JPH02211462A - Image forming device - Google Patents

Abstract

PURPOSE:To relieve the strains accumulated in a transfer medium and superpose images always with high accuracy so that the high-quality images can be formed by releasing the press-contact force of an image carrier and the medium before image formation. CONSTITUTION:A transfer drum 7 as the transfer medium is connected by a gear mechanism, etc., to a photosensitive drum 1 of the image carrier and is rotated synchronously therewith. The drum 7 is mounted to one end of an arm 12 for driving and the other end is pivoted to a device body. The arm 12 is oscillated by turning of an eccentric cam 13 which comes into contact with the intermediate part thereof to allow switching of the drum 7 to the transfer operation section where the drum comes into contact with the drum 1 and the non-transfer operation position where the drum parts therefrom. The drum is moved to the non-transfer operation position at the time of a preparation operation mode, such as when the transfer medium is under idling, when the image transfer end or when the image forming device is reset, by which the strains in the thrust direction generated between the drums 1 and 7 are relieved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to an electrophotographic or electrostatic recording type image forming apparatus, and particularly to an image forming apparatus that forms an image on an image carrier by an image forming means.

The image is transferred to a transfer material support such as a transfer drum or a transfer belt, or a transfer material supported on a transfer medium such as a drum or belt-like intermediate transfer body, to obtain an image.2 For example, a color copying machine, etc. The present invention relates to an image forming apparatus such as the above.

Conventionally, for example, in a color electrophotographic copying machine, a drum-shaped electrophotographic photoreceptor (photosensitive drum) is used as an image carrier, and a drum-shaped transfer material support (transfer material support) is used as a transfer medium. A color image is obtained by overlappingly transferring an image (toner image) formed on a photosensitive drum to a transfer material on a transfer drum multiple times using a photosensitive drum.

During this multiple transfer, so-called "offset" may occur, in which a toner image already transferred onto the transfer material adheres to the photosensitive drum again during idle rotation of the transfer drum.

Therefore, in order to prevent such offset, the transfer drum has conventionally been placed in contact with or close to the photosensitive drum.
It is configured to be movable from a "transfer operating position" to a "non-transfer operating position" spaced apart from the photosensitive drum, and is configured to be movable during idling rotation of the transfer drum, that is, after the transfer process of one color is completed and the transfer process of the next color is started. Until this happens, the transfer drum is moved to a non-transfer operating position relative to the photosensitive drum.

In this specification, "idle rotation" of the transfer drum refers to the formation of an image of the next color during one rotation of the transfer drum due to, for example, switching of the developing device or returning the document reading optical means to the starting position. This refers to the transfer drum being rotated one more time because the preparation cannot be completed.

For example, if you use a transfer drum whose circumferential length on the surface of the transfer material support roughly corresponds to that of an A3 size transfer material,
When forming three-sized color images, the transfer drum is set to idle between the transfer steps of each color, so the four-color images (magenta image, cyan image, yellow image, and black image) are superimposed and transferred. In an image forming apparatus that obtains a full-color image, three idle rotations are required.

In addition, when forming an A4 size color image using a transfer drum in which the circumferential length of the surface of the transfer material support is set to approximately correspond to the length of the A3 size transfer material, the following color image transfer method is used. Since the A4 size transfer paper is not supported on the transfer drum until color image formation, preparations for the next color image formation can be made, so idle rotation is not required.
The transfer drum was always held in the transfer operating position.

When forming an A3 size image after forming an A4 size image multiple times in such a color electrophotographic copying machine, l! The optical drum and the transfer drum continue to rotate multiple times while being in pressure contact, and only after the A3 size magenta image is transferred, the pressure between the photosensitive drum and the transfer drum is released, and the transfer drum is brought to the non-transfer operating position. It will be done. Then, in order to transfer the cyan image of the original color during idle rotation, the transfer drum is again brought into pressure contact with the photosensitive drum and held at the transfer operation position.

The contact and separation operations at this time cause a slight positional shift between the photosensitive drum and the transfer drum in the long direction, resulting in a relative shift between the magenta image and the cyan image of the A3 image.

This relative misalignment has the problem of causing subtle color misalignment or changing the overall color tone.

Further, even in the first image when the transfer drum is separated from the photosensitive drum due to jam processing or the like, a relative shift occurs between the first color and the second color.

According to the results of the inventor's research experiments, these discrepancies are
It has been found that this is caused by the fact that when the photosensitive drum and transfer drum are rotated multiple times in a state in which they are in pressure contact, the transfer drum moves in the longitudinal direction relative to the photosensitive drum. Additionally, this amount of movement is determined by the backlash of the transfer drum, including the thrust play of bearings, and the rigidity of the transfer drum. Experiments have shown that if these amounts of movement exceed 30 IL, the hue of the copied image will be different from the original. I discovered that things look different.

