Abstract
This paper introduces the realization of a tool radius compensation algorithm for NURBS trajectory. First, a single-segment NURBS trajectory tool radius compensation algorithm is developed. Different from the straight line and arc trajectory, the self-intersection phenomenon is prone to happen when calculating a single NURBS tool center trajectory, and the self-intersection will cause the overcut of workpiece. To avoid this situation, the algorithm introduced in this paper can detect whether the NURBS tool center track has caused overcut, and deal with the self-processing. Second, the tool radius compensation algorithm with multi-segment NURBS trajectory is implemented. The focus of this part is the tool radius compensation of the trajectory transfer, and the trajectory transfer is divided into two types: the extension type and the shortened type. For the shortened type transfer, cross-processing is needed to avoid the overcut of workpiece at the transfer. When calculating the tool radius compensation of the shortened type, we not only need to find the intersection of the tool center trajectory of two adjacent NURBS curves, but also need to select the intersection we need when a number of intersections exist. For the extension type transfer, in order to ensure the continuity of the tool center trajectory, we need to extend the tool center trajectory or add arc-segment at the transfer. The proposed algorithm can automatically decide where to extend the tool center trajectory or add arc-segment to achieve the best efficiency. Finally, the algorithm can output the calculated NURBS tool center trajectory in the form of linear segment interpolation G code or NURBS interpolation G code according to the processing needs. Simulations on VERICUT and experiments on three-axis CNC machine tool shows the effectiveness and validation of the tool path compensation algorithm.
Highlights
CAM system has been able to use NURBS curve to describe contour trajectory
We focus on the NURBS tool radius compensation problem for tool geometry path rather than the speed planning and interpolation of NURBS trajectories studied in previous papers
For elongated tool radius compensation, the existing processing method only considers the geometric information of the trajectory [19,20], but ignores some parameter information given by the actual machine processing, such as turning time, tool radius, maximum acceleration for machine tools, and so on
Summary
CAM system has been able to use NURBS curve to describe contour trajectory. NURBS interpolation has been studied [1,2,3] and seems to work well. Many high-end systems have been supporting NURBS curve interpolation, such as FAUNC, Siemens and other manufacturers These CNC systems do not support tool radius compensation for flat NURBS. In the NURBS trajectory tool radius compensation algorithm, we need to consider the calculation of the NURBS equidistant curve, and need to consider the Intersection of NURBS equidistant curve. There is no self-intersection phenomenon for the straight lines and arcs, as shown in Figure 2a and b It is possible for NURBS equidistant curve to contain self-intersection, which can lead to overcut of workpiece. To avoid this phenomenon, we need to calculate the self-intersection of the NURBS equidistant curve and remove the trajectory segments which will lead to overcut. To obtain the discrete points of the equidistant curve, firstly we need to discrete the original NURBS curve
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