JP2019139145A - Image forming apparatus - Google Patents

Abstract

To prevent the occurrence of discharge streaks and the occurrence of exposure memory even when the characteristics of a photoreceptor and a contact charging member are changed.SOLUTION: An image forming apparatus comprises: a contact charging member that charges the surface of a photoreceptor for electrophotography; a static eliminator lamp that irradiates the surface of the photoreceptor after development and transfer with light to eliminate static electricity; a control unit that controls the operation of image formation including a charging bias voltage applied to the contact charging member and turn-on/off of the static eliminator lamp; and an environmental sensor that detects a use environment during image formation. The control unit determines whether to turn on or turn off the static eliminator lamp during image formation on the basis of the detected use environment.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus in which a roller is brought into contact with a photosensitive member to charge the surface thereof.

An electrophotographic image forming apparatus forms a visible image to be printed on the surface of an electrophotographic photosensitive member through processes of charging, exposure, and development, and the visible image formed in the transfer process is formed on a printing sheet. Transcript. The surface of the photoconductor has an endless shape such as a cylinder, for example, and undergoes a cleaning process and, if necessary, a static elimination process to form the next visible image on the photoconductor surface after transfer. Thereafter, charging, exposure, development, and transfer processes are repeated.
In recent years, there are many contact charging systems that charge the surface of a photoreceptor using a contact charging member (for example, a roller or blade) that generates less ozone.

However, in the contact charging unit method, a phenomenon in which streaky charging unevenness (discharge streaks) occurs depending on conditions is known (see, for example, Patent Documents 1 and 2). However, in the case of the contact charging method, the discharge streak does not always occur, and the discharge streak may or may not occur depending on the material of the photoconductor, the material of the contact charging member, the charging voltage, and other various conditions.
In Patent Document 1, the surface of the photoconductor is charged on the upstream side of the abutting portion where the photoconductor and the contact charging member are asymptotically disposed by disposing a static eliminating device upstream of the abutting portion between the photoconductor and the contact charging member. As a result, discharge streaks due to occurrence of peeling discharge downstream of the contact portion are suppressed.
In order to solve the problem that discharge streaks occur when the moving speed of the surface of the photoconductor is slowed even if the charge upstream side of the contact portion is neutralized, Patent Document 2 discloses that Whether to irradiate light on the upstream side of the contact portion with the charging member is changed according to the moving speed of the photosensitive member.

JP-A-5-341626 JP 2012-13951 A

Although the thing of patent document 1 pays attention to suppression of a discharge stripe, and removes the upstream of a contact part, as described in patent document 2, it cannot necessarily suppress a discharge stripe under all conditions. On the other hand, there is a case where no discharge streak occurs even if the configuration as in Patent Document 1 is not taken.
Further, in Patent Document 1, since static elimination (in the embodiment, photo neutralization) is performed to suppress charging on the surface of the photoconductor near the upstream side of the contact portion, the photoconductor is charged immediately after static elimination. This is a condition where fatigue tends to accumulate.
By the way, a method for irradiating substantially uniform light onto the surface of the photoconductor after transfer is known in order to suppress the exposure memory of the photoconductor, although the purpose is different from the suppression of the discharge stripe. Photostatic discharge for the purpose of exposure memory is different from photostatic charge for the purpose of suppressing discharge streaks. The position at which the surface of the photoconductor is irradiated with light is not limited to the vicinity of the upstream side of the contact portion, and may be any downstream side of the transfer process. For example, the irradiation position may be further upstream than the cleaning process.

The inventor has found that discharge streaks may occur when the photoconductor surface after transfer is subjected to photostatic discharge in order to suppress exposure memory during image formation, and in that case, discharge streaks will not occur when photostatic discharge is stopped. It was. That is, it has been found that the suppression of exposure memory and the suppression of discharge streak conflict with respect to the presence or absence of photostatic discharge after transfer.
Furthermore, it has been found that depending on the change in characteristics of the photosensitive member and the contact charging member, discharge streaks are likely to occur or exposure memory is likely to be generated. It has been found that the characteristics of the photoreceptor and the contact charging member change depending on the ambient temperature and humidity during image formation.

