JP5693690B2 - Optical scanning device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to an optical scanning apparatus that exposes a photosensitive member by irradiating light, and particularly relates to an optical scanning apparatus having a structure that dissipates heat inside the apparatus.

  An electrophotographic image forming apparatus includes an optical scanning device that irradiates a photoconductor with light and exposes the photoconductor. This optical scanning device passes through a light source such as a laser beam, a polygon mirror that reflects light from the light source, a motor that rotates the polygon mirror, an fθ lens that forms an image of light from the polygon mirror on a photoconductor, and an fθ lens. A reflection mirror that reflects light to the photosensitive member is provided. In this type of optical scanning device, the components are housed in a highly airtight case so that dust does not enter inside.

  When the inside of the case is made highly airtight, heat generated from the components housed therein, in particular, the motor and the driving driver of the motor is not easily radiated, and the internal temperature rises. When the inside becomes high temperature, the polygon mirror, the reflection mirror and the like are distorted, and a phenomenon that the light scanned by the polygon mirror is curved (scanning line bending) occurs. For this reason, various cases for radiating the heat inside the optical scanning device have been conventionally applied to the case. For example, Patent Document 1 discloses an exposure apparatus in which a polygon mirror and a motor are accommodated in an inner case, and an outer case is provided that covers the inner case from the outside. Further, Patent Document 2 includes a case having an opening and a cooling fan provided therein, and further, the opening is opened by wind force when the cooling fan is driven, and the opening is caused by its own weight when the cooling fan is stopped. An optical writing device having a lid member for closing the cover is disclosed.

JP 2007-328335 A JP 2009-175455 A

  However, in the exposure apparatus described in Patent Document 1, since the inner case is blocked from the outside by the outer case, the inner space of the outer case causes a heat insulating effect on the inner case, and directly from the inner case. There is a problem that it becomes impossible to dissipate heat. In addition, since the optical writing device described in Patent Document 2 has an opening in the case, it cannot completely prevent dust and dust from entering from the opening. Specifically, when the cooling fan is stopped and the wind power is exhausted, the lid member rotates in a direction to close the opening. At this time, an entrainment airflow is generated by the rotation of the lid member, and the airflow is reduced. Therefore, there is a risk that fine dust or dust may enter the inside through the opening. Further, since the optical writing device requires two driving means for the polygon mirror motor and the cooling fan, the number of steps such as assembly and wiring of the cooling fan increases, resulting in an increase in manufacturing cost. Further, the case needs to have a structure in which two driving means can be fixed, and it is necessary to have a structure that suppresses vibration by each driving means, so that the configuration of the apparatus becomes complicated.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to efficiently cool the polygon mirror driving means by circulating the internal air with a simple configuration without providing a driving means such as a cooling fan. It is an object of the present invention to provide an optical scanning device that can be operated and an image forming apparatus including the same.

Optical scanning apparatus according to an aspect of the present invention includes a case, a gas-tight space, and one of the tube member, a. The case contains at least a polygon mirror and driving means for rotating the polygon mirror, and the inside thereof is kept airtight. The airtight space is provided outside the outer wall surface on the vertically upper side of the case and is separated from the case, and an airtight space is formed inside. The tube member communicates with the interior of the internal and the airtight space portion of the casing, the passage of the opposite direction of the air flow with causing natural convection between said casing airtight space.

  An image forming apparatus according to another aspect of the present invention includes the optical scanning device.

When the optical scanning device of the present invention is driven, the driving means is rotated to rotate the polygon mirror. When the driving means is driven, the driving means generates heat and the surrounding air is warmed. The warmed air moves upward while gradually diffusing in the case. On the other hand, since the airtight space does not have a heat generating portion like the driving means, the temperature of the air in the airtight space is lower than the temperature in the case, particularly the temperature of the air around the driving means. . For this reason, natural convection occurs between the air in the airtight space and the air in the case. In other words, air warmed in the case through the tube member moves to the airtight space, air in the hermetic space is moved within the case through the tube member. The warm air (warm air) that has moved to the airtight space is cooled by heat exchange with the outside air using the outer wall of the airtight space as a heat transfer medium. On the other hand, the cold air (cold air) that has moved into the case is warmed by heat exchange with the drive means. As described above, the optical scanning device according to the present invention is provided with the airtight space, so that natural convection of air occurs between the airtight space and the case, and the heat of the driving means is efficiently used. It can be well discharged outside the device.

