JP2001175041A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the extension of an image from becoming different at the leading edge part and the back half part of a transfer material in an image forming device having an image carrier moved by carrying an image to be transferred, a transfer means which is made to press-contact with the image carrier through the transfer material at a transfer part on the image carrier and moved in the same identical direction as the moving direction of the image carrier and which feeds the transfer material while transferring the image to be transferred on the transfer material, a resist roller feeding the transfer material toward the transfer part and a feeding guide guiding the transfer material fed out from the resist roller to the transfer part. SOLUTION: This image forming device is provided with adjustment means (10R, 23R, 25 and 28) adjusting the nip pressure of the resist roller 3 by giving different between the feeding speed of the transfer material at roller 3 and that at the transfer part 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and a printing machine which conveys a transfer material at a proper timing by a registration roller, and an image obtained by combining some of these image forming functions. The present invention relates to a forming apparatus.

[0002]

2. Description of the Related Art As shown in FIG. 7, a drum-shaped image carrier (hereinafter, referred to as a photoconductor) 1 which carries an image to be transferred and moves.
The transfer unit 5 on the photosensitive member 1 presses the photosensitive member through the transfer material via the transfer material and moves in the same direction as the moving direction of the photosensitive member to transfer the transferred image onto the transfer material. A transfer unit 2 for conveying the material, a registration roller 3 for feeding the transfer material toward the transfer unit 5, a conveyance guide 4 u for guiding the transfer material sent from the registration roller 3 to the transfer unit 5,
There is an image forming apparatus having 4d.

In FIG. 7, a transfer means 2 includes a transfer roller,
The registration roller 3 includes a pair of rollers. The transfer section 5 includes a peripheral portion including a nip portion between the photosensitive member and the transfer means, and a so-called transfer paper is used as a transfer material.

Conventionally, in such an electrophotographic copying machine, one of the problems in transferring a toner image, which is an image to be transferred, to a transfer material is a transfer failure phenomenon referred to as so-called hollowing.

[0005] The hollow portion is a phenomenon in which the toner at the edge portion of a character or an image is transferred only to the peripheral portion and the inner toner remains on the photoconductor side, so that the central portion of the image is lost. It is said that hollowing occurs because excessive pressure acts on the toner and the toner aggregates.

In order to eliminate such a hollow phenomenon, the following means have been proposed. Japanese Unexamined Patent Publication No. Hei 6-35345 discloses that in order to prevent dropout, the maximum pressing force of a transfer material to a photoreceptor caused by pressure contact by a contact-type transfer unit and pressure contact due to rigidity of the transfer material is determined by a transfer roller. There is disclosed an image forming apparatus that controls a pressing force on a body drum within a predetermined range. Japanese Patent Application Laid-Open No. Hei 6-348152 discloses that, in order to eliminate a hollow portion, a part or all of a recording material guide member to an entrance to a transfer portion of a recording paper is movable, and a conveyance member is adjusted according to the thickness of the recording paper. And an image forming apparatus in which the recording paper is moved upstream of a contact nip portion between the photosensitive member and the transfer means by moving the recording paper. Japanese Patent Application Laid-Open No. 7-319302 discloses that the peripheral speed of a transfer roller is 3 to 15% higher than that of an image carrier in order to prevent toner fixation and filming of the image carrier and to prevent poor transfer of a hollow image.
There is disclosed an image forming apparatus in which the transfer speed of the transfer material is increased by 0.5 to 2.5%, and the coefficient of friction between the transfer material and the transfer roller, the hardness of the transfer roller, and the pressing force are set. Japanese Patent Application Laid-Open No. 6-239489 discloses that a transfer material is not displaced or an image is displaced without suddenly generating tension in the transfer material.
To prevent image loss and wrinkles, after a loop is formed at the leading end of the transfer material, the transport speed by the transport means is switched to be lower than the peripheral speed of the photoconductor to reduce the loop and reduce the transfer material. A transfer material conveying device that generates tension is disclosed.

[0007] In each of the above disclosed technologies, the situation of each transfer material is taken into consideration in order to eliminate the voids, but the extension of the image at the leading end and the latter half of the transfer paper is considered. It does not control in consideration of the deviation (magnification deviation of the transferred image).

