Image forming apparatus

Abstract

To set an appropriate transfer voltage even in an environment in which prevention of patch void and prevention of strong void are difficult, such as a high temperature and high humidity environment.SOLUTION: An image forming apparatus 100 has an image carrier 10, a transfer member 20, an application unit 21, and a control unit 210. In performing constant voltage control on a transfer voltage so that a voltage that the application unit 21 applies to the transfer member 20 becomes substantially constant, the control unit 210 perform control to define the transfer voltage as a first voltage when the amount of toner used for a toner image is a first amount of toner, and defines the transfer voltage as a second voltage that has an absolute value smaller than the absolute value of the first voltage when the amount of toner is a second amount of toner larger than the first amount of toner.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to image forming apparatus such as printers, copiers, and facsimile machines that use electrophotographic or electrostatic recording methods. [Background technology]

[0002] In image forming apparatuses using electrophotography or the like, the toner image formed on the image carrier is transferred onto a recording material such as paper that passes through a transfer section formed between the image carrier and the transfer member. In image forming apparatuses using an intermediate transfer method, the toner image formed on a photoreceptor or the like, which serves as the first image carrier, is first transferred onto an intermediate transfer body, which serves as the second image carrier, and then secondarily transferred onto a recording material that passes through a secondary transfer section formed between the intermediate transfer body and the secondary transfer member.

[0003] The transfer of the toner image from the image carrier to the recording material is performed by applying a transfer voltage to the transfer member. Setting an appropriate transfer voltage is crucial for obtaining high-quality results (printed materials).

[0004] Patent Document 1 discloses a configuration that changes the transfer current according to the print density and number of pixels in order to obtain a uniform final image regardless of the image pattern and print density. In this configuration, the transfer current is increased as the print density and number of pixels increase, that is, as the amount of toner transferred to the recording material increases, in an attempt to suppress transfer defects in high-print images. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-191088 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, if the control that increases the transfer current as the amount of toner transferred to the recording material increases, as in the configuration of Patent Document 1, is implemented, for example, in a high-temperature, high-humidity environment, the following two types of image defects may occur.

[0007] (1) When transferring low-print images including isolated patch patterns, etc. Generally, in high-temperature and high-humidity environments, the electrical resistance of transfer components such as transfer rollers and recording materials decreases. As a result, the transfer current tends to selectively flow to areas where there is no toner (hereinafter also referred to as "white areas" or "white background areas"), rather than to areas where there is toner (hereinafter also referred to as "toner areas" or "patch areas"), which have low electrical resistance. Therefore, in order to transfer isolated patch patterns well, a large amount of transfer current is required. Here, an "isolated patch pattern" refers to an image pattern in which clusters of highly printed toner images are scattered within the width of the recording material (length in the width direction approximately perpendicular to the transport direction). However, in the configuration of Patent Document 1, the amount of toner is judged to be small in images containing isolated patch patterns, which leads to a reduction in the absolute value of the transfer voltage. As a result, it is not possible to supply sufficient transfer current to the toner areas, which may cause image defects (hereinafter also referred to as "patch defects") in which toner is not transferred to the recording material.

[0008] (2) When transferring high-resolution images including full-surface solid images In this case, the transfer current does not selectively flow to the white areas, so sufficient transfer current is supplied to the toner area. If the transfer voltage is set so that the above-mentioned patch blemishes do not occur, that is, so that sufficient transfer current is supplied to isolated patch patterns, then a transfer current greater than the minimum current required for toner transfer is supplied to the full-surface solid image. Here, "full-surface solid image (full-surface solid pattern)" means an image pattern in which a toner image of the highest density level exists throughout the entire image-forming area in the width direction of the recording material. However, in the configuration of Patent Document 1, the absolute value of the transfer voltage becomes even larger than the transfer voltage required to transfer a "full-surface solid image (full-surface solid pattern)". As a result, excessive transfer current is supplied to the toner area, which may cause image defects (hereinafter also called "strong bleeds") in which toner is not transferred to the recording material due to the reversal of charge polarity by discharge, etc.

[0009] Therefore, the objective of the present invention is to set an appropriate transfer voltage even in environments where it is difficult to suppress both patchiness and strong break-off, such as high temperature and high humidity environments. [Means for solving the problem]

[0010] The above objective is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier that carries a toner image, a transfer member that forms a transfer section for transferring the toner image from the image carrier to a recording material, an application section that applies a transfer voltage to the transfer member, and a control unit that controls the application section, wherein the control unit controls the transfer voltage to be a constant voltage so that the voltage applied to the transfer member by the application section is substantially constant, setting the transfer voltage to a first voltage when the amount of toner used for the toner image is a first amount of toner, and setting the transfer voltage to a second voltage whose absolute value is smaller than the absolute value of the first voltage when the amount of toner is a second amount of toner greater than the first amount of toner. Furthermore, when the amount of toner is a third amount greater than the second amount of toner, the transfer voltage is set to a third voltage whose absolute value is smaller than the absolute value of the first voltage and whose absolute value is larger than the absolute value of the second voltage. This image forming apparatus is characterized by its ability to perform control in such a manner. [Effects of the Invention]

[0011] According to the present invention, an appropriate transfer voltage can be set even in an environment where it is difficult to achieve both suppression of patching boss and suppression of strong removal, such as in a high-temperature and high-humidity environment.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic cross-sectional view of an image forming apparatus. [Figure 2] It is a block diagram showing the control mode of the image forming apparatus. [Figure 3] It is a functional block diagram related to the calculation of the toner amount. [Figure 4] It is a graph diagram for explaining the method of determining the secondary transfer voltage in Example 1. [Figure 5] It is a flowchart diagram showing the control procedure of the secondary transfer voltage. [Figure 6] It is a schematic diagram for explaining the effect of the example. [Figure 7] It is a timing chart diagram showing the control timing of the secondary transfer voltage. [Figure 8] It is a schematic cross-sectional view of another example of the image forming apparatus. [Figure 9] It is a graph diagram for explaining the method of determining the secondary transfer voltage in Example 2. [Figure 10] It is a graph diagram for explaining the method of determining the secondary transfer voltage in other configurations of Example 2. [Figure 11] It is a graph diagram for explaining the method of determining the secondary transfer voltage in Example 3. [Figure 12] It is a schematic diagram of the configuration around the primary transfer portion of the image forming apparatus in Example 4. [Figure 13] It is a schematic diagram showing the cross-sectional configuration of the intermediate transfer belt in Example 4. [Figure 14] It is an equivalent circuit diagram related to the secondary transfer portion in Example 4.

Modes for Carrying Out the Invention

[0013] The image forming apparatus according to the present invention will be described in more detail below with reference to the drawings.

[0014] [Example 1] <Overall configuration and operation of the image forming apparatus> Figure 1 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is an electrophotographic full-color laser printer employing an in-line method and an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a recording material P (e.g., recording paper, plastic sheet, etc.) according to image information. Image information is input to the image forming apparatus 100 from an image reading device (not shown) provided in or connected to the image forming apparatus 100, or from a host device 199 such as a personal computer (Figures 2 and 3) that is communicatively connected to the image forming apparatus 100.

[0015] The image forming apparatus 100 has a plurality of image forming stations, the first, second, third, and fourth image forming stations Sa, Sb, Sc, and Sd, each for forming images of yellow (Y), magenta (M), cyan (C), and black (K). In this embodiment, the first, second, third, and fourth image forming stations Sa, Sb, Sc, and Sd are arranged in a line in a direction intersecting the vertical direction. In this embodiment, the configuration and operation of the first, second, third, and fourth image forming stations Sa, Sb, Sc, and Sd are substantially the same except for the different colors of the images they form. Elements having the same or corresponding functions or configurations in each image forming station Sa, Sb, Sc, and Sd may be described collectively by omitting the suffixes a, b, c, and d of the symbols indicating that they are elements for one of the colors. The image forming unit S is composed of the following components: a photosensitive drum 1 (1a, 1b, 1c, 1d), charging rollers 2 (2a, 2b, 2c, 2d), exposure device 3 (3a, 3b, 3c, 3d), developing device 4 (4a, 4b, 4c, 4d), primary transfer rollers 14 (14a, 14b, 14c, 14d), drum cleaning device 5 (5a, 5b, 5c, 5d), and the like.

[0016] The photosensitive drum 1, which is a rotatable drum-shaped (cylindrical) photoreceptor (electrophotographic photoreceptor) serving as the first image carrier, is driven to rotate at a predetermined peripheral speed (process speed) in the direction of arrow R1 (counterclockwise direction) in Figure 1 by a drive motor serving as the driving means (driving source). The surface of the rotating photosensitive drum 1 is uniformly charged to a predetermined potential with a predetermined polarity (negative polarity in this embodiment) by a charging roller 2, which is a roller-type charging member serving as the charging means. The charged surface of the photosensitive drum 1 is scanned and exposed according to image information by an exposure device (laser scanner unit) 3 serving as the exposure means, and an electrostatic latent image (electrostatic image) according to the image information is formed on the photosensitive drum 1. The exposure device 3 irradiates the photosensitive drum 1 with laser light L based on the output calculated by a CPU 221 (Figure 3), which will be described later, from image information input from, for example, a host device 199 (Figures 2 and 3). The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) by a developing device 4, which is a developing means, when toner is supplied as a developer, and a toner image (toner image, developer image) is formed on the photosensitive drum 1. In this embodiment, toner charged with the same polarity as the charge polarity of the photosensitive drum 1 (negative polarity in this embodiment) adheres to the exposed area (image area) on the photosensitive drum 1, where the absolute value of the potential has decreased after uniform charging treatment and exposure (reverse development). In this embodiment, the normal charge polarity of the toner, which is the charge polarity of the toner during development, is negative polarity.

[0017] An intermediate transfer belt 10, which is an intermediate transfer body composed of an endless belt as a second image carrier, is positioned opposite the four photosensitive drums 1a to 1d. The intermediate transfer belt 10 is stretched over a plurality of support members (tension rollers), namely drive rollers 11, tension rollers 12, and secondary transfer opposing rollers 13, and is taut with a predetermined tension. The intermediate transfer belt 10 contacts the four photosensitive drums 1a to 1d at the transfer surface M formed between the secondary transfer opposing rollers 13 and the drive rollers 11. The drive rollers 11 are rotated by a drive motor, which is a driving means (driving source), in the direction of arrow R2 in Figure 1 (clockwise). As a result, the intermediate transfer belt 10 rotates (circular movement, reciprocal movement) in the direction of arrow R3 in Figure 1 (clockwise) at a peripheral speed (process speed) corresponding to the peripheral speed of the photosensitive drum 1. On the inner circumferential surface of the intermediate transfer belt 10, primary transfer rollers 14a, 14b, 14c, and 14d, which are roller-type primary transfer members serving as primary transfer means, are arranged corresponding to each photosensitive drum 1a, 1b, 1c, and 1d. The primary transfer rollers 14 press the intermediate transfer belt 10 toward the photosensitive drum 1, forming a primary transfer section (primary transfer nip section) N1, which is the contact area between the photosensitive drum 1 and the intermediate transfer belt 10. The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the rotating intermediate transfer belt 10 in the primary transfer section N1 by the action of the primary transfer rollers 14. During primary transfer, a primary transfer voltage (primary transfer bias) with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner is applied to the primary transfer rollers 14 by a primary transfer power supply (high voltage power supply) 15, which serves as a primary transfer voltage application means (primary transfer voltage application section). In this embodiment, as an example, a primary transfer voltage of +100V is applied to the primary transfer rollers 14. For example, when forming a full-color image, the toner images of yellow, magenta, cyan, and black, formed on each of the photosensitive drums 1a, 1b, 1c, and 1d, are sequentially transferred onto the intermediate transfer belt 10 in a primary transfer process.

[0018] On the outer circumferential surface of the intermediate transfer belt 10, a secondary transfer roller (secondary transfer outer roller) 20, which is a roller-type secondary transfer member serving as a secondary transfer means, is positioned opposite the secondary transfer opposing roller (secondary transfer inner roller) 13. The secondary transfer roller 20 is pressed toward the secondary transfer opposing roller 13 and contacts the secondary transfer opposing roller 13 via the intermediate transfer belt 10, forming a secondary transfer section (secondary transfer nip section) N2, which is the contact area between the intermediate transfer belt 10 and the secondary transfer roller 13. The toner image formed on the intermediate transfer belt 10 is transferred (secondary transfer) in the secondary transfer section N2 to the recording material P, which is being transported sandwiched between the intermediate transfer belt 10 and the secondary transfer roller 20, by the action of the secondary transfer roller 20. During secondary transfer, a secondary transfer voltage (secondary transfer bias) with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner is applied to the secondary transfer roller 20 by a secondary transfer power supply (high voltage power supply) 21, which serves as a secondary transfer voltage application means (secondary transfer voltage application section). In this embodiment, the secondary transfer opposing roller 13 is connected to ground potential. For example, when forming a full-color image, the four toner images on the intermediate transfer belt 10 are transferred collectively onto the recording material P in the secondary transfer section N2. The recording material P is housed in a cassette 51, which serves as a recording material storage section. The recording material P is separated one sheet at a time from the cassette 51 by a feeding roller 50, which serves as a feeding means, and transported to the register roller 60. The register roller 60 then transports the recording material P to the secondary transfer section N2 in a manner that matches the timing with the toner image on the intermediate transfer belt 10. The transport timing of the recording material P by the register roller 60 is controlled based on the detection result of a resist sensor 61 that detects the leading edge of the recording material P in the transport direction.

