JP7350537B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine using an electrophotographic method or an electrostatic recording method.

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic method, a toner image is electrostatically transferred from an image bearing member such as a photoreceptor or an intermediate transfer member to a recording material such as paper. This transfer is often performed by applying a transfer voltage to a transfer member such as a transfer roller that comes into contact with the image carrier to form a transfer portion. If the transfer voltage is too low, "image density is low" may occur, in which transfer is not performed sufficiently and the desired image density cannot be obtained. In addition, if the transfer voltage is too high, discharge occurs in the transfer section, and the polarity of the toner charge in the toner image is reversed due to the influence of the discharge, resulting in "white spots" where the toner image is not partially transferred. This may occur. Therefore, in order to form a high quality image, it is required to apply an appropriate transfer voltage to the transfer member.

The amount of charge required for transfer varies depending on the size of the recording material and the area ratio of the toner image. Therefore, the transfer voltage is often applied using constant voltage control that applies a constant voltage corresponding to a predetermined current density. When the transfer voltage is applied under constant voltage control, the transfer is performed in accordance with the predetermined voltage to the area where the target toner image is located, regardless of the current flowing outside the recording material or in the areas where there is no toner image on the recording material. This is because it is easy to secure electric current. However, the electrical resistance of the transfer member that makes up the transfer section changes depending on product variations, member temperature, cumulative usage time, etc., and the electrical resistance of the recording material passing through the transfer section also changes depending on the type of recording material and the surrounding environment. (temperature, humidity), etc. Therefore, when controlling the transfer voltage at a constant voltage, it is necessary to adjust the transfer voltage in response to fluctuations in the electrical resistance of the transfer member and recording material.

Patent Document 1 discloses the following transfer voltage control method in a configuration in which the transfer voltage is controlled at a constant voltage. Immediately before the start of continuous image formation, a predetermined voltage is applied to the transfer section in a state where there is no recording material, the current value is detected, and the voltage value at which a predetermined target current is obtained is determined. Then, a recording material shared voltage corresponding to the type of recording material is added to this voltage value to set a transfer voltage value to be applied under constant voltage control during transfer. With such control, it is possible to apply a transfer voltage according to a desired target current by constant voltage control, regardless of fluctuations in the electrical resistance value of a transfer unit such as a transfer member or fluctuations in electrical resistance value of a recording material. .

Here, the types of recording materials include, for example, types that differ in the smoothness of the surface of the recording material, such as high-quality paper and coated paper, and types that differ in the thickness of the recording material, such as thin paper and thick paper. . The recording material shared voltage can be determined in advance according to the type of recording material, for example. However, there are many types of recording materials in circulation. Also, the electrical resistance of a recording material varies depending on the wet state of the recording material (the amount of moisture contained in the recording material), but even if the environment (temperature and humidity) is the same, the amount of moisture contained in a recording material varies depending on the time it is left in the environment, etc. fluctuate. Therefore, it is often difficult to accurately determine the recording material shared voltage in advance. If the transfer voltage is not at an appropriate value, including fluctuations in the electrical resistance of the recording material, image defects such as low image density and white spots may occur as described above.

To address these issues, Patent Documents 2 and 3 disclose that in a configuration in which the transfer voltage is controlled at a constant voltage, the upper and lower limits of the current supplied to the transfer section when the recording material is passing through the transfer section are disclosed. It is proposed to provide a value. With this kind of control, the current supplied to the transfer section when the recording material is passing through the transfer section can be controlled within a predetermined range, thereby preventing the occurrence of image defects due to insufficient or excessive transfer current. Can be suppressed. In Patent Document 2, the upper limit value is determined based on environmental information. In Patent Document 3, the upper limit value and the lower limit value are determined based on the front and back sides of the recording material, the type of recording material, and the size of the recording material in addition to the environment.

Note that in a configuration in which the transfer voltage is controlled at a constant voltage, when the recording material passes through the transfer section, if the current flowing through the transfer member deviates from a predetermined range, the transfer is performed so that the current falls within the predetermined range. Control that changes the target voltage of constant voltage control is also called "limiter control." Further, here, the magnitude (high/low) of voltage and current is compared in absolute value.

Japanese Patent Application Publication No. 2004-117920 Patent No. 4161005 Japanese Patent Application Publication No. 2008-275946

The current that flows through the transfer section when the recording material is passing through the transfer section is divided into "paper passing section current (passing section current)" and "non-paper passing section current (non-passing section current)" . The paper passing section current is a current that flows in a region of the transfer section through which the recording material passes ("paper passing section (passing region)") in a direction substantially perpendicular to the conveyance direction of the recording material. Further, the non-sheet passing current is a current that flows in a region of the transfer unit through which the recording material does not pass (“non-sheet passing portion (non-passing region)”) in a direction substantially perpendicular to the conveyance direction of the recording material. The non-paper passing portion occurs because transfer members such as transfer rollers are designed to stably transport recording materials of various sizes and transfer toner images, so their longitudinal length is limited to the size of the image forming device. This is because the width is larger than the maximum width of the recording material guaranteed by . In order to suppress the above-mentioned image defects, it is important that the paper passing section current is within an appropriate range. However, the current that can be detected when the recording material is passing through the transfer section is the sum of the paper passing section current and the non-paper passing section current. Therefore, when there is no recording material in the transfer section, information regarding the electrical resistance of the transfer section is acquired as voltage-current characteristics, etc., and this information and information on the width of the recording material (the length in the direction approximately perpendicular to the transport direction) are combined. Based on this, it is possible to determine the non-sheet passing current that flows when a predetermined voltage is applied. Then, a predetermined current range for limiter control can be set based on the range of current that may be allowed to flow in the paper passing portion and the current in the non-paper passing portion.

Furthermore, conventionally, in order to set an appropriate transfer voltage, a test voltage or a test current is supplied to the transfer section before image formation to obtain voltage-current characteristics.

Here, in order to set a predetermined current range in limiter control, it is desirable to obtain voltage-current characteristics using a plurality of test voltages or test currents in a relatively wide range. This is because the voltage-current characteristics of the transfer section may be expressed by a polynomial of quadratic or higher order, or from the perspective of improving control accuracy, it is necessary to collect information near the upper limit (or even lower limit) of the transfer current. Depends on what it is desired to obtain.

On the other hand, if the operation of acquiring the voltage-current characteristics of the transfer section using a relatively wide range of test voltages or test currents as described above is performed before each image formation, the electrical resistance of the transfer member will increase due to the supply of large currents and voltages. As a result, the life of the transfer member may be shortened due to an increase in the temperature. Therefore, when setting the transfer voltage, an operation is performed to obtain the voltage-current characteristics of the transfer section using a relatively narrow range of test voltage or test current, and a relatively wide range of test voltage or test current as described above is used. It is conceivable that the operation of acquiring the voltage-current characteristics of the transfer section using the method is not performed before each image formation, but is performed, for example, every time a predetermined number of images are formed.

However, it has been found that with this method, image defects such as white spots may occur during the first image formation after the transfer member is replaced with a new one due to periodic replacement or the like. According to studies conducted by the present inventors, it was found that this is because the electrical resistance is different between the transfer member before replacement and the new transfer member after replacement. For example, as the amount of use (voltage application time, etc.) of a transfer member such as a transfer roller constructed using an ion conductive material increases, the internal ion distribution becomes uneven, and the electrical resistance increases. Therefore, when using a new transfer member after replacement, the voltage-current characteristics obtained using a relatively narrow range of test voltage or test current cannot determine the appropriate current range for limiter control, and the transfer current If the current is outside the appropriate current range, image defects such as white spots may occur.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus that can appropriately control the transfer voltage in the first image formation after the transfer member is replaced while suppressing the shortening of the life of the transfer member. That's true.

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier that carries a toner image, a transfer member that transfers the toner image carried on the image carrier to a recording material in a transfer section by applying a voltage, and a transfer member that is connected to the transfer member. The control unit includes a power source that applies a voltage, a current detection unit that detects a current flowing through the transfer member, and a control unit that controls the power supply, and the control unit controls when the recording material is passing through the transfer unit. If the detection result of the current detection unit is within a predetermined range defined by at least one of an upper limit value and a lower limit value , a constant voltage is set so that the voltage applied from the power source becomes a target voltage. When the detection result is outside the predetermined range when the recording material is passing through the transfer section by executing the control, the target voltage is adjusted so that the detection result is within the predetermined range . , an image forming apparatus that executes the constant voltage control with the adjusted target voltage , the image forming apparatus having an acquisition unit that acquires replacement information indicating that the transfer member has been replaced, the control unit recording the information on the transfer unit. At least one level of test voltage or test current is supplied to the transfer member in a state where there is no material, and when the test voltage is supplied, the current detected by the current detection section or the test current is supplied. a first test mode in which information on the voltage output from the power source is acquired , and at least the target voltage can be set based on the information acquired in the first test mode; A plurality of levels of test voltages or test currents are supplied to the transfer member in a state in which there is no recording material, and the current detected by the current detection unit when the test voltage is supplied or the test current is supplied. A second test mode is executed to obtain information on the voltage output from the power source at the time of the test, and the target voltage and the predetermined range can be set based on the information obtained in the second test mode. The absolute value of the voltage output by the power supply when supplying at least one level of the test voltage or the test current in the second test mode is the absolute value of the voltage output by the power supply when supplying the test voltage or the test current in the first test mode. is larger than the largest value among the absolute values of the voltages outputted by the power supply when the transfer member is replaced, and if the replacement information is acquired by the acquisition means, The second test mode is executed before image formation, and the target voltage and the predetermined range at the time of the first image formation are set based on the information acquired in the second test mode. and the absolute value of the voltage output by the power supply when supplying the at least one level of the test voltage or the test current in the second test mode is the first value after execution of the second test mode. The image forming apparatus is characterized in that the target voltage is 80% or more of the absolute value of the target voltage set in the image forming job to be performed and is less than or equal to the absolute value of the outputtable voltage of the power source.
According to another aspect of the present invention, an image carrier that carries a toner image, a transfer member that transfers the toner image carried on the image carrier by applying a voltage to a recording material in a transfer section, and the transfer member a current detection section that detects a current flowing through the transfer member; and a control section that controls the power supply; When the detection result of the current detection unit is within a predetermined range defined by at least one of an upper limit value and a lower limit value, the voltage applied from the power source is set to be a target voltage. When voltage control is executed and the detection result is outside the predetermined range while the recording material is passing through the transfer section, the target voltage is adjusted so that the detection result is within the predetermined range. The image forming apparatus executes the constant voltage control using the adjusted target voltage, and the image forming apparatus includes an acquisition unit that acquires replacement information indicating that the transfer member has been replaced, and the control unit provides information on the transfer unit. At least one level of test voltage or test current is supplied to the transfer member in the absence of a recording material, and the current detected by the current detection unit when the test voltage is supplied or the test current is supplied. A first test mode is executed in which information on the voltage output from the power source is acquired, and at least the target voltage can be set based on the information acquired in the first test mode. A plurality of levels of test voltages or test currents are supplied to the transfer member in a state where there is no recording material in the transfer member, and when the test voltage is supplied, the current detected by the current detection unit or the test current is supplied. The target voltage and the predetermined range can be set based on the information acquired in the second test mode by executing a second test mode in which information on the voltage output from the power supply is obtained when the voltage is output from the power supply. , the absolute value of the voltage output by the power supply when supplying at least one level of the test voltage or the test current in the second test mode is higher than the test voltage or the test current in the first test mode. is larger than the largest value among the absolute values of the voltages output by the power supply when supplying the voltage, and the control unit is configured to control the voltage at the first time after the transfer member is replaced, when the replacement information is acquired by the acquisition means. The second test mode is executed before the image formation, and the target voltage and the predetermined range at the time of the first image formation are set based on the information acquired in the second test mode. The control unit acquires voltage-current characteristics based on the information acquired in the second test mode, and performs the transfer with no recording material in the transfer unit based on the voltage-current characteristics. A voltage value for supplying a predetermined current to the member is acquired, the target voltage is set based on the voltage value, and the transfer member is set in a state where there is no recording material in the transfer section based on the voltage-current characteristics. An image forming apparatus is provided, characterized in that a value of a current flowing through the transfer member is obtained when a predetermined voltage is applied to the transfer member, and the predetermined range is set based on the current value.

