JPH0540430A - Both-side printing device - Google Patents

Abstract

PURPOSE:To prevent faulty transfer from occurring in the case of transferring a toner image on a back surface side, and also to prevent paper jamming from being caused when a paper is rolled up to the side of a paper carrying roller which is set just behind a fixing device by the viscosity of melted toner with inexpensive constitution as to a paper carrying mechanism for a both-side printing device in which the paper is turned over and carried to the transfer part again after performing printing on the surface of the paper, and the toner image is transferred on the back surface side and fixed. CONSTITUTION:The paper carrying roller 28R which is set just behind the thermal fixing device is obtained by disposing plural roller parts 291-29n on the outer periphery of a roller shaft 25 at small intervals G, a paper guide 34 advances in each small interval G, and the sum total of the width RW of the roller parts 291-29n is made larger than the sum total of the interval G of the roller parts 291-29n so that at least equal to or above half of the paper width P may contact to the roller part 29R in the paper interposing area RP of the roller part 29R.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet in a double-sided printing apparatus in which after printing on the front surface of a sheet, the sheet is turned over and transferred to a transfer section again, and a toner image is transferred and fixed on the back side. Concerning the transport mechanism.

[0002]

2. Description of the Related Art FIG. 5 is a side view of a conventional double-sided printing apparatus. Reference numeral 1 denotes a photosensitive drum, on the outer periphery of which an exposure unit 2, a developing device 3, a transfer device 4, a cleaner 5, and a uniform charging device 6 are arranged in the counterclockwise order. When the photosensitive drum 1 reaches the exposure unit 2 after the entire width of the photosensitive drum 1 has been charged by the uniform charger 6, the exposure unit 2 is irradiated with the information light 8 reflected by the rotating mirror 7, so that the electrostatic latent image is generated. An image is formed. Toner is attached to the electrostatic latent image by the developing device 3, and the toner image is transferred to the sheet at the position of the transfer device 4, and then the cleaner 5 removes the residual toner and electric charge, and the uniform charging device 6 is again provided. Move to position.

On the other hand, when a sheet is fed from the sheet feeding section 9, it is transferred to the transfer unit 4 by the sheet conveying rollers 10 and 11. Transfer device 4
Consists of a transfer charger, and by corona discharge,
By applying an electric charge having a polarity opposite to that of the toner image to the paper, the toner image on the photosensitive drum 1 is attracted to the paper.

The sheet on which the toner image is transferred is transferred to the fixing device 13 by the suction and conveyance unit 12 and is heated and fixed. That is, since the roller 13a on the side of the photosensitive drum 1 is a heat roller having a built-in heater, when the paper on which the toner image is attached passes through the roller fixing device 13, the paper and the toner image are heated and the toner image is melted. The paper is soaked in the paper and fixed.

In the case of single-sided printing, the sheet on which the toner image is fixed is discharged to the sheet stacker via the sheet conveying roller 14 and the sheet discharging rollers 15 and 16. In the case of double-sided printing, the sheet is conveyed to the switchback roller 19 via the sheet conveying roller 14 immediately after the fixing device 13 and the rollers 17 and 18 of the sheet reversing unit.

The trailing edge of the paper is the roller 1 of the path switching unit.
When passing through 7 and 18, the switchback roller 19 and the rollers 17 and 20 of the traveling path switching unit reversely rotate, so that the paper is guided to the upper traveling path 24 by the rollers 17 and 20 of the traveling path switching unit, Guide rollers 21, 22,
The paper is fed backward at 23, and makes a U-turn, and is transported between the transfer device 4 and the photosensitive drum 1 by the paper transport roller 11. As the sheet moves backward and makes a U-turn in this manner, the sheet is supplied to the transfer portion in an upside down state.

When the back surface reaches the photosensitive drum 1 in this way, the toner image on the photosensitive drum 1 is transferred to the back surface of the paper. Then, the fixing device is attached via the adsorption and transport unit 12.
After being transferred to 13 and thermally fixed, it is ejected to the stacker via the sheet conveyance roller 14, the sheet conveyance roller 15 and the ejection roller 16 immediately after the fixing device.

