JP7553302B2 - Image forming device - Google Patents

Description

The present invention relates to image forming devices such as copying machines, printers, facsimile machines, printing machines using electrophotography or electrostatic recording methods, or multifunction machines that have multiple functions among these.

Conventionally, for example, electrophotographic image forming apparatuses have been widely used in which a transfer section is formed in which a transferee (intermediate transfer member or recording material) is sandwiched between an image carrier (photoconductor or intermediate transfer member) and a transfer member, and a toner image is transferred from the image carrier to the transferee. During transfer, a transfer voltage is applied to the transfer section. In image forming apparatuses that apply a transfer voltage to the transfer section under constant voltage control during transfer, a setting mode is executed prior to image formation to set a target voltage value for the transfer voltage to be applied to the transfer section under constant voltage control when a toner image is transferred from the image carrier to the transferee passing through the transfer section.

The following setting modes are known. When the toner image is not being transferred, a test voltage or test current is applied to the transfer section, and a target voltage value is set based on the current value or voltage value detected at that time. The following is also known. When the toner image is not being transferred, a multi-stage test voltage or test current is applied to the transfer section to obtain the voltage-current characteristic (IV curve) of the transfer section. Then, based on the obtained voltage-current characteristic, a target voltage value corresponding to a predetermined target current value is set. According to the setting mode, the transfer voltage can be automatically adjusted so that a current of a predetermined target current value flows in the transfer section according to the resistance value of the transfer member or image carrier, which varies depending on individual differences, ambient temperature, usage history (accumulated time of voltage application), etc. Therefore, transfer voltage control using such a setting mode is called ATVC (Automatic Transfer Voltage Control).

For example, a transfer roller as a transfer member may experience relatively large changes in electrical resistance due to the influence of circumferential electrical resistance variations, temperature characteristics of electrical resistance, and changes in electrical resistance with use. For this reason, ATVC control is generally performed before image formation begins at the start of a job.

Patent document 1 proposes ATVC control in which a predetermined voltage is applied to the transfer roller, the current is measured, and the next output voltage is set according to the current value.

Patent Document 2 also proposes ATVC control that changes the voltage value initially applied depending on the environment detected by the environment detection means.

Japanese Patent Application Publication No. 2-264278 JP 2006-72207 A

Conventionally, in ATVC control, in order to determine the target voltage value of the transfer voltage to be applied to the transfer section during image formation, a voltage is often applied to the transfer section so as to flow a current of the target current value during image formation by constant current control. In a configuration capable of constant current control and constant voltage control of the voltage applied to the transfer section, when a voltage is applied to the transfer section so as to flow a current of the target current value during image formation by constant current control, a voltage with an absolute value larger than expected may be output. Here, as described above, ATVC control is known in which the voltage value to be initially applied to the transfer section is determined according to the environment. However, there may be an increase in electrical resistance due to deterioration of the transfer member with use, or an increase in electrical resistance due to adhesion of the transfer member (paper dust, toner, etc.). This may result in a voltage with an absolute value larger than the maximum output value determined by the high voltage output upper limit value (high voltage transformer upper limit value, constant voltage high voltage power supply upper limit value), etc. Therefore, it is insufficient to simply predict the voltage output value in ATVC control based on the environment.

If a voltage with an absolute value greater than the maximum output value (assumed voltage value) is output when ATVC control is being performed, the detection result in ATVC control will differ from the actual result, and so ATVC control must be performed again to grasp the voltage-current characteristics. In addition, if a voltage with an absolute value greater than the maximum output value (assumed voltage value) is output when ATVC control is being performed, there is a risk of fluctuations in the reference potential of the high-voltage board, failure of the high-voltage board, and creeping discharge on the high-voltage board.

Therefore, the object of the present invention is to provide an image forming apparatus that can determine the voltage-current characteristics of the transfer section by preventing the transfer power supply from outputting a voltage whose absolute value is greater than the assumed voltage value.

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier that carries a toner image, a transfer member to which a voltage is applied to transfer the toner image from the image carrier to a transferee in a transfer section, a power source that applies a voltage to the transfer member, a current detection section that detects a current that flows through the transfer member when the power source applies a voltage to the transfer member, and a control section that is capable of executing a setting mode in which, when there is no toner image in the transfer section, a test voltage is applied to the transfer member to set a transfer voltage to be applied to the transfer member when there is a toner image in the transfer section, and the control section controls the power source in the setting mode so that the current value detected by the current detection section becomes a first current value, applies the test voltage to the transfer member, and obtains a first voltage value of the test voltage, and determines a second voltage value based on the first voltage value. a second current value, a second current value is determined, the power source is controlled so that a current value detected by the current detection unit becomes the second current value, the test voltage is applied to the transfer member to obtain a second voltage value of the test voltage, the transfer voltage is set based on the first and second current values and the first and second voltage values, the first current value is set so that an absolute value of the first voltage value is equal to or less than an absolute value of a predetermined voltage value, and the absolute value of the second current value is greater than an absolute value of the first current value, and the control unit sets the second current value to a second value when the first voltage value is a first value, and sets the second current value to a fourth value whose absolute value is smaller than the second value when the first voltage value is a third value whose absolute value is greater than the first value .
According to another aspect of the present invention, a printing apparatus includes an image carrier that carries a toner image, a transfer member to which a voltage is applied and which transfers the toner image from the image carrier to a transferee in a transfer section, a power source that applies a voltage to the transfer member, a current detection section that detects a current that flows through the transfer member when the power source applies a voltage to the transfer member, and a control section that is capable of executing a setting mode in which, when there is no toner image in the transfer section, a test voltage is applied to the transfer member to set a transfer voltage to be applied to the transfer member when there is a toner image in the transfer section, and the control section, in the setting mode, controls the power source so that the current value detected by the current detection section becomes a first current value, applies the test voltage to the transfer member, and obtains a first voltage value of the test voltage, an image forming apparatus including: determining a second current value based on a first voltage value; controlling the power supply so that a current value detected by the current detection unit becomes the second current value, applying the test voltage to the transfer member to obtain a second voltage value of the test voltage; setting the transfer voltage based on the first and second current values and the first and second voltage values; the first current value is set so that the absolute value of the first voltage value is equal to or less than the absolute value of a predetermined voltage value, and the absolute value of the second current value is greater than the absolute value of the first current value; and in the setting mode, the control unit determines a voltage-current characteristic based on the first and second current values and the first and second voltage values, and sets the transfer voltage based on the voltage-current characteristic.

According to the present invention, it is possible to determine the voltage-current characteristics of the transfer section by preventing the transfer power supply from outputting a voltage whose absolute value is greater than the assumed voltage value.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 2 is a schematic block diagram for explaining a control mode of the image forming apparatus. 5A and 5B are schematic diagrams for explaining electrical characteristics of a secondary transfer portion. FIG. 11 is a graph showing a relationship between a secondary transfer current and a secondary transfer efficiency. FIG. 4 is a flowchart of the ATVC control according to the first embodiment. FIG. 4 is a graph for explaining the ATVC control according to the first embodiment. FIG. 11 is a flowchart of the ATVC control according to the second embodiment. FIG. 11 is a graph for explaining the ATVC control according to the second embodiment.

