JPS62100777A - Image forming device - Google Patents

Abstract

PURPOSE:To suppress toner offset in respective transfer process of a multi- transfer system by slightly separating a transfer material carrying means from an image carrier when a transfer material is opposed to an image carrier carrying no toner image. CONSTITUTION:A solenoid 520 is connected to the other side of a coupling plate 516 through a tension spring 519. When the solenoid 520 is turned on, a transfer drum 5 is separated from a photosensitive drum 1 against the force of springs 517, 517' and the moving distance of the drum 5 is adjusted by stoppers 521, 521'. The separated distance is set up so that a photosensitive drum gear 524 is not disengaged from a transfer drum gear 523 and synchronous rotation is always maintained between both the drums 1 and 5. Sequence control is executed so that the solenoid 520 is turned off and the drum 1 is pressed against the drum 5 at the transfer of a toner image on the drum 1, and at the time of non-transfer, the solenoid 520 is turned on and the drum 1 is separated from the drum 5.

Description

DETAILED DESCRIPTION OF THE INVENTION Product No. 1) The present invention provides a method for holding a transfer material on an endlessly rotating transfer material supporting means such as a drum or an endless belt.

By applying a transfer electric field to the transfer material, a plurality of toner images sequentially formed on an image bearing member L such as a photosensitive drum or an insulating drum are sequentially superimposed and transferred onto the transfer material. The image forming apparatus according to the present invention is applicable to, for example, a color electrophotographic copying machine, a color printer with a computer output section, and other various color printing apparatuses. is embodied in.

Although the invention is described herein in connection with a color electrophotographic reproduction apparatus, the invention is not limited thereto.

``Rainbow'' L Technique Conventionally, as in an electrophotographic image forming apparatus, especially a color electrophotographic copying apparatus, a method of obtaining a color image by superimposing and transferring multiple color toner images onto the same transfer material is: jS5v4
A color copying apparatus having the configuration shown in FIG.

To briefly explain such a color copying apparatus with reference to FIG. 5, the photosensitive drum 1, which is an image carrier, rotates in the direction of the arrow.
A corona discharger 2, a tip optical system 3, a developing device 14, a transfer material carrying means 5, which is a transfer drum, and a cleaner 6 are arranged around it. The optical system 3 is rXX constant scanning 3
a and a color separation filter part 3b. The developing device 4 is a rotary developing device that integrally includes a yellow developing device 4Y having yellow toner, a magenta developing device 4M having magenta toner, a cyan developing device 4C having cyan toner, and a black developing device 4B having black toner. Each developing device is held by a support 4a and rotated about a central shaft 4b to change the developing device to the developing position.On the other hand, the transfer drum 5 can be better understood by referring also to FIG. The cylinder 5a and the transfer corona discharge provided inside the cylinder 5a: I! 5b. The cylinder 5a has a peripheral opening 5c stretched with a transfer material holding sheet 5d made of a sheet such as a film or screen mesh, and the cylinder has a plurality of grippers 5e for gripping the transfer material as described later. are provided in the longitudinal direction.

To form a full-color image, first, a color-separated electrostatic latent image is formed on the photosensitive drum 1, and then developed by the yellow developer 4Y. On the other hand, the transfer drum 5 grips the leading edge of the transfer material P fed from the paper feeder 7 with a gripper 5e, wraps the transfer material around a supporting sheet) 5d, and then uses a transfer corona discharger 5b to grip the transfer material P on the photosensitive drum l- Next, the toner image of L is transferred onto the transfer material, and the transfer material is electrostatically attracted to the Y1 holding sheet.
A green color-separated latent image is formed and developed by a magenta developing device 4M, and the resulting toner image is transferred to the transfer material A in alignment with the previously transferred toner image. Similarly, red color separation latent image formation, development by cyan developer 4C, and transfer,
Furthermore, a latent image is formed by exposure to white light.

Development and transfer are performed by the black developing device 4B. When the transfer of the four-color toner image is completed, the transfer material is separated from the transfer drum 5 by the separating means 8 and discharged to the tray 10 via the heat roller fixing device 9. .

