JP2008070818A - Roller transfer device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roller transfer device, wherein displacement and color shift of an image by impact applied when cardboard paper is inserted and discharged, are prevented, flexibility in the design of the pressing mechanism of the roller transfer device is not lowered, and the size of the pressing mechanism is not increased, and also to provide an image forming apparatus. <P>SOLUTION: Using the pressing mechanism, the roller transfer device presses a transfer roller 1 against a counter roller 2a rotating while supporting a belt-like image carrier 3 with a toner image held thereon, and thus forms a nip part. The roller transfer device also passes recording paper 4 through the nip part, thereby transferring the toner image to the recording paper. When a toner image is transferred to cardboard 40, an inter-shaft distance between the transfer roller 1 and counter roller 2a is longer than that set as a transfer condition for transferring a toner image to thin paper 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a roller transfer device that uses a roller to transfer a toner image onto the surface of a sheet-like recording medium (hereinafter referred to as recording paper or recording body), and a printer, a facsimile machine, and a copying machine that use the roller transfer device. The present invention relates to an electrophotographic image forming apparatus that visualizes an image using colored particles, such as a machine or a multifunction machine.

  An image forming apparatus using an electrophotographic method includes a development / transfer process in which colored particles are visualized as an image on the surface of a recording medium such as recording paper, and a fixing process in which the visualized colored particle image is fixed to the recording medium. Then, an image is formed on the recording medium. As the colored particles, a powder called toner exclusively for electrophotography is used.

  The toner is charged in the developing process to become charged particles, and is visualized (referred to as a toner image) as an image on a photoreceptor or an intermediate transfer belt. In the transfer step, a toner image of charged particles is placed in an electric field, and an electrostatic force is applied to the toner image to transfer it from the photosensitive member or intermediate transfer belt to the recording member.

  Conventionally, a clamping portion is formed by pressing a semiconductive or conductive transfer roller against a photosensitive member or an intermediate transfer belt using a coil spring or the like, and a voltage is applied to the roller, the photosensitive member or the intermediate transfer belt to hold the holding member. A roller transfer system is often used in which a recording medium is inserted into the holding portion while an electric field is applied to the portion.

  In this roller transfer device, particularly when transferring the toner image to the thick paper, when the thick paper is inserted into the sandwiching portion, a rush impact at the front end of the recording paper or a discharge impact at the rear end of the recording paper occurs during ejection. In particular, the speed of the photoconductor and the intermediate transfer belt fluctuates, and there is a problem that image misregistration and color misregistration occur in the case of a color recording apparatus.

  The rush impact and the discharge impact that cause this are conventionally known as causes that cause offset in roller fixing of electrophotography (see, for example, Patent Document 1). The rush impact and discharge impact (hereinafter collectively referred to as “rush discharge impact”) are not large in a thin recording medium (hereinafter referred to as “thin paper”), and image positional displacement and color shift due to the rush discharge impact do not become a problem. When a thick recording medium (hereinafter referred to as “thick paper”) is passed, a large rush / discharge impact is generated, and image misregistration and color misregistration are at an unacceptable level.

  Conventionally, in order to prevent image displacement and color misregistration due to rush discharge impact when passing thick paper, it is necessary to keep the range of the impact coefficient of the pressing mechanism low. For example, as in Patent Document 1, a pressure roller (backup roller) is supported at an intermediate position of an arm-shaped pressing member, and one end side of the pressing member is a fulcrum, and the other end side is a power point. When the pressure mechanism is configured to press the pressure roller against the heat roller by pulling the free end side of the pressure member with an elastic force using a spring at a power point at a distance, to reduce the impact coefficient. However, it is necessary to reduce the spring constant of the spring and the arm ratio (E / 1) of the pressing member, and there is a problem that the degree of freedom in designing the pressing mechanism is lowered. In addition, lowering the spring constant and arm ratio (E / 1) of the spring used in the pressing mechanism increases the free length of the spring of the pressing mechanism, leading to the enlargement of the pressing mechanism. is there.

JP-A-6-19357

  The present invention does not reduce the degree of freedom in design of the pressing mechanism of the roller transfer device, and does not cause an enormous increase in the pressing mechanism. Good roller transfer without image misalignment or color misregistration due to a rush / discharge impact during cardboard insertion An object is to provide an image forming apparatus and an image forming apparatus.

