CONSTANT INERTIAL ROTOR SPEED DRIVE

摘要

Improved method and means to initiate and maintain a rotor at substantially constant speed with respect to an inertial frame of reference, comprising surrounding the rotor with a rotor enclosure which rotates substantially in step with the rotor in order to isolate the rotor from contact with the outside environment and to provide a stationary relative environment for the rotor. In the preferred embodiment the rotor, of conventional cylindrical shape, is maintained within a similarly shaped rotor enclosure by rotor support means which comprises anti-friction bearings. The rotor enclosure is driven by a stepper motor: at startup, a simple mechanical clutch mechanism is employed to couple the rotor to the rotor enclosure to initiate motion of the rotor. An optical pickoff detects marks on the rotor through an optically transparent portion of the rotor enclosure and generates a signal which is employed to control the stepper motor and thereby the motion of the rotor enclosure. Various alternative embodiments of the invention are feasible. Alternative enclosure drive means include brushless D.C. motors and switched reluctance motors. Alternative rotor support means include nested bearings and flexure supports, and alternative rotor support methods include dithering and selective torque rectification. Alternative pickoff means include various precisions of incremental or absolute encoders. Alternative overall arrangements of the means of the invention include locating an 'inside-out' drive motor within the rotor.