Optimum Form of Capacitive Transducer for Displacement Measurement

Abstract

A comb-shaped capacitive transducer for displacement measurement is used as a manufacturing machine controller, a step-and-repeat camera, and an electrical micrometer. In this transducer one of the comb-shaped electrodes is fixed and the other is moved parallel to it. For an accurate measurement it is desirable to increase the difference between the maximum and the minimum values of the capacitance. It has been reported that putting dielectric protective layers on the surfaces of the electrodes effectively increases that difference. To find the optimum form of the transducer, a simulation based on the finite-element method is introduced, and the simulation is experimentally verified. To achieve the optimum form, the distance between the electrode must be made as narrow as possible, and the width of the tooth should be 20 ~ 30 percent of one pitch. The effect of dielectrics put in the capacitor is also discussed.