Patent Publication Number: US-6992690-B2

Title: Multi-beam scanning apparatus

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a multi-beam scanning apparatus used for a laser beam printer, digital copying machine, and the like. 
   2. Related Background Art 
   In recent years, multi-beam scanning apparatuses for simultaneously writing a plurality of lines using a plurality of laser beams are being developed in electrophotographic apparatuses such as a laser beam printer. 
   The multi-beam scanning apparatus simultaneously scans a plurality of laser beams apart from each other. As shown in  FIG. 1 , in the multi-beam scanning apparatus, a multi-beam semiconductor laser  111  serving as a light source for a multi-beam light source unit  101  emits two laser beams P 1  and P 2 . The laser beams P 1  and P 2  are collimated by a collimator lens  112 , irradiate a reflecting surface  103   a  of a rotary polygon mirror  103  via a cylindrical lens  102 , and form an image on a photosensitive member on a rotary drum  105  via an imaging lens  104 . 
   The two laser beams P 1  and P 2  are incident on the reflecting surface  103   a  of the rotary polygon mirror  103 , scanned in the main scanning direction, and form an electrostatic latent image on the photosensitive member along with main scanning by rotation of the rotary polygon mirror  103  and subscanning by rotation of the rotary drum  105 . 
   The cylindrical lens  102  linearly focuses the laser beams P 1  and P 2  on the reflecting surface  103   a  of the rotary polygon mirror  103 . The cylindrical lens  102  has a function of preventing a point image formed on the photosensitive member in the above manner from being distorted due to surface tilt of the rotary polygon mirror  103 . The imaging lens  104  is made up of a spherical lens and toric lens. The imaging lens  104  has a function of preventing distortion of a point image on the photosensitive member, similar to the cylindrical lens  102 , and a correction function of scanning the point image on the photosensitive member in the main scanning direction at a constant speed. 
   The two laser beams P 1  and P 2  are respectively split by a detection mirror  106  at the end of the main scanning plane (X-Y plane), guided to a photosensor  107  on an opposite side to the main scanning plane, and converted into write start signals in a controller (not shown) to be transmitted to the multi-beam semiconductor laser  111 . The multi-beam semiconductor laser  111  receives the write start signals to start write modulation of the two laser beams P 1  and P 2 . 
   By adjusting the write modulation timings of the two laser beams P 1  and P 2 , the write start (write) position of an electrostatic latent image formed on the photosensitive member on the rotary drum  105  is controlled. 
   The cylindrical lens  102 , rotary polygon mirror  103 , imaging lens  104 , and the like are mounted on the bottom wall of an optical box  108 . After the respective optical components are mounted in the optical box  108 , the upper opening of the optical box  108  is closed with a lid (not shown). 
   As described above, the multi-beam semiconductor laser  111  simultaneously emits the laser beams P 1  and P 2 . The multi-beam semiconductor laser  111  is integrated via a laser holder  111   a  with a lens barrel  112   a  incorporating the collimator lens  112 , and the integral unit is mounted on a sidewall  108   a  of the optical box  108  together with a laser driving circuit board  113 . 
   In mounting the multi-beam light source unit  101 , the laser holder  111   a  holding the multi-beam semiconductor laser  111  is inserted into an opening  108   b  formed in the sidewall  108   a  of the optical box  108 . The laser holder  111   a  is fitted in the lens barrel  112   a  of the collimator lens  112 , the focal point and optical axis of the collimator lens  112  are adjusted, and the lens barrel  112   a  is adhered to the laser holder  111   a . As shown in  FIG. 2A , the laser holder  111   a  is rotated through a predetermined angle θ to adjust a straight line connecting the emission points of the laser beams P 1  and P 2 , i.e., the inclination angle of a laser array N. More specifically, as shown in  FIG. 2B , the beam interval between the laser beams P 1  and P 2  emitted by the multi-beam semiconductor laser  111  is adjusted to make a pitch S between imaging points A 1  and A 2  on the rotary drum  105  in the main scanning direction, and a pitch, i.e., line interval T in the subscanning direction coincide with design values. After this adjustment, the laser holder  111   a  is fixed to the sidewall  108   a  of the optical box  108  with a screw or the like. 
