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