GB2227608A

GB2227608A - Solenoid actuators

Info

Publication number: GB2227608A
Application number: GB9001536A
Authority: GB
Inventors: Jerzy Hoffman; Krzysztof J Ciezarek
Original assignee: H U Dev Corp
Current assignee: H U Dev Corp
Priority date: 1989-01-25
Filing date: 1990-01-23
Publication date: 1990-08-01
Also published as: DE3940242A1; IL91042A0; JPH02208905A; FR2642223A1; GB9001536D0

Description

:2--:2-;:-col- C) PATENTS ACT 1977 CASIPLIA 5837 GB Title: "Improved

Solenoid Actuator"

Description of the Invention

This invention relates to solenoid actuators for switches and other electrical devices.

Although there have been many recent advances in the technology related to all electronic switching devices, electromagnetic actuators are still required in many applications for which all electronic devices are not suitable. As a result, there is a need for reliable electromagnetic actuators, particularly in applications where the device is subject to vibration, high impact, high acceleration and fluctuating thermal and humidity conditions.

In the past, electromagnetic switching devices such as relays which were capable of withstanding these adverse conditions, have often been internally complex. As a result, many such prior devices are expensive and difficult to manufacture. For example, a typical prior relay is a model 412K Series TO-5 relay manufactured by the Teledyne Corporation. This relay includes a clipper type armature having two small push pins with an insulating glass bead to push a contact reed from a first position to a second position when the electromagnetic force attracts the armature, and a larger return spring to push the armature to its first position when the electromagnet is deactivated. The construction of the armature as well as the complex arrangement of its contact members makes this relay difficult to manufacture. This design also has a relatively high number of moving parts and welded joints which are subject to failures. As a result, the reliability of this relay limits its usefulness in many applications.

Another previous design replaces the spring and armature system with a bar-shaped slider actuator which is mechanically coupled to the contact reed. The slider is provided with an off-axis permanent magnet which is normally attracted to the yoke and core of the electromagnet; thus, holding the slider and the contact reed in a first position. Activation of the electromagnet repels the permanent magnet moving the slider and the reed to a second position. Although an improvement over the aforementioned TO-5 relay, this 0 design has a single stable position and consumes a substantial amount of power to repel the permanent magnet.

In still another design, an armature made of a ferro-magnetic material is positioned below an electromagnet. To increase resistance to shock and vibration, a permanent magnet is located such that the armature is held in one position by the attractive force of the permanent magnet. When the electromagnet of the actuator is activated, the attractive force of the electromagnet overcomes that of the permanent magnet, moving the armature to a second position. Such a design also consumes substantial power to overcome the permanent magnet.

In yet another design, an armature coupled to movable conductors slides co-axially in the core of the coil of the electromagnet. The magnetic field of the electromagnet when activated overcomes the attraction force of a fixed permanent magnet, actuating the armature and movable conductor. This design also consumes substantial power.

It is an object of the present invention to provide an improved solenoid actuator obviating for practical purposes the above mentioned limitations, particularly in a manner requiring a relatively uncomplicated mechanical arrangement.

It is a further object to provide a solenoid actuator that is highly reliable, simple in construction, relatively inexpensive to manufacture and is able to withstand the environmental conditions typical in applications requiring such actuators.

An actuator in accordance with a preferred embodiment of the present invention includes a slider having a permanent magnet co-axially positioned below the core of a core of the electromagnet. The slider is coupled to the element to be actuated and is held in a first position by the attractive force of the permanent magnet for the electromagnet. When the electromagnet is activated, the electromagnet repels the permanent magnet, moving the slider and the actuated element to a second position.

In a preferred embodiment, the actuator further includes a cup-shaped mass of ferro-magnetic material located adjacent the second position. Once the electromagnet is activated the attraction of the slider permanent magnet for the ferro-magnetic mass combines with the repulsive force of the electromagnet to move the slider to the second position. The cup-shape of the mass is made from magnetic material to close the magnetic circuit.

1 0 It has been found that such an arrangement reduces the amount of repulsive force required of the electromagnet and hence reduces power consumption of the actuator.

