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Team 7: Hydraulic Integrated Test Stand Design Report Patrick Anderson, ME Jonathan Crow, ME Jake DeRooy, ME John Sherwood, ME ENGR 340 Senior Design Project May 15, 2015
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Team 7: Hydraulic Integrated Test Stand
Design Report
Patrick Anderson, ME
Jonathan Crow, ME
Jake DeRooy, ME
John Sherwood, ME
ENGR 340 Senior Design Project
May 15, 2015
ENGR 340 Team 7
© 2015 Team 7 and Calvin College
ENGR 340 Team 7
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Executive Summary
The Calvin College Engineering Program’s senior capstone project is composed of two courses, ENGR
339 and ENGR 340. ENGR 339, the first half of the capstone, focuses on the feasibility study of a design
project; ENGR 340, the second half of the capstone, focuses on the implementation and results of the
design project. This report is the final product of ENGR 340. Both courses integrate Christian design
norms into the design process, which have also been included within this design project.
The engineering team designing this project (HITS) consists of four mechanical engineering students. The
design work completed by HITS provides the framework for a general purpose hydraulic test stand
capable of loaded cylinder testing for Best Metal Products (BMP), a local hydraulic cylinder
manufacturer.
The team designed and analyzed key features of the hydraulic integrated test stand, including the force
generation method, the components required, and the hydraulic circuit. A prototype, shown in Figure 1,
was developed and built in order to test these features. The design concept consisted of a bank of two
force generating cylinders (red) surrounding the cylinder undergoing testing (yellow). The cylinders are
connected via a moving wall (blue). The hydraulic circuit is controlled by a LabVIEW graphical
programming interface (computer screen), connected through a data acquisition device to a web of
sensors and control circuits (black instrumentation board).
Figure 1: Hydraulic test stand prototype.
The prototype highlighted a number of difficulties which much be overcome in order create a
functioning full scale system. The control system for the hydraulic pressure will require extensive
calibration. The prototype had a pressure ramp up time of less than three seconds, so a full scale system
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should respond similarly. The prototype showed that the hydraulic system designed by HITS will rely
heavily on a system of rails to stabilize the moving wall.
HITS used the results of analysis and prototype testing to specify a list of recommendations to consider
when designing a full scale hydraulic integrated test stand. HITS recommends maintaining an area ratio,
defined as the effective piston area of the test cylinder divided by the effective piston areas of the force
generating cylinders, between 0.40 and 1.33 in order to maintain acceptable flows and pressures within
the hydraulic system. HITS determined that three banks of two hydraulic cylinders would be necessary
to maintain area ratios within these bounds while still covering the desired product range.
Testing of the prototype showed that synchronizing a bank of force generating cylinders will require
more than a simple T-connection within a manifold to connect the cylinder flows together. The
prototype HITS built relied heavily on a system of rails and rollers to maintain cylinder alignment.
Applying this method to a full scale system would require high strength rails.
Testing also showed that the proportional flow control valve used in the prototype was difficult to
control. Recommendations to limit this difficulty in the implementation of a full scale system include: 1)
using a proportional pressure relief valve and 2) hiring electrical and controls engineers to establish and
calibrate the electronic systems. Additionally, directional control valves should be powered with direct
current rather than alternating current to avoid heat buildup in electrical components.
HITS believes that despite the difficulties presented by the prototype, the chosen method could be
applied to a full scale system. Using the recommendations as a starting point, BMP can reasonably
expect to develop a hydraulic integration test stand in the near future.
Figure 2: Prototype and team.
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Table of Contents
Executive Summary ....................................................................................................................................... 1
Table of Contents .......................................................................................................................................... 3
Table of Figures ............................................................................................................................................. 7
Table of Tables .............................................................................................................................................. 9
1 Introduction ........................................................................................................................................ 10
1.1 Course ......................................................................................................................................... 10
1.2 Team ........................................................................................................................................... 10
1.2.1 Patrick Anderson ................................................................................................................. 10
1.2.2 Jonathan Crow .................................................................................................................... 10
1.2.3 Jake DeRooy ........................................................................................................................ 11
1.2.4 John Sherwood .................................................................................................................... 11
1.3 Chapter Overview ....................................................................................................................... 11
2 Project Definition ................................................................................................................................ 13
2.1 Need ............................................................................................................................................ 13
2.2 Customer ..................................................................................................................................... 13
2.3 Reason for Selection ................................................................................................................... 13
2.4 Requirements .............................................................................................................................. 14
2.4.1 Team Requirements ............................................................................................................ 14
2.4.2 Team Goals .......................................................................................................................... 14
2.5 Design Norms .............................................................................................................................. 15
2.5.1 Stewardship ........................................................................................................................ 15
2.5.2 Integrity ............................................................................................................................... 15
2.5.3 Trust .................................................................................................................................... 15
2.6 Project Scope .............................................................................................................................. 15
2.7 Project Breakdown ...................................................................................................................... 16
3 Project Management .......................................................................................................................... 17
3.1 Team Member Responsibilities................................................................................................... 17
3.1.1 Design Assignments ............................................................................................................ 17
3.1.2 Administrative Assignments ............................................................................................... 18
3.2 Course Milestones ...................................................................................................................... 18
3.3 Project Deliverables .................................................................................................................... 19
3.4 Time Tracking .............................................................................................................................. 19
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3.5 Team Work Philosophy ............................................................................................................... 20
3.5.1 Initial Approach ................................................................................................................... 20
3.5.2 Agile Product Development ................................................................................................ 20
3.6 Data Management and Validation .............................................................................................. 21
4 Concept Design ................................................................................................................................... 22
4.1 Test Stand Concepts .................................................................................................................... 22
4.1.1 Test Scenarios ..................................................................................................................... 22
4.1.2 Method of Force Generation .............................................................................................. 22
4.1.3 Sliding Wall .......................................................................................................................... 23
4.1.4 Cylinder Bank Arrangement ................................................................................................ 23
4.1.5 Cylinder Synchronization Method ...................................................................................... 24
4.2 Force Generating Bank Design .................................................................................................... 24
4.2.1 Pressure and Flow Calculation Tool .................................................................................... 24
4.2.2 Cylinder Optimization Tool ................................................................................................. 24
4.2.3 System Sensitivity Extension ............................................................................................... 25
4.2.4 Rod Buckling Extension ....................................................................................................... 26
4.3 Hydraulic Circuit Design .............................................................................................................. 26
4.3.1 Hydraulic Schematic ............................................................................................................ 26
4.3.2 Hydraulic Power Unit .......................................................................................................... 27
4.3.3 Test Cylinder ....................................................................................................................... 28
4.3.4 Force Generation Cylinders ................................................................................................. 28
4.3.5 Metering Device .................................................................................................................. 28
4.3.6 Circuit Explanation .............................................................................................................. 29
5 Prototype Design ................................................................................................................................ 30
5.1 Cylinders and Frame ................................................................................................................... 30
5.1.1 Cylinder Sizing ..................................................................................................................... 30
5.1.2 Frame Design ...................................................................................................................... 30
5.1.3 Shield Design ....................................................................................................................... 32
5.1.4 Wall Design ......................................................................................................................... 32
5.2 Hydraulic System ......................................................................................................................... 33
5.2.1 Hydraulic Design ................................................................................................................. 33
5.2.2 System Review .................................................................................................................... 34
5.2.3 Hydraulic Power Unit .......................................................................................................... 34
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5.2.4 Pressure Control Valve ........................................................................................................ 34
5.3 Hydraulic Assembly ..................................................................................................................... 36
5.4 Sensors and Electronics .............................................................................................................. 39
5.4.1 DAQ ..................................................................................................................................... 39
5.4.2 Sensors ................................................................................................................................ 39
5.4.3 Amplification and Control Circuits ...................................................................................... 40
5.4.4 Sensor Calibration ............................................................................................................... 43
5.5 LabVIEW Control ......................................................................................................................... 45
5.5.1 DAQ Interfaces .................................................................................................................... 45
5.5.2 Conditional Structure .......................................................................................................... 45
5.5.3 PID control .......................................................................................................................... 46
5.5.4 Boolean Control and Safety ................................................................................................ 46
5.5.5 User Interface ...................................................................................................................... 47
5.5.6 Force Calculations ............................................................................................................... 49
5.6 Control System Assembly ............................................................................................................ 49
5.6.1 Main Electrical Panel ........................................................................................................... 49
5.6.2 Power Supplies .................................................................................................................... 50
5.6.3 Electrical Signal Interference .............................................................................................. 50
6 Testing Results .................................................................................................................................... 52
6.1 Calibration Development ............................................................................................................ 52
6.1.1 Control Curve Development ............................................................................................... 52
6.1.2 Wait Stage Development .................................................................................................... 53
6.1.3 Calibration Error .................................................................................................................. 53
6.2 System Synchronization .............................................................................................................. 54
6.3 Proof of Force Generation Concept ............................................................................................ 54
7 Recommendations .............................................................................................................................. 56
7.1 Maintain proper area ratio between test and force cylinders ................................................... 56
7.2 Use three or more banks of FG cylinders .................................................................................... 56
7.3 Test stand should be mechanically robust .................................................................................. 57
7.4 Use a proportional pressure relief valve ..................................................................................... 57
7.5 Hire electrical and control systems engineers ............................................................................ 57
7.6 Use DC valves instead of AC valves ............................................................................................. 58
8 Costs .................................................................................................................................................... 59
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9 Conclusion ........................................................................................................................................... 60
10 Acknowledgements ......................................................................................................................... 63
11 Works Cited .................................................................................................................................... 64
12 Appendices ...................................................................................................................................... 65
12.1 Hydraulic Power Unit Sizing ........................................................................................................ 66
12.2 Wall Deflection Calculations ....................................................................................................... 68
12.3 Excel Macros ............................................................................................................................... 69
12.4 Electronic Circuit schematics ...................................................................................................... 73
12.5 Cavitation Calculations ................................................................................................................ 77
12.6 LabVIEW program ....................................................................................................................... 78
12.7 Sensitivity Derivation .................................................................................................................. 82
12.8 Datasheets .................................................................................................................................. 87
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Table of Figures
Figure 1: Hydraulic test stand prototype. ..................................................................................................... 1
Figure 2: Prototype and team. ...................................................................................................................... 2
Figure 3: Breakdown of project focus areas. .............................................................................................. 16
Figure 4: Team member responsibilities. ................................................................................................... 17
Figure 5: Cylinder arrangement. ................................................................................................................. 23
Figure 6: Cylinder optimization tool flow chart. ......................................................................................... 25
Figure 7: Full system hydraulic schematic. ................................................................................................. 27
Figure 8: Example pressure control curve for PPRV [1]. ............................................................................. 29
Figure 9: CAD model of prototype frame. .................................................................................................. 31
Figure 10: Constructed prototype frame. ................................................................................................... 31
Figure 11: Prototype hydraulic schematic. ................................................................................................. 33
Figure 12: Control curve (shown in yellow) for prototype pressure control curve [5]. .............................. 35
Figure 13: Hydraulic power unit. ................................................................................................................ 36
Figure 14: Prototype cylinders and frame. ................................................................................................. 37
Figure 15: Force generating valve block. .................................................................................................... 37
Figure 16: Proportional flow control valve. ................................................................................................ 38
Figure 17: Original force generating valve block design. ............................................................................ 38
Figure 18: National Instruments USB 6008 DAQ. ....................................................................................... 39
Figure 19: Pressure and linear displacement sensor (courtesy Omega and Unimeasure). ........................ 39
Figure 20: Flyback diode schematic [7]. ...................................................................................................... 40
Figure 21: Voltage-current control circuit for pressure control valve. ....................................................... 41
Figure 22: LTspice simulation results for voltage-current control circuit. .................................................. 42
Figure 23: Voltage-current control circuit on breadboard. ........................................................................ 42
Figure 24: Voltage-current control printed circuit board mounted with large heat sink. .......................... 43
Figure 25: Pressure sensor calibration. ....................................................................................................... 44
Figure 26: Pressure sensor calibration curve. ............................................................................................. 44
Figure 27: Example of HITS user interface (LabVIEW Front Panel) while test is running. .......................... 47
Figure 28: Example of LabVIEW graphical output while test is running (images move from left to right). 48
Figure 29: Main electrical panel. ................................................................................................................. 50
Figure 30: Power Supply. ............................................................................................................................ 50
Figure 31: Pressure-voltage control curve. ................................................................................................. 52
Figure 32: Effect of temperature on kinematic viscosity [11]. ................................................................... 53
Figure 33: Successful PID pressure control. ................................................................................................ 55
Figure 34: Differential amplifier circuit for pressure sensors (schematic). ................................................ 73
Figure 35: Differential amplifier circuit for pressure sensors (board layout). ............................................ 73
Figure 36: Relay trigger circuit for 115V components (schematic). ........................................................... 74
Figure 37: Relay trigger circuit for 115V components (board layout). ....................................................... 74
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Figure 38: Relay circuit for 115V components (schematic). ....................................................................... 75
Figure 39: Relay circuit for 115V components (board layout). ................................................................... 75
Figure 40: Relay circuit for 24V valve (schematic). ..................................................................................... 76
Figure 41: Relay circuit for 24V valve (board layout). ................................................................................. 76
Figure 42: Potential Percent Error in Force as a function of the Area Ratio .............................................. 83
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Table of Tables
Table 1: Product capability range. .............................................................................................................. 14
Table 2: Key milestones of ENGR 339/340. ................................................................................................ 19
Table 3: Project time summary. .................................................................................................................. 19
Table 4: Summary of hours for second semester, ENGR 340. .................................................................... 20
Table 5: Test scenario summary for test cylinder and force generation cylinder bank. ............................ 22
Table 6: Suggested force generating cylinder bank sizes. .......................................................................... 56
Table 7: Total cost of hydraulic integrated test stand. ............................................................................... 59
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1 Introduction
1.1 Course
The Calvin College Engineering Program’s senior capstone project is composed of two courses:
ENGR 339 and ENGR 340. Both courses combine to create a six credit hour, year-long
engineering project that all graduating seniors complete. ENGR 339, the first half of the
capstone, focuses on team formation, project identification, and a feasibility study. ENGR 340,
the second half, focuses on the in-depth analysis needed to create a finished product or final
design. The final deliverables include this final design report, along with a presentation to the
engineering department faculty, friends, and family at an open house in early May 2015. Both
courses integrate Christian design norms into the design process with a focus on a holistic
understanding of the role of Christians in engineering careers.
