SHEET FEEDER, IMAGE READING APPARATUS AND IMAGE FORMING APPARATUS

Abstract

A paper press member 240 configured to be capable of advancing and retracting with respect to a paper guide 220 is provided between a paper feed roller 234 and the front end in the paper feed direction of paper loaded in a manual feed tray 230. When a plurality of sheets of paper enter into the press-contact section between the paper feed roller 234 and a reverse roller 235, the reverse roller 235 is rotated in the reverse direction to retract the sheet on the reverse roller side to the manual feed tray 230. At this time, by causing the paper press member 240 to project from the upper surface of the paper guide 220, the sheet to be retracted and the paper press member 240 come into contact with each other, so that the travel amount of the sheet when retracting the sheet is reduced.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2007-124930 filed in Japan on May 9, 2007, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present application relates to a sheet feeder capable of certainly preventing multi-feeds (feeding two or more sheets at a time), and an image reading apparatus and an image forming apparatus comprising the sheet feeder.

2. Description of Related Art

As the paper feeding system in an image forming apparatus, two types of feeding systems are used. One is a paper feeding cassette system in which one sheet of paper is taken out of the paper feeding cassette at one time and fed to a printing section, and the other is a manual feedtray system in which paper of irregular size, or only a small amount of paper to be used, is loaded in the manual feed tray, and the paper is taken out of the manual feed tray and supplied to the printing section.

Since a number of sheets of paper corresponding to a print request are often loaded in the manual feed tray, the load of paper in the manual feed tray is small. However, with high-speed processing (high-speed image processing, high-speed print processing etc.) in recent years, there is a tendency toward an increase in the load of paper in the manual feed tray. FIG. 1 is a schematic view showing a schematic structure of a conventional manual paper feed unit, and FIGS. 2A to 2C are explanatory views for explaining the operation of the manual paper feed unit. A manual paper feed unit 53 shown in FIG. 1 comprises a manual feed tray 530 for loading paper, and a paper regulating plate 531 for preventing skew of the transported paper by being adjusted suitably according to the paper size. In order to regulate the paper load position in the direction orthogonal to the paper feed direction, the paper regulating plate 531 is configured to be able to slide in the above-mentioned direction with a mechanism such as, for example, lack and pinion gears.

Thus, in the direction orthogonal to the paper feed direction, the paper position is regulated by the paper regulating plate 531. However, a member for regulating the paper position is not generally provided for the paper feed direction (particularly for the rear end of the paper loaded in the manual feed tray 530). In other words, in order to avoid paper feeding errors, the manual feed tray 530 is arranged on a side face of an apparatus in an inclined manner so that the paper loading surface is lower on the apparatus side and higher on the rear end side of the loaded paper. Since the paper feed performance is improved, it is not necessarily to regulate the position of the rear end of the paper.

In such a manual feed tray 530, when a large amount of paper is loaded and a large amount of paper is used for one printing as in recent days, like the above-mentioned paper feeding cassette system, frictional electrification occurs between a sheet P1 to be taken out by a pickup roller 532 and a sheet P2 to be fed next, and the frictionally electrified charge accumulates in the paper loading section, and thus there is a possibility that a multi-feed in which a plurality of sheets of paper are simultaneously fed may occur in feeding the paper (see FIG. 2A). If the paper is transported to the printing section in the multi-feed condition, not only the print quality is degraded, but also friction with peripheral members may cause a paper jam and damage to the peripheral members.

Therefore, in the manual paper feed unit 53, the sheet P1 taken out of the manual feed tray 530 and the sheet P2 to be fed next are separated using a paper feed roller 534 and an opposing reverse roller 535 pressed against the paper feed roller 534, so that one sheet of paper is transported to the printing section. The reverse roller 535 is not always rotated in the reverse direction during the paper feeding process, but is rotated in the reverse direction when a predetermined load is applied to a torque limiter placed on the rotation shaft of the reverse roller 535 and the shaft axis is coupled to the driving shaft. Hence, during normal feed in which one sheet is transported, since the driving load is small, the driving shaft is not coupled to and the reverse roller 535 is rotated according to the paper feed roller 534. On the other hand, during multi-feed in which a plurality of sheets of paper are fed at a time, since the driving load is large, the driving shaft is coupled to and the reverse roller 535 is rotated in the direction opposite to the rotation direction of the paper feed roller 534 (see FIG. 2B).

