JPH1087116A - Sheet feeder and image forming device provided with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet feeder capable of feeding a sheet in a reduced period and an image forming device provided with the sheet feeder. SOLUTION: A sensor means S ascertains whether a sheet P mounted on a sheet platen 1 and having reached a separator means 6A is a short sheet of a length in the feed direction as to be separated from widthwise regulation guides 2 or a long sheet of a length in the feed direction as to still touch the widthwise regulation guides 2. A control means controls an obliquity-correcting means 8 so as to correct obliquity of the sheet based on information from the sensor means S only when the sensor means S decides that the sheet is a short sheet, to thereby feed the sheet P in a reduced period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying apparatus for conveying sheets of different sizes and an image forming apparatus provided with the same, and more particularly, to an apparatus for correcting skew of a sheet.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus has a sheet conveying device for conveying a document, which is an example of a sheet stacked on a document table as a sheet mounting table, to an image forming section. The sheet conveying device includes a document table, a width-direction regulating guide that is provided on the document table, and abuts on an edge of the document in the width direction to regulate the movement of the document, and a sheet feeding unit that feeds the document. The apparatus includes a paper roller, a transport roller that rotates in the document feeding direction, and a separating unit that is a separating unit that includes a separating roller that rotates in a direction opposite to the transport roller.

As shown in FIG. 9, the conveying roller and the separating roller constituting the separating section are each in the form of a comb and are slightly inserted into each other.
Further, the transporting force of the transporting roller 6 is higher than that of the separating roller 7 due to the difference in material and hardness. With this configuration, when the document is fed by the feed roller, the transporting force of the transport roller 6 overcomes the return force generated by the reverse rotation of the separation roller 7 and transports the document. You can do it.

By the way, a plurality of originals may be conveyed at the same time depending on the state of overlapping of the originals. In this case, the uppermost document is sent by the transport roller 6 as in the case of one sheet, but the second and subsequent documents do not come into contact with the transport roller 6 and are returned to the separation roller 7 by the return force of the separation roller 7. You can be dammed. When the uppermost document is transported, the transport roller 6 comes into contact with the second document, so that the second document is transported next, but the third and subsequent documents are not transported. It is dammed at the separation roller 7 as described above. By repeating the above, even if a plurality of originals are fed, the originals are separated and conveyed one by one by the separation unit.

[0005]

However, in such a conventional sheet conveying apparatus and an image forming apparatus having the same, variations in the arrangement, outer diameter, surface condition, etc., of the conveying roller 6 and the separation roller 7 are present. As a result, the balance between the conveyance force and the return force for the document is different between the left and right, and as a result, the force for conveying the document is slightly different between the left and right.

Therefore, when the leading edge of the document arrives at the separation section, if the document is regulated by the width regulating guide, the document does not skew even if the force for transporting the document is slightly different between the left and right. However, if the original is short and comes off the width regulating guide before the leading end of the original arrives at the separation section, the original may be skewed. Therefore, in the case where such skew of the document occurs, in order to correct the skew, for example, in a state where the skew is corrected as a skew correcting means, the skew is corrected by contacting the skewed document. Rollers are provided.

However, when the registration roller having such a configuration is used, the skew can be corrected by temporarily stopping the registration roller, but the skew is not corrected, that is, the skew correction is required. The registration roller must be temporarily stopped even when a document that is not conveyed is conveyed, which wastes time when the document is conveyed.

On the other hand, in image forming apparatuses such as recent printers and copiers, higher speeds are desired. However, if wasteful time is required for document conveyance, the speed cannot be increased. There is a problem.

Accordingly, the present invention has been made to solve such a conventional problem, and has a sheet conveying apparatus capable of conveying a document (sheet) without wasting time, and a sheet conveying apparatus having the same. It is an object of the present invention to provide an image forming apparatus.

