Abstract:
A multi-channel fiber-optic rotary joint having an elongate housing with a passageway extending therethrough. Fiber optic containing bundles are oriented in hollow shafts at the opposite ends of the passageway, which hollow shafts are rotatively supported in the housing. An alignment mechanism is provided inside the housing for effecting an optimizing of signal strength of signals transmitted between the respective fiber optic bundles.

Description:
This invention relates a multi-channel fiber-optic rotary joint and, more particularly, to a rotary joint, as aforesaid, wherein an adjustment mechanism is provided for optimizing the signal strength transmitted through the rotary joint from one set of fiber strands in a bundle to another set of fiber strands in a separate bundle disposed axially from the first mentioned bundle. 
     BACKGROUND OF THE INVENTION 
     Multi-channel fiber-optic rotary joints are known in the art and one example thereof is described in U.S. Pat. No. 5,271,076. As is explained in this patent, the extreme tolerances associated with multi-channel rotary joints exhibit high optical loss and variation of that loss with rotation. 
     Accordingly, it is an object of this invention to provide a multi-channel fiber-optic rotary joint which is capable of effecting an optimization of signal strength through the rotary joint and rendering the signal strength essentially constant during rotation of one end of the rotary joint with respect to the other end. 
     It is a further object of the invention to provide a multi-channel fiber-optic rotary joint, as aforesaid, which facilitates a setting of the alignment for a central one of the fiber strands before facilitating alignment of the strands that are oriented radially outwardly therefrom. It is a further object of the invention to provide a multi-channel fiber-optic rotary joint wherein the respective ends of the joints are supported for rotation and when adjustment is needed, the two ends are rotatively linked to facilitate rotation in opposite directions to bring the outer fiber optic strands into an optimal signal strength relation. 
     SUMMARY OF THE INVENTION 
     Other objects and purposes of this invention will be apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings, in which: 
     FIG. 1 is an isometric view of a multi-channel fiber-optic rotary joint embodying the invention; 
     FIG. 2 a fragmentary isometric view of a fragment of the aforesaid rotary joint; 
     FIG. 3 is an isometric view of a prism stage; 
     FIG. 4 is a isometric sectional view of the prism stage; 
     FIG. 5 is a side view of the control mechanism utilized for rotatively linking the respective ends of the rotary joint; 
     FIG. 6 is an end view of a hollow shaft containing a plurality of fiber optic strands therein; and 
     FIGS. 7 and 8 are schematic illustrations of related gear arrangements disclosed herein. 
    
    
     DETAILED DESCRIPTION 
     Certain terminology will be used in the following description for convenience and reference only and will not be limiting. The words “up”, “down”, “right” and “left” will designate corrections in the drawings to which reference is made. The words “in” and “out” will refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. Such terminology will include derivatives and words of similar import. 
     A multi-channel fiber-optic rotary joint  10  is illustrated in FIG.  1 . It includes a housing  11  having an elongate passageway  12  extending axially therethrough. The housing  11  consists of two housing parts  11 A and  11 B that are coupled together by a plurality of screws (not illustrated). When the housing parts  11 A and  11 B are assembled, a cylindrical housing is defined with an axially extending passageway  12  extending therethrough. 
     The left end of the housing illustrated in FIG. 1 includes a support section  13  for rotatably supporting a hollow shaft  14  in plural coaxially oriented bearings  16 . A spur gear  17  is oriented between the bearing sets  16  as illustrated in FIG.  1  and projects through a gap  18  in the support section  13 . The left end of the hollow shaft  14  terminates in a radial flange  19 , which flange can be used for securing the hollow shaft  14  to either a fixed or rotatable member not illustrated. 
     The right end of the housing  11  includes a support section  21  rotatably supporting a hollow shaft  22  on sets of bearings  23  supported on the support section  21 . A spur gear  24  identical in size and having an equal number of teeth as the spur gear  17  is mounted on the hollow shaft  22  and oriented between the sets of bearings  23  as illustrated in FIG.  1 . The axis of rotation  26  of the hollow shaft  14  is coaxial with the axis of rotation  27  of the hollow shaft  22 . A radial flange  25  is mounted on the hollow shaft  22  in a manner similar to the radial flange  19  on the hollow shaft  14 . As with the radial flange  19 , the radial flange  25  also provides facilitation of a mounting to either a fixed or rotatable member. 
