JP2017223902A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can eliminate the influence of a surface shape of a sheet surface on sheet surface detection outputs to suppress wrong detection of a waste sheet.SOLUTION: An image forming apparatus 1A comprises: an image forming unit 11 that forms an image on a sheet; a first sheet surface detection sensor 102a that optically reads a sheet surface of the sheet before the image formation; a second sheet surface detection sensor 102b that optically reads the sheet surface of the sheet after the image formation; and a control unit 100 that corrects sheet surface detection outputs from the amount of attached toner acquired from sheet surface detection outputs acquired by the first sheet surface detection sensor 102a and second sheet surface detection sensor 102b and image data of the image formed on the sheet on the basis of data of correlation between the shape of the sheet surface and the amount of attached toner.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus that forms an image by transferring and fixing a toner image onto a sheet.

  As a technique for detecting a deviation of an output image, an output image is detected using an optical reading sensor in a paper passing path after image formation, and a deviation is determined from the detected output. In this detection method, the threshold value for detection of deviation is determined from the information of the input image data. For example, by shifting the threshold value based on the presence or absence of an image based on the input image data, it is possible to detect the error regardless of the presence or absence of the image.

  However, the above-described detection method has a problem in that when a paper whose shape of the paper surface is not constant, such as embossed paper, is detected, it cannot be distinguished whether the variation in the detection result is due to the paper or the error, and the reliability of the determination is reduced. For example, there is a possibility that it is determined that the image is not distorted even though it is a distorted image, and that it is determined that it is a distorted image although the image is not distorted.

  In an image forming apparatus, a technique for suppressing erroneous detection is known. For example, there is a technique for avoiding erroneous detection due to the influence of noise due to electrical noise / unevenness of a detection symmetry plane by raising and lowering a threshold level during color resist correction. It has been proposed (see, for example, Patent Document 1).

  Further, a technique has been proposed in which two illumination means are used to detect defects by detecting the surface shape and density change of the detection surface from the brightness change (see, for example, Patent Document 2). Furthermore, a technique has been proposed in which a paper type detection sensor discriminates paper before printing, and the image printing method is changed according to the characteristics of the paper (see, for example, Patent Document 3).

JP 2011-059637 A JP 2008-070273 A JP 2006-039025 A

  However, since the influence of the paper shape on the output changes depending on the presence and amount of toner, it is impossible to calculate only the influence of the paper surface accurately with any technique, and to the paper surface detection output of the paper surface shape. Since it was not possible to eliminate the influence of the error, misdetection of the file occurred.

  The present invention has been made to solve such a problem, and provides an image forming apparatus capable of suppressing an erroneous detection of a file by eliminating the influence of the surface shape of the paper surface on the paper surface detection output. With the goal.

  In order to solve the above-described problems, an invention according to claim 1 includes an image forming unit that forms an image on a sheet, a sheet surface detection sensor that optically reads the sheet surface of the sheet, and a sheet surface detection output acquired by the sheet surface detection sensor. The image forming apparatus includes a control unit that corrects the paper surface detection output based on correlation data between the paper surface shape and the toner adhesion amount from the toner adhesion amount acquired from the image data of the image formed on the paper.

  In the invention according to claim 2, the control unit reads the non-image forming surface before image formation with the paper surface detection sensor, acquires the paper surface shape data from the paper surface detection output, and the image formation surface after image formation with the paper surface detection sensor. The image forming apparatus according to claim 1, wherein the toner surface detection data is acquired from the paper surface detection output, and correlation data between the paper surface shape and the toner adhesion amount is calculated and stored.

  According to a third aspect of the present invention, the control unit calculates the length of the boundary line between the paper surface and the toner surface from the image data, and corrects the paper surface detection output from the correlation between the sum of the boundary lines and the error of the toner adhesion amount. Item 3. The image forming apparatus according to Item 1 or 2.

  According to a fourth aspect of the present invention, the paper surface detection sensor includes a separation unit that separates polarized light into S-polarized light and P-polarized light, and the control unit selects a paper surface detection output acquired with a polarization component having high sensitivity with respect to the paper surface shape. The image forming apparatus according to claim 1.

  The invention according to claim 5 is the image according to any one of claims 1 to 4, wherein the control unit changes a back surface color at the time of paper surface detection to control variation in paper surface detection output due to a paper surface shape. Forming device.