[0010]

According to the present invention, a sheet placed on a sheet mounting table is separated one by one by a sheet feeding means and a separating means and sent to the skew correcting means. After correcting the skew, in the sheet conveying device for conveying to the recording means, while being provided on the sheet mounting table,
A width-direction regulating guide that abuts on both ends of the sheet to regulate the movement of the sheet in the width direction; and a sheet placed on the sheet placing table, when the sheet reaches the separation unit, the width-direction regulating guide. Detecting means for detecting whether the sheet is a short sheet having a length in the conveying direction such that the sheet does not deviate from the width direction or a long sheet having a length in the conveying direction so as not to deviate from the width direction regulating guide; And control means for controlling the skew correcting means so as to perform the skew correcting operation only when the sheet is determined to be the short sheet based on the information from.

[0011] The present invention also provides the detecting means provided on the sheet mounting table, wherein the detecting means is provided at a rear end position of the short sheet when the short sheet is mounted on the sheet mounting table; The long sheet is placed between the rear end position of the long sheet when the long sheet is placed on the table.

Further, according to the present invention, when the long sheet and the short sheet are mixedly loaded on the sheet mounting table, the detecting means is provided on a conveying path between the skew correcting means and the separating means. The installation position is set to a position that is at least distant from the skew correcting means with respect to the length of the short sheet.

Further, the present invention is characterized in that an auxiliary conveying means for conveying the sheet to the skew correcting means is provided between the skew correcting means and the separating means.

Further, according to the present invention, the sheets placed on the sheet mounting table are separated one by one by a sheet feeding means and a separating means and sent to the skew correcting means, and the skew is corrected by the skew correcting means. And a sheet conveying device that conveys the sheet to a recording unit. The sheet conveying device is provided on the sheet mounting table, and is in contact with an end of the sheet to restrict the widthwise movement of the sheet. When the sheet placed on the mounting table is a short sheet having a length in the transport direction such that the sheet is detached from the width direction regulating guide when reaching the separation unit, or the sheet is not detached from the width direction regulating guide. A first detecting unit for detecting whether the sheet is a long sheet having a length in the conveying direction, and a sheet having a narrow width having a length in the width direction in which both ends of the sheet cannot abut on the width direction regulating guide. Ah A skew correcting operation only when the sheet is determined to be a short sheet and when the sheet is determined to be a narrow sheet based on information from the first and second detecting means. And control means for controlling the skew correcting means to perform the skew correction.

In the present invention, when the long sheet, the short sheet and the narrow sheet are mixedly loaded on the sheet mounting table, the first and second detecting means may include the skew correcting means and the separating means. , And the installation position is set at a position distant from the skew correcting means by at least the length of the short sheet.

In the present invention, the width-restricting guide is provided on the sheet mounting table so as to be movable in the width direction of the sheet, and moves in the width direction in conjunction with the width-restricting guide, and the skew correction is performed. An interlocking plate having a protruding portion protruding into the transport path between the means and the separating means is provided, and the first and second detecting means are attached to the protruding portion of the interlocking plate.

Further, the present invention comprises a sheet conveying device for conveying a sheet placed on a sheet placing table to an image forming section, and recording means for recording data on the sheet on a recording medium such as a film or an optical disk. In the above image forming apparatus, the sheet conveying device is the sheet conveying device according to any one of claims 1 to 7.

Further, as in the present invention, the detecting means allows the sheet placed on the sheet placing table to be a short sheet having a length in the transport direction such that the sheet is separated from the width direction regulating guide when it reaches the separating means. And if the control unit determines that the sheet is a short sheet based on information from the detection unit, while detecting whether the sheet is present or a long sheet having a length in the conveyance direction that does not deviate from the width direction regulating guide. The sheet is conveyed without wasting time by controlling the skew correcting means so as to perform the skew correcting operation only when the sheet is skewed.

