Image forming apparatus

Abstract

To provide a technique to suitably supply toner to a developer carrier by using a supply roller in an image forming apparatus.SOLUTION: An image forming apparatus is used, which has: a developer carrier that conveys developer to an electrostatic latent image formed on an image carrier; a supply roller that supplies the developer to the developer carrier and includes a foam elastic body; a power supply device that applies developing voltage to the developer carrier and supply voltage to the supply roller; a power supply control unit that controls the supply of the developer from the supply roller to the developer carrier by controlling the developing voltage and the supply voltage to change a supply bias; and an image control unit that controls formation of the electrostatic latent image on the basis of image information. The image control unit controls the amount of change of the supply bias in a period during which image formation is performed on the basis of a first value that is a value based on the image information.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] In electrophotographic image forming devices such as laser printers, copiers, and facsimiles, the surface of a photosensitive drum is uniformly charged by a charging means, and the charged photosensitive drum surface is exposed by an exposure means to form an electrostatic latent image. This electrostatic latent image is then developed by a developing means having a developer carrier to form a toner image using a developer (hereinafter, referred to as toner). This toner image is then transferred to a recording material by a transfer means. Thereafter, the toner image is fixed on the recording material by a fixing means, and the resulting image is output as a printout.

[0003] In the development process, forming a uniform toner layer on the surface of the developer carrier is essential for improving image quality, such as the color and clarity of the printed matter. In order to stably supply toner to the developer carrier, a supply roller is generally installed. According to Patent Document 1, a potential difference is formed between the developer carrier and the supply roller, which further stabilises the toner supply. Therefore, the toner can be supplied in a controlled manner. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5093143 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the above method, particularly when printing high-density images on long paper, the supply of toner to the developing roller may be insufficient, resulting in a phenomenon in which the density becomes low (low density) or the toner is scratched (smudged).On the other hand, if too much toner is supplied, the regulating force of the development regulating member, such as a blade, that regulates the amount of toner may become insufficient, resulting in image defects such as fogging.

[0006] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a technique for suitably supplying toner to a developer carrier using a supply roller in an image forming apparatus. [Means for solving the problem]

[0007] The present invention employs the following configuration. An image carrier; a developer carrier that conveys a developer to the electrostatic latent image formed on the image carrier; a supply roller including a foamed elastic body that contacts the developer carrying member and supplies the developer to the surface thereof; a power supply device that applies a development voltage to the developer carrier and a supply voltage to the supply roller; a power supply control unit that controls the developing voltage and the supply voltage, and thereby controls the supply of the developer from the supply roller to the developer carrier by changing a supply bias by controlling the developing voltage and the supply voltage; an image control unit that controls formation of the electrostatic latent image on the surface of the image carrier based on image information; having The image control unit obtains a first value that is a value based on the image information, and controls an amount of change in the supply bias during a period in which an image is formed based on the first value. The image forming apparatus is characterized in that: Effect of the Invention

[0008] According to the present invention, it is possible to provide a technique for suitably supplying toner to a developer carrier using a supply roller in an image forming apparatus. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing an overall view of an image forming apparatus according to a first embodiment. [Diagram 2] FIG. 1 is a schematic diagram showing a flow of information processing related to image formation in the first embodiment. [Diagram 3] Schematic diagram showing the image processing in the first embodiment. [Figure 4] Schematic diagram showing the printing rate of a drawn image in a comparative example and Example 1. [Diagram 5] Schematic diagram showing a supply bias in a comparative example [Figure 6] FIG. 11 is a schematic diagram showing the amount of toner in a supply roller and the amount of toner supplied to a development roller in a comparative example; [Figure 7] Schematic diagram showing the supply bias in Example 1 [Figure 8] FIG. 1 is a schematic diagram showing the amount of toner in a supply roller and the amount of toner supplied to a development roller in the first embodiment; [Figure 9] FIG. 13 is a diagram showing the relationship between the printing rate and the amount of change in the supply bias in the first embodiment. [Figure 10] Flowchart of image forming operation with supply bias control in the first embodiment [Figure 11] FIG. 11 is a schematic diagram showing the printing ratio of a drawn image in the second embodiment. [Figure 12] Schematic diagram showing the supply bias in Example 2 [Figure 13] FIG. 11 is a schematic diagram showing the amount of toner in a supply roller and the amount of toner supplied to a development roller in the second embodiment; [Figure 14] FIG. 13 is a diagram showing the relationship between the printing rate and the change amount of the supply bias in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] A preferred embodiment of the present invention will be described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in the embodiment are not intended to limit the scope of the present invention to those alone. Furthermore, the materials, shapes, etc. of the members once described in the following description are the same as those described initially, unless otherwise specified. Well-known or publicly known technologies in the relevant technical field can be applied to configurations and processes not particularly shown or described. Furthermore, duplicated descriptions may be omitted.

