US3678422A

US3678422A - Miniature crossbar switch

Info

Publication number: US3678422A
Application number: US167314A
Authority: US
Inventors: William A Reimer
Original assignee: GTE Automatic Electric Laboratories Inc
Current assignee: AG Communication Systems Corp
Priority date: 1971-07-29
Filing date: 1971-07-29
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18
Also published as: IT963294B; GB1402171A; CA980468A; BE786866A

Abstract

A miniature crossbar switch adapted to be mounted on and connected through a printed wiring card includes a plurality of orthogonal bus bars; those in a first direction being provided with a fixed electrical contact and those in the orthogonal direction being provided with a movable safety pin type contact element. A like plurality of orthogonally disposed select bars having notches adapted to receive the movable contact element are driven by solenoids in axial translation to urge the movable and fixed electrical contacts together to complete a selected circuit path.

Description

United States Patent Reimer [54] MINIATURE CROSSBAR SWITCH [72] Inventor: William A. Relmer, Wheaton, Ill. [73] Assignee: GTE Automatic Electric Laboratories Incorporated, Northlake, Ill.

22 Filed: July 29,1971

211 Appl.No.: 167,314

52 user ..33s/112, 20o/175 [51] Int. Cl. ..H0lh 67/14 [58] Field ofSearch .....335/1l2, 199; 200/175 [56] References. Cited UNITED STATES PATENTS 2,718,559 9/1955 Lundvist et a1. ..335/112 3,031,550 4/1962 Morrison ...335/l99 3,529,113 9/1970 Vazquez et a1. ..200/175 15] 3,678,422 51 July 18,1972

3,551,631 12/1970 Vazquez et a1. ..200/175 3,460,076 8/1969 Lundkvist ..335/1l2 Primary Examiner-Harold Broome Attorney-K. Mullerheim, R. F. Van Epps and B. E. Franz s7 ABSTRACT A miniature crossbar switch adapted to be mounted on and connected through a printed wiring card includes a plurality of orthogonal bus bars; those in a first direction being provided with a fixed electrical contact and those in the orthogonal direction being provided with a movable safety pin type contact element. A like plurality of orthogonally disposed select bars having notches adapted to receive the movable contact element are driven by solenoids in axial translation to urge the movable and fixed electrical contacts together to complete a selected circuit path.

11 Clairm, l0 Drawing figures PATENTEU JUL 1 81972 SHEET 1 OF 4 INVENTOR WILLIAM A. REIMER BY M #7 Z a M fl" ATTORNEY PATENTEDJUUBIBYZ 3678422 SHEET 2 [1F 4 v PATENTED JUL] 81972 SHEET U 0F 4 MINIATURE CROSSBAR SWITCH BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the field of electrical switching and more particularly to an improved crossbar type switch.

2. Description of the Prior Art Crossbar switches have long been known and widely used particularly in telephone systems as an economical means of providing a large switching capacity. The basic elements of the conventional crossbar switch are a number of vertical units each having a number of spring contacts mounted side by side on a base plate, a holding magnet for each vertical unit having an armature connected to the vertical bar, a number of horizontal select units, each having a number of bar-mounted flexible wire selecting fingers rotatable in two directions from a mid-position by the armature of an associated select electromagnet. The vertical units are generally mounted in a frame such that their spring contacts form horizontal rows and the selecting fingers are pivoted between two adjacent horizontal rows of spring contacts. Through selective operation of a select magnet and a holding magnet the selecting finger operates to close the spring contact at the crosspoint of the selected horizontal and vertical units. Once the selected contact is closed the select unit is released and the selecting finger is held in position by the operated holding unit. A crossbar switch of this general type is described in considerable detail in U.S. Pat. No. 3,445,795 which issued to R. P. Holtfreter et al. on May 20, 1969.

