JP2006084931A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of forming an image on used paper while preventing failure. <P>SOLUTION: The image forming apparatus 1 has an image acquiring device 50, which detects whether an image formed on the backside of used paper is a color image or not, the density of the image formed on the backside of the used paper, and an amount of margin at the leading end of the used paper in a conveyance direction. In the case that the image formed on the backside of the used paper is a color image, the image forming apparatus 1 controls the intensity of a transfer electric field for the transfer of a toner image in accordance with the image density detected. In the case that the amount of margin on the backside at the leading end of the used paper in the conveyance direction is not larger than a predetermined amount, the toner image is transferred so that a predetermined amount of margin is left on the surface of the paper. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and relates to a technique for forming an image on a backing paper.

In view of dealing with environmental issues and reusing resources, in the workplace where a large amount of paper is used in copiers and printers, etc., recording paper (hereinafter referred to as “recording paper”) that has been used with images formed on only one side. In other words, an image is formed on the side of the back paper on which the image is not formed and reused. In recent years, since the backing paper has been used in the image forming apparatus in recent years, for example, an invention relating to the use of the backing paper has been made like the invention disclosed in Patent Document 1. . An image forming apparatus disclosed in Patent Document 1 (hereinafter referred to as a conventional apparatus) includes a reflective optical sensor in the vicinity of a paper feed tray. This sensor irradiates light on the back surface of the paper in the conveyance path, detects reflected light reflected by the paper, and outputs the detected light instead of an electrical signal. If the back side is white paper, the sensor output will be approximately constant, but if an image is formed on the back side of the paper, the reflected light will change and the sensor output will change. By detecting the presence or absence of an image on the paper, it is possible to determine whether or not the paper is a back paper.
JP-A-9-96927

  By the way, when an image is formed on a recording sheet, various controls such as toner image transfer control are performed in order to prevent image quality defects. When unused paper is stored in the paper feed tray, the same paper is always used. Therefore, if a certain control is performed, it is possible to prevent image quality defects from occurring. However, when the back paper is stored in the paper feed tray, the user thinks that paper reuse is the most important, so papers with different thicknesses, black-and-white images, and color images are formed. In some cases, various backing papers such as used paper are mixed and stored in the paper feed tray. When various types of paper are used in this way, poor image quality will occur if various controls are not performed according to the individual paper. In conventional devices, the presence or absence of an image on the paper is detected. However, since various controls cannot be performed according to the paper, it has not been possible to suppress defects that occur when an image is formed on the back paper.

  The present invention has been made under the above-described background, and an object thereof is to provide a technique for forming an image on a backing paper while suppressing the occurrence of defects.

In order to solve the above-described problems, the present invention forms a toner image on an image carrier in accordance with a conveyance unit that conveys a recording sheet along a conveyance path, and input image data, and the toner image is formed along the conveyance path. A toner image forming means for transferring to the recording sheet conveyed in the recording medium, and a recording sheet in the conveying path on the upstream side in the conveying direction of the sheet as viewed from the position where the toner image is transferred to the recording sheet. An image density detecting means for detecting an image density of the image, and when the toner image forming means transfers the toner image to the recording sheet when the image density detected by the image density detecting means is equal to or higher than a predetermined density. There is provided an image forming apparatus having a transfer electric field control means for controlling the intensity of the transfer electric field according to the image density measured by the image density detection means.
If the image is already formed on the recording sheet like the backing paper and the image density of the image is equal to or higher than a predetermined density, a large amount of the color material on which the image is already formed is on the paper surface. When the transfer electric field is the same as when a toner image is transferred to unused paper, the transfer electric field is not sufficient to transfer the toner image with the color material on the back surface, resulting in poor image quality. Therefore, in the image forming apparatus according to the present invention, the image density of the image on the recording sheet is detected, and the transfer electric field is controlled according to the detected image density.

  According to the present invention, it is possible to form an image on a backing paper while suppressing the occurrence of defects.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Constitution]
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is a so-called tandem type color copier, and has a display 39 that displays various menu screens, messages, and the like, and an operation unit 41 that includes operation keys 40 for a user to perform various operations. is doing.

