Transmission cable storing and positioning mechanism

Aug. 11, 1964 _c. _F.tepe 3,144,218

TRANSMISSION CABLE STORING AND POSITIONING MECHANISM

Filed June 26, 1961

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ATTORNEY

United States Patent Office

3,144,218

Patented Aug. 11, 1964

3,144,218 TRANSMISSION CABLE STORING AND POSITIONING MECHANISM

Charles F. Tepe, Fairport, N.Y., assignor to General Dynamics Corporation, Rochester, N.Y., a corporation of

Filed June 26,1961, Ser. No. 119,638

Claims. (CI. 242—107.1)

This invention relates to a positioning mechanism and more particularly to a device capable of taking up a length of transmission line within a relatively small volume without breaking the continuity of the line.

In many cases it is necessary to move a pickup or detecting device attached to a length of transmission line along a path of considerable length. For example, in measuring the neutron flux density in a nuclear reactor, it is often necessary to position selectively a detector, such as a fission chamber, into the reactor throughout a range which may be of the order of twenty to forty feet.

Owing to the low signal levels involved and to the fact that the indicating device may be at a remote point, a low noise shielded cable must be used. The detector and indicator can be connected directly to opposite ends of the cable. The high noise level inherent in arrangements using slip rings precludes their use in such applications and necessitates a means for positioning the detector without breaking the continuity of the cable.

Because of space limitations often encountered, it is frequently required that the cable be taken up within a relatively small volume; this places a restriction upon the size of the drum or reel upon which the cable is wound. Moreover, it is desirable to avoid winding several layers of cable over one another lest the cable develops kinks and loose turns which interfere with an even motion of the detector within the reactor. Furthermore, it is desirable to avoid twisting of the suspended length of the cable and the appended detecting device which is inserted within the reactor.

The device according to the invention is characterized by an ability to take up or absorb a continuous cable within a relatively small volume without imparting a twist to any device which may be connected at either end thereof. The device according to the invention includes a hollow drum about which a portion of the cable is wound. The outer periphery of this drum may be grooved to accept the cable and prevent the turns from running together. The drum can be rotated by means of a motor whenever the position of the detector within the reactor is to be varied. The cable on the outside of the drum is clamped to the drum adjacent one end thereof and passes through an aperture in the drum to the interior. The portion of the cable within the drum is preformed into a helical configuration; this helical portion of the cable is positioned between the inner periphery of the drum and an elongated stationary rod or mandrel disposed coaxially within the drum. The helical portion of the cable is clamped to the stationary rod at a point remote from the point of entrance of the cable into the interior of the drum. Since the helical prestressed portion of the cable surrounds the stationary rod, it is restrained from kinking as the cable is taken up on the drum. An unstressed portion of the cable continues past the point of clamping of the helical portion to stationary rod out through one end of the drum; this portion of the cable is connected to an indicator or readout device which may be positioned at any desired distance of the lifting mechanism. As the drum is rotated to unwind or wind the cable, the diameter and pitch of the preformed helically coiled portion of the cable changes, thereby allowing a given length of cable to be wound or unwound with a relatively few turns of cable on the periphery of the drum.

In order to insure that the coiled portion of the cable will not bind on the stationary rod, the latter may include a number of rotating members each free to rotate about a common axis coincident with the axis of the rod, each rotating member being just long enough to allow one turn of the helical portion of the cable to bear against it. As the stress on the coiled portion of the cable changes, the rotating members are free to rotate under the turns of the coiled portion of the cable, thus preventing binding of the cable on the rod.

Other objects of this invention will become apparent from examination of the specification and of the drawing wherein FIG. 1 is a view, partly in cross-section, showing an embodiment of the invention.

