Image forming apparatus and method of controlling developing unit thereof

A controlling method of a developing unit comprising a photoconductive medium, first to fourth developing apparatuses each comprising a developing roller mounted near the photoconductive medium to adhere toner to an electrostatic latent image formed on the photoconductive medium, a toner supply part, and a supplying roller to supply the toner to the respective developing roller through the toner supply part, the toner supply part being formed between the developing roller and the supplying roller, the controlling method comprising:

• adhering the toner of the first developing apparatus to the electrostatic latent image of the photoconductive medium, comprising applying a first bias voltage to cause a potential difference between the first developing roller and the first supplying roller;
• collecting the toner of the first developing roller comprising applying a first reverse bias voltage to the first supplying roller;
• adhering the toner of the second developing apparatus to the electrostatic latent image of the photoconductive medium by applying a second bias voltage to cause a potential difference between the second developing roller and the second supplying roller;
• collecting the toner of the second developing roller comprising applying a second reverse bias voltage to the second supplying roller;
• adhering the toner of the third developing apparatus to the electrostatic latent image of the photoconductive medium, comprising applying a third bias voltage to cause a potential difference between the third developing roller and the third supplying roller;
• collecting the toner of the third developing roller comprising applying a third reverse bias voltage to the third supplying roller;
• adhering the toner of the fourth developing apparatus to the electrostatic latent image of the photoconductive medium, comprising applying a fourth bias voltage to cause a potential difference between the fourth developing roller and the fourth supplying roller;
• and
• collecting the toner of the fourth developing roller comprising applying a fourth reverse bias voltage to the fourth supplying roller.

An apparatus comprising:

• a photoconductive medium to form electrostatic latent images thereon;
• first and second developers, each comprising:
• a developing roller to receive color toner and transfer the received color toner to the respective electrostatic latent image,
• a supplying roller to supply the toner to the developing roller, and
• a toner supply part formed between the developing roller and the supplying roller to adhere the toner onto the developing roller;
• a voltage supplier to supply a bias voltage to the developing rollers and the supplying rollers of the respective developers to enable the developers to perform respective developing operations, and
• a controller to control the voltage supplier such that the developers perform the developing operations one by one with respect to the respective electrostatic latent images which are formed on the photoconductive medium.

A method comprising:

• forming an electrostatic latent image on a photoconductive medium;
• applying a voltage to a first developing roller while a second developing roller receives no voltage, to attach a first color developer to the first developing roller and not the second developer;
• transferring the attached developer to the electrostatic latent image;
• and
• applying a neutral bias voltage to a supplying roller adjacent to the first developing roller to stop the attaching of the first color developer to the first developing roller.

An apparatus comprising:

• a photoconductive medium to form electrostatic latent images thereon;
• first and second developers, each comprising:
• a developing roller to receive color toner and transfer the received color toner to the respective electrostatic latent image,
• a supplying roller to supply the toner to the developing roller, and
• a toner supply part formed between the developing roller and the supplying roller to adhere the toner onto the developing roller;
• and
• a voltage supplier to sequentially supply a bias voltage to the developing roller and the respective supplying roller performing a developing operation, the developer not performing the developing operation not receiving the bias voltage.