  The paper feed trays 9A and 9B are trays for storing recording paper (recording sheet) 10 such as white paper or back paper, both of which are front and back, the paper feed tray 9A stores the back paper, and the paper feed tray 9B is not yet installed. Store paper for use. Above the paper feed trays 9A and 9B, paper feed rolls 33A and 33B for separating recording sheets one by one and feeding them to the paper transport path 36 are disposed. Note that the image forming apparatus 1 has a plurality of paper feed trays, but only two paper feed trays are shown in FIG. 1 to prevent the drawing from becoming complicated. Further, in the following description, when it is not necessary to distinguish each tray, it is referred to as a paper feed tray 9. The transport roll 34 is a roll for transporting the recording paper 10 delivered from the paper feed tray 9 along the paper transport path 36. The recording paper 10 delivered to the paper transport path 36 by the paper feed roll 33 is transported to the position of the registration roll 37 by the transport roll 34. The registration roll 37 is a roll that conveys the recording sheet 10 to the position of the secondary transfer roll 30, and conveys the recording sheet 10 to the position of the secondary transfer roll 30 at a predetermined timing under the control of the control unit 5. In the recording paper 10 in the paper transport path 36, an image is formed on the surface facing upward in FIG. 1, and therefore, the surface facing upward is hereinafter referred to as the front surface and facing downward. The surface that is present is referred to as the back surface. Further, since the image is formed on the front surface, when the back paper is stored in the paper feed tray 9A, the surface on which the image has already been formed is stored face down.

  An image acquisition device 50 is provided on the upstream side of the registration roll 37 and in the vicinity of the paper transport path 36 to acquire an image of the back side of the backing paper in the paper transport path 36. The image acquisition device 50 includes a light source and an image sensor (both not shown). The image sensor receives light emitted from the light source and reflected by the back surface of the backing paper, and images on the back surface of the backing paper are received. The image data shown is generated and stored for each color of R (red), G (green), and B (blue). In the present embodiment, each pixel representing a read image is represented by 8-bit digital data for each color of RGB.

  The image reading unit 3 includes a platen glass 12, a light source 13, a full rate mirror 14, half rate mirrors 15 and 16, an imaging lens 17, and an image reading element 18. In the image reading unit 3, light is emitted from the light source 13 to the document 2 placed on the platen glass 12. The light reflected by the document 2 is guided to the imaging lens 17 by the full rate mirror 14 and the half rate mirrors 15 and 16, and forms an image on the image reading element 18. The image reading element 18 includes a photodiode and a CCD (Charge Coupled Device). The image reading element 18 generates an electrical signal for each color of RGB according to the intensity of incident light, converts the generated electrical signal into 8-bit digital data, and outputs the digital data.

  The image processing unit 4 performs various processes such as shading correction, positional deviation correction, and gamma correction on the image represented by the digital data output from the image reading unit 3 or the image represented by the digital data output from the control unit 5. Apply. Then, raster data is generated and output for each color of yellow (Y), magenta (M), cyan (C), and black (K) from the image subjected to various processes.

  The image output unit 6 forms an image on the recording paper 10 based on the raster data output from the image processing unit 4. As shown in FIG. 1, the image output unit 6 includes image forming units 7Y, 7M, 7C, and 7K corresponding to each color of YMCK, and the image forming units are spaced apart from each other in the horizontal direction. Has been placed. Since each image forming unit has the same configuration except that the color of the image to be formed is different, hereinafter, when there is no need to distinguish between the individual image forming unit and each part of the image forming unit, YMCK The reference numeral is omitted.

  The image forming unit 7 includes a photosensitive drum 20 that rotates in the direction of arrow A in the figure, a corotron 21 for primary charging that uniformly charges the surface of the photosensitive drum 20, and the surface of the photosensitive drum 20 by laser light. ROS (Raster Output Scanner) 19 for forming an electrostatic latent image on the surface, a developing device 22 for developing the electrostatic latent image formed on the photosensitive drum 20, and a predetermined color in the developing device 22 A toner supply device 23 that supplies toner and a cleaning device 24 are provided. A primary transfer corotron 25 is provided below the photosensitive drum 20 with the intermediate transfer belt 8 interposed therebetween.