Referring to the drawing, a hollow drum 12 of generally cylindrical configuration is shown upon whose outer periphery a helically disposed groove 13 is formed to accept a cable, indicated generally by the reference numeral 15. A stationary rod or mandrel 17 is positioned inside the drum 12. The drum 12 and rod 17 are mounted in coaxial relationship with one another from a supporting member 19 by means of brackets 21 and 22 which are fastened, as by bolts 23, to the supporting member. A shaft 24 terminating in a hub portion 25 is attached at one end of the drum 12, as by screws 27; alternately, the hub 25 could be made integral with the drum. A bearing 28 fitting tightly in bracket 22 serves to permit rotation of the hub 25 within bracket 22. Support for the other end of drum 12 is provided by a hub 29 attached to the drum, as by screws 31, and cooperating with the bearing 32 retained in fixed bracket 21 to allow rotation of the drum with respect thereto. The shaft 24 is connected to any suitable prime motor, such as an electric motor 33. The centrally disposed rod 17 passes through a central aperture in bracket 21 and hub 29 and a recess 26 in hub 25. One end of the rod 17 bears lightly against a ball 34 located in the recess 25. By proper adjustment of the threaded end of the rod 17 which passes through a nut 37, the hub 25 may be permitted to rotate freely about stationary rod 17 without binding, while still maintaining suitable support for one end of the rod. The cable 15 includes a first portion 15a which is connected to a detector 4®. This portion of the cable is adapted to be wound about the drum 12 and is guided by the peripheral helical groove 13. The cable is clamped to the drum near one end thereof by a clamp 42 and passes through an aperture 43 in the drum and thence into the interior of the drum. Cable 15 then assumes the preformed configuration of a helix 15b surrounding rod 17; this portion of the cable, which may be referred to as the second portion or the intermediate portion, is secured by clamp 45 to the rod 17 near the end supported by bracket 21. The cable then assumes an untwisted configuration and passes out through the end of the drum and through an aperture 47 in the bracket 21 and eventually is connected to an indicator device 50. The portion 15c of the cable 15, also referred to as the third portion, may be of any length, depending upon how close the indicator is to the positioning mechanism. In some instances, rod 17 may be tubular and the portion 15c of the cable may be inserted into the tubular rod and brought out through one end thereof.

The intermediate portion 155 of cable 15 is preformed into the helical configuration, in the manner of coiled telephone cords, prior to being inserted into the drum 12. The technique for prestressing the cable to form such a coil is well known and may consist, for example, of coiling portion 155 of the cable about a mandrel and curing at an elevated temperature while it is held in the desired position.

3,144,218

As the drum 12 is rotated, and the first portion 15α of cable 15 is wound or unwound about the drum, the diameter and pitch of the preformed coil 15b increases or decreases. When the coil 15Z&gt; is wound as shown in the drawing, the pitch of the coil 15b will increase and the diameter will increase as the cable is taken up on the drum; similarly, the pitch in diameter of coil 15b will decrease as the cable is reeled off. On the other hand, if coil 15b were to be wound in the opposite direction from that shown in the drawing, the pitch and diameter of helix 15b would decrease as the cable is wound upon the drum.

The motive means for rotating the drum may include limit switches for limiting the rotation of the drum so that the length of cable wound about the drum does not exceed the length of the helical groove 13, on the one hand, or exert tension on the clamped end of the cable, on the other hand.

The rod 17 must have a diameter smaller than the minimum cable bend diameter so that the cable will not bind on the rod as the coil 15b tightens. One method of insuring that the cable does not bind is to provide a number of sleeves or bearings 52 which are free to rotate about rod 17. Each of the sleeves may have a length about equal to the diameter of the cable so that only one turn of the coil contacts a given sleeve. The portions of the sleeves which contact one another may be of reduced diameter in order to reduce friction therebetween. If the coil turns start to touch the rod, they contact the associated sleeve which is free to rotate about the rod and thus prevent binding. Since the greatest tension appears in the region adjacent the clamped end of the coil 15b, it is also possible to use a rod 17 which is of somewhat smaller cross-section in the aforesaid region. For the same reason, the sleeves may be limited to the region adjacent the clamped end of coil 15b.

Binding of the coil can also be minimized by designing the cable so that in the unbiased or unstressed position of coil 15b, the periphery of the drum is approximately half filled with cable. Then, the coil becomes stressed only during half of the total angular excursion of the drum.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. For example, stress relieving means may be provided for connecting the detector to one end of the cable. Furthermore, the rod may be supported at one end by a bracket separate from that used to support the drum. In this instance, the portion 15c of the cable could extend out through the open end of the drum. It is desired, accordingly, that the claims be given a broad interpretation commensurate with the scope of the invention within the art.