Abstract:
The present invention is a limited rotation through-bore optical slip ring. This will enable one or more optical signals to pass across a rotational interface while leaving a center bore free. The present invention is passive, unlike many off axis or through bore optical slip rings and is low loss by nature.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This application claims priority of U.S. Provisional Patent Application No. 61/365,977, filed date: Jul. 20, 2010. 
         [0002]    The present invention relates generally to the field of apparatus for fiber optic communication, and more particularly, to through-bore fiber optic slip ring to provide transmission of an optical signal through a mechanically rotational interface with a through-bore. 
         [0003]    An optic device to transmit optic signal from a rotating member to a stationary member is called fiber optic rotary joint, or fiber optic slip ring. There are many different types of fiber optic rotary joint, or fiber optic slip ring. They can be a single-channel, multi-channel, and hybrid one (electrical/optical). Fiber optic rotary joint, or fiber optic slip ring are generally categorized as either an on-axis or an off-axis type. In an on-axis fiber optic rotary joint the optic signal occupies the central space along the axis of rotation. In an off-axis type, the central space along the rotational axis is not accessible and the optic signal would not be allowed to path through this central space along the rotational axis. Usually there is a through bore along the rotational axis to provide routing space for hydraulics, pneumatics, RF, or other physical media. So the off-axis fiber optic sip ring is also called through-bore fiber optic slip ring. Application examples of through-bore fiber optic slip ring, include CT scan, MRI scan, tank turret, marine propulsion systems, helicopters, machine tools, and winches. While some of these applications require an infinite number of rotations in both directions others, such as a winch, only require a limited number of rotations in either direction. 
         [0004]    Most of the single channel on-axis fiber optic rotary joint need two relatively rotatable members to hold two ends of optic fibers, one on each side of the rotating interface that are opto-mechanically aligned along the common rotational axis. By employing the expanded beam technology, the light beam from the fiber is expanded when it is coupled through the rotational interface. The light beam is then refocused and aligned with the receiving fiber. The details are described in U.S. Pat. Nos. 5,039,193, 4,124,272, 5,633,963, and 5,949,929. 
         [0005]    Most of multi channel on-axis fiber optic rotary joints also include two relatively rotatable members to hold two bundles of optic fibers, one on each side of the rotating interface, which are mechanically arranged around the common rotational axis. By using the expanded beam technology and de-rotating technology, like a Dove Prism, the light beams from fiber bundles can be transmitted through the rotational interface. The details are described in U.S. Pat. Nos. 6,301,405, 5,157,745 and 5,271,076. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  shows a cross section view of the mechanical embodiment of a preferred embodiment of an through-bore fiber optic slip ring of present invention; 
           [0007]      FIG. 2  illustrates how the optical fiber ( 11  in  FIG. 1 ) is wound around the rotor spool ( 1 ) and the off-axis spool ( 40 ); 
           [0008]      FIG. 3  is a cross section view of another preferred embodiment of a through-bore fiber optic slip ring. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0009]    As shown in  FIG. 1 , a preferred embodiment of an through-bore fiber optic slip ring in the present invention comprises a rotor spool ( 1 ), a off-axis spool ( 40 ), housing members ( 2 ), ( 3 ), and ( 4 ), a control rotor ( 75 ), a slider ( 77 ), a rod ( 78 ), on-axis fiber optic rotary joint members ( 45 ) and ( 49 ), bearings, ( 5 ), ( 6 ), ( 73 ), ( 74 ), ( 43 ) and ( 44 ), optic fibers, or optic cables, ( 11 ) and ( 50 ). 
         [0010]    Rotor spool ( 1 ) has an axial through bore ( 70 ), includes two flanges, facing each other and separated by a cylindrical barrel ( 7 ). An optic fiber ( 11 ) stored on the rotor spool ( 1 ) is wound around the barrel ( 7 ). The rotor spool ( 1 ) is mounted within the housing members ( 2 ), ( 3 ), and ( 4 ) through a pair of bearings ( 5 ) and ( 6 ) so that the rotor spool is rotatable relative to the housing members ( 2 ), ( 3 ), and ( 4 ). 
         [0011]    The off-axis spool ( 40 ) includes two flanges, facing each other and separated by a cylindrical barrel ( 46 ). The optic fiber ( 11 ) stored on the off-axis spool ( 40 ) is wound around the barrel ( 46 ). The off-axis spool ( 40 ) is supported by a pair of bearings ( 43 ) and ( 44 ) between holder ( 41 ) and ( 42 ), which are secured in the housing members ( 2 ), ( 3 ), and ( 4 ). The rotational axes ( 10 ) of the rotor spool ( 1 ) and ( 20 ) of the off-axis spool ( 40 ) are parallel each other. 
