Image forming apparatus

Abstract

To provide a technique to obtain an output image having higher quality and density when outputting a single-color image in an image forming mode for expanding the color gamut of an output image compared with that in a normal mode.SOLUTION: An engine control unit 202 of an image forming apparatus 100 has, as an image forming mode, a normal mode (first mode) and an expanded color gamut mode (second mode) for expanding a color gamut of an image formed on a recording material compared with that in the normal mode. The engine control unit 202 further has, as the expanded color gamut mode, expanded color gamut modes for a single color and multiple colors (second single color mode and second multicolor mode), which correspond to formation of a single-color image and a multicolor image, respectively. The engine control unit 202 is configured to cause only an image forming unit 30K of a plurality of image forming units 30 to form a toner image in the K color in the expanded color gamut mode for a single color (second single color mode).SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an electrophotographic image forming apparatus.

Background Art

[0002] In an electrophotographic image forming apparatus such as a laser beam printer, there is a color gamut as one of the quality indexes of an output image. The color gamut represents the range of colors (color reproduction range) that the image forming apparatus can reproduce. Patent Document 1 discloses an image forming apparatus capable of executing image formation in a mode (wide color gamut mode) for expanding the color reproduction range of an image formed on a recording material as an electrophotographic image forming apparatus. In the wide color gamut mode of Patent Document 1, the peripheral speed of the developing roller is set faster than the peripheral speed (rotation speed) of the photosensitive drum, and the amount of toner per unit area carried on the photosensitive drum is increased, thereby expanding the color reproduction range.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, in an image forming apparatus having a wide color gamut mode, usually, even when forming a single-color image (for example, a black single-color image) in the wide color gamut mode, the same image forming conditions as when forming a multi-color image (for example, a full-color image) are used. However, using such image forming conditions when forming a single-color image in the wide color gamut mode does not necessarily meet the user's needs. For example, it may be required to apply image forming conditions suitable for forming a black single-color image to output an image having higher quality and density.

[0005] The present invention aims to provide a technique for obtaining output images with higher quality and density when outputting a monochrome image in an image formation mode that expands the color gamut of the output image compared to normal. [Means for solving the problem]

[0006] An image forming apparatus according to one aspect of the present invention comprises: a first image forming unit having a first image carrier and a first developing means for forming a toner image by developing an electrostatic latent image formed on the first image carrier; a second image forming unit having a second image carrier and a second developing means for forming a toner image by developing an electrostatic latent image formed on the second image carrier; and a control means for controlling the first image forming unit and the second image forming unit, wherein the control means controls to enable the execution of an image forming mode for forming an image on a recording material, which includes a first mode and a second mode that expands the color gamut of the image formed on the recording material compared to the first mode, and the second mode is characterized by comprising a second monochromatic mode in which image formation is performed only by the first image forming unit and a second multicolor mode in which image formation is performed by both the first and second image forming units. [Effects of the Invention]

[0007] According to the present invention, when outputting a monochrome image in an image formation mode that expands the color gamut of the output image compared to normal, it becomes possible to obtain an output image with higher quality and density. [Brief explanation of the drawing]

[0008] [Figure 1] A cross-sectional view showing an example of the hardware configuration of an image forming apparatus. [Figure 2] Block diagram showing a schematic control configuration example of an image forming apparatus. [Figure 3] A schematic diagram showing an example of the drive configuration of the image forming unit and the intermediate transfer belt. [Figure 4] A schematic diagram showing an example of a voltage application configuration in an image forming apparatus. [Figure 5] This figure shows examples of the driving conditions for the image forming unit in each image forming mode. [Figure 6] A flowchart illustrating an example of the image formation process. [Modes for carrying out the invention]

[0009] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0010] [Embodiment 1] As an example of an image forming apparatus, an electrophotographic laser beam printer will be described. However, the image forming apparatus is not limited to laser beam printers, but may also be other types of image forming apparatus such as printers, copiers, facsimile machines, microfilm reader printers, and recording machines.

[0011] <Configuration of an image forming apparatus> Embodiment 1 describes an image forming apparatus having a normal mode (first mode) and a wide color gamut mode (second mode) that expands the color gamut of the image formed on the recording material compared to the normal mode, as image forming modes for forming an image on the recording material. The image forming apparatus according to this embodiment has a wide color gamut mode for monochrome (second monochrome mode) corresponding to the formation of a monochrome image, and a wide color gamut mode for multicolor (second multicolor mode) corresponding to the formation of a multicolor image, as wide color gamut modes. In the wide color gamut mode for monochrome (second monochrome mode), the image forming apparatus is configured to form a toner image only in the first image forming unit corresponding to the first color (K color) among a plurality of image forming units that each form toner images of different colors. An example of such an image forming apparatus will be described in detail below.

[0012] Figure 1 is a cross-sectional view showing an example of the hardware configuration of an image forming apparatus 100 according to Embodiment 1. The image forming apparatus 100 is configured to form an image on a recording material using an electrophotographic method. The image forming apparatus 100 is also configured as an in-line laser beam printer employing an intermediate transfer method, and is capable of forming full-color images. The image forming apparatus 100 uses an intermediate transfer belt as an intermediate transfer body. Alternatively, the image forming apparatus may be configured as a laser beam printer employing a direct transfer method that transfers the toner image from the photosensitive drum to the recording material without using an intermediate transfer body (intermediate transfer belt). The recording material to which the image is formed may be referred to as a sheet, recording paper, recording medium, paper, transfer material, transfer paper, etc.

[0013] The image forming apparatus 100 includes multiple image forming units 30Y, 30M, 30C, and 30K, each forming an image (toner image) of a different color. The image forming units 30Y, 30M, 30C, and 30K are arranged in a line from upstream to downstream in the moving direction R1 of the surface of the intermediate transfer belt 8 that carries the toner image. The image forming units 30Y, 30M, 30C, and 30K each form an image using yellow, magenta, cyan, and black toners, respectively. The image forming units 30Y, 30M, 30C, and 30K have the same configuration. The letters Y, M, C, and K assigned to the reference numbers indicate the toner colors: yellow (Y), magenta (M), cyan (C), and black (K), and are omitted when explaining matters common to each color.

[0014] The image forming unit 30 includes a process cartridge 40 that is detachable from the image forming apparatus 100. The process cartridge 40 includes a photosensitive drum 1, a charging roller 2, a developing unit 20 including a developing roller 3, a cleaning blade 4, and a waste toner container 24. The developing unit 20 includes the developing roller 3. The image forming unit 30 further includes a primary transfer roller 6 and a laser unit 7. The primary transfer roller 6 is positioned inside the intermediate transfer belt 8, facing the photosensitive drum 1 via the intermediate transfer belt 8. The laser unit 7 is positioned below the process cartridge 40.

[0015] The photosensitive drum 1 is an image carrier that carries an electrostatic latent image and a toner image formed by developing the electrostatic latent image with toner. The photosensitive drum 1 is driven to rotate at a predetermined peripheral speed (peripheral velocity) in the direction of the arrow shown in FIG. 1 (clockwise direction).