Since the paper feed roller 534 and the reverse roller 535 are rotated in mutually opposite directions, the fed sheet on the paper feed roller 534 side is transported to the downstream side in the paper feed direction and transported to the printing section as a predetermined supply destination, while the fed sheet on the reverse roller 535 side is transported to the upstream side in the paper feed direction and returned to the manual feed tray 530.

When retracting the extra sheet fed by the multi-feed to the manual feed tray 530 by the function of the reverse roller 535, the travel amount (return amount) varies depending on the type of paper. In other words, when the rotation speed of the reverse roller 535 is fixed, the function (returning force) acting on the paper is fixed. Therefore, if the type of paper is thin paper, since the paper has small flexibility, the returning force is not sufficiently transmitted, the paper is bucked, and the return amount is relatively small. In this case, since the multi-feed problem is solved by slightly retracting the sheet from the paper feed roller 534 to the upstream side, a multi-feed does not occur when feeding the next sheet.

However, when the paper type is thick paper, the paper has strong flexibility, and therefore the returning force of the reverse roller is directly transmitted to the paper and the return amount is large. In particular, when the paper is small-sized thick paper such as a post card, since the weight of the paper is light with respect to the returning force, the return amount is large and the following problem occurs.

Specifically, as shown in FIG. 2C, if the front end in the sheet feed direction of the sheet P2 to be moved back to the manual feed tray 530 returns upstream of the point where the pickup roller 532 is lowered when feeding paper, a sheet P3 placed under the returned sheet P2 is picked up by the pickup roller 532 in the next paper feeding process and two sheets P2 and P3 are fed at one time, and thus a multi-feed occurs definitely.

SUMMARY

The present application has been made with the aim of solving the above problems, and it is an object of the present application to provide a sheet feeder comprising, between a paper feed roller and the front end of a stored sheet in a sheet feed direction, a contact member configured to be capable of advancing and retracting and capable of coming into contact with an extra sheet fed by a multi-feed, and thereby capable of reducing the travel amount of sheet when retracting the extra sheet fed by the multi-feed and capable of certainly preventing multi-feeds, and to provide an image reading apparatus and an image forming apparatus comprising the sheet feeder.

A sheet feeder according to the present application is a sheet feeder comprising: a sheet storing section for storing sheets; a paper feed roller for feeding a sheet taken out of the sheet storing section to a predetermined supply destination; detecting section for detecting a multi-feed of sheets in the paper feed roller; and a sheet retracting unit for retracting, when the detecting means detects a multi-feed of sheets, an extra sheet fed by the multi-feed to an upstream side in a sheet feed direction, and characterized by comprising, between the paper feed roller and the front end in the sheet feed direction of the sheet stored in the sheet storing section, a contact member configured to be capable of advancing and retracting and capable of coming into contact with an extra sheet fed by a multi-feed.

In this application, since the contact member capable of advancing and retracting and capable of coming into contact with the sheet fed by a multi-feed is provided between the paper feed roller and the front end of the stored sheet in the sheet feed direction, it is possible to reduce the travel amount of sheet when retracting the sheet fed by the multi-feed to the sheet storing section, and it is possible to prevent a multi-feed in the next paper feeding process.

The sheet feeder according to the present application is characterized in that the contact member comes into contact with the front surface or the back surface of the extra sheet when retracting the sheet.

In this application, since the contact member is configured to come into contact with the front surface or the back surface of the sheet when retracting the sheet, friction is caused between the contact member and the sheet to be retracted when a multi-feed of sheets occurs.

The sheet feeder according to the present application is characterized by further comprising a driving section for moving, when feeding a sheet to the supply destination, said contact member not to come into contact with the sheet, and for moving, when said detecting means detects a multi-feed of sheets, said contact member to come into contact with the extra sheet fed by the multi-feed.

In this application, since the contact member is configured to be separated from a sheet during normal feeding and come into contact with a sheet when a multi-feed is detected, the transport operation in the normal paper feeding process is not interfered, and the travel amount of sheet when retracting the sheet is reduced by bringing the contact member into contact with the sheet only when a multi-feed occurs.

