JP2016114727A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that discharge current control and constant voltage control cannot be appropriately changed when there is deviation between detected environmental information and temperature of a charging device itself.SOLUTION: An image formation device comprises a charging member for charging an image carrier body, measurement means for measuring current or voltage generated when voltage is applied to process means including the charging member, environmental information detection means for detecting environmental information, and control means for, according to a current value or a voltage value measured by the measurement means and the environmental information detected by the environmental information detection means, determining whether an applied voltage value of the charging member is based on the current value or the voltage value measured by the measurement means or an applied voltage value of the charging member is based on the environmental information.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus that charges a surface of an image carrier by applying a bias in which direct current and alternating current are superimposed on a charging member arranged in contact with or close to the surface of the image carrier.

  Conventionally, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a non-contact charging method such as a corona discharger is used as a method for charging the surface of an image carrier that is a charged body such as a photosensitive member or a dielectric. Instead, the contact charging method is becoming mainstream.

  In this contact charging method, the surface of the image carrier is charged by applying a voltage to a charging member in contact with or close to the image carrier. The charging member includes a roller-shaped charging roller and a blade-shaped charging blade. In particular, the charging roller has an advantage that the image carrier can be stably charged over a long period of time.

  The voltage applied to such a charging member may be only a DC voltage, but by applying an oscillating voltage in which an AC voltage is superimposed on the DC voltage, the discharge between the charging member and the image carrier is repeated alternately. In this case, the surface of the image carrier can be uniformly charged.

  For example, an oscillating voltage in which an alternating voltage having a peak-to-peak voltage that is at least twice the discharge start threshold voltage (charging start voltage) Vth of the image carrier when a direct current voltage is applied and a direct current voltage (direct current offset bias) are superimposed. Is applied to the charging member. By doing so, there is an effect of leveling the charged potential on the surface of the image carrier. Note that the waveform of the oscillating voltage is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or a pulse wave. In addition, the oscillating voltage includes a rectangular wave voltage formed by periodically turning the DC voltage OFF / ON, and a superimposed voltage of the AC voltage and the DC voltage by periodically changing the value of the DC voltage. Includes the same output.

  In the following description, a contact charging method in which an oscillating voltage is applied to a charging member for charging is referred to as an “AC charging method”, and a contact charging method in which only a DC voltage is applied for charging is referred to as a “DC charging method”. "

  In the AC charging method, compared with the DC charging method, since the amount of discharge to the image carrier increases, there is a problem that the deterioration of the image carrier is promoted, for example, the image carrier is scraped. Furthermore, there is a problem that abnormal images such as image flow in a high-temperature and high-humidity (H / H) environment due to discharge products occur.

  In order to solve these problems, it is effective to minimize the discharge generated alternately between the charging member and the image carrier by applying the necessary minimum voltage.

  However, in practice, the relationship between the applied voltage and the discharge amount is not always constant, and the discharge amount varies depending on the film thickness of the photosensitive layer and dielectric layer of the image carrier, the environmental variation of the charging member and air, and the like.

  For example, in a low-temperature and low-humidity environment where the temperature is 15 ° C. and the humidity is 10%, the resistance value of the image carrier and the charging roller is increased and the discharge is less likely to occur. The peak-to-peak voltage is required. In addition, even at the lowest voltage value at which charging uniformity can be obtained in this low-temperature and low-humidity environment, if charging is performed in a high-temperature and high-humidity environment where the temperature is 30 ° C. and the humidity is 80%, an excessive discharge occurs. It will be. As a result, the amount of discharge increases, causing problems such as image flow, blurring, toner fusion, and wear and shortening of the life of the image carrier due to deterioration of the surface of the image carrier.

  In order to suppress the increase / decrease in discharge due to environmental fluctuations, in addition to the “AC constant current control method” in which a constant AC current flows, as described above, the AC current is applied to the charging member. An “AC constant voltage control method” for controlling an alternating current value has been proposed.

  According to the AC constant current control method, the AC voltage peak value can be lowered in the L / L environment where the resistance of the material increases, and conversely the peak-to-peak voltage value can be lowered in the H / H environment. It is possible to suppress increase / decrease in discharge compared to the method.

  Here, the charging member is not necessarily in contact with the surface of the image carrier, and a dischargeable area determined by the voltage between the gap and the modified Paschen curve is ensured between the charging member and the image carrier. If so, for example, it may be arranged in a non-contact proximity with a 10 μm gap. In the following description, the case of contact charging includes the case of proximity charging.

  When aiming to extend the life of the image carrier, even in the AC constant current control system, the variation in the resistance value due to manufacturing variation and contamination of the charging member, the capacitance fluctuation of the image carrier due to durability, It is difficult to sufficiently suppress the increase and decrease in the discharge amount due to variations and the like.

