Abstract:
Simple and small-sized equipment which continuously afford alternate twists to an optical fiber and a method using the apparatus are provided. The equipment includes: a guide roller for causing the fiber to roll; a roller supporting member for holding the roller in a manner allowing the roller to freely turn about an axial center X; and a driving unit to cause the roller to oscillate by making the supporting member to turn about an axial center Y that is inclined relative to the axial center X. The method includes: arranging a guide roller to intersect the fiber, the roller being held by a roller supporting member to freely turn about an axial center X; oscillating the roller by driving the supporting member to revolve about the axial center Y which is inclined relative to the axis center X; and causing the fiber to roll to afford alternate twists to the fiber.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to equipment and methods for manufacturing an optical fiber. 
         [0003]    2. Description of the Background Art 
         [0004]    It is difficult to form the core portion and the cladding portion in a perfectly circular and concentric shape in manufacturing an optical fiber. It is often the case that the core portion and the cladding portion become slightly ellipsoidal or distorted such that the cross-sectional refractive index profile of the optical fiber is not axial symmetry. As a result, the group velocities of mutually orthogonal two polarization modes that propagate in the optical fiber tend to differ from each other, and accordingly the polarization mode dispersion (PMD) increases. It is known that for manufacturing an optical fiber from an optical fiber preform, the drawing process is performed while affording twists to the optical fiber so that the PMD may be reduced. 
         [0005]      FIGS. 5A and 5B  are drawings illustrated in Japanese Patent Application Publication No. H9-243833:  FIG. 5A  is a conceptional schematic diagram and  FIG. 5B  is a perspective view. In this method, the twists are afforded to an optical fiber  1  by using an oscillating guide roller  2 . In the oscillating guide roller  2 , the axial center X, about which it turns, oscillates alternately in the range of +θ and −θ, and as the arrow “a” indicates, the roller surface  2   a  sways between the position defined by the solid line and the position defined by the dotted line. Accordingly, an optical fiber  1  which has passed a guide bar  3  rolls on the top of the swaying roller surface  2   a  so that twists are afforded thereto in an alternate twisting direction. 
         [0006]    The oscillating mechanism  10  has a pinion gear  12  arranged to turn on a base  11 , and the oscillating guide roller  2  is supported by means of a supporting shaft  14  so as to be mounted to a roller support body  13  that is fixed on the pinion gear  12 . Also, one end of a drive arm  16  is connected with a pin  16   a  to a turning plate  15  driven by a motor on the base  11  and the other end is connected to a slide member  19  arranged on a movable member  17 . The movable member  17  has a rack gear  18  which is meshed with the pinion gear  12  so as to afford a turning drive to the pinion gear  12 , and a guide part  17   a  helps the movable member  17  to move to and fro in the direction indicated by an arrow “b” along the guide groove provided on the base  11 . Also, a guide protrusion  19   a  guides a slide member  19  to slide in the direction indicated by an arrow “c”. 
         [0007]    When the turning plate  15  is driven to turn at a constant speed, the pin  16   a  of the drive arm  16  moves in a circle such that the arm  16  moves to and fro. As a result of the movement of the drive arm  16 , the slide member  19  moves in the direction of the arrow “c” on the guide protrusion  19   a  while the movable member  17  performs a linear movement in the direction of the arrow “b”. The pinion gear  12 , which meshes with a rack gear  18 , is caused to perform an oscillating rotational movement in the direction of an arrow “d” by the linear movement of the movable member  17 . The oscillating rotational movement “d” of the pinion gear  12  causes the oscillating guide roller  2  to oscillate in the oscillating range “a”. 
         [0008]      FIGS. 6A and 6B  are drawings which illustrate the method described in Japanese Patent Application Publication No. 2002-226229:  FIG. 6A  is a side view and  FIG. 6B  is a front view. In this method, twists are afforded to an optical fiber  1  by reciprocating rollers  21  and  22 . 
         [0009]    The reciprocating rollers  21  and  22  are supported in parallel by a base frame  25 , and a first guide roller  23  arranged above the roller  21  and a second guide roller  24  arranged below the roller  22  push the optical fiber  1  onto the surface of the reciprocating rollers  21 ,  22 . The surfaces of the reciprocating rollers  21 ,  22  have a coefficient of friction which is sufficient for the optical fiber  1  to roll without sliding thereon. The reciprocating rollers  21 ,  22  are caused to turn by the running of the optical fiber  1 , while the reciprocating rollers  21  and  22  are moved to and fro in mutually opposite directions at a given period. Thus, the optical fiber  1  rolls on the surface of the reciprocating rollers  21  and  22 , so that twists are afforded to the optical fiber  1 . The number of the reciprocating rollers provided in such case is supposed to be one or more than two. 
         [0010]    These known mechanisms are complicated and the relevant equipment is inevitably large-sized. Also, the driving direction of the rollers is reversed so that the direction of twist in the optical fiber may be reversed. And, at the time of such reversion, the twisting operation is interrupted temporarily. Therefore, the twisting speed is slow, and the number of twisting times becomes less, resulting in increase of variation in the PMD characteristics. 
       SUMMARY OF THE INVENTION 
       [0011]    The object of the present invention is to provide equipment and a method for manufacturing an optical fiber, such that the structure for affording twists to the fiber is simple and small-sized, allowing continuous and effective twisting operation without interruption at the time of reversing the twisting direction. 
         [0012]    To achieve the object, equipment for manufacturing an optical fiber is provided, which is capable of affording alternate twists to the optical fiber and which comprises (1) a guide roller arranged in a manner intersecting the traveling direction of the optical fiber and causing the optical fiber to roll in contact with the surface thereof, (2) a roller supporting member for holding the guide roller in a manner allowing the guide roller to freely turn about an axial center X, and (3) a driving unit to cause the guide roller to oscillate by making the roller supporting member to turn about its turning axis, that is, an axial center Y, which is inclined relative to the axial center X. 
         [0013]    According to one embodiment of the invention, the roller supporting member is a roller supporting shaft which is along the axial center X, and in another embodiment, the guide roller is supported by a cantilever lying along the axial center Y. Preferably, the inclination angle of the axial center X relative to the axial center Y is changeable. It is preferable that the guide roller have a brim portion having a taper spreading outward at each end of the roller and that the inclination angle θ of the axial center X with respect to the axial center Y satisfy the following formula: 
         [0000]    
       
