JP6890771B2 - Image forming apparatus, image forming method and image forming program - Google Patents

Description

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

In a touchdown development type image forming apparatus, a rear end pool is likely to occur at the rear end portion of the photoconductor in the peripheral speed direction in a solid image. To solve such a problem, for example, Patent Document 1 proposes a method of suppressing trailing edge accumulation by reproducing a solid image in a state where the dot area ratio is reduced. Specifically, the technique proposed in Patent Document 1 determines the initial area ratio of a half patch, which is a patch with a reduced dot area ratio, and steps the control value within a range within the upper limit of development bias or laser power. By changing the ratio, a plurality of half patches having an initial area ratio are formed on the intermediate transfer body. Next, this technology creates a table showing the relationship between the toner concentrations of multiple half patches and the control values used to form each half patch, and sets the control values and the initial area ratio of the half patches to solid. Register as a control value used for printing an image.

Japanese Unexamined Patent Publication No. 2016-51006

However, in the method of suppressing the rear end accumulation using a half patch, while the rear end accumulation can be effectively suppressed by reducing the dot area ratio, the fine line breakage and jaggies are likely to occur, and the opposite is true. In addition, there was a trade-off problem that when the dot area ratio was increased, it became difficult for fine lines to be interrupted, and it was not possible to effectively suppress the accumulation at the rear end.

The present invention has been made in view of such a situation, and provides a technique for solving a trade-off problem and effectively suppressing rear end accumulation while suppressing breakage of thin lines and generation of jaggy. The purpose.

The image forming apparatus of the present invention includes a rotatable photoconductor that forms a solid image in an unsaturated state, an exposure unit that exposes the photoconductor to form an electrostatic latent image based on image data, and a magnetic roller. A developing roller is provided, and 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 development bias potential, which is the potential of the developing roller, is used. Based on the electrostatic latent image, at least one developing unit for adhering toner from the toner layer to the photoconductor and the image data are analyzed to estimate the degree of occurrence of rear end pooling, and based on the estimation. An image forming condition setting unit that selects one of a plurality of image forming conditions in which the dot area ratios for forming a solid image are different from each other, and the plurality of dot area ratios assuming the plurality of dot area ratios. It includes a calibration processing unit that calibrates each development bias potential for forming the solid image with a dot area ratio, 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 method of the present invention includes a rotatable photoconductor that forms a solid image in an unsaturated state, an exposed portion that exposes the photoconductor to form an electrostatic latent image based on image data, and a magnetic roller. Using 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 the development bias potential which is the potential of the developing roller and the development bias potential are described. A development step of adhering toner from the toner layer to the photoconductor based on the electrostatic latent image and the image data are analyzed to estimate the degree of occurrence of trailing edge pools, and a solid image is obtained based on the estimation. Assuming an image formation condition setting step of selecting one of a plurality of image formation conditions in which the dot area ratios for formation are different from each other and the plurality of dot area ratios, the plurality of dot area ratios are used. It includes a calibration processing step of calibrating each development bias potential for forming the solid image, and an image forming step of forming an image on an image forming medium under the selected image forming conditions and outputting the image.

The present invention provides an image forming program for controlling an image forming apparatus. The image forming apparatus includes a rotatable photoconductor that forms a solid image in an unsaturated state, an exposure unit that exposes the photoconductor to form an electrostatic latent image based on image data, a magnetic roller, and development. The developing roller has a roller, and 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 the developing bias potential which is the potential of the developing roller and the static. The image forming program includes at least one developing unit for adhering toner from the toner layer to the photoconductor based on the electron latent image, and the image forming program analyzes the image data to estimate the degree of occurrence of rear end pooling. An image forming condition setting unit that selects one of a plurality of image forming conditions in which the dot area ratios for forming a solid image are different from each other based on the above estimation, assuming the plurality of dot area ratios. , A calibration processing unit that calibrates each development bias potential for forming the solid image with the plurality of dot area ratios, and image formation that forms and outputs an image on an image forming medium under the selected image forming conditions. The image forming apparatus functions as a unit.

According to the present invention, the problem of trade-off can be solved, and the rear end accumulation can be effectively suppressed while suppressing the breakage of thin lines and the generation of jaggy.