According to the present invention, it is possible to appropriately control the transfer voltage in the first image formation after the transfer member is replaced while suppressing the shortening of the life of the transfer member.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 3 is a schematic diagram of a configuration related to secondary transfer. FIG. 2 is a schematic block diagram showing a control mode of main parts of the image forming apparatus. FIG. 3 is a flowchart of control in the first embodiment. FIG. 3 is a graph diagram showing an example of the relationship between voltage and current of a secondary transfer section. FIG. 3 is a graph diagram showing voltage-current characteristics before and after replacing the secondary transfer roller. FIG. 7 is a graph diagram showing differences in accuracy of voltage-current characteristics due to differences in ATVC control after replacing the secondary transfer roller. FIG. 3 is a schematic diagram showing an example of table data of recording material shared voltages. FIG. 7 is a schematic diagram showing an example of table data of a paper passing section current range. FIG. 7 is a graph diagram showing differences in accuracy of voltage-current characteristics due to differences in ATVC control after replacing the secondary transfer roller. FIG. 3 is a flowchart of control in Example 2. FIG. FIG. 7 is a flowchart of control in Example 3;

Hereinafter, the image forming apparatus according to the present invention will be explained in more detail with reference to the drawings.

[Example 1]
1. Overall Configuration and Operation of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem multifunction device (having the functions of a copying machine, a printer, and a facsimile machine) that employs an intermediate transfer method and is capable of forming a full-color image using an electrophotographic method. ).

The image forming apparatus 100 includes a plurality of image forming sections (stations) including first, second, third, and fourth image forming sections SY, SM, which form images of yellow, magenta, cyan, and black, respectively. Has SC and SK. For elements with the same or corresponding functions or configurations in each image forming unit SY, SM, SC, SK, the suffix Y, M, C, K is omitted to indicate that the element is for one of the colors. This may be explained comprehensively. In this embodiment, the image forming section S includes a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, and a drum cleaning device 6, which will be described later.

A photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member), serves as a first image carrier that carries a toner image (toner image). clockwise). The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2, which is a roller-type charging member serving as a charging means. The charged surface of the photosensitive drum 1 is scanned and exposed by an exposure device (laser scanner device) 3 as an exposure means based on image information, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. Ru.

The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by being supplied with toner as a developer by a developing device 4 serving as a developing means, and a toner image is formed on the photosensitive drum 1. In this embodiment, the exposed area (image area) on the photosensitive drum 1, whose absolute value has decreased by being exposed to light after being uniformly charged, is charged to the same polarity as the charging polarity of the photosensitive drum 1. Toner adheres (reverse development method). In this embodiment, the normal charging polarity of the toner, which is the charging polarity of the toner during development, is negative polarity. The electrostatic image formed by the exposure device 3 is a collection of small dot images, and by changing the density of the dot images, the density of the toner image formed on the photosensitive drum 1 can be changed. In this embodiment, the maximum density of each color toner image is about 1.5 to 1.7, and the amount of toner applied at the maximum density is about 0.4 to 0.6 mg/ ^cm2. It has become.

An intermediate transfer belt 7, which is an intermediate transfer body formed of an endless belt and serves as a second image carrier carrying a toner image, is arranged so as to be able to come into contact with the surfaces of the four photosensitive drums 1. ing. The intermediate transfer belt 7 is an example of an intermediate transfer body that transports a toner image that has been primarily transferred from another image carrier to a recording material for secondary transfer. The intermediate transfer belt 7 is stretched around a drive roller 71, a tension roller 72, and a secondary transfer opposing roller 73 as a plurality of tension rollers. Drive roller 71 transmits driving force to intermediate transfer belt 7 . Tension roller 72 controls the tension of intermediate transfer belt 7 to be constant. The secondary transfer opposing roller 73 functions as an opposing member (counter electrode) of the secondary transfer roller 8, which will be described later. The intermediate transfer belt 7 rotates (circumferentially moves) in the direction of arrow R2 (clockwise) in the drawing at a conveyance speed (circumferential speed) of about 300 to 500 mm/sec by rotationally driving the drive roller 71. The tension roller 72 is applied with a force that pushes the intermediate transfer belt 7 from the inner peripheral surface side to the outer peripheral surface side by the force of a spring serving as a biasing means, and this force pushes the intermediate transfer belt 7 in the conveyance direction. A tension of about 2 to 5 kg is applied. On the inner peripheral surface side of the intermediate transfer belt 7, a primary transfer roller 5, which is a roller-type primary transfer member serving as a primary transfer means, is arranged corresponding to each photosensitive drum 1. The primary transfer roller 5 is pressed toward the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 1 and the intermediate transfer belt 7 are in contact with each other. . The toner image formed on the photosensitive drum 1 is electrostatically transferred (primary transfer) onto the rotating intermediate transfer belt 7 by the action of the primary transfer roller 5 in the primary transfer portion N1. . During the primary transfer process, a primary transfer voltage (primary transfer bias) is applied to the primary transfer roller 5 from a primary transfer power source (not shown), which is a DC voltage with a polarity opposite to the normal charging polarity of the toner. is applied. For example, when forming a full-color image, yellow, magenta, cyan, and black toner images formed on each photosensitive drum 1 are sequentially transferred onto the intermediate transfer belt 7 so as to be superimposed.

On the outer peripheral surface side of the intermediate transfer belt 7, a secondary transfer roller 8, which is a roller-type secondary transfer member serving as a secondary transfer means, is arranged at a position facing the secondary transfer opposing roller 73. The secondary transfer roller 8 is pressed toward the secondary transfer opposing roller 73 via the intermediate transfer belt 7 to form a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 7 and the secondary transfer roller 8 contact each other. ) form N2. The toner image formed on the intermediate transfer belt 7 is transferred to a recording material that is being conveyed between the intermediate transfer belt 7 and the secondary transfer roller 8 by the action of the secondary transfer roller 8 in the secondary transfer portion N2. (Sheet, transfer material) Electrostatically transferred to P (secondary transfer). The recording material P is typically paper, but is not limited to this, and may include synthetic paper made of resin such as waterproof paper, plastic sheets such as OHP sheets, cloth, etc. Sometimes it happens. During the secondary transfer process, a secondary transfer voltage (secondary transfer bias) is applied to the secondary transfer roller 8 from a secondary transfer power source (high voltage power supply circuit) 20, which is a DC voltage with a polarity opposite to the normal charging polarity of the toner. ) is applied. The recording materials P are stored in a recording material cassette (not shown) or the like, and are fed one by one from the recording material cassette by a feeding roller (not shown) or the like and sent to the registration rollers 9 . The recording material P is temporarily stopped by the registration rollers 9, and then is supplied to the secondary transfer portion N2 in synchronization with the toner image on the intermediate transfer belt 7.

The recording material P onto which the toner image has been transferred is conveyed to a fixing device 10 as a fixing means by a conveying member or the like. The fixing device 10 fixes (melts, fixes) the toner image on the recording material P by heating and pressurizing the recording material P carrying the unfixed toner image. Thereafter, the recording material P is discharged (output) to the outside of the main body of the image forming apparatus 100.

Further, toner remaining on the surface of the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 and collected by a drum cleaning device 6 serving as a photosensitive member cleaning means. Further, toner remaining on the surface of the intermediate transfer belt 7 after the secondary transfer process (secondary transfer residual toner) and deposits such as paper dust are removed from the intermediate transfer belt 7 by a belt cleaning device 74 serving as intermediate transfer body cleaning means. removed from the surface and collected.

In this embodiment, the intermediate transfer belt 7 is an endless belt having a three-layer structure from the inner peripheral surface to the outer peripheral surface: a resin layer, an elastic layer, and a surface layer. As the resin material constituting the resin layer, polyimide, polycarbonate, etc. can be used. The thickness of the resin layer is preferably 70 to 100 μm. Further, as the elastic material constituting the elastic layer, urethane rubber, chloroprene rubber, etc. can be used. The thickness of the elastic layer is preferably 200 to 250 μm. Further, as the material for the surface layer, it is desirable to use a material that reduces the adhesion force of the toner to the surface of the intermediate transfer belt 7 and makes it easier to transfer the toner to the recording material P in the secondary transfer portion N2. For example, one or more resin materials such as polyurethane, polyester, and epoxy resin can be used. Alternatively, one or more types of elastic materials such as elastic materials (elastic material rubber, elastomer) and butyl rubber can be used. In addition, one or more types of powders or particles such as fluororesin, or one or more types of these powders or particles can be added to these materials to reduce surface energy and increase lubricity. can be used by dispersing them with different particle sizes. Note that the thickness of the surface layer is preferably 5 to 10 μm. The intermediate transfer belt 7 has its electrical resistance adjusted by adding a conductive agent such as carbon black for adjusting electrical resistance, and preferably has a volume resistivity of 1×10 ⁹ to 1×10 ¹⁴ Ω·cm.