[0011] [Example 1] (Overall configuration of image forming apparatus) The overall configuration of an image forming apparatus will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to the present invention, with each component being shown in a simplified manner.

[0012] The image forming apparatus 100 according to this embodiment is generally provided with a photosensitive drum 1 as a photoconductor, a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a fixing device 6. The charging device 2 charges the surface of the photosensitive drum 1. The exposure device 3 exposes the charged photosensitive drum 1 to light, and forms an electrostatic latent image corresponding to image information on the surface. The developing device 4 develops the electrostatic latent image formed on the surface of the photosensitive drum 1 with a developer (toner T). The transfer device 5 comes into contact with the photosensitive drum 1 and transfers the toner image to a recording material R. The fixing device 6 heats and presses the recording material R, and fixes the toner image onto the recording material.

[0013] The photosensitive drum 1 is an image carrier in which a negatively charged organic photosensitive body is formed on a cylindrical conductive cylinder at ground potential. The photosensitive drum 1 has a diameter of 24 mm and is driven to rotate in a predetermined direction (clockwise direction in the figure: arrow E) at a predetermined process speed by a motor. The process speed S1 of the photosensitive drum 1 in this embodiment is 130 mm / sec.

[0014] The charging device 2 is a charging roller to which a desired charging voltage is applied by a power supply device 160 described later. The charging device 2 is a charging means that comes into contact with the rotating photosensitive drum 1 with a predetermined pressure and uniformly charges the surface of the photosensitive drum 1 to a predetermined potential. In this embodiment, the photosensitive drum 1 is negatively charged by the charging device 2.

[0015] The exposure device 3 is an exposure means that performs exposure corresponding to image information input from an external device or a reading device. As the exposure device 3, a laser scanner unit that scans the surface of the photosensitive drum 1 with a semiconductor laser, an LED exposure device having an LED array in which multiple LEDs are arranged along the longitudinal direction of the photosensitive drum 1, or the like can be used. In this embodiment, a laser scanner unit (hereinafter also referred to as a scanner) is used as the exposure device 3.

[0016] The developing device 4 (developing means) includes a developing roller 41 as a developer carrier that carries a developer, a developing container 44 that is a frame of the developing device 4, a supply roller 42 that is a supply member that can supply the developer to the developing roller 41, and a developing blade 43 as a regulating member that regulates the amount of developer. The developing roller 41 and the supply roller 42 are supported by the developing container 44 so as to be rotatable about a rotation shaft 41a. The developing roller 41 is disposed at the opening of the developing container 44 so as to face the photosensitive drum 1. The developing roller 41 in this embodiment has a diameter of φ10 mm, and is driven by a motor in a predetermined direction (counterclockwise direction in the figure: arrow F) at a predetermined process speed S2 = 100 mm / sec. The peripheral speed ratio S1 / S2 = 1.3 between the photosensitive drum 1 and the developing roller 41 means that the distance on the surface of the photosensitive drum 1 corresponding to one circumference of the developing roller 41 is 10π / 1.3 ≒ 24.16 mm.

[0017] The supply roller 42 has a configuration in which an open-cell foamed elastic body is formed around a metal core 42a, and is disposed in rotatable contact with the developing roller 41. The supply roller 42 is driven to rotate in the direction of arrow G by a motor.

[0018] The toner T as the developer contained in the developing container 44 is applied to the surface of the developing roller 41 by the supply roller 42. A supply voltage is applied to the supply roller 42 by the power supply device 160 (power supply means). Here, the difference in potential of the supply roller 42 with respect to the potential of the developing roller 41 is called a supply bias. The developing blade 43 is an elastic member, and is arranged in contact with the developing roller 41 while being bent against the elasticity. The toner T carried on the surface of the developing roller 41 by the developing blade 43 becomes a predetermined layer thickness. The toner T having the predetermined layer thickness is transported to a developing section (developing area) where the photosensitive drum 1 and the developing roller 41 face each other. In the illustrated example, the rotation direction F and the rotation direction G are the same, and the developing roller 41 and the supply roller 42 are in counter contact. The peripheral speed ratio of the supply roller 42 to the developing roller 41 is 90%. However, this is not limited to this, and the developing roller 41 and the supply roller 42 may be in with contact in which the rotation directions are different. In this case, the peripheral speed ratio of the supply roller 42 to the developing roller 41 is, for example, 140%. However, in either case, the peripheral speed ratio is not limited to this, and it is sufficient if the toner supply can be ensured.

