JP2020046561A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can output a pattern image that has less difference in visual density between a background part and a character part.SOLUTION: An image forming apparatus forms a pattern image including a character part and a background part, and comprises: toner patch forming means that forms, on an image holding body, a toner patch for the background part at a predetermined density and toner patches for a plurality of Cin character parts different in area gradation ratio; density detection means that detects the density of the toner patches; and determination means that determines the area gradation ratio Cin of a toner patch for the character part most proximate to a detected detection value of the toner patch for the background part.SELECTED DRAWING: Figure 6

Description

  The present invention relates to an image forming apparatus.

  In an image forming apparatus for printing a tint block image including a latent image portion and a background portion, the gradation for the latent image portion and the background portion are adjusted such that the density of the latent image portion and the density of the background portion become predetermined densities, respectively. Correction means for correcting at least one of the gray scales, output means for respectively outputting an image signal for the latent image part and an image signal for the background part based on the corrected gray scale, and 2. Description of the Related Art An image forming apparatus including a printing unit that prints a copy-forgery-inhibited pattern image is known (Patent Document 1).

JP 2007-081750 A

  SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of outputting a tint block image having a small visual density difference between a background portion and a character portion.

In order to solve the above problem, the image forming apparatus according to claim 1
An image forming apparatus for forming a copy-forgery-inhibited pattern image including a character portion and a background portion,
A toner patch forming unit for forming, on an image carrier, a toner patch of the background portion having a predetermined density and a toner patch of the character portion having a plurality of Cins having different area gradation ratios;
Density detection means for detecting the density of the toner patch,
Determining means for determining the area gradation ratio Cin of the toner patch of the character portion most similar to the detected value of the detected toner patch of the background portion,
It is characterized by the following.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
The density detection unit detects the toner patch detection value, a value obtained by subtracting the dark voltage value of the density detection unit from the detection value obtained by detecting the density of the toner patch, and a detection value obtained by detecting the bare surface of the image holding member. Converted to a standardized detection value obtained by dividing the dark voltage value of the density detection unit from the obtained value, and used as the detection value of the toner patch,
It is characterized by the following.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
The determining unit is configured to determine, based on a density value obtained by linearly approximating a detection value for the plurality of Cin toner patches of the text portion, the area gradation ratio of the toner patch of the text portion that matches the density value of the toner patch of the background portion. Determine Cin,
It is characterized by the following.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
The toner patch forming unit forms each of the toner patches by applying screens having different numbers of lines in the character portion and the background portion,
It is characterized by the following.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect,
The toner patch forming unit sets each of the toner patches by setting a screen ruling applied to the character part higher than a screen ruling applied to the background part.
It is characterized by the following.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects,
The determining unit does not target the linear approximation when the detected density value of the toner patch of the character portion is lower than a predetermined threshold.
It is characterized by the following.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects,
The determining unit determines the Cin of the character portion to be a maximum value or a minimum value when the detected density value of the toner patch of the background portion does not match any of the density values that resemble the character portion linearly. , To that effect,
It is characterized by the following.

  According to the first aspect of the invention, it is possible to output a copy-forgery-inhibited pattern image having a small visual density difference between the background portion and the character portion.

  According to the second aspect of the invention, it is possible to reduce the variation error of the detection value.

  According to the third aspect of the invention, it is possible to reduce a variation error in the detection value.

  According to the fourth aspect of the invention, it is possible to suppress the density fluctuation of the background portion.

  According to the invention described in claim 5, it is possible to suppress the density fluctuation of the background portion.

  According to the invention described in claim 6, it is possible to reduce a variation error of the detection value.

  According to the seventh aspect of the present invention, it is possible to determine the Cin of the character portion and then notify the maintenance person of the device.

