JP2003345181A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can suppress an in- machine residual jam by judging whether binding is possible or impossible by a binding method of binding a bundle of sheets according to image density, and discharging the sheets from a machine and generating an alarm when it is judged that the binding is possible. <P>SOLUTION: The image forming apparatus which forms images on sheets and bundles and folds the image-formed sheets in two is characterized by having an image forming means main body having an image forming means of forming an image corresponding to an image information signal on a sheet, a 1st sheet storage means of temporarily storing a sheet carried from the image forming means main body, and a binding means of binding a bundle of sheets stored in the 1st sheet storage means. <P>COPYRIGHT: (C)2004,JPO

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 having a sheet processing apparatus capable of sequentially taking in sheets on which images are formed by image forming means, binding a plurality of sheets by binding means, and folding the sheets in half. Regarding

[0002]

2. Description of the Related Art Today, there is an image forming apparatus such as a copying machine that can be bound by combining a sheet processing apparatus, binding a plurality of sheets and folding them in two. In such an apparatus, images are formed on both sides of a sheet by the main body of the image forming apparatus, the sheets are sequentially taken in, the stapler unit is driven to bind the sheets in the vicinity of the center of the sheet bundle, and the sheets are conveyed to the folding unit to be conveyed. It will be folded.

As the structure for folding in two, a folding roller composed of a roller pair and a projecting means composed of a thrust plate or the like are used to project the bound position of the sheet bundle to the nip portion of the roller pair by the thrust plate. Fold in,
The folded sheet bundle is pressed and conveyed by a pair of rollers to be folded in two. As a result, the sheet bundle discharged to the discharge tray is discharged in the state where the sheet bundle is folded in two and bound at the binding position in the center of the sheet.

When a folding process is performed in the sheet processing apparatus, if the friction coefficient between the sheets is low, a slip occurs when the folded sheet bundle is pulled in by a folding roller, and a tear occurs at the binding position. There is a risk. This tear is likely to occur immediately after the start of folding. At this time, if an image is formed on the entire sheet or on the folding start portion and a large amount of toner adheres,
Even when the number of sheets is small, when the sheet is pulled in by the folding roller, the folded sheet in the inner portion is likely to return and tear easily occurs. And because of the tear,
The bound sheet bundle is separated, and the sheet in contact with the folding roller is discharged from the machine, but the folded inner portion sheet remains inside the machine, and residual jam occurs.

Therefore, in order to solve such a problem,
For example, as disclosed in Japanese Patent Laid-Open No. 11-322180, a method has been proposed in which a margin portion is provided at the folding start portion. As a result, when the sheet bundle is folded by the sheet processing apparatus, since the margin portion is provided in advance on the sheet, the frictional force at the portion is increased, and the sheet bundle can be folded without tearing or wrinkling. Will be possible.

[0006]

However, in the case of providing a margin portion on the sheet for the above-mentioned purpose, for the image formed over two pages in the spread during bookbinding, the folding start portion, that is, the central portion of the image. The image information of is missing. This has been solved by making it possible to cancel the setting for providing a margin in the above proposal, but once the setting is made, the binding will not be provided until another setting is made next time. Therefore, if the paper breaks or wrinkles occur during the bookbinding, which causes a residual jam in the machine, the usefulness of the image forming apparatus itself decreases.

The present invention has been made in view of the above points, and an object thereof is to determine whether or not a sheet on which an image is formed by an image forming apparatus can be bound during bookbinding.
When it is determined that bookbinding is impossible, a warning is given to the user, and the sheet is ejected to a storage means other than the bookbinding storage means to prevent the occurrence of residual jam inside the machine. A device is provided.

[0008]

A typical configuration according to the present invention for achieving the above object is to form an image on a sheet, and to bind the image-formed sheets in a bundle and to fold in two. An image forming means main body having an image forming means for forming an image corresponding to an image information signal on a sheet, a first sheet storage means for temporarily storing the sheet conveyed from the image forming means main body, and the first Bundle binding means for binding the sheet bundle stored in the sheet storage means, half-folding means for half-folding the sheet bundle from the central portion of the sheet bundle stored in the first sheet storage means, and the image forming means Second sheet storing means for storing the sheet conveyed from the main body, image density detecting means for detecting the image density of the image formed on the sheet in the image forming means main body, and the image density detecting means. And a destination selection unit for selecting a destination of the sheet from the first sheet storage unit and the second sheet storage unit based on the density obtained by the detection unit. In the conveyance destination selecting means, the bundle binding of the sheet bundle is performed by the bundle binding means based on the density obtained by the image density detecting means and the number of sheets obtained by the sheet number detecting means. It is characterized in that it has a warning means for giving some warning to the user when it is judged that it is impossible, and in the image density detecting means, in particular, the central portion of the sheet bundle of the image formed on the sheet. The image density of a portion corresponding to is detected.

