Global calibration of an on-machine measurement system using a chromatic confocal sensor

In ultra-precision machining, real-time measurement is typically conducted using non-contact on-machine measurement (OMM) systems to satisfy the stringent accuracy requirements of manufactured workpieces. However, during the OMM process, deviations in the beam direction of sensor may introduce measurement errors, thereby compromising machining precision. To address this challenge, this study proposes an on-machine measurement system based on a chromatic confocal sensor, capable of accurately inspecting freeform surfaces, such as spherical workpieces. Initially, an OMM system was implemented on a three-axis alignment turning lathe, followed by the calibration of the beam direction of sensor using a standard sphere. To simultaneously estimate the beam direction vector and sphere center coordinates, a novel hybrid optimization algorithm combining a Genetic Algorithm (GA) and the Levenberg–Marquardt (L–M) method was developed. Compared to conventional optimization methods, the proposed algorithm reduces calibration residual error by approximately 61.4 %, as measured by the sum of squared residuals. Finally, planar surface measurement experiments were conducted using the developed OMM system alongside a precision interferometer to validate calibration accuracy. This study achieves submicron measurement precision, facilitating accuracy, enabling integrated machining and measurement on ultra-precision turning platforms and ensuring reliable process control.