In the above-described disclosed technique, the transport speed is changed after the loop is formed, but before and after the change, the speed is switched between a case where the speed is faster than the peripheral speed of the photosensitive drum and a case where it is slower.

In the above prior arts (1) to (4), adjustment of the transfer pressure and the method thereof, the peripheral speed difference of the transfer roller and the like are devised.
In particular, in the above, the linear speed of the registration roller after paper feeding is set to be faster than the transport speed in the transfer unit, and the moving speed of the transfer unit is increased to transport the transfer material faster than the photoconductor. As a result, not only electrostatic force but also mechanical force is applied to the toner on the photoreceptor to eliminate hollow holes,
These days, it is generally done.

However, if a difference is made between the moving speed of the photosensitive member and the moving speed of the transfer material as described above, the transfer amount of the transfer material during the transfer will be between the leading end of the transfer material in the transfer section and the latter half thereof. Therefore, there is a problem that the image elongation differs between the leading end portion and the rear half portion of the transfer material. This also changed the state of improvement in hollowing between the tip and the second half.

The possible causes are described below. Normally, the transfer speed of the transfer material is set to be slightly higher at the registration roller portion than the transfer speed at the transfer section so that the transfer material is not pulled by the registration roller. Otherwise, the transfer material is pulled by the registration roller, and the image is blurred, or the transfer material is not normally conveyed, so that a paper jam easily occurs.

When the speed at the registration roller portion is slightly higher than the speed at which the transfer material is conveyed to the transfer portion, and when the transfer material is observed, a short time after the transfer material arrives at the transfer portion and is fed, the transfer material is in the middle of the guide. And it gradually becomes larger in the shape of a mountain.

When the flexure occurs, the transfer material is pushed toward the transfer portion due to the rigidity of the transfer material, and the force of the transfer material causes the speed of the transfer material to be faster than when the leading end of the transfer material passes through the transfer portion.
For this reason, the degree of elongation of the image changes at the leading end and the latter half of the transfer paper, and a magnification deviation occurs in the transferred image.

Another problem during transfer is transfer dust. Transfer dust is a phenomenon in which the periphery of an image is blurred by toner. In order to prevent the transfer dust, the position where the transfer material enters the transfer portion is set at the upstream position of the transfer nip so that the transfer material is in close contact with the photoconductor.

If the leading end of the transfer material is directly applied to the photosensitive member before the transfer portion, the photosensitive member vibrates, causing jitter, which is blurring of writing. At the exit of the guide, adjust the shape of the guide that guides the transfer material to the transfer unit so that the transfer material goes downward toward the transfer nip at the exit of the guide so that the leading end does not directly hit the photoconductor. The feed direction is adjusted.

For the above reasons, the upper guide 4u shown in FIG.
The lower guide 4d is configured as follows. Upper guide 4u
Is a guide that rises from a position obliquely above the nip portion of the pair of registration rollers 3 constituted by the upper roller 3u and the lower roller 3d and rises with a gentle inclination toward the transfer unit 5, and has a gentle upward convex near the photoconductor 1. It becomes curved, and the leading end is made closer to the position before the transfer unit 5 along the peripheral surface of the photoconductor 1.

On the other hand, the lower guide 4d is a guide toward the transfer portion 5 with a gentle inclination from a position obliquely below the nip portion of the registration roller 3, and has a sharply convex upper end near the front end thereof. Becomes substantially the same height as the transfer unit 5 and thereafter, is inclined downward and the leading end is located at a position close to the upstream position in the rotation direction of the transfer unit 2.

As described above, the shape of the guide that is curved upward and convex in the vicinity of the transfer portion has a tendency to promote the deflection of the transfer material. The transfer material is bent in the middle of the transfer, and a new feeding force due to the bending acts on the transfer material in the transfer portion, and the feed speed of the transfer material in the transfer portion is increased.

In order to avoid such a phenomenon, it is desirable that the transfer material is transported straight from the registration roller toward the transfer portion. However, such a layout is required depending on the size of the apparatus and the position of the developing apparatus. It is not always possible to design.

In this way, the guide having a convex shape in the vicinity of the transfer portion has a linear velocity difference between the transfer member and the photosensitive member in order to prevent centering, and the velocity difference is maintained. Therefore, when the transfer speed of the transfer material at the registration roller is set to be slightly higher than the transfer speed of the transfer material at the transfer unit, the transfer material is bent in a chevron shape, and the front end and the rear half of the transfer material are distorted. The problem that the elongation of the image was different occurred.

