Image forming apparatus and transfer bias control method

Abstract

To prevent the occurrence of a transfer failure in a transfer unit on the upstream side in the time of adjustment of a transfer bias of the transfer unit of an adjustment target.SOLUTION: An image formation apparatus (1) comprises: a plurality of image carriers (22K, 22Y, 22M, 22C); a plurality of transfer units (40K, 40Y, 40M, 40C); a transfer voltage generation unit (75) which applies a transfer bias to each of the plurality of transfer units; and a control unit (90). The control unit, when receiving a command of adjustment of the first transfer bias being the transfer bias to be applied to the transfer unit of the adjustment target in the plurality of transfer units (40K, 40Y, 40M, 40C), executes the first adjustment which increases or decreases an absolute value of the first transfer bias on the basis of the content of the command, and executes the second adjustment which increases or decreases an absolute value of the second transfer bias being the transfer bias to be applied to the transfer unit on the upstream side of the transfer unit of the adjustment target on the basis of the content of the command.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] This disclosure relates to an image forming apparatus and a method for controlling transfer bias. [Background technology]

[0002] Conventionally, in image forming apparatuses, multiple toner images formed on multiple photosensitive drums are sequentially transferred onto the printing medium by a transfer bias applied to multiple transfer units (e.g., multiple transfer rollers) to form a color image consisting of multiple toner images on the printing medium. Since the appropriate transfer bias applied to each color transfer roller differs depending on the type of printing medium, the image forming apparatus allows the user to change the value of the transfer bias applied to each color transfer roller. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2005-077598 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in conventional image forming apparatuses, if a user changes the transfer bias of one of the multiple transfer sections to be adjusted, this can cause transfer defects in other transfer sections (especially those upstream of the one being adjusted). Therefore, there was a problem in properly adjusting the transfer bias.

[0005] This disclosure aims to prevent the occurrence of transfer failures in other transfer regions when adjusting the transfer bias of a transfer region that is being adjusted. [Means for solving the problem]

[0006] The image forming apparatus of the present disclosure comprises: a plurality of image carriers arranged in the transport direction of a printing medium and each carrying a plurality of developer images; a plurality of transfer units arranged opposite to the plurality of image carriers and sequentially transferring the plurality of developer images onto the printing medium by a transfer bias; a transfer voltage generation unit that applies the transfer bias to each of the plurality of transfer units; and a control unit that controls the transfer voltage generation unit. When the control unit receives a command to adjust a first transfer bias, which is the transfer bias applied to a transfer unit to be adjusted among the plurality of transfer units, it determines a first adjustment amount based on the content of the command using adjustment amount information stored in advance in a storage unit, performs a first adjustment to the absolute value of the first transfer bias using the first adjustment amount, determines a second adjustment amount based on the content of the command using the adjustment amount information, and applies the transfer bias to the transfer unit upstream of the transfer unit to be adjusted using the second adjustment amount. The This method is characterized by performing a second adjustment to the absolute value of the transcription bias. [Effects of the Invention]

[0007] The image forming apparatus and transfer bias control method disclosed herein have the effect of preventing the occurrence of transfer defects in other transfer parts when adjusting the transfer bias of the transfer part to be adjusted. [Brief explanation of the drawing]

[0008] [Figure 1] This is a longitudinal cross-sectional view schematically showing the configuration of an image forming apparatus according to an embodiment. [Figure 2] This is a block diagram showing the configuration of the control system of the image forming apparatus according to the embodiment. [Figure 3] This figure shows the items in the transfer bias adjustment menu for the image forming apparatus according to the embodiment. [Figure 4] This figure shows an example of a basic table for transcription bias. [Figure 5] This figure shows an example of a transfer bias adjustment table for high-resistance printing media. [Figure 6]It is a diagram showing an example of a transfer bias adjustment amount table for a low-resistance printing medium. [Figure 7] (A) is a diagram showing an attenuation curve of the amount of charge charged on the printing medium, and (B) is a diagram showing the time change of the amount of charge charged on the printing medium in tabular form. [Figure 8] It is a flowchart specifically showing the calculation process of the transfer bias in the image forming apparatus according to the embodiment.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an image forming apparatus according to an embodiment and a transfer bias control method implemented by the image forming apparatus will be described with reference to the drawings. The following embodiments are merely examples, and various modifications are possible within the scope of the present disclosure. In the following description, an example in which the developer (that is, toner) supplied onto the photosensitive drum as an image carrier is a negatively charged developer that is negatively charged will be described. However, the present invention is also applicable to an image forming apparatus in which the developer supplied onto the photosensitive drum is a positively charged developer that is positively charged.

[0010] 《Configuration of Image Forming Apparatus 1》 FIG. 1 is a longitudinal sectional view schematically showing the configuration of an image forming apparatus 1 according to an embodiment. FIG. 2 is a block diagram showing the configuration of the control system of the image forming apparatus 1. The image forming apparatus 1 is, for example, a color printer that forms an image on a printing medium using an electrophotographic method. Inside the image forming apparatus 1, a plurality of image forming units 20K, 20Y, 20M, 20C, which are four independent printing mechanisms corresponding to black (K), yellow (Y), magenta (M), and cyan (C), are arranged in a line in the conveyance direction D1 of the printing medium by a transfer belt 50 that is an endless belt. The transfer belt 50 is also called a conveyance belt.

[0011] Each of the image forming units 20K, 20Y, 20M, and 20C is also called an image drum (ID) unit. The image forming unit 20K is a printing mechanism that forms a black developer image (toner image), the image forming unit 20Y is a printing mechanism that forms a yellow toner image, the image forming unit 20M is a printing mechanism that forms a magenta toner image, and the image forming unit 20C is a printing mechanism that forms a cyan toner image. Note that the number of image forming units is not limited to four. Also, the order of arrangement of the image forming units 20K, 20Y, 20M, and 20C is not limited to that in the example of FIG. 1. Further, the colors of the developers used by the image forming units 20K, 20Y, 20M, and 20C are not limited to black, yellow, magenta, and cyan.

