CNC centralized control for digitizing freeform surfaces by means of a conoscopic holography sensor integrated in a machining centre

Abstract This paper presents the integration of a conoscopic holography sensor (CH) in a machining centre (MC) by means of a centralized control on the machine's CNC (CNC centralized control). Besides the installation and extrinsic calibration of the sensor, the primary focus is the automation of the freeform digitizing process on the MC itself. To overcome the usual lack of compatibility between the respective interfaces of the CNC machine and the non-contact sensor, a system was developed to centralize the control intelligence on the machine's own CNC, enabling digitizing operations to be performed directly with the execution of an NC subroutine. In addition, three digitizing strategies are proposed: Non-Adaptive, Adaptive and Predictive-Adaptive. These require no planning tools or off-line programming prior to the digitizing process. The effectiveness of the extrinsic calibration method was validated by measuring a certified ballbar, and the integrated measuring system was checked by comparing the metrological results obtained by digitizing a freeform surface with those obtained by a CMM contact probe and with the CAD model used for machining the surface.