JPH11255366A - Sheet conveyance device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly convey sheets of plural kinds of sizes by moving a structural member so that after the trailing end of a sheet passes through a conveyance part by a first conveyance means, conveys by a second transport means is enabled. SOLUTION: A guide of a conveyance belt table unit 12 is set to be lowered to a designated position, and then a transfer material is guided upward toward a nip part 8d, the sectional form thereof is a V-shape with a wide angle, a driving shaft 40 for a conveyance belt is provided in the valley part of the conveyance path, a first driven shaft 49 is provided on the secondary transfer roller 11 side, and a second driven shaft 42 is provided on a fixing device side. A distance L1 from the driving shaft 40 to the nip part 8d is set to be shorter than the spec. paper which can be conveyed by several tens mm, and the trailing end of the minimum paper sheet is pressed by the first conveyance belt to be surely pushed into a nip part of the fixing rollers. The width of two second conveyance belts is smaller than the width of the minimum spec. paper sheet, and the first conveyance belt is provided with a projecting part 12d in which the trailing end of the transfer material is caught, so that the sheet can be properly conveyed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying device for conveying a sheet, for example, from a transfer unit to a fixing unit provided in an image forming apparatus such as a copying machine, a printer, a facsimile, etc. using an electrophotographic system. It is applied as a sheet conveying device for conveying a sheet up to.

[0002]

2. Description of the Related Art Conventionally, as this type of electrophotographic image forming apparatus, there are, for example, a copying machine, a printer, and a facsimile.

A copying machine generally has a function of reading an image of an original or the like and forms an image on a sheet based on the read image information. Some copiers have a function of inputting image information to be sent.

[0004] A printer is generally an external device,
For example, it is to form an image on a sheet based on image information sent from a device such as a computer, fax is generally a function of reading an image such as a document, and,
It has a communication function, sends read image information to the outside, and forms an image on a sheet based on information sent from the outside.

[0005] In these image forming apparatuses, unfixed images (toner images) are converted into various sizes (plain paper, envelopes, postcards).
Transfer means for transferring an unfixed image formed on the sheet, a fixing means for fixing an unfixed image formed on the sheet, and a sheet conveyance for conveying the sheet from a transfer part by the transfer means to a fixing part by the fixing means A device is provided.

Hereinafter, a conventional sheet conveying apparatus will be described with reference to FIGS. FIG. 11 and FIG. 12 are schematic configuration diagrams of a sheet conveying apparatus and an image forming apparatus according to the related art, in which a sheet conveyed from a nip of a transfer unit reaches a nip of a fixing unit. Is shown.

FIG. 11 is a main sectional view of a black-and-white laser printer (LBP), and FIG. 12 is a main sectional view of a black-and-white copying machine.

In FIG. 11, a transfer material (cut paper or the like) S as a sheet sent from a cassette tray 7a by a half-moon-shaped pickup roller 7e is separated into one sheet by a roller pair of a feed roller 7f and a retard roller 7g. Is transported by the transport roller pair 7b to reach the registration roller pair 7d.

Thereafter, the transfer material S is conveyed by a pair of registration rollers 7d in accordance with the rotation of a photosensitive drum 1 as an electrophotographic photosensitive member disposed in a process cartridge B serving as a recording means, and is transferred by a transfer roller 5. The toner image on the photosensitive drum 1 is transferred onto the material S.

The transfer material S transported by the nip between the photosensitive drum 1 and the transfer roller 5 is transported by a transport guide unit 12.
Are conveyed along the downwardly moving conveyor belt 12a, the flat conveyance guide ribs 12b, and the fixing entrance guide 8c.

Thereafter, the transfer material S is heated and pressed by the nip portion of the heating roller 8b and the pressure roller 8a, and the toner image on the transfer material S is fixed as a permanent image. The sheet is then conveyed along the conveyance guide ribs 15 and is discharged and stacked on a face-down tray 10 in the upper part of the apparatus main body by the discharge roller pair 9.

In the black-and-white copying machine shown in FIG. 12, the transfer material S sent out from the cassette tray 7a by the pickup roller 7e is transferred by a roller pair of a feed roller 7f and a retard roller 7g in the same manner as the LBP described above. The sheet is separated, transported to the transport roller pair 7b, and reaches the registration roller pair 7d.

Thereafter, the transfer material S is conveyed from a pair of registration rollers 7d in accordance with the rotation of the photosensitive drum 1 as an electrophotographic photosensitive member disposed in a process cartridge B serving as a recording means. S, the toner image on the photosensitive drum 1 is transferred onto the
The sheet is conveyed by 2a, is sandwiched between the nip portions of the fixing roller pair, and is discharged and stacked on the face-up tray 17.

