JPH0552494B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multicolor image forming apparatus, and more particularly, the present invention relates to a multicolor image forming apparatus, and more particularly, to an image bearing member in which a toner visible image based on a formed latent image is sequentially formed in different colors. The present invention relates to a multicolor image forming apparatus in which images of the respective colors are superimposed on the surface of a rotating transfer material or an intermediate transfer member to form a multicolor image.

In general, a multicolor image forming apparatus, for example, a so-called color copying apparatus called a multi-transfer type copying apparatus, uses a filter to expose an original to color separation, forms an electrostatic latent image for each color on a photoreceptor, and then It is known as a method in which a multicolor image is obtained by developing the image with a developer having a complementary color relationship with those filters, and then sequentially transferring each color onto a transfer material supported on a transfer drum or belt, one on top of the other. ing. Generally, the filters are of blue, green, and red, and the developers are of yellow, magenta, and cyan.

Here, we will explain the outline of a color copying machine using electrophotography as an example. Color separation exposure is performed by scanning an optical system such as a mirror back and forth with respect to the original on the original table, and A drum-shaped body and transfer drum are generally used. In the case of multiple transfer, the rotation speed ratio of the photosensitive drum and transfer drum is 1:1 to align the images.
They are rotatably synchronously interlocked by mechanical means such as gears so that n (n is an integer). In addition, the transfer drum is placed in contact with the photosensitive drum in the generatrix direction or with a minute gap approximately equivalent to the thickness of the transfer material, and the corresponding points of the photosensitive drum and the transfer drum are always aligned at the contact position. There seems to be no misalignment.

As described above, the transfer drum rotates one or two times to obtain a one-color image, depending on the diameter of both drums and the size of the transfer material, and generally the rotation of the transfer drum and photosensitive drum is relative to the size of the transfer material. Generally, the closer the number ratio, that is, the ratio of circumferential lengths (>1) is to 1, the more the transfer drum and photosensitive drum need to rotate twice for each image. The reason for this is that there is always a demand for each drum to have a diameter as small as practical, and the optical system that exposes the original is usually constructed as a type that moves with respect to a stationary original. In this case, the optical system scans in synchronization with the photosensitive drum during forward movement, then shifts to backward movement after exposure, and must return to the starting position by the time the leading edge of the image on the photosensitive drum is at a predetermined position. .

Therefore, in order to make the optical system move forward and backward during one rotation of the photosensitive drum, it is necessary to increase the backward movement speed of the optical system from the viewpoint of reducing the size of the photosensitive drum. There is a limit to such speed increase, and if the photosensitive drum is made smaller, it will be difficult to leave room for the optical system to move back and forth during one rotation of the photosensitive drum, and eventually the photosensitive drum will have to move back and forth to the optical system. This is because it is common to provide a total of two rotations, one rotation for exposing the original image according to the image exposure, and one rotation for synchronizing the timing with the return movement of the optical system regardless of the image exposure. Furthermore, it will be understood that when the ratio of the photosensitive drum to the transfer drum is 1:2, the photosensitive drum only needs to rotate once, but the transfer drum needs to rotate twice.

Now, as described above, the photosensitive drum or the transfer drum simply returns the device to its initial position ( In order to return the optical system to its initial position, rotation is performed between the formation of multiple images of each color. (between these), the toner transferred to the transfer material on the transfer drum may adhere to the photosensitive drum again, a so-called offset phenomenon. When this occurs, when multiple colors are layered, the hue changes to the desired color. This will lead to the problem of not being able to obtain a copy of the file.

The present invention has been made in view of the above circumstances,
The purpose of this is to prevent the above-mentioned offset, and when each drum that does not contribute to transfer rotates, the transfer drum (if an intermediate transfer body is provided) is separated from the photosensitive drum. This is to prevent offset.

The gist of the present invention to achieve these objects is that, in the first invention, a multicolor toner image formed on an image carrier is carried on a transfer material carrier at a transfer position for each color. In a multicolor image forming apparatus that performs multiple transfer onto a transfer material, the toner image transferred to the transfer material passes through the transfer position after the first toner image is transferred and before the second toner image is transferred. In a second aspect of the present invention, there is provided a multicolor image forming apparatus characterized in that when the image bearing member and the transfer material supported on the transfer material bearing member are separated from each other, when the image bearing member is In a multicolor image forming apparatus that multiple-transfers multicolor toner images to an intermediate transfer member at a transfer position for each transfer, and transfers the multicolor images transferred to the intermediate transfer member to a transfer material, the image bearing When the toner image transferred to the intermediate transfer body passes through the transfer position after the first toner image is transferred from the body to the intermediate transfer body and before the second toner image is transferred, the image bearing The multicolor image forming apparatus is characterized in that the intermediate transfer body and the intermediate transfer body are separated from each other.

