Image forming apparatus

Abstract

An image forming apparatus is disclosed. The image forming apparatus 100 is capable of performing constant voltage control on a voltage applied to a transfer member 8 and performing limit value control for controlling the voltage applied to the transfer member 8 based on a detection result of a current detection portion 21 so that the detection result of the current detection portion 21 is within a predetermined range. The image forming apparatus 100 is capable of performing a first mode in which a toner image is transferred onto a recording material P and a second mode in which a plurality of different voltages are applied to the transfer member 8 and a plurality of test toner images are transferred onto the recording material P, wherein: when the first mode is performed, the controller 50 is capable of performing the limit value control when the recording material P passes through a transfer portion N1, and when the second mode is performed, the controller 50 does not perform the limit value control when a region on which the plurality of test toner images are transferred passes through a transfer portion N2.

Description

[0001] This application is a divisional application of Chinese invention patent application No. 202080046543.0, filed on June 25, 2020, entitled "Image Forming Apparatus". Technical Field

[0002] The present invention relates to image forming apparatuses such as copiers, printers, and fax machines that use electrophotographic methods and / or electrostatic recording methods. Background Technology

[0003] Conventional image forming apparatuses using electrophotographic methods electrostatically transfer toner images from an image-bearing component, such as a photosensitive element or intermediate transfer element, to a recording material, such as paper. This transfer is typically performed by applying a transfer voltage to a transfer element, such as a transfer roller, which contacts the image-bearing component to form the transfer portion. If the transfer voltage is too low, the transfer is not sufficiently performed, and the desired image density cannot be obtained, potentially resulting in "sparse image density." If the transfer voltage is too high, discharge may occur in the transfer portion, and the effect of the discharge may reverse the polarity of the toner charge in the toner image, resulting in "white holes" where the toner image has not been transferred. Therefore, it is necessary to apply an appropriate transfer voltage to the transfer element in order to form a high-quality image.

[0004] The amount of charge required for transfer depends on the size of the recording material and the area ratio of the toner image. Therefore, a constant voltage control, applying a constant voltage corresponding to a given current density, is typically used to apply the transfer voltage. This is because it is easy to ensure a transfer current based on a specified voltage in the area where the desired toner image is located, regardless of the current flowing outside the recording material or in areas where no toner image is present on the recording material. However, the resistance of the transfer component, including the transfer portion, varies depending on product variations, component temperature, cumulative usage time, etc., and the resistance of the recording material passing through the transfer portion also varies depending on the type of recording material, the surrounding environment (temperature, humidity), etc. Therefore, when using constant capacity control to control the transfer voltage, it is necessary to adjust the transfer voltage in response to changes in the resistance of the transfer component and the recording material.

[0005] Japanese Patent Application Publication No. 2004-117920 discloses a transfer voltage control method in which the transfer voltage is controlled by constant voltage control. Immediately before the start of continuous image formation, a predetermined voltage is applied to the transfer portion without recording material to detect the current value and calculate a voltage value at which a predetermined target current can be obtained. Then, the recording material-sharing voltage, depending on the type of recording material, is added to this voltage value to set the transfer voltage value to be applied by constant voltage control during transfer. With this control, a transfer voltage corresponding to the desired target current can be applied by constant voltage control, regardless of changes in the resistance value of the transfer portion, such as the transfer member and the recording material.

[0006] For example, due to differences in surface smoothness, there are different types of recording materials, such as high-grade paper and coated paper, and due to differences in thickness, there are different types of recording materials, such as thin paper and thick paper. For example, the recording material's voltage sharing can be pre-calculated based on these types of recording materials. However, many types of recording materials are available on the market. The resistance of the recording material also depends on its humidity level (the moisture content contained within the recording material), but even with the same environmental conditions (temperature and humidity), the moisture content of the recording material varies depending on the time it has been exposed to the environment. For this reason, it is generally difficult to accurately determine the recording material's voltage sharing in advance. As mentioned above, if the transfer voltage, which includes variations in the resistance of the recording material, is not set to an appropriate value, image defects such as sparse image density and white voids may occur.

[0007] In response to these issues, Japanese Patent Application Publication Nos. 2008-102258 and 2008-275946 propose a configuration for controlling the transfer voltage using constant voltage control, in which an upper and lower limit of the current supplied to the transfer section is set when the recording material passes through the transfer section. This control allows the current supplied to the transfer section when the recording material passes through to be set to a predetermined current range, thereby suppressing image defects caused by insufficient or excessive transfer current. In Japanese Patent Application Publication No. 2008-102258, the upper limit is calculated based on environmental information. In Japanese Patent Application Publication No. 2008-275946, in addition to the environment, the upper and lower limits are determined based on the front and back sides of the recording material, the type of the recording material, and the size of the recording material.

[0008] On the other hand, there are methods to solve the above-mentioned problems by adjusting the transfer voltage by performing adjustment operations separately from the usual image formation. In Japanese Patent Application Publication No. 2013-37185, it is proposed to form multiple test images (hereinafter referred to as "patches") on a recording material when switching transfer voltages, and to adjust the transfer voltage based on the detection results of the concentration of each patch.

[0009] In methods such as those described in Japanese Patent Application Publication Nos. 2008-102258 and 2008-275946, the transfer voltage is automatically adjusted during image formation. This reduces the burden on the user in adjusting the transfer voltage, the time required to adjust the transfer voltage, and the amount of recording material (waste paper) needed to adjust the transfer voltage. However, in this method, the transfer voltage is not adjusted by actually viewing the image formed on the recording material or by detecting its density. Therefore, the desired results may not be achieved; for example, the density of the output image may not match the user's preferences.

[0010] Therefore, when enabling automatic adjustment as described in Japanese Patent Application Publication No. 2008-102258 and Japanese Patent Application Publication No. 2008-275946, in order to meet the needs of various users, it is desirable to be able to perform an adjustment mode as described in Japanese Patent Application Publication No. 2013-37185, in which the image is actually formed on the recording material and adjusted.

[0011] However, in configurations that automatically adjust the transfer voltage based on the current detected as the recording material passes through the transfer section, blocks may not be output under expected conditions, and proper adjustment may not be possible. In other words, for example, multiple blocks can be formed on a single recording material by gradually increasing the absolute value of the transfer voltage for each block. In this case, if the current supplied to the transfer section is limited as the recording material passes through the transfer section, then... Figure 10As shown in sections (a) and (b), the transfer voltage can only be varied within a predetermined current range. For example, in areas where a small absolute value of the transfer voltage is applied, the current supplied to the transfer section may drop below the lower limit of the predetermined current range, and adjustments may be made to increase the absolute value of the transfer voltage. This may result in blocks that should be output with a small absolute value of the transfer voltage not being output properly. Conversely, in areas where a large absolute value of the transfer voltage is applied, the current supplied to the transfer section exceeds the upper limit of the predetermined current range, and adjustments are made to decrease the absolute value of the transfer voltage. This may also result in blocks that should be output with a large absolute value of the transfer voltage not being output properly. If a transfer voltage that satisfies the user's preferred image density can be achieved in a region where the current supplied to the transfer section is outside the predetermined current range as described above, then if the above-described automatic adjustment is performed, the output of blocks at the transfer voltage in that region will be inappropriate. As a result, adjustments may not be possible according to user preferences.

[0012] In a configuration where the transfer voltage is controlled by constant voltage control, the control that changes the target voltage of the constant voltage control to bring the current into the predetermined range when the current flowing to the transfer member as the recording material passes through the transfer section is outside a predetermined range is also called "limiter control." In this part, the magnitude (high or low) of the voltage or current is compared in absolute values.

[0013] [The problem this invention aims to solve]

[0014] Therefore, the object of the present invention is to provide an image forming apparatus capable of performing adjustment by forming a test image on the recording material in an adjustment mode that is configured to perform limit control of the transfer voltage based on the transfer current when the recording material passes through the transfer section.

[0015] [Problem-solving methods]

[0016] According to one embodiment of the present invention, an image forming apparatus is provided, comprising: an image carrier member for carrying a toner image; a transfer member to which a voltage is applied to transfer the toner image carried on the image carrier member to a recording material at a transfer portion; a voltage source for applying a voltage to the transfer member; a current detection portion for detecting a current flowing through the transfer member; and a controller for performing constant voltage control when the recording material passes through the transfer portion, such that the voltage applied to the transfer member is a predetermined voltage, wherein the controller is capable of executing a first mode and a second mode, wherein in the first mode, a toner image is formed onto the recording material based on image information, and in the second mode, multiple test toner images are formed onto the recording material by applying multiple different voltages to the transfer member to set a voltage to be applied to the transfer portion in the first mode, and wherein the controller performs limit control when the recording material passes through the transfer portion in the first mode, and does not perform limit control when an area with the multiple test images transferred passes through the transfer portion in the second mode. Attached Figure Description

[0017] Figure 1 This is a schematic cross-sectional view of an image forming apparatus.

[0018] Figure 2 This is a schematic diagram of the configuration for secondary transfer printing.

[0019] Figure 3 This is a schematic block diagram showing the control scheme of the main part of the image forming apparatus.

