JPH0729070Y2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Use The present invention relates to an image forming apparatus such as a facsimile or a laser printer, and more specifically, a forward rotation roller and a reverse rotation roller as a double feed prevention mechanism for primary paper feed. The present invention relates to an image forming apparatus having a pair.

(B) Conventional Technology In this type of apparatus, a forward rotation roller and a reverse rotation roller are opposed to each other via a sheet conveyance path, thereby preventing double feeding of sheets.

(C) Problems to be solved by the invention However, when an automatic conveyance mechanism such as ADF or RADF is used, the average jam rate of the paper (for example, when one out of 200 sheets is double-fed, the average jam rate is 200). ) Is high, and there is a risk that paper will be repeatedly fed. Moreover, it is difficult to avoid double-feeding on paper that easily accumulates electric charges, such as OHP sheets.

One of the objects of the present invention is to provide an image forming apparatus capable of reducing the average jam rate in sheet feeding.

(D) Means for Solving the Problem The present invention is directed to an image forming apparatus including a pair of rollers for preventing double feed in a sheet conveying path of an image forming apparatus main body. It is composed of a forward rotation roller and a reversing roller, which are provided to face each other above and below, respectively, and the paper transport path is curved toward the reversing roller side once on the downstream side in the transport direction of the both rollers. A U-turn curve along the peripheral surface of the diversion roller, and a sheet that is sandwiched between the rollers and conveyed is once curved toward the reversing roller side, and then a U-turn shape along the peripheral surface of the forward rotation roller. The image forming apparatus includes a curved conveyance unit that is curved in a curved direction and can apply a downward force to the double-feed sheet to contact the reversing roller side.

That is, in this invention, a forward rotation roller and a reverse rotation roller are provided respectively above and below via the paper transport path, and at the downstream side of both rollers in the transport direction, the forward rotation roller is curved once toward the inversion roller side. U along the circumference
The gist of the present invention is to provide a curved conveyance section that curves in a turn shape. Even if the double-fed sheet on the side of the reversing roller that is about to be multi-fed intrudes on the upper side of the double-fed sheet and the conveyed sheet that is about to be conveyed on the downstream side position of both rollers in the conveyance direction. , A so-called waist-elasticity or stickiness-generated on the conveying paper that is conveyed in advance in the curved conveying unit imparts a downward force for bringing the lower double-feeding paper into contact with the reversing roller side. The multi-fed sheet is pressed against the reversing roller by this, and as a result, the multi-fed sheet is reliably fed back.

(E) Embodiments The present invention will be described in detail based on the embodiments shown in the drawings.
However, the present invention is not limited to this.

In this embodiment, a facsimile is used as the image forming apparatus for description.

In FIG. 1, the facsimile is provided with a pair of rollers for preventing double feed in a sheet conveying path P of the machine body 1, and the pair of rollers for preventing double feeding is provided above and below the sheet conveying path P so as to face each other. The normal rotation roller 2 and the reversal roller 3 are formed. The paper transport path P is curved transport that is curved downstream in the transport direction of both rollers 2 and 3 toward the reversing roller 3 side and then curved in a U-turn shape along the circumferential surface of the normal rotation roller 2. It has a U-turn part 5 as a road. A pair of registration rollers 4 is arranged diagonally above the forward rotation roller 2 so as to align the leading ends of a sheet (not shown) to be conveyed.
Is provided. The U-turn section 5 is curved until just before the registration roller pair 4, and after the sheet (not shown) conveyed by being sandwiched between the rollers 2 and 3 is once curved toward the reversing roller 3 side. U along the peripheral surface of the forward rotation roller 2
It is a portion that can be curved in a turn shape and can be applied with a downward force F for bringing the multi-feed sheet into contact with the reversing roller 3 side.

Further, the forward rotation roller 2 is normally rotated in the direction A in the figure at a peripheral speed of 48 mm / sec, and this is made of a soft elastic member (trade name Mu-rubber: manufactured by Hokushin Rubber Co., Ltd.), while the reversal roller 3 is It is rotated in the direction B in the figure at a peripheral speed of 35 mm / sec, and is made of urethane with a hardness of 60 °.

The sheet conveying path portion 6 between the rollers 2 and 3 has a clearance, and the clearance is preferably 0.2 to 0.4 mm and 0.3 mm.
Is more preferable. This width is set by the linear distance formed by connecting the centers of both rollers. The registration roller pair 4 has a peripheral speed of 48 mm / sec.