In an alternative embodiment, the slider may be further provided with an armature magnetically coupled to the permanent magnet of the slider. The armature further assists in the closing of the magnetic circuit when the permanent magnet is in the second position adjacent the ferro-magnetic mass. Similarly, when the permanent magnet is in the first position adjacent the core of the electromagnet, the armature assists in the closing of the magnetic circuit of the electromagnet.

In another embodiment, the actuator may have tandem permanent magnets coaxially aligned with the core of the electromagnet in the illustrated embodiment. These permanent magnets may be coupled to each other so as to move in tandem betwen first and second positions in accordance with the direction of the field of the electromagnet. A slider coupled to one of the permanent magnets actuates the movable conductor in accordance with the movement of the magnets. Such an arrangement may be made either bistable and latching, or monostable. Alternatively, one of the permanent magnets may be eliminated to also provide monostable operation.

In yet another alternative embodiment, a permanent magnet may be positioned between two co-axially aligned coils and adapted for movement between the two coils. By selected energisation of the coils to produce the appropriate magnetic fields, the permanent magnet and a slider coupled to the permanent magnet may be actuated between first and second positions, either bi-stable or monostable as desired.

Further advantages and structures will be better understood in view of the detailed description below and the accompanying drawings.

FIGURE 1 is a cross-sectional view of a solenoid actuator in accordance with one embodiment of the invention, illustrating the position of the slider in the electromagnet deactivated mode; FIGURE 2 is a cross-sectional view of the actuator shown in Figure 1, illustrating the position of the slider in the electromagnet activated mode; FIGURE 3 is a cross-sectional view of an actuator in accordance with an alternative embodiment, illustrating the position of the slider and the electromagnet in the deactivated mode; FIGURE 4 is a cross-sectional view of a bi-stable and latching actuator in accordance with another alternative embodiment having tandem magnets; 0 FIGURE 5 is a cross-sectional view of an actuator in accordance with still another alternative embodiment having a single permanent magnet, illustrating the position of the slider in the electromagnet deactivated mode; FIGURE 6 is a cross-sectional view of a bi-stable and latching actuator in accordance with yet another alternative embodiment having tandem coils.

Figures 1 and 2 show a solenoid actuator 10 in accordance with a preferred embodiment of the present invention. The actuator 10 is shown in cross-section, the actuator being generally symmetrical (round) about a centre axis A-A. The actuator 10 may be used to actuate any of a number of electromechanical devices including RF and DC relays and reed switches and RF attenuators, power dividers and the like.

The actuator 10 includes an electromagnet 12 having a wire coil 14 wound around a generally cylindrical bobbin (not shown). Centred within the coil 14 is a core 18 made of a ferro-magnetic material. Completing the magnetic circuit is a yoke 20, also of ferro-magnetic material. The actuator 10 actuates a movable member such as the reed conductor 22 of Figure 1 which illustrates a first (or open) position. The conductor reed 22 may be moved to engage stationary contacts 24 to define a second (closed) position (Figure 2).

In order to actuate the conductor reed 22 (or other movable element) of a relay or other electrical device, the actuator 10 further has a generally cylindrical slider 28 which is adapted to move along the centre axis A-A within an aperture 32 of the actuator body 34. In the illustrated embodiment, the outer surface of a probe 36 of the slider 28 and the inner surface of the aperture 32 are cylindrically shaped with the outer diameter of the probe 36 being sized somewhat smaller than the inner diameter of the aperture 32 to allow free axial movement of the slider 28 within the aperture 32. It is recognised, of course, that the slider 28 may have other shapes as well.

The probe 36 couples the slider 28 to the movable member to be actuated. In the illustrated embodiment, the probe 36 is fabricated from a nonmagnetic insulative material so that the probe 36 can directly engage electrically conductive members such as reed conductors, if desired.

