Patent Publication Number: US-11036178-B1

Title: Exposure device of image forming apparatus

Description:
FIELD 
     Embodiments described herein relate to an exposure device of an image forming apparatus. 
     BACKGROUND 
     In some exposure devices used in image forming apparatuses such as an electrophotographic apparatus, a print head such as an LED print head (LPH) is used. In such an exposure device, a technique for determining a focal position of a print head with respect to a photoreceptor drum using a gap spacer is known. In this technique, the following configuration is adopted. A gap spacer for providing a focal length is provided between the photoreceptor drum and the print head. In addition, a positioning unit that abuts on the gap spacer is provided on the print head side. Further, a coil spring is provided between the print head and a print head holding unit. The position of the print head is determined with respect to the photoreceptor drum in a state in which the print head receives a predetermined abutting load by causing the gap spacer and the positioning portion to abut on each other and compressing the coil spring. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing an image forming apparatus according to an embodiment; 
         FIG. 2  is a perspective view showing a basic configuration of a photoreceptor drum and an exposure device shown in  FIG. 1 ; 
         FIG. 3  is a view showing an example of a print head shown in  FIG. 2 ; 
         FIG. 4  is a view showing a light emitting element array on a transparent substrate of the print head shown in  FIG. 3 ; 
         FIG. 5  is a perspective view showing the exposure device shown in  FIGS. 1 and 2 ; 
         FIG. 6  is a perspective view showing the exposure device shown in  FIG. 1  and a photoreceptor unit; 
         FIG. 7  is a cross-sectional view showing the exposure device and the photoreceptor unit shown in  FIG. 6 ; 
         FIG. 8  is a view showing a part surrounded by an ellipse shown in  FIG. 7  in an enlarged manner; 
         FIG. 9  is a view showing the exposure device in which a lifting holder is at a lowest position and the exposure device in which the lifting holder is at a highest position in a situation where the photoreceptor drum does not exist; 
         FIG. 10  is a cross-sectional view of the exposure device and the photoreceptor unit in a state in which the lifting holder and a cleaner case are separated from each other; and 
         FIG. 11  is a cross-sectional view of the exposure device and the photoreceptor unit in a state in which the lifting holder and the cleaner case abut on each other. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, there is provided an exposure device including: a print head that exposes a photoreceptor to form a latent image on the photoreceptor; a lifting mechanism that lifts or lowers the print head relative to the photoreceptor; and a biasing member that biases the print head toward the photoreceptor. The lifting mechanism has a lifting holder that holds the print head and is liftable with respect to the photoreceptor. The biasing member is provided between the print head and the lifting holder. 
       FIG. 1  shows an image forming apparatus  100  according to an embodiment. The image forming apparatus  100  is a quadruple tandem type color image forming apparatus. The image forming apparatus  100  is an image forming apparatus such as a printer, a copy machine, or a multifunction peripheral. 
     The image forming apparatus  100  includes an image forming unit  102 -Y that forms a yellow (Y) image, an image forming unit  102 -M that forms a magenta (M) image, an image forming unit  102 -C that forms a cyan (C) image, and an image forming unit  102 -K that forms a black (K) image. The image forming units  102 -Y,  102 -M,  102 -C, and  102 -K form yellow, cyan, magenta, and black images, respectively, and transfer the images to a transfer belt  103 . Thus, a full-color image is formed on the transfer belt  103 . 
     The image forming unit  102 -Y includes a charging charger  112 -Y, an exposure device  113 -Y, a developing device  114 -Y, a transfer roller  115 -Y, and a cleaner  116 -Y around a photoreceptor drum  111 -Y. The image forming units  102 -M,  102 -C, and  102 -K have the same configuration. 
     In  FIG. 1 , a symbol “−Y” is attached to the configuration of the image forming unit  102 -Y that forms a yellow (Y) image. A symbol “−M” is attached to the configuration of the image forming unit  102 -M that forms a magenta (M) image. A symbol “−C” is attached to the configuration of the image forming unit  102 -C that forms a cyan (C) image. A symbol “−K” is attached to the configuration of the image forming unit  102 -K that forms a black (K) image. 
