A position control system converts a position input position to a position output response. Position control systems find widespreadapplications in antennas, robot arms, and computer disk drives. The radio telescope antenna in Figure 1.8 is one example of a system that uses position control systems. In this section we will lookin detail at an antenna azimuth position control system that could be used to position a radio telescope antenna. We will see how the system works and how we can effect changes in its performance.The discussion here will be on a qualitative level, with the objective of getting an intuitive feeling for the systems with which we will be dealing.
An antenna azimuth position control system isshown in Figure 1.9(a), with a more detailed layout and schematic in Figures 1.9(b) and 1.9(c), respectively. Figure 1.9(d) shows a functional block diagram of the system. The functions are shown abovethe blocks, and the required hardware is indicated inside the blocks. Parts of Figure 1.9 are repeated on the front endpapers for future reference.
The purpose of this system is to have the azimuthangle output of the antenna, o (t), follow the input angle of the potentiometer,i(t). Let us look at Figure 1.9(d) and describe how this system works. The input command is an angular displacement.The potentiometer converts the angular displacement into a voltage. Similarly, the output angular displacement is converted to a voltage by the potentiometer in the feedback path. The signal andpower amplifiers boost the difference between the input and output voltages. This amplified actuating signal drives the plant.
The system normally operates to drive the error to zero. When the inputand output match, the error will be zero, and the motor will not turn. Thus, the motor is driven only when the output and the input do not match. The greater the difference between the input and...