JPH07267424A - Sheet conveying device and image forming device - Google Patents

Abstract

PURPOSE:To obviate the complex control in response to the type of a sheet by providing a one-way clutch on the transmission mechanism of the third conveying means, driving the third conveying means and the first conveying means in common, and specifying the distance from the first conveying means to the second conveying means. CONSTITUTION:Multiple conveying vertical pass roller pairs 22a-22c are provided between a heat roller pairs 19a and a reverse roller pair 23b of an image forming device to satisfy the relation L1>=L2, where L1 is the distance between the heat roller pair 19a and the reverse roller pair 23b, and L2 is the maximum length in the conveying direction of a usable sheet. The heat roller pair 19a and conveying vertical pass roller pairs 22a-22c are rotatively driven by a common driving motor 35 via driving gears 19a1, 22a1, 22b1, 22c1. The driving gears 22a1, 22b2, 22c1 store one-way clutches 36 each transmitting only the rotating force in one way, i.e., in the sheet conveying direction, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus capable of recording on both sides of a sheet, and more particularly to a sheet conveying apparatus equipped in the image forming apparatus. The image forming apparatus may be, for example, a copying machine,
Laser beam printers, LED printers, facsimile machines, etc. are included.

[0002]

2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and laser beam printers record at least two or more colors in addition to an image forming apparatus that records a single color (usually black and white) image. A so-called color image forming apparatus has been put into practical use.

Further, in order to improve the amount of information that can be recorded on a sheet, a double-sided image forming apparatus or the like has been put into practical use, which records a single-color or multi-color image on the front and back surfaces of the sheet.

In these image forming apparatuses, it is necessary to change the amount of heat supplied according to the type of the sheet at the time of fixing the image due to the diversification of the sheet used (difference in material, thickness, size, etc.). It is necessary to change the driving speed of the fixing device. Therefore, the drive motor for driving the fixing device is provided separately from the drive motors for driving the other sheet conveying systems, and the drive speed of the fixing device (fixing while conveying the sheet is performed according to the type of the sheet used. It is configured so that the speed at which it is performed) can be changed independently.

Further, in the double-sided image forming apparatus, a plurality of conveying roller pairs interposed between the fixing device and a reversing device for reversing and conveying the sheet downstream of the fixing device in the sheet conveying direction are driven. Is configured to be driven by a drive motor that is separate from the drive motor that drives the fixing device.

[0006]

However, in the above-mentioned conventional example, the driving of the fixing device and the driving of the plurality of conveying roller pairs on the downstream side in the sheet conveying direction are driven by separate driving motors. Normal sheet (plain paper)
When an image is formed on both sides of a sheet (resin film, cardboard, postcard, etc.) other than the above, control to change the drive of the plurality of conveyance roller pairs according to the change of the drive of the fixing device according to the type of the sheet Is required.

When the distance from the fixing device to the reversing device is shorter than the length of the maximum size sheet to be used, in addition to the above control, the control of the reversing device (acceleration start timing, sheet conveyance speed change, etc.) is performed. ) And the control of the sheet conveyance interval, etc., and the control of the apparatus itself changes according to the type of the sheet, so that there is a problem that the image recording time per sheet greatly increases.

Further, since the inspection points at the time of the sheet jam when the above-mentioned construction is carried out differ depending on the type of the sheet used, there is a problem that the operability of the apparatus is impaired.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to have a sheet conveying system which does not require complicated drive control according to the type of sheet used. An object is to provide an image forming apparatus having good properties.

[0010]

A typical constitution of the present invention for achieving the above object is to provide a first transporting means for transporting a sheet and a downstream side of the first transporting means in the sheet transporting direction. A second conveyance unit that conveys the sheet at a higher conveyance speed than the first conveyance unit; and a third conveyance unit that intervenes between the first conveyance unit and the second conveyance unit and conveys the sheet. Then, a one-way clutch is interposed in the power transmission mechanism of the third transfer means to drive the third transfer means and the first transfer means by a common drive source, and the first transfer means The relation between the distance L ₁ from the means to the second conveying means and the maximum length L ₂ of the usable sheet in the conveying direction is set so that L ₁ ≧ L ₂ .

