JP2022018663A - Image forming apparatus, control method for image forming apparatus, and control program for image forming apparatus - Google Patents

Abstract

To supply a fogging toner within a proper range to a surface of a photoreceptor to form an appropriate amount of stationary layer between the surface of the photoreceptor and a cleaning blade.SOLUTION: In an image forming apparatus 1, an electrifying member 12a electrifies a surface of an image carrier 11. An exposure device 13 exposes the surface of the image carrier 11 to form an electrostatic latent image. A developing unit 14 includes a developer carrier 14a that carries developer including toner and carrier and develops the electrostatic latent image with the toner supplied from the developer carrier 14a. A cleaning member 15a is in contact with the surface of the image carrier 11 to remove the toner. A control unit 60 adjusts, according to the operation frequency of the developing unit 14, at least either one of the electrification potential on the surface of the image carrier 11 applied by the electrifying member 12a or the bias potential on the developer carrier 14a, so that a fogging toner within a proper range is supplied to the image carrier 11.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to an image forming apparatus, a control method of the image forming apparatus, and a control program of the image forming apparatus.

In an electrophotographic image forming apparatus, a phenomenon in which toner adheres to a portion where toner should not originally adhere, a so-called "blurring phenomenon", may cause a problem in terms of image quality.

For example, Japanese Patent Application Laid-Open No. 2006-301479 (Patent Document 1) has an object of preventing the occurrence of ground fog for a long period of time when a non-magnetic one-component developer is used as a toner. Specifically, in order to compensate for the decrease in the amount of electric charge of the toner due to the increase in the number of integrated prints, the development bias voltage without increasing the potential difference between the time average voltage of the development bias voltage and the background potential of the electrostatic latent image. The potential difference between the peak voltage and the background potential is controlled to be small.

Further, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-140917 (Patent Document 2), the rotation speed of the developing roller changes when the charge amount of the developer changes according to the operating condition of the developing device, humidity and the like. By adjusting the image density, the image density is maintained and the fog phenomenon is prevented.

Japanese Unexamined Patent Publication No. 2006-301479 Japanese Unexamined Patent Publication No. 2005-140917

By the way, it is known that a rest layer is formed between the surface of the photoconductor and the cleaning blade by the toner and the external additive. By blocking the toner with this stationary layer, the surface of the photoconductor can be satisfactorily cleaned.

In order to maintain good image quality, it is necessary to always form an appropriate amount of rest layer. The inventor of the present application has found that it is effective to supply an appropriate amount of fog toner from the developer to the photoconductor in order to always form an appropriate amount of the rest layer (for details, refer to the details. It will be described in the embodiment).

The present disclosure has been made on the basis of the above study results, one of the purposes of which is to provide an appropriate range of fog toner to form an appropriate amount of rest layer between the photoconductor surface and the cleaning blade. It is to provide an image forming apparatus to supply to the surface of a photoconductor.

The image forming apparatus of one embodiment includes an image carrier, a charging member, an exposure apparatus, a developing device, a cleaning member, and a control unit. The charging member charges the surface of the image carrier. The exposure apparatus forms an electrostatic latent image by exposing the surface of the image carrier. The developer includes a developer carrier that carries a developer containing toner and carriers, and develops an electrostatic latent image on the surface of the image carrier with toner supplied from the developer carrier. The cleaning member abuts on the surface of the image carrier to remove the toner. The control unit carries the image by the charging member so that the cover toner is supplied to the image carrier in an amount within a predetermined range according to the operating frequency of the developing device or the amount related to the operating frequency of the developing device. Adjust at least one of the charging potential on the surface of the body or the bias potential of the developer carrier.

In one embodiment, the quantity related to the operating frequency of the developer is the number of prints within the evaluation period up to the present time or the integrated rotation speed of the developer carrier within the evaluation period.

In one embodiment, the control unit increases the potential difference between the charging potential of the image carrier and the bias potential of the developer carrier as the evaluation amount, which is an amount related to the operating frequency of the developing device or the operating frequency of the developing device, increases. Increase the amount of manipulation, which is an absolute value.

In one embodiment, the control unit does not change the operation amount until the evaluation amount reaches the threshold value, and increases the operation amount when the evaluation amount exceeds the threshold value.

In one embodiment, the control unit changes the threshold and the manipulated variable depending on at least one of the average coverage of the image printed by the image forming apparatus, the in-flight humidity of the image forming apparatus, or the print linear velocity.

In one aspect, the control unit reduces the threshold and increases the manipulated variable as the average coverage decreases.

In one embodiment, the control unit reduces the threshold value and increases the operation amount as the in-flight humidity decreases.

In one embodiment, the control unit reduces the threshold value and increases the operation amount as the print line speed increases.

In another embodiment, a method for controlling the above-mentioned image forming apparatus is provided. The control method consists of a step in which the control unit stores the operating status of the image forming apparatus in the storage device over time, and the control unit operates the developing device or the operating frequency of the developing device based on the operating status over time. The step of calculating the amount related to the image carrier as the evaluation amount, and the image support by the charging member so that the control unit supplies the cover toner in an amount within a predetermined range according to the evaluation amount to the image carrier. It comprises a step of adjusting at least one of the charging potential on the surface of the body or the bias potential of the developer carrier.

In still another embodiment, a control program for the image forming apparatus described above is provided. The control program stores the step of storing the operating status of the image forming apparatus in the storage device over time in the computer, and the amount related to the operating frequency of the developing device or the operating frequency of the developing device based on the operating status over time. The charge potential or developer on the surface of the image carrier by the charging member so that the step calculated as the evaluation amount and the fog toner in an amount within a predetermined range are supplied to the image carrier according to the evaluation amount. The step of adjusting at least one of the bias potentials of the carrier is performed.

