Image forming apparatus

Abstract

An image forming apparatus includes an image bearing member, a transfer member, an applying portion, a detecting portion, and a controller. The controller controls the applying section such that the second test bias voltage is higher than the absolute value of the first test bias voltage in a case where the adjustment operation is performed during a period from reception of the imaging start signal to start transfer of the image on the first sheet in the transfer section. And controls the applying section such that a time for applying the first test bias to the transfer section is set to a first time and a time for applying the second test bias to the transfer section is set to a second time that is longer than the first time.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus using an electrophotographic or electrostatic recording method, such as a copier, a printer, a facsimile machine, a printing device, or a multifunctional machine having multiple functions of these machines. Background Art

[0002] In an image forming apparatus adopting an electrophotographic type or the like, an image is formed and outputted by an image forming process including a step of transferring a toner image formed on an image bearing member to a toner image receiving member. For example, in the image forming apparatus, when a recording material as a toner image receiving member passes through a transfer portion formed in a contact portion between the image bearing member and the transfer member, a transfer bias is applied to the transfer member, thereby transferring the toner image from the image bearing member to the recording material by the action of an electric field formed in the transfer portion. As the transfer member, a transfer roller composed of a rotatable roller is widely used.

[0003] The transfer roller is configured to have, for example, approximately 1×10 6 Up to 1×10 10 The transfer roller is composed of an elastic layer arranged around a conductive core metal. According to the way of imparting conductivity to the elastic layer, the transfer roller is roughly divided into two categories, namely, an electron conductive transfer roller and an ion conductive transfer roller. As an electron conductive transfer roller, there can be cited a roller composed of a conductive filler such as carbon black or a metal oxide as an electron conductive agent dispersed in an elastic layer formed of EPDM (ethylene propylene diene monomer rubber), polyurethane rubber, etc. In addition, as an ion conductive transfer roller, there can be cited a roller in which the material of the elastic layer formed of polyurethane rubber, etc. itself has ion conductivity and a roller composed of a surfactant, etc., dispersed in the elastic layer as an ion conductive agent.

[0004] Transfer bias control includes constant current control and constant voltage control. In order to obtain good transfer performance, it is ideal to control the charge amount of the electric charge supplied to the transfer section to a predetermined charge amount. As one of the methods, constant current control of the transfer bias can be considered. However, the load impedance of the transfer roller to the photosensitive drum is different from each other between the part with recording material and the part without recording material in the transfer section, so that the load impedance becomes smaller at the part without recording material. Therefore, depending on the size of the recording material used, it is possible that a large amount of current flows through the part without recording material, resulting in poor transfer in the part with recording material. On the other hand, in the case of constant voltage control of the transfer bias, the charge amount of the electric charge supplied from the transfer roller to the transfer section is always almost the same. Therefore, in many cases, constant voltage control is performed on the transfer bias.

[0005] It is known that the resistance value of the ion conductive transfer roller in particular easily fluctuates due to the temperature and humidity of the surrounding environment. If a desired transfer current cannot be obtained due to the fluctuation of the transfer roller resistance value, transfer failure may occur.

[0006] Therefore, the following ATVC (active transfer voltage control) for setting the transfer bias according to the resistance value of the transfer portion (mainly the transfer roller) is proposed (Japanese Laid-Open Patent Application 202027144). That is, for example, in the preparatory operation (pre-rotation step, pre-multi-rotation step) before imaging, a plurality of levels of test bias (test current or test voltage) are applied to the transfer roller, and a voltage-current characteristic (VI characteristic) as information on the resistance value of the transfer portion (mainly the transfer roller) is obtained. Then, based on the voltage-current characteristic, the transfer voltage under constant voltage control of the transfer bias applied to the transfer roller is determined so that the desired transfer current flows during imaging (during transfer).

[0007] Incidentally, in some cases, the transfer roller may have uneven resistance value in the circumferential direction (rotation direction) (hereinafter, such unevenness is referred to as "circumferential unevenness"). Such circumferential unevenness not only causes unevenness in the material used to adjust the resistance value of the transfer roller, but also becomes significant due to partial influence of temperature or humidity changes in some cases. Specifically, due to the heat from the fixing device, there is a difference in resistance value between the position of the transfer roller opposite to the fixing device and the position on the opposite side thereof.

[0008] Therefore, in the conventional ATVC, a plurality of levels of test bias are applied to the transfer roller during a period corresponding to approximately one full rotation of the transfer roller. In addition, the average value of the current or voltage detected when the plurality of levels of test bias are applied to the transfer roller is used to obtain the voltage-current characteristic.

[0009] However, in the above-mentioned conventional ATVC, time for obtaining voltage-current characteristics is required depending on the number of levels of the test bias voltage. For example, in the case of using 3 levels of the test bias voltage, time corresponding to 3 weeks is required. Therefore, due to the time used for ATVC, downtime (a period during which an image cannot be output) becomes long in some cases.

[0010] In recent years, there is a trend to further shorten FCOT (First Copy Out Time) in multifunction machines, etc. Therefore, it is necessary to shorten the time required for ATVC. However, the image quality of imaging devices is also improving, and it is necessary to shorten the control time while fully maintaining the accuracy of test bias control. Summary of the invention

[0011] The main purpose of the present invention is to shorten the control time while fully maintaining the test bias control accuracy.

[0012] This object is achieved by an imaging device according to the invention.

[0013] According to one aspect of the present invention, there is provided an image forming apparatus comprising: an image bearing member configured to bear a toner image; a transfer member configured to form a transfer section in which the toner image is transferred from the image bearing member to a toner image receiving member; an applying section configured to apply a bias voltage to the transfer section; a detecting section configured to detect a voltage applied to the transfer section or a current flowing through the transfer section when the bias voltage is applied to the transfer section by the applying section; and a controller capable of controlling the applying section to perform an adjustment operation in which, based on the application of a first test voltage to the transfer section during a non-image forming period, a first test voltage is applied to the transfer section by the applying section. The transfer bias applied to the transfer section by the applying section during the transfer is set based on the detection results of the detection section when multiple test biases including a test bias voltage and a second test bias voltage are applied; wherein, when an adjustment operation is performed from the receipt of an imaging start signal to the start of transfer of an image on a first sheet in the transfer section, the controller is configured to control the applying section so that the second test bias voltage is higher than the absolute value of the voltage of the first test bias voltage, and is configured to control the applying section so that the time for applying the first test bias voltage to the transfer section is set to a first time and the time for applying the second test bias voltage to the transfer section is set to a second time longer than the first time.

[0014] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a schematic cross-sectional view of an imaging device.

[0016] Figure 2 It is a schematic diagram for explaining the structure of the secondary transfer section.

[0017] Figure 3 This is a diagram showing the transition of the voltage applied to the transfer unit in the control of Example 1.

[0018] Figure 4 This is a flowchart for explaining the control of the first embodiment.

[0019] Figure 5 (a), (b) and (c) are diagrams for explaining the effects of Example 1.

[0020] Figure 6 (a) and (b) are diagrams for explaining the effects of Example 1.

[0021] Figure 7 This is a diagram showing the transition of the voltage applied to the transfer unit in the control of the second embodiment.

[0022] Figure 8 (a) and (b) are diagrams for explaining the effects of Example 2.

[0023] Fig. 9 (a) and (b) are diagrams for explaining the effects of Example 2.

[0024] Fig.10 This is a diagram showing the transition of the voltage applied to the transfer unit in the control of the third embodiment.

[0025] Fig.11 (a) and (b) are each a schematic diagram showing another example of the configuration of the secondary transfer portion. DETAILED DESCRIPTION

[0026] An image forming apparatus according to the present invention will be described in detail with reference to the accompanying drawings. [Example 1]

[0027] 1. Overall construction and operation of imaging equipment

[0028] Figure 1 is a schematic cross-sectional view of an image forming apparatus 100 of Embodiment 1. The image forming apparatus 100 in this embodiment is a tandem printer capable of forming a full-color image on a sheet-like recording material P using an electrophotographic type, and adopts an intermediate transfer type.

[0029] The image forming apparatus 100 includes four image forming units UY, UM, UC, and UK for forming yellow (Y), magenta (M), cyan (C), and black (K) images as a plurality of image forming sections. With regard to elements provided for the respective colors and having the same or corresponding functions or configurations, suffixes Y, M, C, and K indicating elements for the relevant colors are omitted in some cases and will be described uniformly. In the present embodiment, the image forming unit U is constituted by including a photosensitive drum 1, a charging roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, a drum cleaning device 6, and the like, which will be described later.

