Image forming apparatus, determination method, and control program

Abstract

To determine, accurately in a short time, the voltage-current characteristics of an application target member.SOLUTION: An image forming apparatus 1000 has a control unit 10 that determines first voltage-current characteristics of an application target member according to a detection current or a detection voltage detected by a detection unit 82 when an application unit 80 applies one or more levels of voltage or current. The control unit 10 controls detection time or the number of times of detection when the levels of voltage or current is applied and the detection current or detection voltage is detected, according to the levels of voltage or current to be applied.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, a method for determining the current-voltage characteristics of a member to be applied, and a control program.

Background Art

[0002] In image forming apparatuses such as electrophotographic printers and copiers, toner images of a plurality of colors are respectively formed on a plurality of image carriers such as a photoreceptor. Then, the formed toner images are transferred to an intermediate transfer belt by a primary transfer roller, and after being superimposed, they are transferred onto a sheet by a secondary transfer roller, and then the sheet on which the toner image is formed is obtained by heating and pressure fixing.

[0003] The resistance of transfer members such as transfer rollers and intermediate transfer belts varies due to durability or according to the ambient temperature and humidity. In order to appropriately control the appropriate transfer voltage according to the variation in the resistance of the transfer member, in the image forming apparatus disclosed in Patent Document 1, the following control is performed to calculate the applied voltage for outputting a desired current value by the transfer roller. Voltage control is performed by transfer PTVC control performed in constant voltage control, and the current value for one rotation of the transfer roller is detected in a state where the output current value has approached a desired current value to some extent. Then, the average of the voltage applied at that time is set as the applied voltage for outputting the desired current value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the technology disclosed in Patent Document 1, since the current value for one rotation of the transfer roller, that is, the same time is always detected, the detection time may not be appropriate. That is, in the technology disclosed in Patent Document 1, depending on the level of the voltage value, the detection time may be insufficient and there is a risk that stable detection cannot be performed.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to accurately determine the voltage-current characteristics (VI characteristics) of a member to which a voltage is applied in a short time.

Means for Solving the Problems

[0007] The above object of the present invention is achieved by the following means.

[0008] (1) An image forming apparatus that forms an image by an electrophotographic process, a member to which a voltage or current is applied, an applying unit that applies a voltage or current to the member to which the voltage is applied, a detection unit that detects a detection current or a detection voltage obtained through the member to which the voltage is applied when the applying unit applies a voltage or current to the member to which the voltage is applied, a control unit that determines a first voltage-current characteristic of the member to which the voltage is applied based on the detection current or the detection voltage detected by the detection unit when the applying unit applies one or more levels of voltage or current, and has, The control unit controls a detection time or a detection number when detecting a detection current or a detection voltage by applying the voltage or the current of the level according to the level of the voltage or the current to be applied, an image forming apparatus.

[0009] (2) The second voltage-current characteristic of the member to which the voltage is applied in the past obtained from the detection current or the detection voltage when a plurality of levels of voltage or current are applied is recorded, Based on the second voltage-current characteristic, the control unit determines whether the level of the voltage or current applied by the application unit is in a region where the variation in the detected current or detected voltage is large with respect to the variation in voltage or current. In the region where the variation is large, the image forming apparatus according to (1) above lengthens the detection time or increases the number of detections.

[0010] (3) The application of the voltage or current at one or more levels by the application unit and the detection of the detected current or detected voltage when determining the first voltage-current characteristic are performed between sheets of paper or between images of a print job. The image forming apparatus according to (2) above.

[0011] (4) The second voltage-current characteristic is obtained by applying voltages or currents at a plurality of levels and detecting the detected current or detected voltage before the start of execution of a print job or by interrupting an ongoing print job. The image forming apparatus according to (2) or (3) above.

[0012] (5) When the second voltage-current characteristic is linear, the detection time or the number of detections is set to be the same for any of the plurality of levels. The image forming apparatus according to (2) above.

[0013] (6) When the second voltage-current characteristic is non-linear, In a region where the level of the current up to the voltage applied by the application unit has a large variation in the detected current or detected voltage with respect to the variation in voltage or current, the control unit lengthens the detection time or increases the number of detections. The image forming apparatus according to (2) above.

[0014] (7) When the second voltage-current characteristic is non-linear, In a region where the level of the current up to the voltage applied by the application unit has a small variation in the detected current or detected voltage with respect to the variation in voltage or current, the control unit shortens the detection time or decreases the number of detections. The image forming apparatus according to (2) above.

[0015] (8) When determining the first voltage-current characteristic, the application of the voltage or current of the one or more levels by the application unit and the detection of the detection current or detection voltage are performed between sheets of paper or between images of a print job, The image forming apparatus according to (2) above, wherein the level is set based on the value of the voltage or current applied to the member to be applied immediately before the previous image formation.

[0016] (9) The image forming apparatus according to (1) above, wherein the member to be applied is composed of a plurality of layers having different layer resistances.

[0017] (10) The image forming apparatus according to (1) above, wherein the member to be applied is an intermediate transfer belt to which a toner image developed on a photoreceptor drum is transferred, or a primary transfer member.

[0018] (11) The image forming apparatus according to (1) above, wherein the member to be applied is a transfer member that transfers a toner image from an image carrier that carries the toner image to a recording medium.

