A special type of brushless motor is called a limited-angle torquer (LAT). LATs are constrained to produce torque through a rotation angle of less than 180 degree, But they are widely used to operate servovalves, direct laser mirrors, position missile-guidance radar antennas, open shutters for heat-seeking sensors, and power other systems that rotate through small angles.

The rotor in a limited-angle torquer carries field magnets, and the stator supports armature windings (similar to the construction of conventional brushless motors). LATs, however, are wound single phase, unlike conventional brushless types, which are typically wound for two or three-phase operation. Single-phase construction eliminates the need for commutation circuitry.

Conventional brushless motors can also be used for limited-angle service. But when conventional three-phase brushless motors are used as LATs, only two of the three leads are used.

Armature windings in some limited-angle torquers are embedded in slots around the inside periphery of a laminated stator, a construction similar to that used with conventional brushless motors. In another design, the armature is toroidally wound on a slotless stator. Here, some stators are laminated and others are solid

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A special type of brushless motor is called a limited-angle torquer (LAT). LATs are constrained to produce torque through a rotation angle of less than 180 degree, The motor consists of two main assemblies, a rotor assembly contained within a rotor casing and a stator and housing assembly surrounding the rotor casing. One end of the casing is closed, whereas the other end is open to eliminate the need for a dynamic shaft seal. Fluid enters the casing at the open end thereof to provide a lubricating fluid for the rotor bearings and a heat conductive path. The rotor casing isolates the critical movement of the rotor from the contaminated atmosphere of the stator environment and allows replacement of the stator assembly without disturbing the rotor assembly. A permanent magnet rotor may be formed using one or more rare earth magnets which may be suitably bonded to the rotor shaft. A protective cover surrounds the rotor magnets to eliminate potential rotor magnet breakage contamination. The relationship between the rotor magnet angle and stator winding may be such as to produce a relatively large output work potential. Also, the lamination slot configuration and stator winding may be graded to optimize the torque versus rotation profile to more closely match the cosine function of various rotary to linear output gearing to provide a substantially constant force output. A two pole stationary coil rotary magnet motor which provides for increased work and reduced rotary inertia.


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