WO2021206791A1

WO2021206791A1 - Organic photo conductor charger

Info

Publication number: WO2021206791A1
Application number: PCT/US2021/016145
Authority: WO
Inventors: Jin Yun Park; Jong Hwa Cho; Kwang Hoon CHEON
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-04-09
Filing date: 2021-02-02
Publication date: 2021-10-14
Also published as: KR20210125762A

Abstract

An example image forming apparatus includes a printing engine including a charging member to charge a photoconductor, a power supply including a direct current (DC) power circuit to generate a DC power, an alternating current (AC) power circuit to generate an AC power and to superimpose the DC power on the generated AC power to provide the superimposed power to the charging member, and a sensing circuit to detect an output value of a comparator of the DC power circuit, and a processor to control the AC power circuit to vary a magnitude of the AC power and search for a current saturation point of the charging member based on the output value detected by the sensing circuit while varying the magnitude of the AC power.

Description

ORGANIC PHOTO CONDUCTOR CHARGER

BACKGROUND

[0001] An image forming apparatus may include an apparatus for generating, printing, receiving, and transmitting image data, and a representative example thereof may include a printer, a scanner, a copier, a facsimile, and a multi-function printer that integrally implements functions thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0002] FIG. 1 is a block diagram illustrating an image forming apparatus according to an example;

[0003] FIG. 2 is a block diagram illustrating an image forming apparatus according to an example;

[0004] FIG. 3 is a diagram illustrating a printing engine according to an example;

[0005] FIG. 4 is a diagram illustrating a power supply according to an example;

[0006] FIG. 5 is a circuit diagram of a power supply having a sensing circuit according to a an example;

[0007] FIG. 6 is a circuit diagram of a sensing circuit according to a an example;

[0008] FIG. 7 is a diagram illustrating a relationship between a charging current and a sensing current according to an example; and [0009] FIG. 8 is a diagram for describing a charging control method according to an example. DETAILED DESCRIPTION

[0010] Hereinafter, examples will be described with reference to the accompanying drawings. The examples described below may be modified and implemented in various different forms. In the disclosure, when a component is referred to as being “connected to” another component, it means that the component and the other component may be ‘directly connected to’ each other or may be ‘connected to’ each other while having another component interposed therebetween. In addition, when a component is referred to as “including” another component, it means that other components are not excluded but may be further included, unless explicitly described to the contrary.

[0011] As used herein, the term “image forming job” may refer to various jobs (e.g., copy, print, scan, or fax) related to an image, such as forming of an image or creating/storing/transmitting of an image file, and the term “job” may refer to the image forming job and also to a series of processes necessary to perform the image forming job.

[0012] An image forming apparatus may refer to an apparatus for performing an image forming job such as printing print data generated by a terminal device such as a computer onto a recording medium, such as paper. Examples of such an image forming apparatus may include a printer, a scanner, a copier, a facsimile, or a multi-function peripheral (MFP) that complexly implements the functions of the printer, the scanner, the copier, and the facsimile through a single device.

[0013] The image forming apparatus may perform a charging operation for charging a photoconductor to a constant potential. If a charging voltage is higher than a reference value, the life of the photoconductor may be reduced, and if the charging voltage is lower than the reference value, a print quality may deteriorate. Therefore, an appropriate charging voltage should be used.

[0014] To supply an appropriate charging voltage to a photoconductor, a current saturation point of a charging member may be measured. Hereinafter, an example of an image forming apparatus capable of measuring a current saturation point will be described. In the following example, the current saturation point is obtained without the expense of a current sensor.

[0015] FIG. 1 is a block diagram illustrating an image forming apparatus according to an example.

[0016] Referring to FIG. 1 , an image forming apparatus 100 may include a power supply 110, a printing engine 120, and a processor 130.

[0017] The power supply 110 may supply power to a component in the image forming apparatus 100. For example, the power supply 110 may receive an alternating current (AC) power and convert the received AC power into a direct current (DC) power. The AC power received by the power supply 110 may be provided by a commercial AC power supplier.

[0018] The power supply 110 may generate a charging power and provide the generated charging power to a charging member 121. Flere, the charging power may be a power in which a DC power of a predetermined magnitude and an AC voltage of a peak voltage of a predetermined magnitude are superimposed. [0019] For such an operation, the power supply 110 may include an AC power circuit 200 and a DC power circuit 300. Flere, the DC power circuit 300 may generate a DC power of a predetermined magnitude and the AC power circuit 200 may generate a sinusoidal AC power wave having a predetermined peak voltage. The power supply 110 may superimpose the generated AC power and the DC power and output the superimposed power. An example of the AC power circuit 200 and the DC power circuit 300 will be described later with reference to FIG. 5.

