JP2019120728A - Image forming apparatus, image forming method, and image forming program - Google Patents

Abstract

To efficiently prevent rear-end accumulation of toner, while solving the problem of trade-off and preventing a break of thin lines and the occurrence of jaggies.SOLUTION: An image forming apparatus comprises: developing units each include a photoreceptor, an exposure 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 difference in toner layer formation potential between the magnetic roller and 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; an image forming condition setting unit that analyzes the image data to estimate the degree of occurrence of rear end accumulation of toner, and selects, on the basis of the estimate, any one of a plurality of image forming conditions in which dot area ratios for forming a solid image are different from each other; a calibration processing unit that calibrates the developing bias potential for forming a solid image with the assumption of the plurality of dot area ratios; and an image forming unit that forms and outputs an image onto an image forming medium with the selected image forming condition.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus, an image forming method, and an image forming program, and more particularly to calibration processing.

  In the image forming apparatus of the touch-down development system, the trailing end stagnation is likely to occur at the trailing end portion in the circumferential speed direction of the photosensitive member in the solid image. To address such a problem, for example, Patent Document 1 proposes a method of suppressing the trailing edge accumulation by reproducing a solid image in a state where the dot area ratio is reduced. Specifically, the technique proposed by Patent Document 1 determines the initial area ratio of a half patch which is a patch in which the dot area ratio is reduced, and steps the control value within the upper limit value of the developing bias or the laser power. A plurality of half patches of the initial area ratio are formed on the intermediate transfer member by changing the positions in the above manner. Next, the present technology creates a table showing the relationship between the toner density of a plurality of half patches and the control value used to form each half patch, and the control value and the initial area ratio of the half patch are solid. Register as a control value used to print an image.

JP, 2016-51006, A

  However, in the method of using the half patch to suppress the trailing edge accumulation, if the dot area ratio is reduced, the trailing edge accumulation can be effectively suppressed, but the thin line breaks and jaggies are more likely to occur. However, if the dot area ratio is increased, there is a trade-off problem that it is difficult to effectively suppress the trailing edge accumulation, which is a step where thin line breaks are less likely to occur.

  The present invention has been made in view of such a situation, and it is an object of the present invention to solve the problem of trade-off and to provide a technique for effectively suppressing rear end accumulation while suppressing occurrence of thin line breaks and jaggies. To aim.

  An image forming apparatus according to the present invention includes: a rotatable photosensitive member that forms a solid image in a non-saturated state; an exposure unit that exposes the photosensitive member based on image data to form an electrostatic latent image; A toner layer having a thickness corresponding to a toner layer forming potential difference between the magnetic roller and the developing roller, and a developing bias potential which is the potential of the developing roller; Based on the electrostatic latent image, at least one developing unit for causing toner to adhere from the toner layer to the photosensitive member, and analyzing the image data to estimate the degree of occurrence of trailing edge accumulation, based on the estimation Image forming condition setting unit for selecting any one of a plurality of image forming conditions having mutually different dot area rates for forming a solid image, and the plurality of dot area rates, At dot area rate Serial includes a calibration processing unit for calibrating each developing bias potential for forming a solid image, an image forming unit that forms and outputs an image on the image forming medium in the selected image forming conditions.

  The image forming method of the present invention comprises: a rotatable photosensitive member that forms a solid image in a non-saturated state; an exposure unit that exposes the photosensitive member based on image data to form an electrostatic latent image; A toner layer having a thickness corresponding to a toner layer forming potential difference between the magnetic roller and the developing roller is formed on the developing roller using the developing roller, and the developing bias potential which is the potential of the developing roller and Based on the electrostatic latent image, a developing step of attaching toner from the toner layer to the photosensitive member based on the electrostatic latent image, and the image data are analyzed to estimate the degree of occurrence of trailing edge accumulation, and a solid image is determined based on the estimation. Assuming an image forming condition setting step of selecting any one of a plurality of image forming conditions in which dot area rates for forming are different from one another, and the plurality of dot area rates, the plurality of dot area rates Said solid image Comprising a calibration process of calibrating each developing bias potential to form, and an image forming step of forming and outputting an image on the image forming medium in the selected image forming conditions.

  The present invention provides an image forming program for controlling an image forming apparatus. The image forming apparatus comprises: a rotatable photosensitive member that forms a solid image in a non-saturated state; an exposure unit that exposes the photosensitive member based on image data to form an electrostatic latent image; a magnetic roller; A toner layer having a thickness corresponding to a toner layer forming potential difference between the magnetic roller and the developing roller is formed on the developing roller, and the developing bias potential which is the potential of the developing roller The image forming program analyzes at least one of the image data and estimates the degree of occurrence of the trailing edge accumulation based on the electrostatic latent image and at least one developing unit for adhering the toner from the toner layer to the photosensitive member based on the electrostatic latent image. An image forming condition setting unit for selecting any one of a plurality of image forming conditions having mutually different dot area rates for forming a solid image based on the estimation; and assuming the plurality of dot area rates , A calibration processing unit that calibrates each developing bias potential for forming the solid image with a plurality of dot area rates; and an image forming unit that forms and outputs an image on an image forming medium under the selected image forming conditions The image forming apparatus functions as

  According to the present invention, it is possible to solve the problem of the trade-off, and to effectively suppress the trailing end accumulation while suppressing the occurrence of thin wire breaks and jaggies.