In the known crossbar switches of the above-described type the alignment of the critical components of the switch has been a continuing problem and the replacement of a worn component is not only difiicult due to the arrangement of the arts but also involves a realignment of the switch. Further, the switches of this type are generally hard wired; i.e., the wires leading to and from the switch are connected directly to the individual switch contacts thus complicating the removal and replacement of a crossbar switch unit from a rack of switches. Prior art cross-bar switches have typically not been optimized for economy of manufacture and in their normal use are not well adapted to having their mechanical components effectively protected from dust and moisture thus compounding the environmental control problems in the facility in which the switching system is housed. Finally the prior art crossbar switches are generally rather bulky and since relatively large numbers of switches are required, as in a telephone exchange, the available space is quickly taken up.

OBJECTS AND SUMMARY OF THE INVENTION From the foregoing discussion it will be understood that among the various objectives of the present invention are included the following:

to provide a new and novel crossbar switch;

to provide a switch of the above-described character which is economical of manufacture and of improved volumetric efficiency;

to provide a switch of the above-described character which is adapted for mounting on, and electrically coupling to a printed wiring card base;

to provide apparatus of the above-described character which is adapted to provide environmental protection of the mechanical components thereof; and

to provide a crossbar switch which is optimized for ease of repair and replacement.

These and other objectives of the present invention are efiiciently achieved by providing a printed wiring card base member adapted to receive an alignment guide frame in which are mounted a plurality of orthogonal, electrically conductive bus bars. Each bus bar arranged in a first direction is provided with a plurality of spaced fixed electrical contacts electrically coupled through the bus bar to the printed wiring card. The orthogonal busbars are each provided with a like plurality of movable safety pin type electrical contacts. A like plurality of orthogonally disposed, electrically non-conductive select bars are disposed in a select bar frame disposed adjacent the alignment guide frame. Each select bar is notched such as to engage the movable contacts when driven in axial translation by a selected solenoid. The activation of one solenoid in each of two directional arrays of solenoids operates to translate two orthogonal select bars thereby urging the movable contact at the crosspoint of the select bars together with a corresponding fixed contact to thereby complete a selected circuit path.

The foregoing as well as other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded schematic view of a miniature crossbar switch constructed in accordance with the principles of the present invention;

FIG. 2 is a more detailed schematic view of the elements of one crosspoint of the switch of FIG. 1;

FIGS. 3A-3E is a schematic diagram of the operation of a crossbar switch constructed in accordance with the principles of the present invention;

FIG. 4 is a detailed partial elevation view of the alignment guide frame of the switch illustrated in FIG. 1;

FIG. 5 is a detailed partial elevation view of a select bar actuating solenoid structure of utility in the practice of the present invention; and

FIG. 6 is a detailed schematic view with portions cut away of a select bar which may advantageously be used in the practice of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to FIG. 1 there is illustrated a printed wiring card 10 of conventional construction to which a plurality of signal lines (not shown) may be coupled. A first area 12 of the card 10 includes the circuitry 14 for providing the electrical connections to the orthogonal bus bars to be presently described. Second areas 16 of the printed wiring card 10 provide the electrical circuitry 18 necessary for the select bar activating solenoids also to be presently described. Electrical connections to the printed wiring card circuitry 14 and 18 is made via plated through holes 20 only several of which are shown for the purposes of illustration. The printed wiring card 10 is further provided with several alignment holes 21 adapted to receive corresponding projections (not shown) on the bus bar alignment guide frame 22, the detailed construction of which will be described hereinbelow. The alignment guide frame holds the orthogonal bus bars, only one pair of which, 24 and 26 are shown, in a spaced relationship with respect to one another. The lower or x bus bar 24 is provided with upstanding electrical. contacts 28 and with downward projecting tabs 30 adapted to mate with associated plated through holes 20 in the printed circuitry 14. In a like manner the upper or y bus bar 26 is provided with downward projecting tabs 32 which mate with associated plated through holes in the circuitry 14. Each y bus bar is provided with a plurality (only one being shown) of safety pin type movable electrodes 34 which under proper urging may be moved into electrical contact with the fixed electrical contact 28 on the x bus bar 24. The bus bar alignment guide frame 22 is provided with alignment holes 36 adapted to receive corresponding projections (not shown) on the select bar frame 38. The notched portions 40 of the alignment guide frame 22 and select bar frame 38 provide mounting channels for a plurality of orthogonal

