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?
Reply to
Buerste
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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.
Reply to
Pete C.
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
Reply to
co_farmer
(...)
Use light through a 0.014" aperture normal to a 0.118" gap, for a buck!
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--Winston
Reply to
Winston
How does one keep the lenses clean in a manufacturing environment?
I rather like the vacuum idea.
Gunner
Reply to
Gunner Asch
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.
Reply to
Larry Fishel
You can blow back through them as a cleaning cycle.
Reply to
John R. Carroll
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
Reply to
Gunner Asch
"Buerste" fired this volley in news:hubi6l$an2$1 @speranza.aioe.org:
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
Reply to
Lloyd E. Sponenburgh
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.
Reply to
Pete C.
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
Reply to
Wes
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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
Reply to
Wes
When the wire is pressed into the cup, against what to you push? The side of the pin, or the ends of the wires?
If it's the side of the pin, the pusher blade can have a shallow slot the joins two drilled holes. From one hole compressed air flows. The other hole connects to a fast-acting pressure switch of some kind. If the pin is in place while the bundle of wires is being pushed into place, there will be a fairly good seal between pin side and blade end, communicating compressed air to the pressure switch. Loose wires will not be able to seal the blade-end slot well enough.
I would think that optical and magnetic approaches would require far too much maintenance, given the typically dirty environment.
A vacuum approach would also tend to clog, but could be periodically blown clean, perhaps as part of the machine cycle. But if it does clog, pinless brushes will not be detected, so it is not fail safe.
As for my two-port-compressed-air approach, I would arrange it such that the pressure-switch port could be blown clean as well. While there is no vacuum, it will still clog from time to time. The good news is that clogging will be read as no pin present, so it's fail-safe.
Can one determine if the pin is present by accurate weighing of the completed assembly? The issue will be if the natural variation in the weight of all but the pin exceeds the weight of the pin.
Joe Gwinn
Reply to
Joseph Gwinn
For even smaller parts.
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The convergent models cast a .010" spot up to 12" away.
Reply to
Ned Simmons
Sounds like the assembly can't be released from whatever holds the wires in place until after it's determined that the pin is present. I assume that would make it difficult to weigh.
Reply to
Larry Fishel
Could you use a larger pin?
jsw
Reply to
Jim Wilkins
Without the pin in place, doesn't the ram pushing the bundle travel a longer distance? Could you measure ram travel as a check to see if the pin is there?
Reply to
Denis G.
The link below is to a reliable supplier of photo detectors which use opticat fibre about 2 mm in diameter which detect whether there is something between the ends of the fibre or not. They are pretty sensitive and rugged as the electronics are mounted up to a couple of metres away from the product detected. I've used them a lot in packaging operation with good results.
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Reply to
Grumpy
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
Reply to
Buerste
At least this machine in is a clean part of the plant
Reply to
Buerste

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