JPH02301790A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the offset to an image holding body of a toner image caused by pressure of a backup member, and the irregularities in a transfer image caused by ironing by constituting the backup member being a transfer auxiliary means so that press-contacting is started to a tapered part at the time of passing through a transfer position. CONSTITUTION:A transfer electrifier 24 is outputted in accordance with the moving timing of transfer paper and a movement of a connecting member 5c of a transfer drum, and a backup member 61 is pressed against a suction sheet 53. In this case, the member 5c moves to a transfer position by gripping the tip of the transfer paper by a gripper 51. Subsequently, when a tapered part E provided on the tip side of the transfer paper comes to the transfer position, the member 61 is moved, and moved to a prescribed position, while bumping the member 61 against the tapered part E. In this case, the tip of the member 61 hits against the tapered part E of the member 5c first, but it is extremely near the sheet 54 in the radial direction since the tapered part E is inclined, therefore, buckling of the member 61 is not generated. Also, an impact given to the member 53 is also small. In such a way, the offset and the irregularities in a transfer image can be prevented.

Description

Detailed Description of the Invention 1.1') The present invention forms a latent image on an image bearing member using an electrophotographic method or an electrostatic recording method, and converts the latent image into an IIf visual image using a developing means. , relates to an image forming apparatus that obtains an image by transferring the visible image to a transfer material using a transfer device, and in particular,
The present invention is suitably embodied in a multicolor image forming apparatus having a plurality of developing devices, which develops a latent image formed on an image carrier, and sequentially transfers the toner image onto a transfer material using a transfer device to obtain an image. It's something you get.

A variety of multicolor image forming apparatuses have been proposed and reprinted in the past, and FIG. 5 shows an example of a typical color electrophotographic copying machine.

In FIG. 5, the color electrophotographic copying machine forms a latent image on an image bearing member L, which is an electrophotographic photosensitive drum in this example, and transfers the latent image to a plurality of colors, for example, yellow, magenta, etc., which will be described in detail later. , cyan, and black developing devices 132 ~
A rotary developing device 13 equipped with a rotary developing device 134 forms a color toner image, and these toner images are superimposed and transferred onto a sheet-like transfer material such as paper attached to a drum-shaped transfer device 5 disposed close to the surface of the photosensitive drum 1. The configuration is such that a color image can be obtained.

As schematically shown in FIG. 6, the transfer device 5 used in such a color electrophotographic copying machine includes a pair of annular members, cylindrical members 5a and 5b in this example, arranged concentrically. Both were integrally connected by a connecting member 5C, and the entire circumference was covered with a transfer material support, that is, an adsorption sheet 53, usually made of a dielectric material such as a polyester sheet, to form a cylindrical shape. A transfer drum is used.

Further, a gripper 51 is disposed at an appropriate position on the outer surface of the connecting member 5C of the transfer drum 5, and grips the transfer material supplied in synchronization with the toner image on the photosensitive drum 1'', conveys it, and transfers it. Each time the toner image of each color is transferred to the transfer material at the transfer position where the charger 24 is placed, and the photosensitive drum 1 approaches, a color image is formed, and then the gripper 51 is released to separate the transfer material from the transfer drum. do. The separated transfer material is conveyed to the fixing means 30 by the conveying means 29. Conventionally, in the transfer drum 5, the suction sheet 53 is made uniform and the transfer nip is adjusted to improve the transfer efficiency. In order to push up the suction sheet 53 from the inside of the transfer drum 5 toward the photosensitive drum l in the vicinity of the transfer charger 24, as shown in FIGS. is provided. This backup member 61 is made of a flexible material such as Mylar, and applies appropriate pressure to the suction sheet 53.

Further, in such a color electrophotographic copying machine, since the toner image on the photosensitive drum is transferred for one color during one rotation of the transfer drum 5, the yellow image,
In order to transfer the four-color toner images of magenta, cyan, and black to the transfer material, the transfer drum 5 rotates at least four times.

However, depending on the size of the transfer material, after one color is transferred by one rotation of the transfer drum, the image forming process of the next color is not completed at the next rotation, and the transfer drum 5 rotates one more rotation. Then, the next color may be transferred during the next rotation. In other words, the transfer drum 5 performs one rotation for the transfer process and one idle rotation, and at least three rotations are required to complete the four-color transfer process.