[0021]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus in which the extension of an image is not different between a leading end portion and a rear half portion of a transfer material while preventing a hollow portion.

[0022]

The present invention has the following configuration to achieve the above object. (1). An image carrier that carries and moves an image to be transferred; and a transfer unit presses against the image carrier via a transfer material and moves in the same direction as the moving direction of the image carrier to be transferred to the transfer material. An image having transfer means for transferring the transfer material while transferring an image, a registration roller for transferring the transfer material toward the transfer portion, and a transfer guide for guiding the transfer material sent from the registration roller to the transfer portion; In the forming apparatus, an adjusting means for adjusting the nip pressure of the registration roller by providing a difference between the transfer speed of the transfer material at the registration roller and the transfer speed of the transfer material at the transfer section is provided. (2). In the image forming apparatus described in (1), the nip pressure is changed during the passage of the transfer material in the transfer section (Claim 2). (3). In the image forming apparatus described in (1) or (2), the nip pressure is changed according to the type of the transfer material. (4). In the image forming apparatus described in (1), (2) or (3), the timing at which the nip pressure is changed is changed according to the type of the transfer material. (5). In the image forming apparatus described in (1), (2), (3) or (4), the nip pressure is changed according to the curl state of the transfer material before being conveyed to the registration roller. Item 5). (6). In the image forming apparatus described in (1), (2), (3), (4) or (5), the nip pressure adjusting means presses the movable roller against the fixed roller forming the registration roller. An urging means and a switching means for switching the strength of the urging means are provided.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [1] Outline of Image Forming Apparatus FIG. 1 is a schematic diagram showing a configuration of an image forming section of a printer to which the present invention is applied. The basic configuration of the image forming unit is as described with reference to FIG. 7, and will be supplemented with the description of FIG.

Around the photoreceptor 1, a charging roller 6, a developing device 7, a transfer means (hereinafter referred to as a transfer roller) 2, and the like are arranged in the order of rotation indicated by arrows. The photoconductor 1 is charged by a charging roller 6 during rotation, and the negatively charged photoconductor 1 is exposed to exposure light Ld emitted from a writing device (not shown) to form an electrostatic latent image.

In the developing device 7, a developing roller 7a is disposed so as to face the photosensitive member 1. The developing roller 7a forms a toner image as a transferred image by attaching positive toner to the electrostatic latent image carried on the photoreceptor 1. The toner image is
It is transferred to a transfer material in a later step. In this image forming apparatus,
A so-called negative-positive developing system in which the photosensitive member 1 is negatively charged and positive polarity toner is used is employed.

The toner image formed on the photosensitive member 1 reaches the transfer section 5 and is transferred to a transfer material. A transfer bias is applied from a power source 8 to the transfer roller 2 that is in pressure contact with the photoconductor 1 at the transfer section under constant current control.

The transfer roller 2 has a thickness of about 10 mm to 30 mm as a resistance layer on a shaft which is not driven and has a single-cell, open-cell,
Or, it is made of a material such as EDPM, BR, and chloroprene rubber having smoothness.

The volume resistance of the transfer roller 2 made of these materials is 10 ⁷ Ωcm to ^{10 10} Ωcm, and the Asker hardness is 3
It is around 0 ° (Japan Rubber Association Standard SRIS0101). The transfer roller 2 is pressed toward the photoconductor 1 by a spring (not shown). The force of the spring is applied to the metal core 2 a of the transfer roller 2.

The transfer roller 2 is driven to rotate in the same direction as the photosensitive member at a portion facing the photosensitive member by a drive source (not shown).
%, And at the same time, rotates at a linear speed as high as about%, conveys a transfer material (hereinafter, referred to as transfer paper) in the direction of arrow C in cooperation with the photoconductor 1, and transfers an image to be transferred on the photoconductor 1 to the transfer paper.

In the transfer section 5, the transfer paper is slightly slipped, so that it is fed at a linear speed of 90 to 97% of the linear speed of the transfer roller 2. Therefore, in writing with the exposure light Ld, the image is reduced correspondingly to form an image on the photoconductor 1.

