JPH11100138A - Sheet feeding device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet feeding device and an image formation device which can stop without damaging sheet even if sheet is jammed when it is transferred from a sheet suction and conveyance part to a conveyance roller. SOLUTION: A duct part 7 which is provided on an inner side of an endless conveyance member 14 of a sheet suction and conveyance part 3 and is communicated with a suction static pressure generation means 12 which generates suction static pressure which sucks sheet S is opened and closed by a static pressure change means 13, and an open amount of the duct part 7 is changed to change suction static pressure. A static pressure control means 34 controls the static pressure change means 13 to change an open amount of the duct part 7 immediately before the sheet S is transferred to a conveyance roller 23 provided on the downstream side of the sheet suction and conveyance part 3 so that suction static pressure immediately before the sheet S is transferred to a conveyance means is lower than suction static pressure at the time of the start of sheet conveyance. Consequently, even if the sheet S causes jamming when it is transferred to the conveyance roller 23, it slips.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet feeding apparatus provided in an image forming apparatus such as a copying machine, a printer, a facsimile, and the like, and more particularly, to a sheet feeding apparatus for sucking and feeding a sheet.

[0002]

2. Description of the Related Art Conventionally, a sheet feeding apparatus provided in an image forming apparatus such as a copying machine, a printer, a facsimile, etc.
In general, the sheet stacked on the sheet stacking means is conveyed by rotation of a sheet feeding roller.

In the sheet feeding apparatus of this type, the sheet feeding roller has a surface made of an elastic material such as rubber, but the sheet feeding performance largely depends on the coefficient of friction of the surface of the elastic material. Due to frictional changes in the outer surface of the paper feed roller, changes in the material over time, changes in the coefficient of friction due to the adhesion of paper dust, etc., the paper feed performance is not stable, and it is not possible to cope with sheets with various surface conditions. There was a disadvantage.

In view of the above, recently, a sheet feeding apparatus of a type in which a sheet stacked on a sheet stacking tray is suctioned and conveyed using an air suction force, a conveying force of an endless belt or the like has been proposed. ing.

FIG. 8 is a view showing the structure of such a sheet feeding apparatus. In FIG. 8, a sheet stacking tray 1 serving as a sheet stacking means for stacking a large number of sheets S is provided.
The sheet suction conveyance unit 3 is provided. The sheet suction and transport unit 3 includes a sheet suction unit 4 having a plurality of suction openings 4A for sucking the sheet S, a transport belt 14 as an endless transport member, and a suction opening 4A of the sheet suction unit 4. And a suction blower 12 for sucking air below the conveyor belt 5 through the suction belt.

Further, near the leading end of the sheets S stacked on the sheet stacking tray 1, a first nozzle 19 for jetting air for floating the upper sheet S, and air to the second and subsequent sheets S are provided. , And a second nozzle 20 for separating only the top sheet S by one sheet.

In the sheet feeding apparatus having such a configuration, the sheets S stacked on the sheet stacking tray 1 are
In order to feed the sheet, first, air is ejected from the first nozzle 19 to cause several sheets S on the sheet stacking tray 1 to float.

Subsequently, the uppermost sheet S is conveyed to the conveyor belt 1 by the suction force of the sheet suction section 4 by the action of the suction blower 12.
Adsorb to 4. Thereafter, the transport belt 14 is rotationally driven in the direction of arrow A, and the sheet S adsorbed on the transport belt 14 is
To the downstream side. At this time, air is blown from the second nozzle 20 to the front end of the sheet S, and the double fed sheet S is blown back and separated.

As a result, only one uppermost sheet S is conveyed to the conveying roller 23 which is a conveying means provided on the downstream side of the sheet suction conveying section 3. In the present sheet feeding apparatus, the sheet S that floats with the air from the first nozzle 19 and is attracted to the conveyor belt 14 by the suction force of the sheet attracting unit 4 has a shape from its leading end to its trailing end. The transfer belt 14 is attracted to the conveyor belt 14 in a horizontal state.

A jam detection sensor 11 is provided on the downstream side of the conveyance roller 23, and the conveyance belt 14
If the jam detection sensor 11 does not detect the sheet S within a certain period of time after the conveyance of the sheet S attracted to the sheet S is started, it is determined that the sheet is jammed, and the apparatus stops.

