Image forming apparatus

An image forming apparatus of a type causing a toner image transferred by a primary image transfer to again move via a primary image transfer region before a secondary image transfer, said image forming apparatus comprising:

• means for carrying the toner image to be transferred by the primary image transfer;
• means for transferring the toner image transferred thereto by the primary image transfer to a recording means by the secondary image transfer;
• means for forming a first electric field for the primary image transfer;
• means for forming, when said transferring means again conveys the toner image via the primary image transfer region while running idle, a second electric field weaker than the first electric field in said primary image transfer region;
• and
• sensing means for sensing a surface potential of said image carrier;
• control means for variably controlling, in accordance with the sensed surface potential of said image carrier, the second electric field during the idle run of said intermediate image transfer body.

An image forming apparatus of a type causing a toner image transferred by a primary image transfer to again move via a primary image transfer region before a secondary image transfer, said image forming apparatus comprising:

• an image carrier configured to carry the toner image to be transferred by the primary image transfer;
• an intermediate image transfer body configured to transfer the toner image transferred thereto by the primary image transfer to a recording medium by the secondary image transfer, said intermediate image transfer body forming the primary image transfer region in contact with said image carrier;
• a bias roller configured to apply a bias to said primary image transfer region to thereby form an electric field for the primary image transfer;
• an electric field generator configured to generate when said intermediate image transfer body again conveys the toner image via the primary image transfer region while running idle, an electric field weaker than an electric field assigned to the primary image transfer in said primary image transfer region;
• and
• a surface potential sensor configured to sense a surface potential of said image carrier;
• a controller configured to variably control, in accordance with the sensed surface potential of said image carrier, the bias for forming the electric field during the idle run of said intermediate image transfer body.

An image forming method for a toner image transferred by a primary image transfer to again move via a primary image transfer region before a secondary image transfer, in an image forming apparatus including an image carrier for carrying the toner image to be transferred by the primary image transfer and an intermediate image transfer body for transferring the toner image transferred thereto by the primary image transfer to a recording medium by the secondary image transfer, said intermediate image transfer body forming the primary image transfer region in contact with said image carrier, said image forming method comprising the steps of:

• applying a bias to said primary image transfer region to thereby form an electric field for the primary image transfer;
• forming, when said intermediate image transfer body again conveys the toner image via the primary image transfer region while running idle, an electric field weaker than an electric field assigned to the primary image transfer in said primary image transfer region;
• sensing a surface potential of said image carrier;
• and
• variably controlling, in accordance with the sensed surface potential of said image carrier, the bias for forming the electric field during the idle run of said intermediate image transfer body.