JP2004177928A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably form a toner image having good image quality by performing processing for optimizing a density control factor in appropriate timing. <P>SOLUTION: Density control processing is performed when a parameter showing the state of toner in a developing device reaches predetermined threshold. The threshold (shown by a dashed line) which triggers performance of the density control processing is set on each of two parameters, namely, a dot count value (an integrated value of the number of dots formed using an exposing beam) which is indicative of the amount of consumption of the toner and a developing roller rotating time which is indicative of the degree of toner fatigue. The density control processing is performed at the timing ((1)-(6)) that the path (d) of dots shown by the combination of the parameters intersects each dashed line. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
According to the present invention, an electrostatic latent image is formed on an image carrier, and a developing bias is applied to a developing unit containing toner to apply the toner to the surface of the image carrier, thereby revealing the electrostatic latent image. The present invention relates to an image forming apparatus and an image forming method for forming a toner image by forming an image.
[0002]
[Prior art]
In image forming apparatuses such as copiers, printers, and facsimile machines that apply electrophotographic technology, the image density of the toner image varies due to individual differences, changes over time, and changes in the surrounding environment such as temperature and humidity. There is. In view of this, various techniques for stabilizing the image density have been proposed. As such a technique, for example, a test small image (patch image) is formed on an image carrier, and a density control factor that affects the image density is optimized based on the density of the patch image. There is. This technique forms a predetermined toner image on the image carrier while changing the density control factor in various ways, and also transfers the toner image on the image carrier or the toner image to another transfer member such as an intermediate transfer medium. The image density is detected using the toner image transferred to the patch image as the patch image, and the density control factor is adjusted so that the patch image density matches the preset target density, thereby obtaining a desired image density. It is what.
[0003]
In general, such adjustment of the density control factor is executed at regular time intervals or every time the number of formed images reaches a certain number because of easy management. On the other hand, in order to perform more appropriate density control in view of the actual change in apparatus characteristics over time, the interval at which density control processing (density control factor optimization processing) is executed is varied according to the number of images formed. (For example, refer to Patent Document 1). That is, in this image forming apparatus, when the number of image forming sheets is small and the developing device is new (initial stage), and when the number of image forming sheets is large and the developing unit seems to be deteriorating (performance deterioration period), the change in image density Therefore, the density control process is executed at a relatively short interval. On the other hand, the interval of the density control process is lengthened during a period when the number of formed images is medium and the image density is stable (stable period). This makes it possible to form an image with a stable image density, and to reduce the time and toner loss associated with the density control process.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-186769 (FIG. 3)
[0005]
[Problems to be solved by the invention]
As pointed out in the above publication, the degree of change in image density with time is not uniform, and the degree of change in density varies depending on the operating status of the apparatus. Therefore, there may be a case where a stable image density cannot be obtained only by adjusting the density control factor every certain time or every certain number of sheets. That is, the image density may change greatly before the readjustment of the density control factor, or the density of the image formed before and after the density control factor may be greatly changed.
[0006]
The image density gradually changes as the number of formed images increases, but the degree of the change affects not only the number of formed images but also the contents thereof. For example, the number of images formed is the same between an image that has a relatively high density due to heavy painting or a large number of characters, and a relatively low density image that is composed of fine lines and a small number of characters. However, the amount of toner consumed is greatly different, and the degree of change in image density with time varies with this difference.
[0007]
Therefore, as described in the above publication, it is not sufficient to change the execution timing of the density control process according to the number of image formations. In order to form a stable image with little density change, the image density Therefore, it is required to execute the optimization process of the concentration control factor at a more appropriate timing in accordance with the change with time.
[0008]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an image forming apparatus and an image forming method capable of stably forming a toner image with good image quality by executing optimization processing of a density control factor at an appropriate timing. The purpose is to provide.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention has an image carrier configured to carry an electrostatic latent image, and contains toner therein, and the toner is placed on the surface of the image carrier. A developing device that transports the toner toward the image carrier, and a predetermined developing bias applied to the developing device to move the toner to the image carrier, whereby the electrostatic latent image formed on the surface of the image carrier is visualized with toner. Image forming means for forming a toner image and storage means for storing toner status information relating to the status of the toner contained in the developing device, and updating the toner status information according to the operating status of the apparatus A density control factor that stores a toner image as a patch image when the toner status information reaches a predetermined control start condition and affects the image density based on the toner density of the patch image It is characterized by controlling the image density by optimizing.
[0010]
In the invention configured as described above, the density control factor is optimized based on the information indicating the state of the toner in the developing device. That is, the state of the toner in the developing device that changes with time can be grasped by the toner state information updated as needed. Then, when the toner status information reaches a predetermined condition, that is, the control start condition is satisfied, optimization of the density control factor is executed, so that an appropriate timing according to the status of the toner in the developing device can be obtained. To adjust the concentration control factor. As a result, this image forming apparatus can stably form an image with good image quality.
[0011]
Note that the density control factor optimization process is executed as frequently as possible, so that the change in the image density can be further suppressed. However, if the frequency is increased too much, the waiting time of the user increases for the processing, or the amount of toner consumed without contributing to image formation increases and the running cost increases. Produce. Therefore, it is desirable that the density control factor optimization process be executed at a timing that satisfies the two requirements that the above-described problems do not occur and the change in the image density is not so noticeable.
[0012]
Therefore, this control start condition can be determined as follows, for example. That is, the change in the image density with respect to the change in the toner state information is obtained in advance by experiment or the like, and the toner state information when the change in the image density reaches the upper limit or the lower limit of the allowable range may be used as the control start condition. By doing this, optimization of the density control factor is performed before the fluctuation of the image density exceeds the allowable range, and the time and time are controlled while keeping the change in the image density within the predetermined range. It is possible to reduce toner loss.
[0013]
Further, in the image forming apparatus that optimizes the density control factor by setting the density control factor so that the toner density of the patch image substantially matches a predetermined density target value, according to the toner state information The target density value of the patch image may be changed and set. In the invention configured as described above, the density target value of the patch image is changed and set in accordance with the toner state information in view of the fact that the density of the image formed by the change in the toner state also varies. That is, since the density target value corresponding to the toner state at that time is set as needed, an image with a stable density can be formed regardless of the change in the toner state.
[0014]
Then, for example, the density control factor is optimized when the density target value is changed, and the density control factor is set so that the toner density of the patch image substantially matches the density target value after the change. If it is set, that is, if the control start condition is when the density target value needs to be changed based on the toner state information, the timing at which the density target value is changed and the density control factor needs to be readjusted Thus, the optimization of the concentration control factor can be reliably executed. Further, if the density target value is not changed or the amount of change is equal to or less than a predetermined value, if the optimization of the density control factor is not executed, the number of executions can be suppressed to the minimum necessary, and toner and Time loss can be reduced.
[0015]
Further, the toner state gradually changes from the new state to the end of its life, but the change in image density with respect to the state change is not necessarily uniform. Accordingly, a plurality of the control start conditions are set for the toner state information, and the density control is performed more frequently when the change rate of the image density with respect to the change of the toner state information is large than when the change rate is small. The plurality of control start conditions may be set so that factor optimization is performed.
[0016]
In this way, when the rate of change of the image density is large, optimization of the density control factor can be executed with a relatively high frequency to effectively suppress the change of the image density, while the change of the image density is small. In the state, the frequency can be lowered to suppress the toner loss.
