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(11) | EP 0 000 635 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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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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| 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). |
[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.
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.