FIG. 7 shows an example of a time sequence of the color electrophotographic copying apparatus in which the diameter of the photosensitive drum 1 is 80 mm and the diameter of the transfer drum 5 is 160 mm (that is, the diameter of the photosensitive drum: the diameter of the transfer drum is 1=2). , which shows the image exposure time and the transfer charging time by the transfer corona discharger with respect to the rotational speed of the photosensitive drum and the transfer drum for the case where the size of the transfer material is A4 and A3, respectively. Note that the transfer charging is turned on and off in Fig. 7 to make it easier to understand the timing of transfer depending on the size of the transfer material.
Although it is indicated to be turned off, it is not necessary to turn it off.

As can be seen from the on/off timings of image exposure and transfer charging shown in FIG. 7, when making an A3 size full color copy, the image exposure interval is at least one rotation of the transfer drum. This requires time for the original scanning optical system to return to the starting position after scanning, or travel time for replacing the developer, and it is not possible to copy A3 size transfer material at the same transfer drum rotation speed as A4 size. In this case, one rotation of the transfer drum is required. That is, after the first color toner image is transferred until the two color toner images are transferred, after the second color toner image is transferred and until the three color toner images are transferred, and the third color toner image is transferred. After the color toner images are transferred and until the four color toner images are transferred, a step is required in which the transfer material comes into contact with a photosensitive drum on which no toner images are formed.

In this way, when the transfer material contacts the photosensitive drum 1 due to idle rotation of the transfer drum 5, the toner that has already been transferred to the transfer material adheres to the photosensitive drum (offset phenomenon), resulting in unevenness in the full-color image written. The image quality of A3 size copies is lower than that of A4.
It was significantly inferior in size.

It is thought that the offset phenomenon as shown in , L occurs due to the effects of mechanical adhesion force and electrostatic adhesion force with the photosensitive drum due to an increase in the number of times the toner on the transfer material contacts the photosensitive drum.

Therefore, the first objective of the present invention is to eliminate the above-mentioned problems, and in particular, to prevent toner offset between each transfer step in multi-hair transfer in a color image forming apparatus. An object of the present invention is to provide an image forming apparatus that can obtain high-quality images.

Eight l　U　　　　 The above object is achieved by an image forming apparatus according to the present invention.

In summary, the present invention applies a transfer electric field to a transfer material carried on a transfer material carrying means, and transfers toner images sequentially formed on an image carrier onto the transfer material in a superimposed manner. In an image forming apparatus that forms a visible image on a transfer material, the toner images are transferred to a transfer material during each transfer process, and when the transfer material faces an image carrier that does not carry a toner image. The image forming apparatus is characterized in that the transfer material carrying means moves synchronously with the image carrier and is slightly separated from the image carrier.

The image forming apparatus according to the present invention will now be described in more detail with reference to the drawings.The present invention can be suitably embodied in a color copying apparatus as shown in FIG. The description will be given assuming that the invention is also applied to such a copying apparatus.

In FIG. 1 shown in red, one embodiment of the present invention shows a photosensitive drum l.
Various electrophotographic means are arranged around the color copying apparatus shown in FIG. It is shown.

In this embodiment, the transfer material carrying means is a transfer drum 5 similar to that shown in the drawings, and has a cylinder 5a, and the cylinder 5a has a transfer material carrying sheet (5d) in the peripheral opening area 5C.
is stretched, and a plurality of grippers 5e are provided in the longitudinal direction.

As best illustrated in FIG. 2, grooves 5f are formed at both ends of the cylinder 5a of the transfer drum 5, and rollers 511.51 supported by side plates 514.514' are provided in the grooves 5f.
2.513; 511', 512', 513'' are in contact,
Thereby, the transfer drum 5 is rotatably supported. Further, the transfer drum 5 is pressed against the photosensitive drum l via abutment members 522 and 522' made of elastic bodies provided on the outer peripheral surface of both ends of the cylinder 5a, so that the transfer drum 5 is pressed against the photosensitive drum l. The integrated transfer drum gear 523 meshes with the photosensitive drum gear 524, and the external drive source M
The driving force is transmitted from the photosensitive drum l which is driven as shown in FIG.

