JP2009159490A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which controls toner refilling in combination of pixel refilling control and sensor refilling control, to calculate the upper limit value of an appropriate amount of toner even when desired image processing is performed for input image data and an image is formed based on the image data subjected to image processing. <P>SOLUTION: Image data read by a reader is input to an image processing device 1000, first pixel information 1002 is obtained by a pixel information calculation part 1001, and based on attribute information 1003, the first pixel information is converted to second pixel information 1005 by a pixel information conversion part 1004. On the basis of the second pixel information and density detected by a toner density detecting device which is not shown in the figure, the upper limit value of the amount of toner to be refilled to a developing device from tanks, bottles, or the like of various colors of toner is calculated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method such as a copying machine, a facsimile, a printer, a plotter, and a multifunction machine.

  In recent years, image forming apparatuses tend to be faster and have higher image quality, and in particular, much attention has been paid to high stability of image density. In order to stabilize the image density, optimal control of toner replenishment is necessary, and the control method is an important issue at present.

  Further, in recent image forming apparatuses, the particle size of the developer has been reduced in order to improve the image quality. In particular, reducing the particle size of the carrier in the two-component development deteriorates the fluidity of the developer. For this reason, even if replenishment toner enters, it is difficult to mix, and if a large amount of toner is replenished, toner that does not mix with the carrier is generated, causing toner scattering and high image quality. That is, in order to reduce the particle size of the developer, more appropriate replenishment control is required.

  The means for calculating the replenishment amount in the toner replenishment control can be roughly divided into a method for calculating and replenishing toner density from the density sensor value (sensor replenishment control), the number of pixels to be written, or the image area to be written. There are two methods (pixel replenishment control) in which toner consumption is converted from pixel information such as rate and the amount is replenished.

  This pixel replenishment control is a control method in which toner is replenished by the amount of the output image (consumed toner), so there is an advantage that the toner replenishment amount can be calculated with relatively high accuracy. The amount of toner used depends on the ratio of the line image to the solid image of the image data, and even the line image, the vertical line image ratio, the horizontal line image ratio, etc. Therefore, it is difficult to control the image density to be constant only by replenishment control (pixel proportional control) proportional to the image area ratio. For example, a line image and a solid image have the same number of pixels but have different toner consumption. Therefore, if there are many line images, the toner consumption will be greater than that of a solid image. This is because, in the line image, the toner adhesion amount increases compared to the solid portion due to the edge effect of the latent image.

  On the other hand, as sensor replenishment control, a replenishment control method using a density sensor or the like utilizing the fact that the magnetic permeability of the developer in the developing device varies with the toner density is known. However, in this replenishment control method, as described in many prior arts, there are fluctuation factors such as a decrease in sensor output due to empty developer agitation and an increase in sensor output due to long-term standing. On the other hand, if it is so large that it cannot be ignored, if it is replenished without correction such as the upper limit processing, density fluctuation will occur.

  Therefore, as a toner replenishment control method, a control method combining pixel replenishment control and sensor replenishment control is generally used. However, even with this combination control, the replenishment amount may fluctuate. For example, when an image having a high image density (high area image) or the like is output, control for supplying toner at once is performed from both pixel supply control and sensor supply control. At this time, troubles such as toner scattering due to excessive supply may occur.

  Therefore, in order to solve such a problem, a toner density detection device and a pixel information detection device that acquires pixel information from the input image data are provided, and the detected toner density information and the acquired pixel information are used. There has been proposed an image forming apparatus that calculates an upper limit value of the replenishment amount of toner to be replenished from each color toner tank, bottle, or the like to the developing device (see Patent Document 1).

  However, in this image forming apparatus, when image processing desired by the user is performed on input image data read by an external device or a reading apparatus, and image formation is performed based on the image data after the image processing, image formation is performed. There is a problem that it is impossible to obtain pixel information that conforms to. For example, considering 50% reduction / magnification processing, the number of pixels in the main scanning direction and the sub-scanning direction is halved, but pixel information corresponding to the number of pixels cannot be obtained, and therefore an appropriate upper limit value of the toner correction amount is calculated. I can't.

JP 2007-156411 A

  The present invention has been made to solve such a problem, and its purpose is to perform desired image processing on input image data and form an image based on the image data after the image processing. However, an appropriate upper limit value of the toner supply amount can be calculated.