[0011]

However, in such a conventional sheet feeding apparatus, if the sheet S is not detected within a predetermined time after the conveyance of the sheet S is started, the apparatus stops. The tip is the transport roller 23
If the paper jam occurs before the nip, the sheet is conveyed by the distance L from the conveyance roller 23 to the jam detection sensor 11 even though the sheet is jammed.

When the sheet is conveyed with the leading end jammed, the leading end of the sheet becomes accordion-shaped,
There is a problem in that the sheet S is damaged, and particularly in the case of document feeding, the master document is damaged.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to stop the apparatus without damaging the sheet even when the sheet is jammed when the sheet is conveyed from the sheet suction conveyance section to the conveyance rollers. It is an object of the present invention to provide a sheet feeding apparatus and an image forming apparatus that can perform the above.

[0014]

According to the present invention, a sheet stacked on a sheet stacking means is suctioned by an endless conveyance member provided in a sheet suction conveyance section and then provided downstream of the sheet suction conveyance section. In the sheet feeding apparatus for conveying toward the conveyed conveying means, a static suction pressure generating means for generating a static suction pressure for adsorbing the sheet, and the endless conveying member communicating with the static static pressure generating means. And a duct portion for applying the static suction pressure to the transport member, and opening and closing the suction duct portion, and changing an opening amount of the suction duct portion so as to change the suction static pressure in the duct portion. Static pressure changing means for changing the opening amount of the suction duct portion immediately before the sheet is delivered to the conveying means, and changing the opening amount of the suction duct portion to a value just before the sheet is delivered to the conveying means, compared with the suction static pressure at the start of sheet conveyance. A static pressure control means towards the suction static pressure and controls the static pressure changing means so as to be lower, and is characterized in that it comprises a.

Further, the present invention is characterized in that the static pressure changing means is a valve, and the static pressure control means performs static pressure control by switching an opening / closing angle of the valve.

Further, in the present invention, the static pressure changing means is a relief valve, and the static pressure control means performs static pressure control by switching an opening / closing angle of the relief valve.

Further, in the present invention, the static pressure changing means is a valve and a relief valve, and the static pressure control means performs static pressure control by switching the opening and closing angles of the valve and the relief valve in conjunction with each other. It is assumed that.

Further, according to the present invention, sheet detecting means is provided between the sheet suction and conveying section and the conveying means, and the static pressure control means controls the static pressure changing means based on a detection signal from the sheet detecting means. It is characterized by the following.

Further, the present invention is characterized in that the static pressure changing means changes the opening amount of the suction duct portion in multiple steps by a stepping motor.

Further, according to the present invention, the static suction pressure immediately before the sheet is delivered to the transporting means is such that when the sheet is jammed without being delivered to the transporting means, the sheet slips on the transporting member. It is characterized by pressure.

According to the present invention, there is provided an image forming apparatus having a sheet feeding device and an image forming section, wherein the sheet feeding device is one according to any one of claims 1 to 7. Things.

Further, as in the present invention, the static-static-pressure changing means is provided inside the endless conveying member provided in the sheet-sucking and conveying section, and generates a static suction pressure for generating a static suction for sucking the sheet. The opening and closing of the duct portion communicating with the opening and closing is changed, and the static opening pressure is changed by changing the opening amount of the duct portion. The static pressure control means controls the static pressure changing means to change the opening amount of the duct immediately before the sheet is transferred to the conveying means provided on the downstream side of the sheet suction and conveying part, so that when the sheet is conveyed, The static suction pressure immediately before being delivered to the conveying means is lower than the static suction pressure.

[0023]

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

FIG. 1 is a view showing the overall configuration of a sheet feeding apparatus according to a first embodiment of the present invention. 8, the same reference numerals as those in FIG. 8 indicate the same or corresponding parts.

In FIG. 2, reference numeral 2 denotes a trailing end stopper guide plate provided at the rear end of the sheet stacking tray 1 on which the sheets S are stacked, and when the sheets S are stacked on the sheet stacking tray 1, the rear end of the sheet S Are abutted against the rear end stopper guide plate 2. The rear end stopper guide plate 2 is provided with a sheet level detection sensor 35 for positioning the document surface at an appropriate height with respect to the sheet suction / conveyance unit 3.