     As shown in FIG. 1, the leftmost bearing  23  has a radially outwardly extending flange  23 A which is received in a groove  23 B in the support section  21 . A load ring  23 C is threadedly engaged with the support section  21  immediately to the right of the rightmost bearing  23  and, when turned, effects an application of an axial force on the rightmost bearing and directed toward the radial flange  23 A to compress the bearings  23  and the hub for the spur gear  24  therebetween. This axially applied force also removes any unwanted radial play or clearance in the bearings  23  so as to keep the position of the axis of the shaft  22  from varying in the support structure  13 . 
     A similar construction exists for the bearings  16 . Here, the rightmost bearing  16  has a radially outwardly extending flange  16 A thereon received in a not illustrated groove in the support section  13 , which is similar to the groove  23 B in the support section  21 . A load ring  16 B is threadedly secured to the support section  13  to effect, when turned, an application of an axial force toward the radial flange  16 A to compress the bearings  16  and the hub for the spur gear  17  therebetween to accomplish the same objective as was done with the bearings  23 . 
     A plurality of fiber optic strands  28  and  29  forming a bundle  30  are oriented in each of the hollow shafts  14  and  22 . In this particular embodiment, the central fiber optic strand  28  of the fiber optic bundle  30  in each of the hollow shafts  14  and  22  is oriented centrally of the hollow shaft whereas the remaining, here six, fiber optic strands  29  are oriented circumferentially thereof as illustrated in FIG.  6 . Thus, there are present in the disclosed invention a 7-channel rotary joint, each channel being designated by a single fiber optic strand. 
     As is illustrated in FIG. 1, the terminal ends of the fiber optic strands  28  and  29  of the two bundles  30  in each of the hollow shafts  14  and  22  oppose one another through the passageway  12  in the housing  11 . An adjustable prism apparatus  31  is oriented in the signal path transitioning between the terminal ends of the fiber optic strands  28  and  29  in both bundles. The adjustable prism apparatus  31  includes a prism stage  32  best illustrated in FIGS. 2-4. The prism stage  32  includes an elongated base wall  33  and a pair of upstanding and parallel sidewalls  34  and  36  upstanding from the lateral edges of the base wall  33 . The sidewall  36  has a reduced thickness section  37  in which is housed a leaf spring  38  bowing inwardly into the lateral space between the sidewalls  34  and  36 . As is illustrated in FIG. 4, the bottom wall  33  has an opening  39  in generally the central region thereof adjacent the right end. The bottom wall also includes a laterally extending groove  41  adjacent the left end. The groove  41  opens through the bottom portion of the sidewall  36  as at  42 . A pin  43  is received into the opening  42  and the groove  41  so that the upper surface thereof projects above the surface of the bottom wall  33  as illustrated in FIG.  3 . 
     The upstanding wall  32  has at the end thereof adjacent the hole  39  an upstanding groove  44  adapted to receive therein a pin  46  as illustrated in FIG. 2. A hole  47  is provided in the upstanding sidewall  34  adjacent the groove  41 . The aforesaid holes  39  and  47  are adapted to receive a threaded set screw for applying respective forces onto the prism yet to be described. 
     A post  48  depends downwardly from the underside of the base wall  33 . The base wall is also provided with upstanding stops adjacent the longitudinal ends thereof. 
     To accommodate the prism stage  32  in the housing  11 , a region between the terminal ends of the fiber optic strands  28  and  29  the bundles  30  in the respective hollow shafts  14  and  22  includes a recess  51  having upstanding sidewalls, only one sidewall  52  being illustrated in FIG. 2, end walls  53  and  54  and a bottom wall  56 . The bottom wall  56  includes a pocket  57 , polygonal in cross section, with a hole  58  extending from the bottom wall thereof. The hole  58  is adapted to receive an externally threaded set screw. 
