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JPS59114995

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DESCRIPTION JPS59114995
[0001]
Industrial Applicability The present invention is a magnetic recording in which the mechanical
height d of a one-rotation magnetic head is changed by using an electro-mechanical transducer
called a so-called "5 imorph" composed of a piezoelectric element. The present invention relates
to an automatic vibration suppression method for removing the automatic vibration of an electromechanical transducer element in a playback device (VTR) or the like. The structure of the prior
art and the problems thereof In the rotary magnetic head type VTR, the method of displacing the
mechanical height position of the single-rotation magnetic head in the direction of the rotational
axis using the pie% JL 17 composed of piezoelectric elements is already known. The present
invention is applied to a method of following a curve of a recording track, a method of following
a reproducing head faithfully on a recording track at the time of special reproduction such as still
image, slow speed, double speed reproduction and the like. -As shown in FIG. 1, the bimorph (1)
composed of piezoelectric elements comprises 2 'piezoelectric elements (2) (3) with polarization
in the direction of the arrow (P) as common electrodes (4). The two electrodes (5) and (6) are
further formed. A bimorph of such a configuration (in the case of displacing a terminal, a
terminal drawn out from the common electrode (4) (a terminal drawn out from a line electrically
connected between the terminal and the both electrodes (5) and (6) A voltage may be applied
between 8) and 8). For example, terminal (7) is positive. When a voltage is applied so that the
terminal (8) becomes negative, the piezoelectric element (2) stretches in the longitudinal
direction and the piezoelectric element (3) contracts. As a result, the displacement of the
piezoelectric elements (2) and (3) causes a bend in the direction of the bimorph (arrow (4) from
January). It is well known that this bending direction depends on the voltage polarity applied
between the terminals (7) +8) and the polarization direction of the piezoelectric elements (2) and
(3). A magnetic head movable device using a bimorph having such a configuration is shown in
FIG. In FIG. 2, Ql) is a bimorph composed of the piezoelectric element (b) side, and the magnetic
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head ??? is fixed at one end, and the other end is fixed on a member (g) by adhesion. ing. For
mounting, the member (f) is fixed on a rotating disk (not shown) by means of screws or the like.
Thus the movable device shown in FIG. 2 rotates with the rotating disc. If a voltage is not applied
to the piezoelectric element a (2), the magnetic head 94 only performs circular motion in a plane
perpendicular to the rotation axis like the magnetic head used in a conventional rotary head type
VTR. (Lead wire connected to each electrode of the piezoelectric element O ? (1) (+1 when a
voltage is applied from outside to the brush (not shown), the magnetic head is circular as shown
by the arrow) direction (rotation Axial displacement).
The frequency characteristic of the bimorph used in the magnetic head movable device is shown
in FIG. When a sine wave signal of a constant voltage is applied to the bimorph, the amplitude n
is incinerated according to the frequency of the applied signal as shown in (2) in the figure, and
the positive resonance characteristic at one frequency f and the negative resonance characteristic
at one frequency f2 Show. The phase characteristics change rapidly at the positive resonance
portion as shown in FIG. 2B, and the phase delay at this time is 180 degrees. Therefore, bimorphs
can be treated as a second-order system in the vicinity of the positive resonance part. The
resonance frequency is determined by a bimorph shape, which is determined by the diameter of
the rotating disk, the required vibration amount, the intensity, and the like. For example, in the
case of a length of 12 mm, a width of 8 mm and a thickness of 0.4 mm, the resonance frequency
f1 is I KHz "C". Also, Q at f at this time is usually about 10, which is a relatively large value. When
a step voltage as shown in 41i $ '(a) is applied to a bimorph having such characteristics, the
deflection amount of the bimorph produces self-excited oscillation (i) in the rapid change (as
shown in the daughter). The self-oscillation frequency coincides with the positive resonance
frequency f, and the amplitude has Jt at the abrupt change, and then attenuates later. Therefore,
the deflection amount of the bimorph finally settles at the displacement position ?S according to
the applied voltage Vs. Assuming that the resonance frequency is ? n, the transfer function G (s)
of the second-order system can generally be expressed as the following equation (0). The
transient response of the system represented by the equation (0) changes as shown in FIG. 5, and
the overshoot amount increases as the reduction coefficient ? decreases, and the overshoot
amount becomes 1 at ??0 and indicates the maximum value. The relationship between the
damping coefficient and Q is shown by the following equation 0, and when Q is infinity, it
becomes zero. Apply these control theories to the rri imorph described above. Since Q of the
bimorph is 1 G, ? = 0.05, and 1 overshoot is almost close to l. This shows that ?t = 2t s in FIG. 4
(b). Next, a specific example of the magnetic head movable device will be described. Helical scan
type VTR: A 2-head type VTR in which A and B 2 magnetic heads are built in 1 rotation disk is
used to record video signals of 1 field as 1 track alternately with each head on a magnetic tape.
