Design Of Metal Thermal Expansion Coefficient Measuring Device Based On Feature Point Matching

High-precision machining is the core and foundation of industrial automation.Temperature is one of the important factors affecting mechanical processing,and the thermal deformation error caused by temperature changes occupies a non-negligible proportion of the total error.Therefore,research on the thermodynamic properties of materials to reduce thermal errors and compensate is gradually becoming one of the research hotspots in the industrial field.Among them,the thermal expansion coefficient is a key parameter to characterize the thermodynamic properties of materials.Based on the research results of thermal deformation at home and abroad,based on the method of image sensing,this paper researched and designed a metal material thermal expansion coefficient measuring instrument,which realized the real-time online measurement of the thermal expansion coefficient of metal materials in the high and low temperature box.The main research work of the thesis is as follows:First,in response to the technical requirements for real-time online measurement of metal materials in high and low temperature boxes,a complete image sensor-based thermal expansion measuring instrument imaging device was designed.Aiming at the technical problem that the measuring instrument needs to perform high-resolution imaging of the samples in the box through the optical window of the high and low temperature box,the long-distance microscopic imaging optical path and the corresponding mechanical adjustment structure are designed through Zemax software.A long-distance microscopic imaging with a working distance of 400mm and a spatial resolution of 10um is realized.Secondly,the measurement software design of the thermal expansion measuring instrument,including multi-channel image acquisition and processing,real-time thermal expansion coefficient calculation and other programs.On the basis of the aforementioned mechanical device and optical imaging optical path research,the thermal expansion image offset calculation research based on feature point matching is carried out,and four feature point detection algorithms of SIFT,FAST,ORB,and SURF are analyzed and compared.At the same time,in view of the problem of thermal expansion image blurring,the blade edge method is used to restore the blur image to improve the accuracy of feature point matching.Finally,on the basis of the above-mentioned hardware and software research and design,the thermal expansion coefficient of aluminum alloy material was measured experimentally.In the laboratory environment,the aluminum alloy calibration board is driven by the electronically controlled lifting platform,and the repeatability test of the thermal expansion coefficient measuring instrument is carried out,and the repeatability is 2.4%.In the high and low temperature box,the aluminum alloy material is used as the object,and the thermal expansion coefficient from-50?to+50?is measured.According to the data fitting,the average thermal expansion coefficient of the aluminum alloy is 2.192×10^-5?^-1.At 20?,the calculated thermal expansion coefficient of aluminum alloy is 2.3×10^-5?^-1,and the thermal expansion coefficient of 20?aluminum alloy is 2×10^-5?^-1?2.4×10^-5?^-1,The results calculated in this paper are within the scope of the table lookup.In summary,this paper has completed a design of a real-time online thermal expansion coefficient measuring instrument for samples in a high and low temperature box based on image sensing,which meets the predetermined design requirements.