JP2008309848A - Detecting method of fog in image forming apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically detect the presence or absence of fog with ease without wastefully consuming a recording medium such as paper. <P>SOLUTION: While fog toner images are absent on an intermediate transfer belt 18, the density of the surface of the belt 18 is detected by a density sensor 20. Fog toner images are formed on a photoreceptor 11 and the transfer of these images to the intermediate transfer belt 18 is carried out over more than one time, thereby superimposing the fog toner images onto the intermediate transfer belt 18. The density of the fog toner images formed by the superimposition is detected by the density sensor 20. The density of the detected fog toner images and the density of the surface of the intermediate transfer belt 18 when fog toner images are absent are compared with each other. If a difference between them is equal to a specified value or greater, the fog is determined to be present. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fog detection method and an image forming apparatus in an image forming apparatus provided with an electrophotographic image forming unit.

  In an image forming apparatus using an electrophotographic technique, defective charged toner having a reduced charge amount may increase in the developing device due to various factors such as environmental changes or changes with time. As a result, the poorly charged toner adheres to the white background (background) of the image, and so-called fogging occurs.

  Such fog may also occur due to factors such as deterioration in charging performance due to durability deterioration of the photosensitive member and charger, and the surface potential of the photosensitive member not reaching a specified potential.

  The fog is transferred to the recording paper (paper), and is recognized by the user as a stain on the background image. When the fog occurs, not only the image quality is deteriorated but also the inside and outside of the apparatus of the image forming apparatus are contaminated, and the consumption of toner increases, so that there is a possibility that the specified number of sheets cannot be printed.

  By the way, since the amount of toner in the fog itself is very small, it is difficult to detect the presence or absence of fog with an existing optical detector, and it is not easy to detect fog and perform automatic control to eliminate fog. . Therefore, in the market, there is a problem that a user or a serviceman must visually check the fogged image and adjust it manually.

  Conventionally, there are those described in Patent Documents 1 and 2 as prior art for detecting fog. That is, Patent Document 1 discloses a method for visualizing a fogged image on a recording medium by controlling a developing bias and a transfer bias. Also, after forming a fogged image superimposed on the intermediate transfer member a plurality of times, the fogged image is transferred to a recording medium, and the fogging curve plotted with the fog density on the recording medium and the number of fogging images becomes close to the initial fogging curve. A method of setting a combination in which the surface potential and the developing bias are changed is disclosed.

Patent Document 2 discloses a method of detecting fog with an optical detector when the development bias potential is fixed and the output of the charging grid potential is changed stepwise.
JP 2005-62858 A JP-A-11-160930

  However, in the method disclosed in Patent Document 1, it is necessary to form a fog by changing the charging potential and the developing bias in order to obtain a fogging curve. The fog image forming process is required. In addition, since the fog density is detected on the recording medium, a new device for detecting the fog density is required, and the recording medium such as paper is wasted only for the fog detection. . Furthermore, there is a problem that the user and the serviceman are bothered to detect the fog density.

  The method disclosed in Patent Document 2 is effective when the amount of fog toner is large, but there is a problem that detection is difficult when the amount of fog toner is small.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to easily and automatically detect the presence or absence of fog without wastefully consuming a recording medium such as paper.

  In the method according to the present invention, an electrostatic latent image formed on a photoconductor by exposure is developed by a developing unit, and the obtained toner image is transferred to an image carrier by a transfer unit and further transferred to a recording medium. A method for detecting the presence or absence of fog in a configured image forming apparatus, wherein the density of a surface of the image carrier is detected by a density sensor in the absence of a fog toner image on the image carrier, A fog toner image formed by overlapping a plurality of fog toner images on the image carrier by forming a fog toner image and transferring the image to the image carrier a plurality of times. The density sensor detects the density of the fog toner image and compares the density of the detected fog toner image with the density of the surface of the image carrier in the absence of the fog toner image. It determines that fog is present if the value or more.

