JP2018063357A - Image forming apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that has a higher transfer efficiency than the prior art while suppressing a reduction in productivity.SOLUTION: An image forming apparatus (200) comprises: a conductive member (9) that is arranged to be in contact with a recording medium on a conveyance path (R1); a power supply device (80) for transferring a toner image to the recording medium by applying a transfer bias to the conductive member; a sensor (85) for acquiring an electrical characteristic value of the conductive member; and a control part (70) that controls the magnitude of the transfer bias applied to the conductive member on the basis of the electrical characteristic value acquired by the sensor and the number of continuously printed recording media.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an image forming apparatus, and more particularly to a technique for controlling the magnitude of a transfer bias in the image forming apparatus.

  An image forming apparatus according to an electrophotographic method charges an image carrier such as a photoconductor and irradiates a laser beam to form an electrostatic latent image on the surface of the image carrier, and visualizes the electrostatic latent image with a developing device. To form a toner image. A transfer roller is in contact with the image carrier via an intermediate transfer belt or a recording medium, and a transfer bias having the same polarity as the toner charging polarity is applied to the transfer roller, whereby a toner image on the image carrier is obtained. Is transferred to an intermediate transfer belt or a recording medium.

  When transferring a toner image onto a recording medium using a transfer roller, it is necessary to set the current (transfer current) flowing through the transfer roller within an appropriate range from the viewpoint of transfer efficiency. In general, the resistance value of the transfer roller varies depending on the environmental temperature, the cumulative energization time, and the like. Therefore, the voltage applied to the transfer roller needs to be adjusted according to the resistance value of the transfer roller.

  ATVC (Active Transfer Voltage Control) control is known as a method for setting a transfer current flowing in a transfer portion via a transfer roller within an appropriate range. This is because a voltage obtained when a constant current is passed through the transfer roller (hereinafter also referred to as “ATVC voltage”) is substituted for the resistance value of the transfer roller and applied to the transfer roller based on the ATVC voltage value. The bias voltage is controlled (Patent Documents 1 and 2).

JP 2013-178485 A JP 05-006112 A

  The ATVC control disclosed in the above patent document is a configuration in which the ATVC voltage (or current) of the transfer roller is periodically acquired and the transfer bias voltage is controlled based on the acquired result. Transfer between ATVC voltage measurements is performed. It is assumed that the resistance value of the roller does not change. However, the resistance value of the transfer roller fluctuates based on various factors such as the environmental temperature as described above. Therefore, if the ATVC voltage measurement interval is long, the transfer current is likely to be out of the appropriate range. On the other hand, if the ATVC voltage measurement interval is shortened, the productivity of the image forming apparatus is reduced.

  The present disclosure has been made in order to solve the above-described problems, and an object in one aspect thereof is to provide an image forming apparatus with higher transfer efficiency than the conventional one while suppressing a decrease in productivity. It is. An object in another aspect is to provide a method for improving transfer efficiency as compared with the conventional one while suppressing a decrease in productivity.

  An image forming apparatus according to an embodiment includes a conductive member disposed so as to contact a recording medium on a conveyance path, and a power supply device for transferring a toner image to the recording medium by applying a transfer bias to the conductive member. The size of the transfer bias applied to the conductive member is controlled based on the sensor for acquiring the electrical characteristic value of the conductive member, the electrical characteristic value acquired by the sensor, and the number of continuous prints on the recording medium. A control unit.

  Preferably, the control unit controls the transfer bias to increase as the number of continuous prints increases.

  Preferably, the control unit acquires an electrical characteristic value during execution of the first continuous print job, and based on the electrical characteristic value acquired during execution of the first continuous print job, the magnitude of the transfer bias. Is further corrected.

  Preferably, the control unit is configured to acquire the electrical characteristic value of the conductive member by the sensor before executing the continuous printing corresponding to the continuous printing number.

  Preferably, when the electrical characteristic value is acquired during the execution of the first continuous print job, the control unit is based on the number of continuous prints when the electrical characteristic value is acquired in the first continuous print job. Controls the magnitude of the transfer bias in the second print job after the first continuous print job.

  Preferably, the conductive member includes an ion conductive member. The image forming apparatus further includes at least one of a temperature sensor that measures temperature and a humidity sensor that measures humidity. The control unit controls the magnitude of the transfer bias applied to the conductive member based on at least one of the temperature acquired by the temperature sensor and the humidity acquired by the humidity sensor, the electrical characteristic value, and the number of continuous prints.

  Preferably, the control unit controls the magnitude of the transfer bias applied to the conductive member based on the electrical characteristic value, the number of continuous prints, and the type of recording medium corresponding to the number of continuous prints.

  Preferably, the image forming apparatus is configured to be capable of duplex printing on a recording medium. The control unit controls the magnitude of the transfer bias applied to the conductive member based on the electrical characteristic value, the continuous print number, and whether or not the print corresponding to the continuous print number is double-sided printing.

  According to another aspect, a method for controlling a transfer bias applied to a conductive member disposed in contact with a recording medium on a conveyance path includes a step of obtaining an electrical characteristic value of the conductive member, and continuous printing of the recording medium. A step of counting the number of sheets, and a step of determining the magnitude of the transfer bias to be applied to the conductive member based on the acquired electrical characteristic value and the counted number of continuous prints.