It is a block diagram which shows the functional structure of the image forming apparatus 1 which concerns on one Embodiment of this invention. It is sectional drawing which shows the whole structure of the image forming apparatus 1 which concerns on one Embodiment. It is a side sectional view which showed the structure of the developing part 100 which concerns on one Embodiment. It is a conceptual diagram which shows the state that the rear end accumulation occurs in the development process which concerns on one Embodiment. It is a flowchart which shows the content of the image formation process which concerns on one Embodiment. It is a flowchart which shows the content of the image data analysis processing in the image forming apparatus 1 which concerns on one Embodiment. It is a flowchart which shows the content of the print condition proofreading process which concerns on one Embodiment. It is explanatory drawing which shows the light amount adjustment patch and the hybrid patch for bias voltage setting used in the image forming apparatus 1 which concerns on one Embodiment. It is a flowchart which shows the content of development bias calibration processing which concerns on one Embodiment. It is a flowchart which shows the content of the dot area ratio adjustment processing which concerns on one Embodiment. It is explanatory drawing which shows the patch for gamma adjustment used in the gamma calibration processing which concerns on one Embodiment. It is explanatory drawing which shows the registration adjustment chart used in the registration adjustment processing which concerns on one Embodiment.

Hereinafter, embodiments 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 the original 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 a photoconductor drum (image carrier) 30c to 30k which is an amorphous silicon photoconductor. It has a developing unit 100c to 100k and a charging unit 25c to 25k. The color conversion processing unit 21 color-converts the image data ID, which is RGB data, into CMYK data. The halftone processing unit 22 executes 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 CMYK toner, 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 representing a non-solid image (also referred to as an image area other than the solid image area). 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 main storage means such as RAM and ROM, and control means such as MPU (Micro Processing Unit) and CPU (Central Processing Unit). Further, the control unit 10 has controller functions 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, a flash memory, or the like which is a non-temporary recording medium, and stores control programs and data of processes executed by the control unit 10. In the present embodiment, the storage unit 40 further stores the calibration data storage area R1 and the 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 the embodiment. The image forming apparatus 1 of the present embodiment is a tandem type color printer. The image forming apparatus 1 has photoconductor drums (image carriers) 30m, 30c, 30y, and 30k arranged in a row in a housing 70 corresponding to magenta, cyan, yellow, and black colors. Development units 100m, 100c, 100y and 100k are arranged adjacent to the photoconductor drums 30m, 30c, 30y and 30k, respectively.

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

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

At the upstream position of the photoconductor drum 30k, the cleaning device 200 is arranged at a position opposite to the driven roller 26b with the intermediate transfer belt 27 in between. The cleaning device 200 has a fur brush 210 in which fine fibers are planted and 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 a brush cleaning method using a fur brush 210 that abuts on the intermediate transfer belt 27, and scrapes and discards the used toner.

For example, the black toner image on the photoconductor drum 30k is primarily transferred to the intermediate transfer belt 27 by sandwiching the intermediate transfer belt 27 between the photoconductor drum 30k and the primary transfer roller 23k and driving the intermediate transfer belt 27 to circulate. Toner. This point is the same for 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 that the intermediate transfer belts 27 are superposed on each other at predetermined timings. The calibration density sensor 28 is arranged at a position where the density of the toner image before the primary transfer is completed and the density of the toner image before the secondary transfer can be measured.

The full-color toner image is then secondarily transferred to the printing paper P supplied from the paper feed cassette 60, and fixed to the printing paper P by the fixing roller pair 81 of the fixing unit 80. The cleaning device 200 can also remove the residual toner remaining on the intermediate transfer belt 27 from the intermediate transfer belt 27 for the calibration patch. The print medium is also called an image forming medium.

FIG. 3 is a side sectional view showing the structure of the developing unit 100k according to the 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 transporting 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. A partition portion 145b is provided at the lower part of the developing container 145. The partition portion 145b partitions the inside of the developing container 145 into a first transport chamber 145a and a second transport chamber 145c. The first transport chamber 145a and the second transport chamber 145c extend in a columnar direction in the direction perpendicular to FIG. 3, and accommodate a two-component developer (also simply referred to as a developer) composed of a magnetic carrier and black toner.

The developing container 145 further holds a magnetic roller 143 and a developing roller 144. The developing container 145 is formed with an opening 147 that exposes the developing roller 144 toward the photoconductor drum 30 (30k).

The two stirring and transporting members 141 and 142 are cyclically moved while stirring the developer inside the first transport chamber 145a and the second transport chamber 145c, respectively. The stirring and transporting member 142 supplies a positively charged developer to the magnetic roller 143 as a magnetic brush. The magnetic roller 143 has a non-magnetic 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 preset predetermined height.

