Close proximiy sensor

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Klemko
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Posted by Klemko: Sun. Nov 5, 2017 - 08:42 AM
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Hello,

 

currently i am planning a PCB that would detect objects at near proximity. The distance from sensor to object is 10mm to 20mm. Also the objects are 20mm wide and 5mm apart. So i plan to make around 25cm long PCB, whit sensors placed 25mm apart, so i will detect if there is an object at that slot or not. The object positioning is +/-few mm, so the question if i am detecting object center or edge is not really that important, i jsut ned to know if there is someting in front of that sensor. And also the sensors must be cheap as possible, since i need 340 sensor PCB (so around 3400 sensors) just for first from first costumer.

 

Originally i was planning to go whit LDR (or another kind of ambient light sensor whit analog/linear output), since the sensor PCB is gonna be placed in a well litt room and the MCU on main pcb would just take the value of the LDR in "direct line of light" as limit and anything under that would be treated as object detection. But then there could be other obstacles or humans in front the reference sensors and a lot of other problems.

 

So then i started lookign at IR photo detectors and found some nice whit emmitor and receiver in 1 small SMD package, but the price of those is around 3€ to 5€, 2x time or more of LDR or similar solution. But they do seem as a better and more professional solution, since they rely on the light that they emitt themself. 

 

So what i am asking the community is if you guys and girls know for any sort or even particular type of sensor that would fit perfectly in my PPCB. So to recap, the sensor needs to have sensing range of 5mm to 20mm(can be max 150mm), sensor package needs to be smaller then 1cm hegiht(width doesnt matter) and it would be great if at 1000 units, the price for one would be under 1€.

 

Just for exmple, this is my favorite at the moment: http://si.farnell.com/broadcom-l...

 

 

Thanks in advance :D

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Last Edited: Tue. Nov 7, 2017 - 08:42 PM
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Kartman
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Posted by Kartman: Sun. Nov 5, 2017 - 10:23 AM
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Something like this?
http://www.st.com/en/imaging-and-photonics-solutions/proximity-sensors.html?querycriteria=productId=SC1934

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valusoft
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Posted by valusoft: Sun. Nov 5, 2017 - 10:39 AM
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Klemko.

 

I guess that you realise that you also have to sense the gap between two objects because at 20mm wide with a spacing of only 5mm between each, a single object will  be sensed as being in two adjacent "slots".

 

ps... and you haven't said how quickly the objects are moving through each "slot". Your sensors, including the gap sensor, need to be fast enough.

Ross McKenzie ValuSoft Melbourne Australia

Last Edited: Sun. Nov 5, 2017 - 10:42 AM
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sparrow2
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Posted by sparrow2: Sun. Nov 5, 2017 - 11:09 AM
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I would look into separate LED and photo diodes, and then either use a 3D printer to make light guides, or drill small holes in a plate.

If you have a good back light then perhaps you don't need the LEDs.

 

once I made a similar thing 120cm long with 64 diodes, each having a 2 cm long black pipe glues to it. The light was a florescent tube, (it had to be controlled otherwise the diodes would react on the 100Hz flashing ) placed on the other side about 50 cm away. It was used as a line scanning camera for a automatic window frame painting machine.    

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Scroungre
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Posted by Scroungre: Sun. Nov 5, 2017 - 02:24 PM
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Dunno how you feel about the analog side, but here's a suggestion I've seen in many light-sensing devices: 

 

Switch the light at a fairly high frequency (20kHz or so) and then, on the detector side, put in an analog bandpass filter that only passes your frequency.  This gets rid of any ambient light level issues (dc goes away...) and quite a lot of other noise.

 

Strongly recommended.  S.

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DocJC
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Posted by DocJC: Sun. Nov 5, 2017 - 06:21 PM
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I interpret the description to be something like the diagram below.

 

You mention needing to know "if there is something in front of that sensor", and yet with your suggested 25 mm sensor spacing you could easily have an object "in the middle", and not be able to detect that one is present.

