Abstract:
A fixation method for fixing an optical member to a holding member using irradiation of a laser beam. The method includes the steps of inserting the optical member into the holding member, providing a fixing member, mounting the fixing member to the holding member having the optical member positioned therebetween, and irradiating laser beams on the holding member through the fixing member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fixation method for an optical member, such as a photographic lens, in which the optical member is joined and fixed to a holding member using laser welding, and also relates to an optical unit having such an optical member fixed. 
     2. Description of the Related Art 
     In conventional optical apparatuses, such as still cameras or video cameras, a variety of methods for fixing a lens have been employed. In recent years, since the size of a still camera or video camera has become smaller and a space usable for fixing a lens has also become smaller, a method for fixing a lens using adhesives is generally employed. Moreover, a method for fixing a lens using so-called thermal caulking in which a part of a lens holder is thermally deformed is also known. 
     However, in the case of the method for fixing a lens to a lens holder or the like using adhesives, which is generally employed, the adhesive may intrude into the effective diameter of the lens or may protrude from the lens holder, thus causing difficulty in production control. In addition, contraction of the adhesive being cured may distort the lens. Furthermore, the amount of applied adhesive may vary with the applied positions, thereby causing distortion of the lens, so that a desired optical performance may not be obtained. Furthermore, while an ultraviolet curable resin can be taken as an example of an adhesive usable for bonding an optical element, such as a lens, the time of irradiation of ultraviolet rays required to cure the ultraviolet curable resin is several seconds to several tens of seconds. It takes further time to completely cure the adhesive. Therefore, even if the position of a lens is adjusted, for example, by the correction for decentering, the lens position may gradually vary due to the unevenness of contraction of the adhesive until the adhesive is completely cured. Accordingly, the lens position may deviate from a desired position. Furthermore, in the case of a plastic lens, the lens may become yellowed by the intense irradiation of ultraviolet rays. Therefore, the color balance of the lens may vary. 
     In the fixation method using the thermal caulking, heat is also conducted to portions other than that required to be heated. Therefore, a portion of the lens holder other than a portion required to be heated may be deformed. If the lens or the lens holder is reduced in size and portions for mounting other parts are close to each other, the influence of heat further increases. If heat is excessively conducted to the lens, the lens may be deformed. 
     As a method for solving the problems with the bonding by the ultraviolet curable resin or with the thermal caulking for fixing a lens, Japanese Laid-Open Patent Application No. 2004-20867 discloses a technique of fixing a lens to a part, such as a lens holder, using laser welding. In this technique, a laser beam is radiated to a lens holder, a viewfinder holder or the like, which is made of plastic, so as to fix a plastic lens thereto. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method for fixing an optical member to a holding member and to an optical unit. In one aspect of the present invention, a fixation method for fixing an optical member to a holding member includes the steps of inserting the optical member into the holding member, providing a fixing member, mounting the fixing member to the holding member having the optical member positioned therebetween, and irradiating laser beams on the holding member through the fixing member. In another aspect of the present invention, an optical unit includes an optical member having an outer circumference portion; a holding member configured to hold the optical member, the holding member including a wall portion configured to face the outer circumference portion of the optical member and having an end face, the holding member being made of a laser beam absorbent plastic; and a fixing member configured to contact with the outer circumference portion of the optical member and to contact with the end face of the wall portion of the holding member, the fixing member being made of a laser beam transparent plastic, the fixing member being fixed to the holding member by a part of the holding member being melted by a laser beam impinging on the part of the holding member through the fixing member. 
     Other features and advantages of the present invention will become apparent to those skilled in the art upon reading of the following detailed description of embodiments thereof when taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a perspective sectional view showing a lens unit according to a first embodiment of the invention in a condition before assembling the lens unit. 
         FIG. 2  is a perspective sectional view showing the lens unit according to the first embodiment in a condition after completing assembling the lens unit. 
         FIG. 3  is a perspective sectional view showing a lens unit according to a second embodiment of the invention in a condition before assembling the lens unit. 
