A Simple Approach to Design a Capacitive Rotary Encoder

In order to optimise the mechanical error and to avoid electrical interface from a rotating plate of the capacitive rotary encoder, a state-of-the-art designing approach is presented in this article. In contrast to the multi-electrode capacitive sensing pattern, the proposed structure is very simple. It has three pairs of stator electrodes and a rotor plate (RP). In each stator plate, three isolated conductive arc sectors are fabricated using standard PCB technology. Likewise, an arc sector, an aluminium oxide-based metallic plate is placed between the stator pairs and the plate is firmly attached with a shaft. This plate is named as RP. Since the RP acts as a dielectric medium hence; it is free from any electrical interface. Henceforth, the angular position of an object has been determined by analysing the variation of three parallel capacitances, which develops due to the rotation of dielectric medium inside the stator pairs. In this preliminary investigation, a prototype has been designed, developed and tested in laboratory condition to proof of this concept. A satisfactory result has been found with an accuracy of ±0.6°, resolution of 0.0003° and repeatability of ±1° in the measured range of 0-360°.