Design Optimization And Feedforward Control Research Of Microgripper Based On Flexible Mechanism

The microgripper is an important end-effector in the high-precision microoperations,and its performance directly affects the efficiency and quality of the microoperation.This paper proposed a microgripper with high structure rigidity,large working band-width and a large magnification ratio for micromanipulation and assembly.The structural design,characteristic analysis,and feedforward compensation control of the microgripper have been systematically re-searched,and the experimental setups have been established to test the dynamic and static performances of the microgripper.The main research work of this paper is as follows.Firstly,the mechanical structure of the microgripper has been determined.The piezoelectric actuator has been selected as the driver of the microgripper.This paper presents a three-stage flexure-based amplification mechanism that mainly consists of two bridge-type parallelogram amplification mechanisms and one leverage mechanism.The first two stages are configured as two bridge-type parallelogram amplification mechanisms connected in serial to provide advantages in terms of high structural stiffness and compactness.The third-stage leverage mechanism with a larger amplification ratio is designed to ensure a large displacement output for the whole microgripper.Secondly,the displacement amplification theoretical modeling of the proposed microgripper has been established and its structural optimization and performance simulation has been performed based on the finite element method.A theoretical model of the displacement magnification has been established based on the pseudo-rigid body theory,then the relationship between the key design variables and the displacement magnification has obtained.The range of key design variables has been determined through the analysis of this model.The final value of design variables is obtained based on the response surface method.The static characteristics of the microgripper,the first to sixth-order vibration modal shapes and their corresponding resonance frequencies have been analyzed.Thirdly,a feedforward control method for the hysteresis compensation of the microgripper has been proposed.The inverse model of the hysteresis curve of the microgripper has been established based on the improved PI model,and its unknown parameters have been identified by the particle swarm algorithm.Subsequently,the feedforward control of the microgripper based on the inverse model has been performed,which improves the linearity between the output displacement and the input voltage.Finally,the experimental test systems have been established to investigate the dynamic and static performances of the microgripper.The gripper prototype has been fabricated based on the wire electro-discharge machining technique,and its performances have been validated through pick-and-place of microbeads experiments and dynamic tests.The experimental results have demonstrated the large amplification ratio of 31.88 with an excellent linearity,and the motion stroke of 218 μm with a large grasping force up to 1993 m N.They match well with the outcomes from both simulation and theoretical calculation in terms of motion range and amplification ratio.