JP2003316206A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate problems even if a backing paper where images are already formed on one surface is used for printing. <P>SOLUTION: An image detection means 12 is provided on a form transfer path 21 between a paper supply section 2 and an image transfer section, where the image detection means 12 comprises a photosensor 16 and a light receiving sensor 17 for detecting whether images are already formed or not on a form that is being carried on the path 21. Then, a control apparatus 50 is provided, where the apparatus 50 for prohibiting double-sided printing on the paper by judging that the form is a back one when the image detection means 12 detects that images are formed on the form P. In the image detection means 12, the light receiving sensor 17 detects light that is generated by the photosensor 16 and is transmitted through the form, and the control apparatus 50 judges whether the form is a backing paper or not according to the intensity of the quantity of received light depending on output. <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 of a copying machine, a printer, a facsimile apparatus, etc., which is suitable for reusing a backing paper having an image already formed on its back side and forming a new image there. Forming apparatus

[0002]

2. Description of the Related Art In recent years, for the purpose of resource saving, waste reduction, office cost reduction, etc., in an image forming apparatus such as a copying machine, a facsimile machine, a printer, etc., a sheet of paper on which an image is once formed (printed) , Called backing paper)
It has become common to form a desired image on a surface on which the image is not formed. In addition, it is strongly desired to improve the adaptability when forming an image on such a backing paper. On the other hand, the need for double-sided image formation (double-sided printing), which forms images on both sides of new paper that has no images on both sides, has led to resource saving and waste reduction in recent years, as well as the use of backing paper. Are being strengthened for the purpose of cost reduction in Further, in recent years, the usage of image forming apparatuses such as copying machines and printers does not use them individually, but connects those image forming apparatuses to a network of a plurality of personal computers to commonly use the printer function. There are many cases.

[0003]

However, when a new image is formed on such a backing paper, the backing paper on which an image is once formed uses a general toner. In such a copying machine, the image is passed through the fixing section once to fix the image there, but there is a problem that a small amount of oil component adheres to the surface of the sheet at that time. In addition, due to the influence of the toner image (which may be ink) attached to the surface of the paper, the separation performance of the paper in the paper feed unit is likely to deteriorate. Furthermore, when using multiple backing papers in a paper feed cassette, etc., the backing papers are not limited to the same type, but can be mixed in various paper qualities and thicknesses. In such a case, the paper separating performance performed in the paper feeding unit is likely to be further deteriorated because the paper is used. Therefore, it is desired to improve the problems when such backing paper is used.

Further, when a backing sheet having an image formed with toner on one side is already used and an image is formed on the side on which the image is not formed,
In some cases, the toner of the already formed image absorbs heat for fixing at the time of fixing, so that the temperature of the fixing portion is lowered, and thus the fixing performance is likely to be deteriorated. Further, the toner of the already formed image may be melted again by the heat of the fixing unit and adhere to the roller of the fixing unit, and the toner may not be removed. Also, since the backing paper has an image already formed on one side, it is not possible to perform double-sided printing using that paper, but the user can perform double-sided printing without noticing that it is backing paper. If it happened, it would be a waste of work. Furthermore, even when printing on one side, the backing paper cannot be used for documents that are officially issued outside the company, but even in such cases, image formation is performed without noticing that the backing paper is set. When it happened, there were times when I would end up doing unnecessary work.

On the other hand, as described above, when an image forming apparatus having a printer function connected to a network is commonly used by a plurality of personal computers respectively connected to the image forming apparatus, all of the plurality of personal computers are operated. It is difficult for the user to use it after recognizing whether the backing sheet is set in the sheet feeding unit of the image forming apparatus. Therefore, in such a case, there is a possibility that double-sided printing may be erroneously performed on the backing paper even though the backing paper is set. Therefore, as an image forming apparatus capable of using a conventional backing paper, there is one described in, for example, Japanese Patent Laid-Open No. 2000-305323. In this image forming apparatus, a transfer surface onto which a toner image on a recording sheet is transferred is irradiated with light from a linear light source such as an LED array, the reflected light is received by a solid-state image sensor, and a signal output from the solid-state image sensor. Thus, it is determined whether or not an image has already been formed on the transfer surface (blank paper). When it is determined that an image has already been formed on the transfer surface of the recording paper, the recording paper is discharged to the back paper tray without forming an image.

However, in this image forming apparatus, although it is possible to prevent double-sided image formation on the backing paper, a slight amount of oil component or the like adheres to the surface of the paper when the paper once passes through the fixing section as described above. The paper separation performance may deteriorate, or the paper separation performance may deteriorate when multiple types of backing paper with different paper qualities and thicknesses are mixed and set in the paper cassette of the paper feeder. There was a problem that it could not be prevented. Further, since the image detection by the linear light source and the solid-state image sensor is performed only on the transfer surface of the paper, it is not known whether or not an image is formed on the back surface of the paper. However, even when it is difficult to use the backing paper because it is a document that is officially issued to the outside, there is a risk that an image is formed on the backing paper. This invention
The present invention has been made in view of the above problems, and an object thereof is to prevent double-sided printing on a backing paper having an image already formed on one side. It is also an object to determine the backing paper with the minimum number of parts.

[0007]

In order to achieve the above object, the present invention provides an image forming apparatus for transferring an image to a sheet fed from a sheet feeding section by an image transfer section, wherein the sheet feeding section and the image transfer section are provided. An image detecting means for detecting whether or not an image has already been formed on the sheet conveyed through the sheet conveying path is provided on the sheet conveying path between and, and the image detecting means forms an image on the sheet. When it is detected that the sheet is a backing sheet, a control unit is provided to control so as to prohibit double-sided printing on the sheet. The image forming apparatus is provided with a backing paper prohibition setting means for setting a backing paper prohibition mode when the backing paper prohibition mode is set by the backing paper prohibition setting means when the backing paper prohibition mode is set when the backing paper prohibition mode is not used. When the image detecting means detects an image on the back surface of the paper, it may be a means for controlling so as to prohibit printing on the paper. In the image forming apparatus, when the image detecting unit detects that an image is formed on a sheet, conditions for image formation such as conditions for sheet separation, process conditions such as image formation and transfer, and fixing conditions are determined. It is advisable to provide means for switching to the backing paper mode for switching to conditions suitable for image formation on the backing paper.

