JPH11322135A - Paper oblique carrying correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paper oblique carrying correction device which is remarkably shortened in carrier time per sheet to be carried to an image forming part and is suitable in a high speed processing of continuous images, in particular. SOLUTION: On the upstream sides of feed rollers 23, 24 carrying paper (a) to an image forming part (transfer device), rollers 27, 28 for oblique carrier correction of paper (a), an actuator 31 changing these correction rollers 27, 28 in attitude and oblique carrying detection sensors 32a, 32b of paper (a) nipped by the correction rollers 27, 28 are provided. Further, a control means 40 correcting the degree of skew to zero while paper (a) is nipped by the feed rollers 23, 24, based on detection information on the degree of skew from the sensors 32a, 32b and returning the correction rollers 27, 28 to a home position P after paper (a) is nipped by the feed rollers 23, 24 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper skew correction device provided in an image forming apparatus such as an electrostatographic copying machine, a printer or a facsimile.

[0002]

2. Description of the Related Art Conventionally, a pair of registration rollers driven at a predetermined timing are arranged in the middle of a paper transport path to an image forming unit in order to correct oblique transport of a paper transported to an image forming unit. Then, the leading end of the sheet conveyed by the feed roller is brought into contact with the nip portion of the registration roller, and the feeding of the leading end of the sheet is momentarily stopped. The skew of the leading edge of the sheet is corrected, and the registration roller is driven here to convey the skew-corrected sheet to the image forming unit.

[0003]

However, if the feeding of paper is stopped for an instant, the transport time per sheet becomes longer by the time of the stop, and in forming a continuous image, Since the distance between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet becomes longer, there is a problem in terms of high-speed processing of continuous images.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and does not use a registration roller dedicated to skew correction, and therefore does not stop the feeding of the paper for a moment, and obliquely transports the paper. Device that can correct
In particular, it is an object of the present invention to provide a paper skew conveyance correction device suitable for high-speed processing of continuous images.

[0005]

In order to achieve the above object, the present invention provides an apparatus for correcting the oblique conveyance of a sheet conveyed to an image forming section. A pair of rollers for skewed conveyance correction for nipping and conveying the sheet, an actuator for changing the position of the correction roller around an axis perpendicular to the paper surface of the sheet of conveyance, and an oblique line for the leading end of the sheet nipped by the correction roller. A sensor for detecting the degree of skew due to conveyance, and further, based on the skew degree detection information from the sensor, the skew is reduced to zero before the sheet is nipped by the feed roller. Control means for changing the posture of the correction roller in a direction to make the correction roller return to the home position after the paper is nipped by the feed roller. It is characterized in that made.

According to the above feature, when the sensor detects the skew of the leading edge of the sheet nipped by the correction roller, the skew of the sheet before the sheet is nipped by the downstream feed roller. The posture of the correction roller is changed so as to make the degree zero, and thereby the oblique conveyance of the sheet is corrected without stopping the sheet feeding.

[0007] When the sheet whose skew conveyance has been corrected is nipped by the feed roller on the downstream side, the correction roller whose posture has been changed once is returned to the original home position, and the next skew conveyance is performed. Since the oblique conveyance of the sheet is corrected while the conveyance of the sheet is continued, the conveyance time per sheet is greatly reduced.

Accordingly, in forming a continuous image, the interval between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet is reduced, so that high-speed processing of the continuous image can be performed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an electrostatographic copying machine (an example of an image forming apparatus) configured to be capable of forming a two-sided image, in which a photosensitive drum 3 is horizontally mounted on an apparatus main body 2 having a document holder 1 on an upper part. Around the photosensitive drum 3, a charging device 4, a developing device 5, a transfer device (image forming unit) 6, a paper separating device 7, and a cleaning device 8 are arranged in this order. An optical system movable exposure apparatus 9 is arranged in the upper space of the main body 2.

Further, a sheet feeding and conveying device 12 for conveying sheets fed from a sheet feeding deck 11 having a plurality of vertically arranged sheet feeding cassettes 10 to a transfer device 6, and a sheet after image formation. A suction-type paper feed path 14 for conveying the sheet to the fixing device 13 and a pair of discharge rollers 16 for discharging the sheet for fixing to a sheet discharge tray 15 outside the apparatus are provided. Tray 17, a paper feed path 18 for feeding fixing processing paper to the intermediate tray 17, and a paper feed path for turning the stock paper upside down and feeding it again to the transfer device 6. 19 and
In addition, a path switching unit 20 is provided upstream of the discharge roller pair 16 so that the fixing processing paper can be switched between the discharge tray 15 and the stock paper supply path 18 and fed.

