Design of Miniaturized Capacitive Angle Encoder Using Semi-Cylindrical-Shaped Shaft Electrode

In this article, a miniaturized, easy-to-apply, low-cost capacitive angle encoder is designed. Compared to traditional capacitive encoders, the encoder is more compact. The encoder is composed of a stator and a rotor. An electrode made of flexible printed circuit board (FPCB) is attached to a 3D-printed cylindrical shell to form the stator. The rotor is a semi-cylindrical-shaped shaft electrode manufactured by using computer numerical control (CNC) machining. To enhance encoder stability, electrodes between the stator and rotor are configured into two sets of differential equivalent capacitances: rough-channel capacitance and fine-channel capacitance. The absolute rotational angle of the encoder is obtained by these capacitances. Furthermore, a new algorithm is proposed to avoid the non-linear errors caused by the edge effect of small-size capacitors. Then, a capacitance measurement module is designed to measure capacitance in the picofarad range. Finally, a prototype of the capacitive angle encoder and capacitance measurement module are fabricated, and a series of experiments are carried out to test the performance of the proposed encoder.