Abstract
LIGA process in MEMS is at present expensive and has brought pollution problem. In this study, a novel device provides functions with environmental protection and being a physical process is developed to promote MEMS technology.A micro EDM that is based on EDM waveform discrimination is researched and developed in this study. In this design, a thin-disc edge-driving ultrasonic actuator, which developed by our group, is used to drive thin wire electrode. This actuator, possessing micro stepping capability simplifies the design of the micro EDM system. Using this actuator as a driving element of thin wire electrode feeding mechanism, an action with non-interrupted electrode feeding is achieved.This micro EDM device has a set of adjustable EDM circuits and an on-line EDM waveform discrimination system. The EDM waveform discrimination system with programmable chips can calculate the average spark delay time and provide useful electrical discharge (open-spark-arc-short) information according to logical combination between different levels of gap voltage and discharge current. The electrical discharge information thus obtained provides data as input parameters for the fuzzy controller. By this discrimination system, a closed loop controller without any sensor is obtained.The control system consists of two fuzzy controllers. One is gap fuzzy controller with amplitude and pulse width modulation. This controller can follow fuzzy inference to select pulses of different amplitudes, active frequencies and duration periods to keep the balance of electrode feeding and machining rate. The other one is discharge off time fuzzy controller that can adjust discharge off time when the circumstance between electrode and workpiece is inadequate. With these two fuzzy controllers, a stable iso-energy micro EDM device is completed.