Image forming apparatus

Abstract

To provide an image forming apparatus that can supply toner at appropriate timing.SOLUTION: An image forming apparatus 100 comprises: a photoreceptor drum 3; a developing unit 2 that forms a toner image on the photoreceptor drum 3; a developing power supply 2h that supplies a developing bias to the developing unit 2; an image sensor 74 that detects the density of the toner image; an environmental sensor 80 that detects a temperature and humidity; a supply unit 141 that supplies toner to the developing unit 2; and a control unit 91 that executes image quality adjustment of changing the developing bias. The control unit 91 has a storage unit 92 that stores a supply condition in which timing to supply the toner is set, a correction value for the supply condition, and an ideal bias, and corrects the correction value until the next image quality adjustment on the basis of a bias difference that is a difference between an adjustment bias and the ideal bias and a previous correction value set in the previous image quality adjustment.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus that forms a toner image on an image carrier. [Background technology]

[0002] Conventionally, electrophotographic image forming devices form images by transferring a toner image formed on a photosensitive member onto paper. In recent years, because repeated image formation consumes toner (developer), a method of replacing cartridges (containers) containing toner has been adopted. In image forming devices using this method, developer is contained in a developing device, and when the developer is consumed during image formation, developer is replenished from the cartridge as needed.

[0003] Furthermore, in an image forming apparatus for forming a color image, a plurality of image carriers are provided to form toner images of a plurality of colors, and a method for controlling the toner density and developing bias of each color has been proposed to form a desired color image (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-28004 Summary of the Invention [Problem to be solved by the invention]

[0005] In a conventional image forming apparatus, an electrostatic latent image is formed on the surface of a photoreceptor charged by a charging means using an exposure means based on an image signal, and the electrostatic latent image is developed using a two-component developer consisting of toner and carrier contained in a developing means while applying a development bias voltage to form a toner image, which is then transferred and fixed onto a recording material. The image forming apparatus also includes a toner adhesion amount detection sensor that detects the amount of toner adhesion on the toner image carrier, a toner concentration detection sensor that detects the toner concentration in the developer in the developing means, and a control means that controls the development bias voltage and toner concentration. The control means sets the same development bias voltage for all developing means based on the development bias voltage that achieves a target toner adhesion amount and the toner concentration that achieves the target toner adhesion amount, and sets individual control target values ​​for the toner concentration for each developing means.

[0006] In conventional image forming apparatuses, a toner concentration detection sensor is provided to detect the toner concentration in the developing unit, but if a toner concentration detection sensor is not provided, there is a problem that the toner concentration in the developing unit cannot be detected. Also, providing a toner concentration detection sensor increases the number of parts, which increases costs.

[0007] The present disclosure has been made to solve the above-mentioned problems, and aims to provide an image forming apparatus that can replenish toner at the appropriate time without having to install a sensor that detects the amount of toner. [Means for solving the problem]

[0008] The image forming apparatus according to the present disclosure comprises an image carrier whose surface is charged to a predetermined potential, a developing unit that forms a toner image on the image carrier, a developing power supply that supplies a developing bias to the developing unit, an image sensor that detects the density of the toner image formed by the developing unit, an environmental sensor that detects temperature and humidity, a supply unit that supplies toner to the developing unit, and a control unit that performs image quality adjustment by changing the developing bias based on the detection results of the image sensor, wherein the control unit has a memory unit that stores supply conditions that set the timing at which the supply unit supplies toner, a correction value for the supply conditions that is set in the image quality adjustment, and an ideal bias that is set based on the detection results of the environmental sensor, and corrects the correction value until the next image quality adjustment based on the bias difference, which is the difference between the adjusted bias calculated during the image quality adjustment and the ideal bias, and the previous correction value set in the previous image quality adjustment.

[0009] In the image forming apparatus according to the present disclosure, the memory unit may store a correction table in which a reflection rate corresponding to the bias difference is set, and the control unit may be configured to correct the correction value by referring to the reflection rate of the correction table when adjusting the image quality.

[0010] In the image forming apparatus according to the present disclosure, the control unit may be configured to change the interval until the next image quality adjustment based on the bias difference.

[0011] In the image forming apparatus according to the present disclosure, the image carrier may include a plurality of photosensitive drums and an intermediate transfer belt onto which the toner images on the plurality of photosensitive drums are transferred, and a plurality of the developing units and the supply units may be provided corresponding to the plurality of photosensitive drums.

[0012] The image forming apparatus according to the present disclosure may be configured such that, in the image quality adjustment, the bias difference is calculated for each of the multiple developing units, and the control unit changes the interval until the next image quality adjustment based on the bias difference with the largest value.

