JP5885688B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  A certain image forming apparatus calculates toner consumption from the value of image data before gamma correction for the image data of the gradation portion of the image data, and calculates the toner amount from the number of dots for the image data of the character / line drawing portion. The consumption is calculated (for example, refer to Patent Document 1).

  On the other hand, an image forming apparatus performs calibration for adjusting the characteristics of gamma correction applied to the gradation portion. In the calibration, a halftone toner pattern is developed, and the gamma correction characteristic is adjusted based on the measured density of the toner pattern.

JP 2012-48055 A

  As described above, the characteristics of gamma correction applied to the gradation part are appropriately adjusted by calibration. However, when calibration is not separately performed for adjusting the density characteristic of the character / line drawing part, The density varies depending on the state, and there is a possibility that the toner consumption amount for the character / line drawing portion may not be accurately calculated.

  Therefore, it is conceivable that the density sensor measures the density of the solid toner patch and calculates the toner consumption for the character / line drawing portion in consideration of the measured density.

  For example, it is conceivable to correct the toner consumption amount of a character / line drawing portion based on the measured density. In this case, the calculation of the toner consumption is accurate, but the image quality of the character / line drawing portion is not improved.

  Further, for example, based on the measured density, it is conceivable to adjust the processing conditions (quantization threshold, etc.) so as to match the calculated toner consumption. In that case, the calculation accuracy of the toner consumption is improved, but the image quality of the character / line drawing portion is likely to be lowered.

  As described above, it is difficult to accurately calculate the toner consumption amount for the character / line drawing portion while improving the image quality of the character / line drawing portion.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus that accurately calculates the toner consumption amount for a character / line drawing portion while improving the image quality of the character / line drawing portion. To do.

An image forming apparatus according to the present invention performs calibration using an image carrier that carries a calibration toner pattern, a sensor that detects the density of the calibration toner pattern, and the density detected by the sensor. A correction amount adjustment unit to perform, a pixel count unit that counts the value of the image data of the gradation unit before gamma correction, and a dot count unit that counts dots in the image data of the character / line drawing unit immediately before the pulse width modulation, A toner consumption calculation unit that specifies a toner consumption amount of a gradation part based on a count value by the pixel count unit and a toner consumption amount of a character / line drawing part based on a count value by the dot count unit ; Prepare. The calibration toner pattern has a plurality of patches each having a screen pattern corresponding to each of a plurality of densities, and some or all of the plurality of patches are linear with a dot width corresponding to the density. Has a pattern. The correction amount adjustment unit adjusts the density correction amount for the gradation part by adjusting the correction amount of the gamma correction for the gradation part based on the density detected by the sensor, and also adjusts the character / line drawing. The density correction amount for the character / line drawing portion is adjusted by adjusting the correction amount of the pulse width in the pulse width modulation for the portion. Further, the correction amount adjustment unit applies different correction amounts to the edge portion and the portions other than the edge portion for the character / line drawing portion. Then, the toner consumption calculation unit applies different coefficients to the count value by the pixel count unit and the count value by the dot count unit, respectively, and calculates the toner consumption of the gradation unit and the character / line drawing unit. .

  According to the present invention, the image quality of the character / line drawing part as well as the gradation part is improved by the calibration, and the toner consumption amount for the character / line drawing part is accurately calculated.

FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a block diagram illustrating details of a processing unit in the arithmetic processing apparatus in FIG. FIG. 4 is a diagram illustrating an example of a patch in the calibration toner pattern used by the correction amount adjustment unit in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a side view showing a part of a mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus is an apparatus having an electrophotographic printing function, such as a printer, a facsimile machine, a copying machine, or a multifunction machine.

  The image forming apparatus of this embodiment has a tandem color developing device. The color developing device includes photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing devices 3a to 3d. The photoconductor drums 1a to 1d are four-color photoconductors of cyan, magenta, yellow, and black. The photosensitive drums 1a to 1d are made of amorphous silicon, for example.

