GB2149974A - Two-state electromagnetic device comprising a permanent magnet - Google Patents

Abstract

A two-state electromagnetic device comprises an energizing winding (305) and a magnetic circuit comprising yokes and at least one armature (301), the armature comprising a permanent magnet (302) and two pole pieces (303, 304) forming with at least two yoke surfaces two air-gap zones each comprising two opposing air gaps. The yoke surfaces bounding the opposing air gaps of each air-gap zone are associated with respective yoke arms (308, 310, 309, 311) which are magnetically insulated from one another. A permanent magnet (314) is interposed between the two yoke arms (308 and 310 or 309 and 311) associated with each air-gap zone so that the flux flow in each air gap is boosted by the presence of permanent magnets upstream and downstream of the air gap. <IMAGE>

Description

SPECIFICATION Two-state electromagnet device comprising a permanent magnet This invention relates to a two-state electromagnet device comprising a permanent magnet.

French patent specification 2 271 654 discloses an electromagnetic device comprising a rotatable H-section armature and a permanent magnet disposed at the centre of the H.

The electromagnetic device disclosed by French patent specification 2 388 386 also has an H-section armature but in this case the same moves parallel to the axis of the permanent magnet disposed at the centre of the H.

The armature has plane pole pieces. This device may have two armatures and two parallel windings.

The Applicants' French patent specification 2 466 844 discloses an electromagnetic device comprising a H-section armature movable in a winding perpendicular to the axis of the permanent magnet disposed at the centre of H. The armature has a pole piece whose opposite ends are bent at right-angles.

The electromagnetic devices described in the patent specifications hereinbefore referred to operate as basically bistable (two-state) devices.

According to the applicants' French patent 2 520 152 and European patent 00 86121, the structures of the electromagnetic devices hereinbefore referred to were modified to provide operation with a single stable state. To this end, a second permanent magnet was introduced into the magnetic circuit of the yokes.

German patent specification 2 1 35 1 71 discloses an electromagnet comprising an energising winding extending around two bars or rods separated by a permanent magnet.

The armature of this device has no permanent magnet.

French patent specification 2 486 303 discloses an electromagnetic device with a structure similar to that of the device disclosed by French patent specification 2 271 654 except that there are two parallel windings and two armatures rotatable by the magnetic forces arising when the windings are energized.

All these prior-art electromagnetic devices have technical limitations.

The result of adding a second permanent magnet in the case of the devices disclosed by the Applicants' French patent specification 2 528 1 52 and European patent specification 0086121, is that two magnets are in the normal state magnetically in series with one another by way of an air gap which in the normal state is closed, so that the magnetic force determining the normal position can be increased.

For bistable operation of the device the second permanent magnet is eliminated, thus reducing the magnetic force produced by the closed air gaps.

However, since it is often necessary to provide a single electromagnetic construction which can be arranged to operate either as a monostable or bistable device just by means of a minor modification, it is a disadvantage for bistable operation not to be able to benefit from the magnetic force produced by the second permanent magnet.

Also, on bistable operation the energizing ampere-turns for causing the device to change its position are more than adequate and appear with a time constant which is low in relation to the operating time of the device because of its total mechanical inertia, but a leakage flux may extend through a closed air gap in the opposite direction to the flux flow before energization. In this case the movement of the electromagnetic device cannot occur since the attractive force of an air gap does not depend upon the direction of the magnetic flux in it.

To mitigate this disadvantage it is desirable to reduce leakage fluxes by placing permanent magnets as close as possible to the air gaps.

In the extreme case, if an air gap surface was embodied by the pole face of a permanent magnet with no pole piece, the stray attractive force would be replaced by a repulsion force.

The point is that a permanent magnet whose flux flow is opposed by another magnet or by ampere-turns produces a repulsion in a given direction if a movement in such a direction serves to decrease the flux flow stress to approach the state of flow in the absence of permanent magnet or ampereturns.