In order to achieve the above object, the invention according to claim 1 is directed to a clamping unit that presses a transfer roller using a pressing mechanism against a counter roller that rotates while supporting a belt-like image carrier on which a toner image is carried. And transferring the toner image onto a thick sheet-like medium in a roller transfer device that transfers the toner image onto the sheet-like medium by inserting a sheet-like medium through the sandwiching portion. The distance between the axes of the opposing rollers is set to be longer than the transfer conditions for transferring the toner image to a thin sheet-like medium.
According to a second aspect of the present invention, in the transfer device according to the first aspect, the minimum value suitable for transfer of a thin sheet-like medium is set to Lo, and the distance between the transfer roller and the opposite roller is suitable for the transfer of the thin sheet-like medium. When the thickness of the medium is D and the thickness of the thin sheet-like medium is Do, the axis between the transfer roller and the opposing roller when the toner image is transferred to the thick sheet-like medium by the pressing mechanism. The distance L is set to a range defined by the following expression “Lo + (D−Do) ≦ L <Lo + D”.
According to a third aspect of the present invention, there is provided the roller transfer device according to the first aspect, wherein a thickness detecting means for detecting a thickness of the sheet-like medium before the sheet-like medium reaches the roller transfer device, and the paper thickness An inter-axis distance calculation unit that calculates an inter-axis distance between the transfer roller and the counter roller based on a detection value of the detection unit, and an adjustment of the inter-axis distance based on a value calculated by the inter-axis distance calculation unit. And an inter-axis distance adjusting means.
According to a fourth aspect of the present invention, in the roller transfer device according to the fourth aspect, the minimum distance suitable for the transfer of the thin sheet medium is set to Lo, and the thick sheet is the distance between the transfer roller and the opposing roller. When the thickness of the sheet-like medium is D and the thickness of the thin sheet-like medium is Do, when the toner image is transferred to the thick sheet-like medium, the shaft between the transfer roller and the opposing roller is transferred by the pressing mechanism. The distance L is set to a value determined by the following expression “L = Lo + (D−Do)”.
The invention according to claim 5 comprises at least a photosensitive member, a developing device, a roller transfer device, and a fixing device. The latent image formed on the photosensitive member is converted into a toner image by the developing device, and the toner image is converted into the roller. 5. The image forming apparatus according to claim 1, wherein the toner image transferred to the sheet-like medium is transferred by the transfer device, and the toner image is fixed by the fixing device and output. The roller transfer device described in 1) was provided.

  According to the present invention, the degree of freedom of design of the pressing mechanism of the roller transfer device is not lowered, and the pressing mechanism is not enormous. A roller transfer device and an image forming apparatus can be provided.

Embodiment 1
Hereinafter, an example of the first embodiment will be described with reference to FIGS.
FIG. 1 schematically shows an image forming engine of a recording apparatus which is an image forming apparatus of the present invention. This recording apparatus is a tandem type full-color electrophotographic process using an intermediate transfer belt. In FIG. 1, reference numeral 1 is a transfer roller, reference numeral 2 a is an opposing roller that forms a clamping portion, reference numeral 3 is an intermediate transfer belt, reference numeral 4 is recording paper, reference numeral 5 is an image forming unit (cyan), and reference numeral 6 is an image forming unit. (Magenta), 7 is an image forming unit (yellow), 8 is an image forming unit (black). In each of the image forming units 5, 6, 7, and 8, an electrostatic latent image is formed on a photosensitive member (not shown), and each electrostatic latent image is developed with primary and black toners, which are used as an intermediate for image transfer. Transfer to belt 3. This transfer is called primary transfer. The intermediate transfer belt 3 is supported by support rollers 2b and 2c in addition to the opposing roller 2a.

[Roller transfer device having a conventional pressing mechanism as a comparative example]
FIG. 2 shows a state in which the transfer roller 1 is pressed against a counter roller 2a that rotates while supporting an intermediate transfer belt (belt-shaped image carrier) 3 carrying a toner image by using a conventional pressing mechanism. A configuration part in which a pinching part P is formed, a sheet-like medium is inserted into the pinching part, and a toner image is transferred to the sheet-like medium is shown in an enlarged manner. Here, the pinching portion P is a portion where the recording paper 4 is sandwiched between the transfer roller 1 and the opposing roller 2a via the intermediate transfer belt 3, and the recording paper 4 passes through the pinching portion P and rotates each roller indicated by an arrow. Sent in the direction.
The roller transfer device and the pressing mechanism in FIG. 2 generally include an arm 10 and an extensible spring 9. The transfer roller 1 is pivotally supported at the intermediate portion of the arm 10. One end of the arm 10 on the downstream side in the recording paper conveyance direction is pivotally supported by a fulcrum 11. The other end side of the arm 10 is located on the downstream side in the recording paper conveyance direction, and is urged by the spring 9 in the clockwise direction around the fulcrum 11. The transfer roller 1 is pressed against the opposing roller 2a by the urging force of the spring to constitute the pinching portion P.