The sheet feeder according to the present application is characterized in that the sheet retracting unit includes a reverse roller placed opposite to the paper feed roller, and a torque limiter supported on a driving shaft of the reverse roller, wherein when the torque limiter detects an increase in load and the reverse roller is coupled to a drive source and starts to be driven, the detecting means determines that a multi-feed was detected.

In this application, a multi-feed is detected by detecting a rotation of the reverse roller which is conventionally provided to separate sheets fed by a multi-feed.

The sheet feeder according to the present application is characterized in that the travel amount of sheet when the sheet retracting unit retracts the sheet is restrained by the contact between the sheet and the contact member.

In this application, since the travel amount of sheet when retracting the sheet is restrained by the contact between the sheet and the contact member, the possibility of reoccurrence of multi-feed in the next paper feeding process is decreased.

The sheet feeder according to the present application is characterized by comprising a pickup roller arranged to be able to come into contact with the sheet stored in the sheet storing section, wherein the sheet feeder restrains the front end in the feed direction of a sheet to be retracted from returning upstream of a contact section between the pickup roller and the sheet stored in the sheet storing section.

In this application, since returning of the sheet to the upstream of the contact section between the pickup roller and the stored sheet is restrained, a sheet to be fed in the next paper feeding process is the sheet retracted by the retracting means.

The sheet feeder according to the present application is characterized in that the contact member has elasticity.

In this application, by using an elastic member, such as rubber, foam sponge, and cork, as the contact member, even if the contact member is brought into contact with a sheet to be retracted, there is no possibility that the sheet is damaged or torn, and it is possible to prevent wasteful disposal of sheets and degradation of the print quality.

The sheet feeder according to the present application is characterized in that the sheet storing section is a manual feed tray.

In this application, by applying the sheet feeder to a manual feed tray having no regulating member for regulating the position of the rear end of a sheet in the sheet feeding direction, it is possible to reduce the occurrence of multi-feeds in the paper feed unit of the manual feed tray.

An image reading apparatus according to the present application is characterized by comprising: a sheet feeder of the above-mentioned application; and image reading means for reading an image recorded on a sheet fed by the sheet feeder.

In this application, since multi-feeds are prevented, the processing efficiency is not decreased even when reading a large amount of images.

An image forming apparatus according to the present application is characterized by comprising: a sheet feeder of the above-described application; and image forming means for forming an image on a sheet fed by the sheet feeder.

In this application, since multi-feeds are prevented, the processing efficiency is not decreased even when printing a large amount of images.

According to the present application, since the contact member capable of advancing and retracting and capable of coming into contact with an extra sheet fed by a multi-feed is provided between the paper feed roller and the front end of the stored sheet in the sheet feed direction, it is possible to reduce the travel amount of sheet when retracting the sheet fed by the multi-feed to the sheet storing section, and it is possible to prevent a multi-feed in the next paper feeding process.

According to the present application, since the contact member is configured to come into contact with the front surface or back surface of a sheet when retracting the sheet, it is possible to reduce the travel amount of sheet when retracting the sheet by the friction between the contact member and the front surface or back surface of the sheet.

According to the present application, since the contact member is configured to be separated from a sheet during normal feeding and come into contact with a sheet when a multi-feed is detected, the transport operation in the normal paper feeding process is not interfered, and it is possible to reduce the travel amount of sheet when retracting the sheet by bringing the contact member into contact with the sheet only when a multi-feed occurs.

According to the present application, it is possible to detect a multi-feed by detecting a rotation of the reverse roller which is conventionally provided to separate sheets fed by the multi-feed.

According to the present application, since the travel amount of sheet when retracting the sheet is restrained by the contact between the sheet and the contact member, it is possible to decrease the possibility of reoccurrence of multi-feed in the next paper feeding process.

According to the present application, since returning of the sheet to the upstream of the contact section between the pickup roller and the stored sheet is restrained, the sheet retracted by the retracting means is certainly transported in the next paper feeding process, and thus it is possible to prevent reoccurrence of multi-feed.

According to the present application, by using an elastic member such as rubber, foam sponge, and cork as the contact member, even if the contact member is brought into contact with a sheet to be retracted, there is no possibility that the sheet is damaged or torn, and thus it is possible to prevent wasteful disposal of sheets and degradation of the print quality.