The developing roller 144 has a rotatable non-magnetic 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 development bias potential Vslv is applied to the developing roller 144.

In the present embodiment, the surface potential of the photoconductor drum 30 is set to 20 V, and a developing electric field is formed between the photoconductor 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 a development bias potential Vslv and a sinusoidal potential having a peak-to-peak value of 2000 V at a frequency of 2 kHz are superimposed is applied to the developing roller 144. A direct current potential of 200 V is applied to the magnetic roller 143 as the magnetic roller potential Vmag during development, and a direct current potential of −200 V is applied to the magnetic roller 143 during non-development.

As a result, at the time of development, the time of the development bias potential Vslv <magnetic roller potential Vmag (potential state in which the toner is supplied to the development roller 144) becomes longer, and the time for the toner to be supplied to the development roller 144 becomes longer. During non-development, the development bias potential Vslv> magnetic roller potential Vmag (potential state in which the toner is recovered from the developing roller 144) becomes longer, and the time for the toner to be recovered from the developing roller 144 becomes longer.

Further, 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 between the development bias potential Vslv and the magnetic roller potential Vmag during development is changed. Can be done. As a result, the developing roller 144 has a thin toner layer (simply 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. Also called a layer.) Is formed.

The developing roller 144 attaches toner to the photoconductor drum 30 via an opposing portion (development nip) having a predetermined clearance with the photoconductor drum 30, and forms a toner image on the surface of the photoconductor drum 30. .. The toner image is formed based on the potential difference between the potential of the electrostatic latent image on the surface of the photoconductor drum 30 and the potential difference of the development bias potential Vslv applied to the developing roller 144.

Amorphous silicon photoconductors have a relative permittivity about three times higher than that of organic photoconductors (OPC), and have a feature that the amount of toner that the photoconductor can hold is large with respect to the development contrast potential. Therefore, the amorphous silicon photoconductor can retain more toner than the solid concentration normally used. Therefore, when the amorphous silicon photoconductor is used in a saturated state, it retains an amount exceeding the amount required for the solid concentration. Therefore, in the present embodiment, the amorphous silicon photoconductor is used in a non-saturated state even at a solid density, and almost all the toner formed on the developing roller 144 is developed into the photoconductor and the development is completed to complete the solid density. Is used to determine.

FIG. 4 is a conceptual diagram showing how a rear end pool is generated in the developing process according to the embodiment. FIG. 4A shows how an image is formed at the tip and center of the image. FIG. 4B shows how 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 photoconductor drum 30.

In the present embodiment, as shown in FIG. 4A, the photoconductor drum 30 receives toner from the developing sleeve 144a of the developing roller 144 while neutralizing the potential of the latent image image. At this time, the developing step is configured to be completed not by the saturation of the potential but by the exhaustion of the toner thin 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 speed Vs and is configured to form an image while overtaking the photoconductor drum 30 having a peripheral speed Vd. Therefore, during solid development, the surface of the developing sleeve 144a in which toner is not consumed exists in the vicinity of the rear end portion of the solid. The surface on which the toner is not consumed overtakes the rear end portion of the solid latent image in the amorphous silicon photoconductor 30.

At this time, since the photoconductor drum 30 as the amorphous silicon photoconductor is in an unsaturated state, the toner is further developed from the surface of the developing sleeve 144a in which the toner is not consumed. By this development, the rear end pool (thickness T2) as a solid density higher than the density assumed in advance becomes apparent.

FIG. 4C shows, as an example, the state of adhesion (lamination state) of toner at the time of image formation of the solid image TP. In the solid image TP, the toner layer is raised at the rear end portion at the time of image formation. This swelling of the toner layer is called a rear end pool.

Such a problem of rear end accumulation can be suppressed by expressing solidness with a half patch, which is a patch having a reduced dot area ratio. In this example, the image forming apparatus 1 is assumed to express a solid image 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 development bias potential Vslv and the dot area ratio, which are the applied potentials of the developing units 100m, 100c, 100y and 100k.

However, the problem of rear end accumulation is when the central portion is extremely small in the traveling direction of the photoconductor drum 30, for example, when reproducing a thin ruled line in a direction perpendicular to the traveling direction (peripheral speed direction) of the photoconductor drum 30. Increases the density of the entire ruled line. Therefore, such a ruled line does not cause deterioration of image quality as color unevenness such as a pool at the rear end, and only increases the density of the entire ruled line. INDUSTRIAL APPLICABILITY The present invention can suppress reduction of image quality deterioration due to the accumulation at the rear end.