[0012] The structures of the image forming units 20K, 20Y, 20M, and 20C are the same or similar to each other except for the color of the toner they contain. The image forming units 20K, 20Y, 20M, and 20C each have charging rollers 21K, 21Y, 21M, and 21C as charging members and photosensitive drums 22K, 22Y, 22M, and 22C as image carriers whose surfaces are uniformly charged by the charging rollers 21K, 21Y, 21M, and 21C. Also, the image forming units 20K, 20Y, 20M, and 20C each have developing rollers 23K, 23Y, 23M, and 23C, developing blades 24K, 24Y, 24M, and 24C, supply rollers 25K, 25Y, 25M, and 25C, cleaning blades 26K, 26Y, 26M, and 26C, and toner cartridges 27K, 27Y, 27M, and 27C. The developing rollers 23K, 23Y, 23M, and 23C, the developing blades 24K, 24Y, 24M, and 24C, and the supply rollers 25K, 25Y, 25M, and 25C constitute a developing unit that supplies toner onto the photosensitive drums 22K, 22Y, 22M, and 22C.

[0013] Toner supplied from toner cartridges 27K, 27Y, 27M, and 27C into the toner storage section is strongly rubbed against the supply rollers 25K, 25Y, 25M, and 25C and the developer rollers 23K, 23Y, 23M, and 23C, thereby becoming triboelectrically charged. The toner is supplied to the developer rollers 23K, 23Y, 23M, and 23C via the supply rollers 25K, 25Y, 25M, and 25C, where it is thinned on the developer rollers 23K, 23Y, 23M, and 23C by the developer blades 24K, 24Y, 24M, and 24C, and then carried to the contact area with the photosensitive drum 22K, 22Y, 22M, and 22C.

[0014] LED (light-emitting diode) heads 30K, 30Y, 30M, and 30C are arranged on the photosensitive drum 22 of the image forming units 20K, 20Y, 20M, and 20C, which serve as print heads. The print head is also called an exposure device. The LED heads 30K, 30Y, 30M, and 30C each have an LED array, a substrate equipped with a drive IC for driving the LED array and a group of registers for data retention, and an erect, 1:1 imaging lens array for focusing the light emitted from the LED array. The LED head 30K, 30Y, 30M, and 30C emit light according to the image data input from the interface unit 91 (Figure 2). The print head is not limited to the LED heads 30K, 30Y, 30M, and 30C, but may also be a light-emitting thyristor head using a light-emitting thyristor array, or a laser scanning optical system equipped with a semiconductor laser, etc.

[0015] The LED heads 30K, 30Y, 30M, and 30C of the image forming units 20K, 20Y, 20M, and 20C receive the black, magenta, yellow, and cyan image data from the color image data, respectively. In the image forming units 20K, 20Y, 20M, and 20C, the uniformly charged surface of the photosensitive drums 22K, 22Y, 22M, and 22C is exposed by the light emitted from the LED heads 30K, 30Y, 30M, and 30C, and an electrostatic latent image is formed on the surface of the photosensitive drums 22K, 22Y, 22M, and 22C.

[0016] The toner on the developing rollers 23K, 23Y, 23M, and 23C moves onto the photosensitive drums 22K, 22Y, 22M, and 22C by electrostatic force, forming a toner image corresponding to the electrostatic latent image. The toner cartridges 27K, 27Y, 27M, and 27C contain black, cyan, magenta, and yellow toner, respectively. Below the photosensitive drums 22K, 22Y, 22M, and 22C of the image forming units 20K, 20Y, 20M, and 20C, the transfer rollers 40K, 40Y, 40M, and 40C are positioned as transfer sections, sandwiching the transfer belt 50. The transfer rollers 40K, 40Y, 40M, and 40C are pressed against the photosensitive drums 22K, 22Y, 22M, and 22C, sandwiching the transfer belt 50, forming a transfer nip section. The toner image formed on the photosensitive drums 22K, 22Y, 22M, and 22C is transferred to the printing medium, such as paper, at the transfer nip. The transfer rollers 40K, 40Y, 40M, and 40C are also referred to as transfer roller 40.

[0017] The transfer belt 50 is stretched with a predetermined tension by a drive roller 51 and a driven roller 52. The drive roller 51 is rotated by a belt motor 83 (Figure 2), moving the transfer belt 50 and transporting the printing medium in the transport direction D1. The driven roller 52 rotates along with the transfer belt 50. The transfer belt 50 has a glossy surface and is used as a reference reflector for adjusting the light emission current of the infrared LED of the density sensor 53.

[0018] The lower part of the housing of the image forming apparatus 1 is equipped with a storage cassette 11 for storing printing media (e.g., paper media, resin film, etc.) supplied to the transport path, a hopping roller 12 for feeding out the printing media one sheet at a time from the storage cassette 11, registration rollers 13 and 14 for correcting the skew (i.e., the state of being fed at an angle) of the printing media, a guide 15 for guiding the printing media to the transfer belt 50, and media sensors 16 and 17 for detecting the printing media.

[0019] Downstream of the transfer belt 50 (i.e., on the left side in Figure 1), an ejection sensor 18 is provided for detecting when the printing medium has not been properly separated from the transfer belt 50, or for detecting the position of the trailing end of the paper that has passed through.

[0020] The printing medium, having passed through the transfer belt 50 and formed with toner, is separated from the transfer belt 50 and transported to the fuser 60.

[0021] The fuser 60 includes a heat roller 61 and a pressure roller 62. The heat roller 61 is driven by a heater motor 84 (Figure 2), and the pressure roller 62 rotates in conjunction with the heat roller 61. The heat roller 61 incorporates a heater 61a (Figure 2), which consists of a halogen lamp that functions as a heat source. The fuser 60 heats and melts the toner image on the printing medium, fixing the toner image onto the printing medium. A fuser thermistor 64 is positioned near the surface of the heat roller 61 to monitor its temperature.

[0022] Downstream of the fuser 60, a medium sensor 65 is provided to detect the printing medium and monitor whether a jam occurs in the fuser 60 or if the paper becomes entangled with the heat roller 61. Downstream of the medium sensor 65, a guide 66 is provided to transport the printing medium to the stacker 67 on the top of the housing of the image forming apparatus 1. The printed medium, on which the image has been formed and fixed, is discharged onto the stacker 67.

