JP2019119560A - Paper feeding device and image forming apparatus - Google Patents

Abstract

To provide a paper feeding device and an image forming apparatus which are capable of suppressing the occurrence of double feeding by reducing a friction force between sheets that are stacked and surely separating the sheets.SOLUTION: A paper feeding device comprises: a sheet stacking table 511 for storing sheets in a stacked state; a rear end suction part 57 for sucking a rear end part, in a paper feeding direction, of the uppermost sheet P on the sheet stacking table; and a send-out part 55 for sending the sheet in the paper feeding direction, with the rear end suction part comprising a movable part 571 which is movable in a vertical direction with respect to the sheet surface of the sheets that are stored on the sheet stacking table and a second fan 573 which generates suction power for making the sheet sucked onto the moving part. The movable part is configured in such a manner that it moves downward and comes into contact with the uppermost sheet on the sheet stacking table when the sheet is not sucked and that it moves upward and separates the rear end from the other sheets when the sheet is sucked.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a sheet feeding device and an image forming apparatus.

2. Description of the Related Art Conventionally, in an image forming apparatus for forming an image on a sheet, there is known an air suction type sheet feeding device for stocking sheets in a stacked state and supplying the sheet to an image forming unit (see, for example, Patent Document 1). .
In this air suction type sheet feeding apparatus, the upper sheet is blown from the both sides (side end side) to the upper sheet along the direction orthogonal to the sheet conveyance direction, and the sheet stacked on the sheet stacking unit is lifted. An end air blower, a tip air blower that blows air from the leading end side of the uppermost sheet in the conveyance direction to float up the upper sheet and separate the uppermost sheet and the other sheets; And a suction conveyance unit that feeds the sheet in the conveyance direction while adsorbing the sheet by the conveyance belt disposed above the sheet. By suctioning only the top sheet by these mechanisms and reliably separating it from other sheets, the sheets can be sent out one by one onto the sheet conveyance path.

  However, in such a sheet feeding apparatus, in the case of a sheet long in the sheet feeding direction such as a long sheet, it is necessary to allow the separated air to reach the trailing end of the sheet in order to reliably separate it from the sheet below. If the separation air is weak, the separation of the sheets becomes insufficient, and the risk of double feeding due to contact between the sheets increases, but if the separation air is too strong, the sheets move to the rear end side or the sheets May cause buckling.

  In order to cope with such a problem, in Patent Document 2, a pressing unit for pressing the sheet is provided above the space between the trailing end regulating plate for regulating the trailing end position of the sheet and the suction conveyance unit, and the sheet is separated by separation air. However, when the sheet moves in the direction opposite to the sheet feeding direction, a configuration is disclosed in which the pressing unit is driven to restrict the movement of the sheet in the direction opposite to the sheet feeding direction. Thereby, the problem in the case where the separation air as described above is too strong can be solved.

JP, 2016-117589, A JP 2012-046278 A

  However, as in the method of Patent Document 2, when the sheet is pressed from above, the frictional force between the uppermost sheet and the lower sheet is increased, and the double feed multi feed is deteriorated. Therefore, in the prior art, it is difficult to simultaneously achieve the separation of the sheet to the rear end by the separation air and the reduction of the frictional force between the sheets.

  The present invention has been made in view of the above problems, and a sheet feeding device and an image forming apparatus capable of reducing the frictional force between stacked sheets, reliably separating the sheets and suppressing the occurrence of double feeding. Intended to be provided.

In order to solve the above-mentioned subject, a sheet feeding device according to claim 1 is
A sheet stacking unit for storing sheets in a stacked state;
A rear end suction unit that suctions the rear end side of the uppermost sheet of the sheet stacking unit in the sheet feeding direction;
A delivery unit for delivering the sheet in the sheet feeding direction;
The rear end suction portion is
A movable unit movable in the vertical direction perpendicular to the sheet surface of the sheet accommodated in the sheet stacking unit;
An adsorption force generation unit that generates an adsorption force for attracting the sheet to the movable unit;
Equipped with
The movable portion is
When the sheet is not adsorbed, it moves downward to contact the sheet at the top of the sheet stacking unit, and when the sheet is adsorbed, the sheet moves upward to move the rear end of the sheet from the other sheet It is characterized in that it is configured to be separated.

The invention according to claim 2 is the sheet feeding apparatus according to claim 1;
The movable portion is characterized by moving downward by its own weight.

The invention according to claim 3 is the sheet feeding device according to claim 1 or 2
The suction force generation unit includes a negative pressure generation unit that generates a negative pressure between the movable unit and the sheet to attract the sheet.
The movable portion may move upward by a negative pressure generated between the negative pressure generating portion and the sheet.

According to a fourth aspect of the present invention, in the sheet feeding device according to the third aspect,
The movable portion has a suction hole at a contact portion with the sheet,
The force by the negative pressure generated by the negative pressure generating part in the closed state of the suction hole is larger than the force by the weight of the movable part, and the negative pressure generated by the negative pressure generating part in the open state of the suction hole The force is characterized in that it is smaller than the force by its own weight.

According to the fifth aspect of the present invention, in the sheet feeding device according to the third or fourth aspect,
The apparatus may further include a spray unit configured to blow air, which is exhausted as negative pressure is generated by the negative pressure generation unit, to the rear end of the loaded sheet.

The invention according to claim 6 is the sheet feeding device according to any one of claims 3 to 5,
A negative pressure control unit that controls the generation of negative pressure by the negative pressure generation unit;
The negative pressure control unit determines whether or not negative pressure is generated by the negative pressure generation unit based on at least one of the sheet type, the paper feeding direction length, the basis weight, and the environment of the stacked sheets. It is characterized in that the magnitude of pressure is controlled.

The invention according to claim 7 is the sheet feeding device according to any one of claims 1 to 6,
The moving distance of the movable portion in the vertical direction can be changed based on at least one of a sheet type of stacked sheets, a length in a sheet feeding direction, a basis weight, and an environment.

