Cam Actuated Switch

This invention relates to the field of electrical switches and within that field to cam actuated switches.

Essentially all telephones include a switch that is actuated by the removal of the telephone handset from and replacement of the handset on the telephone base. Basically, the actuation of the switch serves to connect the telephone to an associated telephone line responsive to the removal and to disconnect responsive to the replacement. This switch is therefore often referred to as the line switch. Nearly all line switches, however, perform functions in addition to the basic one. Consequently, they generally include between four and six contact pairs that are operated in a particular sequence.

The force necessary to operate the line switch is derived from the weight of the telephone handset, and over the years not only has the weight of the handset been reduced, but telephone base designs have been introduced wherein only a portion of the handset weight is applied to the line switch. Thus line switches have had to be designed that operate in response to smaller and smaller forces. More recently, this problem has been drastically compounded by the introduction of multiple line business sets that rely on the weight of the handset to both operate the line switch and operate a mechanism for releasing one or more latched down pushbuttons of a multiple pushbutton switch.

The magnitude of this problem is best understood by comparing existing line switches with the requirements imposed by this latest telephone set design. The line switch used in the general purpose telephone of the Bell System, which switch is of the type described on pages 266 and 267 of an article entitled, "An Improved Telephone Set" appearing in the April 1951 issue of the Bell System Technical Journal, has an operating force of 300 grams. The line switch used in the dial-in-handset telephone of the Bell System, which switch is of the type disclosed in U.S. Pat. No. 3,027,432 issued to Messrs. H. G. Jordan, L. J. Purgett, W. E. Restall, Jr., and P. E. Schweizer on Mar. 27, 1962, has an operating force of 160 grams. The line switch for the new business telephone design must operate with a force of only 20 grams.

In addition, the line switch for this new design needs to be small in size, that is, no bigger than about a cubic inch in volume. It also needs to be comprised of relatively inexpensive components that are readily asembled so that the cost of the switch is kept low. Furthermore, to facilitate use of the switch in the wide variety of business sets being made available to telephone customers, the switch should permit the sequence in which the contact pairs are actuated to be readily changed. While it may seem that these combined requirements pose an impossible object to meet, a switch in accordance with the present invention can be designed to satisfy them all.

A switch in accordance with the present invention comprises a number of coplanar cantilever movable contact springs that overlie a like number of coplanar cantilever stationary contact springs. The free ends of the movable contact springs extend beyond and are biased toward the free ends of the stationary contact springs. In addition, the fixed ends of the movable and stationary contact springs are insulated from one another by a dielectric spacer and are fastened to a base portion of a molded dielectric support member.

The support member includes a pair of spaced integral guide portions that extend from the base portion and define a channel for accommodating an actuator that is reciprocally displaceable beneath and generally parallel to the contact spring pairs. The support member also includes a plurality of cam follower portions that are equal in number to the contact spring pairs and are situated between the guide portions. The cam follower portions have a hammer-like configuration in that each comprises (1) a shank portion that is integrally hinged to the base portion and extends generally parallel to both the contact springs and the channel and (2) a head portion at the free end of the shank portion that extends transverse to the shank portion.

One end of each head portion extends into juxtaposition with the free end of an associated movable contact spring. The other end of each head portion extends into juxtaposition with the actuator, and cam surfaces on the actuator serve to sequentially deflect the cam follower portions responsive to displacement of the actuator. The cam follower portions in turn deflect the movable contact springs to effect corresponding sequential actuation of the contact pairs.

Because the movable contact springs are deflected sequentially and once deflected the force required to maintain them deflected is essentially zero, the force required to actuate the switch is low. Also, because the contact spring mounting surface, the cam followers, and the guide for the actuator are all integral elements of a unitary molded member and therefore do not need to be assembled, these elements and thereby the switch can be made quite small and the spatial relationship between these elements is accurately controlled. In addition, because these elements do not need to be assembled, and because the unitary support member, actuator, and contact springs are inexpensive to manufacture, and the contact springs do not need to be manually adjusted to provide the desired contact force, the cost of the switch is comparable to or less than any of the line switches presently in use by the Bell System. Finally, because the sequence in which the contact springs are actuated is determined by the actuator and because the actuator just slides into place, the same basic switch structure can be combined with any one of a number of different actuators to provide any desired sequence of contact actuation.

FIG. 1 is an exploded perspective view of a switch embodying the present invention;

FIG. 2 is a top view of the unitary support member of the switch;

FIG. 3 is a sectional view of the support member taken along line 3--3 of FIG. 2;

FIG. 4 is a front view of the support member;

FIG. 5 is a top view partially in section showing the structure of the contact spring assembly of the switch at the time it is fastened to the support member;

FIG. 6 is an exploded perspective view showing the switch inverted and all components, other than the actuator and cover, assembled; and

FIG. 7 is a side view of the assembled switch without the cover.

