US 3826885 A
An electrical switch utilizing a diaphragmtype contact element. The contact element includes a central contact-making portion and leg portions flexibly attached thereto that extend partially circumferentially about the central portion and out of the plane of the central portion. The contact element is prebiased by pre-flexing the legs so that a predetermined threshold force must be exceeded before any movement of the contact-making portion takes place.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 Allen et al. 1 July 30, 1974  PUSHBUTTON SWITCH HAVING 3,582,596 .0/1971 Woodhead 200/159 R 5,002,077 8/1971 A0000 200/159 B x gggfi CONTACT CONTACT 3,019,520 11/1971 Riley 200/100 M x 3,070,017 7/1972 Miller 200/44 lnventors: William J. Allen, Stratford, Conn;
Walter M. Tomasulo, Jr., Wayne, NJ
Assignee: Wild Rover Corp., Norwood, NJ.
Filed: June 23, 1972 Appl. No.: 265,452
U.S. Cl..... 200/159 B, 200/166 BH, 200/166 .1, 200/83 N Int. Cl. H01h 13/52, H01h l/06 Field of Search 200/166 BH, 166 .1, 166 SD, 200/159 R, 159 B, 16 R, 83 N;335/15, 192; 337/349 References Cited UNITED STATES PATENTS 8/1964 Gaynor 200/5 F Primary ExaminerB. Dobeck Assistant Examiner-William .1. Smith Attorney, Agent, or Firm-Cooper, Dunham, Clark, Griffin & Moran 5 7 ABSTRACT An electrical switch utilizing a diaphragmtype contact element. The contact element includes a central contact-making portion and leg portions flexibly attached thereto that extend partially circumferentially about the central portion and out of the plane of the central portion. The contact element is prebiased by preflexing the legs so that a predetermined threshold force must be exceeded before any movement of the contact-making portion takes place.
17 Claims, 7 Drawing Figures BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION This invention relates to electrical switches, and more particularly to switches involving low-throw of the movable contact-making element thereof. US. Pat. No. 3,602,677 discloses switch forms involving lowthrow and also touch operation. There, a flexiblecontact element is employed containing a plurality of parallel and extended contact segments that constitute the contact-making portion of the element. Enhanced electrical effectiveness is achieved through close tolerance construction and borad area contact between the contact-making portion and a base contact structure, utilizng independent segment contacting through the flexibility of the element. In the present invention, electrical simultaneity of contact between a plurality of extended, parallel contact segments and a base contact structure is achieved through the use of a relatively rigid diaphragm containing the extended contact segments. Advantages accrue from broad area simultaneity of contact without independence of contacting by the individual contact segments. The diaphragm is supported by a resilient leg structure permitting the diaphragm to move in parallel relation to the base contact structure.
The invention involves prebiasing, namely, the preloading of a spring-mounted contact element so that a predetermined threshold force must be exceeded before any movement of the contact element takes place. Such a prebiasing has the advantage of minimizing force variations from switch to switch due to gross imprecision in contact separations.
In switch construction in accordance with present invention a spring structure is employed which has polar symmetry. Superimposed upon the polar symmetrical springstructure is a contact-making structure comprising a plurality of physically parallel and extended contact segments. The orientation of the extended contact segments is correlated with the polar symmetrical structure to provide an overall spring element contact-making structure which is stable in operation and which tends to self-correct for offcenter forces applied to this structure.