[0020] Figure 4 This is a flowchart of the control process in Example 1.

[0021] Figure 5 This is a graph illustrating an example of the relationship between voltage and current in the secondary transfer section.

[0022] Figure 6 This is a schematic diagram illustrating an example of voltage table data for recording material distribution.

[0023] Figure 7 This is a schematic diagram showing an example of tabular data on the current range of the paper feed section.

[0024] Figure 8 This is a diagram illustrating the adjustment of the chart and showing an example of the adjustment mode settings screen.

[0025] Figure 9 It is a graph showing the changes in secondary transfer voltage and secondary transfer current when the output of the adjustment chart in Example 1 is displayed.

[0026] Figure 10 It is a graph used to illustrate the problem.

[0027] Figure 11 It is a graph showing the changes in secondary transfer voltage and secondary transfer current when the output of the adjusted graph in Example 2 is displayed. Detailed Implementation

[0028] The following is a more detailed description of the image forming apparatus of the present invention with reference to the accompanying drawings.

[0029] [Example 1]

[0030] 1. Overall configuration and operation of the image forming apparatus

[0031] Figure 1 This is a schematic diagram of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem multi-function machine (having the functions of a copier, printer, and fax machine) that uses an intermediate transfer method and is capable of forming a full-color image using an electrophotographic method.

[0032] The image forming apparatus 100 has a first image forming section SY, a second image forming section SM, a third image forming section SC, and a fourth image forming section SK, which respectively form images of yellow, magenta, cyan, and black, as multiple image forming sections (stations). Elements having the same or corresponding functions or configurations in each of the image forming sections SY, SM, SC, and SK can be generally described by omitting the Y, M, C, and K at the end of the symbol indicating one of the colors. In this embodiment, the image forming section S consists of a photosensitive drum 1, a charged roller 2, an exposure device 3, a developing device 4, a primary transfer roller 5, and a drum cleaning device 6, as described below.

[0033] The photosensitive drum 1, a rotatable drum-shaped (cylindrical) photosensitive component (electrophotographic photosensitive component) serving as the first image-carrying member for the toner image (toner picture), is driven in the direction of arrow R1 (counterclockwise) in the figure. The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charged roller 2, which is a roller-shaped charged component. Based on image information, the charged surface of the photosensitive drum 1 is scanned and exposed by an exposure device (laser scanner device) 3, which serves as an exposure component, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1.

[0034] The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by a toner supplied as a developer by the developing device 4, which is a developing component, and a toner image is formed on the photosensitive drum 1. In this embodiment, a toner charged with the same polarity as the photosensitive drum 1 is attached to the exposed portion (image portion) of the photosensitive drum 1, and its absolute value decreases by exposure after uniform charging (reverse development method). In this embodiment, the toner, which is charged with the same polarity as the toner during development, is usually negatively charged. The electrostatic image formed by the exposure device 3 is a collection of small dot images, and the concentration of the toner image formed on the photosensitive drum 1 can be changed by changing the density of the dot images. In this embodiment, the toner image of each color has a maximum concentration of approximately 1.5 to 1.7, and the amount of toner applied at the maximum concentration is approximately 0.4 to 0.6 mg / cm³. 2 .

[0035] An intermediate transfer belt 7, consisting of an unterminated strip, is arranged as a second image carrier carrying a toner image, allowing it to contact the surfaces of the four photosensitive drums 1. The intermediate transfer belt 7 is an example of an intermediate transfer component that feeds a toner image, already transferred once from another image carrier, to the recording material for secondary transfer. The intermediate transfer belt 7 is stretched on a drive roller 71, a tension roller 72, and a secondary transfer counter-roller 73, which are multiple tension rollers. The drive roller 71 transmits driving force to the intermediate transfer belt 7. The tension roller 72 controls the tension of the intermediate transfer belt 7 to a constant level. The secondary transfer counter-roller 73 serves as the counter member (counter electrode) of the secondary transfer roller 8, which will be described later. As the drive roller 71 is driven, the intermediate transfer belt 7 rotates (moves circumferentially) in the direction of arrow R2 (clockwise) in the figure at a feed speed (circumferential speed) of approximately 300 to 500 mm / s. The tension roller 72 is subjected to the force of a spring, which acts as an attachment member, to push the intermediate transfer belt 7 from the inner circumferential surface to the outer circumferential surface, and this force applies a tension of approximately 2 kg to 5 kg in the feeding direction of the intermediate transfer belt 7. A primary transfer roller 5 is mounted on the inner circumferential surface of the intermediate transfer belt 7 corresponding to each photosensitive drum 1. The primary transfer roller 5 is a roller-type primary transfer member that serves as a primary transfer component. The primary transfer roller 5 is pressed against the photosensitive drum 1 by the intermediate transfer belt 7 to form a primary transfer portion (primary transfer clamping portion) N1 where the photosensitive drum 1 contacts the intermediate transfer belt 7. In the primary transfer portion N1, by the action of the primary transfer roller 5, the toner image formed on the photosensitive drum 1 is electrostatically transferred (primarily transferred) to the rotating intermediate transfer belt 7. During a single transfer process, a primary transfer voltage (primary transfer bias) is applied from a primary transfer voltage source (not shown) to the primary transfer roller 5. This primary transfer voltage is a DC voltage with the opposite polarity to the toner's usual polarity. For example, when forming a panchromatic image, toner images of yellow, magenta, cyan, and black formed on each photosensitive drum 1 are sequentially transferred, such that they are superimposed on the intermediate transfer belt 7.

[0036] On the outer peripheral side of the intermediate transfer belt 7, a secondary transfer roller 8 is disposed opposite to a secondary transfer opposing roller 73. The secondary transfer roller 8 is a roller-type secondary transfer component that serves as a secondary transfer part. The secondary transfer roller 8 is pressed against the secondary transfer opposing roller 73 via the intermediate transfer belt 7 to form a secondary transfer portion (secondary transfer clamping portion) N2 where the intermediate transfer belt 7 and the secondary transfer roller 8 are in contact. In the secondary transfer portion N2, by the action of the secondary transfer roller 8, the toner image formed on the intermediate transfer belt 7 is electrostatically transferred (secondary transfer) to the recording material (sheet, transfer material) P conveyed between the intermediate transfer belt 7 and the secondary transfer roller 8. The recording material P is typically paper (paper used for printing), but is not limited to this; synthetic paper made of resin, such as waterproof paper, plastic sheets such as OHP sheets, cloth, etc., may also be used. During the secondary transfer process, a secondary transfer voltage (secondary transfer bias voltage) is applied to the secondary transfer roller 8 from a secondary transfer voltage source (high voltage source circuit) 20. This secondary transfer voltage is a DC voltage with the opposite polarity to the toner's normal polarity. Recording material P is stored in a recording material cassette (not shown) or similar, and is fed one sheet at a time from the cassette via a feed roller (not shown) or similar, and then fed to a stop roller 9. After recording material P stops passing the stop roller 9, it is timed to match the toner image on the intermediate transfer belt 7 and fed to the secondary transfer section N2.

[0037] Recording material P, on which a toner image has been transferred, is fed to a fixing member 10, which serves as a fixing component. The fixing member 10 heats and pressurizes the recording material P, which carries the unfixed toner image, to fix (melt, adhere) the toner image to the recording material P. Afterward, the recording material P is ejected (output) to the outside of the main assembly of the image forming apparatus 100.

[0038] After the first transfer process, the toner remaining on the surface of the photosensitive drum 1 (first transfer residual toner) is removed and collected from the surface of the photosensitive drum 1 by the drum cleaning device 6, which is a photosensitive drum cleaning component. In addition, after the second transfer process, the toner remaining on the surface of the intermediate transfer belt 7 (second transfer residual toner) and adhering materials such as paper dust are removed and collected from the surface of the intermediate transfer belt 7 by the belt cleaning device 74, which is an intermediate transfer component cleaning component.

[0039] In this embodiment, the intermediate transfer belt 7 is an annular belt with a three-layer structure consisting of a resin layer, an elastic layer, and a surface layer, extending from the inner circumference to the outer circumference. Polyimide, polycarbonate, etc., can be used as the resin material constituting the resin layer. A thickness of 70 μm to 100 μm is suitable for the resin layer. Polyurethane rubber, chloroprene rubber, etc., can be used as the elastic material constituting the elastic layer. The thickness of the elastic layer is preferably 200 μm to 250 μm. As the material for the surface layer, it is desirable to reduce the adhesion of the toner to the surface of the intermediate transfer belt 7 and promote the transfer of the toner to the recording material P in the secondary transfer section N2. For example, one or more types of resin materials such as polyurethane, polyester, epoxy resin, etc., can be used. Alternatively, one or more types of elastic materials (elastic rubber, elastomer), butyl rubber, or other elastic materials can be used. Furthermore, these materials can be dispersed with powders and particles of one or more types of materials that reduce surface energy and increase lubricity, such as fluoropolymers, or one or more of these powders or particles with different particle sizes. A thickness of 5 μm to 10 μm is suitable for the surface layer. The resistance of the intermediate transfer belt 7 is adjusted by adding a conductive agent, such as carbon black, to adjust the resistance, and the volume resistivity is preferably set to 1×10⁻⁶. 9 Ω·cm~1×10 14 Ω·cm.