According to an eighth aspect of the present invention, in the sheet feeding device according to any one of the first to seventh aspects,
A rear end position regulation unit that regulates the rear end position of the stacked sheets in the sheet feeding direction;
The rear end suction portion is provided in the rear end position regulating portion.

The invention according to claim 9 is the sheet feeding apparatus according to claim 8;
The rear end position regulation unit is movable in the sheet feeding direction,
The rear end suction unit moves along with the length of the sheet stacked in the sheet feeding direction along with the rear end position regulating unit.

The image forming apparatus according to claim 10 is
The sheet feeding device according to any one of claims 1 to 9.
And an image forming unit that forms an image on a sheet fed by the sheet feeding device.

  According to the present invention, it is possible to provide a sheet feeding device and an image forming apparatus capable of reducing the frictional force between stacked sheets, reliably separating sheets, and suppressing the occurrence of double feeding.

FIG. 1 is an entire configuration view showing an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing a control system of the image forming apparatus according to the present invention. FIG. 2 is a perspective view of a sheet feeding unit of the image forming apparatus. FIG. 6 is a side view in which a part of the sheet feeding unit is cut away. FIG. 6 is a plan view showing a delivery unit and a tip suction unit of a sheet feeding unit. FIG. 6 is a perspective view in which a part of a rear end suction portion of the sheet feeding unit is cut away. FIG. 6 is a diagram for explaining a floating state of a sheet in a sheet feeding unit having no trailing end suction unit. FIG. 6 is a view for explaining the sheet suction and gripping operation by the trailing end suction unit. 5 is a flowchart of operation control of continuous sheet feeding. 5 is a timing chart of operation control of continuous sheet feeding. 5 is a timing chart of operation control of continuous sheet feeding. It is a figure showing the modification of the back end adsorption part concerning the present invention.

  Hereinafter, embodiments of the present invention will be described using the drawings. However, although various limitations preferable for carrying out the present invention are given to the embodiments described below, the scope of the invention is not limited to the following embodiments and the illustrated examples.

[Overview of Image Forming Apparatus]
FIG. 1 is an overall configuration diagram of an image forming apparatus 100 according to the present invention, and FIG. 2 is a block diagram showing a functional configuration of the image forming apparatus 100. As shown in FIG.
As shown in FIGS. 1 and 2, the image forming apparatus 100 mainly includes an image forming apparatus main body 100a, an image reading apparatus SC, an automatic document feeder DF, an image processing unit 30, a sheet feeding unit 500, and a control unit 400. It is done. The control unit 400 and the sheet feeding unit 500 constitute a sheet feeding device.

The image forming apparatus main body 100 a includes an image forming unit 110 including a photosensitive member 1, a charging unit 2, an image exposing unit 3, a developing unit 4, a transfer unit 5, and a cleaning unit 6, a fixing unit 7 and a sheet conveyance system 120. It is configured.
A sheet conveyance system 120 includes upper and lower two-stage sheet feeding cassettes 10 and 10 for storing sheets, sheet feeding and conveying sections 11 and 11 for feeding sheets one by one from each sheet feeding cassette 10, and sheet feeding and conveying sections 11 and 11 11, a first conveying unit 12 for conveying the sheet conveyed to the front of the image forming unit 110, a second conveying unit 13 for conveying the sheet from the first conveyance unit 12 to the downstream of the fixing unit 7, A sheet between the sheet discharge unit 14 for conveying the sheet to the sheet, the circulation refeed unit 15 branching from the second conveyance unit 13 and joining the first conveyance unit 12 again, the sheet discharge unit 14 and the circulation refeed unit 15 A conveyance path switching unit 16 switches the conveyance, and a reverse paper discharge unit 17 branches from the circulation re-feed unit 15 and reverses the front and back of the sheet.
Further, the sheet feeding unit 500 is configured of three first sheet feeding units 50a, a second sheet feeding unit 50b, and a third sheet feeding unit 50c which are disposed side by side vertically.

[Automatic Document Feeder and Image Reader]
The automatic document feeder DF conveys the document d placed on the document table to the image reading device SC. The image reader SC reads an image of one side or both sides of the conveyed original d by the image sensor CCD. The image processing unit 30 performs analog processing, A / D conversion, shading correction, image compression processing, and the like on an analog signal photoelectrically converted by the image sensor CCD, and then transmits it to the image exposure unit 3 as an image signal. .
In addition, the control unit 400 can communicate with an external device (for example, a personal computer) connected to a communication network from a communication unit (not shown), and performs image processing on an image signal received from the external device. The image exposure unit 3 may also be sent via the unit 30.

[Image formation unit]
In the image forming unit 110, the charging unit 2 applies an electric charge to the photosensitive member 1, the image exposing unit 3 forms an electrostatic latent image by irradiating the photosensitive member laser light, and the developing unit 4 forms an electrostatic latent image. Are visualized to form a toner image.
Then, the sheet P accommodated in the sheet feeding cassette 10 and conveyed from the sheet feeding and conveying unit 11 is conveyed in synchronization with the toner image by the registration roller 12 a of the first conveying unit 12. Thereafter, the sheet P is fixed by the fixing unit 7 after the toner image is transferred at the transfer unit 5.
Further, not the sheet P accommodated in the sheet feeding cassette 10 but the sheet P accommodated in the sheet feeding unit 500 is also fed to the image forming apparatus main body 100a, and the toner image is transferred and fixed on the sheet P .

  The sheet P after fixing is discharged by the second conveyance unit 13 out of the apparatus. On the other hand, the cleaning unit 6 removes the residual toner on the photosensitive member 1. In the case of double-sided printing, the sheet P on which the image is formed on the first side is sent to the circulation refeed unit 15 by the conveyance path switching unit 16 and inverted, and the image forming unit 110 After the formation, the sheet is discharged by the second conveyance unit 13 out of the apparatus. In the case of reverse sheet discharge, the sheet P branched from the normal sheet discharge path is switched back in the reverse sheet discharge portion 17 and turned upside down, and then discharged out of the apparatus by the second conveyance portion 13.