1.2 Team
The engineering team responsible for completing this project consists of four senior mechanical
engineering students, hereafter referred to as HITS (Hydraulic Integrated Test Stand). Their
broad range of skills includes undergraduate research, manufacturing environment experience,
consumer product design, energy auditing, and economic analysis. The team is well suited for
the design project, which requires an interdisciplinary approach.
1.2.1 Patrick Anderson
Patrick Anderson is a mechanical concentration engineering student
from Ann Arbor, Michigan who expects to graduate in May 2015.
He has gained research experience through internships at the
University of Florida and Carnegie Mellon University. Next year, he
will pursue a PhD in mechanical engineering at Vanderbilt
University, where he will research surgical robotics. Patrick primarily
contributed to the hydraulic circuit and control system of this
project. In his free time, he enjoys rock climbing, playing soccer,
backpacking, and going to concerts.
1.2.2 Jonathan Crow
Jonathan was born and raised in San Diego, California. He will
graduate in May 2015 with a BS in engineering, international
mechanical concentration, and a BA in French. Jonathan has
industry experience in DoD network systems (SAIC) and product
development (Steelcase). While interning for Steelcase, Jonathan
has developed a unique set of research interests including product
design, human factors, and efficient use of space. He will begin an
MS in Engineering Design and Innovation at Northwestern
University in September 2015. In his free time, Jonathan enjoys
playing ultimate frisbee and badminton, cooking, backpacking,
traveling, and optimizing every aspect of his life.
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1.2.3 Jake DeRooy
Jake is an international mechanical concentration engineering
student from Grand Rapids, MI, who will graduate in May, 2015. Jake
will be working for Best Metal Products as a manufacturing engineer
upon graduation and hopes to return to graduate school soon. Jake’s
interests in hydraulics and experience in programming will be
valuable to the design of this product. As an intern at Best Metals
Products, Jake provides experience with hydraulics as well as strong
customer relations. In his free time, Jake enjoys cooking and
photography.
1.2.4 John Sherwood
John Sherwood is an international mechanical concentration
engineering student, and expects to graduate with honors in May,
2015. John grew up in Hoffman Estates, Illinois. John gained
engineering experience as the Calvin Energy Recovery Fund intern.
He will attend Clemson University to pursue an Environmental
Engineering PhD to research the interactions between energy,
economics, and public policy. John primarily contributed to the
electrical components, sensors, and control system of the project. In
his free time, John enjoys photography and rock climbing.
1.3 Chapter Overview
This report contains the final design report for the hydraulic integrated test stand project. A
brief description of each chapter of the report is given below.
Chapter 1: Introduction
Chapter 1 gives a general overview of the Calvin Engineering senior design course. It also
introduces Team 7 (HITS) and provides a brief background of each team member.
Chapter 2: Project Definition
Chapter 2 introduces the hydraulic integrated test stand project, including the customer, Best
Metal Products. This chapter lists the requirements and goals for the project as well as a
breakdown of its different technical components.
Chapter 3: Project Management
Chapter 3 details the technical and managerial tasks assigned to each team member. It also
provides a year-long schedule for the project and a list of deliverables for the fall and spring
semesters.
Chapter 4: Concept Design
Chapter 4 explains design decisions and analysis for the concepts of the test stand. This includes
the force generation method, pressure and flow analysis, hydraulic cylinder selection, and
hydraulic circuit design.
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Chapter 5: Prototype Design
Chapter 5 details the prototype that was built and used to test the concepts of Chapter 4. The
design and construction of the frame, the hydraulic system, and the control system are
explained.
Chapter 6: Testing Results
Chapter 6 summarizes the results of Chapters 4 and 5. Prototype testing results are discussed,
the outcomes of design decisions are analyzed.
Chapter 7: Recommendations
Chapter 7 provides a series of recommendations to be considered when developing a full scale
test stand using the concepts described in previous chapters.
Chapter 8: Costs
Chapter 8 provides the team's expenditures in completing the project. It also lists the
components supplied by several generous donors.
Chapter 9: Conclusion
Chapter 9 contains a final evaluation of the senior design project. It summarizes the successes
and shortcomings of the project, the challenges faced by the team, and the lessons learned.
Chapter 10: Acknowledgments
Chapter 10 thanks the many individuals and groups who contributed time, ideas, and funds to
this project.
Chapter 11: Works Cited
Chapter 11 lists the many sources used throughout the design report.
Chapter 12: Appendices
Chapter 12 provides further background information for several chapters, including calculations,
computer models, and figures.
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2 Project Definition
2.1 Need
The design created by HITS will address the need for more extensive testing of hydraulic
cylinders at Best Metal Products (BMP), a local hydraulic cylinder manufacturer. The chief
engineer at BMP, Kurt Skov, expressed a desire to expand the current testing equipment at BMP
to include a machine capable of loaded testing. This test stand would be a valuable asset to BMP
as they continue to design complex cylinders with unique applications.
2.2 Customer
This design is being created to meet the specific need of Best Metal Products. BMP specializes in
producing custom welded hydraulic cylinders, including cylinders with multiple rods and valves.
BMP has designed several complex cylinders with valves integrated into the cylinders. These
designs can require large amounts of testing to perfect the valve selection process. BMP already
has numerous test stands, including several testing rigs designed to allow for specific loaded
testing of select cylinders. However, the company would like to obtain a universal test stand
capable of simulating a variety of loading situations.
Best Metal Products currently produces around 700 hydraulic cylinders per day for a wide range
of applications. BMP’s cylinders can be found on snowplows, concrete screeds, stump grinders,
pizza crust cutters, recreational vehicles, and minesweeping tanks. Each application requires a
different testing simulation, underscoring the need for a hydraulic integrated test stand for
simulation testing.
2.3 Reason for Selection
There are two primary reasons for selecting the hydraulic integrated test stand as the HITS
senior design project. First, it provided an opportunity to solve an actual design problem for a
local engineering firm. All aspects of the project, such as defining project parameters, managing
a budget, and working with a customer, helped to develop the abilities of each team member.
This experience will prove invaluable for future long-term projects in both industry and graduate
school.
Second, the hydraulic integrated test stand project serves as the culmination of four years of
engineering classes and internships. Almost every engineering class required for mechanical
engineering majors at Calvin College is utilized in some way, including: Engineering Graphical
Communication, Statics and Dynamics, Circuits Analysis and Electronics, Mechanics of Materials,
Machine Design, Dynamics of Machinery, Control Systems, and Thermal/Fluid Sciences. The
hydraulic integrated test stand project integrates multiple engineering fields, creating a uniquely
interdisciplinary work environment. Not only did the project utilize skills that have been
developed throughout our engineering classes at Calvin, but it also required exploration of
previously unknown topics. For instance, HITS had the opportunity to learn a great deal about
hydrostatic fluid circuits, an area that is not normally discussed in undergraduate classes. This
project is comprehensive in its scope of mechanical engineering subjects yet requires detailed,
in-depth analysis in each area.
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2.4 Requirements
2.4.1 Team Requirements
HITS selected the following performance requirements when exploring recommendations for
the full scale hydraulic design.
Req 1. Device shall perform compression and tension loaded testing with a force
accuracy of 5%.
Req 2. Device shall allow for loaded testing when the test cylinder is both extending and
retracting.
Req 3. Device shall accept test cylinders within ranges seen in Table 1.
Table 1: Product capability range.
Given Product Range Min Max
Cylinder Bore [in] 1.0 4.0
Static Pressure [psi] 1000 5000
Dynamic Pressure [psi] 1000 3000
Retracted Length [ft] 0.5 4.0
Flow rate [gpm] 2 20
Rod Velocity [ft/s] 0 1.4
Req 4. Device shall measure the stroke of the test cylinder to an accuracy of less than
1/16 inches.
Req 5. Device shall record and locally store displacement and force information for each
test.
Req 6. Device shall operate in a safe manner under normal conditions.
Req 7. Device shall safely deactivate the hydraulic system in case of an emergency stop.
2.4.2 Team Goals
HITS has also identified a number of project goals which will be considered when analyzing
design alternatives.
Goal 1. Device should minimize floor space requirements.
Goal 2. Device should be intuitive and easy to use.
Goal 3. Device should minimize cost while maintaining safety and performance.
Goal 4. Device should minimize changeover time necessary between tests.
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2.5 Design Norms
As a team of Christian engineers who strive to apply reformed principles, HITS is guided by
Stephen Monsma’s seven design norms detailed in his 1986 book, Responsible Technology: A
Christian Perspective. These design norms provide an engineering framework to ensure the
flourishing of God’s people and God’s creation. HITS has selected three norms which relate most
directly to the project proposed by BMP.
2.5.1 Stewardship
HITS practiced responsible stewardship of resources, both material and human. The concept of
an integrated test stand is to reduce defective products before they become widespread in
production and go out for shipment to customers. A hydraulic integrated test stand could alert
BMP to design flaws as early as product development, thereby limiting the use of unnecessary
resources at the start. While there is not presently a shortage of steel or hydraulic oil, HITS
pursued all necessary measures to design a system which limits the consumption of non-
renewable resources.
2.5.2 Integrity
HITS contributed towards the design of a complete system that functions as a united whole and
is aesthetically pleasing. In recognition of the operator who will eventually use the test stand,
HITS strived to make the user interface intuitive and easy to use. Ergonomic design should be
incorporated into the full sale test stand layout to encourage proper posture and preserve the
health of the operator. Where possible, HITS reduced clutter and provided documentation in
simple terms to facilitate user interaction with the system.
2.5.3 Trust
HITS worked diligently to establish a bond of trust between the customer and the team. Because
of the high pressure nature of any project with hydraulic cylinders, trust is necessary to ensure
the safety of all involved. Emergency stops were be incorporated into all hardware and software
to ensure that all system functions can be stopped in the event of a system malfunction. Hard
limits were incorporated into the software to limit pressure spikes and unstable states of
motion. HITS assured that the test stand prototype performed in a safe, consistent manner
within conservative operating limits.
2.6 Project Scope
When BMP originally approached HITS with the project concept, the problem definition included
a full physical design that included safety shielding analysis and crane loading design. HITS
determined that a full system design was not feasible given the limited time and resources
available. Due to this reason, BMP requested that HITS focus on the hydraulic design and force
generation components of the stand. Therefore, HITS focused on the design of the hydraulic
circuit for the full scale system and development of a small scale prototype. HITS built this
prototype to test several key aspects of this full design. The smaller scope allowed for a more in-
depth analysis of the difficult components of the system to better meet the client’s needs.
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2.7 Project Breakdown
Before undertaking any design work, the project was segmented into manageable focus areas.
Figure 3 provides a visual representation of the project breakdown. At a high level, the project
consists of three major design domains: component, system, and prototype. Component design
is broken down into four focus areas which relate to specific components. System design is
divided into three focus areas which apply to the system as whole. Prototype design consists of
three large focus areas which relate to the prototype. While this schema does not reflect time
spent in each domain or demonstrate the integral nature of the project, it provided direction to
the research and development process.
Figure 3: Breakdown of project focus areas.
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3 Project Management
3.1 Team Member Responsibilities
Each member of HITS brought a unique skill set to the team. These skill sets were considered in
the project definition phase to ensure maximum work satisfaction and productivity. Using the
project breakdown in Section 2.7, functional areas were assigned to each member. However,
these assignments changed throughout the year and evolved to match project needs.
Administrative tasks were also divided among the members of HITS to assure equilibrium and
peace. Figure 4 provides a visual representation of principal functional areas for each member.
Figure 4: Team member responsibilities.
3.1.1 Design Assignments
Initially, co-leaders were assigned to four functional areas: testing capabilities, geometric layout,
control system, and force generation system. For the larger functional areas, hydraulic circuit
and power unit, all members were tasked with development as these areas were central to the
project and required direct involvement from all team members. As time progressed, tasks
became more fluid and team members completed design tasks as needed. New functional areas
were assigned to cover control system integration, electric circuit design and integration,
calibration, tuning, and prototype construction.
