Cable retraction system

A cable retraction system is described which includes a windup reel (16) and power springs (24, 26, 28) that urge the reel to turn and wind up a signal-carrying cable (20). An outer end (25) of each power spring is bent about 180.degree. to form a hook that projects through a slot (72) in a windup drum (36) of the reel. A screw (44) projects through a lug (38) at the end of a cable wire, through a hole (71) in the spring, and into a threaded insert (50) set in the windup drum. A stationary axle (30) at the center of the reel, comprises a dielectric body (71) and a plurality of conductors (73, 75, 77) embedded in the body, each conductor having an outer end (58, 60, 62) at the end of the body to connect to wires of a second cable, and each conductor having an inner end (74, 76, 78) lying at the periphery of the axle and attached to an inner end ( 32) of a spring.

BACKGROUND OF THE INVENTION 
The present invention relates to cable retraction systems where springs 
turn a windup drum and carry currents. 
One type of cable windup system uses spiral springs to turn a windup drum 
and to carry currents between a windup cable and a stationary cable. A 
flat slotted end of each spring is pressed against a surface of the windup 
reel to extend tangentially thereto, and a screw is used to hold the 
spring end in place. Because of the varying force constantly acting on the 
outer spring end, it is difficult to reliably connect the spring end to 
the windup drum and to a wire of the windup cable. 
SUMMARY OF THE INVENTION 
In accordance with one embodiment of the present invention, a cable 
retraction system is provided which is of reliable construction. The 
system includes a plurality of spiral windup springs for turning a windup 
drum of a reel. Each spring has an inner end mounted on an axle and an 
outer end mounted on a windup drum. The drum has a plurality of through 
slots, and the outer end of each spring is bent into a largely 180.degree. 
loop that extends through a slot in the drum, with an outer leg of each 
loop lying on the windup surface of the drum. Each wire of the windup 
cable has a lug at its end. The outer leg of the spring loop is sandwiched 
between the wire lug and a metal insert embedded in the drum, with a screw 
extending through them and threadably connected to the insert to hold them 
together. 
The axle includes a dielectric body and a plurality of axle conductors 
embedded in the body. Each axle conductor extends primarily parallel to 
the axis of the axle. Each conductor has an outer end lying at an end of 
the axle where it connects to a wire of a stationary second cable. Each 
conductor has an inner end that extends to the periphery of the axle where 
it connects to an inner end of the spring. The inner end of each spring is 
permanently deformed to substantiate the radius of curvature of the axle 
periphery, and a screw extends through a hole in the spring inner end and 
through a hole at the inner end of the axle conductor. 
The novel features of the invention are set forth with particularity in the 
appended claims. The invention will be best understood from the following 
description when read in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a cable retraction system 10 for electrically coupling a pair 
of audio transceivers 12, 14 that each may comprise a headset (earphone 
and microphone). In one example, one transceiver is worn by a person on an 
airplane that is being serviced at a noisy airport, and the other is worn 
by a person who is servicing equipment that may lay one hundred feet away. 
The system comprises a cable reel 16 that is rotatably mounted on a frame 
18 that is designed to rest on the ground. A windup cable 20 that is 
coupled to the first audio transceiver at 12, is retractably wound about 
the reel 16. A second cable 22 that is coupled to the second audio 
transceiver, extends from a stationary axle 30 lying at the axis 31 of the 
apparatus, about which the reel 16 turns. 
As shown in FIG. 2, the windup cable 20 has three wires 37, 39, and 41, 
that each has a conductive lug 38, 40, 42 at its end (each lug is 
connected to a conductor of the wire). Each lug is mounted on the outer 
surface or periphery of a windup drum 36 of the reel. The system includes 
three power springs, including power spring 24 which has an outer end 25 
connected to a corresponding wire lug 38, and which has an inner end 32 
mounted on the axle 30. The inner end 32 of the power spring is connected 
to a corresponding axle conductor 58 which connects to a wire of the 
second cable. 
FIG. 4A shows the manner in which the outer end 25 of the spring 24 is 
connected to the wire 37 of the windup cable. The windup drum 36 is 
substantially in the form of a hollow cylinder, with the windup cable 
being wrapped about its outer surface 34. The windup drum has a plurality 
of slots 72. The outer end 25 of each spring is bent into a substantially 
180.degree. loop 43 that has outer and inner loop sides 45, 47. The center 
of the loop at 43 extends through a slot 72 in the windup drum, with the 
outer loop side 45 lying on the outer surface 34 of the drum. A threaded 
insert 50 is set (as by force fit) in a hole in the windup drum. The outer 
loop side 45 of the spring is sandwiched between the lug 38 and the insert 
50, and a screw 44 projects through holes in the lug and spring and is 
threadably connected to the threaded insert 50. Tension on the spring 24 
can lead to slight bending of the loop 43 and pressure of it on one side 
72A of the slot 72 in the drum. As a result, the changing forces on the 
outer end 25 of the spring, as the cable is wound and unwound from the 
windup drum, are largely isolated from the outer leg 45 of the spring 
loop. This minimizes the tendency for the mounted location of the spring 
end at outer loop side 45 to loosen the screw. This arrangement provides a 
relatively simple and reliable mounting of the spring outer end and its 
electrical coupling to one of the cable wires 37. 