  Each primary color toner image is successively overlaid on the intermediate transfer belt 3 by the image forming units 5, 6, 7, and 8 and is carried as a superimposed color image, and is recorded on a transfer sheet composed of a transfer roller 1 and a counter roller 2. 4 is collectively transferred. This is called secondary transfer.

Since the conventional pressing mechanism does not include a means for adjusting the inter-axis distance L (= Lo) between the opposing roller 2a and the transfer roller 1, the opposing roller 2a and the transfer roller 1 are elastic of the spring 9 when paper is not passed. Thus, they are in contact via the intermediate transfer belt 3.
In this situation, there is no particular problem when passing thin paper (so-called thin recording paper). However, when passing thick paper (so-called thick recording paper), if the recording paper 4 is thick paper, the secondary A rush impact occurs at the front end of the recording paper 4 when the transfer is inserted. At that time, each of the image forming units 5, 6, 7, and 8 is forming an image of the previous page in a print job different from the image to be secondarily transferred to the recording paper 4.

  At the moment when the rush impact occurs, the speed of the intermediate transfer belt 3 decreases, and the primary transfer of each of the image forming units 5, 6, 7, and 8 is performed at a distance shorter than the image length that should be primarily transferred. And the image becomes shorter. The speed drop due to this rush impact is instantaneous, and then recovers.

  For example, when the cyan component is primarily transferred by the image forming unit 5 and the corresponding magenta component image is to be superimposed by the image forming unit 6, the second transfer is performed at the timing of the primary transfer by the image forming unit 5. When a rush impact occurs at the transfer portion, the image length of the cyan component is shortened, and in the next image forming unit 6, the speed of the intermediate transfer belt 3 is restored, so that the magenta component image has a normal image length. As a result, since the image length is different between cyan and magenta, color misregistration occurs. Similarly, when the recording paper 4 is discharged, color misregistration due to the discharge impact occurs.

  A similar problem occurs not only in the image forming apparatus using the intermediate transfer belt 3 shown in FIGS. 1 and 2, but also in the image forming units 5, 6 using a photosensitive belt instead of the intermediate transfer belt 3 (not shown). , 7 and 8, an image forming unit having exposure means and developing means for each color image is formed, and cyan, magenta, yellow, and black toner images are sequentially superimposed on the photosensitive belt, and a transfer roller This also occurs in an image forming apparatus of a type that batch-transfers to the recording paper 4 in the transfer portion composed of 1 and the opposing roller 2, and the same cause causes a color shift due to the same discharge impact. That is, both the image forming apparatus having the photosensitive belt (image carrier belt) and the image forming apparatus having the intermediate transfer belt 3 (image carrier belt) have a common problem in transferring to the recording paper. Have Since the configuration of the transfer unit is common, an example using the intermediate transfer belt 3 will be described below.

[Roller transfer device provided with pressing mechanism of the present invention]
FIG. 3 shows a roller transfer device provided with the pressing mechanism of the present invention. 3, members that are the same as those already described in FIG. 2 are given the same reference numerals, and descriptions thereof are omitted. A characteristic point in this example is that an inter-axis distance adjusting cam (hereinafter simply referred to as a cam) 12 is provided. The cam 12 is disposed on the free end side of the arm 10 so that the arm 10 can be pushed by the spring 9 with the arm 10 therebetween.

  The cam 12 has an equilateral triangular shape, and is displaced when the rotation shaft 12a at the center is driven to rotate by the motor M. As shown in FIG. 3, the cam 12 is not in contact with the arm at a rotational position for thin paper where the portion corresponding to the triangular side of the cam 12 is parallel to the arm 10, and the transfer roller 1 and the opposing roller 2a are intermediate. The contact is made by the elasticity of the spring 9 through the transfer belt 3. At this time, the distance between the axes of the opposing roller 2a and the transfer roller 1 is L (= Lo).

  As described in the comparative example, when the recording paper 4 is a thin paper, even if the inter-axis distance L is not adjusted and the paper is thin even when L (= Lo), the color deviation of the image due to a relatively small rush discharge impact does not cause a problem. However, if thick paper is inserted without adjusting the inter-axis distance L, color misregistration of the image due to rush / discharge impact occurs.

  Therefore, in the present invention, when inserting thick paper, the distance between the axes of the transfer roller and the opposing roller is set in advance to be longer than the transfer condition for transferring the toner image to the thin sheet-like medium. The inter-axis distance L was adjusted. The adjustment of the inter-axis distance L is performed by controlling the rotation stop position of the cam 12.

