Modeling and synchronous control of a single-axis stage driven by dual mechanically-coupled parallel ball screws

摘要

This paper presents a synchronous control scheme and system modeling technique for a single-axis stage driven by dual parallel ball screws/servo motors. The slide tables of the two ball screws are bridged with an aluminum bar, and each end of the bar is firmly fixed to one slide table. The thrust can, thus, be jointly output via this coupling. Such an arrangement aims to solve the potential skew problem that would occur on large scale machine tools whose stages have a long span between the two linear guides. This layout can also improve the system dynamics, speed and accuracy for large gantry-type machine tools. However, the precise synchronization of the two coupled parallel ball screws is a major challenge to overcome. Hence, in this paper, a system identification technique is first developed to construct a mathematical model of the coupled system, which is experimentally verified to be effective in improving performance. Three types of synchronous control schemes are then employed for control of the system. The performances of the three control schemes are experimentally compared in terms of positioning accuracy, tracking ability and reduction of the synchronization error between the two ball screws. Appropriate control schemes are suggested based on the experimental results.