Uncertainty analysis of an in-situ part measurement system for micromilling applications

The capacity to detect geometrical errors on the workpieces during the machining process is a key enabling technology for obtaining in-tolerance parts. Being able to use a non-contact in-situ measurement system can improve the limited productivity of standard contact probes. This work characterizes the uncertainty of an optical measurement system, based on a CMOS sensor, installed in-situ on a micromilling machine. A repeatable procedure for system characterization purposes is presented along with a task-specific analysis of the expanded uncertainty associated to the optical measurements. Different geometrical features were measured on a specifically developed metallic artefact calibrated by a CMM machine. The measurements, carried out at different machine conditions showed that: I) the expanded uncertainty (ISO15530-3), varies from 0.4 µm to 29.2 µm, II) the uncertainty sources are feature-dependent, III) machine conditions do not play a main role, IV) illumination is a key factor. The presented results prove that optical measurement systems can be feasibly integrated on the harsh micromilling machine environment to support machining processes optimization and control and machine/cycle setup only if the uncertainty budget is adequately characterized.