The upper roller 3u constituting the registration roller 3
Is a metal roller, and the lower roller 3d is a rubber roller. As will be described later, the lower roller 3d is a fixed roller because it is supported between the side plates and does not change its position, and the upper roller 3u is a movable roller because it is movably supported by the side plate.
The upper roller 3u is pressed against the lower roller 3d by a spring.

The lower roller 3d is connected to a motor (not shown) so that the lower roller 3d is rotated in a direction for feeding the transfer paper. Transfer paper is fed from the tray to the registration roller 3. The transfer paper is fed at a predetermined timing, temporarily stops at the position of the registration roller 3, and is sent to the transfer unit 5 at a predetermined timing in synchronization with the image writing on the photoconductor 1.

The transfer paper fed between the upper guide 4u and the lower guide 4d as a transport guide has a toner image on the photoreceptor 1 by the action of a transfer bias supplied from a power source 8 while passing through the transfer section 5. Is transferred. The transfer paper exiting the transfer unit 5 is discharged by a separation device (not shown) and then discharged to a paper discharge unit via a fixing device.

Here, in order to facilitate understanding of the present invention,
The transfer paper transfer mode when the present invention is not applied, that is, when the nip pressure of the registration roller 3 is not adjusted, will be described with reference to FIG.

In FIG. 1, the transfer paper S1 shown by the solid line shows the state when the leading end of the transfer paper S has passed through the transfer nip of the transfer unit 5 by 10 mm. Under this condition,
The transfer paper S1 is fed only by the transfer force of the transfer roller 2.

The transfer conditions of the transfer paper at this time are as shown in Table 1.

[0037]

[Table 1]

In Table 1, the linear velocity of the transfer roller is set to 213.4 mm / sec with respect to the linear velocity of the photosensitive member of 200 mm / sec in order to prevent the dropout, and the linear velocity of the registration roller 3 is too high. Determined by experience, so as not to wrinkle the paper too much, the linear velocity is 206.2 mm / s
ec, and consequently, a transfer paper transport speed of 203.8 mm / sec in the transfer unit 5 is obtained with respect to a transfer paper transport speed of 206.2 mm / sec in the registration roller unit. The transfer speed of the transfer paper is set higher than the transfer speed of the transfer paper in the transfer unit, so that the registration roller 3 does not pull back the transfer paper in the transfer unit 5 in a direction opposite to the traveling direction of the transfer paper. .

Each of these feed speeds is empirically determined to be an appropriate amount. Note that a force of 1600 gf is applied to the registration roller 3 as a whole, and no slippage occurs between the registration roller 3 and the transfer paper.

As described above, when the leading end portion and the vicinity of the leading end portion of the transfer sheet are located at the transfer section 5, the transfer sheet is still slightly bent between the transfer section 5 and the registration roller 3. Therefore, the force generated in the bending portion does not push the transfer paper toward the transfer nip 5, and most of the force for feeding the transfer paper is due to the transfer force of the transfer roller 2.

When the transfer of the transfer sheet progresses and the latter half of the transfer sheet approaches the transfer section 5, the transfer speed at the registration roller section is originally set to be slightly higher than the transfer rate at the transfer section. In some cases, the curvature of the transfer paper becomes stronger. That is, as shown in the data of the leading end portion of the transfer sheet in Table 1, the transfer speed of the transfer sheet (206.2 mm / sec.)
c) and the transfer speed of the transfer paper in the transfer section 5 (203.8)
mm / sec), the deflection of the transfer paper between the transfer section 5 and the registration roller 3 section due to the speed difference increases cumulatively with the passage of time and forms a large mountain-shaped deflection.

The transfer paper S2 indicated by a broken line in FIG. 1 shows a state in which the rear half of the transfer paper has passed through the transfer unit 5, and the upstream position immediately before the transfer unit 5 is bent in a mountain shape. When a large bending occurs in the chevron, a force for eliminating the bending is generated, and acts to push the transfer paper to the transfer unit 5.

When the paper strain is strong, the guide shapes of the upper guide 4u and the lower guide 4d are also assisted, and the force for pushing the rear half of the transfer paper located at the transfer section 5 in the traveling direction is increased. The transport speed in the latter half is faster than the initial state when the leading end enters the transfer unit 5.

