Analysis And Control On The Dynamic Creep Of A Stack Piezoelectric Actuator In Low Speed And Wide Range Applications

A piezoelectric actuator(PEA)is a solid actuator with a smart material as its main component.It is a dominant actuator on ultra-precision application because of its subnano-resolution.PEAs have four known non-linearities,namely,hysteresis,creep,vibration and drift.The first two inherent non-linearities are investigated extensively.Effective methods are obtained to model and control them in terms of materials or physics from the macro/micro level.Researches on rate-dependent and rate-independent hysteresis have been intensively conducted.Meanwhile,efforts have been exerted to suppress creeps in the stable stage or in single step.However,research on the dynamic creep,which is defined as the effect of creep in the transient stage and relationship of steps,has just attracted increasing attention.Therefore,the dynamic creep needs to be further investigated.The main focus of this dissertation is developed as follows:determine the dynamic creep through experiments,model it,and then attempt to suppress or control it.First,the dynamic characteristics of creep are verified by performing experiments when PEA is applied in a low frequency and extensive range of applications.Second,a hypothesis concerning the separation point between creep and hysteresis is proposed by considering in the rate-independent hysteresis under 1%of the natural resonant frequency.The separation point is investigated according to this hypothesis.Third,a low bi-directional voltage spike is used to suppress the dynamic creep to avoid high voltage spikes caused by using advanced algorithms.Fourth,a fuzzy PI composite controller is proposed to compensate for the dynamic creep with different voltage discretizations.Experiments show the effectiveness of the proposed controller.Meanwhile the results also reveal that this type of controller cannot decrease the spike amplitude any further.Fifth,PEA is intrinsically a fractional order actuator,thus a fractional order controller is designed.The fractional order composite controller is capable of suppressing the non-linearities and can produce a considerably low spike voltage with compensation of hysteresis by the direct inverse.The main contributions are listed as follows.1.The effect of the dynamic creep in low-speed and wide range application is explored by performing a series of experiments.The definition of the dynamic creep is preliminarily elaborated.Thereafter,the change rules of the dynamic creep are investigated.The hysteretic characteristics of the dynamic creep parameters are verified using a modified log-type model and an inverse proportion function.A hypothesis on the separation point of creep and hysteresis is proposed,and forward prediction ability is verified.2.The voltage spike direction is the key to creep suppression.Moreover,the voltage spike amplitude and duration substantially influence the creep suppression.The direction is correct when it has the same trend with the applied voltage variation;otherwise,the voltage spike has no good effect.The spike amplitude also has non-linear influence on the dynamic creep.Results show that the spike amplitude has an optimal value in a certain situation.A considerably long spike duration facilitates the creep suppression.However,a substantially long duration can delay the stable moment.3.A fuzzy PI composite controller is developed to suppress the rate-independent hysteresis and the dynamic creep.The experiments verify that the composite controller plays an effective role in suppressing the rate-independent hysteresis and the dynamic creep.4.A composite controller with a fractional order PI is proposed to the dynamic creep suppression by considering the intrinsic fractional order of PEA.Results show that the controller has a good capability on the dynamic creep suppression.Meanwhile,the proposed controller can also decrease the spike amplitude,as well as possesses a rapid and small tracking error.This dissertation presents a substantial exploration on the intrinsic non-linearities of PEA;therefore,the results have an important application value.Researches on the separation point of hysteresis and creep leads to a new theoretical research direction of PEA.