The recording magnetization locus as shown in FIG. 6 is obtained. Fig. 6 fc (+ 'Qi (TA) (TB) is the
magnetization locus recorded by the A head and B head respectively, and the gart band (No
signal is recorded between the magnetization loci (TA) and (TB)) TG) is provided.
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When the running direction of the tape is the direction of the arrow (c) and the scanning
direction of the one-rotation magnetic head is the direction from the point (a) to the point (b), the
still image locus is (7). When still image reproduction is performed in the state where voltage is
not applied to the bimorph, a noise band is generated on the reproduction image ml because the
head passes all over the gart band (TG). In order to prevent the generation of a noise band, a
predetermined voltage may be applied to the bimorph such that the trajectory of the head is a
straight line connecting the points (a) and (c). FIG. 7 shows an applied voltage waveform to the
bimorph. FIG. 7 (a) shows a head switching signal, and the period when the A head is in contact
with the tape is tl-12, t3-t4. ... and the period during which the B head is in contact with the tape
is b?ts et 4-ts * ░░. The triangular wave voltage shown in (b) of the figure is a voltage applied
to the bimorph for driving the A head, and the triangular wave voltage shown in the figure is a
voltage applied to the bimorph for driving the B head. When the head starts to abut against the
tape at the time of still image reproduction, as shown in FIG. 6, if it starts from the center (a) of
the recording locus, the triangular wave applied to the A head driving bimorph 1. The voltage at
the time is set to zero, and at time t2, a voltage corresponding to the amount of displacement
between the point CbJ and the point (c) shown in FIG. 6 may be applied. Similarly, the voltage at
time t2 of the triangular wave applied to the B head driving bimorph is set to zero, and a voltage
corresponding to the amount of displacement between points (b) and (C) may be applied at time
sj3. . The same operation is repeated below. Therefore, the period in which each head is in
contact with the tape corresponds to one rise period of each triangular wave, and the fall period
is the initial position of the mechanical height position of the head before the head begins to abut
the tape next time. It is a period to return. Therefore, basically, the falling period of each
triangular wave voltage may be made any number. For example, when head A is taken as an
example, even if the waveform shown in FIG. 7 (b) is a sawtooth wave as shown in FIG. 7 (d), the
head will be a tape if the bimorph produces the same displacement as the applied waveform.
During the period of contact with the recording track, the on-track on the recording track is
faithfully reproduced on the recording track. However, in this case, the bimorph itself causes the
above-mentioned self-excited oscillation in a sudden change portion such as t2 + j4 in fact. The
self-oscillation does not attenuate sufficiently within 1 field period (1/60 sec) when Q is about
l?, so the self-oscillation generated at 12 o'clock does not converge between t2-t3 and between
+ t3-t4 Will also affect.
The amount of self-excited vibration at this time corresponds to the mistrack amount at the time
of reproduction. In order to avoid such self-excited vibration, in the 2-head type VTR, it is usual
to gradually return the mechanical height position of the head to an initial value while the head is
not in contact with the tape. Here, consider the case of reproducing at a higher tape speed than
at the time of recording. The necessity of performing reproduction at a speed faster than that at
the time of recording is effective 1 at 9 points or 6 points when a predetermined content 0 is
recorded and the part is recorded while looking at the reproduced image at the time of fast
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forward. In FIG. 8, (TA) (TB) is a magnetization locus recorded at a normal tape speed, and ? is a
head scanning locus at the time of fast feed. When the tape speed at the time of fast-forwarding
is 10 times that at the time of recording, the head crosses ten recording tracks in V60 seconds.
At this time, if no voltage is applied to the bimorph, nine noise bands occur on the reproduced
screen, resulting in an unsightly screen. The noise band can be avoided by applying a voltage to
the bimorph in the same way as in the above-mentioned still image reproduction, and faithfully
performing on-track reproduction on the first recording track where the head starts to abut the
tape. The bimorph displacement required in this case corresponds to a 9-track pitch interval,
which is larger than the maximum displacement of the bimorph. In the above 12 mm bimorph,
the amount of displacement of the 8- to 4-track pinch interval is the limit. Therefore, when
reproducing in the fast-forwarding state, it is effective to adopt the scanning locus 4 indicated by
a broken line in FIG. 8 instead of the method of on-tracking and reproducing on the same
recording locus. Trajectory (2) is reproduced by on-track recording on a predetermined
recording track for a fixed period, and the head is displaced in the direction perpendicular to the
guard band when passing the guard band so as to shorten the guard band passing time of the
head It is The direction in which the mechanical height position of the head is changed is the
direction perpendicular to the still locus. Because the gart band is almost parallel to the still
locus. It is possible to displace the head in a direction perpendicular to the guard band.