  The intermediate transfer belt 8 is formed into an endless belt shape by, for example, forming a synthetic resin film such as polyimide having flexibility in a band shape, and connecting both ends of the synthetic resin film formed in the band shape by means such as welding. It is a thing. The intermediate transfer belt 8 is suspended with a constant tension by a drive roll 26, a tension roll 27, a steering roll 28, and a backup roll 29 in contact with the contact roll 90.

  The tension roll 27 applies a certain tension to the intermediate transfer belt 8 and is urged toward the intermediate transfer belt 8. The drive roll 26 is a roll for rotating the intermediate transfer belt 8 and is rotated by a motor (not shown) to move the intermediate transfer belt 8 in the direction of arrow B in the figure.

  The backup roll 29 and the secondary transfer roll 30 are rolls for transferring the toner image transferred to the intermediate transfer belt 8 onto the recording paper 10. The backup roll 29 is a secondary transfer with the intermediate transfer belt 8 interposed therebetween. It is provided at a position facing the roll 30. The secondary transfer roll 30 contacts the intermediate transfer belt 8 immediately before the recording paper 10 is transported between the backup roll 29 and the secondary transfer roll 30, and the toner image on the intermediate transfer belt 8 is transferred onto the recording paper 10. Let them transcribe. When the transfer of the toner image is completed, the toner image is separated from the intermediate transfer belt 8. Further, the backup roll 29 and the contact roll 90 form a transfer electric field for transferring the toner image onto the recording paper 10. A voltage source (not shown) is connected to the contact roll 90, and a voltage is applied under the control of the control unit 5. Since the contact roll 90 is in contact with the backup roll 29, when the secondary transfer roll 30 contacts the intermediate transfer belt 8, a potential difference is generated between the secondary transfer roll 30 and the grounded secondary transfer roll 30, and the applied voltage A transfer electric field corresponding to the above is formed.

  A belt cleaner 38 and a transport roll 31 are provided downstream of the backup roll 29 and the secondary transfer roll 30. The belt cleaner 38 is in contact with the intermediate transfer belt 8 and removes toner remaining on the intermediate transfer belt 8 after the toner image is transferred onto the recording paper 10. The conveyance roll 31 is rotated by a motor (not shown) and conveys the recording paper 10 onto which the toner image is transferred to the fixing device 11.

  The fixing device 11 includes a heating roll 80 and a pressure roll 81 with the paper transport path 36 interposed therebetween. The heating roll 80 has a heat lamp 80 </ b> A that generates heat therein, and the heat generated by the heat lamp 80 </ b> A is controlled by the control unit 5. The pressure roll 81 is in a position facing the heating roll 80 with the paper transport path 36 interposed therebetween, and is in pressure contact with the heating roll 80.

  The communication unit 110 is connected to a communication network 200 such as a local area network (LAN) (not shown), and receives data transmitted from a personal computer 210 connected to the same communication network.

  Next, the configuration of the control unit 5 will be described. FIG. 2 is a block diagram illustrating the control unit 5 and each unit controlled by the control unit 5. The control unit 5 includes a CPU 102, a ROM 103, a RAM 104, and a nonvolatile memory 105 that can read and write various data, and each unit is connected to a bus 101. Further, the control unit 5 has an interface 106 for controlling each unit. The control unit 5 controls each unit such as the driving unit 100 that rotates each roll through the interface 106, and receives a signal output from each unit. The CPU 102 controls each unit of the image forming apparatus 1 based on a control program stored in the ROM 103. When the operation key 40 is operated by the control unit 5 or the user, the image reading unit 3 is controlled to read the document 2, and the read image is processed by the image processing unit 4. Then, each unit of the image forming apparatus 1 is controlled to form the read image on the recording paper 10 conveyed from the paper feed tray 9, and the original placed on the image reading unit 3 is copied.

