JP5172259B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to an image forming apparatus using an intermediate transfer system.

  As charging means for uniformly charging the photosensitive member, those utilizing discharge are known. When the discharge is used, discharge products such as ozone and nitrogen oxide are generated along with the discharge. In the charging roller method, discharge occurs only between the charging roller and the photoconductor, so that the amount of discharge products generated is smaller than that in the charging charger method.

  However, since the discharge concentrates in a narrow space between the charging roller and the photoconductor, the amount of discharge products adhering to the surface of the photoconductor increases. In particular, in the case of a charging roller to which an AC voltage is applied, this tendency is more remarkable because the number of discharges is increased. Since the discharge product adhering to the surface of the photoreceptor is a hydrophilic substance, the electrical resistance on the surface of the photoreceptor may be reduced, and the image may flow in a high temperature and high humidity environment. In particular, when a photosensitive member that is difficult to remove the photosensitive layer, such as an amorphous silicon photosensitive member, is used, the image flow becomes remarkable.

  In order to suppress this image flow, it is known that a method in which the surface of the photosensitive member is heated to scatter the discharge product, which is a hydrophilic substance, is effective. As a heating method, there are a method of providing a heater inside the photosensitive member or in the vicinity of the surface of the photosensitive member, a method of guiding the heat of the fixing device into the photosensitive member, and the like. In order to suppress image flow by providing a heater inside the photoreceptor, as disclosed in Patent Document 1, it is possible to energize the heater only when the image forming apparatus is turned on from the viewpoint of energy saving. desirable. Further, in order to shorten the rise time of the image forming apparatus (the time until an image that does not cause image flow can be output), the surface of the photoconductor is heated in a short time from the start of energization of the heater. It is necessary to suppress the occurrence.

  In order to effectively heat the surface of the photoconductor, it is desirable to provide a heater in or near the photoconductor, but it is difficult to mount a heater or the like inside the photoconductor, particularly in a small image forming apparatus. Installation in the vicinity of the photoreceptor is also difficult in terms of space. Further, in a color image forming apparatus using an intermediate transfer member, since the heat capacity of the intermediate transfer member is large, the heat of the photosensitive member is easily taken away by the intermediate transfer member, so that the surface of the photosensitive member can be efficiently heated. Have difficulty. In many cases, the intermediate transfer member itself absorbs water, and the transfer of moisture from the intermediate transfer member to the surface of the photosensitive member also hinders image flow suppression.

  In order to solve these problems, Patent Document 2 discloses an image forming apparatus in which a heater is provided below the intermediate transfer member. Since the space below the intermediate transfer member is often more space-wise than the vicinity of the photosensitive member, it is easy to install a heater. Further, there is no problem that the heat of the photosensitive member is taken away by the intermediate transfer member.

JP 2002-40876 A JP 2004-191790 A

  However, since an intermediate transfer member exists between the heater and the photosensitive member, it is necessary to set the output of the heater to be high in order to suppress the image flow by heating the surface of the photosensitive member in a short time. As a result, the temperature of the intermediate transfer member also becomes high, and there is a concern that the influence of heat on the intermediate transfer member itself and the intermediate transfer member peripheral element is a new problem.

  Therefore, a main object of the present invention is to provide a small-sized and low-cost image forming apparatus that can suppress an image flow due to a discharge product and that is less affected by heat on the intermediate transfer member itself and the intermediate transfer member peripheral element. That is.

The invention according to claim 1 includes at least a charging roller, a photosensitive member, an intermediate transfer member, a cleaning unit disposed in the vicinity of the photosensitive member , and a sensor that detects an in-machine temperature, an outside temperature, and an outside humidity of the image forming apparatus. An image forming apparatus comprising:
A heater that can be energized only when the image forming apparatus is powered on is installed near the intermediate transfer member,
The start of energization of the heater is determined according to the detection value of the sensor,
Almost simultaneously with the start of energization of the heater, a refresh operation is performed in which the non-transfer toner supplied to the surface of the photoconductor and developed is supplied to the cleaning unit, and the cleaning unit rubs the surface of the photoconductor through the non-transfer toner. ,
The heater output is set to be low when a predetermined time has elapsed since the start of energization of the heater, and even within the predetermined time, the sensor responds to detected values of the in-machine temperature and the outside temperature of the image forming apparatus. The heater output is set low,
While the heater is energized, the AC voltage applied to the charging roller is 77% to 91% of the voltage applied to the charging roller during image formation in an environment of a temperature of 23 ° C. and a humidity of 50%. That it is configured,
An image forming apparatus characterized by the above.
The invention according to claim 2 is an invention dependent on the invention according to claim 1, and the AC voltage applied to the charging roller is set to 850 V to 1000 V while the heater is energized. An image forming apparatus.

