Proximity Sensor for Glass Sheet

I've been researching different proximity sensors that I can use with transparent glass panes. Few people have mentioned using LJC18A3-H-Z/BX successfully with glass on top of a PCB heater. LJC18A3-H-Z/BX is a capacitive sensor. Can we not use inductive sensors for an application like this? I found a photoelectric sensor from a German company that is specifically made for detecting transparent objects. http://www.clrwtr.com/PDF/Leuze-Lumiflex/Leuze-RKR-3B-Foils.pdf Can we use something like that? I've no idea how much that sensor is though.

I have not seen anything on the datasheet for the photoelectric sensor that shows how good a resolution it would have at a couple of mm range. As it has a maximum range or 1.8mm I would be quite surprised if it was sufficiently accurate at short range ( I may be wrong thought)
Can I ask why you have concentrated on proximity sensors - inductive, capacitative and optical, rather than nozzle contact sensors?

Mike

My differential IR sensor works quite well on glass if you put a black surface under the glass, e.g. black paper or black paint. The idea is to reduce the reflection from underneath the glass, so that the reflection from the top of the glass dominates. See [miscsolutions.wordpress.com].

Capacitive sensors tend to be sensitive to temperature and moisture, especially when used with insulating materials such as glass.

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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 with Mike on this one tried all the sensors but can't beat the piezo contact sensor for a long list of reasons. Will hopefully be able to supply a ready built module in the near future.

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Simon Khoury

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

A good rundown on the different sensors is here:

[www.youtube.com]

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nebbian
A good rundown on the different sensors is here:

[www.youtube.com]

Thomas Sanladerer's review is very good as far as it goes but it omits all nozzle contact sensors. He has included no FSRs despite their popularity, no accelerometer sensors despite their appearance on some commercial 3D printers and no Piezo sensors even though every argument against Piezo sensors so far has been shown to be wrong.

Mike

Mike what would you say are the key arguments against piezo sensors?

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Simon Khoury

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

So far I have seen none that have stood up, but if we look at many claims that have been made in the past

• Claim: Piezos are not sensitive enough and will need amplification.
  Truth: Piezos put out enough voltage even to be used without any signal conditioning. See for example [www.youtube.com]
• Claim: Piezos have a high impedance and subject to electrical noise.
  Truth: A 20mm piezo can have a capacitance of 18nF and an impedance of 300Ω, both huge in electronic terms so they are a low noise source..
• Claim: Piezos are fragile.
  Truth: When installed they are very robust. They have been used drilled or milled and and still work - they even still work if cut into quarters.
• Claim: Piezos are subject to mechanical noise
  Truth: This is true but is easy to circumvent by allowing a pause between X/Y movements and probing for shaking to settle.
• Claim: Piezos become insensitive at higher temperatures
  Truth: This varies with the make but all that have been tried are satisfactory up to at least 60°C
• Claim: Piezos will trigger from a changing temperature.
  Truth: Fast changing temperatures will cause a voltage to be developed across a piezo disc but this is only seen with bad thermal insulation and/or too high an input impedance in the conditioning circuit.
• Claim: Piezos deteriorate with time.
  Truth: So far no appreciable deterioration has been seen over a period of a year. Manufacturers data sheets would seem to indicate a life of many years but this has yet to be proved or disproved.
• Claim: Using any nozzle contact detection will damages the print surface.
  Truth: With a clean nozzle heated to 240°C, a contact pressure of 20 grams at a speed of 2mm/sec, the time in contact was 16ms and no visible mark was left on Kapton, 3M blue tape or Wolfbite on glass.
• Claim: Nozzle contact methods need a high contact speed.
  Truth: Most of my investigatory work has been done at 1mm per second and my working printers use 2mm per second.

Over the years I have seen many things that bright cookies could find no fault with come to grief over something that they had not considered. Thorium nuclear reactors, NiMH batteries for electric cars, the Dot Com bubble etc., all failed for reasons that were obvious only in hindsight. I have seen many more in my professional life that are covered by NDAs. If there is any problem with Piezo discs and nozzle contact detection I am too close to see it.

If there is then any problem with Piezos that I and others have not seen, please tell us so that we may see the error of our ways - or use the new problems for target practice..

Mike

My hope is that with a turnkey solution hopefully not far away, more and more people will be able to try it, and will instantly be convinced, as almost everyone who has tried it so far has been.

These things are used widely in industry for extremely high precision sensing and motion control such as laser aiming etc.. The fact that they have not been part of 3D printing from day one is as surprising as it is short sighted, given their accuracy and extremely low cost.

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Simon Khoury

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

Quote
DjDemonD
My hope is that with a turnkey solution hopefully not far away

I think this is may be the reason Thomas didn't cover many types of sensors, he seems to concentrate on plug-n-play commercial solutions that seems to be in contrast to much of what I've seen on this site. I get the feeling that there is another group of people who either can't or don't want to tinker with the guts of their printers.

Idris

I think a lot of the youtube guys are really focused on products, rather than reprap-type stuff. Whether its because they have tie-ins to provide revenue with products, or that they are send free machines to test, which isn't going to happen with ANother reprap idea, I don't really know.

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Simon Khoury

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

I'm not pro/anti Piezo... in fact I hadn't heard of them until a couple of weeks ago. Just trying to see what is practically available.

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leadinglights
[*] Claim: Piezos become insensitive at higher temperatures
Truth: This varies with the make but all that have been tried are satisfactory up to at least 60°C[/quote]

But surely that kills their usefulness right there? For PLA, I have my glass bed heated to 70C, and for ABS 100C. How satisfactory are Piezos at those temperatures?

The piezo never comes into contact with the bed, it's really only a consideration for heated enclosures.

Idris

Ps, I do have a financial interest in the promotion of piezo sensors, I make and sell a PCB used to interface piezo sensors to a controller board.

Talking of which I have a hot end piezo sensor in a chamber which runs at around 45-50 deg c and it has performed flawlessly now for a good number of prints now.

I also have an interest in that I am working with Idris and Mike to make these sensors widely available.

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Simon Khoury

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

Quote
frankvdh
I'm not pro/anti Piezo... in fact I hadn't heard of them until a couple of weeks ago. Just trying to see what is practically available.

Quote
leadinglights
[*] Claim: Piezos become insensitive at higher temperatures
Truth: This varies with the make but all that have been tried are satisfactory up to at least 60°C\

But surely that kills their usefulness right there? For PLA, I have my glass bed heated to 70C, and for ABS 100C. How satisfactory are Piezos at those temperatures?

Since this thread was started by lukebarber who sought advise on proximity sensors I think that the discussion on piezos should be transferred to its current thread so I have answered there [forums.reprap.org]

Meanwhile I think that he has two good answers for proximity sensors between dc42's IR sensor and Thomas Sanladerer's review as well as having been introduced to Piezo disc sensors

Mike