[0040] In this embodiment, the secondary transfer roller 8 is composed of a core metal (matrix material) and an elastic layer formed around the core metal by ion-conductive foam rubber (NBR rubber). In this embodiment, the outer diameter of the secondary transfer roller 8 is 24 mm, and the surface roughness Rz of the secondary transfer roller 8 is 6.0 to 12.0 (μm). In this embodiment, when 2 kV is applied at N / N (23°C, 50% RH), the resistance of the secondary transfer roller 8 is measured to be 1 × 10⁻⁶. 5 Up to 1×10 7 The elastic layer has a hardness of Ω, and its hardness on the Asker-C hardness scale is 30 to 40°. In this embodiment, the width (length in the direction substantially perpendicular to the feed direction of the recording material P) of the secondary transfer roller 8 in the longitudinal direction (rotation axis direction) is approximately 310 mm to 340 mm. The longitudinal width of the secondary transfer roller 8 is longer than the maximum width (maximum width) of the recording material P (length in the direction substantially perpendicular to the feed direction) that the image forming apparatus 100 ensures to be conveyed. In this embodiment, the recording material P is fed relative to the center in the longitudinal direction of the secondary transfer roller 8, thus ensuring that all the recording material P is fed. This allows for the stable feeding of recording materials of various sizes and the stable transfer of toner images onto recording materials of various sizes.

[0041] Figure 2This is a schematic diagram of the secondary transfer configuration. The secondary transfer roller 8 contacts the secondary transfer opposing roller 73 via the intermediate transfer belt 7 to form a secondary transfer section N2. A secondary transfer voltage source 20 with a variable output voltage value is connected to the secondary transfer roller 8. The secondary transfer opposing roller 73 is electrically grounded (connected to ground). When the recording material P passes through the secondary transfer section N2, a secondary transfer voltage, which is a DC voltage of the opposite polarity to the toner's normally charged polarity, is applied to the secondary transfer roller 8, and the toner image on the intermediate transfer belt 7 is transferred to the recording material P by supplying a secondary transfer current to section N2. In this embodiment, during the secondary transfer, a secondary transfer current of, for example, +20 μA to +80 μA is applied to the secondary transfer section N2. In this embodiment, the roller corresponding to the secondary transfer counter roller 73 of this embodiment is used as a transfer member, and a secondary transfer voltage with the same polarity as the toner's normal polarity is applied to it, while the roller corresponding to the secondary transfer counter roller 8 of this embodiment can be used as a counter electrode and electrically grounded.

[0042] In this embodiment, the upper and lower limits (“secondary transfer current range”) of the secondary transfer current when the recording material P passes through the secondary transfer section N2 are determined based on various information. This information includes, as described in detail below, the following: First, information regarding the control section 31 on the main component of the image forming apparatus 100 (… Figure 3 ) or by an external device 200 such as a personal computer that is connected to the image forming apparatus 100 via communications. Figure 3 Information regarding the conditions specified by ) (such as the type of material P being recorded). Also regarding environmental sensor 32 ( Figure 3 The information pertains to the detection results of the recording material P. It also pertains to the resistance of the secondary transfer section N2, detected before the recording material P reaches it. When the recording material P passes through the secondary transfer section N2, the secondary transfer voltage output from the secondary transfer voltage source 20 is controlled by constant voltage control while detecting the secondary transfer current flowing in the secondary transfer section N2, so that the secondary transfer current falls within the aforementioned range. Specifically, in this embodiment, the range of the secondary transfer current is varied based on information about the width of the recording material P passing through the secondary transfer section N2. In this embodiment, information about the width and thickness of the recording material P is obtained based on information input from the control unit 31 and the external device 200. However, a detection component for detecting the width and thickness of the recording material P may also be installed in the image forming apparatus 100, and control may be performed based on information obtained from this detection component.

[0043] The secondary transfer voltage source 20 is connected to the current detection circuit 21, which serves as a current detection component (current detection section), to detect the current (secondary transfer current) flowing in the secondary transfer section N2 (i.e., the secondary transfer roller 8 or the secondary transfer voltage source 20). Furthermore, the voltage detection circuit 22, which serves as a voltage detection component (voltage detection section), is connected to the secondary transfer voltage source 20 to detect the voltage output by the secondary transfer voltage source 20 (secondary transfer voltage). The controller 50 can also be used as the voltage detection section and detects the voltage output by the secondary transfer voltage source 20 based on the indicated value of the voltage output from the secondary transfer voltage source 20. In this embodiment, the secondary transfer voltage source 20, the current detection circuit 21, and the voltage detection circuit 22 are disposed in the same high-voltage board.

[0044] 2. Control Scheme

[0045] Figure 3 This is a schematic block diagram illustrating the control scheme of the main component of the image forming apparatus 100 in this embodiment. The controller (control circuit) 50, serving as the control unit, is composed of a CPU 51 as an arithmetic control unit, RAM 52 as a storage unit, and a memory (storage medium) such as ROM 53. The CPU 51 is the central component that performs arithmetic processing. The RAM 52, serving as a rewritable memory, stores information input to the controller 50, detected information, calculation results, etc., while the ROM 53 stores control programs, predetermined data tables, etc. The CPU 51, RAM 52, ROM 53, and other memories can transfer and read data from each other.

[0046] External devices 200, such as an image reader (not shown) or a personal computer installed in the image forming apparatus 100, are connected to the controller 50. Additionally, an operation unit (operation panel) 31 installed in the image forming apparatus 100 is connected to the controller 50. The operation panel 31 consists of a display section and an input section. The display section displays various information to an operator, such as a user or service personnel, under the control of the controller 50. The input section is used by the operator to input various settings related to image forming to the controller 50. The operation section 31 may include a touch panel or similar device equipped with both the display section and the input section. Information about the operation, including control commands for image forming such as the type of recording material P, is input from the operation section 31 or the external device 200 to the controller 50. The type of recording material P encompasses attributes based on general characteristics such as plain paper, thick paper, thin paper, glossy paper, coated paper, etc., including manufacturer, brand name, part number, basis weight, thickness, and any other information that can distinguish the recording material P. The controller 50 can obtain information about the type of recording material P by directly inputting information, or, for example, by selecting the cassette storing the feed portion of the recording material P from information pre-set with the cassette. The secondary transfer voltage source 20, current detection circuit 21, and voltage detection circuit 22 are connected to the controller 50. In this embodiment, the secondary transfer voltage source 20 applies a secondary transfer voltage, which is a DC voltage under constant voltage control, to the secondary transfer roller 8. Constant voltage control is a control that makes the voltage applied to the transfer portion (i.e., the transfer member) a substantially constant voltage value. The controller is also connected to an environmental sensor 32. In this embodiment, the environmental sensor 32 detects the temperature and humidity of the atmosphere inside the housing of the image forming apparatus 100. The temperature and humidity information detected by the environmental sensor 32 is input to the controller 50. The controller 50 can obtain the moisture level (moisture content, absolute moisture level) of the atmosphere inside the housing of the image forming apparatus 100 based on the temperature and humidity detected by the environmental sensor 32. The environmental sensor 32 is an example of an environmental sensing component that detects at least one of temperature or humidity in at least one of the interior or exterior of the image forming apparatus 100. The controller 50 comprehensively controls each part of the image forming apparatus 100 to perform image forming operations based on image information from the image reading device and the external device 200, as well as control commands from the operation section 31 and the external device 200.

[0047] Here, the image forming apparatus 100 executes a job (printing operation) initiated by a single start command (printing command), which is a series of operations to form and output an image on one or more recording materials P. The job typically includes image forming processing, pre-rotation processing, paper-to-paper processing when forming images on multiple recording materials P, and post-rotation processing. Image forming processing is the time period during which the formation of an electrostatic image, toner image, primary transfer of the toner image, and secondary transfer of the toner image are performed to be actually formed on the recording materials P and output; the image forming time (image forming period) refers to this period. More specifically, the timing of the image forming period differs at the locations where these processes of electrostatic image formation, toner image formation, primary transfer of the toner image, and secondary transfer of the toner image are performed. Pre-rotation processing is the preparatory operation period from the time the start command is input until the image forming processing begins, prior to the actual image forming. Paper-to-paper processing is the time period corresponding to the interval between recording materials P when image forming (continuous image forming) is performed continuously on multiple recording materials P. Post-rotation processing is the period during which organization operations (preparation operations) are performed after image forming processing. Non-image forming time (non-image forming period) is the period other than image forming time, and includes the aforementioned pre-rotation processing, paper-to-paper processing, post-rotation processing, and pre-multiple rotation processing as a preparation operation when the voltage source of the image forming apparatus is turned on or when it returns from sleep mode. In this embodiment, during non-image forming time, control is performed to determine the upper and lower limits of the secondary transfer current ("secondary transfer current range"). In this embodiment, the series of operations described below for outputting an adjustment chart in adjustment mode are also considered as operations in adjustment mode for outputting an adjustment chart.

