Image forming apparatus

Abstract

In an image forming apparatus equipped with a photosensitive drum and a developing roller that can be moved in and out of contact, the objective is to reduce the occurrence of lateral streaks in the rotation period of a supply roller containing foam that is in contact with the developing roller. [Solution] When the peripheral speed of the photosensitive drum 1 during the period up to t107 is Vo1, the peripheral speed of the developing roller 42 is Vd1, and the peripheral speed of the supply roller 43 is Vr1, and the peripheral speed of the photosensitive drum 1 during the period from t108 to t110 is Vo2, the peripheral speed of the developing roller 42 is Vd2, and the peripheral speed of the supply roller 43 is Vr2, the control unit 202 will |Vo1-Vd1|<|Vo2-Vd2| |Vd1-Vr1|<|Vd2-Vr2| The drive motor 85 is controlled so as to satisfy the given relationship, and so as to monotonically change the peripheral speed of the photosensitive drum 1 from Vo1 to Vo2, the peripheral speed of the developing roller 42 from Vd1 to Vd2, and the peripheral speed of the supply roller 43 from Vr1 to Vr2.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus using an electrophotographic method or an electrostatic recording method.

Background Art

[0002] An electrophotographic image forming apparatus includes an image forming process including a step of uniformly charging the surface of a photosensitive drum as an image carrier to a predetermined polarity and potential, a step of forming an electrostatic latent image on the charged surface, and a step of developing the electrostatic latent image with toner as a developer. As a developing method for developing the electrostatic latent image formed on the photosensitive drum, a contact developing method in which a developing roller as a developer carrier is brought into contact with the photosensitive drum is generally used. The contact developing method includes a contact separation mechanism between the photosensitive drum and the developing roller at the contact portion between the developing roller and the photosensitive drum in order to prevent deformation of the elastic developing roller. The contact separation mechanism is configured to bring the photosensitive drum and the developing roller into contact during image formation and to separate the photosensitive drum and the developing roller during other periods. In an image forming apparatus provided with a contact separation mechanism, for example, in Patent Document 1, in order to reduce the vibration of the photosensitive drum due to the shock at the time of contact and the occurrence of shock jitter in the image, the peripheral speed of the developing roller is reduced and the photosensitive drum and the developing roller are brought into contact. Thereby, a configuration for reducing the shock at the time of contact has been proposed. Further, for example, in Patent Document 2, in order to prevent image distortion due to rotational unevenness caused by load fluctuations of the photosensitive drum when the photosensitive drum and the developing roller having different peripheral speeds are brought into contact, the peripheral speeds of the photosensitive drum and the developing roller are made the same at the time of contact. Thereby, a configuration for reducing rotational unevenness has been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 1

[0004] According to the inventors' studies, the following problems arise in a configuration in which a developing roller and a supply roller, which serves as a developer supply member with foam formed on the outer circumference of a metal core, are in contact. Specifically, when a photosensitive drum and a developing roller with different peripheral speeds come into contact, there is a problem of horizontal streaks occurring at the rotation period of the supply roller. This is because when a photosensitive drum and a developing roller with different peripheral speeds come into contact, a braking effect occurs on the surface of the developing roller at the time of contact, and peripheral speed fluctuations also occur in the supply roller. Since the supply roller, which is made of foam, changes the amount of toner discharged and absorbed from the foam when peripheral speed fluctuations occur, uneven toner content occurs on the peripheral surface of the supply roller when peripheral speed fluctuations occur. Uneven toner content on the peripheral surface of the supply roller results in uneven frictional resistance, which in turn results in torque unevenness at the rotation period of the supply roller. When image formation is performed with torque unevenness at the rotation period of the supply roller, the peripheral speed of the developing roller fluctuates at the rotation period of the supply roller, resulting in a horizontal streaked image output at the rotation period of the supply roller.

[0005] In the conventional example described above, where only the peripheral speed of the developing roller is reduced to bring it into contact with the photosensitive drum, the braking effect at contact can be reduced, but it is necessary to control the peripheral speed of the developing roller alone. Therefore, separate drive motors are required to drive the photosensitive drum and the developing roller, which leads to the problem of the image forming apparatus becoming larger.

[0006] This invention was made under such circumstances, and aims to reduce the occurrence of lateral streaks in the rotation period of a supply roller containing foam that is in contact with the developing roller, in an image forming apparatus equipped with a photosensitive drum and a developing roller that can be moved in and out of contact. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the present invention has the following configuration.

[0008] (1) An image forming apparatus comprising: a rotatable image carrier on which an electrostatic latent image is formed; a rotatable developing member that applies a developer to the image carrier and develops the electrostatic latent image to form a developer image; a rotatable supply member that contacts the developing member and supplies the developer to the developing member; a moving unit that moves the developing member to a contact position where the developing member is in contact with the surface of the image carrier, or to a separated position where the developing member is separated from the surface of the image carrier; a drive source that drives the image carrier, the developing member and the supply member; and control means that control the moving unit and the drive source, wherein in a first period before an electrostatic latent image is formed on the image carrier and before the developing member is moved from the separated position to the contact position by the moving unit, the image When the peripheral speed of the surface of the image carrier is Vo1, the peripheral speed of the surface of the developing member is Vd1, the peripheral speed of the surface of the supply member is Vr1, the absolute value of the difference between the peripheral speed of the image carrier and the peripheral speed of the developing member is |Vo1-Vd1|, the absolute value of the difference between the peripheral speed of the developing member and the peripheral speed of the supply member is |Vd1-Vr1|, and during the second period while an electrostatic latent image is being formed on the image carrier, the peripheral speed of the image carrier is Vo2, the peripheral speed of the developing member is Vd2, the peripheral speed of the supply member is Vr2, the absolute value of the difference between the peripheral speed of the image carrier and the peripheral speed of the developing member is |Vo2-Vd2|, and the absolute value of the difference between the peripheral speed of the developing member and the peripheral speed of the supply member is |Vd2-Vr2|, the control means, |Vo1-Vd1|<|Vo2-Vd2| |Vd1-Vr1|<|Vd2-Vr2| An image forming apparatus characterized by satisfying the following relationship and controlling the drive source so that the peripheral speed, which is the moving speed of the surface of the image carrier, changes monotonically from Vo1 to Vo2, the peripheral speed, which is the moving speed of the surface of the developing member, changes monotonically from Vd1 to Vd2, and the peripheral speed, which is the moving speed of the surface of the supply member, changes from Vr1 to Vr2. [Effects of the Invention]

[0009] According to the present invention, in an image forming apparatus equipped with a photosensitive drum and a developing roller that can be moved in and out of contact, the generation of lateral streaks in the rotation period of a supply roller containing foam that is in contact with the developing roller can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1] Figures showing the image forming apparatus for Examples 1 and 2. [Figure 2] Block diagram showing the control configuration of the image forming apparatus in Examples 1 and 2. [Figure 3] Diagram showing process cartridges for Examples 1 and 2. [Figure 4] Timing chart of contact / separation interval and peripheral speed of each component in Example 1 [Figure 5] Timing chart of contact / separation interval and peripheral speed of each component for Comparative Example 1 compared to Example 1. [Figure 6] Diagram showing uneven toner distribution of the supply roller during contact and separation in Example 1. [Figure 7] A diagram showing the torque fluctuation of the developing roller in Example 1. [Figure 8] Timing chart of contact / separation interval, developing voltage, and supply voltage in Example 2 [Modes for carrying out the invention]

[0011] Preferred embodiments of this invention will be described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments are not intended to limit the scope of this invention to those components alone. Furthermore, the materials, shapes, etc. of the members described once in the following description will be the same as those described in the initial description unless otherwise specified. [Examples]

[0012] <Overview of the configuration of the image forming apparatus> Referring to FIG. 1, the operation of the image forming apparatus 100 of Example 1 will be described. FIG. 1 is a schematic cross-sectional view showing the image forming apparatus 100 including the process cartridge 88 of Example 1. The image forming apparatus 100 of Example 1 is a full-color laser beam printer employing an in-line system and an intermediate transfer system. The image forming apparatus 100 can form a full-color image on a transfer material P (e.g., recording paper, plastic sheet, cloth, etc.) as a transfer target according to image information. The image information is input to the main body of the image forming apparatus 100 from an image reading device connected to the main body of the image forming apparatus 100 or a host device such as a personal computer communicably connected to the main body of the image forming apparatus 100.

