Patent Publication Number: US-2010119262-A1

Title: Light source device, optical scanning device, and image forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2008-290874 filed in Japan on Nov. 13, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light source device, an optical scanning device, and an image forming apparatus. 
     2. Description of the Related Art 
     In recent years, in a field of an image forming apparatus such as a laser printer and a digital copier, a demand is growing for improving an image forming speed (high speed) and writing density (high density). To meet the demand, a method is proposed, for example, in Japanese Patent Application Laid-open No. 2003-283031 to scan a scanning surface with a plurality of light beams by using an optical scanning device that includes a light source including a plurality of light emitting sources. 
     However, in a high-speed and high-density image forming apparatus, heat generated in a drive circuit that supplies a drive signal to a light source tends to increase. The drive circuit is typically provided near the light source for suppressing delay of the drive signal. Heat generated in the drive circuit may shorten the lifetime of the light source and lower the image quality. Therefore, various methods of radiating heat have been proposed as a countermeasure, such as one disclosed in Japanese Patent Application Laid-open No. 2005-74978. 
     However, an optical scanning device disclosed in Japanese Patent Application Laid-open No. 2005-74978 needs a radiation fin, an air duct, and an exhaust fan, which leads to increase in size and cost of the device. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least partially solve the problems in the conventional technology. 
     According to an aspect of the present invention there is provided a light source device including a light source that includes a plurality of light emitting units; a drive circuit that drives the light source; and a circuit board on which the light source is mounted in a first area and the drive circuit is mounted in a second area and which includes a radiation mechanism between the first area and the second area for heat from the drive circuit. 
     According to another aspect of the present invention there is provided an optical scanning device that scans a scanning surface with a light beam, the optical scanning device including a light source device including a light source that includes a plurality of light emitting units, a drive circuit that drives the light source, and a circuit board on which the light source is mounted in a first area and the drive circuit is mounted in a second area and which includes a radiation mechanism between the first area and the second area for heat from the drive circuit, a deflector that deflects the light beam output from the light source device; and a scanning optical system that focuses the light beam deflected by the deflector on the scanning surface. 
     According to still another aspect of the present invention there is provided an image forming apparatus including at least one image carrier; and at least one optical scanning device that scans the image carrier with a light beam containing image information and that includes a light source device including a light source that includes a plurality of light emitting units, a drive circuit that drives the light source, and a circuit board on which the light source is mounted in a first area and the drive circuit is mounted in a second area and which includes a radiation mechanism between the first area and the second area for heat from the drive circuit, a deflector that deflects the light beam output from the light source device, and a scanning optical system that focuses the light beam deflected by the deflector on the scanning surface. 
     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a configuration of a laser printer according to a present embodiment of the present invention; 
         FIG. 2  is a schematic diagram of an optical scanning device as shown in  FIG. 1 ; 
         FIG. 3  is a schematic diagram for explaining light emitting units of a light source; 
         FIG. 4  is a schematic diagram for explaining a light source package; 
         FIG. 5  is a block diagram for explaining a configuration of a drive control device; 
         FIG. 6  is a schematic diagram for explaining a driving package; 
         FIG. 7  is a schematic diagram for explaining a mounting state of the light source package and the driving package on a control board; 
         FIG. 8  is another schematic diagram for explaining a mounting state of the light source package and the driving package on the control board; 
         FIG. 9  is a cross sectional view taken along line A-A in  FIG. 7 ; 
         FIG. 10  is a schematic diagram for explaining an arrangement of radiation fins shown in  FIG. 7 ; 
         FIG. 11  is a schematic diagram for explaining a radiation fan; 
         FIG. 12  is a schematic diagram for explaining an arrangement position of the radiation fan; 
         FIG. 13  is a schematic diagram for explaining a first modification example of a light source device; 
         FIG. 14  is a schematic diagram for explaining a second modification example of the light source device; 
         FIG. 15  is a schematic diagram for explaining a third modification example of the light source device; 
         FIG. 16  is a schematic diagram for explaining a fourth modification example of the light source device; 
         FIG. 17  is a schematic diagram for explaining a fifth modification example of the light source device; 
         FIG. 18  is a schematic diagram for explaining a sixth modification example of the light source device; 
         FIG. 19  is a schematic diagram for explaining a seventh modification example of the light source device; 
         FIG. 20  is another schematic diagram for explaining the seventh modification example of the light source device; 
         FIG. 21  is a cross sectional view taken along line A-A in  FIG. 19 ; 
         FIG. 22  is a schematic diagram for explaining a radiation fan in the seventh modification example; 
         FIG. 23  is a schematic diagram for explaining an eighth modification example of the light source device; 
         FIG. 24  is another schematic diagram for explaining the eighth modification example of the light source device; 
         FIG. 25  is a cross sectional view taken along line A-A in  FIG. 23 ; 
         FIG. 26  is a schematic diagram for explaining a radiation fan in the eighth modification example; and 
         FIG. 27  is a schematic diagram illustrating a configuration of a color printer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Exemplary embodiments of the present invention are explained in detail below with reference to the accompanying drawings. 