Embedded within an upper cylindrically shaped insulated portion 39 of the slider 28 is a permanent magnet 40. In the illustratred embodiment, the magnet 40 is preferably a raw earth magnet such as samarium cobalt, neodymium-iron or neodymium-lron-boron. The horizontal cross-sectional shape of the magnet 40 is square but other shapes such as round are also 0 useable. As represented by the symbols 'IN" and IISII, the North and South poles of the magnet 40 are co-axially aligned with the centre axis A-A of the coil and core of the actuator electromagnet. When the coil 14 of the electromagnet 12 is de-energised, that is, deactivated, the permanent magnet 40 is attracted to the core 18 of the electromagnet 12, thereby moving the slider 28 to the 'first' position of the actuator 10 illustrated in Figure 1. In this manner, the movable element coupled to the slider 28 by the slider probe 36 is maintained in its first position corresponding to the first position of the slider 28 illustrated in Figure 1.

Upon energisation of the electromagnet, the electromagnet exerts an axial electromagnetic force on the permanent magnet 40 of the slider 28, repelling the permanent magnet 40 away from the core 18 of the electromagnet, and moving the slider 28 axially to the 'second, position illustrated in Figure 2. In order to further minimise the amount of repulsing force (and hence electrical power) required by the electromagnet, the actuator 10 of the illustrated embodiment further includes a mass or yoke 42 of soft ferro-magnetic material such as iron positioned generally adjacent to the second position of the slider 28. The permanent magnet 40 of the slider 28 is attracted to the ferromagnetic means 42 and this attractive force combines with the repulsive force supplied by the electromagnet to move the slider 28 to the second position of Figure 2. In this manner, the movable element coupled to the slider 28 by the probe 12 is actuated to the second (closed) position.

In the illustrated embodiment, the ferro-magnetic mass 42 is generally cup-shaped and is centred about the centre axis A-A. The mass 42 has a "U" cross-sectional shape including a base position 44 and an upstanding wall position 48. This shape is believed to enhance the closing of the magnetic circuit of the permanent magnet 40.

It is recognised that the mass 42 may have other shapes as well. In one embodiment, the ferro-magnetic mass 42 is sized and positioned such that, in the second position of Figure 2, the attractive force of the permanent magnet 40 for the core 18 and yoke 20 of the electromagnet 12 exceeds that of the attraction to the ferro-magnetic mass 42. Consequently, upon deactivation of the electromagnet, the slider 28 returns to the first position illustrated in Figure 1. In such an arrangement, the actuator 10 would be considered to be "normally open" in this monostable position.

C1 Alternatively, the size of the ferro-magnetic mass 42 may be increased such that the attraction of the permanent magnet 40 for the ferromagnetic mass 42 exceeds that of the attraction for the core 18 and yoke 20 of the electromagnet when the slider 28 is in the second position of Figure 2. Consequently, upon deactivation of the electromagnet, the slider 28 will remain in the second position. To move the slider 28 back to the first position of Figure 1, the electromagnet can be activated with the current through the call 14 being reversed, thereby reversing the poles of the electromagnet. As a result, the permanent magnet 40 of the slider 28 is also attracted to the electromagnet by the electromagnetic force exerted by the electromagnet, overcoming the attraction of the permanent magnet 40 for the ferro-magnetic mass 42. Depending upon the respective sizes and distances of the core 18, yoke 20 and yoke 42, this actuator can operate as a normally open or normally closed switch.

Preferably, the range of permissible motion of the movable element coupled to the slider 28 is restricted so that the permanent magnet 40 of the slider 28 is prevented from coming into contact with the core of the electromagnet 12 when the slider 28 is in the first position of Figure 1. Such an arrangement also reduces the amount of power needed to subsequently move the slider 28 to the second position of Figure 2. In a similar fashion, the second position of the slider 28 of Figure 2 may be defined by restricting the range of motion of the movable element towards its second position. For example, a movable element such as a reed conductor may alternately engage two contact terminals which define the first and second positions and hence the range of motion of the reed conductor. Because the slider 28 is coupled to the reed conductor by the slider probe 36, the first and second positions of the slider 28 are defined by the first and second positions of the conductor reed. Consequently, the actuator 10 is self-adjusting. That is, the slider 28 will always move the reed conductor into solid engagement with one of the two contact terminals, ensuring a good electrical connection between the reed conductor and the associated terminal.

Also, the actuator can selectively be made monostable in either the first position or the second position by appropriately distancing the permitted trail of the permanent magnet from the upper yoke 20 and core 18 on the one hand and the lower yoke 42 on the other. Thus, for example, the actuator 110 of Figure 3 will latch in the second position (normally closed) since the distance 8 between the armature 158 and the lower yoke 142 is much smaller than the distance between the armature 158 and the upper yoke 120.

