Imaging equipment

Abstract

The present disclosure relates to an imaging device, which includes an image bearing member; a developer bearing member; a driving unit for driving the image bearing member and the developer bearing member at a varying circumferential speed; a control unit; a developing voltage applying unit; a supply member for supplying developer to the developer bearing member; and a supply member voltage applying unit, wherein the control unit executes a first imaging mode in which the rotational circumferential speed ratio between the surface movement speeds of the developer bearing member and the image bearing member is not greater than 1 and a second imaging mode in which the rotational circumferential speed ratio is greater than 1, and the control unit controls the driving unit so that the difference between the developing voltage and the supply voltage is greater in the second imaging mode than in the first imaging mode.

Description

Technical Field

[0001] The present invention relates to an imaging device. Background Art

[0002] In imaging devices (such as copiers, printers, and fax machines) that use an electrophotographic imaging system (electrophotographic process), an electrophotographic photosensitive member (hereinafter referred to as a "photosensitive member") serving as an image bearing member is uniformly charged by a charging device, and the charged photosensitive member is exposed to light to form an electrostatic image on the photosensitive member. The electrostatic image formed on the photosensitive member is visualized as a toner image by a developing device using a toner in a developer. The toner image formed on the photosensitive member is then transferred to a recording material (such as a recording sheet or plastic sheet). Heat and pressure are applied to the toner image transferred to the recording material. As a result, the toner image is fixed to the recording material, allowing image recording.

[0003] Such imaging devices often require developer replenishment and maintenance of various processing components. To facilitate developer replenishment and processing component maintenance, a technology has been put into practical use in which a photosensitive member, a charging device, a developing device, a cleaning device for cleaning the photosensitive member, and the like are incorporated into a cartridge serving as a process cartridge (attachable to and detachable from the imaging device body) within the main frame. This process cartridge system makes it possible to provide an imaging device with excellent usability.

[0004] In recent years, as one of the widespread market demands, there has been a demand for high image density or enhanced color tone to achieve richer images. To this end, there is a technology that, in addition to a mode for achieving general image density, also provides a mode for changing the peripheral speed ratio between the photosensitive drum and the developing roller, increasing the amount of developer supplied to the photosensitive drum, and increasing the amount of developer on the recording material to achieve high density or enhanced color tone (Japanese Patent Application Laid-Open No. 2017-181964). Summary of the Invention

[0005] However, in recent years, with the increasing speed of processing, the number of rotations of the photosensitive drum or developer roller has increased. Increasing the number of rotations of the photosensitive drum or developer roller can cause torque fluctuations or vibrations in the developer container, leading to unstable rotation of the developer roller. Unstable rotation of the developer roller causes variations in the peripheral rotational speed ratio between the developer roller and the photosensitive drum, and in some cases, density irregularities known as banding appear in the image.

[0006] The present invention has been made in view of the above-mentioned problems, and its object is to provide an imaging device having multiple modes, each of which has a different rotational peripheral speed ratio between the photosensitive drum and the developing roller, wherein the imaging device is capable of forming a high-quality image while suppressing the occurrence of banding in any mode.

[0007] The present invention provides an imaging device, comprising:

[0008] an image bearing member configured to be rotatable;

[0009] a developer carrying member configured to be rotatable and to develop the electrostatic latent image with a developer at a nip region formed between the developer carrying member and the image bearing member;

[0010] a driving unit configured to rotationally drive the image bearing member and the developer bearing member so that the peripheral speeds of the image bearing member and the developer bearing member are individually changed;

[0011] a control unit configured to control the drive unit;

[0012] a developing voltage applying unit configured to apply a developing voltage to the developer carrying member;

[0013] a supply member configured to supply the developer to the developer carrying member; and

[0014] a supply member voltage applying unit configured to apply a supply voltage to the supply member, wherein

[0015] The control unit is configured to perform control so as to be able to execute a first image forming mode in which a rotational peripheral speed ratio representing a ratio between a surface movement speed of the developer bearing member and a surface movement speed of the image bearing member is not greater than 1 and a second image forming mode in which the rotational peripheral speed ratio is greater than 1, and

[0016] The control unit is configured to perform control so that a difference between the development voltage and the supply voltage is larger when the control unit executes the second imaging mode than when the control unit executes the first imaging mode.

