WO2022265683A1

WO2022265683A1 - Toner amount adjustment using offset power

Info

Publication number: WO2022265683A1
Application number: PCT/US2022/012737
Authority: WO
Inventors: Jinyun Park; Seongho Jeong; ByeongNo JEONG
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2021-06-18
Filing date: 2022-01-18
Publication date: 2022-12-22
Also published as: KR20220169319A

Abstract

An image forming apparatus includes an optical photo conductor to receive a surface voltage; a laser scanner to apply an exposure voltage corresponding to an image to a surface of the optical photo conductor; a developing roller to receive a developing voltage and to transfer a toner to the surface of the optical photo conductor; a transfer roller to transfer the toner transferred to the surface of the optical photo conductor to a sheet to form an image on the sheet; and an optical photo conductor power device to apply an offset voltage corresponding to information of the image to the surface of the optical photo conductor to adjust a toner amount of the toner according to a difference between the exposure voltage, to which the offset voltage is applied, and the developing voltage.

Description

TONER AMOUNT ADJUSTMENT USING OFFSET POWER

BACKGROUND

[0001] An image forming apparatus refers to an apparatus which prints print data generated on a terminal apparatus such as a computer on a print paper. Examples of such an image forming apparatus may include a copier, a printer, a facsimile, a multi-function peripheral (MFP) serving functions of these in combination as one apparatus, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS [0002] FIG, 1 is a diagram illustrating a print engine of an image forming apparatus according to an example;

[0003] FIGS, 2A and 2B are diagrams illustrating a control circuit of an offset voltage according to an example;

[0004] FIG. 2C is a diagram illustrating an offset voltage according to a surface voltage according to an example;

[0005] FIG. 3A is a diagram illustrating a toner amount according to a potential according to an example;

[0008] FIG. 3B is a diagram illustrating a concentration of a toner according to the offset voltage according to an example; [0007] FIG. 4 is a flowchart illustrating a toner amount control method according to an example;

[0008] FIG. 5A is a flowchart illustrating a control process of the offset voltage according to an example;

[0009] FIG. 5B is a diagram illustrating the offset voltage according to a temperature according to an example;

[0010] FIG. 6 is a diagram for comparing toner concentrations according to an example;

[0011] FIG. 7 is a diagram illustrating a configuration of the image forming apparatus according to an example; and

[0012] FIG. 8 is a diagram illustrating commands stored in a computer-readable recording medium according to an example.

DETAILED DESCRIPTION

[0013] Hereinafter. various examples will be described in detail with reference to the drawings. The examples described hereinafter may be modified and practiced in various different aspects.

[0014] In the disclosure, the expression that a certain component is “connected" to another component not only includes a case where the components are “directly connected to each other”, but also a case where the components are “connected to each other with another component interposed therebetween”. In addition, when a certain component “includes” another certain component, it implies that a still another component may be further included, rather than excluding it, unless otherwise noted. Meanwhile, each example may be implemented or operated independently or the examples may also be implemented or operated in combination,

[0015] In the disclosure, an “image forming job” may refer to various jobs relating to an image such as forming of an image or generating, saving, or transmitting of an image file (e.g., printing, scanning, or faxing), and the “job” may not only refer to the image forming job, but also refer to all of processes necessary for performing the image forming job,

[0018] The “print data” may refer to data converted into a format that is printable by a printer. Meanwhile, if a printer supports direct printing, a file itself may be the print data.

[0017] The “image forming apparatus” may refer to an apparatus which prints print data generated on a terminal apparatus such as a computer on a recording paper. Examples of such an image forming apparatus may include a copier, a printer, a facsimile, a scanner, and a multi-function peripheral (MFP) realizing functions of these as one apparatus in combination.

[0018] A “user” may refer to a person who manipulates an electronic apparatus by using the electronic apparatus or a device connected to the electronic apparatus in a wired or wireless manner. A “manager” may refer to a person who has authority to access ail functions and system of the electronic apparatus. The “manager” and the “user” may be the same person.

[0019] The disclosure is for reducing an amount of a toner efficiently and obtaining an output object with an excellent quality. [0020] FIG. 1 is a diagram illustrating a print engine of an image forming apparatus according to an example.

[0021] Referring to FIG. 1, a configuration of a print engine of an image forming apparatus 100 is illustrated. The print engine of the image forming apparatus 100 may include an optical photo conductor 11, a laser scanner 12, a developing roller 13, a transfer roller 14, and an optical photo conductor power device (or “power device” )15.