[0016] The charging roller 2 uniformly charges the surface of the photosensitive drum 1 by applying a predetermined charging voltage from a voltage application unit (voltage application units 401 and 402 in FIG. 4). The laser unit 7 forms an electrostatic latent image on the surface of the photosensitive drum 1 by exposing the photosensitive drum 1 based on an image signal (image data). The developing roller 3 forms a toner image on the photosensitive drum 1 by developing the electrostatic latent image formed on the photosensitive drum 1 using a developer (toner) supplied from a toner container in the developing unit 20. Specifically, a predetermined developing voltage is applied to the developing roller 3 from a voltage application unit (voltage application unit 411 in FIG. 4), causing the toner on the developing roller 3 to move and adhere to the photosensitive drum 1. As a result, the electrostatic latent image on the photosensitive drum 1 is developed into a toner image.

[0017] In the present embodiment, the photosensitive drum 1 is an example of an image carrier (photoconductor), and the developing roller 3 is an example of developing means for developing an electrostatic latent image formed on the image carrier with toner to form a toner image on the image carrier. Also, the primary transfer roller 6 is an example of primary transfer means for transferring the toner image formed on the corresponding image carrier to the intermediate transfer member.

[0018] The image forming apparatus 100 includes an endless belt-shaped intermediate transfer belt 8 having flexibility, which is disposed at a position facing each photosensitive drum 1. The intermediate transfer belt 8 is stretched between a driving roller 9 for rotating the intermediate transfer belt 8 and a driven roller 10 for applying an appropriate tension to the intermediate transfer belt 8. The intermediate transfer belt 8 is rotationally driven in the direction of arrow R1 (counterclockwise direction) while contacting the photosensitive drum 1 by transmitting a driving force to the driving roller 9 by a driving motor (not shown). The intermediate transfer belt 8 moves at a speed corresponding to the peripheral speed of the photosensitive drum 1.

[0019] Inside the intermediate transfer belt 8, a primary transfer roller 6 is arranged as a transfer member for transferring the toner image from the photosensitive drum 1 to the intermediate transfer belt 8. By applying a primary transfer voltage to the primary transfer roller 6 by a voltage application unit (voltage application units 421 and 422 in FIG. 4), the toner image formed on the photosensitive drum 1 is transferred onto the intermediate transfer belt 8 at the transfer position (primary transfer unit). For example, by applying a positive voltage to the intermediate transfer belt 8 via the primary transfer roller 6, a negatively charged toner image is transferred from the photosensitive drum 1 onto the intermediate transfer belt 8. At that time, the four-color toner images of yellow, magenta, cyan, and black, which are respectively formed on the photosensitive drums 1Y, 1M, 1C, and 1K, are sequentially superimposed and transferred onto the intermediate transfer belt 8.

[0020] The toner image formed on the intermediate transfer belt 8 is conveyed to a secondary transfer unit 17, which is a contact portion between the intermediate transfer belt 8 and the secondary transfer roller 11, in accordance with the rotation of the intermediate transfer belt 8. In the secondary transfer unit 17, the toner image on the intermediate transfer belt 8 is transferred onto the recording material P that has been conveyed through the conveyance path from the recording material cassette 13. Thus, the intermediate transfer belt 8 of the present embodiment is an example of an intermediate transfer body (transfer target body) onto which the toner images formed on the image carriers (photosensitive drums 1) of the plurality of image forming units 30 are superimposed and transferred, and the toner image transferred onto the intermediate transfer body is transferred onto the recording material.

[0021] The recording material cassette 13 stores the recording material P in a stacked state. The feeding and transporting device 12 has a paper feed roller 14 and a transport roller pair 15. The paper feed roller 14 is configured to feed the recording material P from the recording material cassette 13 to the transport path. The transport roller pair 15 is configured to transport the recording material P fed to the transport path toward the register roller pair 16. The recording material P transported to the register roller pair 16 is transported by the register roller pair 16 to the secondary transfer section 17 at a predetermined control timing at a speed corresponding to the rotation speed of the intermediate transfer belt 8. A secondary transfer voltage is applied to the secondary transfer roller 11 by the voltage application unit (voltage application unit 431 in Figure 4), and the toner image on the intermediate transfer belt 8 is transferred onto the recording material P in the secondary transfer section 17. For example, if a positive voltage is applied to the recording material P via the secondary transfer roller 11, a negative toner image is transferred from the intermediate transfer belt 8 onto the recording material P.

[0022] The recording material P onto which the toner image has been transferred in the secondary transfer section 17 is transported to the fixing unit 18. The fixing unit 18 comprises a fixing roller 18a, which is a heating element, and a pressure roller 18b, which is a pressing element, positioned opposite the fixing roller 18a. The fixing unit 18 performs a fixing process in which the transferred toner image is fixed to the recording material P by applying heat and pressure to the recording material P as it passes through the contact area between the fixing roller 18a and the pressure roller 18b. The fixing process is performed on the recording material P, which is then discharged onto the discharge tray 50 by the discharge roller pair 19.

[0023] After the toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 8, any toner remaining on the surface of the photosensitive drum 1 is removed by the cleaning blade 4. The cleaning blade 4, while in contact with the photosensitive drum 1, collects the toner on the photosensitive drum 1 into the waste toner container 24. In addition, after the toner image is transferred from the intermediate transfer belt 8 to the recording material P, any toner remaining on the surface of the intermediate transfer belt 8, and any paper dust moved from the recording material P to the intermediate transfer belt 8 during the transfer, are removed by the cleaning blade 31. The cleaning blade 31, while in contact with the intermediate transfer belt 8, collects the toner and paper dust on the intermediate transfer belt 8 into the waste toner container 32.

[0024] Figure 2 is a block diagram showing a schematic control configuration example of the image forming apparatus 100. The image forming apparatus 100 includes a control unit 200 that controls the operation of the entire apparatus. The control unit 200 includes a printer control unit 201 and an engine control unit 202.

[0025] The printer control unit 201 communicates with the host computer 211 (external device). When the printer control unit 201 receives a print job from the host computer 211, it expands the print data contained in the print job into image data that can be used for image formation. The printer control unit 201 has the function of performing image processing on the image data received from the host computer 211, such as bitmap conversion of character codes or halftoning of images. The printer control unit 201 transmits the expanded image data to the engine control unit 202.

[0026] The engine control unit 202 communicates with the printer control unit 201, for example, via serial communication, and controls the image forming units 30Y, 30M, 30C, and 30K. When the engine control unit 202 receives image data from the printer control unit 201, it controls the image forming units 30Y, 30M, 30C, and 30K to perform an image forming operation to form an image on the recording material P based on the received image data.