According to each of the above embodiments, an appropriate amount of rest layer can be formed between the surface of the photoconductor and the cleaning blade by supplying a cover toner in an appropriate range to the surface of the photoconductor.

It is a figure which shows an example of the schematic structure of the color image forming apparatus by an electrophotographic method. It is a figure which shows the detailed configuration example of the image formation unit. It is a block diagram which shows an example of the hardware composition of a control part. It is a figure for demonstrating the rest layer formed between a photoconductor and a cleaning blade. It is a figure which shows the relationship between the number of prints in a day, and the amount of a fog toner. It is a figure which shows the change of the fog toner amount when the developer 14 is operated continuously. It is a figure explaining the change of the charge amount distribution according to the operating time of a developer 14. It is a figure for demonstrating the charge amount distribution of FIG. 7C. It is a figure explaining the relationship between the fog margin and the fog toner amount. It is a figure for demonstrating the control of the fog toner amount by the fog margin. It is a flowchart which shows the control procedure of the image forming apparatus by Embodiment 1. FIG. It is a flowchart which shows an example of the detailed procedure of step S130 of FIG. It is a figure which shows an example of the table referred to in step S310 of FIG. It is a figure which shows the relationship between the average charge amount of toner in a developer, and the cumulative use time of a developer. It is a flowchart which shows an example of the detailed procedure of step S130 of FIG. 11 in the image forming apparatus of Embodiment 2. FIG. It is a figure for demonstrating the control of the cover toner amount according to the number of prints in a day, and the average coverage. It is a figure for demonstrating the control of the cover toner amount according to the number of prints in a daytime and the humidity in a machine. It is a figure for demonstrating the control of the cover toner amount according to the number of prints in the daytime and the machine line speed.

Hereinafter, embodiments will be described in detail with reference to the drawings. The same or corresponding parts are designated by the same reference numerals, and the description thereof will not be repeated.

<Embodiment 1>
[Rough configuration of image forming apparatus]
FIG. 1 is a diagram showing an example of a schematic configuration of a color image forming apparatus by an electrophotographic method. Hereinafter, the image forming apparatus of the secondary transfer method will be described as an example, but the method of controlling the amount of fog toner, which will be described later, can also be applied to the image forming apparatus of the direct transfer method. In FIG. 1, the rotation direction of each roller is indicated by an arrow.

With reference to FIG. 1, the image forming apparatus 1 includes a printer 20 configured to form a color image in a tandem manner, a paper feed tray 30 for storing paper as a recording medium, and a transport mechanism for transporting paper. And include. A scanner (not shown) may be arranged on the upper part of the printer 20.

The printer 20 includes four image forming units 10Y, 10M, 10C, 10K, an intermediate transfer belt 21, a primary transfer roller 22, a secondary transfer roller 25, a cleaner 26, and a fixing device 35. The transport mechanism includes a paper feed roller 31, a resist roller 33, and a discharge roller 38.

As shown in FIG. 1, an image forming unit 10Y for forming a yellow image, an image forming unit 10M for forming a magenta image, an image forming unit 10C for forming a cyan image, and a black image for forming a black image. The image unit 10K of is juxtaposed. Hereinafter, the image forming units 10Y, 10M, 10C, and 10K will be referred to as an image forming unit 10 when they are generically or unspecified.

Each image forming unit 10 sequentially transfers a toner image of each color formed on each photoconductor 11 onto an intermediate transfer belt 21 rotating in the direction of arrow Z by an electric field applied from the primary transfer roller 22. As a result, toner images of each color are combined on the intermediate transfer belt 21. The synthesized toner image is transferred onto the recording medium by the electric field applied from the secondary transfer roller 25. Residual toner on the intermediate transfer belt 21 is removed by a cleaner 26 including a cleaning blade (not shown).

FIG. 2 is a diagram showing a detailed configuration example of the image forming unit. With reference to FIG. 2, the image forming unit 10 includes a photoconductor 11 as an image carrier, a charger 12, an exposure device 13, a developer 14, and a cleaner 15 including a cleaning blade 15a as a cleaning member. including.

The charger 12 charges the surface of the photoconductor 11 to a target charging potential. In FIG. 2, the charger 12 by the corona discharge method is shown, but the charging method is not limited to the corona discharge method. Instead of the corona discharge method, either a proximity discharge method or a charge injection method may be used. In the case of the corona discharge method, the charging potential Vs on the surface of the photoconductor 11 can be adjusted by controlling the current Ic flowing through the wire as the charging member 12a. Further, in the case of the proximity discharge method and the charge injection method, the charge potential Vs on the surface of the photoconductor 11 can be adjusted according to the potential Va applied to the charging member 12a (roller or the like) from the high voltage power supply 16.

The exposure apparatus 13 irradiates the surface of the photoconductor 11 with light such as a laser beam based on the original image data. As a result, the surface potential of the irradiated portion is lost, so that an electrostatic latent image is formed on the photoconductor 11.

The developer 14 conveys the charged toner to the surface of the photoconductor 11 by the developing roller 14a as a developer carrier. As a result, the electrostatic latent image on the surface of the photoconductor 11 is developed. In this embodiment, a two-component development process is used. In two-component development, the toner is charged by friction with the carrier. The charged toner is carried to the surface of the photoconductor 11 by an electric field generated by the potential difference between the potential Vb applied to the developing roller 14a from the high voltage power source 17 and the potential of the electrostatic latent image.

The cleaner 15 abuts the cleaning blade 15a as a cleaning member on the surface of the photoconductor 11 to remove residual toner, fog toner, test toner patch, and the like on the surface of the photoconductor 11.