[0030] The photosensitive drum 1 is a rotatable drum-shaped photosensitive member (electrophotographic photosensitive member) as a first image bearing member for bearing a toner image, and is driven to rotate in the direction of arrow R1 (clockwise) at a predetermined peripheral speed by a driving force transmitted from a driving motor (not shown) as a driving device. The charging roller 2 is a roller-shaped charging member as a charging device, and the surface of the rotating photosensitive drum is uniformly charged to a predetermined polarity (negative in this embodiment) and a predetermined potential by the charging roller. The charging roller 2 is arranged to contact the surface of the photosensitive drum 1 and rotates as the photosensitive drum 1 rotates. The charged surface of the photosensitive drum 1 is scanned and exposed according to image data (image information signal) by an exposure device (laser scanner) 3 as an exposure device, thereby forming an electrostatic image (electrostatic latent image) corresponding to the image data on the photosensitive drum 1. The exposure device 3 can be configured as a single unit capable of exposing, for example, four photosensitive drums 1.

[0031] Incidentally, for the sake of convenience, unless otherwise specified, the magnitudes (high / low) of voltage (potential) and current refer to the magnitudes (high / low) when these values ​​are compared with each other in absolute values.

[0032] The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer from the developing device 4 as a developing means, thereby forming a toner image (toner image, developer image) corresponding to the image data on the photosensitive drum 1. In this embodiment, the toner charged with the same polarity as the photosensitive drum 1 is deposited on the exposed portion (image portion) of the photosensitive drum 1 whose potential has been lowered by exposing the surface of the photosensitive drum 1 after the photosensitive drum 1 is uniformly charged (reversal development type). In this embodiment, the toner as the main charged polarity of the toner during development is usually charged with a negative polarity.

[0033] As a second image bearing member for bearing the toner image, an intermediate transfer belt 7 as a rotatable endless belt-shaped intermediate transfer member is provided in a manner opposed to the four photosensitive drums 1. The intermediate transfer belt 7 is extended around a plurality of tension rollers (support rollers) and is tensioned by a plurality of tension rollers at a predetermined tension, the plurality of tension rollers including a drive roller 71, a tension roller 72, idle rollers 73 and 74, and a secondary transfer opposing roller 75. The intermediate transfer belt 7 is composed of an endless belt (film) formed of a material including a resin material (such as polyimide or polyamide) or various rubbers and including a conductive filler (such as carbon black), an ion conductive material, etc. contained and dispersed in the resin material or various rubbers. For example, the surface resistivity of the intermediate transfer belt 7 is 1×10 9 -5×10 11 Ω / sq, thickness is about 0.04-0.05 mm.

[0034] The driving roller 71 is driven to rotate by the driving force transmitted from the motor (not shown) as the driving device, so that the intermediate transfer belt 7 rotates (circular motion, circular motion) in the direction of the arrow R2 (counterclockwise) at a peripheral speed corresponding to the peripheral speed of the photosensitive drum 1. The tension roller 72 applies a certain tension to the intermediate transfer belt 7. The idle rollers 73 and 74 support the surface of the intermediate transfer belt 7 extending along the arrangement direction of the four photosensitive drums 1Y, 1M, 1C and 1K. The secondary transfer opposing roller 75 is used as an opposing member (opposing electrode) of the secondary transfer roller 8 described later. Incidentally, the tension of the intermediate transfer belt 7 relative to the tension roller 72 is about 3-12 kgf. On the inner peripheral surface side of the intermediate transfer belt 7, the primary transfer rollers 5Y, 5M, 5C and 5K, which are primary transfer devices and roller-type primary transfer members, are arranged to correspond to the respective photosensitive drums 1. In this embodiment, the primary transfer roller 5 is composed of a metal roller. The primary transfer rollers 5 press the intermediate transfer belt 7 against the associated photosensitive drum 1, thereby forming a primary transfer portion (primary transfer nip) T1 where the photosensitive drum 1 and the intermediate transfer belt 7 contact each other. The tension rollers excluding the drive roller 71 and the respective primary transfer rollers 5 rotate as the intermediate transfer belt 7 rotates.

[0035] Under the action of the primary transfer roller 5, the toner image formed on the photosensitive drum 1 as described above is primarily transferred to the rotating intermediate transfer belt 7 as a toner image receiving member in the primary transfer portion T1. During the primary transfer, a primary transfer bias (primary transfer voltage) which is a DC voltage of a polarity opposite to the normal charging polarity of the toner (positive in this embodiment) is applied to the primary transfer roller 5 by a primary transfer power supply (high voltage power supply circuit) D1 as a primary transfer voltage applying portion. For example, during full-color image formation, the toner images of the colors Y, M, C, and K formed on the respective photosensitive drums 1 are primarily transferred in sequence in the respective primary transfer portions T1 to be superimposed on the intermediate transfer belt 7.

[0036] On the outer peripheral surface side of the intermediate transfer belt 7, at a position opposite to the secondary transfer opposing roller 75, a secondary transfer roller 8, which is a roller-type secondary transfer member, is provided as a secondary transfer device. The secondary transfer roller 8 is pressed toward the secondary transfer opposing roller 75 via the intermediate transfer belt 7 to form a secondary transfer portion (secondary transfer nip portion) T2 where the intermediate transfer belt 7 and the secondary transfer roller 8 contact each other. In the present embodiment, the secondary transfer roller 8 is driven to rotate by a driving force transmitted from a driving motor (not shown) as a driving device, but it may also be a configuration in which the secondary transfer roller 8 rotates with the rotation of the intermediate transfer belt 7. By the action of the secondary transfer roller 8, the toner image formed on the intermediate transfer belt 7 as described above is transferred (secondary transfer) in the secondary transfer portion T2 to the recording material P as a toner image receiving member that is nipped and conveyed by the intermediate transfer belt 7 and the secondary transfer roller 8 at the secondary transfer portion T2. During the secondary transfer, the secondary transfer power supply (high voltage power supply circuit) D2 ( Figure 2 ) A secondary transfer bias (secondary transfer voltage) is applied to the secondary transfer roller 8, which is a DC voltage having a polarity opposite to the normal charge polarity of the toner.

[0037] A recording material (transfer material, recording medium, sheet) P such as paper is supplied toward the secondary transfer portion T2 by a recording material supply device 10 as a recording material supply portion. The recording material supply device 10 includes a recording material accommodating portion (box, tray, etc.) 11 for accommodating the recording material P, a pickup roller 12 for feeding the recording material P one by one from the recording material accommodating portion 11 at a predetermined timing, a conveying roller pair 13 for conveying the fed recording material P, and the like. The recording material P conveyed by the conveying roller pair 13 is conveyed toward the secondary transfer portion T2 in accordance with the timing of the toner image on the intermediate transfer belt 7 by an alignment roller pair 50 as an alignment correction portion. The recording material P to which the toner image is transferred is conveyed toward a fixing device 9 as a fixing device. The fixing device 9 heats and presses the recording material P carrying the unfixed toner image, thereby fixing (melting, attaching) the toner image on the recording material P.

[0038] In the case where the image forming mode is a single-sided mode (single-sided printing) in which an image is formed only on a single side (surface) of the recording material P, the recording material P on which a toner image is fixed by the fixing device 9 on a single side (surface) is discharged (output) to the outside of the apparatus main assembly of the image forming apparatus 100 by the discharge roller pair 30 as a discharge section. On the other hand, in the case where the image forming mode is a double-sided mode (automatic double-sided printing) in which an image is formed on both (both) sides (surfaces) of the recording material P, the recording material P on which an image is formed (toner image is fixed) on the first side (surface) by the fixing device 9 is re-transferred to the secondary transfer section T2 by the double-sided conveying device 40. In the case of the double-sided mode, before the recording material P on which an image is formed on the first side is discharged to the outside of the image forming apparatus, the discharge roller pair 30 is reversed at a predetermined timing. Thus, the recording material P is guided to the reversing path (double-sided conveying path) 41 of the double-sided conveying device 40. The recording material P guided to the reversing path 41 is conveyed toward the registration roller pair 50 by the re-transfer roller pair 42. Similar to the case of forming an image on the first side, the recording material P is conveyed to the secondary transfer portion T2 by the registration roller pair 50 in timing with the toner image on the intermediate transfer belt 7, so that the toner image is secondarily transferred to the second side (surface) opposite to the first side. The recording material P to which the toner image is transferred on the second side is discharged to the outside of the image forming apparatus by the discharge roller pair 30 after the toner image is fixed on the second side of the recording material P by the fixing device 9.

[0039] Furthermore, the toner (primary transfer residual toner) remaining on the photosensitive drum 1 without being transferred onto the intermediate transfer belt 7 during the primary transfer is removed and recovered by the drum cleaning device 6 as a photosensitive member cleaning device. Furthermore, on the outer peripheral surface side of the intermediate transfer belt 7, at a position opposed to the driving roller 71, a belt cleaning device 76 as an intermediate transfer member cleaning device is provided. Deposits such as the toner (secondary transfer residual toner) remaining on the intermediate transfer belt 7 without being transferred onto the recording material P during the secondary transfer, paper dust, etc. are removed and recovered from the surface of the intermediate transfer belt 7 by the belt cleaning device 76.