However, pole pieces are necessary to concentrate the flux in the air gaps so as to increase the attractive force.

Also, in some of the known constructions simultaneous and total closure of the air gaps calls for expensive precautions.

Another difficulty with known electromagnetic devices is that the inertia of the moving armature is often excessive and makes them useless for purposes requiring very rapid operation as in the case of circuit breakers for limiting short circuits.

The object of this invention is to obviate the disadvantages of known electromagnetic devices.

The two-state electromagnetic device comprising a permanent magnet according to the invention comprises a magnetic circuit and at least one energizing winding extending around a part of the magnetic circuit, the same taking the form of yokes and at least one armature movable relatively to one another, the armature comprising a permanent magnet having disposed on its pole faces, perpendicularly to the axis of the permanent magnet, two pole pieces projecting on at least one side of the permanent-magnet axis to bound with four yoke surfaces two airgap zones, each such zone taking the form of two opposing air gaps between the armature and the yoke and producing oppositely directed magnetic forces, the resultant of such forces tending to move the armature towards one or other of its stable end position according to the direction of energization of the winding.

According to the invention, in such a device for each air-gap zone the two yoke surfaces bounding the opposing air gaps are associated with yoke arms magnetically insulated from one another; and a permanent magnet is interposed between two yoke arms associated with a single air-gap zone so that the flux flow in an air gap is boosted by the presence of permanent magnets upstream and downstream of the flux flow.

Consequently, the presence of the permanent magnets boosts the flow of magnetic flux in an air gap so that the air gaps are closed optimally by very simple means.

Advantageously, the permanent magnet is interposed between two groups each consisting of two arms which are directly interconnected magnetically and which are associated with different air-gap zones.

Consequently, the magnetic circuit of a permanent magnet cannot be open in any of the armature end positions, thus obviating any risk of cold demagnetization of the permanent magnet.

Other features and advantages of the invention will be disclosed in the following description.

In the accompanying exemplary and nonlimitative drawings: Figure 1 is a perspective view, with parts broken away, of a first embodiment of an electromagnetic device according to the invention; Figure 2 is a view in cross-section of a second embodiment of the device according to the invention; Figure 3 is a section on the line Ill-Ill of Fig. 2; Figure 4 is a view in cross-section of a third embodiment of the device according to the invention; Figure 5 is a plan view of the embodiment shown in Fig. 4; Figure 6 is a perspective view of a fourth embodiment of the device according to the invention, the two parts being shown separated from one another for the sake of clarity, and Figure 7 is a perspective view of a fifth embodiment of the device according to the invention, the various parts being shown separated from one another for the sake of clarity.

Referring to Fig. 1, a two-state electromagnetic device comprises a permanent magnet 2 and an energizing winding 5 which extends around a part of the magnetic circuit. The same comprises yokes and an H-section armature 1 which can move relative to the yokes.

Magnet 2 is disposed in the central zone of the armature 1 and has on its pole faces two pole pieces 3, 4 which project on either side of the magnet along the axis thereof.

The winding 5 is retained in a plastics bobbin 6 and is wound around the central zone of the two pole pieces 3, 4 although the same remain free relative to the bobbin 6.

The pole pieces 3, 4 co-operate with four yoke surfaces to bound two air-gap zones.

Each such zone takes the form of two opposing air gaps between the armature and the yoke, magnetic forces of opposite directions being produced, the forces of two air-gap zones being in the same direction, the resultant of these forces tending to move the armature 1 towards one or other of its stable end positions according to the direction or sense of energization of the winding 5.

The features herein before described are present in the construction disclosed by the Applicants' French patent specification 2 466 844.

According to this invention, for each air-gap zone the two yoke surfaces bounding the opposing air gaps are associated with yoke arms 8, 10 on the one hand, and 9, 11, on the other hand, which are insulated from one another. Also, a permanent magnet 14 is interposed between the two arms 8, 10 and 9, 11 respectively associated with a single airgap zone so that, as will be described in greater detail hereinafter, the flux flow in an air gap is boosted by the presence of permanent magnets upstream and downstream of such flow.

