Design and Implementation of a Control System for a DC Servomechanism with an Internal Dither Created by a Limit Cycle

Purpose of this paper is designing of a positional angle control system for a DC servomechanism. The servomechanism system consists of a direct current (DC) motor, a motor driver, a measuring sensor, and a control board to adjust angular position. The motor in the servomechanism has a non-linear element called dead-zone. Presence of dead-zone causes the nonlinear behavior of system. Injecting a high frequency signal called dither to input of nonlinear element is a method to reduce the nonlinear effects in that system. There are two approaches of injecting dither to system, the first is generating dither and injecting independently and the second is generating dither by creating a limit cycle. In this paper, a relay and an appropriate controller are exploited to create a limit cycle with adjustable amplitude and frequency in the servomechanism system. This limit cycle generates an internal dither in the system. The frequency of limit cycle is adjustable by determining controller coefficients. Finally, according to the simulation results, the servomechanism was implemented practically and the validation is performed.