The present invention has an image processing apparatus that performs desired image processing on input image data, forms an electrostatic latent image on an image carrier based on the image data after the image processing, and supplies it from a developing device An image forming apparatus that develops the electrostatic latent image using a developer that is calculated, and that has a means for calculating an upper limit value of a toner replenishment amount to the developing device based on pixel information of the image data after the image processing An image forming apparatus characterized by the above.
The present invention also provides a step of performing desired image processing on input image data, a step of forming an electrostatic latent image on an image carrier based on the image data after the image processing, and a supply from a developing device And developing the electrostatic latent image with a developed developer, wherein an upper limit value of a toner replenishment amount to the developing device is calculated based on pixel information of the image data after the image processing And an image forming method characterized by comprising the step of:
Here, the pixel information of the image data after the image processing can be generated based on the acquired pixel information and desired image processing attribute information by acquiring the pixel information from the input image data. The attribute information includes scaling information, aggregation information, inversion information, erasing information, printing information, and the like.

  According to the present invention, an appropriate upper limit value of the toner replenishment amount can be calculated even when desired image processing is performed on input image data and image formation is performed based on the image data after the image processing. .

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. This embodiment is an example applied to a tandem intermediate transfer type full-color copying machine.

  The full-color copying machine includes an apparatus main body 100, a paper feed table 200 on which the apparatus main body 100 is mounted, a scanner 300 attached to the copying apparatus main body 100, an automatic document feeder (ADF) 400 attached to the scanner 300, and the like. Yes.

  In the center of the apparatus main body 100, yellow (Y), cyan (C), magenta (M), and black (K) image forming units 18Y, 18C, 18M, and 18K for four colors are arranged side by side in tandem. An image forming apparatus 20 is configured. Each image forming unit of the tandem image forming apparatus 20 includes photoreceptors 40Y, 40C, 40M, and 40K on which Y, C, M, and K color toner images are formed, respectively.

  An exposure device 21 is provided above the tandem image forming apparatus 20. The exposure apparatus 21 includes four laser diode (LD) light sources prepared for each color, a pair of polygon scanners composed of a six-sided polygon mirror and a polygon motor, and fθ arranged in the optical path of each light source. It is composed of a lens, a lens such as a long WTL, and a mirror. In accordance with the image data of each color, the laser light emitted from the laser diode is deflected and scanned by the polygon scanner, and is irradiated onto the photoconductor (image carrier) of each color.

  Below the tandem image forming apparatus 20, an endless belt-like intermediate transfer belt 10 is installed. In the illustrated example, the intermediate transfer belt 10 is wound around three first support rollers 14, a second support roller 150, and a third support roller 160, and can be rotated and conveyed in the clockwise direction in the drawing. The support roller 14 is a drive roller that rotationally drives the intermediate transfer belt. Further, between the first support roller 14 and the second support roller 150, primary transfer rollers 62Y, C, M, and Bk are used as primary transfer means for transferring the toner image from the photosensitive member of each color to the intermediate transfer belt. It is provided so as to face each photoconductor with an intermediate transfer belt interposed therebetween.

  An intermediate transfer belt cleaning device 17 that removes residual toner remaining on the intermediate transfer belt 10 after image transfer is provided in the rotational direction indicated by the arrow and downstream of the third support roller 160. As the material of the intermediate transfer belt 10, a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, polyethylene terephthalate, etc. can be molded into a seamless belt and used. These materials can be used as they are, or the resistance can be adjusted with a conductive material such as carbon black. Further, using these resins as a base layer, a surface layer may be formed by a method such as spraying or dipping to form a laminated structure.

  A secondary transfer device 22 is disposed below the intermediate transfer belt 10. In the illustrated example, the secondary transfer device 22 includes a secondary transfer belt 24 that is an endless belt between two rollers 23, and is pressed against the third support roller 160 via the intermediate transfer belt 10. The image on the intermediate transfer belt 10 is transferred to a transfer material. As the secondary transfer belt 24, the same material as that of the intermediate transfer belt 10 can be used.

  Next to the secondary transfer device 22, a fixing device 25 for fixing an image on the transfer material is provided. The fixing device 25 has a configuration in which a pressure roller 27 is pressed against a fixing belt 26 that is an endless belt. The secondary transfer device 22 described above is also provided with a sheet transport function for transporting the transfer material after image transfer to the fixing device 25. Of course, a transfer roller or a transfer charger may be disposed as the secondary transfer device 22, and in such a case, it is necessary to provide this transfer material conveying function separately.