[0013] In the image forming apparatus according to the present disclosure, the development power supply may be configured to supply a common bias common to the plurality of development units as the development bias, and the control unit may be configured to correct the correction value based on the difference between the common bias and the adjustment bias.

[0014] In the image forming apparatus according to the present disclosure, the control unit may be configured to correct the correction value based on a detection result of the environment sensor. [Effects of the Invention]

[0015] According to the present disclosure, by comparing the adjusted bias obtained by image quality adjustment with the ideal bias, it is possible to determine whether the previously set correction value was appropriate and to grasp the toner supply status to the developing unit. Then, by reflecting the grasped results, toner can be replenished at the appropriate timing without providing a sensor to detect the amount of toner in the developing unit. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic cross-sectional view showing a configuration of an image forming apparatus according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a perspective view showing the internal structure of a developing unit. [Figure 3] FIG. 2 is a schematic side view showing members in the vicinity of the photosensitive drum. [Figure 4] 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention; [Figure 5] FIG. 4 is a characteristic diagram showing the relationship between the charge potentials of the photosensitive drum and the developing roller. [Figure 6] FIG. 2 is a development explanatory view showing the intermediate transfer belt and a toner image formed thereon. [Figure 7] 10 is an explanatory diagram showing an example of a supply table. [Figure 8] 10 is an explanatory diagram illustrating an example of an environment table. [Figure 9] 1 is an explanatory diagram showing an example of a charging table. [Figure 10]10 is an explanatory table showing an example of a correction result for a replenishment condition. [Figure 11] 10 is an explanatory diagram showing an example of a correction table. [Figure 12] 10 is an explanatory table showing an example of correction results for replenishment conditions in the second embodiment. [Figure 13] 10 is an explanatory diagram showing an example of a coefficient table. DETAILED DESCRIPTION OF THE INVENTION

[0017] (First embodiment) Hereinafter, an image forming apparatus according to a first embodiment of the present disclosure will be described with reference to the drawings.

[0018] FIG. 1 is a schematic cross-sectional view showing the configuration of an image forming apparatus according to a first embodiment of the present disclosure.

[0019] The image forming device 100 is a multifunction device having a copy function, a scanner function, a facsimile function, and a printer function, and transmits an image of a document read by the image reading device 130 to an external device, and forms an image of a document read by the image reading device 130 or an image received from an external device in color or monochrome on a recording medium such as paper.

[0020] An original transport device 110 that is supported so as to be able to open and close freely is provided above the image reading device 130. The original transport device 110 transports one or more originals one by one. The image reading device 130 scans a scanning optical system 130b to read an original placed on an original placement table 130a, or reads an original transported by the original transport device 110 to generate image data.

[0021] The image forming apparatus 100 is provided with a fixing device 1, a developing unit 2, a photosensitive drum 3 (an example of an image carrier), a drum cleaning device 4, a charger 5, an intermediate transfer belt device 7, a secondary transfer device 11, an exposure unit 12, and a paper feed unit 18.

[0022] Image forming apparatus 100 handles image data corresponding to color images using black (K), cyan (C), magenta (M), and yellow (Y), or monochrome images using a single color (e.g., black). Image forming apparatus 100 is provided with four developing units 2, four photosensitive drums 3, four drum cleaning devices 4, and four chargers 5 for forming four types of toner images, and four image stations Pa, Pb, Pc, and Pd are configured corresponding to black, cyan, magenta, and yellow, respectively.

[0023] The charger 5 uniformly charges the surface of the photosensitive drum 3 to a predetermined potential. The exposure unit 12 is an optical scanning device that exposes the surface of the photosensitive drum 3 to light to form an electrostatic latent image. The development unit 2 develops the electrostatic latent image on the surface of the photosensitive drum 3 to form a toner image on the surface of the photosensitive drum 3. The drum cleaning device 4 removes and collects residual toner on the surface of the photosensitive drum 3. Through the series of operations described above, a toner image of each color is formed on the surface of each photosensitive drum 3.

[0024] The intermediate transfer belt device 7 includes an intermediate transfer roller 6, an endless intermediate transfer belt 71 (an example of an image carrier), an intermediate transfer drive roller 72, an intermediate transfer driven roller 73, and a cleaning device 9. Four intermediate transfer rollers 6 are provided inside the intermediate transfer belt 71 so as to form four types of toner images corresponding to each color. The intermediate transfer rollers 6 transfer the toner images of each color formed on the surface of the photosensitive drum 3 onto the intermediate transfer belt 71, which moves in a rotation direction C.

[0025] The intermediate transfer belt 71 is stretched over an intermediate transfer drive roller 72 and an intermediate transfer driven roller 73. In the image forming apparatus 100, the toner images of each color formed on the surface of each photosensitive drum 3 are sequentially transferred and superimposed to form a color toner image on the surface of the intermediate transfer belt 71. The cleaning device 9 removes and collects waste toner remaining on the surface of the intermediate transfer belt 71 without being transferred to paper.