         
           
             
               
                 tan 
                  
                 
                     
                 
                  
                 ϑ 
               
               ≤ 
               
                 T 
                 
                   
                     
                       
                         ( 
                         
                           R 
                           + 
                           H 
                         
                         ) 
                       
                       2 
                     
                     - 
                     
                       R 
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
         [0000]    where T is a thickness, and H is a height, of the brim portion, and R is a radius of the roller. These preferred embodiments can be combined together. 
         [0014]    In addition, a method of manufacturing an optical fiber is provided as another embodiment of the invention. The method comprises: arranging a guide roller so as to intersect the advancing direction of the optical fiber, the guide roller being held by a roller supporting member so as to freely turn about an axial center X; oscillating the guide roller by driving the roller supporting member to revolve about the axial center Y, the axial center Y being inclined relative to the axis center X; and thereby causing the optical fiber to roll in contact with the surface of the guide roller so as to afford alternate twists to the optical fiber. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIGS. 1A to 1C  is are drawings for illustrating the oscillating mechanism of the guide roller in a first embodiment of optical fiber manufacturing equipment according to the present invention:  FIG. 1A  is a partial sectional view thereof;  FIG. 1B  is a schematic diagram illustrating the positional arrangement; and  FIG. 1C  is a graph showing the oscillating speed of the guide roller in the oscillating mechanism. 
           [0016]      FIG. 2  is a partial sectional view illustrating the oscillating mechanism of a guide roller in a second embodiment of the optical fiber manufacturing equipment of the present invention. 
           [0017]      FIG. 3  is a partial sectional view illustrating the oscillating mechanism of a guide roller in a third embodiment of the optical fiber manufacturing equipment of the present invention. 
           [0018]      FIGS. 4A and 4B  are conceptional schematic diagrams for explaining the positional relationship between an optical fiber and the brim portion of a guide roller in the optical fiber manufacturing equipment of the present invention. 
           [0019]      FIGS. 5A and 5B  are drawings illustrating a conventional method:  FIG. 5A  is a conceptional schematic diagram, and  FIG. 5B  is a perspective view. 
           [0020]      FIGS. 6A and 6B  are drawings illustrating a conventional method:  FIG. 6A  is a side view, and  FIG. 6B  is a perspective view. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The above-mentioned features and other features, aspects, and advantages of the present invention will be better understood through the following description, appended claims, and accompanying drawings. In the explanation of the drawings, an identical mark is applied to identical elements and an overlapping explanation will be omitted. 
         [0022]      FIGS. 1A to 1C  is are drawings for illustrating the oscillating mechanism of the guide roller in a first embodiment of optical fiber manufacturing equipment according to the present invention, and  FIG. 1A  is a partial sectional view. An oscillating mechanism  30  comprises a guide roller  31  that is attached to a roller supporting member (support block)  32  through one pair of bearings  34  so as to be free to turn, the support block  32  being structured to rotate integrally with the rotating shaft  33 . The rotating shaft  33  is supported at both ends by rotating-shaft supporting bodies  35   a  and  35   b  through shaft supports  36  composed of bearings. A drive motor  37  is combined to one end of the rotating shaft  33 , so that the rotating shaft  33  and the support block  32  are turned in one direction at a given number of rotations. 
         [0023]    The guide roller  31  freely turns around the support block  32 , using the axial center X as its center. In the first embodiment, the axial center X has an inclination angle θ to the axial center Y of the rotating shaft  33  of the drive motor  37 . Therefore, the axial hole  32   a  of the support block  32  that rotates integrally with the shaft  33  is formed slantingly with an inclination angle θ relative to the axial center X. 
