From "System Modeling" to "Controller Hardware Testing" in Three Hours: A Robotic Arm Controller Design Lab Using MATLAB Real Time Windows Target to Reinforce Classical Control Theory

A 3 hour hands-on lab experience was designed to give students the opportunity to model, design and test a controller for a nonlinear electro-mechanical robot-arm system as a culminating project in mechanical engineering controls course. Students used linearization to model a nonlinear pendulum DC servo system using first principles. They used experimental frequency response data to derive a numerical transfer function model. Next they used analytical techniques including root locus and Simulink modeling to design a PID controller. Finally they tested their controller design using a hardware-in-the-loop system with MATLAB’s real-time windows target system to assess the performance of their controller. The entire process was started and completed in one three hour lab period. The goals of the exercise were to give students the chance to complete an entire control system design cycle from modeling to hardware testing in one sitting, incorporate as many of the course concepts as possible and give the students a practical understanding of the application of the theory. Assessment was conducted using pre and post online quizzes testing conceptual understanding of the major topics such as linearization, frequency response, and the effect of proportional, integral and derivative control. The assessment indicate a significant improvement in understanding of the theory and positive attitudes regarding the experience. Introduction Our university’s philosophy is that students learn best through a combination of lecture and lab experiences and industry feedback indicates that our undergraduates are unparalleled at hitting the ground running and working with real world problems. While many have reported on the effectiveness of including hands-on laboratory exercises to enhance learning [1], these labs are expensive and there is pressure to eliminate them in the times of increasing budget pressure. This study suggests that the cost is justified because learning outcomes are significantly improved compared to a lecture only course. Mechanical Controls is a four unit, required senior level course that consists of three-one hour lectures and one-three hour lab per week for the ten week quarter. The course covers singleinput single-output linear system modeling, time domain analysis, transfer functions, root locus, frequency response methods, PID and lead lag controllers. The lab is taken concurrently with the lecture and is designed to support the topics covered in lecture while also illustrating the realities of real world systems, modeling and controller implementation. There are currently four exercises: a two week Matlab/Simulink simulation exercise, a two week analog DC servo position control experiment, a two week digital controller tank water level regulator experiment and a two week digital controller hydraulic servo control experiment. The digital control experiments use Matlab Real Time Windows Target (RTWT) with a National Instruments data acquisition board (DAQ) interface to implement a simple PID controller in realtime. This software interface is ideal for the learning environment and is use in many universities because the Simulink code is displayed as a block diagram that is identical to the theory that is presented in the textbook [2] [3] [4]. This makes modifying and developing new controllers simple for the student with minimal programming experience. This hardware was introduced in this lab in 2008 in an experiment using a hydraulic control system [5]. This paper describes the DC servo experiment that is performed early in the term and also the addition of a new one-week PID Design Project that is intended to include elements from many of the lecture topics and end the term with a single creative and self-contained experiment. Assessment of the new project was conducted using a pre and post quiz and surveys. Linear DC Servo Setup The new PID Design project is conducted in the last week of the term. However, students test and analyze the DC servo at the beginning of the quarter with only an inertia disk and gear system as the mechanical load. The experimental apparatus shown in Figure 1 is a DC servo control system based on the Motomatic Inc. hardware. The angular position is measured by an angular potentiometer sensor. The sensor signal is measured by a DAQ interface to a Matlab/Simulink RTWT PID controller. The controller generates an actuator signal via the DAQ analog output channel which is connected to the motor amplifier to close the loop. Figure 1. Photograph of DC servo control apparatus showing DC motor, potentiometer position sensor and motor amplifier. DC Motor Potentiometer Position Sensor