Japanese Patent Application Laid-Open No. 2004-228561 controls on / off of a static eliminator during image formation in response to switching of the moving speed (process speed) of the photoconductor during image formation. However, it does not provide a solution when a discharge streak occurs or does not occur at the same process speed depending on the characteristics of the photosensitive member and the contact charging member.
The present invention has been made in consideration of the above-described circumstances. Even if the characteristics of the photosensitive member and the contact charging member are changed, the generation of discharge streaks and the generation of exposure memory is suppressed, and a high-quality image is obtained. An image forming apparatus obtained is provided.

  The present invention relates to a contact charging member that charges the surface of a photoreceptor for electrophotography, a discharge lamp that discharges light by irradiating the surface of the photoreceptor after development and transfer, a charging bias voltage applied to the contact charging member, and A control unit that controls an image forming operation including turning on and off of the static elimination lamp; and an environment sensor that detects a use environment during image formation. The control unit forms an image based on the detected use environment. An image forming apparatus for determining whether to turn on or off the static elimination lamp is provided.

  In the image forming apparatus according to the present invention, the control unit determines whether to turn on or off the static elimination lamp during image formation based on the detected use environment. Therefore, it is possible to provide an image forming apparatus capable of obtaining a high-quality image by suppressing the occurrence of discharge stripes and the occurrence of exposure memory even if the characteristics of the light body and the contact charging member change depending on the use environment.

In this embodiment, it is explanatory drawing which shows the structure which concerns on the image formation of an image forming apparatus. FIG. 2 is a timing chart showing a waveform of a voltage applied to the charging roller shown in FIG. 1 and on / off of a charge removal lamp. FIG. 2 is a timing chart showing waveforms of a charging bias voltage and a developing bias voltage applied to the charging roller and the developing roller shown in FIG. 1, respectively. 5 is a graph qualitatively showing respective regions where exposure memory and discharge stripes are likely to occur at various ambient temperatures and humidity in this embodiment. In this embodiment, it is explanatory drawing which shows the classification | category of the atmospheric temperature / humidity which an environmental sensor detects. In this embodiment, it is explanatory drawing which shows an example in which a control part controls lighting of a static elimination lamp, light extinction, and a lighting light quantity according to atmospheric temperature and humidity.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. In addition, the following description is an illustration in all the points, Comprising: It should not be interpreted as limiting this invention.

<< Configuration of image forming apparatus >>
First, the configuration of the part related to image formation of the image forming apparatus in this embodiment will be described.
FIG. 1 is an explanatory diagram showing a configuration relating to image formation of the image forming apparatus in this embodiment.
As shown in FIG. 1, the image forming apparatus according to this embodiment includes a photoconductive drum 10 that is provided with a photoconductor for electrophotography on a cylindrical surface and rotates around an axis during image formation. An arrow R indicates a direction in which the photosensitive drum 10 rotates during image formation.

A charging roller 11, an exposure unit 13, a developing unit 14, a transfer unit 17, a charge eliminating lamp 18, and a cleaner unit 19 are arranged in this order around the photosensitive drum 10 along the direction of the arrow R.
The charging roller 11 has a charge discharging member (for example, silicone rubber mixed with a conductive agent) having elasticity arranged on the outer periphery of a shaft (core metal) made of a conductive metal (for example, stainless steel).

An output voltage from the charging bias power supply 21 is applied to the core of the charging roller 11.
The cleaning roller 12 comes into contact with the peripheral surface of the charging roller 11 and cleans the surface of the charging roller 11 when toner or paper dust adheres to the surface. The cleaning roller is obtained by winding a cleaning member (for example, a nonwoven fabric) around the outer periphery of a resin core.

The exposure unit 13 irradiates the surface of the photosensitive drum 10 uniformly charged by the charging device (charging roller 11) with light corresponding to image data (image information for printing) output from an image processing unit (not shown). To expose. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 10.
The specific configuration of the exposure unit 13 is generally a laser scanning unit (LSU), but is not limited to this, for example, a minute light emitting element corresponding to a pixel, specifically, EL (Electro Luminescence). Alternatively, a configuration using a writing head in which LEDs (Light Emitting Diodes) are arranged in an array may be used.

