BASF 6106 - Stepper Motor Control

2.2.2 STEPPER MOTOR CONTROL
The stepper motor is a four phase DC-motor and
is controlled by the integrated circuit
SAA 1027. This Ie comprises the stepper motor
drivers, a synchron counter and control cir-
cuits (~ee Fig. 2-16). Each STEP pulse from
the host system rotates the stepper motor for
one step. Each step corresponds to a rotation
angle of 150. The rotation of the stepper
motor is converted to a linear motion of the
R/W-head(s)
by the spiral wheel. The direction
of the motion of the R/W-head(s) depends on
the input signal DIRECTION IN/. If this signal
is active (low) the R/W-head(s) will be moved
towards track 39 (in). The R/W-head(s) move out
by each STEP pulse when DIRECTION IN/ is in a
high
state. Multiple track positioning is
attained by the host system issuing aseries
I
N
STEP PHASE
AI BI CI DI
-
L
H
L
H
1
H
L L H
2 H L
H
L
3
L
H H
L
4
L
H
L
H
of
STEP pulses at 12 msec intervals. Table 2-4
shows the output signals for "in" and "out"
motion of the R/W-head(s).
The DIRECTION IN-signal
must be at the desired level 1 lusec before the
trailing edge of the STEP pulse. Stepping is
initiated by the trailing edge of the STEP pulse.
The time between two consecutive STEP pulses must
be 12 msec minimum (see Fig. 2-17). As long as
WRITE GATE or WRITE INHIBIT is active during a
write operation the
STEP pulse interface line is
inhibited by the input interface logic. In Fig. 2-16
a
Zener diode is used in addition to the -internal
free wheeling diodes. This
undamps the magnetic
response
at switch off time, causes armature to
oscillate acroSs target position. This reduces the
influence of
friction upon target positioning,
decreases hysteresis error, resulting in precise
settling on target position.
OUT
STEP
PHASE
AI BI
CI
D/
-
L
H
L
H
1 L H H L
2
H
L
H
L
3
H
L L
H
4
L
H
L
H
TAßLE 2 - 4 SEQUENCE OF THE STEPPER MOTOR SIGNALS
2 - 12