The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[Example 1]
1 is a schematic cross-sectional view of an image forming apparatus 100 according to the present embodiment. The image forming apparatus 100 according to the present embodiment is a tandem-type full-color laser printer that employs an intermediate transfer method and is capable of forming full-color images using an electrophotographic method.

The image forming apparatus 100 has four image forming sections (stations, image forming units) SY, SM, SC, and SK that form toner images of the colors yellow (Y), magenta (M), cyan (C), and black (K). The four image forming sections SY, SM, SC, and SK are arranged in a row at regular intervals along the direction of movement of the intermediate transfer belt 56, which will be described later. Elements in each image forming section SY, SM, SC, and SK that have the same or corresponding functions or configurations may be described collectively by omitting the suffixes Y, M, C, and K of the reference numbers indicating that the elements are for one of the colors. In this embodiment, the image forming unit S is configured to include photosensitive drums 50 (50Y, 50M, 50C, 50K), charging rollers 51 (51Y, 51M, 51C, 51K), exposure devices 52 (52Y, 52M, 52C, 52K), developing devices 53 (53Y, 53M, 53C, 53K), primary transfer rollers 54 (54Y, 54M, 54C, 54K), cleaning devices 55 (55Y, 55M, 55C, 55K), etc., which will be described later.

The photosensitive drum 50, which is a drum-type (cylindrical) electrophotographic photosensitive member (photoconductor) as a rotatable (movable) first image carrier, is rotated in the direction of the arrow R1 in the figure (clockwise direction) by a drum drive motor (not shown) as a drive source constituting the drive means. The photosensitive drum 50 is rotated at a preset predetermined peripheral speed (process speed). The surface of the rotating photosensitive drum 50 is charged approximately uniformly to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 51, which is a roller-shaped charging member as a charging means. During charging, a predetermined charging voltage (charging bias) is applied to the charging roller 51 by a charging power source (not shown), which is a high-voltage power source as a charging voltage application means. The surface of the charged photosensitive drum 50 is scanned and exposed by an exposure device 52 as an exposure means according to image information corresponding to each image forming unit S, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 50. In this embodiment, the exposure device 52 is a laser scanner device that scans the photosensitive drum 50 in the longitudinal direction (rotation axis direction) with laser light modulated according to image information.

The electrostatic image formed on the photosensitive drum 50 is developed (visualized) by the developing device 53 as a developing means with toner of a color corresponding to each image forming section S, and a toner image (developer image) is formed on the photosensitive drum 50. In this embodiment, the developing device 53 is a two-component developing method that uses a two-component developer mainly comprising non-magnetic toner particles (toner) and magnetic carrier particles (carrier) as a developer. The developing device 53 conveys the developer to the opposing portion (developing portion) with respect to the photosensitive drum 50 by a developing sleeve as a rotatable developer carrier. Then, a predetermined developing voltage (developing bias) is applied to the developing sleeve by a developing power source (not shown) which is a high-voltage power source as a developing voltage application means. As a result, the toner is transferred from the developer on the developing sleeve to the photosensitive drum 50 according to the electrostatic image. In this embodiment, a developing voltage in which an AC voltage component Vac is superimposed on a negative DC voltage component Vdc is applied to the developing sleeve. In this embodiment, toner charged to the charge polarity of the photosensitive drum 50 (negative in this embodiment) adheres to the exposed portion (image portion) of the photosensitive drum 50, which has been uniformly charged and then exposed to light to reduce the absolute value of the potential (reverse development). In this embodiment, the normal charge polarity of the toner, which is the charge polarity of the toner during development, is negative. Each of the developing devices 53Y, 53M, 53C, and 53K contains toner of the colors yellow, magenta, cyan, and black, respectively.

An intermediate transfer belt 56, which is an intermediate transfer body composed of an endless belt as a rotatable (movable) second image carrier, is arranged to face the four photosensitive drums 50Y, 50M, 50C, and 50K. The inner circumferential surface of the intermediate transfer belt 56 is supported by a plurality of tension rollers (support rollers) including a drive roller 63, a tension roller 60, an upstream auxiliary roller 67, a downstream auxiliary roller 61, and a secondary transfer opposing roller 62, and is stretched with a predetermined tension. The intermediate transfer belt 56 is formed in an endless shape from a dielectric resin such as polyimide. The intermediate transfer belt 56 rotates (moves around) in the direction of the arrow R2 in the figure (counterclockwise direction) by the drive roller 63 being driven to rotate by a belt drive motor (not shown) as a drive source constituting the drive means. The intermediate transfer belt 56 is driven to rotate at a circumferential speed (process speed) that is approximately the same as the circumferential speed of the photosensitive drum 50. On the inner peripheral surface side of the intermediate transfer belt 56, a primary transfer roller 54, which is a roller-shaped primary transfer member as a primary transfer means, is arranged corresponding to each photosensitive drum 50. The primary transfer roller 54 presses the inner peripheral surface of the intermediate transfer belt 56 toward the photosensitive drum 50 to form a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 50 and the intermediate transfer belt 56 come into contact with each other. The toner image formed on the photosensitive drum 50 is transferred (primary transfer) onto the rotating intermediate transfer belt 56 as a transfer target by the action of the primary transfer roller 54 at the primary transfer portion N1. During the primary transfer, a primary transfer voltage (primary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the primary transfer roller 54 by a primary transfer power source (not shown) which is a high-voltage power source as a primary transfer voltage application means. For example, when forming a full-color image, the toner images of the colors Y, M, C, and K formed on each photosensitive drum 50 are sequentially transferred (primary transfer) to the intermediate transfer belt 56 so as to be superimposed on each other at each primary transfer section N1Y, N1M, N1C, and N1K.

On the outer peripheral surface side of the intermediate transfer belt 56, a secondary transfer roller (secondary transfer outer roller) 64, which is a roller-shaped secondary transfer member serving as a secondary transfer means, is disposed at a position facing the secondary transfer opposing roller (secondary transfer inner roller) 62. The secondary transfer roller 64 is pressed toward the secondary transfer opposing roller 62 and abuts against the secondary transfer opposing roller 62 via the intermediate transfer belt 56 to form a secondary transfer portion (secondary transfer nip) N2 where the intermediate transfer belt 56 and the secondary transfer roller 64 come into contact. In the secondary transfer portion N2, the toner image formed on the intermediate transfer belt 56 is transferred (secondarily transferred) by the action of the secondary transfer roller 64 onto a recording material P such as a recording paper that is being conveyed while being sandwiched between the intermediate transfer belt 56 and the secondary transfer roller 64 as a transferee. During the secondary transfer, a secondary transfer voltage (secondary transfer bias), which is a DC voltage of the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer roller 64 by a secondary transfer power source E2 (FIG. 2) which is a high-voltage power source serving as a secondary transfer voltage application means. The secondary transfer opposing roller 62 is electrically grounded (connected to ground). The recording material P is fed from a cassette (not shown) serving as a recording material storage section by a feed roller (not shown) serving as a feeding means, and is conveyed to the pair of registration rollers 11 serving as a conveying member. The pair of registration rollers 11 corrects the skew of the recording material P, and conveys the recording material P to the secondary transfer section N2 in synchronization with the toner image on the intermediate transfer belt 56. The recording material P conveyed by the pair of registration rollers 11 is guided to the secondary transfer section N2 with its conveying trajectory regulated by a pre-transfer guide member 12.

