JP2000067545A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform an optimum focusing by providing an objective lens and allowing an optical pickup device to have a slider holding the lens with respect to a recording medium at a prescribed interval by the airflow generated by a rotating recording medium and providing a wing part whose elevation angle is changable in the slider. SOLUTION: A wing part 200 consisting of a first piezoelectric element body 201 and a second piezoelectric element body 203 is provided in a slider 71. A focus error signal in which outputs of respective light receiving surfaces of bisected photodetector are differentially operated by a differential amplifier is inputted to a control part, which changes voltages to be applied to the first and second piezoelectric element bodies 201, 203 via first and second piezoelectric element driving circuits. Then, quantities of extension and contraction of respective piezoelectric bodies 201, 203 are changed and the elevation angle of the wing part 200 is changed to change the flying hight of the slider 71 to a position where the objective lens is focused. Moreover, the control part performs a tracking by driving a coil based on a tracking error signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device provided with an objective lens and having a slider which is held at a predetermined distance from a recording medium by an air flow generated by a rotating recording medium.

[0002]

2. Description of the Related Art FIG. 12 shows an example of an optical pickup device having a slider which is held at a predetermined distance from a recording medium by an air flow generated by a rotating recording medium.
There are the following.

In FIG. 1, a magneto-optical disk 1 as a recording medium is driven to rotate at high speed by a spindle motor 3. The main body 6 of the optical pickup device 5 is provided with a roller 9 movably engaged with a guide 7 on the base 8 side, and is movable in a direction crossing a track of the magneto-optical disk 1.

Further, the voice coil motor 10
The main body 6 of the optical pickup device 5 is driven in a direction crossing the tracks of the magneto-optical disk 1.
A slider 11 that floats with respect to the magneto-optical disk 1 by an airflow generated by rotation of the magneto-optical disk 1 is attached to a main body 6 of the optical pickup device 5 via a suspension 13.

On the base 8 side, a laser light source for emitting a laser beam in the direction of the guide 7 and a reflected laser beam from the magneto-optical disk 1 are received, and information recorded on the magneto-optical disk 1 is detected. A box 15 provided with a photodetector and the like for detecting a track error signal is provided, and a laser beam emitted from the box 15 is supplied to a prism 17 provided on the main body 6 of the optical pickup device 5.
As a result, the light enters the slider 11 and is focused on the recording surface of the magneto-optical disk 1 by an objective lens (not shown) provided in the slider 11.

Next, the operation of the optical pickup device 5 having the above configuration will be described. When the magneto-optical disk 1 is not rotating, the slider 11
Are pressed on the magneto-optical disk 1.

When the magneto-optical disk 1 is driven to rotate at a high speed by the spindle motor 32, a force (lift) that causes the slider 11 to fly is generated in the slider 11 by the airflow generated on the magneto-optical disk 1, and the suspension is suspended. 1
Ascends against the bias of 3. At a position where the flying force of the slider 11 and the biasing force of the suspension 13 are balanced, the flying of the slider 11 stops, and the slider 11 keeps a certain flying height while the magneto-optical disk 1 is rotating.

When an electric current is applied to the voice coil motor 10,
The main body 6 of the optical pickup device 5 moves in a direction crossing the track of the magneto-optical disk 1 and stops on a desired track.

The laser beam emitted from the laser light source in the box 15 is incident on the slider 11 by the prism 17 and is condensed on the magneto-optical disk 1 by the objective lens in the slider 11. Is read / written.

In the optical pickup having such a configuration, since the flying height of the slider 11 is substantially constant, the focusing control is not particularly performed, and the tracking control is performed by the operating part of the optical pickup device 5, that is, the main body 6, the prism 17, the suspension 13 and the slider 11 are moved along the guide 7 in the direction of the arrow.

[0011]

However, in the optical pickup device having the above configuration, since focusing is not performed, there are the following problems.

(1) When the temperature environment in the apparatus changes greatly, the distance between the objective lens in the slider 11 and the magneto-optical disk changes due to the change in air density, expansion and contraction of the suspension 13, and the like. Sufficient imaging performance cannot be obtained on the magnetic disk 1.