  The exposure devices 2a to 2d irradiate the photosensitive drums 1a to 1d with laser beams, scan the laser beams on the photosensitive drums 1a to 1d, and control the pulse width of the laser beams to form an electrostatic latent image. It is. The laser beam is scanned in a direction (main scanning direction) perpendicular to the rotation direction (sub-scanning direction) of the photosensitive drums 1a to 1d. The exposure apparatuses 2a to 2d have a laser scanning unit including a laser diode that is a light source of laser light and an optical element (lens, mirror, polygon mirror, etc.) that guides the laser light to the photosensitive drums 1a to 1d.

  Further, around the photosensitive drums 1a to 1d, a charger such as a scorotron, a cleaning device, a static eliminator and the like are arranged. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after the primary transfer, and the static eliminator neutralizes the photosensitive drums 1a to 1d after the primary transfer.

  The developing devices 3a to 3d attach the toner cartridge filled with toners of four colors, cyan, magenta, yellow, and black, and the toner conveyed from the toner hopper in the toner cartridge to the photosensitive drums 1a to 1d. A developing unit, and the toner is attached to the electrostatic latent images on the photosensitive drums 1a to 1d to form a toner image. The toner is transported from the toner hopper to the developing unit by a toner transport unit that is operated by a driving device such as a motor (not shown).

  The photosensitive drum 1a, the exposure device 2a, and the developing device 3a develop magenta, and the photosensitive drum 1b, the exposure device 2b, and the developing device 3b develop cyan, the photosensitive drum 1c, and the exposure device. Yellow development is performed by the device 2c and the developing device 3c, and black development is performed by the photosensitive drum 1d, the exposure device 2d, and the developing device 3d.

  The intermediate transfer belt 4 is an annular image carrier (intermediate transfer member) that comes into contact with the photosensitive drums 1a to 1d and primarily transfers the toner images on the photosensitive drums 1a to 1d. The intermediate transfer belt 4 is stretched around the driving roller 5 and circulates in the direction from the contact position with the photosensitive drum 1d to the contact position with the photosensitive drum 1a by the driving force from the driving roller 5.

  The transfer roller 6 brings the conveyed paper into contact with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the paper. The sheet on which the toner image has been transferred is conveyed to the fixing device 9 and the toner image is fixed on the sheet.

  The roller 7 has a cleaning brush, and the cleaning brush is brought into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image onto the paper.

  The sensor 8 irradiates the intermediate transfer belt 4 with a light beam, and detects reflected light from the surface of the intermediate transfer belt 4 or a toner pattern on the surface. For example, at the time of calibration, the sensor 8 irradiates a predetermined region of the intermediate transfer belt 4 with a light beam, detects the reflected light, and outputs an electrical signal corresponding to the light amount.

  That is, at the time of calibration, a calibration toner pattern is carried on the intermediate transfer belt 4, and the sensor 8 detects the density of a patch corresponding to each of a plurality of densities in the calibration toner pattern.

  FIG. 2 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. As illustrated in FIG. 2, the image forming apparatus includes a communication device 11, an arithmetic processing device 12, and a printing device 13.

  The communication device 11 can be connected to a host device via a network or a peripheral device interface, and performs data communication using a predetermined communication protocol.

  The arithmetic processing unit 12 includes a computer having a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an ASIC (Application Specific Integrated Circuit), etc., and software and / or hardware. Various processing units are realized by hardware.

  In this embodiment, processing units such as a communication processing unit 21, a print request processing unit 22, an image processing unit 23, a controller 24, a toner consumption calculation unit 25, and a correction amount adjustment unit 26 are realized by the arithmetic processing unit 12. The FIG. 3 is a block diagram illustrating details of the processing unit in the arithmetic processing unit 12 in FIG.

  The printing apparatus 13 is an internal device that prints a document image with a mechanical configuration as shown in FIG.

