2.6. In-Laboratory Session 2.6.1. QICii Modelling Module 2.6.1.1. Module Description The main tool for this lab is the front panel of the module entitled Modelling in the QICii software, which should be similar to the one shown in Figure 2.4. Figure 2.4 Modelling Module Of The QICii Software As a quick module description, Table 2.3 lists and describes the main elements composing the QICii Modelling module user interface. Every element is uniquely identified through an ID number and located in Figure 2.4. ID # Label Parameter Description Unit 1 Speed! m Motor Output Speed Numeric Display rad/s Document Number: 627! Revision: 01! Page: 35
ID # Label Parameter Description Unit 2 Current I m Motor Armature Current Numeric Display A 3 Voltage V m Motor Input Voltage Numeric Display V 4 Signal Generator Type of Generator For The Input Voltage Signal 5 Amplitude Generated Signal Amplitude Input Box V 6 Frequency Generated Signal Frequency Input Box Hz 7 Offset Generated Signal Offset Input Box V 8 Speed! m Scope With Actual (in red) And Simulated (in blue) Motor Speeds 9 Voltage V m Scope With Applied Motor Voltage (red) V rad/s 10 K K Motor Model Steady-State Gain Input Box rad/(v.s) 11 " " Motor Model Time Constant Input Box s 12 Tf T f Time Constant of Filter for Measured Signal s Table 2.3 QICii Modelling Module Nomenclature The Modelling module program runs the process in open-loop using the motor voltage given by the signal generator. There are two windows that show the time histories of motor speed and motor voltage. A simulation of the system runs in parallel with the hardware. The output of the simulation can be used for model fitting and validation. The input of the simulation is equal to the motor voltage and the output of the simulation is displayed (blue trace) in the same window as the actual motor speed (red trace). The simulation model parameters K and " can be adjusted from the front panel. The simulated motor speed,! s, is obtained from the simulated transfer function and actual motor voltage as follows: # s ( s )!"! K ( s ) V m % s!$! 1 The implemented digital controller in the QIC runs at 100 Hz. Thus the sampling interval is: h!"! 0.01 [ s ] The actual speed is obtained by filtering the position signal using the following filter: Document Number: 627! Revision: 01! Page: 36
s & m # m!"! T f s!$! 1 where # m is the position of the motor shaft measured by the encoder. 2.6.1.2. Module Startup To start and use the Modelling module, follow the steps described below: Step 1. Power up the DCMCT. LED2 should light up while LED3 should flash on and off repeatedly. Step 2. Press the Reset button on the QIC. Again, LED2 should remain on while LED3 should flash on and off repeatedly. Step 3. Press the DCMCT User Switch (i.e. pushbutton next to the two flashing LED's). LED2 and LED3 should both turn off. Step 4. Launch the USB QICii software and select Modelling in the drop-down menu. Step 5. Select the Connect to data source button on top of the QICii window to be able to receive/send data from/to the controller. LED2 should light up while LED3 should still be off, and the controller should start running. Note: The drop-down menu will be disabled (i.e. is unavailable) while the controller is running. You must select the Stop controller button on top of the QICii window to stop the controller (this should also turn off LED2, and enable the drop-down menu again). Once the drop down menu is enabled again and the controller is stopped, you can select any one of the other controller experiments, if you want. After selecting some other controller experiment, you can once again select the Connect to data source button on top of the QICii window to be able to receive/send data from/to the controller of your choice. The default module parameters loaded after download are given in Table 2.4. Signal Type Square Wave Amplitude Frequency [Hz] Offset K [rad/(v.s)]! [s] T f [ s] 2.0 0.4 0.0 10.0 0.2 0.01 Table 2.4 Default Parameters For The Modelling Module Document Number: 627! Revision: 01! Page: 37
2.6.2. Static Relations 2.6.2.1. Initial Experimental Tests Objectives Determine the maximum velocity and compare with calculations. Determine the Coulomb friction. Explain your findings and summarize them briefly. Experimental Procedure A procedure of this type is very useful to make sure that a system functions properly. Please follow the steps described below. Step 1.Run the system open-loop by changing the voltage to the motor. The motor voltage is set by the signal generator. With zero signal amplitude, change the signal offset to generate a constant voltage. Sweep the voltage gently over the full signal range and observe the steady-state speed, current, and velocity. What happens to the variables as you change the offset? Step 2.Determine the maximum velocity and compare with calculations. Note: Although the motor maximum input voltage is 15 V, the Offset numeric input is limited to 5 V. Document Number: 627! Revision: 01! Page: 38
Step 3.Start with zero voltage on the motor and increase the voltage gradually until the motor starts to move. Determine the voltage when this occurs. Repeat the test with negative voltages. Document Number: 627! Revision: 01! Page: 39
2.6.2.2. Estimate The Motor Resistance Some of the parameters of the mathematical model of the system can be determined by measuring how the steady-state velocity and current changes with the applied voltage. To experimentally estimate the motor resistance, follow the steps described below: Step 1.Set the generated signal amplitude to zero. If the signal offset is different from zero then the motor will spin in one direction, since a constant voltage is applied. You can change the applied voltage by entering the desired value in the Offset numeric control of the Signal Properties box. You can also read the actual motor current from the digital display. The value is in Amperes. Fill the following table (i.e. Table 2.5). For each measurement hold the motor shaft stationary by grasping the inertial load to stall the motor. Note that for zero Volts you will measure a current, I bias, that is possibly non-zero. This is an offset in the measurement which you need to subtract from subsequent measurements in order to obtain the right current. Note also that the current value shown in the digital display is filtered and you must wait for the value to settle before noting it down. Sample: i 0 0 V m (i) Offset in Measured Current: I bias [A] Sample: i 1-5 2-4 3-3 4-2 5-1 6 1 7 2 8 3 9 4 10 5 V m (i) Average Resistance: R avg [!] Measured Current: I meas (i) [A] Table 2.5 Motor Resistance Experimental Results Corrected for Bias: I m (i) [A] Resistance: R m (i) [!] Document Number: 627! Revision: 01! Page: 40
Step 2.From Table 2.5, above, calculate for each iteration the motor resistance R m (i) and obtain an average value for it, R avg. Explain the procedure you used to estimate the resistance R m. Step 3.The system parameters are given in Table A.2. Compare the estimated value for R m (i.e. R avg ) with the specified value and discuss your results. 2.6.2.3. Estimate The Motor Torque Constant To experimentally estimate the motor back-emf constant, follow the steps described below: Step 1.With the motor free to spin, apply the same procedure as above and fill the Document Number: 627! Revision: 01! Page: 41