Piezoelectric disks for Z contact detect and bed levelling

An update on the ongoing testing of piezo discs, but first the conclusions: Nothing that these tests has revealed has changed my impression that inexpensive piezo discs offer the most accurate, most affordable and most robust way to both detect the bed level and the nozzle height on FFF 3D printers.
Having said that, some of the results I have obtained are not for those who have a technologically queasy stomach. Anybody who insists on 8AWG gold plated de-oxygenated speaker cables on their home audio please leave this thread now.

I have attached a PDF with the results of my tests and with some sample oscilloscope traces.
morediscs.pdf

Mike

Interesting. Would you be willing to test higher temperatures to determine where a few disks fell to below 0.25V? (Do they recover afterwards, or is this a destructive test?) Undrilled disks would be fine by me, although I'm sure others would be more interested in the drilled numbers.

Hi Mike, interesting, and useful test for polarity. My method so far has been attach piezo to signal conditioning pcb, attempt to probe, if probing unsuccessful reverse polarity and try again.

---

Simon Khoury

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

Quote
JamesK
Interesting. Would you be willing to test higher temperatures to determine where a few disks fell to below 0.25V? (Do they recover afterwards, or is this a destructive test?) Undrilled disks would be fine by me, although I'm sure others would be more interested in the drilled numbers.

They recover fine afterwards. I did a test some time ago on a 27mm Murata disc and it was good up to 100°C so I have started looking to see if I can find Murata leaded 20mm discs to try and will report back if I find these or a better breed of discs.

The problem area - at least if you are a neatness freak, is that the discs are all over the place, some even improving with drilling, some being more temperature sensitive than others etc.. Fortunately all that is really needed is a quick response to a few 10s of millivolts so they will all do.

Mike

I am the author of the product being sold in Brazil via Mercado Livre. I was very surprised to find this topic and, from what I could see, I started to develop my project a long time ago. But as I've never divulged it anywhere, it gives me a sense that they caught my idea of ​​the collective unconscious!

I go very little in this forum, and I came here to talk more about the idea of ​​using polyester films as warm bedding. And also the idea of ​​using a vacuum to fix the film. I am really surprised at the comments made here.

As far as I can understand, they are not yet properly exploiting the sensor in the mechanical sense. And to get a result that I have considered great, I use a differential ADC and a software (ATMEL microcontroller) in order to eliminate vibrations and maximize the response to the type of movement that matters. So I get great sensitivity, good stability and accuracy. Unfortunately I can not share project specific data because I did not do it for this purpose. It was a lot of work for me, and I did not copy anything from anyone.

If someone is interested in getting my sensor, I can try to negotiate a more affordable way. But, as it seems obvious, I notice that I do not speak English.

Why don't you use car detonation sensor??
It has resonance peak typically at 15-25khz so all you need is piezogenerator on this frequency. No false triggering anymore I hope.

Quote
karabas
Why don't you use car detonation sensor??
It has resonance peak typically at 15-25khz so all you need is piezogenerator on this frequency. No false triggering anymore I hope.

I am not sure what you are suggesting as your post gives too little information but perhaps you can clarify.
Is a car detonation sensor a knock sensor? Why would anybody pay £57 for a knock sensor rather than £0.40 for a piezo disc? What would the purpose of the piezogenerator be? Why would 15-25kHz help as the information content in a nozzle contacting a bed is almost entirely in the 4Hz to 500Hz range?
The only false triggering I have had from piezo sensors have been from the printer shaking during moves and from a thermal effect during warmm up - both long since solved.

Mike

Quote
ECJ
I am the author of the product being sold in Brazil via Mercado Livre. I was very surprised to find this topic and, from what I could see, I started to develop my project a long time ago. But as I've never divulged it anywhere, it gives me a sense that they caught my idea of ​​the collective unconscious!

I go very little in this forum, and I came here to talk more about the idea of ​​using polyester films as warm bedding. And also the idea of ​​using a vacuum to fix the film. I am really surprised at the comments made here.

As far as I can understand, they are not yet properly exploiting the sensor in the mechanical sense. And to get a result that I have considered great, I use a differential ADC and a software (ATMEL microcontroller) in order to eliminate vibrations and maximize the response to the type of movement that matters. So I get great sensitivity, good stability and accuracy. Unfortunately I can not share project specific data because I did not do it for this purpose. It was a lot of work for me, and I did not copy anything from anyone.

