QNP3 Hardware Manual
Electrical Specifications and Installation
3.5. Travel Limits
All QNP3 stages purchased with capacitance feedback (-C option) and configured with an Aerotech drive
will have two sets of travel limits: Software Limits and End-of-Travel limits. Stages purchased without
feedback will not have travel limits.
Software Limits
Software limits protect the user from driving or commanding the QNP3 stage outside of the specified closed-
loop travel range. The standard location for software limits on a QNP3 stage is one micron past each end of
closed-loop travel. They are only active when the stage is in closed-loop mode (SERVO ON). When the
stage enters a limit, the controller will stop motion and return a limit fault. Refer to Aerotech controller
documentation for more information on software limits.
End-of-Travel Limits
End-of-travel limits are placed outside of the software limits at the extents of the sensor range. They are a
fail-safe measure used to prevent the stage from losing feedback. The operation of the end-of-travel limits is
very similar to software limits. The CCW End-Of-Travel limit in the direction of travel that corresponds to
negative voltage (refer to
) is always on. When the CCW End-Of-Travel limit is reached, the
controller will disable the stage. This is necessary to protect the capacitance sensor. The CW End-Of-Travel
limit in the direction of travel that corresponds to positive voltage is active in close-loop mode (SERVO ON)
only. The controller will stop motion and return a fault when the CW End-Of-Travel limit is reached.
N O T E :
In open-loop mode (SERVO OFF), the position of a piezo stage will drift when the voltage is held
constant. This may result in the piezo stage drifting into an End-Of-Travel limit over time when held at an
extreme end of the voltage range.
N O T E :
When subjected to high side loads, QNP3 stages with the -C option may experience slightly
reduced open-loop range and may be more likely to encounter End-Of-Travel limits at the extreme ends of
travel.
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Chapter 3
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