Further, in this embodiment, the secondary transfer roller 8 includes a core metal (base material) and an elastic layer formed of ion conductive foam rubber (NBR rubber) around the core metal. Ru. In this embodiment, the outer diameter of the secondary transfer roller 8 is 24 mm, and the surface roughness Rz of the secondary transfer roller 8 is 6.0 to 12.0 (μm). Further, in this embodiment, the electrical resistance value of the secondary transfer roller 8 is 1×10 ⁵ to 1×10 ⁷ Ω when measured by applying 2 kV at N/N (23° C., 50% RH), and the electric resistance value of the elastic layer The hardness is about 30 to 40° in terms of Asker-C hardness. Further, in this embodiment, the width of the secondary transfer roller 8 in the longitudinal direction (rotation axis direction) (length in the direction substantially perpendicular to the conveyance direction of the recording material P) is approximately 310 to 340 mm. In this embodiment, the width in the longitudinal direction of the secondary transfer roller 8 is the maximum width (the length in the direction substantially orthogonal to the conveyance direction) of the recording material P whose conveyance is guaranteed by the image forming apparatus 100. (maximum width). In this embodiment, since the recording material P is conveyed with the center in the longitudinal direction of the secondary transfer roller 8 as a reference, all the recording materials P whose conveyance is guaranteed by the image forming apparatus 100 are in the longitudinal direction of the secondary transfer roller 8. Pass through the length range. This makes it possible to stably transport recording materials P of various sizes and to stably transfer toner images onto recording materials P of various sizes.

FIG. 2 is a schematic diagram of a configuration related to secondary transfer. The secondary transfer roller 8 comes into contact with the secondary transfer opposing roller 73 via the intermediate transfer belt 7, thereby forming a secondary transfer portion N2. A secondary transfer power source 20 whose output voltage value is variable is connected to the secondary transfer roller 8 . The secondary transfer opposing roller 73 is electrically grounded (connected to the ground). While the recording material P is passing through the secondary transfer portion N2, a secondary transfer voltage, which is a DC voltage with a polarity opposite to the normal charging polarity of the toner, is applied to the secondary transfer roller 8, and the secondary transfer portion By supplying the secondary transfer current to N2, the toner image on the intermediate transfer belt 7 is transferred onto the recording material P. In this embodiment, a secondary transfer current of, for example, +20 to +80 μA is applied to the secondary transfer portion N2 during the secondary transfer. Note that a roller corresponding to the secondary transfer opposing roller 73 of this embodiment is used as a transfer member, and a secondary transfer voltage having the same polarity as the normal charging polarity of the toner is applied to the roller, and the secondary transfer roller of this embodiment is A roller corresponding to 8 may be used as a counter electrode and electrically grounded.

In this embodiment, the upper limit value and lower limit value (“2 ``next transfer current range'') is determined. As will be described in detail later, this various information includes the following information. First, conditions (recording This is information regarding the type of material P, etc.). It is also information regarding the detection results of the environmental sensor 32 (FIG. 3). It is also information regarding the electrical resistance of the secondary transfer portion N2 that is detected before the recording material P reaches the secondary transfer portion N2. Then, while the recording material P is passing through the secondary transfer section N2, while detecting the secondary transfer current flowing through the secondary transfer section N2, the secondary transfer current is determined to be within the above secondary transfer current range. The secondary transfer voltage outputted from the secondary transfer power source 20 by constant voltage control is controlled so that the voltage is controlled. Here, particularly in this embodiment, the secondary transfer current range is changed based on information regarding the width of the recording material P passing through the secondary transfer portion N2. Note that in this embodiment, information regarding the width and thickness of the recording material P is acquired based on information input from the operation unit 31 and the external device 200. However, it is also possible to provide a detection means for detecting the width and thickness of the recording material P in the image forming apparatus 100 and perform control based on information acquired by this detection means.

In this embodiment, in order to perform such control, the secondary transfer power source 20 has a current (secondary transfer current) flowing through the secondary transfer portion N2 (that is, the secondary transfer roller 8 or the secondary transfer power source 20). ) is connected to a current detection circuit 21 as a current detection means (current detection section) for detecting the current. Further, a voltage detection circuit 22 is connected to the secondary transfer power supply 20 as a voltage detection means (voltage detection section) that detects the voltage (secondary transfer voltage) outputted by the secondary transfer power supply 20. Note that the control unit 50 may function as a voltage detection unit and detect the voltage output by the secondary transfer power source 20 from the instruction value of the voltage output from the secondary transfer power source 20. In this embodiment, the secondary transfer power source 20, the current detection circuit 21, and the voltage detection circuit 22 are provided within the same high voltage substrate.

2. Control Mode FIG. 3 is a schematic block diagram showing a control mode of main parts of the image forming apparatus 100 of this embodiment. The control unit (control circuit) 50 as a control means includes a CPU 51 as an arithmetic control means which is a central element that performs arithmetic processing, and memories (storage media) such as RAM 52 and ROM 53 as storage means. Ru. The RAM 52, which is a rewritable memory, stores information input to the control unit 50, detected information, calculation results, etc., and the ROM 53 stores control programs, predetermined data tables, etc. The CPU 51 and memories such as the RAM 52 and ROM 53 can transfer and read data between each other. The control unit 50 also includes a storage unit that stores the number of images formed from the start of use of the secondary transfer roller 8 as information (usage history information) that correlates with the usage amount of the secondary transfer roller 8. A counter 54 is provided.

An external device 200 such as an image reading device (not shown) provided in the image forming apparatus 100 and a personal computer is connected to the control section 50 . Further, an operation section (operation panel) 31 provided in the image forming apparatus 100 is connected to the control section 50 . The operation unit 31 includes a display unit that displays various information to operators such as users and service personnel under the control of the control unit 50, and an input unit that allows the operator to input various settings related to image formation to the control unit 50. It is composed of the following. The operation unit 31 may be configured with a touch panel or the like having the functions of a display unit and an input unit. Job information including control commands related to image formation, such as the type of recording material P, is input to the control unit 50 from the operation unit 31 and the external device 200. The type of recording material P can be distinguished by attributes based on general characteristics such as plain paper, thick paper, thin paper, glossy paper, coated paper, manufacturer, brand, product number, basis weight, thickness, etc. It includes any information. Note that the control unit 50 can obtain information on the type of recording material P by directly inputting the information, and also by selecting a cassette of the feeding unit that stores the recording material P, for example. It can also be acquired from information set in advance in association with the cassette. Further, a secondary transfer power source 20 , a current detection circuit 21 , and a voltage detection circuit 22 are connected to the control unit 50 . In this embodiment, the secondary transfer power supply 20 applies a secondary transfer voltage, which is a DC voltage controlled at a constant voltage, to the secondary transfer roller 8 . Note that constant voltage control is control such that the voltage applied to the transfer section (that is, the transfer member) has a substantially constant voltage value. Furthermore, an environmental sensor 32 is connected to the control unit 50 . In this embodiment, the environment sensor 32 detects the temperature and humidity of the atmosphere inside the casing of the image forming apparatus 100. Information on temperature and humidity detected by the environmental sensor 32 is input to the control unit 50. The control unit 50 can determine the moisture content (moisture content, absolute moisture content) of the atmosphere inside the casing of the image forming apparatus 100 based on the temperature and humidity detected by the environment sensor 32. The environment sensor 32 is an example of an environment detection unit that detects at least one of temperature and humidity inside and outside of the image forming apparatus 100 . The control unit 50 performs image forming operations by comprehensively controlling each part of the image forming apparatus 100 based on image information from the image reading device and the external device 200 and control commands from the operation unit 31 and the external device 200. let

Here, the image forming apparatus 100 executes a job (print operation), which is a series of operations to form and output an image on a single or multiple recording materials P, which is started by one start instruction (print instruction). do. A job generally includes an image forming process, a pre-rotation process, a paper spacing process when forming images on a plurality of recording materials P, and a post-rotation process. The image forming process is a period in which the electrostatic image of the image to be actually formed on the recording material P and output, the formation of the toner image, the primary transfer, and the secondary transfer of the toner image are performed. Formation period) refers to this period. More specifically, the timing of image formation differs depending on the position where each of the steps of electrostatic image formation, toner image formation, toner image primary transfer, and secondary transfer is performed. The pre-rotation process is a period from when a start instruction is input until actually starting to form an image, during which preparatory operations are performed before the image forming process. The inter-sheet process is a period corresponding to a period between recording materials P when images are formed on a plurality of recording materials P continuously (continuous image formation). The post-rotation process is a period in which organizing operations (preparatory operations) are performed after the image forming process. The non-image forming period (non-image forming period) is a period other than the image forming period, including the above-mentioned pre-rotation process, paper interval process, post-rotation process, and even when the image forming apparatus 100 is turned on or from the sleep state. This includes a pre-multi-rotation step, which is a preparatory operation for the return. In this embodiment, control for determining the upper limit value and lower limit value ("secondary transfer current range") of the secondary transfer current is executed during non-image formation.

3. Secondary Transfer Voltage Control Next, control of the secondary transfer voltage in this embodiment will be explained. FIG. 4 is a flowchart showing an outline of the procedure for controlling the secondary transfer voltage in this embodiment. For convenience of explanation of the present invention, FIG. 4 shows an example of a procedure for replacing the secondary transfer roller 8 before starting a job.

