Avoiding 5-axis singularities using tool path deformation

This paper deals with a topical method for avoiding the tool to traverse singular positions in 5-axis machining. It is well known that the inverse kinematics transformation generates singular positions for which incoherent movements of rotary axes appear. However, in the paper, we show that due to uncertainties on the positioning, the singular position is actually characterized by a cone. We thus adopt the concept of singular cone. Following, we propose a method to deform the tool path so that the tool does not traverse the singular cone during machining. This method takes advantage of the description of the tool trajectory as B-spline curves. Therefore, the deformation corresponds to the displacements of certain control points wisely chosen. As the corrected tool path must still verify the machining tolerance, the displacement is limited by the admissible displacement which can be calculated in function of the geometrical characteristics of the tool and of the specified machining tolerance. The deformation method we propose can be extended so that the contact point is preserved. Our purpose is illustrated through the example of the machining of a surface in 5-axis high-speed machining (HSM). This illustration shows the efficiency of our method: incoherent movements are eliminated after tool path deformation and the dynamic performance of the machine tool is improved. (C) 2003 Elsevier Ltd. All rights reserved.