JP2015169812A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing toner spill.SOLUTION: An image forming device 1 comprises: a suction duct 160 disposed above a photoreceptor drum 413 and developing roller 110, and forming an air channel for sucking toner dispersing from a surface of the developing roller 110 from a suction port 162; and a suction fan 170 for generating the air flow. On the suction duct 160, on a part R1 which is extending downward with respect to a horizontal direction from the suction fan 170 to the suction port 162, an upper wall 160A has a second bending part 164 bending to outside of the suction duct 160, and a first bending part 166 bending to outside of the suction duct 160 is formed on a bottom wall 160B. The second bending part 164 is formed on an upstream side of the first bending part 166 in a toner suction direction.

Description

  The present invention relates to an electrophotographic image forming apparatus.

  In general, an image forming apparatus (printer, copier, facsimile, etc.) using an electrophotographic process technology generates an electrostatic latent image by irradiating (exposing) a charged photoconductor with a laser beam based on image data. Form. Then, by supplying toner from the developing device to the photosensitive member (image carrier) on which the electrostatic latent image is formed, the electrostatic latent image is visualized to form a toner image. Further, after the toner image is directly or indirectly transferred to the paper, it is fixed by heating and pressurizing to form an image on the paper.

  As a developing device used in an image forming apparatus, one using a two-component developer composed of a toner and a carrier is often used. The developing device includes a developing roller disposed close to the photosensitive drum, and the developing roller has a plurality of magnetic poles therein. The developing roller carries the developer on its outer peripheral surface by the magnetic field generated from the magnetic pole and supplies it to the photosensitive drum.

  When the developer has not been used for a long time or left in a high-temperature and high-humidity environment, the toner and carrier are not triboelectrically charged or difficult to triboelectrically charge. To do. As described above, when the image forming operation is started in a state where the charge amount of the toner is reduced, the electrostatic adhesion force between the toner and the carrier is weakened. The detached toner scatters from the opening of the developing device serving as a developing region facing the photosensitive drum (toner scatter). When toner scattering occurs, the scattered toner accumulates in the vicinity of the developing device and the photosensitive drum. Thereafter, there is a problem that an image defect called toner spillage occurs due to the accumulated toner falling on the developing sleeve or the photosensitive drum due to vibration during image formation or maintenance.

  With respect to the above problem, Japanese Patent Laid-Open No. 2004-228688 discloses that a gap between a developing device and a photosensitive member is provided in the vicinity of a developing device that supplies toner to the photosensitive member, more specifically, directly between a photosensitive drum and a developing sleeve. A technique is disclosed in which a suction device that sucks negatively sucked toner is provided.

  Patent Document 2 discloses a technique for preventing toner scattering from a developing device by providing a duct formed by a duct forming member and a cover and a fan for sucking scattered toner from the duct.

  Patent Document 3 discloses a suction unit provided with an upper duct for sucking toner scattered near the developing sleeve and the peripheral surface of the photosensitive drum on the upper surface of the developing device housing. .

JP 2001-265111 A JP 2008-39965 A JP-A-5-346728

  However, in the technique described in Patent Document 1, since the distance between the suction device and the developing sleeve is large, the toner scattered between the developing device and the photosensitive member is not covered by the upper lid portion of the developing device or the developing sleeve. There is a problem in that it accumulates on the outer wall of the suction device opposite to the surface and may fall on the developing sleeve or the photosensitive drum.

  In the technique described in Patent Document 2, since the distance between the top of the duct and the photosensitive member is very short, the air sucked from the end of the duct reaches the surface of the developing sleeve and is carried on the surface. As a result, the toner flying up causes toner scattering.

  Further, the technique described in Patent Document 3 has a problem that scattered toner accumulates on the outer wall of the upper duct facing the developing sleeve and may fall on the developing sleeve. In addition, the toner scattered in the vicinity of the developing sleeve and the peripheral surface of the photosensitive drum is sucked through the upper duct, but the flow passage cross-sectional area in the upper duct is small, that is, the air intake resistance in the upper duct. Will increase. Therefore, in order to sufficiently suck the toner scattered near the developing sleeve and the peripheral surface of the photosensitive drum, there is a problem that a large electric power is required to drive the suction unit.

  An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of toner spillage.

