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United States Patent 3,622,924
Harcourt November 23, 1971

ELECTRIC SWITCHES

Abstract

A crossbar switch comprising a rectangular array of contact sets formed by intersecting wires. Each contact set is operated by an individual interposer member, each row of interposer members being moved by a select magnet armature into operative positions and each column of interposer members being driven, if in an operative position, to operate their respective contact sets. The travel of the select magnet armature is limited in one direction by a stop member and in the other by the magnet core which is itself biased against the stop member.


Inventors: Harcourt; Michael David (Coventry, EN)
Assignee: The General Electric Company Limited (London, EN)
Appl. No.: 05/064,300
Filed: August 17, 1970


Foreign Application Priority Data

Aug 15, 1969 [GB] 40,950/69

Current U.S. Class: 335/112
Current International Class: H01H 67/26 (20060101); H01H 67/00 (20060101); H01h 067/26 ()
Field of Search: 335/112 200/176,177

References Cited

U.S. Patent Documents
3427575 February 1969 Mustafa
3460076 August 1969 Lundkvist
3478285 November 1969 Haines et al.
3509301 April 1970 De Smet
Primary Examiner: Broome; Harold

Claims



I claim:

1. A crossbar switch comprising an array of contact sets arranged in rows and columns, an interposer member in respect of each contact set, a set of row coordinate members, each row coordinate member being coupled to a respective row of interposer members, means for operating each row coordinate member selectively to drive the associated row of interposer members into respective driving positions, a set of column coordinate members, each column coordinate member being coupled to a respective column of interposer members, means for operating each column coordinate member selectively, to drive any interposer member of the associated column which interposer member is in a said driving position, into operative engagement with the associated contact set, wherein said means for operating the coordinate members of one of said sets comprises electromagnetic armature means, an electromagnetic core, and a stop member in respect of each coordinate member of the set, said armature means having unoperated and operated positions determined by, respectively, said stop member and said electromagnetic core, and further comprising means for biasing said core into engagement with the stop member and means for biasing said armature means into engagement with the stop member in the unoperated position of the armature means.

2. A crossbar switch according to claim 1, wherein said armature means comprises a magnetic armature and a nonmagnetic member.

3. A crossbar switch according to claim 2, wherein said nonmagnetic member is integral with a respective coordinate member of said one set.

4. A crossbar switch according to claim 2, wherein said nonmagnetic member is coupled to a respective coordinate member of said one set.

5. A crossbar switch according to claim 2, wherein said nonmagnetic member engages said stop member to determine the unoperated position of said armature means.

6. A crossbar switch according to claim 5, wherein said magnetic armature and said core have cooperating plane surfaces, said magnetic armature and said nonmagnetic member have plane surfaces in permanent engagement, said nonmagnetic member and said stop member have cooperating plane surfaces, and the plane surfaces of said nonmagnetic member respectively in engagement with said magnetic armature and cooperating with said stop member, are parts of a common plane surface, the movement of said nonmagnetic member between the unoperated and operated positions of the armature means being determined by the displacement between said plane surface of said stop member and the position of engagement of said core with said stop member.

7. A crossbar switch according to claim 2, wherein said stop member is common to a plurality of the armature means and cores associated with said one set of coordinate members.

8. A crossbar switch according to claim 2, wherein said nonmagnetic member is engaged by a respective coordinate member of said one set, the coordinate member being a longitudinal member, the switch further comprising means for biasing said longitudinal member into end-on engagement with the respective said nonmagnetic member so as to be driven against this bias by operation of the associated armature.

9. A crossbar switch according to claim 8, and comprising a rigid housing in which said cores, armatures, nonmagnetic members and the stop member associated with said one set of coordinate members are all mounted to form a subassembly of the switch, the switch further comprising a main frame on which said rigid housing is mounted and means for mounting said coordinate members of said one set on said main frame separately from said subassembly.
Description



This invention relates to electric switches and particularly to crossbar switches such as may be used in telephone exchanges.

Examples of crossbar switches are described in U.S. Pat. No. 3,478,285 dated 11 Nov. 1969 for Electric Crossbar Switches, by Ernest Martin Haines and Henry Bastian Taylor, and the present invention is directed to an improvement in such switches.

