Abstract:
An end face polishing apparatus has a lapping board mounted to undergo rotation and revolving movement, a lapping member having a polishing surface and disposed on the lapping board for rotation and revolving movement therewith, a polishing fixture for supporting a workpiece having an end face, and a pressing member. During a polishing operation, preselected portion thereof to bring the end face of the workpiece into pressure contact with the polishing surface of the lapping member and to dispose the preselected portion at a position closer to the polishing surface than to a center of gravity of the polishing fixture to thereby polish the end face of the workpiece during rotation and revolving movement of the lapping board.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an end face polishing apparatus that polishes an end face of a rod-shaped member such as fibers for optical communication and a ferrule holding fibers for optical communication. 
     2. Description of the Background Art 
     Fibers for optical communication are adhesively secured in the central hole of a ferrule, a main member of a connector, and then the ferrule end face and the end face of fibers are polished together and thus finished into a smooth, mirror surface. If the polished end faces of the ferrule and the fibers are not vertical to the central axis of the ferrule or if there is a flaw on the polished faces, the precision in positioning such ferrules as they are connected facing each other in an optical connector is lowered, and the loss increases. Therefore, the face of the ferrule including the optical fibers must be polished with high precision. 
     A conventional apparatus for polishing the end faces of optical fibers is disclosed for example by Japanese Patent Laid-Open No. 26456/1991. The disclosed end face polishing apparatus includes an eccentric adapter that rotates on a circle concentric with a rotating disc, and a planetary gear that transmits the rotation of a revolution motor to the eccentric adapter. These elements are coupled in a lapping board, so that the lapping board is allowed to rotate and revolve, while the end faces of a plurality of ferrules held by a polishing fixture are pressed against a lapping member secured to the lapping board by a supporting portion provided at the main body of the apparatus. 
     In the conventional end face polishing apparatus, however, the position for pressing the polishing fixture by the supporting portion and the position for polishing the rod-shaped member are different in height, so that a moment is applied upon the polishing fixture as the polishing fixture is pressed, and the operation becomes unstable. The end face of the bar-shape member is therefore polished into a curved surface, and when a ferrule is used as the rod-shaped member, the polishing precision of the ferrule could be low. As a result, when end faces are connected in abutment with each other in optical connection, optical insertion loss could be large. 
     In a multi-fiber optical connector as a ferrule holding a plurality of optical fibers, the curved surface resulting from using the conventional end face polishing apparatus could increase insertion loss caused by optical connection of optical fibers particularly on the outer periphery when end faces of the multi-fiber optical connectors are abutted against each other. 
     Furthermore, in the conventional end face polishing apparatus, the polishing fixture should be secured free from inclination in order to polish the end face not to be curved, while the precision of securing the polishing fixture and the precision of attaching the rod-shaped member to the polishing fixture must be high, which requires much time and complicated operation. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the foregoing disadvantages in the conventional art, and it is an object of the present invention to provide an end face polishing apparatus that allows a rod-shaped member to be polished with improved precision and the polishing process to be simplified. 
     According to a first aspect of the present invention directed to a solution to the above disadvantages, in an end face polishing apparatus polishing an end face of a rod-shaped member mounted at a polishing fixture by pressing the rod-shaped member against a lapping member on a lapping board supported at the main body of the apparatus to rotate and rock, the polishing fixture is pressed through an abutting part against a supporting portion provided at the apparatus main body, and the abutting part is located more on the side of the lapping board than the center of gravity of the polishing fixture. 
     According to a second aspect of the invention, in the end face polishing apparatus according to the first aspect, the abutting part is within the range of ±5.0 mm from the polishing surface of the lapping member in the pressing direction. 
     According to a third aspect of the invention, in the end face polishing apparatus according to the first or second aspect, the abutting part is located about in the center of the polishing fixture. Here, the abutting part may be provided in at least two, preferably at least four positions at the outer periphery of the jig, and still the same effect can be provided 
     According to a fourth aspect of the invention, in the end face polishing apparatus according to any one of the first to third aspects, a recessed portion is provided near the center of the lapping board on the side of the polishing fixture, and the abutting part of the polishing fixture against the supporting portion is provided to project into the recessed portion. 
