JP3120853B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to a driving structure of a transfer medium.

(Prior Art) Generally, in an image forming apparatus such as a copying machine or a printer, an electrostatic latent image corresponding to a document image is formed on a photoreceptor, and visible processing is performed by developing the electrostatic latent image. Then, the visible image is electrostatically transferred to a recording medium such as paper to obtain a copy.

By the way, instead of performing the transfer of the visible image to the transfer paper in the above-described image forming process, a transfer medium such as a transfer belt close to the photoconductor is provided, and the visible image is temporarily transferred to the transfer medium. There is an image forming process.

That is, in the above-described image forming process, in the case of single-sided copying on a recording medium, the visible image on the photoconductor is electrostatically transferred to the recording medium as it is, and in the case of double-sided copying on the recording medium, the first time. The visible image formed on the photoreceptor is transferred to a transfer medium provided as an intermediate transfer member, and a second image is formed on the photoreceptor after the transfer, and the copy paper fed The first image is transferred from the transfer medium and the second image is transferred from the photoconductor at the same time, so that it is not necessary to reversely feed the recording medium. (For example, Japanese Patent Application No. 63-35883 (JP-A-1-209471)).

For this reason, the transfer medium for feeding the recording medium and transferring the visible image is driven by, for example, the structure shown in FIG.

That is, in the structure shown in FIG. 7, a transfer belt made of a dielectric material is used as a transfer medium, and the transfer belt A is transported in a recording medium conveying direction (shown by an arrow in the figure), which will be described later. Direction), and is wound around a pair of rollers B and C arranged along the same direction.

Then, one of the rollers B and C, that is, the belt surface corresponding to the side forming the conveyance path of the recording medium E facing the photoconductor D, and the upper belt surface in FIG. In other words, a drive motor F is connected to the pulley B located on the downstream side in the transport direction, and the drive motor F causes the transfer belt A to direct the transfer surface of the recording medium E to a fixing device (not shown). Have to be moved. In the drawing, reference numeral G denotes a bias roller which is capable of switching charging characteristics and is capable of coming and going to and from the transfer belt A in order to set a bias when transferring the first and second visible images formed. , And the symbol H indicates a registration roller.

(Problems to be Solved by the Invention) By the way, in the above-described transfer medium driving structure,
Since the transfer belt is driven by positioning the drive motor on the downstream side in the transport direction of the recording medium E, the following problem occurs.

That is, the recording medium transport surface of the transfer belt A is
As shown in FIG. 8, the roller B on the driving side receives a considerably large tension (F ₁ ). On the other hand, the recording medium E carried on the transfer belt E receives a sliding resistance (F ₂ ) due to the contact with the bias roller G and the registration roller H and the contact with the transport guide member (not shown).

Therefore, when a visible image is transferred while the recording medium E is in opposition to the photoconductor D, the recording medium E moves in a conveying path having a different action direction from the tension (F ₁ ) acting on the transfer belt A. By receiving the action of the resistance (F ₂ ), the transfer belt A
The movement which always tends to deviate from the above occurs.

For this reason, the visible image located between the transfer belt A and the recording medium E moves from the transfer position with the transfer belt A to the fixing device, which is the next step, in a very unstable state. Depending on the properties of the recording medium, specifically, the paper quality and size of the copy paper as the recording medium, and in the case of full color formed by combining three primary colors or a selected color of any of a plurality of colors, so-called multi-color In the case where the amount of toner adhesion such as color is large and the developing layer is thick, a problem occurs in which the image is displaced, rubbed or further blurred due to the influence of shearing due to the difference in the direction of the acting force.

Further, as the above-described transfer medium, an elastic belt having high transfer efficiency, low cost, and easy to obtain high reliability, for example, 10 ⁻⁸ to
When a medium-resistance rubber belt of about 10 ^-11 Ωcm is used, there is a problem that vibration and pulsation are easily generated due to the mechanical rigidity of the belt itself, and it is difficult to transfer a visible image accurately.

Therefore, an object of the present invention is to improve the transfer efficiency and to prevent the occurrence of transfer unevenness and the omission of the transferred image, and to improve the uniformity in view of the above-mentioned problems in the image forming apparatus using the transfer medium in addition to the conventional recording medium. It is an object of the present invention to obtain a low-cost image forming apparatus capable of performing a smooth transfer.