For the purposes of this specification a crossbar switch is defined as a switch having a plurality of conducting paths in each of two coordinate directions, a path in one of the two directions being connected to a path in the other direction by a contact set at the crosspoint of the two paths, and each contact set being operated by cooperation of a coordinate member in respect of one of the two paths and a coordinate member in respect of the other. Thus the term crossbar switch is not to be taken as limiting the kind of contact set employed-- which may for example be relay contact sets or wire multiples such as will be described.

The present invention is concerned with minimizing the effects of manufacturing and assembly tolerances in the production of crossbar switches.

According to the present invention, a crossbar switch comprises an array of contact sets arranged in rows and columns, each contact set being operable by a respective interposer member, and a set of row coordinate members and a set of column coordinate members together operable to select an interposer member associated with a particular row and a particular column for operative engagement with the associated contact set, the coordinate members of one of said sets being movable by respective electromagnetic armature means, each of which has unoperated and operated positions determined by, respectively, a stop member and a respective electromagnetic core with which the armature means cooperates, the core, and the armature means in its unoperated position, being located by engagement with said stop member.

The armature means may comprise a magnetic armature and a nonmagnetic member which is integral with or coupled to a respective coordinate member of said one set. The unoperated position of the armature is then preferably determined by the engagement of said nonmagnetic member with said stop member.

The arrangement may be such that the armature and the core have cooperating plane surfaces, the armature and the nonmagnetic member have plane surfaces in permanent engagement, the nonmagnetic member and the stop member have cooperating plane surfaces, and the plane surfaces of the nonmagnetic member respectively in engagement with the armature and cooperating with the stop member, are parts of a common plane surface, so that the movement of the nonmagnetic member between the unoperated and operated positions of the armature is determined by the displacement between said plane surface of the stop member and the position of engagement of said core therewith. The stop member is preferably common to a plurality of the armature means and cores associated with said one set of coordinate members.

The nonmagnetic member may be engaged by a respective coordinate member of said one set, the coordinate member being a longitudinal member biased into end-on engagement with the respective said nonmagnetic member so as to be driven against this bias by operation of the associated armature. Each nonmagnetic member may then be individually biased into engagement with the stop member by the associated coordinate member.

The cores, armatures, nonmagnetic members and the stop member associated with said one set of coordinate members may all be mounted in a rigid housing to form a subassembly of the switch, the housing being mounted on a main frame of the switch on which frame, the coordinate members of said one set are then separately mounted.

A crossbar switch in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, of which:

FIG. 1 is an exploded front elevation of the crossbar switch, the upper part being the contact set assembly and the lower part the operating mechanism;

FIG. 2 is a plan view of the contact set assembly;

FIG. 3 is an end view, from the left in FIG. 2, of a particular column of contact sets;

FIG. 4 is an underneath plan of the column of FIG. 3;

FIG. 5 is a sectional elevation on line V--V of FIG. 3 showing a single (level-switching) contact set;

FIG. 6 is a plan view of the operating mechanism shown in the lower part of FIG. 1;

FIG. 7 is a bridge mechanism as seen in the left-hand end view of the operating mechanism of FIG. 6, the magnet assembly being removed and the select bars being shown in section, said figure being taken substantially along the line VII--VII of FIG. 6.

FIG. 8 is a plan view of the bridge mechanism shown in FIG. 7 with the mounting plate (shown in FIG. 6) removed;

FIG. 9 is a perspective view of a molding shown at the left hand ends of FIGS. 7 and 8 by means of which (and a corresponding right hand molding) the bridge mechanism of FIGS. 7 and 8 is mounted to the late shown in FIG. 6;

FIG. 10 is an end view (from the right in FIG. 1) of a pivoted part, an armature assembly, of the bridge mechanism of FIG. 7 (from the rear of FIG. 7);

FIG. 11 is a part-broken away end view of the armature assembly shown in FIG. 10;

FIG. 12 is a section on line XII--XII of FIG. 10;

FIGS. 13 and 14 are plan view and elevation on an enlarged scale of an interposer block shown as a detail in FIG. 12;

FIG. 15 is a perspective view of part of a channel molding shown as a detail in FIGS. 10, 11 and 12;

FIGS. 16 and 17 are front elevation and end-view of a molding for a contact assembly in respect of each bridge mechanism, to be referred to as a bridge off-normal contact set. This molding couples with that of FIG. 9.