In the embodiment shown in Fig. 1, the arms 8, 9 and 10, 11 are parallel to one another. The arms 8, 9 on the side near the pole piece 3 are magnetically interconnected by the yoke 1 2a which extends perpendicu larly to the latter arms. The arms 10, 11 adjacent the pole piece 4 are interconnected by the yoke 1 3a which also extends perpendicularly to the latter arms.

The two yokes 12a, 1 3a are plane and parallel to one another and are interconnected by the permanent magnet 14a.

In the example shown, ends 15, 1 6 of pole piece 3 and ends 17, 1 8 of pole piece 4 are bent at right-angles to increase the air-gap area delimited with the arms 8, 9 and 10, 11.

Also, the arms 8, 9 extend on either side of the ends 15, 1 6 of pole piece 3 whereas the arms 10, 11 are disposed between the ends 17, 18 of the pole piece 4.

Two yokes identical to the yokes 12a, 1 3a and a permanent magnet identical to the magnet 1 4a are disposed at those ends of the arms 8, 9 and 10, 11 which are distal from the yokes 12a, 13a and magnet 14a- i.e., on the other side of the armature 1 - the further two yokes and one magnet being arranged symmetrically of the yokes 12a, 13a and magnet 14a.

Clearly, therefore, the construction just described differs from the construction disclosed by French patent specification 2 466 844 in that the arms 8, 10 and the arms 9, 11 are not directly interconnected.

The point is that in the construction disclosed by the French patent specification just mentioned, the two arms associated with two different air-gap zones are interconnected by a magnet whereas in the construction according to the invention the arms 8, 10 are interconnected by a single magnet 1 4a (and the arms 9, 11 are interconnected similarly) since the arm 8 is connected to the arm 9 by the yoke 1 2a and the arm 10 is connected to the arm 11 by the yoke 13a.

If a first magnet was placed between the arms 8 and 10 and a second magnet between the arms 9 and 11, then in any of the operative positions of the electromagnetic device the magnetic circuit of one permanent magnet would always be open, which would render such magnet liable to cold demagnetization. The construction according to the invention obviates this likelihood.

Also, according to the invention the magnetic circuit of the permanent magnet 1 4a always opens very readily since the latter circuit has another chance of reclosing.

Also, the space between the arms 8, 9 and 10, 11 is delimited very accurately by the yokes 1 2a and 1 3a interconnecting them.

Assembly is very simple and effective thanks to the presence of recesses (not shown) which extend over half the width of the arms 8-11 and yokes 12a, 1 3a and engage in one another.

The two-state electromagnetic device here it before described can readily be converted into a monostable device without elaborate modification of its construction, it merely being necessary to interconnect the arms 8, 10 magnetically and interconnect the arms 9, 11 magnetically and to connect the two pairs of arms together by two stationary permanent magnets, something which can readily be achieved by altering the shape of the yokes 12aand 13a.

Figs. 2 and 3 show an electromagnet of similar construction to a construction disclosed by the Applicants' European patent specification 0086121 but modified in accordance with this invention. Like references denote like elements with the addition of 1 00.

The electromagnetic device shown in Figs.

2 and 3 comprises a substantially H-section armature 101 whose pole pieces 103, 104 are separated from one another by a permanent magnet 102, the whole having around it a winding 105. Pole piece 103 is substantially plane and has two widened opposite ends 115, 116.

Pole piece 104 has two ends 117, 118 bent at right-angles and disposed in two planes extending on either side of ends 115, 116 of pole piece 103.

The bobbin of the winding 105 is in the form of two plastics half-shells 1 06 a, 106 b which are free relatively to the pole pieces 103, 104, armature 101 being adapted to move along the axis of the winding 105.

