On-machine Measurement Scheme Generation and Optimization Method for Multi-axis CNC Machine Tool

The multi-axis CNC machine tool may have some redundant freedoms for being used in on-machine measurement(OMM), which will result in that one measurement task could be done by different servo motion schemes. Thus, how to determine metering schemes to check a workpiece with high accuracy and efficiency is an important problem and also a focus for researchers. To solve this problem, a generation method of task-oriented OMM scheme is proposed. Utilizing multi-body system theory and homogeneous coordinate transformation, geometrical characteristic of workpiece and movements of machine tool are analyzed mathematically. A function relationship between the geometrical characteristic of workpiece as independent variables and motions of machine tool as dependent variables is established. All possible metering schemes are obtained based on the solutions of functional equation and their feasibilities are verified by analyzing the value range of the solution. Considering the influences of the configuration and servo characteristics of CNC machine tool on measuring accuracy, some assessment criterions are presented and so the optimal metering scheme is selected in the end. Finally, the experiment of profile error was carried on a CNC gear forming grinding machine, and the feasibility and efficiency of the methodology has been verified by the experimental resultants. The optimal OMM scheme gained by the method presented in the paper has good characteristic of accuracy and repeatability.