Low Cost Motor Control Systems Laboratory Kit for Distance Learning Courses

Transcription

1 2016 International Conference on Computational Science and Computational Intelligence Low Cost Motor Control Systems Laboratory Kit for Distance Learning Courses Theodore Grosch, Member, IEEE, Hai T. Ho Abstract Certain barriers remain for implementing a handson laboratory in distance learning courses. Many affordable and useful home laboratory kits are available for courses such as circuits, electronics, embedded systems, but some introductory courses remain out of reach. In this paper, we describe a lowcost, turnkey control system laboratory kit that is affordable, safe, and robust enough to satisfy the demands of a college level controls course. This laboratory kit integrates a DC motor, sensor, microcontroller, and a USB interface into an integrated system for home use. The embedded firmware in the kit allow the student to characterize the motor in the kit, design a PID control loop and create Bode plots of the loop response. Index Terms Embedded Control, Laboratory, Low cost, servo, motor control M I. INTRODUCTION OTION control systems employing embedded systems are integrated in a multitude of places from toys to factories, from home appliances to wind turbines. Most of these systems have three components in common: motors, sensors, and controllers. Therefore, it is important to teach DC motor servo control in undergraduate control system courses. Usually, both the theory and lab components are covered in order to achieve complete learning experience. The widely used textbook authored by Nise [1] covers the details of the electromechanical servo system modeling and simulation, and references a rotary servo lab system made by the company Quanser [2,3]. These lab hardware systems, along with others similar to it, were developed for campus laboratories where they can handle heavy long-term use; therefore the dollar costs are high. This has been an acceptable arrangement for traditional learning model where students come to campus to conduct laboratories, Submitted for review: T. Grosch is with the Electrical Engineering Department, Kennesaw University, Marietta, GA, 30090, (phone: ; fax 978= ; tgrosch@kennesaw.edu) H. Ho is with the Electrical Engineering Department, Kennesaw University, Marietta, GA, 30090, ( hho3@kennesaw.edu) often times in groups due to limited number of stations. In the case of distance learning degree programs, there are ongoing efforts to give students a hands-on laboratory experience remotely [4-6]. However, many online engineering programs failed to obtain ABET accreditation [7] due to no hands-on laboratories. In the case of control systems course, existing distance learning laboratory solutions are largely based on using remote access to operate laboratory apparatuses that are housed on campus [8,9]. The challenges of these types of labs are that they are not widely and commercially available, and are usually custom built. Furthermore, students don t get to touch and feel the hardware, which is an important part of the laboratory experience. Current research is ongoing on a low-cost alternative approach to have students buy and/or build their own hardware for a controls system course using Arduino, RaspberryPi [10, 11]. These are appealing in the sense that the institution doesn t have to buy equipment or provide space and the student can work with the hardware anytime and anywhere. Here, we propose a turnkey control system laboratory kit that achieves key hands-on learning objectives and meets three major goals: Affordability, Adaptability, and Accessibility. The proposed work in progress is a portable lab kit that consists of a DC motor, driver, real-time microcontroller, USB, interface, and embedded software using an open Application Programming Interface (API), and lab manuals. This laboratory kit hardware is shown in Fig. 1. All the hardware parts, except for the computer, are housed in an enclosure with the motor shaft and USB interface port exposed. The target retail cost of this system, which includes distribution and retail markups, is less than a typical textbook /16 $ IEEE DOI /CSCI