In the prior art, diaphragm-type contact elements have been employed; see in particular the Woodhead patents among those patens listed below. While Woodhead utilizes flexed diaphragms in the non-actuated states of his switches in many of his applications, there is no appreciation of prebiasing for the purpose of minimizing variations in contactseparations. Rather, Woodhead's flexed contact elements are for the obvious sole purpose of biasing a movable contact element against a fixed contact element as part of a normally on switch structure. The Woodhead patents are all principally directed to electromagnetic switch operation in which a diaphragm element is magnetically actuated to provide for switch actuation. Furthermore, Woodhead does nothing to correlate the contact-making portion of his movable element with the spring portion of his element. In the present invention the orientation of the extended contact segments, as noted above, provides for unique stability in operation. Further a relatively rigid contact making structure is utilized in the diaphragm-type element of the present invention in order to provide for proper orientation of the contact-making segments as they make contact with the fixed base contacts, a factor unappreciated by Woodhead. Representative prior art patents are as follows:
U.S. PATENTS No. 3,636,290 Kucharski Jan. 18, 1972 No. 3,629,749 Woodhead Dec. 21, 1971 No. 3,624,330 Bognar, et al. Nov. 30, 1971 No. 3,626,337 Woodhead Dec. 7, 1971 No. 3,582,596 Woodhead June 1, 1971 No. 3,490,342 Rciss Jan. 20, 1970 No. 3,485,975 Long Dec. 23, 1969 No. 3,407,277 Chapin Oct. 22, 1968 No. 3,388,356 Myatt, at al. June 11, 1968 No..3,331,040 Woodhead July 11, 1967 No. 3,324,432 Ridlcr, ct a1. June 6, 1967 No. 3,300,594 Paine, et a1. Jan. 24, 1967 No. 2,949,520 Schneider Aug. 16, 1960 No. 2,817,725 Rochfort, et 211. Dec. 24, 1957 No. 2,715,169 High Aug. 9, 1955 No. 2,558,412 Baldwin June 26, 1951 No. 2,511,271 Kaminky, et a1. June 13, 1950 No. 2,500,429 Nijland Mar. 14, 1950 No. 2,409,483 Gandelot Oct. 15, 1946 No. 830,209 Conkling, et a1. Sept. 4, 1906 No. 693,416 Merrick, et a1. Feb. 18, 1902 FOREIGN PATENTS No. 870.755- FRANCE No. 1,131,928- BRITISH Woodhead 30 Oct. 1968 No. 1,126,869- BRITISH Woodhead 11 Sept., 1968 No. 1,115.401- BRITISH Woodhead 29 May 1968 No. 1,099,081- BRITISH Woodhead Jan. 17, 1968 No. 1,098,145- BRITISH Woodhead Jan. 10, 1968 No. 1,094.334- BRITISH Woodhead Dec. 6, 1967 No. 91.558 FRANCE 1968 (patcntofaddition of No. 1.399.005) No. 65353il BELGIUM 1964 .326408- GERMAN 1917 The invention will be more completely understood by reference to the following detailed description to be read in conjunction with the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION FIGS. 1 and 2 are perspective views of a capsule-type switch embodying the invention. The switch, of the normally off momentarily on type (the switch is in the on state as long as an actuating force is applied), is shown in exploded view in FIG. 6, and involves only four parts, namely, a housing 22, an energy directing actuating element 24, a contact element 26 and a base structure 28 that includes two base contacts 30 and 32 connected to output terminals 34 and 36. As shown in FIG. 6, the housing 22 is advantageously formed with two shoulders or ledges 22a and 22b, as well as with a slot 22d in the side thereof. The housing 22 is open at both ends thereof. As shown in FIG. 3, the energy directing actuating element 24 is positioned within the housing 22 so that an annular shoulder 24a thereof is seated upon housing ledge 22a. In this regard it will be noted that the outwardly directed surface 24b of the energy directing actuator element 24 is flush with the lower annular outwardly directed surface 222 of the switch housing 22 in the non-actuated state of the switch, as shown in FIG. 3. The energy director 24 includes a dimpled portion 240 that is positioned on the side thereof opposite from the outer surface 24b. The dimpled portion 240 serves to concentrate energy in the actuation of the switch in the center of the contact element 26, to be explained in more detail below.
Referring to FIGS. 4 to 6, the contact element 26 is shown. It is a diaphragm-type element that includes a central portion 26a and a plurality of legs 26b, 26c and 26d flexibly attached to the central portion 26a. The leg portions 26b extend partially circumferentially about the central portion 26a and, in the unstressed or unflexed state thereof, out of the plane of the central portion, as shown in FIG. 5. The leg portions include feet portions thereof, designated 26e, 26f and 26g. The feet portions may be dimpled, e.g., semi-spherical in shape, to reduce friction in the action of the spring 26, to be described in more detail below. The central portion 260 of the contact element includes a plurality-of linearly extending contact-making segments .2611
thereon. These segments may be constituted of wires affixed to a plate 261' that is in turn affixed to the central portion 26a of the contact element.