In any one of the above image forming apparatuses, when the image detecting means detects that an image is formed on a sheet fed from the sheet feeding section, a backing sheet is stored in the sheet feeding section. It is advisable to provide a backing paper use display means for displaying the fact on the display unit. Further, when the image detecting unit detects that an image is formed on the sheet, it is determined that the backing sheet is stored in the sheet feeding unit.
You may make it provide the backing paper use display means to display on the display part of the externally connected apparatus connected by the network. In the image forming apparatus, when the image detecting unit detects that an image is formed on a sheet, all the backing sheets are stored in the sheet feeding unit that has fed the sheet thereafter. It is advisable to provide a backing sheet storage determining means for determining.
Further, in the image forming apparatus, the paper feed section has a plurality of paper feed cassettes each capable of accommodating paper, and when the image detection means detects that an image is formed on the paper, the subsequent operation is performed. It is advisable to provide a backing sheet storage determining means for determining that all the backing sheets have been stored in the sheet feeding cassettes that have fed the sheets. In the image forming apparatus, when the paper feeding from the paper feeding cassette which is determined to contain the backing paper is selected, the backing paper is stored in the selected paper feeding cassette. It is preferable to provide a backing paper storage cassette display means for displaying on the display unit.

Further, in the image forming apparatus, the backing paper storage cassette display means is a means for displaying the display of the paper feed cassette housing the backing paper on the display section of the externally connected device connected by the network. It is good to have it. In the image forming apparatus, when double-sided printing is designated and paper feeding from a paper feeding cassette storing backing paper is selected, control is performed to stop the paper feeding from the paper feeding cassette. It is preferable to provide a paper feed stopping means. Also, when the backing paper prohibition mode that does not form an image on the backing paper is selected and paper feeding is selected from the paper feeding cassette that contains the backing paper, It is advisable to provide a paper feed stopping means for controlling the paper feed to stop. Further, there is provided means for switching to a backing paper mode for switching conditions related to image formation, such as conditions for paper feed separation, process conditions such as image formation and transfer, and fixing conditions, to conditions suitable for image formation on backing paper. When the image detection unit detects that an image is formed on the paper and paper feeding from the paper feeding cassette that has fed the paper is selected, when the paper is fed from the paper feeding cassette, the above-mentioned back paper mode is set. It is good to switch.

In any one of the above image forming apparatuses, the image detecting means includes a light emitting means and a light receiving means which are arranged to face each other so as to sandwich a sheet conveyed through the sheet conveying path, and the image detecting means conveys the sheet. It is preferable to also serve as a sheet detection sensor that detects the leading edge and the trailing edge of the sheet conveyed on the path. Alternatively, the image detecting means comprises a light emitting means and a light receiving means which are arranged so as to face each other so as to sandwich a sheet conveyed in the sheet conveying path, and the image detecting means is configured to perform double feeding of the sheet conveyed in the sheet conveying path. It is preferable to also serve as a double feed sensor for detecting. The image forming apparatus is provided with a light emitting means and a light receiving means for measuring the transmittance of the sheets set in the paper feeding section, and the transmittance measured by the image detecting means and the light emitting means and the light receiving means of the paper feeding section. The number of sheets set in the sheet feeding unit may be detected by comparing the measured transmittance with. In determining the backing sheet, the sheet detected when the output value of the light receiving unit of the image detecting unit that receives and outputs the light transmitted through the sheet changes with an amplitude of a certain value or more is the backing sheet. You should judge that. In any one of the image forming apparatuses described above, it is preferable to provide image detection canceling means for forcibly canceling the image detection of the sheet by the image detecting means.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a component part for detecting whether or not a sheet of an image forming apparatus according to the present invention is a backing sheet together with a sheet feeding system, and FIG. 2 is an example of an embodiment of the image forming apparatus. FIG. 1 is an overall configuration diagram showing a color image forming apparatus. In the color image forming apparatus shown in FIG. 2, the image forming section 20 is arranged in the substantial center of the apparatus main body 1, and a plurality of sheet feeding cassettes 22 are provided just below the image forming section 20.
The sheet feeding unit 2 having the above is arranged. In addition, this paper feeding unit 2
It is also possible to add another sheet feeding device as needed. A reading unit 23 for reading a document is provided above the image forming unit 20, and the reading unit 23 of the image forming unit 20 shown in FIG.
At the left side, there are provided paper discharge storages 24, and the papers P on which images have been formed are discharged and stored in the paper discharge storages 24. The image forming unit 20 includes a belt-shaped intermediate transfer belt 25 that is stretched between a plurality of rollers and rotates in the direction of arrow A.
Around the intermediate transfer belt 25, drum-shaped photoconductors 26Y, 26M, 26C and 26K forming four image forming units are arranged in parallel as shown in the figure.

Around each of the photoconductors, each charging device 62 for charging the surface of the photoconductor, and each of the electrostatic latent images formed on the surface of the photoconductor are visualized with toner of each color. A developing device 63 and cleaning devices 64 for removing and collecting residual toner remaining on each photoconductor after transferring the toner image (visible image) on each photoconductor to the intermediate transfer belt 25 are provided. The photoconductors 26Y, 26M, 26C, 26 of the image forming unit 20 are provided above the image forming unit 20.
K is provided with an exposure device 7 that irradiates a laser beam corresponding to each color image information to form a latent image thereon.
Further, a registration roller 33 is provided on the upstream side of the sheet conveyance of the image forming section 20, and a fixing device 28 is provided on the downstream side of the sheet conveyance of the image forming section 20, and the skew of the sheet is corrected by the registration roller 33 and the photoconductor The paper is fed in time with the image above. Further, the toner image transferred onto the paper is fixed by the fixing device 28. Downstream of this fixing device 28,
A paper discharge roller 41 is provided for discharging the paper that has passed through the fixing device 28 onto the paper discharge storage unit 24. In addition, in FIG.
Is an automatic document feeder that automatically conveys a document onto the contact glass 31.

When the color image forming apparatus starts a full-color image forming operation, the photoconductors 26Y, 26M and 26 charged by the charging devices 62 of the image forming section 20 are charged.
The charged surfaces on C and 26K are exposed by the exposure device 7 to yellow (Y), magenta (M), cyan (C), and black (B).
K) is exposed by the operation light corresponding to each color, and a latent image is formed there. Each photoconductor 26 by the exposure device 7
Writing to Y, 26M, 26C and 26K is performed by the reading unit 2
The image of the original set on the contact glass 31 provided in FIG. 3 is read and scanned by reciprocating left and right movements of the reading traveling bodies 32a and 32b composed of the original illuminating light source and the mirror in FIG. This is performed based on the image information read as an image signal in the CCD 35 installed behind the lens 34. Ie CCD
The image signal read by 35 is digitized and image-processed. Based on the image-processed signal, the laser diode in the exposure device 7 emits light to cause the photoconductor 26
Each surface of Y, 26M, 26C, and 26K is exposed to form an electrostatic latent image on it. At that time, the light from the laser diode reaches each photoconductor through a polygon mirror and a lens.