(Means for Solving the Problems) To achieve this object, the present invention provides an optical writing means for writing an image on a writing target as a normal image or a mirror image,
A rotatable photoreceptor to be written, developing means for visualizing the electrostatic latent image written on the photoreceptor by the optical writing means as a primary toner image, and a photoconductor; A belt as an intermediate transfer member set so as to allow the transfer paper as a recording medium to pass through the opposing position, and a secondary toner image formed on the belt by transferring the primary toner image to the transfer paper. An image forming apparatus having a secondary toner image transfer unit for transferring the toner image onto the transfer paper, using a transfer structure having a bias roll capable of coming in contact with and separating from the transfer paper as the secondary toner transfer image transfer unit. A drive source for the bias roll and the belt is located on the upstream side in the transport direction of the transfer paper in the transport path, and a surface other than the transfer paper passing surface of the belt is set as a tension side. A charging device that is disposed facing the photoconductor to charge the secondary toner image on the belt for polarity conversion, and a pair of opposing electrodes disposed at positions facing the photoconductor with the belt interposed therebetween. A roller, and a grounded roller-shaped secondary toner image transfer counter electrode disposed between the counter electrode roller and the driving source; the charging device, the counter electrode roller, and the secondary toner The method is characterized in that a primary toner image and a secondary toner image are simultaneously transferred onto transfer paper by operating an image transfer counter electrode.

(Operation) According to the present invention, the transfer paper passing surface of the belt as the intermediate transfer member is in a state where it is not subjected to tension, and the transfer paper and
The next toner image moves integrally between the transfer position and the fixing position.

(Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS.

The feature of the present embodiment resides in that the driving position with respect to the transfer belt is set so as not to exert a tension effect on the paper passing surface of the transfer paper forming the recording medium in the transfer belt as the intermediate transfer body.

That is, FIG. 1 is a layout diagram for explaining the overall configuration of the image forming apparatus according to the embodiment of the present invention, and the image forming apparatus 1 according to the present embodiment is shown inside (FIGS. 3, 4 and the like). ) Direction.

Around the photosensitive member 2, a charging device 3, an optical writing device 4, a developing device 5, an intermediate transfer member 6, and a cleaning device 7 for performing an image forming process are arranged along the rotation direction. is there.

In the case of the present embodiment, the above-described optical writing device 4 has a structure in which an electrostatic latent image is formed on the photoreceptor 2 by scanning using a laser beam. And a writing unit 4B.

That is, the above-described document reading section 4A
A light source 4A2, a reflecting mirror 4A3, and an imaging lens 4A4, which can reciprocate in the direction of the arrow to expose the original on 4A1, and a color CCD image sensor disposed at an imaging position of exposure light guided by these optical members. 4A5, the reflected light from the original is color-separated by a color CCD image sensor 4A5, converted into a digital signal, input to a storage unit (not shown), and controls the output of a laser light source of a writing unit 4B described later. It has become.

On the other hand, the writing unit 4B is a rotating polygon mirror 4B that deflects laser light from a light source constituted by a semiconductor laser (not shown).
An imaging advanced member including an fθ lens and a reflecting mirror having a well-known structure and a reflecting mirror are arranged, and a laser beam emitted from a light source is scanned in the axial direction of the photoconductor 2 to write an original image. Has become. In the writing unit 4B, since the image information is converted into a digital signal, the writing order is changed to form an electrostatic latent image corresponding to a normal image or an electrostatic latent image corresponding to a mirror image on the photoconductor 2. The formation of an image can be arbitrarily selected.

The developing device 5 for visualizing the electrostatic latent image formed on the photoreceptor 2 has a structure corresponding to color copying in the present embodiment, and is provided inside a rotatable holder 5A. Is a magnetic material containing cyan, magenta, and yellow color developers which are complementary colors to the three primary colors (red, green, and blue) and a black developer used for monochromatic copying to obtain gradation. Brush development unit
5B, 5C, 55, 5Y are equipped. This developing device 5
Is such that each magnetic brush developing unit is selected in accordance with the copying type, and the developing sleeve in the unit is opposed to the photoconductor 2.

On the other hand, the intermediate transfer member 6 has a surface resistance of, for example, 10 ⁻⁸ to
The belt is made of medium resistance rubber set to 10 ^-11 Ωcm, and is arranged close to the photoconductor 2. The details of the intermediate transfer member 6 will be described later.