[0017]
In the case where the toner state is further provided with exposure means for forming an electrostatic latent image on the surface of the image carrier by exposing the surface of the image carrier charged to a predetermined surface potential with a light beam. As information, the number of dots formed on the surface of the image carrier by exposure to the light beam and the operating time of the developing device are used, and at least one of the number of dots and the operating time is set to a predetermined threshold value. You may make it make the said control start condition reach | attained.
[0018]
The amount of toner that moves from the developing device to the image carrier to form a toner image increases as the number of dots formed on the image carrier as an electrostatic latent image increases. Therefore, an approximate toner consumption can be estimated from the number of dots. In addition, the characteristics of the toner remaining in the developing unit gradually change with use, but the degree of the characteristic change can be estimated from the length of the operating time of the developing unit. Therefore, it is possible to estimate the remaining amount of toner in the developing device and its characteristics from these pieces of information. Further, these pieces of information have a property of being accumulated and increased as the apparatus is used. Therefore, by setting a threshold value for these information in advance and optimizing the concentration control factor when the information reaches the threshold value as it accumulates as it is used, The execution timing is in accordance with the state of toner in the developing device.
[0019]
Here, in the apparatus in which the developing device includes a toner carrier that conveys the toner to a position facing the image carrier by rotating in a predetermined direction while carrying the toner on the surface thereof, The rotation time of the toner carrier can be set as the operation time of the developing device. The change in the toner characteristics with the lapse of time with the operation of the developing device is mainly caused by repeated adhesion and separation of the toner on the toner carrier. Therefore, by representing the operation time of the developing device by the rotation time of the toner carrier, it is possible to obtain toner state information that more accurately reflects the toner state.
[0020]
Further, target value correspondence information in which a density target value is associated with each of a plurality of toner status information is set in advance, and when the toner status information corresponding to the operation status of the apparatus reaches a predetermined threshold value, The density target value corresponding to the toner state information may be changed and set. By the way, when the density target value does not change at all or when the fluctuation value is small, the density fluctuation is small. Therefore, even if the optimization of the density control factor (density control processing) at these timings is omitted, the fluctuation of the image density is almost negligible. Also, by omitting this, the toner consumption can be suppressed, and it is possible to extend the life of the developing device and reduce the waiting time of the user. Therefore, the control starts that the difference between the density target value corresponding to the toner state information when the threshold value is reached and the density target value before reaching the threshold value is equal to or greater than a predetermined fluctuation value. It can be a condition. Even if the toner status information corresponding to the operating status of the apparatus reaches a predetermined threshold value, the density target value corresponding to the toner status information when the threshold value is reached and the threshold value When the difference from the target concentration value before reaching it is less than the predetermined fluctuation value, the concentration control factor may not be optimized. As the variation value, for example, the optical density can be set to 0.03 or less.
[0021]
Further, in an image forming apparatus that forms a color image using a plurality of different color toners and forms a single color image using a black toner of the plurality of colors, the black color corresponds to the target value The information and the target value correspondence information other than the black color may be different from each other. This is due to the fact that the density fluctuation accompanying the fluctuation of the black toner state is different from the density fluctuation accompanying the fluctuation of the toner state of the other colors. Thus, by setting the target value correspondence information for each color, it is possible to change and set to a more appropriate density target value. As a result, the concentration control factor can be optimized at a more appropriate timing.
[0022]
In addition, in an image forming apparatus that forms a color image using a plurality of different colors of toner, the target value correspondence information is set in advance using the most frequently consumed color among the plurality of colors as a reference color. The target value correspondence information of color may be configured to match the target value correspondence information of the reference color. In this way, by setting the target value correspondence information based on the color with the most selective consumption, the density control factor can be optimized at a more appropriate timing.
[0023]
In such an image forming apparatus, the control start condition may be changed and set according to the initial state of the toner contained in the developing device. The characteristics of the toner contained in the developing unit are not necessarily the same among the individual developing units, and may vary slightly from one developing unit to another due to manufacturing variations, for example. The degree of change in image density is also different. Therefore, for example, when using a developing device containing toner that tends to have a large density change, the density control factor is optimized at a relatively early timing, while the toner that does not easily change the density. When the toner is used, the density control factor can be optimized at a timing according to the initial state of the toner so that the execution frequency is reduced.
[0024]
The “initial state” here refers to various characteristics of the toner at the time when the developing device is filled with toner, and in the newly manufactured developing device, it represents the characteristics of the toner filled at the time of manufacture. In addition, when the used developer is refilled with toner and used for reuse, it represents the characteristics of the refilled toner. Various characteristics such as the initial state of the toner, that is, its particle size distribution and chargeability, can be obtained by actual measurement at the time of toner production.
[0025]
In the image forming apparatus, the developing unit may be configured to be detachable from the apparatus main body, and may include a storage element that functions as at least a part of the storage unit. In this way, management of information relating to the internal toner state is facilitated, and it is possible to manage the consumption status of the developing device and facilitate maintenance during replacement.
[0026]
In the image forming method according to the present invention, an electrostatic latent image is formed on the surface of the image carrier, and a predetermined developing bias is applied to a developing unit that contains toner to move the toner to the image carrier. An image forming method for forming a toner image by visualizing the electrostatic latent image with toner, and in order to achieve the above object, the toner accommodated in the developing device according to the operation status of the apparatus In addition, the toner status information relating to the current status is updated, and when the toner status information reaches a predetermined control start condition, a toner image is formed as a patch image, and the image density is affected based on the toner density of the patch image. The image density is controlled by optimizing the density control factor to be given.
[0027]
In the invention configured as described above, the execution timing of the density control factor optimization processing is determined based on the state of the toner in the developing device, as in the above-described image forming apparatus. Therefore, it is possible to optimize the density control factor at an appropriate timing according to the state of the toner, and by forming an image under the conditions optimized in this way, a toner image with good image quality can be stably obtained. It is possible to form.
[0028]
Further, in this image forming method, when an electrostatic latent image is formed on the surface of the image carrier by exposing the surface of the image carrier charged to a predetermined surface potential with a light beam, the above apparatus is used. Similarly to the toner state information, the number of dots formed on the surface of the image carrier by the exposure of the light beam and the operation time of the developing unit are used, and at least one of the number of dots and the operation time is used. The control start condition may be that has reached a predetermined threshold value. In this way, the density control factor can be optimized at an appropriate timing according to the remaining amount of toner in the developing device and its characteristics.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. This image forming apparatus forms a full color image by superposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), or uses only black (K) toner. This is an apparatus for forming a monochrome image. In this image forming apparatus, when an image signal is given to the main controller 11 from an external device such as a host computer in response to an image formation request from the user, the “image forming means” of the present invention is in response to an instruction from the main controller 11. The engine controller 10 functioning as “controls each part of the engine unit EG to form an image corresponding to the image signal on the sheet S.
[0030]
In the engine unit EG, the photosensitive member 2 is provided so as to be rotatable in an arrow direction D1 in FIG. Further, a charging unit 3, a rotary developing unit 4 and a cleaning unit 5 are arranged around the photosensitive member 2 along the rotation direction D1. The charging unit 3 is applied with a charging bias from the charging controller 103 and uniformly charges the outer peripheral surface of the photoreceptor 2 to a predetermined surface potential.