During idle rotation without this transfer process, the toner image that has already been transferred to the transfer material comes into contact with the surface of the photosensitive drum 1 again, and this contact causes the toner image on the transfer material 2 to be transferred to the surface of the photosensitive drum. A problem occurred in that the transferred image was disturbed due to the toner being offset or the image flowing at the transfer nip. ``To solve this problem, it has been proposed to retract the backup member from the suction sheet during idle rotation.

However, there is another problem with regard to the pressure contact and withdrawal of this backup member from the suction seal I. This problem will be explained with reference to FIGS. 7 to 9.

7 to 9 show a portion of the transfer drum 5 where the connecting member 5C is present, the transfer charger 24, and the backup member 61.
FIG. 2 is an enlarged cross-sectional view of main parts showing the relative arrangement thereof.

Inside the transfer drum 5, adjacent to the transfer charger 24, a backup member 61 is arranged so as to be movable toward and away from the adsorption sheet 53.

In the transfer drum 5 having such a configuration, if the backup member 61 is already in pressure contact with the suction sheet 53 before the connecting member 5C reaches the transfer position where the transfer charger 24 is located (FIG. 7), When the connecting member 5C reaches the transfer position, the backup member 61 and the connecting member 5C collide,
This causes sudden braking to be applied to the transfer drum 5. This causes uneven rotation and vibration in the transfer drum 5,
This is not desirable as it causes image quality deterioration.

Furthermore, as shown in FIG. 8, when the backup member 61 is held in pressure contact with the connecting member 5C when the connecting member 5c is in the transfer position, the thickness S of the connecting member 5C decreases.
Because of the large amount, the bar 2-qua-7 member 61 buckles and a large impact is applied to the connecting member 5C, which also causes image quality deterioration.

Furthermore, as can be understood from FIG. 9, at the moment the connecting member 5C passes the transfer position, the connecting member 5C has a thickness S, and by the time the backup member 61 comes into contact with the suction sheet 53, the connecting member 5C has a thickness S. Since it takes time for the back-up member 53 to come into contact with the back-up member 53, the area indicated by reference numeral A near the connecting member 5C becomes a region. This has caused a problem in that the effect of the backup member 61 at the leading edge of the image cannot be expected, and transfer gaps occur at the leading edge of the image.

Therefore, it is an object of the present invention to prevent image quality deterioration such as uneven rotation of the transfer device, vibration (shock) caused by the backup member in the transfer device coming into contact with and separating from the transfer material support, and image quality deterioration such as missing transfer at the leading edge of the image. An object of the present invention is to provide an image forming apparatus that can obtain high-quality images.

-1 for -゛ The above object is achieved by an image forming apparatus according to the present invention.

To summarize, the present invention provides an image forming apparatus that obtains an image by forming a visible image on an image carrier and transferring the visible image to a transfer material using a transfer device, wherein the transfer device includes at least a pair of annular members, a connecting member that connects the annular members, a sheet-shaped transfer material support disposed on the outer surface of each of the members for holding a transfer material, and a sheet-shaped transfer material support located inside the transfer material support. and a backup member that urges the transfer material support toward the image carrier, and the downstream end of the connection member located on the leading edge side of the transfer material has a tapered cross-sectional shape, and at least the connection member The image forming apparatus is characterized in that when the tapered portion of the image forming apparatus reaches the transfer position, the backup member is brought into contact with the connecting member.

1 Next, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

FIG. 5 shows an embodiment of the present invention in a color electrophotographic copying machine. In the wooden embodiment, the photosensitive drum l constituting the image carrier is rotating in the direction of the arrow. Arranged around the photosensitive drum l are a charger 12, a rotary developing device i13 including developing devices 132 to 134, a transfer drum 5 constituting a transfer device, and a cleaning device 27. Image information signals color-separated by a laser optical system consisting of a polygon mirror 10 and a laser reflection mirror 11 are irradiated onto the photosensitive drum 1, and a latent image is formed on the photosensitive drum 1.

The latent image on the photosensitive drum 1 is developed into a visible toner image by a predetermined developing device placed at a developing position facing the photosensitive drum 1 as the rotary developing device rotates.

Transfer material 14 in cassette 15 (hereinafter referred to as transfer paper)
is sent out from the cassette (cassette) 15 by the paper feed roller 16, and then transferred to the second registration roller 17 and the second registration roller pair 1.
8 and is sent to the paper feed guide 19. The transfer paper is timed by the first and second registration rollers 17 and 18, its leading edge is gripped by the gripper 51 on the transfer drum 20, and the transfer paper is transferred to the adsorption charger 23 and the squeezing roller 2.
2, and is suction-held over the entire area by the transfer material support of the transfer drum 5'', that is, the suction sheet 53.