According to the data, as shown in Table 1, the transfer speed at which the second half of the transfer paper 200 mm from the leading end advances in the transfer section 5 is 207 mm / sec, and the transfer speed is 10 mm from the leading end.
The transport speed at which the part advances in the transfer unit 5 is 203.8 m
It is larger than m / sec. As a result, a phenomenon occurs in which the image elongation differs between the leading end portion and the rear half portion of the transfer paper.

In the present invention, the speed of the transfer sheet in the transfer section is controlled so that the difference between the leading end and the rear half of the transfer sheet is as small as possible. In this embodiment, in the latter half of the transfer of the transfer paper, the transfer speed of the transfer paper by the registration roller 3 is set to be lower than the transfer speed of the leading end of the transfer paper.

As means for this, the registration roller 3
An adjusting means for adjusting the nip pressure of the transfer material at
When the rear half of the transfer paper is only applied to the transfer portion, the nip pressure at the registration roller 3 is reduced to cause slippage between the transfer paper and the transfer speed at the registration roller 3 to be lower than before. By adjusting the degree of bending of the chevron in the transfer section, the transfer speed of the rear half of the transfer paper in the transfer section is made closer to the transfer speed of the leading end of the transfer paper in the transfer section. [2] Examples corresponding to the claims Examples of the adjusting means for adjusting the nip pressure of the registration roller will be described below.

In this embodiment, an adjusting means for adjusting the nip pressure of the registration roller 3 is provided at the position of the registration roller 3. This adjusting means includes a fixed lower rotor 3d constituting the registration roller 3, a movable upper roller 3u, and a lower roller 3d.
And a switching means for switching the strength of the urging means.

This adjusting means weakens the nip pressure of the registration roller, slides the transfer sheet at the registration roller 3, and reduces the transfer speed of the transfer sheet at the registration roller portion as compared with the case where there is no slip. Aim for.

FIG. 2 shows the configuration of the registration roller 3 when viewed from the direction of arrow A in FIG. FIG. 3 shows a cross section taken along the line BB in FIG. 2 and 3, the lower roller 3d, which is a fixed-side roller, has side plates 9R and 9L.
It is pivoted on. However, the shaft and the bearing are omitted from the figure for simplicity.

As shown in FIG. 2, the right shaft 11 of the upper roller 3u is supported by a swing bearing 10R, and the left shaft 11 is supported by a swing bearing 11R.

The oscillating bearing 10R includes a bearing piece 10R1 located inside the side plate 9R and a bearing piece 1 located outside the side plate 9R.
0R2, the bearing piece 1 penetrating through the side plate 9 and being pivotally attached to the side plate 9
0R and a fulcrum shaft 10R3 that integrally connects the bearing piece 10R1 and the bearing piece 10R2. The bearing pieces 10R1 and 10R2 have substantially the same shape.

The opening 13 of the side plate 9R through which the shaft 11 of the upper roller 3u penetrates has a larger diameter than the shaft 11 and is formed with a margin. The shaft 11 is supported at one end of each of the bearing pieces 10R1 and 10R2.

The bearing pieces 10R1 and 10R2 each have a bent portion for receiving a spring on the opposite side of the one end side with the fulcrum shaft 10R3 therebetween. The above-mentioned bent portion of the bearing piece 10R1 is provided with an elastic spring 23.
One end of R and the bent portion of the bearing piece 10R2 are hooked to one end of an elastic spring 24R. The other end of the spring 23R is hung on the movable shaft 25, and the other end of the spring 24R is hung on the fixed shaft 14R implanted on the side plate 9R.
Similarly, a bearing 11R is supported at one end of the bearing pieces 11R1 and 11R2.

A bent portion for receiving a spring is formed on each of the bearing pieces 11R1 and 11R2 on the side opposite to the one end side with the fulcrum shaft 11R3 therebetween. The bending portion of the bearing piece 11R1 is provided with an elastic spring 23.
One end of L and the bent portion of the bearing piece 11R2 are hooked to one end of an elastic spring 24L.

