Laboratory 6a Closed Loop Analog Control Of DC Motor Velocity
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1. 4 To drive the motor using the analog voltage output from the DAQ board connect your motor control module to the CB 68LP connector block according to Table 1 Table 1 CB 68LP connector block pin assignments for open loop control of DC motor velocity DC Motor Control Module Vin socket Analog voltage on MOTOR DRIVE INPUT panel Vour socket Analog voltage on TACHOGENERATOR OUTPUT panel Ground on DC power supply AIGND Ground on DC power supply AOGND The connector block can also be grounded to the breadboard if the breadboard is grounded to the DC power supply 5 Before connecting the DC power supply to the motor module turn ON the DC power supply and make sure the variable output terminals are properly configured to provide 12 V and 12 V Turn OFF the DC power supply then connect the power supply to the DC motor module Make sure that no wires or cables interfere with the moving parts of your motor Turn ON the DC Power Supply oman a Make sure the Eddy Current Brake is disengaged That is make sure it is in the 0 position 10 Connect your DC motor control module to your oscilloscope such that the reference r Vin is viewed on Channel 1 and the velocity feedback Vout Y is viewed on Channel 2 For best viewing set your vertical scales to 1 volt division and your horizontal scale to 400 ms division 11 Open and run yourname_MotorDrive_AcquireVoltage vi created for Lab 4 by clicking the Run Continuousl2. ME 104 Sensors and Actuators Laboratory 6a Closed Loop Analog Control Of DC Motor Velocity Department of Mechanical Engineering University of California Santa Barbara Rev 2007 Introduction In this laboratory you will build analog circuits on a breadboard to implement proportional P and integral I control of a DC motor NOTE e For this lab you will need yourname_MotorDrive_AcquireVoltage vi which you created for Lab 4 e You will write ONE REPORT FOR EACH Labs 6a and 6b Background Reading Please read the following material prior to this lab 1 Histand and Alciatore Introduction to Mechatronics Sections 5 1 5 8 and Sections 5 10 5 11 2 DC Motor Control Module User Manual Pages 3 7 and 14 16 LJ Technical Systems Inc Experiment 1a Open Loop Control of DC Motor Velocity In this experiment you will use a LabVIEW VI to drive a DC motor similar to what you did in Laboratory 4 You will observe both the motor drive input Vin and the tachogenerator output Vout velocity feedback on an oscilloscope PORE REECE E EEE E Eee eee ete e eee eee eee tees DAQ board Velocity Shaft Sensor Rotation Ch 1 Ch 2 Oscilloscope Figure 1 Open loop control of DC motor velocity In control system terminology the system shown in Figure 1 is described as an open loop control system This is because the control drive signal Vin to your plant the DC motor module does not directly automatically de
3. e 3 shows the closed loop control system in block diagram form in which the following notation has been used P s Plant DC Motor module e error signal r y K s Controller u control input to Vij socket on Motor Drive I Identity block D A Converter Input panel ry reference signal from LabVIEW VI y plant output from Vout socket on r reference signal Tachogenerator Output panel Controller Plant vi r e u E D A a Converter Figure 3 Closed loop feedback control block diagram Mathematically the proportional controller can be described in the time domain as up t K e t where up is the output and Kp is a constant gain Figure 4 shows the system diagram for the closed loop control system of the DC motor Drive Circuits Velocity Shaft a Sensor Rotation Oscilloscope Figure 4 Closed loop control of DC motor velocity Note that you need to provide power to both the DC motor module and the analog circuits on the breadboard The DC motor module requires voltage supplies of 12 V 12 V 5 V and ground The analog circuits include LMC6484 op amps which require voltage supplies of V 5 V and V 5 V Since the DC power supply at each station has only three output terminals and four different voltage outputs 12 V 12 V 5 V and 5 V are needed an L7905ACV negative voltage regulator is used to convert the 12V signal from the power supply to 5 V for the op amp Build the v
