Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
2001-03-30
2003-01-14
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C335S272000, C335S279000, C335S229000, C310S036000
Reexamination Certificate
active
06507257
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a latching permanent magnet brushless torque actuator (PMBTA) and particularly a bi-directional PMBTA capable of being latched in two different rotational positions and remaining in the latched positions even when the latching coil is de-energized.
2. Discussion of Prior Art
U.S. Pat. No. 5,337,030 was issued on Aug. 9, 1994 to David Mohler (the “Mohler patent”), an inventor of the present invention, and the subject matter is herein incorporated by reference in its entirety. The Mohler patent discloses a permanent magnet brushless torque actuator (PMBTA) having the stator assembly supporting the permanent magnet rotary assembly, the stator assembly including stator poles and an electromagnet winding and the rotor assembly including a rotor shaft supporting the rotor assembly for rotation about a rotational axis and a plurality of arcuate permanent magnet poles disposed around the rotor shaft in a north-south-north-south sequence. Energization of the electromagnet winding induces the stator poles as north and south poles which coact with the permanent magnet poles in the rotor to generate a torque rotating the rotor assembly relative to the stator assembly.
Although the rotor assembly of the PMBTA disclosed in U.S. Pat. No. 5,337,030 will reach an intermediate rest position when the electromagnet winding is de-energized (as aided by spring
70
), when energized it reaches a rest position achieved when the magnetically induced clockwise torque balances the magnetically induced counter-clockwise torque (and any centering spring force). Thus variation of the coil current increases torque in one direction and decreases it in the other and the rotor moves until a new steady state position is reached. Unfortunately, when the coil is de-energized, with the centering spring, the energized position is not latched and the rotor returns, under the spring bias, to the centered position. Even without the centering spring, when de-energized, the rotor of the PMBTA because of the symmetrical pull between the magnets and the stator pole pieces there is little or no net torque and it reaches a neutral position only gradually (if at all), and can be disturbed from this position by relatively small outside magnetic influences.
Thus, it is desirable in certain application to have a bi-directional latching actuator which upon energization will go to one position and upon de-energization, remain latched in that position. Upon energization with the opposite polarity current, it is desirable for the latching actuator to move to the opposite position and, latch so that, upon de-energization, it remains latched in the new position.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a permanent magnet brushless torque latching (PMBTL) actuator having clockwise and counter-clockwise latched rest positions.
It is a further object of the present invention to provide a PMBTL actuator having clockwise and counter-clockwise latched positions to one of which the rotor assembly will return when the electromagnet winding of the actuator is de-energized.
In accordance with all embodiments of the present invention, there is provided a PMBTA comprising a rotor assembly supported for rotation relative to a stator assembly. The rotor assembly has a rotor shaft defining an axis of rotation and at least one rotor rotatable about the rotor axis with respect to stator assembly. At least one stator assembly is located axially above or below the rotor and, in preferred embodiments, sandwiches the rotor between two stator assemblies.
At least one electromagnet coil is provided such that, when energized, the coil generates a toroidal magnetic field having a flux component parallel to the rotor's axis of rotation and passing through the rotor and the at least one stator. The coil's electromagnetically induced field, when energized with the correct polarity of current, causes movement of the rotor to a latched position whereupon permanent magnets hold the rotor in that latched position when current through the coil is terminated. An abutment prevents the rotor from rotating such that the permanent magnets on one structure are axially aligned with the void on the other structure. A reverse current through the coil, unlatches the rotor and torques it into movement to the other latched position. In all embodiments, the flux field created by the winding aids the flux field through one of the permanent magnets and opposes the flux field through an opposing permanent magnet resulting in a torque applied to the rotor causing it to rotate until contacting a rotational stop.
In a first embodiment, the rotor is only partially comprised of at least two circumferentially spaced permanent magnets generating opposing magnetic flux fields, each field having a component in a direction parallel with the rotor's axis of rotation. The at least two permanent magnets are non-symmetrically disposed at differing circumferential positions around the rotor shaft with a non-magnetic or void area separating the opposing magnets at one circumferential position for each pair of opposing permanent magnets.
In this first embodiment, the stator assembly includes ferromagnetic stators providing a low resistance path for the flow of magnetic flux from said permanent magnets where the stators have one or more circumferentially defined portions whose flux conductivity is enhanced. Because of the void portion of the rotor, the rotor stays in its rotated position against the abutment stop due to the greater pull of one magnet on a corresponding enhanced conductivity portion of the stator and the lesser pull of the void and opposite polarity magnet with respect to a lesser conductivity portion of the stator assembly.
In a second embodiment, a stator has at least two circumferentially spaced permanent magnets generating opposing magnetic flux fields, each field having a component in a direction parallel with the rotor's axis of rotation. The at least two permanent magnets are disposed asymmetrically about the stator at differing circumferential positions around the rotor shaft with a non-magnetic or void area separating the opposing magnets at one circumferential position for each pair of opposing permanent magnets.
In the second embodiment, the rotor is comprised of at least one segment of ferromagnetic material with a corresponding segment of non-ferromagnetic material (or an absence of ferromagnetic material). Because of the void portion of the stator and/or the non-ferromagnetic portion of the rotor, the rotor stays in its rotated position against the stop due to the greater pull of one stator magnet on the ferromagnetic portion of the rotor and the lesser pull of the stator magnet. The proximity void on the stator insures that the magnetic pull on the rotor is not stable thereby pulling the ferromagnetic portion of the rotor into a latched position.
REFERENCES:
patent: 2930974 (1960-03-01), From
patent: 2987687 (1961-06-01), Buchtenkirch et al.
patent: 5337030 (1994-08-01), Mohler
Donovan Lincoln
Nixon & Vanderhye P.C.
SAIA-Burgess Inc.
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