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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
February 16, 2017 05:27PM
Let me know when you've got the wiki page up and I'll see if there's anything I can contribute.

Idris
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 05:39PM
Quote
Lykle
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

I'd have to do some customizing of your design for sure. My rods are I believe 48.15mm apart, have to check. It evolved over a series of different effectors and carriages and this is the standard that I settled on for no particular reason. I had my carriages SLA printed in nylon externally so I knew they'd be straight and consistent, so I'd be hesitant to abandon them for a new rod distance. I'm pretty solid at editing though, so if you have the source files in any standard format that'd be much appreciated, otherwise, I could even edit the STL to fit my rod spacing.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 16, 2017 06:20PM
Lykle's effector system for piezo hotend, working:


Will be published shortly.
No nozzle wobble and clear triggers.

We will adapt this design for some other mounting options soon.


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 10:18PM
Any chance of getting that setup as openscad customizable or thingiverse customizer or anything like that? I'm drooling to try this but my rod spacing is unique.... sad smiley
Re: Piezoelectric disks for Z contact detect and bed levelling
February 17, 2017 03:38AM
I have the stl's for this effector now on my thingiverse. Lykle will publish it also (with step files) if anyone needs to edit it to suit their setup. Please feedback to us on how you are getting on with it, any additions and improvement you make as well.

[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 17, 2017 07:18AM
Hi all,

I published my version of the same thing on Thingiverse.

It was a pleasure working with DJDemonD to get this thing wrapped up. All I did was the final design, the bulk of the research and work was done by LeadingLights, Huntley, Moriquendi and of course DJDemonD. It does look like a very nice system.

All I need to do now is finish the 64 mm wide effector for Doug and finish the design of the next version, but that is only for good looks, no functional changes to this device.
Then I will move on to finishing the Diamond nozzle adapter for the Nimble.
After that I will have a look to see how we could fit a peizo sensor into the Chimera mount.


So many things to do, so little time. But hey, my own choice, right?

Happy printing!


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 18, 2017 05:46AM
Quote
DjDemonD
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.

I will be pleased to make any contribution to the wiki page that I can.

Mike

Edited 1 time(s). Last edit at 02/18/2017 05:48AM by leadinglights.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 18, 2017 05:53AM
Thanks Mike that would be great.


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 18, 2017 06:38AM
I have been investigating the behaviour of piezoelectric disks used in the configuration that DjDemonD uses and have got some useful traces which show just how sensitive this can be.
To do this I modified a jig that I made for earlier work. Instead of being compressed between two surfaces the disc was suspended around the outer edge and pressure was applied to the centre, the disc having been drilled 4.5mm and a small pad made to fit the hole. This should be a fair approximation to the way DjDemonD uses. The jig was preloaded with a force of 5N, about 500 grams to approximate the weight of a hot-end and small extruder. The drilledd disk with edge ring and centre button is on the left in the picture below.

The center pad was pushed down at 1mm per second for 20µm, 40µm, 60µm, 80µm and 0.1mm at a speed of 1mm/sec. The traces that I got are shown below. Scope set 100ms/cm and 2V/cm

The second picture shows the output change with different speeds, the traces being at 0.5mm/sec, 1.0mm/sec, 1.5mm/sec, 2.0mm/sec, 2.5mm/sec and 3.0mm/sec. Scope set to 20ms/cm and 2V/cm The small wiggles in the line are caused by the steps from the stepper motor - 1.8°, half stepping and a 1mm leadscrew so each wiggle is 2.5µm.

Incidentally, I tested the three piezo disks that I fitted to one machine back in March last year and have used regularly since: One disc has lost about 10% of it's mojo but the others are not measurably different.

Mike
Re: Piezoelectric disks for Z contact detect and bed levelling
February 18, 2017 06:51AM
Those are very interesting results Mike. Just for clarification, by how much are you bending the piezo disc?

Do you have any 20mm piezos that you could test? A 20mm piezo based probe unit would be a much neater package, they will be stiffer, presuming the same material thickness, and the 5mm hole out of the centre will take a relatively bigger bite out of the piezoelectric material so I have no idea if they will have sufficient signal/noise. I was planning to get some and just make a unit with a much smaller contact area on the clamp. The minimum would probably be a ring 1.5mm thick, with an ID of 4.5mm, since a 4mm bowden tube has to pass through 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 18, 2017 07:31AM
I have just ordered some 20mm disks from ebay. Can you do a sketch of how you want the disks to be clamped or suspended, middle as well as outside.