       FIG. 1  is a schematic diagram illustrating a configuration of a laser printer  1000  as an image forming apparatus according to a present embodiment of the present invention. The laser printer  1000  includes an optical scanning device  1010 , a photosensitive element  1030 , a charging unit  1031 , a developing roller  1032 , a transfer charging unit  1033 , a neutralizing unit  1034 , a cleaning unit  1035 , a toner cartridge  1036 , a feeding roller  1037 , a feed tray  1038 , a pair of registration rollers  1039 , a fixing roller  1041 , a discharging roller  1042 , a discharge tray  1043 , a communication control device  1050 , and a printer control device  1060  that collectively controls the above units. The above units are accommodated at predetermined positions in a printer housing  1044 . 
     The communication control device  1050  controls a bilateral communication with an upper-level device, such as a personal computer (PC), via a network or the like. 
     The photosensitive element  1030  having a cylindrical shape has a photosensitive layer on its surface. The photosensitive layer functions as a scanning surface. The photosensitive element  1030  rotates in a direction indicated by an arrow in  FIG. 1 . 
     The charging unit  1031 , the developing roller  1032 , the transfer charging unit  1033 , the neutralizing unit  1034 , and the cleaning unit  1035  are arranged around the photosensitive element  1030  in this order along a direction in which the photosensitive element  1030  rotates. 
     The charging unit  1031  uniformly charges the surface of the photosensitive element  1030 . 
     The optical scanning device  1010  irradiates the surface of the photosensitive element  1030  charged by the charging unit  1031  with a light beam that is modulated based on image information from the upper-level device. Consequently, a latent image corresponding to the image information is formed on the surface of the photosensitive element  1030 . The latent image moves along with the rotation of the photosensitive element  1030  in a direction toward the developing roller  1032 . 
     Toner is accommodated in the toner cartridge  1036  and is supplied to the developing roller  1032 . 
     The developing roller  1032  develops the latent image by causing the toner supplied from the toner cartridge  1036  to adhere to the latent image on the surface of the photosensitive element  1030  to obtain a visible image based on the image information. The latent image (hereinafter, “toner image” for convenience in some cases) to which the toner is adhered moves in a direction toward the transfer charging unit  1033  along with the rotation of the photosensitive element  1030 . 
     Recording sheets  1040  are accommodated in the feed tray  1038 . The feeding roller  1037 , which is arranged near the feed tray  1038 , picks up the recording sheets  1040  one by one from the feed tray  1038  to convey it to the registration rollers  1039 . The registration rollers  1039  once hold the recording sheet  1040  picked up by the feeding roller  1037  and conveys it toward a nip formed between the photosensitive element  1030  and the transfer charging unit  1033  in synchronization with the rotation of the photosensitive element  1030 . 
     The transfer charging unit  1033  is applied with a voltage having a polarity opposite to that of the toner to electrically attract the toner on the surface of the photosensitive element  1030  to the recording sheet  1040 . With this voltage, the toner image on the surface of the photosensitive element  1030  is transferred onto the recording sheet  1040 . The recording sheet  1040  with the toner image transferred thereon is conveyed to the fixing roller  1041 . 
     The recording sheet  1040  is applied with heat and pressure by the fixing roller  1041 , so that the toner image on the recording sheet  1040  is fixed thereto. Then, the recording sheet  1040  with the toner image fixed thereto is conveyed to the discharge tray  1043  by the discharging roller  1042  to be stacked thereon in order. 
     The neutralizing unit  1034  neutralizes the surface of the photosensitive element  1030 . 
     The cleaning unit  1035  removes toner (residual toner) remaining on the surface of the photosensitive element  1030 . The surface of the photosensitive element  1030  from which the residual toner is removed returns to a position opposing the charging unit  1031  again. 
