JP2019128369A - Image forming apparatus, image forming method, and image forming program - Google Patents

Abstract

To reduce an edge effect in electrophotography in which development is performed with photoreceptors in a non-saturated state.SOLUTION: An image forming apparatus comprises: developing units that each have a photoreceptor, an exposing unit that exposes the photoreceptor on the basis of image data to form an electrostatic latent image, a magnetic roller, and a developing roller, form, on the developing roller, a toner layer having a thickness according to a toner layer forming potential difference between the magnetic roller and the developing roller, and attach a toner from the toner layer to the photoreceptor on the basis of a developing bias potential that is the potential of the developing roller and the electrostatic latent image; a calibration unit that adjusts a dot area ratio for forming a solid image when the developing bias potential of the developing unit reaches a potential limiting value within an adjustment range set in advance to execute calibration processing; and an image processing unit that, when determining that the total amount of toner consumed in formation of an image is reduced when a rear end direction of an image set in advance and a leading end direction that is a direction opposite to the rear end direction are reversed, processes the image data and reverses the leading end direction and rear end direction of the image.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus, an image forming method, and an image forming program.

  Various techniques have been proposed to suppress an edge effect which is a phenomenon in which toner as a developer is concentrated on the edge portion (end portion) of an image area and the density of an image becomes uneven. Specifically, for example, Patent Document 1 discloses edge detection means for detecting an edge portion of output image data, and edge correction means for performing density correction on data of the edge portion detected by the edge detection means. An exposure unit control apparatus is proposed. Japanese Patent Application Laid-Open No. 2004-228561 has an apparatus for estimating a transfer toner amount (also referred to as a toner adhesion amount in this specification) from an accumulated value of image data and performing appropriate heat amount control to reduce power consumption. In the forming apparatus, even when the line width of the image is different, a technique capable of outputting a good image without deteriorating the fixability of the image is proposed. Japanese Patent Laid-Open No. 2004-26883 detects an end portion in which peripheral pixels have a predetermined gradation difference pattern, and for each target pixel within a predetermined range from the end portion, the pixel value of a predetermined pixel region ahead of the target pixel is determined. A technique has been proposed in which the toner amount of the pixel of interest is adjusted based on the difference between the sum and the sum of the pixel values of the pixel area behind the pixel of interest.

JP, 2009-118378, A Japanese Patent Laid-Open No. 5-333728 Unexamined-Japanese-Patent No. 2014-068084

  However, in electrophotography in which development is performed on a non-saturated photoconductor, there is room for improvement in a method for reducing the edge effect by paying attention to the characteristics of the photoconductor.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique for reducing the edge effect in electrophotography in which development is performed with a non-saturated photoreceptor.

  The present invention provides an image forming apparatus that forms an image based on image data. The image forming apparatus includes a rotatable photosensitive member, an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image, a magnetic roller, and a developing roller, A toner layer having a thickness corresponding to a toner layer forming potential difference between the roller and the developing roller is formed on the developing roller, and the developing bias potential which is the potential of the developing roller and the electrostatic latent image are used. A first calibration process is executed by adjusting a developing unit for adhering toner from the toner layer to the photosensitive member, and a developing bias potential of the developing unit within a preset adjustment range. In the first calibration process, A calibration unit that adjusts a dot area ratio for forming a solid image and executes a second calibration process when the potential limit value is within the adjustment range, and a preset rear end direction of the image And opposite direction of the rear end When it is determined that the total amount of toner consumed for forming the image is reduced when the leading edge direction is reversed, the leading edge direction and the trailing edge direction of the image are processed by processing the image data. And an image processing unit that inverts.

  The present invention provides an image forming method for forming an image based on image data. The image forming method uses a rotatable photoconductor, an exposure unit that exposes the photoconductor to form an electrostatic latent image based on the image data, a magnetic roller, and a developing roller. Forming on the developing roller a toner layer having a thickness corresponding to the toner layer forming potential difference between the toner and the developing roller, and based on the electrostatic latent image and the developing bias potential which is the potential of the developing roller The first calibration process is performed by adjusting the development bias potential in the development process and the development process in which the toner adheres from the layer to the photosensitive member within a preset adjustment range, and the first calibration process performs the first calibration process. A calibration step of adjusting the dot area ratio for forming a solid image when the potential limit value is within the adjustment range and executing the second calibration process; and a rear end direction set in advance for the image; In the direction of the rear end When it is determined that the total amount of toner consumed for forming the image decreases when the opposite end direction, which is the opposite direction, is reversed, the image data is processed to adjust the end direction of the image and the back direction of the image. An image processing step of inverting the end direction is provided.