The recording material P with the transferred toner image is transported to a fixing device (not shown) as a fixing means. The fixing device pressurizes and heats the recording material P while nipping and transporting it in the fixing nip between the fixing roller and the pressure roller, thereby fixing (melting and bonding) the toner image onto the recording material P. The recording material P with the fixed toner image is discharged (output) outside the main body of the image forming apparatus 100.

On the other hand, the toner remaining on the photosensitive drum 50 after the primary transfer (primary transfer residual toner) is removed from the photosensitive drum 50 by the cleaning device 55 as a cleaning means and collected. In this embodiment, the cleaning device 55 scrapes off and collects the primary transfer residual toner from the surface of the rotating photosensitive drum 50 by using a cleaning blade as a cleaning member that contacts the surface of the photosensitive drum 50. In addition, a belt cleaning device 65 as an intermediate transfer body cleaning means is disposed at a position facing the drive roller 63 on the outer peripheral surface side of the intermediate transfer belt 56. The toner remaining on the intermediate transfer belt 56 after the secondary transfer (secondary transfer residual toner) and paper powder and other adhesions are removed from the intermediate transfer belt 56 by the belt cleaning device 65 and collected. In this embodiment, the belt cleaning device 65 scrapes off and collects adhesions such as secondary transfer residual toner from the surface of the rotating intermediate transfer belt 56 by using a cleaning blade as a cleaning member that contacts the surface of the intermediate transfer belt 56.

In this embodiment, in each image forming section S, the photosensitive drum 50 and the charging roller 51, developing device 53, and cleaning device 55 acting on the photosensitive drum 50 as process means integrally constitute a process cartridge that is detachably attached to the main body of the image forming device 100.

The image forming apparatus 100 of this embodiment has a double-sided transport section (not shown) that transports the recording material P, which has a toner image fixed on its first surface, again to the secondary transfer section N2. The image forming apparatus 100 can then form a toner image on the second surface, opposite the first surface, of the recording material P transported again to the secondary transfer section N2 by the double-sided transport section, fix the toner image, and output the recording material. In this way, the image forming apparatus 100 of this embodiment is configured to enable automatic double-sided printing.

In addition, the image forming apparatus 100 of this embodiment is capable of forming images in a full-color mode in which a toner image can be formed using the image forming units SY, SM, SC, and SK for the colors Y, M, C, and K, and in a black monochrome mode in which a toner image can be formed using only the image forming unit K for the color K.

2. Secondary Transfer Configuration In this embodiment, the secondary transfer roller (transfer roller) 64 as the secondary transfer member (transfer rotating body) has a conductive shaft core (conductive shaft) and an elastic layer (outer peripheral layer) formed on the outer periphery of the shaft core. The shaft core of the secondary transfer roller 64 is a cylindrical member formed of a conductive material (conductor) such as metal (e.g., stainless steel). The elastic layer of the secondary transfer roller 64 is formed of a sponge-like or solid elastic material with a thickness of, for example, about 4 mm. In this embodiment, the entire outer diameter (roller diameter) of the secondary transfer roller 64 is about 20 mm.

As the elastic material constituting the elastic layer of the secondary transfer roller 64, elastomers such as NBR (acrylonitrile butadiene rubber) and EPDM (ethylene propylene rubber) and other synthetic resins can be used. In addition, an ionically conductive conductive agent (ion conductive agent) such as a metal complex is added to the material constituting the elastic layer of the secondary transfer roller 64 to impart appropriate conductivity (semiconductivity). As the ionically conductive conductive agent, a semiconductive polymer such as epichlorohydrin rubber may be kneaded into the base material of the elastic layer, or a semiconductive polymer and a metal complex may be used in combination. In addition, an electronically conductive conductive agent (electronic conductive agent) such as carbon or metal oxide and the above-mentioned ionically conductive conductive agent may be dispersed in the material constituting the elastic layer of the secondary transfer roller 64.

In this embodiment, the secondary transfer opposing roller 62, which serves as an opposing roller facing the secondary transfer roller 64 across the intermediate transfer belt 56, has an elastic layer made of an elastic material such as EPDM and having a thickness of about 0.5 mm, and a metal shaft core that supports the elastic layer. In this embodiment, the overall outer diameter (roller diameter) of the secondary transfer opposing roller 62 is about 16 mm.

The material constituting the elastic layer of the secondary transfer opposing roller 62 is given appropriate electrical conductivity by adding the above-mentioned ionic conductive agent or electronic conductive agent such as carbon. In addition, the hardness of the elastic layer of the secondary transfer opposing roller 62 is set to 70° using, for example, an Asker C-type measuring device.

3. Control Mode Fig. 2 is a schematic block diagram for explaining the control mode of the image forming apparatus 100 in this embodiment.

The image forming apparatus 100 has a controller 110 as a control unit. The controller 110 is configured with a CPU 111 as an arithmetic control means (arithmetic control unit) that is a central element for performing arithmetic processing, and a memory (storage medium) 112 such as a ROM or RAM as a storage means (storage unit). The RAM, which is a rewritable memory, stores information input to the controller 110, detected information, arithmetic results, etc., and the ROM stores a control program, a data table that has been determined in advance, etc. The CPU 111 and the memory 112 such as the ROM or RAM can transfer and read data to and from each other. The controller 110 is also provided with an input/output circuit (not shown) that controls communication between the controller 110 and external devices.

A secondary transfer power supply (high voltage circuit) E2 is connected to the secondary transfer roller 64. A voltage control unit (voltage control circuit) 120 is connected to the secondary transfer power supply E2, which controls the voltage applied by the secondary transfer power supply E2 to the secondary transfer roller 64 (secondary transfer section N2) under the control of the controller 110. In this embodiment, the secondary transfer power supply E2 is configured to have a constant voltage high voltage power supply circuit. The voltage control unit 120 can detect the voltage output by the secondary transfer power supply E2 from a control signal (indication value) that controls the output of the secondary transfer power supply E2. Note that the voltage control unit 120 may be provided with a voltage detection unit (voltage detection circuit) that detects the voltage output by the secondary transfer power supply E2. The voltage control unit 120 inputs a signal indicating the detection result of the voltage value to the controller 110. In this embodiment, the voltage control unit 120 is provided with a current detection unit (current detection circuit) 121. The current detection unit 121 can detect the current flowing through the secondary transfer roller 64 (secondary transfer unit N2 or secondary transfer power supply E2) when the secondary transfer power supply E2 applies a voltage to the secondary transfer roller 64 (secondary transfer unit N2). The current detection unit 121 inputs a signal indicating the detection result of the current value to the controller 110.

