US20070007716A1

US20070007716A1 - Sheet discharging device

Info

Publication number: US20070007716A1
Application number: US11/434,619
Authority: US
Inventors: Kenji Tanaka
Original assignee: Toshiba Corp; Toshiba TEC Corp
Current assignee: Toshiba Corp; Toshiba TEC Corp
Priority date: 2005-07-11
Filing date: 2006-05-15
Publication date: 2007-01-11
Also published as: CN100587613C; JP2007015838A; CN1896880A

Abstract

A sheet discharging device includes a sheet discharging section which discharges sheets, and a sheet discharging tray including a stacking wall portion on which discharged sheets are stacked. The stacking wall portion includes a first wall portion having a first surface which becomes higher in a direction in which sheets are discharged, and a second wall portion connected to an upstream end of the first wall portion in the sheet discharging direction and having a second surface including at least one of a horizontal surface, an inclined surface having a smaller gradient than that of the first surface, and an inclined surface having a gradient opposite to that of the first surface.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-201875, filed Jul. 11, 2005, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a sheet discharging device mounted in, for example, an auto document feeder in an image forming apparatus to discharge loaded sheets to a sheet discharging tray or the like.
2. Description of the Related Art
Some image forming apparatuses such as copiers are provided with an auto document feeder (ADF). The auto document feeder takes out each of the documents (sheets) stacked in a sheet feeding tray and feeds it to a read position in the image forming apparatus. Then, after an image is read, the auto document feeder discharges the sheet to a sheet discharging tray. The auto document feeder is thus provided with a sheet feeding device consisting of a sheet discharging portion that discharges documents from which images have been read and a sheet discharging tray that accommodates the discharged documents.
One problem with the conventional sheet discharging device is that a variation in document discharging speed, document size, or the like suppresses the alignment of documents on the sheet discharging tray, that is, the alignment of discharged sheets. The main cause of the suppressed alignment of discharged sheets is that the leading end of a discharged document hangs down owing to gravity and comes into contact with the surface of the documents already discharged onto the sheet discharging tray, thus moving the documents on the sheet discharging tray.
To solve this problem, a technique has been developed which corrugates documents to be discharged to allow them to advance straight more properly when discharged. When a discharged document advances straight more properly, its leading end comes into contact with documents on the sheet discharging tray at a position farther than the one achieved without using this technique. This reduces the time for which and the area over which the discharged document contacts the surface of the documents on the sheet discharging tray. The alignment of discharged documents is thus improved.
Another technique has been developed which uses an inclined sheet discharging tray to slide down discharged documents backward to align their trailing ends together at a rear end wall of the sheet discharging tray. However, the inclined sheet discharging tray requires an increase in the vertical size of the sheet discharging tray and thus in the size of the device. A technique has thus been developed which forms the rear end of the sheet discharging tray into a gently inclined or flat surface to avoid an increase in the height of the sheet discharging tray.
A technique has also been developed which provides the sheet discharging tray with a leading end wall to align the leading ends of discharged documents together at the leading end wall instead of aligning their trailing ends at the trailing end wall of the sheet discharging tray.
Another technique has been developed which makes the inclination of rear of the sheet display tray smaller to avoid an increase in the vertical size of the sheet discharging tray, while providing the sheet discharging tray with a leading end wall to align the leading ends of discharged documents together at the leading end wall. This leading end wall is movable with respect to the sheet discharging tray to adjust to documents of multiple sizes (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 7-277579).
A considerably marked corrugation is required to prevent the leading end of a document from coming into contact with the documents on the sheet discharging tray until the document is completely discharged. However, a marked corrugation significantly stresses the document, which may thus be damaged.
