Image forming apparatus

Abstract

To make uniform the surface potential of a photoreceptor according to the arrangement position of an electrification electrode relative to the photoreceptor.SOLUTION: An image forming apparatus 1 comprises: an electrification device that has an electrification grid arranged along an outer peripheral surface of a photoreceptor 131b and supported by both ends in a longitudinal direction, in which the electrification grid faces the outer peripheral surface of the photoreceptor, and the aperture ratio of the electrification grid is adjusted according to its arrangement position relative to the photoreceptor 131b; and a control unit 16 that changes an operation condition for the electrification device according to a difference in the surface potential of the outer peripheral surface of the photoreceptor 131b.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Image forming devices use scorotron charging electrodes that generate corona discharge in components that charge the surface of a photoconductor (latent image carrier) and components that transfer a toner image from the latent image carrier. The scorotron charging electrode includes a charging grid and a charging wire. Applying a voltage to the charging grid and the charging wire generates a corona discharge between the charging grid and the latent image carrier, charging the surface of the latent image carrier. However, gravity causes the charging grid to bend, changing the distance between the photoconductor and the edges and center of the charging grid. This change in the distance between the charging grid and the photoconductor increases the amount of charge imparted to the portion of the photoconductor closest to the charging grid. This creates a potential difference on the surface of the photoconductor, which can lead to image defects such as uneven density. To address this issue, techniques for equalizing the surface potential of a photoconductor have been proposed, such as those described in Patent Document 1.

[0003] Patent Document 1 describes that an electric field having a larger absolute value is generated between the discharge electrode and the ionization region control electrode at both ends in the axial direction of the discharge electrode than at the central portion. Patent Document 1 also describes that the ionization region control electrode is made of a plate-like member having a slit. Patent Document 1 also describes that the slit width at both ends in the axial direction of the ionization region control electrode is smaller than that at the central portion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-15232 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, a technique has been proposed to equalize the surface potential of a photoconductor by narrowing the slit width at both ends of the charging grid compared to the center, thereby generating a larger absolute value of the electric field between the discharge electrodes and the ionization region control electrodes at both ends than at the center. However, depending on the specifications of the image forming device, the charging electrode may be positioned above the photoconductor, causing the charging grid to be oriented positively relative to the direction of gravity. In this case, gravity narrows the distance between the longitudinal center of the charging grid and the surface of the photoconductor. In this case, applying the technique described in Patent Document 1 results in a larger slit width at the center of the grid, i.e., a larger aperture ratio, than at both ends. A larger aperture ratio at the center of the grid increases the amount of charge passing through the center, strengthening the potential at the center of the photoconductor and resulting in uneven density.

[0006] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to make the surface potential of a photosensitive member uniform depending on the position of a charging electrode relative to the photosensitive member. [Means for solving the problem]

[0007] The image forming apparatus of the present invention includes a charging device that is arranged along the outer peripheral surface of a photosensitive body and has a charging grid that is supported at both longitudinal ends, the charging grid facing the outer peripheral surface of the photosensitive body, and the aperture ratio of the charging grid is adjusted according to its position relative to the photosensitive body, and a control unit that changes the operating conditions of the charging device according to the surface potential difference of the outer peripheral surface of the photosensitive body. [Effects of the Invention]

[0008] According to the present invention having the above-described configuration, the surface potential of the photosensitive member can be made uniform depending on the position of the charging electrode relative to the photosensitive member. 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] 2 is a block diagram showing an example of the hardware configuration of a control unit of an image forming apparatus according to an embodiment of the present invention; FIG. [Figure 3] 10A and 10B are diagrams illustrating deflection of a charging grid that occurs depending on the arrangement position of a charging electrode relative to a photosensitive member. [Figure 4] 10A and 10B are diagrams showing an example of a halftone image density profile when density unevenness occurs due to deflection of a charging grid; [Figure 5] 10A and 10B are diagrams for explaining a method of representing the position of a charging electrode relative to a photosensitive member. [Figure 6] 10A and 10B are diagrams for explaining a method of adjusting the aperture ratio depending on the arrangement position of the charging electrode in the image forming apparatus according to the embodiment of the present invention. [Figure 7] 10 is a diagram showing adjustment data for the aperture ratio according to the arrangement position of the charging grid in the image forming apparatus according to one embodiment of the present invention; [Figure 8] 10A and 10B are diagrams showing an image of adjustment of the aperture ratio according to the arrangement position of the charging grid in the image forming apparatus according to one embodiment of the present invention. [Figure 9] FIG. 2 is a diagram showing a first example of a control table for controlling the surface potential of a photosensitive member to be uniform in the image forming apparatus according to one embodiment of the present invention. [Figure 10] 10 is a diagram showing an example of a halftone image density profile after charge amount uniformization control is performed in an image forming apparatus according to an embodiment of the present invention. FIG. [Figure 11] FIG. 10 is a diagram showing a second example of a control table for controlling the surface potential of a photosensitive member to be uniform in an image forming apparatus according to one embodiment of the present invention. [Figure 12] FIG. 10 is a diagram showing a third example of a control table for controlling the surface potential of a photosensitive member to be uniform in an image forming apparatus according to one embodiment of the present invention. [Figure 13] FIG. 10 is a diagram showing a fourth example of a control table for controlling the surface potential of a photosensitive member to be uniform in an image forming apparatus according to one embodiment of the present invention. [Figure 14]FIG. 10 is a diagram showing a fifth example of a control table for controlling the surface potential of a photosensitive member to be uniform in an image forming apparatus according to one embodiment of the present invention. [Figure 15] FIG. 10 is a diagram showing Example 6 of a control table for controlling the surface potential of a photosensitive member to be uniform in an 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 1 according to this embodiment.