In this way, the photoconductors 26Y, 26
The latent images formed on M, 26C and 26K are
Toner images are developed by the developing devices 63 corresponding to the four colors of yellow (Y), magenta (M), cyan (C), and black (BK). As for the toner image, the yellow image on the photoconductor 26Y is first shown in FIG.
Is transferred onto the intermediate transfer belt 25 which is rotating in the direction of arrow A, and when the yellow image is moved to the position of the photoconductor 26M, the magenta image is superposed and transferred thereon. To do. When the portion to which the magenta image is transferred moves to the position of the photoconductor 26C, the cyan image is superposed and transferred thereon, and the part to which the cyan image is transferred is the position of the photoconductor 26K. When it moves to, the black image is overlaid and transferred. Then, when the yellow, magenta, cyan, and black four-color superimposed image is moved to a certain transfer position of the transfer roller 51 by the rotation of the intermediate transfer belt 25, the images are fed in synchronization so as to coincide with the timing. The transfer rollers 51 collectively transfer the transferred sheets. In this way, this color image forming apparatus performs an image forming process in which the intermediate transfer belt 25 rotates once to form one color image.

After the four-color superposed toner images on the intermediate transfer belt 25 are collectively transferred to the sheet, the toner remaining on the intermediate transfer belt 25 is removed and collected by the intermediate transfer cleaning device 52. The sheet on which the toner image has been fixed and which has passed through the fixing device 28 is discharged to the discharged sheet storage unit 24 by the sheet discharge roller 41 when the sheet is for single-sided image formation. When a double-sided image formation instruction is issued, the sheet is image-formed by the branching claw 43 provided on the conveyance path between the fixing device 28 and the sheet discharge roller 41.
It is sent to the double-sided device 29 disposed below the sheet, is reversed, and is conveyed again to the registration roller 33. This time, after the image is formed on the second surface, the sheet discharge roller 41 is used to discharge the sheet. Is discharged onto 24.

On the other hand, the paper feed unit 2 for feeding paper is provided with a paper feed device 4 for each paper feed stage. As shown in FIG. 1, the sheet feeding device 4 of each sheet feeding stage rotates a bottom plate 5 which is a sheet stacking unit for stacking sheets and a sheet P stacked on the bottom plate 5 in a counterclockwise direction in FIG. The pickup roller 6 that is a sheet feeding unit that feeds the sheet by doing so, and when there are a plurality of sheets P fed by the pickup roller 6, a separation including a feed roller and a reverse roller that separate the sheets P into one sheet. And means 8. The bottom plate 5 is rotatable in the direction of the arrow B in FIG. 1 with the end portion on the left side in FIG. 1 as a fulcrum with the paper P placed thereon. It is pushed up by the lift lever that rotates to the upside by the drive source such as
The paper delivery end side is raised.

For the paper feeding from the paper feeding device 4, the paper P stored on the bottom plate 5 of the paper feeding cassette 22 is picked up by picking up the uppermost paper as the bottom plate 5 rotates upward. 6 is lifted up to a position where it abuts on 6, and the pickup roller 6 is rotated in this state to be fed from the paper feed cassette 22. Therefore, when two or more sheets of paper P are sent out, they are separated into one by the separating means 8. Then, the sheet P is conveyed to the registration roller 33 in the stopped state, is temporarily stopped there, and the registration roller 33 is stopped at the timing when the positional relationship between the leading end and the toner image on the photoconductor exactly matches. By starting the rotation, the sheet is conveyed toward the image forming unit 20 shown in FIG. After that, an image is formed on the sheet through the above-described process, and the image is discharged to the discharged sheet storage unit 24.

In this color image forming apparatus, an image is transferred to the paper P fed from the paper feed cassette 22 of the paper feed unit 2 at an image transfer unit having a transfer roller 51. 1 and an image detecting means 12 for detecting whether or not an image has already been formed on the paper P conveyed through the paper conveying path 21 shown in FIG. Detects that an image is formed on the sheet P, the sheet is determined to be a backing sheet (reused sheet having an image already formed on one side), and double-sided printing on the sheet is prohibited. A control device 50 which is a control means for controlling is provided. The image detecting means 12 is composed of, for example, a light emitting sensor 16 which is a light emitting means and a light receiving sensor 17 which is a light receiving means which are paired so as to sandwich a conveyed sheet, and these are formed by the registration roller 3 of the sheet conveying path 21.
3 is provided on the upstream side in the sheet conveying direction (immediately before the registration roller 33 in this example). The light receiving sensor 17 receives the light emitted from the light emitting sensor 16 and outputs a signal according to the intensity of the received light.

The light emitting sensor 16 and the light receiving sensor 17 of the image detecting means 12 are, for example, a pair of guide plates 18, 1.
It is preferable that the distances between them are fixed to 9 so that the distance therebetween is always kept constant. Further, a reflection type photo sensor can be used as the image detecting means. However, in that case, the presence / absence of an image is detected only on one side of the sheet, so if the sheets are stored in a mixture of front and back sides, it is not possible to detect even the images on both sides. .

The control device 50 shown in FIG. 1 is a central processing unit (CPU) having various judgment and processing functions, a ROM storing each processing program and fixed data, and a RAM serving as a data memory for storing the processing data. And a microcomputer including an input / output circuit (I / O). Then, the microcomputer of the control device 50 inputs the output value output from the light receiving sensor 17.
Next, a method of determining whether the paper is a backing paper using the light emitting sensor and the light receiving sensor will be described with reference to FIGS. When the paper is conveyed between the light emitting sensor 16 and the light receiving sensor 17, the light emitted by the light emitting sensor 16 and received by the light receiving sensor 17 is blocked by the paper and changes according to the transmittance of the paper. (Attenuation). When, for example, a character image (indicated by ◯, Δ, □ for convenience) as shown in FIG. 3 is formed on the back surface of the sheet, the sheet is positioned on the light receiving sensor detection line of the character portion. When the portion reaches the position of the light receiving sensor 17, the light transmittance of the portion decreases, so that the output value received and output by the light receiving sensor 17 decreases (small pulse).

