JP2004205558A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To change an uneven amount of transfer nip, which results from inclinations of an image carrier and a transfer member and shape errors (eccentric center and ununiform layer thickness), to an even amount, thereby effectively avoiding image defects such as ununiform transfer, color slurring. <P>SOLUTION: The image forming apparatus includes: the image carrier 1 on which an image is held; and a transfer member 3 that forms a nip area between the image carrier 1 and itself and transfers the image formed on the image carrier 1 to a body 2 to be subjected to transfer. The image forming apparatus is provided with: a swingable support member 4 that supports the transfer member 3 such that the member 3 freely swings; and a pressing member 6 that has a pressure application point 5 on the swingable support member 4 located on a line perpendicular to the substantially middle part of the transfer member 3 in its axial direction, and thus presses the transfer member 3 to the image carrier 1 side. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic copying machine, and more particularly, to an improvement of an image forming apparatus in which a transfer member is arranged in contact with an image carrier and an image on the image carrier is transferred to a transfer body. About.
[0002]
[Prior art]
As an example of a conventional image forming apparatus, for example, an image forming apparatus of an intermediate transfer type is used. For example, primary transfer of each color component toner image formed on a photosensitive drum or the like to an intermediate transfer belt or the like is performed by a primary transfer device. 2. Description of the Related Art There is known an apparatus in which multicolor toner on a transfer belt is collectively transferred to a recording medium by a secondary transfer device.
In this type of image forming apparatus, as a primary transfer device, for example, a transfer member formed by using a semiconductive elastic material is disposed in pressure contact with the back surface of the intermediate transfer belt at a portion where the photosensitive drum and the intermediate transfer belt are opposed to each other. There is used a roller having a roll and transferring a color component toner on the photosensitive drum onto the intermediate transfer belt by forming a transfer electric field between the photosensitive drum and the intermediate transfer belt.
[0003]
When the transfer nip area between the transfer roll and the photosensitive drum is not constant during transfer, there are problems such as image defects such as transfer unevenness, and wrinkles and skew of the recording medium. Further, in the case of color printing, it causes color shift when the respective colors are superimposed.
For this reason, when pressing the transfer roll against the photosensitive drum or the like, bearings disposed at both ends of the axis of the transfer roll are pressed by a pressing spring. An image defect or the like is prevented by making the contact nip area constant (see, for example, Patent Document 1).
[0004]
[Patent Document 1]
JP-A-5-333719 (page 1-2, FIG. 1)
[0005]
[Problems to be solved by the invention]
In the image forming apparatus of the above aspect, the contact member (photosensitive drum, backup roll) that abuts on the transfer roll may be lost due to the variation in the strength of the pressure spring or the tolerance of the assembly dimension in forming the intermediate transfer belt unit. Alignment occurs, and the nip amount and pressure of the transfer roll in the axial direction with respect to the contact member are not uniform.
Further, in Patent Document 1, for example, the distance between the photosensitive drum shaft and the transfer roller shaft is maintained constant by pressing a bearing that supports the axis of the transfer roller against a contact surface such as a photosensitive drum unit. However, a proposal for configuring a constant nip displacement amount is also disclosed.
[0006]
However, also in the above-described embodiment, for example, due to variations in the position of the contact surface on the photoconductor drum and the shape error (eccentricity and layer thickness unevenness) of the transfer roll and photoconductor drum, the photoconductor drum and the transfer roll There is a technical problem that the nip amount is not constant.
[0007]
SUMMARY OF THE INVENTION In order to solve the above-mentioned technical problems, the present invention is to fix the inclination of the image carrier and the transfer member and the non-uniform transfer nip amount due to a shape error (eccentricity and unevenness in the layer thickness), and to improve transfer unevenness and color. An object of the present invention is to provide an image forming apparatus capable of effectively avoiding image defects such as displacement.
[0008]
[Means for Solving the Problems]
That is, according to the present invention, as shown in FIGS. 1A and 1B, a nip area is formed between an image carrier 1 on which an image is carried, and the image carrier 1, In an image forming apparatus including a transfer member 3 for transferring an image formed thereon to a transfer-receiving member 2, a swing support member 4 for swingably supporting the transfer member 3, and a shaft of the transfer member 3 The swing support member 4 located on a line perpendicular to the center of the direction has a pressing action point 5, and the transfer member 3 includes a pressing means 6 for pressing the transfer member 3 toward the image carrier 1. .
Although FIG. 1A illustrates an intermediate transfer type image forming apparatus, the image forming apparatus is not limited to this.