  At that time, when the surface of the image carrier is cleaned by a toner cleaning unit so that there is no fog toner image on the image carrier, and a plurality of fog toner images are overlapped on the image carrier, The cleaning by the toner cleaning means may not be performed.

  Further, when it is determined that fog is present, the absolute value of the voltage of the charging means for charging the photosensitive member is changed so as to increase, and then the method according to claim 2 is executed again. When the determination is made, a value based on the voltage of the charging unit at that time may be set as the voltage value of the charging unit in normal image formation.

  The voltage of the charging unit may be changed in a stepwise manner until the voltage reaches a limit value determined by using values relating to an environmental state of the image forming apparatus and an operation time of the photoconductor as parameters. preferable.

  According to the present invention, the presence / absence of fog can be easily detected without wastefully consuming a recording medium such as paper.

  FIG. 1 is a front sectional view showing a schematic configuration of an image forming apparatus 1 according to an embodiment of the present invention, FIG. 2 is a diagram showing an imaging unit U around a development, which is a part of the image forming apparatus 1, and FIG. FIG. 4 is a diagram showing the relationship between the surface potential of the photoconductor 11 and the image, FIG. 4 is a diagram showing the relationship between the toner adhesion amount on the intermediate transfer belt 18 and the output of the density sensor 20, and FIG. 5 is the fog detection in the image forming apparatus 1. 6 is a block diagram showing the configuration of the control device KS, FIG. 6 is a diagram showing a setting state of each part in the fog detection control, FIG. 7 is a diagram showing a change in toner density on the intermediate transfer belt 18 in the fog detection control, and FIG. It is a figure which shows the example of the upper limit table GV which stored the data of the upper limit of the change of the output voltage Vg of the apparatus 12.

  In FIG. 1, an image forming apparatus 1 has a tandem transfer unit, and sequentially superimposes four color toners of yellow (Y), magenta (M), cyan (C), and black (K). Is formed. The image forming apparatus 1 develops the electrostatic latent image formed on the photoconductor 11 by exposure by the developing device 13, and the obtained toner image is transferred to the intermediate transfer belt 18 as an image carrier by the primary transfer roller 16. It is configured to transfer and further transfer to a recording sheet.

  That is, in the image forming apparatus 1, four color imaging units UY, UM, UC, UK of Y, M, C, and K are arranged in a tandem arrangement, and each color formed by these imaging units U is arranged. A toner image (toner image) is superimposed on the intermediate transfer belt 18 to be transferred and synthesized.

  When the toner images of the respective imaging units UY, UM, UC, UK are transferred to the intermediate transfer belt 18, one corresponding primary transfer roller 16Y, 16M, 16C, 16K is pressed against the intermediate transfer belt 18, and the others The primary transfer roller 16 is separated.

  The “primary transfer roller 16” indicates all or part of the “primary transfer rollers 16Y, 16M, 16C, 16K”. The same applies to other elements.

  As shown in FIG. 2, each imaging unit U is configured by arranging a charging device 12, a developing device 13, a cleaner 15, and the like around a drum-shaped photoconductor 11. The surface of the photoconductor 11 is charged to a predetermined voltage (charging potential) V0 by the charging device 12, and an electrostatic latent image is formed by exposure from the exposure unit. The electrostatic latent image is supplied with toner charged from the developing roller 13a to the potential gap ΔV between the electrostatic latent image potential and the developing bias voltage Vdc by the developing roller 13a to which the developing bias voltage Vdc is applied. The toner image is formed by developing the image.

  The toner image visualized on the surface of the photoreceptor 11 is primarily transferred to the intermediate transfer belt 18 by the primary transfer roller 16. The toner remaining on the photoreceptor 11 is scraped off by the cleaner 15. The toner image on the intermediate transfer belt 18 is secondarily transferred onto the recording paper conveyed from the paper supply unit 22 by the secondary transfer roller 23. The recording paper is fixed by the fixing unit 24 and discharged onto the paper discharge tray 25 as an electrophotographic image.