FIG. 18 is a part broken away end view of the operating mechanism shown in FIG. 1 from the left hand end;

FIG. 19 is a part section on line XIX--XIX of FIG. 18, no bridge mechanism being shown: and

FIGS. 20 and 21 are front and end elevations of a coordinate operating member shown in position in FIGS. 7 and 8.

The scales of the various figures have been adjusted for convenience and clarity and are in groups of increasing scale as follows: 20, 21; 1, 2, 6; 7-12, 15, 18, 19; 16, 17; 3, 4, 5; 13, 14.

FIGS. 22-29 show modifications of various features of the switch.

FIGS. 22 and 23 correspond to FIGS. 10 and 11 and show views of a bridge armature assembly;

FIG. 24 is an end elevation of a channel molding corresponding to that of FIG. 15;

FIG. 25 is a part section elevation of the operating mechanism for one coordinate of the system and corresponds to FIG. 19;

FIGS. 26, 27 and 28 are part sectional elevation, end elevation and sectional elevation on the line X--X of FIG. 26 respectively, of a member which corresponds to the left-hand end of the member shown in FIG. 20; and

FIG. 29 is a plan view of a coordinate member corresponding to the right-hand end of the member shown in FIG. 20.

Referring to FIGS. 1-21 of the drawings, the switch comprises a matrix 51 (FIG. 2) of contact sets mounted on an operating mechanism 52 as shown in FIG. 1.

The contact set matrix is described in detail in copending Pat. application, Ser. Nos. 33,615, 33,616 and 33,617, all filed on May 1, 1970.

The contact set matrix comprises a rectangular array of contact set assemblies 53 of which columns one and ten are shown in FIG. 2, the remaining columns being shown only in block form. There are 13 assemblies 53 in each column, numbered as shown in FIG. 2. An extra column, at the left of FIG. 2, and an extra row at the top of FIG. 2, consist of connector housing 14 by means of which connections are made to and from the switch. The row of housings 14 carry inlet connectors 41 and the column of housings 14 carry outlet connectors 43. The housings 14 are so shaped as to accommodate row and column connectors equally.

It can be seen from FIG. 2 that rows one, two and three are not provided with connectors 43, these three rows being what will be called level-switching rows, as will be explained. As shown in columns one and ten, each assembly 53 comprises a contact set housing 4 and a comb member 25, which moves within the housing 4 perpendicular to the plane of FIG. 2.

The columns of assemblies 53 are clamped between clamping strips 54 extending the length of the matrix at the top edge and by clamping strips 55 extending beyond the matrix at the lower edge. The columns are located with respect to each other by means of accurately positioned holes in the clamping strips 54 and 55, in which holes, spigots on the assemblies 53 (at the row 13 side of the switch) and on the connector housing 14 (on the row-one side) locate.

Feet 56 on the lower clamping strip provide a mounting means for the matrix.

On the row 13 side of the matrix, a side plate 57 in the form of a thin sheet of insulating material closes off the row 13 assemblies 53. The clamping strips 54 and 55 on this side of the matrix separate the side plate 57 from a cover plate 58 which is attached by means of tie rods which extend through the assemblies 53.

The conductor matrix itself, which provides the contact sets, comprises ten row conductors 2 in rows 4 to 13 in each of 12 tiers, and 10 column conductors 3 in each of the 12 tiers. Thus each assembly 53 comprises the crosspoint of a row conductor 2 and a column conductor 3 in each of the 12 tiers.

FIGS. 3 and 4 show the details of a column of the assemblies 53, and FIG. 5 shows the details of a contact set assembly in a level-switching row (row three). From FIG. 4 the row conductors 2 can be seen to extend through the assemblies 53 in the `normal` rows while terminal wires 18 in the level-switching rows relate to a particular column only. The column wires 3 are looped, as shown, to provide a redundant contact at each corsspoint. Access to a column wire 3 in a particular column is obtained by way of a terminal wire 18 in the same column and tier, by operation of an appropriate level-switching crosspoint in that column, and access from that column wire 3 to a row wire 2 of a particular row is obtained by way of a crosspoint in the particular row and column.

It can be seen from FIGS. 3 and 5 that the terminal wires 18 are in groups of four in each column plane, each group of four terminal wires extending to a different one of the level-switching rows one, two and three. The three groups are commoned outside the matrix so that a four-wire inlet to a particular column can be connected to the column wires 3 of tiers 1-4, 5-8 or 9-12 according as a crosspoint is operated in level-switching row one, two or three.

