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EP 0 000 635 B1 |
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EUROPEAN PATENT SPECIFICATION |
(45) |
Mention of the grant of the patent: |
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29.07.1981 Bulletin 1981/30 |
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Date of filing: 12.07.1978 |
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(54) |
Snap acting switch blade and method for manufacturing it
Schnappfeder und Verfahren zu deren Herstellung
Lame à action brusque et sa méthode de fabrication
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Designated Contracting States: |
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DE FR GB |
(30) |
Priority: |
15.07.1977 GB 2988977
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(43) |
Date of publication of application: |
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07.02.1979 Bulletin 1979/03 |
(71) |
Applicant: Ranco Incorporated |
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Columbus
Ohio 43201 (US) |
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(72) |
Inventor: |
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- Rossi, Guglielmo
D-7515
Linkenheim-Hochstetten (DE)
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(74) |
Representative: Stephens, Michael John |
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M.J. Stephens & Co.
46 Tavistock Place Plymouth PL4 8AX Plymouth PL4 8AX (GB) |
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Note: Within nine months from the publication of the mention of the grant of the European
patent, any person may give notice to the European Patent Office of opposition to
the European patent
granted. Notice of opposition shall be filed in a written reasoned statement. It shall
not be deemed to
have been filed until the opposition fee has been paid. (Art. 99(1) European Patent
Convention).
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[0001] This invention relates to snap action switch blades.
[0002] Various configurations of snap action switch blades are known in the art of electrical
switches and controls which effect snap opening of switch contacts when an operating
force applied to a part of the switch blade reaches a predetermined threshold value.
The snap action of the switch blade results from a prestressing of the blade so that
the blade tends to adopt stable configurations of minimum stress in which a switch
contact carried by the blade is in different positions relative to a point of anchorage
of the blade. In moving between the stable configurations the blade is unstable, and
accordingly it moves rapidly to one stable position or the other, according to the
direction in which a force is applied to the blade, moving the switch contact with
a snap action.
[0003] A known snap-acting switch blade of the type to which the present invention relates
is described in French Patent Specification FR A 2291598. This type of blade is made
of resilient sheet metal and comprises a base portion, an inwardly projecting tongue,
an outwardly projecting tongue, two resilient legs projecting from opposite sides
of the base portion and terminating beyond the inwardly projecting tongue, and a contact
element interconnecting the two legs in a stressed condition in which the legs are
drawn together, causing a dish deformation of the base portion, and prestressing the
blade for snap movement of the contact element when an operating force is applied
to one of the tongues while the end of the other tongue is anchored.
[0004] In a preferred practical use of the switch blade the outwardly projecting tongue,
which preferably terminates in a flat portion of enlarged width, is anchored to a
fixed support. The blade as a whole acts as a cantilever resisting elastically the
operating force applied to the inwardly projecting tongue. The elasticity of this
mounting cantilever can be predetermined by appropriate choice of the length and width
of the outwardly projecting tongue to predispose the blade for monostable or bistable
snap movement according to the practical application for which the switch is intended.
[0005] An object of the present invention is to improve the damping qualities of the snap
action switch blade of the aforesaid type by resisting elastically any tendency for
'contact bounce' to occur when the contact element engages a fixed contact upon snap-closure
of a switch employing the switch blade.
[0006] Accordingly the present invention provides a snap action switch blade of the aforesaid
type which is characterised in that the two legs terminate in respective resilient
arms which project laterally towards each other, the contact element being affixed
to the laterally inner ends of the said arms, and in that the centre of the contact
element, which in use of the blade is its area of contact, is spaced from the longitudinal
centre line of the two resilient arms so that contact pressure exerted at the centre
of the contact element causes torsional stress in the two arms.
[0007] The resilience of the two laterally inwardly projecting arms to which the contact
element is affixed affords a degree of elasticity in the mounting of the contact element,
which serves to resist and dampen any tendency for 'contact bounce' when the contact
element closes upon a fixed contact in use of the switch blade.
[0008] Furthermore, the torsional stress which exists in the two laterally inwardly projecting
arms carrying the contact element when the latter is held by the switch blade against
a fixed switch contact tends to effect, upon contact separation, a wiping action between
the two contacts breaking any welds which may tend to form in use of the switch blade.
This wiping action and the effective damping of any tendency to contact bounce may
be enhanced by so dimensioning the switch blade that the two laterally inwardly projecting
arms which carry the contact element are narrower in width than the two legs of the
switch blade upon which the arms are formed.