  The communication processing unit 21 is a processing unit that controls the communication device 11 to execute data communication with a host device or the like. For example, the communication processing unit 21 receives document data as a print request from the host device.

  The print request processing unit 22 receives a print request based on a user operation on the operation panel or a print request supplied from the host device, and executes a print job corresponding to the request. For example, when document data in a predetermined data format such as PDL (Page Description Language) or PDF (Portable Document Format) is received as a print request from the host device, the print request processing unit 22 reads image data from the document data. Is generated. This image data is bitmap data after rasterization.

  In addition, the image processing unit 23 specifies the pixel attribute of each pixel from the attribute data of each pixel in the rasterized image data, and the character / line drawing unit (solid area such as a character or line drawing) and the floor in the image data. Tone parts (regions having a halftone such as photographs) are identified and separated from each other. Further, the image processing unit 23 converts the color space of the image data. Here, the image processing unit 23 converts RGB image data into CMYK image data of toner color.

  The image processing unit 23 includes a gamma correction unit 31, a screen processing unit 32, and an edge correction unit 33.

  As shown in FIG. 3, the image data of the gradation part is input to the gamma correction part 31. The gamma correction unit 31 corrects the halftone value of the image data so that the relationship between the value of the image data and the toner density is linear for each color of CMYK. For example, the gamma correction unit 31 has a conversion table, and corrects the image data of the gradation unit with reference to the conversion table. In that case, the conversion table is adjusted in the calibration.

  The screen processing unit 32 performs screen processing on the image data after the gamma correction, and outputs print data generated by the screen processing.

  The edge correction unit 33 performs edge correction processing such as smoothing.

  The controller 24 also monitors and controls internal devices such as the printing apparatus 13. Further, the controller 24 controls the drive source (not shown) for driving the above-described roller, the bias application circuit for applying the development bias and the primary transfer bias, and the exposure devices 2a to 2d to develop and transfer the toner image. And fixing, feeding, printing, and paper discharge are executed. The developing bias is applied between the photosensitive drums 1a to 1d and the developing devices 3a to 3d, respectively, and the primary transfer bias is applied between the photosensitive drums 1a to 1d and the intermediate transfer belt 4, respectively.

  Further, the controller 24 has a pulse width setting unit 41.

  The pulse width setting unit 41 performs pulse width modulation on each pixel value of the print data, and sets a period during which the exposure apparatus 2i (i = a, b, c, d) is lit for each pixel. Specifically, the pulse width setting unit 41 specifies whether each pixel belongs to the gradation part or the character / line drawing part based on the pixel attribute data, and the screen processing part 32 for the gradation part pixel. The print data from the edge correction unit 33 is used for the pixels of the character / line drawing part, and the pulse width corresponding to the value of the print data (the width of the exposure pulse of the exposure apparatus 2i) is used. Set.

  The pulse width setting unit 41 has an edge correction table for designating a correction amount for pixels around the edge. For the pixels of the character / line drawing unit, the character / line drawing unit is referred to by referring to the edge correction table. For these pixels, the pulse width is corrected according to the pixel value pattern around the pixel.

  Further, the toner consumption calculation unit 25 calculates the toner consumption accompanying printing by the printing apparatus 13. Further, the toner consumption calculation unit 25 calculates the remaining amount of toner in the toner cartridge from the toner consumption. Further, the toner consumption amount calculation unit 25 displays the toner consumption amount and the toner remaining amount on an operation panel (not shown), or displays a warning message on an operation panel (not shown) when the toner remaining amount is low. To do.

  The toner consumption amount calculation unit 25 accumulates, for example, one page of toner consumption amount values for each pixel attribute for each pixel attribute, and, for example, according to Equation (1), the accumulated value and coefficient for each of the plurality of pixel attributes. The toner consumption is calculated based on the sum of the products.

  Tp = a * Xp + b * Yp (1)

  Where Tp is the total toner consumption for one page, a is a coefficient for the character / line drawing part, b is a coefficient for the gradation part, and Xp is one page for the character / line drawing part. Yp is an integrated value for one page for the gradation part.