[0017] The present invention further provides an imaging device, comprising:

[0018] an image bearing member configured to be rotatable;

[0019] a developer carrying member configured to be rotatable and to develop the electrostatic latent image with a developer at a nip region formed between the developer carrying member and the image bearing member;

[0020] a driving unit configured to rotationally drive the image bearing member and the developer bearing member so that the peripheral speeds of the image bearing member and the developer bearing member are individually changed;

[0021] a control unit configured to control the drive unit;

[0022] a developer container configured to accommodate a developer to be supplied to the developer carrying member; and

[0023] a conveying member disposed inside the developer container and configured to rotate about a rotation axis to stir and convey the developer, wherein

[0024] The control unit is configured to perform control so as to be able to execute a first image forming mode in which a rotational peripheral speed ratio representing a ratio between a surface movement speed of the developer bearing member and a surface movement speed of the image bearing member is not greater than 1 and a second image forming mode in which the rotational peripheral speed ratio is greater than 1, and

[0025] The control unit is configured to perform control such that the rotation speed of the conveying member is changed between a case where the control unit executes the first imaging mode and a case where the control unit executes the second imaging mode.

[0026] According to the present invention, it is possible to provide an image forming apparatus having a plurality of modes each having a different rotational peripheral speed ratio between a photosensitive drum and a developing roller, wherein the image forming apparatus is capable of forming a high-quality image while suppressing the occurrence of banding in any mode.

[0027] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a sectional view showing a schematic configuration of an image forming apparatus according to the present invention;

[0029] Figure 2 is a sectional view showing a schematic configuration of a cartridge according to the present invention;

[0030] Figure 3 is a graph for describing the relationship between development contrast and image density according to the present invention; and

[0031] Figure 4A and Figure 4B : is a view for describing a situation where the load on the toner conveying sheet according to the present invention changes. DETAILED DESCRIPTION

[0032] Hereinafter, with reference to the accompanying drawings, embodiments for implementing the present invention will be described in detail based on exemplary examples. However, unless otherwise specified, the dimensions, materials, shapes, and relative arrangements of the components described in the embodiments should be appropriately modified according to the configuration of the device to which the present invention is applied or various conditions. In other words, the scope of the present invention is not limited to the following embodiments.

[0033] Example

[0034] Imaging equipment

[0035] The overall configuration of an electrophotographic image forming apparatus (hereinafter referred to as an image forming apparatus) according to an embodiment will be described. Figure 1 FIG2 is a cross-sectional view of an imaging apparatus 100 according to an embodiment. The imaging apparatus 100 is a full-color laser beam printer that employs an inline system and an intermediate transfer system. The imaging apparatus 100 is capable of forming a full-color image on a recording material (e.g., a recording sheet, a plastic sheet, or fabric) based on image information. The image information is input to the imaging apparatus main body from an image reading device connected to the imaging apparatus main body or a host device, such as a personal computer, that is communicatively connected to the imaging apparatus main body.

[0036] In the image forming apparatus 100, a plurality of process cartridges 7 include image forming units SY, SM, SC, and SK to form images of corresponding colors of yellow (Y), magenta (M), cyan (C), and black (K). In the embodiment, the image forming units SY, SM, SC, and SK are arranged in a row in a direction intersecting the vertical direction.

[0037] The process cartridge 7 is attachable to and detachable from the image forming apparatus 100 via mounting means (e.g., attachment guides and positioning members) provided in the image forming apparatus main body. In the embodiment, the process cartridges for the respective colors have the same shape, and toners of the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) are accommodated in the process cartridges 7 for the respective colors. Note that, although the process cartridge will be described in the embodiment, the developing device 3 may be configured to be independently attachable to and detachable from the image forming apparatus main body.

[0038] The photosensitive drum 1 is rotationally driven by a drive device (drive source) not shown. A scanner unit 30 (exposure device) is arranged around the photosensitive drum 1. The scanner unit 30 is an exposure device for applying laser light based on image information and forming an electrostatic image (electrostatic latent image) on the photosensitive drum 1. For each scan line in the main scanning direction (a direction orthogonal to the conveying direction of the recording material 12), writing of laser exposure is performed based on a position signal called BD (beam detection) inside the polygon scanner. On the other hand, writing of laser exposure is performed in the sub-scanning direction (the conveying direction of the recording material 12) after a predetermined time delay from the TOP signal starting from a switch (not shown) in the conveying path of the recording material 12. Therefore, laser exposure is always allowed to be performed at the same position on the photosensitive drum 1 in the four processing stations Y, M, C and K.

[0039] An intermediate transfer belt 31 serving as an intermediate transfer member for transferring the toner image on the photosensitive drum 1 to the recording material 12 is arranged facing the four photosensitive drums 1. The intermediate transfer belt 31, which is formed of an endless belt and serves as an intermediate transfer member, is in contact with all the photosensitive drums 1 and moves along the recording material 12. Figure 1 The intermediate transfer belt 31 circulates (rotates) in the direction indicated by arrow B (counterclockwise). Four primary transfer rollers 32, serving as primary transfer devices, are arranged side by side on one side of the inner peripheral surface of the intermediate transfer belt 31 so as to face their respective photosensitive drums 1. A bias voltage having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer rollers 32 from a primary transfer bias power supply (high voltage power supply) (not shown), serving as a primary transfer bias applying device. Consequently, the toner image on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 31.

