Research On High Bandwidth Precision Positioning System Based On Compliant Mechanism

With the development and profound use of precision positioning technology in all walks of life,people's requirements for precision positioning technology are no longer limited to high precision and large range,and more attention is paid to the response speed of precision positioning.The rapid response precision positioning system can be used in the fields of high speed scanning probe microscope,high speed micro-nano machining and high speed micro-nano operation.The high speed precision positioning system requires the high bandwidth performance of the system,and the key and difficult point of constructing the high bandwidth precision positioning system lies in the structure design of the nanopositioning stge and the corresponding control strategy and method.In this paper,aiming at the low bandwidth of traditional precision positioning,a high-bandwidth two-degree-of-freedom nanopositioning system based on compliant mechanism is designed.The main research contents are as follows:(1)Structure design of nanopositioning stage.In terms of structure,the bandwidth performance of nanopositioning stage mainly depends on the natural frequency of the stage.In order to obtain high natural frequency stage,the article designed a two degree of freedom parallel nanopotitioning stage based on the kinematics of structure characteristics and design requirements,adoptting two kind of flexures including doubly clamped beam and parallelogram hybrid beam by which not only contribute significantly to high stiffness for but also accuracy and decoupling performance of stage.The theoretical stiffness model of stage is established by using Castigliano's second theorem.According to the Lagrange equation,two theoretical natural frequency models of the stage structure itself and the stage attached actuator are obtained.In order to further improve the natural frequency of the stage,an optimization model of the natural frequency based on the size of the flexible element was established.According to the design objective,constranits concerning with the stroke of stage,the flexibility ratio between compliant beams,the range of size variables and the maximum stress constraints are set to obtain the optimal natural frequency.Finally,finite element simulation is used to verify the accuracy of stiffness model,natural frequency model and optimization results in this chapter.(2)Research on closed loop control system.Nanopositioning stage under the open-loop can't precisely position,so a suitable closed-loop control algorithm must be established in positioning system.Considering the hysteresis effect of piezoelectric stack actuators and the errors caused by other disturbances,the feed-forward polynomial hysteresis inverse model conbined with PI controller and fuzzy PI controller are used to control the stage quickly and accurately.In consideration of dynamic tracking,tracking performance of high-frequency periodic signals of a stage is an important index to measure the bandwidth performance of stage.Both the errors in the movement of stage and the hysteresis model derived from the first order differential equation of the Duhem model can be regarded as periodic errors so repetitive control is used to compensate these two periodic errors in this paper,(3)Experimental system construction and experimental research.The designed stage is machined and related components are selected according to the high bandwidth requirement in system.The performance experiments of the precision positioning system are conducted,including experiments of motion stroke,coupling,dynamic performance and periodic triangular wave tracking in open loop.PI control,hysteresis feed-forward PI control and fuzzy PI control closed-loop experiments are also conducted,including continuous step performance,precision positioning and circular trajectory tracking;triangular wave tracking experiment under repetitive controller metioned above is carried out.The experimental results show that stage not only has the ability of rapid positioning at the nanometer level under static conditions,but also can track the periodic triangular waves with the frequency below 1kHz at the nanometer level.The stage can effectively improve the moving speed of traditional precision positioning,and will be applied in the field of high-speed precision positioning in the future.