JPH10177307A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image blur, etc., caused by shock occurring when a transfer guide is returned to an initial position by providing a fixing means fixing the transfer guide when the transfer guide is rocked by a specified amount by the stiffness of a sheet guided by the transfer guide. SOLUTION: A locking member 14 capable of rocking centering a hinge 14a provided on a device main body frame is arranged on a position corresponding to an engaging part 11c provided on the bottom part of the transfer guide 11. A torsion coil spring 15 is provided on the member 14, and the member 14 is always pressed in a direction shown by an arrow (a) by the pressing force of the spring 15. When the guide 11 rocks in a direction shown by an arrow (b) centering a hinge 11a against the pressing force of a pressing means 12 by the stiffness of the transfer sheet P having comparatively high stiffness such as a cardboard guided by an upper guide 13 and the transfer guide 11, supported between a pair of a resist roller 5 and carried a hook part 14b provided on the leading end of the member 14 is engaged with the engaging part 11c of the guide 11, and the guide 11 is fixed.

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 provided with a transfer device for electrostatically transferring a toner image formed on an image carrier to a sheet surface.

[0002]

2. Description of the Related Art Conventionally, in a general image forming apparatus such as an electrophotographic copying machine, a transfer apparatus for transferring a toner image formed on an image carrier to a transfer sheet such as paper is known.
2. Description of the Related Art An image forming apparatus including an electrostatic transfer type transfer device is known.

In the above-described image forming apparatus, as shown in FIG. 7, a surface of a photosensitive drum 1 serving as a uniformly charged image carrier is scanned by a laser exposure optical system (not shown) to form an electrostatic latent image. After the formation, the developing device 2 forms a toner image. On the other hand, the transfer sheet P fed out by the pickup roller 3 is conveyed to the registration roller pair 5 by the conveyance roller pair 4, and the registration roller pair 5 synchronizes with the rotation of the photosensitive drum 1 on which the toner image is formed. Is transferred to the image transfer portion T between the photosensitive drum 1 and the transfer charger 6 facing the photosensitive drum 1, and the toner image on the photosensitive drum 1 is transferred onto the transfer sheet P by the action of the transfer charger 6. Is transferred to

When an image is transferred, a transfer bias voltage is applied to the transfer charger 6, whereby a transfer electric field formed in an image transfer portion T between the photosensitive drum 1 and the transfer charger 6 causes The toner image on the photosensitive drum 1 is transferred to the transfer sheet P.

In the image transfer section T, the transfer sheet P on which the toner image has been transferred is separated from the surface of the photosensitive drum 1 by the separation charger 7, and is conveyed to the fixing device 10 via the conveyance belt 8 and the fixing guide 9. Then, the toner image transferred to the transfer sheet P is heated and pressurized, is permanently fixed, and is discharged outside the apparatus.

A transfer guide 11 for guiding the transfer sheet P conveyed by the pair of registration rollers 5 to the image transfer portion T is provided between the pair of registration rollers 5 and the photosensitive drum 1. The transfer guide 11 is configured to be swingable about a hinge 11a, and an urging means 12 constituted by a coil spring or the like is arranged at the bottom of the transfer guide 11. Then, the transfer gap G in which the leading end 11 b of the transfer guide 11 is appropriately separated from the surface of the photosensitive drum 1 by the urging means 12.
Is formed.

In the image transfer section T, it is particularly important to transfer the toner image on the photosensitive drum 1 onto the transfer sheet P without deterioration. As the deterioration of the toner image, there is a so-called scattering phenomenon in which a very small amount of toner scatters in the vicinity of a substantial image to lower the sharpness of the image.

It is known that this scattering phenomenon occurs remarkably when contact between the transfer sheet P and the photosensitive drum 1 is unstable, and a transfer gap between the photosensitive drum 1 and the transfer guide 11 is known. By making G as small as possible and stably bringing the transfer sheet P into contact with the photosensitive drum 1, the above-mentioned scattering phenomenon can be avoided.

However, in recent years, even in an image forming apparatus such as a copying machine, the transfer sheet P is not limited to a so-called plain paper of 100 g / mm ² or less, but is formed on a thick paper of about 200 g / mm ² to form an image. Demand is increasing for use on the cover. In such a transfer sheet P, since the rigidity is extremely high, not only the thickness, the transfer sheet P such as thick paper is transferred by the transfer guide 11 in which the transfer gap G is adjusted to be small in order to avoid the scattering phenomenon as described above. When the transfer sheet P is nipped between the photosensitive drum 1 and the transfer guide 11, when the transfer sheet P is conveyed, a large conveyance resistance is generated, the conveyance speed of the transfer sheet P changes, and an image transferred to the transfer sheet P is transferred. There is a possibility that so-called transfer blurring may occur.