In the present invention , by setting the heater output high for a predetermined time from the start of energization of the heater, the surface of the photoreceptor is heated in a short time, and the rise time of the image forming apparatus (an image that does not cause image flow is output). The time until it becomes possible. When a predetermined time elapses from the start of energization of the heater, the output of the heater decreases, so that the influence of heat on the intermediate transfer member itself and the intermediate transfer member peripheral elements can be suppressed.

In general, when the AC voltage applied to the charging roller is too high, the amount of discharge products adhering to the surface of the photoconductor increases, and image flow tends to occur. Conversely, when the AC voltage applied to the charging roller is too low, the surface of the photoreceptor becomes non-uniform. That is, there is an optimum value for the AC voltage applied to the charging roller. The optimum value decreases when the temperature of the charging roller becomes high. In the present invention , the photosensitive member is heated by the heater, and the charging roller in contact with the photosensitive member is also heated, so that an AC voltage applied to the charging roller is normally formed in an environment of, for example, a temperature of 23 ° C. and a humidity of 50%. The voltage is set to 77% (850 V) to 91% (1000 V) of the voltage (1100 V) applied to the charging roller. As a result, the amount of discharge products adhering to the surface of the photoreceptor is suppressed, and the image flow is further less likely to occur.

In addition, when the external environment is not high temperature and high humidity when the image forming apparatus is turned on, the discharge product absorbs less water and the image flow due to the discharge product is less likely to occur, so there is no need to energize the heater. Rather, thermal damage to the intermediate transfer member and peripheral elements is likely to occur. In the present invention , unnecessary heating is prevented by determining whether to energize the heater according to the detection values of the sensors that detect the in-machine temperature, the outside temperature, and the outside humidity of the image forming apparatus. Thus, the intermediate transfer member and peripheral elements are protected from heat damage.

In the present invention, the output control of the heater is controlled by the elapsed time from the power-on of the image forming apparatus. For example, when continuous printing is performed immediately after the start of the image forming apparatus, before the heater output is switched low, There is a concern that the temperature may rise and cause toner fusing. In the present invention , the temperature inside the machine and the temperature outside the machine are detected, and if the difference is greater than or equal to a predetermined value, it is determined that the inside of the image forming apparatus is sufficiently warmed (and the surface of the photoreceptor is also sufficiently heated). Control to lower the output low. As a result, toner fusion can be suppressed, and the intermediate transfer member and peripheral elements can be protected from thermal damage.

A third aspect of the invention is an image forming apparatus according to the first or second aspect of the invention, wherein the photoconductor is made of amorphous silicon.

According to the third aspect of the present invention, a good image can be provided in the long term even with an image forming apparatus using an amorphous silicon photoconductor that is liable to cause image flow.

  According to the image forming apparatus of the present invention, since the heater output is set to be low when a predetermined time has elapsed from the start of energization to the heater, the heater output is increased for a predetermined time from the start of energization to the heater. By setting to, the photosensitive member surface can be heated in a short time, and the rise time of the image forming apparatus can be shortened. When a predetermined time elapses from the start of energization of the heater, the output of the heater decreases, so that the influence of heat on the intermediate transfer member itself and the intermediate transfer member peripheral element can be suppressed. As a result, it is possible to obtain a small and low-priced image forming apparatus that can suppress the image flow due to the discharge product and has little influence of heat on the intermediate transfer member itself and the intermediate transfer member peripheral element.

  The above-described object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

  FIG. 1 is a schematic diagram showing an example of an image forming apparatus (color laser printer) according to the present invention.

  In the lower part of the main body of the image forming apparatus 1, a paper feed unit 2 such as a paper feed cassette that accommodates a stack of stacked paper is provided. At one end portion of the paper feeding unit 2, a separation feeding unit 3 for feeding the stacked paper P one by one from the uppermost paper is provided.

