Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Patent
1998-05-15
2000-02-01
Donovan, Lincoln
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
335266, 310154, H01F 708
Patent
active
06020804&
DESCRIPTION:
BRIEF SUMMARY
TITLE OF THE INVENTION
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to an electromagnetic actuator intended to operate devices such as valves or switches and having a plurality of possible states, controlled by the positioning of a rotary element.
Discussion of Background
The displacement detween two consecutive stable positions constitutes a rapid transition achieved by application of a current in at least one pair of coils. The operation of such devices by electric motors usually necessitates the use of locking mechanisms to guarantee positioning at rest in one of the sought positions after a rotary displacement, and to prevent untimely displacements in the absence of control signals. The prior art teaches the technique of actuators provided with a rotor disposed in the air gap of a stator structure formed by a first magnetic circuit provided with four pole shoes, each equipped with an exciting coil. The rotor has a magnetized thin portion comprising two pairs of thin poles magnetized transversely in opposite directions. Such actuators are intended in particular for control of valves or switches. These actuators exhibit the feature of having a broad zone in which the force is constant. As a result, it is possible to construct actuators having very great reproducibility and very great angular precision under automatic control.
To achieve positions that are stable in the absence of current, the prior art actuators are usually provided with a ratchet wheel to lock the position of the actuator after a displacement. The mechanical parts employed for locking are a source of noise and wear. In addition, they lead to higher ts for manufacture and assembly of such actuators.
SUMMARY OF THE INVENTION
The object of the present invention is to construct an actuator provided with at least two stable positions, with a strong locking torque with or without current, not necessitating mechanical locking parts.
To this end the present invention relates to an electromagnetic actuator having four positions that are stable in the absence of current, for operation of a device such as a valve or switch, the actuator being provided with a thin rotationally movable magnet, having two pairs of magnetic poles magnetized transversely in alternate directions, and a stator structure provided with four pole shoes of developed length P, each equipped with an exciting coil, two consecutive poles of the thin magnet being separated by a distance d. The thin magnet is movable in an air gap of dimension E, the dimensional ratios P/E and P/d being larger than 8.
Such an actuator has a locking torque of almost 30% of the motor torque when the diametral plane separating the two magnets is in one of the planes passing between two pole shoes.
Such an actuator can be constructed in two variants: a first variant in which the movable portion has the shape of a disk, and a second variant in which the movable portion has the shape of a tube.
According to the first variant, the movable portion comprises a yoke of circular cross section integral with a thin magnet in the shape of a disk, having two complementary sectors extending for about 180.degree. and magnetized in two opposite axial directions, the pble shoes of the stator portion disposed facing the movable magnet having an annular shape extending for about 90.degree..
Advantageously, the semi-annular surface of the pole shoes of the stator portion is extended by a foot of smaller cross section, the exciting coil encircling the said foot.
Preferably the shoes are integral with a disk-shaped magnetic-flux closing part.
According to one particular embodiment, the stator structure comprises a first ferromagnetic part having two pole shoes and a second ferromagnetic part having two pole shoes, the two stator parts being disposed on both sides of the thin disk-shaped magnet, the planes passing through the top surface of the pole shoes being spaced apart by a distance d, and the two stator parts being offset by 90.degree..
According to a second construct
REFERENCES:
patent: 3889219 (1975-06-01), Larner
patent: 3959672 (1976-05-01), Walker et al.
patent: 4698535 (1987-10-01), Shiraki et al.
patent: 4899073 (1990-02-01), Takeuchi et al.
Donovan Lincoln
Sonceboz S.A.
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