JP2001206587A - Sheet feeder and image forming device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet feeder that can feed sheets without having adverse effects on transfer images and causing a jam and the like via a simple structure, and an image forming device having the sheet feeder. SOLUTION: A guide member 49 interposed between a first feeding means 19 and second feeding means 11, 12 guides a sheet S delivered from the first feeding means 19 to the second feeding means 11, 22, and a pressing means 43 presses the sheet S against the guide member 49, thus leading the sheet S to the second feeding means 11, 22. The pressing means 43 is pressed back from the position to press the sheet S against the guide member 49, by the sheet S flexing between the first and second feeding means 19 and 11, 22 due to the difference in feed speed therebetween after the leading edge reaches the second feeding means 11, 22, consequently the flexure of the sheet S caused by the feed speed difference is absorbed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying apparatus and an image forming apparatus having the same, and more particularly, to a sheet conveying apparatus for correcting skew of a sheet and conveying the sheet to an image forming section at a predetermined timing. The configuration of the pair of registration rollers.

[0002]

2. Description of the Related Art Conventionally, as a sheet conveying apparatus provided in an image forming apparatus such as a copying machine or a printer adopting an electrophotographic system, there is a sheet conveying apparatus in which a pair of registration rollers is arranged upstream of an image forming section. In the image forming apparatus having such a sheet conveying device, the leading end of the sheet is brought into contact with the nip of the stopped registration roller pair to correct the skew of the sheet, and to register the registration roller at a predetermined timing. In some cases, the sheet is conveyed to an image transfer unit by rotating a pair, and the toner image formed in the image forming unit is transferred to a predetermined position on the sheet.

FIG. 8 is a view showing a schematic structure of such a conventional image forming apparatus. In FIG. 8, reference numeral 101 denotes a feed roller, 102 denotes a pair of registration rollers, and 103 denotes an upstream side near the pair of registration rollers 102. And a registration sensor that detects the leading edge of the sheet S.

In the image forming apparatus having such a configuration, when the sheet feeding operation is started, first, the sheet S is fed from the cassette 100 by the feeding roller 101, and the leading end is detected by the registration sensor 103. Thereafter, the leading end abuts on the nip of the pair of registration rollers 102 stopped in advance by a clutch or the like. Thereafter, when the feeding roller 101 further rotates, the sheet S forms a loop, and the skew is corrected by the strength of the waist of the sheet itself.

Next, after a predetermined time period for forming a loop necessary for correcting the skew of the sheet S has elapsed since the registration sensor 103 detects the leading end of the sheet S, the registration roller pair 102 rotates. As a result, the sheet S is conveyed to the image transfer unit 106, where the toner image formed on the photosensitive drum 105 disposed in the process cartridge 104 is transferred to a predetermined position on the sheet S. You.

In such an image forming apparatus, for example, as shown in FIG. 9, a transfer between a registration roller pair 102 and an image transfer section (transfer roller) 106 is performed so that stable image transfer can be performed. The upper and lower conveyance guide plates 107 and 108 are provided in the path, and the leading end of the sheet can be stably entered at a predetermined position of the nip between the photosensitive drum 105 and the image transfer section (transfer roller) 106 at a predetermined entry angle. Like that.

[0007]

In such a conventional sheet conveying apparatus and an image forming apparatus provided with the same, the image transfer unit 106 conveys the sheet at a speed higher than that of the registration roller pair 102 (hereinafter, referred to as a conveying speed). When the leading edge of the sheet reaches the image transfer unit 106 in a case where the transfer speed is high, the sheet is in a tension state, which adversely affects the transferred image (color shift, banding, etc.). , Are set slightly faster than the image transfer unit 106.

However, the registration roller pair 10
2 is increased, the registration roller pair 102
(Loop) occurs due to a difference in conveyance speed between the image transfer unit 106 and the image transfer unit 106. Further, when the distance between the registration roller pair 102 and the image transfer unit 106 is narrow, a jam or breakage of the sheet occurs due to the warp. May be. If the distance between the registration roller pair 102 and the image transfer unit 106 is increased in order to prevent the occurrence of a jam due to such bending, the size of the apparatus is increased.