[0019] (12) A member to which a voltage or current is applied, An application unit that applies a voltage or current to the member to be applied, A detection unit that detects a detection current or a detection voltage obtained through the member to be applied when the application unit applies a voltage or current to the member to be applied, and a method for determining the voltage-current characteristic of the member to be applied, which is executed by an image forming apparatus that forms an image by an electrophotographic process, The method has a step (a) of determining a first voltage-current characteristic of the member to be applied based on the detection current or detection voltage detected by the detection unit when the application unit applies a voltage or current of one or more levels, In step (a), the detection time or the number of detections when detecting the detection current or detection voltage by applying the voltage or current of the level is controlled according to the level of the voltage or current to be applied.

[0020] (13) A member to which a voltage or current is applied, An applying unit that applies a voltage or current to the member to which voltage or current is to be applied, A detecting unit that detects a detected current or a detected voltage obtained through the member to which voltage or current is to be applied when the applying unit applies a voltage or current to the member to which voltage or current is to be applied, and a control program executed in an image forming apparatus that forms an image by an electrophotographic process, Including step (a) of determining a first voltage-current characteristic of the member to which voltage or current is to be applied based on the detected current or detected voltage detected by the detecting unit when the applying unit applies a voltage or current at one or more levels, In step (a), a control program for executing a process of controlling a detection time or a detection frequency when detecting a detected current or a detected voltage by applying the voltage or current at the level according to the level of the voltage or current to be applied.

Advantages of the Invention

[0021] According to the present invention, an image forming apparatus has a control unit that determines a first voltage-current characteristic of a member to which voltage or current is to be applied based on a detected current or detected voltage detected by a detecting unit when an applying unit applies a voltage or current at one or more levels, and the control unit controls a detection time or a detection frequency when detecting a detected current or a detected voltage by applying the voltage or current at the level according to the level of the voltage or current to be applied. By doing so, it is possible to accurately determine the voltage-current characteristic of the member to which voltage or current is to be applied in a short time.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6A

Figure 6B

Figure 6C

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0023] Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. However, the scope of the present invention is not limited to the disclosed embodiments. In the description of the drawings, the same reference numerals are assigned to the same elements, and duplicate descriptions are omitted. Also, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may be different from the actual ratios.

[0024] (Member to be applied, and applied voltage or applied current) In the present embodiment, the member to be applied includes at least one of a primary transfer member (primary transfer rollers 32Y, 32M, 32C, 32K), a secondary transfer member (secondary transfer roller 34), and an intermediate transfer belt 33. Also, the primary transfer rollers 32Y, 32M, 32C, 32K, the secondary transfer roller 34, and the intermediate transfer belt 33 are also referred to as transfer members. In the following description, for example, the case where the primary transfer roller 32 is used as the member to be applied will be described as a representative example.

[0025] (Output current when a bias voltage is applied, or output voltage when a current is applied) In the following, taking the case of using a constant voltage power supply as the high-voltage power supply 81 of the bias application unit 80 that outputs a bias to the member to be applied as an example for explanation. For example, the high-voltage power supply 81 of the bias application unit 80 that applies a transfer bias to the transfer member is a constant voltage power supply. The control unit 10 of the image forming apparatus 1000 obtains a transfer voltage (transfer voltage setting vt) that results in a predetermined output current from the current-voltage characteristics (hereinafter also referred to as VI characteristics), and outputs that transfer voltage during image formation. However, it is not limited to this, and a constant current power supply may be applied as the high-voltage power supply 81 of the bias application unit 80. For example, the high-voltage power supply 81 of the bias application unit 80 that applies a transfer bias to the transfer member is a constant current power supply, obtains a transfer current (transfer current setting It) that results in a predetermined output voltage from the VI characteristics, and outputs that transfer current during image formation.

[0026] (VI characteristics, first and second VI characteristics) In the present embodiment, the VI characteristics describe the relationship between the voltage applied to the member to be applied and the current flowing at that time, or the current applied to the member to be applied and the voltage at that time. The determination of the VI characteristics of the member to be applied is performed by the VI characteristics determination unit 120.

[0027] Details will be described later, but the first VI characteristic is a VI characteristic with a certain degree of high precision within a narrow range and is the latest VI characteristic. The second VI characteristic (second current-voltage characteristic) is a VI characteristic with high precision over a wide range and is a past VI characteristic.

[0028] Although the overall shape (profile of the VI graph) of the VI characteristics of the member to be applied does not change, the resistance changes due to short-term use of the member to be applied or environmental changes, and thereby the VI characteristics shift. In the present embodiment, the overall shape is grasped by the second VI characteristic that is sampled at a low frequency, and the shift of the VI characteristics in a short time is compensated by the first VI characteristic that is sampled at a high frequency.

[0029] The determination of the "second VI characteristic" is performed relatively slowly at the timing when the image is not being formed (or just before image formation). For example, the determination of the "second VI characteristic" is performed immediately before the start of execution of a print job. When determining the second VI characteristic, the VI characteristic determination unit 120 sequentially outputs application voltages at many levels and detects the current flowing through the member to which the voltage is applied at that time. The number of levels here (n levels, described later) is, for example, 10 to 20 levels and spans the output range of the high-voltage power supply.

[0030] The determination of the "first VI characteristic" is performed in a relatively short time during the execution of a print job, such as between sheets of paper or between images. Since the determination of the first VI characteristic is performed in a short time, the number of levels of the voltage applied to the member to which the voltage is applied is smaller than that at the time of determining the second VI characteristic. For example, the number of levels (m levels, described later) when the VI characteristic determination unit 120 determines the first VI characteristic is from 1 to several, and a more preferable number of levels is 2 or 3.

