JP2011219221A - Paper feeding device and image forming system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paper feeding device capable of surly conveying paper sheets abutting on a conveying roller, and preventing a following paper sheet from buckling.SOLUTION: The paper feeding device includes: a suction conveying means for sucking and conveying paper sheets loaded on a paper sheet loading tray; the conveying roller for conveying the paper sheets conveyed by the suction conveying means; a paper feeding sensor for detecting the paper sheets; and a control means for separately controlling the drive of the suction conveying means and the conveying roller. After the paper feeding sensor detects the tip of the conveyed paper sheet, the control means drives the suction conveying means for a certain time so that the tip of the paper sheet abuts on the conveying roller, and thereafter, the control means stops the drive of the suction conveying means. After the tip of the paper sheet abuts on the conveying roller, the control means starts the drive of the conveying roller, and at the same time, restarts the drive of the suction conveying means to convey the paper sheets. After a predetermined time passes, the control means controls to stop the drive of the suction conveying means.

Description

  The present invention relates to a sheet feeding apparatus that separates and feeds a bundle of sheets stacked on a sheet stacking tray one by one, and an image forming system having the sheet feeding apparatus.

  In recent years, with the development of digital information technology, a printing method called “print on demand” for directly printing data created by a computer or the like without obtaining a plate making process has become widespread and used in the printing field. In such a production market, various sizes, thicknesses and types of paper are used. Accordingly, paper feeding apparatuses used in image forming systems are required to support a wide range of papers of various sizes, thicknesses, and types.

  2. Description of the Related Art Conventionally, various methods have been used for separating and transporting the top sheet of a sheet stacking tray on which sheets are stacked in a sheet feeding device of an image forming system.

  As one of the methods, a method of separating and transporting the uppermost sheet of the stacking tray while air suction (air suction) is used.

  A paper feeding device using air suction, such as a perforated belt that is formed with an air inlet that sucks air stretched on a plurality of rollers by blowing air onto the front end surface or side surface of the stacked paper and separating the paper. A sheet is sucked by the suction surface, and a belt (hereinafter referred to as a sheet feeding belt) is rotationally driven to transport the sheet.

  When feeding paper with a short length in the paper transport direction with this paper feeder, when the paper feed belt is driven to feed the paper to the transport roller downstream of the transport path, the trailing edge of the paper is inside the belt. If it comes out of the negative pressure generation area (hereinafter also referred to as an adsorption area), the middle part of the next paper may be adsorbed and the next paper may buckle. (Hereinafter, long and short paper means the length in the paper transport direction).

  On the other hand, a paper feeding device is disclosed in which the distance from the downstream transport roller to the upstream end of the suction region in the transport direction is shorter than the corresponding shortest paper length (see, for example, Patent Document 1).

JP-A-5-116783

  In such a paper feeding device using air suction, there are design restrictions such as a blowout port of separation air blown from the front end surface of the paper, and the downstream transport roller cannot approach the front end side of the paper more than a certain amount. For this reason, it is necessary to reduce the length of the suction area, but reducing this shortens the area for sucking the paper.

  For example, in the case of a 60 mm device from the sheet abutting portion of the regulating member that regulates the front edge of the paper loaded on the paper stacking tray to the transport roller, in order to cope with a postal length of 148 mm, the upstream end of the suction area Can only secure a maximum of 88 mm from the paper abutment.

  In order to secure the necessary transport force, when the maximum suction area is secured in the constraints, the distance from the transport roller to the upstream end of the suction area in the transport direction is brought closer to the minimum length of the corresponding paper size. Is preferred. However, the paper feed belt that conveys the paper at a high speed and the roller that stretches the paper feed belt continue to move for a while after receiving a stop signal from the control means. Due to this inertia, the paper feeding belt rotates (overruns) and the trailing edge of the paper comes out of the suction area inside the belt. As described above, the middle of the next paper is sucked with negative pressure and the leading edge is buckled. There is a risk of letting you. This is particularly noticeable with thin paper among short-size paper.

  FIG. 4 is a schematic diagram showing the process of buckling of the paper.