  For example, when the communication unit 110 receives page data described according to a page description language such as PostScript (registered trademark), the control unit 5 interprets the received page data and converts the digital data representing the image of the page. Generate. The generated data is output to the image processing unit 4, and each unit of the image forming apparatus 1 is controlled to form an image represented by the digital data on the recording paper 10. Note that the control unit 5 determines whether the image formed on the back side of the back paper is a color image or a black and white image from the image acquired by the image acquisition device 50, and the image density of the back side of the back paper (occupies the paper surface). Image amount) and whether or not an image is formed on the end of the back side of the backing paper, and an image is formed on the surface of the backing paper according to the detection result. When the controller 5 forms an image on the back paper according to the detection result, the non-volatile memory 105 stores the margin amount at the leading edge of the back paper in the paper feed direction and the voltage applied to the contact roll 90. Read from various tables and control.

[Operation]
Next, the operation of this embodiment will be described with reference to FIG. When the personal computer 210 connected to the communication network 200 performs an operation to instruct the image formation of the document on the back paper stored in the paper feed tray 9A, the page data representing the document is transmitted via the communication network 200. It is transmitted to the image forming apparatus 1. When this data is received by the communication unit 110 of the image forming apparatus 1, the control unit 5 controls each unit of the image forming apparatus 1 and starts processing to form an image represented by the received data.

  First, the control unit 5 interprets the received page data and determines whether to perform image formation on only one side of the recording paper 10 or to perform image formation on both sides. When the image forming is performed only on one side of the recording paper 10 (FIG. 3: Step SA1; YES), the control unit 5 controls the driving unit 100 to rotate the paper feed roll 33A and transfer the backing paper to the paper transport path 36. Send out (step SA2). On the other hand, when image formation is performed on both sides of the recording paper 10 (step SA1; NO), the drive unit 100 is controlled to rotate the paper feed roll 33B and send unused paper to the paper transport path 36 (step SA15). ).

  When the backing paper is sent to the paper transport path 36 and the leading edge of the backing paper reaches the image acquisition device 50, the image acquisition device 50 scans the image formed on the back surface of the backing paper and forms it on the back surface. Image data representing an image is generated and stored for each color of RGB (step SA3).

  When the trailing edge of the backing paper passes through the image acquisition device 50, the control unit 5 generates a GR color difference signal and a GB color difference signal for each pixel from the generated data. Then, as shown in FIG. 4, a histogram of the generated color difference signal is generated (step SA4).

  Next, the control unit 5 determines whether or not the image represented by the page data received by the communication unit 110 is a monochrome image. The control unit 5 interprets the page data, and if the image represented by the page data is a color image (step SA5; NO), the process proceeds to step SA9.

  On the other hand, when the image represented by the page data is monochrome (step SA5; YES), the control unit 5 interprets the page data and determines whether or not the image represented by the page data is a character-only image. When it is determined that the image represented by the page data includes an image (photograph, graphic) other than characters (step SA6; NO), the control unit 5 advances the process to step SA9.

  When it is determined that the image represented by the page data is only characters (step SA6; YES), the control unit 5 determines that the image formed on the back side of the backing paper is a color image or black and white according to the histogram generated in step SA4. It is determined whether the image is an image (step SA7). When a black and white image is read by the image acquisition device 50 and a histogram is generated, a color difference signal histogram is generated as in region A of FIG. On the other hand, when a color image is read by the image acquisition device 50 and a histogram is generated, a histogram of color difference signals is generated as in a region B in FIG. When the color difference signal of a certain value (32 in FIG. 5) or more is not generated as in the region A, the control unit 5 determines that the read image is a monochrome image (step SA7; YES) ).

  If it is determined YES in step SA7, the control unit 5 supplies the image processing unit 4 with the image data of the image represented by the data received by the communication unit 110. Then, the image output unit 6 is controlled in the same manner as when forming an image on unused paper, and an image is formed on the surface of the backing paper (step SA8). Specifically, the control unit 5 first supplies the image processing unit 4 with the image data of the image represented by the data received by the communication unit 110. In the image processing unit 4, raster data for each color of YMCK is generated, and the generated raster data is output to the image output unit 6.

  When raster data for each color of YMCK is output from the image processing unit 4, the output raster data is input to the ROS 19 corresponding to each color. The ROS 19 scans the laser beam LB based on the input raster data, and forms an electrostatic latent image on the photosensitive drum 20. The electrostatic latent image formed on the photosensitive drum 20 is developed with toner supplied to the developing device 22. The toner images of the respective colors formed on the photosensitive drum 20 are transferred onto the intermediate transfer belt 8 by the primary transfer corotron 25 so that the toner images of the respective colors overlap. When the transfer of the toner image is completed, the residual toner remaining on the photosensitive drum 20 is removed by the cleaning device 24.