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3.1.2 Administrative Assignments
Industry Liaison
This team member was responsible for communicating regularly with the customer (BMP) and
the industrial consultant (Professor Ren Tubergen). The liaison discussed all design decisions
with the customer and solicited feedback. Additionally, the liaison coordinated meetings with
Professor Ned Nielsen and took meeting minutes for all team meetings. Jake was well-suited for
this position. As an intern for BMP, Jake had frequent contact with the customer. Jake was
diligent in his note taking and well-versed in sharing documents using Microsoft OneDrive.
Team Manager
This team member was responsible for coordinating the project schedule, tracking progress, and
facilitating team meetings. The team manager tracked task completion and performed time
tracking analysis. Additionally, the team manager moderated conflicts among teammates and
looked for ways for team members to collaborate. Jonathan was well-suited for this position
due to his affinity for Microsoft Excel and his interest in the project management.
Budget Manager
This team member was responsible for managing the prototype budget. The budget manager
created the bill of materials and assured that all team accounts are in good standing, both with
Calvin College and BMP. Patrick was a well-suited for this position due to his role as treasurer for
the American Society of Mechanical Engineers, Calvin Chapter.
Media Coordinator
This team member was responsible for team communications to the general public in print and
online. The media coordinator managed the team website and generated all posters and
pamphlets. This person created all graphics for the team and assured consistent visual style
throughout all publications, including reports. John was well-suited for this position due to his
interest in photography and his affinity for graphic design.
3.2 Course Milestones
A list of the key milestones for the class portion is presented in Table 2. While not specific to the project
objectives of HITS, this defined the overall timeline of project deadlines.
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Table 2: Key milestones of ENGR 339/340.
Milestone Date
Project Proposal 10 Sept 2014 Project Objectives and Requirements 17 Sept 2014 PPFS Outline 24 Sept 2014 Work Breakdown Schedule 8 Oct 2014 First Oral Presentation 17 Oct 2014 Project Poster 31 Oct 2014 PPFS Draft 10 Nov 2014 Website Live 21 Nov 2014 Second Oral Presentation 3 Dec 2014 PPFS Final Draft 8 Dec 2014 Third Oral Presentation 6 Mar 2015 CEAC Design Review 24 Apr 2015 Fourth Oral Presentation 1 May 2015 Final Poster 1 May 2015 Final Presentation 9 May 2015 Final Report 13 May 2015 Faculty Review 14 May 2015
3.3 Project Deliverables
HITS produced a variety of deliverables including presentations, briefs, a website, a prototype,
and design recommendations. The primary deliverables to BMP are a small scale prototype to
prove key concepts (Section 5 and 6) and a list of recommendations for the construction of a full
scale hydraulic system (Section 7). The recommendations are provided in lieu of a full scale
schematic because the complexity of such a system is outside the scope of this project, as
outlined in Section 2.6.
3.4 Time Tracking
At weekly meetings, HITS tracked the time contributed by each team member.
Table 3 shows that actual time spent on the project far exceeded projections, especially in the
second semester course, ENGR 340. A detailed breakdown of the time spent in ENGR 340 can be
found in Table 4.
Table 3: Project time summary.
Projected Actual
First Semester (ENGR 339) 250 300
Second Semester (ENGR 340) 400 891
Total (Hours) 650 1191
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Table 4: Summary of hours for second semester, ENGR 340.
Tasks Estimated Time
Excel Sheet 57 Hydraulic schematic 42 Hydraulic component selection 28 Company Meetings 26 LabVIEW 140 Prototype design 12 Prototype build 15 Moving wall 12 Safety shields 15 Frame 20 Wheels 12 Physical assembly 40 Electronic assembly 40 Sensors and electronics 77 Professor consulting 10 Circuit boards 50 Control board design 10 Calibration 100 Reports / documentation 110 leak control 35 Errands/travel/admin 12 Team Meetings 28
Total 891
3.5 Team Work Philosophy
3.5.1 Initial Approach
For the first semester, HITS used a design approach which centered on long range goals
discussed at Saturday meetings. Key topics were discussed and action items were assigned to
each member. The team coordinator tracked and analyze time spent on the project each week.
Informal meetings between two or more group members took place throughout the week to
discuss focus areas.
Unfortunately, this approach did not facilitate communication between team members and
resulted in general discord. Since estimated date of completion was not made clear for action
items, team members sometimes discovered that their action items had already been
completed by another team member. Additionally, this approach did not establish clear
expectations for daily task completion.
3.5.2 Agile Product Development
Halfway through the year, a new approach was adopted which is similar to a framework known
as agile product development. Saturday meetings were replaced with short, daily meetings to
communicate daily and weekly tasks. This improved daily accountability and allowed team
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members to share real time scheduling data for tasks. A progress board with sticky notes of
completed and uncompleted tasks was placed in the workspace to serve as a visual reminder of
current progress. Additionally, tasks were made more relevant by limiting their range to a
maximum of 2 weeks. This boosted team morale by making tasks more realistic and attainable
in both the short run and the long run.
3.6 Data Management and Validation
HITS stored all documents, spreadsheets, and presentations in Microsoft One Drive for ease of
collaboration and reliable formatting. CAD data and any calculations performed using programs
on Calvin College computers were stored on the Calvin server. Backup copies of key documents
stored on the Calvin server and backed up on flash drives.
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4 Concept Design
4.1 Test Stand Concepts
4.1.1 Test Scenarios
The first step in selecting a design concept was to identify all of the scenarios which the test
stand would be required to test. The hydraulic integrated test stand’s primary function is to
simulate physical loading situations that occur in real-world applications. Tensile force can be
applied to a hydraulic cylinder’s rod in either direction. At the same time, the rod can move in,
out, or stay static while under load. Considering these factors, HITS developed six primary
loading scenarios that were the focus of the hydraulic circuit and control system design. Each
scenario involves specific types of fluid flow in the test cylinder and the driving cylinder bank,
where hydraulic fluid can be pumped into or metered out of either side of the cylinders.
"Metering" means that the system limits the amount of flow leaving a cylinder; this creates
pressure in the cylinder and generates force. See Section 4.1.2 for more details. As a result, the
driving cylinder bank can provide a driving force against the test cylinder or a resistive force
against the movement of the test cylinder. The rods of the test and driving cylinders must move
in the same direction in each case. Table 5 shows the details of the six primary loading
scenarios. Please refer to HITS’ Project Proposal and Feasibility Study for a more complete
explanation of each test scenario. It is most important to notice that pumping and metering
capabilities are required for both chambers of the test cylinder as well as for both chambers of
the driving cylinder bank. Without these capabilities, the six test scenarios are not possible and
it would not be feasible for HITS to design a robust variable loading test stand.
Table 5: Test scenario summary for test cylinder and force generation cylinder bank.
Test Cylinder Force Generation Cylinder(s)
Test Scenario Force Direction Velocity Flow Type Force Type Velocity Flow Type
1 ← → Pump In Resistive → Meter Out
2 ← ← Meter Out Driving ← Pump In
3 ← 0 No Flow 0 No Flow
4 → → Meter Out Driving → Pump In
5 → ← Pump In Resistive ← Meter Out
6 → 0 No Flow 0 No Flow
The design process and decisions for the test scenarios was an important first step for HITS.
These decisions impact the requirements and decisions of almost every other component of the
test stand, including the force generation system, frame design, hydraulic circuit, and control
system.
4.1.2 Method of Force Generation
HITS chose to use a bank of hydraulic cylinders to provide a resistive force to the system. The
Force Generation (FG) bank houses several cylinders that apply loads to the test cylinder.
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Because hydraulic cylinders are being tested with other cylinders, it is paramount that adequate
safety factors are applied to the driving cylinder bank to ensure a long operating lifetime. HITS
chose to orient the FG cylinders around the test cylinder rather than juxtaposing the cylinders in
order to save on floor space of the system. See Section 4.1.4 for more details on the
arrangement of the FG cylinders. HITS analyzed the requirements of this FG system in detail.
More details on the analysis can be found in Section 4.2.
The FG cylinders exert a force on the test cylinder by maintaining pressure using a method
called metering. Metering is the act of adding resistance to flow by the use of an orifice. This is
the same concept present when placing a thumb over the end of a garden hose, building up
pressure in the hose, which allows the water exiting the hose to spray further. Metering can be
used to control either flow or pressure. HITS specified the use of a proportional pressure relief
valve in order to achieve the necessary metering for the system. More details on the metering
device selection process can be found in Section 4.3.5.
4.1.3 Sliding Wall
In order to apply forces to the test cylinder, the test cylinder must be physically connected to
the FG bank. This can be accomplished through a movable steel wall. The wall should mount on
a sliding rail system, allowing it to move along with the extension and retraction of the cylinder
rods. More details on the wall design can be found in Section 5.1.4.
4.1.4 Cylinder Bank Arrangement
The driving cylinders should be oriented evenly around the moving wall as shown in Figure 5.
The green cylinders in the figure represent the driving cylinders while the purple cylinder
represents the testing cylinder. This distribution is pertinent to reduce moments on the moving
wall, a topic which is discussed in Section 4.1.5 and the Project Proposal and Feasibility Study.
Figure 5: Cylinder arrangement.
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4.1.5 Cylinder Synchronization Method
HITS showed in the Project Proposal and Feasibility Study that the FG cylinders could exert a
high load on the guide rails if the cylinders were to become unsynchronized. Ideally, most of the
synchronization would be accomplished by dividing fluid flow equally between the cylinders.
Since this is not always possible, a system of rails and rollers can be used to absorb force and
moment imbalances and bring the system into equilibrium. However, further study was required
to determine how high these loads could become synchronized in order to properly size the
rails. This was an important question for the team to answer. HITS used the prototype to test
the effectiveness of flow division and the necessity of rails. See Section 5.1.2 for the design of
these prototype components and Section 6.2 for testing results.
4.2 Force Generating Bank Design
The initial concept was to specify a pair of FG cylinders with a combined area slightly larger than
the largest bore test cylinder. Unfortunately, these FG cylinders would have to run at extremely
low pressure (10psi) for the smaller test cylinders, which is not enough to overcome static
friction. After a few attempts to generalize results with two pairs of FG cylinders and a chosen
test cylinder, HITS discovered that an appropriate set of force generation cylinders needed to be
specified for each test cylinder. In the absence of suitable software solutions, a macro-enabled
Microsoft Excel sheet was used to design the FG bank.
4.2.1 Pressure and Flow Calculation Tool
The most important criterion for a FG bank is the ability to generate force on a cylinder with a
give bore-rod combination over the entire range of flow rates (0-20 gpm) and dynamic pressures
(0-3000psi). A key variable in this analysis was the area ratio, which is the ratio between the
effective area of the test cylinder and that of the FG cylinder bank. A list of 150 test cylinders
was provided by BMP, specified as a set of bore-rod combinations. A macro was written to
calculate flow and pressure data for one pair of FG cylinders applying force to the cylinders on
this list. The macro was then expanded to generate a data table for any set of FG cylinders
acting on any set of test cylinders. The inputs for this program can be seen on the left of the
optimization tool diagram (Figure 6, below). Conditional logic was used to determine if proposed
FG cylinders sizes matched the pressure and flow boundaries specified in the system
requirements (Section 2.4). Additionally, a minimum pressure of 400 psi was specified for the FG
cylinders based on a conservative estimate of the pressure necessary to overcome static friction.
Initial guess values for three FG cylinder pairs satisfied requirements for only 10% of test
cylinder sizes.
4.2.2 Cylinder Optimization Tool
To increase the proportion of test cylinders accommodated, HITS used a Microsoft Excel Solver
routine to optimize FG cylinder sizes. The solver was allowed to change cylinder sizes while
respecting basic rules of cylinder design: 1) bore size must be at least 1/2 inch larger than rod
size and 2) 1/8 inch increments should be used for ease of manufacturing. This was a process
that involved many trials and optimizations, but the software greatly increased productivity. A
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schematic of the process is shown in Figure 6. Conditional formatting was used to figure out
which cylinders needed attention and which requirement were not being met. Having the data
for each cylinder combination was extremely helpful for analysis, even though a table of 4000 or
more rows was initially daunting. This optimization process increased the proportion of
cylinders accommodated to well over 90%.
Figure 6: Cylinder optimization tool flow chart.
4.2.3 System Sensitivity Extension
HITS extended the optimization tool to automatically select the best combination of FG banks
for each test cylinder. Before this revision, the optimization tool stated that at least one
combination FG banks would allow for acceptable flows and pressures in the FG system, but had
no criteria to select the best option. In cases where more than one FG bank combination met
the criteria, HITS needed a criteria to select the preferred combination. HITS used the force’s
sensitivity to the pressure measurement uncertainty, cylinder manufacturing tolerances, and
estimated cylinder deflections as the selection criteria. Stated another way, the optimization
tool selected the cylinder bank combination which had the least potential for error in the force
generated by the system.
Appendix 12.7 walks through the process used to derive the formula determining the force’s
sensitivity to the pressure measurement uncertainty, cylinder manufacturing tolerances, and
estimated cylinder deflections. Implementation of this formula into the optimization tool
showed that a FG cylinder combination has less potential for error as the area ratio decreases.