Here, the fog toner means toner that flies from the developing roller 14a to the surface of the photoconductor 11 regardless of image formation. The causes of fog toner generation are as follows. (i) Toner having a normal charge amount physically (for example, due to the centrifugal force received from the rotating developing roller 14a) flies to the surface of the photoconductor 11. (ii) Since the amount of charge of the toner is low, it cannot sufficiently attract the carrier on the surface of the developing roller 14a and flies to the surface of the photoconductor 11. (iii) Since it is counter-charged with normal toner, it repels electrically and flies from the developing roller 14a to the surface of the photoconductor 11.

With reference to FIG. 1 again, the paper feed trays 30 arranged in two stages load and store paper as a recording medium. The paper feed roller 31 takes out the paper one by one from the printer 20. The tip of the fed paper abuts on the contact portion of the stopped resist roller 33. After that, the resist roller 33 starts rotating at the timing when the synthetic toner image is transferred on the intermediate transfer belt 21, so that the paper is transferred to the secondary transfer roller 25. As a result, the synthetic toner image is secondarily transferred to the paper. After that, the synthetic toner image formed on the paper is fixed by heating and pressurizing by the fixing roller 35a of the fixing device 35. Finally, the paper is ejected to the ejection unit 5 by the ejection roller 38.

The image forming apparatus 1 further includes a control unit 60 that controls the operation of the image forming apparatus 1 as a whole, a storage device (65 in FIG. 2), a temperature sensor 67, and a humidity sensor 68.

FIG. 3 is a block diagram showing an example of the hardware configuration of the control unit. With reference to FIG. 3, the control unit 60 is a computer including at least one CPU (Central Processing Unit) 61, at least one RAM (Random Access Memory) 62, and at least one ROM (Read Only Memory) 63. Is configured on the basis of. Instead of at least one CPU 61, the control unit 60 may be configured by at least one FPGA (Field Programmable Gate Array) or at least one ASIC (Application Specific Integrated Circuit). Alternatively, the control unit 60 may be configured by any combination of the CPU, FPGA, and ASIC.

The control unit 60 is connected to an operation panel 64, a printer 20, a storage device 65, a temperature sensor 67, a humidity sensor 68, and the like via a bus. The operation panel 64 functions as a display device for displaying information to the user and an input device for receiving input from the user.

The control unit 60 reads the control program from the storage device 65 or the ROM 63 into the RAM 62 based on the reception of the control program execution command via the operation panel 64. The RAM 62 functions as a working memory and temporarily stores various data necessary for executing a control program. The control program may be stored in a non-temporary recording medium and provided, or may be provided via a network.

The storage device 65 is, for example, a hard disk, an SSD (Solid State Drive), or other storage device. The storage device 65 stores, for example, the above-mentioned control program and data. In the case of the image forming apparatus 1 of the present embodiment, the storage device 65 stores the operation history information 66 indicating the operation status (that is, whether or not it is operating) of the image forming apparatus 1 (particularly the developing device 14) over time. do.

The temperature sensor 67 and the humidity sensor 68 detect the temperature and humidity inside the housing of the image forming apparatus 1. The control unit 60 stores the detected temperature and humidity data in the storage device 65. Further, the control unit 60 controls the printer 20 based on the detected temperature and humidity data.

[Technical issues in this disclosure]
Next, the technical issues in the present disclosure will be described in detail. FIG. 4 is a diagram for explaining a stationary layer formed between the photoconductor and the cleaning blade.

Usually, the toner is externally supplemented with a lubricant. The reasons for this are the improvement of the releasability of the toner on the photoconductor 11, the suppression of wear of the cleaning blade 15a, the suppression of reduction of the torque of the photoconductor 11 due to the contact between the cleaning blade 15a and the photoconductor 11, and the charging device 12. This is for suppressing the discharge deterioration of the photoconductor 11.

Therefore, as shown in FIG. 4, a stationary layer is formed between the cleaning blade 15a and the photoconductor 11 on the upstream side in the rotation direction of the photoconductor 11 by the toner and the lubricant. The rest layer blocks the toner and scrapes it off. The toner on the surface of the photoconductor includes a fog toner, a transfer residue toner, a toner patch for testing, and the like.

From the viewpoint of image quality, it is necessary to always form an appropriate amount of stationary layer. For example, if the amount of rest layer is too small, the toner will not be cleaned and will be left behind. As a result, streak-like image noise is generated on the surface of the photoconductor 11. On the contrary, if the amount of the rest layer is too large, the amount of lubricant on the surface of the photoconductor 11 becomes excessive, and the lubricant adheres to the photoconductor 11. As a result, toner adheres to the adhered lubricant, and spot-like image noise called raindrops is generated.

In order to constantly form an appropriate amount of rest layer, it is most effective to supply an appropriate amount of fog toner. This is because the transfer residual toner is supplied only at the time of image formation and the toner patch is supplied only at the time of non-image formation, whereas the fog toner is always supplied at the time of image formation and non-image formation. ..

Here, it should be noted that the supply amount of the fog toner changes depending on the operating frequency of the developer 14. For example, when printing is executed at a uniform frequency, the amount of fog toner varies depending on the total number of printed sheets per day (hereinafter referred to as “number of printed sheets within the day”).

