JP7484743B2 - Image forming apparatus, image forming method, and image forming program - Google Patents

Description

The present invention relates to an image forming apparatus, an image forming method, and an image forming program.

In an electrophotographic image forming apparatus, for example, a charged photoconductor is exposed to light to form an electrostatic latent image, which is then developed with toner to form a toner image on the surface of the photoconductor. The toner image is then transferred to an intermediate transfer body, which then transfers the toner image onto paper. The toner image on the paper is then fixed by applying heat and pressure to form an image on the paper.

In the transfer process in which a toner image is transferred from a photoconductor to an intermediate transfer body, the toner image can be transferred by a current generated by applying a constant voltage controlled voltage to a transfer section such as a transfer roller. In a transfer process using constant voltage control, a constant transfer rate can be obtained even if the amount of toner adhesion in the main scanning direction varies. The voltage controlled by constant voltage control is determined by ATVC (Active Transfer Voltage Control). ATVC is a process that determines the transfer voltage by reading the voltage value when a predetermined constant current controlled current is applied to the transfer section.

ATVC is normally performed when image formation begins, but as image formation continues, the temperature and humidity inside the image forming apparatus change due to heat from the fixing device and changes in the external environment, causing the resistance of the members in the transfer section to fluctuate. This causes a constant voltage controlled by constant voltage control to be applied to the transfer section, reducing the current applied to the toner, lowering the transfer rate and potentially causing problems such as poor color tone. As a countermeasure, in the past, after image formation began, ATVC was performed again during non-image formation periods such as between sheets of paper, correcting the applied voltage and changing the constant voltage controlled voltage applied to the transfer section to maintain the current applied to the toner.

However, if ATVC or similar is performed during non-image formation, such as between sheets of paper, productivity decreases because the transfer member or other parts need to be rotated more than once.

The following prior art is disclosed in the following Patent Document 1. A correction formula for correcting the voltage drop in the transfer roller when ATVC is performed before image formation to the corresponding voltage drop during image formation based on the temperature change during image formation is registered in advance for each humidity level. When the humidity level during image formation is the same as when ATVC is performed, an applied voltage corresponding to the corrected voltage drop calculated using the above correction formula is applied to the transfer roller by constant voltage control to perform the transfer process. When the humidity level during image formation is different from when ATVC is performed, ATVC is performed again, and the transfer process is performed using the determined applied voltage. This makes it possible to maintain an appropriate electrostatic force in the transfer process by constant voltage control while suppressing a decrease in productivity.

JP 2007-183309 A

However, the transfer members used in the transfer section have resistance variations due to lot differences, and also undergo deterioration due to durability, adhesion of discharge products due to corona discharge during charging and post-transfer static elimination, and resistance changes due to adhesion of lubricants to increase the lubricity of the cleaning section. The above prior art has the problem that it cannot prevent the effects of such resistance changes on the transfer rate, etc. Furthermore, the above prior art performs ATVC again when the absolute humidity changes relatively greatly and the humidity level during image formation differs from when ATVC was performed. However, performing ATVC again reduces productivity, and there is also the problem that it cannot be used when no non-image formation time is provided, such as when forming images on continuous paper.

The present invention has been made to solve these problems. In other words, the objective is to provide an image forming apparatus, an image forming method, and an image forming program that can suppress deterioration of transfer performance caused by manufacturing variations and changes over time in the resistance of the transfer unit, and prevent a decrease in productivity.

The above-mentioned problems of the present invention are solved by the following means.

(1) An image forming apparatus having a transfer unit that transfers a toner image formed on an image carrier to a transferee with a constant-voltage controlled transfer voltage, and a control unit that performs a determination process to determine the transfer voltage for generating a predetermined transfer current, and corrects the transfer voltage based on a correction ratio corresponding to the amount of change from the time of the determination process in a fluctuation factor that causes the transfer current generated by the transfer voltage to fluctuate.

(2) The image forming apparatus according to (1) above, in which the control unit corrects the transfer voltage by correcting the variable portion of the determined transfer voltage, excluding the invariant portion that does not fluctuate due to the fluctuation factor, with the correction ratio.

(3) The image forming device according to (2) above, in which the fluctuation factor is temperature, and the control unit corrects the fluctuation part based on the rate of change of the temperature.

(4) The image forming device according to (2) above, in which the fluctuation factor is relative humidity, and the control unit corrects the fluctuation portion based on the rate of change in relative humidity.

(5) The image forming device according to (2) above, in which the fluctuation factor is absolute humidity, and the control unit corrects the fluctuation portion based on the rate of change in absolute humidity.

(6) The image forming device according to (2) above, in which the control unit calculates the transfer voltage determined by performing the determination process as the invariant portion when the temperature becomes equal to or higher than a predetermined threshold.