Therefore, as shown in FIG.
Are arranged so as to be swingable about a hinge 11 a, and the leading end 11 b of the transfer guide 11 is
, The transfer gap G is appropriately changed according to the rigidity of the transfer sheet P, thereby preventing image deterioration at the time of transfer.

[0011]

However, in the above-mentioned conventional technique, when the transfer sheet P is a thick paper or the like, the rigidity of the transfer sheet P is used to swing the transfer guide 11 so that the transfer gap G is increased.
However, when the rear end of the transfer sheet P passes through the registration roller pair 5, the rigidity of the transfer sheet P does not act on the transfer guide 11, and the transfer guide 11 is Is applied to the transfer sheet P, and the rear end of the transfer sheet P is strongly pressed against the photosensitive drum 1 so that the transfer gap G becomes extremely small. Transfer failure such as image blurring may occur.

The present invention has been made to solve the above problems, and
The purpose is to fix the transfer guide that guides the sheet between the image carrier and the transfer charger until the image formation on the sheet is completely completed, so that the transfer guide returns to its initial position. It is an object of the present invention to provide an image forming apparatus that prevents transfer failure such as image blurring caused by the above.

[0013]

A typical configuration according to the present invention for achieving the above object is a swingable transfer guide for guiding a sheet between an image carrier and a transfer charger. A fixing means for fixing the transfer guide when the transfer guide swings by a predetermined amount due to the rigidity of a sheet guided by the transfer guide. Image forming apparatus.

Since the present invention is constructed as described above, the oscillating transfer guide is once fixed by a fixing means using a highly rigid sheet such as thick paper until all the image transfer to the sheet is completed. Even after the trailing edge of the sheet has passed through the pair of registration rollers, a predetermined transfer gap is ensured, and transfer failure such as image blurring can be prevented.

When the fixing means is supported via an impact buffering member, the impact when the transfer guide is fixed is absorbed by the impact buffering member and transmitted to the sheet without being transmitted to the sheet. Can be fixed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of an image forming apparatus according to the present invention will be specifically described with reference to the drawings. 1 to 3 are cross-sectional explanatory views showing the configuration of a first embodiment of the image forming apparatus according to the present invention.

In FIG. 1, reference numeral 1 denotes an electrophotographic photosensitive drum serving as an image carrier, which is rotationally driven by driving means (not shown). A primary charger (not shown) is disposed on the outer periphery of the photosensitive drum 1, and the surface of the photosensitive drum 1 is uniformly charged by the primary charger. Correspondingly, the surface of the photosensitive drum 1 is scanned with a laser beam to form a latent image.

A developing device 2 is arranged on the outer periphery of the photosensitive drum 1, and the developing device 2 controls the photosensitive drum 1.
A toner image is formed on the latent image formed on the surface. A transfer charger 6 is disposed at a position facing the photoconductor drum 1, and an image transfer unit T is configured between the photoconductor drum 1 and the transfer charger 6.

The transfer charger 6 is for transferring the toner image formed on the surface of the photosensitive drum 1 to the surface of the transfer sheet P conveyed to the image transfer section T. A transfer bias voltage is applied to the charging device 6, whereby a transfer electric field formed in the image transfer portion T between the photosensitive drum 1 and the transfer charger 6 causes the photosensitive drum 1 to move.
The upper toner image is transferred to the transfer sheet P.

A separation charger 7 is disposed adjacent to the transfer charger 6 and separates the transfer sheet P from the surface of the photosensitive drum 1 by the separation charger 7. In the image transfer section T, the transfer sheet P on which the toner image has been transferred is separated from the surface of the photosensitive drum 1 by the separation charger 7 and then on the transport belt 8 disposed downstream of the separation charger 7. And transported.

The transfer sheet P conveyed by the conveyance belt 8 is guided to a fixing device 10 by a fixing guide 9, where the toner image transferred to the transfer sheet P is heated and pressed by the fixing device 10. After being permanently fixed, it is discharged outside the machine.

On the other hand, a transfer sheet P made of paper, synthetic resin, or the like stored in a sheet cassette or a sheet deck is
After being fed out by the pickup roller 3, the sheet is separated and fed one by one by separation means (not shown), and is conveyed to the registration roller pair 5 by the conveyance roller pair 4.

The skew of the transfer sheet P is corrected before the registration roller pair 5, and the transfer sheet P waits. The registration roller pair 5 synchronizes the transfer sheet P with the rotation of the photosensitive drum 1 on which the toner image is formed. The sheet is nipped and conveyed to an image transfer section T between the photosensitive drum 1 and the transfer charger 6.

