Development of on-machine measurement for ultra-precision machining

Surface measurement is playing an increasingly important role in ultra-precision manufacturing. Nowadays, there is a technological shift from offline measurement to on-machine measurement, forming a closed-loop control for manufacturing processes. Conventionally, the transportation operations between the measurement and machine coordinates are time-consuming and inevitably induce more errors, which cannot be neglected, especially at the ultra-precision level. Development of on-machine measurement for ultra-precision machining processes will enable the reduction of measurement cycle time as well as potential improvement of machining accuracy. In the present study, an in-house designed interferometer probe, called Dispersed Reference Interferometer (DRI) is integrated on an ultra-precision diamond turning machine (Precitech Nanoform 250). The alignment method of DRI is firstly described, in order to establish the measurement coordinate. Different on-machine measurement strategies are also discussed, including multiple radial, multiple circular, and spiral trajectories. Experimental study has shown that the on-machine measurement results of a cosine form sample agree well with the offline measurement. The measurement error difference is less than 10% and correlation coefficient is 0.991.