A Forward and Reverse Bidirectional Nurbs Curve Interpolation Method Based on Multiple Constraints

Abstract

The present invention provides a forward and reverse NURBS curve interpolation method based on multi-constrained conditions. The method comprises: taking out a curve section required being processed at present in order from a preprocessing curve section set, and calculating the maximum feeding step at the same time from forward and reverse direction; obtaining the position information of a current interpolation point according to the maximum feeding step, storing the forward interpolation point to an interpolation data queue, and storing a reverse interpolation point to an LIFO buffer zone; when the forward and reverse interpolation is performed to an intersection zone, regulating the acceleration value of an intersection point to allow the speed to be smoothly transited; after the forward interpolation is finished, storing the reverse interpolation point temporarily stored in the LIFO buffer zone into the interpolation data queue; and after the forward interpolation point is continued, completing the interpolation preprocessing of one curve section, issuing the interpolation point data to a servo control system, and realizing feeding of each shaft through a driving motor so as to ensure the processing efficiency and improve the interpolation precision.

Description

technical field [0001] The invention relates to a forward and reverse bidirectional NURBS curve interpolation method based on multiple constraint conditions. Background technique [0002] High-speed and high-precision machining not only requires the CNC system to have a real-time interpolation algorithm, but also the control accuracy must reach the sub-micron level. The real-time performance of the interpolation algorithm even determines the possibility of high-speed machining. Non-uniform rational B-spline (Non-uniform Rationa1 B-spline, NURBS) curve has good shape expression ability, and it is more and more widely used in the modeling design and manufacturing of automobile, aircraft, shipbuilding and other surface parts, and has become a STEP curve. -The only form of expressing free curved surfaces in NC. The processing file code expressed in NURBS form is concise, and there is no loss of precision, and its code volume is only that of the traditional NC code It has inco...

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Problems solved by technology

[0046] Firstly, the actual interpolation step length should be smaller than the maximum feed step length interpolated at the command speed within the interpolation cycle T; secondly, during NURBS curve interpolation, all interpolation points are on the curve, and there is no radial error (neglected and discarded) error), but there is a contour error caused by the short straight line approaching the actual curve with the feed step as the unit. The short straight line formed by the actual feed step should make the contour error within the allowable range; in addition, due to the existence of the curvature of the curve, When performing high-speed machining, it will also cause a large acceleration in the normal direction (abbreviated as normal acceleration). If the normal acceleration is too large and exceeds the design capacity of the dynamic stiffness of the machine tool feed system, it will cause damage to the feed system and the workpiece. The processing quality, or even the entire machine tool has a serious impact

[0047] From the above problems, it can be seen that when various constraints are met, the change of feed speed and acceleration during interpolation may be inconsistent with the acceleration and deceleration mode adopted

At the same time, the traditional acceleration and deceleration is carried out in one direction along the interpolation curve, and the interpolation constraint information of the rest of the curve is unknown, and the acceleration process cannot be associated with the subsequent deceleration.

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