[Summary of Paper Feeder]
FIG. 3 is a perspective view schematically showing the first sheet feeding unit 50 a of the sheet feeding unit 500. As described above, the first sheet feeding unit 50a, the second sheet feeding unit 50b, and the third sheet feeding unit 50c are provided in the sheet feeding unit 500 side by side vertically as described above, for example, all of them are the same. The first sheet feeding unit 50a will be described here.
The first sheet feeding unit 50a includes a sheet storage unit 51, a tip air blowing unit 52, side end air blowing units 53 and 54, a delivery unit 55, a tip suction unit 56, a rear end suction unit 57, a conveyance unit 58, and the like. Configured

[Configuration of paper storage unit and its surroundings]
The sheet storage unit 51 has a sheet stacking table 511 as a horizontally-oriented sheet stacking unit on which a plurality of sheets P are stacked in a stacked state, and a rear side of the sheet stacking table 511, that is, an upstream side of the sheet feeding direction a. The rear end regulating member 512 is provided, and a front end regulating member 513 provided on the front side of the sheet stacking table 511, that is, on the downstream side in the sheet feeding direction a.
In the following description of the sheet feeding unit 50, the left direction is the horizontal direction orthogonal to the sheet feeding direction a and is the horizontal direction orthogonal to the sheet feeding direction a with the left direction facing the sheet feeding direction a. It is assumed that the direction of the right hand is “right” while the sheet is directed in the sheet feeding direction a.

The sheet stacker 511 is supported by the sheet feeding unit 50 so as to be movable up and down.
The upper end of the leading end regulating member 513 is slightly lower than the upper end of the trailing end regulating member 512. On the other hand, the sheet stacking tray 511 is moved up and down by an actuator (not shown), and the top of the sheets P stacked on the sheet stacking tray 511 maintains a prescribed height slightly lower than the upper end of the leading edge regulating member 513 The actuator is controlled by the controller 400 as described above. The height control by the actuator is performed based on sensing by a sensor (not shown) that detects the height of the uppermost sheet P provided on the rear end regulating member 512 side.
In addition, at the time of non-sheet feeding such as replenishment of the sheet P, the sheet stacking table 511 can be lowered.

The trailing end regulating member 512 is moved up and down by an actuator (not shown), and moves in the height direction integrally with the trailing end suction portion 57 as described later. It is possible to lower the sheet stacker 511 and raise the trailing end regulating member 512 when the sheet P is not fed for supplying the sheet P or the like.
Further, the rear end regulating member 512 is provided movably along the sheet feeding direction a by an actuator (not shown) according to the length of the sheet P in the sheet feeding direction.

[Front end air blowing unit and side end air blowing unit]
A leading end air blower 52 is provided adjacent to the leading end regulating member 513 and downstream of the leading end regulating member 513 in the sheet feeding direction a. Further, side end air blowers 53 and 54 are provided on the left and right sides of the sheet loading table 511, respectively, and the inner side surfaces of the side end air blowers 53 and 54 are along smooth and vertical directions. Functions as a restricting member that restricts the position of the sheet in the left-right direction.

  Blower fans 521, 531, 541 are respectively provided inside the tip air blower 52 and the side end air blowers 53, 54, and the air is blown from the blower ports 522 (see FIG. 4), 532, 542 It is configured as follows. The tip end air blower 52 and the side end air blowers 53 and 54 function as an air blower.

FIG. 4 is a cross-sectional view showing the configuration of the periphery of the leading end portion of the uppermost sheet P in the sheet feeding direction a in the sheet stacking stand 511. As shown in FIG.
The tip air blower 52 has a nozzle 523 for blowing air from the air outlet 522 in a direction slightly upward to the downstream side in the sheet feeding direction a. The tip air blower 52 has a switching valve (not shown) inside the nozzle 523 and can switch the air blowing direction to two stages of upward blowing and downward blowing. When the air is blown downward, air is blown to the end face of the stacked sheets P, and the floating effect is high. When air is blown upward, air is blown to the leading end of the sheet P that has floated, so that the so-called separation effect is high, in which the sheet P at the top is separated from the sheet P that floats with the sheet P. .

As shown in FIG. 3, the side end air blowers 53, 54 are slightly higher in the horizontal direction or in the horizontal direction from the left and right sides of the uppermost sheet P located at the regulated height toward the sheet P. The nozzles 533 and 543 are provided for blowing air downward in an inclined manner. The air outlets 532 and 542 of the nozzles 533 and 543 are formed such that the upper edge is higher than the lower edge of the uppermost sheet P located at the regulated height.
Thus, by blowing air from the air outlets 532 and 542 of the side edge air blowing units 53 and 54, air can be applied to the upper sheet P in the stacked state, and the upper sheet P can be lifted. There is.

The downward air blowing by the leading end air blowing unit 52 and the air blowing by the side end air blowing units 53 and 54 function as floating air for causing the stacked sheets P to float. Note that the floating air may be either the downward air blowing by the tip air air blowing unit 52 or the air blowing by the side end air air blowing units 53 and 54.
The upward air blowing by the leading end air blowing unit 52 functions as separation air for separating the floated sheet P into the top sheet P and the sheet below it.