[0048] 3. Secondary transfer voltage control

[0049] Next, the control of the secondary transfer voltage in this embodiment will be explained. Figure 4 A flowchart illustrating the process for controlling the secondary transfer voltage in this embodiment is shown. Figure 4 An example is shown of a situation where an operation is performed on a single recording material P to form an image (also referred to herein as a "normal image") or adjust a chart based on arbitrary image information specified by the operator.

[0050] First, when the controller 50 obtains job information from the operation unit 31 or the external device 200, the controller 50 begins the job operation (S101). In this embodiment, the information includes the dimensions (width, length) of the recording material P on which the image is to be formed, the thickness of the recording material P and related information (thickness or basis weight), and information related to the surface properties of the recording material P, such as whether the recording material P is coated paper (paper type category information). The controller 50 writes the job information to the RAM 52 (S102).

[0051] Next, the controller 50 acquires environmental information detected by the environmental sensor 32 (S103). In the ROM 53, information showing the correlation between the environmental information and the target value (target current) Itarget of the transfer current used to transfer the toner image on the intermediate transfer belt 7 to the recording material P is stored as tabular data, etc. Based on the environmental information read in S103, the controller 50 obtains the target current Itarget corresponding to the environment from the information showing the relationship between the above environmental information and the target current Itarget, and writes it to the RAM 52 (S104).

[0052] The target current Itarget changes based on environmental information because the amount of toner charge varies depending on the environment. Information demonstrating the relationship between this environmental information and the target current Itarget is obtained beforehand through experiments. Besides the environment, the amount of toner charge may also be affected by usage history, such as the timing of refilling the developing unit 4 with toner and the amount of toner from the developing unit 4. The image forming apparatus 100 is designed to maintain the amount of toner charge in the developing unit 4 within a certain range to suppress these effects. However, if factors other than environmental information that affect the amount of toner charge on the intermediate transfer belt 7 are known, the target current Itarget can be changed based on that information. Furthermore, the image forming apparatus 100 may be equipped with a measuring component for measuring the amount of toner charge, and the target current Itarget can be changed based on the information about the amount of toner charge obtained from this measuring component.

[0053] Next, the controller 50 obtains information about the resistance of the secondary transfer section N2 before the toner image on the intermediate transfer belt 7 and the recording material P with the toner image transferred thereon reach the secondary transfer section N2 (S105). In this embodiment, information about the resistance of the secondary transfer section N2 (mainly the secondary transfer roller 8 in this embodiment) is obtained by ATVC control (Active Transfer Voltage Control). In other words, when the secondary transfer roller 8 is in contact with the intermediate transfer belt 7, a predetermined voltage (test voltage) or current (test current) is supplied to the secondary transfer roller 8 from the secondary transfer voltage source 20. Then, the current value when the predetermined voltage is supplied or the voltage value when the predetermined current is supplied is detected, and the relationship between voltage and current (voltage-current characteristic) is obtained. This voltage-current relationship varies depending on the resistance of the secondary transfer section N2 (mainly the secondary transfer roller 8 in this embodiment). In this embodiment, the relationship between voltage and current does not change linearly (proportionally) with respect to voltage, but rather... Figure 5 As shown, the current is changed in such a way that it is expressed as a second-order or higher-order polynomial of voltage. Therefore, in this embodiment, when information about the resistance of the secondary transfer portion N2 is obtained, the predetermined voltage or current to be supplied is set to multiple levels with three or more points (three levels), such that the above voltage-current relationship can be expressed as a polynomial equation. From the viewpoint of being able to obtain the voltage-current characteristics with sufficient accuracy without making the control time longer than required, the number of these levels can be appropriately selected, but in many cases, typically 10 levels or less are sufficient.

[0054] Next, the controller 50 obtains the target value (target voltage) of the secondary transfer voltage to be applied from the secondary transfer voltage source 20 to the secondary transfer roller 8 (S106). In other words, the controller 50 calculates the voltage value required to apply the target current Itarget when no material P is recorded in the secondary transfer section N2, based on the target current Itarget written in RAM 52 in S104 and the voltage-current relationship calculated in S105. This voltage value Vb corresponds to the voltage shared by the secondary transfer section. Additionally, as... Figure 6As shown, ROM 53 stores information for determining the recording material sharing voltage Vp. In this embodiment, this information is set as tabular data showing the relationship between the atmospheric moisture content and the recording material sharing voltage Vp for each category of the recording material P's basis weight. Controller 50 obtains the atmospheric moisture content based on environmental information (temperature and humidity) detected by environmental sensor 32. Controller 50 obtains the recording material sharing voltage Vp from the above tabular data based on the information about the basis weight of the recording material P included in the information about the operation obtained in S102 and the environmental information obtained in S103. Then, controller 50 calculates Vb+Vp, which is the sum of the above Vb and Vp, as the initial value of the secondary transfer voltage Vtr applied from the secondary transfer voltage source 20 to the secondary transfer roller 8 when the recording material P passes through the secondary transfer section N2, and stores it in RAM 52. In this embodiment, the initial value of the secondary transfer voltage Vtr is obtained before the recording material P reaches the secondary transfer section N2, and preparations are made for timing when the recording material P reaches the secondary transfer section N2.

[0055] like Figure 6 The tabular data shown for calculating the recording material sharing voltage Vp is obtained experimentally beforehand. Here, in addition to information related to the thickness (basis weight) of the recording material, the recording material sharing voltage (the transfer voltage relative to the resistance of the recording material) Vp can vary depending on the surface properties of the recording material P. Therefore, the above tabular data can be set such that the recording material sharing voltage Vp varies depending on the surface properties and related information of the recording material P. In this embodiment, information related to the thickness of the recording material P (and information related to the surface properties of the recording material P) is included in the job information obtained in S102. However, the image forming apparatus 100 is equipped with a measuring component for detecting the thickness and surface properties of the recording material P, and the recording material sharing voltage Vp can be calculated based on the information obtained by the measuring component.

[0056] Next, the controller 50 determines whether the image to be formed on the recording material P is a "normal image" based on any image information actually output by the operator as a deliverable, or a predetermined "adjustment chart" (S107) used to adjust the operating settings (output conditions) of the image forming apparatus 100. The controller 50 can make the above determination based on information included in the job information, which indicates whether the job is in a normal image forming mode (first mode) for outputting a normal image or in an adjustment mode (second mode) for outputting an adjustment chart.

[0057] If the controller 50 determines in S107 that the image to be formed on the recording material P is an adjustment chart, then when the recording material P used to output the adjustment chart passes through the secondary transfer section N2, the controller 50 does not perform the limit control (current limit control) described below (S108). In other words, in this case, the controller 50 performs constant voltage control when the recording material P passes through the secondary transfer section N2, such that the voltage applied from the secondary transfer voltage source 20 to the secondary transfer roller 8 becomes a predetermined secondary transfer voltage based on the secondary transfer voltage Vtr (=Vb+Vp) determined in S106. As described in detail below, this predetermined secondary transfer voltage is set to Vb+Vp or Vb+Vp+ΔV (adjustment amount) so that multiple blocks of the adjustment chart are transferred at different secondary transfer voltages. The controller 50 continues the processing in S108 until the output of the adjustment chart is completed (S109). Here, the case of performing the operation of forming an adjustment chart on a single recording material P is taken as an example. In the case of a job that continuously forms adjustment charts on multiple recording materials P, it is sufficient not to perform limit control during the secondary transfer of each adjustment chart. The adjustment mode for forming and outputting adjustment charts on recording material P in this embodiment will then be described in more detail.

[0058] On the other hand, if the controller 50 determines in S107 that the image to be formed on the recording material P is a normal image, then when the recording material P used to output the normal image passes through the secondary transfer section N2, the controller 50 performs the limit control as described below. In other words, in this case, when the recording material P passes through the secondary transfer section N2, the controller 50 controls the secondary transfer voltage determined in S106, such that when the current is outside the predetermined range, the current flowing in the secondary transfer roller 8 enters the predetermined range. In other words, in this case, the controller 50 limits the range of current flowing to the secondary transfer roller 8 when the recording material P passes through the secondary transfer section N2.

[0059] The controller 50 determines the upper and lower limits of the secondary transfer current (“secondary transfer current range”) when the recording material P passes through the secondary transfer section N2, as follows. In other words, as... Figure 7As shown, information used to determine the range of current that can flow through the paper passage portion when the recording material P passes through the secondary transfer portion N2 ("paper passage portion current range") from the viewpoint of suppressing image defects is stored in ROM 53. In this embodiment, this information is set as tabular data showing the relationship between the atmospheric moisture content and the upper and lower limits of the current that can be applied to the paper passage portion. This tabular data is obtained in advance through experiments, etc. First, the controller 50 calculates the range of current that can be applied to the paper passage portion from the above tabular data based on the environmental information obtained in S103 (S110). The range of current that can flow through the paper passage portion varies depending on the width of the recording material P. In this embodiment, the above tabular data is set assuming a recording material P with an A4 size equivalent width (297 mm). Here, in addition to environmental information, the range of current that can be applied to the paper passage portion from the viewpoint of suppressing image defects can also vary depending on the thickness and surface properties of the recording material P. Therefore, the data in the table above can be set such that the range of current varies depending on information related to the thickness (weight) of the recording material P and information related to the surface properties of the recording material P. The range of current that can be applied to the portion through which the paper passes can be set as a formula. The range of current that can be applied to the portion through which the paper passes can be set as multiple tables or formulas for each dimension of the recording material P.

