Non-circular Contouring Measurement for Servo Tuning and Dynamic Performance of a CNC Machine

To achieve high quality and productivity, it is important to know what is the maximum feed rate while meeting the required part accuracy. Laser interferometers and telescoping ballbars have been used for the positioning and circular contouring measurement. However, a conventional laser is limited by the line-of-sight, and cannot tolerate large lateral deviations. A telescoping ballbar is limited to circular contouring test at low speed and large radius. However, motion errors due to the mistuning of CNC servo control system are often easier to observe on non-circular tool paths. To make sure that the CNC on the high-velocity machine tools are tuned properly and at its optimum performance, a laser/ballbar is developed by Optodyne to perform circular and non-circular contouring tests. The laser/ballbar is non-contact and not limited to circular contours. By comparing non-circular contouring errors profiles at different feed-rate, motion errors due to mechanical structures, acceleration/deceleration, and those due to CNC servo control system can be identified. The basic theory, test setup, and test results are described.