JP2007065241A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize high-definition printing by adjusting an image at a transfer nip part with a simple mechanism, and also, to maintain the durability of a member, regarding an image forming apparatus where a toner image on an image carrier is transferred onto a transfer material sheet by introducing a secondary transfer system. <P>SOLUTION: A sheet guiding member constituted of an inner guide 1 and an outer guide 2 is arranged on the upstream side just before the transfer material sheet S rushes into a transfer nip part (a) (contact point) of a curved surface formed by an intermediate transfer belt 130 and a pair of secondary transfer rollers 3 and 4 arranged facing each other at the inside and outside of the belt 130. The sheet guiding member is moved to establish X=Y, provided that X denotes a distance between the intersection of the center line linking between the roller center points of the pair of secondary transfer rollers 3 and 4 and a vertical line orthogonal to a straight line at the exit end (b) extending from the straight guiding part 1a of the sheet guiding member and the contact point at the transfer nip part (a), and Y denotes a distance between the intersection and the exit end (b) of the straight guiding part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

   The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a laser beam printer.

  In the field of image forming apparatuses, the intermediate transfer method is well known, and a toner image formed on a photosensitive drum (image carrier) is temporarily transferred onto the surface of an endless intermediate transfer belt (image carrier) to obtain a color image. In the case of printing, such primary transfer is repeated for each of a plurality of color toners to superimpose toner images. Next, the superimposed toner images are collectively transferred from the intermediate transfer belt onto the surface of the transfer material sheet, and the image is recorded on the sheet (see Patent Document 2).

  The intermediate transfer belt is configured by winding an endless flat belt body between a plurality of rollers such as a driving roller, a driven roller, and a tension roller. One of the plurality of winding rollers is for secondary transfer, and another secondary transfer roller is disposed opposite to the secondary transfer roller from the outside with the flat belt body interposed therebetween. A sheet that has been fed from the sheet feeding roller is fed into a transfer nip portion between the contact points where the secondary transfer roller inside and outside the belt and the flat belt main body contact each other. The secondary transfer roller on the outer side of the belt presses the fed sheet against the flat belt body, and the toner images on the surface of the flat belt body are transferred to the sheet all at once, and the secondary transfer is finished.

  Image adjustment to eliminate image non-uniformity that occurs after transfer at the transfer nip, or a method or structure for adjusting to a desired image magnification, such as changing the writing interval when a latent image is formed on the photosensitive drum, Measures such as providing a speed difference between the flat belt main body and the sheet have been taken (see Patent Document 1).

JP 2002-311676 A JP 2002-244449 A

  However, in the case of such an image adjustment method, a complicated and highly accurate control program and control device are required for variable control of the latent image writing and speed difference control, resulting in high cost. Further, if a speed difference is provided between the members, rubbing occurs between the members, and the members are easily damaged or worn, leading to a decrease in the life.

  An object of the present invention is to provide an image forming apparatus capable of realizing high-quality printing by enabling image adjustment at a transfer nip portion with a simple mechanism, and also effective in maintaining durability of members. .

In order to achieve the above object, a transfer unit that transfers an image on an image carrier carrying an image onto a sheet by a pair of transfer rollers facing each other across the image carrier, and an upstream side of the transfer unit. A sheet guide member for guiding the sheet, and an image forming apparatus comprising:
A linear guide portion for feeding the sheet linearly to the outlet side of the sheet guide member;
An intersection point between a central straight line connecting the roller center points of the pair of transfer rollers and a vertical line orthogonal to a straight line at the exit end extended from the linear guide portion of the sheet guide member is defined as s, and this intersection point s and the transfer When the distance between the contact point of the transfer nip portion of the means is X and the distance between the intersection s and the exit end of the linear guide portion is Y,
X = Y
The sheet guide member is moved while maintaining the state as described above.

  According to the image forming apparatus of the present invention, it is possible to perform image adjustment at the transfer nip portion with a simple mechanism without depending on complicated control and the like, and it is also effective in maintaining the durability of the members.

  Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 shows an image forming apparatus according to the present embodiment. A document table 102 made of a transparent glass plate is provided on the upper part of the apparatus main body 101, and the document pressing plate 103 has an image surface at a predetermined position on the document table 102. The original 100 set downward is pressed and fixed. An optical system including a lamp 104 that illuminates the document 100 and reflecting mirrors 105, 106, and 107 for guiding an optical image of the illuminated document 100 to the image processing unit 108 is provided below the document table 102. . Note that the lamp 104 and the reflection mirrors 105, 106, and 107 move at a predetermined speed to scan the document 100.

  The image forming unit 120 includes a photosensitive drum 121, a charging roller 122 that uniformly charges the surface of the photosensitive drum 121, and a rotary developing unit 125 that forms a toner image on the photosensitive drum 121. The image forming unit 120 includes an intermediate transfer belt (image carrier) 130 formed of an endless flat belt onto which the developed toner image is temporarily transferred onto the surface of the photosensitive drum 121. The image forming unit 120 further includes a secondary transfer unit 131 that collectively transfers the toner image of the intermediate transfer belt 130 to the sheet S as a transfer material, and the toner remaining on the photosensitive drum 121 after the toner image is transferred. Is provided with a cleaner 123 for removing water. The photosensitive drum 121 develops an electrostatic latent image formed by a light image irradiated from the laser unit 109 on the surface of the photosensitive drum 121 charged by the charging roller 122 and transfers it to the intermediate transfer belt 130. It has become. The sheet S is supplied from the sheet cassette 110.

  As shown in each figure in FIG. 2 and subsequent figures, the secondary transfer unit 131 as a transfer unit is a plurality of rotating rollers (for driving, for driving, for tension, etc.) that wind and stretch the intermediate transfer belt 130. A secondary transfer roller 3 on the inner side of the belt, and a secondary transfer roller 4 facing the secondary transfer roller 3 on the inner side of the flat belt body from the outer side. Hereinafter, the belt inner and outer secondary transfer rollers 3 and 4 are simply referred to as a transfer roller pair 3 and 4. A transfer nip portion a is formed at a contact portion between the intermediate transfer belt 130 and the pair of transfer rollers 3 and 4 that sandwich the flat belt body from inside and outside, and a toner image on the flat belt body is transferred with the sheet S interposed therebetween. The next transfer process is performed. The toner image is transferred to the sheet in a state where the sheet is bent at the transfer nip a (a state having a curvature).

  On the other hand, on the downstream side of the image forming unit 120, a fixing device 135 that fixes the toner image on the conveyed sheet S as a permanent image, and the sheet S on which the toner image is fixed in the fixing device 135, are copied. A pair of discharge rollers 112 for discharging from the nozzles are arranged in order. A discharge unit 113 that receives the sheet material S discharged by the discharge roller pair 112 is provided outside the copying machine main body 101.

  Here, the concept of image adjustment in the transfer nip portion, which is the basis of the present invention, will be schematically described with reference to FIG.

Assuming that the thickness dimension of the sheet S is t and the radius of curvature up to the transfer surface of the sheet S is r1, the curvature radius r2 at half t / 2 of the thickness dimension t of the sheet S is
r2 = r1 + t / 2
It is. If the size of the image 10 at the time of transfer that is in a contracted state with a radius of curvature r1 is represented by A1, the size A2 of the image 10 ′ after the transfer expands flatly and becomes A1 <A2. . The image elongation ratio ε after the transfer from A1 to A2 is expressed by the ratio of r2 and r1.
ε = A2 / A1 = r2 / r1 = 1 + t / (2r1)
It becomes. That is, by changing the sheet curvature radius, the image elongation rate ε1 also changes. Therefore, the concept of image adjustment of the present invention is to make the image magnification after transfer desired by adjusting the curvature radius r of the sheet S on the upstream side immediately before entering the transfer nip a.

