JP2008058740A - Image forming apparatus and exposure correcting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of holding effective developing potential within a suitable range and reducing the number of times of forming density patch even when its environment is changed and even when it is used over a long term. <P>SOLUTION: An applied voltage decision means 14 decides the value of voltage to be applied to an exposure means 4 from a result obtained by detecting temperature and humidity near a photoreceptor 2 and a data table input in a storage means 13, and an applied voltage correction means 15 corrects the value of the voltage to be applied so that the effective developing potential may be a value within a predetermined range. An updating means 16 updates the data table stored in the storage means 13 and showing relation between the value of voltage to be applied to the exposure means 4 and the temperature and humidity near the photoreceptor 2 to a new data table where relation between the value of voltage to be applied corrected by the applied voltage correction means 15 and the result of detection by a temperature and humidity detection means is set as referencee. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an exposure amount correction method.

  An image forming apparatus using an electrophotographic method includes an electrophotographic photosensitive member (hereinafter sometimes simply referred to as a “photosensitive member”), a charging unit, an exposing unit, a developing unit, a transfer unit, a fixing unit, and a cleaning unit disposed around the electrophotographic photosensitive unit. Means and static elimination means. The charging unit charges the surface of the photoreceptor. The exposure unit irradiates the charged photosensitive member surface with signal light to form an electrostatic latent image corresponding to the image information. The developing means supplies toner in the developer to the electrostatic latent image formed on the surface of the photoreceptor to form a toner image. The transfer unit transfers the toner image formed on the surface of the photoreceptor to a recording medium. The fixing unit fixes the transferred toner image on the recording medium. The cleaning unit cleans the surface of the photoreceptor after the toner image is transferred by a cleaning member such as a cleaning blade. The neutralizing unit neutralizes the photoconductor after the toner image is transferred. With such an image forming apparatus, a desired image is formed on a recording medium.

  In such an image forming apparatus, the electrostatic latent image on the surface of the photosensitive member is developed by the forward rotation developing method or the reverse developing method. In the forward development method, the electrostatic latent image on the surface of the photoreceptor is developed by attaching toner having a polarity opposite to the charged polarity of the photoreceptor to an unexposed portion of the photoreceptor. In the reverse development method, the electrostatic latent image on the surface of the photoconductor is developed by attaching a toner having the same polarity as the charged polarity to the exposed portion of the photoconductor. In a printer such as a laser printer, a facsimile machine, and a digital copying machine, the reversal development method is mainly used.

  The potential of the photosensitive member after being charged by the charging unit and before being exposed by the exposure unit is likely to change due to a change in temperature and humidity of the environment in which the image forming apparatus is used. When temperature and humidity changes in the environment in which the image forming apparatus is used, electrical characteristics such as a resistance value and a dielectric constant of the charging member change. Also, the charge mobility of the photoreceptor itself changes. As a result, there is a problem that the surface of the photoconductor cannot always have a constant potential regardless of environmental conditions.

  Organic photoreceptors (OPC: Organic Photo Conductor), which are widely used as photoreceptors and on which photosensitive layers such as charge generation layers and charge transport layers are laminated, reduce the film thickness of the photosensitive layer due to wear due to long-term use. Reduction of film thickness occurs. This film reduction reduces the charge retention capability of the photoreceptor, and the surface potential of the photoreceptor changes with long-term use.

  As described above, the surface potential of the photoconductor changes depending on the environment in which the image forming apparatus is used and the film thickness of the photoconductor. Therefore, uneven density and image fogging occur in the formed image, and high-quality images are stabilized. There is a problem that cannot be obtained.

  In view of such a problem, a charging device for controlling a charging unit according to a temperature change of an environment in which an image forming apparatus is used, a reduction in film thickness of the photoconductor, and the like, and keeping the surface potential of the photoconductor constant Has been proposed (see, for example, Patent Documents 1 and 2).

  The charging means disclosed in Patent Document 1 includes a discharge electrode provided at a position facing the photosensitive layer on the surface of the photoreceptor, and a counter electrode provided so as to cover the opposite side of the discharge electrode to the photoreceptor. And a grid electrode provided between the discharge electrode and the photosensitive member. In such a charging means, a difference is set by subtracting the current value of the current flowing through the grid bias power source that applies the voltage to the grid electrode and the counter electrode from the current value of the current flowing through the DC power source that applies the voltage to the discharge electrode. The voltage output of the DC power supply or grid bias power supply is controlled so as to approach the value.

  The charging means disclosed in Patent Document 2 uses the information signal of the number of copies as a film thickness change signal of the photosensitive layer, and in accordance with the input of the film thickness change signal, the surface potential of the photoconductor approaches the set value. The applied voltage to the charging member is corrected.

  By such charging means disclosed in Patent Documents 1 and 2, etc., the surface potential of the photoreceptor can be brought close to a set value, and there is no high density unevenness or image fogging due to environmental changes and long-term use. It is expected that high quality images can be formed. However, in the image formation using the electrophotographic method, even after the charging by the charging unit and the potential before the exposure by the exposure unit can be set to a suitable value, the exposed portion after the exposure by the exposure unit If the potential is not a suitable value, a high-quality image cannot be formed if there is a change in the environment or if it is used for a long time.

  A semiconductor laser is used as the light emitting element of the exposure means. Even when the same voltage is applied to the semiconductor laser, the emission intensity changes as the environmental temperature changes. Thus, if the environment changes, the potential of the exposed portion after exposure by the exposure means cannot be set to a suitable value. Further, when the developing bias is not corrected by, for example, the number of printed sheets, the effective developing potential, which is the difference between the developing portion and the potential of the exposed portion after exposure by the exposure means, changes when used for a long time.

  In order to cope with such a change in the effective development potential, in the image forming apparatus, a density patch made of toner is formed on the surface of the photoreceptor before the toner image to be transferred to the recording medium is formed on the surface of the photoreceptor. Implement process control. In this process control, the density of the density patch made of toner is detected, and operations of the charging unit, the exposure unit, the developing unit, etc. are controlled so that the density of the density patch becomes a predetermined density. As a result, even if the effective development potential deviates from a suitable value, the effective development potential is corrected to a suitable value, and it is possible to prevent density unevenness and image fogging from occurring in the formed image.

  Process control is performed until the density of the density patch reaches a predetermined density. Therefore, when the effective development potential is out of the preferred value, the operation of the charging unit, the exposure unit and the development unit is controlled so that the effective development potential is set to a suitable value, and the density patch is formed each time. This increases the number of density patch formations. As the number of density patch formation increases, the amount of toner consumption increases. In addition, the time until image formation is started is lengthened.

  Accordingly, there is a demand for an image forming apparatus that can maintain the effective development potential within a suitable range even when the environment changes or is used for a long period of time, and can reduce the number of density patch formations.

JP-A-5-197261 JP-A-5-27557

  An object of the present invention is to provide an image forming apparatus and an exposure device that can maintain the effective development potential within a suitable range even when there is a change in environment or when used for a long period of time, and can reduce the number of density patch formations. It is to provide a quantity correction method.

The present invention provides an electrophotographic photoreceptor having a photosensitive layer on the surface;
Charging means for charging the electrophotographic photosensitive member;
Exposure means for exposing the surface of the electrophotographic photosensitive member in a charged state to form an electrostatic latent image by exposing signal light according to image information;
Voltage applying means for applying a voltage to the exposure means;
Temperature and humidity detecting means for detecting the temperature and humidity in the vicinity of the electrophotographic photosensitive member;
Storage means for inputting a data table indicating the relationship between the voltage applied to the exposure means by the voltage application means and the temperature and humidity in the vicinity of the electrophotographic photosensitive member;
An applied voltage determining means for determining an applied voltage value to the exposure means by the voltage applying means from a detection result by the temperature / humidity detecting means and a data table input to the storage means;
An applied voltage correcting means for correcting the applied voltage value determined by the applied voltage determining means so that the effective developing potential is a value in a predetermined range;
Control means for controlling the voltage applying means so as to apply the applied voltage value corrected by the applied voltage correcting means to the exposure means;
When the applied voltage value corrected by the applied voltage correcting unit is different from the applied voltage value previously input as a data table in the storage unit, the data table input in the storage unit in advance is corrected by the applied voltage correcting unit. An image forming apparatus comprising: a data table updating unit that updates a new data table based on a relationship between a voltage value and a detection result by a temperature and humidity detection unit.