As shown in FIG. 4 the leg portions 26b, 26c and 26d of the contact element extend partially circumferentially about the central portion 26a. Each leg portion subtends an are approximately 90 in the form shown in FIG. 4, although a 90 arc is not critical and the arc may differ from 90,and the leg portions are equiangularly spaced about the central portion 26a of the contact element. In other words, the leg portions of the contact element exhibit polar symmetry about the central portion. Specifically, the feet portions 26e, 26f and 26g thereof are angularly spaced from each other by 120. The regions at which the leg portions are joined to the central portion, designated 26j, 26k and 26m in FIG. 4, are also angularly speaced from each other by 120.
As shown in FIG. 4, the feet portions 26e, 26f and 26g are located at the ends of the corresponding leg portions and are unattached to the central portion 26a of the contact element. While this construction is preferred, it is possible to include the leg portions as part of a continuous ring of material (not shown) constituting the leg portions, which ring of material is attached to the central portion of the contact element at angularly spaced regions of connection. Such a continuous ring leg portion structure would provide a stiffer diaphragm-type spring element. Further, it should be noted that the stiffness of the contact element may be varied by variation of the material of the element and its thickness, as well as by variation of the circumferential extend of the leg portions. Shorter leg portions, in the sense that they each extend over less of an angular segment than do the 90 leg portions shown specifically in FIG. 4, would tend to provide a relatively stiffer spring action in the contact element. The curvature of the leg portions may be in the form of an arc of a circle, as in the presently preferred embodiment, or they may range in curvature from that shape to straight line segments, all as viewed in plan. 7
While three leg portions have been utilized in the presently preferred embodiment switch, it should be noted that a different number of leg portions may be employed. It is believed that an odd number of leg portions should be utilized, exhibiting polar symmetry with respect to the central portion 26a.
The linearly extending contact-making segments 26h that are affixed to the central portion 26a of the contact element providea stiffening of that portion of the contact element. In particular, the contact element is typically made of beryllium copper, and is relatively flexible. The contact segments 26h as well as the plate 261' upon which they are affixed provides a stiffening of the central portion 26a so that it is relatively regid. Nonetheless, the entire contact element 26 is flexible, and exhibits a definite spring action by virtue of the flexing of the leg portions 26b, 26c and 26d.
The orientation of the linearly extending, physically parallel contact-making segments 26h is believed to be important. In particular, it is presently preferred to have such contact-making segments extend in lines that are parallel to a line between the center of the central portion 26a and one of the feet portions of the contact element. In particular, in the contact element 26 shown in FIG. 4, the segments 26h are parallel to a line between the center of the central portion 26a and the foot portion 26f. Such orientation of contact-making segments is believed advantageously to compensate for off center actuation of the contact element by the energy director 24, to be explained in more detail below.
The contact element 26 is mounted within the switch housing 22 as shown in FIG. 3, so that the feet portions 26e, 26f and 26g ride upon the surface 28a of the base element 28. As shown in FIG. 3, which is the nonactuated state of the switch 20, the contact element 26 is in a prebiased or bowed state in which the leg portions 26b, 26c and 26d are flexed from the unlfexed state shown in FIG. 5. For example, the distance between the feet portions of the contact element and the central portion in the unflexed state may be approximately 0.070 inch, while in the flexed state shown in FIG. 3 the same distance may be approximately 0.040 inch. Thus the central portion 26a of the contact element bears against the energy director dimple 24c urging the energy director shoulder 24a against the housing ledge 22a and providing a predetermined bias or threshold in the switch which must be exceeded in order to actuate the switch from the non-actuated state shown in FIG. 3.
The contact element 26 may be maintained in place within the housing through use of an extension 26n of one of the leg portions which fits into the corresponding groove 22d of the housing 22. As shown in FIG. 3 the assembly of the housing is completed by the positioning of the base structure 28 against the ledge 22b. A tab 28b fits within housing groove 22d to properly position the base structure so that the base contacts 30 and 32 are bridged by the contact-making segments 26h when the switch is actuated. The lower part 22f of the housing may be bent over as shown in FIG. 3 to maintain the switch in assembled condition.
The operation of the switch will be more completely understood by reference to FIG. 6A. That figure is a force/deflection diagram for the contact element 26 in both unassembled and assembled form. The curve segment designated 40 represents the force/deflection characteristic of the unassembled contact element. The
in FIG. 6A (the values of forces and deflections in FIG.