     The charging chargers  112 -Y,  112 -M,  112 -C, and  112 -K uniformly charge the photoreceptor drums  111 -Y,  111 -M,  111 -C, and  111 -K, respectively. The exposure devices  113 -Y,  113 -M,  113 -C, and  113 -K expose the photoreceptor drums  111 -Y,  111 -M,  111 -C, and  111 -K respectively to form latent images on the photoreceptor drums  111 -Y,  111 -M,  111 -C, and  111 -K, respectively. The developing device  114 -Y attaches (develops) a yellow toner, the developing device  114 -M attaches (develops) a magenta toner, the developing device  114 -C attaches (develops) a cyan toner, and the developing device  114 -K attaches (develops) a black toner to electrostatic latent image portions of the photoreceptor drums  111 -Y,  111 -M,  111 -C, and  111 -K, respectively. 
     The transfer rollers  115 -Y,  115 -M,  115 -C, and  115 -K transfer toner images developed on the photoreceptor drums  111 -Y,  111 -M,  111 -C, and  111 -K to the transfer belt  103 , respectively. The cleaners  116 -Y,  116 -M,  116 -C, and  116 -K clean the remaining toner without transfer of the photoreceptor drums  111 -Y,  111 -M,  111 -C, and  111 -K, respectively. Thus, the photoreceptor drums  111 -Y,  111 -M,  111 -C, and  111 -K enter the standby state for the next image formation. 
     A paper  121 - 1  of a first size (small size) is stored in a paper cassette  117 - 1 . A paper  121 - 2  of the second size (large size) is stored in a paper cassette  117 - 2 . 
     The toner image is transferred from the transfer belt  103  by a pair of transfer rollers  118  to the paper  121 - 1  or  121 - 2  picked up from the paper cassette  117 - 1  or  117 - 2 . The paper  121 - 1  or  121 - 2  onto which the toner image is transferred is heated and pressurized by a fixing roller  120  of a fixing unit  119 . The toner image is firmly fixed on the paper  121 - 1  or  121 - 2  by heating and pressurizing with the fixing roller  120 . By repeating the above process operation, an image forming operation is continuously performed. 
     Hereinafter, the photoreceptor drums  111 -Y,  111 -M,  111 -C, and  111 -K and the exposure devices  113 -Y,  113 -M,  113 -C, and  113 -K shown in  FIG. 1  will be described. The image forming units  102 -Y,  102 -M,  102 -C, and  102 -K are substantially the same structures except for different toner colors. Accordingly, in the following description, the exposure devices  113 -Y,  113 -M,  113 -C, and  113 -K are typically represented by the exposure device  113  without being distinguished, and the photoreceptor drums  111 -Y,  111 -M,  111 -C and  111 -K are also typically represented by the photoreceptor drum  111  without being distinguished. 
       FIG. 2  is a perspective view showing the basic configuration of the photoreceptor drum  111  and the exposure device  113  shown in  FIG. 1 . 
     The exposure device  113  has the print head  1  that exposes the photoreceptor drum  111  to form a latent image on the photoreceptor drum  111 . The print head  1  is arranged so as to face the photoreceptor drum  111 . 
     The photoreceptor drum  111  rotates in a direction of an arrow shown in  FIG. 2 . Hereinafter, the rotation direction of the photoreceptor drum  111  is referred to as a sub-scanning direction SD. In addition, a direction perpendicular to the rotation direction of the photoreceptor drum  111 , that is, a direction parallel to the rotation axis of the photoreceptor drum  111  is referred to as a longitudinal direction or a main scanning direction MD. 
     The photoreceptor drum  111  is uniformly charged by a charging device and exposed by light from the print head  1  of the exposure device  113  to lower the potential in the exposed portion thereof. That is, by controlling light emission and non-light emission of the print head  1 , an electrostatic latent image is formed on the photoreceptor drum  111 . 
