Calibration and capability assessment of on-machine measurement by integrating a laser displacement sensor

Abstract

On-machine measurement is being used increasingly to inspect the features of machined components without removing the workpiece from the machine tool. In the present work, a laser displacement sensor is integrated on a machine tool to measure the elementary features of a step, hole, cylinder, and plane. An iterative calibration method is introduced to obtain the position and direction of the sensor accurately, and data processing is performed for filtration and edge recognition. The accuracy and uncertainty of detecting the characteristic parameters of height, diameter, roundness, and flatness by the laser-based on-machine measurement are evaluated and are compared with those of a mechanical probe. Furthermore, the capability of the on-machine measurement process on the adopted machine tool is assessed according to ISO 22514-7. The results show that the difference between the calibrated and actual sphere center is reduced to 4.7 μm after five iterations. The on-machine measurement by the mechanical probe is more accurate, while that by the laser displacement sensor is more efficient. The uncertainties of the two methods are evaluated as being in the ranges of 2.4–3.7 μm and 4.8–5.8 μm, respectively. The accessible tolerances can be obtained to determine whether the machine tool is competent for requirement as a measuring device.