JP2009103785A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively discharge heat generated inside a developing device to the outside with comparatively simple structure. <P>SOLUTION: The developing device 21 installed in an image forming device such as a printer includes a case body 21b which accommodates a toner as a developer. A stirring screw for stirring and conveying the toner is set inside the case body 21b. A lot of heat-releasing ribs 21c, which extend in the stirring screw rotating direction, are formed on the upper and side surfaces of the case body 21b to ensure a heat-releasing area. When air is blown from the side of the developing device 21, the air flow is guided by the heat-releasing ribs 21c to circulate from the side surface of the case body 21b to the under surface thereof. Accordingly, uniform cooling can be achieved. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image by developing a latent image formed on the surface of a photoreceptor with a developing device, and particularly relates to a technique for improving heat dissipation or cooling performance of the developing device.

  As a prior art relating to this type of image forming apparatus, a developing device provided with a cooling means is known (see, for example, Patent Document 1). This prior art arranges a metal heat conduction member at the bottom of the developer container (below the stirring screw), and conducts heat accumulated by this heat conduction member to a heat sink provided elsewhere, The container is cooled by releasing heat from the heat sink.

As another prior art, there is known a technique in which a developing device is forcibly air-cooled (see, for example, Patent Document 2). In this prior art, a number of cooling fins are provided in a housing of a developing device, and cooling air is blown onto the cooling fins with a blower to cool the housing.
JP 2002-365888 A JP-A-5-188754

  In the former prior art, heat generated during the rotation of the stirring screw is absorbed by a metal plate disposed below the agitating screw, thereby radiating heat. However, when such a metal plate is disposed below the stirring screw, the contact range between the screw portion and the inner wall surface is reduced accordingly, and the stirring and transport (fluidity) of the developer is significantly reduced. Further, since the metal plate is integrally formed with the resin developer container, and it is necessary to mold the developer container with various kinds of materials such as resin and metal, an increase in manufacturing cost is inevitable. Furthermore, when recycling used containers as resources, even if you try to separate them by material, the structure in which the resin and metal are integrally molded is poorly decomposable and can only be disposed of, causing a load on the environment. There is.

  In the latter prior art, cooling fins are formed in the longitudinal direction on both the lower surface and the side surface of the housing. In this case, the lower surface of the housing is cooled because the wind hits from below, but the direction of the cooling fins becomes a wall on the side surface of the housing, and sufficient cooling cannot be obtained. For this reason, there is a problem that only the local cooling can be obtained in the latter prior art, and the overall cooling effect cannot be obtained.

  Accordingly, an object of the present invention is to provide a technique capable of effectively discharging the heat generated inside the developing device to the outside with a relatively simple structure.

  The present invention is an image forming apparatus that forms a latent image by exposing the surface of a charged photoreceptor and developing the latent image with a developing device. The developing device includes a case body that contains the developer, a stirring screw that is disposed inside the case body, rotates around an axis extending in the longitudinal direction of the case body, and stirs the developer, and the case body. And a developing roller that supplies the developer agitated by the agitating screw to the surface of the photoconductor for development, and a concavo-convex portion that is formed on the outer surface of the case body and extends in a direction along the rotation direction of the agitating screw. It is a configuration.

  The agitating screw agitates the developer contained in the case body, and conveys the developer toward the developing roller (magnetic brush roller in the case of the two-component developer) as it rotates. The developing roller develops the latent image on the photoreceptor by supplying the developer while rotating with the developer layer supported on the peripheral surface thereof.

  At this time, the developer comes into contact with the rotating stirring screw and generates heat due to the friction generated there. In addition, in order to ensure the transportability of the developer by the stirring screw, the gap between the stirring screw and the inner surface below the inside of the case body is narrow, and here the developer is transported while being compressed. Therefore, heat is also generated by friction in the developer. For this reason, in this invention, sufficient heat dissipation area is ensured with the uneven | corrugated | grooved part formed in the outer surface of a case body, the contact area with an external air layer is increased, heat dissipation is improved, and the overheating is suppressed.