Therefore, the optimization tool selected the FG bank combination with the smallest area ratio
within the acceptable area ratio bounds.
Test Cylinders (150)
Pressure/Flow Requirements
(8)
FG Cylinder Pairs (3+)
Cylinder Combinations
(4000)
% of BMP Cylinders
Accommodated
Final Force Generation Cylinder Selection
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4.2.4 Rod Buckling Extension
HITS developed an additional extension to the optimization tool to evaluate rod buckling stress.
This extension calculated the critical stresses to avoid buckling on each cylinder in the FG bank.
It then calculated the load seen by each cylinder in each situation based on the given pressure
and the combination of active FG cylinders. This load was used to calculate the stress on the
cylinder rods. This stress was compared to the critical stress for the cylinder design to give a
safety factor against buckling. This outcome was incorporated into the optimization tool as an
additional acceptance criterion for each FG bank combination.
As a result of this rod buckling extension, HITS reduced the range of test cylinders that the test
stand could accommodate and ruled out a subset of advantageous FG cylinders. Due to buckling
concerns, maximum rod length was reduced to 4 feet or less and small bore-rod cylinder options
were removed from consideration for the FG bank. This second change was detrimental to BMP
product accommodation because the smaller rod FG cylinders had allowed for more consistent
area ratios between extend and retract. HITS determined with this extension that 3 banks of
cylinders would be required to cover 97% of BMP’s product line assuming the FG system could
not exceed 4000 psi, drop below 390 psi, or exceed 30 gpm. This 97% includes all bore and rod
combinations for bore sizes 4.000 inches and smaller with one exception. The 1.500 inch bore
with a 1.250 rod cylinder would not be able to function during the retract stroke within these
bounds.
4.3 Hydraulic Circuit Design
4.3.1 Hydraulic Schematic
HITS developed a full-sized test stand hydraulic schematic that utilizes the force generation and
metering concepts in Section 4.1.2, as well as the cylinder bank optimization results in Section
4.2. The system was designed to allow fluid from the pump to be delivered to the extend or
retract side of the test cylinder, as well as to the extend or retract side of the force generating
cylinder bank. In this way, all of the test scenarios described in Section 4.1.1 can be achieved
with a single test stand. The schematic is shown in Figure 7, below.
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Figure 7: Full system hydraulic schematic.
4.3.2 Hydraulic Power Unit
The green box (lower left) shows the hydraulic power unit (HPU). This includes a pump, motor,
safety relief valve, and flow control valve. The variable displacement pump works in conjunction
with a variable flow divider to control the hydraulic flow through the system. The safety relief
valve is standard in hydraulic circuits. This is a very simple, mechanical valve which prevents the
system from exceeding an absolute maximum pressure. Relief valves are designed to fail in the
relief position; therefore, a single valve can act as the pressure relief for the entire system. The
HPU also includes a mechanically actuated relief valve which opens if the test stand door is
opened. This prevents pressurized flow from reaching the system in case the safety shielding
around the system is opened to insert a new test cylinder.
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4.3.3 Test Cylinder
The orange box (upper left) shows the hydraulic cylinder that is being tested. There is also a
directional control valve to send fluid from the pump to either the extend or retract side of the
cylinder. This directional control valve works in tandem with the directional control valves in the
Force Generation circuit.
4.3.4 Force Generation Cylinders
The blue box (upper right) shows the three sets of two force generation cylinders and the
directional control valves that control them. Section 4.2 provides more details about the design
of the Force Generating circuit.
An external review of the system by Michigan Fluid Power concluded that this design for the
Force Generating circuit could allow for cavitation at higher temperatures under extremely high
fluid flow conditions (See Section 5.2.2). Future development of the force generating system
should account for this issue by replacing the three reservoirs seen in the blue box with a low
pressure centrifugal pump with a mechanically actuated relief valve to prevent pressurizing the
cylinders when the door to the system is open.
In addition, issues could arise when dividing fluid flow to several sets of different size cylinders.
This complication was not explored with the prototype built by HITS, so a detailed analysis on its
effects was never performed.
4.3.5 Metering Device
The yellow box (lower right) contains the key component that allows flow to be metered and
force to be generated: a proportional pressure relief valve (PPRV). PPRVs are “designed to
regulate pressure in a hydraulic system in proportion to an applied electrical input” [1]. The user
can dictate a command signal and in term specify an exact pressure in the system (Figure 8,
below). The functionality of this valve is the most critical component of the test stand, because
it the component by which pressure and force are generated in the system.
A typical PPRV controls pressure by changing the force applied to a valve poppet that covers an
orifice. The electrical command signal activates a solenoid, which adjusts the force on an
armature, changing the amount of pressure required to move the poppet and allow fluid to pass
[2] [3]. A greater command signal increases system pressure, which in turn generates force in
the test stand (Figure 8).
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Figure 8: Example pressure control curve for PPRV [1].
4.3.6 Circuit Explanation
The advantage of this hydraulic circuit design is that all of the test scenarios discussed in Section
4.1.1 can be accomplished in a single test stand. This is accomplished in the following manner
for Test Scenario 1:
1. Center directional control valve (component 9) directs high pressure fluid from the
pump to the test cylinder. Simultaneously, this action connects the force generation
cylinder banks to the PPRV.
2. Test cylinder directional control valve (component 10) directs high pressure fluid to the
extend side of the test cylinder. Simultaneously, this action connects the retract side of
the test cylinder to an open hose that goes to the reservoir.
3. Any combination of force generating cylinder banks is “turned on” by shifting the
directional control valves (components 11, 12, and 13) to direct oil from the retract side
of the cylinders to the PPRV. The combination of banks depends on the size of the test
cylinder. If this is not done, the force generation cylinder bank dumps oil to the
reservoir.
4. The PPRV meters fluid coming from the retract side of the FG cylinder banks is metered,
pressure builds in the FB cylinder banks, and force is applied to the test cylinder.
The same process can be used for the rest of the test scenarios. The key to the system is that
high pressure fluid from the pump can be sent to either the test cylinder or the FG cylinder
banks. In either case, it can then sent to either the extend or retract side of the cylinder (or
cylinder banks). Fluid coming out of the opposite side of the cylinders on other half of the
hydraulic system is sent to the PPRV. Any other fluid exiting a cylinder is sent to the reservoir.
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5 Prototype Design
HITS fabricated a prototype to test several aspects of the full system design. First, the prototype
focused on determining the extent to which the full system can use the hydraulic circuit to
balance the moving wall. Second, the prototype required HITS to determine the electrical
requirements of the system to allow for LabVIEW control. Third, the prototype explored the
accuracy of the system’s force generation method.
5.1 Cylinders and Frame
5.1.1 Cylinder Sizing
HITS decided to design the prototype to only work with one test cylinder and one set of FG
cylinders rather than with a bank of FG cylinders and allow for multiple test cylinders. This
decision was made in order to reduce system complexity, cost, and to limit control variables.
HITS decided to size the prototype cylinders to allow for a rod speed of approximately 1 inch per
second and a maximum operating pressure of approximately 2000 psi. The rod speed was
chosen to allow for enough time for emergency shut down while still allowing for a
representative stroke duration. The maximum operating pressure was chosen to minimize
system loads while still allowing for representative pressures. The exact rod speed and operating
pressures were determined by the hydraulic power unit donated by Mason Dynamics.
HITS generated a list of matching FG and test cylinder bore and rod combos using a Mathcad
calculator (Appendix 12.1). This list was then compared to existing cylinders produced by BMP
until two suitable cylinders were found. The chosen cylinders had an 8 inch stroke, allowing for a
desktop sized frame to be designed. The test cylinder, painted yellow on the prototype, has a
2.5 inch bore and a 1.25 inch rod. The FG cylinders, painted maroon on the prototype, have 1.5
inch bores and 1 inch rods. The maximum operating pressure with the selected cylinders was
2250 psi on the FG side of the system, and 900 psi in the test cylinder. All three of the cylinders
involved had pressure ratings above 3500 psi, ensuring that the cylinders would be safe to
operate at these conditions. The rod speeds on extend is 0.78 inches per second, and 1.05
inches per second on retract.
5.1.2 Frame Design
A frame was designed and constructed out of ½ inch steel plate and 1 inch angle iron. The
design was selected to use available materials and to allow for disassembly. See Figure 9 to see
the CAD model of the frame and Figure 10 to see a photograph of the constructed frame.
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Figure 9: CAD model of prototype frame.
Figure 10: Constructed prototype frame.
The side wall supporting the cylinders was modeled as a modified simply supported beam to
determine if reinforcement would be necessary to minimize deflection. The calculations in
Appendix 12.2 showed that extra reinforcement would be required for the side wall of the
frame. HITS designed the side wall to use 1 inch angle iron welded to the back of the frame for
reinforcement. HITS switched to welding a large C-bracket to the back wall when constructing
the prototype to simplify construction.
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The rails were constructed out of 1 inch angle iron. This provided enough support to hold the
side walls together and to support the weight of the moving wall. However, the pinned
connection between the angle iron and the side walls allowed for a significant amount of
deflection without failure when the hydraulic cylinders moved out of sync, applying excessive
loads to the rails. This pinned connection did not provide enough stability to the system, so
metal tabs were welded to the rails to limit the amount of deflection permitted in these joints.
The rails were initially sized with the assumption that the hydraulic system would provide a high
level of synchronization to the system. Initial testing showed that this did not happen at low
pressures, so HITS revised the rails to be able to handle more load. The revised rails consisted of
1 inch square tubing welded inside of the angle iron for additional stability. Section 6.2 discusses
the conclusion about rail sizing and system synchronization in more depth.
5.1.3 Shield Design
A polycarbonate enclosure was built to surround the hydraulic cylinders and frame for
additional safety. This shield was built out of three ¼” polycarbonate sheets, attached with bolts
through 1 inch angle iron. Slots were cut into the shield to allow for sensors and hydraulic hoses
to exit the enclosure, and then the shield was placed over the frame and cylinders. The installed
shield protects against any mechanical failures of the frame, including weld separation, rail
failure, or hose ruptures.
An additional acrylic shield was constructed to surround the HPU and system valves. This was
built to contain high pressure oil leaks. The presence of several pin-hole leaks in the hydraulic
system were discovered after initial testing. Several of these leaks allowed oil to leave the
secondary oil containment tray when the system operated at high pressures. In response, HITS
repaired the leaks as well as building the additional acrylic shield for safety considerations.
5.1.4 Wall Design
The moving wall connects the FG and test cylinders and must withstand the entire loads exerted
by the cylinders. These loads exceed 2 tons in worst case test scenarios. The strength of the wall
was calculated by modeling it as a modified simply supported beam. Initial calculations showed
that the wall should be reinforced to reduce deflections. Two pieces of 1 inch angle iron was
welded onto the back of the moving wall to minimize deflections.
Custom rollers were built for the moving wall. These were built to allow for using available
supplies. The design also allowed for machining larger or smaller rollers to account for tolerance
stack ups in the frame design.
The moving wall was initially designed and built with one roller per rail. This allowed the FG
cylinders de-synchronize in order to test the extent which system would rely on rails to
synchronize the system. Early testing showed that the hydraulic system was not able to properly
synchronize the system, so additional rollers were added to the moving wall to increase the
stability of the wall as it moved along the rails.
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5.2 Hydraulic System
5.2.1 Hydraulic Design
A small hydraulic circuit was successfully designed for the test stand prototype. The prototype
circuit does not allow supplying pressurized fluid to the FG system, driving the test cylinder back.
It also only includes one set of FG cylinders, as discussed in Section 5.1.1. These simplifications
allow for the system to be built with a minimum amount of components while still allowing for
basic functionality.
The hydraulic system is shown in Figure 11. The prototype’s hydraulic system is separated into
two separate systems. The first system powers the test cylinder. This includes an HPU, relief
valve, directional control valve, and a single cylinder. The hoses and cylinder in the prototype
are color coded as yellow. The HPU, relief valve, and directional control valve, shown in the
dotted blue box, were supplied by Mason Dynamics. The second system powers the FG system.
This system has a reservoir, a small centrifugal pump, a directional control valve, two cylinders,
and a proportional flow control valve. The initial prototype design also featured a flow relief
valve for the centrifugal pump and a proportional pressure relief valve rather than a
proportional flow control valve. The flow relief valve was removed since it was found that the
centrifugal pump did not allow for a great enough pressure differential to justify the flow relief
valve. The proportional pressure relief valve was replaced with a proportional flow control valve
since BMP donated the proportional flow control valve.
Figure 11: Prototype hydraulic schematic.
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5.2.2 System Review
HITS requested that Michigan Fluid Power Automation Engineering (MFP) review the hydraulic
design to ensure proper functionality and safety. MFP noted that the original prototype design
had a potential risk of cavitation. Cavitation occurs when a fluid drops below its vapor pressure.
In hydraulics, cavitation causes bubbles, which then implode under pressure, causing damage to
hydraulic circuits. MFP suggested HITS implement the low pressure centrifugal pump seen in
Figure 11 to power a fluid resupply system, preventing cavitation.
