Hi,
the problem with current monitoring is that it is so coarse.
Imagine if you have a servo drive the torch downwards until it impacts the material. As the motor stalls you will see a major increase in current but by then the servo has happily
crunched the torch so bad it'll be wrecked. You could set the current sensor to be very sensitive, but the if the servo accelerates up or down as its meant to those current spikes
could be mistaken for torch contact events.
What wrong with just an Ohmic contact. ie like a probe? When the torch touches material the voltage would get pulled low whereon the servo would decelerate to a stop.
You can often have the servo stop within a few milliseconds and so the torch would 'press' down just a few um, not enough to do any damage.
Craig