Contour smoothing processes

The contour-influencing processes described below are available to be able to operate at a higher machining speed even with discontinous block transitions and relatively short blocks. All the processes modify the programmed nominal contour in such a way that the transition between the individual programmed interpolation points or partial contours is continuous. To what degree this continuity is achieved depends on the process used.

When using the processes 1, 2, 4 and 5, by specifying corresponding parameters the user can additionally decide to what extent deviations from the programmed nominal contour are permissible. Here, the nominal contour is understood to be the NC program generated by the CAD/CAM system (i.e. the interpolation points). Slight permissible deviations from the nominal contour in the case of highly discontinuous block transitions generally lead to lower machining speeds.

In the case of the spline process 3, the possible contouring error cannot be influenced. It results from the specified interpolation points and the spline algorithm. The Akima spline has the characteristic that it links up the programmed interpolation points. By contrast, the B-spline algorithm uses the programmed interpolation points as check points only and therefore generally does not lead through the interpolation points. The processes are especially suitable for joining smooth and harmonious interpolation point profiles (e.g. joining of circular blocks or elliptical description via linear blocks) because non-linear transitions are smoothed as required. The spline processes listed as number (3) are not suitable for the interpolation of prismatic contour descriptions. Due to the typical characteristics of the B-spline algorithm, this is also partly suitable for generating curves out of scanned surfaces.

The HSC B spline mode 5 offers the possibility to combine automatically spline segments. Beside the smoothing effect of the B spline the roughness of the interpolation points is removed, and the block performance is increased. During this the process monitors the contour deviation, parametrized by the user.

The operating principle of all the processes is not limited to main axis motions but, except for process 4, at least one main axis must be involved in a motion.

Processes 2 and 3 are not suitable for smoothing short circular blocks with transitions that are not tangent-constant because spline generation is deactivated automatically before the entry into a circular block! Process 1 or 4 must be used in this case. If the preservation of discontinuous block transitions is desirable (prismatic contour segment), processes 2 and 4 must be given preference. Here, the user can also retain required prismatic contour segments by specifically using the contouring process 4 or by suitably parameterizing the limit angle at discontinuous block transitions with process 2.

If interpolation points generated by a CAD/CAM system are used, the actual nominal contour error depends considerably on the scanning process in the CAD/CAM system. Generally, the nominal contour error becomes smaller than the tolerance hose programmed in the CAD/CAM system because the spline curve positioned over the interpolation points comes closer to the original curve than the polygon. As shown by way of example in Figure 1-2, the contour description is approximated via polygons and/or circular blocks, i.e. the generated interpolation points each lie on the original curve or the generated circular blocks approximate the curvature of the original curve locally and end on the original curve.

+: suitable -: not suitable