  In particular, in the present invention, a concavo-convex portion extending in a direction along the rotation direction of the stirring screw is formed on the outer surface of the case body. Since the rotation direction of the stirring screw is a direction substantially perpendicular to the longitudinal direction of the case body (rotation axis of the stirring screw), this direction coincides with the short direction of the case body. It is getting shorter. If the length of the concavo-convex portion is short, the air passage (flow) in the concave portion is improved accordingly, so that the cooling performance by natural convection and ventilation can be improved.

  Here, the “direction along the rotation direction of the stirring screw” may be parallel to the rotation direction or may be a slightly inclined direction. If the concavo-convex portion is provided with an inclination, the length of the concavo-convex portion can be increased even in the short direction of the case body, and a large heat radiation area can be ensured.

  In addition, it is preferable that the uneven | corrugated | grooved part is formed in the at least lower surface and one side surface adjacent to this at least among the outer surfaces of a case body.

  That is, since the concavo-convex portion extends in the direction along the rotation direction of the stirring screw (short direction of the case body) as described above, it can be formed continuously within the range from the lower surface to the side surface. In this case, since the heat radiation area can be secured in a wider range, the heat radiation efficiency is increased accordingly. Moreover, since it becomes easy to guide the flow of the air which goes to a side surface from the lower surface of a case body, the cooling performance by natural convection and ventilation can be improved further.

  Moreover, the aspect which has a some heat radiating rib distributed and formed in the longitudinal direction on the outer surface of a case body may be sufficient as an uneven | corrugated | grooved part.

  In this case, the flow of air between the heat radiating ribs (recesses) can be improved by shortening the heat radiating ribs one by one as described above. In addition, if the heat dissipating ribs are formed from the lower surface to the side surface of the case body, it becomes easier to induce an air flow from the lower side of the case body to the side, and cooling by natural convection or ventilation as described above. Can be improved.

  The present invention may further include a blowing unit that supplies a cooling air flow to the outer surface of the case body.

  In this case, when an air flow is supplied from the lower side or the side to the uneven portion (heat radiating rib) formed relatively short as described above, the air flow is guided along the uneven portion in the entire range without peeling. As a result, the air flow widely spreads around the outer surface of the case body, and cooling can be performed uniformly and efficiently over a wide range.

  As described above, according to the present invention, high cooling performance can be exhibited with a simple configuration without providing a separate member on the case body of the developing device. In addition, since it is not necessary to provide a separate member such as a heat conducting member, the inner surface shape of the case body can be designed in consideration of the stirring performance of the stirring screw. Further, since the wide range of the case body can be uniformly cooled, the performance of the developing device can be sufficiently stabilized.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically showing the structure of a printer 1 which is an example of an image forming apparatus. The cross section shown in FIG. 1 is seen from the right side surface of the printer 1, and the front surface of the printer 1 is located on the left side and the back surface is located on the right side. First, the basic structure of the printer 1 will be described.

  A paper feed cassette 4 is disposed below the inside of the apparatus main body 2 of the printer 1. Inside the paper feed cassette 4, sheets of paper P are stored in a stacked state. A paper feed unit 8 is installed above the paper feed cassette 4, and the paper P is sent out by the paper feed unit 8 toward the upper left of the paper feed cassette 4 in FIG. The fed paper P is reversed toward the back side by the feed roller 10 and is conveyed toward the back side as it is. The paper feed cassette 4 can be pulled out in the left direction in the figure, and in this pulled out state, a new paper P can be replenished in the paper feed cassette 4 or another paper P can be loaded. It can be replaced with different types of paper.

  Further, inside the apparatus main body 2, the sheet conveyance path 12, the registration roller 14, the sheet conveyance path 24, the image forming unit 16, the transfer unit 30, The fixing unit 32 is arranged in order. Among these, the image forming unit 16 is provided with a photosensitive drum 18, and the photosensitive drum 18 rotates around a rotation axis located at the center thereof. A charger 19 and a laser scanning unit 15 are provided above the photosensitive drum 18. Further, a cleaning unit 17 and a developing device 21 are arranged on both sides of the photosensitive drum 18, respectively.