  The toner (transfer residual toner) that is not completely transferred in the secondary transfer and remains on the intermediate transfer belt 18 is removed and collected by the cleaning unit 19. That is, the surface of the intermediate transfer belt 18 is cleaned by the cleaning unit 19 after the secondary transfer. In this embodiment, the cleaning unit 19 is a cleaning blade type that is movable between the pressure contact and the separation with respect to the intermediate transfer belt 18. However, in addition to this, the intermediate transfer belt 18 is used. It is possible to use various types or mechanisms, such as a brush type in which the voltage applied to is controlled on and off.

  Incidentally, in order to set the toner adhesion amount on the surface of the photoconductor 11 to a target amount, the charging potential V0, the exposure amount, and the development bias voltage Vdc of the photoconductor 11 execute an operation mode called stabilization control. It is adjusted by doing. The stabilization control is performed when the output of the temperature / humidity detector (environmental sensor) 21 inside or outside the image forming apparatus 1 changes from a specified value, when the print counter CT (see FIG. 5) reaches a specified value, or This is activated when a change occurs in the image forming apparatus 1, such as when the operating time of the photoconductor 11 reaches a predetermined time, or when the mounting of a new imaging unit U is detected. The value of the print counter CT is a value related to the operation time.

  The image forming apparatus 1 is provided with an optical density sensor (also referred to as an adhesion amount sensor or IDC sensor) 20 in order to detect the toner concentration (toner adhesion amount) on the surface of the intermediate transfer belt 18. The output of the sensor 20 is used for stabilization control. The output of the density sensor 20 is also used in fog detection control described later.

  The control device 101 controls the entire image forming apparatus 1 by performing stabilization control, fog detection control, other control, image processing, or communication with an external device such as a network. The control device 101 includes a CPU, a DSP, a ROM, a RAM, and other peripheral elements. Image formation is performed by the CPU executing an appropriate program, by hardware circuit elements, or a combination thereof. Various functions in the device 1 are realized.

  In the present exemplary embodiment, an example based on a two-component development tandem configuration is described as the image forming apparatus 1, but the configuration is not limited thereto. For example, a density sensor for detecting the toner adhesion amount of a toner image formed on various types of image carriers other than the photoconductor 11 or the intermediate transfer belt 18 and cleaning of residual toner on the image carrier. As long as a cleaning unit that can be switched on and off is provided, another developing method such as a one-component developing method or a liquid developing method may be used, or a multi-transfer method or a direct transfer method may be used.

  Next, an image forming mechanism on the photoconductor 11 and a fog generation mechanism will be described. In the present embodiment, it is assumed that the photoconductor 11 is an organic photoconductor that is negatively charged.

  Due to the output voltage Vg of the charging device 12, the surface of the photoreceptor 11 is charged to the charging potential V0. When a scorotron is used as the charging device 12, the output voltage Vg is substantially equal to the voltage applied to the grid.

  In FIG. 3, the non-exposed portion (non-image portion) on the surface of the photoconductor 11 has the same voltage V0 as the charging potential V0, and the exposed portion (image portion) decreases to the voltage Vi. The image background portion on the surface of the photoconductor 11 is slightly reduced in voltage from the non-exposed portion to the voltage V0 ′ by the amount of exposure bias light.

  In this state, by applying a negative developing bias voltage Vdc to the developing roller 13a, the negatively charged toner has a total toner charge amount corresponding to the potential of the potential gap ΔV (= | Vdc | − | Vi |). Minutes adhere to the surface of the photoreceptor 11.

  Further, the fog is regulated by the fog margin potential Vm (= | V0 ′ | − | Vdc |). When Vm is increased, the fog amount is decreased, and when Vm is decreased, the fog amount is increased. If the fog margin potential Vm is to be increased, (1) the charging potential V0 is increased, so that the carrier adhesion to the photosensitive member 11 occurs in the two-component development method, and (2) the potential gap ΔV is decreased. There arises a problem that a prescribed toner adhesion amount may not be obtained. Usually, the fog margin potential Vm is determined by a value at which the presence / absence of fog and these two problems (1) and (2) are optimal.

