Controller Design for Cable-Suspended Robots Considering Actuator Saturation

This paper discusses the performance of a controller on parallel cable-suspended robots considering the saturation problem of the actuators. Controllers utilized with an integrator face problems when the motor passes its saturation limit. The phenomenon called integral wind-up” impedes the correct tracking of the set point and causes unpleasant over-shoots in control variable. The overshoot usually remains even after the saturation is over and might result in a complete instability. This effect is more remarkable when a sharp settling time in control system is required. Many anti wind-up techniques have been proposed to solve this problem. Some have a simple algorithm though inadequate transient response. Others have more efficiency with more complexity. There has been a challenge to choose a strategy with the proper trade off. In this paper, a modified back-calculation strategy has been augmented to a PID controller that has been used to control the speed of a DC PM motor. A model of the motor is established. Both electrical and mechanical equations of DC motors are considered in order to fulfill the most realistic model of the motor. Simulations on the control system of a cable-suspended robot are conducted in SIMULINK to verify the efficiency of the taken algorithm. The results show a reliable control on input voltage compared to the other anti-wind-up strategy.

Keywords:

motor control , saturation , wind-up , back calculation