According to the present application, by applying the sheet feeder to a manual feed tray having no regulating member for regulating the position of the rear end of a sheet in the sheet feeding direction, it is possible to reduce the occurrence of multi-feeds in the paper feed unit of the manual feed tray.

According to the present application, since it is possible to prevent multi-feeds, it is possible to automatically read a large amount of images without decreasing the processing efficiency.

According to the present application, since it is possible to prevent multi-feeds, it is possible to print a large amount of images at a time without decreasing the processing efficiency.

The above and further objects and features of the application will more fully be apparent from the following detailed description with accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view showing a schematic structure of a conventional manual paper feed unit;

FIGS. 2A to 2C are explanatory views for explaining the operation of the manual paper feed unit;

FIG. 3 is a cross sectional view showing the entire structure of a digital all-in-one apparatus comprising a sheet feeder according to the present application;

FIG. 4 is a schematic view for explaining the structure of a manual paper feed unit according to an embodiment;

FIGS. 5A and 5B are schematic views showing the structure of a paper press member;

FIGS. 6A to 6C are explanatory views for explaining an operation performed by the manual paper feed unit when a multi-feed occurs;

FIGS. 7A to 7C are explanatory views for explaining an operation performed by the manual paper feed unit when a multi-feed occurs;

FIG. 8 is a block diagram showing the structure of a control system of the manual paper feed unit; and

FIG. 9 is a flowchart showing the steps of a paper feeding process performed by the manual paper feed unit.

DETAILED DESCRIPTION

The following description will explain in detail the present application, based on the drawings illustrating an embodiment thereof.

FIG. 3 is a cross sectional view showing the entire structure of a digital all-in-one apparatus comprising a sheet feeder according to the present application. The digital all-in-one apparatus shown in FIG. 3 comprises a printer unit 1 for forming an image on a sheet of paper, OHP film etc. (hereinafter just referred to as the paper); a paper feed unit 2 for supplying the paper to the printer unit 1; and a scanner unit 3 for generating image data by optically reading a document image.

The scanner unit 3 comprises a light source unit 32, a mirror unit 33 and a reading unit 34 as optical image reading means. The light source unit 32 applies reading light to a document placed on a document platen 31, or a document sent from an automatic document feeder 35. The mirror unit 33 comprises a pair of mirrors whose reflection surfaces placed at a right angle to each other to guide reflected light from the document to the reading unit 34. The reading unit 34 comprises a reading element, such as a CCD, for converting the light guided by the mirror unit 33 into an analog signal; an AD converter for converting the analog signal obtained by the reading element into a digital signal; and a DSP for correcting the converted digital signal, based on the variation in the sensitivity of the CCD etc., and outputting the resulting signal as image data.

The printer unit 1 comprises an exposure unit 10, a developing device 11, a photosensitive drum 12, an electrifier 13, a cleaner unit 14, a transfer unit 15, and a fixing unit 16, and forms an image on paper fed from the paper feed unit 2, based on image data generated in the scanner unit 3, or print data obtained by communication means, not shown.

The exposure unit 10 comprises a laser scanning unit (LSU) including a laser irradiating section and a reflection mirror, and exposes the photosensitive drum 12 charged evenly by the electrifier 13 to light, according to the inputted image data, thereby forming an electrostatic latent image on the surface of the photosensitive drum 12 according to the image data. The electrifier 13 is electrifying means for evenly charging the surface of the photosensitive drum 12 to a predetermined electric potential, and, for example, a charger type electrifier is used.

The developing device 11 visualizes the electrostatic latent image formed on the photosensitive drum 12 with toner as developer. The cleaner unit 14 removes and collects the toner remaining on the surface of the photosensitive drum 12 after the development and transfer of the image.

The toner visualizing the image on the photosensitive drum 12 is transferred to the paper transported from the sheet feed unit 2. The transfer unit 15 used for this is a mechanism for transferring the toner image onto the paper by the application of an electric field of the opposite polarity to the toner. For example, when the electrostatic image has negative charge, the polarity of the electric field applied to the transfer unit 15 is positive.

