Image forming apparatus

Abstract

To provide a charging device and an image forming apparatus that, when an environmental condition changes, can set appropriate voltage and reduce the time of operations other than an image forming operation.SOLUTION: A charging device 101 switches, according to atmospheric temperature, between constant voltage control of applying predetermined voltage to a charging member 2 and discharge current control of applying, to the charging member 2, a voltage in which a current measured by a charging AC current detection circuit 403 is predetermined current, and before switching from the constant voltage control to the discharge current control, corrects the voltage applied to the charging member 2 in the constant voltage control on the basis of the atmospheric temperature and applies the corrected voltage to the charging member 2.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a charging device that charges an image carrier, and an image forming apparatus such as a copier, printer, facsimile, or multifunction machine having a plurality of these functions that is equipped with the charging device and forms an image on a recording material. [Background technology]

[0002] Conventionally, in an image forming apparatus that prints images by electrophotography, the surface of a photosensitive drum, which is a drum-shaped electrophotographic photosensitive member, is uniformly charged to a predetermined potential by a charging unit. Conventionally, the charging method of such a charging unit has generally been corona charging, which is a non-contact charging method in which a corona generated by applying a high voltage to a thin corona discharge wire acts on the surface of the photosensitive drum to charge the photosensitive drum.

[0003] Meanwhile, in recent years, the contact charging method has become mainstream as a charging method for charging units, because of its advantages of low voltage process, low ozone generation, low cost, etc. The contact charging method is a method in which a charging member such as a charging roller is brought into contact with the surface of a photosensitive drum and a voltage is applied to the charging member to charge the photosensitive drum.

[0004] To the charging member of the contact charging method, only a DC voltage is applied, or an AC voltage is applied superimposed on a DC voltage. When an AC voltage is applied superimposed on a DC voltage, the photosensitive drum can be charged more uniformly by alternately generating discharge to the positive side and discharge to the negative side. For example, it is known that the charged body can be charged uniformly by applying to the charging member an oscillating voltage in which an AC voltage having a peak-to-peak voltage at least twice the discharge start threshold voltage to the photosensitive drum when a DC voltage is applied and a DC voltage are superimposed.

[0005] As a method for setting the voltage applied to such a charging member, constant voltage control is known, which applies a constant voltage according to the environment. When a voltage is applied to the charging member, a resistive load current flows through a resistive load between the charging member and the photosensitive drum, a capacitive load current flows through a capacitive load between the charging member and the photosensitive drum, and a discharge current flows between the charging member and the photosensitive drum. A current that is the sum of these currents flows through the charging member.

[0006] At this time, it is empirically known that in order to obtain stable charging performance, it is good to set the amount of discharge current (hereinafter referred to as "discharge current amount") to a predetermined value or more, while it is also known that increasing the discharge current amount increases the amount of wear of the photosensitive drum. Therefore, in order to achieve both stable charging performance and suppression of wear of the photosensitive drum, it is necessary to set the discharge current amount appropriately. In view of this situation, an image forming apparatus that performs discharge current control to control the discharge current amount has been proposed (for example, Patent Document 1).

[0007] Furthermore, when a charging member is used in a low-temperature, low-humidity environment, the resistance of the charging member increases, and therefore a voltage higher than that required for image formation must be applied in order to obtain the amount of discharge current required for calculations, resulting in a problem of wasted power consumption.

[0008] In response to this, Patent Document 2 discloses an image forming apparatus that sets an appropriate voltage by correcting a reference voltage obtained by executing discharge current control in accordance with the atmospheric temperature, and Patent Document 3 discloses an image forming apparatus that determines a voltage suitable for environmental conditions by switching between constant voltage control and discharge current control in accordance with a predetermined environment. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2001-201921 A [Patent Document 2] JP2018-84756A [Patent Document 3] JP2011-150309A Summary of the Invention [Problem to be solved by the invention]

[0010] However, in Patent Document 3, when the environmental conditions change from those under which constant voltage control is performed to those under which discharge current control is performed, a process must be performed to set an appropriate voltage for the discharge current control. In particular, in Patent Document 3, when the environment frequently changes near the environmental conditions under which constant voltage control and discharge current control are switched, a process is performed to set an appropriate voltage every time the environmental conditions change from those under which constant voltage control is performed to those under which discharge current control is performed. As a result, Patent Document 3 has a problem in that the downtime, which is the time during which operations other than image formation operations are performed, becomes longer.