Jpn. Pat. Appln. KOKAI Publication No. 7-277579 reliably reduces the size of the device. However, the movability of the leading end wall prevents the alignment of discharged documents from being improved unless the position of the leading end wall adjusts to the document size.
For example, if the leading end wall lies distally with respect to the document size, the leading end of a discharged document cannot reach the leading end wall. The discharged document thus fails to be aligned with the documents on the sheet discharging tray. On the contrary, if the leading end wall lies proximally with respect to the document size, the leading end of the document collides against the leading end wall before the document is completely discharged. The document may thus be bent.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a sheet discharging device that can reliably improve the alignment of discharged sheets on a sheet discharging tray without imposing a heavy load on the sheets and without the need to increase the size of the entire device.
An aspect of the present invention configures a sheet discharging device as described below.
The sheet discharging device comprises a sheet discharging portion which discharges sheets, and a sheet discharging tray including a stacking wall portion on which discharged sheets are stacked. The stacking wall portion comprises a first wall portion having a first surface which becomes higher in a direction in which sheets are discharged, and a second wall portion connected to an upstream end of the first wall portion in the sheet discharging direction and having a second surface including at least one of a horizontal surface, an inclined surface having a smaller gradient than that of the first surface, and an inclined surface having a gradient opposite to that of the first surface.
Another aspect of the present invention configures a sheet discharging device as described below.
The sheet discharging device comprises a sheet discharging portion which discharges sheets, and a sheet discharging tray including a stacking wall portion on which discharged sheets are stacked. The sheet discharging tray comprises a projecting portion having a wall portion provided in a central portion of the sheet discharging tray in a width direction substantially orthogonal to the sheet discharging direction to raise a width-wise central portion of the sheets stacked on the sheet discharging tray. The wall portion comprises a first wall portion having a first surface which becomes higher in a direction in which sheets are discharged, and a second wall portion connected to an upstream end of the first wall portion in the sheet discharging direction and having a second surface including at least one of a horizontal surface, an inclined surface having a smaller gradient than that of the first surface, and an inclined surface having a gradient opposite to that of the first surface.
The present invention reliably improves the alignment of discharged documents on the sheet discharging tray without imposing a heavy load on the sheets and without the need to increase the size of the device.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.
FIG. 1 is a front view showing a digital copier in accordance with an embodiment of the present invention;
FIG. 2 is a perspective view showing an auto document feeder in accordance with the embodiment;
FIG. 3 is a perspective view showing an auto document feeder from which a sheet feeding tray has been removed in accordance with the embodiment;
FIG. 4 is a sectional view showing the internal configuration of the auto document feeder in accordance with the embodiment;
FIG. 5 is a schematic diagram showing a sheet discharging device in accordance with the embodiment as viewed from a downstream side in a direction in which documents are conveyed;
FIG. 6 is an enlarged sectional view showing a sheet discharging tray in accordance with the embodiment; and
FIG. 7 is an enlarged sectional view showing a variation of the sheet discharging tray in accordance with the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below in detail with reference to the drawings.
(Configuration of a Digital Copier)
FIG. 1 is a diagram showing the appearance of a digital copier in accordance with an embodiment of the present invention. As shown in FIG. 1, the digital copier comprises an auto document feeder (ADF) 10, a scanner unit 20, and a printer engine section 30.
With the digital copier, the maximum copy document size is called a full size. Half the maximum copy document size is called a half size. Accordingly, in the present embodiment, in which the maximum copy document size is A3, the A3 size corresponds to the full size and an A4 size, which is half the A3 size, corresponds to the half size.
The auto document feeder 10 loads and supplies each document (sheet) D to a predetermined read position R (described later).
The scanner unit 20 optically reads an image from the document D supplied by the auto document feeder 10 or manually to convert the image into image data.