[0031] (First Embodiment) FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 1000 according to the first embodiment. FIG. 2 is a block diagram showing a main hardware configuration of the image forming apparatus 1000. FIG. 3 is a diagram for explaining a configuration around the image forming unit 30. As shown in FIGS. 1 and 2, the image forming apparatus 1000 includes a control unit 10, a storage unit 20, an image forming unit 30, a paper feeding and conveying unit 40, an operation panel 60, a transfer bias application unit 80, and a communication I / F (interface) 90, which are mutually connected by signal lines.

[0032] The control unit 10 includes a CPU, a RAM, a ROM, etc., and the CPU executes a control program stored in the storage unit 20 to perform various controls on the entire image forming apparatus 1000. The control unit 10 also functions as an image control unit 110 and a VI characteristic determination unit 120. Although details of these functions will be described later, the outline is as follows.

[0033] When a print job is input, the image control unit 110 executes the print job based on the print job setting information of the input print job. The print job is input by an instruction sent from an external terminal such as the operation panel 60 or a network-connected PC operated by the user. The image control unit 110 controls the paper feeding and conveyance of the paper S by controlling the paper feeding and conveyance unit 40. Also, the image control unit 110 sets the image formation conditions (also referred to as process conditions) of the image forming unit 30 according to the settings of the print job and the VI characteristics. As the image formation conditions, the image control unit 110 calculates the resistance of the transfer member based on the VI characteristics, and determines the transfer bias setting (vt) so as to obtain a predetermined output current based on this resistance or directly from the VI characteristics. The VI characteristic determination unit 120 applies a transfer bias output of a plurality of levels to the member to be printed (transfer member) by the high-voltage power supply 81a (or 81b). Then, the VI characteristic determination unit 120 determines the first VI characteristic and the second VI characteristic (for example, FIG. 5 described later) based on the measured value of the ammeter 82a (or 82b) at that time.

[0034] The storage unit 20 is composed of an auxiliary storage device composed of a semiconductor SSD and / or a magnetic disk. The storage unit 20 stores various control programs, setting values of the apparatus main body, settings of print jobs, and image data. Also, the first and second VI characteristics are stored in the storage unit 20.

[0035] (Image forming unit 30) The image forming unit 30 forms an image on the paper S by an electrophotographic process. The image forming unit 30 has a plurality of image forming units 31Y, 31M, 31C, 31K. The image forming units 31Y, 31M, 31C, 31K correspond to the respective primary colors of yellow (Y), magenta (M), cyan (C), and black (K). In the following, when these are collectively referred to, they are simply called the image forming unit 31 (the same applies to the primary transfer roller 32 described later).

[0036] The image forming unit 30 includes a primary transfer roller 32Y, 32M, 32C, 32K corresponding to each image forming unit 31, an intermediate transfer belt 33, a secondary transfer roller 34, a fixing device 35, and the like. As described above, among these, the primary transfer rollers 32Y, 32M, 32C, 32K, the intermediate transfer belt 33, and the secondary transfer roller 34 function as members to be applied. Further, the intermediate transfer belt 33 functions as an image carrier that carries a toner image.

[0037] The image forming unit 31 includes a photosensitive drum 311, a charging electrode, an exposure unit, a developing device 312, a cleaning unit, etc. (some configurations are omitted in the figure). Each image forming unit 31 has the same configuration except that the toner color of the developer stored in the developing device 312 is different.

[0038] The photosensitive drum 311 is an organic photosensitive member in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer peripheral surface of a drum-shaped metal substrate. The photosensitive drum 311 rotates counterclockwise as indicated by the arrow in FIG. 1. After the surface of the photosensitive drum 311 is charged substantially uniformly by the charging electrode, exposure in pixel units based on image data is performed by the exposure unit, and an electrostatic latent image is formed on its surface. The electrostatic latent image is developed by the developing device 312 to form a toner image.

[0039] The developing device 312 of each image forming unit 31 has a developing roller disposed opposite to the photosensitive drum 311. Each developing device 312 contains a two-component developer composed of small-particle-size toner of different colors of yellow, magenta, cyan, and black and a carrier.

[0040] The intermediate transfer belt 33 is rotatably stretched by a plurality of inscribed rollers including a counter roller r3, and rotates and moves clockwise as indicated by the arrow in FIG. 1. On the inner peripheral surface side (back side) of the intermediate transfer belt 33, a plurality of primary transfer rollers 32 are disposed opposite to the photosensitive drum 311. A transfer bias is applied to the primary transfer roller 32 by a high-voltage power supply 81a during transfer.

[0041] (Example of Printed Component) The system speed (also called the process speed) of the image forming apparatus 1000 is, for example, 400 mm / sec.

[0042] The intermediate transfer belt 33 is configured using, for example, a polyimide resin, has a thickness of 80 μm, and a surface resistance of 9.95 to 10.75 LogΩ / □. Further, the intermediate transfer belt 33 may be configured with a three-layer structure of a base polyimide resin layer, an elastic layer, and a surface layer. The resistance of each layer has a different value. The elastic layer can be formed of a material mainly composed of a thermoplastic elastomer (TPE), a material mainly composed of a vulcanized rubber, or a foam of a polymer material. The surface layer is a layer formed on the elastic layer and is composed of, for example, an acrylic-based material.