More specifically, in an image forming apparatus capable of recording on both sides of a sheet, an image forming means for forming an image according to image information, and an image formed by the image forming means. The transfer means for transferring the sheet onto the sheet, the conveying speed can be changed according to the type of the sheet used, the fixing means for fixing the image transferred by the transferring means onto the sheet, and the sheet conveying rather than the fixing means. A reversing conveyance unit that is located on the downstream side in the direction and that conveys a sheet at a higher conveyance speed than the fixing unit, and a reversing conveyance unit that intervenes between the fixing unit and the reversal conveyance unit and conveys the sheet. And a means for driving the conveying means and the fixing means by a common drive source with a one-way clutch interposed in the power transmission mechanism of the conveying means, and
A distance L ₁ from the fixing means to the reversal conveying means,
The relation with the maximum length L ₂ of the usable sheet conveyance direction is
The feature is that it is set so that L ₁ ≧ L ₂ .

[0012]

In the above structure, the fixing means and the conveying means on the downstream side in the sheet conveying direction are driven by a common drive source. Therefore, the fixing means can be used depending on the type of sheet used. The drive of the transporting means is also changed by simply changing the drive of. This simplifies drive control of the device itself. Further, by simplifying the control, the inspection location at the time of sheet jam and the image recording time per sheet are not largely changed depending on the type of sheet, and the operability of the apparatus is improved.

Further, since the distance from the fixing means to the reversing conveying means is set to be equal to or longer than the maximum length of the sheet to be used in the conveying direction, the conveying speed is faster than that of the fixing means. The fixing unit does not restrain the sheet conveyance by the reverse conveyance unit that rotates in the normal and reverse directions. That is, the sheet conveyance by the reversal conveyance means is performed after the image fixing over the entire area of the maximum length sheet is completed. Further, since the one-way clutch is interposed in the power transmission mechanism of the conveying means interposed between the both means, the conveying means does not restrain the sheet conveyance by the reversing conveying means.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a sheet conveying apparatus to which the present invention is applied and an image forming apparatus equipped with the sheet conveying apparatus will be described below with reference to the drawings. In this embodiment, a color copying machine capable of double-sided recording is used as an image forming apparatus, and the sheet conveying apparatus is applied as a sheet conveying system from a fixing device to a reversing roller of the copying machine. FIG. 1 is a schematic sectional view showing a schematic configuration of a color copying machine, and FIG. 2 is a driving state explanatory view showing a sheet conveying state by a sheet conveying system from a fixing device to a reversing roller.

First, a schematic structure of a color copying machine will be described with reference to FIG. The color copying machine has, as image forming means, a digital color image reader section at the upper part of the apparatus and a digital color image printer section at the lower part of the apparatus. In the digital color image reader unit, the original 1 is an original platen glass 2
The image is reflected on the document 1 by the lens 4 by being placed on it and scanned by the exposure lamp 3 to obtain a color-separated image signal.
This color separated image signal is processed by a video processing unit (not shown) through an amplifier circuit (not shown),
Transferred to the digital color image printer unit.

In the digital color image printer section, the photosensitive drum 6 as an image bearing member is rotatably supported in the direction of the arrow, and a pre-exposure lamp 7, a primary charger 8 and laser exposure are provided around the photosensitive drum 6. Optical system 9, potential sensor 10, four developing devices 11y, 11c, 11m, 11B of different colors
k, an on-drum light amount detection means 12, a transfer device 13, and a cleaning device 14 are arranged.

In the laser exposure optical system 9, the image signal from the reader section is converted into an optical signal at the laser output section, the converted laser light is reflected by the polygon mirror 9a, and the lens 9b and the mirror 9c. And is projected onto the peripheral surface of the photosensitive drum 6. At the time of image formation, the photosensitive drum 6 is rotated in the direction of the arrow, the photosensitive drum 6 after being discharged by the pre-exposure lamp 7 is uniformly charged by the primary charger 8, and an optical image is emitted for each separated color. To form an electrostatic latent image.

Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 6, and a toner image based on resin is formed on the photosensitive drum 7. Developing device 11y, 11c, 11
The m and 11 Bk are configured to selectively approach the photosensitive drum 6 according to each separated color by the operation of the eccentric cams 15 y, 15 c, 15 m and 15 Bk.

Further, the toner image on the photosensitive drum 6 is supported by the transfer drum 13a of the transfer device 13 with the sheet P supplied from the sheet cassette 16 through the sheet conveying system 17, and is opposed to the photosensitive drum 6. Then, the toner image is transferred to the sheet P by applying a voltage having a polarity opposite to that of the toner image by the transfer charger 13b. The transfer device 13 includes a transfer drum 13a, a transfer charger 13b, and an attraction charger for electrostatically attracting the sheet P to the transfer drum 13a.
13c, a suction roller 13 arranged to face the suction charger 13c
d, an inner charger 13e, and an outer charger 13f are provided, and a carrier sheet 13g made of a dielectric material is stretched in a cylindrical shape on the peripheral surface of a transfer drum 13a which is rotatably supported. The supporting sheet 13g uses a dielectric sheet such as a polycarbonate film.

Further, a carrying sheet 13g for the transfer drum 13a.
A backup brush 13j facing the fur brush 13i, an oil removing roller 13k, and a carrying sheet are provided in order to prevent scattering of the upper toner and adhesion of oil on the sheet P.
Cleaning is performed by the action of the backup brush 13l facing the oil removing roller 13k via 13g. Such cleaning is performed before or after image formation, and at any time when a paper jam (sheet jam) occurs.

Further, in this embodiment, the eccentric cam 13m is operated at a desired timing and the cam follower 13n integrated with the transfer drum 13a is operated to arbitrarily set the gap between the carrying sheet 13g and the photosensitive drum 6. It has a configurable configuration. For example, during standby for image formation or when the power is off, the transfer drum 13a and the photosensitive drum 6 are separated from each other.

As the transfer drum 13a of the transfer device 13 is rotated, the toner image on the photosensitive drum 6 is transferred to the sheet P carried on the carrying sheet 13g by operating the transfer charger 13b. In this way, the desired number of each color image is transferred to the sheet P that is sucked and conveyed to the carrying sheet 13g, and a full color image is formed. In this example, the transfer drum 13a and the photosensitive drum 6 are set to have the same outer diameter.

In the case of the above-mentioned full-color image formation, when the transfer of the four color toner images is completed, the sheet P is transferred onto the transfer drum 13a.
Are separated by the action of the separation claw 18a, the separation push-up roller 18b, and the separation charger 13h, and are discharged to the discharge tray 20 provided outside the apparatus through the fixing device 19 having the heat roller pair 19a. Further, after the image transfer, the toner remaining on the photosensitive drum 6 is removed by the cleaning device 14, and then the image forming step is prepared again.

Explaining the structure for performing double-sided image formation, the conveyance path switching guide 21 provided on the downstream side of the fixing device 19 is driven to switch the sheet conveyance path in the vertical path 22 direction. As a result, the sheet P after the image fixing has a vertical pass.
When the trailing edge is guided to 22 and further to the reverse path 23a and the rear end passes through the branch portion, the reverse roller pair 23b is driven in the reverse direction and the horizontal path is passed.
Transport to 23c. At this time, the flapper 24 corresponding to the sheet size is rotated to convey the sheet P conveyed on the horizontal path 23c.
Is discharged to the stacking tray section 26 of the intermediate tray 25 and is stacked with the image side facing up.

A gate provided at the tip of the intermediate tray 25
Numeral 27 is closed when the sheets are stacked, and every time one sheet P is stacked, the sweeping roller 28 is operated to bring the leading edge of the sheet into contact with the gate 27 and align the leading edge. Loading is completed by repeating the above operation for a predetermined number of sheets.