4. ep 5 8 Set yourMotor Drive Input Control to 0 00 and stop running the VI by clicking the Abort Execution stop button Your plant P s should show zero steady state error for all reference values However this has been achieved at a price Namely your system experiences transient oscillations that you did not observe previously In other words although the velocity signal y Vour will equal the reference value r after a sufficient amount of time has passed the velocity has a tendency to overshoot its intended target at the onset By combining proportional and integral control the desired zero steady state error condition can be maintained but with significantly reduced overshoot You will investigate in next week s lab Retain your P and I control circuits for next week s lab Laboratory Report 1 For the VI s you used in this laboratory provide a printout that shows the front panel and block diagram 2 Using the data you collected with the Eddy Current Brake in the 0 position provide a graph of steady state velocity voltage output y versus reference voltage signal r for the following control methods a open loop b proportional and c integral For comparison all three control methods should be plotted on the same graph Clearly indicate which plot corresponds to which control method and compare the steady state performance of the different control methods 3 Repeat Question 2 for the data you collected wi
5. f r and y as displayed by the digital indicators on your VI front panel Set the Eddy Current Brake to the 1 position and repeat Step 5 Set your Motor Drive Input Control to 0 00 and stop running the VI by clicking the Abort Execution stop button Although the velocity signal y Vout is closer to the reference value r than in the open loop case Experiment 1 the two signals are still unequal In other words tracking has improved but your plant P s still shows a steady state error for nonzero reference values This steady state error can be eliminated using closed loop integral control Experiment 3a Integral I Control of DC Motor Velocity In this experiment you will use a LabVIEW VI and an integral feedback control circuit to control a DC motor as shown in Figures 3 and 4 Mathematically the integral I controller can be described in the time domain as u K edn where u is the output and K is a constant gain Use the two remaining op amps on the left LMC6484 chip to build the integral control circuit shown in Figure 8 Provide the error input e to this circuit from the first half of the circuit you built in Experiment 2a Choose your resistors and capacitor such that R 100 KQ Rr Ry 1 MQ and C 0 1 uF Then Figure 8 Integral control circuit This circuit consists of an integrator that calculates the error integral followed by an inverting amplifier that multiplies the error integ
6. ges DSON7 14 4 Figure 7 LMC6484 op amp connection diagram 3 Connect the reference signal rfrom AOO Analog Output 0 to the proportional control circuit as shown in Figure 6 4 To drive the motor using the proportional control signal Up from the proportional control circuit connect your motor control module and proportional control circuit to the CB 68LP connector block according to Table 3 Table 3 CB 68LP connector block pin assignments for proportional control of DC motor velocity Vin socket Analog voltage on MOTOR DRIVE INPUT panel P feedback circuit output Up connection Vout socket Analog voltage on TACHOGENERATOR OUTPUT AIO and P feedback circuit input panel y connection 5 Retain the ground connections from Experiment 1a 6 Retain your oscilloscope connections from Experiment la That is connect your DC motor control module to your oscilloscope such that the reference r A00 is viewed on Channel 1 and the velocity feedback y Vout AI 0 is viewed on Channel 2 7 Make sure the Eddy Current Brake is disengaged That is make sure it is in the O position 10 Run yourname_MotorDrive_AcquireVoltage vi from Lab 4 by clicking the Run Continuously button Increment the Motor Drive Input Control by 1V from 4 00 V to 4 00 V inclusive and observe the voltage signals on Channels 1 and 2 of your oscilloscope Make a sketch of the transient behavior and write down the steady state values o
7. oltage regulator circuit shown in Figure 5 Follow the wire color scheme in Table 2 Vin 12V 0 L7905ACV 3 IN OUT Vour 5V GND 0 1 uF L7905ACV WK0040342 CHINA N l z pe Cc 0 1 uF 1 GROUND a b Figure 5 a Voltage regulator circuit b Pin assignment for L7905ACV negative voltage regulator Table 2 Wire color scheme Wire color Voltage Red 12 V Purple 12 V White 5 V Green 5 V Black 0 V Ground 1 Using a voltmeter verify that the output voltage of the voltage regulator circuit is 5 V 2 Build the proportional control p control circuit shown in Figure 6 Two LMC6484 op amps have been pre inserted on your breadboard Build the p circuit on the LEFT op amp on the breadboard Pin assignments for the op amp are shown in Figure 7 Remember to provide positive power V 5V from 5V FIXED 3A terminal on power supply to Pin 4 and negative power V 5V from voltage regulator circuit to Pin 11 Choose your resistors such that R 100 kQ and Rp 4 7 MQ Then R Kp 1 48 R Figure 6 Proportional control circuit The circuit consists of a difference amplifier that calculates the error followed by a noninverting amplifier that multiplies the error by a constant gain Kp Note Power supply connections are not shown for clarity As a safety precaution use your voltmeter to verify the values of your positive and negative supply volta