  Even if the driving of the paper feed belt 64 is stopped at the timing when the paper P1 being transported reaches the transport roller 39, the paper feed belt 64 continues to move due to inertia (overrun). This overrun varies, for example, 8 to 16 mm, and an accurate amount cannot be predicted. When the rear end of the paper P1 comes out of the suction area inside the belt due to the overrun (FIG. 4A, portion L1), the paper feed belt 64 sucks the rear side of the next paper P2 and the next paper. P2 will be pushed downstream. Since the leading edge of the next sheet P2 stays below the sheet conveyance path, the leading edge of the sheet P2 pressed thereby is between the regulating member that regulates the leading edge of the stacked sheets and the sheet after the next sheet P2. Clogged in the corner. (See FIG. 4 (a)).

  Here, the cause of the leading edge of the next sheet P2 staying downward includes being pushed down by the wind pressure of the air separating the sheet and hanging down by its own weight.

  In this way, the next paper P2 is stressed because the leading edge is clogged under the regulating member, and therefore cannot be raised in the direction of the paper feeding belt and adsorbed to the paper feeding belt. For this reason, simultaneously with the driving of the paper feed belt, the next paper P2 buckles and becomes jammed. (See FIG. 4 (b)).

In Patent Document 1, the movement of the paper feeding belt due to this inertia is not taken into consideration. In Patent Document 1, if the influence of the movement of the paper feeding belt due to this inertia is prevented, the distance from the downstream transport roller to the upstream end in the transport direction of the suction area is further shortened, and A3 is used with thick paper exceeding 300 g / m ^2. It may be difficult to secure a necessary conveying force for a heavy paper having a large size exceeding the above.

  As a countermeasure, it is known that the downstream transport roller is stopped in advance and the leading edge of the paper transported by the paper feed belt is abutted against the nip of the transport roller. According to this configuration, even if the driving of the paper feeding belt is stopped after the leading edge of the paper hits the nip of the conveying roller, and even if the paper feeding belt continues to move to some extent due to inertia, a slip is caused between the paper and the paper feeding belt. And the paper will not travel downstream further. That is, it is possible to stop the conveyance of the sheet due to the movement of the sheet feeding belt due to inertia.

  If the movement of the paper feeding belt stops due to inertia, that is, if the overrun is removed, the transport roller is driven, the paper is fed downstream, and the suction area of the paper feeding belt is exposed to the next paper. Even if it comes, since the paper feed belt is stopped, the leading edge of the next paper does not buckle.

  However, just by abutting the leading edge of the paper against the nip of the conveying roller, it cannot be said that the leading edge of the paper is securely held between the conveying rollers composed of a pair of rollers, and the paper is conveyed even if the conveying roller is driven. There was a risk of problems that could not be done.

  The present invention has been made in view of the above-described situation, and can feed the paper abutted against the transport roller reliably and does not cause buckling of the next paper, and is supplied from the paper feeding device. An object of the present invention is to provide an image forming system having an image forming apparatus for forming an image on a printed sheet.

  The above object is achieved by the following configuration.

1. A paper stacking tray for loading paper,
An adsorbing and conveying means located above the sheets stacked on the sheet stacking tray and adsorbing and conveying the sheets;
A transport roller disposed downstream of the suction transport means in the paper transport direction and transports the paper;
A paper feed sensor disposed between the suction conveyance means and the conveyance roller to detect the paper;
Control means for independently controlling the suction conveyance means and the driving of the conveyance rollers,
The control means detects the leading edge of the sheet conveyed by the paper feed sensor, and then drives the suction conveying means for a predetermined time so that the leading edge of the sheet abuts against the conveying roller. Stop driving,
Next, after the leading edge of the sheet is abutted against the conveying roller, the driving of the conveying roller is started, and at the same time, the driving of the sucking and conveying unit is restarted to convey the sheet. The sheet feeding device is controlled to stop driving.

  2. 2. The sheet feeding device according to 1, wherein the predetermined time is set based on a length of the sheet in a conveyance direction.

  3. In transporting the paper having the smallest usable transport direction length, when the suction transport unit is stopped after the predetermined time, the rear end of the paper is the upstream end in the transport direction of the suction region of the suction transport unit The sheet feeding device according to 1 or 2, wherein

  4). 4. An image forming system comprising: the sheet feeding device according to any one of items 1 to 3; and an image forming apparatus that forms an image on a sheet supplied from the sheet feeding device.

