Reaserch And Application On The Segmenting Algorithm For NURBS Tool Paths Generation In CNC Surface Machining

NURBS representation has been widely used in CAD/CAM for its sophisticated geometric properties, which is also specified by international standard as a unique mathematical tool for describing the geometry form of industrial production. In CNC machining, NURBS interpolation that is regarded as the best way for tool path planning involving high speed and high accuracy needs more concise NC codes, smoothens the speed and produces high machining accuracy. To use the NURBS interpolation in the free-form surface machining, NURBS tool path should be calculated through the CAD model of the surface. Taken this as the background, the segmentation algorithm for NURBS tool path generation and the boundary conditions in the NURBS fitting is investigated on this thesis.By analyzing the property of the NURBS tool path, the boundary points and the connection of the tool paths in line with the properties of NURBS tool paths are classified. A segmentation approach is proposed by using hierarchical clustering algorithm. According to the segmenting result, the points fitted with the NURBS curve can be determined by justifying the type of the boundary points.A new NURBS fitting method with the constraint condition that is obtained from the segmentation algorithm is used in this study. The fitting technique can make the NURBS tool path smoother. A new method that allows determining the initial value of NURBS fitting is proposed. The matrix expression of NURBS curve subsection is derived.NURBS tool path which is generated by using the algorithm proposed in this thesis is applied to machine the sophisticated sculptured surface. The case studies showed that the new algorithm is robust, effective and highly adaptable to the different surfaces and curves.The proposed algorithm is easy to achieve in the applications. NURBS tool path can improve the stability of machining processes and decrease frequent acceleration-deceleration to enhance the cutting efficiency, while these tool paths can make accurate and smooth sculpture surfaces. This approach may be of potential to be widely implemented in the manufacturing industry.