[0019] In this embodiment, it is also possible to apply a voltage with the same polarity as the normal charging polarity of the toner to the inner roller corresponding to the secondary transfer opposing roller 13, and connect the outer roller corresponding to the secondary transfer roller 20 to ground potential.

[0020] The recording material P onto which the toner image has been transferred is transported to a fixing device 30, which serves as a fixing means. The fixing device 30 includes a fixing roller 31 equipped with a heat source and a pressure roller 32 that presses against the fixing roller 31. At the fixing nip section, which is the contact area between the fixing roller 31 and the pressure roller 32, the fixing device 30 applies heat and pressure to the recording material P carrying the unfixed toner image, thereby fixing (melting and solidifying) the toner image onto the recording material P. For example, when forming a full-color image, the four-color toner images on the recording material P are heated and pressurized at the fixing nip section, causing them to melt and mix, and then fixed onto the recording material P. The recording material P with the fixed toner image is discharged (output) from the main body of the image forming apparatus 100.

[0021] The image forming apparatus 100 in this embodiment is capable of performing double-sided printing (automatic double-sided printing) by transporting the recording material P, on which a toner image has been transferred and fixed to the first surface, to a secondary transfer unit N2, transferring and fixing a toner image to the second surface of the recording material P, and then discharging it outside the main body of the apparatus. The image forming apparatus 100 has a double-sided transport mechanism (not shown) for transporting the recording material P, on which a toner image has been fixed to the first surface, back to the secondary transfer unit N2 in order to perform double-sided printing. In the case of single-sided printing, the recording material P on which a toner image has been fixed to the first surface is directly discharged outside the main body of the apparatus.

[0022] On the other hand, any toner or other deposits remaining on the photosensitive drum 1 after the primary transfer (primary transfer residue toner) are removed and recovered from the photosensitive drum 1 by the drum cleaning device 5, which serves as a photoreceptor cleaning means. In addition, any toner or other deposits remaining on the intermediate transfer belt 10 after the secondary transfer (secondary transfer residue toner) are removed and recovered from the intermediate transfer belt 10 by the belt cleaning device 16, which serves as an intermediate transfer body cleaning means.

[0023] Furthermore, the image forming apparatus 100 can also form monochrome or multicolor images using only one image forming unit S or some (but not all) of the image forming units S.

[0024] Furthermore, in each image forming unit S, the photosensitive drum 1, the charging roller 2 which acts on the photosensitive drum 1 as a process means, the developing device 4, and the drum cleaning device 5 together constitute a process cartridge 6 that can be attached to and detached from the main body of the image forming apparatus 100. The process cartridge 6 can be attached to and detached from the main body of the apparatus via mounting means such as mounting guides and positioning members provided on the main body of the apparatus.

[0025] Furthermore, the image forming apparatus 100 of this embodiment can form and output images on A5 size paper, A4 size paper, LTR size paper, etc., at a process speed of 148 mm / sec.

[0026] In this embodiment, the primary transfer roller 14 is a cylindrical metal roller with an outer diameter of 6 mm, and nickel-plated stainless steel is used as the material. The primary transfer roller 14 is positioned 8 mm downstream of the center of the photosensitive drum 1 in the direction of movement of the intermediate transfer belt 10, so that the intermediate transfer belt 10 wraps around the photosensitive drum 1. The primary transfer roller 14 is positioned 1 mm higher than the horizontal plane formed by the photosensitive drum 1 and the intermediate transfer belt 10, so as to ensure the amount of wrapping of the intermediate transfer belt 10 around the photosensitive drum 1. The primary transfer roller 14 presses the intermediate transfer belt 10 toward the photosensitive drum 1 with a force of approximately 200 gf. The primary transfer roller 14 also rotates in conjunction with the rotation of the intermediate transfer belt 10.

[0027] In this embodiment, the secondary transfer roller 20 contacts the intermediate transfer belt 10 with a pressure of 50 N, forming the secondary transfer section N2. The secondary transfer roller 20 rotates in conjunction with the rotation of the intermediate transfer belt 10. The recording material P, such as paper, is held and conveyed between the intermediate transfer belt 10 and the secondary transfer roller 20 in the secondary transfer section N2. The secondary transfer roller 20 has a nickel-plated steel rod with an outer diameter of 8 mm as a core, surrounded by an elastic layer with a volume resistivity of 10 8This is a roller with an outer diameter of 18 mm, covered with a 5 mm thick foamed sponge body mainly composed of NBR and epichlorohydrin rubber adjusted to Ω·cm. In this embodiment, the secondary transfer power supply 21 is capable of outputting in the range of 100V to 5000V. In this specification, numerical ranges indicated using "~" mean the range including the numbers before and after "~".

[0028] In this embodiment, the fixing roller 31, which serves as the fixing member, is a roller with an outer diameter of 18 mm, in which an elastic layer of insulating silicone rubber is formed around a metal tube, and the outer circumference of the elastic layer is further coated with an insulating PFA tube. This fixing roller 31 incorporates a halogen heater (not shown) as a heating means. The halogen heater is not in contact with the fixing roller 31 and generates heat when voltage is supplied by a power source (not shown). In this embodiment, the pressure roller 32, which serves as the pressurizing member, is a roller with an outer diameter of 18 mm, in which an elastic layer of conductive silicone rubber is formed around a metal core, and the outer circumference of the elastic layer is further coated with a conductive PFA tube. The fixing roller 31 and the pressure roller 32 are pressed together with a pressure of 10 kgf to form a fixing nip. The pressure roller 32 is rotationally driven by a drive motor, which serves as the driving means (driving source). The fixing roller 31 rotates in conjunction with the rotation of the pressure roller 32. The recording material P is held between a heating roller 31 and a pressure roller 32 at the fixing nip section and transported. The pressure roller 32 is connected to ground (earth potential) via a 1000 MΩ resistive element (not shown) from its core. By discharging the charge on the fixing roller 31 and the pressure roller 32 to ground via the pressure roller 32 and the resistive element, it is possible to suppress the charging of the surfaces of the fixing roller 31 and the pressure roller 32.

[0029] Figure 2 is a block diagram illustrating the configuration of the engine control unit 210, which controls the entire image forming apparatus 100 in this embodiment. The engine control unit 210 incorporates a CPU circuit unit 150, a ROM 151, and a RAM 152. The CPU circuit unit 150 comprehensively controls the primary transfer control unit 201, secondary transfer control unit 202, development control unit 203, exposure control unit 204, charging control unit 205, etc., according to the control program stored in the ROM 151. Control tables related to the control of the secondary transfer voltage (environment table, recording material width / recording material thickness correspondence table, etc.), which will be described later, are stored in the ROM 151 and are called by the CPU 221 (Figure 3) implemented in the CPU circuit unit 150 and reflected in the control. The RAM 152 temporarily holds control data and is also used as a work area for calculation processing associated with the control.

[0030] The primary transfer control unit 201 and the secondary transfer control unit 202 control the primary transfer power supply 15 and the secondary transfer power supply 21, respectively. Based on the current value detected by their respective current detection units (current detection circuits), the primary transfer control unit 201 and the secondary transfer control unit 202 control the voltage output from the primary transfer power supply 15 and the secondary transfer power supply 21, respectively. The control of the secondary transfer voltage will be explained in detail later.

[0031] The engine control unit 210 is connected to an environmental sensor 300, which serves as an environmental detection means (environmental detection unit) for detecting at least one of the temperature or humidity inside or outside the image forming apparatus 100. In this embodiment, the environmental sensor 300 incorporates a temperature sensor 301 as a temperature detection means (temperature detection unit) and a humidity sensor 302 as a humidity detection means (humidity detection unit), and detects the temperature and humidity around the image forming apparatus 100. The environmental sensor 300 inputs a signal (temperature information) indicating the temperature detection result from the temperature sensor 301 and a signal (humidity information) indicating the humidity (relative humidity) detection result from the humidity sensor 302 to the engine control unit 210.

[0032] Furthermore, a controller 200 is connected to the engine control unit 210. The controller 200 receives print information (image information, various setting information) and print commands (instructions to start a print job) from the host device 199, which is an external device. The engine control unit 210 then controls each control unit (primary transfer control unit 201, secondary transfer control unit 202, development control unit 203, exposure control unit 204, charging control unit 205, etc.) to execute the print job. In this embodiment, the engine control unit 210 obtains environmental information from the detection results of the environmental sensor 300 and information on the recording material P from the print information from the host device 199 in order to control the secondary transfer voltage, which will be described later. The print information is input from the host device 199 to the controller 200 via a printer driver installed on the host device 199.

[0033] Here, the image forming apparatus 100 executes a print job (printing job, image output operation), which is a series of operations that start with a single start instruction and form and output an image on one or more recording materials P. A print job generally has an image forming process, a pre-rotation process, a paper-to-paper process when forming an image on multiple recording materials P, and a post-rotation process. The image forming process is the period during which the electrostatic latent image, toner image, primary transfer, and secondary transfer of the toner image are performed for the image to be actually formed and output on the recording material P, and this period is referred to as the image forming time (image forming period). More specifically, the timing of the image forming time differs depending on the position where each of these processes—formation of the electrostatic latent image, formation of the toner image, primary transfer, and secondary transfer of the toner image—is performed. The pre-rotation process is the period during which preparatory operations are performed before the image forming process, from when a start instruction is input until the image is actually formed. The paper-to-paper process (inter-recording material process) is the period corresponding to the space between recording materials P when image forming is performed continuously on multiple recording materials P (continuous image forming). The post-rotation process is the period during which tidying operations (preparation operations) are performed after the image forming process. The non-image forming period (non-image forming period) is the period other than the image forming process, and includes the pre-rotation process, inter-paper process, post-rotation process, and pre-multi-rotation process, which is the preparation operation when the image forming apparatus 100 is powered on or when it returns from sleep mode.

[0034] <Overview of Secondary Transfer Voltage Control> Next, an overview of the control of the secondary transfer voltage in this embodiment will be described.

[0035] As shown in Figure 1, the secondary transfer power supply 21 is connected to the secondary transfer roller 20, and the secondary transfer voltage output from the secondary transfer power supply 21 is supplied to the secondary transfer roller 20. When the secondary transfer voltage is applied from the secondary transfer power supply 21 to the secondary transfer roller 20, an electric field is formed between the secondary transfer roller 20 and the secondary transfer counter roller 13 installed opposite it. As a result, inductive polarization is generated between the intermediate transfer belt 10 and the recording material P, and an electrostatic attraction force is generated between them.

[0036] As shown in Figure 2, the secondary transfer control unit 202 has a current detection unit (ammeter) 241 as a current detection means that detects the current flowing through the secondary transfer unit N2 (secondary transfer roller 20) when the secondary transfer power supply 21 applies voltage to the secondary transfer roller 20. The secondary transfer control unit 202 can control the voltage value output by the secondary transfer power supply 21 so that the current flowing through the secondary transfer unit N2 is approximately constant at (approaching) a target current value. During image formation (secondary transfer), the current flowing through the secondary transfer unit N2 is detected by the current detection unit 241 at a predetermined period (current detection period). The secondary transfer control unit 202 then determines the voltage value of the secondary transfer voltage to be applied to the secondary transfer roller 20 in the next current detection period. The secondary transfer control unit 202 determines the voltage value of the secondary transfer voltage in the next current detection period by feeding back the difference between a preset target current value and the detected current value detected by the current detection unit 241, which is the actual output value, to the secondary transfer power supply 21. In other words, the voltage value of the secondary transfer voltage applied to the secondary transfer roller 20 in the next current detection cycle is adjusted so that the detected current value approaches the target current value. As a result, the secondary transfer voltage applied from the secondary transfer power supply 21 to the secondary transfer roller 20 is controlled so that the current flowing through the secondary transfer section N2 is approximately constant. Here, this control, in which the secondary transfer voltage is applied from the secondary transfer power supply 21 to the secondary transfer roller 20 so that the current value detected by the current detection section 241 is approximately constant at a predetermined current value, is called "constant current control".