[0011] An object of the present invention is to provide a charging device and an image forming apparatus that can set an appropriate voltage and reduce the time for operations other than image forming operations when environmental conditions change. [Means for solving the problem]

[0012] The charging device according to the present invention comprises a charging member that contacts an image carrier and charges the image carrier by applying a voltage to the charging member, an environmental information detection means that detects environmental information, a measurement means that measures a current that flows through the charging member when a voltage is applied to the charging member, and a control means that switches between a first control that applies a predetermined voltage to the charging member and a second control that applies a voltage to the charging member such that the current measured by the measurement means becomes a predetermined current, depending on the environmental information, and is characterized in that before switching from the first control to the second control, the control means corrects the voltage applied to the charging member by the first control based on the environmental information and applies the corrected voltage to the charging member. Effect of the Invention

[0013] According to the present invention, when the environmental conditions change, it is possible to set an appropriate voltage and to reduce the operation time other than the image forming operation. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention; [Diagram 3] 5 is a flowchart showing an AC voltage determination process executed by the charging device according to the embodiment of the present invention. FIG. [Figure 4] 5 is a diagram showing an example of a table used in constant voltage control performed by the charging device according to the embodiment of the present invention; FIG. [Diagram 5] 6 is a diagram showing the relationship between AC voltage and total current amount in discharge current control performed by the charging device according to the embodiment of the present invention. FIG. [Figure 6] 5 is a flowchart showing an AC voltage correction process executed by the charging device according to the embodiment of the present invention. [Figure 7] 6 is a diagram showing an example of a table used in an AC voltage correction process executed by the charging device according to the embodiment of the present invention; FIG. [Figure 8] 13 is a diagram showing an example of another table used in the AC voltage correction process executed by the charging device according to the embodiment of the present invention. FIG. [Figure 9] 5A to 5C are diagrams for explaining the effects of the charging device according to the embodiment of the present invention. [Figure 10] 11A and 11B are diagrams for explaining the operation of the charging device when AC voltage correction processing is not executed, as a comparison with the effect of the charging device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0016] <Configuration of Image Forming Apparatus> The configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described in detail with reference to FIGS.

[0017] The image forming apparatus 100 is exemplified here as an electrophotographic laser beam printer that employs a contact charging method.

[0018] The image forming apparatus 100 includes photosensitive drums 1Y, 1M, 1C, and 1K, latent image devices 3Y, 3M, 3C, and 3K, developing members 4Y, 4M, 4C, and 4K, primary transfer members 5Y, 5M, 5C, and 5K, and cleaning devices 6Y, 6M, 6C, and 6K. The image forming apparatus 100 also includes an intermediate transfer body 7, a secondary transfer section 8, a pair of registration rollers 9, a fixing device 10, a feeding device 11, and charging devices 101Y, 101M, 101C, and 101K. The image forming apparatus 100 also includes a photosensitive drum driving motor M1, a charging power source PS1, and a developing power source PS2.

[0019] In addition, Y, M, C, and K added to the end of the reference numerals of each member or device indicate that the member or device is used for image formation of each color, Y (yellow), M (magenta), C (cyan), and K (black). Since each member has the same configuration, the Y, M, C, and K added to the end of each reference numeral will be omitted in the following description.

[0020] The photosensitive drum 1 as an image carrier is a rotating drum-type organic electrophotographic photosensitive drum with negative charging characteristics. The photosensitive drum 1 has a structure in which a charge generating layer made of an organic material, a charge transport layer (about 20 μm thick), and a hardened layer using a hardening resin as a binder resin, which is a surface layer, are coated on the surface of an aluminum cylinder (conductive drum base) in this order from the bottom. The thickness of the hardened layer is, for example, 8 μm.

[0021] The surface layer of the photosensitive drum 1 is not limited to the above-mentioned hardened layer, and may be a charge transport hardened layer formed by hardening and polymerizing a monomer having a carbon-carbon double bond and a charge transport monomer having a carbon-carbon double bond by heat or light energy. The surface layer of the photosensitive drum 1 may be a charge transport hardened layer formed by hardening and polymerizing a hole transport compound having a chain polymerizable functional group in the same molecule by electron beam energy. Furthermore, the surface layer of the photosensitive drum 1 does not have to have a hardened layer.

[0022] The photosensitive drum 1 has an axial length of 340 mm and an outer diameter of 30 mm, and is driven to rotate around a central shaft at a process speed (circumferential speed) of 200 mm / sec in the direction of the arrow in FIG. 1 (counterclockwise in FIG. 1).

