Development of an on-machine measurement system for ultra-precision machine tools using a chromatic confocal sensor

In ultra-precision machining, the accuracy of a workpiece can be generally improved by surface measurement and compensation machining. Since on-machine surface measurement can avoid the errors caused by reposi-tioning workpieces and use the machine axes to extend the measuring range, there has been a trend from offline measurement to on-machine measurement in recent years. However, the workpiece surfaces inspected by on -machine measurement system in previous studies generally have small slopes and depths. In this paper, an on-machine measurement device based on a chromatic confocal sensor is designed, which can inspect workpiece surfaces with larger slopes and depths. The on-machine measurement system and measurement procedure are introduced first. A nonlinear least squares method is then used to further reduce the adverse influence of the alignment error between the axes of the sensor and the spindle of the machine tool. Finally, machining and measuring experiments of the spherical and free-form surfaces are performed using a Nanotech 650FG ultra-precision machine lathe to validate the proposed on-machine measurement method. The profile pattern and the form error obtained from the on-machine measurement device are compared with those obtained from a Taylor-Hobson 3D stylus profilometer. There is good agreement between the two results, which verifies the effectiveness of the proposed on-machine measuring method.