  The charger 19 charges the surface of the photosensitive drum 18 with, for example, a charging roller (not shown). Further, from the laser scanning unit 15, the scanning light L (laser light beam) is irradiated toward the photosensitive drum 18 as indicated by a one-dot chain line in the drawing. The laser scanning unit 15 exposes the surface of the charged photosensitive drum 18 to form a latent image thereon.

  The developing device 21 incorporates a developing roller 22, and the developing roller 22 is disposed so as to be rotatable in the vicinity of the surface of the photosensitive drum 18. The developing roller 22 develops the latent image formed on the photosensitive drum 18 with toner while rotating while carrying toner as a developer on the surface thereof.

  A cooling fan 29 is installed as a blowing means on the side of the developing device 21 (on the left side in FIG. 1). For example, the cooling fan 29 sends air introduced from the outside of the apparatus main body 2 to the developing device 21 as cooling air. The cooling action using the cooling fan 29 will be described later with reference to another drawing.

  The transfer unit 30 is provided with a transfer roller 31, and the transfer roller 31 is configured to be able to press against the photosensitive drum 18 from below. The photosensitive drum 18 and the transfer roller 31 form a transfer nip portion for transferring the toner image onto the paper P using the toner supplied from the toner container 20 and the developing device 21. The paper P carried into the transfer nip portion is conveyed while being carried on the surface of the photosensitive drum 18 between the transfer roller 31 and the toner image is transferred in this process.

  The paper P is conveyed to the transfer unit 30 via the feed roller 10 and the registration roller 14 described above. The registration roller 14 temporarily stops while holding the paper P, and feeds the paper P at a timing synchronized with the rotation of the photosensitive drum 18 while correcting the inclination and skew of the paper P. As a result, the toner image for one page is accurately transferred to a predetermined position on the paper P. The cleaning unit 17 is located in the vicinity of the transfer unit 30, and the cleaning unit 17 removes residual toner and the like attached to the photosensitive drum 18 after the toner image is transferred.

  A sheet conveyance path 26, a fixing unit 32, a sheet discharge side sheet conveyance path 34, and a sheet discharge tray 36 are sequentially arranged on the downstream side of the transfer unit 30 when viewed in the sheet conveyance direction. Among these, the sheet conveyance path 34 extends upward from the downstream of the fixing unit 32 along the back surface of the apparatus main body 2, and is further bent toward the front side at the upper position of the apparatus main body 2. When printing only on one side of the paper P, the paper P that has passed through the fixing unit 32 is discharged to the paper discharge tray 36 via the discharge roller 35 and stacked in the height direction. The printed paper P stacked on the tray 36 can be easily taken out from the outside.

  Further, a paper conveyance path 38 for double-sided printing is installed between the paper feed cassette 4 and the transfer unit 30 or the fixing unit 32. The sheet conveyance path 38 branches from the middle of the sheet conveyance path 34 at a position along the back surface of the apparatus main body 2 and extends downward, and is bent toward the front surface of the printer 1 and extends in the horizontal direction. . The paper conveyance path 38 is connected to the upstream side of the registration roller 14, for example, between the rollers 8 and 10, and joins the paper conveyance path 12. The sheet P transported through the sheet transport path 38 is transported toward the sheet transport path 12 by the transport roller 40 and further supplied to the registration roller 14.

  The basic configuration of the printer 1 and the image forming operation have been described above. In FIG. 1, a monochrome type printer 1 is taken as an example. However, the image forming apparatus of the present embodiment may be a color printer, a monochrome / full color copying machine, or a multifunction machine. In these cases, the image forming apparatus can include an image reading unit in addition to the image forming unit 16. The image reading unit includes, for example, a reading optical system on which a scanner lamp and a mirror are mounted, and an optical element such as a condenser lens and a CCD. In addition, an automatic document feeder (ADF) may be provided along with the image reading unit.

