Rockwell Automation GMLC Reference Manual - Manual (Page 225)

Publication GMLC-5.2 - November 1999
188 Control Setting Blocks
Command Position
When you select Command from the Position menu, the motion controller
directly applies the new position value to the command position of the
servo or imaginary axis. Because master only axes do not have a
command position, you can select only Actual from the position menu for
master only axes. The motion controller also adjusts the actual position of
servo axes to reflect the new command position, and to preserve any
position error that exists. This ensures that there is no unexpected axis
motion when the positions are redefined.
Command position is the desired or commanded position of a servo or the
imaginary axis, as generated by any previous motion blocks. Actual
position is the current position of a physical or virtual axis as measured by
the encoder or other feedback device. Position error is the difference
between these two and is used to drive the motor to make the actual
position equal to the command position. The figure below shows the
relationship of these three positions.
See your motion controller’s Installation and Setup manual for
information about the nested digital servo loop used in the motion
controllers.
Synchronizing Redefine Position Blocks
When you select Synchronize with next block, the action of this Redefine
Position block occurs simultaneously with the following Redefine
Position block. This lets you redefine the position of multiple axes
simultaneously, as shown below.