[0037] On the other hand, as shown in Figure 2, the secondary transfer control unit 202 has a voltage detection unit 242 as a voltage detection means for detecting the voltage value that the secondary transfer power supply 21 applies to the secondary transfer roller 20. The secondary transfer control unit 202 can control the voltage value output by the secondary transfer power supply 21 so that it becomes approximately constant at (approaches) the target voltage value. The voltage detection unit 242 may detect (recognize) the voltage value from the output voltage value instructed to the secondary transfer power supply 21. In high temperature and high humidity environments, the electrical resistance of the recording material P, secondary transfer roller 20, intermediate transfer belt 10, etc. decreases due to moisture absorption. If "constant current control" of the secondary transfer voltage is performed in such a state, the absolute value of the secondary transfer voltage required to output the target current value becomes small, which may result in a transfer failure because the electric field necessary to transfer toner to the recording material P is not formed. Therefore, a lower limit is set for the secondary transfer voltage, and if the secondary transfer voltage falls below this lower limit when constant current control is performed in a high-temperature, high-humidity environment, the secondary transfer voltage is controlled so that the voltage value becomes approximately constant at a target voltage value corresponding to that lower limit. This ensures that the minimum voltage required to transfer toner to the recording material P is secured, and secondary transfer can be performed. Here, this control, which applies an approximately constant secondary transfer voltage at a predetermined voltage value from the secondary transfer power supply 21 to the secondary transfer roller 20 (control that makes the applied voltage approximately constant regardless of the current value), is called "constant voltage control".

[0038] In this embodiment, the CPU 221 (Figure 3) of the engine control unit 210 calculates the absolute moisture content of the environment in which the image forming apparatus 100 is installed based on the detection results of the temperature sensor 301 and humidity sensor 302 of the environmental sensor 300. Then, according to the calculated absolute moisture content, the CPU 221 decides whether to control the secondary transfer voltage by the secondary transfer control unit 202 using "constant current control" or "constant voltage control," and commands the secondary transfer control unit 202. In this embodiment, the absolute moisture content is 21.7 g / m². 3 In the above cases, "constant voltage control" of the secondary transfer voltage is implemented, and the absolute moisture content is 21.7 g / m². 3If the value is less than the specified value, "constant current control" of the secondary transfer voltage is implemented.

[0039] <Details of the control of the secondary transfer voltage in this embodiment> One of the features of this embodiment is that, in constant voltage control of the secondary transfer voltage, the amount of toner to be transferred to the recording material P is calculated based on image information, and a correction is applied to a preset reference secondary transfer voltage value based on the calculation result. In particular, one of the features of this embodiment is that the absolute value of the secondary transfer voltage is decreased as the amount of toner increases (and the absolute value of the secondary transfer voltage is increased as the amount of toner decreases).

[0040] (Regarding the calculation of toner quantity) Referring to Figure 3, the method for calculating the amount of toner transferred to the recording material P in this embodiment will be explained. Figure 3 is a functional block diagram relating to the calculation of the amount of toner transferred to the recording material P in the image forming apparatus 100 of this embodiment. Here, the toner amount information related to the amount of toner transferred to the recording material P used in controlling the secondary transfer voltage of this embodiment, that is, the method for calculating the amount of toner X per page and its physical meaning will be explained.

[0041] The controller unit 200 is capable of communicating with the host device 199 and the engine control unit 210. When the controller unit 200 receives print information input from the host device 199, it expands the print information and converts it into image data for forming an image. Based on this image data, the controller unit 200 generates four video signals for exposure, allowing the exposure apparatus 3 to expose the photosensitive drum 1 in the four image forming units S. Once the generation of the video signals is complete, the controller unit 200 inputs a print job start instruction to the video interface unit 220 of the engine control unit 210. Subsequently, when the CPU 221 of the engine control unit 210 receives the print job start instruction from the video interface unit 220, it activates various actuators and begins preparations for image formation. When the CPU 221 is ready for image formation, it notifies the controller 200 via the video interface unit 220 that the image formation preparations are complete. When the controller 200 receives the signal indicating that the image formation preparations are complete, it transmits a video signal to the video interface unit 220.

[0042] The video interface unit 220 transmits the received video signal to the image processing GA 222 of the engine control unit 210. The image processing GA 222 receives the video signal from the video interface unit 220, converts it into a laser drive signal, and transmits the laser drive signal to the laser drive unit 230 of the exposure apparatus 3. The laser drive unit 230 controls the current supplied to the laser diode 231, which serves as the light source of the exposure apparatus 3, according to the laser drive signal, thereby controlling the emission of light from the laser diode 231. The image data count unit 223 of the engine control unit 210 samples the laser drive signal and counts the number of times the signal becomes High (light emitted) (hereinafter referred to as "H"). The image data count unit 223 does not count when the signal is Low (light off) (hereinafter referred to as "L") when sampling the laser drive signal. In this embodiment, the video interface unit 220, the image processing GA, and the image data count unit 223 are implemented by ASICs mounted on the CPU circuit unit 150 of the engine control unit 210.

[0043] The CPU 221 counts the number of times the laser drive signal for each of the four colors Y, M, C, and K is "H" as determined by the image data counting unit 223, and counts the pixel count values ​​ny, nm, nc, and nk for each color for one page. Subsequently, the CPU 221 calculates the total pixel count value n (=ny+nm+nc+nk), which is the sum of the pixel count values ​​for each color. If N is the total number of samples per color per page, the amount of toner X[%] in one page is calculated by the following formula (1). In this embodiment, the calculation of the amount of toner X in one page is performed by the toner amount calculation unit 224, which is implemented by the CPU 211 mounted in the CPU circuit unit 150 of the engine control unit 210. Toner amount per page X[%] = {(pixel count value n) / (total number of samples per color N)} × 100 ...(1)

[0044] The sampling of each color, with a total sampling count of N, is performed at different timings because the laser is driven at different timings for each color. In this embodiment, the sampling period was set to a short period (100 MHz) so that all pixels on one page could be counted. Therefore, the total sampling counts Ny, Nm, Nc, and Nk for the four colors Y, M, C, and K were Ny=Nm=Nc=Nk=N. In this embodiment, the maximum value of the pixel count values ​​ny, nm, nc, and nk for each color is the total sampling count N per color, so X can take values ​​from 0 to 400[%] (a value from 0 to 100[%] per color). In other words, in this embodiment, the toner amount information regarding the amount of toner transferred to the recording material P is the toner amount X[%], which is the ratio of the amount of toner transferred to the recording material P to the total amount of toner for each color that can be transferred to the recording material P.

[0045] As described above, the amount of toner X per page refers to the total amount of toner transferred to one recording material P (more precisely, its image-forming area) (more precisely, its predicted value). An amount of toner X per page of less than 100% roughly indicates how much of the recording material P is covered with toner. In this case, a smaller value for the amount of toner X per page means that there is more white space. In particular, an amount of toner X per page of less than 10% roughly indicates a state where there are several texts or isolated patch patterns (described later) within a white area that covers almost the entire surface of the recording material P. An amount of toner X per page of 100% or more indicates a state where almost the entire surface of the recording material P is covered with toner, and also roughly indicates how much toner is distributed in the height direction for the four colors. In this case, a larger value for the amount of toner X per page means that there is more toner in the height direction. A state where the toner amount X on a page is between 10% and 100% indicates a condition where a relatively large area on a single recording material P may be covered by toner from isolated patch patterns (described later) or halftone images (described later).

[0046] In this embodiment, the purpose of calculating the amount of toner X on one page is to predict how the inside of this single recording material P is coated with toner. Then, in this embodiment, the correction amount (correction value) ΔV of the secondary transfer voltage is determined based on this predicted toner coating state inside the single recording material P.

[0047] (Regarding the method for determining the secondary transfer voltage) This embodiment describes the method for determining the reference secondary transfer voltage when performing constant voltage control of the secondary transfer voltage, and the method for correcting the secondary transfer voltage based on the amount of toner X per page (method for determining the secondary transfer voltage).

[0048] First, we will explain how to determine the voltage V1 (reference value), which is the reference secondary transfer voltage when performing constant voltage control of the secondary transfer voltage. In this embodiment, the voltage V1 is determined by the CPU 221 based on information about the recording material P obtained from the print information input from the host device 199, and environmental information obtained from the detection results of the environmental sensor 300. In this embodiment, the information about the recording material P includes information about the size of the recording material P (hereinafter also referred to as "paper size"), including information about the length in the width direction (here, simply referred to as "width") which is approximately perpendicular to the transport direction of the recording material P, information about the thickness of the recording material P and related indicators (thickness, basis weight, etc.), and information about the category of the recording material P (plain paper, cardboard, glossy paper, etc.; hereinafter also referred to as "paper quality"). In addition, in this embodiment, the environmental information includes information about the absolute moisture content of the environment calculated by the CPU 221 based on the detection results of the temperature sensor 301 and humidity sensor 302 of the environmental sensor 300. The information about the recording material P includes any information that can distinguish the recording material P, such as attributes based on general characteristics (so-called category (paper quality)) such as plain paper, fine paper, glossy paper, coated paper, embossed paper, cardboard, and thin paper, numerical values ​​or ranges of values ​​such as basis weight, thickness, size, and rigidity, or brand name (including manufacturer, product name, product number, etc.). Each recording material P distinguished by its information can be considered to constitute a type of recording material P. The information about the recording material P may be specified directly, for example, or it may be included in the print mode information that specifies the operation settings of the image forming apparatus 100, such as "plain paper mode" or "cardboard mode," or it may be replaced by the print mode information. In other words, in this embodiment, for each type of recording material P, information showing the relationship between paper size, basis weight, paper quality, absolute moisture content, and voltage V1 is pre-set and stored in the ROM 151 as a table. Then, the CPU 221 retrieves the necessary information from the table above based on the acquired information about the recording material P and environmental information, and determines the voltage V1 corresponding to the paper size, basis weight, paper quality, and absolute moisture content.

[0049] Next, the method for determining the correction amount ΔV of the secondary transfer voltage (the method for determining the secondary transfer voltage) in this embodiment will be explained. Figure 4 is a graph illustrating the method for determining the correction amount ΔV of the secondary transfer voltage in this embodiment. In Figure 4, the horizontal axis represents the amount of toner X in one page, and the vertical axis represents the secondary transfer voltage V that is actually applied. The amount of toner X in one page on the horizontal axis can take values ​​from 0 to 400 [%]. The voltage value at which the amount of toner X in one page = 0 [%] is defined as voltage V1, which is the reference value of the secondary transfer voltage in this embodiment. The voltage value at which the amount of toner X in one page = 400 [%] is defined as V2. In this embodiment, voltage V2 is determined based on information about the recording material P and environmental information, similar to voltage V1. That is, in this embodiment, for each type of recording material P, information showing the relationship between paper size, basis weight, paper quality, absolute moisture content and voltage V2 is pre-set and stored in ROM 151 as a table. Then, the CPU 221 retrieves the necessary information from the table above based on the acquired information about the recording material P and environmental information, and determines the voltage V2 corresponding to the paper size, basis weight, paper quality, and absolute moisture content.

[0050] As shown in Figure 4, in this embodiment, the absolute value of the secondary transfer voltage V actually applied is monotonically decreased as the amount of toner X on a page increases, relative to the voltage V1 at which the amount of toner X on a page is 0%. That is, the correction amount ΔV is the difference between the voltage V1 and the secondary transfer voltage V actually applied, and is determined (calculated) by the following equation (2). In this embodiment, the determination (calculation) of the secondary transfer voltage correction amount ΔV is performed by the secondary transfer voltage correction amount calculation unit 225, which is realized by the CPU 221 implemented in the CPU circuit section 150 of the engine control unit 210. ΔV={(V1-V2) / 400}×X[V] (0≦X≦400) ···(2)

[0051] Then, the secondary transfer voltage V is determined (calculated) by the following equation (3) so as the amount of toner X on a page increases, the absolute value of the secondary transfer voltage decreases. In this embodiment, the determination (calculation) of the secondary transfer voltage V using the correction amount ΔV is performed by the CPU 221 implemented in the CPU circuit section 150 of the engine control unit 210. V = V1 - ΔV ... (3)

[0052] Table 1 shows an example table of voltages V1 and V2 for plain paper. In the example shown in Table 1, the table sets voltages V1 and V2 for the surface (first or second surface) of the recording material P to which the toner image is transferred, the absolute moisture content, and the paper size. Note that the paper size refers to the width of the recording material P.