[0014]

However, in the case of the above-described prior art, the following problems have occurred.

In the transfer unit 12 provided in the conventional LBP shown in FIG. 11, after the nip portion between the photosensitive drum 1 and the transfer roller 5 is discharged, the transfer roller 12 having the length L1 or less is heated by the heating roller 8b and Since the belt does not reach the nip of the pressure roller 8a, the transport belt 12 is provided at an angle.
a cannot push the rear end portion to apply a conveying force to the transfer material S, and the transfer material S stays on the transfer unit 12 to cause a jam.

Alternatively, a cardboard having a length of about L6 (a medium which is stiff and not conveyed along the conveyance path, such as an envelope, a postcard, a card, etc.) is provided immediately after the transfer roller 5 as shown in FIG. Static eliminator and fixing entrance guide 8
c, the transfer material stretches during the transfer belt 12a.
In some cases, a gap is formed in the transfer material and the conveying force is not transmitted, resulting in a stagnant jam.

Therefore, the type and size of the transfer material that can be conveyed are limited, or in order to cope with this, the apparatus must be increased in size.

In the black-and-white copying machine shown in FIG. 12, the transfer material S on which the toner image has been transferred by the photosensitive drum 1 and the transfer device 5 is transferred by a flat transport belt 12a extending from the rear of the transfer section to the fixing entrance guide. The sheet is conveyed to the fixing roller nip portion, and the distance L2 from the rear end of the conveying belt to the fixing roller nip portion is sufficiently short so that the transfer material of almost any size can be conveyed.

However, in order to surely convey the transfer material shorter than the nip portion of the fixing roller from the registration roller pair 7d, a large number of holes are provided on the surface of the conveyance belt 12a. It is necessary to take measures such as attracting the paper to the conveyor belt, and there is a problem that the structure becomes complicated.

In addition, there is a problem that the above-described suction structure must be used, and that the entire apparatus becomes large due to the configuration of the transport belt that extends flat.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a sheet capable of properly conveying sheets of a plurality of sizes without increasing the size of the apparatus. An object of the present invention is to provide a transport device and an image forming apparatus.

[0022]

In order to achieve the above object, according to the present invention, a first conveying means for conveying a sheet and a position lower than a conveying position by the first conveying means are provided. A second conveying means for conveying the sheet conveyed by the first conveying means further downstream while placing the sheet thereon. A moving means for moving at least one of the constituent members of the conveying means is provided, and after the rear end of the conveyed sheet passes through the conveying section by the first conveying means, the conveyed sheet is The component is moved by the moving means so as to be able to be conveyed by the second conveying means.

Therefore, even when the rear end of the conveyed sheet is caught by the component on the first transporting means side and is not subjected to the transporting force by the second transporting means, the component is moved by the moving means. (Only the components on the first transporting means side are moved downward, only the components on the second transporting means side are moved upward, or any of them is moved). The moved sheet moves to a position where it can be conveyed by the second conveying means, and the sheet receives the conveying force of the second conveying means.

A first conveying means for conveying the sheet, a second conveying means for conveying the sheet conveyed by the first conveying means, and further conveying the sheet further downstream; And a guide member for guiding the sheet conveyed by the conveying unit upward. In the sheet conveying device, a moving unit for moving at least one of the constituent member and the guide member on the second conveying unit side is provided. After the leading edge of the conveyed sheet reaches the guide member, the member can be moved by the moving means so that the conveyed sheet can be conveyed by the second conveying means.

Therefore, even if the leading end of the sheet is caught by the guide member and is not subjected to the conveying force by the second conveying means, the sheet conveyed by the moving means can be conveyed by the second conveying means. After moving to a certain position, the sheet receives the conveying force of the second conveying unit.

The second transport means includes a first transport belt that guides the sheet gradually downward, and a second transport belt that gradually guides the sheet guided by the first transport belt upward. It is preferable to form a V-shaped conveyance path, and drive the first conveyance belt and the second conveyance belt by a drive shaft provided at the intersection of the V-shape.

It is preferable to provide an identification means for identifying the size of the sheet to be conveyed, and to judge whether or not to move the constituent members by the movement means based on the identification result of the identification means.

The identification means is provided upstream of the first conveying means, and the passage timing of the rear end of the sheet in the conveying section by the first conveying means is recognized based on the detection of the passage of the rear end of the sheet by the identification means. It is good to let.

The type of the transport sheet can be identified by the identification means.