[0043] Also, the primary transfer roller 32 is configured using, for example, an NBR (Nitril-Butadiene Rubber) sponge rubber roller, has a resistance of 6.7 to 7.1 logΩ, a hardness of Aske-C 35°, an outer diameter of φ20 mm, and a pressing force of 10 N. The sponge rubber roller is formed by forming sponge rubber on the surface of a metal roller. The opposing roller r3 is configured using, for example, an NBR sponge rubber roller, has a resistance of 7.5 logΩ, a hardness of Aske-C 30°, an outer diameter of φ38 mm, and a pressing force of 10 N. The secondary transfer roller 34 is an NBR solid roller, has a resistance of 7.5 logΩ, a hardness of Aske-C 30°, an outer diameter of φ38 mm, and a pressing force of 10 N.

[0044] The fixing device 35 has a pressure roller and a heating roller, and is controlled to reach a predetermined temperature by a heater inside the heating roller. By passing the paper S through the fixing nip formed by both rollers, heating and pressing processes are performed on the paper S.

[0045] The sheet feeding and conveying unit 40 includes a plurality of sheet feeding trays 41 and conveying paths 42 and 43. A plurality of sheets S are stacked on the sheet feeding tray 41, and the uppermost sheet S is fed one by one. The sheet feeding and conveying unit 40 includes a plurality of conveying roller pairs arranged along the conveying paths 42 and 43 and a drive motor (not shown) for driving the same, and conveys the sheet S fed from the sheet feeding tray 41 to the transfer position of the secondary transfer roller 34 and the fixing device 35 on the downstream side thereof. When performing double-sided printing in which an image is also formed on the back surface (second surface) of the sheet S, the sheet S on which an image is formed on one side is conveyed to the conveying path 43 for double-sided image formation at the lower part of the apparatus main body. The sheet S conveyed to this conveying path 43 is reversed in front and back by a switchback path, then merges into the single-sided conveying path 42, and an image is formed on the other side of the sheet S again by the image forming unit 30.

[0046] The toner images formed on the photoreceptor drums 311 of the respective image forming units 31 are sequentially primary transferred to the surface of the intermediate transfer belt 33 by the respective primary transfer units. Thereby, an overlapped toner image is formed on the intermediate transfer belt 33. The overlapped toner image on the intermediate transfer belt 33 is secondary transferred to the sheet S conveyed in synchronization with the position of the toner image by the secondary transfer unit. The sheet S to which the overlapped toner image is transferred is conveyed to the fixing device 35 on the downstream side, and a full-color image is formed on the sheet S by being subjected to heating and pressurizing treatment by the fixing device 35.

[0047] The operation panel 60 includes a touch panel, numeric keys, a start button, a stop button, etc., and is used for inputting various settings related to the apparatus, displaying the state of the apparatus, and inputting various instructions.

[0048] (Bias application unit 80) The bias application unit 80 includes a high-voltage power supply 81a that applies a transfer bias to the primary transfer roller 32, a high-voltage power supply 81b that applies a transfer bias to the secondary transfer roller 34, and ammeters 82a and 82b that measure the currents output from the high-voltage power supplies 81a and 81b. Hereinafter, these are collectively referred to as the high-voltage power supply 81 and the ammeter 82. The ammeter 82 functions as a detection unit. The high-voltage power supply 81a and the ammeter 82a apply independent transfer biases to each of the plurality of primary transfer rollers 32Y, 32M, 32C, and 32K and measure the flowing current.

[0049] The communication I / F 90 is an interface for various local connections such as a network interface for wired communication according to a standard such as Ethernet (registered trademark), and an interface for wireless communication according to a standard such as Bluetooth (registered trademark) and IEEE 802.11. The communication I / F 90 communicates with a user terminal such as a PC (personal computer) connected to the network.

[0050] (Determination process of the second VI characteristic) Next, with reference to FIGS. 4A, 4B, and 5, the determination process of the second VI characteristic will be described. FIG. 4A is a flowchart showing the determination process of the second VI characteristic, and FIG. 4B is a subroutine flowchart showing the VI characteristic determination process of step S12 in FIG. 4A.

[0051] Hereinafter (the same applies to the process in FIG. 6A), as a representative, the case where the member to be applied is the primary transfer roller 32K will be described. In this case, the transfer bias setting vt of the high-voltage power supply 81a that supplies bias to the primary transfer roller 32K is controlled by the process described below. The control of the transfer bias setting for other members to be applied (primary transfer rollers 32Y, 32M, 32C, intermediate transfer belt 33, secondary transfer roller 34) is performed in parallel, but the description thereof is omitted.

[0052] (Step S11) If it is the determination timing of the second VI characteristic, the control unit 10 proceeds to step S12. As a determination condition for determining whether it is the determination timing, at least any one of the following can be applied. For example, according to condition 3, when executing for each number of printed sheets, every time the running print job reaches a predetermined number of sheets, the print job is interrupted and the processing below step S12 is executed. (Condition 1) Before (immediately before) the start of execution of the print job. (Condition 2) When the image forming apparatus 1000 is powered on. (Condition 3) For each predetermined number of printed sheets (for example, every 1000 sheets). (Condition 4) When the second VI characteristic is not stored in the storage unit 20 (no history).

[0053] (Step S12) The control unit 10 executes the second VI characteristic determination process. The process here will be described using the subroutine flowchart of FIG. 4B.

[0054] (Step S210) The VI characteristic determination unit 120 sets a plurality of levels x1 to xn of the transfer bias (voltage) to be applied. This setting is stored in the storage unit 20 in advance. For example, the levels are n (for example, a dozen or so) level settings evenly arranged from the lower limit to the upper limit of the use range of the transfer member.

