Page 1
SPECIFICATIONS,
Track system
Motor
4-track 2-channel
2-moîor system
. Capstan drive section
Uni-torque motor (DD motor)
o Reel disc drive section
DC motor (with mechanical gov-
erno r)
OUTLINE OF DEVELOPMENT
ln cassette decks using direct drive motors, the capstan and
the motor are directly connected, so principal perform-
ance items such as wow & flutter, etc. depend directly on
the performance of the motor.
Multi-pole DC servo-motors and AC motors have been
conventionally used for cassette decks; they have various
advantages and d isadvantages.
Hitachi has conducted research into direct drive motors
with the advantages of both types of motor and succeeded
in developing a flat, brushless DC servo direct drive motor.
This motor is called a uni-torque motor because its torque
is constant; vibration is minimized and rotation is
smooth.
A uni-torque motor, as developed for direct drive record
players, has been adapted for use in cassette decks. ln
addìtion, single-chip lC. which contains the speed detector
circuit, speed control cìrcuit and motor drive circuit has
been developed to minimize the number of parts.
Fig. 3 is a block diagram of this lC.
(1) Servo control
A magnetic induction detection cìrcuit is to detect
the motor speed. The principle used is that when the
magnetic flux changes when there is a conductor in
the magnetic f ield, an electromotive force proportional
Speed detect ion (Magnetic inductionl
Tape speed
Wow & flutter
Fast-forward time
Rewind time
Heads
4.7Scm/s
0.03% wRMs
90 sec (C-60)
90 sec (C-60)
3-head system
(REC/PLAY combination
head, erase head)
* This specif ication may be changed for improvement without notice.
DESCRIPTION OF UNI-TOROUE MOTOR
to the rate of change of the magnetic flux occurs in
the conductor.
Fis. 1
As is shown in Fig. 1, there are 9 conductors for each
pole; 72 conductors under the whole circumference.
Assuming these conductors arg numbered 1-72, volL-
age is generated in the 1st, 1Oth, 'lgth. 28th, 37th,
46th, 55th and 64th conductors which are positioned
where polarity changes, and the direction of the
voltage is the opposite for every other conductor, so
directions of 8 voltages are same and added together.
When the magnet turns, the voltage is induced in the
(
next conductor in sequence.
A signal which is inverted 72 times
rotations of the magnet is obtained.
the number of
Since this signal
l2t4 561A9 l5 l7 l9 t6 t8
Referencevo ltage Limiteramplilier
Bolor magnet
-2-
Page 2
Drive coil
(-B I
Hall elements
consists of voltages from 8 positions on the circum-
ference, it is a highly precise signal with a constant
output even if there is any unevenness or instabiliîy
in the magnet.
The conductors are arranged as a highly precise prlnt-
ed pattern.
(2) Amplification, wave-shaping of the speed detection
signal
The speed detection signal has low level and an AM
component remains in it, so errors will occur if it is
used as it is. Accordingly, it is over-saturated and
amplified by an amplifier with high gain and a shaping
circuit forms it into a square wave signal. By making
it a square wave signal, any AM component is llmited
and errors become negligible.
English
Fis. 3
72
Sped detection pailern
Pulse generator, f-V converter
The voltage of the capacitor is inversely proportional
to the speed because it is repeatedly charged and dis-
charged at îhe speed deteclion frequency.
The pulse generator generates a trigger signal synchro-
nized with the speed detection signal.
This trigger signal operates the capacitor charging/
discharging circuit and îhe voltage of the capacitor
is converted to a DC voltage by a low-pass f ilter.
Reference voltage, comparison amplification
The DC voltage generated by the f-V converter and the
reference voltage are compared and a difference volt-
age is output. Since the reference voltage is îhe speed
reference, its stability is very important, so a stabi-
lization circuit is provided.
(3)
Differential amp - lnput stage
_?_
(4)