[0019] The developing device 4 of this embodiment uses a contact development method as a developing method. That is, a toner layer carried by the developing roller 41 comes into contact with the photosensitive drum 1 in a developing area. A developing voltage is applied to the developing roller 41 by a power supply device 160. Under the developing voltage, the toner T carried by the developing roller 41 is transferred from the developing roller 41 to the drum surface in accordance with the potential of the surface of the photosensitive drum 1, and the electrostatic latent image is developed into a toner image.

[0020] The image forming apparatus 100 may be of a multi-color type capable of forming an image using toner T of multiple colors (for example, four colors of cyan C, magenta M, yellow Y, and black K). In that case, the image forming apparatus 100 includes an image forming section for each of the multiple colors of toner, which forms an image on the surface of the photosensitive drum 1 with toner T supplied from the developing device 4. In that case, it is also preferable to use an intermediate transfer type in which toner images of multiple colors are superimposed and formed on an intermediate transfer belt, and then transferred to a recording material R. The image forming apparatus 100 may also adopt a process cartridge type in which the developing device 4, the photosensitive drum 1, the charging device 2, the cleaning device 7, etc. are integrated into a cartridge that is detachable from the image forming apparatus main body.

[0021] As an example of the toner T of this embodiment, a polymerized toner produced by a polymerization method, spherical with a particle size of 6 μm, and having a normal charging polarity of negative polarity can be used. The toner T of this embodiment does not contain a magnetic component, and is a so-called non-magnetic one-component developer in which the toner T is carried on the developing roller 41 mainly by intermolecular forces and electrostatic forces. The one-component developer may contain additives (e.g., wax and silica particles) for adjusting the fluidity and charging performance of the toner T in addition to the toner particles. The developer may be a magnetic one-component developer containing a magnetic component or a two-component developer composed of a non-magnetic toner T and a carrier having magnetism. When a magnetic developer is used, a cylindrical developing sleeve with a magnet arranged inside is used as the developer carrier.

[0022] The transfer device 5 has a transfer roller to which a transfer voltage is applied from a power supply device 160. The transfer device 5 is a transfer means for transferring the toner image carried on the photosensitive drum 1 to a recording material R. The recording material R to which the toner image has been transferred is conveyed to a fixing device 6.

[0023] The fixing device 6 is a fixing means of a thermal fixing type that heats and melts the toner T on the recording material R to fix the image. The fixing device 6 includes a fixing film 6a, a fixing heater 6b such as a ceramic heater that heats the fixing film, and a pressure roller 6c that presses against the fixing film, and a thermistor that measures the temperature of the fixing heater 6b is provided inside the fixing film. The recording material R that has passed through the fixing device 6 is discharged outside the image forming apparatus 100 (outside the machine) and loaded onto a discharge tray 28 formed on the top of the printer body.

[0024] The cleaning device 7 is a cleaning means for removing toner T that has not been completely transferred by the transfer means and remains on the surface of the photosensitive drum 1. The cleaning device 7 has an elastic rubber blade 71 arranged in contact with the photosensitive drum 1 with its tip facing the upstream side in the rotation direction (arrow E) of the photosensitive drum 1, thereby removing the toner T.

[0025] (Control Method) The image analysis and supply bias control method that characterizes this embodiment and is executed in the image forming apparatus 100 having the above configuration will be described below.

[0026] The toner T supplied from the supply roller 42 and carried on the surface of the developing roller 41 is regulated by the developing blade 43 so that it becomes a predetermined layer thickness. Here, when an image with a high print density or a large print area and a high print coverage is repeatedly printed, the toner supply from the supply roller 42 temporarily becomes insufficient, which may result in image defects such as fading. For this reason, it is required to suppress image defects such as fading caused by an insufficient toner supply.

[0027] The configuration for image analysis and toner supply determination processing in this embodiment and the flow of information processing will be described with reference to Fig. 2. The image forming apparatus 100 operates according to programs and user instructions and includes a CPU 150 as a control unit that controls each component of the apparatus. When a print command is issued to the printer from a terminal such as a personal computer 200, the CPU The CPU 150 controls the exposure device 3 as a scanner, the power supply device 160, the drive source 170, etc. to perform image forming operations. Note that the CPU 150 may be considered to have an image control unit 150a and a power supply control unit 150b as functional blocks such as program modules that execute predetermined functions. The image control unit 150a divides image information, calculates density, and determines the printing rate. The power supply control unit 150b determines the control conditions for the power supply device 160, and adjusts the development voltage, supply voltage, and supply bias based on them.