The present invention will be described below with reference to the drawings as an embodiment in which the present invention is applied to an electrophotographic color copying apparatus in which the circumferential length ratio of a transfer drum, which is a transfer material carrier that holds a transfer material to a photosensitive drum, is set to 2:1. .

Figure 1 is a side view of the copying device, Figure 2 is a top view in the depth direction of the transfer drum, Figures 3 and 6 are side views of the vicinity of the transfer drum, and Figure 4 is the image surface of the photosensitive drum and transfer drum. The diagram showing the relationship, FIG. 5, is a sequence diagram.

In FIGS. 1 and 2, reference numeral 1 denotes an electrophotographic photosensitive drum having an insulating layer on its surface, which is rotatably supported by a shaft 2, and starts rotating in the direction of arrow 3 in response to a copy command. When the drum 1 rotates to the normal position, the original O placed on the original platen glass 4 is illuminated by an illumination lamp 6 integrated with the first scanning mirror 5, and the reflected light is transmitted to the second scanning mirror 7. is scanned. The first scanning mirror 5 and the second scanning mirror 7 are 1:
By moving at a speed ratio of 1/2, the document O and lens 8
The document is scanned while the optical path length is always kept constant. The reflected light image passes through a lens 8 and a third mirror 9, and then is color separated by a color separation filter 10, and is further color-separated by a fourth mirror 11 and a dust-proof sealing glass 1.
2, and is imaged onto the drum 1 at the exposure section 13.

After the drum 1 is neutralized by the static eliminator 14 and then charged (for example, positive) by the primary charger 15,
In the exposure section 13, the image illuminated by the illumination lamp 6 is subjected to slit exposure. At the same time, AC or primary static electricity removal with a polarity opposite to that of the primary (for example, negative) is performed using a static eliminator 16, and then a high-contrast electrostatic latent image is formed on the drum 1 by full-surface exposure using a full-face exposure lamp 17.

The electrostatic latent image on the photosensitive drum 1 is then developed into a toner image by a developing device 18. Developing device 18
is yellow 181, magenta 182, cyan 18
The developing device is composed of three developing devices (3), and a designated developing device works in accordance with the color separation filter used for exposure to obtain a toner image of the required color.

On the other hand, the transfer paper 201 in the cassette 191 is fed into the machine by the paper feed roller 211, and the first register roller 221 takes rough timing, then the second register roller 23 takes precise timing, and the leading edge is the gripper 24 of the transfer drum 33
is grasped by. The details of the transfer drum will be described later, but as the transfer drum 33 rotates, it is transported while being wrapped around the drum 33, and is transferred to the transfer charger 25.
The transfer position where the photosensitive drum 1 faces the transfer paper 2
01 passes, the toner image on the photosensitive drum 1 is transferred onto the transfer paper. The transfer drum 33 rotates at a required number of rotations while gripping the leading edge of the transfer paper 201 with the gripper 24, and images of the required number of colors are transferred.

The copying apparatus shown in the figure is equipped with two cassettes loaded with transfer papers of different sizes and types, and these papers are fed selectively.

After the transfer is completed, the transfer material is released from the gripper 24 at a separation position 56, separated by the action of the separation claws 26, and guided to the conveyor belt 27. The image is further guided to a pair of fixing rollers 28 and 29, where it is fixed by pressure and heat, and then discharged onto a tray 30.
After the transfer, the surface of the photosensitive drum 1 is cleaned by a cleaning device 31 composed of an elastic blade.
It's time to move on to the next cycle.

Reference numerals 41 and 42 denote the front and rear side plates (both ends of the shaft) of the transfer drum 33, which are connected by a stay (not shown) to form a frame. Swing plates 44 and 45 are provided along the inner sides of the front and rear side plates 41 and 42 to support the shaft 43 of the transfer drum 33, and are swingable about a shaft 46 eccentric to the transfer drum shaft 43. It is configured. This rocking plate 44, 4
5 is rotated counterclockwise around the first shaft 46 by its own weight (or biased by a spring, etc.), and the photosensitive drum 1
The transfer drum 33 is swung to the side to press the transfer drum 33 against the photosensitive drum 1.

The entire body including the transfer drum, ie, the transfer device 32, is composed of the front and rear side plates, etc. described above.
By movably supporting it on a rail (not shown) provided on the main body of the copying apparatus, it can be pulled out to the operation side (the front side in FIG. 1). In this case, the swing plates 44, 45 and the transfer drum 33 are It is preferable that the drum be separated from the photosensitive drum 1 by a cam mechanism (not shown) or the like so that both drums are not damaged. Further, the photosensitive drum 1 and the transfer drum 33 in this example have a gear 10 on the back side.
1 and 301, and both drums mechanically rotate in synchronization, thereby ensuring two rotations of the transfer drum for each rotation of the photosensitive drum described above.

