The Principle Research On Small Optical Pattern Rotary Encoder With High Resolution

The optical rotary encoder is an instrument for measuring the angular position, whichis also named angular displacement photoelectrical sensor. The devices of optics,mechanics and electricity are integrated in the optical rotary encoder. It is widely usedin the dynamic measurement and real-time control system in the aerospace, defenceand the technology fields, because of its simple structure, high precision andresolution. With the development of space technology, it is not only needed toimprove the measurement accuracy of the optical rotary encoder, but also to controlthe device’s volume and weight. In this thesis, an optical pattern rotary encoder isstudied, which can achieve the miniaturization and high resolution for optical rotaryencoder by optical imaging and digital image processing technology. It is significantfor the aerospace instrumentFirstly, the current research on optical pattern rotary encoder and the analysis about itscharacteristics and principle are described, in reference to a large number of domesticand foreign scientific literatures. And the theory for optical pattern rotary encoder isstudied, including optical imaging, pattern recognition, and displacement detectiontechnology.Secondly, the design guidelines are given for encoder’s coarse code and precisioncode, which use the binary code unit and the baseline to reduce the code disc’sdiameter. And the encoder’s codes are arranged radially. Through selecting the opticalmaterials, a code disc is designed for the small optical pattern rotary encoder.Based on balancing the image internal data, the centroid detection algorithm is studiedto calculate the precision code and improve the encoder’s resolution. An improvedalgorithm for the precision codes subdivision is also studied to reduce the amount ofcalculated data. The coarse code recognition and correction algorithm is also studied. Using imagerecognition technology, the coarse code is calculated by marking the code discimage’s binary code value. Because of scratch or attachment, the error code track canbe detected by recognizing the coarse code.Thirdly, the data acquisition and processing system of the optical pattern rotaryencoder is designed. The array image sensor which replaces the traditional separationof optical receiver devices receives the image signal as the encoder’s data. The imageprocessing circuit which includes CPLD, DSP and SDRAM electronic devicesconverts the image information of the code disc for angular information.Finally, the optical pattern rotary encoder’s resolution and precision were tested by theexperiment. And the experimental results were analyzed. In the experiment, weapplied this method in an optical pattern rotary encoder which diameter was φ38mm.The results showed that the encoder’s angular resolution reached5arcseconds and thepeak to peak value of the angular measurement error was61arcseconds.