JPS6235145Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a drive circuit for a bimorph element, and is particularly suitable for use in a helical scan type VTR that uses a bimorph element to perform tracking correction.

In a rotating head type helical scan VTR, a recording track is normally formed on the magnetic tape with an inclination depending on the inclination of the wound tape with respect to the drum, the tape running speed, the rotational speed of the rotary head, etc. Therefore, when playing back a magnetic tape by running it at a speed different from the speed at which it was recorded, for example, when playing in various modes such as still, slow motion, and double speed, the scanning locus of the head is The different slope from the track causes the head to scan off the predetermined recording track. If the magnetic head scans off the predetermined recording track in this way, guard band noise and crosstalk will occur, which is undesirable. Therefore, in this type of VTR,
Tracking correction means is required to ensure that the magnetic head correctly scans the recording track in any mode. As such a tracking correction means, a magnetic head support device using a bimorph element is known.

FIG. 1 shows the basic structure of such a bimorph plate. As shown in FIG. 1, a bimorph plate 1 includes a piezoceramic element 4 having electrodes 2 and 3 adhered to both sides thereof by plating or the like, and electrodes 5 and 6 also adhered to both sides thereof. Piezo・
It consists of a ceramic element 7. The electrodes 3 and 5 of these ceramic elements 4 and 7 are in contact with the shim 8 via the shim 8 so that their polarization directions are opposite to each other as shown by the arrows in FIG. They are joined by adhesive. The shim 8 is for reinforcement and is made of phosphor bronze, carbon fiber, or the like.

As shown in FIG. 2, a voltage is applied to such bimorph plate 1 through a drive circuit consisting of a pair of diodes 15 and 16 and a pair of Zener diodes 17 and 18. Note that the pair of diodes 15 and 16 are for rectification, and the pair of Zener diodes 17 and 18 are for each piezo
This is to prevent depolarization of the piezo ceramic elements 4, 7 by suppressing the voltage applied to the piezo ceramic elements 4, 7 in the opposite direction to the polarization direction to a predetermined value or less. When a voltage is applied by this circuit, the electrode 2
Since an electric field is applied in the direction of the electrode 3 (polarization direction), the piezoelectric effect deforms the ceramic element 4 in the direction shown by the arrow. Further, since an electric field is applied to the ceramic element 7 in the direction from the electrode 5 to the electrode 6 (in the direction opposite to the polarization direction), the ceramic element 7 is deformed in the direction of shrinkage. Therefore, the bimorph plate 1 bends as shown by the chain line in FIG. 2, and its displacement corresponds to the magnitude of the electric field. Furthermore, if the direction of the electric field is reversed, the direction of displacement will also be reversed. That is, bimorph plate 1
Both ends of the ceramic element are displaced to the side of the ceramic element to which an electric field is applied in the opposite direction to the polarization direction. When one end of the bimorph plate 1 is cantilevered at a predetermined position on the head drum 9 and a magnetic head 10 is attached to the other end, that is, the free end, the magnetic head 10 extends along the outer surface of the head drum 9. It will be supported to be movable in the height direction. Therefore, if the displacement of the magnetic head 10 is appropriately controlled by the applied voltage, the above-mentioned tracking correction becomes possible.

That is, the magnetic tape 11 is helically wound around the outer peripheral surface of the head drum 9 by a pair of tape guides 12 and 13, as shown in FIG.
This magnetic tape 11 is run at a speed of _V1 by a drive means not shown. On the other hand, the magnetic head 10 is held by the rotating head drum 9 via the bimorph plate 1 as described above, and protrudes from the outer circumferential surface of the drum 9 through the slit 14 formed in the drum 9 _. The magnetic tape 11 is in contact with the magnetic tape 11 while traveling. Therefore, when recording is performed with this device, a large number of mutually parallel recording tracks _T1 are recorded on the magnetic tape 1, as shown in FIG.
It is formed on this tape 11 at an angle with respect to the length direction of the tape 11 . Therefore, during normal reproduction in which the magnetic tape 11 is run at the same speed _V1 as during recording, the magnetic head 10 correctly tracks the recording track.
Since the scanning is performed on _T1 , the recording track _T1 will not be deviated from.

