An automatic visual-servo microassembly system is installed and tested. With a compliant polyurethane microgripper, a visual-servo system is implemented for micropeg alignment, micropeg transportation, and peg-in-hole assembly. The microassembly process is controlled by developing dynamic position-based servo through image calibration, regional-scanning with edge-fitting, and shadow-aided positioning algorithm. The main specifications of the system are gripping range of 60–90 μm, working space of 7 mm × 5.74 mm × 15 mm, and system bandwidth of 25 Hz. In performance test, cylindrical copper micropegs of diameter 80 μm and 88 μm are automatically aligned, gripped, transported, and assembled to a stainless rod with a mating hole of 100 μm.
An innovative design of a polyurethane microgripper system with force sensor is developed for the measurement of gripping force in vision-based control. A microgripper mechanism integrated with a force sensing arm is fabricated by an excimer laser. The microgripper is actuated by a self-biased-SMA (Shape Memory Alloy) actuator. A computer-vision method through the ERES (Extended Regional Edge Statistics) algorithm is employed to track the motion of gripper. The position information of the gripping point together with the deflection of the force sensing arm is utilized for sensing force. A fuzzy expert with a PI controller in a visual servo is employed to test the performance of sensing the gripping force in grasping of 38μm diameter metal rod. In the performance test, the microgripper system provides a maximum gripping size of 40μm, a maximum force resolution of 1μN and a maximum gripping force of 58μN.
A methodology to integrate FEA, pseudo-linkages model, and experimental test for input-output modeling and error analysis of compliant micromachine is developed. A four-bar micromachine fabricated from polyethylene is employed for investigations. The integration of FEA and pseudo-linkages model is simulated through the equivalence of force system and strain energy along with motion estimated under kinematic constraints. The method to integrate linear FEA and experimental test is realized through the information of stress and strain along with the data average and offset compensation of experimental creep-recovery process. Two types of four-bar micro-machines with either convex or concave joint are selected to investigate the effects of variations of compliant joints under loading. Proportional factor and indices of RMS error are defined to help the selection of joint types in the micromachines. The validity of utilizing linear model is finally supported by experimental test through data analysis and processing.
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