[0027] The engine control unit 202 includes a processor (CPU), ROM, and RAM. The ROM is a non-volatile memory device that stores programs such as control programs for controlling the operation of the image forming apparatus 100. The RAM is a volatile memory device used as a temporary storage area for programs and data, and as a work area for the CPU. The CPU controls the operation of each device (image forming unit 30, etc.) of the image forming apparatus 100 by reading the programs stored in the ROM into the RAM and executing them. Thus, the engine control unit 202 (or control unit 200) in this embodiment is an example of a control means for controlling the first image forming unit and the second image forming unit. In this embodiment, the image forming unit 30K is an example of the first image forming unit, and the image forming units 30M, 30C, and 30K are each examples of the second image forming unit.

[0028] <Drive configuration> Figure 3 is a schematic diagram showing an example of the drive configuration of the image forming unit 30 and the intermediate transfer belt 8 in the image forming apparatus 100 of this embodiment. The image forming apparatus 100 includes drive units 301 to 305. The operation of the drive units 301 to 305 is controlled by the engine control unit 202. Each image forming unit 30's developing unit 20 includes a developing roller 3, a supply roller 21, and an agitation member 22. The agitation member 22 is configured to agitate the toner in the toner container of the developing unit 20 by being driven to rotate. The supply roller 21 is configured to supply the toner in the toner container to the developing roller 3 by being driven to rotate.

[0029] The photosensitive drums 1Y, 1M, and 1C are rotationally driven by the drive unit 301. The drive unit 301 includes a drive motor (first drive source) and a gear train that transmits the driving force from the drive motor. The photosensitive drum 1K is also rotationally driven by the drive unit 302. The drive unit 302 includes a drive motor (second drive source). The drive unit 302 is further configured to rotate (circulate) the intermediate transfer belt 8 by driving a drive roller 9 for the intermediate transfer belt 8.

[0030] The developing rollers 3Y, 3M, 3C, and 3K are rotationally driven by the drive unit 303. The drive unit 302 includes a drive motor (third drive source) and a gear train that transmits the driving force from the drive motor. Although not shown in Figure 3, the drive unit 303 is further configured to rotationally drive the rotation axes of the stirring members 22Y, 22M, 22C, and 22K via another gear train.

[0031] The image forming apparatus 100 includes a drive unit 304 for switching the state of each developing roller 3 between a contact state in contact with the corresponding photosensitive drum 1 and a separated state in which it is separated from the photosensitive drum 1. The drive unit 304 includes a drive motor (fourth drive source), a gear train and a clutch that transmit the driving force from the drive motor. The engine control unit 202 can individually switch each developing roller 3 between the contact state and the separated state in contact with the corresponding photosensitive drum 1 using the drive unit 304 (developing contact / separation mechanism).

[0032] The image forming apparatus 100 includes a drive unit 305 for switching the state of each primary transfer roller 6 between a contact state, in which it is in contact with the corresponding photosensitive drum 1 via an intermediate transfer belt 8, and a separated state, in which it is separated from the photosensitive drum 1. The drive unit 305 includes a drive motor (fifth drive source), a gear train and a clutch that transmit the driving force from the drive motor. The engine control unit 202 can individually switch each primary transfer roller 6 between the contact state and the separated state with respect to the corresponding photosensitive drum 1 using the drive unit 305. Although not shown in Figure 3, the drive unit 305 is further configured to drive the fixing roller 18a.

[0033] When the photosensitive drum 1 and the developing roller 3 are driven by the same drive source (drive motor) via a gear train, the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3 is fixed to a value determined by the gear ratio of the corresponding gears. In contrast, the image forming apparatus 100 of this embodiment is configured such that the photosensitive drum 1 and the developing roller 3 are driven by different drive sources (drive motors) in each image forming unit 30. As a result, the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3 in each image forming unit is variable.

[0034] <Voltage Application Configuration> Figure 4 is a schematic diagram showing an example of the voltage application configuration in the image forming apparatus 100 of this embodiment. As shown in Figure 4, the image forming apparatus 100 includes voltage application units 401, 402, 411 (411Y, 411M, 411C, 411K), 421, 422, and 431, and each voltage application unit includes a high-voltage power supply. The voltage application (power supply) from each voltage application unit in the image forming apparatus 100 is controlled by the engine control unit 202.

[0035] Voltage application units 401 and 402 are configured to generate a charging voltage using a high-voltage power supply and apply the charging voltage to the charging roller 2. Voltage application unit 401 is provided in common for image forming units 30Y, 30M, and 30C and is configured to apply the charging voltage to the respective charging rollers 2Y, 2M, and 2C. Voltage application unit 402 is provided for the image forming unit 30K and is configured to apply the charging voltage to the charging roller 2K of the image forming unit 30K.

[0036] The voltage application units 411Y, 411M, 411C, and 411K are configured to generate a developing voltage using a high-voltage power supply and apply the developing voltage to the developing roller 3. The voltage application units 411Y, 411M, 411C, and 411K are provided for the image forming units 30Y, 30M, 30C, and 30K, respectively, and are configured to apply the developing voltage to the respective developing rollers 3Y, 3M, 3C, and 3K.

[0037] Voltage application units 421 and 422 are configured to generate a primary transfer voltage using a high-voltage power supply and apply the primary transfer voltage to the primary transfer roller 6. Voltage application unit 421 is provided in common for image forming units 30Y, 30M, and 30C and is configured to apply the primary transfer voltage to the respective primary transfer rollers 6Y, 6M, and 6C. Voltage application unit 422 is provided for image forming unit 30K and is configured to apply the primary transfer voltage to the primary transfer roller 6K of image forming unit 30K. Note that separate power supplies may be provided for each image forming unit for applying the primary transfer voltage, or a common power supply may be provided for all image forming units.

[0038] The voltage application unit 431 is configured to generate a secondary transfer voltage using a high-voltage power supply and apply the secondary transfer voltage to the secondary transfer roller 11. Alternatively, the image forming apparatus 100 may be configured so that, without the above-mentioned voltage application units 421 and 422, the voltage output from the voltage application unit 431 is applied to each primary transfer roller 6 as a primary transfer voltage via the intermediate transfer belt 8.

[0039] <Normal mode and wide color gamut mode> As described above, the image forming apparatus 100 of this embodiment has a drive configuration that allows the photosensitive drum 1 and the developing roller 3 to be driven at individual rotation speeds for each image forming unit. Utilizing this drive configuration, the image forming apparatus 100 (engine control unit 202) has, as image forming modes, a normal mode (first mode) and a wide color gamut mode (second mode) that expands the color gamut of the image formed on the recording material (output image) compared to the normal mode. The color gamut represents the range of colors that the image forming apparatus can reproduce when forming an image on the recording material (color reproduction range). The normal mode is an image forming mode for obtaining normal density as the density of the output image. Furthermore, as will be described later, the image forming apparatus 100 of this embodiment has monochrome and multi-color (full-color) modes for both the normal mode and the wide color gamut mode.

