JP2003002490A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of improving productivity and a durable life of a component by optimizing operation of a sheet skew correcting means. SOLUTION: When a sheet skew amount detected by a pre-resist sensor 2k is not more than a previously set tolerance, or when an image discriminating part 100e discriminates that an image to be formed is an image of which a skew is not distinctive, a sheet skew correcting means is not operated by a controller 100, but it is controlled so that an interval for feeding a sheet is changed by a pickup roller 3c. This control enables to feed with reduced paper intervals by a loop for correcting the skew. Thereby the productivity and the durable life of the component are improved.

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 of, for example, a printer, a facsimile, a copying machine, or a composite machine having these functions.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer or a facsimile, a recording material (transfer material, photosensitive paper or the like) is recorded by an appropriate image forming process mechanism such as electrophotographic method, electrostatic recording method, magnetic recording method. -A device for fixing an unfixed toner image formed and carried on a recording medium such as electrostatic recording paper or printing paper) by a transfer method (indirect method) or a direct method corresponding to the target image information is widely used. There is.

Further, there is also used an image forming apparatus such as an ink jet system which directly forms an image on a recording material with a liquid containing a dye or a pigment.

Image forming apparatuses typified by these copying machines, printers, facsimiles, etc. have been digitized in recent years. For example, in an electrophotographic copying machine, the reflected light of the illumination of the reader is read by a photoelectric element such as a CCD. , A / D
Convert and emit a laser beam, and rotate the polygon mirror to scan in the generatrix direction of the photoconductor to write on the photoconductor, or write on the photoconductor with LEDs arranged at a minute pitch or directly drop ink droplets on the sheet An inkjet method for forming an image or a thermal recording method is used. In addition, a number of multi-function machines that combine the functions of copying machines, printers, and facsimiles, which take advantage of the digital advantage of image compatibility, have been released.

In the above image forming apparatus, it is always required to increase the image forming speed in order to increase the copying speed (the number of copies per unit time) and the printing speed (the number of copies per unit time). Is.
However, in order to increase the image forming speed while advancing the above digitization, for example, the rotation speed of the polygon mirror, LE
Since it is necessary to increase the driving frequency of the D head and the inkjet head to increase the rotation speed and the frequency, there are many technical problems to be solved, which requires a lot of cost or time.

Further, it is desirable to increase the copying speed or the like without increasing the image forming speed and improve the productivity in terms of energy or durability of all the moving or rotating parts.

On the other hand, the copying speed is not determined only by the image forming speed, but the size of the interval between the sheets when a transfer material such as a sheet on which an image is formed is fed from the feeding unit and conveyed to the image forming unit. It is also preferable that the distance between the sheets is as small as possible, and as a result, the copying speed and the like are increased even in the image forming apparatus having the same image forming speed.

However, in a copying machine, for example, there is a problem that the image forming speed cannot catch up with the sheet conveying speed unless the distance between the sheets is opened to some extent in order to secure the time for back scanning in the reader section. There was a limit to shortening the interval.

As a method of solving such a problem, there is a method of having a memory for the entire surface of an image that can be read by one scan of the reader. In this case, by repeatedly ejecting the image read once from the memory, the back scan time of the reader can be omitted, so that the interval between the sheets can be reduced. In the past, the memory was expensive, but in recent years, the price has decreased remarkably, and a device equipped with a means for storing an image such as a memory or a hard disk has been put on the market.

Therefore, according to the above method, when the image forming speed is higher than the sheet conveying speed, it is the sheet conveying speed of the image forming apparatus that determines the copying speed and the printing speed, and the sheet conveying speed is constant. For example, the spacing between the sheets determines the copying speed in the image forming apparatus.

Therefore, even if the sheets have the same image forming speed, it is possible to increase the copying speed and the productivity more easily by reducing the distance between the sheets as much as possible.

Further, as another factor that determines the distance between the sheets, an operation for correcting the skew is performed in order to prevent the sheet from being obliquely conveyed and the image not being properly formed on the sheet. The required space between sheets can be increased.

