JPH026495Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a bimorph drive device for a magnetic head suitable for auto-tracking in a video tape recorder or the like.

BACKGROUND TECHNOLOGY In general, the higher the recording density of a video tape recorder, the higher the tracking ability of the magnetic head is required.In order to meet this requirement, the magnetic head itself is displaced perpendicular to the track scanning direction. Dynamic tracking methods have been developed and are approaching the stage of practical use. In this dynamic tracking system, for example, a bimorph drive device 1 for a magnetic head as shown in FIG. 1 is used, and a magnetic head 2 is
is attached to the tip of the bimorph diaphragm 3. This bimorph diaphragm 3 has a piezoelectric material 3a such as barium zirconate titanate and a central electrode plate 3b.
The bimorph diaphragm 3 is sandwiched between upper and lower electrode plates 3c, with polarization directed in the same direction with the boundary between the electrode plates 3c and 3b. The whole thing is made to vibrate.

However, the conventional bimorph drive device 1 for a magnetic head requires a certain length of the bimorph diaphragm 3 in order to obtain a large amount of displacement of the magnetic head 2, which makes it difficult to make it compact. If 3 is forcibly shortened, a large voltage must be applied to obtain the required amount of displacement, and as a result, a piezoelectric material with high withstand voltage is required, and the bimorph drive circuit becomes expensive, etc. There were some shortcomings.

In addition, if a piezoelectric material with low rigidity is used, sufficient amplitude in the low range can be obtained, but the amplitude in the high range cannot be obtained due to the reduction in the resonance frequency. When using this, the amplitude characteristics in the high range are improved by the increase in the resonant frequency, but there are drawbacks such as the inability to obtain amplitude in the low range.

Furthermore, in the case of special reproduction, the characteristics required of the bimorph diaphragm become particularly severe. In other words, during speed playback, still image playback, and reverse playback, the bimorph diaphragm must be displaced greatly depending on each mode, and must operate quickly.Meeting these demands requires more variety than normal playback. This was accompanied by many difficulties.

DISCLOSURE OF THE INVENTION The present invention eliminates the above-mentioned drawbacks by constructing a bimorph diaphragm that supports and drives a magnetic head using piezoelectric materials with different rigidities at the fixed end and free end. An object of the present invention is to provide a bimorph drive device for a magnetic head, which is capable of vibrating a magnetic head attached to the free end side of a bimorph diaphragm with desired amplitude characteristics.

To achieve this objective, the present invention includes a first bimorph diaphragm made of a low-rigidity piezoelectric material that vibrates in a cantilevered state, and a distal end connected to the tip of the first bimorph diaphragm. A second bimorph diaphragm made of a highly rigid piezoelectric material is provided with a magnetic head attached to the second bimorph diaphragm.

According to the present invention, since the magnetic head is driven by connecting bimorph diaphragms with different rigidities, each bimorph diaphragm can be driven in different vibration modes depending on the respective drive voltage. For example, a voltage ranging from DC to several hundred Hz (hereinafter referred to as low frequency) is applied to the first bimorph diaphragm with low rigidity, and a voltage of several hundred Hz to several KHz (hereinafter referred to as high frequency) is applied to the second bimorph diaphragm with high rigidity. By applying a voltage of It can be driven with a displacement locus in which a small amplitude displacement of a high frequency wave to be corrected is superimposed, and is therefore suitable for cases where it is necessary to faithfully track a magnetic head over a narrow track using a high-density recording method. It has excellent effects such as

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to FIG. 2 and subsequent figures. FIG. 2 is a schematic configuration diagram showing an embodiment of the bimorph drive device for a magnetic head of the present invention, and FIGS. 3A and 3B show the voltage applied to the first and second bimorph diaphragms shown in FIG. 2, respectively. A waveform diagram showing an example of voltage, and FIG. 4 is an amplitude characteristic diagram of the bimorph drive device for a magnetic head shown in FIG. 2.

