Roller Drive Mechanism

Many many moons ago, 444 moons ago, as a lad of 16, I worked for a summer in a food plant. One of the products was peanut butter. Apparently, for "quality" peanut butter, only roasted peanuts of a certain "doneness" are desirable. To reject peanuts that were either roasted to much or not enough, automatic peanut sorters were used.

One peanut at a time would fall through a clear glass tube. Photocells, mounted on a 360º bracket around the tube, looked at the peanuts from all sides. The photocells were connected to an electronics package, made by "Icore Acurex", this equipment would then decide if the peanut was "good or bad". If good, the peanut would fall through the glass tube to a funnel where it continued along the processing chain.

A bad one... would fall out of the tube then be blown by a jet of air into a hopper. It was really something out of a side scene from Dante's Inferno as there were peanuts literally flying everywhere... but it worked, after a fashion.

Perhaps such a system would meet your needs. I will try and find a URL.

I think this idea is worth a try.

Thanks, North of 60.

I'm usually good at visualizing alternatives for such things, but the only thing coming to me is to spin it between centers. The driving center could have a rubber tip to provide friction for spinning the item being inspected.

Thanks, pantaz.

There are a couple of problems that I foresee with this approach.

Firstly, the rollers are small - only 2.5 mm dia. Obviously they are without centers and in order to rotate them between centers I will need to use hollow (inverse) centers. Now, the rollers are not guarranteed to have a chamfer on which these hollow centers may rest. So, when we attempt to drive the rollers it may result in non-uniform motion and this will spoil the image.

Secondly, I cannot use rubber (or teflon, or any other non metallic material) to drive the rollers as any contamination of the rollers is strictly to be avoided.

I know nothing about this sort of thing so just ignore me if this is rubbish.

I think I'd try to do it with air: create a trough which is the complement of half the cylinder you're working with, and, blow in a tiny amount of air through holes which are slightly away from the bottom.

In this picture I've drawn the holes freehand at the side: I think they'd need to be a lot closer to the bottom of the trough:-

Adjusting the rate of air flow should enable you to get approximately the correct rate of rotation (of course you will never be able to adjust the speed exactly).

Thanks, Randall for an innovative solution.

However, I am not sure how effective this will be. The reason is, this arrangement may not ensure uniformity of motion of rollers which is so necessary for correctly imaging the part.