The side walls of the two half-shells 106a, 106bare moulded on two pairs of parallel arms 108, 109 and 110, 111 which extend perpendicularly to the axis of the winding 105 and on either side of the pole pieces 103, 104. The arms 108-111 have the same function as the arms 8-11 of Fig. 1.

Also, the arms 108, 110, on the one hand, and the arms 109, 111, on the other hand, are coplanar.

As with the construction shown in Fig. 1, the arms 108, 110 and 109, 111 respectively are magnetically insulated and define opposing air-gap zones with the corresponding ends of the pole pieces 103, 104.

As can be seen in Fig. 3, the arms 108, 109 have their opposite ends interconnected by plane yokes 112a, 11 2b perpendicular to the arms and disposed on either side of the armature 101.

Similarly, the arms 110, 111 have their opposite ends interconnected by plane yokes 113a, 11 3b which extend parallel to the yokes 112a, 112 b. Permanent magnets 1 14a and 11 4b are disposed between each yoke pair 112a-113aand 112b1l3b.

The yokes 112a, 113a, 112b, 113b can be secured to the arms 108-111 by-means of nested slotting, just as in the construction of Fig. 1.

The device shown in Figs. 2 and 3 operates in just the same way as the construction shown in Fig. 1.

With reference to the electromagnetic device shown in Fig. 4, one hundred has been added to like references previously used. The basic difference between the constructions hereinbefore described and the device shown in Fig. 4 is that the same comprises two substantially H-section armatures 201 a, 201 b, the pole pieces 203a, 204a and 203b, 204b of each armature being separated by a permanent 202a, 202b and having around them a winding 205 a, 205b.

The armatures 201 a, 201 band the windings 205 a, 205b are disposed parallel and symmetrically on either side of the axis X-X' of the electromagnetic device.

The pole pieces 203a, 203b nearest the axis X-X' are plane whereas the other pole pieces 204a, 204b have ends 217a, 218a, 217b, 21 8b bent at right-angles, the coplanar ends 217 a, 21 7b extending towards the axis X-X' whereas the ends 218a, 218bwhich are coplanar in a different plane extend away from the axis X-X'.

The air-gap zones of the device shown in Fig. 4 are opposite one another. Near the ends 218a, 218b of the pole pieces 204a and 204b the air-gap zones are bounded by arms 209a, 211 a and 209b, 211 b cut in a metal sheet, all the arms being coplanar with one another and symmetrical of the axis X-X'.

These arms have the same function as the arms of the devices shown in Figs. 1-3.

In contrast to the previous embodiments, in which each arm is connected to an arm of a different air-gap zone but is associated with the same pole piece, the arms of opposite airgap zones are interconnected in the embodiment of Fig. 4.

For instance, the arm 209a is directly connected to the arm 211 b by a loop or yoke 219 disposed rearwardly of the armatures 201 a and 201 b relatively to the plane of Fig.

4, the yoke 219 forming part of the metal sheet in which the arms are cut (see Fig. 5).

Similarly, the arms 211 a, 209b are directly interconnected by a loop or yoke 220 identical to the yoke 219 and disposed forwardly of the armatures 201 a, 201 b in relation to the plane of Fig. 4.

Also, the arms 211 a and 211 bare interconnected by way of two permanent magnets 214a1, 214a2 stuck to the arm 211 a and 211 b respectively and partly covering the same. The arms are connected in series by means of a sheet metal plate 221 placed above them (and not shown in Fig. 5).

As a variant, the arms 211 a, 211 b could have been directly interconnected, et sim, the arms 209a, 209b, these two systems being interconnected by a permanent magnet placed between them.

Also, in this case the polarities of one of the permanent magnets 202a or 202b must be changed round. The resulting operation is such that the two armatures 201 a, 201 b have opposite directions of movement.

