Model and Experiments for Compound Control of a Piezoelectric Micro-gripper

To improve the gripping performance of a piezoelectric micro-gripper, a compound control system is designed. The hysteresis model of the piezoelectric micro-gripper is presented through improving the PI (proportional-integral) model by using the dead zone operator, and the feedforward controller based on the hysteresis model is designed. Then a PID (proportional-integral-derivative) feedback controller with a parabola integral and differential forward is designed by improving the conventional PID control algorithm. Finally, a compound controller is proposed, which consists of the feedforward controller and the modified PID feedback controller. Under the compound control, the response time of the micro-gripper descends to 0.09s for a desired step signal of 5um, which is a little faster than the feedforward control, and significantly faster than the PID feedback control. Under the input of a maximum displacement of 15.2um, the steady-state error of compound control is almost zero if excluding the sensor noise. Experimental results indicate that the proposed compound control possesses better performance comparing with the feedforward control and the PID feedback control, such as faster response speed and higher steady-state accuracy.