JP4301010B2 - Paper feeder - Google Patents

Description

  The present invention relates to a paper feeding device that is used in, for example, an image forming apparatus such as a copying machine, a printer, and a facsimile machine and supplies paper to a predetermined portion.

  In recent years, for example, in the field of image forming apparatuses such as copiers, printers, and facsimiles, image forming apparatuses that form images on paper cut to a predetermined size are widely used. In this type of image forming apparatus, reliability has been remarkably improved due to recent performance improvements, and as a result, there are very few paper feeds, that is, two or more sheets are transported while being overlapped. However, in the field where the printed matter output from the image forming apparatus is used as a product, even if one double feed occurs, it becomes a big problem, and therefore, higher reliability is required.

  In general, this type of image forming apparatus includes a pickup unit that presses a stacked sheet and conveys the sheet in a predetermined direction, and a sheet separating unit that is disposed on the downstream side of the sheet and separates the conveyed sheet. A paper device is provided. The paper separating means transports only one sheet in a predetermined direction when a plurality of sheets are conveyed from the pick-up means, and the other sheets are returned in the reverse direction to prevent double feeding. is doing. However, when the sheet immediately below the sheet to be conveyed is in a so-called reverse wedge state, the sheet immediately below is conveyed together with the sheet immediately above, and so-called double feeding occurs.

  In addition to the above causes, for example, when a user sets paper in the paper feed tray, the paper guide does not align properly due to poor setting of the paper guide, and the lower part of the paper is lower than the upper part of the paper bundle. May come to the downstream side in the conveying direction, which may cause a reverse wedge state. However, the reverse wedge state caused by such a cause is not a problem in terms of frequency and quantity, and the reverse wedge state that occurs during paper conveyance due to the structure of the paper feeder itself is prevented. is important.

  FIG. 5 is a schematic configuration diagram of a conventional paper feeding device.

  In FIG. 5, a paper feed tray 91 on which paper P is stacked, a pick-up roll 92 that presses the paper P loaded on the paper feed tray 91 and picks up the paper P and conveys it in the A direction, downstream of the pick-up roll 92. The feed roll 93 and the retard roll 94 which are arranged on the side and which is fed from the pick-up roll 92, and the paper which is arranged on the downstream side of the feed roll 93 and is conveyed from the feed roll 93 further downstream. A paper feeding device 90 having a takeaway roll 96 and the like is shown.

  FIG. 6 is a diagram illustrating a reverse wedge state of a sheet in a conventional sheet feeder.

  When the paper is continuously fed using the above-described paper feeding device 90 (see FIG. 5), the paper P1 is pulled out in the A direction by the takeaway roll 96 as shown in FIG. Immediately after the trailing edge passes through the nip portion 95 between the feed roll 93 and the retard roll 94, as indicated by the chain line, the lower sheet to be conveyed after the sheets P2 and P3 to be conveyed next. There is a case where P4 is in a position downstream of the sheets P2 and P3 in the transport direction, that is, a reverse wedge state.

  When the paper is in the reverse wedge state in this way, the paper bundle (P2, P3, P4) in the reverse wedge state may enter the nip portion 95 as it is at the start of the next conveyance. Here, in the case of a paper feeding device in which the retard roll 94 does not reverse, the conveyance of the paper P4 in contact with the retard roll 94 can be stopped, but the braking force does not act on the paper P2, P3 thereabove as it is. It is transported and double fed. Even in the case where the retard roll 94 is reversed, the sheets P4 and P3 contacting the retard roll 94 can be returned to the sheet feed tray 91 by the reverse rotation of the retard roll 94 until the sheet P4 reaches the downstream takeaway roll 96. Otherwise, double feed occurs.

  FIG. 7 is a diagram illustrating a mechanism of occurrence of a reverse wedge state in the sheet feeding device.

  As shown in FIG. 7A, when the sheet P1 is picked up by the pick-up roll 92, pulled through the nip portion 95 between the feed roll 93 and the retard roll 94, and taken out in the A direction by the take-away roll 96. In the vicinity of the nip portion 95, the following sheets P2, P3, and P4 exist as indicated by chain lines.

