Piezo Z-probe Mk III Beta version now available

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By dc42 16 February 2017 11:54

Administrator · 2,297 comments

You can adjust the debounce time by adjusting the threshold in the G31 P parameter. Lower values give lower debounce times.


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com

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By Moriquendi 16 February 2017 21:44

Member · 39 comments

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

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By DjDemonD 16 February 2017 21:57

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Idris. That's great news. I think it might be a good idea to possibly start a wiki page on reprap for this system as it is coming together nicely, and all the relevant information such as how to use the board and how to assemble the units would be well placed.

David - I will experiment with this. I have been setting the P parameter dependant on the analogue value but it might be worth revisiting the digital setup as it does seem to work extremely well on smoothie as a digital sensor with 1ms debounce.

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By DjDemonD 16 February 2017 23:18

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Okay so this is the current incarnation of the sensor mounted in Lykle's latest effector system (which will be able to have a Nimble extruder bolted straight on - or just used with your current Bowden/flying extruder):
IMG_20170216_231632.jpg

Nozzle wobbly practically non-existent and calibrating to a 0.02 precision over a 330mm bed.

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By DjDemonD 17 February 2017 08:38

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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.

http://www.thingiverse.com/thing:2069480

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By Dougal1957 17 February 2017 08:43

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DJ did you get his larger one I sent you you will need that to go with the Alloy carriages that I am getting cut it has a hole to take the Bardair cooling tube integrated into it (Reminder to self to order a bardAir system)

Doug

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By DjDemonD 17 February 2017 12:16

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Thanks Doug, I did get it yet. I will reprint and upgrade the effector when the carriages are in. I am looking forward to that.

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By DjDemonD 18 February 2017 13:21

Member · 415 comments

This seems to be a nice way to use the probe for automatic perfect first layers:
https://www.duet3d.com/forum/thread.php?id=940

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By Zesty_Lykle 18 February 2017 14:10

Member · 86 comments

Yes, DJDemonD did a great job there, getting it done.

I published the designs on our Thingiverse page as well. http://www.thingiverse.com/thing:2117069
Included is a 64mm wide effector and a Prism effector, which is the standard Kossel type width, but pretty looking. (I think)

All three effectors already have holes in them for a Bard-air type cooling pipe.


Lykle
Design, make and enjoy life

Co Creator of the Zesty Nimble

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By Moriquendi 19 February 2017 12:40

Member · 39 comments

I'm writing up documentation for these new boards, does anyone know whether the inputs of the Duet are 5V tolerant?

Idris

Edit: Tuning instructions for the Z-probe v2 board are here https://www.dropbox.com/sh/3q38ew98kt7f … jm2Ra?dl=0, feedback would be very welcome, particularly from anyone whose using a v1 board.

Last edited by Moriquendi (19 February 2017 13:17)

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By dc42 19 February 2017 13:57

Administrator · 2,297 comments

Although they are fairly tolerant of over-voltage, the Duet inputs should not be fed more than 3.3V under normal operating conditions. If you power your interface board from the 3.3V supply provided on the Z probe connector, all will be well.


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com

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By Moriquendi 19 February 2017 16:05

Member · 39 comments

I thought that would be the case. The reason I ask is that I'm using a Smoothieboard which uses 5v IO. The board specifies 5v power so I'd hate for someone to give it 5v then plug it into the Duet and fry something. I don't have a 3.3v powersupply so I can't test the boards on 3.3v, nobody reported any problems with the v1 at 3.3v.

Idris

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By DjDemonD 19 February 2017 19:52

Member · 415 comments

Moriquendi, I'm using your one-Piezo board at 3.3v on duetwifi with no issue.

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By kraegar 21 February 2017 16:26

Member · 138 comments

Got my piezos today, a test fit is perfect, though I may need to get creative to insulate the edges of the copper from the retaining screws.  I plan to use some nylon washers to insulate it from the mount plates, we'll see what I can come up with there.

I'll probably cut some small notches in the copper plate and put an insulator around the m3 screws.

http://imgur.com/hdlaqlQ

Looking forward to getting the board from Moriquendi so I can try it out.

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By briangilbert 21 February 2017 22:10

Member · 80 comments

@dc42

What are the chances of this sensor also being used as a crash sensor during prints?


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By dc42 22 February 2017 06:36

Administrator · 2,297 comments
briangilbert wrote

@dc42

What are the chances of this sensor also being used as a crash sensor during prints?

That depends on whether the sensor has any tendency to trigger during normal printing.


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com

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By leadinglights 22 February 2017 08:40

Member · 8 comments

As most firmware does not look at the sensor other than when probing this does not normally create a problem. However, the LED on the piezo sensor boards on my 3D printers flash a lot during printing so there is signal to work with. If the amplifier put out an analogue signal instead of a logic one then perhaps the firmware could be set to look for error indicating values.

