How to detect a small pin

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.

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

(...)

Use light through a 0.014" aperture normal to a 0.118" gap, for a buck!

--Winston

How does one keep the lenses clean in a manufacturing environment?

I rather like the vacuum idea.

Gunner

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.

You can blow back through them as a cleaning cycle.

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

"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

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.

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

-- "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

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

For even smaller parts.

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.

Could you use a larger pin?

jsw

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?

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.

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

At least this machine in is a clean part of the plant