         FIG. 4  is a perspective sectional view showing the lens unit according to the second embodiment in a condition after completing assembling the lens unit. 
         FIG. 5  is a perspective sectional view showing a lens unit according to a third embodiment of the invention in a condition before assembling the lens unit. 
         FIG. 6  is a perspective sectional view showing the lens unit according to the third embodiment in a condition after completing assembling the lens unit. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the invention will be described in detail below with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a perspective sectional view showing a lens unit according to a first embodiment of the invention in a condition before assembling the lens unit.  FIG. 2  is a perspective sectional view showing the lens unit in a condition after completing assembling the lens unit. The sequence for assembling the lens unit according to the first embodiment is described below with reference to  FIGS. 1 and 2 . 
     First, a first lens  12  made of glass or plastic and a lens holder  11  made of a laser beam absorbent plastic are aligned with respect to their optical axes Z by using a given method. The first lens  12  is then fitted into the lens holder  11  from below in  FIG. 1  in such a manner that an outer circumference portion  12   a  of the first lens  12  abuts on a lens-contacting portion  11   a  of an inner circumference portion of the lens holder  11 . Subsequently, a first lens presser frame  13  made of a laser beam transparent plastic is fitted into the lens holder  11  from below the first lens  12 . More specifically, the lens holder  11  includes, in addition to the lens-contacting portion  11   a , a frame-abutting portion  11   b  serving to position an outer circumference portion of the first lens presser frame  13 . The first lens  12  includes a frame-abutting portion  12   b  serving to position an inner circumference portion of the first lens presser frame  13 . The first lens presser frame  13  is fitted to both frame-abutting portions  11   b  and  12   b . Accordingly, the lens holder  11 , the first lens  12  and the first lens presser frame  13  are substantially aligned with respect to their optical axes Z. 
     Next, laser beams  14  are simultaneously radiated onto a plurality of sections of the first lens presser frame  13  from below in  FIG. 1 . More particularly, the laser beams  14  are applied only to a plurality of sections of the outer circumference portion of the first lens presser frame  13  that correspond in position to the frame-abutting portion  11   b  of the lens holder  11 . Since the first lens presser frame  13  is formed of a laser beam transparent plastic, the laser beams  14  pass through the first lens presser frame  13  and are then absorbed by the frame-abutting portion  11   b  of the lens holder  11 , which is formed of a laser beam absorbent plastic. Then, at the frame-abutting portion  11   b , the laser beams  14  are converted into heat to melt some portions of the lens holder  11 . This heat also melts some portions of the first lens presser frame  13 . In this instance, the laser beams  14  do not impinge on the first lens  12 , and the first lens  12  is positioned somewhat away from the welding zones. Accordingly, the first lens  12  is not affected by the heat. After that, when the laser radiation is stopped, the melted plastics are quickly cooled, and the first lens presser frame  13  and the lens holder  11  are welded and bonded together, as shown in  FIG. 2 . 
     The inner diameter portion of the first lens presser frame  13 , which is in contact with the frame-abutting portion  12   b , functions as an optical aperture limiter for eliminating undesired light beams coming from an aperture portion. While, in  FIG. 1 , the first lens presser frame  13  provides a circular aperture, it may be configured to provide a quadrilateral aperture. 
     Subsequently, a second lens  15  made of glass or plastic is aligned with the lens holder  11  with respect to their optical axes Z by using a given method. The second lens  15  is then fitted to a wall  11   c  and a lens-contacting portion  11   d  which are formed in the lens holder  11 . Then, a second lens presser frame  16  made of a laser beam transparent plastic is fitted into the lens holder  11  from above the second lens  15 . More specifically, the lens holder  11  further includes presser-frame guides  11   e  configured to engage with recess portions  16   a  of the second lens presser frame  16  so as to position the second lens presser frame  16 . By causing the recess portions  16   a  to engage with the presser-frame guides  11   e , the second lens presser frame  16  is positioned with respect to the lens holder  11 . Accordingly, laser welding portions  11   f  of the lens holder  11  are kept in close contact with laser receiving portions  16   b  of the second lens presser frame  16 . In this instance, a plurality of lens presser portions  16   c  formed on the inner circumference portion of the second lens presser frame  16  keep the second lens  15  pressed against the lens holder  11 . 