  The present invention provides an image forming program for controlling an image forming apparatus that forms an image on an image forming medium according to image data. The image forming apparatus includes a rotatable photosensitive member, an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image, a magnetic roller, and a developing roller. A toner layer having a thickness corresponding to a toner layer forming potential difference between the roller and the developing roller is formed on the developing roller, and the developing bias potential which is the potential of the developing roller and the electrostatic latent image are used. A developing unit that attaches toner from the toner layer to the photoconductor, and the image forming program executes a first calibration process by adjusting a developing bias potential of the developing unit within a preset adjustment range; A calibration unit that adjusts a dot area ratio for forming a solid image when the potential limit value is within the adjustment range in the first calibration process, and executes a second calibration process; Set When it is determined that the total amount of toner consumed for forming the image decreases when the rear end direction and the front end direction opposite to the rear end direction are reversed, the image data is processed. The image forming apparatus functions as an image processing unit that reverses the front end direction and the rear end direction of the image.

  According to the present invention, it is possible to reduce the edge effect in electrophotography in which development is performed with a non-saturated photosensitive member.

2 is a block diagram illustrating a functional configuration of the image forming apparatus 1 according to an embodiment of the present disclosure. 1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus 1 according to an embodiment. FIG. 2 is a side cross-sectional view showing the structure of the developing unit 100 according to an embodiment of the present invention. It is a conceptual diagram which shows a mode that a back end accumulation generate | occur | produces in the image development process which concerns on one Embodiment. 4 is a flowchart showing the contents of a half patch calibration processing procedure of the image forming apparatus 1 according to an embodiment. 6 is a graph showing a relationship between an input tone value at a rear end and a toner consumption amount (ratio) in the image forming apparatus 1 according to an embodiment. 6 is a flowchart showing the contents of an image drawing direction determination processing procedure (step S100) of the image forming apparatus 1 according to an embodiment. FIG. 6 is an explanatory view showing a state in which an image drawing direction is reversed in the image forming apparatus 1 according to an embodiment. It is an explanatory view showing a compound half patch concerning a modification.

  Hereinafter, modes for carrying out the present invention (hereinafter, referred to as “embodiments”) will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a functional configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 includes a control unit 10, an image forming unit 20, a storage unit 40, an image reading unit 50, and a fixing unit 80. The image reading unit 50 reads an image from a document and generates an image data ID that is digital data.

  The image forming unit 20 includes a color conversion processing unit 21, a halftone processing unit 22, a density sensor 28 for calibration, an exposure unit 29, and photosensitive drums (image carriers) 30c to 30k, which are amorphous silicon photosensitive members. , And developing units 100c to 100k and charging units 25c to 25k. The color conversion processing unit 21 performs color conversion of image data ID, which is RGB data, into CMYK data. The halftone processing unit 22 performs halftone processing on the CMYK data to generate print data PD as CMYK halftone data. The halftone data represents the formation state of dots formed by each toner of CMYK, and is also called dot data.

  The control unit 10 includes an end detection unit 11 and a toner consumption calculation unit 12. The control unit 10 uses the edge detection unit 11 and the toner consumption calculation unit 12 to calculate the toner consumption as an aggregation of the toner consumption of each image area based on the print data PD. The print data PD represents an image area group including a plurality of image areas.

  The end detection unit 11 detects the end (edge pixel) of the image area, and the rear end and the front end of the end. The edge detection unit 11 may detect the edge based on the relationship between the pixel of interest and the pixel value of the adjacent pixel, or may detect the edge using a filter such as a differential filter or a Sobel filter. Good. The rear end portion is an end portion on the rear end side that is defined as a front end portion, a central portion, and a rear end portion in order from the traveling direction with reference to a circumferential speed direction of a photosensitive drum (described later). The rear end portion can be detected by setting of the relationship of pixel values or setting of directivity of the filter. A direction from the front end side toward the rear end side is called a rear end direction and is set in advance. The opposite direction of the back end direction is called the tip direction.

  The control unit 10 includes main storage means such as RAM and ROM, and control means such as MPU (Micro Processing Unit) and CPU (Central Processing Unit). The control unit 10 also has a controller function related to interfaces such as various I / O, USB (Universal Serial Bus), bus, and other hardware, and controls the entire image forming apparatus 1.

  The storage unit 40 is a storage device including a hard disk drive or a flash memory that is a non-temporary recording medium, and stores a control program and data for processing executed by the control unit 10. In the present embodiment, the storage unit 40 further stores calibration data CD1 and correction data CD2. The calibration data CD1 and the correction data CD2 can be configured, for example, as a LUT (Look Up Table). The contents of the calibration data CD1 and the correction data CD2 will be described later.

  FIG. 2 is a cross-sectional view showing the overall configuration of the image forming apparatus 1 according to an embodiment. The image forming apparatus 1 of the present embodiment is a tandem type color printer. In the image forming apparatus 1, photosensitive drums (image carriers) 30 m, 30 c, 30 y and 30 k are arranged in a line in a casing 70 corresponding to each color of magenta, cyan, yellow and black. Developing units 100m, 100c, 100y and 100k are disposed adjacent to the photosensitive drums 30m, 30c, 30y and 30k, respectively.

