Incremental Optical Encoder Based on a Sinusoidal Transmissive Pattern

In this paper, a high-precision rotary encoder based on a sinusoidal transmissive pattern (STP) is proposed for detecting shaft rotation. The STP disk can be realized by coating bell-shaped transmissive area on a transparent glass. We optimize the STP design shape and parameters to achieve sinusoidal transmissive characteristics. The STP-based encoder consists of a light-emitting diode, a STP disk, and a photodetector array. Experimentally, the produced STP disk had a diameter of 60 mm. 256 columns of STPs were arranged on the circumference of this disk to provide a detection pitch of 1.40625°. Each column consisted of 50 bell-shaped STPs. In principle, an incident beam from a blue-ray light emitting diode illuminates the STP of the disk, and the angle of rotation is decoded from the sinusoidal distribution of transmissive spots on the PD. Compared with a conventional incremental rotary encoder, the proposed STP-based encoder achieves a superior angular resolution.