JP2871237B2 - Head actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small head actuator used in a VTR or the like, which generates a driving force by using elastic vibration of a piezoelectric body.

[0002]

2. Description of the Related Art In recent years, in VTR equipment, the video track width has been narrowed due to the enhancement of the quality of recorded / reproduced images, the advancement of special reproduction functions, and the progress of magnetic materials. A head actuator capable of tracking is demanded. Hereinafter, the conventional composite bimorph and parallel spring bimorph piezoelectric head actuators will be described.

FIG. 14 is a perspective view of a head actuator having a composite bimorph structure developed by Ampex Corporation. FIG. 15 shows the principle of operation. 29, 3
Reference numerals 0, 31, and 32 are actuator electrodes, 33 is a sensor electrode, 34 is a support, and 35 is a head.

In the head actuator constructed as described above, when the actuator electrodes 29 and 31 and 30 and 32 are connected, and the actuator electrodes 29 and 30 bend in one direction, the actuator electrodes 31 and 30 connected in the opposite direction are connected. At 32 and 32, the tip of the piezoelectric body 28 is bent in the opposite direction, so that the whole is deformed into a shape close to an S-shape.

[0005] As a result, the head 35 provided at the tip of this actuator can make the spacing angle θ with respect to the tape 36 significantly smaller than that of a head actuator having a single bimorph structure. In addition, the sensor electrode 33 is used to control the position of the head 35 by detecting electric charges generated from distortion caused by bending of the piezoelectric body 28.

FIG. 16 is a perspective view of a head actuator having a parallel spring type bimorph structure. FIG. 17 shows the principle of operation. As shown in the figure, two piezoelectric elements 37 and 38 having a bimorph structure are arranged in parallel, a flexible head holder 39 having flexibility in a bending direction is provided at the tip, and a head 35 is attached to the tip. I have. As shown in FIG. 17, when a DC voltage is applied to the piezoelectric elements 37 and 38, the tip is displaced in accordance with Expression (1).

[0007]

(Equation 1)

Here, d ₃₁ is the piezoelectric constant, l is the length of the piezoelectric element, t is the thickness of the piezoelectric element, and V is the applied voltage.

The mechanical resonance frequency f of the piezoelectric elements 37 and 38 follows (Equation 2).

[0010]

(Equation 2)

Here, ρ is a density and s ₁₁ is an elastic constant. When the piezoelectric elements 37 and 38 are displaced by the above relationship,
The flexible head holder 39 is deformed so as to be parallel to the tape 36. Therefore, as compared to the composite bimorph structure of FIG.
As a result, the head 34 moves in parallel, so that the spacing angle θ can be made almost zero.

[0012]

However, in the above-mentioned conventional configuration, there is a problem that the head actuators having the composite bimorph structure or the parallel spring type bimorph structure both have a large shape.

According to the relationship between (Equation 1) and (Equation 2),
The displacement ξ is proportional to the square of the ratio (l / t) between the length and the thickness of the piezoelectric element. On the other hand, the resonance frequency f is proportional to the square of the thickness and length (t / l ² ) of the piezoelectric body.

For example, the length l of the piezoelectric element is 20 mm, the thickness is 1 mm, d ₃₁ ≒ −10 ⁻¹⁰ (m / v), Young's modulus s ₁₁
≒ 10 ¹¹ (N / m ² ), density ρ = 7.8 × 10 ³ (kg /
m ³ ), a displacement amount of about 300 μm and a resonance frequency f of about 1400 Hz can be obtained at a voltage V = 1 Kv.

In the case of such a large number of heads, the diameter of the head cylinder is 50 mm or more and a high DC voltage is required. On the other hand, if the dimensions are reduced, the mechanical strength of the piezoelectric element will decrease and the resonance frequency f will decrease, and the current control that can be controlled only at a control frequency of about half the resonance frequency will be further reduced. There is a major problem that must be used.

An object of the present invention is to provide a head actuator which solves the above problems.