  The laser beams Lm, Lc, Ly and Lk for respective colors are irradiated (exposed) from the exposure unit 29 to the photosensitive drums 30m, 30c, 30y and 30k. By this irradiation, electrostatic latent images are formed on the photosensitive drums 30m, 30c, 30y and 30k. The developing units 100m, 100c, 100y and 100k cause the toner to adhere to the electrostatic latent images formed on the surfaces of the photosensitive drums 30m, 30c, 30y and 30k while stirring the toner. Thus, the developing process is completed, and toner images of respective colors are formed on the surfaces of the photosensitive drums 30c to 30k.

  The image forming apparatus 1 has an endless intermediate transfer belt 27. The intermediate transfer belt 27 is stretched around a tension roller 24, a drive roller 26a and a driven roller 26b. The intermediate transfer belt 27 is driven to circulate by the rotation of the driving roller 26a.

  For example, a black toner image on the photosensitive drum 30k is primarily transferred to the intermediate transfer belt 27 by sandwiching the intermediate transfer belt 27 between the photosensitive drum 30k and the primary transfer roller 23k, and the intermediate transfer belt 27 being driven to circulate. Ru. The same applies to the three colors of cyan, yellow and magenta.

  A full-color toner image is formed on the surface of the intermediate transfer belt 27 by performing primary transfer so as to be superimposed on each other at a predetermined timing. The calibration density sensor 28 is disposed at a position where the primary transfer is completed and the density of the toner image before the secondary transfer can be measured. Thereafter, the full-color toner image is secondarily transferred to the printing paper P supplied from the paper feed cassette 60 and fixed on the printing paper P as a printing medium by the fixing roller pair 81 of the fixing unit 80.

  FIG. 3 is a side sectional view showing the structure of the developing unit 100k according to an embodiment of the present invention. The developing units 100m, 100c, and 100y have the same configuration as the developing unit 100k, and these are also simply referred to as the developing unit 100. The developing unit 100 includes two agitating and conveying members 141 and 142, a magnetic roller 143, a developing roller (developer carrying member) 144, a developing container 145, and a regulating blade 146.

  The developing container 145 constitutes the outline of the developing unit 100. At the lower part of the developing container 145, a partition part 145b is provided. The partitioning portion 145 b partitions the inside of the developing container 145 into a first transfer chamber 145 a and a second transfer chamber 145 c. The first transfer chamber 145a and the second transfer chamber 145c extend in a column shape in a direction perpendicular to FIG. 3, and contain a two-component developer (also simply referred to as a developer) made of a magnetic carrier and black toner.

  The developing container 145 further holds the magnetic roller 143 and the developing roller 144. The developing container 145 is formed with an opening 147 for exposing the developing roller 144 toward the photosensitive drum 30 (30 k).

  The two agitating and conveying members 141 and 142 are cyclically moved while stirring the developer inside the first conveying chamber 145a and the second conveying chamber 145c, respectively. The stirring and conveying member 142 supplies a positively charged developer to the magnetic roller 143 as a magnetic brush. The magnetic roller 143 includes a nonmagnetic rotating sleeve 143a and a fixed magnet body 143b fixed inside the rotating sleeve 143a. The magnetic roller 143 and the developing roller 144 face each other with a predetermined clearance. The regulation blade 146 adjusts the magnetic brush to a predetermined height.

  The developing roller 144 includes a rotatable nonmagnetic developing sleeve 144a and a developing roller side magnetic pole 144b fixed inside the developing sleeve 144a. A magnetic roller potential Vmag is applied to the magnetic roller 143. A developing bias potential Vslv is applied to the developing roller 144.

  In the present embodiment, in the photosensitive drum 30, the surface potential is set to 20 V, and a developing electric field is formed between the photosensitive drum 30 and the developing roller 144. On the other hand, an alternating bias in which a DC potential of 20 to 80 V as the developing bias potential Vslv and a sine wave potential of a peak-to-peak value of 2000 V at a frequency of 2 kHz are superimposed is applied to the developing roller 144. A DC potential of 200 V is applied to the magnetic roller 143 as a magnetic roller potential Vmag during development, and a DC potential of −200 V is applied during non-development.

  As a result, during development, the time of developing bias potential Vslv <magnetic roller potential Vmag (the potential state in which toner is supplied to developing roller 144) is lengthened, and the time for supplying toner to developing roller 144 is lengthened. At the time of non-development, the time of developing bias potential Vslv> magnetic roller potential Vmag (a potential state in which toner is collected from the developing roller 144) becomes longer, and the time for collecting toner from the developing roller 144 becomes longer.