(7) The image forming device according to (2) above, in which the control unit calculates the transfer voltage determined by performing the determination process after image formation by the print job is completed as the invariant portion.

(8) The image forming device described in (7) above, wherein the print job includes double-sided printing.

(9) The image forming apparatus according to (2) above, wherein the control unit determines the transfer voltage by the determination process when a plurality of conditions are set in which the resistance of the path through which the transfer current flows is different, and calculates the invariant portion based on the determined transfer voltage.

(10) The image forming device according to (2) above, wherein the control unit changes the invariant portion when an influencing factor that affects the invariant portion and is different from the variable factor changes.

(11) The image forming device according to (10) above, in which the influencing factor is temperature, and the control unit calculates the invariant portion based on the temperature.

(12) The image forming device according to (10) above, in which the influencing factor is relative humidity, and the control unit calculates the invariant portion based on the relative humidity.

(13) The image forming device according to (10) above, in which the influencing factor is absolute humidity, and the control unit calculates the invariant portion based on the absolute humidity.

(14) An image forming method comprising: a step (a) of transferring a toner image formed on an image carrier to a transferee with a constant-voltage controlled transfer voltage; and a step (b) of performing a determination process of determining the transfer voltage for generating a predetermined transfer current, and correcting the transfer voltage for transferring the toner image to the transferee in the step (a) based on a change rate corresponding to the amount of change from the time of the determination process of a fluctuation factor that causes the transfer current generated by the determined transfer voltage.

(15) An image forming program for causing a computer to execute the steps of: (a) transferring a toner image formed on an image carrier to a transfer recipient with a constant-voltage controlled transfer voltage; and (b) performing a determination process to determine the transfer voltage for generating a predetermined transfer current, and correcting the transfer voltage for transferring the toner image to the transfer recipient in (a) based on a change rate corresponding to the amount of change from the time of the determination process of a variable factor that causes the transfer current generated by the determined transfer voltage.

A determination process is performed to determine a constant-voltage controlled transfer voltage that generates a predetermined transfer current for transferring a toner image formed on an image carrier to a transfer medium, and the transfer voltage is corrected based on a correction ratio corresponding to the amount of change from the determination process in the variable factor that causes the transfer current generated by the transfer voltage to fluctuate. This makes it possible to suppress deterioration of transfer performance caused by manufacturing variations and fluctuations over time in the resistance of the transfer unit, and to prevent a decrease in productivity.

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. 1 is a block diagram showing a configuration of an image forming apparatus; FIG. 4 is an explanatory diagram showing the configuration of a circuit that applies a transfer voltage to a primary transfer roller. 11 is a graph for explaining correction of a transfer voltage. 11 is a graph showing an approximation of the relationship between the amount of change in temperature and the transfer voltage under different resistance conditions. 1 is a graph showing an approximation of the relationship between the amount of change in temperature and the rate of change of the fluctuation part. 13 is a graph for explaining an immutable portion update process. 4 is a flowchart showing an operation of the image forming apparatus. 1 is a graph for explaining a conventional technique. 11 is a graph for explaining calculation of a corrected transfer voltage.

Below, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. Note that in the drawings, identical elements are given the same reference numerals, and duplicate explanations will be omitted. Also, the dimensional ratios in the drawings have been exaggerated for the convenience of explanation, and may differ from the actual ratios.

First Embodiment
Fig. 1 is a schematic diagram showing the configuration of an image forming apparatus 100. Fig. 2 is a block diagram showing the configuration of the image forming apparatus 100.

The image forming device 100 includes a control unit 110, a memory unit 120, a communication unit 130, an operation display unit 140, an image reading unit 150, an image control unit 160, an image forming unit 170, and a sensor 180. These components are communicatively connected to each other via a bus 190. The image forming device 100 may be configured as an MFP (MultiFunction Peripheral). The control unit 110, the memory unit 120, and the operation display unit 140 form a computer.

The control unit 110 includes a CPU (Central Processing Unit) and various memories, and controls the above-mentioned components and performs various calculation processes according to a program. The operation of the control unit 110 will be described in detail later.

The storage unit 120 is configured with a solid state drive (SDD) or a hard disc drive (HDD) and stores various programs and data.

The communication unit 130 is an interface for communicating between the image forming apparatus 100 and external devices. As the communication unit 130, a network interface based on a standard such as Ethernet (registered trademark), SATA, or IEEE 1394 is used. Also, as the communication unit 130, various local connection interfaces such as wireless communication interfaces such as Bluetooth (registered trademark) or IEEE 802.11 are used.

The operation display unit 140 is equipped with a touch panel, a numeric keypad, a start button, a stop button, etc., and is used to display various information and input various instructions.

