Abstract:
A through-door security intercom that clamps on the free edge of a door of any conventional thickness. Clamping is effected by constant-force flat springs, which springs also provide current paths. The springs are pre-bent at acute angles at predetermined points, to aid in mounting of the outside unit on the door. The inside unit is mounted on the door due to the force created by the constant-force springs which are coiled on spools. Brushes in the inside unit engage the springs and complete the electric circuit.

Description:
BACKGROUND OF THE INVENTION 
     It has long been recognized that shouting through closed doors is an unsatisfactory way for persons in apartments, hotel rooms, vacation condominiums, etc., to communicate with attempted visitors in order to be sure that the attempted visitors are not impostors or criminals. The door muffles the sound, and makes it difficult for the apartment dwellers to recognize voices with accuracy. 
     Many apartment (for example) doors do not have peep holes, and it is not authorized for holes to be drilled in the doors. The same applies to hotel room doors, where the danger of unwanted intruders is perhaps even greater than relative to apartments. 
     It has been proposed several times to mount outside and inside intercom units on the doors of dwellings, using the peep holes for the mounting and connecting means. Such proposals are of no value to persons who wish to speak through doors of apartments, hotel rooms, condominiums, etc., where there are no peep holes. Furthermore, and very importantly, such apparatus is not readily portable, nor is it quickly mountable and demountable. 
     SUMMARY OF THE INVENTION 
     The present invention provides compact, portable intercom units that do not require the peep hole, and that are quickly and easily mounted on and removed from any door. 
     In accordance with one aspect of the present invention, outside and inside intercom units are mounted at the edge of a door, and are electrically and mechanically connected to each other by elements going around the edge of the door. 
     In accordance with another aspect of the present invention, the elements that go around the edge of the door are the same elements that effect mounting of the outside and inside intercom units to the door, such mounting elements being adjustable for mounting of the intercom units to the surfaces of doors of different thicknesses. 
     In accordance with another aspect of the present invention, the same elements that mount the intercom units to the outside and inside of the door provide electrical connection between such units. 
     In accordance with another aspect of the present invention, resilient means are provided to hold the outside and inside intercom units in full engagement with the door surfaces. 
     In the preferred embodiment of the present invention, constant-force springs are coiled on spools in one of the intercom units, and extend outwardly from the housing of such unit, and are connected to the other intercom unit, the constant-force springs being adapted to cause the outside and inside intercom units to engage the door surfaces. 
     Stated more specifically, and again referring to the preferred embodiment, the constant-force springs conduct electricity between the intercoms. Furthermore, the coiled portions of such springs generate torque which causes one of the intercoms to be parallel to the associated door surface instead of inclined relative thereto. The spring portions remote from the coiled portions are pre-bent at acute angles, the relationships being such that the other of the intercom units is held in parallel relationship to the associated door surface by the spring force resulting from such pre-bending. Furthermore, the pre-bent corners provide sharp breaks causing the spring portions to substantially hug the door edge. 
     It is a feature of the invention that the constant-force springs are substantially impervious to being damaged due to being pinched between the door edge and the door jamb. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view showing the outside and inside intercom units in condition for carrying and storing, the units being held by the spring elements in substantially parallel engagement with each other; 
     FIG. 2 is an isometric view showing the intercom units in position on the free edge of a door, the door being shown in phantom line, portions being broken away; 
     FIG. 3 is a horizontal sectional view taken on either of lines 3--3 of FIG. 2; and 
     FIG. 4 is a fragmentary view of one of the springs at the corner thereof, showing the free condition of each spring at its corner. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 2, and also to FIGS. 1 and 3, there is shown an electrical intercom comprising an inside unit 10 and an outside unit 11 that are connected to each other by elements 12,13 that go around the edge of the door 14. Door 14 is a conventional door of any thickness, being pivoted on suitable hinges (not shown) at the door edge remote from the illustrated door edge 15. Such hinges are contained in a conventional rectangular door frame or jamb 16 having the usual stop element 17 for the door edge 15. 
     The door frame and door are those which are part of (and permit or prevent entrance into and exit from) apartments, vacation (or other) condominiums, hotel rooms, mobile homes, motorhomes, houses, etc. 
     The inside and outside electrical intercom units 10,11 are shown, in the present drawings, as being mounted on the free left vertical edge (as viewed from the inside of the dwelling space) 15 of door 14. For doors that pivot the other way, by which it is meant that the hinges are on the left side as viewed from the inside of the dwelling space, and the free edge is on the right, it is merely necessary to invert both the inside and outside units 10,11 and mount them at the right edge of the door. 
     Inside unit 10 has a rectangular housing 18 formed of two mated portions or sections 19,20 that are secured together by screws, not shown. The housing portions or sections 19,20 are injection molded of synthetic resin. 
     Similarly, outside unit 11 has an injection-molded synthetic-resin rectangular housing 21 formed of mated portions or sections 22,23 held together by unshown screws. The housing 21 of the outside unit is substantially smaller than is that of the inside unit. The outside unit preferably contains no electronics or moving parts, and represents only a small fraction of the manufacturing cost of the through-door intercom system. 
