EP0057130B1 - Mercury switch using the surface tension of mercury to reset the movable element - Google Patents

Description

The present invention relates to a switch with mercury wetted contacts arranged in a housing consisting of a base and a cover, comprising first and second electrodes, a movable element which can take at least two different positions, respectively a position of working under the action of an external control force and a rest position under the action of a restoring force generated by mercury disposed between the mobile element and a fixed element, the distance of which is at most equal to the value for which the mercury is maintained between said elements by capillary forces, the respective surfaces of the fixed element and of the movable element in contact with the mercury being such that they are wetted by the latter.

Such switches generally include a spring at the height of the cepillarity force generated by the mercury between the fixed element and the mobile element. The spring can take the form of either a blade (flat spring) or a helix (coil spring). In particular in so-called monostable switches, having a stable position (rest position) and a non-stable position (working position) in which the switch is held by the action of an external means (magnetic field in the case of 'a relay), a metal blade or flat spring is frequently used as a means of returning to the stable position.

The return spring used in this case is generally made of a material different from that constituting the mobile element to which it is fixed by welding or any other suitable means. In the case of miniature relays, the use of which is spreading more and more in the field of electronics, this flat spring is then of extremely reduced dimensions which makes on the one hand its manipulation difficult and on the other hand the precise adjustment of its extremely delicate position. The same applies to the operations for fixing to the moving part and in general for all the operations in which this spring is concerned.

Furthermore, such springs are of a fairly high cost price: they are not only made of fairly special fairly special materials such as beryllium copper, but it is also necessary to subject them to a treatment which makes them good. elastic properties.

Finally, any mechanical spring is subject to an aging phenomenon which causes its characteristics to change over time.

Document DE-B-1 257 285 discloses a switch controlled by a magnetic field comprising, inside a glass or ceramic envelope, a first and a second electrode on which a non-magnetic plate is fixed, a ball, under the action of an external magnetic field which can move from the second electrode towards the first and being recalled when the external magnetic field is suppressed towards the second electrode under the action of the surface tension of the mercury which is exerts on the ball and on the plate secured to the second electrode. This closes the electrical circuit between the two electrodes, via mercury and the ball. In addition, the fact that such a structure makes it possible to produce only simple switches with two electrodes and not inverter type switches with three electrodes, it also has the serious drawback of operating only in a predetermined position or in the vicinity of this one. A 180 ° turn of the switch generates a random operation of the switch. This is particularly troublesome when the switch is to be used in materials subject to overturning. We find a similar structure with the same drawbacks in US-A-2,309,953.

The switch according to the invention makes it possible to avoid these drawbacks. For this purpose, it is characterized in that the movable element has the form of a pallet, one of the sides of which constitutes an axis of rotation of the latter from the rest position to the working position and vice versa , this axis of rotation penetrating into a groove carried by the base of the housing which is integral with said fixed element and in that said mobile element is connected to a third electrode electrically connected to the first or to the second electrode according to the rest position or working (or vice versa) of the movable element.

Preferably also, the mobile element and / or the fixed element will have the form of flat metal tongues.

According to a preferred embodiment, the switch according to the invention is characterized in that it comprises a dihedral-shaped part, one of the planes of which is secured to the base and provided with an opening through which passes the movable element, the axis of rotation thereof being held in the groove by said plane, the fixed element being constituted by the other plane of said dihedral.

The dihedral is obtained simply from a metal plate preferably, in which an opening is drilled and which is then folded into two parts making an angle of the order of 90 ° between them. The axis of rotation of the movable part, which is arranged in a groove inside the support, a groove also containing mercury, is then maintained by the plane of the dihedron provided with an opening. We thus easily realize such a switch from a plate pierced with an opening, bent at 90 ° and a support such as a transistor base provided with its working and rest contacts, on which we practiced a groove. The axis of rotation of the movable part is then placed in the groove, then there is added over the plane of the dihedral pierced with its opening, which is fixed to the support and which thus maintains the movable part, allowing only a rotation thereof. Then a drop of mercury is introduced into the corresponding cover which is welded to the base. The switch according to the invention has the advantage of being an "all position" switch.

All the parts having been treated to be wetted by mercury, the latter will then automatically be housed, on the one hand in the groove ensuring easy tilting of the mobile part and on the other hand between the mobile and fixed parts. Taking care to introduce a reducing gas before closing the housing, we then obtain a switch in which the return device does not undergo any aging.

Concerning the distance which must be respected between the fixed and mobile parts so as to allow the liquid to act by capillarity, one will refer for example to the well-known work of physical mechanics of G. BRUHAT with editions MASSON AND CIE., pages 470 et seq. - 1934 - Paris.

The invention in principle, in fact, calls upon a law of physics well known under the name of law of JURIN.

