A Comprehensive Model For The Piezoelectric Stick-slip Actuator And Strategy For Compensating The Thermal Effect Of The Actuator

The high resolution (several nanometers) and large range motion characteristics (theoretically unlimited or only limited to the mechanical structure) of the piezoelectric stick-slip (PZT-SS) actuator make it distinct from other types of actuators. By taking into account the linear dynamics and hysteretic behaviour of the piezoelectric actuator, the presliding friction between the end-effector and stage, thermal effect, as well as the mass of the end-effector, a comprehensive model representative of the end-effector displacement of the PZT-SS actuator is presented in this thesis. The parameters of the model are determined using the system identification techniques with a careful procedure. The model with the identified parameters is simulated in Matlab/Simulink and the simulation results obtained are compared with the experimental results drawn from the literature to validate the model. The validated model represents the effects on the displacement of end-effector more comprehensively.The proportional derivative (PD) controllers are applied to control the piezoelectric actuator and whole system, respectively. It is found that the maximum overshoots are reduced significantly. However, the transient time of the whole system is not shortened.Two control strategies are developed to compensate the thermal effect of the PZT-SS actuator. The first strategy is that the PD controller only looks after the piezoelectric actuator while an accessory controller controls a mechanical system that allows adjusting the pressure between the end-effector and stage. The second strategy is that the self-adjusting PD/PID controller to control the whole system and compensate the thermal effect. As a result, in the first control strategy, the compensating temperature range can be in any range using the accessory controller. However, the mechanism system to adjust the pressure between the end-effector and the stage should be designed. The first strategy will increase the cost. In the second control strategy, the results of the self-adjusting PD/PID controller is more accurate, and the algorithm is less complex as well. However, the compensating temperature range is limited (30℃～38℃). PID controller is better than self-adjusting PD controller to compensate the thermal effects.