(Operation) According to the image forming apparatus of claim 1, the density of the image formed on the sheet to be bound is detected,
Based on the detected image density, it is determined whether or not bookbinding is possible, and when it is determined that bookbinding is possible, the sheets are conveyed to the first sheet storage means for bookbinding, and are bound and folded in two. To do. On the contrary, when it is determined that the bookbinding is impossible, the sheet is conveyed to the second storage unit arranged outside the machine body.

In the bookbinding by the sheet processing apparatus, it is judged whether or not the bookbinding is possible by using the judgment method utilizing the relation characteristic between the image density and the success rate of the bookbinding, and all the sheets are judged even when the bookbinding is judged to be impossible. The remaining jam inside the machine is prevented by discharging the inside of the machine.

According to the image forming apparatus of claim 4, whether or not bookbinding is possible is determined based on the density of the image formed on the sheets to be bound and the number of sheets to be bound, and when it is determined that bookbinding is impossible. By issuing a warning to the user, when the warning is issued before the image formation, it is possible to suppress the image formation on the sheet corresponding to the bookbinding failure.

According to the image forming apparatus of claim 9, the time required for the image density detection is shortened by detecting the image density of the binding margin portion at the time of bookbinding to judge whether or not bookbinding is possible.
Further, it becomes possible to perform binding on a sheet on which an image of high density is formed, other than the binding margin portion.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) FIGS. 1 to 4 are views showing the configuration of an image forming apparatus according to an embodiment of the present invention. The basic configuration will be described based on them.

The image forming apparatus shown in FIG. 1 is constructed by connecting a sheet processing apparatus to the main body of the image forming apparatus. Here, first, the configuration of the image forming apparatus main body will be described, and then the configuration of the sheet processing apparatus (finisher unit) will be described.

Structure of image forming apparatus main body Color reader configuration First, the configuration of the color reader unit will be described.

FIG. 3 shows the overall structure of the image forming apparatus. Here, 101 is a CCD, 311 is a CCD 10
1, a control unit 300 for controlling the entire image forming apparatus, and a printer processing unit 312 including a portion of the image processing unit of FIG. 1 excluding 101 and portions of 201, 202 to 205 of FIG. 301 is a platen glass,
Reference numeral 302 denotes a document feeder (ADF) (note that there is also a configuration in which a mirror pressure plate (not shown) is mounted instead of the document feeder 302), and 303 and 304 denote light sources (halogen lamps or fluorescent lamps) for illuminating the document. , 305 and 306 are light sources 3
Reflector that focuses the light of 03.304 on the original, 307-3
Reference numeral 09 is a mirror, 310 is a lens for condensing reflected light or projection light from the document on the CCD 101, 314 is halogen lamps 303/304, reflectors 305/306, and mirror 3.
A carriage 307 for housing 07 is a mirror 308.
A carriage 313 for accommodating 09 is an external interface (I / F) with another device. The carriage 314 has a speed V and the carriage 315 has a speed V / 2.
Then, the CCD 101 is mechanically moved in the direction perpendicular to the electrical scanning (main scanning) direction to scan (sub-scan) the entire surface of the document.

As shown in FIG. 4, the control unit 300 includes a digital image processing unit 312 and a printer control I / F 355.
The CPU 501, the operation unit 502, and the memory 50, each having an I / F for exchanging information for controlling each of them.
It is composed of three. The operation unit 502 is composed of a liquid crystal with a touch panel for inputting process execution contents by the operator, information regarding the process to the operator, and notification of warnings.

Next, the digital image processing section 312 will be described in detail. FIG. 1 is a block diagram showing a detailed configuration of the digital image processing unit 312.

