CAD-based measurement path planning for free-form shapes using contact probes

Dimensional inspection of engineering components comprising free-form surfaces demands accurate measurement of a large number of discrete points, such that the actual shape may be fully characterised. This paper presents a methodology for CAD-based measurement of such components using a coordinate measuring machine equipped,vith a touch-trigger probe. The main shortcomings of the conventional methodology have been identified to be in relation to registration and probe radius compensation. The proposed measurement process involves the following main steps: registration, definition of measurement points, probe path generation, path optimisation and verification, measurement and probe radius compensation. By employing the CAD model at every step, the implemented methodology maximises the measurement accuracy and this is verified through a detailed simulation study. In addition, the implemented tools for CMM programming achieve accurate control of the overall measurement process and provide a high level of confidence when dealing with complex component geometry.