If someone is interested in getting my sensor, I can try to negotiate a more affordable way. But, as it seems obvious, I notice that I do not speak English.

Hi ECJ,
Can you reveal a little more about why you use software, why a differential ADC is useful and in what way "they" are not properly exploiting the sensor in the mechanical sense?

Mike

Hi ECJ, inventions/innovations are often throughout history discovered simultaneously, its not that hard to see how the same technology, conditions and problems exist at the same time in different places and people try to solve them in parallel. I am not accusing you of copying, but there were some surprising similarities in the way the technology is presented and the youtube videos we both produced.

However it makes sense to me that you have been working on it for a while now, as your product is more well developed than ours, which is only just coming together now. I am personally okay with it as this is an open source hardware project, all my data, techniques and stl's etc.. are public, my cad files are public. I think the world is quite large enough for us both to be selling piezo hotend sensors, though I suspect many people here would like to make their own.

What is a great shame is that whilst our information is free and open to all, your project is closed source and only benefits yourself. Please consider the benefits to everyone including yourself of working with us, sharing your data and electronics, so that we can all benefit from it. Its by doing things this way the world changes.

---

Simon Khoury

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

Quote
DjDemonD
Hi ECJ, inventions/innovations are often throughout history discovered simultaneously, its not that hard to see how the same technology, conditions and problems exist at the same time in different places and people try to solve them in parallel. I am not accusing you of copying, but there were some surprising similarities in the way the technology is presented and the youtube videos we both produced.

However it makes sense to me that you have been working on it for a while now, as your product is more well developed than ours, which is only just coming together now. I am personally okay with it as this is an open source hardware project, all my data, techniques and stl's etc.. are public, my cad files are public. I think the world is quite large enough for us both to be selling piezo hotend sensors, though I suspect many people here would like to make their own.

What is a great shame is that whilst our information is free and open to all, your project is closed source and only benefits yourself. Please consider the benefits to everyone including yourself of working with us, sharing your data and electronics, so that we can all benefit from it. Its by doing things this way the world changes.

Yes, I understand what you mean and understand your indignation. I also really want the world to change for the better. But I am afraid that someone with more capacity for dissemination and production, can copy the project. I am poor, I no have own home and the situation here in Brazil is somewhat critical.

This device despite being very good, suffers from the competition of other solutions that already exist in the market. And it seems that it suffers also with a certain skepticism. So far, almost no one has been interested in buying it. With more time and more exposure maybe more people might be interested.

No I have no indignation... I sympathise with your situation and I accept that selling them successfully might have more impact on your life than mine, I do this for a hobby and for the innovation. I am more interested to see people use this technology than the other much less suitable sensor systems out there (I have tried almost all of them, and found them all lacking) rather than in making money.

Perhaps we can work together to raise awareness and market these devices, maybe some more Youtube videos etc... I am quite happy to mention you and your product aiming at the South American (and North American?) markets, given that I am fairly sure most of my orders (when I get them) will be UK/Europe just by nature of the cost of postage, if you are willing to mention us (we're called Precision Piezo).

Edited 2 time(s). Last edit at 04/07/2017 07:05AM by DjDemonD.

---

Simon Khoury

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

Quote
leadinglights

Quote
ECJ
I am the author of the product being sold in Brazil via Mercado Livre. I was very surprised to find this topic and, from what I could see, I started to develop my project a long time ago. But as I've never divulged it anywhere, it gives me a sense that they caught my idea of ​​the collective unconscious!

I go very little in this forum, and I came here to talk more about the idea of ​​using polyester films as warm bedding. And also the idea of ​​using a vacuum to fix the film. I am really surprised at the comments made here.

As far as I can understand, they are not yet properly exploiting the sensor in the mechanical sense. And to get a result that I have considered great, I use a differential ADC and a software (ATMEL microcontroller) in order to eliminate vibrations and maximize the response to the type of movement that matters. So I get great sensitivity, good stability and accuracy. Unfortunately I can not share project specific data because I did not do it for this purpose. It was a lot of work for me, and I did not copy anything from anyone.

If someone is interested in getting my sensor, I can try to negotiate a more affordable way. But, as it seems obvious, I notice that I do not speak English.