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

In step S120, the control unit 10 executes the image data analysis process. In the image data analysis process, the control unit 10 quantitatively quantifies the degree of occurrence of the rear end pool 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 the embodiment. In step S121, the solid image detection unit 11 executes the image attribute determination process. The image attribute determination process is a process of determining whether or not 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 pays attention to each image area in order, and whether or not it is a solid image area, that is, a solid image area and a non-solid image area (which can also be said to be an image area other than the solid image area). ) Is determined. The solid image detection unit 11 is an image area having a size equal to or larger than a preset size, and the image area is a solid image area having a substantially uniform gradation value such as a maximum gradation value or a substantially maximum gradation value. Is determined. The image area of interest is called the image area of interest.

In step S122, the solid image detection unit 11 proceeds to step S126 when the image area of interest is not a solid image area, that is, when it is a non-solid image area, and when the image area of interest is a solid image area. The process proceeds to step S123.

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

In step S124, the image analysis unit 13 executes the specific rear end portion detection process. In the specific rear end portion detection process, the image analysis unit 13 has a rear end adjacent to the central portion having a size (for example, a length of 3 to 7 mm or the number of pixels) equal to or larger than a preset threshold value in the peripheral speed direction. The portion is extracted as a specific rear end portion (see FIG. 4). The specific rear end portion is a rear end portion adjacent to the central portion having a size sufficient to generate a rear end pool.

In step S125, the image analysis unit 13 executes the specific rear end portion counting process. In the specific rear end counting process, the number of pixels constituting the specific rear end of the image region of interest is counted. The control unit 10 pays attention to each image area in order, and executes the processes of steps S121 to S125 for all the image areas (step S126).

In step S127, the image analysis unit 13 executes the specific rear end aggregation process. In the specific rear end portion aggregation process, the image analysis unit 13 adds and aggregates the number of pixels constituting the specific rear end portion of each image area, and calculates the total number of the specific rear end portions.

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

FIG. 5B shows four printing conditions (printing conditions 1 to 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 ratios are different from each other.

The printing condition 1 is a dot area ratio of 70% when forming a solid image, a bias 1 which is a bias voltage for forming a solid with a dot area ratio of 70%, and a solid with a dot area ratio of 70%. Gamma 1, which is an input / output gamma for realizing a linear input / output relationship, is set at the time of printing. On the other hand, the printing condition 4 has a dot area ratio of 100% when forming a solid image, a bias 4 which is a bias voltage for forming a solid with a dot area ratio of 100%, and a solid with a dot area ratio of 100%. Gamma 4, which is an input / output gamma for realizing a linear input / output relationship, is set when forming the above. The input / output gamma is also called an input / output gamma correction value.

The printing condition 1 (dot area ratio 70%) is the most effective in suppressing the accumulation at the rear end, but is a printing condition that causes breakage of fine lines and occurrence of jaggies. The printing condition 4 (dot area ratio 100%) is the most effective in suppressing the breakage of fine lines and the occurrence of jaggies, but is a printing condition that causes the rear end to accumulate. The printing condition 2 (dot area ratio 80%) is a printing condition that gives priority to the suppression of the rear end accumulation. The printing condition 3 (dot area ratio 90%) is a printing condition that gives priority to the suppression of the breakage of fine lines and the occurrence of jaggies.

The image analysis unit 13 can select, for example, the printing condition 1 that is most effective in suppressing the rear end accumulation for an image in which the total number of specific rear end portions is 10,000 or more and the rear end accumulation is likely to occur. For an image in which the total number of specific rear end portions is 0 and the occurrence of rear end accumulation is not expected, the printing condition 4 that is most effective in suppressing the breakage of thin lines and the occurrence of jaggies can be selected.

In the past, the suppression of rear end accumulation and the breakage of thin lines and the occurrence of jaggies have been the targets of trade-offs. On the other hand, the present invention can predict the degree of occurrence of the rear end pool based on the image data PD and switch the printing conditions based on the predicted degree of the occurrence of the rear end pool.

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

In this way, the image forming apparatus 1 can predict (estimate) the degree of occurrence of the rear end pool based on the image data PD, and switch the printing conditions based on the predicted degree of the occurrence of the rear end pool. Therefore, it is possible to solve the trade-off problem of suppressing the accumulation at the rear end and breaking the thin line or generating jaggies.

