Surface-opening feature measurement using coordinate-measuring machines

Abstract

Coordinate-measuring machines (CMM) with contact probes have been widely used in industry for quality inspection and reverse engineering. Despite its lower scanning speed, its tactile nature and precision level leads to more reliable measurement results compared with non-contact probes. Although extensive research effort has been spent on CMM-based measurement, the current research status does not lend an immediate application of CMM machines to the measurement of surface-opening features. When opening spaces are not taken into account in CMM path planning, the probing stylus would enter opening spaces, thus leading to significant measurement errors. This paper presents a methodology to measure surface-opening features using CMM with contact probes. Starting from estimated boundary points through extrapolating cubic spline curves, the probing styluses are able to search and compensate to the boundaries of opening features. The probing method is implementable in both computer-aided design (CAD)-guided mode and non-CAD-guided mode. In CAD-guided mode the probing stylus approaches along surface normal direction, while in non-CAD-guided mode the normal direction is first estimated through triangular method, and then followed by a correction procedure. The presented method is able to use contact probes to track and measure the boundaries of surface-opening features directly without using complicated data processing and sophisticated instrumentation.