[0009] A further practical advantage of the blade according to the invention is that the
contact element interconnects the resilient arms at the outer ends of the two legs
of the blade, serving both as an electrical contact and drawing the two arms together
to stress the blade and predispose it for snap action. Since it is not necessary to
affix a separate contact element to the blade, after deformation thereof and interconnection
of the arms, the blade construction is simplified considerably and is therefore potentially
economical in mass production.
[0010] The contact element of the switch blade should be of a material which can easily
be welded to the arms of the switch blade, while presenting a suitable contact surface.
Preferably, therefore, the contact element of the switch blade comprises a base portion
which is affixed to the two laterally inwardly projecting arms and an electrically
conductive contact layer which is deposited on, or bonded to, the base portion. The
contact element may conveniently be of square or rectangular shape, severed from a
continuous strip, each contact element being formed with two raised parallel ribs
on its base portion along which the contact element is welded to the arms of the blade.
[0011] The invention also comprehends a method of making the snap action switch blade herein
defined, comprising stamping or otherwise forming a flat blank or resilient sheet
metal with a base portion, inwardly and outwardly projecting tongues, two legs projecting
from opposite sides of the base portion and extending generally parallel to the inwardly
projecting tongue, terminating beyond the latter in respective arms which project
laterally inwardly towards each other, the inner ends of the said arms being spaced
from each other by a gap, anchoring the base portion of the blade blank while deforming
the outer ends of the two legs laterally towards each other to reduce the gap between
the arms and stress the blade, and affixing to the two arms a contact element which
interconnects the arms and maintains the blade in its stressed condition. The contact
element would in practice preferably be affixed to the two arms by a welding operation,
the steps of deforming the blade blank and welding the contact element in position
being conveniently performed in an automatic sequence, using a suitable jig. To assist
the accurate deformation of the blade blank the two legs of the latter may be formed
at their ends with laterally outwardly projecting lugs to which laterally inwardly
directed forces are applied to deform the outer ends of the two legs laterally inwardly
towards each other, prior to the affixing of the contact element to the laterally
inwardly projecting arms carried by the legs.
[0012] The invention will be further described and illustrated, by way of example, with
reference to the accompanying purely diagrammatic drawings, in which:
Figure 1 is a diagrammatic perspective view of a snap action switch blade;
Figure 2 is a plan view of a blank from which a switch blade according to one embodiment
of the invention may be made;
Figure 3 is a perspective view of a contact element adapted to be welded to the blade
blank shown in Figure 2;
Figure 4 is a plan view of a switch blade according to the invention made from the
blank shown in Figure 2, and the contact element shown in Figure 3, and
Figure 5 is a side elevation of the blade shown in Figure 3.
[0013] The snap action switch blade shown in Figure 1 comprises a sheet of resilient sheet
metal, for example beryllium copper having a thickness of 0.25 millimetre. The blade
is formed with a base portion 1, an inwardly projecting tongue 2, an outwardly projecting
tongue 3, and two resilient legs 4, 5 projecting from opposite sides of the base portion
1, the legs 4, 5 being substantially parallel to each other and terminating beyond
the end of the inwardly projecting tongue 3 in respective laterally inwardly projecting
arms 6, 7. The base portion 1, the tongues 2, 3 the legs 4, 5 and the arms 6, 7 are
all formed integrally with each other from a single resilient metal sheet.
[0014] The two laterally inwardly projecting arms 6, 7 are interconnected by a contact element
8 which is welded to the two arms 6, 7, interconnecting them in a stressed condition
in which the arms are drawn together, causing stressing of the two legs 4, 5 and resulting
in a slight dished deformation of the base portion, as illustrated in Figure 1.
[0015] The outwardly projecting tongue 2 terminates in a flat integral mounting tab 9 of
greater width than the remainder of the tongue 2, the tab 9 having two holes 10 by
means of which it can be anchored firmly to a fixed support, so that the entire blade
projects cantilever-fashion from this support. When mounted in this way, and prestressed
for snap action as described above, the switch blade is predisposed to effect snap
movement of the contact element 8 relative to the fixed blade support and, therefore,
relative to a fixed switch contact (not shown) when an operating force is applied
to the end of the inwardly projecting tongue 3. The tongue 3 may be formed with a
raised protuberance 11 near its free end, forming a well defined surface for engagement
by a switch operating member (not shown) which applies an operating force indicated
by the arrow P in Figure 1.
