I do like the piezo approach in theory… don’t have one yet though so I can’t really comment.
There are LOTS of measurable physical properties that change when the nozzle tip touches the bed. Capacitive, conductive, acoustic, etc sensors can all detect that directly. In fact, they may measure contact much more accurately than anything triggering off a contact force. All force-detecting schemes rely on the nozzle/bed positions having some interference (ie flexing something) before enough contact force builds up to trigger a force sensor. This was always my complaint with FSRs; there’s still a Z offset because the nozzle has to keep moving and pushing down after making initial contact so the FSR triggers.
@Ryan_Carlyle The key question here is whether we can detect the physical force of mechanical contact with sufficient accuracy. If we cannot, then we have to use another approach.
Piezoelectric sensors offer (practically) zero-displacement, so … (off to figure out the next experiment).
Heh. Piezoelectric sensors are very tolerant of high temperatures. So future hotends could conceivably clamp the sensor just-behind the nozzle? (Whether this makes sense is another question.)
Would knowing the up-force against the nozzle in real time during a print give feedback useful to improve the quality of the print?
@Brook_Drumm BTW, seems one outfit offering piezo sensors is in Rocklin, not far from you.
https://www.parallax.com/product/30056
@Preston_Bannister there’s an argument that extruding plastic causes a meaningful up-force from mashing viscous plastic onto the print. In which case, nozzle force detection could correlate to excessive backpressure, eg when the print is overextruding.
@Preston_Bannister I know the guys at Parallax pretty well. Great company!
Brook