   In the prior art, however, when the multi-beam light source unit is to be fixed to the optical box, the whole multi-beam light source unit is rotated through the predetermined angle θ together with the laser driving circuit board, thereby obtaining the line interval T. To realize this, a space enough to rotate the large-area laser driving circuit board must be prepared outside the optical box, which interferes with downsizing of the whole apparatus. 
   Further, an error allowable value for adjustment of the line interval T is as strict as several μm or less. If the angular adjustment range in assembling the multi-beam light source unit to the optical box is wide, high-precision adjustment is difficult to complete within a short time. The multi-beam light source unit cannot be assembled with high working efficiency and high reliability. 
   SUMMARY OF THE INVENTION 
   The present invention has been made to eliminate the conventional drawbacks, and has as its object to provide a multi-beam scanning apparatus which can be downsized and allows adjusting of the beam interval within a short time with high precision. 
   To achieve the above object, according to the present invention, there is provided a multi-beam scanning apparatus comprising a multi-beam light source unit having a multi-beam semiconductor laser and a laser holder holding the multi-beam semiconductor laser, scanning imaging means for scanning a plurality of laser beams emitted by the multi-beam semiconductor laser to form an image on a surface to be scanned, and a housing supporting the scanning imaging means and the multi-beam light source unit. The multi-beam semiconductor laser is fixed to the laser holder with an inclination at or near a predetermined rotational angle for adjusting a beam interval between the plurality of laser beams. 
   In the multi-beam scanning apparatus, the multi-beam semiconductor laser preferably has a laser array fixed with an inclination with respect to a reference surface of the laser holder. 
   The multi-beam semiconductor laser preferably has a plurality of aligned emission points. 
   The multi-beam semiconductor laser preferably has a plurality of two-dimensionally arrayed emission points. 
   The laser holder is preferably integrated with a lens barrel holding a collimator lens. 
   In mounting the laser holder in the housing after the multi-beam semiconductor laser is fixed to the laser holder, the whole multi-beam light source unit is inclined (rotated) to adjust the beam interval. In this arrangement, however, angular adjustment is difficult to perform precisely, and takes a long time. In addition, an extra space is required to incline the large-area laser driving circuit board mounted on the multi-beam light source unit. To avoid this, in a unit assembly step of assembling the multi-beam semiconductor laser to the laser holder, the multi-beam semiconductor laser is rotated (inclined) through an angle necessary for adjusting the beam interval or an angle approximate to the necessary angle. In this state, the multi-beam semiconductor laser is fixed to the laser holder into a unit. 
   In mounting the multi-beam light source unit in the housing, the whole multi-beam light source unit is rotated through a small angle in order to finally adjust a small error arising from the component precision and the like. 
   Since final angular adjustment in mounting the multi-beam light source unit in the housing is done within a small angular range, the angle can be quickly adjusted with high precision. 
   Since the large-area laser driving circuit board need not be greatly inclined, the whole apparatus can be downsized. 
   The present invention has been made to eliminate the conventional drawbacks, and has as its object to provide a low-cost, high-performance multi-beam scanning apparatus which can easily ensure the installation positional precision of the multi-beam light source unit in terms of the structure, can improve the adjustment precision of the multi-beam line interval, can efficiently mount the multi-beam light source unit, and can maintain high image quality without generating any error upon mounting. 