[0031]
Then, the light beam L is irradiated from the exposure unit 6 toward the outer peripheral surface of the photosensitive member 2 charged by the charging unit 3. The exposure unit 6 functions as an “exposure unit” of the present invention. The exposure unit 6 exposes the light beam L onto the photoconductor 2 in accordance with a control command given from the exposure control unit 102, and generates a static image corresponding to the image signal. An electrostatic latent image is formed. For example, when an image signal is given from an external device such as a host computer to the CPU 111 of the main controller 11 via the interface 112, the CPU 101 of the engine controller 10 sends a control signal corresponding to the image signal to the exposure control unit 102 at a predetermined timing. In response to this, a light beam L is irradiated onto the photosensitive member 2 from the exposure unit 6, and an electrostatic latent image corresponding to the image signal is formed on the photosensitive member 2. When forming a patch image, which will be described later, as necessary, a control signal corresponding to a predetermined pattern of patch image signals is given from the CPU 101 to the exposure control unit 102, and the electrostatic image corresponding to the pattern is output. A latent image is formed on the photoreceptor 2. Thus, in this embodiment, the photoreceptor 2 functions as the “image carrier” of the present invention.
[0032]
The electrostatic latent image thus formed is developed with toner by the developing unit 4. In other words, in this embodiment, the developing unit 4 is configured to be detachably attached to the support frame 40 that is rotatably provided about the shaft center, a rotation drive unit that is not shown, and the support frame 40, and each color toner. Are provided with a yellow developing device 4Y, a cyan developing device 4C, a magenta developing device 4M, and a black developing device 4K. The developing unit 4 is controlled by the developing device controller 104 as shown in FIG. Based on a control command from the developing device controller 104, the developing unit 4 is driven to rotate, and the developing devices 4Y, 4C, 4M, and 4K are selectively opposed to the photoreceptor 2 at a predetermined developing position. The toner of the selected color is applied to the surface of the photoreceptor 2. As a result, the electrostatic latent image on the photoreceptor 2 is visualized with the selected toner color. FIG. 1 shows a state in which the developing device 4Y for yellow is positioned at the developing position.
[0033]
These developing units 4Y, 4C, 4M, and 4K all have the same structure. Therefore, the configuration of the developing device 4K will be described in more detail with reference to FIG. 3, but the structures and functions of the other developing devices 4Y, 4C, and 4M are the same.
[0034]
FIG. 3 is a cross-sectional view showing a developing device of the image forming apparatus. In the developing device 4K, a supply roller 43 and a developing roller 44 are axially attached to a housing 41 that accommodates toner T therein, and when the developing device 4K is positioned at the development position described above, “ A developing roller 44 functioning as a “toner carrying member” is positioned in contact with the photosensitive member 2 or with a predetermined gap therebetween, and a rotation driving unit (not shown) provided on the main body side. ) And rotate in a predetermined direction. The developing roller 44 is formed in a cylindrical shape from a metal or alloy such as copper, stainless steel, or aluminum so that a developing bias described later is applied. Then, the two rollers 43 and 44 rotate while being in contact with each other, whereby the black toner is rubbed against the surface of the developing roller 44 and a toner layer having a predetermined thickness is formed on the surface of the developing roller 44.
[0035]
In the developing device 4K, a regulating blade 45 for regulating the thickness of the toner layer formed on the surface of the developing roller 44 to a predetermined thickness is disposed. The regulation blade 45 is composed of a plate-like member 451 such as stainless steel or phosphor bronze and an elastic member 452 such as rubber or resin member attached to the tip of the plate-like member 451. The rear end portion of the plate member 451 is fixed to the housing 41, and the elastic member 452 attached to the front end portion of the plate member 451 is the rear end portion of the plate member 451 in the rotation direction D3 of the developing roller 44. It arrange | positions so that it may be located in the upstream rather than. Then, the elastic member 452 elastically contacts the surface of the developing roller 44, and the toner layer formed on the surface of the developing roller 44 is finally restricted to a predetermined thickness.
[0036]
Each toner particle constituting the toner layer on the surface of the developing roller 44 is charged by being rubbed with the supply roller 43 and the regulating blade 45, and here, the toner will be negatively charged. Toner that is positively charged by appropriately changing the potential of each part of the apparatus can also be used.
[0037]
The toner layer thus formed on the surface of the developing roller 44 is sequentially conveyed to a position facing the photoreceptor 2 on which the electrostatic latent image is formed by the rotation of the developing roller 44. When the developing bias from the developing device controller 104 is applied to the developing roller 44, the toner carried on the developing roller 44 partially adheres to each surface portion of the photoreceptor 2 according to the surface potential. Thus, the electrostatic latent image on the photoreceptor 2 is visualized as a toner image of the toner color. Further, the toner that does not move to the photosensitive member 2 and remains on the developing roller 44 is further conveyed downstream, and is scraped off by the supply roller 43.
[0038]
As the developing bias applied to the developing roller 44, a DC voltage or a voltage obtained by superimposing an AC voltage on the DC voltage can be used. In particular, the photosensitive member 2 and the developing roller 44 are separated from each other, and toner is supplied between them. In a non-contact development type image forming apparatus that develops toner by flying, in order to efficiently fly toner, a voltage waveform in which an AC voltage such as a sine wave, a triangular wave, or a rectangular wave is superimposed on a DC voltage is used. Is preferred. The magnitude of the DC voltage and the amplitude, frequency, duty ratio, etc. of the AC voltage are arbitrary. Hereinafter, in the present specification, the DC will be applied regardless of whether or not the developing bias has an AC component. The component (average value) is referred to as a direct current developing bias Vavg.
[0039]
Further, as shown in FIG. 2, each of the developing units 4Y, 4C, 4M, and 4K is provided with memories 91 to 94 for storing data relating to the manufacturing lots and usage histories of the developing units, characteristics of the built-in toner, and the like. Yes. These memories 91 to 94 function as “storage means” of the present invention. Further, connectors 49Y, 49C, 49M, and 49K are provided in the developing devices 4Y, 4C, 4M, and 4K, respectively. If necessary, these are selectively connected to a connector 108 provided on the main body side, and data is transmitted and received between the CPU 101 and each of the memories 91 to 94 via the interface 105 to relate to the developing device. It manages various information such as consumables management. In this embodiment, the main body side connector 108 and each developing device side connector 49K and the like are mechanically fitted to each other to exchange data, but for example using electromagnetic means such as wireless communication. Data transmission / reception may be performed without contact. The memories 91 to 94 for storing data unique to each of the developing devices 4Y, 4C, 4M, and 4K are nonvolatile memories that can store the data even when the power is off or the developing device is removed from the main body. As such a nonvolatile memory, for example, a flash memory, a ferroelectric memory, an EEPROM, or the like can be used.
[0040]
Returning to FIG. 1, the description of the device configuration will be continued. The toner image developed by the developing unit 4 as described above is primarily transferred onto the intermediate transfer belt 71 of the transfer unit 7 in the primary transfer region TR1. The transfer unit 7 includes an intermediate transfer belt 71 stretched between a plurality of rollers 72 to 75, and a drive unit (not shown) that rotates the intermediate transfer belt 71 in a predetermined rotation direction D2 by rotationally driving the roller 73. It has. Further, a secondary transfer roller 78 is provided at a position facing the roller 73 with the intermediate transfer belt 71 interposed therebetween, and is configured to be able to contact and separate with respect to the surface of the belt 71 by an electromagnetic clutch (not shown). Yes. When a color image is transferred to the sheet S, the color toner images formed on the photoreceptor 2 are superimposed on the intermediate transfer belt 71 to form a color image, and the color image is taken out from the cassette 8 to be intermediate. The color image is secondarily transferred onto the sheet S conveyed to the secondary transfer region TR2 between the transfer belt 71 and the secondary transfer roller 78. Further, the sheet S on which the color image is formed in this way is conveyed via the fixing unit 9 to a discharge tray portion provided on the upper surface portion of the apparatus main body.
