Research On Workpiece Thickness Measurement System Based On Laser Triangulation

Improving production quality has become a high priority objective since the implementation of the manufacturing power plan.The requirements for measuring the thickness of high-end workpieces such as spaceship thin walls and rocket fuel tanks have risen in parallel.Traditional contact manual sampling measurement has some drawbacks,including simple workpiece damage,low measurement efficiency and accuracy,and a low scrap rate.As a result,the use of an online,non-contact measurement device has become the recommended method.Laser triangulation's accuracy,range,and dependability are outstanding,given its wide application in the field of non-contact automatic measurement.In this paper,the laser triangulation method is used to measure the workpiece thickness by image detection,and an on-line and non-contact thickness measurement system is built.The main research is as follows:(1)The optical path structure of the non-contact thickness measurement system is constructed.The direct laser triangulation suitable for diffuse reflection is used as the optical measurement structure of the system;The constant focus optical path is designed to fully ensure the clarity of imaging focus and improve the imaging quality of light spot,and the optical system parameters are deduced;Aiming at the shortcomings of traditional optical parameter selection methods,an intelligent optimization algorithm is proposed to select the optical system parameters,and the SSA-LT optical parameter optimization model is established.The sparrow global combination optimization of optical parameters can be carried out according to the set objectives,which reduces the experimental workload and improves the selection efficiency,providing a new idea for the intelligent optimization of optical system parameters.(2)A CCD driving,and data acquisition system based on FPGA and virtual instrument technology is designed,and the CCD spot data with good quality is successfully obtained.The hardware design based on image sensor module,CCD acquisition module and timing control module,and the software design based on CCD driving timing,analog-to-digital conversion timing,data acquisition program and image detection have been completed;The idea of two-stage programming of timing is put forward,and a strict driving timing is designed to ensure the signal quality;The system combines the advantages of FPGA and virtual instrument to obtain stable spot signal,and can quickly build a reliable and flexible thickness measurement system,which lays the foundation for the on-line measurement of the system.(3)The image detection system is developed,which can realize the functions of CCD gray data display,VMD image noise reduction,sub-pixel spot center positioning algorithm,thickness calculation and so on.It is of great significance to improve the spot center accuracy;To extract the effective characteristic signal of the spot,a CCD image denoising method based on variational modal decomposition(VMD)is proposed,which eliminates all kinds of noise and obtains high-quality spot image data with good symmetry,while the traditional denoising method will lose the detailed features of the image;The Gaussian fitting method is used to locate the sub-pixel spot center of the denoised image,and the accurate and stable spot center coordinates are obtained,reaching the sub-pixel level.According to the overall measurement scheme of the system,the experimental platform is built;Carry out the system calibration experiment and get the fitting curve;The system performance is tested.In the measurement range of 10 mm,the measurement error is no more than ±8.45 ?m and the mean square deviation is less than 1.21 ?m.The source of error is described.Experiments show that the system can realize on-line,non-contact and high-precision workpiece thickness measurement.