The printer engine section 30 comprises a charger, a laser unit, a photosensitive drum, a developing device, a transfer roller, and a fixing device (none of them are shown). The charger charges a surface of the photosensitive drum to a predetermined potential. The laser unit forms an electrostatic latent image on the surface of the photosensitive drum on the basis of image data from the scanner unit 20. The developing device develops the electrostatic latent image on the photosensitive drum using toner. The transfer roller transfers the toner image formed on the photosensitive drum to a sheet. The fixing device fixes the toner image transferred to the sheet. In this configuration, the printer engine section 30 copies the document image read by the scanner unit 20 to the sheet.
(Configuration of the Auto Document Feeder 10)
FIG. 2 is a perspective view showing the auto document feeder 10 in accordance with the embodiment of the present invention. FIG. 3 is a perspective view showing the auto document feeder 10 from which the sheet feeding tray 11 has been removed in accordance with the embodiment. FIG. 4 is a sectional view showing the internal configuration of the auto document feeder 10 in accordance with the embodiment.
As shown in FIGS. 2 to 4, the auto document feeder 10 is composed of a sheet feeding tray 11 on which a plurality of documents D are placed, a conveying device 12 that takes each of the documents D out of the sheet feeding tray 11 to convey the document D along a conveying path C (described later), and a sheet discharging tray 13 that accommodates a plurality of documents D discharged by the conveying device 12.
The conveying device 12 comprises a first and second guide members 121 and 122. The first and second guide members 121 and 122 comprise respective smooth guide surfaces inside. The U-shaped conveying path C is provided in the gap between the guide surfaces so that the document D can be conveyed along the conveying path C.
The conveying path C connects the sheet feeding tray 11 and the sheet discharging tray 13 together. The read position R is provided in a portion of the conveying path C which is closest to the scanner unit 20; a document image is read at the read position R.
The first guide member 121 is placed outside the second guide member 122. The first guide member 121 has a rectangular opening 121 a formed in its area corresponding to the read position R. This allows the document D conveyed along the conveying path C to be located opposite the scanner unit 20 on passing through the read position R.
The conveying path C has a pickup roller 123, a separate roller 124, a registration roller 125, a first conveying roller 126 a, a second conveying roller 126 b, a stabilizing roller 127, a third conveying roller 126 c, and a sheet discharging roller 128 which are arranged in this order from an upstream side in a direction in which the document D is conveyed.
The pickup roller 123 picks up each of the documents D in the sheet feeding tray 11 and loads it into the conveying path C of the conveying device 12. When a plurality of documents D are loaded by the pickup roller 123, the separate roller 124 passes only the uppermost document D through, while blocking the passage of the remaining documents D. The registration roller 125 registers the document D the passage of which is not blocked by the separate roller 124. The first to third conveying rollers 126 a to 126 c convey the document D registered by the registration roller 125, along the conveying path C. The stabilizing roller 127 stabilizes the behavior of the document D conveyed by the first to third conveying rollers 126 a to 126 c. The sheet discharging roller 128 constitutes a sheet discharging device 40 together with the sheet discharging tray 13. The sheet discharging roller 128 discharges the document D conveyed by the first to third conveying rollers 126 a to 126 c, from the conveying path C.
Each of the rollers 123 to 128 has a plurality of (in the present embodiment, four) roller pieces around a horizontally supported drive shaft at predetermined intervals. When each of the drive shafts is rotated, all roller pieces provided around the drive shaft rotate concurrently.
Pinch rollers 129 are arranged immediately below the respective sheet discharging roller pieces 128. Each of the pinch rollers 129 is rotatably disposed in a groove portion 121 b (shown only in FIG. 5) of the first guide member 121. Each of the pinch rollers 129 is contacted with an outer peripheral surface of the sheet discharging roller 128 under pressure by elastic means such as a leaf spring.
The separate roller 124, registration roller 125, first to third conveying roller 126 a to 126 c, and sheet discharging roller 128 constitute respective roller pairs together with driven rollers arranged opposite them across the conveying path C. For example, the separate roller 124 constitutes a separate roller pair together with a corresponding driven roller.