[0040] 2. Secondary transfer structure

[0041] Figure 2 1 is a schematic diagram for illustrating the configuration of the secondary transfer portion T2 of the image forming apparatus 100 of the present embodiment.

[0042] The secondary transfer roller 8 is pressed into contact with the intermediate transfer belt 7 whose inner surface is supported by the secondary transfer opposing roller 75 connected to the ground potential, thereby forming a secondary transfer portion T2 between the intermediate transfer belt 7 and the secondary transfer roller 8. By applying a positive (polarity) DC voltage as a secondary transfer bias (secondary transfer voltage) from the secondary transfer voltage source D2 to the core metal (rotation shaft) of the secondary transfer roller 8, a transfer electric field is formed at the secondary transfer portion T2. ​​As a result, the toner image of the negative polarity toner carried on the intermediate transfer belt 7 is transferred (secondary transfer) to the recording material P passing through the secondary transfer portion T2.

[0043] The secondary transfer opposing roller 75 is formed by forming a 0.5 mm thick conductive rubber layer as an elastic layer around a stainless steel roller with a diameter of 15 mm as a core metal (base material). In the present embodiment, the outer diameter of the secondary transfer opposing roller 75 is 16 mm. As the material of the conductive rubber, a rubber obtained by mixing an ion conductive agent into nitrile rubber, EPDM rubber, polyurethane rubber, etc. is used. In the present embodiment, the resistance value of the secondary transfer opposing roller 75 is adjusted to 1×10 5 Ω or less. Incidentally, the resistance value is obtained in the following manner. 10N is applied to the secondary transfer opposing roller 75 so that the secondary transfer opposing roller 75 is pressed into contact with the conductive cylinder. Then, while the secondary transfer opposing roller 75 is rotated by the rotation of the conductive cylinder, the current flowing when a voltage of 50V is applied to the rotating shaft (core metal) of the secondary transfer opposing roller 75 is measured. Based on the current, the above-mentioned resistance value is obtained. In addition, in the present embodiment, the surface hardness of the secondary transfer opposing roller 75 is 70 degrees in terms of the ASKER C hardness value.

[0044] The secondary transfer roller 8 is constituted by forming a 6 mm thick conductive rubber sponge as an elastic layer around a stainless steel rotating shaft with a diameter of 12 mm as a core metal (base material). In the present embodiment, the outer diameter of the secondary transfer roller 8 is 24 mm. As the material of the conductive rubber sponge, a rubber sponge obtained by mixing an ion conductive agent into nitrile rubber, EPDM rubber, polyurethane rubber, etc. is used, and is adjusted to have a 1×10 7 -1×10 8 Ω resistance value. Incidentally, the resistance is obtained in the following manner. 10N is applied to the secondary transfer roller 8 so that the secondary transfer roller 8 is pressed into contact with the conductive cylinder. Then, while the secondary transfer roller 8 is rotated by the rotation of the conductive cylinder, the current flowing when a voltage of 2kV is applied to the rotating shaft (core metal) is measured. Based on the current, the above resistance value is obtained. In addition, in this embodiment, the surface hardness of the secondary transfer roller 8 is 35 degrees in terms of ASKER C hardness value.

[0045] Here, the conductive sponge layer of the secondary transfer roller 8 generally generates unevenness in the resistance value in the circumferential direction (rotational direction) of the secondary transfer roller 8 ("circumferential unevenness"). In the present embodiment, when the circumferential unevenness is represented by the difference between the common logarithm of the maximum value and the common logarithm of the minimum value of the circumferential resistance value of the secondary transfer roller 8, the circumferential unevenness is 1.1 (i.e., = (common logarithm of the maximum value) - (common logarithm of the minimum value)).

[0046] exist Figure 2 , a control configuration of a main portion of the imaging apparatus 100 in this embodiment is shown.

[0047] The controller (DC controller) 150 is constituted by including a CPU 151 as a control device, which is a main element for executing processing, and a memory (storage medium) 152 such as a ROM, RAM, etc. as a storage device. Information input to the controller 150, detected information, calculation results, etc. are stored in the RAM as a rewritable memory. A pre-obtained data table, etc. are stored in the ROM. The CPU 151 and the memory 152 such as a ROM, RAM, etc. can transmit and read data between them. In addition, the controller 150 is provided with a communication section (I / F) 153 for exchanging information with an external device (not shown) such as a personal computer. The CPU 151 is connected to the external device in a communicable manner via the communication section 153, and can receive data from the external device.

[0048] The secondary transfer power source D2 is connected to the controller 150. The secondary transfer power source D2 can apply a bias voltage controlled by a constant voltage at a predetermined target voltage and a bias voltage controlled by a constant current at a predetermined target current in a switching manner. The controller 150 controls the secondary transfer power source D2 and determines the secondary transfer bias voltage applied to the secondary transfer roller 8 during the secondary transfer. Then, during the secondary transfer, the controller 150 causes the secondary transfer power source D2 to apply the secondary transfer bias voltage to the secondary transfer roller 8.

[0049] In the present embodiment, the controller 150 is capable of performing constant voltage control of the bias voltage applied from the secondary transfer power source D2 to the secondary transfer roller 8 by controlling the voltage output from the secondary transfer power source D2 so that the voltage value detected by the voltage detection circuit 19 described later is a predetermined voltage value. In addition, the controller 150 is capable of performing constant current control of the bias voltage applied from the secondary transfer power source D2 to the secondary transfer roller 8 by controlling the voltage output from the secondary transfer power source D2 so that the current value detected by the current detection circuit 18 described later is a predetermined current value. In addition, in the present embodiment, as described in detail later, the controller 150 determines the target voltage of the secondary transfer bias voltage during the non-image forming period before the image forming, and performs constant voltage control of the secondary transfer bias voltage during the secondary transfer in such a manner that the secondary transfer bias voltage is kept substantially constant at the target voltage.

[0050] A current detection circuit 18 as a current detection device (current detection portion) is connected to the controller 150. The current detection circuit 18 detects the current output from the secondary transfer power source D2 to the secondary transfer roller 8 and flowing through the secondary transfer portion T2. ​​The current detection circuit 18 outputs a 0-5V analog voltage corresponding to the current value, which is AD-converted by the controller 150 into an 8-bit digital signal and used for calculation.

[0051] In addition, a voltage detection circuit 19 as a voltage detection device (voltage detection portion) is connected to the controller 150. The voltage detection circuit 19 detects the voltage output from the secondary transfer power source D2 to the secondary transfer roller 8 and flows through the secondary transfer portion T2. ​​The voltage detection circuit 19 outputs a 0-5V analog voltage corresponding to the voltage value, which is AD-converted into an 8-bit digital signal by the controller 150 and used for calculation.

[0052] In addition, an environment sensor 17 as an environment detection device for detecting an environment (the use environment of the imaging device 100) which is at least one of the temperature and humidity of at least one of the inside and the outside of the imaging device 100 is connected to the controller 150. In the present embodiment, the environment sensor 17 detects the temperature and humidity in the housing of the imaging device 100. Information on the temperature and humidity detected by the environment sensor 17 is input to the controller 150.

[0053] Furthermore, an operation panel 120 as an operation section is connected to the controller 150. The operation panel 120 is configured by including a display section as a display device for displaying information under the control of the controller 150 and an input section as an input device for inputting information to the controller 150.

[0054] In the present embodiment, the operation panel 120 includes a touch panel that serves as both a display unit and an input unit. An operator such as a user or a service person operates the operation panel 120 and can input settings regarding image formation to the controller 150. For example, the operation panel 120 displays a selection screen for a recording material P and can allow the operator to select the type of recording material P used for image formation.

[0055] Furthermore, information on the print job is input from an external device to the controller 150. The information on the print job includes image data, and information (control instructions) on settings for image formation such as data for specifying the kind of recording material P used for image formation.

[0056] By the way, a print job is a series of operations that form and output an image on a single recording material P or a plurality of recording materials P, which is started by a single start instruction. A print job generally includes an imaging step, a pre-rotation step, a sheet (paper) interval step in the case of forming an image on a plurality of recording materials P, and a post-rotation step. The imaging step is a period during which electrostatic image formation, toner image formation, and primary transfer, secondary transfer, and fixing of the toner image are performed for the image actually formed and output on the recording material P, and the imaging period refers to this period. Specifically, the timing during the imaging period is different in the positions where the respective steps of charging, exposure, development, primary transfer, secondary transfer, and fixing are performed. The pre-rotation step is performed during the preparatory operation before the imaging step from the input of the start instruction until the actual image formation is started. The sheet interval step (image interval step) is a period corresponding to the interval between one recording material P and the next recording material P when images are continuously formed (continuous imaging) on ​​a plurality of recording materials P. The post-rotation step is a period during which the post-operation (preparatory operation) after the imaging step is performed. The non-imaging period (non-imaging period) is a period other than the imaging period, and includes a front rotation step, a sheet interval step, a rear rotation step, and also includes a front multi-rotation step, which is a preparatory operation during turning on the main switch (power) of the imaging device 100 or during recovery from a sleep state.