Operation of a crosspoint contact set, both normal and level-switching is effected by a comb 25 shown in FIG. 5. The teeth 26 of the comb, interleave the twelve contact pairs and movement of the comb vertically upwards as shown in FIG. 5 deflects the row wires 2 (or the terminal wires 18 if in a level-switching row) into contact with a column wire 3. The comb 25 has a lower extension 32 (also shown in FIG. 1) which engages the operating mechanism.

The operating mechanism, shown in the lower part of FIG. 1 and in FIG. 6, comprises two sets of coordinate members which are aligned with the rows and columns of the conductor (i.e., contact set) matrix. The row coordinate members are referred to herein as select bars and the column coordinate members as bridge bars.

An interposer member individual to each crosspoint contact set is mounted so as to be movable along the switch by a select bar (which similarly couples with each interposer member in the particular row) from an inoperative position to a driving position, and to be moved transversely to the conductor matrix by the associated bridge bar. When an interposer member is in a driving position and is then driven vertically by a bridge bar, the associated comb is similarly driven vertically and the contact set is operated.

The operating mechanism to be described embodies the select bars, bridge bars, interposer members, and their mounting and control arrangements.

Referring to FIGS. 1 and 6 the operating mechanism is supported by a mounting plate 61 which serves as a main frame for the switch. This plate 61 is rigid and is used as a datum for the positioning of the conductor matrix and the various parts of the operating mechanism.

Considering first the column coordinate members, i.e., the bridge bars, these are embodied in a bridge assembly 62 of which there are ten, as shown in FIG. 1. The bridge assemblies are independent of each other and are individually mounted on the plate 61 by screws 63 on each side of the plate. A spigot 64 on each end of the bridge assembly 62 engages a corresponding hole in the plate 61 and locates the assembly accurately.

Referring to FIGS. 7 to 17 additionally, each bridge assembly 62 comprises a magnetic core 65 of U-form which is mounted in moldings 66 and 67. The molding 66 on the left in FIGS. 7 and 8 is the rear molding (shown in broken lines) in FIG. 6 and the molding 67 is at the front in FIG. 6. The rear molding 66 is shown in perspective in FIG. 9.

Two screws 71 clamp the core 65 laterally in the moldings 66 and 67 and two screws 72 locate the core vertically in the same moldings. A spring 73 is positioned in a recess 74 in each molding 66 and 67, this spring engaging the mounting plate 61 at its upper end and bearing on the top of a limb of the core 65 at its lower end. The core 65 is thus positioned accurately and adjustably with respect to the mounting plate 61.

A magnetizing coil 76 is mounted on the lower limb of the core 65, the coil having terminal connections 77.

The bridge armature 78 and all of the parts which move as one with the armature are shown in FIGS. 10 and 11. This armature assembly is pivoted on the upper edges of the limbs of the core 65, on the inner portions 81 of these edges, on the near face of the yoke in FIG. 7.

A bridge frame 83 extends above the armature 78 and has arms 84 to which the armature is fixed by screws 82. Further arms 85 of the frame 83 extend downwardly below the armature 78, these arms 85 carrying an interposer assembly which is fixed by clamping strips 86 and screws 87.

The frame 83 incorporates, at its junction with the arms 84, a metal insert 91 (the frame 83 being of plastics material) which insert is angled to receive, and pivot on, the edge 81 of the core 65. Movement of the armature 78, in and out of engagement with the core 65, on energization of the coil 76, causes the whole armature assembly to pivot on the edges 81 of the core. A cantilevered leaf spring 92 held by the armature fixing screw 82 constitutes a return spring and biases the armature 78, and associated assembly, out of engagement with the core. Return movement of the armature assembly is limited by stops 90 on the moldings 66 and 67 which abut the arms 84 in the return (unenergized) position.

The armature assembly is retained in its pivoted position on the limbs of the core 65 by retaining members 89 which are attached by screws to the core 65 and extend around the edge of the frame 83 retaining the frame but permitting its pivoting action.