Specifically, the sheets fed one by one from the sheet stacking unit (cassette) by the sheet feeding unit are temporarily placed in the nip of the pair of stopped registration rollers adjacent to the sheet conveying upstream of the image forming unit. bump into. At that time, the sheet detection sensor arranged near the upstream of the registration roller pair detects the sheet front end, and generally 5 to 15 mm after the sheet front end hits the registration roller, the conveying roller upstream of the registration roller is fed at a predetermined timing. Stop. Therefore, the skew of the sheet is corrected by aligning the leading edge of the sheet in parallel with the nip line of the registration roller by the waist of the sheet. After that, the registration roller is driven in synchronization with the image of the image forming unit to form an image on the conveyed sheet, thereby aligning the sheet and the image.

As the sheet detecting sensor, a rotatable lever biased in one direction by a spring and a transmissive photointerrupter in which a light emitting element and a light receiving element are arranged so as to face each other are combined, and when the lever is tilted by the sheet, A lever detects the presence or absence of a sheet by blocking or not blocking the light of a transmissive photointerrupter, or a light that emits light from a light emitting element to the sheet and the reflected light or diffused light is directly detected by a light receiving element. Type photointerrupters are the mainstream.

Further, regarding the arrangement of the sheet detecting sensors in the direction perpendicular to the sheet conveying direction, when conveying a sheet having a different sheet width, the sheet detecting sensor is arranged near the center in a device which distributes the sheet to both sides with the center of the sheet as a reference. In an apparatus that conveys a sheet based on one end of the largest sheet, the sheet is arranged close to the reference side.

In addition, an abutting plate that does not have a resist roller and is located immediately before the sheet conveying roller in front of the image forming unit is selectively retractable, and a sheet detection sensor similar to the above is arranged upstream of the abutting plate. In some cases, the conveying roller upstream of the registration roller is stopped at a predetermined timing from the detection signal. Similar to the registration rollers, skew is corrected by aligning the sheet in parallel with the abutting plate, and the sheet and image are aligned by retracting the abutting plate in synchronization with the image of the image forming means. ing.

In the case of performing the skew feeding correction, when trying to reduce the interval between the conveyed sheets, the minimum conveying interval between the sheets is a condition that the sheet detection sensor upstream of the registration rollers can detect the sheet. Therefore,
Except for small items such as detection error, the minimum detection interval between sheets of the sheet detection sensor and the feed amount (loop amount below) when performing skew correction of the sheet as described above (the sheet is not advancing at this time) Therefore, the sheet conveyance interval is the smallest.

[0018]

However, in the prior art, not all sheets are fed to the registration rollers or shutters outside the permissible range with respect to the permissible amount of skew according to the apparatus. Nevertheless, the skew feeding correction operation is performed by turning on / off the roller or the shutter even for a sheet for which skew feeding need not be corrected.

Further, generally, among images to be copied or printed, there are many images which are formed on a skewed sheet, such as memo writing, which are not so noticeable. Whether or not it is noticeable depends on the person, for example, on an image with a frame line, depending on the situation, but skew correction is uniformly performed on such an image.

By performing the skew feeding correcting operation which is not so necessary, it is difficult to reduce the distance between the sheets, the copying speed cannot be increased, and the productivity cannot be improved. Also, using unnecessary energy, clutches,
It is also a factor that reduces the durability of the drive connecting parts such as the motor and the gear.

The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to reduce the distance between sheets when an operation for correcting skew is not required. To increase the copy speed and print speed,
An object is to provide an image forming apparatus capable of improving productivity.

[0022]

In order to achieve the above object, in the image forming apparatus of the present invention, a feeding means for feeding the stacked sheets one by one, and an image on the fed sheets. Image forming means for forming a sheet, sheet skew correcting means arranged upstream of the image forming means for correcting a skewed sheet, and operation of the sheet feeding means and the sheet skew And a control unit capable of selectively controlling the operation of the correction unit, the control unit not operating the sheet skew correction unit with respect to the sheet feeding interval when the sheet skew correction unit operates. The operation of the feeding means is controlled so as to change the sheet feeding interval.

It is preferable to have a sheet detecting means for detecting the sheet skew amount upstream of the sheet skew correcting means.

The control means may include an image identifying section for identifying image information, and the operation of the sheet skew correcting means may be controlled according to the image information identified by the image identifying section.

The control means may control the operation of the skewed sheet correcting means in accordance with the skewed sheet amount detected by the sheet detecting means.

The control means has a comparison operation part for performing a comparison operation on the sheet skew amount detected by the sheet detection means and the image information identified by the image identification part, and depending on the operation result by the comparison operation part. The operation of the skewed sheet correcting means may be controlled by the following.