  Furthermore, by adjusting the magnetic roller potential Vmag applied to the magnetic roller 143 during development and non-development, the toner layer formation potential difference ΔV during development between the development bias potential Vslv and the magnetic roller potential Vmag is changed. Can. Accordingly, a thin toner layer (simply a toner) having a thickness D (see FIG. 4A described later) corresponding to the toner layer forming potential difference ΔV between the developing bias potential Vslv and the magnetic roller potential Vmag is applied to the developing roller 144. Also called a layer) is formed.

  The developing roller 144 attaches toner to the photosensitive drum 30 through a facing portion (developing nip) having a predetermined clearance with the photosensitive drum 30 to form a toner image on the surface of the photosensitive drum 30. . The toner image is formed based on the potential difference between the electrostatic latent image potential on the surface of the photosensitive drum 30 and the developing bias potential Vslv applied to the developing roller 144.

  Amorphous silicon photoconductors have a characteristic that the relative permittivity is about three times higher than that of organic photoconductors (OPC), and the amount of toner that can be held by the photoconductor is larger than the development contrast potential. For this reason, the amorphous silicon photosensitive member can hold more toner than the solid density which is usually used. Therefore, when used in a saturated state, the amorphous silicon photosensitive member is held in excess of the amount required for the solid density. Therefore, in the present embodiment, the amorphous silicon photosensitive member is used in the non-saturated state even in the solid density, and the toner formed on the developing roller 144 is almost entirely developed on the photosensitive member, and the development is completed. Is used to be determined.

  FIG. 4 is a conceptual diagram illustrating how the trailing edge accumulation occurs in the developing process according to the embodiment. FIG. 4A shows a state in which an image is formed at the front end portion and the center portion of the image. FIG. 4B shows that the image is formed at the rear end of the image. In the present specification, the front end portion, the central portion, and the rear end portion are defined as the front end portion, the central portion, and the rear end portion in order from the traveling direction with reference to the traveling direction of the photosensitive drum 30.

  In this embodiment, as shown in FIG. 4A, the photosensitive drum 30 is supplied with toner from the developing sleeve 144a of the developing roller 144 while neutralizing the potential of the latent image. At this time, the developing process is configured to be completed when the toner thin layer formed on the developing sleeve 144a is consumed in the non-saturated state, not in the saturation of the potential. The thickness D of the toner thin layer is set to have a thickness T1 for achieving the maximum density at the time of solid development in image formation.

  As shown in FIG. 4B, the developing sleeve 144a has a peripheral speed Vs and is configured to form an image while overtaking the photosensitive drum 30 at the peripheral speed Vd. For this reason, the surface of the developing sleeve 144a in which the toner is not consumed exists near the rear end of the solid at the time of solid development. The surface on which the toner is not consumed will overtake the rear end of the solid latent image on the amorphous silicon photosensitive member 30.

  At this time, since the photosensitive drum 30 as the amorphous silicon photosensitive member is not saturated, the toner is further developed from the surface of the developing sleeve 144a where the toner is not consumed. By this development, the trailing edge stagnation (thickness T2) as a solid density higher than the density assumed in advance becomes apparent.

  FIG. 4C shows, as an example, the adhesion state (stacked state) of the toner at the time of image formation of the line image TP. In the line image TP, the toner layer is raised at the rear end portion at the time of image formation. This rise of the toner layer is called a rear end reservoir.

  FIG. 5 is a flowchart showing the contents of the half patch calibration process procedure (step S100) of the image forming apparatus 1 according to an embodiment. In the present embodiment, since the amorphous silicon photosensitive members are adopted for the photosensitive drums 30c to 30k, the image forming apparatus 1 is configured to express a solid by a half patch in order to suppress the problem of the rear end accumulation. There is.

  Such a problem of rear end accumulation can be suppressed by expressing a solid with a half patch. In this example, the image forming apparatus 1 represents a solid with a half patch having a dot area ratio of 70% to 90%. In the present embodiment, the solid density by the half patch is calibrated by adjusting the developing bias potential Vslv, which is the applied potential of the developing units 100m, 100c, 100y, and 100k, and the dot area ratio.

  In step S <b> 110, the control unit 10 functions as a calibration unit, and forms a chart on the intermediate transfer belt 27 having a plurality of half patches in which the development bias potential Vslv is changed stepwise. Specifically, the control unit 10 forms, on the intermediate transfer belt 27, a chart having a plurality of half patches having different development bias potentials Vslv with a dot area ratio (70% in this example) as an initial value before calibration. . The plurality of half patches include those having the development bias potential Vslv having the maximum value.

  A plurality of half patches in which the development bias potential Vslv is changed in stages are used because the toner image has an electrostatic latent image potential on the surface of the photosensitive drum 30 and a development bias potential Vslv applied to the development roller 144. It is because it is formed based on the potential difference. A plurality of half patches are formed for each of CMYK. Hereinafter, a cyan (C) half patch will be described as an example.

