Abstract:
An optical scanning device includes a light source that emits a light beam, an optical deflector at which a light beam emitted from the light source is incident, the optical deflector deflecting the incident light beam, an optical system that guides the deflected light beam to surface to be scanned by the deflected light beam, a driving device that drives at least a portion of the optical deflector, a thermal storage member mounted on the driving device, the thermal storage member absorbing and storing heat generated by the driving device, thereby controlling a temperature gradient of the driving device, and a casing body that accommodates the light source, the optical deflector, the optical system, the driving device, and the thermal storage member.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority under 35 USC 119 from Japanese Patent Application No. 2005-217657, the disclosure of which is incorporated by reference herein. 
   BACKGROUND 
   1. Technical Field 
   The present invention relates to an optical scanning device and an image forming apparatus, and more particularly relates to an optical scanning device at which plural optical systems and a heat-generating component are disposed in a single container, the optical systems respectively guiding plural light beams which have been deflectingly scanned by a light-deflecting element, and to an image forming apparatus which is equipped with this optical scanning device. 
   2. Related Art 
   An electrophotographic-system color image forming apparatus deflectingly scans plural light beams corresponding to the colors Y (yellow), M (magenta), C (cyan) and K (black), or the like, with an optical deflector which is mounted at an optical scanning device, and forms a color image by focusing the respective colors through plural optical systems onto a photosensitive drum. In such a color image forming apparatus, image formation timings of the colors are regulated in accordance with a device temperature, which is measured by an environment sensor (a temperature sensor). Thus, color shifts between color images (reading registration errors) that are caused by temperature variations of the device are corrected for (“color registration correction”). 
   In recent years, in order to suppress costs, housings of optical scanning devices have come to be made of molded resin components, and as optical deflectors, inexpensive general purpose unitized components formed as units are being used. In such units, a polygon mirror and a motor are disposed on a circuit board, which serves as a base for the optical deflector, and a motor-driving IC, for controlling rotary driving of the motor, and the like are also mounted at the circuit board. 
   However, with an optical deflector which is formed as a unit in this manner, because the whole of the optical deflector is accommodated in the housing of the optical scanning device, heat which is generated by heat-generating components, such as the motor-driving IC and the like, tends to accumulate within the housing. Hence, with a housing made of resin, which has lower thermal conductivity (heat absorption and heat dissipation characteristics) than a metal model made of die-cast aluminum or the like, interior heat is less easily propagated through the housing and dissipated. Therefore, particularly just after the device starts to operate, when the amount of temperature increase is large, there is a difference in temperature gradient between an interior temperature of the optical scanning device (the housing) and the temperature that is measured by an environment sensor. Thus, there is a problem in that color registration errors will occur. 
   As is shown in  FIG. 14 , when, for example, the temperature variation of a color image forming apparatus is observed over a 30-minute period after startup, the motor-driving IC of the optical deflector rapidly rises in temperature for about 3 minutes after startup, and then gradually stabilizes. Meanwhile, the interior of the optical scanning device (housing) gradually rises in temperature for about 25 minutes after startup, and substantially stabilizes at an increase of about 3.5° C. 
   On the other hand, because propagation of heat through the housing is low and propagation of heat through the air is dominant after startup, a rate of heat conduction to the environment sensor is slow, and the environment sensor has no observable rise in temperature for about 8 minutes after startup, thereafter rises only gradually, and does not match the temperature in the optical scanning device until about 30 minutes has passed. 
   Thus, just after the device starts operation, there is a difference between a gradient of the temperature in the optical scanning device and a gradient of the device temperature that is measured by the environment sensor, and the rise of the environment sensor is slower than the temperature rise of the optical scanning device interior. Therefore, when a reading registration difference between, for example, the color C and the color K is observed, as is shown in the graph for an IOT (Image Output Terminal) in  FIG. 15 , a registration error just before input of a registration control cycle is large. Furthermore, when the polygon mirror of the optical scanning device (ROS: Raster Output Scanner) is rotated and laser light sources are illuminated, a graph showing the reading registration difference between the color C and the color K at the optical scanning device (‘ROS unit body’) is similar to the above-mentioned graph for the IOT. From this, it is understood that effects of heat sources other than the optical scanning device on deterioration in color registration at the IOT just after startup are small, and the deterioration in color registration is mainly determined by characteristics of the optical scanning device. 
