Siemens SINUMERIK 840D sl Programming Manual page 172

Special Motion Commands
5.2 Spline interpolation (ASPLINE, BSPLINE, CSPLINE, BAUTO, BNAT, BTAN)
A-Spline
The A spline (Akima spline) passes exactly through the intermediate points. While it
produces virtually no undesirable oscillations, it does not create a continuous curve in the
interpolation points. The akima spline is local, i.e. a change to an interpolation point affects
only up to six adjacent points. The primary application for this spline type is therefore the
interpolation of digitized points. A polynomial of third degree is used for interpolation.
B spline
With a B spline, the programmed positions are not intermediate points, but merely check
points of the spline, i.e. the curve is "drawn towards" the points, but does not pass directly
through them. The lines linking the points form the check polygon of the spline. B splines are
the optimum means for defining tool paths on sculptured surfaces. Their primary purpose is
to act as the interface to CAD systems. A third degree B spline does not produce any
oscillations in spite of its continuously curved transitions.
5-8
Programming Manual, 03/2006 Edition, 6FC5398-2BP10-1BA0
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