The present invention further includes density detecting means for detecting the density of the density patch formed on the electrophotographic photosensitive member,
The applied voltage correction means is
The applied voltage value determined by the applied voltage determining means is corrected according to the density of the density patch detected by the density detecting means.

The present invention further includes a potential detecting means for detecting the potential of the electrophotographic photosensitive member,
The applied voltage correction means is
The applied voltage value determined by the applied voltage determining means is corrected according to the potential of the exposed portion of the electrophotographic photosensitive member after exposure detected by the potential detecting means.

The present invention further includes a film thickness detecting means for detecting the film thickness of the photosensitive layer of the electrophotographic photoreceptor,
The charging means is
A charging member, and charging voltage applying means for applying a voltage to the charging member,
The applied voltage determining means includes
According to the detection result by the temperature and humidity detection means and the film thickness detection means, determine the applied voltage value to the charging member by the charging voltage application means,
The control means includes
The charging voltage applying unit is controlled so that the applied voltage value determined by the applied voltage determining unit is applied to the charging member.

In the present invention, the data table updating means
When the electrophotographic photosensitive member is replaced with a new electrophotographic photosensitive member, the data table input to the storage means is updated to a data table of a predetermined applied voltage value.

In the present invention, the applied voltage determining means includes
When the detection result by the temperature / humidity detection means is the same as the previous detection result, the applied voltage value applied to the exposure means by the voltage application means is determined to be the previous applied voltage value applied to the exposure means by the voltage application means. It is characterized by.

The present invention also includes a temperature and humidity detection step for detecting the temperature and humidity in the vicinity of the electrophotographic photosensitive member,
A voltage value determining step for determining an applied voltage value for the exposure means of the voltage applying means according to the detection result by the temperature and humidity detecting means;
A voltage value correcting step for correcting the applied voltage value determined by the applied voltage determining means so that the effective developing potential is a value in a predetermined range;
And a storage step of storing a data table indicating a relationship between the applied voltage value corrected in the voltage value correction step and the temperature and humidity in the vicinity of the electrophotographic photosensitive member detected in the temperature / humidity detection step. This is an exposure correction method.

  According to the present invention, an image forming apparatus includes an electrophotographic photosensitive member (hereinafter simply referred to as “photosensitive member”), a charging unit, an exposing unit, a voltage applying unit, a temperature / humidity detecting unit, a storage unit, an application unit. A voltage determining unit, an applied voltage correcting unit, a control unit, and a data table updating unit (hereinafter simply referred to as “updating unit”) are configured. The image forming apparatus of the present invention is configured to apply an applied voltage to the exposure unit by the voltage application unit from the detection result of the temperature and humidity in the vicinity of the photoconductor by the temperature and humidity detection unit and the data table of the applied voltage value input to the storage unit. And an applied voltage correcting means for correcting the applied voltage value determined by the applied voltage determining means so that the effective developing potential is in a predetermined range. And In addition, the data table for determining the applied voltage input in advance to the storage means is based on the latest detection result by the temperature / humidity detecting means and the applied voltage value determined and corrected from the detection result, if necessary. Update means for updating to a new data table is provided. The effective development potential is the difference between the potential of the exposed portion of the electrophotographic photoreceptor after exposure and the development bias.

  The applied voltage value to the exposure means is determined by the applied voltage determination means from the detection result of the temperature and humidity in the vicinity of the photoconductor and the data table of the applied voltage value input to the storage means. Since the exposure potential of the electrostatic latent image formed on the surface of the photoreceptor by the exposure unit varies depending on the temperature and humidity conditions in the vicinity of the photoreceptor, the effective development potential can be obtained simply by applying a constant voltage to the exposure unit. Cannot be maintained within a substantially constant range. Therefore, as described above, the applied voltage determining means determines the applied voltage value according to the temperature and humidity, and corrects the applied voltage value so that the effective developing potential is in a predetermined range. The applied voltage value is applied to the exposure means. By applying the applied voltage value thus corrected to the exposure means, the effective developing potential can be set to a predetermined suitable value. As a result, even if there is a change in the environment, the exposure potential and hence the effective development potential can be maintained in a substantially constant range, and a high-quality image with a high image density can be formed.

  In addition, when the application voltage value corrected by the application voltage correction unit is different from the application voltage value of the data table input to the storage unit, the update unit converts the data table input to the storage unit to the application voltage correction. The data is updated to a new data table based on the relationship between the applied voltage value corrected by the means and the detection result by the temperature / humidity detecting means. That is, the applied voltage value corrected by the applied voltage correcting unit is stored as a data table related to the detection result by the temperature / humidity detecting unit in accordance with the latest detection result of the surface potential of the photoreceptor. As a result, the applied voltage value stored in the storage means is set to a value that is equal to or close to a suitable applied voltage value, for example, than the applied voltage value in the data table stored in advance as a default value. Can do.

  When the applied voltage value stored in the storage means is the same as or close to the preferred applied voltage value, the applied voltage value determined by the applied voltage determining means is the same as the preferred applied voltage value. The applied voltage correction means can correct the applied voltage value in a short time. Thus, for example, when the density of a density patch made of toner is detected and the process control for controlling the operation of the charging unit, the exposure unit, the developing unit, etc. is performed so that the density of the density patch becomes a predetermined density, it is less. By forming the density patch a number of times, the density of the density patch can be set to a predetermined density, and the voltage value applied to the exposure unit can be set to a suitable applied voltage value. If the number of density patch formations can be reduced, an increase in toner consumption for density patch formation and an increase in time required for image formation can be prevented.

  According to the invention, the image forming apparatus further includes a density detecting unit, and the applied voltage correcting unit applies the applied voltage value determined by the applied voltage determining unit according to the density of the density patch detected by the density detecting unit. Correct. In such an image forming apparatus, the applied voltage value to the exposure unit is corrected so that the density of the formed density patch falls within a predetermined range, and process control is performed so that the effective development potential becomes a predetermined value. Therefore, even if the environment changes or the photoconductor is used for a long time, an image having a stable and uniform image quality can be formed.

  According to the invention, the image forming apparatus further includes a potential detecting unit, and the applied voltage correcting unit determines the applied voltage according to the potential of the exposed portion of the electrophotographic photosensitive member after the exposure detected by the potential detecting unit. The applied voltage value determined by the means is corrected. In such an image forming apparatus, since the applied voltage value to the exposure unit is corrected so that the surface potential of the photosensitive member becomes a predetermined value, process control is performed so that the effective developing potential becomes a predetermined value. Even if there is a change in the environment and the photoreceptor is used for a long time, an image having a stable and uniform image quality can be formed. Further, in the image forming apparatus that corrects the voltage applied to the exposure means so that the surface potential of the photosensitive member becomes a predetermined value, process control can be performed without forming a density patch. Therefore, no toner is consumed.

  According to the invention, the image forming apparatus further includes a film thickness detecting unit, and the charging unit provided in the image forming apparatus includes a charging member and a charging voltage applying unit. In such an image forming apparatus, the applied voltage determining unit determines an applied voltage value to the charging member by the charging voltage applying unit in accordance with detection results by the temperature / humidity detecting unit and the film thickness detecting unit. When the voltage applied to the charging member is determined according to the detection result by the temperature / humidity detection means, the voltage applied to the charging member according to the electrical characteristics such as the resistance value, dielectric constant, etc. Since the voltage value is determined, the surface of the photoreceptor can always be charged to a suitable potential even if the environment changes. Further, when the voltage applied to the charging member is determined according to the detection result by the film thickness detecting means, the voltage applied to the charging member is changed according to the change in the charge holding ability of the photosensitive member caused by the reduction in the film thickness of the photosensitive member. Therefore, the surface of the photoreceptor can always be charged to a suitable potential even after long-term use.

  According to the invention, the data table update means updates the data table input to the storage means to a predetermined applied voltage value data table when the photoconductor is replaced with a new photoconductor. In this way, the data table input to the storage means when the photoconductor is replaced with a new photoconductor is returned to the initial data table, which is a data table of predetermined applied voltage values, to the storage means. The stored applied voltage value may be equal to or close to a suitable applied voltage value than the voltage value applied to the exposure unit that exposes the photoconductor used for a long time before replacement. it can. As a result, the time required for process control after replacement with a new photoreceptor can be shortened.