The applications of the switches according to the invention, as described above, are manifold: it is possible, for example, to use them with magnetically controlled relays of the monostable, bistable type, or having several different stable positions. In this case, the movable pallet will be moved under the action of an external force and will come into contact with one of the electrical contacts wetted with mercury. The position will be stable insofar as the restoring force exerted by the liquid on the movable pallet will remain less than the capillary attraction force caused by the liquid on the upper part of the movable tongue, at the level of the electrical contact.

Those skilled in the art will without any particular problem determine the various parameters of the switch according to the invention by applying on the one hand JURIN's law, and on the other hand the moments theorem.

• - la figure 1 sous forme de deux vues (a) et (b), les deux phases de déplacement d'une lame mobile par rotation à rappel par tension de surface d'un liquide telle qu'utilisée dans l'interrupteur selon l'invention,
• - la figure 2, un interrupteur à contacts mouillés au mercure en ampoule fermée muni d'un dispositif de rappel selon l'invention,
• - la figure 3, une vue en coupe d'un mode préférentiel de réalisation de l'interrupteur selon l'invention,
• - la figure 4, une vue de dessus du dispositif de la figure 3 avant cambrage du support pour réaliser la languette fixe,

The invention will be better understood with the aid of the following exemplary embodiments, given without limitation, together with the figures which represent:

• - Figure 1 in the form of two views (a) and (b), the two phases of movement of a movable blade by rotation to return by surface tension of a liquid as used in the switch according to invention,
• FIG. 2, a switch with wet mercury contacts in a closed bulb fitted with a return device according to the invention,
• FIG. 3, a sectional view of a preferred embodiment of the switch according to the invention,
• FIG. 4, a top view of the device in FIG. 3 before bending the support to produce the fixed tongue,

Figure 1 shows, in two sectional views (a) (b), the two phases of movement of a movable blade return by surface tension forces used in the switch according to the invention.

The return device uses a liquid 21, a certain amount of which is located between the movable part 1 in the form of a blade, and a fixed part 22, arranged opposite, and integral with the base 3.

The distance between the two parts being chosen such that the liquid is maintained there by capillarity, the displacement of the blade 1 between the close position (a) and the separated position (b) makes the free surface 23 presented by the liquid vary considerably . And, as will be shown below, this results in the creation of a restoring force tending to bring the two parts closer in the direction of the arrow 25.

• L'écartement entre la pièce mobile 1 et la pièce fixe 22 sous l'action d'une force extérieure au système lui procure une énergie potentielle due à l'augmentation de la surface extérieure du liquide qui, lorsque la force extérieure disparait, replace la pièce mobile dans sa position initiale grâce à la libération de cette énergie par réduction de la surface du liquide et retour dans l'état d'énergie interne minimum.

The operation is as follows:

• The spacing between the moving part 1 and the fixed part 22 under the action of a force external to the system gives it potential energy due to the increase in the external surface of the liquid which, when the external force disappears, replaces the moving part in its initial position thanks to the release of this energy by reduction of the surface of the liquid and return to the state of minimum internal energy.

This effect is achieved when the dimensions of the parts 1 and 22 are sufficiently small and close enough for there to be an ascent of the liquid under the action of the surface tension forces of this liquid and the force due to the action of the gravity on the moving part 1 is sufficiently low compared to the surface tension forces involved.

• - d W étant la variation d'énergie interne de la goutte de liquide lorsque la pièce mobile 1 se déplace sous l'action d'une force extérieure,
• - d S étant la variation de la surface extérieure du liquide engendrée lorsque la pièce mobile 1 se déplace,
• - 8 est le coefficient de tension superficielle du liquide.

The energy stored under the effect of the displacement of the moving part 1 is equal to:

• - d W being the variation of internal energy of the drop of liquid when the moving part 1 moves under the action of an external force,
• - d S being the variation of the external surface of the liquid generated when the moving part 1 moves,
• - 8 is the coefficient of surface tension of the liquid.

• - de la hauteur de l'ascension capillaire du liquide entre les pièces 1 et 22,
• - des dimensions respectives des pièces 1 et 22,
• -- de l'écartement provoqué entre les pièces 1 et 22,
• - de la nature du liquide,

(l'action de la gravitation peut être négligée sur des pièces de taille suffisamment réduite telle, par exemple, que celle des interrupteurs miniatures en enceinte hermétique). Pour plus de détails sur ces différents paramètres, on se reportera à l'ouvrage de G. BRUHATcité plus haut.Knowing that the restoring force exerted on the moving part 1 depends on the stored energy and the spacing caused between the moving part 1 and the fixed part 22, this restoring force directly depends:

• - the height of the capillary rise of the liquid between parts 1 and 22,
• - the respective dimensions of parts 1 and 22,
• - the spacing caused between parts 1 and 22,
• - the nature of the liquid,

(the action of gravitation can be neglected on sufficiently small parts such as, for example, that of miniature switches in an airtight enclosure). For more details on these different parameters, see the work by G. BRUHATcité above.

