Dual 721 - Speed Regulation; Tacho Voltage Feedback; Speed Control Mechanism

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6
Thus the following sequence
of movement ta-
kes place:
After the 1.
rotation phase (Fig. 7 b) the
Hall generator H 1 is located in the neutral
zone of a pair of magnetic
poles. One south
pole is now directly
above Hall generator
H 2 and now also produces at its
connection
7 a Hall voltage maximum
of negative polar-
ity
which switches on phase winding W 3 via
transistor T 6. All other transistors are
blocked. The rotor now rotates again through
22 1/2 0 through the magnetic fields genera-
ted in
phase winding W 3.
After elapse of the second rotation
phase
(Fig. 7 c) the Hall generator H
2 is now in
the neutral zone of
a pair of magnetic po-
les. Hall generator H 1
is now directly un-
derneath a north pole and a
Hall voltage of
reversed
polarity occurs, i. e.
the negative
polarity
Hall voltage maximum is
now present
at connection 9 which
connects through phase
winding W 2
via transistor T 5.
The other
transistors are
blocked. The rotor
again advances by 22 1/2°.
After this 3.
rotation phase (Fig. 7 d)
Hall
generator H 1
is in the
neutral zone. A
north pole
is above Hall
generator H 2 and
produces a negative
Hall voltage at
its con-
nection 5
which switches
on phase winding
W 4 via
transistor T 7.
The rotor
advances
by a further 22 1/2°.
After
conclusion of this 4.
rotation phase
the process starts again.
Thus, a continuous
rotating field
occurs which drives
the rotor
at an uniform
rate.
If the
rotor is, for
example, between two
phase windings, a
partial flux of a pair of
magnetic poles passes
through both Hall
ge-
nerators and thus two
switching
transistors
are partly
opened. The
current
is divided
accordingly between two
phase windings. Both
phase windings
participate
simultaneously
in the
torque formation and
together produce
the
torque of a
fully-connected phase um -
ding. The torque is,
therefore, almost
con-
stant in any position of the rotor.
Speed Regulation
As a result of the rotary movement of the
rotor, voltages are induced in the
phase
windings not connected through
which are
coupled out via diodes D 9
to D 12. Thus, a
tacho voltage proportionate to the speed is
obtained.
The tacho voltage passes via a voltage divi-
der to connection 4 of the
operation ampli-
fier in the control section and counteracts
the voltage present there. A stabilized vol-
tage is
present at connection 5 of the
ope-
ration
amplifier.
On start-up and during run-up of the motor
the potential at connection 4 of the
opera-
tion amplifier is more or less positive in
relation to
connection 5. In this condition
the operation amplifier fully drives tran-
sistor T 7. T 7 is present as variable
re-
sistance in the common emitter circuit of
the four switching transistors
through which
practically the full switching current can
flow in sequence.
Fig. 7
Robar
zwejam -
H2
HI
H2
H1
W3
H2
H2
-1ZIN
HI
2
HI
W4
The nominal or controlled speed is reached
when the same potential is present at con-
nection 4 of the operation amplifier as at
connection 5, because at this moment the
operation amplifier closes transistor T 7.
As a result the motor current drops and
the
speed cannot, therefore, increase any fur-
ther.
By
switching over or altering the voltage
divider in the control circuit the controlled
speed can be
preselected or altered. With
reducing speed the potential at connection
4 of the operation amplifier would change
so that
transistor T 7
would
be
fully
driven.
T 7 would thus become of low resistance, the
result would be
a sharp rise in the motor
current and thus of the speed.
As this control process takes place
even at
minor deviations from the
nominal speed, a
constant speed independent of
load fluctua-
tions is obtained.
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