Ricoh GR-C1 Series Service Training page 139

Two coils agitate the toner/developer mixture.
If the toner density sensor detects that the density is not sufficient, the
toner supply unit adds toner from the toner bottle.
The ID sensor (below the ITB) detects the density of a standard patch that
is transferred to the ITB. This sensor is also used for toner supply control.
Slide 139
The toner supply hopper mechanism is explained later.
Mixing
139
Toner Mixing Coil
(Upper)
Toner Mixing Coil
(Lower)
Toner Density
Sensor
GR-C1 Training