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(5-5-2. Principle of Arbitrary
Playback)
2. Tracking Control
A tracking error will occur if the DT head is simply displaced at
the angle of the video track at the arbitrary playback. This is due
to a phase shift of the track or the linearity of the DT head path
and video track.
In order to safeguard against this tracking error, the bimorph ,
onto which the DT head is mounted, is wobbled at a constant
frequency (720Hz with NTSCIPAL,
700Hz with PAL/SECAM)
in the direction
parallel
to the recording
head gap, and the
tracking
error
is detected
from
the
amplitude-modulated
playback RF signal.
A strain gauge is adhered to the bimorph leaf to indicate the DT
head movement
but, since sawtooth
waves for driving
the
bimorph indicating the head jump are also included along with
the wobbling signal, the undesirable
components
are removed
and filtered out by a subtracter and high -pass filter, and only the
wobbling components
are taken out. The wobbling signal which
indicates
the head movement
is multiplied
by the amplitude
modulated
RF envelope signal, it passes through the low -pass
and notch
filters, and it is detected
as the tracking
error
information.
The detected tracking error information
is returned
to the drive signal and the track is traced.
Recorded Track
Head Trace without
Tracking correction.
(Head off-track
+
Wobbling)
(a)
When the relation
between
the recorded
track and
head trace are not
phase.
TRACK CURVE~___
_ __
-~----~
DT
HEAD
Head Trace with
Track ing Correction
(Head off-track
+
Wobbling)
PB RF SIGNAL
.
(b)
When the DT head traces a recorded
track.
DYNAMIC
TRACKING
SYSTEM
5-5-2
BV H-2000 (U /C) IPS/PM
BVH-2180(U/C)/PS/PM
Summary of Contents for BVH-2000
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