  In the illustrated example, a transfer material is disposed below the secondary transfer device 22 and the fixing device 25 in parallel with the above-described tandem image forming device so as to reversely discharge the transfer material or to form an image on both sides of the transfer material. And a reversing device 28 for re-feeding and refeeding. When copying using this full-color copying machine, a document is set on the document table 30 of the ADF. Alternatively, the ADF 400 is opened and a document is set on the contact glass 32 of the scanner, and the ADF 400 is closed and the document is pressed.

  When a start switch of an operation unit (not shown) is pressed, when a document is set on the ADF 400, the document is transported and moved onto the contact glass 32, and then when the document is set on the other contact glass 32, immediately. The scanner 300 is driven to cause the first traveling body 33 and the second traveling body 34 to travel. The first traveling body 33 emits light from the light source and further reflects reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and is read through the imaging lens 35. The light is incident on 36 and the content of the original is read.

  Thereafter, when the mode setting is set in the operation unit or the automatic mode selection is set in the operation unit, the image forming operation is started in the full color mode or the monochrome mode according to the reading result of the original.

  When the full color mode is selected, each of the photoreceptors 40Y, 40C, 40M, and 40K rotates counterclockwise in FIG. Then, the surfaces of the photoreceptors 40Y, 40C, 40M, and 40K are uniformly charged by the charging rollers 16Y, 16C, 16M, and 16K that are charging devices. Next, laser light corresponding to the image of each color is irradiated from the exposure device 21 to the photoconductors 40Y, 40C, 40M, and 40K of the respective colors, and electrostatic latent images corresponding to the image data of the respective colors are formed.

  Each electrostatic latent image is developed with each color toner by each color developing device 15Y, 15C, 15M, 15K as each photoconductor 40Y, 40C, 40M, 40K rotates. Here, each developing device is appropriately replenished with toner from a toner storage unit such as a toner tank or a toner bottle (not shown) via a toner replenishing device (not shown). The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 10 along with the conveyance of the intermediate transfer belt 10 to form a full color image on the intermediate transfer belt 10.

  On the other hand, one of the paper feed table paper feed rollers 42 is selected and rotated so that the transfer material is fed from one of the paper feed cassettes 44 provided in multiple stages to the paper feed table 43 and separated one by one by the separation roller 45. The paper is put into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the main body, and abutted against the registration roller 49 and stopped. Alternatively, the transfer roller 50 is rotated to feed the transfer material on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped. Then, the registration roller 49 is rotated in synchronization with the full-color image on the intermediate transfer belt 10, the transfer material is fed between the intermediate transfer belt 10 and the secondary transfer device 22, and transferred by the secondary transfer device 22. The toner image is transferred onto the transfer material.

  The transfer material onto which the toner image has been transferred is conveyed by the secondary transfer device 22 and sent to the fixing device 25, where the heat and pressure are applied to the fixing device 25 to be fixed. Next, it is switched by the switching claw 55, discharged by the discharge roller 56, and stacked on the discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and fed again to the secondary transfer position 22. Here, after the image is also recorded on the back surface, the image is discharged onto the discharge tray 57 by the discharge roller 56. Thereafter, when the formation of two or more images is instructed, the above-described image forming process is repeated.

  When the monochrome mode is selected, the support roller 150 moves downward to separate the intermediate transfer belt 10 from the photoreceptors 40Y, 40C, 40M, and 40K. Only the black photoconductor 40K rotates counterclockwise in FIG. 1, the surface of the photoconductor 40K is uniformly charged by the charging roller 16K, the laser beam corresponding to the black image is irradiated, and the electrostatic latent image is formed. A toner image is formed and developed with black toner. This toner image is transferred onto the intermediate transfer belt 10. At this time, the three color photoconductors and developing devices other than K are stopped, and unnecessary consumption of the photoconductor and the developer is prevented.

  On the other hand, the transfer material is sent out from the paper feed cassette 44 and is sent out again at a timing coincident with the toner image formed on the intermediate transfer belt 10 after being temporarily stopped by the registration roller 49. The transfer material on which the toner image is transferred by the secondary transfer device 22 is fixed by the fixing device 25 as in the case of a full-color image, and processed through a paper discharge system corresponding to a designated mode. Thereafter, when the formation of two or more images is instructed, the above-described image forming process is repeated.