In this embodiment, the voltage control unit 120 adjusts the voltage output by the secondary transfer power supply E2 so that the value of the current detected by the current detection unit 121 becomes (approaches) a target value (target current value), thereby enabling constant current control of the voltage applied by the secondary transfer power supply E2 to the secondary transfer roller 64. Also, in this embodiment, the voltage control unit 120 adjusts (sets) the output voltage of the secondary transfer power supply E2 so that the output voltage value of the secondary transfer power supply E2 becomes (approaches) a target value (target voltage value), thereby enabling constant voltage control of the voltage applied by the secondary transfer power supply E2 to the secondary transfer roller 64.

The controller 110 is also connected to an environmental sensor 130 as an environmental detection means for detecting at least one of the temperature and humidity inside or outside the image forming device 100. In this embodiment, the environmental sensor 130 is configured as a temperature and humidity sensor, and is provided inside the main body of the image forming device 100, and is capable of detecting the temperature and humidity inside (inside the machine) of the image forming device 100. The environmental sensor 130 inputs a signal indicating the detection result of the temperature and humidity to the controller 110. The controller 110 is capable of calculating the absolute moisture amount based on the detection result of the temperature and humidity by the environmental sensor 130. In this embodiment, the environmental sensor 130 is provided to detect the temperature and humidity near the developing device 53.

The controller 110 controls each part of the image forming apparatus 100 in an integrated manner to perform sequence operations. The controller 110 receives an image formation signal (image data, control command) from an external device (host device) 200, such as an image reading device or a personal computer, connected to the image forming apparatus 100. The controller 110 controls each part of the image forming apparatus 100 according to the image formation signal (job information) to perform image formation operations. The control command includes an image formation start instruction, information about the recording material P, and information about image formation conditions such as the number of images formed. The information about the recording material P includes any information that can distinguish the recording material P, such as attributes based on general characteristics such as plain paper, fine paper, glossy paper, glossy paper, coated paper, embossed paper, thick paper, thin paper, and paper quality (so-called paper type categories), numerical values or numerical ranges such as basis weight, thickness, size, and stiffness, or brands (including manufacturers, product names, product numbers, etc.). Each recording material P distinguished by information about the recording material P can be considered to constitute a type of recording material P. The information about the recording material P may be included in information about an image forming mode that specifies the operation settings of the image forming apparatus 100, such as "plain paper mode" or "gloss paper mode," or may be replaced by the information about the image forming mode. In addition, a part or all of the image forming signal (job information) may be input to the controller 110 from an operation unit (not shown) equipped with a display means and an input means provided in the image forming apparatus 100.

Here, the image forming apparatus 100 executes a job (print job, image output 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. A job generally has an image forming process, a pre-rotation process, a paper-interval process when forming an image on multiple recording materials P, and a post-rotation process. The image forming process is a period during which the electrostatic image of the image to be actually formed on the recording material P and output, the toner image, the primary transfer of the toner image, and the secondary transfer are performed, and the image forming time refers to this period. More specifically, the timing during image formation differs depending on the positions at which the electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer are performed, and corresponds to the period during which the image forming area on the photosensitive drum 50 or the intermediate transfer belt 56 passes through each of the above positions. The pre-rotation process is a period during which a preparatory operation is performed before the image forming process, from when a start instruction is input until the image actually starts to be formed. The sheet interval process is a period corresponding to the interval between recording materials P when image formation is continuously performed on a plurality of recording materials P (continuous printing, continuous image formation). The post-rotation process is a period during which a rearrangement operation (preparatory operation) is performed after the image formation process. The non-image formation time is a period other than the image formation time, and includes the pre-rotation process, the sheet interval process, the post-rotation process, and the pre-multiple rotation process, which is a preparatory operation when the image forming apparatus 100 is turned on or when the image forming apparatus 100 returns from a sleep state. More specifically, the timing during the non-image formation time corresponds to a period during which the non-image formation area on the photosensitive drum 50 or the intermediate transfer belt 56 passes through each position where the electrostatic image formation, the toner image formation, the primary transfer of the toner image, and the secondary transfer are performed. The image formation area on the photosensitive drum 50 or the intermediate transfer belt 56 is an area in which an image that is transferred to the recording material P and output from the image forming apparatus 100 can be formed, and the non-image formation area is an area other than the image formation area. In this embodiment, the controller 110 is capable of executing the ATVC control described below when no image formation is taking place.

4. Electrical Characteristics of the Secondary Transfer Section FIG. 3 is a schematic diagram for explaining the electrical characteristics of the secondary transfer section N2 in this embodiment. In this embodiment, during image formation (secondary transfer), a voltage (secondary transfer voltage) is applied to the secondary transfer roller 64 (secondary transfer section N2) by the secondary transfer power source E2, so that a current (secondary transfer current) flows from the secondary transfer roller 64 to the electrically grounded secondary transfer opposing roller 62. As a result, a transfer electric field (secondary transfer electric field) is formed in the secondary transfer section N2, which moves the toner charged to the normal charging polarity from the intermediate transfer belt 56 to the recording material P passing through the secondary transfer section N2. In this embodiment, the secondary transfer power source E2 is a constant voltage source that outputs a voltage of the polarity opposite to the normal charging polarity of the toner to the secondary transfer roller 64 (positive polarity in this embodiment).

In this embodiment, the maximum output value (maximum possible output voltage value) Vmax of the secondary transfer power source E2 is set to 6500 [V]. This maximum output value Vmax is the maximum absolute value of the voltage that the secondary transfer power source E2 can apply to the secondary transfer roller 64 (secondary transfer section N2), which is determined based on the high voltage output upper limit value (high voltage transformer upper limit value, constant voltage high voltage power supply upper limit value), etc. This maximum output value Vmax does not necessarily have to be the high voltage output upper limit value itself, and may be set to a value lower than the high voltage output upper limit value.

In addition, in this embodiment, the process speed of the image forming device 100 is 320 mm/s (corresponding to the peripheral speed of the intermediate transfer belt 56).

Figure 4 is a graph diagram showing a schematic relationship between the secondary transfer current and the secondary transfer efficiency. The secondary transfer efficiency is expressed by the ratio of the toner transferred to the recording material P among the toner carried on the intermediate transfer belt 56. As shown in Figure 4, the secondary transfer efficiency generally peaks (white circle in the figure) at a certain secondary transfer current value. Therefore, it is desirable that the secondary transfer voltage is controlled (set) so that the secondary transfer current of the value at which the secondary transfer efficiency peaks flows to the secondary transfer roller 64 (secondary transfer section N2). Since the electrical resistance of the secondary transfer section N2 (mainly the secondary transfer roller 64 in this embodiment) varies depending on the amount of use of the member and the environment, the secondary transfer voltage value at which the desired secondary transfer current value is obtained also changes. Therefore, during non-image formation, a voltage is applied to the secondary transfer roller 64 (secondary transfer section N2) in a state where there is no recording material P in the secondary transfer section N2, and information on the relationship between the voltage and the current is obtained. This allows information regarding the electrical resistance of the secondary transfer section N2 (mainly the secondary transfer roller 64 in this embodiment) to be obtained. Then, based on this information, the secondary transfer voltage to be applied to the secondary transfer roller 64 (secondary transfer section N2) during image formation (secondary transfer) is set. This type of control (setting mode) is the ATVC control mentioned above.