[0040] The wide color gamut mode has different image formation conditions than the normal mode. In the wide color gamut mode, the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3 is changed from the peripheral speed ratio in the normal mode. Here, the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3 is the ratio of the peripheral speed (rotational speed) of the developing roller 3 to the peripheral speed (rotational speed) of the photosensitive drum 1. Specifically, in the wide color gamut mode, the engine control unit 202 sets the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3 for each image formation unit to be higher than the peripheral speed ratio in the normal mode. This operation, in which the photosensitive drum 1 and the developing roller 3 rotate at a higher peripheral speed ratio than in the normal mode, corresponds to an operation that increases the amount of toner per unit area supplied to the photosensitive drum 1 from the developing roller 3 (toner supply capacity) compared to the normal mode.

[0041] In wide-gamut mode, the development contrast may also be changed from the development contrast in normal mode. Here, development contrast is the potential difference (absolute value of the difference) between the potential of the exposed area (image area) on the surface of the photosensitive drum 1 (bright area potential) and the potential of the development roller 3. Specifically, in wide-gamut mode, the engine control unit 202 sets the development contrast for developing the electrostatic latent image formed on the photosensitive drum 1 with toner to be greater than the development contrast in normal mode for each image forming unit. This ensures that, for example, the maximum amount of toner that can adhere to the development roller 3 is used to develop the electrostatic latent image. In this way, increasing the development contrast compared to normal mode is equivalent to increasing the amount of toner per unit area supplied to the photosensitive drum 1 from the development roller 3 (toner supply capacity) compared to normal mode.

[0042] As described above, by increasing the amount of toner per unit area supplied from the developing roller 3 to the photosensitive drum 1, a wide color gamut mode can be realized that expands the color range of the image (output image) formed on the recording material compared to the normal mode. Table 1 shows examples of setting image formation conditions in the normal mode and the wide color gamut mode. Table 1(A) shows examples of setting various process speeds and the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3, and Table 1(B) shows examples of setting various potentials and development contrasts.

[0043] [Table 1]

[0044] In the example shown in Table 1(A), the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3 in wide-gamut mode is set to 1.28 times (≒115 / 90) the peripheral speed ratio in normal mode. By making the peripheral speed ratio in wide-gamut mode higher than that in normal mode, the amount of toner supplied per unit time from the developing roller 3 to the photosensitive drum 1 can be increased compared to normal mode. Note that the method of changing the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3 is not limited to this. For example, a method may be used in which the peripheral speed ratio is changed by fixing the linear speed of the photosensitive drum 1 and increasing the linear speed of the developing roller 3.

[0045] In the example shown in Table 1(B), the development contrast in wide-gamut mode is set to be greater than that in normal mode. This setting is intended to allow the maximum amount of toner that can adhere to the development roller 3 to be used for developing the electrostatic latent image. Specifically, in normal mode, the potential of the charging roller 2 is set to V0 = -1100 [V], the dark area potential (potential of the non-image area) on the photosensitive drum 1 after charging is set to Vd = -550 [V], the bright area potential (potential of the image area) is set to Vl = -130 [V], and the potential of the development roller 3 is set to Vdev = -400 [V]. As a result, the development contrast (=|Vdev-Vl|) is 270 [V]. On the other hand, in wide-gamut mode, the settings are set to V0 = -1250 [V], Vd = -700 [V], Vl = -150 [V], and Vdev = -450 [V]. As a result, the development contrast is 400 [V], which is greater than in normal mode.

[0046] Furthermore, in wide-gamut mode, the potential difference between the dark area potential Vd and the bright area potential Vl is set to be larger than in normal mode in order to improve the reproducibility of fine lines. That is, in wide-gamut mode, the engine control unit 202 sets the potential difference between the dark area potential Vd and the bright area potential Vl in the photosensitive drum 1 where the electrostatic latent image is formed to be larger than the potential difference in normal mode for each image forming unit. This makes it possible to improve the reproducibility of fine lines in the output image in wide-gamut mode. In the image forming apparatus 100 of this embodiment, it is possible to prepare multiple image forming modes in which the potential difference of the electrostatic latent image (i.e., the potential difference between the bright area potential and the dark area potential) is different for each mode.

[0047] <Wide color gamut mode for single colors> Next, we will describe the case in which a monochrome image (e.g., a monochrome image of black (K color)) is formed on a recording material in a wide color gamut mode in the image forming apparatus 100. As will be described below, in addition to the wide color gamut mode (wide color gamut mode for multicolor) described above, the image forming apparatus 100 of this embodiment has a wide color gamut mode (wide color gamut mode for monochrome) that is suitable for forming a monochrome image on a recording material (i.e., suitable for forming a monochrome image).

[0048] As described above, in an image forming apparatus with a wide color gamut mode, the same image forming conditions are usually used when forming a K-monochromatic image in wide color gamut mode as when forming a multi-color image such as a full-color image. That is, in each of the image forming units 30Y, 30M, 30C, and 30K, image forming conditions (transfer settings, etc.) corresponding to the amount of toner that expands the color gamut of the image formed on the recording material are used.

[0049] However, using such image formation conditions when forming a monochrome image in wide color gamut mode does not always meet user needs. For example, there is a need to be able to output images with higher quality and density by applying image formation conditions suitable for (corresponding to) the formation of a monochrome black image. Thus, when forming a monochrome image in wide color gamut mode, there are problems such as the following:

[0050] For example, in image forming apparatuses that typically employ an intermediate transfer method, the transfer settings are configured to prevent the toner image transferred to the intermediate transfer belt in the upstream image forming section from being re-transferred to the photosensitive drum in the downstream image forming section, in the direction of movement of the intermediate transfer belt. Therefore, it is difficult to configure a unique transfer setting only for the image forming section corresponding to the K color to generate an electric field of appropriate strength in the primary transfer section when forming a K-monochromatic image. - An excessively strong electric field may be generated in the secondary transfer area, which can cause the charge of the toner image to reverse, leading to a decrease in transfer efficiency. - In the fuser unit, if excessive heat is supplied by the heating element, toner offset occurs, where a portion of the toner image adheres to the heating element, which can lead to a decrease in gloss or density in the output image. - When using a wide color gamut mode that supports the formation of multi-color images, and forming an image with a low toner coverage ratio relative to the entire output image as a K-monochromatic image, it is not possible to obtain a sharp monochromatic image (monochrome image). This is due to the effect of color-shifting toner, which occurs because primary transfer of the toner image from the photosensitive drum 1 is possible in multiple image forming units. - In the image forming unit 30 corresponding to each toner color other than K, the developing unit 20 (developing roller 3) is driven even though no electrostatic latent image development using toner is performed. This leads to a shortened lifespan for the developing units corresponding to each toner color other than K.

[0051] Therefore, in order to address one or more of the above-mentioned problems, the image forming apparatus 100 of this embodiment has a wide color gamut mode for monochrome (second monochrome mode) that is suitable for forming monochrome images. In the wide color gamut mode for monochrome, the engine control unit 202 causes only the image forming unit 30K (first image forming unit) corresponding to the K color (first color) among the multiple image forming units 30 to perform image formation. In this embodiment, when forming a monochrome image with a wider color gamut than usual (a K monochrome image), using the wide color gamut mode for monochrome makes it possible to form an image according to image forming conditions corresponding to the formation of a monochrome image. This makes it possible to output a monochrome image of higher quality and density.