  Further, according to the present invention, the applied voltage determining means is configured to expose the applied voltage value applied by the voltage applying means to the exposure means when the detection result by the temperature / humidity detecting means is the same as the previous detection result. The previous applied voltage value applied to the means is determined. In this way, when it is expected that a suitable applied voltage value that the voltage application means should apply to the exposure means is the same as or close to the previous applied voltage value, exposure is performed without performing process control. By determining the applied voltage value applied to the means, it is possible to prevent an increase in toner consumption and an increase in time required for image formation due to the process control.

  Further, according to the present invention, an exposure amount correction method for determining the exposure amount on the photoconductor is realized by the temperature / humidity detection step, the voltage value determination step, the voltage value correction step, and the storage step. In the voltage value determination step, an applied voltage value for the exposure unit of the voltage application unit is determined according to the detection result in the temperature and humidity detection step. In the voltage value correcting step, the applied voltage value determined by the applied voltage determining means is corrected so that the effective developing potential is in a predetermined range.

  The applied voltage value determined in the voltage value determining step is determined in the voltage value determining step so that the applied voltage value corresponding to the temperature and humidity is determined, and in the voltage value correcting step, the effective developing potential is in a predetermined range. And the corrected applied voltage value is applied to the exposure means. By applying the applied voltage value thus corrected to the exposure means, the effective developing potential can be set to a predetermined suitable value. As a result, even if there is a change in the environment, the exposure potential and hence the effective development potential can be maintained in a substantially constant range, and a high-quality image with a high image density can be formed.

  In the storage step, a data table indicating the relationship between the applied voltage value corrected in the voltage value correction step and the temperature and humidity in the vicinity of the electrophotographic photosensitive member detected in the temperature and humidity detection step is stored in the storage means. . Thus, the applied voltage value corrected in the voltage value correcting step is stored as a data table related to the detection result by the temperature / humidity detection unit according to the latest detection result of the surface potential of the photosensitive member, and stored in the storage unit. The stored applied voltage value can be set to a value that is the same as or close to a suitable applied voltage value, for example, than the applied voltage value in the data table stored in advance as a default value. As a result, the voltage value determined in the voltage value determination step is the same as or close to a suitable applied voltage value, and the applied voltage value can be corrected in a short time by the applied voltage correcting means. .

  FIG. 1 is a cross-sectional view showing a simplified configuration of an image forming apparatus 1 according to an embodiment of the present invention. The following description includes a description of the exposure amount correction method. The image forming apparatus 1 includes an electrophotographic photosensitive member (hereinafter simply referred to as “photosensitive member”) 2, a charging unit 3, an exposing unit 4, a developing unit 5, a transfer unit 6, a fixing unit 7, and a cleaning unit 8. And the static elimination means 9. Further, the image forming apparatus 1 of the present embodiment includes a voltage applying unit 10 that applies a voltage to the exposure unit 4, a temperature / humidity detecting unit 11, a control unit 12, a storage unit 13, an applied voltage determining unit 14, An application voltage correction unit 15, a data table update unit (hereinafter simply referred to as “update unit”) 16, a print number detection unit 17 that functions as a film thickness detection unit, and a density sensor 18 that is a density detection unit. Is done. The image forming apparatus 1 of the present embodiment forms an image by a reverse development method using negatively charged toner.

  In the image forming apparatus 1 of the present embodiment, the charging unit 3, the exposure unit 4, the developing unit 5, and the transfer unit 6 are arranged around the photoconductor 2 from the upstream side to the downstream side in the rotation direction 19 of the photoconductor 2. The cleaning means 8 and the charge eliminating means 9 are provided in this order. In the present embodiment, a temperature / humidity detecting unit 11 is provided between the charge eliminating unit 9 and the charging unit 3, and a density sensor 18 is provided between the developing unit 5 and the transfer unit 6.

  The photoreceptor 2 includes a cylindrical conductive substrate (not shown) and an organic photosensitive layer formed on the surface of the conductive substrate. The photoreceptor 2 is supported by a driving unit (not shown) so as to be rotatable around an axis. As the photoreceptor 2, those commonly used in this field can be used. For example, a photoreceptor having a diameter of 30 mm including an aluminum base tube as a conductive substrate and an organic photosensitive layer formed on the surface of the aluminum base tube. A drum is used. The organic photosensitive layer is formed by laminating a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. The organic photosensitive layer may include a charge generation material and a charge transport material in one layer.

  The temperature / humidity detecting means 11 detects the temperature and relative humidity (also simply referred to as “humidity”) in the vicinity of the photoreceptor 2. The temperature / humidity detecting means 11 may be any temperature / humidity sensor capable of measuring the temperature and humidity in the vicinity of the photoreceptor 2 in a non-contact manner. For example, an insertion type temperature detector (trade name: HTY78, manufactured by Yamatake Corporation) ) Etc. can be used. The temperature / humidity detecting means 11 is provided 3 to 5 mm away from the surface of the photoreceptor 2. The temperature / humidity detection means 11 detects the temperature and humidity in the vicinity of the photoreceptor 2 and outputs the detection result to the control means 12 described later.

  The density sensor 18 detects the density of the density patch made of toner formed on the surface of the photoconductor 2 when performing process control for forming a density patch made of toner on the surface of the photoconductor 2. As the density sensor 18, for example, a sensor including a light emitting element, a light receiving element, a condenser lens, and an imaging lens can be used. The density sensor 18 detects the density of the density patch by receiving, with the light receiving element, light that is emitted from the light emitting element and reflected by the density patch. The density detection result of the density patch detected by the density sensor 18 is input to the control means 12 described later.

  The charging unit 3 charges the surface of the photoreceptor 2 to a potential having a predetermined polarity. The charging means 3 according to the present embodiment includes a charging member 3a including a grid electrode, a discharge electrode, and a shield case, and a charging voltage applying means 3b that applies a voltage to the charging member 3a. The charging member 3a is configured such that its length in the longitudinal direction is substantially the same as or longer than the length in the longitudinal direction of the photoreceptor 2.

  The grid electrode is provided between the photosensitive member 2 and the discharge electrode, and receives a voltage applied from the charging voltage applying unit 3b, for example, adjusts the variation in the charged state of the surface of the photosensitive member 2 to make the surface potential uniform. Turn into. For the grid electrode, for example, a metal plate member having a plurality of through holes in the thickness direction can be used. The through hole is formed in a mesh shape, for example. The material for forming the plate member of the grid electrode is not particularly limited as long as it is a conductive material, but for example, metals such as stainless steel, aluminum, nickel, copper, and iron are preferable. On the surface of the plate-like member, a nickel layer containing fluororesin particles having a particle diameter of about 2 to 20 μm is formed with or without a nickel layer in order to further enhance the effect of uniformizing the surface potential of the photoreceptor 2. May be. The discharge electrode is provided so as to extend from the opposite side of the surface facing the peripheral surface of the photoreceptor 2 in the short side direction toward the peripheral surface of the photoreceptor 2 in the shield case, and is supported by a support member (not shown). When a voltage is applied from a power source (not shown), the discharge electrode performs corona discharge toward the photoconductor 2 to charge the surface of the photoconductor 2. As the discharge electrode, a needle electrode commonly used in this field can be used. The acicular electrode is a thin plate member including, for example, a flat plate portion formed in a plate shape, and a sharp protrusion formed so as to protrude in the short direction from one end surface of the flat plate portion in the short direction. This thin plate member is formed of, for example, stainless steel. The shield case is a container-like member having a rectangular parallelepiped external shape having an internal space and having a surface facing the peripheral surface of the photoreceptor 2 opened. The shield case accommodates at least a discharge electrode and a support member for the discharge electrode in its internal space. The shield case is made of, for example, stainless steel.

  The operation of the charging voltage applying unit 3b is controlled by a control unit 12 described later, and an applied voltage value (hereinafter simply referred to as “a”) determined by an applied voltage determining unit 14 based on a data table stored in a storage unit 13 described later. A voltage value ”may be applied to the charging member 3a. In the present embodiment, since the image forming apparatus 1 uses negatively charged toner and forms an image by a reversal development method, the charging voltage applying unit 3b applies a voltage having the same polarity as the toner, that is, a negative voltage. The photosensitive member 2 is charged by applying to 3a.

  The exposure unit 4 exposes the surface of the charged photoreceptor 2 to signal light corresponding to image information to form an electrostatic latent image. In the present embodiment, since the image forming apparatus 1 forms an image by the reversal development method, the exposure unit 4 irradiates signal light to a portion where an image is formed, that is, a portion where development is performed by attaching toner. A semiconductor laser or the like is used as the signal light source.