[0040] Furthermore, a secondary transfer roller 33, serving as a secondary transfer device, is disposed on one side of the outer peripheral surface of the intermediate transfer belt 31. A bias voltage having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 33 from a secondary transfer bias power source (high voltage power source) (not shown), serving as a secondary transfer bias applying device. Consequently, the toner image on the intermediate transfer belt 31 is transferred (secondarily transferred) onto the recording material 12. For example, when forming a full-color image, the above-described process is performed sequentially in the image forming units SY, SM, SC, and SK, thereby primary transferring the toner images of the corresponding colors onto the intermediate transfer belt 31 so as to overlap with one another.

[0041] Thereafter, the recording material 12 is conveyed to the secondary transfer area in synchronization with the movement of the intermediate transfer belt 31. Then, the secondary transfer roller 33 contacts the intermediate transfer belt 31 with the recording material 12 interposed therebetween, and the four color toner images on the intermediate transfer belt 31 are collectively and secondarily transferred onto the recording material 12.

[0042] The recording material 12 to which the toner image has been transferred is conveyed to a fixing device 34 serving as a fixing means. When heat and pressure are applied to the recording material 12 by the fixing device 34, the toner image is fixed to the recording material 12.

[0043] Processing box

[0044] The overall configuration of the process cartridge 7 attached to the image forming apparatus 100 according to the embodiment will be described. Figure 2 1 is a sectional view (main sectional view) of one of the process cartridges 7 according to the embodiment when viewed in the longitudinal direction (rotational center axis direction) of the photosensitive drum 1. Note that, in the embodiment, the configuration and operation of the process cartridges 7 for the respective colors are substantially the same except for the type (color) of toner accommodated.

[0045] The process cartridge 7 has a photosensitive unit 13 including a photosensitive drum 1 serving as an image bearing member and the like, and a developing unit 3 including a developing roller 4 serving as a developer carrying member and the like.

[0046] The photosensitive drum 1 is rotatably attached to the photosensitive unit 13 via an unillustrated bearing. The photosensitive drum 1 rotates in accordance with an image forming operation when receiving a driving force of a driving motor serving as a drum driving device 401 (driving source a). Figure 2 The photosensitive drum 1 is driven to rotate in the direction (clockwise) indicated by the arrow A. In the embodiment, an organic photosensitive drum is used as the photosensitive drum 1 which plays a core role in the image forming process. In the organic photosensitive drum, an undercoat layer, a carrier generating layer, and a carrier transferring layer serving as functional films are sequentially coated on the outer peripheral surface of an aluminum cylinder.

[0047] Furthermore, the charging roller 2 and a cleaning blade 6 serving as a cleaning member are arranged in the photosensitive unit 13 so as to contact the circumferential surface of the photosensitive drum 1. The cleaning blade 6 is in contact with the photosensitive drum 1 in an opposed manner, and the residual toner removed from the surface of the photosensitive drum 1 by the cleaning blade 6 falls and is accommodated in the cleaning frame main body 14.

[0048] When the roller portion formed of conductive rubber is brought into pressure contact with the photosensitive drum 1, the charging roller 2, serving as a charging member, is driven to rotate. A predetermined DC voltage is applied to the core of the charging roller 2 from a charging bias applying unit 303 (charging voltage applying device), serving as a high-voltage power source. Consequently, a uniform dark potential (Vd) is formed on the surface of the photosensitive drum 1.

[0049] When the charged photosensitive drum 1 is exposed to a spot pattern of laser light emitted from the scanner unit 30 in a manner corresponding to image data, the charge on the surface disappears during the exposure period due to carriers from the carrier generation layer, and the potential decreases. As a result, an electrostatic latent image is formed on the photosensitive drum 1, having a predetermined bright potential (Vl) in the exposed section and a predetermined dark potential (Vd) as the surface potential in the unexposed section.

[0050] On the other hand, the developing unit 3 includes a toner storage container serving as a developer container for storing a non-magnetic single-component developer (toner 9) as a developer. In the toner storage container, a developing roller 4 serving as a developer carrying member for carrying the toner 9 and a supply roller 5 serving as a supply member for supplying the toner 9 to the developing roller 4 are arranged. Furthermore, a developing blade 8 is arranged that controls the amount of toner supplied by the supply roller 5 and applied to the developing roller 4, and applies an electric charge to the toner.

