Fiber Optic Rotary Joint

The present invention is in the field of rotary joints or connectors for passing optical signals or other power or communication media through an interface between a stationary and a relatively rotating reference frame.

The field of fiber optics for conveying of communication data, voice, and data pulse trains has expanded greatly in recent years. The use of fiber optics transmission techniques is now well accepted in the telephone and data transmission arts. Optical multiplexing to enable each fiber to carry a great multitude of data and voice channels is well understood.

However, several technologies require the passage of power or communication signals (voice or data streams) across an interface between a rotary reference frame and a non rotary or stationary reference frame. One such application is the instrumentation of rotary devices, such as the rotors of electrical generators, when it is desired to collect stress, vibration, temperature, pressure, and other data form the apparatus in operation. In such a case, the necessary sensors and transducers mounted on the rotor of the apparatus, many of which are electrical, may have their data converted to optical signals, and passed through an optical rotary joint during operation of the apparatus. Similarly, command signals for the test apparatus on the rotor may be passed across the joint to the electrical test instruments while the apparatus is in operation. The techniques of optical multiplexing allow a limited number of optical fibers to suffice in this usage.

A conventional fiber optic rotary joint is provided by Focal Technologies of Dartmouth, Nova Scotia, Canada, which allows up to 10 optical fibers to feed into and out of the joint. This rotary joint permits unlimited members of rotations between the stationary and rotary parts of the joint. However, as noted above, the sensors and control devices aboard the rotating reference frame may be electrical powered, in which case either an on board power source must be provided, or power must be fed to the rotary apparatus another way. To this end, frequently, a fluidic, or electrical slip ring device is used in conjunction with a conventional fiber optic rotary joint. In the former case, the fluidic slip ring may simply carry pressure signals to a non rotational interpretation, recording, or indicating device. In the latter case, the electrical slip ring is employed to feed electrical power onto the rotary device, there to power electrical sensors, as well as the electrical-to-optical converters and optical multiplexing devices.

However, there exists a desire to provide communication with a device associated with a relatively rotating reference frame, which device is entirely optically powered. That is, only optical signals are to cross the rotating-stationary interface to and from the device. Further, in connection with the definition of this need it appears that unlimited numbers of relative rotations of the rotary reference frame are not required. A limited number of rotations of the rotary frame in each direction of rotation will suffice.

More particularly, a need exists to provide communication from a stationary frame to a plurality of sensors arrayed along a length of elongate sensor-carrier cable reeled upon or unreeled from a storage drum. Because the sensor-carrier cable is of finite length, a sufficient number of rotations of the storage drum to completely reel and unreel the cable will suffice. This use may require from a few turns to a few hundred turns of the storage drum. However, an unlimited number of turns of the storage drum is not required. However, communication with the sensors on the cable must be continuous, without interruption while or alteration of the transmittal optical signal the storage drum turns or is stationary. Communication to be provided may be via optical fibers, or with the use of electrical conductors, or other communication media conduits.

In view of the above, the present invention provides a rotary joint having a pair of coaxial and radially congruent annular surface-defining bodies which are relatively rotatable. The two bodies define radially disposed circumferential surfaces confronting one another across a radial gap defined therebetween. In the radial gap a flexible shape-retaining carrier ribbon extends spirally from the one body to the other. The carrier ribbon includes at least one conduit member extending continuously from end to end. The conduit member may be an optical fiber, or optionally may be an electrical conductor or fluid conduit. Each of the bodies has means for interfacing the one or more conduit members of the carrier ribbon with like conduits extending externally of the joint apparatus. Finally, each one of the bodies of the rotary joint is fixably associated with a respective one of a pair of relative rotatable reference frames.

More particularly, one of the bodies of the inventive rotary joint may be secured to a winch frame while the other body of the joint is rotational with the winch drum. A sensor-carrier cable on the winch drum is communicable with the non rotational reference frame where the winch apparatus is mounted via the conduit members of the rotary joint.

FIG. 1 is a perspective view of an optical rotary joint embodying the present invention;

FIG. 2 provides a partially cross sectional view taken generally along arrow 2--2 of FIG. 1, and viewing in the direction of the arrows;

FIG. 2A provides a fragmentary sectional view of the structure shown within the encirclement referenced on FIG. 2, and with component parts shown in alternative relative positions to better depict salient features of the invention;

FIG. 3 is a fragmentary cross sectional view taken at line 3--3 of FIG. 2.