That portion of the first guide member 121 which lies downstream of the read position R is located below that portion of the second guide member 122 which lies downstream of the read position R. Thus, in the description below, the portion of the first guide member 121 located downstream of the read position R is called a lower guide portion 121 c. The portion of the second guide member 122 located downstream of the read position R is called an upper guide portion 122 c.
FIG. 5 is a schematic diagram showing the sheet discharging device 40 in accordance with the embodiment as viewed from a downstream side in the direction in which the document D is conveyed. As shown in FIG. 5, the lower guide portion (guide member) 121 c has a guide surface located below the lowermost portion of the sheet discharging roller 128. The lower guide portion 121 c comprises a plurality of (in the present embodiment, four) projecting portions 130 located substantially immediately below the drive shaft of the sheet discharging roller 128. The number of projecting portions 130 is not particularly limited.
The projecting portions 130 are disposed so that two of the four sheet discharging roller pieces 128 arranged at the opposite ends of the sheet discharging roller are each sandwiched between the projecting portions 130. The upper end of each projecting portion 130 projects upward from the lowermost portion of the sheet discharging roller 128.
Each projecting portion 130 comprises a scoop-up surface in its area located upstream in the conveying direction of the document D; the scoop-up surface becomes higher as it approaches its downstream end in the conveying direction. Thus, when the document D reaches the projecting portions 130, a portion of the document D which corresponds to the projecting portions 130 is scooped up by the scoop-up surface and runs onto the projecting portions 130. On the other hand, a portion of the document D which corresponds to the sheet discharging roller 128 is guided by the upper and lower guide portions 121 c and 122 c as it is and then advances between the sheet discharging roller 128 and the pinch roller 129.
(Configuration of the Sheet Discharging Tray 13)
Now, the sheet discharging tray 13 will be described with reference to FIG. 6.
FIG. 6 is a sectional view showing the sheet discharging tray 13 in accordance with the embodiment. In the description below, a sheet discharging direction refers to the direction in which the document D is discharged. A width direction refers to the direction orthogonal to the sheet discharging direction in a horizontal plane.
As shown in FIG. 6, the sheet discharging tray 13 comprises a bottom wall portion (stacking wall portion) 131 on which the discharged documents D are stacked, a rear wall portion 132 provided upstream of the bottom wall portion 131 in the sheet discharging direction to align the trailing ends of the documents D stacked on the bottom wall portion 131, and side wall portions 133 provided at the opposite ends of the bottom wall portion 131 in the width direction to prevent the documents D stacked on the bottom wall portion 131 from falling down.
The bottom wall portion 131 comprises a horizontal portion (fourth wall portion 131 a) and a ridge portion 131 b (shown only in FIG. 3); the horizontal portion 131 a is closer to the rear wall portion 132 than the ridge portion 131 b. A protruding portion 134 is provided in a central portion of the bottom wall portion 131 in the width direction to raise the width-wise central portion of the documents D stacked on the bottom wall portion 131.
The protruding portion 134 extends from a middle portion of the horizontal portion 131 a to a rear end of the ridge portion 131 b. A top wall portion 140 is placed at a top portion of the protruding portion 134. The upper wall portion 140 comprises a first inclined portion (third wall portion) 134 a, a second inclined portion (second wall portion) 134 b, a third inclined portion (first wall portion) 134 c, and a fourth inclined portion 134 d which are arranged in this order; the first inclined portion 134 a is closest to the rear wall portion 132, and the fourth inclined portion 134 d is farthest from the rear wall portion.
Each of the first to fourth inclined portions 134 a to 134 d is inclined so as to become higher in the sheet discharging direction. The document D placed on the sheet discharging tray 13 thus slides down toward the rear wall portion 132.
The first inclined portion 134 a extends both upstream and downstream in the sheet discharging direction by a predetermined length from a position located at that distance from the rear wall portion 132 which is almost equal to half of the vertical size of an A4-sized document D. In other words, the first inclined portion 134 a is formed within an area including the position of the leading end of the A4-sized document D with its trailing end abutting against the rear wall portion 132.
