Design Of The Intelligent Calibration System Of The Absolute Grating Ruler With Double Reading Heads

With the progress of science and society,the demand of large range and high precision measurement and processing is increasing.The splicing absolute grating r uler plays an important role in the large length and high precision measurement.When the absolute grating scale is used for measurement,there is a measurement blind area at the interface when it works with a single reading head which inevitably results in the accumulated errors.At the same time,the splicing grating ruler is inevitably interfered by internal and external factors,resulting in errors.The measurement data need to be corrected.Therefore,it is of great practical significance to develop an absolute grating ruler with double reading heads and intelligent correction.On the basis of the previous researches,this thesis analyzes the working principle of the absolute grating ruler and measurement principle of the double reading heads and the main interference factors that cause the measurement errors.With the analysis of the results,the overall scheme of error correction for the ruler with double reading heads is put forward.In this thesis,hardware circuits are designed for the absolute grating ruler with double reading heads.FPGA chip is used as the main controller which is selected according to the demand.Its configurations of the interface and storage are set according to the chip manual.The matching USB chip is selected.The interfaces are configured according to the communication process and principles in the slave chip FIFO mode.The related signal processing chip is selected to complete the internal signal conversion.According to the power supply demand of each chip,the external input voltage and the corresponding voltage conversion chips are selected.Also,the related voltag e conversion circuit is designed.After testing,the designed circuits meets the system requirements.Verilog HDL is used in Quartus II,the Altera FPGA software development environment to implement the overall FPGA program.The main work includes: the realization of Bi SS communication protocol between the hardware system and the reading heads of the absolute grating ruler,the measurement algorithm realization of double reading heads,the least square method fitting correction algorithm realization,and the realization of USB communication between FPGA chip and USB chip.The detailed design is given,and some functional modules are s imulated and tested in Model Sim.The results show that the FPGA hardware program meets the design requirements.Finally,the testing system is set up with the host computer program written by Matlab GUI and the Signal Tap logic analyzer of Quartus.Two working modes of the designed absolute grating ruler with double reading heads and intelligent correction.The experimental results show that the ruler can quickly acquire positions and realize double reading heads and least square method fitting correction algorithms.After intelligent correction,the measurement precision is improved from ±3?m to ±1.8?m,which indicates that the designed splicing grating ruler implements the measuring fuction in large range and high precision.