  At this time, a motor (not shown) for driving the feed roll 93 and the retard roll 94 is stopped, and the paper P1 is pulled out in the A direction by the takeaway roll 96, but is nipped by the nip portion 95. An upward retard pressure is always applied from the retard roll 94 to the paper P1. Usually, since rubber is used for the feed roll 93 and the retard roll 94, the feed roll 93 and the retard roll 94 are crushed and distorted by this retard pressure. Further, the retard roll 94 is applied with a reaction force of a braking force in a direction opposite to the rotational direction. When the paper P1 passes through the nip portion 95 in this state, at that moment, as shown in FIG. 7B, the retard roll 94 is pushed down to open the nip portion 95 by the thickness of the paper. Thus, the feed roll 93 and the retard roll 94 rotate in the reverse direction. Then, since the retard pressure that has been stably applied to the feed roll 93 and the retard roll 94 is reduced to the initial pressure, the retard roll 94 is pushed downward, and at the same time, the feed roll 93 and the retard roll 94 As a result of the sudden release of the stored distortion, the retard roll 94 rotates in the reverse direction by the amount of backlash between the gear backlash and the torque limiter. Therefore, the sheet bundle (P2, P3, P4) that has been in contact with the retard roll 94 is returned in the direction opposite to the transport direction. If all the sheets P2, P3, and P4 of the sheet bundle are returned by the same distance, the reverse wedge state will not occur. However, there are sheets that are easy to return and sheets that are difficult to return due to variations in the friction coefficient between the sheets. When the upper sheets P2 and P3 are returned too much than the lower sheet P4, a reverse wedge state occurs as shown in FIG.

  In particular, when a back paper once used is reused as a paper, a reverse wedge state is likely to occur due to a difference in the coefficient of friction between the papers. In this case, the reverse wedge state frequently occurs as the difference in the friction coefficient between the sheets increases.

  Usually, in order to prevent this reverse wedge phenomenon, for example, a feed unit equipped with a so-called reverse roll type separation means that prevents double feed by reversing the retard roll and sequentially returning it from the lower sheet of the retard roll. Paper devices have been proposed.

  However, even in a paper feeder equipped with a reverse roll type separation means, when a large amount of paper enters the nip portion in a bundle state, the paper is transported downstream in the transport direction. There is a problem that all the sheets cannot be returned before reaching the takeaway roll on the side, and double feed eventually occurs.

Therefore, in a paper feeding device having a pickup roll and a pair of feed rolls and a retard roll incorporating a torque limiter on the downstream side of the pickup roll, when the pickup roll is separated from the paper at a position upstream of the pickup roll. Also, there is disclosed a paper feeding device that is provided with a paper pressing roll that presses the upper surface of the paper to prevent the paper from being returned too much when the paper is double fed (see, for example, Patent Document 1). .
JP-A-1-92137 (page 1-3, FIG. 1-2)

  However, the paper feeder disclosed in Patent Document 1 has a problem in that the cost increases because a paper pressing roll must be provided separately.

  In view of the above circumstances, an object of the present invention is to provide a low-cost paper feeding device that can reliably prevent double feeding of paper.

The paper feeding device of the present invention that achieves the above object is as follows.
A paper tray that contains paper,
A pick-up roll that is disposed on the upper surface of the paper feed tray so as to be able to come into contact with and separate from the surface of the paper stored in the paper feed tray, and picks up the paper in the paper feed tray in a predetermined transport direction;
The second sheet when the sheet is disposed downstream of the pickup roll in the transport direction and only one of the sheets picked up by the pickup roll is sent to the downstream side of the transport direction, and two or more sheets are picked up simultaneously. A paper separation unit that pushes back the subsequent paper to the upstream side in the transport direction;
A paper delivery unit that is disposed downstream of the paper separation unit in the transport direction, receives a paper sent to the downstream side of the transport direction by the paper separation unit, and sends the paper further downstream;
When sending out one sheet in the sheet feeding tray, the pickup roll picks up the sheet in the sheet feeding tray at a first timing and the sheet delivered from the sheet separating unit to the sheet feeding unit. It is characterized in that it contacts and separates the paper in the paper feed tray twice so as to come into contact with the paper in the paper feed tray twice with the second timing immediately before the rear end of the paper separating portion leaves. And

  According to the paper feeding device of the present invention, since the pickup roll is in contact with the paper until the trailing edge of the paper is separated from the paper separating portion, the paper is prevented from being returned too much from the paper separating portion, and double feed occurs. Can be prevented.

  Here, the paper feeding device may include a solenoid that brings the pickup roll into and out of contact with the surface of the paper stored in the paper feeding tray.