FIG. 3 shows an example in which characters are formed using three colors, and
The part indicated by is the black character part, the part indicated by △ is the red character part, and the part indicated by □ is the blue character part, so the red character part of △ and the blue character part of □ respectively When the portion of the light receiving sensor detection line reaches the position of the light receiving sensor 17, the output value from the light receiving sensor 17 becomes different in magnitude from the pulse of the black character portion indicated by ◯. In this way, since the light transmittance varies depending on the color of the character, the output of the light receiving sensor also varies accordingly. The detection judgment of the backing paper by the light emitting sensor 16 and the light receiving sensor 17 is
The control device 50 shown in FIG. 1 performs the change amount of the output value output by the light receiving sensor 17, that is, the output value output by the light receiving sensor 17 by receiving the light transmitted through the character portion,
Immediately after the leading edge of the paper reaches the position of the light receiving sensor 17, when the difference from the output value Sa output by the light receiving sensor 17 is equal to or more than a preset value, the paper is judged to be the backing paper. ing.

The output value output from the light receiving sensor 17 upon receiving the light thus transmitted through the character portion and the light receiving sensor 17 immediately after the leading edge of the paper reaches the position of the light receiving sensor 17.
The output value (position of Sa) is compared with the signal immediately after the paper reaches the light receiving sensor 17 is the signal at the leading end of the paper, and this part is usually the part where the image is not formed. This is because it is assumed. That is, most of the backing paper on which an image has already been formed on one side usually has a certain amount of margin around the front and rear edges and the left and right edges of the paper. This is because it is a portion where an image is not formed.

FIG. 4 is a diagram for explaining the output signal of the light receiving sensor when a character image is formed on substantially the entire surface with some margins left and right. The entire surface of the character image formed on the back surface of the sheet is green (indicated by ⋄ in FIG. 4 for convenience). When the character portion reaches the position of the light receiving sensor 17, the light transmittance of the portion decreases,
The output value that the light receiving sensor 17 receives and outputs is small as shown. Since the image on the back surface of the sheet is formed over substantially the entire surface of the sheet as described above, the degree of change in the output value of the light receiving sensor 17 in the image portion is higher than that in the case shown in FIG. Small. Then, the amount of change in the output value output by the light receiving sensor 17, that is, the output value output by the light receiving sensor 17 after receiving the light transmitted through the character portion, and immediately after the leading edge of the paper reaches the position of the light receiving sensor 17. When the difference from the output value Sa output from the light receiving sensor 17 is equal to or more than a preset value, the sheet is determined to be the backing sheet.

FIG. 5 is a diagram for explaining an output signal of the light receiving sensor when a sheet on which images are not formed on both sides is detected. As described above, when the light receiving sensor 17 detects the light transmitted through the paper on which no image is formed on both sides, the signal output by the light receiving sensor 17 is the output value Sa when the paper is detected. Although it slightly fluctuates with respect to the signal before the sheet is detected, the amount of change is smaller than the previously set value. Therefore, in this case, it is determined that the detected sheet is not the back sheet. Even if the paper is blank on both sides in this way, the output of the light receiving sensor 17 slightly changes as shown in the figure due to the flapping of the paper, the variation in the transmittance depending on the measurement position of the paper itself, and the like. In this way, in this color image forming apparatus, it is determined from the change in the output of the light receiving sensor 17 whether the paper conveyed to the registration roller 33 is the backing paper. By the way, a signal output by the light receiving sensor 17 when an image is detected is not compared with an output value Sa output by the light receiving sensor 17 immediately after the sheet reaches the light receiving sensor 17, and only the output value of the light receiving sensor 17 is used. When it is judged whether or not it is the backing paper, the transmissivity of the paper differs depending on the type of paper, so the paper with small transmissivity (such as thick paper)
Therefore, even if it is not the backing sheet, it is likely to be erroneously detected as the backing sheet.

However, in the color image forming apparatus according to this embodiment, when the light receiving sensor 17 receives the light transmitted through the paper, when the output output according to the detected light amount changes with a certain amplitude or more, it is detected. Since it is determined that the current sheet is a back sheet, erroneous detection does not occur even if the sheet has a small transmissivity such as a thick sheet. That is, in this embodiment, the light receiving sensor 17
The output value output by the light receiving sensor 17 immediately after the sheet reaches the position detected by the sensor is compared with the output value output by the light receiving sensor 17 when the image is detected, and the value changes with a certain amplitude or more. At this time, since it is determined that the detected sheet is the back sheet, it is possible to prevent erroneous detection. In this way, in this color image forming apparatus, it is determined whether or not the sheet conveyed to the registration roller 33 is the back sheet. Then, when it is determined (detected) that the sheet is a backing sheet having an image formed on one side of the sheet, even when the print instruction for this sheet is double-sided printing (double-sided image formation),
The double-sided printing on the sheet is prohibited, and the two sheets are replaced by single-sided printing, and the image forming operation is continued. And all the control is performed by the control device 50 shown in FIG.

That is, the microcomputer of the control device 50 starts the routine of the backing paper detection process shown in FIG. 7 at a predetermined timing. First in step 1,
It is determined whether or not the feeding of the sheet from the sheet feeding unit 2 is started,
If it has not been conveyed yet, it waits as it is, and when it is conveyed, it proceeds to step 2. In the step 2, it is judged whether or not the conveyed sheet is conveyed to the position where the image detecting means 12 is present, and when it reaches the position where the image detecting means 12 is reached, the process proceeds to step 3. In step 3, the output value Sa (see FIGS. 3 to 5) of the light receiving sensor 17 immediately after the sheet reaches the position of the light receiving sensor 17 is detected and stored in the storage unit. Then, in the next step 4, the output value Sb of the light receiving sensor 17 is detected again, that is, at the timing when the image portion normally reaches the position of the light receiving sensor 17.
In the next step 5, it is determined whether or not the output value Sb−Sa ≧ specified amount (preset value) is reached. If NO is determined, the process proceeds to step 6 and the sheet is at the position where the light receiving sensor 17 is located. If it has not been removed, the process returns to step 4 to repeat the processing and determination. If it has been removed, the process proceeds to step 7 and it is determined that the detected paper is not a backing paper. The detection process ends. If YES is determined in step 5, the process proceeds to step 8, and it is determined that the detected paper is a backing paper, and the backing paper detection process is ended.

As described above, the color image forming apparatus according to this embodiment determines whether or not the sheet conveyed to the sheet conveying path 21 shown in FIG. 1 is the backing sheet. This can prevent the user from mistakenly performing double-sided printing on the backing paper. In addition, it is possible to save resources by preventing wasteful printing mistakes and reduce office costs. Furthermore, the usability for the user is improved. By the way, when the image detecting unit 12 detects that an image is formed on the back surface of the sheet, the control device 50 detects the conditions of the sheet feeding and separation of the separating unit 8 and the process conditions such as image forming and transfer,
Further, control is performed to switch to a backing paper mode in which conditions related to image formation such as fixing conditions (raising the fixing temperature) are switched to conditions suitable for image formation on a backing paper. Thereby,
In this color image forming apparatus, when the image detecting means 12 detects a backing sheet, the backing sheet mode is automatically switched to a mode suitable for forming an image on the backing sheet, so that an image is formed on the backing sheet. It is possible to prevent the deterioration of the separation performance of the paper, which is likely to occur in the second step, the deterioration of the fixing performance due to the temperature decrease of the fixing section, and the tendency of the back surface toner to be easily attached to the roller of the fixing section.