HITS implemented MFP’s suggestion with a centrifugal pump found in Calvin’s part’s storage
room. However, HITS found that the pressure loss in the hydraulic system was high enough to
limit the flow from this centrifugal pump. HITS analyzed the pressure losses in the hydraulic
circuit and used Bernoulli’s Equation to determine that the centrifugal pump provided enough
flow to prevent cavitation under the predicted operating temperatures and flows. See Appendix
12.5 for these calculations.
5.2.3 Hydraulic Power Unit
HITS determined the approximate Hydraulic Power Unit (HPU) size based on the desired flow
and pressures while sizing the hydraulic cylinders in the system. HITS then contacted Mason
Dynamics, who offered to donate a HPU with the desired flow and pressure characteristics. The
HPU donated by Mason allows for 1 gallon per minute of hydraulic flow and was pressure
limited to 1000 psi for safety considerations. The HPU contained a pressure relief valve and a
directional control valve which was used to control the test cylinder.
5.2.4 Pressure Control Valve
The prototype requires a pressure control valve to meter the fluid leaving the force generating
cylinders. Ideally, this would be a proportional pressure relief valve (PPRV). See Section 4.3.5 for
an explanation of PPRV function. HITS originally selected the Eaton KBCG-3-160-D-Z-M-1-2-A-
PR7-10 as an excellent valve for the prototype [1]. It is a PPRV that can handle flow rates up to
1.3 US gpm and control pressure from 58 – 2300 psi. However, this valve and others like it are
very expensive; listed at approximately $1500, it was well above the price range of a Calvin
Senior Design team or even BMP for this purpose [4].
Instead of using the Eaton valve, BMP donated a Command Controls Corp. flow control valve. It
is an EPFI-10-N-0-08-0-M-24DG [5]. It has several technical properties of note. First, it is
technically a proportional flow control valve, not a proportional pressure relief valve. This means
that the flow rate passing through the valve can be dictated by the electrical signal that is
applied to it (Figure 12, below). However, through discussions with BMP engineers, HITS
determined that a pressure compensated flow control valve could be used for the same purpose
as a pressure control valve. The valve’s documentation states that the valve has a pressure
compensatory spool that “modulates the flow at 100 PSI/6.9 Bar delta ‘P’ providing the valve
with a constant regulated flow regardless of load or system pressure” [5]. This means that when
HITS changes the current applied to the valve, the flow rate will change, but the pressure will
also change. The metering orifice changes size, dictating flow and indirectly dictating pressure. A
PPRV operates similarly by changing the amount of pressure needed to move a valve poppet off
of an orifice (See Section 4.3.5). While this is not exactly the same as the flow control valve given
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to HITS, which changes an orifice area, a true PPRV does effect orifice size as well when it
changes the force applied to the poppet.
Rather than use the given control curve relating flow and current, HITS decided to build a
control curve relating pressure and voltage, two much more useful variables in this particular
application (See Section 6.1). Therefore, the valve will be referred to as the “pressure control
valve” (PCV) throughout the remainder of this report.
Another important physical characteristic is that the valve is “Normally Open.” This means that
the orifice is fully open when no electrical signal is applied to the valve. This was advantageous
for the test stand application, because HITS could test the functionality of the rest of the
hydraulic system and frame without actually attaching the pressure control valve cords. It was
also an important safety feature, because “in the event of power failure…the normally open
valve will open” [5]. This prevents pressure buildup in the test stand in case of electrical
malfunction.
Finally, the prototype pressure control valve can be controlled up to an 8 gpm flow rate.
However, the hydraulic power unit provided by Mason Dynamics supplies only 1 gpm.
Therefore, HITS was only utilizing a fraction of the capacity of the valve. This proved to be
problematic, as there was a limited voltage signal range that HITS could provide to the valve to
create pressure in the force generating cylinders. A full explanation of this problem and how it
was addressed can be found in Section 6.1.
The cavity required to connect the PCV to hydraulic hoses (#C1020) was donated by Mason
Dynamics.
Figure 12: Control curve (shown in yellow) for prototype pressure control curve [5].
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5.3 Hydraulic Assembly
The HPU, shown in Figure 13, contains a 1 gallon reservoir, pump, motor, pressure relief valve,
and directional control valve. The HPU pushes hydraulic oil through the hose connected to it,
pushing the yellow cylinder out. Return oil from the yellow cylinder re-enters the HPU through
the other hose. The HPU and yellow cylinder combined make up the right side of the Hydraulic
Schematic shown in Figure 11.
As shown in Figure 14, the yellow cylinder pushes the blue wall out as it extends. This blue wall
then pulls the red cylinders out. Fluid is expelled through the red hoses with white strips visible
in Figure 14. This fluid enters the valve block seen in Figure 15 through the top two ports. The
valve block directs this fluid out of the port exiting the right side of Figure 15. The fluid enters
the Command Controls proportional flow control valve, shown in Figure 16 through the port on
the left side.
This flow control valve then meters the fluid, building up pressure in the left most valve,
returning fluid at atmospheric pressure to the reservoir. The pressure builds up through the
entire red hoses with white stripes and into the red cylinders. This pressure is measured with
both an analogue gage and a pressure transducer, seen at the top of Figure 15. This pressure
causes the red cylinders to apply a force onto the yellow cylinders through the blue wall. The
other side of red cylinders receives a replenish supply of oil through the valve block shown in
Figure 15 via a small centrifugal pump. The red cylinders, valve block shown in Figure 15,
proportional flow control valve shown in Figure 16, the reservoir, and the resupply pump make
up the right half of the diagram shown in Figure 11.
Figure 13: Hydraulic power unit.
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Figure 14: Prototype cylinders and frame.
Figure 15: Force generating valve block.
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Figure 16: Proportional flow control valve.
The main manifold in the hydraulic prototype, shown in Figure 15, leaked due to improper
machining of the NPT fittings. The original valve block design is shown in Figure 17.
Figure 17: Original force generating valve block design.
HITS attempted to use pipe sealant to fix this issue. When the system still leaked, HITS decided
to use a newer SAE straight thread O-ring port connections rather than the original NPT
connections. HITS manufactured extensions to the original manifold to allow for the SAE O-ring
ports to be welded onto the system. However, poor weld quality caused the new manifold to
have several pin hole leaks. HITS attempted to repair these leaks with a metal based epoxy, but
that repair did not work. HITS then removed the manifold and re-welded the ports. This entire
process taught HITS to appreciate good workmanship in manufacturing and to design hydraulic
systems with high grade connections.
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5.4 Sensors and Electronics
Sensors and electronics were an integral part of the prototype’s control system. The electronic
components allowed for automated control of the system, while the sensors provided active
feedback. Central to both sensors and electronics was the Data Acquisition device (DAQ).
5.4.1 DAQ
A National Instruments USB 6008 Data Acquisition device (Figure 18) was used to connect
sensors and electronic components to a computer. This DAQ was selected because it is a
relatively low cost device designed for student projects. It is capable of handling both analog
and digital input/output. The HITS team used each of these functionalities in the final prototype
design.
Figure 18: National Instruments USB 6008 DAQ.
5.4.2 Sensors
The HITS team obtained two pressure sensors (a 2 ksi and 5 ksi model, Figure 19 left), and a
linear displacement sensor (Figure 19 right). The pressure sensors help control the forces
generated on the test cylinder, and the linear displacement sensor checks where the cylinder is
within the test scenario. All three sensors are powered by a 5V power supply, and return a
variable voltage based on their reading. The linear displacement sensor could directly connect to
the DAQ, but the pressure sensor signals required amplification.
Figure 19: Pressure and linear displacement sensor (courtesy Omega and Unimeasure).
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5.4.3 Amplification and Control Circuits
HITS built several circuits for the prototype, including amplification and relay circuits. The
National Instruments Data Acquisition device accepts input of -10 – 10V, minimum 10mV, and
output of 0 – 5V at 5 mA [6]. Unfortunately, the pressure sensors could not meet minimum
voltage requirements and the relay circuits required more current. The schematics and board
layouts for all circuits can be found in Appendix 12.4.
Amplification Circuits
Two amplification circuits were constructed to reduce noise from the pressure sensors. HITS
used a differential op-amp that compared two signal lines and amplified only the difference,
which is 1mV – 50mV. A gain of 100 on the op-amp was used to boost the signal to 100mV –
500mV, which are levels readable by the DAQ. By amplifying only the difference, the signal noise
to the DAQ was significantly reduced.
Relay Circuits
Relay circuits were constructed in order to control high voltage valves and pumps within the
system by a digital output signal from the DAQ. Fortunately, fellow student Jeremy Ward had
already developed a suitable circuit to control 115V devices as part of a home automation
system. The circuit consists of a transistor that actuates a relay with a 1V digital signal from the
DAQ. An external power supply was necessary to meet the 20mA current requirement of the
relay because the DAQ could only provide 5mA [6]. The original circuit was also adapted to
control the 24V Parker directional control valve.
Flyback Diodes
Flyback diodes were integrated into every circuit to protect the valves and relays, which are
essentially solenoids. When solenoids are turned off with a switch, they act as inductors and
maintain current for a few milliseconds. This can induce significant reverse voltages on other
circuit components and decrease the usable life of the solenoid [7]. Flyback diodes allow the
current to dissipate safely by cycling current back through the solenoid (Figure 20).
Figure 20: Flyback diode schematic [7].
PCV Control Circuit
Finally, a current-variable voltage control circuit was designed with help from Professor Kim in
order to control the PCV from a computer. The pressure control valve requires an input of 0 –
1.05A at 24V, which is significantly different than the DAQ ranges. Therefore, both the voltage
and current output had to be amplified in order to control the valve with the computer. Using a
digital multimeter, the internal resistance of the valve was determined to be 21Ω. To aid with
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understanding the current control circuit, HITS focused on varying the voltage from 0 – 22V and
using the internal resistance to calculate the current.
HITS knew that a non-inverting amplifier circuit could be used to amplify voltage and that a
common-collector transistor circuit could be used to amplify current. However, the team of
mechanical engineering students was unable to effectively combine these circuits. HITS talked to
Professor Kim, who designed the full circuit (Figure 21, below). The circuit uses a CA320
operational amplifier to amplify voltage and an MJE802 transistor in a common-collector setup
to amplify current (equivalent parts were utilized in the simulated circuit below).
Figure 21: Voltage-current control circuit for pressure control valve.
The circuit was then simulated using LTspice to confirm the behavior of the circuit (Figure 22,
below). The green line is the NI DAQ output from the computer control system, which can be set
from 0 to 5V. The blue line shows the voltage after it has be amplified by the operational
amplifier part of the circuit. This range is approximately 0 – 23V. The red line shows the current
at the R3, which represents the internal resistance of the pressure control valve. The current
range is from 0 – 1.1A. Therefore, the circuit successfully amplifies both voltage and current into
the necessary ranges to control the pressure control valve. As seen in Figure 12, above, the
current must controlled from 0 – 1.05A (or, given the internal resistance, the voltage must be
controlled from 0 – 22V); this circuit, based on the simulation, accomplishes this goal. The
resistor values in the circuit were adjusted to avoid railing and nonlinearity in the outputs.
3.6k
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Figure 22: LTspice simulation results for voltage-current control circuit.
Next, HITS built the circuit on a breadboard with electrical components provided by the Calvin
Engineering laboratories (Figure 23, below). A 100W, 4A power supply provided the 24V input to
the operational amplifier and transistor. In order to protect the NI DAQ from accidents, the 0 –
5V computer signal was provided manually with a separate power supply. Using a digital
multimeter, HITS confirmed that voltage and current could be properly controlled with the
circuit. The black finned component at the bottom of the breadboard is a heat sink for the
transistor. Since over 20W of power is applied to the transistor, a great deal of heat is generated
that could damage the component. A piece of mica was placed between the transistor and the
heat sink to provide thermal conduction but electrical isolation. Later, however, it was found
that this heat sink was not large enough to adequately dissipate heat. A much larger heat sink
was bolted to the existing heat sink and thermal paste was used to ensure good thermal
conduction (Figure 24, below). This ensured proper temperature control of the transistor.
Figure 23: Voltage-current control circuit on breadboard.
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Figure 24: Voltage-current control printed circuit board mounted with large heat sink.
Printed Circuit Boards
When working on a breadboard, it is easy for components to accidentally come into contact
with each other. Since the circuit operates at significant voltage and current levels, this can be
dangerous to the components and to the user. In addition, breadboards can cause signal noise,
which could be detrimental to the finely tuned voltage electrical control needed for the test
stand’s pressure control valve. Finally, breadboards are messy and create a cluttered workspace.
HITS wanted the test stand to be a complete, cohesive, clean system. For these reasons, HITS
designed and constructed a printed circuit board for all system circuits (see Appendix 12.4). The
printed circuit boards significantly improved the safety, overall size, and aesthetics of the
circuits.
5.4.4 Sensor Calibration
After the amplification circuits were constructed, the pressure sensors needed to be calibrated
in order to accurately measure pressure values. The Calvin Metal Shop hydraulic lift was used
for this purpose. A pressure sensor was connected to the lift and raw voltage readings were
taken through the DAQ. Weights were added to the lift and the resultant voltage was recorded
(Figure 25). Because the hydraulic lift cylinder had a bore area of approximately one inch, the
weight increase corresponded to a nearly identical psi increase. Therefore, the calibration curve
shown in Figure 26 could be developed. A manual gage on the hydraulic lift also confirmed
pressure values.