Therefore, if the scanning trajectory of the head at the time of fast-forwarding reproduction is
changed as a locus (good), the amount of noise band generated on the reproduction screen
becomes very small, and a nearly satisfactory reproduced image can be obtained. What is the
voltage waveform applied to the bimorph at this time? A sawtooth wave as shown in FIG. 9 must
be used, which causes self-excited oscillations associated with rapid bimorph displacement. The
number of sawtooth waves shown in FIG. 9 is required for 10 l field periods in the case of lO
double speed / reproduction.
In addition to the above examples, the application of the need to rapidly displace the bimorph
occurs depending on the application, and the actual displacement change of the bimorph at this
time is such that the self-excitation component of the bimorph is superimposed on the drive
waveform. . To eliminate the bimorph's automatic vibration. Some damping means are required,
and one mechanical damping method and electrical damping method have been considered
conventionally. The mechanical damping method is a method in which an elastic body such as
rubber is brought into contact with a part of the ? ии morph, but such a method has the
disadvantage of reducing the displacement amount of the bimorph, and The problem of reliability
due to the change of elastic body with time was also found. On the other hand, the electrical
damping method is a method of feeding back a signal in which the self-oscillation of the bimorph
is detected by some method to the drive stage of the bimorph. In such a method, means for
detecting the self-oscillation and a feedback circuit etc. Is complicated and expensive. SUMMARY
OF THE INVENTION The present invention is a method of suppressing self-oscillation of an
electro-mechanical transducer, which can eliminate the above-mentioned conventional
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drawbacks and can be implemented with a 2 wU single circuit configuration, but can prevent
automatic vibration well. The purpose is to get. SUMMARY OF THE INVENTION In order to
achieve the above object, a method of suppressing self-oscillation of an electro-mechanical
displacement element according to the present invention comprises: converting this electromechanical conversion element into an electro-mechanical conversion element whose damping
coefficient is approximated by one or more secondary systems. A trapezoidal wave drive voltage
having a rise time equal to the period T of the first self-oscillation component of the element or
an integral multiple thereof is applied to obtain a desired displacement amount. According to
such a configuration, the electro-mechanical transducer Can be eliminated without using a
damper member or the like. Description of Embodiments Hereinafter, an embodiment of the
present invention will be described based on one drawing. FIG. 10 shows the applied voltage
waveform to the bimorph and the actual displacement change of the bimorph. In the same figure
(a), the step-like waveform (f) shows the applied voltage waveform of the bimorph, and the
bimorph also shows the applied voltage ?'9 real' '' answer? 6 o'0 displacement change ?. The
step-like waveform represents a bimorph displacement amount corresponding to the applied
voltage. Therefore, when a constant voltage value is applied stepwise, if the bimorph responds
faithfully, the displacement amount of ? 81 will be indicated stepwise. However, an actual
bimorph displacement change causes self-excited oscillation at a rapid displacement change
portion as in the bimorph response waveform (c), and this self-excitation oscillation gradually
attenuates and finally causes a displacement change that settles to ?81.
??? The various self-excited vibrations shown in FIG. 1 ? show self-excited vibrations which
are not attenuated for the convenience of the description. The period T of the self-excited
oscillation is a period corresponding to the positive resonance frequency of the bimorph, and the
time from the rising edge of the applied voltage to the first peak value of the self-excited
oscillation is i in the secondary system It can be said from the theory of transient response.
Further, if the bimorph Q is about l?-, the overshoot amount is 1, so the amplitude ?1 of the
self-excited vibration at this time is 1. Has already been mentioned that is equal to 2?Sl. On the
premise of the above, let us consider the response of the bimorph when the voltage wave / shape
shown in FIG. 1? is applied. The rise time of the trapezoidal wave pulse shown in (b) of the
figure can be created by combining T ? ? ? C-6 and the trapezoidal wave pulse g4 @ of (c) and
(d) of the figure. In other words, the response characteristics for one trapezoidal wave pulse (c)
are equal to the combined response characteristics of bimorphs for one trapezoidal wave pulse
(e) (i). @ ? is a bimorph response waveform to a trapezoidal wave pulse (e), which is expressed
as a combination of a vibration component vector of a self-excited bimorph and a vector of a
trapezoidal wave, as shown in FIG. . In FIG. 11 (a) (d) is a composite waveform of the bimorph
self-excitation vibration shown in FIG. 11 (b) and the trapezoidal wave shown in FIG. 11 (c); It is
expressed as a sum with the vertical vector component of the wave. Vector component of selfoscillation? 3) is a vector component (2) possessed by one trapezoidal wave while the direction
and the magnitude and the magnitude change in the direction and magnitude corresponding to
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the sine wave amplitude from moment to moment, it is a direction perpendicular to ? at the time
of rise. 10 corresponds to the vector component (2) of the step waveform shown in FIG. In the
trapezoidal wave flat portion, the vector component is zero. Accordingly, the response waveform
@ 4 of the high hymorph response to the trapezoidal wave pulse (e) (2) shown in FIG. If the
vector component of the trapezoidal wave pulse (e) (good) is equal to the vector component (d) of
the step waveform shown in FIG. 10 (a), the bimorph response waveform) (4) The amplitude is
equal to ?t, and the period T is also equal. Next, consider the transient response of the bimorph
by the drive waveform which synthesizes the trapezoidal wave pulse (c) (c). The composite
waveform of the trapezoidal wave pulse (E) is a trapezoidal wave pulse (B) as shown in FIG. 10 (e)
due to the relationship of the amplitude 9 phase, and this trapezoidal wave pulse (B) is applied to
the bimorph The transient response of the bimorph is a synthesis of bimorph response molding
(C) and F.
