Research On Piezoelectric Micro-gripper Sensing Displacement And Gripping Force Of Finger

Based on the requirements of that the finger can motion in parallel, the displacement andgripping force of the finger can be detected, the micro-gripper driven by the piezoelectric actuatorwas designed based on the displacement magnifying mechanism with flexible hinge. And thestatic and dynamic characteristic analyses were implemented using finite element method.And the sensing method of the displacement and gripping force of the finger are studied by usingmetal resistance strain gage. The detailed researches are as follows:Firstly, the structure of the micro-gripper was designed and the input/output characteristics wereanalyzed. According to the requirements of that: the finger motions in parallel, the displacementand gripping force of the finger can be detected easily, strain gauge can be integrated easily on themicro-gripper, and the fingertip is sensitive, the detailed structure of the gripper was designed byusing two order lever type displacement magnifying mechanism with the rectangular flexure hinge.The relationships between the displacement and gripping force of the finger and input force wasattained based to the energy method. Since the rectangular flexure hinge existstension/compression deformation and bending deformation, the theoretic errors of the finger outputwere analyzed. The characteristics of the displacement and gripping force of the finger wereanalyzed based on bending deformation theory of cantilever beam. The results show that thedisplacement and gripping force of the finger are in direct proportion to the strains of therectangular flexible hinge C2and finger respectively. The static simulation results show that: thefinger can motion in parallel, the displacement of the finger is125.6μm when the inputdisplacement is5μm, the maximum stress122MPa is in flexible hinge B which is far less than theallowable stress, both the rectangular flexible hinge C2and the finger have good sensingcharacteristics of the displacement and gripping force respectively. The dynamic simulation resultsshow that: the first order natural frequency is300Hz, the steady state displacement and theresponse time of the finger are27μm and0.08s respectively under a step displacement of1μm.According to the above design and analysis, a micro-gripper prototype was fabricated.Thirdly, the piezoelectric coupled-field analysis for the static and dynamic characteristics ofthe micro-gripper was performed. In order to further investigate the actual operating process of themicro-gripper driven by piezoelectric actuator, the micro-gripper and piezoelectric actuator arecombined, and the mechanical and electronic input/output characteristics of the micro-gripper areanalyzed by using ANSYS piezoelectric coupled-field module. The results show that: themaximum displacement of the finger is about233.9μm when the maximum voltage of200V was applied to the piezoelectric actuator, the steady state displacement and the response time of thefinger are20.6μm and0.1s respectively under a step voltage of20V.Finally, the static and dynamic characteristic of the micro-gripper was measured experimentallybased on the sensing method using the metal resistance strain gauge. The relationship between thedisplacement of the finger and the strain of the rectangular flexible hinge C2, as well as the relationbetween the gripping force and the strain of the finger, was calibrated. The results show that thesetwo relationships are linear. The static and dynamic characteristic measurement results indicate:the displacement of the finger is78.4μm when a voltage of150V is applied to the piezoelectricactuator, the gripping force of the finger is9.2mN when a micro shaft (0.3mm8mm) isgripped, the first natural frequency is142Hz.