Tuning the Precision Piezo to not trigger on every move

darookee

I just installed the Percision Piezo probe on my self-designed X carriage on my HyperCube and can't seem to get the tuning right.

It either does not trigger when knocking on the nozzle, or it does trigger on every move of the printer, or even when you touch the printer frame or the table on which is sits… Is there a trick to get it right?

DjDemonD

Sounds like a piezo polarity issue try reversing the piezo connection to the piezo pcb then retune.

Not triggering well on probing is a problem, triggering at any other time is not a problem as it does not cause any undesirable behaviour.

darookee

Thanks, I will try.

The problem is that when the bed moves up it triggers the piezo, so homing is not possible at the moment

DjDemonD

A couple of things to try:
Lower z accel to 50mm/min.
Use M558 R0.5 to pause before probing. Consider reducing the piezo sensitivity but it's a fine line.
You might consider once you've tried those things fitting a noise cancelling piezo disc http://forums.reprap.org/read.php?1,767998,810011#msg-810011

darookee

I tried reversing the polarity, but still got the same results. It's triggering on every movement that in any way affects the printer, be it touching the frame or placing a hand on the table. I already use M558 R0.8, and now also lowered the acceleration. That helped with the triggering right after the probing starts.

The other problem is that it either it is constantly 'triggered' when the coldend fan turns on or, if I adjust the sensitivity while the fan is on, it will still trigger when I touch the printer, but not when the bed touches the nozzle.

I'm thinking maybe my carriage design is not optimal. It looks like this:

The piezo sits in the round part at the top, the idea was to push on it with the triangular part, which is flexed a bit backward when the nozzle touches the bed, but maybe it is too tight when resting?

As this is currently a setup in testing and I only have one piezo disc ( ) I did not glue the piezo in. Do you think the problems could be caused by the disc itself vibrating inside its slot?

darookee

After fiddling a bit more I glued the disc in place, this got rid of the constant triggering when the fan is turned on (YAY!).

Unfortunately I discovered that my design is pretty flawed. As I said the idea was that the bed touching the nozzle would pivot the 'arm' with the triangle on top around the whole in the bottom to press the piezo. Touching the bottom of the motor mount does just that. Touching the coldend part of the Titan Aero does it, too. Touching the nozzle doesn't…

I also found that the top of the triangle is touching the solder point on the piezo, I'm trying to file it down a bit so that it does not touch it anymore and see if that does anything...

darookee

I did a bit more testing and foud out that the piezo will trigger, just much later than I expected. And much less reliable. I did G29 and got this:
Gnah

After moving everything around one lead of my piezo broke and I had to replace it, but just had 27mm discs. I stuck one below the lowest screw of the mount and got this G29 result
YAY

Now I'm happy...

DjDemonD

Apologies for not picking up on this earlier. I'm glad that's working better now. It's remarkable how versatile these things are, if you tune it right you can stick them in a lot of places and get a usable signal from them.

darookee

@djdemond No Problem! Unfortunately I gave up for now, as I could not get it to not trigger before probing or even while probing, but not yet touching the bed as it needed to be very sensitive to trigger when the nozzle touched the bed.
I'm planning on rebuilding my Z and getting rid of the springs on the corners of the bed. Do you think this could help with triggering at a lower sensitivity?

DjDemonD

Yes I think getting rid of springs can help. Play around with probing speeds too. Too slow and you don't get a trigger, too fast and you lose accuracy. Sorry for not picking up this one earlier I've been away travelling.