JPH05278904A - Sheet transport device of image forming device - Google Patents

Abstract

PURPOSE:To prevent generation of wrinkles by furnishing a mechanism to reduce the sheet contacting pressure of a grip roller which is to feed sheets to a register roller couple, and reducing the sheet transport force of the grip roller after the register rollers start pinched transport of sheet. CONSTITUTION:A sheet feeding device feeds each sheet 1 while pinching it with a grip roller 2, and the leading edge of the sheet 1 is left running against a register roller couple 3 at a standstill to cause generation of a deflection, which allows correcting the sheet advancing askew, and the sheet 1 after correction is pinched by the register rollers 3 and fed to a photosensitive body 4 to be subjected to image formation. On a side plate 17 the upper roller 12a of the grip roller 12 is installed through a bearing 15 in such a way as slidable the direction perpendicular to the surface of the sheet, and eventual skew is corrected by the register rollers 3, and sheet transport is started by them 3, when a solenoid 19 is deenergized while the upper roller 12a is energized upward by a pressure spring 18 for separating from the lower roller 12b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a registration roller pair for correcting skew of a sheet by carrying the sheet after abutting the sheet, and a sheet arranged on the registration roller pair upstream of the registration roller pair. The present invention relates to a sheet feeding device of an image forming apparatus having a grip roller for feeding the sheet.

[0002]

2. Description of the Related Art In a sheet feeding apparatus having the above-described structure of an image forming apparatus such as a laser beam printer, a digital copying machine, a plain paper fax, etc., a sheet held by grip rollers toward a pair of stopped registration rollers. Will be delivered. At this time, the sheet may be skewed, and when it is conveyed to the print processing section or the copy processing section through the registration roller pair as it is, it is printed or copied obliquely or protruding on the sheet. As a countermeasure, skewing of the sheet is corrected. In many cases, the leading edge of the sheet is abutted against the pair of stopped registration rollers to cause bending. This will be described with reference to FIGS. 19 to 26.

I. Carrying In FIGS. 16 and 17, the sheet 1 is nipped by the grip roller 2 and fed toward the registration roller pair 3 which is stopped. At this time, the sheet may skew as illustrated. Reference numeral 4 is a photoconductor.

II. Resist abutment The sheet 1 abuts against the resist roller pair 3 whose front end is stopped to cause a slight deflection 5, and this deflection 5
When the occurs, the feeding of the grip roller 2 is stopped (FIGS. 18 and 19). At this time, the leading edge of the sheet follows the nip of the registration roller pair 3 due to the rigidity of the sheet itself, and the skew feeding is corrected. Since the rear end of the sheet is held by the grip roller 2 as it is, as shown in FIG.
As shown in, the flexure 5 is distributed asymmetrically. That is, a large deflection 5a and a small deflection 5b occur. Further, since the leading edge of the sheet is accurately positioned at the position of the registration roller pair 3, the registration roller pair 3 also has the function of relative alignment between the image formation and the sheet position.

III. Image Formation In FIGS. 20 and 21, the registration roller pair 3 starts rotating in synchronization with image formation, and the leading edge of the sheet is guided to the photoconductor 4. At this time, the grip roller 2 is not driven and is rotating together. When the sheet is skewed, an asymmetric sheet load may occur during the period from the elimination of the small flexure 5b to the elimination of the large flexure 5a, which may cause skewing again. Further, when the skew is severe, the sheet is subjected to a rotating force between the registration roller pair 3 and the grip roller 2, so that vertical wrinkles 6 occur near the center of the sheet 1 as shown in FIG. May leave damage to.

IV. After the image formation, if the skewed sheet is not sufficiently corrected and the image is formed, the image is rotated with respect to the sheet, and the sheet or the image is damaged due to wrinkles, which is very undesirable.

In Japanese Patent Laid-Open No. 64-2961, when skew feeding of a sheet is detected, the sheet is asymmetrical in the direction in which the skew feeding is corrected by the load applying means provided upstream of the roller for skew feeding correction. A sheet transport device is shown that provides various loads. This known device attempts to correct skewing of a sheet by utilizing the fact that the sheet conveyance is affected when a load is applied to the sheet upstream of the roller. This is because the load applying means is newly arranged, which complicates the structure and inevitably increases the required space and cost.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and prevent sheet wrinkles, tears, etc., which are likely to occur during skew correction, to effectively correct sheet skew. The present invention provides a sheet feeding device that does this.

[0009]

According to the present invention, the above-mentioned problem is solved by the present invention, in which the sheet feeding device is provided with a mechanism for reducing the sheet contact pressure of the grip roller, and this mechanism is provided until the sheet hits the pair of registration rollers. Maintains the seat contact pressure,
The problem is solved by reducing the sheet contact pressure of the grip roller after the pair of registration rollers starts gripping and conveying the sheet, and reducing the sheet conveyance force of the grip roller.

