User's Manual

PMAC User Manual
Writing Programs for PMAC 189
The added arc prevents the compensated corner from extending too far out on the outside of a sharp
corner. However, as an added move, it has the minimum time of the acceleration time, which can cause a
slowdown on a very shallow angle. While the default value for I89 of 0.9998 (cos1
o
) causes an arc to be
added on any change in angle greater than 1
o
, many users will set I89 to 0.707 (cos45
o
) or 0.0 (cos90
o
) so
arcs are only added on sharp corners.
When coming to a full stop (e.g. Step, Quit, /, or DWELL) at an outside corner with an added arc, PMAC
will include the added arc move before stopping. When coming to a full stop at an outside corner without
an added arc, PMAC will stop at the compensated, but unblended, corner point.
Treatment of Full Reversal
If the change in directed angle at the boundary between two successive compensated moves is 180
o
+ 1
o
(the
included angle is less than 1
o
), this is considered a full reversal and special rules apply. If both the incoming
and outgoing moves are lines, the corner is always considered an outside corner, and an arc move of
approximately 180
o
is added. If one or both of the moves is an arc, PMAC will check for possible inside
intersection of the compensated moves. If such an intersection is found, the corner will be treated as an
inside corner. Otherwise, it will be treated as an outside corner with an added 180
o
arc move.
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Line
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<1
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Arc
Arc
Arc
Arc
Line
Programmed Path
Tool Center
Path Right
Tool Center
Path Left
Line
Arc
Programmed
Path
Tool Center
Path
Arc
Arc
Arc
Arc
Programmed
Path
Tool Center
Path
Arc
Arc
Arc
Arc
Line to Line Line to Arc,
Inside and Outside
Arc to Arc Outside Arc to Arc Inside
Reversal In Cutter Compensation
Arc
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Figure 43 Reversal in Cutter Compensation
Note on Full Circles
If a full-circle move is executed while in cutter compensation, and one or both of the ends produces a
shallow outside corner that is directly blended (no added arc – see the previous section Treatment of
Outside Corners), the compensated arc move will be extended beyond 360
o
, and PMAC may produce just
a very short arc, 360
o
shorter than what is desired (making it appear that the circle has been skipped.
Typically, while this is the result of sloppy programming – an outside corner with a full circle causes an
overcut into the circle – many machine designers may want to permit slight cases of this. Coordinate
system parameter Isx97 defines the shortest arc angle that may be executed; the longest arc angle is 360
o
plus this angle.
The default value of Isx97 sets a minimum arc angle of one-millionth of a semi-circle, enough to account
for numerical round off, but sometimes not enough for compensated full circles. To handle these cases,
Isx97 should be set to a somewhat larger value.