[0022] The power device 15 may apply a surface voltage to the optical photo conductor 11. In an example, the optical photo conductor power device 15 may generate a charger high voltage and supply the generated charger high voltage to a charge roller. The charge roller may be disposed to come into contact with the optical photo conductor 11 and rotate to transfer the supplied charger high voltage to the optical photo conductor 11 and apply a surface voltage to a surface of the optical photo conductor 11.

[0023] The laser scanner 12 may apply an exposure voltage corresponding to an image to the surface of the optical photo conductor 11. The exposure voltage applied to the surface of the optical photo conductor 11 by the laser scanner 12 may refer to a laser scanner unit (LSU) voltage.

[0024] A developing voltage may be applied to the developing roller 13, the developing roller 13 may transfer the toner to the surface of the optical photo conductor 11 , and the transfer roller 14 may transfer the toner transferred to the surface of the optical photo conductor 11 to a sheet to form an image on the sheet. A transfer voltage may be applied to the transfer roller 14. [0025] In an example, the image forming apparatus 100 may form an image on the sheet based on the surface voltage applied to the optical photo conductor 11, the exposure voltage applied to the surface of the optical photo conductor by the laser scanner 12, the developing voltage applied to the developing roller 13. In other words, the image forming apparatus 100 may transfer the toner to the surface of the optical photo conductor 11 in a form corresponding to the image to be formed based on the surface voltage, the exposure voltage, and the developing voltage. In addition, the image forming apparatus 100 may generate an output object on which the image is formed, by transferring the toner of the surface of the optical photo conductor 11 to a sheet supplied through the transfer roller 14.

[0028] Meanwhile, the optical photo conductor power device 15 may apply an offset voltage to the surface of the optical photo conductor 11. A magnitude of the offset voltage may vary depending on information of an image. The offset voltage applied to the surface of the optical photo conductor 11 may adjust the exposure voltage. The optical photo conductor power device 15 may provide the offset voltage to the exposure voltage to adjust the toner amount of the toner according to a difference between the exposure voltage, to which the offset voltage is provided, and the developing voltage.

[0027] In an example, the information of the image may include density information of the image. The optical photo conductor power device 15 may determine the density of the image and apply the offset voltage based on a concentration of a toner correspond to the determined density. The information of the image may further include a type of the image. For example, the type of the image may include an image including a picture, an image including a text, an image including only a text, and the like. When the image includes a picture, the optical photo conductor power device 15 may apply a first offset voltage to the surface of the optical photo conductor 11 and, when the image includes a text, the optical photo conductor power device 15 may apply a second offset voltage to the surface of the optical photo conductor 11 , For example, the first offset voltage and the second offset voltage may be voltages having different magnitudes, and an absolute value of the second offset voltage may be a value greater than an absolute value of the first offset voltage. Alternatively, when the image includes only a text, the optical photo conductor power device 15 may apply an offset voltage having an increased absolute value to reduce the toner amount of the toner. An example in which the image is formed according to the voltage will be described below in detail,

[0028] The optical photo conductor power device 15 may apply the offset voltage based on a duty ratio of a pulse width modulation (PMW) signal. The image forming apparatus 100 may include a memory and store a table of offset voltage corresponding to the exposure voltage and the duty ratio in the memory. Hereinafter, the configuration of the print engine of the image forming apparatus 100 has been described. Hereinafter, an example in which the image forming job is performed by the offset voltage will be described.

[0029] FIGS. 2A and 2B are diagrams illustrating a control circuit of an offset voltage according to an example, and FIG. 2C is a diagram illustrating an offset voltage according to a surface voltage according to an example. The description will be made with reference to FIGS. 2A to 2C.

[0030] FIG. 2A illustrates a control circuit including a transistor. The image forming apparatus, for example image forming apparatus 100 of FIG. 1, may receive print data (image data) and determine a surrounding temperature and a type of an image. The image forming apparatus 100 may determine an offset voltage corresponding to the determined surrounding temperature and type of the image based on the offset voltage table stored in the memory. The image forming apparatus may output a PWM signal (PWM__OPC) to the optical photo conductor power device, when applying a charger bias to the optical photo conductor. A low pass filter (LPF) of the control circuit may change the input PWM signal into a direct current (DC) voltage value according to the duty ratio of the PWM signal. A current amount of a base terminal of the transistor may change according to the DC voltage value, and the transistor may change the offset voltage value applied to the optical photo conductor.