Further, 7 is a sheet detection switch provided in the middle of the U-turn section 5, which is turned on by the passage of the sheet, and after a predetermined time has elapsed, activates the registration roller pair 4. Reference numeral 8 denotes a photosensitive drum disposed further downstream of the paper transport path P, and 9
Is a paper feed roller, which feeds the paper in the cassette set in the paper feed unit 10 to the paper conveyance path P via the paper feed guide 11, and rotates the forward rotation roller 2 in synchronization with the paper feed roller 9. To be done.

Since this embodiment has the above-mentioned structure, when the multi-fed sheet is conveyed to the U-turn section 5, a lower weight is generated by so-called waist-elasticity or stickiness which is generated in the conveyed sheet that is conveyed in advance. A downward force F for contacting the feeding sheet with the reversing roller 3 side is applied and pressed against the reversing roller 3, and as a result, the double feeding sheet is reliably fed in the C direction by the rotation of the reversing roller 3. Then, only the conveyed sheet passes through the U-turn section 5 and is conveyed to the registration roller pair 4.

As described above, in the present embodiment, the forward rotation roller 2 and the reverse rotation roller 3 are curved toward the reverse rotation roller 3 side on the downstream side in the transport direction, and then U along the circumferential surface of the normal rotation roller 2.
Since the U-turn portion 5 that is curved in a turn shape is provided, the double-fed sheet that is on the reversing roller 3 side and is about to be double-fed is on the upper side of the double-fed sheet and is also to be conveyed. Even if the rollers 2 and 3 enter the downstream side of the conveyance direction, the downward force F due to the so-called waist generated on the conveyed sheet preceding the U-turn section 5 causes only the lower double-fed sheet to be conveyed. It is possible to reliably press the reversing roller 3 to reversely feed the double-fed sheet, and it is possible to prevent the double-fed sheet from occurring.

Further, in the present embodiment, the reversing roller 3 is arranged so that the double-fed sheet may come into contact with the reversing roller 3 earlier than the influence of the rotation of the forward rotation roller 2 or the pressure due to the curving of the preceding conveyance sheet. Is positioned slightly upstream of the normal rotation roller 2 with respect to the direction orthogonal to the paper transport direction in the transport direction. Thereby, the effect of preventing the above-mentioned double feeding can be further enhanced.

In this embodiment, the normal rotation roller 2 and the reverse rotation roller 3 are always rotated in the opposite directions, and a roller driving mechanism having no so-called torque limiter is adopted. The present invention can also be applied to a mechanism having a torque limiter that normally rotates the forward rotation roller normally while the reverse rotation roller is driven by the forward rotation roller when the number of sheets is 0 or 1, and reversely when the number of sheets is two or more.

(F) Effect of the Invention As described above, according to the present invention, the forward rotation roller and the reversal roller are provided so as to face each other above and below the paper transport path, and both rollers are provided on the downstream side in the transport direction.
A curving conveyance section is provided that is curved toward the reversing roller side and then curved in a U-turn shape along the peripheral surface of the forward rotation roller. Even if the sheet to be fed is located above the multi-fed sheet and is going to be transported to the downstream side in the transport direction, it occurs in the transported sheet that is previously transported in the curved transport section, that is, the so-called waist- Since the elastic force or the tenacity is such that a downward force is applied to bring the double feed sheet under the conveying sheet into contact with the reversing roller side, the double feed sheet is pressed against the reversing roller by this. As a result, the double-fed sheet is reliably fed back, and the double-fed sheet can be prevented from being fed. Further, since the multi-fed sheets can be fed back by using the waist of the conveyed sheets, there is an advantage that the weight of the sheets can be made wider and the sheets of arbitrary weight can be fed.

[Brief description of drawings]

FIG. 1 is an explanatory view of a main part configuration showing an embodiment of the present invention. 1 ... Machine body, 2 ... Forward rotation roller, 3 ... Reverse rotation roller, 5 ... U-turn section (curved transport section), P ... Paper transport path.

Claims (1)

[Scope of utility model registration request] 1. An image forming apparatus comprising a pair of rollers for preventing double feed in a sheet conveying path of an image forming apparatus body, wherein the pair of rollers for preventing double feeding are opposed to each other above and below the sheet conveying path. It is composed of a forward rotation roller and a reversal roller provided, and the paper transport path is curved toward the reversal roller side downstream of the both rollers in the transport direction, and then U along the peripheral surface of the normal rotation roller. The sheet that is curved in a turn shape and is conveyed by being sandwiched by both rollers is once curved toward the reversing roller side, and then is curved in a U-turn shape along the circumferential surface of the forward rotation roller, An image forming apparatus having a curved conveyance unit capable of applying a downward force for bringing a double feed sheet into contact with a reversing roller side.