FIG. 4 depicts a partial exploded assembly view of a component of the inventive apparatus; and

FIG. 5 schematically depicts on electrical circuit embodied partially in the apparatus illustrated by FIGS. 1-4.

FIGS. 1-3 in conjunction illustrate a fiber optic rotary joint 10 embodying the present invention. Joint 10 includes a two part housing, generally referenced with the numeral 12. In order to sealingly secure the two parts of the housing 12 together, both the generally cup-shaped front part 14, and the plaiar back plate 16 of the housing 12 includes a plurality of circumferentially arrayed bosses 18. At the bosses 18, the housing defines respective bores 20 for receiving fasteners, such as bolts (not visible in FIG. 1). As mentioned, the housing 12 includes a cup-shaped first portion 14, and a generally planar back plate or closure member 16, spanning and closing the open end 22 of the first portion 14.

At the end of housing 12 opposite the opening 22, the housing defines a central axially disposed mounting face 24. The mounting face 24 includes plural bolt holes 26 whereby the housing portion 14 may be secured to a non-rotational mounting frame.

Protruding axially from the center of the mounting face 24, the housing portion 14 includes an elongate bearing and seal carrier boss referenced with numeral 28. Internally of the boss 28, a rotational armature member generally referenced with numeral 30, is freely rotationally and sealingly received. Outwardly of the armature member 30 protrudes a multi-filament fiber optic cable, referenced with numeral 32. The cable 32 is secured to the armature member 30, and because the latter is freely rotational relative to rotary joint 10, the fiber optic cable 32 is also freely rotatable relative to the stationary structure to which the housing 12 is secured.

Viewing more particularly FIG. 2, it will be seen that the housing 12 opposite the mounting face 24, and at the opening 22, defines an axially extending cylindrical recess 34. Recess 34 is cooperatively defined by a back wall 36, and a cylindrical, annular wall 38. The wall 38 defines a radially inwardly disposed annular surface 40.

Centrally of the recess 34, an inner end portion 42 of armature member 30 extends rotationally into the recess 34 toward but short of the back plate 16. The inner end portion 42 defines a radially outwardly disposed annular surface 44 (only a part of which is visible in FIG. 2) which is radially congruent with the annular surface 40. In other words, the surfaces 40 and 44 define a radially extending annular gap, therebetween, which is generally referenced with the numeral 46.

Spirally disposed in the gap 46 within recess 34, is a length of generally flat and flexibly shape-retaining fiber-carrier ribbon 48. The ribbon 48 secures to the outer surface 44 of armature end portion 42 and extends spirally through several rotations outwardly to secure to the inner surface 40 of wall 38. The ribbon 48 is slightly smaller in width than the depth of recess 34 from back wall 36 to the inner face of cover plate 16. Consequently, the ribbon 48 is freely movably captured in the recess 34. That is, ribbon 48 may freely move radially inwardly and outwardly between the surfaces 40 and 44 within the constraints imposed by its own spiral disposition in recess 34. At its inner end, the ribbon 48 is associated with the fiber optic cable 32, while at its outer end the ribbon is associated with an optical fiber connector 50 disposed outwardly on wall 38.

Turning now to FIG. 3, a cross section of the fiber-carrier ribbon 48 reveals that the latter is composed of a first, and a second layer of flexible, but shape-retaining Mylar or Kapton tape, referenced with numerals 52 and 54, respectively. Between the tapes 52-54, is disposed a layer of elongate parallel optical fibers, 58. The optical fibers 58 individually connect with respective optional fibers of the optical cable 32, and with individual optical fibers of connector 50. The element 52-58 are secured together with adhesive (not shown).

Consequently to the above, the fiber optic cable 32 may be connected with a rotational structure, for example, a sensor-carrier cable on a winch drum. The housing 12 may be carried by a non-rotational frame of the winch. As the winch drum turns to reel and unreel cable from the drum the optical cable 32 and armature 30 are freely rotational relative to the housing 12. As the armature 30 turns in one direction or the other relative to housing 12, the fiber-carrier ribbon 48 winds up or unwinds in its spiral configuration. That is, as depicted in FIG. 2, clockwise rotation of the armature 30 will result in a greater part of ribbon 48 unspiraling against the outer wall 38 at surface 40. Conversely, counterclockwise rotation of the armature 30 will spiral the ribbon 48 more tightly upon the surface 44 of end portion 42.