[0023] The latent image device 3 as an exposure means is a laser beam scanner using a semiconductor laser that forms an electrostatic latent image on the surface of the photosensitive drum 1 that has been charged by the charging device 101. The latent image device 3 outputs a laser beam modulated in response to an image signal sent to the image forming apparatus 100 from a host processing device such as an image reading device (not shown) to perform laser scanning exposure on the surface of the photosensitive drum 1. By performing laser scanning exposure, the latent image device 3 reduces the potential of the portion of the surface of the photosensitive drum 1 that has been irradiated with the laser beam, thereby sequentially forming an electrostatic latent image corresponding to the image information on the surface of the photosensitive drum 1.

[0024] The developing member 4 as a developing means is a developing sleeve that supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum 1 by the latent image device 3, and reversely develops the electrostatic latent image as a toner image. The developing member 4 holds a magnetic brush made of a two-component developer consisting of toner and carrier, and performs development while in contact with the photosensitive drum 1. The toner used is, for example, a toner with an average particle size of about 5 μm obtained by kneading a pigment into a resin binder mainly made of polyester and then pulverizing and classifying the mixture. The average charge amount of the toner attached to the photosensitive drum 1 is about -30 μC / g.

[0025] A thin layer of developer is formed on the developing member 4 by a developer regulating blade (not shown) disposed opposite the developing member 4 with a predetermined gap therebetween. The developing member 4 is rotated in the direction of the arrow in FIG. 1 (clockwise direction in FIG. 1), which is the opposite direction to the rotational direction of the photosensitive drum 1, by a developing drive motor (not shown).

[0026] The primary transfer member 5 is pressed against the photosensitive drum 1 via the intermediate transfer body 7 with a predetermined pressing force to form a pressure nip portion which is a primary transfer portion. A transfer voltage of positive polarity, which is opposite to the negative polarity which is the normal charging polarity of the toner, is applied to the primary transfer member 5 from a transfer power source (not shown). The transfer voltage applied to the primary transfer member 5 from the transfer power source is, for example, +600 V here. The primary transfer member 5 electrostatically transfers the toner image formed on the surface of the photosensitive drum 1 to the intermediate transfer body 7 in sequence.

[0027] The cleaning device 6 removes and collects the toner remaining on the photosensitive drum 1 that has not been transferred to the intermediate transfer body 7 by the primary transfer member 5 .

[0028] The intermediate transfer member 7 conveys the toner image transferred from the photosensitive drum 1 by the primary transfer member 5 to a secondary transfer section 8 .

[0029] A predetermined transfer voltage is applied to the secondary transfer unit 8. Here, the transfer voltage is exemplified as +800 V. The secondary transfer unit 8 transfers the toner image transferred to the intermediate transfer body 7 onto the recording material 15 being conveyed by a pair of registration rollers 9. The secondary transfer unit 8 conveys the recording material 15 onto which the toner image has been transferred to the fixing device 10.

[0030] The pair of registration rollers 9 conveys the recording material 15 fed by the feeding device 11 to the secondary transfer section 8 at a predetermined timing.

[0031] The fixing device 10 is a heat roller fixing device that performs a fixing process of fixing the toner image transferred to the recording material 15 conveyed by the secondary transfer unit 8 onto the recording material 15 by applying heat and pressure. The fixing device 10 outputs the recording material 15 onto which the toner image has been fixed to the outside of the image forming apparatus 100 as an image formed product.

[0032] The feeding device 11 stores a recording material 15. The feeding device 11 feeds the stored recording material 15 to the pair of registration rollers 9.

[0033] The charging device 101 includes a charging member 2 of a contact charging type that uniformly charges the surface of the photosensitive drum 1. The configuration of the charging device 101 will be described in detail later.

[0034] The photosensitive drum drive motor M1 rotates the photosensitive drum 1 by being driven under the control of a CPU 201 (to be described later) of the charging device 101.

[0035] The charging power supply PS1 is a DC and AC power supply, and under the control of the CPU 201, applies an oscillating voltage of predetermined conditions, in which a DC voltage and an AC voltage are superimposed, to the charging member 2. For example, the charging power supply PS1 applies an oscillating voltage of a frequency of 1.45 kHz, in which a peak-to-peak voltage of 1980 V and a DC voltage of -500 V are superimposed, to the charging member 2.

