Study On Diffractive Absolute Angular Encoder Technique

Photoelectric rotary encoder is an angular sensor, which is usually applied to transform angular position, angular displacement and angular velocity to electric signals or digital signals. It is widely used in industrial control, precise measurement, aerospace, robot and other fields for its high precision, high resolution, small size and stability.With the development of industry and technology, higher performance is required for rotary encoder. The encoder needs to have higher resolution and precision, and at the same time keep the small size. There is always contradiction between the resolution and size in traditional rotary encoder.To solve the contradiction between the size and resolution, a new absolute angular encoder technique based on grating diffraction is proposed. The positions of diffraction spot are used for absolute encoding, and their intensities are for subdivision. One code unit is composed of four gratings with different direction, and their pitches vary in different angular position. The grating diffraction is generated from the interacting between the laser and gratings. Then the diffraction signals are received by a plane array and sent into the computer. Finally, a specially designed algorithm is used to obtain the angular information.Firstly, a model was built according to the working principle of the encoder, and a simulation was executed on the subdivision signal, which proves the feasibility of diffractive encoder. Then an encoder disc was designed and manufactured. And a software was designed to process the diffractive signal of encoder disc. Finally, an absolute angular encoder system was built to test the performance of diffractive encoder. The light source was a semiconductor laser and its wavelength is 658nm, the diameter of the disc is 40mm, and the array sensor was CMOS with its resolution as 2048*1536. In the experiment, another measurement system was introduced to measure the precision of the rotary encoder. The experiment results show that its measurement error is less 78.00" and the standard deviation is 16.86"...