[0051] The developing blade 8 is formed from a thin plate-like member. The spring elasticity of the thin plate creates contact pressure, and its surface contacts and contacts the toner 9 and the developing roller 4. When the developing blade 8 and the developing roller 4 abut and rub against each other, the toner 9 is charged by friction, and the toner thickness is controlled while the charge is applied. In the embodiment, a predetermined voltage is applied to the developing blade 8 from a blade bias power supply (not shown) to stabilize toner application.

[0052] Furthermore, the toner storage chamber 21 is arranged in the direction in which the toner scraped off from the developing roller 4 by the developing blade 8 falls. The toner is stored in the toner storage chamber 21. Furthermore, a toner conveying member 22 for stirring and conveying the toner 9 is provided inside the toner storage chamber 21. That is, the toner conveying member 22 stirs the toner 9 contained in the toner storage chamber 21 and Figure 2 The toner 9 is conveyed in the direction indicated by the middle arrow G toward the upper region of the toner supply roller 5 .

[0053] The toner conveying member 22 is formed by a rotating shaft 22a and a conveying sheet 22b. The conveying sheet 22b is attached to substantially the entire area in the axial direction (longitudinal direction) of the rotating shaft 22a. The conveying sheet 22b is a rectangular sheet member and can be manufactured using a flexible resin sheet such as a polyester film and a polycarbonate film with a thickness of 50 μm to 250 μm. In addition, the length of the conveying sheet 22b in the direction of the rotation radius of the rotating shaft 22a in the natural state is set to be longer than the distance from the rotation center of the rotating shaft 22a to the wall surface W1 of the toner containing chamber 21 in the same direction.

[0054] The developing roller 4 is configured to be provided with an elastic layer formed of a conductive elastomer and having a diameter of 12 mm on the outer peripheral surface of a SUS (stainless steel) core rod. In the embodiment, polyurethane rubber is used as the elastomer. The developing roller 4 touches and contacts the photosensitive drum 1. The developing roller 4 and the photosensitive drum 1 rotate so that their surfaces move in the same direction (from the bottom to the top in the embodiment) at the facing area (contact area). That is, the developing roller 4 rotates in the direction indicated by the arrow D. In the embodiment, the hardness of the developing roller 4 is set to be lower than the hardness of the photosensitive drum 1, and the developing roller is arranged so that its intrusion amount is 50 μm.

[0055] In order to maintain a uniform contact nip with the photosensitive drum 1, it is preferable to use an elastic rubber layer of the developing roller 4 having an MD-1 hardness of no more than 50°, as measured by an MD-1 durometer manufactured by Kobushi Keiki Co., Ltd. If the MD-1 hardness is too high, it is difficult to ensure a sufficient contact nip with the photosensitive drum 1. Consequently, the effects of the present invention are rarely achieved. In the embodiment, an elastic rubber layer having a rubber hardness of 38° is used.

[0056] Furthermore, the surface roughness of the developing roller 4 is set to at least 1.4 μm as the centerline average roughness Ra, thereby maintaining a desired amount of toner 9 on the surface of the developing roller 4. If the centerline average roughness Ra is less than 1.4 μm, a sufficient amount of toner 9 cannot be developed on the photosensitive drum 1. Consequently, sufficient image density is rarely achieved. In the examples, a developing roller 4 having a centerline average roughness of 2.0 μm is used. The centerline average roughness Ra is measured using a "surfcoder SE 350" manufactured by Kosaka Laboratory Ltd.

[0057] In the embodiment, with respect to a predetermined DC bias (Vdc) applied to the developing roller 4 from a development bias applying unit 301 (development voltage applying device) serving as a high-voltage power source, the toner 9, which is negatively charged by triboelectric charge, moves only to the bright portion potential region due to the potential difference at the developing region where the toner 9 contacts the photosensitive drum 1, and visualizes the electrostatic latent image. The difference between the DC bias Vdc and the bright portion potential V1 is referred to as development contrast, and the magnitude of the development contrast is varied to control the amount of toner developed from the developing roller onto the photosensitive drum 1 and to control image density, line width, and the like.

[0058] The supply roller 5 is arranged on the circumferential surface of the developing roller 4 to form a predetermined contact area (nip area) N. The supply roller 5 is an elastic sponge roller having a foam layer formed on the outer periphery of a conductive core rod, and the supply roller 5 and the developing roller 4 contact each other with a predetermined intrusion amount. Here, the intrusion amount refers to the amount of concavity ΔE obtained when the toner supply roller 5 is deformed into a concave shape by the developing roller 4. In the embodiment, the amount of intrusion of the supply roller 5 into the developing roller 4, that is, the amount of concavity ΔE by which the supply roller 5 is deformed into a concave shape by the developing roller 4, is set to 1 mm.