As shown in FIG. 2 to FIG. 4, the above-described paper feed / conveyance device 12 firstly nips and conveys the paper a.
And the second feed rollers 21, 22, 23, 24,
A section for introducing paper from the paper feed deck 11 (see FIG. 1)
25 and the transfer device 6, and between the first and second feed rollers 21, 22, 23 and 24,
The skew conveyance correcting device 26 for the sheet a is arranged, and the re-feeding path 19 is connected to the middle of the feeding path between the first feed rollers 21 and 22 and the skew conveyance correcting device 26, The oblique conveyance correction device 26 for the sheet a is configured as follows.

That is, a roller holding member 29 provided with a pair of oblique conveyance correcting rollers 27 and 28 for nipping and conveying a sheet a is moved around a support shaft 30 having one end thereof perpendicular to the sheet surface of the sheet to be conveyed. An actuator 31 for rotating the roller holding member 29 around the support shaft 30 and a sensor 32a, 32b for detecting the skew of the leading end of the sheet due to the oblique conveyance are provided with the correction rollers 27, A sensor 33 for detecting the leading end and the trailing end of the sheet a is provided immediately downstream of the second feed rollers 23 and 24.

The above-mentioned actuator 31 is driven, for example, by rotation of a cam 35 connected to a pulse motor 34, and
The roller holding member 29 is rotated around the support shaft 30 against the urging force of the spring 36, and includes, for example, a photo switch 37 and a light shielding plate 38 having a light projecting slit b. The position detecting device 39 is provided. The cam 35 and the light shielding plate 38 are rotated at a reduced speed by a gear G1, a gear G2, and a gear G3 meshing with the gear G.

The reference position detecting means 39 determines the home position P of the correction rollers 27 and 28.
The number of pulses during which the correction rollers 27 and 28 return to the home position P from the reference point is set with reference to the time when the light transmitted through the slit b of the light shielding plate 38 is detected by the photo switch 37. The pulse motor 34 is driven to rotate in the reverse direction by the number of pulses.
The operation of determining the home position P is performed every time the print switch is turned on.

The peripheral speed of the second feed rollers 23, 24 is set to the process speed of image formation, and the peripheral speed of the correction rollers 27, 28 is set to a speed slightly higher than the process speed. And the first feed rollers 21 and 22
Is set to a speed slightly higher than the peripheral speed of the correction rollers 27 and 28.

On the other hand, the sensors 32a and 32b detect the leading edge of two points in the width direction of the sheet of paper a and detect the skew degree of the leading edge of the sheet by oblique transport based on the time difference between the detection of the leading edge. The actuator 31 is controlled by the control means 40 as follows based on information from the sensors 32a and 32b and the paper edge detection sensor 33.

In other words, an example in which a plurality of images are continuously formed will be described. As apparent from the timing chart shown in FIG. 5, when the print switch is first turned on (step S1), the above-described operation is performed. As described above, the roller holding member 29 rotates around the support shaft 30 until the photo switch 37 detects the light blocking plate 38, and thereafter, the roller holding member 29 returns and rotates by a preset number of pulses. The home position P of the correction rollers 27 and 28 is determined (step S2).

During this time, the conveyance of the sheet a is started at a predetermined timing, and the sheet a is fed to the correction rollers 27 and 28 through the first feed rollers 21 and 22.
At this time, the sensors for detecting the oblique conveyance of the sheet a 32a, 32b
When the skew of the leading edge of the sheet nipped by the correction rollers 27 and 28 due to the oblique conveyance is detected (step S3), the second feed rollers 23 and 24 feed the sheet a based on the skew degree detection information. Before the nip, the postures of the correction rollers 27 and 28 are changed in a direction to reduce the skew degree to zero (step S4).

Specifically, based on the detection of two leading edges of the paper a in the width direction, the control means 40 determines whether the oblique transport state of the paper a is rightward or leftward based on the time difference of the leading edge detection. Is determined, and the skew of the leading edge of the sheet is detected, and based on the skew direction and the skew, the roller holding member 29 is pulse-controlled in a direction to reduce the skew to zero. The number of control pulses at this time is stored in the control means 40.