[0012] The image forming apparatus 1 is an example of an image forming apparatus that forms an image on a recording material by electrophotography. The image forming apparatus 1 is a multi-function digital image forming apparatus that has multiple functions, such as a print function, a copy function, and a scan function. The image forming apparatus 1 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.

[0013] As shown in FIG. 1, the image forming apparatus 1 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 electrode 131d, a cleaning unit 131e, and a primary transfer roller 131f.

[0017] During image formation processing, in each image writing unit 131, the charging electrode 131d is arranged along the outer peripheral surface of the drum-shaped photosensitive member 131b and charges the outer peripheral surface of the photosensitive member 131b. The charging electrode 131d is an example of a charging device, and scans the outer peripheral surface of the photosensitive member 131b with a light beam (light beam) emitted by the exposure device 131a based on the document image data, thereby forming an electrostatic latent image.

[0018] The charging electrode 131d includes a charging wire and a charging grid. The outer peripheral surface of the photoconductor 131b is charged by applying a current to the charging wire and a voltage to the charging grid. The charging grid is supported by both longitudinal ends of the charging electrode 131d and faces the outer peripheral surface of the photoconductor 131b. The aperture ratio of the charging grid is typically uniform across the entire surface, at a constant value, such as 70%. In this embodiment, the aperture ratio of the charging grid is adjusted depending on the position of the charging electrode 131d relative to the photoconductor 131b (see FIGS. 6 to 8, described below). When the developing unit 131c supplies a coloring material, such as toner, for development, an image is formed on the outer peripheral surface of the photoconductor 131b. The position of the charging electrode 131d relative to the photoconductor 131b shown in FIG. 1 is merely an example, and the present invention is not limited thereto. The position of the charging electrode 131d may be any position along the outer circumferential surface of the photosensitive member 131b depending on the design specifications of the image forming apparatus 1.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] In addition to the components shown in FIG. 1, the image forming apparatus 1 also includes a control unit 16 shown in FIG. 2. FIG. 2 is a block diagram showing an example of the hardware configuration of the control unit 16 of the image forming apparatus 1 according to this embodiment. The control unit 16 controls the overall operation of the image forming apparatus 1. The control unit 16 also changes the operating conditions of the charging electrode 131d (charging device) according to the surface potential difference on the outer circumferential surface of the photosensitive member 131b. The control unit 16 includes a CPU (Central Processing Unit) 16a, a ROM (Read Only Memory) 16b, a RAM (Random Access Memory) 16c, and a memory 16d. The CPU 16a, the ROM 16b, the RAM 16c, and the memory 16d are connected via a bus B so as to be able to transmit and receive information data to and from each other.

[0024] The CPU 16a performs image forming processing in the image forming apparatus 1, uniform control of the surface potential of the photosensitive member, and the like in accordance with the program read from the ROM 16b. The ROM 16b is configured as a storage medium such as a nonvolatile memory, and stores programs and data executed and referenced by the CPU 16a. The ROM 16b is used as an example of a computer-readable non-transitory storage medium that stores programs executed by the control unit 16. The RAM 16c is configured with a storage medium such as a volatile memory, and temporarily stores information (data) required for each process performed by the CPU 16a. The memory 16d is an image memory that stores image data to be recorded, a control table for uniformly controlling the surface potential of the photosensitive member, and the like.

[0025] Next, we will explain the deflection of the charging grid that occurs depending on the position of the charging electrode 131d relative to the photoconductor 131b. Figure 3 is a diagram showing the deflection of the charging grid that occurs depending on the position of the charging electrode relative to the photoconductor. Figure 3 shows a cross-sectional view along the longitudinal direction of the photoconductor 131b and the charging electrode 131d. Figure 3 also shows an example in which the charging electrode 131d is located directly above the photoconductor 131b and an example in which the charging electrode 131d is located directly below the photoconductor 131b.