The bistable device shown in Figs. 4 and 5 can readily be converted into a monostable device by interconnecting the arms 211 a and 209a and interconnecting the arms 211 band 209 b and placing a permanent magnet between these two systems. Since these arms are coplanar, the conversion can be made very simply by altering the cutting of the arms in the sheet metal carrying them.

The bottom part of the device shown in Fig.

4 could be symmetrical at the top part just described. However, in the example shown the ends 217 a, 21 7b of the pole pieces 204 a, 204b are bent towards the axis X-X' so that the armatures 201 a, 201 b can be engaged in the bobbin 206a, 206b of the windings 205 a, 205b respectively.

Also, the end 217a and 217b of the pole pieces 204a and 204b respectively is far enough away from the ends of the other pole pieces 203a, 203b for the positioning in the resulting air-gap zones of pairs of superposed arms 208a, 210aand 208b, 210bseparated by two permanent magnets 214b1, 214b2.

The latter magnet is disposed between the arm 208a and 21 0a and between the arm 208b and 210b respectively.

Also, if the armatures 201 a, 201 b are required to move in the same direction, the arm 208a associated with the pole piece 203a is connected to the arm 21 0b associated with the pole piece 204b; likewise, the arm 210a is connected to the arm 208b by crossing. The crossing is achieved by means of recesses, as 222, on the axis X-X' in the zone where the system forming the arms 210a and 208b is bent bayonet-fashion so that the two systems do not touch one another and are separated by the magnets 214b1 and 214b2.

Consequently, the latter magnets are connected in parallel and the arms are interconnected directly and not by way of the yokes.

In the example shown in Fig. 4, the arms 208a to 211 b are stationary and the armatures 201 a, 201 b are movable, in both cases in the same direction parallel to the axis X-X'.

The armatures 201 a, 201 b move in the direction F1 (downwardly in the drawing) when the windings 205a, 205b are energized in the direction indicated by arrows Hiaand H,, so that a flux whose path is indicated by solid-line arrows is produced in the magnetic circuit. The path is in shape substantially square and is passed through in the trigonometric direction.

Conversely, the armatures 201 a, 201 b move in the direction F2 (upwards in the drawing) when the windings are energized in the direction indicated by arrows H2a and H2,, so that a flux following the path indicated by chain-line arrows is produced in the magnetic circuit. This path too is substantially square but is passed through in the opposite direction to the previous one.

Also, without departing from the scope of the invention the armatures 201 a, 201 b with their windings can be considered as stationary and the arms 208a to 211 b as moving. In this event a clearance can be left between the two bobbins 206a and 206b of the windings 205a and 205b for the positioning on the axis X-X' of connecting and guiding means, such as a rod, to connect the top arms 209a. .211 to the bottom arms 208a. . .210b.

This is a preferred feature since the arms have less mechanical inertia than the armatures and in this case the plastics bobbins for the windings can be moulded directly on the armatures.

In the embodiment shown in Fig. 6 one hundred has been added to like references.

The electromagnetic device of this embodiment comprises an armature 301 having plane pole pieces 303, 304 separated by a permanent magnet 302. The armature 301 can move in the direction F, or F2 (along the axis of the magnet 302) as in the case of the device disclosed by French patent specification 2 388 386. However, in contrast to the construction disclosed thereby, instead of a single yoke extending into the air-gap zone between the pole pieces 303, 304 disposed at the bottom of the armature 301, two magnetic arms 308, 310 separated by a permanent magnet 314 extend into such zone.

Also, in the air-gap zone at the top of the armature 301, the two pole pieces 303, 304 are framed by two arms 309, 311 bent bayonet-fashion and not directly interconnected but interconnected by way of the magnet 314, in the same way as the arms 308, 310.

Also, the arm 308, 309 adjacent the pole piece 303 are directly interconnected by a yoke 312.

Also, the arms 310, 311 adjacent the pole piece 304 are directly interconnected by a yoke 313.

Each system comprising two arms interconnected by a yoke 308, 309, 312 and 310, 311, 313 is cut in a C shape from sheet metal with a bayonet-like curvature.