[Sending unit and suction unit]
FIG. 5 is a plan view of the delivery unit 55 and the tip suction unit 56. As shown in FIG. As shown in FIGS. 3 to 5, the delivery unit 55 is provided above the sheet stacking table 511. In FIG. 3, the delivery unit 55 is shown shifted to the position indicated by the arrow so as not to hide the surrounding configuration, but in actuality, as shown in FIG. Are disposed above the downstream end of the

The delivery unit 55 includes four pairs of belt mechanisms arranged in the horizontal direction orthogonal to the paper feeding direction a, a motor 551 serving as a paper feed drive source for driving these belt mechanisms, and between each belt mechanism and the motor 551 And a transmission gear train 552 interposed therebetween.
Each belt mechanism includes a large diameter roller 553 provided on the upstream side in the sheet feeding direction a, two small diameter rollers 554 and 555 provided on the downstream side in the sheet feeding direction a, and these rollers 553 and 554. , 555, and a belt 556 which is stretched around. Then, torque is applied from the motor 551 to the large diameter roller 553 of each belt mechanism in the direction in which the lower portion of each belt 556 advances in the sheet feeding direction a. Note that sprockets may be used instead of the rollers 553, 554, 555.
Each belt 556 is formed with a plurality of small holes penetrating the front and back over the entire surface, and a sheet P is formed on the lower portion of each belt 556 through each small hole by suction of a tip suction portion 56 described later. It is possible to adsorb the

On the upstream side of the sheet feeding direction a of the belt mechanism, a suction detection unit 557 for detecting the suction of the sheet to each belt 556 is equipped. The adsorption detection unit 557 includes a substantially rod-like detection body 557a swingably supported, and a photosensitive sensor 557b.
One end of the detection body 557a protrudes lower than the lower portion of the belt 556, and when the sheet P is adsorbed to the belt 556, the detection body 557a swings and one end thereof is pushed back upward. There is. The other end of the detection body 557a descends when one end is pushed back upward, and is disposed so as to shield the sensor 557b, and the sensor 557b controls the change of the light reception amount due to the shielding. And causes the control unit 400 to recognize suction of the sheet P.

As shown in FIGS. 3 to 5, the tip suction portion 56 has a first duct 561 disposed with one end portion inserted inside each belt 556 of the delivery portion 55, and the other end of the first duct 561. And a first fan 562 that makes the inside of the first duct 561 negative pressure.
One end side of the first duct 561 to be inserted into each belt 556 is formed in a substantially rectangular parallelepiped shape, and a first opening 561a is formed in the lower part thereof. And, by setting the inside of the first duct 561 to a negative pressure by the first fan 562, it is possible to suction the outside air from the first opening 561a.
The first duct 561 is disposed such that the first openings 561a straddle the lower portions of the four belts 556, and the area corresponding to the first openings 561a of each belt 556 is the first adsorption area for the sheet It is B.

FIG. 6 is a perspective view in which a part of the rear end suction portion 57 is cut away. As shown in FIG. 6, the rear end suction portion 57 is fixed to the upper end portion of the rear end regulating member 512, and is disposed to be in contact with the rear end of the uppermost sheet P. A movable portion 571 which can be lowered, a second duct 572 whose one end is connected to the movable portion 571, and a second pressure which makes the inside of the second duct 572 negative pressure at the other end of the second duct 572 A fan 573 is provided.
The movable portion 571 is a rectangular cylindrical body with a bottom, and a circular second opening 571 b is formed at the center of the bottom 571 a at the one end side contacting the uppermost sheet P, and the second opening 571 b Forms a second suction area C for the sheet. When the second fan 573 rotates, the outside air is sucked from the second opening 571 b in the direction of D in the drawing and exhausted in the direction of E in the drawing. That is, when the second opening 571 b is attracted to the sheet P by the rotation of the second fan 573, the inside of the second duct 572 has a negative pressure.
Further, one or more pins 571 c are provided on the wall surface of the movable portion 571. The pin 571 c is inserted into the window hole 572 a provided in the second duct 572, and the moving range in the height direction is restricted by the window hole 572 a. That is, as shown in FIG. 6A, the movable portion 571 has a position where the second opening 571b contacts the uppermost sheet P on the sheet stacking stand 511, and the second opening as shown in FIG. 6B. The unit 571 b is provided so as to be movable between the sheet placed on the sheet stacking table 511 and the position farthest from the sheet.

Here, the operation of the feeding unit 55, the leading end suction unit 56, and the rear end suction unit 57 at the time of sheet feeding will be described.
When floating air is blown by the leading end air blowing unit 52 and the side end air blowing units 53 and 54 and one or more sheets of paper P on the upper side of the sheet stacking table 511 rise, the sending unit 55 and the leading end suction unit 56 The leading end portion of the uppermost sheet P floated by the suction force generated in the first adsorption area B is adsorbed to the lower portion of each belt 556.
On the other hand, the rear end suction portion 57 moves the rear end portion of the sheet P by the suction force generated in the second suction area C in a state where the second opening 571 b of the movable portion 571 contacts the sheet P at the top. Adsorb to 571. When the force by the negative pressure in the second duct 572 is larger than the weight of the movable portion 571 and the weight of the rear end portion of the uppermost sheet P, the movable portion 571 ascends to lift the rear end side of the sheet.
In this state, it is possible to feed the sheet P in the sheet feeding direction a by the rotational driving of each belt 556 in the delivery unit 55.

[Transporter]
As shown in FIG. 4, a transport unit 58 is disposed in the vicinity of the delivery unit 55 and downstream of the feeding direction a. The conveyance unit 58 is provided in the middle of the insertion guide portion 581 capable of inserting the sheet P fed from the lower portion of the belt 556 and the insertion guide portion 581, and conveys the sheet P downstream in the sheet feeding direction a. Transport rollers 582 and 583, a motor (not shown) as a drive source for driving the transport rollers 582 and 583 to rotate, reaching the leading end of the sheet P to the insertion guide portion 581, and the rear end of the sheet P And a paper detection unit 584, which is an optical or contact sensor that detects the passage of a sheet.

The insertion guide portion 581 is formed such that the end on the upstream side in the sheet feeding direction a opens wide up and down, and the width in the top and bottom narrows toward the sheet feeding direction a. The upstream end portion is connected to the sheet P conveyance path toward the image forming apparatus main body 100a.
The large diameter conveyance roller 582 and the small diameter conveyance roller 583 are disposed to be in contact with each other, and the insertion guide such that the sheet P passing through the insertion guide portion 581 passes between the conveyance roller 582 and the small diameter conveyance roller 583 It is provided in the unit 581.
The large diameter transport roller 582 uses a motor (not shown) as a drive source, and the drive of the motor is controlled by the control unit 400. Since the small-diameter conveying roller 583 is in contact with the large-diameter conveying roller 582, torque of reverse rotation is transmitted to the large-diameter conveying roller 582 to perform the common rotation.