   To achieve the above object, according to the present invention, there is provided a multi-beam scanning apparatus comprising a multi-beam light source unit having a multi-beam semiconductor laser and a laser holder holding the multi-beam semiconductor, scanning imaging means for scanning a plurality of laser beams emitted by the multi-beam semiconductor laser to form an image on a surface to be scanned, a housing supporting the scanning imaging means and the multi-beam light source unit, and fixing means for fixing the multi-beam light source unit to the housing after the rotational angle of the multi-beam light source unit is adjusted, the fixing means having a plurality of fixing portions. The center of the rotation of the multi-beam light source unit and a plurality of emission points of the multi-beam semiconductor laser are located on a straight line connecting two of the plurality of fixing portions or a planar region defined by straight lines connecting all the plurality of fixing portions. 
   The fixing means preferably has at least three fixing portions. 
   The fixing means preferably has a fixing portion fastened by a screw. 
   The fixing means preferably has a fixing portion adhered with an adhesive. 
   The multi-beam semiconductor laser preferably has a plurality of aligned emission points. 
   The multi-beam semiconductor laser preferably has a plurality of two-dimensionally arrayed emission points. 
   The laser holder is preferably integrated with a lens barrel holding a collimator lens. 
   In mounting the multi-beam semiconductor laser in the housing, the whole multi-beam light source unit is rotated to adjust the line interval. Thereafter, screws or the like are tightened to fix the multi-beam light source unit to the housing. 
   A plurality of fixing portions by screws or the like are set. The emission points of laser beams and the center of rotation of the multi-beam light source unit are located on a straight line connecting two of the fixing portions or a planar region defined by straight lines connecting all the fixing portions. Accordingly, the multi-beam light source unit can be very firmly, stably fixed to the housing. 
   Hence, no rotational shift occurs in the multi-beam light source unit due to shock or the like after the multi-beam light source unit is fixed to the housing. 
   Trouble such as a shift of the rotational angle of the multi-beam light source unit due to free running during screw tightening operation does not occur. Thus, the assembly efficiency and precision can be improved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic plan view showing a conventional multi-beam scanning apparatus; 
       FIGS. 2A and 2B  are views for explaining line interval adjustment in the multi-beam scanning apparatus in  FIG. 1 ; 
       FIG. 3  is a schematic plan view showing a multi-beam scanning apparatus according to the present invention; 
       FIG. 4  is an enlarged perspective view showing the first embodiment of a multi-beam light source unit in the multi-beam semiconductor laser of the apparatus in  FIG. 3 ; 
       FIGS. 5A and 5B  are views for explaining line interval adjustment; 
       FIG. 6  is a perspective view showing a laser holder temporarily fixed to an optical box; 
       FIG. 7  is a view for explaining final line interval adjustment; 
       FIG. 8  is a schematic view showing the second embodiment of the multi-beam light source unit; 
       FIG. 9  is a schematic view showing a multi-beam semiconductor laser in  FIG. 8  together with a laser driving circuit board; 
       FIG. 10  is a schematic view showing the third embodiment of the multi-beam light source unit; 
       FIGS. 11A and 11B  are views showing the fourth embodiment of the multi-beam light source unit, in which  FIG. 11A  is a plan view showing the layout of three fixing portions, and  FIG. 11B  is a sectional view showing the fixing portions; and 
       FIG. 12  is a schematic view showing the fifth embodiment of the multi-beam light source unit. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of the present invention will be described below with reference to the accompanying drawings. 
     FIG. 3  shows a multi-beam scanning apparatus according to the present invention. In this multi-beam scanning apparatus, a multi-beam semiconductor laser  11  serving as a light source for a multi-beam light source unit  1  emits two laser beams P 1  and P 2 . The laser beams P 1  and P 2  are collimated by a collimator lens  12 , irradiate a reflecting surface  3   a  of a rotary polygon mirror  3  via a cylindrical lens  2 , and form an image on a photosensitive member on a rotary drum  5  serving as a surface to be scanned via an imaging lens  4  which constitutes a scanning imaging means together with the rotary polygon mirror  3 . 