An image forming apparatus according to the present invention includes:
A developer carrier disposed opposite to the image carrier, transported while carrying a developer containing toner and carrier, and supplying the toner in the developer to the image carrier;
A suction duct that is disposed above the image carrier and the developer carrier and forms an air flow path for sucking toner scattered from the surface of the developer carrier from a suction port;
A suction fan for generating the air flow;
With
A first bent portion that is bent outward from the suction duct is formed on a bottom wall of a portion of the suction duct that extends downward from the horizontal direction from the suction fan toward the suction port, and an upper wall of the portion. Is formed with a second bent portion that bends outside the suction duct,
The second bent portion is formed on the upstream side of the first bent portion in the toner suction direction.

An image forming apparatus according to the present invention includes:
A developer carrier disposed opposite to the image carrier, transported while carrying a developer containing toner and carrier, and supplying the toner in the developer to the image carrier;
A suction duct that is disposed above the image carrier and the developer carrier and forms an air flow path for sucking toner scattered from the surface of the developer carrier from a suction port;
A suction fan for generating the air flow;
With
The upper wall of the suction duct that extends downward from the horizontal direction from the suction fan toward the suction port is formed in a flat shape, and the bottom wall of the part is bent to the outside of the suction duct. 1 bend is formed,
The first bent portion is formed on a downstream side of an end portion on the suction port side of the upper wall in the toner suction direction.

  According to the present invention, since the peak of the suction air velocity at the suction port of the suction duct approaches the upper wall side, the air reaching the surface of the developer carrier among the air (intake air) guided to the suction duct. The wind speed becomes relatively slow, and the amount of toner scattered from the surface of the developer carrier by the air can be reduced. As a result, the amount of toner that scatters from the surface of the developer carrying member and adheres to and accumulates in the vicinity of the intake port can be reduced. Therefore, it is possible to suppress the occurrence of toner spillage (image defect) caused by the toner accumulated in the vicinity of the air inlet falling on the developer carrier or the image carrier.

1 is a diagram schematically showing an overall configuration of an image forming apparatus in the present embodiment. FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus according to the present embodiment. FIG. 2 is a diagram schematically showing a configuration of a developing device in the present embodiment. It is a figure which shows distribution of the suction wind speed in the nearest cross section. It is a figure which shows roughly the modification of the structure of the image development apparatus in this Embodiment. 1 is a diagram schematically showing a configuration of a developing device in an embodiment. It is a figure which shows schematically the structure of the image development apparatus in a comparative example. It is a table | surface showing the result of evaluation experiment.

Hereinafter, the present embodiment will be described in detail with reference to the drawings.
[Configuration of Image Forming Apparatus 1]
FIG. 1 is a diagram schematically showing an overall configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 shows a main part of the control system of the image forming apparatus 1 according to the present embodiment. An image forming apparatus 1 shown in FIGS. 1 and 2 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 1 transfers the toner images of Y (yellow), M (magenta), C (cyan), and K (black) formed on the photosensitive drum 413 to the intermediate transfer belt 421 (primary transfer). Then, after superposing four color toner images on the intermediate transfer belt 421, the toner images are transferred to the paper S (secondary transfer) to form an image.

  Further, in the image forming apparatus 1, the photosensitive drums 413 corresponding to the four colors of YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and the respective color toner images are sequentially transferred to the intermediate transfer belt 421 in one step. Tandem system is adopted.

  As illustrated in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 100.

  The control unit 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, and the like. The CPU 101 reads a program corresponding to the processing content from the ROM 102 and develops it in the RAM 103, and centrally controls the operation of each block of the image forming apparatus 1 in cooperation with the developed program. At this time, various data stored in the storage unit 72 is referred to. The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 100 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Do. For example, the control unit 100 receives image data transmitted from an external device, and forms an image on the paper S based on the image data (input image data). The communication unit 71 is composed of a communication control card such as a LAN card, for example.

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

  The automatic document feeder 11 transports the document D placed on the document tray by a transport mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents D placed on a document tray all at once.

  The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

  The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, an image status display, an operation status of each function, and the like in accordance with a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 100. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, a compression process, and the like on the input image data in addition to the gradation correction. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 is based on the input image data, and image forming units 41Y, 41M, 41C, 41K, and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component. Etc.

