JP2000198560A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cope with a plurality of kinds of paper by one friction pad and to prevent the misfeeding and multifeeding by providing a central part and both end parts in the paper feeding direction, of the friction pad with the different feeding resistances. SOLUTION: A friction pad 40 has cut parts from a neighborhood of a nip N of a paper feeding roller and the friction pad 40 to a downstream side in the paper feeding direction at both ends in the paper feeding direction. The area of a separation surface of an ordinary friction pad 40 is, for example, 50 mm×8.5 mm. On the other hand, an area of a separation surface of this friction pad 40 is approximately a value obtained by adding 25 mm×8.8 mm of a central part A and 25 mm×5 mm×2 at both ends B. The conveying resistance after passing through the nip P becomes 1/2 of the ordinary one because of the cut parts formed on both ends. Whereby the thick paper with bur can be fed. On the other hand, in a case of thin paper, the lowering of separatability can be reduced, so that the multifeeding of thin paper can be prevented.

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 the like.
The present invention relates to an image forming apparatus having a friction pad type sheet feeding unit.

[0002]

2. Description of the Related Art In this type of image forming apparatus, for example, sheets (including the concept of sheets) stacked and accommodated in a sheet feed tray are included.
same as below. ) Are fed one by one in order from the uppermost one to the image forming unit by a feed roller. The best paper is pulled out by the rotation of the paper feed roller,
A plurality of sheets are easily pulled out at the same time due to the friction between the sheets, and therefore, resistance is given to the lower layer sheet to feed only the uppermost sheet. There are various configurations for providing resistance, such as a claw separation system and a friction pad system. The friction pad system is generally used.

In the friction pad system, a friction pad serving as a friction member is pressed against a paper feed roller at an arbitrary separation angle and separation pressure, and paper is passed through a nip formed between the paper feed roller and the friction pad. ing. Even if two sheets of paper are pulled out by the rotation of the paper feed roller, only the upper paper is fed because the resistance of the lower paper from the friction pad is greater than the resistance due to friction between the papers. You. However, actually, a so-called double feed in which two sheets are fed in a state of being overlapped or a so-called non-feed in which no sheet is fed due to an excessively high resistance of the friction pad or the like occurs.

For this reason, various devices have been conventionally devised. For example, Japanese Unexamined Utility Model Publication No. 6-18344 discloses a technique in which two friction pads are separately arranged on the upstream side and the downstream side in the paper transport direction to perform two-stage separation. Japanese Patent Application Laid-Open No. 9-267936 discloses that a separation surface of a friction pad is divided into an upstream surface and a downstream surface having different separation angles, the separation angle of the downstream surface is made larger than the upstream separation angle, and only the downstream separation surface is separated. To contact the paper feed roller.

[0005]

When a thick paper such as a postcard is fed, if the paper has burrs, non-feed occurs due to the resistance of the friction pad. As a countermeasure to prevent this, it is conceivable to reduce the overall resistance by reducing the width of the friction pad. However, in such a case, there is a problem that as a side effect, multi-feeding increases in the case of thin paper. . The conventional techniques as described above are:
The purpose of the present invention is to eliminate the double feeding of the two types of paper and to surely separate them one by one, and a satisfactory function cannot be obtained when the types of paper are different. In a configuration in which a plurality of friction pads are used for one sheet feed roller, there are problems that the separation pressure and the separation load increase, or the torque of the sheet feed roller increases.

Accordingly, the present invention provides an image forming apparatus which can separate and convey even thick paper with burrs, does not cause double feeding even with thin paper, and can solve the problem of a plurality of friction pads. The purpose is to provide.

According to the present invention, the optimum separation resistance between thick paper and thin paper is obtained by changing the area of one friction pad in the paper transport direction. Specifically, in the image forming apparatus according to the first aspect of the present invention, the paper is passed through a nip between a paper feed roller and a friction pad and separated and transported one by one to an image forming unit. A configuration is adopted in which the conveyance resistance between the center portion in the paper conveyance direction and both end portions is made different.

In the invention according to the second aspect, in the configuration according to the first aspect, portions of both ends of the friction pad from near the nip between the paper feed roller and the friction pad to the downstream side in the sheet transport direction are cut off. The configuration is adopted.

According to a third aspect of the present invention, in the configuration of the second aspect, both ends of the partially cut-out friction pad are formed by friction members having a lower hardness than the central portion. I am taking it.

[0010] According to a fourth aspect of the present invention, in the configuration of the third aspect, the friction member is a composite material.

According to the fifth aspect of the present invention, there is provided the first, second, and third aspects.
5. The configuration according to 3 or 4, wherein a nip position of the friction pad with respect to the paper feed roller is different from a nip position of a center portion and both end portions of the friction pad, and a nip position of both end portions is located upstream of the nip position of the center portion in a sheet conveying direction. It has a configuration.