The alternating current components of the bimorph response waveform (3) are signals having
the same amplitude 1 cycle and one phase different by 180 ░, and the alternating current
components of the synthesized signal cancel each other and become ?. The DC component of
the synthesized signal is the value of the difference between the amplitude of the trapezoidal
wave pulse (e) in FIG. 10 (c) and the amplitude of the trapezoidal wave pulse ? ? shown in FIG.
1 (d), ie, FIG. It becomes the value of the amplitude of the trapezoidal wave pulse (ii) shown.
Therefore, when the trapezoidal wave pulse (ii) shown in FIG. 10 (e) is applied to the bimorph,
the transient response waveform (d) becomes a waveform as shown, and the trapezoidal wave
pulse which is the drive voltage after the rising portion of the period T It becomes constant at the
displacement amount equivalent to the amplitude of (3). This applies if a drive voltage having a
rise time equal to the bimorph's automatic oscillation period T is applied as a trapezoidal wave
pulse (ii). Bimorph means that self-oscillation does not occur. FIG. 12 shows the strength of the
self-oscillation component of the bimorph when the rise time of the trapezoidal wave drive signal
is changed, and the rise time t is the cycle T4 of the self-oscillation component or its integer
multiple nT (n It can be seen that the self-excited vibration weakens when = (positive integer),
and the automatic vibration weakens as the rise time t becomes longer. FIG. 18 shows a bimorph
drive voltage waveform at the time of a still image of a 2-head VTR corresponding to FIG. 7 (d),
and in the head contact period, a drive voltage having a sufficiently larger rise than T is applied
to the bimorph. Self-oscillation hardly occurs. This is also apparent in the description of FIG. Even if it is necessary to return the bimorph to the initial value of the contact period in the head
non-contact section, it is necessary to do this as quickly as possible. It is possible to suppress the
self-oscillation of the bimorph by returning the cycle TS of the self-oscillation component to the
initial value with a fall time equal to its integer multiple nT. As described in detail in the
invention, according to the present invention, self-excited vibration of the bimorph can be well
suppressed by applying a trapezoidal wave having a predetermined rise time to the no-immorph
drive waveform, and in the implementation, It is possible to use an extremely simple and
inexpensive circuit without using a mechanical damper member as in the prior art and without
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having to detect self-excited vibration and apply an electrical feed to the bimorph.
[0002]
Brief description of the drawings
[0003]
1 is an external perspective view of a bimorph composed of piezoelectric elements, FIG. 2 (8) is a
plan view of a magnetic head movable device using the bimorph, FIG. Explanatory diagram of
frequency characteristic of bimorph, FIG. 4 is explanatory diagram of transient response
characteristic of bimorph, FIG. 5 is explanatory diagram of transient characteristic of secondary
system, FIG. 6 is explanatory diagram of recording magnetization locus of VTR, FIG. The figure
shows the waveform of the voltage applied to the inmorph at the time of still image reproduction,
FIG. 8 is an explanatory diagram of the scanning locus of the head at 10 О speed and
reproduction, and FIG. 9 is the voltage applied to the bimorph at 10 О speed reproduction in the
conventional method. Waveform diagrams, FIG. 1? and FIG. 11 are explanatory views of
waveform operation principle for suppressing self-oscillation of bimorph in one embodiment of
the present invention, and FIG. 12 is rise time of trapezoidal wave and self-oscillation of bimorph.
Relationship with.
)) Steplike waveform, H (ha) (ha) ... bimorph response waveform,) (a) cap 1 и и trapezoidal wave
pulse, (7) synthetic waveform. C3 ? и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и
и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и и. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 1-?-nt Fig. 6 Fig. 7 (cb
Fig. 8 Fig. Q Fig. 1 O 1 1 1 1 1 ? (C) 1 1 1 Fig. 11 , ??
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