  According to the present invention, the polygon mirror driving means can be efficiently cooled by circulating internal air with a simple configuration without providing a driving means such as a cooling fan.

1 is a schematic cross-sectional view illustrating a schematic configuration of a printer 10 including an optical scanning device 30 according to an embodiment of the present invention. It is the elements on larger scale of the principal part II of FIG. 1, Comprising: The structure of the optical scanning device 30 which concerns on embodiment of this invention is shown. It is a model perspective view which shows the structure where the case 39 and the box 50 were simplified, (A) is an external appearance block diagram, (B) is an internal arrangement | positioning figure. It is a schematic cross-sectional view showing a central cross-sectional structure of the case 39 and the box 50, (A) is a cross-sectional view showing a connection structure by the communication pipe 64, (B) is an internal arrangement view. It is the schematic which shows the natural convection which generate | occur | produces between the simplified case 39 and the box 50, (A) is a figure which shows the airflow in the box 50, (B) is a figure which shows the airflow in the case 39. is there. It is a heat distribution diagram which shows the verification result of the thermal radiation effect of each of the conventional optical scanning devices 101 and 102 and the optical scanning device 30. It is a model perspective view which shows 30 A of optical scanning apparatuses which concern on other embodiment of this invention. 1 is a schematic perspective view showing a printer 10 provided with an optical scanning device 30A. FIG. 9 is a partial enlarged view showing a modification of the configuration of the protruding piece 76 of the shift guide 73.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. The embodiment described below is merely an example embodying the present invention, and the embodiment of the present invention can be changed as appropriate without departing from the scope of the present invention.

[Printer 10]
First, a schematic configuration of a printer 10 (an example of an image forming apparatus of the present invention) according to an embodiment of the present invention will be described with reference to FIG. Note that the configuration not described here is the same as that of a general electrophotographic image forming apparatus, and thus description of the configuration is omitted. The printer 10 is only an example of the image forming apparatus according to the present invention. For example, a facsimile machine and a multifunction peripheral also correspond to the image forming apparatus according to the present invention. In the following description, the printer 10 is described as a color printing compatible machine, but the present invention can be applied to a monochrome printing compatible machine.

  As shown in FIG. 1, the printer 10 includes four image forming units 11, two optical scanning devices 30 (an example of the optical scanning device of the present invention), an intermediate transfer belt 12, a secondary transfer device 13, and a paper feeding device. 14, a fixing device 15, and a paper discharge unit 16. The printer 10 also includes a control unit (not shown) having a CPU, ROM, RAM, and the like, an operation display unit (not shown) for performing various operation inputs and information display, and the like. Each of the two optical scanning devices 30 corresponds to each of the two image forming units 11 and is disposed below each image forming unit 11.

  In the present embodiment, an example in which two optical scanning devices 30 corresponding to the four image forming units 11 are provided in the printer 10 will be described. For example, four optical scanning devices 30 corresponding to the four image forming units 11 are provided. The present invention can also be applied to a printer 10 having a configuration in which one optical scanning device 30 is provided individually or a configuration in which one optical scanning device 30 corresponding to three or four image forming units 11 is provided. is there.

  The four image forming units 11 are of a general electrophotographic system corresponding to four colors of black, yellow, cyan, and magenta in order from the right in FIG. Each image forming unit 11 includes a photosensitive drum 11A, a charging device 11B, a developing device 11C, a primary transfer roller 11D, and a cleaning device 11E.

  In the printer 10, an image is formed on the recording paper supplied from the paper feeding device 14 according to the following procedure. First, the photosensitive drum 11A is uniformly charged to a predetermined potential by the charging device 11B. Next, the optical scanning device 30 irradiates the surface of the photosensitive drum 11A with laser light based on the image data, and an electrostatic latent image is formed on the surface. Then, the electrostatic latent image on the photosensitive drum 11A is developed (visualized) as a toner image by the developing device 11C. Thereafter, the toner image on the photosensitive drum 11A is transferred to the intermediate transfer belt 12 that travels in the direction indicated by the arrow 19 in FIG. 1 by the primary transfer roller 11D. When the toner image is transferred to the intermediate transfer belt 12, the photosensitive drum 11A is cleaned by the cleaning device 115.

