Research On The Posit Ionmeasurement System Of The Holes In The Battery Case

The location of the hole group of the battery pack box determines the assembly quality of battery pack box and the assembly quality of the whole vehicle,thus affecting the use performance of new energy vehicles.At present,coordinate measuring machine(CMM)is widely used in the production line to sample and measure the hole group of battery case,which is difficult to meet the requirements of fast production pace,high degree of automation and on-line tracing in the automobile industry.At the same time,as a large-scale workpiece,the battery pack box is 2060mm long,with a positioning inclination of 1°,and the height difference between the two ends of the box will be nearly 36mm.Due to the limitation of depth of field and the inability to detect the height information of the hole group,the application of ordinary plane camera in large-scale workpiece position detection is limited.In view of the above problems,this paper makes a systematic analysis and research,designs and develops an on-line measurement system for the hole group position of battery case based on line structured light.On the basis of summarizing the hole group position detection technology at home and abroad,aiming at the problems faced in the implementation of the position detection of the large-scale workpieces based on the visual inspection,this paper studies the design of the measurement system,the calibration of the line structured light visual measurement system,the establishment of the hole group position measurement model,the hole group position measurement experiment and error analysis As follows:(1)The design of the hole group position measurement system of the battery case.This paper introduces the principle of measuring the position of the hole group of the battery case,completes the design of the measuring platform and the selection of the hardware.According to the distribution characteristics of the holes in the battery case,a vision measurement scheme of double laser and single camera is proposed,which reduces the use of the camera and improves the detection efficiency.Assemble and debug the closed-loop motion system based on the linear motor module,linear motor driver and grating ruler driven by gantry structure.The positioning accuracy and repetition accuracy are all within ± 3 μm measured by laser interferometer.(2)Calibration of line structured light vision measurement system.In this paper,the characteristics of linear structured light stripe imaging are analyzed,the gray-scale Gaussian distribution model of light stripe image is established,and the stability and accuracy of different light stripe center extraction algorithms are compared.The experimental results show that Steger algorithm is better than curve fitting method in the stability and accuracy of extracting the central point of metal material strip image.The hand eye calibration of depth map is completed,and the coordinate system of depth map acquired by left and right laser is unified.Based on the study of the camera model of the structured light measurement system,the camera internal and external parameters are calibrated.In order to facilitate the on-site rapid calibration of light plane,a zigzag target is designed to improve the corner extraction algorithm of calibration image,and the calibration of light plane based on line structured light is completed.(3)The establishment of measurement model of hole group position.The assembly hole with chamfer will produce a lot of noise in the process of data acquisition,which will affect the ellipse fitting,and then affect the measurement accuracy.This paper studies the imaging characteristics of chamfered holes,introduces the concept of "point symmetry distance",improves the robust regression algorithm of LTSD(least trimmed symmetry distance),iteratively removes noise,and accurately extracts ellipse features.In order to reduce the excessive dependence of the position measurement based on vision on the positioning accuracy of the detection platform,the model of hole group position measurement is established to solve the perspective projection distortion caused by the non-parallel of the measured plane and the camera imaging plane,and the problem that the positioning deviation of the detection platform affects the measurement accuracy.(4)Detection system measurement experiment and error analysis of the system.Finally,through the line structured light measurement system and the proposed algorithm to measure the position of the hole group,and compared with the three-dimensional measurement data,the accuracy of the proposed algorithm is verified.The measuring time of the system is about 15 minutes.Compared with the CMM,the testing speed of all hole groups is increased nearly 10 times within the allowable error range.