Limited rotation moving iron motor with novel velocity sensing and feedback

In combination, a limited rotation moving iron electromagnetic motor and a device for providing a voltage indicating the angular velocity of rotation of the armature of said motor, said motor comprising a rotatable armature of ferromagnetic material mounted for rotation about an axis, a stator adjacent to said armature, a stationary permanent magnet, and a stationary drive coil through which a drive current flows, and means for elastic angular restraint attached to said armature wherein said stator, magnet, armature, and drive coil are arranged to apply permanent magnet biasing flux and to apply magnetic flux produced by said drive current to rotate said armature from said neutral position in an amount and direction dependent upon the flow of said drive current and the stiffness of said elastic restraint,

• said device comprising:
• means for providing a first voltage dependent upon said angular velocity of said armature, the self-inductance of said drive coil, and said drive current,
• a compensation coil magnetically coupled through a gap to said drive coil and magnetically isolated from the effects of said rotating armature to provide a second voltage,
• said second voltage appearing across said compensation coil and being dependent upon mutual inductance between said compensation coil and said drive coil and upon said drive current,
• said second voltage being substantially unaffected by angular velocity of rotation of said armature due to said magnetic isolation of said compensation coil from the effects of said rotating armature, and
• combining means for proportionally combining said first and second voltages to provide said voltage indicating said angular velocity of rotation.