Further, when the image detecting means 12 detects that an image is formed on the sheet fed from the sheet feeding section 2, the control device 50 feeds the sheet to the sheet feeding section 2. It also functions as a backing sheet use display means for displaying on the display unit 55 that the backing sheet is stored in the paper feed cassette 22. According to this color image forming apparatus, when it is detected that the sheet conveyed through the sheet conveying path 21 is the backing sheet, the sheet feeding cassette 22 of the sheet feeding unit 2 that has fed the sheet is set to the back side. The display unit 55 shows that paper is stored.
Since it is displayed in, it is possible to call the user's attention. As a result, the user can know the paper feed cassette 22 in which the backing paper is stored at the time of subsequent printing, and when the user does not want to use the backing paper or wants to use the backing paper. On the display 5
The display of 5 is an effective criterion. Therefore, it is possible to prevent the use of the backing paper which is not intended by the user.
The display unit 55 includes, for example, a display panel, an operation panel, a lamp provided in the cassette and turned on when a backing sheet is used. Since the display unit 55 is provided in the image forming apparatus itself, it is particularly effective when operating the image forming apparatus directly near the image forming apparatus.

Further, when the image detecting means 12 detects that an image is formed on a sheet, the control device 50 shown in FIG. 1 stores the sheet in the sheet feeding cassette 22 of the sheet feeding section 4. Indicates that the backing paper is stored on the display of the externally connected device 81 shown in FIG. 6 for instructing the color image forming apparatus to print on a personal computer or a host computer connected by a network. It also functions as a means. Therefore, according to this color image forming apparatus, when the external connection device 81 is connected to the color image forming apparatus, when the image detecting unit 12 detects that the sheet conveyed on the sheet conveying path 21 is the backing sheet, Since the display section of the externally connected device 81 indicates that the backing sheet is stored in the sheet feeding cassette 22 of the sheet feeding section 2 that has fed the sheet, the user is required to issue a subsequent print command. Be careful. As a result, when the user does not want to use the backing paper, or wants to use the backing paper, the display on the display unit is a useful judgment material. Therefore, when the user does not want to use the backing paper,
Unintentional use of backing paper can be prevented. In the color image forming apparatus shown in FIG. 6, the display section 55 provided in the apparatus is connected to the controller control section 92, and the controller control section 92 has the engine control section 93.
It is possible to send and receive signals. Then, the engine control unit 93 sends and receives signals to and from the image forming unit 20, the paper feeding unit 2, the fixing device 28, etc., and controls the driving thereof.

FIG. 8 is a flow chart showing the backing sheet detection processing performed by the microcomputer of the control apparatus of another embodiment of the image forming apparatus according to the present invention. The image forming apparatus according to this embodiment is different from the color image forming apparatus described with reference to FIGS. 1 to 7 only in the control contents performed by the control system, and the mechanical structure of the entire apparatus is the same. The description will be given using the reference numerals shown in FIGS. 1 and 2 as necessary. The color image forming apparatus according to this embodiment is
When the image detection unit 12 detects that an image is formed on a sheet, it is assumed that all the backing sheets are stored in the sheet feeding cassette 22 of the sheet feeding unit 2 that has fed the sheet thereafter. It has a control device that functions as a backing sheet storage determination means for determination. Although not shown, the control device has a microcomputer having the same configuration as the control device 50 described with reference to FIG. The microcomputer executes the backing sheet detection processing routine shown in FIG. 8 at a predetermined timing. That is, when the routine shown in FIG. 8 starts, the microcomputer performs the same judgment and processing as in steps 1 to 8 described in FIG. 7 in steps 11 to 18, and in the next step 19, the backing paper. After the paper detection is completed, it is determined that all the backing paper is stored in the paper feed cassette 22 in which the paper detected as the backing paper is fed, and the result is stored in the storage unit. .

That is, after that, when the paper is fed from the paper feed cassette 22 that has fed the paper judged to be the backing paper, the backing paper is placed there without waiting for the result of the backing paper detection. Handle as if it contains paper. According to this color image forming apparatus, when the image detecting unit 12 detects that the sheet conveyed through the sheet conveying path 21 is the backing sheet, the sheet feeding cassette of the sheet feeding stage that has fed the sheet thereafter. Since it is determined that the backing paper is stored in all of 22 sheets, even if the backing paper of the paper is not detected every time the paper is fed from the paper feeding cassette 22, the problem due to the use of the backing paper can be solved. It can be resolved. Further, it is understood that the paper stored in the paper feed cassette 22 before the print command is issued is likely to be the backing paper. Even if the paper stored in the paper feed cassette 22 is determined to be the backing paper in this way, when the backing paper is generally used,
Since it is rare to mix and use backing paper and new paper (unimaged paper), if the first detected paper is the backing paper, the paper loaded after the next paper will also be the backing paper. Probability of being paper is high.

Further, the information that the paper set in the paper feed cassette 22 is the back paper is preferably reset when the paper feed cassette 22 is pulled out. Then, even if the paper in the paper feed cassette 22 is changed to an unused paper by pulling out the paper feed cassette 22 when the paper is replenished in the paper feed cassette 22, a false detection is made. Since it does not occur, it is possible to improve the detection accuracy of whether it is a backing sheet. Further, since the paper may be replenished while the power of the color image forming apparatus is turned off, the paper is set in the paper feed cassette 22 when the power is turned off or when the power is newly turned on. It is preferable to reset the information as to whether or not the paper being processed is the backing paper. By doing so, it is possible to further improve the accuracy of whether or not the paper is the backing paper. 7 and 8, the light receiving sensor 1 is shown.
7 shows an example of the case where the output is large when the amount of received light is large,
On the contrary, if the light receiving sensor 17 has a characteristic that the output becomes small when the amount of received light is large,
And each judgment of step 15 is Sb−Sa ≦ specified amount.