  In step S120, the control unit 10 measures the density of the patch of each color (for example, cyan (C)) using the calibration density sensor 28. The density of the patch can be measured, for example, the amount of red reflected light which has a complementary color relationship of cyan (C). The same process is performed for MYK.

  In the present embodiment, the calibration concentration sensor 28 emits infrared light from, for example, an LED (not shown), passes through a polarizing filter that transmits only P waves, and irradiates the patches with infrared P waves. The density is detected based on the ratio of P wave and S wave of the reflected light detected by the light receiving element. The calibration density sensor 28 includes a regular reflection method for detecting regular reflection light from the patch and a diffuse reflection method for detecting diffuse reflection light from the patch.

  In step S130, the control unit 10 executes development bias adjustment processing. In the development bias adjustment process, the control unit 10 determines that a patch that has reached a preset solid image target density from among a plurality of cyan (C) half patches whose development bias potential Vslv is changed in stages. If it exists, it is executed by selecting the development bias potential Vslv corresponding to that patch. Specifically, when there is a half patch whose ratio between the P wave and the S wave is equal to or less than a preset threshold, the control unit 10 calibrates the lowest developing bias potential Vslv among the half patches. To the developing bias potential.

  In step S140, if the half patch calibration is possible within the adjustment range of the development bias, the control unit 10 advances the process to step S195, and the half patch calibration is possible within the adjustment range of the development bias potential Vslv. If not, the process proceeds to step S150. In step S195, the control unit 10 stores the development bias potential Vslv after calibration in the storage unit 40 as a part of the calibration data CD1. Calibration by adjusting the development bias potential Vslv is also referred to as first calibration processing.

  The case where half patch calibration is not possible within the adjustment range of development bias means that there is no patch which has reached a preset solid image target density among a plurality of cyan (C) patches. ing. Normally, any one of the plurality of half patches reaches the solid image target density, but the solid image target density may not be reached in a state where the toner charge amount is increased due to, for example, an environmental change.

  In step S150, the control unit 10 sets the development bias potential Vslv to the maximum value, and starts an operation mode in which the dot area ratio is adjusted and calibrated. The maximum value of the developing bias potential Vslv is also referred to as a potential limit value, and is set from the viewpoint of, for example, the output limit of the developing bias and an adverse effect (fogging etc.) on the image.

  In step S160, the control unit 10 forms, on the intermediate transfer belt 27, a chart having a plurality of half patches in which the dot area ratio is changed stepwise. In this example, the dot area ratio is changed stepwise within the range of the dot area ratio from 71% to 90%.

  In step S170, the control unit 10 measures the density of the cyan (C) patch using the calibration density sensor 28. The calibration concentration sensor 28 measures the ratio of the P wave and the S wave. The same process is performed for MYK.

  In step S180, the control unit 10 sets a dot area ratio. Specifically, when there is a half patch whose ratio between the P wave and the S wave is equal to or less than a preset threshold, the control unit 10 determines the half patch with the lowest dot area ratio among the half patches. The dot area rate is acquired as calibration data. Calibration by adjusting the dot area rate is also referred to as a second calibration process. The control unit 10 stores the calibrated dot area ratio in the storage unit 40 as part of the calibration data CD1.

  In step S185, the control unit 10 executes correction formula determination processing. In the correction formula determination process, the control unit 10 determines a correction formula based on the dot area ratio set in step S180. In the present embodiment, the correction equation is used to determine the necessity of the drawing direction reversing process. The correction formula may be used for adjustment of the toner adhesion amount such as determination of a dot thinning rate and change of dot size in the rear edge pixel.

  FIG. 6 is a graph showing the relationship between the input tone value at the rear end and the toner consumption (ratio) in the image forming apparatus 1 according to the embodiment. The horizontal axis indicates the input tone value. The vertical axis represents toner consumption (ratio). The input tone value 100% indicates a solid that is often used for characters and line drawings. Curve CR represents the toner consumption in the area other than the rear end. Three curves C1 to C3 indicate toner consumption in the area of the rear end.

  In FIG. 6, the toner consumption amount is shown as a ratio with respect to the reference consumption amount, with the toner consumption amount (curve CR) in the region other than the rear end portion of the input gradation value 100% as the reference consumption amount. The three curves C1 to C3 are selected based on the dot area ratio set in step S80. In this example, the curve C1 indicates the largest toner consumption, the curve C3 indicates the smallest toner consumption, and the curve C2 indicates an intermediate toner consumption.

  The control unit 10 selects a curve indicating a larger amount of toner consumption as the amount of change from the dot area ratio (70% in this example) as an initial value before calibration is larger. In this example, for example, the curve C1 is selected when the dot area ratio is 90%, the curve C2 is selected when the dot area ratio is 80%, and the dot area ratio is 75%. Curve C3 is selected. On the other hand, for example, when the dot area ratio has a value such as 78% or 85%, it can be determined by interpolation using three curves C1 to C3.