  In such a configuration, the pickup roll can be reliably brought into and out of contact with the surface of the paper by the solenoid.

  In addition, the paper feeding device may include a sensor that detects paper fed to the paper feeding unit and a calculation unit that obtains the second timing based on a detection signal from the sensor.

  In such a configuration, it is not necessary to provide a sensor for obtaining the second timing, so that a low-cost sheet feeding device can be obtained.

  As described above, according to the paper feeding device of the present invention, it is possible to realize a low-cost paper feeding device that can reliably prevent double feeding of paper.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus including a sheet feeding device according to the present embodiment.

  The image forming apparatus 1 includes a transmission / reception unit 5 connected to an external device 3 such as an image reading device 2 or a personal computer via a communication line 4, and an image writing device 6 based on image information from the transmission / reception unit 5. An image recording control unit 7 to be controlled, a cylindrical image carrier 8 on which an electrostatic latent image is written by the image writing device 6, and a charger 9 disposed along the circumferential direction of the image carrier 8 The developing device 10 that develops the electrostatic latent image on the image carrier 8, the transfer roll 12 that transfers the image formed on the image carrier 8 to the paper P, and the toner remaining on the image carrier 8 are removed. Cleaner 11, fixing device 13 for fixing the image transferred onto paper P, discharge roll 14 for discharging the paper from fixing device 13, discharge tray 15 for stacking the paper discharged by discharge roll 14, and paper Image via transport unit 16 Bearing member and a feeder 20 for supplying 8 and the sheet P to the transfer roll 12.

  FIG. 2 is a diagram illustrating a standby state of the sheet feeding device according to the present embodiment, and FIG. 3 is a diagram illustrating a state during sheet feeding of the sheet feeding device according to the present embodiment.

  As shown in FIG. 2 and FIG. 3, the paper feeder 20 includes a paper feed tray 21 that contains paper P, and an upper part of the paper feed tray 21 that is in contact with and separated from the surface of the paper P contained in the paper feed tray 21. A pickup roll 22 that is freely arranged and picks up the paper P in the paper feed tray 21 in the conveyance direction (A direction), and is arranged downstream of the pickup roll 22 in the conveyance direction (A direction) and is picked up by the pickup roll 22. Feeds only one of the received sheets to the downstream side in the transport direction (A direction) and pushes back the second and subsequent sheets to the upstream side in the transport direction (A direction) when two or more sheets are picked up at the same time A paper separation unit 23 composed of a roll 23a and a retard roll 23b, and a downstream side of the paper separation unit 23 in the conveyance direction (direction A), and a conveyance method by the paper separation unit 23 (A direction) A sheet feeding unit 24 composed of a pair of takeaway rolls 24a and 24b that receives the sheet P sent to the downstream side and sends it to the downstream side, and feeds one sheet in the sheet feeding tray 21. In this case, the pick-up roll 22 picks up the paper in the paper feed tray 21 and immediately before the trailing edge of the paper delivered from the paper separation unit 23 to the paper delivery unit 24 is separated from the paper separation unit 23. It is configured to be in contact with and separated from the paper in the paper feed tray 21 so as to come into contact with the paper in the paper feed tray 21 twice at the second timing.

  The paper feeding device 20 includes a pre-feed sensor 26 that detects paper fed to the paper feed unit 24, a feed-out sensor 27 that detects paper sent from the paper feed unit 24, and detection by the pre-feed sensor 26. An arithmetic unit 29 (see FIG. 1) that obtains the second timing based on the signal is provided. The operations of the pre-feed sensor 26, the feed-out sensor 27, and the calculation unit 29 will be described later.

  Note that the feedout sensor 27 in this embodiment corresponds to the sensor referred to in the present invention.

  Next, the pickup roll contacting / separating operation in the paper feeding device 20 will be described.

  In the paper feeding device 20 of the present embodiment, the rotation shafts of the pickup roll 22 and the feed roll 23a are attached to a bracket 30. The bracket 30 is shown in FIGS. 2 and 3 with the rotation shaft of the feed roll 23a as a fulcrum. As shown in the figure, it is configured to be freely contacted and separated from the surface of the paper P. Further, the bracket 30 is pushed down in a direction away from the top cover 31 of the paper feeding device 20 by the elasticity of the spring 32 during paper feeding (see FIG. 3).

