Monocycle Encoder And Its Real-time Error Correction Techniques

Electro-optical shaft encoder is an angular displacement sensor which has been applied most widely and its angle-measuring accuracy is only next to the angular displacement sensor with laser techniques. It has been widely applied to industrial, military, aviation and aerospace techniques. High-accuracy and miniaturization is one of its main development directions. Since the action of light, during signal extracting, large amount of harmonic components must be produced by the electro-optical encoder based on Moire fringe technique. At the same time, the signal accuracy will be seriously affected by the eccentricity of grating disk and jitter of main shaft. These faults are needed to be removed by the complex structural design and processing measures. For the miniature encoder, it is impossible to attain this purpose. At present, the research for the miniature encoder is concentrated on encoding scheme, introduction of laser technique, new method and new principle, etc. A method that extracting shaft displacement information of an axis by using the motion trace of eccentral circle is proposed in the paper. It only exits a periodic signal in one cycle. The structure of the encoder is simple and its adjustment is convenient. The information of shaft displacement is exported with simple harmonic function and it does not consist of harmonic component. The mode of diameter reading inhibits the influence of main shaft jitter and provides conditions for high-power subdivision.The common high-power subdivision can only attain about 1,000 at the utmost, it can attain 20,000 of subdivision in the special-purpose case such as small angular "angular standards". An amplitude segmentation method based on A/D conversion is adopted in the system. By using orthogonal property of encoder signal, 13-bit, i.e., 8192 times of subdivision is implemented in complete period range with 12-bit A/D conversion. It has the advantages of simple interface and large applicability.Another main work in the paper is to apply correlation function to real-time error correction techniques for encoder. The high-precision encoder cannot do without error correction techniques. The common measures are to adopt complicated structure, special design, inhibiting or reducing error source, meticulous adjustment, and point-by-point or piecewise compensation according to error curve after assembling. The real-time error correction method is proposed in the paper. By introducing carrier modulation technique, it can monitor error variation quantity and correct it at real time and dynamically.Combined with real-time error correction techniques, a monocycle 13-bit encoder with a size of φ22×35mm is constructed . Its volume is far less than the traditional encoder with same bits and is the minimum 13-bit encoder at present, and a large compression space is still existed in the encoder structure.As a complement and improvement in electro-optical encoder, the monocycle encoder based on Moire fringe techniques has broad application prospect.