  The Y component, M component, C component, and K component image forming units 41Y, 41M, 41C, and 41K have the same configuration. For convenience of illustration and explanation, common constituent elements are denoted by the same reference numerals, and Y, M, C, or K are added to the reference numerals when distinguished from each other. In FIG. 1, only the components of the Y-component image forming unit 41Y are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 has an undercoat layer (UCL) and a charge generation layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube) having a drum diameter of 80 mm, for example. It is a negatively charged organic photoconductor (OPC) in which a generation layer (CTL) and a charge transport layer (CTL) are sequentially stacked. The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges by exposure by the exposure device 411. The charge transport layer consists of a material in which a hole transport material (electron donating nitrogen-containing compound) is dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The control unit 100 controls the drive current supplied to a drive motor (not shown) that rotates the photosensitive drum 413, thereby rotating the photosensitive drum 413 at a constant peripheral speed.

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity. The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. A positive charge is generated in the charge generation layer of the photosensitive drum 413 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 413 is neutralized. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 is a two-component developing type developing device, and attaches toner of each color component to the surface of the photosensitive drum 413 to visualize the electrostatic latent image to form a toner image.

  The drum cleaning device 415 includes a drum cleaning blade that is slidably contacted with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, it is preferable that the roller 423A disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face a roller 423B (hereinafter referred to as “backup roller 423B”) disposed on the downstream side of the driving roller 423A in the belt traveling direction. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the paper S.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photoconductive drum 413 are primarily transferred onto the intermediate transfer belt 421 in sequence. Specifically, a primary transfer bias is applied to the primary transfer roller 422, and an electric charge having a polarity opposite to that of the toner is applied to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422). It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the sheet S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the sheet S. Specifically, a toner image is applied by applying a secondary transfer bias to the secondary transfer roller 424 and applying a charge having a polarity opposite to that of the toner to the back side of the paper S (the side in contact with the secondary transfer roller 424). Is electrostatically transferred to the paper S. The sheet S to which the toner image is transferred is conveyed toward the fixing unit 60.

  The belt cleaning unit 426 includes a belt cleaning blade that is in sliding contact with the surface of the intermediate transfer belt 421 and removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Instead of the secondary transfer roller 424, a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller is adopted. Also good.

  The fixing unit 60 includes an upper fixing unit 60A having a fixing surface side member disposed on the fixing surface (surface on which the toner image is formed) of the paper S, and the back surface (surface opposite to the fixing surface) of the paper S. A lower fixing unit 60B having a rear side support member to be disposed, a heating source 60C, and the like are provided. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the paper S is formed.

  The fixing unit 60 fixes the toner image on the paper S by heating and pressurizing the paper S on which the toner image is secondarily transferred and conveyed at the fixing nip. The fixing unit 60 is disposed in the fixing device F as a unit. The fixing device F may be provided with an air separation unit that separates the sheet S from the fixing surface side member or the back surface side support member by blowing air.

  The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. In the three paper feed tray units 51a to 51c constituting the paper feed unit 51, paper S (standard paper, special paper) identified based on basis weight, size, or the like is stored for each preset type. . The conveyance path unit 53 includes a plurality of conveyance roller pairs such as registration roller pairs 53a.

  The sheets S stored in the sheet feed tray units 51 a to 51 c are sent one by one from the top and are conveyed to the image forming unit 40 by the conveyance path unit 53. At this time, the registration roller portion provided with the registration roller pair 53a corrects the inclination of the fed paper S and adjusts the conveyance timing. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred onto one side of the sheet S at a time, and a fixing process is performed in the fixing unit 60. The sheet S on which the image has been formed is discharged out of the apparatus by a discharge unit 52 having a discharge roller 52a.

[Configuration of Developing Device 412]
Next, the configuration of the developing device 412 will be described. As shown in FIG. 3, the developing device 412 develops an electrostatic latent image formed on the photosensitive drum 413 (image carrier) using a developer containing toner and a carrier, thereby providing a photosensitive member. A toner image is formed on the drum 413. The developing device 412 includes a developing roller 110 (developer carrier), a supply roller 120, a conveyance guide unit 130, a stirring roller 140, and a conveyance roller 150.

  The stirring roller 140 and the conveyance roller 150 are helical screw members. The stirring roller 140 is housed in the first developer supply chamber 145. The transport roller 150 is accommodated in the second developer supply chamber 155. The stirring roller 140 and the transport roller 150 transport the developer to the supply roller 120 while stirring the developer.

