Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Patent
1996-02-15
2000-02-22
Gellner, Michael L.
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
335229, 335230, 335234, 335274, 335281, H01F 708
Patent
active
060284994
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a single-phase electromagnetic actuator, designed more particularly for applications requiring low-amplitude strokes.
2. Discussion of the Art
Actuators are known in the state of the art that include a first part moving along a direction Y and a second, fixed stator part made of a material with a very high magnetic permeability that contains at least one coil. Such actuators are, for example, claimed in the applicant's French Patent No. 2,648,633. The actuator, according to this embodiment, includes a transversely magnetized thin magnet with the peculiarity of providing a constant force throughout the entire stroke and an absence of magnetostatic force.
Also known from the prior art are actuators described, for example, in European Patent No. 157,632 or U.S. Pat. No. 4,779,582. These actuators contain two electrical coils acting antagonistically on a movable unit containing a thick-walled permanent magnet.
Such devices of the prior art present the disadvantages of the law of nonlinear force in relation to the current injected into the coils, a large amount of occupied space in the radial direction and a low efficiency in force per watt.
SUMMARY OF THE INVENTION
The purpose of the present invention is to provide an actuator optimized for short strokes and to provide an actuator that presents a high level of force per watt.
To this end, the actuator according to the invention has a fixed stator part and a movable ferromagnetic part defining between them two gaps arranged symmetrically with respect to the median plane perpendicular to the movement axis Y of the radially magnetized movable unit which passes through the middle of a permanent magnet, with the length of the movable ferromagnetic part approximately equal to the length of the permanent magnet. The radial gap between the fixed magnet and the ferromagnetic part is made as short as mechanically possible.
When the movable ferromagnetic part is in a median position with respect to the magnet and to the fixed stator part, the magnetic flux due to the magnet is shared equally between both gaps in the absence of a current in the excitation coil.
When current circulates through the excitation coil, it creates flux that is added to or subtracted from that of the permanent magnet. According to the direction of the flux generated by the coil, it will close preferentially in one or the other of the gaps, which causes the movable ferromagnetic part to move in the direction of the gap crossed by the addition of the two fluxes.
This type of actuator presents the particularity of producing a large magnetostatic force in each one of the two stable positions without current at the end of the stroke. In order to reduce the proportion of magnetostatic force in relation to the force due to the current, the gaps may be advantageously tilted with respect to axis Y by an angle on the order of 45.degree..
According to a preferred variation, the fixed stator part consists of an external cylindrical tube made of a soft magnetic material, which is closed at each end by a flange made of the same material with a conical surface. Advantageously, the coil is housed in the external cylinder and the fixed magnet is housed within the internal diameter of the coil; it preferably consists of a high-energy, radially oriented magnet such as those offered by the company DAIDO STEEL Ltd. The movable magnetic part consists of a tubular part made of a soft magnetic material with a conical surface at each end which complements that of the fixed stator part.
Advantageously, the coil is housed in a cylindrical cavity provided in the fixed stator part.
According to one variation, the actuator has two annular coils arranged symmetrically with respect to the median crosswise plane, housed in cylindrical cavities provided in the fixed stator part. This embodiment makes it possible to use the actuator bidirectionally in single-pole control and makes it possible to insert a soft magnetic material between the two
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Gandel Pierre
Oudet Claude
Barrera Raymond
Gellner Michael L.
Moving Magnet Technologies (S.A.)
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