8. pend on the output signal Vout Figure 2 shows the open loop control system in block diagram form in which the following notation has been used P s Plant DC Motor module u control input to Vin socket on Motor I Identity block D A Converter Drive Input panel ry reference signal from LabVIEW VI y plant output from Vout socket on r reference signal Tachogenerator Output panel a P Plant Pe Figure 2 Open loop control block diagram The D A converter is represented by an identity block to indicate that the reference value seen by your system should be equal to the reference value specified by your LabVIEW VI For this experiment you will drive the DC motor such that the reference value is equal to the control input That is r U 1 Set the appropriate switches on your DC motor control module so that you can drive the motor with analog voltage input and also obtain analog velocity feedback from the tachogenerator output e MOTOR DRIVE switch Vin position selects analog motor drive input e TACHOGENERATOR switch Vout position enables analog velocity feedback output 2 Use a banana connector to connect the E Enable Input socket to the OV socket to enable the input to drive the motor 3 Connect the OV sockets Analog ground on MOTOR DRIVE INPUT panel and TACHOGENERATOR OUTPUT panel to common ground The P s notation indicates that the Plant is represented mathematically by its transfer function
9. ral by a constant gain K Note Power supply connections are not shown for clarity 2 To drive the motor using the integral control signal U from the feedback control circuit connect your motor control module and feedback circuit to the CB 68LP connector block as shown in Table 4 Table 4 CB 68LP connector block pin assignments for integral control of DC motor velocity Vin socket Analog voltage on MOTOR DRIVE INPUT panel I feedback circuit output U1 connection Vour socket Analog voltage on TACHOGENERATOR OUTPUT AIO and feedback circuit input panel y connection 3 Retain the ground connections 4 Retain your oscilloscope connections from Experiment la That is connect your DC motor control module to your oscilloscope such that the reference r A00 is viewed on Channel 1 and the velocity feedback y Vout AI 0 is viewed on Channel 2 5 Make sure the Eddy Current Brake is disengaged That is make sure it is in the O position 6 Open and run yourname_MotorDrive_AcquireVoltage vi by clicking the Run Continuously button Increment yourMotor Drive Input Control by 1V from 4 00 V to 4 00 V inclusive and observe the voltage signals on Channels 1 and 2 of your oscilloscope Make a sketch of the transient behavior and write down the steady state values of r and Vout as displayed by the digital indicators on your VI front panel 10 7 Set the Eddy Current Brake to the 1 position and repeat St
10. th the Eddy Current Brake in the 1 position Is there a notable difference between your plots in Question 2 and Question 3 Explain 4 Using the observations you made with the Eddy Current Brake in the 0 position provide a sketch of your DC motor s transient behavior All three control methods should be shown on the same sketch graph for comparison Compare the transient behavior of each of your control methods 5 Repeat Question 4 for the observations you made with the Eddy Current Brake in the 1 position Your x axis should consist of the values r 4 3 2 1 0 1 2 3 4 with units in volts 11 Your Lab Report should clearly state your name Lab Report number Lab date and your laboratory partner s name if any Your lab report should be thorough but concise You will be graded on quality not quantity Lab Report 6a is due at the beginning of Laboratory 6b 12
11. y button Incrementing by units of 1 00 V from 4 00 V to 4 00 V inclusive forthe Motor Drive Input Control observe the voltage signals on Channels 1 and 2 of your oscilloscope For each increment make a sketch of the transient behavior and write down the steady state values of r and Vour as displayed by the digital indicators on your VI front panel 12 Set the Eddy Current Brake to the 1 position and repeat Step 7 This brake acts as an external disturbance to your system 13 Set your Motor Drive Input Control to 0 00 and stop running the VI by clicking the Abort Execution stop button To avoid saturation effects the boundary reference values of 5 00 V to 5 00 V is reset to 4 00 V to 4 00V t Steady state means that you have waited long enough that transient motion has ceased Although one would like and expect Vin y and Voyr f to be equal you should have observed that they are not equal except when V OV That is your plant P s has a steady state error for nonzero reference values In other words in the absence of output information the magnitude of your plant motor velocity is slightly different from what you would like it to be This situation can be improved using closed loop feedback control Experiment 2a Proportional P Control of DC Motor Velocity In this experiment you will use a LabVIEW VI and a proportional P feedback control circuit to control a DC motor Figur
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