The image forming conditions of this image forming apparatus will be specified below.
Photoconductor diameter: 60 mm
Photoconductor rotation speed: 282 mm / sec
Distance between photoconductor and developing roller: 0.3 mm
Developer capacity: 380 g
Toner particle size: 7 μm
Carrier particle size: 35 μm

  In the present image forming apparatus, each of the developing devices 15Y, 15C, 15M, and 15K is provided with a toner density detecting device that detects the toner density, and a control device (not shown) is read by an external device connected to the image forming apparatus or the reading device 36. The input image data (read image data) is input to the image processing apparatus 1000 shown in FIG. 2, first pixel information 1002 is obtained from the pixel information calculation unit 1001, and the pixel information is based on the attribute information 1003. The information is converted into second pixel information 1005 by the information conversion unit 1004. Then, from the second pixel information and the detected density of the toner density detecting device, the replenishment amount of toner to be replenished from each color toner tank, bottle or the like to the developing devices 15Y, 15C, 15M, 15K is calculated.

  The image data input to the image processing apparatus 1000 is subjected to necessary image processing in a scanner γ processing block 1006, a filter processing block 1007, a color conversion block 1008, and a compression processing block 1009, and then a hard disk (HDD) 1010. To remember. The image data read from the hard disk 1010 is subjected to necessary image processing in the expansion processing block 1011, the filter processing block 1012, the scaling block 1013, the color conversion block 1014, and the gradation processing block 1015, and the written image Output data. Since these image processing blocks are publicly known, detailed description thereof is omitted.

  In the present embodiment, the following control technique is applied to the control device in order to stabilize the image density. As a replenishment control method, pixel replenishment control for calculating a replenishment amount from pixel information (for example, the number of pixels) of an input image, and sensor replenishment control for detecting a toner density with a density sensor and calculating a replenishment amount from a change in toner density. The control method which combined these two control methods is introduced.

The total replenishment amount H [mg] is calculated by the following equation [1] as the sum of the replenishment amount P_Pxl [mg] in the pixel replenishment control and the replenishment amount P_Vt [mg] in the sensor replenishment control.
H = P_Pxl + P_Vt [1]

Here, the contents of P_Pxl and P_Vt are expressed by the following equations [2] and [3], respectively.
P_Pxl = (M / A) × Pxl × α1 [2]
In this equation, M / A is the target amount of toner adhesion per unit area [mg / cm ² ] on the intermediate transfer belt, the dot image area [cm ² ] of the input image, that is, the number of pixels calculated from the input image data. A value obtained by converting [dot] data into [cm ² ] units, α1 (first supply coefficient) is a correction coefficient (fixed value) for correcting the pixel supply amount with respect to the supply performance of the apparatus.

P_Vt = sensor sensitivity × (Vtnow−Vtref) × α2 (3)
In this equation, Vtnow is the sensor output value [V] representing the current toner density, Vtref is the sensor output value [V] of the target toner density, and α2 (second replenishment coefficient) is the replenishment of the device in the same manner as α1. This is a correction coefficient (fixed value) for correcting the sensor replenishment amount with respect to performance. The sensor sensitivity is an output value of the sensor with respect to the toner concentration, and its unit is [wt% / V].

In the present embodiment, the following seven types of toner supply control are possible.
First, the upper limit value of the toner replenishment amount replenished to the developing device at a time is changed according to the number of pixels of image data to be written or the image area ratio.

In this example, the replenishment amount upper limit value linked to the toner replenishment amount by the pixel replenishment control is set for the replenishment amount represented by the formula [1]. The replenishment amount upper limit value H_limit [mg] is assumed to be up to 120% of the pixel replenishment amount expressed by the equation [2], and can be expressed by the following equation [4].
H_limit = 1.2 × P_Pxl Expression [4]

  This makes it possible to prevent the image density from fluctuating due to oversupply even when the image areas are different. In order to confirm the actual effect, when replenishment control is performed without an upper limit value (case 1), when the upper limit value is set as a fixed value (case 2), when the upper limit value is calculated from the pixel replenishment value, that is, the pixel When the upper limit of supply amount linked with the supply amount was set (case 3), each experiment was performed, and the image density of the output image was measured.

  As a confirmation method, as shown in FIG. 3, image data in which the image area ratio is changed is output. 3A is an image area ratio of 5%, FIG. 3B is an image area ratio of 10%, FIG. 3C is an image area ratio of 20%, FIG. 3D is an image area ratio of 50%, and FIG. Shown visually. Further, the number of output images for image data having each image area ratio is set to 3, and the set values α1 = 1.05, α2 = 150, and sensor sensitivity = 3.0 [wt% / V] in each replenishment calculation formula. used. However, α1 and α2 may have different values depending on the conditions of the apparatus.

  FIG. 4 is a table and FIG. 5 is a graph showing the measured image density (ID: Image Density) of an image actually output based on image data having each image area ratio. 4 and 5, “no limit” corresponds to the case 1, “limit fixed” corresponds to the case 2, and “limit pixel interlocking” corresponds to the case 3.

