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100

PMAC 2 Software Reference

PMAC I-Variable Specification 75

With the same setup parameters, and the following program segment:

INC F10 TA200 TS0

X20 Y20

X-20 Y20

The rate of acceleration from the program at the corner for motor #1 (X) is ((-7.07-

7.07)units/sec * 10000 cts/unit * sec/1000msec) / 200 msec = -0.707 cts/msec

. The

acceleration of motor #2 (Y) is 0.0. Since motor #1 exceeds its limit the acceleration time

will be lengthened to 200 * 0.707/0.25 = 707 msec.

Note that in the second case, the acceleration time is made longer (the corner is made

larger) for what is an identically shaped corner (90

). In a contouring XY application, this

parameter should not be relied upon to produce consistently sized corners.

See Also

Acceleration Limits (Making Your Application Safe)

LINEAR-mode moves (Writing a Motion Program)

I-variables I13, I50, Ix16, Ix19, Ix22

Ix19 Motor x Maximum Permitted Motor Jog/Home Acceleration

Range

positive floating point

Units

counts/msec

Default

0.015625

Remarks

Ix19 sets a limit to the commanded acceleration magnitude for jog and home moves, and

for RAPID-mode programmed moves, of Motor x. If the acceleration times in force at the

time (Ix20 and Ix21) request a higher rate of acceleration, this rate of acceleration will be

used instead. The calculation does not take into account any feedrate override

Since jogging moves are usually not coordinated between motors, many people prefer to

specify jog acceleration by rate, not time. To do this, simply set Ix20 and Ix21 low enough

that the Ix19 limit is always used. Do not set both Ix20 and Ix21 to 0, or a division-by-

zero error will result in the move calculations, possibly causing erratic operations. The

minimum acceleration time settings that should be used are Ix20=1 and Ix21=0.

The default limit of 0.015625 counts/msec

is quite low and will probably limit

acceleration to a lower value than is desired in most systems; most users will eventually

raise this limit. This low default was used for safety reasons.

Example

With Ix20 (accel time) at 100 msec, Ix21 (S-curve time) at 0, and Ix22 (jog speed) at 50

counts/msec, a jog command from stop would request an acceleration of (50 cts/msec) /

100 msec, or 0.5 cts/msec

. If Ix19 were set to 0.25, the acceleration would be done in 200

msec, not 100 msec.

With the same parameters in force, an on-the-fly reversal from positive to negative jog

would request an acceleration of (50-(-50) cts/msec) / 100 msec, or 1.0 cts/msec

. The

limit would extend this acceleration period by a factor of 4, to 400 msec.