Research On Multi-constrained Feedrate Control For5-axis Interpolation

With the increasing requirement for machining geometrically complex parts, as one of the most popular standards for exchange of production, NURBS are widely used in CAD and CAM files due to its exact analytic representation and the ability of local adjustment. In order to improve the overall performance of the CNC system and the integration of the CAD/CAM and CNC technique, it will be very important to research and develop the CNC system with good NURBS interpolation performance. This paper presents a new approach to dual NURBS interpolator with limited non-linear geometric error, angular feedrate, angular feed acceleration and tangential feed acceleration for precision five-axis machining.The five-axis cutting location data consists of a position vector and an orientation unit vector, representing the tool tip and the tool axis, respectively. In fact, the continuous spatial trajectory of the given cutter in five-axis machining can be essentially described by a ruled surface due to the existence of the dual rotation axes. As a result, a ruled surface expressed by two NURBS curves is used to define the cutter tip position and cutter axis orientation at any moment during machining along the tool path.Different from chord error aroused in three-axis machining, non-linear geometric error in five-axis machining is researched and calculated. The angular feedrate of rotational cutting tool is researched. Meanwhile, the calculation formula of angular feedrate and the relation between angular and linear feedrate is given, and then the adaptive linear feedrate at each sampling cycle is scheduled with the limits of maximum allowable non-linear geometric error and angular feedrate.The concept and calculation formula of the guiding feedrate curver is proposed for the off-line work of the later ACC/DEC smooth control. Combined with the analytical relations of feed acceleration to the arc-length parameter and linear feedrate. the linear feedrate of angular acceleration sensitive points is adjusted using an same coefficient derived formula while that of tangential feed acceleration sensitive points is rescheduled using a look-ahead algorithm.A simulation system with the proposed interpolation algorithm of this paper is designed by VC++software. Four kinds of interpolation algorithms for one tool path are respectively researched. From the simulation results the proposed tangential and angular feed ACC/DEC flexible control adaptive interpolation algorithm can fulfill all of the constraints. At last. Combined with a five-axis CNC machine, a machining example is designed and is performed to validate the good flexibility and feasibility of the algorithm in this paper.