[0009]
In such technical means, as an image forming method of the image forming apparatus to which the present invention is applied, an electrophotographic method, an electrostatic recording method, or the like may be appropriately selected.
The image carrier 1 may be a photoconductor, a dielectric, or the like as appropriate as long as it can support the image T, and its shape may be a drum shape or a belt shape.
Further, the transfer target 2 broadly includes those that transfer the image T on the image carrier 1.
Here, in the direct transfer type image forming apparatus, the recording material K such as a sheet to which the image T on the image carrier 1 is directly transferred is the transfer target 2.
In the intermediate transfer type image forming apparatus shown in FIG. 1A, an image forming carrier (for example, a photosensitive drum) is an image carrier 1 and an intermediate transfer body (for example, an intermediate transfer belt) is a primary transfer portion. Is an image receiving member 2, while an intermediate transfer member (for example, an intermediate transfer belt) is an image carrier 1 and a recording material K such as paper is an image receiving member 2 in a secondary transfer portion.
The secondary transfer portion is provided with a batch transfer unit 8 for transferring the image T on the transfer target body 2 to the recording material K. The batch transfer unit 8 has, for example, a roll-shaped secondary transfer member 9. I have.
[0010]
The swing support member 4 may be appropriately selected as long as it can swing the transfer member 3 in accordance with the inclination of the image carrier 1, and the point of action 5 of the pressing is substantially in the axial direction of the transfer member 3. Any portion on the swing support member 4 located on a line orthogonal to the center may be used.
Further, the pressing means 6 only needs to press the transfer member 3 against the image carrier 1, and the pressing action on the swing support member 4 located on a line perpendicular to the substantially center of the transfer member 3 in the axial direction is sufficient. The point 5 includes a mode in which the swing support member 4 is pulled or pressed, and the like.
The pressing means 6 may be appropriately selected such as a spring, a damper, or a combination thereof.
[0011]
The reason why the point of action 5 of the pressing by the pressing means 6 is arranged on a line orthogonal to the substantially center of the transfer member 3 in the axial direction is as follows.
That is, if the point of action 5 of the pressing by the pressing means 6 is arranged on a line orthogonal to the substantially center of the transfer member 3 in the axial direction, the substantially center of the swinging support member 4 is pushed, and both ends of the swinging support member 4 are uniformly placed. Force can be applied.
At this time, since the swing support member 4 is swingably supported, the shape error of the transfer member 3 is effectively canceled.
In this regard, the aspect in which both ends of the transfer member 3 are pressed by the spring member is different from the present invention because the pressing force at both ends is uneven due to the variation in spring strength.
In such an operation process, the swing fulcrum of the swing support member 4 may be set arbitrarily. For example, a mode in which the swing support member 4 is supported at the swing fulcrum in its axial direction will be described. The swing fulcrum position is set substantially at the center of the swing support member 4.
More specifically, as shown in FIG. 1B, at a position facing the image carrier 1, a transfer member 3 disposed in parallel is provided with a swing support member via a bearing (not shown). 4 and is pressed by the pressing means 6 at a pressing point 5 substantially at the center of the swinging support member 4, so that a nip area is formed between the swinging support member 4 and the image carrier 1.
Here, as shown in FIG. 2A (1), when the swing fulcrum S of the swing support member 4 is not located on a line orthogonal to the substantially center of the transfer member 3 in the axial direction, the transfer member 3 Rotational moments M1 and M2 are received about the swing fulcrum S by the action force F applied from the pressing means 6 such as a spring. Since the rotational moments M1 and M2 have different distances from the swing fulcrum S to both ends, it is apparent that the rotational moments M1 and M2 have different magnitudes at both ends of the transfer member 3.
Further, as shown in FIG. 2 (a) {circle around (2)}, pressures f1 and f2 on the image carrier 1 at both ends of the transfer member 3 (the force by which the nipped transfer member 3 pushes back the image carrier 1 + the pressing means 6). In order to make the transfer force (3) equal, an acting force F must be applied substantially at the center of the transfer member 3 in the axial direction, and the swing fulcrum S must be supported. In this case, since the distances from the swing fulcrum S to both ends are different, the pressures f1 and f2 with respect to the image carrier 1 are not equal at both ends of the transfer member 3.
[0012]
On the other hand, as shown in FIG. 2B, when the swing fulcrum S is freely movable so as not to give the rotational moments M1 and M2, the transfer member 3 is not supported. Stop functioning.
This is the same in a mode in which the transfer member 3 has a tapered shape (see (3) in FIG. 2B).