[0016] When an operating force P is applied to the central inwardly projecting tongue 3
of the blade this force is resisted by resilient flexing of the outwardly projecting
tongue 2 which supports the blade, while at the same time the inwardly projecting
tongue 3 itself bends relative to the base portion 1, until a well defined threshold
value of the force P is reached, when the additional stress imparted to the blade
by the force P results in instability of the blade, when the entire blade will undergo
snap deformation to a condition in which the dish deformation of the base portion
1 is reversed, this deformation being accompanied by movement of the legs 4, 5, and
therefore of the contact element 8, in the opposite direction to the deflection of
the central tongue 3 by the force P. According to the relative positioning of a fixed
contact the resulting snap movement of the contact element 8 will result in snap closure
or opening of a switch.
[0017] The switch blade can be designed so as to be monostable or bistable in operation.
In the monostable version of the switch blade illustrated here, the switch blade reverts
to its original stressed condition when the operating force P is removed or falls
below a further threshold value. In the embodiment illustrated in Figure 1 the application
of the operating force P causes snap movement of the contact element 8 into engagement
with a fixed contact (not shown) of a switch, and the subsequent release of the force
P results in snap opening of the switch contacts.
[0018] By appropriate proportioning of the width of the outwardly projecting tongue 2 which
supports the blade cantilever-fashion, the blade can be predisposed for bistable operation,
whereby, once having undergone snap deformation from its original stressed condition
(Figure 1) it assumes a stable condition with the opposite dished deformation to that
shown in Figure 1.
[0019] The flexural elasticity of the two legs 4, 5 and the arms 6, 7 serves to enhance
the snap movement of the contact element 8 carried thereby by virtue of the inertia
of the relatively massive contact element 8: before the instant of contact separation
the legs 4, 5 and the arms 6, 7 will bend elastically, releasing their stored energy
when the contact element 8 "unsticks" to cause rapid movement of the contact element
8 relative to the fixed contact.
[0020] The fabrication of a snap action switch blade according to one embodiment of the
invention will be described with reference to Figures 2 and 3.
[0021] Figure 2 shows a flat sheet metal blank stamped in a single piece from resilient
conductive material such as, for example beryllium copper sheet. In the flat blank
the legs 4, 5 are parallel to each other and to the central inwardly projecting tongue
3, and the outwardly projecting tongue 2 is coplanar with the inner tongue 3. The
two laterally inwardly projecting arms 6, 7 at the ends of the legs 4, 5 are also
coplanar, and terminate in respective edges 13, 14 which converge towards the base
portion 1 and which are separated by a suitable gap to allow the subsequent prestressing
of the blade. In the illustrated embodiment the edges 13, 14 converge at an angle
of approximately 6°. The two laterally inwardly projecting arms 6, 7 terminate in
end portions 15, 16 of enlarged width, the two arms 6, 7 themselves in this embodiment
being narrower in width than the respective legs 4, 5 which carry them.
[0022] Two shallow outwardly projecting rounded lugs 17, 18 are formed at the ends of the
respective legs 4, 5 adjoining the arms 6, 7.
[0023] After stamping the blade blank shown in Figure 2 and deforming the central inwardly
projecting tongue 3 to form the raised protuberance 11, the blade blank is placed
in a jig with the flat tab 9 anchored in a fixed support or clamp forming part of
a jig which includes pneumatically operated pistons which act upon the external lugs
17, 18 of the blank to deform the legs 4, 5 inwardly towards each other, closing or
substantially closing the gap between the edges 13, 14. The pistons may be arranged
to bring the edges 13, 14 into edge to edge abutment with each other, or alternatively
may incorporate stops to reduce the size of the gap between the edges 13, 14 by a
predetermined amount only. When the pistons have deformed the blade blank in this
way the contact element 8 is placed in position on the end portions 15, 16 of the
arms 6, 7 and welded in position, thereby permanently interconnecting the arms 6,
7 and maintaining the blade in a stressed condition, as illustrated in Figures 4 and
5.
[0024] The contact element 8 is of bimetal construction, having a base layer of suitable
material capable of being welded to the blade blank. The contact element is formed
with two raised parallel ridges 19, 20 (Figure 3). The ridges 19, 20 are pressed into
contact with the respective end portions 15, 16 of the blade blank upon assembly of
the blade, and after inward deformation of the arms 6 and 7 towards each other the
contact element 8 is welded to the end portions along the ridges 19, 20 by the passage
of a suitable welding current between the contact element 8 and the blade itself,
thereby securing the contact element 8 to the arms 6 and 7 and interconnecting the
latter in a stressed condition of the blade. Superimposed upon the base layer of the
contact element 8 is a contact layer of silver cadmium oxide, or some other suitable
conductive material.