[0013] On FIG. 1, the image forming apparatus 100 is provided with four-color image forming stations of yellow, magenta, cyan, and black (hereinafter also referred to as image forming units) from the left side to the right side. Each image forming unit has an electrophotographic image forming mechanism with the same configuration except that the color of the toner 90 as a developer accommodated in each developing device 4 is different. In the following description, when no particular distinction is required, the subscripts Y (yellow), M (magenta), C (cyan), and K (black) given to the reference numerals to indicate that they are elements provided for any one of the colors are omitted and described in a general way.

[0014] The process cartridge 88 is detachable from the image forming apparatus 100 via mounting means such as a mounting guide and a positioning member provided on the main body of the image forming apparatus 100. In Example 1, all the process cartridges 88 for each color have the same shape, and each process cartridge 88 for each color accommodates toners of each color of Y (yellow), M (magenta), C (cyan), and K (black). The process cartridge 88 has a developing device 4, and the developing device 4 has a developing roller 42, a supply roller 43, and a regulating blade 44.

[0015] The photosensitive drum 1 as a carrier is rotationally driven by a drive motor 85 (see FIG. 2). The charging roller 2 uniformly charges the surface of the photosensitive drum 1. A scanner unit 3 is disposed around the photosensitive drum 1. The scanner unit 3 is an exposure means for irradiating a laser based on an image signal to form an electrostatic latent image on the photosensitive drum 1. Opposite to the four photosensitive drums 1, an intermediate transfer belt 53 as an intermediate transfer member for transferring the toner image (developer image) on the photosensitive drum 1 to the transfer material P is disposed. The endless intermediate transfer belt 53 abuts on all the photosensitive drums 1 and circulates (rotates) in the direction of the arrow B shown in the figure.

[0016] On the inner peripheral surface side of the intermediate transfer belt 53, four primary transfer rollers 51Y, 51M, 51C, and 51K as primary transfer means are arranged side by side so as to face each photosensitive drum 1. A voltage having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 51 from a primary transfer voltage power source 73 (see FIG. 2) as primary transfer voltage applying means. Thereby, the toner image on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 53. The portion where the toner image is transferred is transferred from the photosensitive drum 1 to the intermediate transfer belt 53 is called the primary transfer portion.

[0017] Furthermore, a secondary transfer roller 52 (transfer member) is positioned on the outer circumferential surface of the intermediate transfer belt 53 as a secondary transfer means. A voltage with the opposite polarity to the normal charging polarity of the toner is applied to the secondary transfer roller 52 from a secondary transfer voltage power supply 74 (see Figure 2), which serves as a secondary transfer voltage application means. This transfers the toner image on the intermediate transfer belt 53 to the transfer material P (secondary transfer). The area where the toner image is transferred from the intermediate transfer belt 53 to the transfer material P is called the secondary transfer section. For example, when forming a full-color image, the above process is performed sequentially in the image forming sections Y, M, C, and K, and the toner images of each color are sequentially superimposed on the intermediate transfer belt 53 for primary transfer. After that, the transfer material P is transported to the secondary transfer section in synchronization with the movement of the intermediate transfer belt 53. Then, through the action of the secondary transfer roller 52, which is in contact with the intermediate transfer belt 53 via the transfer material P, the four-color toner images on the intermediate transfer belt 53 are collectively transferred to the transfer material P for secondary transfer. The transfer material P onto which the unfixed toner image has been transferred is transported to a fixing device 6, which acts as a fixing means. In the fixing device 6, heat and pressure are applied to the transfer material P, fixing the toner image to the transfer material P, and the resulting image is discharged outside the image forming apparatus 100.

[0018] <Control of image forming apparatus> Figure 2 is a block diagram illustrating the schematic control configuration of the main components of the image forming apparatus 100 in Embodiment 1. The control unit 202 is a means for controlling the operation of the image forming apparatus 100 and is responsible for the exchange of various electrical information signals. The control unit 202 also processes electrical information signals input from various process equipment and sensors, and processes command signals to various process equipment. The controller 200 exchanges various electrical information with the host device and comprehensively controls the image forming operation of the image forming apparatus 100 via the interface 201 and the control unit 202 according to a predetermined control program and reference table.

[0019] The control unit 202, acting as a control means, includes a CPU 155, which is a central element for performing various calculations, and memory 15 such as RAM and ROM, which are memory elements. The RAM stores sensor detection results, counter count results, and calculation results, while the ROM stores control programs and data tables obtained in advance through experiments, etc. The control unit 202 is connected to each control target, sensor, counter, etc. in the image forming apparatus 100. The control unit 202 controls the transmission and reception of various electrical information signals and the timing of the driving of each part, thereby controlling a predetermined image forming sequence.

[0020] The control unit 202 controls the following high-voltage power supplies and devices to form a toner image on the surface of the photosensitive drum 1, for example. Specifically, the control unit 202 controls the charging voltage power supply 71, the developing voltage power supply 72, the supply voltage power supply 75, the regulating blade voltage power supply 76, the scanner unit 3, etc. Here, the charging voltage power supply 71 is a charging voltage application means that applies a charging voltage to the charging roller 2. The developing voltage power supply 72 is a developing voltage application means that applies a developing voltage to the developing roller 42. The supply voltage power supply 75 is a supply voltage application means that applies a supply voltage to the supply roller 43. The regulating blade 44 is a toner regulating member, and the regulating blade voltage power supply 76 is the power supply for the regulating blade 44. Furthermore, the control unit 202 controls the primary transfer voltage power supply 73, the secondary transfer voltage power supply 74, etc. The control unit 202 also controls the contact / separation mechanism 50 that controls the contact and separation between the photosensitive drum 1 and the developing roller 42, and the drive transmission unit 80 that rotates the drum unit 11 (see Figure 3) and the developing device 4. The drive transmission unit 80 transmits the driving force of the drive motor 85 to the drum unit 11 and the developing device 4. The photosensitive drum 1, the developing roller 42, and the supply roller 43 rotate due to the driving force of the drive motor 85.

[0021] <Overview of Process Cartridge Configuration> The overall configuration of the process cartridge 88 installed in the image forming apparatus 100 of Example 1 will now be described. In Example 1, the drum unit 11 and the developing apparatus 4 are integrated as a process cartridge 88. Figure 3 is a main cross-sectional view of the process cartridge 88 of Example 1, viewed along the longitudinal direction (rotation axis direction) of the photosensitive drum 1. In Example 1, the configuration and operation of the process cartridge 88 for each color are substantially the same, except for the type (color) of toner contained.

[0022] The rotational driving force of the drive motor 85 is transmitted to the process cartridge 88 from the drive output section (not shown) of the image forming apparatus 100, and voltage (charging voltage, developing voltage, supply voltage, regulating blade voltage, etc.) is supplied from the contacts of the image forming apparatus 100. The drum unit 11 is equipped with a photosensitive drum 1 and a charging roller 2 which is a charging member.