The operation of the sheet skew correction unit may be controlled according to the distance from the edge of the sheet identified by the image identifying unit to the image to be formed.

The operation of the sheet skew correcting means may be controlled according to the density of the image information to be formed on the sheet identified by the image identifying section.

A selection unit for selecting the operation of the skewed sheet correcting device may be provided.

The sheet skew feeding correcting means may be a shutter which can be selectively moved.

The skewed sheet correcting means may be a pair of rollers which can be selectively rotated.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions of the components described in this embodiment,
Unless otherwise specified, the material, the shape, the relative arrangement, and the like are not intended to limit the scope of the present invention thereto.

Further, this embodiment will be described by using a copying machine adopting an electrophotographic method as an image forming apparatus as an example.

(First Embodiment) FIG. 1 is a sectional view showing the schematic arrangement of an image forming apparatus according to the first embodiment. First, the schematic configuration of the copying machine will be described with reference to FIG. The copying machine photoelectrically converts the image information read by a reader unit 1 as an image reading unit having a scanning optical system, transfers the image information to an image forming unit 2 as an image forming unit, and feeds it by a feeding unit 3 as a feeding unit. Image formation is performed on the fed sheet S in the image forming unit 2. The sheet S on which the image has been formed is conveyed to the fixing unit 4, where heat and pressure are applied to fix the image, and the sheet S is discharged as a recorded image. The series of operations is controlled by the controller 100 as a control means. Since a series of electrophotographic process steps are known, detailed description thereof will be omitted.

(Reader) The document D placed on the platen glass 1a is irradiated with light by the scanning optical system 1b having a light source and a reflection mirror group, and the reflected light is reduced by the reduction lens 1c.
An image is formed on the CCD 1d via the and photoelectric conversion is performed.
After being D-converted, this image information is transferred to the image memory 100c provided in the controller 100 which is the control means. The maximum document size is LTR or A3. In addition, since the present embodiment is configured so that double-sided copying is possible, it has a memory twice the maximum original size.

(Feeding Unit) Paper feeding cassettes 3a and 3b accommodating sheets S of different sizes are removably attached to the lower part of the copying machine. Since the operation is the same, the paper feeding operation from the upper cassette 3a will be described below. When the solenoid connected to the pickup roller 3c is turned on / off at a constant interval, the pickup roller 3c which is rotationally driven feeds the sheets one by one.
Even if a plurality of sheets S are picked up, the retard roller 3f is driven in the opposite direction to the conveying direction via a torque limiter (not shown) when it is nipped by the conveying roller 3e and the retard roller 3f. Therefore, only the topmost sheet is fed and no double feeding is performed.

However, due to a momentary slip at the time of pick-up, instability of the conveying speed of the conveying roller 3e and the retard roller 3f (because it is a soft rubber roller of 25 °, and the sheet is reversely driven). ,
The sheet conveyance speed is often slower than the rotation speed of the roller), and even if the pickup is repeated at regular intervals, the intervals between the sheets are not constant and vary. In addition, the position of the leading edge of the paper at the time of pickup varies from the stacking point 3p to the separating portion (between M), which is also a factor that causes the distance between the sheets to vary.

In the present embodiment, the image forming speed is 200.
mm / s, and all the rollers described above are designed to have a conveying speed of 200 mm / s.

Next, the conveyed sheet passes through the pre-registration sensor 2k, and then reaches the registration roller pair 22 which is the sheet skew correcting means. The pre-registration sensor 2k is a module including a light emitting element and a light receiving element. When infrared light from the light emitting element hits a sheet, the light receiving element reads the reflected light and the presence or absence of the sheet is determined by the voltage level of the device controller. 100 judges. Further, the pre-registration sensors 2k are arranged at two positions in front and in the back in the direction perpendicular to the sheet conveying direction, and the controller 100 of the apparatus determines the difference between the detection times of both sheets as the skew amount. The registration roller pair 22 is a driving roller 22a and a driven roller 22b.
Is urged by a spring (not shown). Drive roller 2
2a is a metal cored bar with rubber fixed to the outer periphery thereof, and the driven roller 22b is made of metal with a small outer peripheral surface roughness.

An electromagnetic clutch 23, which can be selectively connected by a microcomputer of the main body, is arranged on the axis of the drive roller 22a, and the drive force of a motor 25 rotating at a constant speed is transmitted through a gear (not shown) to the drive roller 22a. Have been communicated to. Of course,
A stepping motor with good stopping accuracy may be directly connected to the drive roller for control.

