A capacitive rotary encoder with a novel sensitive electrode

In this paper, a capacitive rotary encoder for contactless angle measurement is presented. The encoder includes a rotor and a stator. The rotor is composed by a coupling electrode and a sensitive electrode and the stator is mainly composed by an excitation electrode and four collection electrodes. A high frequency sinusoidal voltage is acted on stator's excitation electrode to offer a carry voltage on rotor coupling electrode with contactless. The petal-form sensitive electrode together with the four collection electrodes encodes angular position to four variable capacitances. By C-V conversion and subtract, two amplitude-modulated signals are obtained. As specifications of these signals are the same with resolvers, a resolver decoder chip is applied to decode the two modulated signals to the angular position. A prototype is fabricated and measured. The result of the measurement indicates non-linearity over the full range is 0.1deg, which can be enhanced to 0.003deg after compensation. This shows that the capacitive encoder has great prospect to be used in the high precision measurement at a low cost.