[0041]
Note that the surface potential of the photosensitive member 2 after the toner image is primarily transferred to the intermediate transfer belt 71 is reset by a neutralizing unit (not shown), and the toner remaining on the surface is removed by the cleaning unit 5. Then, the charging unit 3 receives the next charging.
[0042]
Further, a cleaner 76, a density sensor 60, and a vertical synchronization sensor 77 are disposed in the vicinity of the roller 75. Among these, the cleaner 76 can be moved toward and away from the roller 75 by an electromagnetic clutch (not shown). Then, the blade of the cleaner 76 abuts on the surface of the intermediate transfer belt 71 that is stretched over the roller 75 while moving to the roller 75 side, and the toner remaining on the outer peripheral surface of the intermediate transfer belt 71 after the secondary transfer. Remove. The vertical synchronization sensor 77 is a sensor for detecting the reference position of the intermediate transfer belt 71 and is used to obtain a synchronization signal output in association with the rotational drive of the intermediate transfer belt 71, that is, a vertical synchronization signal Vsync. Functions as a vertical sync sensor. In this apparatus, the operation of each part of the apparatus is controlled based on the vertical synchronization signal Vsync in order to align the operation timing of each part and accurately superimpose the toner images formed in the respective colors. Further, the density sensor 60 is provided to face the surface of the intermediate transfer belt 71, and measures the optical density of the patch image formed on the outer peripheral surface of the intermediate transfer belt 71 as described later.
[0043]
In FIG. 2, reference numeral 113 denotes an image memory provided in the main controller 11 for storing an image given from an external device such as a host computer via the interface 112, and reference numeral 106 denotes an operation executed by the CPU 101. A ROM for storing control data for controlling the program, the engine unit EG, and the like, and a reference numeral 107 are a RAM for temporarily storing calculation results in the CPU 101 and other data.
[0044]
In the image forming apparatus configured as described above, density control processing is executed at a predetermined timing in order to form a stable image while suppressing a change in image density with time. Specifically, as a density control factor that affects the image density, DC development bias Vavg applied to the developing roller 44 and energy per unit area of the exposure beam L (hereinafter simply referred to as “exposure energy”) E are used. These density control factors are optimized by forming a patch image of a predetermined pattern while changing these variously, and obtaining the DC development bias Vavg and exposure energy E so that the image density substantially matches the density target value. It has become. This concentration control process, that is, a process for optimizing the concentration control factor will be described in detail below.
[0045]
In this image forming apparatus, the timing is as follows:
(a) Immediately after the device is turned on;
(b) When a long time has passed since the previous concentration control process;
(c) The number of dots formed on the photosensitive member 2 by the exposure beam L and the rotation time of the developing roller 44 are counted for each developing device, and when these count values reach a predetermined threshold value;
(d) When the developer is replaced;
Execute density control processing.
[0046]
Here, when the developing device is replaced, the density control process may be executed immediately. However, considering the following points, in addition to the developer replacement (d), the density control process may be executed only when a predetermined condition is satisfied. That is, when a developing device different from that previously taken out is mounted, it is necessary to perform density control processing in order to suppress fluctuations in image density due to variations in characteristics of the developing device. Therefore, it is mounted on the basis of various information stored in the memories 91 to 94 attached to the developing devices 4Y, 4C, 4M, and 4K, for example, information on manufacturing lots and usage history of the developing devices, characteristics of the built-in toner, and the like. It is determined whether or not the developing device is the same as that previously installed. If they are different, the density control process can be executed. On the other hand, when the attached developing device is originally attached to the apparatus main body, the density control process is not necessarily required. In particular, when a developer once taken out by the user is immediately remounted, it is not necessary to perform density control processing, and toner and processing time are wasted. Is preferred.
[0047]
However, if the developer has been removed for a long time, such as when the density adjustment process has been performed for a long time, the ambient environment of the device, such as temperature and humidity, will change significantly. In this case, it is preferable to perform the density control process even if the installed developing device is the same as the previously-developed developing device. Therefore, based on these, in the present embodiment, the following timing:
(d-1) When the developing device is replaced and the developing device is different before and after removal / installation;
(d-2) Even if the developing device is the same before and after removal / mounting, when a predetermined time has elapsed since the previous density control processing;
The density control process is executed.
[0048]
(e) When a new photoconductor 2 is mounted;
Here, when the photoconductor 2 is replaced, it is determined whether or not the photoconductor is the same before and after replacement as in the case of the developing device, and the execution timing of the density control processing is determined according to the difference. You may make it set.
[0049]
As described above, in the image forming apparatus of FIG. 1, the density control processing is executed at various timings. In this specification, the condition (c) will be described in detail below.
[0050]
FIG. 4 is a diagram exemplifying a change in image density with respect to the number of formed images, and FIG. 5 is a diagram showing a setting principle of timing for executing density control processing. FIG. 6 is a diagram showing the relationship between the dot count value and the developing roller rotation time, and FIG. 7 is a diagram showing the timing for executing the density control process.
[0051]
In this type of image forming apparatus, when a large number of images are formed with a constant density control factor, the image density gradually changes as the number of image forming sheets increases. One of the causes of such density change is considered as follows. In other words, it is desirable that the toner contained in the developing device has uniform characteristics such as particle size and chargeability, but in practice there are some variations, and there are various particle sizes in the developing device. Or toner particles having chargeability are mixed. When image formation is performed using toner having such variations, the toner is selectively consumed, that is, only toner particles having specific characteristics are selectively consumed, while other toner particles are not consumed so much. The phenomenon of remaining inside occurs. As a result, as the number of images formed increases, the state of toner characteristic distribution in the developing device changes, and the image density also changes accordingly.
[0052]
Here, as a representative example, a case where the image density increases with an increase in the number of image formations as shown in FIG. 4 will be considered. As shown in FIG. 4, the fluctuation of the image density is large between the number of image formations and the image density in a normal image forming apparatus at the initial stage (when the number of image formations is small), and gradually increases as the number of image formations increases. It is common to show the relationship that the fluctuation is small.
[0053]
Furthermore, the larger the ratio of the area occupied by the portion where the toner is actually attached in the area corresponding to one sheet of printing duty, that is, the initial density fluctuation becomes more prominent. This is presumably because even if the number of formed images is the same, if the printing duty is large, the amount of toner consumption increases, and the toner characteristics in the developing device change more rapidly.
[0054]
In such an image forming apparatus, in order to suppress the change in the image density to be small, a density control process is newly executed before the change in the image density exceeds the allowable range, and the density control factor is set to an optimum state. It is necessary to readjust. For example, as shown in FIG. 5, in an apparatus having an initial image density of D0, unless the density control factor is readjusted, the image density gradually increases as shown by curve a. However, if the density control factor is readjusted before the image density rises to the upper limit density D1 of the allowable range ΔD, the image density is pulled back to the original density D0. In the example of FIG. 5, the density control factor is readjusted when the number of formed images reaches the number N1, N2 at which the image density reaches the upper limit density D1, or before that, the change in the image density is allowed. It becomes possible to suppress within the range ΔD.
[0055]
In the above description, the relationship between the number of image formations and the image density has been described. However, this relationship is strictly established only when the printing duty is constant. In an actual image forming apparatus, the print duty differs for each image to be formed. Therefore, it is not preferable to determine the timing for optimizing the density control factor based only on the number of formed images.