[0057] In addition, the type of recording material P includes arbitrary information that can distinguish the recording material P based on general characteristics such as plain paper, thick paper, thin paper, glossy paper, coated paper, etc., including values, ranges, etc. of attributes, manufacturers, brands, product numbers, basis weights, sizes, etc.

[0058] The controller 150 determines the contents of the operator's operation on the operation panel 120 or the print job information from the external device, and can thereby determine settings related to image formation, such as the type of recording material P used for image formation.

[0059] 3. Secondary transfer bias control

[0060] Next, the secondary transfer bias control in this embodiment will be described.

[0061] <atvc>

[0062] The resistance value of the secondary transfer portion T2 varies depending on the environment (temperature, humidity), fluctuations in the initial resistance values ​​of components such as the secondary transfer roller 8 and the intermediate transfer belt 7 (mainly the secondary transfer roller 8), energization history, etc. In particular, it is known that the resistance value of the ion conductive secondary transfer roller 8 is prone to fluctuate depending on the surrounding environment.

[0063] Here, the secondary transfer efficiency (the rate at which the toner carried on the intermediate transfer belt 7 moves toward the recording material P) generally shows a peak value at a certain secondary transfer current value. Due to the fluctuation of the resistance value of the secondary transfer roller 8, when the secondary transfer current value deviates from the secondary transfer efficiency peak value, the secondary transfer efficiency decreases, and transfer failure may occur.

[0064] Therefore, during the non-image forming period before the image forming (before the secondary transfer step), ATVC (active transfer voltage control) is performed for determining the target voltage of the constant voltage control of the secondary transfer bias according to the resistance value of the secondary transfer portion T2 (mainly the secondary transfer roller 8). In ATVC, the target voltage of the constant voltage control of the secondary transfer bias is determined using the secondary transfer current value when the secondary transfer efficiency is approximately expressed as a peak value as the target current. As the non-image forming period during which ATVC is performed, there can be cited the period during the pre-multi-rotation step when the image forming device 100 is started, the period during the pre-rotation step before the image forming of the print job is started, and the like. By performing ATVC, the share (share) voltage Vb of the secondary transfer portion T2 during the non-image forming period required to determine the target voltage of the secondary transfer bias applied to the secondary transfer roller 8 in the constant voltage control during the secondary transfer period (sheet passing period) can be determined. Then, a voltage value obtained by adding the divided voltage Vb of the secondary transfer portion T2 during the non-sheet passing period and the pre-set divided voltage Vp for the recording material, that is, a voltage Vt (=Vb+Vp) is determined as a target voltage of the secondary transfer bias voltage applied to the secondary transfer roller 8 in the constant voltage control during the secondary transfer period (sheet passing period). In the present embodiment, the divided voltage Vb of the secondary transfer portion T2 is applied to the secondary transfer roller 8 in the constant voltage control during the non-sheet passing period at the initial stage of the secondary transfer step (immediately before the recording material P reaches the secondary transfer portion T2).

[0065] Incidentally, the non-sheet passing period refers to a time when there is no recording material P in the secondary transfer portion T2 . During the non-sheet passing period, the secondary transfer roller 8 contacts the intermediate transfer belt 7 .

[0066] In the ATVC of the present embodiment, the controller 150 performs control so that a plurality of levels of test bias (test current or test voltage) are applied to the secondary transfer roller 8 (secondary transfer portion T2) by the secondary transfer power supply D2 during non-sheet passing. In particular, in the present embodiment, the controller 150 performs control so that three levels of test biases controlled by constant current are applied to the secondary transfer roller 8 by the secondary transfer power supply D2. In addition, the controller 150 calculates the average value of the voltage values ​​sampled at predetermined intervals by the voltage detection circuit 19 during the application of the test biases of each level controlled by constant current to the secondary transfer roller 8. Thus, the controller 150 obtains the voltage-current characteristic as information about the resistance value of the secondary transfer portion T2 (mainly the secondary transfer roller 8). In addition, based on the voltage-current characteristic, the controller 150 determines the divided voltage Vb of the secondary transfer portion T2 during non-image formation. Then, the controller 150 causes the memory 152 to store the divided voltage Vb of the secondary transfer portion T2 during non-image formation.

[0067] Incidentally, in the present embodiment, in the ATVC, a test bias voltage controlled by a constant current is applied to the secondary transfer roller 8 (secondary transfer portion T2), and the voltage generated at this time is detected by the voltage detection circuit 19, but the present invention is not limited to this. In the ATVC, a test bias voltage controlled by a constant voltage is applied to the secondary transfer roller 8 (secondary transfer portion T2), and the current flowing at this time can be detected by the current detection circuit 18. In the ATVC, both a test bias voltage controlled by a constant current and a test bias voltage controlled by a constant voltage can be used. It is sufficient that the voltage-current characteristic as information on the resistance value of the secondary transfer portion T2 (mainly the secondary transfer roller 8) can be obtained.

[0068] <Test bias voltage and its application time>

[0069] Next, a target current determination method for three levels of test bias in ATVC in this embodiment will be described.

[0070] The target currents for the three levels of test bias are taken as the first target current Itarget1, the second target current Itarget2, and the third target current Itarget3. These target currents Itarget1, Itarget2, and Itarget3 satisfy the following relationship: Itarget1 <Itarget2<Itarget3。

[0071] Itarget3 is preset according to the environment (absolute humidity (moisture content) calculated based on temperature and humidity) and the type of recording material P, and is stored in the memory 152 as a data table or the like. The controller 150 calculates the absolute humidity based on the temperature and humidity detected by the environment sensor 17. In addition, the controller 150 determines the type of recording material P according to the operation content in the operation section 120 or the print job input from the external device. Then, based on the absolute humidity and the type of recording material P, the controller 150 determines Itarget3 by referring to the above-mentioned data table. Here, as an example, Itarget3 takes 60 μA.

[0072] In addition, the controller 150 determines Itarget2 by the following formula.

[0073] Itarget2=Itarget3×0.7.

[0074] Furthermore, the controller 150 determines Itarget1 to be 1.0 μA, which is a fixed value.

[0075] Next, the application timing of the three levels of the test bias in the ATVC in this embodiment will be described.

[0076] The application time of the test bias applied to the secondary transfer roller 8 is respectively taken as the first application time Troll1, the second application time Troll2 and the third application time Troll3 by using Itarget1, Itarget2 and Itarget3 as target currents for constant current control. In this embodiment, in order to shorten the time required for ATVC, the times Troll1, Troll2 and Troll3 are preset as shown in the following Table 1. Incidentally, in this embodiment, the peripheral speed (surface movement speed) of the secondary transfer roller 8 during ATVC is 320 mm / sec.

[0077] Table 1

[0078] Troll3 is the time corresponding to approximately one full cycle of the secondary transfer roller 8 in order to be able to detect the voltage value corresponding to one full cycle of the secondary transfer roller 8. Incidentally, in consideration of the time required for the rise and fall of the output voltage of the secondary transfer power source D2, the application time of each level of the test bias is made slightly longer than the voltage value detection time when the relevant test bias is applied to the secondary transfer roller 8. The time corresponding to approximately one full cycle of the secondary transfer roller 8 includes, for example, the time increased or decreased from the time corresponding to one full cycle within the range of the margin or error of the rise or fall of the output voltage of the above-mentioned secondary transfer power source D2, for example, the time within the range of about ±5% of the time corresponding to one full cycle of the secondary transfer roller 8. In addition, Troll2 is shorter than Troll3, and Troll1 is shorter than Troll2. Incidentally, from the viewpoint of shortening the time required for ATVC, Troll1 and Troll2 may preferably be less than 90% of Troll3, and more preferably less than 70%. However, typically, Troll1 and Troll2 are more than 5% of Troll3.

[0079] Figure 3 : is a time chart schematically showing the transition of the voltage applied to the secondary transfer roller 8 (secondary transfer portion T2 ) during the ATVC period and the secondary transfer period in the present embodiment.

[0080] The voltage values ​​in the times Troll1, Troll2, and Troll3 as described above are detected respectively, and the average values ​​V1, V2, and V3 are calculated respectively. Then, based on Itarget1, Itarget2, Itarget3, V1, V2, and V3, the voltage-current characteristic is obtained. In addition, based on the voltage-current characteristic, the divided voltage Vb of the secondary transfer portion T2 during the non-sheet passing period is obtained, where Itarget1 corresponds to the target current during the secondary transfer period (sheet passing period).

[0081] Furthermore, the target voltage Vt of the constant voltage control of the secondary transfer bias during the secondary transfer period (sheet passing period) is obtained based on the divided voltage Vb of the secondary transfer portion T2 during the non-sheet passing period and the preset recording material divided voltage Vp.