  Above the paper feed unit 2, a conveyance path 5 is formed that extends substantially horizontally from the main body right side surface portion to the main body left side surface portion and further extends upward to the paper discharge tray 4 formed on the upper surface of the main body. The separating and feeding means 3, the transport roller pair 6, the secondary transfer roller 7, the fixing roller pair 8, the transport roller pairs 9, 10 and the paper discharge roller pair 11 are arranged in this order along the transport path 5 from the upstream side. Yes.

  An endless intermediate transfer belt 12 is rotatably disposed above the horizontal conveyance path 5. The intermediate transfer belt 12 is suspended from a drive roller 13, a driven roller 14, a tension roller 15 and a primary transfer roller 16, and the drive roller 13 is driven to rotate, so that the intermediate transfer belt 12 and the rollers 14, 15, 16 are indicated by arrows. It is designed to rotate clockwise. The driving roller 13 is in contact with the secondary transfer roller 7 via the intermediate transfer belt 12, and a cleaning blade 17 is driven downstream of the contact portion (secondary transfer region) in the rotation direction of the intermediate transfer belt 12. 13 is in contact with the transfer belt 12 so as to be in pressure contact therewith. The primary transfer roller 16 is in contact with a photosensitive drum 18 that is an image carrier via the intermediate transfer belt 12. The photosensitive drum 18 is made of amorphous silicon.

  The photosensitive drum 18 is rotated counterclockwise by a driving device (not shown), and a charging roller 19, which is a contact charger, a developing unit 20, a primary transfer roller 16, a cleaning roller 21, and a cleaning blade are sequentially arranged along the rotation direction. 22 is disposed. The charging roller 19 abuts on the upper portion of the photosensitive drum 18 and rotates following the rotation of the photosensitive drum 18. A conductive brush roller 23 as a charger cleaning member is disposed in contact with the charging roller 19 in the longitudinal direction on the opposite side of the photosensitive drum 18 from the charging roller 19. A laser optical unit 24 using a known optical system is disposed above the developing unit 20.

  The developing unit 20 has a substantially cylindrical shape as a whole, and is supported rotatably at both ends thereof. The interior of the developing unit 20 is divided into four rooms by a cross-shaped partition wall 20a, which corresponds to yellow (Y), magenta (M), cyan (C), and black (K) toners. Thus, four developing units 25Y, 25M, 25C, and 25K are configured. In addition, arrangement | positioning of the image development apparatus to illustrate is an example, Comprising: It is not limited to this.

  Each of the developing devices 25Y, 25M, 25C, and 25K includes developing rollers 26, 27, 28, and 29 that are individually driven to rotate. Further, a drive unit is connected to the developing unit 20 via a clutch (not shown), and by driving the drive unit, the developing unit 20 rotates to select a developing roller of any developing unit. For example, the developing operation is performed by being disposed opposite to the photosensitive drum 18.

  At the time of image formation, the photosensitive drum 18 is driven to rotate, whereby the charging roller 19 is driven to rotate and the surface 18a of the photosensitive drum 18 is uniformly charged. Based on the input image signal, the laser optical unit 24 operates to irradiate the charged photosensitive drum 18 with the laser light L, and an electrostatic latent image is formed on the surface 18a of the photosensitive drum 18. The The electrostatic latent image thus formed is developed by the developing unit 20 as follows.

  That is, in the case of monochrome image formation, only the developing roller 29 of the developing device 25K is disposed opposite to the photosensitive drum 18 on which the electrostatic latent image is formed to form a black toner image on the surface 18a of the photosensitive drum 18. To do. In the case of color image formation, the developing unit 20 is rotated by driving the driving unit, and the developing rollers 26, 27, 28, and 29 of the four developing units 25Y, 25M, 25C, and 25K are sequentially and selectively exposed. A toner image of each color is formed on the surface 18 a of the photosensitive drum 18 so as to face the photosensitive drum 18.

  The toner image formed on the surface 18 a of the photosensitive drum 18 in this way is primarily transferred onto the intermediate transfer belt 12 that rotates clockwise by the primary transfer roller 16. That is, in the case of monochrome image formation, the black toner image formed on the surface 18a of the photosensitive drum 18 is transferred onto the transfer belt 12 rotated by the primary transfer roller 16 to form a monochrome image. In the case of color image formation, the toner images of the respective colors formed on the surface 18a of the photosensitive drum 18 are transferred onto the intermediate transfer belt 12 that is sequentially rotated by the primary transfer roller 16, and these are superimposed to form a color image. To do. In the case of color image formation, the cleaning blade 17 is separated from the intermediate transfer belt 12 during the primary transfer operation.