[0031] In an example, as the duty lowers, the voltage value applied to the base terminal of the transistor lowers, and the transistor may be saturated. In this case, an OPC output terminal is connected to 3.3 V, and accordingly, a voltage almost close to 0 V may be output to the optical photo conductor 11. On the other hand, as the duty increases, the voltage value applied to the base terminal of the transistor increases, and the transistor may operate in an active area to apply a desired voltage to the optical photo conductor. If a duty for applying a Vbase voltage to the extent that a base current cannot flow is received, the transistor may enter a cut-off area to output a maximum value of voltage. Meanwhile, a maximum voltage may be adjusted based on resistances R1 and R2.

[0032] FIG. 2C illustrates an optical photo conductor output voltage table for each surface voltage (charger bias) and duty. The optical photo conductor voltage table may be changed based on a circuit time constant.

[0033] FIG. 2B illustrates a control circuit including a photocoupler. The photocoupier may be implemented by replacing the transistor of the control circuit described in FIG. 2A. The control circuit of FIG. 2B is capable of electric insulation between a high voltage terminal and a low voltage terminal. Accordingly, the control circuit of FIG. 2B insulates strongly against noise and minimizes an effect between input and output. In addition, the control circuit including the photocoupier may be implemented in an NPN type so as to connect the OPC output terminal to the ground. A basic operation principle of the control circuit including the photocoupier is similar to an operation principle of the control circuit including the transistor.

[0034] In other words, as the PWM duty ratio lowers, a diode cathode terminal voltage lowers, and a light emitting unit of the photocoupier may output a maximum value. Accordingly, a light receiving unit may be turned on and the OPC output terminal may be connected to the ground. As the PWM duty ratio increases, the diode cathode terminal voltage increases, and the output of the light emitting unit may be adjusted. Accordingly, the light receiving unit transistor may control the OPC output voltage by controlling the current according to a light amount. Then, when the voltage at a predetermined level or higher is applied to the cathode, the output of the light emitting unit may be turned off and the transistor of the light receiving unit may be turned off. The control circuit may output a maximum value of voltage.

[0035] FIG. 3A is a diagram illustrating a toner amount according to a potential according to an example, and FIG. 3B is a diagram illustrating a concentration of a toner according to the offset voltage according to an example. The description will be made with reference to FIGS. 3A and 3B.

[0036] Referring to FIG. 3A. the amount of the toner developed on the output object may be determined according to a difference between a developing potential and an exposure potential. As described above, the surface potential may be a voltage applied to the optical photo conductor 11 , and the developing potential may refer to a voltage applied to the developing roller 13. The exposure potential may be a voltage corresponding to an image applied to the surface of the optical photo conductor 11 by the laser scanner 12. For example, ail of the surface potential, the developing potential, and the exposure potential may be negative potentials, and an absolute value of the developing potential may be lower than an absolute value of the surface potential.

[0037] The image forming apparatus 100 may apply the offset voltage to the surface of the optical photo conductor 11 by using the optical photo conductor power device 15. In the case described above, the offset voltage may also be a negative voltage, and the offset voltage applied to the surface of the optical photo conductor 11 may increase the absolute value of the exposure potential. Referring to FIG. 3A, the amount of the toner developed on the output object is determined according to the difference between the developing potential and the exposure potential, and accordingly, if the absolute value of the exposure potential increases, the amount of the toner may be reduced.

[0038] FIG. 3Bconfirms that a concentration of Black 100% may be greatly reduced through the toner amount control of the disclosure, but there is no significant difference between the concentrations of Halftone 60% and Halftone 30%.

[0039] FIG. 4 is a flowchart illustrating a toner amount control method according to an example.

[0040] Referring to FIG. 4, the image forming apparatus 100 may apply the exposure voltage to the surface of the optical photo conductor 11 (8410). The surface voltage (charger bias) may be applied to the optical photo conductor 11 and the exposure voltage may be a voltage corresponding to the image.

