ABSTRACT
Fundamentally, all the above-mentioned systems operate using one or several permanent magnet motors, together with a supply reversing circuit. A typical motor reverse circuit is shown in Figure 16.1. When the switch is moved, one of the relays will operate and this changes the polarity of the supply to one side of the motor. If the switch is moved the other way, then the polarity of the other side of the motor is changed. When at rest, both sides of the motor are at the same potential. This has the effect of regenerative braking so that when the motor stops it will do so instantly. Further refinements are used to enhance the operation of these systems. Limit switches, position memories and force limitations are the most common.