[0026] The secondary transfer device 11 sandwiches and transports the paper that has been transported through the paper transport path 21 in the transfer nip between the secondary transfer roller 11a and the intermediate transfer belt 71. When the paper passes through the transfer nip, the toner image on the surface of the intermediate transfer belt 71 is transferred onto the paper, and the paper is then transported to the fixing device 1.

[0027] An image sensor 74 is provided near the intermediate transfer belt 71, facing the surface of the intermediate transfer belt 71. The image sensor 74 is disposed between any of the image stations (image station Pa in FIG. 1) located on the most downstream side in the rotation direction C and the secondary transfer device 11. The image sensor 74 is an optical sensor that irradiates light onto the intermediate transfer belt 71 and receives the reflected light to detect the density of the toner image on the intermediate transfer belt 71. The relationship between the image sensor 74 and the toner image will be described later with reference to FIG. 6.

[0028] The fixing device 1 includes a fixing belt 31 that rotates around an axis and a pressure roller 32. The fixing device 1 sandwiches a sheet of paper onto which a toner image has been transferred in a nip portion between the fixing belt 31 and the pressure roller 32 and applies heat and pressure to fix the toner image to the sheet. Although not shown in FIG. 1, the fixing device 1 may also include components other than the fixing belt 31 and the pressure roller 32.

[0029] The paper feed unit 18 includes a paper feed cassette that holds recording media (paper) used for image formation, and is provided below the exposure unit 12. The paper is pulled out of the paper feed unit 18 by a pickup roller 16 and transported to a paper transport path 21. The paper transported to the paper transport path 21 passes through the secondary transfer device 11 and the fixing device 1, and is then discharged to a paper output tray 19 by a discharge roller 17.

[0030] Conveyance rollers 13, registration rollers 14, and discharge rollers 17 are arranged on paper conveyance path 21. Conveyance rollers 13 facilitate the conveyance of paper. Registration rollers 14 convey paper at a speed equal to the process speed at which an image is formed on the paper. Registration rollers 14 are provided between paper feed unit 18 and secondary transfer device 11, and adjust the timing of paper conveyance so that the toner image is transferred to the paper by secondary transfer device 11. For example, registration rollers 14 wait (temporarily stop) while clamping paper conveyed from paper feed unit 18, and then start conveying the paper at a constant speed in synchronization with secondary transfer device 11.

[0031] When an image is to be formed on the back side of the paper in addition to the front side, the conveying direction of the paper is changed by discharge rollers 17, and the paper is conveyed to reversing conveying path 22. In reversing conveying path 22, the paper is guided up to registration rollers 14 in a reversed state by reversing conveying rollers 15. Image forming apparatus 100 forms an image on the back side of the paper guided to registration rollers 14 in the same manner as on the front side, and discharges the paper to discharge tray 19.

[0032] The image forming apparatus 100 is configured to have cartridges 140 that contain toner attached thereto, and the toner is supplied from the cartridges 140 to the developing unit 2 via a conveying member (not shown). In this embodiment, four cartridges 140 are attached thereto, one for each color to be used, and each cartridge 140 is detachably attached to the image forming apparatus 100. Note that the cartridges 140 are not limited to being configured to contain only toner, and may be configured to contain a developer containing toner and carrier. Furthermore, when a cartridge 140 that contains toner is employed, the developing unit 2 may be filled with carrier in advance, and the toner and carrier may be mixed in the developing unit 2 to produce a developer.

[0033] 1 shows a configuration in which the toner image is transferred onto paper via the intermediate transfer belt 71 for the image forming apparatus 100, but the present invention is not limited to this and may be configured such that the toner image is transferred directly from the photosensitive drum 3 to the paper. In other words, while FIG. 1 shows a configuration in which the image carrier includes a plurality of photosensitive drums 3 and an intermediate transfer belt 71 onto which the toner images on the plurality of photosensitive drums 3 are transferred, the present invention is not limited to this and may be configured such that the image carrier includes only one photosensitive drum 3.

[0034] 2 is a perspective view showing the internal structure of the developing unit 2. Note that in FIG. 2, a part of the housing of the developing unit 2 has been removed to make it easier to see the inside of the developing unit 2.

