User's Manual

PMAC User Manual
182 Writing Programs for PMAC
Four Programmed Segments
V
time
TA (added) TA (added)TA TA
TA TA
Three Programmed Segments
V
time
TA (added) TA (added)TA TA
TA
Two Programmed Segments
V
time
TA (added) TA (added)TA
TA
One Programmed Segment
V
time
TA (added) TA (added)TA
Figure 36 Cubic Spline Trajectories
(specified)
VEL
TIME
TA
P
V
1
1
(specified)
(calculated)
P ,V
P
1
P
0
P
00
(from
before)
(calculated)
= constant
A
A
dA
dt
0
(calculated)
1
(specified)
PVT200
...
X9000:150
...
Figure 37 PMAC Transition Point Moves (PVT Mode, Parabolic Velocity)
How They Work
In SPLINE1 mode, a long move is split into equal-time segments, each of TA time. Each axis is given a
destination position in the motion program for each segment with a normal move command line like
X1000Y2000. Looking at the move command before this and the move command after this, PMAC
creates a cubic position-vs-time curve for each axis so that there is no sudden change of either velocity or
acceleration at the segment boundaries. The commanded position at the segment boundary may be
relaxed slightly to meet the velocity and acceleration.
PMAC can only work with integer (millisecond) values for the TA segment times. If a non-integer value
is specified for the TA time, PMAC will round it to the nearest integer automatically. It will not report an
error. This rounding will change the speeds and times for the trajectory.
PMAC computes intermediate way points for each axis for each point along the spline by taking a
weighted average of the specified point X(n) and the specified points on either side, according to the
equation:
6
1)X(n4X(n)1)X(n
WP(n)
+++−
=