JP2015219435A - Image forming apparatus, and control method of image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can prevent insufficient charging of an image carrier while suppressing a current flowing through the image carrier, and a controlling method of the same.SOLUTION: In an image forming apparatus 10, a second charging part 42b charges the surface of an image carrier 41 at a position on the downstream side in the direction of rotation of the image carrier 41 with respect to the position of a first charging part 42a, and a control part 8 performs voltage ratio adjustment of increasing a ratio of a voltage to be applied to the first charging part 42a to a voltage to be applied to the second charging part 42b according to a reduction in both temperature and humidity of an environment.

Description

  The present invention relates to an electrophotographic image forming apparatus and a control method thereof.

  In general, it is known that an electrophotographic image forming apparatus includes a charging unit that charges the surface of a drum-shaped image carrier. The charging unit includes a charging roller that rotates in contact with the surface of the image carrier, and a charging voltage is applied thereto.

  In addition, it is known that two charging units are provided around the image carrier in order to shorten the time of one cycle of image formation including charging, development, and image transfer (for example, Patent Document 1). reference).

JP 2001-5256 A

  By the way, when the temperature and humidity of the surrounding environment of the image carrier are lowered, the efficiency with which the charging unit charges the image carrier is deteriorated, and the image carrier may be insufficiently charged.

  On the other hand, in order to avoid the insufficient charging, it is conceivable to set the applied voltage level to the charging unit high. In this case, the level of current flowing through the image carrier increases, which may cause a problem that the life of the image carrier is shortened.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of preventing insufficient charging of an image carrier while suppressing a current flowing through the image carrier and a control method thereof.

  An image forming apparatus according to one aspect of the present invention includes a rotating image carrier, a first charging unit, a second charging unit, and a control unit. The first charging unit charges the surface of the image carrier at a first position around the image carrier. The second charging unit charges the surface of the image carrier at a second position downstream of the first position in the rotation direction of the image carrier. The controller performs voltage ratio adjustment that increases a ratio of an applied voltage to the first charging unit with respect to an applied voltage to the second charging unit in accordance with a decrease in environmental temperature and humidity.

  An image forming apparatus control method according to another aspect of the present invention is an image forming apparatus control method including the image carrier, the first charging unit, and the second charging unit. This control method has an input process and a voltage ratio adjustment process. The input step is a step of inputting environmental temperature and humidity. The voltage ratio control step is a step of increasing a ratio of an applied voltage to the first charging unit with respect to an applied voltage to the second charging unit according to a decrease in each of the temperature and the humidity.

  According to the present invention, it is possible to provide an image forming apparatus and its control method capable of preventing insufficient charging of the image carrier while suppressing the current flowing through the image carrier.

FIG. 1 is a configuration diagram of an image forming apparatus according to the first embodiment of the present invention. FIG. 2 is a block diagram of a charging-related control device in the image forming apparatus according to the first embodiment of the present invention. FIG. 3 is a flowchart illustrating an example of a charging voltage control procedure executed by the control unit of the image forming apparatus according to the first embodiment of the present invention. FIG. 4 is a graph showing an example of a parameter for adjusting the charging voltage ratio based on the temperature in the image forming apparatus according to the first embodiment of the present invention. FIG. 5 is a graph showing an example of a parameter for adjusting the charging voltage ratio based on humidity in the image forming apparatus according to the first embodiment of the present invention. FIG. 6 is a configuration diagram of an image forming apparatus according to the second embodiment of the present invention. FIG. 7 is a graph showing an example of a second charging voltage level adjustment parameter based on the temperature in the image forming apparatus according to the third embodiment of the present invention. FIG. 8 is a graph showing an example of a second charging voltage level adjustment parameter based on humidity in the image forming apparatus according to the third embodiment of the present invention. FIG. 9 is a graph showing the relationship between the transfer charge amount and the reduced charging voltage in the photoreceptor. FIG. 10 is a graph showing the relationship between the charging voltage and the reduced charging voltage of the first charging unit in the photoreceptor.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the following embodiment is an example which actualized this invention, Comprising: It does not have the character which limits the technical scope of this invention.