  In this way, when the toner images are sequentially transferred onto the intermediate transfer belt 12 by the image forming units 11, a color image is formed on the intermediate transfer belt 12. Then, the color image on the intermediate transfer belt 12 is transferred to the recording paper by the secondary transfer device 13. Thereafter, when the toner image on the recording paper is fused and fixed by the fixing device 15, the recording paper is discharged to the paper discharge unit 16.

[Optical scanning device 30]
Next, the optical scanning device 30 will be described with reference to FIGS. 3 to 6 show the optical scanning device 30 with a simplified configuration for easy understanding. The optical scanning device 30 irradiates the photosensitive drum 11A with laser light. As shown in FIG. 2, the optical scanning device 30 includes a laser light source (not shown), a polygon mirror 32 (an example of the polygon mirror of the present invention), a motor 33 (an example of the driving means of the present invention), a driver board 34 ( An example of driving means of the present invention), fθ lenses 35A and 35B, deflection mirrors 37A, 37B, and 37C, and a case 39 (an example of the case of the present invention) that accommodates these. The optical scanning device 30 is provided with two sets of the laser light source, fθ lenses 35A and 35B, and deflection mirrors 37A, 37B, and 37C for one polygon mirror 32.

  The polygon mirror 32 is made of aluminum, and is a rotating multi-faceted boundary having six reflecting surfaces that reflect the laser light from the laser light source. The polygon mirror 32 is formed in a regular hexagonal shape in plan view. A motor 33 is provided below the polygon mirror 32. That is, the polygon mirror 32 is provided vertically above the motor 33. The motor 33 has an output shaft 41 extending vertically upward (vertical direction in FIG. 2), and a polygon mirror 32 is connected to the output shaft 41. Thereby, when the motor 33 is rotationally driven by the driver substrate 34, the polygon mirror 32 is rotated about the output shaft 41 as the rotation center axis.

  When the polygon mirror 32 is rotated by the motor 33, the laser light emitted from the laser light source toward the polygon mirror 32 is reflected by the polygon mirror 32, and the reflected light passes through the optical path 43 (with an arrow in FIG. 2). The image is scanned in a predetermined direction on the surface of the photosensitive drum 11A through the wavy line). Specifically, the horizontal laser light emitted from the laser light source is scanned in the horizontal direction by being reflected by the reflection surface whose reflection angle is changed as needed by the rotation of the polygon mirror 32. Then, the laser light reaches the deflection mirror 27A through the fθ lens 35A and the fθ lens 35B, and is further deflected toward the photosensitive drum 11A by the deflection mirror 27A, the deflection mirror 27B, and the deflection mirror 27C. An image is formed on the surface of the photosensitive drum 11A.

[Case 39]
The case 39 accommodates the polygon mirror 32, the motor 33, the driver board 34, and the like. The case 39 is made of, for example, a synthetic resin having thermal conductivity. As described above, in the optical scanning device 30, the laser light passes through the internal space of the case 39 along the optical path 43. Therefore, when dust such as dust or dust enters the inside of the case 39, the laser light is irregularly reflected by the dust. The electrostatic latent image on the photosensitive drum 11A is disturbed. Therefore, the case 39 is kept airtight so that air cannot enter and exit between the inside and the outside. Specifically, as shown in FIG. 3, the case 39 is hermetically sealed with an upper wall 45 on the upper side, a bottom wall 46 on the lower side, and a side wall 47 that surrounds the sides with four sides. It is formed as follows. A transparent plate 48 (see FIG. 2) is fitted in a portion where the upper wall 45 and the optical path 43 intersect so that the laser light travels from the deflection mirror 37C to the photosensitive drum 11A.