     According to a fifth aspect of the invention, in the end face polishing apparatus according to any one of the first to fourth aspects, the rod-shaped member is a ferrule including a ferrule tubular body for holding optical fibers and a collar member provided at a rear end of the ferrule tubular body for holding coated optical fibers. 
     According to a sixth aspect of the invention, in the end face polishing apparatus according to the fifth aspect, the ferrule is a multi-fiber optical connector. 
     According to a seventh aspect of the invention, an end face polishing method includes pressing an end face of a rod-shaped member against a surface of a rotating and revolving lapping member, and securing the rod-shaped member by an abutting part extended in the radial direction of the rod-shaped member and about in the same level as the surface of the lapping member. 
     According to an eighth aspect of the invention, a polishing fixture has a through hole for receiving a rod-shaped member in the center, an abutting part at the outer periphery for pressing from the upper surface to the bottom surface, and a recessed portion at the bottom surface in the center. 
     According to a ninth aspect of the invention, a method of polishing an end face of a rod-shaped member includes the steps of securing a polishing fixture having a through hole for receiving a rod-shaped member in the center, an abutting part at the outer periphery for pressing from the upper surface to the bottom surface, and a recessed portion at the bottom surface in the center, providing the upper surface of a lapping member facing the bottom surface in the center about in the same level as the upper surface of the polishing fixture, and rotating and revolving the lapping member. 
     According to the present invention, the abutting part where the polishing fixture is pressed by the supporting portion is located below the center of gravity of the polishing fixture, and therefore the moment applied on the polishing fixture can be reduced. In this way, the periphery of the polishing fixture can be prevented from being deviated from the lapping board in the vertical direction, and the polishing surface of the rod-shaped member can be polished perpendicularly to the axial direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a part of an end face polishing apparatus according to a first embodiment of the invention; 
     FIG. 2A is a perspective view of a polishing fixture and a supporting mechanism according to the first embodiment; 
     FIG. 2B is a sectional view of a main part of the polishing fixture and the supporting mechanism; 
     FIG. 3A is a sectional view of a main part of a polishing fixture and a lapping board according to the invention; 
     FIG. 3B is a sectional view of a main part of a conventional polishing fixture and a conventional lapping board; and 
     FIG. 4 is a sectional view of a part of the end face polishing apparatus according to the first embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings. 
     First Embodiment 
     FIG. 1 is a schematic sectional view of an end face polishing apparatus according to a first embodiment of the present invention. 
     As shown in FIG. 1, the central part of a first rotation transmission plate  12  is rigidly coupled to the rotation shaft of a rotation motor  11 . A plurality of first coupling pins  13  are secured to the first rotation transmission plate  12  concentrically around the rotation center of the first rotation transmission plate  12 . The first coupling pins  13  are each rotatably coupled to an eccentric part of a corresponding one of rotation transmission plates  14 . Second coupling pins  15  are each secured at an eccentric part of a corresponding one of the rotation transmission plates  14 . The second coupling pins  15  are rotatably coupled to a second rotation transmission plate  16 . 
     Meanwhile, the central part of a driving gear  18  is rigidly coupled to the rotation shaft of a revolution motor  17  and the driving gear  18  is engaged with a driven near  19 . The driven near  19  is rigidly coupled to the lower periphery of a revolution transmission shaft  20 , the upper periphery of which is engaged with the bearing tube  22  of an apparatus main body  21 . A rotation shaft  23  is rotatably fitted in a position a prescribed distance deviated from the center of the revolution transmission shaft  20 , and the lower end of the rotation shaft  23  is rigidly coupled to the rotation center of the second rotation transmission plate  16 . 
     The rotation shaft  23  has its upper end coupled to a polishing member or lapping board  25  through a coupling member  24 . On the upper surface of the lapping board  25 , a lapping member which is not shown is provided. 
     Meanwhile, at the apparatus main body  21 , a jig board or polishing fixture  40  having a plurality of workpieces in the form of rod-shaped members W such as ferrules secured thereto is supported by a supporting mechansim  30 . 
     The supporting mechanism  30  and the polishing fixture  40  will now be detailed. 
