Developing apparatus using non-magnetic mono-component toner and method of adding toner to same

A developing apparatus comprising:

• an image receptor;
• and
• a developing unit having a developing roller facing the image receptor, and
• two or more agitators disposed in the developing unit to agitate and transfer toner inside of the developing unit to the developing roller,
• wherein toner can be added when existing toner in the developing unit is consumed;
• and
• wherein the existing and added toners comprise cores and external additives, and at least one of the cores or the external additives of the added toner is different than those of the existing toner, and the volume mean diameters of the existing and added toners are in the range of 4 to 12 μm;
• and
• charge amounts of the existing and added toners are Q1 and Q2, respectively, and the ratio Q1/Q2 is in the range of 0.6 to 1.7, and the absolute values of Q1 and Q2 are 10 μC/g or greater, respectively.

A developing apparatus comprising:

• an image receptor;
• and
• a developing unit having a developing roller facing the image receptor, and
• two or more agitators disposed in the developing unit to agitate and transfer toner inside of the developing unit to the developing roller, wherein
• toner can be added when existing toner in the developing unit is consumed,
• the existing and added toners comprise cores and external additives, and the cores of the added toner are different from the cores of the existing toner, and
• the volume mean diameters of the existing and added toners are in the range of 4 to 12 μm, the difference in the volume mean diameters of the existing and added toners are within 1.5 μm, and the difference in the percentages of the particles having a diameter of 5 μm or less is 15 % or less numerically.