  A voltage is applied to the exposure unit 4 by the voltage application unit 10. The operation of the voltage application unit 10 is controlled by a control unit 12 described later, and an applied voltage value determined by the application voltage determination unit 14 is applied to the exposure unit 4 based on a data table stored in a storage unit 13 described later. Apply. The applied voltage value applied to the exposure unit 4 determines the exposure intensity from the light source of the exposure unit 4, that is, the exposure amount, and the exposure amount determines the potential of the exposed portion of the photoreceptor after exposure. Therefore, by adjusting the applied voltage value applied to the exposure means 4, the potential of the exposed portion of the photoreceptor after exposure can be adjusted.

  The developing means 5 includes a toner container 5a for storing toner and a developing roller 5b that faces the photosensitive member 2 and is rotatably provided by a rotating shaft 5c. The developing roller 5b is connected to the rotating shaft 5c. A developing bias is applied from the developing bias applying means 20.

  The toner storage container 5a is a container for storing toner made of, for example, hard synthetic resin. The toner container 5a has an opening facing the photoconductor 2, and a developing roller 5b is provided so as to face the photoconductor 2 in a state where a part of the toner storage container 5a is exposed from the opening and to be slightly separated. A toner stirring roller (not shown) is provided in the toner container 5a, and the toner is frictionally charged by the stirring of the toner stirring roller and supplied to the developing roller 5b.

  The developing roller 5b is a cylindrical member having an outer diameter of 25 mm, for example. The developing roller 5b is rotatably supported by the toner storage container 5a via the rotation shaft 5c, and is driven to rotate by a motor (not shown). The developing bias applying unit 20 applies a developing bias having the same polarity as the toner to the developing roller 5b.

  In the non-contact developing method in which the photosensitive member 2 and the developing roller 5b are provided apart from each other, the developing bias applying unit 20 applies a developing bias having the same polarity as the toner, for example, −400V to the developing roller 5b. As a result, the charged toner supplied onto the developing roller 5b is made to fly and sit on the surface of the photosensitive member by an electric field force, and the toner is supplied to the surface of the photosensitive member 2 to form a toner image.

  The transfer means 6 is formed in a roller shape in this embodiment, and is provided so as to abut on the photosensitive member 2 and to be rotatable around its axis. The transfer means 6 is connected to a transfer voltage applying means 6 a for applying a voltage to the roller-like transfer means 6. At the time of image formation, the transfer unit 6 presses the recording medium 21 against the photosensitive member 2 from the surface opposite to the contact surface of the recording medium 21 such as paper with the photosensitive member 2, and the photosensitive member 2 and the recording medium. In a state in which the recording medium 21 is in pressure contact, a voltage having a reverse polarity to the toner, for example, a voltage of +3 kV, is applied to the transfer unit 6 from the transfer voltage applying unit 10 to charge the recording medium 21 with a reverse polarity to the toner. As a result, the toner image formed on the surface of the photoreceptor 2 is transferred onto the recording medium 21. The recording medium 21 is supplied to the transfer unit 6 in synchronization with the exposure of the exposure unit 4 by a recording medium transport unit (not shown).

  The transfer unit 6 is not limited to the configuration using the transfer roller as described above, and may be configured to include a transfer belt formed in a belt shape instead of the transfer roller, for example. The transfer unit 6 is not limited to a transfer unit that uses a contact transfer method in which a toner image is directly transferred to the recording medium 21, and the transfer unit 6 transfers the toner image to the transfer belt, and the toner image is transferred onto the transfer belt. Transfer means using an intermediate transfer system such as transferring a toner image to a recording medium may be used.

  The fixing unit 7 is a thermocompression fixing unit including a heating roller 22 and a pressure roller 23. The heating roller 22 includes heating means (not shown) and is heated to a predetermined temperature. In the present embodiment, the heating roller 22 is provided so as to contact the surface of the recording medium 21 on which the toner image is transferred. The fixing unit 7 sequentially receives the recording medium 21 onto which the toner image is transferred by the transfer unit 6, passes through a contact portion between the heating roller 22 and the pressure roller 23, and is heated and heated by the heating roller 22 and the pressure roller 23. The toner image is fixed on the recording medium 21 by applying pressure. The recording medium 21 is held between the heating roller 22 and the pressure roller 23 and is conveyed by the rotation of the heating roller 22 and the pressure roller 23.

  The fixing unit 7 is not limited to the one including the heating roller 22 and the pressure roller 23 as described above, and may be configured to include a belt-shaped heating member and a pressure member, for example.

  The cleaning means 8 is made of an elastic material and includes a cleaning blade 8a that scrapes off toner remaining on the surface of the photoreceptor 2, and a toner recovery container 8b that recovers toner scraped off by the cleaning blade 8a. By such cleaning means 8, the toner remaining on the surface of the photoreceptor 2 after the toner image is transferred to the recording medium 21 is removed and cleaned.

  The neutralizing means 9 is constituted by a neutralizing lamp or the like, and removes the charge on the surface of the photoreceptor 2 after the toner image is transferred to the recording medium 21.

  The control means 12 is realized by a central processing unit (abbreviated as CPU: Central Processing Unit). The control unit 12 controls the voltage application unit 10 described later so as to apply the applied voltage value determined by the application voltage determination unit 14 described later to the exposure unit 4, and also controls the operation of the entire apparatus. The control means 12 executes a program stored in the storage means 13 to perform processing shown in a flowchart to be described later, thereby controlling the operation of the entire apparatus.

The storage means 13 includes ROM (Read Only Memory) and RAM (RAM: Random Access).
Memory), a hard disk drive (HDD), and the like. The storage unit 13 includes a data table of voltage values applied to the charging member 3a, a data table of voltage values applied to the exposure unit 4, and a printed sheet counter value used for detecting the number of printed sheets by a printed sheet number detecting unit 17 described later. A program executed by the control unit 12 is input.

Tables 1 and 2 show examples of data tables of voltage values applied to the charging member 3 a stored in the storage unit 13. The storage means 13 is a data table of applied voltage values obtained from the relationship between temperature and humidity as shown in Table 1 as a data table of voltage values applied to the charging member 3a, and will be described later as shown in Table 2. A data table indicating voltage correction values determined according to the cumulative number of printed sheets obtained by the number of printed sheet detecting means 17 is stored. The applied voltage values shown in Table 1 are values obtained by measuring the applied voltage value when the charging potential is −600 V in each environment for an unused photoreceptor. Further, the voltage correction values shown in Table 2 are obtained when the applied voltage value is measured when the charged potential of the photoconductor on which the number of printed images is formed is −600 V in an environment of a temperature of 20 ° C. and a humidity of 60%. These are values obtained by calculating the difference from the applied voltage value under the same environmental conditions in Table 1. The applied voltage value was measured under the following conditions.
Image forming apparatus: MX-5500N remodeling machine (manufactured by Sharp Corporation)
Photoreceptor: Multilayer organic photoreceptor in which the charge transport layer resin is polycarbonate Photoreceptor rotation speed: 355 mm / sec
Film thickness of the photosensitive layer on the photoreceptor surface: 27 μm
Charging means: Scorotron type (saw tooth charging)
Applied voltage value to the discharge electrode: -7 kV
Contact pressure of transfer roller: 1 × 10 ⁻² N / mm
Cleaning blade contact pressure: 200 mN / cm

  The storage unit 13 stores a data table of voltage values applied to the exposure unit 4. In this embodiment, the ratio of the actual laser oscillation time to the total laser oscillation time is stored instead of the voltage value applied to the exposure means 4. The applied voltage value is calculated from the ratio of the laser oscillation time. The storage means 13 stores the ratio of the laser oscillation time as a data table of the ratio of the actual laser oscillation time to the total laser oscillation time obtained from the relationship between temperature and humidity. Further, in the present embodiment, the actual laser oscillation time ratio is stored as a ratio when the total laser oscillation time is 256. The storage means 13 stores the ratio of the laser oscillation time as described above, and determines the applied voltage value from the ratio of the laser oscillation time stored in the storage means 13.

  Table 3 shows an example of a data table of the ratio of the laser oscillation time stored in the storage unit 13 and applied to the exposure unit 4. The storage means 13 of the present embodiment stores the data table of Table 3 as default values. The ratio of the laser oscillation time shown in Table 3 was measured by measuring the ratio of the laser oscillation time when the potential of the exposed portion was −150 V under each environment for an unused photoreceptor charged to −600 V. It is the obtained value.