[0036] The developing power source PS2 is a DC and AC power source, and applies an oscillating voltage in which either or both of a DC voltage and an AC voltage are superimposed to the developing member 4 under the control of the CPU 201. For example, the oscillating voltage applied to the developing member 4 from the developing power source PS2 is an oscillating voltage in which a square-wave AC voltage is superimposed, and here, a frequency of 8.0 kHz and a peak-to-peak voltage of 1800 V are exemplified. The DC voltage applied to the developing member 4 from the developing power source PS2 is appropriately set so as to become an appropriate fog removal potential with respect to the potential of the developing portion of the photosensitive drum 1, and here, -400 V is exemplified.

[0037] In response to a start instruction, the image forming apparatus 100 having the above configuration executes a job such as a print job or a printing operation, which is a series of operations for forming and outputting an image on one or multiple recording materials 15. A job generally includes an image forming process, a pre-rotation process, a paper spacing process when forming images on multiple recording materials 15, and a post-rotation process.

[0038] Here, the image forming process is a process of forming an image on recording material 15 and outputting recording material 15 on which the image has been formed. In the image forming process, formation of an electrostatic image, formation of a toner image, primary transfer of the toner image, and secondary transfer of the toner image are performed. The image forming period is a period during which the image forming process is performed, which is a period during which an image is created. The timings of formation of an electrostatic image, formation of a toner image, primary transfer of the toner image, and secondary transfer of the toner image in the image forming process are each different.

[0039] The pre-rotation process is a process carried out during a period of preparatory operations before the image forming process from when a start command is input until the image actually starts to be formed. The sheet gap process is a process carried out during a period corresponding to the interval between recording materials 15 when the image forming process is carried out continuously on a plurality of recording materials 15 (when carrying out continuous image formation). The post-rotation process is a process carried out during a period of tidying up operations (preparatory operations) after the image forming process.

[0040] The non-image forming period (non-image forming time) is a period other than the image forming period. Specifically, the non-image forming period includes the above-mentioned pre-rotation process, the paper interval process, the post-rotation process, the pre-rotation process which is a preparatory operation when the power is turned on, and the pre-rotation process which is a preparatory operation after returning from the sleep state.

[0041] <Configuration of charging device> The configuration of a charging device 101 according to an embodiment of the present invention will be described in detail with reference to FIGS.

[0042] The charging device 101 includes a charging member 2 , a control unit 200 , an environment sensor 400 , and a charging AC current detection circuit 403 .

[0043] The charging member 2 has an axial length of 330 mm and a diameter of 14 mm. The charging member 2 is formed by overlapping a conductive rubber layer on the outer periphery of a stainless steel core. The charging member 2 is rotatably held at both longitudinal ends of the core by bearing members (not shown), and is pressed toward the photosensitive drum 1 by a pressure spring (not shown) so as to be in pressure contact with the photosensitive drum 1 with a predetermined pressure. The charging member 2 rotates following the rotation of the photosensitive drum 1. The charging member 2 charges the photosensitive drum 1 by utilizing a discharge phenomenon that occurs in a minute gap between the charging member 2 and the photosensitive drum 1.

[0044] A voltage of predetermined conditions is applied from the charging power source PS1 to the core of the charging member 2. For example, when an oscillating voltage of a DC voltage of -500 V superimposed on an AC voltage of 1980 V is applied from the charging power source PS1 to the charging member 2, the charging member 2 performs a charging process to uniformly charge the image forming portion of the photosensitive drum 1 to about -500 V. Note that the DC voltage and AC voltage applied from the charging power source PS1 to the charging member 2 during image formation are not limited to the above values, but are appropriately set to values ​​suitable for good image formation.

[0045] The control unit 200 controls the overall operation of the image forming apparatus 100. The control unit 200 includes a CPU 201 and a memory 202.

[0046] The CPU 201 as a control means reads out and executes a program stored in the memory 202, thereby controlling the operation of the image forming apparatus 100 based on the data stored in the memory 202. Specifically, the CPU 201 executes ON / OFF switching of various motors such as the photosensitive drum drive motor M1, ON / OFF switching and output value control of the charging power supply PS1 and the developing power supply PS2, and control of the image forming operation.