An advantage of this system is its great stability over time since it eliminates any deformation of mechanical parts.

Another advantage lies in the fact that the mechanical parts 1 and 22 do not need to have particular elastic properties.

Another advantage lies in the fact that for systems of reduced dimensions such as, for example, miniature switches in hermetic enclosure, there is no need to operate a connection by precise welding between the moving part 1 and the base fixed (base 3).

FIG. 2 represents an embodiment of a miniature switch with wet mercury contacts according to the invention.

The switch consists of an airtight enclosure completely internally wetted by closing a cover 8 on a base 3 'comprising two electrodes 6 and 7 isolated from the base 3' by insulators 9 and a movable pallet 1 ' , connected via the base 3 'to an external electrical contact 24, said movable pallet coming to establish the electrical contact either between the electrode 6 and the contact 24 or between the electrode 7 and the contact.

A fixed pallet 22 'is positioned on the base 3 near the mobile pallet l' so that there is a capillary rise of the liquid 21 between the pallets l and 22 '.

The fixed electrode 7 is the electrode on which the movable pallet 1 ′ generally comes to rest in the absence of external stress thanks to the restoring force caused by the liquid spring of the invention. The electrode 6 is the working electrode on which the movable pallet 1 'is placed when a force external to the system, for example of magnetic origin, acts on said pallet.

When the ends of the electrodes 6 and 7 (one and / or the other) are not treated to be wetted by mercury, the switch according to the invention operates only by the action of an electromagnetic force on the movable pallet 1 'which switches it in contact with the electrode 6. The removal of the magnetic field generates the return of the movable pallet on the electrode 7. The switch then operates in a monostable manner.

• - la première dans le cas où après basculement de la palette mobile 1' en contact avec l'électrode 6 sous l'action d'un champ magnétique extérieur, le couple de rappel de la charnière liquide selon l'invention est supérieur au couple dû à la force de capillarité qui retient l'extrémité de la lame au contact de l'électrode 6, la disparition du champ électro-magnétique extérieur entraîne le rappel de la palette mobile au contact de l'électrode 7;
• - la seconde dans laquelle le moment de la force s'exerçant au niveau de l'électrode 6 sur la palette mobile 1' est supérieur au moment de la force exerçée par la charnière liquide 21 sur la palette mobile 1' (moment par rapport à l'axe 35 comme précédemment). Dans ce cas, un champ magnétique extérieur est à nouveau nécessaire pour permettre d'arracher la languette mobile de l'électrode 6 et son retour grâce au dispositif de rappel selon l'invention au contact de l'électrode 7. Ce champ magnétique, de sens inverse au champ magnétique précédent, est d'intensité moins élevée que celui-ci ainsi qu'il découle des explications données ci-dessus. En fonction des indications données plus haut, l'homme de l'art déterminera sans difficulté les dimensions respectives et les formes des électrodes 6, 7 de la palette mobile 1' et de la palette fixe 22' de manière à obtenir suivant l'effet recherché un interrupteur monostable ou bistable.

On the other hand, when the end of the electrodes 6 and 7 forming electrical contact as well as the movable pallet in contact with the electrodes are treated so as to be wetted by mercury, two situations can arise:

• - the first in the case where after tilting of the movable pallet 1 'in contact with the electrode 6 under the action of an external magnetic field, the return torque of the liquid hinge according to the invention is greater than the torque due at the capillary force which retains the end of the blade in contact with the electrode 6, the disappearance of the external electromagnetic field causes the movable pallet to return to the contact with the electrode 7;
• - the second in which the moment of the force exerted at the electrode 6 on the movable pallet 1 'is greater than the moment of the force exerted by the liquid hinge 21 on the movable pallet 1' (moment relative to axis 35 as before). In this case, an external magnetic field is again necessary to make it possible to tear off the movable tab of the electrode 6 and its return by means of the return device according to the invention in contact with the electrode 7. This magnetic field, opposite direction to the previous magnetic field, is of lower intensity than this one as it follows from the explanations given above. Depending on the indications given above, those skilled in the art will easily determine the respective dimensions and shapes of the electrodes 6, 7 of the movable pallet 1 'and of the fixed pallet 22' so as to obtain, depending on the effect looking for a monostable or bistable switch.