FIG. 5 is a diagram showing the relationship between the number of sheets printed during the day and the amount of fog toner. As shown in FIG. 5, when the number of sheets printed during the day exceeds a certain threshold value (about 4000 sheets in the case of FIG. 5), the amount of fog toner suddenly starts to increase. Further, as the number of sheets printed during the day increases, the amount of fog toner also increases. In the example shown in FIG. 5, when the amount of fog toner exceeds about 1.3 mg / sheet, point-like image noise called raindrops is generated. Further, when the amount of fog toner is smaller than about 0.7 mg / sheet, streak-like image noise is generated because the toner is left unwiped. Therefore, an appropriate range of the fog toner amount is in the range of about 0.7 mg / sheet to the image forming apparatus 1.3 mg / sheet.

Further, when the developer 14 is continuously operated or continuously stopped, the amount of fog toner changes according to the continuous operation time and the continuous stop time.

FIG. 6 is a diagram showing changes in the amount of fog toner when the developer 14 is continuously operated. In FIG. 6, the case where the developing device 14 is in operation is indicated by a solid line and a black circle, and the case where the developing device 14 is stopped is indicated by a broken line and a white circle. Until the elapsed time is 0, the developing device 14 is stopped for a long period of time.

FIG. 6A shows a change over time in the amount of fog toner when the developer 14 is continuously operated for 11 hours. FIG. 6B shows the temporal change in the amount of fog toner when the developer 14 is continuously operated for 7 hours and then continuously stopped. FIG. 6C shows the temporal change in the amount of fog toner when the developer 14 is continuously operated for 5 hours, then continuously stopped for 2 hours, and then continuously operated for 4 hours. FIG. 6D shows a change in the amount of fog toner when the developer 14 is continuously operated for 4 hours, then continuously stopped for 1 hour, then continuously operated for 5 hours, and then continuously stopped. .. FIG. 6E shows a change in the amount of fog toner when the developer 14 is continuously operated for 2 hours, then continuously stopped for 3 hours, then continuously operated for 3 hours, and then stopped.

In the examples shown in FIGS. 6A to 6E, the amount of fog toner does not increase from the start of operation of the developer 14 to about 2 hours. After about 2 hours from the start of operation of the developer 14, the amount of fog toner starts to increase. After that, the rate of increase increases with the passage of time. However, as shown in FIG. 6A, when the continuous operation time of the developer 14 exceeds about 8 hours, the amount of fog toner generated is saturated.

On the other hand, when the developer 14 is stopped, the amount of fog toner immediately begins to decrease. The amount of fog toner is reduced at a rate of about 0.75 mg / sheet per hour until the original amount of fog toner is returned to 1 mg / sheet.

The factors that change the amount of fog toner according to the operating status of the developing device 14, particularly the operating frequency, as described above will be described below.

FIG. 7 is a diagram illustrating a change in the charge amount distribution according to the operating time of the developer 14. In the following description, it is assumed that the toner is negatively charged.

FIG. 7A is a diagram showing a charge amount distribution immediately after the start of operation of the developing device 14 or when the developing device 14 is operated at a low frequency. FIG. 7B is a diagram showing the charge amount distribution when the developing device 14 is continuously operated for a while or when the developing device 14 is operated at a medium frequency. Compared with the charge amount distribution of FIG. 7A, the charge amount distribution of FIG. 7B shifts to the high charge amount distribution side. This phenomenon occurs because the triboelectric charge amount increases as the number of times the carrier and the toner rub against each other increases as the operating time of the developer 14 increases.

FIG. 7C is a diagram showing the charge amount distribution when the developing device 14 is further continuously operated or when the developing device 14 is operated at a high frequency. The charge amount distribution in FIG. 7 (C) corresponds to the charge amount distribution in FIG. 7 (B) (shown by a broken line in FIG. 7 (C)) in which the tail portion is shifted to the lower charge amount side.

FIG. 8 is a diagram for explaining the charge amount distribution of FIG. 7 (C). With reference to FIG. 8, when the charge amount of the toner becomes high on average, the carrier 72 and the high charge amount toner 70 are strongly attracted to each other in the developing device 14. Therefore, the low-charge amount toner 71 corresponding to the hem portion on the low-charge side of the charge amount distribution is less likely to rub against the carrier 72, and the charge amount decreases. As a result, the hem portion of the charge amount distribution on the low charge amount side shifts to the lower charge amount side.

Compared to the case of FIG. 7C, when the developing device 14 is continuously operated for a longer period of time, or when the developing device 14 is operated at a higher frequency, the developing device 14 is replenished with relatively low charge. Toner does not easily rub against the toner in the developing device 14, so that the amount of charge remains low. Further, the charge amount of the low charge amount toner at the tail portion of the charge amount distribution originally existing in the developing device 14 is further reduced. As a result, the proportion of low-charge toner is further increased. Since the low-charged toner is not strongly attracted to the developer 14 electrically, it becomes a fog toner and flies to the photoconductor 11. As a result, the amount of fog toner increases.

As described above, in order to always form an appropriate amount of static layer between the photoconductor 11 and the cleaning blade 15a, it is necessary to pay attention to the amount of fog toner that changes depending on the operating condition of the developing device 14. In particular, it should be noted that the amount of fog toner suddenly increases when the continuous operating time of the developing device 14 or the operating frequency of the developing device 14 exceeds a certain threshold value.

[Solutions to technical issues]
Next, a solution to the above problem will be described. In the present embodiment, in order to maintain the amount of fog toner within an appropriate range, the absolute value of the potential difference between the bias potential Vb of the developing roller 14a and the charging potential Vs on the surface of the photoconductor 11, that is, | Vb-Vs | , The change is made according to the operating condition of the developer 14. In the present disclosure, the absolute value | Vb-Vs | of this potential difference is referred to as "fog margin" or "manipulation amount". Specifically, the fog margin is increased as the operating frequency of the developer 14 or the amount related to the operating frequency increases. Examples of the amount related to the operating frequency of the developing device 14 include the number of prints within a predetermined evaluation period up to the present time or the integrated rotation speed of the developing roller 14a within the evaluation period. In the present disclosure, the operating frequency of the developer 14 or the amount related to the operating frequency is referred to as an "evaluation amount".