Further, the first detecting means may determine whether the sheet placed on the sheet placing table is a short sheet having a length in the conveying direction such that the sheet is separated from the width direction regulating guide when it reaches the separating means. Or, while detecting whether the sheet is a long sheet having a length in the conveyance direction that does not deviate from the width direction regulating guide, the sheet is not detected by the second detecting means in the width direction in which both ends cannot contact the width direction regulating guide. It is detected whether the sheet is a narrow sheet having a length. The control means controls the skew correcting means to perform the skew correcting operation only when the sheet is determined to be a short sheet or when the sheet is determined to be a narrow sheet based on the information from the first and second detecting means. By controlling, the sheet is conveyed without wasting time.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an external view of an image recording apparatus which is an example of an image forming apparatus having a sheet conveying apparatus according to a first embodiment of the present invention, and FIG. 2 is a schematic sectional view thereof.

In FIG. 1, reference numeral 30 denotes an image recording apparatus main body (hereinafter referred to as a main body), and an original P placed on the original table 1 is separated by a separation unit 6A including a paper feed roller 5, a transport roller 6 and a separation roller 7. The sheet is conveyed in a separated state one by one. When the sheet is skewed, the sheet is corrected by the registration roller 8 and then sent to the image reading section 31.

Further, the original P sent to the image reading section 31 is read by a reading sensor such as a CCD via an optical system 37, and then read by an image recording section 33 as a recording means.
To be recorded on an optical disk or the like. Then, the read document P is conveyed while being sandwiched by the conveyance belt 9 and the like, and is sequentially discharged to the paper discharge unit 35. The recorded image is displayed on the screen 34 or printed on paper by the printer 36.

The document table 1 which is removably mounted on the main body 30 is provided so as to be movable in a width direction orthogonal to the conveyance direction of the document P as shown in FIGS. , A document detecting sensor S for detecting the length of the placed document P, and a pressure plate 1 a for abutting the document P against the paper feed roller 5. And a coil spring 1b.

Here, the document detection sensor S itself has a performance of detecting whether or not the document P exists at the position of the sensor, such as an optical reflection sensor. Then, such a document detection sensor S is moved to a length shorter than a predetermined length, that is, a length in the transport direction such that when the leading end reaches the separating portion 6A, the trailing end is out of the regulation of the width direction regulating guide 2. When a document P having a length of
Is not detected, and a position where the original P is detected when the original longer than the original P is placed on the original platen 1, in other words, after the original P when the shorter original P is placed on the original platen 1 Edge position and original P when long original P is placed on original platen 1
Is provided between the original document P and the rear end position to detect whether or not the placed document P is shorter than a predetermined length.

As shown in FIG. 2, the main body 30 is provided with a control device 50 for controlling the driving of the paper feed roller 5, the transport roller 6, the separation roller 7, and the registration roller 8. Here, based on a signal from the document detection sensor S, the control device 50 determines that a document P shorter than a predetermined length (hereinafter, referred to as a short document) has been placed on the platen 1 and tilts the document P While the rotation of the registration roller 8 is temporarily stopped so that the line can be corrected, the registration roller 8 is driven again to convey the document P after correcting the skew.

The reason for controlling the registration roller 8 in this way is that, in the case of a short original P, one or more sheets are fed by the feed roller 5, but when the original P is separated one by one. This is because the trailing edge of the document P has already been disengaged from the width-direction regulating guide 2 and the force for regulating the movement in the width direction does not work. When the force for restricting the movement in the width direction does not work as described above, as described above, due to the difference between the right and left of the balance of the conveying force and the separating force of the conveying roller 6 and the separating roller 7 with respect to the original P, the original P This is because the skew may occur.

On the other hand, if the control device 50 determines that a document longer than a predetermined length (hereinafter referred to as a long document) has been placed based on a signal from the document detection sensor S, it stops the registration roller 8. And the original P is conveyed. The reason why the registration rollers 8 are not stopped in the case of such a long original P is that the long original P is not deviated from the regulation of the width direction regulating guide 2 at the time of separation, and the originals P are separated one by one at the separation section. At this time, since it is regulated so as not to move in the width direction by the width direction regulating guide 2,
This is because the document P does not skew even if there is a difference between the right and left in the width direction of the separating force.