The sheet detection unit 584 is disposed in the vicinity of the transport rollers 582 and 583 and on the upstream side of the sheet feeding direction a, detects the presence or absence of the sheet P at the position of the sheet detection unit 584, and detects the detection result. Is input to the control unit 400 as needed. That is, when the detection state changes from a state where there is no paper P to a certain state, the control unit 400 recognizes that the leading end of the paper P has reached the position of the paper detection portion 584, and the state where the paper P is present When the detection state is changed to the absence state, it is recognized that the rear end of the sheet P has passed the position of the sheet detection unit 584.
The leading end of the sheet P indicates the downstream end of the sheet P in the sheet feeding direction a, and the rear end of the sheet P indicates the upstream end of the sheet P in the sheet feeding direction a.

[Control unit]
The control unit 400 includes a central processing unit (CPU) 401, a read only memory (ROM) 402, a random access memory (RAM) 403, and the like. The CPU 401 reads out a program corresponding to the processing content from the ROM 402, develops it in the RAM 403, and cooperates with the developed program to cooperate with each block of the image forming apparatus 100 (image reading device SC, automatic document feeder DF, image processing unit 30 Centrally control operations of the image forming apparatus main body 100a, the sheet feeding unit 500, and the like. At this time, various data stored in the storage unit 410 are referred to. The storage unit 410 is configured of, for example, a non-volatile semiconductor memory (so-called flash memory) or a hard disk drive.
The control unit 400 functions as an air control unit and a suction control unit.
Further, the control unit 400 includes a communication unit including a communication control card such as a LAN card (not shown), and is an external device connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network). Various data can be transmitted and received with (for example, a personal computer).

[Feed control of paper feeding device: Separation control by trailing end suction section]
The sheet feeding control for the first sheet feeding unit 50 a of the sheet feeding unit 500 by the control unit 400 will be described. The same paper feed control is executed for the second paper feeding unit 50b and the third paper feeding unit 50c.

First, the relationship between the blowing amount of floating air and the separation accuracy of the sheet P in the sheet feeding operation will be described based on FIG.
When the sheet feeding unit 50 starts the sheet feeding operation, floating air is blown by the leading end air blowing unit 52 and the side end air blowing units 53 and 54 so that the upper sheet P is floated and adsorbed to the lower part of each belt 556 It sends out to the conveyance part 58 side.
At this time, if the air flow rate of the floating air is insufficient, as shown in FIG. 7A, the sheet P can not float up to reach the trailing edge of the uppermost sheet P, and therefore contact with the lower sheet It becomes more likely to cause double feed from one another.
Further, when the air of the floating air is too strong, as shown in FIG. 7B, even if the top sheet P floats and is attracted to the lower part of the belt 556, the second and subsequent sheets of paper P are used. Buckling may occur.
As described above, it is difficult to control the rising of the trailing end of the sheet only by the blowing of air by the leading end air blowing unit 52 and the side end air blowing units 53 and 54. By lifting by 57, the separation of the rear end is assisted.

This will be described in detail with reference to FIG. In the following description, the top sheet is denoted by P0, and the next sheet below it is denoted by P1.
As shown in FIG. 8A, at the start of the sheet feeding operation, the movable portion 571 of the rear end suction portion 57 is in contact with the uppermost sheet P0 at the lowered position. When the sheet feeding operation is started, the second fan 573 is operated under the control of the control unit 400 to make the inside of the second duct 572 negative pressure, so that the outside air is sucked from the second opening 571 b to the movable portion 571. The sheet P0 is attracted.
When the sheet P0 is adsorbed, as shown in FIG. 8B, the negative pressure in the second duct 572 increases and exceeds the weight of the movable portion 571 and the weight of the rear end portion of the uppermost sheet P0, the movable portion 571 moves up while adsorbing the sheet P0, and the trailing edge of the uppermost sheet P0 is lifted. As a result, the rear end of the uppermost sheet P0 and the rear end of the next sheet P1 are separated.

As shown in FIG. 8C, when the uppermost sheet P0 is conveyed and the rear end side passes through the movable portion 571, the second opening 571b is opened. When the suction is released, the negative pressure in the second duct 572 is reduced, and the movable portion 571 is lowered by its own weight and comes in contact with the rear end upper surface of the next sheet P1.
As shown in FIG. 8D, when the movable portion 571 descends and contacts the upper surface of the next sheet P1, the next sheet P1 is attracted to the movable portion 571 by the outside air being sucked from the second opening 571b. Ru. When the movable portion 571 is adsorbed, a grip force is exerted, so that it is possible to prevent the next sheet P1 from being fed to the uppermost sheet P0 and being double-fed.
After the movable portion 571 is attracted to the next sheet P1, the negative pressure in the second duct 572 is increased during conveyance of the uppermost sheet P0, whereby the movable portion 571 is lifted as shown in FIG. And lift and hold the trailing edge of the next sheet P1. Since the separation operation of the next sheet P1 is started without waiting for the topmost sheet P0 to leave the transport unit 58, the waiting time can be reduced and the production efficiency can be increased.