     FIG. 2A is a perspective view of the polishing fixture, FIG. 2B is a sectional view of a main part of the polishing fixture and the supporting mechanism, and FIG. 3A is a sectional view of the polishing fixture and the supporting mechanism. 
     As shown in FIGS. 2A to  3 A, the polishing fixture  40  includes a polishing fixture main body  41  and a plurality of fittings  42  attached at a side surface of the polishing fixture main body  41 . 
     The polishing fixture main body  41  has a polygonal shape, each side of which has V grooves  43  in the thickness-wise direction. 
     In a position of the polishing fixture main body  41  facing the V groove  43 , the fitting  42  is secured through a securing screw  44 . The rod-shaped member W is held between the V groove  43  and the fitting  42 , so that the rod-shaped member W is detachably secured to the polishing fixture  40 . 
     Note that according to the embodiment, two such V grooves  43  are provided at each side, so that twelve rod-shaped members W altogether can be secured for the polishing fixture main body  41  in a hexagon shape. The type of the rod-shaped member W is not specifically limited and may be a cylindrical rod-shaped member such as a ferrule, or a rod-shaped member having a rectangular section such as a multi-fiber ferrule or a multi-fiber optical connector. According to the embodiment, a cylindrical ferrule is used as the rod-shaped member W. The fitting  42  and the securing screw  44  used to secure the rod-shaped member W to the polishing fixture main body  41  are not limited to those described. 
     About in the center of the polishing fixture main body  41 , there is a through hole  45  penetrating in the thickness-wise direction. A tubular member in the form of a boss  46  abutted and pressed against the polishing fixture main body  41  is secured at the opening of the through hole  45  on the side of lapping board  25 , in other words at the polishing fixture main body  41  on the side of the lapping board  25 . As will be detailed, at the upper surface of the boss  46  on the side of the through hole  45 , there are a tapered recessed portion  47  against which the tip end of pressing member or portion  32  of the supporting mechanism  30  abuts about in the same level as the polishing surface of the rod-shaped member W in abutment against the lapping board, and a restriction hole  48  to which a restriction pin  33  to restrict the movement in the rotation direction is engaged. 
     According to the embodiment, in order to provide the polishing surface of the lapping board  25  and the recessed portion  47  of the polishing fixture  40  about in the same level, a recessed portion  25   a  is provided about in the center of the lapping board  25  so that the boss  46  projecting from the polishing fixture  40  does not abut against the lapping board  25 . 
     Meanwhile, the supporting mechanism  30  includes a supporting arm  31  provided at the apparatus main body  21 , the pressing portion  32  supported by the supporting arm  31  as it is urged to press the polishing fixture  40  toward the lapping board  25 , and the restriction pin  33  provided at the supporting arm  31  to restrict the movement of the polishing fixture  40  in the rotation direction. 
     The pressing portion  32  is held as it is urged toward the lapping board  25  by urging means (not shown) which is provided at the supporting arm  31 . A tapered portion  32   a  provided at the tip end of the pressing portion abuts against the recessed portion  47  of the boss  46  at the polishing fixture  40 , so that the polishing fixture  40  is pressed toward the lapping board  25 . 
     According to the embodiment, the abutting part between the tapered portion  32   a  of the pressing portion  32  and the recessed portion  47  of the boss  46  constitutes a preselected portion of the polishing fixture  40  and is provided about in the same level as the end face of the rod-shaped member W to be polished by the lapping board  25 . The height of the abutting part should be more on the side of the lapping board  25  than the center of gravity of the polishing fixture  40  as will be described. 
     Meanwhile, the restriction pin  33  is engaged with the restriction hole  48  of the boss  46  at the polishing fixture  40 , so that the movement of the polishing fixture  40  is restricted as the lapping board  25  rotates in the rotation direction. 
     More specifically, the polishing fixture  40  is urged by the pressing portion  32  toward the lapping board  25  as its movement in the rotation direction is restricted by the restriction pin  33  of the supporting mechanism  30 . Thus, the polishing fixture  40  is supported on the lapping board  25  through the tip ends of the rod-shaped members W secured by the fitting  42 . The lapping board  25  is rotated and rocked to polish the tip end faces of the rod-shaped members W. 