[0028] The image forming apparatus 100 is also provided with a power supply device 160 for applying a predetermined voltage to each of the charging device 2, the developing roller 41 and the supply roller 42 of the developing device 4, and the transfer device 5. The power supply device 160 may be a single power supply device. The power supply device may also be a collective term for a plurality of power supply devices provided in the image forming apparatus 100, in which case each of the plurality of power supplies applies a voltage to one or a plurality of corresponding components. The power supply device 160 in the example of FIG. 2 includes a development power supply 160a that applies a voltage to the developing roller 41, a supply power supply 160b that applies a voltage to the supply roller 42, a transfer power supply 160c that applies a voltage to the transfer device 5, and a charging power supply 160d that applies a voltage to the charging device 2. When a single power supply device 160 is used, it is considered that the power supply device 160 also serves as the development power supply and the supply power supply.

[0029] The image forming apparatus 100 is also provided with a memory 180 that can communicate with the CPU 150 and that can hold various types of information such as image information and tables, and that is configured with a RAM, a ROM, or the like.

[0030] Furthermore, the CPU 150 analyzes image information received from the personal computer 200 or read by a reading device, and converts the color space of the original image information into a color space suitable for the image forming apparatus 100. For example, in the case of the image forming apparatus 100 that performs four-color printing, data in the RGB format is converted into data in the CMYK format. An image expressed in the color space of the image forming apparatus 100 has a correlation with the amount of toner of each color used for drawing. Therefore, the CPU 150 can estimate the amount of toner to be supplied to the developing roller 41 based on the converted image information. Here, a continuous image with a relatively high density and a large area is called an image with a high printing ratio, and an image with a relatively low density or a small area is called an image with a low printing ratio.

[0031] Here, when printing at a high printing rate in the transport direction of the developing roller 41, a large amount of toner T is used. If the amount of toner supplied from the supply roller 42 is insufficient at this time, poor toner supply occurs, increasing the possibility of blurring and the like. Therefore, the CPU 150 analyzes the image density in the direction perpendicular to the rotation axis of the developing roller 41 for the image information for each color printed by the image forming apparatus 100. Then, based on the analysis result, the CPU 150 detects and determines in advance whether there is a high possibility of a toner supply shortage.

[0032] FIG. 3 is a schematic diagram showing the state of analysis in image processing. The image information 65 is two-dimensional data that holds image density information for each color, which is defined by the conveying direction of the recording material R and the rotation axis direction of the developing roller 41. In this embodiment, the CPU 150 divides the image information 65 into a plurality of image regions 66a to 66c in a direction parallel to the rotation axis direction of the developing roller 41. Then, for each image region, analysis of continuous drawing in a direction perpendicular to the rotation axis direction is performed to detect the printing rate. In this embodiment, the CPU 150 determines that a printing rate of 80% or more is a high printing rate when a solid black image has a printing rate of 100% and a solid white (no printing) image has a printing rate of 0%. However, the threshold value is not limited to this and may be determined appropriately. When the CPU 150 calculates the above printing rate, it is preferable to calculate the average printing rate based on image information within the range of one rotation of the developing roller 41.

[0033] Determination of whether the average printing rate within the circumference of the developing roller 41 is equal to or greater than a threshold value (80%) The determination will be explained while showing the relationship with the print rate of the image data. That is, in this embodiment, the case where image data with an average print rate of 80% or more continues for more than the circumference of the developing roller 41 will be explained as an example. Note that, here, the image data for one revolution of the developing roller 41 is considered as the unit of determination, but the present invention is not limited to this.