Therefore, it is meaningless to provide the swing fulcrum S in a portion other than substantially the center of the transfer member 3 in the axial direction, and the swing fulcrum S needs to be provided substantially in the axial center of the transfer member 3.
[0013]
As described above, providing the swing fulcrum S substantially at the center of the transfer member 3 in the axial direction means that the transfer member 3 swings with the pressing point 5 of the swing support member 4 acting as a fulcrum. As shown in FIG. 1B, it is preferable that the pressing force of the pressing means 6 can be directly transmitted to the transfer member 3 without dispersing.
[0014]
Further, from the viewpoint of pressing the surface of the image carrier 1 and the surface of the transfer member 3 in parallel to prevent the transfer member 3 from being twisted, the image carrier 1 It is preferable to provide a guide member 7 that regulates the axis of the transfer member 3 and the axis of the transfer member 3 in parallel.
Further, in the mode in which the guide member 7 is provided, from the viewpoint of reducing the rotational friction given to the guide member 7 by the image carrier 1 and the transfer member 3, the guide member 7 is provided between the bearing of the image carrier 1 and the transfer member 3. It is preferable to be disposed so as to sandwich the bearing. According to this aspect, the rotational load applied to the axis of the image carrier 1 and the transfer member 3 is reduced, and the image carrier 1 and the transfer member 3 can operate stably.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
◎ Embodiment 1
FIG. 3 shows Embodiment 1 of the image forming apparatus to which the present invention is applied.
In FIG. 1, the image forming apparatus is a so-called intermediate transfer type color image forming apparatus, and has, for example, a photosensitive drum 20 that is rotationally driven by a drive motor. 30 and a secondary transfer roll 40 as a secondary transfer device is disposed at a predetermined position of the intermediate transfer belt 30, and a recording material conveying path that has passed through a secondary transfer portion by the secondary transfer roll 40. The fixing device 50 is disposed downstream of the fixing device 50.
[0016]
In the present embodiment, a charger (scorotron in this example) 21 for charging the photosensitive drum 20 is provided around the photosensitive drum 20, and each color component (yellow (Y) in this example) is placed on the photosensitive drum 20. , Magenta (M), cyan (C), black (K)) and an exposure device 22 such as a laser scanning device for writing an electrostatic latent image (a beam from the exposure device is denoted by a symbol in the figure) and a photosensitive drum 20 A developing device (in this example, a rotary developing device) 23 for visualizing the electrostatic latent image of each color component with a corresponding color toner, and cleaning the untransferred toner (residual toner) remaining on the photosensitive drum 20 Cleaning device 24 is provided.
[0017]
The intermediate transfer belt 30 is, for example, stretched over a plurality of stretching rolls 31 to 34, and the photosensitive drum is configured such that the stretching roll 31 is a driving roll, the stretching roll 32 is a driven roll, and the stretching roll 33 is a tension roll. 20 and is circulated and rotated so as to rotate in the same direction.
A primary transfer roll 35 as a primary transfer device is provided on the back surface of the intermediate transfer belt 30 facing the photoconductor drum 20, and a transfer electric field necessary for the primary transfer is formed between the primary transfer roll 35 and the photoconductor drum 20. It is supposed to be.
[0018]
Further, the secondary transfer roll 40 in the present embodiment is disposed to face the intermediate transfer belt 30 using the tension roll 34 as a backup roll, and a transfer electric field required for secondary transfer between the secondary transfer roll 40 and the intermediate transfer belt 30 is formed. Is formed.
Furthermore, the recording material transport system transports the recording material once to a secondary transfer site after positioning the recording material by a resist roll 41 disposed upstream of the secondary transfer roll 40, and then guides the guide plate 42 and a transport belt. The recording material is conveyed to the fixing device 50 via 43.
[0019]
In the present embodiment, the primary transfer roll 35 and the secondary transfer roll 40 are made of a urethane rubber tube in which carbon is dispersed on the surface, and the inside is made of urethane foam in which carbon is dispersed, and the roll surface is further coated with fluorine. ing.
The backup roll 34 is made of a blend rubber tube of EPDM and NBR in which carbon is dispersed on the surface, and the inside is made of EPDM rubber.
[0020]
Further, in the present embodiment, as shown in FIG. 4, the primary transfer roll 35 is supported by a swing support member 60 via a bearing (not shown), and the swing support member 60 is attached by a spring member 70. It is being stressed.
In the present embodiment, the swinging support member 60 has a substantially U-shaped base 61, and a rotatable support 62 is disposed substantially at the center of the base 61 in the longitudinal direction. Is provided with a column 63 extending perpendicular to the base 61. For this reason, the swing support member 60 can swing about the support portion 62 as a fulcrum.