[0055] (Detection processing loop: steps S220 to S250) The VI characteristic determination unit 120 sequentially outputs a transfer bias (voltage) corresponding to the level x from the level x1 to xn from step S220 to step S250 by the high-voltage power supply 81a, applies it to the primary transfer roller 32, and detects the current at that time by the ammeter 82a. In the second VI characteristic determination process, the time constraint is looser than that in the first VI characteristic determination process described later. Therefore, the VI characteristic determination unit 120 increases the detection time or the number of detections in order to emphasize the measurement accuracy. The VI characteristic determination unit 120 performs nine measurements as the same number of detections at each level x. Here, the detection time for one time is 2 msec, and this is performed continuously nine times. Therefore, the detection time for one level is 18 msec. Then, the VI characteristic determination unit 120 records (associates) the average current obtained by averaging the nine measurement values in association with the output value of the transfer bias (step S240).

[0056] (Step S260) The VI characteristic determination unit 120 determines the second VI characteristic based on the applied voltage and the detected current (average current) at each level from the level x1 to xn by the processing from step S220 to step S250. FIG. 5 is an example of the determined second VI characteristic. Thus, the processing of FIG. 4B is completed, and the process returns to the processing of FIG. 4A.

[0057] (Step S13) Here, the VI characteristic determination unit 120 analyzes the obtained second VI characteristic and records (updates) the second VI characteristic in the storage unit 20 together with the analysis result. The VI characteristic determination unit 120 performs the following as the analysis process. · Determination of whether the updated second VI characteristic is non-linear. · When it is determined to be non-linear, further determination of the inflection point. · Further determination of the region with large variation and the region with small variation according to the position of the inflection point.

[0058] In the example shown in FIG. 5, with the voltage V0 at the inflection point as the boundary, depending on the slopes before and after it, the region above it is recognized as the small-variation region and the region below it as the large-variation region. These small-variation region and large-variation region are used in the determination process of the first VI characteristic described below. Thus, the control unit 10 ends the process of FIG. 4A (end). Note that the analysis process in step S13 may not be performed at this timing, but may be performed in FIG. 6C (step S410) described later.

[0059] (Printing process) Next, with reference to FIGS. 6A to 6C and FIGS. 7 to 9, the printing process executed in the image forming apparatus 1000 according to the present embodiment will be described.

[0060] FIG. 6A is a flowchart showing the printing process. FIG. 6B is a table showing the determination timing of step S36. FIG. 6C is a subroutine flowchart showing the first VI characteristic determination process of step S37 in FIG. 6A.

[0061] (Step S31) The control unit 10 reads a print job. The print job includes print data and print settings. The print settings describe the type of paper to be used (thin paper, thick paper, coated paper, etc.), size, number of printed sheets, and the like.

[0062] (Step S32) The image control unit 110 sets image formation conditions according to the print settings and the machine state. The machine state includes the ambient temperature and humidity of the image forming apparatus 1000, the usage history (number of uses, usage time) of each component of the image forming unit 31, information on the paper type, and the like. The ambient temperature and humidity can be detected by a temperature and humidity sensor (not shown) installed inside the apparatus main body. These image formation conditions set by the image control unit 110 include the transfer bias setting (output current value) to the transfer member. The image control unit 110 refers to the second VI characteristic stored in the storage unit 20, calculates the voltage that becomes a predetermined output current value set in the image formation conditions, and sets the calculated voltage as the transfer bias setting. This predetermined output current value is commonly used during the execution of one print job. In the following, similar to FIG. 4A, the transfer bias setting vt by the high-voltage power supply 81a for the primary transfer roller 32K as a representative of the member to which voltage is applied will be described.

[0063] If the determination condition of the second VI characteristic was set immediately before the start of execution of the print job of the above-mentioned "Condition 1", between steps S31 and S32, the determination process of the second VI characteristic shown in FIG. 4A is executed. Then, based on the determined and recorded latest second VI characteristic, the image formation condition setting of this step S32 is performed.

[0064] (Steps S33, S34) The image control unit 110 controls the paper feeding and conveying unit 40 to continuously feed and convey the paper S. Further, the image control unit 110 controls the image forming unit 30 to form an image on the conveyed paper S according to the image formation conditions set in step S32.

[0065] (Step S35) If the control unit 10 reaches the number of printed sheets set in the print settings and the print job ends (YES), the process ends. On the other hand, if the number of printed sheets has not been reached (NO), the control unit 10 advances the process to step S36.

[0066] (Step S36) The control unit 10 determines whether it is the first VI characteristic determination timing. FIG. 6B shows an example of a table of determination timings stored in the storage unit 20. It is the number of prints p (number of pages) since the start of the print job. In the example of FIG. 6B, it is performed at 5p for the first time, and then every 30p. This determination timing is an example and is not limited thereto. For example, there may be multiple types of tables shown in FIG. 6B, and each table may be appropriately selectable according to an instruction by the user via the operation panel 60 or the like. For example, two tables for color printing and monochrome printing may be provided. The table in FIG. 6B is applied to color printing, and for monochrome printing, another table with a lower frequency (for example, half the frequency) may also be prepared.

[0067] When the control unit 10 refers to FIG. 6B and determines that it is the first VI characteristic determination timing (YES), the process proceeds to step S37. When it determines that it is not the determination timing (NO), the process returns to step S33 and the subsequent processes are repeated.

