How to detect a small pin

I make 1/2", 3/4" and 1" solid wire fill end brushes that typically fit into die grinders that spin up to 20k RPM. The wire in folded in half around a
steel pin then pressed into a steel cup. The cup is then crimped. This all takes place in a few seconds. The operator starts by placing a pin into a slot, a bundle of wire into a jig and a cup into a holder. After pressing two palm switches, the operation is automatic. Two hydraulic cylinders do all the work.
The 3/4" and the 1" have a microswitch that detects a pin in the slot and prevents the machine from cycling. On the 1/2", the pin is so small that the microswitch detect system doesn't work very well, the pin is too small. (1/2" x 3/32")
we're rethinking how to detect the pin better. Can we get a laser/photocell or something similar that will "see" this small of a part?
If a brush gets made without a pin it will immediately eject the wire in a poof...NOT GOOD! The wire doesn't have a lot of mass and the tool's not up to speed yet so it's not extremely dangerous if you've got eye protection...who doesn't when using power brushes?
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Buerste wrote:

There are tons of optical sensors available that could do the job. Check the Digi-Key catalog for many examples. In particular look at the Omron modules that include signal conditioning, so they just need power and output a logic signal. The issue you might have with these would be dirt / debris buildup causing false positive detection.
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Some questions: At what point in the operation are you currently doing the pin detection? When the operator puts the pin into the slot, or later when the bundle of wires is wrapped around the pin? Are you relying on the weight of the pin to activate a microswitch, or the when the machine tries to use the pin and there is nothing there?
Perhaps one detection method would be to make the bottom of the pin slot reflective and shine a light into the slot. Have a detector look for the light at the beginning of the cycle. No light, pin is there, reflected light, no pin. A similar scheme might require a hole smaller than the pin, going across the bottom of the slot and look for light or no light at the beginning of a cycle.
Some type of magnetic sensor might work, but since hydraulics are involved, the pin slot is probably in steel.
Another possibility would be to use a vacuum with a tiny hole at the bottom of the slot to detect the pin presence. If low vacuum, no pin. If high vacuum, there is a pin closing the tiny hole. Some experimentation and valving may be necessary. Plus a vacuum detection switch.
Probably other methods, but those are the ones I would start with. The vacuum is probably the most rugged as well as the quickest to implement.
Paul
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Some questions: At what point in the operation are you currently doing the pin detection? When the operator puts the pin into the slot, or later when the bundle of wires is wrapped around the pin? ************************ The microswitch in in the pin slot ************************
Are you relying on the weight of the pin to activate a microswitch, ************************** Yes
or the when the machine tries to use the pin and there is nothing there? ******************************* and, yes
Perhaps one detection method would be to make the bottom of the pin slot reflective and shine a light into the slot. Have a detector look for the light at the beginning of the cycle. No light, pin is there, reflected light, no pin. A similar scheme might require a hole smaller than the pin, going across the bottom of the slot and look for light or no light at the beginning of a cycle.
Some type of magnetic sensor might work, but since hydraulics are involved, the pin slot is probably in steel.
Another possibility would be to use a vacuum with a tiny hole at the bottom of the slot to detect the pin presence. If low vacuum, no pin. If high vacuum, there is a pin closing the tiny hole. Some experimentation and valving may be necessary. Plus a vacuum detection switch. ****************************** Hmmmmm!
Probably other methods, but those are the ones I would start with. The vacuum is probably the most rugged as well as the quickest to implement.
Paul
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On 6/4/2010 11:55 AM, Buerste wrote:
(...)

Use light through a 0.014" aperture normal to a 0.118" gap, for a buck!
http://www.simplemotor.com/images/optointerrupter2.gif
http://www.allelectronics.com/make-a-store/item/OSU-58/OPTO-INTERRUPTER-SWITCH/1.html http://www.fairchildsemi.com/collateral/infrared_psg.pdf#page3
--Winston
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wrote:

How does one keep the lenses clean in a manufacturing environment?
I rather like the vacuum idea.
Gunner
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Wouldn't a vacuum sensor tend to actively suck debris into the tiny hole giving false positives also?
Assuming this is an unpainted steel pin, how about two spring-loaded brass contacts (one at/near the bottom of the hole) and test for continuity? They would be essentially self cleaning, but would wear out periodically.
Just a thought.
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Larry Fishel wrote:

You can blow back through them as a cleaning cycle.
--
John R. Carroll



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On Fri, 4 Jun 2010 14:52:36 -0700 (PDT), Larry Fishel

Not if one used a very small brass filter over the suction port. Or made a cleaner basin just inside the port and use a large port.