[0053] [Table 1]

[0054] Note that voltages V1 and V2 for paper sizes and absolute moisture content not listed in Table 1 are determined by linear interpolation between the paper sizes and absolute moisture content listed in Table 1. Regarding paper size, the LTR setting is selected for widths of LTR (215.9 mm) or greater, and the A5 setting is selected for widths of A5 (148.0 mm) or less. A4 width is 210.0 mm. Regarding absolute moisture content, it is 27.1 g / m². 3 The above is 27.1 g / m 3 The setting selected is 21.7g / m 3 If the value is less than the specified value, constant current control of the secondary transfer voltage is performed as described above.

[0055] Next, we will explain why the difference (absolute value) between voltage V1 and voltage V2 in Table 1 is varied depending on the absolute moisture content, the first and second surfaces, and the width of the recording material P.

[0056] Firstly, it is preferable to increase the difference between voltage V1 and voltage V2 as the absolute moisture content increases. In other words, the greater the moisture absorption of the recording material P, the lower its resistance. Therefore, in this embodiment, from the viewpoint of suppressing patchiness and strong leakage, the difference between voltage V1 and voltage V2 is increased as the absolute moisture content increases.

[0057] Secondly, it is preferable that the difference between voltage V1 and voltage V2 be larger on the first surface than on the second surface. On the second surface, heat is applied to the recording material P after going through the fixing process, causing the moisture in the recording material P to evaporate and increasing the electrical resistance. As a result, the second surface is less prone to patchiness and strong gaps compared to the first surface. Therefore, in this embodiment, the difference between voltage V1 and voltage V2 is larger on the first surface than on the second surface.

[0058] Thirdly, it is preferable to increase the difference between voltage V1 and voltage V2 as the width of the recording material P increases. This is because, when the size of the isolated patch pattern described later is the same, the smaller the width of the recording material P, the larger the area ratio of toner to the white area, making it less likely for patch blemishes to occur. For this reason, in this embodiment, the difference between voltage V1 and voltage V2 is increased as the width of the recording material P increases.

[0059] Note that the table in Table 1 is an example for ordinary paper, and the degree of moisture absorption and the electrical resistance of the recording material P itself will vary depending on the type of recording material P. Therefore, the table can be set appropriately according to the type of recording material P. Generally, the smaller the basis weight of the recording material P, the lower the electrical resistance tends to be. Therefore, from the viewpoint of suppressing patchiness and strong breaks, it is preferable to increase the difference between voltage V1 and voltage V2 as the basis weight of the recording material P decreases. In addition, to increase the difference (absolute value) between voltage V1 and voltage V2, the absolute value of voltage V1 can be increased, the absolute value of voltage V2 can be decreased, or both can be done. In other words, at least one of voltage V1 or voltage V2 can be changed so that the absolute value of the difference between voltage V1 and voltage V2 increases.

[0060] A specific example of a method (calculation method) for determining the secondary transfer voltage is shown. For example, in an environment with an absolute moisture content of 24.4 g / m 3 consider the case of single-sided printing an image with a toner amount X of 160[%] per page on plain paper (width 179 mm).

[0061] First, for the first-side voltages V1 and V2 of sizes A5 (width 148 mm) and A4 (width 210 mm) in an environment with an absolute moisture content of 24.4 g / m 3 interpolate linearly between an absolute moisture content of 27.1 g / m 3 and an absolute moisture content of 21.7 g / m 3 to obtain them. · For A5 size, V1 = 1000 + (1100 - 1000) × (24.4 - 21.7) / (27.1 - 21.7) = 1050 V · For A4 size, V1 = 1200 + (1300 - 1200) × (24.4 - 21.7) / (27.1 - 21.7) = 1250 V · For A5 size, V2 = 900 + (900 - 900) × (24.4 - 21.7) / (27.1 - 21.7) = 900 V · For A4 size, V2 = 800 + (850 - 800) × (24.4 - 21.7) / (27.1 - 21.7) = 825 V

[0062] Next, for the voltages V1 and V2 of the recording material P with a width of 179 mm, interpolate linearly between widths of 148 mm and 210 mm to obtain them. · For a width of 179 mm, V1 = 1050 + (1250 - 1050) × (179 - 148) / (210 - 148) = 1150 V · For a width of 179 mm, V2 = 825 + (900 - 825) × (179 - 148) / (210 - 148) = 862.5 V

[0063] Subsequently, obtain the correction amount ΔV for a toner amount X of 160[%] per page by linearly interpolating between a toner amount X of 0[%] and a toner amount X of 400[%] per page. ΔV = {(1150 - 862.5) / 400} × 160 = 115 [V]

[0064] Finally, the voltage V1 is corrected using the correction amount ΔV obtained above to determine the actual applied secondary transfer voltage V. V = V1 - ΔV = 1150 - 115 = 1035 [V]

[0065] The CPU 221 instructs the secondary transfer control unit 202 to apply the secondary transfer voltage V, determined as described above, from the secondary transfer power supply 21 to the secondary transfer roller 20, thereby performing the secondary transfer.

[0066] (Control procedure) Figure 5 is a flowchart illustrating the general procedure for controlling the secondary transfer voltage in this embodiment, as described above.

[0067] When a print job start instruction is received, the CPU 221 begins preparing for image formation (S101). In this embodiment, control of the secondary transfer voltage begins from the start of the print job (print start (i=1)). The CPU 221 acquires the print information for page i from the host device 199 (S102) and also acquires information on the absolute moisture content from the detection result of the environmental sensor 300 (S103). Based on the information on the absolute moisture content, the CPU 221 decides whether to control the secondary transfer voltage with constant voltage control or constant current control (S104). In this embodiment, the CPU 221 determines that the absolute moisture content is 21.7 g / m². 3 In the above cases, constant voltage control will be performed (S105), and the absolute moisture content is 21.7 g / m³. 3 If the value is less than the specified value, constant current control will be performed (S106). This embodiment is characterized by the control performed when constant voltage control of the secondary transfer voltage is performed, so the control performed when constant voltage control of the secondary transfer voltage will be described.

[0068] While the CPU 221 determines the control method for the secondary transfer voltage, it measures the toner amount X (0-400%) for page i using the method described above, based on the print information from the host device 199 (S107). In other words, the video signal from the controller 200 is transmitted to the image processing GA222 via the video interface unit 220, converted into a laser drive signal, and the toner amount X (0-400%) for page i is measured. The CPU 221 stores the measured toner amount X (0-400%) for page i in the RAM 152 (S108). Based on the toner amount X for page i stored in the RAM 152, the absolute moisture content information obtained from the print information for page i and the detection result of the environmental sensor 300 (S109), the CPU 221 calculates a correction amount ΔV corresponding to the voltage V1 and toner amount X (S110). In parallel with this, if there is a print job for the next page, the CPU 221 measures the toner amount X for page i+1, stores it in RAM 152, and repeatedly determines the voltage V1 and correction amount ΔV for page i+1 in the same way as for page i (S111, S112, S113).

[0069] After the CPU 221 determines the voltage V1 and the correction amount ΔV corresponding to the toner amount X for page i, it applies a secondary transfer voltage of V = V1 - ΔV when the recording material P is passing through the secondary transfer section N2 (S114) to finish printing page i. If there is a subsequent print, the CPU 221 repeats the process of applying the V = V1 - ΔV for page i+1, which was determined in advance as described above, in the same manner, and finishes the print job (S115, S116, S117).

[0070] <Effects and Effects> Next, we will explain the effect of a control mechanism in constant voltage control of the secondary transfer voltage where the absolute value of the secondary transfer voltage decreases as the amount of toner X on a page increases (and increases as the amount of toner X on a page decreases). Figure 6(a) is a schematic diagram showing an example of an image containing an isolated patch pattern, and Figure 6(b) is a schematic diagram showing an example of a solid image (e.g., a solid black image). Figure 6(c) is a schematic diagram of the cross-section of the secondary transfer section N2 during secondary transfer of an image containing an isolated patch pattern, and Figure 6(d) is a schematic diagram of the cross-section of the secondary transfer section N2 during secondary transfer of a solid image (e.g., a solid black image). In Figures 6(c) and (d), the arrows represent the path of the transfer current, and their thickness schematically represents the magnitude of the current. As mentioned above, an "isolated patch pattern" refers to an image pattern in which clusters of high-print toner images are scattered within the width of the recording material P. Furthermore, a "full-surface solid image (full-surface solid pattern)" refers to an image pattern in which the highest density toner image exists across the entire image-forming region in the width direction of the recording material P.

[0071] In this embodiment, constant voltage control of the secondary transfer voltage is performed in a high-temperature, high-humidity environment. In a high-temperature, high-humidity environment, the recording material P, secondary transfer roller 20, intermediate transfer belt 10, etc., absorb moisture, causing their electrical resistance to decrease.

[0072] Therefore, when transferring low-print images, such as isolated patch patterns, where the amount of toner X per page is small, as shown in Figure 6(a), the following occurs. In other words, as shown in Figure 6(c), the transfer current is more likely to selectively flow to the white areas, which have low resistance, rather than to the toner areas (patch areas) T, which have high resistance, and less likely to flow to the toner areas (patch areas) T. In this case, according to the control of this embodiment, the smaller the amount of toner X per page, the larger the absolute value of the secondary transfer voltage can be made, and thus the total amount of secondary transfer current can be increased. That is, the current to the white areas increases, but at the same time the current to the toner areas (patch areas) T also increases, so it becomes possible to supply sufficient current to the toner areas (patch areas) T for secondary transfer, and as a result, "patch blemishes" can be suppressed.

[0073] Conversely, when transferring high-print images, such as full-page solid images, where the amount of toner X per page is large, as shown in Figure 6(b), the following occurs. In other words, as shown in Figure 6(d), there is no escape route for the transfer current, so if constant voltage control is implemented with a large absolute voltage value that takes into account the escape current to the white areas in order to suppress "patch blurring," the current supplied to the toner unit T becomes excessive. In this case, according to the control of this embodiment, the absolute value of the secondary transfer voltage can be made smaller as the amount of toner X per page increases, so that the excessive current supplied to the toner unit T can be suppressed, and as a result, "strong gaps" can be suppressed.

[0074] In accordance with the mechanism described above, ideally, it is preferable to change the correction amount ΔV of the secondary transfer voltage according to the amount of toner present in the secondary transfer section N2 and the area of ​​the toner section. That is, it is preferable to decrease the absolute value of the secondary transfer voltage when the amount of toner present in the secondary transfer section N2 and the area coverage of the toner section are large, and to increase the absolute value of the secondary transfer voltage when the amount of toner present and the area coverage of the toner section are small. However, if the voltage is frequently raised and lowered within a page during constant voltage control, the secondary transfer voltage may not follow the control due to the responsiveness limits of the secondary transfer power supply 21, and as a result, it may become impossible to apply the optimal secondary transfer voltage according to the image pattern. Therefore, in this embodiment, the secondary transfer voltage is corrected according to the amount of toner X in a page in order to improve the image quality on average.

[0075] Here, we will further explain the timing of applying (changing) the secondary transfer voltage. Figure 7 is a timing chart diagram for explaining the timing of applying the secondary transfer voltage. In Figure 7, the horizontal axis represents time, and the vertical axis represents voltage. The period during which recording material P (more specifically, its image-forming region) exists in the secondary transfer section N2 is also called "in-paper". In-paper corresponds to the period during image formation (secondary transfer) in the secondary transfer section N2. The period between a preceding recording material P and the recording material P that follows it is also called "between-paper". "Between-paper" corresponds to the period during the aforementioned "between-paper" process in the secondary transfer section N2. In Figure 7, for convenience, the non-image-forming period before the "in-paper" on the first page (corresponding to the aforementioned pre-rotation process) is also referred to as "between-paper".

[0076] Figure 7(a) shows the timing of the application of the secondary transfer voltage in this embodiment. In this embodiment, the secondary transfer voltage V = V1 - ΔV is applied only when the recording material P is passing through the secondary transfer section N2 (in the paper). In this embodiment, at other timings (between the paper), a paper-to-paper voltage with a smaller absolute value than the above V = V1 - ΔV secondary transfer voltage is applied. There are two reasons for this. First, the timing at which the secondary transfer voltage Vi for page i, as explained in Figure 5, can actually be determined depends on the communication conditions between the host device 199 and the controller 200, and the process speed of the image forming apparatus 100. In other words, since it is unknown at what timing the secondary transfer voltage Vi can be determined, applying the paper-to-paper voltage until just before the application of the secondary transfer voltage for page i allows preparation for determining the secondary transfer voltage Vi in the paper. Second, if a secondary transfer voltage with a large absolute value is applied when the recording material P is not present in the secondary transfer section N2, the load on the secondary transfer power supply 21 becomes heavy, and in some cases, oscillation may occur.

[0077] For these reasons, in this embodiment, when there is no recording material P in the secondary transfer section N2 (between the sheets), a paper-to-paper voltage with an absolute value smaller than the secondary transfer voltage in the sheets is applied. However, if the timing for determining the secondary transfer voltage is sufficiently fast and the response of the secondary transfer power supply 21 to the control is sufficiently fast, for example, as shown in Figure 7(b), the secondary transfer voltage for the i-th page may be applied between the sheets to prepare the sheet in the sheets.

