IBM 5280 Maintenance Information Manual page 73

The stator poles are used in pairs. Stator poles opposite
each other, such as stator poles numbers 2 and 6 in the
preceding figure, are magnetized together to provide the
necessary torque for the rotor to turn. The stator poles
that are magnetized last remain magnetized until the
diskette control circuitry sends signals to move the rotor
again. These poles remaining magnetized provides an
electrical detent to the stepper motor.
The permanent magnetic rotor poles all have thei r north
poles facing the stator poles. When the stator poles have
current flowing through them, their south poles face the
rotor poles. In magnetism, opposite poles attract; therefore
the closest north pole of the rotor is attracted to and moves
to the magnetized stator pole.
D IJ
Stator poles
0
and
fJ
are magnetized. This holds rotor
polesll and
II
electrically detented. When the electrical
current is moved from stator poles
D
and
fJ
to stator
poles
II
and
II,
rotor poles
IJ
and
I!I
are attracted to
and align with stator poles
II
and
II.
The rotor moves
the distance shown by
II .
In the diskette drive, the stepper motor drive band is
attached to the head/carriage assembly. As the motor
turns, the band moves the head/carriage assembly. A 1.8
0
rotation of the motor moves the head/carriage assembly
the distance of one track. A clockwise movement of the
rotor moves the head/carriage assembly toward the center
of the diskette. The stepper motor moves the head/carriage
assembly one track in 5 milliseconds. Thirty-five milli-
seconds are required to stop the moving head/carriage
assembly and to allow the heads to settJe. Total seek time
is 5 milliseconds times the number of tracks traveled plus
35 milliseconds.
Theory 61