Abstract:
An armored cord has flexibility and tensile strength for securing a telephone handset to a telephone housing. The cord includes an outer armored sheath which is designed for increased flexibility in that it allows the cord to bend readily over small radii. Tensile strength between the handset and housing is provided by an internal cable which absorbs the stress applied to the cord when subjected to unusually large longitudinal forces. The service life of the cord is lengthened, and the number of incidents causing out-of-service conditions is thereby reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to armored electric cords and particularly to telephone armored cords that connect telephone handsets to housings of public telephones. 
     2. Description of the Prior Art 
     Many public telephones are located in unattended and isolated areas so as to provide reasonable and continuous access for the general public to the telephone system. Vandalism of these public telephones is a problem, however, with the handset and cord being the most vulnerable. Out-of-service conditions may result from damage sustained by the cord due to pulling and stretching of the outer protective covering when subjected to an unusually large force. 
     Handset cords in public telephones have traditionally been protected by armoring the cord with helically wound metal having adjacent interlocking helices, similar to &#34;BX&#34; or &#34;Greenfield&#34; armor. Unfortunately, these cords when made very strong are also very stiff. Thus, they tend to pull on the hand of the customer holding the handset, thereby adding substantially to its apparent weight. 
     In an effort to overcome the stiffness problem, an arrangement disclosed in U.S. Pat. No. 3,290,429, issued to R. E. Prescott et al. on Dec. 6, 1966, shows a flexible armored cord for connecting a telephone handset to a telephone housing. The cord comprises a number of separate sleeve-like armored elements forming an armored electric line for a central conductor by surrounding the conductor at longitudinal distributed points. Elements in the cord having inwardly flanged sleeves interlink with smaller diameter elements having outwardly flanged sleeves that extend between the larger inwardly flanged sleeves. This arrangement thus allows the cord to drape loosely and turn about comparatively small radii. 
     While the Prescott et al. arrangement enhances flexibility, it is nevertheless desirable to provide a simple and inexpensive armored cord which not only secures the handset to the housing with the desired flexibility but also with an increased longitudinal tensile strength to avoid damage that might result in an out-of-service condition. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, there is provided an armored cord having flexibility and strength for securing a telephone handset to a telephone housing. The cord includes an outer armored sheath which is designed for increased flexibility in that it allows the cord to bend readily over small radii. The outer sheath is also designed to be highly resistant to penetration or cutting by sharp objects. The strength necessary to overcome any strain likely to be caused by an unusually large longitudinal force is provided solely by an internal cable which secures the handset to the housing. With these features of construction, a telephone handset cord containing electrical conductors is provided with sufficient flexibility and longitudinal strength to reduce the likelihood of the forcible disconnection or removal of the handset. The service life of the telephone cord is lengthened and the number of incidents causing out-of-service conditions is thereby reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The invention and its mode of operation will be more clearly understood from the following detailed description when read with the appended drawings in which: 
     FIG. 1 is a perspective view of a public telephone showing a cord connecting a handset to a housing according to the invention; 
     FIG. 2 is a detailed partially broken away view of a portion of a handset cord depicted in FIG. 1 and FIG. 8; 
     FIG. 3 is an exploded perspective view of the handset of FIG. 1 and of mounting members used for securing the handset cord; 
     FIGS. 4 through 7 are detailed views of a mounting member and related components used for securing the handset cord in the housing of FIG. 1; 
     FIG. 8 is a perspective view of another public telephone showing the cord connecting a handset to a housing according to the invention; 
     FIG. 9 is a view of the handset of FIG. 8, partially in section, illustrating the mounting members used for securing the handset cord; 
     FIG. 10 is a perspective view of a transmitter housing arranged for securing an outer sheath of the handset cord; 
     FIG. 11 is a perspective view of a wedge-shaped member located in the handset depicted in FIG. 8 and arranged for terminating a strength member in a handset cord; 
     FIG. 12 is an exploded perspective view of some of the mounting members used for securing the handset cord in the housing of FIG. 8; and 
     FIG. 13 is a fragmentary side elevation view, partially in section, illustrating the mounting member of FIG. 12. 
     Throughout the drawing, the same elements when shown in more than one figure are designated by the same reference numerals. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1 of the drawing, a housing 100 for a public telephone supports a switchhook 101 which is located on a front panel 102 of the housing. The housing 100 receives a handset cord 105 that extends from a mounting member 106 located on a sidewall 107 of the telephone housing to the lower transmitter end 108 of a handset 110. 