Hi ECJ,
Can you reveal a little more about why you use software, why a differential ADC is useful and in what way "they" are not properly exploiting the sensor in the mechanical sense?

Mike

On the mechanical issue, he said this because it is necessary that the piezo disc is kept under a small constant pressure so that variations in pressure from the heating and cooling of the filament do not affect the performance of the sensor. The use of the differential ADC is to eliminate noise and static energy captured by the cables and the disk itself. With the use of the software I can ignore vibrations coming from engines and other undesirable stimuli effectively without the need for additional components. This allows you to take advantage of the sensor sensitivity and apply extremely high pressure on the table during the tests. My sensor is capable of even on E.V.A surfaces, for example.

Quote
DjDemonD
No I have no indignation... I sympathise with your situation and I accept that selling them successfully might have more impact on your life than mine, I do this for a hobby and for the innovation. I am more interested to see people use this technology than the other much less suitable sensor systems out there (I have tried almost all of them, and found them all lacking) rather than in making money.

Perhaps we can work together to raise awareness and market these devices, maybe some more Youtube videos etc... I am quite happy to mention you and your product aiming at the South American (and North American?) markets, given that I am fairly sure most of my orders (when I get them) will be UK/Europe just by nature of the cost of postage, if you are willing to mention us (we're called Precision Piezo).

Yes, I thank you very much for your understanding and for your proposal, and for a partnership to popularize this solution. I'll call my "PieZprobe". I'll think more about it, how I can do it and we'll contact you in the future according to your availability, ok?

Quote
ECJ

..........................

On the mechanical issue, he said this because it is necessary that the piezo disc is kept under a small constant pressure so that variations in pressure from the heating and cooling of the filament do not affect the performance of the sensor. The use of the differential ADC is to eliminate noise and static energy captured by the cables and the disk itself. With the use of the software I can ignore vibrations coming from engines and other undesirable stimuli effectively without the need for additional components. This allows you to take advantage of the sensor sensitivity and apply extremely high pressure on the table during the tests. My sensor is capable of even on E.V.A surfaces, for example.

Thank you ECJ,
I think that those are all good engineering reasons even though I would do it differently.
On last question though: What is the E.V.A. surface that you mention above?

Mike

I mentioned EVA only to demonstrate sensor sensitivity and little pressure that it exerts on the surface during the probes. Obviously there are no EVA coated tables. But I also use this same type of sensor in plotter, cnc, laser and dispenser modules that I have in my 3D printer.

At first I also considered the use of analog hardware, but I soon came to the conclusion that to get the results I want, many components would be needed. It would be more laborious and would not have the same performance and stability. As I have knowledge and ease with microcontrollers, soon I started for this solution. I got very compact hardware, inexpensive, few components, and very efficient.

Edited 1 time(s). Last edit at 04/07/2017 09:20AM by ECJ.

Quote
ECJ

Quote
DjDemonD
No I have no indignation... I sympathise with your situation and I accept that selling them successfully might have more impact on your life than mine, I do this for a hobby and for the innovation. I am more interested to see people use this technology than the other much less suitable sensor systems out there (I have tried almost all of them, and found them all lacking) rather than in making money.

Perhaps we can work together to raise awareness and market these devices, maybe some more Youtube videos etc... I am quite happy to mention you and your product aiming at the South American (and North American?) markets, given that I am fairly sure most of my orders (when I get them) will be UK/Europe just by nature of the cost of postage, if you are willing to mention us (we're called Precision Piezo).

Yes, I thank you very much for your understanding and for your proposal, and for a partnership to popularize this solution. I'll call my "PieZprobe". I'll think more about it, how I can do it and we'll contact you in the future according to your availability, ok?

Makes sense to work together as I don't think we're really in direct competition.

---

Simon Khoury

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

Hi folks,

I just PM'ed Moriquendi, but figured I could've just asked here...sorry for that.

I;ve had some nice probing attempts with the v1.2 board on my delta...and then after some fiddling with stuff, VR1 just stopped working. I'm getting no readings between any of the terminals. What sort of potentiometer can I replace it with ?

Thanks

If you know the resistance you need you could use a resistor and avoid the vr1, we are considering it but it depends on how consistent the piezo are.