  When the intermediate transfer belt 8 is rotationally moved by the drive roll 26, the toner image transferred to the intermediate transfer belt 8 moves to the position of the backup roll 29. When the toner image moves to the position of the backup roll 29, the control unit 5 rotates the registration roll 37 and conveys the backing paper to the secondary transfer roll 30. The controller 5 brings the secondary transfer roll 30 into contact with the intermediate transfer belt 8 immediately before the backing paper is conveyed between the backup roll 29 and the secondary transfer roll 30, and the toner image on the intermediate transfer belt 8 is transferred. Transfer to backing paper. When the transfer of the toner image is completed, the secondary transfer roll 30 is separated from the intermediate transfer belt 8. The backing paper on which the image is formed is subjected to fixing processing by the fixing device 11 and then discharged to the paper discharge tray 32.

  When determining NO in step SA5, determining NO in step SA6, and determining NO in step SA7, the control unit 5 performs various controls according to the image formed on the backing paper, and performs the backing paper. An image is formed on the surface. Specifically, first, the control unit 5 obtains the image density of the image formed on the back paper based on the paper size of the paper stored in the paper feed tray 9A and the histogram generated in Step SA4 (Step S4). SA9). If there is an image on the entire back side of the backing paper, the area of the histogram is large because there are many pixels, whereas if the area where the image is formed is small, the area of the histogram is small because the number of pixels is small. Narrow. The control unit 5 calculates the area of the histogram area, calculates the image density of the image on the backing paper from the calculated area, and if the calculated image density value is smaller than the predetermined threshold Q (step SA10; NO), the step An image is formed on the surface of the backing paper in the same way as when YES is determined in SA7.

  On the other hand, if YES is determined in step SA10, the control unit 5 determines a voltage (transfer voltage) to be applied to the contact roll 90 according to the image density obtained in step SA9 (step SA11). Specifically, the control unit 5 stores the voltage table TBL1 illustrated in FIG. The control unit 5 first determines a voltage to be applied to the contact roll 90 from the record corresponding to the obtained image density. For example, when the image density is less than the density a, a voltage value of T1 [V] is read as a voltage value applied to the contact roll 90. Then, a voltage source (not shown) is controlled so that the read voltage value is applied to the contact roll 90. When a voltage is applied to the contact roll 90, a transfer electric field corresponding to the applied voltage is formed. If the image density of the image on the back surface of the backing paper is equal to or higher than a predetermined density, a large amount of color material that has already formed an image is on the paper surface. For this reason, an air gap is generated between the secondary transfer roll 30 and the back side of the backing paper, and if a voltage for transferring a toner image to unused paper is applied to the contact roll 90, sufficient transfer is achieved. An electric field cannot be obtained, resulting in poor image quality. For this reason, in this embodiment, the voltage applied to the contact roll 90 is controlled in accordance with the image density on the back side of the backing paper so as not to cause image quality defects.

  Next, the control unit 5 analyzes the pixel position of the image on the back side of the backing paper stored by the image acquisition device 50, and obtains the amount of margin from the leading end in the transport direction to the position where the image is formed (step SA12). . When an image is not formed within the predetermined threshold value R from the leading edge in the conveyance direction on the back side of the backing paper (step SA13; NO), the control unit 5 displays image data of the image represented by the data received by the communication unit 110. Is supplied to the image processing unit 4. Then, the image output unit 6 is controlled to form an image on the surface of the backing paper (step SA8).

  On the other hand, when the margin amount is equal to or less than the threshold value R (step SA13; YES), the margin amount of the image formed on the surface of the backing paper is set according to the margin amount from the leading edge of the backing paper in the conveyance direction to the image ( Step SA14). Specifically, the control unit 5 stores a margin amount table TBL2 illustrated in FIG. The control unit 5 reads the margin amount of the image formed on the front surface from the record corresponding to the margin amount obtained in step SA12. For example, when the amount of margin from the front end of the back surface to the image is less than d [mm], a distance of S1 [mm] is read as the amount of margin from the front end of the backing paper. Then, the image represented by the page data is corrected so that the blank portion having the read margin amount is formed from the leading end portion in the conveyance direction of the backing paper. If there is an image at the leading end in the transport direction on the back side of the backing paper, the paper is likely to be wound around the roll of the fixing device 11 at the time of fixing. It is prevented from winding around the roll. Then, the control unit 5 supplies image data representing the corrected image to the image processing unit 4 and controls the image output unit 6 to form an image on the surface of the back paper (step SA8).

