Abstract:
A machine for winding, in a selected and consistent manner, a fiber optic lament on a compliant elastomeric mandrel, which assembly responds to acoustic waves by producing variations in diameter and light transmission characteristics of the fiber optic means. A motor rotates the mandrel at a selectable speed. A timing belt couples the mandrel rotation to a traversing mechanism supporting an optical fiber carrying reel and is adjustable to variably convert the rotary to linear motion. The shaft supporting the reel has brake means for adjusting the tension on the fiber. The fiber feeds over an idler roll which operates to count the number of meters of fiber wound on the mandrel, and then passes under a tension sensing roll. By varying mandrel rotation speed, traversing speed and reel drag, compliant hydrophone mandrels can have optical fibers wrapped therearound having many different fiber lay angles and fiber tensions, thus permitting production of hydrophones of desired characteristics.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates to a precision optical fiber winding device and more particularly to a winding machine which permits precise control of reel drag, traversing speed, mandrel rotation speed, fiber tension and fiber lay angle. 
     (2) Description of the Prior Art 
     Certain interferometric optical hydrophones are based upon the phenomena that an optical fiber, when elongated, will alter the characteristics of the light transmitted in proportion thereto. A compliant, cylindrical mandrel such as a nylon rod or the like, when circumferentially wrapped with optical fiber, can take advantage of this phenomenon. This wrapped elastomeric mandrel, when exposed to an acoustic pressure, changes its length and, due to Poisson Effects, diameter. The optical fiber, being prestretched by tightly wrapping it around the mandrel, follows these diameter changes and thus elongates or contracts the optical path length in proportion to the acoustic signal. By way of example, a more complete description of a typical fiber optic hydrophone is set forth in U.S. Pat. No. 4,238,856. 
     At present interferometric hydrophones have mandrels handwrapped with the delicate optical fiber. A significant drawback of the handwrapped hydrophone is the lack of repeatable performance between one hydrophone and the next. This is because once mandrel material has been chosen, hydrophone performance depends strongly on two constructional parameters. First, the amount of initial fiber elongation present after the winding process dictates how easily the fiber will continue to elongate as the mandrel diameter increases or shrinks with diameter reduction. This fiber prestretch is directly controlled by the amount of back tension applied as the fiber is wound onto the mandrel. Handwrapping the fiber does not allow sufficient tension control during this initial fiber elongation. The second constructional parameter governing hydrophone performance is the distribution pattern of the fiber along the length of the mandrel. This fiber density is entirely dependent upon the lay angle of the fiber as it is wound onto the mandrel. Handwrapping does not permit the angular control necessary for consistent performance from hydrophone to hydrophone. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general purpose and object of the present invention to provide an interferometric fiber optic hydrophone winding machine able to consistently wind delicate optical fibers onto compliant hydrophone mandrels without any degradation of the fiber properties. Another object is that the winding machine be able to vary two important parameters which strongly influence optical hydrophone performance, i.e., fiber lay angle and fiber pretension, thereby permitting the winding machine to serve as a research tool in optimal hydrophone design. A further object is that such a winding machine be able to employ single mode or multimode optical fiber. A still further object is that the machine be capable of producing a plurality of hydrophones having identical performance characteristics. 
     These objects are accomplished with the present invention by providing an interferometric fiber optic mandrel hydrophone winding machine comprising a rigid baseplate having mounted thereon hydrophone mandrel mounting means, optical fiber dispensing means attached to an adjustable traversing mechanism, electric motor means for rotating the mandrel and driving the traversing mechanism, and control panel means for controlling the winding operation and displaying optical fiber length and tension status. The optical fiber dispensing means includes a fiber reel stand, attached to the traversing mechanism, a journal mounted fiber reel, an idler roll and a lead roll, all bearing mounted thereon. Fiber tension is controlled by adjusting the drag on the reel shaft while a tension assembly attached to a force gage permits digital readout of fiber tension at the control panel. A microswitch operated pulse counter device operating in conjunction with the idler roll monitors the total fiber length already wrapped on the mandrel. By controllably varying mandrel rotation speed, reel stand traversing speed and direction, and reel drag, compliant hydrophone mandrels can thus have optical fibers wrapped therearound having preselected fiber lay angles and fiber tensions. This either permits a plurality of hydrophone variants to be produced for research programs or if desired allows production of large quantities of identical hydrophones. 