  Since MAX-MIN (maximum value-minimum value) was calculated and compared in order to see variations in image density for each combination of the above cases and image area ratios, the upper limit value of case 3 was calculated from the pixel replenishment value. In this case, that is, when the replenishment amount upper limit value linked to the pixel replenishment amount is set, it was confirmed that the image density was most stable.

  Second, the amount of toner replenishment is changed according to the ratio of the line image (line drawing) in the output image. The ratio of the line image is calculated by dividing the output image into a line portion and a solid portion, and the ratio The amount of toner replenishment to the developing device is changed according to the above. In that case, the upper limit value of the replenishment amount to be replenished at a time is changed according to the pixel information. For example, the amount of replenishment is slightly increased in the line portion. This will be described below.

  The image data of the output image can be divided into line portion data (edge portion / character portion) Pxl_line and solid portion (photo image portion) Pxl_beta by edge detection in image processing.

Here, the above equation [2] is changed to the following equation [5].
P_Pxl = (M / A) × Pxl × α1 × α3 (5)

In this equation, α3 (third correction factor) is a replenishment amount correction factor based on the solid / line ratio, and is calculated by the following equation [6].
α3 = Pxl_beta / (Pxl_beta + Pxl_line)
+ Coef_B1 × Pxl_line / (Pxl_beta + Pxl_line) (6)

  Coef_Bl in this equation is a solid / line ratio (solid / line adhesion amount ratio).

  As described above, the upper limit value of the toner replenishment amount to the developing device is calculated based on the ratio between the number of pixels to be written and the number of pixels of the line image (line drawing) in the number of pixels to be written.

Thirdly, a replenishment amount upper limit value linked to the toner replenishment amount by pixel replenishment control is set for the replenishment amount represented by Equation [5]. The replenishment amount upper limit value H_limit [mg] is up to 120% of the pixel replenishment amount obtained by applying the equations [5] and [6], and can be expressed by the following equation [4a].
H_limit = 1.2 × P_Pxl ... [4a]

  That is, the upper limit value of the toner replenishment amount to the developing device is calculated based on the ratio between the number of pixels to be written and the number of pixels of the line image (line image) in the number of pixels to be written.

Case 4: For comparison, based on the above equations [5] and [6], an image is output by toner replenishment control using the above equation [2] (corresponding to the above case 3). The image density of the part was measured.
Case 5: An image is output with Coef_Bl = 1.3 by toner replenishment control (solid / line ratio replenishment control) based on the above equations [5] and [6], and the image density of the solid portion at that time is output. It was measured.
In both cases, the images were output at 10 sheet repeats, and the image density fluctuations at the repeats were compared when there was no solid / line ratio replenishment control.

  The comparison results are shown in the table of FIG. 6 and the graph of FIG. In FIG. 6 and FIG. 7, the case 4 is expressed as “no solid / line correction”, and the case 5 is expressed as “solid / line correction”. Since MAX-MIN (maximum value-minimum value) is calculated and compared in order to see the variation in image density for each case, the image density is most stable in “solid / line correction” corresponding to case 5 above. It was confirmed that As a result, it was confirmed that replenishment control with reduced variation due to the image pattern can be realized by adding according to the solid / line ratio.

  Fourth, the toner replenishment amount is calculated from the toner density detection values in the developing devices 15Y, 15C, 15M, and 15K, and the toner replenishment amount calculated from the toner density detection values is linked to the image area ratio of the input image. . Specifically, in the sensor replenishment control of the above equation [3], the replenishment amount by the sensor replenishment control is also optimized by linking the second replenishment coefficient α2 with the image area ratio of the output image.

Here, the value of the second replenishment coefficient α2 is set to be proportional to the value obtained by dividing the output image area Pxl by the transfer paper size S [cm ² ] as in the following equation [7]. The value of Pxl / S corresponds to the image area ratio of the output image with respect to the transfer paper. By multiplying the sensor replenishment amount by the image area ratio, the replenishment amount correction suitable for the output image was realized.
α2 = Pxl / S × α4 [7]
In this equation, the fourth supply coefficient α4 is a fixed value.

  In order to actually confirm the effect, image output evaluation was performed for image area ratios of 5%, 10%, 20%, 50%, and 100% in accordance with the examples obtained when the results of FIGS. In equation [7], 150 is used as the fourth supply coefficient α4, but this value may vary depending on the apparatus.

