362 Rockwell Automation Publication MOTION-RM003I-EN-P - February 2018
Homing Sequence Types Description
Active Unidirectional Home to
Switch then Marker
This active homing sequence is useful for multi-turn rotary applications when
unidirectional motion is required.
When this sequence is performed in the Active Homing Mode, the axis moves in the
specified Home Direction at the specified Home Speed and Home Acceleration until the
home switch is detected. The axis continues in the same direction at the Home Speed
until the first marker event is detected. If the Home Offset is zero, the Home Position is
assigned to the axis position at the precise position where the marker was detected,
and the axis decelerates to a stop at the specified Home Deceleration. The axis position
is updated based on the Home Position and Home Offset.
If Home Offset is non-
zero, then the Home Position will be offset from the point where
the marker was detected by this value. The controller then continues to move the axis
to the Home Position at the specified Home Speed and Home Acceleration using a
trapezoidal move profile.
By setting a Home Offset greater than the deceleration distance, unidirectional motion
to the Home Position is insured. However, if the Home Offset value is less than the
deceleration distance, then the axis is simply decelerated to a stop at the specified
Home Deceleration. The axis does not reverse direction to move to the Home Position.
In this case, the PC-bit leg of the associated MAH instruction is not set when the IP-bit
leg is cleared.
In the case where this homing sequence is performed on a cyclic axis and the Home
Offset value is less than the deceleration dista
nce when the home event is detected, the
control automatically adds one or more revolutions to the move distance. This
guarantees the resulting move to the Home Position is unidirectional.
If the controller detects that the state of the home switch at the start of the homing
sequence is active, the controller immediately establishes the Home Position based on
the current axis position, and if allowed by the unidirectional motion constraint, begins
to move to the Home Position.
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