Further, in the present embodiment, the control unit 400 functions as an air control unit, and after the rear end adsorption unit 57 adsorbs the sheet P, the front end air blower 52 and the side end air blowers 53 and 54 The air blowing timing is switched based on at least one of the sheet type of the stacked sheets P, the length in the sheet feeding direction, the basis weight, and the environment. For example, the ease of separation of the paper P varies depending on the paper type, for example, the rough paper such as recycled paper is easily separated and the paper with high adhesiveness such as coated paper is difficult to separate. Further, the longer the sheet feeding direction length and the smaller the basis weight, the more difficult the separation. Furthermore, in a high-humidity environment or the like where the sheets P contain moisture and the adhesiveness of the individual sheets P is increased, separation becomes difficult. Therefore, by delaying the air blowing timing for a sheet that is difficult to separate, the time for lifting and holding the sheet P by the rear end suction unit 57 becomes long, and the separation property is improved. By changing the air blowing timing of the floating air according to such conditions, the separation can be further enhanced.
Furthermore, the control unit 400 controls the front end air blower 52 and the side end air blower based on at least one of the paper type, the paper feed direction length, the basis weight, and the environment of the sheets loaded as the air control unit. Whether the floating air is blown or blown by the units 53 and 54 is determined. As a result, it is possible to reduce damage to the sheet, such as not to blow the floating air to the sheet P having high separability, and to suppress unnecessary consumption of power.

  Further, the side end air blowers 53, 54 blow the floating air from the start of the sheet feeding operation until the suction detection of the leading end of the sheet P is detected by the suction detection unit 557, and stop the air blowing after the detection. Thus, the air flow of the separated air by the tip air blower 52 can be stabilized.

[Flow of operation control of continuous sheet feeding of sheet feeding device]
A flow of operation control of continuous sheet feeding of the sheet feeding apparatus will be described based on a flowchart of FIG. 9 and a timing chart of FIG. FIG. 10A is a timing chart when suction is not performed by the rear end suction portion 57 while the floating air is being blown, and FIG. 10B is suctioned by the rear end suction portion 57 while the floating air is being blown. It is a timing chart of a case.

  With regard to the topmost sheet P0 of the first sheet of continuous sheet feeding, the preceding sheet is not in a state of being adsorbed to the belt 556, so when receiving a request to start sheet feeding, the control unit 400 immediately responds to the printing conditions. The air blowing timing and air blowing amount of the floating air are determined (step S1). Here, the printing conditions refer to the sheet type of the sheet P, the sheet feeding direction length, the basis weight, and the environment as described above, and the control unit 400 determines based on at least one of these. The printing conditions and the air blowing timing and air flow rate of the floating air are tabulated in advance and stored in the storage unit 410. The printing conditions may be input by the user, or may be determined by the control unit 400 with reference to environment information detected by the humidity detection sensor or job information.

  Subsequently, the air blowing direction of the end air air blowing unit 52 is set to the downward air blowing, and air blowing of the floating air is started by the end air air blowing unit 52 and the side end air air blowing units 53 and 54. As a result, the topmost sheet P 0 of the sheet loading table 511 floats up and is attracted to the first attraction area B of the belt 556. On the other hand, the control unit 400 starts driving of the second fan 573 of the rear end suction unit 57, and the rear end of the uppermost sheet P 0 is sucked by the second suction area C, and the movable portion 571 is the second duct 572. When the internal negative pressure exceeds the weight of the movable portion 571 and the weight of the rear end portion of the topmost sheet P0, it starts to rise (step S2, (t1) in FIGS. 10A and 10B).

The control unit 400 determines whether the suction detection unit 557 is in the "ON" state indicating sheet detection (step S3), and when it is determined that the suction detection unit 557 is not in the "ON" state (step S3: NO), Execute judgment repeatedly.
Subsequently, when the sheet P is detected by the suction detection unit 557 (step S3: YES), the control unit 400 switches the air blowing direction of the tip air air blowing unit 52 to the upper air blowing and starts blowing the separation air. The air blowing by the air blowing units 53 and 54 is stopped (step S4, (t2) in FIGS. 10A and 10B). As a result, separation air is blown to the end portion of the sheet P which has floated up, the separation effect is enhanced, and the sheet P is completely separated from the next sheet P1.
Then, the control unit 400 activates the delivery unit 55 to deliver the uppermost sheet P in the sheet feeding direction a (step S5, (t3 in FIGS. 10A and 10B)).

  When the trailing edge of the uppermost sheet P passes through the trailing edge suction portion 57 in association with the delivery by the delivery portion 55, the second opening 571b is opened, whereby the negative pressure in the second duct 572 is reduced. Then, the movable portion 571 starts to descend by its own weight (step S6, (t4 in FIG. 10B)).

When the trailing edge of the next sheet P1 is adsorbed to the second adsorption area C by the descent of the movable portion 571, the negative pressure in the second duct 572 becomes high and the movable portion 571 starts to ascend again ( Step S7, (t5) in FIG. As a result, the trailing edge of the next sheet P1 is lifted, and is separated from the sheet below.
Subsequently, the control unit 400 switches the air blowing direction of the tip air blowing unit 52 to the downward blowing, and starts blowing the floating air by the tip air blowing unit 52 and the side end air blowing units 53 and 54 (step S8, FIG. 10). (A), (B) (t6). As a result, the leading end of the next sheet P 1 raises the sheet P at the top of the sheet stacking table 511, and is attracted to the first suction area B of the belt 556.

The control unit 400 determines whether the suction detection unit 557 determines that the trailing edge of the sheet P is in the "OFF" state indicating that the rear end of the sheet P has passed the delivery unit (step S9) and determines that it is not the "OFF" state. (Step S9: NO) The determination of step S9 is repeatedly executed.
Subsequently, when the control unit 400 determines that the suction detection unit 557 is in the “OFF” state (step S9: YES), the control unit 400 stops driving the sending unit 55 (step S10, FIGS. 10A and 10B). (T7)).

  Subsequently, the control unit 400 determines whether the top sheet P is the final page in the sheet feeding operation (step S11). If the controller 400 determines that it is not the final page (step S11: NO), it returns to step S2 and continues the feeding operation of the next sheet P1, but if it determines that it is the final page (step S11: YES), End paper feed control.