     The configuration of the optical scanning device  1010  is explained. As shown in  FIG. 2 , the optical scanning device  1010  includes a light source device  14 , a coupling lens  15 , an aperture plate  16 , a cylindrical lens  17 , a polygon mirror  13 , a deflector-side scanning lens  11   a,  an image-plane-side scanning lens  11   b,  g light detecting sensors  18   a  and  18   b,  and light detecting mirrors  19   a  and  19   b.  The above units are arranged at predetermined positions in a housing  21 . 
     In the specification, in an XYZ three-dimensional Cartesian coordinate system, a Y-axis direction is a direction along a longitudinal direction of the photosensitive element  1030 , and an X-axis direction is a direction along an optical axis of the scanning lenses  11   a  and  11   b.  Moreover, in the following explanation, a direction corresponding to the main-scanning direction is indicated as a main-scanning corresponding direction, and a direction corresponding to the sub-scanning direction is indicated as a sub-scanning corresponding direction, for convenience. 
     The light source device  14  includes a light source  100  that includes a plurality of light emitting units and a drive control device  22  that drives the light source  100 . 
     As shown in  FIG. 3  as an example, the light source  100  is a two-dimensional array that is formed by two-dimensionally arranging  32  light emitting units v 1  to v 32  on one substrate. In  FIG. 3 , an M direction corresponds to the main-scanning corresponding direction and an S direction corresponds to the sub-scanning corresponding direction that is the same as a Z-axis direction. Furthermore, a T direction is a direction that is inclined from the M direction toward the S direction, and an R direction is a direction in which a light beam is emitted from each of the light emitting units v 1  to v 32 . 
     The light source  100  includes four rows of light emitting units, in each of which eight light emitting units are arranged at equal intervals along the T direction. The four rows of light emitting units are arranged so that when all of the light emitting units v 1  to v 32  are orthographically projected on a virtual line extending in the S direction, an interval therebetween is the same. In the specification, the term “a light-emitting-unit interval” denotes an interval between the centers of two adjacent light emitting units. 
     Each of the light emitting units v 1  to v 32  is a vertical cavity surface emitting laser (VCSEL) of which oscillation wavelength is 780 nanometer (nm) band. In other words, the light source  100  is a so-called VCSEL array including  32  light emitting units. 
     As shown in  FIG. 4  as an example, the light source  100  is accommodated in a package  100 P of a quad flat package (QFP) type. Terminals in 01  to in 32  in  FIG. 4  correspond to the light emitting units v 1  to v 32 , respectively, and are input terminals to which the respective drive signals are input. Hereinafter, the package  100 P in which the light source  100  is accommodated is also referred to as “light source package  100 P” as a matter of convenience. 
     The coupling lens  15  shown in  FIG. 2  collimates a light beam emitted from the light source device  14  into an approximately parallel light beam. 
     An aperture is formed in the aperture plate  16 , which defines a diameter of the light beam reached thereto via the coupling lens  15 . 
     The cylindrical lens  17  focuses the light beam that has passed through the aperture of the aperture plate  16  near a deflection/reflection surface of the polygon mirror  13  with respect to the sub-scanning corresponding direction (the Z-axis direction). 
     An optical system arranged on the optical path between the light source device  14  and the polygon mirror  13  is also called a pre-deflector optical system. In the present embodiment, the pre-deflector optical system includes the coupling lens  15 , the aperture plate  16 , and the cylindrical lens  17 . 
     The polygon mirror  13  has four mirror surfaces each of which functions as the deflection/reflection surface. The polygon mirror  13  rotates at a constant angular rate around an axis parallel to the Z-axis direction to deflect the light beam from the cylindrical lens  17 . 
     The deflector-side scanning lens lie is arranged on an optical path of a light beam deflected by the polygon mirror  13 . 
     The image-plane-side scanning lens  11   b  is arranged on an optical path of a light beam that has passed through the deflector-side scanning lens  11   a.  The light beam that has passed through the image-plane-side scanning lens  11   b  is irradiated to the surface of the photosensitive element  1030  to form a light spot. The light spot moves in the longitudinal direction of the photosensitive element  1030  along with the rotation of the polygon mirror  13 . In other words, the light spot scans the surface of the photosensitive element  1030 . At this time, the moving direction of the light spot corresponds to the main-scanning direction, and the rotation direction of the photosensitive element  1030  corresponds to the sub-scanning direction. 