The above-mentioned problems also apply to image forming apparatuses that use an intermediate transfer body as a transfer medium and transfer the image transferred onto the intermediate transfer body onto the transfer material again.

The present invention is based on this new knowledge.

An object of the present invention is to solve the above-mentioned problems, and by controlling the timing of movement of the transfer medium between the transfer operation position and the non-transfer operation position with respect to the image bearing member, the distance between the image bearing member and the transfer medium is improved. By releasing the fluctuating force in the thrust direction that occurs in the
An object of the present invention is to provide an image forming apparatus that can obtain high quality images.

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 including an image bearing member on which an image is formed by an image forming means, and a transfer medium for transferring the image formed on the image bearing member to a transfer material. The transfer medium is configured to be movable to a transfer operation position and a non-transfer operation position with respect to the image carrier, and is set before or after image formation on the image carrier by the image forming means. The image forming apparatus is moved to a non-transfer operating position at least in a preparatory operation mode.

The preparatory operation mode is set when the transfer medium is idle, when image transfer from the image carrier is completed, or when the image forming apparatus is reset.

Support 11 Next, the image forming apparatus according to the present invention will be explained in more detail with reference to the drawings.

The image forming apparatus of the present invention shown in FIG. 1 is a laser beam color electrophotographic copying machine, but the present invention is not limited to such an apparatus.

Referring to FIG. 1, in this embodiment, a drum-shaped electrophotographic photosensitive member, ie, a photosensitive drum 1, is used as an image carrier, and is supported rotatably in the direction of the arrow. On the other hand, around the photosensitive drum 1, there is a primary charger 4 for uniformly charging the photosensitive drum 1. Laser beam optical device that exposes and scans the photosensitive drum surface to form a latent image on the photosensitive drum! Image forming means is provided, which includes at least a rotary developing device I15 that develops a latent image on the photosensitive drum 1 into a toner image.

The rotary developing device 5 carries yellow, magenta, cyan, and black developing devices Y, M, and C1B, rotates each developing device in the direction of the arrow, and transfers the selected developing device to the photosensitive drum. 1, and the latent image on the photosensitive drum is visualized.

In this embodiment, a drum-shaped transfer material support (transfer drum) 7 is used as the transfer medium, and a transfer material 9 is held on the transfer drum 7. The transfer drum 7 is rotated by a drive motor 8 in synchronization with the photosensitive drum 1, and the transfer material 9 is supplied onto the transfer drum 7 at a timing from a supply section (not shown), and the transfer material 9 is supplied onto the transfer drum 7 at a timing. is maintained.

The transfer material 9 is conveyed to a transfer position facing the photosensitive drum 1 by the rotation of the photosensitive drum 1, and the toner image on the photosensitive drum 1 is transferred by the transfer charger IO. Transfer dotem 7
rotates by the required number of rotations while supporting the transfer material 9, and therefore images of the required number of colors are transferred onto the transfer material 9 in multiple layers.

On the other hand, the photosensitive drum 1 after the transfer is cleaned by a cleaning device! ll
The surface is then cleaned and the image forming cycle proceeds to the next image forming cycle.

Further, after the transfer material 9 has been transferred, the static electricity is removed by a static eliminator (not shown) or the like, and after it is separated from the transfer dot 7, it is sent to a fixing device (not shown) where it is fixed and discharged from the apparatus. .

The configuration and operation of the image forming means are well known to those skilled in the art, so further detailed explanation will be omitted.

Next, to further explain the operation of the transfer drum 7, the transfer drum 7 is connected to the photosensitive drum 1 by, for example, a gear drive transmission mechanism (not shown), and rotates in synchronization with the photosensitive drum 1. It has become. On the other hand, the rotation shaft 7a of the transfer drum 7 is attached to one end 12a of a driving arm 12, and the other end 12b of the driving arm 12 is pivotally supported by the main body of the apparatus. Furthermore, the drive arm 12 rotates the eccentric cam 13 that is in contact with the midway portion of the drive arm 12.
The transfer drum 7 is swung as shown by the arrow around the end portion 12b, and the transfer drum 7 is moved to the transfer operation position shown by the solid line in the figure, that is, the position where the transfer drum 7 contacts or approaches the photosensitive drum l, and two points. It is possible to switch to a non-transfer operating position indicated by a chain line, that is, a position where the transfer drum 7 is separated from the photosensitive drum 1.

The operation of the eccentric cam 13 is controlled by a drive motor 14.

The transfer drum 7 is configured to be separated from the photosensitive drum 1 within a range where the gears between the transfer drum 7 and the photosensitive drum 1 are not disengaged in the non-transfer operating position. Although the transfer material 9 continues to rotate synchronously, it is set so as not to come into contact with the photosensitive drum 1.

