Sheet re-feed device and image forming apparatus

• US 20010011794A1
• Filed: 01/18/2001
• Published: 08/09/2001
• Est. Priority Date: 01/21/2000
• Status: Active Grant

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Chihara, Hiroshi
• Granted Patent: US 6,736,390 B2
• Time in Patent Office: Days
• US Class Current: 271/8.1
• CPC Class Codes: B41J 13/0045 concerning sheet refeed sections of automatic paper handling systems, e.g. intermediate stackers printing on both faces B41J3/60
• CPC Class Codes: B41J 3/60 for printing on both faces of the printing material
• CPC Class Codes: G03G 15/234 by inverting and refeeding the image receiving material with an image on one face to the recording member to transfer a second image on its second face, e.g. by using a duplex tray; Details of duplex trays or inverters
• CPC Class Codes: G03G 2215/00721 of sheet position

Abstract

An image forming apparatus includes a guide unit for guiding sheets fed by a sheet feed unit to an image forming unit, a discharge guide unit for discharging the sheets onto which images are formed, by the image forming unit, a re-transportation guide unit for branching the sheets from the discharge guide unit and guiding them through the image forming apparatus again, and a plurality of sheet sensors disposed in the re-transportation guide unit at intervals in a sheet transportation direction for determining positions at which the sheets are placed in a standby state, wherein the number of sheets, which are placed in the standby state is selected based on sheet size information so that more sheets are placed in the standby state when a sheet size is short than when it is long. Accordingly, the throughput of short sheets can be increased when images are recorded on both sides thereof.

Claims

1. An image forming apparatus comprising:

sheet feed means for feeding sheets;

guide means for guiding the sheets fed by said sheet feed means to image forming means for forming an image on the sheet;

discharge guide means for discharging the sheets having an image formed thereon by said image forming means;

re-transportation guide means for branching the sheets from said discharge guide means and guiding the sheets through said image forming apparatus again; and

a plurality of sheet sensing devices disposed in said re-transportation guide means at intervals in a sheet transportation direction for determining positions at which the sheets are placed in a standby state,

wherein a number of sheets, which are placed in said re-transportation guide means in the standby state, is determined based on sheet size information so that more sheets are placed in the standby state when a sheet size is short than when the sheet size is long.

2. An image forming apparatus according to

claim 1

, wherein said re-transportation guide means comprises a transportation path connected to said guide means, and said transportation path comprises a reverse path for switching back sheets from said discharge guide means and a re-guide path for guiding the sheets from said reverse path to a connecting section, which connects to said guide means.

3. An image forming apparatus according to

claim 2

, wherein the number of sheets that can be placed in the standby state on said reverse path and said re-guide path is three.

4. An image forming apparatus according to

claim 3

, wherein the size of the sheets is divided into a large group and a small groups.

5. An image forming apparatus according to

claim 4

, wherein said plurality of sheet sensing devices are disposed at a midpoint of said re-guide path and downstream of said re-guide path about said connecting section.

6. An image forming apparatus according to

claim 1

, wherein the sheets are fed from said sheet feed means and from said re-guide path alternately.

7. An image forming apparatus according to

claim 6

, wherein a maximum number of standby sheets is selected by a maximum number of sheets managing unit, and the number of sheets in the standby state is controlled by a number of sheets control means.

8. A re-feed device comprising:

re-transportation guide means for guiding sheets, which are branched after an image is formed thereon by an image forming means, to the image forming means again; and

a plurality of sheet sensing devices disposed in said re-transportation guide means at intervals in a sheet transporting direction for determining positions at which the sheets are placed in a standby state,

wherein a number of sheets, which are placed in said re-transportation guide means in the standby state, is determined based on sheet size information so that more sheets are placed in the standby state when a sheet size is short than when the sheet size is long.

9. A re-feed device according to

claim 8

, wherein said re-transportation guide means comprises a transportation path connected to a guide means for guiding the sheets to the image forming means, and said transportation path comprises a reverse path for switching back the sheets having been branched and a re-guide path for guiding the sheets from said reverse path to a connecting section, which connects to the guide means.

10. A re-feed device according to

claim 9

, wherein a maximum of three sheets can be placed at the maximum in the standby state on said reverse path and said re-guide path.

11. A re-feed device according to

claim 10

, wherein the size of the sheets is divided into a large group and a small group.

12. A re-feed device according to

claim 11

, wherein said plurality of sheet sensing devices are disposed at a midpoint of said re-guide path and downstream of said re-guide path about the connecting section.

13. A re-feed device according to

claim 8

, wherein a maximum number of standby sheets is selected by a maximum number of sheets managing unit, and the number of sheets in the standby state is controlled by a number of sheets control means.