Here, since the peripheral speed of the first feed rollers 21 and 22 is set to a speed slightly higher than the peripheral speed of the correction rollers 27 and 28, the paper a nipped by the correction rollers 27 and 28 Are the first feed rollers 21 and 22
Therefore, the posture of the correction rollers 27 and 28 can be easily changed without causing the paper a to be torn.

After the sheet a whose skew has been corrected in this manner is nipped by the second feed rollers 23 and 24, specifically, the sheet edge detection sensor 33 detects the trailing edge of the sheet (step S5). In the meantime, based on the number of pulses stored by the control means 40, the attitude of the roller holding member 29 is changed in the return direction (step S6),
The correction rollers 27 and 28 are returned to the home position P, whereby the correction rollers 27 and 28 prepare for the correction of the oblique conveyance of the next sheet a. Thereafter, the same control is repeatedly performed.

When returning the correction rollers 27 and 28 to the home position P, the correction rollers 27 and 28
Is set to a speed slightly higher than the peripheral speed of the second feed rollers 23, 24, so that the posture of the correction rollers 27, 28 can be easily changed without the paper a being torn. You can do it.

Correction roller 2 for correcting the above skewed conveyance
The change of the postures of 7, 28 is performed in consideration of the time until the sensors 32a and 32b detect the leading edge of the sheet (step S3) and the sensor 33 detects the leading edge of the sheet (step S7). The speed of the pulse motor 34 is controlled so that the attitude change of the correction rollers 27 and 28 is completed.

Further, the paper edge detection sensor 33 detects the leading edge of the paper (step S7), and this paper a is
Taking into account the time it takes to be nipped by 7,28,
Thereafter, the correction rollers 27 and 28 are moved to the home position P.
, The return movement of the correction rollers 27 and 28 is started (step S8), and the paper end detection sensor 3
The pulse motor 34 is controlled so that the return movement of the correction rollers 27 and 28 to the home position P is completed (step S9) by taking into consideration the time until the sheet 3 detects the trailing edge of the sheet (step S5). The speed is controlled.

According to the above configuration, each time the print switch is turned on, the correction rollers 27, 28 are returned to the reference points, and the home positions P of the correction rollers 27, 28 are determined. The correction is achieved with high accuracy, and the home position P of the correction rollers 27 and 28 is accurately determined.

Further, in addition to reliably correcting the oblique conveyance of the sheet a, the feeding of the sheet a is not stopped during that time.
Since the distance between the trailing edge of the following sheet a1 and the leading edge of the succeeding sheet a1 can be reduced, high-speed processing of a continuous image can be performed.

The feed roller 4 in the re-feeding path 19
It is needless to say that the skewed conveyance of the sheet is surely corrected based on the above-mentioned operation also for the sheet re-supplied to the sheet feeding device 12 through the feed rollers 1 and 42.

[0028]

As described above, in the paper skew conveyance correcting device according to the present invention, the paper conveyance is continued without using the registration roller dedicated to skew correction, which temporarily stops the paper feeding. By correcting the skew of the sheet while keeping it as it is, the conveyance time per sheet can be greatly reduced, and furthermore, when forming a continuous image, Since the distance from the leading edge of the succeeding sheet can be reduced, high-speed processing of a continuous image can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an electrostatographic copying machine (an example of an image forming apparatus) shown together with a sheet feeding deck.

FIG. 2 is a perspective view of a sheet feeding / conveying device including a sheet skew conveyance correcting device.

FIG. 3 is a side view of the paper feeder.

FIG. 4 is a plan view of the paper feeder.

FIG. 5 is a timing chart for correcting oblique conveyance of a sheet.

[Explanation of symbols]

6 image forming section (transfer device), 23, 24 feed roller, 27, 28 correction roller, 31 actuator, 32a, 32b paper oblique conveyance detection sensor,
0: control means, a: paper.

Claims (1)

[Claims] 1. An apparatus for correcting a skew of a sheet conveyed to an image forming unit, comprising: a pair of skew conveyance correcting units for nipping and conveying a sheet upstream of a feed roller for conveying a sheet to the image forming unit. A roller, an actuator for changing the attitude of the correction roller about an axis perpendicular to the paper surface of the transported paper, and a sensor for detecting a skew degree due to oblique transport of the leading edge of the paper nipped by the correction roller,
Further, based on the detection information of the skew degree from the sensor, before the paper is nipped by the feed roller, the attitude of the correction roller is changed in a direction to reduce the skew degree to zero, and And a control unit for returning the correction roller to a home position after the sheet is nipped by the feed roller.