  According to a sixth aspect of the present invention, the control unit forms a paper surface detection image outside the image forming region, and controls fluctuations in the paper surface detection output depending on the paper surface shape. This is an image forming apparatus.

  According to the present invention, it is possible to eliminate the influence of the surface shape of the paper surface on the paper surface detection output.

1 is a configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment. 3 is a functional block diagram illustrating an example of a control function of the image forming apparatus according to the present exemplary embodiment. FIG. 6 is an explanatory diagram illustrating a relationship between a toner adhesion amount and a fluctuation range of a paper surface detection output. FIG. 6 is a graph showing the relationship between the toner adhesion amount and the amplification factor of the fluctuation range of the paper surface detection output due to paper surface unevenness. 6 is an explanatory diagram illustrating an example of conversion of toner adhesion amount. FIG. 4 is a flowchart illustrating an example of an operation of the image forming apparatus according to the present exemplary embodiment. FIG. 10 is an explanatory diagram illustrating an example of threshold calculation in consideration of toner adhesion amount and paper surface shape. FIG. 10 is an explanatory diagram illustrating an example of threshold calculation in consideration of toner adhesion amount and paper surface shape. FIG. 10 is an explanatory diagram illustrating an example of threshold calculation in consideration of toner adhesion amount and paper surface shape. FIG. 10 is an explanatory diagram illustrating an example of threshold calculation in consideration of toner adhesion amount and paper surface shape. 10 is a flowchart illustrating a modification of the image forming apparatus according to the present embodiment. It is explanatory drawing which shows the other modification of the image forming apparatus of this Embodiment. 6 is a graph showing the relationship between the length of the boundary between the toner surface and the paper surface and the error in toner adhesion amount. It is explanatory drawing which shows the other modification of the image forming apparatus of this Embodiment. It is explanatory drawing which shows the relationship between P / S polarization | polarized-light and a paper surface detection output. It is explanatory drawing which shows the other modification of the image forming apparatus of this Embodiment. It is explanatory drawing which shows the relationship between a back surface color and a paper surface detection output. It is explanatory drawing which shows the other modification of the image forming apparatus of this Embodiment. It is explanatory drawing which shows the relationship between the state of a paper surface, and a paper surface detection output.

  Hereinafter, an embodiment of an image forming apparatus of the present invention will be described with reference to the drawings.

<Example of Configuration of Image Forming Apparatus of Embodiment>
FIG. 1 is a configuration diagram illustrating an example of an image forming apparatus according to the present embodiment. The image forming apparatus 1A is an electrophotographic image forming apparatus, and in this example, a plurality of photoconductors face a single intermediate transfer belt and are arranged in the vertical direction to form a full-color image. This is a so-called tandem color image forming apparatus.

  The image forming apparatus 1 </ b> A includes an image forming unit 11 that forms an image on a sheet P. The image forming apparatus 1 </ b> A includes a transport unit 21 that transports the paper P.

  The image forming unit 11 is an example of an image forming unit, and forms an image on the paper P by a process of charging, exposure, development, transfer, and fixing. The image forming unit 11 forms a toner image forming unit 11Y that forms a yellow (Y) toner image, a toner image forming unit 11M that forms a magenta (M) toner image, and a cyan (C) toner image. A toner image forming unit 11 </ b> C and a toner image forming unit 11 </ b> BK for forming a black (BK) toner image are provided.

  The toner image forming unit 11Y includes a photosensitive drum Y and a charging unit 12Y, an optical writing unit 13Y, a developing device 14Y, and a drum cleaner 15Y arranged around the photosensitive drum Y. Similarly, the toner image forming units 11M, 11C, and 11BK are the photosensitive drums M, C, and BK and the charging units 12M, 12C, and 12BK, the optical writing units 13M, 13C, and 13BK, and the developing device 14M that are disposed around the photosensitive drums M, C, and BK. , 14C, 14BK and drum cleaners 15M, 15C, 15BK.

  The developing devices 14Y, 14M, 14C, and 14BK are examples of developing units, and the developing device 14Y supplies toner to the photosensitive drum Y that is a photosensitive member. The developing device 14M supplies toner to the photosensitive drum M that is a photosensitive member, the developing device 14C supplies toner to the photosensitive drum C that is a photosensitive member, and the developing device 14BK is a photosensitive member that is a photosensitive member. Toner is supplied to the body drum BK.

