Abstract:
A light-source device of a multi-beam scanning apparatus including a plurality of semiconductor lasers, collimator lenses provided for the semiconductor lasers and a holder member integrally holding the semiconductor lasers and the collimator lenses. The semiconductor lasers are pressed into the holder member, and the collimator lenses are bonded to the holder member with a part of each edge portion of the collimator lenses adjusted in position relative to said holder member. Positions of press-in portions of the holder member for the semiconductor lasers are relatively deviated and formed in such a manner that adhesive layers for bonding the holder member and the collimator lenses have a same thickness.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a light-source device of a multi-beam scanning apparatus. 
     2. Discussion of the Background 
     It is well known that in an image forming device, such as a printer or a digital copying machine, a scanning apparatus scans a photosensitive surface with light beams of a semiconductor laser for forming an image thereupon. 
     As an example of the above scanning apparatus, there is known a multi-beam scanning apparatus in which a plurality of light emitting devices are used. In the multi-beam scanning apparatus, a plurality of beams emitted by the plurality of light emitting devices are guided to a scanned surface via a common optical system, and converged in a sub-scanning direction as a plurality of mutually separated spots. The plurality of beams are simultaneously deflected by a deflector included in the optical system, and the scanned surface is scanned by the plurality of beams formed as the spots. 
     FIG. 4A illustrates an example of a multi-beam scanning apparatus, in which two beams are simultaneously radiated from a light-source device  10 . These two beams form a parallel light flux, and are converged in a sub-scanning corresponding direction by a cylindrical lens  12  to form longitudinal linear images in a main scanning corresponding direction in the vicinity of a deflecting/reflecting surface of a rotating polygonal mirror  14  as a deflector. The sub-scanning directions is a direction corresponding to a sub-scanning direction on an optical path leading to a scanned surface from a light source, and the main scanning direction is a direction corresponding to a main scanning direction on the optical path to the scanned surface from the light source. Beams reflected in the deflecting/reflecting surface of the rotating polygonal mirror  14  are deflected at an equiangular velocity with uniform rotation of the rotating polygonal mirror  14 . The beams are then incident upon fθ mirror  16  having an image forming function, reflected by the fθ mirror  16 , and turned by a mirror  18 . Then, the beams are transmitted through a longitudinal toroidal lens  20  having a barrel-shaped toroidal surface, and have their optical paths folded by a mirror  22 . Next, the beams are converged in spots on a photosensitive surface of a photoconductor unit  24  as the scanned surface via the fθ mirror  16  and longitudinal toroidal lens  20 . In this case, the fθ mirror  16  mainly converges each deflected beam in the main scanning direction. Moreover, the longitudinal toroidal lens  20  cooperates with the fθ mirror  16  to converge each beam in the sub-scanning direction. 
     In the light-source device  10 , as illustrated in FIG. 4B, beams radiated from two semiconductor lasers  101 ,  102  are formed into a parallel light flux by coupling lenses  103 ,  104  as collimator lenses supported by a holder  60  (see FIG.  5 ), described later, and synthesized by a beam synthesizer  105 . 
     The beam synthesizer  105  is provided for combining optical axes of the parallel flux from the coupling lenses  103 ,  104 , and the beam spots are overlapped with one another on the scanned surface by arranging the semiconductor lasers  101 ,  102  on optical axes of the coupling lenses  103 ,  104 . 
     As illustrated in FIG. 4B, the beam synthesizer  105  is integrally constructed by a ½ wavelength plate  1051  and a prism  1052 . The prism  1052  includes a polarizing/separating film  1053 . The polarizing/separating film  1053  transmits P polarized light, and reflects S polarized light. 
     The beam synthesizer  105  is supported by the holder  60  constructed as illustrated in FIG. 5, in which the holder  60  includes a plate base  61  and a shelf-like portion  62 . 
     The plate base  61  has screw through holes b 1  to b 4  (b 4  not shown) formed in four comers, and is fixed to a casing (not shown) via screws (not shown) passed through the screw through holes b 1  to b 4 . 
     The shelf-like portion  62  includes a member formed integral with the flat plate base  61  and a overhang piece and therefore has an angled side face. The member formed integral with the base plate  61  is formed with semiconductor laser attachment holes  63 ,  64  leading to the plate base  61 . 
     As shown in FIG. 5A, a portion  621  for holding the coupling lenses  103 ,  104  and a portion  622  for holding the beam synthesizer  105  are formed on a top surface of the overhang piece of the shelf-like portion  62 , which is parallel with the optical axes of the semiconductor lasers  101 ,  102  pressed in the attachment holes  63 ,  64  (refer to FIG.  5 B). 