[0052] Specifically, the engine control unit 202 controls the image forming unit 30 according to the driving conditions shown in Figure 5(A). In the wide color gamut mode for single color, the engine control unit 202 controls the drive unit 304 to bring the developing roller 3K into contact with the photosensitive drum 1K, while moving the developing rollers 3Y, 3M, and 3C away from the photosensitive drums 1Y, 1M, and 1C, respectively. In this state, the engine control unit 202 controls the image forming operation of the image forming unit 30 to form a single-color K image using the image forming unit 30K and transfer it to the recording material P. Furthermore, in the wide color gamut mode for single color, the engine control unit 202 controls the drive unit 305 to bring the transfer roller 6K into contact with the photosensitive drum 1K via the intermediate transfer belt 8, while moving the transfer rollers 6Y, 6M, and 6C away from the photosensitive drums 1Y, 1M, and 1C, respectively.

[0053] In this way, in the wide color gamut mode for monochrome, the engine control unit 202 brings the developing roller 3K of the image forming unit 30K into contact with the corresponding photosensitive drum 1K, and separates the developing roller 3 of the image forming units 30 other than the image forming unit 30K from the corresponding photosensitive drum 1. Furthermore, in the wide color gamut mode for monochrome, the engine control unit 202 brings the primary transfer roller 6K of the image forming unit 30K into contact with the photosensitive drum 1K via the intermediate transfer belt 8, and brings the developing roller 3 of the image forming units 30 other than the image forming unit 30K into contact with the photosensitive drum 1K. This makes it possible to set image forming conditions (transfer settings, etc.) for the formation of a monochrome image (a monochrome K image), enabling the output of images of higher quality and density.

[0054] As shown in Figure 5(A), the image forming apparatus 100 may also have a normal mode for monochrome and a normal mode for multicolor. In this case, the engine control unit 202 controls the contact / separation state of the developing roller 3 and the transfer roller 6 with respect to the photosensitive drum 1 in the monochrome normal mode, similar to the wide-gamut multicolor mode. This makes it possible to set image forming conditions (transfer settings, etc.) for the formation of monochrome images (K monochrome images) even in the normal mode.

[0055] <Transfer current setting> In the image forming apparatus 100 of this embodiment, the engine control unit 202 controls the image forming unit 30K (first image forming unit) to form an image in the wide color gamut mode for monochromatic images (second monochromatic mode) according to image forming conditions corresponding to the formation of a monochromatic image. This makes it possible to output an image with higher quality and density when forming a monochromatic image in the wide color gamut mode. Here, with reference to Table 2 below, the transfer current setting as an example of setting the image forming conditions in the image forming apparatus 100 of this embodiment will be further explained. Table 2 shows examples of setting the transfer conditions (target transfer current) in each image forming mode.

[0056] [Table 2]

[0057] The engine control unit 202 adjusts the primary transfer voltage applied to each primary transfer roller 6 from the voltage application units 421 and 422 so that the value of the current flowing through the primary transfer unit (primary transfer current) reaches the target value when not forming an image (for example, during the pre-rotation operation for each print job). During subsequent image formation, the adjusted primary transfer voltage is applied to each primary transfer roller 6 from the voltage application units 421 and 422.

[0058] Specifically, the engine control unit 202 detects the current flowing between the photosensitive drum 1, which is uniformly charged to the dark area potential Vd, and the primary transfer rollers 6, as the primary transfer current, when voltage is applied to each primary transfer roller 6 from the voltage application units 421 and 422. The primary transfer current is detected using a current detection circuit (not shown). The engine control unit 202 performs constant current control using the current detection circuit and target values ​​of the primary transfer current corresponding to the image formation mode, as exemplified in Table 2. That is, the engine control unit 202 adjusts the primary transfer voltage so that the value of the primary transfer current detected using the current detection circuit remains constant at the target value of the primary transfer current corresponding to the image formation mode.

[0059] Furthermore, during non-image formation, the engine control unit 202 adjusts the secondary transfer voltage applied from the voltage application unit 431 to the secondary transfer roller 11 so that the value of the current flowing through the secondary transfer section (secondary transfer current) reaches the target value. During subsequent image formation, the adjusted secondary transfer voltage is applied from the voltage application unit 431 to the secondary transfer roller 11.

[0060] Specifically, the engine control unit 202 detects the current flowing between the drive roller 9 and the secondary transfer roller 11 via the intermediate transfer belt 8 as the secondary transfer current when a voltage is applied from the voltage application unit 431 to the secondary transfer roller 11 while the recording material is not passing through the secondary transfer section. The secondary transfer current is detected using a current detection circuit (not shown). The engine control unit 202 performs constant current control using the current detection circuit and target values ​​of the secondary transfer current corresponding to the image formation mode, as exemplified in Table 2. That is, the engine control unit 202 adjusts the secondary transfer voltage so that the value of the secondary transfer current detected using the current detection circuit remains constant at the target value of the secondary transfer current corresponding to the image formation mode.

[0061] In the example settings in Table 2, the target value of the primary transfer current in the wide-gamut mode for single-color toners is set higher than the target value of the primary transfer current in the wide-gamut mode for multi-color toners. In the wide-gamut mode for single-color toners, the primary transfer rollers 6 corresponding to each toner color other than K are separated from the corresponding photosensitive drums 1. Therefore, when setting the target value of the primary transfer current for the primary transfer of the single-color (K) toner image, it is not necessary to consider suppressing the re-transfer of the toner image to the photosensitive drums 1 corresponding to each toner color other than K. Accordingly, in the example settings in Table 2, the target value of the primary transfer current in the wide-gamut mode for single-color toners is set to a higher target value suitable for forming a solid K image.

[0062] On the other hand, in the example settings in Table 2, the target value of the secondary transfer current in the wide-gamut mode for single colors is set lower than the target value of the secondary transfer current in the wide-gamut mode for multi-colors. In the wide-gamut mode for single colors, it is sufficient for the secondary transfer unit to transfer a single-color toner image (with an increased amount of toner to expand the color gamut) to the recording material P. For this reason, in the wide-gamut mode for single colors, the target value of the secondary transfer current is set lower than the target value for transferring multi-color toner images to the recording material in the wide-gamut mode for multi-colors.

[0063] In the example settings in Table 1, the ratio of the process speed in wide-gamut mode to the process speed in normal mode is set to approximately 1 / 3 for the intermediate transfer belt 8 and recording material P. Nevertheless, in the example settings in Table 2, the ratio of the target value of the primary transfer current in wide-gamut mode to the target value of the primary transfer current in normal mode is set to be greater than the ratio of the process speed for both single-color and multi-color modes. The same applies to the target value of the secondary transfer current. This is because in wide-gamut mode, a larger amount of toner than in normal mode, carried on the photosensitive drum 1 or intermediate transfer belt 8, is required to be transferred to the transfer target (intermediate transfer belt 8 or recording material P) at each transfer section.

