JP3308310B2 - Sheet conveying method in image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying method for an image forming apparatus such as a printer, a digital copying machine, and a facsimile which continuously feeds cut sheets and sequentially forms an image on each sheet.

[0002]

2. Description of the Related Art A conventional sheet conveying method in an image forming apparatus such as a printer, a digital copying machine or the like which continuously feeds a cut sheet and sequentially forms an image thereon is as follows.
The sheet fed at a predetermined interval is positioned so that the leading end thereof abuts against a registration roller in a stopped state in order to synchronize the image with the image in the image forming unit, and the sheet is positioned. It is generally known that the sheet is conveyed again by being driven at a predetermined timing, and the sheet is fed at a predetermined interval.

In recent years, with the advent of digital copiers, the speeding up of image processing apparatuses mounted on printers and facsimile machines, and the improvement of efficiency, the sheet interval is reduced as much as possible and the image per unit time is reduced. The need for high-speed processing to increase the number of sheets that can be formed as much as possible has been required.

Therefore, as described in Japanese Patent Publication No. 63-15577, for example, when an image forming apparatus sequentially feeds sheets stored in a sheet feeding cassette from the upper side, the next sheet is printed. By advancing the start timing of paper feeding, paper is fed in a state where the trailing edge of the preceding sheet and the leading edge of the succeeding sheet are partially overlapped, and is placed on the sheet in the overlapped state. There is one that forms an image.

[0005]

However, an image is formed on the partially overlapped sheet as it is, and the sheet is conveyed in the overlapped state after image formation. Problems could arise when discharged.

That is, for example, an image forming apparatus such as a copying machine or a printer discharges a sheet after forming an image,
Face-up paper discharge, with the image side facing up,
It is possible to select face-down paper discharge to discharge with the image side facing down, or send the sheet after forming the image on one side to the re-feeding conveyance path, turn it upside down, and return it to the image forming unit again Although there is a type capable of forming a double-sided image so that an image is formed on the back side on which an image is not formed by transporting the sheet, the sheet after the image formation is transported on the transport path of such an apparatus. In order to switch the conveyance direction and feed the paper to the path, for example, a conveyance path switching device of a branch claw type as shown in FIG. 6 is provided.

[0007] However, in this branch pawl type transfer path switching device, the pair of rotatable branch pawls 41 and 42 are set to the positions shown in FIG. The sheet S conveyed in the indicated direction is straightly advanced to the conveyance path provided with the conveyance roller pair 45 and discharged face-up, or the branching claw 41 is moved to the position shown in FIG. , The sheet S is guided to the conveying path provided with the conveying roller pair 43 on the upper side in the figure and discharged face-down, and further, the branching claw 42 is switched to the position shown in FIG. As a result, since the sheet is guided to the re-feeding conveyance path provided with the lower conveyance roller pair 44 in the drawing, in a general branching mechanism using such a branching claw, as described above, a part is used. Pile The sheet conveyed by the Align was state, was sometimes can not be fed by securely branched to the conveying path of interest.

Therefore, a special branching mechanism is required to branch the partially overlapped sheet, thus increasing the cost. Further, when the sheet is passed through the fixing unit in a state where a part of the sheet is superimposed, a part of the sheet between the fixing roller heated to a high temperature of the fixing unit and the pressing roller pressed against the fixing unit is partially moved. When the sheets overlap each other, the sheets overlap each other while being heated, so that the marks (pressure marks) of the edges of the other sheets that overlap each other are attached to the paper surface, and the appearance deteriorates. There was a thing.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is possible to perform high-speed processing for increasing the number of images that can be processed per unit time as much as possible, and to perform the conventional branching without providing a special branching mechanism. An object of the present invention is to enable a sheet to be conveyed to be reliably fed into a target conveying path or to be stacked by a general branching mechanism using claws or the like. It is another object of the present invention to prevent a trace of an edge portion of a sheet adjacent to the sheet.

[0010]

SUMMARY OF THE INVENTION The present invention achieves the above object.
To achieveFeed the cut sheet continuously, and
Part of the trailing edge of the next sheet and the leading edge of the following sheet.
Image is sequentially formed on each sheet by the image forming unit
Form the sheet and transfer it to the conveyor belt of the belt conveyor
Image forming apparatus that conveys toward fixing means while holding
In place Above rear endAnd the tip are partially overlapped
Sheet overlapConveyed by the above belt conveyor
When the sheet is conveyed by the fixing unit
VF is set to the sheet conveying speed in the image forming section. ₀ ,
When the transfer speed of the belt transfer device is VB VF> V ₀ = VB Fast enough to satisfy the relationship
Dissolve It provides a sheet conveying method
You.

