Optimum PID control of a servo-motor subjected to frictional loads, inertia and disturbances

Abstract

The control of dc servo-motors has been, and still is, the subject of numerous research activities. These motors are used in wide range of industrial and mobile robot applications. Traditionally, dc motors have been controlled by ON-OFF controllers. With such simple controllers it is very difficult to achieve precise motion and path control as required by many robotic and servo applications. The rise in popularity of microcontrollers and microcontroller based precision data acquisition system, in recent years, have opened up new arenas for creating smart controllers for such robotic systems. Now-a-days, proportional controllers are being investigated for servo-motors. However, proportional controllers have inherent steady-state error and these fail to respond quickly in case of rapid load variations. Therefore, precise trajectories are not achievable in many applications. PID controllers seem attractive for such systems and are now being tried to be implemented in microcontroller. However, PID controllers require an optimum balance of proportional (P), integral (I) and derivative (D) control actions and several procedures are available for disposal. In the present study, Ziegler-Nichols method is used to have optimum control parameters of the PID controller for a dc servo-motor subjected to frictional loads, inertia and disturbances. The control action is implemented in microcontroller based data acquisition and control system - LabJack. Both data acquisition and control actions are implemented in python scripting language. Performance results are obtained using these controlled parameters and results are analyzed to obtain optimum PID control strategy using LabJack for servo-motors.