When forming an image on the second side,
The gate 27 arranged at the front end of the intermediate tray 25 is opened, and the pickup roller 29 pressurizes and rotates the uppermost side of the stacked sheets P to sequentially feed the sheets P. Then, only one uppermost sheet P is separated and conveyed by the retard roller pair 30 and 31, and the downstream auxiliary feed roller pair 32 and 33.
Is sent to the paper feed path 34. After that, the image formation of the second side is performed similarly to the image forming step of the first side.
Then, the transport path switching guide 21 is driven to switch the transport path toward the discharge tray 20. The sheet P having the image fixed on the second side is discharged onto the discharge tray 20 and stacked with the second side facing up. The above operation is repeated until there is no sheet P on the stack tray portion 26 of the intermediate tray 25.

Here, the structure of the sheet conveying system from the heat roller pair 19a to the reversing roller pair 23b of the fixing device 19 will be described in detail with reference to FIGS. In the figure, a plurality of conveying vertical path roller pairs 22a, 22b, 22c are interposed in the vertical path 22 between the heat roller pair 19a and the reversing roller 23b. Here, from the heat roller pair 19a of the fixing device 19 to the plurality of conveying vertical path roller pairs 22a, 22b, in the vertical path 22.
The distance to reach the pair of reversing rollers 23b via 22c is L ₁ , and the maximum length of the usable sheet in the conveying direction (in this example, the maximum length of the sheet that can be held on the transfer drum 13a) is L.
_{If it is 2} , the relationship between the _two is set to L ₁ ≧ L ₂ (see FIG. 2). Therefore, after the image fixing over the entire area of the maximum usable sheet is completed, the sheet is conveyed by the reversing roller pair 23b.

Further, as shown in FIG. 2, the heat roller pair 19a of the fixing device 19 and the conveying vertical path roller pair 22a, 22 are provided.
b and 22c are drive gears 19a1 and
It is rotationally driven by a common drive motor 35 via 22a1, 22b1 and 22c1. The drive motor 35 is drive-controlled so that the rotation speed can be changed according to the types of sheets that can be used in this apparatus. Further, the driving gears 22a1, 22b1, 22c1 for transmitting the driving force from the motor to the respective conveying vertical path roller pairs 22a, 22b, 22c are rotated only in one direction (in the present example, the sheet conveying direction). It has a built-in one-way clutch 36 for transmission.

Further, the pair of reversing rollers 23b is composed of the gears 23b1,
A forward / reverse rotation is performed by a drive motor 37 that is forward / reverse driven via 23b2. The reversing roller pair 23b has a predetermined speed (in this example, when the leading edge of the sheet is fed into the nip portion).
It rotates in the sheet conveying direction at about twice the image forming speed on the photosensitive drum 6) and rotates in the opposite direction at a speed not less than the above speed immediately before the trailing edge of the sheet passes through the nip portion to convey the sheet. To do. The reversing roller pair 23b repeats the above operation every time a sheet is fed.

Here, each roller pair 19a, 22a, 22
The driving states of b, 22c and 23b will be described. Until the leading edge of the sheet reaches the reversing roller pair 23b (the sheet is at the position T _{1 in} the figure), the heat roller pair 19a and the conveying vertical path roller pair 22a, 22 rotated by the common drive motor 35.
The sheets b and 22c are conveyed at a conveying speed corresponding to the type of sheet. Therefore, the desired fixing is surely performed over the entire area of the sheet, and wrinkles due to the discrepancy in the conveying speeds of the roller pairs occur.
No damage such as tearing.