  The supply roller 120 includes a rotatable supply sleeve and a supply magnet roll disposed inside the supply sleeve, and is disposed to face the conveyance roller 150. A plurality of magnetic poles for generating a magnetic field are arranged in the supply magnet roll. By the magnetic field generated by the magnetic pole, the developer is carried on the outer peripheral surface of the supply sleeve, and the supply sleeve is transported to the transport guide unit 130 by rotating counterclockwise in the drawing.

  The conveyance guide unit 130 is installed between the developing roller 110 and the supply roller 120, and supplies the developer conveyed from the supply roller 120 to the development roller 110. A vertically upper surface of the conveyance guide unit 130 is a flat surface, and forms a descending slope toward the developing roller 110 from the supply roller 120. A gap (for example, 0.75 [mm]) is formed between the end of the conveyance guide unit 130 on the supply roller 120 side and the supply roller 120.

  The developing roller 110 includes a rotatable developing sleeve 110A and a developing magnet roll 110B disposed inside the developing sleeve 110A. The developing roller 110 is disposed in the vicinity of the photosensitive drum 413 and conveys the developer to the developing region 115 in the vicinity of the photosensitive drum 413. The developing sleeve 110A rotates counterclockwise in the drawing. A plurality of magnetic poles for generating a magnetic field are arranged in the developing magnet roll 110B. A predetermined gap (for example, 0.50 [mm]) is formed between the end of the conveyance guide unit 130 on the developing roller 110 side and the developing sleeve 110A.

  A regulating blade 180 is arranged in the vicinity of the developing sleeve 110A. The end portion of the regulating blade 180 is located downstream of the vicinity of the conveyance guide portion 130 and upstream of the developing region 115 in the rotation direction of the developing sleeve 110A. The restriction blade 180 is supported by a restriction holder (not shown).

  A part of the developing roller 110, the supply roller 120, the conveyance guide unit 130, the stirring roller 140, the conveyance roller 150, and the regulation blade 180 are accommodated in the development casing 190. In the developing casing 190, a first developer supply chamber 145 and a second developer supply chamber 155 are formed. The first developer supply chamber 145 and the second developer supply chamber 155 are partitioned by the partition wall portion 200.

  The first developer supply chamber 145 is supplied with toner from a toner supply unit (not shown). The agitation roller 140 rotates and mixes and agitates the toner and the carrier supplied to the first developer supply chamber 145 to frictionally charge. The stirring roller 140 conveys the frictionally charged developer to the second developer supply chamber 155. The conveyance roller 150 conveys the developer conveyed from the stirring roller 140 to the supply roller 120 by rotating.

  Due to the magnetic field generated by the supply magnet roll of the supply roller 120, a carrier magnetic brush is generated on the outer peripheral surface of the supply sleeve, and a developer layer containing toner carried on the magnetic brush is formed on the outer peripheral surface of the supply sleeve. It is formed. The supply sleeve rotates counterclockwise in the drawing, and conveys the developer to the conveyance guide unit 130 while holding the developer on the outer peripheral surface of the supply sleeve by a magnetic field.

  The developer on the conveyance guide unit 130 is guided to the developing roller 110. A magnetic brush is generated on the outer peripheral surface of the developing sleeve 110A by the magnetic field generated by the developing magnet roll 110B, and a developer layer is formed on the outer peripheral surface of the developing sleeve 110A. The developing sleeve 110A rotates counterclockwise in the drawing, and conveys the developer to the developing region 115 closest to the photosensitive drum 413 while carrying the developer on the outer peripheral surface of the developing sleeve 110A by a magnetic field. In the middle, the regulating blade 180 regulates the thickness of the developer layer, so that a certain amount of developer is conveyed to the development region 115. In the development region 115, the developer layer contacts the surface of the photosensitive drum 413. In the development region 115, the toner electrostatically moves from the development sleeve 110A to an electrostatic latent image formed on the surface of the photosensitive drum 413. In this way, the developing device 412 visualizes the electrostatic latent image on the photosensitive drum 413 with toner.