select bars

42 and 44, only one pair of which are shown. Each

select bar

42 and 44 is provided with a plurality of notches or cut-outs 46 and is adapted to move in axial translation. Each select bar is notched at one end 50 to receive the armature of a solenoid as will later be described and is provided with a spring biasing means 52 which tends to retain the select bars in a preselected unoperated position against a select bar stop 48.

Low profile x and y solenoid assemblies 54 and 56 are disposed on the printed wiring card 10. In the preferred embodiment of the invention the solenoid cores 58 are formed in a continuous'strip and each core is provided with a solenoid bobbin 60 which is electrically coupled to the printed wiring card via terminals 62 which extend through plated through holes 64. Each solenoid is provided with a pivotal armature 66 retained in a position by a strip keeper spring 68 fixed to the printed wiring card 10.

Once assembled the electrical coupling between the printed wiring card 10 and the x and y bus bars and x and y solenoid windings may be efficiently made through a conventional wave soldering technique. Finally, if desired a cover 70 may beplaced over the entire mechanical assembly such as to leave only the plug portion 72 of the printed wiring card 10 exposed to the environment.

FIG. 2 schematically illustrates one crosspoint element of the crossbar switch wherein elements common to those discussed with reference to FIG. 1 are identified by like reference numerals. The crosspoint electrical coupling is made between a movable contact element 34 positioned by the x and y

select bars

42 and 44 respectively and a stationary electrical contact element 28. The movable contact element 34 is herein termed a safety pin element due to its shape and comprises a first cantilever spring portion 34a affixed to the y bus bar 26, a coil spring portion 34b and a second cantilever spring portion 340 on the free end of which is placed any desired long-life electrical contact material 34d. The fixed element 28 is fixed to or integrally formed with the x bus bar 24 and is preferably formed in a V-shaped and plated with a suitable contact material at the contact end 28a.

In operation, the y select bar 44 is translated along its longitudinal axis in the direction of the arrow thereby engaging movable contact 34 and moving the free end cantilever portion 34c with its electrical contact 34d into alignment with the fixed contact 28. The at select bar 42 is then" translated along its longitudinal axis to engage the cantilever portion 34c near the contact 34d and thereby urge the contacts 34d and 28a into electrical contact. Once the contact is made the y select bar 44 may be released and the contact will be maintained so long as the x select bar 42 remains operated thereby holding the contact 34d against the V-shaped fixed contact 28a. It is preferred that the x select bar 42 engage the movable element 34 very near thecontact area 34d in order to minimize x select bar 42 travel required to effect the connection and to minimize the effects of vibration in the element 34. The round or curved contact 34d engages two separate areas on the fixed contact 28a when contact a is made thereby providing a contact redundancy and thus improved reliability of operation. It is preferred in the practice of the invention that the safety pin contact elements 34 be automatically positioned on and welded to the x bus bar 26 and that the fixed contact 28 be integrally formed with the y bus bar 24 in order that handling is simplified and accurate spacing between adjacent elements is provided. The

connection tabs

30 and 32 on y and x bus bars 24 and 26 respectively are also preferably formed integrally with the bus bars for accuracy in spacing and are formed such that the bus bars do not make electrical contact with circuitry on the card surface.