  As described above, the leading edge of the paper abutted against the transport roller can be reliably held between the transport rollers, and the paper can be reliably transported by the transport roller.

  Further, buckling can be prevented by stopping the driving of the suction conveyance means before the suction area is exposed to the next paper.

1 is an overall configuration diagram of an image forming system including an image forming apparatus, an image reading apparatus, an automatic document feeder, and a large-capacity paper feeder. FIG. 3 is a perspective view illustrating a main part of a sheet feeding device body. FIG. 3 is a schematic cross-sectional view of a sheet feeding device body. It is a schematic diagram showing a process of buckling of the paper. FIG. 6 is a schematic diagram illustrating a conveyance process of the shortest size paper P. 6 is a timing chart of conveyance control in sheet conveyance.

  Embodiments of a paper feeding device according to the present invention will be described below with reference to the drawings. The present invention is not limited to the following.

[Image forming apparatus]
FIG. 1 is an overall configuration diagram of an image forming system including an image forming apparatus A, an image reading apparatus SC, an automatic document feeder DF, and a large capacity sheet feeding apparatus LT.

  The illustrated image forming apparatus A includes an image forming unit including a photosensitive member (image carrier) 1, a charging unit 2, an image exposing unit 3, a developing unit 4, a transfer unit 5, a cleaning unit 6, and the like, a fixing unit 7 and And a paper transport system.

  The paper transport system includes a paper feed cassette 10, a first paper feed means 11, a second paper feed means 12, a paper discharge means 14, a transport path switching means 15, a circulation refeed means 16, a reverse paper discharge means 17, and the like. Has been. In addition, a control unit AS is provided as control means for controlling each part of the apparatus.

  The document d placed on the document table of the automatic document feeder DF is transported by the paper feeding means, the image on one or both sides of the document is read by the optical system of the image reading device SC, and is read by the image sensor CCD. . The analog signal photoelectrically converted by the image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing and the like in the image processing unit 20 and then sent to the image exposure apparatus 3.

  In the image forming unit, processes such as charging, exposure, development, transfer, separation, and cleaning are performed.

  In the image forming unit, a charge (negative charge in the present embodiment) is applied to the photosensitive member 1 by the charging unit 2, and an electrostatic latent image is formed by laser light irradiation from the image exposure device 3. The electrostatic latent image is visualized by 4 and becomes a toner image (in this embodiment, the toner is negatively charged).

  Next, the paper P stored in the paper feed cassette 10 is conveyed from the first paper feed means 11. On the other hand, the transfer residual toner on the photosensitive member 1 is removed by the cleaning unit 6.

  The paper P is conveyed in synchronism with the toner image by the second paper feeding means 12 composed of registration rollers. Thereafter, the paper P is fixed by the fixing device 7 after the toner image is transferred by the transfer means 5. The paper P after fixing is discharged out of the apparatus by the paper discharge means 14.

  In the case of double-sided copying, the paper P on which the image is formed on the first side is sent to the circulation refeed unit 16 and reversed, and after the image is formed again on the second side in the image forming unit, the paper discharge unit 14 is formed. Is discharged out of the apparatus. In the case of reverse paper discharge, the paper P branched from the normal paper discharge path is switched back by the reverse paper discharge means 17 and turned upside down, and then discharged from the apparatus by the paper discharge means 14.

[Paper Feeder]
The large-capacity paper feeding device LT connected to the image forming apparatus A has a plurality of paper feeding devices 30 inside, accommodates a large amount of paper P, and feeds the paper P to the image forming apparatus A one by one. To do.

  The sheet feeding device 30 includes a sheet stacking tray 31 on which sheets are stacked, a sheet leading edge regulating member 32, a sheet trailing edge regulating member 33, and a guide rail 34. In this example, the sheet stacking trays 31 are configured in three stages, and each sheet stacking tray 31 is configured to be able to be pulled out from the large capacity sheet feeding device LT by the guide rail 34. For example, the large-capacity paper feeder LT can accommodate 1300 sheets in the first tray, 1850 sheets in the second and third trays, and can accommodate approximately 5000 sheets as a whole.

  FIG. 2 is a perspective view showing a main part of the paper feeding device 30, and FIG. 3 is a schematic sectional view of the paper feeding device 30. In FIG. 2, the suction conveyance unit 60 that is a suction conveyance unit is shown at a temporary position that is horizontally shifted by an arrow b toward the downstream side in the paper conveyance direction from the position where it is actually installed in the paper feeding device 30. ing.