[0026] As shown in FIG. 3, the charging grid of the charging electrode 131d located directly above the photoconductor 131b sags due to gravity, reducing the distance between the center of the charging grid and the photoconductor 131b. The closer the distance, the greater the amount of charge the charging grid imparts to the photoconductor 131b. Therefore, the amount of charge at the center of the photoconductor 131b, which corresponds to the center of the charging grid, is greater than at both ends. Also, as shown in FIG. 3, the charging grid of the charging electrode 131d located directly below the photoconductor 131b sags due to gravity, reducing the distance between the center of the charging grid and the photoconductor 131b. Therefore, the amount of charge at the center of the photoconductor 131b, which corresponds to the center of the charging grid, is less than at both ends. The difference in the amount of charge between the center and both ends of the photoconductor 131b, i.e., the surface potential difference, causes uneven density in the formed image.

[0027] FIG. 4 is a diagram showing an example of a halftone image density profile when density unevenness occurs due to the deflection of the charging grid. In FIG. 4, the halftone image density profile when the charging electrode 131d is located directly above the photoreceptor 131b, as shown in FIG. 3, is shown. The horizontal axis in FIG. 4 represents each position in the longitudinal direction of the photoreceptor 131b, that is, each position (mm) in the main scanning direction of image formation. The vertical axis in FIG. 4 represents the halftone image density. As shown in FIG. 4, the image density (about 0.53) at the central portion (150 mm) of the photoreceptor 131b is greater than the image densities (about 0.3) at both end sides (0 mm, 300 mm) of the photoreceptor 131b. That is, density unevenness has occurred.

[0028] Next, a method for representing the position of the charging electrode 131d with respect to the photoreceptor 131b in the present embodiment will be described. FIG. 5 is a diagram for explaining a method for representing the position of the charging electrode with respect to the photoreceptor. In FIG. 5, a cross-sectional view along a direction orthogonal to the longitudinal direction of the photoreceptor 131b and the charging electrode 131d is shown. In the present embodiment, an angle θ is defined as the smaller angle formed by the direction of gravity (reference solid arrow) and the line segment direction passing through the center of the photoreceptor from the opening surface of the charging grid (reference dashed arrow). As shown in FIG. 5, when the formed angle θ is an acute angle (when 0 < cos θ ≤ 1), the charging electrode 131d is at a positive position with respect to the direction of gravity, that is, at a position along the outer peripheral surface on the upper half side of the photoreceptor 131b. Further, when the formed angle θ is an obtuse angle (when -1 ≤ cos θ < 0), the charging electrode 131d is at a negative position with respect to the direction of gravity, that is, at a position along the outer peripheral surface on the lower half side of the photoreceptor 131b.

[0029] In the present embodiment, the aperture ratio of the charging grid is adjusted according to the arrangement position of the charging electrode 131d with respect to the photoreceptor 131b. FIG. 6 is a diagram for explaining a method for adjusting the aperture ratio of the charging grid according to the arrangement position of the charging electrode 131d in the image forming apparatus 1 according to the present embodiment. The cross-sectional view along the longitudinal direction of the photoreceptor 131b and the charging electrode 131d shown in FIG. 6 is the same as the cross-sectional view shown in FIG. 5 except for the aperture ratio of the charging grid, so duplicate explanations will be omitted.

[0030] In this embodiment, as shown in FIG. 6, the aperture ratio of the central portion of the charging grid of the charging electrode 131d located directly above the photoreceptor 131b (the formed angle θ is 0°) is adjusted to be smaller than the aperture ratios of both end portions. This is because in a portion where the aperture ratio of the charging grid is small, it is more difficult for charges to pass through compared to a portion where the aperture ratio is large. By adjusting the aperture ratio of the central portion of the charging grid to be small, the amount of charge applied to the central portion of the photoreceptor 131b is reduced. Therefore, an increase in the amount of charge in the central portion of the photoreceptor 131b due to the deflection of the charging grid is reduced. Further, in this embodiment, the above-described adjustment of the aperture ratio is not performed only for the charging electrode 131d located directly above the photoreceptor 131b. The aperture ratio of the central portion of the charging grid of the charging electrode 131d arranged at all positions where the formed angle θ described in FIG. 4 is an acute angle (0 < cos θ ≤ 1) is adjusted to be small.

