Image forming apparatus

Abstract

To reduce the burden on correction of image density unevenness.SOLUTION: An image forming apparatus 100 comprises: an image forming unit 13 that has a developing unit 131c that attaches toner to a surface of a photoreceptor 131b to form a toner image, and forms an image on a recording material; a developing bias detection unit 20 that, when a test chart is formed on the recording material, detects a bias voltage applied to the developing unit 131c; a correction voltage calculation unit 30 that calculates a correction voltage for correcting the bias voltage, on the basis of a change in the density of a read image of the recording material on which the test chart is formed and the detected bias voltage; and a control unit 40 that corrects the bias voltage, on the basis of a change in the density of a read image of the recording material on which a document image is formed and the correction voltage.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] An image forming apparatus that forms an image on a recording material using electrophotography irradiates a charged photosensitive drum with laser light based on image data to form an electrostatic latent image. The developing device of the image forming apparatus then visualizes the electrostatic latent image by depositing toner of each color component onto the surface of the photosensitive drum, forming a toner image. The developing device has a developing sleeve that carries developer while rotating and supplies the toner contained in the developer to the photosensitive drum. A developing bias is applied to the developing sleeve, and a toner image is formed on the surface of the photosensitive drum due to a potential difference generated between the developing sleeve and the surface of the photosensitive drum. If the amount of toner varies significantly due to changes in image density, the developing bias will fluctuate, resulting in density unevenness. Therefore, a developing bias correction technique has been proposed to suppress density unevenness when forming an image with large toner fluctuations in some areas, such as the technique described in Patent Document 1.

[0003] Patent Document 1 describes specifying the amount of toner fluctuation by referring to input image data. Patent Document 1 also describes estimating the amount of voltage fluctuation of the reference developing bias in a portion where the amount of toner fluctuates greatly based on the specified amount of toner fluctuation. Patent Document 1 also describes correcting the developing bias so as to cancel out the estimated amount of voltage fluctuation of the reference developing bias. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-167195 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, a development bias correction technique has been proposed to suppress density unevenness when forming an image with a large amount of toner fluctuation in some areas. However, the technique described in Patent Document 1 makes a correction determination based solely on the toner fluctuation rate, which can lead to an erroneous determination. In such cases, unnecessary corrections are made, which increases the correction load.

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to reduce the load of correcting image density unevenness. [Means for solving the problem]

[0007] The image forming apparatus of the present invention includes an image forming unit that has a developing unit that forms a toner image by adhering toner to the surface of a photosensitive member and forms an image on a recording material, a development bias detection unit that detects a bias voltage applied to the developing unit when a test chart is formed on the recording material, a correction voltage calculation unit that calculates a correction voltage to correct the bias voltage based on the density change of the read image of the recording material on which the test chart is formed and the detected bias voltage, and a control unit that corrects the bias voltage based on the density change of the read image of the recording material on which an original image is formed and the correction voltage. [Effects of the Invention]

[0008] According to the present invention having the above configuration, the load of correcting image density unevenness can be reduced. Problems, configurations, and effects other than those described above will become apparent from the following description of the embodiments. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing an example of the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a block diagram illustrating an example of a functional configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 3]10A and 10B are diagrams illustrating images before and after correction of density unevenness caused by fluctuations in development bias in an image forming apparatus according to one embodiment of the present invention. [Figure 4] 5A and 5B are diagrams for explaining development bias voltage correction in the image forming apparatus according to one embodiment of the present invention. [Figure 5] 10 shows Example 1 of development bias voltage correction in the image forming apparatus according to one embodiment of the present invention. [Figure 6] 10 shows a second example of development bias voltage correction in the image forming apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functions or configurations are designated by the same reference numerals, and redundant description will be omitted.

[0011] <One embodiment> [Configuration example of image forming device] First, a configuration example of an image forming apparatus according to an embodiment of the present invention will be described. Fig. 1 is a schematic cross-sectional view showing a configuration example of an image forming apparatus 100 according to this embodiment.