  Further, if the fog margin potential Vm is constant and the toner charge amount increases, the fog amount decreases. If the toner charge amount decreases, the fog amount increases. That is, fogging occurs when the charging potential V0 is not charged to the specified potential due to durability deterioration of the charging device 12 or the photoconductor 11, or when the toner charge amount is decreased due to durability deterioration.

However, by performing the fog detection control described below, it is possible to suppress the fog that occurs when the charging device 12 or the photoreceptor 11 is deteriorated in durability or when the toner charge amount is reduced.
[Fog detection control]
In this embodiment, the fog detection control is performed by detecting the density of the surface of the intermediate transfer belt 18 with the density sensor 20 in a state where there is no fog toner image on the intermediate transfer belt 18 and forming a fog toner image on the photoconductor 11. The transfer operation to the intermediate transfer belt 18 is performed a plurality of times so that the plurality of fog toner images overlap on the intermediate transfer belt 18, and the density of the fog toner image formed on the intermediate transfer belt 18 is determined by the density sensor 20. The detected density of the fog toner image is compared with the density of the surface of the intermediate transfer belt 18 in a state where there is no fog toner image, and it is determined that there is fog when the difference between them is equal to or greater than a specified value. To do.

  At this time, when the surface of the intermediate transfer belt 18 is cleaned by the cleaning unit 19 so that there is no fog toner image on the intermediate transfer belt 18, and a plurality of fog toner images are overlapped on the intermediate transfer belt 18, The cleaning unit 19 is not cleaned.

  When it is determined that fog is present, the absolute value of the voltage of the charging device 12 that charges the photosensitive member 11 is changed so as to increase, and then the above operation is executed again. When it is determined that there is no fog, a value based on the voltage of the charging device 12 at that time is set as the voltage value of the charging device 12 in normal image formation.

  The voltage of the charging device 12 is changed in a stepwise manner until the voltage reaches a limit value determined by using the values relating to the environmental state of the image forming apparatus 1 and the operation time of the photoconductor 11 as parameters.

  That is, in FIG. 5, the fog detection control device KS includes an adhesion amount detection unit 111, a control determination unit 112, a charging potential control unit 113, and the like.

  The adhesion amount detection unit 111 acquires the reference concentration Sbs and the fog detection value Sn based on the output value from the concentration sensor 20.

  The control determination unit 112 controls the imaging unit U, the primary transfer roller 16, the intermediate transfer belt 18, the cleaning unit 19, and the like so that there is no fog toner image on the surface of the intermediate transfer belt 18, and the intermediate transfer Control necessary for fog detection control is performed such that the fog toner image overlaps the surface of the belt 18 and the value of the output voltage Vg of the charging device 12 in the fog detection control is determined. Further, the control determination unit 112 compares the reference concentration Sbs and the fog detection value Sn to determine the presence or absence of fog.

  The control determination unit 112 is provided with an upper limit value table GV. When determining the value of the output voltage Vg of the charging device 12, the temperature and humidity output from the temperature / humidity detector 21 and the print counter CT are used. The upper limit value (limit value) of the change in the output voltage Vg is read from the upper limit value table GV using information such as the count value and the operation time of the photoconductor 11 from the timer TM as parameters, so that the upper limit value is not exceeded. Take control.

  The charging potential control unit 113 outputs a charging potential V0 to the charging device 12 of the imaging unit U.