[0041] The image forming apparatus 100 may apply the offset voltage to the surface of the optical photo conductor 11 (S420). The image forming apparatus 100 may apply the offset voltage corresponding to the information of the image to the surface of the optical photo conductor 11. The image forming apparatus 100 may adjust the toner amount of the toner according to the difference between the exposure voltage, to which the offset voltage is provided, and the developing voltage. For example, the information of the image may include the density of the image and the type of the image. In other words, the image forming apparatus 100 may determine the density of the image and apply the offset voltage based on the determined density. Alternatively, when the image includes a picture, the image forming apparatus 100 may apply a first offset voltage and, when the image includes a text, the image forming apparatus 100 may apply a second offset voltage. The magnitude of the first offset voltage and the magnitude of the second offset voltage may be different values. If the voltage supplied to the image forming apparatus 100 is a negative voltage, a value of the second offset voltage may be greater than the value of the first offset voltage. When the image includes only a text, the image forming apparatus 100 may increase the absolute value of the offset voltage. Meanwhile, the image forming apparatus 100 may apply the offset voltage based on the duty ratio of the PWM signal and the offset voltage may match to the exposure voltage and the duty ratio and stored in the image forming apparatus as a table.

[0042] The developing voltage is applied, and the image forming apparatus 100 may transfer the toner to the surface of the optical photo conductor (S430), and transfer the toner transferred to the surface of the optical photo conductor 11 to a sheet to form the image on the sheet (S440). The applied offset voltage may increase the absolute value of the exposure potential and reduce the difference from the developing potential. Accordingly, the image forming apparatus 100 may reduce the toner amount to form the image on the sheet.

[0043] FIG. 5A is a flowchart illustrating a controi process of the offset voitage according to an example, and FIG. 5B is a diagram illustrating the offset voitage according to a temperature according to an example. The description will be made with reference to FIGS. 5A and 5B.

[0044] Referring to FIG. 5A, the image forming apparatus 100 may check a surrounding environment (S510). For example, the image forming apparatus 100 may detect the surrounding environment information by using a sensor. For example, the surrounding environment information may include a temperature, humidity, and the like. The image forming apparatus 100 may determine a basic charger bias (surface voltage) level (S520). In addition, the image forming apparatus 100 may receive image data (print data) and analyze the image data to determine whether it is a picture or a text (8530), If the determined image data is a picture, the image forming apparatus 100 may determine the offset voltage as 0 V (8540). If the determined image data is a text, the image forming apparatus 100 may determine the offset voltage as a set value (8550). In an example, the set value may be -30 V.

[0045] If the determined image data is a text, the image forming apparatus 100 may determine the offset voltage as a set value and check the detected environment information. The image forming apparatus 100 may determine whether the detected surrounding information is greater than the set value (S560). If the detected environment information is equal to or lower than the set value, the image forming apparatus 100 may apply a voltage in a PWM form at the time when the charger bias (surface voltage) is turned on and output the exposure potential offset voltage to the optical photo conductor to form an image (8580). If the detected environment information is greater than the set value, the image forming apparatus 100 may determine a final offset voltage based on a stored environment information offset voltage table (S57G), As described above, the environment information may include a temperature, humidity, and the like. In an example, FIG. 5B illustrates the environment information offset voltage table, when the environment information is a temperature. The image forming apparatus 100 may apply a voltage in a PWM form at the time when the charger bias (surface voltage) is turned on, and output the exposure potential offset voltage to the optical photo conductor 11 to form an image (S580).

[0046] FIG. 6 is a diagram for comparing toner concentrations according to an example.

[0047] The image forming apparatus, for example image forming apparatus 100, of the disclosure may apply the offset voltage only when forming a specific image, while maintaining the surface voltage (charger bias). In other words, the image forming apparatus 100 may apply the offset voltage only when forming a specific image to reduce the consumed toner amount, and may not apply the offset voltage or apply a comparatively low offset voltage, when forming other images. For example, the image forming apparatus 100 may apply the offset voltage only when the image includes only a text and the concentration is Black 100%. Generally, a user tends to be unable to recognize the difference in toner amount of the output object of a Black 100% text document. Accordingly, although the toner amount of the output object of the Black 100% text document is reduced to a certain level, the quality of the output object may not be affected. Thus, referring to FIG. 6, the image forming apparatus 100 of the disclosure exhibits an effect of maintaining the quality while reducing the toner consumption amount.

[0048] FIG. 7 is a diagram illustrating a configuration of the image forming apparatus 100 according to an example.