[0035] The developing unit 2 includes a developing roller 2a, a first screw 2d, and a second screw 2e, all of which are housed in a housing 2b. The housing 2b has an internal cavity and is generally rectangular. The housing 2b is divided into two regions by a partition wall 2c extending along the longitudinal direction. The partition wall 2c has openings at its longitudinal ends, through which the developer flows between the two regions. One region of the housing 2b is provided with a first screw 2d, and the other region is provided with a second screw 2e. The first screw 2d and the second screw 2e are arranged with their axes parallel to each other and facing each other. A developing gear 2f is connected to the shaft of the first screw 2d and the shaft of the second screw 2e, respectively. The first screw 2d and the second screw 2e rotate due to the rotational force transmitted from a drive source (not shown) via the developing gear 2f.

[0036] A toner receiving port 2g is provided at an end of the developing unit 2, and the receiving port 2g is connected to the corresponding cartridge 140 and a transport member. In the developing unit 2, the developer (toner) supplied from the receiving port 2g is circulated within the housing 2b by rotating the first screw 2d and the second screw 2e. In the developing unit 2, the toner concentration (the proportion of toner in the developer) varies depending on the amount of toner replenished from the cartridge 140.

[0037] The developing roller 2a is disposed opposite the photosensitive drum 3 and supplies developer to the photosensitive drum 3. In the present embodiment, the developing roller 2a is disposed above the first screw 2d, but this is not limitative, and the developing roller 2a may be disposed facing the part of the developing unit 2 that supplies developer to the outside.

[0038] FIG. 3 is a schematic side view showing members in the vicinity of the photosensitive drum.

[0039] 3 shows one photosensitive drum 3 and some of its associated components. Specifically, the charger 5 includes a charging roller 5a that contacts the photosensitive drum 3, and a bias is supplied to the charging roller 5a from a connected charging power source 5b. The developing roller 2a contacts the photosensitive drum 3 and a bias is supplied to the developing roller 2a from a connected developing power source 2h. Furthermore, a supply unit 141 that supplies toner to the developing unit 2 is connected to the cartridge 140.

[0040] Supply unit 141 is composed of a screw that transports toner, a gear that transmits power to the screw, a motor connected to the gear, the transport members described above, and the amount of toner supplied to development unit 2 is determined according to the amount of operation of supply unit 141. In this embodiment, the supply time for operating supply unit 141 is set as the condition for supplying toner to development unit 2, but the invention is not limited to this, and the supply conditions may be any item related to the amount of toner supplied.

[0041] Fig. 4 is a schematic diagram of an image forming apparatus according to the present embodiment. Note that Fig. 4 shows only a portion of image forming apparatus 100, and other members not shown in Fig. 4 may be included as appropriate.

[0042] In addition to the above-mentioned developing unit 2, developing power supply 2h, photosensitive drum 3, exposure unit 12, intermediate transfer belt 71, image sensor 74, cartridge 140, and supply unit 141, image forming apparatus 100 also includes an environmental sensor 80, control unit 91, and storage unit 92. The environmental sensor 80 detects the temperature and humidity in the environment in which image forming apparatus 100 is installed. The control unit 91 is a CPU mounted in image forming apparatus 100 and controls the operation of image forming apparatus 100, for example, causing image quality adjustment, which will be described later, to be performed. The storage unit 92 stores various information related to the operation of image forming apparatus 100.

[0043] Next, the relationship between the charge potential on the surface of the photosensitive drum 3 and the charge amount of the toner will be described with reference to FIG.

[0044] FIG. 5 is a characteristic diagram showing the relationship between the charge potentials of the photosensitive drum and the developing roller.

[0045] As described above, in the image forming apparatus 100, a toner image is formed by the steps of charging, exposing, and developing the photosensitive drum 3, and the potential (bias) in each step affects the image quality (density) of the toner image. Specifically, the photosensitive drum 3 is charged to a predetermined photosensitive bias Vk by a bias applied to the charging roller 5a. The exposure unit 12 then exposes a portion of the surface of the photosensitive drum 3 to which toner is to be attached, thereby changing the bias to an exposure bias Vr close to 0V. The developing roller 2a is charged to a developing bias Vb, the absolute value of which is smaller than the photosensitive bias Vk. The difference between the developing bias Vb and the exposure bias Vr (toner potential difference ΔV) attracts the toner supplied to the developing roller 2a to the surface of the photosensitive drum 3. In other words, the toner potential difference ΔV changes the amount of toner attached to the surface of the photosensitive drum 3, and also changes the density of the toner image. In the example shown in FIG. 5, the photosensitive member bias Vk is set to -450V, the developing bias Vb is set to -400V, and the exposure bias Vr is set to about -100 to -50V.

[0046] Incidentally, the density of the toner image varies not only depending on the toner potential difference ΔV but also on the density of the toner in the developing unit 2, the temperature and humidity of the environment in which the image forming apparatus 100 is installed, the surface condition of the developing roller 2a, etc. Therefore, the image forming apparatus 100 forms a toner image on the image carrier, and performs image quality adjustment by changing the developing bias Vb based on the result of detecting the density of the toner image with the image sensor 74, so that the desired density of the toner image can be obtained through image quality adjustment.

