Development And Application Of A Calibration System Used For Laser Transverse Deformation Measure Based On Knife-edge Method

When an object is loaded by the axial force resulting in axial deformation,the transverse deformation will occur due to the Poisson's effect.Transverse deformation is an important performance parameter to characterize the mechanical properties of materials.Therefore,the transverse deformation measure can be used as an important method to explore the mechanics response of materials.In this paper,a laser calibration system for transverse deformation measure based on knife-edge method was designed.Through accurately controlled mechanical movement of baffle plate that ran like a knife-edge to cut the rectangular light beam emitted by a diode laser generator,the intensity of laser light collected by photodetector was then changed and the relationship of light intensity with moving displacement of the baffle plate could be established at the same time.Obtained linear relationship of the displacement with the light intensity could be used to explore the homogenization of the beam intensity.Precision displacement of the moving plate was thus used inversely to calibrate the linear relationship—the transverse deformation of the material.The measure of the transverse deformation of the material could be realized.In order to realize the transverse deformation measure method proposed in this paper,the design of the calibration system of laser transverse deformation measure based on the knife-edge method was completed.The calibration system design took the principle of calibration measure as the theoretical support,the calibration measure method as the guide,the mechanical structure system,the motion control system,the laser emission system and the data acquisition system as the core components of the calibration device.Finally,the key components selection of each system,the parameters setting and the function test were completed.After completing the calibration system design,considering that the transverse deformation of the test piece loaded was extremely small and difficult to capture,this paper proposed an optimization scheme to improve the calibration system accuracy from the point of data acquisition.For mechanical structure,the coaxial alignment design of optical path and the optimal design of knife-edge structure were put forward.For motion accuracy control,a motion scheme of equal length step displacement mode and uniform linear motion mode was proposed to verify the system applicability and determined a more precise motion control form.For data acquisition parameters control,the effects of sampling time base control and waveform acquisition mode control on system accuracy control were discussed.After the system accuracy was optimized from data acquisition aspect,this paper analyzed the noise control of the calibration system from the aspect of subsequent calibration curve data processing.The main noise source of the system was determined as background light and photodetector and then the SG algorithm was selected as the filtering method based on the results of Fourier transform analysis of noise characteristics.Through the comprehensive analysis of the calibration curve and the evaluation indexes,it was clear that when the data window value was about 50 and the fitting order was 2,the best SG filtering effect could be obtained.To examine the calibration system and to evaluate the test results,the relative error between the theoretical value and the experimental value at the intersectional points and the slope of the relationship and determining coefficient of the linear fitting line were used as the evaluation indicators to judge the control accuracy of the mechanical motion and the homogenization effect of laser spot in the calibration system.Then the detection effect of the calibration system was discussed by the comparison analysis of two modes of equal step displacement motion and uniform linear motion.The comparative analysis results showed that the relative error of the intersection coordinates of the curve was not more than 1.63% and the uniform motion was more accurate than equal step motion.Meanwhile,the determination coefficient of the 1mm area in the middle of the rectangular spot was 0.998 in different motion modes and knife-edge distance experiments,which means that the test had good spot homogenization detection effect.The results indicate that the calibration system designed in this paper can simulate transverse deformation of material by means of precisely controlled mechanical movement of the baffle plate and provide convenient detection and simulation methods for transverse deformation measure of materials.