         [0024]    When the rotating shaft  33  is driven to rotate in one direction at a given turning speed by the drive motor  37 , the support block  32  is turned integrally with the rotating shaft  33 . Then, the guide roller  31  which is arranged concentrically around the outer circumference of the support block  32  moves as shown by an arrow “a” from the position of a solid line to the position of a dot-dash line by a half rotation of the support block  32 . In the subsequent half rotation, the guide roller  31  moves from the position of the dot-dash line to the position of the solid line. That is, the position of the guide roller  31  oscillates so as to return to the original position by one rotation of the rotating shaft  33 . (The oscillating range “a” of the guide roller can be changed by an inclination angle θ.) Accordingly, twists are afforded to the optical fiber  1  as the optical fiber  1  rolls on the roller surface  31   a.    
         [0025]      FIG. 1B  is a schematic diagram illustrating the positional arrangement of the oscillating mechanism  30 . The oscillating mechanism  30  is arranged between a fixed roller  4  and a guide roller  5 . The optical fiber  1  is led by guide bars  3  to a given position of the oscillating mechanism  30 , so that it is wound around the roller surface  31   a  of the guide roller  31 , with an orbit of 90° or more, for example. Also, the optical fiber  1  can roll without slipping on the roller surface  31   a,  since the roller surface  31   a  of the guide roller  31  is generally formed of a material having a large frictional coefficient. Consequently, alternate twists are afforded to the optical fiber  1  by the oscillation of the guide roller  31 . 
         [0026]    As in the first embodiment, if the oscillating equipment is installed at a position which lies in the range following the step of providing a protective coating onto a glass fiber in the process of drawing an optical fiber from an optical fiber preform, it is possible to afford twists (in this case, it is also called as spins) to the glass fiber itself that is in a fused condition by heating. However, the twists may be afforded to an optical fiber when it is subjected to a coloring or rewinding process after it has been drawn, provided with a protective coating, and wound on a take-up reel. 
         [0027]      FIG. 1C  is a graph showing the oscillating speed of the guide roller in the oscillating mechanism  30 . If the rotation of the rotating shaft  33  is constant, the speed of oscillation (right turn) of the guide roller  31  shown in  FIG. 1A  between the condition indicated by the solid line from the condition indicated by a dot-dash line while the rotating shaft turns by a half rotation is constant. Also, the succeeding oscillating speed (left turn) of the guide roller  31  from the condition indicated by the dot-dash line to the condition indicated by the solid line during the following half-rotation of the rotating shaft is constant. Here, the reverse of the oscillating direction is continuously done without undergoing operational stoppage with one-directional rotation of the rotating shaft  33 , and accordingly the twisting operation of the optical fiber can also be done without interruption of operation. 
         [0028]      FIG. 2  is a partial sectional view illustrating an oscillating mechanism  40  of a guide roller in the second embodiment of the optical fiber manufacturing equipment of the present invention. The oscillating mechanism  40  is an example of supporting a guide roller  41  so as to allowing its free rotation by using a roller supporting member (roller supporting shaft)  42  that is arranged to coincide with the axial center X of the guide roller  41 . The roller supporting shaft  42  is connected at its both ends with rotating shafts  43   a  and  43   b  through angle adjusting members  48   a  and  48   b,  respectively, so as to be fixed to have a given angle θ to the rotating shaft  43   a  and  43   b.    
         [0029]    In the second embodiment, the roller supporting shaft  42  that supports the guide roller  41  is coincident with the axial center X of the guide roller  41 , and not inclined like the rotating shaft  33  of the first embodiment. Thus, the guide roller  41  can be supported with one pair of small-diameter bearings  44 . Supporting the guide roller  41  with the small-diameter bearings enables not only a low-cost bearing mechanism, but also decrease in the rotational resistance (mechanical loss) of the roller. The final rolling-up tension of an optical fiber must be reduced to about tens of grams, and therefore the decrease in the bearing diameter of the guide roller  41  is effective for attaining a preferable value of the rolling-up tension. 
         [0030]    The rotating shafts  43   a  and  43   b  are supported by rotating-shaft supporting bodies  45   a  and  45   b,  respectively, through shaft supports  46  that are composed of bearings. A drive motor  47  is combined with the rotating shaft  43   a,  which turns in one direction at a given number of rotations. The guide roller  41  may be supported using the support block and bearings of large-sized diameter like the first embodiment, instead of supporting with small-diameter bearings  44 . 