[0068] (Step S37) The control unit 10 executes the first VI characteristic determination process. The process here will be described using the subroutine flowchart of FIG. 6C.

[0069] (Step S410) The control unit 10 acquires the second VI characteristic stored in the storage unit 20. Also, the VI characteristic determination unit 120 performs an analysis process using the acquired second VI characteristic and determines the large variation region and the small variation region. Note that this analysis process may be performed in conjunction with the determination of the second VI characteristic. In that case, only the analysis result may be acquired in step S410.

[0070] (Step S420) The VI characteristic determination unit 120 sets a plurality of levels y1 to ym of the transfer bias (voltage) to be applied. The number of levels m is one to several, preferably two or three. In the following, it is assumed that m = 3, and the number of levels of y is three, namely y1 to y3, for explanation. The output setting at each level y is determined based on the current transfer bias setting vt, that is, the transfer bias vt output during the previous image formation. This may be to set a level (geometric progression) obtained by multiplying a predetermined ratio based on the current transfer bias vt, or to add or subtract a predetermined ratio (arithmetic progression). For example, when setting to a level obtained by multiplying a predetermined ratio, the current transfer bias setting vt is set as level y1, and 0.75 times and 0.50 times thereof are set as levels y2 and y3, respectively. This ratio is merely an example, and it may be set to 1.2 times and 0.83 times, or may be set like 1.5 times and 0.67 times. In the following, levels y1, y2, and y3 are described as being set to 1.0 times (the same), 0.75 times, and 0.50 times the current transfer bias setting.

[0071] (Detection count setting processing loop: Steps S430 to S470) The VI characteristic determination unit 120 sequentially sets the number of detections according to the value of the transfer bias (voltage) of level y from level y1 to ym from step S430 to step S470. Specifically, in step S440, the VI characteristic determination unit 120 determines whether the value of level y1 belongs to a region with large fluctuations or a region with small fluctuations. In the example shown in FIG. 5, if the value of level y (each of levels y1 to y3) is equal to or less than the voltage v0 at the inflection point, the VI characteristic determination unit 120 determines that it is in a region with large fluctuations and sets the number of detections to a first value (a large number). On the other hand, if the value of level y is greater than the voltage v0, the VI characteristic determination unit 120 determines that it is in a region with small fluctuations and sets the number of detections to a second value (a small number). The first value is greater than the second value. For example, the first value is 9 times and the second value is 3 times. During the VI detection described later, the VI characteristic determination unit 120 performs current detection for the set number of detections and obtains the output current by averaging. The measurement time for one detection is the same, for example, 2 msec. For example, when the number of detections is set to 2 times, the total measurement time is 4 msec. When the number of detections is set to 9 times, the total measurement time is 18 msec.

[0072] Increasing the number of detections in the region with large fluctuations is to increase the number of detections and improve the detection accuracy because the variation during measurement is large. On the other hand, decreasing the number of detections in the region with small fluctuations is because the variation during measurement is small, so a certain level of detection accuracy can be maintained even with a small number of detections, and the detection time can be shortened to ensure productivity. Note that in the description here, an example of setting the number of detections according to whether the region to which the level belongs is either a region with large fluctuations or a region with small fluctuations is shown, but it is not limited to this. The VI characteristic determination unit 120 may set the detection time instead of setting the number of detections.

[0073] (Step S480) If it is the timing between images or between sheets, the control unit 10 proceeds to step S510.

[0074] (Detection processing loop: steps S510 to S540) The VI characteristic determination unit 120 sequentially outputs a transfer bias (voltage) corresponding to the levels y1 to ym from step S510 to step S540 by the high-voltage power supply 81a, applies it to the primary transfer roller 32, and detects the current at that time by the ammeter 82a. The number of detections at this time is the number of detections set in steps S430 to S470. Since it is performed between sheets of paper, in the first VI characteristic determination process, the time constraint is stricter than in the above-described second VI characteristic determination process. Therefore, the VI characteristic determination unit 120 shortens the detection time while ensuring the detection accuracy by performing the set number of detections. Then, the VI characteristic determination unit 120 records the average current obtained by averaging the measurement values of the set number of detections in association with the output value of the transfer bias (step S530).

[0075] FIG. 7 is a schematic diagram showing VI detection performed between sheets of paper. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the output of the transfer bias (voltage). Before time t0 is the image formation area of the previous page, and after time t9 is the image formation area of the next page. The period between time t0 and time t9 corresponds to between images or between sheets of paper. The length from time t0 to t9 is 50 to 100 msec, for example, 80 msec. The periods from time t0 to t1 and from time t8 to t9 are work prohibited areas. The periods from time t0 to t1, from time t3 to t4, and from time t5 to t6 are periods during which transfer biases of levels y1, y2, and y3 are applied. Hereinafter, it will be described on the assumption that the switching time between adjacent detections is almost zero and can be ignored, and the length of the applied period is the same as the detection time. In the example shown in FIG. 7, for levels y1 and y2, the number of detections is set to the second value (for example, 2 times, a total of 4 msec) in step S460. Also, for level y3, the number of detections is set to the first value (for example, 9 times, a total of 18 sec) in step S450. Level y1 is the same voltage V1 as the transfer bias setting (V1) of the previous page. The voltage v2 of level y2 is 0.75 times the voltage v1, and the voltage v3 of level 3 is 0.50 times the voltage v1. This ratio is stored in the storage unit 20 in advance. The periods from time t2 to t3 and from time t4 to t5 are transition periods of the transfer bias output.