FIG. 9 is a block diagram for explaining an embodiment of a color image forming apparatus having a backing paper prohibition mode. This color image forming apparatus is provided with a backing paper prohibition mode key 71, which is a backing paper prohibition setting means for setting a backing paper prohibition mode when the backing paper is not used, outside the main body of the apparatus. Further, when the backing paper prohibition mode is set by the backing paper prohibition mode key 71, when the image detecting means 12 detects the image of the paper, it is a control means which also controls to prohibit printing on the paper. Device 5
0'is provided. As described above, this color image forming apparatus can select whether or not to use the backing paper before executing the print command. Therefore, when the backing paper is not used, the main body of the apparatus can be used. The backing paper prohibition mode key 71 provided on a panel or the like on the outside is pressed to select the backing paper prohibition mode. Then, when the backing sheet prohibit mode is executed and it is detected that the sheet conveyed to the sheet conveying path is the backing sheet, it is controlled not to form an image on the sheet. It

That is, without transferring the image to the backing paper, the paper is ejected to the paper ejection accommodating section 24 (see FIG. 2) with the printing surface left blank. For the user, for example, a message “printing was not performed because the paper was backing paper” is displayed on the display unit 55 of the apparatus body (display panel, operation panel, alarm lamp, etc.).
Alternatively, when an external connection device 81 such as a personal computer is connected to the color image forming apparatus, the same display is displayed on the display of the external connection device 81. As a result, wasteful printing mistakes can be prevented and resource saving can be achieved. It is also effective in reducing office costs. Furthermore, the usability for the user is improved. Further, even when the backing sheet is not used for the documents to be submitted to the outside of the company, selecting the backing sheet prohibition mode can prevent an image from being accidentally printed on the backing sheet.

FIG. 10 is a block diagram showing an embodiment of a color image forming apparatus in which when a double-sided print is designated and a backing sheet is detected, the sheet feeding from the sheet feeding cassette storing the sheet is stopped. is there. Note that this color image forming apparatus is different from the color image forming apparatus described in FIGS. 1 to 7 only in the control contents performed by the control system, and the configuration of the mechanical portion of the entire apparatus is the same. Accordingly, the description will be given using the reference numerals shown in FIGS. 1 and 2. In the color image forming apparatus according to this embodiment, when double-sided printing is designated and paper feeding from the paper feeding cassette 22 that stores backing paper is selected, paper feeding from the paper feeding cassette 22 is performed. A control device 50 ″ that functions as a paper feed stopping unit that controls the stop is provided. The control device 50 ″ is the control device 5 of FIG.
It has a microcomputer with the same configuration as 0.

According to this color image forming apparatus, when double-sided printing is designated, the paper feeding cassette 22 in which the backing paper is stored is known in advance (by the previous paper feeding history, When the paper feed from the paper feed cassette 22 is selected, the paper feed from the paper feed cassette 22 is automatically stopped by the control device 50 ″. A new image will not be overlaid on the surface where the image has already been formed, preventing unnecessary printing mistakes, saving resources, and reducing office costs. Thus, according to this color image forming apparatus, when double-sided printing is designated, the backing paper set in the paper feed cassette 22 is No wasteful paper feeding operation is performed because the paper is not printed Note that the backing paper is set and unused paper is stored with the same size as the paper in the selected paper feed cassette 22. If there is another paper feed cassette, unused paper may be fed from the paper feed cassette 22.

FIG. 11 is a block diagram showing an embodiment of the image forming apparatus in which the paper feeding from the paper feeding cassette storing the backing paper is stopped when the backing paper prohibit mode is selected. In this color image forming apparatus, the control contents performed by the control system are partly different from those in the color image forming apparatus described with reference to FIGS. 1 to 7, and the configuration of the mechanical portion of the entire apparatus is the same. Description will be made using the reference numerals shown in FIGS. 1 and 2 as necessary. In the color image forming apparatus according to this embodiment, when the backing sheet prohibition mode is selected by the backing sheet prohibition mode key 71, the backing sheet is stored in the plurality (for example, four) of the sheet feeding cassettes 22 provided. When a paper feed from the paper feed cassette 22 is selected, a control device 60 that functions as a paper feed stopping unit that controls to stop the paper feed from the paper feed cassette 22 is provided. The control device 60 has a microcomputer having the same configuration as the control device 50 of FIG.

In this color image forming apparatus, when double-sided printing is designated, the paper feeding cassette 22 in which the backing paper is stored is known in advance (depending on the previous paper feeding history, the If the paper feed from the paper feed cassette 22 is selected, the control device 60 automatically stops the paper feed from the paper feed cassette 22. Therefore, it is possible to prevent a new image from being overlaid on the surface of the paper on which the image has already been formed. As a result, it is possible to save resources by preventing useless printing mistakes, effectively reduce office costs, and improve user friendliness.
As in the case of the color image forming apparatus described with reference to FIG. 10, backing sheets are set and unused sheets of the same size as the sheets in the selected sheet cassette 22 are stored. If there is another paper feed cassette, unused paper may be fed from the paper feed cassette 22. According to this color image forming apparatus, when it is difficult to use the backing paper like a document issued as a formal document to the outside of the company, the backing paper prohibition mode is selected to form an image. In that case, even if the user selects the paper feeding from the paper feeding cassette 22 in which the backing paper is stored, the paper feeding from the paper feeding cassette 22 is not performed, so it is erroneously wasteful. It is possible to prevent image formation.

In FIG. 12, when the paper feed from the paper feed cassette that has fed the paper on which the image is formed on the back side of the paper is selected, the back paper mode is switched to when the paper is fed from the paper feed cassette. FIG. 3 is a block diagram showing an embodiment of the image forming apparatus according to the present invention. In this color image forming apparatus, the control contents performed by the control system are partly different from those of the color image forming apparatus described with reference to FIGS.
Since the structure of the mechanical portion of the entire apparatus is the same, the description will be given using the reference numerals shown in FIGS. 1 and 2 as necessary. The color image forming apparatus according to this embodiment switches a condition related to image formation such as a condition for sheet feeding / separation, a process condition such as image formation and transfer, and a fixing condition to a condition suitable for image formation on a backing paper. A control device 60 'is provided which functions as a means for switching to the mode. Further, the paper feeding unit 2 has a plurality of paper feeding cassettes 22 each capable of storing paper,
When the image detection unit 12 detects that an image is formed on a sheet and selects the sheet feeding from the sheet feeding cassette 22 that has fed the sheet, the back sheet is fed when the sheet is fed from the sheet feeding cassette 22. I'm trying to switch to mode.