  The photosensitive drum Y is an example of an image carrier, and the surface is uniformly charged by the charging unit 12Y, and a latent image is formed on the photosensitive drum Y by scanning exposure by the optical writing unit 13Y. The photosensitive drum Y is supplied with toner from the developing device 14Y, and the latent image is developed to be visualized. As a result, a toner image corresponding to yellow is formed on the photosensitive drum Y as a predetermined color image.

  The photosensitive drum M is an example of an image carrier, and the surface is uniformly charged by the charging unit 12M, and a latent image is formed on the photosensitive drum M by scanning exposure by the optical writing unit 13M. The photosensitive drum M is supplied with toner from the developing device 14M, and the latent image is developed to be visualized. As a result, a toner image corresponding to magenta is formed on the photosensitive drum M.

  The photosensitive drum C is an example of an image carrier, and the surface is uniformly charged by the charging unit 12C, and a latent image is formed on the photosensitive drum C by scanning exposure by the optical writing unit 13C. The photosensitive drum C is supplied with toner from the developing device 14C, and the latent image is developed to be visualized. As a result, a toner image corresponding to cyan is formed on the photosensitive drum C.

  The photosensitive drum BK is an example of an image carrier, and the surface is uniformly charged by the charging unit 12BK, and a latent image is formed on the photosensitive drum BK by scanning exposure by the optical writing unit 13BK. The photosensitive drum BK is supplied with toner from the developing device 14BK, and the latent image is developed to be visualized. As a result, a toner image corresponding to black is formed on the photosensitive drum BK.

  The image forming unit 11 includes a transfer unit 16 that transfers the toner image onto the paper P. The transfer unit 16 is an example of a transfer unit, and an intermediate transfer belt 17 to which a toner image formed on each of the photosensitive drums Y, M, C, and BK is primarily transferred, and a toner that is primarily transferred to the intermediate transfer belt 17. A secondary transfer roller 18 for transferring the image onto the paper P is provided.

  The intermediate transfer belt 17 is an example of an image carrier, and is provided on the side opposite to one surface of the paper P that is transported through the transport unit 21. The toner images formed on the photoconductive drums Y, M, C, and BK are transferred to the intermediate transfer belt 17 by the primary transfer rollers 17Y, 17M, 17C, and 17BK by driving the intermediate transfer belt 17 in the direction of the arrow. The image is sequentially transferred to a predetermined position.

  The secondary transfer roller 18 is an example of a secondary transfer unit, and is provided to face the intermediate transfer belt 17 on the side facing the other surface of the paper P transported through the transport unit 21. The transfer unit 16 is provided so that the secondary transfer roller 18 can move in a direction to be separated from and in contact with the intermediate transfer belt 17, and a transfer nip portion 19 is formed by pressing the secondary transfer roller 18 against the intermediate transfer belt 17. Is done.

  The secondary transfer roller 18 applies a positive voltage from the other side of the sheet or the like. As a result, the sheet P passing between the secondary transfer roller 18 and the intermediate transfer belt 17 is charged with one surface serving as an image forming surface onto which the toner image is transferred to the negative electrode and the other surface charged to the positive electrode.

  In the transfer nip portion 19, the secondary transfer roller 18 is rotationally driven at a constant speed with the intermediate transfer belt 17 in synchronization with the conveyance of the paper P by the conveyance portion 21. As a result, the paper P transported by the transport unit 21 enters between the secondary transfer roller 18 and the intermediate transfer belt 17. The intermediate transfer belt 17 is pressed by the secondary transfer roller 18. Therefore, the toner images of the respective colors primarily transferred to the intermediate transfer belt 17 are secondarily transferred onto the paper P conveyed between the intermediate transfer belt 17 and the secondary transfer roller 18.

  The image forming unit 11 includes a fixing unit 30 that fixes the toner image on the paper P. The fixing unit 30 is an example of a fixing unit, and performs a fixing process for fixing the toner image on the paper P on which the toner image is transferred. The fixing unit 30 includes a fixing belt 31 that heats the paper P and a pressure roller 32 that presses a sheet or the like against the fixing belt 31.