[0023] A cleaning blade 55 is positioned below the transfer belt 50 to remove any toner remaining on the transfer belt 50. The cleaning blade 55 is made of a flexible rubber or plastic material and contacts the transfer belt 50 to scrape off the toner on it. The scraped-off toner is collected in the waste toner storage section 56.

[0024] Furthermore, a concentration sensor 53 is positioned below the transfer belt 50, opposite the transfer belt 50. The concentration sensor 53 is used to detect the concentration of the concentration detection pattern by measuring the intensity of the reflected light from the concentration detection pattern transferred onto the transfer belt 50.

[0025] In Figure 2, the operation unit 95 consists of, for example, a display panel for checking the status and various settings of the image forming apparatus 1, and operation buttons for changing various settings. The operation unit 95 may also be a touch panel. The various setting menus include a "Printing Medium Type" menu for setting the type of printing medium used for printing images (also called "Paper Type"), and a "Transfer Bias Adjustment" menu for setting the amount of transfer bias adjustment. In the "Printing Medium Type" menu, options are displayed for the user to select the type of printing medium, such as "Plain Paper" and "Film". Film is, for example, a sheet made of resin. The type of printing medium is not limited to "Plain Paper" and "Film". Also, the type of printing medium is not limited to just two types.

[0026] Figure 3 shows the items in the transfer bias adjustment menu in the image forming apparatus 1. The "Transfer Bias Adjustment" menu is a menu item that allows the user to change the transfer bias for each color in order to adjust the transfer bias when the user is dissatisfied with the print result of the color to be adjusted (including when the print result is abnormal) after viewing the print result. As shown in Figure 3, when the "Transfer Bias Adjustment" menu is selected, toner color information is displayed so that the menus "Black," "Yellow," "Magenta," and "Cyan" can be selected. When the menu for each color is selected, the transfer bias selection values ​​of "-2," "-1," "0," "+1," and "+2" (-2 is the minimum transfer bias, and +2 is the maximum transfer bias) can be selected. In this embodiment, the amount of transfer bias adjustment is determined by referring to the transfer bias table recorded in the memory 94a, which is a storage unit in the mechanism control unit 94, based on the settings in the "Type of Printing Medium" menu and the settings in the "Transfer Bias Adjustment" menu. However, it is also possible to use the storage device of a server on a network that can communicate with the image forming apparatus 1 as the storage unit.

[0027] The interface unit 91 is the interface unit with the host computer and consists of a connector and a communication chip. The command / image processing unit 92 is the part that expands commands and image data from the host side into a bitmap and consists of a microprocessor (not shown), RAM (random access memory), and hardware for expansion, and controls the entire image forming apparatus 1. The LED head interface unit 93 processes the image data expanded into a bitmap from the command / image processing unit 92 to match the interface of the LED heads 30K, 30Y, 30M, and 30C.

[0028] The mechanism control unit 94 drives the hopping motor 81, resist motor 82, belt motor 83, heater motor 84, and drum motor 85 according to commands from the command / image processing unit 92, and rotates the hopping roller 12, resist roller 14, drive roller 51, heat roller 61, and photosensitive drums 22K, 22Y, 22M, and 22C corresponding to each motor. The mechanism control unit 94 also controls the heater 61a and the high-voltage control unit 71 according to commands from the command / image processing unit 92. The command / image processing unit 92 and the mechanism control unit 94 constitute the control unit 90 that controls the operation of the entire device.

[0029] The high-voltage control unit 71 generates charging voltage, developing voltage, supply voltage, and transfer voltage for the image forming units 20K, 20Y, 20M, and 20C. The charging voltage generation unit 72 generates and stops charging voltage for the charging rollers 21K, 21Y, 21M, and 21C. The developing voltage generation unit 73 generates and stops developing voltage for the developing rollers 23K, 23Y, 23M, and 23C. The supply voltage generation unit 74 generates and stops supply voltage for the supply rollers 25K, 25Y, 25M, and 25C. The transfer voltage generation unit 75 generates and stops transfer voltage for the transfer rollers 40K, 40Y, 40M, and 40C. In this embodiment, a high-voltage power supply with a maximum output of 5000[V] is used as the transfer voltage generation unit 75.

[0030] Figure 4 shows an example of the basic transfer bias table 101. Figure 5 shows an example of the transfer bias adjustment amount table 102 for high-resistance printing media, and Figure 6 shows an example of the transfer bias adjustment amount table 103 for low-resistance printing media. The memory 94a of the mechanism control unit 94 stores the basic table 101 and the adjustment amount tables 102 and 103 as transfer bias tables, which are information used to calculate the transfer bias. The values ​​in the basic transfer bias table 101 in Figures 4 to 6 are determined from experiments to be appropriate for each printing medium.

[0031] When image data is transmitted from the host computer to the command / image processing unit 92 via the interface unit 91, the printing operation of the image forming apparatus 1 begins. When the image data is processed in the command / image processing unit 92, the motors and other components are driven to transport the printing medium and toner images are formed by the image forming units 20K, 20Y, 20M, and 20C. Once the toner image formation operation begins, the calculation of the transfer bias begins, and the command / image processing unit 92 controls the transfer voltage generation unit 75 to apply the calculated transfer bias to each transfer roller 40K, 40Y, 40M, and 40C in accordance with the timing when the printing medium reaches the transfer nip of each color.

[0032] For example, a high-resistance printing medium is a printing medium whose volume resistivity is greater than or equal to a predetermined threshold Rt, and a low-resistance printing medium is a printing medium whose volume resistivity is less than the threshold Rt. The threshold Rt could be, for example, 1.0 × 10⁻⁶. 12 It is possible to use [Ω·cm]. However, the value of the threshold Rt is not limited to this value.