First, the control unit 50 acquires information indicating that the secondary transfer roller 8 has been replaced (S101). In this embodiment, the control unit 50 sequentially adds up and stores the number of images formed since the start of use of the secondary transfer roller 8 as usage history information of the secondary transfer roller 8 in the counter 54 . Further, when the count value of the counter 54 reaches a predetermined threshold value, the control unit 50 sends information prompting the replacement of the secondary transfer roller 8 as information regarding the lifespan of the secondary transfer roller 8 to the operation unit 31 and the external device 200. Display. An operator such as a user or a service person can replace the secondary transfer roller 8 in accordance with this display. Then, the operator replaces the secondary transfer roller 8 with a new secondary transfer roller 8, and presses a button (not shown) for inputting that the secondary transfer roller 8 has been replaced, which is displayed on the operation unit 31. ). As a result, a signal indicating that the secondary transfer roller 8 has been replaced is input to the control section 50, and the control section 50 can acquire information indicating that the secondary transfer roller 8 has been replaced. In this embodiment, the operation unit 31 functions as an acquisition unit that acquires information indicating that the transfer member has been replaced. When the control unit 50 acquires information indicating that the secondary transfer roller 8 has been replaced, it clears the usage history information of the secondary transfer roller 8 stored in the counter 54 (in this embodiment, it sets the count value to 0). reset) (S102). Note that the usage history information of the secondary transfer roller 8 is not limited to the number of images formed, but can be any index value that correlates with the amount of usage of the secondary transfer roller 8. For example, The rotation time, number of rotations, voltage application time, etc. of the secondary transfer roller 8 may be used. Furthermore, almost at the same time as clearing the usage history information of the secondary transfer roller 8, the control unit 50 causes the RAM 52 to store information indicating that the secondary transfer roller 8 has been replaced (S103).

Next, upon acquiring the job information from the operation unit 31 or the external device 200, the control unit 50 starts the operation of the job (S104). In this embodiment, the information for this job includes image information specified by the operator, the size (width, length) of the recording material P that forms the image, information related to the thickness of the recording material P (thickness or tsubo information (paper type category information) related to the surface properties of the recording material P, such as whether the recording material P is coated paper or not. The control unit 50 writes information about this job into the RAM 52 (S105).

Next, the control unit 50 acquires environmental information detected by the environmental sensor 32 (S106). The ROM 53 also contains table data and other information indicating the correlation between the environmental information and the target value (target current) Itarget of the transfer current for transferring the toner image on the intermediate transfer belt 7 onto the recording material P. It is stored as . Based on the environmental information read in S106, the control unit 50 determines a target current Itarget corresponding to the environment from information indicating the relationship between the environmental information and the target current Itarget, and writes this into the RAM 52 (S107).

Note that the reason why the target current Itarget is changed depending on the environmental information is that the amount of charge on the toner changes depending on the environment. The information indicating the relationship between the environmental information and the target current Itarget is obtained in advance through experiments or the like. Here, the amount of electric charge of the toner may be affected not only by the environment but also by usage history such as the timing of replenishing toner to the developing device 4 and the amount of toner coming out of the developing device 4. In order to suppress these influences, the image forming apparatus 100 is configured so that the amount of charge of the toner in the developing device 4 falls within a certain range. However, if factors other than environmental information that affect the amount of charge of toner on the intermediate transfer belt 7 are known, the target current Itarget may be changed based on that information as well. Further, the image forming apparatus 100 may be provided with a measuring means for measuring the amount of electric charge of the toner, and the target current Itarget may be changed based on information about the amount of electric charge of the toner obtained by this measuring means.

Next, the control unit 50 checks whether information indicating that the secondary transfer roller 8 has been replaced is recorded in the RAM 52 (S108).

If the control unit 50 determines in S108 that information indicating that the secondary transfer roller 8 has been replaced is recorded, the toner image on the intermediate transfer belt 7 and the recording material P to which the toner image is transferred are Before reaching the secondary transfer portion N2, information regarding the electrical resistance of the secondary transfer portion N2 is acquired as follows (S109). In this example, in this case, the secondary transfer portion N2 (in this example, Information regarding the electrical resistance of the secondary transfer roller 8) is mainly acquired. That is, with the secondary transfer roller 8 and the intermediate transfer belt 7 in contact with each other, at least three levels of predetermined voltage (test voltage) or current (test current) are applied from the secondary transfer power source 20 to the secondary transfer roller 8. ). Note that this test voltage or test current is also collectively referred to as "test bias." Then, a current value when a predetermined voltage is supplied or a voltage value when a predetermined current is supplied is detected to obtain the relationship between voltage and current (voltage-current characteristics). The relationship between this voltage and current changes depending on the electrical resistance of the secondary transfer portion N2 (mainly the secondary transfer roller 8 in this embodiment). In the configuration of this embodiment, the relationship between the voltage and current is that the current does not change linearly (proportional) to the voltage, but as shown in FIG. It changes as the situation changes. Therefore, in this embodiment, the predetermined voltage or current to be supplied when acquiring information regarding the electrical resistance of the secondary transfer portion N2 is set at three points so that the relationship between the voltage and current can be expressed by a polynomial. (level 3) or higher. In particular, in this example, three levels of test voltages were used as the test bias in this case (see FIGS. 6 and 7).

Note that in this embodiment, the test bias in multi-point ATVC control is set to three levels, but is not limited to this, and may be more than five levels, for example. The number of levels can be selected as appropriate from the viewpoints of obtaining voltage-current characteristics with sufficient accuracy and not making the control time longer than necessary, but typically 10 levels or less may be sufficient. many. However, the absolute value of at least one level of test bias voltage in multi-point ATVC control (second test mode) is greater than the absolute value of the largest test bias voltage in normal ATVC control (first test mode), which will be described later. Also make it bigger. More specifically, the absolute value of the voltage of at least one level of test bias in the multi-point ATVC control (second test mode) is the same as the absolute value of the voltage of at least one level of test bias in the multi-point ATVC control (second test mode). The next transfer voltage is set to be 80% or more of the absolute value of the target voltage and less than or equal to the absolute value of the output possible voltage (guaranteed voltage) of the secondary transfer power source 20. For example, when the target voltage of the secondary transfer voltage is 2500V, the absolute value of the voltage of at least one level of test bias in multi-point ATVC control (second test mode) is 2000V or more and the output of the secondary transfer power supply 20 is possible. The absolute value of the voltage (for example, 3000V) or less. Thereby, it is possible to accurately determine the secondary transfer current range for limiter control in the first image formation after the new secondary transfer roller 8 is installed.

Next, when the voltage is V and the current is I, the control unit 50 approximates the voltage-current characteristics based on the detection results at the three points with a second-order polynomial shown in Equation 1 below. At this time, in this embodiment, the control unit 50 calculates each coefficient A0, B0, C0 in Equation 1 below by the least squares method, and stores it in the RAM 52 (if each coefficient is already stored, its value is ) (S110).
I=A0×V ² +B0×V+C0...Formula 1

On the other hand, if the control unit 50 determines that the information indicating that the secondary transfer roller 8 has been replaced is not recorded in S108, the control unit 50 removes the toner image on the intermediate transfer belt 7 and the recording material to which the toner image is transferred. Before P reaches the secondary transfer portion N2, information regarding the electrical resistance of the secondary transfer portion N2 is acquired as follows (S111). In this embodiment, in this case, the secondary transfer portion N2 (mainly the secondary transfer roller 8 in this embodiment) is controlled by normal ATVC control (“resistance information acquisition processing”) using at least one level of test voltage or test current. Get information about electrical resistance. That is, with the secondary transfer roller 8 and the intermediate transfer belt 7 in contact with each other, a predetermined voltage (test voltage) or current (test current) of at least one level is applied from the secondary transfer power source 20 to the secondary transfer roller 8. ). Then, a current value when a predetermined voltage is being supplied or a voltage value when a predetermined current is being supplied is detected. In particular, in this embodiment, the test current I1 at one point (one level), more specifically, the target current Itarget acquired in S107, is used as the test bias in this case.

Next, the control unit 50 uses the test current I1 at one point, the detection voltage V1 at the time of supplying this test current, and the coefficients A0, B0, C0 acquired by multi-point ATVC control stored in the RAM 52, Based on this, the voltage-current characteristic of the above equation 1 is corrected as shown in the following equation 2 (S112). At this time, in this embodiment, the control unit 50 calculates the coefficients A1, B1, and C1 in the following equation 2 from the following equations 3, 4, and 5, respectively. Note that the current value when voltage V=V1 in the above equation 1 (approximate equation with coefficients A0, B0, and C0) is I0.
I=A1×V ² +B1×V+C1...Formula 2
A1=(I1/I0)×A0
=(I1/(A0×V1 ² +B0×V1+C0))×A0...Formula 3
B1=(I1/I0)×B0
=(I1/(A0×V1 ² +B0×V1+C0))×B0...Formula 4
C1=(I1/I0)×C0
=(I1/(A0×V1 ² +B0×V1+C0))×C0...Formula 5

In other words, Equation 1 is corrected using the ratio between the test current I1 under normal ATVC control and the current value I0 obtained by applying the detected voltage V1 when the test current I1 is supplied under normal ATVC control to Equation 1. Then, the voltage-current characteristics of Equation 2 are obtained.

Here, FIG. 6 is a graph diagram showing the voltage-current characteristics of the secondary transfer portion N2 when the same test bias is applied before and after replacing the secondary transfer roller 8 with a new one. In the secondary transfer roller 8 before replacement, the internal ion distribution becomes uneven due to voltage application during use, and the electrical resistance increases. Therefore, in the secondary transfer roller 8 before replacement, the current flowing when the same test voltage is applied is smaller than that in the new secondary transfer roller 8. In this way, the approximate curve when the voltage-current characteristic of the secondary transfer portion N2 is approximated by a second-order polynomial is significantly different before and after replacing the secondary transfer roller 8. In FIG. 6, the voltage values of the three test bias points are approximately 380V, approximately 1590V, and approximately 2600V.

Further, FIG. 7 shows an approximate curve (dotted line) obtained by determining the voltage-current characteristics with one test bias after replacing the secondary transfer roller 8 and correcting it using the coefficients A0, B0, and C0 before replacing the secondary transfer roller 8. It is a graph figure which shows the approximated curve (solid line) calculated|required with the test bias of 3 points after exchange. The difference between the two approximate curves is small near one test bias point, but the difference increases as the current (or voltage) becomes larger than the test bias or as the current (or voltage) becomes smaller. Therefore, when the secondary transfer roller 8 is replaced, the voltage-current characteristics cannot be determined correctly unless the coefficients A0, B0, and C0 are newly obtained. In FIG. 7, the test bias at one point has a voltage value of about 1590V, and the test biases at three points have voltage values of about 380V, about 1590V, and about 2600V.