Further, conveyance guide plates 107 and 108 are provided on a conveyance path between the pair of registration rollers 102 and the image transfer section 106.
In addition to the complicated shape near the exit on the side of the image transfer unit as shown in FIG. 9, for example, as shown in FIG. In the case of pivoting around the opening 102a, the structure becomes complicated and the cost increases.

The present invention has been made in view of such circumstances, and can convey a sheet with a simple structure without adversely affecting a transferred image and without causing a jam or the like. It is an object of the present invention to provide a sheet conveying apparatus and an image forming apparatus including the same.

[0011]

SUMMARY OF THE INVENTION According to the present invention, there is provided a first conveying means for conveying a sheet, and a sheet disposed downstream of the first conveying means and conveying the sheet at a lower conveying speed than the first conveying means. A second transport unit, the first transport unit, and the second transport unit;
A guide member provided between the first conveying unit and the second conveying unit for guiding a sheet from the first conveying unit to the second conveying unit; and a pressing member for pressing a sheet from the first conveying unit to the second conveying unit against the guide member. Means, the pressing means, after the tip reaches the second transport means,
Due to a difference in the transport speed between the first transport unit and the second transport unit, the sheet is pressed by a sheet that is bent between the first transport unit and the second transport unit, and retreats from a pressing position for pressing the sheet against the guide member. It is characterized by having such a configuration.

Further, according to the present invention, the first transport means is located on a side close to the first transport member and the guide member, and
A second conveying member for nipping and conveying the sheet together with a conveying member, wherein the pressing means is movably held by the first conveying member from the pressing position to the retracted position. It is.

Further, in the present invention, after the pressing means contacts the sheet conveyed from the upstream side, the pressing means is pressed by the sheet toward the second conveying means and moves to the pressing position. It is characterized by the following.

Further, according to the present invention, there is provided an urging means for holding the pressing means at an initial position where the pressing means comes into contact with the sheet conveyed from the upstream side, and the urging force of the urging means is brought into contact with the pressing means. Then, when a predetermined reaction force of the bent sheet is applied to the pressing means, the pressing means is set to have such a size as to move toward the pressing position. .

Further, the present invention is characterized in that the initial position of the pressing means is on the upstream side in the transport direction from the first transport means.

Further, the present invention includes a leading edge detecting means for detecting the leading edge of the sheet, wherein the leading edge detecting means is configured to detect the leading edge of the sheet based on the movement of the pressing means to the pressing position. It is assumed that.

Further, according to the present invention, the first transport means and the second transport means
The transfer means is arranged in a substantially vertical direction.

According to the present invention, there is provided an image forming apparatus provided with an image forming section and a sheet conveying device, wherein the sheet conveying device is one of the above.

The present invention also relates to a second aspect of the present invention, wherein
The transporting means comprises an electrostatic transfer transporting belt and a suction means.

The present invention also relates to a second aspect of the sheet transporting apparatus.
The transporting means comprises an image bearing rotating body constituting the image forming section, and a transfer rotating body facing the image bearing rotating body.

Further, as in the present invention, the first transport means for transporting the sheet and the second transport means disposed downstream of the first transport means and transporting the sheet at a slower transport speed than the first transport means. The guide member provided therebetween guides the sheet from the first transport unit to the second transport unit,
By pressing the sheet from the first transporting means to the second transporting means against the guide member by the pressing means, the sheet is directed to the second transporting means in a stable state. Further, after the leading end reaches the second conveying means, the pressing means is formed by a sheet which is bent between the first conveying means and the second conveying means due to a difference in conveying speed between the first conveying means and the second conveying means. By pressing and retreating from the position where the sheet is pressed against the guide member, the bending of the sheet caused by the difference in transport speed is absorbed.