[0023] The photosensitive drum 1 is a rotatable cylindrical photosensitive body, and a coupling member (not shown) for transmitting driving force to the photosensitive drum 1 is provided at one end of the photosensitive drum 1 in the longitudinal direction. The coupling member engages with the image forming apparatus side drum drive coupling (not shown), which is the drum drive output section of the image forming apparatus 100, and the driving force of the drive motor 85 of the image forming apparatus 100 is transmitted to the photosensitive drum 1. The photosensitive drum 1 rotates around its axis in the first direction, the direction of arrow R1 (counterclockwise). In Embodiment 1, the photosensitive drum 1 is driven to rotate at a rotational speed such that the speed of the outer surface of the photosensitive drum 1 (circumferential speed) is 148 mm / sec at full speed.

[0024] Furthermore, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. In Example 1, the charging roller 2 is a conductive roller with a conductive rubber layer on a metal core, and is arranged in parallel with the photosensitive drum 1 in contact with it at a predetermined pressure, and rotates in conjunction with the rotation of the photosensitive drum 1. In addition, a charging voltage can be applied to the charging roller 2 from a charging voltage power supply 71. In Example 1, the photosensitive drum 1 is charged by applying a DC voltage of, for example, -1350V to the charging roller 2, and the surface potential of the photosensitive drum 1 at that time is approximately -700V. In Example 1, the surface potential (bright area potential) of the photosensitive drum 1 after exposure is set to -150V.

[0025] The developing device 4 contains, for example, a toner 90 whose normal charging polarity (charging polarity for developing an electrostatic latent image) is negative. A developing drive input gear (not shown) for transmitting driving force to the developing device 4 is provided at one longitudinal end of the developing device 4. The developing drive input gear is provided with a developing input coupling section (not shown) that receives drive from the image forming apparatus side developing drive coupling (not shown) of the image forming apparatus 100, and the driving force of the drive motor 85 of the image forming apparatus 100 is input to the developing device 4. The developing device 4 is equipped with a rotatable developing roller 42 (developing member) which is a developer carrier, a rotatable supply roller 43 (supply member) which is a developer supply member, and a regulating blade 44 which is a developer regulating member. The gears and couplings described above are included in the drive transmission section 80.

[0026] Toner 90 is supplied to the surface of the developing roller 42 by the supply roller 43. The toner 90 held on the developing roller 42 is then thinned by the regulating blade 44, which restricts the thickness of the layer (hereinafter referred to as layer thickness). Here, the regulating blade 44 has the function of restricting the layer thickness of the toner 90 on the developing roller 42, and also functions as a developer charging means that imparts a predetermined charge to the toner 90 on the developing roller 42. The thinned toner 90 is transported to the contact area with the photosensitive drum 1 as the developing roller 42 rotates, and the toner 90 is applied to the surface of the photosensitive drum 1, developing the electrostatic latent image formed on the surface of the photosensitive drum 1 with the toner. In addition, toner 90 that remains on the developing roller 42 and is not used for development is removed from the developing roller 42 at the contact area with the supply roller 43. The removed toner 90 is then agitated and mixed with the toner 90 in the developing device 4.

[0027] The developing roller 42 has a conductive elastic rubber layer with a predetermined volume resistance on the outer circumference of a metal core, and its surface is configured to have a predetermined surface roughness. The developing roller 42 can be a single-layer roller or a multi-layer roller. As a single-layer roller, for example, one in which an elastic layer is formed on a metal core using a rubber material such as silicone rubber, urethane rubber, or hydrin rubber is used. As a multi-layer roller, for example, one in which a surface layer is formed by coating the surface of the elastic layer with silicone resin, urethane resin, polyamide resin, fluororesin, etc.

[0028] The supply roller 43 is an elastic sponge roller with a layer (hereinafter also referred to as the foam layer or foam layer) formed on the outer circumference of a metal core using conductive foam. On the surface of this foam layer, foam cells are open, making it easy to hold and transport the toner 90. The supply roller 43 is positioned to contact the developing roller 42 with a predetermined amount of penetration, forming a nip portion N. At the nip portion N, the supply roller 43 is deformed into a concave shape by the developing roller 42. At the nip portion N with the developing roller 42, the supply roller 43 rotates in the direction of arrow R3, opposite to the rotation direction of the developing roller 42, and supplies toner 90 to the developing roller 42. That is, the rotation direction of the supply roller 43 (R3) is the same direction (second direction) as the rotation direction of the developing roller 42 (R2), and opposite to the rotation direction (R1) of the photosensitive drum 1.

[0029] Furthermore, the supply roller 43 scrapes off the toner 90 remaining on the developing roller 42 that was not used for developing the electrostatic latent image on the photosensitive drum 1, through the openings in the foam layer on its surface, and returns it to the inside of the developing container 41. The foam layer of the supply roller 43 deforms just before the nip section N with the developing roller 42, and this deformation causes the toner 90 remaining on the surface and inside to be discharged into region X in the direction of arrow T1. When the foam layer on the surface of the supply roller 43 passes through the nip section N and the deformation is restored, it sucks in the toner 90 in region Y in the direction of arrow T2.

[0030] In Example 1, the supply roller 43 has a urethane foam layer and contains an ionic conductive agent. For example, the supply roller 43 of Example 1 has a structure in which an ionic conductive agent, which is composed of a salt of a cation and anion having a reactive functional group that reacts with an isocyanate group, is chemically bonded to the urethane foam layer via the aforementioned reactive functional group. For example, a supply roller 43 with such a structure can be manufactured by foaming and curing a urethane composition containing an ionic conductive agent.

[0031] The driving force of the drive motor 85 input to the developing device 4 is transmitted to the developing roller gear (not shown), thereby enabling the developing roller 42 to rotate in the direction of arrow R2 in Figure 3. Furthermore, the driving force of the drive motor 85 input to the developing device 4 is transmitted to the supply roller gear (not shown), thereby enabling the supply roller 43 to rotate in the direction of arrow R3 in Figure 3. In Example 1, in order to obtain appropriate image density, it is desirable to set the peripheral speed ratio (hereinafter referred to as the peripheral speed ratio) of the moving speed of the surface of the photosensitive drum 1 to between 1.2 and 1.5 times the moving speed of the surface of the photosensitive drum 1. In Example 1, the developing roller 42 is set to a peripheral speed ratio of 1.4 times, balancing density and durability, and is driven to rotate in the direction of arrow R2 at a moving speed of 207 mm / sec at full speed.

[0032] Furthermore, considering the balance between supplying and scraping toner 90 to the developing roller 42, it is desirable to set the supply roller 43 to 0.85 to 0.95 times the surface movement speed of the developing roller 42. In Example 1, considering durability, the peripheral speed ratio was set to 0.9 times, and the roller was driven to rotate in the direction of arrow R3 at a speed of 186 mm / sec at full speed.

[0033] The regulating blade 44 has a plate-shaped elastic member that is conductive and flexible. One end of the elastic member is fixed to the developing container (frame) and supported in a cantilevered manner, while the other end is a free end that contacts the circumferential surface of the developing roller 42. The regulating blade 44 is positioned downstream in the direction of movement (rotation) of the surface of the developing roller 42 from the opposing part (contact part) between the supply roller 43 and the developing roller 42, and is in contact with the circumferential surface of the developing roller 42. In Embodiment 1, SUS material is used as the elastic member of the regulating blade 44. In Embodiment 1, the regulating blade 44 is positioned such that, at the contact position with the developing roller 42, the tip of the free end of the elastic member faces upstream (counter direction) in the direction of movement of the surface of the developing roller 42.

[0034] Furthermore, predetermined DC voltages are applied to the developing roller 42, supply roller 43, and regulating blade 44 from the developing voltage power supply 72, supply voltage power supply 75, and regulating blade voltage power supply 76 (see Figure 2), respectively, according to the image formation operation. In Example 1, during image formation, DC voltages of -450V are applied to the developing roller 42, -550V to the supply roller 43, and -550V to the regulating blade 44. Since the normal charge polarity of the toner 90 in Example 1 is negative, the potential difference between the supply roller 43 and the developing roller 42 is such that the toner 90 is biased (moves) from the supply roller 43 side to the developing roller 42 side.