[Technical effect of this embodiment]
In the sheet feeding unit 500 mounted in the image forming apparatus 100 according to the present embodiment, the separation effect of the sheet P can be increased.
This will be described using the timing chart of FIG. When the trailing edge of the uppermost sheet P0 is not attracted by the trailing edge adsorbing portion 57, the trailing edge adsorbing portion 57 adsorbs and grips the trailing edge of the next sheet P1. Therefore, from the transport start time of the uppermost sheet P0 ((t3) in FIGS. 10A and 10B), the time to float the next sheet P1 ((t6 in FIGS. 10A and 10B)) The time until ((T1) in FIGS. 10A and 10B) can be shortened.
Further, since the trailing end suction by the rear end suction portion 57 also serves as a grip for the next sheet P1, the blowing of the floating air to the next sheet P1 is started ((t6 in FIGS. 10A and 10B). ) Can be advanced to the middle of the delivery of the uppermost sheet P0 by the delivery unit 55, and when the uppermost sheet P0 leaves the delivery unit 55 ((A) and (B) of FIG. Spraying of separation air can be started from t7). The same effect can be obtained for the following paper P.
Here, the conveyance start time of the next sheet P1 from the conveyance start time ((t3) in FIGS. 10A and 10B) of the uppermost sheet P0 ((t8) in FIGS. 10A and 10B) Assuming that the time until (the total time of (T1), (T2), and (T3) in FIGS. 10A and 10B) is the same as that in the prior art, the time during which the levitation effect is applied to the next sheet P1 10 (A) and (B) (T2), the time for applying the separation effect to the paper P ((T3) in FIGS. 10 (A) and (B)) is increased. Can. Therefore, according to the present invention, it is possible to reduce the frictional force between the stacked sheets, reliably separate the sheets, and to suppress the occurrence of double feeding.

In the above embodiment, as described above, the cleaning effect can be increased, but the productivity can be improved by making the time for applying the cleaning effect equal to that of the prior art.
This will be described using the timing chart of FIG. Similar to the timing chart of FIG. 10, in the present embodiment, T1 and T2 can be shortened. Here, by making T3 the same as the time in the prior art, it is possible to advance the conveyance start time of the next sheet P1 ((t 8) in FIGS. 10A and 10B) compared to the prior art. That is, by delaying the timing of the start of conveyance of the sheet P, the waiting time can be reduced and the productivity can be improved.

  In the sheet feeding unit 500 according to the present embodiment, the movable portion 571 is lowered by its own weight when the sheet P passes through the rear end suction portion 57. Therefore, since an individual mechanism for lowering the movable portion 571 is not required, the effect of the present invention can be obtained with a simple configuration.

  Further, in the sheet feeding unit 500 according to the present embodiment, the movable portion 571 is raised by the negative pressure generated by the second fan 573 when the sheet P is adsorbed. Therefore, since the separate mechanism for raising the movable part 571 is not required, the effect of the present invention can be obtained with a simple configuration.

  Further, in the sheet feeding unit 500 according to the present embodiment, the movable unit 571 is provided with the second opening 571b at the contact portion with the sheet P by the control unit 400, and the force by the negative pressure in the adsorption state of the sheet P is movable. The force by negative pressure in the state where the sheet P is not attracted is larger than the weight of the portion 571, and the force by the negative pressure is controlled to be smaller than the weight of the movable portion 571. Therefore, the raising and lowering of the movable portion 571 can be properly controlled.

  Further, the sheet feeding unit 500 according to the present embodiment is provided with a trailing end regulating member 512 for regulating the trailing end position of the stacked sheets in the sheet feeding direction, and the trailing end adsorption portion 57 is the trailing end regulating member 512. It is provided integrally with the Therefore, the rear end suction portion 57 takes up little space and saves space.

  Further, in the sheet feeding unit 500 according to the present embodiment, the trailing end regulating member 512 is movable in the sheet feeding direction a of the sheet P, and the trailing end adsorption portion 57 is a sheet stacked with the trailing end regulating member 512 It moves according to the length of the sheet feeding direction a of P. Therefore, the rear end can be reliably attracted regardless of the size of the sheet P.

[Modification]
Hereinafter, modifications of the rear end suction portion 57 will be described.
As shown in FIG. 12, the rear end suction portion 57 according to the modification has an exhaust port 572 b as a spray portion provided in the second duct 572 so as to face the rear end side of the stacked sheets P. Then, the air is exhausted by the second fan 573 in the direction of the air F, and the air is blown to the trailing edge of the stacked sheets. That is, by simultaneously performing the floating of the rear end side of the sheet P by the movable portion 571 and the blowing of the air from the exhaust port 573b, the separation effect can be strengthened.

[Others]
In addition to the above-described embodiment, the blowing amount of the separation air and the floating air may be switched according to the sheet type, the basis weight, the sheet size, and the like of the sheet. That is, when feeding thick paper and other hard-to-lift paper, the floating effect is enhanced by increasing the air flow of separation air and floating air, and when feeding thin paper that is easy to float but tends to bend, separation air and floating air Damage to the paper can be reduced by reducing the air flow.

  Further, in the above embodiment, the separation air is switched to the upper air blowing or the lower air blowing according to the sheet feeding condition, but the upper air blowing or the lower air blowing may be always performed according to the paper type or the like. For example, when the sheet has a curl that is convex downward, if the separation air is blown upward, the lower sheet may be pressed against the uppermost sheet, which has an adverse effect on the separation. Therefore, in such a case, it is effective that the separation air is always blown downward and the separation is performed only by lifting the rear end side by the rear end suction portion 57.

  Further, in the above-described embodiment, the air volume and the negative pressure of the second fan 573 may be changed according to the sheet type, the basis weight, the sheet size, the environment, and the like of the sheet. That is, for example, when feeding thick paper that is difficult to float, negative pressure is increased to strengthen the floating assist at the rear end, and when thin paper that is easy to float but bends easily is reduced negative pressure to attract the rear end. Damage to the paper can be reduced.