  As described above, according to the present embodiment, the transfer voltage and the amount of image margin are controlled in accordance with the image formed on the back paper and the image to be printed, resulting in poor image quality. An image can be formed on the backing paper without any problems.

[Modification]
As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above, It can implement with another various form. For example, the present invention may be implemented by modifying the above-described embodiment as follows.

  FIG. 7 is a diagram showing another configuration of the image acquisition device 50. As shown in this figure, the image acquisition device 50 includes a light emitting element array 51, a sheet-like light guide member 52, photosensors 53A, 53B, and 53C, and an image generation unit 54. In FIG. 7, the transport direction D2 is a direction in which the recording paper 10 moves, the width direction D3 is a direction orthogonal to the transport direction D2, and the scanning direction D4 is a direction parallel to the width direction D3.

  The light emitting element array 51 includes a plurality of LED (Light Emitting Diode) chips C1 to Cn that emit white light, and the shape thereof is substantially the same as the full width of the recording paper 10 in the longitudinal direction (width direction D3). It is the same rectangular parallelepiped. The detection position P includes n positions P1 to Pn arranged along the width direction D3 at equal intervals. The light from the LED chip C1 is P1, the light from the LED chip C2 is P2, and so on. The light from the LED chip Cn reaches the position Pn. When the leading edge of the conveyed recording paper 10 reaches the detection position P, the light emitting element array 51 repeats the scanning process until the trailing edge of the recording paper 10 passes the detection position P. The scanning process is a process of sequentially switching the LED chips C1 to Cn to emit light, and this switching is performed so that the light emission position moves in the scanning direction D4. That is, the LED chip that emits light is switched in the order of LED chip C1, LED chip C2,..., LED chip Cn.

  The sheet-like light guide member 52 is a sheet-like member that guides light, and is formed of a transparent member having high transmittance. The shape is a trapezoid having only one hypotenuse with a uniform thickness, and the end surface 521 of the hypotenuse is provided with a reflecting surface. The end surface 522 not adjacent to the end surface 521 is orthogonal to the principal ray of light emitted from the LED chips C1 to Cn of the light emitting element array 51 and reflected at the detection position P. Further, the end face 523 having the thickness of the base of the trapezoid is a light emission face obtained from the end face 522.

  The photosensors 53A, 53B, and 53C receive light emitted from the end surface 523 of the sheet-like light guide member 52, and output a signal (electric signal) at a level corresponding to the intensity (light quantity) of the received light. The photosensor 53A includes a red filter, the photosensor 53B includes a green filter, and the photosensor 53C includes a blue filter.

  Signals output from the photosensors 53A, 53B, and 53C are input to the image generation unit 54. The image generation unit 54 generates and stores, for each color of RGB, an image indicated by light received by the photosensor, that is, image data indicating an image on the back side of the backing paper from the input signal. The image on the back side of the back paper may be detected by such an image acquisition device.

  In the embodiment described above, the image forming apparatus 1 is a tandem type, but the image forming apparatus 1 may be a rotary type.

  The recording sheet on which an image is formed in the image forming apparatus 1 is not limited to paper, and for example, a plastic film or the like may be used as the recording sheet.

  The method for obtaining the image density is not limited to the above-described mode, and the image density may be obtained by counting the number of white pixels and the number of pixels having pixel values.