[0035] In Example 1, the toner 90 used is a non-magnetic toner with negative charge properties manufactured by suspension polymerization. However, the toner 90 is not limited to this, and may also be toner manufactured using other polymerization methods such as pulverization or emulsion polymerization. Furthermore, the volume-average particle size of the toner 90 is preferably 5.0 to 8.0 μm. Here, the volume-average particle size of the toner 90 was measured using a Multisizer3 precision particle size distribution analyzer manufactured by Beckman Coulter, Inc. In Example 1, the volume-average particle size of the toner 90 was approximately 7.0 μm.

[0036] Furthermore, additives (hereinafter referred to as external additives), such as fluidizers, may be added to the toner 90 to improve its fluidity, electrostatic properties, and cleaning properties. Examples of external additives include inorganic oxide microparticles consisting of silica microparticles, alumina microparticles, titanium oxide microparticles, inorganic stearic acid compound microparticles such as aluminum stearate microparticles and zinc stearate microparticles, or inorganic titanate compound microparticles such as strontium titanate and zinc titanate. These can be used individually or in combination of two or more. It is preferable that these inorganic microparticles are gloss-treated with silane coupling agents, titanium coupling agents, higher fatty acids, silicone oils, etc., to improve heat resistance and environmental stability. The BET specific surface area of ​​the external additive is 10 m². 2 / g or more 450m 2 It is preferable that the value be less than or equal to / g.

[0037] The BET specific surface area can be determined by a low-temperature gas adsorption method using a dynamic constant-pressure method, according to the BET method (preferably the BET multi-point method). For example, by using a specific surface area measuring device (product name: Gemini 2375 Ver. 5.0, manufactured by Shimadzu Corporation), nitrogen gas is adsorbed onto the sample surface, and the BET specific surface area (m²) is measured using the BET multi-point method. 2 The amount of these various external additives added should be between 0.05 parts by mass and 5 parts by mass, preferably between 0.1 parts by mass and 3 parts by mass, per 100 parts by mass of toner. In addition, various external additives may be used in combination.

[0038] Furthermore, a considerable amount of residual toner that was not transferred by the intermediate transfer belt 53 remains on the photosensitive drum 1. In the image forming apparatus 100 of Example 1, such residual toner is charged to a negative polarity, which is the normal polarity (normal charging polarity) of toner 90, by discharge from the charging roller 2. The charged residual toner enters the charged area, which is the contact area between the charging roller 2 and the photosensitive drum 1. At this time, since the residual toner is negatively charged by the discharge from the charging roller 2 in the charged area, it remains electrostatically on the photosensitive drum 1 as it passes through the charged area. Subsequently, the residual toner that has passed through the charged area moves to the developing area, which is the contact area between the developing roller 42 and the photosensitive drum 1. In this developing area, if the surface of the photosensitive drum 1 to which the residual toner is attached is a non-image forming area (dark area potential formation area), the toner is recovered from the surface of the photosensitive drum 1 to the developing roller 42 due to the potential relationship between the photosensitive drum 1 and the developing roller 42. Specifically, the negatively polarized residual toner is recovered by the 350V potential difference between the dark area potential of the photosensitive drum 1 (-700V) and the development voltage potential (-350V). Increasing this potential difference improves recovery, but the potential difference is determined considering latent image formation and development during image formation. Furthermore, the difference in surface movement speed between the photosensitive drum 1 and the development roller 42 (hereinafter referred to as the surface movement speed difference) also affects development and recovery, with development and recovery improving as the surface movement speed difference increases. On the other hand, if the surface of the photosensitive drum 1 to which residual toner is attached is the image formation area (bright area potential formation region), the residual toner remains on the surface of the photosensitive drum 1 and is used as toner 90 for image formation.

[0039] The system for recovering residual toner with the developing roller 42 is a so-called cleanerless system. The cleanerless drum unit 11 consists only of a lightweight photosensitive drum 1 with a hollow internal structure and a charging roller 2 that rotates in accordance with the rotation of the photosensitive drum 1, so the load torque during rotational drive is extremely small. For this reason, in Embodiment 1, the drum unit 11 and the developing device 4 are driven by the same drive motor 85, and the image forming apparatus 100 is made smaller by minimizing the number of drive sources.

[0040] <Configuration and operation of the contact-separation mechanism> In Example 1, the following control is performed to avoid unnecessary contact between the photosensitive drum 1 and the developing roller 42 during periods when image formation is not taking place (hereinafter referred to as non-image formation or non-image formation time). Specifically, the control unit 202 controls the presence or absence of contact between the photosensitive drum 1 and the developing roller 42 (developing contact and separation operation) using the contact / separation mechanism 50. During image formation, the developing roller 42 contacts the surface of the photosensitive drum 1 at contact position A (hereinafter referred to as developing contact), and during non-image formation, except during continuous image formation, it moves to a separated position at a predetermined distance G from the surface of the photosensitive drum 1 (hereinafter referred to as developing separation). Figure 3 shows the developing separation state when the developing roller 42 has moved to the separated position.

[0041] Next, the configuration and operation of the contact / separation mechanism 50 as a moving part will be described. The contact / separation mechanism 50 has a lever 81 as an action receiving part provided on the developing device 4, and a moving member 82 as an action part provided on the main body of the image forming apparatus 100. The developing device 4 is also connected to a frame that fixes the position of the photosensitive drum 1 so that it can swing about a rotation axis that is substantially parallel to the rotation axis direction of the photosensitive drum 1. By operating the moving member 82 and moving the lever 81, the developing device 4 can be swung and moved between a contact position and a separated position.

[0042] The development device 4 moves to the contact position by a spring biasing force from a tension spring (not shown) and a rotational moment centered on the drive input to the development device 4 when it is driven. Here, the tension spring functions as a biasing means with both ends attached to the frame that fixes the position of the photosensitive drum 1 and the development device 4. The control unit 202 moves the moving member 82 of the contact / separation mechanism 50 in the direction of arrow P1, thereby releasing the state in which the development device 4 is held in the separated position in conjunction with the movement of the lever 81. Then, due to the spring biasing force and the rotational moment, the development device 4 swings and the development roller 42 moves toward the photosensitive drum 1. This moves the development device 4 to the contact position and brings the development roller 42 into contact with the photosensitive drum 1.

[0043] Conversely, to move the developing device 4 to the separated position, the control unit 202 moves the moving member 82 of the connecting / separating mechanism 50 toward the side away from the photosensitive drum 1 in the direction of arrow P2, and moves the lever 81 in the same direction to hold the developing device 4 in the separated position. This moves the developing device 4 to the separated position, and the developing roller 42 can be separated from the photosensitive drum 1. The movement of the moving member 82 is performed by receiving driving force from a motor or solenoid, which serves as a drive source provided in the image forming apparatus 100, via a drive transmission member.

[0044] In Example 1, during image formation, the developing device 4 is positioned in contact with the photosensitive drum 1, and the developing roller 42 is in contact with the photosensitive drum 1. In standby mode, sleep mode, power-off mode, etc., the developing device 4 is positioned in a separated position, and the developing roller 42 is separated from the photosensitive drum 1. By bringing the developing roller 42 into contact with the photosensitive drum 1 only when necessary, deformation of the elastic developing roller 42 can be prevented, and performance can be maintained for a long period of time.

