IMAGE FORMING APPARATUS AND REMAINING SHEET DETECTION METHOD THEREFOR

Abstract

An image forming apparatus is provided that detects a sheet remaining between a transfer unit and fixing unit using a loop sensor. The loop sensor is configured to detect a loop of a sheet conveyed between the transfer unit and the fixing unit. The image forming apparatus includes a control unit to control, in accordance with an output from the loop sensor, a sheet conveyance speed of the fixing unit so as to form the loop of the sheet conveyed by the transfer unit and the fixing unit. If the loop sensor detects a presence of the sheet while driving of the transfer unit and the fixing unit for conveying the sheet has stopped, the control unit determines that a remaining sheet is present, and outputs a warning signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining the schematic arrangement of a laser printer as an example of an image forming apparatus according to an embodiment;

FIG. 2 is a block diagram for explaining the schematic arrangement of the laser printer according to the embodiment;

FIGS. 3A and 3B are views for explaining sheet conveyance between a transfer roller and fixing unit in the laser printer according to the first embodiment;

FIG. 4 is a flowchart for explaining a jam detecting process in the laser printer according to the embodiment;

FIG. 5 is a flowchart for explaining a sheet jam detection process when the power supply of the printer is ON in an idle state without executing a print job;

FIG. 6 is a view for explaining sheet conveyance between a transfer roller and fixing unit in a laser printer according to the second embodiment;

FIG. 7 is a view for explaining the schematic arrangement of the laser printer as an example of an image forming apparatus according to the second embodiment;

FIG. 8 is a view for explaining sheet conveyance between a transfer roller and fixing unit in a laser printer according to the third embodiment; and

FIG. 9 is a flowchart for explaining a sheet conveyance delay jam according to the embodiment.

Claims

1. An image forming apparatus comprising: an image carrier;a transfer unit configured to transfer, to a sheet, an image formed on the image carrier;a fixing unit configured to fix the image transferred on the sheet by the transfer unit;a loop sensor configured to detect a loop of the sheet conveyed by the transfer unit and the fixing unit; anda control unit configured to control, in accordance with an output from the loop sensor, a sheet conveyance speed in the fixing unit so as to form the loop of the sheet conveyed by the transfer unit and the fixing unit,wherein when the loop sensor detects the sheet while driving of the transfer unit and the fixing unit for conveying the sheet stops, the control unit determines that a remaining sheet is present, and outputs a warning signal.

2. The apparatus according to claim 1, wherein the loop sensor includes a movable element that is pushed down by the sheet to be in a detecting state of the sheet when the loop of the sheet is formed or when a loop amount of the sheet is more than a predetermined amount, andthe movable element of the loop sensor is not pushed down by the sheet to be in an undetecting state of the sheet when the sheet is absent or when the loop amount of the sheet is larger than or equal to the predetermined amount.

3. The apparatus according to claim 1, further comprising: an opening/closing member movable between an opened position and a closed position, anda moving member configured to move the sheet in a direction of the loop sensor in accordance with an opening operation of the opening/closing member.

4. The apparatus according to claim 3, wherein the moving member moves the sheet in the direction of the sensor upon rotating in accordance with the opening operation of the opening/closing member.

5. The apparatus according to claim 4, wherein the moving member comprises a protection member for protecting the fixing unit.

6. The apparatus according to claim 1, wherein the control unit determines that a remaining sheet is present, and outputs a warning signal when the loop sensor detects the sheet upon power-ON of the image forming apparatus.

7. The apparatus according to claim 1, further comprising a sheet detection sensor which detects a sheet on the downstream side in a sheet conveyance direction of the fixing unit,wherein the control unit determines that a remaining sheet is present and outputs a warning signal when determining that a sheet conveyance delay occurs based on an output from the sheet detection sensor, and detecting the sheet based on the output from the loop sensor.

8. A method for an image forming apparatus having a transfer unit which transfers an image to a sheet and a fixing unit which fix the image on the sheet, the method comprising: controlling a sheet conveyance speed in the fixing unit so as to form a loop of the sheet in accordance with an output from a loop sensor which detects the loop of the sheet, while conveying the sheet between the transfer unit and the fixing unit; anddetermining whether a remaining sheet is present in the image forming apparatus in accordance with the output form the loop sensor while driving of the transfer unit and the fixing unit for sheet conveyance stops.

9. The method according to claim 8, wherein the determination of a presence of a remaining sheet is executed upon power-on of the image forming apparatus.

10. The method according to claim 8, wherein the determination of a presence of a remaining sheet is executed when a sheet conveyance delay occurs when the image forming apparatus is in operation.

11. An image forming apparatus comprising: an image carrier;a transfer unit configured to transfer an image formed on the image carrier to a sheet;a fixing unit configured to fix the image transferred on the sheet by the transfer unit;a sensor capable of detecting a slack of the sheet between the transfer unit and the fixing unit; anda control unit configured to control, based on an output from the sensor, a sheet conveyance speed of the fixing unit so that the amount of the slack of the sheet forming between the transfer unit and the fixing unit may become a defined amount, wherein the control unit is configured to determine if a presence of the sheet is detected by the sensor after driving of the transfer unit and the fixing unit for conveying the sheet has stopped.

12. The apparatus according to claim 11, wherein the sensor is a loop sensor disposed between the transfer unit and the fixing unit.

13. The apparatus according to claim 12, wherein the loop sensor includes a movable member that is pushed down by the sheet when a slack of the sheet is formed or an amount of slack of the sheet is more than a defined amount.