  For example, if the apex of the triangular cam 12 as shown in FIG. 4 presses the arm 10 from the rotation stop position of the cam 12 shown in FIG. 3, the arm 10 rotates around the fulcrum 11. Accordingly, the distance L between the shafts becomes long, and the rush / discharge impact at the time of passing through the thick paper can be reduced. The rotation of the cam 12 is performed by the motor M as described above, and the amount of rotation is controlled by the control means 14.

The significance of widening the distance between the transfer roller and the counter roller in advance is as follows.
When the distance L between the axes of the transfer roller 1 and the opposing roller 2 in a state where the recording paper 4 is not sandwiched in the case of thin paper transfer is Lo, and the paper thickness when the recording paper 4 is thin paper is Do, the recording paper The distance between the axes of the transfer roller 1 and the opposing roller 2 while 4 is held is expanded by Do, and the following equation (1) is obtained.
L = Lo + Do (1)

  Under this thin paper passing condition, image color misregistration due to rush discharge impact does not matter. The strength of the rush / discharge impact depends on the spread distance, and the rush / discharge impact increases as the spread distance increases. That is, even in the case of thick paper, if the spread distance is made smaller than Do, image color misregistration due to rush discharge impact will not be a problem.

  Therefore, in the roller transfer device of the present invention, in the case of thick paper, the cam 12 is operated so that the distance between the axes of the transfer roller 1 and the opposing roller 2 is widened in advance, and even when the thick paper is inserted, the pushing distance is increased. Do not exceed Do. In the case of thick paper, the condition is expressed by the following equation (2), where D is the thickness of the thick paper.

      Lo + (D−Do) ≦ L <Lo + D (2)

  In the case of thick paper, if the distance L between the axes of the transfer roller 1 and the opposing roller 2 is widened in advance so as to satisfy the condition of the expression (2), the distance for expanding when the thick paper 40 is inserted as shown in FIG. (ΔD) does not exceed the spread distance Do in the case of thin paper. In FIG. 4, a symbol t indicates a gap between the transfer roller 1 and the opposing roller 2 when L satisfying the expression (2) is set.

  In the pressing mechanism of this example, while the thick paper 40 is being clamped, the arm 10 is further pushed out by the thick paper 40 from the standby position (position where the inter-axis distance L is widened) contacting the cam 12. The cam 12 is naturally separated from the arm 10. If the inter-shaft distance adjusting cam 12 is in contact with the arm 10, the pressing force by the spring 9 is shared by the inter-shaft distance adjusting cam 12 during the transfer, and an appropriate clamping portion This means that no formation has been made.

  In this example, the cam 12 is used for adjusting the distance between the shafts. However, not only the cam but also other mechanisms may be used. Even in this case, this separation is a necessary condition. That is, in general, it is necessary that no pressing force is applied to the member for adjusting the inter-axis distance while the thick paper is being sandwiched.

According to the example described above, even if the thick paper is inserted into the transfer holding portion, the rush / discharge impact does not increase and color misregistration does not become a problem. In this case, it is not necessary to design the spring constant and arm ratio of the pressing mechanism to be low in accordance with the cardboard, so that the degree of freedom in design is not reduced and the pressing mechanism is not enlarged.
The recording paper after the transfer is discharged to a paper discharge tray after the transferred toner image is fixed through a fixing device (not shown).

Embodiment 2
Hereinafter, another embodiment of the present invention will be described with reference to FIG. FIG. 5 shows a roller transfer device and a roller pressing mechanism at the time of thick paper transfer according to the second embodiment. When the roller transfer device in FIG. 5 is compared with the roller transfer device in FIG. 4, the difference is that an inter-shaft distance adjustment cam (hereinafter referred to as an eccentric roller) 120 is used instead of the cam 12. Another difference is that a means for driving and controlling the rotating shaft 120a is added. Others are the same as those shown in FIG. 4 and are denoted by the same reference numerals.

  As means for driving and controlling the rotating shaft 120a, a thickness detecting means 50, an inter-axis distance calculating means 51, a control means 52, a motor M and the like are provided. The thickness detecting means 50 is a paper thickness detecting means for detecting the thickness of the recording paper before the recording paper reaches the clamping portion of the roller transfer device, and uses a thickness measuring sensor such as a light transmission sensor. The inter-axis distance calculation unit 51 plunges the inter-axis distance between the transfer roller 1 and the opposing roller 2a based on the thickness detection value of the recording paper by the thickness detection unit 50 so that the color misregistration of the image does not matter. A calculation unit (CPU or the like) that calculates a value that reduces the discharge impact. Based on the calculated value, the control unit 52 sets and executes the rotation amount of the motor M. The control means 52 is an inter-axis distance adjusting means for adjusting the inter-axis distance L.