[0012] Image forming apparatus 100 is an example of an image forming apparatus that forms an image on a recording material by electrophotography. Image forming apparatus 100 is a multifunction digital image forming apparatus (MFP: Multifunction Peripheral) that has multiple functions, such as a print function, a copy function, a facsimile function, and a scan function. Image forming apparatus 100 forms an image on a recording material based on document image data obtained by reading an image from a document or document image data received from an external terminal device. Hereinafter, recording material will also be referred to as "paper."

[0013] As shown in FIG. 1, the image forming apparatus 100 includes a reading unit 12, an image forming unit 13, an operation display unit 15, a manual feed tray T1, a paper feed tray T2, and a paper discharge tray T3.

[0014] The reading unit 12 scans and exposes an image of a document placed on a document table or an automatic document feeder (ADF) (not shown) using the optical system of a scanning exposure device, reads the reflected light using a line image sensor, and outputs the read image.

[0015] The image forming unit 13 forms an image on the paper P according to the pixel value of each pixel in the document image data. The image forming unit 13 has four image writing units 131 for forming toner images of four colors, cyan (C), magenta (M), yellow (Y), and black (K), respectively. The image writing units 131 include image writing units 131Y, 131M, 131C, and 131K shown in FIG. 1. The image forming unit 13 also includes an intermediate transfer belt 132, a transfer roller 133 (secondary transfer roller), a fixing unit 134, and the like. Hereinafter, the image writing units 131Y, 131M, 131C, and 131K may be referred to collectively or without any particular distinction being made therebetween as the image writing unit 131.

[0016] The four image writing units 131Y, 131M, 131C, and 131K are arranged in series (tandem) along the belt surface of the intermediate transfer belt 132. The four image writing units 131Y, 131M, 131C, and 131K form images of the respective colors of C, M, Y, and K. The image writing units 131 have the same configuration except for the colors of the images they form. As shown in FIG. 1, the image writing unit 131 includes an exposure device 131a and a photosensitive member 131b (an example of an image carrier). The image writing unit 131 also includes a developing unit 131c, a charging unit 131d, a cleaning unit 131e, and a primary transfer roller 131f.

[0017] During image formation processing, in each image writing unit 131, the charging unit 131d charges the outer peripheral surface of the drum-shaped photoconductor 131b. Then, the charging unit 131d scans the outer peripheral surface of the photoconductor 131b with a light beam (light beam) emitted by the exposure device 131a based on the document image data, forming an electrostatic latent image. In this state, the developing unit 131c visualizes the electrostatic latent image by attaching toner of each color component to the surface of the photoconductor 131b, thereby forming a toner image. A developing bias is applied to the developing unit 131c, which supplies toner contained in the developer to the photoconductor 131b. A potential difference is generated between the developing unit 131c to which the developing bias is applied and the surface of the photoconductor 131b, forming a toner image on the surface of the photoconductor 131b.

[0018] The primary transfer roller 131f primarily transfers the image formed on the photosensitive member 131b onto the intermediate transfer belt 132, superimposing the image onto the intermediate transfer belt 132. As a result, an image made up of each color is formed on the intermediate transfer belt 132. The intermediate transfer belt 132 is an image carrier that is wound around multiple rollers and rotates. After the primary transfer, the cleaning unit 131e removes color material remaining on the photosensitive member 131b.

[0019] Furthermore, intermediate transfer belt 132 feeds paper from manual feed tray T1 or paper feed tray T2 in time with the timing at which it reaches the position of transfer roller 133. Transfer roller 133 is one of a pair of rollers, one of which is in pressure contact with intermediate transfer belt 132 and the other of which winds around intermediate transfer belt 132. The pressure of transfer roller 133 causes a second transfer of an image from intermediate transfer belt 132 onto the paper.