  In order to suppress the increase / decrease in the amount of discharge current, it is effective to suppress variations in dimensions and resistance values during manufacture of the charging member, environmental fluctuations, and to suppress high-voltage fluctuations in the power supply. This will increase the cost.

  Therefore, Patent Document 1 proposes the following configuration as a countermeasure.

  (1) The charging means for charging the image carrier is arranged near or in contact with the image carrier and applies a voltage to charge the surface of the image carrier. The charging means includes means for applying a DC voltage and / or AC voltage superimposed on the charging means, and means for controlling each voltage value of the DC voltage and the peak-to-peak voltage of the AC voltage applied to the charging means. Also, there is a means for measuring an alternating current value flowing to the charging means via the image carrier. Then, when the discharge start voltage to the image carrier when a DC voltage is applied to the charging member is Vth, the peak-to-peak voltage less than twice the Vth of at least one point is applied to the charging means at the time of non-image formation. Apply. The current value at this time and the current value when a peak-to-peak voltage that is at least twice the Vth of at least two points is applied are measured. Based on the measured alternating current value, the peak-to-peak voltage of the alternating voltage applied to the charging means during image formation is determined.

  (2) In the discharge current control described in (1), ΔIs is a predetermined constant. A peak-to-peak voltage-alternating current function obtained by connecting a current value obtained when a peak-to-peak voltage less than twice the Vth of one point is applied to the charging means is defined as fI1 (Vpp). Further, a peak-to-peak voltage-alternating current function obtained from a current value when a peak-to-peak voltage more than twice the Vth at least two points is applied is defined as fI2 (Vpp). At this time, a peak-to-peak voltage value satisfying fI2 (Vpp) −fI1 (Vpp) = ΔIs is determined. Based on the determined peak-to-peak voltage value, the peak-to-peak voltage of the AC voltage applied to the charging unit during image formation is controlled at a constant voltage.

  In addition to the above control, Patent Document 2 also proposes the following configuration.

  The charging means includes first applied voltage determining means for determining an applied voltage by the above-described discharge current control, and second applied voltage determining means for determining from voltage values stored in a storage unit stored in advance.

  And control means for controlling charging based on the applied voltage value determined by either one of the first and second applied voltage determining means. When determining the applied voltage value, the control means determines which one of the first and second applied voltage determining means is selected based on the environment information output from the environment detecting means. When the temperature indicated by the environmental information is equal to or higher than the predetermined value, the first determining unit is selected, and when the temperature is lower than the predetermined value, the charging unit is controlled based on the second determining unit.

JP 2001-201921 A Patent No. 4918612

  In the configuration described in Patent Document 2, the control is switched based on the environment information (temperature, humidity) from the environment detection unit. However, there is a difference between the detected environment information and the temperature of the charging device itself. In this case, there is a problem that the discharge current control and the constant voltage control cannot be changed appropriately.

  In addition, since the applied voltage value is determined based on the detected environmental information, if there is a deviation from the temperature of the charging device, the necessary applied voltage is not applied and image defects such as fogging occur. There is a problem that occurs.

  In order to achieve this object, an image forming apparatus according to the present invention includes a charging member that charges an image carrier, and a measuring unit that measures a current or voltage generated when a voltage is applied to a process unit including the charging member. Measured by the measuring means according to the environmental information detecting means for detecting environmental information, the current value or the voltage value measured by the measuring means, and the environmental information detected by the environmental information detecting means. Control means for determining whether the applied voltage value of the charging member based on a current value or a voltage value or the applied voltage value of the charging member based on the environmental information.

  In the present invention, the applied voltage of the charging member based on the current value or the voltage value measured by the measuring unit according to the current value or the voltage value measured by the measuring unit and the environmental information detected by the environmental information detecting unit. Value or applied voltage value of the charging member based on environmental information is determined.

  As a result, even if there is a difference between the environmental information (temperature, humidity) from the environmental information detection means and the temperature of the charging device itself, it is possible to appropriately switch between discharge current control, constant voltage control, and constant voltage output.

  In addition, when there is little difference between the current value assumed from the detection result of the environmental information detection means and the current value flowing through the charging member or the like, the environment is easily affected by an error in the high-voltage output (for example, 20 to 30 ° C./50 to 80%) gives priority to the detection result of the environmental information detection means. This makes it possible to perform optimal control switching while minimizing the influence of errors.

1 is a diagram schematically illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a longitudinal cross-sectional view explaining the layer structure of the photosensitive drum of embodiment of this invention. It is a block circuit diagram of the charging bias application system of the embodiment of the present invention. It is a figure for demonstrating the amount of discharge currents of embodiment of this invention. It is a figure for demonstrating the discharge current control which concerns on embodiment of this invention. It is a figure for demonstrating the problem of the discharge current control in the low temperature environment of embodiment of this invention. It is a flowchart explaining the flow of the charge control of embodiment of this invention. It is a figure which shows an example of the environment table used by the process of FIG. It is a figure which shows an example of the charging current value table used by the process of FIG. It is a figure which shows an example of the environment table at the time of determining the electric current value table of FIG. It is a flowchart explaining the flow of the charge control of other embodiment of this invention. It is a figure which shows an example of the transfer voltage value table used by the process of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<First Embodiment>
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, what attached | subjected the same code | symbol in the same drawing or a different drawing performs the same structure or the same effect | action, The duplication description is abbreviate | omitted suitably about these.