[0031] Also, in this embodiment, as shown in FIG. 6, the aperture ratio of the central portion of the charging grid of the charging electrode 131d located directly below the photoreceptor 131b (the formed angle θ is 180°) is adjusted to be larger than the aperture ratios of both end portions. By adjusting the aperture ratio of the central portion of the charging grid to be large, the amount of charge applied to the central portion of the photoreceptor 131b is increased. Therefore, a decrease in the amount of charge in the central portion of the photoreceptor 131b due to the deflection of the charging grid is reduced. Further, in this embodiment, the above-described adjustment of the aperture ratio is not performed only for the charging electrode 131d located directly below the photoreceptor 131b. The aperture ratio of the central portion of the charging grid of the charging electrode 131d arranged at all positions where the formed angle θ described in FIG. 4 is an obtuse angle (-1 ≤ cos θ < 0) is adjusted to be large.

[0032] FIG. 7 shows adjustment data for the aperture ratio corresponding to the position of the charged grid in the image forming apparatus 1 according to this embodiment. FIG. 7 illustrates an example of adjustment data for the aperture ratio when the charging electrode 131d is located directly below the photoconductor 131b (the angle θ is 180°). As shown in FIG. 7, the aperture ratio adjustment data T0 includes a column for the distance (in mm) from each position on the center line of the etching pattern area of ​​the charged grid to a reference position. The aperture ratio adjustment data T0 also includes a column for the target aperture ratio (in %) corresponding to the distance to the reference position. Here, the length of the charging electrode 131d in the longitudinal direction is assumed to be 340 mm. The center line of the etching pattern area of ​​the charged grid is the line located at the center of the short side of the charged grid and running along the longitudinal direction (see the dashed line in FIG. 8 described below). The reference position is any one of the two longitudinal ends of the charged grid.

[0033] When the charging electrode 131d is located directly below the photoconductor 131b (the angle θ is 180°), as described in FIG. 6, the aperture ratio of the center of the charged grid is set to be greater than the aperture ratio of both ends. Therefore, as shown in FIG. 7, the target aperture ratio for the portion of the charged grid where the distance to the reference position is 154.5 to 185.5 mm, i.e., the center of the charged grid, is set to a maximum value of 80%. The target aperture ratio is set to be smaller as the distance from the center (154.5 to 185.5 mm) approaches the ends (0 mm and 340 mm). For example, the target aperture ratio is adjusted to be smaller by 1% for each specified distance (15.5 mm) from the center. The target aperture ratio corresponding to each position in this case is the target aperture ratio shown in FIG. 7. The target aperture ratios for both ends of the charged grid (0 to 15 mm and 325 to 340 mm) are set to a minimum value of 70%.

[0034] FIG. 8 shows an example of the aperture ratio adjustment of the charged grid based on the aperture ratio adjustment data shown in FIG. 7. FIG. 8 is a diagram illustrating an example of aperture ratio adjustment according to the arrangement position of the charging electrode 131d in the image forming apparatus 1 according to this embodiment. FIG. 8 shows an enlarged view of a portion of the charged grid of the charging electrode 131d. The hatched area in FIG. 8 represents the etching pattern range of the charged grid. The long-dotted dashed line represents the center line of the etching pattern range. Each solid line perpendicular to the center line represents the distance to the reference position. Note that the reference position is not shown in FIG. 8. As shown in FIG. 8, the aperture ratio of the charged grid in the range of 154.5 to 185.5 mm from the reference position (center portion) is 80%. Furthermore, the aperture ratio in the range (139 mm to 154.5 mm) a predetermined distance (15.5 mm) from the center portion is 79%. The aperture ratio in the range (123.5 mm to 139 mm) a predetermined distance (15.5 mm) away from 139 mm to 154.5 mm is 78%.

[0035] Note that simply adjusting the aperture ratio of the charging grid may not be enough to equalize the surface potential of the photoconductor 131b. In this case, the control unit 16 of the image forming apparatus 1 changes the operating conditions of the charging electrode 131d according to the surface potential difference of the photoconductor 131b. Here, the surface potential difference of the photoconductor 131b is the difference between the surface potential of the photoconductor facing the portion of the charging grid with the smallest aperture ratio and the surface potential of the photoconductor facing the portion of the charging grid with the largest aperture ratio. The operating conditions of the charging electrode 131d include at least one of the following: the charging grid voltage applied to the charging electrode 131d, the charging wire current supplied to the charging wire of the charging electrode 131d, the rotational speed of the photoconductor 131b, and the temperature of the charging electrode 131d. Note that in this embodiment, surface potential sensors are located at both the ends and the center of the photoconductor 131b.

