Development of a capacitive sensing technology for the measurement of perpendicularity in the narrow, deep slot-walls of micromolds

This paper presents a novel approach to narrow, deep slot-wall measurement in micromolds. A tabletop hybrid measurement-center combining micro spark erosion and automatic optical inspection technique (AOI) with Capacitive Sensing (CS) technology is developed for measuring the perpendicularity of slot-walls in the very narrow and deep slots of precision molds. A microprobe is machined in-situ using micro wire spark erosion while the AOI system acquires images to help fast position the completed microprobe precisely over the narrow slot to be measured. Capacitive sensing with a high-frequency, low-voltage electric signal is employed between the probe and slot-wall to precisely sense the perpendicularity of the wall. A four-step probe feed approach is utilized to improve measurement accuracy. The technical feasibility of capacitive sensing technology is experimentally confirmed.