The image reading unit 150 has a light source such as a fluorescent lamp and an imaging element such as a CCD (Charge Coupled Device) image sensor. The image reading unit 150 shines light from the light source on a document set at a predetermined reading position, photoelectrically converts the reflected light with the imaging element, and generates image data from the electrical signal.

The image control unit 160 performs layout processing and rasterization processing of the print data contained in the print job etc. received by the communication unit 130, and generates image data in bitmap format.

A print job is a general term for a print command given to the image forming device 100, and includes print data and print settings. Print data is data for a document to be printed, and may include various types of data, such as image data, vector data, and text data. Specifically, print data may be PDL (Page Description Language) data, PDF (Portable Document Format) data, or TIFF (Tagged Image File Format) data. Print settings are settings related to image formation on paper 900, and include various settings such as the number of pages, number of copies to be printed, paper type, color or monochrome selection, and page layout.

The image forming unit 170 includes an image creating unit 40, a fixing unit 50, a paper feeding unit 60, and a paper transport unit 70.

The image forming section 40 has image forming units 41Y, 41M, 41C, and 41K corresponding to the toners of the respective colors Y (yellow), M (magenta), C (cyan), and K (black). Each image forming unit 41Y, 41M, 41C, and 41K forms a toner image on the photoconductor drum 42 through processes of charging, exposure, and development based on image data. Exposure is performed by scanning the photoconductor drum 42 with a laser beam. The toner images formed on the photoconductor drum 42 are sequentially superimposed and primarily transferred onto the intermediate transfer belt 43 by electrostatic force due to a constant-voltage controlled transfer voltage applied to the primary transfer roller 44. As a result, a color toner image is held on the intermediate transfer belt 43. The color toner image on the intermediate transfer belt 43 is secondarily transferred onto the paper 900 by the secondary transfer roller 45. The primary transfer roller 44 constitutes the transfer section.

The intermediate transfer belt 43 is a semiconductive endless (seamless) resin belt having a volume resistivity of about 1.0×10 ⁷ to 1.0×10 ⁹ Ω·cm and a surface resistivity of about 1.0×10 ¹⁰ to 1.0×10 ¹² Ω/□. The resin belt may be a semiconductive resin film having a thickness of 0.05 to 0.5 mm, which is made of engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, etc., in which a conductive material is dispersed. Alternatively, the intermediate transfer belt 43 may be a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm, which is made of silicone rubber, urethane rubber, etc., in which a conductive material is dispersed. The intermediate transfer belt 43 is wound around a plurality of roller members including a tension roller 36, etc., and is supported so as to be rotatable in the vertical direction.

The primary transfer rollers 44 are made of roller-shaped conductive members, for example, a metal shaft and foamed rubber such as silicone or urethane covering the periphery thereof, and are disposed opposite the photoconductor drums 42 for each color, sandwiching the intermediate transfer belt 43 between them, and press against the back surface of the intermediate transfer belt 43 to form a transfer area between the primary transfer rollers 44 and the photoconductor drums 42. A transfer voltage of the opposite polarity to that of the toner is applied to the primary transfer rollers 44 by constant voltage control, and the toner image on the photoconductor drum 42 is transferred onto the intermediate transfer belt 43 by the electrostatic force of the transfer electric field formed in the transfer area.

The photosensitive drum 42 is an image carrier having a hollow cylindrical main body (substrate) and a photosensitive layer, and is configured to rotate at a predetermined speed. The main body (substrate) is made of a metal such as aluminum. The photosensitive layer is made of a resin such as polycarbonate that contains an organic photoconductor (OPC).

Figure 3 is an explanatory diagram showing the configuration of a circuit that applies a transfer voltage to the primary transfer roller 44.

The transfer voltage is applied to the primary transfer roller 44 by the power supply 441. The transfer voltage is set to a reference potential (ground potential) equal to the potential of the photoconductor drum 42, which is pressed against the primary transfer roller 44 via the intermediate transfer belt 43, by grounding the photoconductor drum 42. The power supply 441 outputs the transfer voltage based on the control signal VIN output from the control unit 110 and input to the power supply 441. Specifically, the power supply 441 outputs a transfer voltage based on an analog signal obtained by converting the control signal VIN by the D/A converter 442. The power supply 441 operates as a constant voltage source and outputs a constant voltage controlled transfer voltage.

The power supply 441 can also operate as a constant current source and can be used to determine the transfer voltage by ATVC (Active Transfer Voltage Control). Specifically, the voltage (potential) of the primary transfer roller 44 when a constant current is output from the power supply 441 is detected by the voltage detection circuit 443, converted to a digital signal VOUT by the A/D converter 444, and output to the control unit 110. This allows the control unit 110 to determine the transfer voltage (hereinafter also simply referred to as the "transfer voltage") that needs to be applied to the primary transfer roller 44 to generate a predetermined transfer current. The predetermined transfer current can be appropriately set by experiment from the viewpoint of the quality of the image formed on the paper 900.

