EP0057130A2 - Mercury switch using the surface tension of mercury to reset the movable element - Google Patents

Abstract

The invention relates to a device for returning a pivoting moving part, ensuring its return to a rest position when it is moved away from it. The known solution, using an elastic mechanical part in the form of a spring, is replaced, according to the invention, by a certain amount of liquid 21, introduced between the moving part 1 and a fixed part 22, where it is maintained by capillarity. The displacement of the part 1 in the direction of the arrow 4, develops on the surface of the liquid surface forces which tend to return the part, in the direction of the arrow 25, to its initial position. The applications are notably in the field of miniature relays with wet mercury contacts in a sealed bulb.

Description

The present invention relates to a device for recalling a mobile element, a switch comprising such a device as well as its use in relays with magnetic control. It relates more particularly to a device for returning a mobile element which can take at least two different positions, respectively a working position under the action of an external control force and a rest position under the action of a force of recall.

These return devices are frequently constituted by an element endowed with elasticity, generally designated by the term of "spring". This 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 have a fairly high cost price: they are not only made of fairly special materials such as beryllium copper, but it is also necessary to subject them to a treatment which gives them good elastic properties. .

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

The recall device according to the invention makes it possible to avoid these drawbacks. For this purpose, it is characterized in that it is constituted by a liquid disposed between the mobile element and a fixed element whose distance is at most equal to the value for which the liquid is held between them by the forces capillary, the respective surfaces of the fixed member and the movable member in contact with the liquid being such that they are wetted by the latter.

Preferably, this liquid will be mercury, in particular when the device will be used as a switch in a relay with wet mercury contacts. In this particular case, in fact, the invention is particularly advantageous since the enclosure in which the switch is located already normally contains mercury. This therefore performs the dual function of wetting the contacts of the relay, on the one hand, and of the device for returning the movable element, on the other hand. Preferably also, the mobile element and / or the fixed element will have the form of flat metal tongues. The movable tongue may either move in translation under the action of an external force, such as a magnetic field, when it is made of a material sensitive to such a field, or move by rotation, for example around 'an axis contained in a plane integral with the fixed element.

According to a preferred embodiment, the fixed element will consist of a dihedral-shaped part, one of the planes of which is secured to a support parallel to the axis of rotation of the movable part, an opening being formed in said plan across which passes the movable element having the shape of a tongue located on the same side as the second plane of the dihedral relative to the first. This realization is obviously of great industrial interest since 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 preferably also containing mercury, is then maintained by the plane of the dihedron provided with an opening. It is thus very easily industrially produced 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 there is practiced a groove. The axis of rotation of the mobile 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 mobile part, allowing only a rotation of it. Then a drop of mercury is introduced into the corresponding cover which is welded to the base. According to another variant known to those skilled in the art, the mercury can be introduced after welding of the cover on the base through one of the electrodes having the shape of a hollow cylinder.

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, we will refer for example to the well-known work of physical mechanics of G. BRUHAT with the 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 tab 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 tongue 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 à rappel par tension de surface d'un liquide 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:

• FIG. 1 in the form of two views A and B, the two phases of movement of a movable blade with return by surface tension of a liquid according to the 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 according to the invention.

The reminder device uses a liquid 21, one of which a certain quantity is found 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,
• - 9 est le coefficient de tension superficielle du liquide.

The energy stored under the effect of the movement 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,
• - 9 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,

Knowing that the restoring force exerted on the moving part 1 depends on the stored energy and the spacing 3 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. BRUHAT cited 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 3.

FIG. 2 represents an embodiment of the recall device of the invention in a miniature switch with wet mercury contacts.

The switch consists of a fully wetted sealed enclosure obtained 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 has an external electrical contact 24, said movable pallet coming to establish electrical contact either between the electrode 6 and the electrode 24 or between the electrode 7 and the electrode 24.