A winding 305 is wound around the bobbins 312, 313, between which the magnet 314 is disposed.

Consequently, in this construction the permanent magnet 314 co-operates with the two air-gap zones of the armature 301.

When the winding 305 is energized as indicated by H1, a magnetic flux is produced in the direction indicated by solid-line arrows and causes the armature 301 to move in the direction indicated by the arrow F, perpendicular to the pole pieces of the armature 301.

Conversely, when the winding 305 is energized as indicated by H2, a magnetic flux is produced as indicated by the chain-line arrows and moves the armature 301 in the direction indicated by the arrow F2.

Of course, without departing from the scope of the invention, and as in the case of Fig. 4, two armatures 301 a and 301 b could have been arranged parallel to one another, opposite air-gap zones being interconnected by two systems of arms interconnected by a magnet and surrounded by a winding.

In the embodiment shown in Fig. 7 one hundred has been added to the previous like references. The bistable electromagnetic device of this embodiment has a rotatable armature 401 a as in the case of the construction disclosed by French patent specification 2 271 654.

However, in the example of Fig. 7 the device has two parallel armatures 401 a, 401 b and, disposed there-between, two windings 405a, 405b parallel to the rotational axis, as Y-Y', of the two armatures 401 a, 401 b.

Each H-shaped armature 401 a, 401b has two pole pieces 403a, 404a and 403b, 404b separated by a respective permanent magnet 402a, 402b.

In contrast to the known construction just mentioned, the cores of the windings 405 a, 405b are not solid but each take the form of two yokes 419, 420 and 423, 424 separated by a permanent magnet 414a and 414b respectively and having arm-like projections 409a, 411 a, 409b, 411b and 408a, 410a and 408b, 41 Ob on either side of the permanent magnet.

The resulting magnetic circuit is embodied by four H-shaped systems nested one in another at the four corners of a rectangle, the two systems associated with the windings 405a, 405b being stationary while the other two systems (the armatures 401 a and 401 b) are mobile.

The arrows of Fig. 7 explain the operation.

The flux path has a substantially square shape in this case too.

The description of the previous embodiments shows that in all cases an air gap of the electromagnetic device is framed in the direction of magnetic flux flow by a permanent magnet upstream and a permanent magnet downstream of such flow, one magnet being stationary and the other being mobile. The result is achieved because for each air-gap zone the two yoke surfaces bounding the opposing air gaps are associated with yoke arms magnetically insulated from one another and because a permanent magnet is interposed between two yoke armsXassociated with a single air-gap zone. Also, the permanent magnets are disposed very close to the air gaps so as to minimize stray fluxes.

The invention is not of course limited to the embodiments herein before described, which may be varied in many ways without departing from the scope of the invention.

For instance, instead of having air gaps of the constant-surface kind with variable distance between surfaces, as in the case of the examples described, the air gaps could be of the variable-surface kind and the betweensurfaces distance could be constant. One way of achieving this is by moving the edges of an arm and of a pole piece close together. However, air gaps of this kind are less efficient than those described because of the risks of incomplete closure and friction.

Also, starting from a magnetic circuit construction comprising a number of armatures interconnected by yokes, the armatures being embodied by a permanent magnet having disposed on its pole faces pole pieces projecting beyond the axis of the permanent magnet, a construction according to this invention is provided with elimination of the yokes and with the projecting ends of the armature pole pieces being so shaped as to delimit between them air-gap zones in the form of opposing air gaps. The characteristics claimed hereinafter therefore also apply to the constructions described in the patent of the invention filed today by the Applicants and entitled "Electromagnetic device comprising yokes and an armature having a permanent magnet having disposed on its pole faces pole pieces projecting beyond the axis of the permanent magnet, such axis being perpendicular to the direction of the movement" (Application No.

8428810).