  The applied voltage determining means 14 determines the applied voltage value to the charging member 3a by the charging voltage applying means 3b according to the detection results by the temperature / humidity detecting means 11 and the print number detecting means 17. The applied voltage determination means 14 includes temperature and humidity detection results by the temperature / humidity detection means 11, detection results of accumulated print count by the print count detection means 17 described later, and Tables 1 and 2 stored in the storage means 13. The voltage value applied to the charging member 3a is determined using this data table. Specifically, the applied voltage value is determined as follows. For example, when the temperature is 15 ° C. or more and less than 25 ° C. and the humidity is 45 RH% (also simply referred to as “%”) or more and less than 60%, Table 1 shows that the applied voltage value is −700V. Furthermore, when the cumulative number of printed sheets is 50K or more and less than 100K, it can be seen from Table 2 that the voltage correction value is −20V. Therefore, when the temperature is 15 ° C. or more and less than 25 ° C., the humidity is 45% or more and less than 60%, and the cumulative number of printed sheets is 50 K or more and less than 100 K, the applied voltage value (−700 V) obtained from Table 1 is obtained. A value obtained by adding the voltage correction value (−20V) obtained from Table 2, that is, −720V is determined as the applied voltage value.

  As described above, when the voltage value applied to the charging member 3a is determined according to the detection results by the temperature / humidity detecting means 11 and the number-of-printing-number detecting means 17, the resistance value and dielectric of the charging member 3a that change according to the change in temperature / humidity. The voltage applied to the charging member 3a can be determined according to the electrical characteristics such as the rate. As a result, the surface of the photoreceptor 2 can always be charged to a suitable potential even when the environment changes. When the applied voltage value to the charging member 3a is determined according to the detection result by the number-of-printing-sheet detecting means 17, the charging member 3a is applied to the charging member in accordance with the change in the charge holding capability of the photosensitive member 2 caused by the film reduction of the photosensitive member 2. Since the applied voltage value is determined, the surface of the photoreceptor 2 can always be charged to a suitable potential even after long-term use.

  The applied voltage determining means 14 determines the applied voltage value to the exposure means 4 by the voltage applying means 10 from the detection result by the temperature / humidity detecting means 11 and the data table of the ratio of the laser oscillation time input to the storage means 13. decide. The applied voltage determination means 14 determines the ratio of the laser oscillation time of the exposure means 4 using the temperature and humidity detection results by the temperature / humidity detection means 11 and the data table of Table 3 stored in the storage means 13. Then, the provisional voltage value to be applied to the exposure unit 4 is determined so that the ratio of the laser oscillation time of the exposure unit 4 becomes the determined rate. The voltage value determined by the applied voltage determining means 14 may be referred to as “temporary applied voltage value”. Specifically, the provisional applied voltage value is determined as follows. For example, when the temperature is 15 ° C. or more and less than 25 ° C. and the humidity is 45% or more and less than 60%, it can be seen from Table 3 that the applied voltage value is a value when the ratio of the laser oscillation time is 128 duty. Therefore, under such an environment, the applied voltage determining means 14 determines the provisional applied voltage value as a value when the ratio of the laser oscillation time is 128 duty.

  The applied voltage correcting unit 15 corrects the applied voltage value determined by the applied voltage determining unit so that the effective developing potential is in a predetermined range. In the present embodiment, correction of the applied voltage value applied to the exposure means 4 is performed by process control that forms a density patch made of toner on the surface of the photoreceptor.

  In the present embodiment, the applied voltage value determined by the applied voltage determining means 14 is corrected according to the density of the density patch detected by the density sensor 18 so that the effective development potential becomes a value in a predetermined range. The applied voltage value is corrected. Even if the effective development potential deviates from a suitable value due to environmental changes or the like due to process control for forming such a density patch, the potential of the exposed portion of the photoreceptor 2 after exposure by the exposure means 4, and By correcting the effective development potential, which is the difference from the development bias, to a suitable value, it is possible to prevent density unevenness and image fogging from occurring in the formed image. Such process control is performed, for example, when the image forming apparatus 1 is started up, after printing a predetermined number of sheets, or before image formation.

  The applied voltage correcting unit 15 corrects the applied voltage value determined by the applied voltage determining unit 14 as follows. First, before the process control, the temperature and humidity detection means 11 detects the temperature and humidity in the vicinity of the photoreceptor 2. Depending on the detection result, an image can be formed without correcting the applied voltage value. For example, when the detection result by the temperature / humidity detection unit 11 is the same as the previous detection result, the applied voltage value is determined to be the same as the previous value without correcting the applied voltage value.

  When the applied voltage value is corrected after detection by the temperature / humidity detection means 11, first, a density patch is formed on the surface of the photoreceptor 2. The applied voltage value at this time is a provisional applied voltage value determined from the detection result of the temperature / humidity detecting unit 11 and the data table stored in the storage unit 13. For example, when the temperature is 15 ° C. or more and less than 25 ° C. and the humidity is 45% or more and less than 60%, it can be seen that the ratio of the laser oscillation time of the exposure means 4 is 128 duty. Therefore, in the process control under such an environment, first, a voltage when the ratio of the laser oscillation time is 128 duty, which is the provisional applied voltage value, is applied to the exposure means 4.

  The density patches are, for example, 8 cm square patches made of toner, and a plurality of types having different patch densities are formed at predetermined positions. A plurality of types of formed density patches are detected by the density sensor 18 and the voltage applied to the exposure unit 4 is adjusted so that the detection result by the density sensor 18 has a predetermined density. When the applied voltage value is adjusted and the detection result by the density sensor 18 reaches a predetermined density, the applied voltage value to the exposure unit 4 at this time is determined to be a true applied voltage value applied to the exposure unit 4 in image formation. . As described above, the applied voltage value is corrected.

FIG. 2 is a diagram for explaining the effective development potential. The effective development potential is represented by the difference between the potential (V _L ) of the exposed portion of the photoreceptor 2 after exposure by the exposure means 4 and the development bias (Vbias). In the present embodiment, the developing bias (Vbias) is set to −400V. The effective development potential is preferably set to, for example, about 250 V (245 V to 255 V), and the applied voltage value is corrected so that the effective development potential becomes a value in such a predetermined range. When the value of the predetermined range of the effective development potential is set to about 250 V (245 V to 255 V), the potential (V _L ) of the exposed portion of the photoreceptor 2 after exposure is set to about −150 V (−155 V to −145 V). It is hoped that V ₀ in FIG. 2 is the potential of the photosensitive member 2 after charging by the charging unit 3 and before exposure by the exposure unit 4, and is set to −600 V in the present embodiment.

  The applied voltage correction means 15 uses the provisional applied voltage value determined by the applied voltage determination means 14 according to the temperature and humidity in the vicinity of the photosensitive member 2 as the density determined in advance by the density patch density detection result by the density sensor 18. Correct so that As a result, the corrected applied voltage value is an applied voltage value at which the potential of the exposed portion of the photoreceptor 2 after exposure becomes a suitable potential (about −150 V), that is, an effective development potential is a value within a predetermined range. It is corrected to the voltage value. As a result, even if there is a change in the environment, a change in the surface potential of the photoconductor 2, etc., an effective development potential which is the difference between the potential of the exposed portion of the photoconductor 2 after exposure by the exposure means 4 and the development bias is suitable. Can be held at any value.

  The update means 16 stores in advance storage means when the applied voltage value to the exposure means 4 corrected by the applied voltage correction means 15 is different from the applied voltage value to the exposure means 4 that is previously input to the storage means 13 as a data table. 13 is updated to a new data table based on the relationship between the applied voltage value corrected by the applied voltage correcting means 15 and the detection result by the temperature / humidity detecting means 11.

  The update means 16 of the present embodiment is such that the ratio of the laser oscillation time based on the applied voltage value corrected by the applied voltage correction means 15 is the ratio of the laser oscillation time of Table 3 that is previously input to the storage means 13 as a data table. When the data table is different from the data table, the data table input to the storage means 13 is updated to a new data table. Hereinafter, an example of a method for updating a data table input to the storage unit 13 to a new data table will be described.

  For example, when the data table of Table 3 is stored in the storage means 13, the temperature is 15 ° C. or more and less than 25 ° C., and the humidity is 45% or more and less than 60%, the laser oscillation time stored in the storage means 13 is stored. The ratio is 128 duty as shown in Table 3. Here, when the process control is performed, the temperature is 15 ° C. or more and less than 25 ° C., the humidity is 45% or more and less than 60%, and the voltage is applied with the applied voltage value corrected by the applied voltage correcting means 15. When the ratio of the laser oscillation time becomes 132 duty, the ratio of the laser oscillation time based on the applied voltage value to the exposure unit 4 corrected by the applied voltage correction unit 15 is input to the storage unit 13 in advance as a data table. This is different from the ratio of the laser oscillation time. In such a case, the update unit 16 updates the data table.

