Fast Response Actuation Of Piezoelectric Stacks Based On The Time-sequence Method

Fast response is one of the main advantages of piezoelectric actuators. Currently, the reseaches on piezoelctric actuators are all based on the same driving methodology that all the piezoelectric layers are charged at the same time, in which the piezoelectric stack is treated as an entirety and the influence of the stress wave propagation in the stack on the output is neglected. To solve this issue, a novel ultra-fast time-sequence driving method is proposed in this article. This technique drives each piezoelectric layer in sequence by considering the stress wave propagating in the stack and ensures that the stresses from each piezoelectric layer reach the top of the stack simultaneously. In this method, a linear superposition of stresses generated by each piezoelectric layer is obtained and the response speed of the piezoelectric stack is also greatly improved.First, the equations of the stress wave and the stress propagation in the piezoelec-tric stack are derived and analyzed in this paper. Then a finite element simulation soft-ware COMSOL Multiphysics is used to structure the piezoelectric stack mode and the time sequence driving pulses. The outputs of the stack under the time-sequence driving method and traditional method are simulated when the underside of the stack is directly and rigidly fixed. The results indicate that the response speed of the time-sequence driv-ing method has not been well improved because that the downgoing waves generated by the piezoelectric stack are not linear superposition and they will propagate to the top after the bottom reflection, thus largely lengthening the response speed. To verity this conclusion, an infinite piezoelectric rod base is set in the bottom of the piezoelectric s-tack to absorb the downgoing stress wave. At this time, the simulation results show that the response speed under the time-sequence method is 2.75 times under the traditional driving method. Besides, we have made further selection and optimization for the base and a more suitable base is designed.Finally, to verify the time-sequence method by experiments, a piezoelectric stack that can be charged with time-sequence method is manufactured which consists of four-teen piezoelectric ceramic rings. A time-sequence driving circuit that can engender a series of pulses is built by using the thought of low voltage to control high voltage. The delay time between adjacent pulses is adjustable and the pulses have a very transient rising time. The PVDF piezoelectric films are used to measure the dynamic response of the piezoelectric stack. The experimental results show that the response speed un-der the time-sequence method is 2.67 times under the traditional method and the time-sequence method achieves a linear superposition of the stress from each piezoelectric layer. Moreover, the response speed remains unchanged in despite of the number of charged piezoelectric layer and the amplitude of the driven voltage.By using the time-sequence method proposed in this paper, the piezoelectric stack can output enough displacement with a very momentary response time. It will not only largely improve the dynamic performance of the piezoelectric actuator, but also plays a crucial role in the applications of piezoelectric stacks for high speed driving.