  The image forming apparatus according to an embodiment can control the transfer current flowing through the transfer roller more accurately. Thereby, this image forming apparatus can realize higher transfer efficiency than the conventional one while suppressing a decrease in productivity.

  The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention taken in conjunction with the accompanying drawings.

It is a figure explaining the amount of moisture contained in the ATVC voltage with respect to the continuous printing number of sheets, and a transfer roller. It is a figure explaining the structural example of the image forming apparatus according to a certain embodiment. It is a figure explaining the control part according to a certain embodiment. It is a figure explaining the relationship between the estimated voltage Vp and the continuous printing number according to a certain embodiment. 6 is a flowchart illustrating control of a transfer bias voltage Vt during a continuous print job according to an embodiment. It is a figure explaining the control which estimates the initial voltage V0. It is a figure explaining the relationship between the ATVC voltage which points out the resistance value of the secondary transfer roller containing an ion conductive material, temperature, and humidity. It is a figure explaining the structural example of the image forming apparatus according to a certain embodiment. It is a flowchart explaining control of the transfer bias voltage Vt in a continuous printing job in consideration of temperature and humidity according to an embodiment. It is a figure explaining control of transfer bias voltage Vt according to other embodiments. FIG. 6 is a diagram illustrating a relational expression between a correction voltage corresponding to the type of paper and the number of continuous prints. It is a figure explaining the relational expression of the correction voltage according to the basic weight of a paper, and the number of continuous printing. It is a figure explaining the relational expression of the correction voltage according to print setting, and the number of continuous printing.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

[Technology]
FIG. 1 is a diagram for explaining the ATVC voltage and the amount of moisture contained in the transfer roller with respect to the number of continuously printed sheets.

  In FIG. 1, the horizontal axis indicates the total number of printed sheets, and the vertical axis indicates the ATVC voltage. The ATVC voltage shown in FIG. 1 is a voltage value obtained when a constant current is passed through a transfer roller arranged so as to be in contact with the paper (recording medium) on the transport path.

  An image forming apparatus according to an embodiment measures an ATVC voltage before executing printing according to a print job input. In the example shown in FIG. 1, the image forming apparatus measures the ATVC voltage at the time of the cumulative number of printed sheets NC1 before executing printing according to the input of the first continuous print job, and follows the input of the first continuous print job. Then, the ATVC voltage is measured at the time of the cumulative number of printed sheets NC2.

  When the paper passes through the transfer roller, the paper takes away moisture from the transfer roller in contact therewith. Therefore, as shown in FIG. 1, the amount of water contained in the transfer roller gradually decreases as the number of continuous prints in the first continuous print job increases. Accordingly, the ATVC voltage that indirectly indicates the resistance value of the transfer roller gradually increases as the number of continuous prints in the first continuous print job increases.

  As the first continuous printing job ends, the transfer roller absorbs moisture from the surrounding atmosphere. As a result, the moisture content of the transfer roller returns to a steady state after a certain amount of time has elapsed from the end of the first continuous print job. As a result, the ATVC voltage also returns to the steady state.

  An image forming apparatus according to an embodiment controls the magnitude of the transfer bias voltage applied to the transfer roller in consideration of the increase in resistance of the transfer roller accompanying the decrease in the water content of the transfer roller. More specifically, the image forming apparatus controls to increase the transfer bias voltage as the number of continuous prints increases. As described above, the image forming apparatus according to an embodiment controls the magnitude of the transfer bias voltage by controlling the magnitude of the transfer bias voltage in consideration of the variation in the resistance value of the transfer roller during the measurement of the ATVC voltage. Can be controlled with higher accuracy than in the past. As a result, this image forming apparatus can improve the transfer efficiency as compared with the prior art.

  Further, since this image forming apparatus sets the transfer bias voltage in accordance with the resistance value of the transfer roller predicted from the number of continuous prints, it is not necessary to frequently measure the ATVC voltage. Therefore, this image forming apparatus can suppress a decrease in productivity due to frequent measurement of the ATVC voltage. Hereinafter, a specific configuration and control of the image forming apparatus will be described.

[Embodiment 1]
(Image forming apparatus 200)
FIG. 2 is a diagram illustrating a configuration example of an image forming apparatus 200 according to an embodiment. In an embodiment, the image forming apparatus 200 is an electrophotographic image forming apparatus such as a laser printer or an LED printer. As shown in FIG. 2, the image forming apparatus 200 includes an intermediate transfer roller 1 as a belt member at a substantially central portion inside. Below the lower horizontal portion of the intermediate transfer roller 1, four image forming units 2Y, 2M, 2C, and 2K respectively corresponding to yellow (Y), magenta (M), cyan (C), and black (K) colors. Are arranged side by side along the intermediate transfer roller 1. These image forming units 2Y, 2M, 2C, and 2K respectively include photoreceptors 3Y, 3M, 3C, and 3K configured to be able to carry toner images.