[0082] <Control Order>

[0083] The sequence of ATVC in this embodiment will be further described. Figure 4 : is a flowchart schematically showing the sequence of ATVC in this embodiment.

[0084] When a start instruction of a print job is input, the controller 150 starts ATVC in a pre-rotation step before the toner image and the recording material P reach the secondary transfer portion T2 (S101). Then, the controller 150 determines a first target current Itarget1, a second target current Itarget2, and a third target current Itarget3, which are target currents of the test bias of 3 levels in ATVC (S102). The determination method of Itarget1, Itarget2, and Itarget3 is as described above. Next, based on the detection result of the current detection circuit 18, the controller 150 performs control so that the test bias is applied to the secondary transfer roller 8 from the secondary transfer power source D2 by constant current control with Itarget1 as the target current (S103).

[0085] Furthermore, based on the detection result of the voltage detection circuit 19 in the time Troll1, the controller 150 obtains the average value V1 of the voltage value, and causes the memory (RAM) 152 to store the average value V1 (S104). Then, based on the detection result of the current detection circuit 18, the controller 150 performs control so that the test bias is applied from the secondary transfer power source D2 to the secondary transfer roller 8 by constant current control with Itarget2 (>Itarget1) as the target current (S105). Furthermore, based on the detection result of the voltage detection circuit 19 in the time Troll2, the controller 150 obtains the average value V2 of the voltage value, and causes the memory (RAM) 152 to store the average value V2 (S106). Then, based on the detection result of the current detection circuit 18, the controller 150 performs control so that the test bias is applied from the secondary transfer power source D2 to the secondary transfer roller 8 by constant current control with Itarget3 (>Itarget2) as the target current (S107). Furthermore, based on the detection result of the voltage detection circuit 19 in the time Troll3 , the controller 150 obtains an average value V3 of the voltage values, and causes the memory (RAM) 152 to store the average value V3 ( S108 ).

[0086] Next, based on Itarget1, Itarget2, Itarget3, V1, V2, and V3, the controller 150 obtains the divided voltage Vb of the secondary transfer portion T2 during the non-sheet passing period corresponding to Itarget1 corresponding to the target current during the secondary transfer period (sheet passing period), and causes the memory (RAM) 152 to store the divided voltage Vb (S109). In the present embodiment, the controller 150 approximates the voltage-current characteristic indicating the relationship between Itarget1, Itarget2, Itarget3, V1, V2, and V3. The controller 150 causes the memory 152 to store the obtained voltage-current characteristic. In addition, based on the voltage-current characteristic, the controller 150 obtains the divided voltage Vb of the secondary transfer portion T2 corresponding to Itarget1 (i.e., the target current during the secondary transfer period). The controller 150 causes the memory (RAM) 152 to store the obtained divided voltage Vb of the secondary transfer portion T2 during the non-sheet passing period. Then the controller 150 adds the recording material divided voltage Vp to the obtained divided voltage Vb of the secondary transfer portion T2, and determines the target voltage Vt of the secondary transfer bias applied to the secondary transfer roller 8 by constant voltage control during the secondary transfer (during the sheet passing) (S110). Information of the recording material divided voltage Vp is set in advance according to the type of the recording material P, environmental conditions, etc., and is stored in the memory (ROM) 152 as table data, etc. The controller 150 causes the memory (RAM) 152 to store the determined target voltage Vt of the secondary transfer bias during the secondary transfer (during the sheet passing). During the secondary transfer, the secondary transfer bias subjected to constant voltage control at the target voltage Vt is applied to the secondary transfer roller 8. Thereafter, the controller 150 ends the ATVC (S111).

[0087] Incidentally, the method for obtaining the voltage-current characteristic from the detection results of 3 levels in ATVC is arbitrary in itself, but for example, the least square method may be used. Furthermore, in the present embodiment, in ATVC, the target voltage of the secondary transfer bias is obtained based on the quadratic function obtained from the detection results of 3 levels, but is not limited thereto. Depending on the detection accuracy of the desired voltage-current characteristic of the secondary transfer roller 8, the target voltage of the secondary transfer bias may be obtained based on the quadratic function obtained from the detection results of 4 or more levels. However, by the detection results of 10 or less levels, the voltage-current characteristic can be obtained with sufficient accuracy in many cases. 4. Effects of this embodiment

[0088] Table 2 below shows the results of comparing the fluctuation of the current actually flowing when the target current during secondary transfer is set to 70 μA and the target voltage of the constant voltage control of the secondary transfer bias is determined, between the case where ATVC in the present embodiment (Embodiment 1) is performed and the case where ATVC is performed with Troll1, Troll2 and Troll3 each set to a time corresponding to approximately one full rotation of the secondary transfer roller 8 (238 milliseconds).

[0089] Table 2

[0090] *1: "OFC" refers to approximately one full circumference of the secondary transfer roller 8 for all three points.

[0091] *2: "CT" stands for control time.

[0092] *3: "CF" is the current fluctuation when the target current is set to 70μA.

[0093] As can be seen from Table 2, the current fluctuation in the case of executing ATVC in this embodiment is the same as the current fluctuation in the case of executing ATVC with each of Troll1, Troll2, and Troll3 set to a time corresponding to approximately one full rotation of the secondary transfer roller 8. Therefore, according to this embodiment, a good image can be formed by sufficiently maintaining the control accuracy of the secondary transfer bias while shortening the time required for ATVC.

[0094] The reason for obtaining such a result will be described. The conductive rubber sponge layer of the secondary transfer roller 8 in the present embodiment has a resistance value unevenness ("circumferential unevenness") in the circumferential direction (rotational direction) of the secondary transfer roller 8. In the present embodiment, in the case where the circumferential unevenness is represented by the difference between the common logarithm of the maximum value and the common logarithm of the minimum value of the resistance value in the circumferential direction of the secondary transfer roller 8 (=(common logarithm value of the maximum value) - (common logarithm value of the minimum value)), the circumferential unevenness is 1.1. Figure 5 (a), (b), and (c) are graphs for explaining fluctuations of V1, V2, and V3 respectively obtained in the case where Troll1, Troll2, and Troll3 are respectively changed in this case. Figure 5 (a) shows the relationship between Troll1 and each of the maximum value (Vmax) and the minimum value (Vmin) of V1. Figure 5 (b) shows the relationship between Troll2 and each of the maximum value (Vmax) and the minimum value (Vmin) of V2. Figure 5 (c) shows the relationship between Troll3 and each of the maximum value (Vmax) and minimum value (Vmin) of V3. Figure 5 In (a), (b) and (c), the horizontal axis represents the test bias application time (respectively Troll1, Troll2, Troll3), and the vertical axis represents the voltage value obtained in ATVC (respectively V1, V2, V3). Figure 5 It can be seen that the fluctuation of the voltage value when the application time is shortened becomes larger as the target current of the test bias increases, that is, as the voltage value (measured voltage value) of the test bias increases. In the case where this fluctuation is large, the fluctuation of the divided voltage Vb of the secondary transfer portion T2 obtained during the non-sheet passing period becomes large, and the fluctuation of the secondary transfer current flowing during the secondary transfer relative to the target current also becomes large. That is, in the case where the voltage value (measured voltage value) of the test bias is small, the fluctuation of the voltage value is small even when the application time is shortened, and therefore, the accuracy of the voltage-current characteristic obtained by using the voltage value can be fully maintained.

[0095] Figure 6 (a) and (b) are graphs showing voltage-current characteristics represented by quadratic functions, which are obtained when ATVC in the present embodiment is performed and when ATVC is performed with each of Troll1, Troll2, and Troll3 set to a time corresponding to approximately one full rotation of the secondary transfer roller 8 (238 milliseconds), respectively. Figure 6 (a) shows the voltage-current characteristics when the ATVC in this embodiment is implemented, Figure 6 (b) shows the voltage / current characteristics in the case where ATVC is performed with each of Troll1, Troll2, and Troll3 set to a time corresponding to substantially one full rotation of the secondary transfer roller 8. Figure 6 It can be seen that even when ATVC in this embodiment is executed, the target voltage for constant voltage control of the secondary transfer bias can be determined with an accuracy equivalent to the accuracy of executing ATVC with Troll1, Troll2 and Troll3 each set to a time corresponding to approximately one full cycle of the secondary transfer roller 8 to obtain the desired target current.