Further, a spring member 70 for urging the primary transfer roll 35 toward the photosensitive drum 20 is provided on the other end side of the support portion 63 where the support portion 62 is not provided.
[0021]
Next, the operation of the image forming apparatus according to the present embodiment will be described (see FIGS. 3 and 4).
In the present embodiment, the photosensitive drum 20 is driven to rotate by a drive motor (not shown), uniformly charged to minus several hundred volts by a charger 21, and then exposed by an exposure device 22 to form an electrostatic latent image. The toner image is developed by the developing device 23 and becomes a toner image.
At this time, a developing bias is applied to the developing device 23 from a bias power supply (not shown), and in the case of reverse polarity development, negatively charged toner is developed on the photosensitive drum 20.
Then, the toner image on the photosensitive drum 20 is transferred to the intermediate transfer belt 30 by applying a positive applied bias by the primary transfer roll 35.
[0022]
At this time, in the present embodiment, the primary transfer roll 35 is pivotally supported by the swing support member 60, and the photosensitive drum 20 is supported by the support portion 62 which is located on a line orthogonal to substantially the center of the primary transfer roll 35 in the axial direction. , The nip amount with the photosensitive drum 20 can be kept constant.
For example, even when the photoconductor drum 20 is tilted and attached due to an assembling dimensional error, or when there is a shape error (eccentricity / layer thickness unevenness) between the photoconductor drum 20 and the primary transfer roll 35, the primary transfer roll 35 Both end parts swing. For this reason, the primary transfer roll 35 can rotate following the inclination, shape, and the like of the photoconductor drum 20. As a result, the axial nip amount between the photoconductor drum 20 and the primary transfer roll 35 is constant. Become.
In addition, at the secondary transfer portion where the secondary transfer roll 40 and the backup roll 34 face each other, the swing support member 60 and the spring member 70 are used for the secondary transfer roll 40 so that the swing support member 60 can be used. Has almost the same function as the action on the primary transfer roll 35 at the primary transfer site, and therefore can be applied to the primary transfer site. The same applies to the following embodiments.
[0023]
◎ Embodiment 2
The image forming apparatus used in this embodiment is substantially the same as that of the first embodiment, except that the swing support member 60 and the spring member 70 provided on the primary transfer roll 35 are different from the first embodiment. This is a mode in which the swing fulcrum 35 and the position where the spring member 70 acts are different (see FIG. 4).
In this embodiment, as shown in FIGS. 5A and 5B, the swing support member 80 has a rod-shaped shaft 82, and both ends of the shaft 82 are connected to the frames 81a and 81b via bearings 83. It is supported and is substantially U-shaped.
Supporting portions 84a and 84b are provided at substantially the center in the longitudinal direction of the frames 81a and 81b, respectively. The supporting portions 84a and 84b are supported by an image forming apparatus main body (not shown) so that a swing supporting member is provided. 80 is swingable with each of the support portions 84a and 84b as a fulcrum.
On the other hand, the primary transfer roll 35 is rotatably supported via bearings 83 on the other end sides of the frames 81a and 81b on which the shaft 82 is not provided. The spring member 71 pulls down the swing support member 80 in the direction of arrow A in the figure. Thus, the primary transfer roll 35 is urged toward the photosensitive drum 20 by being pushed up in the direction B in the figure (see FIG. 5B).
Regarding the torsion of the swing support member 80, the shaft of the primary transfer roll 35 and the shaft 82 rotate because the primary transfer roll 35 and the shaft 82 are disposed on the frames 81a and 81b via the bearing 83. Can be absorbed.
[0024]
In the present embodiment, since the frame 81a swings around the support portion 84a as a fulcrum, the frame 81b swings around the support portion 84a as a fulcrum. 35 can rotate following the movement of the photosensitive drum 20.
Therefore, similarly to the first embodiment, the nip area between the primary transfer roll 35 and the photosensitive drum 20 in the axial direction is constant.
[0025]
◎ Embodiment 3
The image forming apparatus used in the present embodiment is substantially the same as that in the first embodiment, but differs from the first embodiment in that a guide member 90 for supporting the photosensitive drum 20 and the primary transfer roll 35 is provided. different.
In the present embodiment, as shown in FIGS. 6A and 6B, the guide member 90 connects the shaft center 20a of the photosensitive drum 20 and the shaft center 35a of the primary transfer roll 35 to a plate-shaped guide frame 90a, 90b. The slits 91 formed by the guide frames 90a and 90b are set to the widths of the diameter of the shaft 20a of the photosensitive drum 20 and the diameter of the shaft 35a of the primary transfer roll 35, respectively. 35a is slidable along the slit 91.
