A Framework for a Large-Scale Machine Tool With Long Coarse Linear Axes Under Closed-Loop Volumetric Error Compensation

A large-scale machine tool is typically very inefficient in size, cost, and energy consumption. Some large parts only have a set of machining features, each of which is within a small local region, and their location should meet position and orientation tolerances. In such a machining application, as a more cost-and energy-effective alternative, this paper presents the concept of a "portable" machine tool, where a small machining platform, with the capability to machine each local machining feature in the required accuracy, is moved by long coarse linear axes. The coarse axes only perform the point-to-point positioning to each machining feature and fixed by servo control during the machining. They do not have sufficient positioning repeatability. To ensure the position/orientation accuracy of each machining feature without having highly repeatable coarse axes, this paper proposes the application of a tracking interferometer to measure all the error motions of coarse axes, and then to perform their compensation. This can be seen as a closed-loop feedback control for coarse axes using the tracking interferometer in the loop. The proposed concept is demonstrated by the experiments with its prototype using a six-degrees of freedom robot moved by two coarse linear axes.