Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
2000-05-11
2001-05-22
Barrera, Ramon M. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C335S270000
Reexamination Certificate
active
06236296
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to electromagnetic actuators.
The invention relates more particularly to an electromagnetic actuator including:
a mobile magnetic member which can reciprocate in translation along a central axis, said mobile magnetic member including stacked rigid ferromagnetic plates and said mobile magnetic member being joined to a fixed yoke by elastomer bodies which allow the mobile magnetic member to reciprocate parallel to the central axis, and
at least one electromagnet which is fastened to said yoke and which is adapted to reciprocate the mobile magnetic member along the central axis when a current that varies with time flows through said electromagnet.
BACKGROUND OF THE INVENTION
The document EP-A-0 544 576 describes an example of an electromagnetic actuator of the above kind whose operation is entirely satisfactory.
Nevertheless, the practical implementation of the mobile magnetic member leads to the following problems:
the assembly of ferromagnetic plates of the mobile magnetic member must be very stiff, especially as the mobile magnetic member is generally slim, with a relatively small thickness in the direction of the central axis,
the assembly of ferromagnetic plates must have a high resistance to fatigue, especially as the mobile magnetic member is subjected during its service life to a very large number (generally several billion) of alternating force cycles due to its reciprocating movement,
because the airgap between the magnetic member and the electromagnet is generally very small, for example of the order of 1 mm, the assembly must be very accurate and must guarantee perfect flatness of the mobile magnetic member, and
the assembly must prevent Eddy currents.
No satisfactory solution to the above technical problems has yet been found, whether by sticking the plates (insufficient fatigue resistance), welding them (insufficient fatigue resistance, residual stresses in the ferromagnetic plates and deterioration of the magnetic properties of the plates) or embedding them in a moulded elastomer (insufficient fatigue resistance).
OBJECTS AND SUMMARY OF THE INVENTION
Thus a particular object of the present invention is to solve the technical problems referred to above.
To this end, in accordance with the invention, an electromagnetic actuator of the kind in question is characterised in that:
each ferromagnetic plate has first and second opposite edges parallel to the central axis, the first edges of the ferromagnetic plates are aligned with each other along a first transverse axis perpendicular to the central axis and the second edges of the ferromagnetic plates are also aligned with each along said first transverse axis,
the ferromagnetic plates are fastened to respective first and second rigid transverse strips which are respectively fixed to the first and second edges of each ferromagnetic plate by crimping,
and the elastomer bodies join each transverse strip to the fixed yoke.
This produces an assembly which is particularly rigid and resistant to fatigue.
Moreover, relative movement of the plates in the stack of ferromagnetic plates is unrestricted prior to crimping, which enables the ferromagnetic plates to be positioned perfectly at the time of crimping, guaranteeing a highly accurate assembly.
Additionally, the assembly method used prevents residual stresses and does not modify the magnetic properties of the ferromagnetic plates in any way, unlike welding.
Finally, the ferromagnetic plates are connected to the transverse strip at the lateral faces of the mobile member, where there is virtually no magnetic flux, which prevents Eddy currents.
Any of the following features may be used in preferred embodiments of the invention:
the transverse strips are plates each of which is parallel to the first transverse axis and to the central axis;
the first and second edges of each ferromagnetic plate each include two fingers which project parallel to a second transverse axis perpendicular to the central axis and to the first transverse axis, a notch is defined between the two fingers and receives the corresponding transverse strip and each finger is crimped to said transverse strip;
the transverse strips are crimped to the ferromagnetic plates: this avoids bending the ferromagnetic plates and interferes as little as possible with their magnetic properties;
each transverse strip has a central part which extends along the first transverse axis between two diverging oblique ends each of which diverges from said central part of the transverse strip and said transverse strip is joined to the fixed yoke by two elastomer bodies stuck between each divergent end of the transverse strip and two support faces of the fixed yoke which are parallel to said divergent ends: the mobile magnetic member is therefore substantially immobilised in the direction perpendicular to the central axis;
the elastomer bodies are each stuck between an outside face of one transverse strip parallel to the central axis and to the first transverse axis and a support face of the fixed yoke parallel to said external face of the corresponding transverse strip;
at least one transverse strip is extended by an electrical connection terminal, the transverse strips and the ferromagnetic plates are electrically conductive and in electrical contact with each other and the electromagnetic actuator further includes at least one fixed conductive plate parallel to the mobile magnetic member and forming with it a capacitive position sensor;
the fixed yoke includes separate first and second rigid spacers respectively disposed along the first and second transverse strips with the mobile magnetic member between them;
the entire mobile magnetic member is covered with a moulded elastomer material which incorporates the elastomer bodies; and
the electromagnetic actuator includes two opposed electromagnets on respective opposite sides of the mobile magnetic member relative to the central axis.
REFERENCES:
patent: 4455496 (1984-06-01), Dean et al.
patent: 4596158 (1986-06-01), Strugach
patent: 5388812 (1995-02-01), Kojima et al.
patent: 5621293 (1997-04-01), Gennesseaux
patent: 5961104 (1999-10-01), Gennesseaux
patent: 0 544 576 (1993-06-01), None
patent: 0 893 620 (1999-01-01), None
French Preliminary Search Report dated Jan. 17, 2000, French Application FR 9906218.
Durand Sylvain
Gastineau Jean-Luc
Gennesseaux Andre
Menager Joel
Barrera Ramon M.
Hutchinson
Marshall O'Toole Gerstein Murray & Borun
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