[0034] (1) As a first example, assume that the average print rate in the first half of the first rotation of the developing roller 41 is 80%, and the average print rate in the second half of the first rotation is 79%. In this case, when considering the image data for one rotation, the average print rate is 79.5%. Therefore, the first example is not subject to the control of this embodiment. (2) As a second example, assume that the average print rate in the first rotation of the developing roller 41 is 80%, and the average print rate in the second rotation is 79%. In this case, the state in which the average print rate is 80% or more continues for more than the circumference, so it is subject to the control of this embodiment. (3) As a third example, assume a case where image data continues in which the average print rate in the first half of the first rotation of the developing roller 41 is 90% and the average print rate in the second half of the first rotation is 79%. In this case, the average print rate is 84.5% when considering the image data for one rotation. Therefore, it is subject to the control of this embodiment. (4) As a fourth example, assume that the average print rate is 0% (solid white image) for the first 1 / 5 of the first revolution of the developing roller 41, and 100% (solid black image) for the remaining 4 / 5 revolutions. In this case, the average print rate is 80% when considering the image data for one revolution. Therefore, this is subject to the control of this embodiment.

[0035] In Fig. 4, the horizontal axis indicates time and the vertical axis indicates the printing rate, showing the change in printing rate over time when drawing is performed at a printing rate of 100% in the section T1-T2. In this case, a comparison is made between the comparative example (Figs. 5 and 6) and the embodiment (Figs. 7 and 8). Here, time T1 is the timing on the photosensitive drum 1 that corresponds to the leading edge of the image forming area on the recording material R excluding margins and the like. Time T2 is the timing on the photosensitive drum 1 that corresponds to the trailing edge of the image forming area on the recording material R. In this embodiment, the period before time T1 is called the pre-processing section, the section T1-T2 is called the image forming section, and the period after time T2 is called the post-processing section.

[0036] 5 shows the supply bias control of the comparative example. In the pre-processing section, the supply bias is V0. At time T1, the CPU 150 instantly changes the supply bias from V0 to V0-200V in the direction of the same polarity as the normal charging polarity of the toner T (negative polarity in this embodiment). In the image formation section, that is, between times T1 and T2, the supply bias is maintained at V0-200V. At time T2, the bias is instantly changed to a bias in the direction of the opposite polarity to that of the toner T. Here, the original supply bias V0 is restored.

[0037] 6, the horizontal axis indicates time and the vertical axis indicates the amount of toner supplied, with the dashed line indicating the amount of toner in supply roller 42 and the solid line indicating the amount of toner supplied to developing roller 41 in the comparative example. In the pre-processing section, the amount of toner supplied is constant according to supply bias V0. When the supply bias is changed in the same polarity as toner T at time T1, the amount of toner in supply roller 42 decreases, and toner T is supplied from the foamed elastic body of supply roller 42 to the surface of developing roller 41. Conversely, when the supply bias is changed in the opposite polarity to toner T at time T2, the amount of toner in supply roller 42 increases, and toner T accumulates in the foamed elastic body of supply roller 42.

[0038] Here, when time has passed since the bias was changed (time T1), the amount of toner in the supply roller 42 is balanced with the electrostatic potential (time T11). As a result, the inflow and outflow of the toner T from the supply roller 42 becomes steady, and the increase in the amount of toner supplied to the development roller 41 due to the supply bias disappears (time T11). In other words, in the case of the comparative example, the amount of toner supplied decreases as time passes from time T1, so there is a high possibility that a toner supply shortage will occur. In the illustrated example, the toner supply amount St1 is sufficient at time T1, but the supply amount gradually decreases and at a certain point falls below the toner supply amount Sts required for high-density printing. After that, the supply amount decreases further and becomes steady at an insufficient toner supply amount St2.

[0039] FIG. 7 shows the supply bias control of this embodiment. In this embodiment, the supply bias is gradually changed in the same polarity as the toner T (negative polarity in this embodiment) in the image forming section T1-T2. FIG. 8 shows the amount of toner in the supply roller 42 in this embodiment with a dashed line, and the amount of toner supplied to the development roller 41 with a solid line. In this embodiment, as the supply bias gradually changes, the amount of toner in the supply roller 42 also gradually decreases. Therefore, the toner T continues to be supplied from the supply roller 42 to the development roller 41. In other words, in this embodiment, the amount of toner supplied to the development roller 41 is maintained throughout the image forming section T1-T2, so that the possibility of a toner supply shortage occurring is reduced.

[0040] 8 in this embodiment is a stable value and exceeds the toner supply amount Sts required for a high-print image. Therefore, even in a situation where high-print images continue, the possibility of image defects such as blurring is reduced.

[0041] In addition, in Fig. 7, the supply bias is changed so that the slope is constant, but the method of changing the supply bias is not limited to this as long as the toner required for the high-print image can be supplied. For example, in the section T1-T2 in Fig. 7, the supply bias may be decreased in small steps.

[0042] Also, the period from time T2 onwards shows a post-processing operation after the end of image formation. At time T2, the supply bias is returned to the value before time T1, so that the toner T can be replenished into the supply roller .