[0064] The reason for this is explained as follows: Equation (1) below represents the transfer current It required to transfer a toner image having a certain amount of charge per unit area, weight M, and width (image width) W onto a transfer target at a predetermined process speed PS. It = Q / M × M / S × PS × W =Q / S × PS × W (1) Here, Q is the total charge of the toner image, Q / M is the charge per unit weight of toner, M / S is the toner weight per unit area, and Q / S is the charge of toner per unit area. In wide-gamut mode, as described above, the amount of toner to be transferred to the transfer target increases compared to normal mode. In accordance with this increase in toner amount, the total charge Q increases. Therefore, in wide-gamut mode, even if the process speed is set to about 1 / 3 of the process speed in normal mode, a transfer current greater than about 1 / 3 of the transfer current in primary normal mode is required for the transfer current in the transfer unit and secondary transfer unit.

[0065] <Processing Procedure> Figure 6 is a flowchart showing an example of the image forming process procedure performed in the image forming apparatus 100 of this embodiment. Each step in Figure 6 is performed by the control unit 200 (printer control unit 201 and engine control unit 202).

[0066] First, in S601, when the printer control unit 201 receives a print job from the host computer 211 (external device), it expands the print data contained in the print job into image data usable for image formation (input image from the print job). The host computer 211 can specify the image formation mode, etc., using the printer driver. The printer control unit 201 sends the expanded image data and the execution instruction for image formation to the engine control unit 202. The execution instruction includes setting information such as the image formation mode specified in the print job.

[0067] Next, in S602, the engine control unit 202 determines the image formation mode to be used for forming an image on the recording material based on the image formation mode specification and input image in the print job received by the printer control unit 201, and proceeds to S603. For example, if the received print job specifies a wide color gamut mode as the image formation mode and the input image is a monochrome image, the engine control unit 202 decides to use a wide color gamut mode for monochrome (second monochrome mode). In this case, the engine control unit 202 controls the multiple image formation units 30 to form an image on the recording material using the wide color gamut mode for monochrome. Also, if the received print job specifies a wide color gamut mode as the image formation mode and the input image is a multicolor image, the engine control unit 202 decides to use a wide color gamut mode for multicolor (second multicolor mode). In this case, the engine control unit 202 controls the multiple image formation units 30 to form an image on the recording material using the wide color gamut mode for multicolor.

[0068] In S603, the engine control unit 202 determines the image formation conditions corresponding to the determined image formation mode. For example, when using the wide color gamut mode for monochrome, the engine control unit 202 determines the image formation conditions corresponding to the formation of a monochrome image. The image formation conditions may include the peripheral speed ratio between the photosensitive drum 1 and the developing roller 3, the development contrast, and the target transfer current values ​​in the primary and secondary transfer sections, as described above with reference to Tables 1 and 2. The image formation conditions may further include the driving conditions of each drive unit (Figure 3) for the image formation section 30, as described above with reference to Figure 5(A).

[0069] Next, in S604, the engine control unit 202 controls the contact / separation state of the developing roller 3 and the transfer roller 6 with respect to the photosensitive drum 1 for each image forming unit, according to the image forming conditions determined in S603. When using the wide color gamut mode for single color, the engine control unit 202 brings the developing roller 3K into contact with the corresponding photosensitive drum 1K, and separates the developing rollers 3Y, 3M, and 3K from the corresponding photosensitive drums 1Y, 1M, and 1K, as shown in Figure 5(A). The engine control unit 202 also brings the primary transfer roller 6K into contact with the corresponding photosensitive drum 1K via the intermediate transfer belt 8, and separates the primary transfer rollers 6Y, 6M, and 6K from the corresponding photosensitive drums 1Y, 1M, and 1K.

[0070] Furthermore, in S605, the engine control unit 202 adjusts the primary transfer voltage output from the voltage application units 421 and 422 and the secondary transfer voltage output from the voltage application unit 431 based on the target transfer current values ​​in the primary and secondary transfer units determined in S603. Then, in S606, the engine control unit 202 starts image formation based on the print job and completes the processing according to the procedure in Figure 6.

[0071] As described above, in the image forming apparatus 100 of this embodiment, the engine control unit 202 controls the image forming mode to enable the execution of a normal mode (first mode) and a wide color gamut mode (second mode) which expands the color gamut of the image formed on the recording material compared to the normal mode. The wide color gamut mode consists of a wide color gamut mode for monochrome (second monochrome mode) and a wide color gamut mode for multicolor (second multicolor mode), corresponding to the formation of monochrome images and multicolor images, respectively. The wide color gamut mode for monochrome (second monochrome mode) is a mode in which image formation is performed only by the first image forming unit (image forming unit 30K). The wide color gamut mode for multicolor (second multicolor mode) is a mode in which image formation is performed by the first image forming unit and the second image forming unit (image forming units 30Y, 30M, 30C). In the wide color gamut mode for single color, the engine control unit 202 is configured to not use any of the multiple image forming units 30 other than the image forming unit 30K corresponding to the K color (first color), and to cause the image forming unit 30K to form a K color toner image.

[0072] This makes it possible to form a monochrome image in accordance with image formation conditions corresponding to the formation of a monochrome image, even when forming a monochrome image in wide color gamut mode. Therefore, according to this embodiment, in an image forming apparatus having a wide color gamut mode, it becomes possible to output a monochrome image of higher quality and density when outputting a monochrome image in wide color gamut mode.

[0073] [Embodiment 2] Embodiment 2 describes another example of the wide color gamut mode for monochromatic toners (second monochromatic mode) described in Embodiment 1. In the wide color gamut mode for monochromatic toners in this embodiment, image formation is performed with not only the developer roller 3K corresponding to the K color, but also the developer rollers 3Y, 3M, and 3C corresponding to toner colors other than K, in contact with the corresponding photosensitive drums 1Y, 1M, and 1C, respectively. Alternatively, image formation is performed with not only the primary transfer roller 6K corresponding to the K color, but also the primary transfer rollers 6Y, 6M, and 6C corresponding to toner colors other than K, in contact with the photosensitive drums 1Y, 1M, and 1C via the intermediate transfer belt 8. In the following, the parts common to Embodiment 1 will be omitted from the explanation, and the parts that differ from Embodiment 1 will be mainly described.

[0074] When forming an image with a high toner coverage ratio relative to the entire output image formed based on the input image, as a K-monochromatic image, the majority of the recording material's background is usually obscured by the K-color toner, which has the lowest brightness among the multiple toner colors. In this case, the effect of color cast toner, which occurs because primary transfer of the toner image from the photosensitive drum 1 is possible in multiple image forming units, becomes relatively small.

[0075] On the other hand, the slipperiness between the recording material and the toner increases when the toner is transferred to the recording material. Depending on the image pattern of the output, blurring and banding (streaks of light and dark) are more likely to occur in the transferred toner image. In the wide color gamut mode for single color in Embodiment 1, the amount of toner supplied to the photosensitive drum 1K increases compared to the normal mode, so the aforementioned slipperiness may increase even further. As a result, blurring and banding may occur more easily in the transferred toner image. Examples of when such phenomena become apparent include blurring of the toner image to be transferred next on the intermediate transfer belt 8, and development blurring on the photosensitive drum 1, which occurs when the rear end of the recording material P leaves the secondary transfer roller 11 on the transport path.