In the present embodiment, the developing method of the developing device 412 is a reverse developing method. That is, the rotation direction of the photosensitive drum 413 and the rotation direction of the developing sleeve 110A are the same direction, and in the developing region 115, the surface of the photosensitive drum 413 and the developer carried on the surface of the developing sleeve 110A contact from the opposite direction. To do. In the reverse development method, the surface of the photosensitive drum 413 and the magnetic brush of the developer held on the developing sleeve 110A are in contact with each other in the reverse direction, and as a result, the amount of contact with the developer increases. And a high density image can be obtained even in high-speed development. In the developing method of the developing device 412, the rotation direction of the photosensitive drum 413 and the rotation direction of the developing sleeve 110A are opposite to each other, and the developing region 115 is carried on the surface of the photosensitive drum 413 and the surface of the developing sleeve 110A. A forward developing method in which the developer contacts from the same direction may be used.
Developed.

  A suction duct 160 formed along the upper surface of the developing casing 190 and a suction fan 170 connected to the suction duct 160 are provided on the upper portion of the developing device 412.

  The suction duct 160 is disposed above the photosensitive drum 413 and the developing roller 110, and is provided at a position facing the photosensitive drum 413 for toner scattered from the surface of the developing sleeve 110A (hereinafter referred to as "scattered toner"). A flow path for air sucked from the suction port 162 is formed. The scattered toner is generated by the following mechanism. That is, when the developer has not been used for a long period of time or is left in a high-temperature and high-humidity environment, the toner and the carrier are not triboelectrically charged or are not easily triboelectrically charged. Decreases. When the image forming operation is started in a state where the charge amount of the toner is reduced, the electrostatic adhesion force between the toner and the carrier is weakened, so that the toner separated from the carrier by the centrifugal force of the rotation of the developing sleeve 110A Are scattered from the opening of the developing device 412 which becomes the developing region 115 facing the photosensitive drum 413. Note that a toner filter or an ozone filter may be provided inside the suction duct 160.

  The suction fan 170 includes the motor and a motor drive circuit that drives the motor, and receives a control command from the control unit 100 to generate an air flow (in the direction of arrow B) for sucking scattered toner. The control unit 100 can change the suction air speed of the suction fan 170 by controlling the drive voltage applied to the motor drive circuit.

  For example, when the image forming apparatus 1 is activated, the control unit 100 sends a signal for lowering the drive voltage to the motor drive circuit to control the suction air speed of the suction fan 170 to be low. When the image forming process for the sheet S is started, that is, when the developing process for the photosensitive drum 413 is started, the control unit 100 sends a signal for increasing the driving voltage to the motor driving circuit, and the suction fan. The suction air speed of 170 is controlled to be high. Thereafter, when the execution of the image forming process on the sheet S is completed, that is, when the developing process on the photosensitive drum 413 is completed, the control unit 100 sends a signal for increasing the driving voltage to the motor driving circuit, and the suction fan The suction air speed of 170 is controlled to be high.

  By the way, when scattered toner is generated, the scattered toner may adhere to and accumulate on the inner wall surface of the suction duct 160. Accumulation of scattered toner is likely to occur inside the suction duct 160 at a location where air (intake air) guided to the suction duct 160 convects. In this case, toner spillage (image defect) is caused by the scattered toner accumulated on the inner wall surface of the suction duct 160 falling on the developing sleeve 110A or the photosensitive drum 413 due to vibration during image formation or maintenance. There was a problem that occurred.

  Therefore, in the present embodiment, in the portion R1 of the suction duct 160 that extends downward from the horizontal direction from the suction fan 170 toward the suction port 162, the upper wall 160A is bent to the outside of the suction duct 160. A bent portion 164 is formed. That is, in the scattering toner suction direction (arrow B direction), the inclination of the upper wall 160A increases with the second bent portion 164 as a boundary.

  In addition, a first bent portion 166 that bends outside the suction duct 160 is formed on the bottom wall 160B. That is, in the scattered toner suction direction, the inclination of the bottom wall 160B decreases with the first bent portion 166 as a boundary. The second bent portion 164 is formed on the upstream side of the first bent portion 166 in the scattering toner suction direction.

  The developing roller 110 passes through a midpoint 214 of a straight line connecting the end 210 of the upper wall 160A on the suction port 162 side and the end 212 of the bottom wall 160B on the suction port 162 side, and a straight line L perpendicular to the straight line L It is arranged so as not to overlap.