     The coupling lenses  103 ,  104  are made integral with the shelf-like portion  62  by an adhesive applied to bonding areas  6211 ,  6212  of the holding portion  621 . Moreover, in FIG. 5A, numeral  6221  denotes an area for bonding the beam synthesizer  105 , and as illustrated in FIG. 5B, the beam synthesizer  105  is bonded and fixed in the bonding area  6221 . 
     The holder  60  is provided with a casing (not shown) attached and fastened via the screw through holes b 1  to b 4 . Also provided is a ¼ wavelength plate for circularly polarizing each synthesized beam and an aperture for shaping the synthesized beam which are arranged in the casing on an optical axis between the beam synthesizer  105  and the cylindrical lens  12  (FIG.  4 A). 
     In the light-source device  10  constructed as described above, when the semiconductor lasers  101 ,  102  and the beam synthesizer  105  are assembled into the light-source device  10 , the semiconductor lasers  101 ,  102  are first pressed into the attachment holes  63 ,  64 . Then, the beam synthesizer  105  is fixed in the bonding area  6221 , after its optical axis position relative to the semiconductor lasers  101 ,  102  is adjusted, by a photo-setting adhesive, e.g., an adhesive using a ultraviolet setting resin. 
     Subsequently, after a beam shaping aperture AP (FIG. 5B) is inserted and fixed into a retaining groove  623  (FIG.  5 A), the coupling lenses  103 ,  104  are adjusted in position relative to the optical axes of the semiconductor lasers  101 ,  102  in such a manner that two spots formed by the beams of the semiconductor lasers  101 ,  102  are separated at a desired distance on the scanned surface. The coupling lenses  103 ,  104  are then fixed in the bonding areas  6211 ,  6212  by the adhesive using the ultraviolet setting resin. 
     The light-source device  10  is rotatable centering on the optical axes of the coupling lenses  103 ,  104 . By rotating the light-source device  10 , the separated amount of the spots on the scanned surface can be adjusted in the sub-scanning direction to change a density of the spots, i.e., a writing density, on the scanned surface. For this purpose, as shown in FIG. 4A, an angle controller  26  is provided to which a writing density switch signal is transmitted. In addition, the entire light-source device  10  can be rotated to obtain a desired writing density by operating a motor  28  in response to the signal. 
     In FIG. 4B, a writing signal for changing the writing density is transmitted to a semiconductor laser drive section  32  (illustrated as LD drive section in the drawing) via a writing controller  30 . The semiconductor laser drive section  32  modulates and controls light of the semiconductor laser  101  in response to an odd line writing signal, and modulates and controls light of the semiconductor laser  102  in response to an even line writing signal. The construction of the light-source device  10  is described in detail in Japanese Patent Application No. 256352/1997 filed by the present applicant. 
     In the above light-source device  10 , a center of the attachment holes  63 ,  64  of the semiconductor lasers  101 ,  102  and a center of the bonding portions of the coupling lens  103 ,  104  are positioned on a straight line. On the other hand, for changing the writing density on the scanned surface by separating the beams in the main scanning direction and sub-scanning direction on the scanned surface, the beams need to be deviated slightly from the optical axes of the semiconductor lasers  101 ,  102 . 
     However, in the above-described light-source device  10 , as illustrated in FIG. 6, center positions S 1 , S 2  of the semiconductor lasers  101 ,  102  are fixed by positions of the attachment holes  63 ,  64 . Therefore, for deviating the optical axes of the semiconductor lasers  101 ,  102 , center positions P 1 , P 2  of the coupling lenses  103 ,  104  are needed to be deviated from the centers of the bonding areas  6211 ,  6212 . 
     In the above light-source device  10 , the centers of the coupling lenses  103 ,  104  are deviated from the center of the bonding areas  6211 ,  6212 , such that the two beam spots are separated by 2 mm in the main scanning direction, and 42.3 μm in the sub-scanning direction on the scanned surface. In this case, a deviation amount of an optical axis is set to ±4.5 mrad (FIG. 6B) in the main scanning direction, and ±0.35 mrad in the sub-scanning direction, after the beams emerge from the coupling lenses  103 ,  104 . 
     Accordingly, the centers of the coupling lenses  103 ,  104  are deviated from the center of the bonding areas  6211 ,  6212  for the coupling lens  103 ,  104  by ±68.2 μm in the main scanning direction, and ±5.3 μm in the sub-scanning direction. In FIGS. 6A and 6B, since the deviation in the sub-scanning direction is smaller than the deviation in the main scanning direction, illustration for the deviation of the sub-scanning direction is omitted. 