Mike

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By DjDemonD 22 February 2017 16:38

Member · 415 comments

Well whether it's designed to or not it does put out an analogue signal. I can read from 216 to 1000 on the duet web control depending on rate of pressure change on the piezo. It's goes to around 500 during rapid moves or over rough previous layers. I set 600-700 as a trigger level for probing.

But even then what would we use as a stop trigger? 1000? Maybe a slowdown to half speed at 700 then gradual increase back to normal at the next layer? It would be interesting to develop as its not been done before that I am aware of.

700 equate to 15g of force on probing, I'll set 1000 (or 999) probing threshold and stick the scales under the nozzle.

Last edited by DjDemonD (22 February 2017 16:38)

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By Moriquendi 22 February 2017 21:02

Member · 39 comments

I'm on holiday at the moment but when I get home I'll dig out the protoboard version of the circuit and have a look at the output of the differentiator section on an oscilloscope during a print. The output of the differentiator should be an analog signal proportional to, in my case, movement of the bed.

If anyone has access to a 'scope you're looking at either pin 1or pin 9 of the IC or the centre most end of either C1 or R3

Idris

Last edited by Moriquendi (22 February 2017 22:50)

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By DjDemonD 23 February 2017 12:05

Member · 415 comments

So a bit of experimenting.
Set the probe to digital in config.g using
M558 P5 I1 F500 X0 Y0 Z0       
G31 X0 Y0 Z0 P100           

And in this mode (I am using inverted setup for piezo board (active low), if you are using active high then remove I1) the G31 P100 is the debounce which filters the signal, so using this config I can probe at normal speed/jerk/accel which brings the probe performance into line with that on smoothieware, which has debounce parameter also.

However in this mode I think it would be less easy/not possible to use data from the probe for crash detection/quality improvement as discussed above by briangilbert, unless we take a feed from the pins Moriquendi suggested above and connect them to a spare analogue input on the duet. And then there is some coding required.

Here is it probing at normal speed:
https://youtu.be/MURqDTL9oVA

Last edited by DjDemonD (24 February 2017 20:05)

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By Moriquendi 25 February 2017 19:14

Member · 39 comments

Piezo endstops? Don't mind if I do 😄

Idris

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By Dougal1957 25 February 2017 20:05

Member · 265 comments

Idris How repeatable it it?  I have a few of them 10.5mm ones now

Doug

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By Moriquendi 25 February 2017 20:14

Member · 39 comments

I've only just got it together but it seems to be pretty good, not sure exactly how I'll measure repeatability but I'll have a look at it tomorrow.

Idris

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By Moriquendi 27 February 2017 12:00

Member · 39 comments

I realise that in my excitement to show off the piezo endstops working I didn't actually show how they were working and how they were set up, I'll try to rectify that now.

Very simply I have a 10.5mm (also very thin, 0.2mm) piezo element centred below an 8mm hole in the mount, the head of the bolt in the carriage touches dead centre in the bottom of the piezo.
2017_02_27_10_52_46.jpg

One of these at the top of each axis connects to the three channel endstop board. The sensitivity and threshold of each channel is linked so they all trigger at the same force.

2017_02_25_18_47_33.jpg

I think I've reached the limits of rigidity of my printer as I'm not seeing any improvement in z-leveling. I think that DJdemonD's printer is rather more robust so hopefully when he gets round to playing with the board I sent him we'll get better data on accuracy and repeatability.

I've got six more of these endstop boards on their way from OSHpark and hopefully they'll be here within two weeks.

I'm still working on the best way to organise piezos as endstops and their signal conditioning requirements, I could use some feedback here.

One option I'm looking at is an integrated board that has a piezo soldered on as well as the signal conditioning circuit, you'd then need one of these per axis. The issue with this is that you wouldn't be able to tune them, or if you could you couldn't guarantee that they were all tuned the same, I don't know how much of a problem this would be. This is likely to be the simplest, mount it, plug it in and forget about it. the difficulty is I'd have to find tuning values that work reliably for everyone.

Option two is the same as one but the piezo mount part of the board can be snapped off and mounted separately, this gives more flexibility without having the have multiple board types.

Option three is what I have at the moment, one board handling three separate piezos, the issue here is that long wires may pick up interference and in the app note we're warned against long wires due to the capacitance affecting the strength of the signal. How long does the cable have to be before this is a problem, no idea, may need further investigation.

Opinions most welcome, or if you've got other ideas I'd love to hear them.

Idris

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By DjDemonD 28 February 2017 00:40

Member · 415 comments

Wiki page http://reprap.org/wiki/Piezo-electric_sensors

Feel free to edit if you have the access or let me know if you want something changed.