Documents on the platen glass are light sources 303 and 30.
The light from No. 4 is reflected, and the reflected light is guided to the CCD 101 and converted into an electric signal (in the case of the CCD 101 being a color sensor, even if the RGB color filters are inline on the one-line CCD in the order of RGB, 3 line C
In the CD, the R filter, the G filter, and the B filter may be arranged in each CCD,
The filter may be on-chip, or the filter may be configured separately from the CCD). Then, the electric signal (analog image signal) is input to the image processing unit 312,
Clamp & Amp. & S / H & A / D section 102 sample-holds (S / H), clamps the dark level of the analog image signal to the reference potential, and amplifies it to a predetermined amount (the above processing order is not limited to the written order). It is D-converted and converted into, for example, an 8-bit digital signal of RGB. The RGB signal is output to the shading unit 103.
Then, after the shading correction and the black correction are performed, in the connection & MTF correction & document detection unit 104, when the CCD 101 is a 3-line CCD, the connection position in the connection processing is different in the connection processing, and therefore the line-by-line processing is performed according to the reading speed. Is adjusted, the signal timing is corrected so that the reading positions of the three lines are the same, and the MTF correction corrects the change because the MTF of the reading changes depending on the reading speed and the scaling factor. The size of the original is recognized by scanning the original on the base glass. The input masking unit 105 outputs the digital signal whose reading position timing is corrected to CC.
The spectral characteristics of D101 and the spectral characteristics of the light sources 303 and 304 and the reflectors 305 and 306 are corrected. The output of the input masking unit 105 is input to the selector 106 that can switch the external I / F signal. The signal output from the selector 106 is a color space compression & background removal & LOG conversion unit 107.
Is input to the background removal unit 115. The signal input to the background removal unit 115 is subjected to background removal, and then input to a black character determination unit 116 that determines whether the original is a black character in the original, and a black character signal is generated from the original. Further, in the color space compression & background removal & LOG conversion unit 107 to which the output of the other selector 106 is input, the color space compression is performed by judging whether or not the read image signal is within the range reproducible by the printer. If it is not, the image signal is corrected so that it falls within the range that can be reproduced by the printer. Then, background removal processing is performed, and RGB signals are converted into CMY signals by LOG conversion. Then, the output signal of the color space compression & background removal & LOG conversion unit 107 has its timing adjusted by a delay 108 in order to correct the timing of the signal generated by the black character determination unit 116. This 2
Moire is removed by the moire removing unit 109 from the types of signals,
At 110, scaling processing is performed in the main scanning direction. 111 is UC
The signal processed by the scaling processing unit in the R & masking & black character reflection unit is a CMYK signal generated by UCR processing in the CMY signal, and the masking processing unit corrects the signal to match the output of the printer and the black character determination unit. The determination signal generated in 116 is fed back to the CMYK signal. U
The signal processed by the CR & masking & black character reflection unit 111 is density-adjusted by the γ correction unit 112 and then filtered by the filter unit 11.
In step 3, smoothing or edge processing is performed. The processed signal is converted from an 8-bit multi-valued signal into a binary signal in the binary conversion unit 201 (the conversion method may be any of the dither method, the error diffusion method, and the improved error diffusion). .

Configuration of Printer Unit Next, the configuration of the printer unit will be described. In FIG. 3, reference numeral 355 is a printer control I / F, which serves as a port for receiving control signals from the CPU 501 of the color reader unit. The printer unit performs the operation described below based on the control signal from the printer control I / F 355.

Next, the image forming section will be described in detail. In FIG. 3, 317 is an M image forming unit, 318 is a C image forming unit, 319 is a Y image forming unit, and 320 is a K image forming unit. Since all the image forming units 317 to 320 have the same configuration, the M image forming unit 317 will be described in detail below, and description of the other image forming units will be omitted.

In the M image forming section 317, 342 is a photosensitive drum, and a light from the LED array 210 forms a latent image on the surface thereof. A primary charger 321 charges the surface of the photosensitive drum 342 to a predetermined potential to prepare for latent image formation. A developing unit 322 is a photosensitive drum 342.
The upper latent image is developed to form a toner image. The developing device 322 includes a sleeve 345 for applying a developing bias and developing. A transfer charger 323 discharges from the back surface of the transfer belt 333 to transfer the toner image on the photosensitive drum 342 to a recording paper or the like on the transfer belt 333. Since the transfer efficiency is high in this embodiment, the cleaner portion is not arranged (it goes without saying that there is no problem even if the cleaner portion is mounted).

Finally, the procedure for forming an image on a sheet (recording paper) will be described.

First, the sheets and the like stored in the cassettes 340 and 341 are picked up by pickup rollers 339 and 338 rotated by a driving means (not shown). At that time, the pickup rollers 339 and 338 are picked up.
Picks up while pushing out by rotating in pressure contact with the leading edge of the recording paper.

