Research On Quadruped Piezoelectric Actuator With Three Degrees Of Freedom And Its Motion Characteristics

Multi degrees of freedom(MDOF)ultraprecision actuating and positioning technology is a common supporting technology in the fields of ultraprecision manufacturing,robotics,optical instruments and life science.It has become one of the core and key technologies for the development of high-end equipment in the direction of high-grade.The rapid development of above fields puts forward strict requirements for the accuracy,stroke and degree-of-freedom of the actuating and positioning system,the common requirements are that the system should have the capability of large travel,nanometer accuracy and MDOF output s,and some of which even exceed the limit values of the existing actuating technologies.The piezoelectric actuating technology,which uses the reverse piezoelectric effect of piezoelectric material,is easy to achieve nanometer resolution,and also has characteristics of large output force,fast response,excellent electromagnetic compatibility,etc.It can be used in various ultraprecision actuating systems and has been commercialized.However,the existing piezoelectric actuating technology has a common problem that large travel,high-precision and multi-dimensional outputs cannot be achieved by a piezoelectric actuator.Aiming at this bottleneck,a quadruped piezoelectric actuator with three degrees of freedom(3-DOF)is presented based on the bionic principle;which imitates three different motion modes of quadruped creatures,i.e."swinging","walking" and "running",and three actuation modes suitable for the actuator are proposed: direct actuation mode,walking actuation mode and inertial actuation mode,and the mechanical output capabilities of the three actuation modes are complementary and crossing.Through their flexible switching,the motion outputs of large travel and high-accuracy are realized.In addition,based on the multi motion modes of quadruped,the gait motion schemes corresponding to the linear and rotary DOF outputs are planned,and the three motion strategies corresponding to the 3-DOF outputs are presented,the 3-DOF outputs are realized by the flexible switch of three motion strategies(two linear DOF and a single rotary DOF in the operating plane).As a result,actuating capability with large-scale traveling range,nanometer accuracy and3-DOF output is realized by the proposed quadruped piezoelectric actuator,which provides a novel feasible scheme for multidimensional ultraprecision actuating in large travel.The design process suitable for the configuration of the quadruped 3-DOF piezoelectric actuator is constructed by analyzing the actuation principle and operating requirements of the proposed actuation modes and motion strategies,and the basic configuration of the quadruped 3-DOF piezoelectric actuator is determined.The dynamic model of a single piezoelectric leg is established by using Timoshenko beam theory,Galerkin discrete theory and Lagrange equation;the contact model between the driving foot and the operating plane is established based on friction theory and two-dimensional contact theory.Integrating the dynamic model of the driving leg and the contact model between the driving foot and the operating plane,the dynamic model of the whole piezoelectric actuator system is developed,and the optimization design of the configuration of the actuator is completed,the structure sizes and material parameters are finally determined.A prototype of the quadruped 3-DOF piezoelectric actuator is developed and its motion characteristics are measured in detail.The experimental results show that the actuator has three-dimensional actuating capability(two linear DOF and a single rotary DOF in the operating plane).In the direct actuation mode,the travel range is6.4?m×6.4?m×79.2?rad,the linear displacement resolution is better than 16 nm and the angular displacement resolution is better than 0.198?rad.The motion with large travel at any position in the operating plane is realized in the walking actuation mode,the resolution is better than 0.1?m,and the load capacity is up to 35 kg.The maximum output speed of 3.65mm/s and displacement resolution better than 1?m are achieved in the inertial actuation mode;the measured output characteristics of the three actuation modes are complementary and crossing.The tested motion characteristics show that the actuator realizes planar 3-DOF large-scale nano positioning and has large load capacity,the characteristic of "one machine with multi functions" has been achieved.Finally,the proposed actuator is used to construct a planar nano positioning platform with large travel,and a coordination control strategy for multi actuation modes is established,a switching controller for multi actuation modes of the actuator is designed,and different actuation modes are selected automatically according to different output targets.The mechanical output characteristic test experiments of the platform are carried out,the experimental results show that the travel range is 15mm×15mm,the closed-loop positioning accuracy is better than±20nm and the planar 2-DOF nano positioning with large travel is realized.The relevant test results fully show that the developed platform has potential to be applied in fields of ultraprecision manufacturing,optical device attitude adjustment and cell manipulation.