Development and testing of an error compensation algorithm for photogrammetry assisted robotic machining

Abstract

Robotic machining of relatively small features on large components potentially offers an opportunity to reduce capital expenditure in various industries. A barrier to this is the inability of robotic machine tools to machine to the tolerances of conventional equipment. This paper proposes and tests a photogrammetry-based metrology assistance algorithm to compensate for robotic machining inaccuracy, as measured in the part, and investigates the associated measurement challenges. The algorithm is executed in a two stage process, whereby the closest point to nominal cutting coordinates on an aligned inspection surface is used for compensation, created a penultimate measured cut. Finally, the finishing program coordinates are compensated to correct under-cuts during the measured cut stage. Conceptual tests using simulated measurement data give confidence that the proposed approach works well. In experiments, a key area for further R&D effort is found to be uneven inspect point coverage, which results in alignment issues and a poor surface finish. Ultimately, direction is given to improve measurement system performance to enable the metrology assistance approach proposed to be implemented and therefore the benefits of “process-to-part” robotic machining to be realised.