[0096] Therefore, in the present embodiment, as the voltage value (measured voltage value) of the test bias increases, the application time becomes longer. Preferably, the application time of at least one level of the test bias is not less than the time corresponding to approximately one full cycle of the secondary transfer roller 8. In the case where the application time is longer than the time corresponding to approximately one full cycle, from the viewpoint of improving the detection accuracy while suppressing the influence of circumferential unevenness, the application time can be made to correspond to, for example, a time of approximately an integer multiple of the secondary transfer roller 8. However, it is sufficient for the application time of at least one level of the test bias to be a time corresponding to not moving more than approximately 5 full cycles of the secondary transfer roller 8, and typically not more than approximately 3 full cycles of the secondary transfer roller 8. In other words, in the present embodiment, the smaller the voltage value (measured voltage value) of the test bias, the shorter the application time. Thus, the fluctuation of the detection result of the voltage value can be reduced while shortening the time required for ATVC, and the fluctuation of the secondary transfer current flowing during the secondary transfer relative to the target current can be reduced.

[0097] Therefore, in the present embodiment, the image forming apparatus 100 includes: an image bearing member (intermediate transfer belt) 7 for bearing a toner image; a transfer member (secondary transfer roller) 8 for forming a transfer portion (secondary transfer portion) T2 in which the toner image is transferred from the image bearing member 7 to a toner image receiving member (recording material) P; an applying portion (secondary transfer power source) D2 for applying a bias voltage to the transfer portion T2; and a detecting portion (in the present embodiment, a voltage detecting portion) 19 for detecting a voltage applied to the transfer portion T2 when the applying portion D2 applies a bias voltage to the transfer portion T2. voltage or current flowing through the transfer section T2; and a controller 150 capable of controlling the applying section D2, wherein the controller 150 is capable of performing control to perform an adjustment operation (ATVC), in which: when no transfer is performed in the transfer section T2, a first test bias and a second test bias having a higher voltage absolute value are applied to the transfer section T2 by the applying section D2, and then the transfer bias applied to the transfer section T2 by the applying section D2 during the transfer is set based on the detection result of the detection section 19 when each of the first test bias and the second test bias is applied to the transfer section T2. ​​In addition, in the present embodiment, in the above-mentioned adjustment operation, the controller 150 performs control so that the first time of applying the first test bias to the transfer section T2 is shorter than the second time of applying the second test bias to the transfer section T2. ​​Here, the first time may be preferably more than 5% and less than 90% of the second time. In addition, the first time may be more preferably more than 5% and less than 70% of the second time.

[0098] In the present embodiment, the transfer member 8 is a roller 8 for contacting with the surface of the image bearing member 7 to form the transfer portion T2, and the second time is a time corresponding to at least approximately one full turn of the roller 8. In particular, in the present embodiment, the image bearing member 7 is composed of an endless belt, and the transfer member 8 is an outer roller (secondary transfer roller) 8 for contacting with the inner roller (secondary transfer opposing roller) 75 contacting the inner peripheral surface of the belt via the belt to form the transfer portion T2. ​​And, the second time is a time corresponding to at least approximately one full turn of the roller 8. In addition, in the present embodiment, the applying portion D2 applies a bias voltage to the roller 8.

[0099] Furthermore, in the present embodiment, the image forming apparatus 100 includes an environment detection device (environmental sensor) 17 for detecting at least one of temperature and humidity, and the controller 150 performs control to change at least one of the first test bias and the second test bias based on the detection result of the environment detection device 17. Furthermore, in the present embodiment, the controller 150 performs control so that the above-mentioned adjustment operation is performed in a preparation operation (pre-rotation step, pre-multi-rotation step) before transfer in a print job for forming an image composed of a toner image on a single recording material P or a plurality of recording materials P. Furthermore, in the present embodiment, the controller 150 performs control so that in the above-mentioned adjustment operation, the first test bias and the second test bias which are controlled by a constant current are applied to the transfer portion T2, and then the above-mentioned transfer bias is set based on the voltage detection result of the detection portion (voltage detection circuit) 19 when each of the first test bias and the second test bias is applied to the transfer portion T2. However, the controller 150 may be configured to perform control such that, in the above-mentioned adjustment operation, the first test bias and the second test bias which are subjected to constant voltage control are applied to the transfer portion T2, and then the above-mentioned transfer bias is set based on the current detection result of the detection portion (current detection circuit) 18 when the first test bias and the second test bias are each applied to the transfer portion T2. ​​Further, in this embodiment, the controller 150 performs control such that, in the above-mentioned adjustment operation, a plurality of different test biases including the first test bias and the second test bias are applied to the transfer portion T2, and the second test bias is a test bias having the highest voltage absolute value among the plurality of different test biases.

[0100] As described above, according to the present embodiment, the control time can be shortened while the secondary transfer bias control accuracy is sufficiently maintained. [Example 2]

[0101] Next, another embodiment of the present invention will be described. The imaging device in this embodiment has the same basic configuration and operation as the imaging device of Embodiment 1. Therefore, in the imaging device of this embodiment, elements having the same or corresponding functions or configurations as those in Embodiment 1 are represented by the same reference numerals or symbols as those in Embodiment 1 and will be omitted from the detailed description.

[0102] In Embodiment 1, in ATVC, three levels of test bias are applied to the secondary transfer roller 8 by the secondary transfer power source D2 to obtain the voltage-current characteristics. In this embodiment, in ATVC, two levels of test bias are applied to the secondary transfer roller 8 by the secondary transfer power source D2 to obtain the voltage-current characteristics.

[0103] In the ATVC of the present embodiment, similar to the embodiment 1, the controller 150 performs control so that a plurality of levels of test bias (test current or test voltage) are applied to the secondary transfer roller 8 (secondary transfer portion T2) by the secondary transfer power supply D2 during the non-sheet passing period. In particular, in this embodiment, the controller 150 performs control so that two levels of test biases controlled by constant current are applied to the secondary transfer roller 8 by the secondary transfer power supply D2. In addition, the controller 150 calculates the average value of the voltage values ​​sampled by the voltage detection circuit 19 at predetermined intervals during the application of the test biases of each level controlled by constant current to the secondary transfer roller 8. Thus, the controller 150 obtains the voltage-current characteristic as information about the resistance value of the secondary transfer portion T2 (mainly the secondary transfer roller 8). In addition, based on the voltage-current characteristic, the controller 150 determines the divided voltage Vb of the secondary transfer portion T2 during the non-image forming period. Then, the controller 150 causes the memory 152 to store the divided voltage Vb of the secondary transfer portion T2 during the non-image forming period.

[0104] Incidentally, in the present embodiment, in the ATVC, the test bias voltage controlled by constant current is applied to the secondary transfer roller 8 (secondary transfer portion T2), and the voltage generated at this time is detected by the voltage detection circuit 19, but the present invention is not limited to this. In the ATVC, the test bias voltage controlled by constant voltage is applied to the secondary transfer roller 8 (secondary transfer portion T2), and the current flowing at this time can be detected by the current detection circuit 18. In the ATVC, both the test bias voltage controlled by constant current and the test bias voltage controlled by constant voltage can be used.

[0105] In this embodiment, the target currents for the two levels of test bias are taken as the first target current Itarget1 and the second target current Itarget2. These target currents Itarget1 and Itarget2 satisfy the following relationship: Itarget1 <Itarget2。

[0106] Itarget2 is preset according to the environment (absolute humidity (moisture content) calculated based on temperature and humidity) and the type of recording material P, and is stored in the memory 152 as a data table or the like. The controller 150 calculates the absolute humidity based on the temperature and humidity detected by the environment sensor 17. In addition, the controller 150 determines the type of recording material P according to the operation content in the operation section 120 or the print job input from the external device. Then, based on the absolute humidity and the type of recording material P, the controller 150 determines Itarget2 by referring to the above-mentioned data table. Here, as an example, Itarget2 takes 60 μA.

[0107] Furthermore, the controller 150 determines Itarget1 to be 1.0 μA, which is a fixed value.

[0108] The application time of applying the test bias to the secondary transfer roller 8 by constant current control using Itarget1 and Itarget2 as target currents is respectively taken as the first application time Troll1 and the second application time Troll2. In this embodiment, in order to shorten the time required for ATVC, the times Troll1 and Troll2 are set in advance as shown in the following Table 3. Incidentally, similar to Embodiment 1, in this embodiment, the peripheral speed (surface moving speed) of the secondary transfer roller 8 during ATVC is 320 mm / sec.

[0109] Table 3

[0110] Troll2 is a time corresponding to approximately one full rotation of the secondary transfer roller 8 in order to be able to detect a voltage value corresponding to one full rotation of the secondary transfer roller 8. Incidentally, similarly to Embodiment 1, in consideration of the time required for the rise and fall of the voltage output of the secondary transfer power source D2, the application time of each level of the test bias is made slightly longer than the voltage value detection time when the relevant test bias is applied to the secondary transfer roller 8.

[0111] Furthermore, Troll1 is shorter than Troll2. By the way, from the viewpoint of shortening the time required for ATVC, Troll1 may preferably be less than 90%, more preferably less than 70% of Troll2. However, typically, Troll1 is more than 5% of Troll2.

[0112] Figure 7 : is a time chart schematically showing the transition of the voltage applied to the secondary transfer roller 8 (secondary transfer portion T2 ) during the ATVC period and the secondary transfer period in the present embodiment.

