Interpolation control algorithm for a three-RPS parallel spindle head

Abstract

A five-axis computer numerical control hybrid machine tool composed mainly of a three-RPS parallel spindle head with one translation and two rotations is investigated; because of its unique machining characteristics, this machine tool has been applied to high-efficiency aerospace monolithic component processing, and its trajectory control is one of the core technologies underpinning its efficacy. This research investigates a new type of five-axis hybrid machine tool which is loaded with a three-RPS parallel spindle head and finds a cutter orientation interpolation algorithm which can ensure its high-precision, and high-speed, operation in machining processes. First, the kinematic model of the hybrid machine tool is established using the vector chain method. Using this model, the virtual reality mapping relationship between the control axis space and the operating space is established. Then a control algorithm governing two interpolation strategies in the operation and joint spaces is proposed; this method disperses the cutter vector in the workspace. Through the mapping relationship, the point data array in the joint space can be obtained from the machining data which are calculated from the mapping model, and then the improved three B-spline interpolation method is used in the joint space. Thereafter, the post-machining module outputs the interpolation data to the motor, and the moving platform can realise the desired tool path. Finally, using the hybrid machine tool for the machining of an ‘S’ test-piece, the results prove the feasibility and effectiveness of the interpolation algorithm. The experiment indicates that the interpolation algorithm can be used in this kind of parallel machine tool control system.