EE312 Control Systems Engineering Lab 1: DC Servo Motor Analog Speed Control System Objective: To introduce the student to feedback control (specifically proportional (P) feedback) for velocity control in the Googol Technology GSMT 2000 series DC Servo Trainer. Specifically the students will be able to: © Identify and explain the functional block diagram of a velocity control system * Construct open-loop and closed-loop velocity control systems from functional block diagrams. Compare open-loop and closed-loop control systems. Duration: 1x3 hour lab session Prerequisites: ‘The students are required to read Chapter 1 — System Introduction of the Gogol Technology Analog Control System Experiment Manual. This provides a brief introduction to the various components of the Analog Control System, Equipment: * Oscilloscopes # Analog Circuit Control Box * DC Servo experimental platform Introduction: This experiment is adapted from the Gogol Technology Analog Control System Experiment Manual. Specifically it is derived from Chapter 3 — Single Closed-Loop Velocity Modulations System of DC Servo Motor Experiment. The Googol Technology Analog Control System (Figure 1) is a device that enables analog control of Gogol ‘Technology equipment such as Magnetic Levitation System, Ball & Beam System, or DC Servo Trainer. The analog control system experimental chamber contains nine modules, the signal source module, the signal-setting module, the signal connector module, the motor connector, the power supply, the analog circuit module, the motor’s velocity detection module, the power amplifier, and a reserved module. Users with the experimental chamber can do analog circuit experiment for typical elements, velocity modulation experiment for the single closed-loop DC servo motor, follow-up system experiment of DC servo motor, the control of magnetic levitation ball, ball and bean system experiment. It is suitable for students majored in mechatronics engineering, machinery manufacturing, and automation, eteil ‘Magnetic Levitation System & Maguetic levitation system, My ntl, PID contro DC Servo Trainer DC motor contol follow seo coat. PID conta Ball Beam System De serve motor coutal 5 ‘alles conto, PID coil Figure 1: Googol Technology Analog Control System. Theory: Single Closed-Loop Velocity Control System DC Servo experimental platform is one series of googoltech’s education products, It can accomplish the various experiment of the DC servo motor control system, so in this term we use DC Servo experimental platform to do experiments(Model: GSMT2012), as shown in Figure 2. Figure 2: DC Servo experimental platform. The single closed-loop velocity control system functional block diagram is shown in Figure 3 and Figure 4. The power amplifier adopts the linear power amplifier, the velocity detection adopts inverse electromotive force detection, and the setting signal is given by a potentiometer. In order to eliminate steady-state error, it uses acontroller. This controller could be a P, PI, PD, or PID controller. We shall only consider a P controller for this lab. Giveii uc | Power | ua a Controller | 5] amplifier >| Motor > Ur Velocity detection Figure 3: Block diagram of single closed-loop speed control system. Given signal PID controller Power Amplifiers Control object Speed detect Figure 4: Block diagram of single closed-loop speed control system with analog circuit control box components, In order to overcome the drawback of the steady-state error of an open-loop velocity control system and enhance the control quality of the system, it should adopt negative feedback velocity control. This can correct the error of the system automatically. The working principle of the single closed-loop velocity control system is as follows. The voltage of the negative feedback Ur which is directly proportional to the rotating speed of the motor is compared with the rotating speed setting voltage U; through the velocity detection element to get the error voltage ¢. The controller then uses the error € to compute an output voltage Uc which is input to the power amplifier. The power amplifier then produces a drive voltage Ud to control the velocity n of the motor Controller of the Single Closed-Loop Velocity Control System The single closed-loop velocity control system adopts serial adjustment, The form of its controller is a Proportional-Integral (PI) adjustor. It can guarantee the stable precision, and realize zero steady-state error, The controller is composed of operational amplifier, resistance and capacitance to form the analog control circuit. Its circuit is shown as Figure 5.ovorce Figure S: Circuit diagram of Proportional-Integral (PI) velocity loop controller. The circuit is comprised of the proportion circuit, integration circuit and inverse summation circuit. The proportion circuit K, et) Rey a Vv. The integration cireuit 1 —— fetnar KiCy J ® The inverse summation circuit Vou =V, Vi 3)‘The transfer function of the controller (via Laplace Transforms) is fon) 3 Is the proportional gain of the Re controller Is the integral gain of the controller One can adjust the proportional gain and integral gain of the controller by adjusting Ks and Ky, respectively. Procedure: First, we will study the response of the open-loop speed control system. Then we will study the closed-loop system when a proportional controller is used. Part 1: Open Loop Speed Control System 1. Check whether the power is turned off or not. If not, tum off the power first. 2. Connect wires. The velocity modulation system of DC servo motor connects to the connection of the motor on the circuit board (voyage plug), M+ of the motor module conneets to P42 of the power module, M- of the motor module connects to P43 of the power module, and REV connects to Pé4 of the signal- setting module. Also connect P42 to P45 and P46 to IR. Check whether the lines connected are right or not again. If you are unsure, ask the lab demonstrator for assistanoe, 3. Turn on the power. Push the dial switch up of the signal-setting module, tune the adjustable potentiometer RPI, and use the oscilloscope to watch the waveforms of P44 and P47. Note the step response of the open loop system and show it to the lab demonstrator. Does the system reach the target (set poini) velocity? 4. Tum off the power, pullout the connected lines between P42 and P44, Part 2: Closed Loop Speed Control System 1. Connect wires. Connect P41 to P44 of the summation circuit, P30 to P38, GND to P39 and P40; P26 to P27, P42 to P46, PAS to IR of the motor module,P25 to P47, connect REV of the setting signal module to P24, Cheek whether the_lines connected are right or not again. If you_are_ut demonstrator for assistance. Implement the proportion control, Tum on the power, push the dial switeh up of the signal-setting module; adjust the knob switch RP7 to change the proportion coefficient of the velocity loop. ‘The coefficient inereases clockwise and decreases counterclockwise. Detect the waveforms of P25 and P24 using oscilloscope. Push down the dial switch of signal-setting module first, then push up, and detect the step response curve of P25. Note the step response of the closed loop system using an oscilloscope and show it to the lab demonstrator. Does the system reach the target (set point) velocity? Does changing the value of Ks make the system reach the target (set point)? What value of K3 produces the smalllest error? Review Questions: Identify/label the following components of a feedback control system in the functional block diagram of Figure 3/4, a. Input Unit b. Comparator/Controller c. Sensor d. Process variable (output) e. Actuator f. PlanvProcess Why does the rotating velocity become low when the load is increased in the open-loop control system? Why can closed-loop velocity control reduce the error of the rotating speed?