Non-contact on-machine measurement using a chromatic confocal probe for an ultra-precision turning machine

On-machine measurement (OMM) involves the interruption of the machining process and the subsequent measurement of the workpiece without its removal from the machining tool. Chromatic confocal sensing is a well-known measurement technique that is able to evaluate the position of a point on an object surface along the optical axis of the system with high accuracy. The present study integrates a chromatic confocal measurement probe with an ultra-precision diamond turning machine to achieve the non-contact OMM of machined components. The procedure for establishing the position of the rotary axis of the spindle based on dual standard spheres is first described in detail, and the relevant OMM procedure for machined components of different surface topographies is explained. Then, a 50-mu m quartz step height standard is employed to investigate the linear measurement accuracy of the chromatic confocal probe. Finally, the measurement accuracy of the proposed OMM method is compared experimentally with that of the stylus method. The results show that the estimated form error value of the OMM method agrees well with the value obtained by the stylus method. The proposed OMM method feasibly achieves non-contact OMM with a nanometer-level accuracy for an ultra-precision turning machine and is capable of reconstructing the 3D surface topography of flat, spherical, and aspheric surfaces. After integrating the OMM method, the ultra-precision turning machine can realize the function of processing-measurement integration.