     Preferably, the housing 21 of outside unit 11 has four feet or pads 24 at corner regions thereof, and adapted to seat on the outside surface 25 of door 14. Correspondingly, there are provided at corner regions of inside housing 18 four feet or pads 26 that rest on the inside door surface 27. Pads 24 and 26 are formed of a soft material, such as rubber or synthetic elastomer, adapted to increase friction relative to the door surfaces and also prevent any possible damage to the finish thereon. 
     Combination speakers/microphones 28,29 are mounted in housings 18,21, respectively, in outwardly-facing relationship relative to door 14. The speakers/microphones are secured to the outer walls of housings 18,21, respectively, at slotted portions of such walls. In the case of outside unit 11, speaker/microphone 29 is preferably the only electrical element other than leads or wires. On the other hand, inside speaker/microphone 28 is connected by leads or wires 31 to electronic circuitry which is schematically represented at 32. Circuitry 32 is mounted on a circuit board 33 that, in turn, is secured by posts 34 to the bottom wall of portion 20 of inside housing 18. 
     The circuitry 32 preferably comprises a differential amplifier that is powered by a battery (not shown). The power is controlled by a volume-control wheel 35. A switch 36 is mounted above the speaker/microphone of inside unit 10 in order to determine when power is supplied to the differential amplifier and associated circuitry from the battery. Preferably, such switch is of the internally-lighted variety so that the user will know when the switch is on. A push-button switch 37 (double-pole double throw) is mounted adjacent switch 36 and is pushed by the householder when it is desired that any person speak into the intercom system, whether from the outside or inside of the door. Switch 37 insures that there will be no eavesdropping on the occupants by a person located outside the door. 
     The electronics portions of the present invention are standard and well known, it being understood, however, that the leads that go from one unit to another constitute a major portion of one aspect of the invention. Electronic circuitry which may be employed includes, for example, that described in U.S. Pat. 4,809,320. The electronics portions of the disclosure of such patent are hereby incorporated by reference herein. 
     Preferred Embodiment of the Elements for Causing Units 10,11 to Remain in Place Against Door 14, and for Electrically and Mechanically Connecting Such Units to Each Other 
     In accordance with a major aspect of the preferred embodiment, spring means are provided to generate torque so directed as to hold one of the units 10,11 flatwise against the door surface. Means are also provided to create a flexural spring force, also a torque, aiding in maintaining the other of the units 10,11 against the opposite door surface. In addition, means are provided to effect electrical connections between the units 10,11 around the door edge 15. 
     In the preferred embodiment, all of the above-mentioned means are incorporated in the same elements 12,13, and associated parts. These elements 12,13 are constant-force flat springs that are so constructed as to tend constantly to coil up upon themselves. Coils 12a,13a are thus present at all times in a housing, preferably housing 18. At all times, including during the winding process, the force exerted by the springs is constant. 
     The springs are formed of metal and therefore are current conductors; they are--very preferably--employed to complete the circuit between the inside and outside units. 
     At one point in each spring, numbered 38, each spring is bent sharply. Preferably, such bend is an acute angle, preferably about forty-five degrees, when the spring is in the free condition shown in FIG. 4. A purpose of the sharp bend is to create a flexural force tending to maintain one of the units 10,11, preferably unit 11, against a door surface. 
     Formed integrally with the bottom wall of portion 20 of inside housing 18 are bearing posts 39. Four such posts 39 are provided, two for each of the springs 12,13. Spools 41, preferably formed of synthetic resin, and flanged at one side, are mounted rotatably between the bearing posts for free rotation about an axis, the axis being indicated at 42 in FIG. 3. The mounting of the spools 41 in freely-rotatable relationship on bearing posts 39 may be effected (for example) by short shafts or bolts that extend through the spools, along axis 42, each shaft extending through two bearing posts and the spool 41 between them. 
     As shown in FIGS. 2 and 3, the bearing posts and the horizontal planes when the inside unit 10 is in mounted condition on the door. Stated otherwise, axis 42 is vertical when the inside unit is thus mounted. Preferably, the posts and spools are located between the electronic circuitry 32 and that sidewall of housing 18 which is nearest the door edge 15 when the inside unit 10 is in mounted condition. Stated otherwise, and preferably, the bearing posts and spools are spaced only a relatively short distance from such housing sidewall nearest door edge 15. 
     The springs 12,13 are coiled on the two spools 41, to form coils 12a,13a, there being a sufficient number of coils that the springs may be pulled off the spools sufficient distances to effect mounting of the unit on a door 14 of any conventional thickness. The inner ends of the springs (adjacent the spool surfaces) may be connected to the spools but need not be. Since the springs 12,13 have the strong natural tendency to coil up, they tend to cause the spools 41 to rotate counterclockwise as viewed in FIG. 3. 
     The springs 12,13 extend outwardly from housing 18 through s openings 43 in the side wall of such housing, the openings being on the opposite side of the spools from electronic circuitry 32, and being spaced away from the bottom housing wall. Thus, the bend points 38 are outside the housing 18 and can be spaced various distances from such housing 18 depending upon the number of coils that are on the spools. 