[First Embodiment]
First, the configuration of the image forming apparatus 10 according to the first embodiment of the present invention will be described with reference to FIGS. The image forming apparatus 10 is an electrophotographic image forming apparatus. As shown in FIG. 1, the image forming apparatus 10 includes a sheet supply unit 2, a sheet conveyance unit 3, an image forming unit 4, an optical scanning unit 5, a fixing unit 6, a temperature sensor 801, and a humidity sensor 802 in a housing 100. And a control unit 8 and the like.

  The image forming apparatus 10 is, for example, a printer, a copier, a facsimile machine, or a multifunction machine.

  The sheet supply unit 2 includes a sheet cassette 21 that can be attached to and detached from the housing 100, and a sheet delivery unit 22 that sends out the recording sheet 9 accommodated in the sheet cassette 21 to the image forming unit 4. The recording sheet 9 is a sheet-like image forming medium such as paper, coated paper, postcard, envelope, and OHP sheet.

  The sheet delivery unit 22 includes a pickup roller 221 and a delivery roller 222. The sheet delivery unit 22 picks up the recording sheets 9 one by one from the sheet cassette 21 and further sends the recording sheets 9 to the conveyance path 30 of the sheet conveyance unit 3.

  The sheet conveyance unit 3 includes a registration roller 31, a conveyance roller 32, a discharge roller 33, and the like. The registration roller 31 and the transport roller 32 transport the recording sheet 9 along the transport path 30, and the discharge roller 33 discharges the recording sheet 9 after image formation from the discharge port 300 of the transport path 30. It is discharged onto the tray 101.

  The image forming unit 4 forms an image on the surface of the recording sheet 9 moving on the conveyance path 30. The image forming unit 4 includes a drum-shaped photoconductor 41, two charging units 42a and 42b, a developing unit 43, a charge eliminating unit 44, a transfer unit 45, a cleaning unit 47, and the like. The photoreceptor 41 is, for example, an organic photoreceptor. The photoreceptor 41 is an example of an image carrier.

  The two charging units 42 a and 42 b include a first charging unit 42 a and a second charging unit 42 b disposed around the photoconductor 41, respectively. The second charging unit 42b is disposed at a position (second position) downstream of the position of the first charging unit 42a (first position) in the rotation direction of the photoconductor 41.

  The photoconductor 41 rotates, and the first charging unit 42a and the second charging unit 42b uniformly charge the surface of the photoconductor 41. The first charging unit 42a and the second charging unit 42b include a charging roller that rotates in contact with the surface of the photoconductor 41 in a state where a charging voltage (charging voltage) is applied. The charging roller charges the photoreceptor 41 with an applied voltage. The charging voltage is, for example, a DC voltage.

  Further, an electrostatic latent image is written on the surface of the photosensitive member 41 charged by the optical scanning unit 5 scanning the laser beam, and the developing unit 43 supplies toner to the photosensitive member 41, thereby The electrostatic latent image is developed into a toner image.

  Further, the transfer unit 45 transfers the toner image of the photoconductor 41 to the recording sheet 9 moving on the first conveyance path 301. Finally, the cleaning unit 47 removes the toner remaining on the surface of the photoreceptor 41.

  Further, the charge removal unit 44 discharges the surface of the photoconductor 41 by irradiating the surface of the photoconductor 41 with light (discharge light). In the present embodiment, the static eliminator 44 is located at a position between the position of the first charging unit 42a (the first position) and the position of the second charging unit 42b (the second position). The surface of the body 41 is neutralized.

  The two charging portions 42a and 42b charge the photoconductor 41 in two stages, so that the photoconductor 41 is reliably charged even when rotating at a higher speed. Further, when the photoconductor 41 is neutralized during the two-stage charging as described above, the charging voltage of the first charging portion 42a can be set higher. It is possible to reliably charge the battery.

  The fixing unit 6 sandwiches the recording sheet 9 on which the toner image is formed between a fixing roller 61 including a heater 610 such as a halogen heater and a pressure roller 62, and sends the recording sheet 9 to a subsequent process. Thus, the fixing unit 6 heats the toner image (image) on the recording sheet 9 and fixes the image on the recording sheet 9.

  The temperature sensor 801 and the humidity sensor 802 are sensors that measure the temperature and humidity of the environment in which the image forming unit 4 (the photoconductor 41) is disposed, respectively. The temperature sensor 801 and the humidity sensor 802 are arranged in the casing 100 or at a position along the casing 100.