[0056]
FIG. 6 shows the correspondence between the developing roller rotation time and the count value of the number of dots formed by the exposure beam L. Here, since the developing roller rotation time corresponds to the total length of the formed image, it can be considered to represent the approximate number of images formed. If the toner adhesion amount per dot is substantially constant, the dot count value can be considered to represent an approximate toner consumption amount. For example, if the printing duty is constant at 5% (a value that is an average printing duty of a document composed only of characters), the number of images formed and the toner consumption amount are substantially proportional (straight line b). On the other hand, if the printing duty is larger than this, for example 20%, the slope of the straight line becomes larger (straight line a), and if the printing duty is small, for example, 1%, the slope of the straight line becomes smaller (straight line c).
[0057]
In an actual image forming operation, since images having various printing duties are mixed, the locus of points representing a combination of the developing roller rotation time and the dot count value does not always have such a linear relationship. Rather, it is generally a curve that goes from the origin to the upper right while drawing a complicated trajectory. Since these values are integrated values, the trajectory cannot advance downward or leftward. However, if the image signal corresponds to a solid image (no printing) or one that does not use any toner color, the dot count value does not increase for that toner color and develops. Only the roller rotation time is added, and the locus in this case is a straight line parallel to the horizontal axis.
[0058]
Further, when a large number of images having a small print duty are formed, toner fatigue in the developing device becomes a problem. That is, as described above, the charged toner that has not been used for image formation is collected in the developing device, peeled off from the developing roller 44, and again used for image formation. For this reason, the amount of toner collected without being used in an image with a low print duty increases, and the toner is fatigued by repeating charging and peeling in this manner, and its characteristics gradually change. As the toner characteristics change, the image density gradually changes even if the image is formed under the same conditions.
[0059]
The amount of toner in the developing unit and the change in its characteristics occur in a shorter cycle than the time-dependent change in other characteristics of the apparatus, for example, the characteristic change due to wear of the photosensitive member 2, and the amount of change is large. Therefore, such a change in toner characteristics is one of the main causes that cause a change in image density over time in the image forming apparatus.
[0060]
As is clear from the above, in order to keep the image density substantially constant, it is extremely important at what timing the optimization of the density control factor is executed. The timing should be determined according to the state of the toner remaining in the developing device. However, it is difficult to accurately grasp the state of such toner based only on the number of images formed or the amount of toner consumed (or the remaining amount of toner). Therefore, it is necessary to determine the execution timing of the density control process based on information that more reflects the toner state. In the conventional image forming apparatus, the density control process is not always performed at an appropriate timing, and as a result, problems such as large fluctuations in image density and increased toner loss may occur.
[0061]
In view of the above, in this embodiment, when image formation is performed, the number of dots formed by the exposure beam L serving as an index representing the amount of toner consumption and the rotation time of the developing roller 44 serving as an index representing the degree of toner fatigue. Are stored in the RAM 107, and when the CPU 101 determines that any of these values has reached a predetermined threshold value, a density control process described later is executed. In other words, by counting the number of dots, it is possible to grasp the approximate toner remaining amount, and it is possible to grasp the degree of toner fatigue from the correspondence between the toner remaining amount and the developing roller rotation time. By setting the execution timing of the density control process based on the combination, the density control process can be performed at an appropriate timing according to the toner state.
[0062]
Specifically, as indicated by the broken lines in FIG. 7, several threshold values are determined in advance for each of the developing roller rotation time and the dot count value, and any one of these values accumulated is determined. When the threshold value is reached, the “control start condition” is set, and the density control process is executed when this condition is satisfied. In this embodiment, the threshold values were determined as follows: 1325 for developing roller rotation time (unit sec, the same applies hereinafter), 3975 and 6625; 1000000, 2000000 and 6666666 for dot count values.
[0063]
Among these, the threshold value of the developing roller rotation time is a value corresponding to 1000 sheets, 3000 sheets, and 5000 sheets, respectively, in terms of the number of images formed when continuous printing is performed on A4 size paper. However, as described above, it is the developing roller rotation time that more accurately reflects the state of the toner in the developing device. Thus, the density control process is executed not based on the number of image formations but the developing roller rotation time. By managing the timing, it is possible to perform density control processing at a more appropriate timing according to the toner state.
[0064]
In this image forming apparatus, the average toner consumption per dot is about 0.015 mg. That is, the threshold value of the dot count value described above is determined as a value corresponding to 15 g, 30 g, and 100 g in terms of toner consumption. In addition to the toner forming the toner image, this numerical value includes the amount of toner consumed by scattering and fogging.
[0065]
As shown in FIG. 4, the variation in image density is large at the beginning of use of the developing device, and the variation gradually decreases. Therefore, as shown in FIG. 7, the threshold value is set to be relatively small when the developing roller rotation time or the dot count value is small, and to be coarser as these values increase. Yes. In other words, the density control process is executed at a relatively high frequency when the density fluctuation is large at the initial stage of use of the developing device, whereas the frequency decreases when the density fluctuation becomes small. In this way, by changing the threshold increment, which is the starting condition of the density control process, according to the degree of fluctuation of the image density, the density control process is executed at a more appropriate timing, thereby stabilizing the image density and reducing the toner loss. It is possible to achieve both reduction.
[0066]
Further, when the remaining amount of toner is extremely reduced or its characteristics are extremely lowered, the image quality is rapidly deteriorated. Therefore, in this embodiment, when the dot count value reaches a value of 120000000 corresponding to the toner consumption amount of 180 g, or when the developing roller rotation time reaches a value of 10600 sec corresponding to the image forming number of 8000 sheets, the CPU 101 determines the life of the developing device. Therefore, a message notifying the toner end is displayed on a display unit (not shown) to prompt the user to replace the developing device.
[0067]
Information representing the toner state, that is, the developing roller rotation time and the dot count value as the “toner state information” of the present invention are individually stored in the RAM 107 provided in the engine controller 10 for each developing device. Updating and reading are performed at any time by access from the CPU 101 performed as necessary. That is, in this embodiment, the RAM 107 functions as the “storage unit” of the present invention.
[0068]
In addition, when the developing device is replaced, the information is written in the memories 91 to 94 provided in the developing devices 4Y, 4C, 4M, and 4K before the developing device is removed. When installed, the information stored in these memories is read and used, so that even if a developing device in use is removed and then reattached or attached to another device, the usage history of the developing device is properly stored. Can be managed.
[0069]
Since it is configured as described above, in consideration of the case where the combination of the developing roller rotation time and the dot count value changes as shown by the curve d in FIG. 7, for example, this image forming apparatus is executed immediately after the power is turned on. In addition to the above, the density control process is executed at timings corresponding to the signs {circle around (1)} to {circle around (6)} corresponding to the intersections of the broken lines indicating the threshold and the curve d. Therefore, it is possible to perform density control processing at an appropriate timing in response to a change in the state of toner in the developing device.
[0070]
FIG. 8 is a flowchart showing density control processing in this embodiment, and FIG. 9 is a diagram showing an example of a lookup table referred to in the processing of FIG. Hereinafter, the operation of the density control process performed at the above timing will be described with reference to FIGS. In this density control process, for each toner color, the target density value of the patch image is set according to the characteristics of the toner remaining in the developing device, the patch image is formed, its density is detected, and the detection result And a concentration control factor are optimized based on the set concentration target value. Here, the density control process using the black toner color will be described as an example, but the same process is performed for other toner colors.
[0071]
In this image forming apparatus, due to variations in toner production, various characteristics of the toner in the developing unit, that is, particle size distribution, charging property, and the like are slightly different for each individual developing unit. The initial characteristics of the toner are actually measured at the manufacturing stage, and these are classified into several types and attached to each developing device. Here, information indicating which type of toner filled in the developing device corresponds to “toner individuality information”. Such variations in toner characteristics may differ between toners manufactured with the same specifications at different manufacturing facilities, and may vary depending on the manufacturing lot even if they are manufactured with the same facilities. .
