Image forming device

Abstract

To reduce the occurrence of horizontal streaks occurring in the rotation period of a supply roller including a foam body in contact with the developing roller in an image forming apparatus having a photosensitive drum and a developing roller that can be brought into contact with and separated from each other. 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, 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 |Vo1-Vd1|<|Vo2-Vd2| |Vd1-Vr1|<|Vd2-Vr2| The drive motor 85 is controlled so as to satisfy the relationship above 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, for example, an image forming apparatus such as a copying machine, a printer, or a facsimile machine that uses an electrophotographic or electrostatic recording method. [Background technology]

[0002] An electrophotographic image forming apparatus has an image formation process including a step of uniformly charging the surface of a photosensitive drum (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 (developer). A contact development method is generally used to develop the electrostatic latent image formed on the photosensitive drum, in which a developing roller (developer carrier) is brought into contact with the photosensitive drum. The contact development method includes a contact / separation mechanism between the photosensitive drum and the developing roller at the contact point between the developing roller and the photosensitive drum to prevent deformation of the elastic developing roller. The contact / separation mechanism is configured to contact the photosensitive drum and the developing roller during image formation and separate the photosensitive drum and the developing roller at other times. In an image forming apparatus equipped with a contact / separation mechanism, for example, in Patent Document 1, the peripheral speed of the developing roller is slowed down when the photosensitive drum and the developing roller are brought into contact with each other to reduce shock jitter in an image caused by vibration of the photosensitive drum due to shock at the time of contact. This configuration reduces the shock at the time of contact. Also, in Patent Document 2, for example, the peripheral speeds of the photosensitive drum and the developing roller are made the same when they are in contact with each other to prevent image distortion caused by rotation unevenness due to load fluctuations on the photosensitive drum when the photosensitive drum and the developing roller have different peripheral speeds. This configuration reduces rotation unevenness. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-085127 [Patent Document 1] Japanese Patent Application Publication No. 05-107902 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the inventors' investigations, a configuration in which a developing roller is in contact with a supply roller serving as a developer supply member, which is made of a metal core and has a foam formed on its outer periphery, has the following problem: When a photosensitive drum and a developing roller, which have different peripheral speeds, come into contact with each other, horizontal stripes occur at the rotational frequency of the supply roller. This problem occurs when a photosensitive drum and a developing roller, which have different peripheral speeds, come into contact with each other. When a photosensitive drum and a developing roller, which have different peripheral speeds, come into contact with each other, a braking effect occurs on the surface of the developing roller and the peripheral speed of the supply roller also fluctuates. When a supply roller made of a foam fluctuates in peripheral speed, the amount of toner discharged and absorbed by the foam changes, resulting in uneven toner content on the peripheral surface of the supply roller. Uneven toner content on the peripheral surface of the supply roller causes uneven frictional resistance, which in turn causes torque unevenness with the rotational frequency of the supply roller. When an image is formed with torque unevenness with the rotational frequency of the supply roller, the peripheral speed of the developing roller fluctuates with the rotational frequency of the supply roller, resulting in an output image with horizontal stripes occurring at the rotational frequency of the supply roller.

[0005] In the above-described conventional configuration in which only the peripheral speed of the developing roller is reduced to bring the photosensitive drum and the developing roller into contact, the braking action during contact can be reduced, but it is necessary to control the peripheral speed of the developing roller alone, which requires separate drive motors to drive the photosensitive drum and the developing roller, resulting in an increase in the size of the image forming apparatus.

[0006] The present invention was made under these circumstances, and aims to reduce the occurrence of horizontal streaks that occur during the rotational cycle of a supply roller that includes a foam material and is in contact with the developing roller in an image forming device that is equipped with a photosensitive drum and a developing roller that can be brought into contact with and separated from each other. [Means for solving the problem]

[0007] In order 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 developer to the image carrier to develop the electrostatic latent image and form a developer image; a rotatable supply member that contacts the developing member to supply 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 a separation position where the developing member is spaced from the surface of the image carrier; a drive source that drives the image carrier, the developing member, and the supply member; and a control means that controls the moving unit and the drive source, wherein, before an electrostatic latent image is formed on the image carrier and until the developing member is moved from the separation position to the contact position by the moving unit, When the peripheral speed that is the moving speed of the surface of the image carrier is Vo1, the peripheral speed that is the moving speed of the surface of the developing member is Vd1, the peripheral speed that is the moving 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 a second period while an electrostatic latent image is 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| and the driving source is controlled so that the peripheral speed, which is the moving speed of the surface of the image carrier, monotonically changes from Vo1 to Vo2, the peripheral speed, which is the moving speed of the surface of the developing member, from Vd1 to Vd2, and the peripheral speed, which is the moving speed of the surface of the supply member, from Vr1 to Vr2. [Effects of the Invention]

[0009] According to the present invention, in an image forming device equipped with a photosensitive drum and a developing roller that can be brought into contact with and separated from each other, the occurrence of horizontal streaks occurring during the rotation period of a supply roller that includes a foam that is in contact with the developing roller can be reduced. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing an image forming apparatus according to first and second embodiments; [Figure 2] Block diagram showing the control configuration of the image forming apparatus according to the first and second embodiments. [Figure 3] 1 is a diagram showing a process cartridge according to first and second embodiments; [Figure 4] Timing chart of contact and separation and peripheral speed of each member in Example 1 [Figure 5] Timing chart of contact and separation and peripheral speed of each member in Comparative Example 1 compared to Example 1 [Figure 6] FIG. 10 is a diagram showing uneven toner content of the supply roller during contact and separation in Example 1. [Figure 7] FIG. 10 is a diagram showing torque fluctuations of the developing roller in Example 1. [Figure 8] Timing chart of contact / separation, developing voltage, and supply voltage in Example 2 DETAILED DESCRIPTION OF THE INVENTION