An example of a general ATVC control will be described. Before the recording material P reaches the secondary transfer portion N2, the target voltage value of the secondary transfer voltage during image formation is determined so that a secondary transfer current of the target current value It at which the secondary transfer efficiency peaks flows when the recording material P is present at the secondary transfer portion N2 during image formation (secondary transfer). More specifically, for example, before image formation, the controller 110 performs constant current control of the voltage applied to the secondary transfer roller 64 (secondary transfer portion N2) so that the current value detected by the current detection portion 121 approaches the target current value It when there is no recording material P at the secondary transfer portion N2. This target current value It is set in advance according to the type (basis weight, material, etc.) of the recording material P and the environment. Then, based on the voltage value detected at this time, the controller 110 determines the target voltage value of the secondary transfer voltage to be applied to the secondary transfer roller 64 (secondary transfer portion N2) when the recording material P is present at the secondary transfer portion N2 during image formation (secondary transfer). More specifically, the target voltage value of the secondary transfer voltage applied to the secondary transfer roller 64 during image formation can be set by adding the recording material voltage to the voltage value determined according to the electrical resistance of the secondary transfer portion N2 as described above. The recording material voltage is set in advance according to the type (basis weight, material, etc.) of the recording material P used in image formation and the environment. However, for simplicity, a detailed explanation of the recording material voltage is omitted here.

An example of typical ATVC control at the secondary transfer section N2 has been described above. However, as mentioned above, in a configuration that allows constant current control and constant voltage control of the voltage applied to the secondary transfer section N2, when a voltage is applied to the secondary transfer section N2 so as to pass a current of a target current value during image formation under constant current control, a voltage with an absolute value larger than expected may be output.

5. ATVC Control of the Present Embodiment Next, the ATVC control of the secondary transfer portion N2 in the present embodiment will be described. Fig. 5 is a flow chart showing an outline of the procedure of the ATVC control in the present embodiment. Fig. 6 is a graph showing a schematic voltage-current characteristic for explaining the ATVC control in the present embodiment.

In this embodiment, the ATVC control (setting mode) of the secondary transfer section N2 is performed in the pre-rotation process each time a job is executed. In this embodiment, the secondary transfer roller 64 is made of an elastic material, and there may be unevenness in electrical resistance. Therefore, in this embodiment, in order to accurately determine the target voltage value of the secondary transfer voltage, in the ATVC control, a voltage is applied to the secondary transfer roller 64 for at least one rotation (one rotation in this embodiment) of the secondary transfer roller 64 with constant current control at a predetermined current value. Then, based on the average value of the voltage value detected at that time, a process for determining the target voltage value of the secondary transfer voltage, which will be described below, is performed. Note that the ATVC control is not limited to being executed for each job, but can be executed during non-image formation at predetermined timings, such as for every predetermined number of image formations (number of prints) or when the environmental change exceeds a predetermined range. In addition, the ATVC control is not limited to being executed during the pre-rotation operation, but may be executed between sheets or during the post-rotation process.

In addition, in this embodiment, the target current value It (also referred to here as the "table value") corresponding to the secondary transfer current value at which the secondary transfer efficiency described with reference to FIG. 4 shows a peak is obtained for each type of recording material P (basis weight, material, etc.) according to the environment (absolute moisture content), and is set as a table as shown in Table 1. This table of target current values It is stored in memory 112 in advance. Table 1 shows the setting of the target current value It for a predetermined type of recording material P (for example, plain paper) as an example. Also, as shown in Table 1, in this embodiment, the table value of the target current value It is set corresponding to each of the full color mode and the black monochrome mode. Also, as shown in Table 1, in this embodiment, the table value of the target current value It is set corresponding to each of the single-sided print (and the first side of the double-sided print) and the second side of the double-sided print in each of the full color mode and the black monochrome mode. Note that, when the image forming apparatus 100 is capable of operating at a plurality of different process speeds, the target current value It may be set for each process speed as a table as shown in Table 1, for example. In addition, the target current value It corresponding to the absolute moisture content not included in the table can be found, for example, by linear interpolation.

When a job is started, the controller 110 starts ATVC control in the pre-rotation process (S101). When the controller 110 starts ATVC control, it obtains the temperature and humidity inside the machine detected by the environmental sensor 130 to determine the absolute moisture content (S102). Next, the controller 110 determines the table value of the target current value It from a table such as that shown in Table 1 according to the type of recording material P selected in the job information (paper type setting) and the above-mentioned absolute moisture content (S103). Next, the controller 110 outputs a constant current controlled voltage from the secondary transfer power source E2 so that the current detected by the current detection unit 121 becomes a predetermined first stage target current value (first current value) I1 that has been set in advance (S104). This first stage target current value I1 has an absolute value smaller than the table value of the above-mentioned target current It. The first-stage target current value I1 is preset so that the output of the secondary transfer power source E2 is equal to or less than the maximum output value, and a voltage equal to or greater than the discharge start voltage is applied to the secondary transfer roller 64 (secondary transfer portion N2). In particular, in this embodiment, the first-stage target current value I1 is set to 5 μA. By performing ATVC control with constant current control, a voltage equal to or greater than the discharge start voltage can be reliably applied to the secondary transfer portion N2. The controller 110 averages the voltage values detected by the voltage control portion 120 while the secondary transfer power source E2 is outputting a voltage controlled by the constant current at the first-stage target current value I1, and obtains the averaged first-stage detection voltage value V1 (S105).

Next, the controller 110 determines the second-stage target current value (second current value) I2 of the voltage to be output from the secondary transfer power source E2. First, if the first-stage detection voltage value V1 is less than 200V (first threshold value), the controller 110 determines the second-stage target current value I2 to be the first second-stage target current value I2-1, which is the table value of the above-mentioned target current value It (S106). In this case, it is determined that the impedance of the secondary transfer unit N2 (mainly the secondary transfer roller 64 in this embodiment) is sufficiently low. Then, the controller 110 causes the secondary transfer power source E2 to output a voltage that is constant current controlled so that the current detected by the current detection unit 121 becomes this first second-stage target current value I2-1 (S107).

On the other hand, when the first-stage detection voltage value V1 is equal to or greater than 200V (first threshold) and less than 400V (second threshold), the controller 110 performs the following. That is, the second-stage target current value I2 is determined to be a second second-stage target current value I2-2 whose absolute value is smaller than the table value of the target current value It described above (S108). In this case, it is possible to determine that the impedance of the secondary transfer portion N2 (mainly the secondary transfer roller 64 in this embodiment) is high. This second second-stage target current value I2-2 has an absolute value larger than the first-stage target current value I1. In addition, this second second-stage target current value I2-2 is set so that the output of the secondary transfer power source E2 is equal to or less than the maximum output value, and a voltage equal to or greater than the discharge start voltage is applied to the secondary transfer roller 64 (secondary transfer portion N2). For example, the second second-stage target current value I2-2 is set to 0.7 times the first second-stage target current value I2-1 (the table value of the target current value It in this embodiment). Then, the controller 110 causes the secondary transfer power source E2 to output a voltage that is constant current controlled so that the current detected by the current detection unit 121 becomes the second second-stage target current value I2-2 (S109).