[0078] Furthermore, the timing of applying the secondary transfer voltage according to the amount of toner will be explained in more detail. In this embodiment, the secondary transfer voltage applied during the period when toner may be present (the timing when the image-forming region in the transport direction of the recording material P passes through the secondary transfer section N2) is controlled to change according to the amount of toner, from the viewpoint of suppressing patchiness and strong gaps. In this embodiment, the voltage applied at the timing when the blank areas at the leading and trailing ends of the recording material P, where no toner is present, pass through the secondary transfer section N2 is not controlled to change according to the amount of toner. The leading and trailing ends of the recording material P refer to the leading and trailing ends in the transport direction of the recording material P, respectively. In this embodiment, at the timing when the leading and trailing ends of the recording material P pass through the secondary transfer section N2, a leading and trailing end voltage different from the secondary transfer voltage V=V1-ΔV is applied. This is for the following reason: At the leading end of the recording material P, the impedance suddenly changes from a low state where the recording material P is not present in the secondary transfer section N2 to a high state when the recording material P suddenly enters the secondary transfer section N2. Therefore, at the leading edge of the recording material P, a leading edge voltage is applied to ensure sufficient transfer voltage. Conversely, at the trailing edge of the recording material P, the impedance gradually decreases as the recording material P passes through the secondary transfer section N2 from a state of high impedance where it exists. Therefore, at the trailing edge of the recording material P, a trailing edge voltage is applied to ensure sufficient transfer current. However, in cases where there is no margin, or the margin is narrow, and toner may be present near the leading edge or trailing edge of the recording material P, the secondary transfer voltage applied to the leading edge or trailing edge of the recording material P may also be corrected according to the amount of toner as described in this embodiment. The leading edge voltage and trailing edge voltage are predetermined voltages set in advance from the above perspective. These voltages are determined based on information about the recording material P and environmental information, similar to the voltages V1 and V2 mentioned above. That is, for example, for each type of recording material P, information showing the relationship between paper size, basis weight, paper quality, and absolute moisture content, and the leading edge voltage and trailing edge voltage is pre-set and stored in the ROM 151 as a table.Then, the CPU 221 retrieves the necessary information from the table above based on the acquired information about the recording material P and environmental information, and determines the leading edge voltage and trailing edge voltage corresponding to the paper size, basis weight, paper quality, and absolute moisture content. Typically, the leading edge voltage and trailing edge voltage have a larger absolute value than the secondary transfer voltage V=V1-ΔV. However, there may be cases where at least one of the leading edge voltage or trailing edge voltage set as described above is approximately the same as the secondary transfer voltage V=V1-ΔV.

[0079] In this example, the absolute moisture content is 21.7 g / m². 3 In environments below a certain temperature, the electrical resistance of the recording material P is high enough that no escape current occurs in the white areas, so "constant current control" of the secondary transfer voltage is performed. In this environment, even with image patterns like those shown in Figures 6(a) and (b), "constant current control" allows for the supply of a transfer current almost uniformly across the width direction of the recording material P to achieve an appropriate secondary transfer voltage.

[0080] Thus, in this embodiment, the image forming apparatus 100 includes an image carrier 10 that carries a toner image, a transfer member 20 that forms a transfer section N2 for transferring the toner image from the image carrier 10 to a recording material P, an application section 21 that applies a transfer voltage to the transfer member 20, and a control unit (engine control unit) 210 that controls the application section 21. In this embodiment, when the control unit 210 controls the transfer voltage to be a constant voltage so that the voltage applied to the transfer member 20 by the application section 21 is substantially constant, it sets the transfer voltage to a first voltage when the amount of toner used for the toner image is a first amount of toner, and sets the transfer voltage to a second voltage whose absolute value is smaller than the absolute value of the first voltage when the amount of toner is a second amount of toner which is greater than the first amount of toner. In this embodiment, the image forming apparatus 100 includes an acquisition unit (CPU) 221 that acquires toner amount information relating to the toner amount, and an exposure unit 3 that exposes another image carrier 1 that carries toner to be transferred to the image carrier 10 according to the image information. The acquisition unit 221 acquires toner amount information based on a drive signal that causes the exposure unit 3 to emit light according to the image information. In this embodiment, toner amount information relating to the toner amount is acquired for each toner image transferred to a single recording material P.

[0081] Here, the control unit 210 can change at least one of the first voltage or the second voltage so that the absolute value of the difference between the first voltage and the second voltage increases when the basis weight of the recording material P onto which the toner image is transferred is a second basis weight which is smaller than the first voltage and the second voltage Furthermore, the image forming apparatus 100 may be capable of transporting the recording material P on which a toner image has been transferred and fixed to the first surface to the transfer unit N2 and performing the operation of transferring a toner image to the second surface of the recording material P. In this case, the control unit 210 can change at least one of the first voltage or the second voltage so that the absolute value of the difference between the first voltage and the second voltage is larger when transferring a toner image to the first surface than when transferring a toner image to the second surface. Furthermore, the image forming apparatus 100 may have an environmental detection unit 300 that detects environmental information relating to at least one of the temperature or humidity of the environment. In this case, the control unit 210 can change at least one of the first voltage or the second voltage so that the absolute value of the difference between the first voltage and the second voltage is larger when the absolute amount of moisture in the environment indicated by the detection result of the environmental detection unit 300 is a second absolute amount which is greater than the first absolute amount.

[0082] In this embodiment, the control unit 210 controls the absolute value of the transfer voltage to gradually decrease as the amount of toner increases, between the transfer voltage when the amount of toner is minimum and the transfer voltage when the amount of toner is maximum. In this embodiment, the control unit 210 is also capable of constant current control of the transfer voltage so that the current supplied to the transfer member 20 by the application unit 21 is substantially constant. Constant voltage control of the transfer voltage is performed when the absolute moisture content indicated by the detection result of the environmental detection unit 300 is above a predetermined value, and constant current control of the transfer voltage is performed when the absolute moisture content indicated by the detection result of the environmental detection unit 300 is below the predetermined value.

[0083] As described above, according to this embodiment, even when controlling the secondary transfer voltage at a constant voltage in environments where it is difficult to suppress both patchiness and strong dropouts, such as high temperature and high humidity environments, an appropriate secondary transfer voltage can be set. Furthermore, as mentioned above, in this embodiment, an appropriate secondary transfer voltage can be supplied by constant current control of the secondary transfer voltage even in environments other than high temperature and high humidity environments. Therefore, according to this embodiment, good secondary transfer can be performed regardless of the environment in which the image forming apparatus 100 is used.

[0084] <Effect Confirmation> To confirm the effectiveness of this embodiment, a high-temperature, high-humidity environment (temperature 30°C / relative humidity 80% / absolute moisture content 21.7 / m³) was used. 3 A test was conducted to verify the presence or absence of image defects. Xerox Business 4200 LETTER size (Xerox, product name) was used as the recording material P. The test was performed on the configuration of this embodiment and the configurations of Comparative Examples 1 and 2. In the configuration of this embodiment, the voltage V1 was 1400V, and the voltage V2 at a toner amount X = 400[%] per page was 1000V.

[0085] In the configurations of Comparative Examples 1 and 2, a substantially constant secondary transfer voltage was applied regardless of the amount of toner X per page. In the configuration of Comparative Example 1, the same voltage V1 as in this embodiment, 1400V, was applied as the secondary transfer voltage. In the configuration of Comparative Example 2, the same voltage V2 as in this embodiment, 1000V, was applied as the secondary transfer voltage. The configurations of Comparative Examples 1 and 2 are substantially the same as the configuration of this embodiment, except for the differences described above.

[0086] Table 2 shows the evaluation results. Table 2 shows the applied voltage V for low print quality (X=5[%]) and high print quality (X=300[%]), and the image level in each case (patch blurring in low print quality images, strong gaps in high print quality images). The image level is categorized into three levels from top to bottom: Good, Fair, and Poor. Fair and Poor are considered to indicate the occurrence of image defects.

[0087] [Table 2]

[0088] In the configuration of Comparative Example 1, in low-print images including isolated patch patterns, sufficient current could be supplied to the toner area (patch area), so "patch bleed" did not occur. However, in the configuration of Comparative Example 1, in high-print images including solid images, the absolute value of the secondary transfer voltage became large, resulting in excessive current supply and "strong gaps" occurred.

[0089] In the configuration of Comparative Example 2, the secondary transfer voltage was set so that excessive current was not supplied to high-print images including solid images, and therefore "strong gaps" did not occur. However, in the configuration of Comparative Example 2, in low-print images including isolated patch patterns, sufficient current could not be supplied to the toner area (patch area), resulting in "patch bleed."

[0090] On the other hand, in the configuration of this embodiment, the absolute value of the secondary transfer voltage could be increased in low-print images including isolated patch patterns, and sufficient current could be supplied to the toner area (patch area), resulting in no "patch blemishes" and good transfer performance. Furthermore, in the configuration of this embodiment, the absolute value of the secondary transfer voltage could be decreased in high-print images including solid images, suppressing the flow of excessive current, resulting in no "strong gaps" and good transfer performance.

[0091] In this example, and in Comparative Examples 1 and 2, the absolute moisture content was 21.7 g / m². 3In environments below a certain level, the transfer performance was equivalent because "constant current control" of the secondary transfer voltage was implemented.

[0092] <Other configurations> In this embodiment, the toner amount was calculated and the secondary transfer voltage was corrected for each page, but the present invention is not limited to this embodiment. For example, the toner amount may be calculated and the secondary transfer voltage corrected at any period, such as every predetermined rotation amount (e.g., one revolution) of the secondary transfer roller 20 or every predetermined rotation amount (e.g., one revolution) of the photosensitive drum 1. Alternatively, as described above, it is preferable to change the secondary transfer voltage according to the amount of toner in the secondary transfer section N2, ideally. Therefore, in configurations where the response of the secondary transfer power supply is sufficiently fast, for example, the secondary transfer voltage may be changed according to the amount of toner in the secondary transfer section N2.

[0093] In this embodiment, the engine control unit 210 samples the laser drive signal and measures the pixel count value n (the number of "H"s) to calculate the toner amount, but the present invention is not limited to this embodiment. For example, the controller 200 may transmit image information (toner amount information) along with the video signal to the engine control unit 210, and the engine control unit 210 may determine the correction amount of the secondary transfer voltage based on that information. Also, in this embodiment, the toner amount was calculated using the pixel count values ​​for four colors relative to the total number of samples per color, but the present invention is not limited to this embodiment. For example, the pixel count values ​​equivalent to a full-page solid image (e.g., a full-page solid black image) for each paper size may be stored in the RAM 152 as constants in advance, and the toner amount may be calculated from the ratio of that number to the actual pixel count value.

[0094] In this embodiment, the decision to perform "constant voltage control" or "constant current control" of the secondary transfer voltage was made based on the detection result of the absolute moisture content by the environmental sensor 300. However, the present invention is not limited to this embodiment. For example, the decision to perform "constant current control" or "constant voltage control" of the secondary transfer voltage may be made by measuring the impedance of the secondary transfer section N2 (secondary transfer roller 20 and intermediate transfer belt 10) before image formation. Specifically, the impedance is measured by applying a predetermined current to the secondary transfer section N during the non-image formation stage before the image formation process of the print job (pre-rotation process or pre-multi-rotation process) and measuring the voltage value applied at that time. Alternatively, the impedance may be measured by applying a predetermined voltage and measuring the current value that flows at that time. If the measured impedance is small, it is considered that the electrical resistance of the secondary transfer roller 20 and intermediate transfer belt 10 has decreased, and similarly, the electrical resistance of the recording material P has also decreased. Therefore, if the impedance is lower than a predetermined threshold, "constant voltage control" of the secondary transfer voltage should be performed to correct the secondary transfer voltage according to this embodiment. In addition to the impedance itself, the voltage value when the predetermined current is applied or the current value when the predetermined voltage is applied may also be used as an index value correlated with the impedance for control. Alternatively, for example, information showing both the relationship between the paper size, basis weight, paper quality, and absolute moisture content and the lower limit voltage value of the secondary transfer voltage, and the relationship between the paper size, basis weight, paper quality, and absolute moisture content and the target current value during secondary transfer may be pre-set and stored in the ROM 151 as a table. Then, when a transfer current of the target current value is applied during secondary transfer, if the voltage value at that time falls below the lower limit voltage value, "constant voltage control" at the lower limit voltage value may be performed. In other words, the image forming apparatus 100 may have resistance detection units (current detection unit, voltage detection unit) 241, 242 that detect an index value correlated with the electrical resistance of the transfer unit N2. In this case, the control unit 210 can perform constant voltage control of the transfer voltage when the electrical resistance of the transfer unit N2, as indicated by the detection results of the resistance detection units 241, 242, is lower than a predetermined value, and can perform constant current control of the transfer voltage when the electrical resistance of the transfer unit N2, as indicated by the detection results of the resistance detection units 241, 242, is equal to or greater than the predetermined value.Alternatively, the control unit 210 may perform constant current control of the transfer voltage, and if the applied voltage of the application unit 21 becomes smaller than a predetermined value, it may perform constant voltage control of the transfer voltage.