(Overall configuration of image forming apparatus)
FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus shown in the figure is a laser beam printer using an electrophotographic method, and further employs a contact charging method and a reversal developing method. This figure is a schematic view corresponding to a longitudinal sectional view of the laser beam printer (hereinafter abbreviated as “printer”) as viewed from the front side, that is, from the side where a user or a serviceman is located when operating the printer.

  The printer shown in the figure includes a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, a charging roller 2 that is a contact charging member as a charging unit and an exposure device 3 as an information writing unit are disposed almost in order along the rotation direction (arrow R1 direction). Further, a developing device 4, a transfer roller 5 (transfer member), and a cleaning device 6 are provided. In addition, a fixing device 7 as a fixing unit is disposed on the downstream side of the transfer roller 5 along the conveyance direction (arrow Kp direction) of the recording material P (for example, paper, transparent film) used for printing. Yes. Hereinafter, description will be made in the order of the photosensitive drum 1 to the fixing device 7.

  In this embodiment, the photosensitive drum 1 is a rotating drum type electrophotographic photosensitive member, more specifically, a negatively chargeable organic photoconductor (OPC).

  FIG. 2 is a diagram showing a layer structure of the photosensitive drum 1.

  FIG. 1 schematically shows a part of a longitudinal sectional view of the photosensitive drum 1 when it is cut along a plane including the central axis O (see FIG. 1). The lower side in FIG. 2 corresponds to the inner side of the photosensitive drum 1, and the upper side corresponds to the outer side. The photosensitive drum 1 is composed of four layers. Three layers of an undercoat layer 1b, a photocharge generation layer 1c, and a charge transport layer 1d, which suppress the interference of light and improve the adhesion of the upper layer, are sequentially formed on the surface of the aluminum cylinder 1a disposed on the innermost side. It has a layered structure. The entire photosensitive drum 1 is configured to have an outer diameter of 30 mm, and is driven to rotate at a process speed (circumferential speed) of 230 mm / sec in the direction of the arrow R1 about the central axis O by a driving unit (not shown). The aluminum cylinder 1a is grounded.

  As shown in FIG. 1, in the charging roller 2, both ends in the longitudinal direction of the core metal 2a are rotatably held by bearing members (not shown), and both ends are pressed by a pressing spring 2e. Is biased in the direction. As a result, the charging roller 2 is pressed against the surface of the photosensitive drum 1 with a predetermined pressing force, and is driven to rotate in the direction of arrow R2 as the photosensitive drum 1 rotates in the direction of arrow R1. The vicinity including the contact portion where the photosensitive drum 1 and the charging roller 2 come into contact is the charging position N1. A charging bias voltage of a predetermined condition is applied to the cored bar 2a of the charging roller 2 from the power source S1. As a result, the surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity (in this embodiment, negative polarity).

  The exposure device 3 forms an electrostatic latent image on the surface of the charged photosensitive drum 1. In this embodiment, a laser beam scanner using a semiconductor laser is employed as the exposure apparatus 3. The exposure device 3 outputs a laser beam modulated in accordance with image information sent from a host device such as an image reading device (not shown) to the printer side. Then, the surface of the charged photosensitive drum 1 is subjected to image scanning exposure at the exposure position N2 by this laser beam. The surface of the photosensitive drum 1 is freed from the charge at the exposure position N2, thereby forming an electrostatic latent image corresponding to the image information.

  The developing device 4 develops the electrostatic latent image formed on the surface of the photosensitive drum 1 with toner. The developing device 4 includes a developing container 4a, a nonmagnetic developing sleeve 4b, a magnet roller 4c, and a regulating blade 4d. In the developing container 4a, a one-component magnetic toner t having a negative charging characteristic is accommodated as a developer. An opening is formed in a portion of the developing container 4a facing the photosensitive drum 1, and a developing sleeve 4b is rotatably disposed in the opening in the direction of arrow R4. A developing bias is applied to the developing sleeve 4b by the power source S2. The magnet roller 4c is fixedly disposed inside the developing sleeve 4b. The toner t in the developing container 4a is carried on the surface of the developing sleeve 4b by the magnetism of the magnet roller 4c, and the layer thickness is regulated by the regulating blade 4d as the developing sleeve 4b rotates in the direction of arrow R4. It is conveyed to position N3. At this time, a developing bias is applied to the developing sleeve 4b by the power source S2. As a result, the toner t on the surface of the developing sleeve 4b is selectively attached to the electrostatic latent image on the surface of the photosensitive drum 1 to develop the electrostatic latent image. In the present embodiment, so-called reversal development is adopted in which development is performed with toner t attached to the exposure position on the photosensitive drum 1. The toner t that has not been developed is returned to the developing container 4a through the developing position N3.

