Piezo20 probe and piezo kit now available
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Awesome thread going on here!
Are you guys aware of this board?
http://wiki.seeedstudio.com/wiki/Grove-_Piezo_Vibration_Sensor
Will test it once I get hold of 20mm discs (and could this be an alternative for Moriquendi's board?) -
That seed studio piezo looks like it might be easier to incorporate into the more rectangular hotentd mounting form factors you get in Cartesian and corexy printers.
Also have you considered two of the smallest possible piezos one on either side of the hotend so you don't have to drill a hole through the center of a piezo?
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I was not aware of the grove unit linked to above but it is worth looking into. That being said we are on the border of using these things as load cells detecting dimension change, and microphones listening for the contact.
Very small piezo's might be the answer to many of the harder to integrate setups.
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I've been lurking around here for a while now.
I'm with Moriquendi on lifting the nozzle close to the plane of the effector. So I took DjDemonDs 20mm piezo design and made an effector to use with Haydn's magnetic arms. Arm spacing is 64mm, goes with a 30mm fan and a Berd-Air like cooling pipe.Here's what I came up with for a delta effector that integrated the piezo elements. There's no need for a drilled piezo or having the leverage of the length of the hot end hanging off it.
Those are 15mm piezos with a brass nut soldered to the back.
Idris
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The picture above got me thinking that maybe I could use piezos on my latest Diamond hot end mount design. I'm planning on using the nozzle as a probe and had intended to use some sort of switch but now you've got me thinking. Sorry but I don't know how to post pictures directly but here is a shareable link to an OpenScad png of what I have. https://drive.google.com/file/d/0B_MwtHtQR_ZvOTJxVklrWGdlN3M/view?usp=sharing
The red part is the X carriage upper section. Ignore the pale blue part which is the X carriage lower section, but the white part is the Diamond hot end assembly complete with heat sinks, fan and shroud with short tube sticking out to represent the Bowden tubes. There are 3 bosses on the x carriage which will have bronze pushes inserted and there are 3 mating bosses on the hot end assembly which will have steel dowel pin inserted (shown in grey). So effectively, the hot end will just drop in but can slide in Z. It weighs 250gms so I'm hoping it'll stay put without any form of retainer but the Bowden tubes will also be under compression so will act as springs to some extent.
So the question I have for you guys is, could I use one or more peizo discs between the bosses on the carriage and the bosses on the hot end assembly? Would it work with just the weight of the hot end? Should I put peizos on all 3 bosses? Any other thoughts?
Thanks
Ian -
deckingman… I think Idris 3 piezo design could work for you.
Idris... I like your idea better. Lightweight effector and no moving/sliding parts. I went the other way to avoid soldering piezos, something I'm not that good at.
How do you solder to last? And they are connected in parallel I presume? -
They are connected in parallel.
Preparation and stress relief is the key to soldering piezos easily and to last. My process goes like this.
For the electrical connections:
Thoroughly clean the piezo with acetone or alcohol
Tin both wires
Tin the brass ring of the piezo
Tin the centre contact (put the solder wire on the contact the the soldering iron (at 360deg) on top of the solder, as soon as the solder melts, remove the iron.
Solder the wires to the piezo, tinned wire on tinned contact, touch momentarily with the iron and you're done.The trick to getting the connection to last is to fix the wires somewhere close to the piezo, the solder joint will pull off with very little force so you need to make sure any force on the wires is taken up before it reaches the piezo.
To solder the nut to the back I'm using solder paste but you could do the same thing by tinning the nut, cleanliness is key, I sand the nut and the piezo with very fine sandpaper before soldering then use a very hot iron on top of the nut to reduce the thermal stress on the piezo ceramic.
Idris
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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.