[0047] Next, the toner image (patch image) formed during image quality adjustment will be described with reference to FIG.

[0048] FIG. 6 is an explanatory development view showing the intermediate transfer belt and the toner image formed thereon.

[0049] 6 shows a portion of the unfolded intermediate transfer belt 71, and schematically illustrates the relative positions of the toner images (patch images PG) and the image sensor 74. In the present embodiment, patch images PG formed on the four photosensitive drums 3 are transferred to the intermediate transfer belt 71 while it is moving in a rotation direction C (upward in FIG. 6). The positions at which the patch images PG are formed are not particularly limited, and they may be formed in positions that can be detected by the image sensor 74 when the intermediate transfer belt 71 is moving in a rotation direction C.

[0050] During image quality adjustment, the developing bias is changed in stages, and multiple patch images PG are formed on each photosensitive drum 3 and transferred to intermediate transfer belt 71. The densities of the multiple patch images PG are then detected by image sensor 74, and an adjusted bias is calculated based on the results as the developing bias value that will result in a desired density. In a configuration with multiple image stations, as in this embodiment, it is preferable to calculate the adjusted bias for each image station.

[0051] As described above, image forming apparatus 100 is configured to replenish toner to developing unit 2 as needed, and replenishment conditions are set according to the amount of toner consumed. Next, a replenishment table relating to replenishment conditions will be described with reference to FIG.

[0052] FIG. 7 is an explanatory diagram showing an example of a supply table.

[0053] The replenishment table shown in FIG. 7 is stored in the memory unit 92 and associates the print rate corresponding to the amount of toner consumed with the replenishment time, which is a replenishment condition. The print rate is a value calculated from image data and corresponds to the proportion of the area of ​​a single sheet of paper that is colored with toner. In other words, the higher the print rate, the greater the amount of toner consumed. Note that when forming images on multiple sheets of paper consecutively, the print rate may be calculated for all of them at once. The replenishment time indicates the time for which the replenishment unit 141 is operated; the longer the replenishment time, the greater the amount of toner replenished to the developing unit 2. The print rate and replenishment time may be set to have an appropriate relationship depending on the configuration of the image forming apparatus 100, and the replenishment amount may be set to compensate for the amount of toner consumed by the developing unit 2.

[0054] As described above, the temperature and humidity in the environment in which image forming apparatus 100 is installed and the operating conditions of developing roller 2a affect the density of the toner image. Therefore, in this embodiment, information related to these factors is collected and reflected in the operation of image forming apparatus 100. Next, tables related to temperature, humidity, and the surface condition of developing roller 2a will be described with reference to FIGS. 8 and 9.

[0055] FIG. 8 is an explanatory diagram showing an example of the environment table.

[0056] The environment table shown in FIG. 8 is stored in the storage unit 92 and is a table related to temperature and humidity. The environment table provides multiple, non-overlapping ranges for the temperature and humidity detected by the environment sensor 80. Specifically, four temperature ranges (first temperature range TE1 to fourth temperature range TE4) are provided, with the temperature increasing in the order of first temperature range TE1, second temperature range TE2, third temperature range TE3, and fourth temperature range TE4. Six humidity ranges (first humidity range HU1 to sixth humidity range HU6) are provided, with the humidity increasing in the order of first humidity range HU1, second humidity range HU2, ..., and sixth humidity range HU6. The environment table assigns an environment frequency corresponding to the temperature and humidity, with values ​​ranging from "1" to "6" being used. The environment frequency in the environment table is assigned as "1" when the temperature and humidity are low, and as the temperature and humidity increase, a higher environment frequency value is assigned. That is, a low environmental degree indicates a low temperature and low humidity environment, and a high environmental degree indicates a high temperature and high humidity environment.

[0057] 8 shows a case where four temperature ranges and six humidity ranges are set, and values ​​from "1" to "6" are used as the environmental frequency, but the present invention is not limited to this, and the number of temperature and humidity ranges may be changed, and the values ​​used for the environmental frequency may be changed. In other words, the temperature and humidity may be divided into smaller ranges, and the values ​​used for the environmental frequency may be increased.

[0058] FIG. 9 is an explanatory diagram showing an example of the charging table.

[0059] 9 is stored in the storage unit 92 and is a table relating to the environmental frequency and the operating status of the developing roller 2a. In the present embodiment, the accumulated running time is recorded as the operating status of the developing roller 2a.