[0076] Furthermore, the image forming apparatus 100 may receive, for example, a print job from the host computer 211 in which multi-color and monochrome images are mixed as input images. When executing such a print job in wide-gamut mode, it is necessary to switch the contact state and separation state of the developing unit 20 with respect to the photosensitive drum 1 for the three colors other than K, depending on whether a multi-color image is being printed or a monochrome image is being printed. It is also necessary to switch the contact state and separation state of the primary transfer roller 6 with respect to the photosensitive drum 1 for the three colors other than K. Repeating these operations increases the time it takes to complete the print job, reducing the productivity of the image forming apparatus 100.

[0077] Therefore, in this embodiment, in order to address one or more of the above-mentioned problems, the engine control unit 202 has settings 1 and 2, as shown in Figure 5(B), as settings for the driving conditions of each drive unit (Figure 3) in the wide color gamut mode for single color. Specifically, if the print job received from the external device does not meet predetermined conditions, the engine control unit 202 uses the driving conditions of setting 1 in the wide color gamut mode for single color. Setting 1 is the same as the setting for the driving conditions for the wide color gamut mode for single color shown in Figure 5(A). On the other hand, if the print job received from the external device meets predetermined conditions, the engine control unit 202 uses the driving conditions of setting 2 in the wide color gamut mode for single color.

[0078] The predetermined conditions described above include, for example, that the input image from the print job is a monochrome image, and that the toner coverage ratio for the entire output image formed based on the input image exceeds a threshold. Alternatively, the predetermined conditions include that the input image from the print job contains a mixture of monochrome and multicolor images. When these conditions are met, the engine control unit 202 uses setting 2 shown in Figure 5(b) in the wide color gamut mode for monochrome.

[0079] When setting 2 shown in Figure 5(B) is used, the engine control unit 202, in the wide color gamut mode for single color, brings not only the developing roller 3K of the image forming unit 30K, but also the developing rollers 3Y, 3M, and 3C of image forming units other than the image forming unit 30K into contact with the corresponding photosensitive drum 1. Furthermore, the engine control unit 202 brings not only the primary transfer roller 6K of the image forming unit 30K, but also the primary transfer rollers 6Y, 6M, and 6C of image forming units other than the image forming unit 30K into contact with the corresponding photosensitive drum 1 via the intermediate transfer belt 8.

[0080] In this embodiment, the control unit 200 (printer control unit 201 and engine control unit 202) performs image formation processing in the same procedure as in Embodiment 1 (Figure 6). However, when using the wide color gamut mode for single color, the engine control unit 202 controls the contact / separation state of the developing roller 3 and the primary transfer roller 6 in S603 and S604 according to the predetermined conditions as described above, using the drive conditions of setting 2.

[0081] As described above, according to this embodiment, when using the wide color gamut mode for monochrome (second monochrome mode), the wide color gamut mode of setting 2 is used according to predetermined conditions. This can accommodate the increased slipperiness between the recording material and the toner when the toner is transferred to the recording material, and can reduce blurring and banding in the transferred toner image caused by the image pattern of the output target. Furthermore, when multi-color images and monochrome images are mixed as input images for a print job, it becomes possible to output higher quality monochrome images while maintaining the productivity of the image forming apparatus 100.

[0082] Furthermore, various modifications are possible to each of the embodiments described above. For example, in the additional mode, the engine control unit 202 may drive the photosensitive drums 1Y, 1M, and 1C to rotate at a different speed than the photosensitive drum 1K in order to obtain a better braking effect (for suppressing rotational unevenness of the photosensitive drum 1 and reducing banding). Also, in the wide color gamut mode for monochrome, the settings for this mode may be adjusted not only for the development settings and transfer settings, but also, for example, for the fixing temperature setting in the fixing unit 18 to a setting suitable for forming a monochrome image.

[0083] The disclosures herein include the following image forming apparatus. (Item 1) An image forming apparatus, A first image forming unit having a first image carrier and a first developing means for forming a toner image by developing an electrostatic latent image formed on the first image carrier, A second image forming unit having a second image carrier and a second developing means for forming a toner image by developing an electrostatic latent image formed on the second image carrier, The system comprises control means for controlling the first image forming unit and the second image forming unit, The control means controls the image formation mode for forming an image on the recording material to be executable as a first mode and a second mode that expands the color gamut of the image formed on the recording material compared to the first mode. The second mode comprises a second monochromatic mode in which image formation is performed only by the first image forming unit, and a second multicolor mode in which image formation is performed by both the first and second image forming units. An image forming apparatus characterized by the following: (Item 2) The control means, in the second monochromatic mode, brings the first developing means into contact with the first image carrier and separates the second developing means from the second image carrier. The image forming apparatus according to item 1, characterized in that it is a picture forming apparatus. (Item 3) An intermediate transfer body on which toner images formed on the first and second image carriers are superimposed and transferred, wherein the toner image transferred to the intermediate transfer body is transferred to a recording material, further comprising the intermediate transfer body, The first image forming unit further includes a first primary transfer means for transferring the toner image formed on the first image carrier to the intermediate transfer body, The second image forming unit further includes a second primary transfer means for transferring the toner image formed on the second image carrier to the intermediate transfer body, In the second monochromatic mode, the control means brings the first primary transfer means into contact with the first image carrier via the intermediate transfer body, and separates the second primary transfer means from the second image carrier. The image forming apparatus according to item 2, characterized in that it is a picture forming apparatus. (Item 4) The control means controls the first and second image forming units to form an image on the recording material in the second monochrome mode if the second mode is specified as the image forming mode in a print job received from an external device, and the input image from the print job is a monochrome image. An image forming apparatus according to any one of items 1 to 3, characterized in that it is an image forming apparatus. (Item 5) The control means further, when a print job received from an external device satisfies predetermined conditions, brings the first and second developing means into contact with the first and second image carriers, respectively, in the second monochromatic mode, and brings the first and second primary transfer means into contact with the first and second image carriers, respectively, via the intermediate transfer body. The image forming apparatus according to item 3, characterized in that it is a picture forming apparatus. (Item 6) The predetermined conditions are that the input image from the print job is a monochrome image, and the toner coverage area ratio for the entire output image formed based on the input image exceeds a threshold. The image forming apparatus according to item 5, characterized in that it is a picture forming apparatus. (Item 7) The aforementioned predetermined condition is that the input image for the print job contains a mixture of monochrome and multicolor images. The image forming apparatus according to item 5, characterized in that it is a picture forming apparatus. (Item 8) The control means controls the first image forming unit to form an image in the second monochromatic mode according to image forming conditions corresponding to the formation of a monochromatic image. An image forming apparatus according to any one of items 1 to 7, characterized in that it is an image forming apparatus. (Item 9) The first image forming unit further includes a first primary transfer means for transferring the toner image formed on the first image carrier to an intermediate transfer body in a primary transfer unit, The second image forming unit further includes a second primary transfer means for transferring the toner image formed on the second image carrier to the intermediate transfer body in a primary transfer unit, The image forming apparatus is The intermediate transfer body is on which the toner images formed on the first and second image carriers are superimposed and transferred, and the toner image transferred to the intermediate transfer body is transferred to a recording material, the intermediate transfer body and A first voltage application means for applying a primary transfer voltage to the first primary transfer means, The system further comprises a second voltage applying means for applying a primary transfer voltage to the second primary transfer means, In the second monochromatic mode, the control means sets the target value of the primary transfer current flowing to the primary transfer unit corresponding to the first image forming unit due to the application of the primary transfer voltage by the first voltage application means to a value higher than the target value of the primary transfer current in the second multicolor mode. The image forming apparatus according to item 8, characterized in that it is a picture forming apparatus. (Item 10) A secondary transfer means for transferring the toner image transferred to the intermediate transfer body to a recording material in a secondary transfer unit, The system further comprises a third voltage application means for applying a secondary transfer voltage to the aforementioned secondary transfer means, In the second monochromatic mode, the control means sets the target value of the secondary transfer current flowing through the secondary transfer section due to the application of the secondary transfer voltage by the third voltage application means to a value lower than the target value of the secondary transfer current in the second multicolor mode. The image forming apparatus according to item 9, characterized in that it is a picture forming apparatus. (Item 11) The control means sets the peripheral speed ratio, which is the ratio of the peripheral speeds of the first and second developing means to the peripheral speeds of the first and second image carriers in the second mode, to be higher than the peripheral speed ratio in the first mode. An image forming apparatus according to any one of items 1 to 10, characterized in that it is an image forming apparatus. (Item 12) The control means sets the development contrast for developing the electrostatic latent images formed on the first and second image carriers with toner in the second mode to be greater than the development contrast in the first mode. An image forming apparatus according to any one of items 1 to 11, characterized by the features described herein. (Item 13) In the second mode, the control means sets the potential difference between the dark area potential and the bright area potential in the first and second image carriers where the electrostatic latent image is formed to be greater than the potential difference in the first mode. An image forming apparatus according to any one of items 1 to 12, characterized in that it is the same as described in item 1 to 12.

