SHEET CONVEYING APPARATUS AND IMAGE FORMING APPARATUS

Abstract

Positioning in the width direction of a sheet is performed by a skew correcting unit which is provided on a re-conveying path for reversing the sheet and conveying it again to an image forming unit and which has a reference surface that is come into contact with a side edge of the sheet and a plurality of diagonal feed units which obliquely convey the sheet so as to be come into contact with the reference surface. The pressures in nip portions of the other diagonal feed units excluding one of the plural diagonal feed units are reduced or cancelled by a reducing/cancelling unit according to a length in the sheet conveying direction of the sheet which is conveyed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a schematic construction of a laser beam printer as an example of an image forming apparatus having a sheet conveying apparatus according to an embodiment of the invention.

FIG. 2 is a perspective view for describing a construction of a duplex unit as a sheet conveying apparatus.

FIG. 3 is a perspective view for describing a lateral registration correcting unit provided for the duplex unit.

FIG. 4 is a top view of the duplex unit.

FIG. 5 is an enlarged diagram of a rail portion provided for the duplex unit.

FIG. 6 is a top view illustrating the state where the lateral registration correcting unit has been moved.

FIG. 7 is a diagram illustrating the state where a sheet is pressed onto a reference surface provided for the lateral registration correcting unit.

FIG. 8 is a perspective view of the duplex unit.

FIGS. 9A and 9B are schematic diagrams for describing the sandwiching state according to a sheet size of a diagonal feed roller pair provided for the duplex unit.

FIGS. 10A, 10B, and 10C are plan views illustrating a construction of a re-conveying path of a conventional sheet conveying apparatus.

FIG. 11 is a plan view illustrating a construction of the re-conveying path on which two diagonal feed roller pairs are arranged according to the conventional sheet conveying apparatus.

FIG. 12 is a diagram illustrating the state where a sheet has been made to approach a reference surface by a large approaching force according to the conventional sheet conveying apparatus.

Claims

1. An image forming apparatus in which a sheet with an image formed on one surface by an image forming unit is reversed and conveyed again to the image forming unit, comprising: a re-conveying path which reverses the sheet having the image formed on one surface by the image forming unit and guides the sheet again to the image forming unit;a skew correcting unit provided on the re-conveying path, having a reference surface to which a side edge of the sheet abuts, and a plurality of diagonal feed units which diagonally convey the sheet and abut the sheet to the reference surface; anda reducing/cancelling unit which reduces or cancels pressures in nip portions of the other diagonal feed units excluding one of the plurality of diagonal feed units,wherein the pressures of nip portions of the diagonal feed units are reduced or cancelled by the reducing/cancelling unit according to a length in a sheet conveying direction of the sheet which is conveyed.

2. An apparatus according to claim 1, further comprises a first conveying unit provided on an upstream side of the skew correcting unit and a second conveying unit provided on a downstream side of the skew correcting unit, wherein if the sheet reaches the second conveying unit before a skew is corrected by the skew correcting unit, the pressures of the nip portions of the other diagonal feed units are reduced or cancelled by the reducing/cancelling unit.

3. An apparatus according to claim 1, further comprising: a holding member which holds the plurality of diagonal feed units; anda moving unit which moves the holding member in a width direction which perpendicularly crosses the sheet conveying direction according to a size of the sheet which is conveyed,wherein the reducing/cancelling unit reduces or cancels the pressure of the other diagonal feed units in an interlocking relational manner with the movement in the width direction of the holding member.

4. An apparatus according to claim 1, wherein each of the diagonal feed units is constructed by a diagonal feed roller and a diagonal feed rotation member which is come into pressure-contact with the diagonal feed roller andthe reducing/cancelling unit has: a rotation member holding unit which holds the diagonal feed rotation member and movable supports the diagonal feed rotation member to a pressure contact position where it is come into pressure-contact with the diagonal feed roller or a reducing/cancelling position where the pressure with the diagonal feed roller is reduced or cancelled; and an interlocking member which moves the rotation member holding unit to the pressure contact position or the reducing/cancelling position in an interlocking relational manner with the movement in the width direction of the holding member.

5. An apparatus according to claim 3, wherein the reference surface is held to the holding member integratedly with the plurality of diagonal feed units.