Variable-Reluctance Stepper Motor Half-Step Operation Modify the sequence of the applied pulses A A&B B B&C C C&D D

Variable-Reluctance Stepper Motor Half-Step Operation Excite phases A & B Rotor moves a “half-step” to 7.5°

Variable-Reluctance Stepper Motor Half-Step Operation Excite Phase B Rotor moves another “half-step” to 15°

Variable-Reluctance Stepper Motor Holding Torque “Holding” torque “Static” torque The maximum load torque that can be applied to an energized stepper motor without having it “slip” poles Here, A is energized and the rotor is at rest

Variable-Reluctance Stepper Motor Holding Torque Force the rotor one 15° step clockwise The force of attraction on rotor teeth 1 and 4 by the stator teeth 1 and 5 will develop a “restoring” torque Releasing the rotor will cause the rotor to “fall back” to the original position

Variable-Reluctance Stepper Motor Holding Torque Force the rotor two 15° steps clockwise (30°) Rotor teeth 1 & 6 (and 3 & 4) have equal forces of attraction from stator teeth 1 & 5, resulting in an “unstable” equilibrium. If the rotor is released, it could go two steps either clockwise or counter-clockwise

Variable-Reluctance Stepper Motor Holding Torque Here, the rotor is shown to have moved two additional steps clockwise

Static-Torque as a function of the number of steps of displacement