[0033] High-resistance printing media include, for example, media containing resin films. Specific examples of high-resistance printing media are (H1) to (H4) below. (H1) Type: "Waterproof paper", Product name: "Laser Peach WETY-145", Manufacturer: "Daioh Miura", Volume resistivity (measured value): "1.9 × 10 16 [Ω·cm]", Material: Polyester film (H2) Type: "Waterproof paper", Product name: "Lamifree", Manufacturer: "Nakagawa Seisakusho", Volume resistivity (measured value): "5.7 × 10 14 [Ω·cm]", Material: "Film laminated onto base paper" (H3) Type: "Waterproof paper", Product name: "Kareka", Manufacturer: "International Paper & Pulp Trading Co., Ltd.", Volume resistivity (measured value): "8.2 × 10 14 [Ω·cm]", Material: "Film laminated onto base paper" (H4) Type: "OHP (overhead projector sheet)", Product name: "CG3500", Manufacturer: "3M", Volume resistivity (measured value): "1.2 × 10⁻¹⁰15 [Ω·cm], material "film"

[0034] The low-resistance printing medium is, for example, a paper medium. Specific low-resistance printing media include the following (L1) and (L2). (L1) Type "plain paper", product name "Excellent White", manufacturer "OKI", volume resistivity (measured value) "3.5×10 10 [Ω·cm], material "polyester film" (L2) Type "plain paper", product name "Excellent Paper", manufacturer "OKI", volume resistivity (measured value) "2.5×10 11 [Ω·cm], material "film laminated to base paper"

[0035] By applying a transfer bias to the printing medium, the state in which the charge accumulated in the printing medium leaks out can be considered by the time constant τ determined by the electrical resistance and the capacitance component. The charge amount Q of the charge accumulated in the printing medium is expressed by the following formula (1). Q = Q0·e (-t / τ) …(1) Here, Q is the charge amount [C], Q0 is the initial charge amount [C], t is the elapsed time [s], and τ is the time constant [s].

[0036] When R is the resistance value [Ω], C is the capacitance [F], ρ is the volume resistivity [Ω·cm], and ε is the dielectric constant [F / cm], the time constant τ is expressed by the following formula (2). τ = RC = ρε …(2) Here, the dielectric constant of vacuum ε0 = 8.85×10 -12 [F / m] and the relative dielectric constant ε of paper c are assumed to be about 2, then generally ε = ε0×ε c ≒1×10 -11 [F / m] = 1×10 -13 (=1E - 13)[F / cm] is obtained.

[0037] When the volume resistivity ρ [Ω·cm] is 10 11 (=1E + 11), 1012 In the case of (=1E+12), 10 13 In the case of (=1E+13), 10 14 Figures 7(A) and (B) show the results of calculating Q in equation (1) for each of the cases (=1E+14) (where Q0=1). From Figures 7(A) and (B), it can be seen that the lower the volume resistivity ρ[Ω·cm] of the printing medium, the faster the charge Q decays. Here, assuming that the transport speed of the printing medium is 100[mm / s] and the distance (spacing) between the color to be adjusted, the transfer roller and the transfer roller of the downstream color is 100[mm], if there is still charge remaining in the printing medium at the following elapsed time ta[s], adjusting the transfer bias of the transfer roller to be adjusted will easily affect the transfer bias of other transfer rollers. ta = (100 [mm]) / (100 [mm / s]) = 1 [s] Therefore, the threshold Rt, which is the boundary value for determining whether a printing medium is a high-resistance printing medium or a low-resistance printing medium, can be, for example, 1.0 × 10⁻⁶. 12 It is possible to use [Ω·cm].

[0038] Operation of the Embodiment In Embodiment 1, when the control unit 90 receives a command to adjust the transfer bias to be adjusted (first transfer bias), which is the transfer bias applied to the transfer roller to be adjusted among the plurality of transfer rollers 40K, 40Y, 40M, and 40C, it performs a first adjustment to increase or decrease the absolute value of the transfer bias to be adjusted based on the content of the command, and performs a second adjustment to increase or decrease the absolute value of the second transfer bias, which is the transfer bias applied to the transfer roller upstream of the transfer section to be adjusted (for example, the nearest upstream transfer roller), based on the content of the command.

[0039] For example, when the control unit 90 receives a command to adjust the transcription bias, it uses a table of adjustment amount information (Figures 4 to 6) pre-stored in the memory 94a as a storage unit to determine a first adjustment amount based on the content of the command, performs a first adjustment on the absolute value of the first transcription bias using the first adjustment amount, determines a second adjustment amount based on the content of the command using the adjustment amount information, and performs a second adjustment on the absolute value of the second transcription bias using the second adjustment amount.

[0040] Furthermore, the control unit 90 may receive type information indicating the type of printing medium, and based on the type information, select target adjustment amount information from a plurality of tables (for example, adjustment amount tables 102, 103) which are a plurality of adjustment amount information stored in advance in memory 94a, and when it receives a command, it may use the target adjustment amount information to determine a first adjustment amount based on the content of the command, and use the first adjustment amount to perform a first adjustment on the absolute value of the first transfer bias, and use the target adjustment amount information to determine a second adjustment amount based on the content of the command, and use the second adjustment amount to perform a second adjustment on the absolute value of the second transfer bias.

[0041] For example, the control unit 90 receives type information indicating the type of printing medium, and if this type is a high-resistance printing medium having a volume resistivity of a predetermined value or more and the absolute value of the first transfer bias is increased in the first adjustment, it can control the absolute value of the second transfer bias in the second adjustment. If the type is a low-resistance printing medium having a volume resistivity of less than a predetermined value and the absolute value of the first transfer bias is increased in the first adjustment, it can control the absolute value of the second transfer bias in the second adjustment.

[0042] Furthermore, the control unit 90 receives type information indicating the type of printing medium, and if the printing medium is a medium containing a resin film and the absolute value of the first transfer bias is increased in the first adjustment, it can control the system to decrease the absolute value of the second transfer bias in the second adjustment. If the printing medium is a paper medium and the absolute value of the first transfer bias is increased in the first adjustment, it can control the system to increase the absolute value of the second transfer bias in the second adjustment.

[0043] Next, the operation of Embodiment 1 will be described in more detail. Figure 8 is a flowchart that specifically shows the calculation process of the transfer biases V(K), V(Y), V(M), and V(C) in the image forming apparatus 1.

[0044] When the image forming apparatus 1 receives image data and starts printing (step S1), the command / image processing unit 92 of the control unit 90 checks the setting of the "Type of Printing Medium" menu, which has been pre-set by the user on the operation unit 95 (step S2). Note that the setting of the type of printing medium may also be performed by the printer driver when the image data is transmitted.

[0045] Next, the command / image processing unit 92 checks the settings in the "Type of Print Media" menu, refers to the basic transfer bias table 101 in Figure 4, and determines the transfer bias of each color before the adjustment amount in the transfer bias adjustment menu is applied (step S3).