     Next, laser beams  17  are simultaneously radiated onto a plurality of sections (laser receiving portions  16   b ) of the outer circumference portion of the second lens presser frame  16  from above in  FIG. 1 . Since the second lens presser frame  16  is formed of a laser beam transparent plastic, the laser beams  17  pass through the second lens presser frame  16  and are then absorbed by the lens holder  11 , which is formed of a laser beam absorbent plastic. Then, at the lens holder  11 , the laser beams  17  are converted into heat to melt the laser welding portions  11   f  of the lens holder  11 . This heat also melts some portions of the second lens presser frame  16 . In this instance, the laser beams  17  do not impinge on the second lens  15 , and the second lens  15  is positioned somewhat away from the welding zones. Accordingly, the second lens  15  is not affected by the heat. After that, when the laser radiation is stopped, the melted plastics are quickly cooled, and the second lens presser frame  16  and the lens holder  11  are welded and bonded together, as shown in  FIG. 2 . 
     In the first embodiment, the first lens  12  is first fixed using laser welding and, then, the second lens  15  is fixed using laser welding. However, the present invention is not limited to this order. For example, the first lens  12  and the second lens  15  may be approximately simultaneously fixed by approximately simultaneously radiating laser beams from both sides. Furthermore, only one of the first lens  12  and the second lens  15  may be fixed using laser welding or may be installed in the lens holder  11 . 
     According to the above-described first embodiment, welding by laser beams is utilized to fix the first lens  12  between the lens holder  11  and the first lens presser frame  13  and to fix the second lens  15  between the lens holder  11  and the second lens presser frame  16  without using adhesives. Therefore, high-speed and high-precision fixation is possible, and a constant intensity of fixation can be attained. 
     Furthermore, since laser beams do not impinge directly on the first lens  12  and the second lens  15 , the first lens  12  and the second lens  15  are prevented from being subjected to thermal deformation. Also, the first lens  12  and the second lens  15  can be made of glass without the lens material being limited to laser beam absorbent plastics as in the conventional method. Moreover, since the laser beams  14  or  17  are approximately simultaneously radiated onto a plurality of sections to fix the lens  12  or  15 , the position of the lens  12  or  15  is prevented from changing after laser welding as in the conventional method. Accordingly, the positional accuracy of the lens  12  or  15  can be maintained. Furthermore, the inner diameter portion of the first lens presser frame  13  can be configured to serve as an optical aperture limiter for eliminating undesired light beans coming from an aperture portion. 
     Second Embodiment 
       FIG. 3  is a perspective sectional view showing a lens unit according to a second embodiment of the present invention in a condition before assembling the lens unit.  FIG. 4  is a perspective sectional view showing the lens unit in a condition after completing assembly of the lens unit. The sequence for assembling the lens unit according to the second embodiment is described below with reference to  FIGS. 3 and 4 . 
     First, a first lens  22  is fitted into a lens holder  21  from below in  FIG. 3  by using a given method. Accordingly, the first lens  22  is fixed to a first lens fixing portion  21   d  of the lens holder  21 . 
