Rockwell Automation GMLC Reference Manual - Manual (Page 701)

Publication GMLC-5.2 - November 1999
664 Using AxisLink
• Show Axis Status
• Control Setting
See the descriptions of the above blocks in the Function Blocks chapter of
this manual for more information on using virtual axes with each of them.
When a virtual axis in one controller is AxisLinked to the command
position of an axis in a controller using a different servo update rate, the
speed of the virtual axis is different from the speed of the corresponding
physical or imaginary axis due to the different servo update rates. If the
motion controller in which the virtual axis is defined has a faster servo
update rate than the controller to which the virtual axis is linked, the
virtual axis appears to be going faster than the corresponding physical or
imaginary axis and vice versa. For best results, ensure that all motion
controllers connected via AxisLink are using the same servo update rate.
The Servo Update Rate (parameter D47) can be checked using the
Control Setting block in GML Commander by selecting the Show check
box in the Type area, and selecting Servo Update Rate in the Data
Parameter list. See the Control Settings block in the Function Blocks
chapter of this manual for more information.
Homing Virtual Axes
Because the virtual axis has no physical dimensions, only passive homing
can be performed on the virtual axis. You can use the Home Axis block to
passively home a virtual axis. When a virtual axis is passively homed, the
virtual axis’ Actual_Position Axis System Variable changes, and (upon
completion of passive homing) reflects the virtual axis’ new home
position. The position of the physical axis on the motion controller (or
ALEC), to which the virtual axis is linked, is not affected. Thus, the home
position value (entered in the motion controller’s machine setup menu)
need not be the same for both the virtual axis and the physical axis to
which it is linked.
!
ATTENTION: Ensure that all motion controllers and
ALEC(s) on AxisLink are using the same Servo Update Rate.