[0011] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in these embodiments are not intended to limit the scope of the present invention. Furthermore, the materials, shapes, etc. of components that have been described once in the following description will remain the same in subsequent descriptions unless otherwise specified. [Example]

[0012] <Configuration overview of image forming device> The operation of an image forming apparatus 100 according to the first embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view showing an image forming apparatus 100 equipped with a process cartridge 88 according to the first embodiment. The image forming apparatus 100 according to the first embodiment is a full-color laser beam printer employing an inline 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 in accordance with image information. The image information is input to the image forming apparatus 100 from an image reading device connected to the image forming apparatus 100 main body, or from a host device such as a personal computer connected to the image forming apparatus 100 main body so as to be able to communicate with the image forming apparatus 100 main body.

[0013] Image forming apparatus 100 has image forming stations (hereinafter also referred to as image forming units) of four colors, yellow, magenta, cyan, and black, arranged side by side from left to right in FIG. 1. Each image forming unit is an electrophotographic image forming mechanism with the same configuration except for the color of toner 90 contained as developer in each developing device 4. In the following explanation, unless a particular distinction is required, the suffixes Y (yellow), M (magenta), C (cyan), and K (black) given to reference numerals to indicate that the element is provided for one of the colors will be omitted and the explanation will be generalized.

[0014] The process cartridge 88 is detachably mounted to 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 the first embodiment, the process cartridges 88 for each color all have the same shape, and each process cartridge 88 for each color contains toner of each color, namely, 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 drums 1 serving as image carriers are driven to rotate by a drive motor 85 (see FIG. 2). The charging rollers 2 uniformly charge the surfaces of the photosensitive drums 1. A scanner unit 3 is arranged around the photosensitive drums 1. The scanner unit 3 is an exposure means that irradiates the photosensitive drums 1 with a laser based on an image signal to form an electrostatic latent image on the photosensitive drums 1. Facing the four photosensitive drums 1, an intermediate transfer belt 53 is arranged as an intermediate transfer body for transferring the toner image (developer image) on the photosensitive drums 1 to a transfer material P. The intermediate transfer belt 53, formed as an endless belt, abuts against all the photosensitive drums 1 and moves (rotates) in a circular motion in the direction of arrow B in the figure.

[0016] Four primary transfer rollers 51Y, 51M, 51C, and 51K are arranged side by side on the inner circumferential surface of the intermediate transfer belt 53, as primary transfer means, facing each photosensitive drum 1. A voltage of 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 supply 73 (see FIG. 2) as primary transfer voltage application means. This causes the toner image on the photosensitive drum 1 to be transferred (primary transfer) onto the intermediate transfer belt 53. The area where the toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 53 is called the primary transfer section.

[0017] Additionally, a secondary transfer roller 52 (transfer member) serving as a secondary transfer means is disposed on the outer peripheral surface of the intermediate transfer belt 53. A voltage of a polarity opposite 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 FIG. 2) serving as a secondary transfer voltage application means. This causes the toner image on the intermediate transfer belt 53 to be transferred (secondarily transferred) to the transfer material P. The location 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 a full-color image is formed, 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 and primarily transferred onto the intermediate transfer belt 53. Thereafter, the transfer material P is transported to the secondary transfer section in synchronization with the movement of the intermediate transfer belt 53. Then, the four-color toner images on the intermediate transfer belt 53 are collectively secondarily transferred onto the transfer material P by the action of the secondary transfer roller 52, which is in contact with the intermediate transfer belt 53 via the transfer material P. The transfer material P onto which the unfixed toner image has been transferred is conveyed to a fixing device 6 as a fixing means. In the fixing device 6, heat and pressure are applied to the transfer material P, whereby the toner image is fixed to the transfer material P, and the transfer material P is discharged outside the image forming apparatus 100 as an image-formed product.

[0018] <Control of image forming device> 2 is a block diagram showing a schematic control mode of the main parts of the image forming apparatus 100 of the first embodiment. The control unit 202 is a means for controlling the operation of the image forming apparatus 100, and transmits and receives various electrical information signals. The control unit 202 also processes electrical information signals input from various process devices and sensors, and processes command signals to the various process devices. The controller 200 transmits and receives various electrical information to and from the host device, and also controls the image forming operation of the image forming apparatus 100 in an integrated manner via the interface 201 by the control unit 202 in accordance with predetermined control programs and lookup tables.

[0019] The control unit 202 as a control means has a CPU 155 which is a central element that performs various arithmetic processing, and memories 15 such as RAM and ROM which are storage elements. The RAM stores the detection results of the sensors, the count results of the counters, the calculation results, etc., and the ROM stores the control program, 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 sending and receiving of various electrical information signals and the timing of driving each unit, thereby controlling a predetermined image formation sequence, etc.

[0020] The control unit 202 controls, for example, the following high-voltage power supplies and devices to form a toner image on the surface of the photosensitive drum 1. 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 a 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 a contact / separation mechanism 50 that contacts and separates the photosensitive drum 1 and the developing roller 42, and a drive transmission unit 80 that drives the drum unit 11 (see FIG. 3) and the developing device 4 to rotate. The drive transmission unit 80 transmits the driving force of a 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 by the driving force of the drive motor 85.