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

In step S210, the calibration processing unit 14 executes the light quantity calibration processing. 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 preset steps to display a chart having a plurality of light amount adjustment patch PLs. It is formed on the intermediate transfer belt 27. The image data representing the light amount adjusting patch PL is stored in the calibration data storage area R1 of the storage unit 40.

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

The calibration processing unit 14 uses the calibration density sensor 28 to measure the density of patches of each color (for example, black (K)). The calibration processing unit 14 uses the reflected light of the plurality of light amount adjusting patch PLs exposed by the laser light of a plurality of different light amounts to perform, for example, an interpolation calculation to obtain a preset target density. Set the calibration light amount, which is the appropriate amount of light. 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 intensity is commonly used for printing conditions 1 to 4.

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

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

In step S221, the calibration processing unit 14 executes the hybrid patch forming process. In the hybrid patch forming process, the calibration processing unit 14 forms a chart having a plurality of hybrid patch PHs in which the development bias potential Vslv is changed stepwise in a plurality of preset steps on the intermediate transfer belt 27. The 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 for the sake of clarity. The half patch P80 is a patch used for proofreading an image forming bias potential having a dot area ratio of 80% under printing condition 2. The solid patch P100 is a patch having a dot area ratio of 100% used for proofreading a bias potential for registration, that is, a dot area ratio for detecting color shift.

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

To use a plurality of hybrid patch PHs in which the development bias potential Vslv is changed stepwise, the toner image is the potential of the electrostatic latent image on the surface of the photoconductor drum 30 and the development bias potential Vslv applied to the development roller 144. This is because it is formed based on the potential difference of. Multiple half patches are formed for each of the CMYKs. In the following, a cyan (C) half patch will be described as an example.

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

In step S223, the calibration processing unit 14 determines whether or not the previous area ratio deviation read from the calibration data storage area R1 is larger than the threshold value 0. If the previous area ratio deviation is equal to or greater than the threshold value 0, the calibration processing unit 14 advances the processing to step S224, and if the previous area ratio deviation is less than the threshold value 0, the calibration processing unit 14 performs the processing to step S225. Proceed. In this example, the previous area ratio deviation is the deviation of the gradation value finally remaining in the previous I / O gamma calibration. 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 for calibrating the image forming bias potential to set the adjustment target value. The adjustment target value (concentration target value actually used for bias potential calibration) is calculated by, for example, adding the gradation deviation α corresponding to the previous area ratio deviation to the nominal concentration target value (solid concentration value). can do. As a result, the image forming bias potential rises according to the gradation deviation α.

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

The density of the image increases as the bias potential for image formation 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 cancel the previous area ratio deviation.

In step S226, the calibration processing unit 14 executes the image forming bias calibration processing. In the image forming bias calibration process, the calibration processing unit 14 uses the measurement density and the adjustment target value of the half patch P80 of the plurality of hybrid patch PHs in which the development bias potential Vslv is changed stepwise to develop the development bias. The potential Vslv can be calibrated.

Specifically, in the calibration processing unit 14, 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 stepwise is If present, it is performed by selecting the development bias potential Vslv corresponding to the patch. That is, when there is a half patch in which the ratio of the P wave and the S wave is equal to or less than the preset threshold value, the calibration processing unit 14 develops after calibrating the lowest development bias potential Vslv in the half patch. Adjust to the bias potential. As a result, the calibration processing unit 14 can calibrate the development 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 shift. In the registration bias calibration process, the development bias potential Vslv is calibrated using the measurement concentration and the adjustment target value of the solid patch P100 among the plurality of hybrid patch PHs in which the development bias potential Vslv is changed stepwise. Can be done. As a result, the calibration processing unit 14 can calibrate the development bias potential Vslv (development bias potential for color shift detection) for registration bias calibration.

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

In step S230 (FIG. 7), the calibration processing unit 14 advances the processing to step S250 for the printing conditions 1 to 4 when the half patch can be calibrated within the development bias adjustment range, and the half patch is processed. If patch calibration is not possible within the adjustment range of the development bias potential Vslv, the process proceeds to step S240.

If half-patch calibration is not possible within the development bias adjustment range, it means that none of the multiple cyan (C) patches has reached the preset solid image target density. ing. Normally, one of the plurality of half patches reaches the solid image target density, but the solid image target density may not be reached when the toner charge amount is increasing due to, for example, environmental changes.