  As shown in FIGS. 3 and 4, when the sheet S enters the transfer nip portion a, it seems to be curved following the flat belt body curvature radius Rt of the intermediate transfer belt 130, but when viewed macroscopically, Actually, the belt curvature radius Rt and the sheet curvature radius r do not always match. In that case, when the sheet S is guided by a guide member comprising an inner guide 1 and an outer guide 2 provided upstream immediately before entering the transfer nip a, the curvature radius r of the sheet is the guide. It depends on the radius rs formed in the tangential direction of the sheet S immediately after coming out of the member. Focusing on this, adjustment for correcting the enlargement magnification or elongation of the toner image transferred onto the sheet S is possible in the range of Rt ≦ rs ≦ ∞. For example, when Rt = 10 [mm] and t = 0.1 [mm], considering the track effect, the image elongation ε is 0 ≦ ε ≦ 1.005, and is adjusted by 0 to 0.5%. Is done.

In FIG. 2, assuming that the center straight line A connects the center points of the pair of transfer rollers 3 and 4, a contact point between the flat belt body of the transfer nip portion a and the sheet S exists on the center straight line A. On the downstream side of the inner guide 1, there is a sheet linear guide portion 1 a in which the sheet guide surface has a linear cross section. Let the exit point (downstream end) of the sheet linear guide 1a be b. Let s be the intersection of a line that passes through the exit point b and is perpendicular to the sheet guide surface of the sheet linear guide 1b and the center straight line A. That is, the intersection of the vertical line perpendicular to the straight line at the exit point b as the exit end extended from the straight sheet guide portion 1b as the straight guide portion formed on the inner guide 1 and the center straight line A is defined as s. . The linear distance sb connecting the exit point b of the sheet linear guide portion 1a of the inner guide 1 and the intersection point S is equal to the linear distance sa connecting the intersection point s and the transfer nip portion a (sa = sb). Further, the inner guide 1 and the outer guide 2 as the sheet guide members are:
sa = sb
With this state maintained, it is moved by an adjusting mechanism such as a multi-joint link mechanism 5 described later.

  By adjusting the movement of the sheet guide member, the inner guide 1 guides the posture of the sheet S immediately before entering the contact point (symbol a) in the transfer nip portion in a straight and flat manner. In the state of sa = sb, the curvature radius r of the sheet entering the transfer nip portion is equal to the radius rs formed in the tangential direction of the sheet S immediately after exiting from the inner and outer guides 1 and 2. If the inner guide 1 moves while maintaining sa = sb, the curvature radius r of the sheet that has entered the transfer nip portion is equal to the radius rs regardless of the position of the inner guide 1.

  In the state where sa = sb is maintained, the radius rs that determines the curvature radius r of the sheet is the straight line distance sb connecting the intersection point s to the exit point b of the sheet linear guide portion 1a of the inner guide 1 and the intersection point. The length is the same as the linear distance sa from s to the transfer nip part a. In the state of sa = sb, since the curvature radius r of the sheet can be obtained based on the linear distance sb and the radius rs equal to the linear distance sa, the transfer magnification can be easily calculated based on the curvature radius r of the sheet. Therefore, by changing the radius rs according to the configuration described later, it is possible to easily adjust the toner image secondarily transferred from the intermediate transfer belt 130 to the sheet S with the same magnification or the set elongation rate or magnification. By adjusting the toner image in this manner, it is possible to record an image with uniform magnification and no elongation in the recording area from the leading end to the trailing end on one type of sheet S of all kinds.

  2 to 4 showing the adjustment mechanism, a sheet guide member is disposed upstream in front of the transfer nip portion a. The seat guide member is composed of a pair of an inner guide 1 and an outer guide 2, and the position of the entire guide member can be changed by operating the articulated link 5 coupled to the inner guide 1. In this example, the multi-joint link 5 has a structure in which four joint members 5a, 5b, 5c, and 5d are connected to each other by hinge pins. Further, a slider piece 7 is provided for moving the multi-joint link 5 for each joint. The slider piece 7 is guided to the inside of the piece guide frame 8 and moved by receiving power from a driving means (not shown), and an arbitrary link of the multi-joint link 5 is connected via a link support portion 7 a inside the slider piece 7. The joint member can be supported.