     The print head  1  includes a light emitting unit  10 . The light emitting unit  10  includes a transparent substrate  11 . For example, the transparent substrate  11  is a glass substrate which transmits light. The transparent substrate  11  is formed with high surface accuracy. On the transparent substrate  11 , one or more light emitting element arrays  13 L are provided. Each light emitting element array  13 L has a plurality of light emitting elements. Each light emitting element array  13 L is arranged in parallel to the rotation axis of the photoreceptor drum  111 . The light emitting element is formed by, for example, an LED. Alternatively, the light emitting element may be formed by, for example, an organic EL (OLED). 
     The print head  1  also includes a rod lens array  12 . The rod lens array  12  is arranged between the light emitting unit  10  and the photoreceptor drum  111 . Specifically, the rod lens array  12  is arranged between the light emitting element array  13 L and the photoreceptor drum  111 . The rod lens array  12  is arranged in parallel to the rotation axis of the photoreceptor drum  111 . The rod lens array  12  condenses the light emitted from the light emitting element array  13 L of the light emitting unit  10  on the photoreceptor drum  111 . 
     The print head  1  includes, for example, two light emitting element arrays  13 L (a first light emitting element array  13 L 1  and a second light emitting element array  13 L 2 ). In the embodiment, the example in which the print head  1  includes two light emitting element arrays  13 L is described, but the embodiment is not limited. For example, the print head  1  may include one light emitting element array  13 L. 
       FIG. 3  is a view showing an example of the transparent substrate constituting the print head shown in  FIG. 2 . As shown in  FIG. 3 , the two light emitting element arrays  13 L (the first light emitting element array  13 L 1  and the second light emitting element array  13 L 2 ) are provided along the longitudinal direction of the transparent substrate  11  at the central portion on the transparent substrate  11 . In the vicinity of the light emitting element arrays  13 L (the first light emitting element array  13 L 1  and the second light emitting element array  13 L 2 ), a drive circuit array  14 L (a first drive circuit array  14 L 1  and a second drive circuit array  14 L 2 ) for driving (light-emitting) each light emitting element is formed. 
     As shown in  FIG. 3 , for example, the drive circuit array  14 L is arranged on both sides of the two light emitting element arrays  13 L. The drive circuit array  14 L may be arranged on one side of the two light emitting element arrays  13 L. The light emitting element array  13 L and the drive circuit array  14 L are covered with a transparent cover  17  so as not to be exposed to the outside air. 
     In an end portion of the transparent substrate  11 , an integrated circuit (IC)  15  is arranged. In addition, the transparent substrate  11  includes a connector  16 . The connector  16  is electrically connected to the print head  1  and the control system of the image forming apparatus. This connection enables power supply, head control, and image data transfer. When it is difficult to mount the connector  16  on the transparent substrate  11 , a flexible printed circuit (FPC) may be connected to the transparent substrate  11 , and electrical connection with the control system may be achieved through the FPC. 
       FIG. 4  is a view showing an example of the light emitting element arrays (two array head) shown in  FIG. 3 . As shown in  FIG. 4 , each light emitting element array  13 L includes a plurality of light emitting elements  13  aligned along the main scanning direction MD. That is, the alignment direction of the plurality of light emitting elements  13  forming the first light emitting element array  13 L 1  and the arrangement direction of the plurality of light emitting elements  13  forming the second light emitting element array  13 L 2  are parallel to the main scanning direction MD. 
     The light emitting element  13  has a square size of 20 μm, for example. Both the light emitting elements  13  of the first light emitting element array  13 L 1  and the light emitting elements  13  of the second light emitting element array  13 L 2  are arranged at a predetermined arrangement interval D 11  along the main scanning direction MD. The arrangement interval D 11  of the light emitting elements  13  is about 42.3 μm, for example, with a resolution of 600 dpi. 
     The first light emitting element array  13 L 1  and the second light emitting element array  13 L 2  are arranged at a distance D 12  with respect to the sub-scanning direction SD. Further, each light emitting element  13  forming the first light emitting element array  13 L 1  and each light emitting element  13  forming the second light emitting element array  13 L 2  are arranged to be shifted by a predetermined pitch D 13  with respect to the main scanning direction MD. For example, the predetermined pitch D 13  is ½ of the arrangement interval D 11 . Thus, the two light emitting element arrays  13 L are arranged in a staggered manner. 
