Piezo20 probe and piezo kit now available
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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.
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Here's another possible configuration:
1. Drill and tap the top end of an E3D heatsink with 3 small holes, probably M2.5 or possible M3. I hate groove mounts.
2. Take a piezo element with the active element about 20mm diameter. Perhaps this one http://www.digikey.co.uk/product-detail/en/murata-electronics-north-america/7BB-27-4L0/490-7714-ND/4358154. Drill a central hole for the Bowden tube and collet, and 3 smaller holes around it.
3. Attach the disk to the top of heatsink using 3 nylon screws, with a piece of insulation between the piezo and the heatsink. The purpose of the insulation is so that if the heater cartridge develops a short and makes the heatsink live, we don't get a short between the heater and the piezo.
4. Clamp the brass surround of the piezo disc between the effector (which has a hole in it for the top of the heatsink to pass through) and a printed ring.
For the electronics, I would take one of my IR sensors, remove the optical components, and feed the piezo into the analog input. Then program it to produce a nice clean pulse when it detects a shock. Piezos produce a good voltage from a very small mechanical shock if the load resistance is very high.
I'd have a go at this myself, but I don't have a drill press for drilling the top of the E3D heatsink.
David, or anyone else who may know how to answer this, you'd be helping me out of a bind I've found myself in. Once upon a time I had gotten two of DJ's new piezo sensor systems for probing accurately, but since I accidentally fried the spare i had and had to employ the second one, leaving me one more kit, though minus the circuit board with the potentiometer for tuning.
My question is regarding the quoted text. Has anyone actually succeeded in converting an IR sensor board by dc42 into a feasible board to utilize with piezo discs? It certainly would be very helpful and much appreciated if you could explain to me how to go about converting dc's board (which, as s luck would have it, I've got four out five lying around currently so it'd be great to repurpose one to enable be to compete the second Piezo kit that's missing that very component.
Thank you in advance for assisting me on this one.
Cheers!
Jonathan.
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Just to say we have stock currently of Piezo20 ready to use modules, and piezo z-probe kits (hotend or underbed use) at https://www.precisionpiezo.co.uk/shop .
We are also selling printed part kits for both the Piezo20 Module so you can build your own (much cheaper than ready made) and the titan/titan aero piezo bracket enabling use of piezo sensing for these popular extruders (and in theory others that can be attached via this bracket).
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Hi Simon,
i did some tests with the Seedstudio Grove piezzo vibration sensor with your mount.
While it does work, it is not near sensitive enough for probing use.
I am going to buy your board and see how it goes
I see in your shop that I can order the board with one drilled piezzo.
Is it possible to order the board with 2 drilled piezzos? One 20mm and one 27mm (I have a feeling the 20mm is not sensitive enough, but I could be wrong…) -
Yes sure leave a note on your order, or email me the order number and remind me and I'll drill 2 for you.
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Yes sure leave a note on your order, or email me the order number and remind me and I'll drill 2 for you.
Last question, if I buy the full kit, is it already calibrated or is that something I will need to do?
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The kit is not assembled or tuned in any way, you attach the piezo, insert it in a suitable assembly, then attach endstop wires to your controller then tune the board (usually just one pot to set), its not tricky. How well it works will depend on whether the assembly mechanically works, i.e. is as firm as it can be whilst still compressing or flexing the piezo on nozzle contact, and on whether you can set it up in your firmware (easy on duet) and manage mechanical noise from your printer (use the R parameter in M558 to pause after moving to a probe point before diving to probe).
The Piezo20 module is ready assembled and tested and should work out of the box as long as the delivery service haven't bashed it about too much and moved the potentiometers, if they have you re-tune it in the same way as the kit board. Full instructions are on our site).
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Ok, I went ahead and bought the full kit (ref Kryotech) I will see how it goes
/Kris
