Reference Manual
PMAC 2 Software Reference
74 PMAC I-Variable Specifiation
Ix17 Motor x Maximum Permitted Motor Program Acceleration
Range
positive floating point
Units
counts/msec
2
Default
0.5
Remarks
Ix17 sets a limit to the allowed acceleration in LINEAR-mode blended programmed moves
for Motor x, provided I13 equals zero (no move segmentation). If a LINEAR move
command in a motion program requests a higher acceleration of this motor given its TA
and TS time settings, the acceleration for all motors in the coordinate system is stretched
out proportionately so that Motor x will not exceed this parameter, yet the path will not be
changed.
Because PMAC cannot look ahead through an entire move sequence, it sometimes cannot
anticipate enough to keep acceleration within this limit. Refer to LINEAR-mode
trajectories in Writing a Motion Program.
It is possible to have this limit govern the acceleration for all LINEAR-mode moves by
setting very low TA and TS times. Do not set both the TA and TS times to zero, or a
division-by-zero error will occur in the move calculations, possibly causing erratic
movement. The minimum acceleration time settings that should be used are TA1 with
TS0.
Note:
When moves are broken into small pieces and blended together, this
limit can affect the velocity, because it limits the calculated
deceleration for each piece, even if that deceleration is never
executed, because it blends into the next piece.
This limit does not affect PVT, CIRCLE, RAPID, or SPLINE moves. The calculation
does not take into account any feedrate override value other than 100).
Note:
If PMAC’s circular interpolation function is used at all, then I13
must be greater than zero, and Ix17 will not be active as an
acceleration limit.
With the Option 6L special lookahead firmware, Ix17 sets the limit for acceleration of
LINEAR and CIRCLE mode moves with segmentation active (I13 > 0). This mode of
operation permits robust acceleration control by looking ahead far enough to ensure that
these motor acceleration limits can always be obeyed.
Example
Given axis definitions of #1->10000X, #2->10000Y, an Ix17 for each motor of 0.25,
and the following motion program segment:
INC F10 TA200 TS0
X20
Y20
the rate of acceleration from the program at the corner for motor #2 (X) is ((0-10)units/sec
* 10000 cts/unit * sec/1000msec) / 200 msec = -0.5 cts/msec
2
. The acceleration of motor
#2 (Y) is +0.5 cts/msec
2
. Since this is twice the limit, the acceleration will be slowed so
that it takes 400 msec.