Furthermore, spacer rubber 302 that comes into contact with the photosensitive drum is provided at both ends of the transfer drum 33 to ensure backlash of the gear, thereby also reducing the gap between the photosensitive drum 1 and the screen 303 that electrostatically supports the transfer paper 201. Set. The gap D is preferably 0 to (transfer paper thickness) for reasons such as preventing image blurring. This means that the transfer paper 201 is transferred to the photosensitive drum 1 by the screen 303 as shown in FIG.
means to be forced upon.

In this example, the rotation of the photosensitive drum 1 and the transfer drum 33 and the image position relationship are as follows. In other words, in Figures 4 and 5, half size (A4,
B4, etc.) images are formed on a portion of both the A and B sides of the photosensitive drum, and full-size images (A3, etc.)
The image is formed on either side A or B of the photosensitive drum. This is because when the photosensitive drum 1 is full-sized, the reciprocating movement of the first and second mirrors cannot be completed within half a rotation of the photosensitive drum 1 because the scanning length becomes long. In this case, it may be possible to make the photosensitive drum even larger, but as mentioned above, this is not common sense in practice.

Now, as is already clear from the relationship of the usable area of the photosensitive drum 1 when the target is full-size transfer paper, the above means that the transfer drum 33 needs two Rotation means that, for example, the transfer paper on which the image on side A has been transferred comes into contact with side B even though it is not necessary. It has already been mentioned that this causes offset. Therefore, in this embodiment, the transfer drum 33 is connected to the front and rear side plates 41 and 4 via the eccentric shaft 46.
2, the photosensitive drum 1 is supported so as to be able to swing between contact and separation, and is normally brought into contact with the photosensitive drum by its own weight (or biasing force from a spring, etc.), and furthermore, the following separation method is provided. The configuration of the drive mechanism eliminates the above drawback by separating the transfer drum 33 from the photosensitive drum when the toner image transferred to the transfer material passes through the transfer position between the transfer steps. There are some characteristics that make it so.

To explain the configuration of the drive mechanism that separates the transfer drum 33 from the photosensitive drum 1, cam followers 49, 50 are installed on the swing plates 44, 45 by shafts 47, 48, and the front and rear side plates 4
A cam shaft 51 is rotatably installed at 1 and 42, and cams 52 and 53 are installed at positions relative to the cam followers 49 and 50 in the longitudinal direction. An electromagnetic clutch 54 is attached to the rear end of the camshaft 51.
is fixed, and drive from the main body side is transmitted to the camshaft 51 through the gear 55 via the electromagnetic clutch 54. The electromagnetic clutch 54 is the fifth
As shown in the figure, the cams 52 and 53 are connected to the cam follower 4.
9 and 50, it operates only when changing from the contact state to the non-contact state and from the non-contact state to the contact state, therefore, a half-turn clutch may be used instead of the electromagnetic clutch. The cam followers 49 and 50 are pushed by the half rotation of the cams 52 and 53, and the rocking plate 4
4 and 45 rotate clockwise in FIG. 1 about a shaft 46 and move away from the photosensitive drum 1. In this example, the separation amount (movement amount) d (see Figure 6) is gear 101, 3.
It must be less than twice the height of the tooth end of 01. This is because, as mentioned above, the photosensitive drum 1 and the transfer drum 33 are meshed with gears 101 and 301 for image alignment (to prevent color misregistration), and if they are separated by more than the above amount, the coupling will be broken and not only will the drive not be transmitted, but the This is because the alignment will be out of order. Usually half of the tooth end height (0.5mm for module 1)
It is enough. However, if the surface potential of the photosensitive drum 1 is close to 0, the distance d may be less than the above value, and if it is high, the distance d may be increased depending on the degree.

If the final image is separated by the separating claw 26 immediately after the transfer is completed, it is not necessary to separate the transfer drum at the sixth rotation in FIG. (The part indicated by a box in FIG. 5) Due to the separation drive mechanism for the transfer drum 33 as described above, the distance between the photosensitive drum 1 and the transfer drum 33 (strictly speaking, the transfer paper supported on the transfer drum) is , when transfer is necessary, they are in contact with each other, and on the other hand, when the toner image transferred to the transfer material in a process other than the transfer process passes through the transfer position, they are separated, and the surface of the photosensitive drum is covered by the transferred toner. This effectively prevents staining and makes it possible to obtain clear multicolor images.

In addition to the above-described type in which the transfer paper is supported on the transfer drum and brought into direct contact with the photosensitive drum, various modifications of the present invention can be considered. The present invention can also be applied to a multicolor image forming apparatus that transfers multiple color images and then finally transfers the multicolor images onto a transfer material.