Referring to FIGS. 1 through 4 of the drawing, a switch in accordance with the present invention includes a unitary molded dielectric support member 100 comprising a base portion 110, a pair of guide portions 130, and a number of cam follower portions 150. The base portion 110 includes an upper mounting surface 111 and a recessed lower mounting surface 112 that lie in parallel planes. The base portion 110 also includes three spaced openings 114 that extend between the mounting surfaces 111 and 112.

The guide portions 130 extend from the base portion 110 and are spaced from and are essentially a mirror image of one another. As seen in FIGS. 3 and 4, the inside surface of each guide portion 130 includes spaced opposing surfaces 132 and 133 and joining surfaces 134 that combine with identical surfaces on the other guide portion to define a channel 135, best seen in FIG. 4, that extends beneath and generally parallel to mounting surfaces 111 and 112 of the base portion 110. The inside surfaces of each guide portion 130 also includes a recess 136, best seen in FIG. 3, the lower end of which is open and the upper end of which is closed to provide a stop 137 that lies in the plane of the lower mounting surface 112. Finally, the outside surface of each guide portion 130 includes a tongue 138 that extends generally parallel to the mounting surfaces 111 and 112 and the forward end of which is tapered.

The cam follower portions 150 are situated between the guide portions 130 and have a hammer-like configuration in that each comprises (1) a shank portion 152 that is integrally hinged to the base portion 110 and extends generally parallel to the mounting surfaces 111 and 112 thereof, and (2) a head portion 154 at the free end thereof that extends transverse to the shank portion. As most clearly seen in FIG. 3, the upper end of each head portion 154 extends above the plane of the upper mounting surface 111 and advantageously has a blunt shape. The lower end of each head portion 154 extends into close proximity with the channel 135 and advantageously has a tapered shape.

Referring now to FIG. 1, assembled to the upper mounting surface 111 of the base portion 110 is a contact spring pileup. The pileup comprises a stationary contact spring cluster 200, a dielectric spacer 300, a movable contact spring cluster 400, a dielectric spacer 500, and an upper clamping plate 600 respectively having mounting openings 214, 314, 414, 514, and 614 therein that are the same size as or larger than and are adapted to be placed in registration with the openings 114 in the base portion 110.

The stationary and movable contact spring clusters 200 and 400 are advantageously formed from sheet stock of a gauge such that the stationary contact spring cluster is relatively stiff while the movable contact spring cluster is relatively flexible. In addition, the stationary and movable contact spring clusters 200 and 400 are advantageously respectively formed with webs 215 and 415 at the rear thereof, the movable contact spring cluster also having a web 416 at the front thereof. This permits each contact spring cluster to be assembled to the support 100 as a unit. Furthermore, the webs 215, 415, and 416 are advantageously respectively provided with one or more fixture holes 218 and 418 which in combination with an appropriate fixture assure the proper orientation of the contact spring clusters with respect to one another and the support 100. Thus it is seen that the webs 215, 415, and 416 greatly facilitate and reduce the cost of the assembly operation, and after assembly to the support 100 is completed, the webs are readily trimmed off along the lines A--A shown in FIG. 5.

When the trimming operation is completed, it is seen that the stationary contact spring cluster 200 comprises a plurality of coplanar contact springs 250 equal in number to the cam follower portions 150 of the support 100. Each stationary contact spring 250 has an upward facing contact 252 at the forward end thereof and a terminal post 254 at the rear end thereof. In somewhat similar fashion, the movable contact spring cluster 400 comprises the same number of coplanar contact springs 450, but the forward portion of each contact spring is bifurcated, the bifurcations having downward facing contacts 452. The forward portions of both the stationary and movable contact springs 250 and 450 are shaped so that the forward ends have the same spacing as the cam follower portions 150, and the contacts 452 are located so as to be in registration with the contacts 252.

The movable contact springs 400 are longer than the stationary contact springs 250 and therefore the forward ends of the movable contact springs extend for a distance beyond the contacts 452 thereof. Furthermore, the forward portion of the movable contact springs 450 are provided with a permanent set so that the forward portions incline toward the stationary contact springs 250. This permanent set provides a predetermined contact force once the contacts are assembled. Finally, the rear ends of the movable contact springs 450 are provided with a bend to increase the spacing of terminal posts 454 thereat from the terminal posts 254 of the stationary contact spring 250.