[0095] In this embodiment, the secondary transfer voltage V was calculated as V = V1 - ΔV from the voltage V1 and the correction amount ΔV, but the present invention is not limited to this embodiment. For example, as in the image forming apparatus 100 of Figure 8, there is a configuration in which the primary transfer current can be supplied from the secondary transfer power supply 21. In such a configuration, further correction is required to determine the secondary transfer voltage V. In the image forming apparatus 100 of Figure 8, elements having the same or corresponding functions or configurations as those in the image forming apparatus 100 of Figure 1 are denoted by the same reference numerals as in Figure 1. In the image forming apparatus 100 of Figure 8, the secondary transfer opposing roller 13 (and furthermore, the drive roller 11 and tension roller 12) and each primary transfer roller 14 are connected to ground potential via a Zener diode 17 as a voltage maintenance element (voltage stabilization element). As a result, by supplying a voltage of a predetermined value or higher from the secondary transfer power supply 21, the potential of each primary transfer roller 14 (and secondary transfer opposing roller 13) can be maintained at a predetermined potential and primary transfer current can be supplied to each primary transfer section N1. Furthermore, the voltage stabilization element (voltage maintenance element) used to stabilize the primary transfer voltage Vt1 is not limited to the Zener diode 17; other voltage stabilization elements such as varistors may be used as long as they can achieve a similar effect. In the configuration shown in Figure 8, the primary transfer voltage Vt1 is applied to the secondary transfer opposing roller 13. Therefore, the effective voltage for secondary transfer is the difference between the voltage applied to the secondary transfer roller 20 and the voltage applied to the secondary transfer opposing roller 13. Consequently, the secondary transfer voltage to be actually applied must be the value calculated by equation (4) below, taking into account the primary transfer voltage Vt1. V=(V1-ΔV)+Vt1 ···(4)

[0096] In this embodiment, the correction amount of the secondary transfer voltage was changed linearly in response to the change in the amount of toner X, but the present invention is not limited to this embodiment, and the correction amount of the secondary transfer voltage may be changed by any curve.

[0097] In this embodiment, the normal charge polarity of the toner was negative polarity, but the present invention is not limited to this embodiment, and the normal charge polarity of the toner may be positive polarity. In that case, the polarity of the bias, such as the secondary transfer voltage, will be the opposite polarity to that in this embodiment. Also, in that case, the relationship of increase and decrease of the secondary transfer voltage value, including the sign, in the control of the secondary transfer voltage will be the opposite to that in this embodiment, but the relationship of increase and decrease of the absolute value of the secondary transfer voltage will be the same as in this embodiment.

[0098] Furthermore, in this embodiment, the image forming apparatus 100 was configured to use four toners: Y, M, C, and K. However, the present invention is not limited to this configuration. The image forming apparatus 100 may also be configured to use transparent toner, metallic toner, or the like in addition to Y, M, C, and K, or in place of any one of these colors. In that case, the maximum value of the toner amount X is not limited to 400% in this embodiment, but may be changed according to the total amount of the types of toners used.

[0099] [Example 2] Next, other embodiments 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, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus in Embodiment 1 are denoted by the same reference numerals as in Embodiment 1, and detailed descriptions are omitted.

[0100] In Example 1, a correction was applied to the reference secondary transfer voltage V1, such that the absolute value of the secondary transfer voltage monotonically decreases as the amount of toner X per page increases. In this example, there is a range of toner amounts X in which the absolute value of the secondary transfer voltage remains approximately constant with respect to changes in the amount of toner X per page.

[0101] A method for determining the correction amount ΔV of the secondary transfer voltage in this embodiment will be described. FIG. 9 is a graph for explaining the method for determining the correction amount ΔV of the secondary transfer voltage in this embodiment. In FIG. 9, the horizontal axis represents the toner amount X in one page, and the vertical axis represents the secondary transfer voltage V actually applied. The toner amount X in one page on the horizontal axis can take values from 0 to 400 [%]. The voltage value in the section (section a) where 0 ≦ X ≦ A [%] of the toner amount X in one page is defined as V1. Also, the voltage value in the section (section c) where B ≦ X ≦ C of the toner amount X in one page is defined as V2. Further, the voltage value in the section (section e) where D ≦ X (D ≦ X ≦ 400) [%] of the toner amount X in one page is defined as V3. Here, the relationship among the voltages V1, V2, and V3 is V1 > V2 > V3. Also, the voltage in the section (section b) where A < X < B is determined by linearly interpolating the voltages V1 and V2. Also, the voltage value in the section (section d) where C < X < D is determined by linearly interpolating the voltages V2 and V3.

[0102] That is, the correction amount ΔV of the secondary transfer voltage is as shown in the following formula (5). ΔV = 0 (0 ≦ X ≦ A) ΔV = V1 - { (V2 - V1) / (B - A) × (X - B) + V2} (A < X < B) ΔV = V1 - V2 (B ≦ X ≦ C) ΔV = V1 - { (V3 - V2) / (D - C) × (X - D) + V3} (C < X < D) ΔV = V1 - V3 (D ≦ X ≦ 400) ···(5)

[0103] Thus, in this embodiment, correction is performed to reduce the absolute value of the secondary transfer voltage when the toner amount X is larger than the section of the toner amount X where the voltage is V1. Also, in other words, in this embodiment, the absolute value of the secondary transfer voltage is increased when the toner amount X is less than the section of the toner amount X where the voltage is V2, and correction is performed to reduce the absolute value of the secondary transfer voltage when the toner amount X is larger than the section of the toner amount X where the voltage is V2. In this embodiment, the voltages V1 and V2 can be considered as reference values of the secondary transfer voltage.

[0104] In this embodiment, the voltages V1, V2, V3 and toner amounts A, B, C, and D are determined based on information about the recording material P and environmental information. Specifically, in this embodiment, for each type of recording material P, information showing the relationship between paper size, basis weight, paper quality, and absolute moisture content, and the voltages V1, V2, V3, and toner amounts A, B, C, and D is pre-set and stored in the ROM 151 as a table. The CPU 221 then retrieves the necessary information from the table based on the acquired information about the recording material P and environmental information, and determines the voltages V1, V2, V3, and toner amounts A, B, C, and D corresponding to the paper size, basis weight, paper quality, and absolute moisture content.

[0105] Next, the effects of this embodiment will be explained. Generally, "patch blurring" is likely to occur at very low printing levels, while "severe blackout" can occur not only in full-bleed images like the one shown in Figure 6(b), but also in full-bleed halftone images. Here, a full-bleed halftone image is an image with an average amount of toner less than a full-bleed image like the one shown in Figure 6(b). A halftone image is typically an image with a toner amount X of 20-100%. Full-bleed halftone images are prone to "severe blackout" through the same mechanism as explained in Example 1. That is, "patch blurring" is likely to occur in a narrow range of printing levels at very low printing levels with a very small amount of toner, while "severe blackout" is likely to occur in a relatively wide range of printing levels with a medium or larger amount of toner.

[0106] As a result of the inventor's diligent research, it was found that "patch blurring" is more likely to occur with toner amounts X of 0-20%, and "severe patchiness" is more likely to occur with toner amounts X of 100% or more. Furthermore, it was found that in the case of full-page halftone images, "severe patchiness" is more likely to occur even with toner amounts X of 20% or more, and in images where a large area of ​​the page is covered with toner and only a part has an isolated patch pattern, "patch blurring" may occur even with toner amounts X of 20% or more. In other words, it was found that in the range of toner amounts X of 20-100%, both "severe patchiness" and "patch blurring" can occur depending on the image pattern. Therefore, the appropriate transfer voltage differs for each toner amount X range of low, medium, and high printing, and it is not always desirable to change the transfer voltage too much in each range. Also, for very low printing, it is not always desirable to change the transfer voltage from the perspective of the load on the secondary transfer power supply 21 described later.

[0107] Based on the above, it was found that the following ranges are preferable for the values ​​of A, B, C, and D used to determine the range of toner amount X to which voltage V1 is applied to suppress patchy printing at very low printing levels (0% to A), the range of toner amount X to which voltage V2 is applied to suppress both patchy printing and patchy printing at medium printing levels (B to C), and the range of toner amount X to which voltage V3 is applied to suppress patchy printing and above (D to 400%). In other words, it was found that it is preferable for A to be 3 to 10% to suppress patchy printing, B to be 15 to 25%, C to be 75 to 90% to suppress both patchy printing and patchy printing, and D to be 95% or more (typically 150% or less) to suppress patchy printing.

[0108] Therefore, in this embodiment, in order to suppress patch blurring at extremely low printing levels, a voltage V1 (a voltage with a large absolute value that does not cause patch blurring) was set in the range where the toner amount X is 0 ≤ X ≤ A = 5 [%]. In addition, in order to suppress strong patch blurring and patch blurring in images where a large area on the page is covered with toner, such as full-page halftone images, or when isolated patch patterns exist in some parts, a voltage V2 (a voltage that is unlikely to cause patch blurring or strong patch blurring) was set in the range where the toner amount X is B = 20 ≤ X ≤ C = 80 [%]. Furthermore, in order to suppress strong patch blurring at high printing levels, a voltage V3 (a voltage that does not cause strong patch blurring in solid images of one or more colors) was set in the range where the toner amount X is X ≥ D = 100 [%]. As a result, compared to the control in Embodiment 1, it became possible to set voltage values ​​that are more appropriate for each image defect, and better transfer performance was obtained compared to Embodiment 1.

[0109] As an example, the absolute moisture content of the first side of the plain paper in this embodiment is 21.7 g / m². 3 The set values ​​for voltages V1, V2, and V3 in this case are shown in equation (6) below. V=V1=1400V (0≦X≦5%) V = (V2 - V1) / (BA) × (XB) + V2 (5%) <X<20%) V = V2 = 1000V (20% ≤ X ≤ 80%) V = (V3 - V2) / (DC) × (XD) + V3 (80%) <X<100%) V = V3 = 900V (100% ≤ X ≤ 400%) ...(6)

[0110] Patch blurring occurs in low-print images such as isolated patch patterns, and is a phenomenon caused by the transfer current escaping to the white areas. Therefore, as shown in equation (6), in order to supply the appropriate transfer current to the toner area, the difference (absolute value) between voltage V1 and voltage V2 is made larger than the difference (absolute value) between voltage V2 and voltage V3, taking into account the escape current. The reason why the difference between voltage V2 and voltage V3 is smaller than the difference between voltage V1 and voltage V2 is as follows: In other words, strong breaks, unlike patch blurring, are a phenomenon that occurs when there is no escape current to the white areas and current is supplied to the entire toner area, and the increase or decrease in the secondary transfer voltage directly corresponds to the increase or decrease in current to the toner area. The reason why the secondary transfer voltage is gradually changed in the section from A to B and the section from C to D is that if the secondary transfer voltage changes discontinuously with respect to the amount of toner, it may not be possible to apply the appropriate secondary transfer voltage at that discontinuous amount of toner.

[0111] Thus, in this embodiment, the control unit 210 performs control so that there is an interval of toner amount in which the transfer voltage is substantially constant with respect to the change in the toner amount between the transfer voltage when the toner amount used for the toner image is minimum and the transfer voltage when the toner amount is maximum. In this embodiment, in the interval of 0≦X≦A defined by the value A (0<A) of the toner amount, the transfer voltage is substantially constant with respect to the change in the toner amount. In particular, in this embodiment, the toner amount indicates the toner amount X [%], which is the ratio of the toner amount transferred to the recording material P to the total amount of toner amount per color that can be transferred to the recording material P. When the intervals defined by the values A, B, C, D (0<A<B<C<D) of the toner amount X are interval a for 0≦X≦A, interval b for A<X<B, interval c for B≦X≦C, interval d for C<X<D, and interval e for D≦X, and the average value of the absolute value of the transfer voltage in interval a is Vave1, the average value of the absolute value of the transfer voltage in interval c is Vave2, and the average value of the absolute value of the transfer voltage in interval e is Vave3, Vave1>Vave2>Vave3 is satisfied. Also, in this embodiment, the value A is 3 to 10 [%], the value B is 15 to 25 [%], the value C is 75 to 90 [%], and the value D is 95 [%] or more. Also, in this embodiment, (Vave1-Vave2)>(Vave2-Vave3) is satisfied. Also, in this embodiment, in intervals a, c, and e, the transfer voltage is substantially constant with respect to the change in the toner amount X. Also, in this embodiment, in intervals b and d, the absolute value of the transfer voltage gradually decreases as the toner amount X increases. The reason for using the average values Vave1, Vave2, and Vave3 is that, as will be described later, it is also possible to change the absolute value of the transfer voltage in intervals a, c, and e.