[0049] Referring to FIG. 7, the image forming apparatus 100 may include a power device 110, a processor 120, an input interface 130, a sensor 140, a communication interface 150, a display 160, a speaker 170, a memory 180, and a print engine 190. The print engine 190 performs the same function as the print engine described in FIG. 1, and therefore the overlapped description will not be repeated.

[0050] The power device 110 may supply the power to each configuration of the image forming apparatus 100. In an example, the power device 110 may apply a voltage to a roller of the print engine 190. Meanwhile, the power device 110 may include an optical photo conductor power device, for example optical photo conductor power device 15 of FIG. 1 , and apply an offset voltage corresponding to information of an image to a surface of an optical photo conductor by using the optical photo conductor power device 15.

[0051] The processor 120 may control general operations of the image forming apparatus 100. Th processor 140 may control a voltage applied to each roller of the print engine 190. In addition, the processor 140 may control the optical photo conductor power device 15 to apply the offset voltage to the optical photo conductor. [0052] The input interface 130 may receive selection of a function and a control command of the corresponding function from the user. Here, the function may include a print function, a copying function, a scanning function, a fax transmission function, and the like. The input interface 130 may be referred to as an input device, an input unit, an input module, or the like.

[0053] The sensor 140 may detect the surrounding environment information of the image forming apparatus. For example, the sensor 140 may detect a surrounding temperature, humidity, and the like. For example, the sensor 140 may include a temperature sensor, a humidity sensor, and the like.

[0054] The communication interface 150 may communicate with an external device. For example, the external device may include a server, an A! cloud, a terminal device, and the like. The communication interface 150 may be formed to connect the image forming apparatus 100 to the external apparatus and may also be connected via a universal serial bus (USB) port or a wireless communication (e.g., Wi-Fi 802.11 a/b/g/n, near field communication (NFC), or Bluetooth) port, in addition to the connection to the external apparatus via a local area network (LAN) or the Internet. The communication interface 150 may receive the print data from the external apparatus. The communication interface 150 may be referred to as a communication device, a communication unit, a communication module, or a transceiver, or the like.

[0055] The display 160 may display a user interface window for receiving selection of functions supported by the image forming apparatus 100, and various pieces of information. The display 160 may be a monitor such as a liquid crystal display (LCD), a Cathode Ray Tube (CRT), an Organic Light Emitting Diodes (OLED), or the like, and may also be implemented as a touch screen for simultaneously performing the functions of the input interface 130. [0056] The speaker 170 may output state information of the image forming apparatus 100 as a sound. For example, if the state is an error state, the image forming apparatus 100 may output a sound corresponding to the error state. [0057] The memory 180 may store at least one instruction for the image forming apparatus 100. For example, the memory 180 may store various programs (or software) for the image forming apparatus 100 to operate according to various examples of the disclosure. In addition, the memory 180 may store the offset voltage table.

[0058] FIG. 8 is a diagram illustrating commands stored in a computer-readable recording medium according to an example.

[0059] The toner amount control process executed by the image forming apparatus described above may be implemented in a form of a computer- readable recording medium storing a command or data executable by a computer or a processor, for example processor 120 of FIG. 7. A computer- readable recording medium 800 may store commands related to the operations of the image forming apparatus described above. For example, the computer- readable recording medium 800 may include commands 810 for applying an exposure voltage corresponding to an image to a surface of an optical photo conductor, commands 820 for applying an offset voltage to the surface of the optical photo conductor, for example optical photo conductor 11 of FIG. 1 , commands 830 for applying a developing voltage and transferring a toner to the surface of the optical photo conductor 11 , and commands 840 for transferring the toner transferred to the surface of the optical photo conductor 11 to a sheet to form an image on the sheet.

[0080] Such a computer-readable recording medium may be a read-only memory (ROM), a random-access memory (RAM), a flash memory, CD-ROMs, CD-Rs, CD+Rs, CD-RWs, CD+RWs, DVD-ROMs, DVD-Rs, DVD+Rs, DVD- RWs, DVD+RWs, DVD-RAMs, BD-ROMs, BD-Rs, BD-R LTHs, BD-REs, a magnetic tape, a floppy disk, a magneto-optical data storage device, an optical data storage device, a hard disk drive, a solid-state drive (SSD), and any device capable of storing instructions or software, related data, data files, and data structures, and providing instructions or software, related data, data files, and data structures to a processor or a computer so that the processor or the computer executes the instructions.