  With such a configuration, the fog detection control device KS first detects the surface of the intermediate transfer belt 18 by the cleaning unit 19, and detects the toner concentration on the surface of the cleaned intermediate transfer belt 18 by the density sensor 20. The second step of acquiring the reference density Sbs, the third step of setting the output voltage Vg of the charging device 12 to a predetermined value, and forming a fog toner image on the photoreceptor 11 and transferring it to the intermediate transfer belt 18 A fourth step in which a plurality of fog toner images are overlapped and accumulated on the intermediate transfer belt 18, and the density sensor 20 detects the density of the fog toner image formed on the intermediate transfer belt 18 in an overlapping manner. Then, the fifth step of obtaining the fog detection value Sn which is the fog density, the fog detection value Sn and the reference density Sbs are compared. In the sixth step, when the difference between the fog detection value Sn and the reference concentration Sbs is equal to or larger than a specified value (allowable value) ε, the absolute value of the output voltage Vg of the charging device 12 is changed to be larger, If the difference between the fog detection value Sn and the reference concentration Sbs is equal to or less than the specified value ε, the fog detection is terminated by determining that there is no fog. The eighth step is executed.

As described above, the fog detection control (fogging detection control mode) is performed by direct instruction from the user or service person to the image forming apparatus 1, an instruction by a service center connected by a network protocol, or when an installation environment of the image forming apparatus 1 is changed. Triggered when one of the specified number of prints has elapsed. The fog detection control is performed for all colors Y, M, C, and K, and is not limited to a specific system speed. This will be described in more detail below.
[Acquisition of Reference Concentration Sbs]
The density sensor 20 is a reflection type density sensor, and as shown in FIG. 4, the amount of reflected light decreases and the output value decreases as the toner adhesion amount increases. That is, a decrease in the output value of the density sensor 20 indicates an increase in the toner adhesion amount. In the fog detection control, the output value of the density sensor 20 is used for determination of fog detection, but instead of the output value, a converted toner adhesion amount as shown in FIG. 4 may be used.

  First, in the TB cycle of FIG. 7, the density (reference density) Sbs of the surface (base surface) to which the toner of the intermediate transfer belt 18 is not attached is acquired. That is, in a state where the surface of the intermediate transfer belt 18 is cleaned, the output value of the density sensor 20 is acquired as the reference density Sbs and stored in the memory.

  By acquiring the reference density Sbs, whether the change in the output value of the density sensor 20 during fog detection control is due to the running of the intermediate transfer belt 18, or a slight fog is detected with respect to the base surface. It is possible to accurately discriminate whether it is due to the fact. Note that the amount of change (increase) from the reference concentration Sbs corresponds to the fog amount.

  Upon detection of the base surface (acquisition of the reference density Sbs), as shown in FIG. 6, the cleaning unit 19 is brought into pressure contact with the intermediate transfer belt 18, and the primary transfer roller 16 and the secondary transfer roller 23 are separated from each other. To do. In this state, the intermediate transfer belt 18 is run and the output value of the density sensor 20 is acquired.

Note that the primary transfer roller 16 and the secondary transfer roller 23 do not necessarily need to be separated from each other as long as the base surface is not contaminated. For example, the transfer current, the charging potential, or the developing bias potential may not be driven or a reverse voltage may be applied. The acquisition of the reference concentration Sbs is not necessarily performed every time the fog detection control is activated, and the reference concentration Sbs acquired before the activation of the fog detection control, the reference concentration Sbs acquired in the previous fog detection control, or the like is used. May be.
[Acquisition of fog detection value Sn]
Next, in order to perform the fog detection, as shown in FIG. 6, the cleaning unit 19 is set in the separated state, and the primary transfer roller 16 for the target color for fog detection is set in the pressure contact state. In this state, the developing bias voltage Vdc at the time of normal image formation and the output voltage Vg of the charging device 12 are set to be used, and the image formation of the imaging unit U is performed with the exposure light amount of 0 gradation data similar to the image background portion. The toner image (fog toner image) is transferred to the intermediate transfer belt 18. Since the amount of fog is small, the image formation in the imaging unit U and the transfer to the intermediate transfer belt 18 are repeated a plurality of times in each cycle of T1 to TN in FIG. Overlap (N times). Then, the density of the fog toner image superimposed on the intermediate transfer belt 18 is detected by the density sensor 20, and the output value at that time is set as the fog detection value Sn.

