GB2149975A

GB2149975A - Electromagnetic device comprising a permanent magnet

Info

Publication number: GB2149975A
Application number: GB08428810A
Authority: GB
Inventors: Gerard Koehler
Original assignee: Telemecanique Electrique SA
Current assignee: Telemecanique SA
Priority date: 1983-11-16
Filing date: 1984-11-14
Publication date: 1985-06-19
Also published as: FR2554959A1; GB8428810D0; DE3441427A1; GB2149975B; JPH0219607B2; JPS60117603A; FR2554959B1

Abstract

An electromagnetic device comprises at least one permanent magnet (2, 5) having pole pieces (3, 4, 6, 7) the ends of which define two air-gap zones each producing opposing forces along different axes parallel to the direction of movement of a moving part (1), and at least one winding (10, 12) extending around a part of the magnetic circuit. At least one flux-routeing system is provided in the form of the winding (10, 12) which extends around the magnet (2, 5) having pole pieces (3, 4; 6, 7). A crossover (8 9) of the pole-piece ends enables the air-gap surfaces to be in only two planes (P1, P2) so that the moving part (1) may be disposed in an hermetic enclosure which extends across the air-gap surfaces. <IMAGE>

Description

SPECIFICATION Electromagnetic device comprising a permanent magnet and with provision for displacement This invention relates to an electromagnetic device having a permanent magnet, a part being displaceable between two end positions, the displaceable or moving part co-operating with ends of the remainder of the magnetic circuit to bound two air-gap zones disposed on separate parallel axes, each such zone being adapted to produce alternately two opposing forces in directions parallel to the direction of the movement of the moving part, the magnetic circuit also comprising at least one permanent magnet having on its two pole faces pole pieces whose ends bound the two air-gap zones, at least one winding so extending around a part of the magnetic circuit as to be adapted to change the direction of flux flow in the magnetic circuit by means of an energization in the appropriate sense and thus to move the moving part from one end position to the other.

French patent specification 2 388 386 discloses an electromagnetic device constructed as just defined, the moving part or armature taking the form of the permanent magnet plus its plane pole pieces and moving parallel to the axis of the permanent magnet.

For the movement to be a displacement it is necessary to have in this construction, on one side of the permanent magnet, a stationary yoke which extends between the two pole pieces and, on the other side of the permanent magnet, two stationary interconnected yokes framing the outside surfaces of the pole pieces. The flux path is therefore asymmetrical and the forces in the two air-gap zones are not identical, so that the armature takes up a skewed position unless appropriate guide means are provided. Also, when the energization increases the forces decrease and change their sign. However, if energization becomes substantial the stray fluxes may produce a further attraction in the same direction as that operative in the absence of energization. Because of the asymmetry referred to, the force reversals on both sides of the armature do not occur simultaneously.Consequently, when energization increases progressively due to the winding being energized, there is a chance of having a resulting force which does not change its sign or which is less than the weight of the armature, so that the same is prevented from moving.

The stray or leakage fluxes are all the greater because the winding is disposed far from the permanent magnet and separated therefrom by air gaps.

There are also constructional difficulties in ensuring simultaneous closure of the air gaps, for the same are disposed in four different planes and the height tolerance of the magnet reacts on the positioning of the air-gap surfaces.

The main object of this invention is to obviate the disadvantages mentioned. Another object of the invention is to enable the armature to be positioned on its own in a hermetic enclosure in which at least one armatureoperated contact is disposed.

The electromagnetic device having a permanent magnet in accordance with the invention comprises a part displaceable between two end positions, the displaceable or moving part co-operating with ends of the remainder of the magnetic circuit to bound two air-gap zones disposed on separate parallel axes, each such zone being adaptdd to produce alternately two opposing forces in directions parallel to the direction of the movement of the moving part, the magnetic circuit also comprising at least one permanent magnet having on its two pole faces pole pieces whose ends bound the two air-gap zones, at least one winding so extend- ing around a part of the magnetic circuit as to be adapted to change the direction of flux flow in the magnetic circuit by means of an energization in the appropriate sense and thus to move the moving part from one end position to the other, means being adapted to cross the ends of the pole pieces bounding the two air-gap zones so that two ends of pole pieces associated with different air-gap zones and of opposite magnetic polarities are disposed in the same plane.

The electromagnetic device according to the invention comprises at least one flux-routeing system in the form of a permanent magnet having pole pieces on its pole faces too and having around it a winding whose field is perpendicular to the direction of magnetization of the latter permanent magnet and directed towards one or the other of the pole piece ends which extend from the winding.

