Vimantra 2010 NITK Entry

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Title of the Application: Study of FPGA based vibration control of amass varying two-degree of freedom system

Name of Institution:NITK Surathkal, Mangalore, 575025(KARNATAKA)

Author(s): Prashant Kumar Tripathi1, Ashwin B N1, Mayand PratapSingh1, Dr. Gangadharan K V31Post-graduate Student, Department of Mechanical Engineering.3Professor, Department of Mechanical Engineering.

Contest Category: Student

NI Products used

NI LabVIEW 2009 NI CompactRIO 9012 NI 9215 NI 9505 NI 9477

The ChallengeVibration isnt always easy to predict, which is why engineers must bothdesign systems to eliminate vibrations and also use vibration isolation to

control the problem after a system is designed to the best of theengineers ability. There may be serious problems in these areas due tovibration-

Tall and slender free-standing structures (bridges, pylons ofbridges, chimneys, TV towers) which tend to be excited dangerously

in one of their mode shapes by wind,

Steel structures like factory floors excited in one of their naturalfrequencies by machines , such as screens, centrifuges, fans etc.,

Ships exited in one of their natural frequencies by the main enginesor even by ship motion.

This proposed system can control the vibration of base excited mass

varying 2-DoF system in these cases at wideband range of frequencies.

The SolutionThe system has been designed to be used as tool to demonstrate the

capability of mass variable tuned damper for wide frequency application.For changing the mass of systems, specially designed water containerswith controllable inlet and outlet flow has been used. The inlet flow to thecontainers was controlled by pumps and outlets were controlled bysolenoid valves. All valves and pumps were controlled by a CompactReconfigurable Input Output device (cRIO) with onboard FPGA (Field

Programmable Gate Array). CRIO with FPGA enable the designer toimplement different control algorithms that can be used for real time wide


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spectrum vibration control. LabVIEW with real time suite was used foralgorithm implementation and device control. A variable speed motor with

rotating unbalance was used as the excitation to the system.Mass variation has been achieved through variation of water level in thecontainer hence the effect of water in the system toward modifying the

characteristics of the system was also studied. To create a fully filled

container at every water column height a floating roof was used. Its effecton damping was also studied.This system is also used to perform different real-time controlexperimentation, as use of sensors, PWM generation, level control of

liquid in a tank and as tuned mass damper.

Introduction

Controlling of vibration in any system is very challenging problem. Thereare many methods of controlling the vibration such as passive control,active control, and semi-active control of vibration. In passive control no

external energy is required and these are best within the frequency region

for which it is designed. In active control system an additional active forceis introduced as a part of absorber subsection. The absorber is controlled

using different algorithms to make it more responsive to primarydisturbances. The disadvantage of this system is that energy required forcontrol action and the complexity of the control system coupled with high

cost of implementation. Semi-active control system has continuouslyadjustable elements like stiffness, damping or mass. There are two widelyused methods (i) variable rate damper and (ii) variable rate springelements. In variable rate damper vibratory energy is dissipated byincreasing the damping present in the system. In case of variable rate

spring elements, variation in stiffness shifts the natural frequency away

from the excitation frequency. There is another possibility of changing themass of the system to shift the natural frequency to desired value.

In the present work a design, fabrication and testing of a variable mass 2-DoF system was presented.

System ConfigurationThe system setup consists of the following shown in Figure 1:

CompactRIO 9012 NI C Series module (NI 9505,NI 9477,NI 9215) Laser pick-up (L-GAGE model LG10 series) Universal motor(either AC or DC power) Two Solenoid Valves Two Small Submersible pumps

Sensors and data acquisition are very much important for measurementor feedback in control. Actuators are used to regulate the processaccording to feedback from the sensors. In this project two solenoid

valves and two small submersible pumps were used to control water flowin tanks. A universal motor was used to produce disturbance at primarysystem. Control of these valves and pumps was done by NI CompactRIO


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9012, with different NI modules. NI 9505 was used for motor speedcontrol by PWM generation, NI 9477 is used for digital output to control

pumps and solenoid valves and NI 9215 is used for analog input from thelaser pickup.

