Theoretical And Experimental Research On Low Stiffness Contact Stick-slip Inertial Piezoelectric Actuators

The frontier science fields such as large-scale integrated circuit,microscopic observation and nanotechnology are important research areas pointed out by the National 14th Five-Year Plan,and the further research of these frontier science fields is inseparable from the precision/ultra-precision driving and positioning technology.The inertial piezoelectric actuators based on inverse piezoelectric effect have the characteristics of high resolution,small size,fast response,immunity to electromagnetic interference and high compatibility.It is one of the important supporting technologies in the above advanced technology fields.Stick-slip inertial piezoelectric actuators use friction as the driving force to achieve large-stroke linear or rotary motion by means of step accumulation.However,the existing stick-slip inertial piezoelectric actuators still have some shortcomings,such as the unclear relationship between the contact force and output characteristics,the difficulty of contact force adjustment and the lack of single-step motion characteristics control methods,which seriously restrict the application of actuators.In this paper,a low stiffness contact method was proposed to overcome the shortcomings of the existing stick-slip inertial piezoelectric actuators,and on this basis,the related theoretical analysis of the low stiffness contact inertial piezoelectric actuators was carried out,as well as the structural design,simulation,prototype manufacturing and assembly,and experimental testing of a series of low stiffness contact stick-slip inertial piezoelectric actuators.The main research contents of the paper are as follows:(1)The realization method of the low stiffness and brief configuration of the low stiffness contact stick-slip inertial piezoelectric actuator were proposed.According to the brief configuration,the static equivalent model of the low stiffness contact stick-slip inertial piezoelectric actuator was established by comprehensively considering the stiffness of piezoelectric stack and compliant mechanism,the preload deformation embedded by piezoelectric stack,as well as external load.The system dynamics model of the actuator was built based on the dynamics models of piezoelectric stack and the compliant mechanism as well as the brief configuration of the low stiffness contact stick-slip inertia piezoelectric actuator,which provides the theoretical basis for this type actuator.(2)The structure design and analysis of the low stiffness contact stick-slip inertial piezoelectric actuator were carried out,and the actuator prototype was developed.And then the basic output characteristics of the actuator contact were systematically tested from the aspects of contact force measurement and assembly interchangeability.The analysis and test showed that the low stiffness contact stick-slip inertial piezoelectric actuator can achieve the contact force measurement without sensors.At the same time,the relationship between the contact force and single-step motion characteristics of the low stiffness contact inertial piezoelectric actuator is clarified.That is,with the increase of contact force,the single-step motion characteristics of the actuator will gradually evolve from sudden jump,smooth to backward motion,the stepping displacement will gradually decrease,the operating bandwidth of frerquency will gradually increase,and the loading capacity will gradually increase.In addition,the theoretical analysis and experimental test also prove that the low stiffness contact stick-slip inertial piezoelectric actuator has high assembly interchangeability.(3)The shape regulation and amplitude regulation of the single-step motion of the actuator were explored by using the developed low stiffness contact stick-slip inertial piezoelectric actuator.On the one hand,the switching rules between single-step motion curves with different shapes are studied.The test results showed that the switching of different single-step motion curives(sawtooth shaped,stepwise shaped and S shaped smooth)could be achieved by controlling the driving frequency.Increasing the mass of the mover can not only realize the transition from S shaped smooth to linear smooth,but also reduce the driving frequency required for the single-step motion curve transition.At the same time,the actuator could achieve low driving voltage high speed movement(238.46 mrad/s:36 V,150 Hz)as well.On the other hand,the potential of the actuator designed by the low stiffness contact to regulate the amplitude of the single-step motion is studied.The analysis and test results showed that the designed actuator has good amplitude control ability of single-step motion and could significantly improve its motion speed.Under the locking force of 2 N,driving voltage of 100 V and driving frequency of 700 Hz,the fastest speed of the actuator reached 20.05 mm/s.(4)To achieve smooth linear motion under low frequency and low mass of mover,a low stiffness contact stick-slip inertial piezoelectric actuator was developed by coupling two driving units and an auxiliary friction unit.And then the mechanism of smooth linear motion of the actuator is studied and analyzed.The dynamic simulation and experimental results showed that the actuator could achieve continuous,smooth,high linearity and long stroke motion under the condition of external load or no external load.In particular,the actuator can still move smoothly and linearly in the range of 0-30 g horizontal load.At the same time,the vertical load and preload deformation have little effect on the single-step motion curve of the actuator.The actuator can work stably in the range of 0-700 g of vertical load and 0-0.5 mm of preload deformation,and its motion curve is basically the same.In this paper,the related theory and experiment of low stiffness contact inertial piezoelectric actuator provide the basis for the design,analysis and application of subsequent this type of actuators.At the same time,the measurable contact force without sensors and high assembly interchangeability of low stiffness contact piezoelectric actuators are of great significance for mass production.The four single-step motion characteristics of sawtooth shaped,stepwise shaped,S shaped smooth and linear smooth and their controllability play an important role in broadening the application field of piezoelectric actuators.