[0046] In this embodiment, when plain paper is selected as the "Type of Printing Medium" in the "Type of Printing Medium" menu settings, the basic transfer bias V0(K) for the black transfer roller 40K is set to V0(K)=2000[V], the basic transfer bias V0(Y) for the yellow transfer roller 40Y is set to V0(Y)=2200[V], the basic transfer bias V0(M) for the magenta transfer roller 40K is set to V0(M)=2400[V], and the basic transfer bias V0(C) for the cyan transfer roller 40C is set to V0(C)=2600[V]. However, these voltage values ​​are merely examples, and the basic transfer bias is not limited to these values.

[0047] Furthermore, when "Film" is selected as the "Type of Printing Medium" in the "Type of Printing Medium" menu settings, the basic transfer bias V0(K) for the black transfer roller 40K is set to V0(K)=3900[V], the basic transfer bias V0(Y) for the yellow transfer roller 40Y is set to V0(Y)=4300[V], the basic transfer bias V0(M) for the magenta transfer roller 40M is set to V0(M)=4700[V], and the basic transfer bias V0(C) for the cyan transfer roller 40C is set to V0(C)=5000[V]. However, these voltage values ​​are merely examples, and the basic transfer bias is not limited to these values.

[0048] The values ​​in the basic transfer bias table 101 in Figure 4 are determined through experiments to be appropriate for each printing medium. In this embodiment, the "Type of Printing Medium" menu is limited to two types: plain paper and film, but it is not limited to these two, and there may be three or more types of printing mediums. Furthermore, the basic transfer bias table 101 in Figure 4 may be different tables for each printing speed, temperature and humidity, printing medium thickness, or combinations of two or more of these conditions. In addition, the calculation of the transfer bias in this process may be performed by measuring the resistance value information of the transfer roller at the timing before the application of the transfer bias and during the pre-printing operation, and reflecting the results.

[0049] Next, the command / image processing unit 92 checks the settings of the "Type of Printing Medium" menu, which have been pre-configured by the user on the operation unit 95, and determines whether to use the transfer bias adjustment amount table for high-resistance printing medium or the transfer bias adjustment amount table for low-resistance printing medium (step S4).

[0050] In this embodiment, the image forming apparatus 1 refers to different tables for adjusting the transfer bias for each color in the "Transfer Bias Adjustment" menu, depending on whether the printing medium is high-resistance or low-resistance. In this embodiment, when the setting in the "Type of Printing Medium" menu is "Film," the transfer bias adjustment amount table 102 for high-resistance printing mediums (Figure 5) is used, and when the setting is "Plain Paper," the transfer bias adjustment amount table 103 for low-resistance printing mediums (Figure 6) is used. In this embodiment, film is used as the high-resistance printing medium, but other examples of high-resistance printing mediums include OHP sheets, water-resistant paper, synthetic paper, film labels, and synthetic paper labels. Examples of low-resistance printing mediums include plain paper, thin paper, recycled paper, envelopes, and postcards.

[0051] In this embodiment, the boundary value for volume resistivity is set such that the volume resistivity of the printing medium is approximately 1.0 × 10⁻⁶. 12 Printing media with a resistance of [Ω·cm] or higher are classified as high-resistance printing media, and those with a resistance of less are classified as low-resistance printing media. Printing media with high resistance values ​​have a slower rate at which the charge accumulated on the printing media leaves the media when a transfer bias is applied, which affects the transfer bias downstream. As will be explained in detail later, it will be necessary to change the transfer bias adjustment amount table to take into account the effect of this charge accumulation on the printing media.

[0052] Here, the characteristic of the transfer bias adjustment amount table 102 for high-resistance printing media shown in Figure 5 is that when the transfer bias of the transfer roller of the color to be adjusted is increased, the transfer bias of the transfer roller of the upstream color of the transfer roller of the color to be adjusted is decreased, and the transfer bias of the downstream color of the transfer roller of the color to be adjusted is increased. The characteristic of the transfer bias adjustment amount table 103 for low-resistance printing media shown in Figure 6 is that when the transfer bias of the transfer roller of the color to be adjusted is increased, the absolute value of the transfer bias of the upstream color of the transfer roller of the color to be adjusted is increased, and the absolute value of the transfer bias of the downstream color of the transfer roller of the color to be adjusted is increased.

[0053] Next, we will explain the procedure for determining the transfer bias when film (high-resistance printing medium) is selected in the "Type of Printing Medium" menu, and the procedure for determining the transfer bias when plain paper (low-resistance printing medium) is selected in the "Type of Printing Medium" menu.

[0054] If the printing medium to be printed is a high-resistance printing medium (film) (when "film" is selected in the "Printing Medium Type" menu), use the transfer bias adjustment amount table 102 for high-resistance printing media shown in Figure 5 (step S5).

[0055] In the transfer bias adjustment table 102 for high-resistance printing media, the setting value for the transfer roller of the color to be adjusted in the "Adjust Transfer Bias" menu is set to a negative value, which lowers the transfer bias of the transfer roller of that color. Conversely, the setting value for the transfer roller of the color to be adjusted is set to a positive value, which increases the transfer bias of the transfer roller of that color. Furthermore, when the transfer bias of the transfer roller of the color to be adjusted is increased, the upstream color of the transfer roller of the color to be adjusted is set to have a lower transfer bias, while the downstream color of the transfer roller of the color to be adjusted is set to have a higher transfer bias.

[0056] For example, if the transfer bias adjustment for magenta (M) is set to "+2", the adjustment amounts for the transfer bias will be as follows: M1 = +500[V] for magenta (M), the color being adjusted; Ym1 = -200[V] for yellow (Y) upstream of the transfer roller of the color being adjusted; and Cm1 = +250[V] for cyan (C) downstream of the transfer roller of the color being adjusted.

[0057] Here, we will explain how to adjust the transfer bias of the upstream and downstream colors of the transfer roller for the color being adjusted. With high-resistance printing media, charge accumulates on the media when a transfer bias is applied. With high-resistance printing media, the accumulated charge remains on the media until it reaches the downstream color to be transferred next, so the transfer bias required for the next transfer becomes higher. Therefore, if the transfer bias of the transfer roller for the color being adjusted is increased, the transfer bias required to properly transfer the downstream color of the transfer roller for the color being adjusted increases, so it is necessary to increase the transfer bias of the downstream color of the transfer roller for the color being adjusted.