[0022]

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

FIG. 1 is a diagram showing a configuration of a full-color laser beam printer which is an example of an image forming apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 100 denotes a full-color laser beam printer (hereinafter, referred to as LBP). The LBP 100 includes an image forming unit 101 and a paper feeder for feeding a transfer material S as a sheet to the image forming unit 101. Part 17
And a fixing unit 20 for fixing the toner image formed on the sheet by the image forming unit 101 to the transfer material S.

Here, the image forming unit 101 is a photosensitive drum 1 which is four image-bearing rotating bodies arranged in a vertical direction.
(1a, 1b, 1c, 1d) and a charging device 2 (2a, 2) of a contact charging type for uniformly charging the surface of the photosensitive drum 1.
b, 2c, 2d), a scanner unit 3 (3a, 3b, 3c, 3d) for irradiating a laser beam based on image information and forming an electrostatic latent image on the photosensitive drum 1, and an electrostatic latent image Developing device 4 (4a, 4b, 4c, 4d) for forming a toner image by adhering toner to the toner, and electrostatic transfer constituting a transfer unit for transferring the toner image on the photosensitive drum 1 to the transfer material S The apparatus 5 includes a cleaning device 6 (6a, 6b, 6c, 6d) for removing transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer of the toner image.

In this embodiment, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6
Are integrated into a cartridge to form a process cartridge 7 (7a, 7b, 7c, 7d).

On the other hand, in the present embodiment, the photosensitive drum 1 (1a, 1b, 1c, 1d) has a diameter of, for example, 30 m.
m photoconductive layer (OPC)
(Photoconductor). The photosensitive drum 1 (1a, 1b, 1c, 1d) is rotatably supported at both ends by supporting members, and a driving force from a driving motor (not shown) is transmitted to one end. As a result, it is driven to rotate counterclockwise.

The charging device 2 (2a, 2b, 2c, 2
d) is a conductive roller 21 (21a, 2a) as a charging member.
1b, 21c, and 21d), the conductive roller 21 is brought into contact with the surface of the photosensitive drum 1, and a charging bias voltage is applied to the conductive roller 21 to clean the surface of the photosensitive drum 1. In the same way.

The scanner unit 3 includes a laser diode (not shown) and a polygon mirror 9 (9a, 9b, 9b, 9b, 9b, 9c, 9
d) and the imaging lens 10 (10a, 10b, 10c, 1)
0d).

The scanner unit 3 irradiates the image light corresponding to the image signal to the polygon mirror 9 rotating at high speed by a laser diode, reflects the image light by the polygon mirror 9, and further reflects the reflected light. By selectively exposing the charged photosensitive drum surface through the imaging lens 10, an electrostatic latent image is formed on the photosensitive drum surface.

The developing device 4 includes toner containers 41 (41a, 41b, 41c, 41d) containing toners of yellow, magenta, cyan, and black, respectively.
Developing rollers 42 (42a, 42b, 42c,
42d).

The electrostatic transfer device 5 includes an electrostatic transfer belt 11 circulating and moving so as to face and contact all the photosensitive drums 1 (1a, 1b, 1c, 1d).
And the electrostatic transfer belt 11
The transfer roller 12 (1), which is a transfer rotating body,
2a, 12b, 12c, 12d).

Here, the electrostatic transfer belt 11 is formed of a film-like member having a peripheral length of 700 mm and a thickness of 150 μm having a volume resistivity of, for example, 10 ¹¹ to 10 ¹⁴ Ω · cm. The electrostatic transfer belt 11 has four rollers arranged in the vertical direction, that is, the support driving roller 1.
3. The transfer member S is vertically wound around the first driven roller 14a, the second driven roller 14b, and the tension roller 15, and is rotated in the direction of the arrow while electrostatically adsorbing the transfer material S to the outer peripheral surface on the left side in the figure. It has become.