         [0012]    A pair of gears ( 61 ) and ( 62 ) is made as part of one of the flanges on rotor spool ( 1 ) and one of the flanges on off-axis spool ( 40 ) respectively. The gear ( 61 ) and ( 62 ) are engaged with each other and is selectively designed so that the off-axis spool ( 40 ) would rotate in a reverse direction as that of the rotor spool ( 1 ). 
         [0013]    A single channel on-axis fiber optic rotary joint usually has a rotor member ( 45 ) and stator member ( 49 ), which are secured in the central area of the off-axis spool ( 40 ) and the central area of one of the holder ( 42 ) or ( 41 ) respectively. The optic signal can be transmitted through the rotational interface between the off-axis spool ( 40 ) and the holder ( 42 ) or ( 41 ). The single channel on-axis fiber optic rotary joints are available on market. 
         [0014]    The control rotor ( 75 ) is supported by bearing ( 73 ) and ( 74 ) and is rotatable by the engagement of gear ( 76 ) and gear ( 61 ). In the middle portion of the control rotor ( 75 ) is the ball screw ( 80 ), which drives slider ( 77 ) to move along rod ( 78 ). There are two surfaces ( 81 ) and ( 82 ) on control rotor ( 75 ). If the slider ( 77 ) contact with either surfaces ( 81 ) or ( 82 ), it would make the whole system stop moving. The pitch of ball screw ( 80 ) and the distance between surfaces ( 81 ) and ( 82 ) should be determined by the total fiber length used in the system. Different application requires different fiber lengths. 
         [0015]      FIG. 2  illustrates how the optical fiber ( 11  in  FIG. 1 ) is wound around the rotor spool ( 1 ) and the off-axis spool ( 40 ). 
         [0016]    It is to be understood that the size of the optical fiber relative to barrels ( 7 ) and ( 46 ) is somewhat exaggerated for better illustrating the effects upon the optical fiber as its being wound on and off barrels ( 7 ) and ( 46 ). 
         [0017]    Without loss of generality we shall assume the optical fiber is wound around the barrel ( 7 ) in clockwise direction for a couple of layers. Then after straight section ( 60 ) of the fiber it wound around barrel ( 46 ) in counterclockwise direction for more layers. The fiber end of the optical fiber is opto-mechanically secured with the rotor member ( 45  in  FIG. 1 ) of an on-axis fiber optic rotary joint. 
         [0018]    So when the rotor ( 1 ) rotates clockwise the off-axis spool ( 40 ) would rotate counter-clockwise due to the engagement of gears ( 61 ) and ( 62 ). The optic signal would go through the optical fiber to the rotor member of on-axis fiber optic rotary joint and coupled into the stator member ( 49  in  FIG. 1 ), then exit from optical fiber ( 50  in  FIG. 1 ). If the signal were to originate in other optical fiber ( 50  in  FIG. 1 ) then the signal would travel the same path but in reverse. 
         [0019]    Another preferred embodiment of a through-bore fiber optic slip ring in the present invention is illustrated in  FIG. 3 . It is a two-channel through-bore fiber optic slip ring, in which the fiber cable ( 12 ) includes  2  fibers—fiber ( 47 ) and fiber ( 48 ). The fiber cable ( 12 ) is wound around the rotor spool ( 1 ) and the off-axis spool ( 40 ) in the same way as optical fiber ( 11  in  FIG. 1 ) is shown in  FIG. 2 . The second single channel on-axis fiber optic rotary joint has a rotor member ( 55 ) and stator member ( 52 ), which are secured in one side of the central area of the off-axis spool ( 40 ) and the central area of one of the holder ( 41 ) respectively. The  2 -channel optic signals can be transmitted from the fiber cable ( 12 ) to the rotor members ( 45 ) and ( 55 ) through fibers ( 47 ) and ( 48 ) respectively, then coupled into the stator members ( 49 ) and ( 52 ) and exit from fibers ( 50 ) and ( 51 ) respectively. Vise versa. The single channel on-axis fiber optic rotary joints are available on market. 
         [0020]    Obviously the continuous bi-directional rotation of rotor ( 1 ) relative to housing ( 2 ) is limited by the length of fiber ( 11  in  FIG. 1 ), or the fiber cable ( 12  in  FIG. 3 ). 
         [0021]    The above-described embodiments of the present invention can be modified by replacing the single fiber with a fiber bundle and using any multi channel on-axis fiber optic rotary joint to replace the single channel on-axis fiber optic rotary joint in  FIG. 1 , or  FIG. 2  to achieve a multi-channel through-bore fiber optic slip ring, in which the fiber cable  12  would include multi-fibers and at the rotational interface between  45  and  49 , or between  52  and  55 , there would be a de-rotating mechanism.