[0020] The power supply 110 may include a sensing circuit 400 for detecting saturation of a charging current. In an example, the sensing circuit 400 may detect an output value of a comparator of the DC power circuit 300. An example sensing circuit 400 will be described later with reference to FIGS. 5 and 6.

[0021] The printing engine 120 is to form an image. For example, the printing engine 120 may form the image in an electrophotographic manner and may include the charging member 121 .

[0022] The charging member 121 may charge the photoconductor to a predetermined potential. For example, the charging member 121 may charge the photoconductor using the charging power provided from the power supply 110. An example of the charging member 121 will be described later with reference to FIG. 3.

[0023] The processor 130 is to control an operation of the image forming apparatus 100. The processor 130 may be a single device such as a central processing unit (CPU) or a microcontroller (MCU), and may also be a plurality of devices such as a clock generation circuit, a CPU, and a graphics processor. [0024] The processor 130 may determine whether it is necessary to determine the charging voltage. For example, when the image forming apparatus 100 is in an initially installed state, when consumables (e.g., a photoconductor, a toner, etc.) in the image forming apparatus 100 are changed, when the image forming apparatus 100 prints a predetermined number of copies or more, etc., the processor 130 may determine that it is necessary to determine the charging voltage.

[0025] When it is necessary to determine the charging voltage, the processor 130 may control the power supply 110 to supply the power in which the DC power of the predetermined magnitude and the AC power of the predetermined peak voltage magnitude are superimposed to the charging member 121.

[0026] The processor 130 may detect the output value of the comparator of the DC power circuit 300 using the sensing circuit 400. A reason for using the output value of the comparator will be described later with reference to FIG. 5. [0027] When the output value of the comparator is detected in a state in which an initial AC power is supplied, the processor 130 may control the power supply 110 to vary a peak voltage of the AC power. In an example, the processor 130 may control the power supply 110 to increase the peak voltage of the AC power in a stepwise manner. For example, if the initial AC power is 300 Vpp, the processor 130 may increase the peak voltage of the AC power by + 100 Vpp per step. That is, the processor 130 may gradually increase the peak voltage of the AC power such as 300 Vpp, 400 Vpp, 500 Vpp, ... .

[0028] In an example, the processor 130 may maintain the DC power at a predetermined value and continuously detect the output value of the comparator of the DC power circuit 300 using the sensing circuit 400.

[0029] The processor 130 may determine whether a current of the charging member 121 is saturated by checking whether a change in the output value of the comparator is less than a predetermined value according to a change in the peak voltage of the AC power.

[0030] If it is determined that the charging member 121 is saturated, the processor 130 may stop an operation of searching for a current saturation point of the charging member 121 , and set the peak value of the AC voltage at a saturation point to an AC voltage value at the time of charging.

[0031] Accordingly, if a print command is input after the charging voltage is determined, the processor 130 may control the power supply 110 to provide the charging power in which the predetermined DC power and the previously determined AC voltage are superimposed to the charging member 121 .

[0032] While an example image forming apparatus is illustrated and described above with reference to FIG. 1 , various components may be additionally provided at the time of implementation. Examples of such various components will be described below with reference to FIG. 2.

[0033] FIG. 2 is a block diagram illustrating an image forming apparatus according to an example.

[0034] Referring to FIG. 2, the image forming apparatus 100 may include the power supply 110, the printing engine 120, the processor 130, a communication device 140, a memory 150, a display 160, and a manipulation input device 170.

[0035] The power supply 110, the printing engine 120, and the processor 130 have been described with reference to FIG. 1 , and a redundant description thereof will be thus omitted.

[0036] The communication device 140 may be formed to connect the image forming apparatus 100 with an external device, and may be connected through a universal serial bus (USB) port, a wireless module, a local area network (LAN), an internet network, or the like. Here, the wireless module may be WiFi, WiFi Direct, near field communication (NFC), Bluetooth, or the like.

[0037] The communication device 140 may receive print data from the external device. Here, the print data refers to data converted to a format that is printable by the image forming apparatus, and may be, for example, data in a printer language such as postscript (PS) or printer control language (PCL).

[0038] The memory 150 may store the print data. The memory 150 may be implemented as an external storage medium, a removable disk including a USB memory, a web server through a network, a storage medium in the image forming apparatus 100, or the like.