[0036] 9 is a diagram showing Example 1 of a control table for uniformly controlling the surface potential of the photoconductor in the image forming apparatus 1 according to this embodiment. The control table Tb1 shown in FIG. 9 includes the following items: Δsurface potential T11 (V), charging grid voltage value T12 (−V), and charging wire current value T13 (−μA). In other words, in the example shown in FIG. 9, the control unit 16 of the image forming apparatus 1 controls the charging grid voltage and charging wire current as operating conditions for the charging electrode 131d.

[0037] The Δ surface potential T11 item stores the range of the surface potential difference of the photosensitive element 131b, for example, −5≦Δ surface potential<0.

[0038] The charged grid voltage value T12 field stores a charged grid voltage value corresponding to the Δ surface potential, such as 105% of the target grid voltage value. Here, the target grid voltage value is the initially set charged grid voltage value. Alternatively, a specific voltage value may be stored in the charged grid voltage value T12 field.

[0039] The charging wire current value T13 field stores the charging wire current value corresponding to the Δ surface potential, such as 720 (-μA). Here, the charging wire current value is the current value applied to the charging wire of the charging electrode 131d. Note that the charging wire current value T13 field may store an adjustment value for the initially set charging wire current value.

[0040] When Δsurface potential<0, the surface potential corresponding to the small-aperture area is lower than the surface potential corresponding to the large-aperture area. In this case, charge is less likely to pass through the small-aperture area of ​​the charged grid than through the large-aperture area. Therefore, increasing the charging wire current does not significantly increase the amount of charge transferred to the photoconductor. Therefore, in this case, the control unit 16 of the image forming apparatus 1 controls the charging grid voltage to increase and the charging wire current to decrease. As shown in control table Tb1, when Δsurface potential<0, the larger the absolute value of Δsurface potential, the greater the change in the charging grid voltage value T12. Increasing the charging grid voltage value increases the amount of charge in the small-aperture area of ​​the charged grid. Furthermore, the larger the absolute value of Δsurface potential, the smaller the change in the charging wire current value. Decreasing the charging wire current value decreases the amount of charge passing through the large-aperture area of ​​the charged grid. As a result, the difference in surface potential of the photoconductor is eliminated, and the amount of charge on the photoconductor surface becomes uniform.

[0041] Furthermore, when Δsurface potential > 0, the surface potential corresponding to the area with a small aperture ratio is higher than the surface potential corresponding to the area with a large aperture ratio. In this case, charge passes through the area with a large aperture ratio of the charged grid more easily than through the area with a small aperture ratio. Therefore, increasing the charged grid voltage does not significantly increase the amount of charge transferred to the photoconductor. Therefore, in this case, the control unit 16 of the image forming apparatus 1 controls the charging grid voltage to be lowered and the charging wire current to be increased. As shown in control table Tb1, when Δsurface potential > 0, the larger the absolute value of Δsurface potential, the smaller the charging grid voltage value T12 is changed. By lowering the charging grid voltage value, the amount of charge in the charged grid area with a small aperture ratio decreases. Furthermore, the larger the absolute value of Δsurface potential, the larger the charging wire current value is changed. By increasing the charging wire current value, the amount of charge passing through the charged grid area with a large aperture ratio increases. As a result, the difference in surface potential of the photoconductor is eliminated, and the amount of charge on the photoconductor surface becomes uniform.

[0042] FIG. 10 is a diagram showing an example of a halftone image density profile after the surface potential equalization control of the photoconductor has been performed in the image forming apparatus 1 according to this embodiment. Here, the surface potential equalization control of the photoconductor adjusts the aperture ratio of the charging grid according to the arrangement position of the charging electrode 131d, and further changes the operating conditions of the charging electrode 131d according to the control table Tb1 shown in FIG. 9. The horizontal and vertical axes in FIG. 10 are the same as those in FIG. 4, and therefore a redundant explanation will be omitted. As shown in FIG. 10, after the surface potential equalization control of the photoconductor has been performed, the density of the formed image is uniform without any significant change.

[0043] The present invention is not limited to controlling the surface potential uniformity of the photoconductor in accordance with the control table Tb1 shown in Fig. 9. For example, if the design specifications impose an upper limit on the charging wire current value, the process speed may be controlled instead of the charging wire current value. The process speed is the rotation speed of the photoconductor, i.e., the image formation speed.

[0044] FIG. 11 shows Example 2 of a control table for uniformly controlling the surface potential of the photoconductor in the image forming apparatus 1 according to this embodiment. Control table Tb2 shown in FIG. 11 includes fields for Δsurface potential T11 (V), charging grid voltage T12 (-V), and charging wire current T13 (-μA), as well as a field for process speed T24 (mm / sec). In other words, in the example shown in FIG. 11, the control unit 16 of the image forming apparatus 1 controls the charging grid voltage, charging wire current, and photoconductor rotation speed as operating conditions for the charging electrode 131d. Here, the upper limit set for the charging wire current is assumed to be 880 (-μA). Note that descriptions of fields that overlap between control table Tb2 and control table Tb1 will be omitted.