In FIG. 1, a side plate 514 supporting the rollers 511, 512, 513 has an arm 514a projecting outward, and the arm 514a is rotatably supported on a fixed shaft 515. Therefore, the transfer drum 5 is allowed to swing around the shaft 515.

Further, a lever 514b protruding outward is provided at a portion of the side plate 514 that is substantially diametrically opposed to the arm 514a.

Further, the side plate 514' is also formed in the same manner as the side plate 514, and the levers 514b and 514b' of both side plates are connected by a plate 516. The connecting plate 516 has tension springs 517 and 517' connected to one side thereof, and pushes the transfer drum 5 toward the photosensitive drum L side and presses the transfer drum 5 toward the photosensitive drum 1 with an appropriate pressing force. I'm guessing. In addition, stoppers 518 and 518' are provided to restrict movement of the connecting plate 516 so that excessive pressing force is not applied between both drums. A solenoid 520 is connected to the other side of the connecting plate 516 via a tension spring 519. When the solenoid 520 is energized, that is, turned on, the transfer drum 5 is moved by the spring 5.
It is separated from the photosensitive drum 1 against the force of 17.517', and its movement is adjusted by stoppers 521.521'. This separation distance is set to such an extent that the photosensitive drum gear 524 and the transfer drum gear 523 are not disengaged from each other, so that the driving force from the photosensitive drum 1 to the transfer drum 5 is continuously transmitted. Thereby, synchronous rotation is always maintained between the photosensitive drum and the transfer drum.

In the configuration described in 1-, when transferring the toner image on the photosensitive drum l-, the solenoid is turned off and the photosensitive drum and the transfer drum are in pressure contact, and when the transfer material is not transferred, that is, when the transfer material is facing the photosensitive drum, the solenoid is turned off. Inside, sequence control is performed so that the solenoid is turned on and the photosensitive drum and transfer drum are separated. The timing of this contact/separation is set at the end of the toner image transfer between each transfer process in order to prevent latent images or uneven development caused by shocks generated on the photosensitive drum during contact/separation or uneven rotation due to fluctuations in driving torque. The design is such that the solenoid is then turned on to separate the transfer drum, and immediately after the idle rotation of the transfer drum 5 ends and the trailing edge of the transfer material leaves the transfer area, the solenoid is turned off and the transfer drum is brought into contact with the photosensitive drum. is preferred.

It is preferable that this separation distance be at least 0.1 mm or more in order to obtain the effect of preventing offset. By providing such a small separation distance, the transfer material held on the transfer drum and the photosensitive drum are not in contact with each other. Even if the two are in contact with each other, the contact pressure between the two becomes weaker, and the effect of offset prevention I can be obtained. In order to obtain a more reliable effect, it is necessary to increase the separation distance, but it is 0.5 to 1
.

A sufficient effect can be obtained if the amount is about 0 mm. Moreover, if the separation distance is one time, even if general gears are used as the photosensitive drum gear 524 and the transfer drum gear 523, it is easy to drive the gears to rotate synchronously while maintaining their meshing state.

Incidentally, the multi-hair transfer rate can be increased by turning off the transfer charging during the time period when the idle Matsunai photosensitive drum and the transfer drum are separated from each other. That is, if the transfer charging is turned on and charging is continued even while the idling Matsunai photosensitive drum and the transfer drum are separated, the charge J is multiplied on the transfer material carrying sheet, approaching the saturated state jE, and the two colors 11 and onwards. Since it becomes difficult to further charge the transfer material carrying sheet during transfer charging, development occurs in which the multi-hair transfer rate of two colors [1 and subsequent colors] is low.

As a countermeasure to this problem, by turning off the transfer belt in the idle rotation direction, it is possible to reduce charge accumulation on the transfer material carrying sheet and improve the multi-hair transfer rate.