The other end of the spring 23L is hung on the movable shaft 25, and the other end of the spring 24L is hung on the fixed shaft 14L implanted on the side plate 9R. The movable shaft 25 has side plates 9R and 9L.
Grooves 26R, 26 formed in the same position and in the same shape and size
L is movably fitted. The grooves 26R and 26L have a U-shape. By moving the movable shaft 25 from one end to the other end of the grooves 26R and 26L, the spring 23
By changing the locking position of one of the R and 23L to change the length of the spring, the biasing force by the springs 23R and 23L can be changed.

On the other hand, since the springs 24R, 24L are hung on the stationary fixed shafts 14R, 14L, the grooves 2
Even when the movable shaft 25 is moved from one end of the 6R, 26L to the other end, the biasing force of the springs 24R, 24L does not change and is constant.

As shown in FIG. 3A, the movable shaft 25 is
When located above the 6R, 26L, the spring 23R
(23L) becomes the most extended state, so the fulcrum shaft 10R
The urging force applied to the lower roller 3d of the upper roller 3u provided together with the oscillating bearings 10R and 10L that are oscillating about the center 2 (11R2) becomes the largest, and generates the maximum nip pressure in the registration roller 3.

As shown in FIG. 3B, the movable shaft 25 is
When moved to the other end of 6R, 26L, the spring 23
Since R (23L) shrinks most, the upper roller 3u comes into pressure contact with the lower roller 3d with the smallest force, resulting in a small nip pressure. FIG. 3C shows that the movable shaft 25 has the groove 26.
It shows a state in the middle of moving from one end to the other end in R and 26L.

As shown in FIG. 4, while the movable shaft 25 is pulled by the elastic spring 27, the solenoid 28
When the solenoid 28 is turned on, the movable shaft 25 can be pulled to pull the movable shaft 25 into the state shown in FIG. 3B. When the solenoid 28 is turned off, the movable shaft 2 can be moved.
5 can be in the state shown in FIG.

As described above, the pair of springs 24R and 24L for making the biasing force constant and the pair of springs 2 for making the biasing force variable.
The nip pressure adjusting means of the registration roller is constituted by the combination of 3R and 23L. Springs 23R, 23L, 24
R and 24L are examples of urging means for urging the movable roller with respect to the fixed roller, and the grooves 26R and 26L, the movable shaft 2
5 and the solenoid 28 are examples of switching means for switching the strength of the urging means.

At a certain timing during the transfer of the transfer paper, the operation of the pair of springs 23R and 23L is released, and the other pair of springs 24R and 23L are released.
Only the functions of R and 24L were used, and the pressure between the rollers sandwiching the transfer paper was reduced so that the sandwiched transfer paper slipped between the registration rollers 3.

That is, under the state shown in FIG.
A pair of springs 24R, 24L and a pair of springs 23R, 23
Each of the Ls exerted a force of 400 gf on the upper roller 3u, and was set to 1600 gf as a whole.

When it is desired to reduce the nip pressure at the registration roller, the force by the pair of springs 23R and 23L is released as shown in FIG. 3B, so that the force applied to the entire upper roller 3u is 800 gf.

When the nip pressure is reduced as shown in FIG. 3 (b) from the state shown in FIG. 3 (a) in the course of passing the registration roller 3, slippage occurs between the registration roller 3 and the transfer paper. 1% slower than the linear velocity of the transfer paper.

The transfer paper transfer conditions are as follows.
The condition at the time of passing 10 mm is the same as the condition shown in Table 1, and when the portion 200 mm from the leading end of the transfer paper is located in the transfer portion 5, the adjusting means in the registration roller 3 is shown in FIG. The nip pressure was reduced by switching from the state as shown in FIG.

Table 2 shows the data at this time.

[0067]

[Table 2]

The transfer speed of the transfer paper at the registration roller portion in the latter half of the transfer paper where the portion 200 mm from the leading end of the transfer paper is located at the transfer portion is due to the slip of the transfer paper due to the release of the spring pressure by the adjusting means. The linear velocity at the time when the leading end is fed by the registration roller 3 is 204.5 mm / sec, which is 14.5 less than the linear velocity of 206.2 mm / sec. Of the transfer paper is weakened.

As a result, the transfer speed (204.9 mm / sec) of the transfer paper in the transfer section is substantially the same as the transfer speed (203.8 mm / sec) when the leading end passes through the transfer section 5. .

