Adaptive Adjustment Method And Technology Of Coupling Gap In Ultrasonic Non-contact Scanning Thickness Measurement

Wall thickness parameter is an important index to measure the processing quality of thin-walled parts in aerospace and national defense military equipment fields.Water spray ultrasonic thickness measurement has the advantages of non-contact nondestructive measurement and high speed scanning,and it is an effective method for automatic ultrasonic thickness measurement of large thin-walled parts.However,due to the large size and low stiffness of thin-walled parts,it is easy to be deformed by forces such as transportation and clamping.As a result,it is difficult to maintain a stable coupling gap between ultrasonic sensor and workpiece within an appropriate range during actual measurement.If the coupling gap is too large,it will cause multi-component coupling of ultrasonic echo signal,which will lead to unreliable thickness measurement results.On the contrary,it may cause the thickness measuring device to scratch or even collision with the workpiece,which will not only damage the workpiece and equipment,but also have safety risks.Therefore,in the process of ultrasonic non-contact scanning thickness measurement,it is of positive significance to improve the accuracy and stability of thickness measurement by dynamically adjusting coupling gap to an appropriate range to adapt to the real surface shape of the workpiece after deformation.Aiming at the three key problems of coupling gap "state discrimination","adjustment value determination" and "shape adaptive adjustment path generation" in ultrasonic non-contact scanning thickness measurement.The ultrasonic thickness measuring device integrated with the eddy current sensor pathfinder was designed.Based on the three-axis linkage measurement platform,the unified coordinate model of multiple sensors and the coupling gap state discrimination model were established.Combining kernel function probability density estimation and k-nearest neighbor probability density estimation,a kind of coupling gap data density estimation function is constructed to guide the determination of coupling gap adjustment value.The least square method(MLS)is used to fit the workpiece shape and generate the coupling gap shape adaptive adjustment path.The fitting accuracy and speed are improved by implementing the basis function normalization and selecting the tight support weight function.In order to realize the application of coupling gap adaptive adjustment function in NC measurement platform,Sinumerik 840 D sl CNC system HMI interface was developed by using XML,Qt and C++ Programming language based on the Operating Programming Package,and realized the embedding of coupling gap adaptive adjustment algorithm and the interactive communication between HMI,NC and PLC.By activating the "position-independent temperature compensation function" of Sinumerik 840D sl CNC system and modifying the PLC program of the CNC system,the NC system can realize the dynamic offset of the spindle of the machine tool based on the adaptive adjustment algorithm of the coupling gap while executing the NC program.Based on the self-developed measuring platform,the ultrasonic non-contact scanning thickness measurement experiment of coupling gap adaptive adjustment was carried out,and the coupling gap and thickness measurement error before and after the coupling gap adaptive adjustment were respectively compared to verify the effectiveness of the research method and technology.The coupling gap can be maintained relatively stable within the preset range,and the thickness measurement accuracy in the adjustment area can be improved effectively.