Mechanics Mechanisms for Conveyors

I am interesting to know about the mechanics mechanisms that use the conveyors in products lines automations systems.

I am interesting to know more about "span" roller (I am not sure that I wrote "span" correct, I think that this mechanics mechanism have a wheel that stretched) and about roller drive systems, and about others mechanics mechanisms for conveyors and I am interesting to know the different between these different kinds of mechanics mechanisms for conveyors.

I will glad to receive some relevant links.