  The transfer roller 5 is pressed against the surface of the photosensitive drum 1 from below to form a transfer position N4 between the transfer roller 5 and the photosensitive drum 1. The transfer roller 5 is driven to rotate in the direction of arrow R5 as the photosensitive drum 1 rotates in the direction of arrow R1. A transfer bias is applied to the transfer roller 5 from a power source (transfer bias application power source) S3. The recording material P to be transferred is conveyed in the direction of the arrow Kp by a feeding / conveying means (not shown) and is supplied to the transfer position N4. When the recording material P passes through the transfer position N4, a positive transfer bias is applied to the transfer roller 5 by the power source S3. As a result, the toner image on the photosensitive drum 1 is electrostatically transferred onto the recording material P.

  The cleaning device 6 includes a cleaning blade 6a that contacts the surface of the photosensitive drum 1 and cleans the surface of the photosensitive drum 1 at the cleaning position N5, and a cleaning container 6b. The transfer residual toner that is not transferred onto the recording material P and remains on the surface of the photosensitive drum 1 when the toner image is transferred is wiped off by the cleaning blade 6a and collected in the cleaning container 6b. The photosensitive drum 1 whose surface has been cleaned in this way is used for the next image formation.

  The fixing device 7 includes a fixing roller 7a incorporating a heater (not shown) and a pressure roller 7b pressed against the fixing roller 7a from below. A fixing nip N6 is formed between the fixing roller 7a and the pressure roller 7b. The recording material P on which the toner image has been transferred to the surface by the transfer described above is heated and pressurized when passing through the fixing nip N6. As a result, the toner image is fixed on the surface of the recording material P.

  The printing on the surface of one sheet of recording material P is completed by the processes of charging, exposure, development, transfer, cleaning, and fixing described above.

(Charging bias application system)
FIG. 3 is a block circuit diagram of a charging bias application system for the charging roller 2.

  A predetermined vibration voltage (charging bias voltage Vdc + Vac) obtained by superimposing a DC voltage and an AC voltage having a frequency f from the power source S1 is applied to the charging roller 2 through the cored bar 2a, whereby the rotating photosensitive drum 1 The outer peripheral surface (surface) is charged to a predetermined polarity and potential.

  A power source S1 that is a voltage application unit for the charging roller 2 includes a DC power source 11 (DC power source) and an AC power source 12 (AC power source). These DC power supply 11 and AC power supply 12 are controlled by a control circuit (control means) 13. The control circuit 13 has a function of controlling the DC power supply 11 and the AC power supply 12 to be turned on / off so that one or both of the DC voltage and the AC voltage are applied to the charging roller 2. Further, it has a function of controlling the DC voltage value applied from the DC power source 11 to the charging roller 2 and the peak-to-peak voltage value of the AC voltage applied from the AC power source 12 to the charging roller 2.

  The control circuit 13 is connected to a measurement circuit 14 as a means for measuring an alternating current value and a peak-to-peak voltage value. The alternating current value information and the peak-to-peak voltage value measured by the measurement circuit 14 are input to the control circuit 13.

  The control circuit 13 is connected to an environmental sensor 15 (environmental information detection means). The environment sensor 15 detects the environment where the printer is installed, for example, temperature and humidity. The environmental information detected by the environmental sensor 15 is input to the control circuit 13 described above.

  The control circuit 13 has the following functions based on the AC current value information input from the measurement circuit 14 and the environment information input from the environment sensor 15. That is, the control circuit 13 has a function of executing an appropriate peak-to-peak voltage value calculation / determination program applied to the charging roller 2 in the charging process during printing.

[Discharge current amount]
FIG. 4 is a graph for explaining the discharge current amount according to the present embodiment.

  In an electrophotographic apparatus, a DC voltage and an AC voltage are generally applied to a charging roller for the purpose of charging uniformity and image unevenness prevention. The “discharge current amount” in the present embodiment refers to a current amount at the time of discharge, which has discharge characteristics based on a current amount curve at the peak voltage Vpp of the AC voltage applied mainly to the charging roller.

  Normally, when the AC current amount Iac is measured on the support side of the photoconductor while increasing the peak-to-peak voltage Vpp of the AC voltage applied to the charging roller shown on the horizontal axis of the graph of FIG. 4, Vpp as shown in FIG. Iac relationship is obtained.