     An optical system arranged between the polygon mirror  13  and the photosensitive element  1030  is also called a scanning optical system. In the present embodiment, the scanning optical system includes the deflector-side scanning lens  11   a  and the image-plane-side scanning lens  11   b.  At least one reflecting mirror can be arranged on at least one of optical paths between the deflector-side scanning lens  11   a  and the image-plane-side scanning lens  11   b  and between the image-plane-side scanning lens  11   b  and the photosensitive element  1030 . 
     Part of light beams before writing enters the light detecting sensor  18   a  via the light detecting mirror  19   a  from among light beams that are deflected by the polygon mirror  13  and pass the scanning optical system. Part of light beams after writing enters the light detecting sensor  18   b  via the light detecting mirror  19   b  from among the light beams that are deflected by the polygon mirror  13  and pass the scanning optical system. 
     Each of the light detecting sensors  18   a  and  18   b  generates an electrical signal (photoelectric conversion signal) corresponding to light intensity of the received light, and outputs the signal to the drive control device  22 . 
     As shown in  FIG. 5  as an example, the drive control device  22  includes a pixel-clock generating circuit  215 , an image processing circuit  216 , a write control circuit  219 , and a light-source driving circuit  221 . Arrows in  FIG. 5  indicate flows of representative signals and information and thus do not indicate all connection relations between the blocks. 
     The pixel-clock generating circuit  215  determines time required for a light beam to scan between the light detecting sensors  18   a  and  18   b  based on signals output from the light detecting sensors  18   a  and  18   b,  sets the frequency so that the preset number of pulses is contained in the determined time, and generates a pixel clock signal PCLK having the set frequency. The generated pixel clock signal PCLK is supplied to the image processing circuit  216  and the write control circuit  219 . The signal output from the light detecting sensor  18   a  is output to the write control circuit  219  as a synchronization signal. 
     The image processing circuit  216  rasterizes the image information received from the upper-level device via the communication control device  1050  and the printer control device  1060  and generates image data representing gradation of each pixel with the pixel clock signal PCLK as a reference for each light emitting unit after performing a predetermined halftone process and the like. Then, when the image processing circuit  216  detects a scan start based on the signal output from the light detecting sensor  18   a,  the image processing circuit  216  outputs image data to the write control circuit  219  in synchronization with the pixel clock signal PCLK. 
     The write control circuit  219  generates a pulse modulation signal based on the image data from the image processing circuit  216  and the pixel clock signal PCLK and the synchronization signal from the pixel-clock generating circuit  215 . 
     The light-source driving circuit  221  drives each of the light emitting units v 1  to v 32  based on the pulse modulation signal from the write control circuit  219 . 
     The drive control device  22  is stored in a QFP type package  22 P as shown in  FIG. 6  as an example. Therefore, the pixel-clock generating circuit  215 , the image processing circuit  216 , the write control circuit  219 , and the light-source driving circuit  221  are arranged close to each other. Because these circuits are arranged close to each other, a high-frequency clock, various signals, and the like can be transmitted between the circuits with good quality, thereby enabling to accomplish high-speed and high-density image formation. The terminals out 01  to out 32  in  FIG. 6 , corresponding to the light emitting units v 1  to v 32 , are output terminals through which the respective drive signals are output. Hereinafter, the package  22 P in which the drive control device  22  is stored is also referred to as the drive package  22 P″ as a matter of convenience. Terminals out 01  to out 32  are arranged near the two sides that form a corner portion C of the drive package  22 P. 
     As shown in  FIGS. 7 and 8  as an example, the light source package  100 P and the drive package  22 P are both mounted on the +R side of a control board  14 B, apart from each other on one area and another area. 
     Four radiation fins  14 D are provided around the drive package  22 P on the control board  14 B. 
     As shown in  FIG. 9 , each of the radiation fins  14 D is in contact with a ground pattern of the control board  14 B at its end on the -R side. Moreover, each of the radiation fins  14 D has a shape in which a side in one direction is longer than a side in the other direction. 
     As shown in  FIG. 10 , the radiation fin  14 D provided between the drive package  22 P and the light source package  100 P is arranged so that a longitudinal direction thereof is orthogonal to a virtual line connecting the centers of the drive package  22 P and the light source package  100 P. 
     Moreover, as shown in  FIG. 11  as an example, a radiation fan  22 X that sends the wind blowing in a direction from the side of the light source package  100 P to the side of the drive package  22 P is provided. 
     The radiation fan  22 X is attached to the housing  21  as shown in  FIG. 12  as an example. 
     As is apparent from the above explanation, the light source device  14  is such that the drive circuit is composed of the drive control device  22  and the circuit board is composed of the control board  14 B. 