[0039] The memory 150 may store setting information for a printing environment. Here, the setting information may include various setting values related to a printing job operation, such as a charging voltage, a fixing temperature for an environment such as a type of printing paper, a temperature, a humidity, and the like, and may store information on a peak voltage of the AC power corresponding to a current saturation point.

[0040] The display 160 may display a variety of information provided from the image forming apparatus 100. For example, the display 160 may display a user interface window for selecting various functions provided by the image forming apparatus 100. The display 160 may include a liquid crystal display (LCD), a cathode ray tube (CRT), a light emitting diode (LED), an organic LED (OLED), or the like.

[0041] The manipulation input device 170 may receive a function selection and a control command for the corresponding function from a user. Here, the function may include a print function, a copy function, a scan function, a fax transmission function, and the like. The function control command may be received through a control menu displayed on the display 160.

[0042] The manipulation input device 170 may be implemented as a button, a keyboard, a mouse, or the like, and may also be implemented as a touch screen capable of simultaneously performing the functions of the display 160 described above.

[0043] As described above, the image forming apparatus 100 according to the example may effectively check the current saturation point without using a separate current sensor for measuring a surface current of the photoconductor. In addition, the image forming apparatus 100 may provide a charging power corresponding to the current saturation point detected at the time of printing to the photoconductor. That is, the image forming apparatus 100 may perform a charging operation using a minimum AC power. Accordingly, it is possible to prolong the life of the photoconductor while decreasing a deterioration of image quality.

[0044] In illustrating and describing FIGS. 1 and 2, although the sensing circuit 400 is illustrated and described as included in the power supply 110, the sensing circuit 400 may be included in the printing engine 120. The AC power circuit and the DC power circuit in the power supply 110 may also be included in the printing engine 120.

[0045] FIG. 3 is a diagram illustrating a printing engine according to an example.

[0046] Referring to FIG. 3, the printing engine 120 may operate in a tandem manner. Flere, the tandem manner is a color printing manner in which a photoconductor for each color individually performs a job of forming an image for high-speed output hereinafter, the printing engine 120 is described as including a plurality of photoconductors and a plurality of charging members on the assumption that color printing is possible. However, a printing engine capable of black-and-white printing may include one photoconductor and one charging member.

[0047] An electrostatic latent image may be formed on photoconductors 123-1 , 123-2, 123-3, and 123-4. Each photoconductor 123 may be referred to as an organic photo conductor (OPC), a photosensitive drum, a photosensitive belt, or the like depending the form thereof. Here, a first photoconductor 123-1 may be a yellow photoconductor to form a yellow image, a second photoconductor 123-2 may be a magenta photoconductor to form a magenta image, a third photoconductor 123-3 may be a cyan photoconductor to form a cyan image, and a fourth photoconductor 123-4 may be a black photoconductor to form a black image.

[0048] Charging members 121-1 , 121-2, 121-3, and 121-4 may respectively charge a surface of each of the photoconductors 123-1 , 123-2, 123- 3, and 123-4 to a uniform electric potential using the charging power provided from the power supply 110. The charging members 121-1 , 121-2, 121-3, and 121- 4 may be implemented in various configurations such as corona charging members, charging rollers, charging brushes, and the like.

[0049] An exposure device (not illustrated) may form the electrostatic latent image on the surfaces of the photoconductors 123-1 , 123-2, 123-3, and 123-4 by changing surface potentials of the photoconductors 123-1 , 123-2, 123-3, and 123- 4 according to image information to be printed. A developing device (not illustrated) may accommodate a developer therein and may supply the developer to the electrostatic latent images to develop the electrostatic latent images into visible images.

[0050] The visible images formed on the photoconductors 123-1 , 123-2, 123-3, and 123-4 may be primarily transferred to an intermediate transfer belt (ITB). In addition, the images on the intermediate transfer belt (ITB) may be transferred to a printing medium such as paper by a transfer machine.

[0051] In addition, the image may be fixed on the printing medium by a fuser (not illustrated). The printing job may be completed by a series of processes as described above.

[0052] The power supply 110 may separately supply the charging power in which the DC power and the AC power are superimposed to each of the charging members 121-1 , 121-2, 121-3 and 121-4 during the charging operation described above. An example of the power supply 110 that supplies a plurality of charging powers will be described below with reference to FIG. 4.

[0053] FIG. 4 is a diagram illustrating a power supply according to an example.

[0054] Referring to FIG. 4, the power supply 110 may include a plurality of AC power circuits 200-1 , 200-2, 200-3, and 200-4, a plurality of DC power circuits 300-1 , 300-2, 300-3, and 300-4, a plurality of sensing circuits 400-1 , 400-2, 400- 3, and 400-4, and a multiplexer (MUX) 115.