However, at a speed slower than V ₁ above, magnetic tape 1
When performing reproduction while running the magnetic head 10, for example in slow motion or still motion (V=0) mode, the inclination angle of the scanning trajectory _T2 of the magnetic head 10 is as shown by the dotted line in FIG. It becomes larger than the inclination angle of the recording track _T1 . As a result, the recording track _T1 and the locus of the magnetic head 10 no longer match, resulting in guard band noise and crosstalk. Therefore, by applying a voltage to appropriately deform the bimorph plate 1 and displacing the magnetic head 10 as shown in FIG. 2, it is possible to scan the predetermined recording track _T1 without deviating from it.

Tracking correction is also performed by deforming the bimorph plate 1 even when the running speed of the magnetic tape 11 is faster than _V1 . That is, at double speed (V=2V ₁ ), for example, the inclination angle of the scanning trajectory _T3 of the magnetic head 10 becomes smaller than the inclination angle of the recording track _T1 , as shown by the chain line in FIG. Therefore, in this case as well, the bimorph plate 1 can be appropriately deformed to match the recording track _T1 .

However, when the bimorph plate 1 as shown in FIGS. 1 and 2 is used, since the piezo ceramic elements 4 and 7 are insulating materials, variations in poling and dimensions of these elements may cause Due to the piezoelectric effect when the bimorph plate 1 is attached to the head drum 9, a voltage is charged to the shim 8 without applying an external voltage. This voltage causes the tip of the bimorph plate 1 to be slightly displaced. This displacement is for example 40
The magnetic head 1 is of the order of μm to 50 μm.
The accuracy of mounting 0 on the head drum 9 is ±10μ.
Considering that the distance is about m, the displacement of the tip of the bimorph plate 1 cannot be ignored. This displacement causes a problem in that the magnetic head 10 supported by the bimorph plate 1 cannot be statically positioned.

The present invention was devised in view of these problems. A bimorph element is constructed by bonding a pair of piezo ceramic elements with different polarization directions via a shim, and one piezo ceramic element A series circuit of a diode and a Zener diode is connected between the electrodes of one piezo ceramic element and between the electrodes of the other piezo ceramic element.
an electrode on the opposite side of the ceramic element to the shim;
By applying a driving voltage between the electrode of the other piezoceramic element which is opposite to the shim and which is grounded, a driving voltage in the polarization direction is applied to each piezoceramic element through the series circuit. and a driving voltage in the direction of depolarization, respectively, and resistors are connected in parallel with the series circuit, so that the static charge charged in the shim is discharged through these resistors. The present invention relates to a characteristic drive circuit for a bimorph element. Therefore, according to the present invention, a bimorph element with high strength can be used, and a stable drive voltage can be supplied to the pair of piezo ceramic elements constituting the bimorph with a drive circuit having a simple circuit configuration. Also, Figure 2 (Figure 5)
Even if a drive circuit with a simple circuit configuration in which the shim is not grounded, as shown in Figure 2, is configured to supply drive voltage to a pair of piezo ceramic elements, the bimorph element will still achieve static stability. be able to.

An embodiment of the present invention will be described below with reference to FIG. Note that portions corresponding to those of the conventional device shown in FIGS. 1 to 4 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 5, in this example,
A resistor 19 is connected in parallel to the series circuit of the diode 15 and the Zener diode 17, and a resistor 20 is connected in parallel to the series circuit of the diode 16 and the Zener diode 18. Accordingly, the charges stored in the center shim 8 of the bimorph plate 1 and the electrodes 3, 5 in contact with the shim 8 are discharged through the resistors 19, 20, and the static position of the bimorph plate 1 is stabilized. Therefore, the position of the magnetic head 10 supported at the tip of the bimorph plate 1 is also stabilized. This makes it possible to statically position the head 10 and mount the magnetic head 10 on the head drum 9 with high precision.