FIGS. 3A-3E serve to better illustrate in a schematic top view the operation of the present invention. Again elements previously described are identified with common reference numerals. FIG. 3A shows a segment of the crossbar switch including x select bars 42, through 42 y select bars 44, through 44 and a movable electrical contact element 34 and fixed contact 28 associated with each intersection of x and y

select bars

42 and 44. In FIG. 3B y select bar 44, has been translated in the direction of the arrow engaging the free end of movable contact 34 preferably near its furthest point from its bus bar such that minimum select bar movement produces maximum movement of the free end of contact 34. The x select bar 42 acts as a stop when the y select bar 44, moves the free end of element 34 into alignment with the fixed contact 28. In this stage of operation the protrusions of the x select bars 42 mask the stationary contacts 28 such that inadvertent connections cannot be fonned. To complete the desired connection as shown in FIG. 3C x select bar 42 is translated in the direction of the arrow engaging the free end of movable contact 34 proximate the contact area urging the contact 34 into the V- shaped portion of fixed contact 28. As illustrated in H6. 3D the y select bar 44, may be returned to its original position although x select bar 42 must remain displaced so long as the connection is to be maintained. The movable contact element 34 cannot return to its disconnected position since it is trapped between the x select bar 42 and the V-shaped fixed contact element 28. With one x select bar 42 holding a crosspoint connection all of the y select bars 44 are unaffected and may be used in establishing other connections. When the connection is to be broken, as shown in FIG. 3E, the x select bar 42 is returned to its original position releasing the movable contact element 34 which disconnects from fixed contact 28 due to its spring characteristics.

With reference now to FIG. 4 there is shown an elevation view of a portion of the bus bar alignment guide frame 22 mounted on printed wiring card 110. The guide frame 22 may be easily molded of one of a variety of plastic materials and is used to provide alignment of the x and y bus bars normal to the surface of the wiring card 10 and to provide a guide surface for the x and y select bars. When affixed to the printed wiring card 10 the alignment guide frame also serves to provide additional structural integrity and removal of any card warpage which may be encountered. The alignment guide frame is provided with slots 74 and 76 the latter being deeper than the former to permit the y bus bars to be maintained beneath the x bus bars. The notches 40 in the guide frame 22 provide a guide surface over which the x and y select bars move and are again stepped to provide the necessary elevation differential between the orthogonal select bars.

FIG. 5 illustrates in greater detail a segment of the low profile x and y select bar operating solenoid subassemblies 54 and 56 preferred in the practice of the present invention as described with reference to FIG. 1. Although conventional solenoids may be used in the present crossbar switch it is preferred for ease of construction to provide a plurality of solenoid cores 58 formed of a single continuous strip of suitable material. This strip of cores may then be affixed to the printed wiring card 10 by any convenient means such as eyelets 78. Each core 58 on the strip is fitted with a wire wound solenoid bobbin 60 with the ends of the winding brought out to terminals 62 adapted to engage plated through holes 20 in the printed wiring card 10. Individual solenoid armatures 66 are formed to pivot about the lower front edge of each solenoid core 58 and have an upward extending portion 82 adapted to engage the notched end of the select bars as illustrated in FIG. 1. Solenoid keeper springs 68 are preferably formed in a continuous strip and are affixed to the printed wiring card 10 such as by clinch tabs 84 extending therethrough. Each keeper spring 68 engages a depression 86 formed in the outer surface of each armature 66. When a current is passed through the solenoid winding an attractive force is applied to the armature 66 moving the extended portion inwardly as the armature pivots about the lower front edge 80 of core 58.

Finally, with reference to FIG. 6 there is schematically shown a partial view of the end detail of a typical select bar such as 42. The select bars are preferably molded from any suitable plastic material and as stated hereinabove are provided at their operated end with a notch or cut-out 50 adapted to receive the upward extending portion 82 of an individual solenoid armature 66. A select bar spring biasing means 52 is affixed to the top edge of the select bar frame 38 and engages a notch 84 in the upper surface of each select bar 42 providing an outward biasing force which retains the select bar stop 48 against the inside of the select bar frame 38. Notches 40 in the alignment guide frame 22 and select bar frame 38 align to provide the select bar 42 with a guide surface or channel in which the select bar is free to move in translation when activated by inward movement of the solenoid armature 66.

