Research On The Direct Interpolation Of NURBS Based On DSP

NURBS is more and more widely applied in the field of CAD/CAM and computer graphics because of its unique advantages in modeling complex parts. However, traditional CNC machine tools only have the direct interpolation function of line and arc, so it's necessary to turn the curves into tiny segments with CAM and then transfer the data to CNC systems. It can't meet the demand of high efficiency and high precision. So the direct interpolation of NURBS is of great significance to the development of CNC machine tools of high efficiency and precision.This paper proposed a new direct interpolation algorithm of NURBS with the support of the Science and Technology Project of Zhejiang Province (NO. 2006C11067).There are two steps to realize the direct interpolation of NURBS, first mapping the path into parameters and then mapping the parameters into path. Nonlinear equation method and de Boor algorithm are used to simplify the process and improve the efficiency. In addition, the feed rate optimization is another important task for the direct interpolation of NURBS. Feed rate Adaptation Control Algorithm modifies the feed rate according to the curvature of the curve, meanwhile the look-ahead algorithm with back tracking and re-interpolation strategy keeps the dynamics parameters under control to prevent shocks and vibrations. To take the effect of dangerous points into consider during the planning of feed rate, segment interpolation scheme is proposed in Chapter Four. The symmetry of NURBS is used to predict position of the decelerating point precisely.The algorithm is transplanted to the motion control card based on TMS320F2812. In term of hardware, the settings of EV are explained in details, including I/O, GP Timer, Period Register, and so forth. Meanwhile, the tech of circular buffer and IQ math library are introduced in term of software.Finally, analysis of simulations and experiments are conducted to verify the viability and reliability of the algorithm. Xk713 CNC miller and an specific designed NURBS curve are applied in the experiments. The performance of the algorithm in efficiency, precision and axis dynamics is compared with the traditional methods.