[0043] On the other hand, if excessive toner is supplied to areas where toner T is not used, such as white areas, the developing blade 43 may not be able to regulate the toner layer thickness to an appropriate level. In this case, image defects such as "fog" occur, where toner T is developed in the white areas. Therefore, it is necessary to determine whether toner T is being supplied excessively and to appropriately control the supply bias.

[0044] 9 shows the relationship between the printing rate and the supply bias change amount (V / mm) in the control of this embodiment. In the control of this embodiment, in order to supply toner T in a high print image, in an image area determined to be a high print image, the supply bias is changed by -0.4 V / mm with respect to the length of the image area in the rotation direction of the developing roller 41 (reference symbol 75b). On the other hand, in an area determined not to be a high print image, the supply bias is controlled to be constant (here, 0.0 V / mm, reference symbol 75a). Here, in this embodiment, the change amount of the supply bias is a negative value, but it may be a positive value if the direction is such that toner T is supplied to the developing roller 41.

[0045] In addition, the supply roller 42 in this embodiment is configured such that the open-cell foamed elastic body rotates while being pressed by the developing roller 41. Therefore, the foamed elastic body is compressed upstream of the contact portion and expanded downstream of the contact portion. This change in compression / expansion promotes the replacement of the toner T in the foamed elastic body of the supply roller 42, and smooths the change in the amount of toner due to the supply bias.

[0046] (Processing flow) A specific control in this embodiment will be described with reference to the flow chart of FIG. (Step S101) A print command is issued from a terminal such as personal computer 200 to image forming apparatus 100.

[0047] (Step S102) CPU 150 converts image information 65 into a color space in image forming apparatus 100. For example, conversion from the RGB system to the CMYK system suitable for handling by image forming apparatus 100 is performed.

[0048] (Step S103) CPU 150 determines whether a high print image is printed in each image area. First, CPU 150 divides image information 65 into a plurality of image areas 66. Then, in each image area 66, it obtains density information for each color. Then, for each divided image area 66 and for each color, it determines whether a high print image that would result in a toner supply shortage will be printed in the direction parallel to the rotation axis of developing roller 41.

[0049] (Step S104) CPU 150 determines the supply bias and its change amount for the image area determined to be a high print image. The supply bias change amount at this time is determined by referring to FIG.

[0050] (Step S105) CPU 150 judges whether the high print image determination has been performed for all image regions of the image. If there are regions that have not yet been determined, the process returns to S103 and continues. On the other hand, if the determination has been performed for all image regions, the process proceeds to S106.

[0051] (Step S106) Image forming apparatus 100 performs an actual image forming operation based on the determined supply bias. (Step S107) After the image formation is completed, the process goes to a standby state.

[0052] By doing so, a sufficient amount of toner T can be supplied even when printing a high-resolution image, so image defects such as blurring do not occur. Also, since excessive toner T is not supplied even when printing a low-resolution image, fogging can be suppressed.

[0053] Here, the method of this embodiment is applicable whether the image forming apparatus 100 is a monochrome printer capable of rendering only monochrome images, or a full-color printer using a CMYK four-color system.

[0054] [Example 2] Next, a description will be given of Example 2. The same components as those in Example 1 described above are given the same reference numerals, and detailed descriptions thereof will be omitted.

[0055] In the above-mentioned first embodiment, the case where a high print image continues is considered. In this embodiment, the case where a low print image such as a halftone image is printed after a high print image in a direction perpendicular to the rotation axis of the developing roller 41 is considered. Note that, here, an image that has a lower print rate than the high print image and is not a white image (no print) is called a low print image. In such a case, compared with the case where a high print image is not printed before a low print image, the amount of toner T used on the surface of the developing roller 41 in the high print image is large, so the amount of toner immediately before the toner is supplied by the supply roller 42 for the low print image is small. Therefore, even after the toner T is supplied by the supply roller 42, the toner layer thickness on the developing roller 41 is likely to be thin. As a result, depending on the control of the supply bias, the density of the low print image may be low.

[0056] In this embodiment, therefore, a control method for supplying sufficient toner T to the developing roller 41 even when many low print images are printed will be described. Typically, a low print image is printed after a high print image. A method for suppressing image defects in low print images even when the section is printed will be described.

