Method and apparatus for use in image forming apparatus

An image forming apparatus comprising:

• a photosensitive unit which can hold, as a latent image, a potential difference between an exposed portion thereof which is irradiated with light, and a non-exposed portion thereof which is not irradiated with light, when light has been emitted onto the photosensitive unit charged with a predetermined potential;
• a charger unit which can output a first voltage used to supply a predetermined surface potential to the photosensitive unit, and also output a second voltage differing from the first voltage;
• an exposure unit which can emit light onto the photosensitive unit supplied with the predetermined surface potential from the charger unit, the light having its intensity varied in accordance with image data;
• a developing unit including a sleeve opposed to the photosensitive unit with a predetermined space defined therebetween, the developing unit supplying the surface of the photosensitive unit with toner, thereby developing the latent image held on the photosensitive unit, the toner being formed of a resin material containing first magnetic particles, the ratio of the first magnetic particles to the resin material being predetermined, second magnetic particles, of a same material as the first magnetic particles, being attached to a surface of the toner;
• a recording-medium conveyance mechanism which can convey, to the photosensitive unit, a recording medium which can electrostatically hold the toner supplied by the developing unit to the latent image on the photosensitive unit;
• a transfer unit which can electrostatically transfer the toner supplied by the developing unit to the latent image on the photosensitive unit, onto the recording medium conveyed to the photosensitive unit by the recording-medium conveyance mechanism;
• a recording-medium discharge mechanism which can convey, to a predetermined position, the recording medium with the toner electrostatically transferred by the transfer unit from the photosensitive unit;
• a developing-bias-voltage supply unit which can supply the sleeve of the developing unit with a third voltage that differs by a predetermined potential from the first voltage applied to the photosensitive unit by the charger unit;
• a voltage control circuit which can change a voltage, applied by the charger unit to the photosensitive unit, from the first voltage to the second voltage for a predetermined time period in which no toner is electrostatically transferred by the transfer unit onto the recording medium conveyed by the recording-medium conveyance mechanism, so as to set a difference between the second voltage and the third voltage applied to the sleeve of the developing unit by the developing-bias-voltage supply unit, larger than a difference between the first and third voltages;
• and
• a collecting unit which can collect the second magnetic particles separated from the toner and existing on the photosensitive unit.

An image forming method of supplying a visualizing agent onto a latent image to form an image, comprising:

• forming a latent image on an optical semiconductor by emitting light selected portions of the optical semiconductor with a predetermined potential applied to the optical semiconductor;
• supplying toner to the latent image formed on the optical semiconductor, while applying a predetermined bias voltage to the optical semiconductor;
• and
• collecting, in a predetermined time period in which a recording medium does not exist in a transfer region defined between the optical semiconductor and a transfer unit, other than when the toner is being transferred onto the recording medium, magnetic particles separated from the toner attached to the optical semiconductor, into a predetermined collecting section, by increasing the potential of the optical semiconductor, so as to set a difference between the developing bias voltage and the potential of the optical semiconductor larger than a difference therebetween assumed when the toner is being transferred onto the recording medium.