     Accordingly, if the thickness of an adhesive layer for the bonding areas is set, for example, to 150 μm when the deviation amount of optical axis is zero, thicknesses d 1 , d 2  of adhesive layers A 1 , A 2  for the coupling lens  103 ,  104  (FIG. 6A) become as follows: 
     d 1 =150−68.2=81.8 μm 
     d 2 =150+68.2=218.2 μm 
     In this manner, the adhesive layers A 1 , A 2  for the coupling lenses  103 ,  104  are different in thickness by about 2.7 times or a width of 136.4 μm. 
     In the light-source device  10  constructed as above, when the coupling lenses  103 ,  104  are mounted to the light-source device  10 , after the adhesive of ultraviolet setting resin is dropped in the bonding areas  6211 ,  6212  for the coupling lenses  103 ,  104 , the coupling lenses  103 ,  104  are adjusted in position by monitoring collimating properties and light axis values. When the collimating properties and light axis values reach desired values, ultraviolet rays are irradiated to set the adhesive to bond the coupling lens  103 ,  104  in the bonding areas  6211 ,  6212 . However, since the adhesive contracts at the time of ultraviolet radiation, the position of the coupling lenses  103 ,  104  are deviated from the adjusted positions and thereby the collimating properties and light axis values are deviated from the desired values. 
     Therefore, the desired values for the collimating properties and light axis values are adjusted to target values beforehand in consideration of the deviation amount which will be caused by contracting of the adhesive. 
     However, when the bonding areas  6211 ,  6212  for the coupling lenses  103 ,  104  differ in adhesive thickness, the adhesive contraction amount differs between the bonding areas  6211 ,  6212 , causing a problem that the deviation amount (offset amount) that has been considered when the desired values for the collimating properties and light axis are adjusted changes. 
     Additionally, when there is a difference of 136.4 μm in thickness between the adhesive layers A 1 , A 2  for the coupling lenses  103 ,  104 , the thicker adhesive layer necessarily has a larger change in the contraction amount. As a result, this causes a large change in the collimating properties and light axis values of the coupling lens  103 ,  104  at the time of ultraviolet radiation. 
     Furthermore, when the adhesive layers for the coupling lens  103 ,  104  are different in thickness, the changes in the contraction amount of the adhesive layers due to changes of environmental temperature or other environmental conditions differ from each other. Therefore, the changes in the collimating properties and light axis value of the coupling lenses  103 ,  104  differ from each other between the coupling lens  103  and  104 . 
     Particularly, when the adhesive layers have a thickness difference of about 2.7 times, as described above, the thicker adhesive layer has a larger change in the contraction amount. As a result, the change in the collimating properties and light axis value of the coupling lens bonded by the thicker adhesive layer becomes large. When the adhesive layers have the same thickness, although the light axis of each of the coupling lens  103 ,  104  is deviated by changes in the environmental conditions, the light axes of the coupling lens  103 ,  104  are deviated by the same amount, because the adhesive for each of the coupling lenses  103 ,  104  contracts by the same amount. Therefore, the relative position of the beams as an important multi-beam property is not deviated. On the other hand, when the adhesive layers differ in thickness, the deviation amounts of the collimating properties and light axis of the coupling  103  and  104  due to changes in the environmental conditions differ. Therefore, the relative position of the beams itself is deviated, which adversely affects the image writing density. 
     The adverse effect on the image writing density results in a change in the image gradation, color tone, or character sharpness according to the changes in the environmental conditions. 
     Moreover, when the aperture AP (FIG. 5B) is engaged into the retaining groove  623  (FIG. 5A) of the holder  60 , and the ¼ wavelength plate is successively mounted on the casing (not shown) integral with the holder  60 , the assembly operation takes a long time because these members are very small components and therefore are inferior in assembly properties. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to solve the above-described and other problems with background devices. 
     Another object of the present invention is to provide a light-source device of a multi-beam scanning apparatus in which, when an adhesive for bonding by ultraviolet radiation is used for fixing coupling lenses to a holder, collimating properties and light axis values of the coupling lenses can be prevented from being deviated from desired values at the time of the ultraviolet radiation or changes in environmental conditions, so that stabilized position adjustment can be performed. 
     Yet another object of the present invention is to provide a light-source device of a multi-beam scanning apparatus in which beam pitch changes due to changes in environmental conditions can be prevented to prevent images from being deteriorated by the changes in the environmental conditions. 
