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The growing demand for miniaturized products motivates the advancement in micromanufacturing processes research and development. Micro Ultrasonic Machining (Micro USM) is a downscaled version of a macro USM process that is developed to fabricate complex features in chemically inert, nonconductive, hard, brittle materials such as quartz, glass, and ceramics. These materials have many applications in various fields such as optics, electronics, MEMS, and biotechnology. The micro USM process stability is hard to accomplish, because it is highly influenced by the accuracy of the machining system and the variation of the process control parameters. The repeatability of micro USM machined features is greatly influenced by the cutting force variations. Therefore, designing a robust cutting force controller for the micro USM process is essential for stabilizing the material removal mechanism and improving machining characteristics.
A new micro USM machining system has been developed to enhance the cutting force control by improving the cutting force sampling and servo control frequencies. An Autoregressive Moving Average Model with Exogenous Input (ARMAX) is then used to develop a linear dynamic model for the micro USM cutting force based on experimental data. Proportional (P), Proportional-Integral (PI), and Model Reference Adaptive Control (MRAC) controllers are designed and implemented to stabilize the cutting force for themicro USM process based on the ARMAX model. The process stability is analyzed to study the effects of these cutting force controllers on the micro USM cutting force stability, machining rate, and surface roughness of the machined features. The results show that the MRAC controller reduced both the cutting force variations (by 66% compared to the P controller) and the cutting force steady state error (< 1%). Moreover, the MRAC controller improves the repeatability of the micro USM machining characteristics.