     Next, a second lens  25  made of glass or plastic is fitted to a wall portion  21   a  and a lens-contacting portion  21   b  of the lens holder  21  from above the lens holder  21 . In this case, the diameter of the second lens  25  is configured to be slightly smaller than the diameter of a lens housing portion constituted by the wall portion  21   a  and the lens-contacting portion  21   b  of the lens holder  21 . Therefore, the second lens  25  is fitted in the lens holder  21  with a slight clearance kept therebetween in a direction perpendicular to the optical axis Z. Next, a second lens presser frame  26  made of a laser beam transparent plastic is mounted on the second lens  25  from above the second lens  25 . Then, by moving the second lens presser frame  26  mounted on the second lens  25  in a direction perpendicular to the optical axis Z by using a given method, the optical axis Z of the second lens  25  is aligned with the optical axis Z of the first lens  22 . The second lens presser frame  26  includes lens presser portions  26   a  that are elastically deformable. After the second lens  25  and the first lens  22  are aligned with respect to their optical axes Z in the above-described manner, laser welding portions  21   c  of the lens holder  21  and laser receiving portions  26   b  of the second lens presser frame  26  are kept in close contact with each other by a clamping device (not shown). 
     Subsequently, laser beams  27  are simultaneously radiated from above in  FIG. 3  onto the laser receiving portions  26   b , which are formed at a plurality of sections on the outer circumference portion of the second lens presser frame  26 . Since the second lens presser frame  26  is formed of a laser beam transparent plastic, the laser beams  27  pass through the second lens presser frame  26  and are then absorbed by the lens holder  21 , which is formed of a laser beam absorbent plastic. Then, at the lens holder  21 , the laser beams  27  are converted into heat to melt the laser welding portions  21   c  of the lens holder  21 . This heat also melts some portions of the second lens presser frame  26 . In this instance, the laser beams  27  do not impinge on the second lens  25 , and the second lens  25  is somewhat positioned away from the welding zones. Accordingly, the second lens  25  is not affected by the heat. After that, when the laser radiation is stopped, the melted plastics are quickly cooled, and the second lens presser frame  26  and the lens holder  21  are welded and bonded together, as shown in  FIG. 4 . 
     Then, the lens holder  21  and the second lens presser frame  26  are released from close contact by the clamping device (not shown). In this respect, since the lens presser portions  26   a  of the second lens presser frame  26  have elastic force serving to constantly press the second lens  25  against the lens-contacting portion  21   b  of the lens holder  21 , the second lens  25  is highly precisely positioned without becoming unstable with respect to the lens holder  21 . In addition, even if a large impact is accidentally applied to the second lens  25 , the lens presser portions  26   a  absorb the impact by being elastically deformed, so that the second lens  25  can be prevented from cracking. 
     The above-described second embodiment has the following advantages in addition to the advantages of the first embodiment. The position of the second lens  25  can be shifted in order to perform positioning adjustment prior to the laser radiation. Even if the position of the second lens  25  is somewhat shifted, a condition of the welding zones does not change, and it is not necessary to change the position or setting of a laser apparatus. Therefore, the second lens  25  can be fixed between the second lens presser frame  26  and the lens holder  21  with a constant fixation strength. In addition, since elastically-deformable portions having weak elasticity (lens presser portions  26   a ) are provided at a plurality of sections of the second lens presser frame  26 , the second lens  25  can be prevented from becoming unstable when being fixed to the lens holder  21 . Furthermore, if an impact is accidentally applied to the second lens  25 , the elastically-deformable portions absorb the impact by being elastically deformed, so that the second lens  25  can be prevented from cracking. 
     Third Embodiment 
       FIG. 5  is a perspective sectional view showing a lens unit according to a third embodiment of the invention in a condition before assembling the lens unit.  FIG. 6  is a perspective sectional view showing the lens unit in a condition after completing assembling the lens unit. The sequence for assembling the lens unit according to the third embodiment is described below with reference to  FIGS. 5 and 6 . 
     First, a first lens  32  is fitted into a lens holder  31  from below in  FIG. 5  by using a given method. Accordingly, the first lens  32  is fixed to a first lens fixing portion  31   e  of the lens holder  31 . 
