Mixing device for blending a developer consisting of carrier particles and toner

Claim 1

Apparatus for mixing carrier and toner particles of a developer mix in a developer station housing divided by a partition wall into a principal chamber, containing a main body of developer mix on housing floor and at least one rotatable developer drum for carrying developer mix into contact with a charge image carrier surface, and a mixing chamber, communicating at a first end through an opening in said partition wall with said principal chamber and receiving a supply of fresh toner particles through feed means in an opposed second end, comprising; a first screw mounted for rotation in said principal chamber on the floor of said housing along the length of said developer drum for conducting developer mix from the first end of said mixing chamber toward the second end, a second screw mounted for rotation in said mixing chamber for conducting fresh toner particles from the second end of said mixing chamber to the first end for passage into said principal chamber through said partition wall opening, and a flow means disposed in said housing between said developer drum and said mixing chamber for conducting only that portion of the developer mix carried by said developer drum adjacent the mixing chamber second end into said mixing chamber second end for blending with the fresh toner particles, such that the major portion of the developer mix carried by said developer drum is spilled back directly into said principal chamber and said first screw serves to convey the spilled back mix progressively along the length of said developer drum for pick up by the developer drum adjacent the second end of said mixing chamber.