Next, the sheet conveying operation of the sheet conveying apparatus thus configured will be described.

First, when a document transport instruction is issued by pressing a start button (not shown) provided on the main body 30,
Document detection is performed by the document detection sensor S. Here, assuming that a short original P is placed on the original platen 1, since the original detection sensor S does not detect the short original P, the control device 50 based on a signal from the original detection sensor S It is determined that the short document P is placed on the document table 1.

Next, the control device 50 drives the paper feed roller 5 to feed one or a plurality of originals P. Here, when one short document P is fed, this document P is transported by the transport roller 6 that has overcome the return force of the separation roller 7.
Is conveyed by the conveyance force.

When a plurality of sheets are conveyed, the uppermost original is sent in the same manner as described above, but the second and subsequent originals are blocked at the separation roller 7 by the return force of the separation roller 7. . When the top document is conveyed, the conveyance roller 6 comes into contact with the second document, so that the second document is conveyed next. As described above, it is dammed at the separation roller 7. By repeating the above, the document P is separated and conveyed one by one in the separation unit.

On the other hand, the control device 50 temporarily stops the rotation of the registration roller 8 before the document P reaches the registration roller 8 after a predetermined time has elapsed after driving the transport roller 6 in this manner, The leading edge of the document P is made to strike the registration roller 8 in a stopped state. Then, the skew of the document P is corrected by abutting the leading end of the document P against the registration rollers 8 in the stopped state.

Next, after the registration roller 8 is once stopped to correct the skew of the document P, the control device 50
Drives the registration roller 8 again, whereby the original P
Go through the registration rollers 8. Thereafter, the document P is photographed on a film via an optical system, recorded on a medium such as an optical disk, or stamped by a stamping device.

On the other hand, if it is assumed that a long document is placed on the document table 1, the document detection sensor S detects the document, so that the controller 50 controls the document table 1 based on the detection signal from the document detection sensor S. It is determined that a long document is placed on the.

Next, the control device 50 drives the paper feed roller 5, whereby the document is separated one by one by the separation unit 6A. In the case of a long document, the document is restricted in the width direction during this separation. Since the guide 2 restricts movement in the width direction, even if there is a difference between the left and right in the width direction of the separating force, there is no skewing. Therefore, the control device 50 rotates the registration roller 8 without stopping, and conveys the document.

As described above, the size of the document P is detected by the document detection sensor S, and in the case of a short document that may be skewed, the registration roller 8 is temporarily stopped to correct the skew. In addition, it is possible to record an image without skew. Further, by stopping the registration roller 8 once for a long document that is unlikely to be skewed, wasteful time for stopping the document can be eliminated.

In the above description, the case where the document detection sensor is provided on the document table 1 has been described. However, the present invention is not limited to this, and the document detection sensor is provided between the separation unit 6A and the registration roller 8. May be provided in the transport path of the first embodiment.

Next, a description will be given of a second embodiment of the present invention in which a document detection sensor is provided at such a position.

FIG. 5 is a plan view of a main part of a sheet conveying apparatus according to a second embodiment, and FIG. 6 is a schematic sectional view. In FIGS. 5 and 6, P1 and P2 are mixedly mounted on the document table 1. Documents having different lengths in the conveying direction are shown. Note that P1 is a short document whose rear end is separated from the width-direction regulating guide at the time of separation, and P2 is a long document regulated by the width-direction regulating guide 2 at the time of separation.

Reference numeral S1 denotes a document detection sensor disposed on the conveyance path R between the separation section 6A and the registration roller 8, and the document detection sensor S1 is at least located on the conveyance path R from the registration roller 8. The short document P1 is provided at a position more distant than the length in the transport direction. By providing the document detection sensor S1 at such a position, the document detection sensor S1 can detect the leading edge and the trailing edge of the document P1 before the short document P1 reaches the registration roller 8. ing.