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

FIG. 10 is a flowchart showing the contents of the dot area ratio adjustment process (step S240) according to the embodiment. In step S241, the calibration processing unit 14 sets the development bias potential Vslv to the maximum value, adjusts the dot area ratio, and starts the processing of proofreading. The maximum value of the development bias potential Vslv is also called a potential limit value, and is set from the viewpoint of, for example, the output limit of the development bias and the adverse effect on the image (fog, etc.).

In step S242, the calibration processing unit 14 forms a chart having a plurality of half patches whose dot area ratio is changed stepwise on the intermediate transfer belt 27. In this example, the dot area ratio is changed stepwise (for example, three stages of 73%, 75%, and 77%) in the range of the dot area ratio of 71% to 79%. This is because it was determined that the half patch can be calibrated within the adjustment range of the development bias for the printing condition 2 (dot area ratio 80%).

In step S243, the calibration processing unit 14 measures the concentration of the cyan (C) patch using the calibration density sensor 28. The calibration density sensor 28 measures the ratio of the P wave and the S wave. The same processing is performed for MYK.

In step S244, the calibration processing unit 14 executes the dot area ratio setting process. Specifically, when the calibration processing unit 14 has a half patch in which the ratio of the P wave and the S wave is equal to or less than a preset threshold value, the half patch (for example, 73%, 75%, 77%) is used. The dot area ratio of the half patch with the lowest dot area ratio in (3 steps) is acquired as print condition setting data. In this example, it is assumed that the adjusted dot area ratio is equal to or less than a preset threshold value of the ratio of P wave and S wave in the half patch P73 (dot area ratio 73%).

The calibration processing unit 14 updates the data of the print 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 the gamma setting process. In the gamma setting process, the proofing process unit 14 sets the maximum dot area ratio to 73% for the printing condition 1. As a result, the calibration processing unit 14 linearly outputs an output gradation value as an image density of 0 to 255 (density 0% to 100%) with respect to an input gradation value of 0 to 255 (density 0% to 100%). The input / output gamma for realizing (dot area ratio 0% to 73%) can be set.

For the print condition 2, the print condition 3, and the print condition 4, the calibration processing unit 14 sets the maximum dot area ratios to 80%, 90%, and 100% with respect to the input gradation values of 0 to 255, respectively. .. As a result, the calibration processing unit 14 linearly linearly outputs 0 to 255 output gradation values (dot area ratio 0% to 80%, dot area ratio 0% to 90%) with respect to the input gradation values of 0 to 255. And the input / output gamma for realizing the dot area ratio 0% to 100%) can be set.

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

For printing condition 1 (updated to a dot area ratio of 73%), the proof processing unit 14 sets the development bias potential Vslv to bias 1 and has a half patch P20, a half patch P40, a half patch P60, and a half patch P73. The chart 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, and the half patch P73, and linearly linearly outputs 0 to 255 output gradation values with respect to the input gradation values of 0 to 255. The input / output gamma (gamma 1) for realizing (dot area ratio 0% to 73%) is set.

For printing condition 2 (dot area ratio 80%), the proof processing unit 14 sets the development bias potential Vslv to bias 2, and intermediates the chart having half patch P20, half patch P40, half patch P60, and half patch P80. It is formed on the transfer belt 27. 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 linearly linearly outputs 0 to 255 output gradation values with respect to the input gradation values of 0 to 255. The input / output gamma (gamma 2) for realizing (dot area ratio 0% to 80%) is set.

For printing condition 3 (dot area ratio 90%), the proof processing unit 14 sets the development bias potential Vslv to bias 3, and half patch P20, half patch P40, half patch P60, half patch P80, and half patch P90 (half patch P20, half patch P40, half patch P60, half patch P80, and half patch P90. A chart having a dot area ratio (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 0 to 255 with respect to the input gradation values of 0 to 255, respectively. The input / output gamma (gamma 3) for realizing the output gradation value (dot area ratio 0% to 90%) is set.

For printing condition 4 (dot area ratio 100%), the proof processing unit 14 sets the development bias potential Vslv to bias 4, and applies half patch P20, half patch P40, half patch P60, half patch P80, and solid patch P100. The chart to have 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 0 to 255 with respect to the input gradation values of 0 to 255, respectively. The input / output gamma (gamma 4) for realizing the output gradation value (dot area ratio 0% to 100%) is set.

In order to realize the target output gradation value (density), the inventor of the present application inputs / outputs from the dot area ratio (for example, 80% in the case of printing condition 2) assumed when setting the development bias potential Vslv. It was found that the dot area ratio after setting the gamma may be released.