In the case of the present embodiment, the cleaning device 7 has a structure provided with a blade, and the blade removes the developer remaining on the photoreceptor 2 so that the developer is removed. After passing through the cleaning device 7, the photoreceptor 2 has a residual charge removed by the discharging lamp 8 and faces the next charging device 3.

The above-described intermediate transfer body 6 is wound around a pair of rollers 6A and 6B arranged along the transfer direction of the transfer paper S (the direction of the arrow in FIG. 2) in FIG. It moves in the same direction as the photoconductor 2.

Of the pair of rollers, the roller 6A, which is located on the upstream side in the transport direction of the transfer sheet S on the belt surface corresponding to the transport surface of the transfer sheet S, has its rotating shaft connected to the drive motor 6C and the drive side roller. The belt surface corresponding to the transfer surface of the transfer paper S in the intermediate transfer body 6 is set to the slack side, and the belt surface corresponding to the opposite side to the transfer surface of the transfer paper S is set to the tension side. ing.

Further, a transfer device 9 having a polarity switching circuit 9A as shown in FIG. 4 is provided at a position facing the photoconductor 2 with the above-described intermediate transfer member 6 interposed therebetween. The image can be electrostatically transferred to the intermediate transfer member 2. further,
A tension roller 6D (see FIG. 1) is disposed near the roller 6B, and is provided for the photosensitive member 2 at a position facing the tension roller 6D and the intermediate transfer member 6 therebetween. A cleaning device 10 (see FIG. 1) having a blade having a structure similar to that of the cleaning device 10 is provided. This cleaning device 10 has a blade (not shown) that can be brought into contact with and separated from the intermediate transfer member 6. When a secondary toner image, which will be described later, is carried on the intermediate transfer member 6, the blade moves from the intermediate transfer member 6. The blades are separated.

Further, in FIG. 2, a bias roll 11 is disposed at a position of the intermediate transfer member 6 opposite to the driving roller 6A with the intermediate transfer member 6 interposed therebetween.

That is, the bias roll 11 is, as shown in FIG.
A bias circuit 12 is connected to the intermediate transfer body 6 so as to be able to come into contact with and separate from the intermediate transfer body 6, so that a bias having a polarity necessary for contact and subsequent transfer can be set.

A charging device 13 is disposed at a position facing the driving roller 6A with the intermediate transfer member 6 interposed therebetween, as shown in FIG. The secondary toner image is charged for polarity conversion.

A blade provided inside the bias roll cleaner 14 is in contact with the peripheral surface of the bias roll 11, so that the toner adhered to the peripheral surface is removed.

On the other hand, in FIG. 1, a feeding mechanism 15 is provided on the upstream side in the transport direction of the transfer sheet S with the intermediate transfer body 6 described above, and a fixing device 16 and a paper discharge mechanism 17 are provided on the downstream side in the transport direction. positioned.

That is, the paper feed mechanism 15 includes paper feed cassettes 15A and 15B storing transfer papers S of a plurality of sizes and a manual paper feed tray 15C, respectively. Registration roller 15D located at the end of the
The paper feed timing for the image position on the photoreceptor 2 is set, and the sheet is conveyed toward the photoreceptor 2.

Further, a paper discharge mechanism 17 for the transfer paper S passing through the fixing device 16 is provided.
In the case of the present embodiment, the paper discharge tray 17A, a sorter (not shown), or a structure in which a paper discharge direction can be selected toward the recycle path 17B or the like is selected. Switching claw 17 for setting the paper discharge direction at the branch position
C is located.

Since the present embodiment has the above structure, the copy mode shown in FIGS. 3 to 6 is executed.

It should be noted that the copy modes shown in FIGS. 3 to 6 are based on the premise that a toner image is transferred by a single color developer, for example.

That is, FIG. 3 shows a process in which an image is directly transferred from the photoconductor 2 to the transfer paper S. In this case, the transfer device 9 controls the transfer of the toner image carried on the photoconductor 2. The charging characteristics of the polarity opposite to the polarity are set, and the bias roll 11 and the charging device 13 are set in a state where they do not function. The bias roll 11 is set in a state of contact with the intermediate transfer member 6 and cooperates with the intermediate transfer member 6 to enable the nipping and conveying of the transfer sheet S.