  The developing unit 14 visualizes the electrostatic latent image formed on the photosensitive drum 10 with toner. As shown in FIG. 1, the developing unit 14 includes a developing roller 15 that is disposed to face the photosensitive drum 10 and rotates. The developer 16 is supplied from the inside of the developing unit 14 to the outer periphery of the developing roller 15, and the electrostatic latent image formed on the photosensitive drum 10 is visualized by the developer 16.

An output voltage from the developing bias power supply 22 is applied to the developing roller 15.
Note that a two-component developing method using a developer in which a carrier and toner that form a spike on a portion of the developing roller 15 facing the photosensitive drum 10 is used, and a one-component using a powder having both functions. There is a development system, but the development unit 14 does not matter which development system it is.
The transfer unit 17 has a transfer member disposed on the outer periphery of a shaft (core metal) made of a conductive metal (for example, stainless steel). The transfer member is a member having elasticity and a predetermined electrical resistivity (in the present embodiment, a range of 1 × 10 ⁹ to 1 × 10 ¹³ Ω · cm). For example, a silicone rubber or foaming resin containing a conductive agent is included. It is a soft member such as. The transfer member is disposed in contact with the photosensitive drum 10.
The transfer unit 17 conveys a printing sheet (not shown) while pressing it against the photosensitive drum 10.

An output voltage from the transfer bias power source 23 is applied to the transfer unit 17.
In FIG. 1, the transfer unit 17 is composed of one transfer roller, but is not limited thereto. For example, a configuration in which a belt-shaped transfer member is bridged between a plurality of rollers may be employed.
In order to suppress the occurrence of the afterimage phenomenon (exposure memory) of the photoreceptor whose surface is selectively exposed by the exposure unit 13, the static elimination lamp 18 emits uniform light on the surface of the photoreceptor drum 10 via the reflection lens 18L. Irradiate. For example, a discharge lamp in which EL and LEDs are arranged can be used. However, unlike the exposure unit 13, the discharge lamp is intended to irradiate the photosensitive drum 10 uniformly. There is no need to dispose ELs or LEDs and drive them independently, as long as they can be turned on and off collectively. Preferably, the amount of light at the time of lighting can be adjusted. The discharge lamp 18 may be disposed anywhere in the direction along the arrow R as long as it is between the downstream side of the transfer unit 17 and the upstream side of the charging roller 11. The neutralizing lamp 18 in this embodiment is configured by arranging a plurality of LEDs that irradiate light in a direction opposite to the surface of the photosensitive drum 10 in a direction along the rotation axis of the photosensitive drum 10. The reflection lens 18L reflects the light so that the light emitted from the LED is directed toward the surface of the photosensitive drum 10 and is made uniform in the rotation axis direction of the photosensitive drum 10.

  The cleaner unit 19 is a mechanism for cleaning the surface of the photosensitive drum 10 after transfer. The cleaner unit 19 includes a cleaning blade 20. One end of the cleaning blade 20 contacts the surface of the photosensitive drum 10 to remove the toner remaining on the surface of the photosensitive drum 10 after transfer. The toner removed from the surface of the photoreceptor by the cleaning blade 20 is collected in the cleaner unit 19.

Operations of the exposure unit 13, the charge removal lamp 18, the charging bias power source 21, the developing bias power source 22, and the transfer bias power source 23 are controlled by the control unit 25. Further, a drive motor (not shown) is controlled to drive and rotate the photosensitive drum 10 to stop.
Specifically, the control unit 25 controls the exposure unit 13 to control the exposure start timing. Further, the static elimination lamp 18 is controlled to control turning on and off. Furthermore, it may be possible to control the intensity of light emitted during lighting.
For the charging bias power source 21, the developing bias power source 22, and the transfer bias power source 23, the control unit 25 controls on / off and the magnitude (absolute value) of the output voltage.

  From the viewpoint of hardware resources, the control unit 25 includes a CPU, a memory, a timer circuit, an input / output interface circuit, and the like. Further, the CPU executes processing according to a control program stored in the memory. In other words, the function of the control unit 25 is exhibited by organically combining hardware and software.