In FIG. 1, reference numeral 22 denotes an electrostatic attraction roller which is an attraction means for pressing against the outer periphery of the electrostatic transfer belt 11;
By applying a voltage between the electrostatic attraction roller 22 and the electrostatic transfer belt 11, the transfer material S, which is a dielectric material, and the electrostatic transfer belt 11
Is induced in the dielectric layer, and the transfer material S is electrostatically attracted to the outer periphery of the electrostatic transfer belt 11. By electrostatically attracting the transfer material S to the electrostatic transfer belt 11 in this manner, the transfer material S can be stably transported to the position of the most downstream photosensitive drum 1d.

On the other hand, the transfer roller 12 is
The negative charge toner image is transferred to the transfer material S being in contact with the photosensitive drum 1 by the electric field generated by the charge. It is supposed to be.

Then, the electrostatic transfer device 5 having such a configuration is used.
When the electrostatic transfer belt 11 circulates so as to electrostatically attract the transfer material S to the outer peripheral surface and bring the transfer material S into contact with the photosensitive drum 1, the transfer material S
1 transfers the toner image on the photosensitive drum 1 to the transfer position.

The paper feed unit 16 feeds the transfer material S to the image forming unit 101, and includes a paper feed cassette 17 for storing a plurality of transfer materials S, and a paper feed roller (half moon roller).
18, a registration roller pair 19, a transfer material leading edge detection sensor 40 as leading edge detecting means for detecting the leading edge of the transfer material S, and the like. Note that, in the present embodiment, the sheet transporting device uses the paper feed roller (half moon roller) 18.
A pair of registration rollers 19 serving as a first transport unit;
It is constituted by the electrostatic transfer belt 11 and the electrostatic attraction roller 22, which are conveying means, a registration shutter 43 described later, an electrostatic transfer belt entrance guide 49, and the like.

During image formation, the transfer material S in the paper feed cassette 17 is separated and fed one by one by a paper feed roller 18 driven and rotated in accordance with the image forming operation. After being separated and fed by the feed roller 18 in this way, the transfer material S abuts against the pair of registration rollers 19, and temporarily stops to form a loop, thereby performing skew correction. The sheet is fed to the electrostatic transfer belt 11 by a pair of registration rollers 19 whose rotation starts at the timing.

Before the transfer material S is fed to the electrostatic transfer belt 11 as described later, the transfer material S is detected by a transfer material front end detection sensor 40 provided downstream of the registration roller pair 19. It has become. Further, when the transfer material leading edge detection sensor 40 detects the transfer material S, it outputs a detection signal to a control device (not shown), and the control device transmits the detection signal and the four photosensitive drums 1a, 1b, 1
After the latent images are formed on the photosensitive drums 1a, 1b, 1c, 1d in synchronization with the image writing positions on c, 1d, a toner image is formed by the developing device 4.
Thus, when the toner image is conveyed by the electrostatic transfer belt 11, the toner images are sequentially transferred to the transfer material S.

The fixing section 20 fixes a plurality of color toner images transferred onto the transfer material S, and applies heat and pressure to the transfer material S by pressing against a rotating heating roller 21a. A fixing roller pair 21 including a pressure roller 21b is provided. When the transfer material S onto which the toner image has been transferred passes through the fixing unit 20, the transfer material S is conveyed by the fixing roller pair 21 and is given heat and pressure, so that a plurality of color toner images are formed on the surface of the transfer material S. It has become established.

Next, the LBP 100 configured as described above will be described.
Will be described.

In the image forming operation, first, the four process cartridges 7 (7a, 7b, 7c, 7d) are sequentially driven in accordance with the print timing, and the photosensitive drum 1 rotates counterclockwise in accordance with the drive. When driven, the charging roller 2 applies a uniform charge to the peripheral surface of the photosensitive drum 1. Further, the scanner units 3 corresponding to the respective process cartridges 7 are sequentially driven, and an electrostatic latent image corresponding to the image signal is formed on the peripheral surface of the photosensitive drum 1 by the scanner unit 3.

Next, the developing roller 42 in the developing device 4 transfers the toner to the low potential portion of the electrostatic latent image, and
A toner image is formed (developed) on the peripheral surface.