In step S260, the calibration processing unit 14 executes the area ratio deviation acquisition processing. In the area ratio deviation acquisition process, the calibration processing unit 14 uses the calibrated input / output gamma correction value to determine the dot area ratio corresponding to the input gradation value for reproducing the solid image, and the determination is made. The deviation between the dot area ratio and the predetermined dot area ratio as the target value is calculated. The proofreading unit 14 converts the deviation between the dot area ratio and the target value into a gradation deviation α of 0 to 255 using, for example, the input / output gamma correction value, and each gradation under the printing conditions 1 to 4. The deviation α (α1 to α4) is stored in the calibration data storage area R1 of the storage unit 40. In this way, the calibration processing unit 14 also functions as a deviation management unit.

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

In step S270, the calibration processing unit 14 executes the 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 the color shift between a plurality of images of CMYK formed on the intermediate transfer belt 27 by the plurality of developing units 100c to 100k, and suppresses the color shift between the plurality of images. Adjust the image formation timing in multiple developing units and the relative image formation position in the main scanning direction.

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

The registration adjustment chart PR shows K main patch Km, M main patch Mm, C main patch Cm and Y main patch Ym, and K sub patch Ks and M sub patch Ms, respectively, at predetermined timings with each toner of CMYK. The C subpatch Cs and the Y subpatch 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 shift in the main scanning direction (direction perpendicular to the transport direction). The K sub-patch Ks, the M sub-patch Ms, the C sub-patch Cs, and the Y sub-patch Ys are patches for detecting the amount of color shift in the sub-scanning direction (parallel to the transport direction).

The calibration processing unit 14 detects the timing of the density increase on the tip side of each patch, and measures the positional relationship of the images formed by the plurality of developing units 100c to 100k. The proofreading unit 14 can detect color shifts 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 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 a registration adjustment chart PR is formed with a dot area ratio of about 70%, jaggies (jagged contours) are generated in the contours (in this case, the contours on the tip side), and the amount of color shift cannot be detected accurately. Because.

However, conventionally, a development bias potential for achieving a solid density with a dot area ratio of about 70% (a dot area ratio lower than the dot area ratio for color shift detection) for suppressing trailing edge accumulation has been used. It was. 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 amount of toner in the patch becomes excessive, resulting in deterioration of patch cleanability and color shift. It was found that the detection varies.

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

In step S280, the proofing process unit 14 executes the print parameter setting process. In the print parameter setting process, the dot area ratio, the development bias potential Vslv, and the input / output gamma are set for each of the print conditions 1 to 4, and are stored in the print setting data storage area R2. On the other hand, the range of the specific rear end device number can be determined by conducting experiments and simulations for each size print medium.

As described above, in the image forming apparatus 1 according to the embodiment, in the image forming apparatus that reproduces the solid density with the photoconductor in the unsaturated state, there are mainly three features for realizing high image quality while suppressing the accumulation at the rear end. have.

The first feature is that the degree of occurrence of rear end pools is predicted based on the image data PD, and printing conditions (also referred to as image formation conditions) are switched based on the predicted degree of occurrence of rear end pools. it can. As a result, it is possible to solve the trade-off problem of suppressing the accumulation at the rear end and breaking the thin line or generating jaggies.

The second feature is to focus on the dot area ratio after gamma calibration and correct the target value at the time of calibration to set the development bias potential Vslv next time, so that the dot area ratio after gamma calibration approaches the target value. be able to. As a result, it is possible to suppress the accumulation of the rear end and to realize the breakage of the thin line and the generation of jaggies with a high precision balance.

The third feature is that the registration adjustment chart PR can be formed by using the development bias potential Vslv individually set for the registration adjustment assuming a dot area ratio of 100%. As a result, it is possible to suppress deterioration of cleanability and detection variation due to excessive toner in 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 photoconductor is used, but the present invention is not limited to the use of an amorphous silicon photoconductor. The present invention can generally be applied to an image forming apparatus that reproduces a solid density with a photoconductor in an unsaturated state.