In a first embodiment in which the electromagnetic device comprises two flux-routeing systems, the same are parallel to one another and have their pole pieces disposed in two parallel planes; and the means for crossing the ends of the pole pieces bounding the two air-gap zones take the form of two intermediate yokes interconnecting the respective ends of pole pieces disposed on the same side of the two windings associated with different flux-routeing systems and disposed in different planes.

In a second embodiment, the means for crossing the ends of the pole pieces bounding the two air-gap zones take the form of rightangled bends, along axes parallel to the axis of the winding, of tongue-shaped ends of two pole pieces, the four tongues being bent on the same side relative to the winding axis, two tongues which are associated with the same pole piece being disposed in different parallel planes.

In a bistable version, the moving part takes the form of a flat bar interconnecting the two air-gap zones and moving inside facing surfaces of the ends of the stationary pole pieces bounding such zones.

In another version for monostable operation, the moving part takes the form of a permanent magnet having mobile pole pieces on its two pole faces, one end of each mobile pole piece contacting one or the other of the facing inside surfaces of the ends of the stationary pole pieces disposed on one side of the winding.

According to one embodiment, the moving part is disposed in a hermetic enclosure whose thin walls engage the inside surfaces of the ends of the stationary pole pieces bounding the air-gap zones. It is therefore possible ta operate an electric contact in a hermetic enclosure without the winding having to be disposed therein and without the need for magnetic lead-throughs as in the case of the device disclosed by the Applicants' European patent specification 0 086 121.

Other features and advantages of the invention will become apparent from the following description.

In the accompanying exemplary and nonlimitative drawings: Figure 1 is a sectioned plan view of a first embodiment of an electromagnetic device according to the invention in a bistable form; Figure 2 is a side view in section on the line Il-Il of Fig. 1; Figure 3 is an end view corresponding to the front of Fig. 1; Figure 4 is an end view of the rear of Fig.

1; Figure 5 is a developed diagram showing the flux flow in the electromagnetic device of Fig. 1; Figure 6 is a view similar to Fig. 3 after the device has been placed in a hermetic enclosure; Figure 7 is a plan view of a second embodiment in a monostable form; Figure 8 is a sectioned side view on the line VIll-VIll of Fig. 7, and Figure 9 is another section side view on the line IX-IX of Fig. 7.

Referring to the embodiment shown in Figs.

1 to 4, a magnetic circuit has a moving part or armature 1 embodied by an ordinary flat bar. A first permanent magnet 2, has a pole piece 3 on its pole face S and a pole piece 4 on its pole face N.

A second permanent magnet 5 has a pole piece 6 on its pole face N and a pole piece 7 on its pole face S. The unit or system consisting of the permanent magnet 2 and its pole pieces 3, 4 has around it a winding 10 wound on a bobbin 11. Similarly, the system or unit formed by the permanent magnet 4 and its pole pieces 6, 7 has around it a winding 12 wound on a bobbin 13. The windings with their magnet and pole piece systems are disposed in side-by-side parallel relationship to one another and the pole pieces 4, 7 are disposed in one plane P1 while the pole pieces 3, 6 are disposed in a plane P2 parallel to the plane P1.

On one side of the windings 10, 1 2 the pole pieces 3, 4 and 6, 7 have plane ends 3b, 4b, 6b, 7b extending from the windings.

Also, the ends 3b and 7b associated with different permanent-magnet-and-pole-piece systems and disposed in different planes P1 and P2 are interconnected by an intermediate yoke 8. The ends 4b and 6b are similarly interconnected by an intermediate yoke 9.

However, the ends 4b, 6b are longer then the ends 3 b, 7b to prevent the yokes 8, 9 from touching one another. There is therefore a crossover in the connection between the pole pieces of the two systems. The yokes 8, 9 can, for instance, have a slight bayonetshaped curvature or bending and be secured by screws 14.

On the other side of the windings 10, 1 2 the pole pieces 3, 4, 6, 7 also have plane ends 3a, 4a, 6a, 7a which extend from the windings, and the moving part of armature 1 is disposed between the facing surfaces of the ends 3a and 4a and between the surfaces of the facing ends 6a and 7a.

Two air-gap zones are therefore bounded on separate parallel axes perpendicular to the planes P1 and P2, each such zone being adapted to produce alternately two opposing forces whose directions are perpendicular to the planes P1 and P2 and parallel to the direction of the displacement of the moving part 1. Because of the crossover just described, two pole-piece ends, as 3a and 6a or 4a and 7a, associated with different air-gap zones and having opposite magnetic polarities are disposed in a single plane P2 or a single plane P1.