[0011]

[0012]

[0013]

According to the sheet conveying method in the image forming apparatus having the above-described configuration, a large number of sheets are fed in a unit time to efficiently form an image. Even if the sheet is fed in a state where the leading end of a succeeding sheet is partially overlapped and an image is sequentially formed thereon, the overlapped sheet passes through the image forming section after the overlapping section passes through the image forming section. Since the sheet is conveyed at a predetermined sheet interval after the alignment state is eliminated, the sheet can be conveyed to the conveyance path or discharge path intended for the sheet with the conventional branching mechanism or paper discharge mechanism using a conventional branching claw or the like. Can be sent reliably.

Further, the superposed portion of the sheet having the rear end portion and the front end portion partially overlapped is conveyed by a belt conveying device.
When the sheet is being fed,
In order to speed up , the sheet on which the image is formed and conveyed to the fixing unit has already been released when the rear end portion passes through the fixing unit . Since the ends do not pass between the rollers of the fixing unit in a state where they overlap each other, it is possible to prevent the occurrence of pressure marks caused by the edge of the sheet being pressed against the sheet surface. In addition, superposition of sheets
The overlapping state can be eliminated by using the belt conveyor
Is performed when the sheet is conveyed by the
The rear end of the
Just slide on the belt to eliminate sheet stacking
It is .

[0015]

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a schematic diagram showing a portion from an image forming section to a fixing device of an image forming apparatus for implementing a sheet conveying method according to the present invention, and FIG. 2 is a sheet continuously fed from a sheet feeding section of the image forming apparatus. FIG. 4 is a schematic diagram for explaining a mechanism for overlapping a part of the parts with each other.

In this image forming apparatus, a cut-sheet (hereinafter simply referred to as a sheet) S in a sheet feeding cassette 30 of a sheet feeding section shown in FIG. 1, the front end of the preceding sheet and the front end of the succeeding sheet are separated by the crank 7
A part of the sheets is overlapped by using a sheet rear end separation mechanism including a push-up member 6 and the like which is moved up and down, and a predetermined image is sequentially formed on each sheet S in that state.

That is, when the image forming apparatus starts a sheet feeding operation, the image forming apparatus is rotated in the direction indicated by an arrow by a stepping motor (not shown) on the top of the sheets S stacked in the sheet feeding cassette 30. The circumference of the pickup roller 1 is pressed against the sheet S, whereby the sheet S is sent to the left in the drawing. At this time, the sheet S is separated into one sheet by the action of separating claws 12 provided at both corners of the front end of the upper surface, and the photosensitive drum 10 is separated therefrom.
And a transfer / separation charger 9 provided to the image forming unit 2.

From the paper feed cassette 30 to the photosensitive drum 1
In the sheet conveyance path reaching 0, a registration sensor 3, a timing roller 4, a timing sensor such as a reflection type optical sensor for detecting the sheet, and a rear end of the preceding sheet S are arranged in this order from the sheet conveyance upstream side. A push-up member 6, a crank 7, and a transport roller 8, which constitute rear-end separating means for lifting the sensor to a position outside the detection area of the timing sensor 5, are provided.

The registration sensor 3 is an optical sensor for detecting that the rear end of the sheet S is sufficiently separated from the sheet bundle in the sheet cassette 30. The timing roller 4 can freely control the rotation speed and rotation direction by a stepping motor (not shown) or the like.

In this embodiment, the rear end separating means rotatably connects the base end (lower side in FIG. 2) of the push-up member 6 to the crank 7 by a pin, and moves the push-up member 6 onto the transport path. The tip 6a contacts the rear end of the sheet S and pushes it up when protruded. In addition to this, a push-up member is connected to the movable shaft of the solenoid, and the push-up member can be moved up and down. , A combination of a groove having a circular cross section and a pressing member having a cross section engaged with the groove, a structure in which the rear end of the sheet is lifted by an attractive force of electrostatic suction or negative pressure, and Various configurations are conceivable, such as a configuration in which the rear end of the sheet is lifted by airflow.

Next, the operation when the sheet S is continuously fed at regular intervals in the image forming apparatus in FIG. 2 will be described with reference to FIG.
4 and the timing chart shown in FIG. The numbers (a), (b),... (G), (h) of the titles of the respective operations shown in FIG. 3 and (a), (b) written on the time axis (horizontal line) shown in FIG. ), ……… (g),
The timing of (h) corresponds to each other. Further, a V ₀ is the conveying speed of the sheet in the image forming portion (photosensitive drum 10) in FIG. 3, V ₁ is the transport speed of the sheet by the transport roller 8, V ₂ is the conveying speed of the sheet by the timing roller 4 Shown respectively.