2 II. OBJECTIVES OF HARDWARE CONTROLS LAB Unlike simulations, hardware labs give realworld-like experience on physical components and witness real-time signals and responses. For Fig. 1 Concept Diagram of the controls systems laboratory kit. example, a student can feel how the torque of the motor changes when he or she attempts to disturb the loop. They further observe the effects of real world constraints and limitations such as voltage saturation and mechanical nonlinearities. The following are the design objectives of this servo laboratory lab system: 1. The kit shall contain a motor, driver, and position sensor. 2. The kit shall also include a real-time controller that is capable of executing of the control algorithm. 3. Have an open Application Programming Interface (API) with which the students can set configure and monitor the control system with a PC and USB interface. 4. Provide hands-on debug and operation of the servo control system. 5. The laboratory kits should cost less than a typical textbook 6. The controller firmware shall be upgradable when new algorithms and procedures become available. III. ARCHITECTURE AND DESIGN A distance learning laboratory kit should meet the objectives stated above at minimal cost to reach as many students as possible. This is the ideal application for embedded systems where timers, counters, digital and analog I/O are integrated in one low-cost platform. These systems are perfectly suited to facilitate distance learning in control theory and provide an affordable turnkey platform. A. Archetecture To minimize the cost to the student, the kit includes everything on the right side of the laptop computer in Fig. 1 in a single package only the motor shaft, an LED, and USB port exposed. The function of the PC is to accept user input and help the student work with the data. For the kit described here, any general purpose PC, laptop, or tablet with a USB port can be used with a suitable application, such as a simple terminal program. The USB interface Application Programming Interface (API) consists of series of ASCII serial strings terminated by a carriage return character and is shown Table 1. This was done to meet the accessibility objectives by making the interface platform independent. Key p i d s t a b k l TABLE 1 LIST OF API KEYWORDS THE THEIR MEANING Description The PID proportional constant or Bang-Bang (float) The PID integral parameter (float) The PID differential parameter (float) Step parameter input to the loop (rad) Inject test sinusoid at location t Test sinusoid parameter 2000*cos( t/1000) Test sinusoid parameter 500*sin( t/1000) Kill the motor Put motor online In the system here, the control loop is closed in the box by the microcontroller firmware, which runs a general-purpose control loop shown in Fig.2. The loop coefficients kp, ki, and kd are configured with the API. I facilitate this, we wrote a basic Windows Graphical User Interface (GUI) as shown in Fig. 3 for the majority of students who can run a Windows application. This all serves to Fig. 2 PID control system implemented in firmware

3 lower the cost of ownership while maximizing functionality for the student. Furthermore, the USB interface facilitates retrieving control and position data from the embedded processor. The processor streams ASCII data as comma separated values of desired and actual shaft position and motor control voltage, other analysis options are open to the student and instructor. An example of one such text stream is shown in Table 2. TABLE 2 EXAMPLE OF STREAMING OUTPUT SHOWING DESIRED POSITION, MEASURED POSITION, AND MOTOR PWM DRIVE LEVEL , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , B. Hardware and Software Design The basic system consists of the hardware components shown in Fig. 1, firmware running in the controller, and an application interface on a PC or laptop. Fig. 3 is a photo of the prototype hardware. The Bill of Materials (BOM) is shown in Table 3 and suggests that the cost of the servo box will be affordable given additional manufacturing-, distribution-, and retail-pricing markups. There are multiple ARM-based microcontroller off-the-shelf development kits that can be used to develop a low cost electronics controller platform. When choosing a suitable microcontroller, we considered cost, speed, ALU core, and a possibility of a hardware quadrature decoder. The current Fig. 3 TABLE 3 BILL OF METERIALS 1 DRV8830 H-Bridge Driver CY ARM PSoC CP2102 USB to serial interface DC Motor/Encoder Enclosure USB cable prototype has a Cyprus SoC with a Cortex M0 processor. Since this processor has a fixed point ALU, the loop calculations in the set the time to 2 ms. For faster loops, fixed-point loop algorithms or floating point ALU would be necessary. This determination should be made in conjunction with the motor, encoder, and output shaft gearing system. The driver is an integrated H-bridge that provides forward or reverse current to the motor. The controller firmware sets up and controls a pulsewidth-modulator and the H-bridge with the control algorism as to the pulse width, motor direction and breaking. The PWM output also drives an LED where the student has a visual indication of how hard the motor is being driven in real time. The user chooses the control scenario and enters the necessary parameters. These are sent to the controller and the loop is closed. Data is streamed to the application for analysis and control. The user can then change the mode, change parameters, or stop the loop at any time using the GUI as shown in Fig. 4. The lower part of the window shows a plot of a step function from 0 to + radians as executed by the prototype. Fig. 5 shows the graph window

4 Fig. 4 Example of the PID window using the Windows GUI Fig. 6 Example of the PID window using the Windows GUI Fig. 5 Example of the graph window using the Windows GUI shortly after a step command from + to 0 radians. In addition, the embedded firmware contains a digital sinusoidal synthesizer. This sinusoid can be applied to the position input to the systems or inside the loop. The purpose is to measure the frequency response of the open or closed loop. A display of one such test is shown in Fig. 6. Amplitude and phase is plotted on a standard Bode plot. The student has the option to use higher-level applications to design and simulate the loop, then load the stimulus and parameters with API calls. If the student has Simulink, control experiments can be designed, simulated, and tested with the controller API commands as summarized in Table 2 and streaming data as shown in Table 3. Fig. 7 ARM firmware block diagram C. Laboratory Manuals The ongoing work is assessing and refining a series of laboratories that integrate with classroom instruction as shown in Table 4. Students start out with first lab where they derive the transfer function of the plant based on the schematic and parameters of DC motor obtained