   Further, as shown in  FIG. 16 , reading registration offsets of the color C and the color K are set in relatively opposite directions, with the color C at a minus side, and the color K at a plus side. Thus, offset amounts are large. Note that differences between offset amounts of the color C and offset amounts of the color K in  FIG. 16  constitute the graph of reading registration errors of the ROS unit body shown in  FIG. 15 . 
     FIG. 17  shows a schematic diagram of the structure of the optical scanning device at which the various data shown in  FIGS. 14 to 16  have been measured. At an optical scanning device  110 CK shown in  FIG. 17 , two different optical systems corresponding to the color C and the color K are provided at a single housing (optical casing)  112 , which is made of resin. A light beam K corresponding to the color K, which is deflectingly scanned by a polygon mirror  54  of an optical deflector, passes through f-θ lenses  56  and  58 , is reflected by a total of four mirrors—a cylindrical mirror  60 K, a reflection mirror  62 K, a cylindrical mirror  64 K and a reflection mirror  66 K—and is focused on a photosensitive drum  24 K. Similarly, a light beam C corresponding to the color C, which is deflectingly scanned by the polygon mirror  54 , passes through the f-θ lenses  56  and  58 , is reflected by a total of three mirrors—a cylindrical mirror  60 C, a reflection mirror  62 C and a cylindrical mirror  64 C—and is focused on a photosensitive drum  24 C. 
   Now, just after startup of the device, besides the motor-driving IC of the optical deflector, a driving IC at which a laser light source driver (LDD) or the like is mounted also rapidly rises in temperature at the time of startup. Air inside the optical scanning device  110 CK is warmed by these heat-generating components, and the air is agitated by rotation of the polygon mirror  54 . Consequently, a distribution of temperature in the optical scanning device  110 CK alters or a hot air flow impinges on the optical system (for example, on a reflection mirror directly or on a support of a reflection mirror), and a temperature thereof is increased. Thus, when, for example, the light beams C and K pass through the f-θ lenses  56  and  58  and are initially incident on the cylindrical mirrors  60 C and  60 K and are inclined in the same direction, the light beams C and K that have been reflected by the cylindrical mirrors  60 C and  60 K are shifted as shown by the broken lines, and the reading registrations on the photosensitive drums  24 C and  24 K are offset to respectively opposite sides (see  FIG. 16 ). Thus, the difference which is a color registration error becomes large. 
   As countermeasures for the color registration error which is generated in this manner, for example, reducing a time interval between temperature measurements by the environment sensor and increasing a number of registration control cycles have been considered. However, in such cases, while the color registration error described above can be avoided, the number of down-times, at which image output operations are stopped, increases and usability deteriorates. 
   SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, an optical scanning device includes a light source that emits a light beam, an optical deflector at which a light beam emitted from the light source is incident, the optical deflector deflecting the incident light beam, an optical system that guides the deflected light beam to surface to be scanned by the deflected light beam, a driving device that drives at least a portion of the optical deflector, a thermal storage member mounted on the driving device, the thermal storage member absorbing and storing heat generated by the driving device, thereby controlling a temperature gradient of the driving device, and a casing body that accommodates the light source, the optical deflector, the optical system, the driving device, and the thermal storage member. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the present invention will be described in detail based on the following figures, in which: 
       FIG. 1  is a schematic view showing the structure of an image forming apparatus relating to a first exemplary embodiment of the present invention; 
       FIG. 2  is a perspective view showing optical scanning devices relating to the first exemplary embodiment of the present invention; 
       FIG. 3  is a plan view showing principal structural components of an optical scanning device relating to the first exemplary embodiment of the present invention; 
       FIG. 4  is a perspective view showing the principal structural components of the optical scanning device relating to the first exemplary embodiment of the present invention; 
       FIG. 5  is a diagram showing light paths of the optical scanning devices relating to the first exemplary embodiment of the present invention; 
       FIG. 6  is a front view showing an optical deflector at which a thermal storage member relating to the first exemplary embodiment of the present invention is provided; 
       FIG. 7  is a perspective view showing a vicinity of an optical deflector mounting portion of a housing relating to the first exemplary embodiment of the present invention; 
       FIG. 8  is a graph showing comparative results of temperature gradients of a motor-driving IC with and without presence of the thermal storage member; 
       FIG. 9  is a graph showing comparative results of temperature gradients of an ROS interior with and without presence of the thermal storage member; 
       FIG. 10  is a graph showing comparative results of reading registration differences between a color C and a color K at a ROS unit body with and without presence of the thermal storage member; 
       FIG. 11  is a graph showing comparative results of reading registration differences between the color C and the color K at an IOT with and without presence of the thermal storage member; 
       FIG. 12  is a front view showing an optical deflector at which a thermal storage member relating to a second exemplary embodiment of the present invention is provided; 
       FIG. 13  is a front view showing an optical deflector at which a thermal storage member relating to a third exemplary embodiment of the present invention is provided; 
       FIG. 14  is a graph showing differences between temperature gradients of a conventional motor-driving IC, ROS interior and environment sensor; 
       FIG. 15  is a graph showing reading registration differences between the color C and the color K at a conventional ROS unit body and IOT; 
       FIG. 16  is a graph showing a difference between reading registration offset directions of the color C and the color K at a conventional ROS unit body; and 
       FIG. 17  is an explanatory view for explaining light paths of a conventional optical scanning device and directions of offsetting of light beams of the color C and the color K. 