FIG. 15 shows part of a channel molding of which there are two, 93 and 94, mounted underneath the bridge frame 83 (FIG. 10). The longer one of these, 93, relates to the ten `normal` rows of the switch and the shorter one, 94, to the three level-switching rows. The two channel moldings are biased into engagement with the underside of the frame 83 in the following manner. A spring 95 has a closely wound upper end which engages a screw 96 in the frame 83 in the manner of a nut (FIGS. 11 and 12). The lower end of the spring is anchored by a pin in the bottom of the channel 93 (or 94). The long channel molding 93 has three such fixings and the short channel molding 94 has one. Both of the channel moldings have a flange, constituting the bridge bar 97, extending along their length, which, as can be seen from FIG. 1, is vertically aligned with a step on the lower ends 32 of a column of the combs 25. Operation of the bridge magnet causes the whole armature assembly of FIGS. 10 and 11 to rock on the pivots 91 to allow the armature 78 to close the magnetic circuit of the core 65. The channel moldings 93 and 94 move with the rest of the assembly with the result that the bar 97 moves upwardly towards the combs 25. However, the spacing is such that the bar cannot normally reach the combs. Coupling between the bar 97 and the combs 25 is effected as follows.

The interposer assembly comprises a comb stamped out of thin spring metal sheet the root of which is clamped between the clamping strips 86. Each interposer arm 101 (i.e., each tooth of the comb) terminates in a fork in which an interposer block 102 is trapped. The interposer block is shown in FIGS. 13 and 14 and has two slots 103 at its rear end which receives the `prongs` of the fork. The interposer block can thus be driven forwards and backwards by the interposer arm 101 parallel to the rows of the switch.

Referring again to FIGS. 12 and 15, the channel moldings 93 and 94 have the top of one wall, adjacent the bar 97, shaped in the manner of battlements, the alternate, low parts being at the level of the upper surface of the bar 97. The bar 97 is spaced from, and joined to, the channel wall by portions 98 aligned with the high parts of the `battlements.` There is thus a hole 104 (FIG. 12) in front of each battlement `low.` These holes 104 are at the pitch of the interposer arms 101 which extend through them and carry the interposer blocks 102 in a position just overlying the battlement `low` (to the rear) and the bar 97 (to the front).

The portions 98 are proud of the surface of the bar 97 by an amount slightly greater than the thickness of the interposer blocks 102 which can therefore be trapped by a lid 99 shown in FIGS. 8 and 10. There are two lids 99, one for each of the channels 93 and 94 and these are fitted extending along the portions 98 against a small projection at the rear of each portion 98. The lids are secured by pegs 100, over which they are a force fit. The interposer blocks 102 are thus trapped in position being free to move only forwards and backwards within the limits of the interposer arm 93 in the hole 104.

In the normal, relatively unstressed, position of the interposer arms 10, that is, as shown in FIG. 12, the arm 101 is to the rear of the hole 104 and the bar 97 is not covered by the interposer block 102. Operation of the bridge magnet in this position of the block 102 causes no engagement of the comb 25. If the interposer arm is moved to the front of the hole 104, the interposer block 102 is moved to what may be called a driving position in which, if the bridge magnet is operated the block 102 is interposed between the bar 97 and the end 32 of the comb 25 and is of sufficient thickness to cause vertical movement of the comb 25 and operation of the associated contact set.

The channel moldings 93 and 94 have an end web 105 to brace the channel although this has been removed from FIG. 11 for clarity. The rear wall of the channel 93 is curved at the top to provide a sharp pivot edge 106 which beds into a slightly obtuse corner recess of the frame 83. At each end of this corner recess is a square projection which engages a cut-out 107 in the edge 106 (one in the channel 93 and one in the channel 94).

The effect of spring mounting of the channel 93 and its integral bar 97 is to provide a lost-motion coupling in the drive between the bridge magnet armature and the contact set comb 25. Thus the travel of the interposer blocks 102 is limited by the stop provided for the comb 25 and not by any stop to the travel of the main body of the bridge assembly 78. Any movement of the armature which is excessive for the operation of the comb 25 is `lost` by the spring mounting of the driving bar 97, the channel 93 pivoting on its edge 106 when further movement of the bar 97 is resisted by the comb. Thus the operating pressure on the combs 25 is kept much more nearly constant and accuracy of positioning of the contact set matrix with respect to the operating mechanism is somewhat relaxed.

Two channels 93 and 94 are necessary in each column as the three level-switching rows have to be operable independently of the ten normal rows.