The third inclined portion 134 c extends both upstream and downstream in the sheet discharging direction by a predetermined length from a position located at that distance from the rear wall portion 132 which is almost equal to the vertical size of the A4-sized document D.
Thus, when the A4-sized document is placed on the sheet discharging tray 13, its middle portion corresponds to the first inclined portion 134 a, while its leading end corresponds to the third inclined portion 134 c.
If an A3-sized document is placed on the sheet discharging tray 13, two different areas in the middle portion of the document D correspond to the first and third inclined portions 134 a and 134 c.
The first inclined portion 134 a is steeper than the horizontal portion 131 a, connected to an upstream end of the first inclined portion 134 a in the sheet discharging direction, and the second inclined portion 134 b, connected to a downstream end of the first inclined portion 134 a in the sheet discharging direction. The inclination of the first inclined portion 134 a is utilized to prevent the documents D already stacked on the sheet discharging tray 13 from moving in the sheet discharging direction.
The third inclined portion 134 c is steeper than the second inclined portion 134 b, connected to an upstream end of the third inclined portion 134 c in the sheet discharging direction, and the fourth inclined portion 134 d, connected to a downstream end of the third inclined portion 134 c in the sheet discharging direction. The inclination of the third inclined portion 134 c is utilized to prevent the documents D already stacked on the sheet discharging tray 13 from moving in the sheet discharging direction.
When the subsequently discharged document D exerts a frictional force acting in the sheet discharging direction, on the documents D already stacked on the sheet discharging tray 13, the first and third inclined portions 134 a and 134 c exert a resistance force on the documents D on the sheet discharging tray 13 to offset the frictional force.
In particular, if the documents stacked on the sheet discharging tray are of the A4 size, their leading ends contact the first inclined portion 134 a at a large friction angle. Accordingly, even if the subsequently discharged document D exerts a strong frictional force in the sheet discharging direction, a resistance force is exerted which is sufficient to offset the frictional force.
Thus, even when the subsequently discharged document D applies a frictional force acting in the sheet discharging direction, to the documents D stacked on the sheet discharging tray 13, the resistance force of the first and third inclined portions 134 a and 134 c prevents the stacked documents D from moving in the sheet discharging direction.
The inclination of the third inclined portion 134 c is designed so that while an A3-sized document D is being discharged by the sheet discharging roller 128, the advancement of the document D is not hindered by the third inclined portion 134 c. Specifically, while the force of the sheet discharging roller 128 is acting directly on the A3-sized document to push it out, the document D can slide on the third inclined portion 134 c. This enables the A3-sized document discharged onto the sheet discharging tray 13 to advance smoothly to the fourth inclined portion 134 d without stopping at the third inclined portion 134 c.
A sub sheet discharging tray 135 is housed in the leading end of the sheet discharging tray 13 so that it can project from and withdraw into the sheet discharging tray 13. The sub sheet discharging tray 135 is disposed at a distance from the rear wall portion 132 that is almost equal to the vertical size of the A3-sized document D. Thus, when A3-sized documents D are stacked on the sheet discharging tray 13, their leading end corresponds to the sub sheet discharging tray 135.
The sub sheet discharging tray 135 is steeper than the fourth inclined portion 134 d. The sub sheet discharging tray 135 utilizes its inclination to prevent A3-sized documents D stacked on the sheet discharging tray 13 from moving in the sheet discharging direction.
When the subsequently discharged document D exerts a frictional force on the A3-sized documents D already stacked on the sheet discharging tray 13, the first and third inclined portions 134 a and 134 c and sub sheet discharging tray 135 exert a resistance force on the A3-sized documents D on the sheet discharging tray 13 to offset the frictional force.
Thus, even when the subsequently discharged document D applies a frictional force acting in the sheet discharging direction, to the A3-sized documents D stacked on the sheet discharging tray 13, the resistance force of the first and third inclined portions 134 a and 134 c and sub sheet discharging tray 135 prevents the stacked A3-sized documents D from moving in the sheet discharging direction.