Reference numeral 31 denotes a tray motor for moving the sheet stacking tray 1 up and down.
Is controlled by a CPU 34 which is a control means for controlling the overall operation of the image forming apparatus.

That is, the CPU 34 operates the sheet stacking tray 1
When stacking the sheets S on the upper side, the tray motor 31 is rotated in the reverse direction to lower the sheet stacking tray 1 to a predetermined position, and after the stacking of the sheets S is completed, the tray motor 31 is rotated.
Is rotated forward to raise the sheet stacking tray 1 to a predetermined position. Then, after this, the sheet level detection sensor 3
When a signal indicating that the document surface has reached an appropriate height with respect to the sheet suction / conveyance unit 3 is input from 5, the tray motor 31 is stopped. The control operation of the CPU 34 is performed every time the sheet S is fed.

Reference numeral 5 denotes a planar bottom surface facing the sheet bundle of the sheet suction unit 4, and a plurality of air suction openings 6 are formed in the planar bottom surface 5. Reference numeral 7 denotes a suction chamber which is a duct formed in the sheet suction section 4, and the suction chamber 7 communicates with a suction blower 12 which is a suction static pressure generating means for generating a suction static pressure for sucking a sheet. I have.

Here, between the suction chamber 7 and the suction blower 12, an example of a static pressure changing means for opening and closing the suction chamber 7 and changing the opening amount of the suction chamber 7 so as to change the static suction pressure. A certain suction valve 13 is provided, and the suction valve 13 is rotatably provided around a shaft 21 provided at the center of the suction valve 13 as shown in FIG. By rotating the suction valve 13 in this way, the opening amount of the suction chamber 7 is changed to adjust the amount of sheet suction air.

The end of this shaft 21 is
A pulley 21 is provided, as shown in FIG. 2, and this pulley 21 is connected via a timing belt 20A to a pulley 23 provided on a stepping motor 20 for opening and closing the suction valve 13. Then, by the rotation of the stepping motor 20, the suction valve 13 is rotated.

In the figure, reference numeral 24 denotes a flag provided coaxially with the pulley 23, and reference numeral 25 denotes the flag 24.
And flag detection means connected to the CPU 34 as shown in FIG. 4. When the flag detection means 24 detects the flag 24, the flag detection means 24
4 is input. Based on this detection signal, the CPU 34 controls the driving of the stepping motor 20 as a static pressure control means to adjust the opening / closing angle of the suction valve 13.

On the other hand, in FIG. 1, reference numerals 15 and 16 denote two rollers arranged so as to sandwich the sheet suction portion 4 so as to stretch the conveyor belt 14 at a predetermined tension.
Is driven intermittently in the direction of arrow A by these rollers 15 and 16 to convey the sheet S.
In this embodiment, the downstream roller 15 is a driving roller, and the upstream roller 16 is a driven roller.

As shown in FIG. 2, a large number of air holes 14A are formed in the transport belt 14, and the air below the transport belt 14 is supplied to the air holes 14A and the sheet suction section 4 by the suction blower 12. The air is sucked into the suction chamber 7 through the air suction opening 6.
Then, the sheet is conveyed by the suction of the air to the transport belt 1.
4 to be adsorbed.

In FIG. 1, reference numeral 21 denotes a blower for blowing air, and first and second nozzles 19 and 20 are connected to the blower 21.

On the other hand, reference numeral 17 denotes a leading edge detection sensor which is provided between the transport roller 23 and the sheet suction and transport section 3 and is a sheet detecting means for detecting the leading edge of the sheet. CPU3
4 is input. Then, the CPU 34
The stepping motor 20 reduces the suction pressure (static suction pressure) based on the detection signal from the tip detection sensor 17.
Is driven to set the release angle of the suction valve 13 from the maximum angle shown in FIG. 2B to a predetermined angle shown in FIG.

Here, by setting the release angle of the suction valve 13 to a predetermined angle in this manner, the suction pressure immediately before the sheet S is transferred to the conveying roller 23 can be used to convey the sheet S at a constant speed (conveying without acceleration / deceleration). If the sheet S can be conveyed without slipping on (the suction surface of) the conveyance belt 14 and the sheet tip is jammed without being transferred to the conveyance roller 23, a pressure such that the sheet slips on the conveyance belt 14. I am trying to do it.

