Image forming apparatus and transfer bias application device therein

The image forming apparatus according to claim 1, wherein the sheet absent period is a time from which a trailing edge of the recording medium passes through the transfer region to a time at which a leading edge of a successive recording medium enters the transfer region during continuous image forming operation.

The image forming apparatus according to claim 1, wherein as the image bearing member bearing toner passes through the transfer region during the sheet absent period, the controller allows the transfer bias application device to selectively apply to the transfer region one of the transfer bias without the AC component and the transfer bias with the peak-to-peak voltage of the AC component less than that applied upon image formation.

The image forming apparatus according to claim 1, further comprising:na DC transfer bias application device to apply to the transfer region a DC transfer bias without the AC component; anda mode changing device to change an image forming mode between a first mode in which the transfer bias application device applies to the transfer region the transfer bias including the DC component and the AC component and a second mode in which the DC transfer bias application device applies to the transfer region the DC transfer bias to form an image,wherein during the bias change period, when the transfer bias application device is not selectively applying to the transfer region the one of the transfer bias without the AC component and the transfer bias with a peak-to-peak voltage of the AC component less than that applied upon image formation, the controller stops application of the transfer bias by the transfer bias application device while allowing the DC transfer bias application device to apply the DC transfer bias to the transfer region to form the image.

The image forming apparatus according to claim 9, further comprising a toner detector that detects a test toner image formed on the image bearing member,nwherein the controller controls the transfer power source to output the second bias when the test toner image passes through the transfer nip.

The image forming apparatus according to claim 9, wherein the transfer member is a transfer roller, and the transfer roller includes a conductive layer.

The image forming apparatus according to claim 9, wherein a polarity of the first bias is alternately inverted when the toner image is transferred to the sheet at the transfer nip.

The image forming apparatus according to claim 9, further comprising a toner detector that detects a test toner image formed on the image bearing member,nwherein application of the bias to the transfer nip is turned oft when the test toner image passes through the transfer nip.

The image forming apparatus according to claim 9, further comprising a toner detector that detects a test toner image on the transfer member,nwherein the controller controls the transfer power source to output the second bias when the test toner image passes through the transfer nip, and the test toner image is transferred from the image bearing member to the transfer member.

The image forming apparatus according to claim 21, further comprising a toner detector that detects a test toner image formed on the image bearing member,nwherein the controller controls the transfer power source to output the second bias when the test toner image passes through the transfer nip.

The image forming apparatus according to claim 21, wherein the transfer member is a transfer roller, and the transfer roller includes a conductive layer.

The image forming apparatus according to claim 21, wherein a polarity of the first bias is alternately inverted when the toner image is transferred to the sheet at the transfer nip.

The image forming apparatus according to claim 21, further comprising a toner detector that detects a test toner image formed on the image bearing member,nwherein application of the bias to the transfer nip is turned off when the test toner image passes through the transfer nip.

The image forming apparatus according to claim 21, further comprising a toner detector that detects a test toner image on the transfer member,nwherein the controller controls the transfer power source to output the second bias when the test toner image passes through the transfer nip, and the test toner image is transferred from the image bearing member to the transfer member.