[0017]

In order to solve the above-mentioned problems, a head actuator according to the present invention comprises a rod-shaped vibrator having a square cross-sectional shape in which a piezoelectric body is provided on at least one set of intersecting planes. It is composed of a pressure mechanism for pressing a moving body provided on a guide shaft or a leaf spring on the ridge line of the moving body, and a position detecting unit such as an optical type or a strain detecting element for detecting the position of the moving body.

Further, the moving body is moved in one direction by applying an AC voltage to one of the piezoelectric bodies, and the other piezoelectric body is driven by applying a driving method based on a combined vibration excited by the first and second piezoelectric bodies. By switching the AC voltage to the body, it is possible to move the moving body in the opposite direction.

[0019]

According to the above construction, since the pressure between the moving body and the vibrating body is not a plane but a point or a line, there is no restriction on the planar accuracy and the parallelism between the moving body and the vibrating body, and mass production and low cost are achieved. Is easily peeled off. Further, the control frequency is not limited by the mechanical resonance frequency unlike the conventional bimorph structure. Further, since the frictional force is transmitted to the moving body as a driving force using the resonance phenomenon of the piezoelectric element of the vibrating body, the driving voltage can be reduced and the moving body can be driven at high speed.

Furthermore, since the head moves on the guide shaft, the deflection width of the head is not limited by the structure, and the moving angle of the head moves along the ridge of the vibrating body, so that the spacing angle of the head can be made almost zero. .

In this driving method, since the moving body is pressed against the ridge of the vibrating body having a certain angle with respect to the vibration displacement in the X and Y directions, the moving body is pressed by the cosine component of the vibration displacement. It is possible to drive the moving body in one direction only by the vibration of the piezoelectric body on one side in the X and Y directions, and to reverse the moving direction only by switching the AC voltage so as to excite the vibration in the other piezoelectric body. You can do it.

As another driving method, an alternating voltage having a different phase is simultaneously applied to the piezoelectric body in the X and Y directions to excite the vibration of an elliptical locus on the ridge portion of the vibrating body and to move by changing the phase. It is also possible to easily change the direction of movement of the body.

[0023]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of a head actuator according to the present invention will be described with reference to FIG.

FIG. 1 is a perspective view of the head actuator of this embodiment. In FIG. 1, reference numeral 1 denotes an elastic body having a square cross section, and 2a denotes a first piezoelectric body, not shown, and 2b.
Is a second piezoelectric body, and the first and second piezoelectric bodies 2 are
The vibrating body 3 is formed by affixing a and 2b. 4 is a support hole, 5 is a support member, 6 is a moving body, 7 is a guide shaft, 8 is a pressure spring, 9 is an optical position detector, and 10 is a signal detection head.

FIG. 2 is a diagram showing a displacement distribution of the first-order free vibration of the rod. Reference numeral 11 denotes a node (node) corresponding to the position of the support hole 4.
1 (1: vibrating body length). From FIG. 1, the moving body 6
Is in pressure contact with the ridge 1a of the vibrating body 3 at the maximum position of the amount of vibration displacement at the center of the vibrating body 3. The vibrating body 3 is made of a supporting member 5 such as a plastic pin having a low Young's modulus or a material having a low sound velocity, and is supported and fixed by a supporting hole 4. At this time, the support hole 4 is provided with the vibrating body 3 in the X and Y directions.
It is preferable to provide them symmetrically in order to make the stiffness equal, but this is not the case if the effect of the support holes 4 can be ignored.

Next, the driving principle will be described with reference to FIGS. 3 and 4A and 4B. FIG. 3 is a driving principle diagram when the combined vibration of the first and second piezoelectric bodies 2a and 2b is used, and FIG. 4 is a diagram when the single vibration is used for the first and second piezoelectric bodies 2a and 2b. FIG. 4 is a driving principle diagram of FIG.

Now, an AC voltage v ₁ represented by (Equation 3) is applied to the _first piezoelectric body 2 a to excite vibration in the X direction, and a second piezoelectric body 2 b is represented by (Equation 4). The AC voltage v ₂ having a different phase of π / 2 is applied to excite vibration in the Y direction.