[0084] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of symbols]

[0085] 100: Image forming apparatus, 200: Control unit, 201: Printer control unit, 202: Engine control unit, 1: Photosensitive drum, 2: Charging roller, 3: Developing roller, 6: Primary transfer roller, 8: Intermediate transfer belt, 11: Secondary transfer roller, 20: Developing unit, 30: Image forming section

Claims

1. An image forming apparatus, a first image forming section including a first image carrier and a first developing unit that forms a toner image by developing an electrostatic latent image formed on the first image carrier; a second image forming section including a second image carrier and a second developing unit that forms a toner image by developing the electrostatic latent image formed on the second image carrier; a control unit that controls the first image forming unit and the second image forming unit, the control means controls to execute a first mode and a second mode in which a color gamut of the image formed on the recording material is expanded more than that in the first mode as an image forming mode in which an image is formed on the recording material, The second mode includes a second monochromatic mode in which image formation is performed only by the first image forming unit, and a second multicolor mode in which image formation is performed by the first image forming unit and the second image forming unit. An image forming apparatus characterized by:

2. The control unit causes the first developing unit to contact the first image carrier and the second developing unit to separate from the second image carrier in the second monochromatic mode.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. an intermediate transfer member onto which the toner images formed on the first and second image carriers are transferred in a superimposed state, and the toner images transferred onto the intermediate transfer member are transferred onto a recording material; the first image forming unit further includes a first primary transfer unit that transfers the toner image formed on the first image carrier to the intermediate transfer member, the second image forming unit further includes a second primary transfer unit that transfers the toner image formed on the second image carrier to the intermediate transfer member, In the second monochromatic mode, the control unit causes the first primary transfer unit to contact the first image carrier via the intermediate transfer unit, and causes the second primary transfer unit to separate from the second image carrier.

3. The image forming apparatus according to claim 2, wherein the image forming apparatus is a recording medium.

4. The control means controls the first and second image forming units to form an image on a recording material in the second monochrome mode when the second mode is specified as the image forming mode in a print job received from an external device and an input image according to the print job is a monochrome image.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. The control unit further controls, in the second monochrome mode, the first and second developing units to contact the first and second image carriers, respectively, and the first and second primary transfer units to contact the first and second image carriers, respectively, via the intermediate transfer unit, when a print job received from an external device satisfies a predetermined condition.

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

6. The predetermined condition is that the input image of the print job is a monochrome image, and the toner coverage area ratio of the entire output image formed based on the input image exceeds a threshold value.

6. The image forming apparatus according to claim 5,

7. The predetermined condition is that the input image of the print job is a mixture of monochrome images and multicolor images.

6. The image forming apparatus according to claim 5,

8. The control means controls the first image forming unit to form an image in the second monochrome mode according to image forming conditions corresponding to the formation of a monochrome image.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

9. the first image forming unit further includes a first primary transfer unit that transfers the toner image formed on the first image carrier to an intermediate transfer member in a primary transfer unit; the second image forming unit further includes a second primary transfer unit that transfers the toner image formed on the second image carrier to the intermediate transfer member in a primary transfer unit; the image forming apparatus, an intermediate transfer member onto which the toner images formed on the first and second image carriers are transferred in a superimposed state, and the toner images transferred onto the intermediate transfer member are transferred onto a recording material; a first voltage applying means for applying a primary transfer voltage to the first primary transfer means; a second voltage applying unit that applies a primary transfer voltage to the second primary transfer unit, The control unit sets, in the second monochromatic mode, a target value of a primary transfer current flowing in the primary transfer unit corresponding to the first image forming unit by application of the primary transfer voltage by the first voltage application unit to a value higher than a target value of the primary transfer current in the second multicolor mode.

9. The image forming apparatus according to claim 8,

10. a secondary transfer unit that transfers the toner image transferred to the intermediate transfer body onto a recording material in a secondary transfer unit; a third voltage application unit that applies a secondary transfer voltage to the secondary transfer unit, The control unit sets, in the second monochromatic mode, a target value of a secondary transfer current flowing in the secondary transfer unit due to application of the secondary transfer voltage by the third voltage application unit to a value lower than a target value of the secondary transfer current in the second multicolor mode.

10. The image forming apparatus according to claim 9,

11. The control unit sets a peripheral speed ratio, which is a ratio of the peripheral speed of the first and second developing units to the peripheral speed of the first and second image carriers, in the second mode to be higher than the peripheral speed ratio in the first mode.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

12. The control means sets, in the second mode, a development contrast for developing the electrostatic latent images formed on the first and second image carriers with toner to be greater than the development contrast in the first mode.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

13. In the second mode, the control unit sets a potential difference between a dark area potential and a light area potential of the first and second image carriers on which the electrostatic latent images are formed to be larger than the potential difference in the first mode.

4. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

Images