[0020] The paper is then transported to the fixing unit 134, where it is subjected to a fixing process and then discharged to the paper output tray T3. The fixing process involves applying heat and pressure to the paper with the fixing roller 134a to fix the image to the paper. When forming images on both sides of the paper P, the paper is transported to the reversing path 135 to reverse the paper surface, and then the paper is fed again to the position of the transfer roller 133.

[0021] The operation display unit 15 is composed of a display unit and an operation unit. The display unit is composed of a display device such as an LCD (Liquid Crystal Display) or an organic EL (Electro-luminescence) display. The operation unit is composed of a touch sensor or the like. The display unit and operation unit are integrally formed as, for example, a touch panel. It is also possible to configure the operation unit as a mouse, tablet, or the like, separate from the display unit.

[0022] [Example of functional configuration of image forming device] Next, the functional configuration of the image forming apparatus 100 will be described. Fig. 2 is a block diagram showing an example of the functional configuration of the image forming apparatus 100 according to this embodiment. In addition to the components shown in Fig. 1, the image forming apparatus 100 also includes an IDC (Image Density Control) sensor 16, a density measuring device 17, a development bias detection unit 20, a correction voltage calculation unit 30, a control unit 40, and a storage unit 50 shown in Fig. 2. The components of the image forming apparatus 100 are connected via a bus B so as to be able to send and receive information data to and from each other.

[0023] The IDC sensor 16 is a light intensity sensor made of a reflective photosensor. The IDC sensor 16 measures the intensity of light reflected from the surface of the paper on which an image is formed, and detects the amount of bitmap toner adhesion based on the measured intensity of reflected light, and outputs the result to the correction voltage calculation unit 30.

[0024] The density measuring device 17 is configured, for example, by a spectrophotometer, and measures the bitmap density of the read image of the test chart for density unevenness correction output from the reading unit 12, and outputs the result to the correction voltage calculation unit 30. Note that the density measuring device 17 may be configured integrally with the reading unit 12.

[0025] The developing bias detection unit 20 detects the bias voltage applied to the developing unit 131c and the developing output current when a test chart for correcting density unevenness is formed on the recording material, and outputs the results to the correction voltage calculation unit 30.

[0026] The correction voltage calculation unit 30 calculates a correction voltage for correcting the bias voltage based on the change in density of the read image of the recording material on which the test chart is formed and the bias voltage detected by the development bias detection unit 20 .

[0027] Specifically, the correction voltage calculation unit 30 calculates the bitmap toner charge amount using the toner concentration value measured by the IDC sensor 16 and the development output current value detected by the development bias detection unit 20, using the formula: toner charge amount = development output current value × application time ÷ toner adhesion amount. The correction voltage calculation unit 30 also calculates a correction voltage based on the bitmap density of the scanned image of the test chart measured by the density measurement device 17 and the calculated bitmap toner charge amount. When a density change in the scanned image of the test chart exceeds a pre-registered threshold, the correction voltage calculation unit 30 calculates a correction voltage to cancel the bias voltage oscillation caused by the density change in the scanned image (see FIG. 4, described later). The correction voltage calculation unit 30 also calculates the above-described correction voltage each time the density of the scanned image of the test chart changes. In this embodiment, the test chart is generated to include multiple levels of density change (see FIG. 6, described later). A test chart is also generated for each toner color. The above-mentioned predetermined threshold value is registered in advance in the image forming apparatus 100 by the user in accordance with his / her requirements for image quality, for example.

[0028] The control unit 40 is configured to include a CPU (Central Processing Unit), RAM (Random Access Memory), etc. (not shown). The CPU reads various processing programs stored in the storage unit 50, loads them into the RAM, and controls the operation of each component of the image forming apparatus 100. The control unit 40 also corrects the bias voltage to be applied to the developing unit 131c based on the density change of the original image and the correction voltage corresponding to the density change stored in the storage unit 50. Note that a GPU (Graphics Processing Unit) may be used instead of the CPU, or a CPU and a GPU may be used together.