In order to change the fog margin, at least of the potential Va applied to the charging member 12a of the charger 12 (or the current Ic flowing through the charging member 12a in the case of the corona discharge method) or the bias potential Vb of the developing roller 14a. Change one. From the time when the image stabilization is performed until the next image stabilization is performed, the bias potential Vb applied to the developing roller 14a as the developer carrier is kept constant, so that the charger 12 is used. It is desirable to operate the potential Va applied to the charging member 12a (or the current Ic flowing through the charging member 12a in the case of the corona discharge method).

FIG. 9 is a diagram illustrating the relationship between the fog margin and the fog toner amount. With reference to FIG. 9, it is assumed that the normally charged toner is negatively charged. When the bias potential Vb of the developing roller is −300V and the charging potential Vs on the surface of the photoconductor is −350V (fog margin: 50V) and −400V (fog margin: 100V) are compared.

The fog toner is generated by being blown off the developing roller by the centrifugal force of the developing roller. At this time, when the charging potential Vs on the surface of the photoconductor is −400V, the electrical repulsive force received by the negatively charged toner becomes larger than when it is −350V. As a result, the amount of fog toner flying to the surface of the photoconductor is smaller when the charging potential Vs on the surface of the photoconductor is −400 V (that is, when the fog margin is larger) than when it is −350 V.

FIG. 10 is a diagram for explaining control of the fog toner amount by the fog margin. FIG. 10A is a diagram showing an appropriate setting value of the fog margin according to the number of printed sheets within the day. FIG. 10B is a diagram showing the relationship between the amount of fog toner corresponding to the set value of the fog margin in FIG. 10A and the number of printed sheets within the day. In FIG. 10B, the case where the fog margin is changed according to the number of sheets printed in the daytime is shown by a solid line, and the case where the fog margin is set to a constant value (100V) regardless of the number of sheets printed in the daytime is shown by a broken line.

As shown in FIGS. 10A and 10B, the fog margin is kept constant until the number of sheets printed during the day reaches a certain threshold value (about 4000 sheets in the example of FIG. 10). When the number of sheets printed within the day exceeds the threshold value, the amount of the cover toner can be maintained within an appropriate range by gradually increasing the fog margin as the number of sheets printed within the day increases. As a result, it is possible to prevent the generation of image noise.

[Control procedure of image forming apparatus]
FIG. 11 is a flowchart showing a control procedure of the image forming apparatus according to the first embodiment. Hereinafter, the control procedure of the image forming apparatus will be described while summarizing the explanations so far.

In step S100 of FIG. 11, the control unit 60 of the image forming apparatus 1 receives print settings from the user. In the next step S110, the control unit 60 starts a job according to the print settings.

First, before starting printing by the printer 20, in step S120, the control unit 60 reads out the operation history information 66 of the image forming apparatus 1 from the storage device 65. In the next step S130, the control unit 60 determines the suitability of the fog margin based on the operation history information 66.

FIG. 12 is a flowchart showing an example of the detailed procedure of step S130 of FIG. In step S300, the control unit 60 calculates the operating time of the developing device 14 within the evaluation period up to the present time as the operating frequency of the developing device 14. Instead of the operating time of the developing device 14, a value related to the operating frequency of the developing device 14 may be calculated. For example, the control unit 60 may calculate the number of prints of the image forming apparatus 1 within the evaluation period up to the present time based on the operation history information 66.

In the next step S310, the control unit 60 determines the optimum cover margin corresponding to the operating time of the developer 14 (or the number of prints of the image forming apparatus 1) by referring to the table or according to a mathematical formula.

FIG. 13 is a diagram showing an example of the table referred to in step S310 of FIG. FIG. 13 shows the correspondence between the number of prints and the fog margin within the evaluation period from 3 hours before the present time to the present time. The control unit 60 determines the optimum fog margin corresponding to the number of prints within the evaluation period according to the table of FIG. The control unit 60 determines the optimum cover margin corresponding to the number of prints not shown in the table of FIG. 13 by interpolation.

For the evaluation period, an appropriate value is selected experimentally or by simulation so that the amount of fog toner is maintained in an appropriate range. Multiple evaluation periods may be set. For example, set three evaluation periods, such as 1 hour to the present, 2 hours to 1 hour before the present, and 3 hours to 2 hours before the present, and printing for each evaluation period. The fog margin may be determined based on the average value of the number of sheets. The average value of the number of printed sheets for each of the plurality of evaluation periods may be a weighted average that is more important as the average value of the newer evaluation periods.

With reference to FIG. 11 again, when it is necessary to change the cover margin as a result of the suitability determination of the cover margin in step S130 (YES in step S140), the control unit 60 advances the process to step S150.

In step S150, the control unit 60 has a high voltage so as to change the bias potential Va (or the current Ic flowing through the charging member 12a in the case of the corona discharge method) applied to the charging member 12a so as to have an optimum cover margin. Controls the power supply 16. Alternatively, the control unit 60 controls the high-voltage power supply 17 so as to change the bias potential Vb applied to the developing roller 14a so as to have an optimum fog margin. After that, the control unit 60 proceeds to the process in step S160.

On the other hand, if it is not necessary to change the cover margin as a result of the suitability determination of the cover margin in step S130 (NO in step S140), the control unit 60 proceeds to step S160 while maintaining the current cover margin.