[0025] The contact element 8 may conveniently be cut from a continuous strip of the aforesaid
bimetal, extruded with the raised ridges 19, 20 extending longitudinally, the strip
being cut transversely of the ridges to form the contact element 8, without any subsequent
finishing operation being necessary.
[0026] It will be seen that in the finished switch blade the centre of the contact element
8, indicated C in Figure 4, at which contact pressure is applied when the contact
element 8 engages a fixed contact, is spaced from the centreline axis X-X of the aligned
laterally inwardly projecting arms 6, 7 of the blade. This results in the generation
of a moment about the axis X-X when the centre C of the contact element 8 is engaged
by a fixed contact, leading to an elastic torsional deformation of the two arms 6,
7 about the axis X-X due to the contact pressure exerted on the contact element, upon
its closure against a fixed contact. Such torsional deformation serves to absorb the
kinetic energy of the contact element 8 upon closure of the switch contacts, acting
in a shock-absorbing capacity and minimising the tendency for contact bounce to occur.
The torsional deformation and therefore the shock absorbing effect will be proportional
to the kinetic energy to be absorbed.
[0027] The torsional deformation of the arms 6, 7 also has the effect of imparting a slight
twisting action to the contact element 8 about a transverse axis parallel to the axis
X-X of the arms 6, 7, resulting in a rocking or wiping movement of the contact element
8 upon the fixed contact prior to separation of the contacts and serving to break
any welds between the contacts.
[0028] The contact element 8 in the switch blade of Figures 4 and 5 is on the opposite face
of the blade from the contact element 8 in the embodiment of Figure 1: either position
may be adopted for the contact element according to the switch requirement.
1. A snap action switch blade of resilient sheet metal comprising a base portion (1),
an inwardly projecting tongue (3), an outwardly projecting tongue (2), two resilient
legs (4, 5) projecting from opposite sides of the base portion and terminating beyond
the inwardly projecting tongue (3), and a contact element (8) interconnecting the
legs (4, 5) in a stressed condition in which the legs (4, 5) are drawn together, causing
a dish deformation of the base portion and prestressing the blade for snap movement
of the contact element (8) when an operating force is applied to one of the tongues
while the end of the other tongue is anchored, characterised in that the two legs
(4, 5) terminate in respective resilient arms (6, 7) which project laterally towards
each other, the contact element (8) being affixed to the laterally inner ends of the
said arms (6, 7), and in that the centre of the contact element (8), which in use
of the blade is its area of contact, is spaced from the longitudinal centre line of
the two resilient arms (6, 7) so that contact pressure exerted at the centre of the
contact element (8) causes torsional stress in the two arms (6, 7).
2. A switch blade according to Claim 1, in which the two laterally inwardly projecting
arms (6, 7) terminate in end portions of enlarged width to which the contact element
(8) is affixed.
3. A switch blade according to Claim 2, in which the two laterally inwardly projecting
arms (6, 7) are narrower in width than the two legs (4, 5) of the switch blade which
carry the said arms (6, 7).
4. A switch blade according to any one of the preceding claims, in which the contact
element comprises a base portion which is affixed to the two laterally inwardly projecting
arms (6, 7) and an electrically conductive contact layer which is deposited on or
bonded to the base portion.
5. A method of making the snap action switch blade defined in Claim 1, comprising
stamping or otherwise forming a flat blank of resilient sheet metal with a base portion
(1), inwardly and outwardly projecting tongues (3, 2), two legs (4, 5) projecting
from opposite sides of the base portion (1) and extending generally parallel to the
inwardly projecting tongue (3), terminating beyond the latter in respective arms (6,
7) which project laterally inwardly towards each other, the inner ends of the said
arms (6, 7) being spaced from each other by a gap, deforming the outer ends of the
two legs (4, 5) laterally towards each other to reduce the gap between the arms (6,
7) and stress the blade, and affixing to the adjacent ends of the two arms (6, 7)
a contact element (8) which interconnects the arms (6, 7) and maintains the blade
in its stressed condition.
6. A method according to Claim 6, in which the contact element (8) is affixed to the
two arms (6, 7) by welding.
7. A method according to Claim 7, in which the contact element (8) has two raised
parallel ridges (19, 20) on a base portion which are brought into contact with the
two arms (6, 7) in the welding operation so that welding is effected along the two
ridges.