The identification means may identify whether or not the sheet transmits light.

It is also possible to provide a setting means for setting the type of sheet to be conveyed, and to judge whether or not to move the discharging means by the moving means based on the setting result of the setting means.

According to another aspect of the present invention, there is provided an image forming apparatus including the above-described sheet conveying device, wherein the first fixing means provided on the sheet conveying device is used to fix unfixed sheets on the sheet. An image is formed, and the sheet on which the unfixed image is formed is conveyed to the fixing unit for fixing the unfixed image by the second conveying unit.

The first transporting means has a carrying means for carrying the unfixed image and a transferring means for transferring the unfixed image carried by the carrying means onto a sheet. During the operation of carrying the attached image, the carrying means and the transfer means are located apart from each other, and after the carrying operation is completed, the unfixed image is transferred onto the sheet while holding and transporting the sheet by the carrying means and the transfer means. Good.

The fixing means has a pair of rotating members,
The unfixed image may be fixed by nipping the sheet by the rotating member and transporting the sheet while applying heat and pressure.

The component moved by the moving means is preferably the transfer means.

The transfer means may be provided with a charge removing means for removing charge on the sheet, and the charge removing means may move together with the transfer means.

The discriminating means may also have a function of a sensor for determining a timing for forming an unfixed image on the sheet by the first conveying means.

[0038]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The material, shape, relative arrangement, and the like are not intended to limit the scope of the present invention only to them unless otherwise specified.

With reference to FIGS. 1 to 10, a sheet conveying apparatus and an image forming apparatus according to an embodiment of the present invention will be described.

{Outline of Image Forming Operation of Color Image Forming Apparatus} First, an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention, and is a longitudinal sectional view illustrating a schematic configuration of an electrophotographic four-color full-color laser beam printer.

First, the photosensitive drum 1 is rotated in the direction of the arrow (counterclockwise) in the figure in synchronization with the rotation of the intermediate transfer belt 5a, and the surface of the photosensitive drum 1 is uniformly charged by the charging device 2; The exposure unit 3 irradiates light of a yellow image to form a yellow electrostatic latent image on the photosensitive drum 1.

Simultaneously with the formation of the electrostatic latent image, the developing device 4 is driven to dispose the yellow developing unit 4Y at the developing position, and the photosensitive member is set so that the yellow toner adheres to the electrostatic latent image on the photosensitive drum 1. A voltage having the same polarity as the charging polarity of the drum 1 and substantially the same potential is applied to cause the yellow toner to adhere to the electrostatic latent image for development.

Thereafter, a voltage having a polarity opposite to that of the toner is applied to the pressing roller (primary transfer roller) 5j of the intermediate transfer member 5 to transfer the yellow toner image on the photosensitive drum 1 to the intermediate transfer belt 5a. I do.

When the primary transfer of the yellow toner image is completed as described above, the next developing unit rotates and moves to the developing position facing the photosensitive drum 1, and the magenta image is formed in the same manner as in the case of yellow. , Cyan, and black, an electrostatic latent image is formed, developed, and primary transferred sequentially, and four color toner images are superimposed on the intermediate transfer belt 5a.

During this time, as shown in FIG. 5, the secondary transfer roller 11 is not in contact with the intermediate transfer belt 5a.

At this time, the charging roller 5f of the cleaning unit 5e is also in a non-contact state with the intermediate transfer belt 5a.

After the formation of the four color toner images on the intermediate transfer belt 5a, the secondary transfer roller 11 is pressed against the intermediate transfer belt 5a (the state shown in FIGS. 1 and 6), and the rotation of the intermediate transfer belt 5a is further increased. Synchronously with this, the transfer material S waiting at a predetermined position near the registration roller pair 7d, which is a feeding means, is sent out to the nip portion between the intermediate transfer belt 5a and the secondary transfer roller 11.

The first transfer means is constituted by the intermediate transfer belt (support means) 5a and the secondary transfer roller 11 (transfer means).

Immediately before the registration roller pair 7d, a pre-registration sensor 39 which detects the leading end of the transfer material S, shuts off the rotational driving force of the registration roller pair 7d, and waits the transfer material S at a predetermined position. Is provided.

Further, a voltage having a polarity opposite to that of the toner is applied to the secondary transfer roller 11, and the toner image on the intermediate transfer belt 5a is secondarily transferred onto the surface of the transfer material S which has been conveyed at once. I will do it.