[0045] Figure 4 is a timing chart of the contact and separation intervals and the peripheral speed of each component in Example 1. In Figure 4, (i) shows the contact and separation (contact, separation) state t101 of the developing roller 42, (ii) shows the speed of the drive motor 85 (drive motor speed t102) (full speed, low speed, stopped), (iii) shows the moving speed of the surface of the photosensitive drum 1 (photosensitive drum speed t103) (full speed, low speed, stopped), (iv) shows the moving speed of the surface of the developing roller 42 (developing roller speed t104) (full speed, low speed, stopped), (v) shows the moving speed of the surface of the supply roller 43 (supply roller speed t105) (full speed, low speed, stopped), (vi) shows the developing voltage t113 (0V, -450V), and (vii) shows the supply voltage t114 (0V, -550V). Furthermore, a to c for t102-t105, a and b for t113 and t114, t106-t108, and t110-t112 are the respective timings, and t109 is the period.

[0046] In Example 1, in order to prevent horizontal streaks caused by the rotation period of the supply roller 43 (hereinafter referred to as the supply roller period) due to development contact during full-speed printing, the control unit 202 performs the following control. As shown in the timing chart of Figure 4, after the control unit 202 receives the print signal at t106, it drives the drive motor at a low speed t102 (t102a) when the contact / separation interval t101 is separated. As a result, the peripheral speeds of the photosensitive drum speed t103a, the development roller speed t104a, and the supply roller speed t105a are uniformly reduced. Therefore, at the time of development roller 42 contact at timing t107, the photosensitive drum 1, development roller 42, and supply roller 43 are all driven at a lower speed than during full-speed image formation. At this time, the peripheral speed of the photosensitive drum 1 is 49 mm / sec, the peripheral speed of the development roller 42 is 69 mm / sec, and the peripheral speed of the supply roller 43 is 62 mm / sec.

[0047] (Regarding full-speed mode and low-speed mode) The image forming apparatus 100 of Example 1 is capable of operating in multiple modes with different image forming speeds for image formation. The image forming apparatus 100 is configured to perform image formation in a low-speed mode to improve fixation when printing on thick paper, and in a full-speed mode when printing on plain paper. In Example 1, the low-speed mode corresponds to the first mode, which has the slowest image forming speed among the multiple modes, and the full-speed mode corresponds to the second mode other than the first mode. When performing image formation in full-speed mode, the control unit 202 controls the rotation of the photosensitive drum 1, the developing roller 42, and the supply roller 43 at the rotation speed of the low-speed mode from the development separation state until development contact is completed.

[0048] On the other hand, when image formation is performed in low-speed mode, the control unit 202 is configured to maintain the low-speed mode from development separation to completion of development contact, and further until the end of image formation, while controlling the rotation of the photosensitive drum 1, the developing roller 42, and the supply roller 43. As will be described in detail later, to reduce lateral streaks in the supply roller cycle, it is important to reduce the absolute speed difference between the photosensitive drum 1 and the developing roller 42 at the time of development contact, and the absolute speed difference between the supply roller 43 and the developing roller 42. If each absolute speed difference during image formation is effective against lateral streaks in the supply roller cycle, the low-speed mode may be maintained from development separation to the end of image formation. However, if further effect against lateral streaks in the supply roller cycle is desired, this is not the case, and the rotation speed may be controlled at a slower speed than the rotation speed during image formation in low-speed mode from development separation to development contact.

[0049] On the other hand, by rotating at a lower speed and making contact with the developing roller, the absolute speed difference between the photosensitive drum 1 and the developing roller 42 is reduced, which is effective against lateral streaks in the supply roller cycle. However, if either the photosensitive drum 1 or the developing roller 42 makes contact while not rotating, the toner 90 on the developing roller 42 may solidify. Therefore, to prevent toner solidification, it is desirable for the photosensitive drum 1 and the developing roller 42 to make contact while rotating. In Example 1, the photosensitive drum 1 rotates between 1 mm / sec and 88 mm / sec, the developing roller 42 rotates between 1.4 mm / sec and 123 mm / sec, and the supply roller 43 rotates between 1.3 mm / sec and 111 mm / sec, and makes contact with the developing roller. As a result, improvement in lateral streaks in the supply roller cycle was confirmed. The absolute speed difference between the photosensitive drum 1 and the developing roller 42 at this time is in the range of 0.4 mm / sec to 35 mm / sec, and the absolute speed difference between the supply roller 43 and the developing roller 42 is in the range of 0.1 mm / sec to 12 mm / sec. In Example 1, the peripheral speed ratio between the photosensitive drum 1 and the developing roller 42, and the peripheral speed ratio between the developing roller 42 and the supply roller 43 during development contact, are the same as the peripheral speed ratio during image formation, which are 1.4 times and 0.9 times, respectively.

[0050] Furthermore, after receiving the print signal at t106, the control unit 202 drives the drive motor 85 at a low speed (t102a) and applies a voltage of -450V (t113a) to the developing roller 42 and -550V to the supply roller 43 (t114a).

[0051] In this state, the control unit 202 performs development contact at t107, and after development contact is completed (from t107 onwards), increases the drive motor speed t102 to full speed (t102b) between t108 and the start of image exposure by the scanner unit 3. As a result, the control unit 202 increases the peripheral speed of the photosensitive drum 1 (t103b), the developing roller 42 (t104b), and the supply roller 43 (t105b) to the peripheral speed for image formation (full speed). After that, the control unit 202 starts image exposure at t108 and performs image formation during the period t109. After image exposure is completed at t110, the control unit 202 performs development separation at t111, and stops the drive motor 85 (t102c) after development separation, thereby stopping the rotation of the photosensitive drum 1 (t103c), the developing roller 42 (t104c), and the supply roller 43 (t105c). At the same time, the control unit 202 stops applying voltage to the developing roller 42 (t113c) and the supply roller 43 (t114c), and terminates image formation at t112.

[0052] <Verification of effectiveness> Image evaluation was performed using the image forming apparatus 100 and process cartridge 88 of Example 1. A fully black image was printed on A4 size plain paper under conditions of 25°C / 50%RH and sensory evaluation was performed. As a comparative example, Figure 5 shows the timing chart of Comparative Example 1. Note that (i) to (vii) in Figure 5 correspond to (i) to (vii) in Figure 4, and t301 to t314 correspond to t101 to t114. Also, 'd' in t302 to t305, t313, and t314 indicates the timing.

[0053] In Comparative Example 1, the control unit 202 drives the drive motor 85 at full speed (t302d) after receiving the print signal (t306). This causes the control unit 202 to drive the photosensitive drum 1 (t303d), the developing roller 42 (t304d), and the supply roller 43 (t305d) at full speed. In addition, after receiving the print signal (t306), the control unit 202 drives the drive motor 85 (t302d) and applies a voltage of -450V (t313d) to the developing roller 42 and -550V (t314d) to the supply roller 43 to perform development contact (t307). The subsequent operation from the start of image exposure (t308) to the end of image formation (t312) is the same as in Example 1, so the explanation is omitted.

[0054] Table 1 shows the results of the sensory evaluation conducted by the inventors regarding lateral streaks in the supply roller cycle. The symbols A, B, C, and D in Table 1 represent, respectively: A: Excellent, B: Good, C: Acceptable, and D: Bad. In other words, in Table 1, C is better than D in the sensory evaluation, and A is better than B in the sensory evaluation (A > B > C > D). [Table 1] As shown in Table 1, Example 1 achieved a rank of B, which is superior to Comparative Example 1's rank of D in terms of the occurrence of lateral streaks during the supply roller cycle. The reasons will be explained using Figures 6 and 7.