Next, the control unit 50 determines a target value (target voltage) of the secondary transfer voltage to be applied to the secondary transfer roller 8 from the secondary transfer power source 20 (S113). That is, the control unit 50 determines whether there is no recording material P in the secondary transfer unit N2 based on the target current Itarget written in the RAM 52 in S107 and the relationship between the voltage and current determined in S110 or S112. A voltage value Vb required to cause the target current Itarget to flow is determined. This voltage value Vb corresponds to the secondary transfer partial charge voltage. Further, the ROM 53 stores information for determining the recording material shared voltage Vp as shown in FIG. In this embodiment, this information is set as table data indicating the relationship between the moisture content of the atmosphere and the recording material shared voltage Vp for each basis weight category of the recording material P. Note that the control unit 50 determines the amount of moisture in the atmosphere based on environmental information (temperature and humidity) detected by the environmental sensor 32. The control unit 50 determines the recording material shared voltage Vp from the table data based on the basis weight information of the recording material P included in the job information acquired in S105 and the environmental information acquired in S106. . Then, the control unit 50 sets the above-mentioned Vb and Vb+Vp is obtained by adding up Vp, and this is written into the RAM 52. In this embodiment, the initial value of the transfer voltage Vtr is determined before the recording material P reaches the secondary transfer portion N2, and preparation is made for the timing when the recording material P arrives at the secondary transfer portion N2. Alternatively, in the process of S113 after the normal ATVC (S111, S112), the detection voltage V1 when the target current Itarget is supplied in the normal ATVC control is used as the secondary transfer shared voltage Vb, and the secondary transfer voltage is An initial value of Vtr may also be determined.

Note that the table data for determining the recording material shared voltage Vp as shown in FIG. 8 is determined in advance through experiments or the like. Here, the recording material shared voltage (transfer voltage corresponding to the electrical resistance of the recording material P) Vp changes not only depending on the thickness of the recording material P and information related to it (basis weight) but also depending on the surface properties of the recording material P. There is. Therefore, the table data may be set so that the recording material shared voltage Vp also changes depending on information related to the surface properties of the recording material P. Further, in this embodiment, information related to the thickness of the recording material P (further information related to the surface properties of the recording material P) is included in the job information acquired in S105. However, the image forming apparatus 100 may be provided with measuring means for detecting the thickness of the recording material P and the surface properties of the recording material P, and the recording material shared voltage Vp may be determined based on the information obtained by this measuring means. .

Next, the control unit 50 determines the range of current that may be passed through the paper passing portion (“paper passing portion current range (passing portion current range)”) when the recording material P is passing through the secondary transfer portion N2. A determining process is performed (S114). The ROM 53 contains information for determining the range of current that can be passed through the paper passing portion when the recording material P is passing through the secondary transfer portion N2 from the viewpoint of suppressing image defects, as shown in FIG. Stored. In this embodiment, this information is set as table data indicating the relationship between the moisture content of the atmosphere and the upper and lower limits of the current that may be allowed to flow through the paper passing portion. Note that this table data is obtained in advance through experiments and the like. Here, the range of current that can be passed through the paper passing portion changes depending on the width of the recording material P. In this embodiment, the table data is set assuming a recording material P having a width equivalent to A4 size (297 mm). In this embodiment, first, the control unit 50 determines the range of current that can be passed through the paper passing portion corresponding to A4 size from the table data, based on the environmental information acquired in S106. Next, the control unit 50 corrects the range of current that may be applied to the paper passing portion corresponding to A4 size based on the information on the width of the recording material P included in the job information acquired in S105. In other words, the range of current determined based on the above table data corresponds to the width equivalent to A4 size (297 mm). For example, when the width of the recording material P actually used for image formation is the width equivalent to A5 vertical feed (149 mm), that is, half the width equivalent to A4 size, the following procedure is performed. In other words, the current range is corrected to be proportional to the width of the recording material P so that the upper limit value and lower limit value corresponding to A4 size are each halved.

Note that the range of current that may be applied to the paper passing portion from the viewpoint of suppressing image defects may vary depending on not only environmental information but also the thickness and surface properties of the recording material P. Therefore, the table data may be set such that the current range changes depending on information related to the thickness of the recording material P (basis weight) and information related to the surface properties of the recording material P. The range of current that may be passed through the paper passing portion may be set as a calculation formula. Furthermore, the range of current that may be passed through the paper passing portion may be set as a plurality of table data or calculation formulas for each size of recording material P.

Next, the control unit 50 determines the current flowing in the non-sheet passing portion (“non-sheet passing portion current (non-passing portion current)”) based on the following information (S115). Information on the width of the recording material P included in the job information acquired in S105, and the voltage and current of the secondary transfer portion N2 when there is no recording material P in the secondary transfer portion N2 determined in S110 or S112. These are related information and information on the secondary transfer voltage Vtr obtained in S113. For example, if the width of the secondary transfer roller 8 is 338 mm, and the width of the recording material P obtained in S105 is equivalent to the width of A5 vertical feed (149 mm), the width of the non-sheet passing portion is 338 mm. The width is 189 mm, which is obtained by subtracting the width of the recording material P from the width. It is assumed that the secondary transfer voltage Vtr obtained in S113 is, for example, 2500V, and from the relationship between the voltage and current obtained in S110 or S112, the current corresponding to the secondary transfer voltage Vtr is 80 μA. Note that this is an example based on an approximate curve of voltage-current characteristics obtained using three test bias points after replacing the secondary transfer roller 8 shown in FIG. In this case, the current flowing through the non-sheet passing portion corresponding to the secondary transfer voltage Vtr can be calculated using the following proportional calculation:
80μA×189mm/338mm=44.7μA
It can be found from In other words, the current flowing through the non-sheet passing portion is determined by a proportional calculation in which the current 80 μA corresponding to the secondary transfer voltage Vtr is reduced by the ratio of the width of the non-sheet passing portion, 189 mm, to the width of the secondary transfer roller 8, 338 mm. be able to.

In the example shown in FIG. 7, suppose that after replacing the secondary transfer roller 8, the voltage-current characteristics are determined using one point of test bias, and using an approximate curve corrected with the coefficients A0, B0, and C0 before replacement, the secondary transfer roller 8 is Consider the case where the current flowing through the non-sheet passing portion is determined after the transfer roller 8 is replaced. In this case, in the approximate curve, when the secondary transfer voltage Vtr is 2500 V, the current is 70 μA, and the current flowing in the non-sheet passing portion is as follows, based on the approximate curve obtained using the three test bias points above. (44.7 μA), a difference of about 5.6 μA occurs.
70μA×189mm/338mm=39.1μA

Next, the control unit 50 determines the upper limit value and lower limit value (“secondary transfer current range”) of the secondary transfer current when the recording material P passes through the secondary transfer portion N2, and calculates the determined secondary transfer current range. The transfer current range is stored in the RAM 52 (S116). That is, the control unit 50 adds the non-paper passing section current obtained at S115 to the upper limit value and lower limit value of the paper passing section current obtained at S114 to obtain the secondary transfer current range. For example, consider a case where the upper limit of the range of current that may be passed through the paper passing portion corresponding to the width equivalent to A4 size is 40 μA, and the lower limit is 30 μA. In this case, when the width of the recording material P actually used for image formation is equivalent to A5 vertical feed, the upper limit of the range of current that can be passed through the paper passing portion is 20 μA, and the lower limit is 15 μA. Then, when the current flowing through the non-sheet passing portion determined in S115 is 44.7 μA as in the above example, the upper limit value of the secondary transfer current range is 64.7 μA, and the lower limit value is 59.7 μA.

In this way, by detecting information regarding the electrical resistance of the secondary transfer portion N2, it is possible to accurately determine the current flowing through the non-sheet passing portion. Then, the current that is the sum of the current range that is allowed to flow through the sheet passing portion and the current flowing through the non-sheet passing portion is set as the secondary transfer current range in limiter control. As a result, an appropriate image can be output regardless of the electrical resistance of the secondary transfer portion N2 and the recording material P, the size of the recording material P, the thickness of the recording material P, etc., which vary depending on various situations and user usage conditions. becomes possible.

Next, the control unit 50 controls the secondary transfer current when applying the secondary transfer voltage Vtr while the recording material P is present in the secondary transfer portion N2 after the recording material P reaches the secondary transfer portion N2. is detected by the current detection circuit 21 (S117). Further, the control unit 50 compares the detected secondary transfer current value with the secondary transfer current range obtained in S116, and corrects the secondary transfer voltage Vtr output by the secondary transfer power source 20 as necessary. (S118). In other words, if the detected secondary transfer current value is within the secondary transfer current range determined in S116 (more than the lower limit value and less than the upper limit value), the control unit 50 determines that the secondary transfer current value output by the secondary transfer power source 20 is The next transfer voltage Vtr is maintained unchanged (S119). On the other hand, if the detected secondary transfer current value is out of the secondary transfer current range determined in S116 (less than the lower limit value or more than the upper limit value), the control unit 50 sets the detected secondary transfer current value to the value of the secondary transfer current range. The secondary transfer voltage Vtr output from the secondary transfer power source 20 is corrected so that the voltage Vtr is adjusted so that the voltage Vtr is outputted from the secondary transfer power source 20 (S120). In this embodiment, when the upper limit value is exceeded, the secondary transfer voltage Vtr is lowered, and when the secondary transfer current falls below the upper limit value, the correction of the secondary transfer voltage Vtr is stopped, and the The next transfer voltage Vtr is maintained. In this embodiment, the secondary transfer voltage Vtr is lowered stepwise by a predetermined change width ΔVp. In addition, in this embodiment, when the secondary transfer voltage Vtr is below the lower limit value, the secondary transfer voltage Vtr is increased, and when the secondary transfer current exceeds the lower limit value, the correction of the secondary transfer voltage Vtr is stopped, and at that point The secondary transfer voltage Vtr is maintained. In this embodiment, the secondary transfer voltage Vtr is increased stepwise by a predetermined change width ΔVp. In this embodiment, the operations in S117 to S120 are performed by alternately repeating a predetermined detection time (period for detecting current) and a predetermined response time (period for changing voltage). Further, this detection time and response time are repeated while the recording material P is in the secondary transfer portion N2 (more specifically, while the image forming area of the recording material P is passing through the secondary transfer portion N2). As a result, the secondary transfer voltage Vtr is corrected so that the secondary transfer current detected when the recording material P passes through the secondary transfer portion N2 falls within the secondary transfer current range determined in S113. go.