The transfer material S subjected to the secondary transfer in this manner is
Reaches a nip portion between a heating roller 8b and a pressure roller 8a which are a pair of rotating members constituting the fixing device 8 via a conveyance belt base unit 12 as a second conveyance means, where a toner image of a plurality of colors is formed. After fixing the paper, the discharge roller pair 1
The paper is conveyed along the paper discharge guide 15 by the rollers 3 and 16 and discharged to the paper discharge tray 10 above the image forming apparatus 14 by the discharge roller pair 9 to complete the image formation.

{Structure of Secondary Transfer Roller Unit}
In particular, the configuration of the secondary transfer roller unit will be described with reference to FIGS.

FIGS. 5 and 6 are enlarged longitudinal sectional views of a secondary transfer roller unit constituting a sheet conveying device provided in the image forming apparatus according to the embodiment of the present invention, and FIG. 6 shows a state in which the toner image is retracted from the intermediate transfer body unit 5 and a toner image is formed on the intermediate transfer body belt 5a. FIG. 6 shows that the secondary transfer roller 11 is pressed by the intermediate transfer body unit 5, This shows a state when the secondary transfer is performed on the transfer material S.

In FIG. 5, the secondary transfer frame 21 is made of a mold and is fixed to a secondary transfer substrate 24 made of sheet metal.

At both ends of the secondary transfer frame 21, a cylindrical positioning abutting portion 21f is provided coaxially, and a bearing 20 for receiving the metal shaft center 11a of the sponge portion of the secondary transfer roller 11 at both ends is substantially provided. A guide portion 21b that slides in the vertical direction, a retaining portion 21c for the bearing 20, a static elimination needle 43
Is provided, and the static elimination needle 43 falls to the ground via the secondary transfer substrate 24. (The static elimination needle 43 and the static elimination needle guide 21a constitute a static elimination means.) There).

Between the boss 20a of the bearing 20 and the boss 21d of the secondary transfer frame 21, secondary transfer roller pressing springs 19 are provided at both ends.

As a result, the secondary transfer roller 11 is in the state of being lifted to the position shown in FIG. 5, but the tip portion δ2 of the retaining portion 21c of the bearing 20 is
Has a smaller snap-fit shape than the diameter of the metal shaft center 11a, and the secondary transfer roller 11 does not fall off during normal operation.

The secondary transfer substrate 24 is swingably provided via bearings 30 provided on both ends of the shaft 22 at both ends (see FIG. 6). A play d2 is provided in the radial direction of 30 so that both ends can be independently slid.

Further, a secondary transfer frame pressing plate 26 is rotatably provided coaxially with the swing shaft 22 of the secondary transfer substrate 24, and a stopper 24b of the secondary transfer substrate 24 is provided with a secondary transfer frame pressing plate. 26, and the state as shown in FIG. 5 is maintained.

Between the boss 24a of the secondary transfer substrate 24 and the boss 26a of the secondary transfer frame pressing plate 26, a secondary transfer frame pressing spring 25 is provided near both ends.

An eccentric cam 18 is provided below the secondary transfer substrate 24.
Is provided, and the contact portion 2 of the secondary transfer frame pressing sheet metal 26 is provided.
6a.

A shaft 29 coaxial with a cylindrical abutting portion 21 f provided coaxially at both ends of the secondary transfer frame 21.
a secondary transfer entrance guide 29 oscillating at a, and a U-groove slide guide portion 29b provided at the tip of the entrance guide.
(Two-dot chain line) is the metal axis 11 of the secondary transfer roller 11.
It is configured to be slidably fitted to a.

Further, positioning members 27 having V grooves 27a are provided at both ends of the intermediate transfer body unit 5.

Here, when the eccentric cam 18 rotates in the direction of the arrow (clockwise) from the state of FIG. 5, the eccentric cam 18 pushes up the contact portion 26a of the secondary transfer frame pressing sheet metal 26, The next transfer substrate 24 is pushed up via the secondary transfer frame pressure spring 25.

The secondary transfer frame pressing sheet metal 26 and the secondary transfer substrate 24 rotate about the swing shaft 22 to push up the secondary transfer frame 21.

The coaxial cylindrical positioning abutments 21f provided at both ends of the secondary transfer frame 21 gradually move to the V-groove positioning 27a provided at both ends of the secondary transfer facing roller 5c of the intermediate transfer unit 5. The secondary transfer frame 21 is pressed by the force of the next transfer frame pressurizing spring 25, and the position of the secondary transfer frame 21 with respect to the intermediate transfer body unit 5 is gradually determined.

Further, the bearing play d2 of the secondary transfer substrate 24
Thus, the secondary transfer facing roller 5 of the secondary transfer frame 21
The degree of parallelism in the axial direction with respect to c also appears.