  As can be seen from the graph of FIG. 4, while Vpp is small, Iac increases linearly with increasing Vpp, but when Vpp reaches a point A1 (discharge start point) at which the predetermined threshold Vth is reached. The relationship between voltage and current changes. In other words, it is considered that the increase A4 in which the current amount Iac increases beyond the linear relationship beyond the point A1 is caused by the discharge current.

  Therefore, the current at Vpp (A5) in the discharge region where the direct proportional line A2 (broken line) obtained by plotting the points below the discharge start point A1 and the actual flowing current curve A3 (solid line) deviate from each other. The difference A4 is referred to as a discharge current amount.

[Discharge current control]
The discharge current control refers to controlling the discharge current by obtaining a value of Vpp from which a predetermined amount of discharge current is obtained from an approximate line in order to obtain the amount of discharge current.

  FIG. 5 is a graph for explaining the discharge current control.

  As shown in the figure, three voltage points of Vpp values V1, V2, and V3 of an AC voltage that is an undischarged region are sequentially applied to the charging roller 2, and then Vpp values V4, V5, and V6 that are discharged regions. These three voltages are sequentially applied.

Of the values P1, P2, P3, P4, P5, and P6 of the total current Iac flowing with respect to the Vpp value of each AC voltage, approximation is performed using the least square method at three points P1, P2, and P3 in the undischarged region. The equation that draws a straight line is the following equation (2):
Approximate straight line of undischarged area: Y = βX + B (2)
An expression obtained by drawing an approximate line using the least square method at three points P4, P5, and P6 in the discharge region is defined as the following expression (3).

Approximate straight line of discharge region: Y = αX + A (3)
The discharge current amount ΔAC is obtained from the difference between the equations (3) and (2).

  Specifically, the peak-to-peak voltage Vx at which the discharge current amount is D is determined by the following equation based on the difference between the approximate straight line of the discharge region of Equation (3) and the approximate straight line of the undischarged region of Equation (2). To do. That is, if the Y value of the expression (2) with respect to Vx is Yβ, the Y value of the expression (3) is Yα, and these values are substituted into the expressions (2) and (3), the following expressions (2) ′ (3) ′ Is obtained.

Yβ = βVx + B (2) ′
Yα = αVx + A (3) ′
From these equations (2) ′ (3) ′, Vx is obtained as in the following equation.

Vx = (D−A + B) / (α−β) (4)
(Here, D = Yα−Yβ.)
The voltage applied to the charging roller 2 is defined by the peak-to-peak voltage Vpp. The peak-to-peak voltage Vpp is switched to Vx obtained by Expression (4), and the process proceeds to the printing process.

  Now, if the necessary discharge current amount D (ΔAC) is given, the target Vpp value = V7 can be found. Charge control is performed by feeding back the target Vpp value to the control unit. V7 at this time must satisfy the relationship of V1 <V2 <V3 <V7 <V4 <V5 <V6. Otherwise, the difference between the actual discharge current amount A4 and the necessary discharge current amount ΔAC becomes large and an error occurs.

  FIG. 6 is a graph for explaining the problem of discharge current control in a low temperature environment.

  As shown in the figure, the discharge current curve A3 in the high temperature environment is shifted like a curve A3 ′ in which discharge is difficult in the low temperature environment, and the discharge start point A1 ′ is also shifted compared to the high temperature environment. As a result, the voltage values V4 ′, V5 ′, and V6 ′ of the discharge current control must be applied at a high portion.

  The mutual relationship between the voltage values V4, V5, and V6 is a relationship of V4 <V5 <V6, and the condition of 1.934 <(V4 + V6) / V5 <1.993 from the viewpoint of discharge characteristics and discharge current amount. Has been experimentally confirmed that must be satisfied. When 1.993 ≦ (V4 + V6) / V5, the inclination becomes too large, the discharge becomes excessive, and an image defect occurs. Further, if (V4 + V6) /V5≦1.934, the error with respect to the actual discharge current amount becomes too large, and the charge is estimated to be less than the actual value.

[Constant voltage control]
The constant voltage control here is a method of stably controlling the charging voltage to a desired voltage value in the charging control. In this operation, when the control unit applies a voltage with the PWM value fixed, the output voltage is monitored via a resistor, and the monitored voltage is fed back to the voltage setting circuit unit to set the PWM signal. This is an operation for controlling the output voltage value according to the set value.

[Environmental sensor]
The environment sensor that constitutes the environment detection means is a general term for sensors that detect an installation environment such as temperature, humidity, and a specific gas concentration. In the present embodiment, a humidity sensor and a temperature sensor are applicable. As the temperature sensor, a thermistor that measures the temperature in the air is generally used. The humidity sensor generally detects humidity in the air based on a change in capacitance, and each output is output as an electrical signal. Although various products are sold as environmental sensors, HSU-01F1V2-N manufactured by Hokuriku Electric Industry Co., Ltd. is used as the environmental sensor in this embodiment.

