JPH0739298B2 - Sheet conveying device in image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to various types of copy paper used in an electrostatographic copying machine, a document to be copied, thermal transfer paper used in a thermal printer, an ink ribbon, and the like. The present invention relates to a sheet conveying device in an image forming apparatus for conveying the sheet.

[Prior Art] For example, in an electrostatographic copying machine, a sheet conveying device including a pair of upper and lower rollers is provided on the downstream side of the sheet feeding section and the upstream side of the transfer section.

In the conventional sheet conveying device provided on the downstream side of the sheet feeding section, each of them is disposed on the downstream side of the sheet feeding guide in a state in which, for example, a metal roller and a rubber roller for registration are brought into contact with each other in the vertical direction. And the peripheral speeds of both rollers are set so as to match the sheet feeding speed based on a predetermined sheet feeding speed. , Sheet) is brought into contact with the nip portion of the rollers to bend the sheet in the vertical direction, thereby aligning the leading edges of the sheets and synchronizing the exposure optical system with the rollers. By driving and rotating the sheet, the sheet is fed to the transfer portion at a predetermined timing with respect to the developing area of the photoconductor.

[Problems to be solved by the invention]

By the way, in the above-described sheet conveying device in which both rollers are driven and rotated, although the generation ratio to the number of sheets per unit is extremely small, it also depends on the paper quality of the sheet and the degree of softness and the like, but passes through both rollers. Wrinkles were found on the formed sheet.

As a result of diligent study on the mechanism of wrinkle generation, the present inventor has come to speculate that wrinkles may occur as follows.

That is, in the above-described sheet conveying apparatus, as described above, conventionally, the peripheral speeds of both rollers are set so as to match the sheet feeding speed based on a predetermined sheet feeding speed. Passing a sheet between rollers set to the same peripheral speed means that the rollers roll on the sheet surface while sandwiching the sheet, and the rollers simply push the sheet. It is in a situation where the sheet is conveyed while being crushed.Therefore, when the sheet is in a wavy state and is fed out between both rollers and conveyed, the bending itself of the sheet before being conveyed is crushed, which leads to wrinkles. I came to guess.

The occurrence of the wrinkles is more prominent in the sheet conveying device on the downstream side of the sheet feeding unit than in the sheet conveying device before the transfer, which is caused by the bending of the sheet formed for aligning the leading ends. It is considered that the wrinkles are generated in the sheet conveying device before the transfer due to the bending due to the corrugated conveyance of the sheet by the preceding sheet conveying device.

[Means for solving problems]

The present invention is made on the basis of the above-mentioned consideration results, in which a pair of upper and lower sheet feeding rollers having different sheet feeding surface friction coefficients are provided so as to be rotatable in the sheet feeding direction. It is characterized in that the peripheral speed of the roller on the side where the friction coefficient is small is set to be slightly higher than the peripheral speed of the other roller.

[Action]

According to the above-mentioned characteristic configuration, the sheet feeding speed by the driving rotation of the pair of rollers depends on the peripheral speed of the roller having the large friction coefficient, and thus the friction coefficient is smaller than that of this roller. A roller having a slightly higher peripheral speed will slip on the sheet surface by the slight difference in peripheral speed.

The slipping of the rollers in this manner means that a sheet stretching force is applied to the surface on the roller slip side of the sheet that is nipped and conveyed by the rollers, which causes wrinkles in the sheet itself. Since the above factor is removed, the occurrence of wrinkles in the sheet passing between the rollers is suppressed.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an outline of an electrostatographic copying machine as an example of an image forming apparatus, and a copying machine main body provided with a document table 1 and a document retainer 2 on an upper portion thereof. Three
The photoconductor 4 is laid horizontally, and around the photoconductor 4,
A charging device 5, a developing device 6, a transfer unit 7, a sheet separating device 8 and a cleaning device 9 are arranged in this order in the rotation direction of the photoconductor 4, and an optical system movable exposure is performed in the space below the original table 1. A device 10 is provided.

Then, a sheet feeding and conveying device 13 that conveys the sheets in the cassette case 12 loaded in the sheet feeding portion 11 to the transfer portion 7, and a sheet discharging and conveying device that conveys the transferred and separated sheets to the fixing device 14.
15, and a paper discharge roller pair 17 for discharging the fixed sheet to the tray 16.

As shown in FIG. 2, the paper feeding / conveying device 13 is provided with a pair of upper and lower paper feeding guide plates 18 and 19 on the downstream side of the paper feeding unit 11, and is provided downstream of the paper feeding guide plates 18 and 19. Side is provided with a first sheet conveying device 20, and a second sheet is provided upstream of the transfer section 7.
And a pair of upper and lower guide plates 22, 23 between the first and second sheet conveying devices 20, 21.
Is provided, and the first sheet conveying device 20 is configured as follows.

That is, the surface of the metal roller material is coated to reduce the friction coefficient of the sheet feeding surface S ₁ , and the first resisting roller 24 is placed above the sheet feeding and conveying path in a state where the vertical position can be changed. And a second roller 25 for lower resist made of rubber having a large friction coefficient of the sheet feeding surface S ₂ is provided below the sheet feeding and conveying path, and the sheet feeding surface S ₁ of the first roller 24 is provided. A biasing member (not shown) is provided on both sides of the first roller 24 so that the sheet feeding surface S ₂ of the second roller 25 is biased and abutted, and a driving system (not shown) for both rollers 24, 25 is provided. The rollers 24 and 25 are configured to be driven and rotatable in the sheet feeding direction.