     Still another object of the present invention is to provide a light-source device in which assembly properties of small components, such as an aperture and a ¼ wavelength plate, are improved and the time necessary for assembly is shortened. 
     These and other objects are achieved by providing a light-source device of a multi-beam scanning apparatus which includes a plurality of semiconductor lasers, collimator lenses provided for the semiconductor lasers and a holder member integrally holding the semiconductor lasers and the collimator lenses. The semiconductor lasers are pressed into the holder member, and the collimator lenses are bonded to the holder member with a part of each edge portion of the collimator lenses adjusted in position relative to the holder member. Positions of press-in portions of the holder member for the semiconductor lasers are relatively deviated and formed in such a manner that adhesive layers for bonding the holder member and the collimator lenses have a same thickness. 
     In the light-source device, a beam synthesizing device may be integrally fixed to the holder member and an aperture for shaping each beam of the semiconductor lasers in common may be integrally bonded to the beam synthesizing device. 
     Further, a ¼ wavelength plate to convert a polarized state of each beam of the semiconductor lasers from linear polarization to circular polarization may be bonded to the beam synthesizing device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description thereof when considered in conjunction with accompanying drawings, wherein: 
     FIG. 1A is a plan view of a light-source device according to an embodiment of the present invention; 
     FIG. 1B is a sectional view of the light-source device as viewed in a direction shown by arrows B in FIG. 1A; 
     FIG. 2 is a perspective view of a holder member for use in the light-source device according to the embodiment of the present invention; 
     FIG. 3 is a sectional view of the holder member as viewed in a direction shown by arrows  3  in FIG. 2; 
     FIG. 4A is a schematic perspective view of a multi-beam scanning apparatus; 
     FIG. 4B is a perspective view of a beam synthesizer for use in the multi-beam scanning apparatus of FIG. 4A; 
     FIG. 5A is a perspective view of a holder member of a light-source device for use in the multi-beam scanning apparatus of FIG. 4; 
     FIG. 5B is a sectional view of the holder member as viewed in a direction shown by arrows B in FIG. 5A; 
     FIG. 6A is a front view illustrating a position adjustment state of collimator lenses in the holder member illustrated in FIGS. 5A and 5B; and 
     FIG. 6B is a sectional view as viewed in a direction shown by arrows B in FIG.  6 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described hereinafter in detail with reference to the drawings. In FIGS. 1A,  1 B and subsequent drawings, the same components as those shown in FIGS. 5A,  5 B and subsequent drawings are denoted with alike reference characters. 
     FIG. 1A is a front view of a holder (denoted by numeral  60 ′ for convenience) in a light-source device of a multi-beam scanning apparatus according to an embodiment of the present invention. The numeral  61 ′ corresponds to the plate base illustrated in FIGS. 5A and 5B, and the numeral  62 ′ corresponds to the shelf-like portion illustrated in FIGS. 5A and 5B. In the embodiment, however, the shelf-like portion  62 ′ is not provided with the aperture retaining groove  623  illustrated in FIG.  5 A. 
     The shelf-like portion  62 ′ is constructed by a member formed integral with the flat plate base  61 ′ and an overhang piece extending from the member. Therefore, the shelf-like portion  62 ′ has an angled side face. The member formed integrally with the plate base  61 ′ is formed with semiconductor laser attachment holes  63 ′,  64 ′ leading to the plate base  61 ′. 
     As illustrated in FIG. 1A, in the shelf-like portion  62 ′, a portion (denoted by the numeral  621  shown in FIGS. 5A and 5B for convenience) for holding the coupling lenses  103 ,  104  (FIG. 5B) is formed on a top surface of the overhang piece, which is parallel with the optical axes of the semiconductor lasers  101 ,  102  pressed in the attachment holes  63 ′,  64 ′ (FIG.  1 B). 
     In FIGS. 1A and 1B, the attachment holes  63 ′,  64 ′ for the semiconductor lasers  101 ,  102  are constructed in such a manner that, as illustrated in FIG. 1B, light axes of the semiconductor lasers  101 ,  102  are deviated by ±4.5 mrad in the main scanning direction relative to the centers of the bonding areas (corresponding to the numerals  6211 ,  6212  in FIG. 5A) for the coupling lenses  103 ,  104 . The light axes are similarly deviated in the sub-scanning direction, but deviation amounts are so slight that they are omitted from the drawing. 