On the downstream side of the registration roller pair 5, an upper guide 13 fixed to the apparatus body frame is provided.
A transfer guide 11 is provided so as to be able to swing around a hinge 11a provided on the apparatus main body frame, and to transfer the transfer sheet P nipped and conveyed by the registration roller pair 5. The image is guided to the image transfer unit T.

An urging means 12 composed of a coil spring or the like is disposed at the bottom of the transfer guide 11, and the leading end 11b of the transfer guide 11 is appropriately separated from the surface of the photosensitive drum 1 by the urging means 12. A transfer gap G is formed. Then, the transfer guide is provided by the urging means 12.
The transfer gap G is appropriately changed in accordance with the rigidity of the transfer sheet P by urging the front end 11b of the transfer roller 11 toward the photosensitive drum 1, so that the image deterioration at the time of transfer such as the scattering phenomenon described above is prevented. Has become.

An engagement portion 11c is provided at the bottom of the transfer guide 11.
Is provided, and at a position corresponding to the engagement portion 11c,
A locking member 14 serving as fixing means is provided so as to be swingable about a hinge 14a provided on the apparatus body frame. The locking member 14 is provided with a torsion coil spring 15 as urging means, and the locking member 14 is constantly urged in the direction of arrow a in FIG. 1 by the urging force of the torsion coil spring 15.

With this construction, the transfer guide 11 is biased by the rigidity of the relatively rigid transfer sheet P, such as thick paper, which is guided by the upper guide 13 and the transfer guide 11 and conveyed while being nipped by the registration roller pair 5. As shown in FIG. 2, when the hinge 11a swings about the hinge 11a in the direction of arrow b in FIG. 2 by a predetermined amount against the urging force of the hinge 12, the tip of the locking member 14 is engaged with the engaging portion 11c of the transfer guide 11. The transfer guide 11 is locked and fixed by engagement of the hook portion 14b provided on the transfer guide 11.

Therefore, even after the rear end of the transfer sheet P having relatively high rigidity such as thick paper has passed through the pair of registration rollers 5, the transfer guide 11 is fixed in a state of swinging by a predetermined amount as shown in FIG. Therefore, as in the conventional example described above, the transfer guide
11 is not urged by the urging means 12 to rise to the initial position, and its impact is not transmitted to the transfer sheet P. Therefore, the rear end of the transfer sheet P is strongly pressed against the photosensitive drum 1. Therefore, there is no possibility that transfer failure such as image blurring due to extremely small transfer gap G will occur.

A solenoid 16 serving as a driving means is connected to the back surface of the locking member 14, and after the image is transferred to the transfer sheet P, the fixing of the toner image by the fixing device 10 is completed. After the skew of the succeeding transfer sheet P by the registration roller pair 5 is corrected, the solenoid 16 is turned on when the registration roller pair 5 starts to be driven to rotate when being conveyed toward the image transfer unit T, and the solenoid is turned on. 16, the locking member 14 is hinged against the biasing force of the torsion coil spring 15.
The hook portion 14b of the locking member 14 is disengaged from the engaging portion 11c of the transfer guide 11, and the transfer guide 11 is centered on the hinge 11a by the urging force of the urging means 12. Then, it swings in the direction of arrow d in FIG. 3 to return to the initial position.

After that, the solenoid 16 is turned off, and the locking member 14 is turned on the hinge 14 by the urging force of the torsion coil spring 15.
It swings in the direction of arrow a in FIG. 1 around a and returns to the initial position shown in FIG.

In this embodiment, after the toner image transferred to the transfer sheet P is fixed by the fixing device 10, and
Before the leading end of the succeeding transfer sheet P passes through the registration roller pair 5 and contacts the transfer guide 11, the transfer guide 11 is configured to return to the initial position shown in FIG. Is not transmitted to the transfer sheet P. Accordingly, there is no fear that the impact due to the transfer guide 11 returning to the initial position shown in FIG. 1 is transmitted to the transfer sheet P and transfer failure such as image blur occurs.
High quality image formation is possible.

Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. 4 and 5 are cross-sectional explanatory views showing the configuration of an image forming apparatus according to a second embodiment of the present invention, and FIG. 6 is a cross-sectional explanatory view showing a configuration in which the electromagnet of the second embodiment is supported by an impact buffer. . The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the present embodiment, as shown in FIG. 4, the transfer guide 11 is made of a magnetic material such as a metal part such as a gin coat.
An electromagnet 21, which is an adsorption means as a fixing means driven by a power supply (not shown), is fixed to the apparatus body frame. The electromagnet 21 is energized at a timing when an unillustrated electromagnetic clutch as a drive switching unit of the registration roller pair 5 is turned on.