In Fig. 2, bimorph drive device 1 for magnetic head
1 is a device for driving a magnetic head 12 of a high-density recording video tape recorder along a track of a magnetic tape during dynamic tracking. The magnetic head 12 is supported by a series combination of two types of bimorph diaphragms 13 ₁ and 13 ₂ made of piezoelectric materials with different stiffnesses. The first bimorph diaphragm 13 ₁ has a structure in which an electrode plate 13 b that also serves as a shim material is sandwiched in the center of a low-rigidity piezoelectric material 13 _{1 a} , and a pair of electrode plates 13 _{1 c are sandwiched on both sides of the piezoelectric material 13 1 a .} The electrode plate 13 _1c is fixed in a cantilevered manner at a portion slightly away from the end thereof.

The second bimorph diaphragm 13 ₂ has the electrode plate 3 b sandwiched in the center of a highly rigid piezoelectric material 13 _{2 a} ,
Further, both sides of the piezoelectric material 13 _2a are sandwiched between a pair of electrode plates 13 _2c which are insulated from the pair of electrode plates 13 _1c , and the end portion of the piezoelectric material 13 _2a serves as the first bimorph diaphragm 13 ₁ The piezoelectric material 13 _1a matches the tip of the piezoelectric material 13 1a. That is, the first bimorph diaphragm 13 ₁ and the second bimorph diaphragm 13 ₂ are
Piezoelectric materials 1 having a common electrode plate 13b and different rigidities
3 _1a and 13 _2a are connected in series and integrated. Therefore, the magnetic head 12 provided at the tip of the second bimorph diaphragm ₁₃₂ is a pair of bimorph diaphragms 1 with different resonance frequencies and vibration modes.
3 ₁ and 13 ₂ , and vibrates according to the composite vibration mode of both bimorph diaphragms 13 ₁ and 13 ₂ . In other words, by applying a low frequency voltage as shown in Figure 3A, the amount of displacement can be adjusted, and by applying a high frequency voltage as shown in Figure 3B, the amplitude response characteristics are improved and the response reaches high frequencies. do.

Note that the rigidity of the piezoelectric materials 13 _1a and 13 _2a can be varied in various ways by changing the composition of the piezoelectric materials used.

Generally, when a bimorph diaphragm is used in a cantilevered state, the displacement δ of the tip of the bimorph diaphragm is
It is shown by the following formula.

δ=K·d ₃₁ ·l ² /t ² ·V where K: constant, d ₃₁ : piezoelectric constant, t: plate thickness, l: length, and V: applied voltage.

Therefore, in order to obtain a piezoelectric material with low rigidity, the composition of the piezoelectric material may be selected so that the piezoelectric constant d ₃₁ is large. Furthermore, in order to obtain a piezoelectric material with high rigidity, the composition of the piezoelectric material may be selected so that the piezoelectric constant d ₃₁ is small. Piezoelectric materials with different rigidities are sold by various manufacturers.For example, as piezoelectric materials with low rigidity,
There is N10 material (trade name) manufactured by TOKIN, and 91A material (trade name) manufactured by TDK, which is a highly rigid piezoelectric material.

14 are first and second bimorph diaphragms 13 ₁ ,
This is a bimorph drive circuit that applies a voltage to the first bimorph diaphragm 13 ₂ , but in the case of this embodiment, drive voltages with different frequencies are applied to the first bimorph diaphragm 13 ₁ and the second bimorph diaphragm 13 ₂ . ing. For example, during normal playback, there is no need to displace the first bimorph diaphragm 13 ₁ , so only the second bimorph diaphragm 13 ₂ is vibrated with a desired high frequency voltage to prevent tracking errors and achieve noise reduction. Achieve regeneration. Furthermore, during special playback, a sawtooth low frequency drive voltage of 30 cycles is applied to the first bimorph diaphragm ₁₃₁ , which has low rigidity, in correspondence with the period in which the magnetic head 12 tracks one track of the video tape. The second part is displaced perpendicularly to the scanning direction of the track and
A desired high-frequency drive voltage is applied to the bimorph diaphragm 13 ₂ .Thus, noiseless reproduction during special reproduction is achieved. The frequencies of these driving voltages are the same as those of the corresponding bimorph diaphragm 1.
Although the frequency is set to be lower than the resonance frequencies f ₁ and f ₂ of _{3 1} and 13 ₂ , in order to avoid unnecessary resonance, the bimorph drive circuit 14 and the first bimorph diaphragm 1
A low _{-pass filter 15 1 whose} cutoff frequency is slightly lower than the resonant frequency f ₁ is connected between the bimorph drive circuit 14 and the second bimorph diaphragm 1 .
Band-pass filters 15 ₂ each having a pass band between resonance frequencies f ₁ and f ₂ are inserted between the filters 15 1 and 15 ₂ , and the amplitude characteristics when passing through each filter 15 ₁ and 15 ₂ are as follows. It is shown in Figure 4.

