Rockwell Automation 8520-ARM2 9/Series CNC AMP Reference Manual Documentation Set - Manual (Page 110)

Home Parameters
Chapter 5
5-8
Here are some common variations that can be accommodated:
use a momentary contact home limit switch; if the axis passes the
switch, it reverts to the “OFF” state
hold a home limit switch in the “ON” state whenever the axis is on one
side of it; hold it in the “OFF” state when the axis is on the other side
after tripping the home limit switch, the axis can move in either
direction to the home position
add a positive or negative home calibration distance to the
home position
Axes with linear scales that incorporate distance--coded markers (DCMs)
do not home to a limit switch. Instead, these systems find absolute
position when any three consecutive markers are passed on the scale.
Since all consecutive markers are a different distance apart, the control can
identify which three markers it just passed by identifying how many counts
are between these markers.
For manual homing, the operator selects the direction and speed at which
these markers are to be found, using the same procedure as the Manual
Homing Sequence Using Home Switch describes; however, no limit
switch is used. Homing is complete when three consecutive markers are
passed.
Automatic homing is also available. This allows AMP to select the
direction and speed of the G28 homing operation when using G28 Homing
of Linear Scales with DCMs.
The following parameters are needed to home linear scales using DCMs:
G28 Direction to Home (refer to page 5-17)
G28 Home Speed (refer to page 5-18)
Machine Pos. at DCM Scale 0 (refer to page 5-23)
5.1.2
Homing Linear Scales with
Distance Coded Markers