1. Field of the Invention
The present invention relates to an image forming apparatus, such as a copying machine, a laser beam printer, a laser facsimile machine, and a multifunction machine thereof, by which an image is formed on a sheet material.
2. Description of the Related Art
A number of image forming apparatuses such as a color copying machine and a color laser beam printer, by which an image is formed according to an electrophotographic type or an electrostatic recording type, adopt an intermediate transfer type in which an image forming apparatus has a configuration provided with a photosensitive drum and an intermediate transfer belt as an image bearing member. According to the intermediate transfer type, an image born on a photosensitive drum is transferred (primary transfer) onto the surface of an intermediate transfer belt, and the images on the intermediate transfer belt are transferred at a time onto a sheet material as a recording medium (secondary transfer), as disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-244449. A number of image forming apparatuses adopting the intermediate transfer belt type have been proposed.
In the secondary transfer portion, the sheet material S is guided along the guide path formed with the secondary transfer feeding guides 1 and 2, and the images on the intermediate transfer belt 3 are transferred at a time onto the sheet material S, while the sheet material S is being pressed between the secondary transfer rollers 4 and 5, when the sheet material S is fed out through the pair of resistration rollers 7 and 8 which rotate by rotating power received from a motor (not shown) as a driving source. In this case, the resistration roller 8 as one of the roller pair, together with a roller bearing 9, is energized with a pressing spring 11, and is pressed against the resistration roller 7 as the other of the roller pair, and the secondary transfer roller 5 as one of the roller pair, together with a bearing arm 6, is energized with a pressing spring 10, and is pressed against the secondary transfer roller 4 as the other of the roller pair.
Following
Incidentally, the behavior of the sheet material S just before the sheet material S is fed into the secondary transfer portion has been shown as a general example in
As shown in
Furthermore, the conveying path frame 12 is set with the maximum dimensional tolerance between the front and the far-side at positioning in some cases. Then, there is caused a front and far-side difference between the both sides, that is, for the width of a guide path in a conveying segment between the resistration rollers 7 and 8, and the secondary transfer roller 4 and 5. Thereby, timing at which the sheet material S enters into a nip portion between the secondary transfer rollers 4 and 5 is different from each other at the both sides of the tip of the sheet material S, and there is caused a phenomenon in which an image is transferred in a state in which the image is inclined in the front and far-side direction relative to the sheet material S. Accordingly, image magnifications are different from each other between the front and the far-side to cause an abnormality in an image.
Considering the above circumstances, an object of the present invention is to provide an image forming apparatus by which, by adjusting the feeding of a sheet material during conveying in such a way that there is caused no displacement between feeding amounts at the both ends in the sheet-width direction, a high-quality image can be printed without causing an abnormality, such as a displacement, in an image transferred on the sheet material.
In order to achieve the above-described object, an typical image forming apparatus according to the present invention is provided with: a first sheet conveying member arranged at upstream side of a sheet conveying path;
a second sheet conveying member arranged at downstream side of said sheet conveying path;
a guide member which is provided between said first and said second sheet conveying members and guides a sheet material conveyed from said first sheet conveying member to said second sheet conveying member; and
a movable portion which is movably provided in said guide member, wherein said movable portion has an abutment portion against which the sheet material conveyed toward to said second sheet conveying member by said first sheet conveying member is abutted, and said abutment portion is adjusted by movement of said movable portion so that the tip of the sheet material guided by said guide member is in parallel to a sheet width direction perpendicular to a conveying direction.
Hereinafter, preferred embodiments of an image forming apparatus according to the present invention will be explained in detail, referring to drawings. Here, members similar to those previously described with reference to the structure examples shown in
(Explanation of Image Forming Apparatus)
In the first place,
An image formation device 160 has a configuration provided with a photosensitive drum 1 as an image bearing member, a charging roller 8 for uniformly charging the surface of the photosensitive drum 1, a drum cartridge 50 including a cleaner 9 which removes toners remained in the photosensitive drum 1 after transferring of a toner image, and the like, a rotary developing unit 151 forming a toner image on the photosensitive drum 1, an intermediate transfer belt unit 60, onto which the toner image developed on the surface of the photosensitive drum 1 is transferred, and the like.
The photosensitive drum 1 has a configuration in which the optical image is irradiated from a laser unit 109 onto the surface of the photosensitive drum 1 charged by the charging roller 8, and an electrostatic latent image formed with the optical image is developed and is transferred onto the intermediate transfer belt 3. The toner images on the intermediate transfer belt 3 are transferred at a time onto a sheet material S as a material, onto which an image is transferred, in the secondary transfer portion by one pair of the secondary transfer rollers 4 and 5 which are facing with each other, holding the intermediate transfer belt 3 therebetween. The sheet material S is supplied from a sheet cassette 127.
Here, as shown in
In
(Explanation of Sheet Conveying Apparatus)
That is, assuming that, in the above-described sheet correcting plate 20 forming the secondary transfer feeding guide 1, an abutment portion provided in the correcting portion 21 is A, a nip portion of the pair of the secondary transfer rollers 4 and 5 is B, and a nip portion of the pair of the registration rollers 7 and 8 (second sheet conveying member) is C, the point A exists on an ellipsoidal orbit P with focal points of the point B and the point C. That is, AB+AC obtained by adding the distances from the point A to the focal points B and C corresponds to a guide path length L meaning a distance in which the sheet material S is guided in the conveying section between the secondary transfer rollers 4 and 5 and the registration rollers 7 and 8.