Next, the sequence will be described. The registration roller pair 22 is driven at the expected arrival time of the distance from the position of the pre-registration sensor 2k to the registration roller pair 22 with reference to the timing of one of the pre-registration sensors 2k detected with a delay.

After that, the sheet is driven until it passes through the registration roller pair 22, and is stopped again in preparation for the arrival of the next sheet. In the present embodiment, the stop timing is controlled by the value calculated from the sheet length and the transport speed, but the sheet detection sensor (for example, 2i, 2k) disposed near the registration roller pair 22 (including upstream and downstream). ) The control may be performed based on the signal.

In the present embodiment, the pre-registration sensor 2k
Since the distance from the registration roller pair 22 to 10 mm,
The registration roller pair 22 is driven 50 msec after the timing of one of the pre-registration sensors 2k detected with a delay. Further, the drive timing may be corrected in proportion to the sheet width in the direction perpendicular to the sheet conveyance in accordance with the sheet size. The pre-registration sensor 2k is preferably arranged parallel to the pair of registration rollers 22, but when position adjustment is necessary due to mechanical intersection, the parallel deviation between the two is measured in advance and corrected to the drive timing. It is also possible to improve the ease of assembly by multiplying by.

In the present embodiment, the distance between both sensors is 260 mm, which can detect the longitudinal direction of the LTR size sheet.
I am trying. Of course, it is preferable to detect the edge of the sheet width as much as possible to detect the skew feed amount. Therefore, when conveying sheets of various sizes, arrange multiple sensors according to the size, or before registering in the direction perpendicular to the sheet conveyance. A means for moving the sensor 2k may be provided.

(Image Forming Section) A sheet detection sensor 2i is arranged immediately after the registration roller pair 22. The distance L ′ from the sheet detection sensor 2i to the transfer point is L ≦ L with respect to the distance L from the latent image point to the transfer point.
It is arranged so as to be L ′. Therefore, the laser light emission unit 2a emits a laser beam by the laser driver, based on the image information read by the reader unit 1 from the memory by the detection of the sheet front end of the sheet detection sensor 2i. Then, the rotation of the polygon mirror 2b causes the photosensitive drum 2c to scan in the generatrix direction to form a latent image on the drum surface that has been charged in advance by the charger 2d. This latent image is developed by the developing device 2e provided around the photosensitive drum 2c, and the toner image is transferred to the sheet S conveyed by the registration roller pair 22 by the transfer charging device 2g. The toner remaining on the drum surface after the image transfer is removed by the cleaning device 2h.

(Fixing Section) The sheet S to which the toner image is transferred in the image forming section 2 is guided to the fixing device 4 by the conveyor belt 8 and is applied with heat and pressure when passing through the pair of fixing rollers 4a and 4b. To fuse the toner image to the sheet S.

(Discharge Section) The sheet S after the image fixing is discharged to the outside of the apparatus via the discharge roller pair 5a and 5b.

(Double-sided Conveying Section) When performing double-sided copying, the sheet S after image fixing is guided to the reversing roller 6a by operating the flapper 5c by an actuator (not shown), and the reversing roller 6b while tilting the flexible sheet 6b. 6a is reached. The reversing roller 6a is a roller that can be driven in the normal and reverse directions, and the rear end of the sheet is detected by the detection sensor 6f.
Reverse when you exit. The flexible sheet 6b guides the sheet to the conveying roller 6c side without backflow. The sheet passes through the transport rollers 6d and 6e, and the registration roller 22 again.
Then, under the same control as that for the first side, the image for the second side is written on the sheet this time, and after fixing, the image is discharged to the outside of the apparatus.

(Controller) The controller 100 controls a series of operations of the image forming apparatus, such as control of an image forming operation and a feeding operation when the sheet is conveyed from the feeding section, and the image output from the CCD 1d. It has an image memory 100c for fetching information. Further, the skew feed amount calculation unit 1 for calculating the skew feed amount from the detection signal of the pre-registration sensor 2k.
Has 00f. In addition, a user mode selection unit 100a that can select whether or not to perform skew correction and an allowable skew amount that can select an allowable skew amount that serves as a reference for whether or not to perform skew correction It has a selection unit 100b.