1 is a block diagram showing a functional configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 1 is a cross-sectional view showing an entire 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. 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. 5 is a flowchart showing the contents of an image forming process according to an embodiment. 5 is a flowchart showing the contents of image data analysis processing in the image forming apparatus 1 according to an embodiment. 7 is a flowchart showing the contents of a printing condition calibration process according to an embodiment. FIG. 2 is an explanatory view showing a light amount adjustment patch and a hybrid patch for setting a bias voltage, which are used in the image forming apparatus 1 according to one embodiment. 5 is a flowchart showing the contents of development bias calibration processing according to an embodiment. It is a flowchart which shows the content of the dot area ratio adjustment process which concerns on one Embodiment. FIG. 7 is an explanatory view showing a gamma adjustment patch used in gamma correction processing according to an embodiment. It is an explanatory view showing a chart for registration adjustment used by registration adjustment processing concerning one embodiment.

  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 which 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 a solid image detection unit 11, a rear end detection unit 12, an image analysis unit 13, and a calibration processing unit 14. The print data PD represents an image area group including a plurality of image areas. Each image area of the image area group is classified into a solid image area and a non-solid image area (other than solid image area) representing areas other than the solid image. The functions of the solid image detection unit 11, the rear end detection unit 12, the image analysis unit 13, and the calibration processing unit 14 will be described later.

  The control unit 10 includes a main storage unit such as a RAM and a ROM, and a control unit such as an MPU (Micro Processing Unit) and a 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, which is a non-temporary recording medium, and stores control programs and data of processing executed by the control unit 10. In the present embodiment, the storage unit 40 further stores a calibration data storage area R1 and a print setting data storage area R2.

  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 drive roller 26 a.

  At the upstream position of the photosensitive drum 30k, the cleaning device 200 is disposed at a position opposed to the driven roller 26b with the intermediate transfer belt 27 interposed therebetween. The cleaning device 200 has a fur brush 210 on which fine fibers are planted and which rotates at high speed. The fur brush 210 can mechanically remove the toner on the intermediate transfer belt 27 by the scraping force of the brush tip. As described above, the image forming apparatus 1 adopts the brush cleaning method using the fur brush 210 in contact with the intermediate transfer belt 27, and scraps and discards the used toner.

  For example, the black toner image on the photosensitive drum 30k is primarily transferred to the intermediate transfer belt 27 by the intermediate transfer belt 27 being driven to circulate by nipping the intermediate transfer belt 27 between the photosensitive drum 30k and the primary transfer roller 23k. 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 by the fixing roller pair 81 of the fixing unit 80. The cleaning device 200 can remove residual toner remaining on the intermediate transfer belt 27 from the intermediate transfer belt 27 also for the calibration patch. Print media are also referred to as imaging media.

  FIG. 3 is a side sectional view showing the structure of the developing unit 100k according to an embodiment. 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 stirring and conveying members 141 and 142, a magnetic roller 143, a developing roller (developer carrier) 144, a developing container 145, and a regulating blade 146.

  The developing container 145 constitutes the outer shell 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 columnar shape in the direction perpendicular to FIG. 3, and accommodates a two-component developer (also referred to simply as a developer) composed of a magnetic carrier and a 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 stirring and conveying members 141 and 142 move the developer cyclically while stirring the developer in the first conveyance chamber 145a and the second conveyance 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 has a nonmagnetic rotation sleeve 143a and a fixed magnet body 143b fixed inside the rotation 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 has a rotatable nonmagnetic developing sleeve 144 a and a developing roller side magnetic pole 144 b fixed inside the developing sleeve 144 a. The magnetic roller potential Vmag is applied to the magnetic roller 143. The 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. At the time of development, a DC potential of 200 V is applied to the magnetic roller 143 as the magnetic roller potential Vmag, and at a time of non-development, a DC potential of -200 V is applied.

  As a result, at the time of development, the time of developing bias potential Vslv <magnetic roller potential Vmag (the state in which the toner is supplied to developing roller 144) becomes longer, and the time of supplying toner to developing roller 144 becomes longer. At the time of non-developing, the time of developing bias potential Vslv> magnetic roller potential Vmag (potential state where toner is recovered from developing roller 144) becomes longer, and time of recovering toner from 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. As a result, the toner thin layer (simply, toner) having a thickness D (see FIG. 4A described later) corresponding to the toner layer forming potential difference .DELTA.V 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 causes toner to adhere to the photosensitive drum 30 via an opposing portion (developing nip) having a predetermined clearance with the photosensitive drum 30, and forms 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 on the surface of the photosensitive drum 30 and the developing bias potential Vslv applied to the developing roller 144.

  The amorphous silicon photosensitive member is characterized in that the relative dielectric constant is about three times as high as that of the organic photosensitive member (OPC), and the amount of toner that can be held by the photosensitive member is large with respect to 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 as determined.