Then, the eccentric cam 18 stops at a position where it has rotated a half turn. At this time, the state shown in FIG. 6 is reached, and the secondary transfer roller 11 is moved by being pressed by d1 as shown in FIG.

Accordingly, the secondary transfer roller 11 is pressed against the intermediate transfer belt 5a only by the force of the secondary transfer roller pressing spring 19. The secondary transfer frame pressing spring 25 has a sufficiently stronger force than the secondary transfer roller pressing spring 19.

The secondary transfer entrance guide 29 is swung by a coaxial 29a with the cylindrical abutting portion 21f of the secondary transfer frame 21, and the U-groove slide guide portion 29b at the front end thereof is driven by a double guide.
Since the secondary transfer roller 11 is fitted to the metal shaft center 11a, the gap δ1 between the secondary transfer roller 11 and the distal end portion of the secondary transfer entrance guide 29 is always kept constant.

In addition, since it is configured to swing around the positioning portion for the intermediate transfer unit 5, the position of the secondary transfer entrance guide 29 with respect to the intermediate transfer unit 5 is also determined.

{Structure of Conveyor Belt Unit} Next, the structure and the like of the conveyor belt unit will be described with reference to FIGS. FIG. 2 is a schematic configuration diagram of a transport belt unit constituting a sheet transport device provided in the image forming apparatus according to the embodiment of the present invention, and FIG. 3 is a plan view (view from above).

As shown in FIG. 2, the transfer material S is composed of the secondary transfer opposing roller 5C and the secondary transfer roller 1 of the intermediate transfer unit 5.
1 is discharged downward from the horizontal direction, the guide of the conveyor belt base unit 12 is set in a direction in which the guide is lowered to a predetermined position, and thereafter the nip portion 8d of the fixing roller pair is set. The transfer material S is set so as to guide the transfer material S upwardly, and has a wide-angle V-shaped cross section.

A drive shaft 40 for the transport belt is provided at the valley of the V-shaped transport path, and the first driven shaft 41 of the transport belt at the peak at the side of the secondary transfer roller 11 and the drive shaft 40 at the fixing unit 8 A second driven shaft 42 of the transport belt is provided at the mountain portion, and each is rotatably attached to the transport belt table 12c.

As shown in FIG. 3, a first transport belt 12a (endless belt) is hung between the central coupling portion 40a of the drive shaft 40 and the central portion of the first driven shaft 41. .

Further, both ends 40b of the drive shaft and the second driven shaft 4
The second conveyor belt 12b is hung between the two.

When a rotational driving force is applied to the drive shaft 40 in the direction of arrow Y in FIG. 2 through the coupling portion 40a provided at one end of the drive shaft 40,
a and the second transport belt 12b rotate in the direction of transporting the transfer material S to the fixing device 8 side.

Here, in FIG. 2, the distance L1 from the drive shaft 40 to the nip 8d of the fixing device 8 is a cut sheet (spec sheet) set to be transportable by the image forming apparatus itself.
Is set to be several tens mm shorter than the length.

Thus, the rear end of the smallest paper among the specification papers can be pushed by the first conveyor belt 12a, and can be reliably pushed into the nip portion of the fixing roller.

The width L5 of the two second conveyor belts 12b
Is smaller than the width of the minimum specification paper, and as shown in FIG.
The first transport belt 12a is provided with a projection 12d, but the second transport belt has no projection and is flat.

Here, the first conveyor belt 12a is provided with the protrusion 1
The reason why 2d is provided is that even when the transfer material S slides on the surface of the first transport belt 12a, the rear end of the transfer material S is caught by the protrusion 12d and is transported.

On the other hand, when the projections are provided on the two left and right second transport belts, the transfer material shorter than the transport length L7 of the first transport belt is required if the left and right projections are not aligned. Is transported, there is a difference in the contact of the leading end thereof, and the transfer material S is rotated at the transfer section of the first transport belt 12a to the second transport belt 12b. The transport belt 12b has no projections and is flat.

Here, as shown in FIG. 3, the central portion of the drive shaft 40 on which the first and second transport belts 12a and 12b are hung, and both ends thereof are parallel portions 40a,
40b is shaped like a drum with both sides narrowing,
The belt always moves to the center.

Note that the first and second driven shafts have the same configuration.

{Structure in which the transfer means is retracted by detecting the trailing end of the transfer material by the pre-registration sensor to move the charge eliminating means} Next, moving means for moving the charge eliminating means, which is a feature of the present embodiment, will be described. .