[0059] Furthermore, at the contact area N where the supply roller 5 faces the developing roller 4, the supply roller 5 Figure 2 The supply roller 5 rotates in the direction indicated by the arrow E, causing their surfaces to move in opposite directions. Thus, the supply roller 5 supplies the toner 9 to the developing roller 4 while collecting the residual toner on the developing roller 4. Note that the supply roller 5 may rotate in the direction opposite to the direction indicated by the arrow E.

[0060] Furthermore, a predetermined DC bias (supply voltage) is applied to the supply roller 5 from a supply roller bias applying unit 302 (supply member voltage applying means) serving as a high voltage power source, whereby the negatively charged toner 9 is easily supplied from the supply roller 5 to the developing roller 4 .

[0061] About the appearance of stripes

[0062] Here, we will discuss the occurrence of banding in an image. Banding occurs due to a change in the rotational peripheral speed ratio between the photosensitive drum 1 and the developing roller 4. The rotational peripheral speeds of the photosensitive drum 1 and the developing roller 4 can be expressed as the surface movement speeds of each of these components. The rotational peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 can be expressed as the ratio between the surface movement speed of the developing roller 4 and the surface movement speed of the photosensitive drum 1. Changes in the rotational peripheral speed ratio between the photosensitive drum 1 and the developing roller 4 occur, for example, in the following situations.

[0063] In the embodiment, the toner conveying member 22 and the developing roller 4 are connected to each other by a gear (not shown), and are configured to be driven when receiving the driving force of the driving motor serving as the developing drive device 402 (driving source b). Therefore, in the embodiment, the developing roller 4 and the toner conveying member 22 rotate simultaneously. The peripheral speed of the toner conveying member 22 increases as the peripheral speed of the developing roller 4 increases. The above-mentioned developing drive device 402 and drum drive device 401 can be understood as a driving unit that operates according to the control of the control unit 201 to be described later.

[0064] Will use Figure 4A and Figure 4B The case where the load on the conveying sheet 22b of the toner conveying member 22 changes is described below. Figure 4AAs shown, the load becomes maximum in a state where the conveying sheet 22b contacts the wall surface W1 of the toner accommodating chamber 21 during its rotation and is deformed and the toner 9 is placed in the upper region of the conveying sheet 22b. Figure 4B As shown, the load becomes minimum in a state where the conveying sheet 22b is released from its deformed state and restored to its natural state (original shape) by the elastic restoring force of the conveying sheet 22b itself.

[0065] When the load on the conveying sheet 22b changes as described above, the load applied to the developing roller 4 via the coupling gear changes, and the rotational peripheral speed of the developing roller 4 sometimes temporarily fluctuates. As a result, the rotational peripheral speed ratio between the photosensitive drum 1 and the developing roller 4 changes. As a result, the amount of toner developed from the developing roller 4 to the photosensitive drum 1 changes, which causes the appearance of a banding image.

[0066] Here, when the rotational peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 is not greater than 1, that is, when the photosensitive drum 1 rotates faster than the developing roller 4, a force acts on the photosensitive drum 1 in a direction in which the developing roller 4 is assisted in its rotation. That is, when rotational vibration of the developing roller 4 is likely to occur, a force for assisting the rotation of the developing roller 4 acts on the developing roller 4 from the photosensitive drum 1. Therefore, the rotational vibration of the developing roller 4 is suppressed, which makes it possible to prevent the occurrence of a banding image.

[0067] On the other hand, when the rotational peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 is greater than 1, that is, when the developing roller 4 rotates faster than the photosensitive drum 1, the force for assisting the rotation of the developing roller 4 does not act on the developing roller 4 from the photosensitive drum 1. In this case, rotational vibration of the developing roller 4 may occur. Therefore, rotational vibration of the developing roller 4 is likely to occur. In this case, reducing the process speed while maintaining the rotational peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 makes it possible to moderate the change in torque, suppress the rotational vibration of the developing roller 4, and prevent the occurrence of banding.

[0068] Note that the toner conveying member 22 and the developing roller 4 are configured to be driven when receiving the driving force of the driving motor serving as the developing driving means 402 (driving source b) in the embodiment, but may be driven independently.

[0069] Furthermore, in the embodiment, the peripheral speed of the developing roller 4 is set to be lower in a mode where the peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 is greater than 1 (a high-density mode, described later) than in a mode where the peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 is not greater than 1 (a normal mode, described later). Consequently, as described above, the peripheral speed of the toner conveying member 22 is also reduced. Consequently, it is possible to moderate torque variations and prevent the occurrence of banding.