When the leading end of the sheet is jammed without being transferred to the conveying roller 23, the suction pressure is set so that the sheet S slips. It is possible to prevent the sheet S from becoming accordion-like.

In this embodiment, at the time of the start of sheet conveyance, that is, the state in which the suction / suction valve 13 is fully opened (FIG.
The static pressure in the chamber at the time of (b) is 35 mmH
_The blower 12 is set to be ₂ O. As a result, sheets up to thick paper (200 g / m ² ) can be adsorbed. Before the sheet conveyance is started, that is, the suction valve 1
Chamber 7 when 3 is closed (see FIG. 2C)
Is zero, and the sheet does not stick.

On the other hand, the static pressure in the chamber immediately before the transfer of the sheet to the conveyance roller 23 is such that the sheet of 200 g / m ² can be conveyed without slipping, and the leading end of the sheet is not transferred to the conveyance roller 23. so that when the jammed sheet from slipping, has set a 10~15mmH ₂ O, and opens the suction suction valve 13 so as to obtain such a static pressure at a predetermined angle (see FIG. 3 (a) ).

The following table shows the static pressure that does not cause accordion jam and the static pressure that does not cause slippage during steady-state conveyance at the time of sheet suction, sheet conveyance start, and accordion jam in the chamber 7 according to the present embodiment.

[0041]

[Table 1] Next, the sheet feeding operation of the sheet feeding apparatus thus configured will be described.

First, the CPU 34 operates the ejection blower 21 to eject air from the first nozzle 19 toward the leading end of the sheet bundle on the sheet stacking tray 1. Thereby, several sheets S are blown up and float.

Subsequently, the suction blower 12 is operated, and thereafter, the stepping motor 20 is driven to switch the suction valve 13 from the closed position shown in FIG. 2C to the fully opened position shown in FIG. 2B. As a result, the air under the conveyor belt 14 is sucked through the suction opening 6 and the air hole 14A, and the first (uppermost) sheet S1 as shown in FIG. And is brought into close contact with the conveyor belt 14.

Next, the conveyor belt 14 is driven by a driving means (not shown), whereby the sheet S1 is moved in the direction indicated by the arrow A in FIG.
Conveyed in the direction. In addition, even when the sheet S1 is double-fed by the air blown out from the second nozzle 20, the gap between the first sheet S1 and the second sheet S2 (FIG.
(See (a)), air is blown into the sheet S2, and the sheet S2 is reliably separated from the sheet S1. Thus, only the sheet S1 is transported downstream.

Next, when the leading edge of the sheet reaches the leading edge detecting sensor 17, a detection signal is input from the leading edge detecting sensor 17, and the stepping motor 20 is driven based on the detected signal, as shown in FIG. The opening angle of the suction valve 13 is reduced, and the suction pressure in the chamber 7 is reduced. Thus, the sheet S1 is, 10~15mmH ₂ O
Is conveyed by suction pressure.

On the other hand, after passing through the tip detection sensor 17,
The sheet S <b> 1 is passed to the conveying roller pair 23. Thereafter, when the sheet reaches the jam detection sensor 11 downstream of the conveyance roller 23, a detection signal is input from the jam detection sensor 11, and the sheet S1 is transferred from the conveyance belt 14 to the conveyance roller 23 based on the detection signal. When it is determined that the operation has been completed, the stepping motor 20 is driven to close the suction valve 13 (see FIG. 2C). This prevents the second sheet from being taken out together with the first sheet S1.

By the way, the sheet S1 is transferred to the conveying roller pair 23.
When the sheet S1 is passed to the transfer roller 23, the leading end of the sheet may be clogged without being transferred to the conveyance roller 23. In this case, the suction pressure in the chamber 7 is set to a pressure at which the sheet S1 slips with the conveyance belt 14. Therefore, the sheet S1 slips,
The sheet S1 does not become accordion-like.