As shown in FIG. 2, when a multi-sheet is fed as a transfer material, a thick paper having a length in the vicinity of L2 to L4 (a medium which is strong and is not conveyed along the conveyance path, such as an envelope, a postcard, a card, etc.) is used. The operation will be described.

FIG. 8 is a block diagram relating to the image forming apparatus according to the embodiment of the present invention, and FIG. 9 is a timing chart relating to the image forming apparatus according to the embodiment of the present invention.

In FIG. 4, the transfer material S separated from the multi-sheet feeding tray 30 by the middle plate (not shown), the separation pad (not shown), and the multi-pickup roller 31 and sent out is registered by the conveying roller pair 32. The sheet is conveyed along the front upper guide 7h, and the leading end of the transfer material S kicks the pre-registration sensor flag 39a.

The pre-registration sensor flag 39 rotates about the bearing 39c, turns the photo-interrupter 39b into the transmitting state and turns on, and detects the leading end of the transfer material S.

At a predetermined time t1, after detecting the leading end of the transfer material S, the electromagnetic clutch (not shown) that is rotating the pair of registration rollers 7d is disengaged, and the rotation of the pair of registration rollers 7d is stopped.

After the leading end of the transfer material S hits the nip of the registration roller pair 7d and stops, the electromagnetic clutch is turned off.
After a predetermined time t2, a driving source such as a stepping motor (not shown) that drives the entire sheet feeding system is stopped.

Thus, the leading end of the transfer material S stops at the nip portion of the pair of registration rollers 7d, and the pair of registration rollers 7d
A loop is formed between the transfer roller pair 32 and the transfer roller pair 32, and the transfer material ends are aligned to enter a standby state.

On the other hand, after the completion of the formation of the four color toner images on the intermediate transfer belt 5a, the electromagnetic clutch for secondary transfer UP / DOWN (not shown) is turned on and the eccentric cam 18 rotates half a turn.
The next transfer roller 11 is pressed against the intermediate transfer belt 5a.

The rotation of the electromagnetic clutch for secondary transfer UP / DOWN is controlled every 180 degrees by two photo interrupters.

After that, the registration electromagnetic clutch is turned on, the registration roller pair 7d is set in a rotatable state, and then the drive source (stepping motor) is restarted in synchronization with the rotation of the intermediate transfer belt 5a, and re-feeding means is provided. The transfer material S that has been waiting at the nip portion of the registration roller pair 7d is sent out to the nip portion between the intermediate transfer belt 5a and the secondary transfer roller 11.

The rear end of the transfer material S is the pre-registration sensor flag 3
After passing through 9a, the photointerrupter 39b is shielded from light and turned off, and it is recognized that the rear end of the transfer material S has passed through the pre-registration sensor 39.

Secondary transfer roller 11 and intermediate transfer belt 5a
Speed V1 at the nip portion of the pair and the registration roller pair 7d
The transfer speed V2 is set slightly higher than V2 so that the loop generated between the transfer unit and the registration roller unit does not contact the exterior of the intermediate transfer unit 5.

Assuming that the distance from the pre-registration sensor 39 to the nip of the secondary transfer means is R (see FIG. 4), a fixed time t3 has elapsed since the rear end of the transfer material S passed the pre-registration sensor 39.
After (t3 = R / V1), the rear end of the transfer material S passes through the nip of the secondary transfer means.

As shown in FIG. 2, in the case where the transfer material S is a thick paper (medium, such as an envelope, a postcard, a card, etc., which is strong and is not conveyed along the conveyance path) near the length L2 to L4, the rear end thereof is Transfer roller 11 and intermediate transfer belt 5
a from the nip portion, it falls on the static elimination needle guide portion 21a provided immediately after the transfer roller 11, and the leading end portion abuts against a fixing inlet guide (guide member) or a nip portion of a fixing roller pair, and the transfer material. S is in a state of being stretched.

At this time, as shown in FIG. 2, the transfer material S is not in contact with the transfer belt, and the transfer force is not transmitted to the transfer material S.

Therefore, after a predetermined time t3 after the trailing end of the transfer material S has passed through the pre-registration sensor 39, the secondary transfer electromagnetic clutch is turned off and the eccentric cam 18 is rotated half a turn, as shown in FIG. Then, the secondary transfer roller unit is retracted to a position where the static elimination needle guide 21a is lower than the vertex of the first driven shaft of the transport belt 12a.

As a result, the rear end of the transfer material S falls on the conveyor belt 12a, and the conveyance force is transmitted to the transfer material S and sent to the nip portion of the fixing roller pair.