  Around each of the photoreceptors 3Y, 3M, 3C, and 3K, which are image carriers, charging rollers 4Y, 4M, 4C, and 4K for charging the corresponding photoreceptors in order along the rotation direction, and a print head Primary transfer rollers 7Y, 7M, and 7C that face the photoreceptors 3Y, 3M, 3C, and 3K across the intermediate transfer roller 1 with the portions 5Y, 5M, 5C, and 5K, the developing rollers 6Y, 6M, 6C, and 6K , 7K are arranged.

  A secondary transfer roller 9 is pressed against a portion of the intermediate transfer roller 1 supported by the intermediate transfer belt driving roller 8. The secondary transfer roller 9 is disposed so as to be in contact with the sheet on the transport path R1. Further, a power supply device 80 is electrically connected to the secondary transfer roller 9. A voltmeter 85 is disposed between the intermediate transfer belt driving roller 8 and the ground potential. The control unit 70 that controls the operation of the image forming apparatus 200 is electrically connected to the power supply device 80 and the voltmeter 85.

  Secondary transfer is performed in a region where the secondary transfer roller 9 and the intermediate transfer belt driving roller 8 are in contact with each other. A fixing device 20 including a fixing roller 10 and a pressure roller 11 is disposed at a downstream position of the transport path R1 behind the secondary transfer region.

  A paper feed cassette 30 is detachably disposed below the image forming apparatus 200. The sheets P stacked and accommodated in the sheet feeding cassette 30 are sent out one by one from the uppermost sheet to the transport path R <b> 1 by the rotation of the sheet feeding roller 31.

  An operation panel 90 is disposed on the upper part of the image forming apparatus 200. As an example, the operation panel 90 includes a screen in which a touch panel and a display are superimposed on each other, and physical buttons.

  In the above example, the image forming apparatus 200 employs a tandem intermediate transfer method, but is not limited thereto. Specifically, it may be a configuration having a transfer roller in contact with a sheet, and may be an image forming apparatus that adopts a cycle method.

(Schematic operation of image forming apparatus 200)
Next, a schematic operation of the image forming apparatus 200 having the above configuration will be described. When an image signal is input from an external device (for example, a personal computer) to the control unit 70 of the image forming apparatus 200, the control unit 70 creates a digital image signal obtained by color-converting the image signal into yellow, cyan, magenta, and black. Then, based on the input digital signal, each print head unit 5Y, 5M, 5C, 5K of each image forming unit 2Y, 2M, 2C, 2K is caused to emit light to perform exposure.

  As a result, the electrostatic latent images formed on the photoreceptors 3Y, 3M, 3C, and 3K are respectively developed by the developing rollers 6Y, 6M, 6C, and 6K to become toner images of the respective colors. The toner images of the respective colors are primarily transferred in a superimposed manner on the intermediate transfer roller 1 moving in the direction of arrow A in FIG. 1 by the action of the primary transfer rollers 7Y, 7M, 7C, and 7K.

  The toner image formed on the intermediate transfer roller 1 in this way is secondarily transferred collectively onto the paper P by the action of the secondary transfer roller 9. At this time, the control unit 70 appropriately controls the magnitude of the transfer bias voltage applied from the power supply device 80 to the secondary transfer roller 9. Details of the control of the transfer bias voltage will be described later.

  The toner image secondarily transferred to the paper P reaches the fixing device 20. The toner image is fixed on the paper P by the action of the heated fixing roller 10 and the pressure roller 11. The paper P on which the toner image is fixed is discharged to the paper discharge tray 60 via the paper discharge roller 50.

(Control unit 70)
FIG. 3 is a diagram illustrating the control unit 70 according to an embodiment. The control unit 70 includes a central processing unit (CPU) 310, a random access memory (RAM) 320, a read only memory (ROM) 330, and an interface (I / F) 340 as main control elements.

  The CPU 310 controls the operation of the image forming apparatus 200 by reading and executing a control program stored in the ROM 330 or the storage device 360 described later.

  The RAM 320 is typically a DRAM (Dynamic Random Access Memory) or the like, and can temporarily store data and image data necessary for the CPU 310 to operate the program. Therefore, the RAM 320 can function as a so-called working memory.

  The ROM 330 is typically a flash memory or the like, and can store programs executed by the CPU 310 and various setting information related to the operation of the image forming apparatus 200.

  The CPU 310 is electrically connected to the power supply device 80, the voltmeter 85, the operation panel 90, the communication interface 350, and the storage device 360 via the interface 340, and transmits and receives signals to and from various devices.

  As an example, the communication interface 350 is a wireless LAN (Local Area Network) card. The image forming apparatus 200 is configured to be able to communicate with an external device (a personal computer, a smartphone, a tablet, or the like) connected to a LAN or a WAN (Wide Area Network) via a communication interface 350.

  The storage device 360 is typically constituted by a hard disk drive. The storage device 360 holds the relational expression 365. This relational expression 365 will be described later.

(Control of transfer bias voltage)
In one aspect, the transfer bias voltage Vt applied to the secondary transfer roller 9 can be expressed by the following formula (1).