[0070] Furthermore, in the embodiment, the peripheral speed of the developing roller 4 is set to be lower in the high-density mode, in which the peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 is greater than 1, compared to the normal mode, in which the peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 is no greater than 1. In the embodiment, a configuration is employed in which the peripheral speed of the toner conveying member 22 is also reduced, as described above. However, other configurations may be employed. For example, in an image forming mode (described later) designed to increase the peripheral speed ratio between the photosensitive drum 1 and the developing roller 4 to achieve high density or a wider range of tones, the rotational speed of the toner conveying member 22 may be controlled to be higher. By setting the rotational speed of the toner conveying member 22 higher than in the normal mode, in which the peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 is no greater than 1, after reducing the peripheral speed of the developing roller 4 to a certain extent to suppress the occurrence of banding, the toner conveying capability can be improved. Specifically, the rotational speed of the toner conveying member 22 can be increased to provide the capability to convey toner corresponding to the high-density image, described later.

[0071] Imaging mode

[0072] The image forming apparatus according to the embodiment can operate in two image forming modes. The first mode (first image forming mode) is an image forming mode for obtaining a normal image density (hereinafter referred to as the "normal mode"). The second mode (second image forming mode) is an image forming mode for increasing the rotational peripheral speed ratio between the photosensitive drum 1 and the developing roller 4 to obtain a high density or increase the range of color selection while reducing the dark portion potential on the photosensitive drum (hereinafter referred to as the "high density mode").

[0073] The specific differences in control between the normal mode and the high-density mode in the embodiment are shown in Table 1 below. Here, the bias voltages applied by the development bias applying unit 301, the supply roller bias applying unit 302, and the charging bias applying unit 303, and the amount of laser light from the scanner unit 30 are controlled by the control unit 201 based on information obtained by the imaging mode information acquisition unit 200. The imaging mode information acquisition unit 200 acquires information input from an unillustrated operation panel or printer driver in the imaging apparatus 100 or the host PC, and the like.

[0074] As the control unit 201, for example, a control circuit or a computer having computing resources such as a processor and a memory can be used. The control unit 201 is used to perform various control operations related to image formation, such as exposure control, voltage control, and drive control. The control unit 201 can also variably control the rotation speed of the toner conveying member 22.

[0075] For example, the control unit 201 is capable of variably controlling the peripheral speed at which the developing roller 4 is rotationally driven by controlling the driving force of the driving motor serving as the developing drive device 402. The control unit 201 is also capable of variably controlling the peripheral speed at which the photosensitive drum 1 is rotationally driven by controlling the driving force of the driving motor serving as the drum drive device 401, or is capable of individually and variably controlling the peripheral speeds of the developing roller 4 and the photosensitive drum 1. The above-described configuration allows the control unit 201 to change the rotational peripheral speed ratio between the developing roller 4 and the photosensitive drum 1 and to execute a first mode in which the rotational peripheral speed ratio is not greater than 1 and a second mode in which the rotational peripheral speed ratio is greater than 1. The control unit 201 can also control (execute control) so that the surface movement speed of the photosensitive drum 1 in the second mode becomes smaller than the surface movement speed of the photosensitive drum 1 in the first mode.

[0076] [Table 1]

[0077]

[0078] In the embodiment, the rotational peripheral speed ratio represents the rotational peripheral speed of the developing roller 4 when the rotational peripheral speed of the photosensitive drum 1 is assumed to be 1. Specifically, in normal mode, the rotational peripheral speed of the photosensitive drum 1 is set to 300 mm / sec, and the rotational peripheral speed of the developing roller 4 is set to 270 mm / sec. That is, in normal mode, a relationship is established in which the rotational peripheral speed of the developing roller 4 is less than the rotational peripheral speed of the photosensitive drum 1. By establishing this relationship, the photosensitive drum 1 assists the rotation of the developing roller 4. Therefore, the occurrence of banding can be suppressed. In order to fully exert the function and effectively reduce the occurrence of banding caused by changes in the rotational peripheral speed of the developing roller 4, the rotational peripheral speed ratio is desirably set to not more than 0.95.

[0079] Furthermore, in order to obtain sufficient concentration in the normal mode, the rotational peripheral speed is desirably set to at least 0.7.

[0080] On the other hand, in the high density mode, the rotational peripheral speed of the photosensitive drum 1 is set to 100 mm / sec, and the rotational peripheral speed of the developing roller 4 is set to 120 mm / sec. Figure 3 As shown, when the rotational peripheral speed of the developing roller 4 is greater than the rotational peripheral speed of the photosensitive drum 1, the amount of toner developed from the developing roller 4 to the photosensitive drum 1 becomes larger for the same development contrast, and the image density becomes higher. Therefore, the desired density in high-density mode can be achieved without reducing the quality of characters. In high-density mode, the rotational peripheral speed ratio is desirably not greater than 1.5. This is because as the rotational peripheral speed ratio increases, the rotational peripheral speed of the developing roller 4 becomes faster, and therefore, banding caused by the change in the rotational peripheral speed of the developing roller 4 is more likely to occur.

