Feedback Control of a DC Servomotor with Time Delays Subjected to Disturbance Signals

The time delay imposed in the wireless control systems makes it difficult to guarantee stable response in many cases. Especially, delays in feedforward path combined with feedback path may result in some stability problems of the controlled system response. For the remote control of servomotors used on unmanned aerial or underwater vehicles, space manipulators and humanoid robots time delays has got great importance in real time remote control of those systems. The time delay in the feedforward path may be caused by computer control algorithm processing, buffering, transmitting process of control signals through antenna, receiving process of control signals through antenna on the vehicle and the complementary hardware processing. Similarly, on the feedback path, position feedback signal measured by encoder is transmitted in reverse order of the control signal with some delay time. In this paper, the PID control of a DC servomotor with constant time delays will be discussed in detail. After specifying the effects of the delays in the system, Smith predictor will be added to the model to minimize the undesired effects on the output response of the servomotor. For the wireless control of the servomotors actuating some mechanical systems, a modified Smith predictor is designed to drive the system efficiently to take care of the disturbance effects coming from the dynamics of the driven parts. The success of the calculated predictors together with the tuned PID controller and the controllable range for disturbance to controller signal ratio are shown on a low power DC servomotor by simulations.