Manual

Detailed Descriptions of ACL Commands 3-3
Skipping occurs if either: the specified slew speed exceeds approximately 2200 microsteps
per second; or the circumference of the arc (i.e. the actual distance traveled) exceeds 65535
microsteps. Note that other internal errors may cause small endpoint discrepancies even
though none of the above conditions is exceeded and thus no microsteps are skipped.
The actual final carriage position as given by the OA command may differ from the "ideal"
position by several microsteps. The Commanded Position, as given by the OC command,
will not reflect this difference. Any discrepancy will disappear at the next MA or MR
command. (For an exception, see the BC command.)
The AA command is ignored while the machine is in the Emergency Stopped state. If the
STOP button is pressed (or an external Emergency Stop switch closes) during the arc, the
motors stop immediately and the Home position reference is lost. See the STOP button in
Chapter 4 and the FH command in this chapter.
The behavior of the AA command can be altered by changing the Vector Mode. See the VM
command.
Example: the sequence MA 2000, 2000; AA 3000, 2000, -360; moves the carriage to
(2000,2000) and then performs a clockwise circle with a radius of 1000 microsteps, centered
about (3000,2000). The carriage is left at approximately (2000,2000).
Example: the sequence MA 1000, 0; AA 1000, 6000, 45; produces an arc which ends at
approximately (5243,1757). But the sequence MA 1000, 0; AA 1000, 6000, -45;
produces Error 6 and a vector to (0,1757), because a portion of the arc lies outside the travel
limits.
AB [<flag>] Antibacklash Vectors
If <flag> is nonzero, antibacklash vectors are enabled. When antibacklash vectors are
enabled, each move performed by the MA, MR, and MT commands and GO TO ORIGIN
button is divided into two vectors. The first vector moves to a point 15 microsteps to the left
of and 15 microsteps below the Commanded position. The second vector moves to the
Commanded position. The effect of this extra vector is to improve endpoint repeatability by
applying a consistent bias to the backlash of the mechanical system.
If mid-move Digital Outputs changes have been established via the MD or MM command,
they are performed during the first vector; the Digital Outputs do not change between the
two vectors or during the second vector.
The <flag> parameter is optional. If is zero or is omitted, and also at IN and power up,
antibacklash vectors are disabled. They can also be temporarily disabled via the VM
command.
The size of the antibacklash vector (15 by 15) can be changed via the PE command; it can
be made any length or direction, or can be restricted to one axis.
The AA and AR commands do not produce antibacklash vectors. If it is necessary to be
exactly at the "right" physical position following an arc, send MR 0,0; after the arc
command; this generates a pair of vectors which wind up at the right spot.