Fig. 1 System setup

Pumps used here were AC pumps but output was digital output, whichwas taken from NI 9477, so DC driven relays were used to control AC

pumps. Output form NI 9477 first go to relay and from relay to pumpFigure 2. There was some delay in control system which was due to use ofseparate relays and due to time taken by water to reach in to tank. These

delays were added in program so pumps on time was increased tocompensate this delay.

Fig. 2cRIO 9012 With NI C Series module (NI 9505, NI 9477, NI 9215)


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System Implementation1. Use of LabVIEW FPGA with LabVIEW Simulation Module

A simple analog input and analog output operation written with LabVIEWFPGA is shown in Figure 3. The analog I/O will run at the maximum rateallowed by the FPGA since a timing VI has not been added to the

program. The timing is then limited only by the conversion rate for I/O on

the FPGA-based device.

Fig. 3 Simple analog input and digital output VI in LabVIEW FPGA for I/O

Figure 4.shows the front panel for this VI when the analog output is takenfrom laser pickups by using NI 9215 module. The user can adjust theswitches to give the digital output to the motor and pumps and stop

buttons are given to stop the operation instantaneously.Once the basic entities have been specified in the FPGA target, the nexttask is to create a host controller as it gives more flexibility (more

features) in the architecture of LabVIEW program using FPGA interfacemethod.

Fig. 4 Front panel of Analog input and Digital output VI in LabVIEW FPGA


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2. Mass control of the systemHere, water was used as a variable mass. So for controlling the water

mass, water height has to be controlled in the tank. An open loop systemwas used for controlling water height after collecting all the data fromvalves output and pumps input.

For adding mass to the system water was pumped inside the tank. For

this purpose mass flow rate of the pump was calculated. Theprogramming was done in such a manner that it gives synchronismbetween the varying mass and on time of pump. The scenario is differentin the case of outflow. The water outflow depends on the height of the

water and there is no linear relationship. Hence the outflow rate wasmeasured at every 5 mm reduction in height and the results weretabulated in 1-D lookup table using LabVIEW. Block diagram made byusing LabVIEW can be seen in figure 5.For this system a 2-D lookup tablewas made, after collecting all the data, some qualified data has beenchosen for putting in control table. All qualified data was given in lookup

table. When this program will run the output data was chosen according

to the motor speed (on X-Axis) and bottom water height (on Y-Axis).

Fig. 5 Water height control or mass control VI

3. Control and data representation front panelA front panel of the tank control and acquires data from laser pickup is

shown in figure 6. Motor control was done by a slider on front panel;speed of the motor varies according to the slider movement. In figure 7

top graph represents time domain data of primary system acquired bylaser pickup and bottom graph represents time domain data of absorbersystem. Primary system mass can be fixed by fixing height of water inprimary system and absorber water height changes according to the

required value at that instant for controlling the vibration. In figure 8frequency domain data from the sensors are presented with differentcontrol and indicators to monitor the control process.


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Fig. 6 Front panel with time domain data and tank level control

Fig. 7 Front panel with frequency domain data and motor control


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Benefits of using Graphical System Design approachThe NI LabVIEW environment makes interfacing with any hardware

measurement simple, besides quickly acquiring and generating signals aswell as allowing configuration-based data acquisition. Field programmablegate arrays (FPGAs) are being used for an increasing number of

embedded control and monitoring systems. They are less expensive than

ASICs in terms of development and can also be reprogrammed in thefield. FPGAs also have advantages over microprocessors in that all of thecontrol logic is implemented in hardware.

ConclusionThis system can be used at offshore applications to control the vibration.It can also be use in structures where time delay is permitted to control

the vibration. This time delay is due to inlet and outlet flow rateconstraints of the system.The setup is kept prepared for remotely use forSOLVE (Student Online Laboratory through virtual experimentation), so

students can perform real time experimentation through internet. This

system has the capability of performing different experiments.

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