Study On NC Complex Curve And Surface Interpolation Technology

With the development of the science and technology, there are more and more products with complex curve, and the requirement of the process accuracy keeps increasing. At present, there are only two methods of interpolation, circular and liner interpolation, in most of the NC systems in China. In complex curve processing, off-line tool path approximation processing method is usually used, curve is divided into tiny straight-line portions, and linear interpolation is used to fit. In order to fulfill the accuracy requirement, the number of straight-line portions is great. This leads to huge burden in NC system transfer, at the same time, tools needs to accelerate and decelerate in each procedure, the processing efficiency is seriously affected.Non-Uniform Rational B-Spline (NURBS) curve and its features, related parameters calculation was researched in this thesis. Curve and surface interpolation algorithm on NURBS was studied and analyzed in-depth.First of all, with integrating before and after difference instead of differentiations, parameter rapid recursive approach was developed by improving initial iterative approach. By utilizing parameter rapid recursive approach, proper interpolated pretreatment and reasonable approximate computation, considering contour error control and acceleration feed control, an adaptive dynamic variable step size NURBS curve interpolation method was achieved. Within machine error requirement, the machine can maximize the feed rate of parts for interpolation processing. Interpolation accuracy and speed was optimized so that processing quality and efficiency was improved.Secondly, regarding to acceleration and deceleration control, by predicting deceleration point in real-time interpolation according to NURBS curve's symmetrical characteristics, we proposed parabola--linear--parabolic S-type acceleration and deceleration control method in this thesis. This method has the advantages of high positional accuracy and smooth speed transition. In addition, it changed the situation that using strings instead of arc, complicated arc length calculation in each interpolation in the old control method, which was beneficial to improve the high interpolation accuracy and instantaneity.Finally, based on NURBS curve real-time interpolation algorithm and S-type acceleration and deceleration control put up by this thesis, a NURBS curve interpolator was developed using MATLAB Programming Language. The tool path was formed by the tool-contact-point. Compared with the traditional method, that the tool path was formed by the position of the tool, this approach practically improved the accuracy and efficiency of the processing curve. An open NC platform based on embedded industrial PC+Movement Control Card was built to analyze extensively on various features of this interpolator, correctness and feasibility of the related algorithms, by demonstrating and simulating on the exemplified surface of impeller vane.