In the present embodiment, the shaft core 20 a of the photosensitive drum 20 is fitted to a bearing 101 provided on the apparatus main body 100, and the guide frame 90 a is located axially inward of the photosensitive drum 20 from the bearing 101. , 90b. Further, the shaft core 35a of the primary transfer roll 35 is sandwiched between the guide frames 90a and 90b, and is axially supported by the swing support member 60 inside the guide member 90 in the axial direction.
The swing support member 60 and the spring member 70 used in the present embodiment are substantially the same as those used in the first embodiment.
[0026]
In the present embodiment, as described above, the axis 20a of the photosensitive drum 20 and the axis 35a of the primary transfer roll 35 are sandwiched by the guide member 90, and slide along the slit 91 provided in the guide member 90. Therefore, the photosensitive drum 20 and the primary transfer roll 35 are not twisted.
Therefore, the spring member 70 pressing the swing support member 60 can always press the surface of the photosensitive drum 20 and the surface of the primary transfer roll 35 in parallel.
[0027]
Further, in the present embodiment, the guide member 90 does not sandwich the shaft core 20a of the photosensitive drum 20 and the shaft core 35a of the primary transfer roll 35, but is provided on the respective shaft cores 20a and 35b (not shown). When the bearing is sandwiched between the photosensitive drum 20 and the primary transfer roll 35, the rotational load of the photosensitive drum 20 and the primary transfer roll 35 is reduced, and the guide member 90 is not affected by the friction received from the photosensitive drum 20 and the primary transfer roll 35. This is a preferred embodiment.
[0028]
【The invention's effect】
As described above, according to the present invention, in an image forming apparatus that forms a nip area between an image carrier and a transfer member, a swing support member that swingably supports the transfer member is provided. Since the transfer member is provided with a pressing means for pressing the transfer member toward the image carrier at the point of application of the rocking support member located on a line perpendicular to the substantially center in the axial direction of the image carrier, the image carrier may be inclined due to an assembly dimensional error or the like. Even if the transfer member has been attached or has been tapered as a whole due to uneven thickness of the image carrier and the transfer member, both ends of the transfer member swing and follow the shape of the image carrier. The transfer member swings, and as a result, the axial nip amount becomes constant.
For this reason, the voltage applied to the transfer member is uniformly generated without bias at both ends of the transfer member, and image quality defects such as transfer unevenness do not occur.
Furthermore, since the nip amount is uniform, it is possible to prevent the transfer medium such as the recording paper from being skewed or wrinkled due to the non-uniform nip amount.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to the present invention.
FIG. 2 is an explanatory diagram illustrating a relationship between a fulcrum and an action point in a transfer member.
FIG. 3 is a schematic diagram illustrating the image forming apparatus according to the first embodiment;
FIG. 4 is an explanatory diagram illustrating a swing support member according to the first embodiment.
FIG. 5A is a perspective view illustrating a swing support member according to a second embodiment, and FIG. 5B is a side view of the swing support member.
FIG. 6A is a front view illustrating a swing support member and a guide member according to a third embodiment, and FIG. 6B is a side view illustrating the swing support member and a guide member.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Transfer receiving body, 3 ... Transfer member, 4 ... Swing support member, 5 ... Pressing point, 6 ... Pressing means, 7 ... Guide member, 8 ... Batch transfer means, 9 ... 2 Next transfer member, T: image, K: recording material

Claims (4)

An image forming apparatus comprising: an image carrier on which an image is carried; and a transfer member that forms a nip area between the image carrier and transfers an image formed on the image carrier to a transfer object. At
A swing support member for swingably supporting the transfer member,
An image having a pressing action point on a swing support member positioned on a line perpendicular to a substantially center in the axial direction of the transfer member, and a pressing means for pressing the transfer member toward the image carrier. Forming equipment. The image forming apparatus according to claim 1,
The image forming apparatus is characterized in that the transfer member swings around a pressing point of the swing support member as a fulcrum. The image forming apparatus according to claim 1,
An image forming apparatus, comprising: a guide member for regulating the axis of the image carrier and the axis of the transfer member to be parallel to each other when the transfer member is in contact with the image carrier. The image forming apparatus according to claim 3,
The image forming apparatus is characterized in that the guide member is disposed so as to sandwich the bearing of the image carrier and the bearing of the transfer member.

Images