Image forming method and apparatus capable of effectively performing charging operation

An image forming apparatus comprising:

• a plurality of image forming means for forming toner images of different colors, the plurality of image forming means including at least two common image forming means having a common structure;
• toner supplying means for supplying toners of the different colors to corresponding development means of the plurality of image forming means;
• common-unit detecting means for detecting each one of the at least two common image forming means at installation thereof;
• initial operation executing means for executing an initial operation of supplying an amount of toner to developing means of each one of the at least two common image forming means detected by the common-unit detecting means and mixing to charge the toner by friction for a preset time period before a formation of a reference image on an image carrier;
• and
• determining means for detecting a status as to whether the toner in the development means is charged to a threshold level upon completion of the initial operation, and for determining whether to mix the toner one more time for another time period based on the status detected.

An image forming method comprising:

• providing a plurality of image forming units including at least two common image forming units having a common structure, each including a development device;
• confirming installment of each one of the at least two common image forming units in the image forming apparatus;
• executing an initial operation of supplying an amount of toner from a toner supply device to a corresponding development device of each one of the at least two common image forming units confirmed as installed in the confirming step and mixing to charge the toner by friction for a preset time period before forming of a reference image on an image carrier;
• detecting a status as to whether the toner in the development device is charged to a threshold level upon completion of the initial operation;
• and
• determining whether to mix the toner one more time for another time period based on the status detected.