[0060] The running time of the developing roller 2a corresponds to the distance (number of rotations) it rotates when forming a toner image, and as the running time of the developing roller 2a increases, it becomes more difficult for the toner to be charged, and the amount of charge decreases. The amount of charge on the toner affects the amount consumed in image formation. Temperature and humidity also affect the amount of charge on the toner, increasing the amount of charge in a low-temperature, low-humidity environment and decreasing the amount of charge in a high-temperature, high-humidity environment.

[0061] The charge table provides six non-overlapping ranges (first life range LA1 to sixth life range LA6) for the running time of the developing roller 2a, with the running time increasing in the order of first life range LA1, second life range LA2, ..., and sixth life range LA6. The charge table assigns charge frequencies corresponding to the environmental frequency and the running time of the developing roller 2a, with values ​​of "1" to "6" used as the charge frequencies. The charge frequency in the charge table is assigned "1" when the environmental frequency and the running time of the developing roller 2a are low, and higher values ​​of the charge frequency are assigned as the environmental frequency and the running time of the developing roller 2a increase. In other words, a low charge frequency indicates a situation in which the charge amount is high, and a high charge frequency indicates a situation in which the charge amount is low.

[0062] The image forming apparatus 100 calculates an ideal bias, which is an appropriate development bias for the current situation, by referring to the charge table shown in FIG. 9. In this embodiment, a reference value for the development bias is set in advance, and the ideal bias is calculated by adding a charge correction value corresponding to the charge frequency to the reference value. The ideal bias may be calculated at any time; for example, it is calculated in accordance with image quality adjustment and stored in the storage unit 92.

[0063] For example, if the reference value is set to -300V and the charge correction value when the charge number is "1" is set to -30V, the ideal bias will be -330V. In other words, in a situation where the charge amount is high, the ideal bias will be corrected to lower the charge amount. Also, if the reference value is set to -300V and the charge correction value when the charge number is "6" is set to 65V, the ideal bias will be -235V, and the ideal bias will be corrected to increase the charge amount.

[0064] In the charge table shown in FIG. 9, similarly to the environment table shown in FIG. 8, the running time of the developing roller 2a may be divided into smaller ranges and the number of values ​​used for the charge frequency may be increased.

[0065] In image forming apparatus 100, the toner supply conditions are corrected based on the result of image quality adjustment. The relationship between the result of image quality adjustment and the correction of the supply conditions will now be described with reference to FIG.

[0066] FIG. 10 is an explanatory table showing an example of the correction results for the replenishment conditions.

[0067] 10 shows an example of the correction results for the replenishment conditions, and shows a table summarizing the correction results for each of the four image stations. Note that, for the sake of explanation, the four image stations Pa, Pb, Pc, and Pd will be abbreviated below using the corresponding colors and may be referred to as black, cyan, magenta, and yellow.

[0068] In the table shown in FIG. 10, the following items are provided for black, cyan, magenta, and yellow: "previous correction ratio," "adjusted bias," "bias difference," "reflection rate," and "correction ratio." In this embodiment, correction of the replenishment conditions is performed in conjunction with image quality adjustment, and the values ​​of each item are determined. Image quality adjustment is performed at preset intervals, and the storage unit 92 stores the values ​​of each item (especially the correction ratio). Hereinafter, image quality adjustment may be distinguished by referring to it as the previous image quality adjustment, the current image quality adjustment, and the next image quality adjustment in order to clarify when the image quality adjustment was performed.

[0069] The "previous correction ratio" corresponds to the correction ratio (Hz) calculated during the previous image quality adjustment, and the correction ratio is calculated using Formula A, which will be described later. The "adjusted bias" corresponds to the adjusted bias calculated during the current image quality adjustment. The "bias difference" corresponds to the bias difference, which is the difference between the adjusted bias calculated during the current image quality adjustment and the ideal bias; specifically, it is the value obtained by subtracting the adjusted bias from the ideal bias. The "reflection rate" corresponds to the reflection rate (α) determined by referring to the correction table shown in FIG. 11, which will be described later, and the reflection rate is a value according to the bias difference. The "correction rate" corresponds to the correction rate (H) calculated during the current image quality adjustment using Formula A, "H = Hz × α / 100." In Formula A, H represents the correction rate, Hz represents the previous correction ratio, and α represents the reflection rate.

[0070] FIG. 11 is an explanatory diagram showing an example of the correction table.

[0071] The correction table shown in FIG. 11 is stored in the storage unit 92 and is a table relating to bias difference, reflection rate, and number of adjustments. In the correction table, multiple non-overlapping ranges are set for the bias difference, and a reflection rate and number of adjustments corresponding to each range are set. In the correction table, when the bias difference is "0 (-20 to 20)," the reflection rate is set to "100," and as the absolute value of the bias difference increases, the reflection rate is set to increase or decrease from "100." In this way, by providing a correction table and setting the reflection rate in advance, the correction process can be simplified.