     The regions of springs 12,13 on the opposite sides of bends 38 from the spools extend into housing 21 of outside unit 11. Such extensions are through openings 44 formed in section 23 of housing 21 adjacent the bottom housing wall. Each opening 43,44 is preferably a vertical slot the walls of which are closely adjacent the associated spring 12,13. 
     Inside the housing 21, each spring 12,13 is secured to a post 46, it being understood that there are two such posts 46, one above the other, one for each of the springs 12,13. The securing is effected by screws 47 threaded into the post ends. Preferably, though not necessarily, the posts are located relatively near openings 44. 
     There is caused to be a predetermined spacing between each bend 38 and the adjacent side of housing 21. This spacing is such that when bends 38 are nested over the inside corner of door edge 15, housing 21 will be spaced from such corner a substantial distance that is sufficient to prevent contact with stop element 17. 
     The electric circuit in the present system is as follows. Two leads 48 connect the two terminals of speaker/microphone 29 of outside unit 11 to the two springs 12,13, the connections being effected at the ends of the respective posts 46 by means of the s crews 47. Current can thus flow between speaker/microphone element 29 and the respective spring coils 12a,13a on spools 41. 
     Brushes 49 make sliding connections with the exterior surfaces of the coils at regions adjacent electronic circuitry 32. Preferably, these brushes are sharply-bent discrete sections of the constant-force spring. There are two such brush sections, one for each coil of spring element, and they have portions sandwiched between circuit board 33 and the posts 34 which mount such circuit board and the electronics 32. The brushes 49 make electric connection with conductive portions of circuit elements of the circuitry 32. Preferably, the portion of each brush 49 that engages a coil is convex toward the left as viewed in FIG. 3. 
     Method of Transporting, Mounting on the Door, and Using 
     For transporting in a suitcase, box, etc., the units 10 and 11 are held in the positions shown in FIG. 1. Such holding results automatically from coiling of the springs 12,13 on spools 41, and also results from the coil-generated torque described below. A flexible plastic container may be provided into which the units 10,11 fit snugly so as to facilitate carrying in a suitcase to a vacation condo, hotel, etc. 
     To mount the through-door intercom on a door, it is merely necessary to position the outside unit 11 in the position shown (for example) in FIG. 3, with bends 38 nested over the door corner. The outside unit is thus spaced sufficiently far from the door frame or jamb 16 that it will not be in danger of contacting the stop element 17 of conventional door frames, when the door opens or closes. 
     Not only do the bends 38 determine the spacing, but they cause the constant-force springs to be closely adjacent the edge surface of the door as well as adjacent the outside door surface 25. Because of the bend relationship described above relative to FIG. 4, by which the springs when in their free conditions are bent at acute angles, it follows that placing the outside unit 11 flatwise (parallel) against the door surface 25 is accompanied by substantial flexing of the springs 12,13, so that the (for example) forty five-degree angles become substantially right angles. The resulting spring flexure generates torque tending to hold the outside unit 11 flatwise against door surface 25. 
     In constructions where the springs 12,13 are not thick and wide enough to generate sufficient flexural spring force to hold outside unit 11 flatwise against door surface 25, double-sided adhesive strips, incorporating pressure-sensitive adhesive that is subsequently removable from the door surface, are adhesively provided on the feet or pads 24 of the outside housing 21, to adhesively secure such outside housing to the door. 
     After unit 11 is mounted and positioned, and while the door is in open condition, the inside unit 10 is pulled to thereby uncoil sufficient lengths of spring 12,13 to permit the inside unit to be positioned at the location illustrated in FIGS. 2 and 3. Such position is close to the door edge. 
     The coiled springs 12,13 generate torque that causes the inside housing 18 to pivot counterclockwise about those feet or pads 28 that are nearest the door edge, so that the feet or pads 26 remote from the door edge are caused to be firmly in contact with inside door surface 27. 
     The described torque results from interaction between the spring coils 12a,13a, and the adjacent spring and housing portions, which interaction is believed to create force vectors that pass generally through the axis 42 and through the bottom bearing posts 39 as viewed in FIG. 3. 
     The intercom apparatus is thus mounted in a matter of seconds or (in those situations where adhesive may be required relative to the pads 24 of the outside unit 11) in about a minute. 
     The spring elements 12,13 are not harmed by opening and closing of the door, this being because they are flat, and because they have no insulation thereon that becomes pinched, etc. On the other hand, the elements 12,13 are rugged and long lasting, and will create both technical connection and electrical connection for long periods of time. 
     It is to be understood that different numbers of springs 12,13 may be employed, as desired for strength and for production convenience. Preferably, however, there are at least two springs so as to provide two leads for the electric circuitry. 
     When the through-door intercom is employed in a vacation condo, hotel, etc., it may be removed in a matter of seconds after the vacation or hotel stay is over. 
     The foregoing detailed description is to be clearly understood as given by way of illustration and example only, the spirit and scope of this invention being limited solely by the appended claims.