(Charge roller voltage application control)
FIG. 7 is a flowchart showing the operation of voltage application control of the charging roller 2.

  As shown in the figure, first, when the power of the image forming apparatus is turned on or after the image forming apparatus is instructed to print (step S100), the environmental sensor 15 confirms the temperature and humidity of the atmosphere ( Step S101). Next, an assumed current value Ix in the detection environment is set from a temperature / humidity table (not shown) set based on the combination of temperature and humidity (step S102). Next, the idle rotation operation (pre-rotation operation) of the photosensitive drum 1 is executed, and the photosensitive drum 1 is rotationally driven (step S103). A charging voltage is applied to the charging roller 2 (step S104), and the current value Ir is detected by the current detecting means (step S105). It is determined whether or not the difference between the assumed current value Ix and the detected current value Ir is equal to or greater than a predetermined value X (a predetermined value) (step S106). If the deviation is equal to or greater than the predetermined value X, it is determined from the set current value table based on the detected current value whether the current region is the discharge current control execution region (step S107). When performing the discharge current control, after determining the target current value of the discharge current control (step S108), the discharge current control is performed (step S109). When the discharge current control is not performed, the application during the constant voltage control is performed. A voltage value is determined (step S110). If it is determined in step 106 that the divergence is not equal to or greater than the predetermined value X (less than the predetermined value), it is determined whether the current region is the discharge current control execution region based on the temperature / humidity table (step S111). When performing the discharge current control, after determining the target current value of the discharge current control (step S112), the discharge current control is performed (step S113). When the discharge current control is not performed, the applied voltage value during the constant voltage control is determined (step S114), and image formation is started when the applied voltage is finally determined (step S115).

  Note that step S108 and step S109 constitute first applied voltage determination means. Step S110 constitutes a second applied voltage determination unit. Further, step S112 and step S113 constitute a first applied voltage determining means. Furthermore, step S114 constitutes a second applied voltage determination unit.

  FIG. 8 is a table showing an environment table used for voltage application control of the charging roller 2 described above. This environment table defines the type of charge control suitable for the environment according to the temperature and humidity of the atmosphere.

  The region where the temperature is less than 15 ° C. may be further divided into a plurality of ranges, and the constant voltage control A, B, C with different voltage values may be switched. In this case, the constant voltage control A is employed in the range of 0 to 5 ° C, the constant voltage control B is employed in the range of 5 to 10 ° C, and the constant voltage control C is employed in the range of 10 to 15 ° C. The voltage value to be applied to the charging means is determined from the voltage values in the charging control table in the storage unit so that the constant voltage Vpp used in the constant voltage control A, B, C decreases in this order.

  If the discharge is excessive in an environment where there is a large amount of absolute moisture in the air, image defects will occur, so the area above 15 ° C is further divided into multiple ranges depending on the combination of temperature and humidity. You may make it switch. In the example of FIG. 8, the discharge current control A is employed in a relatively high temperature and humidity range, the discharge current control B is employed in a medium temperature and humidity range, and the discharge current control C is employed in a relatively low temperature and humidity range. The required discharge current amount ΔAC used in the discharge current controls A, B, and C is set to increase in this order. In this example, instead of calculating the absolute water content, the type of discharge current control (that is, the value of the predetermined discharge current amount) can be determined depending on which range the combination of temperature and humidity belongs to.

  FIG. 9 is a graph showing a current value table in voltage application control of the charging roller 2 of the present embodiment. FIG. 10 is a table showing the environment zones of the environment table shown in FIG. The current value table shown in FIG. 9 defines the current values measured when a constant voltage is applied in each zone of the environment table shown in FIG.

  Similarly to the control based on the environment table shown in FIG. 8, the voltage control means and the voltage value set for each current value shown in FIG. 9 are set so as not to cause image defects when the temperature and humidity are combined.

  This process may be executed when the photosensitive drum 1 is rotated in the next printing operation every time a predetermined number of sheets are printed, in addition to the rotation of the first image carrier after the power of the image forming apparatus is turned on. it can. Further, this process can be executed only when the environmental information detected by the environmental sensor 15 changes with respect to the previous detected environmental information.

  As described above, according to the configuration of the present embodiment, the current value flowing when a predetermined voltage is applied to the charging roller 2 is compared with the current value assumed from the environmental information. In addition, even if there is a difference between the environmental information (temperature, humidity) from the environmental sensor 15 and the temperature of the charging device itself, it is possible to appropriately switch between discharge current control, constant voltage control, and constant voltage output, thereby suppressing image defects. It is possible to provide an image forming apparatus capable of performing the above.

Second Embodiment
Next, an image forming apparatus according to another embodiment of the present invention will be described. In the present embodiment, the outline of the image forming apparatus and the charge control apparatus similar to those of the first embodiment are the same, and thus a duplicate description is omitted.