   The two laser beams P 1  and P 2  are incident on the reflecting surface  3   a  of the rotary polygon mirror  3 , scanned in the main scanning direction, and form an electrostatic latent image on the photosensitive member along with main scanning by rotation of the rotary polygon mirror  3  and subscanning by rotation of the rotary drum  5 . 
   The cylindrical lens  2  linearly focuses the laser beams P 1  and P 2  on the reflecting surface  3   a  of the rotary polygon mirror  3 . The cylindrical lens  2  has a function of preventing a point image formed on the photosensitive member in the above manner from being distorted due to surface tilt of the rotary polygon mirror  3 . The imaging lens  4  is made up of a spherical lens and toric lens. The imaging lens  4  has a function of preventing distortion of a point image on the photosensitive member, similar to the cylindrical lens  2 , and a correction function of scanning the point image on the photosensitive member in the main scanning direction at a constant speed. 
   The two laser beams P 1  and P 2  are respectively split by a detection mirror  6  at the end of the main scanning plane (X-Y plane), guided to a photosensor  7  on an opposite side to the main scanning plane, and converted into write start signals in a controller (not shown) to be transmitted to the multi-beam semiconductor laser  11 . The multi-beam semiconductor laser  11  receives the write start signals to start write modulation of the two laser beams P 1  and P 2 . 
   By adjusting the write modulation timings of the two laser beams P 1  and P 2 , the write start (write) position of an electrostatic latent image formed on the photosensitive member on the rotary drum  5  is controlled. 
   The cylindrical lens  2 , rotary polygon mirror  3 , imaging lens  4 , and the like are mounted on the bottom wall of an optical box  8  serving as a housing. After the respective optical components are mounted in the optical box  8 , the upper opening of the optical box  8  is closed with a lid (not shown). 
   As described above, the multi-beam semiconductor laser  11  simultaneously emits the laser beams P 1  and P 2 . The multi-beam semiconductor laser  11  is integrated via a laser holder  11   a  with a lens barrel  12   a  incorporating the collimator lens  12 , and the integral unit is mounted on a sidewall  8   a  of the optical box  8  together with a laser driving circuit board  13 . 
   In mounting the multi-beam light source unit  1 , the laser holder  11   a  holding the multi-beam semiconductor laser  11  is inserted into an opening  8   b  formed in the sidewall  8   a  of the optical box  8 . The laser holder  11   a  is fitted in the lens barrel  12   a  of the collimator lens  12 , three-dimensional adjustment such as focus adjustment and optical axis adjustment of the collimator lens  12  is done, and the lens barrel  12   a  is adhered to the laser holder  11   a.    
   As shown in  FIG. 4 , the multi-beam semiconductor laser  11  comprises a laser chip  22  fixed to a pedestal  21   a  integrated with a stem  21 , a photodiode  23  for monitoring the emission amounts of laser beams P 1  and P 2  emitted from two emission points  22   a  and  22   b  on the laser chip  22 , and an enerigization terminal  24  for energizing the laser chip  22  and the like. The laser chip  22  and the like are covered with a cap  25 . 
   In a unit assembly step of mounting the multi-beam semiconductor laser  11  in the laser holder  11   a , the multi-beam semiconductor laser  11  is rotated through a predetermined rotational angle θ or angle approximate to the angle θ with respect to a reference surface V of the laser holder  11   a , as shown in  FIG. 5A , thereby adjusting in advance the inclination angle of a straight line, i.e., laser array N connecting the emission points of the laser beams P 1  and P 2 . More specifically, the beam interval between the laser beams P 1  and P 2  emitted by the multi-beam semiconductor laser  11  is adjusted to make a pitch S between imaging points A 1  and A 2  on the rotary drum  5  in the main scanning direction, and a pitch, i.e., line interval T in the subscanning direction coincide with design values in advance (see  FIG. 5B ). After this adjustment, the multi-beam semiconductor laser  11  is fixed to the laser holder  11   a  to obtain a unit. 