[0081] Furthermore, in the embodiment, the development contrast value in the high density mode is set to be larger than that in the normal mode, as shown in Table 1. Therefore, a higher density and a further increase in the selection range of hues can be obtained in the high density mode.

[0082] Furthermore, in both normal mode and high-density mode, a supply roller bias is applied such that the difference between the development potential and the supply roller bias generates a negative electric field in the toner supply direction. Furthermore, the difference between the development potential and the supply roller bias is set to be larger in high-density mode than in normal mode. This increases the amount of toner supplied to the developer roller in high-density mode, achieving a higher density. Furthermore, insufficient toner supply due to continuous printing of high-density images can be prevented.

[0083] In the above-described configuration and control, in high-density mode, the process speed is reduced by lowering the respective rotational circumferential speeds of the developing roller 4 and the photosensitive drum 1 while maintaining the developing roller 4 rotating faster than the photosensitive drum 1. Consequently, changes in torque are mitigated, and rotational vibrations of the developing roller 4 are suppressed. Consequently, the occurrence of banding can be prevented. Thus, the normal mode and high-density mode in this embodiment can be set to the control shown in Table 1, providing the high-quality images required by users while preventing the occurrence of banding.

[0084] experiment

[0085] To verify the above effects, the following verification experiment was conducted. A two-page intermittent printing durability test was conducted at a temperature of 23°C and a humidity of 50%. In this print durability test, the character "E" was printed with an image ratio of 1%. In this mode, 30,000 sheets were printed, periodically printing halftone images, and confirming the occurrence of horizontal streaks due to banding. "×" indicates the occurrence of horizontal streaks, and "○" indicates the absence of horizontal streaks.

[0086] Furthermore, pure black was printed in the high-density mode, and the density of the pure black was measured using SPECTRODENSITOMETER 500 manufactured by X-Rite.

[0087] Furthermore, for comparison with the effect of the present configuration, experiments of Comparative Examples 1 to 3 were conducted in which the control values were changed relative to the values of the embodiment.

[0088] [Table 2]

[0089]

[0090] In Comparative Example 1, the rotational peripheral speed ratio in the normal mode was changed to 1.2. In Comparative Example 2, the rotational speed of the photosensitive drum in the high-density mode was changed to 300 ms / sec. In Comparative Example 3, the rotational peripheral speed ratio in the high-density mode was changed to 0.9.

[0091] Table 3 shows the results. In the banding evaluation, "×" indicates that horizontal streaks appeared due to banding, and "○" indicates that no horizontal streaks appeared. In the density evaluation based on the measurement of pure black in the high-density mode, "○" indicates that the density is at least 1.5, and "×" indicates that the density is not greater than 1.5.

[0092] [Table 3]

[0093]

[0094] In the configuration of the embodiment, it is possible to suppress the occurrence of banding in both the normal mode and the high-density mode and to obtain a desired density in the high-density mode.

[0095] On the other hand, in the configuration of Comparative Example 1, the rotation speed of the developing roller 4 is greater than the rotation speed of the photosensitive drum 1 in the normal mode. Therefore, when rotation unevenness occurs in the developing roller 4, the photosensitive drum 1 does not assist the rotation of the developing roller 4. As a result, a banding image appears.

[0096] Furthermore, in the configuration of Comparative Example 2, the rotation speed of the photosensitive drum 1 in the high-density mode remains the same as the rotation speed of the photosensitive drum 1 in the normal mode. Therefore, the change in torque cannot be mitigated and the rotational vibration of the developing roller 4 cannot be suppressed. As a result, a banding image occurs.

[0097] Furthermore, the occurrence of banding images can be suppressed in the configuration of Comparative Example 3. However, since the toner 9 is not sufficiently supplied in the high-density mode, a desired density cannot be obtained.

[0098] As described above, the rotational peripheral speed ratio is set so that in normal mode the rotational speed of the developing roller 4 becomes slower than the rotational speed of the photosensitive drum 1. This allows the occurrence of banding images to be suppressed even when there may be unevenness in the rotational peripheral speed of the developing roller 4. Furthermore, even when the rotational speed of the developing roller 4 is set faster than the rotational speed of the photosensitive drum 1 in high-density mode, the process speed can be reduced, thereby suppressing the occurrence of banding images. By adopting these two modes, it is possible to respond to user demands for high-density images while suppressing the occurrence of banding images.

