Developer apparatus having toner concentration control

A developer apparatus comprising:

• a developer unit having agitating means for agitating a developer containing a magnetic carrier and a non-magnetic toner;
• a toner concentration sensor which detects a toner concentration in the developer unit;
• toner replenishing means for replenishing the toner into the developer unit according to an output of the toner concentration sensor;
• and
• controlling means for controlling the agitating means so as to conduct an initial agitation of the developer when power is provided to the developer apparatus so as to turn the developer apparatus on and for periodically agitating the developer subsequent to the initial agitation of the developer;
• and said controlling means further comprising means for, when copying is performed during agitation, increasing the reference level from a predetermined value and then stepwisely returning the reference value to the predetermined value.

A developer apparatus comprising:

• a developer unit having agitating means for agitating a developer containing a magnetic carrier and a non-magnetic toner and said developer unit further comprising means for supplying toner to an electrostatic latent image support so as to form a toner image on said support;
• transfer means for transferring the toner image on said support to a substrate;
• a toner concentration sensor which detects a toner concentration in the developer unit;
• toner replenishing means for replenishing the toner into the developer unit according to an output of the toner concentration sensor;
• controlling means for controlling the agitating means so as to conduct an initial agitation of the developer when power is first provided to said developer apparatus, said controlling means including timer means for determining predetermined time intervals following completion of said initial agitation, and said controlling means, upon said timer means determining one of said predetermined time intervals has passed without said means for transferring being active, again activating said agitating means so as to avoid an inaccurate reading by said toner concentration sensor due to a reduction in volume of the developer which can occur due to non-operation of said agitating means over a period of time.