Study On Accuracy Improvement Technology Of On-machine Thickness Measuring System With Tool Holder

Manufacturing is the basic industry of the national economy,among which aviation manufacturing is the representative of advanced manufacturing.In the aviation manufacturing industry,the five-axis CNC machine tool system is the only means of processing many complex parts.After the complex thin-walled structural parts are processed by the five-axis CNC machine tool,manual hand-held ultrasonic thickness gages are sometime required to verify their thickness.In order to achieve the goal of automatic thin-wall thickness measurement in five-axis CNC machining,a shank-type on-machine ultrasonic thickness measurement system is developed.In actual measurement applications,there are problems of insufficient accuracy and stability for small thickness parts.This thesis aims at the problem of insufficient accuracy of the toolshank on-machine thickness measurement system,according to the principle of ultrasonic echo thickness measurement,the hardware circuit and mechanical structure of the tool handle type on-machine ultrasonic thickness measurement system,the main influencing factors of its accuracy decline are analyzed,and the high-precision measurement scheme for small thickness is proposed.Through improvement of ultrasonic echo analog signal from hardware,and improvement of processing method of ultrasonic echo digital signal from software,the precision improvement of tool-shank on-machine ultrasonic thickness measurement system is finally realized.The main contents of this thesis are as follows:(1)The error source of the tool-shank on-machine ultrasonic thickness measurement system is studied,and the characteristics and advantages of the peak-peak method and the emit-echo method are analyzed according to the physical principle to extract TOF(time of flight)of the ultrasonic thickness measurement.According to the main structure of the tool holder on-machine ultrasonic thickness measurement system,the error source of the tool holder type on-machine ultrasonic thickness measurement system is analyzed,and the advantages and disadvantages of the peak-peak method and the vibration-echo method are verified by experiments.(2)The aliasing of ultrasonic echo signals in small thickness measurement is analyzed and processed.For thin-walled parts,when the thickness is very small,there is waveform aliasing,which leads to the feature unable to be directly extracted and calculated.In this thesis,an ultrasonic echo aliasing separation method is used to separate ultrasonic echoes through parameter echo waveform matching.Based on this echo feature extraction,the TOF of thin-walled parts is accurately calculated,and the accuracy and stability of the on-machine ultrasonic thickness measurement device are improved.(3)The specific plan for improving the accuracy of the tool-shank thickness measuring system has been formulated,and accuracy is improved by the combination of software and hardware.The gain amplifier circuit is controlled by FPGA to achieve stable amplification of ultrasonic echoes and improve the sampling resolution.In the QT software of the host computer,the peak fitting of the ultrasonic echo is realized and the thickness information is extracted from the ultrasonic echo.Finally,the accuracy improvement effect of the tool-shank on-machine ultrasonic thickness measurement system is verified by the ultrasonic thickness measurement experiment.