[0058] Furthermore, high-resistance printing media require a high transfer bias for proper transfer, necessitating the use of a high-voltage power supply near its maximum output specification for applying the transfer bias. In this case, even if one attempts to increase the transfer bias using the adjustment menu, it may not be possible due to insufficient voltage. In this embodiment, since a power supply with an upper limit of 5000[V] for the transfer bias output is used, for magenta and cyan, even if the transfer bias is increased, the power supply's upper limit may be reached. To use an even higher transfer bias, a higher-spec high-voltage power supply is required, resulting in increased costs. However, as in this embodiment, by lowering the transfer bias of the color upstream of the transfer roller of the color to be adjusted, the amount of charge accumulated on the printing media can be reduced, thereby lowering the transfer bias required for the color to be adjusted.

[0059] Next, the command / image processing unit 92 checks the adjustment amount for each color in the "Transfer Bias Adjustment" menu, which has been pre-set by the user on the operation unit 95, and calculates the transfer bias adjustment amount for each color from the transfer bias adjustment amount table 103 for low-resistance printing media and the adjustment amounts in the transfer bias adjustment menu (step S6).

[0060] Furthermore, if the transfer bias adjustment menu is adjusted for multiple colors, the transfer bias adjustment amount for each color is determined by the sum of the adjustment values ​​in each table. Therefore, in the case of high-resistance printing media, the transfer bias adjustment amounts ΔV(K), ΔV(Y), ΔV(M), and ΔV(C) for each color are determined by referring to the transfer bias adjustment amount table in Figure 5, as shown in equations (3) to (6) below. ΔV(K)=K1+Ky1+Km1+Kc1…(3) ΔV(Y)=Yk1+Y1+Ym1+Yc1…(4) ΔV(M)=Mk1+My1+M1+Mc1…(5) ΔV(C)=Ck1+Cy1+Cm1+C1…(6)

[0061] Then, the transcription biases V(K), V(Y), V(M), and V(C) are determined using the following equations (7) to (10), which are the sum of the transcription bias value determined in step S3 of the transcription bias calculation flowchart in Figure 8 and the transcription bias adjustment amount determined in S7 (step S7). V(K) = V0(K) + ΔV(K) …(7) V(Y) = V0(Y) + ΔV(Y) …(8) V(M) = V0(M) + ΔV(M) …(9) V(C) = V0(C) + ΔV(C) …(10)

[0062] If the printing medium to be used is plain paper, which is a low-resistance printing medium (when plain paper is selected in the "Printing Medium Type" menu), use the transfer bias adjustment amount table 103 for low-resistance printing media shown in Figure 6 (step S8).

[0063] The transfer bias adjustment table 103 for low-resistance printing media is configured such that when the setting value of the transfer roller for the color to be adjusted is set in the "Adjust Transfer Bias" menu to a negative direction, the transfer bias of the transfer roller for the color to be adjusted becomes lower, and when the setting value of the transfer roller for the color to be adjusted is set to a positive direction, the transfer bias of the transfer roller for the color to be adjusted becomes higher. Furthermore, when the transfer bias of the transfer roller for the color to be adjusted is increased, the upstream color of the transfer roller for the color to be adjusted is set to a value that increases the transfer bias, and the downstream color of the transfer roller for the color to be adjusted is also set to a value that increases the transfer bias.

[0064] For example, if "+2" is set for adjusting the transfer bias of magenta (M), the adjustment amounts for the transfer bias are as follows: M2 = +600[V] for magenta (M), the color being adjusted; Ym2 = +200[V] for yellow (Y) upstream of the transfer roller of the color being adjusted; and Cm2 = +200[V] for cyan (C) downstream of the transfer roller of the color being adjusted.

[0065] Here, we will explain how to adjust the transfer bias of the upstream and downstream colors of the transfer roller for the color being adjusted. On plain paper, increasing the transfer bias of the transfer roller for the color being adjusted increases reverse transfer as the toner of the upstream color of the transfer roller passes through the transfer nip of the transfer roller for the color being adjusted, resulting in a decrease in the density of the upstream color of the transfer roller for the color being adjusted. Here, reverse transfer is the phenomenon in which the toner image transferred onto the transfer belt 50 or recording medium is transferred to the photosensitive drum when it passes through the transfer nip of the downstream color. Toner has a charge distribution, and among the negatively charged toner, which is normally charged, there is a certain amount of positively charged toner that is charged with the opposite polarity. It is thought that reverse transfer occurs mainly because the positively charged toner with the opposite polarity is transferred to the photosensitive drum. Therefore, increasing the transfer bias of the transfer roller for the color being adjusted makes it easier for the positively charged toner of the upstream color of the transfer roller to transfer to the photosensitive drum, thus increasing reverse transfer.

[0066] To reduce reverse transfer, one method is to increase the transfer bias of the upstream color of the transfer roller of the color being adjusted. When transfer is performed with a high transfer bias, discharge is more likely to occur near the transfer nip, increasing the amount of charge on the toner. Since the toner's charge increases in the negative direction of its normal charge, the toner's charge distribution shifts to the negative side, resulting in less positively charged toner and thus a reduction in reverse transfer. Therefore, to reduce reverse transfer of the toner of the upstream color of the transfer roller of the color being adjusted, the transfer bias of the upstream color of the transfer roller of the color being adjusted is increased in conjunction with the transfer bias of the upstream color of the transfer roller of the color being adjusted.

[0067] Furthermore, increasing the transfer bias of the transfer roller for the color being adjusted reduces reverse transfer of the toner downstream of the transfer roller for that color, resulting in a higher density of that color. Therefore, to prevent the density of the color being adjusted from becoming too high, the transfer bias of the downstream color of the transfer roller for that color is increased.

[0068] Next, the command / image processing unit 92 checks the adjustment values ​​for each color in the "Transfer Bias Adjustment" menu, which have been pre-set by the user on the operation unit 95, and calculates the transfer bias adjustment amount for each color from the transfer bias adjustment amount table 103 for low-resistance printing media and the adjustment values ​​in the transfer bias adjustment menu (for example, -2, -1, 0, +1, +2) (step S9).

