Image forming apparatus with developing roller cleaning capability

An image forming apparatus comprising:

• a photosensitive member having a surface on which a latent image is formable;
• a developing roller having a surface on which toner is held, the toner being made of a single-component non-magnetic material;
• a toner supply roller that is disposed in contact with the developing roller, the toner supply roller being configured to supply the toner to the developing roller in a developing mode wherein the developing roller develops the latent image with the toner held on the developing roller, the toner supply roller being configured to remove the toner from the developing roller in a toner cleaning mode wherein the toner supply roller removes the toner held on the developing roller;
• a charging member configured to charge the toner held on the developing roller to a first polarity;
• a bias circuit configured to apply bias voltages to the developing roller, the toner supply roller, and the charging member;
• and
• a controller configured to control the bias circuit to produce the bias voltages such that a potential difference between the charging member and the toner supply roller is greater than a potential difference between the developing roller and the toner supply roller in the toner cleaning mode, such that a potential difference between the developing roller and the toner supply roller in the cleaning mode is greater than a potential difference between the developing roller and the toner supply roller in the developing mode, and that a potential difference between the charging member and the toner supply roller in the cleaning mode is greater than a potential difference between the charging roller and the toner supply roller in the developing mode.