Siemens sinumerik 840d Programming Manual page 153

04.00
5
840D 840D
NCU 571 NCU 572
NCU 573
B SPLINE
With a B spline, the programmed positions are not
interpolation points, but merely check points of the
spline, i.e. the curve is "drawn towards" the points,
but does not pass directly 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 3rd-degree B spline does not produce
any oscillations in spite of its continuously curved
transitions.
Programmed supplementary conditions (please see
below for more information) have no effect on B
splines. The B spline is always tangential to the
check polygon at its start and end points.
Point weight:
A weight can be programmed for every interpolation
point.
Programming:
PW = n
Value range:
0 <= n <= 3; in steps of 0.0001
Effect:
n > 1 The check point exerts more "force" on
the curve
n < 1 The check point exerts less "force" on
the curve
Spline degree:
A 3rd-degree polygon is used as standard, but a 2nd-
degree polygon is also possible.
Programming:
SD = 2
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SINUMERIK 840D/840Di/810D/FM-NC Programming Guide Advanced (PGA) − 04.00 Edition
FM-NC 810D 840Di
Special Motion Commands
5.2 Spline interpolation
B spline
Check polygon
P4
P5
P3
P2
P1
P1 to P7: Predefined coordinates
5
P6
P7
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