     When the light emitting elements of the first light emitting element array  13 L 1  and the light emitting elements of the second light emitting element array  13 L 2  emit light at the same timing, a staggered exposure pattern is formed on the photoreceptor drum  111 . Here, for convenience, the upstream side light emitting element array  13 L with respect to a moving direction of the photoreceptor drum  111  is referred to as a first light emitting element array  13 L 1 , and the downstream side light emitting element array  13 L is referred to as a second light emitting element array  13 L 2 . A control unit that controls an image forming operation causes the first light emitting element array  13 L 1  and the second light emitting element array  13 L 2  to emit light at different timings according to the moving speed of the photoreceptor drum  111  and the distance D 12 . That is, the control unit delays the light emission timing of the second light emitting element array  13 L 2  with respect to the first light emitting element array  13 L 1  for a predetermined time according to the moving speed of the photoreceptor drum  111  and the distance D 12 . In other words, the control unit outputs first light emitting element image data to the first light emitting element array  13 L 1  and second light emitting element image data to the second light emitting element array  13 L 2  at different timings according to the moving speed of the photoreceptor drum  111  and the distance D 12 . Here, the first light emitting element image data and the second light emitting element image data correspond to the image data for one line in the main scanning direction. Thus, a latent image is formed on the photoreceptor drum with a resolution of 1200 dpi. 
     In this manner, the control unit can increase image density by controlling the light emission timing (image data transfer timing) of the plurality of light emitting element arrays  13 L. In the case of the two light emitting element arrays  13 L, it is possible to increase the density of the image by twice the density of the light emitting elements  13  per array, and in the case of n (n≥3, n: integer) light emitting element arrays  13 L, it is possible to increase the density of the image by n times the density of the light emitting elements  13  per array. 
       FIG. 5  is a perspective view showing the exposure device shown in  FIGS. 1 and 2 . The exposure device  113  has the print head  1  shown in  FIG. 2 . The exposure device  113  is arranged inside the image forming apparatus  100  so that the longitudinal direction of the print head  1  extends in the front-rear direction of the image forming apparatus  100 . 
     The print head  1  includes the light emitting unit  10  and the rod lens array  12  as described with reference to  FIG. 2 . Further, the print head  1  includes a holder  20  which holds the light emitting unit  10  and the rod lens array  12  in addition to these components. The holder  20  has a slit extending in the longitudinal direction and the rod lens array  12  is accommodated and fixed in this slit. 
       FIG. 6  is a perspective view showing the exposure device shown in  FIG. 1  and a photoreceptor unit. In addition,  FIG. 7  is a cross-sectional view of the exposure device and the photoreceptor unit shown in  FIG. 6 . As shown in  FIGS. 6 and 7 , the photoreceptor drum  111  is accommodated in a photoreceptor unit  130 . The photoreceptor unit  130  has a case  131 . The case  131  holds the photoreceptor drum  111  rotatably. 
     The photoreceptor unit  130  is attached to the image forming apparatus  100  to be replaceable. For example, the photoreceptor unit  130  is attached to and detached from the image forming apparatus  100  by being inserted into and removed from the front side of the image forming apparatus  100 . The photoreceptor unit  130  is mounted on the image forming apparatus  100  so that the photoreceptor drum  111  is parallel to the print head  1  of the exposure device  113 . 
     In order to clean the print head  1  and replace the photoreceptor unit  130 , the print head  1  needs to be lifted and lowered so that the print head  1  can about on and separate from the photoreceptor unit  130 . Therefore, as shown in  FIGS. 5 to 7 , the exposure device  113  has a lifting mechanism  30  that lifts or lowers the print head  1 . The lifting mechanism  30  has a function of lifting the print head  1  and a function of lowering the print head  1 . Here, lifting the print head  1  means that the print head  1  approaches the photoreceptor drum  111 . In addition, lowering the print head  1  means that the print head  1  is separated from the photoreceptor drum  111 . 