[0113] The ATVC sequence in this embodiment is the same as that in Embodiment 1, except that the test bias voltage is at two levels.

[0114] Table 4 below shows the results of comparing the fluctuation of the current actually flowing when the target current during secondary transfer is set to 70 μA and the target voltage of the constant voltage control of the secondary transfer bias is determined, between the case where ATVC in the present embodiment (Embodiment 2) is performed and the case where ATVC is performed with Troll1 and Troll2 each set to a time corresponding to approximately one full rotation of the secondary transfer roller 8 (238 milliseconds).

[0115] Table 4

[0116] *1: "OFC" refers to approximately one full circumference of the secondary transfer roller 8 for all two points.

[0117] *2: "CT" stands for control time.

[0118] *3: "CF" is the current fluctuation when the target current is set to 70μA.

[0119] As can be seen from Table 4, the current fluctuation in the case of executing ATVC in the present embodiment is equal to the current fluctuation in the case of executing ATVC with each of Troll1 and Troll2 set to a time corresponding to approximately one full rotation of the secondary transfer roller 8. Therefore, according to the present embodiment, a good image can be formed by sufficiently maintaining the control accuracy of the secondary transfer bias while shortening the time required for ATVC.

[0120] The reason for this result is as described in Example 1.

[0121] That is, in this embodiment, similar to Embodiment 1, when the circumferential unevenness is represented by the difference between the common logarithm of the maximum value and the common logarithm of the minimum value of the resistance value in the circumferential direction of the secondary transfer roller 8 (= (common logarithm of the maximum value) – (common logarithm of the minimum value)), the circumferential unevenness of the secondary transfer roller 8 is 1.1. Figure 8 (a) and (b) are related to Figure 5 Similar graphs are used to illustrate fluctuations of V1 and V2 respectively obtained in this case when Troll1 and Troll2 are respectively changed. Figure 8 (a) shows the relationship between Troll1 and each of the maximum value (Vmax) and the minimum value (Vmin) of V1. Figure 8 (b) shows the relationship between Troll2 and each of the maximum value (Vmax) and minimum value (Vmin) of V2. Figure 8 It can be seen that the fluctuation of the voltage value when the application time is shortened increases with the increase of the target current of the test bias, that is, increases with the increase of the test bias voltage value (measured voltage value). In the case where this fluctuation is large, the fluctuation of the obtained partial voltage Vb of the secondary transfer portion T2 during the non-sheet passing period becomes large, and the fluctuation of the secondary transfer current flowing during the secondary transfer relative to the target current also becomes large.

[0122] also, Fig. 9 (a) and (b) are graphs showing voltage-current characteristics expressed by a linear function obtained in the case where ATVC in the present embodiment is performed and in the case where ATVC is performed with Troll1 and Troll2 each set to a time (238 milliseconds) corresponding to substantially one full rotation of the secondary transfer roller 8, respectively. Fig. 9 (a) shows the voltage-current characteristics when the ATVC in this embodiment is implemented, Fig. 9 (b) shows the voltage-current characteristics in the case where ATVC is performed with Troll1 and Troll2 each set to a time corresponding to substantially one full rotation of the secondary transfer roller 8. Fig. 9 It can be seen that even when ATVC is executed in this embodiment, the target voltage for constant voltage control of the secondary transfer bias can be determined with an accuracy equivalent to the accuracy when ATVC is executed with Troll1 and Troll2 each set to a time corresponding to approximately one full cycle of the secondary transfer roller 8 to obtain the desired target current.

[0123] Therefore, according to the present embodiment, fluctuations in the voltage value detection result can be made smaller, and fluctuations in the secondary transfer current flowing during the secondary transfer with respect to the target current can be made smaller.

[0124] As described above, according to this embodiment, it is possible to obtain effects similar to those of Embodiment 1, and furthermore, simplification of ATVC can be achieved. [Example 3]

[0125] Next, another embodiment of the present invention will be described. The imaging device in this embodiment has the same basic configuration and operation as the imaging device of Embodiment 1. Therefore, in the imaging device of this embodiment, elements having the same or corresponding functions or configurations as those in Embodiment 1 are represented by the same reference numerals or symbols as those in Embodiment 1 and will be omitted from the detailed description.

[0126] In the above-mentioned embodiments, ATVC in the front rotation step or the front multi-rotation step is described, but in this embodiment, ATVC performed in the sheet interval will be described. In this embodiment, ATVC performed in the front rotation step or the front multi-rotation step described in the above-mentioned embodiments is called "normal ATVC", and ATVC performed in the sheet interval is called "sheet interval ATVC".

[0127] During continuous image formation, the heat generated by the fixing device 9 causes the temperature inside the housing of the image forming apparatus 100 to rise. In addition, in some cases, friction heat is generated due to the sliding between the rotation shaft and the bearing portion of the secondary transfer roller 8. Therefore, during continuous image formation, the temperature of the secondary transfer roller 8 rises over time, and the resistance value of the secondary transfer roller 8 fluctuates, etc., so that the voltage-current characteristics of the secondary transfer portion T2 change in some cases. Therefore, during continuous image formation, in the case where the set value of the secondary transfer bias is made constant, due to the change in the resistance value of the secondary transfer roller 8, etc., the secondary transfer current deviates from the target current in some cases.

[0128] Therefore, in the present embodiment, during continuous image formation, at a predetermined timing, the sheet interval ATVC is executed in the sheet interval step, and the set value of the secondary transfer bias is corrected (set again). The timing for executing the sheet interval ATVC may be, for example, a case where any index such as the passage of time or environmental fluctuation satisfies a predetermined condition in addition to the case where the number of sheets imaged during continuous image formation reaches a predetermined number of sheets.

[0129] Here, in the sheet interval ATVC, in some cases, the sheet interval step time is short, so that it is impossible to ensure the application time of a horizontal test bias (voltage or current detection time). In this embodiment, in this case, the average value of the detection results in multiple sheet interval steps is used as the detection result of the test bias.

[0130] In addition, in the present embodiment, in the sheet interval ATVC, similar to the usual ATVC, the higher the voltage value (measured voltage value) of the test bias, the longer the application time. In other words, the lower the voltage value (measured voltage value) of the test bias, the shorter the application time. In addition, in this embodiment, the application time of at least one level of the test bias is longer than the time of a single sheet interval step. Therefore, in the present embodiment, in the sheet interval ATVC, the number of sheet interval steps to which the test bias is applied increases as the voltage value (measured voltage value) of the test bias increases. In other words, the number of sheet interval steps to which the test bias is applied becomes smaller as the voltage value (measured voltage value) of the test bias decreases. Thus, the overall detection time in the sheet interval ATVC can be shortened. As a result, it is possible to correct fluctuations in the voltage-current characteristics of the secondary transfer portion T2 during continuous imaging more quickly while maintaining the control accuracy of the secondary transfer bias.

[0131] Fig.10 : is a timing chart schematically showing a portion of the transition of the voltage applied to the secondary transfer roller 8 (secondary transfer section T2) during continuous image formation in this embodiment. Three levels of test bias voltages that are constant current controlled at target currents Itarget1, Itarget2, and Itarget3, which are the same as in the normal ATVC described in Example 1, are applied to the secondary transfer roller 8. The application time of each level of the test bias voltage is Troll1, Troll2, and Troll3, which are the same as in the normal ATVC described in Example 1 (see Table 1). In addition, the time of the sheet interval step (the time required for a single sheet interval to pass through the secondary transfer section T2) is set to 20 milliseconds.

[0132] When the execution timing of the sheet interval ATVC comes during continuous image formation, similarly to the normal ATVC, the target current of the test bias used in the sheet interval ATVC is determined.

[0133] Furthermore, in the case where the detection result of the test bias voltage at one level can be obtained in a single sheet interval step, the detection result obtained in the single sheet interval step is stored in the memory 152 as the detection result of the test bias voltage. Fig.10 In the example shown, the detection result of the test bias voltage with Itarget1 as the target current is obtained in a single sheet interval step. On the other hand, in the case where the detection result of the test bias voltage of one level cannot be obtained in a single sheet interval, the average value of the detection results obtained in a plurality of sheet interval steps is stored in the memory 152 as the detection result of the test bias voltage. Fig.10 In the example shown, the test bias detection result with Itarget2 as the target current is obtained as the average value of the detection results in two sheet interval steps. In addition, the test bias detection result with Itarget3 as the target current is obtained as the average value of the detection results in 12 sheet interval steps.