FIG. 7 shows an embodiment of such a type, and to describe its structure, in FIG. a shaft 51 of the roller 50;
A spring 54 is installed. As a result, the intermediate roller 50 is pressed against the photosensitive drum 1 at the transfer position. The intermediate roller 50 has a surface made of a conductive material (such as rubber) 502 and a core made of an insulating material 501, to which a voltage is applied by a bias device 55. As a result, the toner image on the photosensitive drum 1 is transferred to the intermediate roller 50. After the required number of toners are transferred to the intermediate roller 50, the transfer charger 57 transfers the toner onto the transfer material sent from the guide 56 all at once. After the transfer, the transfer material is separated by a separation charger 58 and sent to a fixing device 60 by a conveyor 59. The rest of the structure of the copying apparatus is the same as that shown in FIG. 1, and illustrations except for the photosensitive drum 1 are omitted.

The intermediate roller 50 is separated from the photosensitive drum 1 by a cam 61. That is, when the toner image transferred to the intermediate roller 50 passes through the transfer position in a process other than the transfer process from the photosensitive drum 1 to the intermediate roller 50, the cam 61 is rotated and the lever 52 is moved against the spring 54 as shown in the figure. The spacing is effected by rotating it counterclockwise.

In the case of this embodiment, there is no need to consider the timing of separating the transfer material, so there is no need to separate the intermediate roller 50 after the last image is transferred to the intermediate roller 50.

In each of the above embodiments, a cam mechanism is used as the separation drive mechanism, but it goes without saying that this may be replaced with other mechanical mechanisms, electromagnetic means, etc. This can be done by adjusting the timing of transfer and non-transfer, and it goes without saying that the photoreceptor, transfer drum, etc. may be of a belt type.

As described above, according to the present invention, in a multi-transfer type multicolor image forming apparatus, it is possible to reliably eliminate the phenomenon of offset of transferred toner to a photoreceptor, and its usefulness is great. .

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and FIG. 1 is a longitudinal sectional front view of an electrophotographic color copying apparatus to which the present invention is applied, FIG. 2 is a side view of the transfer drum portion, and FIGS. 3 and 6. 4 is a diagram showing the positional relationship between the photosensitive drum and the transfer drum, FIG. 4 is a diagram showing the image area on the photosensitive drum, and FIG. 5 is a sequence diagram showing the timing relationship when the transfer drum contacts and separates from the photosensitive drum. FIG. 7 is a schematic diagram showing an embodiment in which an intermediate transfer body is used. DESCRIPTION OF SYMBOLS 1... Photosensitive drum, 2... Axis, 4... Original table glass, 5... First scanning mirror, 6... Illumination lamp, 7... Second scanning mirror, 8... Lens, 9...
... Third mirror, 11 ... Fourth mirror, 12 ... Dust-proof sealed glass, 13 ... Exposure section, 14 ... Static eliminator, 15 ... Primary charger, 16 ... Static eliminator, 17
...Full exposure lamp, 18...Developer, 23...
Second register roller, 24... Gripper, 25...
... Transfer charger, 26 ... Separation claw, 27 ... Conveyance belt, 28, 29 ... Fixing roller, 30 ... Tray, 31 ... Cleaning device, 32 ... Transfer device, 33 ... Transfer drum, 41, 42... Front and rear side plates, 43... Shaft, 44, 45... Rocking plate, 46...
... shaft, 47, 48 ... shaft, 49, 50 ... cam follower, 51 ... cam shaft, 52, 53 ... cam,
54... Electromagnetic clutch, 55... Gear, 101,
301...gear, 191...cassette, 201...
... Transfer paper, 211 ... Paper feed roller, 221 ... First register roller, 302 ... Spacer rubber, 3
03...Screen.

Claims (1)

[Scope of Claims] 1. In a multicolor image forming apparatus that transfers multicolor toner images formed on an image carrier in a multiple manner to a transfer material carried on a transfer material carrier at a transfer position for each color, a first When the toner image transferred to the transfer material passes through the transfer position after the toner image is transferred and before the second toner image is transferred, the transfer carried by the image carrier and the transfer material carrier A multicolor image forming apparatus characterized by separating the material from the material. 2 Multicolor image formation in which a multicolor toner image formed on an image carrier is multiple-transferred to an intermediate transfer member at a transfer position for each transfer, and the multicolor image transferred to this intermediate transfer member is transferred to a transfer material. In the apparatus, after the first toner image is transferred from the image carrier to the intermediate transfer member and before the second toner image is transferred, the toner image transferred to the intermediate transfer member passes through the transfer position. A multicolor image forming apparatus characterized in that, when the image bearing member and the intermediate transfer member are separated from each other.