     Here, the photoreceptor drum  111  naturally refers to a photoreceptor drum accommodated in the photoreceptor unit  130  mounted on the image forming apparatus  100 . In the following description, the photoreceptor drum  111  means a photoreceptor drum in the photoreceptor unit  130  mounted on the image forming apparatus  100 . 
     The lifting mechanism  30  has a liftable lifting holder  31  that holds the print head  1 . The lifting holder  31  is movable so as to approach the photoreceptor drum  111  or separate from the photoreceptor drum  111 . 
     The lifting mechanism  30  also has a lifting slider  35  that is movable in the longitudinal direction, a guide  36  that guides the lifting slider  35 , a lifting spring  37  that biases the lifting slider  35 , and a lifting lever  38  for moving the lifting slider  35 . 
     The lifting slider  35  is supported by the guide  36  to be movable in the longitudinal direction. One end of the lifting spring  37  is attached to the guide  36  and the other end thereof is attached to the lifting slider  35 . The lifting spring  37  biases the lifting slider  35  toward the lifting lever  38 . 
     The lifting lever  38  has a structure that moves the lifting slider  35  against the biasing force of the lifting spring  37  by a rotating operation thereof. 
     The lifting lever  38  has, for example, a pin that moves in the longitudinal direction of the guide  36  according to the rotation thereof. By pushing the pin of the lifting lever  38  toward the lifting spring  37 , the lifting slider  35  is moved toward the lifting spring  37  against the biasing force of the lifting spring  37 . In contrast, by pulling the pushed pin of the lifting lever  38 , the lifting slider  35  is moved toward the lifting lever  38  by the biasing force of the lifting spring  37 . 
     The lifting mechanism  30  further has a pair of link mechanisms  40  that connect the lifting holder  31  and the lifting slider  35 . The link mechanism  40  is a Scott Russell type link mechanism. The Scott Russell type link mechanism  40  converts the movement of the lifting slider  35  in the longitudinal direction into the movement of the lifting holder  31  in a direction perpendicular to the longitudinal direction. 
     The link mechanism  40  has a first link  41  and a second ink  42 . The first link  41  is longer than the second link  42 . One end of the first link  41  is rotatably connected to the lifting slider  35 . The other end of the first link  41  is rotatably connected to the lifting holder  31 . For example, the other end of the first link  41  is engaged with the long hole of the lifting holder  31 . One end of the second link  42  is rotatably connected to the guide  36 . One end of the second link  42  is rotatably connected to the central portion of the first link  41 . 
     According to the movement of the lifting slider  35  in a direction from the lifting lever  38  to the lifting spring  37 , the other end of the first link  41 , that is, the connection portion with the lifting holder  31  is lifted, that is, approaches the photoreceptor drum  111 . As a result, the lifting holder  31  is lifted, that is, approaches the photoreceptor drum  111 . 
     In contrast, according to the movement of the lifting slider  35  in a direction from the lifting spring  37  to the lifting lever  38 , the other end of the first link  41 , that is, the connection portion with the lifting holder  31  is lowered, that is, separated from the photoreceptor drum  111 . As a result, the lifting holder  31  is lowered, that is, separated from the photoreceptor drum  111 . The direction of lifting and lowering of the lifting holder  31 , that is, the direction of approach and separation of the lifting holder, is substantially perpendicular to the moving direction of the lifting slider  35 . 
     The lifting mechanism  30  further has a biasing member that biases the print head  1  toward the photoreceptor drum  111 , for example, a pair of coil springs  50 . The coil spring  50  is arranged between the print head  1  and the lifting holder  31 . That is, the coil spring  50  is arranged between a head holder  20  and the lifting holder  31 . 
       FIG. 8  is a view showing a part surrounded by an ellipse shown in  FIG. 7  in an enlarged manner. As shown in  FIG. 8 , the head holder  20  has a dowel  21  protruding toward the photoreceptor unit  130  attached to the image forming apparatus  100 . In addition, a cleaner case  131  has a dowel hole  132  for receiving the dowel  21 . The dowel hole  132  has a size that allows the dowel  21  to be just fitted. 
