An On-Machine Error Measurement System for Micro-Machining

Technology development trends towards the ability to manufacture ever smaller parts and feature sizes with increased precision and decreased cost. Micro machining is one of the important manufacturing methods to fulfill the requirements from the industry. The objective of this paper is to develop an on-machine error measurement system that can identify the micro machining errors for error compensation so that the machining accuracy of a meso-scale machine tool (mMT) can be enhanced. Because of the difficulty in handling and repositioning the miniature workpiece, the error measurement system should be non-contact and on-machine executable. To meet this requirement, a vision-based error measurement system integrating image re-constructive technology, camera pixel correction, and model comparison algorithm error was developed in this study. The proposed measurement system consists of a CCD with CCTV lens, a precision 3-DOF platform, image re-construction sub-system, and contour error calculation sub-system. By adopting Canny Edge Detection algorithm and camera pixel calibration method, the contour of a machined workpiece can be identified and compared to the pixel-based theoretical contour model of the workpiece to determine the micro machining errors. Because the system does not have to remove the machined workpiece from the CNC machine tool, errors due to re-installing and re-positioning can be avoided. To prove the feasibility of the developed algorithm and system, measurement results obtained from the vision-based measurement system were compared with the measurements of CMM, and error compensation experiment conducted on a 3-DOF mMT was also conducted. The results have shown the good feasibility and effectiveness of the developed system.