Even when the sheet correcting plate 20, that is, the correcting portion 21 is moved for adjustment in the tangential direction (in the direction of the arrow Y shown in the drawing) to the ellipsoidal orbit P passing the abutment portion A, the guide path length L (=AB+AC) moves approximately on an ellipsoidal orbit. Thereby, when the correcting portion 21 is moved in the direction (in the direction of the arrow X shown in the drawing) approximately perpendicular to the tangential direction to the ellipsoidal orbit P passing the abutment portion A under a state that the guide path length L is not changed, the sensitivity for the change in the guide path length L becomes the highest.
Thereby, the whole of the secondary transfer feeding guide 1 is moved for adjustment in the direction (in the direction of the arrow X shown in the drawing) approximately perpendicular to the tangential direction to the ellipsoidal orbit P passing the abutment portion A, and fine adjustment is executed, in such a way that the front and far-side difference of the guide path length L is removed. Accordingly, an image shift at the tip portion of the sheet material S is prevented, and generation of an image with an abnormal image magnification is effectively suppressed. Incidentally, assuming that a bending angle ∠BAC at the abutment portion A is θ, and an incident angle ∠ABC to the secondary transfer portion is φ, a preferable θ is, for example, 140 degrees.
Moreover, when the hitting portion (not shown) of the conveying path frame 12 is abutted within a maximum tolerance, or even when the dimensional tolerance of a portion for positioning of the conveying path frame 12 is swung to the maximum, the front and far-side difference of the guide path length L is not caused by fine adjustment of the secondary transfer feeding guide 1 as shown in
Here, a relation among a bending angle θ at the abutment portion A of the secondary transfer feeding guide 1, a guide path length L, and an incident angle φ to the secondary transfer portion may be obtained from a trigonometric-function model, as shown in
Now, a guide path variation ΔL by guide adjustment, and an incident angle Δφ to the secondary transfer portion bye guide adjustment are expressed in the following formulae (1) and (2), respectively, for simplification of the model, when an adjusting amount is assumed to be Y at adjusting the abutment portion A to the portion A′ on condition of meeting a similar triangle figure ΔABM≡ΔACM at a point M.
ΔL=L′−L={d−sin (θ/2)}−{d−sin (θ′/2)} (1)
Δφ=φ′−φ=(θ/2)−(θ′/2) (2)
Then, when the bending angle θ is equal to, or smaller that, for example, 160 degrees, it is found in the guide configuration than angle variation in the neighborhood of the transfer roller can be reduced because, when the bending angle θ is smaller than about 160 degrees, the inclination of Δφ to the change in the bending angle θ becomes sharp according to the graph
Moreover, when the bending angle θ is equal to, or smaller than, for example, 120 degrees, it is found according to the graph shown in
Though the first secondary transfer feeding guide 1 is moved in the direction (in the direction of the arrow X shown in the drawing) approximately perpendicular to the tangential direction to the ellipsoidal orbit P passing the abutment portion A in the present embodiment, the adjusting direction of the abutment portion A may be set approximately parallel to the straight line AB connecting the nip portion B of the secondary transfer rollers 4 and 5 and the abutment portion A, giving priority to a configuration in which angle variation in the vicinity of the transfer roller can be made smaller. Thereby, there may be provided a guide adjusting mechanism in which angle variation in the vicinity of the transfer roller is controlled, though there may be attended by some sacrifices of the guide adjusting efficiency.
Moreover, generation of front and far-side shift of an image at the tip of the sheet material S, or an abnormal image caused by an abnormality in the image magnification and the like may be prevented according to the present embodiment, because the front and far-side difference of the guide path length L may be efficiently adjusted by adjusting the secondary transfer feeding guide 1 to be slid and moved in the direction approximately perpendicular to the tangential direction to the ellipsoidal orbit P passing the abutment portion A. At the same time, the present invention has an advantage that a defective image due to air discharge just before entering into a nip portion of the secondary transfer rollers 4 and 5, may be prevented, and an abnormality in an image caused by transfer abnormality may be also prevented, because the angle variation in the neighborhood of the transfer roller of the sheet material S can be reduced.
Subsequently, a point of a second embodiment is a configuration in which, as shown in
That is, referring to
Moreover, the secondary transfer feeding guide 1 is controlled with a stepped machine screw 16 to move only in the direction (in the direction of the arrow X shown in the drawing) approximately perpendicular to the tangential direction to the ellipsoidal orbit P passing the abutment portion A, wherein the orbit has focal points of the point B and the point C. Thereby, the distance between the axis for the registration rollers 7 and 8 and that for the secondary transfer roller 4 and 5, that is, the guide path length L as a distance between the nips is automatically kept constant, and generation of front and far-side shift of an image at the tip of the sheet material S, or an abnormal image caused by an abnormality in the image magnification and the like may be prevented.
Here, the present invention is not limited to the first and second embodiments described above, and other embodiments or combinations thereof, and variants or applications may be possible without departing from the scope of the present invention.
For example, the first and second embodiments have disclosed a configuration in which fine adjustment of the secondary transfer feeding guide 1 by sliding for moving is manually or automatically executed. On the other hand, another embodiment adopting a configuration in which, when the rotational speeds V1 of the secondary transfer rollers 4 and 5 shown in
Moreover, though the first and second embodiments have been explained, assuming that concrete examples of two conveying means of the present invention are the registration rollers 7 and 8 and the secondary transfer rollers 4 and 5, even a combination of the registration rollers 7 and 8 and the fixing roller (not shown in the drawing), instead of the combination of the registration rollers 7 and 8 and the secondary transfer rollers 4 and 5, is also effective for the present invention.
This application claims the benefit of priority from the prior Japanese Patent Application No. 2005-146528 filed on May 19, 2005 the entire contents of which are incorporated by reference herein.
Number | Date | Country | Kind |
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2005-146528 | May 2005 | JP | national |
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Number | Date | Country |
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Number | Date | Country | |
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20060263128 A1 | Nov 2006 | US |