  FIG. 2 is a cross-sectional view showing the developing device 21 in more detail. The cross section shown in FIG. 2 corresponds to a cross section obtained by cutting the developing device 21 in a direction orthogonal to the longitudinal direction.

  The developing device 21 includes, for example, a cover member 21a and a case body 21b that can be divided into upper and lower parts. Of these, the lower case body 21b is a toner container, and the upper cover member 21a is the cover. Yes.

  The case body 21b contains toner and the developing roller 22 described above. In this embodiment, for example, a two-component toner is used, and in addition to the developing roller 22, a magnetic brush roller 23 and two stirring screws 25 and 27 are provided inside the case body 21b.

  The agitation screws 25 and 27 have shaft members 25a and 27a at the centers, respectively, and rotate in the direction of the arrow shown in the figure with the shaft members 25a and 27a as the center. The periphery of the shaft members 25a, 27a is formed in a spiral (auger) shape. The agitating screws 25 and 27 have blade members (not shown) (not shown), for example, and these blade members project radially from the shaft members 25a and 27a and come into contact with the inner surface of the case body 21b. is doing.

  When the developing device 21 is activated during image formation by the printer 1, the stirring screws 25 and 27 rotate to stir the toner, and the stirred toner is supplied to the magnetic brush roller 23. The magnetic brush roller 23 rotates while adsorbing toner on its peripheral surface, and supplies the toner layer regulated to a constant layer pressure by the regulating member 23 a to the developing roller 22. The toner supplied to the developing roller 22 forms a thin toner layer on its peripheral surface, and is used for developing the electrostatic latent image formed on the surface of the photosensitive drum 18 as described above.

  At this time, friction occurs due to contact between the agitating screws 25 and 27 (blade members) and the toner inside the case body 21b, and frictional heat is generated there. Further, as shown in FIG. 2, below the agitation screws 25 and 27, the gap with the bottom surface of the case body 21b is narrowed in order to ensure toner transportability. For this reason, the toner is transported while being compressed below the stirring screws 25 and 27, and heat due to friction is easily generated here.

  For this reason, in this embodiment, the surface area of the case body 21b is increased by integrally forming a large number of heat radiation ribs 21c on the outer surface of the case body 21b, and cooling is performed by heat radiation therefrom. The heat radiating ribs 21c extend in the direction along the rotation direction of the stirring screws 25 and 27. The rotation direction of the stirring screws 25 and 27 here is a direction orthogonal to the longitudinal direction of the case body 21b, and coincides with the short direction of the case body 21b. Further, the heat radiating rib 21c is formed, for example, from the lower surface of the case body 21b to the left side surface adjacent thereto as viewed in FIG.

  Next, the following 1st form and 2nd form are mentioned as an example as a preferable form of the thermal radiation rib 21c. First, the first embodiment will be described.

[First form]
FIG. 3 is a perspective view showing the developing device 21 from obliquely below. In this first embodiment, the heat radiating ribs 21c are formed in the direction of rotation of the stirring screws 25 and 27, that is, in the direction orthogonal to the longitudinal direction of the case body 21b (or the developing device 21 and the photosensitive drum 18). A plurality of heat radiating ribs 21c are formed on the outer surface of the case body 21b so as to be distributed at regular intervals in the longitudinal direction. In FIG. 3, all of the heat dissipating ribs 21c are not provided with reference numerals, and only a part thereof is provided with reference numerals.

  A plurality of the cooling fans 29 are installed at intervals in the longitudinal direction of the developing device 21. The direction of air blowing by the cooling fan 29 coincides with the direction substantially orthogonal to the longitudinal direction of the developing device 21, that is, the direction in which the heat radiating ribs 21c are formed.