---

Simon Khoury

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

Quote
leadinglights

Quote
karabas
Why don't you use car detonation sensor??
It has resonance peak typically at 15-25khz so all you need is piezogenerator on this frequency. No false triggering anymore I hope.

I am not sure what you are suggesting as your post gives too little information but perhaps you can clarify.
Is a car detonation sensor a knock sensor? Why would anybody pay £57 for a knock sensor rather than £0.40 for a piezo disc? What would the purpose of the piezogenerator be? Why would 15-25kHz help as the information content in a nozzle contacting a bed is almost entirely in the 4Hz to 500Hz range?
The only false triggering I have had from piezo sensors have been from the printer shaking during moves and from a thermal effect during warmm up - both long since solved.

Mike

Ok. Sensor has internal narrow band frequency filter with only one big resonance peak. My old car sensor marked as 18.6kHz so it does not detect vibrations on other
frequencies. That is why I want to use it as nozzle probe detector.

Attach piezogenerator to nozzle and sensor to bed.
Tune piezogenerator to frequency your sensor is able detect.
When nozzle touches the bed, sensor detects its vibration.

Edited 1 time(s). Last edit at 04/07/2017 10:04AM by karabas.

Unfortunately I didn't get to finding out what exactly I need. Roughly...what values can I expect ? I have a big leftover pot from an arduino set...maybe that one will work

It's very variable look back through the thread there are some values posted.

As for the acoustic pickup idea it's got merit but why go active when passive works just fine? I use a version of this on the micro delta which has a noisy fan and the nozzle vibrates on the bed when I manually calibrate it.

---

Simon Khoury

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

I'm posting a replacement out to RandomFactoid, for reference VR1 is a 1Mohm 3mm single turn SMD trimmer pot (Murata PVZ3A105C01R00 or equivalent)

The pots do need to be treated with respect, they're designed to be set once then left alone, to put that in perspective they're rated for 10 rotational cycles.

Idris

Quote
ECJ
At first I also considered the use of analog hardware, but I soon came to the conclusion that to get the results I want, many components would be needed. It would be more laborious and would not have the same performance and stability. As I have knowledge and ease with microcontrollers, soon I started for this solution. I got very compact hardware, inexpensive, few components, and very efficient.

There is a lot of good things to be said for using digital signal processing but I would feel uncomfortable without having some high frequency filtering for anti aliasing, overvoltage protection to stop the piezos from hurting the ADC and possibly a buffer to present a high DC impedance to the signal. Combine that with the programming time for a microcontroller and I am happier with a simple analogue circuit - I took longer today trying to get to grips with the Goertzel algorithm than I originally took to decide, design and layout my amplifier and that didn't give me a headache.

In the end though, if we didn't have the ability to look at different ways of doing things we would all use microswitches on model aircraft servos - or be flint knapping outside our caves.

Mike

OK... so I finally got around to fitting the piezo sensor to my mini kossel, replacing the servo operated optical sensor I had there for bed probing. Can I just say that you guys have the right approach as far as I am concerned... KISS. It works as described..no need to go digital or over complicate the thing.... it is perfect. If I can bludgeon a hole in the middle(ish) of a piezo sensor then anybody can... and it just works. Many thanks to Moriquendi for supplying the board I wouldn't be able to solder surface mount components any more (I can't see them for one thing!!) and ,thanks to everyone else for developing the design and for the ideas...I have re-gained 40mm by remounting the hotend up into the effector with the peizo mount...superb!!...Happy days!!!





Edited 1 time(s). Last edit at 04/07/2017 05:17PM by dart16.

Quote
leadinglights

Quote
ECJ
At first I also considered the use of analog hardware, but I soon came to the conclusion that to get the results I want, many components would be needed. It would be more laborious and would not have the same performance and stability. As I have knowledge and ease with microcontrollers, soon I started for this solution. I got very compact hardware, inexpensive, few components, and very efficient.

There is a lot of good things to be said for using digital signal processing but I would feel uncomfortable without having some high frequency filtering for anti aliasing, overvoltage protection to stop the piezos from hurting the ADC and possibly a buffer to present a high DC impedance to the signal. Combine that with the programming time for a microcontroller and I am happier with a simple analogue circuit - I took longer today trying to get to grips with the Goertzel algorithm than I originally took to decide, design and layout my amplifier and that didn't give me a headache.