[0029] The storage unit 50 is configured as a computer-readable, non-transitory recording material storing a program executed by the CPU. The storage unit 50 is configured as a storage device such as an HDD (Hard Disk Drive). The storage unit 50 stores programs for the CPU to control each unit, an OS (Operating System), controller programs, and other data. The storage unit 50 also stores original images of the test chart and images read by the reading unit 12. The storage unit 50 also stores correction voltages calculated by the correction voltage calculation unit 30 corresponding to changes in image density. The computer-readable, non-transitory recording material storing a program executed by the CPU is not limited to an HDD. For example, a solid-state drive (SSD), a compact disc (CD)-ROM, a digital versatile disc (DVD)-ROM, or other recording material may be used.

[0030] Next, we will explain the images before and after correction of density unevenness due to fluctuations in the development bias. FIG. 3 is a diagram showing images before and after correction of density unevenness due to fluctuations in the development bias in the image forming apparatus 100 according to this embodiment. Image P1 in FIG. 3 shows an image of a scanned image of a printed test chart. As shown in image P1, the test chart is composed of a striped image. When switching from white to black during image formation, the amount of toner fluctuation increases, which in turn causes a large fluctuation in the bias voltage applied to the developing unit 131c, resulting in density unevenness (see the gray area). Image P2 shows an image of a printed image of the test chart corrected by the bias voltage correction of the present invention. As shown in image P2, the density unevenness has been eliminated by the bias voltage correction.

[0031] Next, the development bias voltage correction corresponding to density changes will be described with reference to Fig. 4. Fig. 4 is a diagram for explaining the development bias voltage correction in the image forming apparatus 100 according to this embodiment.

[0032] Image P3 shown in FIG. 4 is an enlarged view of a portion of image P1 shown in FIG. 3. Below image P1, bias voltage B11, correction voltage B12, and corrected bias voltage B13 corresponding to the density changes in image P1 are displayed in this order. As shown in FIG. 4, at the black-and-white color change positions (positions p1 to p4 in the main scanning direction) in image P3, the bias voltage B11 oscillates due to density changes (fluctuations in the toner amount). As a result, density unevenness (gray areas) occurs.

[0033] Below the bias voltage B11, the correction voltage B12 (see dashed line) calculated by the correction voltage calculation unit 30 is displayed. As shown in the figure, the correction voltage calculation unit 30 calculates the correction voltage B12 so as to cancel out the oscillations in the bias voltage caused by density changes in the image P1. The control unit 40 corrects the bias voltage B11 based on the correction voltage B12, resulting in the corrected bias voltage B13 shown in the figure. Because the bias voltage B13 no longer oscillates, the density unevenness has been eliminated, as shown in the corrected image P4.

[0034] Next, an example of development bias voltage correction will be described with reference to Fig. 5 and Fig. 6. Fig. 5 shows Example 1 of development bias voltage correction in the image forming apparatus 100 according to this embodiment. Image P5 shown in Fig. 5 is an example of a test chart. Below image P5, density change C21, bias voltage B21, and correction voltage B22 corresponding to image P5 are displayed in this order.

[0035] As shown in Figure 5, each of positions p1 to p6 represents a position of density change in the main scanning direction. Multiple density values ​​exist within each range from positions p1 to p2, positions p3 to p4, and positions p5 to p6, but density change C21 is drawn to indicate the largest density difference before and after each position. For example, density change C21 immediately before position p3 displays the highest density of black, and density change C21 immediately after position p3 displays the lowest density of white.

[0036] Below the density change C21, the corresponding bias voltage B21 is displayed. A dashed line indicating the correction range is drawn around the bias voltage B21. The dashed line indicating the correction range represents the bias voltage corresponding to a predetermined threshold value for the density change, which has been registered in advance. Because the density change corresponding to the bias voltage fluctuation within the dashed line is within the predetermined threshold value, it is considered to be outside the correction range. In other words, the bias voltage B21 that exceeds the dashed line is subject to correction. Therefore, the correction voltage calculation unit 30 corrects only the bias voltage B21 within the range of positions p1 to p3. The correction voltage B22 calculated by the correction voltage calculation unit 30 is output only for the range of positions p1 to p3, as shown in the figure.