Here, the change width ΔVp of the secondary transfer voltage in limiter control can be set, for example, as follows. From the viewpoint of suppressing density unevenness, the amount of change in the secondary transfer current per unit transport distance of the recording material P can be set in advance. In addition, from the amount of change in the secondary transfer current per unit conveyance distance of the recording material P, the conveyance speed of the recording material P, and the sampling time of the secondary transfer current, the The amount of change in the next transfer current can be set. The change width ΔVp, which is the amount of change in the secondary transfer voltage per time, can be set to the amount of change in the secondary transfer voltage that corresponds to the amount of change in the secondary transfer current. In this case, information on the amount of change in the secondary transfer current per time can be set in advance and stored in the ROM 53. Then, the control unit 50 can determine the change width ΔVp, which is the amount of change in the secondary transfer voltage per time, from the amount of change in the secondary transfer current using the voltage-current characteristics determined by the ATVC control. That is, the change width ΔVp, which is the amount of change in the secondary transfer voltage corresponding to the amount of change in the predetermined secondary transfer current, is determined in accordance with the information regarding the electrical resistance of the secondary transfer portion N2 determined by ATVC control. This makes it possible to suppress rapid changes in the secondary transfer current and suppress density unevenness.

Alternatively, using the voltage-current characteristics determined by ATVC control, the lower limit value (if it is below the lower limit value) or the upper limit value (if it exceeds the upper limit value) of the detection current and secondary transfer current range. You may also obtain a change width ΔVp corresponding to the difference between the two. In other words, it is possible to determine the change width ΔVp that can eliminate the difference between the detection current and the lower limit value or upper limit value of the secondary transfer current range, according to the information regarding the electrical resistance of the secondary transfer portion N2 determined by ATVC control. can. Thereby, by changing the secondary transfer voltage once, the secondary transfer current can be corrected to around the secondary transfer current range (typically, the lower limit value or the upper limit value). In this case, the change width ΔVp may be set to a voltage larger than a voltage sufficient to eliminate the difference between the upper limit value and the lower limit value of the secondary transfer current range. In this case, if the secondary transfer current can be sufficiently corrected to around the predetermined current range, the secondary transfer current supplied by the corrected secondary transfer voltage will be sufficiently within the predetermined current range due to control errors, etc. It may deviate within a small range.

After that, the control unit 50 repeats the processes of S117 to S120 until all images of the job are transferred to the recording material P and outputted (S121).

Note that here, for convenience of explanation of the present invention, the procedure for replacing the secondary transfer roller 8 before the start of a job has been described; however, the procedure for replacing the secondary transfer roller 8 before starting the job is not performed. In this case, the control unit 50 may perform the processing from S104 onwards.

As described above, in the present embodiment, the image forming apparatus 100 includes a control section that performs constant voltage control so that the voltage applied to the transfer member becomes a predetermined voltage while the recording material P passes through the transfer section N2. It is equipped with 50. The control section 50 controls the voltage applied to the transfer member 8 based on the detection result of the current detection section 21 so that the detection result of the current detection section 21 falls within a predetermined range. The image forming apparatus 100 also includes an acquisition unit 31 that acquires replacement information indicating that the transfer member 8 has been replaced. Further, the control unit 50 supplies at least one level of test voltage or test current to the transfer member 8 in a state where there is no recording material P in the transfer unit N2, and the voltage and current detection unit 21 output by the power supply 20 at that time. Execute a first test mode to obtain information on the current detected by the method, and set at least the predetermined voltage (target voltage of the transfer voltage) during image formation based on the information obtained in the first test mode. It is possible. At the same time, the control section 50 supplies a plurality of levels of test voltages or test currents to the transfer member 8 in a state where there is no recording material P in the transfer section N2, and the voltage and current detection section 21 output from the power supply 20 at that time. A second test mode is executed to acquire information on the current detected by range) can be set. Here, the absolute value of the voltage output by the power supply 20 when supplying at least one level of test voltage or test current in the second test mode is the same as that when supplying the test voltage or test current in the first test mode. It is larger than the largest value among the absolute values of the voltages output by the power supply 20. Then, when the exchange information is acquired by the acquisition means 31, the control unit 50 executes the second test mode before the first image formation after the exchange of the transfer member 8, and performs the second test mode. The predetermined voltage and the predetermined range for the first image formation are set based on the information acquired in the mode. More specifically, the absolute value of the voltage output by the power supply 20 when supplying the at least one level of test voltage or test current in the second test mode is determined by 80% or more of the absolute value of the predetermined voltage set in the image forming job to be performed and less than or equal to the absolute value of the outputtable voltage of the power source 20. In this embodiment, the control unit 50 executes the first second test mode after the transfer member 8 is replaced during a preparatory operation when starting a job for forming the first image after the replacement.

Further, in this embodiment, the control unit 50 acquires the voltage-current characteristics based on the information acquired in the second test mode, and determines whether the recording material P is not present in the transfer section N2 based on the voltage-current characteristics. A voltage value for supplying a predetermined current to the transfer member 8 is obtained, and the predetermined voltage is set based on the voltage value. At the same time, the control unit 50 acquires the value of the current flowing through the transfer member 8 when a predetermined voltage is applied to the transfer member 8 when there is no recording material P in the transfer portion N2 based on the voltage-current characteristics, The predetermined range is set based on the current value. Furthermore, in this embodiment, the control unit 50 uses the voltage-current characteristics acquired in the second test mode executed before the first test mode based on the above information acquired in the first test mode. and obtain a voltage value for supplying a predetermined current to the transfer member 8 in a state where there is no recording material P in the transfer portion N2 based on the voltage-current characteristics after the correction, and obtain the above-mentioned predetermined current based on the voltage value. Set the voltage. Furthermore, in this embodiment, the control unit 50 further determines the voltage-current characteristics obtained in the second test mode executed before the first test mode based on the above information obtained in the first test mode. The current value flowing through the transfer member 8 when a predetermined voltage is applied to the transfer member 8 with no recording material P in the transfer portion N2 is obtained based on the voltage-current characteristics after the correction. The predetermined range is set based on the current value. In this embodiment, the processes in S109 and S110 correspond to the first test mode. Furthermore, in this embodiment, the processes of S111 and S112 correspond to the second test mode.

Note that the second test mode can be executed not only before the first image formation after replacing the secondary transfer roller 8 but also in the following cases, for example. For example, it can be executed before the first image formation after the image forming apparatus 100 is powered on. Further, it can be executed when the index value correlated with the usage amount of the secondary transfer roller 8 since the previous execution of the second test mode satisfies a predetermined condition (for example, exceeds a predetermined threshold value). Further, the second test mode can be executed when the change in the environment (temperature, humidity, or absolute moisture content) since the previous execution of the second test mode satisfies a predetermined condition (for example, exceeds a predetermined threshold). This is because in these cases, it is considered that the electrical resistance of the secondary transfer roller 8 changes relatively greatly.

Furthermore, in this embodiment, the target voltage of the secondary transfer voltage is set based on the results of the first test mode, and the secondary transfer current range of limiter control is adjusted by correcting the results of the second test mode. However, the present invention is not limited thereto. A target voltage for a secondary transfer voltage subsequent to the first test mode is set based on the results of the first test mode, and a secondary transfer current for limiter control during image formation subsequent to the first test mode is set. As for the range, one set before the first test mode may be used.

As explained above, in this embodiment, multi-point ATVC control (second test mode) is executed before the first image formation after replacing the secondary transfer roller 8, and based on the result, the The target voltage of the transfer voltage and the secondary transfer current range of limiter control are set. In this multi-point ATVC control, information regarding the electrical resistance of the secondary transfer portion N2 is obtained using at least three levels of test bias. On the other hand, if the secondary transfer roller 8 has not been replaced, normal ATVC control (first test mode) is executed, and at least a target voltage for the secondary transfer voltage is set based on the result. Furthermore, the secondary transfer current range for limiter control may be set by correcting the results of multi-point ATVC control based on the results of normal ATVC control. The absolute value of the largest test bias voltage in this normal ATVC control is smaller than the absolute value of at least one level of test bias voltage in multi-point ATVC control. Thereby, it is possible to accurately determine the secondary transfer current range for limiter control in the first image formation after replacing the secondary transfer roller 8 while suppressing the shortening of the life of the secondary transfer roller 8. Furthermore, by setting the target voltage of the secondary transfer voltage and the secondary transfer current range of limiter control in one second test mode after replacing the secondary transfer roller 8, these can be set in separate test modes. The control can be simplified and the time required for control can be shortened compared to the case in which the control is performed.

[Example 2]
Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are designated by the same reference numerals as in Embodiment 1, and detailed explanations are omitted. do.

In Example 1, information regarding the electrical resistance of the secondary transfer portion N2 was obtained using one level of test bias in normal ATVC control. On the other hand, it is also possible to obtain information regarding the electrical resistance of the secondary transfer portion N2 by using a plurality of levels of test bias under normal ATVC control. In the following cases, it may be desirable to obtain information regarding the electrical resistance (voltage-current characteristics) of the secondary transfer portion N2 using two or more levels (for example, two to three levels) of test bias. For example, jobs that change the target current during job execution, such as double-sided image formation jobs, jobs that form images on multiple different types of recording materials P, and jobs that include switching between color image formation and monochrome image formation, etc. For example, when executing.

When using multiple levels of test bias in normal ATVC control, it is preferable to set the current value of the test bias to a current value close to the target current Itarget. This is because if a large current or voltage is supplied to the secondary transfer roller 8 frequently, such as during the pre-rotation process of each job, the electrical resistance of the secondary transfer roller 8 will increase, and the secondary transfer roller 8 will This is because the lifespan will be shortened.

FIG. 10 is a graph diagram showing the following two approximate curves. One is an approximate curve (dotted line) in which the voltage-current characteristics are determined using test bias at three points near the target current Itarget after replacing the secondary transfer roller 8 and corrected using the coefficients A0, B0, and C0 before the replacement. The other one is an approximate curve (solid line) obtained by using test biases at three points that are greatly varied with respect to the target current Itarget after replacing the secondary transfer roller 8. The difference between the two approximate curves is small near the test bias at the three points near the target current ITarget, but the difference increases as the current (or voltage) becomes larger than the test bias or as the current (or voltage) becomes smaller. growing. Therefore, when the secondary transfer roller 8 is replaced, the voltage-current characteristics cannot be determined correctly unless the test bias is greatly changed relative to the target current and the coefficients A0, B0, and C0 are newly acquired. In FIG. 10, the test biases at three points near the target current have voltage values of approximately 1300V, approximately 1425V, and approximately 1550V, and the test biases at three points that are significantly swung relative to the target current have voltage values of approximately 380V, They are approximately 1590V and approximately 2600V.

