Electromechanical Servomechanism - Internal Model Control Design Virtual Laboratory
Summary
Electromechanical servosystems are frequently encountered in
practice. The goal of this laboratory is to study the dynamics and
control of a DC electromechanical servosystem and specifically in this
laboratory of the package show that using the advanced techniques of
Internal Model Control and Anti-Windup achieve better performance than
a simple PI controller.
The non-ideal features of the physical setup have been replicated in this virtual laboratory including the power amplifier output limits, potentiometer “wrap-around” and signal noise is included. The laboratory is based on this typical “classroom” style apparatus found in many University laboratories.
Figure 1.1: Screenshot of Program
The Physical Apparatus
Electromechanical servo-mechanisms are frequently encountered in industry. In this laboratory, the servo-mechanism will be used as a positioning system. Fundamentally the system comprises of a simple Direct Current (DC) motor, a gearbox and two metal discs rigidly coupled.
The DC motor is an actuator that converts electrical energy into rotational mechanical energy. The motor itself has a permanent magnet field and external terminals connecting to the armature winding. Direct Current motors are widely used in many control applications including robotics, machine tools, valve actuators and also tape, disk and CD drives.
Shaft position is measured by a sensor located on the disc and shaft speed is provided by a tacho-generator connected directly to the motor.
The aim of this laboratory is to implement a controller to position a disc mounted on the servomechanism shaft at a desired angle. The physical system emulated by this virtual laboratory is shown in Figure 1.2. The setupconsists of a servo-mechanism, signal generator, power supply, power amplifiers and a personal computer that contains an analog input/output card that runs the control software.
Figure 1.2: The Physical Laboratory Setup
The physical servo-mechanism is shown in Figure PS.14. The tachometer is directly connected to one end of the motor shaft, whilst the other end of the motor shaft is connected to an inertial mass and gearbox. The gearbox has a reduction ratio in the order of 30:1. The gearbox output drives both an angular marker disc and a potentiometer. Note that non-ideal features of the physical system have been replicated in the virtual laboratory which include the power amplifier output limits, potentiometer “wrap-around” and signal noise. A schematic of the proposed position control system for this laboratory is shown in Figure 1.3.
Figure 1.3: The Servo Kit
<>Note that the non ideal features of the physical setup have been replicated in this virtual laboratory including the power amplifier output limits, potentiometer ‘wraparound’ and signal noise. A simplified representation of the system is given in Figure 1.4.
Figure 1.4: Position Control System
In this virtual laboratory, we will design a controller with the configuration shown in Figure 1.5.
Figure 1.5: Anti-windup scheme for bi-proper controller
Prerequisites
This virtual laboratory has been designed with the same fundamental properties as a physical laboratory located at the University of Newcastle, Australia. Assumed knowledge:
- Ziegler-Nichols tuning rules
- Controller design using Affine parametrisation
- Anti-windup control strategies
Learning Objectives
The learning objectives of this virtual laboratory include:
- Application of the Ziegler-Nichols tuning rules
- Reinforce theory on affine parametrisation through a application
- Implementation of an anti-windup controller