The stationary contact spring cluster 200, spacer 300, movable contact spring cluster 400, spacer 500, and upper clamping plate 600 are secured to the support 100 by a pair of fasteners 650 only one of which is shown. The heads of the fasteners 650 engage the upper clamping plate 600 while the stems of the fasteners extend through the two outside holes 614, 514, 414, 314, 214, and 114 of the associated components and thread into correspondingly spaced tapped holes 714 in the lower clamping plate 700, the plate being positioned in engagement with the lower mounting surface 112 of the base portion 110. The fasteners 650 draw the upper and lower clamping plates 600 and 700 toward one another and thereby clamp the stationary and movable contact spring clusters 200 and 400 in place. The center holes in these components are used to accommodate a fastener that secures the switch to an appropriate mounting bracket.

The lower clamping plate 700 includes a forward extending portion 750 including laterally extending tabs 752, and as seen most clearly in FIG. 6, the tabs are accommodated within the recesses 136 of the guide portions 130 of the support 100. The tabs 752 engage the stops 137 (FIG. 3) provided by the closed ends of the recesses 136, and as viewed in FIG. 6, serve to prevent any counterclockwise deflection of the guide portions 130 with respect to the base portion 110.

Further rigidity for the guide portions 130 is provided by a transparent protective cover 800 that is snap mounted on the support 100. The cover 800 comprises a front portion 810, a top portion 820, and a pair of side portions 830. The side portions 830 include short inner walls 832 and long outer walls 834, and as indicated in FIG. 6, these walls are adapted to embrace the forward ends of the guide portions 130 and thereby prevent any lateral deflection of the guide portions when the cover 800 is in place.

The cover 800 is secured in place by means of grooves 838 in the outer walls 834 that are adapted to accommodate the tongues 138 of the guide portions 130. The spacing of the outer walls 834 is such that as the cover 800 is moved rearwardly with the grooves 838 in the plane of the tongues 138, the outer walls are spread apart by the tongues. Continued rearward movement of the cover 800 moves the grooves 838 into registration with the tongues 138 at which time the outer walls 834 return to their normal spacing and capture the tongues within the grooves. The cover 800 is advantageously mounted on the support 100 immediately after the webs 215, 415, and 615 are respectively severed from the stationary and movable contact spring clusters 200 and 400. The contact springs are then protected by the front and top portions 810 and 820 of the cover 800 from any damage that might occur during subsequent handling of the switch.

Referring now to FIGS. 6 and 7, it is seen that with the contact spring pileup assembled to the support 100, the free ends of the movable contact springs 450 extend into juxtaposition with the blunt ends of the head portions 154 of the cam follower portions 150. Furthermore, the dimensions of the spacer 300, the contacts 252 and 452 of the stationary and movable contact springs 250 and 450 respectively, and the cam follower portions 150 are such that when the contacts are closed, the free ends of the movable contact springs are immediately adjacent to the blunt ends of the head portions 154 and the tapered ends of the head portions are immediately adjacent to the channel 135. As a result of these relationships, an actuator 900 of a size to be slidably displaceable within the channel 135, provides the means for operating the contact spring pairs.

Referring now also to FIG. 1, the actuator 900 includes a plurality of cam portions 950, each of which is adapted to engage a tapered end of the head portion 154 of an individual cam follower portion 150 during a portion of the travel of the actuator. Each cam portion 950 protrudes above the channel 135 a distance such that when it engages its associated head portion 154, the head portion and thereby the movable contact spring 450 in engagement with the head portion is deflected to separate the contacts 452 on the movable contact spring from the contact 252 on the associated stationary contact spring 250. When, on the other hand, one of the head portions 154 moves off of an associated cam portion 950, the contacts 452 on the movable contact spring 450 associated with the head portion move into engagement with the contact 252 on the associated stationary contact spring 250.

With the cam portions 950 staggered such as shown in FIG. 1, the movable contact springs 450 are operated sequentially and only a very low force is required to displace the actuator 900. This force is reduced even further by choosing the materials from which the support 100 and the actuator 900 are formed to have the lowest possible coefficient of friction with respect to one another. Since the actuator 900 is a relatively inexpensive component to mold, the sequence of contact operation can be altered by merely replacing one actuator with another of the appropriate configuration. Leg portions 960 extending from the side opposite to the cam portions 950 provide the means for displacing the actuator 900, the laterally extending tab portions 970 at one end of the actuator provide a known starting point for that displacement.

Although but one embodiment of the invention has been shown and described, it will be understood that it is but illustrative and that various modifications may be made herein without departing from the scope and spirit of this invention as defined in the appended claims.