The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Motors with a rotor having permanently magnetized poles and a stator having electrically energized field poles suffer numerous disadvantages. The current for such motors is usually supplied from an alternating current source or from communicators rotating with the rotor. However, the maximum speed of such motors is limited by the frequency of the alternating current or by the ability to rapidly reverse the flow of the current in the field coil.
To address these problems, U.S. Pat. No. 2,968,755 to Baermann discloses a motor, which includes stator poles with permanent magnet means for magnetizing each stator pole. Baermann's stator poles also have a remotely actuated magnetic means of a greater magnetic strength than the permanent magnetic means, which could be used to reverse the magnetic polarity of its corresponding stator pole without needing to provide reversing alternating current. However, Baermann's stator only makes use of magnetic flux from one pole of each permanent magnet, and reversing the magnetic polarity of Baermann's stator is energetically demanding.
In U.S. Pat. No. 5,825,113, Lipo et al. discloses permanent magnetic machines that employ a field winding that can be used to weaken or boost an existing magnetic field. Lipo's motors comprise a pair of arched permanent magnets embedded in a stator yoke, a field winding, and armature windings. Half of Lipo's stator poles are dedicated magnetic north poles and half are dedicated magnetic south poles diametrically opposing the dedicated magnetic north poles. U.S. Pat. No. 2,816,240 to Zimmerman also employs similar principles to those disclosed by Lido. However, both Lipo and Zimmerman only use field windings to weaken or boost the variable magnetic fields.
All publications identified herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Thus, there is still a need for permanent magnet offset systems that vary the strength and quality of magnetic fields in a more energy-efficient manner.