[0021] <Process cartridge configuration overview> The overall configuration of the process cartridge 88 to be mounted in the image forming apparatus 100 of the first embodiment will be described. In the first embodiment, the drum unit 11 and the developing device 4 are integrated as the process cartridge 88. Figure 3 is a main cross-sectional view of the process cartridge 88 of the first embodiment as seen along the longitudinal direction (direction of the rotation axis) of the photosensitive drum 1. In the first embodiment, the configuration and operation of the process cartridges 88 for each color are substantially the same, except for the type (color) of toner contained therein.

[0022] The process cartridge 88 receives the rotational driving force of the drive motor 85 from a drive output unit (not shown) of the image forming apparatus 100, and receives voltages (charging voltage, developing voltage, supply voltage, regulating blade voltage, etc.) from contacts of the image forming apparatus 100. The drum unit 11 includes 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 a 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 an image forming apparatus-side drum drive coupling (not shown) that serves as a drum drive output unit of the image forming apparatus 100, and the driving force of a 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 direction of arrow R1 (counterclockwise), which is a first direction. In the first embodiment, the photosensitive drum 1 is rotated at a rotational speed such that the speed (circumferential speed) of the outer circumferential surface of the photosensitive drum 1 is 148 mm / sec at full speed.

[0024] The surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. In the first embodiment, the charging roller 2 is a conductive roller having a conductive rubber layer provided on a metal core, and is disposed in parallel with the photosensitive drum 1 in contact with it at a predetermined pressure, rotating as the photosensitive drum 1 rotates. A charging voltage can be applied to the charging roller 2 from a charging voltage power supply 71. In the first embodiment, the photosensitive drum 1 is charged by applying a DC voltage of, for example, -1350 V to the charging roller 2, and the surface potential of the photosensitive drum 1 at this time is approximately -700 V. The surface potential (light area potential) of the photosensitive drum 1 after exposure in the first embodiment is set to -150 V.

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

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

[0027] The developing roller 42 is made of a metal core and a conductive elastic rubber layer having a predetermined volume resistivity provided on the outer periphery thereof, and is further configured to have a predetermined surface roughness. The developing roller 42 can be a single-layer roller or a roller with a multi-layer configuration. A single-layer roller is used in which an elastic layer made of a rubber material such as silicone rubber, urethane rubber, or hydrin rubber is formed on a core. A multi-layer roller is used in which a surface layer is formed by coating the surface of an elastic layer with a material such as silicone resin, urethane resin, polyamide resin, or fluororesin.

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

[0029] Furthermore, the supply roller 43 scrapes off remaining toner 90 on the developing roller 42 that has not been used to develop the electrostatic latent image on the photosensitive drum 1 through openings in the foam layer on its surface, and returns it to the inside of the developer container 41. The foam layer of the supply roller 43 deforms just before the nip N with the developing roller 42, and this deformation causes the toner 90 that had remained on the surface and inside to be expelled 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 N and recovers its deformation, it sucks in the toner 90 in region Y in the direction of arrow T2.

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

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

[0032] Furthermore, in order to strike a balance between supplying and scraping off toner 90 to developing roller 42, it is desirable to set the speed of supply roller 43 to 0.85 to 0.95 times the moving speed of the surface of developing roller 42. In the first embodiment, in consideration of durability, the peripheral speed ratio is set to 0.9 times, and the supply roller 43 is rotated in the direction of arrow R3 at a speed of 186 mm / sec at full speed.

[0033] The regulating blade 44 has a plate-like elastic member that is conductive and flexible. One end of the elastic member is fixed to the developer container (frame) and supported as a cantilever, and the other end is a free end that abuts against the circumferential surface of the developing roller 42. The regulating blade 44 is disposed in contact with the circumferential surface of the developing roller 42 at a position downstream of the opposing portion (contact portion) of the supply roller 43 and the developing roller 42 in the moving direction (rotation direction) of the surface of the developing roller 42. In Example 1, a stainless steel material is used as the elastic member of the regulating blade 44. In Example 1, the regulating blade 44 is disposed such that, at the contact position with the developing roller 42, the tip end of the free end of the elastic member faces upstream in the moving direction of the surface of the developing roller 42 (counter direction).

[0034] Furthermore, predetermined DC voltages are applied to the developing roller 42, the supply roller 43, and the regulating blade 44 from a developing voltage power supply 72, a supply voltage power supply 75, and a regulating blade voltage power supply 76 (see FIG. 2), respectively, depending on the image forming operation, etc. In the first embodiment, during image formation, a DC voltage of −450 V is applied to the developing roller 42, a DC voltage of −550 V is applied to the supply roller 43, and a DC voltage of −550 V is applied to the regulating blade 44. Since the normal charging polarity of the toner 90 in the first embodiment is negative, the potential difference between the supply roller 43 and the developing roller 42 has a polarity that urges (moves) the toner 90 from the supply roller 43 side toward the developing roller 42 side.

[0035] In Example 1, the toner 90 is a negatively charged non-magnetic toner produced by a suspension polymerization method. However, the toner 90 is not limited to this, and may be a toner produced by other polymerization methods, such as a pulverization method or an emulsion polymerization method. The volume average particle size of the toner 90 is preferably 5.0 to 8.0 μm. The volume average particle size of the toner 90 was measured using a precision particle size distribution analyzer, Multisizer 3, manufactured by Beckman Coulter, Inc. In Example 1, the volume average particle size of the toner 90 was approximately 7.0 μm.