In other words, the amount of fogging at the first time is ΔK1, which is very small and cannot be detected by the concentration sensor 20, but the amount of fogging increases as the second and third times are repeated, and the detection by the concentration sensor 20 occurs. Is possible.
[Fog judgment]
The reference density Sbs and the fog detection value Sn acquired as described above are compared to determine the presence or absence of fog. A predetermined value ε is used to determine whether fog is present. If the difference between the reference concentration Sbs and the fog detection value Sn is equal to or less than the specified value ε, that is,
Sbs-Sn <ε
If so, it is determined that there is no fog. If it is determined that there is no fog, the fog detection control ends and the normal image forming mode is restored. At this time, the output voltage Vg used for the fog detection control may be used as it is as the output voltage Vg in the image forming mode, or a voltage slightly higher than that may be used as the output voltage Vg in the image forming mode. Good. In the fog detection control, when the output voltage Vg in the image forming mode is not changed, the output voltage Vg used in the image forming mode may be used as it is.

On the contrary, if the difference between the reference concentration Sbs and the fog detection value Sn is equal to or greater than the specified value ε, that is,
Sbs-Sn> ε
If so, it is determined that there is fog. If it is determined that there is fogging, the output voltage Vg is changed by performing charging potential control described later.

  The fog detection and fog determination may be performed every time the fog toner image is superimposed on the intermediate transfer belt 18 N times. In this case, if it is determined that fogging has occurred before reaching N times, the formation and transfer of the fogging toner image thereafter are immediately interrupted, and charging potential control described later may be performed.

In the fog determination, if the difference between the reference density Sbs and the fog detection value Sn is equal to the specified value ε, the fog may or may not be fogged. Note that the prescribed value ε may be set to a value that does not reveal fog on the recording paper. Actually, the value varies depending on the number of times the fog toner image is superimposed.
[Charging potential control]
When it is determined that fog is present, the offset output potential Vg ′ is added to the output voltage Vg set for fog detection. That is, the output voltage Vg for the next fog detection is changed to | Vg | + | Vg ′ |.

  The value of the offset output potential Vg ′ is set to “10” in this embodiment, and the fog determination is performed in 10V steps. However, other appropriate voltage values can be used as the offset output potential Vg ′.

  In the repetition of the operation described above, the upper limit of the total value of the offset output potential Vg ′, that is, the upper limit of the change in the output voltage Vg is determined. The upper limit is recorded in the upper limit value table GV as described above.

  In the upper limit value table GV shown in FIG. 8, for example, when the absolute humidity is “10” and the print counter CT is “100”, the upper limit value of the change in the output voltage Vg is “40”. Therefore, when the value of the offset output potential Vg ′ is “10”, fog detection is performed four times at the maximum. When the absolute humidity or the count value is not recorded in the upper limit value table GV, the upper limit value may be obtained by interpolation using the value in the vicinity thereof, or the upper limit value in the vicinity may be used.

  In this way, the output voltage Vg is changed stepwise up to an upper limit value corresponding to the environmental state such as temperature or humidity, the operation time of the photoconductor 11, etc., so that the output voltage Vg corresponds to the current state of the image forming apparatus 1. It is possible to easily find and adjust the optimum output voltage Vg without fog.

The fog detection value Sn immediately before changing the output voltage Vg can be used as the reference density Sbs without performing the operation for obtaining the reference density Sbs as described above. From the point of accuracy, it is desirable to detect again by pressing the cleaning unit 19.
[Charging potential setting]
The value of the offset output potential Vg ′ determined in fog detection is added to the output voltage Vg set in normal image formation, that is, | Vg | = | Vg | + | Vg ′ | An output voltage Vg for forming is set.