On the other hand, in response to the signal from the original detection sensor S1, the controller 50 determines whether or not to detect the rear end within a predetermined time after the original detection sensor S1 has detected the front ends of the originals P1 and P2. Thus, it can be determined whether or not the short document P1 is placed on the document table 1. By providing the document detection sensor S1 on the transport path R and determining the length of the document placed on the document table 1 as described above, documents P1 and P2 having different lengths as shown in FIG. Even if the originals are mixed on the original table 1, the control device 50 can control the driving of the registration rollers 8 each time according to the length of the originals P1 and P2 to be conveyed.

When the document detection sensor S1 is provided at such a position, the separation from the separation unit 6A to the registration roller 8 is large and the short document P1 cannot be transported to the registration roller 8. An auxiliary transport roller 10, which is an auxiliary transport unit, is provided between 6A and the registration roller 8. Then, the rotation of the registration roller 8 is stopped by the auxiliary transport roller 10 immediately before the leading end reaches the registration roller 8, and even when the leading end of the document P1 is dammed, the document P1 can be further pushed. The skew can be corrected.

Next, the sheet conveying operation of the sheet conveying apparatus thus configured will be described.

First, when a document transport command is issued, the document is separated and transported by the separating unit into one sheet. Here, if the conveyed document is a short document P1, the leading edge is detected by the document detecting sensor S1 provided on the transport path R, and then the rear edge is detected within a predetermined time. Then, based on the detection signal from the document detection sensor S1, the control device 50
It is determined that the document being conveyed is the short document P1.

Next, the control device 50 determined in this way.
Stops the rotation of the registration roller 8 immediately before the leading edge of the document P1 reaches the registration roller 8. As a result, the leading edge of the document P1 is blocked, but the auxiliary transport roller 10
Skew is corrected by further pressing the document P1. Next, after the registration roller 8 is once stopped to correct the skew of the document P1, the registration roller 8 is driven again to pass the document P1.

On the other hand, if the document to be conveyed is a long document P2, the leading edge is detected by the document detecting sensor S, but the trailing edge is not detected within a predetermined time.
Determines that the document P2 is being transported is a long document P2, and does not stop the registration roller 8, whereby the document P2 is transported as it is.

As described above, by providing the document detection sensor S1 on the transport path R and determining the length of the document placed on the document table 1, the documents P1 and P2 having different lengths can be read. , The control such as stopping the registration roller 8 can be performed according to the length of the document.

By the way, in the above two embodiments, the case where the control such as the stop of the registration roller 8 is controlled according to the length of the original has been described. However, the present invention is not limited to this, and the present invention is not limited thereto. Control such as stopping of the registration roller 8 may be performed in accordance with not only the length but also the length of the document in the width direction.

Next, a third embodiment of the present invention will be described.

FIG. 7 is a plan view of a main part of a sheet conveying apparatus according to a third embodiment, and FIG. 8 is a schematic sectional view of the sheet conveying apparatus. In FIGS. Documents that are mixed and have different lengths in the transport direction and the width direction. Here, P1 is a short document which is separated from the width-direction regulating guide 2 at the time of separation, and P2 is a width-direction regulating guide 2 at the time of separation.
Long document whose both ends are regulated by P3, P3 is short document P1
And a document that is narrower than the long document P2 (hereinafter referred to as a long document). When the elongated document P3 is separated, only one end thereof is regulated by the width-direction regulating guide 2, so that the document P3 may be skewed.

On the other hand, reference numeral 3 denotes an interlocking plate interlocked with the movement of the width direction regulating guide 2 in the width direction indicated by the arrow A, and arm portions 3a extending from both side ends of the interlocking plate 3 toward the auxiliary transport roller 10 are provided. The arm 3 has a protruding portion 3b that protrudes toward the transport path R at each end of the arm portion a. Then, first and second document detection sensors S2 and S3 as first and second detection means are attached to the protruding portion 3b.