(A) Detection of the rear end of the sheet S ₁ : The uppermost sheet S ₂ loaded in the sheet cassette 30 (FIG. 2) is in a state where the rear end of the preceding sheet S ₁ is sufficiently separated. Is detected by the registration sensor 3, and then the pickup roller 1 is rotated once to get over the separation claw 12 to be separated and sent out.

In this state, the rotation of the crank 7 is stopped (O
FF), and the push-up member 6 is stopped at the home position as shown in the drawing, that is, at a position where the tip 6a of the push-up member 6 is lower than the upper surface of the transport guide 11. Therefore, normal sheet feeding is not hindered.

(B) Start of trailing edge lifting / sheet S ₂ registration: The timing roller 4 is temporarily stopped based on the timing when the registration sensor 3 detects the leading end of the sheet S ₂ . Thereby, the leading end of the sheet S ₂ is abutted to the timing roller 4 is stopped, parallel tip (skew) is corrected. At the same time, the rotation of the crank 7 is started (the rotation direction is clockwise in the figure).

(C) Feeding the sheet S ₂ : When the crank 7 rotates, the push-up member 6, one end of which is rotatably connected to the pin 7 by a pin, is guided by the sliding guide portion 11 a and rises. The leading end 6a of the sheet S protrudes above the upper surface of the conveyance guide 11, and the sheet S being fed is
Lift the rear end from the bottom side of ₁ .

[0027] Thereby, the rear end of the sheet S ₁ is in a state of being separated from the timing sensor 5, the timing sensor 5 is released from the rear end of the detection state of the sheet S _1, it is possible to the leading edge detection of the sheet S ₂ . At the same time, the timing roller 4 is driven again, and the sheet S _{2 is} transported at a transport speed Vf higher than the transport speed (image forming speed) V ₀ of the sheet S ₁ by the photosensitive drum 10 and the transport roller 8.
Feeding is resumed, feeding the leading edge of the sheet S ₂ to the lower surface side of the rear end portion of the raised sheet S _1.

The (d) The sheet S ₂ leading edge detecting: When the leading end of the sheet S ₂ is detected in the timing sensor 5 again to stop the timing roller 4. Although this time the rear end of the sheet S ₁ is in a state of being lifted upward by the push-up member 6, and in a state overlapping the rear end portion and the sheet S ₂ of the distal end portion of the sheet S ₁ at this point , in a state where it is possible to immediately start imaging of the sheet S ₂ after the image formation completion of the sheet S _1.

(E) Aligning the tip of the sheet S ₂ : crank 7
As the rotation proceeds, the push-up member 6 starts to descend. Conveyed by a very low speed of the sheet S ₂ in the feeding direction and a reverse direction by reversing drives timing roller 4, the leading end of the sheet S ₂ by the timing sensor 5 stops the conveyed at a position that is no longer detected. In other words, to align the leading end of the sheet S ₂ on the upstream side of accurately timing sensor 5. This operation can be precisely positioned than the state of the leading end of the sheet S ₂ (d).

(F) Sheet superposition: The crank 7 is further rotated and stopped at the time of one rotation. Therefore, the push-up member 6 connected thereto via the pin is also stopped at the illustrated home position. At this point, the tip portion 6a of the push-up member 6 is located below the upper surface of the conveying guide 11, the rear end of the sheet S ₁ which has been moved away to fall toward the upper surface of the conveying guide 11, the sheet S ₁ of the rear end and the front end portion of the sheet S ₂ overlap.

(G) Adjustment of the amount of superposition of sheets: The timing roller 4 drives the photosensitive drum 10 and the transport roller 8 to convey the conveying speed V ₀ in synchronization with the progress of image formation.
In with a certain overlapping amount accurately resume feeding of the sheet S _2.

(H) Realization of continuous sheet feeding: The sheet S ₂ is kept in the image forming section 2 while maintaining a constant overlapping amount.
(See FIG. 1), and high-speed and efficient image formation is continuously performed.

Thereafter, by repeating the operations (a) to (g) successively with the sheets S ₃ , S _4, ..., Sn, a constant sheet overlapping amount is provided with high accuracy, and
An image is formed.

FIG. 5 is a block diagram showing a control system of the image forming apparatus. Upon receiving a print command from the external device (host computer) 15, the controller 16 sends image information to the main body control device 17.

The main body controller 17 comprises a CPU (central processing unit), ROM, RAM and the like.
A signal is taken in from the timing sensor 5 and the like, and the signals are picked up by a pickup roller O, a timing roller drive circuit 19, a transport roller drive circuit 20, and a rear end lifter drive circuit 21, respectively.
N / OFF clutch 24, stepping motor 25, transport motor 26, and rear end lifter drive motor 2
7 to control the sheet feeding.

