A novel high resolution miniaturized capacitive rotary encoder

In this paper, design and prototyping of a novel, high resolution, and low-cost capacitive encoder were presented. Detailed analysis showed that the number of poles on the rotor should be as high as possible to keep the gain high and to reduce the non-linearity. Moreover, contrary to the common intuition, inter-electrode gap is found to have an optimum non-zero value, corresponding to a particular number of poles, in order to maximize the gain. However, increasing number of poles brings practical problems due to manufacturing limits and digital electronic frequency load. As the electronics, micro-controller based digital signal processing is used to keep the cost as low as possible. With miniaturizing the encoder geometry as a design target, the number of plates were increased to three to increase the capacitances. One prototype, which is around 3 cm in diameter could be successfully mounted to an industry oriented DC motor and tested. The tests of this miniaturized encoder showed non-linearity error of 0.12% and resolution of 0.02°. One source of the non-linearity error is the DC motor itself, and we believe that with a better setup, the error could be measured to be even better.