I guess, it's not speed but acceleration one has to think about - then It is clearer, at least for me 🙂
Yesterday, I tried how a piezo speaker I had lying around might react by gluing one onto the frame holding my printbed, roughly where the Andromeda would be mounted if I followed my initial idea. It turned out my spings are too stiff: the bed spring would rather bend the frame if I pressed onto the bed instead of giving in - and the piezo would barely detect anything.
After some attempts on how to fit everything into the available space (my printer has just 32mm beneath the printing surface with the z-axis being at its lower limit and the printer housing, meaning 13mm for the Andromeda and the adjustment screw), as far away as possible from the heating element and still keeping the adjustment screws accessible, the whole design - with the piezos nicely covered with a housing - looks like this now:
Druckbett.png
(the thin aluminum plate is L-shaped to give it more stiffness; that is cut away in the view. So it not quite as flimsy as it might look)
While this means I will have to drill some more holes into the z-axis frame, I definitely will see a signal now whenever I tap onto the bed with something. Now It's up to finding the correct settings for sensitivity - as soon as the sensors have arrived and I have assembled all this. Some miniature coaxial cable is also ordered 🙂
When this is running, I want to find a way if I can use the Piezos as "second" z-endstop (i.e. z-endstop controlled by the piezo elements - but in case these fail for some reason, the exisiting less precise endstop detection should kick a bit above that and force the Duet to retry...) but I will open a new thread for that topic unless I find something here in the forum.
