A Grating Ruler Segmentation Technology Research

As a kind of sensor of displacement or angle, grating has been widely used in mordenindustry and national defence and other domains. The development of technology andincreasing of practical application demanding have put forward higher requirement formeasurement accuracy of grating measuring system. Electronics subdivision technology ofgrating Moire Fringe signal, has been a kind of effective method to improve measurementaccuracy.By researching the principle of grating displacement measuring and subdivisiontechnology for photoelectric Moire Fringe signal, a new subdividing method and systemdesign scheme was proposed in this paper. This paper analyses the differential amplifer andphase shifter circuit for analog signal and the AD converter circuit and the digital circuit basedon FPGA. It mainly analyses the principle of Coordinate Rotation algorithm which is used asmethod of nonlinefit subdivision for1/8period of Moire Fringe signal. This paper uses VHDLto describe the CORDIC algorithm for phase decoding and has realized it. This is an effectiveway to avoid the subdividing error which is caused by the traditional linear-fitting process ofarctan function and keep the high times and nonlinefit subdivision data valid in the process ofdisplacement calculation. Meanwhile, the IEEE-754format single-precision floating-pointcalculation is applied in subdivision which is more accurate then fixed_point calculation.This paper has designed and realized the hardware platform based on FPGA for thesubdividing technology. The designed hardware system utilizes the parallel pipelinetechnology, so that it can simultaneously implement the function of counting,direction-judgement, driving the AD9826to complete data acquisition, decoding thenonlinefit phase with CORDIC algorithm, floating-point calculation for displacement, BCDdecoding of float-point data, driving the LCD to display the measurement result real time andserial communication on a piece of FPGA.Finally, this paper gives an experimental verification for the measuring accuracy of thehardware circuit system, and then analyses the experimental result and the error factors whichinfluences the measuring accuracy. At last, the improving methods are proposed.