In step S160, the control unit 60 causes the printer 20 to print an image on one sheet of paper. In the next step S170, the control unit 60 updates the operation history information 66 of the image forming apparatus 1 stored in the storage device 65.

In the next step S180, if there is another paper to be printed (YES in step S180), the control unit 60 returns the process to step S120 and repeats the above steps S120 to S170. On the other hand, if there is no other paper to print (NO in step S180), the control unit 60 ends the print job (step S190).

[Effect of Embodiment 1]
As described above, in the image forming apparatus 1 of the first embodiment, in order to always form an appropriate amount of a stationary layer between the surface of the photoconductor and the cleaning blade, the amount of fog toner produced is within an appropriate range. To control. Specifically, the control unit 60 increases the fog margin as the operating time of the developer or the number of printed sheets of paper within the evaluation period up to the present time increases. As a result, the amount of fog toner can be kept substantially constant. As a result, it is possible to form a good image without spot-like image noise called raindrop and streak-like image noise.

Hereinafter, the differences between this embodiment and JP-A-2006-301479 (Patent Document 1) and JP-A-2005-140917 (Patent Document 2) will be described.

FIG. 14 is a diagram showing the relationship between the average charge amount of toner in the developer and the integrated usage time of the developer. FIG. 14A shows the case of a non-magnetic one-component developer as disclosed in JP-A-2006-301479 (Patent Document 1) as a comparative example. FIG. 14B shows the case of a two-component developer as in the present embodiment.

With reference to FIG. 14 (A), in the case of a non-magnetic one-component developer, the average charge in the developer gradually decreases with the passage of time. Similarly, for a short time interval, the average charge in the processor gradually decreases. When the developer reaches the end of its life, the average amount of charge in the developer is considerably lower than that at the start of use.

With reference to FIG. 14 (B), in the case of a two-component developer as in the present embodiment, when the developer continues to operate, the toner and the carrier rub against each other, so that the average charge amount of the toner increases and the developer develops. If the device does not operate, the average toner charge will decrease. In the present embodiment, by adjusting the fog margin, the average charge amount can be repeatedly slightly increased or decreased at a certain short time interval, but the average charge amount can be kept substantially constant as a whole.

Further, in the image forming apparatus disclosed in Japanese Patent Application Laid-Open No. 2005-140917 (Patent Document 2), the image density is maintained by adjusting the rotation speed of the developing roller to prevent the occurrence of the fog phenomenon.

By using the method of adjusting the rotation speed of the developing roller, for example, if the rotation speed of the developer carrier is slowed down, the amount of fog toner generated by the centrifugal force can be suppressed. However, since the rotation speed is slow, the development nip time between the developing roller 14a and the photoconductor 11 becomes long, and the amount of back-charged fog toner electrically attracted to the photoconductor 11 increases. Therefore, it is difficult to control the amount of fog toner by the method of adjusting the rotation speed of the developing roller. In the image forming apparatus 1 of the present embodiment, since the fog toner amount is controlled only by the electric force without changing the fog toner generated by the centrifugal force, it is possible to control the fog toner amount with higher accuracy.

<Embodiment 2>
In addition to the operating time of the developer, the average coverage of the image printed on the paper, the in-flight humidity of the image forming apparatus, and the printing line speed (also referred to as the machine line speed) are also related to the change in the amount of fog toner. In the image forming apparatus 1 of the second embodiment, the fog margin is controlled based on the average coverage of these images, the in-flight humidity, and the printing line speed, in addition to the operating time (or the number of printed sheets) of the developing device.

Since the hardware configuration of the image forming apparatus 1 shown in FIGS. 1 to 3 and the basic control procedure shown in FIG. 11 are the same in the case of the second embodiment, the description will not be repeated.

[Procedure for determining the suitability of the cover margin]
FIG. 15 is a flowchart showing an example of a detailed procedure of step S130 of FIG. 11 in the image forming apparatus of the second embodiment. The following steps S400 to S430 may be executed in any order or may be executed in parallel.

In step S400, the control unit 60 calculates the operating time of the developing device 14 within the evaluation period up to the present time based on the operating history information 66. Instead of the operating time of the developing device 14, the amount associated with the operating time of the developing device 14 may be calculated. For example, the control unit 60 may calculate the number of prints of the image forming apparatus 1 within the evaluation period up to the present time.

In step S410, the control unit 60 acquires information on the average coverage of the image for each sheet of paper based on the original image data of the print job.

In step S420, the control unit 60 acquires the detection value of the humidity sensor 68 provided in the housing of the image forming apparatus 1.

In step S430, the control unit 60 acquires information on the print line speed based on the job conditions set in step S100 of FIG. The printing line speed is the transport distance of the paper per unit time when the image is transferred to the paper.

In the next step S440, the control unit 60 uses the information acquired in the above steps S400 to S430 to determine the operating time (or number of prints) of the developer, the average coverage, the in-machine temperature, and the print line speed within the determination period. Determine the optimum cover margin corresponding to. Hereinafter, the relationship between each parameter and the fog margin will be further described.

[Average coverage]
FIG. 16 is a diagram for explaining control of the amount of fog toner according to the number of prints during the day and the average coverage. FIG. 16A is a diagram showing the relationship between the amount of fog toner and the number of printed sheets within the day when the average coverage is 1% and 5%. FIG. 16B is a diagram showing an appropriate fog margin setting value according to the number of printed sheets within the day when the average coverage is 1% and 5%. In FIGS. 16A and 16B, the case where the average coverage is 1% is shown by a solid line, and the case where the average coverage is 5% is shown by a broken line.