The fixing unit 50 includes a fixing roller 51a and a pressure roller 52, and the fixing roller 51a and the pressure roller 52 are pressed against each other to form a fixing nip between them. The fixing unit 50 heats and presses the paper 900 conveyed to the fixing nip at the fixing nip, and rotates the fixing roller 51a and the pressure roller 52 to melt and fix the toner image on the paper 900 to the surface of the paper 900.

The sensor 180 may include a thermometer and a hygrometer. The sensor 180 is disposed inside the image forming apparatus 100, for example at a position relatively close to the imaging unit 40, and measures the temperature and humidity inside the apparatus. The sensor 180 may also measure the temperature and humidity outside the apparatus. In this case, the temperature and humidity are measured within a predetermined distance from the image forming apparatus 100. The predetermined distance may be appropriately set through experiments from the viewpoint of the quality of the image formed on the paper 900. The humidity may be relative humidity or absolute humidity.

The function of the control unit 110 will be explained.

The control unit 110 performs a determination process (hereinafter simply referred to as the "determination process") to determine the transfer voltage using the ATVC. Hereinafter, the transfer voltage determined by the determination process is referred to as the "ATVC determined value." The ATVC determined value is determined before the execution of a print job, and is applied as the transfer voltage when image formation is performed by executing the print job. It is preferable that the ATVC determined value is determined immediately before the execution of a print job.

The control unit 110 corrects the transfer voltage with a correction ratio (hereinafter also simply referred to as "correction ratio") according to the amount of change from the determination process in the variable factor that changes the transfer current caused by the application of the ATVC determined value to the primary transfer roller 44. The correction ratio will be described later. The variable factors include temperature, relative humidity, and absolute humidity. Specifically, these may be the temperature, relative humidity, and absolute humidity inside the image forming apparatus 100. For simplicity of explanation, the following explanation will be given assuming that the variable factor is temperature.

Figure 4 is a graph to explain the correction of the transfer voltage. The horizontal axis of the graph represents the amount of change in temperature, and the vertical axis represents the transfer voltage. Specifically, the amount of change in temperature is calculated by subtracting the temperature at the time of the determination process (at the time of the determination process before the start of the print job) from the current temperature. The amount of change in the current temperature is indicated by a dashed line on the graph.

As shown in Figure 4, the transfer voltage changes with temperature. The transfer voltage changes because the resistance of the path through which the transfer current flows (hereinafter simply referred to as "resistance") changes due to temperature, etc. The path through which the transfer current flows is considered to be the path from the primary transfer roller 44, through the intermediate transfer belt 43, and the photosensitive drum 42 to the ground point. The transfer voltage is divided into a variable portion that changes with temperature and an invariant portion that does not change with temperature. Note that there may be no invariant portion.

The control unit 110 corrects the transfer voltage by correcting the variable portion of the ATVC determined value, excluding the constant portion, based on a correction ratio corresponding to the amount of change in temperature since the determination process. Hereinafter, the corrected transfer voltage is referred to as the "corrected transfer voltage." The correction ratio is given by the following formula.

Correction ratio [%] = A x e^(B x (current temperature [°C] - temperature at time of decision process [°C]))
Here, the current temperature [°C] - the temperature at the time of determination processing [°C] is the temperature change amount. A and B are coefficients, and as described later, they are determined by calculating an approximation formula from a graph of the relationship between the actual measured value of the transfer voltage by ATVC for each temperature change amount and the temperature change amount.

The variable portion is the ATVC determined value minus the constant portion, and is given by the following formula:

Variable part [V] = ATVC decision value [V] - Invariant part [V]
As described later, the invariant portion can be calculated as the voltage at the intersection of two approximate equations calculated from a graph of the relationship between the measured value and the temperature change amount by actually measuring the transfer voltage for each temperature under two conditions with different resistances, as described below. Such calculation of the variable portion can be performed by experiment before the start of image formation by a print job.

The corrected transfer voltage is calculated by multiplying the variable portion by the correction ratio to calculate the variable portion correction value, and adding it to the unchanging portion, for example, as shown in the following formula. Note that there may be cases where there is no unchanging portion.

Fluctuation part correction value [V] = Fluctuation part [V] x correction ratio [%]
Corrected transfer voltage [V] = Unchanging part [V] + Variable part correction value [V]
In this way, by dividing the transfer voltage into a variable portion and an invariant portion, and correcting only the variable portion with a correction rate based on the amount of change in temperature, it is possible to flexibly suppress deterioration of transfer performance due to various factors such as differences in the components that change the optimal transfer voltage.

