External Sensor-less On-machine Measurement of Workpiece for Ultra-precision Machine Tools

The on-machine measurement of a machined workpiece has numerous advantages such as reducing the man-hours and operator-dependent measurement errors, and improving work-efficiency. In this paper, we propose an external sensor-less on-machine measurement system by only utilizing internal servo information in order to add a workpiece-measurement function to ultra-precision machine tools without increasing the cost. The cutting force observer developed for monitoring the process has the ability to estimate the external force with a resolution of 0.05 N based on servo information. Sensor-less contact force control with the cutting force observer is applied to an on-machine measurement system. To evaluate the performance, several tests are carried out. The results show that the proposed on-machine measurement system is effective at measuring the accuracy of the machined form.