Case 6: The replenishment coefficient α2 is not linked to the image area ratio of the output image. In other words, the toner replenishment amount calculated from the toner density detection value is not linked to the image area ratio of the input image, and is a case where “no α4” is displayed in FIGS.
Case 7: The supply coefficient α2 is linked to the image area ratio of the output image. In other words, this is a case where the toner replenishment amount calculated from the toner density detection value is linked to the image area ratio of the input image, and “α4 is present” is displayed in FIGS.

  Since MAX-MIN (maximum value-minimum value) is calculated and compared in order to see variations in image density for each combination of the above cases and image area ratios, the replenishment coefficient α2 of case 7 is the image area of the output image. It was confirmed that the image density was most stable when linked to the rate, that is, when the toner replenishment amount calculated from the detected toner density value was linked to the image area rate of the input image. From this result, it was confirmed that by linking the replenishment coefficient α2 with the image area ratio of the output image, the image density stability is improved particularly in a region where the image area ratio is low, and the variation in the image density is further improved. .

  Fifth, a small particle size carrier is used for the developer to improve image quality. By reducing the particle size of the carrier, the bulk density of the developer is increased. The bulk density of the developer corresponds to the filling rate of the developer per unit volume. Since the carrier has a smaller particle size, the extra space is reduced and the bulk density is increased. However, the degree of sealing of the developer is increased correspondingly, and there is a problem that the developer and the replenishment toner are not easily mixed.

However, in the replenishment control in the examples described so far, it is possible to provide a stable image density even when using a carrier having a small particle diameter of 40 μm or less in volume average particle size, and satisfies the demand for high image quality. did.
As shown in the above example, it is possible to realize an image forming apparatus that prevents an oversupply state and provides a stable image density even if the image area ratio or line ratio changes in the output image. It was. In addition, an image forming apparatus that provides high image quality and high stability can be realized.

  A comparative example with the prior art will be described below. In some prior arts, the upper limit value of the toner replenishment amount is determined according to the pixel of the output image. Whereas the prior art determines the upper limit of the replenishment amount from the average value and cumulative value of the output pixels, in the present embodiment, the upper limit of the replenishment amount is always determined from the pixel of the image at the time of image output or immediately before it. Is different.

  The optimum control method of toner replenishment control is to replenish only the consumed toner. However, in reality, it is difficult to supply the correction amount as calculated, and an upper limit process is usually provided for the supply amount in order to avoid oversupply. If the upper limit value used in this upper limit process is a fixed value, the supply of toner is insufficient for images with a large amount of toner consumption, and conversely, the supply of toner is excessive for images with a small amount of toner consumption, resulting in fluctuations in image density. End up.

  When this upper limit processing is calculated from the average value of the output pixels, there is no problem if only images with the same image area ratio are output. However, if the image area ratio of the output image changes greatly, the fixed value is used. As with the case, supply shortage and excessive supply occur. In particular, in an apparatus that outputs a full-color image, the fluctuation of the image area ratio greatly changes in the output image.

  For example, after outputting Excel data with a low color image area ratio, etc., if you output a full color map etc. with a high image area ratio, the replenishment amount upper limit is set with a low image area ratio, Insufficient replenishment causes image density fluctuations. An example is shown in FIG. In this example, even if the image area ratio rapidly increases by about 6 times (4% → 25%), the average value initially increases only 1.5 times (4% → 6%). The replenishment amount upper limit value set to a constant multiple (1.2 times here) of the average value of the rate also increases only 1.5 times. For this reason, a shortage of toner supply continues for a while after the image area ratio suddenly increases, and image density decreases during that time.

  Particularly in recent years, the amount of the developer has been reduced due to the downsizing of the unit, so that the image density fluctuation and toner scattering are likely to occur due to insufficient supply or excessive supply. In order to prevent such problems from occurring, in order to set the optimum replenishment amount and the replenishment amount upper limit value at the time of image output, instead of determining the replenishment amount upper limit value from the average value or cumulative value of the image area ratio, It is always necessary to calculate the replenishment amount upper limit value according to the image area ratio of the output image.

  Sixth, when the image area is increased, much of the toner in the developing device is used as an image, and fresh toner is supplied from the toner supply device, the toner is not sufficiently charged in the developing device. Under such circumstances, the toner charge amount decreases, the toner adhesion amount to the latent image increases, and as a result, the image density increases. Because of this phenomenon, when the image replenishment amount is large, it is necessary to suppress the toner replenishment amount by making the relationship between the image area and the upper limit value of the toner replenishment amount lower.

