Control Digital De La Ieee

Session 24B2

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Digital Control Workstation
John R. James Lawrence A. Rapisarda Lieutenant Colonels E l e c t r i c a l Engineering U.S. M i l i t a r y Academy West Point, New York

NI"TODUCTI0N Automatic Controls, a required course for Electrical Engineering majors at the United States Military Academy (USMA) has a significant laboratory component. Students conduct experiments on a DCservo trainer which may be configured to mimic the behavior of commonly encounted analog plant structures. The cability for the student to apply compensation and feedback networks to and observe behavior of a mechanical system is a valuable learning tool. Extensive developments in digital signal processing and the use of DSP systems in control networks makes the addition of a course on DigitalControl desirable. Unfortunately the large core course requirement for students at USMA limits the number of courses available for satisfaction of the requirements for the Elecmcal Engineering Major. Adding a new course requirement for EE Majors forces the deletion of some other required course. For this reason we have chosen to add limited coverage on digital control in the existing course intendingto make the most of the time allotted. These digital control lessons culminate with the conversion of a conventional control design for implementation by a digital system. The control system is a Lead Compensator for the servo trainer configured for position control. The analog design technique is a modification of Sinha's' method for designing lead compensation to meet phase margin and magnitudecrossover specifications. The 2 resulting technique designs lead-lag compensation to achieve phase margin, closed loop bandwidth and low frequency gain specifications. The conversion of the design to digital precompensator employs the z-transform and the model for a Zero-Order Hold. The workstation described in the next section is an upgrade to the existing servo trainer that allows the actualimplementation of the digital design. We have employed it for the last two years as a demonstrationof the solution to the digital design problem. We have found this a valuable addition to the course and hope to incorporate some form of the workstation into the course laboratory sequence to provide a fuller "hands on" dimension to the digital coverage. The workstation has also functioned as a platformfor testing a knowledge-based system capable of designing and implementing digital compensators. For the remainder of the paper we will describe the workstation components and outline the digital design problem and solution that forms the basis for the workstation demonstration.

WORKSTATION CONFIGURATION HARDWARE The system hardware has the following components: 1. An IBM/PC-AT compatiblecomputer (Zenith, 2-248),

2. A PC expansion board built by Atlanta Signal Processors Inc. (ASPI) which implements the compensator, and

3. A Feedback Inc. ES151 InstructionalDC Servo Trainer.
The PC is a Zenith, 2-248 (a PC/AT look-alike), equipped with an EGA monitor, 1.1 Megabyte of memory, 20 Megabyte hard disk drive, 2 360 kilobyte floppy disk drives, a parallel port, two serial ports andmouse. TMS 320 10
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A/D

TT
MEMORY Circuits

Personal Computer Bus

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Figure 1. Block diagram of the ASPI 32OPC-10 The expansion board, Model ASPI 32OPC-10, includes a digital-to-analog @/A) converter, an analog-to-digital (A/D) converter, a Texas Instrument TMS32010 microprocessorand dual port memory. A simplified block diagram of the 320PC10 board appears in Fig. 1. The TMS32010 is a16 bit microprocessor which may be programmed to implement virtually any discrete-time system. The D/A and A D converters connect the system to the outside analog world. Internally they connect to the processor with 12 significant bits. There are 8 kbyte of dual port memory, accessible to the
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TMS32010...