[0055] Each of the plurality of DC power circuits 300-1 , 300-2, 300-3, and 300-4 may generate a DC power. For example, the DC power circuit 300 may receive a control signal from the processor 130 and generate the DC power having a magnitude corresponding to the received control signal. Flere, the received control signal may be a pulse width modulation (PWM) signal. An example of the DC power circuit 300 will be described later with reference to FIG. 5.

[0056] Each of the plurality of AC power circuits 200-1 , 200-2, 200-3, and 200-4 may generate an AC power. For example, the AC power circuit 200 may receive a control signal from the processor 130 and generate the AC power having a magnitude corresponding to the received control signal. In addition, the AC power circuit 200 may superimpose the generated AC power and the DC power generated by the DC power circuit 300 and output the superimposed power to the charging member 121. An example the AC power circuit 200 will be described later with reference to FIG. 5.

[0057] The plurality of sensing circuits 400-1 , 400-2, 400-3, and 400-4 may sense an output voltage value of a comparator of each of the DC power circuits 300-1 , 300-2, 300-3, and 300-4. An example of finding a saturation point of the charging current using a voltage value of an output node of the comparator among various nodes in the power supply 110 will be described later with reference to FIG. 7.

[0058] The MUX 115 may selectively output the output values of the plurality of sensing circuits 400-1 , 400-2, 400-3, and 400-4 to the processor 130 (e.g., MCU). For example, the MUX 115 may be individually connected to the output values of the plurality of sensing circuits 400-1 , 400-2, 400-3, 400-4, and output the output value of one of the plurality of sensing circuits 400-1 , 400-2, 400-3, and 400-4 to an analog-digital converter (ADC) port of the processor 130 according to a control signal.

[0059] In an example, when the processor 130 has a sufficient number of ADC ports, the output voltage value of each of the plurality of sensing circuits 400-1 , 400-2, 400-3, and 400-4 may be directly connected to the processor 130. Flowever, when the number of ADC ports of the processor 130 is insufficient, the processor may receive the output values of the plurality of sensing circuits 400-1 , 400-2, 400-3, and 400-4 through one ADC port using the MUX 115 as illustrated. [0060] In this way, when searching for saturation points for a plurality of charging voltages, the processor 130 may simultaneously control four channels and sequentially sense an output voltage value of each of the four channels. [0061] If the processor 130 finds the saturation point for any one channel during the above-described process, the processor 130 may end the control of the channel on which the saturation point is found, and perform an operation of continuously finding the saturation points for the remaining channels. In addition, if the processor 130 finds the saturation points for all channels, the processor 130 may end the operation of determining the charging voltage.

[0062] The processor 130 may control the power supply 110 to supply the charging power corresponding to the corresponding channel for each channel during the printing process.

[0063] FIG. 5 is a circuit diagram of a power supply having a sensing circuit according to an example.

[0064] Referring to FIG. 5, the power supply 110 may include the AC power circuit 200, the DC power circuit 300, and the sensing circuit 400.

[0065] The AC power circuit 200 may include an AC frequency circuit 210, a low pass filter 220, an amplifier 230, an AC switching circuit 240, a transformer 250, and an AC feedback circuit 260.

[0066] The AC frequency circuit 210 may perform a switching operation at a predetermined frequency. For example, the AC frequency circuit 210 may receive a control signal of a PWM form and perform the switching operation at a frequency corresponding to the received control signal. In an example, the frequency may be 3 kFIz to 5 kFIz. In addition, the control signal may serve to adjust a frequency of the AC power generated by the AC power circuit 200. [0067] The low pass filter 220 may receive a signal corresponding to a target AC voltage and output a voltage value corresponding to the target AC voltage. For example, the low pass filter 220 may include a resistor-capacitor (RC) circuit that charges according to two resistors connected in series with a predetermined voltage and an input signal. Flere, the target AC voltage may include a PWM signal having a PWM duty and may serve to adjust a peak-to- peak value of the AC power supply according to the PWM duty.

[0068] The amplifier 230 may compare and amplify a feedback value of the AC power circuit 200 and an output value of the low pass filter 220. The amplifier 230 may be implemented as an operational-amplifier (OP-AMP), a negative terminal of the OP-AMP may be commonly connected to each of an output terminal of the AC feedback circuit 260, and a capacitor and a resistor connected in parallel, and a positive terminal thereof may be connected to the output terminal of the low pass filter 220 through a resistor.

