Modular Multi-scale Assembly System For MEMS Packaging
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A multi-scale robotic assembly problem is approached here with focus on mechanical design for precision positioning at the microscale. The assembly system is characterized in terms of accuracy/repeatability and calibration via experiments. The MEMS packaging requirements are studied from an assembly point of view. The tolerance budget of the assembly ranges from 4 microns to 300 microns. The system components include robots, microstages, end-effectors and fixtures that accomplish the assembly tasks. Task assignment amongst this hardware has been accomplished based on precision and dexterity availability. Various end-effectors and fixtures have been designed for use with off-the-shelf hardware (robots and microstages) to develop a coarse-fine positioning system. These end-effector and fixture designs are tested for precision performance. The robots and the vision system are calibrated to an accuracy of 11 microns or less. Inverse kinematics solutions for one of the robots have been developed in order to position parts in the global coordinate frame. Conclusions have been drawn with regard to implementation of calibration, fixturing, visual servoing or a combination of these techniques to achieve assembly within the specified tolerance budget as required by the target application. End-effector performance is improved by tuning the PID gains of the controller such that tool oscillations are minimized.