     As explained above, in the light source device  14  in the present embodiment, the light source  100  including a plurality of light emitting units is accommodated in the light source package  100 P to be mounted on the control board  14 B. Moreover, the drive control device  22  that drives the light source  100  is accommodated in the drive package  22 P to be mounted on the control board  14 B. Furthermore, four pieces of the radiation fins  14 D are arranged around the drive package  22 P. 
     In this case, increase in temperature of the drive package  22 P can be suppressed and transfer of heat from the drive package  22 P to the light source package  100 P can be suppressed compared with the conventional technology. Therefore, increase in temperature of the light source  100  can be suppressed without increasing the size and cost. 
     Moreover, because each of the radiation fins  14 D is in contact with the ground pattern of the control board  14 B at its end on the -R side, an amount of heat that is conducted from the drive package  220  to the light source package  100 P via the ground pattern can be reduced. 
     Furthermore, because the longitudinal direction of the radiation fin  14 D provided between the drive package  22 P and the light source package  1000  is orthogonal to a virtual line connecting the centers of the drive package  22 P and the light source package  100 P, heat from the drive package  22 P can be suppressed from conducting to the light source package  100 P in the shortest distance. 
     Moreover, because the radiation fan  22 X that sends the wind blowing in a direction from the side of the light source package  100 P to the side of the drive package  22 P is provided, heat radiated from the radiation fins  14 D can be suppressed from transferring to the side of the light source package  100 P. 
     According to the present embodiment, because the optical scanning device  1010  includes the light source device  14 , the optical scanning device  1010  can perform optical scanning stably without increasing the size and cost. 
     Moreover, according to the present embodiment, because the laser printer  1000  includes the optical scanning device  1010 , the laser printer  1000  can form a high-quality image at high speed without increasing the size and cost. 
     In the present embodiment, if the amount of heat generated in the drive package  22 P is not so large, the radiation fan  22 X can be omitted. 
     Moreover, in the present embodiment, the four radiation fins  14 D have approximately the same length; however, it is not limited thereto. For example, the radiation fin  14 D arranged between the drive package  22 P and the light source package  100 P can be longer than the other radiation fins  14 D. 
     Furthermore, in the present embodiment, the four radiation fins  14 D are provided around the drive package  22 P. However, if the amount of heat generated in the drive package  22 P is not so large, the number of the radiation fins  14 D can be three or less. For example,  FIG. 13  shows a case in which three radiation fins  14 D are provided, and  FIG. 14  shows a case in which one radiation fin  14 D is provided. 
     Moreover, in the present embodiment, the drive package  22 P and the light source package  100 P are arranged along the M direction; however, it is not limited thereto. For example, as shown in  FIG. 15 , the drive package  22 P and the light source package  100 P can be arranged such that a virtual line extending a diagonal line VL 1  of the drive package  22 P passing the corner portion C is approximately aligned with a virtual line extending a diagonal line VL 2  of the light source package  100 P. 
     In this case, the L-shaped radiation fin  14 D can be provided between the drive package  222  and the light source package  1002 , which can have the same effect as the radiation fin  14 D in the present embodiment. 
     Moreover, as shown in  FIG. 16 , each side of the light source package  100 P can be arranged to be in parallel with or orthogonal to a virtual line extending a diagonal line of the drive package  22 P passing one corner portion and the light source package  100 P can be divided approximately into two by the virtual line when viewed in the R direction. Even in this case, the same effect as that in the present embodiment can be achieved. 
     Furthermore, instead of the L-shaped radiation fin  14 D, the radiation fin  14 D having the same shape as that in the present embodiment can be arranged so that the longitudinal direction thereof is orthogonal to a virtual line connecting the centers of the drive package  22 P and the light source package  1002  as shown in  FIGS. 17 and 18 . 
     Moreover, in the present embodiment, the light source package  1002  and the drive package  22 P are mounted on the same side of the control board  14 B; however, the light source package  100 P and the drive package  22 P can be mounted on different sides of the control board  14 B. 
     For example, as shown in  FIGS. 19 and 20 , the light source package  100 P can be mounted on the surface of the +R side and the drive package  22 P can be mounted on the surface of the −R side of the control board  14 B, apart from each other on one area and another area. 
     In this case, as shown in  FIG. 21  as an example, a metal plate  14 E can be inserted into the control board  14 B to be parallel to the surface of the control board  14 B. Consequently, heat of the drive package  22 P can be suppressed from conducting to the light source package  100 P. Moreover, the radiation fin  14 D can be provided to the end of the metal plate  14 E. 