Specifically, the above-described upper limit value [4] of the toner replenishment amount is changed to the following formula [4b] to suppress the increase in the upper limit value as the image area of the input image increases. did.
H_limit = 1.2 × P_Pxl (P_Pxl <312)
H_limit = 1.0 × P_Pxl + 62.4 (P_Pxl ≧ 312) (4b)

  As described above, when the image area exceeds a predetermined value, the relationship between the image area and the replenishment amount upper limit value is changed to lower the replenishment amount upper limit value per image area, thereby suppressing an increase in image density. it can.

  Seventh, when more toner is replenished in the developing unit, the toner in the developing unit is transferred to the developing sleeve without being mixed with the carrier, and falls as a lump onto the latent image, so-called toner. This is to prevent dropping, and it is dealt with by limiting the replenishment amount above a predetermined amount.

Specifically, the following conditional expression [4c] is added to the replenishment amount upper limit expression [4b].
However, when H_limit> 560, H_limit = 1100 (4c)

  Addition of this condition can suppress toner dropping. Further, when toner is supplied to such an extent that toner drops, the amount of toner that remains uncharged increases, resulting in an increase in image density. Therefore, by adding the condition of equation [4c], the toner replenishment amount can be limited, the charge amount of the replenishment toner can be stabilized to a predetermined value or more, and an increase in image density can be suppressed.

  Eighth, under the condition that the image area is small and the toner is not consumed, if the toner staying in the developing device is continuously consumed without being consumed, the charge amount of the toner increases and the toner adhesion amount to the latent image decreases. As a result, the image density is lowered. For this reason, if the formula of the upper limit value of the replenishment amount is maintained, the replenishment amount is limited to be small, so that the image density is lowered.

  In view of this, it is necessary to set the upper limit value of the toner replenishment amount higher than the pixel under the condition that the image area where the toner is hardly consumed is small. In addition, even when the toner is not consumed at all, since the developer is continuously stirred, it may be desirable to supply a certain amount of toner in order to suppress an increase in the charge amount.

Specifically, the following conditional expression [4d] is added to the above-described replenishment amount upper limit expression [4b] along with conditional expression [4c].
However, when H_limit <10, H_limit = 10 (4d)
By raising the lower limit of H_limit using this conditional expression, a constant amount of toner can be replenished even when toner is not consumed at all or when toner consumption is too low, and a decrease in image density can be suppressed. it can.

Next, toner supply control when desired image processing is performed on image data input to the image processing apparatus 1000 will be described with a specific example.
<1> When Image Processing is Scaling When the user designates a scaling factor from an operation unit (not shown), attribute information 1003 is input to the image information conversion unit 1004. The image information conversion unit 1004 obtains the number of pixels or the image area ratio by multiplying the first pixel information 1002 by multiplying the magnification by converting it to the second pixel information 1005, and converts it into the toner consumption amount. Calculate the replenishment amount. In other words, this means that the amount of toner adhering to the transfer paper is changed by changing the magnification.

In this example, Pxl in the expression [2] is converted into Pxl1 according to the scaling factor.
In the case of reduction scaling, Pxl1 is calculated by equation [8].
Pxl1 = Pxl × A × 0.01 Formula [8]
In this equation, A is the scaling factor [%].

In the case of enlarging / magnifying, if the enlarged image fits on the transfer paper, it is calculated by equation [8]. On the other hand, if the enlarged image does not fit on the transfer paper, it is calculated which part of the original is to be transferred, and the area where dots are formed is multiplied by the scaling factor. That is, it is calculated by equation [9].
Pxl1 = Pxlcut × A × 0.01 (9)
In this equation, Pxlcut is the dot image area [cm ² ] of the transfer range on the document.

<2> When Image Processing is Aggregation When the user designates aggregation from an operation unit (not shown), attribute information 1003 is input to the image information conversion unit 1004. The image information conversion unit 1004 calculates the number of pixels or the image area ratio by converting the first pixel information 1002 into the second pixel information 1004 according to the aggregation condition, and calculates the toner replenishment amount by converting into the toner consumption amount. . That is, it means that the amount of toner adhering to the transfer paper is changed by the aggregation.

In this example, Pxl of the expression [2] is converted into Pxl2 according to the aggregation condition. For example, in the case of aggregation of 2IN1, the calculation is performed by the equation [10].
Pxl2 = (Pxl × B × 0.01 of the first document) + (Pxl × B × 0.01 of the second document) Equation [10]
B in this equation is a scaling factor [%] according to the aggregation condition (when 2IN1: B = 50). The same calculation is performed for repeat and double copy.

