Piezoelectric disks for Z contact detect and bed levelling

I've started a spreadsheet with data collected, so far just the control test.

[1drv.ms]

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Need me to re-work any designs?
Or are you guys all set now?

Lykle

Thats very kind of you Lykle. The answer is yes, but the 20mm version isn't really ready yet, I'm going to do some "proper" science and test it. But I'd be very grateful for your take on it/rework design-wise once I'm confident it works.

First proper go on the test rig (thanks Idris for the extra piezo board) and it just slams into the print surface and breaks the mount. But working on it now, might be with the 5mm screw its not hitting it fast enough to trigger.

Edited 1 time(s). Last edit at 03/09/2017 09:32AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

My bad, note to self (and everyone else - not that you need it) if it just slams into the bed, reverse the polarity of the piezo.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

100 data points for 20mm piezo with v1.1 board now on spreadsheet.

Edited 1 time(s). Last edit at 03/09/2017 01:47PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Are you probing with your rig horizontal or vertical? If horizontal, do you think that the hot end cantilevered out by the piezo might be affecting the results?

Idris

I can mount it vertically. Ill do 100 vertical and see if it makes a difference. I might email Tom and ask him if I can have a copy of his arduino code for his rig, might save some time.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Updated spreadsheet. Ran a 100 vertical and yes it has improved the repeatability. Standard deviation dropped to average 0.0045 over 2 x50 probe runs, with spread at 0.01 rather than 0.02.

Unless I learn how to program in the next few minutes I am not going to be able to improve the accuracy of the rig as marlin will only give me 2 decimal places.

What is apparent is that I could build a really good rig; ballscrews, linear guides, metal parts and I suspect the numbers for the probe would be spectacular. However as a tool for testing and benchmarking new designs without having to tie up a printer its going to be very useful. Looking forward to seeing how quickly I can wear out an m5 threaded rod too.

Apologies the online spreadsheet either updates slowly or is missing some information. My bad (again) must be tired. working normally. I will add an image of each module being tested.

Edited 2 time(s). Last edit at 03/09/2017 02:38PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Good work, I thought the range for the piezo looked a little high (if 20 microns can be called high). I reckon we may be beyond the accuracy of threaded rod and printed parts now anyway.

Let me know whether Tom will share his code, if not I'll have a look at writing something but no point doing the work twice if its not needed.

Idris

I have a favour to ask of anyone who's got their piezo board set up and tuned. I'd like to know how widely peoples tuning settings are varying. What I'd like to know is the resistance setting of VR1 and VR2.

On V1 boards you can measure the resistance between the PZ - pin and the metal adjuster on the top of VR1, range will be up to 1Mohm. Measure VR2 between the GND pin and the metal adjuster, range up to 100Kohm

On V1.1 boards you're measuring the resistance between any PZ - pin and the centre pin of VR1, range up to 1Mohm. Measure VR2 between the GND pin and the centre pin of VR2, range up to 47Kohm

Please also note whether it's a v1 (two tiny horizontal pots) or a v1.1 two vertical black pots. It's also be good to know if you're using hot end piezo mounting or underbed mounting and how many piezo elements you're using.

Thanks very much

Idris

Hotend probe
Piezo - 20mm no name ebay [www.ebay.co.uk]
V1.1 board
VR1 10.04 Kohm
VR2 - not measuring anything between GND and VR2 centre pin. Getting 1.5Mohm between piezo pin and VR2 centre pin.

hope this helps.

Hotend probe 27mm murata piezo
V1 board
VR1 0.45 Mohm
VR2 4.95Kohm

This was with the power off, so I remeasured the first one
Hotend probe
Piezo - 20mm no name ebay [www.ebay.co.uk]
V1.1 board
VR1 10.04 Kohm
VR2 - 12.15 Kohm

So measure this with power off.

Edited 2 time(s). Last edit at 03/10/2017 06:24PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Measure my other machine too
Hotend probe 27mm murata piezo
V1 board
VR1 0.56 Mohm
VR2 29Kohm (but it was jumping around all over the place with the power off).

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Hmm, pretty wide range, that's going to make it difficult to make a board that the end user doesn't have to tune...

Thanks DjDemonD.

I have the new batch of boards in and mostly made up. I also have endstop boards for anyone who wants to pursue that.