A plurality of ribs 136 (only shown in FIG. 3) are formed on the bottom wall portion 131, protruding portion 134, and sub sheet discharging tray 135 of the sheet discharging tray 13 along the sheet discharging direction. These ribs 136 reduce the frictional force acting on the moving document D. The ribs 136 allow the documents D placed directly on the bottom wall portion 131 of the sheet discharging tray 13 to slide down smoothly toward the rear of the sheet discharging tray.
(Configuration of the Scanner Unit 20)
The scanner unit 20 comprises a glass plate (not shown) at a position corresponding to the read position R. The glass plate 21 is colorless and transparent and has a reader (not shown) provided on its scanner unit 20 side. The reader comprises a first carriage, a second carriage, an image forming lens, and a CCD sensor (none of them are shown).
The first carriage is provided with an exposure lamp (not shown) that irradiates the document D passing on a surface of the glass plate, and a first mirror that reflects reflected light from the document surface in a predetermined direction. Second and third mirrors (not shown) are attached to the second carriage to reflect the reflected light from the first mirror in a predetermined direction.
The light emitted from the exposure lamp passes through the glass plate to the surface of the document D passing through the read position R. Then, the light reflected off the document surface passes through the glass plate back to the scanner unit 20. The light is reflected by the first to third mirrors and then guided to the image forming lens. The light converged by the image forming lens is detected by the CCD sensor. The detection signal is used to create image data.
A document glass board (not shown) is provided on the top surface of the scanner unit 20 so that the document D is manually placed on the document glass board. The document glass board is used to read a document image without the use of the auto document feeder 10.
(Operation of Discharging the Document D)
The document D from which the document image has been read is conveyed to the sheet discharging roller 128 while being guided by the upper and lower guides 121 c and 122 c. Once the conveyed document D reaches the projecting portions 130 of the lower guide portion 121 c, a portion of the document D which corresponds to the projecting portions 130 is scooped up by the scoop-up surface and runs onto the projecting portions 130. However, a portion of the document D which corresponds to the sheet discharging roller 128 is guided by the upper and lower guide portions 121 c and 122 c as it is and then advances between the sheet discharging roller 128 and the pinch roller 129.
This causes the different portions of the document D discharged onto the sheet discharging tray 130 to advance in the respective directions. As a result, the document D discharged to the sheet discharging tray 13 has a locally substantially S-shaped cross section, that is, the document is corrugated.
During the discharging process, the corrugated document D hangs down progressively from its leading end and finally comes into contact with the surface of the documents already stacked on the sheet discharging tray 13. The discharged document D advances continuously in the sheet discharging direction until its trailing end sandwiched between the sheet discharging roller 128 and the pinch roller 129 is released. In the meantime, a frictional force acting in the sheet discharging direction is continuously exerted on the documents D stacked on the sheet discharging tray 13.
However, if the documents stacked on the sheet discharging tray 13 are of the A4 size, their leading end corresponds to the third inclined portion 134 c of the sheet discharging tray 13, while their middle portion corresponds to the first inclined portion 134 a. Consequently, even when a frictional force is exerted by the subsequently discharged document D, the resistance force of the third inclined portions 134 a and 134 c prevents the documents D on the sheet discharging tray 13 from moving in the sheet discharging direction.
Even when the documents stacked on the sheet discharging tray 13 are of the A3 size, their middle portion corresponds to the first and third inclined portions 134 a and 134 c, while their leading end corresponds to the sub sheet discharging tray 135. Consequently, even when a frictional force is exerted by the subsequently discharged document D, the resistance force of the first and third inclined portions 134 a and 134 c and sheet discharging tray 135 prevents the documents D on the sheet discharging tray 13 from moving in the sheet discharging direction.
The present embodiment therefore prevents the positions of the documents stacked on the sheet discharging tray 13 from being disturbed by the subsequently discharged document D. This improves the alignment of the discharged documents D housed in the sheet discharging tray 13.