It is desirable that a signal be available when any bridge magnet is operated and for this reason a set of `off-normal` contacts are provided for each bridge. The housing 107 for these contacts is shown in FIGS. 16 and 17 and is mounted on the rear core molding 66 (FIGS. 7, 8 and 9). Two angled lugs 111 and 112 mate with corresponding holes 113, 114 in the molding 66, these holes extending first inwards and then sideways (not visible in FIG. 9) to provide a bayonet fixing. A leaf spring (not shown) extends between two slots 115 in the molding 66 and is deflected, to the right in FIG. 9, by a peg 116. To assemble the housing 107 it is presented to the molding 66 so that the peg 117 deflects the leaf spring further to the right until the lugs 111 and 112 are aligned with the holes 113 and 114. The lugs are then pressed home and the leaf spring acting on the peg 117 biases the lugs into their trapped position.

Referring to FIGS. 7, 8 and particularly 10, a projection 116 of the arm 84 of the bridge frame, moves with the armature 78 and drives a contact comb (not shown) which projects from the housing 107. Off-normal contacts not shown but within the housing 107 are thus operated or not according to the condition, operated or not, of the particular bridge.

Having now described the bridge assemblies the other coordinate members, the select bars will be described. The bars 120 are shown in FIGS. 20 and 21 and for the main part of their length are of angle section (as can be seen in FIG. 7). The bars extend substantially the whole length of the switch and the horizontal flange is notched (as shown in FIGS. 20 and 8), the notches being referenced 121. Each bar 120 has a right-angled forked end 122 by means of which the bar is driven longitudinally. The end face of this forked portion 122 is plane and perpendicular to the bar for engagement by a plane armature. One select bar is used for each row of the switch and to accommodate the driving magnets of thirteen select bars the forked portions 122 on alternate bars 120 are inverted so that seven select magnets are arranged side-by-side above the bars and six side-by-side below the bars. The select magnet assembly 123 is shown in FIGS. 12 and 19 and, in position, to the left of FIGS. 1 and 6.

The notches 121 have a smoothly curved rear edge which, in the normal (unenergized) position of the bar 120, lies to the rear (the left in FIGS. 1, 11 and 12) of a respective interposer arm 101. On driving a select bar to the right therefore, all ten interposer arms of the particular row will be deflected forward (if not already in that position) and the interposer blocks 102 will be interposed between the bars 97 and the lower ends of the row of combs 25. Operation of any bridge magnet will then cause a single comb 25 to be driven upwards to operate its contact set.

In FIG. 8, which shows only one bridge assembly, the rear edges of one column of notches 121 in the select bars 120 are shown and the leading edges of the next column of notches.

At the leading end of the select bars a support and guide member 124 is provided which is mounted on the main plate 61 by screws 125. Immediately ahead of this guide member is a `select off-normal` contact assembly 126 which comprises a column of 13 contact sets each operable by a respective arm 127 (FIG. 1). As a select bar is driven forward the associated arm 127 is driven against a return spring (not shown) to `make` the contact set. Thus an indication is provided of the operation of any select bar.

Referring now to FIGS. 6, 18 and 19 the select magnet assembly comprises two identical magnet housings 131 and 132 which are placed against each other in (with one small exception) mirror image fashion. The adjoining faces are recessed to provide guide channels for the select bars 120. The two housings are clamped together by two tie-rods 133 and by a `stop` molding 134 the purpose of which will be explained. Each of the housings 131 and 132 has one spigot hole which is off center (this being the exception to mirror symmetry) and which receives one of two spigots 135 on the stop molding. The stop molding is fixed to the two housings, thus locking their relative positions accurately, by screws 136. One pair of screws 136 is employed at each end of the stop molding 134 and a rib 137 extending between the two pairs of screws maintains the rigidity of the stop molding.

The tie rods 133 are also used to fix the assembly 123 to the main plate 61, spigots 138 in the upper housing 131 engaging in corresponding holes in the plate 61 locating the assembly accurately on the plate.

Each of the two housings contains thirteen parallel slots which extend in the `mirror wall` and partly in the forward wall (to the right in FIG. 19). In the upper housing 131 seven U-shaped magnets 141 are placed, with their open ends to the rear, in alternate ones of the 13 slots. The magnets 141 are thus located transversely in the assembly. Similarly six magnets 141 are positioned in the set of alternate slots in the lower housing 132.