Accordingly, a toner image in which the electrostatic latent image formed on the photoconductor 2 via the writing unit 4B is made visible by a developer of a desired color in the developing device 5 When the toner image is opposed to the transfer member 6, the toner image on the photosensitive member 2 is electrostatically transferred to the transfer sheet S conveyed from the sheet feeding mechanism in synchronization with the movement of the toner image by the operation of the transfer device 9.

This mode is equivalent to the normal single copy mode,
It does not require structural changes to a general device of this type.

Next, FIG. 4 shows a process for transferring a toner image from the photoreceptor 2 to the intermediate transfer member 6, and a toner image formed on the photoreceptor 2 (hereinafter referred to as a primary toner image). ) Is transferred to the intermediate transfer member 6 to obtain a secondary toner image, the transfer device 9 operates similarly to the case shown in FIG. Is set, and the bias roll 11 and the charging device 13 are set to a non-functional state. The paper feed mechanism 15 is provided with a transfer paper S
Is not performed.

Therefore, the secondary toner image carried on the photoconductor 2 is electrostatically transferred onto the intermediate transfer body 6 by the operation of the transfer device 9.

FIG. 5 shows a process for transferring the secondary toner image on the intermediate transfer member 6 shown in FIG. 4 to the transfer paper S. In this case, the transfer device 9 and the charging device 13 In the non-functioning state, the bias roll 11 is set to have a charging characteristic of a polarity opposite to the polarity of the secondary toner image on the intermediate transfer member.

Accordingly, the secondary toner image on the intermediate transfer body 6 is
When the transfer paper S for which the paper feed timing is set is conveyed by the registration rollers 15D, the bias roll 11
, The secondary toner image is electrostatically transferred onto the transfer paper S.

FIG. 6 shows a process for transferring a toner image to both surfaces of the transfer paper S. In this case, the transfer device 9 is opposed to the photoconductor 2 with the intermediate transfer member 6 interposed therebetween instead of the transfer device 9. A pair of opposing electrode rollers 18 are in contact with each other via a bias circuit 18A at a position. Further, between the opposing electrode roller 18 and the driving roller 6A, a pair of grounded rollers
The next toner image transfer counter electrode 19 is in contact.

In the double-sided copying process in which the configuration is changed as described above, first, the primary toner image is transferred to the intermediate transfer body 6 to carry the secondary toner image on the intermediate transfer body 6, and then, again. After the primary toner image is formed on the photoreceptor 2, the transfer paper S is fed out from the paper feed mechanism 15, and both sides of the transfer paper S are transferred from the intermediate transfer body 6 side and the photoreceptor 2 side. The primary and secondary toner images are simultaneously transferred.

According to this process, since the toner image is simultaneously transferred to both sides of the transfer sheet S, there is an advantage that it is not necessary to perform the reverse feeding of the transfer sheet.

In executing this process, the photosensitive member 2
When the first toner image formed on the photosensitive member 2 is transferred to the intermediate transfer member 6, the same operation as that shown in FIG. 4 is obtained. The charging characteristic of the polarity opposite to the polarity of the toner image is set, and the bias roll 11 and the charging device 13 are set in a non-functional state.

Therefore, the primary toner image on the photoreceptor is
Is electrostatically transferred onto the intermediate transfer member 6 by the action of
This is the next toner image.

Then, after the primary toner image is formed on the photosensitive member 2 again, the bias roll 11 is brought close to the intermediate transfer member 6 so as to be able to come into contact with the transfer paper S. The charging characteristic is set to the polarity opposite to the polarity of the secondary toner image carried thereon, and the charging device 13 sets the charging characteristic of the polarity opposite to the polarity of the secondary toner image transferred from the photoconductor 2 for the first time. Is set.

Accordingly, the 2 transferred from the photoconductor 2 onto the intermediate transfer body 6
The next toner image moves toward the bias roll 11 with the polarity being changed from negative to positive by the charging device 13 as shown in the figure. Then, when the transfer paper S is conveyed with the paper feed timing set, the secondary toner image on the intermediate transfer body 6 is electrostatically transferred onto the transfer paper S by the action of the bias roll 11, and The primary toner image on the photoreceptor 2 is electrostatically transferred to the transfer paper S by the action of the charging device 13, which means that the toner images have been simultaneously transferred to both surfaces of the transfer paper S.