  The paper feeding device 20 is provided with a solenoid 33 for bringing the pickup roll 22 into and out of contact with the surface of the paper P stored in the paper feeding tray 21. Now, when the solenoid 33 is operated at a predetermined timing and the link 34 is pulled down in the direction of arrow B during the standby state shown in FIG. 2, the shaft 35 via the link 34 rotates and the plate 36 attached to the shaft 35 is watched. Rotate in the direction. Accordingly, the bracket 30 positioned by the plate 36 and the stud 37 is pushed down by the spring 32, and the pickup roll 22 fixed to the bracket 30 comes into contact with the surface of the paper P with a predetermined pressure, and the feeding shown in FIG. It will be in the state of paper.

  When the paper feeding operation is completed, when the solenoid 33 is activated and the link 34 is pulled up in the direction of the arrow B ', the shaft 35 via the link 34 rotates and the plate 36 attached to the shaft 35 rotates counterclockwise. Accordingly, the bracket 30 is pushed up, and the pickup roll 22 fixed to the bracket 30 is in a standby state separated from the surface of the paper P (see FIG. 2).

  Next, the operation of the paper feeding device of this embodiment will be described.

  As already described with reference to FIGS. 6 and 7, in order to prevent the occurrence of the reverse wedge state of the sheet, the sheet is pulled out by the sheet feeding unit and the trailing end of the sheet passes through the nip portion of the sheet separating unit. Sometimes the paper should not be returned too much. Therefore, the pickup roll is dropped immediately before the trailing edge of the sheet passes through the nip portion of the sheet separation unit, and pressure is applied to the sheet, thereby suppressing the return of the sheet and preventing the occurrence of a reverse wedge state.

  In the paper feeding device 20 of the present embodiment, as shown in FIG. 2, the pickup roll 22 is in a position separated from the paper P on the paper feeding tray 21 during standby, and during paper feeding, as shown in FIG. The solenoid 33 is moved to a position where it contacts the paper P by the operation of the solenoid 33 and contacts the paper P with a predetermined pressure. If the pickup roll 22 is rotated in this state, the paper P is delivered to the nip portion 23c between the feed roll 23a and the retard roll 23b on the downstream side in the transport direction. When the paper P that has passed through the nip portion 23c turns on the pre-feed sensor 26, the pickup roll 22 returns to the standby position. Then, the pickup roll 22 is dropped again at a predetermined timing, so that the nip portion 23c is moved. It is possible to prevent the sheet P from being excessively returned in the reverse direction after being pulled out.

  FIG. 4 is a timing chart of the paper feeding operation of the paper feeding device of this embodiment.

  As shown in FIG. 4, when a paper feed start command is issued from the image recording control unit 7 (see FIG. 1) of the image forming apparatus 1 (t1), the solenoid 33 (see FIG. 2) is first turned on (see FIG. 4). t2) Next, rotation of a feed motor (not shown) that drives the pickup roll 22 and the feed roll 23a is started (t3). After a predetermined time delay after the solenoid 33 is turned on, the pick-up roll 22 comes into contact with the paper and a contact pressure is applied as shown in the drawing to start paper feeding (t4). When the first sheet reaches the nip portion 23c between the feed roll 23a and the retard roll 23b and the prefeed sensor 26 is turned on (t5), the solenoid 33 is turned off (t6), and the solenoid 33 Is turned off, the pickup roll 22 is separated from the paper (t7), and the paper is delivered to the paper delivery unit 24.

  Next, when the paper that has passed through the paper delivery unit 24 turns the feedout sensor 27 “on” (t8), the solenoid 33 is turned “on” after a predetermined time T from the time t8 (t10), As a result, as shown in the figure, contact pressure from the pickup roll to the paper starts to be applied (t11).

  Thus, at the moment (t12) when the trailing edge of the sheet passes through the nip portion 23c, the pickup roll 22 is in contact with the sheet, and the contact pressure on the sheet by the pickup roll 22 at this time causes the pickup roll 22 to contact the sheet as shown in FIG. The reverse wedge state of the paper is prevented.

  Next, the pre-feed sensor 26 is turned “off” (t13), the solenoid 33 is turned “off”, and as a result, the pickup roll 22 is separated from the paper (t14). When the sheet turns off the feedout sensor 27, one sheet feeding operation is completed.

  In order to obtain the above-described time T, the paper feeding device 20 according to the present embodiment includes a calculation unit 29 (see FIG. 1). 24 is configured to obtain the second timing immediately before the trailing edge of the sheet delivered to 24 is separated from the sheet separating unit 23.

