Rockwell Automation 8520-ARM2 9/Series CNC AMP Reference Manual Documentation Set - Manual (Page 109)

Home Parameters
Chapter 5
5-7
Mechanical Considerations
ATTENTION: If the encoder marker is exactly 180 degrees
away from the point at which the home limit switch transitions
from “ON” to “OFF,” an undesirable condition is created that
could affect homing repeatability. To avoid this condition, we
recommend that the encoder or the home limit switch be
mounted so that the encoder marker is near or within that switch
transition range. Refer to Figure 5.2. This applies only to
revision 12.x or earlier.
Figure 5.2
Encoder/Home Limit Switch Positioning Considerations
Home limit switch
YES
NO
Off On
Control will consistently select this
as nearest encoder marker
Control may pick either of these as nearest
encoder marker depending on home limit switch
transition. This may only occur with revision 12.x
or earlier. With revision 13.x or greater this
condition would generate a “HOME TOLERANCE
EXCEEDED” error message.
Correct by relocating home limit switch or
rotating encoder through axis drivetrain
Home limit switch
“ON” to “OFF”
transition range
Encoder marker
detected during
axis homing
The control allows for a variety of homing hardware configurations and
homing procedures. These variations require proper AMP and PAL
programming to perform effectively.