[0047] The CPU 201 stores in the memory 202 temperature information of the temperature (ambient temperature) indicated by the electrical signal input from the temperature sensor 401, and also stores in the memory 202 humidity information of the humidity indicated by the electrical signal input from the humidity sensor 402. The CPU 201 stores in the memory 202 total current amount information of the total current amount flowing through the charging member 2 indicated by the electrical signal input from the charging AC current detection circuit 403. The total current amount is the total current amount of a resistive load current flowing through a resistive load between the charging member 2 and the photosensitive drum 1, a capacitive load current flowing through a capacitive load between the charging member 2 and the photosensitive drum 1, and a discharge current flowing between the charging member 2 and the photosensitive drum 1.

[0048] The CPU 201 controls ON / OFF of the DC power supply and AC power supply of the charging power supply PS1 to apply an AC voltage or an oscillating voltage (superimposed voltage) in which a DC voltage and an AC voltage are superimposed, to the charging member 2. The CPU 201 controls the value of the DC voltage applied to the charging member 2 from the charging power supply PS1, and the AC voltage or AC current applied to the charging member 2 from the charging power supply PS1. Here, a peak-to-peak voltage is used as the AC voltage. Note that the AC voltage is not limited to the peak-to-peak voltage, and a maximum voltage, a minimum voltage, or an effective voltage value may also be used.

[0049] The CPU 201 executes an AC voltage determination process (to be described later) for determining a voltage to be applied to the charging member 2 based on the temperature indicated by the electrical signal input from the temperature sensor 401 and the temperature information stored in the memory 202 .

[0050] The memory 202 stores programs, data such as tables, temperature information, humidity information, or total current amount information.

[0051] An environment sensor 400 serving as an environment information detection unit acquires environment information relating to the installation environment of the image forming apparatus 100, and outputs the information to the CPU 201. The environment sensor 400 includes a temperature sensor 401 and a humidity sensor 402.

[0052] The temperature sensor 401 is a thermistor that measures the temperature in the air as a value indicated by the environmental information, and outputs an electrical signal to the CPU 201 according to the measured temperature.

[0053] The humidity sensor 402 detects the humidity in the air as a value indicated by the environmental information from a change in capacitance, and outputs an electric signal according to the detected humidity to the CPU 201.

[0054] A charging AC current detection circuit 403 as a measuring means measures the total amount of current flowing through the charging member 2 via the photosensitive drum 1, and outputs an electric signal according to the measured total amount of current to the CPU 201.

[0055] <AC voltage determination process> The AC voltage determination process executed by the charging device 101 according to the embodiment of the present invention will be described in detail with reference to FIGS.

[0056] The AC voltage determination process shown in FIG. 3 is started when the image forming apparatus 100 starts the pre-multiple rotation process or the pre-rotation process.

[0057] First, the CPU 201 controls the driving of the photosensitive drum driving motor M1 to perform the idling operation of the photosensitive drum 1 (S101).

[0058] Next, the CPU 201 obtains the ambient temperature T1 based on an electrical signal input from the temperature sensor 401 of the environment sensor 400, and stores the obtained temperature in the memory 202 (S102).

[0059] Next, the CPU 201 reads out and acquires the ambient temperature T2 stored in the memory 202 when the previous constant voltage control or discharge current control was executed (S103).

[0060] Next, the CPU 201 calculates the absolute value |ΔT| of the difference ΔT between the current ambient temperature T1 and the previous ambient temperature T2 (S104).

[0061] Next, the CPU 201 determines whether the absolute value |ΔT| is equal to or greater than an AC voltage determination control threshold ΔTth (S105). The AC voltage determination control threshold ΔTth is 3° C., for example.

[0062] Here, the AC voltage determination control threshold ΔTth is set based on daily temperature fluctuations in the installation environment of the image forming apparatus 100, the detection accuracy or productivity of the environmental sensor 400, and specifically, is set based on temperature, humidity, moisture content, time, number of sheets passed, etc. For example, the AC voltage determination control threshold ΔTth is set based on daily temperature fluctuations in the average installation environment of the image forming apparatus 100, and is set so as to minimize downtime caused by daily temperature fluctuations.

[0063] When the absolute value |ΔT| is equal to or greater than the AC voltage determination control threshold ΔTth (step S105: Yes), the CPU 201 starts executing control for setting the voltage and determines whether the ambient temperature T1 is equal to or greater than the control switching threshold Tth (S106). The control switching threshold Tth is exemplified as 15° C. here.

[0064] When the ambient temperature T1 is equal to or higher than the control switching threshold Tth (step S106: Yes), the CPU 201 performs discharge current control as the second control (S107). Here, the discharge current control is a control for setting a voltage to be applied to the charging member 2, and is a control for obtaining an AC voltage required to output an appropriate amount of discharge current. The details of the discharge current control will be described later.