     The prism stage  32  is inserted into the recess  51  with the post  48  being slidingly received into the pocket  57 . The sidewalls  34  and  36  of the prism stage  32  slidingly engage the sidewalls  52  of the recess  51 . The post  48  has a polygonal cross section and corresponds to the polygonal cross section of the pocket  57  so as to prevent the prism stage from pivoting about an upright axis defined by the longitudinal axis of the post  48 . 
     A dove prism  61  is received in the space between the sidewalls  34  and  36  of the prism stage  32  as illustrated in FIGS. 1 and 2. Dove prisms are also known as reversion prisms. The entry and exit faces are inclined and are anti-reflection coated. The width of the dove prism is slightly less than the spacing between the upstanding sidewalls  34  and  36  of the prism stage  32  so that the spring  38  will urge the dove prism against the sidewall  34  while maintaining a small space between the sidewall of the dove prism and the sidewall  36  of the prism stage. As a result, a turning of a set screw in the hole  47  will apply a force F 1  to the corresponding side of the dove prism  61  to cause the dove prism  61  to pivot about a vertically upright axis defined by the pin  46 . Similarly, the turning of a set screw in the hole  58  will apply a force F 2  to the bottom end of the post  48  to raise and lower the prism stage  32 . Turning of a set screw in the hole  39  will generate a force F 3  on one end of the dove prism  61  to cause the dove prism  61  to tilt about the axis defined by the pin  43 . A spring  62 , schematically illustrated in FIG. 2 applies a downwardly directed force F 4  onto the top surface of the dove prism  61  so that when the respective set screws in the holes  39  and  58  are backed-off, the spring force F 4  will be sufficient to return the dove prism  61  to an original position thereof. Similarly, a backing off of the set screw in the hole  47  will enable the spring  38  to return the dove prism laterally to the original position thereof about the upright pivot axis defined by the pin  46 . The stops  49  retain the dove prism  61  therebetween and prevent a longitudinal shifting of the dove prism  61  relative to the housing  11 . 
     Utilizing the adjustment features on the prism stage  32 , a signal S 1  exiting the central fiber optic strand  28  in the hollow shaft  14  can be adjusted so that the output signal S 2  from the dove prism  61  will be optimized into the central fiber optic strand  28  oriented in the hollow shaft  22 . Once this has been accomplished, the signal strength from the outer fiber optic strands  29  oriented in the hollow shaft  14  now need to be optimized into the fiber optic strands  29  oriented in the hollow shaft  22 . The following structure accomplishes that objective. 
     As is illustrated in FIG. 1, the thickness of the wall of the housing part  11 A is reduced as at  62  and  63  so that the spur gears  17  and  24  project through their respective gaps  18 ,  20  into the regions  62  and  63 . Three longitudinally extending holes are cut lengthwise through the wall thickness of the housing part  11 A, only two of the holes  64  and  66  being illustrated in FIG.  1 . The third not illustrated hole is immediately adjacent the hole  64 . All three holes open into the respective regions  62  and  63 . 
     Turning now to FIG. 5, the hole  66  receives therein an elongate shaft  67  rotatably supported on spaced bearings  68 . A spur gear  69  is secured to the end of the shaft  67  adjacent the exposed portion of the spur gear  17  projecting through the gap  18 . 
     An elongate shaft  71  is received into the hole  64  and is rotatably supported thereon by axially spaced bearings  72 . A spur gear  73  identical to the spur gear  69  is secured to the right end of the shaft  71  and is oriented adjacent the exposed portion of the spur gear  24  projecting through the gap  20 . A spus gear  74  secured to the end of the shaft  71  adjacent both of the spur gears  17  and  69  and has a sufficient width to enable the teeth thereof to mesh with the teeth of the spur gears  17  and  69 . A spring  76 , schematically illustrated in FIG. 5, applies a force F 5  on the bearing  72  to urge the spur gear  74  into tight engagement with the teeth on both of the spur gears  17  and  69  so as to eliminate any backlash that might be present therebetween. 
     A unique feature of the gear  74  is that it is secured to a collet mechanism  77  which supports the gear  74  for rotation with respect to the shaft  71 . The gear  74  can be rendered fixed to the shaft  71  by tightening the screw  78  on the collet mechanism  77 . In other words, a loosening of the screw  78  will enable the collet to slip with respect to the shaft  71  thereby enabling the gear  74  to freely rotate with respect to the shaft  71 . 