  The fixing belt 31 is an example of a heating rotator. The fixing belt 31 is provided on the side opposite to one surface of the sheet P on which the toner image is transferred by the transfer unit 16, and the energization of the heater 31a is controlled. The temperature of the fixing belt 31 to be applied is controlled. The pressure roller 32 is an example of a pressure rotator, and is provided on the side facing the other surface of the sheet or the like. The fixing belt 31 and the pressure roller 32 are independently driven to rotate.

  In the fixing unit 30, a fixing nip portion 33 is formed when the pressure roller 32 is pressed against the fixing belt 31. While the pressure roller 32 is in pressure contact with the fixing belt 31, the pressure roller 32 is rotationally driven and the heater 31a is energized, whereby the paper P sandwiched by the fixing nip portion 33 is conveyed. At the same time, the image is fixed on the paper P by pressure and heat.

  Next, a configuration for conveying the paper P will be described. The image forming apparatus 1A includes an external paper feed port 22 through which paper P and the like are fed from the outside, and a paper feed cassette 23 in which the paper P is stored. The external paper feed port 22 is provided on one side of the apparatus main body 10. The paper feed cassette 23 is provided in the lower part of the apparatus main body 10 so as to be able to be pulled out.

  The transport unit 21 is an example of a transport unit, and includes a main transport path 24 through which the paper P on which an image is formed by the image forming unit 11 is transported, and a reverse transport path 20 that reverses the front and back of the paper P.

  Further, the transport unit 21 includes an external paper feed transport path 25 that transports a sheet of paper P or the like fed from the external paper feed port 22 to the main transport path 24, and a paper fed from the paper feed cassette 23. A paper feed conveyance path 26 for conveying P to the main conveyance path 24 is provided.

  The main conveyance path 24 is provided inside the apparatus main body 10 and on the upper part of the paper feed cassette 23 and extends from one side of the apparatus main body 10 to the other side. One end of the main transport path 24 is connected to the external paper feed transport path 25 and the paper feed transport path 26. Further, the other end of the main transport path 24 is connected to a discharge port 27 provided on the other side of the apparatus main body 10.

  One end of the external paper feed transport path 25 is connected to the external paper feed port 22, and the other end is connected to the main transport path 24. The paper feed conveyance path 26 is provided on one side inside the apparatus main body 10, and extends in the vertical direction from the paper feed cassette 23 to the main conveyance path 24. An upper end portion of the paper feed conveyance path 26 is connected to the main conveyance path 24, and a lower end portion is connected to the paper feed cassette 23.

  The reverse conveyance path 20 is provided between the sheet feeding cassette 23 and the main conveyance path 24 inside the apparatus main body 10 and extends from the other side of the apparatus main body 10 to one side. The reverse conveyance path 20 is a first reflux conveyance branching downward from the main conveyance path 24 on the downstream side of the fixing unit 30 constituting the image forming unit 11 with respect to the conveyance direction of the paper P conveyed on the main conveyance path 24. A path 20 a and a second reflux conveyance path 20 b that merges with the main conveyance path 24 on the upstream side of the transfer section 16 constituting the image forming section 11 are provided.

  In the image forming apparatus 1 </ b> A, an image is formed on the surface of the paper P that has been transported through the main transport path 24 and passed through the fixing unit 30. When images are formed on both sides of the sheet P, the sheet P on which an image is formed on one side facing upward is conveyed from the main conveyance path 24 to the reverse conveyance path 20 through the first reflux conveyance path 20a. Then, the sheet P is reversed in the conveyance direction and conveyed from the reverse conveyance path 20 to the main conveyance path 24 through the second reflux conveyance path 20b, so that the image forming surface faces downward. As a result, the paper P is turned upside down, and an image can be formed on the other side facing upward.

  The transport unit 21 includes a switching gate 24a that switches the transport direction at a location where the main transport path 24 and the first reflux transport path 20a branch, and the transport path is switched based on settings such as the presence / absence of duplex printing.

  The image forming apparatus 1 </ b> A includes a document reading unit 40. The document reading unit 40 scans and exposes an image of a document with the optical system of the scanning exposure apparatus, reads the reflected light with a line image sensor, and obtains an image signal. Note that the image forming apparatus 1A may have a configuration in which an automatic document feeder (not shown) that feeds a document is provided at the top.

<Example of Control Function of Image Forming Apparatus of Present Embodiment>
FIG. 2 is a functional block diagram illustrating an example of a control function of the image forming apparatus according to the present embodiment. The image forming apparatus 1A includes a control unit 100 that performs a series of controls for feeding paper P, forming an image, and discharging the paper. The control unit 100 is an example of control means, and includes a microprocessor called CPU and MPU, and memory such as RAM and ROM as storage means.