≪Control of charging bias voltage and static elimination lamp during image formation≫
Next, control of the charging bias voltage and the charge removal lamp during image formation in the image forming apparatus shown in FIG. 1 will be described.
FIG. 2 is a timing chart showing the control of the charging bias voltage Vc applied to the charging roller 11 shown in FIG.
In FIG. 2, the vertical axis of the charging bias voltage Vc graph represents the magnitude (absolute value) of the charging bias voltage Vc applied to the cored bar portion of the charging roller 11. On the other hand, the vertical axis of the graph of the static elimination lamp indicates whether the static elimination lamp 18 is on or off.

When starting image formation, the control unit 25 activates a drive motor (not shown) to rotate the photosensitive drum 10.
Then, as shown in FIG. 2, the control unit 25 controls the charging bias power source 21 to gradually raise the charging bias voltage Vc from zero (OFF state) to a target value. As the charging bias voltage Vc rises, the surface potential of the photosensitive drum 10 gradually increases. In principle, the target value is maintained during image formation. After the image formation is completed, the control unit 25 controls the charging bias power source 21 to gradually lower the charging bias voltage Vc toward zero (OFF state).

Further, as indicated by a solid line in FIG. 2, the control unit 25 turns on the charge removal lamp 18 simultaneously with the rise of the charge bias voltage Vc, and turns off the charge removal lamp 18 at the same time when the fall of the charge bias voltage Vc ends.
Alternatively, as indicated by a chain line in FIG. 2, the control unit 25 keeps the charge removal lamp 18 off during image formation, and turns on the charge removal lamp 18 simultaneously with the start of the fall of the charging bias voltage Vc.
The purpose of lowering the charging bias voltage Vc is to make the surface potential of the photosensitive drum 10 asymptotically approach zero, but the charge on the surface of the photosensitive member supplied by the charging roller 11 does not escape unless the charge is removed. . Accordingly, the surface potential of the photosensitive drum 10 does not decrease. Therefore, the static elimination lamp 18 is turned on simultaneously with the fall of the charging bias Vc. As a result, the photoconductor becomes conductive and charges accumulated on the surface escape to the substrate, so that the surface potential of the photoconductor drum 10 is lowered following the fall of the charging bias voltage Vc.

Then, at the same time as the fall of the charging bias voltage Vc is completed, the static elimination lamp 18 is turned off.
The controller 25 determines whether or not the static elimination lamp 18 is turned on during image formation based on the use environment (temperature and humidity of the atmosphere in this embodiment) detected by the temperature / humidity sensor 26. Details will be described later.
Next, control on the charging bias voltage Vc of the developing bias voltage Vdv applied to the developing roller 15 will be described.

FIG. 3 is a timing chart showing waveforms of the charging bias voltage Vc and the developing bias voltage Vdv during image formation in the image forming apparatus shown in FIG. As shown in FIG. 3, the developing bias voltage Vdv applied to the developing roller 15 by the developing bias power source 22 is preferably applied at a timing in which a waveform similar to the charging bias voltage Vc is synchronized with the charging bias voltage Vc.
The surface potential of the photosensitive member uniformly charged by the charging roller 11 corresponds to the density of the background of the image (the density of the white background of the image) where the toner does not adhere even if developed. The magnitude of the development bias voltage Vdv is preferably maintained at an absolute value level slightly smaller than the surface potential corresponding to the white background density so that background fog does not occur. The difference between the absolute values of the charging bias voltage Vc and the developing bias voltage Vdv at the time of image formation is shown by the fog margin in FIG.

That is, in order to prevent unnecessary toner from adhering to the surface of the photosensitive drum, it is preferable that the developing bias voltage Vdv always maintains a value slightly smaller than the charging bias voltage Vc. It is preferable that the magnitude relationship between the two is the same (that is, the magnitude relationship is not reversed) during the fall.
The surface potential of the photoconductor in the portion exposed by the light of the maximum intensity by the exposure unit 13 corresponds to the high density portion of the image, and the gap between the surface potential of the photoconductor in that portion and the developing bias voltage Vdv It is the range of the surface potential corresponding to the gradation.