[0045] As shown in control table Tb2, when Δ surface potential<0, process speed T24 is controlled to maintain a constant value (e.g., 500 mm / sec). In this case, the control of the charging grid voltage value and the charging wire current value is the same as the control described in FIG. 9, so a duplicated description will be omitted.

[0046] If Δsurface potential > 0, the process speed T24 is maintained at a constant value until the charging wire current reaches its upper limit. The control of the charging grid voltage and charging wire current is the same as that described in FIG. 9. Once the charging wire current reaches its upper limit, it is maintained at that upper limit, and the process speed T24 is changed. In this case, the control unit 16 of the image forming apparatus 1 controls the charging grid voltage and the rotation speed of the photoconductor 131b to decrease. As shown in control table Tb2, the larger the absolute value of Δsurface potential, the smaller the charging grid voltage. By decreasing the charging grid voltage, the amount of charge passing through the charging grid portion with a small aperture ratio decreases. Furthermore, the larger the absolute value of Δsurface potential, the slower the process speed (rotation speed of the photoconductor 131b) becomes. By decreasing the process speed, the amount of charge passing through the charging grid portion with a large aperture ratio increases. As a result, the surface potential difference of the photoconductor disappears, and the amount of charge on the photoconductor surface becomes uniform.

[0047] Furthermore, the control unit 16 according to the present invention may control the charging grid voltage value and the process speed in accordance with the surface potential difference of the photoconductor. FIG. 12 shows a third example of a control table for uniformly controlling the surface potential of the photoconductor in the image forming apparatus 1 according to the present embodiment. The control table Tb3 shown in FIG. 12 includes the following items: Δsurface potential T11 (V), charging grid voltage value T12 (−V), and process speed T24 (mm / sec). In other words, in the example shown in FIG. 12, the control unit 16 of the image forming apparatus 1 controls the charging grid voltage and the rotational speed of the photoconductor as operating conditions for the charging electrode 131d.

[0048] If Δsurface potential<0, the control unit 16 of the image forming apparatus 1 controls the photoconductor 131b to increase the charging grid voltage and increase the rotation speed. As shown in control table Tb3, if Δsurface potential<0, the larger the absolute value of Δsurface potential, the larger the change in charging grid voltage value T12. By increasing the charging grid voltage value, the amount of charge in the charging grid portion with a small aperture ratio increases. Furthermore, the larger the absolute value of Δsurface potential, the faster the process speed is changed. By increasing the process speed, the amount of charge passing through the charging grid portion with a large aperture ratio decreases. As a result, the surface potential difference of the photoconductor disappears, and the amount of charge on the photoconductor surface becomes uniform.

[0049] Furthermore, if Δsurface potential>0, the control unit 16 of the image forming apparatus 1 controls the photoconductor 131b to lower the charging grid voltage and slow down the rotation speed of the photoconductor 131b. As shown in control table Tb3, if Δsurface potential>0, the larger the absolute value of Δsurface potential, the smaller the charging grid voltage value T12 is changed to. By lowering the charging grid voltage value, the amount of charge on the charging grid portion with a small aperture ratio is reduced. Furthermore, the larger the absolute value of Δsurface potential, the slower the process speed is changed to. By slowing down the process speed, the amount of charge passing through the charging grid portion with a large aperture ratio increases. As a result, the surface potential difference of the photoconductor is eliminated, and the amount of charge on the photoconductor surface becomes uniform.

[0050] Furthermore, the control unit 16 according to the present invention may control the charging grid voltage value and the temperature of the charging electrode 131d in accordance with the surface potential difference of the photoconductor. When performing this control, it is assumed that the image forming apparatus 1 is equipped with a temperature sensor for detecting the temperature of the charging electrode 131d and a temperature control device for adjusting the temperature of the charging electrode 131d. The temperature control device may be, for example, a heater for heating the charging electrode 131d or a Peltier element for cooling the charging electrode 131d. This control will be described with reference to FIG. 13. FIG. 13 shows Example 4 of a control table for uniformly controlling the surface potential of the photoconductor 131d in the image forming apparatus 1 according to the present embodiment. The control table Tb4 shown in FIG. 13 has the following fields: ΔSurface Potential T11 (V), Charging Grid Voltage T12 (-V), and Temperature T43 (°C). The Temperature T43 field stores the temperature of the charging electrode 131d.

