Electrical generator or motor structure – Dynamoelectric – Oscillating
Reexamination Certificate
1999-11-12
2001-11-06
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Oscillating
C310S156450, C310S156320, C310S268000, C310S254100
Reexamination Certificate
active
06313553
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention regards the field of single-phase rotating electromagnetic actuators, that is, electromagnetic devices that have a limited stroke, as opposed to engines that have an unlimited stroke. Actuators are designed for precise positioning, with good repeatability, of an associated mechanism, with constant torque throughout the length of the stroke with a simple control law, preferably linear, avoiding the use of complex control circuits.
2. Discussion of the Background
In the current state of the art there are many types of rotating single-phase actuators that comprise a stationary component consisting of a first stator magnetic circuit made of a material with very high magnetic permeability energized by at least one energizer coil and a mobile component consisting of an axially magnetized disk.
For example, American patent U.S. Pat. No. 4,510,403 describes an actuator comprising a thick central magnet. Such actuators do not supply constant torque, and have central position restoring torque.
In general, we know how to eliminate these disadvantages by using thin magnets transversely magnetized in the direction of the smallest dimension, perpendicular to the polar surfaces. This magnetized disk has 2N pairs of magnetic poles magnetized in alternating directions. The magnetization is virtually uniform. The magnetized disk is attached to a second magnetic circuit made of a material with high magnetic permeability. The mobile component is equipped with a coupling shaft designed to transmit the torque.
By way of example, these types of actuators are described in French patent application EP558362 filed by the applicant.
These actuators have constant torque for a given current, and a torque proportional to the current applied to the energizer coil. However, they have one disadvantage concerning their price: they require high energy magnets, Neodymium-Iron-Boron magnets, for example, whose cost price is high.
Additionally, the structures of the prior art use multipolar magnets or assemblies of several magnets in alternating direction, which prohibits magnetizing after assembly and requires handling high energy magnets when the actuators are being assembled. This type of handling is delicate, since high energy magnets can introduce particles, metal shavings, for example, into the actuators when they are positioned on the mobile component. To prevent this disadvantage, we know how to encapsulate the magnets, a costly solution that has the disadvantage of further increasing the cost price of the actuators.
SUMMARY OF THE INVENTION
To eliminate these disadvantages, the invention proposes a high-performance rotating electromagnetic actuator at a lower cost price that comprises at identical torques a smaller magnet mass than those of the prior art. These magnets are preferably all magnetized in the same direction, which permits magnetization subsequent to assembly of the mobile component, and therefore makes it possible to avoid handling high energy magnets likely to introduce metal shavings into the actuator during manufacture. The invention also targets the enhanced performance of the actuators of the prior art, particularly with regard to the torque at the beginning of the stroke and the overall size of the actuator.
In its most general sense, the invention regards a rotating electromagnetic actuator comprising a stationary component consisting of at least a first stator magnetic circuit with at least 2N poles, N being a whole number, energized by at least one energizer coil and a mobile component comprising at least one magnet wherein the mobile component comprises N magnets juxtaposed with at least one ferromagnetic part with a thickness e between 0 and E, defining one or two air gaps, with a total length of E-e.
As a result, the mobile component has a ferromagnetic thickness stairway that creates an effect of variable reluctance that produces a gap at the start of the stroke proportional to the square of the ampere-turns applied to the coils.
Advantageously, the width of one of the magnetized parts Y
a
measured along its mean diameter is equal to
C+S+2E′
where C is the width of the angular arc travelled by the rotor on the mean diameter of the magnetized parts, S is the width measured on the mean diameter of the magnetized parts between two adjacent stator poles and E′ is between E/2 and E, with
C
+
2
E
′
E
>
3
and
L
E
>
0.75
,
preferably
0.8
L
E
<
0.9
L designates the thickness of a magnetized part in the direction of magnetization, in order to ensure torque due to the roughly constant current along the length of the stroke and roughly proportional to the current.
According to a preferred variation, the interposed ferromagnetic portions of the mobile part have a thickness e in the direction of magnetization of the magnetized parts with a thickness L, so that: 0<e/L<0.6.
According to a special mode of embodiment, the stationary component comprises a stator part that has 2N semi-annular polar parts each surrounded by an energizer coil.
According to a first variation, the stationary component comprises a second stator part symmetrical to the first stator part, also having 2N semi-annular polar parts each surrounded by an energizer coil.
According to a second variation, the mobile component is formed by a rotating yoke bearing N magnets magnetized axially and N interposed ferromagnetic parts.
According to another mode of embodiment, the mobile part is tubular in shape and bears N tile-shaped magnets magnetized radially and N interposed ferromagnetic parts. The stationary component has 2N stator poles that are semi-tubular in shape.
According to a preferred variation, the mobile component comprises N magnets magnetized after they are positioned on the mobile component.
According to a preferred mode of embodiment, the mobile component comprises N magnets housed in cavities provided in the yoke of the mobile part, the complementary areas to these cavities forming the interposed ferromagnetic parts.
In the various embodiment variations, the volume of an interposed ferromagnetic part can be equal to the volume of a magnet; however, this is not a necessary constraint but a special case. When the magnet or magnets are housed in a cavity or a groove made in the rotor, the magnet can be level with the surface of the rotor or can be sunk into the rotor or, on the contrary, can extend beyond the surface of the rotor.
When the actuator is not saturated, within the effective stroke the torque may be broken down into three components: magnetostatic torque C
0
(without current), often negligible, a period of polarized torque C
ni
proportional to the ampere-turns, and a period of torque C
ni2
proportional to the square of the ampere-turns, due to the variable reluctance created by the interposed ferromagnetic parts with a thickness e:
C=C
0
+C
ni
+C
ni2
Without interspersed ferromagnetic parts, e=0, C
ni2
=0.
For a given ampere-turns value, the three torque periods increase when the thickness e of the interposed ferromagnetic parts increases.
For slight thicknesses e of interposed ferromagnetic parts and/or for low values of ampere-turns, the actuator has a torque virtually proportional to the current and virtually constant along the length of the stroke (C
ni2
is negligible). On the other hand, the torque is increased in the case without any interposed ferromagnetic parts (e=0).
For significant thicknesses of interposed ferromagnetic parts, the torque is significantly increased, but when the ampere-turns become significant, the torque is no longer proportional to the current. Its course is no longer constant along the length of the stroke due to the variable reluctance created by the interposed ferromagnetic parts, which is not problematic in certain applications and may sometimes be exploited.
When a torque peak from 2 to 3 times the nominal torque is necessary along the entire stroke, it is necessary to limit the ratio e/L where e
Besson Christophe
Gandel Pierre
Moving Magnet Technologies (S.A.)
Mullins Burton S.
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