The transfer paper adsorbed on the adsorption sheet 53 is transferred to the transfer charger 24.
The toner image on the photosensitive drum 1'' is transferred by this process.

The transfer process is repeated for each color, and when the transfer is completed, the gripper 51 opens and the separation claw 28 moves the transfer means 2
Guided by 9. The transfer paper guided to the conveying means 29 is fixed by a fixing means 30 equipped with a pair of rollers, and then transferred to a tray 32.
-1- is discharged.

After the transfer process, the toner image remaining on the photosensitive drum 1''2 is cleaned by a cleaning device 27, and the photosensitive drum 1 is prepared for the next image formation. Also, the gripper 51 has a cam 21.25.
It is opened and closed at .

Furthermore, as shown in FIG. 1, a buffer member 61 is disposed close to the transfer charger 24 in order to even out the adsorption sheet 53 and to improve the transfer efficiency by blocking the transfer nip. . The backup member 61 is configured to push up the suction sheet 53 from inside the transfer drum 5 toward the photosensitive drum 1, and therefore, the backup member 6
1 is configured to be able to move toward and away from the suction sheet 53.

The specific structure will be explained next.

In FIGS. 3 and 4, a cam 97 is fixed on a shaft 94 fixed to the side plate 50 of the transfer drum 5, and a cam follower roller 68 is arranged to move along the circumferential surface of the cam 97. t will be done. The roller 68 is rotatably supported at one end of an arm 65, and the arm 65 is rotatably supported around a pivot 66 fixed to the side plate 50 of the transfer drum 5. This arm 65
One end side of the support stand 60 of the backup member 61 is connected to the other end side via a pivot 67, and one end side of the arm 62 is connected to the other end side of the support stand 60 via a pivot shaft 63. The other end of the arm 62 is rotatably attached to a pivot 64.

Therefore, the arm 65, the arm 62, and the support base 60 of the backup member 61 are a four-bar linkage mechanism with the pivots 64, 63, 67 and the pivot 66 as joints, and the arm 65 swings around the pivot 66 of the arm 65. The movement is arm 62
The oscillations about the pivot 64 are interlocked.

Furthermore, a torsion coil 69 for urging the roller 68 of the arm 65 in a direction that follows the circumferential surface of the cam 97 is suitably disposed, and the one end portion 65a of the arm 65 and the support base 60
A spring 99 is stretched between the one end side portion 60a and the
The support base 60 is rotated counterclockwise around a pivot 67, and receives the urging force of the support base 60 as a stopper of the arm 65.

In the above configuration, when the stepping motor (not shown) connected to the shaft 94 continues to rotate in the direction of the arrow in the figure,
The cam 97 rotates counterclockwise, as shown by the arrow in FIG. 3, and changes from the state shown in FIG. 3 to the state shown in FIG. 4. Here, the cam 97 is configured to move the backup member 61 away from contact, or from away to contact, every time it rotates about 1800 times.

Next, with the above configuration, control of the bar 2 cup member 61 at the transfer position will be explained with reference to FIGS. 1 and 2.

FIG. 2 shows a case where the size of the transfer paper on the transfer drum 5 is long in the direction of rotation, for example, A3 size paper, and preparation for image formation of the next color is completed within the period of one rotation of the transfer drum. This is an example of a timing chart for a case where this is not possible.

Therefore, in this case, one more idle rotation is performed in addition to the transfer process.

A charger 12 is used to form a first color yellow (Y) image.
Corona discharge is performed for a time depending on the paper size, and the surface of the photosensitive drum 1 is uniformly charged.

Then, a laser beam is irradiated according to the image information, and a latent image of a Y image is formed on the photosensitive drum 1.

At the developing position, a Y developing device whose movement has been completed in advance is waiting, and the developing drive is started to visualize the Y image. The development drive is started tz earlier than the leading edge of the image at the development position, taking into account the time tZ for the development sleeve to rise to a constant rotational speed.

At the transfer position, the transfer charger 24 is output in accordance with the movement timing of the transfer paper held on the transfer drum 5 and the movement of the transfer drum connecting member 5C, and the backup member 61
comes into pressure contact with the suction sheet 53.