  Thereby, the control unit 10 calculates the toner consumption amount in a pixel group (also referred to as a rear end pixel) constituting the rear end region which is an end region in the rear end direction (for example, an approximate expression, a table or correction Coefficient) can be determined. The control unit 10 stores the calculation formula of the toner consumption amount in the storage unit 40 as a part of the correction data CD2. The end region in the distal direction is referred to as a tip region.

  In step S190, the control unit 10 executes an inversion necessity determination flag setting process. In the reversal necessity determination flag setting process, the control unit 10 sets a flag indicating that it is necessary to determine whether the reversal of the drawing direction is necessary from the viewpoint of suppressing the trailing edge accumulation. The control unit 10 stores in the storage unit 40 the setting of a flag indicating that it is necessary to determine whether reversal is necessary as part of the correction data CD2.

  FIG. 7 is a flowchart showing the contents of the image forming process (step S200) in the image forming apparatus 1 according to the embodiment. In step S210, the control unit 10 executes dot data generation processing. In the dot data generation processing, the control unit 10 generates dot data (print data PD) representing the dot formation state using color conversion processing and halftone processing.

  In step S220, the control unit 10 functions as an image processing unit, and determines whether it is necessary to determine whether or not the drawing direction needs to be reversed. The control unit 10 determines whether or not it is necessary to perform inversion based on a flag set in the correction data CD2. If the flag indicating that the necessity for reversal is necessary is set, the process proceeds to step S230. If the flag indicating that the necessity for reversal is necessary is not set, the process is performed. The process proceeds to step S270.

  FIG. 8 is an explanatory diagram illustrating a state in which the image drawing direction is reversed in the image forming apparatus 1 according to the embodiment. FIG. 8A shows the pre-inversion image LA1 in the drawing state before the inversion. FIG. 8B shows an inverted image LA2 of the drawing state after the inversion. The after-inversion image LA2 is an image obtained by rotating, that is, inverting, the image of the pre-inversion image LA1 by 180 degrees. The unreversed image LA1 has seven rear end pixels A to G. The inverted image LA2 has three rear end pixels L to N. The rear end pixel means the rear end pixel (edge) of the image area with reference to the circumferential speed direction of the photosensitive drums (image carriers) 30c to 30k.

  The rear end pixel constitutes an edge of the rear end, and means a pixel in which no pixel in the image area is present in the rear end direction of an adjacent pixel adjacent in the vertical direction (main scanning direction) to the rear end direction. The tip pixel is a pixel which constitutes an edge of the tip and in which there is no pixel in the image area in the tip direction of the adjacent pixel adjacent in the direction perpendicular to the tip direction (main scanning direction). The rear end pixel is a pixel group within a certain range (for example, about 25 pixels) in the sub-scanning direction in the image from the rear end pixel. The leading edge pixel is a pixel group within a certain range (for example, about 25 pixels) from the leading edge pixel in the sub-scanning direction in the image. The rear end pixel and the front end pixel have a broad meaning and include the rear end pixel and the front end pixel, respectively.

  Four pixels H to K of the image LA2 after inversion are pixels in which pixels in the image area exist in the rear end direction of the adjacent pixels adjacent in the vertical direction (main scanning direction) to the rear end direction. Since the four pixels H to K of the inverted image LA2 can fly toner obliquely downstream (rear end side) in the circumferential speed direction of the photosensitive drum 30 (see arrows from the pixel H to the pixel K). , It is hard for the rear end accumulation to occur. On the other hand, the rear end pixels (pixels A to G) of the pre-inversion image LA1 do not have toner on the downstream side (rear end side), so that rear end accumulation is likely to occur.

  In this example, the four pixels H to K form a rear end contour having an inclination in the main scanning direction by one pixel for each pixel. However, for example, when the rear end contour having a gentle inclination in the main scanning direction is formed by one pixel in two pixels, since the inclination is gentle, the destination of the toner is small and the rear end accumulation is likely to occur. become. On the other hand, since one pixel is the rear end pixel in two pixels of the pixels constituting the outline of the rear end, the number of rear end pixels has a positive correlation with the likelihood of rear end accumulation.

  In this way, the control unit 10 can estimate the likelihood of rear end accumulation by counting the rear end pixels. However, the control unit 10 may estimate the degree of occurrence of rear end accumulation using pattern matching or other methods.

  In step S230, the toner consumption amount calculation unit 12 of the control unit 10 executes a total toner amount calculation process. In the total toner amount calculation process, the control unit 10 calculates the total toner amount before and after the reversal. In step S240, the control unit 10 executes difference calculation processing. In the difference calculation process, the difference between the total toner amount before reversal and the total toner amount after reversal is calculated. In the above example, the difference between the total toner amount before and after inversion is the difference between the seven rear end pixels A to G (pre-inversion image LA1) and the three rear end pixels L to N (pre-inversion image LA2) (this This is equivalent to the product of the toner increase amount (correction coefficient, etc.) at the rear end pixel.