By the way, in the conventional apparatus, there is a problem that the sheet is deformed when the sheet passes through the sheet conveying roller 14 immediately after the fixing device after being heated and fixed in the fixing device 13. Since this deformation is such a minute amount that it is inconspicuous, there is no particular problem in the case of single-sided printing. Moreover, when time passes, it returns to the original state. However, in the case of double-sided printing, since the front and back sides are immediately reversed and transferred to the transfer portion and transferred to the back surface, transfer failure occurs during back surface printing.

That is, when printing on the surface of the paper, the paper deformed by the paper transport roller 14 is guided to the backward running path 24 by the switchback roller 19 and the rollers 17, 20 of the running path switching unit as described above, and the U-turn is performed. Then, when the toner image is transferred from the photosensitive drum 1 to the transfer portion in an upside down state, the entire surface is deformed due to the deformation of the paper.
Can not be adhered to and there is a gap. As a result, the toner on the photosensitive drum is not reliably transferred onto the paper on the surface that cannot be in close contact, which causes image defects such as character blurring, transfer omission, and insufficient density.

In the case of the roller type transfer device, since the transfer roller presses the sheet against the photosensitive drum 1, no noticeable transfer failure occurs, but in the case of a corona discharge type transfer device in which no mechanical pressing force is generated. Will be a particular problem.

The deformation of the paper which causes such a transfer failure occurs when the hot paper immediately after being thermally fixed in the fixing device 13 is sandwiched by the paper conveying rollers 14. 6A and 6B are views showing a conventional sheet conveying roller, where FIG. 6A is a plan view and FIG. 6B is a side view. All the conventional paper transport rollers have a structure in which a metal shaft 25 is provided with a rubber roller 26 having a width W at a constant interval D.

As described above, in the conventional paper conveying roller, the area (W) where the rubber roller 26 exists and the area (D) where the rubber roller 26 does not exist.
Therefore, the area w where the pressure of the rubber roller 26 is applied and the area d where the pressure of the rubber roller 26 is not applied (hatched area) d are alternately generated on the sheet 27. In this way, there are regions where the rubber roller 26 receives pressure and regions where it does not. In particular, since the width W of the rubber roller 26 is small to save material, in the area d that does not contact the rubber roller 26 of the paper 27, Small deformations such as gentle waves on 27 are likely to occur.

Immediately after the heat fixing, the paper is heated and therefore easily deformed. Therefore, the sheet is deformed by the sheet conveying roller 14 immediately after the fixing device. Since the heat is dissipated when the sheet reaches the other sheet transport rollers, the other sheet transport rollers do not deform.

In order to solve such a problem, the inventors of the present invention describe in Japanese Patent Application No. 3- (91-7824):
By improving the paper transport roller immediately after the heat fixing device, we have proposed a means that can prevent transfer defects when transferring to the back side in a double-sided printing device.

FIG. 7 is a plan view and a side view illustrating this solution. 28 is a paper carrying roller, and this paper carrying roller 28 is applied only to the paper carrying roller immediately after the heat fixing device. That is, the pair of sheet conveying rollers 28, 28 that sandwich the sheet 27 and rotate include the roller shaft 25 and the roller portion 29 made of rubber or resin. The roller portion 29 is provided over the entire width P of the sheet. In addition, the outer diameter is the same over the entire length, and the entire front and back surfaces of the paper 27 are in contact with the roller portions 29, 29.

In this way, the roller portion 29 of the paper carrying roller 28
Since the entire surface of the sheet 27 contacts, the entire surface of the sheet 27 is sandwiched between the pair of roller portions 29, 29, and the entire surface is uniformly pressed by the roller portions 29, 29. As a result, it is possible to prevent the paper 27 from being deformed when passing through the paper transport roller 28 immediately after the heat fixing device, and it is possible to prevent transfer failure during back surface printing.

Further, the roller portion 29 is provided with a sheet conveying roller 28 having the same outer diameter over the entire length, and the peripheral speed of the roller portion 29 is
By configuring V1 to be faster than the peripheral speed V2 of the heat roller 13a of the fixing device, the tension T acts between the fixing device 13 and the roller portion 29 over the entire width of the sheet 27. That is, the difference in peripheral speed between the heat roller 13a and the roller portion 29 of the paper transport roller 28 causes the paper 27 to be pulled uniformly over the entire width, so that the deformation is less likely to occur and the paper generated by the heat fixing device is not easily deformed. Even minute deformations can be removed.