According to a sixth aspect of the present invention, in the configuration of the fifth aspect, the nip position is different because the height of both ends of the friction pad is higher than the center.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, an overall configuration of the image forming apparatus 2 will be schematically described with reference to FIG. A normal paper feed tray 4 is provided at the lower part of the apparatus main body, and paper P1 (a frequently used paper such as A4 size or B5 size) loaded and stored in the paper feed tray 4 is fed to a paper feed roller 6 by the paper feed roller 6. The sheet is separated one by one by the friction pad 8 and is conveyed by the conveying roller 10 toward the registration roller pair 12. Registration roller pair 12
Is stopped, a slack is formed, the skew of the sheet P1 is corrected, and the sheet P1 is rotated at the timing of alignment with the leading end position of the toner image on the photoconductor 14 as an image carrier.

An electrostatic latent image is formed on a uniformly charged photoreceptor 14 by an optical writing unit (not shown) based on image information read from an original image reading unit (not shown). The developing unit 16 develops the toner image. The toner image on the photosensitive member 14 is transferred to the sheet P1 sent at the above timing by the registration roller pair 12 by the transfer roller 18 as a transfer unit.
The sheet P1 onto which the toner image has been transferred is sent to a fixing unit having a heating roller 20 and a pressure roller 22, where the toner image is fixed as a permanent image on the sheet P1 by heat and pressure. The fixed sheet P1 is discharged to a discharge tray 26 by a discharge roller pair 24.

On the right side of the image forming apparatus 2, a manual paper feed tray 28 capable of feeding special paper such as postcards is provided so as to be openable and closable. In FIG. 1, the manual feed tray 2
8 is open. Manual paper feed tray 2
Reference numeral 8 denotes a tray body 30, a bottom plate 34 provided on the tray body 30 so as to be rotatable in a vertical direction about a shaft 32 as a fulcrum, and an elastic member for constantly urging the bottom plate 34 upward. As a coil spring 36. On the free end side of the bottom plate 34, a paper feed roller 38 for the manual paper feed tray 28 and a friction pad 40 are provided. The paper P2 separated one by one by the paper feed roller 38 and the friction pad 40, the rotation of which is controlled by control means (not shown) by a print command, is sent by the transport roller 10 toward the registration roller pair 12, and thereafter the paper P1 Through the same transporting process.

As shown in FIG. 2, the friction pad 40 is provided with a pad holding member 44 provided rotatably in a vertical direction about a shaft 42 as a fulcrum below the feed roller 38.
Is held in. A pin 46 is integrally provided on the lower surface of the pad holding member 44 and is constantly urged upward by a coil spring 48 engaged with the pin 46.
The separation pressure of the friction pad 40 with respect to the paper feed roller 38 is determined by the urging force of the coil spring 48. Although not shown, the urging force of the coil spring 48 can be adjusted.

Next, the structure of the friction pad 40 in this embodiment will be described with reference to FIGS. The friction pad 40 has a configuration in which a portion from the vicinity of the nip N between the paper feed roller 38 and the friction pad 40 to the downstream side in the paper transport direction is cut off at both ends in the paper transport direction. For example, the area of the separation surface of the conventional friction pad 40 is 50 mm × 8.5 m.
m. On the other hand, in the present embodiment, the area of the separation surface of the friction pad 40 is 25 mm × 8.
5 mm and (25 mm × 5 mm × 2) of both end portions B are added.

The transport resistance of the flash part of the cardboard is Fp = A · H
It is represented by the following equation. Here, A: the true contact area or the area dug up by burrs, and H: the yield stress of the pad. When using a conventional friction pad with the above area,
Fp = 50H. In the present embodiment, the transport resistance after passing through the nip N is approximately Fp = 25H, which is の of the conventional one, since both ends are notched. For this reason, even if the cardboard has burrs, it can be transported. The inventor of the present invention has determined that the cause of non-feeding of the thick paper with burrs is due to the magnitude of the transport resistance after passing through the nip N, and adopted a shape that reduces the transport resistance after passing through the nip N. It is.

On the other hand, in the case of thin paper, the position up to the nip N greatly contributes to the separation property, but that portion has the same transport resistance as the conventional one, that is, in the width direction orthogonal to the paper transport direction. Has a length of 50 mm, and the separability is little reduced, thereby preventing double feeding of thin paper. The dimensions shown in FIG. 3 are merely examples, and the optimal dimensions for achieving both the prevention of non-feed of thick paper used and the prevention of double-feed of thin paper may be determined based on experimental data.

Next, another embodiment will be described with reference to FIGS. Note that the same parts as those in the above embodiment are denoted by the same reference numerals, and repeated description will be omitted unless necessary. The friction pad 50 in this embodiment is similar in shape to the above embodiment, but the hardness of both ends B is set lower than the hardness of the center A. The hatched display in FIG. 5 is for distinguishing the difference in hardness, and is not a sectional display. As described above, the transport resistance of the burr portion of the cardboard is Fp =
The transport resistance before the nip N (upstream side) is Fp = 50H in the above embodiment, but the friction pad 50 in this embodiment has a low hardness at both ends B, so that Fp '= 25H + 25H'(H> H '), and the transport resistance is reduced. The hardness of the central portion A is set to a rubber hardness of 70 ° (JISA). Both ends B
As shown in FIG. 6, a thin plate 52 of cork as a friction member
(Surface material) and a composite material in which the foam rubber 54 of the base is bonded, and has a hardness of 35 ° (JIS).
A) is set.