[0065] Next, CPU 201 stores ambient temperature T1 acquired in the process of step S102 as ambient temperature T2 in memory 202 (S108), and then ends the AC voltage determination process.

[0066] On the other hand, when the ambient temperature T1 is less than the control switching threshold Tth (step S106: No), the CPU 201 executes the constant voltage control as the first control, and then executes the process of step S108. Here, the constant voltage control is a control for setting the voltage to be applied to the charging member 2, and is a control for stabilizing the voltage at a desired predetermined voltage value.

[0067] 4, which shows an example of a table in which the ambient temperature T1 and the AC voltage Vx are associated with each other and which is stored in the memory 202. The CPU 201 then monitors the output voltage of the charging power supply PS1 via a resistor (not shown), feeds back the monitored output voltage to a voltage setting circuit (not shown), and performs control so that the determined AC voltage Vx is applied to the charging member 2 from the charging power supply PS1.

[0068] Furthermore, when the absolute value |ΔT| is less than the AC voltage determination control threshold ΔTth (step S105: No), the CPU 201 executes the AC voltage correction process (S110) without starting the execution of control for setting the voltage to be applied to the charging member 2. Then, the CPU 201 ends the AC voltage determination process. The AC voltage correction process will be described later.

[0069] Then, the CPU 201 performs image formation in the image forming process while controlling the charging power source PS1 so as to apply the AC voltage Vx set in the above-mentioned AC voltage determination process to the charging member 2.

[0070] The above-described AC voltage determination process is started at the timing when the pre-multiple rotation process is started or at the timing when the pre-rotation process is started. However, the AC voltage determination process is not limited to this, and may be started at the timing when the image forming apparatus 100 is turned on, when it returns from a sleep state, or when a print command is issued.

[0071] <Discharge current control> The discharge current control performed by the charging device 101 according to the embodiment of the present invention will be described in detail with reference to FIG.

[0072] The CPU 201 controls the charging power supply PS1 to sequentially apply to the charging member 2 three voltages, namely, voltage values ​​V1, V2, and V3 of the AC voltage Vpp in the non-discharge region, and then sequentially apply three voltages, namely, voltage values ​​V4, V5, and V6 of the AC voltage Vpp in the discharge region.

[0073] The relationship between the voltage values ​​V1, V2, and V3 in the undischarged region and the current values ​​P1, P2, and P3 of the total current Iac that flows when the voltages V1, V2, and V3 are applied is obtained as an approximation straight line of equation (1) using the least squares method.

[0074] Y = βX + B (1)

[0075] In addition, the relationship between the voltage values ​​V4, V5, and V6 in the discharge region and the current values ​​P4, P5, and P6 of the total current Iac that flows when the voltages V4, V5, and V6 are applied is obtained as an approximation straight line of equation (2) using the least squares method.

[0076] Y = αX + A (2)

[0077] The discharge current amount ΔAC can be calculated by subtracting the amounts of currents other than the discharge current, such as the resistive load current and the capacitive load current, from the total current amount Iac, and can therefore be calculated from the difference between equation (2) and equation (1). Therefore, the value Vx of the AC voltage Vpp at which the discharge current amount becomes the target discharge current amount ΔAC can be calculated based on the difference between the approximation line of the discharge region of equation (2) and the approximation line of the undischarged region of equation (1).

[0078] Specifically, the target discharge current amount ΔAC is expressed by the difference between equation (4) in which the Y value of equation (2) is Yα and the X value is Vx, and equation (3) in which the Y value of equation (1) is Yβ and the X value is Vx, as shown in equation (5).

[0079] Yβ=βVx+B (3) Yα=αVx+A (4) Yα-Yβ=(αVx+A)-(βVx+B)=ΔAC (5)

[0080] Then, the voltage value V7 of the voltage Vx can be obtained from equation (6) obtained by modifying equation (5).

[0081] Vx = (D-A+B) / (α-β) (6)

[0082] The CPU 201 controls the charging power source PS1 to apply the voltage Vx having the voltage value V7 calculated by the formula (6) to the charging member 2. The target discharge current amount ΔAC is exemplified as 60 μA here.

[0083] <AC voltage correction processing> The AC voltage correction process performed by the charging device 101 according to the embodiment of the present invention will be described in detail with reference to FIG.