The sheet fed onto the transfer belt 333 after the roller 336 is charged by the adsorption charger 346. A transfer belt roller 348 drives the transfer belt 333 and charges the sheet or the like by pairing with the adsorption charger 346 to adsorb the sheet or the like to the transfer belt 333. A sheet leading edge sensor 347 detects the leading edge of a sheet or the like on the transfer belt 333. The detection signal of the sheet leading edge sensor is sent from the printer section to the color reader section and is used as a sub-scanning synchronization signal when sending a video signal from the color reader section to the printer section.

Thereafter, the sheet or the like is conveyed by the transfer belt 333, and is transferred to the image forming units 317 to 320 by M.
A toner image is formed on the surface in the order of CYK. The sheet or the like that has passed through the K image forming unit 320 is transferred to the transfer belt 33.
In order to facilitate separation from the transfer belt 3, the charge is removed by the discharge charger 349 and then separated from the transfer belt 333. 350
Is a peeling charger, which prevents image disturbance due to peeling discharge when a sheet or the like is separated from the transfer belt 333. The separated sheets or the like have pre-fixing chargers 351 and 352 in order to supplement the toner suction force and prevent image disturbance.
The toner image is thermally fixed by the fixing device 334 and then conveyed to the sheet processing device (finisher unit) 335.

FIG. 2 is a block diagram showing the detailed arrangement of the printer processing section. LED image recording will be described with reference to FIG. Binary C generated by the image processing unit in FIG.
The MYK image signal is generated by the binary conversion unit based on the sheet leading edge signal from the sheet leading edge sensor 347, and the delay units 202 to 205 adjust the difference in distance between the sheet leading edge sensor and each image forming unit. By doing so, it becomes possible to print four colors at predetermined positions. LE
The D drives 206 to 209 generate signals for driving the LEDs 210 to 213.

Configuration of Sheet Processing Apparatus Next, the configuration of the sheet processing apparatus (finisher unit) will be described. The sheet processing apparatus is configured as shown at 335 in FIG. 3, and aligns sheets discharged from the image forming apparatus main body in units of units, staples them with a staple unit, and folds them in half. It is what is bound. This will be roughly described. The sheet discharged from the image forming apparatus main body is conveyed to the vertical path 409 in the sheet processing apparatus 335, and the lower end of the sheet is stopped by the stopper 401.
The stacking unit 403 stacks and aligns the sheets so that the sheets come into contact with each other, and the staple unit 403 binds the staples at two positions at the center position in the sheet length direction (sheet conveying direction).

Next, the stopper 401 is moved downward to a position 400 by a driving means (not shown) to move the sheet bundle so that the binding position reaches the nip position of the folding roller 404, and the binding plate 402 is used to set the binding position. As you poke
The folding roller 404 carries the nip so that the sheet bundle is folded in two at the binding position. As a result, the sheet bundle, which is bound at the center in the sheet length direction and folded in half and bound, is discharged to the stack tray 408.

As described above, when the sheet bundle is pulled in by the folding roller, an image is recorded in the center portion of the sheet bundle, or if a high-density image is recorded on the entire sheet, the image is recorded. Since the sheet friction coefficient is reduced by the (toner), the sheet is not reliably pulled in by the folding roller, which may cause wrinkles or tears in the sheet.

The mechanism of sheet breakage and wrinkle generation during folding will be briefly described with reference to FIG. In addition, here, a sheet bundle including two sheets P11 and P12 will be described as an example.

The folding roller 404 and the first sheet P11
Let F1 be the frictional force between the first sheet P11 and the second sheet P12 be F2, and F3 be the binding force of the binding needle that bundles the sheet bundle. = F
When the expression 2 + F3 is established, normal folding processing is performed. However, in order to satisfy the above formula when the frictional force F2 between the sheets P11 and P12 becomes small, it is necessary that the binding force F3 of the binding needle becomes larger.
At this time, even if the strength of the sheet can withstand the binding force F3 of the binding needle, the second sheet P12 is pulled by the binding needle, causing a deviation as shown in FIG.
Bending occurs as shown in (b). Then, when it passes through the folding roller 404 in the above state, wrinkles as shown in FIG. Further, when the strength of the sheet cannot withstand the binding force F3 of the binding needle, the sheet breaks as shown in FIG. 5D, and sometimes a plurality of sheets including the sheet P12 remain inside the machine body.