[0069] The AC switching circuit 240 may selectively provide power to a primary coil of the transformer 250 according to an output of the amplifier 230 and an output of the AC frequency circuit 210. For example, the AC switching circuit 240 may switch a DC value output from the amplifier 230 to a level of 3 kHz to 5 kHz.

[0070] The transformer 250 may include a primary coil and a secondary coil and may amplify and output a voltage on the primary coil side to a secondary side according to a turns ratio of the two coils. For example, one end of the primary coil of the transformer 250 may be connected to the AC switching circuit 240 and the other end thereof may be grounded, and one end of the secondary coil may be connected to an output terminal of the power circuit and the other end thereof may be connected to an output terminal of the DC power circuit.

[0071] The AC feedback circuit 260 may provide magnitude information of an output value of the secondary coil of the transformer 250 to the amplifier 230. For example, in order to provide AC magnitude information, the AC feedback circuit 260 may extract the AC magnitude information using circuit elements such as capacitors and diodes and provide the extracted AC magnitude information to the amplifier 230. By feeding back the AC magnitude information, it is possible to maintain a constant Vpp even when an output load changes.

[0072] The DC power circuit 300 may generate and output a DC power having a predetermined magnitude. For example, the DC power circuit 300 may include a low pass filter 310, a comparator 320, a DC switching circuit 330, a transformer 340, a rectifying circuit 350, and a DC feedback circuit 360.

[0073] The low pass filter 310 may receive a signal corresponding to a target DC voltage and output a voltage value corresponding to the target DC voltage. For example, the low pass filter 310 may include an RC circuit that charges according to two resistors connected in series with a predetermined voltage and an input signal. Here, the target DC voltage may be a PWM signal having a PWM duty.

[0074] The comparator 320 may compare a feedback value of the DC power circuit and an output value of the low pass filter 310. For example, the comparator 320 may be implemented as an OP-AMP, a negative terminal of the OP-AMP may be connected to an intermediate node of two resistors connected in series of the low pass filter 310, and a positive terminal thereof may be commonly connected to a capacitor node of the low pass filter 310 and an output node of the DC feedback circuit 360.

[0075] The DC switching circuit 330 may selectively provide power to a primary coil of the transformer according to an output of the comparator 320. For example, the DC switching circuit 330 may include a switching element that selectively turns on/off a section (e.g., the middle) of the primary coil of the transformer 340 and an RC circuit connected to one end of the primary coil. [0076] The transformer 340 may include the primary coil and a secondary coil and may amplify and output a voltage on the primary coil side to a secondary side according to a turns ratio of the two coils. For example, one end of the primary coil may be connected to a predetermined power, the other end thereof may be connected to the RC circuit of the DC switching circuit 330, and both ends of the secondary coil may be connected to the rectifying circuit 350.

[0077] The rectifying circuit 350 may rectify and output an output voltage of the secondary coil. For example, the rectifying circuit 350 may include two capacitors and two diodes and may be a double voltage amplifying circuit that simultaneously performs voltage amplification and rectification.

[0078] The DC feedback circuit 360 may provide a voltage value of an output terminal of the rectifying circuit 350 to the comparator 320. For example, the DC feedback circuit 360 may include a resistor. As described above, because an amount of change in a DC current at the output terminal is fed back to the comparator 320, the DC power circuit 300 may maintain a constant voltage even when an output load changes.

[0079] The sensing circuit 400 may sense an output value of the comparator 320. The sensing circuit 400 may include a resistor 410, a rectifying circuit 420, and a voltage distribution circuit 430.

[0080] One end of the resistor 410 may be connected to the output terminal of the comparator 320 of the DC power circuit 300 and the other end thereof may be connected to one terminal of the rectifying circuit 420.

[0081] The rectifying circuit 420 may rectify an output voltage of the comparator 320. For example, the rectifying circuit 420 may include two diodes and a capacitor.

[0082] The voltage distribution circuit 430 may perform voltage distribution on an output value of the rectifying circuit 420. For example, the voltage distribution circuit 430 may include two resistors, and an intermediate node of the two resistors may be connected to the ADC port of the processor 130.

[0083] FIG. 6 is a circuit diagram of a sensing circuit according to an example. The example of FIG. 6 is an example in which an output value of a comparator is amplified and used to improve recognition when the output value of the comparator is low.

[0084] Referring to FIG. 6, a sensing circuit 500 may detect an output value of a comparator. For example, the sensing circuit 500 may be positioned to replace the sensing circuit 400 of FIG. 5. The sensing circuit 500 may include a resistor 510, an amplifying circuit 520, and a voltage distribution circuit 530. [0085] The resistor 510 may include a fifth resistor R5. One end of the fifth resistor R5 may be connected to the output terminal of the comparator of the DC power circuit and the other end thereof may be connected to one terminal of the amplifying circuit 520.