The transfer unit 15 of the image forming apparatus comprises a transfer belt stretched between rollers, such as a driving roller and a driven roller, and having a predetermined resistance value. A transfer roller capable of applying a transfer electric field is disposed in the contact section between the photosensitive drum 12 and the transfer belt. The transfer roller has electrical conductivity and elasticity, and the photosensitive drum 12 and the transfer belt are brought into surface contact with each other by a predetermined width (transfer nip) by the function of the transfer roller. Hence, the transfer efficiency to the paper being transported is improved. The paper to which the toner image has been transferred by the transfer unit 15 is transported to the fixing unit 16 disposed on the downstream side in the paper feed direction.

The fixing unit 16 comprises a heat roller and a press roller, melts the unfixed toner on the transported sheet by heating the toner with the temperature of the surface of the heat roller, and fixes the toner image on the sheet with the pressing force of the press roller in the press-contact section (fixing nip) between the heat roller and the press roller.

The paper feed unit 2 includes paper feed cassettes 21a to 21d for storing paper of different types and sizes, a large-capacity paper feed cassette 22 capable of storing a large amount of paper of regular size, and a manual paper feed unit 23 for mainly picking up paper of irregular size.

The paper supplied from the paper feed unit 2 is transported to a resist roller 18 by the function of transport rollers provided along a predetermined path. The sheet that has reached the resist roller 18 is once stopped, and the resist roller 18 is rotated again at the timing of aligning the front end of the stopped paper and the toner image on the photosensitive drum 12. At this time, the toner image on the photosensitive drum 12 is transferred to the paper by the function of the transfer unit 15. The paper to which the toner image has been transferred is guided to the fixing unit 16, and the toner image on the paper is fixed as an image. The paper on which the image has been fixed is discharged onto a paper output tray 20 by the function of a paper discharge roller 19.

The following will explain the structure and operation of the manual paper feed unit 23 according to this embodiment. FIG. 4 is explanatory views for explaining the structure of the manual paper feed unit 23 according to this embodiment. The manual paper feed unit 23 comprises a manual feed tray 230 capable of storing a plurality of sheets of paper of a size and material desired by the user; a paper regulating plate 231 for regulating the paper position in a direction orthogonal to the paper feed direction with respect to the manual feed tray 230; a pickup roller 232 for picking up the topmost sheet of the paper stored in the manual feed tray 230; a paper feed roller 234 for feeding the paper picked up by the pickup roller 232 from the manual feed tray 230 to a downstream transport path 221 for supplying the paper to a print section; and a reverse roller 235 for separating sheets when a multi-feed occurs.

The pickup roller 232 is mounted to an end of an arm section (not shown) supported on the rotation shaft of the paper feed roller 234. The pickup roller 232 does not reach the feed point of the loaded paper and waits above the feed point until the normal feed timing. A drive coupling is made by an electromagnet etc. supported on the rotation shaft of the paper feed roller 234 which rotates upon a paper feed request, a drive belt 233 which links the paper feed roller 234 and the pickup roller 232 rotates, and the pickup roller 232 is lowered to the feed point by the rotational moment. The topmost sheet of the loaded paper is taken out of the manual feed tray 230 by the friction with the surface of the pickup roller 232.

The paper taken out by the pickup roller 232 passes over a paper guide 220 provided between the paper feed roller 234 and the manual feed tray 230, and reaches the press-contact section between the paper feed roller 234 and the reverse roller 235. The paper which has reached the press-contact section is fed to the transport path 221 on the downstream side by the function of the paper feed roller 234.

The reverse roller 235 is placed in a state in which it is pressed against the paper feed roller 234. The reverse roller 235 has a function of rotating in a direction reverse to the paper feed direction when a multi-feed occurs and retracting an extra sheet fed by the multi-feed (that is, a sheet fed together with a sheet intended to be transported) to the manual feed tray 230. Whether or not the reverse roller 235 is to be rotated in the reverse direction is determined as follows.