  According to the present embodiment configured as described above, as shown in FIG. 4, the peak position of the suction wind speed at the suction port 162 of the suction duct 160 approaches the upper wall 160A side. FIG. 4 is a diagram showing a suction wind speed distribution of air sucked from the suction fan 170 in the cross section 220 where the second bent portion 164 of the upper wall 160A and the surface of the developing sleeve 110A are closest to each other. The amount of change in inclination of the upper wall 160A with the second bent portion 164 as a boundary is smaller than the amount of change in inclination of the bottom wall 160B with the first bent portion 166 as a boundary. Therefore, for the air (intake air) guided to the suction duct 160, the suction wind speed does not decrease so much in the vicinity of the upper wall 160A that is smooth along the air flow line, but is not smooth along the air flow line. In the vicinity of the bottom wall 160B, a strong turbulent flow is generated, so that the suction flow velocity is reduced. As a result, the peak of the suction wind speed is closer to the upper wall 160A side. The air velocity reaching the surface of the developing sleeve 110A out of the air (intake air) guided to the suction duct 160 becomes relatively slow, and the amount of toner scattered from the surface of the developing sleeve 110A by the air can be reduced. it can. Further, there is no place in the suction duct 160 where air (intake air) guided to the suction duct 160 is convected. As a result, the amount of toner that scatters from the surface of the developing sleeve 110A and adheres to and accumulates near the suction port 162 (the upper wall 160A and the bottom wall 160B) can be reduced. Therefore, it is possible to suppress the occurrence of toner spillage (image defect) caused by the toner accumulated in the vicinity of the air inlet 162 dropping onto the developing sleeve 110A or the photosensitive drum 413.

  In the present embodiment, the cross-sectional area of the suction duct 160 on the upstream side of the first bent portion 166 formed on the bottom wall 160B in the suction direction of the scattered toner is the suction on the downstream side of the first bent portion 166. It is larger than the cross-sectional area of the duct 160 (the cross-sectional area of the portion R2). The cross-sectional area of the suction duct 160 does not change until the upper wall 160 </ b> A and the bottom wall 160 </ b> B once become parallel in the direction of sucking the scattered toner and then passes through the downstream portion R <b> 2 of the first bent portion 166. In this way, by increasing the cross-sectional area of the suction duct 160 on the suction port 162 side, the suction air velocity around the developing sleeve 110A is suppressed to reduce the amount of scattered toner, and the cross-sectional area of the suction port 162 is narrow. A large amount of air can be sucked with less electric power than in the case. This is because the flow passage cross-sectional area in the suction duct 160 is large in the vicinity of the suction port 162, that is, the intake resistance in the suction duct 160 can be reduced. Further, as a result of reducing the cross-sectional area of the suction duct 160 (the cross-sectional area of the portion R2) on the downstream side of the first bent portion 166 formed on the bottom wall 160B in the suction direction of the scattered toner, as a result, the developer sleeve 110A is positioned above the developing sleeve 110A. A high suction wind speed can be obtained at the position R2. Therefore, the amount of toner that scatters from the surface of the developing sleeve 110A and adheres to and accumulates on the portion R2 (the upper wall 160A and the bottom wall 160B) can be reduced. From the viewpoint of obtaining a higher suction wind speed at the portion R2, the suction duct 160 is disconnected until the upper wall 160A and the bottom wall 160B once become parallel and then pass through the portion R2 on the downstream side of the first bent portion 166. The suction duct 160 may be configured to reduce the area.

[Modification]
In the above embodiment, the suction duct 160 may be configured as shown in FIG. 5 from the viewpoint of obtaining the same effect as that described above. That is, in the portion R1 of the suction duct 160 that extends downward from the horizontal direction from the suction fan 170 toward the suction port 162, the upper wall 160A of the inner wall is formed flat. That is, the inclination of the upper wall 160A does not change in the scattered toner suction direction (arrow B direction). In addition, a first bent portion 166 that bends outside the suction duct 160 is formed on the bottom wall 160B. That is, in the scattered toner suction direction, the inclination of the bottom wall 160B decreases with the first bent portion 166 as a boundary. The second bent portion 164 is formed on the upstream side of the first bent portion 166 in the scattering toner suction direction.

  The developing roller 110 passes through a midpoint 214 of a straight line connecting the end 210 of the upper wall 160A on the suction port 162 side and the end 212 of the bottom wall 160B on the suction port 162 side, and a straight line L perpendicular to the straight line L It is arranged so as not to overlap. In the suction direction of the scattered toner, the sectional area of the suction duct 160 on the upstream side of the first bent portion 166 formed on the bottom wall 160B is the sectional area of the suction duct 160 on the downstream side of the first bent portion 166 (part R2). Larger than the cross-sectional area).