Another embodiment of the invention is shown in FIGS. 3 and 4. In this embodiment, the transfer drum 5 is connected to the photosensitive drum l.
The contact/separation action of A is the developing unit;! It is synchronized with the rotational movement of I4.

The transfer drum 5A has substantially the same structure as the transfer drum 5 described in connection with FIGS. 1 and 2, except that the side plate 51
4, and rotatably roller 52 is formed on the roller 8-514b.
5 is provided, and the roller 525 is urged by a spring 527 so as to come into contact with the photosensitive drum l with an appropriate pressing force.

In the rotary developing device 4 of the color copying machine shown in FIG. 4, each developing device 2!14Y, 4M, and 4C14B is set at the developing position only during development. (In FIG. 3, the developing device 4Y is located at the developing position).

Rotating developing bag in this example? '14 is a guide plate 526 on the side of the rotary support base 4a that supports these four developing units.
is attached to the guide plate 526, and the transfer drum 5 is attached to the guide plate 526.
The rollers 525 come into contact with each other.

There is a groove 526 on the outer periphery of the guide plate 526 into which the roller 525 falls.
There are a total of four locations a between each developing device, and when each developing device is set at the developing position, the rollers 525 are placed in the groove 5 of the guide plate.
The transfer drum 5 is configured to fall into contact with the photosensitive drum 1 at 26a.

Also, if the developing device is not in the developing position as shown in Figure 4,
That is, at the standby position of the developing device 4 in the free rotation pin where the transfer material faces the photosensitive drum in the non-image area, the roller 525 comes off the groove 526a and hits a portion of the outer periphery of the guide plate 526 other than the groove. The rollers 525 are pressed outward, and the transfer drum 5 is moved away from the photosensitive drum l by the shaft 51.
Rotate around 5.

Although two embodiments regarding the Ja #'P stage of the photosensitive drum 1 and the transfer drum 5 have been described above, those skilled in the art will be able to conceive of various other embodiments.

In addition to the photosensitive drum, the image carrier may be a belt provided with a photosensitive member, and the first stage for carrying the transfer material may be a transfer belt that holds and conveys the transfer material outside the transfer drum, and performs the transfer. It is also possible to set it as T.

The image forming apparatus configured as described above is capable of retaining the image on the transfer material even if there is an idling process in which the transfer material faces the image carrier in the non-image area where the toner image is not transferred during multi-hair transfer. The phenomenon of toner offset to the photosensitive drum can be prevented or suppressed.
As a result, a good image without uneven transfer or loss of density can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a transfer device portion of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view taken along 1ll-1 in FIG. 1. FIG. 2 is an explanatory diagram of the structure of a photosensitive drum in the axial direction. FIG. 3 is a schematic cross-sectional view showing a transfer device and a developing device according to another embodiment of the image forming bag according to the present invention, and shows a state in which the photosensitive drum and the transfer drum are in contact with each other. FIG. 4 is a schematic cross-sectional view showing the image forming apparatus according to the present invention similar to FIG. 3, and shows a state in which the photosensitive drum and the transfer drum are separated from each other. FIG. 5 is a sectional view illustrating the main parts of a conventional color electrophotographic copying apparatus. FIG. 6 is a perspective view showing the relationship between the photosensitive drum and the transfer drum of the apparatus shown in FIG. FIG. 7 is an explanatory diagram showing a part of the timing chart of the color copying apparatus shown in FIG. l: Photosensitive drum (image carrier) 2: Corona discharger, 3: Exposure optical system 4: Developing device 5: Transfer drum (transfer material carrying means) 5a Rainbow cylinder 520: Solenoid 525: Roller 526: Guide plate

Claims (1)

[Claims] 1) An image forming apparatus that applies a transfer electric field to a transfer material carried on a transfer material carrying means, and transfers toner images sequentially formed on an image carrier onto the transfer material in a superimposed manner to form a visible image. In the step of transferring each toner image to a transfer material, and when the transfer material faces an image carrier that does not carry a toner image, the transfer material carrying means is synchronized with the image carrier. An image forming apparatus characterized by moving slightly away from an image carrier.