[0036] Toner 90 may also contain additives (hereinafter referred to as external additives) such as fluidizing agents to improve fluidity, charging properties, cleaning properties, etc. Examples of external additives include inorganic oxide particles such as silica particles, alumina particles, and titanium oxide particles; inorganic stearic acid compound particles such as aluminum stearate particles and zinc stearate particles; and inorganic titanic acid compound particles such as strontium titanate and zinc titanate. These may be used alone or in combination of two or more. These inorganic particles are preferably gloss-treated with a silane coupling agent, a titanium coupling agent, a higher fatty acid, a silicone oil, or the like to improve heat-resistant storage properties and environmental stability. The BET specific surface area of ​​the external additive is 10 m or less. 2 / g or more 450m 2 / g or less is preferable.

[0037] The BET specific surface area can be determined by a low-temperature gas adsorption method using a dynamic constant pressure method in accordance with the BET method (preferably the BET multipoint method). For example, a specific surface area measuring device (trade name: Gemini 2375 Ver. 5.0, manufactured by Shimadzu Corporation) is used to adsorb nitrogen gas onto the surface of a sample, and the BET multipoint method is used to measure the BET specific surface area (m 2 / g) can be calculated. The total amount of these various external additives added is 0.05 parts by mass or more and 5 parts by mass or less, and preferably 0.1 parts by mass or more and 3 parts by mass or less, relative to 100 parts by mass of toner. Various external additives may also 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 the first embodiment, such residual toner is charged to a negative polarity, which is the normal polarity (normal charging polarity) of the toner 90, by discharge from the charging roller 2. The charged residual toner enters a charging section, which is a contact point between the charging roller 2 and the photosensitive drum 1. At this time, the residual toner in the charging section is negatively charged by discharge from the charging roller 2, and therefore passes through the charging section while remaining electrostatically on the photosensitive drum 1. Subsequently, the residual toner that has passed through the charging section moves to a developing section, which is a contact point between the developing roller 42 and the photosensitive drum 1. In this developing section, if the surface of the photosensitive drum 1 to which the residual toner adheres is a non-image forming area (dark potential forming area), the toner is collected from the surface of the photosensitive drum 1 by the developing roller 42 due to the potential relationship between the photosensitive drum 1 and the developing roller 42. That is, negative residual toner is collected by a potential difference of 350 V between the dark area potential of the photosensitive drum 1, which is -700 V, and the development voltage potential, which is -350 V. Increasing this potential difference improves collection efficiency, but the potential difference is determined taking into consideration latent image formation and developability during image formation. Furthermore, the development collection efficiency also changes depending on the difference in the movement speed of the surfaces of the photosensitive drum 1 and the development roller 42 (hereinafter referred to as the surface movement speed difference), and the development collection efficiency improves as the surface movement speed difference increases. On the other hand, when the surface of the photosensitive drum 1 to which the residual toner adheres is in the image formation area (light area potential formation area), the residual toner remains on the surface of the photosensitive drum 1 and is used as toner 90 for image formation.

[0039] A system in which residual toner is collected by the developing roller 42 is a so-called cleanerless system. The cleanerless drum unit 11 is composed only of the photosensitive drum 1, which has a hollow interior and is lightweight, and the charging roller 2, which rotates following the rotation of the photosensitive drum 1, so the load torque during rotation is extremely small. For this reason, in the first embodiment, the drum unit 11 and the developing device 4 are driven by the same drive source, the drive motor 85, and the number of drive sources is minimized, thereby reducing the size of the image forming apparatus 100.

[0040] <Configuration and operation of contact / separation mechanism> In the first embodiment, 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 being performed (hereinafter referred to as non-image formation or non-image formation time). That is, the control unit 202 controls the presence or absence of contact between the photosensitive drum 1 and the developing roller 42 (development contact / separation operation) using the contact / separation mechanism 50. The developing roller 42 contacts the surface of the photosensitive drum 1 at a contact position A during image formation (hereinafter referred to as development contact), and during non-image formation, moves to a separation position where it is separated from the surface of the photosensitive drum 1 by a predetermined distance G (hereinafter referred to as development separation) except during continuous image formation. Note that FIG. 3 shows the development separation state in which the developing roller 42 has moved to the separation 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 connected to a frame that fixes the position of the photosensitive drum 1 so that it can swing around a rotation axis that is approximately parallel to the rotation axis direction of the photosensitive drum 1. By operating the moving member 82 to move the lever 81, the developing device 4 can be swung and moved between the contact position and the separation position.

[0042] The movement of the developing device 4 to the contact position is caused by the spring force of a tension spring (not shown) and a rotational moment centered on the drive input to the developing device 4 when the developing device 4 is driven. Here, the tension spring functions as a biasing means, with both ends attached to a frame that fixes the position of the photosensitive drum 1 and to the developing 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 developing device 4 is held at the separated position in conjunction with the movement of the lever 81. Then, the spring force and the rotational moment cause the developing device 4 to swing, and the developing roller 42 moves toward the photosensitive drum 1. This moves the developing device 4 to the contact position, allowing the developing roller 42 to contact 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 contact / separation mechanism 50 in the direction of arrow P2 away from the photosensitive drum 1, and moves the lever 81 in the same direction to hold the developing device 4 at 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 a driving force from a motor or a solenoid, which serves as a driving source provided in the image forming apparatus 100, via a drive transmission member.