  For example, the temperature sensor 801 and the humidity sensor 802 are attached to the position of the control unit 8 or a position around it. It is also conceivable that the temperature sensor 801 and the humidity sensor 802 are arranged at a position closer to the photoconductor 41.

  The temperature sensor 801 is, for example, a thermistor. The humidity sensor 802 is, for example, a polymer capacitive humidity sensor or a polymer resistance humidity sensor. In addition, a temperature / humidity sensor in which the temperature sensor 801 and the humidity sensor 802 are integrated may be employed.

  The control unit 8 controls various devices of the image forming apparatus 10 including the first charging unit 42a and the second charging unit 42b. For example, as shown in FIG. 2, the control unit 8 includes a microprocessor unit 81 (MPU 81), a memory 82, a signal interface 83, and a charging driver 84. The control unit 8 is an example of a fan control unit.

  The MPU 81 is a processor that executes various arithmetic processes. The memory 82 is a non-volatile memory in which information such as control programs Pr1, Pr2, Pr3, Pr4 for causing the MPU 81 to execute various processes is stored in advance. Further, the memory 82 is a memory that allows the MPU 81 to read and write various information.

  The control unit 8 performs overall control of the image forming apparatus 10 by the MPU 81 executing various control programs Pr1, Pr2, Pr3, and Pr4 stored in the memory 82 in advance.

  The signal interface 83 is an interface circuit that relays signal transfer between the MPU 81 and the sensors and control target devices. The MPU 81 inputs detection signals (measurement signals) from various sensors such as the temperature sensor 801 and the humidity sensor 802 via the signal interface 83. Further, the MPU 81 outputs a control signal via the signal interface 83.

  The charging driver 84 individually applies the charging voltage to each of the first charging unit 42a and the second charging unit 42b in accordance with a control signal output from the MPU 81 via the signal interface 83. Circuit. That is, the MPU 81 can individually control the voltage applied to each of the first charging unit 42a and the second charging unit 42b via the signal interface 83 and the charging driver 84.

  The control unit 8 also includes another circuit (driver) (not shown) that drives a control target device other than the charging unit. The MPU 81 controls other devices to be controlled through the signal interface 83 and other drivers.

[Charging Characteristics of the Photoreceptor 41]
By the way, when the temperature and humidity of the surrounding environment of the photoreceptor 41 are lowered, the efficiency of the first charging unit 42a and the second charging unit 42b charging the photoreceptor 41 is deteriorated, and the charging of the photoreceptor 41 is insufficient. May occur. Hereinafter, this efficiency is referred to as charging efficiency.

  On the other hand, it is conceivable to set the applied voltage level to the first charging unit 42a and the second charging unit 42b high in order to avoid the insufficient charging. In this case, the level of the current flowing through the photoconductor 41 increases, which may cause a problem that the life of the photoconductor 41 is shortened.

  FIG. 9 is a graph showing the relationship between the transfer charge amount Ct and the reduced charging voltage ΔVo in the photoconductor 41 when continuous image formation is performed on the three recording sheets 9. This graph is a graph of experimental data.

  9, the photoconductor 41 is an organic photoconductor, and the charging voltage ratio of the first charging unit 42a and the second charging unit 42b is 1. The charging voltage (voltage applied to the charging unit) is a positive DC voltage.

  Further, the experimental data D1 in FIG. 9 is data obtained under the condition that the charging voltage is set to 1167 [V] in an environment where the temperature is 32.5 ° C. and the humidity is 80%. The experimental data D2 is data obtained under the conditions where the temperature is 22.8 ° C. and the humidity is 30% and the charging voltage is set to 1245 [V]. The experimental data D3 is data obtained under conditions where the temperature is 10.0 ° C. and the humidity is 15% and the charging voltage is set to 1403 [V].

  The charging voltage is set so that the surface state of the photoconductor 41 immediately after charging is equivalent in each ambient environment.

  As shown in FIG. 9, as the number of continuous image formation increases, the transfer charge amount Ct per unit area of the photoconductor 41 sequentially increases, and the surface potential of the photoconductor 41 decreases sequentially. The reduced charging voltage ΔVo is a value obtained by subtracting the surface potential immediately after charging of the photoconductor 41 from the surface potential of the photoconductor 41 at each time point.