The rear (forked) end of each select bar 120 has two short rearward projections 142 which carry an armature 143. The armature, shown in FIGS. 18 and 19 comprise a flat plate having an upper (for the top seven) end of reduced width which is guided in the row direction by a slot 144 in the housing 131. The lower end (again for the top seven) has a hole which is an easy fit laterally on the upper of the two bar projections 142, and, extends above this projection 142 to form a clearance fit around a pin 145 which projects from the stop molding 134. For the upper seven armatures 143, their weight is taken on the lower of the two bar projections 142.

The remaining six select bars 120 carry identical armatures 143 in similar manner but inverted.

Movement of each armature 143 is limited in the forward direction by the magnet core 141 and in the rearward direction by a rib 146 integral with the stop molding 134. There is in fact a thin sheet of relatively nonmagnetic nickel-silver alloy disposed between the armature 143 and the core 141 for the purpose of reducing the residual holding flux on deenergization of the magnet and thus allowing the select bar return spring to release the armature. This `residual` member will be assumed present in further mention of the armature. Although the rib 146 acts at only one point of the length of the armature 143 the `normal` armature position is determined by the forked projections 122 of the select bar which engage a substantial length of the armature 143 above and below the rib 146. The select bar is, it will be recalled, biased to the rear to press the armature 143 against the rib 146. This is achieved by the return spring of the select off-normal contact set at the forward end of the switch.

The position of the core 141 is determined by the pin 145 projecting from the stop molding 134 through the armature 143 and against which pin the core 141 is pressed by a spring 147 in the forward wall of the core slot. Thus the position and travel of the armature are both determined with respect to the stop molding 134, the position and travel of the select bars 120 thus being similarly determined.

On the upper limbs of the upper seven cores 141 and on the lower limbs of the lower six cores, energizing coils 152 are mounted on bobbins 151. Connection to these coils is provided by terminal connections 153.

Further pins 148, one for each select magnet, project from the stop molding 134 beside each armature 143 to retain the bobbins 151 in position on the cores 141. No accurate positioning of these bobbins is required and the pins 148 only prevent excessive `play`.

It can be seen that most of the critical tolerances involved in the location of the select bar and its operative edges (121) with respect to the combs 25 of the contact set matrix, are concentrated in the stop molding 134, which, being a single, unitary molding does not suffer from assembly or part variations.

Several modifications of the bridge mechanism of the above embodiment will now be described with reference to FIGS. 22, 23 and 24.

It may be seen from FIGS. 8, 10, 12 and 15, that the channel moldings 93 and 94 have detachable lids 99 which are force fits over pegs 100. In the alternative modification shown in FIGS. 22, 23 and 24 the lids 160 are molded integrally with the channel moldings 93 and 94. The form of the channel molding 93 and 94 in the region of the interposer blocks 161 is also changed. It can be seen from FIG. 22 that each interposer block 161 runs only in side recesses 162, the bridge bar 163 being relieved throughout the travel of the interposer block for the major part of the width of the interposer block. This relieving is indicated by the recesses 164. The lid portion 160 is also relieved over a corresponding width, giving clearance for the upwardly protruding ends 165 of the interposer arms 101.

The ends 165 of the interposer arms are also of different form, being simply of reduced width rather than of fork form. The interposer blocks 161 are, correspondingly, formed with a single slot extending most of the way across rather than with two slots 103 as shown in FIG. 13.

In FIG. 11 the arms 85, on which the interposer assembly is mounted, are integral with the bridge frame 83 and pivot with the rest of the bridge assembly about the pivot point provided by the insert 91 on the edge of the bridge magnet core 65. The position of the interposer block 102 at substantially the same level as the pivot point is such that its movement on energization of the bridge magnet might be expected to be substantially vertical, that is, as required. However, in the operative condition, when a select bar 120 has deflected an interposer arm 101 the bridge assembly of FIG. 11 does not pivot entirely as a rigid assembly. The deflected interposer arm 101 tends to pivot about the edge 121 of the select bar 120 which has deflected it so that the deflected interposer block 102 tends to return to its undeflected position on the bridge bar. The extent of this tendency depends upon various factors such as the displacement of the select bar and its point of engagement with the interposer arm, however FIGS. 22 and 23 show an alternative solution. The integral arm 85 of FIG. 11 is changed for a pivoted arm 167 in FIGS. 22 and 23, pivoted on a pin 168.