[0072]
This toner individuality information is written in the memory 94 in the developing device when the toner is filled in the developing device 4K. The CPU 101 of the engine controller 10 can read out this information when the developing unit 4K is attached to the developing unit 4 and can grasp the initial characteristics of the toner. By setting the operating conditions, an image with higher image quality can be stably formed regardless of toner manufacturing variations. Thus, in this embodiment, the memories 91 to 94 function as “memory elements” of the present invention.
[0073]
More specifically, in this image forming apparatus, as illustrated in FIG. 9, the ROM 106 has a lookup table for setting the density target value of the patch image according to the developing roller rotation time and the dot count value. This table is prepared for each toner type, and one of them is selected and used based on the toner individuality information, so that a density target value corresponding to the toner type is set. FIG. 9A shows a density target value of a high density patch image to be described later, which is determined for the black toner corresponding to “type 0”, and FIG. The density target value of the density patch image is shown. The target density value is a value normalized so that the maximum density of the toner color is 1.
[0074]
Here, the density target value of the patch image is changed depending on the developing roller rotation time and the dot count value for the following reason. That is, as will be described later, the density of the toner image as a patch image is measured in a state of being carried on the intermediate transfer belt 71. For this reason, there is a slight deviation between the density of the toner image thus measured and the density of the image finally transferred onto the sheet S. Here, when the toner particle size distribution in the developing device 4K changes with time due to selective consumption of the toner, the particle size of the toner constituting the toner image also changes. It changes depending on the state of the toner inside. Therefore, in order to correct this deviation, in this embodiment, the state of the residual toner in the developing device is estimated from the developing roller rotation time and the dot count value, and the density target value of the patch image is changed based on the estimated state. . That is, as shown in the figure, the look-up table includes a density target value for each of the developing roller rotation time and the dot count value (in this embodiment, these correspond to the “toner state information” of the present invention). Correspondingly, the look-up table functions as “target value correspondence information” of the present invention. Of course, it goes without saying that the target value correspondence information may be set in advance in the function format instead of the table format. This is also true for the look-up table of FIG. 13 described later.
[0075]
The interval for changing the density target value matches the threshold values of the developing roller rotation time and the dot count value, which are the density control start conditions. Therefore, every time these values reach the threshold value, a new density target value corresponding to the toner state at that time is newly set, and the density control factor is optimized based on the density target value. It becomes. However, in the table of FIG. 9, the density target value may be the same between adjacent columns. In this case, the newly set density target value is the same as the value before setting.
[0076]
In this density control process, as shown in FIG. 8, first, one look-up table is selected in accordance with the toner individuality information attached to the developing device 4K (step S1), and the toner status information, that is, the current point in time is selected. The table is referred to based on the developing roller rotation time and the dot count value, and the density target value at that time is set (step S2). For example, if the developing roller rotation time is 2000 sec and the dot count value is 1500,000, the values corresponding to these combinations, that is, 0.984 for the high density patch image and 0.181 for the low density patch image in this case. It is a target value.
[0077]
Then, for example, a solid image is formed as a high density patch image with each developing bias while keeping the exposure energy E constant and changing and setting the DC developing bias Vavg in multiple stages (step S3). The patch image formed in this way and transferred to the intermediate transfer belt 71 is conveyed by the movement of the intermediate transfer belt 71, and the optical density of each patch image is detected by the density sensor 60 at the timing when it reaches the position facing the density sensor 60. (Step S4).
[0078]
When the density of the patch image at each developing bias is thus obtained, the optimum value of the DC developing bias Vavg is obtained based on the detection result and the previously obtained density target value (step S5). Here, for example, the bias value at which the density closest to the density target value is obtained may be set as the optimum value, or the correlation between the DC developing bias Vavg and the image density is obtained from the detection result, and the image density is determined based on the correlation. A bias value that matches the density target value may be calculated.
[0079]
If the optimum value of the DC developing bias Vavg is thus obtained, then the optimum value of the exposure energy E is obtained. First, the DC developing bias Vavg is set to the optimum value just obtained (step S6), and the exposure energy E is changed and set in multiple stages, and for each energy, for example, a 1-on 10-off thin line image is formed as a low-density patch image. Form (step S7). In the same manner as described above, the density of each patch image is detected by the density sensor 60 (step S8), and the optimum value of the exposure energy E is obtained based on the detection result and the previously obtained density target value (step S9). ).
[0080]
The optimum values of the DC developing bias Vavg and the exposure energy E thus obtained are stored in the RAM 107 of the engine controller 10, and thereafter, these values are called when performing image formation in black, and based on this value. By setting the DC developing bias Vavg and the exposure energy E and performing image formation, an image with excellent image quality can be formed.
[0081]
Such density control processing is executed in a timely manner in accordance with changes in the developing roller rotation time and dot count value, so that stable image formation with little change in image density can be performed.
[0082]
In the image forming apparatus configured as described above, in order to verify the effect of the present invention, the change in the image density when a large number of images were continuously formed was examined. As an example of the result, FIG. 10 and FIG. 11 show changes in image density when a solid image is formed using black toner.
[0083]
FIG. 10 is a graph showing changes in image density when image formation is performed at each print duty without performing density control processing. FIG. 11 is a graph showing changes in image density when the density control processing according to the present invention is performed and when it is not performed. In these figures, the image density on the vertical axis is plotted as the optical density (OD value) of the image finally transferred and fixed on the sheet S.
[0084]
When the density control process is not performed, as shown in FIG. 10, the on-sheet OD value rapidly increases as the dot count value increases, and then the rate of increase gradually decreases. The initial density change varies depending on the print duty, and increases as the print duty increases. Such a tendency of density change is the same even if the developing roller rotation time is plotted on the horizontal axis. In this way, if the density control process is not performed, the image density greatly changes with time.
[0085]
Next, a change in image density according to whether or not the density control processing according to the present invention is performed when the printing duty is constant (for example, 5%) is compared. A curve e in FIG. 11 corresponds to the curve with a print duty of 5% in FIG. 10 and is a change in image density when the density control process is not performed. On the other hand, when the density control process according to the present invention is performed, as shown by a curve f in FIG. 11, the density control process is executed and the density control factor is readjusted before the density change becomes larger than a certain level. The change in concentration is kept within a certain range. Although not shown, the same experiment was performed by changing the print duty in various ways, and in any case, the density control process as described above is executed to keep the change in the image density within a predetermined range. It was confirmed that it could be suppressed.
[0086]
FIG. 12 is a chart for explaining another setting method of the density control start condition. As described above, the state of the toner in the developing device can be estimated from the developing roller rotation time and the dot count value. In the above embodiment, one of these values is provided independently for each. When the threshold value is reached, the density control process is started. More precisely, however, the toner state is expressed as a combination of these two pieces of information. Therefore, it is preferable to determine the density control start condition based on these combinations.
[0087]
For example, an image density obtained from a combination of the developing roller rotation time and the dot count value is experimentally measured in advance, and a coordinate space represented by (developing roller rotation time, dot count value) is represented as shown in FIG. Then, it is divided into a plurality of areas in which combinations that can obtain substantially the same image density belong to the same area. Then, if the density control process is started when the point Q corresponding to the current developing roller rotation time and the dot count value reaches the boundary line between these areas, the above request is achieved. However, if such a determination is made, the processing becomes complicated, and more memory is required, resulting in an increase in apparatus cost. Therefore, for example, in a device with more demanding image quality, the density control process is executed based on the chart of FIG. 12, while in a simpler apparatus, the density control process is executed based on the threshold value of FIG. Thus, it is desirable to use properly according to the device configuration and its specifications.