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Figure 25: Pressure sensor calibration.
Figure 26: Pressure sensor calibration curve.
Additionally, the linear displacement sensor was calibrated with a tape measure and a DAQ
voltage output LabVIEW program.
0
200
400
600
800
1000
1200
1400
1600
1800
0 0.5 1 1.5 2 2.5 3
Pre
ssu
re [
psi
]
Voltage
Sensor PSI
Mech gage PSI
Linear (Sensor PSI)
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5.5 LabVIEW Control
LabVIEW is a visual programming tool for managing control systems and conducting laboratory
experiments. Its applications include data acquisition and analysis, instrument control,
embedded control systems, and automated test systems [8]. LabVIEW has a Front Panel with a
user interface and a Block Diagram that contains the graphical code. The HITS team designed a
LabVIEW program to control the test stand. The program included conditional structures,
Boolean switches for valve control and safety consideration, DAQ interfaces, and a PID control
system.
5.5.1 DAQ Interfaces
A key LabVIEW component was the interface with the DAQ. The DAQ Assistant Express VI was
used to import sensor signals. The signals were sampled at a rate of 100 Hz. Then, the signals
were routed through a low pass filter to reduce high frequency noise.
Two DAQ Assistant outputs were also used; one for analog output and one for digital output.
The analog output sent signals to the pressure control valve, while the digital output sent
Boolean values to the directional control valves and the pump.
5.5.2 Conditional Structure
A LabVIEW conditional structure is similar to an if/else statement in traditional programming.
Utilizing a conditional structure allowed the program to progress through several stages in the
test cycle; idle, extend, wait, and retract. Each stage altered the DAQ Assistant outputs,
changing the behavior of the prototype.
Idle
The Idle stage in the LabVIEW conditional structure is the default stage and is activated when
the LabVIEW program is executed. The Idle stage only turns on the small centrifugal pump. This
ensures that the force generating cylinders will immediately replenish fluid as the test begins.
The Idle stage switches to the Extend stage as soon as the “Start Test” button is activated.
Extend
After the “Start Test” button is pressed, the extend stage is activated. This stage turns on the
HPU and switches the directional control valves to the extend position. The test runs in this
stage until the cylinders extend six inches, or 3/4ths of their total stroke. The extend stage also
contains a PID controller to control pressure if loaded testing is desired.
Wait
The wait stage is activated once the cylinder is extended past 3/4ths of the stroke length. The
wait stage continues to extend the cylinders to their full stroke, but deactivates the PID
controller. This resets the pressure control valve, which allows for a consistent pressure ramp-
up during the next stage (regardless of pressure during the Extend stage). See calibration section
for further explanation of why this was necessary (Section 6.1).
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Retract
The retract stage is activated once the cylinder reaches its full stroke length. This stage keeps
the HPU active, but switches the directional control valves to the retract position. As with the
extend stage, there is also a PID controller if loaded testing is desired during cylinder retraction.
Once the cylinder fully retracts, the program goes back to the Idle stage. This loop allows for
multiple tests to be conducted without restarting the LabVIEW program.
5.5.3 PID control
A proportional-integral-derivative controller is a control system feedback mechanism that
attempts to minimize the error between a desired value (the set-point) and the actual value (the
process variable). In order to minimize this error, the controller alters a system variable [9]. For
the HITS prototype, the pressure control valve was controlled by a PID controller. In this case,
the set-point was a user-specified pressure value (e.g., 800 psi), the process variable was the
pressure sensor output from either the extend or retract side, and the system variable was the
analog voltage output from the DAQ to the PCV.
Guess Value Calibration
Initially, the PID controller was given full control over the modifiable variable (voltage output to
the PCV). However, this caused too much fluctuation. Therefore, a new system was devised to
use a PID controller to only fine-tune values. Guess values were determined by cycling the PCV
through its voltage range and recording pressure data (See Section 6.1.1). This is an approach
commonly used for hydraulic systems because the mechanical lag time during pressure buildup
causes a standard PID controller to oscillate rapidly between lower and upper signal limits in a
behavior known as “railing” [10]. When pressure is generated in a cylinder, it can take several
seconds to reach the full pressure. This can confuse the PID controller: it sees the low initial
pressure and outputs a high voltage to increase the pressure when in fact the system is still
building pressure. Guess values coupled with a small margin for PID control ensure system
stability and fine control over the response variable, which in this case is pressure.
PID Values
The PID controller was allowed to alter guess values by approximately +2%, -9%. While this
range varied slightly depending on test conditions, it is nevertheless a small percentage that the
PID can control. Ultimately, this decision created a more stable system with minimal oscillations
compared to the initial set-up.
Set Point Values
During the initial testing process of the prototype, it quickly became apparent that the control
system would need to be calibrated for a single pressure set point at first. This proved to be a
sufficiently challenging task for the scope of this project. HITS decided on a pressure set point of
800 psi because this point is within the controllable range for this particular pressure control
valve (Figure 31).
5.5.4 Boolean Control and Safety
LabVIEW utilized a digital output to control relays that powered the pumps and directional
control valve. The origins of these signals is in the case structure, so that the signals will alter
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based on the test stage. However, all signals were further modified to shut down if a stop
button was pressed. This software based emergency stop would terminate all digital signals,
fully open the pressure control valve, and shut down the LabVIEW program.
5.5.5 User Interface
An attractive feature of LabVIEW is its ability to easily build a user interface. It offers a wide
variety of switches, button, indictors, dials, and graphs that can be added to the Front Panel of
the program. HITS created a user interface with several groupings of such items (Figure 27 and
Figure 28).
Figure 27: Example of HITS user interface (LabVIEW Front Panel) while test is running.
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Figure 28: Example of LabVIEW graphical output while test is running (images move from left to right).
Start/Stop
This block contained a large stop button, a large stop button, and a button for writing the
collected data to a file. The stop button takes advantage of the Boolean logic described in
Section 0 to shut down the entire LabVIEW program and stop all analog and digital outputs from
the DAQ.
Manual Override
This block allows the user to set the maximum and minimum lengths to which the test cycle can
go. By setting the maximum length to zero inches, the test stand will automatically retract to the
cylinders’ fully retracted state.
Indicators
This block contained indicator lights for the test status (Idle, Extend, Wait, or Retract), which
components were turned on (Small Pump, HPU, Extend side of valves, Retract side of Valves),
and the relay output to each of these components (which should always match the previous
set).
PID Controller
This block contained controllable variables for the PID control system. This included the P, I, and
D values for both extend and retract cycles, as well as the guess value upper and lower limits.
Sensor Outputs
This block outputs sensor data to the user, from flow rates to pressures to while loop iterations.
This allows the user to easily monitor various processes and components in the test stand and
control system.
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Pressure Calibration Curves
HITS built calibration curves relating PID output voltages to resulting system pressures for both
the extend and retract stroke. These values can be adjusted by the user as needed; however, in
a final design, these values would be inaccessible to a normal user and would only be able to be
changed by a qualified control systems engineer.
Cylinder Information
In this block, the user can alter the dimensions of the test cylinder and the force generating
cylinders. These values alter the calculated force on the test cylinder according to standard force
calculations (see Section 5.5.6).
Output File Information
Here, the user can set names and units for each data stream that is outputted to an Excel file.
These names are automatically placed at the top of each column of data.
Graphs
Graphs are critical for monitoring the system, evaluating the effectiveness of the PID controller,
and detecting problems. The user interface included graphs for force, each pressure sensor
compared to the set point, displacement, velocity, and PID voltage output.
5.5.6 Force Calculations
Since the primary purpose of the hydraulic integrated test stand is to apply forces to cylinders,
force calculation is a critical component of the LabVIEW control system. First, the total area of
the force generating cylinders is calculated using basic geometry. Then, within the conditional
structure, the area is multiplied by pressure to calculate the force applied to the cylinder with
the moving wall. By placing this calculation within the conditional structure, the pressure signal
from the correct signal is automatically selected (2 ksi sensor for the extend stroke, 5 ksi sensor
for the retract stroke). This results in a single data stream for force throughout the duration of
the test cycle, rather than a separate data stream for the extend and retract portions of the
cycle. This data stream is then outputted to a graph in the Front Panel and written to an Excel
file.
5.6 Control System Assembly
The control system assembly consisted of a main electrical panel that held most circuits along
with the DAQ. Additionally, three power supplies were used for the circuits.
5.6.1 Main Electrical Panel
The DAQ is the center component on the main electrical panel (Figure 29: Main electrical
panel.). It sends signals to each of the four boards surrounding it. The top left board is the PCV
Control Circuit (see Section 5.4.3). The PCV Control Circuit receives a 0-5 V signal from the DAQ,
and outputs high power 0-24V to the PCV. The bottom left board contains the signal amplifiers
for the two pressure sensors (Section 405.4.3). The top right board contains parts to the 115V
relay circuits, which control both pumps and a valve. The bottom right board contains the relay
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circuits for the 24V valve. Finally, the bottom center connections contain inputs from the various
power supplies, along with a ground.
Figure 29: Main electrical panel.
5.6.2 Power Supplies
HITS utilized three power supplies for the circuits. Two were HP dual dc power supplies, the
third was a 100W, 25V power supply. One of the dual power supplies were used to supply ± 12V
to the sensor amplifiers. The other dual power supply provided a 5V signal when needed (for
sensors and relay circuits). The second output was used as a simulated LabVIEW analog output
for the PCV current control circuit for testing purposes. Finally, the 100W power supply provided
a signal to the 24V directional control valve, in addition to the PCV.
Figure 30: Power Supply.
5.6.3 Electrical Signal Interference
Electrical signal interference was discovered in the system during various calibration stages of
the project. When calibrating the pressure sensors, issues with floating voltages arose. When
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calibrating the PID controller, HITS discovered interference from the 100W power supply in
sensor readings.
Floating Voltages
During the pressure sensor calibration, the two HP power supplies provided inputs to the
system. Both HP dual dc power supplies were used to power the sensor and amplifier circuit,
and the sensor’s output was connected to the DAQ. The sensor was the only common point
within this system, resulting in erroneous voltage readings throughout the system. There was no
common ground. To solve this electrical issue, HITS connected all grounds together, including
the DAQ, sensors, and power supplies. The team ensured that the chassis ground was being
used, as well. This change to the circuit fixed the floating voltages problem, and calibration
could continue.
100W Power Supply Interference
HITS discovered that the 100W power supply signal interfered with sensor readings during the
PID calibration. Some of the high power wires were not heavily shielded and rested next to the
sensor outputs. The proximity caused higher than normal sensor noise. HITS fixed this issue by
rerouting the wires to be farther apart. However, aspects of the problem persisted.
Occasionally, the sensors would see an increasing noise oscillation up to 100 psi or 2% of the
sensor range. Then, the oscillation would decrease to a reasonable noise level. This process
would take about 30 seconds on average. HITS could not directly fix the issue, but determined
the source of noise was the 100W power supply. Resetting the power supply would immediately
eliminate the noise. Therefore, the team suspects that the power supply may not always be
performing as expected. It is possible that the ground on the 100W power supply occasionally
floats or oscillates in value, because it is not a true chassis ground. This could affect the rest of
the system, as the ground is the only common connection between the 100W power supply and
the sensors.
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6 Testing Results
6.1 Calibration Development
The primary function of the test stand is to take a user-entered pressure set point into the
LabVIEW control system and use the pressure control valve and hydraulic system to set and
maintain that desired pressure in the force generating cylinders. In addition to a fully functional,
leak-free hydraulic system and a robust, strong physical frame, extensive calibration was
necessary to achieve this goal.
6.1.1 Control Curve Development
As mentioned in Section 5.2.4, HITS developed a control curve that related the LabVIEW output
voltage to the resulting pressure in the FG cylinders. Using an external power supply, HITS
carefully adjusted the voltage applied to the voltage-current control circuit described in Section
5.4.3. Then, the resulting pressure was recorded using a LabVIEW indicator output. This data
was used to build the control curve seen in Figure 31.
At first, voltage increments of 0.5V were used. However, it quickly became clear that, at a
certain voltage level, very small increases in voltage resulted in very large increases in pressure.
HITS accounted for this exponential behavior by fine-tuning these sections of the control curve
with smaller voltage increments. Since HITS used a flow control valve rated up to 8 gpm of flow
instead of a properly rated pressure control valve, this calibration process was difficult. The
exponential behavior seen in Figure 22 is significantly more challenging to predict than the linear
behavior exhibited by an ideal PPRV in Figure 8. The pressure values in the control curve were
averaged from two or three tests, but still considered to be approximate.
Figure 31: Pressure-voltage control curve.
