In an image forming apparatus, when a first sheet and a second sheet are subjected to printing and the second sheet is being conveyed at a particular timing after a sheet sensor detected passage of a trailing end of the first sheet, and when a sheet interval between the first sheet and the second sheet is equal to or greater than a particular threshold interval, a controller positions first and second developing rollers to first and second separated positions, respectively, after developing of images to be transferred onto the first sheet has been completed, positions the developing rollers to be used for printing on the second sheet to respective contact positions, and starts developing images to be transferred on the second sheet. The controller is further configured to perform a color printing using both the first and second developing rollers, and a monochromatic printing using only the second developing roller.

An image forming apparatus, having first, second, third, and fourth photosensitive drums, first, second, third, and fourth developing rollers, a development-driving gear, a development motor, a first development gear train having a first gear, a second development-gear train having a second gear, a process-driving gear, a process motor, a first process-gear train having a third gear, and a second process gear-train having a fourth gear, is provided. The first development-gear train transmits a driving force from the development motor to the first and second developing rollers. The second development-gear train transmits the driving force from the development motor to the third and fourth developing rollers. The first process-gear train transmits a driving force from the process motor to the first and second photosensitive drums. The second process-gear train transmits the driving force from the process motor to the third and fourth photosensitive drums.

An image forming apparatus, having a first photosensitive drum, a second photosensitive drum, a first developing roller, a second developing roller, a first moving mechanism, a second moving mechanism, a driving gear, a motor, a first gear train, a second gear train, and a third gear train, is provided. The first gear train having a first gear transmits a driving force from the motor to the first developing roller. The second gear train having a second gear transmits the driving force from the motor to the second developing roller. The second gear train is provided separately from the first gear train. The third gear train having a third gear transmits the driving force from the motor to at least one of the first moving mechanism and the second moving mechanism. The third gear train is provided separately from the first gear train and the second gear train.

An image forming apparatus, having a first developing roller, a second developing roller, a third developing roller, a fourth developing roller, a first photosensitive drum, a second photosensitive drum, a third photosensitive drum, a fourth photosensitive drum, a motor, a first output gear, a first gear train, and a second gear train, is provided. The first output gear is arranged coaxially with the motor and outputs a driving force from the motor. The first gear train includes a first intermediate gear meshing with the first output gear and transmits the driving force from the motor through the first output gear to the first, second, third, and fourth developing rollers. The second gear train includes a second intermediate gear meshing with the first output gear and transmits the driving force from the motor through the first output gear to the first, second, third, and fourth photosensitive drums.

A drum unit includes a photosensitive drum, a developing unit, a toner cartridge, a connector and a relay board. The photosensitive drum is rotatable about a first axis extending in an axial direction. The developing unit includes a magnetic roller, a developer container, a conveyer member and a toner sensor. The developer container accommodate therein carrier, and has an inlet. The conveyer member is positioned in the developer container, and configured to convey the toner and the carrier from the inlet toward the magnetic roller. The toner cartridge accommodate therein toner and is attachable to the developer container to replenish the toner in the developer container through the inlet. The connector is electrically connected to the image forming apparatus. The relay board electrically connects the toner sensor to the connector. The relay board is configured to transmit a detection signal from the toner sensor to the image forming apparatus.

A printing apparatus includes: plural image forming units accommodating colorants of the same color; and a controller that forms an image of one color using the plural image forming units.

In response to determining that image forming in a color mode is performed on a first sheet and then image forming in a monochrome mode is successively performed on the second sheet, perform charging bias reduction processing gradually reducing a charging bias from first to second charging bias and developing bias reduction processing of gradually reducing a developing bias from first to second developing bias during a first inter-sheet period after the first sheet passes a first photosensitive drum and before the second sheet reaches the first photosensitive drum, and perform separation processing such that an execution period of the separation processing overlaps at least one of an execution period of the charging bias reduction processing and an execution period of the developing bias reduction processing, the separation processing being processing of controlling a moving mechanism to move a first developing roller from a contact position to a separation position.

A method of converting a CMYK toner printer to print with a white toner, comprising the steps: providing a CMYK toner printer; wherein the toner printer has four printing cartridges; wherein the four printing cartridges comprise a black toner printing cartridge, a cyan toner printing cartridge, a magenta toner printing cartridge, and a yellow toner printing cartridge; removing the black toner printing cartridge from the toner printer, such that there is an empty toner cartridge slot; providing a white toner printing cartridge that is filled with a white toner; installing the white toner printing cartridge into the empty toner cartridge slot; and providing raster image processor (RIP) software, such that the printer is able to incorporate the white toner into one or more images printed by the printer.

A method of converting a CMYW toner printer to a CMYK printer that prints with black toner, comprising the steps: providing a CMYW toner printer; wherein the CMYW toner printer has four starting toner printing cartridges; wherein the four starting toner printing cartridges comprise a white toner printing cartridge, a cyan toner printing cartridge, a magenta toner printing cartridge, and a yellow toner printing cartridge; removing one or more of the four starting toner printing cartridges from the CMYW toner printer, such that there are one or more empty toner cartridge slots; providing a black toner printing cartridge that are each filled with black toner; and installing the black toner printing cartridge into the one or more empty toner cartridge slots.

In an image forming apparatus, when a first sheet and a second sheet are subjected to printing and the second sheet is being conveyed at a particular timing after a sheet sensor detected passage of a trailing end of the first sheet, and when a sheet interval between the first sheet and the second sheet is equal to or greater than a particular threshold interval, a controller positions first and second developing rollers to first and second separated positions, respectively, after developing of images to be transferred onto the first sheet has been completed, positions the developing rollers to be used for printing on the second sheet to respective contact positions, and starts developing images to be transferred on the second sheet. The controller is further configured to perform a color printing using both the first and second developing rollers, and a monochromatic printing using only the second developing roller.