As described above, the suction pressure in the chamber 7 is set to be lower than the static suction pressure at the start of sheet conveyance immediately before the sheet S1 is transferred to the conveyance roller 23 of the sheet suction conveyance section 3. Even if the sheet S1 is jammed and the conveyance is continued in this state, it is possible to prevent the sheet S1 from becoming accordion-shaped.

Next, a second embodiment of the present invention will be described.

FIG. 5 is a sectional view of the sheet suction portion of the sheet feeding device according to the present embodiment. 2, the same reference numerals as those in FIG. 2 indicate the same or corresponding parts.

In the figure, reference numeral 41 denotes a relief valve provided in the suction chamber 7 for stabilizing the pressure (static pressure) in the chamber after the sheet is adsorbed, and the relief valve 41 is provided on the upper surface of the suction chamber 7. Pressure adjustment opening 4
2 is swingably held so that it can be opened and closed.

When the sheet S is not attracted to the attraction belt 3, the relief valve 41 is provided with an urging means 4 such as a spring.
Although the sheet S is closed by the urging force, when the sheet S is attracted to the suction belt 14, the sheet S operates as a static pressure changing unit, and swings downward due to an increase in suction pressure in the chamber 7 due to sheet suction, and the pressure adjustment opening is opened. 42 is opened to change the suction pressure.

On the other hand, in the figure, reference numeral 44 denotes a stopper provided in the sheet suction / conveyance section 3 for regulating the opening angle of the suction relief valve 41. The stopper 44 is slidable. Note that the stopper 44 can adjust the slide amount by a stopper stepping motor 45, and by adjusting the slide amount in this manner, the opening angle of the suction relief valve 41 can be changed.
Thereby, the pressure in the chamber when the sheet S is sucked by the suction belt 14 can be adjusted. Reference numeral 46 denotes a home sensor for detecting the home position of the stopper 44.

Next, the operation of the sheet feeding apparatus having such a configuration will be described.

First, similarly to the above-described first embodiment, the CPU 34 operates the ejection blower 21 to eject air from the first nozzle 19 toward the leading end of the sheet bundle on the sheet stacking tray 1. This makes several sheets S
Is blown up and rises.

Subsequently, the suction blower 12 is operated, and thereafter, the suction valve 13 is driven by driving the stepping motor 20.
Is switched from the position shown in FIG. 5 (c) to the fully open position shown in FIG. 5 (b). Thereby, the suction opening 6 and the air hole 1
4A, the air under the conveyor belt 14 is sucked,
The second sheet (the uppermost sheet) S <b> 1 is sucked by the sheet suction unit 4 and closely adheres to the transport belt 14.

When the sheet S1 comes into close contact with the conveyor belt 14, the suction pressure in the suction chamber increases, and the relief valve 41 swings downward to open the pressure adjustment opening 42. Here, the opening amount of the relief valve 41 is controlled by the stopper 44, and the opening amount is set in advance so that the static pressure required at the start of sheet conveyance is 30 mmH ₂ O or more.

Next, the transport belt 14 is driven, thereby transporting the sheet S1. Then, after that, when the leading edge of the sheet reaches the leading edge detection sensor 17 and a detection signal is input from the leading edge detection sensor 17, the stopper stepping motor 45 is driven based on the detection signal, and FIG. The stopper 44 is moved in the direction of arrow E as shown in FIG. As a result, the release angle of the relief valve 41 increases, and the suction pressure in the chamber 7 decreases.
Note that the static pressure in the chamber at this time is the first pressure described above.
As with the embodiment, it is set in advance so as to 10~15mmH ₂ O.

On the other hand, after passing through the tip detection sensor 17,
The sheet S <b> 1 is passed to the conveying roller pair 23. When the sheet subsequently reaches the jam detection sensor 11, a detection signal is input from the jam detection sensor 11, and based on the detection signal, it is determined that the sheet S1 has been transferred from the conveyance belt 14 to the conveyance rollers 23, and the stepping motor is determined. 20 is driven to close the suction valve 13, and the stopper stepping motor 45 is driven to return the stopper 44 to the original home position as shown in FIG. 5C.

This prevents the second sheet from being taken out together with the first sheet S1. Note that the return of the stopper 44 to the original home position is determined by the home sensor 4.
When the detection is performed by the detection signal from 6, the driving of the stopper stepping motor 45 is stopped.