  As shown in FIG. 2, the sheet bundle Ps and the uppermost sheet P are stacked on the sheet stacking tray 31 and are housed together with the sheet stacking tray 31 so as to be moved up and down by a mechanism (not shown).

  The pair of paper side edge regulating portions 70 regulates the paper bundle Ps in the width direction orthogonal to the paper transport direction, and has a paper side edge regulating member 71 adjacent to the side edge of the paper bundle Ps inside. . The sheet-side end regulating unit 70 can freely change the relative distance in the sheet width direction, and regulates the position of the sheet bundle Ps in the width direction corresponding to the sheet size.

  The sheet-side edge restricting portion 70 has a box-like structure that is sufficiently long in the sheet conveyance direction and has a large rigidity, and the sheet-side edge restricting member 71 and the sheet side edge are formed at the uppermost portion of the sheet bundle Ps. This gap can be kept below a predetermined value even for a wide range of paper sizes.

  The paper leading edge regulating member 32 regulates the leading edge of the sheet bundle Ps on the paper stacking tray 31 and is fixed to the paper feeding device 30.

  The sheet trailing edge regulating member 33 is movable in the length direction of the sheet P and regulates the position of the trailing end in the sheet conveying direction, and is supported by the sheet feeding device 30 so as to be displaceable in the sheet conveying direction. Yes. The sheet-side edge regulating member 71 and the sheet trailing edge regulating member 33 have a height and a shape that can always regulate a sheet that has been lifted by blowing wind, which will be described later.

  Further, as shown in FIG. 3, a height sensor PS <b> 3 that detects the height of the uppermost portion of the sheet bundle Ps stacked on the sheet stacking tray 31 is disposed on the sheet rear end regulating member 33.

  The uppermost position of the sheet bundle Ps stacked on the sheet stacking tray 31 is maintained at an optimum height at which air can be blown based on a signal from the height sensor PS3. That is, based on the detection result of the height sensor PS3 shown in FIG. 3, a lifting motor (not shown) is driven to raise the bottom plate 34 of the paper stacking tray 31 so that the uppermost part of the paper stack Ps is always maintained at a predetermined height. Is doing the right control.

  Further, on the exit side of the large-capacity paper feeding device LT, a pair of transport rollers 39 including two main and driven rollers that transport the paper P transported by the suction transport unit 60 to the image forming apparatus A is disposed. ing.

  A paper feed sensor PS <b> 2 is provided between the suction conveyance unit 60 and the conveyance roller 39.

<Blower part>
The blower unit 50, which is a sheet separating unit disposed on the downstream side of the sheet stacking tray 31 in the sheet P feeding direction, will be described.

  The blower unit 50 includes an electric fan 51 and a blower guide 52 connected to the electric fan 51. The blower 50 blows air from the blower opening 53A of the blower guide 52 to the front end / upper direction (in the direction of arrow A1 in FIG. 2) of the sheet bundle Ps stacked on the paper stacking tray 31.

  The air blown from the first air outlet 53A is for rolling up and floating the uppermost sheet P of the sheet bundle Ps, and is directed to the upper front end of the sheet bundle Ps. The upper portion of the air blowing guide 52 has a second air blowing port 53B on the downstream side of the air blowing port 53A, and the second air blowing port 53B opens upward from the air blowing port 53A.

  The air blown from the second air blowing port 53B is for separating the paper P sucked and conveyed by the suction conveyance unit 60 into one sheet.

  As shown in FIG. 3, the air guide 52 is formed in a duct structure that connects the first air outlet 53 </ b> A and the electric fan 51, or connects the second air outlet 53 </ b> B and the electric fan 51. The duct is branched into a first duct 54A and a second duct 54B. A shutter 55 is provided at the branch point, and the shutter 55 enables switching of the amount of air flowing through the first duct 54A and the second duct 54B.

  In other words, the blower unit 50 of this example is used both for the purpose of separating and floating the uppermost sheet P of the sheet bundle Ps and for separating the sheet sucked and conveyed by the suction conveyance unit 60 into one sheet. However, the present invention is not limited to this, and it is only necessary to blow air (corresponding to the second air outlet) so that at least the paper sucked and transported by the suction transport unit 60 is separated into one sheet.