Claims (14)

1. A two-state electromagnetic device comprising a magnetic circuit and at least one energizing winding extending around a part of the magnetic circuit, the magnetic circuit comprising yokes and at least one armature movable relative to the yokes, the armature comprising a permanent magnet having disposed on the pole faces thereof, perpendicular to the axis of the permanent magnet, two pole pieces projecting on at least one side of the axis of the permanent magnet to bound with four yoke surfaces two air-gap zones, each such zone comprising two air gaps between the armature and the yoke, the two air gaps producing oppositely directed magnetic forces and the resultant of the forces tending to move the armature towards one or other of two stable end positions thereof according to the direction of energization of the winding, wherein the two yoke surfaces bounding the air gaps of each air-gap zone are associated with respective yoke arms which are magnetically insulated from one another and between which is interposed a permanent magnet, whereby the flux flow in each of the said air gaps is boosted by the presence of a permanent magnet upstream and a permanent magnet downstream of the flux flow.

2. A device according to Claim 1, wherein the permanent magnet is interposed between two groups each consisting of two yoke arms which are directly interconnected magnetically and which are associated with respective different air-gap zones.

3. A device according to Claim 2, wherein the armature is disposed in the winding and has at least one pole piece the ends of which are bent at right-angles, and wherein each yoke arm has two ends secured to yokes which are perpendicular to the arms, two of the yokes in the same side of the armature being separated by a permanent magnet.

4. A device according to Claim 2, comprising two armatures magnetically connected in series, wherein two groups of each of the two interconnected yoke arms, together with the permanent magnet thereof, interconnect two air-gap zones associated with respective diffeent and oppositely disposed armatures.

5. A device according to Claim 4, wherein each armature is disposed in a winding and has at least one pole piece the ends of which are bent at right-angles, and wherein the movement of the electromagnet is picked up on two systems comprising, on the one hand, the arms (209a, 211 b; 211 a, 209b) and the magnets (214a1, 214a2) and, on the other hand, the arms (208a, 210b; 210a, 208b), which are rigidly interconnected and which have provision for guidance along the axis of the electromagnetic device.

6. A device according to Claim 5, wherein the bobbins of the windings are moulded on the armatures.

7. A device according to Claim 5 or 6, wherein one of the arm-and-permanent-magnet systems comprises two coplanar arms, each of which is partly covered by a permanent magnet, and a plate covers the tops of the latter magnets to connect the same in series.

8. A device according to Claim 5 or 6, wheren one of the arm-and-permanent-magnet systems comprises two arms which are curved bayonet-fashion at central portions thereof and formed with recesses therein enabling the same to cross without touching one another; two permanent magnets are interposed between the two arms for connection in parallel; and the two arms are engaged in a space between the pole pieces and ends, curved towards one another, of the other two pole pieces.

9. A device according to Claim 2, the armature having plane pole pieces and being movable along the axis of the permanent magnet thereof, wherein each system comprising two arms and a yoke interconnecting the same comprises a C-shaped plate, one of the arms being curved bayonet-fashion; and the permanent magnet is interposed between the yoke-forming parts of the C-shaped plates.

10. A two-state electromagnetic device comprising a permanent magnet, substantially as herein before described with reference to, and as shown in, Fig. 1 of the accompanying drawings.

11. A two-state electromagnet device comprising a permanent magnet, substantially as hereinbefore described with reference to, and as shown in, Figs. 2 and 3 of the accompanying drawings.

1 2. A two-state electromagnetic device comprising a permanent magnet, substantially as herein before described with reference to, and as shown in, Figs. 4 and 5 of the accompanying drawings.

1 3. A two-state electromagnetic device comprising a permanent magnet, substantially as hereinbefore described with reference to, and and shown in, Fig. 6 of the accompanying drawings.

14. A two-state electromagnetic device comprising a permanent magnet, substantially as herein before described with reference to, and as shown in, Fig. 7 of the accompanying drawings.

1 5. Any novel feature or combination of features described herein.