As shown in FIGS. 3 and 4, the upper wall 45 of the case 39, the communicating pipe 64 of the cylindrical (an example of a tubular member of the present invention) is provided. The communication pipe 64 is formed of the same material as that of the case 39, that is, a synthetic resin having the same thermal conductivity. The communication pipe 64 is a resin pipe whose upper end and lower end are both open, and its cross-sectional area is sufficiently smaller than the plane area of the case 39. Also, as shown in FIGS. Is sufficiently smaller than the plane area. The communication pipe 64 is erected at the center of the upper wall 45 and is connected to the case 39 so that the lower end thereof penetrates the upper wall 45 (see FIG. 4A). Thereby, the inside of the communication pipe 64 and the inside of the case 39 communicate so that air can enter and exit. Of course, the connecting portion between the communication pipe 64 and the upper wall 45 has an airtight structure so that dust cannot enter. In the present embodiment, the communication pipe 64 is provided outside the upper wall 45 and on an extension line of the rotation center axis 66 of the polygon mirror 32.

  One box 50 (an example of an airtight space portion of the present invention) is provided vertically above the case 39. The box 50 is provided for the purpose of efficiently releasing the heat generated from the motor 33 and the driver board 34 in the case 39 when the optical scanning device 30 is driven. The box 50 is provided on the outer side of the outer wall facing the polygon mirror 32, that is, on the outer side of the upper wall 45 on the vertically upper side of the case 39, separated from the case 39. The box 50 has a rectangular parallelepiped shape that is flat in the vertical direction, and is formed of the same material as the case 39, that is, a synthetic resin having the same thermal conductivity. Nothing is contained inside the box 50, and there is only a space surrounded by the upper wall 55 in the vertical upper side, the bottom wall 56 in the lower vertical side, and the side wall 57 that surrounds the sides with four sides. doing. As with the case 39, the box 50 is formed so that the internal space is airtight.

  The upper end of the communication pipe 64 is connected to the center of the bottom wall 56 of the box 50. Specifically, the communication pipe 64 is connected to the box 50 so that the upper end thereof penetrates the bottom wall 56 (see FIG. 4A). Thereby, the inside of the communication pipe 64 and the inside of the box 50 communicate so that air can enter and exit. That is, the communication pipe 64 connects the case 39 and the box 50 so that the inside of the case 39 and the inside of the box 50 communicate with each other and air can enter and exit between the inside of the case 39 and the inside of the box 50. doing.

In the present embodiment, the heat transfer coefficient of the outer wall in the box 50 is set to be larger than the heat transfer coefficient of the outer wall in the case 39. Specifically, the top wall 55 of the box 50 has a heat transfer coefficient of 15 W / m ² , the bottom wall 56 has a heat transfer coefficient of 3.5 W / m ^2, and the heat transfer of the side wall 57. Each thickness and shape are determined so that the rate is 7.5 W / m ² . On the other hand, the thickness and shape of each outer wall of the case 39 are determined so that the heat transfer coefficient is less than 7.5 W / m ² . Specifically, it is conceivable that the outer wall of the box 50 has a fin structure or is formed thinner than the outer wall of the case 39. Further, the outer wall of the box 50 may be formed of a material having a higher thermal conductivity than the case 39.

When the thus configured optical scanning device 30 is driven, the motor 33 and the driver board 34 generate heat, and the surrounding air is warmed. On the other hand, since the box 50 does not have a heat generating part such as the motor 33 inside, the temperature of the air in the box 50 is lower than the temperature in the case 39, particularly the temperature of the air around the motor 33 and the driver board 34. For this reason, natural convection occurs between the air in the box 50 and the air in the case 39 using the communication pipe 64 as an air passage. Specifically, as shown in FIG. 5B, since the polygon mirror 32 is rotated in the direction of the arrow 68 by the motor 33, the air warmed in the vicinity of the motor 33 (warm air) While moving around the rotation center axis 66 by a vortex-like rotating airflow generated by the rotation, it gradually moves upward by natural convection. When the warm air that has moved upward reaches the lower end of the communication pipe 64, it moves to the box 50 through the inside of the communication pipe 64 (see FIG. 5A). The warm air is cooled by convection in the box 50 and heat exchange with the air outside the box 50 using each outer wall as a heat exchange medium.