8. A method according to any of Claims 5 to 7, in which the two legs (4, 5) of the
blade blank are formed at their ends with laterally outwardly projecting lugs (17,
18) to which laterally inwardly directed forces are applied to deform the outer ends
of the two legs laterally towards each other.
1. Eine auf Schnappbewegung beruhende Schalterplatte aus Federblech, bestehend aus
einem Fuss (1), einer nach innen vorstehenden Zunge (3), einer nach aussen vorstehenden
Zunge (2), zwei federnden, von gegenüberliegenden Seiten des Fusses hervorstehenden
und über der innen vorstehenden Zunge (3) hinaus endenden Seitengliedern (4, 5), und
einem die Seitenglieder (4, 5) unter Spannung zusammenhaltenden Anschlussbestandteil
(8), wobei die Seitenglieder (4, 5) zueinander hingezogen werden, derart, dass der
Fuss leicht gebogen und die Platte zur Schnappbewegung des Anschlussbestandteils (8)
beim Belasten einer der Zungen vorgespannt wird, während die andere Zunge geankert
ist, dadurch gekennzeichnet, dass, die beiden Seitenglieder (4, 5) in je einen gefederten
Endbestandteil (6, 7) auslaufen, die seitlich auf den anderen Endbestandteil zu verlaufen,
wobei der Anschlussbestandteil (8) an der seitlich inneren Enden der benannten Endbestandteile
(6, 7) befestigt ist und dadurch, dass der Mittelpunkt des Anschlussbestandteils (8),
der bei Benutzung der Platte die Anschlussfläche bildet, von der Längsmittellinie
der beiden gefederten Endbestandteile (6, 7) abgelegen ist, so dass der auf den Mittelpunkt
des Anschlussbestandteils (8) ausgeübte Schliessdruck zu einer Drehbeanspruchung in
den beiden Endbestandteilen (6, 7) führt.
2. Eine Schalterplatte gemäss Anspruch 1, wobei die beiden seitlich nach innen vorstehenden
Endbestandteile (6, 7) an ihrem Ende, wo der Anschlussbestandteil (8) befestigt ist,
erweitert dimensioniert sind.
3. Eine Schalterplatte gemäss Anspruch 2, wobei die beiden seitlich nach innen vorstehenden
Endbestandteile (6, 7), breitenweise schmäler sind als die beiden Seitenglieder (4,
5) der Schalterplatte, die in die benannten Endbestandteile (6, 7) auslaufen.
4. Eine Schalterplatte gemäss irgendeinem der vorangehenden Ansprüche, wobei der Anschlussbestandteil
aus einem an den beiden seitlich nach innen vorstehenden Endbestandteilen (6, 7) befestigten
Fuss und einer die Elektrizität leitenden, auf den Fuss aufgetragenen oder aufgehafteten
Kontaktschicht besteht.
5. Ein Verfahren zur Herstellung der in Anspruch 1 bezeichneten, auf Schnappbewegung
beruhenden Schalterplatte, bestehend aus dem Stanzen oder der anderweitigen Fertigung
eines flachen Federblechrohlings mit einem Fuss (1), nach innen und aussen vorstehenden
Zungen (3, 2) zwei sich gegenüberliegenden Seiten des Fusses (1) und in Grossen Ganzen
parallel zu der nach innen vorstehenden Zunge (3) verlaufenden Seitengliedern (4,
5), welche über die Zunge hinaus in je einen sich seitlich nach innen gegeneinander
vorstehenden Endbestandteil (6, 7) verlaufen, wobei die inneren Enden der besagten
Endbestandteile (6, 7) voneinander durch einen Abstand getrennt sind, so dass die
äusseren Enden der beiden Seitenglieder (4, 5) seitlich gegeneinander verzogen werden,
um den Abstand zwischen den Endbestandteilen (6, 7) zu verringern und die Platte unter
Spannung zu setzen, und an den anliegenden Enden der beiden Endbestandteile (6, 7)
ein Anschlussbestandteil (8) befestigt wird, der die Endbestandteile (6, 7) miteinander
verbindet und die Platte unter Spannung hält.
6. Ein Verfahren gemäss Anspruch 6, worin der Anschlussbestandteil (8) an den beiden
Endbestandteilen (6, 7) durch Schweissen befestigt wird.
7. Ein Verfahren gemäss Anspruch 7, worin der Anschlussbestandteil (8) auf einem Fusse
zwei erhabene Grate (19, 20) besitzt, die während der Verschweissens mit den beiden
Endbestandteilen (6, 7) in Berührung gebracht werden, so dass das Schweissen länge
der beiden Grate stattfindet.