  FIG. 4 is a conceptual view showing how trailing end accumulation occurs in the developing step according to one embodiment. FIG. 4A shows a state in which an image is formed at the front end portion and the central 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 center portion and the rear end portion are defined as the front end portion, the center portion and the rear end portion in order from the traveling direction with reference to the traveling direction of the photosensitive drum 30.

  In the present embodiment, as shown in FIG. 4A, the photosensitive drum 30 receives supply of 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 completed not by the saturation of the potential but by the consumption of the thin toner layer formed on the developing sleeve 144a in the non-saturated state. 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 velocity Vs, and is configured to form an image while passing over the photosensitive drum 30 at the peripheral velocity 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 in a non-saturated state, the toner is further developed from the surface of the developing sleeve 144 a 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 solid image TP. In the solid image TP, at the time of image formation, the toner layer is raised at the rear end. The rise of the toner layer is called trailing edge accumulation.

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

  However, the problem of the rear end accumulation is that, for example, when the central portion is extremely small in the traveling direction of the photosensitive drum 30, for example, in the case of reproducing a thin ruled line in a direction perpendicular to the traveling direction (circumferential velocity direction) of the photosensitive drum 30. The density of the entire ruled line is high. Therefore, such a ruled line does not cause the image quality deterioration as color unevenness such as the trailing edge accumulation, but only the density of the entire ruled line becomes high. The present invention can suppress the reduction in image quality deterioration caused by the rear end accumulation.

  FIG. 5 is an explanatory view showing the contents of the image forming process in the image forming apparatus 1 according to one embodiment. FIG. 5A is a flowchart showing the contents of the image forming process (step S100) according to an embodiment. In step S110, the image forming unit 20 executes dot data generation processing using the color conversion processing unit 21 and the halftone processing unit 22. In the dot data generation processing, the image forming unit 20 generates dot data (print data PD) representing the dot formation state by color conversion processing or halftone processing.

  In step S120, the control unit 10 executes an image data analysis process. In the image data analysis process, the control unit 10 quantitatively quantifies the degree of occurrence of the trailing edge accumulation for each page to be printed.

  FIG. 6 is a flowchart showing the contents of the image data analysis process (step S120) in the image forming apparatus 1 according to an embodiment. In step S121, the solid image detection unit 11 executes an image attribute determination process. The image attribute determination process is a process of determining whether each image area included in the image area group represented by the print data PD is a solid image area.

  In the image attribute determination process, the solid image detection unit 11 focuses on each image area in order and determines whether it is a solid image area or not, that is, it can be said to be a solid image area and a non-solid image area (an image area other than solid image area). Determine which of the two). The solid image detection unit 11 is an image area having a size equal to or greater than a preset size, and the image area has a substantially uniform tone value such as a highest tone value or a substantially highest tone value as a solid image region. It is determined that The focused image area is called a focused image area.

  In step S122, if the focused image area is not a solid image area, that is, if the focused image area is a non-solid image area, the process proceeds to step S126, and the focused image area is a solid image area. The process proceeds to step S123.

  In step S123, the rear end detection unit 12 executes rear end detection processing. In the rear end detection process, the rear end detection unit 12 detects pixels that constitute the rear end of the solid image area as the target image area. The detection of the rear end portion (pixel) can be realized by detecting the contour in the direction perpendicular to the circumferential speed direction of the photosensitive drums 30c to 30k using a filter such as a differential filter or a Sobel filter, for example. .

  In step S124, the image analysis unit 13 executes a specific trailing edge detection process. In the specific rear end detection process, the image analysis unit 13 detects the rear end adjacent to the central portion having a size (for example, the length or the number of pixels such as 3 to 7 mm) larger than a threshold set in advance in the circumferential speed direction. The part is extracted as a specific rear end (see FIG. 4). The specific rear end portion is a rear end portion adjacent to the central portion having a size sufficient to generate rear end accumulation.

  In step S125, the image analysis unit 13 executes a specific trailing edge count process. In the specific rear end counting process, the number of pixels forming the specific rear end of the target image area is counted. The control unit 10 executes the processing of step S121 to step S125 on all the image areas, focusing on each of the image areas in order (step S126).

  In step S127, the image analysis unit 13 executes a specific trailing edge tabulation process. In the specific rear end tallying process, the image analysis unit 13 adds up and counts the number of pixels forming the specific rear end of each image area, and calculates the specific rear end total number.

  In step S130 (see FIG. 5), the image analysis unit 13 executes a printing condition setting process. In the printing condition setting process, the image analysis unit 13 selects any one of the printing conditions 1 to 4 prepared in advance based on the total number of the specific rear end portions. The print conditions 1 to 4 are stored in the print setting data storage area R2 of the storage unit 40.

  FIG. 5B shows four print conditions (print condition 1 to print condition 4) that can be set in the image forming apparatus 1 according to the embodiment. The four printing conditions are characterized in that the dot area rates are different from one another.

