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Piezoelectric disks for Z contact detect and bed levelling

Posted by leadinglights 
Re: Piezoelectric disks for Z contact detect and bed levelling
January 28, 2017 07:10PM
Okay so have moved to a beta version this time with some rods to support the sensor assembly and to control lateral movement, whilst allowing vertical movement for probing.

Been testing it for the last few hours, and it seems to be the optimum between sensitivity and lateral nozzle looseness - very little of this at all.

[www.thingiverse.com]


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 01, 2017 05:02AM
Tested it on ramps/mega/Marlin rcbugfix working well with bilinear levelling. Details on thingiverse listing above.

Also you can make it with acetal rods, almost as stiff as the steel rods but some mass saved.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 01, 2017 05:54AM
Good idea, acetal.
Was getting a bit worried about the weight. But then I am now working on a Diamond nozzle with 3 Nimbles on top. Weighs a bit more.

BTW I receive the sensors yesterday. I see what you mean in flex. I will have to find a little time to play with them.

Lykle
Re: Piezoelectric disks for Z contact detect and bed levelling
February 12, 2017 11:27AM
OK, DJ, this is going to get complicated.

I was working on the effector for Doug, to mount the Nimble on the peizo sensor with a larger effector.

This is the overall look.



I reverted to 3 acetal posts to guide it all, seems enough and the whole effector is set up in 120 deg anyway.
The original design of the clamp worried me a little. 2 pins in one half of the clamp and 2 pins in the other. So if the clamp is a little off, like too big, the pin position is never consistent. So now the pins are all in 1 piece of the clamp.



This made for pretty funky clamping system. With angled screws to provide the clamping force.



Bolting all this together makes for a pretty sandwich. Finding places to put all the bolts and keeping the areas free. Tricky.



But it is do-able, by the look of it.
There is one little twist in the whole assembly. I feel it is important for the sensor to be pressing against a smooth and flat surface, but you did want a little recess for it. But since I need the lock-in shapes on top, By slicing 2 parts, this is solved. By printing the bottom part upside down, you can print the recess without supports. This way we can get the smoothest surfaces where needed.

All in all, it is a little more complex than I would have liked but all the bits are in there and it all seems to fit well. The proof of the pudding...

Any comments?

Edited 1 time(s). Last edit at 02/12/2017 11:29AM by Lykle.


Lykle
________________________________________________

Co-creator of the Zesty Nimble, worlds lightest Direct Drive extruder.
[zesty.tech]
Re: Piezoelectric disks for Z contact detect and bed levelling
February 12, 2017 01:03PM
That looks great, although I haven't yet looked at it hard yet, but no categorically, the sensor needs to be supported around its circumference and triggered by being bent by something smaller. The signal generated by a sensor squeezed between two flat surfaces is 100 times smaller than when you bend it. Try it though if you have time. Otherwise the clamping system looks good.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 12, 2017 01:11PM
Quote
DjDemonD
The signal generated by a sensor squeezed between two flat surfaces is 100 times smaller than when you bend it.

That isn't necessarily an issue, provide there's still enough signal to reliably detect it against the noise. A smaller signal and more gain on the detector might be a reasonable trade-off for a simpler physical design. The original tests I did were with a piezo element squeezed between two flats, and it didn't look like there would be a problem picking out the signal. To be fair, I never got as far as you have with putting it into an actual printer though smiling smiley
Re: Piezoelectric disks for Z contact detect and bed levelling
February 12, 2017 01:20PM
Well when I introduced the recess for the sensor and made the clamp top narrower it became much easier to pick out the signal. Perhaps with more development of the electronics if will be easier. My "optimum" means high enough gain for there to be a fair bit of noise. But the signal is fairly clear. Truth be told I'd make the clamp top narrower if it was easy to print.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 12, 2017 02:18PM
I am not sure of perovskites like the PZT used in these crystals, but most piezoelectric crystals output a voltage at almost any applied force. e.g., quartz will output a big voltage across one face, a somewhat smaller voltage on another plane and a reverse voltage at the third plane - different planes are used for high and low frequency crystals. Obviously there will be some position at which the opposite direction voltages cancel - but this is not likely to be easy to find a point that is 100 times smaller.
The reason that the bending signal is larger is that the PZT is polarised in a radial direction to give what is called a bimorphic element which is sensitive to bending and should give a bigger signal. This voltage is bigger although only by about 3 times and comes with the risk of breaking the piezo element and also introducing a lot of compliance. The results that I obtained at the beginning of this thread have proven true for two batches of no-name discs and one batch of Murata discs. You could try try clamping the disk between two flat surfaces, covering as much of the sensitive PZT crystal as possible and then simply releasing the pressure. If your voltmeter has a fairly high input resistance you should see something between 8 and 20 volts.