[0088]
Note that the numbers in parentheses in FIG. 12 show examples of density target values in each region, and correspond to the numerical values in the table in FIG. 9A. As described above, even when the timing for executing the density control process is set based on this chart, if the density target value is changed and set according to the state of the toner at that time, the fluctuation of the image density can be further increased. It can be kept small.
[0089]
As described above, in this embodiment, the developing roller rotation time and the number of dots formed are counted for each developing device, and the density control factor is optimized based on the combination of these count values. Concentration control processing is executed. These count values reflect the state of toner remaining in the developing unit. Therefore, by managing the execution timing of the density control process based on these values, the density control process can be executed at an appropriate timing corresponding to the change in the image density accompanying the change in the toner state. As a result, this image forming apparatus can effectively suppress fluctuations in image density and stably form a toner image with good image quality.
[0090]
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, the DC development bias Vavg and the exposure energy E are used as the density control factors. However, other than the density control factors that affect the image density, the AC amplitude of the development bias, the charging Parameters such as the bias and the amount of toner transported by the developing roller 44 are known, and the present invention can also be applied to an image forming apparatus using these parameters as a density control factor.
[0091]
Further, for example, in the above embodiment, the timing for executing the density control process is defined by the dot count value and the developing roller rotation time value, but the toner state information is not limited to this. Other information indicating the state of the toner in the developing device in the above may be used. For example, in an apparatus equipped with a toner remaining amount sensor that analyzes an externally supplied image signal to calculate the toner consumption amount or detects the toner remaining amount in the developing device, the toner remaining amount is obtained from the detection result, and thus The obtained toner amount may be used as one of the toner status information. Further, the developing roller rotation speed may be integrated instead of the developing roller rotation time.
[0092]
Further, the dot count value and the developing roller rotation time threshold value that trigger the density control processing are not limited to the above-described examples, and may be appropriately changed according to the characteristics of the toner to be used. Needless to say.
[0093]
For example, in the above-described embodiment, based on the look-up table illustrated in FIG. 9, the toner state represented by a combination of (developing roller rotation time, dot count value) is shifted from one column to another column. Sometimes the density control process is executed regardless of whether or not the density target value is changed. However, for example, in FIG. 9A, among the columns belonging to the column of the developing roller rotation time “˜3975”, the density of the column where the dot count value is “˜66666666” and the column “˜12000000”. Both target values are common with 0.982. Therefore, even if the dot count value exceeds the threshold value 6666666, the density target value is not changed as long as the developing roller rotation time belongs to the column “˜3975”. The reason why the density target value is not changed is that the expected fluctuation in image density is considered to be small (see FIG. 4). Therefore, the execution timing of the density control process may be as follows.
[0094]
That is, when the dot count value or the developing roller rotation time reaches the threshold value, it is determined whether there is a change in the density target value with reference to the lookup table illustrated in FIG. On the other hand, the density control process may be executed in the same manner as in the above embodiment, but the density control process may not be executed when there is no change or when the amount of change is small (for example, less than 0.001). That is, this change amount corresponds to the “predetermined fluctuation value” of the present invention. The “predetermined fluctuation value” is not limited to 0.001 described above, and is arbitrary. For example, in the embodiment using the lookup table shown in FIG. 13 described in detail later, the optical density (OD value) is set to 0.003 or 0.002 as the “predetermined fluctuation value”.
[0095]
Here, as an example, consider the case where the combination of (developing roller rotation time, dot count value) changes as shown by a curve d shown in FIG. In this case, referring to FIG. 9A, since there is no change in the density target value at the timings indicated by reference numerals (4) to (6), the density control processing at these timings is omitted. . Here, for example, as shown in FIG. 4, as the use of the developing device progresses, the fluctuation of the image density decreases. Therefore, the fluctuation of the image density by omitting the density control processing at these timings does not increase so much. On the other hand, by reducing the number of executions of the density control process, the toner consumption can be suppressed, and the life of the developing device can be extended and the waiting time of the user can be reduced.
[0096]
In the above embodiment, a lookup table is prepared for each toner type, and the density target value of the patch image is changed according to the toner type. However, the timing for executing the density control process is any type. The same applies to the toner. On the other hand, the execution timing of the density control process may be varied for each toner type. That is, the threshold value of the dot count value or the developing roller rotation time is set individually for each toner type, and the timing for executing the density control processing is determined based on this threshold value. Alternatively, the density control process may be executed at different timings.
[0097]
This makes it possible to selectively use toners having different characteristics and form an image with a stable image density. As a result, the range of characteristics of toner that can be used in the apparatus is widened, and the user has a higher degree of freedom in selecting the type of toner. On the other hand, the quality requirements for the toner characteristics are eased for the toner supplier, and the manufacturing cost is reduced. The yield can be improved.
[0098]
Further, the number of threshold values is arbitrary. A lookup table may be created corresponding to the toner color. For example, the density control process may be executed as follows based on a lookup table as shown in FIG.
[0099]
FIG. 13 is a diagram showing another example of the lookup table. FIG. 5A shows the density target value of the high density patch image determined for the black toner corresponding to “type 0”, and FIG. 5B shows the magenta toner corresponding to “type 0”. The density target value of the high density patch image determined for the image is shown. The density target value is a value normalized so that the maximum density of the toner color is 1.
[0100]
As is clear from the comparison between FIG. 9 and FIG. 13, the following points are greatly different. First, in this embodiment, the number of threshold values of the dot count value and the developing roller rotation time is larger than in the previous embodiment (FIG. 9). That is, fine control can be performed by increasing the threshold value. Further, in this embodiment, since the magenta toner has a characteristic that the density fluctuation accompanying the fluctuation of the toner state is large, the lookup is created using the magenta toner as a reference color. That is, when the density target value is a fixed value, the threshold value is set so that the density fluctuation value exceeds 0.03 in the optical density (OD value) as shown in FIG. Yes. For other color colors, that is, yellow and cyan, a lookup table similar to magenta toner is provided. Here, it is considered that the reason why the density fluctuation of the magenta toner is large is that the selective consumption of the toner is larger than that of other colors. Since this selective consumption is considered to depend on the type of pigment, it is desirable to determine the reference color of the lookup table in consideration of these points.
[0101]
On the other hand, with black toner, since the density fluctuation accompanying the fluctuation of the toner state is smaller than that of magenta toner, the density fluctuation value exceeds 0.02 in optical density (OD value) as shown in FIG. However, the threshold is set. Thus, in this embodiment, the look-up tables are different for color (magenta, yellow and cyan) and black. Here, only the high density patch image is shown, but the threshold value and the density target value setting policy are the same for the low density patch image.
[0102]
Further, when the set number of thresholds is increased as described above, it is desirable to limit the execution timing of the density control process as follows. The reason is as follows. Here, as in the previous embodiment, if the density control process is unconditionally executed when the threshold value is reached, the frequency of execution of the density control process increases as the threshold value increases, resulting in density fluctuations. There is a problem that the density control process is executed despite the small amount. In general, the dot count value and the developing roller rotation time are different for each color, and it is rare that all colors reach the threshold value at the same timing. Therefore, the negative effect of executing the density control process every time the threshold value is reached is significant from this point. Therefore, especially when the set number of thresholds is increased, density control is performed only when the condition that there is a change in the density target value when the dot count value or developing roller rotation time reaches the threshold value is added. It is desirable to execute processing. That is, even if the dot count value or the developing roller rotation time reaches the threshold value, if the density target value is not changed, the optical density (OD value) is less than 0.03, and the density fluctuation is small. Therefore, even if the density control processing at these timings is omitted, the fluctuation of the image density is almost negligible. Further, by omitting the density control process, the amount of toner consumption can be suppressed, and the life of the developing device can be extended and the waiting time of the user can be reduced.