     The dowel  21  of the head holder  20  and the dowel hole  132  of the cleaner case  131  are configured to determine the position of the print head  1  with respect to the cleaner case  131  in a direction perpendicular to the lifting direction of the print head  1  by the lifting mechanism  30  by fitting the dowel  21  into the dowel hole  132  of the cleaner case  131  when the print head  1  is lifted. 
     That is, by the dowel  21  of the head holder  20  and the dowel hole  132  of the cleaner case  131 , the position of the print head  1  with respect to the cleaner case  131  is determined for the position of the print head  1  in the longitudinal direction and the position of the photoreceptor drum  111  in a direction perpendicular to both the diameter direction and the longitudinal direction. 
     The head holder  20  has a pair of head position determining units  22  at both ends in the longitudinal direction. The pair of head position determining units  22  respectively abut on a pair of gap spacers  140  arranged between the print head  1  and the photoreceptor drum  111  when the print head  1  is lifted, that is, the print head  1  approaches the photoreceptor drum  111 . The head position determining unit  22  is configured by, for example, a cam. 
     The lifting holder  31  has a pair of lifting holder position determining units  32  at both ends in the longitudinal direction. The pair of lifting holder position determining units  32  respectively abut on the cleaner case  131  holding the photoreceptor drum  111  when the print head  1  is lifted, that is, the print head  1  approaches the photoreceptor drum  111 . 
     The head position determining units  22  of the head holder  20  and the lifting holder position determining units  32  of the lifting holder  31  are provided for determining the positions of the print head  1  with respect to the photoreceptor drum  111  when the print head  1  is lifted to the maximum. For example, the head position determining units  22  and the lifting holder position determining units  32  are provided for determining a distance between the print head  1  and the photoreceptor drum  111 , in other words, for accurately arranging a focal position of the print head  1  on the surface of the photoreceptor drum  111 . 
     Thus, the pair of lifting holder position determining units  32  determines the position of the print head  1  with respect to the photoreceptor drum  111 . For example, the pair of lifting holder position determining units  32  determines a distance from the photoreceptor drum  111  to the print head  1 . 
     The lifting holder position determining units  32  and the head position determining units  22  are configured such that, when the print head  1  is lifted, the head position determining units  22  of the head holder  20  abut on the gap spacers  140  before the lifting holder position determining units  32  of the lifting holder  31  abut on the cleaner case  131 . 
     The coil spring  50  arranged between the head holder  20  and the lifting holder  31  applies a predetermined abutting load with respect to the photoreceptor drum  111  to the print head  1  when the print head  1  is lifted to the maximum, in other words, in a state in which the lifting holder position determining units  32  of the lifting holder  31  abut on the cleaner case  131 . 
     The stroke of the lifting mechanism  30  is larger than the maximum distance between the print head  1  and the photoreceptor drum  111 . Here, the stroke of the lifting mechanism  30  means a distance in which the print head  1  is moved by the lifting mechanism  30  in a situation where the photoreceptor drum  111  does not exist, in other words, in a situation where the movement of the print head  1  is not obstructed by anything. The maximum distance between the print head  1  and the photoreceptor drum  111  means a distance between the print head  1  and the photoreceptor drum  111  in the lowest state of the print head  1 , in other words, in a state in which the print head  1  is most distant from the photoreceptor drum  111 . 
       FIG. 9  is a view showing the exposure device  113  in which the lifting holder  31  is at the lowest position and the exposure device  113  in which the lifting holder  31  is at the highest position in a situation where the photoreceptor drum  111  does not exist. In  FIG. 9 , the exposure device  113  in which the lifting holder  31  is at the lowest position is shown on the left side and the exposure device  113  in which the lifting holder  31  is at the highest position is shown on the right side. 
     In addition, the position of the lifting holder position determining units  32  of the lifting holder  31  at the lowest position is indicated by P 1 , and the position of the lifting holder position determining units  32  of the lifting holder  31  at the highest position is indicated by P 2 . Further, the position of the lifting holder position determining units  32  of the lifting holder  31  in a state in which the lifting holder  31  actually abuts on the cleaner case  131  is indicated by P 3 . Here, the positions P 1 , P 2 , and P 3  mean the positions in the lifting direction of the lifting holder  31  by the lifting mechanism  30 . 