  Further, FIG. 9 shows that the lower the temperature and humidity of the surrounding environment of the photoconductor 41, the greater the decrease in the surface potential of the photoconductor 41 due to the increase in the transfer charge amount Ct per unit area. . This indicates that the charging efficiency deteriorates as the temperature and humidity of the surrounding environment of the photoreceptor 41 are lower.

  On the other hand, FIG. 10 shows the first charging voltage V1c, which is the charging voltage of the first charging portion 42a in the photoconductor 41, when the continuous image formation is performed on the three recording sheets 9. It is a graph showing the relationship with the fall electrification voltage (DELTA) Vo. This graph is a graph of experimental data.

  The experimental data of FIG. 10 is data of the reduced charging voltage ΔVo under a plurality of conditions in which the charging voltage of the second charging unit 42b is the same and the charging voltage V1c of the first charging unit 42a is different. is there. The reduced charging voltage ΔVo is a value obtained by subtracting the surface potential immediately after charging of the photoconductor 41 from the surface potential of the photoconductor 41 after continuous image formation on the three recording sheets 9. .

  FIG. 10 shows that if the charging voltage V1c of only the first charging unit 42a of the two charging units 42a and 42b is adjusted to be high, a decrease in the surface potential of the photoconductor 41 can be suppressed. .

  As will be described below, the control unit 8 controls the charging voltage using the charging characteristics shown in FIG. If the image forming apparatus 10 having such a control unit 8 is employed, insufficient charging of the photoconductor 41 can be prevented while suppressing a current flowing through the photoconductor 41.

[Charging voltage control method]
Next, an example of charging voltage control executed by the control unit 8 in the image forming apparatus 10 will be described with reference to FIGS. FIG. 3 is a flowchart showing an example of the charging voltage control procedure executed by the control unit 8. FIG. 4 is a graph showing an example of an adjustment parameter for the charging voltage ratio based on the temperature measured by the temperature sensor 801. FIG. 5 is a graph showing an example of the adjustment parameter of the charging voltage ratio based on the temperature measured by the humidity sensor 802.

  The charging voltage ratio is a ratio of the charging voltage of the first charging unit 42a to the charging voltage (applied voltage) of the second charging unit 42b. Hereinafter, the adjustment parameter illustrated in FIG. 4 is referred to as a first voltage ratio adjustment parameter Rvt, and the adjustment parameter illustrated in FIG. 5 is referred to as a second voltage ratio adjustment parameter Rvh.

  The control unit 8 starts the process shown in FIG. 3 when the image forming process by the image forming unit 4 is started, for example. In the following description, S1, S2,... Represent processing procedure identification codes. The processing of the control unit 8 shown below is realized by the MPU 81 executing a control program stored in the memory 82.

<Step S1>
First, the control unit 8 inputs measurement results of the temperature sensor 801 and the humidity sensor 802. This step S1 is a step in which the MPU 81 executes the input program Pr1, and is an example of an input process. The MPU 81 that executes the input program Pr1 is an input processing unit that inputs measurement results of the sensors 801 and 802.

  In the following description, the measurement result of the temperature sensor 801 is referred to as measurement temperature, and the measurement result of the humidity sensor 802 is referred to as measurement humidity.

<Step S2>
Next, the control unit 8 sets a second charging voltage level that is the magnitude of the voltage applied to the second charging unit 42b. For example, the control unit 8 sets a predetermined constant value as the second charging voltage level. This step S2 is a step in which the MPU 81 executes the charging voltage level setting program Pr2. As will be described later, a voltage corresponding to the second charging voltage level set in step S2 is applied to the second charging portion 42b.

<Step S3>
Further, the control unit 8 sets a charging voltage ratio, which is a ratio of the voltage applied to the first charging unit 42a to the voltage applied to the second charging unit 42b, using the measurement result obtained in step S1. To do. This step S3 is a step in which the MPU 81 executes the charging voltage ratio setting program Pr3. As will be described later, a voltage calculated by multiplying the voltage applied to the second charging unit 42b by the charging voltage ratio is applied to the first charging unit 42a.

  For example, in step S3, the control unit 8 sets the first voltage ratio adjustment parameter Rvt according to the measured temperature Tm, and sets the second voltage ratio adjustment parameter Rvh according to the measured humidity Hm. Further, the control unit 8 sets the charging voltage ratio reflecting the first voltage ratio adjustment parameter Rvt and the second voltage ratio adjustment parameter Rvh based on a predetermined calculation rule.

