Research On A New Type Of Grating Sensor

Grating displacement sensor has the advantage of high precision, good stability, fastresponse speed and strong anti-jamming capability, which is widely used in the highprecision position measurement field such as measuring instrument and CNC machinetools. At present, incremental grating is widely used in precision grating lineardisplacement measurement system.The linear displacement quantity is converted to moirefringe signal light which is converted to electrical signals after received by photoelectricdevice,and then it is sent to the signal processing circuit, after processing, the relativedisplacement is output. The domestic linear grating rulers are mostly incremental gratingrulers. This kind of grating ruler needs to search’zero position’ when open or reset, andthe phenomenon of cumulative error exist which affect the precision of the workpieceprocessing and measurement.The output of absolute type grating ruler is absolute positioninformation, which can effectively solve the problems of incremental grating ruler.Firstly, the grating measuring system is analyzed to understand how it works. Thetheoretical basis of grating measurement is moire fringe and it is conducive to improveaccuracy and resolution of grating ruler by understanding the mechanism andcharacteristics of moire fringe and quality indicators.Besides, methods to identify thedirection of moire fringe is studied deeply.Secondly,the coding method and coding principle of the current grating displacementsensor and encoder is analyzed and researched. New coding methods of relative codingand absolute coding integration which have high resolution and large measuring range, andcan realize grating displacement sensor miniaturization and structure simplification ispresented. A distance code encoding method and a coding method based on pseudorandom code are including. The method of the encoding and decoding is discussed,thenthe location uniqueness and advancement of coding method are proved.Thirdly, incremental signal processing system and absolute signal acquisition system are desinged. The absolute signal uses a high sensitivity, low dark current TCD1254GFGtype linear CCD as a receiving device.Incremental signals use a specialized DSP devicewhich is an integration of differential amplification, filtering, correction, plastic,segmentation to process signal processing.Finally, the mathematical model of absolutely encoding is derived and have got10pseudo-random code. The simulation is conducted and its correctness is verified. Theaccuracy test of grating ruler prototype is made on the contrast test platform and the causeof generated error is analyzed according to the experimental data.