On-machine Measurement of Large-scale Workpiece Based on Machine Vision

On-machine measurement(OMM) based on machine vision has been hot research topic in recent years because coordinate measuring machine(CMM) measurement requires significant resources in operating time and cost. This paper aims to develop an OMM method with a manipulator and industry camera. First, an on-machine calibration method of industry camera based on image sequence is studied. A set of monocular stereo system was established on the NC milling machine. A calibration target was designed to meet the requirements of finding enough and accurate correspondence relationship. Calibration method is illustrated involving taking image sequence, detecting the position of the calibration board and the marking points, finding the marking points’ correspondence with their projection, determining the camera parameters through optimization algorithm. Accuracy of calibration shows that choosing 10 calibration images is appropriate for on-machine calibration. Second, image mosaic method for on-machine measurement of large-scale workpiece is investigated. Image sequences were acquired by controlling the moving of working table. Image mosaic of large-scale workpiece was realized with high precision. Size measurement result proved the effectiveness and high efficiency of this OMM system.