[0028]

(Equation 3)

[0029]

(Equation 4)

Here, V ₀ is the instantaneous value of the AC voltage, ω is the angular frequency, and t is the time. Thereby, the bending vibration of the elliptical locus expressed by (Equation 5) is excited over the entire circumference of the vibrating body 3. As an example, the state of the elliptical locus is indicated by an arrow in FIG.

[0031]

(Equation 5)

[0032] Here, the amplitude value of xi] is bending vibration, xi] ₀ is the instantaneous value of the bending vibration. Due to the vibration of the elliptical locus, the ridge of the vibrating body 3 is pressed against the moving body 6 by the pressing spring 8 of the pressing mechanism, and driven in the moving direction of the elliptical locus by the frictional force. By changing the phase to ± π / 2 as shown in (Equation 4), the moving direction of the moving body 6 can be reversed.

Another driving method will be described with reference to FIG. FIG. 4A shows a state of vibration of the ridge portion of the vibrating body 3 when vibration in the X direction is excited by the first piezoelectric body 2a. In the ridge line portion, the vibration displacement xi] _x can be decomposed into components of xi] _x2 direction and xi] _x1. Therefore, the moving body 6 that is pressure contact with the ridge portion is moved in xi] _x2 direction by xi] _x2 component of the vibration displacement xi] _x, which is excited by the first piezoelectric 2a.

Similarly, FIG. 4B shows a state of the vibration of the ridge portion of the vibrating body 3 when the vibration in the Y direction is excited by the second piezoelectric body 2b. In the ridge line portion, the vibration displacement xi] _y can be decomposed into xi] _y1 and xi] _y2 direction component. Therefore, the moving body 6 that has been brought into pressure contact with the ridge portion moves in the _2y2 direction due to the _ξy2 component of the vibration displacement 励_y excited by the second piezoelectric body 2b.

As described above, the cosine-direction components ξ _x2 and ξ _y2 of the vibrations independently excited by the first and second piezoelectric bodies 2 a and 2 b are components in directions opposite to each other. The moving direction of the moving body 6 can be controlled by driving the piezoelectric body, and the moving direction can be reversed by switching and inputting one AC voltage to each piezoelectric body.

Then, by either of the above driving methods,
A head 10 is provided on a moving body 6 that moves along a guide shaft 7 shown in FIG. 1, and a recording signal is extracted by a flexible P plate or the like.

At this time, a high-precision head actuator can be obtained by feeding back the position information of the moving body 6 from the position detector 9 in order to accurately track the head 10 on the track on which the video signal is recorded. It is.

As shown as an example of the position detector 9 in FIG. 5, a semiconductor laser 14, a light detecting element 15 such as a photodiode, and a reflecting mirror 16 are provided on each surface of a polarizing element 13 such as a beam splitter as shown in the figure. The movable body 6 is provided with a reflective film 17 made of an aluminum film or the like.

The principle of detection is that a laser beam emitted from a semiconductor laser 14 is split into two by a polarizing element 13, and one laser beam 18 is reflected by a reflecting mirror 16 and enters a photodetecting element 15, while the other laser beam 18 The light 19 is reflected on the reflection film 16 on the moving body 6.
, And again reflected by the polarization element 13 to enter the light detection element 15. At this time, due to a change in light intensity due to a difference in optical path length between the laser beams 18 and 19 to the photodetector 15,
The position is determined.

The position detector 9 may be of any type, such as a device using the principle of an optical lever or an optical encoder, as long as it is a small and non-contact detecting element with the moving body 6.

As described above, according to the present embodiment, the moving body 6
Moves along the guide shaft 7, the run-out width is not restricted in principle, the spacing angle between the tape and the head 10 becomes zero, and an ideal head actuator can be obtained.

Further, since the control frequency is not limited by the conventional mechanical resonance frequency, a high-speed response can be achieved. In addition, since the driving principle of the moving body is basically frictional driving, a head actuator having good damping performance and no ringing can be obtained.

Further, since the moving body 6 is brought into pressure contact with the ridge of the vibrating body 3, there is no restriction on the parallelism and plane accuracy between the moving body and the vibrating body, and it is inexpensive, excellent in mass productivity, and reliable. Of the head actuator can be obtained.