In general, the lower the average coverage of an image, the lower the toner consumption in the developer. As a result, the number of times that a large amount of toner remaining in the developer and the carrier rub against each other increases, so that the average amount of charge of the toner in the developer increases. Therefore, under the condition that the operating frequency of the developing device (that is, the number of printed sheets within the day) is constant, the lower the average coverage, the larger the amount of fog toner. The threshold of the operating frequency of the developing device at which the amount of fog toner starts to increase is smaller as the average coverage is lower.

Specifically, as shown in FIG. 16A, when the average coverage is 5%, the fog toner amount increases when the number of printed sheets within the day exceeds about 4000, whereas the average coverage is 1. In the case of%, the amount of fog toner increases when the number of printed sheets within the day exceeds about 3400 sheets. Further, for the same number of prints within the day, the amount of fog toner is larger when the average coverage is 1% than when the average coverage is 5%.

Therefore, when the operating frequency of the developing device is the same, the control unit 60 increases the fog margin as the average coverage is lower. Further, the control unit 60 reduces the threshold value of the operating frequency of the developing device, which starts to increase the fog margin, as the average coverage is lower. As a result, the amount of fog toner can be kept within an appropriate range regardless of the difference in average coverage.

Specifically, as shown in FIG. 16B, for the same number of prints within the day, the fog margin is set to a larger value when the average coverage is 1% than when the average coverage is 5%. Will be done. Further, when the average coverage is 1%, the fog margin is increased even for a smaller number of daily prints as compared with the case where the average coverage is 5%.

[In-flight humidity]
FIG. 17 is a diagram for explaining control of the amount of fog toner according to the number of prints during the day and the humidity inside the machine. FIG. 17A is a diagram showing the relationship between the amount of fog toner and the number of printed sheets during the day when the humidity inside the machine is 15% and when the humidity is 65%. FIG. 17B is a diagram showing an appropriate fog margin setting value according to the number of prints during the day when the in-machine humidity is 15% and 65%. In FIGS. 17A and 17B, the case where the in-flight humidity is 15% is shown by a solid line, and the case where the in-flight humidity is 65% is shown by a broken line.

Generally, when the humidity inside the image is low, the amount of water in the developing device is reduced, so that it becomes difficult for the charge to escape from the charged toner in the developing device. As a result, the average charge amount of the toner in the developer becomes high. Therefore, under the condition that the operating frequency of the developing device (that is, the number of printed sheets during the day) is constant, the lower the humidity inside the machine, the larger the amount of fog toner. The threshold value of the operating frequency of the developing device at which the amount of fog toner starts to increase becomes smaller as the humidity inside the machine becomes lower.

Specifically, as shown in FIG. 17A, when the in-flight humidity is 65%, the amount of fog toner increases when the number of printed sheets in the day exceeds about 4000, whereas the in-flight humidity is 15. In the case of%, the amount of fog toner increases when the number of printed sheets within the day exceeds about 3400 sheets. Further, for the same number of prints within the day, the amount of fog toner is larger when the in-flight humidity is 15% than when the in-flight humidity is 65%.

Therefore, when the operation frequency within the evaluation period is the same, the control unit 60 increases the fog margin as the in-machine humidity is lower. Further, the control unit 60 reduces the threshold value of the operating frequency of the developing device, which starts to increase the fog margin, as the humidity in the machine becomes lower. As a result, the amount of fog toner can be kept within an appropriate range regardless of the difference in the humidity inside the machine.

Specifically, as shown in FIG. 17B, for the same number of prints within the day, the fog margin is set to a larger value when the in-flight humidity is 15% than when the in-flight humidity is 65%. Will be done. Further, when the in-flight humidity is 15%, the fog margin is increased even for a smaller number of daily prints as compared with the case where the in-flight humidity is 65%.

[Machine speed]
FIG. 18 is a diagram for explaining control of the amount of fog toner according to the number of sheets printed during the day and the machine linear speed. FIG. 18A is a diagram showing the relationship between the amount of fog toner and the number of printed sheets within the day when the machine line speed is 290 mm / s and 145 mm / s. FIG. 18B is a diagram showing an appropriate fog margin setting value according to the number of printed sheets within the day when the machine linear speed is 290 mm / s and 145 mm / s. In FIGS. 18A and 18B, the case where the machine line speed is 290 mm / s is shown by a solid line, and the case where the machine line speed is 145 mm / s is shown by a broken line.

Generally, as the machine linear speed of an image increases, the rotation speed of the developing roller increases. As a result, the speed at which the toner and the carrier are agitated in the developer also increases, so that the number of times the toner and the carrier rub against each other increases, and as a result, the average charge amount of the toner in the developer increases. Therefore, under the condition that the operating frequency of the developing device (that is, the number of printed sheets within the day) is constant, the larger the machine line speed, the larger the amount of fog toner. The threshold value of the operating frequency of the developing device at which the amount of fog toner starts to increase becomes smaller as the machine line speed increases.

Specifically, as shown in FIG. 18A, when the machine line speed is 145 mm / s, the fog toner amount increases when the number of daily prints exceeds about 4000, whereas the machine line increases. When the speed is 290 mm / s, the amount of fog toner increases when the number of printed sheets within the day exceeds about 3400. Further, for the same number of prints within the day, the amount of fog toner is larger when the machine line speed is 290 mm / s than when the machine line speed is 145 mm / s.

Therefore, when the operating frequency of the developing device is the same, the control unit 60 increases the fog margin as the machine line speed increases. Further, the control unit 60 reduces the threshold value of the operating frequency of the developing device, which starts to increase the fog margin, as the machine linear velocity increases. As a result, the amount of fog toner can be kept within an appropriate range regardless of the difference in machine linear speed.