  When the cooling fan 29 is operated, the cooling air is just blown onto the side surface of the case body 21b. At this time, the blown air is guided through the recessed portions formed between the plurality of heat radiation ribs 21c, and can flow from the side surface of the case body 21b to the lower surface. Therefore, since the air flow smoothly flows without being blocked by the heat radiating rib 21c on the outer surface of the case body 21b, the whole can be cooled uniformly.

  Here, although the cooling fan 29 is disposed on the side of the developing device 21, the cooling fan 29 may be disposed below the developing device 21. In this case, cooling air is blown from the lower side of the case body 21b to the lower surface, but the air blown to the lower surface is guided through the concave portions formed between the plurality of heat radiation ribs 21c, and the case body 21b. It can wrap around from the lower surface to the side surface above it. Therefore, the air flows smoothly along the outer surface without being blocked by the heat radiating ribs 21c, so that the whole can be cooled uniformly.

[Second form]
FIG. 4 is also a perspective view showing the developing device 21 obliquely from below. In the second embodiment, the heat radiating rib 21c is oblique to the rotational direction of the agitating screws 25 and 27, that is, the direction obliquely intersecting the longitudinal direction of the case body 21b (or the developing device 21 and the photosensitive drum 18). Is formed. A plurality of heat radiating ribs 21c are formed on the outer surface of the case body 21b so as to be distributed at regular intervals in the longitudinal direction, and these heat radiating ribs 21c are arranged in parallel to each other.

  The arrangement of the cooling fan 29 is the same as in the first embodiment. When these cooling fans 29 are operated, the cooling air is just blown onto the side surface of the case body 21b. At this time, the blown air can be guided from the side surface of the case body 21b to the lower surface while being guided in an oblique direction through the concave portions formed between the plurality of heat radiation ribs 21c. Thereby, since the air flow smoothly flows without being blocked by the heat radiating rib 21c on the outer surface of the case body 21b, the whole can be cooled uniformly.

  In the second embodiment, in order to obtain a smoother air flow, it is preferable that the inclination angle of the heat radiation rib 21c is, for example, 45 degrees or less with respect to the first embodiment. Thus, by forming the heat radiating rib 21c obliquely, the length of the heat radiating rib 21c can be maximized in the short direction of the case body 21b, and the heat radiating area can be increased accordingly.

  Similarly in the second embodiment, the cooling fan 29 may be disposed below the developing device 21. The air blown to the lower surface of the case body 21b is guided through the concave portions formed between the plurality of heat radiating ribs 21c, and circulates from the lower surface of the case body 21b to the side surface above it. can do.

  In the second embodiment, the heat dissipating ribs 21c are not formed at both ends as viewed in the longitudinal direction of the case body 21b, but heat dissipating ribs shorter than the other may be formed at both ends. In particular, both end portions are portions where the toner returns inside the case body 21b, and since the frictional heat due to the agitating screws 25 and 27 is less likely to be generated, the heat radiating ribs 21c are shorter or not formed. There is no problem with cooling performance.

  In the first and second embodiments described above, the case where forced cooling is performed using the cooling fan 29 is described. However, even if the cooling fan 29 is not used, a cooling effect is obtained by natural heat radiation from the heat radiation rib 21c. You can also.

  In particular, in the present embodiment, since the heat radiating rib 21c is formed so as to extend from the lower surface to the side surface of the case body 21b, the air warmed by heat radiation is guided upward through the concave portion between the heat radiating ribs 21c, thereby A natural air flow along the outer surface of the case body 21b can be generated. Thereby, for example, even if the temperature of the developing device 21 is raised after the printer 1 is stopped, natural cooling can be promoted without operating the cooling fan 29. In addition, since the heat hardly accumulates around the developing device 21 inside the apparatus main body 2, it is possible to eliminate the influence of heat inside the apparatus main body 2.

[Contrast with comparative example]
Although the usefulness of this embodiment has already been clarified from the above description, the superiority of this embodiment will be verified below by comparing the conventional technique as a comparative example.

[Comparative Example 1]
FIG. 5 is a perspective view of the developing device 210 of Comparative Example 1 shown obliquely from below. In the comparative example 1, the radiation fins 210 c are formed in the longitudinal direction of the developing device 210.