In particular, when the vibrating body is driven by one of the piezoelectric bodies, it is possible to apply only an AC voltage to the piezoelectric body corresponding to the moving direction of the moving body. It can be configured. further,
Even when one piezoelectric body is driven, the same amount of vibration displacement as in the combined vibration in the X and Y directions can be obtained, so that the input power can be reduced and the driving efficiency can be greatly improved.

Similarly, since the driving is performed on one side only, the elastic body 1 can be controlled even if the resonance frequencies in the X and Y directions are different due to a change in the shape and dimensional accuracy of the elastic body 1, and strict shape accuracy is not required. Therefore, a head actuator having stable characteristics can be obtained with a very simple configuration and a drive circuit.

Note that the first and second piezoelectric bodies 2a and 2b are not limited to only two intersecting planes as shown in FIG. 1, but to opposing planes as shown in FIG. The piezoelectric body 2 is arranged so as to be arranged in the polarization direction as indicated by the arrow.
a ', 2b' are provided, and driven by a set of the piezoelectric bodies 2a, 2a 'and the piezoelectric bodies 2b, 2b', a low resonance impedance and a high coupling coefficient are obtained, and the driving frequency for low voltage driving and load fluctuation is obtained. This provides advantages such as simplification of a control circuit that tracks changes.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 7 is a plan view of a head actuator according to a second embodiment of the present invention. In this figure, a leaf spring 21 provided with a position detector 20 such as a strain gauge is added to the moving body 6 except for the optical position detector 9 of the first embodiment. Thereby, the leaf spring 21 is moved by the movement of the moving body 6.
Is deformed, and the amount of deformation changes the resistance value of the position detector 20 or the like, thereby controlling the position of the moving body 6. Other configurations are the same as those of the first embodiment.

As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained, but in the first embodiment,
Although it was difficult to use the expensive optical position detector 9 and read out the recording signal from the head 10, in this embodiment, the position detector 20 such as a strain gauge using an inexpensive resistance change is used.
In addition to the position control, the wiring on the leaf spring 21 can prevent a problem such as disconnection that is likely to occur in the first embodiment due to the driving of the moving body.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG.

FIG. 8 is a plan view of a head actuator according to a third embodiment of the present invention. In this figure, the guide of the moving body 6 by the guide shaft 10 of the first and second embodiments is stopped, and the moving body 6 is sandwiched by the parallel springs 22 and brought into pressure contact with the vibrating body 3. .

As described above, according to this embodiment, since the parallel spring 22 is used, the guide shaft 1 of the first and second embodiments is used.
With the zero structure, the problem of wear due to sliding with the moving body 6 and the problem of nonlinearity of the moving amount of the moving body due to sliding resistance can be solved. In addition, since the position detector can have the same configuration as that of the second embodiment, an inexpensive and highly reliable head actuator can be obtained.

Here, in the present embodiment, a parallel spring configuration is used, but it goes without saying that a single-spring configuration may be used.

Embodiment 4 Next, a fourth embodiment of the present invention will be described with reference to the drawings.

FIG. 9 is a plan view of a head actuator according to a fourth embodiment of the present invention. This figure shows a parallel spring 24 having a semi-cylindrical bent portion 23 in the third embodiment. Other configurations are the same as in the third embodiment.

In the structure using the parallel springs 22 of the third embodiment, the deflection width of the moving body 6 depends on the amount of extension of the parallel springs.
According to the present embodiment of the structure using the parallel spring 24 having
The deflection width of the moving body 6 can be greatly increased by the deformation of the bending portion 23.

Embodiment 5 Next, a fifth embodiment of the present invention will be described with reference to the drawings.

FIG. 10 is a perspective view of a head actuator according to a fifth embodiment of the present invention. In FIG.
In this embodiment, the cross-sectional shape of the elastic body 1 in the fourth embodiment is a triangular elastic body 25. Other configurations are the same as those of each embodiment.