[0055] Figure 6(a) shows the state in which the photosensitive drum 1 and the developing roller 42 are rotating with a gap G between them. When they are separated for development, the photosensitive drum 1 rotates at a peripheral speed of Vo, the developing roller 42 at Vd, and the supply roller 43 at Vr, with the peripheral speeds in the order Vd > Vr > Vo. Figure 6(b) shows the state in which the photosensitive drum 1 and the developing roller 42 are in contact for development. Because the peripheral speed Vo of the photosensitive drum 1 and the peripheral speed Vd of the developing roller 42 are different (Vd > Vo), a braking effect indicated by arrow B occurs on the surface of the developing roller 42. If the absolute speed difference |Vo-Vd| between the peripheral speed Vo of the photosensitive drum 1 and the peripheral speed Vd of the developing roller 42 is large, the kinetic energy increases, and therefore the braking effect also increases.

[0056] Furthermore, the peripheral speed of the supply roller 43, which was rotated by Vr during the development separation, decreases due to the braking action of the development roller 42 when it makes contact. As mentioned above, the supply roller 43 repeatedly deforms and recovers the foam layer as it comes into contact with and rotates the development roller 42, ejecting toner 90 in the T1 direction toward region X in Figure 6(b) and drawing in toner 90 in the T2 direction from region Y. The larger the absolute speed difference |Vr-Vd| between the peripheral speed Vr of the supply roller 43 and the peripheral speed Vd of the development roller 42, the greater the kinetic energy, and therefore the greater the deformation and recovery of the foam layer. If the peripheral speed of the supply roller 43 changes in a part of its circumferential direction, the amount of toner ejected and drawn in at the position where the peripheral speed changed will change, resulting in uneven toner content U on the circumferential surface of the supply roller 43. As a result, uneven frictional resistance is formed on the surface of the supply roller 43.

[0057] Figure 7 shows the torque data of the developing roller 42 when there is an uneven toner-containing area U on the circumferential surface of the supply roller 43. In Figure 7, the horizontal axis represents time, and the vertical axis represents the torque of the developing roller 42. The ▼ indicates the timing when the uneven toner-containing area U of the supply roller 43 passes the contact point with the developing roller 42. As shown in the graph of Figure 7, the torque of the developing roller 42 fluctuates due to frictional resistance unevenness when the uneven toner-containing area U of the supply roller 43 passes the contact point with the developing roller 42. As a result, the peripheral speed Vd of the developing roller 42 after development contact fluctuates with the supply roller cycle, causing horizontal streaks to appear in the image during the supply roller cycle. For this reason, in Comparative Example 1, horizontal streaks occurred during the supply roller cycle, resulting in a sensory evaluation rank of D.

[0058] On the other hand, in the configuration of Example 1, since development contact is performed with the rotation drive at a low speed, the absolute speed difference |Vo-Vd| between the peripheral speed Vo of the photosensitive drum 1 and the peripheral speed Vd of the developing roller 42 can be made smaller compared to the case where contact is made at full speed. Also, the absolute speed difference |Vr-Vd| between the peripheral speed Vr of the supply roller 43 and the peripheral speed Vd of the developing roller 42 can be made smaller compared to the case where contact is made at full speed. Table 2 shows the |Vo-Vd| and |Vr-Vd| values ​​for Example 1 and Comparative Example 1. [Table 2]

[0059] In the above embodiment 1, the control unit 202 performs the following control. First, the period before an electrostatic latent image is formed on the photosensitive drum 1 (Figure 6 ~ t108) and until the developing roller 42 moves from the separated position to the contact position by the contact / separation mechanism 50 (Figure 6 ~ t107) is defined as the first period. During the first period, the peripheral speed of the photosensitive drum 1 is Vo1, the peripheral speed of the developing roller 42 is Vd1, and the peripheral speed of the supply roller 43 is Vr1. Also, during the first period, the absolute value of the difference between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the developing roller 42 is |Vo1-Vd1|, and the absolute value of the difference between the peripheral speed of the developing roller 42 and the peripheral speed of the supply roller 43 is |Vd1-Vr1|. Furthermore, the period while an electrostatic latent image is being formed on the photosensitive drum 1 (Figure 6 t108~t110) is defined as the second period. During the second period, the peripheral speed of the photosensitive drum 1 is Vo2, the peripheral speed of the developing roller 42 is Vd2, and the peripheral speed of the supply roller 43 is Vr2. Also, during the second period, the absolute value of the difference between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the developing roller 42 is |Vo2-Vd2|, and the absolute value of the difference between the peripheral speed of the developing roller 42 and the peripheral speed of the supply roller 43 is |Vd2-Vr2|. At this time, the control unit 202, |Vo1-Vd1|<|Vo2-Vd2| |Vd1-Vr1|<|Vd2-Vr2| The drive motor 85 is controlled to satisfy the following relationship: The control unit 202 controls the drive motor 85 so that the peripheral speed of the photosensitive drum 1 changes monotonically from Vo1 to Vo2, the peripheral speed of the developing roller 42 changes from Vd1 to Vd2, and the peripheral speed of the supply roller 43 changes from Vr1 to Vr2.

[0060] Furthermore, the ratio of the peripheral speed of the photosensitive drum 1 to the peripheral speed of the developing roller 42 during the first period is Vd1 / Vo1, and the ratio of the peripheral speed of the supply roller 43 to the peripheral speed of the developing roller 42 is Vr1 / Vd1. During the second period, the ratio of the peripheral speed of the photosensitive drum 1 to the peripheral speed of the developing roller 42 is Vd2 / Vo2, and the ratio of the peripheral speed of the supply roller 43 to the peripheral speed of the developing roller 42 is Vr2 / Vd2. At this time, the control unit 202, Vd1 / Vo1 = Vd2 / Vo2 Vr1 / Vd1 = Vr2 / Vd2 The drive motor 85 is controlled to satisfy the relationship.

[0061] In other words, in terms of modes, the control unit 202 controls the drive motor 85 so that the peripheral speed of the photosensitive drum 1, the peripheral speed of the developing roller 42, and the peripheral speed of the supply roller 43 are the same as the peripheral speed in low-speed mode during the first period when operating in full-speed mode. The control unit 202 then controls the drive motor 85 so that it operates in full-speed mode during the second period. On the other hand, when operating in low-speed mode, the control unit 202 controls the drive motor 85 so that the peripheral speed of the photosensitive drum 1, the peripheral speed of the developing roller 42, and the peripheral speed of the supply roller 43 are the same as the peripheral speed in low-speed mode during the first period, and maintains low-speed mode during the second period as well.

[0062] By reducing the absolute speed difference |Vo-Vd| between the peripheral speed Vo of the photosensitive drum 1 and the peripheral speed Vd of the developing roller 42, the braking effect on the developing roller 42 during development contact can be reduced. At the same time, the absolute speed difference |Vr-Vd| between the peripheral speed Vr of the supply roller 43 and the peripheral speed Vd of the developing roller 42 is also reduced, so the amount of deformation and recovery of the foam layer of the supply roller 43 can be reduced. As a result, uneven toner inclusion on the peripheral surface of the supply roller 43 can be reduced, and torque fluctuations of the developing roller 42 can be suppressed. Therefore, the developing roller 42 can rotate stably even after development contact, resulting in a rank B in the sensory evaluation in Example 1, and an improvement in the lateral streaks of the supply roller cycle.

[0063] As explained above, in a developing apparatus 4 in which the photosensitive drum 1 and the developing roller 42 are separable and the developing apparatus 4 includes a supply roller 43 containing foam that is in contact with the developing roller 42, the following configuration can be used to achieve the following effect. Specifically, in Embodiment 1, the absolute speed difference between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the developing roller 42 at the time of development contact, and the absolute speed difference between the peripheral speed of the supply roller 43 and the peripheral speed of the developing roller 42 are made smaller than at the time of image formation. This makes it possible to improve the horizontal streaks in the supply roller cycle. With this configuration, there is no need to change the peripheral speed ratio between the photosensitive drum 1 and the developing roller 42, or the peripheral speed ratio between the developing roller 42 and the supply roller 43 at the time of development contact. Furthermore, even in a configuration in which the photosensitive drum 1, the developing roller 42, and the supply roller 43 are driven by the same drive motor 85, the horizontal streaks in the supply roller cycle can be improved.