The crossbar switch of the present invention when assembled is particularly well suited for mounting in conventional printed wiring card shelves or racks with the connector plug portion engaging a suitable rack mounted connector to which input and output wiring connections may easily be made. An entire switch may be replaced by simply unplugging it from its associated connector and plugging in the replacement. Repairs to the switch are facilitated since the alignment of the various electrical and mechanical components is provided by stamped and/or molded structural elements which automatically locate the various elements in their proper position without the necessity of manual adjustment procedures.

It will thus be seen that through the practice of the present invention there is provided a new and improved crossbar switch wherein the objectives set forth hereinabove are efficiently achieved. Since certain changes in the above-described construction will occur to those skilled in the art without departure from the scope of the invention it is intended that all matter contained in the foregoing description or shown in the appended drawings shall be interpreted as illustrative and not in a limiting sense.

Having described what is new and novel and desired to secure by Letters Patent, what is claimed is:

l. A crossbar switch for coupling any selected one of a first plurality of signal lines to any selected one of a second plurality of signal lines, said switch comprising a printed wiring card having a plurality of signal lines coupled to the circuit portions thereof;

a first plurality of spaced apart, substantially parallel, electrically conductive bus bars each provided at one edge with a plurality of spaced upstanding fixed electrical contact elements and at the opposite edge with downward extending electrically conductive tabs adapted to selectively engage circuit portions of said printed wiring card;

a second plurality of spaced apart, substantially parallel, electrically conductive bus bars oriented orthogonally in a spaced relation with respect to said first plurality of bus bars, each provided at one edge with a plurality of spaced upstanding safety pin type movable electrical contact elements and at the opposite edge with downward extending electrically conductive tabs adapted to selectively engage circuit portions of said printed wiring card;

a first plurality of spaced apart, substantially parallel, electrically non-conductive select bars arranged parallel with and in spaced relation with respect to said first plurality of bus bars, each said select bar adapted for axial translation, and having a plurality of spaced vertically oriented notches adapted to engage said movable electrical contacts;

a second plurality of spaced apart, substantially parallel, electrically non-conductive select bars arranged parallel with said second plurality of bus bars and in orthogonal spaced relation with respect to said first plurality of select bars, each said select bar adapted for axial translation, and having a plurality of spaced vertically oriented notches adapted to engage said movable electrical contacts;

means for driving a selected orthogonal pair of said select bars in axial translation such that said notches therein engage a movable contact element at the crossing of said orthogonal pair and urge it into electrical contact with said fixed electrical contact element.

2. Apparatus as recited in claim 1 wherein said select bar driving means comprises a solenoid associated with each said select bar, disposed on and having the windings thereof coupled to said printed wiring card and having an armature engaging one end of said select bar such that operation of said solenoid drives said select bar in axial translation.

3. Apparatus as recited in claim 1 further including a select bar frame adapted. to retain said first and second pluralities of select bars in a preselected disposition with respect to one another and permitting only axial translation of each said select bar; spring biasing means affixed to said select bar frame, engaging each said select bar, and providing an outwardly directed biasing force of preselected magnitude to each said select bar;

a select bar stop disposed on eachsaid select bar inwardly of said select bar frame, and operative to restrict outward axial translation of said select bar to a predetermined maximum; and

each said select bar driving means being operative to selectively drive said select bar inwardly with respect to said select bar frame against said spring biasing force.

4. Apparatus as recited in claim 2 wherein the solenoids associated with each of said first and second pluralities of select bars include a plurality of solenoid cores formed of a single continuous strip of ferromagnetic material, each said core being provided with a wire wound bobbin having terminals adapted to selectively engage circuit portions of said printed wiring card, and an armature adapted to pivot about one edge of said solenoid core.

5. Apparatus as recited in claim 4 further including a solenoid keeper spring associated with each of said plurality of solenoids, affixed to said printed wiring cards and engaging each said armature such as to retain same in pivotal contact with said solenoid core.