FIG. 2 is a schematic sectional view illustrating an internal configuration of the image forming apparatus. FIG. 2 is a functional block diagram illustrating a functional configuration of the image forming apparatus. FIG. 2 is a functional block diagram illustrating a configuration of a tint block image printing of the image forming apparatus. FIG. 7A is a diagram illustrating toner patches in a background portion and a text portion, and FIG. 7B is a diagram illustrating reading of toner patches in a background portion and a text portion. FIG. 9 is a diagram illustrating an example of a relationship between an area gradation ratio Cin and a density of a toner patch of a character portion. 6 is a flowchart illustrating a flow of a copy-forgery-inhibited pattern image printing operation in the image forming apparatus. FIG. 7A is a diagram illustrating an example of each patch pattern density read by an ADC sensor, and FIG. 7B is a diagram illustrating an example of a patch pattern density obtained by linearly approximating a standardized ADC sensor reading. FIG. 7 is a diagram illustrating an example of a copy-forgery-inhibited pattern image in which an area gradation ratio Cin of a character portion is determined. FIG. 9 is a diagram illustrating an example of linear approximation when there is a patch pattern having a density value lower than a predetermined density value threshold. FIG. 9 is a diagram illustrating determination of a patch pattern of a character portion when a density value of a character portion substantially matching a density value of a background portion cannot be selected. FIG. 9 is a diagram illustrating determination of a patch pattern of a character portion when a density value of a character portion substantially matching a density value of a background portion cannot be selected. It is a figure showing the example of information displayed on an operation display part. It is a schematic diagram explaining a tint block image.

Next, the present invention will be described in more detail with reference to the drawings and embodiments and specific examples, but the present invention is not limited to these embodiments and specific examples.
In the following description using the drawings, it should be noted that the drawings are schematic and ratios of respective dimensions and the like are different from actual ones. Illustrations other than members are omitted as appropriate.

"First Embodiment"
(1) Overall Configuration and Operation of Image Forming Apparatus (1.1) Overall Configuration of Image Forming Apparatus FIG. 1 is a schematic sectional view showing an internal configuration of an image forming apparatus 1 according to the present embodiment.
The image forming apparatus 1 includes an image forming unit 10, a sheet feeding device 20 mounted below the image forming unit 10, a reading device 30 mounted above the image forming unit 10, an operation display unit 40, The processing unit 50 and the system control device 60 are provided, and an image is printed on a recording medium such as paper by executing a print function or a copy function.

  The image forming unit 10 includes an exposure device 12, a photoreceptor unit 13, a developing device 14, a transfer device 15, and a fixing device 16. The image information received from the image processing unit 50 is sent from the paper feeding device 20. To form a toner image on the paper.

  A paper feeder 20 having paper trays 21 and 22 is provided at the bottom of the image forming unit 10, and further below the paper feeder 20, are arranged in multiple stages (in the present embodiment, two stages). The tray module TM including the paper trays T1 and T2 for storing paper is connected to supply paper to the image forming unit 10.

  A reading device 30 is disposed above the image forming unit 10. The reading device 30 reads an image of a sheet with an image sensor (not shown) such as a CCD (Charge Coupled Device) line sensor and converts the image into image data which is an electric signal.

  On the front side of the reading device 30, an operation display unit 40 as a user interface is arranged. The operation display unit 40 is configured by combining a liquid crystal display panel, various operation buttons, a touch panel, and the like, and a user of the image forming apparatus 1 inputs various settings and instructions through the operation display unit 40. Further, various information is displayed to the user of the image forming apparatus 1 via the liquid crystal display panel.

  The image processing unit 50 generates image data from print information captured from an external device (digital camera, mobile terminal, personal computer, or the like), and performs various image processing using the image data input by the reading device 30. Do.

(1.2) Configuration and Operation of Image Forming Unit 10 In the image forming apparatus 1 having such a configuration, the sheet specified by the print job is sent from the sheet feeding device 20 to the image forming unit 10 in synchronization with the image forming timing. Sent in.

  The photoconductor unit 13 includes a photoconductor drum 31 that is provided in parallel above the paper feeding device 20 and that is driven to rotate. On each photosensitive drum 31 on which an electrostatic latent image has been formed by the exposure device 12, a yellow (Y), magenta (M), cyan (C), and black (K) toner image is formed by each developing device 14. Is formed.