     Specifically, in the embodiment, instead of deviating the center positions (denoted by P 1 , P 2  in FIG. 6A) of the coupling lenses  103 ,  104  from the center positions in the bonding areas  6211 ,  6212  as illustrated in FIG. 6B, the center positions S 1 ′,S 2 ′ of the attachment holes  63 ,  64  for the semiconductor lasers  101 ,  102  are deviated from the center positions of the bonding areas  6211 ,  6212  beforehand. 
     On the other hand, the shelf-like portion  62 ′ of the holder member  60 ′ is, as shown in FIG. 2, provided with a retaining concave portion (denoted by the numeral  622  used in FIGS. 5A and 5B for convenience) overhanging at a right angle with the member having the attachment holes  63 ′,  64 ′ for the semiconductor lasers  101 ,  102 . A bonding area  6221  for fixing a beam synthesizer  105 ′, described later, is provided on a top surface of the concave portion. 
     In the beam synthesizer  105 ′, as illustrated in FIG. 3, a ¼ wavelength plate  80  is integrally bonded on a common beam emerging side of a polarized light separating film  1053  in a prism  1052 . An aperture AP is bonded on an exterior surface of the ¼ wavelength plate  80 . 
     When the light-source device  10  constructed as above is assembled, first an adhesive of ultraviolet setting resin is dropped in the bonding areas  6211 ,  6212  for the coupling lenses  103 ,  104 . The bonding positions of the coupling lenses  103 ,  104  are then adjusted by monitoring the collimating properties and light axis values of the coupling lenses  103 ,  104 , and the adhesive is irradiated with ultraviolet rays to set when the parameters reach desired values. Thus, the coupling lenses  103 ,  104  are fixed to the bonding areas  6211 ,  6212 . 
     On the other hand, since the center positions of the attachment holes  63 ′,  64 ′ are deviated beforehand relative to the coupling lenses  103 ,  104  in accordance with the light axis deviation amounts, the semiconductor lasers  101 ,  102  are pressed while deviated from the light axes of the coupling lenses  103 ,  104 . Since the semiconductor lasers  101 ,  102  are deviated beforehand in accordance with the light axis deviation amounts as above, the thickness d 1 , d 2  of adhesive layer A 1 ′, A 2 ′ for the coupling lens  103 ,  104  can be set to the uniform thickness, as illustrated in FIG. 1A, such as for example, d 1 =d 2 =150 μm. 
     Therefore, the difference in the contraction amount, which is caused by the difference in thickness between the adhesive layers A 1 ′ and A 2 ′ at the time of ultraviolet radiation, is suppressed. Accordingly, the difference in the deviations of collimating properties or light axis values of the coupling lenses  103 ,  104  are also suppressed. Further, the adverse effect of changes in the environmental conditions on the beam pitch is prevented. 
     When the beam synthesizer  105 ′ is bonded to the retaining portion  621  of the holder member  60 , the ¼ wavelength plate  80  and the aperture AP formed beforehand integrally with the beam synthesizer  105 ′ are bonded together. Therefore, the ¼ wavelength plate  80  and the aperture AP which have been previously assembled in a separate process can be assembled at the same time the beam synthesizer  105 ′ is assembled. 
     As clearly seen from the above-mentioned embodiment, according to the present invention, since the positions of semiconductor laser attachment holes are deviated in such a manner that the adhesive layers for the coupling lenses as the collimator lenses have the same thickness, the change of contraction amount of each adhesive layer at the time of ultraviolet radiation can be uniformed. Therefore, the difference in the deviations of the collimating properties and the light axis values caused by the difference in the change of the contraction amount of the adhesive layers for the coupling lenses can be prevented. Additionally, since the lenses can be prevented from differing in the deviation amount of the collimating properties and the light axis values due to the changes in the environmental conditions, the position adjustment of the coupling lenses can correctly be performed even under the influence of changes in environmental conditions. This can prevent undesired changes in the beam pitch, lowering of image sharpness or other image deterioration from occurring. 
     According to the present invention, since the aperture and the ¼ wavelength plate are formed integrally with the holder member and the beam synthesizer, the aperture and the ¼ wavelength plate can be assembled with the holder member at the same time the beam synthesizer is fixed to the holder member. Therefore, the aperture and ¼ wavelength plate do not have to be separately assembled, and they can be assembled in one process. This can reduce the number of assembly processes for the light-source device of a multi-beam scanning apparatus and particularly simplify the process for assembling the small components such as the aperture and the ¼ wavelength plate. 
     Numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein. 
     The present application claims priority and contains subject matter related to Japanese Patent Application No. 10-081117 filed in the Japanese Patent Office on Mar. 27, 1998, and the entire contents of which are hereby incorporated by reference.