Design,Modeling And Experiment Of Micro-Gripper Based On Piezo Actuator

Micro-gripper was widely applied in biological engineering,medical sciences,MEMS,aerospace and other frontier fields.The design has important theoretical and practical significance in clamping micro objects with irregular shapes,avoiding damage micro objects and releasing stability micro objects.Two micro grippers are designed by using the method of experimental design,and carries on the performance optimization and the release operation.The main content is listed as follows:A novel plane micro gripper is designed by adopting lever principle.In order to tradeoff the opening distance,gripping force sensitivity and rapid response of the micro gripper,a performance optimization method was proposed based on Kriging model.The parametric finite element model of the micro gripper was established by using the finite element software ANSYS.The performance index corresponding to different structural parameters,such as amplification ratio,natural frequency,output stiffness and maximum stress can be obtained based on the model.Latin hypercube sampling method was used to select test points,and the response values corresponding to each test point are calculated by using ANSYS.The correlation analysis is carried out according to the test points to determine the structural parameters affecting greatly the performance of the micro gripper,and the parameters are selected as the optimization design variables.The nonlinear model reflecting the relationship between the performance index and the design variables is built by using the Kriging theory according to the experimental sample points,and it can provide accurate theoretical model for the multi-objective optimization of the micro gripper.The multi-objective optimization model was established with the objective of the magnification ratio,the natural frequency and output stiffness,the strength as the constraint.The multi-objective genetic algorithm is applied to obtain the optimal Pareto set of three goals,and the optimal design scheme can be determined from the Pareto set by weighing three performance indexes.The comparative analysis of the performance indexes of the micro-gripper before and after optimization shows that the magnification ratio increases 7.4 %,the natural frequency increases 16.46 %,the output stiffness increases 9.84 %,the maximum stress decreases by 5.75 %.It illustrate that the proposed performance optimization method is effective.In order to avoid the injury or loss of small objects when plane micro gripper operating the small objects,the gripper force needs to be predicted and controlled.A structure – sensing integration design idea is presented,which the structure of micro gripper is integrated with resistance strain.The optimization design of the structural parameters of the sensing unit was carried out,by taking the maximum of the strain caused by gripping force,the minimum of the strain caused by piezoelectric ceramic driving force.The least square method is applied to calibration the relationship between the input voltages of piezoelectric actuator,the gripping force and the strains of the force sensing unit respectively.The results showed that the relationship between the driving voltage and the strain of sensing unit is three-order polynomial and the relationship between the strains of the force sensing unit and the gripping force is linear.The relationship between gripping force and drive voltage can be obtained,and the relationship is three-order polynomial in order to forecast and control gripping force.The proposed design idea and calibration method provides a novel thought for micro gripper.A release operation method based on piezoelectric vibration control is proposed in order to solve the adhesion problem of plane micro gripper in the process of clamping tiny objects.Based on the theory of elastic adhesive,it is proved that the inertia force caused by the piezoelectric vibration can be used to overcome the adhesion between the micro gripper and small object.And it is illustrated that the proposed method is feasible.The dynamic model illustrated the vibration a characteristic of the piezoelectric micro-gripper is established by using the experimental method.The conditions on the amplitude and frequency of input voltage of the actuator are obtained based on the model when the micro objects can be released.The experiment stage with a micro gripper is built in order to carry on the experiments on the release of small objects.The experimental results show that the proposed method is feasible.Meanwhile,the experimental results show that the smaller the size of the tiny objects,more difficult the release.The greater inertia force is needed to overcome the adhesion force.For plane micro gripper clamping tiny objects for 2 point contact,can’t adapt to the irregular shape of tiny objects clamping operation,to design a novel spatial micro gripper which can holding different size and shape objects.Two clamping branched chain placed perpendicular form 4 point contact and holding space.The clamping branched chain is designed by two-stage lever principle,including the upper and lower channels structure,two branched chain are driven by a drive at the same time with the upper channels nested with the lower channels.Establish the regression model between its performance and structure parameters based on support vector machine in order to improve the clamping stability and range of micro gripper.To optimize the performance index based on this model.The proposed spatial micro-gripper is used to manipulate the small bolt and resistance.The result shows that the micro gripper can hold them stability.And it illustrates that the design and optimization method of micro gripper is effective.