[0086] The amplifying circuit 520 may amplify and output an output voltage of the comparator. For example, the amplifying circuit 520 may include an OP- AMP, a first capacitor C1 , a second capacitor C2, a first resistor R1 , and a second resistor R2.

[0087] A positive terminal of the OP-AMP may be commonly connected to one end of the fifth resistor R5 and one end of the first capacitor C1 , a negative terminal thereof may be commonly connected to the first resistor R1 , one end of the second capacitor C2, and one end of the second resistor R2, and an output terminal thereof may be commonly connected to the other end of the second capacitor C2, the other end of the second resistor R2, and one end of the third resistor R3.

[0088] One end of the first capacitor C1 may be commonly connected to the positive terminal of the OP-AMP and one end of the fifth resistor R5, and the other end thereof may be grounded.

[0089] One end of the second capacitor C2 may be commonly connected to the negative terminal of the OP-AMP, one end of the first resistor R1 , and one end of the second resistor R2, and the other end thereof may be commonly connected to the output terminal of the OP-AMP, the other end of the second resistor R2, and one end of the third resistor R3.

[0090] One end of the first resistor R1 may be commonly connected to the negative terminal of the OP-AMP, one end of the second capacitor C2, and one end of the second resistor R2, and the other end thereof may be grounded. [0091] One end of the second resistor R2 may be commonly connected to the negative terminal of the OP-AMP, one end of the second capacitor C2, and one end of the first resistor R1 , and the other end thereof may be commonly connected to the output terminal of the OP-AMP, the other end of the second capacitor C2, and one end of the third resistor R3.

[0092] In the above described example, when a voltage Vin is input, the amplifying circuit 520 may output a voltage amplified to (1 +R2/R1)^*Vin. Through an amplification operation as described above, resolution of the ADC port of the processor may be improved.

[0093] The voltage distribution circuit 530 may perform voltage distribution on an output value of the amplifying circuit 520. For example, the voltage distribution circuit 530 may include a third resistor and a fourth resistor.

[0094] One end of the third resistor R3 may be connected to an output terminal of the amplifying circuit 520, and the other end thereof may be connected to the ADC port of the processor 130 and one end of the fourth resistor R4. [0095] One end of the fourth resistor R4 may be connected to the ADC port of the processor 130 and the other end of the third resistor R3, and the other end thereof may be grounded.

[0096] In the above described example, the voltage distribution circuit 530 may perform voltage distribution at an R3/R4 ratio for the output voltage of the amplifying circuit 520 and output the voltage-distributed output voltage.

[0097] FIG. 7 is a diagram illustrating a relationship between a charging current and a sensing current according to an example.

[0098] A surface potential of a photoconductor may be determined by an amount of DC current flowing between the photoconductor and a charging member. Therefore, even if the surface potential of the photoconductor is not measured, it is possible to detect the surface potential of the photoconductor by measuring the amount of DC current flowing between the photoconductor and the charging member.

[0099] For example, in a case in which it is necessary to form a surface potential of 500 V on the photoconductor, even if the surface potential of the photoconductor is not measured, if a current of 36 mA flows between the photoconductor and the charging member, the surface potential of the photoconductor may be 500 V.

[00100] In an example, when the photoconductor is charged using the DC power, uniform charging may not occur depending on the life of the photoconductor, which may adversely affect an image quality. Conversely, if the AC voltage is applied, the surface potential of the photoconductor may be uniform, but there is a disadvantage in that the life of the photoconductor is shortened. [00101] Therefore, to reduce degradation of the image quality while prolonging the life of the photoconductor, the DC power and the AC power may be used together, and a minimum AC power may be used. Accordingly, in an example, a charging power in which the minimum AC power is superimposed in a state in which the DC power having a predetermined magnitude is applied is used.

[00102] Flere, the minimum AC power corresponds to a point at which the amount of DC current flowing between the photoconductor and the charging member is saturated. In an example, a fixed DC power and a gradually increasing AC power are used to find such a point.

[00103] As illustrated in FIG. 7, as a peak voltage of the AC power increases, the amount of DC current supplied to the photoconductor also increases. Furthermore, in proportion to the increasing amount of DC current, an output value measured by the sensing circuit also increases.

[00104] In addition, when an AC voltage is a certain level or more (e.g., 500 Vpp), it may be seen that the charging DC current is saturated and an actual charging current (i.e. , dashed line in FIG. 7) maintains a constant value. In addition, it may be seen that the output value detected by the sensing circuit 400 also maintains a substantially constant value when the charging DC current is saturated.