1 Image forming device 10 Control unit 20 Image forming unit 21 Color conversion processing unit 28 Calibration density sensor 29 Exposure unit 40 Storage unit 50 Image reading unit 60 Paper feed cassette 70 Housing

Claims (6)

It has a rotatable photoconductor that forms a solid image in a non-saturated state, an exposed portion that exposes the photoconductor to form an electrostatic latent image based on image data, 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 is based on the developing bias potential which is the potential of the developing roller and the electrostatic latent image. At least one developing unit for adhering toner from the toner layer to the photoconductor, and
A plurality of images in which the dot area ratios for forming a solid image are different from each other based on the estimation by analyzing the image data and estimating the degree of image quality deterioration as color unevenness due to the occurrence of the rear end pool. An image formation condition setting unit that selects any one of the formation conditions,
Assuming the plurality of dot area ratios, a calibration processing unit that calibrates each development bias potential for forming the solid image with the plurality of dot area ratios, and
An image forming unit that forms and outputs an image on an image forming medium under the selected image forming conditions, and an image forming unit.
Equipped with a,
The estimation is the total number of pixels constituting the specific rear end portion adjacent to the central portion having a size equal to or larger than a preset threshold value in the peripheral speed direction of the photoconductor. The total number of edges
The image forming condition setting unit is configured the more specific the rear end total, an image forming apparatus wherein the dot area rate you select a lower said image forming condition. 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 have a dot area ratio of 100 as an image forming condition for forming a patch for detecting color deviation between a plurality of images formed by the plurality of developing units. Including %
The calibration processing unit forms the patch for color shift detection under the image forming conditions for forming the patch for color shift detection, and develops the plurality of developments so as to suppress the color shift between the plurality of images. An image forming device that adjusts the relative image forming position of each part. The image forming apparatus according to claim 1 or 2, further
An intermediate transfer belt in which the toner is transferred from the plurality of photoconductors and the transferred toner is transferred onto an image forming medium.
A density sensor that measures the concentration of toner transferred to the intermediate transfer belt, and
With
The calibration processing unit is an image forming apparatus that calibrates the development bias potential for each of the plurality of dot area ratios according to the density of the solid image formed assuming the plurality of dot area ratios. The image forming apparatus according to any one of claims 1 to 3.
The photoconductor is an amorphous silicon photoconductor, and the photoconductor is an amorphous silicon photoconductor.
The amorphous silicon photoconductor is an image forming apparatus that forms a solid image in an unsaturated state. Using a rotatable photoconductor that forms a solid image in a non-saturated state, an exposed unit that exposes the photoconductor to form an electrostatic latent image based on image data, 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. A developing step of adhering toner from the toner layer to the photoconductor, and
A plurality of images in which the dot area ratios for forming a solid image are different from each other based on the estimation by analyzing the image data and estimating the degree of image quality deterioration as color unevenness due to the occurrence of the rear end pool. An image formation condition setting process for selecting any one of the formation conditions, and an image formation condition setting step,
Assuming the plurality of dot area ratios, a calibration process step of calibrating each development bias potential for forming the solid image with the plurality of dot area ratios, and
An image forming step of forming and outputting an image on an image forming medium under the selected image forming conditions,
Equipped with a,
The estimation is the total number of pixels constituting the specific rear end portion adjacent to the central portion having a size equal to or larger than a preset threshold value in the peripheral speed direction of the photoconductor. The total number of edges
The image forming condition setting step is an image forming method including a step of selecting the image forming condition in which the dot area ratio is lower as the total number of the specified rear end portions is larger. An image forming program for controlling an image forming apparatus.
The image forming apparatus includes a rotatable photoconductor that forms a solid image in a non-saturated state, an exposure unit that exposes the photoconductor to form an electrostatic latent image based on image data, a magnetic roller, and development. The developing roller has a roller, and 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 the developing bias potential which is the potential of the developing roller and the static. It is provided with at least one developing unit for adhering toner from the toner layer to the photoconductor based on an electro-latent image.
The image formation program
A plurality of images in which the dot area ratios for forming a solid image are different from each other based on the estimation by analyzing the image data and estimating the degree of image quality deterioration as color unevenness due to the occurrence of the rear end pool. Image formation condition setting unit that selects any one of the formation conditions,
Assuming the plurality of dot area ratios, a calibration processing unit that calibrates each development bias potential for forming the solid image with the plurality of dot area ratios, and an image forming medium under the selected image forming conditions. The image forming apparatus is made to function as an image forming unit for forming and outputting an image.
The estimation is the total number of pixels constituting the specific rear end portion adjacent to the central portion having a size equal to or larger than a preset threshold value in the peripheral speed direction of the photoconductor. The total number of edges
The image forming condition setting unit is configured the more specific the rear end total, the image forming program the dot area ratio you select a lower said image forming condition.

Images