Feasibility Study of Replacing an Industrial Hydraulic Lift System with an Electro-Mechanical Lift System

Critical Design Review

Thursday, 21 September 2000

Professors:

Dr. Ram & Dr. Buckner

Students:

Jeremy Bridges & David Herring

OverviewProblem StatementPotential Candidate DesignsSelecting Candidate DesignsFinalizing Design SolutionProposed Design ImplementationConclusionQuestions & Comments

Problem Statement

Hydraulic lift systems occasionally leak fluid. This raises environmental issues. A high number of NACCO’s customers are concerned with this issue and have expressed a willingness to pay a little more for an electro-mechanical lift system. NACCO now would like to research the feasibility of replacing this hydraulic lift system with an electro-mechanical lift system in the most cost effective way so the customer can justify the increased cost.

Potential Design Solutions

1. Ball Screw Jac

2. Machine Screw Jac

3. Electric Cylinder Linear Actuator

4. Cam/Cylinder Lift

5. Rack and Pinion

6. Cable/Chain Lift

7. Scissor Truss (Car Jack)

Ball Screw Jac 1. Accurate lifting with little drift 2. Smooth performance 3. Little horsepower required from motor (1/3 Torque needed

compared to Machine Screw Jac) 4. Compact system 5. Can operate at high speeds 6. Capable of lifting more than 2 tons that lift desires 7. Horizontal input with vertical output 8. Duty cycle can be extended longer than Machine Screw Jac 9. Corrosion resistant 10. Long predictable life 11. A motor needs to be added 12. Reasonable cost 13. Reasonable size that can work within space constraints

Machine Screw Jac 1. Accurate lifting with little drift 2. Smooth operation 3. Compact system 4. Self-locking during manual operation with no vibration when using

20:1 or higher gear ratio. 5. Will not back-drive during mechanical failure with 20:1 or higher ratio. 6. Corrosion resistant 7. Preferred for static vibration 8. Slower travel speed compared to hydraulic, ball screw, or electric

cylinder actuator 9. A motor needs to be added 10. Reasonable cost 11. Reasonable size that can work within space constraints

Electric Cylinder Linear Actuator

1. Extremely accurate

2. High cost

3. Smooth operation

4. Limit switches included

5. Requires input voltage rather than a shaft or other mechanical input

6. Integrated motor

7. Includes ball screw with long life

8. Recommended as ideal solution to hydraulic (per Nook Linear Motion Design Guide, pg. ajec-6)

9. Perfect size that can work within space constraints

Cam/Cylinder Lift 1. Smooth operation

2. Will back-drive without brake during mechanical failure

3. Medium cost

4. Relatively equal travel time compared to hydraulic system

5. Size that may cause problems within space constraints

Rack and Pinion

1. Best during manual operation

2. Mechanical brake preventing back-drive on pinion

3. Low cost

4. Fast travel cycle time

5. Reasonable size that can work within space constraints

Cable/Chain Lift 1. Requires new lift point for lift truck forks

2. High torque

3. Cable wrapping is potential problem

4. If cable or chain break there is a sudden and quick back-drive

5. Medium cost

6. Slower travel time compared to the hydraulic system

7. Reasonable size that can work within space constraints

Scissor Truss (Car Jack) 1. Will not back-drive

2. Can be operated manually

3. Needs large amount of space for mounting

4. Low cost

5. Slower travel time compared to the hydraulic system

6. Size not ideal to work within space constraints

Criteria for Decision Matrix Cost (5%): evaluated on single mechanism basis for

general price ranges

Safety (40%): evaluated on back driving risk during a mechanical failure

Performance (20%) : educated comparison against current hydraulic system

Reliability (35%): evaluated with expected life and risk for a mechanical failure