[0084] The AC voltage correction process shown in FIG. 6 is started at the timing when it is determined in step S105 of the AC voltage determination process shown in FIG. 3 that the absolute value |ΔT| is less than the AC voltage determination control threshold ΔTth (step S105: No).

[0085] First, the CPU 201 reads and acquires the AC voltage Vx determined in the immediately preceding discharge current control or constant voltage control stored in the memory 202 (S201).

[0086] Next, the CPU 201 determines whether the ambient temperature T2 at the time of the previous constant voltage control or discharge current control stored in the memory 202 is equal to or higher than the control switching threshold Tth (S202). The control switching threshold Tth is exemplified as 15° C. here.

[0087] When the ambient temperature T2 is equal to or higher than the control switching threshold Tth (step S202: Yes), the CPU 201 selects the correction value C1 (S203). Specifically, the CPU 201 selects the correction value C1 associated with the ambient temperature T1 in a discharge current control correction value C1 table shown as an example in Fig. 7 stored in the memory 202. Here, the discharge current control correction value C1 table is a table that associates the ambient temperature T1 with the fluctuation amount ΔT from the ambient temperature T2 to the ambient temperature T1, and the correction value C1, and is a table for correcting the AC voltage Vx determined in the discharge current control.

[0088] Next, the CPU 201 corrects the AC voltage Vx based on the AC voltage Vx acquired in the process of step S201 and the correction value C1 selected in the process of step S203 (S204).

[0089] Specifically, CPU 201 corrects AC voltage Vx by adding correction value C1 to AC voltage Vx. For example, if AC voltage Vx determined in discharge current control executed when ambient temperature T2 is 20° C. is 1580 V and a print job is executed when ambient temperature T1 subsequently changes to 18° C., CPU 201 selects correction value C1 of 72 V from FIG. 7. CPU 201 then adds correction value C1 of 72 V to AC voltage Vx of 1580 V to obtain corrected AC voltage Vx of 1652 V.

[0090] The correction of the AC voltage Vx is not limited to adding the correction value C1 to the AC voltage Vx, but may be performed by multiplying the AC voltage Vx by the correction value C1 or by any other method.

[0091] Next, the CPU 201 sets the corrected AC voltage Vx as the AC voltage to be applied from the charging power source PS1 to the charging member 2 (S205), and then ends the AC voltage correction process.

[0092] After completing the AC voltage correction process, the CPU 201 ends the AC voltage determination process shown in FIG.

[0093] On the other hand, when the ambient temperature T2 is less than the control switching threshold Tth (step S202: No), the CPU 201 selects the correction value C2 (S204). Specifically, the CPU 201 selects the correction value C2 associated with the ambient temperature T1 in a constant voltage control correction value C2 table stored in the memory 202 and shown as an example in Fig. 8. Here, the constant voltage control correction value C2 table is a table that associates the ambient temperature T1 with the fluctuation amount ΔT from the ambient temperature T2 to the ambient temperature T1, and the correction value C2, and is a table for correcting the AC voltage Vx determined in the constant voltage control.

[0094] The reason for distinguishing between the discharge current control correction value C1 table and the constant voltage control correction value C2 table in the above AC voltage correction process will be described.

[0095] The AC voltage Vx set in the discharge current control is set in consideration of the variation in the high voltage output. Therefore, the correction amount of the AC voltage Vx set in the discharge current control does not need to take the variation in the high voltage output into consideration. On the other hand, the AC voltage Vx set in the constant voltage control is set assuming the case where the high voltage output is the lowest.

[0096] Therefore, when the AC voltage Vx set in the constant voltage control is corrected using the correction value C1 of the discharge current control correction value C1 table that corrects the AC voltage Vx set in the discharge current control, the amount of discharge current may be insufficient. Therefore, it is necessary to switch between the discharge current control correction value C1 table and the constant voltage control correction value C2 table, which has a larger correction amount than the discharge current control correction value C1 table.

[0097] <Effects of the charging device> The effects of the charging device 101 according to the embodiment of the present invention will be described in detail with reference to FIGS.

[0098] 9 and 10 show a case where a total of nine print jobs are performed in a state where the ambient temperature fluctuates around the control switching threshold Tth. FIG. 9 also shows the implementation state of the AC voltage determination process, the implementation state of the AC voltage correction process, and the set AC voltage and discharge current amount in this embodiment. FIG. 10 shows, as a comparison with this embodiment, the implementation state of the AC voltage determination control, the set AC voltage, and the discharge current amount in a case where the AC voltage correction process is not executed. Note that FIGS. 9 and 10 show an example where the control switching threshold Tth is set to 15° C.