Specifically, a torque limiter 206 (see FIG. 8) is supported on a driving shaft 235a of the reverse roller 235. When one sheet is fed, the drive load of the torque limiter 206 is small and a coupling to a drive source 204b is not made (see FIG. 8). Thus, the reverse roller 235 is rotated by the transport force of the transported paper and apparently feeds the transported paper to the transport path 221 together with the paper feed roller 234. On the other hand, if a multi-feed occurs and plural sheets of paper are transported, when plural sheets of transported paper enter into the press-contact section between the paper feed roller 234 and the reverse roller 235, the load of the torque limiter 206 increases, a coupling to the drive source 204b is made, the reverse roller 235 is rotated in the direction reverse to the rotation direction of the paper feed roller 234 as the driving shaft 235a of the reverse roller 235 turns, and the sheet on the reverse roller 235 side (the extra sheet fed by the multi-feed) is returned to the manual feed tray 230. In short, the sheet retracting unit 250 according to the present application comprises the reverse roller 235 and the torque limiter 206, and is designed to drive the reverse roller 235 and retract the transported sheet to the upstream side in the paper feed direction when simultaneous feeding of multiple sheets of transported paper is detected by a later-described multi-feed detecting section 205 (see FIG. 8).

Disposed in the manual feed tray 230 is a paper regulating plate 231 for preventing paper from being wrinkled or torn and missing of a part of printed image due to skew of the transported paper by adjusting the paper position in a direction orthogonal to the paper feed direction of the loaded paper. The paper regulating plate 231 is connected to the rack/pinion gear so that it is movable according to the paper size and slidable with respect to the manual feed tray 230. On the other hand, for the position of the rear end of the loaded paper, no member for regulating the position is provided. As shown in FIG. 8, the manual feed tray 230 is mounted in an inclined manner so that its end on the apparatus side is lower and the other end on the paper rear-end side is higher, and thus the position of the front end of the loaded paper is naturally determined.

In the manual feed unit 34 having such a structure, after occurrence of multi-feed, when the paper is returned to the manual feed tray 230 by the function of the reverse roller 235, the above-mentioned problem occurs. In other words, when a multi-feed occurs, the sheet on the reverse roller 235 side is returned to the upstream side in the paper feed direction, but if the sheet is returned upstream of the paper feed point of the pickup roller 232 by the returning force of the reverse roller 235, the sheet under the returned sheet (the next sheet intended to be transported after the returned paper) is taken out by the pickup roller 232 in the next paper feeding process and transported together with the paper returned to the top of that paper, and therefore there is an extremely high possibility of multi-feed.

The condition of multi-feed occurred at this time is very bad, and when the lower sheet is held between the paper feed roller 234 and the reverse roller 235, the load of the torque limiter 206 does not increase and the lower sheet enters into the transport path 221, but when the upper sheet advances to a position where the upper sheet is held between the paper feed roller 234 and the reverse roller 235, the load of the torque limiter 206 increases. As a result, the reverse roller 235 starts rotating in the reverse direction. However, since the function of the reverse roller 235 is to return the front end of the paper fed by the multi-feed with the returning force of the reverse roller 235, the reverse roller 235 does not have a sufficient transport force for transporting the lower sheet. Therefore, even when the upper sheet passes through the transport path by the rotation force of the paper feed roller 234, the lower sheet stays in a state in which it is held between the paper feed roller 234 and the reverse roller 235, and a paper entry sensor, not shown, is kept in an on-state. As a result, a transport jam is caused and the apparatus is stopped.

In order to solve such a problem, in this embodiment, a paper press member 240 is provided between the paper feed roller 234 and the manual feed tray 230. FIGS. 5A and 5B are schematic views showing the structure of the paper press member 240. FIG. 5A shows a partial cross section seen from a direction orthogonal to the paper feed direction, and FIG. 5B shows a partial cross section seen from the paper feed direction. The paper press member 240 comprises a contact member 241 capable of coming into contact with paper passing through the upper surface of the paper guide 220, and a solenoid 242 for advancing and retracting the contact member 241 from an aperture 220a formed in the paper guide 220.