  If it is determined that there is fogging even if the upper limit value is set by the upper limit table GV, if (Sbs−Sn) tends to decrease as the output voltage Vg approaches the upper limit value, Set the upper limit. If (Sbs−Sn) is not changed, the output voltage Vg immediately before the fog detection control is not changed, and a fog warning is displayed on the display unit of the image forming apparatus 1 or fog occurs. The imaging unit U is instructed to be replaced.

  Next, fog detection control will be described based on a flowchart.

  FIG. 9 is a flowchart showing an example of a procedure of fog detection control in the fog detection control device KS.

  In FIG. 9, the cleaning unit 19 is brought into a pressure contact state, and the primary transfer roller 16 and the secondary transfer roller 23 are brought into a separated state (# 11). As a result, the fogging toner image is not present on the base surface of the intermediate transfer belt 18, and the reference density Sbs is acquired by the density sensor 20 (# 12). The cleaning unit 19 is separated (# 13), the development bias voltage Vdc and the output voltage Vg of the target color are set (# 14) to detect fog, and the primary transfer roller 16 of the target color for fog detection is pressed. (# 15).

  A fog toner image is formed on the photoconductor 11 and transferred N times on the intermediate transfer belt 18 (# 16), and the fog detection value Sn is obtained by the density sensor 20 (# 17). The presence / absence of fog is determined based on whether or not the difference between the reference concentration Sbs and the fog detection value Sn exceeds a specified value ε (# 18).

  When it is determined that there is fogging, a value obtained by adding the offset output potential Vg ′ to the output voltage Vg is set as a new output voltage Vg (# 20), and fogging detection in step # 11 is executed.

  If it is determined that there is no fog, the output voltage Vg at that time is set to the output voltage Vg for normal image formation (# 19).

  According to the embodiment described above, the reference density Sbs and the fog detection value Sn are obtained using the existing density sensor 20 by overlapping the fog on the intermediate transfer belt 18 a plurality of times, and the charging potential of the photoconductor 11 is obtained. By controlling V0, it is possible to form an image without fog. In addition, since the fog detection control is easily and automatically performed in the image forming apparatus 1, it is possible to reduce the consumption of recording paper, which has conventionally been necessary for checking the adjustment time and the degree of fogging performed by a service person. The cost can be reduced.

  In the above-described embodiment, the fog detection control device KS, the control device 101, or the entire or each part of the image forming apparatus 1, the structure, the shape, the number, the content or order of processing or operation, various voltage values, the upper limit The contents of the value table GV can be appropriately changed in accordance with the spirit of the present invention.

1 is a front sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the imaging unit of an image forming apparatus. It is a figure which shows the relationship between the surface potential of a photoconductor and an image. It is a figure which shows the relationship between a toner density | concentration and the output of a density sensor. It is a block diagram which shows the structure of a fog detection control apparatus. It is a figure which shows the setting state of each part in fog detection control. FIG. 6 is a diagram illustrating a change in toner density on an intermediate transfer belt. It is a figure which shows the example of an upper limit table. It is a flowchart which shows the example of the procedure of fog detection control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Photoconductor 12 Charging apparatus (charging means)
13 Developing device (Developing means)
16 Primary transfer roller (transfer means)
18 Intermediate transfer belt (image carrier)
19 Cleaning unit (toner cleaning means)
20 Concentration sensor 101 Control device 111 Adhesion amount detection unit (means for acquiring fog density)
112 Control determination unit (control means, determination means, voltage change means)
113 Charging Potential Control Unit KS Fog Detection Control Device Sn Fog Detection Value Sbs Reference Concentration GV Upper Limit Table

Claims (8)