By changing the nip pressure of the registration roller during the passage of the transfer material in the transfer section, the transfer paper is not pulled by the registration roller in the direction opposite to the traveling direction. The transfer paper is conveyed while maintaining the image quality while preventing the transfer paper from being bent more than necessary, so that a high-quality image with no hollow portion and a small deviation in magnification of the transferred image can be obtained.

The force by which the chevron-shaped deflection pushes the transfer paper differs depending on the type of transfer paper. For example, there is little change in the transport amount because thin paper does not have much strain. Conversely, thick paper has a strong stiffness and a large amount of change. Further, the position of the thin paper and the thick paper that hit the registration roller 3 also changes.

Therefore, if the control of the nip pressure of the registration roller is changed according to the thickness of the transfer sheet, the transfer sheet speed can be controlled more accurately.

Therefore, as shown in FIG. 4, a paper thickness detector 30 is provided to detect the thickness of the transfer paper before entering the registration roller 3. The detection information is sent to the control unit 32, and the spring pressure for setting the nip pressure of the registration roller 3 is changed to change the transfer speed of the transfer paper.

In this manner, an image having a small magnification error can be obtained even when the type of paper is changed. An example of the operation will be described. FIG. 3C shows the position of the movable shaft 25 in order to reduce the amount of change in the nip pressure at the registration rollers 3 when thin paper or plain paper having a thickness of 50 μm to 90 μm is detected. 3 (a) and 3 (b), while holding at the intermediate position of the groove 26R (26L), the strength of the pair of springs 23R, 23L is reduced.
To the middle strength of the condition. When it is detected that the transfer paper is a thick paper of 1 mm or more, the movable shaft 25 is moved to the position shown in FIG. 3B, and the spring pressure by the springs 23R and 23L is released. In the case of three-stage switching in FIGS. 3A, 3B, and 3C, it is difficult to use only the solenoid 28, so two solenoids having different strokes are used together.

In the case of a postcard or an OHP (overhead projector paper), since the rigidity is strong even if the amount of bending is small, the speed change occurs at a shorter distance from the leading end than in the case of plain paper.

Therefore, the leading edge of these transfer papers is
, The nip pressure of the registration roller is reduced at a timing of about 10 mm from the point in time at which the spring is released, and the release of the spring is released all at once until the state shown in FIG. Thereby, the magnification deviation is reduced.

Further, it is conceivable that the magnitude of the deflection of the transfer paper also differs depending on the paper size, and it is desirable to change the transfer nip change timing also depending on the size of the transfer paper.

Since the transfer paper size is preset in the paper feed tray, for example, the paper feed trays 33,
The accuracy can be further improved by changing the timing of changing the nip pressure (timing of releasing the spring pressure) in the registration unit based on the size information as to which of the paper feed trays 4 is selected and performed. Therefore, paper feed tray 3
Information from 3 and 34 is input to the control unit 32.

Further, the paper feeding position differs between the case where paper is fed from the manual tray and the case where paper is fed from the large-volume paper feeding tray. In this example, the manual feed tray is at the same level as the transfer unit 5 and is sent in a substantially horizontal state, so that almost no curling occurs. On the other hand, since the large-volume paper feed tray is located below the transfer unit 5, it is greatly curled during the conveyance.

As shown in FIG. 5, the conveyance path from the large-volume sheet feeding tray to the registration rollers 3 is large in the curved line shown by a solid line.
The curve in the conveyance path shown by the broken line from the manual feed tray to the registration roller 3 is small. In the drawings, reference numerals 35 and 36 indicate sheet feeding devices, respectively.

The state of the curl of the transfer sheet upstream of the registration roller 3 is indicated by the transfer sheet S from the manual feed tray indicated by a broken line.
Transfer paper S4 from the large-volume paper feed tray indicated by a solid line compared to
As shown in FIG. 6, the transfer paper S4 conveyed from the large-volume paper feed tray on the conveyance path shown by the solid line is smaller than the transfer paper S3 from the manual feed tray fed on the conveyance path shown by the broken line, as shown in FIG. The larger the curl, the larger the deflection of the transfer paper S4 immediately before the transfer unit 3.

For this reason, compared with the transfer paper S3, the transfer paper S4
The change in speed with the tip occurs earlier. On the other hand, the paper sent from the manual feed tray has no curl at the time the leading edge enters, and no speed change has occurred.