Since the present embodiment has an image memory for two sheets, by alternately writing the images on the first side and the second side, it is possible to endlessly perform double-sided copying up to the number of stacked sheets even in continuous image formation. There is.

Next, the control of the sheet feeding interval according to the present embodiment will be described.

In the above-described feeding operation, the distance between the sheets at the time of LTR is 24 mm, and the feeding must be repeated. The distance M from the leading edge of the sheet to the conveying roller 3e is 10 mm,
The distance N between the conveying roller 3e and the sheet detection sensor 3k is designed to be 4 mm as the distance required for detecting the sheet interval (Hi / Lo) of the sensor. After the front end of the conveyed sheet is detected by the pre-registration sensor 2k, it strikes the registration roller pair 22 and is fed by 10 mm by the conveyance roller pair 20 to form a loop. Due to the waist of the sheet at this time, the leading edge of the sheet is parallel to the pair of registration rollers 22, so that the skew feeding is corrected. After the sheet forms a loop, until the vibration of the loop subsides 1
After waiting for 00 msec, the registration roller pair 22 is driven and sent to the image forming unit. When this is converted into a distance, it becomes 0.1 × 200 = 20 mm. Therefore, the required sheet spacing is 44 mm, which is the sum of all the above values, and CPM is LTR and 46 CPM is the basic productivity of the apparatus of this embodiment.

However, in this embodiment, the skew feed amount calculating section 100 is calculated from the signal detected by the pre-registration sensor 2k.
When the skew amount calculated by f is 1 mm or less, the controller 100 controls so as not to perform the above loop formation. Therefore, a distance of 20 mm for transporting a subsequent sheet is not required in the waiting time for loop formation of 10 mm and loop vibration to be settled, so that the timing of the next sheet feeding is advanced by 30 mm (150 msec). If all sheets have skew of 1 mm or less, 52C
PM (LTR) productivity will be obtained. In the actual test, about 50% or more did not require skew correction, although it depends on the type of sheet and how to insert the cassette 3a.

In addition, since the present embodiment has the user mode selection section 100a which allows the user to select the skew feed correction priority mode and the productivity priority mode, the user does not have to worry about skewing as much as a memo. In the case of a document that is not set to "Yes", it is possible to prioritize productivity by selecting the productivity priority mode. Further, an allowable skew amount selection unit 100b capable of inputting an allowable skew amount and varying the skew amount range for automatically performing skew correction is also provided. As a result, it is possible to prevent unnecessary skew feeding correction operation depending on the type of document and the content of the image, and it is possible to increase the copying speed and the printing speed and improve the productivity.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. It should be noted that the same or corresponding components as those of the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 2 shows a sectional view of the image forming apparatus according to the second embodiment. The controller 100, which is the control unit in the present embodiment, has an image identification unit 100d that captures the read image information into the memory 100c and identifies the image information.

In FIG. 3, the letters "ABC" are inclined by the same angle, and the sizes of the frames are different between (a) and (b).
In (c), there is no frame, and in (d), the character position is moved to the end.

Due to the illusion, a normal person is most concerned with skew in (a), and is less concerned with (b) and (c) and (d) next. That is, the closer the image is to the frame line, the worse the impression, and the more linear the image is with respect to the sheet edge, the worse the impression.

Therefore, as shown in FIG. 4, 15 m from the sheet edge.
When the image identifying unit 100d identifies that there is no image within m, the skew correction is not performed, and the controller 100 controls the interval between the sheets to be 14 mm to improve productivity. However, as shown in (d), when there are few parallel image portions such as characters from the sheet edge, for example, line images such as frame lines, the productivity priority mode is entered even if there are images within 15 mm. . 15 mm of the image detection area can be made variable by the user.

Further, the controller 100 has a comparison calculation unit 100e for comparing and calculating the skew amount detected by the pre-registration sensor 2k and the image of the image detection area identified by the image identification unit 100d. 100e
It is also possible to operate the sheet skew feeding correcting means according to the combination of each condition from the calculation result of

FIG. 5 shows whether or not the skew feeding correction operation is performed in relation to the skew feeding amount and the image detection area from the sheet edge. When it is determined that there is a line image in the image detection area, the skew feeding correction operation is not performed in the area below the solid line. In the case of a character image, the area in which the skew feed correction operation is not performed expands, and the skew feed correction operation is not performed below the dotted line, and the productivity priority mode is entered.