         [0031]    Angle adjusting members  48   a  and  48   b  having a plurality of adjusting pins  49   a  and  49   b  are installed at the inner end of the rotating shafts  43   a  and  43   b,  respectively. The roller supporting shaft  42  can be connected with the rotating shafts  43   a  and  43   b  so as to be fixed at a given angle, such as 5°, 10°, 15°, or the like with respect to the axial center Y of the rotating shafts  43   a  and  43   b,  by choosing the adjusting pins  49   a  and  49   b,  and thereby the roller supporting shaft  42  can be rotated integrally with the rotating shaft  43   a  and  43   b.    
         [0032]    In the oscillating mechanism  40 , when the rotating shaft  43   a  is rotated at a give speed by the drive of the drive motor  47 , the roller supporting shaft  42  is caused to turn together with the rotating shaft  43   a  and  43   b.  Then, the guide roller  41  which is arranged concentrically on the roller supporting shaft  42  moves, as shown by the arrow “a”, from the position of the solid line to the position of the dot-dash line according to a half rotation of the rotating shafts  43   a  and  43   b  like the guide roller  31  of the first embodiment. At the subsequent half rotation, the guide roller  41  moves from the position of the dot-dash line to the position of the solid line. That is, the position of the guide roller  41  oscillates, returning to the original position by one rotation of the rotating shaft  43   a.  Thus, by the oscillation of the guide roller  41 , the optical fiber  1  is caused to roll on the roller surface  41   a,  changing the rolling direction alternately, and thereby alternate twists are afforded to the optical fiber. 
         [0033]      FIG. 3  is a partial sectional view illustrating the oscillating mechanism  50  of a guide roller in the third embodiment of the optical fiber manufacturing equipment of the present invention. In the oscillating mechanism  50 , the guide roller  51  is supported through one pair of bearings  54  so as to be free to turn at a roller supporting member (support joint)  52 . The support joint  52  is connected to one end of a rotating shaft  53  through a joint member  58  provided in its inside. The rotating shaft  53  is supported by a rotating-shaft supporting body  55  through a shaft support  56  composed of bearings. A drive motor  57  is combined with the other end of the rotating shaft  53 , and the rotating shaft  53  is turned in one direction at a given number of rotations. In the oscillating mechanism  50 , the guide roller is supported by cantilever and its oscillating angle is variable. 
         [0034]    The guide roller  51  turns about the axial center X of the guide roller  51 , freely revolving around the support joint  52 . The support joint  52  is connected so as to be fixed at a given angle θ with respect to the axial center Y of the rotating shaft  53 . The rotating shaft  53  is provided with an adjusting sleeve  59   b  for installing the support joint  52  at a given angle, and the adjusting sleeve  59   b  is connected to one end of the angle adjusting arm  59 . The other end of angle adjusting arm  59  is connected to a tab  59   a  that is provided on the support joint  52 . By adjusting the position of the adjusting sleeve  59   b  in a direction of the arrow on the rotating shaft  53 , the axial center X of the guide roller  51  and the axial center Y of the rotating shaft  53  can be set to a given angle θ. 
         [0035]    When the rotating shaft  53  is driven at a given turning speed by the drive motor  57 , the support joint  52  is rotated together with the rotating shaft  53  through the angle adjusting arm  59  and the joint member  58 . Then, the guide roller  51  which is arranged concentrically on the support joint  52  moves as shown by arrow “a” from the position of the solid line to the position of the dot-dash line at a half rotation of the rotating shaft  53  as in the case of the guide roller  31  of the first embodiment. At the subsequent half rotation, the guide roller  51  moves from the position of the dot-dash line to the position of the solid line. That is, the position of the guide roller  51  oscillates, returning to the original position by one rotation of the rotating shaft  53 . Thus, by the oscillation of the guide roller  51 , the optical fiber  1  is caused to roll on the roller surface  51   a,  changing the rolling direction alternately, and thereby alternate twists are afforded to the optical fiber. 
         [0036]      FIGS. 4A and 4B  are conceptional schematic diagrams for explaining the positional relationship between an optical fiber and the brim portion of a guide roller in the optical fiber manufacturing equipment of the present invention. Depending on the conditions under which twists are afforded to an optical fiber by the oscillating mechanism of a guide roller, the optical fiber might hit the brim portion provided at both ends of the guide roller such that the optical fiber that is being rolled up might suffer from vibration or damage. Therefore, preferably the brim portion prepared at both ends of the guide roller is provided with a taper (taper angle γ) according to the inclination angle θ and the guide roller radius R. In order to avoid the optical fiber from hitting the outer circumferential periphery of the brim portion of the guide roller, the following formula must be satisfied: 
         [0000]    
       