     In this case, as shown in  FIG. 22  as an example, the radiation fan  22 X that sends the wind blowing in a direction from the side of the light source package  100 P to the side of the drive package  22 P when viewed in the R direction can be provided. 
     Furthermore, as shown in  FIGS. 23 ,  24 , and  25  which is a cross sectional view taken along line A-A illustrated in  FIG. 23  as an example, the metal plate  14 E can be inserted into part of the drive package  22 P on the +R side in the control board  14 B to be parallel to the surface of the control board  14 B. 
     In this case, four radiation fins  14 D of which one ends are in contact with the metal plate  14 E can be provided around the drive package  22 P. 
     Moreover, in this case, as shown in  FIG. 26 , the radiation fan  22 X that sends the wind blowing in a direction from the side of the light source package  100 P to the side of the drive package  22 P when viewed in the R direction can be provided. 
     Furthermore, in the present embodiment, the light source  100  includes  32  light emitting units; however, the number of the light emitting units of the light source  100  is not limited thereto. 
     Moreover, in the present embodiment, the laser printer  1000  is explained as the image forming apparatus; however, it is not limited thereto and any image forming apparatus including the optical scanning device  1010  can be employed. 
     For example, the image forming apparatus can be employed, which includes the optical scanning device  1010  and directly irradiates a medium, such as a sheet of paper, which is developed by a laser beam, with a laser beam. 
     Furthermore, the image forming apparatus can be configured to use a silver halide film as an image carrier. In this case, a latent image is formed on a silver halide film by optical scanning, which can be developed by a process equivalent to a developing process in a typical silver halide photographic process. The developed latent image can be transferred onto a printing paper by a process equivalent to a printing process in the typical silver halide photographic process. Such image forming apparatus can be applied to an optical plate making apparatus or an optical drawing apparatus that draws a computed tomography (CT) scan image. 
     Moreover, as shown in  FIG. 27  as an example, the image forming apparatus can be a color printer  2000  including a plurality of photosensitive elements. 
     The color printer  2000  is a tandem-type multi-color printer that forms a full color image by superimposing four color (black (K), cyan (C), magenta (M), and yellow (Y)) images. The color printer  2000  includes photosensitive elements K 1 , C 1 , M 1 , and Y 1 , charging units K 2 , C 2 , M 2 , and Y 2 , developing units K 4 , C 4 , M 4 , and Y 4 , cleaning units K 5 , C 5 , M 5 , Y 5 , and transferring units K 6 , C 6 , M 6 , and Y 6 , for the four colors. The color printer  2000  further includes an optical scanning device  2010 , a transferring belt  2080 , and a fixing unit  2030 . 
     Each photosensitive element rotates in a direction indicated by an arrow in  FIG. 27 . The charging unit, the developing unit, the transferring unit, and the cleaning unit are arranged around each photosensitive element in this order in a direction in which the photosensitive element rotates. Each charging unit uniformly charges the surface of a corresponding photosensitive element. The optical scanning device  2010  irradiates the surface of each photosensitive element charged by the corresponding charging unit with a light beam, so that a latent image is formed on each photosensitive element. Then, each latent image is developed into a toner image by a corresponding developing unit. Each toner image is transferred onto a recording sheet by a corresponding transferring unit. Finally, the toner images transferred onto the recording sheet is fixed thereto by the fixing unit  2030 . 
     The optical scanning device  2010  includes a light source device similar to the light source device  14 , a pre-deflector optical system similar to the above descried one, and a scanning optical system similar to the above descried one for each color. 
     A light beam emitted from each light source device is deflected by a common polygon mirror through the corresponding pre-deflector optical system, and irradiated to the corresponding photosensitive element through the corresponding scanning optical system. 
     According, the optical scanning device  2010  can have an effect similar to the optical scanning device  1010 . Thus, the color printer  2000  can have an effect similar to the laser printer  1000 . 
     The color printer  2000  can include the optical scanning device for each one or two colors. 
     According to one aspect of the present invention, a light source device can suppress temperature increase of light source units accommodated therein without enlarging size and cost thereof. 
     According to another aspect of the present invention, an optical scanning device, having the light source device in the present invention therein, can stably scan without enlarging size and cost thereof. 
     According to still another aspect of the present invention, an image forming apparatus, having the optical scanning device in the present invention therein, can form image with high speed and good quality without enlarging size and cost thereof. 
     Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.