[0051] If Δsurface potential<0, the control unit 16 of the image forming apparatus 1 controls the temperature regulator to increase the charging grid voltage and decrease the temperature of the charging electrode 131d. As shown in control table Tb4, the greater the absolute value of Δsurface potential, the greater the change in the charging grid voltage value T12. Increasing the charging grid voltage value increases the amount of charge in the charging grid portion with a small aperture ratio. Furthermore, the greater the absolute value of Δsurface potential, the lower the temperature of the charging electrode 131d is adjusted. Lowering the temperature of the charging electrode 131d slows the movement speed of charged ions, decreasing the amount of charge passing through the charging grid portion with a large aperture ratio. As a result, the surface potential difference of the photoconductor is eliminated, and the amount of charge on the photoconductor surface becomes uniform.

[0052] Furthermore, if Δsurface potential>0, the control unit 16 of the image forming apparatus 1 controls the temperature adjustment device to lower the charging grid voltage and raise the temperature of the charging electrode 131d. As shown in control table Tb4, the larger the absolute value of Δsurface potential, the smaller the charging grid voltage value T12 is changed to. By lowering the charging grid voltage value, the amount of charge in the charging grid portion with a small aperture ratio decreases. Furthermore, the larger the absolute value of Δsurface potential, the higher the temperature of the charging electrode 131d is adjusted to. By raising the temperature of the charging electrode 131d, the movement speed of charged ions increases, and the amount of charge passing through the charging grid portion with a large aperture ratio increases. As a result, the surface potential difference of the photoconductor is eliminated, and the amount of charge on the photoconductor surface becomes uniform.

[0053] Furthermore, the control unit 16 according to the present invention may control the charging grid voltage value, the temperature of the charging electrode, and the charging wire current value in accordance with the surface potential difference of the photoconductor. Fig. 14 shows a fifth example of a control table for uniformly controlling the surface potential of the photoconductor in the image forming apparatus 1 according to the present embodiment. The control table Tb5 shown in Fig. 14 has the following items: Δ surface potential T11 (V), charging grid voltage value T12 (-V), temperature T43 (°C), and charging wire current value T13 (-μA).

[0054] When Δsurface potential<0, the control unit 16 of the image forming apparatus 1 does not adjust the temperature of the charging electrode 131d, but instead increases the charging grid voltage and decreases the charging wire current. As shown in control table Tb5, when Δsurface potential<0, no temperature control of the charging electrode 131d is performed. Furthermore, the control of the charging grid voltage value and the charging wire current value in this case is the same as the control when Δsurface potential<0 described in FIG. 9, and therefore a repeated description will be omitted.

[0055] Furthermore, when Δ surface potential>0, the control unit 16 of the image forming apparatus 1 maintains the charging wire current at a predetermined value. The control unit 16 also controls the temperature regulator to lower the charging grid voltage and increase the temperature of the charging electrode 131d. As shown in control table Tb5, when Δ surface potential>0, the charging wire current value is maintained at a predetermined value (e.g., 800 μA). Furthermore, the control of the charging grid voltage value and the temperature of the charging electrode 131d in this case is the same as the control when Δ surface potential>0 described in FIG. 13, and therefore a repeated description will be omitted.

[0056] Furthermore, the control unit 16 according to the present invention may control the charging grid voltage value, the temperature of the charging electrode, and the process speed in accordance with the surface potential difference of the photoconductor. Fig. 15 is a diagram showing Example 6 of a control table for uniformly controlling the surface potential of the photoconductor in the image forming apparatus 1 according to this embodiment. The control table Tb6 shown in Fig. 15 has the following items: Δsurface potential T11 (V unit), charging grid voltage value T12 (-V unit), temperature T43 (°C unit), and process speed T24 (mm / sec unit).

[0057] When Δsurface potential<0, the control unit 16 of the image forming apparatus 1 does not adjust the temperature of the charging electrode 131d, but instead increases the charging grid voltage and controls the rotation speed (process speed) of the photoconductor 131b. As shown in control table Tb6, when Δsurface potential<0, the temperature of the charging electrode 131d is not controlled. Furthermore, the control of the charging grid voltage value and process speed in this case is the same as the control when Δsurface potential<0 described in FIG. 12, and therefore a repeated description will be omitted.

[0058] Furthermore, when Δsurface potential>0, the control unit 16 of the image forming apparatus 1 maintains the rotational speed (process speed) of the photoconductor 131b at a predetermined speed. The control unit 16 also controls the temperature regulator to lower the charging grid voltage and increase the temperature of the charging electrode 131d. As shown in control table Tb6, when Δsurface potential>0, the rotational speed (process speed) of the photoconductor 131b is maintained at a predetermined speed (e.g., 500 mm / sec). Furthermore, the control of the charging grid voltage value and the temperature of the charging electrode 131d in this case is the same as the control when Δsurface potential>0 described in FIG. 13, and therefore a repeated description will be omitted.