In the end though, if we didn't have the ability to look at different ways of doing things we would all use microswitches on model aircraft servos - or be flint knapping outside our caves..

Mike

Yes, but in my case the filtering is done by the algorithm itself. The current generated by the piezo is very low and the ADC itself has its overvoltage protection with diodes and ESD protection up to 5kv. The input impedance is about 100MOhms! Nothing has been forgotten and everything is as it should be. On the contrary I have very easy with programming since I am a hobbyist programmer for more than 30 years. But you are quite right in stating that each has its own way of implementing. But do not forget that the control board of the printer is predominantly digital, from microcontroller that commands everything, to the drivers of the motors that also have a microcontroller and software. The temperature sensors are connected to ADC's and all other sensors are fully digital.
Analog electronics are indispensable in certain specific parts, but in general digital electronics is an evolution and so much that allows greater precision and control in almost all aspects.

Edited 1 time(s). Last edit at 04/07/2017 05:17PM by ECJ.

Quote
dart16
OK... so I finally got around to fitting the piezo sensor to my mini kossel, replacing the servo operated optical sensor I had there for bed probing. Can I just say that you guys have the right approach as far as I am concerned... KISS. It works as described..no need to go digital or over complicate the thing.... it is perfect. If I can bludgeon a hole in the middle(ish) of a piezo sensor then anybody can... and it just works. Many thanks to Moriquendi for supplying the board I wouldn't be able to solder surface mount components any more (I can't see them for one thing!!) and ,thanks to everyone else for developing the design and for the ideas...I have re-gained 40mm by remounting the hotend up into the effector with the peizo mount...superb!!...Happy days!!!
]

The digital system does not complicate. Instead. Decreases the number of components, reduces cost, increases immunity to noise and instabilities, etc. I think so too have those who developed the first 3D printers.
But it's great to have an open source project that works well. I'm glad that you have progressed and are happy with the result. I would also like to have opened my project from the beginning and shared everything, but for private issues, I could not do it.

Is it possible to use digital mode with smoothieware as well ?

If you mean run the sensor as a digital sensor then yes thats the only mode possible. Only RRF/Duet allows for analogue sensors, unless someone else knows better. I am running one on a re-arm running smoothie just configure it as a z_probe and/or z_min and it just works. Heres the relevant sections from my smoothie config:

# optional Z probe
zprobe.enable                                true           # set to true to enable a zprobe
zprobe.probe_pin                             1.29!^          # pin probe is attached to if NC remove the !
zprobe.slow_feedrate                         5             # mm/sec probe feed rate
zprobe.debounce_ms                           1             # set if noisy
zprobe.fast_feedrate                         50            # move feedrate mm/sec
zprobe.probe_height                          5               # how much above bed to start probe

gamma_min_endstop                            1.29!^            #

A couple of things - the pin listed is for re-arm only, on a real smoothieboard or azteeg board it will be different. The debounce_ms command is quite important and it improves the sensor accuracy and cuts down false triggers. Probing at reduced speed helps also. Also if you have it set for the LED to come ON when triggered then remove the ! from after the pin definition, this inverts the logic, I use it with the LED going OFF when triggered, for reasons listed above somewhere.

Just a point of clarification I want to distinguish for anyone reading between using the probe as a digital switch i.e. ramps/smoothie where it just goes high, or low when triggered (depending on how you set the VR2 on the piezo board) and using it as an analogue probe on RRF where you can specify a trigger value; from the discussion about analogue electronics i.e. Leadinglights's, Moriquendi's and my implementation using an analogue PCB and ECJ's system using his digital microcontroller board. These are two separate but potentially confusing discussions.

Edited 4 time(s). Last edit at 04/07/2017 05:52PM by DjDemonD.

---

Simon Khoury

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

Quote
DjDemonD
from the discussion about analogue electronics i.e. Leadinglights's, Moriquendi's and my implementation using an analogue PCB and ECJ's system using his digital microcontroller board. These are two separate but potentially confusing discussions.

Yes! They are two distinct segments, each with its different challenges and results. It is not very pleasant to make comparisons and that is not the intention. I just came here to answer mentions that I would have copied the idea of DjDemonD. It was not my intention to advertise my product.