초록 ▼

An image forming apparatus which can prevent the electric discharge when the trailing edge of a recording material passes a transferring position, and yet can stabilize the surface potential of a photosensitive drum. A controller changes a transfer bias voltage Vt during the supply of paper to 0 V b

An image forming apparatus which can prevent the electric discharge when the trailing edge of a recording material passes a transferring position, and yet can stabilize the surface potential of a photosensitive drum. A controller changes a transfer bias voltage Vt during the supply of paper to 0 V before the trailing edge of recording paper arrives at a transferring nip part, changes it to a transfer bias voltage V0 during the non-supply of paper after the trailing edge of the recording paper has passed the transferring nip part, and changes a charging bias voltage to a charging bias voltage smaller than a normal charging bias voltage when an area on the photosensitive drum to which 0 V has been applied passes a charging nip portion. The transfer bias voltage V0 during the non-supply of paper is smaller than the transfer bias voltage Vt during the supply of paper.

대표청구항 ▼

1. An image forming apparatus comprising:an image bearing member, which bears a toner image; a charging member to which a charging voltage is applied to charge said image bearing member; a transfer member to which a first transfer voltage of a polarity opposite to a polarity of the charging voltage

1. An image forming apparatus comprising:an image bearing member, which bears a toner image; a charging member to which a charging voltage is applied to charge said image bearing member; a transfer member to which a first transfer voltage of a polarity opposite to a polarity of the charging voltage is applied to transfer the toner image on said image bearing member to a recording material at a transfer position; and a controlling portion for controlling a voltage applied to said transfer member, wherein said controlling portion changes the voltage applied to said transfer member from said first transfer voltage to 0 V before a trailing edge of the recording material passes said transfer position, and thereafter changes the voltage to a second transfer voltage after the trailing edge of the recording material passes said transfer position, said second transfer voltage having the same polarity as said first transfer voltage, and an absolute value of a voltage value of said second transfer voltage being smaller than an absolute value of a voltage value of said first transfer voltage. 2. An image forming apparatus comprising:an image bearing member, which bears a toner image; a charging member to which a charging voltage is applied to charge said image bearing member; a transfer member to which a first transfer voltage of a polarity opposite to a polarity of the charging voltage is applied to transfer the toner image on said image bearing member to a recording material at a transfer position; and a controlling portion for controlling a voltage applied to said transfer member, wherein said controlling portion turns off said first transfer voltage applied to said transfer member before a trailing edge of the recording material passes said transfer position, and applies a second transfer voltage to said transfer member after the trailing edge of the recording material passes said transfer position, said second transfer voltage having the same polarity as said first transfer voltage, and an absolute value of a voltage value of said second transfer voltage being smalller than an absolute value of a voltage value of said first transfer voltage. 3. An image forming apparatus comprising:a movable image bearing member, which bears a toner image; a charging member to which a charging voltage is applied to charge said image bearing member; a transfer member to which a first transfer voltage of a polarity opposite to a polarity of the charging voltage is applied to transfer the toner image on said image bearing member to a recording material at a transfer position; and a controlling portion for controlling a voltage applied to said transfer member and the charging voltage applied to said charging member, wherein said controlling portion changes the voltage applied to said transfer member from said first transfer voltage to a second transfer voltage before a trailing edge of the recording material passes said transfer position, and thereafter changes the voltage to a third transfer voltage after the trailing edge of the recording material passes said transfer position, and said controlling portion makes a first charging voltage of the charging voltage when an area, to which said first transfer voltage is applied, on said image bearing member opposes said charging member, and makes a second charging voltage of the charging voltage when an area, to which said second transfer voltage is applied, on said image bearing member opposes said charging member, an absolute value of a voltage value of said second charging voltage being smaller than an absolute value of a voltage value of said first charging voltage, and a voltage value of said third transfer voltage being between a voltage value of said first transfer voltage and a voltage value of said second transfer voltage. 