By the way, the sheet S1 is transported to the conveying roller pair 23.
When the sheet is clogged without being transferred to the conveyance roller 23 when the sheet is transferred to
Has a pressure that causes the sheet S1 to slip with the transport belt 14, so that the sheet S1 slips and the sheet S1 does not become accordion-shaped.

With this configuration,
The same effect as that of the first embodiment can be obtained. Further, since the static suction pressure is controlled by using the relief valve 41, the static suction pressure can be controlled more accurately and stably.

Next, a third embodiment of the present invention will be described.

FIG. 6 is a sectional view of the sheet suction portion of the sheet feeding device according to the present embodiment. In this figure, the same reference numerals as those in FIG. 5 indicate the same or corresponding parts.

In the figure, reference numeral 51 denotes a stopper for restricting the opening angle of the relief valve 41, and a rack 5 is provided at an end of the stopper 51 opposite to the end in contact with the relief valve 41.
3 are provided. Here, the rack 53 is engaged with the motor gear 52 of the stepping motor 20 that rotates the suction valve 13, and
Is driven in the counter-clockwise direction in the same figure, the stopper 51 moves in the arrow F direction (the direction regulating the opening / closing angle of the relief valve 41) in (c), and the suction valve 13 moves in the arrow G direction. Become like

Then, with this configuration,
At the time of sheet suction, FIG.
When bite 3 occurs, the state is as shown in FIG. 6A, and the same effect as in the second embodiment described above can be obtained. Also,
By configuring the driving means for moving the stopper 51 with the stepping motor 20 for rotating the suction valve 13, the simplification and miniaturization of the device can be realized.

In the above description, the case of the sheet feeding apparatus having the sheet suction and conveyance section 3 provided above the sheet stacking tray 1 has been described. However, the present invention is not limited to this. Needless to say, the same effect can be obtained even in a sheet feeding apparatus having a configuration in which the sheet suction conveyance section 3 is provided below the stacking tray 1.

FIG. 7 is a view showing an example of an image forming apparatus provided with the sheet feeding apparatus of the present invention. The image forming apparatus main body (hereinafter simply referred to as “apparatus main body”) 900 includes a document table. (Platen glass) 906, a light source 907, a lens system 908, a paper feeding unit 909, an image forming unit (image forming unit) 902, and the like. An automatic document feeder is provided on a document table (platen) 906.

A paper feeding unit 909 is provided with a cassette 91 in which recording sheets S are stored and which can be detachably attached to the apparatus main body 900.
0, 911 and a deck 913 arranged on the pedestal 912. Further, the above-described paper feeding device is employed as a feeding mechanism for feeding the sheets (sheets) S stored in the cassette 910 or the like.

The image forming section 902 includes a cylindrical photosensitive drum 914, a developing device 915, a transfer charger 916, a separation charger 917, a cleaner 918, a primary charger 919, and the like. Further, on the downstream side of the image forming unit 902, a transport device 920, a fixing device 904, a discharge roller pair 905, and the like are provided. The main controller 930 controls and controls the entire image forming apparatus.

The operation of the image forming apparatus will be described.

When an image formation start signal is output from main controller 930, the automatic document feeder conveys the document through a predetermined conveyance path, and sets the document table (platen glass) 90.
This is placed at a predetermined position on the device 6.

Thereafter, at a predetermined timing, the image forming unit 902 and the paper feeding unit 909 are driven. Paper feed unit 909
Feeds the sheet S from one of the cassettes 910 and 911 or the deck 913 to the image forming unit 902. The details of the feeding are as described above.
The skew of the sheet S fed from the sheet feeding unit 909 is corrected by the registration rollers 901, and the sheet S is sent to the image forming unit 902 at a timing appropriate for image formation described later.

On the other hand, the image forming section 902 irradiates the light emitted from the light source 907 to the original D placed on the original placing table (platen) 902 and irradiates the reflected light to the photosensitive drum 914 via the lens system 908. . Since the photosensitive drum 914 is charged in advance by the primary charger 919, an electrostatic latent image is formed on the surface of the photosensitive drum 914 when reflected light is incident thereon.
Next, the developing device 915 develops the electrostatic latent image,
Form a toner image.