   After the lens barrel  12   a  of the collimator lens  12  is adhered to the laser holder  11   a , as described above, the laser holder  11   a  is temporarily fixed to the sidewall  8   a  of the optical box  8  with screws  11   b  fitted in slots of the laser holder  11   a , as shown in  FIG. 6 . While emitting the laser beams P 1  and P 2 , the laser holder  11   a  is rotated through a small angle Δθ for final adjustment of the line interval T in order to compensate for the precision of each apparatus component and an error at the fit portion of the multi-beam semiconductor laser  11  itself. In practice, as indicated by the broken line in  FIG. 7 , this adjustment is done after the laser driving circuit board  13  is mounted on the laser holder  11   a . Upon the final adjustment, the screws  11   b  are tightened to fix the laser holder  11   a  to the optical box  8 . 
   The line interval T on the rotary drum must be adjusted with submicron-order precision. In the first embodiment, when the multi-beam semiconductor laser is mounted in the laser holder, the laser array N is roughly adjusted to or near to the predetermined inclination angle θ. When the laser holder is mounted in the optical box together with the laser driving circuit board, the angle is finally slightly adjusted to correct an assembly error and the like. Therefore, the final line interval adjustment precision is very high, and the adjustment time can be greatly shortened compared to the conventional wide-range angular adjustment on the optical box. In addition, the large-area laser driving circuit board need not be rotated outside the optical box, and the apparatus can be downsized. 
   As a result, this embodiment can realize a small-size, high-precision multi-beam scanning apparatus with low assembly cost. 
   Note that this embodiment uses the laser chip with two emission points. However, the number of emission points, i.e., laser beams can be arbitrarily changed. The assembly procedure of the laser driving circuit board, lens barrel, collimator lens, and the like can also be arbitrarily changed. The laser holder can be fixed to the optical box not only with a fastening means such as a screw, but also by another method such as adhesion. 
     FIG. 8  shows the second embodiment of the multi-beam light source unit. This multi-beam light source unit uses a disk-like laser holder  31   a  instead of the rectangular laser holder  11   a  having a reference surface V as an end face. In this case, a reference surface U with a rotational angle θ in mounting a multi-beam semiconductor laser  31  in the laser holder  31   a  is defined at a notched portion  31   b  at the circumferential portion of the laser holder  31   a.    
   As shown in  FIG. 9 , a laser driving circuit board  33  is mounted on the laser holder  31   a  such that an upper end face  33   a  serves as an attachment reference for an optical box (not shown). 
   The edge-emission-type multi-beam semiconductor lasers  11  and  31  on each of which a plurality of emission points are aligned may be replaced with a multi-beam semiconductor laser  41  having a surface-emission-type laser chip  42  on which a plurality of emission points  42   a  to  42   d  are two-dimensionally arrayed, as shown in  FIG. 10 . This multi-beam semiconductor laser  41  can advantageously reduce optical aberration because all the emission points can be made close to the optical axis of the collimator lens. A positioning hole  41   b  is formed in a disk-like laser holder  41   a  as a positioning reference used to adjust the rotational angle θ for adjusting beam intervals T 1  to T 3 . 
   The surface-emission-type laser can increase the degree of freedom for the positions of the emission points to facilitate distribution of the mounting tolerance. 
   As described above, in the multi-beam scanning apparatus of the present invention, the two laser beams P 1  and P 2  emitted by the multi-beam semiconductor laser  11  are scanned by the rotary polygon mirror inside the optical box  8 , and form an image on the photosensitive member on the rotary drum via the imaging lens. To adjust the line interval T and the like on the photosensitive member, when the multi-beam semiconductor laser  11  is to be mounted in the laser holder  11   a , the multi-beam semiconductor laser  11  is rotated to incline the laser array N at the predetermined inclination angle θ. Then, the multi-beam semiconductor laser  11  is fixed to the laser holder  11   a . In mounting the multi-beam light source unit  1  in the optical box  8 , the whole multi-beam light source unit  1  is only slightly inclined to compensate for the component precision and the like. 