Mike

Edited 1 time(s). Last edit at 02/12/2017 03:42PM by leadinglights.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 12, 2017 04:00PM
Have had a proper look now, was on my phone before. Okay it seems that it is probably a small change to add the recess for the sensor if it is needed. Its only one part out of four that would need to be reprinted. The clamp looks great that's real move forwards and I totally agree with the idea of having the rods all within one part. It should be much more stable with three rods in a triangular arrangement than the 4, with 2 relatively close together. Great work.

Any volunteers to make one and try it?


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 13, 2017 02:43AM
Hi, thanks.
The recess is already in there, but it has a diam of 28 mm. Now in the discussion with Mike I realise you want a smaller recess?so that there is more bend.
What diameter?
BTW I shot the files over to Doug, it sounded as if he was going to have a look.

Lykle
Re: Piezoelectric disks for Z contact detect and bed levelling
February 13, 2017 09:24AM
The piezo is 27mm diameter so I made mine 25mm diameter leaving 2mm to hold the sensor in place, I recessed it 0.75mm (I think).


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 13, 2017 10:50AM
Thinking about it, this thing works on bending forces, right.

So where is the bend? Inside the gray area, not in the brass. So the recesses could be something like this:



The disc is bending in the small area between the 20 mm diameter recess edge and the 18 mm pressure pad.
To make it even more stable, we could the raise the middle of the 20 mm recess up again, so it falls inside the 10 mm hole in the clamp. Say a raised area of 8 mm diameter in the center.
(just thought of that while writing this so it is not in the image, sorry)

That way you can double the bending output. And make for a much more stable nozzle.

Comments?
Re: Piezoelectric disks for Z contact detect and bed levelling
February 13, 2017 11:24AM
This is where theory is all well and good but you'll have to try it to see if it works. I would estimate that the piezo disc bends more like this (apologies for back of fag-packet diagram):

This is obviously exaggerated to demonstrate the point, the amount it bends is only 0.15mm.
The entire disc bends, the grey area (the piezo-electric material) bends with it.


So its not just the zone indicated on your diagram above which is the area that bends.

So it might work but you'll have to make it and try it. My two pence worth is that it will be harder to see the signal above the noise, but I will be happy to be proved wrong.

Edited 2 time(s). Last edit at 02/13/2017 11:33AM by DjDemonD.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions

Re: Piezoelectric disks for Z contact detect and bed levelling
February 13, 2017 11:48AM
Quote
Lykle
Hi, thanks.
......................................................... Now in the discussion with Mike I realise you want a smaller recess?so that there is more bend.
What diameter?
BTW I shot the files over to Doug, it sounded as if he was going to have a look.
Lykle

That was not a discussion, simply a technical disagreement. DjDemonD's design unconditionally works but both he, and dc42 in a posting on the duet3d forum, have stated that the output from a piezo disk in bending is 100 times (DjDemonD) and 200 times (dc42) higher that which is obtained from a compression force. My fairly extensive measurements put it closer to 3 times higher - we are not even two orders of magnitude in disagreement.

With that, I will return to fighting with my CAD program (Turbocad) and CAM program (CamBam) which are definitely not fighting fair.

Mike
Re: Piezoelectric disks for Z contact detect and bed levelling
February 13, 2017 01:37PM
Lykle if its possible I would print two of the part with the recess for the piezo disc. One with a 25mm diameter recess (I will confirm the depth I used when I get home later on) and one as above, it will take 20 minutes to swap them out to compare them. I can try printing them later on, I am quite keen to see if I can incorporate your new clamp into the underslung/retrofit version (or the smaller circular effector).


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 13, 2017 08:40PM
Quote
DjDemonD
This is where theory is all well and good but you'll have to try it to see if it works. I would estimate that the piezo disc bends more like this (apologies for back of fag-packet diagram):

This is obviously exaggerated to demonstrate the point, the amount it bends is only 0.15mm.
The entire disc bends, the grey area (the piezo-electric material) bends with it.
[attachment 90514 IMG_20170213_161132Medium.jpg]

So its not just the zone indicated on your diagram above which is the area that bends.

So it might work but you'll have to make it and try it. My two pence worth is that it will be harder to see the signal above the noise, but I will be happy to be proved wrong.

My understanding (based on speaker design, which is what the piezo element is designed to be) is that DJDemonD is correct. When you pull apart a device that uses this speaker element, it's usually supported right around the edge, and the middle is free to oscillate. There is usually a small hole to let the sound out, located axially in the middle of the speaker. I doubt that a double bending force will help, in fact I think it will reduce sensitivity a lot. My understanding is that the piezoelectric material isn't in a narrow ring, it's in a flat plate all the way underneath the middle metal element.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 13, 2017 08:43PM
By the way Lykle, that green cutaway drawing above is excellent!! Man I wish I had the skills to make a picture like that.

I think that to reduce the amount of compliance of the nozzle, you could use a smaller diameter piezo element, however I'm not going to get into how to design such a beast!!
Re: Piezoelectric disks for Z contact detect and bed levelling
February 14, 2017 06:12AM
+1 for Lykle's CAD he is a master.