[0018]

However, in the structure in which the sheet conveying roller 28 having the roller portion 29 over the entire width of the sheet is provided immediately after the fixing device as described above, there is an advantage that the deformation of the sheet can be prevented, but at the time of fixing the sheet. The viscosity of the melted toner causes the paper 27 to stick to the paper transport roller 28, causing a new problem of causing paper jam.

That is, as shown in FIG. 7B, the fixing device
Separation claws 30 for preventing the paper sheet 27 from adhering to each other are provided at several positions on the outer circumferences of the heat roller 13a and the pressure roller portion 13b in the inside 13.

In the case of a toner image having a high print density, a large amount of toner adheres to the surface of the paper, so the paper is pressed between the rollers 13a and 13b of the fixing device, and then the toner image side due to the viscosity of the molten toner. The paper 27 adheres to the heat roller 13a, and the paper 27 moves in such a manner as to be rolled up on the heat roller 13a side. But,
As described above, since the rollers 13a and 13b of the fixing device are provided with the separation claw 30 for peeling off the sheet to be stuck, the sheet is not caught by the rollers 13a and 13b of the fixing device.

However, even when the paper passes through the paper carrying roller 28 immediately after passing through the fixing device, the heat of the fixing device heats the paper, so that the molten toner on the paper adheres to the surface of the paper carrying roller 28, and the paper is It may get caught in the paper transport roller 28 side and cause a paper jam. In the case of the fixing device 13,
Measures have been taken such as supplying release oil from the oil roller 31 so that the roller surface is not damaged even if the paper separating claw 30 is pressed against the rollers 13a and 13b by the spring force. Providing the separation claw 30 and the oil roller 31 is costly.

On the other hand, in the conventional paper conveying roller as shown in FIG. 6, as shown in FIG. 8, the paper guide 33 is arranged in the gap 32 between the separated rubber rollers 26. There is. For this reason, the leading edge of the paper 27 is fed to the paper guide before the paper 27 is rolled up on the rubber roller 26 side due to the viscosity of the molten toner.
Since it is scooped up by 33 and guided to the paper transport path 39, paper jam does not occur.

However, as mentioned above, the rubber roller
Since the area d not pressed by 26 is large, there is a problem that minute deformation occurs and transfer failure occurs when the toner image is transferred to the back surface side in the double-sided printing apparatus.

The technical problem of the present invention is to pay attention to such a problem, and in the double-sided printing apparatus, no transfer failure occurs when the toner image is transferred to the back side, and the paper is fixed by the viscosity of the molten toner. Immediately after being caught in the paper transport roller side,
The purpose is to prevent paper jams with an inexpensive structure.

[0025]

FIG. 1 is a plan view and a side view for explaining the basic principle of a double-sided printing apparatus according to the present invention.
The present invention combines the idea proposed by the inventors of the present invention to prevent the minute deformation of the sheet by providing the roller portion over the entire width of the sheet and the idea of scooping the leading edge of the sheet by the sheet guide in FIG.

That is, after printing on one side of the sheet 27, the sheet 27 is turned upside down and transferred to the transfer section again, and the toner image is transferred and fixed on the back side as well. Immediately after the sheet conveyance roller 28R, it is constituted by the roller shaft 25 and a roller portion 29R made of rubber or resin provided on the outer periphery thereof. However, the roller portion 29R is not a single roller 29 longer than the paper width P described above, but a plurality of roller portions 29 ₁ ... Guide 34 is entering.

In the paper holding region RP of the roller portion 29R, at least half of the paper width P is the roller portion 29R.
29n, the total width RW of the roller portions 29 ₁ ... 29n is larger than the total roller gap portion G.