  The photosensitive drum 10 moves at a predetermined peripheral speed (also referred to as process speed) during rotation. Therefore, there is a certain time delay from when a certain part on the circumference passes through the contact part with the charging roller 11 until it passes through the part irradiated with light by the static elimination lamp 18. Therefore, the timing set as “simultaneous” in the above control may be shifted by the time delay described above.

That is, the timing at which the charge removal lamp 18 is turned on simultaneously with the rise of the charge bias voltage Vc may be turned on after the period of time delay from the rise of the charge bias voltage Vc. Good.
By controlling in such a manner, a certain portion on the circumference of the photosensitive drum 10 that has passed through the charging roller 11 when the charging bias voltage Vc is started up is irradiated with light from the static elimination lamp 18 after the time delay. When the irradiated part is reached, the static elimination lamp 18 is controlled to be lit. The same applies to the fall of the charging bias voltage Vc.

That is, the timing of charging and discharging is synchronized with reference to the position on the circumference of the photosensitive drum 10 that rotates (relatively moves) with respect to the image forming apparatus. Not only charging and charge removal, but also the timing related to exposure, development, transfer and the like may be synchronized.
In particular, the developing bias voltage Vdv is preferably applied at a timing in which a waveform similar to the charging bias voltage Vc is synchronized with the charging bias voltage Vc. More preferably, the synchronization timing is shifted by a time delay from a certain portion on the circumference of the photosensitive drum 10 passing through the charging roller 11 to the developing roller 15.

≪About the control of the static elimination lamp according to the usage environment≫
The inventor's knowledge about the control of the discharge lamp will be described.
The exposure unit 13 performs area-selective exposure (photostatic discharge) on the surface of the charged photoconductor to generate an electrostatic latent image corresponding to the image pattern on the photoconductor. Therefore, there is a difference between the exposed area on the photoconductor and the unexposed area regarding the history of charging and discharging. Due to this, if a charge that cannot be completely discharged remains in a part of the photosensitive member that is repeatedly used for image formation, it is developed and visualized during the next image formation. This is an afterimage phenomenon called exposure memory.
Whether or not the exposure memory is generated, and the extent to which the afterimage is noticeable when it occurs, depends on the use environment.

The inventor believes that the ease of occurrence of exposure memory depends on the usage environment, and the ease of occurrence of discharge streaks due to contact charging also depends on the usage environment. It was found that the neutralizing light to be irradiated and the ambient temperature and humidity have a great influence.
FIG. 4 is a graph qualitatively showing the findings described above. In FIG. 4, the vertical axis represents the atmospheric humidity during image formation, and the horizontal axis represents the atmospheric temperature during image formation. An area where exposure memory is likely to occur is indicated by a dot pattern.

As shown in FIG. 4, the exposure memory is particularly likely to occur in a low temperature and low humidity environment, but tends to be somewhat likely to occur in a high temperature and high humidity environment. In comparison, it is less likely to occur in an environment between the two (in a room temperature and humidity environment).
When uniform discharge light is applied to the photosensitive member using the discharge lamp 18 after the transfer, exposure memory is less likely to occur than when no discharge light is irradiated.
On the other hand, the occurrence of discharge streaks is also affected by the presence or absence of static elimination light, and the region where discharge streaks are likely to change.

That is, the region where discharge streaks are likely to appear appears on the low temperature side when the static elimination light is not applied, and appears on the higher temperature side when the static elimination light is applied. That is, it has been found that the region where the discharge streaks are likely to move depends on whether or not the static elimination light is applied.
It was found that controlling the presence / absence of neutralizing light during image formation may avoid the generation of discharge streaks while avoiding the occurrence of exposure memory.
Here, the neutralizing light may be in the vicinity of the upstream side of the charging roller as in Patent Document 1, but it may not be so long as it is on the downstream side of the transfer unit.