   

   DETAILED DESCRIPTION 
   Herebelow, exemplary embodiments of the present invention will be described in detail with reference to the drawings. 
   First Exemplary Embodiment 
   An image forming apparatus  10  according to this exemplary embodiment is provided with an optical scanning device  28 CK and an optical scanning device  28 YM, as shown in  FIG. 1 . The optical scanning device  28 CK scans for exposing a photosensitive drum  24 C and a photosensitive drum  24 K, and is provided with optical systems corresponding to the colors C (cyan) and K (black). The optical scanning device  28 YM scans for exposing a photosensitive drum  24 Y and a photosensitive drum  24 M, and is provided with optical systems corresponding to the colors Y (yellow) and M (magenta). 
   The image forming apparatus  10  is also provided with electrophotographic units  12 Y,  12 M,  12 C and  12 K, which form toner images of the four colors Y (yellow), M (magenta), C (cyan) and K (black). The electrophotographic unit  12 Y is structured with a charging device  26 Y, the optical scanning device  28 YM, a developing device  30 Y, a first transfer device  14 Y and a cleaning device  32 Y disposed around the photosensitive drum  24 Y. The electrophotographic units  12 M,  12 C and  12 K have similar structures thereto. 
   The image forming apparatus  10  is also provided with an intermediate transfer belt  16 , a second transfer device  20  and a fixing device  22 . Respective toner images are layered by the first transfer devices  14 Y to  14 K to form a color toner image on the intermediate transfer belt  16 . The second transfer device  20  transfers the color toner image that has been transferred onto the intermediate transfer belt  16  to paper, which is supplied from a tray  18 . The fixing device  22  fuses and fixes the color toner image that has been transferred onto the paper. 
   As shown in  FIG. 2 , the optical scanning devices  28 CK and  28 YM are provided with rectangular box-form housings  34  made of resin (which are molded components). Herein, because internal structures of the optical scanning devices  28 CK and  28 YM are substantially the same, only the optical scanning device  28 CK will be described. 
   As shown in  FIGS. 3 and 4 , a light source portion  40 K, which emits a light beam K corresponding to the color K, and a light source portion  40 C, which emits a light beam C corresponding to the color C, are disposed in the housing  34  such that emission directions thereof are substantially at 90° to one another. In this exemplary embodiment, surface emission-type semiconductor lasers are employed as the emitting light sources. As shown in  FIG. 4 , the light source portions  40 C and  40 K are structured with surface emission laser chips  41 C and  41 K and retaining members  43 C and  43 K. The surface emission laser chips  41 C and  41 K are formed to be capable of simultaneously emitting plural optical lasers. The retaining members  43 C and  43 K are members for retaining the surface emission laser chips  41 C and  41 K, are referred to with the usual term ‘LCC’ (leadless chip carrier), and ceramics are employed as materials thereof herein. The surface emission laser chips  41 C and  41 K are electrically connected, through the retaining members  43 C and  43 K, to circuit boards  45 C and  45 K, respectively, at which electrical circuits are mounted. 
   The light source portion  40 C which emits the light beam C is disposed to be offset in a height direction relative to the light source portion  40 K which emits the light beam K, and the light beam C and the light beam K are arranged so as to be a predetermined distance apart in the height direction. 