Also, it is detected at a position on the transfer drum 7 that is equal to the distance from the laser writing position (exposure position) on the photosensitive drum l to the transfer position! 115 is provided to detect that the leading edge of the transfer material 9 held on the transfer drum 7 is located at the position. That is, the laser beam optical device 2 has a detector 15
When the leading edge of the transfer material 9 is detected, the control means S, such as a CPU, operates at the appropriate timing to start writing an image onto the photosensitive drum 1. By adjusting the timing of starting image writing, the image transfer start position to be transferred onto the transfer material 9 is positioned at a predetermined position.

On the other hand, FIG. 2 shows the timing of switching the transfer drum 7 between the transfer operating position and the non-transfer operating position.

According to this embodiment, 1. When performing multiple transfers onto a transfer material 9 of, for example, A3 size, first, during the preparatory operation mode for initial setting performed before image formation of the first color, that is, the pre-rotation of the transfer drum 7. (1st rotation), move the transfer drum 7 once from the transfer operation position to the non-transfer operation position,
The force in the thrust direction applied to the transfer drum 7 is released.

Then, from the second rotation of the transfer drum 7, writing of the image of the first color is started. At this time, the transfer drum 7 completes its movement from the non-transfer operative position to the transfer operative position immediately before the start of image writing on the photosensitive drum 1.

After the first color transfer is completed, the image forming apparatus returns to the preparation mode 2.
The transfer drum 7 reaches the non-transfer operating position in the third rotation, and the transfer r ram performs one idle rotation. Then, the printer moves to the transfer operation position again and performs the second color transfer process.

In this way, by sequentially transferring four colors and setting a preparatory mode in between, a four-color full-color image of A3 size can be obtained.

FIG. 3 is a timing chart when forming an A4 size image. When obtaining a four-color full-color image, idle rotation of the transfer drum is not required, so there is no need to operate in the preparatory mode, and the first color The transfer drum 7 is maintained at the transfer operation position until the fourth color is transferred.
Before the formation of the first color image, a preparation mode is provided, so the transfer drum 7 is rotated once, and during that period, the transfer drum 7 is moved from the transfer operation position to the non-transfer operation position once, and the transfer drum 7 is released from the photosensitive drum 1. and then form an image.

In this way, even in image formation that does not require idle rotation, it is undesirable for the photosensitive drum and the transfer drum to continue rotating for a long time in the state S (transfer operation position) where they are in pressure contact, and the thrust that accumulates inside the transfer drum is undesirable. It is necessary to release distortion caused by directional force, etc.

It is preferable to release the pressure between the photosensitive drum and the transfer drum once during operation in the preparatory mode provided before image formation, thereby obtaining a higher quality image.

The movement of the transfer drum from the transfer operation position to the non-transfer operation position in the preparation mode, which is performed according to the present invention, or the strain release operation of the transfer drum, may be performed before image formation as described above, or may be performed after image formation is completed. You can.

The preparation mode can also be set during standby operation (warm-up operation) when the image forming apparatus is powered on, or when it is necessary to reset the main body for work such as jam removal (reset time).

In this embodiment, the cylindrical photosensitive drum 1 and the transfer drum 7 are used as the image carrier and the transfer material support, but belt-shaped ones can also be used, and a drum-shaped one can be used as the transfer medium. Alternatively, a belt-shaped intermediate transfer body can also be used.

Furthermore, although the above embodiments have been described with respect to a color electrophotographic copying machine, the present invention can also be applied to a machine that performs multiple transfers in a single color.
Moreover, it is also applicable to an LED liquid crystal shutter type device instead of a laser beam optical device. Furthermore, it can be similarly applied not to such a digital exposure method but to a normal analog exposure method.
It can be applied to various other image forming apparatuses.

The image forming apparatus according to the present invention is configured as follows:
Before image formation on the image carrier, the pressure between the image carrier and the transfer medium is released, and the transfer medium is once freed, thereby releasing the strain accumulated inside the transfer medium. Since the relative position between the transfer medium and the transfer medium is adjusted to a normal position, images can always be superimposed with high precision, and a high-quality image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of an image forming apparatus according to the present invention. FIGS. 2 and 3 are timing charts illustrating the image forming mode operated according to the present invention. 1: Image carrier 7: Transfer medium 9: Transfer material

Claims (1)

[Claims] 1) an image carrier on which an image is formed by an image forming means;
In an image forming apparatus including a transfer medium for transferring an image formed on the image carrier to a transfer material, the transfer medium is moved to a transfer operating position and a non-transfer operating position with respect to the image carrier. The image is configured to be movable, and is moved to a non-transfer operation position at least in a preparatory operation mode that is set before or after image formation on the image carrier by the image forming means. Forming device.