In an image forming apparatus configured to develop an electrostatic latent image formed on a photosensitive member by exposure by a developing unit, and transfer the obtained toner image to an image carrier by a transfer unit and further transfer the toner image to a recording medium. A method for detecting the presence or absence of fog,
The density of the surface of the image carrier is detected by a density sensor in a state where there is no fog toner image on the image carrier,
An operation of forming a fog toner image on the photoreceptor and transferring it to the image carrier is performed a plurality of times so that the plurality of fog toner images overlap on the image carrier.
The density sensor detects the density of the fog toner image formed on the image carrier in an overlapping manner,
Comparing the density of the detected fog toner image with the density of the surface of the image carrier in the absence of the fog toner image, and determining that there is fog when the difference between them is a specified value or more;
A method for detecting fog in an image forming apparatus. By cleaning the surface of the image carrier with a toner cleaning means, the image carrier is in a state where there is no fog toner image,
When the plurality of fog toner images are overlapped on the image carrier, the cleaning by the toner cleaning unit is not performed.
The method for detecting fog in the image forming apparatus according to claim 1. When it is determined that fog is present, the absolute value of the voltage of the charging unit that charges the photosensitive member is changed to be large, and then the method according to claim 2 is performed again,
When it is determined that there is no fogging, a value based on the voltage of the charging unit at that time is set as a voltage value of the charging unit in normal image formation.
The method for detecting fog in the image forming apparatus according to claim 2. The voltage of the charging unit is changed in a stepwise manner until the voltage reaches a limit value determined by using values relating to the environmental state of the image forming apparatus and the operation time of the photoconductor as parameters.
The method for detecting fog in the image forming apparatus according to claim 3. An image forming apparatus configured to develop an electrostatic latent image formed on a photosensitive member by exposure by a developing unit, and transfer the obtained toner image to an image carrier by a transferring unit and further to a recording medium. There,
A density sensor for detecting the density of the surface of the image carrier;
Means for detecting a density in a state where there is no fog toner image on the image carrier by the density sensor to obtain a reference density;
Means for performing a plurality of operations of forming a fog toner image on the photosensitive member and transferring the image to the image carrier, and controlling the plurality of fog toner images to overlap on the image carrier;
Means for detecting a density of a fog toner image formed on the image carrier in an overlapping manner by the density sensor to obtain a fog density;
Means for comparing the fog density with the reference density, and determining that fog is present when a difference between the fog density and the reference density is equal to or greater than a specified value;
An image forming apparatus comprising: A voltage changing unit that changes the absolute value of the voltage of the charging unit that charges the photosensitive member when it is determined that fog is present;
The image forming apparatus according to claim 5. The voltage changing unit performs stepwise until the voltage reaches a limit value determined by using a value related to an environmental state of the image forming apparatus and an operation time of the photoconductor as parameters.
The image forming apparatus according to claim 6. An image forming apparatus configured to develop an electrostatic latent image formed on a photosensitive member by exposure by a developing unit, and transfer the obtained toner image to an image carrier by a transferring unit and further to a recording medium. There,
Charging means for charging the photoreceptor;
Toner cleaning means for removing toner adhering to the surface of the image carrier;
A density sensor for detecting the density of the surface of the image carrier;
A fog detection control device for detection of fog on the photoreceptor;
With
The fog detection control device includes:
A first step of cleaning the surface of the image carrier by the toner cleaning means;
A second step of obtaining a reference density by detecting the density of toner on the surface of the cleaned image carrier with the density sensor;
A third step of setting the voltage of the charging means to a predetermined value;
A fourth step in which a fog toner image is formed on the photosensitive member and transferred to the image carrier a plurality of times, and a plurality of fog toner images are superimposed on the image carrier;
A fifth step of acquiring a fog density by detecting a density of a fog toner image formed on the image bearing member by the density sensor;
A sixth step of comparing the fog density with the reference density;
When the difference between the fog density and the reference density is equal to or greater than a specified value, a change is made so that the absolute value of the voltage of the charging means becomes larger, and the seventh step is repeated from the first step to the sixth step. And the steps
When the difference between the fog density and the reference density is equal to or less than a specified value, an eighth step of determining that there is no fog and ending fog detection is configured to be executed.
An image forming apparatus.

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