In addition, when the first-stage detection voltage value V1 is 400V (second threshold value) or more, the controller 110 determines the second-stage target current value I2 to be a third second-stage target current value I2-3, which has an even smaller absolute value than the second second-stage target current value I2-2 (S108). In this case, it is determined that the impedance of the secondary transfer portion N2 (mainly the secondary transfer roller 64 in this embodiment) is more likely to be high. This third second-stage target current value I2-3 has a larger absolute value than the first-stage target current value I1. In addition, this third second-stage target current value I2-3 is set so that the output of the secondary transfer power source E2 is equal to or less than the maximum output value, and a voltage equal to or greater than the discharge start voltage is applied to the secondary transfer roller 64 (secondary transfer portion N2). For example, the third second-stage target current value I2-3 is set to 0.5 times the first second-stage target current value I2-1 (the table value of the target current value It in this embodiment). Then, the controller 110 causes the secondary transfer power source E2 to output a voltage that is constant current controlled so that the current detected by the current detection unit 121 becomes the third second-stage target current value I2-3 (S110).

Then, the controller 110 averages the voltage values detected by the voltage control unit 120 while the secondary transfer power source E2 is outputting a constant current controlled voltage at the second stage target current value I2 (I2-1, I2-2, or I2-3), and obtains the averaged second stage detected voltage value V2 (S111).

Next, the controller 110 calculates a linear function (linear curve) as the voltage-current characteristic in this embodiment based on the first-stage target current value I1, the second-stage target current value I2 (I2-1, I2-2, or I2-3), the first-stage detection voltage value V1, and the second-stage detection voltage value V2 (S112). Then, the controller 110 determines the target voltage value (voltage value corresponding to the target current value It) of the secondary transfer voltage to be applied to the secondary transfer roller 64 (secondary transfer section N2) during image formation (secondary transfer) based on the calculated linear function (S113). Thereafter, the controller 110 ends the ATVC control (S114).

As mentioned above, by performing ATVC control with constant current control, a voltage equal to or greater than the discharge start voltage can be reliably applied to the secondary transfer section N2. However, as mentioned above, if the target current value in ATVC control is increased, depending on the environment and durability conditions, it may exceed the maximum output value of the constant voltage high voltage board, which may cause the reference potential of the high voltage board to fluctuate, the high voltage board to break down, or creeping discharge on the high voltage board.

Therefore, in this embodiment, in order to output a voltage from the secondary transfer power source E2 at a target current value that ensures a voltage value below the maximum output value under ATVC control, the absolute value of the first-stage target current value is made sufficiently small. Although not limited to this, it is preferable that the absolute value of the first-stage target current value is 5 μA or less. However, the absolute value of the first-stage target current value is a value or greater at which a voltage equal to or greater than the discharge start voltage is applied to the secondary transfer portion N2. Note that, although the first-stage target current value is 5 μA in this embodiment, it is not limited to this, and it is sufficient to output a voltage that ensures that the output of the secondary transfer power source E2 is equal to or less than the maximum output value under constant current control.

Thus, in this embodiment, the image forming apparatus 100 comprises an image carrier 56 that carries a toner image, a transfer member 64 to which a voltage is applied to transfer the toner image from the image carrier 56 to the transferee P at the transfer section N2, a power source E2 that applies a voltage to the transfer member 64, a current detection unit 121 that detects the current flowing through the transfer member 64 when a voltage is applied to the transfer member 64 by the power source E2, and a control unit 110 that is capable of executing a setting mode in which, when there is no toner image at the transfer section N2, a test voltage is applied to the transfer member 64 to set the transfer voltage to be applied to the transfer member 64 when there is a toner image at the transfer section N2. Then, in the setting mode, the control unit 110 controls the power source E2 so that the current value detected by the current detection unit 121 becomes the first current value I1, applies a test voltage to the transfer member 64, and obtains a first voltage value V1 of the test voltage, determines a second current value I2 based on the first voltage value V1, controls the power source E2 so that the current value detected by the current detection unit 121 becomes the second current value I2, applies a test voltage to the transfer member 64, and obtains a second voltage value V2 of the test voltage, and sets the transfer voltage based on the first and second current values I1, I2 and the first and second voltage values V1, V2. At this time, the first current value I1 is set so that the absolute value of the first voltage value V1 is equal to or less than the absolute value of a predetermined voltage value, and the absolute value of the second current value I2 is greater than the absolute value of the first current value I1. In this embodiment, the control unit 110 sets the second current value I2 to a second value I2-1 when the first voltage value V1 is a first value, and sets the second current value I2 to a fourth value I2-2 (or I2-3) whose absolute value is smaller than the second value when the first voltage value V1 is a third value whose absolute value is larger than the first value. In this embodiment, the absolute value of the first current value I1 is 5.0 μA or less. In this embodiment, the first current value I1 is set so that a voltage whose absolute value is equal to or greater than the discharge start voltage is applied to the transfer section N2. In this embodiment, the predetermined voltage value is a maximum output value of the power source E2 that is set in advance. In this embodiment, the control unit 110 determines the voltage-current characteristic based on the first and second current values I1 and I2 and the first and second voltage values V1 and V2 in the setting mode, and sets the transfer voltage based on the voltage-current characteristic. In this embodiment, the control unit 110 determines a linear function as the voltage-current characteristic. In this embodiment, the image carrier 56 is an intermediate transfer body that carries the toner image transferred from another image carrier 50 and transports it for transfer onto a recording material P as a receiving body.

6. Effects In the conventional ATVC control of the secondary transfer section N2, the impedance of the secondary transfer roller 64 may be greater than expected due to the influence of the environment, durability conditions, paper dust, etc., and the absolute value of the output of the secondary transfer power source E2 may be greater than the maximum output value when the ATVC control is executed. In such a case, the detection result in the ATVC control differs from the actual result, so that it is necessary to execute the ATVC control again to grasp the voltage-current characteristic (IV curve). In addition, if the absolute value of the output of the secondary transfer power source E2 becomes greater than the maximum output value when the ATVC control is executed, there is a risk of the reference potential of the high-voltage board fluctuating, the high-voltage board breaking down, and creeping discharge on the high-voltage board.

In contrast, according to this embodiment, it is possible to prevent the secondary transfer power source E2 from outputting a voltage whose absolute value is greater than the maximum output value (assumed voltage value) when ATVC control is being performed. This makes it possible to suppress the need to redo ATVC control. It is also possible to reduce the risks of fluctuations in the reference potential of the high-voltage board, failure of the high-voltage board, and creeping discharge on the high-voltage board. Furthermore, according to this embodiment, by providing multiple detection points in ATVC control, a wide range of voltage-current characteristics can be grasped without the need for additional components that would increase costs and space.

