Rockwell Automation 8520 9/Series CNC Integration Maintenance Manual Documentation Set - Manual (Page 312)

Section 5B
9/440HR CNC/Drive System
5B-22
The time delay between the 9/440HR receiving the touch probe trigger and
latching the current axis position is negligible. However, you should be
aware of any external delays that may introduce position “staleness” in the
probing operation, especially at high probing speeds.
It is a good idea to establish an offset for the distance between the actual
location, as sensed by the probe at a very low speed, and the location
sensed by the probe at the intended probing speed. The offset can then be
added or subtracted to any future values obtained through probing. This
helps make sure that if there are any external delays in the trigger signal,
the position staleness shows up as a constant position offset error and is
removed from the measurement (assuming the external delay is
repeatable).
The touch probe interface is intended for use with units that offer 5V dc
compatible solid state relay outputs (see Figure 5B.10). Other
configurations can be supported as long as the user operates within the
published electrical specifications.
The touch probe circuitry resident on the 9/440HR only responds to the
trigger probe edge changes. Polarity transition (high to low or low to high)
is selectable through the AMP parameter Probe Transition. Specify the
probe transition in AMP as rising edge or falling edge. Once the active
edge occurs, position data is captured by the module, and additional
occurrences of the trigger signal have no effect until the probe is
re-enabled under program control.
Refer to the 9/Series CNC AMP Reference Manual, publication 8520-6.4,
for more information.
ATTENTION: From a safety standpoint, it is preferred that the
touch probe relay be closed at rest and open when the touch
probe stylus deflects. Then, if a wire breaks or shorts to ground,
it will appear to the system as a probe fired and the probing
cycle in process will stop commanding motion towards the part.
The user should make every effort towards the fail-safe
operation of the touch probe. Not all vendor’s touch probe
control units conform to this safety consideration.