[0059] [effect] As described above, the image forming apparatus 1 according to this embodiment adjusts the aperture ratio of the charging grid of the charging electrode 131d depending on the position of the charging electrode 131d relative to the photoconductor 131b. Furthermore, the image forming apparatus 1 detects the surface potential of the photoconductor 131b. Depending on the detected surface potential of the photoconductor 131b, the image forming apparatus 1 controls and changes the operating conditions of the charging electrode 131d so that the surface potential of the photoconductor 131b is uniform. Therefore, the image forming apparatus 1 according to the present invention can uniform the surface potential of the photoconductor depending on the position of the charging electrode relative to the photoconductor.

[0060] 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]

[0061] 1...image forming apparatus, 131b...photosensitive member, 131d...charging electrode, 16...control unit, Tb1 to Tb6...control tables

Claims

1. a charging device having a charging grid disposed along the outer peripheral surface of the photosensitive member and supported at both ends in the longitudinal direction, the charging grid facing the outer peripheral surface of the photosensitive member, and an opening ratio of the charging grid adjusted according to its position relative to the photosensitive member; a control unit that changes the operating conditions of the charging device in accordance with the surface potential difference of the outer circumferential surface of the photosensitive member; Image forming device.

2. The operating conditions of the charging device include at least one of a charging grid voltage applied to the charging device, a charging wire current supplied to a charging wire of the charging device, a rotation speed of the photoconductor, and a temperature of the charging device. The image forming apparatus according to claim 1 .

3. The opening ratio is set to the smaller angle between the direction of gravity and the direction of a line segment passing from the opening surface of the charging grid through the center of the photosensitive member, and when the angle is acute, the opening ratio of the central portion of the charging grid in the longitudinal direction is adjusted to be smaller. The image forming apparatus according to claim 1 .

4. When the angle is an obtuse angle, the opening ratio of the central portion in the longitudinal direction of the electrified grid is adjusted to be large. The image forming apparatus according to claim 3 .

5. The surface potential difference is the difference between the surface potential of the photoconductor facing the portion of the charging grid where the aperture ratio is smallest and the surface potential of the photoconductor facing the portion of the charging grid where the aperture ratio is largest. The image forming apparatus according to claim 4 .

6. When the surface potential difference is less than 0, the control unit controls the charging device to increase a charging grid voltage applied to the charging device and to decrease a charging wire current supplied to a charging wire included in the charging device; If the surface potential difference exceeds 0, the control unit controls the charging grid voltage to decrease and the charging wire current to increase. The image forming apparatus according to claim 5 .

7. an upper limit is set for the charging wire current, and when the surface potential difference exceeds 0 and the charging wire current reaches the upper limit, The control unit controls the charging grid voltage to be lowered and the rotation speed of the photoconductor to be lowered. The image forming apparatus according to claim 6 .

8. When the surface potential difference is less than 0, the control unit controls the charging device to increase a charging grid voltage applied to the charging device and to increase a rotation speed of the photosensitive member; When the surface potential difference exceeds 0, the control unit controls the charging grid voltage to be lowered and the rotation speed of the photoconductor to be lowered. The image forming apparatus according to claim 5 .

9. A temperature control device is provided to adjust the temperature of the charging device. The image forming apparatus according to claim 5 .

10. When the surface potential difference is less than 0, the control unit controls the temperature adjustment device to increase a charging grid voltage applied to the charging device and decrease a temperature of the charging device; When the surface potential difference exceeds 0, the control unit controls the temperature adjustment device to lower the charging grid voltage and increase the temperature of the charging device. The image forming apparatus according to claim 9 .

11. The temperature control device is a heater that heats the charging device or a Peltier element that cools the charging device. The image forming apparatus according to claim 9 .

12. When the surface potential difference is less than 0, the control unit does not adjust the temperature of the charging device, but controls the charging grid voltage applied to the charging device to be increased and the charging wire current supplied to the charging wire included in the charging device to be decreased; When the surface potential difference exceeds 0, the control unit controls the temperature regulator to maintain the charging wire current at a predetermined value, reduce the charging grid voltage, and increase the temperature of the charging device. The image forming apparatus according to claim 9 .

13. When the surface potential difference is less than 0, the control unit does not adjust the temperature of the charging device, but increases a charging grid voltage applied to the charging device, and controls the photosensitive member to increase a rotation speed; When the surface potential difference exceeds 0, the control unit controls the temperature adjustment device to maintain the rotation speed of the photosensitive member at a predetermined speed, reduce the charging grid voltage, and increase the temperature of the charging device. The image forming apparatus according to claim 9 .

Images