6A are representative). In the assembled form of switch shown in FIG. 3, the permanent preload or deflection given the leg portions is represented in FIG. 6A by the point designated 42. For example, the initial flexing of the leg portions may be such that the feet portions move 0.035 inch from the unflexed position shown in FIG. 5. This amount of prebiasing or initial flexing corresponds to a force of about 30 grams, for example. Accordingly, in order to provide further flexing of the leg portions of the contact element, this initial prebiasing or threshold force (of 30 grams, for example) must be exceeded. In other words no movement of the central portion 26a that carries the contact-making segments 2612 will take place toward the base contacts 30 and 32 until the predetermined threshold force has been exceeded. The heavily inked curve portion designated 44 in FIG. 6A representes the force/deflection characteristic of the assembled contact element 26 and hence of the switch shown in FIG. 3. Thus the segment 44a represents the initial prebias, and any force applied to the energy directing element 24 from up to about 30 grams in the example will result in no deflection of the contact element. As the initial prebiasing or threshold force is exceeded, movement of the contact element takes place as represented by the curve segment 44b. As an example, the contact-making segments 26h may be spaced by a distance of about 0.005 inch from fixed base contacts 30 and 32. For this separation, to provide for contact between the contact-making segments and the base contacts an additional or incremental force of grams, for example, is required. After such contact is made, the application of additional force to the energy directing element 24 will result in no further movement of the central portion 26a of the contact element. This is represented in FIG. 6A by the curve segment 44c.
Through the use of prebiasing so that an appropriate predetermined threshold force must be exceeded in order to actuate the switch, an important advantage, besides the attaining of spring operation in a desired range, is secured tending to nullify the effects of variations in switch parameters, primarly variations in contact spacings. In the practical production of switches, it is possible to closely control and render uniform the spring constant of diaphragm type contact elements of the type utilized herein. It is much more difficult to control and maintain within close limits the spacing between contact elements. It is necessary, however, to avoid the noticeable effects of contact spacing variations. This has important application in the use of a single type of switch for a keyboard, for example, when a plurality of such switches is utilized. In such an environment it is desirable that the person manipulating the switches does not experience any difference in operating characteristics from switch to switch. Through the use of prebias, the effect of variations in contact separations is minimized, as will now be explained.
Consider a typical electrical switch involving no bias, for example, a switch of the type shown in U.S. Fat.
NO. 3,602,677. The equation for contact element movement is as follows:
1 where F is the applied force, k,. is the spring constant of the contact element. Partially differentiating equation (1) results in the following:
2 Equation 2 may be rewritten in the following form, substituting from equation (1):
Equation 3 expresses the percent variation in applied force as a function of the percent variations in displacement and spring constant. Assume as an example that the displacement Z is 5 mils i 2 mils. Accordingly, dz/Z 2/5 40 percent; If k is approximately equal to 10 grams per mil i /2 gram per mil, then dke/ke /z/l0 5 percent. Accordingly, the variation in applied force in such a switch is as much as 45 percent (Spercent plus 40 percent). Where the applied force is normally in the neighborhood of 50 grams, for example, the 45 percent variation possible means that actuation in some applications may be as little as 27.5 grams and as high as 72.5 grams, with actuation of the switch varying between these limits. This is very wide possible variation, which has been experimentally observed in switches, and is unsatifactory from the standpoint of providing switches presenting uniform actuating characteristics to a user.
Consider now the case of an electrical switch that is prebiased so that the force/deflection characteristic is in accordance with a curve of the type of curve 44 shown in FIG. 6A the following equation represents the movement of the contact element:
4 where F is the applied force, F b is the prebias force (the prebias of 5 grams, for example, shown in FIG. 6A), k is the spring constant of the precompressed spring, and Z is the deflection of the central portion 26 of the diaphragm-type spring, considering the prebiased position of the central portion as shown in FIG. 3 to be Z 0.