  The printing condition 1 forms a solid at a dot area rate of 70% when forming a solid image, a bias 1 which is a bias voltage for forming a solid at a dot area rate of 70%, and a dot area ratio of 70% In this case, gamma 1 which is an input / output gamma for realizing a linear input / output relationship is set. On the other hand, printing condition 4 includes 100% dot area ratio when forming a solid image, bias 4 which is a bias voltage for forming a solid with 100% dot area ratio, and 100% dot area ratio. In order to realize a linear input / output relationship when forming the input image, gamma 4 which is input / output gamma is set. Input / output gamma is also referred to as input / output gamma correction value.

  The printing condition 1 (dot area ratio 70%) is the printing condition that is the most effective for suppressing the trailing edge accumulation, but causes a thin line break or jaggies. The printing condition 4 (dot area rate 100%) is the printing condition that is the most effective for suppressing the occurrence of the thin line break and the occurrence of jaggies, but causes the trailing edge accumulation. The printing condition 2 (dot area ratio 80%) is a printing condition that prioritizes the suppression of the trailing edge accumulation relatively. The printing condition 3 (dot area ratio 90%) is a printing condition that prioritizes the suppression of thin line breaks and jaggy generation relatively.

  The image analysis unit 13 can select, for example, the printing condition 1 that is most effective for suppressing the trailing edge accumulation for an image in which the trailing edge accumulation having a specific total number of trailing end portions of 10000 or more is likely to occur. For an image in which the occurrence of the trailing end accumulation is not assumed to be the specific trailing end total number is 0, it is possible to select the printing condition 4 that is most effective in suppressing the thin line interruption and the occurrence of jaggies.

  In the past, suppression of trailing end accumulation and interruption of thin lines and occurrence of jaggy have been the objects of trade-off. On the other hand, according to the present invention, it is possible to predict the degree of occurrence of trailing edge accumulation based on the image data PD, and switch the printing conditions based on the predicted degree of occurrence of trailing edge accumulation.

  In step S140, the image forming unit 20 executes a printed matter output process. In the printed matter output process, the control unit 10 sets the dot area ratio, the developing bias potential Vslv and the input / output gamma based on the selected printing conditions, and controls the image forming unit 20 to form an image on the image forming medium. . The control unit 10 also has functions as an image forming condition setting unit and a gamma correction unit.

  As described above, the image forming apparatus 1 can predict (estimate) the degree of generation of the trailing edge accumulation based on the image data PD, and switch the printing conditions based on the predicted degree of generation of the trailing edge accumulation. Therefore, it is possible to solve the problem of the trade-off between the suppression of the rear end accumulation and the interruption of thin lines and the occurrence of jaggies.

  FIG. 7 is a flowchart showing the contents of the printing condition calibration process (step S200) according to the embodiment. FIG. 8 is an explanatory view showing a light amount adjustment patch PL and a hybrid patch PH for setting a bias voltage used in the image forming apparatus 1 according to an embodiment. Such printing conditions of printing condition 1 to printing condition 4 can be realized by printing condition calibration processing.

  In step S210, the calibration processing unit 14 executes a light amount calibration process. In the light amount calibration process, the calibration processing unit 14 exposes the exposure unit 29 with laser light of a plurality of light amounts changed stepwise in a plurality of stages set in advance, and has a chart having a plurality of light amount adjustment patches PL. The intermediate transfer belt 27 is formed. The image data representing the light amount adjustment patch PL is stored in the calibration data storage area R1 of the storage unit 40.

  The calibration processing unit 14 exposes the photosensitive drums 30c to 30k so as to form the light amount adjustment patches PL with laser beams of a plurality of different light amounts. In this example, the light amount adjustment patch PL has a dot area ratio of 25% as a dot area ratio suitable for light amount adjustment.

  The calibration processing unit 14 measures the density of the patch of each color (for example, black (K)) using the density sensor 28 for calibration. The calibration processing unit 14 performs, for example, interpolation calculation to obtain a preset target density using reflected light of the plurality of light amount adjustment patches PL exposed by the plurality of different amounts of laser light. Set the calibration light amount which is the light amount. The calibration processing unit 14 stores the calibration light amount in the print setting data storage area R2 of the storage unit 40. In this example, a single calibration light amount is commonly used for printing conditions 1 to 4.

  In the present embodiment, the calibration concentration sensor 28 emits infrared light from, for example, an LED (not shown), transmits the polarization filter that transmits only the P wave, and irradiates the P wave of the infrared light to the patch 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 also has a regular reflection method for detecting regular reflection light from a patch and a diffuse reflection method for detecting diffuse reflection light from a patch.

  FIG. 9 is a flow chart showing the contents of the developing bias calibration process (step S220) according to one embodiment. In step S220, the calibration processing unit 14 executes development bias calibration processing. In the developing bias calibration process, the calibration processing unit 14 calibrates the image forming bias potential and the registration bias potential at the calibration light amount. The registration bias potential is a development bias potential for detecting color misregistration.

  In step S221, the calibration processing unit 14 executes a hybrid patch formation process. In the hybrid patch formation process, the calibration processing unit 14 forms, on the intermediate transfer belt 27, a chart having a plurality of hybrid patches PH in which the development bias potential Vslv is changed stepwise in a plurality of preset stages. Image data representing the hybrid patch PH is stored in the calibration data storage area R1 of the storage unit 40.