≪Specific example of static elimination lamp control≫
Hereinafter, a specific method of controlling the static elimination lamp will be described.
The inventor performed image formation by changing the light quantity of the static elimination lamp using the image forming apparatus according to this embodiment under various temperature and humidity environments, and examined the presence or absence of discharge streaks and exposure memory. For example, the presence or absence of discharge stripes and exposure memory was examined under the following conditions.
Verification 1 :
An image was formed using a static elimination lamp light amount of 30% in an environment of 22 ° C./50% Rh.
In that case, no exposure memory occurred in the output image, but a discharge streak occurred.
Verification 2 :
The static elimination lamp was turned off in an environment of 22 ° C / 50% Rh to form an image.
In that case, neither an exposure memory nor a discharge streak occurred in the output image.

Verification 3 :
In the environment of 8 ° C / 20% Rh, the static elimination lamp was turned off to form an image.
In that case, no discharge streaks occurred in the output image, but exposure memory occurred.
Verification 4 :
An image was formed using a 30% static elimination lamp light amount in an environment of 8 ° C./20% Rh.
In that case, no discharge streaks occurred in the output image, but a slight exposure memory occurred.
Verification 5 :
An image was formed using a 100% static elimination lamp light amount in an environment of 8 ° C./20% Rh.
In that case, neither an exposure memory nor a discharge streak occurred in the output image.

Verification 6 :
The static elimination lamp was turned off in an environment of 30 ° C / 60% Rh to form an image.
In that case, no discharge streaks occurred in the output image, but a slight exposure memory occurred.
Verification 7 :
An image was formed by using a 30% static elimination lamp light amount in an environment of 30 ° C./60% Rh.
In that case, neither an exposure memory nor a discharge streak occurred in the output image.

Based on the verification results described above, the charge removal lamp is controlled as described below for the image forming apparatus according to this embodiment.
FIG. 5 is an explanatory diagram showing classification of ambient temperature and humidity detected by the environmental sensor in this embodiment.
In this embodiment, the ambient temperature is classified into four ranges for convenience, and the ambient humidity is classified into five ranges for detection. About atmospheric temperature, it classify | categorizes into the range of 0 degreeC or more and less than 10 degreeC, 10 degreeC or more and less than 20 degreeC, 20 degreeC or more and less than 30 degreeC, and 30 degreeC or more. The atmospheric humidity is classified into ranges of 0% to less than 20%, 20% to less than 40%, 40% to less than 60%, 60% to less than 80%, and 80% or more in terms of relative humidity.
The combinations of the four temperature ranges and the five humidity ranges described above are classified into eight types, and environmental area numbers 1 to 8 are assigned to the combinations.

For example, the range of temperature 0 ° C. or higher and lower than 10 ° C. and relative humidity 0% or higher and lower than 20% is classified as environmental area 1. The range of temperature 0 ° C. or higher and lower than 10 ° C. and relative humidity 20% or higher and lower than 40% is also classified as the same environmental area 1.
In addition, the range of temperature 10 ° C to less than 20 ° C and relative humidity 0% to less than 20% is classified as environmental area 2, and the range of temperature 0 ° C to less than 10 ° C and relative humidity 40% to less than 60% is the same. Are classified into environmental area 2.

The environmental area 3 is wider than the environmental areas 1 and 2, the temperature is 20 ° C. or higher and lower than 30 ° C. and the relative humidity is 0% or higher and lower than 20%, the temperature is 10 ° C. or higher and lower than 20 ° C., and the relative humidity is 20% or higher and 80% or higher. And a range where the temperature is 0 ° C. or more and less than 10 ° C. and the relative humidity is 60% or more.
The environmental areas 4 to 8 are as shown in FIG. 5, and as a tendency, the ambient temperature and humidity from the low temperature and low humidity environment to the high temperature and high humidity environment are classified into a plurality of layers. As shown in FIG. 5, when the humidity and temperature are respectively corresponded vertically and horizontally and are tabulated, they are classified along substantially diagonal lines. This is because the boundary between the area where the exposure memory is likely to occur and the area where the discharge streak is likely to occur tends to follow the hierarchy.