Idris

Yeah I can see the challenge here, might be worth seeing what happens if I set them all to the same settings. Maybe there's a wider range of useful, than I presume.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Just thinking out loud but might there be a way to autocalibrate the piezo? It would, I presume, need a more sophisticated programmable chip, that could be set to "calibrate mode" then move the head around and try a few tentative probes and set the two parameters to a value that gives good performance.

My apologies if my lack of electronics expertise has lead me to suggest something that is 100x more difficult or expensive than what we have now.

Edited 1 time(s). Last edit at 03/12/2017 05:10AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

It's feasible but it would complicate things and would increase the price. I don't know how much of an issue it is, most people who are looking to upgrade their printer are relatively technically able and the tuning process isn't that complicated. I think it would be fairly easy to have a fixed value for VR1, the endstop boards all have a fixed VR1 and seem to work fine. That would leave just a single pot, most people can handle "if you get false triggers turn the pot clockwise" type of thing.

Idris

True. I've yet to try the endstop board I'll put it on the test rig and have a play.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
Just thinking out loud but might there be a way to autocalibrate the piezo? It would, I presume, need a more sophisticated programmable chip, that could be set to "calibrate mode" then move the head around and try a few tentative probes and set the two parameters to a value that gives good performance.

That is what I have in mind with the PCB/piezo effector that I have designed with T3P3, assuming we find that the piezos vary in output as you did. Something like:

- Drop the nozzle so it is just touching the bed, send G92 Z0
- Raise the nozzle 2mm
- Put the probe in calibration mode, using the MOD signal from the Duet
- Send G1 Zxx Fyy where xx is a small negative value that we will need to determine (and might depend on how hard the bed surface is) and yy is an appropriate feed rate
- The probe will then indicate whether it has received a big enough signal to calibrate itself

Another possibility: instead of probing the bed, perform calibration by moving the head up a few mm and then stopping abruptly. The mass of the hot end should cause a trigger when the movement stops. This could be repeated a number of times to ensure consistency.

With luck we will have prototypes by the end of the week. Currently we are still learning how to drill piezos!

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I'm sure if this takes off we could find out if they can be manufactured with holes in, perhaps a big group buy of enough units to keep everyone happy. Even if they're £1 unit instead of £0.40...

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Quote
DjDemonD
I'm sure if this takes off we could find out if they can be manufactured with holes in, perhaps a big group buy of enough units to keep everyone happy. Even if they're £1 unit instead of £0.40...

Good idea! I am in touch with a Taiwanese supplier of piezo devices (they make the sounders we use in Panel;Due) so I will ask them about this.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

1.1 board

VR1 250kohm
VR2 11.5k ohm

Running in analogue mode. I couldn't tune it for digital....

27mm piezo unit (originally from a DJD thingiverse ebay link)

Edited 1 time(s). Last edit at 03/12/2017 03:50PM by Phytone.

Thanks Phytone

Quote
dc42

Quote
DjDemonD
I'm sure if this takes off we could find out if they can be manufactured with holes in, perhaps a big group buy of enough units to keep everyone happy. Even if they're £1 unit instead of £0.40...

Good idea! I am in touch with a Taiwanese supplier of piezo devices (they make the sounders we use in Panel;Due) so I will ask them about this.

Perhaps along those lines if we can determine/agree what properties we want from a piezo for 3d printer use we might even be able to commission some units specifically for this purpose. Do they have to be round? If they were long and thin they might make better endstops? Again just thinking out loud.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Data for a couple of runs using the endstop board now on sheet 3 at [1drv.ms]

Measuring 23 Kohm at the single adjuster (VR2).

No issues with using this board (as a probe in this case) with the one adjuster. Getting a slightly higher spread 0.03mm but still a standard deviation of 0.007-0.008mm.

I am using it as I am with all these boards with the signal inverted i.e. LED's on when open and off when triggered.

If I reverse the logic on the piezo board and firmware and re-run the test I get the same results (sheet 4) so I think I have validated that its a question of personal choice whether to run with normal or inverted logic.

I think the reason I like using it inverted is that the board does not have a power LED (I'm sure it would be easy to add one) so I can visually verify its operational before printing if I use inverted logic, as the LED's are on when the sensor is open.

Also you have to reverse the piezo polarity to run inverted logic. This explains why I had the issue earlier with polarity of the piezo on one machine being reversed compared to another and yet they both worked, one machine was on inverted logic and one machine on normal logic.