On the other hand, after the transfer material S is fed by the paper feed roller 18, skew correction is performed by the registration roller pair 19, and thereafter, the rotation is started by the registration roller pair 19, which starts rotating at a predetermined timing. The paper is fed to the electrotransfer belt 11.

When the transfer material leading edge detection sensor 40 detects the transfer material S before the sheet is fed to the electrostatic transfer belt 11 as described above, the control device operates based on the detection signal from the transfer material leading edge detection sensor 40. When the leading edge of the toner image on the peripheral surface of the most upstream photosensitive drum 1a is rotated and conveyed to a point facing the electrostatic transfer belt 11, the printing start position of the transfer material S coincides with the point. In this way, the detection signal of the transfer material S is synchronized with the start of image writing on the four photosensitive drums 1a, 1b, 1c, 1d.

Thereafter, the transfer material S fed to the electrostatic transfer belt 11 is transferred to the electrostatic attraction roller 22 and the electrostatic transfer belt 1.
1 and the electrostatic transfer belt 11
Is electrostatically attracted to the outer periphery of the electrostatic transfer belt 11 by the voltage applied between the electrostatic transfer roller 11 and the electrostatic attraction roller 22, and is conveyed to the position of the most downstream photosensitive drum 1 d with the rotation of the electrostatic transfer belt 11. You. Then, while being conveyed in this manner, the toner image on each photoconductor drum 1 is sequentially transferred onto the transfer material S by an electric field formed between each photoconductor drum 1 and the transfer roller 12.

Next, the transfer material S onto which the four color toner images have been transferred in this manner is separated from the electrostatic transfer belt 11 by the curvature of the belt drive roller 13, and the fixing unit 20.
It is carried in. Thereafter, the transfer material S is transferred to the fixing unit 20.
After the toner image is heat-fixed, the sheet is ejected from the main body by the sheet ejection roller pair 23 from the sheet ejection section 24 with the image side down.

FIG. 2 is a perspective view of a portion of the pair of registration rollers 19 viewed from the upstream side in the transfer material transport direction.
A registration roller as a second conveying member and a first conveying member.
This is a resist roller as a transport member.

The registration roller 19A has a metal shaft 191 having both ends supported by a fixed bearing (not shown), and a plurality of rubber rollers 192 fixed to the metal shaft 191.
, And is rotated by a rotational driving force transmitted from a driving unit (not shown) to the metal shaft 191.

The resist roller 19B has a metal shaft 1 slidably supported at both ends by a slide bearing (not shown).
93 and a plurality of rollers 194 rotatably provided on the metal shaft 193. The rollers 194 are pressed by a pressing spring (not shown) with a predetermined pressing force.
To form a nip. The rubber roller 192 and the roller 194 are provided symmetrically in a direction orthogonal to the transfer material transport direction.

On the other hand, in FIG.
8 is a registration shutter that causes the transfer material S to form a loop by abutting against the transfer material S before entering the nip of the registration roller pair 19. A plurality of rotation support portions 45 (45a, 45b, 45c, 45) having abutment surfaces 44 (44a, 44b, 44c, 44d) abutting on the tips of
It is rotatably attached to the metal shaft 193 of the resist roller 19B via d). Reference numeral 47 denotes a pre-registration conveyance guide plate provided on the upstream side of the registration shutter 43.

The metal shaft 1 of the resist roller 19B
As shown in FIG. 4, a torsion coil spring 48 as an urging means is provided at one end of 93. The torsion coil spring 48 causes the abutting portion 44 to abut against a stopper (not shown) provided on the pre-registration conveyance guide plate 47 when the registration shutter 43 is in the non-sheet passing state, and as shown in FIG. Are held at an initial position where they abut against the abutting portion 44 at right angles.

In this embodiment, the transfer material S
As shown in the drawing, the abutting surface 44 of the registration shutter 43 is located δ upstream of the nip of the registration roller pair 19 in the transfer material transport direction so that a loop can be formed more reliably.

