The Absolute Angular Encoder Technique Using Linear Detector

Photoelectric rotary encoder is an angle sensor of high precision, which is usually applied to transform the angular position, angular displacement and angular velocity into digital electrical signals. It is widely used in aerospace, industrial automation and other fields because it has simple structure, small size, high resolution and the sensing process is non-contact, stable and reliable.With the increasing requirement of rotary encoder in defense, automation and other industries, the rotary encoder trends to be smaller, more intelligent and of higher-resolution. In traditional rotary encoder, there is always contradiction between the size and resolution, which means one can not obtain both small size and high resolution at the same time.In order to solve the problem, at the same time to improve the frequency response, a new photoelectric absolute angular encoder is proposed. A new single-track absolute coded disc is used in the encoder. The encoded units are directly carved on one track. In the disc, the light sectors stand for the binary "1" while the shade ones stand for the binary "0". The 7 bits binary code according to certain rules is directly carved on the track. The image of coded disc is magnified by the imaging lens, and received by the linear detector. The FPGA control circuit transforms analog signals into digital signals, which is sent to the computer. Finally the software is used for data decoding processing—An integrated 7 bits binary code is obtained by binary image processing, and the subdivision code unit is gained by subdivision technique respectively, which are both contributed to the angular information.Using the above technology, a 7 bits one-track absolute coded disc with a diameter of 40 millimeter, was presented and developed; the hardware circuit based on FPGA was designed for video acquisition and transmission; the software under Microsoft Visual C# was used to receive data and obtain angular information. In this paper, experiment had been carried out using our system. The result was compared with the laser triangulation angle measurement method. And the absolute error was about 7.51 ". Through experimental verification, the resolution of the encoder attained 16 bits.