Next, the leading end of the sheet is a pair of reversing rollers 23.
When it reaches b, the reversing roller pair 23b moves to the drive motor.
By transmitting the driving force from 37, the roller pairs 19a, 22a, 22
Rotates at a higher speed than b and 22c to carry the sheet. At this time (the sheet is at the position T _{2 in} the figure), the pair of conveying vertical path rollers 22a, 22b, 22c which are in contact with the sheet reach the rotational speed of the reversing roller pair 23b which rotates at a high speed by the action of the one-way clutch 36. It rotates at the driven speed. That is, the rotational speed of the roller pair 22a, 22b, 22c that rotates following the sheet conveyed by the reversing roller pair 23b is higher than that of the drive gears 22a1, 22b1, 22c1 that rotate by the transmission of the driving force from the drive motor 35. Since the rotational speed is higher than the rotational speed, the one-way clutch 36 becomes free and the drive force transmission from the drive motor 35 is cut off. Therefore, a drive motor for driving the roller pair 19a, 22a, 22b, 22c
Even if the drive speed is changed depending on the type of sheet, the drive motor 37 can drive the reversing roller pair 23b at a predetermined drive speed and timing. This does not require a special control method, and
The above-mentioned transport trouble does not occur.

[Other Embodiments] In the above-described embodiments, an example in which the present invention is applied to a color copying machine in which a sheet is held by a transfer drum has been described. However, the present invention is not limited to this and, for example, FIG. As shown, it may be applied to a color copying machine that holds a sheet by a transfer belt. still,
In the color copying machine shown in FIG. 3, members having the same functions and configurations as those of the above-described embodiment are designated by the same reference numerals.

Also in the color copying machine shown in FIG. 3, the distance L ₁ from the heat roller pair 19a of the fixing device 19 to the reversing roller pair 23b is set in the usable sheet conveying direction in the same manner as in the above-described embodiment. equal to the maximum length L _2, or it is set longer than and, and the roller pair 19a, with intervening one-way clutch to the power during transmission mechanism of the plurality of conveying roller pairs interposed between 23b the heat rollers 19a It is configured such that a plurality of conveyance roller pairs are driven by a common drive motor.

In this example, several sheets of the maximum length that can be used by the transfer belt 6a can be held, and more specifically, four A3 size sheets can be held. Therefore, the distance between the roller pair 19a and 23b is obtained by dividing the length of the outer circumference of the transfer belt by 4, that is, A
The length is set to be equal to or longer than the length of the three size sheets in the conveyance direction. Further, the color copying machine having the transfer belt has image forming means (comprising a photosensitive drum and process means acting thereon) Y for each color Y,
It has C, M and Bk.

Further, in the above-described embodiment, the conveying vertical path roller pair 22 interposed between the fixing device 19 and the reversing roller pair 23b.
Although the one-way clutch 36 is provided on all of the a, 22b and 22c, the present invention is not limited to this. For example, the leading end of the maximum usable sheet is fed to the reversing roller pair 23b. Sometimes, the one-way clutch does not have to be provided on the pair of conveying vertical path rollers that do not contact the sheet. With this, the same functions and effects as described above can be obtained.

In the above-described embodiment, a color copying machine is exemplified as an image forming apparatus capable of double-sided recording to which the present invention is applied, but the invention is not limited to this, and for example, a monochrome image forming a normal monochrome image or the like. The present invention can also be applied to other copying machines. The image forming apparatus capable of double-sided recording is not limited to the copying machine described above, but may be a laser beam printer, an LED printer, a facsimile machine, or the like.

[0037]

As described above, the fixing unit and the conveying unit on the downstream side in the sheet conveying direction are driven by a common drive source, so that the fixing unit can be used depending on the type of sheet used. The drive control of the apparatus itself is simplified because the drive control of the transporting means is performed only by changing the drive of the means. By simplifying this control, the inspection location at the time of sheet jam and the image recording time per sheet do not largely change depending on the type of sheet, and the operability of the apparatus is improved.

Further, since the distance from the fixing means to the reverse conveying means is set to be equal to or longer than the maximum length of the sheet to be used in the conveying direction, the conveying speed is faster than that of the fixing means. The fixing unit does not restrain the sheet conveyance by the reverse conveyance unit that rotates in the normal and reverse directions. That is, the sheet conveyance by the reversal conveyance means is performed after the image fixing over the entire area of the maximum length sheet is completed. Further, since the one-way clutch is interposed in the power transmission mechanism of the conveying unit interposed between the fixing unit and the reversing conveying unit, the sheet conveying by the reversing conveying unit is not restricted by the conveying unit. .