Thats good too!
Gunner
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wrote:

Wouldn't a vacuum sensor tend to actively suck debris into the tiny hole giving false positives also?
Assuming this is an unpainted steel pin, how about two spring-loaded brass contacts (one at/near the bottom of the hole) and test for continuity? They would be essentially self cleaning, but would wear out periodically.
Just a thought.
I LIKE IT!
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At least this machine in is a clean part of the plant
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On 6/4/2010 9:35 PM, Buerste wrote:

(...)
OK then, how about a mini inductive prox sensor?
http://www.omron247.com/marcom/pdfcatal.nsf/4772377C87AB017986256B05005069D0 /$FILE/D06E2EC1101.pdf
Parametric Search: <http://omrwsc.am.omron.com/webapp/wcs/stores/servlet/ProductExplore?catalogId 001&storeId001&categoryId704&langId=-1>
--Winston
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They can get quite dirty before they stop working. We had optical with small incandesant lights in card and check sorters in the 1960's. Ran for a week with no errors and only a vacuum of the transport couple times a week. Check reader ran 100's of checks a minute. Card reader ran 1000 a minute. Make the lens and light big enough and the light will make it.
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Boy does that date you and me, also. The lights you mention usually had bulbs that were flat on the tip and that tip was actually in and part of the flight path of the card or check. The paper cleaned the bulb as it went past the bulb. On Burroughs equipment they were called BOLs, Beam of light. Don't remember what they were called on IBM equipment.
Then before light there were the wire brushes that would make electrical contact with a drum when a hole in a punched card was being read.
I programmed for the IBM 1419 check reader/sorter on IBM 360 model 30, then moved to a company with Burroughs medium systems check readers. Then to Burroughs/Unisys check reader/sorters that were controlled by Motorola 68005, 68010, and 68030 microprocessors. By then the checks were being read at 1,000 or 1800 documents per minute and from 4 pockets to 48 pockets.
Retired from all that in 1997, so don't know what they are doing, now.
Paul
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wrote:

I worked my way through college (EE degree) working on mainframe 315 systems for NCR corp. Then the Century 100 systems. Was a hardware guy who did some programming. Ended up designing embedded systems. Hardware and software. Disk controllers for System Industries (DEC) and disk drives for Maxtor and apps engineer on disk drives for TI and programming DSP's for TI and contract jobs. then retired after a Biomed employer screwed up. 8 years ago. Funny that I ended up as an EE was going to either be an ME or geologist as a kid. Dad owned one of the larger machine shops in the East side of the SF Bay area.
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How about just having the pin bear on two electrical contacts. Conductance means "present".
If the contacts bear on the ends of the pin, normal wiping, even in a dirty environment, will make the connection reliable over time. If they're made of some fairly thick beryllium bronze, they'll also hold up to friction well.
LLoyd
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"Lloyd E. Sponenburgh" wrote:

I like this idea for a crud resistant solution. I would add a nice little rare earth magnet (presuming the pin isn't stainless) to add a bit of pull for more reliable contact.
On the other side of things, the vacuum idea is sort of there, but I'd change it to pressure. A low pressure, low volume air exhaust and a pressure sensor to measure the back pressure when the pin is in place. The same magnet idea could help ensure the pin sits in place, and the positive pressure should keep crud out.
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

I like this idea the best, I only have to have one insulated contact where the limit switch is and the machine as the other.
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Heck yes. Banner Engineering has sender emitter pairs that use a laser to sense. We use them to look for small orings. Fairly cheap too.
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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http://www.bannerengineering.com/en-US/products/8/Sensors/38/Laser-Sensors/142/WORLD-BEAM-QS18-Laser-Series /
Wes -- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
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