0
200
400
600
800
1000
1200
1400
1600
2 2.2 2.4 2.6 2.8 3 3.2 3.4
Pre
ssu
re [
psi
]
LabVIEW Voltage Output [V]
Extend
Retract
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6.1.2 Wait Stage Development
The exponential behavior of the control curve was complicated by the fact that individual tests
cycles, run in succession with no alternations to voltage supplied to the PCV, were not
generating the same pressure levels every time. At first, HITS attributed this to friction in the
rails, wobbling of the moving wall, voltage signal noise, and other potential factors. However,
after extensive experimentation, HITS determined that the pressure control valve behaves
differently when its supply voltage is ramped up from 0 V compared to when it ramps down
from a voltage of 3.5 V to 2.8 V, for example. The extend stroke, which occurs first, requires a
higher voltage to achieve a given pressure set point because the smaller area (due to the rod)
cause lower flow rates through the PCV. Then, when the test cycle switches to the retract stroke
and wants to maintain the same pressure set point, the LabVIEW control must reduce the
voltage supplied to the PCV. When this happens, the PCV is working against high pressure fluid
when attempting adjust the orifice size. HITS found that the pressure in the system was almost
always higher when the adjusting the voltage down rather than ramping the voltage up from 0
V. For this reason, HITS added the “Wait” stage to the conditional structure. The last few inches
of the extend stroke are unpressurized by the FG cylinders, allowing the PCV to return to its
original 0 V state.
6.1.3 Calibration Error
HITS also noticed major differences between tests conducted immediately after the system was
turned on compared to tests conducted after the system had been running for 30 minutes. At
first, pressures would spike to very high levels (greater than 2000 psi) very quickly. Later, after
running many tests in a row, pressures would be much closer to the set point. HITS believes that
this is due to fluid temperature and its effect on viscosity (Figure 32).
Figure 32: Effect of temperature on kinematic viscosity [11].
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When the pressure control valve limits flow rate through the valve body, energy must be
dissipated. In this case, it causes heat generation. HITS believes that the oil is at room
temperature when the test stand is first operated; then, as more and more cycles are run and
the PCV is used, the oil reaches a higher equilibrium temperature. The resulting change is
viscosity alters the behavior of the PCV. The control curve is only accurate for oil at the higher
equilibrium temperature. When the oil is at room temperature, the same LabVIEW output
voltage that normally results in a pressure of 700 psi might result in a pressure of 2100 psi. To
address this problem, the test stand should be equipped with thermocouples, temperature
control equipment, and a temperature control system in LabVIEW.
6.2 System Synchronization
Initial testing showed that the existing prototype hydraulic system was not able to self-
synchronize the FG cylinders. The original wall allowed for a very loose fit between the walls and
rails to minimize the effects of the rails on the hydraulic synchronization. The system was run
with the loosely fitting wall. The wall “walked” down the rails rather than rolled. The term
“walked” is used to describe the stepping motion of the wall. The rollers would contact the top
rail, where they would stop. The bottom FG cylinder would then extend faster than the top FG
cylinder until the bottom rollers contacted the bottom rail. The top FG cylinder would then
increase in velocity until it was extending faster than the bottom FG cylinder. The bottom roller
would remain in place while the top roller “steps forward.” This motion was repeated
throughout the stroke, giving the appearance of walking.
The result of this test showed that the hydraulic system had too many uncontrollable variables
such as fluid temperature, viscosity, and pressure losses. This resulted in pressure and flow
differentials to be capable of synchronizing the FG cylinders. As a result, HITS increased the
strength of the rails on the prototype and added an additional set of rollers to add stability to
the system. This extra stability provided by the rails minimized the walking effects of the wall.
Flow divider and combiner valves should be considered and tested for the full scale
implementation of this system. These valves may be capable of reducing the pressure and flow
differentials which result in the walking effects in the moving wall. The full scale system should
also be designed with rails strong enough to withstand a significant amount of moment caused
by an unsynchronized FG bank.
6.3 Proof of Force Generation Concept
The purpose of designing and constructing a test stand prototype was to evaluate several key
concepts of the design. The most important concept was the prototype’s ability to generate
forces on the test cylinder using a bank of cylinders, a pressure control valve, and a LabVIEW
control system.
As was explained in Section 6.1, HITS spent a significant amount of time calibrating the test
stand in order to achieve stable pressure generation. The PID controller successfully adjusted
the LabVIEW output voltage to the PCV to maintain a fairly constant pressure and force
throughout the duration of the stroke (Figure 33, below). The prototype could maintain these
values with an approximate error of ±5%.
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However, while the prototype’s ability to maintain a single value was excellent, its ability to
match an exact set point was limited. When given a pressure set point of 800 psi, the prototype
would often set and maintain a pressure value up to 300 psi above or below the set point. HITS
attributed this error to factors such as temperature variation and a rough calibration curve.
However, the team developed a method to further hone the prototype’s control system.
First, HITS found PID gain values that produced excellent response shape with no overshoot, fast
rise time, and fast settling time (Section 5.5.3). Then, HITS minutely adjusted the control curve
voltages and PID guess value limits to bring the “missed” pressure line closer to the set point.
This was a slow, delicate process because successive test cycles with the same parameters
sometimes resulted in “missed” lines above the set point for one test cycle and below the set
point for the next test cycle.
This process improved the overall accuracy of the pressure control, but the line was still often
held constant 100 psi above or below the set point. Regardless, HITS is confident that with
several improvements to the design (a properly rated PPRV, temperature control, and a fully
developed control system), the test stand could consistently meet the specified pressure. In
order for the control system to be able to successfully meet any pressure set point within the
operational range, extensive development would be necessary.
Nevertheless, the prototype successfully proved the concept of generating force with a bank of
hydraulic cylinders controlled by a pressure control valve and a LabVIEW control system.
Figure 33: Successful PID pressure control.
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7 Recommendations
As a result of this project and the lessons learned during prototyping, HITS suggests that BMP consider
the following findings while completing any future design work.
7.1 Maintain proper area ratio between test and force cylinders
HITS determined that the area ratio, defined as the effective piston area of the test cylinder
divided by the effective piston area of the FG cylinders, is critical to maintain acceptable
pressures and flows within the system. The area ratio changes between extend and retract due
to the rod’s effect on the effective areas. The area ratio is used in the following equations.
𝑃𝐹𝐺 𝑐𝑦𝑙𝑠 = (𝐴𝑟𝑒𝑎𝑅𝑎𝑡𝑖𝑜)(𝑃𝑇𝑒𝑠𝑡 𝑐𝑦𝑙) Equation 1
𝐹𝑙𝑜𝑤𝐹𝐺 𝑐𝑦𝑙𝑠 =
𝐹𝑙𝑜𝑤𝑇𝑒𝑠𝑡 𝑐𝑦𝑙
𝐴𝑟𝑒𝑎𝑅𝑎𝑡𝑖𝑜 Equation 2
HITS constrained the FG cylinders to operate at a pressure greater than 390 psi but less than
4000 psi and at a flow less than 30 gpm. These constraints, paired with the above equations and
the system requirements, led to an acceptable area ratio between 0.40 and 1.33. While these
limits on the area ratio hold true at all times when looking at pressure and flows, these bounds
on the area ratio do not eliminate FG and test cylinder combinations that would allow for
buckling.
Additionally, it was found that force’s sensitivity to pressure measurement uncertainty, cylinder
tolerances, and cylinder deformation increases linearly with an increasing area ratio.
Information regarding this relationship can be found in Section 4.2.3 and Appendix 12.7.
7.2 Use three or more banks of FG cylinders
HITS determined that at least 3 banks of two hydraulic cylinders will be needed in order to
maintain an area ratio between 0.40 and 1.33 for the desired product range. These 3 cylinder
banks were selected using the Excel Macro discussed in Section 4.2 and includes considerations
for rod buckling. Table 6 shows the suggested bore and rod combinations for the three cylinder
banks.
Table 6: Suggested force generating cylinder bank sizes.
Bore Rod
Bank #1 2.500 1.375
Bank #2 1.625 1.000
Bank #3 1.000 0.625
A 1.500 bore, 1.250 rod cylinder will have issues reaching the low pressures with this current
design as the pressures inside the FG cylinders would just drop below the minimum threshold of
390 psi. However, testing showed that the FG bank could feasibly be operated below this 390 psi
range, meaning the suggested combination of FG cylinders should still function for this
application.
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7.3 Test stand should be mechanically robust
The proposed test stand will be capable of generating very high levels of force. A 4.000 inch
bore cylinder pressurized to 5000 psi will generate over 30 tons of force. The walls of the test
stand, including the moving wall, must be able to withstand this force. HITS discovered the
importance of this detail after forgetting to install the designed wall reinforcements onto the
prototype. The side wall of the prototype deflected over 0.25 inches under high pressures.
Additionally, the prototype showed that the hydraulic system is not reliable enough to account
for synchronizing the FG cylinders with the current design. A system of very heavy duty rails will
be required to withstand the moments exerted on the wall by a hydraulic system which is out of
synchronization. Purchasing and installing flow splitting and combining valves rather than simply
relying on a machined T in a manifold may decrease the extent to which the system will rely on
rails to provide hydraulic synchronization.
HITS also suggests using solid guarding around the entire system to protect workers from any
forms of failure. This guarding should be solid rather than steel mesh to protect from oil leaks.
Several pinhole leaks in HITS’ hydraulic manifold proved the importance of this guarding early in
the prototype testing.
7.4 Use a proportional pressure relief valve
BMP generously donated a proportional flow control valve for the purpose of prototyping the
system. While the proportional flow control valve did allow for pressure control since it is a
proportional orifice, the calibration curve provided with the valve did not account for the valve
being used for this use. Purchasing a proportional pressure relief valve will likely save money in
engineering costs by reducing time needed to calibrate the system.
Additionally, the prototype operated on the extremes of the proportional flow control valve’s
operating window. Selecting a proportional pressure relief valve designed to operate within the
bounds of the system will help in calibrating the system.
7.5 Hire electrical and control systems engineers
The interface between LabVIEW, sensors, and valves requires extensive circuit design and
selection. Investing in the time of an electrical and control systems engineer will likely pay off
long term as these engineers will be able to solve the electrical problems faster and more
effectively than HITS was capable of doing. HITS suggests assigning the following tasks to an
electrical or controls engineer.
1. Data Acquisition Device selection
2. Sensor selection and calibration
3. Relay design or selection
4. Proportional voltage or current control design and calibration
5. Full LabVIEW system development, with proper error handling
6. PID controller calibration
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7.6 Use DC valves instead of AC valves
HITS burned out a Parker D1VW directional control valve which was powered using 115V AC
power. In response to this accident, HITS learned from Michigan Fluid Power (MFP) that AC
valves allow for an influx of current when the valve is triggered. This influx of current generates
heat. This means that if an AC powered valve is triggered on and off rapidly, heat will build up
faster than it can dissipate, ruining the coil in the valve. Because this test stand is being designed
to allow for continuous cycle testing, HITS suggests that all valves should be powered by DC
power to prevent having issues with influx current.
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8 Costs
This chapter contains cost information for the hydraulic integrated test stand project. While several
components were purchased by HITS within the $500 budget provided by the Calvin College Engineering
Department, most components were provided by generous external sources.
Table 7: Total cost of hydraulic integrated test stand.
Component Provider Quantity Unit Cost [$] Total Cost [$]
Hydraulic Power Unit Mason Dynamics 1 0 0
Directional Control Valve Mason Dynamics 1 0 0
Hoses Mason Dynamics 8 0 0
Hose Fittings Mason Dynamics 0 0
Hydraulic Cylinders Best Metal Products 3 0 0
Pressure Control Valve Best Metal Products 1 0 0
Directional Control Valve Michigan Fluid Power
Automation Engineering 1 0 0
Electrical Components and Power Supplies
Calvin Engineering Department
Many 0 0
Solenoid Valve Connector Calvin Budget 3 4.16 12.48
UniMeasure Linear Transducer Calvin Budget 1 69.99 69.99
National Instruments Data Acquisition Device
Calvin Budget 1 199.00 199.00
OMEGA 2000 psi Pressure Transducer
Calvin Budget 1 175.00 175.00
OMEGA Power Relay, 15A Calvin Budget 2 4.48 8.96
OMEGA Power Relay, 10A Calvin Budget 4 1.48 5.92
Aavid Thermalloy Mica Insulator Mounting Kit
Calvin Budget 1 2.40 2.40
Hydraulic Integrated Test Stand Prototype 473.75
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9 Conclusion
In order to evaluate the success of the project, HITS refers to Section 2.4 for the list of project
requirements. Each requirement is listed below and is followed by an evaluation of HITS’ success
in achieving the requirement.
Req 1. Device shall perform compression and tension loaded testing with a force accuracy
of 5%.
The prototype designed, constructed, and calibrated by HITS successfully maintained
force values with an accuracy of 5% throughout the stroke length. The PID controller
successfully held the force at a single value. However, the prototype was unable to
match the set point during every test cycle, often missing the desired pressure value
by 100 psi or more. In addition, the prototype was only calibrated for one pressure set
point. Selecting a proportional pressure relief valve rather than a proportional flow
control valve and investing more time in establishing a calibration curve could
improve the force control of the system. Additionally, fluid temperature control would
increase the repeatability of the system by controlling the temperature, and therefore
the viscosity of the fluid.
Req 2. Device shall allow for loaded testing when the test cylinder is both extending and
retracting.
The prototype successfully showed that the proposed design is capable of loaded
testing when the test cylinder is both extending and retracting.
Req 3. Device shall accept test cylinders within ranges seen in Table 1.
Analysis showed that the proposed design should be able to fulfill the requirements in
Table 1 with three banks of two FG cylinders. See Section 4.2 for more details.