     Here, the state of the polishing fixture at the time of polishing will be described in comparison between the conventional end face polishing apparatus and the end face polishing apparatus according to the embodiment in conjunction with FIGS. 3A and 3B. FIG. 3B is a sectional view of a main part of the conventional end face polishing apparatus. 
     As shown in FIG. 3B, a conventional polishing fixture  40 A is provided with a boss  46 A at the upper surface of the polishing fixture main body  41 A, and the tapered portion  32   a  of the pressing portion  32  abuts against the upper part of the boss  46 A. More specifically, in the conventional end face polishing apparatus, the abutting part where the polishing fixture  40 A is pressed against the pressing portion  32  is more on the side of the pressing portion  32  than the center of gravity of the polishing fixture  40 A. 
     In the polishing fixture  40 A, a load is applied on the recessed portion  47 A a distance L1 apart from the polishing surface, i.e., from the reference point at which the end face of the rod-shaped member W abuts against the lapping board  25 . Therefore, when the lapping board  25  is rotated and rocked, the polishing fixture  40 A has its circumferential edge deviated up and down and is not operated stably, so that the polishing surface of the rod-shaped member W is finished into a curve. 
     Meanwhile, as shown in FIG. 3A, in the end face polishing apparatus according to the embodiment, the boss  46  is provided at the bottom of the polishing fixture main body  41 , and the tapered portion  32   a  of the pressing portion  32  is abutted against the upper part of the boss  46 . Therefore, the abutting part where the polishing fixture  40  is pressed against the pressing portion  32  is about in the same level as that of the surface of the rod-shaped member W polished by the lapping board  25 . 
     More specifically, in the polishing fixture  40  according to the embodiment, the distance from the polishing surface as a reference to the recessed portion  47  is zero, and therefore when the lapping board  25  is rotated and rocked to polish the rod-shaped member W, the periphery of the polishing fixture  40  is not deviated up and down, and the end face of the rod-shaped member W can be polished into a surface perpendicular to the axial direction with high precision. 
     Therefore, the abutting part where the polishing fixture  40  is pressed against the supporting mechanism  30  is in a position whose distance from the polishing surface as a reference where the end face of the rod-shaped member W is abutted against the lapping board  25  is as small as possible i.e. is more on the side of the lapping board  25  than the center of gravity of the polishing fixture  40 . In this way, the deviation of the periphery of the polishing fixture  40  can be reduced. 
     The abutting part is preferably positioned about in the same level as the polishing surface, while as long as the abutting part is positioned in the range of ±5.0 mm in the pressing direction of the polishing fixture  40  from the polishing surface as a reference, the effect is similarly remarkable as when they are positioned about in the same level. 
     In this way, the abutting part where the polishing fixture  40  is pressed against the supporting mechanism  30  is provided more on the side of the lapping board  25  than the center of gravity of the polishing fixture  40 , so that the periphery of the polishing fixture  40  can be prevented from being deviated in the vertical direction from the lapping board  25 . Thus, the end face of the rod-shaped member W can be polished into the surface vertical to the axial direction with high precision. When a ferrule is used for the rod-shaped member W, the insertion loss by optical connection can be reduced. Since the lapping board does not have to be secured to prevent the vertical deviation, the structure of the end face polishing apparatus can be simplified. Since positioning with high precision is not necessary, the polishing process can be simplified as well. 
     In the above description, the center of the polishing fixture is pressed, while the polishing fixture may be pressed in at least two positions in the outer periphery, so that the moment of the polishing fixture can be reduced and the polishing surface of the rod-shaped member can be formed into a smooth surface perpendicular to the axis of the rod-shaped member with no chamfer or waviness. 
     The operation of the end face polishing apparatus according to the embodiment will now be described. As shown in FIG. 1, for the revolution, the revolution motor  17  is driven to rotate the revolution transmission shaft  20  through the gears  18  and  19 , and the lapping board  25  revolves by a prescribed amount of eccentricity. In this case, the rotation shaft  23  is located in the revolution transmission shaft  20 , while a plurality of rotation transmission plates  14  are provided in the space between the rotation shaft  23  and the first rotation transmission plate  12 . The rotation transmission plates  14  rotate around the first coupling pins  13  in the same rotation phase as the revolution transmission shaft  20 . Therefore, regardless of whether the first rotation transmission plate  12  is stationary or rotates, the rotation of the revolution transmission shaft  20  is not restricted. 