[0081] While examples of the disclosure have been shown and described, the disclosure is not limited to the aforementioned specific examples, and it is apparent that various modifications can be made by those having ordinary skill in the technical field to which the disclosure belongs, without departing from the gist of the disclosure as claimed by the appended claims. Also, it is intended that such modifications are not to be interpreted independently from the technical idea or prospect of the disclosure.

Claims

WHAT [S CLAMED IS:

1. An image forming apparatus comprising; an optical photo conductor to receive a surface voltage; a laser scanner to apply an exposure voltage corresponding to an image to a surface of the optical photo conductor; a developing roller to receive a developing voltage and to transfer a toner to the surface of the optical photo conductor; a transfer roller to transfer the toner transferred to the surface of the optical photo conductor to a sheet to form an image on the sheet; and an optical photo conductor power device to apply an offset voltage corresponding to information of the image to the surface of the optical photo conductor to adjust a toner amount of the toner according to a difference between the exposure voltage, to which the offset voltage is applied, and the developing voltage.

2. The image forming apparatus according to claim 1. wherein the optical photo conductor power device to determine a density of the image and to apply the offset voltage to the surface of the optical photo conductor based on the determined density.

3. The image forming apparatus according to claim 1, wherein the optical photo conductor power device to apply a first offset voltage to the surface of the optical photo conductor when the image includes a picture, and to apply a second offset voltage to the surface of the optical photo conductor when the image includes a text.

4. The image forming apparatus according to claim 3. wherein the optical photo conductor power device to apply the offset voltage having an increased absolute value to reduce the toner amount of the toner when the image includes only a text.

5. The image forming apparatus according to claim 1, wherein the optical photo conductor power device to apply the offset voltage to the surface of the optical photo conductor based on a duty ratio of a PWIVI signal.

6. The image forming apparatus according to claim 5, further comprising: a memory to store the offset voltage in a table, wherein the offset voltage matches to the exposure voltage and the duty ratio.

7. A method of controlling a toner amount comprising: applying an exposure voltage corresponding to an image to a surface of an optical photo conductor to which a surface voltage is applied; applying an offset voltage to the surface of the optical photo conductor; applying a developing voltage to transferring a toner to the surface of the optical photo conductor; and transferring the toner transferred to the surface of the optical photo conductor to a sheet to form an image on the sheet; wherein the applying the offset voltage comprises applying an offset voltage corresponding to information of the image to the surface of the optical photo conductor to adjust a toner amount of the toner according to a difference between the exposure voltage, to which the offset voltage is applied, and the developing voltage.

8. The toner amount control method according to claim 7, wherein the applying the offset voltage comprises determining a density of the image and applying the offset voltage based on the determined density.

9. The toner amount control method according to claim 7, wherein the applying the offset voltage comprises applying a first offset voltage when the image includes a picture, and applying a second offset voltage when the image includes a text.

10. The toner amount control method according to claim 9, wherein the applying the offset voltage comprises increasing an absolute value of the offset voltage to reduce the toner amount of the toner when the image includes only a text.

11. The toner amount control method according to claim 7, wherein the applying the offset voltage comprises applying the offset voltage to the surface of the optical photo conductor based on a duty ratio of a PWM signa

12. The toner amount control method according to claim 11 , wherein the offset voltage matches to the exposure voltage and the duty ratio and is stored in a table.

13. A non-transitory computer-readable recording medium to store instructions which, when executed by a processor, cause the processor to execute a toner amount control method comprising: applying an exposure voltage corresponding to an image to a surface of an optical photo conductor; applying an offset voltage to the surface of the optical photo conductor; applying a developing voltage and transferring a toner to the surface of the optical photo conductor; and transferring the toner transferred to the surface of the optical photo conductor to a sheet to form an image on the sheet, wherein the applying the offset voltage apply an offset voltage corresponding to information of the image to the surface of the optical photo conductor to adjust a toner amount of the toner according to a difference between the exposure voltage, to which the offset voltage is applied, and the developing voltage.

14. The non-transitory computer-readable recording medium according to claim 13, wherein the applying the offset voltage apply a first offset voltage when the image includes a picture, and apply a second offset voltage when the image includes a text,

15, The non-transitory computer-readable recording medium according to claim 14, wherein the applying the offset voltage increase an absolute value of the offset voltage to reduce the toner amount of the toner when the image includes only a text.