Dual 704 - DUAL EDS 900 Electronic Direct Drive System; System Description

Fig. 2
Electronic Direct
Drive
System Dual EDS
900
rotor
axle
resting
surface
for
platter
annular
magnet
coils
return
path plate
motor housing- --
generator
coil
cup
magnet
toothed
dish
return path plate
Dual
EDS 900
Electronic
Direct Drive System
stop cam bearing
cup end journal bearing
The Dual EDS 900 electronic direct drive
Sy-
stem
is a slow-running,
no-commutator DC
electronic
motor. The
electro-mechanical
commutation normally carried out on DC mo-
tors by the
commutator is electronically
controlled in the case of
the Dual EDS 900
by two Hall generators.
These Hall genera-
tors -
dependent on the rotor position -
control via four switching transistors
four coils of the motor
succesively. The
cyclic switching of the field
coils exerts
rotating
magnetic field on the eight-pole
annular magnet of the
rotor. The field coils
are located in the air gap
between the annu-
lar magnet and the return
path plate which
form the magnetic
return path. The speed is
controlled by a frequency generator which
is
coupled to the rotor rigidly. A
fixed
flat coil is located in
a magnetic circle
which is formed by a 200
pole permanent
annular magnet, a
toothed disk and a return
path cup.
The toothed disk
rotates with
the rotor and generates a
frequency in the
coil which is proportional to the
speed. Any
error which might be
caused by eccentricity
between the permanent magnet and
toothed
disk is compensated thus generating a fre-
quency of high uniformity which
controls
the regulating
circuit. This frequency is
transformed by a special
electronic circuit
into a DC voltage which
is proportional to
speed (digital/analog
transformation). The
voltage thus generated is
compared to a
highly stabilized
reference voltage and
used
to control current of the
direct drive.
plug-in
board
The
unique design of drive
and control re-
sults in distinct
advantages: no pole sen-
sitivity, hysteresis,
eddy current
losses,
and
disturbing groove
frequencies;
high-
definition speed control
without interfer-
ence,
thus enabling a
momentary control of
speed
drop. These
characteristics guarantee
a
completely vibration
free and uniform
drive
source for the EDS
900.
Description of Fumaion
The four bifilar coils of the electronic mo-
tor and the two Hall
generators are rigidly
connected to the motor
flange. The 8 pole
annular magnet forms the rotor and also mo-
ves the magnetic return. The four coils and
the two Hall generators are arranged between
the annular
magnet and the magnetic return.
When a north pole is above the Hall genera-
tor H 1 (Fig. 3 a),
the base of transistor
T 17 becomes
positive and the
transistor
conductive or low-ohmic.
Current flows
through coil 3 which has
the effect of a
south pole. The
north pole of the annular
magnet displaced by
22.5° from coil 3
is
attracted.
A section of
coil 1 is also
con-
nected to the
collector of
transistor T 17,
which, as
related to coil
3 will be
subject-
ed
to current
flow in
counter direction.
This section of
coil 1 has the
function of
the north pole
and attracts
the south pole
of
the annular
magnet
displaced by 22.5 0 .
The north pole
of the annular
ring which was
above the
Hall
generator H 1 has been
rotated
by 22.5° and is
now above the
Hall generator
H 2
(Fig. 3 b).
5