FIG. 4 is a qualitative graph, but the vertical and horizontal axes are the same as in FIG. In both cases, the vertical direction is humidity, and it indicates lower humidity as it goes upward. In both cases, the horizontal direction is the temperature, and the temperature increases toward the right.
Therefore, the area where the exposure memory shown in FIG. 4 is likely to occur, the area where the discharge streak is likely to occur when the static elimination lamp is turned off, and the area where the discharge streak is likely to occur when the static elimination lamp is turned on are considered in FIG. The correspondence with the environmental areas 1 to 8 will be understood.

FIG. 6 is an explanatory diagram illustrating an example in which the control unit controls lighting and extinguishing of the static elimination lamp in accordance with the ambient temperature and humidity in this embodiment. FIG. 6 further shows the relative intensity of irradiation light in% when the static elimination lamp is turned on.
As shown in FIG. 6, in the environmental areas 1 to 3 and 7 to 8, the static elimination lamp is turned on during image formation, while in the environmental areas 4 to 6, the static elimination lamp is extinguished during image formation.
That is, in the former case, the static elimination lamp is turned on during image formation as shown by a solid line in FIG. 2, and in the latter case, the static elimination lamp is turned off during high voltage start-up and image formation as shown by a chain line in FIG. Turn on the static elimination lamp at the fall.

  Furthermore, in FIG. 6, the light quantity at the time of lighting a static elimination lamp, ie, irradiation intensity | strength, is shown. The amount of light is the largest in the low-temperature and low-humidity environment area 1, and the light amount is gradually reduced from the environment area 1 toward the environment area 4 where the static elimination lamp is turned off. On the other hand, since exposure memory is slightly generated under high temperature and high humidity, in the environmental areas 7 and 8 under high temperature and high humidity, the exposure memory is suppressed by turning on the light at 30%.

4, 5, and 6, in an environment where the ambient temperature and humidity are low and low, control is performed to suppress the generation of exposure memory by irradiating the static elimination lamp strongly in an area where exposure memory is likely to be generated. You will understand that. In that region, the discharge streaks can be suppressed by turning on the static elimination lamp.
On the other hand, in an environment where the ambient temperature and humidity are normal temperature and normal humidity, it is difficult to generate exposure memory even if the static elimination lamp is turned off. On the other hand, if the static elimination lamp is turned on, discharge streaks are likely to occur. Turn off the lamp.

In an environment where the ambient temperature is high and high, exposure memory is likely to occur, so the static elimination lamp is turned on. In this region, even when the static elimination lamp is turned on, a discharge streak is unlikely to occur.
By controlling not only lighting and extinguishing of the static elimination lamp, but also by controlling the amount of light at the time of lighting, finer control is realized, and the occurrence of exposure memory and discharge stripes can be suppressed according to the ambient temperature and humidity.

As mentioned above,
(I) An image forming apparatus according to the present invention comprises a contact charging member for charging a surface of a photoreceptor for electrophotography, a charge eliminating lamp for irradiating the surface of the photoreceptor after development and transfer with light, and the contact charging member. A control unit that controls charging bias voltage to be applied to and an image forming operation including lighting and extinguishing of the static elimination lamp, and an environmental sensor that detects a use environment during image formation. It is determined whether to turn on or off the static elimination lamp during image formation based on the usage environment.

  In this invention, the electrophotographic photoreceptor is an optical semiconductor which is formed into a film on the surface of a conductive substrate and changes from insulating to conductive when irradiated with light. The static elimination lamp discharges the charge accumulated on the surface of the photosensitive member to the substrate by irradiating the photosensitive member with light to make it conductive. The contact charging member is a member that charges the photosensitive member by contacting the surface of the photosensitive member that is not irradiated with light and supplying an electric charge. Specific examples thereof include a charging roller and a charging blade. The charging roller in the above-described embodiment corresponds to this contact charging member.

  The environment sensor detects a use environment at the time of image formation. The specific aspect is, for example, a sensor that detects ambient temperature and humidity. The temperature / humidity sensor in the above-described embodiment corresponds to this environmental sensor.

  Furthermore, the control unit controls the static elimination lamp based on the detection of the environmental sensor. The specific aspect is comprised by the electronic circuit containing memory and an input / output circuit centering on CPU, for example.