    
    
     A more complete understanding of the invention and many of the attendant advantages thereto will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a front view of a fiber optic hydrophone winding machine built according to the teachings of the present invention. 
     FIG. 2 is a top view of the winding machine of FIG. 1. 
     FIG. 3 is a sectional view of the device shown in FIG. 2 taken along line 3--3 thereof. 
     FIG. 4 is a sectional view of the device shown in FIG. 1 taken along line 4--4 thereof. 
     FIG. 5 is a cross-sectional view of the mandrel gripping device with mandrel inserted taken along line 5--5 of FIG. 2. 
     FIG. 6 illustrates the cam actuated micro switch which feeds the meters counter, viewed along line 6--6 of FIG. 2. 
     FIG. 7 is a block diagram of the electrical control system of the present invention. 
     FIG. 8 is a circuit diagram of the divide-by-six functional block of FIG. 7. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1 there is shown a front view of an interferometric optical hydrophone winding machine 10 comprising a rigid horizontal base plate 12 having first and second rigid vertical side plates 14 and 16 spaced a preselected distance apart and fixedly attached thereto. Side 14 and 16 are each braced by a plurality of rigid gussets 18 affixed so as to maintain 90° alignment with respect to plate 12 while remaining essentially parallel and coaxial to each other. Plates 12, 14 and 16 may be of any strong, lightweight material although aluminum is preferred. In addition to alignment considerations, such plate mounting of machine 10 also provides for machine portability without requiring disassembly. A long threaded shaft 20 passes through threaded support 21 which is fixedly attached to vertical plate 14 having the axis thereof parallel to plate 12. Shaft 20 has attached thereto a handle 22 and is used to center one end of compliant hydrophone mandrel 24. The other end of mandrel 24 is gripped by a collet housed within a bore in shaft 26, the collet being compressed by the knurled compression nut 28. A reel 30 is mounted atop an adjustable traversing mechanism 32. Reel 30 has a preselected length of optical fiber 34 wrapped therearound. Traversing mechanism 32 is coupled to shaft 26, via a timing belt 36 housed beneath belt guard 38 which may be aluminum or the like. An electric motor 40 is geared down and clutch coupled to shaft 26 which holds mandrel 24. 
     Machine 10 is operated using control panel 42. Power is supplied to machine 10 through main power switch 44. An emergency stop button 46 permits disengagement of electrically engaged clutch 48 at any time. Jog button 50, a momentary contact switch, allows the machine operator to incrementally rotate mandrel 24 to an appropriate starting position. An upper digital counter 52 is a preset type such as an Electronic Counters and Controls Inc., (ECCI) Model MU115A-1. The desired number of meters is set using a series of thumbwheels 52a. Display 52b shows the total number of meters of fiber that has been wound onto mandrel 24. Upon reaching the desired preset fiber length, counter 52 deactivates a relay coil disengaging drive shaft clutch 48. Button 52c is a reset device which zero&#39;s out display 52b. Lower counter 54, which may be an ECCI Model MU105A-1 or the like, totalizes and displays the number of revolutions of drive shaft 26, and hence mandrel 24, which is used as a check on the &#34;meters&#34; display 52b. A potentiometer 56 is used to regulate the mandrel rotational speed over a preselected range, e.g., from 0.4 to 12 revolutions per minute. Potentiometer 56 may be part of panel 42 or may be fixedly attached to the side of panel 42 within a separate box 57 such as a Boston Gear Ratiopax or the like. 
     Variable speed motor 40, controlled by motor run switch 58, attaches to the rear face of electrically operated clutch 48 through a suitable reduction gear box 60 having an output shaft 62. A clutch guard 64 fixedly attached to and protruding from belt guard 38, has mounted thereon a proximity switch 66, which provides the count pulse for &#34;totalizer&#34; counter 54 by sensing the number of times indicator 68 passes by. 