The operation of the electromagnetic device is illustrated in the developed diagram of Fig.

5 in which two windings 10, 1 2 have been pivoted so that their axis is disposed in the plane of Fig. 5.

The moving part 1 is shown in its bottom position in the plane P1. It is in contact with the end 4a of north polarity and with the end 7a of south polarity. A flux therefore flows in the direction indicated by arrows. The flux then splits into two, a part I going through the yoke 8 and the magnet 2 and a part II going through the magnet 5 and the yoke 9. The flow of this flux has been produced by the fields H 1 and H' 1 of the windings 10 and 1 2.

If these fields are reversed, in the flux of the magnet 2 cannot issue by way of the end 4a but is routed to the opposite end 4b and will therefore go by way of the yoke 9 to the end 6a. Similarly, the flux of the magnet 5 cannot issue by way of the end 6b but is added to the previous flux at the end 6b but is added to the previous flux at the end 6a.

Each system comprising the winding, a magnet and pole pieces therefore acts as a flux-routeing device able to cancel a previous flux present in the air gaps in order to produce a flux in the open opposing air gaps and thus cause the moving part to move from its bottom end position to its top end position or vice versa. Unlike what occurs in the case of the disclosure by French patent specification 2 388 386, the field of a winding acts directly on the magnet it surrounds without going through an air gap, while the winding is very close to the air gaps. Also, the air gaps are completely symmetrical so that identical forces are produced in the two air-gap zones.

Also, the air gaps can readily be closed completely, possibly with slight skewing of the moving part as a result of loose guidance thereof.

The feature of the crossing yokes 8 and 9 means that the air-gsp surfaces lie just in two planes and not in four as in the prior art.

Referring to Fig. 6, which is similar to Fig.

3, there can be seen in section a bottom dished member 1 5. Thin walls thereof engage the inside surfaces of pole-piece ends 4a and 7a. Also, a top dished member 1 6 has thin walls which engage the inside surfaces of pole-piece ends 3a and 6a. Member 16 is prolonged upwardly by a closed chamber (not shown) in which at least one electric contact is disposed. The moving part thereof is operated by an insulating arm 1 7 secured at its other end of the centre of the moving part 1.

After the contact and the part 1 have been positioned, the two dished members 1 5, 1 6 are nested sealingly one in another. The resulting hermetic enclosure can be filled with a gas appriopriate to the nature of the metals used for the contacts and to the nature of the electrical load controlled. Clearly, the enclosure can be introduced or withdrawn as required from the remainder of the magnetic circuit. The thin walls have an anti-remanence effect and cause little loss of force if they are thin enough in relation to the air-gap area.

Figs. 7-9 show a second embodiment of the electromagnetic device.

In this case the means for crossing the ends of the pole pieces defining the two air-gap zones take the form of right-angled bends 108a, 108b, 109a, 109b, along axes parallel to the axis of the winding 110, of tongue-like ends 103a, 103b, 104a, 104b of the two pole pieces 103, 104. The four tongues are bent on the same side relatively to the winding axis. Two tongues 103a, 103b and 104a, 1 04b associated with the same pole piece 103, 104 respectively are disposed in different parallel planes P1, P2.

Also, the moving part of the electromagnet is a permanent magnet 1 20 having moving pole pieces 121, 122 on its two pole faces.

End 121a of pole piece 121 contacts one or other of the facing inside surfaces of the ends 1 03a or 1 04a of the stationary pole pieces disposed on one side of the winding 11 0.

Another end 1 22b of the moving pole piece 1 22 contacts one or the other of the facing inside surfaces of ends 1 03b or 1 04b of the stationary pole pieces disposed on the other side of the winding 110. The device then operates a monostable device.

As in the embodiment of Fig. 6, the moving part 120, 121, 122 of the device of Figs. 7 to 9 can be placed in a hermetic enclosure whose thin walls engage the inside surfaces of the ends of the stationary pole pieces bounding the air-gap zones.

The operation of the monostable device shown in Figs. 7 to 9 is similar to that described in European patent specification EP 0086121.

An electric contact can therefore be operated in a hermatic enclosure without the winding having to be received therein and without the need for magnetic lead-throughs as in the case of the device disclosed by the European patent specification referred to.

Also, the invention ensures complete closure of the air gaps despite slight asymmetry in the magnetic flux applied to the moving part.