[0103]
In the above embodiment, even if the density (for high density / low density), toner color, toner individuality information, and the like are different, the threshold value of the lookup table is made common, so the density target value is the same. However, it is necessary to set a threshold value. However, the common use of the threshold value in the lookup table is not an essential matter, and the threshold value may be set where the density target value changes. As a result, the number of threshold values set can be reduced, and the capacity of the lookup table can be reduced, which greatly contributes to memory saving.
[0104]
The above-described embodiment is an image forming apparatus having the intermediate transfer belt 71 that temporarily carries the toner image developed on the photosensitive member 2, but the image having other transfer bodies such as a transfer drum and a transfer roller. The present invention is also applied to a forming apparatus and an image forming apparatus configured to directly transfer a toner image formed on the photosensitive member 2 without a transfer member to a sheet S as a final transfer material. be able to.
[0105]
In the above-described embodiment, the image forming apparatus is configured to be capable of forming a full-color image using toners of four colors of yellow, cyan, magenta, and black. For example, the present invention can be applied to an apparatus that forms a monochrome image using only black toner.
[0106]
Furthermore, in the above-described embodiment, the present invention is applied to a printer that executes an image forming operation based on an image signal from the outside of the apparatus. However, in response to a user's image formation request, for example, a copy button push, The present invention can also be applied to a copying machine that creates an image signal and executes an image forming operation based on the image signal, and a facsimile machine that executes an image forming operation based on an image signal given through a communication line. Needless to say.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.
2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG.
FIG. 3 is a cross-sectional view illustrating a developing device of the image forming apparatus.
FIG. 4 is a diagram exemplifying a change in image density with respect to the number of formed images.
FIG. 5 is a diagram illustrating a setting principle of timing for executing density control processing;
FIG. 6 is a diagram illustrating a relationship between a dot count value and a developing roller rotation time.
FIG. 7 is a diagram illustrating timing for executing density control processing.
FIG. 8 is a flowchart showing density control processing in this embodiment.
FIG. 9 is a diagram illustrating an example of a lookup table.
FIG. 10 is a graph showing changes in image density at each printing duty.
FIG. 11 is a graph showing changes in density when density control processing is performed.
FIG. 12 is a chart for explaining another setting method of density control start conditions.
FIG. 13 is a diagram illustrating another example of a lookup table.
[Explanation of symbols]
2 ... photosensitive body (image carrier), 4Y, 4C, 4M, 4K ... developer, 6 ... exposure unit (exposure means), 10 ... engine controller (image forming means), 44 ... developing roller (toner carrier), 91-94 ... memory (storage element), 107 ... RAM (storage means)

Claims (15)

An image carrier configured to carry an electrostatic latent image;
A developing device that contains toner therein and conveys the toner toward the surface of the image carrier;
An image that forms a toner image by applying a predetermined developing bias to the developing device and moving the toner to the image carrier to visualize the electrostatic latent image formed on the surface of the image carrier with toner. Forming means;
Storage means for storing toner state information relating to the state of toner contained in the developing unit;
The toner status information is updated and stored according to the operating status of the apparatus, and
When the toner status information reaches a predetermined control start condition, a toner image is formed as a patch image, and a density control factor that affects the image density is optimized based on the toner density of the patch image. An image forming apparatus that controls image density. Optimizing the density control factor by setting the density control factor so that the toner density of the patch image substantially matches a predetermined density target value;
The image forming apparatus according to claim 1, wherein the density target value is changed and set according to the toner state information. When the density target value is changed, the density control factor is optimized, and the density control factor is set so that the toner density of the patch image substantially matches the density target value after the change. Item 3. The image forming apparatus according to Item 2. A plurality of the control start conditions are set for the toner status information, and
The plurality of control start conditions are set so that when the change rate of the image density with respect to the change in the toner state information is large, the density control factor is optimized more frequently than when the change rate is small. The image forming apparatus according to claim 1. Exposure means for forming an electrostatic latent image on the surface of the image carrier by exposing the surface of the image carrier charged to a predetermined surface potential with a light beam;
As the toner status information, the number of dots formed on the surface of the image carrier by the light beam exposure and the operation time of the developing device are used, and at least one of the number of dots and the operation time is a predetermined value. 5. The image forming apparatus according to claim 1, wherein the control start condition is that a threshold value has been reached. The developing device includes a toner carrier that conveys the toner to a position facing the image carrier by rotating in a predetermined direction while carrying toner on the surface thereof,
The image forming apparatus according to claim 5, wherein a rotation time of the toner carrier is an operation time of the developing device. Target value correspondence information in which the density target value is associated with each of the plurality of toner state information is preset,
The toner status information corresponding to the operating status of the device reaches a predetermined threshold value,
The control start condition is that a difference between a density target value corresponding to the toner state information when the threshold value is reached and a density target value before reaching the threshold value is greater than or equal to a predetermined fluctuation value. The image forming apparatus according to claim 1. Even if the toner status information according to the operating status of the device reaches a predetermined threshold value,
When the difference between the density target value corresponding to the toner state information when the threshold is reached and the density target value before reaching the threshold is less than a predetermined fluctuation value, the density control factor is optimal. The image forming apparatus according to claim 7, wherein the image forming is not performed. The image forming apparatus according to claim 8, wherein the fluctuation value is 0.03 or less in optical density. The image forming apparatus according to claim 7, wherein a color image is formed using a plurality of different color toners, and a single color image is formed using a black toner among the plurality of colors. ,
The image forming apparatus in which the target value correspondence information for the black color is different from the target value correspondence information for the non-black color. The image forming apparatus according to claim 7, wherein a color image is formed using toners of different colors.
While the target value correspondence information is set in advance using a color having the most selective consumption among the plurality of colors as a reference color,
An image forming apparatus in which the target value correspondence information of other colors matches the target value correspondence information of the reference color. The image forming apparatus according to claim 1, wherein the control start condition is changed and set according to an initial state of the toner accommodated in the developing device. The image forming apparatus according to claim 1, wherein the developing device is configured to be detachable from the apparatus main body and includes a storage element that functions as at least a part of the storage unit. An electrostatic latent image is formed on the surface of the image carrier, and a predetermined developing bias is applied to a developing unit that contains toner to move the toner to the image carrier, whereby the electrostatic latent image is visualized with toner. In an image forming method for forming a toner image by converting
According to the operating status of the apparatus, the toner status information regarding the status of the toner stored in the developing device is updated, and
When the toner status information reaches a predetermined control start condition, a toner image is formed as a patch image, and an image density is adjusted by optimizing a density control factor that affects the image density based on the toner density of the patch image. An image forming method comprising controlling the image forming method. The image forming method according to claim 14, wherein an electrostatic latent image is formed on the surface of the image carrier by exposing the surface of the image carrier charged to a predetermined surface potential with a light beam.
As the toner status information, the number of dots formed on the surface of the image carrier by the light beam exposure and the operation time of the developing device are used, and at least one of the number of dots and the operation time is a predetermined value. An image forming method wherein the control start condition is that a threshold has been reached.

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