In addition, in this embodiment, in an image forming apparatus 100 with a process speed of 320 mm/s (corresponding to the peripheral speed of the intermediate transfer belt 56), it is possible to set the time for calculating the voltage value for outputting a certain current value to, for example, less than one revolution of the secondary transfer roller 64. In other words, according to this embodiment, it is possible to increase the number of detections within a range that does not affect FCOT (the time from input of an image formation start instruction to output of the first sheet of recording material on which an image is formed). If the detection points of the ATVC control can be increased within a range that does not affect FCOT, it is possible to set a high-precision secondary transfer voltage. Therefore, it is advantageous in improving the accuracy of prediction of the output possible voltage value determined by the high-voltage output upper limit value (high-voltage transformer upper limit value) and improving the accuracy of calculation of the limiter voltage value of the upper and lower limiter control of the secondary transfer voltage. Note that the upper and lower limiter control is a control that sets upper and lower limits on the output of the secondary transfer power source during secondary transfer in order to prevent the secondary transfer current from being too high or too low, for example, when a recording material P with an unexpected electrical resistance is used.

[Example 2]
Next, another embodiment 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 embodiment 1. 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 given the same reference numerals as those of embodiment 1 and detailed description is omitted. In this embodiment, the ATVC control of the secondary transfer portion N2 is different from that of embodiment 1.

1. ATVC Control of the Present Embodiment In the present embodiment, in the ATVC control of the secondary transfer portion N2, voltage values are detected at three or more stages of target current values, and the voltage-current characteristics are grasped by a quadratic function.

Currently, the market is seeing progress in (1) faster print speeds, (2) cost reductions, and (3) smaller device bodies. In other words, this means that the transfer voltage required to ensure transferability at higher speeds is rising, there is a shortage of transformer capacity margins due to reduced transformer capacity as a result of cost reductions, and the wiring on high-voltage boards is becoming smaller due to miniaturization. In recent years, the results of ATVC control are also used for purposes other than determining the secondary transfer voltage (understanding the possible output voltage value determined by the high-voltage output upper limit (upper transformer capacity limit), determining life span, etc.). For this reason, there are many advantages to be gained from being able to understand a wide range of voltage-current characteristics (IV curves).

Figure 7 is a flow chart showing an outline of the ATVC control procedure in this embodiment. Also, Figure 8 is a graph showing a schematic voltage-current characteristic to explain the ATVC control in this embodiment.

In this embodiment, similar to the first embodiment, ATVC control of the secondary transfer portion N2 is performed in the pre-rotation process each time a job is executed. Also, in this embodiment, similar to the first embodiment, in the ATVC control, a voltage is applied to the secondary transfer roller 64 (secondary transfer portion N2) for at least one rotation of the secondary transfer roller 64 (one rotation in this embodiment) with constant current control at a predetermined current value. Then, based on the average value of the voltage value detected at that time, a process for determining the target voltage value of the secondary transfer voltage, which will be described below, is performed. Also, in this embodiment, in the secondary transfer voltage control, a table of target current values It as shown in Table 1, similar to that described in the first embodiment, is used.

When a job is started, the controller 110 starts ATVC control in the pre-rotation process (S201). When the controller 110 starts ATVC control, it obtains the temperature and humidity inside the machine detected by the environmental sensor 130 to determine the absolute moisture content (S202). Next, the controller 110 determines the table value of the target current value It from a table such as that shown in Table 1 according to the type of recording material P selected in the job information (paper type setting) and the above-mentioned absolute moisture content (S203). Next, the controller 110 outputs a constant current controlled voltage from the secondary transfer power source E2 so that the current detected by the current detection unit 121 becomes a predetermined first stage target current value I1 that has been set in advance (S204). This first stage target current value I1 is the same as that described in the first embodiment. Then, the controller 110 averages the voltage values detected by the voltage control unit 120 while the secondary transfer power source E2 is outputting a voltage that is constant current controlled at the first stage target current value I1, and obtains the averaged first stage detected voltage value V1 (S205).

Next, the controller 110 determines the second-stage target current value I2 of the voltage to be output from the secondary transfer power supply E2 in the same manner as described in the first embodiment (see S106 to S110 in FIG. 5). Then, the controller 110 causes the secondary transfer power supply E2 to output a constant current controlled voltage such that the current detected by the current detection unit 121 becomes the second-stage target current value I2 (I2-1, I2-2, or I2-3) (S206). Then, the controller 110 averages the voltage value detected by the voltage control unit 120 while the constant current controlled voltage at the second-stage target current value I2 (I2-1, I2-2, or I2-3) is being output from the secondary transfer power supply E2, and obtains the averaged second-stage detected voltage value V2 (S207).

Next, the controller 110 calculates a linear function (linear curve) based on the first-stage target current value I1, the second-stage target current value I2 (I2-1, I2-2, or I2-3), the first-stage detection voltage value V1, and the second-stage detection voltage value V2 (S208). Then, the controller 110 determines a third-stage target current value (third current value) I3 based on the calculated linear function (S209). This third-stage target current value I2-3 has an absolute value greater than the second-stage target current value I2. In addition, this third-stage target current value I3 is set so that the output of the secondary transfer power source E2 is equal to or less than the maximum output value, and a voltage equal to or greater than the discharge start voltage is applied to the secondary transfer roller 64 (secondary transfer portion N2). In this embodiment, as shown in FIG. 8, the third-stage target current value I3 is determined from the intersection of the linear function (slope) calculated as described above and the maximum output value Vmax of the secondary transfer power source E2. That is, in this embodiment, the voltage-current characteristics of the secondary transfer portion N2 (mainly the secondary transfer roller 64 in this embodiment) follow a quadratic or higher function (quadratic function in this embodiment). And, by determining the third-stage target current value I3 as described above, it is possible to prevent the voltage value used to obtain the third-stage target current value I3 from exceeding the maximum output value.

Next, the controller 110 causes the secondary transfer power source E2 to output a constant current controlled voltage such that the current detected by the current detection unit 121 becomes the third stage target current value I3 (S210). The controller 110 then averages the voltage values detected by the voltage control unit 120 while the secondary transfer power source E2 is outputting a constant current controlled voltage at the third stage target current value I3, and obtains an averaged third stage detection voltage value V3 (S211).

Next, the controller 110 calculates a quadratic function (quadratic curve) as the voltage-current characteristic in this embodiment based on the target current values I1, I2 (I2-1, I2-2, or I2-3), and I3 of the first, second, and third stages and the detected voltage values V1, V2, and V3 (S212). Then, the controller 110 determines the target voltage value (voltage value corresponding to the target current value It) of the secondary transfer voltage to be applied to the secondary transfer roller 64 (secondary transfer section N2) during image formation (secondary transfer) based on the calculated quadratic function (S213). Thereafter, the controller 110 ends the ATVC control (S214).