Of course, as appears from the description of the switch according to the invention shown in this figure 2, it is necessary in the case shown in this figure that the axis of rotation of the pallet is located at the end of it, that is to say that said pallet rocks about this axis which is substantially fixed and in the case of Figure 2 embedded in the base 3 'of the housing. The restoring force to which the mobile pallet is subjected is exerted near the axis of rotation 35 of the latter and its intensity is all the greater as the mobile pallet moves away from the fixed pallet.

In addition, it is easy to produce an all-position switch according to the invention so that the capillary forces between fixed and movable pallets are in all cases greater than the weight of the mercury placed between them.

In Figure 3, there is shown a very enlarged view of a preferred variant of the device according to the invention. The support 32 is coated with a flat metal part 31 pierced with an opening 37 through which passes the movable pallet 34 provided with its axis 35 located in the corresponding housing 36 of the support 32. The part 31 is extended by a support 30 substantially oriented at 90 ° and forming a dihedral therewith which contains the liquid 33 also present in the groove 36. The surfaces in contact with the liquid 33 of the pallet 34 and of the support 30 are of course treated to be wetted by the latter this. A drop of liquid being deposited on the part 31 above the groove 36, it rises by capillarity between the pallet 34 and the support 30, over a height determined by the various parameters described above. It is understood that the distance between the two pallets has been greatly increased to better understand the phenomenon which is the basis of the invention but that the respective dimensions of the elements of this figure are not to scale.

4 shows a schematic top view of the device of Figure 3. In this figure, the same elements as those of the previous figure have the same references. Unlike the previous figure 3, the fixed pallet (support 30) has not been straightened to form a dihedral with the part 31. This makes it possible to better understand the simplicity of manufacture of the device according to this preferred embodiment of the 'invention. To make a switch in a closed housing as shown for example in FIG. 2, it is therefore sufficient to take a support 32, such as a transistor base, to create a groove 36 therein, then to place the pallet 34 provided with its axis of rotation 35, so that it is placed in said groove. We then bring the assembly 30, 31, provided with the opening 37 of size slightly greater than the width of the pallet 34 and we come to cap it so as to maintain the axis 35 in the groove 36 to the using the lateral parts of part 31. This holding is represented by the dotted parts 38 and 39 of the axis 35. The dihedral 30, 31 is then formed by bending along the axis 40. It then suffices to put a drop of mercury in the cover corresponding to the base then assemble this hermetically without protective gas, so as to avoid oxidation of the mercury (of course, for the sake of simplification, FIG. 4 does not represent the electric electrodes such as 6 and 7 in Figure 2).

With regard to the control of the switch according to the invention, use will be made, for example, of at least one coil or a permanent magnet, arranged near the housing containing the switch, in order to attract the movable pallet in its function of job. The magnetic field applied to this pallet to switch it to the working position of the switch will be adapted to the different parameters of the latter. When the magnetic field is moved away or reduced, the tab returns to the rest position, thanks to the liquid spring of the invention.

For more details concerning the control of switches as represented on figure 2, one will be able to refer to the article "New construction for a mercury-wetted switch for operation in any position" of Messrs LE-GRAND and FRANCES published in volume 2 pages 625 to 634 of "Proceeding of the 1 Oth international conference on electric contact pheno mena", conference held from 25 to 29 August 1980 in Budapest.

Claims (3)

1. Switch having contacts wetted by mercury and located within a casing constituted by a base (3', 32) and a cap (8), comprising a first and a second electrode (6, 7), a movable element (1', 34) adapted to be placed in at least two different positions, to wit, a working position under the action of an external actuating force and a rest position under the action of a return force generated by the mercury located between said movable element (1', 34) and a fixed element (22', 30), the distance between said elements being at most equal to the value at which the mercury ist maintained between them by the capillary forces, the respective surfaces of the fixed element (22', 30) and the movable element (1', 34) which are in contact with the mercury being such that they are wetted by the same, characterized in that said movable element (1', 34) has the shape of a plate one side of which constitutes an axis of rotation (35) of the plate from the rest position toward the working position and vice-versa, said axis of rotation (35) engaging a groove (36) provided in the base (3', 32) of the casing, which is integral with said fixed element (22', 30), and in that said movable element (1') is connected to a third electrode (24) which is electrically connected to the first or the second electrode (6, 7) depending on whether said movable element (1') is inthe rest position or in the working position (or vice-versa).

2. Switch according to claim 1, characterized in that it comprises a dieder-shaped piece (30, 31) one face of which is integral with the base (32) and provided with an aperture (37) through which passes said movable element (1', 34), the axis of rotation (35) of the latter being maintained in said groove (36) by said face (31), and the fixed element being constituted by the other face of said dieder (30, 31).

3. Switch according to one of claims 1 or 2, characterized in that the dimensions of said movable plate and the distance between the contact point of the electrode corresponding to the working position and the axis of rotation (35) of said plate are so selected that the working position is a position of stable equilibrium.

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