On the other hand, the relatively cool air (cold air) present in the box 50 is replaced with the warm air that has moved from the case 39 to the box 50 and moves to the case 39 through the communication pipe 64 (FIG. 5A). )reference). The cool air that has moved from the box 50 to the case 39 is gradually moved downward by natural convection while moving in the direction of the arrow 68 on the rotating air current generated by the rotating polygon mirror 32. When reaching the periphery of the motor 33 and the driver board 34, heat is exchanged with the motor 33 and the driver board 34, and the cold air is warmed. Then, the warmed air rises again by natural convection and travels to the box 50 through the communication pipe 64. In this way, natural convection of air is generated between the box 50 and the case 39, and an air flow in the opposite direction is generated inside the communication pipe 64 as shown in FIG. Since air circulates between the motor 39 and the case 39, the heat of the motor 33 and the driver substrate 34 can be efficiently released to the outside of the optical scanning device 30.

  Here, with reference to FIG. 6, the verification result of the heat dissipation effect of this invention is demonstrated. FIG. 6A is a heat distribution diagram of a conventional optical scanning device 101 having only a case 39 whose inside is hermetically sealed. FIG. 6B is a heat distribution diagram of a conventional optical scanning device 102 having an inner case 39A whose inside is airtight and an outer case 39B covering the inner case 39A. FIG. 6C is a heat distribution diagram of the optical scanning device 30 having the case 39, the communication pipe 64, and the box 50. In the figure, H1 indicates the highest temperature region, and H9 indicates the lowest temperature region. In these heat distribution diagrams, the heat dissipation effect is simulated by a computer under the same conditions, that is, the driving time, rotation speed, and simulation time of the motor 33 are the same.

6A, it can be understood that the heat in the case 39 is relatively high in the conventional optical scanning apparatus 101. FIG. Further, according to FIG. 6B, although there is a heat radiation effect than the optical scanning device 102, the heat insulation effect by the outer case 39B is acting, so there is a part that is sufficiently cooled, but the high temperature is still high. It can be understood that there is a part that is kept. Moreover, according to FIG.6 (C), it can be understood that the heat radiation effect of the air has appeared notably in the box 50. FIG. Further, even in the case 39, there is no lowest temperature region, but it can be understood that the inside of the case 39 is maintained at an equal temperature. From this heat distribution chart, it can be understood that air circulation by natural convection is smoothly performed in the optical scanning device 30 . Further, since the inside of the case 39 is kept at a uniform temperature, the fθ lenses 35A and 35B and the deflecting mirrors 37A, 37B, and 37C housed in the case 39 do not have partially biased temperatures. Distortion caused by temperature changes is less likely to occur in the components.

  Further, as described above, in this embodiment, when a spiral rotating airflow is generated around the rotation center axis 66 of the polygon mirror 32, the center of the rotating airflow has a lower pressure than the portion where the rotating airflow is generated. This makes it easier for air to move upward. A communication pipe 64 is provided on an extension line of the rotation center shaft 66. Therefore, the air that has moved upward through the vicinity of the rotation center axis 66 of the polygon mirror 32 is guided to the communication pipe 64 without any resistance and moves to the box 50 provided outside the upper wall 45 of the case 39. As a result, air is smoothly circulated between the box 50 and the case 39 by natural convection. As a result, heat from the motor 33 and the like can be efficiently released to the outside of the optical scanning device 30.

  Further, since the heat transfer coefficient of the outer wall of the box 50 is larger than the heat transfer coefficient of the outer wall of the case 39, stronger natural convection can be generated between the box 50 and the case 39.

  In the above-described embodiment, the communication pipe 64 is provided on the extension line of the rotation center axis 66 of the polygon mirror 32. However, the communication pipe 64 is provided at a position off the extension line of the rotation center axis 66. Even so, since the air is smoothly circulated by natural convection, the heat of the motor 33 and the like can be efficiently released to the outside of the optical scanning device 30.