[0044] In the first embodiment, during image formation, the developing device 4 is disposed in the contact position, and the developing roller 42 is in contact with the photosensitive drum 1. Also, during standby, sleep, power-off, and other times other than during image formation, the developing device 4 is disposed in the separated position, and the developing roller 42 is in a separated state from the photosensitive drum 1. In this way, 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 contact / separation and the peripheral speed of each member in Example 1. In Figure 4, (i) indicates the contact / separation (contact, separation) state t101 of the developing roller 42, (ii) indicates the speed of the drive motor 85 (drive motor speed t102) (full speed, low speed, stopped), (iii) indicates the movement speed of the surface of the photosensitive drum 1 (photosensitive drum speed t103) (full speed, low speed, stopped), (iv) indicates the movement speed of the surface of the developing roller 42 (developing roller speed t104) (full speed, low speed, stopped), (v) indicates the movement speed of the surface of the supply roller 43 (supply roller speed t105) (full speed, low speed, stopped), (vi) indicates the development voltage t113 (0 V, -450 V), and (vii) indicates the supply voltage t114 (0 V, -550 V). Furthermore, a to c of t102 to t105, t113, a and b of t114, t106 to t108, and t110 to t112 are timings, and t109 is a period.

[0046] In the first embodiment, the control unit 202 performs the following control to prevent horizontal streaks that occur during full-speed printing at the rotational period of the supply roller 43 (hereinafter referred to as the supply roller period) due to development contact. As shown in the timing chart of FIG. 4, after receiving a print signal at t106, the control unit 202 drives the drive motor at a low speed t102 (t102a) while the contact / separation interval t101 is in the separation state. This causes the peripheral speeds of the photosensitive drum 1, the development roller 42, and the supply roller 43 to be uniformly slowed down. Therefore, when the development roller 42 contacts the photosensitive drum 1 at timing t107, the photosensitive drum 1, the development roller 42, and the supply roller 43 are all driven at speeds slower than those during full-speed image formation. The peripheral speeds of the photosensitive drum 1, the development roller 42, and the supply roller 43 are all 49 mm / sec, 69 mm / sec, and 62 mm / sec, respectively.

[0047] (Full speed mode, low speed mode) The image forming apparatus 100 of the first embodiment is operable in a plurality of modes with different image formation speeds for forming images. The image forming apparatus 100 is configured to perform image formation in a low-speed mode to improve fixation when printing on cardboard or the like, and to perform image formation in a full-speed mode when printing on plain paper. In the first embodiment, the low-speed mode corresponds to a first mode having the slowest image formation speed among the plurality of modes, and the full-speed mode corresponds to a second mode other than the first mode. When performing image formation in the 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 speeds in the low-speed mode from the developer separation state until the developer contact state is completed.

[0048] On the other hand, when forming an image in the low-speed mode, the control unit 202 is configured to control the rotation of the photosensitive drum 1, the developing roller 42, and the supply roller 43 while maintaining the low-speed mode from the developer separation to the completion of developer contact and further until the end of image formation. To prevent horizontal streaks occurring during 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 developer contact, and the absolute speed difference between the supply roller 43 and the developing roller 42. If the absolute speed differences during image formation are effective in preventing horizontal streaks occurring during the supply roller cycle, the low-speed mode may be maintained from the developer separation to the end of image formation. However, if it is desired to further prevent horizontal streaks occurring during the supply roller cycle, this is not the only option, and the rotation speed may be controlled to be slower than the rotation speed during image formation in the low-speed mode from the developer separation to the developer contact.

[0049] On the other hand, by rotating and contacting at a slower speed, the absolute speed difference between the photosensitive drum 1 and the developing roller 42 is reduced, which can be effective in reducing horizontal streaks due to the supply roller cycle. However, if either the photosensitive drum 1 or the developing roller 42 contacts while not rotating, the toner 90 on the developing roller 42 may adhere. Therefore, to prevent toner adhesion, it is desirable to have the photosensitive drum 1 and the developing roller 42 contact each other 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 during development contact. This confirmed an improvement in the horizontal streaks due to the supply roller cycle. At this time, the absolute speed difference between the photosensitive drum 1 and the developing roller 42 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 during development contact and the peripheral speed ratio between the developing roller 42 and the supply roller 43 are the same as the peripheral speed ratio during image formation, 1.4 times and 0.9 times, respectively.

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

[0051] In this state, the control unit 202 performs development contact at t107, and after completion of development contact (after t107), increases the drive motor speed t102 to full speed (t102b) until image exposure is started by the scanner unit 3 at t108. ​​As a result, the control unit 202 increases the peripheral speeds of the photosensitive drum 1 (t103b), the development roller 42 (t104b), and the supply roller 43 (t105b) to the peripheral speeds (full speeds) used during image formation. Thereafter, the control unit 202 starts image exposure at t108 and performs image formation during period t109. After image exposure is completed at t110, the control unit 202 performs development separation at t111, and after development separation, stops the drive motor 85 (t102c) to stop the rotation of the photosensitive drum 1 (t103c), the development 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 ends 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. An all-black image was printed on A4-size plain paper in an environment of 25°C / 50% RH, and a sensory evaluation was performed. As a comparative example, a timing chart of Comparative Example 1 is shown in FIG. 5. Note that (i) to (vii) in FIG. 5 correspond to (i) to (vii) in FIG. 4, and t301 to t314 correspond to t101 to t114. Also, the d in t302 to t305, t313, and t314 indicates timing.

[0053] In Comparative Example 1, the control unit 202 drives the drive motor 85 at full speed (t302d) after receiving a print signal (t306). As a result, the control unit 202 drives the photosensitive drum 1 (t303d), the developing roller 42 (t304d), and the supply roller 43 (t305d) at full speed. Furthermore, after receiving a print signal (t306), the control unit 202 drives the drive motor 85 (t302d) and applies a voltage of −450 V (t313d) to the developing roller 42 and −550 V (t314d) to the supply roller 43, respectively, to perform development contact (t307). The subsequent operations from the start of image exposure (t308) to the end of image formation (t312) are the same as those in Example 1, and therefore will not be described again.