  In addition, the image forming apparatus 1A includes an operation unit 101 that performs various operations such as setting of a sheet on which an image is formed and setting of the number of image formations. Further, the image forming apparatus 1A includes a first paper surface detection sensor 102a that optically reads the paper surface of the paper P before image formation, and a second paper surface detection sensor 102b that optically reads the paper surface of the paper P after image formation. Is provided.

  The first paper surface detection sensor 102a and the second paper surface detection sensor 102b are examples of the paper surface detection sensor. The paper surface detection output corresponding to the unevenness of the paper surface, the presence / absence of toner adhesion, the amount of toner adhesion, and the like, for example, voltage Output as a value. The first paper surface detection sensor 102a and the second paper surface detection sensor 102b are configured to irradiate the paper P with infrared rays by the light emitting unit and receive reflected light from the paper P with the light receiving unit, thereby eliminating the influence of the toner color. Paper surface detection output is obtained.

  As shown in FIG. 1, the first paper surface detection sensor 102 a is provided in the main transport path 24 upstream of the transfer unit 16 in the transport direction of the paper P. The second paper surface detection sensor 102 b is provided in the main transport path 24 on the downstream side of the fixing unit 30 with respect to the transport direction of the paper P.

  The image forming apparatus 1A includes a storage unit 103 that stores image data and the like. The storage unit 103 is an example of a storage unit, and holds correlation data between a paper surface shape and a toner adhesion amount, which will be described later, for each paper type.

<Example of Operation of Image Forming Apparatus of Present Embodiment>
The paper surface detection output V obtained by reading the paper surface of the paper P with an optical sensor varies depending on the uneven shape of the paper surface, and the variation width ΔV due to the paper surface shape varies depending on the toner adhesion amount.

  FIG. 3 is an explanatory diagram showing the relationship between the toner adhesion amount and the fluctuation range of the paper surface detection output. FIG. 3A schematically shows the amount of toner adhesion on the surface of the paper P, and shows a case where the image formation region B has a larger amount of toner adhesion than the image formation region A. FIG.

  When the image forming area A and the image forming area B having different toner adhesion amounts are read by an optical sensor, it can be seen that the fluctuation range ΔVn varies depending on the toner adhesion amount as shown in FIG. Then, it can be seen that the fluctuation range ΔVn is larger in the image forming region B where the toner adhesion amount is larger than that in the image forming region A.

  As described above, the fluctuation range ΔV depending on the paper surface shape is amplified as the toner adhesion amount increases. Therefore, the control unit 100 holds in advance correlation data between the amplification factor of the fluctuation range ΔV due to the paper surface shape and the toner adhesion amount. Points where there is no image data are interpolated by logarithmic approximation shown in FIG.

  FIG. 4 is a graph showing the relationship between the toner adhesion amount and the amplification factor of the fluctuation range of the paper surface detection output due to paper surface unevenness. The amplification width α of the fluctuation range of the paper surface detection output due to the paper surface unevenness varies depending on the toner adhesion amount, and the amplification factor α increases as the toner adhesion amount increases, but can be approximated by a logarithmic function f (x). Thereby, the relationship between the toner adhesion amount and the amplification factor is acquired in advance for each paper type.

When the variation width due to the paper surface shape of the non-image forming surface is ΔV0 and the variation width due to the paper surface shape of the image formation surface is ΔVn, the amplification factor α of the variation width due to the toner adhesion amount can be obtained by the following equation (1).
α = ΔVn / ΔV0 (1)

  It can be seen that the fluctuation range ΔVn increases as the adhesion amount of the toner increases, so that the amplification factor α increases. Further, when the paper type is different, the variation width ΔV0 due to the paper surface shape is different. Therefore, the control unit 100 holds correlation data between the paper surface shape and the toner adhesion amount for each paper type.

  Here, the toner adhesion amount in the image data is the adhesion amount converted from the gradation data of each color of Y (yellow), M (magenta), C (cyan), and BK (black) when outputting a certain image. It is.