The control device 60 'has a microcomputer having the same structure as the control device 50 of FIG. This color image forming apparatus has a paper feed cassette 2 in which backing paper is stored in advance before a print command is issued.
2 is known (which is determined based on the previous paper feeding history), and when the paper feeding from the paper feeding cassette 22 is selected, the backing paper suitable for forming an image on the backing paper is selected. The mode is automatically switched. As a result, the separation performance of the paper tends to decrease when an image is formed on the backing paper, and the fixing performance decreases due to the temperature decrease of the fixing unit.
Further, it is possible to prevent the occurrence of problems that are likely to occur when a backing paper is used, such as the fact that the toner on the back surface is likely to adhere to the rollers of the fixing unit due to melting. The image detecting unit 12 including the light emitting sensor 16 and the light receiving sensor 17 described in each of the above-described embodiments detects the leading edge and the trailing edge of the sheet conveyed through the sheet conveying path 21 (see FIG. 1). Also serves as a detection sensor. Therefore,
Since it is not necessary to add a dedicated sensor for detecting the leading edge and the trailing edge of the sheet, the cost of the apparatus can be reduced and the configuration can be simplified. Further, the image detecting means 12 including the light emitting sensor 16 and the light receiving sensor 17 is
It also serves as a double feed sensor that detects double feed of the sheets conveyed through the sheet conveyance path 21. The double feed detection by the light emitting sensor 16 and the light receiving sensor 17 is performed by comparing the light transmittance of one sheet (by the signal of the light receiving sensor) with the light transmittance of two sheets. Is about 1/2 and about 1/3 at a constant rate, it is determined that the paper is double-fed with two or three sheets.

FIG. 13 is a schematic configuration diagram showing an embodiment of an image forming apparatus having a function of detecting the number of sheets set in the sheet feeding section, and parts corresponding to those in FIG. I am doing it. The color image forming apparatus according to the present embodiment is provided with a light emitting sensor 13 which is a light emitting means and a light receiving sensor 14 which is a light receiving means for measuring the transmittance of a sheet set in a paper feeding cassette of the paper feeding section 2, and a light emitting sensor 16 And the light-receiving sensor 17 are included in the image detecting means 12 (which is arranged closer to the separating means 8 than in the embodiment of FIG. 1), and the transmittance and the light-emitting sensor 13 and the light-receiving sensor 14 of the paper feeding unit 2 are measured.
The number of sheets of paper P set in the paper feed unit 2 is detected by comparing the transmittance measured by and. That is, the transmittance of one sheet conveyed from the sheet feeding unit 2 is measured by the light emitting sensor 16 and the light receiving sensor 17 provided in the sheet conveying path 21, and the light emitting sensor 13 and the light receiving sensor provided in the sheet feeding unit 2 are measured. 14 and the bottom plate 5 of the paper feed unit 2
The transmittance of the upper sheet P is measured. Then, by comparing the two transmittances, the microcomputer of the control device 70 calculates the remaining number of sheets of the paper P on the bottom plate 5. By doing so, the number of remaining sheets on the bottom plate 5 can also be detected. Therefore, the cost of the device can be reduced and the configuration can be simplified.

FIG. 14 is a block diagram showing an embodiment of a color image forming apparatus provided with image detection canceling means for forcibly canceling the image detection of the paper by the image detecting means. It should be noted that in this color image forming apparatus as well, FIG.
The control contents performed by the control system and the color image forming apparatus described in 1 above are partially different, and the configuration of the mechanical portion of the entire apparatus is the same. This color image forming apparatus is provided with an image detection canceling unit 73 for forcibly canceling the detection of the image of the sheet by the image detecting unit 12. The image detection canceling means 73 is, for example, a switch provided in the apparatus main body or various keys provided in an external connection device for instructing printing such as a personal computer or a host computer connected to the color image forming apparatus via a network. When a signal from the image detection canceling unit 73 is input to the control device 60 ″ (having the same configuration as the control device 50 in FIG. 1), the image detection of the sheet by the image detecting unit 12 is forcibly cancelled. According to the color image forming apparatus, for example, when a sheet (form paper or the like) on which a ruled line or a character is previously printed is used and an image is to be formed thereon, the ruled line or the character is reused. However, if the image detection canceling means 73 is used in such a case, the image detecting means 12 can detect It is possible to release the image detection, it is possible to prevent the erroneous detection.

[0043]

As described above, according to the image forming apparatus of the present invention, when the image detecting means provided on the sheet conveying path between the sheet feeding section and the image transferring section detects the backing sheet, Since double-sided printing on a sheet is prohibited, it is possible to prevent erroneous double-sided printing on a backing sheet having an image already formed on one side. Further, even when there are a plurality of paper feed cassettes in the paper feed unit, it is not necessary to provide an image detection means for detecting the backing paper for each paper feed cassette, so that the configuration is simple and the apparatus is inexpensive. Can be

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing, together with a sheet feeding system, components that detect whether a sheet of an image forming apparatus according to the present invention is a backing sheet.

FIG. 2 is an overall configuration diagram showing a color image forming apparatus which is also an embodiment of the image forming apparatus.

FIG. 3 is a diagram for explaining an output signal of a light receiving sensor when a sheet on which an image of three-color characters is formed is detected.

FIG. 4 is a diagram for explaining an output signal of a light receiving sensor when a character image is formed on the entire surface except for some marginal areas on the front, rear, left and right.

FIG. 5 is a diagram for explaining an output signal of a light receiving sensor when a sheet on which images are not formed on both sides is detected.

FIG. 6 is a block diagram showing an example of a color image forming apparatus to which an externally connected device is connected.

7 is a flowchart showing a backing sheet detection process performed by a microcomputer of the control device shown in FIG.

FIG. 8 is a flowchart showing a backing sheet detection process performed by a microcomputer of a control device of another embodiment of the image forming apparatus according to the present invention.

FIG. 9 is a block diagram illustrating an embodiment of a color image forming apparatus having a backing paper prohibition mode.

FIG. 10 is a block diagram showing an embodiment of a color image forming apparatus in which when a double-sided print is designated and a backing sheet is detected, the sheet feeding from the sheet feeding cassette storing the sheet is stopped.

FIG. 11 is a block diagram showing an embodiment of an image forming apparatus in which, when the backing sheet prohibition mode is selected, the sheet feeding from the sheet feeding cassette storing the backing sheet is stopped.

FIG. 12: When paper feeding from a paper feeding cassette that has fed a paper on which an image is formed on the back side of the paper is selected, the back paper mode is switched when the paper is fed from the paper feeding cassette 1 is a block diagram showing an embodiment of an image forming apparatus.

FIG. 13 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus having a function of detecting the number of sheets set in a sheet feeding unit.

FIG. 14 is a block diagram showing an embodiment of a color image forming apparatus provided with image detection canceling means for forcibly canceling the image detection of the paper by the image detecting means.