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

For instance, the system 3, 8, 7 of Figs. 1 to 4 could be embodied as a single cut and curved piece just like the system 4, 9, 6.

Also, a flat armature 1 of Fig. 3 could be used instead of the composite armature 120, 121, 122 of Fig. 7 and vice versa. It would also be possible to have a H-shaped armature with the pole-piece ends on its outside surfaces.

It would be possible to have just a single winding in the device of Fig. 1 if for symmetry another system comprising a permanent magnet and pole pieces was to be added on the other side of the winding, the conductors of the additional winding also affecting the permanent magnets of the lateral arms.

The device shown in Figs. 7-9 could have a second armature added on the other side of the winding, the tongues 103a, 103b. 104a, 1 04b also being prolonged on the latter side.

Another possibility would be to have two systems of the kind shown in Fig. 1 disposed opposite one another near the pole-piece ends 3a, 4a, 6a, 7a so as to have a common armature 1 at the centre of the electromagnetic device.

The ideal solution of the problem so far as iron circuit lengths and magnetic leakages are concerned is to have stationary pole pieces 3, 4 separated by their rubber magnet and curved helically over a fraction of a turn above the planes P1 and P2 in which the first ends of the pole pieces are disposed, the second ends of such pole pieces then being returned to the planes P1 and P2, the winding being distributed over the fractional torus thus formed.

Claims

1. An electromagnetic device having a magnetic circuit, a part of which is displaceable between two end positions, the displaceable or moving part co-operating with ends of the remainder of the magnetic circuit to bound two air-gap zones disposed on separate parallel axes, each such zone being arranged to produce alternately two opposing forces in directions parallel to the direction of movement of the moving part, the magnetic circuit also comprising at least one permanent magnet having on the two pole faces thereof pole pieces the ends of which bound the two airgap zones, at least one winding extending around a part of the magnetic circuit so as to be arranged to change the direction of flux flow in the magnetic circuit by means of an energization of the winding in the appropriate sense and thus to move the moving part from one end position thereof of the other, means being provided to cross the ends of the pole pieces bounding the two air-gap zones so that two ends of pole pieces associated with respective different air-gap zones and of opposite magnetic polarities are disposed in the same plane wherein the electromagnetic device further comprises at least one flux-routeing system comprising a permanent magnet having pole pieces on the pole faces thereof and having disposed therearound a winding, the field of which is perpendicular to the direction of magnetization of the said permanent magnet and directed towards one or the other of the pole piece ends which extend from the winding.

2. A device according to Claim 1 comprising two flux-routeing systems, wherein the flux-routeing systems are parallel to one another and have the pole pieces thereof disposed in two parallel planes, and the means for crossing the ends of the pole pieces bounding the two air-gap zones comprise two intermediate yokes interconnecting the respective ends of pole pieces disposed on the same side of the two windings and associated with different flux-routeing systems and disposed in different planes.

3. A device according to Claim 1, wherein the means for crossing the ends of the pole pieces bounding the two air-gap zones comprise right-angle bends, along axes parallel to the axis of the winding, of tongue-shaped ends of two pole pieces, the four tongues being bent on the same side relative to the winding axis and two tongues which are associated with the same pole piece being dis posed in different parallel planes.

4. A device according to any one of the preceding claims, wherein the moving part comprises a flat bar interconnecting two airgap zones and so moving between facing surfaces of the ends of the stationary pole pieces bounding the said zones as to have a bistable operation.

5. A device according to any one of Claims 1 to 3, wherein the moving part comprises a permanent magnet having mobile pole pieces on the two pole faces thereof, one end of one moving pole piece contacting one or other of the facing inside surfaces of the ends of the staionary pole pieces disposed on one side of the winding while one end of the other moving pole piece contacts one or other of the facing inside surfaces of the ends of the stationary pole pieces disposed on the other side of the winding, so as to provide monostable operation.

6. A device according to any one of the preceding claims, wherein the moving part is disposed in an hermetic enclosure the thin walls of which engage the inside surfaces of the ends of the stationary pole pieces bounding the air-gap zones.

7. An electromagnetic device, substantially as hereinbefore described with reference to, and as shown in, Figs. 1 to 5 of the accompanying drawings.

8. An electromagnetic device, substantially as herein before described with reference to, and as shown in, Fig. 6 of the accompanying drawings.

9. An electromagnetic device, substantially as hereinbefore described with reference to, and as shown in, Figs. 7 to 9 of the accompanying drawings.

10. Any novel feature or combination of features described herein.