Research On Absolute Linear Time Grating Displacement Sensor Based On Decimal Shift Coding

With the increases in the requirements of displacement measurement technology,high precision,high efficiency,and high integration have become the main performance indicators for evaluating modern precision displacement sensors.The absolute displacement sensor based on absolute coding and decoding theory.It corresponds the absolute displacement value to the encoding sequence,and realizes the measurement of absolute displacement by identifying the encoded information.It can immediately obtain the current absolute displacement value after power on,and without the need to perform a "return to zero" operation,which improves the efficiency and reliability of the measurement.Although through continuous development,there have been a variety of encoding methods,such as gray code,matrix code,and pseudo-random code.However,as the range of these coding methods increases,the amount of coded data increases correspondingly,resulting the number of coded data bits in the same space and the encoding complexity in a rapid increase,which will bring about the difficulty of coding algorithms and manufacturing.At the same time,the incremental code channel generally adopts the grating moiré measurement method,and its measurement accuracy is determined by the size of the equally spaced grating pitch.The measurement accuracy is improved by precision scribing.This also objectively leads to absolute measurement with the increase in absolute measuring range and accuracy requirements,the complexity of absolute encoding algorithm and the difficulty of manufacturing is growing.In response to the above problems,a simple displacement coding measurement method based on time-grating technology is proposed.The method uses the time-grating measurement method of light intensity modulation to increase the grid pitch of the incremental code,and uses the decimal shift coding and image coding methods to reduce the difficulty of coding and decoding.This method takes advantage of the large time-grating measurement grating period,and uses the micron-level resolution capability of the image sensor to achieve a large range of coding and decoding.Meanwhile the coding complexity of the coding method does not increase with the increase of the range.The research content is as follows:(1)Based on the general coding methods of the absolute displacement sensor,a decimal shift coding method based on time-grating technology is proposed.Compared with the traditional coding methods,it is a large-range absolute position coding method through image recognition,which can realize a large-range and high-precision absolute position measurement without increasing the number of coding bits and complexities.It adopts the decoding method of simple mathematical formula and the decimal coding mechanism,which improves the efficiency and reliability of the measurement.(2)According to the measuring principle of absolute displacement sensor with decimal shift coding,the design of the overall scheme of the sensing system is carried out.It mainly includes sensor structure model,plate structure and test system.The test system consists of hardware circuits such as image acquisition module,FPGA control module,signal processing module,and software modules such as analog-to-digital conversion and data transmission.(3)According to the overall plan of the sensing system,an experimental platform for the absolute displacement sensor is built,and the experimental research of the sensor is also carried out.Carry out experimental tests on the key signals of the test system and the principle experiment to verify the theoretical correctness of the sensor.The error components are analyzed and eliminated.Performance experiments show that this method can achieve large-range,high-precision absolute displacement measurement.