  In the present embodiment, the timing from t4 when the pickup roll 22 comes into contact with the paper and feeding is started to t7 when the pickup roll 22 is separated from the paper corresponds to the first timing in the present invention. In addition, the timing from t11 when contact pressure from the pickup roll to the paper is applied to t14 when the pickup roll is separated from the paper corresponds to the second timing according to the present invention.

  The time T is a time delay from when the solenoid 33 is turned on until the pickup roll 22 actually contacts the paper, the paper size in the transport direction, the paper pulling speed of the takeaway roll 24, and the time of control processing. It can be calculated from the delay.

  In order to prevent the reverse wedge state, the time from t11 to t14 when the pickup roll 22 is in contact with the sheet is at least from immediately before the trailing edge of the sheet exits the nip 23c to immediately after the trailing edge of the sheet exits the nip 23c. Is necessary. After that, there is no problem even if the pickup roll 22 is kept in contact therewith, but in this case, since the solenoid is used, the minimum necessary time only during the trailing edge of the sheet exiting the nip portion 23c as much as possible. It is desirable to set with a timer or the like so that the pickup roll comes into contact. In the present embodiment, the value of the time T is calculated and calculated based on the time when the feedout sensor 27 is “ON”, the paper size in the transport direction, the transport speed, and the like so that the variation is minimized.

1 is a schematic configuration diagram of an image forming apparatus including a sheet feeding device according to an embodiment. It is a figure which shows the state at the time of standby of the paper feeder of this embodiment. It is a figure which shows the state at the time of paper feeding of the paper feeder of this embodiment. 6 is a timing chart of a paper feeding operation of the paper feeding device of the present embodiment. It is a schematic block diagram of the conventional paper feeder. It is a figure which shows the reverse wedge state of the paper in the conventional paper feeder. It is a figure which shows the mechanism of reverse wedge state generation | occurrence | production in a paper feeder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image reading apparatus 3 External apparatus 4 Communication line 5 Transmission / reception part 6 Image writing apparatus 7 Image recording control part 8 Image carrier 9 Charger 10 Developing apparatus 11 Cleaner 12 Transfer roll 13 Fixing apparatus 14 Discharge roll 15 Discharge Tray 16 Paper transport unit 20 Paper feed device 21 Paper feed tray 22 Pickup roll 23 Paper separation unit 23a Feed roll 23b Retard roll 23c Nip part 24 Paper feed part 24a, 24b Takeaway roll pair 26 Pre-feed sensor 27 Feed-out sensor 29 Calculation Part 30 Bracket 31 Top cover 32 Spring 33 Solenoid 34 Link 35 Shaft 36 Plate 37 Stud 90 Paper feed device 91 Paper feed tray 92 Pickup roll 93 Feed roll 94 Retarder roll 95 Nip part 96 Take away roll

Claims (3)

A paper tray that contains paper,
A pick-up roll that is disposed on the upper side of the paper feed tray so as to be able to come into contact with and separate from the surface of the paper stored in the paper feed tray, and picks up the paper in the paper feed tray in a predetermined transport direction;
The second sheet when the sheet is disposed downstream of the pickup roll in the transport direction and only one of the sheets picked up by the pickup roll is sent to the downstream side of the transport direction and two or more sheets are picked up at the same time. A paper separating unit that pushes back the subsequent paper to the upstream side in the transport direction;
A paper delivery unit that is disposed downstream of the paper separation unit in the transport direction, receives a paper sent to the downstream side of the transport direction by the paper separation unit, and sends the paper further downstream;
When sending out one sheet in the sheet feeding tray, the pickup roll picks up the sheet in the sheet feeding tray at a first timing and the sheet delivered from the sheet separating unit to the sheet feeding unit. It is characterized in that it is in contact with and separated from the paper in the paper feed tray twice so as to be in contact with the paper in the paper feed tray twice with the second timing immediately before the trailing edge is separated from the paper separation unit. A paper feeder. The sheet feeding device according to claim 1, further comprising a solenoid that contacts and separates the pickup roll from a surface of a sheet stored in the sheet feeding tray. The sheet feeding device according to claim 1, further comprising: a sensor that detects a sheet fed to the sheet feeding unit; and a calculation unit that obtains the second timing based on a detection signal from the sensor.

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