[00105] As described above, even if the AC peak voltage increases, there occurs a point at which a change in the magnitude of the DC current is very small or starts to be maintained at a constant value. At this point, the amount of DC current is saturated. Therefore, the saturation point of the charging DC current may be determined by using a change in the voltage value of the output terminal of the comparator.

[00106] In an example, when a voltage of another node (e.g., an output node) in the DC power circuit is detected, even if there is no change in the amount of DC current, there is a problem in that a value of the corresponding node is also increased by AC noise caused by the connected AC power. Flowever, from the fact that the output terminal of the comparator in the DC power circuit has little influence of the AC noise, the voltage of the output terminal of the comparator of the DC power circuit may be used to find the saturation point.

[00107] As described above, from the fact that, when the AC peak voltage is a certain level or more, that is, when the charging DC current is saturated, the sensed output value also no longer increases, the processor 130 may stepwise increase the peak voltage of the AC power and use the AC power as the magnitude of the charging AC power when the change in the sensed output value becomes a predetermined value or less.

[00108] For example, when the AC peak voltage is increased in the order of 300 Vpp, 400 Vpp, 500 Vpp, 600 Vpp, and 700 Vpp, a difference between a preceding output value and a current output value may be 0.1 (300 Vpp vs 400 Vpp), 0.06 (400 Vpp vs 500 Vpp), 0.01 (500 Vpp vs 600 Vpp), and 0 (600 Vpp vs 700 Vpp). In this case, a preceding peak voltage (500 Vpp) corresponding to the point at which the difference becomes 0.01 may be set as the AC charging voltage at the time of a charging operation.

[00109] In an example, a current peak voltage (e.g., 600 Vpp) may be set as the AC charging voltage at the time of a charging operation, and the AC voltage may also be determined using an intermediate value (e.g., 550 Vpp) of two values or using a mathematical expression.

[00110] FIG. 8 is a diagram for describing a charging control method according to an example.

[00111] Referring to FIG. 8, a charging power in which a DC power is superimposed on an AC power may be supplied to a charging member in operation S810. For example, a minimum AC power may be superimposed on the DC power of a predetermined magnitude. For example, the DC power may be -300 V, and the minimum AC power may be 300 Vpp. Such numerical values are examples and may be changed according to the image forming apparatus, a surrounding environment at the time of implementation, etc.

[00112] An output value of a comparator whose value changes in response to the magnitude of a current flowing through a charging member may be detected in operation S820. For example, an output value of a sensing circuit may be checked (e.g., measured) and the checked output value may be stored.

[00113] A peak voltage of an AC power may be varied and a current saturation point of the charging member may be searched based on the detected output value during the variation of the peak voltage in operation S830. For example, the peak voltage of the AC power may be stepwise increased and an output value of a sensing voltage at the increased point may be detected. It may be determined whether the charging current is saturated by determining whether a difference between the detected output value and a preceding detected output value is a predetermined value or less.

[00114] An AC voltage and a DC voltage of the current saturation point may be determined as a charging voltage in operation S840. For example, if the difference between the detected output value and the preceding detected output value is the predetermined value or less, an AC power value and a DC voltage value constituting the charging power at the corresponding point may be set as a charging voltage value.

[00115] A charging control method according to an example may effectively determine the current saturation point without using a separate current sensor for measuring a surface current of the photoconductor. In addition, in an example charging control method, because the charging power using the detected current saturation point may be provided to the photoconductor, it is possible to prolong the life of the photoconductor while reducing deterioration of the image quality. [00116] An example charging control method as described above may be implemented by an execution program for executing a driving control method and the execution program may be stored in a non-transitory computer readable recording medium.

[00117] Here, the non-transitory computer readable medium may be a compact disc (CD), a digital video disc (DVD), a hard disk drive (HDD), a solid state drive (SSD), a Blu-ray disc, an universal serial bus (USB), a memory card, a read-only memory (ROM), or the like.

[00118] Although examples of the disclosure have been illustrated and described hereinabove, the disclosure is not limited thereto, but may be variously modified and altered by those skilled in the art to which the disclosure pertains without departing from the spirit and scope of the disclosure claimed in the claims. These modifications and alterations are to fall within the scope of the disclosure.

