Calibration Technology Of A Visual Measuring System On The Manipulator

In the field of industrial robots,visual measuring technology of the manipulator plays an important role to achieve automated processing,assembly and measurement.It can effectively improve the flexibility,accuracy and intelligence of the Manipulator control.However,we could not ignore the disadvantages of the visual measuring technology,such as low accuracy,complicated program,large distortion with large field of view camera calibration.These shortcomings restrict the development of high-precision robots.This paper focused on the calibration technology of the visual measuring system on manipulator around these important issues.They were camera distortion model,collinear distortion correction and cross ratio invariance calibration.The main contents were summarized as follows:(1)In order to determine the distortion calibration model and experimental environment suitable for this paper.We sorted out and analyzed the current application and development of manipulator measurement technology,learned the theoretical knowledge of camera calibration methods and camera distortion causes.Finally,a suitable distortion calibration model was determined.In order to further improve the accuracy and efficiency of distortion calibration,the influencing factors of camera calibration were thoroughly investigated.We studied the effects of light intensity,number of calibration images and calibration plate size on camera distortion calibration,and given the camera parameter distribution curve and reprojection error data table on the influence of these factors.(2)Because of the complicated steps of camera distortion calibration,a lens distortion correction method is proposed to calibrate the parameters of the vision system.First,an objective function of points on a line was built based on the principle of constant linear projection and the radial distortion relationship.Second,the objective function was optimized by Levenberg-Marquardt(LM)algorithm to get the optimum estimate of the lens distortion coefficients.A lens distortion correction method was proposed to calibrate the parameters of the vision system.(3)Since the distortion of a camera varies from large Field of View(FOV)to FOV,a sub-regional camera distortion correction method was proposed based on cross ratio invariance,in this paper,to calibrate the visual model with equal precision at the same time.The region of the FOV was divided into several parts by the distance weighting principle according to optical center of the camera.The distortion coefficient-solving model for each sub-region of FOV was built by using multiple sets of data with four points of a line based on the cross-ratio invariance principle.The sub-region of the FOV could be calibrated by the calculated distortion coefficients.The measurement error of the method was evaluated by the Average Linear Offset(ALO).