Figure 5 is a graph of an approximation of the relationship between temperature and transfer voltage under different resistance conditions. The horizontal axis of the graph is temperature, and the vertical axis is transfer voltage. The circular and triangular plots on the graph are actual measurement results of the transfer voltage measured by the ATVC for each temperature change during image formation. The circular plots are actual measurement results under high resistance conditions, and the triangular plots are actual measurement results under low resistance conditions. The high resistance and low resistance conditions can be achieved by changing the type of primary transfer roller 44, respectively. The high resistance and low resistance conditions may also be achieved by using a relatively worn roller and a new roller, for example.

In the example of Figure 5, the approximate equation for the relationship between temperature (x) and transfer voltage (y) under high resistance conditions is y = 11815e^(-0.075x). The approximate equation under low resistance conditions is y = 5104e^(-0.057x). The intersection of the two approximate equations corresponds to the constant part, which is 358V.

Figure 6 is a graph of an approximation of the relationship between the amount of change in temperature and the rate of change in the fluctuating portion. The horizontal axis of the graph is the amount of change in temperature, which can be a value calculated from the temperature at the start of image formation. The vertical axis is the rate of change in the fluctuating portion.

The approximate equation for the relationship between the amount of change in temperature and the rate of change in the variable portion is calculated as follows. The transfer voltage actually measured by the ATVC at the start of image formation (corresponding to the ATVC determined value) is set to 100%, and the unchanged portion is set to 0%, and the variable portion change rate is calculated by normalizing the transfer voltage actually measured by the ATVC for each temperature. The variable portion change rate corresponds to the correction ratio described above. In the example of FIG. 5, the actual measured value of the transfer voltage by the ATVC at the start of image formation under high resistance conditions is 4807V. The actual measured value of the transfer voltage by the ATVC at the start of image formation under low resistance conditions is 2800V. The unchanged portion is 358V. The normalized transfer voltage can be used to calculate the approximate equation for the relationship between the amount of change in temperature and the rate of change in the variable portion without distinguishing between the calculation results under high resistance conditions and low resistance conditions. In the example of FIG. 6, coefficient A is 0.9806 and coefficient B is -0.075. Therefore, the approximate equation for the relationship between the amount of change in temperature and the fluctuation part change rate (correction rate) is: Fluctuation part change rate (correction rate) = 0.9806 x e^ (-0.075 x amount of change in temperature).

Specifically, the control unit 110 corrects the transfer voltage according to a correction ratio according to the amount of change in temperature as follows, and applies the corrected transfer voltage to the primary transfer roller 44 to perform primary transfer of the toner image formed on the photosensitive drum 42 onto the intermediate transfer belt 43. The control unit 110 determines the ATVC determination value by a determination process at the start of image formation. As image formation continues, the temperature inside the machine increases due to the temperature of the fixing unit 50, for example. For this reason, the transfer voltage is corrected at a predetermined frequency according to a correction ratio according to the amount of change in temperature from the time of the determination process. For example, if the correction is made every time the temperature rises by 5°C, the correction ratio (change rate of the variable part) of the first correction is 0.9806 x e^ (-0.075 x 5V) = 67.4% according to the correction formula for the correction ratio described above. If the ATVC determination value is 3000V, the invariant part is 358V, so the variable part is 3000V-358V = 2642V. The variable portion correction value is 2642V x 67.4% = 1781V. Therefore, the corrected transfer voltage is 1781V + 358V = 2139V. By continuously correcting the transfer voltage in this way, the optimal transfer voltage can be maintained.

When the update condition for the invariant portion is met, the control unit 110 may perform the determination process again and execute a process for updating the invariant portion by calculating the determined ATVC determination value as the invariant portion (hereinafter also referred to as the "invariant portion update process"). The update condition for the invariant portion is, for example, when image formation for all pages is completed by executing a print job.

Figure 7 is a graph to explain the invariant portion update process. The horizontal axis of the graph in Figure 7 is the amount of change in temperature, and the vertical axis is the transfer voltage.

As shown in FIG. 7, image formation (primary transfer) is started with the ATVC determined value (black circle point) determined by the determination process before image formation by the print job as the transfer voltage, image formation is performed while correcting the transfer voltage, and image formation is terminated. The ATVC determined value (white circle point) determined by the determination process at the end of image formation almost corresponds to the invariant part, so an invariant part update process is possible to update the invariant part with the ATVC determined value. This is because when image formation by the print job is terminated, the temperature inside the image forming device 100 has risen sufficiently, and even if the ATVC determined value is determined by the determination process after a further temperature rise, it is estimated that the same ATVC determined value will be obtained and the transfer voltage required to generate a predetermined transfer current will not change. In addition, the invariant part update process is performed because the resistance may change due to wear of members such as the primary transfer roller 44, adhesion of discharge products due to corona discharge during charging and post-transfer de-electrification, and adhesion of lubricant to increase the lubricity of the cleaning part. By performing the determination process at the end of image formation by the print job, a decrease in productivity can be prevented.

