Electrical generator or motor structure – Dynamoelectric – Oscillating
Patent
1994-05-19
1996-08-27
Stephan, Steven L.
Electrical generator or motor structure
Dynamoelectric
Oscillating
310114, 310 905, H02K 2600, H02K 709
Patent
active
055504132
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a brushless torque motor with an angular displacement less than 180.degree. and an application of this motor to controlling the angular displacement of a shaft, for example a shaft carrying a scanning mirror (or an antenna support, a filter, a lens, etc.), preferably but not exclusively in space applications.
Many kinds of torque motors are already known. The operation of these motors is based on producing a torque by causing an appropriate electric current to flow in wires, in practice portions of coils, disposed in a permanent magnetic field. However, known torque motors usually have a large overall dimension transversely or parallel to the rotation axis and a rotor (i.e., the rotating part of the motor) with a high inertia, especially if the latter carries the members generating the permanent magnetic field (in practice permanent magnets).
The term "armature" refers to the part of the motor carrying the wires carrying the current and the term "field assembly" refers to the complementary part of the motor carrying the members generating the permanent magnetic field.
SUMMARY OF THE INVENTION
An object of the invention is to provide a brushless torque motor combining low rotational inertia, compact overall dimensions (especially in the radial direction), a high angular displacement (although below 180.degree.), a constant torque (with no ripple) over virtually all of the angular displacement (for a given current), great precision and freedom from divergent magnetic force (facilitating a combination with mounting of the rotor in bearings) and which is easy and simple to manufacture (leading to low unit cost and high reliability).
To this end the invention proposes a torque motor including a field assembly coupled to a shaft rotating within a given angular displacement about a given axis relative to a stator part including an armature.
In accordance with the invention, the field assembly includes an elongate central bar along the axis and a ferromagnetic tubular portion extending circumferentially all around the central bar at a predetermined distance therefrom. The central bar includes two portions of the same cylinder diametrally opposed and coaxial with the given axis, subtending substantially equal angles less than 180.degree., and separated by two globally parallel longitudinal flats, and a permanently magnetized central bar disposed along the given axis with its magnetization direction substantially parallel to the flats.
The armature is a tubular member disposed radially between the central bar and the ferromagnetic tubular portion and includes at least one coil having an input and an output and including separate parallel longitudinal strands connected by strands disposed transversally to the given axis. The longitudinal strands are divided into two diametrally opposed groups, all the strands of a group carrying current in the same direction when current is applied between the input and the output of the coil. Each group faces a respective cylinder portion, and the given angular displacement is less than the difference between the angle subtended by the cylinder portions and the groups.
According to preferred features of the invention, some of which may be combinable with others:
The permanently magnetized central bar extends from one flat to the other.
The central bar extends axially over a distance less than the length of the longitudinal strands and the transverse strands are axially offset to either side of the central bar.
The flats are plane and parallel.
The angle subtended by each cylinder portion is between 90.degree. and 170.degree..
The angle subtended by each group is less than 30.degree..
The angle subtended by each cylinder portion is approximately 150.degree., the angle subtended by each group is approximately 30.degree. and the amplitude of angular displacement is approximately 120.degree..
The tubular armature is in the form of a plurality of coils in series formed of radially stacked layers electrically insulated from each other
REFERENCES:
patent: 4607180 (1986-08-01), Stoody
patent: 4831296 (1989-05-01), Nagaba
patent: 5124606 (1992-06-01), Eisenbeis
patent: 5319274 (1994-06-01), New
Bernus Christophe
Jamain Patrice
Roland Jean-Pierre
Aerospatiale - Societe Nationale Industrielle
Jones Judson H.
Meehan Thomas A.
Stephan Steven L.
VanOphem John
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