Further, according to the present invention, in order to solve the above-mentioned problems, the sheet conveying means includes a driving roller that does not come into contact with the sheet, and a magnet roller that comes into contact with the sheet attracted by the magnetic force to the driving roller. While the driving roller is being driven, the magnet roller receives a force in the biting direction against the sheet to generate a conveyance force, the driving roller stops driving, and the sheet is sandwiched and conveyed by the registration roller pair. In the meantime, it is proposed that the force in the biting direction of the magnet roller is eliminated and the sheet conveying load is reduced.

[0011]

The grip roller, which is arranged upstream of the pair of registration rollers for abutting the sheet to correct the skew, and which feeds the sheet to the pair of registration rollers, is provided with a mechanism for reducing or eliminating the sheet contact pressure, The sheet contact pressure is maintained until the sheet hits the roller pair, and the contact pressure is reduced or eliminated after the registration roller pair starts gripping and conveying the sheet. The contact pressure can be reduced by adjusting the restraint length of the pressure spring, and the contact pressure can be released by separating the upper and lower rollers of the grip roller.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the embodiments shown in the drawings.

The steps of conveying the sheet and abutting the resist shown in FIGS. 1 to 4 are the same as those described in "I. Conveying" and "II. Resist abutting" of the prior art shown in FIGS. Therefore, the present invention will be described with reference to the image forming process.

In FIGS. 5 and 6, when the registration roller pair 13 starts rotating in synchronization with image formation to guide the leading edge of the sheet to the photoconductor 14, both rollers of the grip roller 12 are separated from each other, whereby the grip roller 12 is separated. The holding of the seat 11 by 12 is eliminated. As a result, sheet 1
Since the rear end of 1 rotates freely, the asymmetrical load and rotational force applied to the seat 11 are reduced, and the above-described problems such as wrinkles in the case of the conventional technique can be eliminated.

In the above-described embodiment, the gripping of the sheet 11 by the grip roller 12 is completely eliminated, but the same effect can be achieved by reducing the contact pressure by the grip roller. It

7 and 8, both rollers 12a, 12b of the grip roller 12 are supported by the side plate 17 via bearings 15, 16. The upper bearing 15 which supports the grip roller 12a is mounted slidably in a direction orthogonal to the sheet surface to be fed, and normally a pressing spring 18 generates a contact pressure between the rollers 12a and 12b. ing. An electromagnetic solenoid 19 is provided on the upper side of the side plate 17.
And its plunger 20 is in contact with the upper end of the pressure spring 18. The electromagnetic solenoid 19 generates a magnetic force when energized and pushes the plunger 20 downward.

In FIG. 7, the electromagnetic solenoid 19 is energized to generate a magnetic force, and the plunger 20 is pushed downward. Thereby, the pressure spring 18 is compressed,
A sufficient contact pressure is generated between the grip rollers 12a and 12b.

In FIG. 8, the energization of the electromagnetic solenoid 19 is cut off, so that the plunger 20 cannot withstand the force of the pressure spring 18 and remains in the raised position. Therefore, since the restraining length of the pressure spring 18 extends from L ₁ to L ₂ and the spring force is reduced, both grip rollers 12a,
The contact pressure between 12b is reduced.

In the embodiment shown in FIGS. 9 and 10,
The upper bearing 25 is pressed downward by a pressure spring 28. The lever 31 is attached to the plunger 30 of the electromagnetic solenoid 29.
Is pivoted at one end and reaches the lower end of the upper bearing 25 at the other end. The lever 31 can turn around the fulcrum 31a.

In FIG. 9, since no current is supplied to the electromagnetic solenoid 29 and the upper bearing 25 is not interfered with by the lever 31, both grip rollers 12a, 12b.
A contact pressure is generated by the pressure spring 18 between them.

In FIG. 10, a current is supplied to the electromagnetic solenoid 29 and the plunger 30 is attracted. This causes the lever 31 to pivot about the fulcrum 31a and lift the upper bearing 25 against the action of the pressure spring 28,
The grip rollers 12a and 12b are separated from each other. Thus, the contact between the grip rollers 12a and 12b is released, and the influence on the sheet is eliminated.

In the embodiment shown in FIGS. 11 and 12, the grip roller is a drive roller 32 which is axially supported so as not to contact the sheet, and a magnet roller 32a which is supported by being attracted by magnetic force thereto. It is composed of. The following effects can be obtained by using such a transmission mechanism called a magnet drive system.

(1) As shown in FIG. 11, the drive roller 3
When 2 exerts the driving force to convey the sheet 11, the magnet roller 32a firmly wedges between the driving roller 32 and the sheet due to the wedge effect of the driving component force 34 generated at this time, and securely. Transmits the driving force to.

(2) As shown in FIG. 12, when the registration roller pair 13 starts to rotate and the driving roller 32 stops or rotates together, the biting force is canceled, and the sheet is extremely damaged. It only gives a small load.

In the embodiment shown in FIGS. 11 and 12, in order to assist the contact between the magnet roller 32a and the sheet 11, the roller guide 35 is provided so as to face the magnet roller 32a. Instead of the roller guide 35, it is also possible to arrange a pinch roller in order to obtain it.