Next, one side of the piezoelectric element shown in FIGS.
The operation principle will be described by taking the case of driving by a body as an example. Basic
Specifically, it is the same as FIG. As shown in FIGS. 11 (a) and 11 (b)
When the vibration in the normal direction of the hypotenuses A and B is excited,
The amount of each vibration displacement 変 位_AAnd ξ_BHuh _A1And ξ_A2Direction and ξ_B1
And ξ_B2The moving object 6 can be decomposed into_A2And ξ_B2To
Therefore, it is driven in the opposite direction.

As described above, according to the present embodiment, in a vibrating body structure having a triangular cross section, the resonance frequency of each piezoelectric body is less likely to shift than that of a square vibrating body. Can be.

Further, as shown in FIG. 10, when the angles sandwiched between the hypotenuse and the base are θ ₁ and θ ₂ , ξ _A2 and ξ _B2 can be expressed by (Equation 6) and (Equation 7),

[0062]

(Equation 6)

[0063]

(Equation 7)

At this time, for example, if the vibrating body is a regular triangle, θ _A2 and ξ _B2 are about 87 of ξ _A and ξ _B at θ ₁ = θ ₂ = 60 degrees.
%, Which is larger than about 71% when the square θ ₁ = θ ₂ = 45 degrees, and a head actuator that can be driven with high efficiency can be obtained. The shape of the triangle of the vibrating body is preferably an equilateral triangle or an isosceles triangle, but is not limited thereto.

(Embodiment 6) Further, a sixth embodiment of the present invention will be described with reference to the drawings.

This embodiment is different from the first to fifth embodiments in that at least the ridge 1a of the vibrating body 3 where the moving body 6 comes into pressure contact as shown in the sectional view of the vibrating body in FIG. , A head actuator having a rounded shape and no edges, and the other configuration is the same as that of each embodiment.

As described above, according to the present embodiment, the wear of the moving body 6 due to the edge of the vibrating body 3 which is generated at the time of driving in the first to fifth embodiments is extremely reduced. The life of the actuator can be remarkably increased, and a highly reliable actuator can be obtained for a long time, and the industrial merits are enormous.

(Embodiment 7) Next, a seventh embodiment of the present invention will be described with reference to the drawings.

FIG. 13 is a sectional view of a moving body according to the seventh embodiment. FIGS. 7A and 7B show a movable body 2 having a cantilever structure.
6 (c) shows a movable body 27 having a doubly supported structure. Other configurations are the same as those of each embodiment.

As described above, according to the present embodiment, the same structure as the pressure spring mechanism can be provided in the cantilevered portion or the both-sided portion by this moving body configuration, so that the pressing mechanism can be omitted. . Needless to say, a pressing mechanism may be provided. Further, since the moving bodies 26 and 27 have a function of adjusting the pressing force, fine adjustment at the time of assembling the head actuator is very easy, and the range of application can be expanded. In addition, since the unnecessary vibration of the vibrating body 3 is absorbed by the cantilevered portions or both-sided portions of the moving bodies 26 and 27, it is possible to further reduce the uniform contact property and the generation of noise.

[0071]

As described above, according to the present invention, the moving body is pressed into contact with the ridge portion of the vibrating body having a square or triangular cross section through the pressing mechanism to drive the vibrating body. There is no restriction on the degree of parallelism with the body, and a low cost, excellent mass productivity, and stable head actuator can be realized.

Further, by driving the vibrating body at the ridge, the moving body can be driven in one direction by the cosine component of the vibration displacement excited by the AC voltage applied to one piezoelectric body, and the other piezoelectric body can be driven by the other piezoelectric body. Since the moving direction of the moving body can be reversed by switching and applying the AC voltage, a low-input drive and high-efficiency head actuator can be easily realized with a simple configuration.

By moving the movable body with a guide shaft or a parallel spring structure, it is possible to realize a small and lightweight head actuator having a substantially zero spacing angle, a large swing width, and no ringing due to friction driving. is there.

[Brief description of the drawings]

FIG. 1 is a perspective view of an embodiment of a head actuator according to the present invention.

FIG. 2 is a first-order free vibration distribution diagram of a rod.

