Stepper Motor - Three phase: Many variable-reluctance stepper motors use three-phase windings. In modified mode, two adjoining phases are excited simultaneously and the rotor indexes to a minimum reluctance position corresponding to the resultant of the two magnetic fields. Since two stepper motor windings are excited, twice as much power is required as the standard mode (one phase at a time). The stepper motor's output is not increased, but damping is improved.
Stepper Motor - Four phase: Each of the stepper motor's half winding is regarded as a separate phase, and phases are energized two at a time. Although this mode isn't very efficient, the controller is simple. Compared to single-phase excitation, twice the input energy is required. Torque output is increased by about 40%, and maximum response rate is increased.
Stepper Motor - Five phase: Five-phase stepper motors have 10 poles rather than the 8 poles typically used in other stepper motors. Rotor-to-stator offset becomes one-fourth to one-tenth the rotor tooth pitch. A 50-tooth rotor provides a full-step of 0.72°, and a 100-tooth version produces a 0.36° full-step (0.18° half-step). The stepper motors run at 500, 1,000, or 2,000 steps/rev with improved loaded-position accuracy and stiffer response. In addition to higher resolution, five-phase stepper motors produce less vibration than two to four-phase stepper motors with virtually no resonance effects.
Stepper Motor - Variable reluctance: These stepper motors have soft iron multipole rotors and a wound stator. The number of teeth on the rotor and stator, as well as the number of winding phases, determines the step angle. Variable-reluctance stepper motors are generally medium step-angle devices (5 to 15°) which operate at high step speeds. The stepper motor's torque is generally low. Rotor inertia and, thus, inertial load capacity are extremely low. Motors of this type operate at maximum pulse rates from 300 to 1,000 steps/sec and have a maximum load inertia capacity of about two-thirds of rotor inertia. When excited in an overlap mode, these stepper motors can move at half step angles and double pulse rates. These stepper motors produce a net output velocity, which remains the same.
Stepper Motor: Basics of Stepper Motor Design Engineering
Previous Page Next Page