1 is a diagram illustrating a configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a configuration of a control unit 5. 3 is a flowchart showing a flow of processing performed by the image forming apparatus 1. It is the figure which illustrated the histogram produced | generated by the control part. It is a figure for demonstrating the histogram produced | generated by the control part. It is the figure which illustrated the format of voltage table TBL1 and margin amount table TBL2. It is the figure which showed typically the structure of the image acquisition apparatus 50 in the modification of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Original, 3 ... Image reading part, 4 ... Image processing part, 5 ... Control part, 6 ... Image output part, 7 ... Image Forming unit, 8 ... intermediate transfer belt, 9A, 9B ... feed tray, 10 ... recording paper (recording sheet), 11 ... fixing device, 26 ... drive roll, 29 ... Backup roll, 30 ... secondary transfer roll, 31 ... transport roll, 33 ... paper feed roll, 34 ... transport roll, 36, 36A ... paper transport path, 37 ... registration roll , 41 ... operation unit, 50 ... image acquisition device, 90 ... contact roll, 110 ... communication unit, 200 ... communication network, 210 ... personal computer.

Claims (9)

Conveying means for conveying the recording sheet along the conveying path;
Toner image forming means for forming a toner image on an image carrier in accordance with input image data, and transferring the toner image to a recording sheet conveyed along a conveyance path;
Image density detection means for detecting the image density of an image formed on the recording sheet in the conveyance path on the upstream side in the conveyance direction of the sheet as viewed from the position where the toner image is transferred to the recording sheet;
When the image density detected by the image density detecting means is equal to or higher than a predetermined density, the intensity of the transfer electric field when the toner image forming means transfers the toner image to the recording sheet is determined by the image density detecting means. An image forming apparatus comprising: a transfer electric field control unit configured to control according to the measured image density. Identify whether the image formed on the recording sheet in the transport path is a color image or a black and white image on the upstream side in the transport direction of the sheet as viewed from the position where the toner image is transferred to the recording sheet Having identification means,
The toner image forming unit recognizes that the image formed on the recording sheet in the conveyance path is a color image by the identifying unit, and the image density detected by the image density detecting unit is a predetermined density. 2. The image formation according to claim 1, wherein the intensity of a transfer electric field for transferring the toner image to the recording sheet is controlled according to the image density measured by the image density detection unit. apparatus. The toner image forming unit controls the strength of the transfer electric field according to the image density measured by the image density detecting unit when the toner image to be formed is a color toner image. Alternatively, the image forming apparatus according to claim 2. The toner image forming unit controls the strength of the transfer electric field according to the image density measured by the image density detecting unit when the toner image to be formed includes a photographic image or a graphic image. The image forming apparatus according to any one of 1 to 3. A margin amount detecting means for detecting a margin amount at a leading end portion in the conveyance direction of the recording sheet in the conveyance path on the upstream side in the conveyance direction of the sheet as viewed from a position where the toner image is transferred to the recording sheet;
When the margin amount detected by the margin amount detection unit is less than a predetermined amount, the toner image forming unit forms a predetermined amount of margin at the leading end of the recording sheet in the conveyance direction according to the detected margin amount. The image forming apparatus according to claim 1, wherein the image is transferred. The toner image forming unit recognizes the image formed on the recording sheet in the conveyance path as a color image by the identifying unit, and the margin amount detected by the margin amount detecting unit is less than a predetermined amount. 6. The image forming apparatus according to claim 5, wherein an image is transferred with a predetermined amount of margin provided at a leading end portion in the conveyance direction of the recording sheet in accordance with the detected amount of margin. When the margin amount detected by the margin amount detection unit is less than a predetermined amount and the toner image to be formed is a color toner image, the toner image forming unit performs the recording according to the detected margin amount. The image forming apparatus according to claim 5, wherein an image is transferred with a predetermined amount of margin provided at a leading end in a sheet conveying direction. When the margin amount detected by the margin amount detection unit is less than a predetermined amount and the toner image to be formed includes a photographic image or a graphic image, the toner image forming unit is configured according to the detected margin amount. The image forming apparatus according to claim 5, wherein an image is transferred with a predetermined amount of margin provided at a leading end portion in a conveyance direction of the recording sheet. A first paper feed tray for storing a recording sheet having an image formed on the back surface;
A second paper feed tray for storing a recording sheet on which no image is formed on either the front surface or the back surface;
And a recording sheet supply unit that sends out the recording sheet stored in the first paper feed tray to the transport path when the toner image forming unit transfers an image to only one side of the recording sheet. The image forming apparatus according to claim 1.

Images