The contact member 241 is made of elastic material, such as rubber, foam sponge and cork, so that it has a predetermined width in a direction orthogonal to the paper feed direction and a semicircular cross section. When the paper is transported normally, the contact member 241 is located under the paper guide 220 and does not come into contact with the passing paper. On the other hand, when a multi-feed is detected and the paper is to be retracted to the manual feed tray 230 by the function of the reverse roller 235, the contact member 241 is moved up by the operation of the solenoid 242 to cause a part of the contact member 241 to project from the aperture 220a of the paper guide 220, so that the contact member 241 and the retracted paper come into contact with each other. The projecting amount of the contact member 241 from the aperture 220a is controlled by the operation of the solenoid 242. When the projecting amount is increased, the friction force between the contact member 241 and the paper being retracted increases, and the retracting amount to the upstream side in the paper feed direction is reduced. On the other hand, when the projecting amount is decreased, the friction force between the contact member 241 and the paper being retracted decreases, and the retracting amount to the upstream side in the paper feed direction is increased. In this application, the projecting amount of the contract member 241 from the aperture 220a is adjusted so that, when the paper is retracted, the paper end (the front end in the feed direction) does not return upstream of the paper feed point of the pickup roller 232.

The following will explain the operation of the manual paper feed unit 23 when a multi-feed occurs. FIGS. 6A to 6C and FIGS. 7A to 7C are explanatory views for explaining the operation performed by the manual paper feed unit 23 when a multi-feed occurs. Before a paper feed request is made, as shown in FIG. 6A, the pickup roller 232 is in a standby state above the paper feed point. When a paper feed request is made, the drive belt 233 which links the paper feed roller 234 and the pickup roller 232 is rotated and the pickup roller 232 is lowered to the paper feed point by the rotation moment.

A topmost sheet P1 among the paper loaded in the manual feed tray 230 is taken out of the manual feed tray 230 by the function of the pickup roller 23 which has reached the paper feed point, and, if an electrostatic force acts between the topmost sheet P1 and a sheet P2 below, the sheet P2 is also transported together with the sheet P1 (FIG. 6B). Thus, when a plurality of sheets P1 and P2 enter into the press-contact section between the paper feed roller 234 and the reverse roller 235, a multi-feed occurs (FIG. 6C).

When a plurality of sheets P1 and P2 enter into the press-contact section between the paper feed roller 234 and the reverse roller 235, the driving load of the reverse roller 23 is increased compared to that in transporting one sheet, and therefore the load of the torque limiter 206 supported on the driving shaft 235a of the reverse roller 235 increases. Hence, the reverse roller 235 is coupled to the drive source 204b for driving the reverse roller 235, so that the drive force is transmitted to the reverse roller 235, and the reverse roller 235 is rotated in the opposite direction to the rotating direction of the paper feed roller 234 (FIG. 7A).

When it is recognized that the reverse roller 235 is drive-coupling, the solenoid 242 of the paper press member 240 located under the paper guide 220 is activated to cause a part of the contact member 241 to project upward from the upper surface of the paper guide 220 (FIG. 7B). The contact member 241 projecting upward from the upper surface of the paper guide 220 comes into contact with the back surface of the sheet P2 returning to the manual feed tray 230 by the function of the reverse roller 235, the friction force between them acts as a load with respect to the returning force, and the return amount is reduced compared to that when there is no load. As a result, the position of the front end of the retracted sheet P2 is prevented from returning upstream of the paper feed point of the pickup roller 232, and the sheet P2 is taken out of the manual feed tray 230 in the next paper feeding process (FIG. 7C), thereby preventing reoccurrence of multi-feed.

FIG. 8 is a block diagram showing the structure of a control system of the manual paper feed unit 23. The manual paper feed unit 23 comprises a control section 200 composed of a microcomputer etc., and controls the paper feeding process. Connected to the control section 200 is an I/O 201 for inputting and outputting signals for sending and receiving various kinds of information to/from the printer unit 1; an I/O 203 for inputting and outputting signals for sending and receiving various kinds of information to/from the scanner unit 3; the drive section 204a for driving the drive source 204b of the paper feed roller 234 etc.; a multi-feed detecting section 205 for detecting a multi-feed occurring in the press-contact section between the paper feed roller 234 and the reverse roller 235; and the paper press member 240 for reducing the travel amount of the paper to be retracted in the event of a multi-feed.

FIG. 9 is a flowchart showing the steps of the paper feeding process performed by the manual paper feed unit 23. First, the control section 200 determines whether or not there is a paper feed request by determining whether or not a paper feed start signal has been inputted from the printer unit 1 through the I/O 201 (step S11). When there is no paper feed request (S11: NO), the control section 200 waits until a paper feed request is made.