  FIG. 5 is an explanatory diagram illustrating a conversion example of the toner adhesion amount. The ratio of each color of Y, M, C, and BK in the gradation data of arbitrary image data and the converted value of the toner adhesion amount of each color are determined in advance. The conversion value of the adhesion amount of toner of each color is acquired from the color and gradation data of the image in the section delimited by the size of the detection spot Sp. The processing is repeated over the entire image to calculate the total adhesion amount of toner of each color, and the obtained total adhesion amount of toner is held as the toner adhesion amount in the image data.

  FIG. 6 is a flowchart showing an example of the operation of the image forming apparatus according to the present embodiment. Hereinafter, an example of feedback to the paper surface detection output will be described with reference to each drawing. The control unit 100 stores image data for forming an image on the paper P in the storage unit 103 in step SA1 in FIG. In step SA2, the control unit 100 reads the non-image forming surface before image formation with the first paper surface detection sensor 102a, and acquires the paper surface detection output V0 on the non-image forming surface and the variation width ΔV0 depending on the paper surface shape.

  The control unit 100 selects correlation data used for correction due to the influence of the uneven shape of the paper surface from the paper surface detection output when determining the paper type of the paper P stored in the paper feed cassette 23 or when detecting the paper surface before printing. .

In step SA3 in FIG. 6, the control unit 100 calculates the toner adhesion amount from the image data, calculates the amplification factor α corresponding to the toner adhesion amount, and corrects the paper surface detection output V0 by the following equation (2). β = α × V0 (2)

In step SA4 of FIG. 6, the control unit 100 reads the image forming surface with the second paper surface detection sensor 102b, and acquires the paper surface detection output Vn on the image forming surface. In step SA5 of FIG. 6, the control unit 100 subtracts the amplification factor β from which the influence of the variation width ΔV0 due to the paper surface shape is excluded from the paper surface detection output Vn on the image forming surface, according to the following equation (3).
Vm = Vn−β (3)

  In step SA6 in FIG. 6, the control unit 100 sets a threshold value for detecting the deviation using the paper surface detection output Vm from which the influence of the paper surface shape is eliminated. These calculations are performed using the same calculation device as that used in feedback control for stabilizing the printing state during normal printing.

  7 to 10 are explanatory diagrams illustrating threshold calculation examples in consideration of the toner adhesion amount and the paper surface shape. In the following example, detection is performed on a line at one point in the width direction of the first paper surface detection sensor 102a and the second paper surface detection sensor 102b, but actually the entire image is detected.

  FIG. 7A shows a state in which a normal image E1 is formed by transferring and fixing the toner image on the paper P. FIG. In this case, as shown in FIG. 7B, the paper surface detection output is amplified by the toner adhesion amount, so that the occurrence of the error is erroneously detected at the threshold value obtained by the conventional method even though the error does not occur. May be detected.

  Therefore, as shown in FIG. 7C, correction is performed to eliminate the influence of the uneven shape of the paper surface, and the threshold value is set, so that the image E1 is erroneously detected as being distorted as shown in FIG. 7D. Can be suppressed.

  FIG. 8A shows a state in which the toner adheres to the white background portion of the paper P as a sag to form a sag portion E2. In this case, as shown in FIG. 8B, due to the uneven shape of the paper surface, there is a case where the threshold obtained by the conventional method is erroneously detected that no deviation occurs even in the deviation portion E2.

  Therefore, as shown in FIG. 8C, correction is performed to eliminate the influence of the uneven shape of the paper surface, and the threshold value is set, so that the deviation occurs in the deviation portion E2 as shown in FIG. 8D. If it is not done, it can be suppressed from being erroneously detected.

  In FIG. 9A, the toner image is transferred and fixed on the paper P to form a normal image E1. A state in which a toner adheres to the part of the image E1 to form a shading part E2 is shown. In this case, as shown in FIG. 9B, the paper surface detection output is amplified by the toner adhesion amount, so that the occurrence of the error is erroneous even though the error is not generated at the threshold value obtained by the conventional method. May be detected. Further, due to the uneven shape of the paper surface, it may be erroneously detected that no burrs have occurred even in the burred portion E2.

  Therefore, as shown in FIG. 9C, correction is performed to eliminate the influence of the uneven shape on the paper surface, and the threshold value is set, so that the image E1 is erroneously detected as being distorted as shown in FIG. 9D. Can be suppressed. In addition, it is possible to suppress erroneous detection that no deviation has occurred in the deviation portion E2.