Claims

WHAT IS CLAIMED IS:

1 . An image forming apparatus comprising: a printing engine including a charging member to charge a photoconductor; a power supply including a direct current (DC) power circuit to generate a DC power, an alternating current (AC) power circuit to generate an AC power and to superimpose the DC power on the generated AC power to provide the superimposed power to the charging member, and a sensing circuit to detect an output value of a comparator of the DC power circuit; and a processor to control the AC power circuit to vary a magnitude of the AC power and search for a current saturation point of the charging member based on the output value detected by the sensing circuit while varying the magnitude of the AC power.

2. The image forming apparatus as claimed in claim 1 , wherein the processor is to control the power supply to vary a peak voltage of the AC power in a state in which a DC power of a predetermined magnitude is output.

3. The image forming apparatus as claimed in claim 1 , wherein the processor is to control the power supply to stepwise increase a peak voltage of the AC power in units of a predetermined magnitude.

4. The image forming apparatus as claimed in claim 3, wherein the processor is to determine that a current of the charging member is saturated based on a change in the output value being a predetermined value or less according to a change in the peak voltage of the AC power.

5. The image forming apparatus as claimed in claim 1 , wherein the processor is to control the printing engine to perform a printing job and control the power supply to supply the AC power and the DC power corresponding to the current saturation point to the charging member during the printing job.

6. The image forming apparatus as claimed in claim 1 , wherein the DC power circuit includes: a low pass filter to receive a signal corresponding to a target DC voltage and to output a voltage value corresponding to the target DC voltage; a comparator to compare a feedback value of the DC power circuit and an output value of the low pass filter; a transformer including a primary coil and a secondary coil; a DC switching circuit to selectively provide a power to the primary coil of the transformer according to an output of the comparator; and a rectifying circuit to rectify and output an output voltage of the secondary coil.

7. The image forming apparatus as claimed in claim 6, wherein the sensing circuit includes: a rectifying circuit to rectify an output voltage of the comparator; and a voltage distribution circuit to perform voltage distribution for an output value of the rectifying circuit.

8. The image forming apparatus as claimed in claim 6, wherein the sensing circuit includes: an amplifying circuit to amplify an output voltage of the comparator; and a voltage distribution circuit to perform voltage distribution for an output value of the amplifying circuit.

9. The image forming apparatus as claimed in claim 6, wherein the rectifying circuit includes a double voltage amplifying circuit to perform rectification and double amplification for the output voltage of the secondary coil.

10. The image forming apparatus as claimed in claim 1 , wherein the AC power circuit includes: a low pass filter to receive a signal corresponding to a target AC voltage and to output a voltage value corresponding to the target AC voltage; an amplifier to compare and amplify a feedback value of the AC power circuit and an output value of the low pass filter; a transformer including a primary coil and a secondary coil; an AC frequency circuit to perform a switching operation at a predetermined frequency; and an AC switching circuit to selectively provide a power to the primary coil of the transformer according to an output of the amplifier and an output of the AC frequency circuit, wherein the secondary coil of the transformer has one end connected to an output terminal of the DC power circuit and another end connected to the charging member.

11. The image forming apparatus as claimed in claim 10, wherein the signal includes a signal having a pulse width modulation (PWM) duty corresponding to the target AC voltage, and wherein the processor is to transmit a signal whose PWM duty is stepwise varied to the low pass filter.

12. The image forming apparatus as claimed in claim 1 , wherein the printing engine includes a plurality of charging members, wherein the power supply includes a plurality of DC power circuits, a plurality of AC power circuits, and a plurality of sensing circuits that correspond to the plurality of charging members, and wherein the power supply includes a multiplexer that selectively provides output values of the plurality of sensing circuits to the processor.

13. The image forming apparatus as claimed in claim 1 , wherein the AC power circuit generates a sinusoidal AC wave having a frequency within 3 kHz to 5 kHz.

14. A non-transitory computer-readable recording medium on which a program for performing a charging control method of an image forming apparatus is recorded, the non-transitory computer-readable recording medium comprising: instructions to supply a charging power in which a direct current (DC) power is superimposed on an alternating current (AC) power to a charging member; instructions to detect an output value of a comparator in a DC power circuit whose value changes in response to a magnitude of a current flowing through the charging member; instructions to vary a peak voltage of the AC power and search for a current saturation point of the charging member based on the detected output value while varying the peak voltage; and instructions to determine an AC voltage and a DC voltage of the current saturation point as a charging voltage.

15. The non-transitory computer-readable recording medium as claimed in claim 14, further comprising: instructions to determine that a current of the charging member is saturated based on a change in the output value being a predetermined value or less according to a change in the peak voltage of the AC power, wherein the instructions to search for the current saturation point comprise instructions to increase the peak voltage of the AC power in units of a predetermined magnitude in a state in which a DC power of a predetermined magnitude is output.