  In the first embodiment, in order to determine the difference between the detected environmental information and the temperature of the charging device itself, a predetermined voltage is applied to the charging device, and the current value flowing at that time is assumed from the environmental information. , And compared with a preset current value.

  In this embodiment, in order to determine the temperature and resistance state of the charging device, a predetermined current value is passed through the transfer roller 5, and the voltage value generated at that time is set to a preset voltage value assumed from environmental information. Compare.

  FIG. 11 is a flowchart showing the voltage application control operation of the charging roller 2.

  As shown in the figure, first, when the power of the image forming apparatus is turned on, or after the image forming apparatus is instructed to print (step S200), the ambient temperature and humidity are confirmed by the environmental sensor (step S200). S201). Then, the assumed transfer voltage value Vx in the detection environment is set from the temperature / humidity table set from the combination of temperature and humidity (step S202). Next, the idle rotation operation (pre-rotation operation) of the photosensitive drum 1 is executed, and the photosensitive drum 1 is rotationally driven (step S203). A transfer current is applied to the transfer roller 5 (step S204), and the detected transfer voltage value Vr is detected by the transfer voltage detecting means (step S205). Then, it is determined whether or not the difference between the assumed transfer voltage value Vx and the detected transfer voltage value Vr is equal to or greater than a predetermined value Y (step S206). If the deviation is equal to or greater than the predetermined value Y, it is determined from the set detection transfer voltage value table whether or not it is a discharge current control execution region based on the detection transfer voltage value (step S207). When performing the discharge current control, after determining the target current value of the discharge current control (step S208), the discharge current control is performed (step S209). When the discharge current control is not performed, an applied voltage value at the time of constant voltage control is determined (step S210). If it is determined in step 206 that the divergence is not equal to or greater than the predetermined value Y, it is determined whether the current region is the discharge current control execution region based on the temperature / humidity table (step S211). When performing the discharge current control, after determining the target current value of the discharge current control (step S212), the discharge current control is performed (step S213). When the discharge current control is not performed, an applied voltage value at the time of constant voltage control is determined (step S214), and image formation is started when the applied voltage is finally determined (step S215).

  Note that step S208 and step S209 constitute first applied voltage determination means. Step S210 constitutes a second applied voltage determining means. Furthermore, step S212 and step S213 constitute a first applied voltage determining means. Furthermore, step S214 constitutes a second applied voltage determination unit.

  FIG. 12 is a graph showing a transfer voltage value table in the present embodiment. This transfer voltage value table defines current values measured when a constant voltage is applied in each zone of the environment table shown in FIG.

  The effect similar to 1st Embodiment was acquired also by the structure and control of this embodiment.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made. For example, in the above-described embodiment, the image forming apparatus main body is provided with environment detecting means for detecting environment information, thereby obtaining environment information. Instead of this, an environment detection unit is not provided, and a user or the like who uses the image forming apparatus inputs an environment to be used from the operation unit or the like of the image forming apparatus, or selects from the display of the operation unit or the like. The environmental information may be obtained.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 2 ... Charging roller 5 ... Transfer roller 11 ... DC power supply 12 ... AC power supply 13 ... Control circuit 14 ... Measurement circuit 15 ... Environmental sensor

Claims (16)