If I were (and I'd quite like to) make a 20mm version it would look broadly the same, though smaller which would be great, these are quite a big unit at present, but have a much narrower flange on the clamp attached to the hot end, to try to achieve enough of a bend on nozzle contact, to get a good signal.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 15, 2017 05:32PM
Okay so I built Lykle's latest effector. Quite a piece of engineering, very impressed.

So the big positive: it works, the nozzle is quite stable even with the PTFE rods (which are easier to work with than the acetal), I can get a 0.02 deviation calibration using it.

The piezo will trigger just fine with the reduced recess, so as I said before, happy to be proved wrong, as the result is great probing.

There are a few tweaks and changes to make it easier to assemble and more robust, but its a working design.

Excellent work.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 03:37AM
New version is in your mailbox.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 03:51AM
Thinking about it its possible that having a less flexible clamping arrangement might reduce signal but probably reduces noise also.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 05:58AM
How far along is this project? I'm currently using an IR probe on a delta, I've messed with FSR in the past. I miss the 0 offset of FSR but the repeatability wasn't there for me. Is this far along that I should print one and give it a shot? Parts list?
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 06:07AM
Hi,

Is this for a delta? If so what arm-system/effector are you using? You can try my mkIII version [www.thingiverse.com] which attaches to the underside of your effector (you need to drill a couple of holes). The main issue is the signal requires a conditioning board like the FSR's. Moriquendi here has made one and can make a few for people who want them. PM him to see if he can help. DC42 said it might be possible for his IR sensor board to be adapted to perform this function also so thats another possibility.

If you're using Haydn's magnetic arms system, then Lykle is producing a fairly definitive effector/sensor design (which I am testing right now) which should be available very soon.

I haven't tried accelerometers yet, but so far this system is the best z probe I have used and I've tried inductive, capacitative, microswitch, IR.

Hope this helps.

Edited 2 time(s). Last edit at 02/16/2017 06:08AM by DjDemonD.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 06:17AM
I'm on a delta, with Haydn's arms indeed! I have my FSR board (john something or other) and my IR board which is my main probe currently. I'd be happy to get my hands on a board made for this purpose though.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 08:46AM
JohnSL board. Certainly not possible to use this with piezo units. Speak with Moriquendi he might well be happy to make one for you, if not they are open source so you could get one made or make one yourself. A new version is in the works but currently no news on that.

Edited 1 time(s). Last edit at 02/16/2017 08:47AM by DjDemonD.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 09:11AM
Hi ClearlynotStafan,

What is the distance between the balls of your magentic arms. Not the length of the arms, but on the effector.
I have a 48 mm one and a 64 mm one ready.

Once DJ gives the go-ahead I will post them on the Zesty Thingiverse page and DJDemonD will probably put them up on his as well.

Let me know.

Currently tweaking the design to make sure all the screws needed are standard lengths and such.
I will generate a list of needed nuts and bolts to be used.

Lykle

Edited 1 time(s). Last edit at 02/16/2017 10:33AM by Lykle.


Lykle
________________________________________________

Co-creator of the Zesty Nimble, worlds lightest Direct Drive extruder.
[zesty.tech]
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 11:52AM
Hi Guys,

Just made some eye candy for you all.



Most nuts and bolts are sorted out and it all seems to fit nice and tidy. Next challenge is to make it work on a Chimera.

I have added holes to pass tubing through in case you want to use Bard-air type cooling.

Lykle
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 04:43PM
New boards have arrived and are made up, I'm currently testing them and they should be ready to post early next week.

Of the the first batch of 12 I've sent out 10 and donated I think £55 to the charity. Unfortunately I'm not in a position to keep doing that, I had to buy more parts to make the new batch and the boards are larger and more expensive so now I'm going to be selling them. If you've already been told that the money is going to the charity then that is where it will go but in the interests of transparency, from this point on, the money is going in my pocket.

I will be writing up documentation (hopefully this weekend) and I will publish that free for anyone to use.

I didn't foresee the demand for these boards so I only ordered six this time, I think three or four are already spoken for. I'll be ordering more asap.

I've previously discussed a piezo endstop handling board, they are also made up and being tested and will be ready to post next week to beta testers.

Idris

Edited 1 time(s). Last edit at 02/16/2017 04:44PM by Moriquendi.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 04:47PM
That's great news Idris.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 05:13PM
I will begin writing a wiki page for piezo hotend probes, with perhaps a tie in with the piezo under-bed sensors, Mike?

We can add the circuit diagram for the piezo boards, the assembly instructions to make a hotend sensor in a fairly generic sense, since there are a few versions but they all share certain features.


Simon.

[www.precisionpiezo.co.uk] Accurate, repeatable, versatile z-probe plus piezo discs, endstop cables, pt100, 50w heaters. PT1000 cartridge sensors plug straight into duet boards and others.
Published:Inventions
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