<Suction conveyance part>
As shown in FIG. 3, the suction conveyance unit 60 is located above the sheet bundle Ps stacked on the sheet stacking tray 31 and is disposed on the downstream side in the sheet conveyance direction.

  The suction conveyance unit 60 includes two endless sheet feeding belts 64 having a large number of small-diameter through holes, a large roller 61 that stretches the sheet feeding belt 64, small rollers 62a and 62b, and an intermediate roller 63. Yes. The large roller 61 is connected to a motor M1 (see FIG. 2) and rotationally drives the paper feed belt 64. In the present embodiment, the small rollers 62a and 62b having small diameters are used as the driven rollers for stretching the paper feed belt 64, but a single roller may be used. Further, the number of paper feed belts 64 is not limited to this.

  The two paper feed belts 64 are stretched between the large roller 61 and the intermediate roller 63 so as to be substantially parallel to the paper P. Further, the intermediate roller 63 and the small roller 62a are stretched with an inclination with respect to the paper P.

  Note that the tension of the paper feeding belt 64 may be substantially parallel to the paper P between the large roller 61 and the small roller 62a without providing such an inclination. In this case, the intermediate roller 63 can be omitted.

  In addition, a suction duct 65 that is an air suction unit that sucks air through the through hole and a suction fan 66 are disposed inside the paper feed belt 64. Air sucked by the suction fan 66 is discharged to the side through the suction duct 65.

  The suction area that sucks the paper P formed by the suction duct 65 is configured such that the distance from the transport roller 39 to the upstream end of the suction area in the transport direction is shorter than the length of the shortest-size paper P.

  Next, sheet conveyance of the sheet feeding device 30 according to the present invention will be described.

  FIG. 5 is a schematic diagram illustrating a conveyance process of the shortest size paper P.

  When a paper feed instruction is issued for the paper P, the control unit AS controls the paper feed drive.

  First, the blower 50 separates the uppermost sheet P of the sheet bundle Ps stacked on the stacking tray 31 into one sheet.

  The suction conveyance unit 60 sucks the uppermost sheet P separated into one sheet onto the sheet feeding belt 64 by air suction, and starts conveyance. At this time, the conveyance roller 39 is stopped.

  The driving of the paper feed belt 64 that sucks and conveys the paper P is stopped after a predetermined time (first constant time) has elapsed after the paper feed sensor PS2 detects the leading edge of the paper P. This fixed time is the time from when the paper feed sensor PS2 detects the leading edge of the paper P until the leading edge of the paper P hits the transport roller 39. This fixed time is set for each model based on the distance between the transport roller 39 and the paper feed sensor PS2 and the transport speed of the paper P.

  In this way, the paper P is transported until the leading edge hits the transport roller 39.

  By the way, as described above, even if the driving of the paper feed belt 64 is stopped, the paper feed belt 64 moves due to inertia and overrun occurs. For this reason, the downstream conveying roller 39 is stopped in advance, and the driving of the sheet feeding belt 64 is stopped by adopting a configuration in which the leading end of the sheet P conveyed by the sheet feeding belt 64 abuts against the nip of the conveying roller 39. Even if an overrun of the paper feed belt 64 due to the inertia occurs later, a slip occurs between the paper P and the paper feed belt 64, whereby the conveyance of the paper P can be stopped.

  FIG. 5A is a diagram illustrating a state in which the feeding of the paper P is started and the paper feeding sensor PS2 detects the leading edge of the paper P, and then the paper P is transported for a predetermined time and the leading edge of the paper P is abutted against the transport roller. It is.

  Here, in FIG. 5A, the suction area for sucking the paper P formed by the suction duct 65 has a distance Lb from the transport roller 39 to the upstream end in the transport direction of the suction area, which is the length of the shortest paper P. It is configured to be shorter than La. That is, by configuring so that La> Lb, it is possible to prevent the rear end of the paper P from coming out of the upstream end in the transport direction of the suction area when the leading edge of the paper P is abutted against the transport roller 39.

