Research On Size Measurement System Of Power Battery Module Based On Machine Vision

In recent years the lean and intelligent production technology,which is one of the core technologies in the field of new energy vehicle manufacturing,has been received more and more attention from all aspects with the rapid development of new energy vehicles.The power battery module is the basic unit of the power battery of a new energy vehicle.The dimensional accuracy has an important impact on the compression resistance,explosion-proof performance and airtightness of the power battery module,so it is an important indicator to ensure the safety of the battery.Therefore,it is one of the keys in power battery production technology to realize measurement of battery module size quickly and accurately online in the production process.Then the research on the battery module size online measurement technology,which is based on machine vision,is introduced in this paper.(1)The direct laser triangulation method is selected as non-contact measurement method to measure the three-dimensional of the battery module according to the measurement accuracy,measurement range and various requirements in the actual production process of the battery module.The measurement program is designed for measuring the end plate’s flatness and the thickness of the battery module.Then the calibration of the 3D size measurement system for the power module is finished and the three-dimensional information that is composed of the depth map and the point cloud data is obtained by using laser profiler sensors to scan the measured object according to the direct laser triangulation method.(2)A plane fitting algorithm based on the variance of the point cloud clusters is proposed to measure the end plate’s flatness of the power battery.This method divides the acquired point cloud data of the measured plane into several point cloud clusters,judges the dispersion degree of the point cloud data according to the coordinate variance of the point cloud clusters,removes the points that are discrete from the overall point cloud data,and reuses the rest of the data for plane fitting,so as to realize the measurement of the flatness of the end plate of the battery module.(3)Firstly,the affine relationship between the point cloud coordinate system and the world coordinate system is established by using the two laser profile sensors to scan the calibration piece and calculating the characteristic points’ coordinate of the calibration piece.Secondly,the two laser contours is used to scan the top and bottom surfaces of the module respectively and the point cloud data of the top and bottom plane is transformed to the world coordinate system by the affine relationship.Lastly,the thickness of the battery module is measured by calculating the average distance between the top surface and the bottom surface.(4)The battery module size measurement system software is developed.The software contains the two-dimensional size measurement module,three-dimensional size measurement module,human-computer interaction module,servo motor system control module,image acquisition module and other functional modules and so on.It realizes template matching,circular measurement,line search,line construction,flatness calculation,plane correction,point cloud merging and other functions.