The urging force of the torsion coil spring 48 is
After coming into contact with the registration shutter 43, the reaction force of the transfer material S on which the loop is formed due to the transfer material conveying force of the paper feed roller 18 and the stiffness of the bending (loop) of the transfer material S is reduced by the registration shutter 4.
3, the register shutter 43 is set to have a size such that the register shutter 43 can be rotated by being pressed by the sheet S, and in this embodiment, a (moment) force of about 200 g · cm. . In the present embodiment, the biasing force of the torsion coil spring 48 is set slightly higher because of the vertical path of the transport system, but about 10 in the horizontal transport system.
It can be set to 0 g · cm.

With this configuration, when the paper is fed, the transfer material S fed by the paper feed roller 18 first enters the nip of the registration roller pair 19 as shown in FIG. The transfer material S abuts against the abutting surface 44 of the registration shutter 43, whereby the transfer material S forms a loop.

After that, when the transfer material S forms a predetermined nip, the registration shutter 43 is pushed by the reaction force of the transfer material S and rotates around the metal shaft 193 of the resist roller 19B as shown in FIG. While moving, the leading end of the transfer material S enters the nip of the registration roller pair 19 in the stopped state.

When the registration roller pair 19 rotates after entering the nip of the registration roller pair 19, the transfer material S is transferred to the electrostatic transfer belt 11 and the electrostatic attraction roller 22 as shown in FIG. At this time, the registration shutter 43 which is a pressing means at this time,
The tip portion of the transfer material S is moved to a position where the tip portion of the transfer material S is pressed against an electrostatic transfer belt entrance guide to be described later while resisting the urging force of the torsion coil spring 48.

On the other hand, in FIG. 3, reference numeral 41 denotes a photo interrupter, and 46 denotes a sensor flag constituting the transfer material leading edge detection sensor 40 together with the photo interrupter 41. The sensor flag 46 is provided integrally with the registration shutter 43. ing.

As described above, the registration shutter 4 is moved by the reaction force of the transfer material S fed by the paper feed roller 18.
When the sensor flag 46 rotates, and the sensor flag 46 rotates accordingly, the photo interrupter 41 is shielded from light by the sensor flag 46, so that the transfer material leading end detection sensor 40 (photo interrupter 41) detects by the control device. It is designed to output a signal.

Reference numeral 49 denotes a roller provided between the registration roller pair 19 and the electrostatic attraction roller 22,
An electrostatic transfer belt entrance guide, which is a guide member for guiding the transfer material S from 9 to the nip between the electrostatic attraction roller 22 and the electrostatic attraction belt 11. In this embodiment, the electrostatic transfer belt entrance guide 49 is provided on the side near the registration roller 19A.

In the present embodiment, the transport speed of the registration roller pair 19 is set slightly higher than the transport speed of the electrostatic transfer belt 11 in order to prevent adverse effects (color shift, banding, etc.) on the transferred image. Is set to

Here, the registration roller pair 19
When the transfer speed is increased, as shown in FIG. 7 described later, the transfer material S bends due to the transfer speed difference between the registration roller pair 19 and the nip between the electrostatic transfer belt 11 and the electrostatic attraction roller 22. (Loop) occurs. When the transfer material S is bent (looped) as described above, the transfer material S is at a position where the transfer material S is pressed against the electrostatic transfer belt entrance guide 49 by a reaction force due to the stiffness of the loop of the transfer material S. The registration shutter 43 is pushed to rotate and retreat.

Next, the sheet conveying operation of the sheet conveying apparatus provided with the registration shutter 43 configured as described above will be described.

The transfer material S fed by the paper feed roller 18
First, as shown in FIG. 3, the abutting portion 44 of the registration shutter 43 abuts on the abutting portion 44, and thereafter, as shown in FIG. Line correction), a loop is formed within the width of the transport path from the state shown by the two-dot chain line to the state shown by the solid line.

Next, when the loop becomes a predetermined size, the leading end of the transfer material S presses the abutting portion 44 due to the reaction force due to the stiffness of the loop and the conveying force of the paper feed roller 18, and the registration shutter By rotating 43, the nip of the pair of registration rollers 19 is held.

