Image forming apparatus, sheet conveying method, and program for sheet conveyance

1. An image forming apparatus which turns back a sheet from a first conveying direction toward the outside of the apparatus to a second conveying direction toward the inside of a reversal conveyance path to reverse a front side and a back side of the sheet, the apparatus comprising:

an intermediate conveyance unit and an outer conveyance unit, the intermediate conveyance unit being positioned upstream from the reversal conveyance path in the second conveying direction and midway in a sheet conveyance path on which the sheet is conveyed during the conveyance involving the turning back, the intermediate conveyance unit being configured to be pulled out of the apparatus together with a portion of the sheet conveyance path, the outer conveyance unit being positioned adjacent to the intermediate conveyance unit upstream from the intermediate conveyance unit in the second conveying direction;

a roller which conveys the sheet within the sheet conveyance path in the second conveying direction;

a sheet length determining section which determines whether or not the sheet to be turned back is long enough in a sheet conveying direction so as to extend into the outer conveyance unit during the conveyance of the sheet involving the turning back; and

a conveyance control section which controls the roller such that the sheet to be turned back and directed into the reversal conveyance path is caused to wait until the sheet can be conveyed into the reversal conveyance path, the conveyance control section setting, as a standby position of the sheet while the sheet is caused to wait, a position such that an upstream end portion in the second conveying direction of the sheet to be directed into the reversal conveyance path does not extend for a predetermined length or longer into the outer conveyance unit, and causing the sheet to wait at the standby position only if the sheet length determining section determines that the sheet is long enough so as to extend into the outer conveyance unit during the conveyance involving the turning back.

2. The apparatus of claim 1 , further comprising an output tray in which a sheet discharged from the image forming apparatus is put,

wherein the outer conveyance unit is placed below the entire output tray or below a portion of the output tray.

3. The apparatus of claim 1 , wherein the predetermined length is set in a range from more than 0 mm to 20 mm.

4. The apparatus of claim 1 , further comprising a sensor which is placed at a position in the outer conveyance unit and detects the passage of the sheet, the position being at the predetermined length from an upstream end of the outer conveyance unit in the first conveying direction,

wherein the sheet length determining section determines based on the result of sensing by the sensor whether or not the sheet to be turned back is long enough in a sheet conveying direction so as to extend into the outer conveyance unit during the conveyance of the sheet involving the turning back.

5. The apparatus of claim 4 , wherein a lower conveyance guide constituting a bottom surface of an inner wall of a conveyance path in the outer conveyance unit is openable downward about a predetermined rotation axis, and

wherein the sensor is placed downstream from the rotation axis in the first conveying direction.

6. A sheet conveying method in an image forming apparatus which turns back a sheet from a first conveying direction toward the outside of the apparatus to a second conveying direction toward the inside of a reversal conveyance path to reverse a front side and a back side of the sheet, the apparatus including an intermediate conveyance unit, an outer conveyance unit, and a roller, the intermediate conveyance unit being positioned upstream from the reversal conveyance path in the second conveying direction and midway in a sheet conveyance path on which the sheet is conveyed during the conveyance involving the turning back, the outer conveyance unit being positioned adjacent to the intermediate conveyance unit upstream from the intermediate conveyance unit in the second conveying direction, the intermediate conveyance unit being configured to be pulled out of the apparatus together with a portion of the sheet conveyance path, and the roller conveying the sheet within the sheet conveyance path in the second conveying direction, the method comprising:

determining whether or not the sheet to be turned back is long enough in a sheet conveying direction so as to extend into the other conveyance unit during the conveyance of the sheet involving the turning back;

controlling a roller such that the sheet to be turned back and directed into the reversal conveyance path is caused to wait until the sheet can be conveyed into the reversal conveyance path;

setting, as a standby position of the sheet while the sheet is caused to wait, a position such that an upstream end portion in the second conveying direction of the sheet to be directed into the reversal conveyance path does not extend for a predetermined length or longer into the outer conveyance unit adjacent to the intermediate conveyance unit upstream from the intermediate conveyance unit in the second conveying direction; and

causing the sheet to wait at the standby position only if it is determined that the sheet is long enough so as to extend into the outer conveyance unit during the conveyance involving the turning back.

7. The method of claim 6 , wherein the image forming apparatus further includes an output tray in which a sheet discharged from the image forming apparatus is put,

wherein the outer conveyance unit is placed below the entire output tray or below a portion of the output tray.

8. The method of claim 6 , wherein the predetermined length is set in a range from more than 0 mm to 20 mm.

9. The method of claim 6 , wherein the image forming apparatus further includes a sensor placed at a position in the outer conveyance unit and detecting the passage of the sheet, the position being at the predetermined length from an upstream end of the other conveyance unit in the first conveying direction,

wherein it is determined on the basis of the result of sensing by the sensor whether or not the sheet to be turned back is long enough in a sheet conveying direction so as to extend into the outer conveyance unit during the conveyance of the sheet involving the turning back.

10. The method of claim 9 , wherein a lower conveyance guide constituting a bottom surface of an inner wall of a conveyance path in the outer conveyance unit is openable downward about a predetermined rotation axis, and

wherein the sensor is placed downstream from the rotation axis in the first conveying direction.