For example, in the case of so-called A4 longitudinal paper (total distance of 297 mm), in which A4 size transfer paper is fed so that the traveling direction of the paper is aligned with the longitudinal direction of the paper, a magnification error occurs from the leading end by 50
mm, the nip pressure of the registration roller is increased by 50% after the leading edge of the transfer paper has passed through the transfer section.
mm.

On the other hand, the transfer paper S3 sent directly from the manual feed tray has almost no curl.
In the case of A4 lengthwise paper (total distance of 297 mm), a portion of 180 mm, which is halfway from the leading end of the transfer paper, reaches the transfer portion 5,
The image began to stretch. Therefore, 180 degrees from the leading end of the transfer paper
The control is performed so that the nip pressure of the registration roller 3 is weakened when the portion exceeding mm reaches the transfer portion 5.

As described above, by controlling the timing of releasing the nip pressure at the registration rollers 3 in accordance with the position of the tray, or more precisely, the state of the curl, the paper feed tray can be controlled regardless of the presence or absence of the curl. Irrespective of the large paper feed tray or the manual feed tray, the change rate of the magnification deviation of the transferred image can be optimized.

[0086]

According to the first aspect of the present invention, the transfer performance is improved by controlling the transfer material feeding speed at the registration roller portion by the adjusting means so that the transfer speed of the transfer material at the transfer portion is not changed. it can. According to the second aspect of the present invention, the transfer can be performed without causing the expansion and contraction of the image in one transfer material.

According to the third and fourth aspects of the present invention, the transfer speed of the transfer sheet at the transfer section can be controlled with higher accuracy according to the type of the transfer material.

According to the fifth aspect of the present invention, it is possible to prevent the image elongation from being different between the leading end portion and the rear half portion of the transfer material according to the state of the curl of the transfer material.

According to the sixth aspect of the invention, the nip pressure can be easily adjusted.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram around a registration roller and a transfer unit in an image forming apparatus.

FIG. 2 is a diagram illustrating a main part of a nip pressure adjusting unit of a registration roller unit.

3 (a) shows the state of the nip pressure adjusting means when the nip pressure is increased, FIG. 3 (b) shows the state of the nip pressure adjusting means when the nip pressure is reduced, and FIG. 3 (c) FIG. 4 is a diagram showing a state of a nip pressure adjusting unit when a nip pressure is set to a medium.

FIG. 4 is a schematic configuration diagram around a registration roller and a transfer unit in the image forming apparatus.

FIG. 5 is a schematic configuration diagram around a registration roller and a transfer unit in the image forming apparatus.

FIG. 6 is a schematic configuration diagram around a registration roller and a transfer unit in the image forming apparatus.

FIG. 7 is a schematic configuration diagram around a registration roller and a transfer unit in the image forming apparatus.

[Explanation of symbols]

 3 Registration Roller 5 Transfer Section 10R, 10L Swing Bearing 23R, 23L, 24R, 24L Spring 26R, 26L Groove 25 Movable Shaft

Claims (6)

[Claims] An image carrier which carries an image to be transferred and moves;
Transfer means for pressing the image carrier through the transfer material at the transfer section and transferring the transfer material while transferring the transferred image to the transfer material by moving in the same direction as the moving direction of the image carrier; A registration roller that conveys a transfer material toward the transfer unit, and an image forming apparatus that has a conveyance guide that guides the transfer material sent from the registration roller to the transfer unit. An image forming apparatus, comprising: an adjusting unit that adjusts a nip pressure of the registration roller by providing a difference in a transfer speed of a transfer material in the transfer unit. 2. An image forming apparatus according to claim 1, wherein said nip pressure is changed during passage of said transfer material in said transfer section. 3. An image forming apparatus according to claim 1, wherein said nip pressure is changed according to a type of said transfer material. 4. The image forming apparatus according to claim 1, wherein the timing at which the nip pressure is changed is changed in accordance with the type of the transfer material. 5. An image forming apparatus according to claim 1, wherein said nip pressure is changed according to a curl state of a transfer material before being conveyed to said registration roller. Forming equipment. 6. An image forming apparatus according to claim 1, wherein said nip pressure adjusting means presses the movable roller against a fixed roller constituting a registration roller. An image forming apparatus comprising: a switching unit configured to switch the strength of the urging unit.