[0060] Next, the controller 50 modifies the range of current that can be applied to the paper passage portion, obtained in S110, based on the information about the width of the recording material P included in the job information obtained in S102 (S111). The range of current obtained in S110 corresponds to a width equivalent to an A4 size (297 mm). For example, if the width of the recording material P actually used for image formation is equivalent to the width of an A5 vertical feed (148.5 mm), that is, half the width of an A4 size, then the upper and lower limits obtained in S110 are halved respectively, making the range of current proportional to the width of the recording material P. In other words, from Figure 7 The table data obtained before correction showed that the upper and lower limits of the current through the paper were Ip_max and Ip_min, respectively, and when determined... Figure 7 The width of the recording material P in the table data is determined as Lp_bas. The actual width of the fed recording material P is Lp, and the upper and lower limits of the current passing through the corrected paper are Ip_max_aft and Ip_min_aft, respectively. The upper and lower limits of the current passing through the corrected paper can be obtained using the following formulas 1 and 2, respectively.

[0061] Ip_max_aft=Lp / Lp_bas×Ip_max…(Formula 1)

[0062] Ip_min_aft=Lp / Lp_bas×Ip_min...(Formula 2)

[0063] Next, the controller 50 calculates the current flowing in the non-paper passage section ("non-paper passage section current (non-passage section current)") Inp (S112) based on the following information: the job information obtained in S102 includes information on the width of the recording material P, information obtained in S105 on the relationship between the voltage and current of the secondary transfer section N2 when there is no recording material P in the secondary transfer section N2, and information obtained in S106 on the relationship between the voltage and current of the secondary transfer section N2. For example, if the width of the secondary transfer roller 8 is 338 mm and the width of the recording material P obtained in S102 is equivalent to the width of A5 vertical feed (148.5 mm), then the width of the non-paper passage section is 189.5 mm, which is the width of the secondary transfer roller 8 minus the width of the recording material P. The secondary transfer voltage Vtr obtained in S106 is, for example, 1000 V, and according to the voltage and current relationship obtained in S105, the current corresponding to the secondary transfer voltage Vtr is 40 μA. In this case, the current Inp flowing in the non-paper passage portion corresponding to the secondary transfer voltage Vtr above can be calculated according to the following proportion.

[0064] 40μA x 189.5mm / 338mm=22.4μA

[0065] In other words, the current flowing in the non-paper passage section can be calculated by reducing the ratio of the 40μA current corresponding to the secondary transfer voltage Vtr to the ratio of the width of the non-paper passage section (189.5mm) to the width of the secondary transfer roller 8 (338mm).

[0066] Next, the controller 50 obtains the upper and lower limits (“secondary transfer current range”) of the secondary transfer current when the recording material P passes through the secondary transfer section N2, and stores the obtained secondary transfer current range in RAM 52 (S113). In other words, the controller 50 adds the non-paper-passing current Inp calculated in S112 to the upper and lower limits of the paper-passing current calculated in S111, and stores it in RAM 52. In other words, when the recording material P passes through the secondary transfer section N2, the upper and lower limits of the secondary transfer current are I_max and I_min, respectively. At this time, the upper and lower limits of the secondary transfer current can be calculated using the following formulas 3 and 4, respectively.

[0067] I_max=Ip_max_aft+Inp…(Formula 3)

[0068] I_min=Ip_min_aft+Inp...(Formula 4)

[0069] For example, consider a case where the upper and lower limits of the range of current that can be applied to the paper passage portion corresponding to the width of the A4 size obtained in S110 are 20 μA and 15 μA, respectively. In this case, when the width of the recording material P actually used for image formation is equivalent to the width of the A5 vertical feed, the upper and lower limits of the range of current that can flow through the paper passage portion are 10 μA and 7.5 μA, respectively. Furthermore, when the current flowing to the non-paper passage portion obtained in S112 is 22.4 μA as in the example above, the upper and lower limits of the secondary transfer current range are 32.4 μA and 29.9 μA, respectively.

[0070] Next, after the recording material P arrives at the secondary transfer section N2, and while the recording material P is present in the secondary transfer section N2, the controller 50 detects the secondary transfer current via the current detection circuit 21 when the secondary transfer voltage Vtr is applied (S114). The controller 50 compares the detected secondary transfer current value with the secondary transfer current range obtained in S113, and adjusts the secondary transfer voltage Vtr output by the secondary transfer voltage source 20 as needed (S115). In other words, if the detected secondary transfer current value is within the secondary transfer current range determined in S113 (above the lower limit and below the upper limit), the controller 50 maintains the secondary transfer voltage Vtr output by the secondary transfer voltage source 20 as is (S116) without changing it. On the other hand, if the detected secondary transfer current value is outside the secondary transfer current range determined in S113 (below the lower limit or above the upper limit), the controller 50 corrects the secondary transfer voltage Vtr output by the secondary transfer voltage source 20 so that it falls within the secondary transfer current range (S117). In this embodiment, when the upper limit is exceeded, the secondary transfer voltage Vtr is decreased, and when the secondary transfer current drops below the upper limit, the adjustment of the secondary transfer voltage Vtr is stopped, and the secondary transfer voltage Vtr is maintained. In this embodiment, the secondary transfer voltage Vtr gradually decreases by a predetermined change range ΔVp. In this embodiment, when the secondary transfer voltage Vtr is below the lower limit, the secondary transfer voltage Vtr is increased, and when the secondary transfer current exceeds the lower limit, the adjustment of the secondary transfer voltage Vtr is stopped, and the secondary transfer voltage Vtr is maintained. In this embodiment, the secondary transfer voltage Vtr gradually increases by a predetermined change range ΔVp. In this embodiment, operations S114 to S117 are performed by alternately repeating a predetermined detection time (the period for detecting the current) and a predetermined response time (the period for changing the voltage). This detection time and response time are repeated when recording material P is present in the secondary transfer section N2 (more specifically, when the image forming area of ​​recording material P passes through the secondary transfer section N2). As a result, the secondary transfer voltage Vtr is corrected so that the secondary transfer current detected when the recording material P passes through the secondary transfer section N2 is within the range of the secondary transfer current calculated in S113. The controller 50 continues the processing of S114 to S117 until the desired image output is completed (S118). Here, the case of performing a job of forming a normal image on a single recording material P is taken as an example. In the case of continuously forming normal images on multiple recording materials P, the processing of S114 to S117 should be repeated until all passed images have been ejected.

[0071] Here, the variation range ΔVp of the secondary transfer voltage in the limit control can be set, for example, as follows. From the viewpoint of suppressing concentration irregularities, the change in secondary transfer current per unit feed distance of the recording material P can be preset. The change in secondary transfer current caused by a single change in secondary transfer voltage can be set based on the change in secondary transfer current per unit transfer distance of the recording material P, the transfer speed of the recording material P, and the sampling time of the secondary transfer current. Then, the variation range ΔVp of each change in secondary transfer voltage can be set to the change in secondary transfer voltage corresponding to that change in secondary transfer current. In this case, information about the change in secondary transfer current each time can be preset and stored in ROM 53. Then, the controller 50 can use the voltage-current characteristics determined by ATVC control to determine the variation width ΔVp of each change in secondary transfer voltage from the above change in secondary transfer current. In other words, based on the information about the resistance of the secondary transfer section N2 obtained by ATVC control, the range ΔVp of the change in secondary transfer voltage corresponding to a predetermined change in the secondary transfer current is obtained. This allows concentration non-uniformity to be suppressed by suppressing abrupt changes in the secondary transfer current. In this way, the controller 50 can change the target voltage of the secondary transfer voltage for each predetermined change range in limit control. Furthermore, the controller 50 can change the target voltage of the secondary transfer voltage in limit control based on the voltage-current characteristics obtained by applying voltage to the secondary transfer roller 8 when no material P is recorded in the secondary transfer section N2.

[0072] Alternatively, the voltage-current characteristics determined by ATVC control can be used to determine the change range ΔVp, which corresponds to the difference between the detected current and the lower limit (if below the lower limit) or upper limit (if above the upper limit) of the secondary transfer current range. In other words, based on the information about the resistance of the secondary transfer section N2 obtained by ATVC control, a change range ΔVp that can eliminate the difference between the detected current and the lower or upper limit of the secondary transfer current range can be obtained, and this allows the secondary transfer current to be corrected to be near the secondary transfer current range (typically, the lower or upper limit) by changing the secondary transfer voltage once. In this case, a voltage larger than that sufficient to eliminate the difference between the upper or lower limit of the secondary transfer current range can be used as the change range ΔVp. In this case, as long as the secondary transfer current can be sufficiently adjusted to be near the predetermined current range, the secondary transfer current supplied by the corrected secondary transfer voltage can deviate from the predetermined current range within a sufficiently small range due to control errors, etc. Therefore, in limit control, the controller 50 controls the secondary transfer voltage so that, through a single change, the difference between the secondary transfer current range and the current indicated by the detection result of the current detection circuit 21 becomes less than a predetermined value (which can be zero).