  The respective color toner images formed on the photoconductor drums 31 of the respective photoconductor units 13 are sequentially electrostatically transferred (primary transfer) onto the intermediate transfer belt 51 of the transfer device 15 to form a superimposed toner image in which the respective color toners are superimposed. Is done. The superimposed toner image on the intermediate transfer belt 51 is sent out from the pair of registration rollers 24 and is collectively transferred by a secondary transfer roller 52 to a sheet guided by a conveyance guide.

In the fixing device 16, a fixing nip NP (fixing region) is formed by a pressure contact region of the pair of heating module 16A and pressure module 16B.
The sheet on which the toner image has been collectively transferred in the transfer device 15 is transported to the fixing nip portion NP of the fixing device 16 via the transport guide in a state where the toner image has not been fixed, and is heated by a pair of the heating module 16A and the pressure module 16B. Then, the toner image is fixed by the action of pressing and heating.

The sheet on which the fixed toner image is formed is guided by a conveyance guide, and is discharged and accommodated from a discharge roller pair 69 to a discharge tray TR1 on the upper surface of the image forming apparatus 1.
When double-sided printing is performed automatically, the sheet is turned over and sent again to the image forming unit 10. Then, after the transfer of the toner image and the fixing of the transferred image are performed, the toner image is discharged to the discharge tray unit TR1.

(2) Functional Configuration and Operation of Image Forming Apparatus (2.1) Functional Configuration of System Control Apparatus FIG. 2 is a functional block diagram showing a functional configuration of the image forming apparatus 1 according to the present embodiment.
The image forming apparatus 1 includes a system control device 60 including a print control unit 61, a density information detection unit 62, a character part condition determination unit 63, and a copy-forgery-inhibited pattern data creation unit 64, and executes a control program stored in a memory. The operation control of the entire image forming apparatus 1 is performed.

  The print control unit 61 controls the information exchange with the sheet feeding device 20, and also includes the exposure device 12, the photoconductor unit 13, the developing device 14, the transfer device 15, and the fixing device 16 included in the image forming unit 10. Is given an operation control instruction.

  The density information detection unit 62 as an example of the density detection unit reads a toner patch (patch pattern: P [i]) formed on the intermediate transfer belt 51 as an example of an image holding member at the time of forming a copy-forgery-inhibited pattern image. The area gradation ratio Cin of the character portion data when forming the copy-forgery-inhibited pattern data is determined.

  The character part condition determining unit 63 as an example of the determining unit includes a plurality of Cin character part patch patterns having different area gradation ratios Cin from the patch pattern P [0] of the background part of the copy-forgery-inhibited pattern image acquired by the density information detecting unit 62. From the density detection values of P [i] (i = 1 to n), the area gradation ratio Cin of the character portion patch pattern closest to the background portion patch pattern P [0] is determined.

  The copy-forgery-inhibited pattern data creating unit 64 determines the image data of the background part according to the predetermined condition (dot pattern, number of lines), the predetermined condition (dot pattern, number of lines), and the character part condition determining unit 63. Based on the image data of the character portion formed in accordance with the obtained area gradation ratio Cin, copy-forgery-inhibited pattern image data to be image-synthesized with image data to be output is created.

(2.2) Copy-forgery-inhibited pattern image FIG. 3 is a functional block diagram showing a configuration of a copy-forgery-inhibited pattern image printing of the image forming apparatus 1 according to the present embodiment, and FIG. FIG. 5B is a diagram for explaining the reading of toner patches in the background portion and the character portion, FIG. 5 is a diagram showing an example of the relationship between the area gradation ratio Cin and the density of the toner patch in the character portion, and FIG. FIG. Hereinafter, printing of a tint block image in the image forming apparatus 1 according to the present embodiment will be described with reference to the drawings.

  Some receipts, securities, and various certificates have special patterns printed on the background so that characters and images emerge when copied so that they are not easily copied. This special pattern is generally called a "background pattern". By adding the background pattern to the background of the image data, a mechanism is provided to prevent the original from being easily duplicated by copying. Deterrence is being done.

  As shown schematically on the left side of FIG. 13, the copy-forgery-inhibited pattern image includes a copy-forgery-inhibited pattern character portion (hereinafter referred to as a character portion) in the background image and a portion other than the character portion (hereinafter referred to as the background portion) in the background image. It is formed by making the number of halftone dots (dot pattern) of the character part different from the number of halftone dots (dot pattern) of the background part while keeping the visual density substantially the same.