It should be further appreciated from the above that the actuator 10 has only one moving part, the slider 28, apart from the movable element being actuated. As a consequence of the minimum number of moving parts, the reliability of the actuator 10 is increased. Furthermore, the ease of manufacture is increased with a corresponding decrease in the cost of manufacture. Still further, it is believed that the actuator 10 of the illustrated embodiment is capable of actuating at higher speeds than many prior actuators. The simplicity of the design also provides a high resistance to degradation caused by the environmental extremes of shock, acceleration, vibration, temperature and humidity.

Similar advantages may be obtained in the alternative embodiments depicted in Figures 3-6. Figure 3 shows an actuator 110 which is similar to the actuator 10 of Figures 1 and 2 except that the actuator 110 further includes an armature 150 coupled to a permanent magnet 140 of the slider 128. The armature 150 is generally disc-shaped and defines a central aperture 152 sized to admit an extension member 154 of the electromagnet core 118. As shown in Figure 3, the armature 150 has a generally cylindrical portion 156 coupled to the co-axially aligned magnet 140 and a generally planar portion 158 which extends between the yoke 142 of the slider 128 and the yoke 120 of the electromagnet 112. The armature 150 of the illustrated embodiment is shaped to assist in the completion of the magnetic circuit through the permanent magnet 140 and the yoke 142 of the slider 128 when the slider 128 (and the movable member 122) are in the second position illustrated in Figure 2. Conversely, when the slider 128 is in the first position adjacent the core 118, the armature 150 assists in completing the magnetic circuit of the electromagnet 112. Such an arrangement has also been found to reduce power consumption and increase reliability. It is recognised that the yoke 150 may have other shapes as well.

In the illustrated embodiment, the gap 160 between the movable member 122 and the body 134 is preferably less than that of the gap 162 between the armature 150 and the core and yoke of the electromagnet 112. This ensures that the movable member 122 contacts the body 134 before the armature 158 can contact the electromagnet 112 which prevents actual contact of the armature 158 with the yoke 120. Such an arrangement reduces the force necessary to magnetically disengage the permanent magnet 140 from C1 - -Bthe electromagnet yoke and core as the slider 128 is moved from the first position back to the second position illustrated in Figure 3. Similarly, the contacts 124 are positioned to ensure a gap 163 between the armature 158 and the lower yoke 142.

Figure 4 shows another alternative embodiment having a pair of tandem permanent magnets 340 and 364. The permanent magnet 340 is secured to one end of a slider 328 similar to the slider 28 of Figure 1. The magnets 340 and 364 are spaced apart a predetermined distance by a rod 366 of nonferromagnetic material, which is adapted to slide in a central aperture 368 of the core 318 of the coil 314 of an electromagnet 312. As shown in Figure 4, the magnetic poles of the permanent magnets 340 and 364, the aperture 368 of the core 318 and the rod 366 are co-axially aligned.

Figure 4 illustrates the actuator 310 in the second position in which the movable member 322 engages stationary contacts 324 (closed position). TO move the movable member 322 to the first position (open position) the coil 314 is energised in a manner so as to produce a magnetic field which repels the permanent magnet 364 and attracts the permanent magnet 340. If the movable member 322 allows the permanent magnet 340 to approach sufficiently close to the core 318 of the electromagnet 312, the actuator 310 will "latch" in the first position even after the coil 314 is deenergised. To return the movable member 322 to the second position illustrated in Figure 4, the coil 314 is energised in the opposite direction to produce a magnetic field which repels the permanent magnet 340 driving the slider 328 and movable contact 322 to engage the stationary contacts 324. In the illustrated embodiment, a gap is preferably provided between the non-magnetic material 369 encasing the permanent magnet 364 and the electromagnet 312 to ensure good contact between the movable member 322 and the stationary contacts 324 in the second position.

It is appreciated that the central rod 366 need not be physically attached to the permanent magnet 340 or 364. Since the rod 366 is constrained to co-axial translational movement within the core 318 of the electromagnet 318 in the illustrated embodiment, attachment of the permanent magnets to the rod 366 provides co-axial guidance for the permanent magnets and slider as well.