According to a second aspect of the present invention, in the double-sided printing apparatus in which the fixing device has a heat roller fixing structure, a plurality of roller portions 29 ₁ ... Paper transport roller 28R with a large sum of ₁ ... 29n
Is provided immediately after the fixing device, and the paper transport roller 28
The peripheral speed V1 of the R roller portion 29R is relatively faster than the peripheral speed V2 of the heat roller 13a of the fixing device. It should be noted that this difference in peripheral speed is sufficient.

[0029]

The paper conveying roller 28R immediately after the fixing device of the present invention is
The roller portion 29R is not a single roller longer than the paper width P, but the roller portion 29R is composed of a plurality of roller portions 29 ₁ ... 29n. However, since the sum of the roller portions RW is larger than the sum of the roller gap portions G, at least the paper width P is at least More than half of them are sandwiched by the roller portions 29R and pressed. Therefore, by making the roller gap G as small as possible and making the roller portion 29R as large as possible,
Since most of the area of 27 can be sandwiched and pressed, minute deformation of the paper 27 is suppressed, and when transferring the toner image to the back surface of the paper, the same good transfer performance as on the front surface side can be obtained.

Further, at the interval G between the roller portions 29 ₁ ... 29 n,
Since the paper guide 34 has entered, even if the hot paper 27 transferred from the fixing device passes between the paper conveyance rollers 28R and 28R, the leading edge of the paper 27 is picked up by the paper guide 34, and the paper conveyance path You will be guided to 39. As a result, the sheet 27 does not wind around the sheet conveying roller 28R on the toner image side or cause a sheet jam.

Further, as in claim 2, the heat roller type fixing device 13 is used, and the roller gap G immediately after the fixing device is used.
The total number of roller parts RW is larger than the total number of
By making the peripheral speed V1 of R relatively faster than the peripheral speed V2 of the heat roller 13a of the fixing device, the tension T acts uniformly over the entire width of the paper 27, so that the deformation of the paper is more reliably prevented. be able to.

[0032]

EXAMPLES Next, examples of practical application of the double-sided printing apparatus according to the present invention will be described. FIG. 2 is a side view showing an embodiment of the double-sided printing device according to the present invention. 13
Is a heat roller type fixing device 13, and the transfer device 4 is a corona charger. In such a double-sided printing apparatus, a large number of sheet conveying rollers are used while the sheet is guided from the heat roller fixing device 13 through the backward path 24 to the transfer portion. 28R, 28R
Is provided only immediately after the heat roller type fixing device 13.
That is, the sheet becomes the hottest immediately after being ejected from the heat roller fixing device 13 and is likely to be deformed, and the other sheet conveying rollers are the same as those used conventionally.

FIG. 3 is a side view showing an embodiment of the sheet conveying mechanism immediately after the fixing device according to the present invention. The fixing device 13 shown is
The heat roller 13a and the pressure roller 13b are provided, and the separation claws 30 and 30 and the oil rollers 31 and 31 are arranged on the outer circumferences thereof.
Incidentally, 35 is a blade for removing toner, 36 is a felt for cleaning, 37 is a static elimination brush, and 38 is a thermistor for temperature detection.

Reference numeral 28R is a sheet conveying roller according to the present invention, and a roller portion 29R (consisting of a plurality of roller portions 29 ₁ ... 29n) made of rubber or synthetic resin is arranged on the outer periphery of the roller shaft 25. .. Then, as shown in FIG. 1, each roller unit 29 ₁
The total sum of the roller widths RW of the roller portions 29 ₁ ... 29n is larger than the total sum of the gaps G of 29n.

As shown in FIG. 1, since the roller gap G is actually very small, the total roller width RW is much larger than the total roller gap G. Therefore, it is possible to reliably prevent minute deformation of the sheet by the sheet conveying roller immediately after the fixing device, which is comparable to the case of the conveying roller having the single roller portion 29 over the sheet width P shown in FIG.

Further, the paper guide 34 enters into the space G between the roller portions 29 ₁ ... 29 n, and the fixing device 13 of the paper guide 34 is fixed.
The end on the side is open like a trumpet. A connecting rod 40 is welded to the back surface of each paper guide 34 (opposite side of the paper transport path 39), and is fixed to the apparatus frame via the connecting rod 40.