[0057] In Fig. 11, the horizontal axis indicates time and the vertical axis indicates the printing rate. During the image formation section (T3-T7), section T3-T4 indicates a high printing rate, section T4-T5 indicates a low printing rate, section T5-T6 indicates no image (white image), and section T6-T7 indicates a medium printing rate. Time T3 is the timing on the photosensitive drum 1 corresponding to the leading edge of the recording material R, and time T7 is the timing on the photosensitive drum 1 corresponding to the trailing edge of the recording material R. In this embodiment, the operation before time T3 is called a pre-processing operation, the operation in section T3-T7 is called an image forming operation, and the operation after time T7 is called a post-processing operation.

[0058] Fig. 12 shows the change over time of the supply bias in this embodiment. Fig. 13 shows the change over time of the toner amount, where the solid line shows the amount of toner supplied to the developing roller 41 and the dashed line shows the amount of toner in the supply roller 42. CPU 150 controls the supply bias so that the required amount of toner is supplied to the developing roller 41 in each section according to the printing rate.

[0059] First, in the high print section T3-T4, the supply bias is controlled to gradually decrease. The gradient of the supply bias at this time may be controlled according to FIG. 9, for example, as in the first embodiment. By such supply bias control, as shown in FIG. 13, the toner supply amount to the developing roller 41 exceeds the toner supply amount Sts required for the high print image in the entire section T3-T4. Next, the supply bias is controlled to gradually decrease in the low print section T4-T5, but the gradient of the decrease is gentler than that in the section T3-T4. As a result, as shown in FIG. 13, stable toner supply is performed for the low print image. In this way, in this embodiment, it is possible to supply the required amount of toner even when a low print image follows a high print image.

[0060] 14 shows the relationship between the printing rate and the amount of change in the supply bias in this embodiment. If the ratio of the amount of toner used at a given printing rate to the amount of toner that develops the entire toner layer on the surface of the developing roller 41 is a, the supply bias is changed by an amount of change of -a x 0.4 (V / mm) relative to the length in the rotational direction of the developing roller 41. In addition, in the image formation section, the amount of change in the supply bias is always negative (or positive), and therefore has the characteristic of being monotonic with respect to the distance of image formation, that is, the operation time (monotonically decreasing or increasing).

[0061] Here, the amount of change in the supply bias (i.e., the gradient of the supply bias) may be expressed as the amount of change in the supply bias per unit time, or may be expressed as the amount of change in the supply bias per unit distance in a direction perpendicular to the rotation axis of the developing roller (the conveying direction of the recording material R). In other words, it is sufficient to be able to express the relationship between the position of the image information in the conveying direction and the amount of change. For example, in FIG. 12, when the supply bias at an arbitrary time t1 is V(t1), the amount of change in the supply bias may be dV / dt, which is the differential over time.

[0062] By doing so, even when a low print image is printed after a high print image, the high print image can be prevented from becoming faint without causing low density.

[0063] As described above, in the embodiment of the present invention, the printing rate of an image to be formed based on image information is obtained by a method such as calculation based on image information or reading from a memory, and is used for controlling the amount of change such as controlling the slope of the supply bias. However, the supply bias control of the present invention is not limited to the printing rate, and can be implemented using other values ​​related to the amount of toner supplied. For example, the CPU 150 can obtain the amount of toner in a predetermined range, such as during one rotation of the developing roller 41, based on the image information in the form of an absolute value of weight or a relative value specific to the device. Alternatively, when using an absolute value of weight, actual measurement may be performed. In other words, the present invention can be considered as controlling the amount of change in the supply bias according to a first value based on image information. In that case, the printing rate may be used as the first value, or, as described above, Calculated or measured amounts of toner usage may also be used.

[0064] As described above, in the embodiment of the present invention, the printing rate (for example, the average printing rate during one rotation of the developing roller 41) is calculated based on the image information, and is used to control the amount of change in the supply bias by the CPU 150. Here, the image forming apparatus 100 is provided with a configuration for detecting the density of the toner image actually printed, and may be used to correct the applied voltage based on the image data. As the density detection target, in the case of a monochrome printer as shown in FIG. 1, a density detection mechanism for the patch of the toner image formed on the surface of the photosensitive drum 1 may be provided inside the apparatus main body, or the density of the toner image transferred onto the recording material may be detected. In addition, in the case of a monochrome printer having multiple photosensitive drums corresponding to multiple colors and transferring the toner images of each color to an intermediate transfer body such as an intermediate transfer belt in a superimposed manner, a toner image density detection mechanism formed on the surface of the intermediate transfer body may be provided inside the apparatus main body, or the density of the toner image transferred onto the recording material may be detected. The CPU 150 adjusts the control value of the apparatus (for example, the applied voltage from the power source, etc.) based on the difference between the toner image density assumed to be formed based on the image information and the actual density detected by the density detection mechanism, thereby adjusting so that the intended printing is performed.

