Modeling and cross-coupled contouring control of multi-axis CNC machine tools

Abstract

Nowadays, multi-axis computer numerical controlled (CNC) machine tools are widely used in machining dies, mold, turbine blades, and aerospace parts. These parts usually have complex geometry, represented by parametric or free-form surfaces. With the increasing demands for better machining precision and higher productivity, methods for improving the performance of machine tools are continuously being sought. One objective is to minimize the contour error through proper design of a motion controller, since accurate contour tracking is essential to ensure high machining quality of a CNC machine tool. In this thesis study, a five-axis CNC machine tool is developed with detailed investigation on kinematics and dynamics modeling, and then a cross-coupled controller for reducing contour error is proposed and applied to the machine tool. The objectives of this study are fourfold. First, the kinematics of the five-axis machine system is analyzed, using Denavit-Hartenberg (D-H) coordinate transformation methodology. The homogeneous transformations, direct and inverse kinematics, and transformation between the workpiece and machine coordinate frames are all derived. Second, a dynamics model of the five-axis machining system is developed using Lagrange’s equation. Thirdly, a cross-coupled contouring controller is developed with a stability analysis. In the proposed control approach, each axis is required to track its desired trajectory while maintaining a certain kinematic relationship with the other axes, through motion synchronization. The proposed controller involves the contour error model and a cross-coupling control strategy to ensure that the machine tool tracks its desired contour. Finally, experiments are performed on the home-made machine tool to demonstrate the effectiveness of the proposed control approaches in the multi-axis motion control tasks.

Date of Award	3 Oct 2006
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Dong SUN (Supervisor)