Here, by attaching the first and second document detection sensors S2 and S3 to the protruding portion 3b protruding toward the conveyance path R side, the first and second document detection sensors S2 and S3 are When a short document P1 and a long document P2 each having a predetermined document width pass, the document P1,
Although P2 can be detected, when the elongated document P3 passes, only the first document detection sensor S2 in this embodiment detects the passage of the document P3.

When the detection signal is input from only one of the document detection sensors S2, the control device 50 determines that the document being conveyed is the elongated document P3,
Since there is a possibility that the document P3 may be skewed, the registration rollers 8 are stopped.

The first and second original detection sensors S2 and S2
If the trailing edge is detected within a predetermined time after the leading edge is detected in S3, the control device 50 determines that the document is a short document P1, and determines the registration roller as described in the second embodiment. Stop rotation of 8 and correct skew. Also,
The leading edge of the long document P2 is detected by the first and document detection sensors S2 and S3, but if the trailing edge is not detected within a predetermined time, the control device 50 determines that the document is the long document P2,
The registration rollers 8 are conveyed without stopping.

Next, the sheet conveying operation of the sheet conveying apparatus thus configured will be described.

First, when a document transport command is issued, the document is separated and transported by the separating unit into one sheet. Here, when the elongated document P3 is transported, the leading end of the document P3 is moved to the first position.
It is detected by the document detection sensor S2, but not detected by the second document detection sensor S3. When only the first document detection sensor S2 detects the passage of the document P3,
The controller 50 determines that the document P3 is an elongated document P3, stops the registration roller 8, stops the leading edge of the document P3, further presses the document P3 by the auxiliary conveyance roller 10, and corrects the skew. The roller 8 rotates to transport the document P3.

On the other hand, when the short document P1 is conveyed,
In the same manner as described in the second embodiment, the leading and trailing edges are detected by the first and second document detection sensors S2 and S3, whereby the control device 50 determines that the document is a short document P1. Then, the control device 50 stops the rotation of the registration roller 8 and dams the leading edge of the document to correct the skew, and then rotates the registration roller 8 again to convey the document.

When a long document P2 is conveyed,
The leading edge is detected by the document detection sensor S1 and the document detection sensor S3, but the trailing edge is not detected within a predetermined time. Therefore, the control device 50 determines that the document is a long document P2. As a result, the document P2 is transported as it is.

As described above, the first and second document detection sensors S2 and S3 are connected to the conveyance path R in conjunction with the width direction regulating guide 2.
In the case where originals P1, P2, and P3 having different lengths and widths in the width direction are mixed, control such as stopping the registration roller 8 can be performed according to the length and the length in the width direction. it can.

[0061]

As described above, according to the present invention, the detecting means detects whether or not the sheet placed on the sheet mounting table is a sheet which may be skewed, and causes skew. By performing the skew correction operation only on a sheet that has a possibility, the sheet can be conveyed without wasting time. Thus, for example, when a large number of documents are conveyed and recorded by an electronic file device or the like, an image without skew can be recorded, and wasteful time can be reduced as compared with a case where the skew correction device is applied to all documents. This has the effect of reducing the time required to record the same number of documents.

[Brief description of the drawings]

FIG. 1 is an external view of an image recording apparatus which is an example of an image forming apparatus having a sheet conveying apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of the image recording apparatus.

FIG. 3 is a plan view of a main part of the sheet conveying apparatus.

FIG. 4 is a schematic sectional view of the sheet conveying device.

FIG. 5 is a plan view of a main part of a sheet conveying apparatus according to a second embodiment of the present invention.

FIG. 6 is a schematic sectional view of the sheet conveying apparatus.

FIG. 7 is a plan view of a main part of a sheet conveying apparatus according to a third embodiment of the present invention.

FIG. 8 is a schematic sectional view of the sheet conveying apparatus.