FIG. 11 is a flowchart showing an outline of the procedure for controlling the secondary transfer voltage in this embodiment. For convenience of explanation of the present invention, FIG. 11 shows an example of a procedure for replacing the secondary transfer roller 8 before starting a job.

The processing from S201 to S208 is the same as the processing from S101 to S108 in the first embodiment shown in FIG. 4, so the explanation will be omitted.

If the control unit 50 determines in S208 that information indicating that the secondary transfer roller 8 has been replaced is recorded, the toner image on the intermediate transfer belt 7 and the recording material P to which the toner image is transferred are Before reaching the secondary transfer portion N2, information regarding the electrical resistance of the secondary transfer portion N2 is acquired as follows (S209). In this embodiment, in this case, information regarding the electrical resistance of the secondary transfer portion N2 (mainly the secondary transfer roller 8 in this embodiment) is acquired by coarse multipoint ATVC control (“coarse multipoint resistance information acquisition processing”). do. In other words, when the secondary transfer roller 8 and the intermediate transfer belt 7 are in contact with each other, the secondary transfer power source 20 outputs at least three levels of voltage to the secondary transfer roller 8 and the voltage that the secondary transfer power source 20 can output. Provide a test bias that includes near the upper limit and near the lower limit of the absolute value of. Note that at least one level of test bias between the test bias near the upper limit and the test bias near the lower limit is preferably set near the target current. Then, a current value when a predetermined voltage is being supplied or a voltage value when a predetermined current is being supplied is detected. In particular, in this example, three levels of test voltages were used as the test bias in this case (see FIG. 10).

In this embodiment, the test bias in the coarse multi-point ATVC control is set to three levels, but is not limited to this, and may be more than five levels, for example. The number of levels can be selected as appropriate from the viewpoints of obtaining voltage-current characteristics with sufficient accuracy and not making the control time longer than necessary, but typically 10 levels or less may be sufficient. many. However, the absolute value of the voltage of at least one level of test bias in coarse multipoint ATVC control (second test mode) is the absolute value of the voltage of the largest test bias in normal ATVC control (first test mode), which will be described later. Make it bigger than. More specifically, the absolute value of the voltage of at least one level of test bias in the coarse multi-point ATVC control (second test mode) is determined during image formation subsequent to the coarse multi-point ATVC control (second test mode). 80% or more of the absolute value of the target voltage of the secondary transfer voltage and less than or equal to the absolute value of the output possible voltage (guaranteed voltage) of the secondary transfer power source 20. Note that the coarse multi-point ATVC control in this embodiment is substantially the same as the multi-point ATVC control in the first embodiment.

Next, when the voltage is V and the current is I, the control unit 50 approximates the voltage-current characteristics based on the detection results at the three points using the second-order polynomial shown in Equation 1 above. At this time, similarly to the first embodiment, the control unit 50 calculates each coefficient A0, B0, C0 in the above-mentioned equation 1 by the least squares method, and stores it in the RAM 52 (if each coefficient is already stored, updates its value) (S210).

On the other hand, if the control unit 50 determines that the information indicating that the secondary transfer roller 8 has been replaced is not recorded in S208, the control unit 50 removes the toner image on the intermediate transfer belt 7 and the recording material to which the toner image is transferred. Before P reaches the secondary transfer portion N2, information regarding the electrical resistance of the secondary transfer portion N2 is acquired in the following manner. In this embodiment, in this case, the secondary transfer portion N2 (in this embodiment, the main Information regarding the electrical resistance of the secondary transfer roller 8) is acquired. That is, in this embodiment, three levels of test currents I1, I2, and I3 are applied from the secondary transfer power source 20 to the secondary transfer roller 8 while the secondary transfer roller 8 and the intermediate transfer belt 7 are in contact with each other. supply

Here, the test bias near the target current Itarget in this normal ATVC control is such that, for example, the absolute value of the current is within ±20 μA of the target current Itarget, typically within ±10 μA. Further, the test bias near the target current Itarget in this normal ATVC control is such that, for example, the absolute value of the voltage is within ±500V, typically within ±200V of the voltage (Vb) corresponding to the target current Itarget. Note that in this embodiment, the test bias in normal ATVC control is set to three levels, but it is not limited to this, and more levels such as five levels may be used, for example. The number of levels can be selected as appropriate from the viewpoint of being able to obtain the voltage-current characteristics near the target current ITarget with sufficient accuracy and not making the control time longer than necessary, but typically it is 10 levels or less. Often enough.

Next, the control unit 50 corrects the voltage-current characteristics obtained by coarse-multipoint ATVC control as follows (S212). First, the control unit 50 calculates the secondary transfer partial voltage Vb corresponding to the target current Itarget by linear approximation from the test currents I1, I2, I3 at the three points and the detection voltages V1, V2, V3. Next, the control unit 50 uses the above-described The voltage-current characteristic of Equation 1 is corrected as shown in Equation 2 above. At this time, in this embodiment, the control unit 50 calculates the coefficients A1, B1, and C1 in the above-mentioned equation 2 from the following equations 6, 7, and 8, respectively. In addition, in the above-mentioned formula 1 (approximate formula with each coefficient A0, B0, C0), the current value when voltage V=Vb is assumed to be I0.
A1=(Itarget/I0)×A0
=(Itarget/(A0×Vb ² +B0×Vb+C0))×A0...Formula 6
B1=(Itarget/I0)×B0
=(Itarget/(A0×Vb ² +B0×Vb+C0))×B0...Formula 7
C1=(Itarget/I0)×C0
=(Itarget/(A0×Vb ² +B0×Vb+C0))×C0...Formula 8

In other words, the ratio between the target current Itarget and the current value I0 obtained by applying the secondary transfer partial charge voltage Vb (voltage corresponding to the target current Itarget) obtained from the approximate straight line obtained by normal ATVC control to Equation 1. is used to correct Equation 1 and obtain the voltage-current characteristics of Equation 2.

The processing from S213 to S221 is the same as the processing from S113 to S121 in the first embodiment shown in FIG. 4, so the description thereof will be omitted. However, in this embodiment, in the process of S213 after the normal ATVC control (S211, S212), the secondary transfer partial charge voltage Vb obtained from the approximate straight line obtained in the normal ATVC control as described above is used. An initial value of the secondary transfer voltage Vtr is determined.

As described above, in the present embodiment, the control unit 50 determines the voltage-current characteristics based on the voltage and current information obtained by supplying a plurality of levels of test voltages or test currents to the transfer member 8 in the first test mode. A voltage value for supplying a predetermined current to the transfer member 8 when there is no recording material in the transfer section N2 is obtained based on the voltage-current characteristics, and a predetermined voltage (of the transfer voltage) is obtained based on the voltage value. target voltage). In this embodiment, the processes of S209 and S210 correspond to the first test mode. Furthermore, in this embodiment, the processes of S211 and S212 correspond to the second test mode.

As explained above, in this embodiment, coarse multi-point ATVC control (second test mode) is executed before the first image formation after replacing the secondary transfer roller 8, and based on the result, two The target voltage for the next transfer voltage and the secondary transfer current range for limiter control are set. In this coarse multi-point ATVC control, information regarding the electrical resistance of the secondary transfer portion N2 is obtained using test biases that have at least three levels and include near the upper limit and near the lower limit of the absolute value of the voltage that the secondary transfer power source 20 can output. get. On the other hand, if the secondary transfer roller 8 has not been replaced, normal ATVC control (first test mode) using multiple levels of test bias is executed, and based on the results, at least the target of the secondary transfer voltage is Set the voltage. Furthermore, the secondary transfer current range for limiter control may be set by correcting the result of coarse multi-point ATVC control based on the result of normal ATVC control. The absolute value of the voltage of the largest test bias in this normal ATVC control is smaller than the absolute value of the voltage of at least one level of test bias in coarse multi-point ATVC control. As a result, the same effects as in the first embodiment can be obtained, and the setting accuracy of the target voltage corresponding to the target current by normal ATVC control is improved.

[Example 3]
Next, other embodiments of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of Embodiment 1 are designated by the same reference numerals as in Embodiment 1, and detailed explanations are omitted. do.

In Embodiments 1 and 2, the control unit 50 executes the first second test mode after replacing the secondary transfer roller 8 during a preparation operation when starting a job for forming the first image after the replacement. did. In this embodiment, the control unit 50 executes the first second test mode after replacing the secondary transfer roller 8 before an instruction to start a job for forming the first image after the replacement is input. .

FIG. 12 is a flowchart schematically showing a procedure for acquiring information regarding the electrical resistance of the secondary transfer portion N2 immediately after acquiring information indicating that the secondary transfer roller 8 has been replaced.

First, the control unit 50 acquires information indicating that the secondary transfer roller 8 has been replaced (S301). Note that in this embodiment as well, the secondary transfer roller 8 is replaced in the same manner as in the first embodiment. Also, in this embodiment, as in the first embodiment, the operator operates a button (not shown) displayed on the operation unit 31 for inputting that the secondary transfer roller 8 has been replaced. As a result, a signal indicating that the secondary transfer roller 8 has been replaced is input to the control unit 50. When the control unit 50 acquires the information indicating that the secondary transfer roller 8 has been replaced, the control unit 50 clears the usage history information of the secondary transfer roller 8 stored in the counter 54 (in this embodiment, the number of sheets of images formed) is cleared. (reset the count value to 0) (S302).

Next, the control unit 50 executes coarse multi-point ATVC control similar to that described in Example 2 (S303), and acquires information regarding the electrical resistance of the secondary transfer unit N2 (S304). Then, the control unit 50 approximates the detection result in the coarse multipoint ATVC control with the second-order polynomial shown in the above-mentioned equation 1, as in the second embodiment, and calculates each coefficient A0, B0, C0 in the equation 1. It is stored in the RAM 52 (if each coefficient is already stored, its value is updated) (S305). As described above, in this embodiment, the control unit 50 controls the first second test mode after the replacement of the secondary transfer roller 8 in conjunction with the acquisition of replacement information by the operation unit 31, which is an acquisition unit. , is executed before an instruction to start a job for forming the first image after the exchange is input. However, it is not limited to this. For example, the operator may operate a button for instructing execution of coarse-multipoint ATVC control, which is displayed on the operation unit 31 separately from a button for inputting that the secondary transfer roller 8 has been replaced. Then, the second test mode may be executed.