Partially differentiating equation (4) results in the following equation:
dF dF,, kedZ Zdke 5 Equation (5) may be rewritten as follows, substituting from equation (4): dF/F dF kedZ Zdke/F keZ 6 Equation (6) is subject to the following approximation in those cases where the term k Z is much less than F,, (i.e., the incremental applied force necessary to actuate the switch is much less than the prebiasing force) Approximation (7) utilizes the following approximation, which also depends upon the stated relationship between prebias and incremental actuating forces:
keZ 1+ Fb 9 Compare approximation (9) with equation (3). Assuming that the variation in prebias is negligible, the term dF /F in approximation (9) can be dropped. The last term in the approximation F is then the same as equation (3). The twoother terms in the approximation are each less than unity, and since these terms are multipliers, the righthand side of the resulting approximation must be much less than the righthand side of equation (3). This means, then, that the variation is applied force, expressed as a percentage of the applied force, is much less in the case of a switch involving prebiasing of a spring-type than in such a switch in which the spring-type contact element is not prebiased.
An example will be useful. Assume a deflection distance Z of 5 mils t 2 mils. Accordingly, dZ/Z 2/5, i.e., the variation if 40 percent. Assume further a prebiasing force F,, of 45 mils i 5 percent, and a spring constant k, of 1 gram per mil i 1/20 gram per mil. Accordingly, the variation in spring constant dk /k is equal to 5 percent.
Substituting these values into the full approximation (9) results in the following:
dF/F (8/9 [5 percent H9 (40 percent 5 percent) 8.8 percent Accordingly, the variation in applied force as a percentage is roughly 9 percent in the case of a prebiased spring, where, for the same approximate switch parameters subject to the same variations in a non-prebiased switch a 45 percent variation in applied force is possible. This results in a 5:1 suppression of the variations in contact spacing that may occur from switch to switch, even with a 5 percent variation in prebias.
As noted above. the salutary effect of prebiasing is possible in those cases when the precompression or threshold force (F0) is greater than the incremental force (k,.Z) needed to complete actuation of the switch. It is believed that the precompression force should be at least about 2 to 3 times the incremental force to achieve this effect.
Returning to the drawing and particularly to FIG. 3, it will be noted that the feet portions 26e, 26f and 26g rest upon the base surface 2811. An additional ring (not shown) may be employed, if desired, upon which the feet portions rest. The semi-spherical shape of the feet portions reduces friction during movement of the central portion 260 of the contact element. It will be noted that there is a slight spacing between the edges of the leg portions of the contact element and the walls of the housing 22, which permits movement of the leg portions to take place. This further allows an optimally soft equivalent spring action which is required to enable a relatively rigidtranslation of the diaphragm or central contact portion 26a.
It has beenfound thatthe central portion 26a of the contact element 26 moves rectilinearly, which movement is enhanced by the stiffening of the central portion 26a by the contact segments 26h. As noted above the preferred orientation of the contact-making segmens is as shown in FIG. 4 and described above, namely, parallel to a line between the center of the central portion 26a and one of the feet portions (26]). It is believed that such an orientation of the contactmaking segments overcomes the effect of wandering of the energy directing dimple 24c from the centerpoint of the central region 26a of the contact element. Such wandering of the energy directing dimple produces an off-center force which tends to urge the central portion 26a of the contact element to move in other than rectilinear fashion. -It essentially is immaterial if the contactmaking segments 26h together strike one of the base contacts 30 and 32 before they strike the other base contact, as long as all segments strike each contact simultaneously. However," an undesirable condition is that in which only one or a few of the contact-making segments 26h concurrently strike the two base contacts while the others of the contact-making segments are not in contact with the base contacts. In such a case, the current flow is shifted to only a portion of the contact-making segments, which may result in an excessive current flow'through this portion of the switch. Accordingly it is desirable to overcome the possible tilting of the central portion 26a of the contact element which would result in this undesirable condition. The orientation of the contact-making segments shown in FIG. 4 is believed to have this effect. Consider wandering of the energy directing dimple 24c in a right or left direction with respect to FIG. 4 from the centerpoint of the central region 26a (movement along axis X-X). Movement to the left places the dimple 24c closer to the two feet portions 26f and 26g (in the exact center of the contact element the dimple is spaced equally from the three feet portions). Accordingly the force exhibited by the dimple is counteracted by two of the feet portions which tend to resits tilting of the central portion. The same is true for movement to the right with respect to FIG. 4; in this case the feet portions 26e and 26f have this salutary effect. On the other hand, consider movement of the dimple 24c toward the foot portion 26f (movement along axis Y-Y). In this case only the single foot portion 26f is approached, and the contact central portion 26a might tend to tilt toward that foot portion. As noted above, however, tilting in this direction is not objectionable, inasmuch as all the contact-making segments 26h still contact one of the base elements simultaneously and then the other base element simultaneously.