[0073] In this embodiment, the current flowing in the secondary transfer section N2 when the recording material P passes through it is considered as "paper-passing current" and "non-paper-passing current". The passing current is the current flowing through the recording material P when it passes through the secondary transfer section N2. The paper-passing current is the current flowing in the area ("paper-passing area") of the secondary transfer section N2 in a direction substantially perpendicular to the feed direction of the recording material P. The non-paper-passing current is the current flowing in the area ("non-paper-passing area") of the secondary transfer section N2 in a direction substantially perpendicular to the feed direction of the recording material P. Non-passing areas occur because the longitudinal length of the secondary transfer roller 8 is greater than the maximum width of the recording material guaranteed by the image forming apparatus 100 to ensure stable transfer and toner image transfer for recording materials P of various sizes. The detectable current when the recording material P passes through the secondary transfer section N2 is the sum of the current in the paper-passing section and the current in the non-paper-passing section. Importantly, the current in the paper-passing section must be within an appropriate range to suppress image defects such as white voids and image densification as described above; however, it is not sufficient to detect only the current in the paper-passing section. On the other hand, upper and lower limits (“secondary transfer current range”) of the secondary transfer current suitable for each size of the recording material P are predetermined, and the secondary transfer current when the recording material P passes through the secondary transfer section N2 is controlled to a value within the secondary transfer current range, based on the size of the recording material P. However, even if an appropriate secondary transfer current range is predetermined, the resistance of the secondary transfer roller 8 forming the non-paper-passing section may vary under various conditions. These various conditions include product variability, environment (temperature and humidity), temperature and moisture absorption of components, and cumulative usage time (operating state and repeated use state of the image forming apparatus). Therefore, changes in the resistance of the secondary transfer roller 8 may lead to changes in the appropriate secondary transfer current range. In this embodiment, the non-paper current is predicted based on information about the resistance of the secondary transfer portion N2 when the recording material P is not in the secondary transfer portion N2. However, the invention is not limited to this, and for example, as described above, an appropriate secondary transfer current range can be obtained in advance for each size of recording material P, and limit control can be performed using the secondary transfer current range according to the size of the recording material P. Furthermore, depending on the desired accuracy, limit control can be performed without considering the non-paper current.

[0074] 4. Adjust mode

[0075] Next, the adjustment mode in this embodiment will be further explained. Various possible adjustment modes exist for forming and outputting adjustment charts on the recording material P. For example, the following can be mentioned: There are adjustment modes for adjusting the latent image formation conditions and development conditions for forming a toner image on the photosensitive drum 1. There are also adjustment modes for adjusting the positional conditions for transferring the toner image onto the recording material P. There are also adjustment modes for adjusting the transfer voltage conditions when transferring the toner image onto the recording material P. In this embodiment, the adjustment mode for forming and outputting adjustment charts on the recording material P is an adjustment mode for adjusting the secondary transfer voltage.

[0076] In other words, this embodiment enables automatic adjustment of the secondary transfer voltage through the aforementioned limit control, and also allows the user to adjust the secondary transfer voltage by outputting an adjustment chart to the recording material P actually used by the user, in order to achieve a concentration that meets the user's preferences. Specifically, in this embodiment, the adjustment mode outputs an adjustment chart as a predetermined test image when switching the secondary transfer voltage, showing multiple blocks formed on a single recording material P. In this embodiment, the type (size, thickness, paper type, etc.) of the recording material P used to output the adjustment chart can be specified, and the adjustment mode can be executed. In this embodiment, when the adjustment chart is output, the aforementioned limit control is not executed, and Vb+Vp (=Vtr) determined according to the type of the recording material P, etc., or Vb+Vp+ΔV (adjustment amount) based on the above, is used to control the secondary transfer voltage using constant voltage control. Furthermore, this embodiment allows the user or other operator to visually inspect the output adjustment chart or use a colorimeter, and set the secondary transfer voltage (more specifically, ΔV) corresponding to the blocks with favorable results.

[0077] Adjustment charts output in adjustment mode are not particularly restricted. Each block in the adjustment chart can be square or rectangular. The color of the block can be determined based on the image defects to be inspected and the ease of inspection. For example, as the secondary transfer voltage increases from low to high, the lower limit of the secondary transfer voltage can be determined based on the voltage value of blocks that can appropriately transfer secondary colors such as red, green, and blue. As the secondary transfer voltage increases further, the upper limit of the secondary transfer voltage can be determined based on the voltage value of image defects appearing in halftone blocks due to high secondary transfer voltage.

[0078] Figure 8Part (a) is a schematic diagram of an example of an adjustment chart 300 output in the adjustment mode of this embodiment. The adjustment chart 300 has a group of blocks arranged in a direction substantially perpendicular to the feed direction (also referred to herein as the "width direction"), comprising one blue solid block 301, one black solid block 302, and two halftone blocks 303. The block groups 301-303 in the width direction are arranged in 11 pairs in the feed direction. In this embodiment, the halftone blocks 303 are gray (black halftone) blocks. Here, the solid image is the image with the highest density level. In this embodiment, when the toner loading level of the solid image is 100%, the halftone image is an image with a toner loading level of 10% to 80%. Additionally, in this embodiment, the adjustment chart 300 has identification information 304 corresponding to each of the 11 groups of blocks 301-303 in the feed direction, the identification information 304 identifying the setting of the secondary transfer voltage applied to each group of blocks 301-303. This identification information 304 corresponds to the adjustment value described below. In this embodiment, there are 11 identification information corresponding to 11 secondary transfer voltage settings (in this embodiment, -5 to 0 to +5).

[0079] In this embodiment, the maximum size of the recording material P that can be used in the image forming apparatus 100 is 13 inches (≈330 mm) in the width direction and 19.2 inches (≈487 mm) in the feed direction, and the adjustment chart 300 corresponds to this size. If the size of the recording material P is 13" × 19.2" or smaller (longitudinal feed) and A3 size (longitudinal feed) or larger, a chart corresponding to the image data cut from the chart data shown in the figure according to the size of the recording material P is output. In this embodiment, the image data is cut at the central reference at the top according to the size of the recording material P. In other words, the top of the recording material P in the feed direction is aligned with the top of the adjustment chart 300 in the feed direction (the upper edge in the figure), and the center of the recording material P in the width direction is aligned with the center of the adjustment chart 300 in the width direction, and the image data is cut out. In this embodiment, the image data is cut with a margin of 2.5 mm at the edges (in this embodiment, both ends in the width direction and both ends in the feed direction). For example, when an adjustment chart 300 is output on an A3-sized (vertically fed) recording material P, image data with a short side of 292mm × a long side of 415mm is cut out at each edge with a 2.5mm gap. Then, the image corresponding to the cut image data is output onto the A3-sized recording material P with the top center as the reference. When using a recording material P with a width dimension less than 13 inches, the width dimension of the halftone blocks 303 at the edges in the width direction becomes increasingly smaller. When using a recording material P with a width dimension less than 13 inches, the gap at the rear edge in the feed direction becomes smaller. In this embodiment, when using a recording material P smaller than A3 size, adjustment charts can be formed on multiple recording materials P, and as many blocks as the required adjustment value can be output. In addition to standard sizes, this embodiment can also output adjustment charts using recording material P of any size (free size) by inputting and specifying it from the operation section 31 or external device 200.

[0080] The size of the blocks must be large enough for the operator to easily determine the presence of image defects. For the transferability of the blue solid block 301 and the black solid block 302, since it is more difficult to determine if the block size is small, the block size should be 10 square millimeters or larger, and more preferably 25 square millimeters or larger. Image defects caused by abnormal discharges occurring when the secondary transfer voltage increases in the halftone block 303 typically result in image defects such as white spots. Compared to the transferability of solid images, such image defects tend to be easier to identify even in small images. However, if the image is not too small, it is easier to see; therefore, in this embodiment, the width of the feed direction of the halftone block 303 is the same as the width of the feed direction of the solid blue block 301 and the solid black block 302. Additionally, the spacing between the block groups 301-303 in the feed direction should be set so that the secondary transfer voltage can be switched. In this embodiment, the blue solid block 301 and the black solid block 302 are 25.7mm × 25.7mm squares (one side is approximately parallel to the width direction). In this embodiment, the halftone blocks 303 at both ends of the width direction are each set to be 25.7mm wide in the feed direction, and extend to the end of the adjustment chart 300 in the width direction. In this embodiment, the interval between the block groups 301-303 in the feed direction is set to 9.5mm. The secondary transfer voltage is switched when the portion of the adjustment chart 300 corresponding to this interval passes through the secondary transfer section N2. The 11 block groups 301 to 303 in the feed direction of the adjustment chart 300 are arranged within a length of 387mm, such that when the size of the recording material P is A3, they fit a feed direction length of 415mm.

