The Research And Realization Of Coding And Demodulation Method For Absolute Single Encoder

Based on single-track coding and linear CCD image sensor technology, the feature ofsingle-track absolute angular encoder is high resolution, small size, high precision andun-touch photolithographic method. The encoder disc is made by glass on which there are twowidth of bar specify two kinds of code and the center of the bar specify the angular interval ofthe circle. The work principle is: a LED is used as light source, and a linear CCD is used toconvert position light signal into timing electrical signal. The data is sampled by AD and is sentto FPGA to have the angular value. And then FPGA calculates the integer parts of the angularvalue first, then refine and obtain the residuum parts of the angular value.The coding and encoding theory of the single ring absolute encoder disc and therealization of them are detailed presented in this paper, based on analyzing and studying themeasuring theory of the single ring absolute encoder disc and the theory of high resolutionrefining. Firstly, a novel approach for coding and programming has been proposed andperformed. Secondly, the photo-electronic detecting and image data collection system wassetup through the FPGA and linear CCD. Thirdly, an algorithm to calculate the center of thedisc image by means of second order polynomial cure fitting with interpolation method hasbeen proposed and performed. The error of angular measurement is reduced by calculating thecenter of multi coding bar’s image. And0.0125pixel sensitivity of object center detecting fromlinear CCD image has been obtained.Lastly, precision of linear CCD is analyzed based on MATLAB, the factors that have aneffect on the encoder are analyzed and given, and some advice which can be good for theencoder is presented, which is suitable for the engineering application of the encoder.