  As shown in FIG. 4, the first voltage ratio adjustment parameter Rvt is a parameter that increases as the measured temperature Tm (environment temperature) decreases. Further, as shown in FIG. 5, the second voltage ratio adjustment parameter Rvh is a parameter that increases as the measured humidity Hm (environmental humidity) decreases.

  In the example shown in FIG. 4, the first voltage ratio adjustment parameter Rvt is adjusted in an adjustment range from a value larger than 0 and smaller than 1 to a value exceeding 1 according to the measured temperature Tm. Similarly, the second voltage ratio adjustment parameter Rvh is adjusted in an adjustment range ranging from a value greater than 0 and less than 1 to a value exceeding 1 according to the measured humidity Hm.

  For example, the control unit 8 sets a representative value of both values of the first voltage ratio adjustment parameter Rvt and the second voltage ratio adjustment parameter Rvh as the charging voltage ratio. The representative value is an average value or a maximum value. Accordingly, the voltage level applied to the first charging unit 42a is changed from the state where the voltage level applied to the first charging unit 42a is lower than the voltage level applied to the second charging unit 42b. The voltage level of the first charging unit 42a is adjusted within an adjustment range that extends to a state higher than the applied voltage level.

<Step S4>
Next, the control unit 8 applies a voltage corresponding to the second charging voltage level set in step S2 to the second charging unit 42b. Further, the control unit 8 applies a voltage calculated by multiplying the voltage applied to the second charging unit 42b by the charging voltage ratio set in step S3 to the first charging unit 42a. This step S4 is a step in which the MPU 81 executes the charging voltage application program Pr4.

  In steps S3 and S4 described above, the first charging unit 42a with respect to the voltage applied to the second charging unit 42b according to the decrease in the measured temperature Tm and the measured humidity Hm (environmental temperature and humidity) It is an example of the process (voltage ratio adjustment process) which performs voltage ratio adjustment which increases the ratio of the applied voltage to. This step is a step for preventing the insufficient charging of the photoconductor 41 by utilizing the charging characteristics of the photoconductor 41 shown in FIG.

  By executing steps S3 and S4, the insufficient charging of the photoconductor 41 can be prevented even when the measured temperature Tm and the measured humidity Hm are lowered and the charging efficiency is deteriorated. Moreover, in a situation where the measured temperature Tm and the measured humidity Hm are not low, the applied voltage level to the first charging unit 42a is set to be relatively low. Therefore, the problem that the life of the photoconductor 41 is shortened due to an increase in the level of the current flowing through the photoconductor 41 hardly occurs.

  Therefore, if the image forming apparatus 10 that executes steps S3 and S4 is employed, the insufficient charging of the photoconductor 41 can be prevented while suppressing the current flowing through the photoconductor 41.

  In step S2, when a predetermined constant value is set as the second charging voltage level, the voltage ratio adjustment is performed while keeping the voltage applied to the second charging unit 42b constant. As a result, simple and highly stable charge control is possible.

  Further, when the applied voltage to the first charging unit 42a and the second charging unit 42b is a positive DC voltage, and when the photoconductor 41 is an organic photoconductor, the temperature and humidity are reduced. The problem of insufficient charging is likely to occur. In such a case, the voltage ratio adjustment by adjusting the positive DC voltage is particularly effective.

  Further, in the image forming apparatus 10, the charge removing unit 44 removes the surface of the photoreceptor 41 at a position between the position of the first charging unit 42 a and the position of the second charging unit 42 b. Further, when the voltage ratio adjustment parameters Rvt and Rvh shown in FIGS. 4 and 5 are adopted, the voltage ratio adjustment is performed by changing the applied voltage level to the first charging unit 42a to the applied voltage level to the second charging unit 42b. The adjustment range is from a lower state to a higher state.

  As described above, when the photoconductor 41 is neutralized during the two-stage charging, the applied voltage level to the first charging portion 42a can be set higher, so that the photoconductor 41 can be more reliably connected. It can be charged.

[Second Embodiment]
Next, an image forming apparatus 10X according to a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a configuration diagram of the image forming apparatus 10X. 5, the same components as those shown in FIGS. 1 and 2 are given the same reference numerals. Hereinafter, differences of the image forming apparatus 10X from the image forming apparatus 10 will be described.