     Next, a second lens  35  made of glass or plastic is fitted to a wall portion  31   a  and a lens-contacting portion  31   b  of the lens holder  31  from above the lens holder  31 . Then, a second lens presser frame  36  made of a laser beam transparent plastic is mounted on the second lens  35  from above the second lens  35 . In this instance, the second lens  35  is approximately coaxially fitted in an inner diameter portion of the second lens presser frame  36 . In addition, the second lens presser frame  36  is configured such that the center of its outer circumference portion slightly deviates from the center of its inner circumference portion, that is, the thickness in the radial direction slightly differs between outer circumference portions  36   a  and  36   b  of the second lens presser frame  36 . The second lens presser frame  36  configured as described above is fitted to a wall portion  31   c  of the lens holder  31 . In general, it is difficult to exactly adjust the first lens  32 , which is already fixed to the lens holder  31 , to the optical axis Z, and it is considered that the first lens  31  is fixed while slightly deviating from the optical axis Z. Therefore, the optical axis Z of the second lens  35  is adjusted to a desired position, i.e., to the optical axis Z of the first lens  32 , by rotating the second lens presser frame  36  along the wall portion  31   c  of the lens holder  31 . The second lens presser frame  36  includes lens presser portions  36   c  that are elastically deformable. 
     After the optical axis Z of the second lens  35  is aligned with the optical axis Z of the first lens  32  as described above, laser welding portions  31   d  of the lens holder  31  and laser receiving portions  36   d  of the second lens presser frame  36  are kept in close contact with each other by a clamping device (not shown). 
     Subsequently, laser beams  37  are simultaneously radiated from above in  FIG. 5  onto the laser receiving portions  36   d , which are formed at a plurality of sections on the outer circumference portion of the second lens presser frame  36 . Since the second lens presser frame  36  is formed of a laser beam transparent plastic, the laser beams  37  pass through the second lens presser frame  36  and are then absorbed by the lens holder  31 , which is formed of a laser beam absorbent plastic. Then, at the lens holder  31 , the laser beams  37  are converted into heat to melt the laser welding portions  31   d  of the lens holder  31 . This heat also melts some portions of the second lens presser frame  36 . In this instance, the laser beams  37  do not impinge on the second lens  35 , and the second lens  35  is positioned somewhat away from the welding zones. Accordingly, the second lens  35  is not affected by the heat. After that, when the laser radiation is stopped, the melted plastics are quickly cooled, and the second lens presser frame  36  and the lens holder  31  are welded and bonded together, as shown in  FIG. 6 . 
     Then, the lens holder  31  and the second lens presser frame  36  are released from close contact by the clamping device (not shown). In this respect, since the lens presser portions  36   c  of the second lens presser frame  36  have elastic force serving to constantly press the second lens  35  against the lens-contacting portion  31   b  of the lens holder  31 , the second lens  35  is highly precisely positioned without becoming unstable with respect to the lens holder  31 . In addition, even if a large impact is accidentally applied to the second lens  35 , the lens presser portions  36   c  absorb the impact by being elastically deformed, so that the second lens  35  can be prevented from cracking. 
     The above-described third embodiment has the following advantages in addition to the advantages of the first embodiment. Since the second lens presser frame  36  is configured such that the center of its outer circumference portion slightly deviates from the center of its inner circumference portion, the optical axis Z of the second lens  35  can be adjusted to a desired position, i.e., to the optical axis Z of the first lens  32 , by rotating the second lens presser frame  36  along the wall portion  31   c  of the lens holder  31 . 
     While, in the above-described first to third embodiments, laser beams are simultaneously radiated onto a plurality of sections, the exactly simultaneous laser radiation is not required. Laser beams may be radiated with such a time difference as to have no influence on the positional accuracy of a lens, for example, with a time difference of several tens of milliseconds to several hundred milliseconds. Furthermore, an object to be fixed is not limited to a lens, but may include a transparent glass or plastic plate, an optical member such as an optical filter, and the like. 
     Moreover, the first lens  22  or  32  described in the second or third embodiment is not essential for the present invention. An apparatus having another reference optical system (not shown) may be used to adjust the optical axis Z of the second lens  25  or  35 . 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims priority from Japanese Patent Application No. 2004-163921 filed Jun. 2, 2004, which is hereby incorporated by reference herein.