I'm going to run this part as a separate mini-project I think, until it's working, and then integrate it back into the rest of the machine.

The idea is twofold:

1. Make a short section of Vee channel which works much more like a traditional vibratory feeder than the current 'jiggler'. By that, I mean the pieces are simply transported along, rather than subjected to significant upward impulses to try to get them to untangle and separate. That's such a useful function that I have to keep it, but this new feeder is in addition. Assuming high-frequency, small vibrations, it should be possible to transport them along a horizontal section of channel and, crucially, switching off the vibrations should cause them to stop dead in their tracks. This excellent article describes what I mean.
2. Then, fit the end of the feeder with another light sensor to detect the precise moment a piece topples off the end. The vibrator can then be temporarily switched off - just a few 100 milliseconds - to give the piece a chance to get on its way past the colour sensor, before resuming the flow.

I'm hoping this stop-start mechanism will enlarge the spacing between the pieces enough for them to be dealt with individually. Thanks to this recent HAD article, I've now learnt there's a word for this: "singulator". Nice.

So I've bought a small solenoid (the sort that is used as a simple out-in piston actuator) and I'm going to attempt driving it at a few 10's of Hz or more using PWM to see if it will work as a vibrator/driver.

Watch this space!