  From Table 3, the ratio of the laser oscillation time based on the applied voltage value corrected by the applied voltage correction means 15 is 4 duty larger than the ratio of the laser oscillation time of the exposure means 4 that is previously input to the storage means 13 as a data table. Therefore, the data table of the laser oscillation time ratio obtained by adding 4 duty to the laser oscillation time ratio input to the data table in advance in the storage means 13 is stored as a new data table, and the data table is updated. That is, the data table in Table 3 is updated to the data table shown in Table 4 below, in which 4 duty is added to the ratio of the laser oscillation time under each environment.

  Next, the data table of Table 4 is stored in the storage means 13, and for example, when the temperature is 25 ° C. or more and less than 35 ° C. and the humidity is 45% or more and less than 60%, the laser stored in the storage means 13 is stored. As shown in Table 4, the ratio of the oscillation time is 128 duty. Here, when the process control is performed, the temperature is 25 ° C. or more and less than 35 ° C., the humidity is 45% or more and less than 60%, and the ratio of the laser oscillation time corrected by the applied voltage correcting means 15 is 124 duty, the applied voltage The ratio of the laser oscillation time based on the voltage value applied to the exposure means 4 corrected by the correction means 15 is different from the ratio of the laser oscillation time of the exposure means 4 that is previously input to the storage means 13 as a data table. Even in such a case, the updating unit 16 updates the data table.

  From Table 4, the ratio of the laser oscillation time based on the applied voltage value corrected by the applied voltage correction means 15 is 4 duty smaller than the ratio of the laser oscillation time of the exposure means 4 that is previously input to the storage means 13 as a data table. Therefore, the data table of the applied voltage value obtained by subtracting 4 duty from the ratio of the laser oscillation time input to the data table in advance in the storage unit 13 is stored as a new data table, and the data table is updated. That is, the data table of Table 4 is updated to the data table of Table 5 below.

  As described above, under the process control environment, the ratio of the laser oscillation time based on the applied voltage value corrected by the applied voltage correction means 15 and the ratio of the laser oscillation time stored in the storage means 13 are as follows. If they are different, the difference of the laser oscillation time ratio is subtracted or added to correct the laser oscillation time ratio of the storage means 13 under the process control environment, and the laser oscillation time ratio of the exposure means 4 is applied voltage correction. It is made to correspond with the ratio of the laser oscillation time used as the ratio of the laser oscillation time corrected by the means 15. Next, the difference is similarly subtracted or added in the ratio of the laser oscillation time in an environment other than the environment where the process control is performed. As a result, a new data table is created and stored in the storage means 13 to update the data table.

  According to the updating means 16 for updating the data table as described above, the ratio of the laser oscillation time stored in the storage means 13 is set as, for example, the laser oscillation time in the data table of Table 3 stored in advance as a default value. Rather than the ratio, the effective development potential can be set to a value that is the same as or close to the ratio of a suitable laser oscillation time that can be a predetermined value. As a result, the applied voltage value when the ratio of the laser oscillation time in the data table of Table 3 is set to be the same as or close to the suitable applied voltage value.

  When the ratio of the laser oscillation time stored in the storage means 13 is the same as or close to the ratio of the suitable laser oscillation time, the applied voltage value determined by the applied voltage determining means 14 is suitable. The applied voltage value is the same as or close to the applied voltage value, and the applied voltage correction means 15 can correct the applied voltage value in a short time. Thus, as in the present embodiment, the density of the density patch made of toner is detected, and process control is performed to correct the applied voltage value to the exposure means 4 so that the density of the density patch becomes a predetermined density. In this case, the density patch density can be set to a predetermined density by forming the density patch a smaller number of times, and the voltage value applied to the exposure means 4 can be set to a suitable applied voltage value. If the number of density patch formations can be reduced, an increase in toner consumption for density patch formation and an increase in time required for image formation can be prevented.

  When the photoconductor 2 is replaced with a new photoconductor 2, the update unit 16 preferably updates the data table input to the storage unit 13 to a predetermined applied voltage value data table. In the present embodiment, when the photosensitive member 2 is replaced with a new photosensitive member 2, the data table input to the storage means 13 is shown in a data table of a predetermined laser oscillation time ratio, for example, Table 3. Update to default value data table.

  When the data table input to the storage means 13 when the photosensitive body 2 is replaced with a new photosensitive body 2 is returned to the initial data table which is a data table of a predetermined laser oscillation time ratio, the storage means The effective development potential is set in advance to the voltage value applied to the exposure means for exposing the photosensitive member 2 used for a long time before replacement, when the applied voltage value stored in 13 is the ratio of the laser oscillation time. It can be a value that is the same as or close to a suitable applied voltage value that can be a predetermined value. This makes it possible to reduce the number of density patch formations in process control after replacement with a new photoconductor 2, reduce toner consumption, and shorten process execution time.

  The number-of-printing-sheet detecting means 17 accumulates the number of printed sheets after the photosensitive member 2 is mounted on the image forming apparatus 1 as a new product. For example, when the print command is input to the control unit 12, the print number detection unit 17 measures the time until the rotation of the photosensitive member 2 is completed, and inputs it to the control unit 12 as the number of prints. The input number of printed sheets is stored in a storage unit described later. At this time, the print number data originally existing in the storage means 13 is rewritten with the new print data after the addition. Thereby, the cumulative number of printed sheets in the image forming apparatus 1 can be obtained. When the number of prints on the recording medium 21 increases, the number of rotations of the photoconductor 2 increases, and the amount of film loss of the photoconductor 2 can be grasped. Therefore, the number-of-printing-sheet detecting means 17 of the present embodiment is used as a film thickness detecting means for detecting the film thickness of the photoreceptor. The film thickness detection means is not limited to the print number detection means as in the present embodiment, and may be, for example, a means for detecting the number of rotations of the photoreceptor 2.

  FIG. 3 is a flowchart for explaining the exposure correction method according to the present embodiment. Unless otherwise specified, the control entity of this flow is the control means 12. For example, the process proceeds to step s1 under a start condition in which the power of the image forming apparatus 1 is turned on from off or a start condition in which a print command is input to the control unit 12.

  In step s1, the control unit 12 causes the print number detection unit 17 to detect the print number. The number of printed sheets detected by the number-of-printed-sheet detecting means 17 is input to the control means 12, and then the process proceeds to step s2.

  In step s2, the controller 12 causes the temperature / humidity detector 11 to detect the temperature and humidity in the vicinity of the photoreceptor 2. Thus, in step s2, a temperature / humidity detection process for detecting the temperature and humidity in the vicinity of the photoreceptor 2 is performed. The temperature and humidity in the vicinity of the photoconductor 2 detected by the temperature / humidity detection unit 11 are input to the control unit 12 and stored in the storage unit 13. Next, the process proceeds to step s3.

  In step s3, the control unit 12 causes the applied voltage determining unit 14 to determine an applied voltage value to be applied to the charging member 3a. The applied voltage determining means 14 reads the data tables shown in Tables 1 and 2 from the storage means 13 using the number of printed sheets obtained in Step s1 and the temperature and humidity obtained in Step s2. Thus, the voltage applied to the charging member 3a by the charging voltage applying means 3b is determined according to the detection results by the temperature / humidity detecting means 11 and the number-of-printing number detecting means. When the voltage value applied to the charging member 3a is determined, the process proceeds to step s4.

  In step s4, the control means 12 determines whether the detection result by the temperature / humidity detection means 11 obtained in step s2 is the same as the detection result by the temperature / humidity detection means 11 at the time of determining the previous exposure amount. To do. In this embodiment, when it is determined that the detection result by the temperature / humidity detection unit 11 obtained in step s2 is the same as the detection result by the temperature / humidity detection unit 11 at the time of determining the previous exposure amount, the exposure unit 4 is referred to. The applied voltage value is the same as the applied voltage value at the time of determining the previous exposure amount, and the control procedure for determining the exposure amount is terminated without performing process control.

