Siemens SINUMERIK 840D sl Programming Manual page 172

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Table of Contents

Special Motion Commands

5.2 Spline interpolation (ASPLINE, BSPLINE, CSPLINE, BAUTO, BNAT, BTAN)

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.

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.

Programming Manual, 03/2006 Edition, 6FC5398-2BP10-1BA0

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