[0081] Preferably, no lumps are formed near the leading and trailing edges of the recording material P in the feed direction (e.g., within approximately 20-30 mm inward from the edge). This is because, within the edges of the recording material P in the feed direction, there may be image defects that do not appear at the edges in the width direction but only at the leading or trailing edges. In such cases, it may be difficult to determine whether the image defects are caused by variations in the secondary transfer voltage.

[0082] The processing conditions for each block in chart 300 are adjusted to be identical until each block is formed on the intermediate transfer belt 7. Then, for each block group 301-303 arranged in rows in the feed direction, the secondary transfer voltage when the block is transferred to the recording material P at the secondary transfer section N2 is different. Due to the difference in secondary transfer voltage, it is assumed that the concentration of each block group 301-303 output on the recording material P will be different.

[0083] Figure 9 (a) and Figure 9(b) is a graph schematically illustrating the changes in secondary transfer voltage and secondary transfer current when the output of the adjustment graph 300 in this embodiment is adjusted. Block groups 301-303, corresponding to the adjustment value "0" indicated by the identification information 304 of the adjustment graph 300, are used in... Figure 4 The initial value of the secondary transfer voltage, Vb + Vp (=Btr), determined in S106, is transferred to the recording material P. Then, blocks 301-303 (at the top end of the feed direction) corresponding to adjustment values ​​less than "0" are transferred to the recording material P with a secondary transfer voltage whose absolute value is less than the initial value. In contrast, blocks 301-303 (at the rear end of the feed direction) corresponding to adjustment values ​​greater than "0" are transferred to the recording material P with a secondary transfer voltage whose absolute value is greater than the initial value. In this embodiment, for each "1" difference in the adjustment value, the secondary transfer voltage changes by a predetermined voltage width (in this embodiment, the absolute value increases), and the secondary transfer voltage changes in a stepwise manner. This change ranges from tens of volts to hundreds of volts, and in this embodiment, it is 150 volts. For example, the secondary transfer voltage applied to blocks 301-303 with an adjustment value of "-5" is Vb + Vp + (-5 × 150V).

[0084] The user or other operator confirms the blocks of the output adjustment chart 300 by visual inspection or by measurement with a colorimeter (not shown). The user then selects an adjustment value for the secondary transfer voltage that enables the operator to output the desired image and inputs it to the controller 50 via a setting screen displayed on the operation section 31 or external device 200. This allows the secondary transfer voltage to be adjusted according to the type and conditions of the recording material P actually used by the operator, resulting in a result tailored to the operator's preferences. Figure 8 Part (b) is a schematic diagram of an example of a setting screen 400 for the operator to input adjustment mode settings. This setting screen 400 has a voltage setting section 401 for setting the adjustment values ​​of the secondary transfer voltage for the front and rear surfaces of the recording material P. This setting screen 400 also has an output surface selection section 402 for selecting whether to output the adjustment chart 300 on one or both sides of the recording material P. This setting screen 400 also has an output indication section 403 for indicating the output of the adjustment chart 300. This setting screen 400 also has a confirmation section (OK button) 404 for confirming the settings and a cancel button 405 for canceling the setting changes. When the adjustment value "0" is selected in the voltage setting section 401, the secondary transfer voltage is set to... Figure 4The initial value Vb+Vp (=Vtr) determined in S106 is set to this voltage, and the center voltage value of the secondary transfer voltage when adjusting the output of chart 300 is set to this voltage. Additionally, when an adjustment value other than "0" is selected, the secondary transfer voltage is adjusted by an adjustment amount ΔV of 150V for each level of the adjustment value, and the center voltage value of the secondary transfer voltage when adjusting the output of chart 300 is set to this voltage. After selecting an adjustment value, the adjustment chart 300 is output at the selected center voltage value by selecting the output indication section 403. After selecting an adjustment value, the setting of the secondary transfer voltage is terminated by selecting the termination section 404 and stored in RAM 52. If no optimal result is found in the adjustment chart, the center voltage value of the secondary transfer voltage when adjusting the output of chart 300 can be changed, and the output of chart 300 can be repeated.

[0085] In this embodiment, the operator visually inspects the blocks of the adjustment chart 300 or uses a colorimeter to adjust the secondary transfer voltage, but the invention is not limited to this. For example, the operator can set the output adjustment chart 300 in an image reading device (not shown) provided in the image forming apparatus 100, and have the image reading device read the density information (brightness information) of each block of the adjustment chart. Then, based on the detection result of the density information, the controller 50 can determine the adjustment amount corresponding to the block that meets a predetermined condition (e.g., the darkest density) and adjust the secondary transfer voltage. Alternatively, an embedded image sensor can be set to read the density information (brightness information) of each block of the adjustment chart 300 when the adjustment chart 300 is output from the image forming apparatus 100. In this case, as above, the controller 50 can adjust the secondary transfer voltage based on the detection result of the image sensor. The colorimeter mentioned above can be a colorimeter external to the image forming apparatus 100 or a colorimeter connected to the image forming apparatus 100. When using an external colorimeter, the operator can input the desired setting to the controller 50 based on the measurement result. When a colorimeter connected to the image forming apparatus is used, the measurement results are read into the controller 50, and the controller 50 reflects the measurement results in the adjustment value of the secondary transfer voltage so that the image density is appropriate.

[0086] In this embodiment, when not in adjustment mode, the limit control described in "3. Secondary Transfer Voltage Control" is executed. In addition to this limit control, from the viewpoint of overcurrent suppression, the secondary transfer voltage source (high-voltage source circuit) 20 may be provided with a current limit through the protection circuit or a high-voltage upper limit for the applied voltage. This current limit through the protection circuit is set to be wider than the current range used to ensure the image during normal image formation via the aforementioned limit control. For example, the secondary transfer voltage source 20 used in this embodiment has a 300μA to 400μA protection circuit to suppress overcurrent, and when a current exceeding this value flows in the secondary transfer section N2, the secondary transfer voltage source 20 is temporarily shut down to protect the circuit. The voltage that can be applied by the secondary transfer voltage source 20 is approximately 7kV to 10kV, and even if the secondary transfer voltage needs to be increased via the limit control described in "3. Secondary Transfer Voltage Control," the secondary transfer voltage does not increase beyond this value.

[0087] If the secondary transfer voltage source 20 has a current limit through the protection circuit and a high voltage limit on the applied voltage from the viewpoint of overcurrent suppression as described above, these should also be effective in the adjustment mode. In other words, in this embodiment, as described above, when outputting the adjustment chart, the limit control that limits the current range used to ensure the image during normal image formation is disconnected. However, even in this case, the current limit through the protection circuit and the high voltage limit on the applied voltage from the viewpoint of overcurrent suppression as described above should be effective.

[0088] 5. Effects

[0089] Unlike this embodiment, Figure 10 (a) and Figure 10 (b) schematically illustrates the changes in secondary transfer voltage and secondary transfer current when limit control is applied during the output of the adjustment chart. The adjustment chart itself is essentially the same as the adjustment chart in this embodiment. As mentioned above, when limit control is applied during the output of the adjustment chart, the secondary transfer voltage can only be changed within a specified range of secondary current. Furthermore, if the secondary transfer voltage that can achieve an image density that satisfies the operator's preference is located in a region where the secondary transfer current is outside the predetermined range, then if limit control is applied, the output of the block at the secondary transfer voltage in that region will be inappropriate. As a result, the block may not be able to be adjusted according to the operator's preference.

[0090] On the other hand, such as Figure 9 (a) and Figure 9 As shown in (b), this embodiment does not perform any limit control when outputting the adjustment chart. Therefore, the block can be output appropriately within the assumed range of the secondary transfer voltage. As a result, adjustments can be made according to operator preferences.

[0091] In this embodiment, the case where no limit control is performed during the entire period when the recording material P that outputs the adjustment chart passes through the secondary transfer section N2 is described. However, the invention is not limited to this, and limit control can be performed in areas where no block is formed relative to the feed direction of the recording material P. In the adjustment chart, blocks are not always formed without gaps from the top to the rear end of the feed direction of the recording material P, and there may be at least one blank area where no block is formed on the top side or the rear end side. In this case, limit control can be performed when the blank area passes through the secondary transfer section N2. When an adjustment chart for adjusting the secondary transfer voltage is output, for example, the setting of the secondary transfer voltage corresponding to the adjustment value "0" is set to a value adjusted by limit control at the blank area on the leading edge of the feed direction of the recording material P. As a result, the adjustment chart can be output with the secondary transfer voltage setting adjusted to make the secondary transfer current close to the optimal state, and more appropriate adjustments can be made. In addition, for example, when adjustment charts are formed continuously on multiple recording materials P, it is also effective to perform limit control in the blank area at the rear end of the previous recording material P to prepare for the subsequent recording material P. In other words, limit control is not performed when the area of ​​the block forming in relation to the feed direction of the recording material P for output adjustment charts passes through the secondary transfer section N2. The area forming the block extends from the top of the area where the block is transferred to the feed direction of the recording material P to the rear end of that area. When multiple blocks are transferred in the feed direction of the recording material P, this ranges from the top of the leading edge block to the rear edge of the trailing edge block in the feed direction of the recording material P. Limit control can then be performed when the blank areas of blocks not formed on the leading edge side of the recording material P and the blank areas of blocks not formed on the trailing edge side pass through the secondary transfer section N2. Alternatively, limit control can be performed only when at least one of the leading edge side or the trailing edge side passes through the secondary transfer section N2.