   With this arrangement, the present invention exhibits the following effects. 
   The beam interval between a plurality of laser beams emitted by the multi-beam semiconductor laser can be adjusted within a short time with high precision. Accordingly, the apparatus can attain high resolution, the assembly cost can be greatly reduced, and the whole apparatus can be downsized. 
   The fourth embodiment of the present invention will be described below.  FIGS. 11A and 11B  are schematic views showing the fourth embodiment of the multi-beam light source unit. The whole arrangement of the multi-beam scanning apparatus is the same as that shown in  FIG. 3 , and a description thereof will be omitted. The multi-beam light source unit will be explained. 
   As shown in  FIGS. 11A and 11B , after a lens barrel  12   a  of a collimator lens  12  is adhered to a laser holder  11   a , the laser holder  11   a  is temporarily fixed to a sidewall  8   a  of an optical box  8  with screws  14  (see  FIGS. 11A and 11B ) serving as fixing means fitted in holes in the laser holder  11   a . While emitting laser beams P 1  and P 2 , the laser holder  11   a  is rotated to adjust the inclination angle θ in order to adjust the line interval T, as shown in  FIG. 5A . 
   This adjustment is to adjust the beam interval between the two laser beams P 1  and P 2  emitted by the multi-beam semiconductor laser  11 , i.e., to make the pitch S between imaging points A 1  and A 2  on a rotary drum  5  in the main scanning direction, and a pitch, i.e., line interval T in the subscanning direction coincide with design values. 
   After the angular adjustment, the screws  14  are tightened to fix the laser holder  11   a  to the optical box  8 . 
   In this adjustment, the laser holder  11   a  is rotated while the spot positions, i.e., imaging points A 1  and A 2  of the two laser beams P 1  and P 2  that displace in submicron order are monitored with a CCD camera or the like. 
   As shown in  FIG. 11A , the three screws  14  fasten the laser holder  11   a  to the sidewall  8   a  of the optical box  8 . Fixing portions  14   a  to  14   c  surround the emission points of the laser beams P 1  and P 2 . That is, the three screws  14  are laid out to locate the emission points of the laser beams P 1  and P 2  on straight lines L 1  to L 3  connecting the fixing portions  14   a  to  14   c  or within a planar region N (shadow portion) defined by the straight line L 1  to L 3 . 
   The laser holder  11   a  has a cylindrical boss  11   c . As shown in  FIG. 11B , the boss  11   c  is fitted in a cylindrical opening  8   b  in the sidewall  8   a  of the optical box  8  so as to rotate the laser holder  11   a . The center O of rotation is also positioned on the straight lines L 1  to L 3  connecting the fixing portions  14   a  to  14   c  or within the planar region N defined by the straight lines L 1  to L 3 . 
   With this layout, the emission points of the two laser beams P 1  and P 2  always fall within the range defined by lengths obtained by converting the intervals between the fixing portions  14   a  to  14   c  into main scanning and subscanning components. The wide range including the center O of rotation can be firmly fixed to effectively prevent vertical and horizontal tilt of the multi-beam light source unit  1 . 
   Particularly, when the screws  14  are used as fixing means, the laser holder  11   a  and the sidewall  8   a  of the optical box  8  are pressed against each other via a fastening surface M. A clearance K is set as an adjustment margin for angular adjustment rotation. The laser holder  11   a  is moved within this range. 
   The fastening surface M at the fixing portions  14   a  to  14   c  of the screws  14  provides the highest fastening reliability and high stability because the laser holder  11   a  and sidewall  8   a  contact each other at fastening pressure generation positions. Note that if the fastening surface M does not completely coincide with the positions of the screws  14 , the same effects can be obtained so long as they are close to each other. The position and shape of the fastening surface M and the number of fastening surfaces M need not be limited. 
