Piezo20 probe and piezo kit now available
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Well broadly speaking I think this is the basis for the new UM3 bed probing, the probe presses on the glass which triggers a capacitative sensor underneath. I think it might be useful to start a new thread call it "new z-probe technologies" or something similar and we can discuss some of these alternative ideas there. I would like to try to keep this thread focused on the piezo z-probe and its development.
Hi,
Ok true i erase my reply and Start A New thread New z probes technologies…
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In any case question for the electronics experts. On the kossel XL the piezo is wired with red-positive and black-negative going into the piezo board, normal operation. On my corexy I noticed the polarity is reversed (same brand piezo) but I also get normal operation - if I reverse it on either machine it doesn't work. So why does one setup happily work with the piezo in reverse polarity compared to the other?
I've been thinking about this for a couple of days and I can't explain it.
Idris
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Are the Piezo's in the same orientation on both ie brass side up on both or down on both could that make any difference?
Just thinking out loud again
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I'll check again maybe my error. But yes they were the same way around.
Edit - no the corexy has the piezo element wired in reverse polarity, and if anything I'd say works slightly better than the kossel XL where it is the right way around. I might try reversing the polarity on the kossel XL and re-tuning the piezo board.
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So this doesn't work, if I reverse the polarity on the kossel XL I cannot tune the piezo board to get a usable output.
So two things to consider:
- my piezos are not very consistent and I bought the branded ones.
- if you cannot get it tuned with the piezo connected one way around, turn the plug from the piezo element so it is reverse polarity and being the tuning again.
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Just a quick observation on consistency: I found that the branded ones (Murata) were polarised in the opposite direction to the unbranded ones and had a wider spread of sensitivity, the most sensitive being about twice as good as the least. By comparison the unbranded ones fell into less than a 10% spread.
Mike
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I think there would be something in it to buy a lot of these and test them, how many different types did you test in total Mike?
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I purchased to batches of 10 no-name 27mm discs on ebay from two different suppliers and tested about 17 of them. I also got 10 Murata discs from Farnell and tested only 5 of them as they had to have leads soldered on and this was a destructive learning curve.
The Murata did score on giving a decent output at temperatures at just over 100C while the no-name were really poor - see http://forums.reprap.org/read.php?1,635075,655510#msg-655510
Mike
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I've soldered wires to piezo transducers before. Apart from heat damage to the piezo, the other risk is that the silver coating gets sucked off the piezo. You need to make the joints as quickly as possible, using as little solder as possible. It's best to use solder that contains silver, which some but not all lead-free solders do.
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Thankfully as we are implementing it above the hotend, temperature is unimportant, I would not expect the piezo to be at more than 40 deg C (if that) in use. I am more interested to see which transducer has the right amount of flexibility versus signal. The optimum between the least flexible transducer with the highest signal is surely our best unit.
If we could get the same signal out of a smaller transducer this would make packaging the sensor (which Lykle is grappllng with right now) much easier, but I suspect the piezo-electric material is only capable of so much voltage for a given tap, and the more of it you have the more signal you get. Perhaps a 20mm unit would give the same output if the top of the clamp that bends it was 6-7mm diameter, instead of the 18mm pressing into (effectively due to the recess) a 25mm disc.
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Just to see how it goes, I plan to test one with the hotend mount I have, http://713maker.com/mounts.html
I think a drilled piezo will fit nicely in the existing mount, and I can trap some nylon washers around it as an insulator.
I need to figure out the max radius I can fit under the mount is, appears to be ~25mm diameter, and then figure out the spacing. Any advice is welcome while I wait on the board to be available again.
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Kraegar, Thats the same mount I have for mine and modified the top clamping mount. 27mm fits
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Awesome, Sakey, good to know. How's it working for you? Any otheer tips or considerations? Are you just compressing it?
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Guys I have a quick question for you. What do your Z homing file and config.g look like? I'm only used to using DC's probe so in my config.g I have a positive offset in G31 because the probe triggers before the nozzle touches the bed. Do you simply use a negative offset in G31 (because the probe triggers after the nozzle touches the bed)? If so, how do you determine the offset? Trial and error or a more scientific approach? I ask because if my sliding mount works, I'll need to do similar. Cheers
Ian -
Its been trial and error to be honest, but the theory I am using is that z=0 with the piezo probe being so precise should be the nozzle at exactly z=0, so I have been using +0.1 z offset, that being said I've just changed that to +0.07 as I couldn't get the print I'm doing right now to stick for love or money.
In theory with the piezo you might get away with no offset and print at exactly your first layer height, no thickness of a piece of paper nonsense.
With FSR's generally you needed a +ve offset equal to the compliance in the sensors/bed mounting/whatever.
Sorry if thats clear as mud.
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Hi DJ,
Er yeah - bit confused TBH. With a probe such as DC's, the trigger point is some way above the point where the nozzle touches the bed. That is to say if Z=0 is the point where the nozzle touches the bed but the probe triggers say 2mm before that, then I need a 2mm positive trigger height in my G31. So I'm thinking that with your Piezo sensor and my moving mount, the trigger point will be after the nozzle touches the bed so the trigger height would need to be negative. In your case it's only 0.1 or less but in my case, it's likely to be nearer 1mm. So, I guess my question really should be does G31 accept a negative offset value to "tell" the machine that Z=0 is below the point where the probe triggers? Or, should I use M208 to define the Z axis minimum as being something other than zero?
Is my mud any clearer than yours?
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Yes G31 accepts negative values, which is what you need to use for any sort of nozzle-contact probe.
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Yes G31 accepts negative values, which is what you need to use for any sort of nozzle-contact probe.
Thank you.
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Yes you can have a negative offset, but I am curious to find out if you will actually need one. If I set -0.1mm as my offset I'd be milling a line in my print bed.
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Yes you can have a negative offset, but I am curious to find out if you will actually need one. If I set -0.1mm as my offset I'd be milling a line in my print bed.
No actually you won't. It works kind of back to front to what one might expect. When it's positive, a larger value moves the nozzle closer to the bed because what you are telling the machine is that the distance from the trigger point to the nozzle tip is greater and to get from the trigger point to Z=0 it must move further. In your case, if you set a positive offset, you are telling the machine that it must move the nozzle closer to the bed after it sees the trigger point but in your case, the trigger point happens after the nozzle touches the bed so Z=0 is in the opposite direction.
Edit. Having re-read that, it seems clear as mud - just try it and see.