   A collimator lens unit  42 K, for making light of the light beam K parallel, is disposed on an optical path of the light beam K emitted from the light source portion  40 K. The light beam K that has passed through the collimator lens unit  42 K passes beneath a reflection mirror  44 , is incident at a slit plate  46 K and is incident on a half-mirror  48 , which is disposed on the optical path. The half-mirror  48  divides the light beam K into a transmitted light beam K and a reflected light beam BK in a predetermined ratio. The light beam BK is reflected and is incident at an optical power monitor  50 . Because a surface emission optical laser is employed in this exemplary embodiment, it is not possible to obtain light for light amount control from a backbeam. Therefore, a portion of the light beam emitted in a forward direction is utilized by this division with the half-mirror  48 . The light beam K that has been transmitted through the half-mirror  48  passes through a cylindrical lens  52 K and is incident at a polygon mirror  54  of an optical deflector  70  which is disposed on the optical path, as shown in  FIG. 3 . 
   Meanwhile, a collimator lens unit  42 C, for making light of the light beam C parallel, is disposed on an optical path of the light beam C emitted from the light source portion  40 C. The light beam C that has passed through the collimator lens unit  42 C is deflected by the reflection mirror  44 , is incident at a slit plate  46 C and is incident on the half-mirror  48  disposed on the optical path. The half-mirror  48  divides the light beam C into a transmitted light beam C and a reflected light beam BC in a predetermined ratio. The light beam BC is reflected and is incident at the optical power monitor  50 . The light beam C that has been transmitted through the half-mirror  48  passes through a cylindrical lens  52 C and is incident at the polygon mirror  54  of the optical deflector  70  which is disposed on the optical path as shown in  FIG. 3 . 
   Plural reflection mirror faces are provided at the polygon mirror  54 . As shown in  FIG. 5 , the light beams C and K that are incident at the polygon mirror  54  are deflectingly reflected by the reflection mirror faces and enter f-θ lenses  56  and  58 . The polygon mirror  54  and the f-θ lenses  56  and  58  are of sizes which are capable of scanning the light beams C and K simultaneously. 
   The light beams for the two colors C and K which have passed through the f-θ lenses  56  and  58  are separated and are reflected at respective cylindrical mirrors  60 C and  60 K, which have power in a sub-scanning direction. The light beam K that has been reflected by the cylindrical mirror  60 K is doubled back to a reflection mirror  62 K, is then deflected by a cylindrical mirror  64 K and a reflection mirror  66 K, and is focused at the photosensitive drum  24 K to form an electrostatic latent image. 
   Meanwhile, the light beam C that has been reflected by the cylindrical mirror  60 C is doubled back to a reflection mirror  62 C, is then deflected by a cylindrical mirror  64 C, and is focused on the photosensitive drum  24 C to form an electrostatic latent image. 
   Thus, at the optical scanning device  28 CK (or  28 YM) of this exemplary embodiment, plural (two) different optical systems are provided in one of the housings  34 . 
     FIG. 6  shows the optical deflector  70  relating to this exemplary embodiment as described above.  FIG. 7  shows a state in which the optical deflector  70  has been assembled to be accommodated inside the housing  34  of the optical scanning device  28 CK or the optical scanning device  28 YM. 
   This optical deflector  70  is a commercially available product (a general purpose component). As shown in  FIG. 7 , a printed circuit board  72 , with a rectangular shape in plan view, is provided to serve as a base of the optical deflector  70 . The polygon mirror  54 , which rotates about an axis L, and a motor  74 , which drives to rotate the polygon mirror  54 , are disposed to be offset to one side relative to a central portion of the printed circuit board  72 . The polygon mirror  54  is made of aluminum and is formed in a polygonal column shape, and a mirror face is machined at the surface of each side of the polygon mirror  54 . 
   As shown in  FIG. 6 , a driving IC  78  for controlling rotary driving of the polygon mirror  54  and the motor  74  is mounted toward the other side of an upper face of the printed circuit board  72 . A connector  76 , at which power source and signal cables are connected, is mounted at an end portion of this other side. The driving IC  78  is an electronic component in the form of a package, with a package portion  78 A being formed of a resin material. 
   A thermal storage member  80  is mounted at an upper face of the driving IC  78 , via an adhesion member  82  with high thermal conductivity, such as a thermally conductive adhesive agent, a thermally conductive adhesive tape or the like. 
   The thermal storage member  80  is fabricated of an aluminum alloy, is formed in a cuboid shape (a block shape) which is larger than the driving IC  78 , and has a larger thermal capacity than the package portion  78 A of the driving IC  78 . Further, because the thermal storage member  80  is formed in this cuboid shape, surfaces with planar form which are free of protrusions can be smoothly formed at all (six) faces thereof. 