The operation of the actuator 310 has been described as a bistable, latching actuator. However, it is appreciated that the operation may be modified to a monostable operation so as to latch in only one of the first or Cl second positions by adjusting the spacing among the permanent magnets and the electromagnet so as to produce an imbalance in the respective attractive forces. For example, the actuator 310 may be configured as a normally closed actuator by restricting the movement of the permanent magnet 340 towards the electromagnet 312 so that in the first position, the attraction of the permanent magnet 364 for the core 318 exceeds that of the permanent magnet 340 for the core 318 upon de-energisation of the coil 314. Consequently, the actuator 310 will return to the second position (normally closed position)!Illustrated in Figure 4 from the first position automatically after the coil is de-energised.

Figure 5 shows an embodiment which is similar to the embodiment of Figure 4 wherein one of the tandem permanent magnets has been eliminated. Thus, the actuator 410 of Figure 5 has a permanent magnet 470 on one side of the core 418 of a coil 414 of an electromagnet 412, and a slider 428 on the other side of the core 418. As shown in Figure 5, the slide 428 does not have a permanent magnet and is coupled to the permanent magnet 470 on the other side of the core 418 by a rod 466 similar to the rod 366 of Figure 4. The actuator 410 of Figure 5 is monostable in the second (i.e. closed position) illustrated in Figure 5. Activating the coil 414 produces a magnetic field which repels the permanent magnet 470 drawing the rod 466 and the slider 428 with the permanent magnet 470, thereby causing a movable member 422 to disengage the stationary contacts 424. Upon de-energisation of the coil 414, the permanent magnet 470 returns the rod 466, slider 428 and movable contact 422 to their respective positions illustrated in Figure 5.

Figure 6 shows another alternative embodiment which in effect combines two actuators similar to the actuator 410 of Figure 5 to produce a bistable, latching actuator 510. Thus, the actuator 510 has two co-axial electromagnets 512 and 572 coupled by a bushing 574 of non-magnetic material. Disposed between the two electromagnets 512 and 572 are a pair of permanent magnets 570 and 576, the poles of which are co-axially aligned with the coils 518 and 578 of the electromagnets 512 and 572, respectively. It is recognised that a single magnet may be used, but it has been found that this embodiment is somewhat easier to construct with two magnets as shown.

In the illustrated embodiment, the magnets 570 and 576 are guided between first and second positions by a pair of guide rods 566 and 580 which are adapted for translational sliding motion within co-axial apertures of the cores 518 and 582 of the electromagnets 512 and 572, respectively. Figure 6 shows the actuator 510 in the first position in which the movable contacts C 1 522 are disengaged from the stationary contacts 524. To actuate the movable contacts 522 to the second (closed) position, the upper coil 578 may be energised to produce a magnetic field which repels the magnets 570 and 576 toward the lower coil 514 until the movable contacts 522 engage the stationary contacts 524 at the second (closed) position. Upon de- energisation of the upper coil 578, the actuator 510 will remain in the second position (latched) if the attraction of the magnets 570 and 576 for the core 518 of the lower electromagnet 512 exceeds that of the magnets for the core 582 of the upper electromagnet 572.

Once latched in the second position, the actuator 510 may be actuated back to the first position by energising the lower electromagnet 512 which produces a magnetic field which repels the magnets 570 and 576 back towards the core 582 of the electromagnet 572 as shown in Figure 6. Here, the actuator 510 will remain latched in the first position if the attractive force of the magnets 570 and 576 for the core 582 of the upper electromagnet 572 exceedsthatof the magnets fort hecore 51 8of thelowerelectro magnet512. Although the bistable, latching operation of the actuator 510 has been described, it is recognised that a mono-stable operation may be obtained by providing an imbalance in the magnetic attractive forces. In addition, the coils may be operated one at a time or together, depending upon the needs of the particular application.

