Reference Manual

Turbo PMAC/PMAC2 Software Reference
Turbo PMAC Global I-Variables 183
Isx78 is expressed in the user length units for the linear axes (usually millimeters or inches) divided by
the square of the user “feedrate time units” set by Isx90 for the coordinate system (usually seconds or
minutes).
Example 1:
You want to limit the centripetal acceleration to 1.0g with Isx78. Your length units are millimeters, and
your time units are seconds. Isx78 can be calculated as follows:







2
2
9800
1000
*
8.9
*0.178
s
mm
m
mm
g
s
m
gIsx
Example 2:
You want to limit your circular interpolation calculation errors to 0.001 inches. Your length units are
inches, your time units are minutes, and your Isx13 segmentation time is 10 milliseconds. Isx78 can be
calculated as follows:







22
22
222
2
min
216000
min
60
*
01.0
001.0*66
78
ins
s
in
T
E
R
V
Isx
Example 3:
Your system is capable of 10 m/s
2
acceleration (about 1g). Your length units are millimeters, your time
units are minutes, and your Isx13 segmentation time is 2 milliseconds. Isx78 can be calculated as
follows:







22
2
2
min
000,000,36
min
3600
*
1000
*1078
mms
m
mm
s
m
Isx
At this setting, your maximum circular interpolation calculation errors can be computed as:
mm
s
s
mmT
Isx
R
TV
E 0067.0
60
min
*002.0*
min
6
000,000,36
6
*78
6
22
2
22
2
222

Isx79 Coordinate System ‘x’ Rapid Move Mode Control
Range: 0 .. 1
Units: none
Default: 0
Isx79 controls how Turbo PMAC computes the speed of “shorter” axes in a multi-axis RAPID-mode
move. If Isx79 is set to the default value of 0, Turbo PMAC will compute the ratio of move distance to
rapid-speed (Ixx16 or Ixx22, depending on the setting of Ixx90) for each motor in the move. Only the
motor with highest distance/speed ratio will actually be commanded at its specified speed. The
commanded speeds for other motors will be lessened so that they have the same ratio of distance to speed,
yielding the same move time for all motors (before acceleration and deceleration are added). This makes
the move path in a Cartesian system at least approximately linear (and truly linear if the acceleration and
deceleration times set by Ixx19 – Ixx21 are the same).