  Then, in a predetermined secondary transfer region, the secondary transfer roller 7 feeds the paper P fed from the paper feed unit 2 by the separation feeding unit 3 and further transported along the transport path 5 by the transport roller pair 6. The monochrome image or color image on the intermediate transfer belt 12 is secondarily transferred at once.

  In this way, the paper P on which the monochrome image or color image is transferred is transported in the substantially horizontal direction on the transport path 5, and the toner image on the paper P is heated and fixed by the fixing roller pair 8. After fixing, the paper P is changed in the transport direction upward at the downstream portion of the transport roller pair 9, further transported on the transport path 5 by the transport roller pair 10, and finally onto the paper discharge tray 4 by the paper discharge roller pair 11. The paper is ejected.

  The untransferred toner that is not primarily transferred and remains on the photosensitive drum 18 is removed by the cleaning roller 21 and the cleaning blade 22. Untransferred toner that has not been secondarily transferred and remains on the intermediate transfer belt 12 is removed by the cleaning blade 17. The removed toner is conveyed to a waste bottle (not shown) by a toner collecting device such as a collecting screw.

  A heater 30 is installed below the intermediate transfer belt 12. The heater 30 has an output of 8 W when 24 V is applied. By continuously turning on / off the energization of the heater 30, it is possible to artificially change the power consumption of the heater 30 to 4W. Further, the image forming apparatus 1 is provided with an in-machine temperature sensor and an outside temperature / humidity sensor (not shown).

  Next, the image flow preventing operation of the image forming apparatus 1 will be described with reference to the flowchart shown in FIG. First, after the power of the image forming apparatus 1 is turned on, in step S1, the ambient temperature / humidity sensor detects the ambient temperature / humidity to determine whether the environment is a high temperature / humidity environment. That is, when the condition of the temperature of 26 ° C. or higher and the humidity of 70% or higher (condition that moisture easily adheres to the surface of the photosensitive drum 18) is satisfied, it is determined that the external environment is high temperature and high humidity, and the heater 30 is determined in step S2. Is energized to heat the surface of the photosensitive drum 18 via the intermediate transfer belt 12.

  On the other hand, if the above condition is not satisfied, it is determined that the external environment is not high temperature and high humidity (the image does not easily flow due to the discharge product because moisture hardly adheres to the surface of the photosensitive drum 18), and the heater 30 is determined. In step S8, printing is enabled and printing is performed as appropriate. This prevents unnecessary heater heating and protects the intermediate transfer belt 12 and peripheral elements from thermal damage.

  When energization of the heater 30 is started in step S2, the image forming apparatus 1 performs a refresh operation described in detail below in order to remove moisture and discharge products on the surface of the photosensitive drum 18 almost simultaneously in step S3. I do.

  With the photosensitive drum 18 and the intermediate transfer belt 12 being driven, black toner is supplied from the developing unit 25K to the photosensitive drum 18 by bias development for 100 milliseconds. By setting the primary transfer bias to a reverse bias, most of the black toner is not transferred but sent to the cleaning roller 21 and the cleaning blade 22. By rubbing the surface of the photosensitive drum 18 with the cleaning roller 21 and the cleaning blade 22 through the black toner, moisture on the surface of the photosensitive drum 18 and discharge products are removed. In the refresh operation, the bias development is repeated 6 times every 30 seconds.

  The image forming apparatus 1 starts energizing the heater 30 after the power is turned on and performs the refresh operation. After that (after about 3 minutes after the image forming apparatus 1 is turned on), the image forming apparatus 1 becomes ready for printing in step S4. Thereafter, printing is appropriately performed. At this time, since the surface of the photosensitive drum 18 is heated and heated by the heater 30, an AC voltage applied to the charging roller 19 is applied to the charging roller during normal image formation in an environment of, for example, a temperature of 23 ° C. and a humidity of 50%. It is set to 77% (850V) to 100% (1100V) of the current voltage (1100V). As a result, the amount of discharge products adhering to the surface of the photosensitive drum 18 is suppressed, and the image flow is further less likely to occur.

