Manual

3-2 Detailed Descriptions of ACL Commands
AA <x center>, <y center>, <angle> Arc Absolute
The Automove System moves the carriage in a smooth circular arc. The center of the arc is
specified by <x center> and <y center>, in absolute Calibrated Units as affected by the
SO, CF, and CR commands.
The range of <x center> and <y center> is -32768.0000 through 32767.9999, but they
must be limited such that the radius of the arc does not exceed 32700 microsteps and such
that the arc center lies within the range -32768 through 32767 microsteps in each axis.
(Further constraints are in effect if the BC command is active.) Certain microstep resolutions
may further restrict the radius; see below.
The arc is circular on the microstep grid; in other words, its shape is not affected by the CF
and CR commands.
The arc begins at the current carriage position and proceeds for <angle> degrees in the
counterclockwise direction. If <angle> is negative the arc sweeps clockwise. <angle>
must be in the range -360.0000 through 360.0000.
The carriage accelerates smoothly from zero velocity to the speed given by the SR
command, up to a maximum of about 17000 microsteps per second. If the SR command's
parameter was greater than 17000, arcs are performed at 17000 microsteps/second but
vectors are performed at the higher speed. The rate of acceleration is as specified by the AC
command. Small radii may cause slew speed to be limited in order to limit radial
acceleration; see the SR and AC commands. Continuous Path and certain microstep
resolutions may also cause the slew speed to be limited; see the BC and RE commands.
The travel limits are applied as follows. The arc center is not required to be within the travel
limits. If any portion of the arc itself would lie outside the travel limits or if the arc radius
exceeds 32700, no arc is generated. Instead, a Position Overflow error is logged and the
system behaves as though an MA (Move Absolute) to the final position had been received.
(If the final position is within the travel limits, the carriage moves in a straight line to this
position. Otherwise, it moves to a position on the edge of the travel limits. See the MA
command.)
If mid-move Digital Outputs changes have been established via the MD or MM command,
they will be executed as though the arc were "unrolled" into a straight line. In other words,
the MD command's <count1> and <count2> parameters (or the MM command's <count>
parameter) are treated as distances along the arc, in microsteps. If the arc length exceeds
32767 there will be a region near the end of the arc which is unreachable by positive
<count> values, and another near the beginning which is unreachable by negative values. If
arc length exceeds 65535 there will be a region in the middle of the arc which is unavailable
for mid-move Digital Output changes; the Digital Outputs will not change in this region.
Several conditions may force the Automove System to skip some intermediate microstep
positions during the generation of the arc. This skipping is done in a regular, smooth pattern
and does not affect the overall shape of the arc, but it does affect the dynamic resolution and
the accuracy with which the "ideal" endpoint can be reached. Also, available motor torque
may be reduced.