     Meanwhile, for the rotation, the rotation motor  11  is driven to rotate the first rotation transmission plate  12 , while the first coupling pins  13  are located concentrically with the first rotation transmission plate  12 , and therefore move in the same trajectory as the above. The rotation shaft  23  is deviated by a prescribed distance from the center, while the shaft is coupled through the rotation transmission plates  14 , and therefore the rotation at the same number of revolutions as that of the first rotation transmission plate  12  is transmitted to the rotation shaft  23 . 
     Thus, the lapping board  25  revolves as it rotates by the rotation of the revolution transmission shaft  20  and the rotation shaft  23 . 
     Meanwhile, with respect to the lapping member provided at the lapping board  25 , the polishing fixture  40  has its movement in the rotation direction restricted by the restriction pin  33  of the supporting mechanism  30 , and as the polishing fixture is urged toward the lapping board  25  by the pressing portion  32 , the end face of the rod-shaped member W is pressed onto the lapping board  25 . In this way, the tip end of the rod-shaped member W is polished. 
     Second Embodiment 
     FIG. 4 is a sectional view of another embodiment of the present invention. A multi-fiber optical connector as a rod-shaped member W is perpendicularly secured to the polishing fixture main body  41 , and both ends of the polishing fixture main body  41  are secured by screws  51  as they are pressed downward using a spring  52 . The bottom surface of the polishing fixture main body is secured to the upper surface of the apparatus main body  21  through a spacer  50 . An end face of the rod-shaped member W is in contact with the surface of the lapping board  25 , so that the lapping board  25  is rotated by the rotation shaft  26  and the end face of the rod-shaped member W can be polished. The lapping board  25  rotates as it revolves. 
     The surface of the lapping board  25  is about in the same level as the upper surface of the outer periphery of the polishing fixture main body. As a result, the moment applied on the polishing fixture is reduced, and the deviation of the rod-shaped member W in the radial direction is reduced. The end face of the rod-shaped member W is polished into a smooth surface in the direction normal to the axis of the rod-shaped member with no waviness or distortion. 
     Other Embodiments 
     The basic structure of the end face polishing apparatus according to the present invention is not limited to those of the embodiments described above. 
     In the above description of the first embodiment, the polishing fixture  40  holds a cylindrical ferrule as the rod-shaped member W, while the member is not limited to this and may for example be a multi-fiber optical connector or an optical connector holding a ferrule. 
     The end face polishing apparatus according to the present invention can polish the end surface of the rod-shaped member W perpendicularly to the axial direction, and therefore insertion loss at the time of optical connection can surely be reduced particularly when a multi-fiber optical connector is polished. 
     In the above description of the first embodiment, there is a single abutting part between the recessed portion  47  of the boss  46  at the polishing fixture  40  and the tapered portion  32   a  of the pressing portion  32 , while there may be a plurality of abutting parts instead. Such a plurality of abutting parts should be provided to allow the polishing fixture  40  to be uniformly pressed. 
     Furthermore, in the above description of the end face polishing apparatus according to the first embodiment, the driving system is provided with the rotation shaft  23  in a position a prescribed distance deviated from the center in the revolution transmission shaft  20 , while the end face polishing apparatus may have a driving system provided with a revolution transmission shaft within a rotation shaft. The driving system for the end face polishing apparatus is not particularly limited. 
     In the foregoing, construction of the end face polishing apparatus according to the present invention, the abutting part of the polishing fixture to be pressed by the pressing portion is positioned below the center of gravity of the polishing fixture, and the moment applied upon the polishing fixture is reduced, so that the periphery of the polishing fixture can be prevented from being deviated from the lapping board in the vertical direction. Thus, the surface of the rod-shaped member can be polished perpendicularly to the axial direction. Neither a device to secure the polishing fixture nor positioning with high precision is necessary and, therefore, the polishing process can be simplified.