Performance Analysis And Control Technology Of A Microgripper Based On Monolithic Compliant Mechanism

Micro-assembly and micromanipulation, which assemble parts with extremely small dimensional size as a complicated micro-electro mechanical system (MEMS), is a rapidly developed field with development of micro/nanotechnology and MEMSs. Microgrippers, which directly contact the operated objects as the end-effectors of micro-assembly and micromanipulation systems, play a crucial role in micro-assembly and micromanipulation. Microgripper technology, which involves micro-machinery, materials, sensors, automation, electronics, and computers, is widely applied to MEMS, microelectronics, optics, microfluidics and biological sciences, and other fields. The size and shape of operated objects are not fixed and fragile. On the one hand, microgrippers should possess large tip displacement with high resolution and be moved accurately in vision field of microscopes. On the other hand, in order to avoid damaging micro-parts, the gripping force should be monitored and feedback controlled. Therefore, microgrippers with large tip displacement, high resolution, integrated gripping force and tip displacement sensors, and feedback controller are desired.In this thesis, based on a piezoelectric-driven microgripper with parallel movement of gripping jaws, the relationships between the input and output of the gripping force/tip displacement are established, and the dynamic model is improved. The monolithic compliant mechanism (MCM) is integrated with gripping force sensor (GFS) and tip displacement sensor (TDS) based on analyzing the strain of the MCM, and both the gripping force sensor and tip displacement sensor are calibrated. The gripping force characteristics of the developed microgripper are tested using the established experimental setup. Based on the integrated gripping force sensor tip displacement sensor, the relationships between the applied voltage and the gripping force and tip displacement are modeled. The PID feedback control and model reference adaptive control (MRAC) are applied to improve the control accurary of the gripping force and tip displacement.The major research works completed in this thesis include:1.Based on the developed piezoelectric-driven microgripper, the characteristics of the gripping force and tip displacement are analyzed, and the relationships between the gripping force, input force, tip displacement, and input displacement of the MCM for microgrippers are established with the pseudo-rigid-body-model (PRBM) method and analyzed. The original dynamic model of the MCM has been improved. The theoretical analyses have established a theoretical foundation for monitoring and control of the gripping force.2.The strain characteristics of the MCM and the possibility of monitoring griping force and tip displacement are analyzed. The relationships between the maximum strain of the single-notch flexure hinges with the tip displacement and input force, and the relationships between the maximum strain of the cantilever beams with the gripping force and the deformation cantilever beams are established, respectively. Comparisons between the theoretical models of strain characteristics for the MCM and the simulation results using FEM are carried out. The strain characteristics of the MCM and the strain distribution of the strain gauges bonded onto the MCM are analyzed using ANSYS software. The research results indicate that the strain gauges can be bonded onto the single-notch flexure hinges and the cantilever beams as tip displacement sensor and gripping force sensor, respectively, and the outputs of sensors are linear.3.The tip displacement and gripping force are measured by semiconductor strain gauges pasted at the single-notch flexure hinges and the cantilever beams, and the outputs of strain gauges are transformed and processed by Wheatstone bridge. Based on the parallel movement of the jaws and the cantilever beam bending theory, a method to calibrate the gripping force sensor by using a non-contact displacement sensor to measure the deformation of the cantilever beam is proposed.4.The gripping force sensor and tip displacement sensors are calibrated using the established experimental setup. The gripping force characteristics are tested and compared with the theoretical model, a case of gripping a micro object to simulate the gripping process is shown. The experimental results indicate that the relationship between the tip displacement and input force, and the relationship between the gripping force and input force are linear. Theoretical model of the gripping force can predict the actual gripping process.5.Based on the integrated gripping force sensor and tip displacement sensor, the relationships between the applied voltage and the gripping force and tip displacement are modeled. The PID feedback control and model reference adaptive control are applied to improve the control accurary of the gripping force and tip displacement. In order to evaluate the proposed method, the corresponding simulation system is established and experimently verified. The simulation results indicate that the control error by the PID feedback control is periodical, while the tracking control error of the adaptive control for the gripping force and tip displacement is small, and the control accurary by the adaptive control is better than the PID control.The research works in this thesis provide theoretical basis and method for design, analysis, and control of MCMs for microgrippers.