FIG. 3 is an explanatory diagram of the operation of the composite driving of the embodiment.

FIG. 4A is an operation explanatory diagram of a first piezoelectric body of the embodiment; FIG. 4B is an operation explanatory diagram of a second piezoelectric body of the embodiment;

FIG. 5 is a configuration diagram of an optical position detector in FIG. 1;

FIG. 6 is a layout diagram of the piezoelectric body of the embodiment.

FIG. 7 is a plan view of a second embodiment of the present invention.

FIG. 8 is a plan view of a third embodiment of the present invention.

FIG. 9 is a plan view of a fourth embodiment of the present invention.

FIG. 10 is a perspective view of a fifth embodiment of the present invention.

FIG. 11 is an operation explanatory diagram of the embodiment.

FIG. 12 is a perspective view of a sixth embodiment of the present invention.

FIG. 13 is a sectional view of a movable body having a cantilever structure according to a seventh embodiment of the present invention.

FIG. 14 is a perspective view of a conventional head actuator having a composite bimorph structure.

FIG. 15 is an explanatory diagram of a driving principle of the actuator of FIG. 14;

FIG. 16 is an explanatory view of a driving principle of a head actuator having a conventional parallel spring type bimorph structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Elastic body 2a, 2a '1st piezoelectric body 2b, 2b' 2nd piezoelectric body 3 Vibration body 6 Moving body 7 Guide shaft 9, 20 Position detector 10 Head 22 Parallel spring 24 Parallel spring 25 Triangular elastic body 26 Moving body 27 Moving body 28 Bimorph structure piezoelectric body 35 Head 39 Flexible head holder

────────────────────────────────────────────────── ─── Continued on the front page (72) Osamu Kawasaki, Inventor 1006 Odakadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-5-91765 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G11B 5/592 H02N 2/00

Claims (9)

(57) [Claims] 1. A rod-shaped elastic body having a square cross section,
A vibrating body having a first piezoelectric body provided on one surface of at least one set of intersecting elastic bodies and a second piezoelectric body provided on the other surface;
A moving body that contacts at least one ridge portion of the vibrating body and moves along a guide axis; a pressing mechanism that presses the moving body and the vibrating body; and a signal detection unit provided on the moving body. And a position detecting unit for optically detecting the position of the moving body. 2. A rod-shaped elastic body having a square cross section,
A vibrating body having a first piezoelectric body provided on one surface of at least one set of intersecting elastic bodies and a second piezoelectric body provided on the other surface;
A moving body that contacts at least one ridge line of the vibrating body and moves along the guide axis, a leaf spring provided with a position detection element fixed to the moving body, and pressurizes the moving body and the vibrating body A head actuator comprising: a pressure mechanism; and a signal detector provided on the moving body. 3. A rod-shaped elastic body having a square cross section,
A vibrating body having a first piezoelectric body provided on one surface of at least one set of intersecting elastic bodies and a second piezoelectric body provided on the other surface;
A moving body that is in contact with at least one ridge line portion of the vibrating body and is sandwiched by a parallel spring, a position detection unit provided on the parallel leaf spring, and a pressing mechanism that presses the moving body and the vibrating body; And a signal detection unit provided on the moving body. 4. The head actuator according to claim 1, wherein the head actuator is driven by a combined vibration excited by applying an AC voltage to the first and second piezoelectric bodies. 5. The driving method according to claim 1, wherein the AC voltage applied to the first and second piezoelectric bodies is switched for each of the piezoelectric bodies, thereby driving each of the vibrations according to the moving direction component of the moving body. Head actuator. 6. An elastic body having a triangular cross-sectional shape, wherein first and second piezoelectric bodies are provided on at least two surfaces.
The head actuator according to any one of the above. 7. The head actuator according to claim 1, wherein at least a portion of the ridge portion of the vibrating body that comes into contact with the moving body is rounded. 8. The head actuator according to claim 3, wherein a semi-cylindrical bent portion is provided in a part of the parallel spring. 9. The head actuator according to claim 1, wherein the movable body has a cantilever or a double-supported beam structure to impart spring properties.