4. An image forming apparatus comprising:a movable image bearing member, which bears a toner image; a charging member to which a charging voltage is applied to charge said image bearing member; a developing member to which a developing voltage having the same polarity as the charging voltage is applied to form the toner image on said image bearing member; a transfer member to which a first transfer voltage of a polarity opposite to a polarity of the charging voltage is applied to transfer the toner image on said image bearing member to a recording material at a transfer position; and a controlling portion for controlling a voltage applied to said transfer member and the developing voltage, wherein said controlling portion changes the voltage applied to said transfer member from said first transfer voltage to a second transfer voltage before a trailing edge of the recording material passes said transfer position, and thereafter changes the voltage to a third transfer voltage after the trailing edge of the recording material passes said transfer position, and said controlling portion makes a first developing voltage of the developing voltage when an area, to which said first transfer voltage is applied, on said image bearing member opposes said developing member, and makes a second developing voltage of the developing voltage when an area, to which said second transfer voltage is applied, on said image bearing member opposes said developing member, an absolute value of a voltage value of said second developing voltage being larger than an absolute value of a voltage of said first developing voltage, and a voltage value of said third transfer voltage being between a voltage value of said first transfer voltage and a voltage value of said second transfer voltage. 5. An image forming apparatus according to claim 3 or 4, wherein the voltage value of said second transfer voltage is 0 V.6. An image forming apparatus according to claim 3 or 4, wherein said second transfer voltage has the same polarity as the charging voltage.7. An image forming apparatus comprising:a movable image bearing member, which bears a toner image; a charging member to which a charging voltage is applied to charge said image bearing member; a transfer member to which a first transfer voltage of a polarity opposite to a polarity of the charging voltage is applied to transfer the toner image on said image bearing member to a recording material at a transfer position; and a controlling portion for controlling a voltage applied to said transfer member and the charging voltage applied to said charging member, wherein said controlling portion turns off said first transfer voltage applied to said transfer member before a trailing edge of the recording material passes said transfer position, and applies a second transfer voltage to said transfer member after the trailing edge of the recording material passes said transfer position, and said controlling portion makes a first charging voltage of the charging voltage when an area, to which said first transfer voltage is applied, on said image bearing member opposes said charging member, and makes a second charging voltage of the charging voltage when an area, to which a transfer voltage is not applied, between the area to which said first transfer voltage is applied and an area to which said second transfer voltage is applied, on said image bearing member opposes said charging member, an absolute value of a voltage value of said second charging voltage being smaller than an absolute value of a voltage value of said first charging voltage, said second transfer voltage having the same polarity as said first transfer voltage, and an absolute value of a voltage value of said second transfer voltage being smaller than an absolute value of a voltage value of said first transfer voltage. 8. An image forming apparatus comprising:a movable image bearing member, which bears a toner image; a charging member to which a charging voltage is applied to charge said image bearing member; a developing member to which a developing voltage having the same polarity as the charging voltage to form the toner image on said image bearing member; a transfer member to which a first transfer voltage of a polarity opposite to a polarity of the charging voltage is applied to transfer the toner image on said image bearing member to a recording material at a transfer position; and a controlling portion for controlling a transfer voltage applied to said transfer member and the developing voltage applied to said developing member, wherein said controlling portion turns off said first transfer voltage applied to said transfer member before a trailing edge of the recording material passes said transfer position, and applies a second transfer voltage to said transfer member after the trailing edge of the recording material passes said transfer position, and said controlling portion makes a first developing voltage of the developing voltage when an area, to which said first transfer voltage is applied, on said image bearing member opposes said developing member, and makes a second developing voltage of the developing voltage when an area, to which a transfer voltage is not applied, between the area to which said first transfer voltage is applied and an area to which said second transfer voltage is applied, on said image bearing member opposes said developing member, an absolute value of a voltage value of said second developing voltage being smaller than an absolute value of a voltage value of said first developing voltage, said second transfer voltage having the same polarity as said first transfer voltage, and an absolute value of a voltage value of said second transfer voltage being smaller than an absolute value of a voltage value of said first transfer voltage. 9. An image forming apparatus comprising:an image bearing member, which bears a toner image; a charging member to which a charging voltage is applied to charge said image bearing member; a transfer member to which a first transfer voltage of a polarity opposite to a polarity of the charging voltage is applied to transfer the toner image on said image bearing member to a recording material at a transfer position; and a controlling portion for controlling a voltage applied to said transfer member, wherein said controlling portion changes, regardless of whether the recording material is a front side or a backside, the voltage applied to said transfer member from said first transfer voltage to a second transfer voltage before a trailing edge of the recording material passes said transfer position, and thereafter changes the voltage to a third transfer voltage after the trailing edge of the recording material passes said transfer position, a voltage value of said third transfer voltage being between a voltage value of said first transfer voltage and a voltage value of said second transfer voltage.