The update condition for the invariant part may be that image formation for all pages is completed by the execution of the print job and that the temperature is equal to or higher than a predetermined threshold. The predetermined threshold may be a value empirically estimated as the temperature at which the ATVC determination value does not change with further temperature increase. The predetermined threshold may be an experimental value obtained by experimentally measuring the minimum value of the temperature at which the ATVC determination value does not change with further temperature increase. The update condition for the invariant part may be that image formation by the print job for double-sided printing is completed. In order to measure the variable part more accurately, it is preferable that the temperature is as high as possible, so it is preferable to perform the update process for the variable part after the image formation of double-sided printing is completed, when the paper 900, which has become heated by the fixing process of the front side of the paper 900 in the fixing unit 50, returns to the image forming unit 40 for image formation on the back side, and the temperature of the image forming unit 40 (the ambient temperature of the primary transfer roller 44) is likely to rise.

The invariant portion updated by the invariant portion update process can be used to calculate the corrected transfer voltage when the next print job is executed.

The operation of the image forming device 100 is explained.

Figure 8 is a flowchart showing the operation of the image forming device 100. This flowchart can be executed by the control unit 110 in accordance with a program stored in the storage unit 120.

The control unit 110 determines whether a print job has been acquired (S101). The control unit 110 may determine that a print job has been acquired, for example, when the print job is received by the communication unit 130.

If the control unit 110 determines that a print job has not been received (S101: NO), it repeats step S101.

When the control unit 110 determines that a print job has been received (S102: YES), it executes a determination process to determine the ATVC determination value (S102).

The control unit 110 applies the determined ATVC value as a transfer voltage to the primary transfer roller 44 using constant voltage control, and performs image formation through an image formation process that includes a process of primarily transferring the toner image formed on the photosensitive drum 42 onto the intermediate transfer belt 43 (S103).

When the control unit 110 determines that image formation for all pages has not been completed (S104; NO), it corrects the transfer voltage with a correction ratio according to the amount of change in temperature measured by the sensor 180 (S105). That is, the control unit 110 corrects the transfer voltage by calculating a corrected transfer voltage by adding a variable part correction value obtained by multiplying the unchanging part by the correction ratio to the unchanging part.

When the control unit 110 determines that image formation for all pages has been completed (S104: YES), it determines whether the update condition for the invariant portion is met (S106). As described above, the update condition for the invariant portion may be that the temperature is equal to or greater than a predetermined threshold, or that the print job is a double-sided print job, etc.

If the control unit 110 determines that the update conditions for the immutable portion are not met (S106: NO), it terminates the process.

If the control unit 110 determines that the update condition for the invariant portion is met (S106: YES), it performs a determination process and updates the invariant portion with the determined ATVC determination value (S107).

In the flowchart of FIG. 8, the transfer voltage is corrected for each sheet of paper 900 (each page), but the correction may be performed at an appropriate predetermined frequency (for example, every 10 pages). The predetermined frequency may be appropriately set through experiments from the viewpoint of the quality of the image formed on the sheet of paper 900. The predetermined frequency may be when the temperature changes by 5° C. or more, for example.

Second Embodiment
A second embodiment will be described. The present embodiment differs from the first embodiment in the following respects. In the first embodiment, the corrected transfer voltage is calculated without considering changes in the invariant portion due to influencing factors such as humidity that affect the invariant portion. On the other hand, in the present embodiment, the corrected transfer voltage is calculated taking into consideration changes in the invariant portion due to influencing factors such as humidity that affect the invariant portion. In other respects, this embodiment is similar to the first embodiment, so duplicated descriptions will be omitted or simplified.

Figure 9 is a graph to explain the conventional technology. The horizontal axis of the graph is the amount of change in temperature, and the vertical axis is the transfer voltage.

In the conventional technology, as in the present embodiment, the transfer voltage is determined by the ATVC before the start of image formation by the print job. The determined transfer voltage is shown by a black circle on the graph. After the start of image formation, the transfer voltage is corrected by a correction formula as shown by a solid line based on the temperature change (temperature rise). When the absolute humidity changes to a threshold value or more, the deviation between the transfer voltage corrected by the correction formula and the ideal value of the transfer voltage for each temperature (transfer current value that generates a specified transfer current) shown by a dashed line becomes significant. Therefore, when the absolute humidity changes to a threshold value or more, the ATVC is re-executed. The transfer voltage determined by re-executing the ATVC is shown by a white circle on the graph. Then, the transfer voltage is corrected by another correction formula corresponding to the absolute humidity after the change. In the conventional technology, when the humidity changes to a threshold value or more, the ATVC needs to be re-executed during non-image formation such as between sheets, even during the execution of a print job, which may reduce productivity.