The arm 167 is prevented from moving arcuately with the rest of the assembly on operation of the bridge magnet by pegs (not shown) mounted on the bridge magnet moldings 66 and 67. Thus only vertical movement of the arms 167, and therefore of the interposer blocks 161, is permitted on operation of the bridge magnet.

Further modifications in the `select` mechanism will now be described with reference to FIGS. 25-29.

In the assembly 123 shown particularly in FIGS. 18 and 19 and, more broadly, in the lower left-hand portion of FIG. 1, the movement of the select armature 143 is limited, in the unoperated position by a stop member 134 and particularly by the rib 148 on the molding 134. The armature 143 is biased against this rib by the forked end (shown in FIG. 21) of the select bar 120. In the operated position, movement of the select armature 143 is limited by the core 141 of the associated magnet. Tolerances on the movement of the select bar therefore include the tolerance on the relative positions of the surfaces of the rib 146 and the pin 145 on the molding 134 and also the tolerance on the thickness of the armature 143.

In the modification of FIG. 25 the second of these is removed from the overall tolerance. Referring to FIGS. 25-28, a nonmagnetic member 170 having an operative face 171, corresponds to the forked end 122 of the select bar 120 of FIG. 20. In this case however, the armature 143 and the member 170 are bound together by a spring clip 172. Notches 173 for the clip are shown in FIG. 27. In addition, six pegs 169 locate the armature on the face 171. The member 170 has two apertures 174 and 175 which extend through the face 171 and receive the ends of the core limbs 141. The same face of the armature 143 which is bound to the face 171 of the member 170 can therefore engage the core 141 in the operated position of the armature.

Again there is a thin sheet of relatively nonmagnetic material disposed on the face of the armature 143 in order to assist in release of the armature in the presence of residual magnetism. This is again considered an integral part of the armature.

A stop member 176 although of somewhat different form from that of the stop member 134 performs similar functions. Periodic bosses 177 along the stop member engage one limb of the cores 141 which are biased against their respective bosses.

The significant difference in this modification is however, that the unoperated position of the armature 143 is determined not by the abutment of the armature itself against any rib 146 of the stop member but by the abutment of the member 170 against the stop member 176. Moreover it is the same face 171 of the member 170 that engages the forward face of the armature 143, that abuts against the stop member.

A rib 178, from which the bosses 177 protrude on alternate sides along its length, provides the abutment surface limiting the rearward movement of the member 170. As shown in FIG. 27, it is the lowest, tapered portion of the face 171 which engages the rib 178, the boss 177 protruding through the aperture 175 in this position. It may be seen therefore that the only tolerances involved are on the `height` of the boss 177 from the face of the rib 178 and the flatness of the surface 171, the mating surface of the armature 143 and the armature/core mating surface.

Clearly, the member 170 could simply constitute a modification of the forked end of the select bar 120 of FIG. 20. However a further modification consists of the separation of the select bar into two parts, the member 170 of FIGS. 26-28 and the coordinate bar 181 itself, shown in FIG. 29. FIG. 29 is a plan view but otherwise corresponds fairly closely to the right hand part of FIG. 20.

Whereas the unoperated position of the armature is produced, in FIG. 19, by the return spring of the select off-normal contact set at the remote end of the select bar, in the modified arrange of FIG. 25 the bias is imposed with the assembly 123. The horizontal section 182, of the member 170, shown in FIG. 26 extends forward through the housing 131 to within a short distance of the forward face of the assembly. A spring member 183, having thirteen teeth after the manner of the interposer spring assembly, is clamped along the root of the teeth so that the free end of each tooth presses on the housing 131 as shown. On assembly the spring is engaged in the recess 184 of the select bar 181 the end face 185 of which is thus biased against the end face of the section 182 of the member 170.

In operation of the switch a four-wire path through it is established as follows. One of the 30 available four-wire outlets is selected i.e., one of the ten rows and one of the three levels in that row. For this purpose two of the select magnets are operated; one of the 10 `normal` ones, and one of the three level-switching ones. Then the bridge magnet of the input in question is operated and the selected two combs 25 are driven vertically upwards to make the connections. The two interposers concerned are thereby trapped between the bridge bar 97 and the ends of the combs 25 so that the select magnets can be released without releasing the connection. The same select magnets can then be used for further routes involving the same row and different level or same level and different row, without affecting the established connections.

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