[0112] As described above, according to this embodiment, in environments where it is difficult to suppress both patchiness and strong dropouts, such as high temperature and high humidity environments, it is possible to set the secondary transfer voltage more appropriately and obtain better transfer performance compared to Example 1. Also, similar to Example 1, in this embodiment, an appropriate secondary transfer voltage can be supplied by constant current control of the secondary transfer voltage even in environments other than high temperature and high humidity environments. Therefore, according to this embodiment, good secondary transfer is possible regardless of the environment in which the image forming apparatus 100 is used.

[0113] <Other configurations> In this embodiment, four thresholds for toner amount X are provided, A, B, C, and D, so that the secondary transfer voltage is approximately constant at voltages V1, V2, and V3 in each of the intervals where toner amount X is 0 ≤ X ≤ A, B ≤ X ≤ C, and D ≤ X (D ≤ X ≤ 400). However, the present invention is not limited to this embodiment. For example, as shown in Figure 10, the amount of correction for the secondary transfer voltage in response to changes in toner amount X may be changed in the interval where toner amount X is 0 ≤ X ≤ A (interval a), the interval where B ≤ X ≤ C (interval c), and the interval where D ≤ X (D ≤ X ≤ 400) (interval e). The amount of correction for the secondary transfer voltage in response to changes in toner amount X can be changed in at least one of these intervals a, c, and e. In this configuration, in addition to voltage V1, voltage V4 at toner amount C, voltage V5 at toner amount D, and the voltage in the interval where toner amount X is C ≤ X ≤ D can be considered as reference values ​​for the secondary transfer voltage.

[0114] First, regarding low print density, the lower the print density, the more likely patch blemishes are to occur. Therefore, increasing the absolute value of the secondary transfer voltage as the toner amount X decreases helps to suppress patch blemishes. However, when the toner amount X is small (low electrical resistance), the transfer current also increases, placing a heavy load on the secondary transfer power supply 21. For this reason, in this embodiment, taking into consideration the load on the secondary transfer power supply 21, the secondary transfer voltage was kept approximately constant at voltage V1 in the interval where the toner amount X is 0 ≤ X ≤ A, as shown in Figure 9. However, if there is sufficient capacity in the secondary transfer power supply 21, control may be performed to gradually increase the absolute value of the secondary transfer voltage from toner amount X A to 0% of a completely white image.

[0115] Furthermore, in the interval B≦X≦C, there is a possibility of a mixture of isolated patch patterns and patterns with large toner coverage areas, but as the amount of toner increases, the likelihood of the toner covering the entire page increases. For this reason, it is possible to control the absolute value of the secondary transfer voltage by gradually decreasing it as the amount of toner X increases from B to C. Similarly, in the interval D≦X (D≦X≦400), as the amount of toner increases, the likelihood of solid images covering the entire page increases, making it easier for strong gaps to occur. For this reason, in the interval where the amount of toner X is D≦X (D≦X≦400), it is possible to gradually decrease the absolute value of the secondary transfer voltage as the amount of toner X increases.

[0116] Furthermore, the voltages V1, V2, V3, V4, V5, V6 and toner amounts A, B, C, D in Figure 10 may be determined based on the information of the recording material P and environmental information, as in the case of the above embodiment.

[0117] In this embodiment, the secondary transfer voltage is monotonically decreased linearly in the section where the secondary transfer voltage is changed in response to the change in toner amount X. However, the present invention is not limited to this embodiment, and any correction of the rate of change may be made, such as changing it in a curve.

[0118] Furthermore, other configurations of Example 1 may be applied to the above-described embodiment, other configurations of the above-described embodiment, or combinations thereof.

[0119] [Example 3] Next, other embodiments 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 apparatuses in Embodiments 1 and 2. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatuses in Embodiments 1 and 2 are denoted by the same reference numerals as in Embodiments 1 and 2, and detailed descriptions are omitted.

[0120] This example is a modification of Example 2. In this example, there is an interval of toner amount X in which the absolute value of the secondary transfer voltage is increased with respect to the change in the toner amount X per page.

[0121] FIG. 11 is a graph for explaining a method of determining the correction amount ΔV of the secondary transfer voltage in this example. In FIG. 11, the horizontal axis represents the toner amount X per page, and the vertical axis represents the actually applied secondary transfer voltage V. The toner amount X per page on the horizontal axis can take values from 0 to 400 [%]. The voltage value in the interval (interval a) where 0 ≦ X ≦ A [%] of the toner amount X per page is set as V1. Also, the voltage value in the interval (interval c) where B ≦ X ≦ C of the toner amount X per page is set as V2. Also, the voltage value in the interval (interval e) where D ≦ X ≦ E of the toner amount X is set as V3. Also, the voltage value in the interval (interval g) where F ≦ X (F ≦ X ≦ 400) [%] of the toner amount X is set as V4. Here, the relationship between the voltages V, V1, V2, V3, and V4 is V1 > V2 > V3, V1 > V4 > V3. This example is different from Example 2 in that it provides a voltage V4 with such a relationship.

[0122] That is, in this example, while maintaining the relationship V < V1, the absolute value of the secondary transfer voltage is increased in some intervals of the toner amount X. In this example, the voltage V1 can be considered as the reference value of the secondary transfer voltage.

[0123] The voltages V1, V2, and V3 are set for the same purposes as described in Example 2. That is, the purpose of setting the voltage V1 is to suppress the patch bos of the isolated patch pattern in extremely low printing. Also, the purpose of setting the voltage V2 is to suppress both strong missing and patch bos in medium printing amounts. Also, the purpose of setting the voltage V3 is to suppress the strong missing of the secondary solid image from the solid monochromatic image covering the entire page.

[0124] And the voltage V4 applied in the range of F ≤ X (F ≤ X ≤ 400) is set for the purpose of suppressing transfer defects when the page is covered with a multi-color solid image of secondary color or more. This transfer defect occurs because the transfer current is insufficient with respect to the weight of the transferred toner, and thus it becomes more likely to occur as the toner weight increases. Therefore, when the toner amount increases such as in multi-color, in order to suppress transfer defects, the absolute value of the secondary transfer voltage is made larger than the secondary transfer voltage V3 for suppressing dropout.

[0125] Also, the voltage in the range of A < X < B (range b) is determined by linearly interpolating the voltage V1 and the voltage V2. Also, the voltage in the range of C < X < D (range d) is determined by linearly interpolating the voltage V2 and the voltage V3. Also, the voltage in the range of E < X < F (range f) is determined by linearly interpolating the voltage V3 and the voltage V4.

[0126] The voltages V1, V2, V3, V4 and the toner amounts A, B, C, D, E, F in FIG. 11 may be determined based on the information of the recording material P and the environmental information as in the case of Example 2.

[0127] Incidentally, the values of A, B, C, D, E, F are preferably in the following ranges. Similar to Example 2, A is 3 to 10% to suppress patch bos, B is 15 to 25%, C is 75 to 90% to suppress dropout and patch bos, and D is preferably 95% to 140% to suppress dropout. Also, it has been found that E and F for coping with transfer defects are preferably such that E is 210 to 240% and F is 260% or more (less than 400%).

[0128] Also, similar to the description of the other configurations in Example 2, it is also possible to change the absolute value of the secondary transfer voltage in ranges a, c, e, and g. In range g, the absolute value of the secondary transfer voltage can be gradually increased as the toner amount X increases. This is to increase the absolute value of the secondary transfer voltage as the toner amount increases such as in multi-color to suppress transfer defects.

[0129] As described above, in this embodiment, when the control unit 210 performs constant voltage control of the transfer voltage so that the voltage applied to the transfer member 20 by the application unit 210 becomes substantially constant, when the amount of toner used for the toner image is the first toner amount, the transfer voltage is set as the first voltage. When the toner amount is the second toner amount larger than the first toner amount, the transfer voltage is set as the second voltage whose absolute value is smaller than the absolute value of the first voltage. When the toner amount is the third toner amount larger than the second toner amount, control is performed such that the transfer voltage is set as the third voltage whose absolute value is smaller than the absolute value of the first voltage and larger than the absolute value of the second voltage. More specifically, in this embodiment, the toner amount indicates the toner amount X [%], which is the ratio of the amount of toner transferred to the recording material P to the total amount of toner per color that can be transferred to the recording material P. When the intervals of 0 ≦ X ≦ A defined by the values A, B, C, D, E, F (0 < A < B < C < D < E < F) of the toner amount X are interval a, the interval of A < X < B is interval b, the interval of B ≦ X ≦ C is interval c, the interval of C < X < D is interval d, the interval of D ≦ X ≦ E is interval e, the interval of E < X < F is interval f, and the interval of F ≦ X is interval g, and the average value of the absolute value of the transfer voltage in interval a is Vave1, the average value of the absolute value of the transfer voltage in interval c is Vave2, the average value of the absolute value of the transfer voltage in interval e is Vave3, and the average value of the absolute value of the transfer voltage in interval g is Vave4, then Vave1 > Vave2 > Vave3 and Vave1 > Vave4 > Vave3 are satisfied. Also, in this embodiment, the value A is 3 to 10 [%], the value B is 15 to 25 [%], the value C is 75 to 90 [%], the value D is 95 to 140 [%], the value E is 210 to 240 [%], and the value F is 260 “%” or more. Further, in this embodiment, in intervals a, c, e, and g, the transfer voltage is substantially constant with respect to the change in the toner amount X. Also, in this embodiment, in intervals b and d, as the toner amount X increases, the absolute value of the transfer voltage gradually decreases. Also, in this embodiment, in interval f, as the toner amount X increases, the absolute value of the transfer voltage gradually increases. Note that the average values Vave1, Vave2, Vave3, and Vave4 are used because, as described above, it is also possible to change the absolute value of the transfer voltage in intervals a, c, e, and g.

[0130] As described above, for very low print volume, voltage V1 is applied to suppress patch bleed. For images that cover the entire page, voltage V3 is applied to suppress strong patch bleed. For print volume between 20% and 100%, which is neither low nor high, voltage V2 is applied to balance both strong patch bleed and patch bleed. This suppresses various image defects. Furthermore, by applying voltage V4 for multi-color high-print images where the entire page is covered and there is a large amount of toner in the height direction, transfer defects caused by insufficient transfer current at high print volume can be suppressed. In this way, appropriate voltage values ​​can be selected to match each type of image defect that may occur depending on the print volume, thereby suppressing image defects.

[0131] In this embodiment, the secondary transfer voltage is increased linearly and monotonically in the section where the secondary transfer voltage is increased in response to a change in the amount of toner X. However, the present invention is not limited to this embodiment, and any correction of the rate of change may be made, such as by changing it in a curve.

[0132] Furthermore, other configurations of Example 1 may be applied to the configuration of this embodiment.

[0133] [Example 4] Next, other embodiments of the present invention will be described. In the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those in the image forming apparatus of Examples 1, 2, and 3 are denoted by the same reference numerals as in Examples 1, 2, and 3, and detailed descriptions are omitted.

[0134] The image forming apparatus of this embodiment is an image forming apparatus that does not have a primary transfer power supply. As an example of a configuration without a primary transfer power supply, a drum voltage configuration, which will be described later, in which the primary transfer member is connected to ground can be considered. In this embodiment, the drum voltage configuration in which the primary transfer member is connected to ground, the intermediate transfer belt used in the drum voltage configuration, and the effects of applying the present invention to the drum voltage configuration will be explained.

[0135] First, let's explain the drum voltage configuration. An image forming apparatus with a drum voltage configuration in which the primary transfer member is connected to ground is an image forming apparatus having a high-voltage power supply configuration as shown in Figure 12. Figure 12 is a schematic diagram showing the connection and grounding status of the high-voltage power supply for each part around the primary transfer section N1 in the image forming apparatus 100 of this embodiment. In this embodiment, the primary transfer roller 14, which is the primary transfer member, is connected to ground (0V) (electrically grounded). Also in this embodiment, during image formation, a voltage of -300V as the drum voltage (reference voltage) is applied from the high-voltage power supply 200 to the core metal (not shown) of the photosensitive drum 1. An image formation potential Vl (-400V) with an absolute value greater than the absolute value of the drum voltage is formed on the surface of the photosensitive drum 1. Then, the toner on the image section (the part with the image formation potential Vl) of the photosensitive drum 1 is primary transferred onto the intermediate transfer belt 10 by the difference (primary transfer contrast) between the potential of the primary transfer roller 14 (0V) and the image formation potential Vl (-400V) on the surface of the photosensitive drum 1.