  In this example, the setting of the inter-axis distance L is changed from the paper thickness to be transferred, and the inter-axis distance L is always fixed to the condition expressed by the following equation (3).

      L = Lo + (D−Do) (3)

  A thickness detecting means 50 comprising a light transmission sensor detects the thickness of the recording paper fed out from a hopper containing the recording paper in the image forming apparatus. If the paper thickness is thicker than the thin paper thickness Do where the image color shift due to the rush discharge impact does not become a problem, the distance L between the axes is calculated based on the equation (3), and the control means 52, the motor M, etc. are driven. Thus, the distance L between the axes is controlled to be a calculated value.

  Since the eccentric roller 120 of this example can set the distance between the axes corresponding to various paper thicknesses, the eccentric roller 120 is used without using the triangular cam as shown in FIGS. In this example, it is the minimum value in the range of the expression (2).

  This condition is the same as the extension distance of the inter-axial distance of the thin paper where the color misregistration of the image does not become a problem when the thick paper is sandwiched, so that the pressing force is shared by the member for adjusting the inter-axial distance. Absent. After the transfer, the recording sheet passes through a fixing device (not shown), and the transferred toner image is fixed.

FIG. 3 is a cross-sectional side view schematically showing an image forming engine of the recording apparatus of the present invention. It is a figure explaining the comparative example of the press means. FIG. 2 is a schematic configuration diagram of a roller transfer device and a pressing mechanism according to the first embodiment. FIG. 2 is a schematic configuration diagram of a roller transfer device and a pressing mechanism according to the first embodiment. FIG. 6 is a schematic configuration diagram of a roller transfer device and a pressing mechanism according to a second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transfer roller 2a Opposing roller 2b, 2c Support roller 3 Intermediate transfer belt 4 Recording paper 5 Image forming unit (cyan)
6 Image creation unit (magenta)
7 Image creation unit (yellow)
8 Image creation unit (black)
9 Spring 10 Arm 11 Support point 12 Axial distance adjusting cam 12a Rotating shaft 13 Axial distance adjusting member 14 Control means 40 Recording paper (thick paper)
50 Thickness detecting means 51 Interaxial distance calculating means 52 Control means 120 Interaxial distance adjusting cam (eccentric roller)
120a Rotating shaft L Distance between shafts P Holding part M Motor δD Spreading distance

Claims (5)

A pressing mechanism is used to press a transfer roller against a rotating roller that supports and rotates a belt-shaped image carrier on which a toner image is carried, and a sheet-like medium is formed on the clamping unit. In a roller transfer device that passes through and transfers a toner image to the sheet-like medium,
When a toner image is transferred to a thick sheet-like medium, the axial distance between the transfer roller and the opposing roller is set to be longer than the transfer condition for transferring the toner image to a thin sheet-like medium. A roller transfer device. The transfer device according to claim 1,
The minimum distance between the transfer roller and the opposing roller that is suitable for transferring a thin sheet medium is Lo, the thickness of the thick sheet medium is D, and the thickness of the thin sheet medium is Do. In this case, the pressing mechanism sets a distance L between the transfer roller and the opposing roller when the toner image is transferred to a thick sheet-like medium within a range defined by the following expression. Transfer device.
Lo + (D−Do) ≦ L <Lo + D The roller transfer device according to claim 1,
Thickness detecting means for detecting the thickness of the sheet-shaped medium before the sheet-shaped medium reaches the roller transfer device, and the axis between the transfer roller and the opposing roller based on the detection value of the paper thickness detecting means A roller transfer device comprising: an inter-axis distance calculating unit that calculates a distance; and an inter-axis distance adjusting unit that adjusts the inter-axis distance based on a value calculated by the inter-axis distance calculating unit. In the roller transfer device according to claim 3,
The minimum distance between the transfer roller and the opposing roller that is suitable for transferring a thin sheet medium is Lo, the thickness of the thick sheet medium is D, and the thickness of the thin sheet medium is Do. In this case, when the toner image is transferred to a thick sheet-like medium, the distance L between the transfer roller and the opposing roller is set to a value determined by the following expression by the pressing mechanism. Transfer device.
L = Lo + (D-Do) At least a photoreceptor, a developing device, a roller transfer device, and a fixing device;
The latent image formed on the photosensitive member is converted into a toner image by the developing device, the toner image is transferred to a sheet-like medium by the roller transfer device, and the toner image transferred to the sheet-like medium is transferred to the fixing device. In an image forming apparatus that fixes and outputs in
An image forming apparatus comprising the roller transfer device according to claim 1 as the roller transfer device.

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