When the paper and the toner image are heated in the fixing device 13, water vapor is generated from the paper 27 and adheres to the paper guide to form a water drop, so that the paper 27 is adsorbed by the water drop on the paper guide and smoothly transported. There is a fear that it will not be done. On the other hand, in the present invention, the paper guide immediately after the fixing device 13 has a structure in which the round bar-shaped paper guide 34 is connected by the connecting rod 40, and the line contact with the paper 27 is made, so that the contact area becomes small. Water drops will not interfere with the transportation of the paper 27.

Next, as a fixing device in the printing apparatus, a heat roller type fixing device and a flash fixing device are known. A flash fixing device including a halogen lamp or the like is used in a high-speed printing device or the like, but heat is generated when the toner image is melted and fixed on the paper 27 by the flash fixing device. Similarly, the sheet 27 is deformed when passing through the sheet conveying roller immediately after the transfer device.

Therefore, according to the present invention, the roller gap G
By using a structure in which the paper conveying roller 28R having a plurality of roller portions 29 ₁ ... 29n having a longer roller portion RW is disposed immediately after the flash fixing device, the paper 27 is deformed even in the flash fixing type device. Can be prevented.

However, when the heat roller type fixing device 13 is used, the deformation of the paper can be prevented more reliably than in the case of the flash fixing device. That is, in the case of the heat roller type fixing device 13, the paper 27 is sandwiched between the heat roller 13a and the pressure roller 13b. Moreover, the entire width of the sheet 27 is sandwiched.

As shown in FIG. 3, the heat roller type fixing device 13 is used as the fixing device, and the peripheral speed V ₁ of the roller portion 29R of the paper conveying roller 28R immediately after the fixing device is the heat roller of the fixing device.
Since it is configured to be relatively faster than the peripheral velocity V _{2 of} 13a, the tension T is uniformly generated over the entire width of the sheet 27. As a result, the deformation of the paper 27 becomes even less likely to occur. The peripheral speed V ₁ of the roller portion 29R and the heat roller 13a
The peripheral speed difference with the peripheral speed V ₂ of V is small.

As the transfer device, a corona transfer system using a corona charger as shown in FIG. 2 and a bias roller transfer system are known, and each has its advantages and disadvantages. In the bias roller transfer method, a high voltage is applied to a metal roller shaft lined with conductive rubber or sponge, and the transfer roller presses the entire width of the paper against the photosensitive drum.
Even if the paper is slightly deformed by the paper conveying roller immediately after the fixing device, the transfer is performed with the deformation corrected. Therefore, the apparatus of the present invention is particularly effective for a corona transfer type double-sided printing apparatus.

The paper carrying roller 28R according to the present invention may be manufactured by the same method as that for manufacturing the paper carrying roller having the rubber rollers 26 at a constant interval. That is,
The outer circumference of the metal roller shaft 25 is lined with rubber or resin only in the areas of the roller portions 29 ₁ ... 29 n. Alternatively, it can be manufactured by a method of press-fitting a metal roller shaft 25 into a cylindrical roller portion 29 ₁ ... 29 n made of rubber or resin.

[0044] The pair of paper conveying rollers 28R, of 28R, if the one of the roller portions 29 ₁ ... 29n and an elastic material such as rubber, the roller portion of the other sheet conveying rollers 28R
29 ₁ ... 29 n are usually made of a relatively hard synthetic resin such as Delrin.

FIG. 4 shows the roller portion 29 ₁ ...
It is a partial cross section / plan view which shows the Example of the paper conveyance roller which comprised 29n. Each of the roller portions 29 ₁ ... 29 n has a cylindrical shape made of synthetic resin, and after inserting the metal roller shaft 25, the pin 42 is inserted into the through hole 41 formed in the roller shaft 25 and the roller portions 29 ₁ ... 29 n. It is fixed by inserting.

[0046]

As described above, according to the present invention, a plurality of roller portions 29 ₁ ... 29 n are arranged at a small interval G, and the paper guide 34 enters the small interval G between the rollers. Because
The paper 27 that has passed through the paper carrying roller 28R can be picked up and guided to the paper carrying path, and the paper 27 is viscous due to the viscosity of the melted toner image.
The problem that paper is caught in the paper transport roller 28R or paper jam occurs is solved. In addition, it can be realized at a lower cost than in the case where a separating claw is provided.