The phenomenon of breakage or wrinkle is caused when the image density of the center portion of the sheet P (sheet bundle) which is the folded portion as shown in FIG. 6 is a threshold value or less, for example, 35/256 gradation or less. If it does not occur. This threshold differs depending on the material, basis weight, and number of sheets (for example,
If the number of sheets is 3 or less, the threshold value is 256/256
Since it is possible to bind even gradations), it is no problem to use a threshold table with materials, basis weights, and number of sheets as items.

As a method of detecting the image density, there can be used a method of dividing the total number of each color (YMCK) by the number of colors (4) by the total number of pixels by using a video count or the like. .

Regarding the range of the center portion of the sheet, which is the object for detecting the image density, the folding margin is t and the width 2t is the image density detection range. In the present embodiment, the configuration is such that it can be set within the range of t = about 5 mm to 8 mm, and the image density within the range of width 2t = 10 mm to 16 mm is detected.

In FIG. 6, Ps is the center of the sheet P (center in the conveying direction), and Pg is the image recording portion of the sheet P.

With this configuration, the digital image processing unit 312 compares the density obtained by detecting the image density of the image area corresponding to the sheet center portion with the density threshold value. It is possible to determine whether or not the wrinkles and tears described above occur before the bookbinding process is performed.

The detection of the image density and the determination as to whether or not the bookbinding is possible are carried out before the sheet on which the image is formed by the printer section is conveyed to the sheet processing apparatus 335. When it is determined that bookbinding is possible, the sheet discharged from the image forming apparatus main body is conveyed to the vertical path 409 in the sheet processing apparatus 335, and the stopper 401 unit performs stacking alignment to perform bookbinding. On the contrary, when it is determined that bookbinding is impossible, the sheet discharged from the image forming apparatus main body is conveyed to the conveyance path 410 and is discharged to the sheet discharge tray 411, thereby suppressing the jam inside the machine.

If the total number of sheets to be bound is unknown at the time when image formation is started on the first sheet in the structure of the image forming apparatus main body, the sheets are conveyed to the sheet processing apparatus 335. Whether or not bookbinding is possible is determined based on the number of sheets and the image density, and when it is determined that bookbinding is impossible at the time of forming an image of the nth sheet, 1 to
The (n-1) th sheet bundle stacked and aligned with the stopper 401 in the sheet processing apparatus 335 is discharged to the stack tray 408, and the nth and subsequent sheets are conveyed to the conveyance path 410 and discharged. The sheet is discharged to the paper tray 411.

(Other Embodiments) In this embodiment, the image density of the center portion of the sheet to be bound is detected as described above, and it is determined whether or not the booklet can be bound based on the detected density. However, the condition used for determining whether or not the bookbinding is possible is not particularly limited to the one based on the image density of the sheet center portion, and is not limited to the center portion t in the sheet layout shown in FIG. It may be based on the image density of the entire area of the sheet including the image area Pg.
As to the setting of the threshold value, since it depends on the material of the sheet, the basis weight, and the number of sheets, as in the above, a threshold value table having these items as an item is prepared and used. For example, FIG. 7 is a correspondence table regarding the basis weight and the density threshold of an A4 size sheet,
When the basis weight of the sheets to be bound is 80 g, the image density is 11
If there are 8 or more sheets of 0/256 gradation or higher, it is determined that bookbinding is impossible.

The configuration of the main body of the image forming apparatus can detect the total number of sheets to be imaged and the image densities of all the images to be formed before the image formation on the first sheet. In such a configuration, a warning or the like notifying that the bookbinding is impossible may be displayed on the operation unit 502 before the first sheet is fed from the cassette 341 or 340.

[0042]

As described above, according to the present invention,
Based on the density of the image formed on the sheet, it is determined whether or not bookbinding is possible, and if it is determined that bookbinding is not possible, a warning is issued to the user before the image formation is started, or Sheets corresponding to the unbound portion are discharged to a discharge tray arranged outside the machine, and as a result,
It is possible to suppress the residual jam inside the machine.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a digital image processing unit.

FIG. 2 is a block diagram showing a configuration of a printer processing unit.

FIG. 3 is a diagram showing an overall configuration of an image forming apparatus main body and a sheet processing apparatus.

FIG. 4 is a block diagram showing a configuration of a control unit.

FIG. 5 is a diagram showing a mechanism of sheet breakage or wrinkle generation during folding processing.

FIG. 6 is a diagram showing an image recording portion and a folding margin portion on a sheet.