In this embodiment, the number of detection points in the ATVC control is three, but it may be four or more. In this case, the target current value of the fourth and subsequent detection points may be determined based on the voltage-current characteristic (e.g., a linear function) obtained from the detection results of the previous detection points. However, if there are too many detection points, the time required for control may become longer. Ten or fewer detection points is often sufficient, and typically five or fewer.

Thus, in this embodiment, in the setting mode, the control unit 110 obtains the voltage-current characteristic based on the first and second current values I1, I2 and the first and second voltage values V1, V2, determines the third current value I3 based on the voltage-current characteristic, controls the power source E2 so that the current value detected by the current detection unit 121 becomes the third current value I3, applies a test voltage to the transfer member 64, obtains the third voltage value V3 of the test voltage, and sets the transfer voltage based on the first, second, and third current values I1, I2, I3 and the first, second, and third voltage values V1, V2, V3. At this time, the absolute value of the third current value I3 is greater than the absolute value of the second current value I2. Also, in this embodiment, the control unit 110 obtains a linear function as the above-mentioned voltage-current characteristic. In addition, in this embodiment, the control unit 110 determines another voltage-current characteristic based on the first, second, and third current values I1, I2, and I3 and the first, second, and third voltage values V1, V2, and V3 in the setting mode, and sets the transfer voltage based on the another voltage-current characteristic. In this embodiment, the control unit 110 determines a quadratic function as the another voltage-current characteristic.

2. Effects According to this embodiment, the same effects as those of the first embodiment can be obtained. Furthermore, according to this embodiment, the voltage-current characteristic can be grasped by a quadratic function in the ATVC control, and the secondary transfer voltage can be set with higher accuracy. Furthermore, according to this embodiment, it is possible to grasp a wider range of voltage-current characteristics than in the first embodiment.

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

In the above embodiment, the absolute moisture content calculated based on the temperature and humidity detection results is used as the environmental information, but the present invention is not limited to such an embodiment. For example, if the electrical resistance of the secondary transfer roller has a sufficient correlation with at least one of the temperature and humidity, control may be performed using at least one of the temperature and humidity as the environmental information.

The present invention is not limited to tandem-type image forming apparatuses, but can also be applied to other types of image forming apparatuses. For example, the present invention is not limited to full-color image forming apparatuses, but can also be applied to monochrome image forming apparatuses. In this case, the present invention is typically applied to a transfer roller as a transfer member that transfers a toner image from a photoreceptor as an image carrier to a recording material. The image forming apparatus may be used for various purposes, such as a printer, various printing machines, copiers, fax machines, and multifunction machines.

In the above embodiment, the transfer member is a roller-shaped member with a conductive elastic layer, but the transfer member is not limited to a roller-shaped member. The transfer member may be a sheet-shaped member made of a conductive resin or the like, or a brush-shaped member with conductive brush fibers.

50 Photosensitive drum 54 Primary transfer roller 56 Intermediate transfer belt 62 Secondary transfer opposing roller 64 Secondary transfer roller 110 Controller 120 Voltage control section 121 Current detection section E2 Secondary transfer power supply P Recording material

Claims (11)

an image carrier that carries a toner image;
a transfer member that transfers a toner image from the image carrier to a transferee in a transfer section when a voltage is applied;
A power source that applies a voltage to the transfer member;
a current detection unit that detects a current flowing through the transfer member when a voltage is applied to the transfer member by the power source;
a control unit capable of executing a setting mode in which a test voltage is applied to the transfer member when a toner image is present on the transfer unit, by applying a test voltage to the transfer member when no toner image is present on the transfer unit;
having
the control unit, in the setting mode, controls the power supply so that the current value detected by the current detection unit becomes a first current value, applies the test voltage to the transfer member, and obtains a first voltage value of the test voltage, determines a second current value based on the first voltage value, controls the power supply so that the current value detected by the current detection unit becomes the second current value, applies the test voltage to the transfer member, and obtains a second voltage value of the test voltage, and sets the transfer voltage based on the first and second current values and the first and second voltage values;
the first current value is set such that the absolute value of the first voltage value is equal to or less than the absolute value of a predetermined voltage value, and the absolute value of the second current value is greater than the absolute value of the first current value;
The control unit sets the second current value to a second value when the first voltage value is a first value, and sets the second current value to a fourth value whose absolute value is smaller than the second value when the first voltage value is a third value whose absolute value is larger than the first value . 2. The image forming apparatus according to claim 1 , wherein the absolute value of the first current value is 5.0 [mu]A or less. 3. The image forming apparatus according to claim 1, wherein the first current value is set so that a voltage having an absolute value equal to or greater than a discharge start voltage is applied to the transfer section. 4. The image forming apparatus according to claim 1, wherein the predetermined voltage value is a maximum output value of the power source that is set in advance. an image carrier that carries a toner image;
a transfer member that transfers a toner image from the image carrier to a transferee in a transfer section when a voltage is applied;
A power source that applies a voltage to the transfer member;
a current detection unit that detects a current flowing through the transfer member when a voltage is applied to the transfer member by the power source;
a control unit capable of executing a setting mode in which a test voltage is applied to the transfer member when a toner image is present on the transfer unit, by applying a test voltage to the transfer member when no toner image is present on the transfer unit;
having
the control unit, in the setting mode, controls the power supply so that the current value detected by the current detection unit becomes a first current value, applies the test voltage to the transfer member, and obtains a first voltage value of the test voltage, determines a second current value based on the first voltage value, controls the power supply so that the current value detected by the current detection unit becomes the second current value, applies the test voltage to the transfer member, and obtains a second voltage value of the test voltage, and sets the transfer voltage based on the first and second current values and the first and second voltage values;
the first current value is set such that the absolute value of the first voltage value is equal to or less than the absolute value of a predetermined voltage value, and the absolute value of the second current value is greater than the absolute value of the first current value;
The image forming apparatus is characterized in that, in the setting mode, the control unit determines a voltage-current characteristic based on the first and second current values and the first and second voltage values, and sets the transfer voltage based on the voltage-current characteristic. The image forming apparatus according to claim 5 , wherein the control unit obtains a linear function as the voltage-current characteristic. the control unit, in the setting mode, determines a voltage-current characteristic based on the first and second current values and the first and second voltage values, determines a third current value based on the voltage-current characteristic, controls the power source so that the current value detected by the current detection unit becomes the third current value, applies the test voltage to the transfer member, and obtains a third voltage value of the test voltage, and sets the transfer voltage based on the first, second, and third current values and the first, second, and third voltage values;
5. The image forming apparatus according to claim 1, wherein an absolute value of the third current value is greater than an absolute value of the second current value. The image forming apparatus according to claim 7 , wherein the control unit obtains a linear function as the voltage-current characteristic. The image forming apparatus according to claim 7 or 8, characterized in that, in the setting mode, the control unit determines another voltage-current characteristic based on the first, second, and third current values and the first, second , and third voltage values, and sets the transfer voltage based on the another voltage-current characteristic. The image forming apparatus according to claim 9 , wherein the control unit obtains a quadratic function as the different voltage-current characteristic. 11. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer body that carries a toner image transferred from another image carrier and transports the toner image to be transferred onto a recording material as the transferee .

Images