A strategy to evaluate and minimize parallelism errors of a rotor system in a precision rotary table

Abstract

Closed hydrostatic rotary table is one of the key units in an ultra-precision machine tool, while the main component of the rotary table is the rotor system, consisting of two thrust plates and a rotor. The kinematic errors of the rotary table are directly affected by the geometric errors of the rotor system. However, geometric errors of the rotor system are difficult to evaluate, due to the closed structure of the system. In this paper, a strategy to evaluate geometric errors of rotor system, using ultra-precision CMM (coordinate measuring machine), is presented. The method is based on coordinate conversion and least squares principle. In this approach, two sets of open structures are established, by dividing the rotor system into two parts. The profiles and cylindrical feature of the components of the rotor system are directly scanned by CMM. Following the compensation of the data from the CMM, the parallelism and perpendicularity errors can be evaluated. Furthermore, based on the aforementioned compensation algorithm, an optimization method for improving assembly precision of the rotor system is proposed. The result shows perpendicularity error between the two thrust plates and the rotor to be 14 μm and 21 μm, respectively, and the parallelism error between the two thrust plates to be 28 μm with measurement uncertainty of 0.5 μm. Additionally, the experimental result on the optimization method of guiding the assemblage of rotor system indicates that the parallelism error reduced to 12.1 μm, noting a 57% improvement.