[0076] As shown in FIG. 7, at the applied voltage v3 at the level y3, since it belongs to a region with large fluctuations, the output period and the measurement time are set long. On the other hand, for the applied voltages v1 and v2 at the other levels y1 and y2, since they belong to a region with small fluctuations, the output period and the measurement time are set short.

[0077] (Step S550) The VI characteristic determination unit 120 determines the first VI characteristic based on the applied voltage and the detected current (average current) at each level from level y1 to level ym through the processing from step S510 to step S540. FIG. 8 is an example of the determined first VI characteristic. FIG. 9 is another example of the determined first VI characteristic. Thus, the control unit 10 ends the processing of FIG. 6C and returns to the processing of FIG. 6A.

[0078] (Step S38) Here, the VI characteristic determination unit 120 updates the transfer bias setting vt in the procedure described below from the obtained first VI characteristic, and repeats the processing below step S33. In step S34 for performing image formation on the next page, the VI characteristic determination unit 120 performs image formation with the updated transfer bias setting vt.

[0079] (Update procedure for transfer bias setting vt) In the examples of FIGS. 8 and 9, the average values i1, i2, and i3 of each level v1, v2, and v3 are plotted, and two adjacent plots are connected by a straight line. As shown in FIG. 8, if a predetermined output current value i4 set under the image formation conditions of step S32 is between i1 and i2, the voltage value v4 when i4 flows is calculated from the straight line calculated from the two points (i1, v1) and (i2, v2). The voltage value v4 is the updated transfer bias setting vt. Also, as shown in FIG. 9, if a predetermined output current value i4 set under the image formation conditions of step S32 is between i2 and i3, the voltage value v4 when i4 flows is calculated from the straight line calculated from the two points (i2, v2) and (i3, v3). The transfer bias setting vt (= v4) calculated in this way is reflected as the image formation conditions at the time of image formation on the next page. In the example shown in FIG. 7, after the time t7 between images, it is changed to the updated transfer bias setting vt (v4) and applied.

[0080] As described above, in this embodiment, the image forming apparatus includes a control unit that determines the first voltage-current characteristic of the member to which voltage is applied based on the detected current when a voltage of one or more levels is applied. The control unit controls the detection time or the number of detections for detecting the detected current by applying a voltage of a level according to the voltage level to be applied. Alternatively, as another embodiment, the image forming apparatus uses a constant current power supply and a voltmeter as the transfer bias application unit 80, and has a control unit that determines the first voltage-current characteristic of the member to which voltage is applied based on the detected voltage when a current of one or more levels is applied. The control unit controls the detection time or the number of detections for detecting the detected voltage by applying a current of a level according to the current level to be applied. In this embodiment and another embodiment, by doing so, even when there are restrictions on the detection time, such as between images, the VI characteristic can be accurately determined in a short time.

[0081] (Modification example) FIG. 10 is a subroutine flowchart showing the VI characteristic determination process of step S37 in FIG. 6A in the modification example. In the modification example, the configuration other than the process shown in FIG. 10 is the same as that of the first embodiment described with reference to FIGS. 1 to 6A, and the description thereof is omitted.

[0082] (Steps S402 to S404) Same as steps S410 and S420 in FIG. 6C, and the description thereof is omitted.

[0083] (Step S406) The VI characteristic determination unit 120 determines whether the second VI characteristic acquired in step S402 is non-linear or linear. For example, the VI characteristic determination unit 120 calculates the coefficient of determination (the square value of the correlation coefficient r) with the linear function of the detection data at a plurality of levels, and determines that it is linear when the coefficient of determination is close to 1 (for example, 0.8 or more), and determines that it is non-linear when the coefficient of determination is low (less than 0.8). When the VI characteristic determination unit 120 determines that the second VI characteristic is non-linear, the process proceeds to step S430. On the other hand, when the VI characteristic determination unit 120 determines that the second VI characteristic is linear, the process proceeds to step S408.

[0084] (Step S408) The VI characteristic determination unit 120 sets the detection times at all levels y1 to ym to the same third value. For example, the third value is the number of times between the first value and the second value.

[0085] (Steps S430 to S550) The processing here is the same as steps S430 to S550 in FIG. 6C, and the description thereof is omitted. In the detection time setting processing loop of steps S430 to S470, when the second VI characteristic is non-linear, the VI characteristic determination unit 120 assigns a large number of detection times to level y when the output of level y is in a region with large fluctuations. Further, when the second VI characteristic is non-linear, the VI characteristic determination unit 120 assigns a small number of detection times to level y when the output of level y is in a region with small fluctuations.

[0086] (Other Modification Examples) The configuration of the image forming apparatus 1000 described above has described the main configuration in explaining the features of the above embodiment, and is not limited to the above configuration, and various modifications can be made within the scope of the claims. Further, it does not exclude the configuration provided in a general image forming apparatus.

[0087] For example, if the time between images (between sheets of paper) is short and the number of detections and detection time from level y1 to ym cannot be assigned to one image interval, it may be divided and assigned to two or more image intervals. For example, when dividing into two image intervals, the VI characteristic determination unit 120 performs a detection at level 3 in the first image interval between 30p and 31p, and performs detections at levels 1 and 2 in the next second image interval between 31p and 32p to determine the first VI characteristic. Then, 32p performs image formation with the transfer bias setting vt (v4) updated based on the first VI characteristic.