     Optical fiber reel 30 is mounted atop a traversing mechanism 32 which permits changes of optical fiber pitch angles and hence mandrel fiber density. While any rotary to linear motion converter may be used, a preferred variable mechanism is a Uhing Variable Pitch Traverses, Type RG 20/25, available commercially from Amacoil Machinery Inc. where the angle changes are accomplished by setting a control lever 69 at the desired position on dial 70. In such a unit rolling rings, controlled by lever 69, convert the rotational motion of shaft 71 driven by belt 36 into to linear travel parallel to the axis of mandrel 24. Shaft 71 is supported at either end by vertical members 72 fixedly attached to plate 12. A pair of limit stops 73 are moveably mounted on traverse rod 74 which is parallel to shaft 71 and is also supported at each end by members 72. A reversing mechanism 75, located on the underside of traversing mechanism 32, upon encountering a limit stop 73 reverses the direction of traverse of mechanism 32. A third cross member 76, parallel to shafts 71 and 74, further adds strutural support. 
     Fiber reel 30 is mounted on a reel stand 77 which is fixedly attached to the top of traversing mechanism 32. Stand 77 further comprises a pair of vertical members 77a  fixedly attached to horizontal member 77b Fiber 34 is fed from reel 30 the shaft of which rotatably mounts in journals having hinged top sections 78 to provide easy removal. Knurled captive screws 80 with springs 82 are used to provide adjustable drag on the reel shaft and thus act as a braking system for controlling tension in fiber 34. Fiber 34 is fed from reel 30 over an idler roll 84 which is arranged so as to provide the meter count for counter 52 of control panel 42. This meter count is provided by counting pulses from a microswitch 86 fixedly attached to one vertical member 77a. Six electrical pulses from switch 86 are stored in an appropriate circuit before one pulse is sent to counter 52 which increments the count by one meter. Switch 86 is connected to counter 52 via cable 88. The output signals of proximity switch 66 are transmitted by cable 90 to totalizer counter 54. Dead shaft 20 has a live center 92 housed in the working end thereof to assist in holding mandrel 24 steady during the winding operation. The length of threaded shaft 20 is selected to accommodate winding of mandrels of varying length. Motor 40 is supported by motor support stand 94 which is fixedly attached to plate 12. 
     FIG. 2 shows a plan view of the machine of FIG. 1. From idler roll 84, fiber 34 is fed to a tension assembly 100. Assembly 100 is pivotably mounted on ball bearings at locations 102 and 104. Fiber 34 is fed under a tension roll 106. Roll 106 runs essentially parallel to mandrel 24 and also to a readout roll 108. Rolls 106 and 108 are secured at each end thereof to cross members 110 and 112 respectively thereby forming the rectangular frame which is tension assembly 100. The distance from locations 102 and 104 to rolls 106 and 108 are equal such that a movement of roll 106 causes an equal and opposite movement of roll 108. The tension assembly readout roll 108 is attached to a force gage 114 which provides a digital readout of fiber 34 tension. Knurled captive screws 80 are loosened or tightened to alter this tension. Tension roll 106 is preferably made of aluminum with a finish of teflon impregnated hard coat anodize. This permits lateral motion of fiber 34 with minimal tension changes and/or abrasion of fiber cladding. From tension roll 106, fiber 34 is then fed over lead roll 116 and onto mandrel 24. Lead roll 116 has an annular groove 118 at the midpoint thereof so that fiber 34 is maintained at the same spatial location relative to traversing mechanism 32 when passing onto mandrel 24 thus providing a constant pitch. Both lead roll 116 and idler roll 84 are bearing mounted. Movement of traversing mechanism 32, in the direction shown by the arrow, at a constant traverse rate causes fiber 34 to be wound onto mandrel 24 at a pitch angle θ. Motor support stand 94 is shown to have a circular cross section for the vertical member thereof. This cross section is optional and may be varied. 