The electrophotographic (monochrome) image forming apparatus has been described above as an example, but other image forming methods such as an electrophotographic apparatus for forming a color image by superposing toner images of a plurality of colors, an ink jet method, a thermal transfer method, etc. The present invention can also be applied by a method.

Further, the skew feeding correction method may be not only the pair of rollers but also another method such as a method using a shutter gate.

[0064]

As described above, according to the present invention, the skewed sheet correcting means in the image forming apparatus is selectively operable in accordance with the content of the document, the type of the image, etc., so that the skewed sheet is corrected. When it is not necessary, the sheet skew correction unit is not operated and the sheet feeding interval can be shortened. As a result, the copying speed and the printing speed of the image forming apparatus can be increased and the productivity can be improved.

[Brief description of drawings]

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

FIG. 2 is a sectional view of an image forming apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram showing an image image when a sheet is skewed.

FIG. 4 is a diagram showing an image detection area according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a range of a skew feeding correction operation according to the second embodiment of the present invention.

[Explanation of symbols]

1 leader 2 Image forming section 2a Laser emission part 2b polygon mirror 2c photosensitive drum 2d charger 2e Developing device 2g transfer charger 2i sheet detection sensor 2k pre-registration sensor 3 paper feeder 3a, 3b cassette 3c pickup roller 3e Conveyor roller 3f retard roller 3k sheet detection sensor 3p loading point 4 fixing device 8 conveyor belt 20 Transport roller pair 22a drive roller 22b driven roller 23 Electromagnetic clutch 25 motor 100 controller 100a User mode selection section 100b Allowable skew amount selection section 100c memory 100d image identification unit 100e Comparison operation part 100f Skew amount calculator

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) G03G 15/00 518 G03G 15/00 518 F term (reference) 2C061 AP03 AP04 AQ04 AQ05 AQ06 AR01 AR03 AS02 HH05 HJ02 HK03 HK11 HX10 2H072 AA03 AA09 AA13 AA22 BA03 BA12 CA01 HB07 JA02 3F048 AA02 AA04 AA05 AB01 BA20 BB02 CC03 DA07 DB06 DB11 DC14 EA15 EB15 EB22 EB24 EB30 EB33 3F102 AA06 AA AB19 BA02 BB02 CA05 CB02 DA06 DA08 DA08 DA08

Claims (10)

[Claims] 1. A feeding means for feeding stacked sheets one by one, an image forming means for forming an image on the fed sheets, and an upstream side of the image forming means, which is skewed. The sheet skew correction unit for correcting the fed sheet, and the control unit capable of selectively controlling the operation of the sheet feeding unit and the operation of the sheet skew correction unit, the control unit Controls the operation of the feeding unit so as to change the sheet feeding interval when the sheet skew correcting unit does not operate with respect to the sheet feeding interval when the sheet skew correcting unit operates. Image forming apparatus. 2. The image forming apparatus according to claim 1, further comprising a sheet detection unit that detects a sheet skew amount upstream of the sheet skew correction unit. 3. The control means has an image identifying section for identifying image information, and controls the operation of the skewed sheet correcting section according to the image information identified by the image identifying section. The image forming apparatus according to claim 1. 4. The image forming apparatus according to claim 2, wherein the control unit controls the operation of the sheet skew correcting unit according to the sheet skew amount detected by the sheet detecting unit. 5. The control means has a comparison operation part for performing a comparison operation on the sheet skew amount detected by the sheet detection means and the image information identified by the image identification part, and an operation result by the comparison operation part. The image forming apparatus according to claim 3, wherein the operation of the skewed sheet correcting unit is controlled in accordance with the above. 6. The image according to claim 3, wherein the operation of the sheet skew correction unit is controlled according to the distance from the edge of the sheet identified by the image identification unit to the image to be formed. Forming equipment. 7. The image forming apparatus according to claim 3, wherein the operation of the sheet skew correcting unit is controlled according to the density of image information to be formed on the sheet identified by the image identifying unit. 8. The image forming apparatus according to claim 1, further comprising a selection unit for selecting an operation of the skewed sheet correcting device. 9. The image forming apparatus according to claim 1, wherein the skewed sheet correcting unit is a shutter that can be selectively moved. 10. The sheet skew correcting means is a pair of rollers which can be selectively rotated.
8. The image forming apparatus according to any one of items 8.