     The stroke of the lifting mechanism  30  is indicated by a distance L 1  between the position P 1  and the position P 2 . In addition, the maximum distance between the print head  1  and the photoreceptor drum  111  is indicated by a distance L 2  between the position P 1  and the position P 3 . 
     Since the stroke of the lifting mechanism  30  is larger than the maximum distance between the print head  1  and the photoreceptor drum  111 , even when the photoreceptor drum  111  is not arranged in parallel to the print head  1  due to the tolerance of the photoreceptor unit  130 , the lifting holder  31  is reliably arranged in parallel to the photoreceptor drum  111 . 
       FIG. 10  is a cross-sectional view of the exposure device  113  and the photoreceptor unit  130  in a state in which the lifting holder  31  and the cleaner case  131  are separated from each other. In addition,  FIG. 11  is a cross-sectional view of the exposure device  113  and the photoreceptor unit  130  in a state in which the lifting holder  31  and the cleaner case  131  abut on each other. 
     As shown in  FIG. 10 , in a state in which the lifting holder  31  and the cleaner case  131  are separated from each other, the photoreceptor drum  111  is not arranged in parallel to the print head  1 . In this case, when the lifting mechanism  30  is lifted by the lifting holder  31 , one lifting holder position determining unit  32  of the lifting holder  31  first abuts on the cleaner case  131 . However, since the lifting holder  31  is then continuously lifted by the lifting mechanism  30 , the other lifting holder position determining unit  32  of the lifting holder  31  also reliably abuts on the cleaner case  131 . As a result, as shown in  FIG. 11 , the lifting holder  31  is reliably arranged in parallel to the photoreceptor drum  111 . 
     As described above, in the exposure device  113  of the embodiment, the print head  1 , the lifting holder  31 , and the coil spring  50  are lifted and lowered together. In a configuration in which only the print head that is generally widely used is lifted and lowered, due to the tolerance of the dimensions of all the components forming the lifting mechanism and warping of the tray surface with the lifting mechanism attached and inclination of the print head that occurs during lifting and lowering, there is a possibility that defects such as the print head not accurately abutting on the gap spacer and a variation in the squeeze amount of the coil spring may be generated. 
     However, since the exposure device  113  of the embodiment has a configuration in which the print head  1 , the lifting holder  31 , and the coil spring  50  are lifted and lowered together, the exposure device has the following advantages. 
     The abutting load of the print head  1  with respect to the photoreceptor drum  111  is determined by the coil spring  50  arranged between the print head  1  and the lifting holder  31 . As described above, when the lifting holder  31  is lifted to the maximum by the lifting mechanism  30 , the lifting holder  31  is reliably arranged in parallel to the photoreceptor drum  111 . Therefore, the abutting load of the print head  1  at both end portions in the longitudinal direction is substantially equal. That is, the abutting load of the print head  1  does not substantially have a variation at both end portions in the longitudinal direction. Further, as the abutting load of the print head  1 , a predetermined abutting load equal to or more than the lower limit value is obtained. Thus, the print head  1  abuts on the gap spacer  140  with a predetermined abutting load having no variation at both end portions in the longitudinal direction. 
     The inclination of the print head  1  with respect to the photoreceptor drum  111  is a factor that deteriorates the quality of an image formed by the image forming apparatus  100 . However, since the print head  1  is reliably arranged in parallel to the photoreceptor drum  111  in the exposure device  113  of the embodiment, such image quality deterioration is prevented. 
     In addition, the variation in the abutting load of the print head  1  with respect to the photoreceptor drum  111  is a factor that causes the photoreceptor drum  111  to wear unevenly, and causes variation in the focal position of the print head  1  in the longitudinal direction position. However, since there is no variation in the abutting load of the print head  1  in the exposure device  113  of the embodiment, the generation of variation in the focal position of the print head  1  is prevented. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the apparatus and methods described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.