Req 4. Device shall measure the stroke of the test cylinder to an accuracy of less than 1/16
inches.
No testing was performed with the prototype to confirm this requirement can be
achieved. However, research shown in the Project Proposal and Feasibility Study
showed that there are many linear displacement sensors capable of this accuracy.
Additionally, the linear sensor used in the prototype did not show significant error and
was used to accurately and confidently control the direction of wall movement.
Req 5. Device shall record and locally store displacement and force information for each
test.
The LabVIEW program constructed for the prototype was capable of recording and
locally storing the system pressures, force exerted, linear displacement, and velocity
of the system.
Req 6. Device shall operate in a safe manner under normal conditions.
The finished prototype did not show reasons for safety concerns under normal
operating conditions. This was achieved by properly sizing load bearing members,
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ensuring proper pressure ratings for all hydraulic components, and by implementing
shields to protect users from any potential mishaps. Limits were implemented in
LabVIEW to prevent excess voltage output to the pressure control valve.
Req 7. Device shall safely deactivate the hydraulic system in case of an emergency stop.
The prototype system implemented physical and virtual emergency stop buttons. An
emergency stop deactivates all pumps supplying hydraulic power to the system.
However, activating an emergency stop left the directional control valves open,
allowing for an operator to manually move the moving wall if necessary.
Goal 1. Device should minimize floor space requirements.
The proposed design uses FG cylinders which surround the test cylinder rather than
sitting juxtaposed to the moving wall. This allows the proposed test stand to be much
shorter as it does not require extra length to store the FG cylinders.
Goal 2. Device should be intuitive and easy to use.
The graphical control system supplied in LabVIEW allows for intuitive system starts
and stops. It also conveniently provides access to graphs and indicators showing key
system parameters. The physical loading and unloading of a cylinder into a test stand
was not covered in this project.
Goal 3. Device should minimize cost while maintaining safety and performance.
No comparison exists to evaluate this goal since no alternative system designs were
explored with enough depth to understand the cost, safety, and system performance.
Goal 4. Device should minimize changeover time necessary between tests.
The loading and unloading of cylinders into the test stand was not covered in this
project.
The combined courses of Engineering 339 and Engineering 340, commonly known as Senior
Design, was instrumental in helping Team 7 learn several valuable lessons. These lessons
spanned beyond learning how to work with and design hydraulic and electronic systems. The
members of HITS improved skills as team players and as project managers.
First, HITS learned to ask early and to ask often. We learned to quickly recognize when we don’t
know something and seek help when needed. We learned that there are a lot of things which
are commonly known to people in the hydraulics or electronics industries which were beyond
our knowledge. For example, we didn’t know that AC powered directional control valves can
overheat due to influx current if actuated too frequently. After burning a valve out for this very
reason, we learned that this is fairly common knowledge among hydraulic engineers. Asking
more questions earlier may have prevented this mistake. This lesson will be valuable as
inexperienced engineers about to enter new realms of engineering.
Second, HITS learned to order spare parts when possible. HITS experienced several delays while
waiting on parts to come after components failed. Several of these components cost less than
$5.00, so purchasing spare parts early on would have been feasible. Additionally, purchasing
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spares would have been more cost effective for Calvin College since it cost Calvin money to
process each new purchase order.
Third, HITS learned to set short term goals. Short term goals help to keep team members
focused and motivated. Short term goals allow for many mini-successes throughout a project,
preventing team members from becoming discouraged at a lack of perceived progress.
Additionally, short term goals help team members deliver results to other team members,
helping work to flow more efficiently.
Finally, HITS learned the importance of meeting with the client frequently. Engineering projects
are often very vague and difficult to define. Meeting with a client to give status updates and ask
questions prevents a team from spending too much time on a solution which may not meet the
client’s needs. This communication is most important during the beginning of the project, but it
is still important to maintain through the project’s completion.
Overall, HITS deems this project a success from both an engineering and educational standpoint.
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10 Acknowledgements
Calvin College has provided significant opportunities and learning experiences that have gone above and
beyond a normal undergraduate degree. We are incredibly thankful for all of the faculty and staff of the
college who have been instrumental in our education by intentionally contributing to our learning within
and outside of the classroom. Particularly, we would like to thank Professors Nielsen and Tubergen for
their direct support on our senior design project.
Best Metal Products has also largely contributed to this senior design project by providing a problem to
solve, along with many resources for support. We would like to thank Kurt Skov in particular for advising
on the project and offering his wisdom in designing various hydraulic components. Kurt was also
instrumental in obtaining a proportional flow control valve to use in the prototype in place of the
proportional pressure relief valve. Best Metal Products also donated three cylinders with very short
notice to the project.
Mason Dynamics, Inc. provided valuable resources to the prototype construction. We would like to
thank John Raider (J.R.) of Mason Dynamics in particular for his willingness to help with very short
notice. J.R. donated the HPU used in the prototype, as well as all of the fittings and hoses. J.R. also
advised the team on which fittings would be best for the given applications.
Michigan Fluid Power Automation Engineering (MFP) donated engineering time to review the project’s
hydraulic design to ensure safety and functionality. HITS would like to thank Roger Betten Jr, Chris
Rozema, and Andrew Hildebrandt for the time and guidance given on this project. Additionally, HITS
would like to thank Chris Rozema and MFP for obtaining a replacement valve within a matter of hours
when HITS burned a valve out.
Phil Jasperse and Chuck Holwerda gave much needed help in the areas of manufacturing the frame,
hydraulic system, and electronic controls. HITS would not have been able to construct their prototype
without Phil and Chuck’s experience.
Professor Kim, Professor Brouwer, and Jeremy Ward also contributed significant amounts of time
helping HITS develop the needed electronic systems to make the prototype function. Jeremy Ward
contributed to the relay design. Professor Brouwer contributed to the design of sensor amplification
circuits. Professor Kim contributed to the current amplifier required to control the pressure control
valve.
In addition, we would like to thank our families and friends for their support and encouragement in
undertaking this project.
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11 Works Cited
[1] Eaton Vickers, "Proportional Pressure Relief Valves - Technical Catalog - KBCG-3-1*," 2003.
[2] Parker Hannifin Corporation, "Electrohydraulic Motion Controls: Proportional Directional &
Pressure Control Valves, Servovalves, Electronics, Accessories," 2014.
[3] Rexroth Bosch Group, "Proportional pressure relief valve, directly operated, without/with
integrated electronics (OBE)," 2013.
[4] SunSource, "Pressure Control Valves," [Online]. Available:
http://www.sunsourceconnect.com/advancedwebpage.aspx?cg=84&cd=3&SBCatPage=. [Accessed
26 March 2015].
[5] Command Controls Corp., "Electro-Hydraulic, Proportional, Pressure Comp, Flow Control Valve -
EPFI-10," 2005.
[6] National Instruments, "NI USB-6008," [Online]. Available:
http://sine.ni.com/nips/cds/view/p/lang/en/nid/201986. [Accessed 3 March 2015].
[7] Wikipedia, "Flyback Diode," Wikimedia Foundation, [Online]. Available:
http://en.wikipedia.org/wiki/Flyback_diode. [Accessed 11 May 2015].
[8] National Instruments, "LabVIEW System Design Software," 2014. [Online]. Available:
http://www.ni.com/labview/. [Accessed 5 November 2014].
[9] Wikipedia, "PID Controller," Wikimedia Foundation, [Online]. Available:
http://en.wikipedia.org/wiki/PID_controller. [Accessed 11 May 2015].
[10] P. Nachtwey, "Closed-loop tuning secrets revealed!," Hydraulics&Pneumatics, 19 Sept 2006.
[Online]. Available:
http://hydraulicspneumatics.com/200/IndZone/Entertainment/Article/False/31840/IndZone-
Entertainment. [Accessed 11 May 2015].
[11] M. C. MEng, "Viscosity of Hydraulic Oil," Webtec, [Online]. Available:
http://www.webtec.com/en/tech/reports/viscosity. [Accessed 12 May 2015].
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12 Appendices
12.1 Hydraulic Power Unit Sizing ………………………………………………………………………………………….. 66
12.2 Wall Deflection Calculations ………………………………………………………………………………………….. 68
12.3 Excel Macros ………………………………………………………………………………………….. 69
12.4 Electronic Circuit schematics ………………………………………………………………………………………….. 73
12.5 Cavitation Calculations ………………………………………………………………………………………….. 77
12.6 LabVIEW program ………………………………………………………………………………………….. 78
12.7 Sensitivity Derivation ………………………………………………………………………………………….. 82
12.8 Datasheets ………………………………………………………………………………………….. 87
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12.1 Hydraulic Power Unit Sizing
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12.2 Wall Deflection Calculations
The moving wall and side wall of the prototype were initially modeled using a simply supported
beam equation. However, the width of the walls are more than 4 times the thicknesses,
meaning the simply supported beam equation does not accurately model the wall deflections.
Instead, the walls would need to be modeled with much more complicated simply supported
plate equations. To simplify calculation, the width of the modeled wall was reduced to allow the
simply supported beam equation to be used. A copy of the modified simply supported beam
calculations is shown below.
Parameter Value Unit
Wall Thickness 0.5 in
Wall Span 11 in
Wall Width 1 in
Moment of Inertia (I) 0.125 in4
Modulus of Elasticity (E) 2.90E+07 psi
Maximum Pressure 1000 psi
Cylinder Bore 2.5 in
Cylinder Area 4.908739 in2
Maximum Force 4908.739 lbf
Maximum Deflection 0.03125 in
Moment of Inertia
Required 0.150196 in4
FS 0.832245
Factor of Safety is < 1. The wall required additional supports.
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12.3 Excel Macros
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12.4 Electronic Circuit schematics
Figure 34: Differential amplifier circuit for pressure sensors (schematic).
Figure 35: Differential amplifier circuit for pressure sensors (board layout).
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Figure 36: Relay trigger circuit for 115V components (schematic).
Figure 37: Relay trigger circuit for 115V components (board layout).
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Figure 38: Relay circuit for 115V components (schematic).
Figure 39: Relay circuit for 115V components (board layout).
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Figure 40: Relay circuit for 24V valve (schematic).
Figure 41: Relay circuit for 24V valve (board layout).
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12.5 Cavitation Calculations
Vapor Pressure Oil: -100 kPa
Minimum oil pressure: -50.87 kPa
Cavitation is not a concern
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12.6 LabVIEW program
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12.7 Sensitivity Derivation
The simulated force’s sensitivity to the pressure measurement uncertainty, cylinder
manufacturing tolerances, and estimated cylinder deflections was found using the error
propagation methods learned in Engineering 382: Engineering Instrumentation Laboratory. The
following pages shows a detailed calculation of this sensitivity. The derivation resulted in
Equation 3.
𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦 =
[ (𝜋
4(𝑁1 (𝐵𝑜𝑟𝑒1
2 − 𝑅𝑜𝑑12) + 𝑁2 (𝐵𝑜𝑟𝑒2
2 − 𝑅𝑜𝑑22) + 𝑁3 (𝐵𝑜𝑟𝑒3
2 − 𝑅𝑜𝑑32))) 2
∗ (𝐸𝑟𝑟𝑜𝑟𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝑆𝑒𝑛𝑠𝑜𝑟2 + 𝐻𝑦𝑠𝑡𝑒𝑟𝑒𝑠𝑖𝑠𝑃𝑃𝑅𝑉
2)𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝐹𝐺2
+ 𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝐹𝐺2 (
𝜋 𝑇𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒𝐵𝑜𝑟𝑒𝑠
2√𝑁1
2𝐵𝑜𝑟𝑒12 + 𝑁2
2𝐵𝑜𝑟𝑒22 + 𝑁3
2𝐵𝑜𝑟𝑒32)
2
]
2
Equation 3
The variables in Equation 3 are defined as:
𝐵𝑜𝑟𝑒𝑖 and 𝑅𝑜𝑑𝑖 designate the bore and rod sizes, in inches, for the FG bank.
𝑁𝑖 designates whether the FG bank is active. 𝑁𝑖 = 2 designates an active system while
𝑁𝑖 = 0 designates that the system is not active in that configuration.
𝐸𝑟𝑟𝑜𝑟𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝑆𝑒𝑛𝑠𝑜𝑟 designates the uncertainty of the pressure sensing measurements
based on the sensors’ data sheets.
𝐻𝑦𝑠𝑡𝑒𝑟𝑒𝑠𝑖𝑠𝑃𝑃𝑅𝑉 designates the hysteresis of the proportional pressure relief valve. This
accounts for non-repeatable actuation of the valve.
𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒𝐹𝐺 designates the pressure in the FG cylinder bank.
𝑇𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒𝐵𝑜𝑟𝑒𝑠 designates the uncertainty in the measurement of the cylinder bores.
This includes manufacturing tolerances and estimates of jacket deflection under
pressure.
The force sensitivity was then plotted as a function of the area ratio. This plot can be seen in
Figure 42.
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Figure 42: Potential Percent Error in Force as a function of the Area Ratio
y = 0.0164x - 0.0007R² = 0.9993
-5%
0%
5%
10%
15%
20%
25%
0 2 4 6 8 10 12 14
Po
ten
tial
Per
cen
t Er
ror
in F
orc
e
Area Ratio
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12.8 Datasheets
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