Real-time 3d Measurement And Reconstruction Of Workpieces For Robotic Powder Coating Lines

Powder coating is an indispensable part of the industry.Traditional powder coating requires workers to be exposed to the environment where toxic and harmful powder coating dust is sprayed.This poses a serious hazard to practitioners,and a lot of manual operations are also not conducive to control spray quality.Therefore,the automatic transformation of powder coating production line is necessary,and it is also a research hotspot in recent years.Many related methods are proposed.However,the basic principle of automatic powder coating is still to use automatic programming technology to plan the powder coating route of the powder coating robot according to the geometric structure of the workpiece to be painted on site.Powder coating robot used in automated powder coating engineering are classified into reciprocating machines and robotic arms.The reciprocating machine only needs to obtain the approximate envelope of the workpiece to perform the powder coating task,and the robotic arm needs to carry out precise and detailed path planning according to the three-dimensional model of the workpiece.Therefore,a reciprocating machine can meet the requirements for a simple workpiece,but it is necessary to use a robot arm for the workpiece with a complicated shape or high coating quality.In view of the above two requirements,and the survey of domestic and international industrial vision imaging measurement programs and considering the actual situation of domestic powder coating factories,this paper proposes a real-time 3D measurement and reconstruction scheme for spray painting lines based on TOF cameras.3D measurement uses depth images to determine the spray area and distance of the target workpiece,which is a rapid powder coating solution,3D reconstruction using point cloud technology to obtain the 3D point cloud model of the workpiece provides point cloud coordinates for trajectory planning,which is a fine powder coating solution.According to the plan,the main work of this paper is as follows:(1)A time-of-flight(TOF)depth camera capable of acquiring depth images and having high sensitivity,low power consumption,and strong anti-interference capability is used as an imaging scheme,and an imaging measurement device is constructed based on the camera.(2)The imaging characteristics of the TOF camera were studied.The calibration of TOF depth camera-reciprocator system was accomplished by calibration,local extreme point marking,distortion calibration and Tsai-Lenz hand-eye calibration.(3)For reciprocator powder coating methods,a real-time 3D envelope measurement method based on depth images is studied: Automatically extract the twodimensional envelope of the workpiece with the contour information of the workpiece edge and the pixel pointer,then use the depth space information of the image to obtain the depth value of each part of the workpiece,so as to determine the spraying plane area and the spraying distance of the reciprocating machine.(4)A method for 3D reconstruction of a point cloud sequence that relies on the insitu rotation of a spliced workpiece is studied for the method of robotic arm powder coating: Firstly,the workpieces in the spraying area are converted into point clouds.After the point cloud is sparsified by the uniform mesh method,the FOVIS algorithm is used for attitude estimation.Then the point cloud function fusion algorithm is used in the directed distance field function(TSDF).Based on the above,CUDA-based spatial hash table operation point cloud data is used for fusion,thereby automatically concatenating continuous point cloud sequences into a complete 3D point cloud model.In this paper,online experiment using three kinds of workpieces provided by the factory,the rate of missed detection is 0%,and the error in measurement is ±7mm;Average 30 frames per second during reconstruction,reconstruction failure rate ≤3%,memory occupancy rate≤25%;Meet the actual spraying production requireme-nts,provides strong support for subsequent spray trajectory planning.The 3D-dimensional measurement part has been put into spraying workshop.