Magnetic actuator

Details Magnetic actuator Magnetic actuator

2000-02-15

2001-06-19

Barrera, Ray (Department: 2832)

Electricity: magnetically operated switches, magnets, and electr

Magnets and electromagnets

With magneto-mechanical motive device

C335S222000, C335S232000, C335S235000, C417S413100, C310S036000

Reexamination Certificate

active

06249198

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a magnetic actuator. The actuator may be used in any applications where a member, for example a diaphragm, piston or plunger mounted for reciprocating motion in a predetermined direction is to be actuated.
Magnetic actuators are known and operate by interaction between a magnetic field and electric current flowing in one or more coils or windings. Typically magnetic actuators include an electromagnet incorporating a fixed core and a winding associated with the core, influencing a movable armature also of soft ferromagnetic material. The armature is one or more permanent magnets mounted on a movable actuator member connected to the member to be actuated, the diaphragm of a diaphragm pump, for example, with the permanent magnets influenced by an electromagnet.
GB 1557453 shows a known moving-magnet actuator, which consists of a fixed soft magnetic E-core stator assembly and two parallely magnetised permanent magnets arranged so that they present opposite poles towards the stator. The magnets are attached to a pair of independent soft magnetic lever arms which are supported by a pivot point and attached to the compressor. A single phase coil is mounted on the core central limb, and when excited by an alternating current, the magnetic arms produce an alternating torque and hence displacement.
The pair of permanent magnets are arranged so the axes of magnetization are in opposition and the motion of the two arms are synchronous, however, this can produce excessive vibration.
The above systems have proved successful for a number of products but their achievable performance is limited by a number of factors and there remain several disadvantages in terms of their manufacture. For example, large air-gaps are required for mechanical clearance due to tolerance problems and allowance for wear of the pivot points, resulting in significant flux leakage and the creation of stray fields. Additionally the use of soft magnetic arms, although improving the magnetic circuit over non-magnetic arms by acting as back-iron for the magnets, introduces problems of significant leakage and stray fields along the arms due to the extension of the soft magnetic component from the magnet back to the pivot point. The interaction of these soft magnetic arms with the coil excitation field also produces a reluctance or saliency force which distorts the excitation force profile. Another inherent feature of such devices is the presence of unbalanced magnetic forces which act in a perpendicular direction to the desired direction of motion due to the attraction of the magnet and the swing arm component towards the soft magnetic stator assembly. These forces can lead to excessive wear on the pivot system, particularly due to the cyclic nature of the force when in operation.
With regard to the electromagnet design in these actuators, current designs are typified by stators of parallel tooth and slot designs which have a large pole area to produce the correct torque-displacement profile. In order to simplify lamination cross section and to allow simple coil location the pole widths may be extended along the entire tooth length. This leads to excessive volumes of material. The material is therefore under utilised due to low levels of flux. Additionally, this feature leads to relatively narrow slots, and in order to accommodate sufficient copper windings whilst also accounting for ‘creepage and clearance’ the slots are typically deep and narrow, leading to slot leakage flux, i.e. flux produced by the coil which does not travel across the slot and is not available at the working air-gap for torque production.
SUMMARY OF THE INVENTION
The present invention seeks to improve the construction and performance of such systems.
The present invention provides an actuator for a member mounted for reciprocating motion in a predetermined direction, the actuator comprising a permanent magnet assembly linked to the member for movement therewith, the magnet assembly providing at least a pair of magnetic poles having similar or opposed pole faces adjacent one another and directed perpendicularly from the member and an electromagnet assembly having a respective pair of opposite poles located opposite so that energisation of the electromagnet produces movement of the permanent magnet poles towards one or other of the electromagnet poles wherein a magnetic backing member interlinks the poles of the permanent magnet to provide a flux return path.
In a preferred embodiment, the member to be actuated is a flexible diaphragm. The backing member acts to minimise leakage, maintain a useful magnet working point and offer an enhanced flux return path whilst reducing the normal force. Preferably, the magnetic backing member is mounted independently of the magnet and more preferably is located in a stationary position with respect to the electromagnet assembly, parallel to the electromagnet poles to define an air space in which the magnets are free to oscillate. Regardless of the magnet arrangement, the backing member improves performance by increasing the component of flux produced by the electromagnet assembly which interacts with the magnet in torque production so that for a given level of excitation a larger portion of flux will extend perpendicularly away from the electromagnet pole faces across the air gap to the backing member, whereas normally the flux would have a significant component of flux fringing, and flux not contributing to the torque production.
Preferably, the backing member comprises an axial dimension comparable with the magnet pole face axial dimension. Conveniently, the backing member may comprise a backing plate.
Preferably, the backing member may be held in a fixed position or more preferably an adjustable mounting may be used to allow adjustment of the air-gap between the backing member and the magnet poles to allow adjustment of the output by altering the magnetic circuit flux and hence torque.
In a preferred embodiment, the backing plate may be contoured with a radius or an approximation of a curve, as per the pole faces of the electromagnet, to maintain the desired air-gap over the moving magnet stroke. Alternatively the backing plate may be straight or ‘v’-ed.
In the preferred embodiment the magnets may be arc segments (as shown in
FIG. 6
) which when combined with a radially contoured backing plate and pole faces, will achieve a minimum variation in air-gap and hence allow minimum mechanical clearance. The magnet segments may be radially or diametrically magnetised. However, for many instances, rectangular magnets may be preferred.
Preferably, the link between the magnet assembly and the diaphragm comprises pivotable arms. More preferably, the arms support the pair of magnetic poles respectively.
Preferably, the magnets may be mounted such that the magnetic-air gap is not extended.
Preferably, the arms may be non-magnetic, thereby avoiding the problems of leakage and stray fields along the arms associated with magnetic arms, due to the extension of the soft magnetic component from the magnet back to the pivot point.
The use of non-magnetic arms allows the use of injection or compression moulded plastics to be considered, hence allowing a reduction in moving mass, whilst maintaining the desired degree of rigidity and strength.
Preferably, the pivot, arm, and diaphragm components may be integrated into a single assembly, which significantly reduces component count and greatly increases reliability whilst minimising possible noise and vibration.
Further the mechanical linkage with the moulded diaphragm components may also be improved by ensuring an air tight seal. The use of injection moulded components also increases tolerance control which combined with the reduction of the unbalanced normal force allows minimisation of the mechanical clearance between magnet and electromagnet backing member and thereby minimising the magnetic air-gap, and improving the magnetic circuit efficiency.
In the preferred embodiment, the electromagnet assembly comprises an E stato

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