Thereafter, before the first image formation, the secondary transfer roller 8 is transferred in the same way as described in Examples 1 and 2 using the voltage-current characteristics obtained by coarse multi-point ATVC control immediately after replacing the secondary transfer roller 8. The target voltage of the transfer voltage and the secondary transfer current range of limiter control can be set. In other words, it is not necessary to execute the second test mode, such as sparse multi-point ATVC control, after the instruction to start the job for forming the first image is input and before forming the first image.

Note that normal ATVC control similar to that described in Embodiments 1 and 2 may be executed before the first image formation after coarse-multipoint ATVC control immediately after the secondary transfer roller 8 is replaced. In that case, as described in Embodiments 1 and 2, the voltage-current characteristics obtained by coarse-multipoint ATVC control immediately after replacing the secondary transfer roller 8 are corrected based on the results of the normal ATVC control. Can be used.

As described above, in this embodiment, immediately after replacing the secondary transfer roller 8, and before an instruction to start a job for forming the first image after the replacement is input, coarse multi-point ATVC control (second test mode) to obtain information regarding the electrical resistance of the secondary transfer portion N2. As a result, the same effects as in Examples 1 and 2 can be obtained, and the preparation operation at the start of the job for forming the first image after replacing the secondary transfer roller 8 can be simplified.

[others]
Although the present invention has been described above with reference to specific examples, the present invention is not limited to the above-mentioned examples.

Limiter control can also be performed by providing only one of the upper limit and lower limit of current. For example, if a recording material having a higher electrical resistance than a standard recording material is used and it is known that the transfer current is often less than the lower limit value, only the lower limit value can be provided. On the other hand, if a recording material having a lower electrical resistance than a standard recording material is used and it is known that the transfer current often exceeds the upper limit value, only the upper limit value can be provided. In other words, for the transfer current to be within a predetermined range in limiter control, the current must be greater than or equal to the lower limit value, the current must be less than or equal to the upper limit value, and the current must be greater than or equal to the lower limit value and less than or equal to the upper limit value. This includes the following.

Further, the acquisition means for acquiring exchange information indicating that the transfer member has been exchanged is not limited to the operation unit operated by the operator. For example, as the acquisition means, a detection means that automatically detects that the transfer member has been replaced (such as a sensor that detects attachment and detachment of the transfer member based on any operating principle such as mechanical, electrical, magnetic, etc.) may be provided in the image forming apparatus.

Further, in the above-described embodiment, the recording material was conveyed with reference to the center of the transfer member in the direction substantially perpendicular to the conveyance direction, but the present invention is not limited to this. For example, the recording material was conveyed with reference to one end side. It may be configured to be transported, and the present invention is equally applicable thereto.

Further, the present invention is equally applicable to a monochrome image forming apparatus having only one image forming section. In this case, the present invention is applied to a transfer section where a toner image is transferred from an image carrier such as a photosensitive drum to a recording material.

7 Intermediate transfer belt 8 Secondary transfer roller 20 Secondary transfer power source 21 Current detection circuit 22 Voltage detection circuit 31 Operation unit 50 Control unit

Claims (11)

an image carrier that carries a toner image;
a transfer member to which a voltage is applied and transfers the toner image carried on the image carrier to a recording material in a transfer section;
a power source that applies voltage to the transfer member;
a current detection unit that detects a current flowing through the transfer member;
A control unit that controls the power supply,
When the detection result of the current detection unit is within a predetermined range defined by at least one of an upper limit value and a lower limit value while the recording material is passing through the transfer unit, the control unit: Constant voltage control is performed so that the voltage applied from the power source becomes a target voltage, and when the detection result is outside the predetermined range while the recording material is passing through the transfer section, the In an image forming apparatus that adjusts the target voltage so that the detection result falls within the predetermined range , and executes the constant voltage control using the adjusted target voltage ,
comprising an acquisition means for acquiring exchange information indicating that the transfer member has been exchanged;
The control unit supplies at least one level of test voltage or test current to the transfer member when there is no recording material in the transfer unit, and the current detection unit detects when the test voltage is supplied. A first test mode is executed to obtain information on a current or a voltage output from the power supply when the test current is supplied , and at least the target voltage is determined based on the information obtained in the first test mode. can be set, and a plurality of levels of test voltages or test currents are supplied to the transfer member in a state where there is no recording material in the transfer unit, and when the test voltage is supplied, the current detection unit detects the A second test mode is executed to obtain information on the current or the voltage output from the power supply when the test current is supplied , and the target voltage is determined based on the information obtained in the second test mode. and the predetermined range can be set,
The absolute value of the voltage output by the power supply when supplying at least one level of the test voltage or the test current in the second test mode is the absolute value of the voltage output by the power supply when supplying the test voltage or the test current in the first test mode. greater than the largest absolute value of the voltage output by the power supply when
When the exchange information is acquired by the acquisition means, the control unit executes the second test mode before the first image formation after the exchange of the transfer member, and performs the second test mode. The target voltage and the predetermined range at the time of the first image formation are configured to be set based on the information acquired in the mode,
The absolute value of the voltage output by the power supply when supplying the at least one level of the test voltage or the test current in the second test mode is determined by the first image after execution of the second test mode. An image forming apparatus characterized in that the absolute value of the target voltage set in a forming job is 80% or more and the absolute value of the voltage that can be outputted from the power source is less than or equal to the absolute value. 2. The control unit executes the second test mode first after the transfer member is replaced during a preparatory operation for starting a job for forming an image for the first time after the replacement. 1. The image forming apparatus according to 1 . The control unit may execute the first second test mode after the transfer member is replaced before an instruction to start a job for forming a first image after the replacement is input. Item 1. Image forming apparatus according to item 1 . The image forming apparatus according to any one of claims 1 to 3 , wherein the test voltage or the test current in the second test mode has at least three levels. The control unit acquires voltage-current characteristics based on the information acquired in the second test mode, and applies a predetermined current to the transfer member when there is no recording material in the transfer unit based on the voltage-current characteristics. A voltage value for supplying the voltage is acquired, the target voltage is set based on the voltage value, and a predetermined voltage is applied to the transfer member when there is no recording material in the transfer unit based on the voltage-current characteristics. The image forming apparatus according to any one of claims 1 to 4 , wherein a value of a current flowing through the transfer member when applied is acquired, and the predetermined range is set based on the current value. an image carrier that carries a toner image;
a transfer member to which a voltage is applied and transfers the toner image carried on the image carrier to a recording material in a transfer section;
a power source that applies voltage to the transfer member;
a current detection unit that detects a current flowing through the transfer member;
A control unit that controls the power supply,
When the detection result of the current detection unit is within a predetermined range defined by at least one of an upper limit value and a lower limit value while the recording material is passing through the transfer unit, the control unit: Constant voltage control is performed so that the voltage applied from the power source becomes a target voltage, and when the detection result is outside the predetermined range while the recording material is passing through the transfer section, the In an image forming apparatus that adjusts the target voltage so that the detection result falls within the predetermined range, and executes the constant voltage control using the adjusted target voltage,
comprising an acquisition means for acquiring exchange information indicating that the transfer member has been exchanged;
The control unit supplies at least one level of test voltage or test current to the transfer member when there is no recording material in the transfer unit, and the current detection unit detects when the test voltage is supplied. A first test mode is executed to obtain information on a current or a voltage output from the power supply when the test current is supplied, and at least the target voltage is determined based on the information obtained in the first test mode. can be set, and a plurality of levels of test voltages or test currents are supplied to the transfer member in a state where there is no recording material in the transfer unit, and when the test voltage is supplied, the current detection unit detects the A second test mode is executed to obtain information on the current or the voltage output from the power supply when the test current is supplied, and the target voltage is determined based on the information obtained in the second test mode. and the predetermined range can be set,
The absolute value of the voltage output by the power supply when supplying at least one level of the test voltage or the test current in the second test mode is the absolute value of the voltage output by the power supply when supplying the test voltage or the test current in the first test mode. greater than the largest absolute value of the voltage output by the power supply when
When the exchange information is acquired by the acquisition means, the control unit executes the second test mode before the first image formation after the exchange of the transfer member, and performs the second test mode. The target voltage and the predetermined range at the time of the first image formation are configured to be set based on the information acquired in the mode,
The control unit acquires voltage-current characteristics based on the information acquired in the second test mode, and applies a predetermined current to the transfer member when there is no recording material in the transfer unit based on the voltage-current characteristics. A voltage value for supplying the voltage is acquired, the target voltage is set based on the voltage value, and a predetermined voltage is applied to the transfer member when there is no recording material in the transfer unit based on the voltage-current characteristics. An image forming apparatus characterized in that a value of a current flowing through the transfer member when applied is acquired, and the predetermined range is set based on the current value. The control unit corrects the voltage-current characteristics acquired in the second test mode executed before the first test mode based on the information acquired in the first test mode, and Obtaining a voltage value for supplying a predetermined current to the transfer member when there is no recording material in the transfer unit based on the corrected voltage-current characteristic, and setting the target voltage based on the voltage value. The image forming apparatus according to claim 5 or 6, characterized in that: The control unit further corrects the voltage-current characteristics acquired in the second test mode executed before the first test mode based on the information acquired in the first test mode, Obtaining a current value flowing through the transfer member when a predetermined voltage is applied to the transfer member with no recording material in the transfer section based on the corrected voltage-current characteristics, and based on the current value. The image forming apparatus according to claim 7, wherein the predetermined range is set. The image forming apparatus according to claim 7 or 8, wherein the test voltage or the test current in the first test mode is one level. The control unit obtains voltage-current characteristics based on the information obtained by supplying the test voltage or the test current of a plurality of levels to the transfer member in the first test mode, and A voltage value for supplying a predetermined current to the transfer member in a state where there is no recording material in the transfer unit is obtained using the transfer unit, and the target voltage is set based on the voltage value. 6. The image forming apparatus according to any one of 6. 11. The image carrier according to claim 1, wherein the image carrier is an intermediate transfer member that transports a toner image that has been primarily transferred from another image carrier to a recording material for secondary transfer. The image forming apparatus described in .

Images