[0099] According to the present invention, an image forming apparatus having a plurality of modes, each having a different rotational peripheral speed ratio between the photosensitive drum 1 and the developing roller 4, is allowed to form high-quality images while suppressing the occurrence of banding in each of the plurality of modes. Therefore, in both the normal mode for obtaining a normal image density and the high-density mode for achieving a high density or tonal enhancement, it is possible to achieve the density requested by the user while suppressing banding in the image.

[0100] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An imaging device, comprising: an image bearing member configured to be rotatable; a developer carrying member configured to be rotatable and to develop the electrostatic latent image with a developer at a nip region formed between the developer carrying member and the image bearing member; a driving unit configured to rotationally drive the image bearing member and the developer bearing member so that the peripheral speeds of the image bearing member and the developer bearing member are individually changed; a control unit configured to control the drive unit; a developing voltage applying unit configured to apply a developing voltage to the developer carrying member; a supply member configured to supply a developer to the developer carrying member; as well as a supply member voltage applying unit configured to apply a supply voltage to the supply member, wherein The control unit is configured to perform control so as to be able to execute a first image forming mode in which a rotational peripheral speed ratio representing a ratio between a surface movement speed of the developer bearing member and a surface movement speed of the image bearing member is not greater than 1 and a second image forming mode in which the rotational peripheral speed ratio is greater than 1, and the control unit is configured to perform control so that a difference between the developing voltage and the supply voltage is larger when the control unit executes the second imaging mode than when the control unit executes the first imaging mode, in, The control unit is configured to perform control so that the surface moving speed of the image bearing member is smaller in a case where the control unit executes the second image forming mode than in a case where the control unit executes the first image forming mode.

2. The image forming apparatus according to claim 1, further comprising an exposure unit configured to expose the surface of the image bearing member based on image information and form an electrostatic latent image, wherein The control unit is configured to control so that a difference between the development voltage and a surface potential formed on the surface of the image bearing member when the surface is exposed by the exposure unit is greater when the control unit executes the second imaging mode than when the control unit executes the first imaging mode.

3. The imaging device according to claim 1, wherein The control unit is configured to perform control so that a rotational peripheral speed ratio between the developer bearing member and the image bearing member is not greater than 0.95 in the first image forming mode.

4. The imaging device according to claim 3, wherein The control unit is configured to perform control so that a rotational peripheral speed ratio between the developer bearing member and the image bearing member is at least 0.7 in the first image forming mode.

5. The imaging device according to claim 1, wherein The control unit is configured to perform control so that a rotational peripheral speed ratio between the developer bearing member and the image bearing member is not greater than 1.5 in the second image forming mode.

6. An imaging device, comprising: an image bearing member configured to be rotatable; a developer carrying member configured to be rotatable and to develop the electrostatic latent image with a developer at a nip region formed between the developer carrying member and the image bearing member; a driving unit configured to rotationally drive the image bearing member and the developer bearing member so that the peripheral speeds of the image bearing member and the developer bearing member are individually changed; a control unit configured to control the drive unit; a developer container configured to accommodate a developer to be supplied to the developer carrying member; as well as a conveying member disposed inside the developer container and configured to rotate about a rotation axis to stir and convey the developer, wherein the control unit being configured to perform control so as to be able to execute a first image forming mode in which a rotational peripheral speed ratio representing a ratio between a surface movement speed of the developer bearing member and a surface movement speed of the image bearing member is not greater than 1 and a second image forming mode in which the rotational peripheral speed ratio is greater than 1, The control unit is configured to perform control such that the rotation speed of the conveying member changes between a case where the control unit executes the first imaging mode and a case where the control unit executes the second imaging mode, and The control unit is configured to perform control so that the surface movement speed of the image bearing member is smaller in a case where the control unit executes the second image forming mode than in a case where the control unit executes the first image forming mode.

7. The imaging device according to claim 6, wherein The control unit is configured to perform control so that the rotation speed of the conveying member is greater when the control unit executes the second imaging mode than when the control unit executes the first imaging mode.

8. The imaging device according to claim 6, further comprising: an exposure unit configured to expose the surface of the image bearing member based on image information and form an electrostatic latent image; as well as a developing voltage applying unit configured to apply a developing voltage to the developer carrying member, wherein The control unit is configured to control so that a difference between the development voltage and a surface potential formed on the surface of the image bearing member when the surface is exposed by the exposure unit is greater when the control unit executes the second imaging mode than when the control unit executes the first imaging mode.

9. The imaging device according to claim 6, further comprising: a developing voltage applying unit configured to apply a developing voltage to the developer carrying member; a supply member configured to supply a developer to the developer carrying member; as well as a supply member voltage applying unit configured to apply a supply voltage to the supply member, wherein The control unit is configured to perform control so that a difference between the development voltage and the supply voltage is larger when the control unit executes the second imaging mode than when the control unit executes the first imaging mode.

Images