More specifically, for example, the length L2 = 20
DL, C existing in the range of 0 mm to L4 = 260 mm
For envelopes such as 5, COM10, B5, and Western-type 4, the user can set the envelope mode to perform the operation of lowering the secondary transfer roller as described above, thereby improving transportability.

On the other hand, even with the same thick paper, the length L2 = 200 mm
The following postcards and cards are conveyed to the first and second conveyor belts without the operation of lowering the secondary transfer roller.

That is, the user need not set the envelope mode.

Alternatively, when the transfer material S pushes the pre-registration sensor flag 39a and the standby time t5 from when the pre-registration sensor is turned ON to the start of re-feeding from the time t4 when the photointerrupter is in the transmitting state, the registration roller pair 7
From d, the actual length L of the transfer material S is calculated from the speed V2 at which the transfer material S is carried out, that is, L = V2 / (t4−t5) +
K (K is the distance between the registration roller pair and the sensor before registration)
When the L dimension matches the length of the envelope set above, the secondary transfer unit can be lowered after the trailing end of the envelope has passed through the secondary transfer roller 11.

In the above description, the timing and the actual length detection of the rear end of the transfer portion of the medium are detected by using the pre-registration sensor using the flag, but the reflection type sensor is used.
The above-described timing and actual length detection may be performed by an OHT sensor (identifying whether or not the sheet transmits light) that distinguishes an OHT sheet from plain paper, or may be performed by a single sensor.

For the reflection type sensor, for example, as shown in FIG.
2, the light is received by the light receiving element 73, and the sheet conveying path 74 is provided at a position where the light path is interrupted. While the light is not being transmitted, the light receiving element 73 receives light to detect whether or not the sheet has passed.

As described above, the contact portion of the static elimination means (the static elimination needle 43 and the static elimination needle guide portion 21a) with respect to the sheet is moved to a position below the conveyance section by the second conveyance means (the conveyance belt base unit 12). By moving the sheet, it is possible to prevent a problem that the sheet is not caught by the second conveying unit while being caught on the charge removing unit.

Therefore, the sheet can be properly conveyed without increasing the size of the apparatus.

Further, only the specific type of sheet needs to be moved by the static elimination means. However, it can be recognized by a user setting as described above or automatically by a sensor. good.

As described above, as the sensor,
A sensor before registration may be used, a dedicated sensor may be provided, a sensor for identifying the type of sheet may be used, or an appropriate sensor provided in another device may be used. .

In the above description, the sheet (the transfer belt unit 1) is moved by moving the components (transfer means and static elimination means) on the first conveyance means side.
Although the configuration to ensure the mounting is described in 2),
The sheet is securely placed on the second transport unit by moving the second transport unit upward by an appropriate driving mechanism or by moving the fixing entrance guide (guide member) downward. It may be configured as follows.

[0114]

According to the sheet conveying apparatus of the present invention, after the rear end of the conveyed sheet passes through the conveying section by the first conveying means, the sheet is moved by the moving means and conveyed by the second conveying means. Therefore, it is possible to prevent a state in which the sheet is caught by the constituent member on the first conveying means side and the conveying force by the second conveying means is not applied.

Alternatively, after the leading edge of the conveyed sheet reaches the guide member, the sheet can be moved by the moving means so that the sheet can be conveyed by the second conveying means. To prevent the transfer force from being applied by the second transfer means.

Therefore, the sheet can be prevented from being caught without increasing the size of the apparatus, and sheets of various sizes can be properly conveyed.

An identification means for identifying the size of the sheet to be conveyed is provided, and it is determined whether or not to move the static elimination means by the movement means based on the identification result of the identification means.
They can be moved only when necessary.

It is also possible to provide a setting means for setting the type of sheet to be conveyed, and to determine whether or not to move the static elimination means by the moving means based on the setting result of the setting means.

Further, if the image forming apparatus of the present invention is provided with a sheet conveying device having excellent sheet conveying performance as described above, the image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a transport belt unit included in a sheet transport device provided in the image forming apparatus according to the embodiment of the present invention.

FIG. 3 is a schematic plan view of a conveyance belt unit included in a sheet conveyance device provided in the image forming apparatus according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a conveying speed and a distance of a registration roller unit and a secondary transfer unit, which constitute the sheet conveying apparatus according to the embodiment of the present invention.

FIG. 5 is an enlarged vertical cross-sectional view of a secondary transfer roller unit included in the sheet conveying device provided in the image forming apparatus according to the embodiment of the present invention.

FIG. 6 is an enlarged vertical cross-sectional view of a secondary transfer roller unit included in a sheet conveying device provided in the image forming apparatus according to the embodiment of the present invention.

