Modeling and Control of Contouring Errors for Five-Axis Machine Tools-Part II: Precision Contour Controller Design

The accurate tracking of tool-paths on five-axis CNC machine tools is essential in achieving high speed machining of dies, molds, and aerospace parts with sculptured surfaces. Because traditional CNCs control the tracking errors of individual drives of the machine, this may not lead to desired contouring accuracy along tool-paths, which require coordinated action of all the five drives. This paper proposes a new control approach where the tool tip and tool orientation errors, i.e., the contouring errors, are minimized along the five-axis tool-paths. The contouring error and kinematic model of the machine, which are presented in Part I of the paper, are used in defining the plant. A multi-input-multi-output sliding mode controller, which tries to minimize path tracking and path following velocity errors, is introduced. The stability of the system is ensured, and the proposed model is experimentally demonstrated on a five-axis machine tool. The path errors originating from the dynamics of five simultaneously active drives are significantly reduced.