A charging member for charging the image carrier;
Measuring means for measuring a current or voltage generated when a voltage is applied to the process means including the charging member;
Environmental information detection means for detecting environmental information;
The voltage applied to the charging member based on the current value or the voltage value measured by the measuring unit according to the current value or the voltage value measured by the measuring unit and the environmental information detected by the environmental information detecting unit. An image forming apparatus comprising: a control unit that determines a value or an applied voltage value of the charging member based on the environmental information. The control means includes
If the difference between the current value or voltage value measured by the measuring means and the current value or voltage value set from the environmental information detected by the environmental information detecting means is less than a predetermined value, the environmental information An applied voltage value of the charging member is determined based on the current value or a voltage value measured by the measuring means when the difference is greater than or equal to a predetermined value. The image forming apparatus according to claim 1. A first applied voltage determining means for determining a relationship between a voltage value applied to the charging member and a discharge current amount, and determining an applied voltage value corresponding to a predetermined discharge current amount;
A second applied voltage determining means for determining an applied voltage value for the charging member from pre-stored voltage values;
The image forming apparatus according to claim 2, wherein the control unit selects one of the first applied voltage determining unit and the second applied voltage determining unit to supply power to the charging member. apparatus.   The control means applies a predetermined voltage to the charging member when determining an applied voltage value to the charging member, and the current value measured by the measuring means and the environmental information detected by the environmental information detecting means. If the difference is less than a predetermined value, either the first applied voltage determining means or the second applied voltage determining means is selected based on the environmental information. When the difference is equal to or greater than a predetermined value, the first applied voltage determining unit and the second applied voltage determining unit are selected based on the current value measured by the measuring unit. The image forming apparatus according to claim 3.   The control means determines the voltage value of the voltage to be applied to the charging member when the difference is a predetermined value or more, and when the current value measured by the measurement means is a predetermined value or more. The voltage value determined by the first applied voltage determining means is selected, and when the current value measured by the measuring means is less than a predetermined value, the voltage value determined by the second applied voltage determining means is determined. The image forming apparatus according to claim 3, wherein a voltage value is selected.   The control means determines the first value when the temperature indicated by the environmental information is equal to or higher than a predetermined value when determining the voltage value of the voltage applied to the charging member when the difference is less than a predetermined value. The voltage value determined by the applied voltage determining means is selected, and when the temperature is less than a predetermined value, the voltage value determined by the second applied voltage determining means is selected. The image forming apparatus according to claim 3.   The control means supplies a predetermined current to the charging member when determining an applied voltage value to the charging member, and a voltage set from the generated voltage value and environmental information detected by the environmental information detecting means When the difference is less than a predetermined value, either the first applied voltage determining means or the second applied voltage determining means is selected based on the environment information, and the difference is predetermined. 4. The method according to claim 3, wherein if the value is equal to or greater than the value, either the first applied voltage determining unit or the second applied voltage determining unit is selected based on the voltage measured by the measuring unit. Image forming apparatus.   The control means determines the voltage value of the voltage to be applied to the charging member when the difference is greater than or equal to a predetermined value, and when the voltage value measured by the measurement means is greater than or equal to a predetermined value. The voltage value determined by the first applied voltage determining means is selected, and when the voltage value measured by the measuring means is less than a predetermined value, the voltage value determined by the second applied voltage determining means is determined. The image forming apparatus according to claim 7, wherein a voltage value is selected.   The control means determines the first value when the temperature indicated by the environmental information is equal to or higher than a predetermined value when determining the voltage value of the voltage applied to the charging member when the difference is less than a predetermined value. The voltage value determined by the applied voltage determining means is selected, and when the temperature is less than a predetermined value, the voltage value determined by the second applied voltage determining means is selected. The image forming apparatus according to claim 7 or 8. A transfer member for transferring to the recording material of the image carrier;
The measuring means measures a voltage generated in the transfer member;
The control means supplies a predetermined current to the transfer member when determining an applied voltage value to the charging member, and a voltage set from the generated voltage value and environmental information detected by the environmental information detection means When the difference is less than a predetermined value, either the first applied voltage determining means or the second applied voltage determining means is selected based on the environment information, and the difference is predetermined. 4. The method according to claim 3, wherein if the value is equal to or greater than the value, either the first applied voltage determining unit or the second applied voltage determining unit is selected based on the voltage value measured by the measuring unit. The image forming apparatus described.   The control means determines the voltage value of the voltage to be applied to the charging member when the difference is greater than or equal to a predetermined value, and when the voltage value measured by the measurement means is greater than or equal to a predetermined value. The voltage value determined by the first applied voltage determining means is selected, and when the voltage value measured by the measuring means is less than a predetermined value, the voltage value determined by the second applied voltage determining means is determined. The image forming apparatus according to claim 10, wherein a voltage value is selected.   The control means determines the first value when the temperature indicated by the environmental information is equal to or higher than a predetermined value when determining the voltage value of the voltage applied to the charging member when the difference is less than a predetermined value. The voltage value determined by the applied voltage determining means is selected, and when the temperature is less than a predetermined value, the voltage value determined by the second applied voltage determining means is selected. The image forming apparatus according to claim 10 or 11.   The voltage applied to the charging member includes an AC voltage, and the voltage value of the voltage applied to the charging member is defined by a peak-to-peak voltage of the AC voltage. The image forming apparatus described in the item.   When the image carrier is rotated for the first time after the image forming apparatus is turned on, a predetermined voltage is applied to the charging member, and the detected current value is set from the environmental information detected by the environmental information detecting means. The image forming apparatus according to any one of claims 3 to 6, wherein one of the first applied voltage determination unit and the second applied voltage determination unit is selected after being compared with a current value to be determined.   Each time a predetermined number of sheets are printed, a predetermined voltage is applied to the charging member during rotation of the image carrier in the next printing operation, and a current value detected at that time is detected by the environmental information detection means. 7. The method according to claim 3, wherein the first applied voltage determination unit and the second applied voltage determination unit are selected after comparison with a current value set based on environmental information. The image forming apparatus described.   A predetermined voltage is applied to the charging member only when the environmental information detected by the environmental information detecting unit changes with respect to the previously detected environmental information, the current value measured by the measuring unit, and the environment The third applied voltage is selected from the first applied voltage determining means and the second applied voltage determining means after comparison with the current value set from the environmental information detected by the information detecting means. The image forming apparatus according to any one of the above.

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