The sub hopper contains 4 transport coils [A] (larger x 2, smaller x 2)
The larger coils agitate toner and the smaller coils transport toner to the downstream part of the sub hopper.
The downstream part of the sub hopper is a toner transport path for supplying the development unit with toner.
If the toner end sensor [C] in the sub hopper detects a toner shortage in the hopper, the toner cartridge supplies toner to the sub hopper.
The 4 transport coils [A] are driven by the sub hopper motor [B] via the gears.