[0064] As described above, in the image forming apparatus equipped with a photosensitive drum and a developing roller that can be moved in and out of contact, the occurrence of lateral streaks in the rotation period of the supply roller, which includes foam in contact with the developing roller, can be reduced. [Examples]

[0065] In Example 2, the supply voltage applied to the supply roller 43 during development contact is controlled, and the configuration further improves the lateral streaks in the supply roller cycle. Note that the image forming apparatus 100, process cartridge 88, and timing chart, which are the same as in Example 1, are omitted from this description.

[0066] <Voltage control during development contact> Figure 8 is a timing chart of the embodiment. Note that (i) to (vii) in Figure 8 correspond to (i) to (vii) in Figure 4, and t201 to t214 and a to c correspond to t101 to t114 and a to c, respectively. Note that t214e indicates the timing.

[0067] The control unit 202 drives the drive motor 85 at a low speed (t202a) after receiving the print signal (t206) and when the development is separated (t201). In this embodiment 2, the control unit 202 is configured to apply a supply voltage to the supply roller 43 that is the same as the development voltage (-450V) applied to the development roller 42 (t214a). With the voltages applied to the supply roller 43 and the development roller 42 being the same, the control unit 202 uniformly reduces the peripheral speed of the photosensitive drum 1 (t203a), the development roller 42 (t204a), and the supply roller 43 (t205a).

[0068] In this state, development contact is performed, and after development contact is completed (t207), the control unit 202 increases the peripheral speed of the drive motor 85 to full speed (t202b) before the scanner unit 3 starts image exposure (t208). As a result, the control unit 202 increases the peripheral speed of the photosensitive drum 1 (t203b), the developing roller 42 (t204b), and the supply roller 43 (t205b) to the peripheral speed for image formation. At the same time, the control unit 202 also increases the supply voltage applied to the supply roller 43 to -550V (t214e). After that, the control unit 202 starts image exposure (t208) and performs image formation (t209). The operation from the end of image exposure (t210) to the end of image formation (t212) is the same as in Example 1, so the explanation is omitted.

[0069] <Verification of effectiveness> Image evaluation was performed using the image forming apparatus 100 and process cartridge 88 of Example 2. A fully black image was printed on A4 size plain paper under conditions of 25°C / 50%RH and sensory evaluation was performed. The results are shown in Table 3. Table 3 shows the results of the sensory evaluation conducted by the inventors regarding lateral streaks in the supply roller cycle. [Table 3] As shown in Table 3, Example 2 achieved rank A, which is superior to Comparative Example 1's rank D in terms of the occurrence of lateral streaks during the supply roller cycle. The reason is explained below.

[0070] Example 2 is a configuration in which the potential difference between the developing roller 42 and the supply roller 43 at the time of development contact is made the same. Factors causing toner ejection from the supply roller 43 include deformation and recovery of the foam and the potential difference with the developing roller 42. By adopting the configuration of Example 2, ejection of toner 90 from the supply roller 43 to the developing roller 42 due to the potential difference can be eliminated. In other words, the amount of toner ejected when the peripheral speed of the supply roller 43 fluctuates can be suppressed. Therefore, it is possible to reduce uneven toner inclusion on the peripheral surface of the supply roller 43.

[0071] In this way, by reducing the speed of the photosensitive drum 1 and the developing roller 42 during development contact to reduce the absolute speed difference, and by making the developing roller 42 and the supply roller 43 at the same potential, uneven toner distribution on the supply roller 43 during development contact can be suppressed. As a result, the developing roller 42 can rotate stably even after development contact, and in Example 2, the sensory evaluation resulted in a rank of A, and the horizontal streaks in the supply roller cycle improved. After development contact, by raising the supply voltage to a voltage value that creates a potential difference that facilitates the movement of toner 90 from the supply roller 43 to the developing roller 42, toner can be stably supplied to the developing roller 42 during image formation.

[0072] In Example 2, the developing roller 42 and the supply roller 43 were configured to be at the same potential when they came into contact with the developing roller. However, the control unit 202 may control the developing voltage power supply 72 and the supply voltage power supply 75 so that the absolute value of the supply voltage in the first period (see Example 1) is less than or equal to the absolute value of the developing voltage. In other words, a potential difference may be created that causes the toner 90 to move towards the supply roller 43. For example, when using a negatively charged toner 90 as in Example 2, the following configuration may be used. Specifically, a voltage value higher on the positive side than the voltage value applied to the developing roller 42 may be applied to the supply roller 43 until it comes into contact with the developing roller, and after it comes into contact with the developing roller, the voltage may be increased so that the potential difference makes it easy for the toner 90 to move from the supply roller 43 to the developing roller 42.

[0073] As explained above, in a developing apparatus 4 in which the photosensitive drum 1 and the developing roller 42 are separable and the developing apparatus 4 includes a supply roller 43 containing foam that is in contact with the developing roller 42, the following configuration is adopted. That is, the absolute speed difference between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the developing roller 42 at the time of development contact is made smaller than at the time of image formation, and the potential difference between the developing roller 42 and the supply roller 43 is set so that the toner 90 does not move from the supply roller 43 to the developing roller 42. This makes it possible to reduce uneven toner absorption on the supply roller 43 at the time of development contact and to improve the lateral streaks in the supply roller cycle. With this configuration, there is no need to change the peripheral speed ratio between the photosensitive drum 1 and the developing roller 42, or the peripheral speed ratio between the developing roller 42 and the supply roller 43 at the time of development contact. For this reason, even in a configuration in which the photosensitive drum 1, the developing roller 42, and the supply roller 43 are driven by the same drive motor 85, it is possible to improve the lateral streaks in the supply roller cycle.

[0074] As described above, in the image forming apparatus equipped with a photosensitive drum and a developing roller that can be moved in and out of contact, the occurrence of lateral streaks in the rotation period of the supply roller, which includes foam in contact with the developing roller, can be reduced.