It will of course be understood that numerous modifications of the present invention, in its various aspects, will be apparent to those skilled in the art, some being apparent only after study and others being matters of routine electromechanical design. For example, other shapes and sizes may be used other than those depicted. Other modifications and variations are also possible, with their specific designs being dependent upon a particular application. As such, the scope of the invention should not be limited by the particular embodiments described above, but should be defined instead by the appended claims and equivalents thereof.

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Claims

CLAIMS:

1. A solenoid actuator comprising a coil having a core, a first permanent magnet disposed on one side of the core and movable between first and second positions, a second permanent magnet disposed on the other side of the core and movable between first and second positions, and a conductor coupled to one of said magnets and movable between first and second positions, wherein activation of the coil produces an electromagnetic field which causes the first and second magnets to move to their respective second positions causing the conductor to move to its second position.

2. A solenoid actuator according to claim 1 wherein the first magnet is spaced from the second magnet by a predetermined distance.

3. A solenoid actuator according to claim 1 or claim 2 further comprising a rod spacing the first magnet from the second magnet.

4. A solenoid actuator according to claim 3 wherein the rod is coupled to both the first and second magnets.

5. A solenoid actuator according to any one of the preceding claims wherein the first and second magnets are constrained to move only translationally between the first and second positions.

6. A solenoid actuator according to any one of the preceding claims wherein the core defines a cylindrical aperture through which the rod is adapted to move translationally between the first and second positions.

7. A solenoid actuator according to any one of the preceding claims further comprising a passageway and a slider adapted for translational sliding movement within the passageway between first and second positions, said slider carrying one of said permanent magnets at one end and insulatively carrying the conductor at the other end.

8. A solenoid actuator according to claim 3 wherein the rod, core and poles of the permanent magnets are co-axially aligned.

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9. A solenoid actuator comprising a coil having a core which defines a central co-axial passageway, a rod adapted for translational sliding motion within the central passageway and between first and second positions, a first permanent magnet disposed on one side of the core, attached to the rod and movable between first and second positions, said first permanent magnet having magnetic poles co-axially aligned with the core of the coil, a slider having a second permanent magnet attached at one end which is in turn coupled to the other end of the rod, said second permanent magnet having magnetic poles co-axially aligned with the core and magnetic poles of the first permanent magnet, and a conductor reed insulatively coupled to the other end of the slider and movable between first and second positions in accordance with movement of the slider.

10. A solenoid actuator comprising a permanent magnet movable between first and second positions, a coil having a core disposed adjacent the first position of the magnet and co-axially aligned with its movement of the magnet, a cup-shaped yoke of magnetically permeable material disposed adjacent the second position of the permanent magnet and co-axially aligned with the core, and a conductor coupled to the permanent magnet and movable between first and second positions in accordance with movement of the permanent magnet, wherein activation of the coil produces a magnetic field which causes the magnet to move to its second position, causing the conductor to move to its second position.

11. A solenoid actuator for actuating a movable element, comprising a slider including a permanent magnet, the slider being coupled to the movable element and being located in the first position, said slider and movable element being movable between said first position and a second position, an electromagnet having a core positioned to attract the slider permanent magnet to the first position, and to repel the permanent magnet of the slider when the electromagnet is activated, and a cup-shaped mass of ferromagnetic material positioned adjacent the second position and coaxially aligned with the permanent magnet and core, and adapted to receive and to attract the permanent magnet, wherein the slider is moved to the second position by the repulsion of the slider permanent magnet by the electromagnet when activated, and the attraction of the ferro- magnetic mass.

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12. The actuator according to claim 11 wherein the ferro-magnetic mass is of sufficient size so as to retain the slider permanent magnet in the second position after the electromagnet is deactivated.

13. A solenoid actuator according to claim 11 and claim 12 wherein the movable element is a reed conductor.

14. A solenoid actuator according to any one of claims 11 to 13 wherein the ferro-magnetic mass is centred around the path of the slider permanent magnet.

15. A solenoid actuator according to claim 14 wherein the ferro-magnetic mass defines a central aperture through which the slider is adapted to slide.

16. The actuator according to any one of claims 11 to 15 further comprising an armature carried by the slider and magnetically coupled to the permanent magnet, said armature being positiond to complete the magnetic circuit with the electromagnet when the permanent magnet is in the first position and to complete the magnetic circuit with the electromagnet when the permanent magnet is in the second position.