     An elongate shaft  79  is received into the hole  65  o 
     (FIG.  5 ), namely, that hole which is behind the shaft  64  illustrated in FIG. 1, and is rotatably supported in the hole  65  by axially spaced bearings  81 . A gear  82  identical to the gear  74  is fixedly secured to the end of the shaft  79  adjacent the exposed portion of the spur gear  24  projecting through the gap  20  and the spur gear  73 . In fact, the teeth on the spur gear  82  are meshed with the teeth on the spur gears  24  and  73 . A spring  83 , schematically illustrated in FIG. 5, applies a force F 6  onto the bearing  81  adjacent the spur gear  82  so as to effect an urging of the teeth of the spur gear  82  into a tightly meshed relation with the teeth on the spur gears  24  and  73  in order to eliminate any backlash that may be present therebetween. 
     FIG. 7 shows very schematically the loading scheme for achieving an antibacklash condition for all three gears. This loading scheme applies to gears of differing diameters as long as the pitch of the teeth is the same. Note that gears  17 ,  24  and  69 ,  73  are not in the same plane and do not mesh. Gears  74 ,  82  are long enough (into the page) to mesh with both gears  17 ,  24  and  69 ,  73 . Gears  17 ,  24  and  69 ,  73  have fixed rotation centers. Thus, gears  74 ,  82  cannot have a fixed rotation center since small eccentricities in manufacture would cause very high stresses in the gear teeth that would cause high friction, yield in the metal tooth face, or both. The gears and their respective shafts are simply too rigid to allow for even small eccentricities in the gears. 
     A lateral load is supplied by a spring which is designed to be compliant enough not to yield while supplying enough load to maintain two tooth contact between gears  17 ,  24  and gears  74 ,  82  and gears  69 ,  73  and gears  74 ,  82 . 
     FIG. 8 shows the effect of this arrangement. The pitch circle of gears  74 ,  82  rides in the v-angle formed by the two tangent lines of contact. Traditionally, antibacklash is achieved by using two gears in a scissors arrangement, but this type of antibacklash device cannot maintain the antibacklash effect between two gears simultaneously. The device presented here can. It also has an advantage in that the spring used to provide the lateral load can be designed independently of the gear set. Thus, the spring load can be corrected to an appropriate setting without starting from scratch on the gear set. 
     Since the adjustable prism apparatus  31  described above has facilitated an optimization of the signal strength transfer between the central fiber optic strand  28  in the fiber optic bundle  30  oriented in the hollow shaft  14  to or from the central fiber optic strand  28  in the fiber optic bundle  30  oriented in the hollow shaft  22 , the next adjustment that needs to occur is an optimization of the signal strength transfer between the outer fiber optic strands  29  in both bundles. This adjustment is accomplished in the following manner. The screw  78  is loosened so that the collet mechanism  77  facilitates the free rotation of the spur gear  74  relative to the shaft  71 . As a result, the spur gear  24  can now be rotated relative to the spur gear  17  until signal strength optimization occurs with the outer fiber optic strands  29 . Once signal strength optimization has occurred, the screw  78  is again tightened to lock the spur gear  74  to the shaft  71 . Any relative rotative movement between the hollow shafts  14  and  22  will not negatively affect the aforesaid obtained signal strength optimization. Thus, if the radial flange  25  is secured to a rotating object and the flange  19  is secured to a fixed object, data can be effectively transmitted from the respective fiber optic bundles without any loss of signal optimization. During a relative rotation between the respective radial flanges  19  and  25 , it is to be understood that the housing  11  is also rotating about the axes  26  and  27 . This rotation of the housing  11  is caused by the spur gear  24  rotating relative to the spur gear  17  to cause the spur gears  82  and  73  to transmit a rotative force through the shaft  71  to the spur gear  74  to the teeth on the fixed spur gear  17 . As a result, the rotating spur gear  74  will effect a rotative drive of the housing  11  in a direction of rotation that is the same as that of the spur gear  24  but half as fast. 
     Although a particular preferred embodiment of the invention has been disclosed in detail for illustrative purposes, it will be recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.