  The toner consumption calculation unit 25 includes a pixel count unit 51 and a dot count unit 52.

  The pixel count unit 51 counts the value of the image data of the gradation part before gamma correction. The pixel counting unit 51 has a built-in lookup table that indicates the correspondence between the image data value and the toner consumption amount, and identifies the toner consumption amount corresponding to the image data value with reference to the lookup table. Then, the specified toner consumption is integrated.

  The dot count unit 52 counts dots in the image data of the character / line drawing unit immediately before the pulse width modulation. That is, the dot count unit 52 counts dots in the image data quantized corresponding to the pulse width resolution (for example, 16 gradations) by the pulse width setting unit 41. The dot count unit 52 has a built-in lookup table that indicates the correspondence between the number of dots and the toner consumption, and the toner consumption corresponding to the number of dots is identified by referring to the lookup table. Accumulate toner consumption.

  That is, the toner consumption calculation unit 25 specifies the toner consumption amount of the gradation part based on the count value by the pixel count unit 51, and calculates the toner consumption amount of the character / line drawing part based on the count value by the dot count unit 52. Identify.

  Here, the toner consumption amount calculation unit 25 applies the above-described coefficients a and b, which are different from each other, to the count value Xp by the pixel count unit 51 and the count value Yp by the dot count unit 52, respectively. Part of toner consumption is calculated.

  Further, the correction amount adjustment unit 26 sets the halftone density correction amount at a timing such as when the image forming apparatus is started up, when a predetermined number of prints have been performed since the previous calibration, or when requested by the user. Tone calibration for adjustment is executed.

  As a result, the gradation characteristics are not easily affected by changes in the charging characteristics of the photosensitive drums 1a to 1d, and the toner consumption characteristics of the gradation portions are not easily affected by changes in the charging characteristics of the photosensitive drums 1a to 1d. In the image forming apparatus of this embodiment, since the total time for calibration becomes long, the density calibration for the character / line drawing part is not performed separately, and based on the measured density obtained by the gradation calibration, Adjust the density correction amount in the text / line drawing area.

  The correction amount adjustment unit 26 supplies the calibration toner pattern print data to the controller 24, develops the calibration toner pattern, and uses the density of the calibration toner pattern detected by the sensor 8 to perform calibration. Perform

  The calibration toner pattern has a plurality of patches each having a screen pattern corresponding to each of a plurality of densities. Some or all of the plurality of patches have a linear pattern with a dot width corresponding to the density.

  FIG. 4 is a diagram showing an example of a patch in the calibration toner pattern used by the correction amount adjustment unit 26 in FIG.

  The linear pattern referred to here is a pattern in which dots are continuous in a linear manner like patches 101-3 to 101-8 in FIG.

  That is, a pattern in which dots are discretely scattered like the patches 101-1 and 101-2 in FIG. 4 is not a linear pattern.

  The patches 101-3 to 101-8 have a linear pattern having a dot width corresponding to the density. That is, the width of each dot becomes longer as the density becomes higher.

  The correction amount adjusting unit 26 adjusts the density correction amount for the gradation portion and the density correction amount for the character / line drawing portion based on the density detected by the sensor 8.

  Specifically, the correction amount adjustment unit 26 adjusts the correction amount of gamma correction for the gradation portion based on the density detected by the sensor 8, and the patches 101-3 to 101-8 having linear patterns. The correction amount of the pulse width in the pulse width modulation for the character / line drawing part is adjusted based on the detected density. That is, if the detected concentration is too high, the pulse width correction amount is adjusted so that the pulse width is shortened. If the detected concentration is too low, the pulse width correction amount is adjusted so that the pulse width is increased. Is adjusted.

  At this time, the correction amount adjustment unit 26 may adjust the correction amount of the pulse width so that different correction amounts are applied to the edge portion and the portion other than the edge portion for the character / line drawing portion.