  In such a comparative example 1, the case where the air for cooling is sprayed from the side as mentioned above is assumed. In this case, the air hitting the side surface of the developing device 210 (case body) is bent in all directions and dispersed. In addition, on the lower surface of the developing device 210 (case body), the radiating fins 210c become walls perpendicular to the air blowing direction, and the air flow is blocked.

  For this reason, in Comparative Example 1, a stable air flow cannot be generated on the outer surface of the developing device 210 (case body), and only one side surface to which the air is blown is locally cooled. .

  In Comparative Example 1, it is assumed that cooling air is blown from below to the lower surface of the developing device 210 (case body). In this case, as already described in the prior art, the lower surface of the developing device 210 can be cooled, but since the heat radiation fins 210c act as walls on the side surfaces to block the air flow, overall cooling is also realized. It is difficult to do.

[Comparative Example 2]
FIG. 6 is a perspective view showing the cooling method of the developing device 210 mentioned as the comparative example 2 from obliquely below. In Comparative Example 2, it is assumed that air is blown in the longitudinal direction of the developing device 210 (case body).

  As shown in FIG. 6, by disposing the cooling fan 29 on the far side of the developing device 210, air can be blown in the longitudinal direction of the developing device 210 (case body). In this case, the radiating fin 210c is certainly not a wall perpendicular to the air flow. However, the concave portion between the heat radiation fins 210c is a narrow and narrow passage as compared with the present embodiment, and even if air is blown into such a passage, the air layer in the passage becomes a resistance. For this reason, as shown by the arrow in FIG. 6, the air flow is gradually separated on the way to the downstream, and a cooling effect is hardly obtained at the downstream end in the longitudinal direction.

  In this respect, in the present embodiment, since the length of each heat radiating rib 21c is short, uniform cooling can be realized up to the downstream end without separation of the air flow on the way.

  The present invention can be implemented with various modifications without being limited to the above-described embodiments. For example, the total number and arrangement interval of the heat radiation ribs 21c are not particularly limited, and may be appropriately modified according to the size of the developing device to be used. In addition, the length, height, width, and the like of each heat radiating rib 21c may be changed according to the developing device to be used.

1 is a diagram schematically illustrating a structure of a printer that is an example of an image forming apparatus. FIG. It is sectional drawing which shows a developing device in detail. It is the perspective view which showed the developing device which has the heat radiation rib of the 1st form from diagonally downward. It is the perspective view which showed the developing device which has the heat radiation rib of the 2nd form from diagonally downward. It is the perspective view which showed the developing device of the comparative example 1 from diagonally downward. FIG. 10 is a perspective view showing a cooling method of a developing device cited as Comparative Example 2 from obliquely below.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 15 Laser scanning unit 18 Photosensitive drum 19 Charger 21 Developer 21b Case body 21c Radiation rib (uneven portion)
22 Developing roller 25, 27 Stir screw

Claims (4)

In an image forming apparatus for exposing a surface of a charged photoreceptor to form a latent image and developing the latent image with a developing unit to form an image.
The developer is
A case body for containing the developer,
An agitation screw that is disposed inside the case body and rotates about an axis extending in the longitudinal direction of the case body to agitate the developer;
A developing roller that is arranged inside the case body and that develops by supplying the developer stirred by the stirring screw to the surface of the photoreceptor;
An image forming apparatus comprising: an uneven portion formed on an outer surface of the case body and extending in a direction along a rotation direction of the stirring screw. The image forming apparatus according to claim 1,
The uneven portion is
An image forming apparatus, wherein the outer surface of the case body is formed on at least a lower surface and one side surface adjacent thereto. The image forming apparatus according to claim 1, wherein
The uneven portion is
An image forming apparatus comprising a plurality of heat dissipating ribs distributed in the longitudinal direction on an outer surface of the case body. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, further comprising a blowing unit that supplies a cooling air flow to the outer surface of the case body.

Images