At this time, as shown in the figure, the sensor flag 46 of the registration shutter 43 also rotates to shield the photo interrupter 41 from light, whereby the photo interrupter 41 outputs a detection signal to the control device. The control device is
Based on this detection signal, a latent image is drawn on the photosensitive drums 1a, 1b, 1c, 1d in synchronization with the leading end position of the transfer material S.

In this embodiment, the relationship between the transfer material leading edge detection sensor 40 and the first transfer position (nip between the photosensitive drum 1a and the transfer roller 12a) is determined by the relationship between the transfer material leading edge detection sensor 40 and the first transfer position. The distance from the toner image on the photosensitive drum 1a to the transfer roller 12 is L1.
Assuming that the distance to a is L2, L1 ≧ L2, so that the toner image can be reliably transferred to the transfer material S.

Next, when the transfer material S is further conveyed from the state shown in FIG. 5 by the registration roller pair 19, the registration shutter 43 further rotates, and the end of the abutting portion 44 of the registration shutter 43 is drawn. As shown in FIG. 6, the leading end of the transfer material S is pressed, and the transfer material S is pressed against the entrance guide of the electrostatic transfer belt. As a result, the transfer material S is conveyed along the electrostatic transfer belt entrance guide 49, and enters the nip between the electrostatic transfer belt 11 and the electrostatic attraction roller 22 in a stable state.

The transfer material S is pressed against the electrostatic transfer belt entrance guide 49 by the registration shutter 43 in this manner, so that the transfer material S is transferred to the electrostatic transfer belt 1.
1 and the nip between the electrostatic attraction roller 22 and the nip. Further, with this configuration, only one guide for guiding the transfer material S to the nip between the electrostatic transfer belt 11 and the electrostatic attraction roller 22 is required, and the structure on the downstream side of the registration roller pair 19 is required. Becomes easier. Also,
Even if a jam occurs, the processing is simplified.

Next, when the transfer material S is further transported, the transfer material S loops due to a difference in transport speed between the registration roller pair 19 and the electrostatic attraction belt 11, and the rigidity of the loop of the transfer material S is increased. As a result, the registration shutter 43 is pressed by the reaction force, and as shown in FIG.
Rotates from the pressing position where the transfer material S is pressed against the electrostatic transfer belt entrance guide 49 and retreats.

By retracting the registration shutter 43 in this manner, it is possible to absorb a loop generated due to a difference in conveyance speed between the registration roller pair 19 and the electrostatic attraction belt 11. As a result, even when a conveyance speed difference is provided between the registration roller pair 19 and the electrostatic attraction belt 11 so that the transfer image is not adversely affected, occurrence of a jam or the like can be prevented, and the transfer material S can be stably maintained. Can be transported.

Further, with this configuration, the transport distance between the registration roller pair 19 and the nip between the electrostatic attraction belt 11 and the electrostatic attraction roller 22 can be shortened. The size can be reduced and the cost can be reduced. This is
Particularly in an apparatus in which the transport system is long, such as a tandem-type multicolor image forming apparatus in which the registration roller pair 19 and the electrostatic attraction belt 11 are arranged in a substantially vertical direction as shown in the present embodiment, the present invention is particularly effective. is there.

In the above description, an image forming apparatus provided with a vertical path transport system has been described.
The present invention is not limited to this, and it is natural that the second conveying means can be applied to an image forming apparatus of a horizontal conveying system composed of an image-bearing rotating body and a transfer rotating body facing the image-bearing rotating body. .

[0074]

As described above, according to the present invention, the structure is simplified by pressing the sheet against the guide member by the pressing means so that the sheet is directed toward the second conveying means in a stable state. be able to. Further, the pressing means is pressed by a sheet that is bent between the first conveying means and the second conveying means, and the sheet is retracted from a position where the sheet is pressed against the guide member. The sheet can be conveyed without adversely affecting the transferred image and without causing a jam or the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a full-color laser beam printer as an example of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view of a pair of registration rollers of a sheet conveying device provided in the full-color laser beam printer as viewed from an upstream side in a transfer material conveying direction.