Then, the transfer guide 11 is guided by the upper guide 13 and the transfer guide 11, and the transfer guide 11 is moved by the urging means 12 by the rigidity of a relatively rigid transfer sheet P such as thick paper which is nipped and conveyed by the registration roller pair 5. When the electromagnet swings by a predetermined amount in the direction of arrow b in FIG. 5 around the hinge 11a against the urging force,
A magnetic force acts on the transfer guide 11 made of a magnetic material to attract the transfer guide 11 against the urging force of the urging means 12, as shown in FIG. It is rocked and fixed in the direction of arrow b in FIG.

Thereafter, when the transfer sheet P reaches the fixing device 10, the electromagnet 21 is turned off by a detection signal of a sensor (not shown) provided at the discharge section, and the transfer guide 11 is moved around the hinge 11a by the urging force of the urging means 12. To return to the initial position shown in FIG. Other configurations are the same as those of the first embodiment, and similar effects can be obtained. Further, in the present embodiment, the number of components is small and the configuration is simple, so that the cost can be reduced.

In the case where the transfer guide 11 is sucked and sucked by the electromagnet 21 as in the present embodiment, if the shock at the time of sucking is transmitted to the transfer sheet P and image blurring may occur, As shown in FIG. 6, by supporting the electromagnet 21 via a spring member 22 such as a coil spring or a leaf spring as an impact buffering member, the spring member 22 absorbs an impact when the transfer guide 11 is attracted and attracted by the electromagnet 21. The shock is not transmitted to the transfer sheet P due to absorption, so that the occurrence of image blur can be prevented.

[0037]

Since the present invention has the above-described structure and operation, the transfer guide is fixed when the transfer guide swings by a predetermined amount by the fixing means. Even after the trailing edge of the sheet has passed through the pair of registration rollers, the transfer guide does not return to the initial position and is held in a state of swinging by the predetermined amount, thereby transmitting an impact to the sheet when the transfer guide returns to the initial position. It is possible to transfer an image without any problem, and it is possible to prevent transfer failure such as image blurring.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view illustrating a configuration of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory cross-sectional view illustrating a configuration of a first embodiment of the image forming apparatus according to the present invention.

FIG. 3 is an explanatory cross-sectional view illustrating a configuration of a first embodiment of the image forming apparatus according to the present invention.

FIG. 4 is an explanatory sectional view showing a configuration of a second embodiment of the image forming apparatus according to the present invention.

FIG. 5 is an explanatory sectional view showing a configuration of a second embodiment of the image forming apparatus according to the present invention.

FIG. 6 is an explanatory sectional view showing a configuration in which the electromagnet of the second embodiment is supported by an impact buffering member.

FIG. 7 is a diagram illustrating a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 2 ... Developing device, 3 ... Pickup roller, 4 ... Conveyor roller pair, 5 ... Registration roller pair, 6 ... Transfer charger, 7 ... Separation charger, 8 ... Conveyor belt, 9 ... Fixing guide, 10: fixing device, 11: transfer guide, 11a: hinge,
11b ... tip, 11c ... engaging part, 12 ... urging means, 13 ... upper guide, 14 ... locking member, 14a ... hinge, 15 ... torsion coil spring, 16 ... solenoid, 21 ... electromagnet, 22 ... spring member, G …
Transfer gap, P: transfer sheet, T: image transfer section

Claims (6)

[Claims] 1. An image forming apparatus in which a swingable transfer guide for guiding a sheet between an image carrier and a transfer charger is urged toward said image carrier by an urging means. An image forming apparatus, comprising: fixing means for fixing the transfer guide when it swings by a predetermined amount due to the rigidity of a sheet guided by the guide. 2. The fixing device according to claim 1, wherein the fixing unit includes: a locking member that is engaged with an engaging portion provided on the transfer guide to lock the transfer guide; and a driving unit that swings the locking member. The image forming apparatus according to claim 1, further comprising: 3. The image forming apparatus according to claim 1, wherein the fixing unit includes a suction unit that suctions the transfer guide. 4. An image forming apparatus according to claim 3, wherein said at least one suction means comprises an electromagnet which applies a magnetic force to a transfer guide made of a magnetic material to attract the transfer guide. 5. The image forming apparatus according to claim 3, wherein the fixing unit is configured to be supported via an impact buffering member. 6. The image forming apparatus according to claim 5, wherein the shock absorbing member is formed of a spring member.