Appeal No. 1998-1819
Application No. 08/364,972
is effected by piezoelectric film 40 (Fig.2) bonded to suspension arm 12, which bends arm
12 when a correction signal is applied. Id. at col. 5, ll. 20-30.
Sakamoto discloses a head tracking system for a rotary magnetic head in a
magnetic video tape recorder, which generates a deflection signal corresponding to the
deflection of the head from a rest position. The reference describes, in columns 1 and 2,
prior art methods of imparting a small oscillatory motion to the magnetic head via its
supporting element, which is typically a piezo-electric element or "bi-morph leaf." The
oscillatory motion is induced by applying a suitable drive signal which causes the
transducer to oscillate transversely about its normal oblique scanning path (e.g., Fig. 2).
The deviations from the path take the form of an amplitude modulation of the envelope of
the reproduced signals. An amplitude modulation detector provides a tracking error
signal, which is used in properly aligning the head transducer with the center of the track.
Mechanical vibrations of the bi-morph leaf were known to cause problems in
tracking control. Sakamoto teaches, to overcome unwanted frequency components due to
mechanical vibrations, securing a strain gauge 15 (Fig. 4) to bi-morph leaf 2. Deflection of
bi-morph leaf 2 thus generates a deflection signal indicating the extent and direction of
deflection of head 1 from its rest position. Sakamoto, col. 5, ll. 20-24 and 44-67. The
reference goes on to describe circuitry for compensating for the unwanted frequencies by
means of the deflection signal, so that the tracking control system may maintain the head
at the optimum tracking position.
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