Vt = a × Vp + b (1)
In equation (1), a and b are coefficients determined by the temperature and humidity in the image forming apparatus 200 and the type of paper to be printed (for example, thick paper, thin paper, etc.). The predicted voltage Vp is an ATVC voltage value predicted at the time of a certain number N of continuous prints, and can be expressed by the following equation (2).

Vp = V0 + Vc (2)
In equation (2), the initial voltage V0 is an ATVC voltage value before continuous printing (that is, an ATVC voltage value when the number N of continuous prints is 0). The correction voltage Vc is the amount of increase in the ATVC voltage corresponding to the increase in the resistance of the secondary transfer roller 9 that is expected at the time of a certain continuous print number N. This increase in resistance of the secondary transfer roller 9 is caused by the moisture contained in the secondary transfer roller 9 being taken away by the paper, as described with reference to FIG.

  The relational expression 365 stored in the storage device 360 is an expression showing the relation between the continuous printing number N and the correction voltage Vc. The relational expression 365 defines the relationship between the continuous print number N and the correction voltage Vc so that the correction voltage Vc increases as the continuous print number N increases. In one aspect, the relational expression 365 can be set based on experimental values.

  In an embodiment, when a print job is input, the control unit 70 supplies a constant current from the power supply device 80 to the secondary transfer roller 9 before executing printing, and the initial voltage V0 measured by the voltmeter 85 is measured. To get. In FIG. 2, the power supply device that supplies a constant current to the secondary transfer roller 9 and the power supply device that applies a transfer bias voltage to the secondary transfer roller 9 have a common configuration. The power supply device may be a separate body.

  FIG. 4 is a diagram illustrating the relationship between the predicted voltage Vp and the continuous print number N according to an embodiment. Referring to the partial diagram (A), the control unit 70 calculates the correction voltage Vc from the continuous print number N1 based on the relational expression 365 at the time of the continuous print number N1 of the first continuous print job. The controller 70 calculates the transfer bias voltage Vt based on the predicted voltage Vp (V1) obtained by adding the correction voltage Vc to the initial voltage V0 acquired from the voltmeter 85 before executing continuous printing.

  The partial diagram (B) is a diagram for explaining an example of a method of correcting the predicted voltage Vp. In the above description, it has been described that the predicted voltage Vp can be expressed by Expression (2). However, there may be a difference between the ATVC voltage (predicted voltage Vp) predicted for a certain number N of continuous printings and the actual ATVC voltage for the number N of continuous printings. Therefore, the control unit 70 according to an embodiment defines the predicted voltage Vp as in the following expression (3).

Vp = V0 + Vc + Voff (3)
In Equation (3), the differential voltage value Voff is a value obtained by subtracting the ATVC voltage value predicted for this continuous printing number from the ATVC voltage value actually measured by the voltmeter 85 at a certain continuous printing number N.

  An example of a specific method for correcting the predicted voltage Vp will be described with reference to a partial diagram (B). When the continuous print number N in the first continuous print job reaches a predetermined number N2 (for example, 100 sheets, 200 sheets, 300 sheets,...), The control unit 70 according to an embodiment performs secondary transfer from the power supply device 80. A constant current is passed through the roller 9 to acquire the ATVC voltage value (V2) measured by the voltmeter 85. The control unit 70 calculates a differential voltage value Voff obtained by subtracting the ATVC voltage value (V2p) predicted for the predetermined number N2 from the measured ATVC voltage value. The control unit 70 calculates the predicted voltage Vp (V1) by adding the correction voltage Vc and the differential voltage value Voff to the initial voltage V0 when the continuous printing number N is N1 (N1> N2).

  According to this configuration, the control unit 70 according to an embodiment can set the transfer bias voltage Vt based on the predicted voltage Vp close to the actual measurement value even when the continuous printing number N is large.

  In the partial diagrams (A) and (B), the correction voltage Vc (predicted voltage Vp) is drawn as being proportional to the number N of continuous prints, but the correction voltage Vc defined by the relational expression 365 and the continuous print are shown. The relationship with the number N is not limited to a proportional relationship. For example, as shown in the diagram (C), the relationship between the correction voltage Vc defined in the relational expression 365 and the continuous print number N is set such that the correction voltage Vc becomes saturated as the continuous print number N increases. May be.

(Flowchart for determining transfer bias voltage Vt)
FIG. 5 is a flowchart illustrating control of the transfer bias voltage Vt during a continuous print job according to an embodiment. The processing shown in FIG. 5 is realized by the CPU 310 executing a control program stored in the ROM 330 or the storage device 360. In other aspects, some or all of the processing may be performed by circuit elements or other hardware.

  In step S <b> 510, CPU 310 receives an input of a continuous print job via operation panel 90 or communication interface 350.

  In step S520, the CPU 310 passes a constant current from the power supply device 80 to the secondary transfer roller 9, and acquires the initial voltage V0 measured by the voltmeter 85.

  In step S530, CPU 310 calculates correction voltage Vc based on relational expression 365 stored in storage device 360. The CPU 310 sets the transfer bias voltage Vt based on the calculated correction voltage Vc. In the relational expression 365, since the correction voltage Vc when the number N of continuous prints is 0 is set to 0, the predicted voltage Vp before printing is equal to the initial voltage V0.