[Example]
Finally, the results of experiments performed by the present inventors to confirm the effectiveness in the above embodiment will be described.

[Configuration of Image Forming Apparatus According to Embodiment]
As the image forming apparatus according to the example, the image forming apparatus 1 having the configuration shown in FIGS. That is, in the portion R1 of the suction duct 160 that extends downward from the horizontal direction from the suction fan 170 toward the suction port 162, a second bent portion 164 that is bent outward from the suction duct 160 is formed on the upper wall 160A. Has been. In addition, a first bent portion 166 that bends outside the suction duct 160 is formed on the bottom wall 160B. The second bent portion 164 is formed on the upstream side of the first bent portion 166 in the scattering toner suction direction. The developing roller 110 passes through the midpoint of a straight line connecting the end of the upper wall 160A on the suction port 162 side and the end of the bottom wall 160B on the suction port 162 side, and does not overlap with a straight line perpendicular to the straight line. Is arranged. The closest distance A1 between the end of the upper wall 160A on the suction port 162 side and the photosensitive drum 413 is 9.0 [mm]. The closest distance B1 between the bottom wall 160B and the developing roller 110 is 10.0 [mm].
[Configuration of Image Forming Apparatus According to Comparative Example]
As the image forming apparatus according to the comparative example, the image forming apparatus 1 having the configuration shown in FIGS. That is, in the portion R1 of the suction duct 160 that extends downward from the horizontal direction from the suction fan 170 toward the suction port 162, a first bent portion 168 that bends inside the suction duct 160 is formed on the upper wall 160A. Has been. In addition, a first bent portion 166 that bends outside the suction duct 160 is formed on the bottom wall 160B. The first bent portion 168 is formed on the upstream side of the first bent portion 166 in the scattering toner suction direction. The developing roller 110 passes through the midpoint of a straight line connecting the end of the top wall 160A on the suction port 162 side and the end of the bottom wall 160B on the suction port 162 side, and overlaps with a straight line perpendicular to the straight line. Is arranged. The closest distance A2 between the end of the upper wall 160A on the suction port 162 side and the photosensitive drum 413 is 2.7 [mm]. The closest distance B2 between the bottom wall 160B and the developing roller 110 is 9.8 [mm].

[First Experimental Method]
In the first experiment, with the photosensitive drum 413 and the developing roller 110 being stationary, only the suction fan 170 is operated, and an anemometer is installed at positions a1 to a5 shown in FIGS. did. At the time of measuring the suction wind speed at the a4 position, a support bar parallel to the axial direction of the developing roller 110 was installed at the a4 position and an anemometer was attached. Further, when measuring the suction wind speed at the a1 and a2 positions, the anemometer at the a4 position was removed. At the positions a1 to a5, the length of the suction duct 160 in the axial direction of the developing roller 110 is substantially constant. Below, the measurement result of the suction | inhalation wind speed (average) in a1-a5 position is shown about each of an Example and a comparative example.

(Measurement results of suction wind speed in the examples)
a1: 0.6 [m / s]
a2: 1.1 [m / s]
a3: 0.5 [m / s]
a4: 0.7 [m / s]
a5: 0.6 [m / s]

(Measurement result of suction wind speed in comparative example)
a1: 0.6 [m / s]
a2: 1.1 [m / s]
a3: 0.9 [m / s]
a4: 0.7 [m / s]
a5: 0.3 [m / s]

[First Experiment Result]
As shown in the above measurement results, in the example, the suction wind speed at the a3 position is lower than the suction wind speed at the a5 position, and the peak position of the suction wind speed at the suction port 162 of the suction duct 160 is on the bottom wall 160B side than the upper wall 160A side. As a result, approached. On the other hand, in the comparative example, the suction wind speed at the a3 position is higher than the suction wind speed at the a5 position, and the peak position of the suction wind speed at the suction port 162 of the suction duct 160 is closer to the upper wall 160A side than the bottom wall 160B side. .