17. The actuator according to claim 16 wherein the armature is generally disc-shaped and extends over the cup-shaped mass.

18. An actuator for actuating a movable element, comprising a slider including a permanent magnet, the slider being coupled to the movable element and being located in a first position, said slider and movable element being translationally movable between said first and second positions, an electromagnet having a core co-axially aligned with the poles of the slider permanent magnet to attract the slider permanent magnet to the first position, and to repel the permanent magnet of the slider with a magnetic field when the electromagnet is activated, to thereby move the slider permanent magnet to the second position and a cupshaped yoke of ferromagnetic material adjacent the magnet second position.

19. A solenoid actuator comprising a coil having a core, a first permanent magnet disposed on one side of the core and movable between first and ( t second positions, and a conductor disposed an the other side of the core and coupled to said magnet and movable between first and second positions, wherein activation of the coil produces an electromagnetic field which causes the magnet to move to its respective second position causing the conductor to move to its second position.

20. A solenoid actuator according to claim 19 wherein the magnet is spaced from the movable contact by a predetermined distance.

21. A solenoid actuator according to claim 19 or claim 20 further comprising a rod disposed within the coil core and coupling the magnet to the movable contact.

22. A solenoid actuator according to any one of claims 19 to 21 wherein the magnet is constrained to move only translationally between the first and second positions.

23. A solenoid actuator according to claim 21 or claim 22 wherein the core defines a cylindrical aperture through which the rod is adapted to move translationally between first and second positions.

24. A solenoid actuator according to any one of claims 19 to 23 further comprising a passageway within the core and a sli der adapted for translational sliding movement within the passageway between first and second positions, said slider carrying said permanent magnet at one end and insulatively carrying the conductor at the other end.

25. A solenoid actuator according to claim 23 or claim 24 wherein the rod, core and poles of the permanent magnet are co-axially aligned.

26. A solenoid actuator comprising a coil having a core of which defines a central co-axial passageway, a rod adapted for translational sliding motion within the central passageway and between first and second positions, a permanent magnet disposed on one side of the core, attached to one end of the rod and movable between first and second positions, said permanent magnet having magnetic poles co-axially aligned with the core of the coil, a conductor reed insulatively coupled to the other end of the rod and movable T 4 between first and second positions in accordance with movement of the magnet.

27. A solenoid actuator comprising a first coil having a core, a second coil having a core, a first permanent magnet disposed between the cores and movable between first and second positions and a conductor coupled to said magnet and movable between first and second positions, wherein selective activation of the coils produces an electromagnetic field which causes the magnet to move to its second position causing the conductor to move to its second position.

28. A solenoid actuator according to claim 27 wherein the magnet is constrained to move only translationally between the first and second positions.

29. A solenoid actuator according to claim 27 or claim 28 further comprising a pair of guide rods coupled to the magnet wherein each core defines a cylindrical aperture through which a rod is adapted to move translationally between the first and second positions.

30. A solenoid actuator according to any one of claims 27 to 29 further comprising a passageway and a slider adapted for transitional sliding movement within the passageway between first and second positions, said slider carrying said permanent magnet at one end and insulatively carrying the conductor at the other end.

31. A solenoid actuator according to claim 29 or claim 30 wherein the rods, cores and poles of the permanent magnet are co-axially aligned.

32. A solenoid actuator comprising a pair of coils, each having a core which defines a central co-axial passageway, a pair of rods, each rod adapted for translational sliding motion within an associated central passageway and between first and second positions, a permanent magnet disposed between the cores, coupled to the rods and movable between first and second positions, said permanent magnet having magnetic poles coaxially aligned with the cores of the coils, and a conductor reed insulatively coupled to a rod and movable between first and second positions in accordance with movement of the rod.

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33. A solenoid actuator substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

34. A solenoid actuator including any novel feature or novel combination of features disclosed herein and/or illustrated in the accompanying drawings.

1 Published 1990atThe Patent Office. State House,C6171 High Holborn, LondonWC1114TP. Further copies maybe obtalnedfrom The PatentOffice. Sees Branch, St Mary Cray, Orpington. Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con- 1187