  Further, the sheet guide member composed of the inner and outer guides 1 and 2 is urged in the direction of being pulled by an elastic member such as a spring in the direction of arrow C in FIG. The inner and outer guides 1 and 2 are guided and moved inside an annular track support guide 6 via a bracket 1 a provided at the rear end of the inner guide 1. Further, the inner guide 1 has a straight guide portion 1a that guides and feeds the sheet S in a straight line. By applying tension to the multi-joint link 5, an exit point b of the seat straight guide portion 1a of the inner guide 1 is provided. The direction of the sheet linear guide portion 1a of the inner guide 1, that is, the sheet feeding direction is perpendicular to the straight line B (see FIG. 3) connecting the multi-joint link 7 and the angle at the exit point b is a right angle (90 °). So that it can be kept. That is, the tangent line that determines the radius of curvature at the time of transfer of the sheet S is obtained by adjusting the entrance and exit dimensions of the exit point b of the sheet linear guide portion 1a of the inner guide 1 by mechanical operation. Further, the correction roller 9 disposed behind the guide member urges the sheet S in that direction so that the sheet S can be guided by being pressed against the inner guide 1, thereby assisting in maintaining a predetermined sheet transfer radius of curvature. ing.

  As shown in FIG. 2, by changing the link length from the portion of one joint member 5b by the movable adjustment of the link support portion 7a of the slider piece 7, the sheet S immediately after coming out of the inner and outer guides 1 and 2 is changed. The radius rs formed in the tangential direction changes. Thereby, the sheet transfer radius can be changed. The sheet transfer curvature radius is changed by moving the slider piece 7 in the same manner (see FIG. 4).

  Driving the link support portion 7a of the slider piece 7 to change the link length by changing any of the multi-joint members 5a to 5d is based on the sheet selection signal input by the user on the operation panel. It is controlled by the control unit. The control unit controls the operation of the link support portion 7a of the slider piece 7 based on the sheet information such as the thickness of the sheet S. However, the means for transmitting the operation from the drive source to the guide member is not limited to the articulated link mechanism 5 as described above, and smooth adjustment drive can be realized if a stepless track mechanism is employed instead. Further, by providing the magnification measuring means, it is possible to perform image adjustment by automatically changing the guide member based on the magnification detected by the magnification measuring means.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 4 is a diagram illustrating the engagement between a secondary transfer unit, which is a main part of the present embodiment, and an adjustment mechanism. The figure which shows typically the view of the image adjustment in this embodiment. The enlarged schematic diagram of the principal part. The figure which shows the operation example of the adjustment mechanism by this embodiment. The figure which illustrates typically the image nonuniformity which arises after a secondary transfer.

Explanation of symbols

1 Inner guide (sheet guide member)
1a Seat linear guide
2 Outer guide (sheet guide member)
3 Secondary transfer roller inside belt (secondary transfer section)
4 Secondary transfer roller outside belt (secondary transfer section)
5 Articulated link mechanism (adjustment mechanism)
130 Intermediate transfer belt (image carrier)
S Transfer material sheet a Transfer nip Rt Transfer curvature rs Sheet transfer curvature radius

Claims (5)

Transfer means for transferring an image on an image carrier carrying an image onto a sheet by a pair of transfer rollers facing each other across the image carrier, and a sheet guide member arranged on the upstream side of the transfer means to guide the sheet In an image forming apparatus comprising:
A linear guide portion for feeding the sheet linearly to the outlet side of the sheet guide member;
An intersection point between a central straight line connecting the roller center points of the pair of transfer rollers and a vertical line orthogonal to a straight line at the exit end extended from the linear guide portion of the sheet guide member is defined as s, and this intersection point s and the transfer When the distance between the contact point of the transfer nip portion of the means is X and the distance between the intersection s and the exit end of the linear guide portion is Y,
X = Y
The image forming apparatus is characterized in that the sheet guide member is moved while maintaining the state. The image forming apparatus according to claim 1, wherein the sheet guide member is moved by an operation signal output based on sheet size information including a thickness dimension of the sheet. The image forming apparatus according to claim 2, further comprising an adjustment mechanism that is driven by the operation signal to move the sheet guide member. The image forming apparatus according to claim 3, wherein the adjustment mechanism is a multi-joint link mechanism in which a plurality of joints are hinge-connected or a stepless displacement mechanism. The image forming apparatus according to claim 1, wherein the sheet guide member is moved according to a magnification detected by a magnification measuring mechanism.

Images