Dual 721 - EDS 1000-2 Motor System; Description of Operation; Hall Generators

Fig. 2
Dual EDS 1000-2
Electronic
Direct Drive System
turntable center plate
centering pin
ring
magnet
steel
plate
conductor
coil
support
plate
field
coi l ls
heddecl
Hall generator
Dual EDS 1000-2
Electronic Direct Drive System
The EDS 1000-2 motor
especially designed
for the Dual 721 is a slow-running no-commu-
tator DC electronic motor which
draus
its
power supply from a
stabilized power pack.
The electro-mechanical
commutation normally
carried out
an
DC motors by the
commutator
is electronically controlled in the case of
the Dual EDS 1000-2 motor by two Hall genera-
tors. These two Hall
generators - dependent
an the rotor position - control four switch-
ing transistors which in turn have the
effect of a rotating
magnetic field occurring
in the field coils of the
motor by means of
which the four pairs of magnets
of the rotor
are continuously attracted or repelled. By
means of the torque thus exerted, uniform
rotation is
induced in the rotor - and with
it the platter.
A
speed-dependent voltage (tacho voltage)
induced in the motor windings not
switched
an is coupled out and controls
the electro-
nic regulator circuit. This
ensures that
even the
slightest deviations from
the nomi-
nal speed are corrected in fractions of
a
second by a change in
the motor current.
Speed
fluctuations are, therefore,
practi-
cally eliminated.
joining centring
for turntable
rotor
plain
bearing
flange
angular bearing
Absolute
maintenance of
the nominal
speed
na langer
presents any
problem with this
control
system.
The
above-mentioned Hall
generator
is a mag-
netically
controllable
semi-conductor ele-
ment
named after
the
physicist E.
Hall. With
the Hall
effect as a
result of the
action
of a
magnetic
field an the
Hall
generator a
voltage
approximately
proportionate to
the
strength
of the
magnetic field
is
generated,
its
polarity being
dependent
an the
direc-
tion
of the
magnetic
flux.
A
control
current
flows
through the
Hall ge-
nerator.
If now a
magnetic
field
becomes
effective at
right
angles to the
area of
the
Hall
generator,
the
so-called Hall
voltage
occurs. With
constant
control
current this
Hall
voltage is
dependent
an the
direction
and
strength of
the
magnetic
field. If the
polarity of the
magnetic
field is
reversed,
the
polarity of
the Hall
voltage
changes as
well.
In the
absence of a
magnetic
field the
Hall
voltage is
zero. This
effect is
utili-
zed to
control the
Dual EDS
1000-2 motor.
As
the motor
is operated
on DC from
a stabi-
lized
power
pack it
operated
independently
of
line
voltage and
frequency
fluctuations.
The motor
is of 8
-pole disk
rotor
design.
The
rotor has a
barium ferrite
annular mag-
net inside
which has 8 -pole
magnetization
an
its lower
face.
6