The basic concept of each process described above is described in the specification of Japanese Patent Application No. 1-130466 according to the present invention.

On the other hand, when the belt surface corresponding to the transfer surface side of the transfer sheet S moves in the transfer direction of the transfer sheet S, as described above, the intermediate transfer body 6 that moves to execute the above-described process Since the drive motor 6C is set to the slack side by setting the disposition position and is a surface that does not receive tension, it is less affected by the drag applied to the transfer paper S, and its resonance frequency is low. The secondary toner image, resonance on the transfer paper transport surface,
That is, flutter is suppressed.

(Effects of the Invention) As described above, according to the present invention, as a drive structure of an intermediate transfer body that directly transfers a toner image on a photoconductor, an upstream side in a transport direction corresponding to a transport surface of a transfer sheet is set as a drive position. When the transfer paper is positioned between the intermediate transfer member and the photosensitive member to transfer the toner image, the transfer paper transfer surface of the intermediate transfer member is set. Does not depend on tension. Therefore, the toner image on the intermediate transfer body can move at a speed corresponding to the movement of the transfer sheet because there is no influence of the drag generated in the transfer path of the transfer sheet. The image quality can be prevented from deteriorating by preventing the omission.

Further, the above-described effect is also obtained when the intermediate transfer member is formed of a belt of medium resistance rubber, by setting the resonance frequency of this surface to be low by setting the transfer paper conveyance surface to the slack side, thereby suppressing the resonance. With this, it is expected that the material can be selected in a wide range, and a low-cost and highly reliable image forming apparatus can be obtained.

[Brief description of the drawings]

FIG. 1 is a layout diagram for explaining an overall configuration of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a perspective view for explaining a main part of the configuration shown in FIG. 1, and FIGS. Fig. 6 shows the first
FIG. 7 is a model diagram for explaining the operation of the configuration shown in FIG. 7, FIG. 7 is a perspective view corresponding to FIG. 2 for explaining an intermediate transfer structure in a conventional image forming apparatus, and FIG. It is an enlarged view of the part shown by VIII. DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Photoconductor, 4 ... Optical writing apparatus, 5 ... Developing apparatus, 6 ... Intermediate transfer body, 6A ... Drive side roller, 9 ... Primary toner image transfer means Barrel transfer device, 11... A bias roll as a means for transferring a secondary toner image.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-209471 (JP, A) JP-A-63-306137 (JP, A) JP-A-64-44457 (JP, A) JP-A-50- 90338 (JP, A) JP-A-63-58387 (JP, A) JP-A-2-10388 (JP, A) JP-A-3-167579 (JP, A) JP-A-3-274076 (JP, A) Japanese Utility Model Application 63-113168 (JP, U) Japanese Utility Model Application 63-84053 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/00 106 G03G 15/00 510-534 G03G 13/14-13/16 G03G 15/14-15/16 103

Claims (1)

(57) [Claims] An optical writing means for writing an image on a writing object as a normal image or a mirror image, a rotatable photoconductor as the writing object, and an electrostatic latent image written on the photoconductor by the optical writing means Developing means for visualizing the toner image as a primary toner image, a belt as an intermediate transfer member which is arranged opposite to the photoconductor and is set at the opposite position so as to allow transfer paper as a recording medium to pass therethrough; An image forming apparatus comprising: a secondary toner image transfer unit configured to transfer a secondary toner image formed on the belt by transferring a secondary toner image to the transfer paper; Using a transfer structure having a bias roll that can be separated from the transfer paper as
A drive source for the bias roll and the belt is located on the upstream side in the transport direction of the transfer paper in the transport path, and a surface other than the transfer paper passing surface of the belt is a tension side, and is disposed to face the drive source. A charging device that performs charging for converting the polarity of the secondary toner image on the belt; a pair of counter electrode rollers disposed at a position facing the photoconductor with the belt interposed therebetween; A roller-like secondary toner image transfer counter electrode disposed between the electrode roller and the drive source and grounded, wherein the charging device, the counter electrode roller, and the secondary toner image transfer counter electrode are provided. And an image forming apparatus for simultaneously transferring the primary toner image and the secondary toner image onto transfer paper by operating the image forming apparatus.