As presented by way of example, a winch with a length of cable reeled thereon requires only a finite number of turns of the winch drum to completely unreel or to completely reel up the cable. Because the tape 48 is comparatively thin (approximately 0.010 inch) while the gap 46 may be on the order of several inches, or more, there is room within recess 34 for a multiturn spiral of tape 48. While the fiber optic rotary joint 10 can not provide an unlimited number of turns between the armature 30 and housing 12, many applications for rotary connectors and joints do not require more than a finite number of turns of the joint. In these applications the rotary joint 10 embodying the present invention offers several advantages. By way of example again, the joint 10 allows a far greater number of optical fibers to pass through the rotary interface than do conventional joints. For example, forty to five-hundred or more optical fibers can be accommodated by the inventive optical rotary joint. Rotation of the rotary joint does not interface with optical communication therethrough. Also, the housing 12 provides very rugged environmental protection for the rotary joint, and may be pressure sealed to allow a pressure differential between the rotary and stationary environments which the joint connects.

Returning once again to FIG. 3, it will be seen that the ribbon 48 includes between the tapes 52, 54, and among the fibers 58, three flexible electrical conductors 60-64. The conductors 60-64 are insulated from one another. FIG. 4 provides an illustration of the armature member 30 and its connection with the inner end of ribbon 48 and transition to optical cable 32. Viewing FIG. 4, it is seen that the armature member 30 defines a partially crescent-shaped recess 66. Into the recess 66 are received, in sequence, the inner end of ribbon 48, a partially crescent-shaped key member 68, and an end 70 of a circumferentially extending leaf spring 72. A threaded fastener 74 passes through a bore 76 of the armature member 30, and threadably engages the key 68 to retain the latter, ribbon 48 and spring 72 in recess 66. The ribbon 48 exits recess 66 along an accurate surface 78 thereof to be disposed circumferentially about the outer surface 44 of armature member 30 depicted by arrow 78'. Similarly, spring 72 is clamped at end 70 thereof between the key 68 and a radially extending surface 80 of the recess 66. An external portion 82 of spring 72 circumscribes the surface 44 of armature 30 to yieldably urge the ribbon 48 into engagement wit the surface 44. On a surface of ribbon 48 confronting the armature member 30 at the surface 44 thereof is a pair of electrically conductive contact pads 84, 86. These contact pads 84, 86 are urged into electrically continuous contact with a conductive contact zone 88 on the surface 44 of armature 30.

Returning to FIG. 2, and viewing fragmentary view 2A also, the housing 12 at front part 14 includes a circumferentially extending leaf spring 90 urging an outer end portion of the tape 48 yieldably outwardly toward surface 40 depicted by force arrow 90'. Similarly to the tape segment seen in FIG. 4, the tape segment overwinding.

FIG. 5 depicts an electrical circuit 94 for safeguarding the fiber optic rotary joint 10, and which includes the conductors 60-64 of the ribbon 48. Viewing FIG. 5, it will be seen that the circuit 94 includes electrical contacts 86 and 88, which are engageable by contact zone 88 to normally close a circuit including conductors 62, 64. Similarly the contacts 96, 98 are normally closed by contact zone 92 (recalling FIG. 2A to complete the circuit of conductors 60, 62. Respective indicators 100, 102 respond to lose of continuity in either of the circuits described, and interface with disabling means (not shown but depicted by dashed lines 104) to stop further relative rotation of the armature seen in FIG. 2A includes a pair of electrical contact pads, which are not visible in the Figure, but which confront an electrical contact zone 92 on surface 40 of wall 38. The normal operative condition of the rotary joint 10 is with the contact pads 84, 86 of FIG. 4, and the pads described by reference to FIG. 2A electrically connecting by the contact zones 88 and 92, respectively. So long as the armature member 30 is not rotated an excessive number of turns in either direction relative to housing 12, this normal operative condition will be pressured by the yieldable bias of the springs 72 and 90. However, if the armature 30 is overwound in either direction, the ribbon 48 will be pulled away from surface 40 or 44, dependent upon the direction of 30 and housing 12.