  In FIG. 10A, the toner image is transferred and fixed on the paper P to form a normal image E1. A state in which a white background portion E3 appears as a spear in a part of the image E1 is shown. In this case, as shown in FIG. 10B, the paper surface detection output is amplified by the toner adhesion amount, so that the occurrence of the error is erroneously detected at the threshold obtained by the conventional method even though the error has not occurred. May be detected.

  Therefore, as shown in FIG. 10C, correction is performed to eliminate the influence of the uneven shape of the paper surface, and the threshold value is set, so that the image E1 is erroneously detected as a gap as shown in FIG. 10D. Can be suppressed. Further, the white background portion E3 can be detected as a scraping.

  As described above, by eliminating the influence of the paper surface shape and setting the threshold for detecting the deviation from the paper surface detection output considering the amount of toner adhesion according to the image data, it is possible to accurately detect the occurrence of the deviation. Is possible.

  In step SA7 in FIG. 6, the control unit 100 determines whether or not the error has been detected. When the error is detected, the control unit 100 executes a predetermined process at the time of the error determination in step SA8. If no error is detected, it is determined in step SA9 whether it is the final image of the job, and if it is the final image, the process ends.

<Modification of Image Forming Apparatus According to Embodiment>
FIG. 11 is a flowchart illustrating a modification of the image forming apparatus according to the present embodiment. When an unknown sheet P that does not hold correlation data between the paper surface shape and the toner adhesion amount is used, the control unit 100 stores image data for forming an image on the sheet P in the storage unit 103 in step SB1 of FIG. save. In step SB2, the control unit 100 reads the non-image forming surface before image formation with the first paper surface detection sensor 102a, and in step SB3, from the paper surface detection output V0 on the non-image forming surface and the variation width ΔV0 depending on the paper surface shape. Acquires the paper shape data.

  In step SB4 of FIG. 11, the control unit 100 reads the image forming surface after image formation by the second paper surface detection sensor 102b, and in step SB5, the paper surface detection output Vn on the image forming surface and the variation width ΔVn depending on the paper surface shape. Toner surface detection data is acquired from

  In step SB6 of FIG. 11, the control unit 100 calculates the toner adhesion amount from the image data as described above, and the correlation data between the paper surface shape and the toner adhesion amount from the toner adhesion amount, the paper surface shape data, and the toner surface detection data. And is stored in the storage unit 103 in step SB7.

  FIG. 12 is an explanatory diagram illustrating another modification of the image forming apparatus according to the present embodiment. As described above, as a result of calculating the toner amount from the image data, the same toner adhesion amount is obtained in FIGS. 12A and 12B.

  However, since the toner adhesion amount at the edge portion of the toner surface E4 increases, the actual toner adhesion amount increases in an image with many edge portions. For example, in FIG. 12A, there are more edge portions than in FIG. 12B, so the actual toner adhesion amount increases.

  FIG. 13 is a graph showing the relationship between the length of the boundary between the toner surface and the paper surface and the error in the toner adhesion amount. The control unit 100 calculates the length of the boundary line E6 between the paper surface E5 and the toner surface E4 from the image data, and corrects the paper surface detection output Vn from the correlation between the sum of the boundary lines and the error of the toner adhesion amount shown in FIG. To do. At this time, as shown in FIG. 12B, the toner surface E4 and the paper surface E5 are distinguished from each other by one line.

  FIG. 14 is an explanatory diagram showing another modification of the image forming apparatus of the present embodiment, and FIG. 15 is an explanatory diagram showing the relationship between P / S polarized light and paper surface detection output. In various optical readers, incoming and outgoing light is separated into S-polarized light and P-polarized light. Therefore, the first paper surface detection sensor 102a and the second paper surface detection sensor 102 separate the reflected light from the paper surface into S-polarized light and P-polarized light by the separation unit 102c. Then, the control unit 100 selects the paper surface detection output acquired with the polarization component having high sensitivity with respect to the paper surface shape.

  In the first paper surface detection sensor 102a and the second paper surface detection sensor 102b, the paper surface detection output obtained by reading the S-polarized light is more resistant to changes in the uneven shape of the paper surface than the paper surface detection output obtained by reading the P-polarized light. High sensitivity. For this reason, this is because S-polarized light is an irregular reflection component. Therefore, the first paper surface detection sensor 102a and the second paper surface detection sensor 102 select S-polarized light. Note that FIG. 14 is established when the diameter of the spot due to light irradiation by the first paper surface detection sensor 102a and the second paper surface detection sensor 102 is smaller than the uneven shape of the paper surface.