Since the hardness of the center portion A and the both end portions B of the friction pad 50 is different, the frequency of vibration with the sheet of the central portion A and the frequency of the sheet of the both end portions B at the time of separation are different. It acts to reduce the energy of stick-slip due to vibration.

Next, another embodiment will be described with reference to FIGS. Note that the same parts as those in the above embodiment are denoted by the same reference numerals, and repeated description will be omitted unless necessary. As shown in FIG. 7, the friction pad 56 in the present embodiment is provided between the center portion A and both end portions B so that the nip position of the center portion A and the nip position of both end portions B with respect to the paper feed roller 38 are different. A step is provided. In the present embodiment, the level difference t between the upstream end of the central portion A in the sheet transport direction and both end portions B is set to about 0.4 mm. For this reason, as shown in FIG.
The nip position of both end portions B with respect to the paper feed roller 38 is N1, and the nip position of the central portion A is N2 on the downstream side in the sheet conveyance direction. Also, the nip position N1 of both ends B
Is a substantially horizontal F1, and the tangent direction of the nip position N2 of the central portion A is F2 which forms an elevation angle.
In the present embodiment, θ is set to 11 °.

In the present embodiment, in the case of thick paper, the paper first reaches the nip N1 at both ends B to obtain the transporting force, and further obtains the transporting force at the nip N2 at the central portion A. Becomes larger. In the case of thin paper, primary separation is performed by reaching the nip N1 at both ends B, and the upper sheet that does not contact both ends B is transported in a substantially horizontal F1 direction. The upper sheet conveyed in a substantially horizontal direction reaches the central portion A at an angle. Here, the pre-separation of the secondary separation performed in the central part A is performed, and finally the secondary separation is performed. This stepwise separation operation prevents double feeding of thin paper.

In the embodiment shown in FIGS. 3 and 4,
Further, by making the nip position of the central portion A different from the nip position of both end portions B, the above function can be obtained.

[0025]

According to the first aspect of the present invention, since the conveyance resistance of the friction pad at the center portion in the paper conveyance direction and the conveyance resistance at the both ends is made different, one friction pad can be used for a plurality of paper types. It is possible to respond and prevent non-feeding and double feeding. Since a single friction pad can be used, there is no problem such as an increase in the torque of the paper feed roller in the related art.

According to the second aspect of the present invention, since both ends of the friction pad are partially cut, the conveyance resistance can be easily varied.

According to the third aspect of the present invention, since both ends of the friction pad are formed of friction members having lower hardness than the central portion, a delicate difference in transport resistance can be obtained, and the frictional pad in thick paper is not affected. The prevention of feeding and the prevention of double feeding of thin paper can be achieved with high accuracy.

According to the fourth aspect of the present invention, since the friction member is made of a composite material, a difference in hardness can be easily obtained by selecting various combinations of materials.

According to the fifth aspect of the present invention, the nip positions at the center and both ends of the friction pad are made different, and the nip positions at both ends are located upstream of the nip position at the center in the sheet transport direction. By the objective separating function, the prevention of non-feeding of thick paper and the prevention of double feeding of thin paper can be achieved with high accuracy.

According to the sixth aspect of the present invention, since the height of the central portion and the height of the both ends are changed, the nip position can be easily shifted without increasing the bulk of the friction pad.

[Brief description of the drawings]

FIG. 1 is a schematic front view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is an enlarged front view of a main part.

FIG. 3 is a plan view of a friction pad.

FIG. 4 is a perspective view of a friction pad.

FIG. 5 is a plan view of a friction pad according to another embodiment.

6 is a sectional view of both ends of the friction pad in the embodiment shown in FIG.

FIG. 7 is a perspective view of a friction pad according to another embodiment.

8 is a schematic front view showing a nip position of a friction pad with respect to a sheet feeding roller in the embodiment shown in FIG.

[Explanation of symbols]

 38 Paper feed rollers 40, 50, 56 Friction pad P2 Paper A Central part B Both ends 52 Cork thin plate as friction member N1, N2 Nip position

Claims (6)

[Claims] 1. An image forming apparatus in which paper is passed through a nip between a paper feed roller and a friction pad and separated one by one and conveyed to an image forming section. An image forming apparatus, wherein the conveyance resistance between the image forming apparatus and the image forming section is different. 2. An image forming apparatus according to claim 1, wherein portions of both ends of said friction pad from near a nip between said paper feed roller and said friction pad to a downstream side in a paper conveying direction are cut off. Image forming apparatus. 3. An image forming apparatus according to claim 2, wherein both ends of said partially cut-out friction pad are formed by friction members having a hardness lower than that of said central portion. . 4. The image forming apparatus according to claim 3, wherein said friction member is a composite material. 5. The image forming apparatus according to claim 1, wherein a nip position of the friction pad with respect to the paper feed roller is different from a nip position of both ends of the friction pad, and a nip position of both ends is set at the center portion. An image forming apparatus which is located upstream of the nip position in the sheet conveying direction. 6. The image forming apparatus according to claim 5, wherein the nip positions are different due to the height of both ends of the friction pad being higher than the center.