Specifically, the number of halftone dots in the character portion is set to a high number of lines that cannot be resolved by the reading device 30 (image scanner), and the number of halftone dots in the background portion is sufficiently resolved by the reading device 30. The number of lines is low.
Therefore, as shown in FIG. 13, when copying a document in which a copy-forgery-inhibited pattern image is embedded, a halftone dot pattern is read for the background portion and the halftone dot pattern is printed as it is, while the character portion is not printed. Since the halftone dot pattern is read as a region having a constant density, the character portion is printed as a non-density region (or a low-density region) by binarization.

As a result, in the printed matter obtained by copying, the density of the character portion is lower than the density of the background portion, and the character portion (that is, a warning embedded as a copy-forgery-inhibited pattern) is visually recognized.
In such a copy-forgery-inhibited pattern image, when an image forming apparatus having poor reproducibility in a low Cin area is used to form a pattern of a character portion and a background portion, isolated dots cannot be stably reproduced. There is a possibility that a difference occurs in the density of the character portion. Further, the image forming apparatus relies on the stability of the installation environment (temperature and humidity conditions) of the apparatus in order to form an image by charging a predetermined toner density to a predetermined charge amount. There is a possibility that the property may be affected. For this reason, there is a problem that the density of the printed character portion and the background portion vary, and the character portion can be seen even in the original (original image) before copying.

(2.3) Printing of Copy-forgery-inhibited Pattern Image As shown in FIG. 3, in the image forming apparatus 1, the character part condition determination unit 63 uses the density of the background part and the character part patch pattern read by the density information detection part 62 to determine Thus, the area gradation ratio Cin of the character portion data is determined. Then, the copy-forgery-inhibited pattern data creating section 64 creates copy-forgery-inhibited pattern data, synthesizes the image data of the original image with the image processing section 50, and prints out the image on the image forming section 10.

  When the image forming apparatus 1 receives such an instruction to form a copy-forgery-inhibited pattern image for copy inhibition, first, as shown in FIG. A toner patch (patch pattern P [0]) of a background portion of density and a toner patch (patch pattern P [i]: i = 1 to 9) of a character portion of a plurality of Cins having different area gradation ratios are formed. The density information detector 62 reads the density of the toner patch. As the density information detection unit 62, an ADC (Auto Density Control) sensor SR for controlling an image forming process provided in the transfer device 15 can be used.

  Here, the patch pattern P [i] of the character portion has nine density levels with different area gradation ratios Cin (P [1] to P [9]), as schematically shown as an example in FIG. . As described above, by setting the patch pattern P [i] of the character portion to a patch pattern having a different area gradation ratio Cin, the density of the background portion formed under the current image forming conditions (apparatus, temperature / humidity conditions, etc.) Image data of a character portion having a density substantially matching with the above can be created.

(3) Determination of Area Gradation Ratio Cin of Character Portion FIG. 6 is a flowchart showing the flow of a copy-forgery-inhibited pattern image printing operation in the image forming apparatus 1, and FIG. 7A shows the density of each patch pattern read by the ADC sensor. FIG. 8B is a diagram illustrating an example, FIG. 8B is a diagram illustrating an example of a patch pattern density obtained by linearly approximating a read value of a standardized ADC sensor, and FIG. 8 is an example of a copy-forgery-inhibited pattern image in which the area gradation ratio Cin of a character portion is determined; FIG. Hereinafter, determination of the area gradation ratio Cin of the character portion in the image forming apparatus 1 will be described with reference to the drawings.

Upon receiving the print job (S101), the image forming apparatus 1 determines whether a copy-forgery-inhibited pattern is set for the print job (S102).
If the copy-forgery-inhibited pattern is set in the print job (S102: Yes), the patch pattern of the background portion and the character portion is formed on the intermediate transfer belt 51 as an image carrier (S103). In this embodiment, the background portion is formed by 47 lines having a low number of lines. Further, the character portion is formed by nine patch patterns having different Cin, each having 144 lines which is a higher number of lines than the background portion.