     The structure of the handset cord 105 is sufficiently limp so that the cord is able to bend readily over small radii. This is achieved by using an armored outer sheath designed for maximum flexibility. The sheath is wrapped using an unpacked fully interlocking construction which makes it extremely difficult to break the cord open by twisting. The outer surface of the cord is also resistant to penetration by objects such as pins or knife blades. Flexibility is further improved by having the sheath unpacked, i.e., the interlocking sections are not packed with a material to make the cord waterproof or airtight. 
     As seen in FIG. 1, where the outer sheath of the handset cord 105 is broken for purposes of illustration, and in greater detail in FIG. 2, the cord 105 comprises a plurality of insulated interior conductors 111 through 114 for carrying electrical signals between the housing 100 and the handset 110. The cord 105 also comprises a longitudinal strength member 115 that extends between the housing 100 and the handset 110 inside the armored outer sheath 116. Although the strength member 115 is illustrated to be collectively a single element in FIGS. 1 and 2, it actually comprises a plurality of twisted wires which could, for example, be made from stainless steel or some other strong material. In the embodiment shown, the strength member has a 3/32nd inch diameter and has 7×19 twisted strands, i.e., seven twisted strands each having 19 smaller wires so that the total number of individual stranded wires is 7×19. In this combination, the wires provide a very flexible arrangement while maintaining a very high tensile strength that is desirable for the handset cord 105. And the breaking strength for this strength member 115 is in excess of 800 pounds. Thus the combination of the strength member 115 when combined with the armored outer sheath 116 as the cover for the handset cord, provides both strength and flexibility in connecting the handset 110 to the telephone housing 100. 
     Referring now to FIG. 3, there is shown the outer sheath 116 and the strength member 115 suitably secured in the handset 110 which comprises a top portion 130 and a bottom portion 131. Also shown are the insulated conductors 111 and 112 which carry electrical signals from the telephone housing 100 to a transmitter housing 132 in the handset 110, and insulated conductors 113 and 114 which carry electrical signals from the housing 100 to a receiver housing 135 also in the handset 110. The outer sheath 116 enters the handset 110 through a rubber grommet 137 and is guided between upstanding walls 138 and 139 attached to the top surface 136 of the transmitter housing 132. The outer sheath 116 is also guided between upstanding walls 140 and 141 into a nested position where it is secured in the handset 110 by a generally U-shaped member 145. A section of the outer sheath 116 is crimped so that the U-shaped member 145 slides around this section and also slides into a pair of inwardly facing opposed grooves 146 and 147 in the spaced upstanding walls 140 and 141, respectively. 
     The upstanding walls 140 and 141 converge beyond the end section 148 of the sheath to a restricted opening 149 having a width corresponding to the diameter of the strength member 115. At the point of the restricted opening, these walls extend outward to provide a stop surface for a swaged end termination 150 which is affixed to the end of the strength member 115. A catch surface is provided by the larger diameter of the swaged end termination forming a shoulder at the common attachment point of the end termination and the strength member 115. The interaction between this stop surface and the catch surface on the swaged end termination 150 is the sole means for providing longitudinal tensile strength in the securing of the telephone cord 105 to the handset 110. When the top portion of the handset 130 is combined with the bottom portion of the handset 131, the top portion covers the upstanding wall pairs 138 and 139, and 140 and 141, thereby retaining the sheath in the channel as well as defining a cavity for retaining the swaged termination 150. 
     With reference to FIGS. 4 through 7, there is shown the details of the mounting member 106 and the termination arrangement for the handset cord 105 in the telephone housing 100. The mounting member 106 comprises a cylinder having a first portion 170 with a first diameter and a second portion 171 with a second smaller diameter sized for inserting in a mating circular opening in the sidewall 107 of the telephone housing 100. Angular rotation of the cylinder in the sidewall of the housing is made possible through use of the mating circular opening. 
     The cylinder is secured to the sidewall 107 of the housing 100 by the combination of (1) a shoulder 172 formed by the difference in the diameter between the first portion 170 and the second portion 171 of the cylinder and (2) a retaining member 175 inserted in the cylindrical groove 176 on that part of the second portion of the cylinder extending inside the sidewall 107 of the housing 100. The first portion of the cylinder also includes a radial slot 178 that is adapted for receiving a crimped portion of the outer sheath 116. The crimped portion of the sheath is buttressed in this slot and secured by the adjacent outer sidewall 107 of the telephone housing 100. 
     As in the telephone handset, the strength member end termination in the telephone housing 100 is that of a swaged termination 180 with a larger diameter than that of the strength member 115. Also a catch surface is provided by the larger diameter of the end termination which forms a shoulder at the common attachment point of the end termination and the flexible strength member 115. The strength member 115 extends from an interior chamber 182 of the cylinder through a notched opening 184 on the second portion of the cylinder and onto a stop surface 186 formed by a hollow in the outer surface 185 of the second portion of the cylinder. The interaction between the stop surface 186 on the second cylinder portion 171 and the catch surface on the end termination 180 provides the sole means for longitudinal tensile strength in the securing of the handset cord 105 to the telephone housing 100. A second cylindrical groove 187 is also located on the second portion of the cylinder for mounting the retaining cover 179. This cover keeps the electrical conductors 111 through 114 in designated slots 188 and 189 formed in the second portion 171 of the cylinder. 