Here, the contact timing of the backup member 61 is set to the first
This will be explained in detail based on the figures.

The connecting member 5C of the transfer drum 5 grips the leading edge of the transfer paper with the gripper 51 and moves to the transfer position. Then, when the tapered portion E provided on the downstream side of the connecting member 5C, that is, on the leading edge side of the transfer paper, reaches the transfer position, the backup member 61 is moved, and the tapered portion E of the connecting member 5c is moved.
The backup member 61 is moved to a predetermined position while abutting against the back-up member 61. At this time, the tip of the backup member 61 first hits the tapered part E of the connecting member 5c, but since the tapered part E is inclined, it is extremely close to the suction sheet 53 in the radial direction, so that the buckling of the backup member 61 is prevented. Does not occur. Furthermore, the impact on the connecting member 53 is very small and does not pose a problem.

At this time, even after the movement of the backup member 61 is completed, since the tapered portion E has a width of 6 mm, its tip is brought into pressure contact with the tip of the connecting member 5c. This allows the backup member 61 to come into contact with the suction sheet 53 from the leading end, thereby preventing the leading end of the image from being transferred.

As described above, the backup member 61 is attached to the suction sheet 53.
is in pressure contact and the transfer charger 24 is output, the transfer drum rotates once and the Y image is transferred to the transfer paper. After the transfer is completed, the backup member 61 is attached to the suction sheet 53.
It is placed in a standby state at a further distance.

Next, the rotary developing device 13 rotates and moves the M developing device to the developing position in preparation for developing a magenta (M) image. Although the transfer drum 5 is in its second rotation and the exposure has stopped, the charger 24 controls the surface potential of the photosensitive drum by corona discharge so that the toner image on the transfer paper is not electrically offset to the photosensitive drum. are doing.

When this idle rotation ends and the transfer drum starts its third rotation, the above process is repeated to transfer the M image onto the transfer paper.

By performing the above steps in the same manner for the cyan image and the black image, a four-color transfer image can be obtained.

Further, according to the present invention, it goes without saying that similar effects can be obtained even when no idle rotation is involved, that is, when A4 size transfer paper is used.

As described above, according to the image forming apparatus of the present invention, in the transfer device having the connecting member, the downstream end cross section (image leading edge side) is tapered, and the backup member serving as the transfer assisting means is used for transfer. Since the configuration is such that pressure contact starts with the tapered portion when passing through the position, it is possible to prevent the toner image from being offset to the image carrier due to the pressure of the backup member, and from flowing or scattering the transferred image due to rubbing. becomes possible,
Further, it has the advantage of preventing uneven rotation of the transfer device, vibrations and shocks near the connecting member, and also preventing the leading edge of the image from being transferred, thereby preventing deterioration of image quality and obtaining a high-quality image. Further, according to the present invention, it is possible to eliminate the need for the backup member to strain against the coupling member of the transfer device, so there is also the advantage that wear and buckling of the backup member can be minimized.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of main parts of an image carrier and a transfer device of an image forming apparatus according to the present invention, and illustrates the relationship between a connecting member and a backup member. FIG. 2 is an operation timing chart of the image forming apparatus according to the present invention. FIG. 3 and FIG. 4 are cross-sectional views showing the approach and separation mechanism of the backup member. FIG. 5 is a schematic diagram of a color electrophotographic copying machine which is an embodiment of the present invention. FIG. 6 is a perspective view of one embodiment of the transfer device. FIG. 7 to FIG. 9 are cross-sectional views of the main parts of a conventional transfer device, illustrating the operation of the transfer device. l: Image carrier 5: Transfer devices 5a, 5b: Annular member 5C: Connecting member 51 Nigeripper 53: Transfer material support

Claims (1)

[Claims] 1) In an image forming apparatus that obtains an image by forming a visible image on an image carrier and transferring the visible image to a transfer material using a transfer device, the transfer device includes at least a pair of annular members disposed in parallel. , a connecting member that connects the annular members; a sheet-shaped transfer material support disposed on the outer surface of each member for holding the transfer material; and a sheet-shaped transfer material support disposed inside the transfer material support and configured to hold the transfer material. a backup member that urges the support toward the image carrier, and the cross-sectional shape of the downstream end of the connecting member located on the leading edge side of the transfer material is tapered, and at least the tapered portion of the connecting member An image forming apparatus characterized in that the backup member is brought into contact with the connecting member when the backup member reaches the position.