Rockwell Automation GMLC Reference Manual - Manual (Page 330)

Publication GMLC-5.2 - November 1999
Output CAM 293
The AxisLink virtual axes are functionally equivalent to physical master
only axes, therefore you can select a virtual axis for output cams.
However, only one of the two available virtual axes can be enabled at one
time—enabling one virtual axis automatically disables the other virtual
axis (if it was previously enabled). Before you use an AxisLink virtual
axis for an output cam, you must first enable it with a Virtual Axis
Control block.
A virtual axis has no command position because they are equivalent to
physical master only axes. When you cam to a virtual axis, only Actual
appears in the Position menu.
Camming to the Imaginary Axis
You can also use the imaginary axis as the axis for output cams. The
output of an imaginary axis is its command position, it has no actual
position, therefore only Command appears in the Position menu when
camming to an imaginary axis.
Camming to Actual Position
When you select Actual from the Position menu, the actual position of the
selected axis is used to generate the output cam transitions.
Actual position is the current position of a physical or virtual axis as
measured by its encoder or other feedback device. This is the usual
selection (the only available selection when the master axis is a master
only axis, physical or virtual,) because it is necessary to activate devices
based on the actual position of the axis.
Camming to Command Position
When you select Command from the Position menu, the command
position of the selected axis is used to generate the output cam transitions.
Command position is only available when the selected axis is a servo or
the imaginary axis and is the intended or commanded position of the axis,
as generated by any previous motion blocks. Virtual axes being equivalent
to physical master only axes have only Actual appear in the Position
menu. (You cannot select Command from the Position menu, if you have
chosen a virtual axis for the output cam.)