  In this way, when it is expected that a suitable applied voltage value that the voltage applying unit 10 should apply to the exposure unit 4 is the same as or close to the previous applied voltage value, process control is performed. The applied voltage value to be applied to the exposure means 4 is determined. Accordingly, it is possible to prevent an increase in toner consumption and an increase in time required for image formation due to the process control.

  If it is determined that the detection result by the temperature / humidity detection unit 11 obtained in step s2 is not the same as the detection result by the temperature / humidity detection unit 11 at the time of determining the previous exposure amount, the process proceeds to step s5, and the process control is performed. To implement.

  In step s5, the control unit 12 causes the applied voltage determination unit 14 to determine a provisional applied voltage value to be applied to the exposure unit 4. In step s5, the voltage value determining step is performed in this way. The applied voltage determination unit 14 determines the ratio of the laser oscillation time from the detection result of the temperature / humidity detection unit 11 and the table data of Table 3 stored in the storage unit 13, and the ratio of the laser oscillation time of the exposure unit 4. However, the provisional applied voltage value to be applied to the exposure means 4 is determined to be a value so that the determined ratio is obtained. For example, when the temperature is 15 ° C. or more and less than 25 ° C. and the humidity is 45% or more and less than 60%, from Table 3, the provisional applied voltage value applied to the exposure means 4 is the laser oscillation time ratio of 128 duty. Decide on a value. When the provisional applied voltage value to be applied to the exposure unit 4 is determined by the applied voltage determination unit 14, the process proceeds to step s6.

  In step s6, the control means 12 causes the charging voltage applying means 3b to apply a voltage to the charging member 3a and causes the charging means 3 to charge the photoreceptor 2. The applied voltage value to the charging member 3a at this time is the applied voltage value determined in step s3. Since such a voltage value is determined according to the detection result by the temperature / humidity detection unit 11 and the detection result by the number-of-printing detection unit 17, even if there is a change in the environment and the film thickness of the photoconductor 2 is decreased. Can always be charged to a predetermined surface potential, for example, a surface potential of -600V. When the photosensitive member 2 is charged by the charging unit 3, the process proceeds to step s7.

  In step s <b> 7, the control unit 12 causes the voltage application unit 10 to apply a voltage to the exposure unit 4 and causes the exposure unit 4 to expose the photoconductor 2. The applied voltage value to the exposure means 4 at this time is a provisional applied voltage value determined in the previous voltage value determining step. The exposure unit 4 exposes a predetermined position on the surface of the photoreceptor 2 where a density patch is to be formed, and forms an electrostatic latent image. When exposure by the exposure unit 4 is performed in step s7, the process proceeds to step s8.

  In step s8, the control unit 12 causes the developing unit 5 to develop the electrostatic latent image formed on the photoconductor 2. In step s8, the electrostatic latent image formed in step s7 is developed with toner to form a density patch. When the density patch made of toner is formed in step s8, the process proceeds to step s9.

  In step s9, the control unit 12 causes the density sensor 18 to detect the density of the density patch. The density of the density patch detected by the density sensor 18 is input to the control means 12. Next, the process proceeds to step s10.

  In step s10, the control means 12 determines whether or not the density of the density patch obtained in step s9 is a predetermined value. If it is determined that the density of the density patch is a predetermined value, the process proceeds to step s11. If it is determined that the density of the density patch is not a predetermined value, the process proceeds to step s12.

  In step s <b> 11, the control unit 12 sets the provisional applied voltage value determined by the applied voltage determination unit 14 as a true applied voltage value to be applied to the exposure unit 4. When the true applied voltage value to be applied to the exposure means 4 is determined, the control procedure for determining the exposure amount is terminated.

  In step s12, the control unit 12 causes the applied voltage correction unit 15 to perform correction according to the density of the density patch obtained in step s9. In step s12, the voltage value correcting step is performed in this way. The correction of the applied voltage value according to the density of the density patch obtained in step s9 is performed as follows, for example.

  When the density of the density patch is higher than a predetermined value, the absolute value of the surface potential of the photosensitive member 2 is smaller than the preferred absolute value of the surface potential, so that the applied voltage value to the exposure means 4 is reduced in order to reduce the exposure amount. Correction to decrease When the density of the density patch is lower than a predetermined value, the absolute value of the surface potential of the photoconductor 2 is larger than the preferred absolute value of the surface potential, so that the applied voltage to the exposure means 4 is increased in order to increase the exposure amount. Perform correction to increase the value. The correction amount of the applied voltage value may be a value determined by the difference between the density of the density patch and a predetermined value, or may be a predetermined correction amount, for example, 1V. When the applied voltage value is corrected in this way, the process proceeds to step s13.

  In step s13, the control unit 12 causes the update unit 16 to update the data table. The storage step is performed by updating the data table and storing it in the storage means 13 as described above. The updating unit 16 stores the data table previously input to the storage unit 13 based on the applied voltage value corrected by the applied voltage correcting unit 15, that is, the temporary applied voltage value corrected in the voltage value correcting step in step s 12. The data is updated to a new data table based on the relationship between the ratio of the oscillation time and the detection result by the temperature / humidity detection means. When the data table is updated in step s13, the process returns to step s5, the provisional applied voltage value is determined again, and process control is performed.

  The applied voltage value to be applied to the exposure unit 4 is set by the control procedure as described above, and the exposure amount from the exposure unit 4 is set by this applied voltage value. In the voltage value determination step (step s5) of the present embodiment, the voltage value applied to the exposure unit 4 of the voltage application unit 10 is determined according to the detection result by the temperature / humidity detection unit 11. The applied voltage value determined in the voltage value determination step is corrected in the voltage value correction step (step s12). Since this correction is performed according to the density of the density patch detected by the density sensor 18, for example, it can be performed according to a change in the surface potential of the photosensitive member 2 by the charging means 3, the developing means 5, and the like. Thus, the effective development potential, which is the difference between the potential of the exposed portion after exposure by 4 and the development bias, can be held at a suitable value.

  In the storage step (step s13), if the ratio of the laser oscillation time based on the applied voltage value corrected in the voltage value correction step is different from the ratio of the laser oscillation time based on the previous applied voltage value, the temperature / humidity detection step. A new data table based on the relationship between the detected temperature and humidity in the vicinity of the photosensitive member 2 and the ratio of the laser oscillation time based on the applied voltage value corrected in the voltage value correction step is the previous laser oscillation time. The percentage is stored by being updated. As a result, the ratio of the laser oscillation time based on the applied voltage value corrected in the voltage value correction step is related to the detection result by the temperature / humidity detection means 11 according to the latest detection result of the surface potential of the photoreceptor 2. Whether the ratio of the laser oscillation time stored as the data table and stored in the storage means 13 is the same as a preferred value, for example, than the ratio of the laser oscillation time of the data table stored in advance as a default value, Or it can be a close value. When the ratio of the laser oscillation time stored in the storage means 13 is the same as or close to the ratio of the suitable laser oscillation time, the process control for setting the effective development potential within a suitable range, The number of density patch formations can be reduced, and an increase in toner consumption for density patch formation and an increase in time required for image formation can be prevented.

  The image forming apparatus 1 and the exposure amount correction method as described above are not limited to the above configuration, and various changes can be made. For example, the storage unit 13 is not limited to a unit that stores the ratio of the laser oscillation time based on the applied voltage value, and may be a unit that stores the applied voltage value itself.

  FIG. 4 is a diagram schematically showing a configuration of an image forming apparatus 31 according to the second embodiment of the present invention. The image forming apparatus 31 according to the present embodiment has the same configuration as the image forming apparatus 1 according to the above-described embodiment except that the image sensor 31 includes a potential detection unit 32 instead of the density sensor 18. The description is abbreviate | omitted and attached | subjected.

  In the image forming apparatus 31 according to the present embodiment, the correction of the applied voltage value by the applied voltage correcting unit 15 detects the potential of the exposed portion of the photoreceptor 2 after exposure instead of performing process control for forming a density patch. Perform by process control.

  The potential detection unit 32 is a surface potential sensor that detects the potential of the photoreceptor 2. The potential detection unit 32 is provided on the downstream side of the exposure unit 4 and on the upstream side of the developing unit 5 in the direction in which the photoreceptor 2 rotates.