  In this example, the hybrid patch PH is composed of a half patch P80 and a solid patch P100 in order to make the description easy to understand. The half patch P80 is a patch used for the calibration of the image forming bias potential in which the dot area ratio of the printing condition 2 is 80%. The solid patch P100 is a patch having a dot area ratio of 100%, that is, a dot area ratio for detecting color misregistration, which is used for calibration of a registration bias potential.

  The hybrid patch PH can be configured as a combination of four patches with dot area rates of 70%, 80%, 90% and 100% respectively corresponding to the printing conditions 1 to 4.

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

  In step S222, the calibration processing unit 14 executes concentration detection processing. In the density detection process, the calibration processing unit 14 measures the density of patches of each color (for example, cyan (C)) of the half patch P80 and the solid patch P100 using the calibration density sensor 28. The density of the patch can be measured, for example, as the amount of red reflected light in a complementary color relationship of cyan (C). The same process is performed for MYK.

  In step S223, the calibration processing unit 14 determines whether the previous area ratio deviation read out from the calibration data storage area R1 is larger than the threshold value 0 or not. If the previous area ratio deviation is greater than or equal to the threshold value 0, the calibration processing unit 14 proceeds to step S224. If the previous area ratio deviation is less than the threshold value 0, the calibration processing unit 14 proceeds to step S225. Advance. In this example, the previous area ratio deviation is the deviation of the gradation value finally remaining in the previous calibration of input / output gamma. In this example, the gradation value has a gradation of 0 to 255.

  In step S224, the calibration processing unit 14 adjusts the density target value used to calibrate the bias potential for image formation to set the adjustment target value. The adjustment target value (the density target value actually used for calibrating the bias potential) is calculated, for example, by adding the tone deviation α corresponding to the previous area ratio deviation to the nominal density target value (solid density value). can do. As a result, the image forming bias potential is increased according to the tone deviation α.

  In step S225, the calibration processing unit 14 subtracts the tone deviation α corresponding to the previous area ratio deviation, for example, from the nominal density target value (solid density value) to actually adjust the adjustment target value (bias potential calibration). The target concentration value to be used can be calculated and set. As a result, the image forming bias potential is lowered according to the tone deviation α.

  The image density increases as the image forming bias potential increases, and increases as the dot area ratio increases. Therefore, an increase in the image forming bias potential causes a decrease in the dot area ratio in reproducing the target density, and a decrease in the image forming bias potential causes an increase in the dot area ratio in reproducing the target density. Therefore, the adjustment of the target value using the gradation deviation α works to offset the previous area ratio deviation.

  In step S226, the calibration processing unit 14 executes a bias calibration process for image formation. In the image forming bias calibration process, the calibration processing unit 14 uses the measured density and the adjustment target value of the half patch P80 among the plurality of hybrid patches PH in which the developing bias potential Vslv is changed stepwise. The potential Vslv can be calibrated.

  Specifically, in the calibration processing unit 14, among the plurality of cyan (C) half patches in which the developing bias potential Vslv is changed stepwise, a patch which has reached a solid image target density set in advance is selected. If it exists, it is executed by selecting the development bias potential Vslv corresponding to that patch. That is, when there is a half patch in which the ratio of the P wave to the S wave is equal to or less than the preset threshold value, the calibration processing unit 14 develops the lowest development bias potential Vslv of the half patches after calibration. Adjust to the potential of the bias. Thus, the calibration processing unit 14 can calibrate the developing bias potential Vslv of the bias 2 under the printing condition 2.

  In step S227, the calibration processing unit 14 executes a registration bias calibration process which is a calibration process for detecting color misregistration. In the bias calibration process for registration, the development bias potential Vslv is calibrated using the measurement density of the solid patch P100 among the plurality of hybrid patches PH in which the development bias potential Vslv is changed stepwise and the adjustment target value. Can. Thus, the calibration processing unit 14 can calibrate the development bias potential Vslv (development bias potential for detecting color misregistration) for calibration of the registration bias.

  The calibration processing unit 14 can calibrate the development bias potential Vslv under the printing conditions 1 and 3 in the same manner. On the other hand, the developing bias potential Vslv for registration bias calibration can be shared as the developing bias potential Vslv under the printing condition 4. The calibration processing unit 14 stores all of the development bias potentials Vslv after calibration in the print setting data storage area R2 of the storage unit 40.

  In step S230 (FIG. 7), if the half patch calibration is possible within the adjustment range of the developing bias for the printing conditions 1 to 4, the process proceeds to step S250 and the half processing is performed for half printing. If the patch calibration is not possible within the adjustment range of the development bias potential Vslv, the process proceeds to step S240.

  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. Usually, one of the plurality of half patches reaches the solid image target density, but may not reach the solid image target density in a state where the toner charge amount is increased due to, for example, environmental fluctuation.

  In this example, the calibration processing unit 14 determines that the printing condition 1 (dot area ratio 70%) is not possible within the adjustment range of the developing bias potential Vslv, and the printing conditions 2 to 4 (dot area ratio 70%) Is considered to be possible within the adjustment range of the development bias. In this case, the process proceeds to step S240 only for the printing condition 1.