FIG. 3 is a diagram illustrating a state in which a transfer material abuts on a registration shutter of the sheet conveying device at a right angle.

FIG. 4 is a perspective view illustrating a biasing unit of the registration shutter.

FIG. 5 is a diagram showing a state in which the registration shutter has begun to be pressed by a transfer material.

FIG. 6 is a diagram illustrating a state in which the registration shutter presses a transfer material against an electrostatic transfer belt entrance guide.

FIG. 7 is a diagram illustrating a state in which the registration shutter is retracted from a pressing position by a transfer material.

FIG. 8 is a diagram illustrating a schematic configuration of a conventional image forming apparatus.

FIG. 9 is a diagram illustrating a configuration of a sheet conveying device of another conventional image forming apparatus.

[Explanation of symbols]

 1 (1a, 1b, 1c, 1d) photoreceptor drum 5 electrostatic transfer device 11 electrostatic transfer belt 12 (12a, 12b, 12c, 12d) transfer roller 19 registration roller pair 19A registration roller 19B registration roller 22 electrostatic suction roller Reference Signs List 40 Transfer material leading edge detection sensor 41 Photo interrupter 43 Registration shutter 46 Sensor flag 48 Torsion coil spring 49 Electrostatic transfer belt front entrance guide 100 LBP 101 Image forming unit S Transfer paper

Claims (10)

[Claims] A first conveying unit that conveys the sheet; a second conveying unit that is arranged downstream of the first conveying unit and conveys the sheet at a lower conveying speed than the first conveying unit; A guide member provided between the first transport unit and the second transport unit to guide a sheet traveling from the first transport unit to the second transport unit; and a sheet traveling from the first transport unit to the second transport unit. And pressing means for pressing the guide member against the guide member. After the leading end reaches the second conveying means, the pressing means determines the first position by a difference in conveying speed between the first conveying means and the second conveying means. A sheet conveying device configured to be pressed by a sheet that is bent between a conveying unit and a second conveying unit to retreat from a pressing position where the sheet is pressed against a guide member. 2. The apparatus according to claim 1, wherein the first transporting unit includes a first transporting member, and a second transporting member located on a side closer to the guide member and sandwiching and transporting the sheet together with the first transporting member. 2. The sheet conveying apparatus according to claim 1, wherein the pressing unit is movably held by the first conveying member from the pressing position to the retracted position. 3. The pressing means is configured to come into contact with a sheet conveyed from an upstream side, and then be pressed by a sheet toward the second conveying means to move to the pressing position. The sheet conveying device according to claim 1, wherein: 4. An urging means for holding the pressing means at an initial position in contact with the sheet conveyed from the upstream side, and after contacting the urging force of the urging means with the pressing means, 4. The sheet according to claim 3, wherein the pressing means moves toward the pressing position when a predetermined reaction force of the bent sheet is applied to the pressing means. Transport device. 5. The sheet conveying apparatus according to claim 4, wherein an initial position of the pressing unit is located upstream of the first conveying unit in a conveying direction. 6. A front end detecting means for detecting a front end of the sheet, wherein the front end detecting means is configured to detect the front end of the sheet based on a movement of the pressing means to a pressing position. Item 2. The sheet conveying device according to Item 1. 7. The sheet conveying apparatus according to claim 1, wherein said first conveying means and said second conveying means are arranged substantially vertically. 8. An image forming apparatus comprising an image forming unit and a sheet conveying device, wherein the sheet conveying device is the one according to any one of claims 1 to 7. . 9. The sheet conveying device according to claim 9, wherein:
9. The image forming apparatus according to claim 8, comprising an electrostatic transfer conveyance belt and a suction unit. 10. The sheet conveying device according to claim 8, wherein said second conveying means comprises an image bearing rotary member constituting an image forming portion and a transfer rotating member facing said image bearing rotary member. Image forming apparatus.