  The image forming apparatus 10X differs from the image forming apparatus 10 shown in FIG. In other words, in the image forming apparatus 10X, the charge eliminating portion 44 is disposed at a position downstream of the position of the first charging portion 42a in the rotation direction of the photoconductor 41.

  It is conceivable that the control unit 8 that performs the voltage ratio adjustment is applied to the image forming apparatus 10X. However, in this case, the first voltage ratio adjustment parameter Rvt is adjusted in an adjustment range greater than 0 and less than or equal to 1 according to the measured temperature Tm, unlike the example shown in FIG. Similarly, the second voltage ratio adjustment parameter Rvh is also adjusted in an adjustment range greater than 0 and less than or equal to 1 in accordance with the measured humidity Hm.

  When the control unit 8 that performs the voltage ratio adjustment is applied to the image forming apparatus 10X, the same effect as that obtained when the image forming apparatus 10 is employed can be obtained.

[Third Embodiment]
Next, an image forming apparatus according to a third embodiment of the present invention will be described with reference to FIGS. FIG. 7 is a graph illustrating an example of a second charging voltage level adjustment parameter based on temperature in the image forming apparatus according to the third embodiment. FIG. 8 is a graph illustrating an example of a second charging voltage level adjustment parameter based on humidity in the image forming apparatus according to the third embodiment. Hereinafter, the adjustment parameter shown in FIG. 7 is referred to as a first voltage level adjustment parameter V2ct, and the adjustment parameter shown in FIG. 8 is referred to as a second voltage level adjustment parameter V2ch.

  In step S2 of the charging voltage control shown in FIG. 3, the control unit 8 in the third embodiment uses the measurement result obtained in step S1 to determine the second charging voltage level (second charging unit 42b). Set the magnitude of the voltage applied to the

  For example, in step S2, the control unit 8 sets the first voltage level adjustment parameter V2ct according to the measured temperature Tm, and sets the second voltage level adjustment parameter V2ch according to the measured humidity Hm. Further, the control unit 8 sets the second charging voltage level reflecting the first voltage level adjustment parameter V2ct and the second voltage level adjustment parameter V2ch based on a predetermined calculation rule.

  As shown in FIG. 7, when the measured temperature Tm is within a predetermined range from the first set temperature T1 to the second set temperature T2, the first voltage level adjustment parameter V2ct is a constant reference voltage level V2x. Set to However, T1 <T2.

  Similarly, when the measured humidity Hm is within a predetermined range from the first set humidity H1 to the second set humidity H2, the second voltage level adjustment parameter V2ch is set to the reference voltage level V2x. However, H1 <H2.

  In addition, when the measured temperature Tm is lower than the first set temperature T1, the first voltage level adjustment parameter V2ct is set to be higher than the reference voltage level V2x according to the decrease in the measured temperature Tm. . Similarly, when the measured humidity Hm is lower than the first set humidity H1, the second voltage level adjustment parameter V2ch is set to be higher than the reference voltage level V2x in accordance with a decrease in the measured humidity Hm. The

  When the measured temperature Tm is higher than the second set temperature T2, the first voltage level adjustment parameter V2ct is set to be lower than the reference voltage level V2x as the measured temperature Tm increases. . Similarly, when the measured humidity Hm is higher than the second set humidity H2, the second voltage level adjustment parameter V2ch is set to be lower than the reference voltage level V2x as the measured humidity Hm increases. The

  Then, for example, the control unit 8 sets a representative value of both values of the first voltage level adjustment parameter V2ct and the second voltage level adjustment parameter V2ch as the second charging voltage level. The representative value is an average value or a maximum value.

  In the present embodiment, the control unit 8 applies the voltage to the second charging unit 42b when the measured temperature Tm and the measured humidity Hm are within a predetermined range (T1 to T2, H1 to H2). The voltage ratio is adjusted while keeping the constant. Thereby, simple and highly stable charge control is performed under the condition where the measured temperature Tm and the measured humidity Hm are not particularly high or low.

  On the other hand, at least one of the measured temperature Tm and the measured humidity Hm is low, the level of the second charging voltage is temporarily set high. Thereby, the insufficient charging due to the deterioration of the charging efficiency is more reliably prevented.