[0072] In this embodiment, the interval for performing image quality adjustment is determined by the number of sheets on which image formation has been performed, and image quality adjustment is performed after image formation has been performed on the number of sheets set as the number of sheets for adjustment. In the correction table, the number of sheets for adjustment is set to be large when the absolute value of the bias difference is small, and the number of sheets for adjustment is set to be small as the absolute value of the bias difference becomes large.

[0073] In image forming apparatus 100, the toner replenishment conditions are corrected based on the results of image quality adjustment, and the bias difference is affected by the toner concentration in developing unit 2. In other words, a large absolute value of the bias difference indicates that the toner concentration in developing unit 2 deviates from the desired value. Therefore, by changing the interval between image quality adjustments, even if the deviation in the toner replenishment amount is larger than expected, the toner replenishment amount can be reviewed before it changes further, and the amount of toner in developing unit 2 can be maintained at an appropriate level.

[0074] Furthermore, if the number of sheets to be adjusted differs among the four image stations, it is preferable to select the smallest number of sheets to be adjusted, and the control unit 91 changes the interval until the next image quality adjustment based on the bias difference with the largest value. In other words, by performing image quality adjustment collectively according to the image station with the largest deviation, it is possible to align the timing of image quality adjustment and appropriately correct the supply amount.

[0075] FIG. 11 shows a correction table in which the bias difference, the reflection rate, and the number of sheets on which adjustments are performed are associated, but this is not limited to this, and multiple correction tables may be provided in which the bias difference is associated with the reflection rate and the number of sheets on which adjustments are performed separately.

[0076] In the image forming apparatus, the correction ratio determined by the above-described method is applied as the correction value until the next image quality adjustment, and the toner replenishment conditions are corrected. For example, the replenishment time determined based on FIG. 7 can be increased or decreased based on the correction ratio. In this way, by comparing the adjusted bias obtained in the image quality adjustment with the ideal bias, it is possible to determine whether the correction value set previously was appropriate, and to grasp the toner replenishment status to the developing unit 2. Then, by reflecting the grasped results, toner can be replenished at the appropriate timing without providing a sensor to detect the amount of toner in the developing unit 2.

[0077] Referring to the correction results shown in Figure 10, for example, for cyan, the "previous correction ratio" is "103" and the "bias difference" is "50", which means that the adjusted bias is higher than the ideal bias, and therefore it is predicted that the amount of toner supplied was less.Then, the "correction ratio" is "105", which means that the amount of toner supplied will be corrected to be more than the previous time.

[0078] (Second embodiment) Next, an image forming apparatus according to a second embodiment of the present invention will be described with reference to the drawings. Note that the configuration of the image forming apparatus according to the second embodiment is substantially the same as that of the first embodiment shown in Figures 1 to 11, so the same reference numerals are used and the description and drawings will be omitted.

[0079] FIG. 12 is an explanatory table showing an example of the correction results for the replenishment conditions in the second embodiment.

[0080] The second embodiment differs from the first embodiment in that a developing power source 2h supplies a common bias common to multiple developing units 2 as a developing bias. In other words, one developing power source 2h is commonly connected to four developing units 2 in four image stations. The control unit 91 then corrects the replenishment conditions based on the difference between the common bias and the adjusted bias. Next, the correction method in this embodiment will be described with reference to an example of the correction result shown in FIG. 12.

[0081] FIG. 12 shows an example of the correction results for the replenishment conditions in the image forming apparatus according to the second embodiment of the present invention, and shows a table summarizing the correction results for each of the four image stations.

[0082] In the table shown in Fig. 12, in addition to the items "previous correction ratio," "adjusted bias," "bias difference," "reflection rate," and "correction ratio" for each of black, cyan, magenta, and yellow, similar to the table shown in Fig. 10, the items "difference value," "reflection coefficient," and "difference correction value" are added. Note that in the table shown in Fig. 12, the items "previous correction ratio," "adjusted bias," "bias difference," and "reflection rate" are the same as those in the table shown in Fig. 10, and therefore their explanation will be omitted.

[0083] The "difference value" corresponds to the difference between the common bias and the ideal bias, and is specifically the value obtained by subtracting the adjusted bias from the common bias. In this embodiment, the common bias is selected from the adjusted biases to be closest to the photosensitive element bias Vk. Specifically, in the example shown in FIG. 12, -400 V is selected for magenta.

[0084] The "reflection coefficient" corresponds to a reflection coefficient (β) determined by referring to a coefficient table shown in Fig. 12 (described later), and the reflection coefficient is a value corresponding to the difference value. The "difference correction value" corresponds to a difference correction value (γ) calculated by calculation formula B, "γ = (α - 100) × β / 100 + 100." In the above-mentioned calculation formula B, β represents the reflection coefficient, and γ represents the difference correction value.