  Next, after the overrun of the paper feed belt 64 disappears and completely stops, the driving of the transport roller 39 is started. The time interval from when the drive of the paper feed belt 64 is stopped until the transport roller is driven (the transport roller drive start time) is the time until there is no overrun after the drive of the paper feed belt 64 is stopped and it completely stops. It is determined in advance by verification in experiments, designs, and the like.

  Here, as described above, it is not possible to say that the leading edge of the sheet is securely held by the conveying roller 39 just by abutting the leading edge of the sheet against the nip of the conveying roller 39. This may cause a problem that it cannot be transported.

  On the other hand, in the present embodiment, the paper feeding belt 64 is driven for a predetermined time simultaneously with the start of driving of the conveying roller 39. As a result, the paper P is attracted and conveyed to the paper feeding belt 64 for a predetermined time, and the paper P is securely held between the conveyance rollers 39.

  FIG. 5B is a diagram illustrating a state in which the paper P is attracted and conveyed to the paper feeding belt 64 for the predetermined time.

  The predetermined time is set based on the length of the paper P so that the transport distance at the predetermined time is the length that the leading edge of the paper P is securely sandwiched between the transport rollers 39. In particular, in the case of the shortest size paper P, in order to maximize the suction area, this predetermined time is such that the transport distance is the minimum length that the leading edge of the paper P is securely held by the transport roller 39. Set to

  The predetermined time is set based on the transport distance and the transport speed with reference to the experiment and the specifications of the existing machine.

  For example, the transport distance in the predetermined time is set to 2 in the case of a light paper P such as the shortest size (for example, length 140 mm) of thin paper because the slip of the paper feed belt 64 and the paper P during transport is small. It is time to carry about 3 mm. In the case of a heavy paper P such as the longest size of the thick paper (for example, a length of 482 mm), slip of the paper feeding belt 64 and the paper P at the time of conveyance becomes large. It is time to do.

  In this way, the predetermined time is set to be a short time under the condition that the paper P is securely held by the transport roller 39, so that the overrun after the drive is stopped is extremely small. In particular, in the shortest size paper P, the predetermined time is very small, and the overrun is extremely small.

  Further, in the conveyance of the shortest size paper P, the conveyance distance Ld conveyed in a predetermined time and the distance Lb from the conveyance roller 39 to the upstream end in the conveyance direction of the suction area are stopped by driving the paper feeding belt 64 for a predetermined time. At this time, the rear end of the sheet P is configured to have a correlation so that the rear end of the sheet P is positioned at least at the upstream end of the suction area in the transport direction. Further, in order to improve safety, it is preferable that the rear end of the paper P at this time is positioned upstream of the upstream end of the suction region in the transport direction.

  That is, in FIG. 5B, the configuration is such that La−Lb ≧ Ld. Therefore, Lc ≧ 0.

  As described above, the overrun of the paper feeding belt 64 after driving for a predetermined time is extremely small, and the paper feeding belt after driving for a predetermined time is configured in this way by configuring the transport distance Ld and the distance Lb for a predetermined time. At the time of stopping 64, it is possible to prevent the trailing edge of the sheet P from coming off from the upstream end in the conveyance direction of the suction area, and it is possible to prevent the next sheet from being sucked.

  In the case of the paper P other than the shortest size, it is preferable that the rear end of the paper P at this time is positioned upstream of the upstream end in the transport direction of the suction region. Therefore, it is preferable that La−Lb> Ld and Lc> 0.

  The paper P sandwiched between the transport rollers 39 is transported in the downstream direction. When the paper feed sensor PS2 detects the trailing edge of the paper P, the driving of the conveying roller 39 is stopped after a certain time (a certain time on the trailing edge side). This fixed time on the trailing edge side is set to a time from when at least the trailing edge of the paper P is detected by the paper feed sensor PS2 until the trailing edge of the paper P passes through the nip of the conveying roller 39.

  As described above, after stopping the driving by stopping the leading end of the paper P against the downstream conveying roller 39 in the stopped state by the paper feeding belt 64, a slight amount is temporarily stored at the timing when the driving of the conveying roller 39 is started. The paper feeding belt 64 is driven, and the leading end of the paper P that is abutted is introduced into the nip of the transport roller 39. Thereby, the paper P can be reliably conveyed. Since the amount of driving is very small, overrun due to inertia can be suppressed to a small extent compared to when transporting at high speed.