When determined that there is a paper feed request (S11: YES), the control section 200 drives the paper feed roller 234 and pickup roller 232 by instructing the drive section 204a to drive the drive source 204b (step S12), and transports the paper taken out of the manual feed tray 230 (step S13).

Next, the multi-feed detecting section 205 determines whether or not the torque limiter 206 was activated and the reverse roller 235 was rotated in the reverse direction (step S14). When the torque limiter 206 is not activated and the reverse roller 235 is not rotated in the reverse direction (S14: NO), the control section 200 can determine that a multi-feed does not occur and therefore continues the paper feeding process (step S18).

When determined that the torque limiter 206 was activated and the reverse roller 235 was rotated in the reverse direction (S14: YES), the multi-feed detecting section 205 determines that a multi-feed was detected (step S15) and reports the detection result to the control section 200.

When the control section 200 receives the report indicating that the multi-feed detecting section 205 detected a multi-feed, it raises the paper press member 240 by activating the solenoid 242 of the paper press member 240 (step S16). Then, the control section 200 transports the upper sheet located on the paper feed roller 234 side to the downstream side in the paper feed direction and transports the lower sheet located on the reverse roller 235 side to the upstream side in the paper feed direction (step S17), and continues the paper feeding process (S18).

Next, the control section 200 determines whether or not there is a sheet to be supplied next (step S19). When determined that there is a sheet to be supplied next (S19: YES), the control section 200 returns the process to step S12. When determined that there is no sheet to be supplied next (S19: NO), the control section 200 moves into a standby state and waits for the input of a new paper feed start signal (step S20).

Note that although this embodiment explains the manual feed tray 23 of the printer unit 1, the present application is of course applicable to a paper feed unit of the automatic document feeder 35 mounted in the scanner unit 3.

As this application may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the application is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.

Claims

1. A sheet feeder comprising:

a sheet storing section for storing sheets;

a paper feed roller for feeding a sheet taken out of said sheet storing section to a predetermined supply destination;

a detecting section for detecting a multi-feed in said paper feed roller;

a sheet retracting unit for retracting, when said detecting section detects a multi-feed of sheets, an extra sheet fed by the multi-feed to an upstream side in a sheet feed direction; and

a contact member configured, between said paper feed roller and a front end in the sheet feed direction of the sheet stored in said sheet storing section, so that said contract member is capable of advancing and retracting and capable of coming into contact with an extra sheet fed by a multi-feed.

2. The sheet feeder according to claim 1, wherein said contact member comes into contact with a front surface or a back surface of the extra sheet when retracting the sheet.

3. The sheet feeder according to claim 1, further comprising a driving section for moving, when feeding a sheet to the supply destination, said contact member not to come into contact with the sheet, and for moving, when said detecting means detects a multi-feed of sheets, said contact member to come into contact with the extra sheet fed by the multi-feed.

4. The sheet feeder according to claim 1, wherein said sheet retracting unit includes a reverse roller placed opposite to said paper feed roller, and a torque limiter supported on a driving shaft of said reverse roller, wherein

when said torque limiter detects an increase in load and said reverse roller is coupled to a drive source and starts to be driven, said detecting section determines that a multi-feed of sheets is detected.

5. The sheet feeder according to claim 1, wherein a travel amount of sheet when retracting the sheet by said sheet retracting unit is restrained by the contact between the sheet and the contact member.

6. The sheet feeder according to claim 5, further comprising a pickup roller arranged to be able to come into contact with the sheet stored in said sheet storing section, wherein

the sheet feeder restrains a front end in the feed direction of the sheet to be retracted from returning upstream of a contact section between said pickup roller and the sheet stored in said sheet storing section.

7. The sheet feeder according to claim 1, wherein said contact member has elasticity.

8. The sheet feeder according to claim 1, wherein said sheet storing section is a manual feed tray.

9. An image reading apparatus comprising:

a sheet feeder as set forth in claim 1; and

an image reading section for reading an image recorded on a sheet fed by said sheet feeder.

10. An image forming apparatus comprising:

a sheet feeder as set forth in claim 1; and

an image forming section for forming an image on a sheet fed by said sheet feeder.