  In step S250, the control unit 10 functions as an image processing unit, and determines whether or not the difference is larger than a preset threshold value Th. If the difference is larger than the threshold value Th, the process proceeds to step S260. If the difference is equal to or less than the threshold value Th, the process proceeds to step S270. The threshold value Th may be zero, and can be set as a result of a trade-off between image processing degradation due to reversal processing cost and trailing edge accumulation, for example.

  In step S260, the halftone processing unit 22 functions as an image processing unit, and executes a drawing direction reversal process. In the drawing direction reversing process, the halftone processing unit 22 rotates dot data by 180 degrees. In step S270, the image forming unit 20 forms dots on the print medium (image forming medium) based on the dot data rotated by 180 degrees, and outputs a printed matter. Since the user can rotate the printed material as necessary, the user can receive the desired printed material with the trailing edge accumulation suppressed.

  As described above, in the image forming apparatus 1 according to the embodiment, in the electrophotography in which development is performed with the non-saturated photoconductor, the non-saturation is performed without depending on the correction processing such as reducing the toner amount of the rear end pixel. The edge effect can be reduced in electrophotography in which development is performed with the photosensitive member in the state.

  The correction process is a predictive control, and must be a uniform correction amount that can take into account changes in the edge effect and trailing edge accumulation due to fluctuations in the charge amount of the toner. In response to such a problem, the present embodiment suppresses image quality degradation caused by the trailing edge accumulation in a method that is essentially different from the conventional method of reducing the edge pixel itself by inverting the image. Can have the inherent effect of being able to Furthermore, the present embodiment has an advantage that the amount of correction processing can be reduced even when it is implemented in combination with correction processing.

  The present invention can be implemented not only in the above embodiment but also in the following modifications.

  Modification Example 1 In the above embodiment, the control unit 10 determines the necessity of the reversing process based on the difference of the total toner amount, but it is not necessary to calculate the difference of the total toner amount. In the determination of necessity of the inversion processing, the control unit 10 calculates the number of rear end pixels (or rear end pixels) and the number of front end pixels (or rear end pixels), and the number of front end pixels is the rear end pixels When the number is larger than the number, it may be determined that the total amount of toner consumed for image formation decreases.

  Modified Example 2 In the above embodiment, the control unit 10 determines the necessity of the reversing process based on the difference of the total toner amount in single-sided printing, but the invention is not necessarily limited to single-sided printing. When the control unit 10 determines that the total amount of toner consumed for forming the image formed on both sides decreases when the front end direction and the rear end direction of the image formed on both sides are reversed, Image data may be processed to invert the leading edge direction and trailing edge direction of images formed on both sides.

  Modification 3: In the above embodiment, the total toner amount which is the total amount of toner of each color of CMYK in the pixel group (specific pixel) in the vicinity of the rear end portion is estimated based on the dot area ratio. For example, the total toner amount may be estimated by measuring the influence of the trailing edge accumulation using a composite half patch as shown in FIG. 9.

  In this modification, the composite half patch is composed of a square solid patch SP of 5 mm square and eight linear ladder patches LP of 1 mm × 5 mm. The density of the solid patch SP is measured at a position 2 mm or more away from the rear end portion in the circumferential speed direction of the photosensitive drum 30 in order to avoid a rear end accumulation region, while the eight ladder patches LP are It is measured as the average value of concentration peaks.

  The density of the solid patch SP is hardly affected by the rear end accumulation, whereas the eight ladder patches LP are strongly affected by the rear end accumulation. Therefore, the density ratio of the solid patch SP and the eight ladder patches LP is used to measure the influence of the rear end accumulation, and the toners of the respective colors of CMYK at specific pixels constituting the end on the rear end side in the rotation direction of the photoreceptor. The total amount of can be estimated.

  Modification 4: In the above embodiment, calibration is performed with the developing bias potential Vslv of the developing units 100c to 100k, and when the calibration cannot be performed with the developing bias potential Vslv, calibration is performed by adjusting the dot area ratio. However, the correction is not limited to the developing bias potential Vslv and the dot area ratio, and calibration may be performed by adjusting the amount of exposure light by the exposure unit 29.

  However, when calibration is performed by adjusting the amount of exposure light, it is preferable to use the calibration preferentially over the dot area ratio. In the present invention, when calibration cannot be performed by adjusting the developing bias potential Vslv and the amount of exposure light, it is preferable to calibrate by adjusting the dot area ratio.