  In the image forming apparatus 1, the output control of the heater 30 is controlled by the elapsed time from the power-on of the image forming apparatus 1. That is, after the power is turned on in step S6, the image forming apparatus 1 is sufficiently warmed (and the surface of the photosensitive drum 18 is also sufficiently heated when a predetermined time (set to 30 minutes in the present embodiment) elapses). In step S7, the output of the heater 30 is switched from 8W to 4W.

  However, for example, when continuous printing is performed immediately after the image forming apparatus 1 starts up, there is a concern that the temperature inside the apparatus rises and the toner is fused before the output of the heater 30 is switched to a low level. Therefore, in step S5, the image forming apparatus 1 detects the in-machine temperature and the outside temperature at every predetermined time (for example, every few minutes) by using the in-machine temperature sensor and the outside temperature / humidity sensor. When the in-machine temperature becomes higher by 4 ° C. or more than the outside temperature, the inside of the image forming apparatus 1 is sufficiently warmed (and the photosensitive drum) even if the elapsed time from the power-on of the image forming apparatus 1 is within 30 minutes. In step S7, the output of the heater 30 is switched from 8W to 4W and lowered. As a result, there is no concern that the temperature inside the apparatus will rise and cause toner fusion or the like before switching the output of the heater 30 to a low level. In the case of this embodiment, the in-machine temperature can be maintained below 50 ° C. by switching the output of the heater 30 from 8 W to 4 W.

  Using this image forming apparatus 1, a total of 10,000 color images were formed at a temperature of 23 ° C. and a humidity of 50% and each color printing rate was 3%, and the discharge product was intentionally formed on the surface of the photosensitive drum 18. Generated. During printing, the value of the AC voltage applied to the charging roller 19 was set to 1100V. This is because when the value of the AC voltage is smaller than 1050 V, image noise caused by uneven resistance and contamination of the charging roller 19 is not at an allowable level. However, the threshold value of the AC voltage applied to the charging roller 19 is lowered in a high temperature and high humidity environment.

  After the color image formation of 10,000 sheets was completed, the image forming apparatus 1 was left in a high temperature and high humidity environment with a temperature of 30 ° C. and a humidity of 85% with the power supply turned off. After being left, the power supply of the image forming apparatus 1 was turned on and the above refresh operation was performed to enable printing, and image flow, image noise caused by the charging roller, and internal temperature were evaluated. Operating conditions and evaluation results are shown in Table 1.

The evaluation of the image flow was that character images were printed immediately after the start-up (after about 3 minutes), 30 minutes after the power was turned on, and 60 minutes later, and the printed state was visually evaluated in four ranks.
Rank A: Little character flow is observed.
Rank B +: Although there is a slight flow of characters, the level is almost inconspicuous.
Rank B: Although the character flow is conspicuous, it is a practical level.
Rank C: The flow of characters is so bad that it is not at a practical level.

The image noise caused by the charging roller 19 is evaluated in three stages immediately after the start-up (after about 3 minutes), 30 minutes after the power is turned on, and 60 minutes after the halftone dot image is printed. Rated by rank.
Rank A: Almost no noise is observed.
Rank B: An acceptable level with some noise due to uneven resistance and dirt on the charging roller 19.
Rank C: Noise due to uneven resistance and dirt on the charging roller 19 is severe.

The in-machine temperature was evaluated by monitoring the temperature of the cleaning blade 17 of the intermediate transfer belt 12 immediately after the start-up and until the end of image printing 60 minutes later, and evaluating the maximum temperature reached in three ranks. When the temperature of the cleaning blade 17 reaches 55 ° C. or more, the toner is likely to be fused to the intermediate transfer belt 12 or the cleaning blade 17.
Rank A: The maximum temperature reached is less than 50 ° C.
Rank B: The highest temperature reached is 50 ° C or higher and lower than 55 ° C.
Rank C: The maximum temperature reached is 55 ° C or higher.

  Comprehensive evaluation is ◯ when the image flow evaluation, image noise evaluation, and in-machine temperature evaluation are all rank A or B +, △ if there is one rank B and no rank C, △ even if one rank C is Some cases were marked with x.