  As described above, when a table is used for gamma correction and pulse width correction, the data value in the table is adjusted.

  Next, an operation during calibration of the image forming apparatus will be described.

  When the correction amount adjustment unit 26 detects the predetermined calibration timing as described above, it executes the following calibration.

  First, the correction amount adjustment unit 26 supplies the print data of the calibration toner pattern including the patches 101-3 to 101-8 having the linear pattern as described above to the pulse width setting unit 41, and performs calibration. The toner pattern is developed on the photosensitive drum 1 i (i = a, b, c, d) with toner, and the toner image of the calibration toner pattern is transferred to the intermediate transfer belt 4.

  When the density of the patches 101-1 to 101-8 in the calibration toner pattern on the intermediate transfer belt 4 is detected by the sensor 8, the correction amount adjusting unit 26 detects all the patches 101-1 to 101-101. The gamma correction table of the gamma correction unit 31 is adjusted using the density of −8, and the correction amount adjustment unit 26 uses only the density of the patches 101-3 to 101-8 having a linear pattern to The pulse width correction table of the width setting unit 41 is adjusted (that is, the pulse width corresponding to each density is adjusted).

  As described above, according to the above embodiment, the table for pulse width correction after adjustment by calibration is used for printing after calibration and calculation of toner consumption. As a result, the image quality of the character / line drawing portion is improved without separately performing density calibration for the character / line drawing portion, and the toner consumption amount for the character / line drawing portion is accurately calculated.

  The above-described embodiments are preferred examples of the present invention, but the present invention is not limited to these, and various modifications and changes can be made without departing from the scope of the present invention. is there.

  The present invention is applicable to, for example, an electrophotographic image forming apparatus.

4 Intermediate transfer belt (an example of an image carrier)
8 Sensor 25 Toner Consumption Calculation Unit 26 Correction Amount Adjustment Unit 51 Pixel Count Unit 52 Dot Count Unit 101-1 to 101-8 Patch

Claims (4)

An image carrier carrying a calibration toner pattern;
A sensor for detecting the density of the calibration toner pattern;
A correction amount adjustment unit that performs calibration using the density detected by the sensor ;
A pixel count unit that counts the value of the image data of the gradation part before gamma correction;
A dot count unit that counts dots in the image data of the character / line drawing unit immediately before the pulse width modulation;
A toner consumption calculation unit that specifies a toner consumption amount of a gradation portion based on a count value by the pixel count unit and a toner consumption amount of a character / line drawing unit based on a count value by the dot count unit. ,
The calibration toner pattern has a plurality of patches each having a screen pattern corresponding to each of a plurality of densities,
A part or all of the plurality of patches has a linear pattern with a dot width corresponding to the density,
The correction amount adjustment unit adjusts the density correction amount for the gradation part by adjusting the correction amount of the gamma correction for the gradation part based on the density detected by the sensor, and for the character / line drawing part. By adjusting the correction amount of the pulse width in the pulse width modulation, the density correction amount for the character / line drawing part is adjusted ,
The correction amount adjustment unit applies a different correction amount between the edge portion and the non-edge portion for the character / line drawing portion,
The toner consumption amount calculation unit applies different coefficients to the count value by the pixel count unit and the count value by the dot count unit, respectively, to calculate the toner consumption amount of the gradation unit and the character / line drawing unit;
An image forming apparatus. The pixel count unit identifies a toner consumption amount corresponding to the value of the image data with reference to a lookup table indicating a correspondence relationship between the value of the image data and the toner consumption amount, and determines the identified toner consumption amount. the image forming apparatus according to claim 1, wherein the by accumulating. The dot count unit, an image forming apparatus according to claim 1, wherein counting the dots in the image data after quantization. The correction amount adjustment unit performs the calibration when the image forming apparatus is activated, when a predetermined number of prints have been performed since the previous calibration, and when requested by the user. The image forming apparatus according to any one of claims 1 to 3 .

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