[Explanation of symbols]

2: Paper feeding unit 4: Paper feeding device 12: Image detecting means 13, 16: Light emitting sensor (light emitting means) 14, 17: Light receiving sensor (light receiving means) 20: Image forming section 21: Paper conveying path 22: Paper feeding cassette 50, 50 ', 50 ", 60, 60', 60", 70:
Control device 55: Display unit 71: Backing paper prohibition mode key 73: Image detection canceling means 81: External connection device P: Paper

Front page continuation (51) Int.Cl. ⁷ identification code FI theme code (reference) B65H 7/06 B65H 7/06 7/12 7/12 G03G 15/00 106 G03G 15/00 106 H04N 1/00 H04N 1 / 00 C F Term (reference) 2C061 AP03 AP04 AR03 HH03 HJ06 HK11 HN02 HN15 HN17 2H027 DC01 DC02 DE02 DE07 EA03 EA12 EA18 EC06 ED17 EE07 EF06 EJ15 EK03 FA13 FA30 A08 A05 A08 A05 A08 A05 A08 A02 A05 A08 A02 A05 A08 A02 A04 A08 A02 A05 A08 A02 A05 A08 A02 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A02 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A05 A08 A02 A05 A08 A05 A08 A05 A08 A05 A08 A02 BA13 BB02 BB05 BB07 BC03 BC07 BC08 BD08 CA02 CA06 CC02 CC03 CC04 DA06 DB12 DC13 EA03 EA15 EB05 5C062 AA02 AA05 AB17 AB22 AB23 AB32 AC58 AF15 BA04

Claims (17)

[Claims] 1. An image forming apparatus for transferring an image to a sheet fed from a sheet feeding section by an image transfer section, wherein the sheet conveying path is conveyed on a sheet conveying path between the sheet feeding section and the image transferring section. The image detection means for detecting whether or not an image has already been formed on the paper to be formed is provided, and when the image detection means detects that the image is formed on the paper, the paper is judged to be a backing paper. An image forming apparatus comprising a control means for controlling so as to prohibit double-sided printing on the sheet. 2. The image forming apparatus according to claim 1,
Backing paper prohibition setting means for setting the backing paper prohibition mode when the backing paper prohibition mode is set when the backing paper prohibition mode is set by the image detecting means is set. An image forming apparatus, which is means for controlling so as to prohibit printing on the sheet when an image on the back side of the sheet is detected. 3. The image forming apparatus according to claim 1,
When the image detection unit detects that an image is formed on the sheet, the conditions for image formation such as the conditions for sheet feeding and separation, the process conditions such as image formation and transfer, and the fixing conditions are used for the image on the backing sheet. An image forming apparatus, comprising means for switching to a backing paper mode for switching to conditions suitable for formation. 4. The image forming apparatus according to claim 1, wherein when the image detecting unit detects that an image is formed on a sheet fed from the sheet feeding unit, An image forming apparatus comprising a backing paper use display means for displaying on the display unit that the backing paper is stored in the paper feeding unit. 5. The image forming apparatus according to claim 1, wherein when the image detecting unit detects that an image is formed on a sheet, a backing sheet is provided in the sheet feeding unit. An image forming apparatus comprising: a backing sheet use display means for displaying on a display unit of an externally connected device that a sheet is stored therein. 6. The image forming apparatus according to claim 4, wherein when the image detecting unit detects that an image is formed on a sheet, the sheet feeding unit that has fed the sheet thereafter An image forming apparatus comprising a backing sheet storage determination means for determining that all backing sheets are stored. 7. The image forming apparatus according to claim 1, wherein the paper feed unit has a plurality of paper feed cassettes capable of accommodating paper, and the image detection unit prints paper. When it detects that an image is formed,
After that, the image forming apparatus is provided with a backing sheet storage determination unit that determines that all the backing sheets have been stored in the sheet feeding cassette that has fed the sheet. 8. The image forming apparatus according to claim 7,
When the paper feed from the paper feed cassette that is determined to contain the backing paper is selected, the display section displays that the backing paper is stored in the selected paper feed cassette. An image forming apparatus comprising a backing paper storage cassette display means. 9. The image forming apparatus according to claim 8,
An image forming apparatus, wherein the backing paper storage cassette display means is a means for displaying a display of a paper feed cassette housing backing paper on a display unit of an externally connected device connected via a network. 10. The image forming apparatus according to claim 7, wherein when double-sided printing is designated and paper feeding from a paper feeding cassette storing backing paper is selected, An image forming apparatus comprising a paper feed stop means for controlling the paper feed from the paper feed cassette to be stopped. 11. The image forming apparatus according to claim 7, wherein the backing paper is stored when a backing paper prohibition mode for preventing an image from being formed on the backing paper is selected. An image forming apparatus comprising: a paper feed stopping unit that controls the paper feed from the paper feed cassette when the paper feed from the paper feed cassette is selected. 12. The image forming apparatus according to claim 7, wherein conditions relating to image formation such as sheet feeding separation conditions, process conditions such as image formation and transfer, and fixing conditions are suitable for image formation on a backing paper. A means for switching to the backing sheet mode for switching to the condition is provided, and when the paper feeding from the paper feeding cassette that has fed the paper in which the image detecting means detects that an image is formed on the paper is selected, the paper feeding is selected. An image forming apparatus characterized in that when the paper is fed from the cassette, the back paper mode is switched. 13. The image forming apparatus according to claim 1, wherein the image detecting unit includes a light emitting unit and a light receiving unit that are arranged to face each other so as to sandwich a sheet conveyed through the sheet conveying path. The image forming apparatus is also characterized in that the image detecting means also serves as a sheet detecting sensor for detecting the leading edge and the trailing edge of the sheet conveyed through the sheet conveying path. 14. The image forming apparatus according to claim 1, wherein the image detecting unit includes a light emitting unit and a light receiving unit that are arranged to face each other so as to sandwich a sheet conveyed in the sheet conveying path. The image forming apparatus is also characterized in that the image detecting means also serves as a double feed sensor for detecting the double feed of the sheets conveyed through the sheet conveying path. 15. The image forming apparatus according to claim 13, further comprising a light emitting unit and a light receiving unit for measuring the transmittance of the sheet set in the sheet feeding unit, and the transmittance measured by the image detecting unit. An image forming apparatus configured to detect the number of sheets set in the sheet feeding unit by comparing the transmittance measured by the light emitting unit and the light receiving unit of the sheet feeding unit. 16. The image forming apparatus according to claim 13, wherein the light receiving means of the image detecting means receives and outputs the light transmitted through the paper and the output value has an amplitude of a certain value or more. An image forming apparatus, which determines that the detected paper is a backing paper when the change occurs. 17. The image forming apparatus according to claim 1, further comprising an image detection canceling unit for forcibly canceling the image detection of the sheet by the image detecting unit. Image forming apparatus.