  FIG. 10 is a flowchart showing the contents of the dot area ratio adjustment process (step S240) according to one embodiment. In step S241, the calibration processing unit 14 sets the development bias potential Vslv to the maximum value, and starts the process of adjusting and adjusting the dot area ratio. The maximum value of the developing bias potential Vslv is also referred to as a potential limit value, and is set, for example, from the output limit of the developing bias or an adverse effect (fogging or the like) on the image.

  In step S 242, the calibration processing unit 14 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 (for example, three steps of 73%, 75%, and 77%) in the range of 71% to 79%. With regard to printing condition 2 (dot area ratio 80%), it was determined that the half patch calibration was possible within the adjustment range of the development bias.

  In step S243, the calibration processing unit 14 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 to the S wave. The same process is performed for MYK.

  In step S244, the calibration processing unit 14 executes dot area ratio setting processing. Specifically, when there is a half patch whose ratio of P wave to S wave is equal to or less than a preset threshold, the calibration processing unit 14 determines that half patch (for example, 73%, 75%, 77%). The dot area rate of the half patch having the lowest dot area rate among the three stages) is acquired as printing condition setting data. In this example, it is assumed that the dot area ratio after adjustment is equal to or less than the threshold value in which the ratio of P wave to S wave is half set in half patch P73 (dot area ratio 73%).

  The calibration processing unit 14 updates the data of the printing condition 1 with the adjusted dot area ratio (73%) and the maximum value of the development bias potential Vslv, and stores the data in the print setting data storage area R2 of the storage unit 40.

  In step S250 (FIG. 7), the calibration processing unit 14 executes gamma setting processing. In the gamma setting process, the calibration processing unit 14 sets the maximum dot area ratio to 73% for the printing condition 1. Thus, the calibration processing unit 14 outputs the output tone value as the image density of 0 to 255 (density 0% to 100%) linearly with respect to the input tone value of 0 to 255 (density 0% to 100%). Input and output gammas can be set to realize (dot area ratio 0% to 73%).

  The calibration processing unit 14 sets the maximum dot area ratio to 80%, 90%, and 100% with respect to the input tone values of 0 to 255 for the printing condition 2, the printing condition 3, and the printing condition 4, respectively. . Thereby, the calibration processing unit 14 linearly outputs output tone values of 0 to 255 (dot area ratio 0% to 80%, dot area ratio 0% to 90%) with respect to input gradation values of 0 to 255, respectively. And an input / output gamma for realizing a dot area ratio of 0% to 100%).

  FIG. 11 is an explanatory view showing a gamma adjustment patch used in the gamma correction process according to an embodiment. The gamma adjustment patches are a half patch P20 of dot area 20%, a half patch P40 of dot area 40%, a half patch P60 of dot area 60%, a half patch P80 of dot area 80% and a solid patch P100 of dot area 100%. have.

  The calibration processing unit 14 sets the developing bias potential Vslv to the bias 1 and has the half patch P20, the half patch P40, the half patch P60, and the half patch P73 for the printing condition 1 (the dot area ratio has been updated to 73%). A chart is formed on the intermediate transfer belt 27. The calibration processing unit 14 measures the density of the half patch P20, the half patch P40, the half patch P60, and the half patch P73, and outputs an output tone value of 0 to 255 linearly with respect to an input tone value of 0 to 255. The input / output gamma (gamma 1) for realizing (dot area ratio 0% to 73%) is set.

  The calibration processing unit 14 sets the developing bias potential Vslv to the bias 2 for the printing condition 2 (dot area ratio 80%), and intermediates the chart having the half patch P20, the half patch P40, the half patch P60 and the half patch P80. The transfer belt 27 is formed. The calibration processing unit 14 measures the densities of the half patch P20, the half patch P40, the half patch P60, and the half patch P80, and outputs an output tone value of 0 to 255 linearly with respect to an input tone value of 0 to 255. The input / output gamma (gamma 2) for realizing (dot area ratio 0% to 80%) is set.

  The calibration processing unit 14 sets the development bias potential Vslv to the bias 3 for the printing condition 3 (dot area ratio 90%), and sets the half patch P20, the half patch P40, the half patch P60, the half patch P80, and the half patch P90. A chart having a dot area ratio of 90% is formed on the intermediate transfer belt 27. The calibration processing unit 14 measures the densities of the half patch P20, the half patch P40, the half patch P60, the half patch P80, and the half patch P90, and linearly measures 0 to 255 for input tone values of 0 to 255, respectively. The input / output gamma (gamma 3) for realizing the output tone value (dot area ratio 0% to 90%) is set.

  The calibration processing unit 14 sets the developing bias potential Vslv to the bias 4 for the printing condition 4 (dot area ratio 100%), and sets the half patch P20, the half patch P40, the half patch P60, the half patch P80, and the solid patch P100. The chart having the above is formed on the intermediate transfer belt 27. The calibration processing unit 14 measures the densities of the half patch P20, the half patch P40, the half patch P60, the half patch P80, and the solid patch P100, and linearly adjusts 0 to 255 for input tone values of 0 to 255, respectively. The input / output gamma (gamma 4) for realizing the output tone value (dot area ratio 0% to 100%) is set.

