Research On Calibration Of Accurate Five-Axis Motion Platform Based On Monocular Vision

Due to factors such as manufacturing and installation,there are various geometric errors in the uncalibrated five-axis motion platform,which have a large impact on the spatial accuracy of the five-axis motion platform.So it is necessary to identify and compensate for each geometric error.However,although the inspection accuracy is high that using the traditional inspection methods including ballbar and laser interferometer,all error terms cannot be measured in one installation,and the installation process is complicated and the instruments are expensive.Therefore,this paper builds a visual calibration system and verifies its feasibility through experiments,and then constructs an error model of the five-axis platform by using the homogeneous coordinate transformation method to calibrate the kinematic geometric parameters of the five-axis platform.The main research contents include:1.The platform of the vision calibration system is built by selecting each hardware.Then a vision algorithm is proposed to recognize rings,fit the ring center and sort the ring targets.Then,comparing it with two other existing recognition algorithms and proving the effectiveness of the algorithm.2.The accuracy of the precision five-axis motion platform hardware is confirmed.After that,the errors of geometric parameters in the platform are analyzed and the positive kinematic errors are modeled based on homogeneous coordinate transformation.3.A ring target is used to calibrate the camera parameters.The target is made to move relative to the camera and the monocular camera is used to take pictures of the target with multiple angles and poses.Finally,the relative position of the target coordinate with respect to the camera coordinate is found.4.The proposed visual calibration method for long-stroke translational axes uses an overlapping partial field-of-view calibration method between multiple cameras to calibrate the entire stroke.Then,a data stitching method to connect the photos taken by multiple cameras.5.The reliability verification experiment of the visual calibration system,the geometric error identification and compensation experiment of the five-axis platform were conducted.By comparing the error parameters identified by using different targets,it can be seen that the highest identification accuracy and the best stability are achieved by using ring targets.Finally,the experimental results show that the maximum integrated error and the average integrated error of the five-axis motion platform after calibration have been reduced by 82.5% and 75%,respectively,compared with those before calibration by making the coordinate system of the target relative to the camera coordinate system,thus verifying the effectiveness of the method.