  In addition, at least in a situation where one of the measured temperature Tm and the measured humidity Hm is high, the level of the second charging voltage is temporarily set low. As a result, it is possible to positively suppress the charging power in a situation where the charging efficiency is high.

[Other application examples]
In the first embodiment, it is conceivable that the first voltage ratio adjustment parameter Rvt and the second voltage ratio adjustment parameter Rvh are set in a range larger than 0 and not exceeding 1.

  In the third embodiment, when the measured temperature Tm is equal to or higher than the first set temperature T1, the first voltage level adjustment parameter V2ct may be always set to the reference voltage level V2x. Similarly, in the third embodiment, when the measured humidity Hm is equal to or higher than the first set humidity H1, the second voltage level adjustment parameter V2ch may be always set to the reference voltage level V2x. .

  Note that the image forming apparatus and the control method thereof according to the present invention can be freely combined within the scope of the invention described in each claim, or the embodiments and application examples described above can be freely combined. It is also possible to configure by appropriately modifying or omitting a part.

2: Sheet feeding unit 3: Sheet conveying unit 4: Image forming unit 5: Optical scanning unit 6: Fixing unit 8: Control unit 9: Recording sheet 10, 10X: Image forming apparatus 21: Sheet cassette 22: Sheet sending unit 30: Conveyance path 31: Registration roller 32: Conveyance roller 33: Discharge roller 41: Photoconductor (image carrier)
42a: first charging unit 42b: second charging unit 43: developing unit 44: neutralizing unit 45: transfer unit 47: cleaning unit 61: fixing roller 62: pressure roller 81: microprocessor unit (MPU)
82: Memory 83: Signal interface 84: Charging driver 100: Case 101: Discharge tray 221: Pickup roller 222: Pickup roller 300: Discharge port 301: First transport path 610: Heater 801: Temperature sensor 802: Humidity sensor Pr1: Input program Pr2: Charging voltage level setting program Pr3: Charging voltage ratio setting program Pr4: Charging voltage application program

Claims (8)

A rotating image carrier;
A first charging unit that charges the surface of the image carrier at a first position around the image carrier;
A second charging unit that charges the surface of the image carrier at a second position downstream of the first position in the rotational direction of the image carrier;
An image forming apparatus comprising: a control unit that adjusts a voltage ratio to increase a ratio of an applied voltage to the first charging unit with respect to a voltage applied to the second charging unit in accordance with a decrease in environmental temperature and humidity. .   2. The image formation according to claim 1, wherein the control unit performs the voltage ratio adjustment while keeping a voltage applied to the second charging unit constant when at least the temperature and the humidity are within a predetermined range. apparatus.   The image forming apparatus according to claim 1, wherein the control unit further performs voltage level adjustment for increasing a voltage level applied to the second charging unit in accordance with a decrease in each of the temperature and the humidity. .   4. The image formation according to claim 1, wherein the control unit performs the voltage ratio adjustment by adjusting a positive DC voltage applied to the first charging unit and the second charging unit. 5. apparatus. A static elimination unit that neutralizes the surface of the image carrier at a position between the first position and the second position;
The control unit applies an applied voltage level to the first charging unit from a state where an applied voltage level to the first charging unit is lower than an applied voltage level to the second charging unit. The image forming apparatus according to claim 4, wherein the voltage ratio adjustment is performed in an adjustment range extending to a state higher than a voltage level.   The image forming apparatus according to claim 1, wherein the image carrier is an organic photoreceptor. A rotating image carrier;
A first charging unit that charges the surface of the image carrier at a first position around the image carrier;
A control method for an image forming apparatus, comprising: a second charging unit that charges the surface of the image carrier at a second position downstream of the first position in the rotation direction of the image carrier.
An input process for inputting the temperature and humidity of the environment;
A voltage ratio adjusting step of increasing a ratio of an applied voltage to the first charging unit to an applied voltage to the second charging unit according to a decrease in each of the temperature and the humidity. . In the case where the image forming apparatus further includes a static elimination unit that neutralizes the surface of the image carrier at a position between the first position and the second position.
In the voltage ratio adjusting step, the applied voltage level to the first charging unit is changed from the state in which the applied voltage level to the first charging unit is lower than the applied voltage level to the second charging unit to the second charging unit. The method for controlling an image forming apparatus according to claim 7, wherein the ratio of the applied voltages is adjusted in an adjustment range over a state higher than the applied voltage level.

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