   In the state in which the thermal storage member  80  has been mounted at the driving IC  78 , an upper face  80 A of the thermal storage member  80  is disposed at a lower side in an axial direction (the direction of arrow Z) relative to a lower face  54 A of the polygon mirror  54 , and a predetermined gap H is provided between the upper face  80 A and the lower face  54 A. 
   As shown in  FIG. 6 , this optical deflector  70  is placed on a bottom face (an optical deflector mounting portion  84 ) of the housing  34  with a length direction of the printed circuit board  72  oriented in a width direction of the housing  34  (the direction of arrow W), and the optical deflector  70  is mounted by fixing the four corners of the printed circuit board  72  with four screws  86 . In this manner, the overall structure, including the driving IC  78  which is a heat-generating component, is accommodated in the housing  34 . Because the housing  34  is a resin-molded component and the optical deflector  70  employs an inexpensive general purpose component formed as a unit, costs of the optical scanning devices  28 YM and  28 CK of this exemplary embodiment are suppressed. 
   Next, operations of this exemplary embodiment will be described. After startup of the image forming apparatus  10 , when an image formation operation commences, at the optical deflector  70 , which is mounted at the optical deflector mounting portion  84  of the housing  34  of the optical scanning device  28 YM or  28 CK as described above, the two light beams emitted from the two light source portions  40  are incident on the polygon mirror  54 , and the two light beams are deflected for scanning by the polygon mirror  54  being rapidly rotated. Here, because two different optical systems are provided in the one housing  34 , directions and amounts of shifts (displacements) in reading registration differ due to differences in numbers of mirrors (particularly subsequent to the optical deflector  70 ), arrangements of optical components, and incidence angles of the light beams at the respective mirrors. 
   Herein, in a stage just after startup of operations, in which the driving IC  78  rises in temperature, heat generated from the driving IC  78  is absorbed at the thermal storage member  80 , via the adhesion member  82 , and is stored (heat sinking/thermal storage). Consequently, a temperature gradient is restrained such that the temperature increase is slowed. This thermal storage member  80  differs from, for example, a heat sink which is cooled to promote dissipation of heat from the driving IC  78  or the like. Because the thermal storage member  80  stores the absorbed heat, amounts of heat dissipated to air in the housing  34  from the thermal storage member  80  just after startup of the device are suppressed. As the amount of heat stored in the thermal storage member  80  increases and the temperature gradually rises, the heat is gradually released. Therefore, the temperature gradient of the temperature in the housing  34  is restrained such that the increase is gentler. Hence, positional shifts due to thermal effects on the optical systems disposed in the housing  34  are mitigated, and gradients of registration variations at scanning-object surfaces which are scanned by the light beams (the photosensitive drums  24 Y,  24 M,  24 C and  24 K) are moderated. 
     FIGS. 8 to 11  show comparative results of various measured values with and without the presence of the thermal storage member  80 . When the thermal storage member  80  is mounted at the driving IC  78 , then as shown in  FIG. 8 , the temperature gradient of the driving IC  78  is made gentler, and accordingly, as shown in  FIG. 9 , the temperature gradient of the housing  34  interior is made gentler. Hence, as shown in  FIGS. 10 and 11 , gradients of color registration variations are also slowed, and color registration variations after corresponding amounts of time have passed can be substantially reduced by half. 
   Thus, with the above-described image forming apparatus  10  which is provided with the optical scanning devices  28 YM and  28 CK, it is possible, with a simple structure in which the thermal storage member  80  is mounted at the driving IC  78  of each optical deflector  70 , to suppress reading registration errors of respective colors that occur in the formation of color images just after startup of the device, and it is possible to form high-quality images. 
   Further, because the thermal storage member  80  of this exemplary embodiment is formed with smooth surfaces which are free of protrusions, a heat dissipation suppression effect of the thermal storage member  80  is enhanced, and it is possible to control the temperature gradient to further make the temperature increase inside the housing  34  gentler. 
   Further again, because the thermal capacity of the thermal storage member  80  is larger than that of the package portion  78 A of the driving IC  78  which is formed of a resin material, it is possible to adequately store heat dissipated from the surface of the driving IC  78  with the thermal storage member  80 , and it is possible to suppress conduction amounts (heat dissipation amounts) which are directly propagated to the air in the housing  34  from the driving IC  78 . 
   Further yet, when the polygon mirror  54  of the optical deflector  70  is driven by the motor  74  and rotates, air currents are generated in radial directions around the polygon mirror  54 . However, in this exemplary embodiment, because the upper face  80 A of the thermal storage member  80  mounted at the driving IC  78  is disposed at the axial direction lower side relative to the lower face  54 A of the polygon mirror  54 , amounts of airflow impinging on the thermal storage member  80  are kept small, and amounts of heat dissipated from the thermal storage member  80  are suppressed. 