  In addition, by changing the driving amount according to the size of the paper P and increasing the amount for a large size, it is possible to reliably introduce paper having a large transport load into the nip, and a small thin paper. Then, the buckling can be prevented by stopping the driving before the suction area is exposed to the next paper.

  FIG. 6 is a timing chart of the conveyance control in the conveyance of the paper P described above.

  When a print instruction is issued and a print preparation such as warm-up is performed and then a paper feed instruction is issued, air suction is started, the drive of the paper feed belt 64 is turned on (B1 in the figure), and the paper P is conveyed. Is started.

  When the paper feed sensor PS2 detects the leading edge of the paper P during the conveyance of the paper P and is turned on (S1), the paper feed belt 64 is continuously driven for a certain time (t1), and then the drive is turned off (B2). Therefore, after the paper feed sensor PS2 detects the leading edge of the paper P and is turned on (S1), the paper P is continuously conveyed for a certain time (t1) and stopped.

  After the feed belt 64 is turned off (B2), when the carry roller drive start time (t2) elapses, the carry roller 39 is turned on (R1) and the carry roller 39 is started to be driven.

  At the timing when the drive of the transport roller 39 is turned on (R1), the drive of the paper feed belt 64 is turned on (B3) and re-driven.

  The re-driven paper feeding belt 64 is driven for a predetermined time (t3), and the driving is turned off (B4) after the predetermined time. The paper P sandwiched between the transport rollers 39 is transported downstream by the transport rollers 39.

  When the paper feed sensor PS2 detects the trailing edge of the paper P and is turned OFF (S2), the driving of the conveying roller 39 is turned off (R2) after a predetermined time (t4) on the trailing edge side, and the conveying roller 39 stops.

  When feeding continuously, the above operation is repeated.

  As described above, after the leading edge of the paper P is abutted against the downstream conveying roller 39 stopped by the paper feeding belt 64 to stop the driving of the paper feeding belt 64, the driving of the conveying roller 39 is temporarily started. A very small amount of the paper feeding belt 64 is driven, and the leading edge of the abutted paper P is introduced into the nip of the conveying roller 39. Thereby, the paper P can be reliably conveyed. Since the amount of driving is very small, overrun due to inertia can be suppressed to a small extent compared to when transporting at high speed.

  In addition, by changing the driving amount according to the size of the paper P and increasing the amount for a large size, it is possible to reliably introduce paper having a large transport load into the nip, and a small thin paper. Then, the buckling can be prevented by stopping the driving before the suction area is exposed to the next paper.

DESCRIPTION OF SYMBOLS 30 Paper feeder 31 Paper stacking tray 50 Air blower 60 Adsorption conveyance part 61 Large roller 62a, 62b Small roller 63 Intermediate roller 64 Paper feed belt 65 Suction duct 66 Suction fan A Image forming apparatus DF Automatic document feeder SC Image reader LT Large-capacity paper feeder P, P1, P2 Paper Ps Paper bundle M1 Motor

Claims (4)

A paper stacking tray for loading paper,
An adsorbing and conveying means located above the sheets stacked on the sheet stacking tray and adsorbing and conveying the sheets;
A transport roller disposed downstream of the suction transport means in the paper transport direction and transports the paper;
A paper feed sensor disposed between the suction conveyance means and the conveyance roller to detect the paper;
Control means for independently controlling the suction conveyance means and the driving of the conveyance rollers,
The control means detects the leading edge of the sheet conveyed by the paper feed sensor, and then drives the suction conveying means for a predetermined time so that the leading edge of the sheet abuts against the conveying roller. Stop driving,
Next, after the leading edge of the sheet is abutted against the conveying roller, the driving of the conveying roller is started, and at the same time, the driving of the sucking and conveying unit is restarted to convey the sheet. The sheet feeding device is controlled to stop driving.   The paper feeding device according to claim 1, wherein the predetermined time is set based on a length in a conveyance direction of the paper.   In transporting the paper having the smallest usable transport direction length, when the suction transport unit is stopped after the predetermined time, the rear end of the paper is the upstream end in the transport direction of the suction region of the suction transport unit The sheet feeding device according to claim 1, wherein the sheet feeding device is located at a position.   An image forming system comprising: the paper feeding device according to claim 1; and an image forming device that forms an image on a sheet supplied from the paper feeding device.

Images