Edited 3 time(s). Last edit at 03/12/2017 08:14PM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Hey all, back from vacation and I've finally got my fancy Piezo setup running. Duet wifi, lykle's effector (printed SLA), M's board version with 2 pots. So far I've gotten great results just fiddling with the sensitivity randomly on a glass bed, but am getting mixed results on PEI. Either the pei is a little squishy, or my actual sheet of PEI is just shot, I have a backup sheet that I'm gluing on shortly to hopefully check that. So far this is the best probe I've used and I've spent a lot of time with both FSR and IR probes. That said, always looking for improvement. It seems my Z0 value is actually about -.301 which suggests that my sensitivity isn't as high as I'd like, but adjusting the pot gives me false triggers during probing on one particular side of the bed, which may indicate a problem in my installation of the peizo disk.

My question is this, the two pots, how do I adjust them optimally on a duet wifi? I'm using the Zprobe pins, so I don't get a flickering endstop light,and the LEDS on the M board themselves don't actually seem to do anything. I'm happy with my results currently but believe they can be better. Should I be adjusting one but not the other? should I set one to some benchmark and adjust the other till perfect? Basically what am I doing with these knobs to get that z0 closer to z0.

Glad you're liking it.

I haven't got any PEI to test but I have tested it on painters tape which must be softer than PEI???

You could expect z=0 to be offset by 0.15-0.2 or so, 0.3 suggests a very soft surface.

I doubt its your installation but regarding your issues there are a couple of things:
1) make sure the holes through the sensor module and piezo are big enough not to rub on the bowden tube. The bowden tube can pull on the sensor at extreme positions (especially with a flying extruder). One solution might be to fit a bowden coupler to the top plate of the sensor module, and just run a guide tube down to the hotend, this decouples the bowden tube from the sensor. I haven't really tested this option but for non-e3d hotends it might be the only way we get the system to work, and it might be the optimal way to use it, so when I get chance I will set one up like this, I would expect an improvement in performance at extreme bed positions.

2) Adjustment of the pots. Decide if you want normal logic (LED off when open) or inverted logic (LED on when open). I recommend LED ON/inverted, you might have to reverse the polarity of the piezo if its not very sensitive, see my post above. Turn VR2 until the LED just illuminates, this is the most sensitive position, then press up on the hotend if the LED flashes off convincingly then have a few probes and see how it goes. If it doesn't turn VR1 and try a few more. Now tap the head and move it around a bit and ensure the led only flickers, if it goes off solidly then its probably too sensitive.

It is worth trying to get it to work digitally on duetwifi Use:
M558 P5 I1 F300 X0 Y0 Z0 - this presumes inverted logic and using the z-probe connector
G31 X0 Y0 Z-0.2 P1 This sets a z offset of -0.2 (you might need more or less) and P1 sets debounce to the shortest time interval possible which reduces false triggers (On my setup anyway) to zero.

Probe at 300mm/s this seems to be the optimum. Too fast and you lose accuracy, too slow and you risk not getting a convincing trigger as you don't bend the disc fast enough.

3) Ensure your hotend is straight, as you do up the screws holding the hotend+clamp to the top plate of the sensor module, if they are uneven, or your piezo disc is unevenly seated, you might get one sided issues.

Hope this helps.

Edited 3 time(s). Last edit at 03/14/2017 05:16AM by DjDemonD.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

You can find tuning instructions Here though that doesn't deal with inverted logic, you're best off following DjDemonDs post for that.

Idris

Edited 2 time(s). Last edit at 03/14/2017 08:16AM by Moriquendi.

Can I make a request for some materials to test?

I've got this test rig setup now (will be modding it a bit to make it a lot stiffer, as I think the values I am getting are partially test rig compliance and that the probe can perform better). I would like to start testing a range of bed materials.

Can I ask if anyone has any small scraps of various print surfaces, they would only need to be 2-3inch pieces?
I am currently using aluminium and I have painters tape, hairspray, glass.

I'd like to test
-Printbite
-PEI
-buildtak
-any other major surfaces I haven't thought of?

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Where are you located? I've got some PEI sitting around.

Quote
DjDemonD
Can I ask if anyone has any small scraps of various print surfaces, they would only need to be 2-3inch pieces?
I am currently using aluminium and I have painters tape, hairspray, glass.

I'd like to test
-Printbite
-PEI
-buildtak
-any other major surfaces I haven't thought of?

That's very thorough of you I'm surprised that print surface makes much of a difference for a physical contact mechanism like this, but I guess the difference between a very hard surface like glass and a thick softer surface could be enough to cause a reduction in signal. I'll certainly be very interested to see the results.