Modelling and Control of Electromechanical Servo System with High Nonlinearity

Electromechanical servo plays important role in automation, robotics and automotive industry. Recent passenger cars are equipped with dozens of such actuators. Often, these actuators replace the original manual and/or mechanical solution by so called mechatronic design –mechanism, electric motor and computer control. Typical example of mechatronic design is the throttle for airflow control of a combustion engine. Conventional mechanical linkage between the driver pedal and the throttle using Bowden cable is in recent cars replaced by the pedal sensor, throttle body (with DC motor, spur gears and potentiometer as position sensor) and the electronic control unit (ECU). The pedal is connected to the throttle only by means of “wire”; therefore this approach is generally called dribe-by-wire or X-by-wire. The research and development is very active in the field of steering-by-wire and brake-by-wire. Due to mass production of automotive parts and related relatively low technical quality, the dry friction is very significant in the actuator. The software implementation of position control in ECU can be challenging and interesting issue if the fast and precise response is required. Moreover, the additional strong spring nonlinearities can complicate the control as we see further.