Soichi Ibaraki, Kyoto University

Large parts are typically machined by using a large-sized machine tool, where all the axes are designed to have sufficient rigidity, repeatability and accuracy. Some large parts only require a set of machining operations within a small “local” region but many “local” features must be machined over the entire large part. In such a machining application, as a more cost-effective alternative to large-sized machine tools, we propose the concept of a "movable" machine tool; a small machine tool, which has the capability to machine the given feature at each local region, moves by long coarse linear axes to each region. To ensure the position accuracy of each machined feature, the long “coarse” axes must also have sufficient positioning accuracy. The paper proposes the application to a laser tracker to measure the three-dimensional positioning accuracy of the coarse axes, and then its real-time compensation to ensure the required positioning accuracy. To demonstrate and validate the proposed design concept, this paper presents an experimental prototype of the “movable” machine tool by applying the proposed concept to a 5-DOF robot, moved by long coarse linear axes.

Keywords: Large machine tool, large parts, volumetric accuracy, laser tracker, compensation.