[Second Experimental Method]
In the second experiment, image formation processing with high coverage (for example, a printing rate of 50 [%] or more) is performed on 35,000 A4 sheets, and the number of printed sheets is 10,000, 20000, 25000, 30000, The number of occurrences of toner spills (image defects) at the time of reaching 35,000 sheets was confirmed. Here, the number of toner spills is defined as “the number of toner spills that occurred during printing on the last 1000 A4 sheets”. For example, the number of occurrences of toner spills when the number of printed sheets reaches 25,000 is the number of occurrences of toner spills while the number of printed sheets is 24,000 to 25,000. FIG. 8 shows the number of toner spills for each of the example and the comparative example.

[Second experiment result]
As shown in FIG. 8, in the example, when the number of printed sheets reached 10,000, 20000, 25000, 30000, and 35000 sheets, the number of toner spills was almost zero. On the other hand, in the comparative example, when the number of printed sheets reached 10,000 and 20000, the number of toner spills was as small as 2 or less, but the number of printed sheets reached 25,000, 30000, and 35000, respectively. The number of toner spills at that time increased to 10 or more. In the comparative example, it is considered that the scattered toner scattered from the surface of the developing sleeve 110A adhered to the inner wall surface of the suction duct 160 and accumulated as the number of printed sheets increased. It is considered that the amount of scattered toner accumulated is large at a location (in the vicinity of the first bent portion 168 in FIG. 7) where air (intake air) guided to the suction duct 160 convects inside the suction duct 160. Then, it is considered that a lot of toner spillage occurred due to the scattering toner accumulated on the inner wall surface of the suction duct 160 falling on the developing sleeve 110A or the photosensitive drum 413 due to vibration during image formation. . As described above, in the example, the occurrence of toner spillage could be suppressed as compared with the comparative example.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Image reading part 20 Operation display part 21 Display part 22 Operation part 30 Image processing part 40 Image formation part 50 Paper conveyance part 60 Fixing part 71 Communication part 72 Storage part 100 Control part 101 CPU
102 ROM
103 RAM
DESCRIPTION OF SYMBOLS 110 Developing roller 120 Supply roller 130 Conveyance guide part 140 Stirring roller 145 1st developer supply chamber 150 Conveyance roller 155 2nd developer supply chamber 160 Suction duct 160A Upper wall 160B Bottom wall 162 Suction port 164 2nd bending part 166 , 168 First bent portion 170 Suction fan 180 Regulating blade 190 Developing casing 200 Partition portion 210, 212 End portion 214 Middle point 412 Developing device 413 Photosensitive drum B Scattered toner suction direction L Linear

Claims (4)

A developer carrier disposed opposite to the image carrier, transported while carrying a developer containing toner and carrier, and supplying the toner in the developer to the image carrier;
A suction duct that is disposed above the image carrier and the developer carrier and forms an air flow path for sucking toner scattered from the surface of the developer carrier from a suction port;
A suction fan for generating the air flow;
With
A first bent portion that is bent outward from the suction duct is formed on a bottom wall of a portion of the suction duct that extends downward from the horizontal direction from the suction fan toward the suction port, and an upper wall of the portion. Is formed with a second bent portion that bends outside the suction duct,
The image forming apparatus, wherein the second bent portion is formed on the upstream side of the first bent portion in the toner suction direction. A developer carrier disposed opposite to the image carrier, transported while carrying a developer containing toner and carrier, and supplying the toner in the developer to the image carrier;
A suction duct that is disposed above the image carrier and the developer carrier and forms an air flow path for sucking toner scattered from the surface of the developer carrier from a suction port;
A suction fan for generating the air flow;
With
The upper wall of the suction duct that extends downward from the horizontal direction from the suction fan toward the suction port is formed in a flat shape, and the bottom wall of the part is bent to the outside of the suction duct. 1 bend is formed,
The image forming apparatus according to claim 1, wherein the first bent portion is formed on a downstream side of an end portion on the suction port side of the upper wall in the toner suction direction.   The developer carrying member passes through a midpoint of a straight line connecting an end portion of the upper wall on the suction port side and an end portion of the bottom wall on the suction port side, and overlaps with a straight line perpendicular to the straight line. The image forming apparatus according to claim 1, wherein the image forming apparatus is arranged so as not to be formed.   The cross-sectional area of the suction duct on the upstream side of the first bent portion in the toner suction direction is larger than the cross-sectional area of the suction duct on the downstream side of the first bent portion. 4. The image forming apparatus according to any one of items 3.

Images