On the noise, there should be no significant electronic noise with the big voltages that you get from piezos and I have no noise problems on my amplifiers. Having said that, I did try making a charge amplifier of the type that is recommended* for piezo sensors and it was very noisy. There is more problems with mechanical noise which can perhaps be solved by the firmware allowing a pre-probing delay and switching off fans etc before probing.

Mike

* [www.mkesc.co.uk]
* [www.ti.com]

edit: I will see if I can measure how much the disk bends with the 500 grams of preload I have got on it but initial indications are that it is not a lot.

Edited 1 time(s). Last edit at 02/18/2017 07:35AM by leadinglights.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 18, 2017 07:50AM
Yes its the mechanical noise I am referring to. There is one development on Smoothie (which I am a total n00b at) you can set debounce_ms 1 on z-probe, this massively improves probing, reducing false triggers to almost 0 at full speed, and to 0 at 60% speed. RRF can do this but I haven't yet worked out how to do this with the piezo setup as I am running it as an analogue sensor on RRF, with the P parameter used to set threshold, whereas David says you can use P as debounce, but this is only when using the sensor in digital mode, which each time I've tried it on RRF it fails, but time to revisit this I think.



Sorry for the crap-arse diagram but hopefully it makes sense, I use a 2mm lip to hold the rim of the piezo, with the piezo-electric element facing downwards, with a 0.5mm-1mm recess above.
The smallest ring possible on the clamp would be 4.5mm ID 6.5mm OD.
If you can try with and without a 5mm hole drilled in the dead centre (spur point wood drill works a charm for me).

Thanks for doing this it should quickly determine if 20mm piezo is feasible.


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 18, 2017 07:51AM
I will contribute on the Wiki what I can, DJ.

Looking forward to the 20 mm results Mike.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 18, 2017 08:12AM
Something else which now seems very doable and might/might not be a new approach to getting a perfect 1st layer (automatically).

[forums.reprap.org]


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 20, 2017 11:53AM
Documentation for the second version of the Piezo Z-probe board (v1.1) can be found here.

Idris
Re: Piezoelectric disks for Z contact detect and bed levelling
February 20, 2017 01:02PM
Hi Idris,
That is nice clear documentation.
There is a thread that you may find interesting at [www.duet3d.com] The o.p. of the thread is using a Cartesian printer and is interested in mountings for piezo sensors and how three or four sensors work in parallel.

Mike
Re: Piezoelectric disks for Z contact detect and bed levelling
February 20, 2017 01:38PM
Thanks for the feedback and the heads up.

Idris
Re: Piezoelectric disks for Z contact detect and bed levelling
February 20, 2017 03:16PM
Hi Idris -

New to this thread - perfect timing as I'm doing a new extruder/effector for my homebrew Delta. I had been using one of Davids IR boards with good success but now I printing mostly on mirror glass with hairspray making IR probing difficult.

I've ordered some piezo disks and want to get my hands on your V2 ( 1.1?) board. I'm US based so it makes sense to go directly to OSH Park. I'll happily make a charity donation or a PayPal to you for the great value you offer to the community. Is there an OSH part number or do I submit the BRD file from your documentation?

I'll likely get a several of the boards so if anyone in the Colonies ( UK joke ! ) wants to join in send me a PM. You need only to make the Idris contribution. FCFS one time only. I'll place the order in 3-4 days.

bob
Re: Piezoelectric disks for Z contact detect and bed levelling
February 20, 2017 03:38PM
Here's a link to order the boards from OSHpark
Order from OSH Park

If you use the OSHpark link I'll get to know how many people order which I quite like the idea of.

The ones I'm making are no longer financially supporting the charity, I cant keep buying the parts to make them and from my point of view, giving them away.

If you make a donation to the charity that is always welcome Great Dane Care

If you choose to make a donation for the work I've done that is also welcome (paypal, idris_nowell15 at hotmail.com)

On the other hand I made the board layout and schematic freely available to everyone and there is no requirement on you to do either.

