Image forming apparatus operable in monochrome and color printing modes

An image forming apparatus operable in a plurality of operation modes including a monochrome printing mode and a color printing mode, the image forming apparatus comprising:

• a first photoconductor drum for use at least in the monochrome printing mode;
• a plurality of second photoconductor drums for use in the color printing mode;
• a plurality of development rollers disposed in positions corresponding to the first and second photoconductor drums, each of the development rollers being configured to be in contact with and supply a corresponding photoconductor drum with developer and operative to collect developer remaining on the corresponding photoconductor drum in contact therewith during an operation thereof;
• a plurality of chargers disposed in positions corresponding to the first and second photoconductor drums to electrically charge surfaces of the photoconductor drums;
• a separation mechanism configured to cause development rollers corresponding to the second photoconductor drums to move away from the corresponding second photoconductor drums and to come back to the positions in which the development rollers are in contact with the corresponding second photoconductor drums;
• a plurality of transfer members disposed in positions corresponding to the first and second photoconductor drums to transfer the developer from surfaces of the photoconductor drums to a medium being transported, wherein the second photoconductor drums are located downstream of the first photoconductor drum in a direction of transport of the medium;
• and
• a controller comprising:
• a separation mechanism control unit configured to exercise control over the separation mechanism such that the development rollers corresponding to the second photoconductor drums are away from the corresponding second photoconductor drums in the monochrome printing mode,
• a developing bias regulator configured to regulate a developing bias for each of the development rollers in such a manner that an absolute value of a developing bias voltage applied to a development roller corresponding to the first photoconductor drum in the monochrome printing mode is smaller than that applied in the color printing mode, and
• a photoconductor potential regulator configured to regulate a surface potential of each of the photoconductor drums by controlling a corresponding charger in such a manner that an absolute value of the surface potential of the first photoconductor drum in the monochrome printing mode is smaller than that in the color printing mode.