Figure 10 is a graph to explain the calculation of the corrected transfer voltage in this embodiment. The horizontal axis of the graph is temperature, and the vertical axis is transfer voltage.

As shown in FIG. 10, when image formation is performed by a print job and the absolute humidity changes (e.g. increases) during image formation, the absolute humidity becomes an influencing factor, and the invariant portion changes before and during image formation. The influencing factor is a factor different from the variable factor. Therefore, the invariant portion for each absolute humidity is calculated in advance, and the transfer voltage is corrected by calculating a corrected transfer voltage during image formation based on the invariant portion corresponding to the absolute humidity after the change. This makes it possible to prevent deterioration of the transfer performance of the primary transfer due to changes in absolute humidity without reducing productivity. The influencing factor can be the relative humidity.

The control unit 110 registers the invariant portion for each absolute temperature by calculating it in advance before executing the print job and storing it in the storage unit 120. The invariant portion can be calculated in the same manner as in the first embodiment.

Before image formation by a print job is performed, the control unit 110 measures the absolute humidity as well as the temperature using the sensor 180, and reads out the invariant portion corresponding to the absolute humidity from the memory unit 120. The control unit 110 determines the ATVC determination value through a determination process. The ATVC determination value is indicated by a black circle on the graph.

The control unit 110 measures the absolute humidity together with the temperature using the sensor 180 while the image is being formed by the print job. When the measured absolute humidity changes by a predetermined threshold or more, the control unit 110 reads out the invariant portion corresponding to the absolute humidity from the memory unit 120 and changes the invariant portion to the read out invariant portion. The predetermined threshold can be appropriately set by experimentation from the viewpoint of the quality of the image formed on the paper 900. The control unit 110 calculates the variable portion by subtracting the read out invariant portion from the ATVC determined value. The control unit 110 calculates the correction rate according to the amount of temperature change using an approximation (see the first embodiment) of the relationship between the amount of temperature change and the correction rate, and multiplies the correction rate by the variable portion to calculate the variable portion correction value. The control unit 110 calculates the corrected transfer voltage by adding the variable portion correction value to the invariant portion. The control unit 110 corrects the transfer voltage by the corrected transfer voltage.

Embodiments of the present invention have the following advantages:

A determination process is performed to determine a constant-voltage controlled transfer voltage that generates a predetermined transfer current for transferring a toner image formed on an image carrier to a transfer medium, and the transfer voltage is corrected at a correction rate according to the amount of change from the determination process in the variable factor that causes the transfer current generated by the transfer voltage to fluctuate. This makes it possible to suppress deterioration of transfer performance caused by manufacturing variations and fluctuations over time in the resistance of the transfer unit, and to prevent a decrease in productivity.

Furthermore, the transfer voltage is corrected by correcting the variable portion of the determined transfer voltage, excluding the constant portion that does not fluctuate due to fluctuation factors, with the correction ratio. This makes it possible to effectively improve transfer performance.

In addition, temperature is treated as a fluctuating factor and the fluctuating portion is corrected based on the rate of change in temperature. This makes it possible to simply and effectively improve transfer performance.

Also, the relative humidity is treated as a variable factor, and the fluctuating portion is corrected based on the rate of change in relative humidity. This makes it possible to improve transfer performance simply and effectively.

In addition, absolute humidity is treated as a variable factor, and the fluctuating portion is corrected based on the rate of change in absolute humidity. This makes it possible to simply and effectively improve transfer performance.

In addition, when the temperature reaches or exceeds a predetermined threshold, the transfer voltage determined by the determination process is calculated as the invariant portion. This improves the calculation accuracy of the variable portion.

Furthermore, after image formation by the print job is completed, the transfer voltage determined by the determination process is calculated as the invariant portion. This makes it easy to calculate the invariant portion.

Furthermore, after image formation by a double-sided printing job is completed, the transfer voltage determined by the determination process is calculated as the invariant portion. This makes it easy to calculate the invariant portion and further improves transfer performance.

The invariant portion is calculated based on the transfer voltage determined by the determination process under multiple conditions in which the resistance of the path through which the transfer current flows is different. This makes it easy to calculate the invariant portion.

Furthermore, the invariant portion is changed when an influencing factor that affects the invariant portion changes. This makes it possible to suppress deterioration of transfer performance caused by changes in the invariant portion during image formation, and to prevent a decrease in productivity.

Furthermore, the invariant portion is calculated based on temperature, with temperature being an influencing factor. This makes it possible to suppress deterioration of transfer performance caused by simple changes to the invariant portion.