  The patch pattern of the background portion and the character portion thus formed on the intermediate transfer belt 51 is read by the ADC sensor (S104). FIG. 7A shows an example of the density of each patch pattern (P [0] to P [9]) read by the ADC sensor. As shown in FIG. 7A, the density information detection unit 62 has a density value ADC [0] corresponding to the density of each patch pattern (P [0] to P [9]) read by the ADC sensor SR. To [9] are obtained.

As described above, since the density values ADC [0] to [9] directly read by the ADC sensor SR include the reflection state of the bare surface of the intermediate transfer belt 51 on which the toner patches are formed, the read value standard is used. (S105). Specifically, the standardized density value R-ADC is expressed by equation (1).
R-ADC = (Vpatch-Vdark) / (Vcln-Vdark) (1)
Here, the read value of the toner patch by the ADC sensor SR is Vpatch, the read value of the elementary surface of the intermediate transfer belt 51 is Vcln, and the dark voltage of the ADC sensor SR is Vdark.
FIG. 7B shows an example of density values R-ADC [0] to [9] standardized corresponding to FIG. 7A.

Next, as shown in FIG. 7B, the density values R-ADC [0] to [9] of the standardized patch patterns (P [0] to P [9]) are linearly approximated to obtain a background image. The density values R-ADC [1] to P [9] of the character portion that substantially match the density value R-ADC [0] of the copy are determined (S106 to S109).
For example, if the density value of the character portion substantially matching the density value R-ADC [0] of the background portion is R-ADC [6], the patch pattern of the character portion matching the patch pattern P [0] of the background portion Becomes P [6].

In this manner, the character part condition determination unit 63 determines the patch pattern P [0] of a plurality of Cin characters having different area gradation ratios Cin from the patch pattern P [0] of the background part of the copy-forgery-inhibited pattern image acquired by the density information detection unit 62. From the density detection values of [i] (i = 1 to 9), the area gradation ratio Cin of the character part patch pattern closest to the background part patch pattern P [0] is determined (S110).
This makes it possible to output a copy-forgery-inhibited pattern image having a small visual density difference between the background portion and the character portion.

FIG. 8 shows an example of the copy-forgery-inhibited pattern image in which the area gradation ratio Cin (P [6]) of the patch pattern of the character portion is determined in this way.
8A, a character portion P [1], FIG. 8B shows a character portion P [2], and FIG. 8C shows a character portion P [3]. (D) is a character part P [4], (e) is a character part P [5], (f) is a character part P [6], (g) is a character part P [7], and (h) is a character part. P [8] and (i) show examples in which the character part P [9] is applied.
As described above, the patch pattern P [i] (i = 1 to 9) of the character portion of a plurality of Cins having different area gradation ratios Cin from the patch pattern P [0] of the background portion of the copy-forgery-inhibited pattern image acquired by the density information detecting section 62 is different. ), By selecting the patch pattern P [6] of the character portion closest to the patch pattern P [0] of the background portion, a tint block image with a small visual density difference between the background portion and the character portion can be obtained. Can be output.

FIG. 9 is a diagram illustrating an example of linear approximation when there is a patch pattern having a density value lower than a predetermined density value threshold value.
As shown as an example in FIG. 9, the character part condition determining unit 63 includes a predetermined density value of a predetermined density value in the patch patterns (P [0] to P [9]) detected by the density information detecting unit 62. If there is a patch pattern (P [1], P [2]) having a density value lower than the threshold value, the patch pattern is not subjected to linear approximation, but is not subjected to linear approximation, and other patch patterns (P [3] to P [9]) Linear approximation is performed using the density values R-ADC [3] to [9].
For example, in the example shown in FIG. 9, the patch patterns (P [1], P [2]) having a low density value are such that the toner patches formed on the intermediate transfer belt 51 depend on the surface condition of the intermediate transfer belt 51 and the like. , Is not reproduced by the set Cin.
As a result, it is possible to reduce a variation error in the reading value of the toner patch by the ADC sensor SR.