[0054] Table 1 shows the results of a sensory evaluation conducted by the inventors regarding horizontal streaks in the supply roller cycle. The symbols A, B, C, and D in Table 1 represent A: Excellent, B: Good, C: Fair, and D: Bad, respectively. In other words, Table 1 shows that C had a better sensory evaluation result than D, and A had a better sensory evaluation result than B (A>B>C>D). [Table 1] As shown in Table 1, Example 1 achieved rank B, which was superior to Comparative Example 1 in terms of the occurrence of horizontal streaks at the supply roller cycle, as compared to Rank D. The reason for this will be explained with reference to FIGS.

[0055] FIG. 6(a) shows a state in which the photosensitive drum 1 and the developing roller 42 are rotationally driven in a development separation state with a gap G between them. During the development separation state, the photosensitive drum 1 rotates at a peripheral speed of Vo, the developing roller 42 rotates at a peripheral speed of Vd, and the supply roller 43 rotates at a peripheral speed of Vr, with the magnitude of the peripheral speeds being in the order Vd > Vr > Vo. FIG. 6(b) shows a state in which the photosensitive drum 1 and the developing roller 42 are in development contact, and because the peripheral speed Vo of the photosensitive drum 1 and the peripheral speed Vd of the developing roller 42 contact each other in a different state (Vd > Vo), a braking action, indicated by arrow B, occurs on the surface of the developing roller 42. When 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 action also becomes greater.

[0056] Furthermore, the supply roller 43, which rotates at Vr during the developer separation, also slows down due to the braking effect of the developing roller 42 when in contact. As previously mentioned, the supply roller 43 repeatedly deforms and recovers its foam layer as the developing roller 42 contacts and rotates, expelling toner 90 in the direction T1 toward region X in FIG. 6B and suctioning toner 90 in the direction T2 from region Y. The greater 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, the greater the kinetic energy, resulting in greater deformation and recovery of the foam layer. If the peripheral speed of the supply roller 43 changes in part of its circumferential direction, the amount of toner 90 expelled and absorbed at the location 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] FIG. 7 shows torque data for the developing roller 42 when there is a toner 90-containing uneven portion U on the circumferential surface of the supply roller 43. In FIG. 7, the horizontal axis represents time and the vertical axis represents the torque of the developing roller 42. Also, ▼ indicates the timing when the toner 90-containing uneven portion U of the supply roller 43 passes through the contact point with the developing roller 42. As shown in the graph in FIG. 7, when the toner 90-containing uneven portion U of the supply roller 43 passes through the contact point with the developing roller 42, the torque of the developing roller 42 fluctuates due to uneven frictional resistance. This causes the peripheral speed Vd of the developing roller 42 after contact to fluctuate with the supply roller cycle, resulting in horizontal streaks in the image with the supply roller cycle. For this reason, horizontal streaks with the supply roller cycle, ranked D in the sensory evaluation, occurred in Comparative Example 1.

[0058] On the other hand, in the configuration of Example 1, development contact is performed at a low rotational drive speed, so 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 than when contact is performed 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 than when contact is performed at full speed. Table 2 shows the |Vo-Vd| and |Vr-Vd| values ​​for Example 1 and Comparative Example 1. [Table 2]

[0059] As described above, in the first embodiment, the control unit 202 performs the following control. First, the period before an electrostatic latent image is formed on the photosensitive drum 1 (FIG. 6 - t108) and until the contact / separation mechanism 50 moves the developing roller 42 from the separated position to the contact position (FIG. 6 - t107) is defined as a first period. During the first period, the peripheral speed of the photosensitive drum 1 is defined as Vo1, the peripheral speed of the developing roller 42 is defined as Vd1, and the peripheral speed of the supply roller 43 is defined as Vr1. Furthermore, during the first period, the absolute value of the difference between the peripheral speeds of the photosensitive drum 1 and the developing roller 42 is defined as |Vo1-Vd1|, and the absolute value of the difference between the peripheral speeds of the developing roller 42 and the supply roller 43 is defined as |Vd1-Vr1|. Furthermore, the period during which an electrostatic latent image is formed on the photosensitive drum 1 (FIG. 6 - t108-t110) is defined as a second period. In 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. In addition, in 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 control unit 202 controls the drive motor 85 so as to satisfy the relationship above and to satisfy the following relationship: That is, the control unit 202 controls the drive motor 85 so that the peripheral speed of the photosensitive drum 1 monotonically changes from Vo1 to Vo2, the peripheral speed of the developing roller 42 monotonically changes from Vd1 to Vd2, and the peripheral speed of the supply roller 43 monotonically 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 in 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. The ratio of the peripheral speed of the photosensitive drum 1 to the peripheral speed of the developing roller 42 in the second period 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 so as to satisfy the relationship:

[0061] In other words, in terms of modes, the control unit 202 controls the drive motor 85 so that the circumferential speeds of the photosensitive drum 1, the developing roller 42, and the supply roller 43 become the circumferential speeds in the low-speed mode during the first period when operating in the full-speed mode. Then, the control unit 202 controls the drive motor 85 so that the full-speed mode is established during the second period. On the other hand, the control unit 202 controls the drive motor 85 so that the circumferential speeds of the photosensitive drum 1, the developing roller 42, and the supply roller 43 become the circumferential speeds in the low-speed mode during the first period when operating in the low-speed mode, and maintains the low-speed mode in 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 and contacting the developing roller 42, the braking action applied to the developing roller 42 during 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, which reduces the amount of deformation and recovery of the foam layer of the supply roller 43. This reduces unevenness in the amount of toner 90 absorbed on the peripheral surface of the supply roller 43, thereby suppressing torque fluctuations in the developing roller 42. Therefore, the developing roller 42 can rotate stably even after contacting the developing roller 42, and therefore Example 1 received a rank B in the sensory evaluation, with improved horizontal streaks occurring during the supply roller cycle.