   Further still, because the thermal storage member  80  is formed of an aluminum alloy, it is possible to fabricate a thermal storage member with small size and large thermal capacity at low cost. Furthermore, because molding, mechanical machining or the like thereof is simple, it is possible to fabricate the thermal storage member in a desired shape with ease. 
   Second Exemplary Embodiment 
   Next, a second exemplary embodiment of the present invention will be described. The second exemplary embodiment is a variant example in which a mounting structure of the thermal storage member is altered. Portions that are the same as in the first exemplary embodiment are assigned the same reference numerals and descriptions thereof are omitted, and only portions that differ from the first exemplary embodiment will be described. 
   As shown in  FIG. 12 , a thermal storage member  90  relating to the second exemplary embodiment is provided with a leg portion  92 , which protrudes downward from an outer side end portion (a left side end portion in the drawing) of a lower face of the thermal storage member  90 . A plate-like fixing portion  94  protrudes to an outer side direction from a lower end portion of an outer side face of the leg portion  92 . Further, an unillustrated hole formed at a distal end portion of this leg portion  92  is fastened together with the optical deflector  70  by one of the screws  86  that fix the optical deflector  70  to the housing  34 . Thus, the thermal storage member  90  is in a state in which a lower face thereof is in contact with the upper face of the driving IC  78 , and the thermal storage member  90  is mounted on the driving IC  78 . 
   Thus, in this exemplary embodiment, because both the thermal storage member  90  and the optical deflector  70  are fixed using the screw  86  which is for fixing the optical deflector  70  to the housing  34 , the thermal storage member  90  is indirectly mounted at the driving IC  78 . Because fixing means constituted by such a screw member is utilized, it is possible to mount the thermal storage member  90  at the driving IC  78  simply and firmly. Further, in comparison with a structure for directly mounting a thermal storage member as in the first exemplary embodiment, it is possible to reduce loads that are applied to lead portions (solder portions) at the driving IC  78  which is formed as a package as in this exemplary embodiment. Moreover, because there is no need to interpose an adhesive member or the like between the driving IC  78  and the thermal storage member  90 , efficiency of thermal conduction from the driving IC  78  to the thermal storage member  90  is enhanced. 
   Third Exemplary Embodiment 
   Next, a third exemplary embodiment of the present invention will be described. The third exemplary embodiment is also a variant example in which the mounting structure of the thermal storage member is altered. Portions that are the same as in the first exemplary embodiment are assigned the same reference numerals and descriptions thereof are omitted, and only portions that differ from the first exemplary embodiment will be described. 
   As shown in  FIG. 13 , a thermal storage member  100  relating to the third exemplary embodiment is provided with a pair of leg portions  102 , which protrude downward from end portions at two sides of a lower face of the thermal storage member  100  (left and right side end portions in the drawing). A protrusion-like fixing portion  104  protrudes to an outer side direction from a lower end portion of the outer face of each leg portion  102 . These fixing portions  104  are fixed with solder  106  to unillustrated copper foil lands which are formed at the upper face of the printed circuit board  72 . Thus, the thermal storage member  100  is also in a state in which a lower face thereof is in contact with the upper face of the driving IC  78 , and the thermal storage member  100  is mounted on the driving IC  78 . 
   Thus, in this exemplary embodiment, because the thermal storage member  100  is soldered to be fixed to the printed circuit board  72  of the optical deflector  70 , the thermal storage member  100  is indirectly mounted at the driving IC  78 . Because solder is employed thus, it is possible to mount the thermal storage member  100  at the driving IC  78  simply and robustly. Further, similarly to the second exemplary embodiment, it is possible to reduce loads that are applied to lead portions (solder portions) of the driving IC  78  and, because there is no need to interpose an adhesive member or the like between the driving IC  78  and the thermal storage member  100 , efficiency of thermal conduction from the driving IC  78  to the thermal storage member  100  can be enhanced. 
   Although in the foregoing embodiments, the present invention has been applied to color image forming apparatus, it is to be understood that the present invention is equally applicable to monochrome image forming apparatus. 
   Hereabove, specific embodiments of the present invention have been exemplified and described in detail. However, the present invention is not limited to these exemplary embodiments, and is to be understood as encompassing various changes and modifications which can be implemented without deviating from the appended claims.