Further, with the above structure, it is possible to prevent the trouble of conveyance due to the disagreement of the conveyance speed between the roller pairs constituting the respective means.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of a color copying machine to which the present invention is applied.

FIG. 2 is a schematic plan view showing a sheet conveying system from a fixing device to a pair of reversing rollers.

FIG. 3 is a schematic sectional view showing a schematic configuration of another color copying machine to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Original 2 ... Original platen glass 3 ... Exposure lamp 4, 9b ... Lens 5 ... Full color sensor 6 ... Photosensitive drum 7 ... Pre-exposure lamp 8 ... Primary charger 9 ... Laser exposure optical system 9a ... Polygon mirror 9c ... Mirror 10 ... Potential sensors 11y, 11c, 11m, 11Bk ... Developing device 12 ... On-drum light amount detecting means 13 ... Transfer device 13a ... Transfer drum, transfer belt 13b ... Transfer charger 13c ... Adsorption charger 13d ... Adsorption roller 13e ... Inner charger 13f Outer charger 13g ... Carrying sheet 13h ... Separation charger 13i ... Fur brush 13j, 13l ... Backup brush 13k ... Oil removing rollers 13m, 15y, 15c, 15m, 15Bk ... Eccentric cam 13n ... Cam follower 14 ... Cleaning device 16 ... Sheet Cassette 17 ... Sheet transport system 18a ... Separation claw 18b ... Separation push-up roller 19 ... Fixer 19a ... Heat roller pair 19a1, 22a1, 22b1, 22c1, 23b1, 23b2 ... 20 ... Ejection tray 21 ... Transport path switching guide 22 ... Vertical path 22a, 22b, 22c ... Transport vertical path roller pair 23a ... Reverse path 23b ... Reverse roller pair 23c ... Horizontal path 24 ... Flapper 25 ... Intermediate tray 26 ... Stack tray section 27 … Gate 28… Sweeping roller 29… Pickup roller 30, 31… Retard roller 32, 33… Auxiliary feed roller 34… Paper feed path 35, 37… Drive motor 36… One-way clutch

Claims (5)

[Claims] 1. A first transporting unit for transporting a sheet, and a second transporting unit located downstream of the first transporting unit in the sheet transporting direction and transporting the sheet at a transporting speed higher than that of the first transporting unit. And interposed between the first transport means and the second transport means,
A third conveying means for conveying the sheet, and driving the third conveying means and the first conveying means with a common drive source by interposing a one-way clutch in the power transmission mechanism of the third conveying means. And the relationship between the distance L ₁ from the first transport means to the second transport means and the maximum length L ₂ of the usable sheet in the transport direction is L ₁ ≧ L
A sheet conveying device characterized by being set to ₂ . 2. The sheet conveying apparatus according to claim 1, wherein the third conveying unit is composed of a plurality of pairs of rotating bodies. 3. It is possible to record on both sides of a sheet
In an image forming apparatus, an image forming unit for forming an image according to image information, and a transfer unit for transferring the image formed by the image forming unit onto a sheet.
The transfer speed can be changed according to the copy means and the type of sheet used.
Yes, the image transferred by the transfer means is fixed on the sheet
And a fixing unit that is located downstream of the fixing unit in the sheet conveying direction.
Forward / reverse in which the sheet is conveyed at a higher conveyance speed than the fixing unit.
A rotatable reversing conveyance unit, and a sheet interposed between the fixing unit and the reversing conveyance unit.
A one-way clutch in the power transmission mechanism of the transport means.
Then, the conveying means and the fixing means are driven by a common drive source.
It is configured to be driven, and the drive from the fixing unit
Distance L to the transfer means₁And the transport of usable sheets
Direction maximum length L ₂Relationship with L₁≧ L₂So that
An image forming apparatus characterized by being set. 4. The image forming apparatus according to claim 3, wherein the conveying unit includes a plurality of pairs of rotating bodies. 5. The image forming apparatus according to claim 3, wherein the image forming apparatus is a multicolor image forming apparatus capable of recording a multicolor image of at least two colors on a sheet.