The operation panel 28 is composed of an operation section composed of a plurality of switches and a display section composed of LEDs, LCDs and the like, and can perform various settings of the image forming apparatus. The controller 16 expands the image information received from the external device 15, and sends a print start command to the main body controller 17 at the time when the development of one page is completed. In the case of image information covering a plurality of pages, similar processing is sequentially performed.

Next, a description will be given of a method of canceling the overlapping state of the sheet in which the rear end portion and the front end portion are partially overlapped. In this embodiment, the sheet S to the trailing and the rear end portion of the sheet S ₂ the preceding superimposed as shown in FIG. 1
₃ to eliminate the overlapping state between the distal end portion, the sheet S
₂ is performed after the overlapping portion lap of the sheet has passed through the image forming portion 2, and the overlapping portion lap of the sheet is the fixing device 1
Perform before reaching 3.

The superposition of the sheets is eliminated by setting the sheet conveying speed VF by the fixing roller 22 and the pressure roller 23 of the fixing device 13 higher than the sheet conveying speed V ₀ of the image forming section 2. Do. Therefore, in this image forming apparatus, the distance L from the transfer position of the transfer / separation charger 9 of the image forming unit 2 to the nip between the fixing roller 22 and the pressure roller 23 of the fixing device 13 is defined as: L> Length in the sheet conveyance direction. The sheet is conveyed between the image forming section 2 and the fixing device 13 by a belt conveying device 29 in which a conveying belt 33 is stretched between rollers 31 and 32.

The transport speed VB of the belt transport device 29
And the conveying speed V _{0 of} the image forming section 2 (photosensitive drum 10).
When the relationship between the conveying speed VF of the fixing device 13, are set to be the VF> V ₀ = VB.

Therefore, the sheet whose leading end has passed through the image forming section 2 is image-formed by the conveying belt 33 which is rotated at the conveying speed VB in the direction indicated by the arrow in FIG. Part 2
Is transported at the same transport speed as the transport speed V ₀ of the fixing device 13, and the leading end side thereof is clamped by the nip between the fixing roller 22 and the pressure roller 23 of the fixing device 13. It is transported at the speed VF.

[0041] At this time, the sheet as the sheet S ₁ in FIG. 1, the rear end side has already passed through the transfer portion. And
The succeeding sheet S ₂ has a conveyance speed V ₀ of the image forming unit 2.
Because it is conveyed by the (same as the conveying speed VB), between the tip of the trailing edge and the sheet S ₂ of the sheet S ₁ is overlapping state of the sheet is eliminated by opening.

Note that the leading end of the sheet S ₁ is
When you are 3 being pinched carried by is its rear end portion is conveyed by a belt conveyor device 29 a slow conveying speed VB than the conveying speed VF of the fixing unit 13, the rear end side of the case sheet S ₁ is conveyed since by being pulled on the belt 33 at a high speed only slide over the belt, or hindered in conveying the sheet, the sheet S ₂ is located in the transfer section to the trailing by the black line jitter (sudden shocks ( A phenomenon in which black streaks occur in the main scanning direction ) does not occur.

As described above, in this embodiment, the overlapping portion lap of the sheet in which the rear end portion and the front end portion are partially overlapped.
Before reaching the fixing device 13, the overlapping state of the sheets is canceled, so that adjacent ones of the continuously fed sheets pass between the rollers of the fixing device 13 while being pressed against the paper surface. Therefore, it is possible to prevent the pressure trace due to the edge portion of the adjacent sheet from sticking to the sheet surface.

The elimination of the superposed state of the sheets is performed by fixing the fixing roller 22 and the pressing roller 23 of the fixing device 13.
Only by increasing the sheet conveying speed, the sheet can be reliably transferred to the target conveying path or discharge path with the conventional branching mechanism and sheet discharging mechanism using the branching claws as described in FIG. Since the apparatus can be fed, the structure of the apparatus can be simplified and the cost can be suppressed.

In the belt conveying device 29 shown in FIG. 1, the sheet immediately after the transfer of the image is fixed on the non-image forming surface side on which the image is not transferred (in the case of double-sided image formation, the fixing is already completed). Since the sheet is conveyed while being sucked and held on the conveying belt 33, the unfixed image immediately after the image transfer is not adversely affected. By the way, the cancellation of the superimposed state of the sheets is performed so that the superimposed portion of the sheets is a branch portion on the downstream side of the fixing device in the sheet conveyance direction, or if there is no branch portion, up to the sheet discharge position. You can also.