FIGS. 10 and 11 are diagrams illustrating the determination of a patch pattern of a character portion when a density value of a character portion substantially matching the density value of the background portion cannot be selected.
In steps S106 to S109, the character part condition determining unit 63 cannot select the density values R-ADC [1] to P [9] of the character part substantially matching the density value R-ADC [0] of the background part ( S107: No), as shown in FIG. 10, it is determined to be P [9] at which the density value of the patch pattern of the character portion becomes maximum (S111).
As shown in FIG. 11, when the density value R-ADC [0] of the background portion is higher than any of the density values R-ADC [1] to P [9] of the character portion, the patch of the character portion It is determined that P [1] at which the density value of the pattern becomes maximum (S111).
Then, the character part condition determining unit 63 determines the area gradation ratio Cin of the patch pattern of the character part (S109).

  FIG. 12 is a diagram illustrating an example of notification displayed on the operation display unit 40. When the image forming apparatus 1 determines the area gradation ratio Cin of the patch pattern of the character portion to the maximum value or the minimum value, as shown in FIG. 12 as an example, the image forming apparatus 1 notifies the operation display unit 40 of the fact. To prompt the maintenance personnel of the device to adjust the device.

In the above description, the copy-forgery-inhibited pattern image is formed with the number of lines of the dot pattern in the background portion being low (47 lines) and the number of lines of the dot pattern in the character portion being high (144 lines). Assuming that the number of lines of the dot pattern of the portion is high (144 lines) and the number of lines of the dot pattern of the character portion is low (47 lines), the density of the character portion becomes higher than the density of the background portion during copying. The copy-forgery-inhibited pattern image may be formed such that the character portion is visually recognized.
Further, in the above description of the embodiment, the number of patches (n = 9) and the area gradation ratio (Cin) of the patch pattern are merely examples, and other numbers and values may be used.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Image forming part 13 ... Photoconductor unit 31 ... Photoconductor drum 14 ... Developing device 15 ... Transfer device 51 ... Intermediate transfer belt 20 ... Paper feeder 30 Reading device 40 Operation display unit 50 Image processing unit 60 System controller 61 Print controller 62 Density information detector 63 Character part condition determining unit 64: background pattern data creating unit P [0] to P [9]: patch pattern SR: ADC sensor

Claims (7)

An image forming apparatus for forming a copy-forgery-inhibited pattern image including a character portion and a background portion,
A toner patch forming unit for forming, on an image carrier, a toner patch of the background portion having a predetermined density and a toner patch of the character portion having a plurality of Cins having different area gradation ratios;
Density detection means for detecting the density of the toner patch,
Determining means for determining the area gradation ratio Cin of the toner patch of the character portion most similar to the detected value of the detected toner patch of the background portion,
An image forming apparatus comprising: The density detection unit detects the toner patch detection value, a value obtained by subtracting the dark voltage value of the density detection unit from the detection value obtained by detecting the density of the toner patch, and a detection value obtained by detecting the bare surface of the image holding member. Converted to a standardized detection value obtained by dividing the dark voltage value of the density detection unit from the obtained value, and used as the detection value of the toner patch,
The image forming apparatus according to claim 1, wherein: The determining unit is configured to determine, based on a density value obtained by linearly approximating a detection value for the plurality of Cin toner patches of the text portion, the area gradation ratio of the toner patch of the text portion that matches the density value of the toner patch of the background portion. Determine Cin,
The image forming apparatus according to claim 1, wherein: The toner patch forming unit forms each of the toner patches by applying screens having different numbers of lines in the character portion and the background portion,
The image forming apparatus according to claim 1, wherein: The toner patch forming unit sets each of the toner patches by setting a screen ruling applied to the character part higher than a screen ruling applied to the background part.
The image forming apparatus according to claim 4, wherein: The determining unit does not target the linear approximation when the detected density value of the toner patch of the character portion is lower than a predetermined threshold.
The image forming apparatus according to claim 1, wherein: The determining unit determines the Cin of the character portion to be a maximum value or a minimum value when the detected density value of the toner patch of the background portion does not match any of the density values that resemble the character portion linearly. , To that effect,
The image forming apparatus according to claim 1, wherein:

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