  In step S540, the CPU 310 prints one sheet with the set transfer bias voltage Vt. In step S550, CPU 310 increments the number N of continuous prints by one. In one aspect, the CPU 310 stores a count value indicating the continuous print number N in the RAM 320.

  In step S560, CPU 310 determines whether or not the continuous print number N has reached a predetermined continuous print number (for example, 100 sheets, 200 sheets, 300 sheets,...). When CPU 310 determines that the number N of continuous prints has reached a predetermined number of continuous prints (YES in step S560), CPU 310 advances the process to step S570. If not (NO in step S560), CPU 310 advances the process to step S580.

  In step S <b> 570, the CPU 310 temporarily interrupts the continuous print job, causes a constant current to flow from the power supply device 80 to the secondary transfer roller 9, and acquires the ATVC voltage measured by the voltmeter 85. The CPU 310 calculates a differential voltage value Voff obtained by subtracting the predicted voltage Vp for the continuous print number reached in step S560 from the acquired ATVC voltage value. The CPU 310 sets the differential voltage value Voff included in the relational expression 365 based on the calculated differential voltage value Voff.

  In step S580, CPU 310 determines whether or not the input continuous print job has ended. When CPU 310 determines that the continuous print job has ended (YES in step S580), CPU 310 ends the series of processing. On the other hand, when CPU 310 determines that the continuous print job has not ended (NO in step S580), CPU 310 returns the process to step S530.

  In step S530, the CPU 310 calculates the correction voltage Vc using the count value stored in the RAM 320, that is, the continuous printing number N, and sets the transfer bias voltage Vt based on the calculated correction voltage Vc. When the differential voltage value Voff is set, the CPU 310 sets the transfer bias voltage Vt based on the predicted voltage Vp obtained by adding the correction voltage Vc calculated to the initial voltage V0 and the differential voltage value Voff. CPU 310 repeats steps S530 to S570 until the continuous print job is completed.

  According to the above, the image forming apparatus 200 according to an embodiment takes into account the increase in resistance of the secondary transfer roller 9 due to the decrease in the water content of the secondary transfer roller 9, and the transfer bias voltage applied to the secondary transfer roller 9. Controls the magnitude of Vt. As described above, the image forming apparatus 200 according to an embodiment controls the magnitude of the transfer bias voltage Vt in consideration of the resistance value variation of the secondary transfer roller 9 in the interval at which the ATVC voltage is actually measured. The magnitude of the transfer current flowing through the next transfer roller 9 can be controlled with higher accuracy than before. As a result, the image forming apparatus 200 can improve the transfer efficiency as compared with the related art.

  Further, since the image forming apparatus 200 sets the transfer bias voltage Vt according to the resistance value of the secondary transfer roller 9 predicted from the continuous printing number N, it is not necessary to frequently measure the ATVC voltage. Therefore, the image forming apparatus 200 can suppress a decrease in productivity due to frequent measurement of the ATVC voltage.

  In the process shown in FIG. 5, the transfer bias voltage Vt is adjusted every time one sheet is printed. However, in another aspect, the image forming apparatus 200 performs the transfer bias every predetermined number (for example, 10 sheets). A configuration for adjusting the voltage Vt may be employed. According to this configuration, since the processing load on the CPU 310 can be reduced, further improvement in productivity can be realized.

(Configuration for predicting initial voltage V0)
In the above, the image forming apparatus 200 is configured to actually measure the initial voltage V0 by the voltmeter 85 before executing printing in accordance with the input of the print job. In another embodiment, the image forming apparatus 200 may be configured to predict the initial voltage V0 without actually measuring it.

  FIG. 6 is a diagram illustrating control for predicting the initial voltage V0. In an embodiment, the CPU 310 actually measures the ATVC voltage of the secondary transfer roller 9 every predetermined number of printed sheets (for example, every 100 sheets). In such a case, the CPU 310 does not necessarily actually measure the initial voltage V0. Therefore, the CPU 310 predicts the initial voltage V0 from the previously measured ATVC voltage.

  Referring to FIG. 6, it is assumed that CPU 310 actually measures the ATVC voltage value (V3) when the number of continuous prints is N3 in the first continuous print job (time T1). The CPU 310 receives the next second continuous print job at time T2 after the end of the first continuous print job.

  Based on the relational expression 365, the CPU 310 calculates a correction voltage Vc corresponding to N3 continuous prints. The CPU 310 predicts a value obtained by subtracting the calculated correction voltage Vc from the previously measured ATVC voltage value (V3) as the initial voltage V0. The CPU 310 uses the predicted initial voltage V0 to control the magnitude of the transfer bias voltage Vt in the second continuous print job.

  According to the above, the image forming apparatus 200 according to an embodiment can predict the initial voltage V0 according to the input of the print job without actually measuring the initial voltage V0 before executing printing. As a result, the image forming apparatus 200 can further suppress a decrease in productivity by reducing the frequency of measurement of the ATVC voltage.

[Embodiment 2]
In recent years, conductive members such as a charging roller, a primary transfer roller, and a secondary transfer roller included in an image forming apparatus that conforms to an electrophotographic system are often formed of an ionic conductive material whose charge is ions. The resistance value of the ion conductive material is affected by temperature and humidity.