   The fourth embodiment adopts the screws as fixing means, but may adopt an adhesion means with an ultraviolet-curing adhesive or the like. The number of emission points is not limited and may be arbitrarily set to two or more. 
   The collimator lens is adhered to the lens barrel preferably with the ultraviolet-curing adhesive, but may be adhered with another adhesive. 
   According to the fourth embodiment, the multi-beam light source unit is fastened to the sidewall of the optical box with screws at three or more fixing portions. The center of rotation of the multi-beam light source unit and the emission points of respective laser beams locate on straight lines connecting the fixing portions or within the planar region defined by straight lines connecting all the fixing portions. Thus, the multi-beam light source unit can be stably, firmly mounted in the optical box. 
   The fourth embodiment can realize a low-cost, high-performance multi-beam scanning apparatus capable of effectively avoiding troubles such as a rotational shift of the multi-beam light source unit upon high-precision line interval adjustment, and free running during fastening upon adjustment. 
     FIG. 12  shows the fifth embodiment of the multi-beam light source unit. When the position of the emission point of a multi-beam semiconductor laser  11  is greatly offset from the center O of rotation of a laser holder  11   a  due to low component precision, the multi-beam semiconductor laser  11  is adjusted again in the laser holder  11   a . To realize this, an adjustment member  15  for adjusting the relative position is used and fastened to the laser holder  11   a  with screws  16 . 
   The adjustment member  15  is relatively moved together with the multi-beam semiconductor laser  11  with respect to the laser holder  11   a  to adjust a laser array connecting laser beams P 1  and P 2  so as to pass through the center O of rotation. Then, the adjustment member  15  is fastened to the laser holder  11   a  with the screws  16 . 
   Even if the positional precision of emission points varies in the component, the adjustment member  15  can adjust the positions of the emission points to locate them on straight lines L 1  to L 3  connecting fixing portions  14   a  to  14   c  or within the planar region N defined by all the straight lines L 1  to L 3 , as shown in  FIG. 11A . 
   The package shape of the multi-beam semiconductor laser can advantageously be selected from a wide range. 
   The edge-emission-type multi-beam semiconductor laser  11  on which a plurality of emission points are aligned may be replaced with a multi-beam semiconductor laser  41  having a surface-emission-type laser chip  42  on which a plurality of emission points  42   a  to  42   d  are two-dimensionally arrayed, as shown in  FIG. 10 . This multi-beam semiconductor laser  41  can advantageously reduce optical aberration because all the emission points can be made close to the optical axis of the collimator lens. A positioning hole  41   b  is formed in a disk-like laser holder  41   a  as a positioning reference used to adjust the inclination angle θ for adjusting line intervals T 1  to T 3 . 
   The surface-emission-type laser can increase the degree of freedom for the positions of the emission points to facilitate distribution of the mounting tolerance. 
   As described above, in the multi-beam scanning apparatus of the present invention, the two laser beams P 1  and P 2  emitted by the multi-beam semiconductor laser are scanned by the rotary polygon mirror inside the optical box  8 , and form an image on the photosensitive member on the rotary drum via the imaging lens. To adjust the line interval and the like on the photosensitive member, the laser holder  11   a  is fixed to the sidewall  8   a  of the optical box  8  after rotation through a predetermined angle. The fixing portions  14   a  to  14   c  are set to locate the emission points of the laser beams P 1  and P 2  and the center O of rotation on straight lines connecting the fixing portions  14   a  to  14   c  by the screws  14  or within the planar region N defined by these lines. The laser holder  11   a  is firmly, stably mounted with high positional precision. 
   With this arrangement, the present invention exhibits the following effects. 
   The line interval between a plurality of laser beams emitted by the multi-beam semiconductor laser can be adjusted with high precision, and the laser holder can be firmly, stably mounted. 
   The present invention can realize a low-cost, high-performance multi-beam scanning apparatus free from any multi-beam line interval error.