  In order to realize the target output gradation value (density), the inventor of the present invention inputs and outputs from the dot area ratio (for example, 80% in the case of printing condition 2) assumed when setting the developing bias potential Vslv. It has been found that the dot area rate after gamma setting may be free.

  In step S260, the calibration processing unit 14 executes area ratio deviation acquisition processing. In the area ratio deviation acquisition process, the calibration processing unit 14 determines the dot area ratio corresponding to the input tone value for reproducing a solid image using the calibrated input / output gamma correction value, and is determined. The deviation between the dot area rate and the predetermined dot area rate as the target value is calculated. The calibration processing unit 14 converts the deviation of the dot area ratio and the target value into a gradation deviation α of 0 to 255 using, for example, the input and output gamma correction values, and the respective gradations under the printing conditions 1 to 4 The deviations α (α 1 to α 4) are stored in the calibration data storage area R 1 of the storage unit 40. Thus, the calibration processing unit 14 also functions as a deviation management unit.

  Specifically, under printing condition 1, the calibration processing unit 14 calculates the deviation of the dot area ratio and the dot area ratio of 73% (target value) with respect to 100% of the input gradation value after the gamma calibration process. For the printing conditions 2 to 4, deviations of the dot area ratio of 80% to 100% (target value) from the dot area ratios under the printing conditions 2 to 4 with respect to the input gradation value of 100% are calculated.

  In step S270, the calibration processing unit 14 executes registration adjustment processing. In the registration adjustment process, the calibration processing unit 14 adjusts the CMYK image formation timing for forming a full color toner image by superimposing the CMYK images on each other. That is, the calibration processing unit 14 detects color misregistration between the plurality of CMYK images formed on the intermediate transfer belt 27 by the plurality of developing units 100 c to 100 k, and suppresses color misregistration between the plurality of images. The image forming timing in a plurality of developing units and the relative image forming position in the main scanning direction are adjusted.

  FIG. 12 is an explanatory view showing a registration adjustment chart used in the registration adjustment process according to the embodiment. The calibration processing unit 14 forms a registration adjustment chart PR on the intermediate transfer belt 27 at a dot area ratio of 100% using a registration bias potential.

  The registration adjustment chart PR includes K main patch Km, M main patch Mm, C main patch Cm and Y main patch Ym, K sub patch Ks, and M sub patch Ms with each of the CMYK toners at a predetermined timing. The C minor patch Cs and the Y minor patch Ys are formed. The K main patch Km, the M main patch Mm, the C main patch Cm, and the Y main patch Ym are patches for detecting the amount of color misregistration in the main scanning direction (the direction perpendicular to the transport direction). The K secondary patch Ks, the M secondary patch Ms, the C secondary patch Cs, and the Y secondary patch Ys are patches for detecting the amount of color misregistration in the secondary scanning direction (direction parallel to the transport direction).

  The calibration processing unit 14 detects the timing of density increase on the leading end side of each patch, and measures the positional relationship of the images formed by the plurality of developing units 100c to 100k. The calibration processing unit 14 can detect color misregistration between a plurality of images based on the positional relationship of the measured images. The calibration processing unit 14 calibrates the relative time difference (timing) of the image formation by the plurality of developing units 100c to 100k and the position in the main scanning direction so as to suppress the detected color shift.

  The registration adjustment chart PR is formed with a dot area ratio of 100%. For example, when the registration adjustment chart PR is formed with a dot area ratio of about 70%, jaggies (jagged outlines) occur in the outline (in this case, the outline on the tip side), and accurate detection of color misregistration can not be performed. It is from.

  However, conventionally, a developing bias potential for achieving a solid density with a dot area rate of 70% (a dot area rate lower than the dot area rate for detecting color misregistration) for suppressing trailing edge accumulation is used. The When the inventor of the present application forms a registration adjustment chart PR with a dot area ratio of 100% using such a development bias potential Vslv, the toner amount of the patch becomes excessive and the patch cleaning performance deteriorates or the color shifts. It has been found that variations in detection occur.

  In this embodiment, since the registration adjustment chart PR is formed using the developing bias potential Vslv set assuming a dot area ratio of 100%, the cleaning performance is deteriorated due to excessive toner in the registration adjustment chart PR. And detection variations can be suppressed.

  In step S280, the proofreading processing unit 14 executes a printing parameter setting process. In the printing parameter setting process, the dot area ratio, the developing bias potential Vslv and the input / output gamma are set in the printing conditions 1 to 4, respectively, and stored in the print setting data storage area R2. On the other hand, the range of the specific number of rear end parts can be determined by carrying out an experiment or simulation for each print medium of each size.

  As described above, in the image forming apparatus 1 according to the embodiment, in the image forming apparatus for reproducing the solid density with the photosensitive member in the non-saturated state, three main features for realizing high image quality while suppressing the trailing edge retention have.