     FIG. 3 shows in cross section the path which fiber 34 traverses during a typical winding operation. Fiber reel 30 plays out fiber 34 which passes over idler roll 84, then under tension roll 106, then over lead roll 116 to and around mandrel 24. Fiber tension is adjusted by tightening or loosening thumb-screws 80 which cause hinges 78 to rotate about pivot points 152 thereby varying the drag on the fiber due to friction imposed on fiber reel shaft 150. The fiber tension so produced causes a load on tension roll 106 which, due to the pivotability of tension assembly 100 about point 102, produces an equal force and opposite movement at roll 108. An analog or digital readout device 114 (although digital is preferred), is mounted on bracket 154, having a vertical actuating linkage 156 extending downward therefrom. Linkage 156 is pivotably connected to horizontal cross member 158 which rests on roll 108 and moves therewith producing proportional vertical movement of linkage 156. Device 114 is calibrated to produce a readout of fiber tension. A typical digital device 114 is a John Chatillion &amp; Sons Model CFG-10. 
     FIG. 4 shows the drive arrangement between mandrel drive shaft 26 and traversing mechanism shaft 71. Drive belt 36 is driven by primary gear 120 which in turn drives secondary gear 122. A typical gear ratio would be about 21/2 to 1 respectively between gear 120 and gear 122, although this can be varied if desired. Both gears may attach to their respective shafts using any of a variety of well known means such as a key, a spline or the like. 
     FIG. 5 shows how mandrel 24 is held securely by drive shaft 26. A compliant collet 174, beneath knurled compression nut 28, is slotted at the mandrel end thereof such that a plurality of evenly spaced gripping segments are formed at the tapered end. Upon tightening of nut 28, pressure is exerted in the direction of the shaft 26 bore, thereby forcing the tapered end of collet 174 against the tapered bore of shaft 26 forcing the gripping segments thereof to press axially against mandrel 24 gripping it securely while the slots extend beyond the mandrel end. The pigtail of fiber 34 is passed through one such slot while collet 174 clamps onto the mandrel. The fiber lead is then passed over the end of mandrel 24 and through the shaft bore. From there it is threaded out through a hole and wound onto a takeup reel 170 which is held in place against shaft 26 by set screw 172. A slot 173 may be utilized in one land of spool 170 for ease of winding. This gripping means protects fiber 34 during the winding operation. 
     Shaft 26 is moveably supported by support 178 which is fixedly attached to plate 16 such that the longitudinal axis thereof is parallel to plate 12. Journal bearings 180 and 182 permit shaft 26 to rotate. 
     FIG. 6 shows the camming arrangement whereby the circumference of idler roll 84 is used to measure the length of fiber wound on mandrel 24. Normally open micro switch 86, fixedly mounted to suport 77a, has an actuating lever 200 extending therefrom. Idler roll 84 has concentric cylindrical protruding hubs 201 of smaller diameter extending from either end. A tapped hole is provided in one hub 201 lying generally parallel to the longitudinal axis of roll 84 and hub 201 but being offset therefrom so that roll rotation produces an eccentric motion by the head of a screw 202 which is installed in the tapped hole. As idler roll 84 rotates, screw 202 trips lever 200 closing switch 86 once per revolution. Roll 84 is sized such that one revolution equals one sixth of a meter. Surface finish of roll 84 is important as it must be rough enough to permit roll rotation at low fiber contact force while not damaging the fiber buffering or jacketing as the fiber passes thereover. A light sandblasted finish was found to work well. 
     FIG. 7 shows in block diagram form, the control circuit 300 used to operate machine 10. An AC source provides power concurrently to; variable speed motor 40, totalizer counter 54, meters counter 52 and DC power supply 302. The DC output of supply 302 is controllably used to engage/disengage clutch 48. Placing power switch 44 in the closed position allows motor 40 to run whenever motor run switch 58 is also closed. The speed at which the output shaft of motor 40 revolves is controlled by potentiometer 56. Motor shaft RPMs are monitored by totalizer counter 54 which counts the number of open/closed cycles of proximity switch 66. Meters counter 52 electricaly connects to a divide-by-six counting circuit 304 which transmits a count signal 306 to counter 52 for every six revolutions of idler roll 84 as sensed by cam operated micro switch 86. A reset connection 308 permits divide-by-six circuit 304 to be reset from counter 52 using button 52c. When counter 52 is set using thumbwheels 52a at some desired, non-zero fiber length (in meters) and while the present sensed count from circuit 304 is less than this preset value, coil 310 is activated which, via connection 312, closes DC contact 314 thus engaging clutch 48. DC power to clutch 48 then passes through emergency stop switch 50 which is normally closed. Upon reaching the preset fiber length, counter 52 deactivates coil 310 opening contact 314 thereby stopping the winding operation. It should be noted that clutch 48 is engaged even when motor 40&#39;s run switch 58 is open which permits the winding operation to commence upon closing switch 58. Conversely, by setting the meters count to zero and closing motor run switch 58, contact 314 is then open permitting the mandrel to be rotated incrementally by selectively closing normally open jog switch 46. 