In addition, the invariant portion is calculated based on the relative humidity, with the relative humidity being an influencing factor. This makes it possible to easily prevent deterioration of transfer performance due to changes in the invariant portion.

In addition, absolute humidity is used as an influencing factor, and the invariant portion is calculated based on the absolute humidity. This makes it possible to easily suppress deterioration of transfer performance due to changes in the invariant portion.

The present invention is not limited to the above-described embodiments.

For example, in the embodiment, the variable factor that changes the transfer current generated by applying a constant-voltage controlled transfer voltage to the transfer section has been described as temperature. However, temperature, relative humidity, and absolute humidity are related to each other, and if relative humidity or absolute humidity significantly changes the transfer current, the variable factor may be used to calculate the corrected transfer voltage.

Also, for example, if the variable factor is absolute humidity, the influencing factor affecting the invariant portion may be temperature or relative humidity. Similarly, if the variable factor is relative humidity, the influencing factor affecting the invariant portion may be temperature or absolute humidity.

In the embodiment, the image carrier, the transferee, and the transfer unit are described as a photosensitive drum, an intermediate transfer belt, and a primary transfer roller, respectively. However, the image carrier, the transferee, and the transfer unit can be an intermediate transfer belt, paper, and a secondary transfer roller, respectively.

In addition, in the embodiment, some or all of the processing executed by the program may be replaced with hardware such as a circuit.

42 photosensitive drum,
43 intermediate transfer belt,
44 Primary transfer roller,
100 Image forming apparatus,
110 control unit,
120 memory unit,
130 Communication department,
140 Operation display unit,
150 Image reading unit,
160 Image control unit,
170 Image forming unit,
180 sensor.

Claims (15)

a transfer section that transfers the toner image formed on the image carrier to a transfer medium with a constant voltage control;
a control unit that performs a determination process to determine the transfer voltage for generating a predetermined transfer current, and corrects the transfer voltage based on a correction rate corresponding to an amount of change from the time of the determination process in a fluctuation factor that causes the transfer current to fluctuate due to the transfer voltage;
An image forming apparatus comprising: The image forming apparatus according to claim 1, wherein the control unit corrects the transfer voltage by correcting the variable portion of the determined transfer voltage, excluding the invariant portion that does not vary due to the fluctuation factor, with the correction ratio. The variable factor is temperature,
The image forming apparatus according to claim 2 , wherein the control unit corrects the fluctuating portion based on a rate of change in temperature. The variable factor is relative humidity,
The image forming apparatus according to claim 2 , wherein the control unit corrects the fluctuating portion based on a rate of change in relative humidity. The variable factor is absolute humidity,
The image forming apparatus according to claim 2 , wherein the control unit corrects the fluctuating portion based on a rate of change in absolute humidity. The image forming apparatus according to claim 2, wherein the control unit calculates the transfer voltage determined by performing the determination process as the invariant portion when the temperature is equal to or higher than a predetermined threshold. The image forming device according to claim 2, wherein the control unit calculates the transfer voltage determined by performing the determination process after image formation by a print job is completed as the invariant portion. The image forming device according to claim 7, wherein the print job includes double-sided printing. The image forming apparatus according to claim 2, wherein the control unit determines the transfer voltage by the determination process when a plurality of conditions are set in which the resistance of the path through which the transfer current flows is different, and calculates the invariant portion based on the determined transfer voltage. The image forming device according to claim 2, wherein the control unit changes the invariant portion when an influencing factor that affects the invariant portion and is different from the variable factor changes. The influencing factor is temperature;
The image forming apparatus according to claim 10 , wherein the control unit calculates the invariant portion based on a temperature. The influencing factor is relative humidity,
The image forming apparatus according to claim 10 , wherein the control unit calculates the invariant portion based on a relative humidity. The influencing factor is absolute humidity,
The image forming apparatus according to claim 10 , wherein the control unit calculates the invariant portion based on absolute humidity. (a) transferring a toner image formed on an image carrier to a transfer medium with a constant voltage control;
a step (b) of performing a determination process of determining the transfer voltage for generating a predetermined transfer current, and correcting the transfer voltage for transferring the toner image to the transfer medium in the step (a) based on a change rate corresponding to an amount of change from the time of the determination process of a fluctuation factor that causes the transfer current to fluctuate due to the determined transfer voltage;
The image forming method according to claim 1, (a) transferring a toner image formed on an image carrier to a transfer medium with a constant voltage control;
a step (b) of performing a determination process of determining the transfer voltage for generating a predetermined transfer current, and correcting the transfer voltage for transferring the toner image to the transfer medium in the step (a) based on a change rate corresponding to an amount of change from the time of the determination process of a fluctuation factor that causes the transfer current to fluctuate due to the determined transfer voltage;
An image formation program for causing a computer to execute the above.