  The first feature is to predict the degree of occurrence of trailing edge accumulation based on image data PD, and to switch the printing condition (also referred to as image forming condition) based on the predicted degree of occurrence of trailing edge accumulation. it can. As a result, it is possible to solve the trade-off problem of the suppression of the rear end accumulation and the interruption of thin lines and the occurrence of jaggies.

  The second feature focuses on the dot area ratio after gamma calibration and corrects the target value at the time of calibration to set the developing bias potential Vslv next time, thereby bringing the dot area ratio after gamma calibration closer to the target value. be able to. As a result, it is possible to realize the suppression of the rear end accumulation and the interruption of thin lines and the occurrence of jaggy in a highly accurate balance.

  The third feature is that a registration adjustment chart PR can be formed using a developing bias potential Vslv individually set for registration adjustment assuming a dot area ratio of 100%. As a result, it is possible to suppress the deterioration of the cleaning performance and the detection variation due to the toner excess of the registration adjustment chart PR.

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

  In the above embodiment, an amorphous silicon photoreceptor is used, but the present invention is not limited to the use of an amorphous silicon photoreceptor. The present invention can be generally applied to an image forming apparatus that reproduces solid density with a non-saturated photosensitive member.

Reference Signs List 1 image forming apparatus 10 control unit 20 image forming unit 21 color conversion processing unit 28 density sensor 29 for calibration exposure unit 40 storage unit 50 image reading unit 60 sheet feeding cassette 70 housing

Claims (6)

A rotatable photosensitive member that forms a solid image in a non-saturated state; an exposure unit that exposes the photosensitive member based on 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 magnetic roller and the developing roller is formed on the developing roller, and a developing bias potential which is the potential of the developing roller and the electrostatic latent image are formed. At least one developing unit for adhering toner from the toner layer to the photoreceptor;
The image data is analyzed to estimate the degree of occurrence of trailing edge accumulation, and one of a plurality of image forming conditions having mutually different dot area ratios for forming a solid image based on the estimation is selected Image forming condition setting unit,
A calibration processing unit that calibrates each developing bias potential for forming the solid image with the plurality of dot area rates, assuming the plurality of dot area rates;
An image forming unit that forms and outputs an image on an image forming medium under the selected image forming condition;
An image forming apparatus comprising: The image forming apparatus according to claim 1,
The at least one developing unit includes a plurality of developing units,
The plurality of image forming conditions include image forming conditions for forming a patch for detecting color misregistration for detecting color misregistration between a plurality of images formed by the plurality of developing units,
The calibration processing unit forms the patch for color shift detection under the image forming condition for forming the patch for color shift detection, and the plurality of developments so as to suppress the color shift between the plurality of images. An image forming apparatus that adjusts a relative image forming position by a unit. The image forming apparatus according to claim 1, further comprising:
An intermediate transfer belt for transferring the toner from the plurality of photosensitive members and transferring the transferred toner onto an image forming medium;
A density sensor that measures the density of toner transferred to the intermediate transfer belt;
Equipped with
An image forming apparatus configured to calibrate the development bias potential for each of the plurality of dot area rates in accordance with the density of the solid image formed on the assumption of the plurality of dot area rates. The image forming apparatus according to any one of claims 1 to 3, wherein
The photosensitive member is an amorphous silicon photosensitive member,
The image forming apparatus wherein the amorphous silicon photosensitive member forms a solid image in a non-saturated state. A rotatable photosensitive member that forms a solid image in a non-saturated state, an exposure unit that exposes the photosensitive member based on 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 forming potential difference between the magnetic roller and the developing roller is formed on the developing roller, and based on the developing bias potential which is the potential of the developing roller and the electrostatic latent image Developing the toner from the toner layer onto the photosensitive member;
The image data is analyzed to estimate the degree of occurrence of trailing edge accumulation, and one of a plurality of image forming conditions having mutually different dot area ratios for forming a solid image based on the estimation is selected Image forming condition setting process,
A calibration processing step of calibrating each developing bias potential for forming the solid image with the plurality of dot area rates assuming the plurality of dot area rates;
An image forming step of forming an image on an image forming medium under the selected image forming condition and outputting the image;
An image forming method comprising: An image forming program for controlling an image forming apparatus, comprising:
The image forming apparatus comprises: a rotatable photosensitive member that forms a solid image in a non-saturated state; an exposure unit that exposes the photosensitive member based on image data to form an electrostatic latent image; a magnetic roller; A toner layer having a thickness corresponding to a toner layer forming potential difference between the magnetic 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 at least one developing unit for adhering toner from the toner layer to the photosensitive member based on an electrostatic latent image,
The image forming program is
The image data is analyzed to estimate the degree of occurrence of trailing edge accumulation, and one of a plurality of image forming conditions having mutually different dot area ratios for forming a solid image based on the estimation is selected Image forming condition setting unit,
A calibration processing unit that calibrates each developing bias potential for forming the solid image with the plurality of dot area rates assuming the plurality of dot area rates, and the image forming medium under the selected image forming condition An image forming program which causes the image forming apparatus to function as an image forming unit that forms and outputs an image.