     FIG. 8 shows another embodiment for the public telephone housing with the handset cord 105 connecting a handset 210 to a telephone housing 200 in accordance with the invention. The housing 200 supports a switchhook 201 which is essentially located on a front panel 202 of the housing 200. The handset cord 105 extends from an opening 206 in the housing to the lower transmitter end 208 of the handset 210. The structure of the handset cord 105 is sufficiently limp for the cord to drape down and form a small loop before extending upwards. 
     As seen in FIG. 8 and in greater clarity in FIG. 2, the cord 105 comprises a plurality of insulated interior conductors 111 through 114 for carrying electrical signals between the housing 200 and the handset 210. The cord 105 also includes a strength member 115 that extends throughout the length of the cord and is secured both in the handset 210 and inside the housing behind the opening 206. 
     FIGS. 9, 10, and 11 show in detail the termination arrangement of the outer sheath 116 and the strength member 115 in the handset 210. The handset cord 105, containing the sheath 116 and the strength member 115, enters the handset 210 via a grommet 227. For securing the sheath 116 in the handset 210, a transmitter housing 232 in a transmitter portion 240 has a surface 236 which includes an upstanding generally U-shaped member 237 situated thereupon. A crimped section of the outer sheath is depressed into the space defined by the legs of the U-shaped member 237 for securing the sheath thereto. A wall forming the back plane of the telephone handset 210 is located adjacent to the U-shaped member and extends transverse to the height of the U-shaped member across the top 242 of its upstanding legs. The sheath is thus securely positioned and retained between the legs of the U-shaped member 237 and the back plane of the handset 210. 
     FIGS. 9 and 11 also show how the strength member 115 is secured in the handset 210. A wedge-shaped member 245 generally located in the receiver portion 260 of the handset housing has its tapered section extending slightly into the yoke portion 270 of the telephone handset 210. The wedge-shaped member 245 also has axially aligned slots of a first and a second diameter extending throughout its length, the first slot 246 defining a passageway for the strength member 115 and the second larger slot 247 being suitably sized for receiving the end termination 250 of the strength member 115 and providing a stop surface 251 extending orthogonally from the first slot 246. The yoke portion 270 of the handset includes a chamber which provides a passageway for the strength member 115 and expands at the common point between the yoke portion 270 and the receiver portion 260. It is at this expansion point that the wedge-shaped member 245 is secured in the handset 210 by having its tapered edge project into the expanded chamber in the yoke portion 270 of the handset 210. The longitudinal tensile strength for securing the cord 105 to the handset 210 is obtained solely from the interaction between the stop surface 251 of the wedge-shaped member and the cylindrically shaped member 250. 
     FIGS. 12 and 13 show the handset cord securing arrangement that is provided inside the telephone housing 200 behind opening 206. After passing through opening 206, the outer sheath 116 passes through a slot 280 on mounting member 281. A crimped section of the sheath is engaged in this slot such that it is secured in a longitudinal direction. A U-shaped spacer member 282 allows clearance for the strength member 115 and the insulated conductors 111 through 114 to pass through. The strength member 115 with its swaged end termination 283 passes through a slot 284 on a securing member 285, with the upper surface of the securing member 285 providing a stop surface for the catch surface 286 of the swage termination 283. And a sidewall surface 287 of the securing member 285 keeps the crimped portion of the sheath depressed in the slot 280. The U-shaped spacer member 282 also retains the strength member 115 in the slot 284 on the upper surface of the member 285 when the arrangement is assembled. An extending tab 290 located on mounting member 281 extends outward for locating underneath a bridge-like frame 291 on a chassis 292 within the telephone housing 200. This chassis is affixed to the telephone housing 200 in this location by threaded fasteners 295 and 297. Threaded fastener 295 is inserted in the opening 296 and attached to the wall of the housing 200. Threaded fastener 297 is inserted in both the opening 298 on securing member 285 and a portion of the slot 280 on mounting member 281 before being attached to the wall of the housing 200. 
     Although only specific exemplary embodiments of this invention have been described in detail, those skilled in the art will appreciate that many variations and/or modifications may be made in the exemplary embodiments without in any way departing from the novel and advantageous features of this invention. Accordingly, all such variations and modifications are intended to be included within the scope of this invention as defined in the appended claims.