In this case, the superimposed portion of the sheet passes through the fixing device 13 so that the superimposed state is canceled. if the non-image forming surface side of the preceding trailing edge of the sheet in contact with the image forming surface side of the sheet front end of the succeeding (see sheet S ₂ and S ₃ in FIG. 1), the photosensitive drum 10 and the fixing roller 22 When the radius of curvature is large, there is a possibility that the leading end of the sheet is not separated from the surface but rotates and winds in close contact, but such a disadvantage can be prevented.

In addition, if the overlapping state of the sheets is eliminated after passing through the fixing device 13 as described above, and the vertical relationship of the overlapping at the end of the sheet is as described above, it has been conventionally used. Even if the peeling mechanism is simplified or omitted to reduce the cost, the leading end of the sheet comes into contact with the surface of the photosensitive drum 10 via the trailing end of the preceding sheet, so that the sheet is wound. In addition to this, damage to the sheet by the peeling mechanism can be removed.

Further, in this case, the sheet is separated from the photosensitive drum only by applying a charging current to only the leading end of the first sheet by the separation charger. The generation of ozone can be reduced by the amount that the charging current need not be applied to the sheet.

[0049]

As described above, when the sheet conveying method according to the present invention is carried out, a rear end portion of a preceding sheet and a rear end portion thereof are formed in order to efficiently form a large number of sheets within a unit time. Even if paper is fed in a state where the leading end of a sheet to be fed is partially overlapped and an image is sequentially formed thereon, the overlapped portion of the sheet is canceled after passing through the image forming unit. As a result, the sheet can be reliably fed to the intended conveyance path or discharge path by using the conventional branching mechanism or paper discharge mechanism as it is. Therefore, the apparatus can be manufactured at low cost while high-speed and efficient image formation can be performed.

Also, the above-mentioned sheet overlapping portion is transported by a belt.
When the sheet is conveyed by the
After the image has been formed and conveyed to the fixing unit, the rear end of the sheet passes through the fixing unit to increase the conveyance speed of the sheet.
In this case, since the overlapping state has already been eliminated, the edges of the sheets adjacent to each other in the conveying direction do not pass between the rollers of the fixing unit in a state of being overlapped with each other. Pressure marks can be prevented from being generated. Further
In addition, the cancellation of the overlapping state of the sheets
Is performed when the paper is being conveyed by the belt conveyor.
The trailing edge of the preceding sheet is pulled on the conveyor belt at high speed.
Sheets can be stacked simply by sliding on the conveyor belt.
The matching state is eliminated. Therefore, it supports sheet conveyance.
It may cause obstacles or sudden impact on the seat.
Black streaks in the main scanning direction.
Can be.

[0051]

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a portion from an image forming section to a fixing device of an image forming apparatus that performs a sheet conveying method according to the present invention.

FIG. 2 is a schematic diagram for explaining a mechanism for overlapping a part of sheets continuously fed from a sheet feeding unit of the image forming apparatus with each other.

FIG. 3 is an operation explanatory view showing step by step an operation of continuously feeding sheets S at a constant interval and overlapping a part of adjacent sheets in the image forming apparatus in FIG. 2;

FIG. 4 is a timing chart showing the operation timing of each unit in the same operation.

FIG. 5 is a block diagram illustrating a control system of the image forming apparatus of FIG. 1;

FIG. 6 is a schematic diagram showing different states of switching between different conveyance paths in a branch-claw type conveyance path switching device provided on a conveyance path of a conventional image forming apparatus.

[Explanation of symbols]

Reference Signs List 2 Image forming unit 6 Push-up member 7 Crank 10 Photoconductor drum 13 Fixing device (fixing unit) 22 Fixing roller 23 Pressure roller 29 Belt transport device

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-60-17456 (JP, A) JP-A-62-30265 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) B65H 5/06 B65H 5/24 G03G 15/00 518

Claims (1)

(57) [Claims] 1. A method for continuously feeding cut sheets,
Part of the trailing edge of the next sheet and the leading edge of the following sheet.
With each sheetIn the image forming sectionSequential image
Line formingThe sheet on the conveyor belt of the belt conveyor.
To the fixing means while holding the paperImage forming device
The weight of the sheet in which the rear end and the front end are partially overlapped
The joint isWhen being transported by the belt transport device
The conveying speed VF of the sheet by the fixing means
The sheet conveyance speed in the image forming unit is set to V ₀ The bell
When the transfer speed of the transfer device is VB VF> V ₀ = VB Fast to satisfy the relationship of the sheet Superposition of
The stateTo resolveCharacteristic sheet conveyance method.