| With the rapid development of precision engineering,biological sciences and microassembly,microgripper as a typical end-effector of micro-nano operation technology which can achieve high precision micro-operation has been widely used in various fields.Because of the increasing vulnerability of the operating object and the complexity of the environment,higher requirements for the force of the end of the gripper are proposed.To realize the constant force micro-operation and reduce the complexity and uncertainty of the whole mechanism,the constant force microgripper based on the principle of zero stiffness and meeting the requirements of high precision,large range and high stability has gradually become the key point in some special environments.In this paper,aiming at the above challenges,a multi-stage amplification constant force microgripper system driven by piezoelectric ceramics is proposed,and the design of the whole micro-gripper system,the establishment of static model,finite element simulation and analysis and experimental verification are studied as follows.Firstly,to reduce the integration of sensors and controllers of the system,a constant force mechanism is designed.Meanwhile,a novel three-stage amplification mechanism is proposed to achieve constant force gripping with high precision,large range and high stability.To increase the natural frequency of the gripper,a guiding mechanism is connected at the end of the amplification mechanism,and the constant force output of the whole mechanism is achieved by series connection of actuated module and passive module.Finally,a piezoelectric-driven microgripper system including mechanism and actuator was designed.Secondly,based on Hooke’s law,the output stiffness of the micro-gripper is obtained.For guiding mechanism and positive stiffness beam,the static model is established by pseudo-rigid body and virtual work principle,and the force-displacement relationship of negative stiffness beam is obtained based on elliptic integral principle.For the three-stage amplification mechanism,the forces in three directions of the compliant hinge are considered,and the statics model of the microgripper under the gripping and free states is established based on the elastic beam theory.Then,the static model is verified by finite element simulation.Through the analysis of the gripping process of the gripping,the relationship between the output force and the input displacement of the constant force microgripper is obtained,and the constant force interval and size of the gripper are analyzed as well.Based on the stress-strain results of the microgripper under gripping and free conditions,the fatigue failure during gripping is obtained.The natural frequencies of the gripper in two states are also obtained by modal analysis.Finally,from the theoretical analysis and simulation results,the constant force microgripper is designed and processed,and the force and displacement sensors are assembled to build the experimental system.Based on the experimental results,the accuracy of the static model was verified.Through the gripping experiment under various states,the characteristics of high precision,large range and high stability of the microgripper were verified.At the same time,according to the sweep frequency experiment,the dynamic characteristics of the gripper under different states were analyzed. |