Then, the rotational peripheral speed of the second roller 25 on the side where the friction coefficient of the sheet feeding surface S ₂ is large matches the predetermined sheet feeding speed, and the friction coefficient of the sheet feeding surface S ₁ is small. The first roller 24 and the second roller 24 are arranged so that the rotational peripheral speed of the first roller 24 on the side is slightly higher than the rotational peripheral speed of the second roller 25.
The rotation number of the roller 25 is set as a predetermined value.

Since the sheet feeding speed by the driving rotation of the pair of rollers 24 and 25 depends on the peripheral speed of the second roller 25 having a large friction coefficient, the friction coefficient is higher than that of the second roller 25. The first roller 24, which has a small peripheral speed and a slightly higher peripheral speed, rotates while slipping on the sheet surface by the peripheral speed difference. In this way, the first roller 24 moves on the sheet surface. By rotating while slipping, the sheet is conveyed in a state in which the stretching force is applied to the roller slip surface of the sheet, and as a result, the cause of wrinkling of the sheet itself is removed. Wrinkling of the sheet when passing between the rollers 24 and 25 is suppressed.

By the way, Asahi Pla Coat ARM on the surface of the iron roller material
The first roller 24 coated with −800 (trade name of Asahi Rubber Kako Co., Ltd.) to make the outer diameter of the sheet feeding surface S ₁ 16.63 mm, and the isoprene having the outer diameter of the sheet feeding surface S ₂ 23.87 mm. The second roller 25 made of rubber (hardness 55 °) is used, the rotation speed of the first roller 24 is set to 404.4 rpm, and the rotation peripheral speed is set to 352.
2 mm / s, the rotation speed of the second roller 25 is set to 280 rpm, and the rotation peripheral speed is set to 350.0 mm / s, and the rotation peripheral speed of the first roller 24 is set to the rotation peripheral speed of the second roller 25. When it was increased by 0.63%, wrinkles did not occur even after repeatedly feeding 50 g / m ² of renewed paper in units of 1,000 sheets.

On the other hand, a roller having an outer diameter of 16.53 mm on the sheet feeding surface which has been subjected to the same surface coating treatment as described above is replaced with the first roller 24 used in the above experiment, and the rotational peripheral speed of the roller is changed to the second. Same as the rotating peripheral speed of the roller 25 (350.0mm / s)
In addition, the result of the experiment in which 50 g / m ² of the changed paper was repeatedly fed in units of 1,000 sheets showed that wrinkles were generated in 50 to 150 changed sheets per 1,000 sheets.

As is clear from this result, by setting the peripheral speed of the roller 24 having the smaller friction coefficient to be slightly larger than the peripheral speed of the other roller 25, it is possible to effectively suppress the occurrence of sheet wrinkles. In the above experiment, the peripheral speed of rotation of the first roller 24 is 0.63 with respect to the peripheral speed of rotation of the second roller 25.
Good results were obtained by increasing by only%, but it may be below or above the above-mentioned increase rate, but if the up-rate is too low, wrinkles tend to occur, or increase If the rate is too high, it is possible that noise may occur between the rollers 24 and 25 or wear of the rollers may be caused due to the difference in peripheral speed during non-feeding.
It is considered that the numerical value of the peripheral speed of rotation, which is determined by the radius of curvature of the rollers 24 and 25 and the copying speed, the difference in the coefficient of friction due to the coating treatment of the roller surface, etc. are also subtly related to the occurrence of wrinkles, Taking these into consideration, it is desirable that the rate of increase in the rotational peripheral speed be in the range of about 0.4 to 1.0%.

In the above embodiment, the present invention has been described with reference to the first sheet conveying device 20 arranged near the paper feeding section.
The sheet conveying device 21 may be targeted, or if the fixing device 14 is of a type in which the upper and lower rollers are driven and rotated, the fixing device 14 may be targeted, and further, the first roller 24 Below the paper feed path and
The roller 25 may be arranged above the sheet feeding / conveying path.

Needless to say, the sheet conveying device in various image forming apparatuses such as a thermal printer and a facsimile is not limited to the electrostatic photocopier and can be implemented.

〔The invention's effect〕

As described above, according to the present invention, in a sheet conveying device in which a pair of upper and lower sheet feeding rollers having different sheet feeding surfaces having different friction coefficients are rotatably driven in the sheet feeding direction, one of the two rollers is rubbed. It is characterized in that the peripheral speed of the roller having the smaller coefficient is set to be slightly larger than the peripheral speed of the other roller.

According to the above characteristic configuration, since the sheet feeding speed depends on the peripheral speed of the roller on the side where the friction coefficient is large,
The roller having a smaller coefficient of friction and a peripheral speed slightly higher than that of the roller rotates while slipping on the sheet surface by the peripheral speed difference, so that the roller slip surface of the sheet is stretched. The sheet is conveyed under the condition that the force is applied, and by removing the factor of the wrinkle generation of the sheet itself by this, the wrinkle generation of the sheet when passing between the both rollers is effectively suppressed. It has been done.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of an electrostatographic copying machine which is an example of an image forming apparatus, and FIG. 2 is a detailed view of a sheet feeding and conveying device. 24,25 …… Sheet feed rollers, S ₁ , S ₂ …… Sheet feed surface.

Claims (1)

[Claims] 1. A pair of upper and lower sheet feed rollers having different sheet feed surfaces having different friction coefficients are rotatably driven in the sheet feed direction, and one roller having a smaller friction coefficient has a lower peripheral speed. A sheet conveying device in an image forming apparatus, which is set to be slightly larger than the peripheral speed of the roller.