Furthermore, the preferable aspect of this invention is demonstrated.
(Ii) The environmental sensor may detect ambient temperature and humidity. That is, the temperature and humidity of the atmosphere may be detected as the use environment (Embodiment 1).
In this way, it is determined whether to turn on or off the static elimination lamp during image formation according to the ambient temperature and humidity that greatly affects the characteristics of the photosensitive member and the contact charging member. Generation of exposure memory can be suppressed.
In addition to or instead of the use environment detected by the environment sensor, the control unit turns on the charge eliminating lamp during image formation based on the use period of the photoconductor and the use period of the contact charging member. It may be determined whether to turn off the light. The same applies to the following preferred embodiments. This is because the characteristics of the photosensitive member and / or the contact charging member change depending on the usage period of the photosensitive member and / or the contact charging member, which affects the ease of occurrence of exposure memory and static elimination stripes. Here, the usage period is not limited to time, but may be determined based on the number of printed sheets. (Embodiment 2)

(Iii) The controller can change the amount of light emitted from the static elimination lamp. When the static elimination lamp is lit during image formation, the control unit may control the quantity of light from the static elimination lamp based on the detected use environment. . (Embodiment 3)
In this way, it is possible not only to control whether to turn on or off, but also to control the light quantity of the static elimination lamp, thereby suppressing the occurrence of discharge stripes and the occurrence of exposure memory.

(Iv) The controller may turn on the charge removal lamp when the charging bias voltage applied to the contact charging member is lowered after the image formation is completed. (Embodiment 4)
In this way, the surface potential of the photoconductor can be lowered following the fall of the charging bias voltage by making the surface of the photoconductor light neutralized by the charge eliminating lamp so that no charge is accumulated.

(V) The control unit further controls the development bias voltage applied to the electrophotographic development unit, and controls the charging bias voltage and the development bias voltage depending on whether the charge removal lamp is turned on or off during image formation. The size may be different.
In this way, a high-quality image can be obtained by selecting appropriate charging bias voltage and developing bias voltage so that ground fog does not occur both when the static elimination lamp is turned on and off during image formation. be able to. (Embodiment 5)

(Vi) The contact charging member may be a charging roller.
Preferred embodiments of the present invention include combinations of any of the plurality of embodiments described above.
In addition to the embodiments described above, there can be various modifications of the present invention. These modifications should not be construed as not belonging to the scope of the present invention. The present invention should include the meaning equivalent to the scope of the claims and all modifications within the scope.

10: Photosensitive drum, 11: Charging roller, 12: Cleaning roller, 13: Exposure unit, 14: Development unit, 15: Development roller, 16: Developer, 17: Transfer unit, 18: Static elimination lamp, 18L: Reflective lens , 19: Cleaner unit, 20: Cleaning blade, 21: Charging bias power source, 22: Development bias power source, 23: Transfer bias power source, 25: Control unit, 26: Temperature / humidity sensor

Claims (6)

A contact charging member for charging the surface of a photoreceptor for electrophotography;
A static elimination lamp that radiates light on the surface of the photoreceptor after development and transfer;
A control unit that controls an operation of image formation including a charging bias voltage applied to the contact charging member and lighting and extinguishing of the static elimination lamp;
With an environmental sensor that detects the usage environment during image formation,
The control unit is an image forming apparatus that determines whether to turn on or off the static elimination lamp during image formation based on the detected use environment.   The image forming apparatus according to claim 1, wherein the environmental sensor detects ambient temperature and humidity. The control unit can further change the lighting amount of the static elimination lamp,
The image forming apparatus according to claim 1, wherein when the static elimination lamp is turned on during image formation, the light amount of the static elimination lamp is controlled based on the detected use environment.   The image forming apparatus according to claim 1, wherein the controller turns on the charge removal lamp when the charging bias voltage applied to the contact charging member is lowered after image formation is completed. The control unit further controls a development bias voltage applied to the electrophotographic development unit,
5. The image forming apparatus according to claim 1, wherein the charge bias voltage and the developing bias voltage are made different depending on whether the static elimination lamp is turned on or off during image formation.   The image forming apparatus according to claim 1, wherein the contact charging member is a charging roller.