[0134] Therefore, in the present embodiment, when an area on the intermediate transfer belt corresponding to the interval between one recording material P and the next recording material P passes through the transfer section T2 in a print job for forming an image composed of colorant images on a plurality of recording materials P (sheet interval step), the controller 150 performs an adjustment operation (ATVC) of applying a first test bias and a second test bias having a voltage absolute value higher than that of the first test bias to the transfer section T2, and further, performs control so that the number of the above-mentioned areas to which the first test bias is applied to the transfer section T2 is less than the number of the above-mentioned areas to which the second test bias is applied when at least one of a first time for applying the first test bias and a second time for applying the second test bias is longer than the time for the above-mentioned areas to pass through the transfer section T2.

[0135] As described above, according to the present embodiment, control (correction, resetting) of the secondary transfer bias during continuous image formation can be performed more quickly by shortening the control time while sufficiently maintaining the control accuracy of the secondary transfer bias in the sheet interval ATVC. Other embodiments

[0136] In the above, the present invention is described based on various specific embodiments, but is not limited to the above embodiments.

[0137] In the above-described embodiments, a secondary transfer bias having a polarity opposite to the normal charge polarity of the toner is applied to the secondary transfer roller 8 in contact with the outer peripheral surface of the intermediate transfer belt 7, and the secondary transfer opposing roller 75 in contact with the inner peripheral surface of the intermediate transfer belt 7 is electrically grounded, but the present invention is not limited to this configuration. Fig.11 As shown in (a), a configuration may be adopted in which a secondary transfer bias having the same polarity as the normally charged polarity of the toner is applied to the inner roller 80 corresponding to the secondary transfer opposing roller 75 in each of the above-mentioned embodiments by a secondary transfer power source D2, and the outer roller 81 corresponding to the secondary transfer roller 8 in each of the above-mentioned embodiments is electrically grounded. That is, the applying portion D2 may be configured to apply a bias to the transfer portion T2 by applying a bias to the inner roller 80. Furthermore, in this configuration, in most cases, the resistance value of the outer roller 81, which is constituted by including a relatively thick elastic layer and forms the secondary transfer portion (secondary transfer nip portion) T2, dominates the resistance value of the secondary transfer portion T2. ​​Therefore, in the case where the resistance value of the outer roller 81 is higher than the resistance value of the inner roller 80, the application time of at least one level of the test bias among the plurality of test biases may preferably be longer than the time corresponding to approximately one full cycle of the outer roller 81. That is, in a case where the image bearing member is composed of an annular belt and the transfer member is an outer roller that contacts the inner circumferential surface of the belt via the belt to form the transfer portion T2, the second time for applying the second test bias having a higher absolute value of the voltage among the first test bias and the second test bias can preferably be at least a time corresponding to approximately one full cycle of the roller with a higher resistance value among the inner roller and the outer roller.

[0138] Furthermore, in the above-described embodiments, the outer member in contact with the outer peripheral surface of the intermediate transfer belt 7 is the secondary transfer roller 8 that directly contacts the outer peripheral surface of the intermediate transfer belt 7, but the present invention is not limited to this configuration. Fig.11 As shown in (b) of FIG. 1 , the image forming apparatus may have a configuration in which a transfer belt (recording material conveying belt) 84 stretched by a plurality of rollers contacts the outer peripheral surface of the intermediate transfer belt 7 to form a secondary transfer portion T2. ​​In this configuration, the outer roller 83 is disposed at a position opposite to the inner roller 80, and the secondary transfer portion T2 in which the intermediate transfer belt 7 and the transfer belt 84 contact each other is formed by pressing the outer roller 83 toward the inner roller 80. In this configuration, a configuration in which a secondary transfer bias having a polarity opposite to the normal charge polarity of the toner is applied to the outer roller 83 by a secondary transfer power source D2 and the inner roller 80 is electrically grounded may also be adopted.

[0139] Alternatively, a configuration may be adopted in which a secondary transfer bias of the same polarity as the normal charge polarity of the toner is applied to the inner roller 80 corresponding to the secondary transfer opposing roller 75 in each of the above-mentioned embodiments by the secondary transfer power source D2, and the outer roller 83 is electrically grounded. In addition, in this configuration, in most cases, the resistance value of the outer roller 83 dominates the resistance value of the secondary transfer portion T2. ​​Therefore, in the case where the resistance value of the outer roller 83 is higher than the resistance value of the inner roller 80, the application time of the test bias of at least one level among the plurality of test biases may preferably be longer than the time corresponding to approximately one full turn of the outer roller 83. That is, the transfer member may be a roller (outer roller) 83 that forms the transfer portion T2 by contacting the image bearing member via an endless belt (transfer belt) 84 that contacts the surface of the image bearing member (intermediate transfer belt) 7, in which case the second time of applying the second test bias having a higher voltage absolute value among the first test bias and the second test bias may preferably be at least the time corresponding to approximately one full turn of the above-mentioned roller 83.

[0140] Furthermore, in each of the above-described embodiments, the present invention is applied to the secondary transfer section, but the present invention is not limited thereto. The present invention is also applicable to, for example, a monochrome image forming apparatus including only a single image bearing member. In this case, the present invention is applicable to a transfer section that transfers a toner image from the image bearing member to a recording material. Incidentally, the image bearing member may be a drum-shaped or belt-shaped photosensitive member or an electrostatic recording dielectric member.

[0141] In addition, in the above-mentioned embodiments, the transfer voltage is described as a voltage that is subjected to constant voltage control during transfer, but the present invention can be applied even in the case where the transfer voltage is subjected to constant current control during transfer. In this case, in ATVC, based on the obtained voltage-current characteristics, the target voltage initial value required to obtain the target current during transfer, or the target current required to obtain the target voltage during transfer, etc. can be obtained.

[0142] In addition, the ATVC executed in the pre-rotation step or pre-multi-rotation step described in the above embodiments is not limited to the ATVC executed in the pre-rotation step every time. ATVC can be executed at a predetermined timing (timing based on the passage of time, environmental fluctuations, component replacement, etc.).

[0143] According to the present invention, it is possible to shorten the control time while sufficiently maintaining the transfer bias control accuracy.

[0144] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications and equivalent structures and functions.< / atvc>

Claims

1. An imaging device, comprising: an image bearing member configured to bear a toner image; a transfer member configured to form a transfer portion in which the toner image is transferred from the image bearing member to the toner image receiving member; an applying portion configured to apply a bias voltage to the transfer portion; a detection section configured to detect a voltage applied to the transfer section or a current flowing through the transfer section when a bias voltage is applied to the transfer section by the application section; and a controller capable of controlling the applying section to perform an adjustment operation in which a transfer bias applied by the applying section to the transfer section during transfer is set based on a detection result of the detecting section when a plurality of test biases including a first test bias and a second test bias are applied by the applying section to the transfer section during a non-image forming period, In which, when an adjustment operation is performed from the time an imaging start signal is received to the time when transfer of an image on a first sheet starts in a transfer section, the controller is configured to control the application section so that the second test bias voltage has a higher absolute value than the voltage of the first test bias voltage, and is configured to control the application section so that the time for applying the first test bias voltage to the transfer section is set to a first time and the time for applying the second test bias voltage to the transfer section is set to a second time that is longer than the first time.

2. The imaging device according to claim 1, wherein The first time is greater than 5% and less than 90% of the second time.

3. The imaging device according to claim 1, wherein: The transfer member is a roller for contacting with the surface of the image bearing member to form a transfer portion, and the second time is a time corresponding to at least substantially one full rotation of the roller.

4. The imaging device according to claim 1, wherein The image bearing member is composed of an endless belt. wherein the transfer member is an outer roller for forming a transfer portion by contacting the inner roller contacting the inner peripheral surface of the belt via the belt, and The second time is a time corresponding to at least approximately one full rotation of the outer roller.

5. The imaging device according to claim 4, wherein: The applying section applies the bias to the transfer section by applying the bias to the outer roller.

6. The imaging device according to claim 4, wherein: The applying section applies the bias to the transfer section by applying the bias to the inner roller.

7. The imaging device according to claim 1, wherein: The transfer member is a roller for forming a transfer portion by contacting the image bearing member via an endless belt contacting a surface of the image bearing member, and the second time is a time corresponding to at least substantially one full rotation of the roller.

8. The imaging device according to claim 1, wherein The image bearing member is composed of an endless belt. wherein the transfer member is an outer roller for forming a transfer portion by contacting the inner roller contacting the inner peripheral surface of the belt via the belt, and The second time is a time corresponding to substantially one full rotation of at least the roller having a higher resistance value among the inner roller and the outer roller.

9. The imaging device according to claim 1, wherein: The second test bias voltage is a test bias voltage having the highest absolute voltage value among the plurality of test bias voltages.

10. The imaging device according to claim 1, wherein The first test bias voltage is a test bias voltage having the lowest absolute voltage value among the plurality of test bias voltages.

11. The imaging device according to claim 1, wherein The plurality of test biases include a third test bias whose voltage absolute value is higher than the first test bias and whose voltage absolute value is lower than the second test bias. wherein the time for applying the third test bias to the transfer portion is set as a third time, and The third time is set to be longer than the first time and shorter than the second time.

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