  FIG. 7 is a diagram illustrating the relationship between the ATVC voltage indicating the resistance value of the secondary transfer roller 9 including an ion conductive material, temperature, and humidity. Referring to FIG. 7, when secondary transfer roller 9 is made of an ion conductive material, the resistance value of the roller changes depending on temperature and humidity.

  Curve 701 shown in FIG. 7 has the lowest humidity, and the humidity gradually increases in the order of curves 702, 703,..., And curve 716 has the highest humidity.

  It can be seen from FIG. 7 that the resistance value of the secondary transfer roller 9 (ion conductive material) increases as the temperature decreases and increases as the humidity decreases. Therefore, when using the secondary transfer roller 9 containing an ion conductive material, it is preferable to set the transfer bias voltage Vt in consideration of the temperature and humidity at that time. Therefore, the configuration and control considering temperature and humidity will be described below.

(Image forming apparatus 800)
FIG. 8 is a diagram illustrating a configuration example of an image forming apparatus 800 according to an embodiment. Since the same reference numerals as those in FIG. 2 are the same, the description of those parts will not be repeated.

  The configuration of the image forming apparatus 800 is different from the configuration of the image forming apparatus 200 described with reference to FIG. 2 in that a temperature sensor 810 and a humidity sensor 820 are provided. The temperature sensor 810 and the humidity sensor 820 are arranged to measure the temperature and humidity near the secondary transfer roller 9.

  The temperature sensor 810 and the humidity sensor 820 are electrically connected to the I / F 340 of the control unit 70 and configured to transmit a measurement result to the CPU 310.

(Control of transfer bias voltage)
The relational expression 365 stored in the storage device 360 of the image forming apparatus 800 has terms of temperature and humidity. As an example, the relational expression 365 can be expressed by the following expression (4).

Vc = k1 × N + k2 × ΔT + k3 × ΔH (4)
N represents the number of continuous prints (count value). The difference temperature ΔT represents a temperature obtained by subtracting the temperature Ta at the time of a certain number N of continuous prints from the initial temperature T0 before starting continuous printing. The differential humidity ΔH represents a temperature obtained by subtracting the humidity Ha at a certain number N of continuous prints from the initial humidity H0 before starting continuous printing. It is assumed that k1 to k3 are variables that vary according to the continuous print number N. It is assumed that the relationship between k1 to k3 and the continuous print number N is stored in the storage device 360. The relational expression 365 is defined so that the correction voltage Vc decreases as the temperature Ta increases and the humidity Ha increases.

(Flowchart for determining transfer bias voltage Vt)
FIG. 9 is a flowchart illustrating control of transfer bias voltage Vt during a continuous print job in consideration of temperature and humidity according to an embodiment. The processing shown in FIG. 9 is realized by the CPU 310 executing a control program stored in the ROM 330 or the storage device 360. In other aspects, some or all of the processing may be performed by circuit elements or other hardware. Note that the portions denoted by the same reference numerals as those in FIG. 5 are the same processing, and therefore the description thereof is not repeated.

  In step S910, the CPU 310 acquires the initial temperature T0 from the temperature sensor 810 and the initial humidity H0 from the humidity sensor 820 before executing printing according to the continuous print job.

  In step S920, CPU 310 obtains temperature Ta and humidity Ha at that time from temperature sensor 810 and humidity sensor 820, respectively, in response to determining that the continuous print job has not ended.

  In step S930, CPU 310 calculates differential temperature ΔT and differential humidity ΔH, respectively.

  In step S940, the CPU 310 calculates the correction voltage Vc based on the relational expression 365 including the difference temperature ΔT term and the difference humidity ΔH term as shown in the equation (4). The CPU 310 sets the transfer bias voltage Vt based on the calculated correction voltage Vc.

  Based on the above, the image forming apparatus 800 according to an embodiment can control the transfer bias voltage Vt applied to the secondary transfer roller 9 including an ion conductive material in consideration of temperature and humidity. Therefore, the image forming apparatus 800 can control the magnitude of the transfer current flowing through the secondary transfer roller 9 with higher accuracy than in the past. As a result, the image forming apparatus 800 can improve the transfer efficiency as compared with the related art.

(Other control)
In one aspect, the storage device 360 of the image forming apparatus 800 has a predetermined relationship between the predicted voltage Vp (predicted ATVC voltage) of the secondary transfer roller 9 as shown in FIG. Is stored for each continuous print number (for example, 0, 1000, 2000,...).

  FIG. 10 is a diagram illustrating control of the transfer bias voltage Vt according to another embodiment. In FIG. 10, the humidity does not vary from the initial humidity H0.

  First, the CPU 310 specifies an initial humidity H0 and a curve 1010 corresponding to zero continuous printing. CPU 310 calculates a voltage (point A) corresponding to initial temperature T 0 based on curve 1010. The CPU 310 sets the transfer bias voltage Vt in the initial continuous printing using the calculated voltage (point A).

