Sensor to detect metal objects moving through a funnel

[maxandy]

I'm looking for a sensor that will detect when hardware such as bolts, washers, screws have been dropped into a funnel. The application is packaging. Workers are loading parts bags by dropping the parts through a funnel into a parts bag which gets sealed and becomes part of the package that is shipped to customers. This is a small start up operation. Sometimes the workers forget if they dropped the parts into the bag. The bags are not easily viewable from their(workers) position. I would like to light an LED that is attached to each individual funnel if the worker dropped the hardware into the bag. The funnels are plastic(like an automotive funnel for adding oil). Any thoughts? Thanks.....

[blnkjns]

Do the items contain iron? Then a hall-effect sensor is your friend, as iron has influence on a electro-magnetic field.
Other thing that is always nice to check is high-accuracy weight measurement as the items you state are having a tiny spread in mass. A friend has a small screw-webshop and he uses weight to see if an order is complete.

[maxandy]

Thank you for your quick response. I will experiment with the hall and see what I get. Regards......

[adafruit_support_mike]

Weight is an excellent go/no-go test for part bags. You only have to double-check the bags whose final weight is out of tolerance from the nominal value.

Pocket boards are also a big help if the parts are the right shapes to cooperate.. washers would be a good example: if you need 5 washers, cut 5 circular pockets wide enough to hold one washer each, and slightly shallower than the thickness of the washers. The idea is that you can dip the board into a bin of washers and shake it a couple of times, then pull it out with washers in all five pockets. You can do the same thing with screws and bolts, just use slots instead of circular pockets.

It takes a bit of trial and error to find the pocket shape and depth that works best. You want parts to fall in the pocket easily when you pour a handful of loose parts across the board, but you want parts that drop halfway into a pocket to go all the way in or all the way out when you shake the board.

A further improvement would be to make a tray that holds a 4x5 array of five-washer pocket boards. Then you can count 100 parts in a few seconds, and pull individual five-washer sets as you need them. Set the empty pocket boards in another 4x5 tray, and they're ready to refill as soon as the last one is dumped.

Using partitioned containers anywhere you need to count things is an industrial best practice. It's easy for people to make mistakes when counting, but anyone can tell if a 20x20 tray is full at a glance. The cost of making the containers pays for itself quickly in speed and reduction in verification/rework.

[maxandy]

Thanks Mike. I'll add weight detection to my testing.