[0069] If the transfer bias adjustment menu is adjusted for multiple colors, the transfer bias adjustment amount for each color is determined by the sum of the adjustment values ​​in each table. Therefore, in the case of low-resistance printing media, refer to the low-resistance transfer bias adjustment amount table 103 in Figure 6, and the transfer bias adjustment amounts ΔV(K), ΔV(Y), ΔV(M), and ΔV(C) for each color are determined by the following equations (11) to (14). ΔV(K)=K2+Ky2+Km2+Kc2…(11) ΔV(Y) = Yk² + Y² + Ym² + Yc² ... (12) ΔV(M)=Mk2+My2+M2+Mc2…(13) ΔV(C) = Ck² + Cy² + Cm² + C² …(14)

[0070] Then, the transcription biases V(K), V(Y), V(M), and V(C) are determined using the following equations (15) to (18), which calculate the sum of the transcription biases V0(K), V0(Y), V0(M), and V0(C) determined in step S3 of the flowchart in Figure 8 and the transcription bias adjustment amounts ΔV(K), ΔV(Y), ΔV(M), and ΔV(C) determined in step S9 (step S10). V(K) = V0(K) + ΔV(K) …(15) V(Y) = V0(Y) + ΔV(Y) …(16) V(M) = V0(M) + ΔV(M) …(17) V(C) = V0(C) + ΔV(C) …(18)

[0071] Furthermore, for the transfer bias adjustment amount tables 102 for high resistance and 103 for low resistance, when the transfer bias of the transfer roller of the color to be adjusted is increased, the transfer bias adjustment amounts on the upstream and downstream sides of the transfer roller of the color to be adjusted are adjusted based on experimental results.

[0072] The settings for each color in the "Transfer Bias Adjustment" menu are to be checked by the user after they have been pre-set on the control unit 95. However, they may also be set by the printer driver or the like when sending image data.

[0073] While the settings in the "Type of Printing Medium" menu allow you to select between a high-resistance transfer bias adjustment table 102 and a low-resistance transfer bias adjustment table 103, it is also possible to obtain the resistance value information of the medium from the transfer bias and transfer current value information when the printing medium passes through the transfer nip and select the transfer bias adjustment table. Furthermore, the high-resistance transfer bias adjustment table 102 and the low-resistance transfer bias adjustment table 103 are not limited to just two types, and the structure may have multiple transfer bias adjustment tables.

[0074] Effects of the Embodiment As described above, according to this embodiment, when the absolute value of the transfer bias applied to the transfer roller of the color to be adjusted is increased or decreased, the absolute value of the transfer bias of the transfer roller upstream of the transfer roller of the color to be adjusted is also increased or decreased.

[0075] Specifically, when the printing medium is a high-resistance printing medium, lowering the absolute value of the transfer bias of the transfer roller upstream of the transfer roller of the color to be adjusted has the effect of preventing voltage deficiency when the absolute value of the transfer bias of the transfer roller of the color to be adjusted is increased in a high-resistance printing medium.

[0076] Furthermore, when the printing medium is a low-resistance printing medium, increasing the absolute value of the transfer bias of the transfer roller upstream of the transfer roller of the color to be adjusted has the effect of preventing a decrease in density when the absolute value of the transfer bias of the transfer roller of the color to be adjusted is increased in a low-resistance printing medium.

[0077] In this way, when the absolute value of the transfer bias of the transfer roller of the color being adjusted is changed, the absolute value of the transfer bias of the transfer roller upstream of that color is also changed appropriately, resulting in the effect of making it easier for the user to adjust the transfer bias. [Explanation of Symbols]

[0078] 1 Image forming apparatus, 20K, 20Y, 20M, 20C Image forming unit, 21K, 21Y, 21M, 21C Charging roller, 22K, 22Y, 22M, 22C Photosensitive drum (image carrier), 23K, 23Y, 23M, 23C Developing roller, 24K, 24Y, 24M, 24C Developing blade, 25K, 25Y, 25M, 25C Supply roller, 26K, 26Y, 26M, 26C Cleaning blade, 27K, 27Y, 27M, 27C Toner cartridge, 30K, 30Y, 30M, 30C LED head, 40K, 40Y, 40M, 40C Transfer roller (transfer section), 50 Transfer belt, 60 Fuser, 90 Control unit, 91 Interface section 92 Command / image processing unit, 94 Mechanism control unit, 94a Memory, 101 Basic table of transfer bias, 102 Adjustment amount table of transfer bias for high-resistance printing media, 103 Adjustment amount table of transfer bias for low-resistance printing media, D1 Transport direction.

Claims

1. Multiple image carriers are arranged in a line in the direction of transport of the printing medium, each carrying multiple developer images, A plurality of transfer units are arranged opposite to the plurality of image carriers and sequentially transfer the plurality of developer images onto the printing medium by a transfer bias, A transfer voltage generating unit that applies the transfer bias to each of the plurality of transfer units, A control unit that controls the transfer voltage generation unit, Equipped with, The control unit, When a command is received to adjust the first transfer bias, which is the transfer bias applied to the transfer unit to be adjusted among the plurality of transfer units, Using adjustment amount information pre-stored in the memory unit, a first adjustment amount is determined based on the content of the command, and a first adjustment is performed on the absolute value of the first transcription bias using the first adjustment amount. Using the adjustment amount information, a second adjustment amount is determined based on the content of the command, and a second adjustment is performed on the absolute value of the second transfer bias, which is the transfer bias applied to the transfer section upstream of the transfer section to be adjusted, using the second adjustment amount. An image forming apparatus characterized by the following:

2. The control unit, The type information indicating the type of the printing medium is received, Based on the aforementioned type information, the target adjustment amount information is selected from a plurality of adjustment amount information pre-stored in the memory unit. Upon receiving the aforementioned command, the system determines a first adjustment amount based on the content of the command using the adjustment amount information of the target, and performs the first adjustment on the absolute value of the first transcription bias using the first adjustment amount. Using the aforementioned adjustment amount information, a second adjustment amount is determined based on the content of the command, and the second adjustment is performed on the absolute value of the second transcription bias using the second adjustment amount. The image forming apparatus according to feature 1.