FIG. 7 is a table showing a relationship between a sheet basis weight and an image density threshold value.

[Explanation of symbols]

101 CCD (charge coupled device) 210 LED array 300 operation part 301 Original glass table (platen) 302 Automatic Document Feeder (ADF) 303, 304 Light source 305, 306 reflective umbrella 307-309 Mirror 310 lens 311 A board on which a CCD is mounted 312 Printer processing unit (digital image processing unit) 313 External interface 314 and 315 carriage 317 M image forming unit 318 C image forming unit 319 Y image forming unit 320K image forming unit 321 Primary charger 322 Developing device 323 Transfer charger 333 transfer belt 334 Fixer 335 sheet processing device 336 Laura 338, 339 Pickup roller 340, 341 cassettes 342 photosensitive drum 345 sleeve 346 Adsorption charger 347 Sheet edge sensor 348 Transfer belt roller 349 Charge elimination charger 350 Peeling charger 351 and 352 Pre-fixing charger 400, 401 Stopper stop position 402 veneer 403 staple unit 404 folding roller 408 loading tray 409 vertical path 410 transport path 411 Output tray 501 CPU 502 memory 503 operation unit;

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C061 AQ06 AR01 AR03 HJ04 HK11                       HK15 HN18 HV01 HV09 HV28                       HV32                 2H027 DA41 DB01 DC01 DC02 DE04                       DE07 ED29 EF09 EK10 FA21                       FA35 GA30 GB07 ZA07                 3F108 GA01 GB01 GB03 HA02 HA39                       HA45

Claims (11)

[Claims] 1. An image forming apparatus for forming an image on a sheet and binding and folding the image-formed sheets together, the image forming means having an image forming means for forming an image corresponding to an image information signal on the sheet. A main body; a first sheet storage means for temporarily storing the sheets conveyed from the image forming means main body; a bundle binding means for binding the sheet bundle stored in the first sheet storage means in a bundle; Half-folding means for half-folding the sheet bundle from the central portion of the sheet bundle stored in the sheet storing means, second sheet storing means for storing the sheet conveyed from the image forming means main body, and the image forming means In the main body, based on the density obtained by the image density detecting means for detecting the image density of the image formed on the sheet, the image density detecting means,
Transport destination selecting means for selecting a transport destination of the sheet from the first sheet storing means and the second sheet storing means,
An image forming apparatus comprising: 2. The image forming means main body further comprises a sheet number detecting means for detecting the number of sheets to be bound at a stage before forming an image on the first sheet. Image forming device. 3. The binding destination selecting means, based on the density obtained by the image density detecting means and the number of sheets obtained by the sheet number detecting means, binding the sheet bundle by the binding means. 3. The image forming apparatus according to claim 2, wherein the second sheet storage unit is selected as a destination for storing the sheet conveyed from the image forming unit main body when it is determined that the sheet cannot be carried out. 4. The bundle binding of sheet bundles by the bundle binding means based on the density obtained by the image density detecting means and the number of sheets obtained by the sheet number detecting means in the destination selecting means. 3. The image forming apparatus according to claim 2, further comprising a warning unit that issues a warning to the user when it is determined that the above is impossible. 5. The image forming apparatus according to claim 1, further comprising a sheet number counting unit that counts the number of sheets placed and stored in the first sheet storing unit. 6. The binding destination selecting means, based on the density obtained by the image density detecting means and the number of sheets obtained by the sheet number counting means, binding the sheet bundle by the binding means. 6. The image forming apparatus according to claim 5, wherein the second sheet storage unit is selected as a conveyance destination for storing the sheet conveyed from the image forming unit main body when it is determined that the above-described is impossible. 7. The binding destination selecting means, based on the density obtained by the image density detecting means and the number of sheets obtained by the sheet number counting means, binding the sheet bundle by the binding means. 6. The image forming apparatus according to claim 5, further comprising a warning unit that issues a warning to the user when it is determined that the above is impossible. 8. The image forming apparatus according to claim 1, wherein the image density detecting unit detects an image density of an image to be formed on a sheet based on the image information signal. 9. The image density detection means, in particular,
The image density of a portion corresponding to the central portion of the sheet bundle of the image formed on the sheet is detected.
8. The image forming apparatus according to item 8. 10. The image forming apparatus according to claim 9, wherein the image density detecting unit is configured to set a width of a central portion of the sheet bundle. 11. The image forming apparatus according to claim 1, wherein the setting of the transport destination selecting unit is configured to be cancelable.