[0063] As described above, in a configuration in which the photosensitive drum 1 and the developing roller 42 are separable and the developing device 4 includes a supply roller 43 that includes a foamed material and is in contact with the developing roller 42, the following configuration can be used to achieve advantageous effects. Specifically, in Example 1, the absolute speed difference between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the developing roller 42 during 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 those during image formation. This makes it possible to improve horizontal streaks occurring during the supply roller rotation. This configuration eliminates the 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 during development contact. Furthermore, horizontal streaks occurring during the supply roller rotation can be improved 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.

[0064] As described above, according to the first embodiment, in an image forming apparatus equipped with a photosensitive drum and a developing roller that can be brought into contact with and separated from each other, it is possible to reduce the occurrence of horizontal streaks that occur during the rotation period of a supply roller that includes a foam that is in contact with the developing roller. [Example]

[0065] In the second embodiment, the supply voltage applied to the supply roller 43 during the development contact in the first embodiment is controlled, and horizontal streaks occurring during the supply roller cycle are further reduced. Note that the description of the image forming apparatus 100, the process cartridge 88, and the timing chart that overlap with the first embodiment will be omitted.

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

[0067] After receiving the print signal (t206), the control unit 202 drives the drive motor 85 at low speed (t202a) in the developer separation state (t201). At this time, in the second embodiment, 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). The control unit 202 uniformly slows down the peripheral speeds of the photosensitive drum 1 (t203a), the development roller 42 (t204a), and the supply roller 43 (t205a) while maintaining the same voltage applied to the supply roller 43 and the development roller 42.

[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) until image exposure is started by the scanner unit 3 (t208). As a result, the control unit 202 increases the peripheral speeds of the photosensitive drum 1 (t203b), the development roller 42 (t204b), and the supply roller 43 (t205b) to the peripheral speeds required for image formation. At the same time, the control unit 202 also increases the supply voltage applied to the supply roller 43 to −550 V (t214e). Thereafter, the control unit 202 starts image exposure (t208) and performs image formation (t209). The subsequent operations from the end of image exposure (t210) to the end of image formation (t212) are the same as those in the first embodiment, and therefore will not be described again.

[0069] <Verification of effectiveness> An image evaluation was performed using the image forming apparatus 100 of Example 2 and the process cartridge 88. An all-black image was printed on A4-size plain paper in an environment of 25°C / 50% RH, and a sensory evaluation was performed. The results are shown in Table 3. Table 3 shows the results of the sensory evaluation performed by the inventors regarding horizontal streaks due to the supply roller cycle. [Table 3] As shown in Table 3, Example 2 was ranked A, which was superior to Comparative Example 1 in terms of the occurrence of horizontal streaks at the supply roller cycle. The reason for this will be explained below.

[0070] In the second embodiment, the potential difference between the developing roller 42 and the supply roller 43 when they are in contact with each other is set to the same potential. Factors that cause toner to be expelled 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 the second embodiment, it is possible to eliminate the expulsion of toner 90 from the supply roller 43 to the developing roller 42 due to the potential difference. In other words, it is possible to suppress the amount of toner 90 expelled when the peripheral speed of the supply roller 43 fluctuates. This makes it possible to reduce unevenness in the toner content on the peripheral surface of the supply roller 43.

[0071] In this way, by slowing down the photosensitive drum 1 and developing roller 42 during development contact, reducing the absolute speed difference, and by making the developing roller 42 and supply roller 43 the same potential, it is possible to suppress uneven toner absorption on the supply roller 43 during development contact. As a result, the developing roller 42 can rotate stably even after development contact, and Example 2 was ranked A in the sensory evaluation, with improved horizontal streaks occurring during the supply roller cycle. After development contact, the supply voltage is increased to a voltage value that creates a potential difference that makes it easy for toner 90 to move from the supply roller 43 to the developing roller 42, allowing for stable toner supply to the developing roller 42 during image formation.

[0072] In the second embodiment, the developing roller 42 and the supply roller 43 are configured to have the same potential when they contact each other for development. 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 during the first period (see the first embodiment) is equal to or less than the absolute value of the developing voltage. That is, a potential difference may be created so that the toner 90 moves toward the supply roller 43. For example, when using a negatively charged toner 90 as in the second embodiment, 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 the developing roller 42 contacts the supply roller 43, and after the developing roller 42 contacts the supply roller 43, the voltage may be increased to create a potential difference that facilitates the movement of the toner 90 from the supply roller 43 to the developing roller 42.

[0073] As described above, the photosensitive drum 1 and the developing roller 42 are separable, and the developing device 4 includes a supply roller 43 that includes a foamed material and is in contact with the developing roller 42. The following configuration is adopted: Specifically, the absolute speed difference between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the developing roller 42 during development contact is made smaller than during image formation, and the potential difference between the developing roller 42 and the supply roller 43 is reduced to prevent the toner 90 from moving from the supply roller 43 to the developing roller 42. This reduces the unevenness of the toner content of the supply roller 43 during development contact, and improves horizontal streaks occurring during the supply roller cycle. This configuration eliminates the 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 during development contact. Therefore, horizontal streaks occurring during the supply roller cycle can be improved even in a configuration in which the same drive motor 85 drives the photosensitive drum 1, the developing roller 42, and the supply roller 43.