Since a normal cylindrical roller has a long contact surface in a direction orthogonal to the sheet conveying direction, as shown by hatching in FIG. 13, when the skewed sheet is rotated, as described above, Produces a relatively large force against. As a countermeasure against this, in the present invention, the grip roller is shaped like a drum, and the contact width in the direction orthogonal to the sheet conveying direction is configured to be small, as shown by the diagonal lines in FIG. With the drum-shaped roller 36 configured in this way, it is possible to smoothly perform sheet rotation when correcting skew of the sheet and prevent wrinkles from occurring.

FIG. 15 shows a configuration in which the grip roller is composed of one drum-shaped roller 36, but it is of course possible to arrange a plurality of drum-shaped rollers in the axial direction of the roller to enhance the conveying force. is there.

[0028]

According to the present invention, after the feeding of the sheet by the registration roller pair is started, the interference of the grip roller with the sheet is reduced or eliminated, so that the rotation of the sheet is smooth due to the sheet hitting the registration roller pair. It is possible to prevent the occurrence of wrinkles due to the restraint of the rotation of the rear end of the seat and the recurrence of skew due to the asymmetric load on the seat.

Further, when the contact pressure of the grip roller is reduced by utilizing the electromagnetic solenoid, it is possible to realize a grip roller load reducing method with a simple structure and high controllability.

[Brief description of drawings]

FIG. 1 is a plan view showing sheet conveyance by a grip roller.

FIG. 2 is a side view thereof.

FIG. 3 is a plan view showing a sheet abutting against a pair of registration rollers.

FIG. 4 is a side view thereof.

FIG. 5 is a plan view showing a sheet in which skew feeding is corrected according to the present invention.

FIG. 6 is a side view thereof.

FIG. 7 is an explanatory diagram of a contact pressure reducing mechanism of a grip roller.

FIG. 8 is an explanatory diagram of a grip roller when a contact pressure is reduced.

FIG. 9 is an explanatory view of another embodiment of the contact pressure reducing mechanism of the grip roller.

FIG. 10 is an explanatory diagram of the grip roller when the contact pressure is released.

FIG. 11 is an illustration of yet another embodiment of the grip roller.

FIG. 12 is an explanatory diagram when the contact pressure of the grip roller is reduced.

FIG. 13 is a perspective view showing a contact width of a cylindrical roller.

FIG. 14 is a perspective view showing a contact width of a drum-shaped roller.

FIG. 15 is a plan view in which one drum-shaped roller is arranged as a grip roller.

FIG. 16 is a plan view showing sheet conveyance by a conventional grip roller.

FIG. 17 is a side view thereof.

FIG. 18 is a plan view showing a sheet abutted against a pair of registration rollers.

FIG. 19 is a side view thereof.

FIG. 20 is a plan view showing a sheet that has been skew-corrected and sent out.

FIG. 21 is a side view thereof.

FIG. 22 shows a sheet having vertical wrinkles near the center after skewing.

[Explanation of symbols]

 1, 11 sheet 2, 12 grip roller 3, 13 registration roller pair 18 pressure spring 19, 29 electromagnetic solenoid 32 drive roller 32a magnet roller 36 drum-shaped roller

 ─────────────────────────────────────────────────── --Continued front page (72) Inventor Tetsuo Yamanaka 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd.

Claims (4)

[Claims] 1. A pair of registration rollers for correcting skew of a sheet by carrying the sheet after abutting and holding the sheet,
In a sheet feeding device of an image forming apparatus having a grip roller arranged upstream of the registration roller pair for feeding a sheet to the registration roller pair, a mechanism for reducing a sheet contact pressure of the grip roller is provided. The mechanism maintains the sheet contact pressure until the sheet hits the pair of registration rollers, and reduces the sheet contact pressure of the grip roller after the pair of registration rollers starts gripping and conveying the sheet. A sheet feeding device characterized by reducing 2. The mechanism for reducing the sheet contact pressure of the grip roller, forcibly separating the grip roller to reduce the sheet contact pressure to almost zero. The sheet feeding device described. 3. A registration roller pair that corrects skew of a sheet by holding and transporting the sheet after the sheet is abutted,
In a sheet feeding device of an image forming apparatus, which is arranged upstream of the pair of registration rollers and has a sheet conveying unit that feeds a sheet to the pair of registration rollers, the sheet conveying unit includes a drive roller that does not contact the sheet, The drive roller is provided with a magnet roller that comes into contact with the sheet attracted by the magnetic force, and while the drive roller is being driven, the magnet roller receives a force in the biting direction with respect to the sheet to generate a conveying force and drive the sheet. A sheet feeding device, characterized in that, while the rollers stop driving, the force of the magnet roller in the biting direction is eliminated while the sheet is being sandwiched and conveyed by the registration roller pair, and the sheet conveying load is reduced. 4. A registration roller pair that corrects skew of a sheet by holding and transporting the sheet after holding the sheet,
In a sheet feeding device of an image forming apparatus having a grip roller arranged upstream of the registration roller pair for feeding a sheet to the registration roller pair, the grip roller is composed of a drum-shaped roller pair. Sheet feeding device.