EFFECTS OF THE PRESENT EMBODIMENT

The sheet discharging tray 13 in accordance with the present embodiment comprises the first to third inclined portions 134 a and 134 c, which offer resistance to the documents D stacked on the sheet discharging tray 13 when they move in the sheet discharging direction. Thus, even when a frictional force is exerted by the subsequently discharged document D, the resistance force of the first and third inclined portions 134 a and 134 c prevents the documents D on the sheet discharging tray 13 from moving in the sheet discharging direction.
The third inclined portion 134 c in accordance with the present embodiment extends both upstream and downstream in the sheet discharging direction by the predetermined length from the position located at that distance from the rear wall portion 132 of the sheet discharging tray 13 which is almost equal to the vertical size of the A4-sized document D.
Thus, when A4-sized documents are stacked on the sheet discharging tray 13, their leading ends contact the third inclined portion 134 c at a large friction angle. This causes a strong resistance force to act on the A4-sized documents on the sheet discharging tray 13. That is to say, the third inclined portion 134 c in accordance with the present embodiment is placed so as to maximize the difficulty of moving the A4-sized documents on the sheet discharging tray 13.
The first inclined portion 134 a in accordance with the present embodiment extends both upstream and downstream in the sheet discharging direction by the predetermined length from the position located at that distance from the rear wall portion 132 of the sheet discharging tray 13 which is almost equal to half of the vertical size of the A4-sized document D.
Thus, when a large number of A4-sized documents D are stacked on the sheet discharging tray 13, even if the thickness of these documents D precludes the leading ends of the documents D on the sheet discharging tray 13 from coming into the third inclined portion 134 c, the first inclined portion 134 c exerts the required resistance force on the A4-sized documents on the sheet discharging tray 13. This prevents the documents D on the sheet discharging tray 13 from moving in the sheet discharging direction.
The sheet discharging tray 13 in accordance with the present invention also comprises the protruding portion 134 in its central portion in the width direction. The first and third inclined portions 134 a and 134 c are provided on the top surface of the protruding portion 134.
This raises the central portion of the documents D on the sheet discharging tray 13 in the width direction to reduce the friction area over which the subsequently discharged document D rubs against the documents D on the sheet discharging tray 13.
The sheet discharging tray 13 in accordance with the present invention comprises the sub sheet discharging tray 135, which offers resistance to A3-sized documents D stacked on the sheet discharging tray 13 when they move in the sheet discharging direction. Thus, even when a frictional force is exerted by the subsequently discharged document D, the resistance force of the first and third inclined portions 134 a and 134 c and sub sheet discharging tray 135 prevents the documents D stacked on the sheet discharging tray 13 from moving in the sheet discharging direction.
The sub sheet discharging tray 135 in accordance with the present embodiment is disposed at a distance from the rear wall portion 132 of the sheet discharging tray 13 that is almost equal to the vertical size of the A3-sized document D. Thus, when A3-sized documents D are stacked on the sheet discharging tray 13, their leading ends contact the sub sheet discharging tray 135 at a large friction angle. This causes a strong resistance force to act on the A3-sized documents D on the sheet discharging tray 13. That is to say, the sub sheet discharging tray 135 in accordance with the present embodiment is placed so as to maximize the resistance against movement of the A3-sized documents D on the sheet discharging tray 13.
In short, the present embodiment improves the alignment of the discharged documents D on the sheet discharging tray 13 without the need for a marked corrugation. This reduces a possible load imposed on the documents D. The present embodiment also eliminates the need to significantly incline the entire bottom wall portion 131 of the sheet discharging tray 13. This prevents an increase in the size of the device. Moreover, even documents D of various sizes discharged by the sheet discharging roller 128 are not hindered from being discharged. This reliably improves the alignment of the discharged documents D on the sheet discharging tray.
If the length of the first inclined portion 134 a in the sheet discharging direction is set to contain the position of the leading end of B5-sized documents D stacked on the sheet discharging tray, effects similar to those exerted on the A4-sized documents are exerted on the B5-sized documents D.
The inclinations of the first and third inclined portions 134 a and 134 c are designed so that even when the sub sheet discharging tray 135 is not drawn out, the combination of the inclined portions 134 a and 134 c prevents A3-sized documents D stacked on the sheet discharging tray 13 from moving in the sheet discharging direction. However, the drawn-out sub sheet discharging tray 135 further improves the alignment of the discharged documents.
The protruding portion 134 in accordance with the present invention comprises the second inclined portion 134 b between the first and third inclined portions 134 a and 134 c. However, for example, as shown in FIG. 7, a bent portion 134 e may be formed between the first and third inclined portions 134 a and 134 c, instead of the second inclined portion 134 b. As shown in FIG. 7, the bent portion 134 e includes a horizontal surface, an inclined surface having a smaller gradient than the third surface, and an inclined surface having a gradient opposite to that of the third surface.
The first to fourth inclined portions 134 a to 134 d in accordance with the present embodiment are formed in the protruding portion 134 of the bottom wall portion 131. However, the present invention is not limited to this. For example, the inclined portion may be formed all over the bottom wall portion 131. Even without the protruding portion 134, substantial effects can be produced by the first to fourth inclined portions 134 a to 134 d formed in the bottom wall portion of the sheet discharging tray.
In the description of the present embodiment, the sheet discharging device 40 is applied to the digital copier. However, this is only illustrative. The present embodiment is expected to produce appropriate effects in any application provided that the application involves discharging of paper.
The present invention is not limited to the above embodiments proper. In implementation, the components of the embodiments can be varied without departing from the spirit of the present invention. Further, various inventions can be formed by properly combining a plurality of components disclosed in the above embodiments. For example, some of the components shown in the embodiments may be omitted. Moreover, components of the different embodiments may be appropriately combined.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. A sheet discharging device comprising:

a sheet discharging section which discharges sheets; and

a sheet discharging tray including a stacking wall portion on which discharged sheets are stacked, the stacking wall portion comprising:

a first wall portion having a first surface which becomes higher in a direction in which sheets are discharged; and

a second wall portion connected to an upstream end of the first wall portion in the sheet discharging direction and having a second surface including at least one of a horizontal surface, an inclined surface having a smaller gradient than that of the first surface, and an inclined surface having a gradient opposite to that of the first surface.

2. The sheet discharging device according to claim 1, wherein the first surface lies within an area including a position corresponding to a leading end of sheets of a size substantially half that of the largest sheet possibly discharged by the sheet discharging section when the sheets are stacked on the stacking wall portion.

3. The sheet discharging device according to claim 1, further comprising:

a third wall portion placed upstream of the second wall portion in the sheet discharging direction and having a third surface which becomes higher in the sheet discharging direction; and

a fourth wall portion connected to an upstream end of the third wall portion in the sheet discharging direction and having a fourth surface including at least one of a horizontal surface, an inclined surface having a smaller gradient than that of the third surface, and an inclined surface having a gradient opposite to that of the third surface.

4. The sheet discharging device according to claim 2, further comprising:

5. The sheet discharging device according to claim 3, wherein the third surface lies within an area including a position corresponding to a central portion of sheets of a size substantially half that of the largest sheet possibly discharged by the sheet discharging section when the sheets are stacked on the stacking wall portion.

6. The sheet discharging device according to claim 4, wherein the third surface lies within an area including a position corresponding to a central portion of sheets of a size substantially half that of the largest sheet possibly discharged by the sheet discharging section when the sheets are stacked on the stacking wall portion.

7. The sheet discharging device according to claim 1, wherein the first surface has an inclination which allows a sheet being discharged by the sheet discharging section to slide on the first surface.

8. A sheet discharging device comprising:

a sheet discharging section which discharges sheets; and

a sheet discharging tray including a stacking wall portion on which discharged sheets are stacked, the sheet discharging tray comprising:

a projecting portion having a wall portion provided in a central portion of the sheet discharging tray in a width direction substantially orthogonal to the sheet discharging direction to raise a width-wise central portion of the sheets stacked on the sheet discharging tray, the wall portion comprising: