Siemens SINUMERIK 840D

5
04.00 Special Motion Commands
5.2 S
p
line inter
p
olation
5
840D
NCU 571
840D
NCU 572
NCU 573
FM-NC 810D 840Di

Siemens AG 2000. All rights reserved
SINUMERIK 840D/840Di/810D/FM-NC Programming Guide Advanced (PGA)
−
04.00 Edition
5-153
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
P1
P2
P3
P4
P6
P7
P5
Check polygon
B spline
P1 to P7: Predefined coordinates