[0037] Fig. 6 shows Example 2 of development bias voltage correction in the image forming apparatus 100 according to this embodiment. Image P6 shown in Fig. 6 shows an example of a test chart. Below image P6, density change C31, bias voltage B31, and correction voltage B32 corresponding to image P6 are displayed in this order.

[0038] As shown in Fig. 6, the density change C31 includes density changes at multiple levels. The fluctuation of the bias voltage B31 within the range of positions p3 to p6 is outside the correction range. Therefore, the correction voltage calculation unit 30 corrects only the bias voltage B31 within the range of positions p1 to p3. The correction voltage B32 calculated by the correction voltage calculation unit 30 is output only for the range of positions p1 to p3, as shown in the figure.

[0039] [effect] As described above, the image forming apparatus 100 according to this embodiment corrects the bias voltage applied to the developing unit 131c when the density change of the scanned image of the test chart exceeds a predetermined threshold. The correction voltage calculation unit 30 of the image forming apparatus 100 calculates the correction voltage only for bias voltage fluctuations within the bias voltage correction range corresponding to the predetermined threshold. In other words, the present invention performs the phenomenon bias correction only when the specified density change level is exceeded, and does not perform unnecessary density unevenness correction, such as correction of density unevenness that cannot be detected visually. Therefore, the image forming apparatus 100 according to this embodiment can reduce the correction load for image density unevenness.

[0040] The present invention is not limited to the above-described embodiment, and it goes without saying that various other applications and modifications are possible without departing from the gist of the present invention as set forth in the claims. For example, the above-described embodiment describes the configuration of an image forming apparatus in detail and specifically in order to clearly explain the present invention, and is not necessarily limited to having all of the described configurations. Furthermore, it is possible to replace part of the configuration of the embodiment described here with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is also possible to add, delete, or replace part of the configuration of an embodiment with other configurations. In addition, the control lines and information lines shown are those that are considered necessary for the explanation, and do not necessarily show all the control lines and information lines in the product. In reality, it can be assumed that almost all components are interconnected. [Explanation of symbols]

[0041] 12...reading unit, 13...image forming unit, 15...operation display unit, 16...IDC sensor, 17...densitometer, 20...development bias detection unit, 30...correction voltage calculation unit, 40...control unit, 50...storage unit, 100...image forming device, 131b...photosensitive member, 131c...developing unit

Claims

1. an image forming section having a developing section that forms a toner image by attaching toner to the surface of a photosensitive member and forms an image on a recording material; a developing bias detection unit that detects a bias voltage applied to the developing unit when a test chart is formed on the recording material; a correction voltage calculation unit that calculates a correction voltage for correcting the bias voltage based on a change in density of the read image of the recording material on which the test chart is formed and the detected bias voltage; a control unit that corrects the bias voltage based on a change in density of the read image of the recording material on which an original image is formed and the correction voltage. Image forming device.

2. The correction voltage calculation unit calculates the correction voltage so as to cancel the fluctuation of the bias voltage caused by the density change of the read image when the density change of the read image of the test chart exceeds a predetermined threshold value registered in advance. The image forming apparatus according to claim 1 .

3. The correction voltage calculation unit calculates the correction voltage every time the density of the read image of the test chart changes. The image forming apparatus according to claim 2 .

4. The test chart is generated to include multiple levels of density variation. The image forming apparatus according to claim 3 .

5. The test chart is generated for each of the toner colors. The image forming apparatus according to claim 4 .

6. The correction voltage corresponding to the density change calculated by the correction voltage calculation unit is stored; The control unit corrects the bias voltage based on a density change of the read image of the recording material on which the original image is formed and the stored correction voltage corresponding to the density change. The image forming apparatus according to claim 5 .

Images