[0065] [Configuration 1] An image carrier; a developer carrier that conveys a developer to the electrostatic latent image formed on the image carrier; a supply roller including a foamed elastic body that contacts the developer carrying member and supplies the developer to the surface thereof; a power supply device that applies a development voltage to the developer carrier and a supply voltage to the supply roller; a power supply control unit that controls the developing voltage and the supply voltage, and thereby controls the supply of the developer from the supply roller to the developer carrier by changing a supply bias by controlling the developing voltage and the supply voltage; an image control unit that controls formation of the electrostatic latent image on the surface of the image carrier based on image information; having The image control unit obtains a first value that is a value based on the image information, and controls an amount of change in the supply bias during a period in which an image is formed based on the first value. 1. An image forming apparatus comprising: [Configuration 2 The image control unit obtains, as the first value, a printing rate in an image formed based on the image information. 2. The image forming apparatus according to claim 1, [Configuration 3] The image control unit obtains, as the first value, an amount of the developer used when forming an image based on the image information. 2. The image forming apparatus according to claim 1, [Configuration 4] The power supply control unit controls the amount of change in the supply bias per unit time. 4. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. [Configuration 5] The power supply control unit controls a change amount of the supply bias per distance in a direction perpendicular to a rotation axis of the developer carrier. 4. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. [Configuration 6] The power supply control unit controls a change amount of the supply bias so that the supply bias gradually changes to the same polarity as the normal charging polarity of the developer. 4. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. [Configuration 7] The power supply control unit performs control so that the supply bias monotonically increases or decreases over time during the period in which the image formation is performed. 5. The image forming apparatus according to claim 4. [Configuration 8] The power supply control unit changes the supply bias by a predetermined amount for a section with a high printing rate determined by analysis of the image information, and controls the supply bias to be constant for a section with a low printing rate. 4. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. [Configuration 9] The power supply control unit performs control such that the amount of change in the supply bias increases as the printing rate of the image formed based on the image information increases. 4. The image forming apparatus according to claim 1, wherein the first and second electrodes are arranged in a first direction. [Explanation of symbols]

[0066] 100: image forming apparatus, 150: CPU, 160: high voltage power supply, T: toner, 1: photosensitive drum, 4: developing device, 41: developing roller, 42: supply roller

Claims

1. Image carrier and, A developer carrier that transports a developer to an electrostatic latent image formed on the image carrier based on image data, A supply roller including a foamed elastic body that contacts the developer carrier and supplies the developer, which is charged to a normal charging polarity, to its surface, A power supply device that applies a developing voltage to the developer carrier and also applies a supply voltage to the supply roller, An acquisition unit that acquires information regarding the printed pixel area obtained from the image data for each of a plurality of regions on the image carrier in the rotational direction of the image carrier, A control unit controls the supply of the developer from the supply roller to the developer carrier by controlling the developing voltage and the supply voltage, It has, The control unit controls the image formation operation, which involves forming an image on the surface of the image carrier with the developer and then transferring the image to the recording material. When performing the image forming operation on one of the recording materials, if, among the plurality of regions on the image carrier, a second region having a second printable pixel area smaller than the first printable pixel area is formed after a first region having a first printable pixel area, The control unit controls the supply voltage so that it increases continuously toward the normal charging polarity from the first region to the second region, and controls the amount of increase in the supply voltage per unit length in the rotational direction of the image carrier within the first region to be greater than the amount of increase in the supply voltage per unit length in the rotational direction of the image carrier within the second region.

2. The image forming apparatus according to claim 1, characterized in that the acquisition unit acquires the amount of developer used to form an image based on the image data when acquiring the information.

3. The image forming apparatus according to claim 1, characterized in that the control unit controls the amount of change in the supply voltage per unit distance in a direction perpendicular to the rotation axis of the developer carrier.

4. In a high print rate section having a print rate above a predetermined threshold, the control unit shall supply the voltage The image forming apparatus according to claim 1, characterized in that the voltage changes by a predetermined amount, and in a low print rate section having a print rate below a predetermined threshold, the supply voltage can be controlled to be constant.

5. The image forming apparatus according to claim 1, characterized in that the control unit controls the amount of change in the supply voltage to increase as the printing density in the image formed based on the image data increases.

Images