Multiaxis On-Machine Inspection Path Planning for Free-Form Impeller Based on Least Rotation Times Optimization Model

To ensure impeller fabrication accuracy, the blades are necessary to be inspected on the machine tool (MT) to correct the machining deviation. Plagued by overlapping structures of the impeller and positioning errors from multiaxis MT, it is a challenge to generate an on-machine inspection (OMI) path that simultaneously guarantee measurement efficiency and accuracy. On the one hand, to improve efficiency, the stylus can stay in the impeller channel during the inspection process to reduce idle paths. On the other hand, the positioning errors from the rotary axis are reduced as much as possible during the measurement process to improve accuracy. For achieving these targets, a least rotation times optimization (LRTO) model for impeller OMI is proposed in this article. An accessible space map (ASM), which is the core of the LTRO model, is innovatively established in terms of the impeller's structure and the to-be-measured point. From this map, the minimum rotation times, the least direction reversions, and the angular velocity of rotary axes are investigated to optimize the stylus orientations, which helps to reduce the inspection errors by controlling the rotations of rotary axes. An impeller, as a typical part with overlapping free-form blades, is used to verify the advantages of the LRTO model with regard to multiaxis OMI. By comparison of the inspection results, the validity of the optimization model in improving measurement efficiency and accuracy is demonstrated.