6. Apparatus as recited in claim 1 further including an alignment guide frame affixed to said printed wiring card, adapted to receive and retain said first plurality of bus bars in a selected first plane parallel to said printed wiring card, and adapted to receive and retain said second plurality of bus bars in a selected second plane parallel to said printed wiring card and spaced apart from said first plurality of bus bars, each of said first and second plurality of bus bars being substantially normal to the plane of said printed wiring card.

7. Apparatus as recited in claim 1 wherein each of said safety pin type movable electrical contact elements comprises a first cantilever spring portion affixed at one end to and upstanding from said second plurality of bus bars, a coil spring portion at the opposite end of said first cantilever spring portion, a second cantilever spring portion extending downwardly from said coil spring portion terminating in a movable free end, and all of said spring portions integrally formed from a single piece of spring material.

8. Apparatus as recited in claim 7 wherein said first plurality of select bars engage said movable electrical contact elements at said second cantilever spring portions proximate the coil spring portions thereof, and said second plurality of select bars engage said movable electrical contact elements at said second cantilever spring portion proximate the free end thereof.

9. Apparatus as recited in claim 1 further including plated through holes disposed in the circuit portions of said printed wiring card and adapted to receive and electrically couple with said downward extending tabs of said first and second pluralities of said bus bars.

10. Apparatus as recited in claim 1 further including protective means engaging said printed wiring card and covering said bus bars, select bars and driving means to thereby substantially prevent the entry of foreign matter into said switch.

11. Apparatus as recited in claim 1 wherein each of said fixed electrical contact elements are integrally formed with said first plurality of bus bars and are formed at the upstanding portion thereof in a V-shape adapted to receive and retain said movable electrical contact element.

Claims

1. A crossbar switch for coupling any selected one of a first plurality of signal lines to any selected one of a second plurality of signal lines, said switch comprising a printed wiring card having a plurality of signal lines coupled to the circuit portions thereof; a first plurality of spaced apart, substantially parallel, electrically conductive bus bars each provided at one edge with a plurality of spaced upstanding fixed electrical contact elements and at the opposite edge with downward extending electrically conductive tabs adapted to selectively engage circuit portions of said printed wiring card; a second plurality of spaced apart, substantially parallel, electrically conductive bus bars oriented orthogonally in a spaced relation with respect to said first plurality of bus bars, each provided at one edge with a plurality of spaced upstanding safety pin type movable electrical contact elements and at the opposite edge with downward extending electrically conductive tabs adapted to selectively engage circuit portions of said printed wiring card; a first plurality of spaced apart, substantially parallel, electrically non-conductive select bars arranged parallel with and in spaced relation with respect to said first plurality of bus bars, each said select bar adapted for axial translation, and having a plurality of spaced vertically oriented notches adapted to engage said movable electrical contacts; a second plurality of spaced apart, substantially parallel, electrically non-conductive select bars arranged parallel with said second plurality of bus bars and in orthogonal spaced relation with respect to said first plurality of select bars, each said select bar adapted for axial translation, and having a plurality of spaced vertically oriented notches adapted to engage said movable electrical contacts; means for driving a selected orthogonal pair of said select bars in axial translation such that said notches therein engage a movable contact element at the crossing of said orthogonal pair and urge it into electrical contact with said fixed electrical contact element.

3. Apparatus as recited in claim 1 further including a select bar frame adapted to retain said first and second pluralities of select bars in a preselected disposition with respect to one another and permitting only axial translation of each said select bar; spring biasing means affixed to said select bar frame, engaging each said select bar, and providing an outwardly directed biasing force of preselected magnitude to each said select bar; a select bar stop disposed on each said select bar inwardly of said select bar frame, and operative to restrict outward axial translation of said select bar to a predetermined maximum; and each said select bar driving means being operative to selectively drive said select bar inwardly with respect to said select bar frame against said spring biasing force.