         
           
             
               
                 tan 
                  
                 
                     
                 
                  
                 ϑ 
               
               ≤ 
               
                 T 
                 
                   
                     
                       
                         ( 
                         
                           R 
                           + 
                           H 
                         
                         ) 
                       
                       2 
                     
                     - 
                     
                       R 
                       2 
                     
                   
                 
               
             
             , 
           
         
       
     
         [0000]    where H represents the height of the brim portion provided at both ends of the roller, and T (tan γ=T/H) represents the thickness of the brim portion. 
         [0037]    The following table shows the minimum value of the thickness T of the brim portion and the taper angle γ in the cases where the roller radius R are 20 mm, 35 mm, and 50 mm, while the height H of the brim portion is 5 mm (constant), and the inclination angle θ of the guide roller are 5°, 10°, 15°, and 16°. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 
               
               
                   
               
               
                 Roller radius 
                 Brim height 
                 Inclination 
                 Brim thickness 
                 Taper angle 
               
               
                 R mm 
                 H mm 
                 angle θ 
                 T mm 
                 γ 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 50 
                 5 
                 16 
                 6.57 
                 52.7 
               
               
                   
                 5 
                 15 
                 6.14 
                 50.8 
               
               
                   
                 5 
                 10 
                 4.04 
                 38.9 
               
               
                   
                 5 
                 5 
                 2.00 
                 21.8 
               
               
                 35 
                 5 
                 16 
                 5.55 
                 48.0 
               
               
                   
                 5 
                 15 
                 5.19 
                 46.1 
               
               
                   
                 5 
                 10 
                 3.41 
                 34.3 
               
               
                   
                 5 
                 5 
                 1.69 
                 18.7 
               
               
                 20 
                 5 
                 16 
                 4.30 
                 40.7 
               
               
                   
                 5 
                 15 
                 4.02 
                 38.8 
               
               
                   
                 5 
                 10 
                 2.64 
                 27.8 
               
               
                   
                 5 
                 5 
                 1.31 
                 14.7 
               
               
                   
               
             
          
         
       
     
         [0038]    The larger the roller diameter, the larger the thickness T of the brim portion and the taper angle γ must be. For example, in order to prevent the optical fiber from hitting the outer circumferential periphery of the brim portion of the guide roller even if the inclination angle θ (oscillation angle) of the guide roller is 15°, the thickness T of the brim portion must be 6.1 mm or more (taper angle γ must be 51° or more) in the case where the roller radius is 50 mm. Also, in the case where the roller radius is 35 mm, the thickness T of the brim portion must be made equal to or more than 5.2 mm (the taper angle γ must be 46° or more), and in the case of the roller radius of 20 mm, the thickness T of the brim portion must be 4.0 mm or more (the taper angle γ: 39° or more). 
         [0039]    In any examples as described above, the oscillating operation of a guide roller on which an optical fiber is caused to roll in contact with the surface thereof can be realized by a simple way of turning just at a constant speed and only in one direction the rotating shaft that supports the guide roller. When the PMD values of coated optical fibers were measured after rewinding with this method, they were reduced by about 40 to 70% as compared with the PMD values obtained before such rewinding, and thus the reduction in the PMD value was of the same degree as in the case of the conventional methods. Also, the PMD values were on the same level as those in the case of the conventional level. 
         [0040]    According to this method, the drive of the rotating shaft to make the guide roller oscillate is done by a motor itself without changing the rotary motion of the motor into the rectilinear motion like the conventional method, and therefore the control of rotation is easy, and the oscillation mechanism can be constituted with a down-sized, simple and low-cost structure. Moreover, the oscillation of the guide roller can be performed continuously at a constant oscillation speed, including the reversing operation, without stoppage, and consequently uniform twists can be afforded to the optical fiber in alternate directions, which is also advantageous in terms of the characteristics (PMD reduction). 
         [0041]    While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.