Further, in the above embodiment, the position at which the movable portion 571 ascends and stops is uniformly set as the position where the pin 571c abuts on the window hole 572a, but the present invention is not limited to this. The height of the pin 571 c may be switched in multiple steps by the window hole 572 a, and the movement of the movable portion 571 in the height direction may be controlled in multiple steps. Thereby, for example, when the sheet is long in the sheet feeding direction and the friction between the sheets is large, the upper limit position is made higher than when feeding short sheets, and the uppermost sheet and the sheet under it are separated as much as possible. For example, the upper limit position can be set according to the sheet condition.
Alternatively, the upper limit position of the movable portion 571 may be set according to the sheet condition by controlling the movement of the rear end regulating member 512 in the height direction in multiple stages.

In the above embodiment, the movable portion 571 is increased by negative pressure. However, the present invention is not limited to this, and the movable portion 571 may be driven and raised by an actuator such as a solenoid.
In the above embodiment, the movable portion 571 is lowered by its own weight. However, the present invention is not limited to this, and may be lowered by a biasing member such as a spring.
Further, in the above embodiment, although the one using a negative pressure as the adsorption force generation part is disclosed, the invention is not limited to this, for example, static electricity may be used, and the sheet can be adsorbed to the movable part 571 It may be anything.

[Other embodiments]
As mentioned above, although it concretely explained based on the embodiment concerning the present invention, the above-mentioned embodiment is a suitable example of the present invention, and is not limited to this.

  For example, in the above-described embodiment, the color image forming apparatus in which the image formed on the photosensitive drum is primarily transferred to the intermediate transfer roller and the image is transferred from the intermediate transfer roller to the sheet by the secondary transfer roller has been described. The present invention is also applicable to a monochrome image forming apparatus in which an image is directly transferred from a photosensitive drum to a sheet by a transfer roller.

  In the above embodiment, the electrophotographic image forming apparatus has been described as an example. However, the paper feeding apparatus according to the present invention can be applied to an inkjet image forming apparatus.

  Further, in the above-described embodiment, the sheet feeding device that sucks and conveys by air is described as an example. However, the present invention can be applied to a sheet feeding device of a friction separation type using sheet feeding rollers.

  In the above description, an example using non-volatile memory, a hard disk or the like as a computer readable medium of the program according to the present invention has been disclosed, but the present invention is not limited to this example. As another computer readable medium, a portable recording medium such as a CD-ROM can be applied. Also, as a medium for providing the data of the program according to the present invention via a communication line, carrier wave (carrier wave) is also applied.

  In addition, the detailed configuration of each device constituting the image forming device and the detailed operation of each device can be appropriately changed without departing from the scope of the present invention.

100 Image forming apparatus 100a Image forming apparatus main body 400 Control unit (negative pressure control unit)
410 storage unit 500 sheet feeding unit 50 a first sheet feeding unit 50 b second sheet feeding unit 50 c third sheet feeding unit 51 sheet storage unit 511 sheet stacking table (sheet stacking unit)
512 Rear end regulating member (rear end position regulating portion)
513 Tip regulating member 52 Tip air blowers 53, 54 Side end air blower 55 Delivery unit 56 Tip suction unit 57 Trailing suction unit 571 Movable portion 571a Bottom portion 571b Second opening (suction hole)
571c pin 572 second duct 572a window hole 572b exhaust port (spray part)
573 Second fan (adsorption force generation part, negative pressure generation part)
58 Transporting Unit P Paper

Claims (10)

A sheet stacking unit for storing sheets in a stacked state;
A rear end suction unit that suctions the rear end side of the uppermost sheet of the sheet stacking unit in the sheet feeding direction;
A delivery unit for delivering the sheet in the sheet feeding direction;
The rear end suction portion is
A movable unit movable in the vertical direction perpendicular to the sheet surface of the sheet accommodated in the sheet stacking unit;
An adsorption force generation unit that generates an adsorption force for attracting the sheet to the movable unit;
Equipped with
The movable portion is
When the sheet is not adsorbed, it moves downward to contact the sheet at the top of the sheet stacking unit, and when the sheet is adsorbed, the sheet moves upward to move the rear end of the sheet from the other sheet A sheet feeding device configured to be separated.   The sheet feeding device according to claim 1, wherein the movable portion moves downward by its own weight. The suction force generation unit includes a negative pressure generation unit that generates a negative pressure between the movable unit and the sheet to attract the sheet.
The sheet feeding device according to claim 1, wherein the movable portion is moved upward by a negative pressure generated between the negative pressure generating portion and the sheet. The movable portion has a suction hole at a contact portion with the sheet,
The force by the negative pressure generated by the negative pressure generating part in the closed state of the suction hole is larger than the force by the weight of the movable part, and the negative pressure generated by the negative pressure generating part in the open state of the suction hole The sheet feeding device according to claim 3, wherein the force is smaller than the force due to the own weight. The sheet feeding device according to claim 3 or 4, further comprising: a blowing portion that blows air, which is exhausted in response to the generation of the negative pressure by the negative pressure generating portion, to the rear end of the stacked sheets. A negative pressure control unit that controls the generation of negative pressure by the negative pressure generation unit;
The negative pressure control unit determines whether or not negative pressure is generated by the negative pressure generation unit based on at least one of the sheet type, the paper feeding direction length, the basis weight, and the environment of the stacked sheets. The sheet feeding device according to any one of claims 3 to 5, wherein the magnitude of pressure is controlled.   The moving distance of the movable portion in the vertical direction can be changed based on at least one of a sheet type of stacked sheets, a length in a sheet feeding direction, a basis weight, and an environment. The sheet feeding device according to any one of Items 1 to 6. A rear end position regulation unit that regulates the rear end position of the stacked sheets in the sheet feeding direction;
The sheet feeding device according to any one of claims 1 to 7, wherein the trailing end adsorbing portion is provided in the trailing end position regulating portion. The rear end position regulation unit is movable in the sheet feeding direction,
9. The sheet feeding apparatus according to claim 8, wherein the trailing end adsorbing portion moves in accordance with the sheet feeding direction length of the stacked sheets together with the trailing end position regulating portion. The sheet feeding device according to any one of claims 1 to 9.
An image forming unit configured to form an image on a sheet fed by the sheet feeding device.

Images