[0075] <Other Embodiments> The present invention can also be realized by supplying a program that implements one or more of the functions of the above embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0076] This embodiment includes the following configuration. (Composition 1) A rotatable image carrier on which an electrostatic latent image is formed, A rotatable developing member that applies a developer to the image carrier, develops the electrostatic latent image, and forms a developer image, A rotatable supply member that contacts the developing member and supplies developer to the developing member, A moving part that moves the developing member to a contact position where the developing member is in contact with the surface of the image carrier, or to a separated position where the developing member is separated from the surface of the image carrier, A drive source that drives the image carrier, the developing member, and the supply member, Control means for controlling the moving part and the drive source, An image forming apparatus comprising, Before an electrostatic latent image is formed on the image carrier, and during the first period until the developing member moves from the separated position to the contact position by the moving part, let Vo1 be the peripheral speed of the surface of the image carrier, Vd1 be the peripheral speed of the surface of the developing member, Vr1 be the peripheral speed of the surface of the supply member, |Vo1-Vd1| be the absolute value of the difference between the peripheral speed of the image carrier and the peripheral speed of the developing member, and |Vd1-Vr1| be the absolute value of the difference between the peripheral speed of the developing member and the peripheral speed of the supply member. During the second period in which an electrostatic latent image is formed on the image carrier, let Vo2 be the peripheral speed of the image carrier, Vd2 be the peripheral speed of the developing member, Vr2 be the peripheral speed of the supply member, and let |Vo2-Vd2| be the absolute value of the difference between the peripheral speed of the image carrier and the peripheral speed of the developing member, and let |Vd2-Vr2| be the absolute value of the difference between the peripheral speed of the developing member and the peripheral speed of the supply member. The control means is |Vo1-Vd1|<|Vo2-Vd2| |Vd1-Vr1|<|Vd2-Vr2| The following conditions must be met, The peripheral speed, which is the moving speed of the surface of the image carrier, is changed from Vo1 to Vo2. The peripheral speed, which is the moving speed of the surface of the developing member, is changed from Vd1 to Vd2. The peripheral speed, which is the moving speed of the surface of the supply member, is changed from Vr1 to Vr2. The drive source is controlled to progress in a monotonous manner. An image forming apparatus characterized by the following: (Configuration 2) During the first period, the ratio of the peripheral speed of the image carrier to the peripheral speed of the developing member is Vd1 / Vo1, and the ratio of the peripheral speed of the supply member to the peripheral speed of the developing member is Vr1 / Vd1. When the ratio of the peripheral speed of the image carrier to the peripheral speed of the developing member during the second period is Vd2 / Vo2, and the ratio of the peripheral speed of the supply member to the peripheral speed of the developing member is Vr2 / Vd2, The control means is Vd1 / Vo1 = Vd2 / Vo2 Vr1 / Vd1 = Vr2 / Vd2 The drive source is controlled to satisfy the relationship, The image forming apparatus according to configuration 1, characterized in that it is a picture forming apparatus. (Composition 3) A developing voltage applying means for applying a developing voltage to the developing member, A supply voltage applying means for applying a supply voltage to the supply member, Equipped with, The control means controls the developing voltage application means and the supply voltage application means so that the absolute value of the supply voltage during the first period is less than or equal to the absolute value of the developing voltage during the first period. An image forming apparatus according to configuration 1 or configuration 2, characterized by the above. (Composition 4) A charging member that charges the image carrier before the electrostatic latent image is formed, A transfer member for transferring the developer image to the object to be transferred, Equipped with, When the polarity of the developer is considered normal polarity, The charging member charges the developer remaining on the surface of the image carrier to the normal polarity after the developer image has been transferred to the transfer object by the transfer member. The developing member recovers the developer that has been charged to the normal polarity by the charging member. An image forming apparatus according to any one of configurations 1 to 3, characterized by the above. (Composition 5) The image forming apparatus can operate in multiple modes with different image forming speeds for performing image formation. The control means is In the first period when operating in a second mode other than the first mode which has the slowest image forming speed among the multiple modes, the drive source is controlled so that the peripheral speed of the image carrier, the peripheral speed of the developing member, and the peripheral speed of the supply member become the peripheral speeds in the first mode. During the first period when operating in the first mode, the drive source is controlled so that the peripheral speed of the image carrier, the peripheral speed of the developing member, and the peripheral speed of the supply member are the peripheral speeds in the first mode. An image forming apparatus according to any one of configurations 1 to 4, characterized by the above. (Composition 6) The image carrier rotates in the first direction, The developing member and the supply member rotate in a second direction opposite to the first direction. An image forming apparatus according to any one of configurations 1 to 5, characterized by the above. (Composition 7) The control means is Vd1>Vr1>Vo1 or Vd2>Vr2>Vo2 The drive source is controlled to satisfy the relationship, An image forming apparatus according to any one of configurations 1 to 6, characterized by the above. [Explanation of symbols]

[0077] 1 Photosensitive drum 42 Developing roller 43 Supply roller 50 Approach / separation mechanism 53 Intermediate transfer belt 85 Drive motor 88 Process Cartridges 90 Toner 202 Control Unit

Claims

1. A rotatable image carrier on which an electrostatic latent image is formed, A rotatable developing member that applies a developer to the image carrier, develops the electrostatic latent image, and forms a developer image, A rotatable supply member that contacts the developing member and supplies developer to the developing member, A moving part that moves the developing member to a contact position where the developing member is in contact with the surface of the image carrier, or to a separated position where the developing member is separated from the surface of the image carrier, A drive source that drives the image carrier, the developing member, and the supply member, Control means for controlling the moving part and the drive source, An image forming apparatus comprising, Before an electrostatic latent image is formed on the image carrier, and during the first period until the developing member moves from the separated position to the contact position by the moving part, let Vo1 be the peripheral speed of the surface of the image carrier, Vd1 be the peripheral speed of the surface of the developing member, Vr1 be the peripheral speed of the surface of the supply member, |Vo1 - Vd1| be the absolute value of the difference between the peripheral speed of the image carrier and the peripheral speed of the developing member, and |Vd1 - Vr1| be the absolute value of the difference between the peripheral speed of the developing member and the peripheral speed of the supply member. During the second period in which an electrostatic latent image is formed on the image carrier, let the peripheral speed of the image carrier be Vo2, the peripheral speed of the developing member be Vd2, the peripheral speed of the supply member be Vr2, the absolute value of the difference between the peripheral speed of the image carrier and the peripheral speed of the developing member be |Vo2 - Vd2|, and the absolute value of the difference between the peripheral speed of the developing member and the peripheral speed of the supply member be |Vd2 - Vr2|, The control means is |Vo1-Vd1|<|Vo2-Vd2| |Vd1-Vr1|<|Vd2-Vr2| The following conditions must be met, The peripheral speed, which is the moving speed of the surface of the image carrier, is changed from Vo1 to Vo2. The peripheral speed, which is the moving speed of the surface of the developing member, is changed from Vd1 to Vd2. The peripheral speed, which is the moving speed of the surface of the supply member, is changed from Vr1 to Vr2. The drive source is controlled to progress in a monotonous manner. An image forming apparatus characterized by the following:

2. During the first period, the ratio of the peripheral speed of the image carrier to the peripheral speed of the developing member is Vd1 / Vo1, and the ratio of the peripheral speed of the supply member to the peripheral speed of the developing member is Vr1 / Vd1. When the ratio of the peripheral speed of the image carrier to the peripheral speed of the developing member during the second period is Vd2 / Vo2, and the ratio of the peripheral speed of the supply member to the peripheral speed of the developing member is Vr2 / Vd2, The control means is Vd1 / Vo1=Vd2 / Vo2 Vr1 / Vd1=Vr2 / Vd2 The drive source is controlled to satisfy the relationship, The image forming apparatus according to feature 1.

3. A developing voltage applying means for applying a developing voltage to the developing member, A supply voltage applying means for applying a supply voltage to the supply member, Equipped with, The control means controls the developing voltage application means and the supply voltage application means so that the absolute value of the supply voltage during the first period is less than or equal to the absolute value of the developing voltage during the first period. The image forming apparatus according to feature 1.

4. A charging member that charges the image carrier before the electrostatic latent image is formed, A transfer member for transferring the developer image to the object to be transferred, Equipped with, When the polarity of the developer is considered normal polarity, The charging member charges the developer remaining on the surface of the image carrier to the normal polarity after the developer image has been transferred to the transfer object by the transfer member. The developing member recovers the developer that has been charged to the normal polarity by the charging member. The image forming apparatus according to feature 1.

5. The image forming apparatus can operate in multiple modes with different image forming speeds for performing image formation. The control means is In the first period when operating in a second mode other than the first mode which has the slowest image forming speed among the multiple modes, the drive source is controlled so that the peripheral speed of the image carrier, the peripheral speed of the developing member, and the peripheral speed of the supply member become the peripheral speeds in the first mode. During the first period when operating in the first mode, the drive source is controlled so that the peripheral speed of the image carrier, the peripheral speed of the developing member, and the peripheral speed of the supply member are the peripheral speeds in the first mode. The image forming apparatus according to feature 1.

6. The image carrier rotates in the first direction, The developing member and the supply member rotate in a second direction opposite to the first direction. The image forming apparatus according to feature 1.

7. The control means is Vd1 > Vr1 > Vo1 or Vd2 > Vr2 > Vo2 The drive source is controlled to satisfy the relationship, The image forming apparatus according to feature 1.

Images