 

Questions:

What do you need to detect?

The presence of an object, or its position on the line?

 

Knowing that an object is present is different than detecting its edge, (the "exact" location of the object.

 

What are the characteristics of a "missing object"?

Are the other objects still located within their "slot", or is the start of the next series of objects now "reset"?

 

Are the objects reflective?

 

What is the line speed?

 

What is the "mission criticality", i.e. how important is it to not miss an object?

 

As already mentioned, a "tube" to "aim" the photodiode receiver's vision will likely be very important, to help decrease ambient light, and increase the sensor's Signal to Noise ratio.

 

If this was mission critical, I'd use a laser diode and a photodiode  receiver for the sensor unit.

It is then trivial to "see" the 5 mm wide gaps, at about any speed the line might run at.

 

A more detailed description of the purpose (spec) would be helpful.

I assume the customer has 340 parallel running production lines, and that you are not placing 340 sensors along one line?

If you detect the presence / absence of the object at the "start" of the line, then clearly you know about the portion of the line that has already passed, particularly if yo also monitor the line's speed, (and hence distance traveled).

 

Low powered laser diodes are cheap these days, and obviously very precise in their aiming and field of view, compared to sensing ambient light, or an IR pair, or ultrasound, etc.

 

If "edge detection" wasn't important, a cheap ultrasound module could tell you when an object is in front of it, or not... as another possibility to be considered.

 

JC

 

 

 

Last Edited: Sun. Nov 5, 2017 - 06:25 PM
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js
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Posted by js: Sun. Nov 5, 2017 - 09:11 PM
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I have used a few of these in a project https://www.pololu.com/search?qu...

 

Of course one can just get the Sharp sensor on one's PCB but for my project I used the ones shown and just plugged them into, long skinny boards.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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avrcandies
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Posted by avrcandies: Sun. Nov 5, 2017 - 10:30 PM
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detect if there is an object at that slot or not

What if an object came along that was only 10mm wide, or 57mm wide---what should happen?  Should those objects be counted, flagged as an error, sound an alarm...etc.

Or is it not possible for a different size object to ever appear?  Saying that will never happen is a very dangerous maneuver, and such thoughts often lead to later catastrophe. 

 

What are ALL of your rules of detection?

When in the dark remember-the future looks brighter than ever.

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Klemko
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Posted by Klemko: Mon. Nov 6, 2017 - 08:23 AM
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The objects speed is variable but is relatively slow (max 10cm/second) and the accuracy i need is very low. Below is drawing of configuration. The Kartmans solution looks liek an interesting one. I will contact suppliers to give me prices for 2, 5 and 10k amounts. Objest that i detect are black coloured metal brackets. 

Diagram

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avrcandies
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Posted by avrcandies: Mon. Nov 6, 2017 - 02:48 PM
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What if an object came along that was only 10mm wide, or 57mm wide---what should happen?  Should those objects be counted, flagged as an error, sound an alarm...etc.

Or is it not possible for a different size object to ever appear?  Saying that will never happen is a very dangerous maneuver, and such thoughts often lead to later catastrophe. 

When in the dark remember-the future looks brighter than ever.

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Klemko
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Posted by Klemko: Tue. Nov 7, 2017 - 07:44 AM (Reply to #10)
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It will never happen since these object are welded to a bar and are the same 10 or 20 objects moving left or right. Its not like i am sensing objects on a conveyour belt or someting like that. :D 

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valusoft
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Posted by valusoft: Tue. Nov 7, 2017 - 08:34 AM
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Well it seems to me that this additional information changes everything! Time wasting...

 

Ross McKenzie ValuSoft Melbourne Australia

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Klemko
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Posted by Klemko: Tue. Nov 7, 2017 - 08:44 AM (Reply to #12)
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Yea, actualy the only thing i have to get is the time it takes for the object to move from one to another sensor. And since the distance beetwen them is almsot fixed (they have move 2mm left or right on the bar), i can still calculate the movement speed ora ccelerating/decelerating whit pretty high accuracy on this low speeds. An the second thing i have to detect is how many objects are stationary and how many are moving.