FIG. 7 is a schematic configuration diagram illustrating a sheet conveying device according to an embodiment of the present invention.

FIG. 8 is a block diagram related to the image forming apparatus according to the embodiment of the present invention.

FIG. 9 is a timing chart for the image forming apparatus according to the embodiment of the present invention.

FIG. 10 is a schematic configuration diagram of a reflection type sensor.

FIG. 11 is a schematic configuration diagram of a sheet conveying apparatus and an image forming apparatus according to the related art.

FIG. 12 is a schematic configuration diagram of a sheet conveying apparatus and an image forming apparatus according to a conventional technique.

DESCRIPTION OF SYMBOLS 5 Intermediate transfer body 5a Intermediate transfer belt 8a Pressure roller 8b Heating roller 11 Secondary transfer roller 12a First transport belt 12b Second transport belt 18 Eccentric cam 21a Static electricity removal needle guide section 39 Pre-registration sensor 40 Drive shaft 43 static elimination needle

Claims (14)

[Claims] A first conveying means for conveying the sheet; and a position lower than a conveying position by the first conveying means.
A second conveying unit that conveys the sheet conveyed by the first conveying unit further downstream while placing the sheet conveyed by the first conveying unit. Moving means for moving at least one of the constituent members on the side of the conveying means, and after the rear end of the conveyed sheet passes through the conveying section of the first conveying means, the conveyed sheet is 2. A sheet conveying apparatus according to claim 1, wherein said component is moved by said moving means so as to be conveyed by said second conveying means. A first conveying means for conveying the sheet; a second conveying means for conveying the sheet conveyed by the first conveying means further downstream while placing the sheet; A guide member for guiding the sheet conveyed by the conveying unit upward, and a moving unit for moving at least one of the constituent member and the guide member on the second conveying unit side. After the leading edge of the conveyed sheet reaches the guide member,
A sheet conveying device, wherein the member is moved by the moving means so that the conveyed sheet can be conveyed by a second conveying means. 3. The first conveying belt for guiding the sheet gradually downward, the second conveying belt for gradually guiding the sheet guided by the first conveying belt upward, and 3. The sheet conveying device according to claim 1, wherein a V-shaped conveying path is formed by the first driving belt, and the first conveying belt and the second conveying belt are driven by a driving shaft provided at the intersection of the V character. apparatus. 4. An apparatus according to claim 1, further comprising identification means for identifying the size of the sheet to be conveyed, and determining whether or not to move the component by said movement means based on the identification result of said identification means. , 2 or 3. 5. A passage timing of a trailing end of a sheet in a conveying section by a first conveying means based on detection of passage of the trailing end of the sheet by the identifying means, the identifying means being provided upstream of the first conveying means. The sheet conveying device according to claim 4, wherein the sheet is recognized. 6. The sheet conveying apparatus according to claim 4, wherein the type of the conveying sheet is identified by the identification unit. 7. The sheet conveying apparatus according to claim 6, wherein said identification means identifies whether or not the sheet transmits light. 8. A method according to claim 1, further comprising setting means for setting a type of the sheet to be conveyed, and determining whether or not to move the charge removing means by the moving means based on a setting result of the setting means. , 2 or 3. 9. A sheet conveying device according to claim 1, wherein an unfixed image is formed on the sheet by a first conveying means provided in the sheet conveying device. An image forming apparatus, wherein a sheet on which an unfixed image is formed is conveyed to a fixing unit for fixing the unfixed image by the second conveying unit. 10. The image forming apparatus according to claim 1, wherein the first transporting means includes: a carrying means for carrying the unfixed image; and a transfer means for transferring the unfixed image carried by the carrying means onto a sheet. During the operation of carrying the unfixed image, the carrying unit and the transfer unit are located separately from each other. The image forming apparatus according to claim 9, wherein the image is transferred. 11. The fixing device according to claim 9, wherein said fixing means has a pair of rotating members, and fixes the unfixed image by transporting the sheet while heating and pressing while sandwiching the sheet with said rotating member. Or the image forming apparatus according to 10. 12. An image forming apparatus according to claim 10, wherein a component moved by said moving means is said transfer means. 13. An image forming apparatus according to claim 12, wherein said transfer means is provided with a charge removing means for removing charge of the sheet, and said charge removing means moves together with the transfer means. 14. The apparatus according to claim 9, wherein said identification means has a function of a sensor for determining a timing for forming an unfixed image on a sheet by the first conveyance means.
The image forming apparatus according to any one of the above.