[0099] In this embodiment, as shown in Fig. 9, when the control switching threshold Tth is frequently crossed, the discharge current control and the constant voltage control are not executed until the absolute value |ΔT| exceeds the AC voltage determination control threshold ΔTth of 3°C. Also, in this embodiment, the AC voltage can be set without falling below the discharge current amount of 60 μA at which charging failure occurs. Furthermore, in this embodiment, the discharge current control that causes downtime is executed only once, and an appropriate AC voltage can be set with little downtime.

[0100] On the other hand, in Fig. 10, the discharge current control or constant voltage control is executed every time the control switching threshold Tth is crossed. In the case of Fig. 10, it is possible to set an AC voltage with a smaller amount of discharge current compared to the case of Fig. 9, but it is found that the discharge current control is executed four times, resulting in an increased downtime.

[0101] Thus, according to this embodiment, when the environmental conditions change from those in which constant voltage control is performed to those in which discharge current control is performed, the AC voltage set in the constant voltage control is corrected in accordance with the environmental information, without executing the discharge current control.

[0102] In this embodiment, before switching from constant voltage control to discharge current control, the voltage applied to the charging member 2 by the constant voltage control is corrected based on the atmospheric temperature and then applied to the charging member 2. This makes it possible to set an appropriate voltage when the environmental conditions change, and also to shorten the operation time other than the image forming operation.

[0103] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention.

[0104] Specifically, in the above embodiment, the AC voltage applied to the charging member 2 is set based on the atmospheric temperature, but this is not limiting, and the AC voltage applied to the charging member 2 may be set based on the atmospheric humidity in addition to or instead of the atmospheric temperature. Also, the AC voltage applied to the charging member 2 may be set using a value indicating an environmental condition other than the atmospheric temperature and the atmospheric humidity. [Explanation of symbols]

[0105] 1Y Photosensitive drum 1M Photosensitive drum 1C Photosensitive drum 1K Photosensitive drum 2Y Electrostatic materials 2M Electrostatic material 2C Electrostatic materials 2K Electrostatic Materials 100 Image forming device 101Y Charging device 101M Charging device 101C Charging device 101K Charging device 200 Control section 201 CPU 202 Memory 400 Environmental Sensors 401 Temperature Sensor 402 Humidity Sensor 403 Charge AC current detection circuit PS1 Charging power supply

Claims

1. a charging member that contacts the image carrier and charges the image carrier by applying a voltage thereto; An environmental information detection means for detecting environmental information; a measuring means for measuring a current flowing through the charging member when a voltage is applied to the charging member; a control means for switching between a first control for applying a predetermined voltage to the charging member and a second control for applying a voltage to the charging member such that the current measured by the measuring means becomes a predetermined current, in accordance with the environmental information; having The control means before switching from the first control to the second control, the voltage applied to the charging member under the first control is corrected based on the environmental information and applied to the charging member; A charging device characterized by:

2. The control means when a difference between a previous value and a current value indicated by the environmental information detected by the environmental information detection means is less than a predetermined value, the voltage applied to the charging member by the first control is corrected based on the environmental information.

2. The charging device according to claim 1.

3. The control means before switching from the second control to the first control, the voltage applied to the charging member by the second control is corrected based on the environmental information and applied to the charging member, and a correction amount when the voltage applied to the charging member by the first control is corrected based on the environmental information is made larger than a correction amount when the voltage applied to the charging member by the second control is corrected based on the environmental information.

3. The charging device according to claim 1, wherein the charging member is a roller.

4. The control means when starting the pre-multiple rotation process or the pre-rotation process, the voltage applied to the charging member by the first control is corrected based on the environmental information.

3. The charging device according to claim 1, wherein the charging member is a roller.

5. The control means applying the predetermined voltage corresponding to the environmental information to the charging member in the first control; 3. The charging device according to claim 1, wherein the charging member is a roller.

6. The charging device according to claim 1 or 2, a charging power source that applies a voltage to the charging device; an image carrier that is charged by the charging device; an exposure unit for exposing the image carrier charged by the charging device to light to form an electrostatic latent image on the image carrier; a developing means for supplying toner to the electrostatic latent image to form a toner image on the image carrier; An image forming apparatus comprising:

Images