In the above-described embodiment, the communication pipe 64 is connected to the upper wall 45 of the case 39, and the box 50 is provided above the upper wall 45. However, as another embodiment of the present invention, FIG. ), A communication pipe 64 is provided on the side wall 47 of the case 39, and an optical scanning device 30A in which a box 50 is connected to an end of the communication pipe 64 is conceivable. In the optical scanning device 30 </ b> A, the communication pipe 64 is connected to the end portion on the side of the upper wall 45 in the side wall 47. Thereby, a part of the box 50 is disposed vertically above the upper wall 45. For this reason, as shown in FIG. 7, natural convection occurs due to the temperature difference of air between the box 50 and the case 39 by using the communication pipe 64 as a passage of airflow, and also in the box 50 due to air convection. Heat exchange with outside air takes place. Thereby, heat of the motor 33 and the like is efficiently released to the outside of the optical scanning device 30 by circulation of air by natural convection. Also, as shown in FIG. 8, the box 50 is arranged on the side wall 47 side, so that when the optical scanning device 30A is provided in the printer 10, the space between the case 39 and the photosensitive drum 11A or the like is narrowed. The size of the printer 10 in the height direction can be made compact.

Further, as shown in FIG. 9, another embodiment of the present invention, the case 39 and the box 50 and the first communicating pipe 64A and the second communicating pipe 64B (an example of a tubular member of any invention) A concatenated optical scanning device 30B is conceivable. In the optical scanning device 30B, the first communication pipe 64A is formed longer than the second communication pipe 64B. The first communication pipe 64 </ b> A is provided on an extension line of the rotation center shaft 66 of the polygon mirror 32. On the other hand, the second communication pipe 64B is provided at the end of the upper wall 45 on the side wall 47 side.

  With this configuration, the air warmed in the case 39 moves to the box 50 through the first communication pipe 64A, and is cooled while exchanging heat with the outside air in the box 50. It moves to the case 39 through the two communication pipes 64B. In this way, circulation in one direction by natural convection is performed, so that air is smoothly circulated between the box 50 and the case 39, and heat from the motor 33 and the like is efficiently transferred to the outside of the optical scanning device 30. To be released.

  Further, since the first communication pipe 64A is formed longer than the second communication pipe 64B, the end 50A on the rotation center shaft 66 side in the box 50 is positioned higher than the end 50B on the side wall 47 side. For this reason, the box 50 is inclined with respect to the upper wall 45 of the case 39. As a result, the air that has moved to the box 50 through the first communication pipe 64A is guided to the second communication pipe 64B while gradually moving downward along the inclination of the box 50 while being cooled. It moves to the case 39 again through the second communication pipe 64B. Thereby, the movement of the air by natural convection becomes smoother, and the air is efficiently circulated between the box 50 and the case 39.

  The present invention is applicable to an optical scanning device that exposes a photosensitive member by irradiating light and an image forming apparatus including the same.

10: Printer 30, 30A, 30B: Optical scanning device 32: Polygon mirror 33: Motor 34: Driver substrate 35A, 35B: fθ lens 37A, 37B, 37C: Deflection mirror 39: Case 45: Upper wall 47: Side wall 50: Box 55: Upper wall 64, 64A, 64B: Communication pipe 66: Center axis of rotation

Claims (6)

A case in which at least a polygon mirror and a driving means for rotating the polygon mirror are accommodated and the inside thereof is kept airtight;
An airtight space portion provided on the outer side of the outer wall surface on the vertical upper side of the case, separated from the case, and having an airtight space formed therein;
Communicates with the interior of the internal and the airtight space portion of the case, the one and the tubular member as the passage opposite the direction of air flow with causing natural convection between said casing airtight space Optical scanning device provided. Sectional area of the tube member includes an optical scanning apparatus according to a small claim 1 than the planar area of each of the case and the airtight space. The whole of the airtight space is provided outside the outer wall surface on the vertical upper side of the case,
Wherein the one end of the tube member is connected to the outer wall surface, the optical scanning device according to claim 1 or 2 and the other end is connected to the airtight space. The airtight space portion is provided outside the side wall of the case so that a part of the airtight space portion is disposed outside the outer wall surface on the vertical upper side of the case,
One end of the pipe member are connected to the side walls, the optical scanning device according to claim 1 or 2 and the other end is connected to the airtight space. The tube member includes an optical scanning device according to claim 4, in the side wall is connected to an end portion of the outer wall surface. An image forming apparatus comprising the optical scanning device according to claim 1.

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