Last Edited: Tue. Nov 7, 2017 - 08:45 AM
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avrcandies
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Posted by avrcandies: Tue. Nov 7, 2017 - 08:55 AM
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Start over with a complete description---you seem to be spewing a collection of random garbage

 

An the second thing i have to detect is how many objects are stationary and how many are moving.

...It will never happen since these object are welded to a bar      ...THEN  HOW CAN SOME BE MOVING WHILE OTHERS ARE NOT

 

Its not like i am sensing objects on a conveyour belt or someting like that ..WHAT ARE YOU DOING

When in the dark remember-the future looks brighter than ever.

Last Edited: Tue. Nov 7, 2017 - 09:05 AM
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sparrow2
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Posted by sparrow2: Tue. Nov 7, 2017 - 09:36 AM
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Perhaps look into using hall sensors, it sounds like you have room for some magnets on some small spring loaded "fingers".

 

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Klemko
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Posted by Klemko: Tue. Nov 7, 2017 - 05:22 PM (Reply to #14)
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There is a metal bar, whit 20 iron brackets on it. The brackets can move left or right individually. I did think about gluing some magnets onto the brackets, but the sensors must work whithout interfering whit the brackets or changin them. I will order few prototype PCBs that will support 4 types of sensors (2x ir reflective, 1 ambient and 1 LDR) and jsut try them all. 

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avrcandies
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Posted by avrcandies: Tue. Nov 7, 2017 - 05:45 PM
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The brackets can move left or right individually

How, you said they are welded to a bar---so they will move together??, or is it magnetic?

 

...It will never happen since these object are welded to a bar       

When in the dark remember-the future looks brighter than ever.

Last Edited: Tue. Nov 7, 2017 - 05:47 PM
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Klemko
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Posted by Klemko: Tue. Nov 7, 2017 - 06:02 PM (Reply to #17)
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Each bracket has hole in the middle, bar goes throught. The bar is welded shut on both ends, so no brackets can fall off and nothing else can get added, but they can move individually. There are also thin aprox. 2mm wide spacers/rubber dampers beetwen each bracket. Sorry for bad explanation in original post.

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avrcandies
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Posted by avrcandies: Tue. Nov 7, 2017 - 06:47 PM
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You can use a hall effect sensor chip (low cost) to detect metal, using a "reflected" magnet approach....I think some chips might combine both (not sure)...then dirt & light & people have no effect.  The distance must be up close.

 

look up gear tooth sensor (the non magnetized tooth type, reluctance) 

 

 

 

look here to see how the metal object distorts the magnet's field to light the LED

http://hades.mech.northwestern.edu/index.php/Hall_Effect_Sensor

 

 

 

When in the dark remember-the future looks brighter than ever.

Last Edited: Tue. Nov 7, 2017 - 06:58 PM
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Klemko
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Posted by Klemko: Tue. Nov 7, 2017 - 08:43 PM (Reply to #19)
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Thaaanks a looot, this solution seams perfect. Did not know i can use hall sensor on ferromagnetic materials whithout mounating an actual magnet on the object itself. I will sure test this out. Thank again :D

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Kartman
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Posted by Kartman: Tue. Nov 7, 2017 - 09:21 PM
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If this is an industrial application, then use industrial sensors. Google prox sensors. They are usually inductive or capacitive. Don’t waste your time reinventing the wheel.

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avrcandies
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Posted by avrcandies: Wed. Nov 8, 2017 - 12:44 AM
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Don’t waste your time reinventing the wheel

The Flintstones said the same thing angel

 

When in the dark remember-the future looks brighter than ever.

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Klemko
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Posted by Klemko: Wed. Nov 8, 2017 - 09:02 AM
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Thanks again to all for help :D

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