FIG. 5 is a diagram for explaining a method of correcting the applied voltage value by the applied voltage correcting means 15. In the graph shown in FIG. 5, the vertical axis represents the surface potential of the photoreceptor 2 after exposure, and the horizontal axis represents the exposure amount of the exposure means 4. As shown in FIG. 5, as the exposure amount of the exposure unit 4 increases, the surface potential of the photoreceptor 2 after exposure decreases. In the exposure correction method using the potential detection means 32, the voltage value to be applied to the exposure means 4 is determined so that the surface potential of the photoreceptor 2 is a predetermined surface potential _VLT . The predetermined surface potential V _LT is determined by the effective development potential and the development bias. For example, when the value of the predetermined range of the effective development potential is 250 V and the development bias is −400 V, it is −150 V.

For example, in the applied voltage correction unit 15, the surface potential of the photoconductor 2 detected by the surface potentiometer when a temporary applied voltage value is applied to the exposure unit 4 is a potential V _LM lower than a predetermined surface potential. In this case, correction is performed to reduce the exposure amount of the exposure unit 4 by Δr so that the surface potential of the photoconductor 2 approaches V _LT . The control means 12 should apply the applied voltage value when the exposure amount is reduced by Δr and the surface potential of the photoreceptor 2 detected by the surface potential meter becomes V _LT to the exposure means 4 at the time of image formation. Set to the true applied voltage value.

  In this way, the applied voltage correction unit 15 applies the voltage so that the potential of the exposed portion of the photoconductor 2 exposed by the exposure unit 4 after charging the photoconductor 2 by the charging unit 3 becomes −150V. Correct the voltage value. A suitable applied voltage value can also be set by process control using such potential detection means 32.

  The process control by the potential detection means 32 is preferable because it is not necessary to form a density patch, so that an increase in toner consumption can be prevented. However, the correction of the exposure amount by the potential detection means 32 is necessary as a precondition that the development bias does not change even if it is used for a long time.

  Therefore, even when there is a possibility that the developing bias may change, in order to perform more accurate control and prevent an increase in toner consumption, an applied voltage that is a surface potential VLT that is predetermined by the potential detecting means 32. It is most preferable to confirm whether or not the corrected applied voltage value is suitable by forming a density patch after correcting the value. Such a method is preferable because the toner consumption can be reduced as compared with the case where the correction of the applied voltage value is performed only by forming the density patch.

  In the image forming apparatus 1 as described above, an image is formed as follows. First, the surface of the photoreceptor 2 is negatively charged by the charging unit 3. Here, the charging voltage applying means 3b for applying a voltage to the charging member 3a of the charging means 3 applies a voltage at which the surface of the photoreceptor 2 has a suitable potential to the charging member 3a by the control means 12 as described above. Controlled.

  The photosensitive member 2 charged and charged by the charging unit 3 is exposed from the exposure unit 4 to form an electrostatic latent image. As described above, the voltage applying means 10 for applying a voltage to the exposure means 4 is set to a voltage at which the density of the density patch becomes a suitable potential or a suitable potential on the surface of the photoreceptor 2 as described above. Such a voltage is controlled to be applied to the exposure means 4.

  The electrostatic latent image formed by the exposure unit 4 is visualized by the toner supplied from the developing unit 5, and a toner image is formed on the surface of the photoreceptor 2. This toner image is transferred to the recording medium 21 by the transfer means 6. After the toner image is transferred to the recording medium 21, the photoreceptor 2 is cleaned by removing the residual toner by the cleaning unit 8 and removing the electric charge by the neutralizing unit 9. By repeating this series of operations, an image can be formed.

  According to such an image forming apparatus, the surface potential of the photosensitive member 2 after being charged by the charging unit 3 and the photosensitive member 2 after being exposed by the exposing unit 4 even if the environment is changed or used for a long time. Since the surface potential of the exposed portion can be set to a suitable potential, and the effective development potential is always in a predetermined range, an image having a uniform image quality can be formed stably.

  Further, in process control that is normally performed before image formation or the like, it is possible to reduce the consumption of toner for forming density patches, and to shorten the time for performing process control.

1 is a cross-sectional view showing a simplified configuration of an image forming apparatus 1 according to an embodiment of the present invention. It is a figure for demonstrating an effective developing potential. It is a flowchart explaining the exposure amount correction method of this Embodiment. It is a figure which shows schematically the structure of the image forming apparatus 31 which is the 2nd Embodiment of this invention. It is a figure for demonstrating the correction method of the applied voltage value by the applied voltage correction means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Electrophotographic photoreceptor 3 Charging means 3a Charging member 3b Charging voltage application means 4 Exposure means 5 Development means 5a Toner container 5b Developing roller 5c Rotating shaft 6 Transfer means 6a Transfer voltage application means 7 Fixing means 8 Cleaning means 8a Cleaning blade 8b Toner recovery container 9 Neutralization means 10 Voltage application means 11 Temperature / humidity detection means 12 Control means 13 Storage means 14 Applied voltage determination means 15 Applied voltage correction means 16 Update means 17 Print number detection means 18 Density sensor 19 Photoconductor rotation Direction 20 Developing bias applying means 21 Recording medium 22 Heating roller 23 Pressure roller 32 Potential detecting means

Claims (7)

An electrophotographic photoreceptor having a photosensitive layer on the surface;
Charging means for charging the electrophotographic photosensitive member;
Exposure means for exposing the surface of the electrophotographic photosensitive member in a charged state to form an electrostatic latent image by exposing signal light according to image information;
Voltage applying means for applying a voltage to the exposure means;
Temperature and humidity detecting means for detecting the temperature and humidity in the vicinity of the electrophotographic photosensitive member;
Storage means for inputting a data table indicating the relationship between the voltage applied to the exposure means by the voltage application means and the temperature and humidity in the vicinity of the electrophotographic photosensitive member;
An applied voltage determining means for determining an applied voltage value to the exposure means by the voltage applying means from a detection result by the temperature / humidity detecting means and a data table input to the storage means;
An applied voltage correcting means for correcting the applied voltage value determined by the applied voltage determining means so that the effective developing potential is a value in a predetermined range;
Control means for controlling the voltage applying means so as to apply the applied voltage value corrected by the applied voltage correcting means to the exposure means;
When the applied voltage value corrected by the applied voltage correcting unit is different from the applied voltage value previously input as a data table in the storage unit, the data table input in the storage unit in advance is corrected by the applied voltage correcting unit. An image forming apparatus comprising: a data table updating unit that updates a new data table based on a relationship between a voltage value and a detection result by a temperature and humidity detection unit. A density detector for detecting the density of a density patch formed on the electrophotographic photosensitive member;
The applied voltage correction means is
2. The image forming apparatus according to claim 1, wherein the applied voltage value determined by the applied voltage determining means is corrected in accordance with the density of the density patch detected by the density detecting means. Further comprising a potential detecting means for detecting the potential of the electrophotographic photosensitive member,
The applied voltage correction means is
3. The image according to claim 1, wherein the applied voltage value determined by the applied voltage determining means is corrected according to the potential of the exposed portion of the electrophotographic photoreceptor after exposure detected by the potential detecting means. Forming equipment. Further comprising a film thickness detecting means for detecting the film thickness of the photosensitive layer of the electrophotographic photosensitive member,
The charging means is
A charging member, and charging voltage applying means for applying a voltage to the charging member,
The applied voltage determining means includes
According to the detection result by the temperature and humidity detection means and the film thickness detection means, determine the applied voltage value to the charging member by the charging voltage application means,
The control means includes
The image forming apparatus according to claim 1, wherein the charging voltage applying unit is controlled so that the applied voltage value determined by the applied voltage determining unit is applied to the charging member. Data table update means
5. When the electrophotographic photosensitive member is replaced with a new electrophotographic photosensitive member, the data table input to the storage means is updated to a data table of a predetermined applied voltage value. The image forming apparatus according to any one of the above. The applied voltage determining means includes
When the detection result by the temperature / humidity detection means is the same as the previous detection result, the applied voltage value applied to the exposure means by the voltage application means is determined to be the previous applied voltage value applied to the exposure means by the voltage application means. The image forming apparatus according to claim 1, wherein: A temperature and humidity detection process for detecting the temperature and humidity in the vicinity of the electrophotographic photosensitive member;
A voltage value determining step for determining an applied voltage value for the exposure means of the voltage applying means according to the detection result by the temperature and humidity detecting means;
A voltage value correcting step for correcting the applied voltage value determined by the applied voltage determining means so that the effective developing potential is a value in a predetermined range;
And a storage step of storing a data table indicating a relationship between the applied voltage value corrected in the voltage value correction step and the temperature and humidity in the vicinity of the electrophotographic photosensitive member detected in the temperature / humidity detection step. Exposure amount correction method.

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