Candidate Design Selection

Scale: 1 = poor

5 = neutral

10 = best

Average Cost Safety Performance Reliability RankWeight 0.05 0.4 0.2 0.35 1

Ball Screw Jac 6 7 9 9 7.65Machine Screw Jac 6 9.5 8.5 8.5 8.975Rack & Pinion 7.5 3.5 7.5 4 3.875Cam/Cylinder Lift 7.5 3 6.5 3.5 3.4Chain/Cable Lift 9 3 7 4 3.65Electric Cylinder Linear Actuator 1.5 7 9.5 9.5 7.6Scissor Truss (Car Jack) 9 8 5.5 6.5 7.525

Candidate Design

1. Ball Screw Jac

2. Machine Screw Jac

3. Electric Cylinder Linear Actuator

Selecting Final Design Size (45%) : evaluate component size and spacing

requirements

Ultimate Cost (30%) : overall cost including additional hardware

Ease of Assembly (5%) : implementation of design

Performance (10%) : travel speed and load handling

Safety (10%) : ability to back-drive

Final Design Decision Matrix

Ultimate Cost

Overall Size

Performance SafetyEase of

AssemblyRank

Weight 0.3 0.45 0.1 0.1 0.05 1

Ball Screw Jac 6.75 3 4 7 6 4.2375

Machine Screw Jac 7 7 4 7.5 7 7

Electric Cylinder Linear Actuator

1 7 9 4 7 6.7

Hydraulic Cylinder 10 10 9 9 9 9.65

Scale: 1 = poor 5 = neutral 10 = best

Ball Screw Jac

Clevis (2)

Drive shaft

Aluminum Housing

Ball Screw Jac - Space Issue

Fork support unit

Ball Screw Jac

Interference w/ Drive Unit

Machine Screw Jac

Aluminum Housing

Drive Shaft

Clevis (2)

Machine Screw JacLower Mounting Option 1

Upper Linkage

Fork Unit Support

Machine Screw Jac

Lower Mounting Bracket(Option 1)

Bracket welded to existing chassis

Option 1:

Stress Analysis must be conducted to select appropriate geometry and ensure structural rigidity

Material must be cut away from interior flanges of fork unit support

Weld strength must be determined

Machine Screw Jac Lower Mounting (Option 2)

Upper Lift Linkage

Fork Unit Support

Machine Screw Jac

Lower Mounting Bracket(Option 2)

Welded to Chassis

Option 2:

Stress Analysis must be conducted in order to determine correct thickness and geometry of bracket

No material will need to be cut away from fork unit support

Strength will be main concern and testing must be conducted

Possible Interference with drive unit at maximum turn radius

Upper Mounting BracketOption 1

Will require additional hole drilled in fork unit support and filling of existing hole

May allow additional undesired degrees of freedom

Upper Mounting BracketOption 2

Additional hole will be drilled and existing hole will be used (No filling will be needed)

More rigid support than Option 1

Machine Screw Jac Assembly

Upper linkage

Fork Unit Support

Machine Screw Jac

Upper Mounting Bracket

Lower Mounting Bracket

Motor InformationBrake Motor

3-Phase, AC Induction 1.5-2 HP depending on desired speed 230/460 VAC Input Voltage NEMA 56-C Motor Size Recommended by Nook Industries (~$1000) Would require DC-AC Inverter (~$500)

Brush DC Motor 1.5-2 HP depending on desired speed 24 VDC Input Voltage Needs to be researched further

Note: More Motor Information will be provided later

Cost of Final Design (Prototype)

Machine Screw Jac: $500AC or DC Motor: $600-$1200 (depending on HP requirements)Limit Switches: $100-$200Fabrication: $200 (if needed)DC-AC Inverter: $200-$300 (if needed)Misc. Hardware: $50

---------------Estimated Total Cost: $1250-$2450 (depending on configuration)

Conclusion

We recommend the Machine Screw Jac as the electromechanical solution

Option 1 - Lower Mounting Bracket

Option 2 - Upper Mounting Bracket

We desire feedback from NACCO on the configuration we have selected before we proceed with prototyping

Questions or Comments???Questions or Comments???

Web Site:

http://www.mae.ncsu.edu/courses/mae586/buckner/index.html