Specifically, as shown in FIG. 18B, for the same number of prints within the day, the fog margin is larger when the machine line speed is 290 mm / s than when the machine line speed is 145 mm / s. Set to a large value. Further, when the machine line speed is 290 mm / s, the fog margin is increased even for a smaller number of daily prints as compared with the case where the machine line speed is 145 mm / s.

[Effect of Embodiment 2]
As described above, in the image forming apparatus 1 of the second embodiment, in addition to the operating frequency of the developing device (or the number of printed sheets within the evaluation period), the average coverage of the image, the humidity in the machine, and the printing line speed (both the machine line speed). The cover margin is changed according to (referred to as). As a result, the amount of fog toner can be kept within an appropriate range with higher accuracy, so that an appropriate amount of static layer can always be formed between the surface of the photoconductor and the cleaning blade. As a result, it is possible to form a good image without spot-like image noise called raindrop and streak-like image noise.

The embodiments disclosed this time should be considered to be exemplary and not restrictive in all respects. The scope of this application is indicated by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 image forming device, 10 image forming unit, 11 photoconductor (image carrier), 12 charger, 12a charging member, 13 exposure device, 14 developer, 14a developing roller (developer carrier), 15, 26 cleaner, 15a Cleaning blade (cleaning member), 16,17 High-pressure power supply, 20 printer, 21 Intermediate transfer belt, 22 Primary transfer roller, 25 Secondary transfer roller, 30 Paper tray, 31 Paper roller, 33 Resist roller, 35 Fixation Equipment, 35a fixing roller, 38 discharge roller, 60 control unit, 64 operation panel, 65 storage device, 66 operation history information, 67 temperature sensor, 68 humidity sensor, 70 high charge toner, 71 low charge toner, 72 carrier, Va, Vb bias potential, Vs charging potential.

Claims (10)

With the image carrier,
A charging member that charges the surface of the image carrier, and
An exposure apparatus that forms an electrostatic latent image by exposing the surface of the image carrier,
A developer that includes a developer carrier that carries a developer containing toner and carriers, and develops the electrostatic latent image on the surface of the image carrier with toner supplied from the developer carrier.
A cleaning member that comes into contact with the surface of the image carrier to remove toner, and
The image by the charging member so that an amount of fog toner within a predetermined range is supplied to the image carrier according to the operating frequency of the developing device or the amount related to the operating frequency of the developing device. An image forming apparatus comprising a control unit for adjusting at least one of a charging potential on the surface of a carrier and a bias potential of the developer carrier. The image forming apparatus according to claim 1, wherein the amount related to the operating frequency of the developer is the number of prints within the evaluation period up to the present time or the integrated rotation speed of the developer carrier within the evaluation period. The control unit increases the potential difference between the charging potential of the image carrier and the bias potential of the developer carrier as the evaluation amount, which is an amount related to the operating frequency of the developing device or the operating frequency of the developing device, increases. The image forming apparatus according to claim 1 or 2, which increases the amount of operation which is an absolute value of. The image forming apparatus according to claim 3, wherein the control unit does not change the operation amount until the evaluation amount reaches a threshold value, and increases the operation amount when the evaluation amount exceeds the threshold value. The control unit changes the threshold value and the operation amount according to at least one of the average coverage of the image printed by the image forming apparatus, the in-flight humidity of the image forming apparatus, or the printing linear velocity. The image forming apparatus according to 4. The image forming apparatus according to claim 5, wherein the control unit reduces the threshold value and increases the operation amount as the average coverage decreases. The image forming apparatus according to claim 5 or 6, wherein the control unit reduces the threshold value and increases the operation amount as the in-machine humidity decreases. The image forming apparatus according to any one of claims 5 to 7, wherein the control unit reduces the threshold value and increases the operation amount as the printing line speed increases. It is a control method of the image forming apparatus.
The image forming apparatus is
With the image carrier,
A charging member that charges the surface of the image carrier, and
An exposure apparatus that forms an electrostatic latent image by exposing the surface of the image carrier,
A developer that includes a developer carrier that carries a developer containing toner and carriers, and develops the electrostatic latent image on the surface of the image carrier with toner supplied from the developer carrier.
A cleaning member that comes into contact with the surface of the image carrier and removes toner is provided.
The control method is
A step in which the control unit stores the operation status of the image forming apparatus over time in the storage device, and
A step in which the control unit calculates an amount related to the operating frequency of the developing device or the operating frequency of the developing device as an evaluation amount based on the operating status over time.
The charging potential of the surface of the image carrier by the charging member or the charging potential of the image carrier so that the control unit supplies the image carrier with an amount of the fog toner within a predetermined range according to the evaluation amount. A method of controlling an image forming apparatus comprising the step of adjusting at least one of the bias potentials of the developer carrier. It is a control program of the image forming apparatus.
The image forming apparatus is
With the image carrier,
A charging member that charges the surface of the image carrier, and
An exposure apparatus that forms an electrostatic latent image by exposing the surface of the image carrier,
A developer that includes a developer carrier that carries a developer containing toner and carriers, and develops the electrostatic latent image on the surface of the image carrier with toner supplied from the developer carrier.
The image carrier is provided with a cleaning member that comes into contact with the surface to remove toner.
The control program is applied to the computer.
A step of storing the operation status of the image forming apparatus over time in the storage device,
A step of calculating an amount related to the operating frequency of the developing device or the operating frequency of the developing device as an evaluation amount based on the operating status over time, and
The charging potential on the surface of the image carrier by the charging member or the developer carrier so that the fog toner is supplied to the image carrier in an amount within a predetermined range according to the evaluation amount. A control program for an image forming apparatus that performs a step of adjusting at least one of the bias potentials.

Images