  The CPU 310 specifies a curve 1020 corresponding to the continuous printing number 1000 when the continuous printing number reaches 1000 sheets, and calculates a voltage (point B) corresponding to the initial temperature T0 based on the curve 1020. Next, the CPU 310 calculates a voltage (point C) corresponding to the temperature Ta when the continuous print number is 1000 based on the curve 1020. The CPU 310 uses this calculated voltage (point C) to set the transfer bias voltage Vt when the number of continuously printed sheets is 1000. Also by such control, the image forming apparatus 800 can set the transfer bias voltage Vt to an appropriate value in consideration of temperature and humidity.

  In the above example, the image forming apparatus 800 is configured to set the transfer bias voltage Vt in consideration of temperature and humidity. However, in another aspect, the image forming apparatus 800 is configured to set the transfer bias voltage Vt in consideration of only temperature. May be adopted. Due to the heat source (for example, the heating device included in the fixing device 20) included in the image forming apparatus, the temperature rises significantly with continuous printing. On the other hand, the humidity does not vary as much as the temperature with continuous printing.

[Embodiment 3]
As described above, the resistance value of the secondary transfer roller fluctuates due to the moisture contained in the secondary transfer roller being taken away by the paper. At this time, how to reduce moisture contained in the secondary transfer roller differs depending on the type of paper and printing conditions. Therefore, a configuration for controlling the transfer bias voltage applied to the secondary transfer roller in consideration of the type of paper and printing conditions will be described below.

(Paper type)
FIG. 11 is a diagram illustrating a relational expression between the correction voltage corresponding to the type of paper and the number of continuous prints. The moisture absorption varies depending on the type of paper. Therefore, the amount of water taken from the secondary transfer roller 9 when passing through the secondary transfer roller 9 differs depending on the type of paper. The moisture absorption of cardboard is higher than that of plain paper. Moreover, the moisture absorption of plain paper is higher than the moisture absorption of coated paper having a surface coated with a paint.

  Therefore, an image forming apparatus according to an embodiment stores a relational expression corresponding to the type of paper (an expression indicating a relation between the number N of continuous prints and the correction voltage Vc) in the storage device 360. In the example illustrated in FIG. 11, the image forming apparatus stores a relational expression 1110 corresponding to thick paper, a relational expression 1120 corresponding to plain paper, and a relational expression 1130 corresponding to coated paper in the storage device 360.

  The CPU 310 specifies the type of paper used in the job according to the input of the continuous print job. The CPU 310 sets a transfer bias voltage Vt to be applied to the secondary transfer roller 9 using a relational expression corresponding to the specified paper type.

  Based on the above, the image forming apparatus according to an embodiment can control the transfer bias voltage according to the type of paper. Therefore, this image forming apparatus can control the magnitude of the transfer current flowing through the secondary transfer roller 9 with higher accuracy, and can further increase the transfer efficiency.

(Paper basis weight)
The image forming apparatus can set the correction voltage using the basis weight of the paper instead of the paper type. This is because the greater the basis weight of the paper (that is, the thicker the paper), the higher the moisture absorption of the paper. For this reason, the image forming apparatus according to an embodiment stores the relational expression such that the correction voltage Vc for a certain number of continuously printed sheets increases as the basis weight of the sheet conforming to continuous printing increases using the above characteristics.

FIG. 12 is a diagram illustrating a relational expression between the correction voltage corresponding to the basis weight of the paper and the number of continuous prints. In the example shown in FIG. 12, the image forming apparatus, the relation 1210 basis weight of the paper corresponds to 300 g / ^{m 2,} a relational expression 1220 basis weight corresponding to 200 g / ^{m 2,} a basis weight of 80 g / The relational expression 1230 corresponding to m ² is stored in the storage device 360.

  The CPU 310 specifies the basis weight of the paper used in the job according to the input of the continuous print job. The CPU 310 sets a transfer bias voltage Vt to be applied to the secondary transfer roller 9 using a relational expression corresponding to the specified paper basis weight.

  According to the above, the image forming apparatus according to an embodiment can control the transfer bias voltage according to the basis weight of the paper. Therefore, this image forming apparatus can control the magnitude of the transfer current flowing through the secondary transfer roller 9 with higher accuracy, and can further increase the transfer efficiency.

(Double-sided printing)
During double-sided printing, the paper once passes through the fixing device 20 and then passes through the secondary transfer roller 9 again. Therefore, the temperature of the paper when passing the secondary transfer roller 9 for the second time is higher than the temperature of the paper when passing the secondary transfer roller 9 for the first time. As the temperature of the paper passing through the secondary transfer roller 9 is higher, the moisture contained in the secondary transfer roller 9 is more easily evaporated. For this reason, the image forming apparatus according to an embodiment stores the relational expression using the above-described characteristics so that the correction voltage Vc for a certain number of continuous prints is larger in double-sided printing than in single-sided printing.

  FIG. 13 is a diagram illustrating a relational expression between the correction voltage corresponding to the print setting and the number of continuous prints. In the example illustrated in FIG. 13, the image forming apparatus stores a relational expression 1310 corresponding to double-sided printing and a relational expression 1320 corresponding to single-sided printing in the storage device 360.

  The CPU 310 specifies whether the job is single-sided printing or double-sided printing according to the input of the continuous print job. The CPU 310 sets a transfer bias voltage Vt to be applied to the secondary transfer roller 9 using a relational expression corresponding to the specified print setting.