Further, in the paper sandwiching area RP of the roller portion 29R, the total sum of the roller portions 29 ₁ ... 29n is larger than the total sum of the small gap portions G, so that at least half or more of the paper width is the roller portion. Contact with 29R. As a result, the front and back of the paper 27 are pressed uniformly over a wide surface by the roller units 29 _{1 to} 29 n, so that minute deformation of the paper can be surely prevented, and after printing on the front surface side, when printing on the back surface, At least half or more of the surfaces are in close contact with the photosensitive drum to ensure reliable transfer, and the back surface of the paper can have the same good printing quality as the front surface side.

As in claim 2, a heat roller type fixing device 13
And the peripheral speed V1 of the roller portion 29R of the paper conveying roller 28R immediately after the fixing device is set to the peripheral speed of the heat roller 13a of the fixing device.
By making the speed relatively faster than V2, the tension uniformly acts on the entire width of the sheet 27, so that the deformation of the sheet can be prevented more reliably.

[Brief description of drawings]

FIG. 1 is a plan view and a side view illustrating a basic principle of a double-sided printing device according to the present invention.

FIG. 2 is a side view showing a double-sided printing device embodying the present invention.

FIG. 3 is a side view showing an embodiment of a sheet conveying mechanism immediately after a transfer device according to the present invention.

FIG. 4 is a partial cross-sectional / plan view showing an embodiment of a paper carrying roller according to the present invention.

FIG. 5 is a side view of a conventional double-sided printing device.

6A and 6B are a plan view and a side view showing a sheet conveying roller immediately after a conventional fixing device.

7A and 7B are a plan view and a side view showing a sheet transport mechanism immediately after the fixing device proposed previously.

FIG. 8 is a plan view and a side view showing a conventional paper guide.

[Explanation of symbols]

1 Photosensitive Drum 4 Transfer Device 13 Fixing Device 13a Heat Roller 13b Pressure Roller 14 Paper Conveying Roller 10,11,15,16,21,22,23 Immediately after the conventional fixing device Paper Conveying Roller 24 Reverse Runway 25 Roller Shaft 26 Rubber Roller 27 Paper 28 Paper transport roller 28R immediately after the fixing device proposed previously 28R Paper transport roller immediately after the fixing device according to the present invention 29R Roller portion 29 ₁ of the paper transport roller immediately after the fixing device of the present invention 29 ₁ ... 29n Roller portion RW Roller portion 29 ₁ ... 29n roller width G Each roller part 29 ₁ ... 29n (small) interval RP Paper nip area V ₁ Peripheral speed of roller part of paper conveying roller immediately after fixing device of the present invention V ₂ Peripheral speed of heat roller of fixing device 30 Separation Claw 31 Oil Roller 32 Rubber Roller Spacing 33 Conventional Paper Guide 34 Paper Guide According to the Present Invention 39 Paper Feed Path 40 Connecting Rod

Claims (2)

[Claims] 1. After printing on one side of the paper (27),
The paper (27) is turned upside down and transferred to the transfer section again,
In a double-sided printing device that also transfers and fixes the toner image on the back side, the paper transport roller (28R) immediately after the heat fixing device is
5) and the roller part made of rubber or resin provided around it
(29R), the roller portion (29R) has a plurality of roller portions (29 ₁ ... 29n) arranged at small intervals (G), and each small interval (G). The paper guide (34) has entered the paper, and the paper width in the paper nipping area (RP) of the roller (29R).
As above, at least half of (P) is in contact with the roller portion (29R), the width of the roller portion than the sum of the spacing portion of the roller portion _{(29 1 ... 29n) (G} ) (29 1 ... 29n) of (RW) A double-sided printing device characterized by a larger total sum. 2. The invention according to claim 1, wherein the fixing device has a heat roller fixing structure, and the sheet conveying roller (2
The peripheral speed of the roller section (29R) of (8R) is
A double-sided printing device characterized by being configured to be relatively faster than the peripheral speed of a).