FIG. 9 is a plan view illustrating a configuration of a separation unit of a conventional sheet conveying apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 document table 2 width direction regulating guide 3 interlocking plate 3 b projecting portion 5 paper feed roller 6 transport roller 6 A separation unit 7 separation roller 8 registration roller 10 auxiliary transport roller S, S1 document detection sensor S2 first document detection sensor S3 second document Detection sensor P Document P1 Short document P2 Long document P3 Slender document R Transport path 30 Image recording device main body 33 Image recording section

Claims (8)

[Claims] 1. A sheet placed on a sheet mounting table is separated one by one by a sheet feeding unit and a separating unit, sent to a skew correcting unit, and skew is corrected by the skew correcting unit. A sheet conveying device configured to convey the sheet to a recording unit, a width direction regulating guide that is provided on the sheet mounting table and that abuts both ends of the sheet to restrict the movement of the sheet in the width direction; The placed sheet is a short sheet having a length in the conveyance direction such that the sheet is separated from the width-direction regulating guide when the sheet reaches the separation unit, or is a sheet in the conveyance direction such that the sheet is not detached from the width-direction regulating guide. A detecting unit that detects whether the sheet is a long sheet having a length, and the skew correcting unit that performs the skew correcting operation only when the sheet is determined to be the short sheet based on information from the detecting unit. A sheet conveying device, comprising: control means for controlling. 2. The method according to claim 1, wherein the detecting unit is provided on the sheet mounting table, and the installation position is set at a rear end position of the short sheet when the short sheet is mounted on the sheet mounting table; 2. The sheet conveying apparatus according to claim 1, wherein the position is set between the position of the long sheet and the rear end of the long sheet. 3. When the long sheet and the short sheet are mixed on the sheet mounting table, the detecting means is provided in a transport path between the skew correcting means and the separating means, and the installation position is set. 2. The sheet conveying device according to claim 1, wherein the position of the sheet is at least distant from the skew correcting unit with respect to a length of the short sheet. 4. The sheet conveying apparatus according to claim 3, further comprising an auxiliary conveying unit for conveying the sheet to the skew correcting unit between the skew correcting unit and the separating unit. 5. After the sheets placed on the sheet mounting table are separated one by one by a sheet feeding unit and a separating unit and sent to a skew correcting unit, and the skew is corrected by the skew correcting unit. In a sheet conveying device for conveying to a recording unit, a width direction regulating guide that is provided on the sheet mounting table and abuts on an end of the sheet to restrict the movement of the sheet in the width direction is mounted on the sheet mounting table. The placed sheet is a short sheet having a length in the conveyance direction such that the sheet is separated from the width-direction regulating guide when the sheet reaches the separation unit, or is a sheet in the conveyance direction such that the sheet is not detached from the width-direction regulating guide. First detecting means for detecting whether the sheet is a long sheet having a length, and whether the sheet is a narrow sheet having a length in a width direction in which both ends cannot contact the width direction regulating guide. Check A second detecting unit that knows that the skew correction operation is performed only when the sheet is determined to be a short sheet and when the sheet is determined to be a narrow sheet based on information from the first and second detecting units. A sheet conveying device comprising: a control unit that controls a skew correcting unit. 6. When the long sheet, the short sheet, and the narrow sheet are mixedly loaded on the sheet mounting table, the first and second detection units are provided between the skew correction unit and the separation unit. 6. The sheet conveying device according to claim 5, wherein the sheet conveying device is provided at a position apart from the skew correcting means by at least a length of the short sheet while being provided on the conveying path. 7. The width-direction regulating guide is provided on the sheet mounting table so as to be movable in the width direction of the sheet, and moves in the width direction in conjunction with the width-direction regulating guide, and is separated from the skew correcting means. 7. An interlocking plate having a protruding portion protruding into a transport path between said interlocking means and said first and second detecting means is attached to said protruding portion of said interlocking plate. Sheet transport device. 8. An image forming apparatus comprising: a sheet conveying device for conveying a sheet placed on a sheet placing table to an image forming unit; and recording means for recording data on the sheet on a recording medium such as a film or an optical disk. An image forming apparatus, wherein the sheet conveying device is the sheet conveying device according to any one of claims 1 to 7.