<3> When Image Processing is Inverted When the user designates inversion from an operation unit (not shown), the attribute information 1003 is input to the image information conversion unit 1004. The image information conversion unit 1004 obtains the number of pixels or the image area ratio by converting the first pixel information 1002 to the second pixel information 1005 by inversion, and converts it into a toner consumption amount to calculate a toner supply amount. In other words, this means that the amount of toner adhering to the transfer paper is changed by performing the inversion.

In this example, Pxl in the expression [2] is converted into Pxl3 according to inversion. The conversion formula [11] is as follows.
Pxl3 = Pxlall−Pxl (11)
Pxall in this equation is the total image area [cm ² ] of the document.

<4> When Image Processing is Erased When the user designates an erasing condition from an operation unit (not shown), the attribute information 1003 is input to the image information conversion unit 1004. The image information conversion unit 1004 calculates the number of pixels or the image area ratio by converting the first pixel information 1002 into the second pixel information 1004 according to the erasure condition, and calculates the toner supply amount by converting it into the toner consumption amount. . In other words, this means that the amount of toner adhering to the transfer paper is changed by erasing.

In this example, Pxl in the expression [2] is converted into Pxl4 according to the erasure condition. The conversion formula [12] is as follows.
Pxl4 = Pxl−Pxlera (12)
Pxlera in this equation is the image area [cm ² ] for erasure.

<5> When Image Processing is Printing When the user designates printing from an operation unit (not shown), attribute information 1003 is input to the image information conversion unit 1004. The image information conversion unit 1004 calculates the number of pixels or the image area ratio by converting the first pixel information 1002 into the second pixel information 1004 according to the printing conditions, and calculates the toner replenishment amount by converting it into the toner consumption amount. . In other words, this means that the amount of toner adhering to the transfer paper is changed by printing.

In this example, Expression [2] Pxl is converted to Pxl5 according to the printing conditions. The conversion formula [13] is as follows.
Pxl4 = Pxl + Pxlsta Formula [13]
Pxlsta in this equation is the image area [cm ² ] for printing.

  As described above in detail, according to the present embodiment, in an image forming apparatus that performs toner replenishment control that combines pixel replenishment control and sensor replenishment control, image scaling, aggregation, and inversion with respect to input image data. Even when desired image processing such as erasure, printing, etc. is performed and image formation is performed based on the image data after the image processing, the pixel information of the input image data is acquired and based on attribute information representing the image processing Thus, by converting the pixel information of the input image data into the pixel information of the image data after image processing and calculating the toner replenishment amount based on the pixel information, an appropriate upper limit value of the toner replenishment amount can be calculated. it can.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is the figure which showed schematic structure of the image processing apparatus of FIG. It is the figure which illustrated the image area rate of the output image. 6 is a table comparing image densities when images are formed under different conditions. FIG. 5 is a graph showing the table of FIG. 4. 6 is a table comparing image densities when images are formed under different conditions. FIG. 7 is a graph showing the table of FIG. 6. 6 is a table comparing image densities when images are formed under different conditions. FIG. 9 is a graph showing the table of FIG. 8. It is explanatory drawing of the comparative example which illustrated image density fall generation | occurrence | production conditions.

Explanation of symbols

  15Y, 15C, 15M, 15K ... developing device, 40Y, 40C, 40M, 40K ... photosensitive member, 1000 ... image processing device, 1003 ... pixel information acquisition block.

Claims (8)

A developer that has an image processing device that performs desired image processing on input image data, forms an electrostatic latent image on the image carrier based on the image data after the image processing, and is supplied from the developing device An image forming apparatus for developing the electrostatic latent image by:
An image forming apparatus comprising: means for calculating an upper limit value of a toner replenishment amount to the developing device based on pixel information of the image data after the image processing. The image forming apparatus according to claim 1.
Means for acquiring the pixel information from the input image data, and means for generating pixel information of the image data after the image processing based on the acquired pixel information and the attribute information of the desired image processing. An image forming apparatus. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the attribute information is scaling information. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the attribute information is aggregated information. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the attribute information is inversion information. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the attribute information is erasure information. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the attribute information is printing information.   The step of applying desired image processing to the input image data, the step of forming an electrostatic latent image on the image carrier based on the image data after the image processing, and the developer supplied from the developing device And developing an electrostatic latent image, the method comprising: calculating an upper limit value of a toner replenishment amount to the developing device based on pixel information of the image data after the image processing. An image forming method.

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