  Modification 5: In the above embodiment, an amorphous silicon photoconductor is used, but the present invention is not limited to the use of an amorphous silicon photoconductor. The present invention is generally applicable to an image forming apparatus that reproduces a solid density with a non-saturated photoconductor.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control part 20 Image forming part 21 Color conversion process part 28 Calibration density sensor 29 Exposure part 40 Storage part 50 Image reading part 60 Paper feed cassette 70 Case

Claims (7)

An image forming apparatus for forming an image based on image data, comprising:
A rotatable photosensitive member; an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image; a magnetic roller; and a developing roller; the magnetic roller and the developing roller; A toner layer having a thickness corresponding to a toner layer forming potential difference between the toner layer and the photosensitive member from the toner layer based on a developing bias potential which is a potential of the developing roller and the electrostatic latent image. A developing unit for attaching toner to
A solid image is obtained by adjusting the developing bias potential of the developing unit within a preset adjustment range and executing a first calibration process, and the potential limit value within the adjustment range in the first calibration process. A calibration unit that adjusts the dot area ratio to form the second and executes the second calibration process;
When it is determined that the total amount of toner consumed for forming the image decreases when the preset rear end direction of the image and the front end direction opposite to the rear end direction are reversed. An image processing unit that processes the image data and inverts the leading edge direction and the trailing edge direction of the image;
An image forming apparatus comprising: The image forming apparatus according to claim 1, further comprising:
The image forming apparatus includes an image forming unit capable of forming an image on both sides of an image forming medium.
The image processing unit reduces a total amount of toner consumed for forming the image formed on both sides when the leading end direction and the trailing end direction of the image formed on the both sides are reversed. If so, an image forming apparatus that processes the image data to invert the leading edge direction and the trailing edge direction of the image formed on both sides. The image forming apparatus according to claim 1, further comprising:
The image processing unit includes a rear end pixel number that is a number of rear end pixels that are pixels constituting a rear end region that is a preset end region in the rear end direction, and a rear end direction pixel. The number of leading edge pixels, which is the number of leading edge pixels that constitute the leading edge region that is the edge region in the leading edge direction that is the opposite direction, is calculated, and the leading edge pixel number is calculated from the number of trailing edge pixels. An image forming apparatus which determines that the total amount of toner consumed for forming the image decreases when the image forming apparatus is too large. The image forming apparatus according to claim 3,
The front end pixel includes a pixel group within a certain range in the sub-scanning direction from the front end pixel in which dots are not formed in a pixel adjacent in the front end direction of an adjacent pixel that is a pixel adjacent in the vertical direction to the front end direction,
The rear end pixel is a pixel group within a certain range in the sub-scanning direction from the rear end pixel in which no dot is formed in a pixel adjacent to the rear end direction of the adjacent pixel that is adjacent to the rear end direction in the vertical direction. An image forming apparatus including: The image forming apparatus according to any one of claims 1 to 4, wherein
The photoconductor is an amorphous silicon photoconductor,
The image forming apparatus, wherein the amorphous silicon photosensitive member forms the solid image in a non-saturated state. An image forming method for forming an image based on image data, comprising:
A rotatable photosensitive member, an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image, a magnetic roller, and a developing roller. A toner layer having a thickness corresponding to the toner layer formation potential difference between the toner layer and the electrostatic latent image is formed on the developing roller based on a developing bias potential which is a potential of the developing roller and the electrostatic latent image. A development process for adhering toner;
A solid image when the first calibration process is performed by adjusting the development bias potential of the development process within a preset adjustment range, and the potential limit value within the adjustment range is reached in the first calibration process. A calibration step of adjusting the dot area ratio to form the second calibration process and executing the second calibration process;
When it is determined that the total amount of toner consumed for forming the image is reduced when the preset rear end direction of the image and the front end direction opposite to the rear end direction are reversed. An image processing step of processing the image data to reverse the front end direction and the rear end direction of the image;
An image forming method comprising: An image forming program for controlling an image forming apparatus for forming an image on an image forming medium according to image data, comprising:
The image forming apparatus includes a rotatable photosensitive member, an exposure unit that exposes the photosensitive member based on the image data to form an electrostatic latent image, a magnetic roller, and a developing roller. A toner layer having a thickness corresponding to a toner layer forming potential difference between the roller and the developing roller is formed on the developing roller, and the developing bias potential which is the potential of the developing roller and the electrostatic latent image A developing unit for attaching toner from a toner layer to the photoreceptor;
The image forming program adjusts the developing bias potential of the developing unit within a preset adjustment range to execute a first calibration process, and the potential limit value within the adjustment range in the first calibration process And a calibration unit that adjusts a dot area ratio for forming a solid image and executes a second calibration process, and a preset rear end direction of the image and an opposite direction of the rear end direction If it is determined that the total amount of toner consumed for forming the image is reduced when the leading edge direction is reversed, the leading edge direction and the trailing edge direction of the image are processed by processing the image data. An image forming program that causes the image forming apparatus to function as an image processing unit that reverses