A fixed pallet 22 is positioned on the base 3 near the movable electrode 1 so that there is a capillary rise of the liquid 21 between the parts 1 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 which makes it tilt in contact with the electrode 6. The removal of the magnetic field generates the return of the movable pallet 1 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 to 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 level of 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 the 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 element. trode 6 and its return by means of the return device according to the invention in contact with the electrode 7. This magnetic field, in the opposite direction to the preceding magnetic field, is of lower intensity than the latter as it follows from explanations given above. Depending on the indications given above, those skilled in the art will without difficulty 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 desired effect, 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 swings around 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.

FIG. 3 shows 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 the movable pallet 34 provided with its axis 35 located in the corresponding housing 36 of the support 32 passes. The support 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 pallets 34 and 30 are of course treated to be wetted by the latter. A drop of liquid being deposited on the support 31 above the groove 36, the latter rises by capillarity between the pallets 30 and 34, over a height determined by the various parameters described above. above. It is understood that the distance between the two pallets 30 and 34 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 30 has not been straightened to form a dihedral with the support 31. This allows 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 therefore suffices to take a base 32, such as a transistor base of the TO 5 type, to create a groove 36 in it, then placing the pallet 34 provided with its axis of rotation 35 so that it is placed in said groove. We then bring the assembly 30 and 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 the support 31. This holding is represented by the dotted parts 38 and 39 of the axis 36. 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 electrical contacts 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, disposed 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 field is moved away or reduced magnetic, 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 LEGRAND and FRANCES published in the volume 2 pages 625 to 634 of "Proceeding of the 10th international conference on electric contact phenomena", conference held from 25 to 29 August 1980 in Budapest.

Claims (10)

1. Return device, of a movable element which can take at least two different positions, respectively a working position under the action of an external control force, and a rest position under the action of a reminder, characterized in that it consists of a liquid (21) disposed between the movable element (1) and a fixed element (22) whose distance is at most equal to the value for which the liquid (21) is held between them by capillary forces, the respective surfaces of the fixed element and of the movable element in contact with the liquid being such that they are wetted by the latter, the transition from the rest position to the working position being effected by rotation of the mobile part (1). 2. Recall device according to claim 1, characterized in that said liquid (21) is mercury. 3. Return device according to one of claims 1 or 2, characterized in that the rotation of the movable part takes place along an axis (35). 4. Return device according to one of claims 1 or 2, characterized in that the axis of rotation (35) of the movable element (34) in the form of a pallet is determined by the penetration of an edge of that -ci in a groove (36) carried by a base (32) integral with the fixed element. 5. Return device according to one of claims 3 or 4, characterized in that it comprises a dihedral-shaped part (30, 31) one of the planes (31) of which is fixed to the base (32) and provided with an opening (37) through which the movable element (34) passes, the axis of rotation (35) thereof being held in the groove (36) by the plane integral with the support. 6. Return device according to claim 5, characterized in that the other plane of the dihedral constitutes the fixed pallet (30). 7. Switch with mercury wetted contacts, characterized in that it comprises at least one electrical contact on which rests a movable element having two equilibrium positions, said switch further comprising a device for recalling the element movable from one to the other equilibrium position according to one of the preceding claims. 8. Switch according to claim 7, characterized in that it comprises at least one electrical contact wetted by mercury on which the movable element (1) comes to bear under the action of an external force, the respective quantities liquid (21) between the two vanes (1, 22) on the one hand and on the electrical contact (7) on the other hand, and the distance from the axis of rotation (35) to the electrical contact (7) being such that the position of said contact (1, 7) is a stable position. 9. Switch with mercury wetted contacts arranged in a housing, characterized in that it comprises two electrical contacts (6, 7), a movable pallet (1) which pivots around an axis (35) formed in a groove (36) of the base (3) of the housing and resting on one or the other of the electrical contacts, as well as a fixed pallet (30) in the form of a dihedral (30, 31), one planes of the dihedron being fixed to the base (3) and provided with an opening through which the movable element passes, these elements being arranged respectively so that mercury introduced into the housing in sufficient quantity allows to exert a restoring force on the movable pallet (1) and an easy tilting thereof around its axis. 10. Use of the switch according to one of the preceding claims in magnetic-controlled relays, the magnetic field making it possible to tilt the movable pallet (1).

Images