| CPC G03G 15/065 (2013.01) [G03G 15/0266 (2013.01); G03G 15/043 (2013.01); G03G 2215/021 (2013.01)] | 10 Claims |
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1. An image forming apparatus comprising:
a rotatable photosensitive drum;
a charging roller configured to electrically charge a surface of the photosensitive drum to a predetermined polarity at a charging position;
a developing roller contacting the surface of the photosensitive drum and configured to form a toner image by supplying toner to the surface of the photosensitive drum at a developing position downstream of the charging position with respect to a rotational direction of the photosensitive drum;
a transfer roller contacting the surface of the photosensitive drum and configured to transfer the toner image from the photosensitive drum onto a recording material at a transfer position downstream of the developing position and upstream of the charging position with respect to the rotational direction of the photosensitive drum;
a charging power source configured to apply a charging voltage of the same polarity as the predetermined polarity to the charging roller;
a developing power source configured to apply a developing voltage to the developing roller;
a transfer power source configured to apply a transfer voltage of an opposite polarity to the predetermined polarity to the transfer roller; and
a control unit configured to control the charging power source, the developing power source, and the transfer power source,
wherein the control unit carries out control so as to be capable of executing an image forming operation in which rotation of the photosensitive drum is started and stopped in a state that the developing roller contacts the photosensitive drum and in which the toner image to be transferred onto the recording material is formed and executing a post rotation operation until the rotation of the photosensitive drum after the image forming operation is ended is stopped, and
wherein during the post rotation operation,
the control unit controls the charging power source so that the charging voltage is changed stepwisely to a first charging voltage lower in absolute value than the charging voltage during the image forming operation and then to a second charging voltage lower in absolute value than the first charging voltage, and thereafter application of the charging voltage is ended, and
when regions of the surface of the photosensitive drum having passed through the charging position under application of the first charging voltage and the second charging voltage are a first region and a second region, respectively,
the control unit ends application of the developing voltage after changing the developing voltage to a first developing voltage when the first region first passes through the developing position and to a second developing voltage when the second region first passes through the developing position,
the control unit controls the developing power source so that a potential difference between a surface potential of the first region when the first region first passes through the developing position and the first developing voltage and a potential difference between a surface potential of the second region when the second region first passes through the developing position and the second developing voltage are maintained within a predetermined range, and
the control unit controls the transfer power source so that a current flows between the transfer roller and the photosensitive drum under application of the transfer voltage when each of the first region and the second region first passes through the transfer position and so that an absolute value of a surface potential of the photosensitive drum is made low when at least one of the first region and the second region first passes through the transfer position.
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