FIGS. 5 and 7 show details of the axle 30. The axle includes a body 71 
(FIG. 7) of dielectric, or insulative material, and a plurality of axle 
conductors 73, 75, and 77 embedded therein. Each axle conductor extends 
primarily parallel to the axis 31, but includes a threaded insert such as 
74 extending to the periphery 79 of the dielectric body. The spring inner 
end 32 is permanently deformed to have about the same radius of curvature 
as the dielectric body (i.e. not more than twice as great), and has a hole 
81 therein. A screw 83 projects through the hole and into the threaded 
insert 74 to anchor the inner end of the spring to the axle and to 
electrically connect the inner end of the spring to a corresponding axle 
conductor 73. The axle has opposite ends 59, 61. Each axle conductor has 
an outer end 58, 60, 62 (FIG. 5) which lies at a first axle end and which 
is opposite the conductor inner end (at one of the inserts 74 etc.). The 
outer ends of the axle conductors are internally threaded, so a screw can 
pass through a lug on a wire of the second cable and connect into a 
threaded conductor end 58, 60, 62. Applicant prefers to embed the axle 
conductors by molding them in place in the axle body. 
FIG. 3 shows how the three power springs 24, 26, 28 are positioned, so they 
are axially spaced apart by insulative sheet-like spacers 66, 67. FIG. 2 
shows that the conductive lugs 38, 40, 42 on wires of the windup cable 20, 
are not only axially spaced along the axis of rotation 31, but are also 
circumferentially spaced. The circumferential spacing helps separate the 
spring ends and wire lugs from one another to avoid contact of one spring 
and/or lug with another. A strain relief device 56 is fixed to the windup 
cable 20 at a location where the cable sheath 57 surrounds the wires, with 
the location being spaced from the wire ends at the lugs 38, 40, 42. The 
strain relief device is mounted on one of the flanges 85 (which lies 
opposite another flange 87) of the reel. As can be seen in FIG. 5, the 
outer ends at 74, 76, 78 of the axle conductors are also circumferentially 
spaced about the axle axis 31. The circumferential spacing corresponds to 
the circumferential spacing of the lugs 38, 40, 42 (FIG. 2) at the outer 
ends of the springs. The circumferential spacing of the inner ends of the 
axle conductors facilitates construction of the axle, and also results in 
substantially equal tension in each of the three springs when 
substantially identical power springs are used. 
FIG. 6 shows additional details of the cable retraction system 10. The 
windup cable 20 includes first and second cable sections 91, 92 which are 
connected by plug and socket connectors 88, 94. The plug and socket 
connectors are designed to unmate when a predetermined force such as 
twenty pounds is applied that tends to pull them apart. This construction 
is used because damage to the windup cable and to instruments it is 
connected to, often occurs by inadvertent pulling of the cable, as where 
the far end of the cable is connected to an instrument on an airplane, and 
is not disconnected when the airplane is taxied to another location. 
The windup cable has a far end with another plug 96, and with a 
handle/protective boot 98 therearound. A mounting bracket 100 is attached 
to the cable a predetermined distance such as six feet from the plug 96. 
The bracket 100 can be hung on an object such as a door or open panel on 
an airplane. FIG. 6 shows at 100A how the bracket can be mounted on a door 
D, the bracket including a substantially 180.degree. loop to allow it to 
be easily hung on a door. Applicant constructs the bracket 100 of 
elastomeric material such as rubber. As a result, if the cable is pulled, 
the elastomeric loop 101 of the bracket will unbend from its loop position 
and will release from the door, at a force such as twenty pounds. 
The cable moves through a hole or passthrough 80 in the frame 18. A hollow 
elastic ball or sphere 82 is fixed to the windup cable, and is larger than 
the hole 80. As a result, if the cable is released to wind up, it will be 
stopped when the sphere 82 hits the walls of the hole 80. The elastomeric 
sphere reduces shock from sudden stopping of the cable, and avoids 
creation of a loud noise. 
Thus, the invention provides a cable retraction system of high reliability. 
The system includes a plurality of windup springs with inner ends mounted 
on a fixed axle and outer ends connected to a windup drum. The outer ends 
of the springs are bent into a largely 180.degree. loop that passes 
through a slot in the windup drum. The outer leg of the loop is sandwiched 
between a metal insert in the drum and a lug at the end of a wire of a 
windup cable, and with a screw holding them together. The stationary axle 
includes a dielectric body and a plurality of axle conductors lying in and 
preferably embedded in the body. Each axle conductor has an inner end 
extending to the periphery of the body and connected to the inner end of 
the windup spring. Each axle conductor also has an outer end lying at an 
axial end of the axle, where the conductor connects to a wire of a second 
cable. Precautions are taken to avoid damage to the cable retraction 
system or to apparatus to which the windup cable is connected, which 
includes providing the windup cable in two sections connected by plug and 
socket connectors that unmate at a predetermined unmating force, and by 
providing a mounting bracket with an elastomeric loop. A hollow elastic 
ball on the cable gently limits cable windup. 
Although particular embodiments of the invention have been described and 
illustrated herein, it is recognized that modifications and variations may 
readily occur to those skilled in the art, and consequently, it is 
intended that the claims be interpreted to cover such modifications and 
equivalents.