Idris

Edited 3 time(s). Last edit at 02/20/2017 06:20PM by Moriquendi.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 20, 2017 06:23PM
Thanks Idris, a Great Dane donation will be made. My only suggestion at this stage is that it would have been nice to have a screw hole or two for attachment. Looks like an M2 screw pad might squeeze between the trim pots.
Re: Piezoelectric disks for Z contact detect and bed levelling
February 21, 2017 11:17AM
I received the 20mm piezo discs this morning and have checked one of them - scope plots below.


Although there are some anomalous differences, I think that there is enough of a signal to be optimistic.
The first set of traces gives a narrower pulse which is as I would expect with a lower electrical capacity. The only strangeness here is that the tail end of the pulse goes negative - this was not seen on the 27mm disks.
The second set is a bit stranger as the pulse width is not narrowed as much as the first set, I would again have expected a faster decay. There is again the negative going tail end and also a little notch in the three fastest traces, I think this may indicate that the plastic ring was too close a fit.
I checked the compliance of the disks by mounting the jig in a vice and using a DTI to check the deflection when I put on an additional 500 grams of load with a dynamometer (spring scale)


The deflection I got with the 27mm disks was 0.035mm and 0.04mm with the 20mm disks - I would have expected a little less but possibly the brass is thinner.
One other thing that was not too good is that only 4 of the disks would be capable of having a 4.5mm hole put in the middle, the other 6 had the soldered connection too close to the middle.

Mike
Re: Piezoelectric disks for Z contact detect and bed levelling
February 21, 2017 01:20PM
Nice going Mike!
That ties in nicely with an integrated Nimble effector I have been working on.



The effector houses an integrated peizo sensor which the back of the Nimble rests on. Underneath the sensor is a little space so the sensor can bend.
Normally the Nimble is already used to clamp the hot end and this allows the sensor to sense the tap on the bed. The extruder is used here as the force transmitting device. The nice thing is that the sensor does not need to be modified in any way. Another benefit is that it takes very little space, so I am sure I can fit it to a lot of the other adapters I have designed so far. The biggest problem I had was making sure I had space to fit all the screws and maintain stiffness of the effector, while still allow the fan of the V6 to be positioned correctly. That took a while but I am confident I have it now.

I still have to play with the tolerances in the disc housing and see how much space needs to be left open for the sensor to be able to bend enough, But with a deflection of 0.04 mm, I am not too worried. I am hampered by the lack of a scope, but I will try and cobble something together. Or perhaps just use my DuetWifi as a scope.
So, in theory it will work, but you know what they say. In theory there is little difference between theory and practice. In practice....


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 21, 2017 04:07PM
Those are interesting and very professionally produced results Mike. Were any of the discs drilled in the test? So potentially promising even if a bit of soldering or discarding less suitable discs applies if they function with holes.


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 21, 2017 04:45PM
Quote
DjDemonD
Those are interesting and very professionally produced results Mike. Were any of the discs drilled in the test? So potentially promising even if a bit of soldering or discarding less suitable discs applies if they function with holes.

Only the one drilled and tested so far but I will do a couple more shortly so that I know that they are consistent.

Mike
Re: Piezoelectric disks for Z contact detect and bed levelling
February 21, 2017 05:09PM
Hi all

It occurred to me the other day that this could also possibly be used as a crash sensor while printing.. Discuss!

Would love to hear David's thoughts on this for the Duet firmware too.

Cheers
Brian
Re: Piezoelectric disks for Z contact detect and bed levelling
February 22, 2017 12:16PM
Well, I guess that is it for tonight.
Was testing with my sensor setup and it simply stopped responding.
I think I must have touched metal with the board and short circuited it.

I will have another look tomorrow, but I think I will be ordering a new board. Lucky Moriquendi has some new ones.

Lykle
Re: Piezoelectric disks for Z contact detect and bed levelling
February 22, 2017 04:05PM
I've got three left but more on their way. These v1.1 boards should be much easier to play with. all the components are on one side and the trimmers are much larger and easier to operate.

Idris
Re: Piezoelectric disks for Z contact detect and bed levelling
February 23, 2017 02:30AM
Nice
Re: Piezoelectric disks for Z contact detect and bed levelling
February 25, 2017 02:14PM
Piezo endstops? Don't mind if I do grinning smiley

Idris
Re: Piezoelectric disks for Z contact detect and bed levelling
February 25, 2017 03:29PM
Hi Idris,

I think that piezo endstops should improve repeatibility over any other kind but I would be a bit worried if the carriage(s) were already against the endstops. How are you actuating the piezo?

Mike
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