     FIG. 8 shows a detail schematic diagram of divide-by-six circuit 304 which supplies corrected control information to meters counter 52. The raw revolution count information from microswitch 86 is first fed to a switch &#34;de-bounce&#34; circuit 320 comprising two logic NAND gates 320a and 320b cross connected so as to prevent false triggering from entering counter circuitry. This conditioned pulse from de-bounce circuit 320 is next fed to a three-stage synchronous counter 322 comprising three J-K flip-flops 324a, 324b and 326 which simultaneously receive the pulse. Two logic NAND gates, 328a and 328b, are connected such that they perform an AND with the flip-flops. Standard logic techniques are used to count the received pulses. When the sixth pulse is received, the &#34;divide-by-six&#34; output line 306 is activated and feeds meter counter 52. Before a winding operation is begun, the &#34;divide-by-six&#34; circuit must be reset. This command is sent by meter counter reset button 52c and is conditioned by a two-stage transistor/driver circuit 330 such that the command voltage levels are compatible with the TTL counter circuitry. 
     The advantages of the interferometric fiber optic hydrophone winding machine are as follows: The machine has the ability to provide increased optical fiber care-in-handling. Careful attention has been given to all fiber bends to provide ample, controlled radii in all cases. Constant tension control eliminates any snap loading of the fiber, and during winding, no twists are introduced into the optical waveguide. The surface finish of the rolls prevent damage to the fiber buffering. These safeguards combine to insure minimal fiber degradation for optical hydrophone operation. Another significant advantage of the winding machine is its ability to aid in hydrophone research. The machine can be used to selectively alter the two constructional parameters which most affect hydrophone performance, i.e., lay angle and fiber tension. A handwrapped version would not permit the small, consistent, changes necessary for optimal design. A final enormous advantage of a hydrophone wound on the present machine over its conventional handwrapped counterpart is in repeatability. Machine 10 provides the ability to fabricate multiple hydrophones having substantially identical response characteristics. This is possible because of the precise control of key constructional parameters; i.e., fiber pretension, fiber lay angle and fiber length. Such repeatability is imperative when constructing multiple sensor array systems. 
     What has thus been described is a hydrophone winding machine comprising a rigid framework, having attached thereto hydrophone mandrel mounting means, optical fiber dispensing means attached to an adjustable traversing mechanism, electric motor means for synchronously rotating the mandrel and driving the traversing mechanism, and control panel means for controlling the winding operation while displaying optical fiber length and tension status. The optical fiber dispensing means further includes a fiber reel stand attached to the traversing mechanism, a journal mounted fiber reel, an idler roll and a lead roll, all bearing mounted thereon. Fiber tension is controlled by adjusting the drag on the reel shaft while a tension assembly attached to a force gage permits digital readout of fiber tension at the control panel. A micro switch/pulse counter device attached to the idler roll monitors the total fiber length already wrapped on the mandrel. By varying mandrel rotation speed, reel stand traversing speed and direction, and reel drag compliant hydrophone mandrels thus can have optical fibers wrapped therearound having preselected fiber lay angles and fiber tensions thereby permitting many hydrophone variants to be produced for research programs and/or allowing production of a quantity of identical hydrophones. 
     Obviously many modifications and variations of the present invention may become apparent in light of the above teachings. For example: Single mode or multimode fiber may be wound on this machine. Materials used for plates, rolls, shafts, etc may be varied. A second fiber tensioning device may be added at roll 108 without deviating from the teachings of the present invention. 
     In light of the above, it is therefore understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.