[0092] Therefore, in this embodiment, the image forming apparatus 100 is equipped with a controller 50, which controls a constant voltage such that the voltage applied to the transfer member 8 when the recording material P passes through the transfer section N2 is a predetermined voltage. This controller can perform limit control to control the voltage applied to the transfer member 8 based on the detection result of the current detection section 21, ensuring that the detection result of the current detection section 21 is within a predetermined range. The image forming apparatus 100 can execute a first mode (normal image forming mode) and a second mode (adjustment mode). In the first mode, a toner image is transferred to the recording material P. In the second mode, multiple test toner images are transferred to the recording material P by applying multiple different voltages to the transfer member 8. When executing the first mode, the controller 50 can perform limit control when the recording material P passes through the transfer section N2. On the other hand, when executing the second mode, the controller 50 does not perform limit control when the area with multiple test toner images transferred passes through the transfer section N2. In this embodiment, the test toner image is a toner image used to set the predetermined voltage (target voltage of the transfer voltage) when executing the first mode. Furthermore, when executing the second mode, the controller 50 can perform limit control when at least some areas outside the areas where multiple test toner images for the feeding direction of the recording material P are transferred pass through the transfer section N2. For example, this at least some area is a blank area where the toner image on the top side of the recording material P is not transferred relative to the feeding direction.

[0093] As explained above, when outputting a normal image, regardless of the type or state of the recording material P, this embodiment can appropriately output the image by suppressing the occurrence of insufficient or excessive secondary transfer current. Simultaneously, according to this embodiment, when outputting an adjustment chart, the adjustment chart can be appropriately output without limiting the operation settings, thereby enabling appropriate adjustments according to operator preferences. Therefore, according to this embodiment, in a configuration where limit control can be performed to adjust the secondary transfer voltage based on the secondary transfer current when the recording material P passes through the secondary transfer section, the secondary transfer voltage can be adjusted based on the secondary transfer current when the recording material P passes through the secondary transfer section.

[0094] [Example 2]

[0095] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus in this embodiment are the same as those of the image forming apparatus in Embodiment 1. Therefore, elements in the image forming apparatus of this embodiment that have the same or corresponding functions or configurations as those in the image forming apparatus of Embodiment 1 are indicated by the same reference numerals as those in Embodiment 1, and detailed descriptions are omitted.

[0096] In Example 1, limit control is not performed when the adjustment chart is output (or when the area where the adjustment chart block is formed passes through the secondary transfer section). On the other hand, by expanding the range of the secondary transfer current (increasing the difference between the upper and lower limits) instead of completely eliminating limit control, a similar effect to that of Example 1 can be expected.

[0097] For further explanation with reference to Embodiment 1, when the controller 50 is in Figure 4 In S107, when determining the image to be formed on the recording material P as an adjustment chart, the same procedure is performed when forming a normal image. Figure 4 The same process applies to S110 through S118. However, the range of secondary transfer current should be wider than that for forming a typical image. Figure 11 Figures (a) and (b) schematically illustrate the transitions in the secondary transfer voltage and secondary transfer current when outputting an adjustment chart in this embodiment. For example, the range of the secondary transfer current when outputting an adjustment chart can be set in a manner that typically disables limit control. However, the upper and lower limits of this secondary transfer current range are values ​​of a current range that can be detected by the current detection circuit 21. By changing at least one of the upper or lower limits of the secondary transfer current range (both in the example shown in the figures) to expand the secondary transfer current range, the range of the secondary transfer current when outputting an adjustment chart can be expanded more than when outputting a normal image.

[0098] Therefore, in this embodiment, when limit control is performed during the execution of the first mode (normal image forming mode), the controller 50 sets the predetermined range of the transfer current to a first predetermined range, and when limit control is performed during the execution of the second mode (adjustment mode), the controller 50 sets the predetermined range of the transfer current to a second predetermined range that is wider than the first predetermined range.

[0099] As described above, this embodiment has the same effect as Embodiment 1.

[0100] [other]

[0101] Although the invention has been described with reference to specific embodiments, the invention is not limited to the embodiments mentioned above.

[0102] Limit control can be performed by setting only one of the upper and lower limits of the current. For example, if a recording material with higher resistance than standard recording material is used and the transfer current is known to typically be below the lower limit, only the lower limit can be set. Conversely, if a recording material with lower resistance than standard recording material is used and the transfer current is known to typically exceed the upper limit, only the upper limit can be set. In other words, maintaining the transfer current within a predetermined range in limit control includes setting the current above the lower limit, below the upper limit, and above both the lower and upper limits.

[0103] Furthermore, in the embodiments mentioned above, the recording material is fed relative to the center of the transfer member in a direction that is substantially perpendicular to the feeding direction, but this is not limited to the above, and for example, the present invention can be equally applied to configurations that transfer recording material based on one end side.

[0104] Furthermore, the present invention can be equally applied to monochrome image forming apparatuses having only one image forming section. In this case, the present invention applies to the transfer section from a toner image to an image carrier member, such as a photosensitive drum, to a recording material.

[0105] [Industrial Applicability]

[0106] According to the present invention, an image forming apparatus will be provided that can appropriately perform adjustments by forming an adjustment mode on a recording material to form a test image.

[0107] This invention is not limited to the embodiments described above, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the appended claims are included to publicly disclose the scope of the invention.

[0108] This application claims priority to Japanese Patent Application No. 2019-122574, filed on June 29, 2019, and Japanese Patent Application No. 2019-206569, filed on November 14, 2019, the entire contents of which are hereby incorporated.

Claims

1. An image forming apparatus, comprising: The image carrier component is configured to carry the toner image; An intermediate transfer belt is used to transfer the toner image from the image carrier to the intermediate transfer belt. A transfer member, to which voltage is applied, the transfer member being configured to transfer a toner image from the intermediate transfer belt to the recording material at a transfer portion; A voltage source is configured to apply voltage to the transfer member; The current detection section is configured to detect the current flowing through the transfer member; as well as The controller is configured to perform constant voltage control such that the voltage applied to the transfer member is a predetermined target voltage. The controller is capable of performing: (i) A first control, wherein, when the recording material with the toner image transferred passes through the transfer section, if the detection result detected by the current detection section is within a predetermined range, the controller performs the constant voltage control such that the voltage applied to the transfer member is the predetermined target voltage; and if the detection result exceeds the upper limit of the predetermined range, the controller changes the predetermined target voltage such that the detection result does not exceed the predetermined range and performs the constant voltage control based on the changed target voltage, and (ii) A second control, wherein when the recording material with the toner image transferred passes through the transfer section, even if the detection result exceeds the upper limit, the controller does not change the predetermined target voltage and performs the constant voltage control such that the voltage applied to the transfer member is the predetermined target voltage.

2. The image forming apparatus according to claim 1, wherein, If the detection result exceeds the upper limit when the first control is executed, the controller gradually reduces the voltage applied to the transfer member.

3. The image forming apparatus according to claim 1, wherein, The controller includes a protection circuit configured to temporarily interrupt the voltage source separately from the first control, such that the current flowing through the transfer member does not become equal to or higher than a predetermined current.

4. The image forming apparatus according to claim 3, wherein, The predetermined current is higher than the upper limit.

5. The image forming apparatus according to claim 3, wherein, The protection circuit is confirmed to be effective when the second control is executed.

6. An image forming apparatus, comprising: The image carrier component is configured to carry the toner image; An intermediate transfer belt is used to transfer the toner image from the image carrier to the intermediate transfer belt. A transfer member, to which voltage is applied, the transfer member being configured to transfer a toner image from the intermediate transfer belt to the recording material at a transfer portion; A voltage source is configured to apply voltage to the transfer member; The current detection section is configured to detect the current flowing through the transfer member; as well as The controller is configured to perform constant voltage control such that the voltage applied to the transfer member is a predetermined target voltage. The controller is capable of performing: (i) A first control, wherein, when the recording material with the toner image transferred passes through the transfer section, if the detection result detected by the current detection section is within a predetermined range, the controller performs the constant voltage control such that the voltage applied to the transfer member is the predetermined target voltage; and if the detection result is lower than the lower limit of the predetermined range, the controller changes the predetermined target voltage such that the detection result is not lower than the predetermined range and performs the constant voltage control based on the changed target voltage, and (ii) Second control, in which, when the recording material with the toner image transferred passes through the transfer section, even if the detection result is below the lower limit, the controller does not change the predetermined target voltage and performs the constant voltage control such that the voltage applied to the transfer member is the predetermined target voltage.

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