[0074] As described above, according to the second embodiment, in an image forming apparatus equipped with a photosensitive drum and a developing roller that can be brought into contact with and separated from each other, it is possible to reduce the occurrence of horizontal streaks that occur during the rotation period of a supply roller that includes a foam that is in contact with the developing roller.

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

[0076] The disclosure of this embodiment includes the following configuration. (Configuration 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 to develop the electrostatic latent image and form a developer image; a rotatable supply member that contacts the developing member to supply 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 spaced position where the developing member is spaced from the surface of the image carrier; a drive source that drives the image carrier, the developing member, and the supply member; a control unit for controlling the moving unit and the drive source; An image forming apparatus comprising: During a first period before an electrostatic latent image is formed on the image carrier and until the developing member is moved from the separated position to the contact position by the moving unit, a peripheral speed that is the moving speed of the surface of the image carrier is defined as Vo1, a peripheral speed that is the moving speed of the surface of the developing member is defined as Vd1, a peripheral speed that is the moving speed of the surface of the supply member is defined as Vr1, an absolute value of a difference between the peripheral speed of the image carrier and the peripheral speed of the developing member is defined as |Vo1-Vd1|, and an absolute value of a difference between the peripheral speed of the developing member and the peripheral speed of the supply member is defined as |Vd1-Vr1|, During a second period while an electrostatic latent image is formed on the image carrier, when 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| and 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. controlling the driving source so as to transition monotonically; An image forming apparatus characterized by: (Configuration 2) a ratio of the peripheral speed of the image carrier to the peripheral speed of the developing member in the first period is Vd1 / Vo1, and a 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 in 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 Vd1 / Vo1=Vd2 / Vo2 Vr1 / Vd1=Vr2 / Vd2 and controlling the driving source so as to satisfy the relationship: 2. The image forming apparatus according to claim 1, (Configuration 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 in the first period is equal to or less than the absolute value of the developing voltage in the first period. 3. The image forming apparatus according to claim 1, wherein: (Configuration 4) a charging member for charging the image carrier before an electrostatic latent image is formed; a transfer member for transferring the developer image to a transfer target; Equipped with When the polarity of the developer is normal, the charging member charges the developer remaining on the surface of the image carrier to the normal polarity after the developer image is transferred to the transfer target by the transfer member; the developing member collects the developer charged to the normal polarity by the charging member; 4. The image forming apparatus according to any one of configurations 1 to 3. (Configuration 5) the image forming apparatus is operable in a plurality of modes with different image forming speeds for forming images; The control means controlling the driving source 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 a second mode other than the first mode having the slowest image forming speed among the plurality of modes; 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; 5. The image forming apparatus according to any one of configurations 1 to 4. (Configuration 6) The image carrier rotates in a first direction, the developing member and the supply member rotate in a second direction opposite to the first direction; 6. The image forming apparatus according to any one of configurations 1 to 5, wherein: (Configuration 7) The control means Vd1>Vr1>Vo1 or Vd2>Vr2>Vo2 The driving source is controlled so as to satisfy the relationship: 7. The image forming apparatus according to any one of configurations 1 to 6, wherein: [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 cartridge 90 toner 202 Control section

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 to develop the electrostatic latent image and form a developer image; a rotatable supply member that contacts the developing member to supply 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 spaced position where the developing member is spaced from the surface of the image carrier; a drive source that drives the image carrier, the developing member, and the supply member; a control unit for controlling the moving unit and the drive source; An image forming apparatus comprising: During a first period before an electrostatic latent image is formed on the image carrier and until the developing member is moved from the separated position to the contact position by the moving unit, a peripheral speed that is the moving speed of the surface of the image carrier is defined as Vo1, a peripheral speed that is the moving speed of the surface of the developing member is defined as Vd1, a peripheral speed that is the moving speed of the surface of the supply member is defined as Vr1, an absolute value of a difference between the peripheral speed of the image carrier and the peripheral speed of the developing member is defined as |Vo1-Vd1|, and an absolute value of a difference between the peripheral speed of the developing member and the peripheral speed of the supply member is defined as |Vd1-Vr1|, During a second period while an electrostatic latent image is formed on the image carrier, when 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| and 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. controlling the driving source so as to transition monotonically; An image forming apparatus characterized by:

2. a ratio of the peripheral speed of the image carrier to the peripheral speed of the developing member in the first period is Vd1 / Vo1, a 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 in 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 Vd1 / Vo1=Vd2 / Vo2 Vr1 / Vd1=Vr2 / Vd2 and controlling the driving source so as to satisfy the relationship:

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

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 in the first period is equal to or less than the absolute value of the developing voltage in the first period.

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

4. a charging member for charging the image carrier before an electrostatic latent image is formed; a transfer member for transferring the developer image to a transfer target; Equipped with When the polarity of the developer is normal, the charging member charges the developer remaining on the surface of the image carrier to the normal polarity after the developer image is transferred to the transfer target by the transfer member; the developing member collects the developer charged to the normal polarity by the charging member; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. the image forming apparatus is operable in a plurality of modes with different image forming speeds for forming images; The control means controlling the driving source 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 a second mode other than the first mode having the slowest image forming speed among the plurality of modes; 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; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

6. The image carrier rotates in a first direction, the developing member and the supply member rotate in a second direction opposite to the first direction; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

7. The control means Vd1>Vr1>Vo1 or Vd2>Vr2>Vo2 The driving source is controlled so as to satisfy the relationship:

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

Images