(Example 1 to Example 6)
In Example 1, the power supply of the image forming apparatus 1 was turned on, and energization was started at an output 8 W of the heater 30. The AC voltage applied to the charging roller 19 at the time of image printing is 850 V (77%: temperature 23 ° C., humidity 50%, and the ratio when the voltage 1100 V applied to the charging roller 19 during image formation is 100%. The same applies hereinafter). Further, after 30 minutes after the image forming apparatus 1 is turned on, the output of the heater 30 is set to 4 W (the power supply to the heater is turned on / off every 30 seconds). In Examples 2, 3, 4, 5, and 6, the AC voltages applied to the charging roller 19 during image printing are 900 V (82%), 950 V (86%), It is the same as Example 1 except the point set to 1000V (91%), 1050V (95%), and 1100V (100%).

  According to the first to sixth embodiments, by controlling the output of the heater 30 and the AC voltage applied to the charging roller 19, an image free from image flow and image noise can be obtained, and the in-machine temperature can be adjusted to the toner fusion. We were able to maintain the level without any problem of wearing.

  Further, by setting the AC voltage applied to the charging roller 19 to 1100 V or less, it was possible to suppress the image flow. In particular, since the surface of the photosensitive drum 18 is not sufficiently heated, it is effective immediately after the start-up that tends to cause an image flow.

  Further, the output of the heater 30 is set high immediately after the image forming apparatus 1 is turned on, and is lowered after 30 minutes, so that the image flow immediately after the start-up is suppressed, and the rise in the in-machine temperature is also suppressed to a level with no problem. I was able to.

(Comparative Examples 1 to 2)
In Comparative Example 1, the power supply of the image forming apparatus 1 was turned on and energization was started at an output 4 W of the heater 30 (energization to the heater 30 was turned on / off every 30 seconds). The AC voltage applied to the charging roller 19 during image printing was set to 900 V (82%). Further, the output of the heater 30 was maintained at 4 W even after 30 minutes after the image forming apparatus 1 was turned on. Immediately after the start-up and 30 minutes later, an image flow occurred, so the overall evaluation was x. This is considered to be because when the output of the heater 30 is 4 W, the surface of the photosensitive drum 18 is not sufficiently heated, and the temperature does not reach a temperature sufficient to suppress the image flow.

  Further, in Comparative Example 2, energization was started at an output 8 W of the heater 30 when the image forming apparatus 1 was turned on. The AC voltage applied to the charging roller 19 during image printing was set to 900 V (82%). Further, the output of the heater 30 was maintained at 8 W even after 30 minutes after the image forming apparatus 1 was turned on. Although there was no problem on the image, the maximum evaluation temperature of the cleaning blade 17 of the intermediate transfer belt 12 reached 55 ° C. or higher.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is carried out within the range of the summary.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. 6 is a flowchart illustrating an image flow prevention operation of the image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 12 Intermediate transfer body 18 Photosensitive drum 19 Charging roller 30 Heater

Claims (3)

An image forming apparatus comprising at least a charging roller, a photosensitive member, an intermediate transfer member, a cleaning unit disposed in the vicinity of the photosensitive member , and a sensor for detecting an in-machine temperature, an outside temperature, and an outside humidity of the image forming apparatus. And
A heater that can be energized only when the image forming apparatus is powered on is installed in the vicinity of the intermediate transfer member,
The start of energization to the heater is determined according to the detection value of the sensor,
Almost simultaneously with the start of energization of the heater, the non-transfer toner supplied to the surface of the photoconductor and developed is supplied to the cleaning unit, and the cleaning unit rubs the surface of the photoconductor through the non-transfer toner. A refresh operation is performed,
When a predetermined time has elapsed from the start of energization of the heater, the output of the heater is set to be low, and even within the predetermined time, the internal temperature and the external temperature of the image forming apparatus by the sensor In accordance with the detected value, the heater output is set to be low,
While the heater is energized, the AC voltage applied to the charging roller is 77% to the voltage applied to the charging roller during image formation in an environment of a temperature of 23 ° C. and a humidity of 50%. Is set to 91%,
An image forming apparatus. The image forming apparatus according to claim 1, wherein an AC voltage applied to the charging roller is set to 850 to 1000 V while the heater is energized. The image forming apparatus according to claim 1 , wherein the photoconductor is made of amorphous silicon.

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