A planar capacitive micro positioning sensor

A planar capacitive micro positioning sensor has been designed and fabricated for positioning a small moving object, for example, a micro mobile robot and small parts (under about 5 millimeters). The sensor system consists of a sensor array, formed by driving and sensing electrodes, and a platform (moving object) with conductive plates. The principle of detecting position is based on the capacitance change proportional to the platform position. The capacitance between the conductive plate and the sensing electrode varies in proportion to the platform displacement. To detect X,Y positions independently and incrementally, sensing electrodes are divided into four kinds of areas, and to improve the linearity of output signals, the area of driving electrode is maximized. Using a prototype 30×30 mm sensor formed by a printed circuit board, the positioning accuracy is about ±10 micrometers. As for a Si base micro machined 4×4 mm sensor, the accuracy is estimated within ±3 micrometers. We also made an absolute type sensor array. As these sensor systems enable us to detect positions by simply adding electrode patterns, it will be very useful for micro positioning and assembly