Rockwell Automation GMLC Reference Manual - Manual (Page 242)

Publication GMLC-5.2 - November 1999
Move Axis 205
When you select Rotary Shortest Path, the axis moves to the specified
position at the specified speed (using the specified acceleration and
deceleration) in the direction that results in the shortest move, regardless
of the current position of the axis. The position must be a positive value
less than the unwind value. Therefore, you cannot perform moves of more
than one revolution (that is, more than 360 degrees) with a single rotary
shortest path Move Axis block.
For example, assume you plan to move a rotary axis, with position units
of degrees, to a position of 225°. As shown in the figure below, using the
standard absolute Move Axis block, the direction of travel depends on the
current position of the axis, and is not necessarily the shortest path to the
endpoint. Starting positions less than the endpoint cause motion in the
positive direction, while starting positions greater than the endpoint cause
motion in the negative direction.
With the rotary shortest path move however, the axis moves to the
specified endpoint—through 0° if necessary—in the direction that results
in the shortest move regardless of the current axis position.
You can use the rotary shortest path move while the axis is moving or
standing still.
0°
225°
315°
Standard
Absolute Move
225°
315°
Rotary Shortest Path
Move
30°
0°
30°