3. The control unit, The type information indicating the type of the printing medium is received, If the aforementioned type is a high-resistivity printing medium having a volume resistivity greater than or equal to a predetermined value, and the absolute value of the first transfer bias is increased in the first adjustment, then the absolute value of the second transfer bias is decreased in the second adjustment. If the aforementioned type is a low-resistivity printing medium having a volume resistivity less than the predetermined value, and the absolute value of the first transfer bias is increased in the first adjustment, then the absolute value of the second transfer bias is increased in the second adjustment. The image forming apparatus according to feature 1.

4. The control unit, The type information indicating the type of the printing medium is received, If the printing medium is a medium containing a resin film and the absolute value of the first transfer bias is increased in the first adjustment, then the absolute value of the second transfer bias is decreased in the second adjustment. If the printing medium is made of paper and the absolute value of the first transfer bias is increased in the first adjustment, the absolute value of the second transfer bias is increased in the second adjustment. The image forming apparatus according to feature 1.

5. It further has an operating section that accepts user input, The control unit receives the command from the operation unit regarding the transfer unit to be adjusted. The image forming apparatus according to feature 1.

6. It further has an operating section that accepts user input, The control unit receives type information indicating the type of printing medium from the operation unit. The image forming apparatus according to feature 1.

7. The upstream transfer unit includes the upstream transfer unit that is closest to the transfer unit to be adjusted among the plurality of transfer units. The image forming apparatus according to feature 1.

8. The upstream transfer section includes a plurality of transfer sections that are upstream of the plurality of transfer sections and are close to the transfer section to be adjusted. The image forming apparatus according to feature 1.

9. A transfer bias control method performed by an image forming apparatus comprising: a plurality of image carriers arranged in the transport direction of the printing medium and each carrying a plurality of developer images; a plurality of transfer units arranged opposite to the plurality of image carriers and sequentially transferring the plurality of developer images onto the printing medium by a transfer bias; and a transfer voltage generating unit that applies the transfer bias to each of the plurality of transfer units, wherein The steps include receiving a command to adjust the first transfer bias, which is the transfer bias applied to the transfer unit to be adjusted among the plurality of transfer units, The steps include: determining a first adjustment amount based on the content of the command using adjustment amount information pre-stored in the memory unit, and performing a first adjustment to the absolute value of the first transcription bias using the first adjustment amount; The steps include: determining a second adjustment amount based on the content of the command using the adjustment amount information; and performing a second adjustment on the absolute value of the second transfer bias, which is the transfer bias applied to the transfer section upstream of the transfer section to be adjusted, using the second adjustment amount; A method for controlling transfer bias, characterized by having the following features.

10. Multiple image carriers are arranged in a line in the direction of transport of the printing medium, each carrying multiple developer images, A plurality of transfer units are arranged opposite to the plurality of image carriers and sequentially transfer the plurality of developer images onto the printing medium by a transfer bias, A transfer voltage generating unit that applies the transfer bias to each of the plurality of transfer units, A control unit that controls the transfer voltage generation unit, Equipped with, The control unit, When a command is received to adjust the first transfer bias, which is the transfer bias applied to the transfer unit to be adjusted among the plurality of transfer units, Based on the content of the aforementioned instruction, a first adjustment is performed to increase or decrease the absolute value of the first transcription bias. Based on the content of the command, a second adjustment is performed to increase or decrease the absolute value of the second transfer bias, which is the transfer bias applied to the transfer section upstream of the transfer section to be adjusted. Furthermore, when type information indicating the type of printing medium is received, If the aforementioned type is a high-resistivity printing medium having a volume resistivity greater than or equal to a predetermined value, and the absolute value of the first transfer bias is increased in the first adjustment, then the absolute value of the second transfer bias is decreased in the second adjustment. If the aforementioned type is a low-resistance printing medium having a volume resistivity less than the predetermined value, and the absolute value of the first transfer bias is increased in the first adjustment, then the absolute value of the second transfer bias is increased in the second adjustment. An image forming apparatus characterized by the following:

11. Multiple image carriers are arranged in a line in the direction of transport of the printing medium, each carrying multiple developer images, A plurality of transfer units are arranged opposite to the plurality of image carriers and sequentially transfer the plurality of developer images onto the printing medium by a transfer bias, A transfer voltage generating unit that applies the transfer bias to each of the plurality of transfer units, A control unit that controls the transfer voltage generation unit, Equipped with, The control unit, When a command is received to adjust the first transfer bias, which is the transfer bias applied to the transfer unit to be adjusted among the plurality of transfer units, Based on the content of the aforementioned instruction, a first adjustment is performed to increase or decrease the absolute value of the first transcription bias. Based on the content of the command, a second adjustment is performed to increase or decrease the absolute value of the second transfer bias, which is the transfer bias applied to the transfer section upstream of the transfer section to be adjusted. Furthermore, when type information indicating the type of printing medium is received, If the printing medium is a medium containing a resin film and the absolute value of the first transfer bias is increased in the first adjustment, then the absolute value of the second transfer bias is decreased in the second adjustment. If the printing medium is made of paper and the absolute value of the first transfer bias is increased in the first adjustment, the absolute value of the second transfer bias is increased in the second adjustment. An image forming apparatus characterized by the following:

12. Multiple image carriers are arranged in a line in the direction of transport of the printing medium, each carrying multiple developer images, A plurality of transfer units are arranged opposite to the plurality of image carriers and sequentially transfer the plurality of developer images onto the printing medium by a transfer bias, A transfer voltage generating unit that applies the transfer bias to each of the plurality of transfer units, An operating unit that accepts user input, A control unit that controls the transfer voltage generation unit, Equipped with, The control unit, When a command is received to adjust the first transfer bias, which is the transfer bias applied to the transfer unit to be adjusted among the plurality of transfer units, Based on the content of the aforementioned instruction, a first adjustment is performed to increase or decrease the absolute value of the first transcription bias. Based on the content of the command, a second adjustment is performed to increase or decrease the absolute value of the second transfer bias, which is the transfer bias applied to the transfer section upstream of the transfer section to be adjusted. The operation unit receives the command for the transfer unit to be adjusted. An image forming apparatus characterized by the following:

Images