5 Lab #1 Lab #2 Lab #3 Lab #4 Lab #5. Plant modeling and measurement Plant validation Basic feedback loops PID design and measurement Closed loop Bode response from datasheet and experimentation (i.e. stimulating the motor using the sinusoid in an open loop test). Then in the second lab, plant validation using the same test signal to drive the hardware. The responses of the system are measured and compared against the simulation to validate the plant model. The students then design and program a basic closed loop control system and measure performance such as settling time, overshoot, and maximum input voltage. In the fourth lab, the student designs, programs and measures a PID control loop. Lastly, the student measures the closed loop frequency response of the system in the fifth lab. It should be recognized that most of the important objectives of a hands-on control laboratory is met through this system and lab exercises. IV. SUMMARY There is a need for remote and portable labs that accommodate distance and individual learning while achieving actual hands-on objectives. We proposed a portable servo lab kit that is low cost and with complete functionality. The hardware integrates a USB interface, microprocessor, H- bridge, motor, and encoder. Firmware in the microcontroller implements a basic PID control loop with variable coefficients, sinusoid synthesizer, and a serial API. We also developed a Windows GUI to interface with the control system in the box. The prototype demonstrates that closing the servo loop using a PID controller was straightforward and the experience enriching. The next step is to productize and made available to students taking undergraduate control system classes in a study to measure effectiveness and refine the laboratory procedures. REFERENCES [1] Nise, Norman S. CONTROL SYSTEMS ENGINEERING, (With CD). John Wiley & Sons, [2] ----, Rotary Servo, Quanser Corp. [3] ----, QUBETM-Servo, Quanser Corp. [4] Ionescu, Clara Mihaela, Ernesto Fabregas, Simona M. Cristescu, Sebastian Dormido, and Robin De Keyser. "A remote laboratory as an innovative educational tool for practicing control engineering concepts." Education, IEEE Transactions on 56, no. 4 (2013): [5] Odeh, Salaheddin, and Eiman Ketaneh. "E-collaborative remote engineering labs." In Global Engineering Education Conference (EDUCON), 2012 IEEE, pp IEEE, [6] Lerro, F., S. Marchisio, S. Martini, H. Massacesi, E. Perretta, A. Gimenez, N. Aimetti, and J. I. Oshiro. "Integration of an e-learning platform and a remote laboratory for the experimental training at distance in engineering education." In Remote Engineering and Virtual Instrumentation (REV), th International Conference on, pp IEEE, [7] Felder, Richard M., and Rebecca Brent. "Designing and teaching courses to satisfy the ABET engineering criteria." JOURNAL OF ENGINEERING EDUCATION-WASHINGTON- 92, no. 1 (2003): [8] Singh, A. K., S. Chatterji, S. L. Shimi, and A. Gaur. "Remote Lab in Instrumentation and Control Engineering Using LabVIEW." (2015). [9] Jara, Carlos A., Francisco A. Candelas, Santiago T. Puente, and Fernando Torres. "Hands-on experiences of undergraduate students in Automatics and Robotics using a virtual and remote laboratory." Computers & Education 57, no. 4 (2011): [10] Reck, Rebecca Marie, BYOE: Affordable and Portable Laboratory Kit for Controls Courses, 2015 ASEE Annual Conference and Exposition. [11] Turner. Mathew, Cooley, Timothy, A low cost and flexible open source inverted pendulum for feedback control laboratory courses, 2015 ASEE Annual Conference and Exposition. Theodore O. Grosch received his BS 82, MS 89, and Ph.D 93. in electrical engineering from The Pennsylvania State University. He worked at Hughes aircraft and General Electric from 1982 to 1986 designing RF, microwave and MMW satellite circuits and systems. He worked at M.I.T. Lincoln Laboratory from 1993 to 2001 on ground penetration radar, ballistic missile defense, and active fuse systems. He designed on cellular base stations and small cell transceivers at Airvana from 2001 to Since 2012, he has been a Lecturer at the University of Massachusetts, Lowell and is now an Assistant Professor at Kennesaw State University and teaches mixed signal applications and embedded systems. Hai Ho: (put more here) Dr. Ho is an associate professor at Kennesaw State University where he teaches control systems and senior project