The transfer charger 916 includes a photosensitive drum 914
The upper toner image is transferred to the fed sheet S.
The separation charger 917 charges the sheet S on which the toner image has been transferred to a polarity opposite to that of the transfer charger 916, thereby separating the sheet S from the photosensitive drum 914.

The conveying device 920 conveys the separated sheet S to the fixing device 904. The fixing device 904 permanently fixes the transferred image on the sheet S. Finally, the discharge roller pair 905 transfers the sheet S on which the image is fixed to
It is discharged from the apparatus main body 900. In the image forming apparatus described above, the speed of image formation can be increased without causing double feeding of sheets.

[0077]

As described above, according to the present invention, by making the static suction pressure immediately before being delivered to the conveying means lower than the static static pressure at the start of sheet conveyance,
Even if the sheet is jammed when it is delivered to the conveying means, the sheet can be slipped until the apparatus stops. This can prevent the document from becoming accordion-like, and can stop the apparatus without damaging the sheet.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a sheet feeding apparatus according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a sheet suction unit of the sheet feeding device.

FIG. 3 is a diagram illustrating a structure of a suction valve provided in the sheet suction unit.

FIG. 4 is a control block diagram of a CPU provided in the sheet feeding apparatus.

FIG. 5 is a cross-sectional view of a sheet suction unit of a sheet feeding device according to a second embodiment of the present invention.

FIG. 6 is a cross-sectional view of a sheet suction unit of a sheet feeding device according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating an overall configuration of an image forming apparatus including a sheet feeding device according to the invention.

FIG. 8 is a diagram showing an overall configuration of a conventional sheet feeding apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sheet loading tray 3 Sheet suction conveyance part 4 Sheet suction part 7 Chamber 11 Jam detection sensor 12 Suction blower 13 Suction valve 14 Conveyor belt 17 Tip detection sensor 20 Stepping motor 23 Conveyance roller 34 CPU 41 Relief valve 44, 51 Stopper 45 Stopper Stepping motor 900 main unit

Claims (8)

[Claims] 1. A sheet stacked on a sheet stacking unit is sucked by an endless conveying member provided in a sheet suction conveying unit, and then conveyed toward a conveying unit provided downstream of the sheet suction conveying unit. A static pressure generating means for generating a static pressure for suctioning the sheet, wherein the static pressure generating means communicates with the static pressure generating means, and is provided inside the endless conveying member; A duct unit for applying a static pressure to the conveying member, a static pressure changing unit that opens and closes the suction duct unit, and changes an opening amount of the suction duct unit to change a suction static pressure in the duct unit; The amount of opening of the suction duct portion is changed immediately before the sheet is delivered to the conveying means, and the static suction pressure immediately before being delivered to the transport means is lower than the static suction pressure at the start of sheet conveyance. As the static and static pressure control means for controlling the pressure change means, that the sheet feeding, characterized in that with a device. 2. The sheet feeding apparatus according to claim 1, wherein said static pressure changing means is a valve, and said static pressure control means performs static pressure control by switching an opening and closing angle of said valve. 3. The static pressure changing means is a relief valve,
2. The sheet feeding device according to claim 1, wherein the static pressure control unit performs static pressure control by switching an opening / closing angle of the relief valve. 4. The static pressure changing means is a valve and a relief valve, and the static pressure control means performs static pressure control by switching the opening and closing angles of the valve and the relief valve in conjunction with each other. Item 2. The sheet feeding device according to Item 1. 5. A method according to claim 1, wherein a sheet detecting means is provided between the sheet suction and conveying section and the conveying means, and the static pressure control means controls the static pressure changing means based on a detection signal from the sheet detecting means. The sheet feeding device according to claim 1, wherein 6. The sheet feeding device according to claim 1, wherein said static pressure changing means changes the opening amount of said suction duct portion in multiple stages by a stepping motor. Feeder. 7. The suction static pressure immediately before the sheet is delivered to the transporting unit is such a pressure that the sheet slips on the transporting member when the sheet is jammed without being delivered to the transporting unit. The sheet feeding device according to claim 1, wherein: 8. An image forming apparatus having a sheet feeding device and an image forming unit, wherein the sheet feeding device is the one according to any one of claims 1 to 7. .