  According to the above, the image forming apparatus according to an embodiment can control the transfer bias voltage according to the print setting. Therefore, this image forming apparatus can control the magnitude of the transfer current flowing through the secondary transfer roller 9 with higher accuracy, and can further increase the transfer efficiency.

  In another aspect, the image forming apparatus can store relational expressions corresponding to single-sided printing and double-sided printing in the storage device 360 for each type or basis weight of the paper. In this case, the CPU 310 sets the transfer bias voltage Vt using a relational expression according to the type or basis weight of the paper used in the job and the print setting according to the input of the continuous print job.

[Other configurations]
In the above, the image forming apparatus is configured to acquire the ATVC voltage indicating the resistance value of the secondary transfer roller 9 using the voltage value obtained when a constant current is passed through the secondary transfer roller 9. The image forming apparatus only needs to be able to acquire the electrical characteristic value of the secondary transfer roller 9. In another aspect, the secondary transfer roller 9 uses a current value obtained when a constant voltage is applied to the secondary transfer roller 9. It may be configured to control the transfer bias voltage applied to the.

  The various functions described in the above embodiment are realized by one CPU 310, but are not limited thereto. These various functions include at least one semiconductor integrated circuit such as a processor, at least one application specific integrated circuit (ASIC), at least one DSP (Digital Signal Processor), and at least one FPGA (Field Programmable). Gate Array), and / or other circuits that include other arithmetic functions.

  These circuits can realize various functions described in the above embodiments by reading one or more instructions from at least one tangible readable medium.

  Such media take the form of magnetic media (eg, hard disk), optical media (eg, compact disc (CD), DVD), volatile memory, any type of memory such as non-volatile memory, etc. The form is not limited.

  Volatile memory can include DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory). The non-volatile memory can include ROM and NVRAM. A semiconductor memory may be part of a semiconductor circuit with at least one processor.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Intermediate transfer roller, 9 Secondary transfer roller, 70 Control part, 80 Power supply device, 85 Voltmeter, 90 Operation panel, 200,800 Image forming apparatus, 310 CPU, 340 interface, 350 Communication interface, 360 Storage device, 365 1110, 1120, 1130, 1210, 1220, 1230, 1310, 1320 relational expression, 810 temperature sensor, 820 humidity sensor, ΔT differential temperature, ΔH differential humidity, T0 initial temperature, H0 initial humidity, R1 transport path, V0 initial voltage, Vc correction voltage, Voff differential voltage value, Vp prediction voltage, Vt transfer bias voltage.

Claims (9)

A conductive member disposed in contact with the recording medium on the transport path;
A power supply device for transferring a toner image to the recording medium by applying a transfer bias to the conductive member;
A sensor for obtaining an electrical characteristic value of the conductive member;
An image forming apparatus comprising: a control unit configured to control a magnitude of the transfer bias applied to the conductive member based on an electrical characteristic value acquired by the sensor and a continuous print number of the recording medium.   The image forming apparatus according to claim 1, wherein the control unit controls the transfer bias to increase as the number of continuous prints increases. The controller is
Obtaining the electrical characteristic value during execution of the first continuous print job;
The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to further correct the magnitude of the transfer bias based on the electrical characteristic value acquired during execution of the first continuous print job.   The said control part is comprised so that the said electrical characteristic value of the said electrically-conductive member may be acquired by the said sensor, before performing the continuous printing corresponding to the said continuous printing number of sheets. The image forming apparatus described in the item.   When the electrical characteristic value is acquired during the execution of the first continuous print job, the control unit is based on the number of continuous prints when the electrical characteristic value is acquired in the first continuous print job. The image forming apparatus according to any one of claims 1 to 3, wherein a magnitude of the transfer bias in a second print job after the first continuous print job is controlled. The conductive member includes an ion conductive member,
It further comprises at least one of a temperature sensor that measures temperature and a humidity sensor that measures humidity,
The control unit applies the transfer bias applied to the conductive member based on at least one of a temperature acquired by the temperature sensor and a humidity acquired by the humidity sensor, the electrical characteristic value, and the number of continuous prints. The image forming apparatus according to claim 1, wherein the size of the image forming apparatus is controlled.   The control unit controls the magnitude of the transfer bias applied to the conductive member based on the electrical characteristic value, the continuous print number, and the type of recording medium corresponding to the continuous print number. Item 7. The image forming apparatus according to any one of Items 1 to 6. The image forming apparatus is configured to be capable of duplex printing on a recording medium,
The control unit controls the magnitude of the transfer bias to be applied to the conductive member based on the electrical characteristic value, the continuous print number, and whether or not the print corresponding to the continuous print number is double-sided printing. The image forming apparatus according to any one of claims 1 to 7. A method for controlling a transfer bias applied to a conductive member arranged to contact a recording medium on a conveyance path,
Obtaining an electrical property value of the conductive member;
Counting the number of continuous prints of the recording medium;
Determining a magnitude of a transfer bias to be applied to the conductive member based on the acquired electrical characteristic value and the counted number of continuous prints.

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