Therefore, in this embodiment, the magnetic head 12
is driven according to a composite vibration mode of the first bimorph diaphragm 13 ₁ of low rigidity and driven at a low frequency and the second bimorph diaphragm 13 ₂ of high rigidity and driven at a high frequency. In this case, as is clear from the amplitude characteristics shown in _{FIG .}
By passing the driving voltage of the second bimorph diaphragm 13 ₂ through the bandpass filter 15 ₂ , the amplitude characteristic shown by the solid line is obtained. Amplitude characteristics without unnecessary resonance peaks can be obtained.
This is because out of the amplitude characteristics of each of the bimorph diaphragms 13 ₁ and 13 ₂ , only those parts convenient for driving the magnetic head 12 are extracted and synthesized.

Therefore, the first and second bimorph diaphragms 13 ₁
and 13 ₂ can obtain sufficient amplitude characteristics even if the total length is short or without applying a high voltage. Furthermore, the magnetic head bimorph drive device 11 can be compactly accommodated even in a narrow installation space, and is particularly suitable for dynamic tracking of a video tape recorder for recording high-density signals.

As explained above, according to the magnetic head bimorph drive device 11 having the above structure, the magnetic head 12 is driven by the bimorph diaphragms 13 ₁ and 13 ₂ having different rigidities connected together.
The low-rigidity bimorph diaphragm 13 ₁ and the high-rigidity bimorph diaphragm 13 ₂ can be driven in different vibration modes depending on their respective drive voltages, so that, for example, the low-rigidity first bimorph diaphragm 13 ₁ By applying a low frequency voltage to the magnetic head and applying a high frequency voltage to the highly rigid second bimorph diaphragm ₁₃₂ , it is possible to more actively utilize each vibration mode. 12 displacements can be driven with a displacement trajectory that superimposes a high-frequency, small-amplitude displacement that corrects tracking errors on a low-frequency, large-amplitude displacement that corresponds to the playback mode. This is suitable for cases where it is necessary to have a magnetic head faithfully track a narrow track.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a conventional bimorph drive device for a magnetic head, FIG. 2 is a schematic diagram showing an embodiment of a bimorph drive device for a magnetic head according to the present invention, and FIG. B is the second
FIG. 4 is a waveform diagram showing an example of the voltages applied to the first and second bimorph diaphragms shown in the figure, respectively. FIG. 4 is an amplitude characteristic diagram of the bimorph drive device for a magnetic head shown in FIG. 2. 11...Bimorph drive device for magnetic head, 1
2... Magnetic head, 13 ₁ ... First bimorph diaphragm, 13 ₂ ... Second bimorph diaphragm, 1
3 _1a , 13 _2a ...Piezoelectric material.

Claims (1)

[Scope of utility model registration request] A first bimorph diaphragm made of a piezoelectric material with a large piezoelectric constant d ₃₁ that vibrates in a cantilevered state, and a piezoelectric device whose end is connected to the tip of the first bimorph diaphragm and a magnetic head is attached to the tip. A bimorph drive device for a magnetic head, comprising a second bimorph diaphragm made of a piezoelectric material with a small constant _d31 .