  FIG. 16 is an explanatory diagram showing another modification of the image forming apparatus of the present embodiment, and FIG. 17 is an explanatory diagram showing the relationship between the back color and the paper surface detection output. When the surface of the paper P is uneven, the thickness of the paper P has changed. For this reason, in the location where the thickness of the paper P is thin, it becomes easy to be influenced by the reflectance of the back color.

  As shown in FIG. 17, the fluctuation of the paper surface detection output is larger in the metal back surface portion between the back surface portion using silver metal and the black back surface portion. FIG. 17 is established when the thickness of the paper P changes due to the uneven shape of the paper surface.

  In order to reduce or amplify the fluctuation of the paper surface detection output due to the change in the thickness of the paper P, the back surface color at the time of paper surface detection is changed to control the fluctuation of the paper surface detection output due to the paper surface shape. Therefore, as shown in FIG. 16, the first paper surface detection sensor 102a and the second paper surface detection sensor 102b are configured to switch the back color of the back surface portion 102d of the reading unit. The back surface portion 102d may be configured such that different members can be replaced, or the back surface color may be switched by switching whether light is transmitted or not.

  FIG. 18 is an explanatory diagram showing another modification of the image forming apparatus of the present embodiment, and FIG. 19 is an explanatory diagram showing the relationship between the paper surface state and the paper surface detection output. As shown in FIG. 18, a predetermined paper surface detection image E8 is formed outside the image forming area E7 to facilitate detection of fluctuations in the paper surface detection output due to the paper surface shape.

  When the paper surface detection image E8 is formed with the transparent toner or the like outside the image forming region E7, the glossiness of the paper surface detection image E8 is increased, so that the paper surface detection output is increased as shown in FIG. When the paper surface of the paper P is uneven, the paper surface detection image E8 is difficult to be printed in the concave portion, so the increase in output is small. Therefore, the difference in the paper surface detection output between the convex and concave portions of the concave and convex shape on the paper surface increases, and the detection accuracy of the paper surface shape increases.

  The present invention is applied to an image forming apparatus that forms an image by transferring and fixing a toner image.

  DESCRIPTION OF SYMBOLS 1A ... Image forming apparatus, 10 ... Apparatus main body, 11 ... Image forming part, 20 ... Reverse conveyance path, 20a ... First reflux conveyance path, 20b ... Second reflux Transport path, 21... Transport section, 22... External paper feed port, 23... Paper feed cassette, 24... Main transport path, 25. Paper transport path, 27... Discharge port, 100... Control unit, 102a... First paper surface detection sensor, 102b.

Claims (6)

An image forming unit for forming an image on paper;
A paper surface detection sensor that optically reads the paper surface of the paper,
A controller for correcting the paper surface detection output based on the correlation data between the paper surface shape and the toner adhesion amount from the paper surface detection output acquired by the paper surface detection sensor and the toner adhesion amount acquired from the image data of the image formed on the paper. An image forming apparatus comprising: The control unit reads a non-image forming surface before image formation by the paper surface detection sensor, acquires paper surface shape data from the paper surface detection output, and reads an image formation surface after image formation by the paper surface detection sensor, thereby detecting the paper surface. 2. The image forming apparatus according to claim 1, wherein toner surface detection data is acquired from the output, and correlation data between a paper surface shape and a toner adhesion amount is calculated and stored. The control unit calculates the length of the boundary line between the paper surface and the toner surface from the image data, and corrects the paper surface detection output from the correlation between the sum of the boundary lines and the error of the toner adhesion amount. Or the image forming apparatus according to 2; The paper surface detection sensor includes a separation unit that separates polarized light into S-polarized light and P-polarized light,
The image forming apparatus according to claim 1, wherein the control unit selects a paper surface detection output acquired with a polarization component having high sensitivity with respect to a paper surface shape. 5. The image forming apparatus according to claim 1, wherein the control unit controls a change in a paper surface detection output depending on a paper surface shape by changing a back color at the time of paper surface detection. . The image according to any one of claims 1 to 5, wherein the control unit forms a paper surface detection image outside an image forming region, and controls variation in paper surface detection output depending on a paper surface shape. Forming equipment.

Images