8. Ein Verfahren gemäss irgendeinem der Ansprüche 5 bis 7, worin die beiden Seitenglieder
(4, 5) des Plattenrohlings mit seitlich nach aussen vorstehenden Ansätzen (17, 18)
versehen sind, die seitlich nach innen gerichteten Kräften unterworfen werden, um
die äusseren Enden der beiden Seitenglieder seitlich gegeneinander zu verziehen.
1. Une lame d'interrupteur à rupture brusque en feuille métallique élastique, comprenant
une pièce de base (1), une languette saillant vers l'intérieur (3), une languette
saillant vers l'extérieur (2), deux bras élastiques (4, 5) s'étendant de chaque côté
opposé de la partie de base et se terminant au-delà de la languette saillant intérieurement
(3), et un contact électrique (8) joignant les bras (4, 5) de façon à communiquer
à ceux-ci (4, 5) une contrainte vers l'intérieur, provoquant une déformation courbée
à la partie du base et précontraignant la lame, occasionnant ainsi un mouvement brusque
du contact électrique (8) dès qu'une force d'opération est appliquée à une des languettes
pendant que l'extremité de l'autre languette est fixe, caracterisée en ce que les
deux bras (4, 5) se terminent tous deux par un organe élastique (6, 7) qui se dirigent
latéralement l'un vers l'autre, le (8) contact électrique étant fixé aux côtés interieurs
et laterals des dits organes (6, 7) et en ce que le centre du contact électrique (8)
qui lors de l'utilisation de la lame créé le contact se trouve à égale distance des
deux organes (6, 7) de façon à ce que la pression de contact exercée au centre du
contact électrique (8) occasion la torsion de deux organes (6, 7).
2. Une lame d'interrupteur selon la Revendication 1 caracterisée en ce que les deux
organes saillent latéralement vers l'intérieur (6, 7) se terminent chacun par une
partie de largeur élargie à laquelle le contact électrique (8) est attachée.
3. Une lame d'interrupteur selon la Revendication 2 caracterisée en ce que les deux
organes saillant latéralement vers l'intérieur (6, 7) sont de largeur plus étroite
que les deux bras (4, 5) de la lame d'interrupteur qui supportent lesdits bras (6,
7).
4. Une lame d'interrupteur selon une quelconque des Revendications précédentes, caracterisée
en ce que le contact électrique comprend une partie de base attachée aux organes saillant
latéralement vers l'intérieur (6, 7) et une pellicule conductrice d'électricité est
soit deposée ou liaisonée à la pièce de base.
5. Une methode de fabrication de la lame d'interrupteur à rupture brusque definie
dans la Revendication 1, comprenant l'estampage ou la formation, d'une façon ou d'une
autre, d'une pièce plate en blanc de feuille métallique élastique avec une partie
de base (1), des languettes faisant saille à l'intérieure et a l'extérieure (3, 2),
deux bras (4, 5) s'avancant des côtés opposés de la partie de base (1) et se prolongeant
en ligne plus ou moins parallel avec la languette saillant vers l'intérieur (3), se
terminant respectivement au-delà de cette dernière par des organes (6, 7) qui se prolongent
latéralement et intérieurement l'un vers l'autre, les extrémités internes de ces organes
(6, 7) étant espacées l'une de l'autre par un écart deformant les extrémités extérieures
des deux bras (4, 5) d'une façon latérale l'une vers l'autre reduisant ainsi l'écart
entre les organes (6, 7) et tendant la lame, tout en attachant aux extrémités adjacentes
des deux organes (6, 7) un contact électrique (8) qui relie les organes (6, 7) et
maintient la lame dans sa condition tendue.
6. Une methode conforme à la Revendication 6 en ce que le contact électrique (8) est
soudé aux deux organes (6, 7).
7. Une method conforme à la Revendication 7 en ce que le contact électrique (8) a
deux arêtes surélevées et parallèles (19, 20) sur une pièce de base et ces arêtes
font contact avec les deux organes (6, 7) pendant la soudure de façon à ce que cette
soudure se fasse le long des deux arêtes.
8. Une methode selon une quelconque des Revendications 5, 6 et 7 en ce que les deux
bras (4, 5) de la lame en blanc ont à leurs extrémités des oreilles en saillie de
projection extérieure et latérale (17, 18) sur lesquelles les forces dirigées latéralement
et vers l'intérieure sont appliquées afin de deformer latéralement et intérieurement
l'une vers l'autre, les extremités des deux bras.