[0085] In this embodiment, the correction ratio is calculated by formula C, "H=Hz×γ / 100." In formula C, the reflection rate (α) in formula A is replaced with a difference correction value (γ), and the difference correction value is calculated by correcting the reflection rate with a reflection coefficient.

[0086] FIG. 13 is an explanatory diagram showing an example of the coefficient table.

[0087] The coefficient table shown in Fig. 13 is stored in the storage unit 92 and is a table relating to difference values ​​and reflection coefficients. In the coefficient table, a plurality of non-overlapping ranges are set for the difference values, and a reflection coefficient corresponding to each range is set. In the reflection table, different columns (values) are set to be referenced depending on whether the bias difference is a plus (positive) value or a minus (negative) value.

[0088] For example, if the difference value is "50 (40 to 60)," the reflection coefficient is set to "50" when the bias difference is negative, and the reflection coefficient is set to "100" when the bias difference is positive. In other words, when the common bias is higher than the adjusted bias, the image is developed darker than when the adjusted bias value is applied to the developing bias, so there is no need to increase the amount of toner replenishment and it can be adjusted to decrease it. Also, when the common bias is lower than the adjusted bias, the image is developed lighter than when the adjusted bias value is applied to the developing bias, so there is no need to decrease the amount of toner replenishment and it can be adjusted to increase it. In this way, even when the developing power supply 2h is shared, an appropriate correction value can be obtained by taking into account the difference from the common bias.

[0089] Referring to the correction results shown in FIG. 12, for example, the "correction ratio" for cyan is "104", which is a correction value that is smaller than the correction results shown in FIG.

[0090] Furthermore, the correction of the replenishment conditions may reflect not only the correction ratio described above but also the detection results of the environmental sensor. Specifically, the correction is performed by referring to the environment table and the charge table described above to determine the environment frequency and the charge frequency. Then, correction coefficients for the environment frequency and the charge frequency are set in advance, and the replenishment time can be increased or decreased based on these coefficients. In this way, by taking into account the influence of the environment in which the image forming apparatus 100 is installed, it is possible to correct to a more appropriate correction value.

[0091] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included. [Explanation of symbols]

[0092] 2 Development section 2a Developing roller 2h development power supply 3 Photosensitive drum 12 Exposure section 71 Intermediate transfer belt 74 Image Sensor 80 Environmental Sensors 91 Control Unit 92 Memory section 100 Image forming device 140 cartridges 141 Supply Department

Claims

1. an image carrier whose surface is charged to a predetermined potential; a developing unit that forms a toner image on the image carrier; a development power source that supplies a development bias to the development unit; an image sensor that detects the density of the toner image formed by the developing unit; an environmental sensor for detecting temperature and humidity; a supply unit that supplies toner to the developing unit; an image forming apparatus including a control unit that executes image quality adjustment by changing the developing bias based on a detection result of the image sensor, The control unit a storage unit that stores a supply condition that sets the timing for the supply unit to supply toner, a correction value for the supply condition that is set in image quality adjustment, and an ideal bias that is set based on the detection result of the environment sensor; Correcting the correction value until the next image quality adjustment based on a bias difference, which is the difference between the adjusted bias calculated during the image quality adjustment and the ideal bias, and a previous correction value set in the previous image quality adjustment. An image forming apparatus comprising:

2. 2. The image forming apparatus according to claim 1, the storage unit stores a correction table in which a reflection rate according to the bias difference is set, The control unit corrects the correction value by referring to a reflection rate of the correction table when adjusting the image quality. An image forming apparatus comprising:

3. 2. The image forming apparatus according to claim 1, The control unit changes the interval until the next image quality adjustment based on the bias difference. An image forming apparatus comprising:

4. 2. The image forming apparatus according to claim 1, the image carrier includes a plurality of photosensitive drums and an intermediate transfer belt onto which the toner images on the plurality of photosensitive drums are transferred; A plurality of the developing units and the supply units are provided corresponding to the plurality of photosensitive drums. An image forming apparatus comprising:

5. 5. The image forming apparatus according to claim 4, In the image quality adjustment, the bias difference is calculated for each of the plurality of developing units, The control unit changes the interval until the next image quality adjustment based on the bias difference having the largest value. An image forming apparatus comprising:

6. 5. The image forming apparatus according to claim 4, the developing power supply is configured to supply a common bias common to the plurality of developing units as the developing bias, The control unit corrects the correction value based on a difference between the common bias and the adjusted bias. An image forming apparatus comprising:

7. 2. The image forming apparatus according to claim 1, The control unit corrects the correction value based on a detection result of the environment sensor. An image forming apparatus comprising:

Images