That is, as described above, the bimorph plate 1 has a pair of piezo ceramic elements 4 and 7 connected to a conductive shim 8.
It is connected via a capacitor and has a capacitance. Therefore, if the circuit is in a non-conducting (oven) state, and if it is deformed by an external force or if internal distortion occurs, the charge generated in the shim 8 will not be released and will be transferred to the shim 8. It remains charged. This state is the same as applying an electric field to the bimorph plate 1, and the tip of the bimorph plate 1 is slightly displaced. Therefore, if this charge is discharged through the discharge resistors 19 and 20, the pair of piezo ceramic elements 4 and 7 will be electrostatically short-circuited, and the tip of the bimorph plate 1 will be stable without being displaced. is maintained.

Note that the piezo ceramic elements 4 and 7 have a relatively large capacitance, for example, 0.04 μF.
Therefore, in order to discharge quickly, resistors 19 and 2 are required.
It is sufficient to reduce the resistance value of resistor 0, but resistor 19,2
If the resistance value of 0 is made too small, current consumption during driving will increase, and conversely, if the resistance value is made too large, the time constant of the drive circuit will become large and responsiveness will deteriorate. Therefore, it is advisable to consider these two conditions and use an appropriate value, for example, about 1 MΩ.

As described above, the present invention constructs a bimorph element by joining a pair of piezo ceramic elements with different polarization directions via a shim,
A series circuit of a diode and a Zener diode is connected between the electrodes of one piezo ceramic element and between the electrodes of the other piezo ceramic element, and the electrode on the opposite side of the shim of one piezo ceramic element By applying a driving voltage between the electrode of the other piezo-ceramic element on the opposite side to the shim and grounded, each piezo-ceramic element is driven in the polarization direction through the series circuit. The shim is configured to supply a voltage and a driving voltage in the direction of depolarization, and a resistor is connected in parallel with the series circuit, so that the static charge charged in the shim is discharged through these resistors. .

Therefore, according to the present invention, since a bimorph element is constructed by joining a pair of piezo ceramic elements via a shim, a bimorph element with high strength can be used.

In addition, each piezo ceramic element is configured to be supplied with a drive voltage in the polarization direction and a drive voltage in the depolarization direction through a series circuit of a diode and a zener diode.
It is possible to drive the ceramic element while keeping the voltage applied to the ceramic element in the opposite direction to the polarization direction below a predetermined value.

In addition, the static charge accumulated on the shim due to the piezoelectric effect when attaching the bimorph element to the head drum can be discharged through the resistor, completely eliminating displacement due to charging of the shim that tends to occur when attaching the bimorph element to the head drum. Therefore, the drive voltage can be supplied to the pair of piezo ceramic elements using a drive circuit with a simple circuit configuration in which the shim is not grounded, as shown in Figure 2 (Figure 5). The static stability of a bimorph element can be obtained even if the structure is configured as follows.

[Brief description of the drawings]

Figure 1 is a side view of the main parts showing the structure of a bimorph board, Figure 2 is a circuit diagram of a bimorph drive circuit in a conventional head support device using this bimorph board, and Figure 3 is a VTR equipped with this support device. FIG. 4 is a plan view of the magnetic tape showing formed tracks, and FIG. 5 is a circuit diagram of a bimorph drive circuit showing an embodiment of the present invention. In addition, in the symbols used in the drawings, 1... bimorph plate, 4... piezo ceramic element, 7...
Piezo ceramic element, 15...diode,
16...Diode, 19...Resistor, 20...Resistor.

Claims (1)

[Claims for Utility Model Registration] A pair of piezos with different polarization directions.
Ceramic elements are bonded via shims to form a bimorph element, and a series circuit of a diode and a Zener diode is connected between the electrodes of one piezo ceramic element and between the electrodes of the other piezo ceramic element, respectively. by applying a driving voltage between an electrode of one piezoceramic element on the opposite side of the shim and an electrode of the other piezoceramic element on the opposite side of the shim and which is grounded. A drive voltage in the polarization direction and a drive voltage in the depolarization direction are respectively supplied to the piezo ceramic element through the series circuit, and resistors are connected in parallel with the series circuit to charge the shim. A drive circuit for a bimorph element, characterized in that the static charge caused by the electrostatic charge is discharged through these resistors.