[0136] Next, the intermediate transfer belt 10 used in the drum voltage configuration will be described. In a configuration without a primary transfer power supply, as in this embodiment, it is difficult to increase the primary transfer contrast. In order to increase the primary transfer contrast, it is necessary to increase the absolute value of the drum voltage, which may lead to an increase in the size and cost of the equipment. Therefore, in order to allow sufficient primary transfer current to flow even with a small primary transfer contrast, it is preferable that the electrical resistance value of the intermediate transfer belt 10 is low.

[0137] Figure 13 is a schematic diagram showing the cross-sectional structure of the intermediate transfer belt 10 in this embodiment. In this embodiment, an endless belt with a circumference of 700 mm and a thickness of 65 μm was used as the intermediate transfer belt 10. As shown in Figure 13, in this embodiment, the intermediate transfer belt 10 consists of two layers: a base layer 10e with a thickness of 64 μm and an inner layer 10f with a thickness of 1 μm. The base layer 10e side (outer surface side) contacts the photosensitive drum 1, and the inner layer 10f side (inner surface side) contacts the primary transfer roller 14. In this embodiment, polyethylene terephthalate (PET) resin mixed with an ionic conductive agent was used as the material for the base layer 10e. In this embodiment, polyester resin mixed with carbon, an electronically conductive agent, was used as the material for the inner layer 10f. The inner layer 10f is formed inside the base layer 10e and contacts the drive roller 11, tension roller 12, and secondary transfer opposing roller 13. In this embodiment, polyethylene terephthalate (PET) resin was used as the material for the base layer 10e, but other materials can also be used. For example, polyester, acrylonitrile-butadiene-styrene copolymer (ABS), and mixed resins thereof can be used as the material for the base layer 10e. Also, in this embodiment, polyester resin was used as the material for the inner layer 10f, but other materials can also be used, such as acrylic resin.

[0138] In this example, the electrical resistance of the inner layer 10f of the intermediate transfer belt 10 is lower than that of the base layer 10e. In this example, the volume resistivity of the intermediate transfer belt 10 is 1 × 10⁻⁶. 10 It is Ω·cm. In this embodiment, the surface resistivity of the inner surface of the intermediate transfer belt 10 is 1.0 × 10⁻⁶. 6 The ratio is Ω / □. In this embodiment, the measurement environment for the electrical properties of the intermediate transfer belt 10 is an indoor temperature of 23°C and an indoor humidity of 50%. In this embodiment, the volume resistivity actually measured for the intermediate transfer belt 10 reflects the electrical resistance of the base layer 10e, based on the relationship between electrical resistance and thickness between the base layer 10e and the inner layer 10f. On the other hand, in this embodiment, the surface resistivity of the inner surface actually measured for the intermediate transfer belt 10 reflects the electrical resistance of the inner layer 10f.

[0139] Volume resistivity was measured using a Hiresta-UP (MCP-HT450) measuring instrument from Mitsubishi Chemical Corporation, with a ring probe of type UR (model MCP-HTP12). Surface resistivity was measured using the same measuring instrument as for volume resistivity, but with a ring probe of type UR100 (model MCP-HTP16). Volume resistivity was measured by applying the probe to the surface side (base layer 10e side) of the intermediate transfer belt 10, with an applied voltage of 100V and a measurement time of 10 seconds. Surface resistivity was measured by applying the probe to the inner side (inner layer 10f side) of the intermediate transfer belt 10, with an applied voltage of 10V and a measurement time of 10 seconds. In this example, the volume resistivity of the intermediate transfer belt 10 is 1 × 10⁻¹⁶. 9 Ω cm or more, 1×10 10 A range of Ω·cm or less is preferred, and the surface resistivity of the inner surface of the intermediate transfer belt 10 is 4.0 × 10 6 Ω / □ or less (typically 1.0 × 10⁻⁶) 5 (Ω / □ or greater) is preferable.

[0140] As described above, the intermediate transfer belt 10 in the electrical resistance range has low electrical resistance, allowing current to flow in the circumferential direction of the intermediate transfer belt 10. Therefore, even if the primary transfer contrast is small, sufficient primary transfer current can be supplied. For this reason, in a drum voltage configuration without a primary transfer power supply, as in this embodiment, it is preferable to use a low-resistance intermediate transfer belt 10 having the electrical resistance value described above.

[0141] Next, the effects of applying the present invention to the drum voltage configuration will be explained. In a high-temperature, high-humidity environment, the lower the electrical resistance of the intermediate transfer belt 10, as in this embodiment, the easier it is for the secondary transfer current to flow to the white area rather than the toner area (patch area). For example, when printing images as shown in Figures 6(a) and (c) above, an equivalent circuit as shown in Figure 14 can be considered for the secondary transfer section N2. Each symbol in Figure 14 represents the following: • Rr: Electrical resistance value of secondary transfer roller 20 • Rp: Electrical resistance value of recording material P • Rt: Electrical resistance of the toner in an isolated patch pattern • Ri: Electrical resistance value of the intermediate transfer belt 10 I1: Current passing through the white area I2: Current passing through the toner section (patch section)

[0142] The ratio of I1 to I2 is given by equation (7) below. I1 / I2 =(Ri+Rt+Rp) / (Ri+Rp) =1+Rt / (Ri+Rp) ...Equation (7)

[0143] As shown in equation (7), the smaller Ri becomes, the larger the ratio of I1 to I2 becomes. In other words, the smaller the electrical resistance value Ri of the intermediate transfer belt 10, the more easily the secondary transfer current flows to the white areas rather than the toner areas (patch areas). Therefore, in a configuration using the low-resistance intermediate transfer belt 10 described above, patch blurring may occur more easily in images with a small amount of toner.

[0144] Therefore, in this embodiment, the present invention is applied to a configuration using the low-resistance intermediate transfer belt 10 described above. As a result, similar to the above embodiment, for images with a small amount of toner that would cause patchy blurring, control can be applied that increases the absolute value of the secondary transfer voltage as the amount of toner decreases. As a result, even with a configuration using the low-resistance intermediate transfer belt 10, it becomes possible to suppress image defects such as patchy blurring. Furthermore, as explained in the above embodiment, strong dropouts can also be suppressed. This makes it possible to realize a simple configuration without a primary transfer power supply, as in this embodiment. Note that any of the methods in Embodiments 1, 2, or 3 may be applied as the method for controlling the secondary transfer voltage in this embodiment.

[0145] Thus, in this embodiment, the image carrier 10 is composed of an endless belt that transports the toner image, which has been primary transferred from another image carrier 1, to the recording material P in the transfer unit N2 for secondary transfer, and the belt is capable of carrying an electric current in the circumferential direction. In this embodiment, the volume resistivity of the belt is 1 × 10⁻⁶. 9Ω cm or more, 1×10 10 It is less than or equal to Ω·cm.

[0146] As explained above, according to this embodiment, even when using a low-resistance intermediate transfer belt 10, patchiness and severe omissions can be suppressed by applying control that increases the absolute value of the secondary transfer voltage as the amount of toner decreases. Therefore, according to this embodiment, patchiness and severe omissions can be suppressed while realizing a simple configuration that does not require a primary transfer power supply.

[0147] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the embodiments described above.

[0148] For example, in the above-described embodiment, the image forming apparatus was a color image forming apparatus having multiple image forming units, but the present invention is not limited thereto, and the image forming apparatus may be a monochrome image forming apparatus having only one image forming unit. In this case, the present invention may be applied to a transfer unit that directly transfers a toner image from a photoreceptor or the like, which serves as an image carrier, to a recording material. [Explanation of symbols]

[0149] 1. Photosensitive drum (photoconductor) 3. Exposure apparatus 10 Intermediate transfer belt 20 Secondary transfer roller 21 Secondary Transfer Power Supply 100 Image forming apparatus P recording material

Claims

1. An image carrier that holds the toner image, A transfer member that forms a transfer section for transferring the toner image from the image carrier to the recording material, An application unit for applying a transfer voltage to the transfer member, It includes a control unit that controls the application unit, The image forming apparatus is characterized in that, when the control unit controls the transfer voltage to be a constant voltage so that the voltage applied to the transfer member by the application unit is substantially constant, the control unit sets the transfer voltage to a first voltage when the amount of toner used for the toner image is a first amount of toner, sets the transfer voltage to a second voltage whose absolute value is smaller than the absolute value of the first voltage when the amount of toner is a second amount of toner greater than the first amount of toner, and sets the transfer voltage to a third voltage whose absolute value is smaller than the absolute value of the first voltage and larger than the absolute value of the second voltage when the amount of toner is a third amount of toner greater than the second amount of toner.

2. An acquisition unit that acquires toner quantity information relating to the toner quantity, The system includes an exposure unit that exposes the image carrier, or another image carrier carrying toner to be transferred to the image carrier, according to image information. The image forming apparatus according to claim 1, characterized in that the acquisition unit acquires toner amount information based on a drive signal for causing the exposure unit to emit light in accordance with the image information.

3. The image forming apparatus according to claim 1 or 2, characterized in that toner amount information relating to the amount of toner is acquired for each toner image transferred to a single recording material.

4. The recording material on which the toner image has been transferred and fixed to the first surface is transported to the transfer unit, and the operation of transferring the toner image to the second surface of the recording material is performed. The image forming apparatus according to any one of claims 1 to 3, characterized in that the control unit changes at least one of the first voltage or the second voltage such that the absolute value of the difference between the first voltage and the second voltage is larger when transferring a toner image to the first surface than when transferring a toner image to the second surface.

5. It has an environmental detection unit that detects environmental information relating to at least one of the temperature or humidity of the environment, The image forming apparatus according to any one of claims 1 to 4, characterized in that the control unit changes at least one of the first voltage or the second voltage such that the absolute value of the difference between the first voltage and the second voltage becomes larger when the absolute amount of moisture in the environment indicated by the detection result of the environment detection unit is a second absolute amount which is greater than the absolute amount of moisture in the environment which is a first absolute amount.

6. The image forming apparatus according to any one of claims 1 to 5, characterized in that the control unit controls the transfer voltage to have a range between the minimum toner amount and the maximum toner amount, in which the absolute value of the transfer voltage is gradually reduced as the toner amount increases.

7. The image forming apparatus according to any one of claims 1 to 5, characterized in that the control unit controls the transfer voltage so that there is a range of toner amounts between the transfer voltage when the toner amount is minimum and the transfer voltage when the toner amount is maximum, in which case the transfer voltage is substantially constant with respect to changes in the toner amount.

8. The image forming apparatus according to claim 7, characterized in that the transfer voltage is substantially constant with respect to changes in the toner amount in the interval 0 ≤ X ≤ A defined by the toner amount value A (0 < A).

9. It has an environmental detection unit that detects environmental information relating to at least one of the temperature or humidity of the environment, The control unit is capable of constant current control of the transfer voltage so that the current supplied to the transfer member by the application unit is substantially constant, and the constant voltage control of the transfer voltage is performed when the absolute moisture content indicated by the detection result of the environmental detection unit is greater than or equal to a predetermined value, and the constant current control of the transfer voltage is performed when the absolute moisture content indicated by the detection result of the environmental detection unit is less than the predetermined value, as described in any one of claims 1 to 8.

10. It has a resistance detection unit that detects an index value correlated with the electrical resistance of the transfer unit, The control unit is capable of constant current control of the transfer voltage so that the current supplied to the transfer member by the application unit is substantially constant, and is characterized in that it performs constant voltage control of the transfer voltage when the electrical resistance of the transfer member indicated by the detection result of the resistance detection unit is lower than a predetermined value, and performs constant current control of the transfer voltage when the electrical resistance of the transfer member indicated by the detection result of the resistance detection unit is equal to or greater than the predetermined value, as described in any one of claims 1 to 8.

11. The control unit is capable of constant current control of the transfer voltage so that the current supplied to the transfer member by the application unit is substantially constant, and when the voltage applied by the application unit becomes less than a predetermined value due to the constant current control of the transfer voltage, the control unit is capable of constant voltage control of the transfer voltage, as described in any one of claims 1 to 8.

12. The image forming apparatus according to any one of claims 1 to 11, wherein the image carrier is composed of an endless belt that transports a toner image, which has been primary transferred from another image carrier, to the recording material in the transfer section for secondary transfer, and the belt is capable of carrying an electric current in the circumferential direction.

13. The volume resistivity of the aforementioned belt is 1 × 10 ９ Ω・cm or more, 1×10 １０ The image forming apparatus according to claim 12, characterized in that it is Ω·cm or less.

Images