Research And Implementation Of Micrometer Grating Ruler System Based On Moiré Fringe

The domestic grating measurement field has made some progress in recent years.The development of precision manufacturing has put forward new requirements for the measurement accuracy and resolution of the Moiré grating ruler.It is of great significance to carry out the research on the measurement technology of the Moiré grating ruler.The thesis studies the working principle of the Moiré grating ruler,and designs a grating ruler measurement system based on Moiré fringes.The main tasks are as follows:1.A new scheme for calculating the position information of Moiré grating ruler is proposed.The linear CCD is used to replace four photocells to collect light intensity signals.The use of linear array CCD to collect Moiré fringes can obtain higher measurement accuracy.The collected signal is filtered after analog-to-digital conversion,and the stable Moiré fringe signal is obtained by shifting after the accumulation of effective digits.The obtained signal is calculated to obtain the phase,and finally the phase is converted into displacement information according to the corresponding counting relationship.2.According to the characteristics of linear array CCD sensors and other devices and the physical constraints of PCB,design a signal acquisition card and simulate it.Use a level conversion chip to meet the power supply requirements of the CCD,use the AD9826 chip to perform analog-to-digital conversion on the output analog signal of the linear array CCD,and design a capacitor after the analog signal to meet the input requirements of the AD chip.The performance of the signal acquisition card under various conditions is obtained through the simulation software,and the signal acquisition card is optimized to meet the design requirements.3.Use Verilog language to complete the program design of Moiré grating ruler measurement,and realize it in FPGA.Complete the drive of the linear array CCD,the drive and configuration of the dedicated AD chip.According to the characteristics of moiré fringe signal collected by CCD,the digital signal is de-noised by median filter.In order to accurately distinguish the moving direction of the Moiré grating ruler,a direction identification module is designed,which can perform real-time identification of the Moirégrating ruler.Solve the phase by the CORDIC algorithm,use the accumulation module to calculate the real-time phase,and use the phase compensation as the final phase of the output.Design the UART serial port module to communicate with the host computer and transmit phase information.4.The Moiré grating scale experimental measurement platform was built,and the Moirégrating scale was calibrated using Michelson interferometer.The scale grating fixture and the indicating grating fixture are designed,and the position of the scale grating can be finetuned by fine-tuning screws.Analyze the error of the Moiré grating ruler and compensate for the error.After compensation,the measurement accuracy of the Moiré grating ruler measurement system can reach ± 3μm,and the resolution can reach 0.08μm.