[0088] The means and methods for performing various processes in the image forming apparatus according to the above-described embodiment can be realized by either a dedicated hardware circuit or a programmed computer. The above program may be provided by a computer-readable recording medium such as a USB memory or a DVD (Digital Versatile Disc)-ROM, or may be provided online via a network such as the Internet. In this case, the control program recorded on the computer-readable recording medium is usually transferred and stored in a storage unit such as a hard disk.

Explanation of Signs

[0089] 1000 Image forming apparatus 10 Control unit 110 Image control unit 120 VI characteristic determination unit 20 Storage unit 30 Image forming unit 31, 31Y, 31M, 31C, 31K Image forming unit 311 Photoconductor drum 32, 32Y, 32M, 32C, 32K Primary transfer roller 33 Intermediate transfer belt 34 Secondary transfer roller 40 Paper feeding and conveying unit 60 Operation panel 80 Bias application unit 81, 81a, 81b High-voltage power supplies 82, 82a, 82b Ammeters 90 Communication I / F

Claims

1. An image forming apparatus that forms an image by an electrophotographic process, comprising: a member to which a voltage or current is applied; an applying unit that applies a voltage or current to the member to which voltage or current is applied; a detecting unit that detects a detected current or a detected voltage obtained through the member to which voltage or current is applied when the applying unit applies a voltage or current to the member to which voltage or current is applied; a control unit that determines a first voltage-current characteristic of the member to which voltage or current is applied based on the detected current or the detected voltage detected by the detecting unit when the applying unit applies a voltage or current at one or more levels; and the control unit controls a detection time or a number of detections when detecting the detected current or the detected voltage by applying the voltage or current at the level according to the level of the voltage or current to be applied, the image forming apparatus.

2. A second voltage-current characteristic of the member to which voltage or current was applied in the past, obtained from the detected current or the detected voltage when applying voltages or currents at a plurality of levels, is recorded; the control unit determines, based on the second voltage-current characteristic, whether the level of the voltage or current applied by the applying unit is in a region where the variation in the detected current or the detected voltage is large with respect to the variation in the voltage or current, and in a region where the variation is large, the control unit lengthens the detection time or increases the number of detections, the image forming apparatus according to claim 1.

3. The application of the voltage or current at one or more levels by the applying unit and the detection of the detected current or the detected voltage when determining the first voltage-current characteristic are performed between sheets of paper or between images of a print job, the image forming apparatus according to claim 2.

4. The second voltage-current characteristic is obtained by applying voltages or currents at a plurality of levels and detecting the detected current or the detected voltage before the start of execution of a print job or by interrupting a print job in execution, the image forming apparatus according to claim 2 or claim 3.

5. When the second voltage-current characteristic is linear, the detection time or the number of detections is set to be the same for any of the plurality of levels, the image forming apparatus according to claim 2.

6. When the second voltage-current characteristic is non-linear, the control unit lengthens the detection time or increases the number of detections in a region where the level of the current is such that the variation in the detected current or the detected voltage is large with respect to the variation in the voltage or current up to the voltage applied by the applying unit, the image forming apparatus according to claim 2.

7. When the second voltage-current characteristic is non-linear, the control unit shortens the detection time or reduces the number of detections in a region where the level of the current is small with respect to fluctuations in the voltage or current up to the voltage applied by the application unit, for fluctuations in the detected current or detected voltage, in the image forming apparatus according to claim 2.

8. The application of the voltage or current at one or more levels by the application unit and the detection of the detected current or detected voltage when determining the first voltage-current characteristic are performed between sheets of paper or between images of a print job, the level is set based on the value of the voltage or current applied to the member to be applied immediately before the previous image formation, in the image forming apparatus according to claim 2.

9. The member to be applied is composed of a plurality of layers having different layer resistances, in the image forming apparatus according to claim 1.

10. The member to be applied is an intermediate transfer belt on which a toner image developed on a photoreceptor drum is transferred, or a primary transfer member, in the image forming apparatus according to claim 1.

11. The member to be applied is a transfer member that transfers a toner image from an image carrier carrying the toner image to a recording medium, in the image forming apparatus according to claim 1.

12. a member to which a voltage or current is applied, an application unit that applies a voltage or current to the member to be applied, a detection unit that detects a detected current or detected voltage obtained through the member to be applied when the application unit applies a voltage or current to the member to be applied, and a method for determining the voltage-current characteristic of the member to be applied, which is executed in an image forming apparatus that forms an image by an electrophotographic process, having a step (a) of determining the first voltage-current characteristic of the member to be applied based on the detected current or detected voltage detected by the detection unit when the application unit applies a voltage or current at one or more levels, in the step (a), according to the level of the voltage or current to be applied, controlling the detection time or the number of detections when detecting the detected current or detected voltage by applying the voltage or current at the level, a determination method.

13. a member to which a voltage or current is applied, an application unit that applies a voltage or current to the member to be applied, a detection unit that detects a detected current or detected voltage obtained through the member to be applied when the application unit applies a voltage or current to the member to be applied, and a control program that is executed in an image forming apparatus that forms an image by an electrophotographic process, Step (a) of determining the first voltage-current characteristic of the member to which voltage or current is applied based on the detected current or detected voltage detected by the detection unit when one or more levels of voltage or current are applied by the applying unit; In step (a), a control program for executing a process of controlling the detection time or the number of detections when detecting a detected current or a detected voltage by applying the voltage or current of the level according to the level of the voltage or current to be applied.

Images