Optimizing the De-Bruijn Code of Rotary Optical Encoders Preventing From the Photocurrent Blooming

Abstract

The De-Bruijn sequences could provide appropriate circular arrangements to achieve a single-track absolute rotary optical encoder in the servo motor application. One example used popularly is the maximum length sequences. High-resolution single-track encoders need a sensor array to obtain the position signal simultaneously. Nevertheless, the individual photocurrents would interference by other adjacent photocurrents, like the photocurrent blooming. The circumstances would increase the bias noise for the digital binarization. The concept in this article would try to find the optimal De-Bruijn sequences to reduce the photocurrent blooming interference intrinsically without signal process remodification. Three different types of the 9-bits codes, the adjacent De-Bruijn code, the quarter De-Bruijn codes, and the optimal De-Bruijn codes, are analyzed, manufactured, and experimented in the actual encoders. Based on the open-factor of the eye-diagram, the adjacent De-Bruijn code has 0.328 and would be the worse signal quality in De-Bruijn sequences. The quarter De-Bruijn codes have 0.386 of the open-factor with 17.7% improvement to adjacent De-Bruijn code. Finally, the optimal De-Bruijn codes have 0.436 of the open-factor with 32.9% improvement to the traditional M-code. The fact would mean the possible ability of 3-bits progress from 9-bits of adjacent De-Bruijn code to 12-bits of the optimal De-Bruijn codes under the same signal-to-noise ratio.