While the above explanation of the self-centering effect of the contact element with respect to the energy directing dimple 24c has been in general terms, an analysis of the moments involved as produced by the forces exerted by the leg portions of the contact element shows that the self-centering effect is indeed present. To elaborate, the supporting forces and actuating force may be vectorially resolved with respect to the transverse and longitudinal directions. The transverse (X-X) is the direction in which an enhanced tilting effect toward the center or stiffness with respect with respect to tilting in that direction is achieved. The lon- 9 gitudinal direction (YY) is the direction in which contact tilt is not significant due to near simultaneity of contact closure as in a knife blade switch action. In particular, due to the precision of design enhanced by a burn-in process and resultant diminished surface roughness, the closure of the contact in that plane exhibits the near angular simultaneity and broadness of area contact within arcing times and capacitive effects.
Considering the leg supporting forces that act in the Z direction (out of the XY plane) and looking along the X-X axis, there are seen a supporting force on the left and two equal balancing supporting forces on the right. As the force transmitted through the energy director resolved in that longitudinal direction tends to wander to either the right or the left, it places a further supporting or moment action on the force in which direction it moves. As the force increases in the proximate supporting leg and since that supporting leg is in fact not rigid but a deflecting spring, the spring tends to slightly deflect. The slight offcentering of the energy director is not compensated for. However, the tilt is inherently limited because the energy director is contained within the switch housing.
Considering now the resolution ofZ axis forces along the transverse XX axis by looking into the Y-Y axis, one observes a center member as well as a left and right hand leg. As the energy director, which is normally on center, wanders slightly off center, the main supporting element is the now proximate leg. Again, since the wander transmits the energy director force closest to this center, instead of having an equal division of forces as in the centered configuration, the center leg tends to adjust to the larger supporting force by deflecting it more than either the right or left hand legs. This action therefore tends to return the off centered energy director toward the center.
Presently preferred embodiments of switch designs have been disclosed. lt will be apparent that modifications are possible within the scope of the principles involved. Accordingly, the invention should be taken to be defined by the following claims.
What we claim is:
1. A diaphragm type contact element for a switch comprising a substantially planar central portion, said central portion including a plurality of linearly extending and substantially parallel contact-making segments, and a plurality of leg portions each flexibly joined to said central portion and extending partially circumferentially about said central portion.
2. A contact element according to claim 1, in which said contact-making segments are wires.
3. A contact element according to claim 2, including a plate to which said wires are affixed, and said plate is affixed to said central portion.
4. A contact element according to claim 3, in which said wires include a coating taken from the following class: gold, gold alloyed with copper, rhodium.
5. A contact element according to claim 3, in which said wires are silver cadmium oxide.
6. A contact element for switch according to claim 1, in which said contact-making segments comprise embossed portions of said central portion.
7. A contact element according to claim 1, which is made of beryllium copper.
8. A contact element according to claim 1, in which said central portion is normally flexible, and the inclusion of said contact-making elements stiffens said central portion.
9. A contact element according to claim 1, in which each leg portion includes a foot portion adapted to support said contact element, and in which said contactmaking segments are substantially parallel to a line between the center of said central portion and one of said feet portions.
10. A contact element according to claim 9, in which each of said leg portions extends out of the plane of said central portion in the unflexed state of said leg portion on the same side of said central portion as said contact-making segments.
11. A switch incorporating a contact element according to claim 10, including means holding said contact element with said feet portions closer to the plane of said central portion than in the non-flexed state of said legportions of prebias said contact element in the nonactuated state of said switch and require a threshold force to be exceeded to actuate said switch.
12. A switch according to claim 11, including energy directing means bearing upon said central portion of said contact element for moving said central portion to actuate said switch.
13. A switch according to claim 12, including housing means for positioning said contact element and said energy directing means with respect to each other.
14. A switch according to claim 13, in which said housing means positions a pair of base contacts in spaced relation to said contact-making segments.
15. A switch according to claim 14, in which said contact-making segments bridge said base contacts in the on state of the switch and which are positioned in the range of from about 0.003 to about 0.030 inch from said base contacts in the off state of said switch.
more than about one half.