Piezo20 probe and piezo kit now available
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I finally got around to finalizing my "simple" piezo mount to work with the 713maker hotend mounts.
Details are here: http://www.thingiverse.com/thing:2268205
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Thats' good, very simple which is always a plus.
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I need to run some repeatability tests with it next time I have some free cycles. Between 1.18 and the new mount, it's very sensitive now, with no false triggers.
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and another, I'm sure theses are $$$$$$
but you know….
https://www.hbm.com/en/3244/paceline-clp-piezoelectric-subminiature-load-washer/
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These both (especially the first one) look wonderful, but I am sure are both very expensive. I asked physik instruments for a quote, there disc looks like it would integrate quite easily, it might be possible to use it as a z-probe, depending on cost, or it might be a nice control to test against.
I think one of the things which makes the current implementation so attractive is that the piezo itself is cheap and (apart from the soldered connections) robust.
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So the first product is £300.
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There are plenty of bare piezo ring transducers available, see https://www.steminc.com/PZT/en/piezo-ring. These are not bimorphs, so they respond directly to pressure instead of to flexing.
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Just a note about electrical interference. I have until recently been saying "its not a problem to have a long lead from the piezo to the signal board", and it hasn't been a problem for me until now.
Maybe its because I am now running dual extruders and new fans and there's more wiring, especially motors, maybe its because I installed a 20mm piezo module on my kossel XL, and 20mm piezo's produce a weaker signal (on average) than the 27mm one it replaced, I am not really sure. However the piezo probe in general had been performing much more poorly than normal, so perhaps it was the second extruder. I was noticing it worked fairly well cold, but almost non-functional with the hotend heated, and the temperature near the piezo was only 30 deg C. I scoped the signal from the piezo at the PCB down the 80cm of wire and and it looked like I'd connected the scope to my TV antenna.
Anyway the short version is - if you're talking about a hotend probe, put the PCB on the effector/carriage, to keep the piezo lead short. The range of usable adjustment on the PCB ("the tuning window" if you want) will be much wider, which will then mean you will be able to work with a better range of temperatures also.
Important lesson for me, I was beginning to think I had bad PCBs (I don't) or that piezo just wasn't doing the job, maybe its not as great as I thought it was, and low and behold there is a perfectly rational explanation for the problem.
Am now calibrating to 0.02mm deviation.
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David - that link's very interesting… I might have to try one of those. I know you have experience with piezo's, any recommendations on specs for one? Or will any of those work as long as it's physically the right shape? How hard are they to solder to?
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StemInc has a note about soldering to their piezos somewhere on their web site. AFAIR the danger is that the soldering iron will soak up the silver coating on the piezo, so you need to solder the wire on as quickly as possible and use solder with a silver content.
You could also use silver-loaded epoxy to make the connection, or perhaps the silver-loaded solution that Maplin sells would hold a fine wire on. Or use spring contacts.
I've only used StemInc piezo transducers for ultrasonic transmission and reception (which is what they are designed for), not for shock sensing, so I can't offer any recommendations.
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So, this may be obvious to others, but I realized that I'd been causing my own headache. I'd been drilling the piezos with as small of a hole as I could fit a bowden through. Had a high number that seemed plenty sensitive in testing, but often failed to trigger. I finally realized that it was due to the bowden being able to touch the piezo, and deadening the vibrations. I drilled a larger (1/4") hole in a new one, and it's just as sensitive in my tests, but also registers every tape since the bowden can't touch it as my delta moves around the plate.
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Yeah I've been using 4.5mm and 5mm for most of them, that being said place the bowden adaptor above the piezo sensor assembly and just run a guide tube down through the piezo, problem solved.
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Yeah, I have a short bit of bowden that passes through the piezo, but it could still flex just enough to make contact… I was drilling the holes so the bowden just passed through them. 1/4" is 6.3mm, and it's still plenty sensitive.
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I was today asked a good question "What dive height should I use with piezo probe in M558?"
This is my reply "I don't specify a dive height and I don't use the H parameter on my printer. I presume the system default is used (which I think is 5mm). Setting a slightly higher dive height might help to smooth mechanical noise as any vibrations and ringing will subside once the effector/carriage comes to a stop above the probing point. However if you are getting no issues with false triggers "probe triggered before probing move" errors, then probing is faster with a smaller dive height. The other advantage would be if you frequently swap printing surfaces which might have different thicknesses.
It is less important than with the IR sensor for example as so long as you are not dragging the nozzle across the bed from one point to the next there is no requirement to begin at any given height above the bed then look for a change in the way the IR sensor goes from open to triggered as the bed approaches. With piezo you either touch it or you don't."
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The first part is true, but not the last paragraph. If the probe trigger height is positive then probing starts with Z = dive height + trigger height. If the probe trigger height is negative then it starts with Z = dive height. So you can use a low dive height with any type of probe once you have the machine calibrated and/or the bed leveled so that the expected height errors are small.
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That's fair enough. I would only use large dive height (combined with a slightly increased starting homed height (H parameter in config.g M665) if I were regularly swapping beds in and out of varying thicknesses, and allowing auto-calibration to adjust for it on a per-print basis.
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I updated my piezo mount: http://www.thingiverse.com/thing:2268205
The changes might be helpful to others. Basically I've learned that you can make the spacer above the hotend that presses on the piezo, and the ring that goes around the hotend both "full width" with just enough of a gap they slide nicely. I'm still using a nylon washer for my center spacer, but uploaded an STL for a spacer the same size. Making both of those wider added even more stability to my nozzle, but didn't lower the sensitivity at all.
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In the end I've modified Idris's effector to work with Hayden's mag arms at 64mm spacing. He also made some 15mm piezos for me
Pict and details here https://www.thingiverse.com/thing:2361081/#files
I coud only make it work in analog mode on my Duet. VR1 is at 11 and VR2 at 4 o'clock
I'm probing on PEI at 210c hotend (Tested and is fine at 220 for 3 seconds) and 65c bed temp.
Z offset is -0.15 and trigger value 500
Deviation aroud 0.023
This mesh is done on the aluminium plate.
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Looks great.