(2) Since the flow velocity of air is different between the inner and outer peripheral sides of the recording medium, a difference occurs in the flying height, and sufficient imaging performance cannot be obtained. The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical pickup device having a slider that is held at a predetermined distance from a recording medium by an air flow generated by a rotating recording medium, An object of the present invention is to provide an optical pickup device capable of performing focusing.

[0014]

According to a first aspect of the present invention, there is provided a slider provided with an objective lens and held at a predetermined distance from a recording medium by an air flow generated by a rotating recording medium. An optical pickup device comprising: a slider having a wing portion capable of changing an elevation angle.

By changing the elevation angle, the lift generated on the wings changes, the flying height of the slider changes, and optimum focusing can be performed. The invention according to claim 2 is
The wing portion according to the first aspect of the present invention includes a plurality of piezoelectric element bodies stacked in a lift generation direction, and changes an elevation angle by changing a voltage applied to each piezoelectric element body. Optical pickup device.

By changing the voltage applied to each of the stacked piezoelectric element bodies and changing the amount of expansion and contraction of each piezoelectric element body,
The elevation angle of the wing changes, the flying height of the slider changes, and optimum focusing is performed.

[0017]

Embodiments of the present invention will be described with reference to the drawings. First, the overall configuration of the optical pickup device according to the present embodiment will be described with reference to FIG. In the figure, a magneto-optical disk 51 as a recording medium is rotationally driven at high speed by a spindle motor 53.

The main body 56 of the optical pickup device 55 includes:
A roller 9 movably engaged with the guide 7 on the base 58 side is provided, and is movable in a direction crossing the track of the magneto-optical disk 51.

Further, the main body 56 is provided with a coil 67 disposed in a gap G of a magnetic circuit 65 comprising a yoke 61 and a magnet 63 provided on a base 58, and the magnetic circuit 65 and the coil 67 provide a moving coil. A main body 56 of the optical pickup device 55 is driven in a direction crossing the tracks of the magneto-optical disk 51 by passing a current through the coil 67.

The main body 56 of the optical pickup device 55
Is a small space with respect to the magneto-optical disk 51 due to the airflow generated by the rotation of the magneto-optical disk 51.
A slider 71 that floats (for example, 100 to 200 nm) is attached via a suspension 73.

On the base 58 side, a laser beam is guided 5
Laser light source and magneto-optical disk 51 emitted in the direction of 7
And a box 75 provided with a light detecting element for detecting a track error signal and a focus error signal while detecting information recorded on the magneto-optical disk 51 by receiving the reflected laser beam from the optical disc 51. I have.

Next, the slider 71 will be described with reference to FIG. 1 which is a cross-sectional view taken along the line AA of FIG. 2 and FIG. 3 which is a top view of FIG. The slider 71 has two stacked piezoelectric element bodies, that is, a first piezoelectric element body 201.
And a second piezoelectric element body 203 are provided.

Then, each of the laminated piezoelectric element bodies 201,
The voltage applied to 203 is changed, and each piezoelectric element body 201, 2
By changing the amount of expansion and contraction of 03, the elevation angle of the wing portion 200 changes.

Next, an optical system of the optical pickup according to this embodiment will be described with reference to FIG. (Emission optical system) Inside a box 75, a laser light source 91 for emitting a laser beam in the direction of the guide 57, and a laser light source 91
A coupling lens 93 for condensing the laser light flux emitted from the light source is provided. The focused laser beam is
The beam passes through the beam splitter 95, and is directed toward the magneto-optical disk 51 by the prism 97 provided at the tip of the main body 56, and enters the slider 71 through the through hole 56a provided in the main body 56.

(Imaging Optical System) A slider 71 has an objective lens 101 and a hemispherical lens (SIL: solid immersion lens) 1 which generates a small spot diameter and enables high density recording.
03 and so on.

(Reproduced Signal Optical System) The laser beam reflected by the magneto-optical disk 51 is reflected by the first beam splitter 95 via the objective lens 101 and the prism 97, and travels toward the second beam splitter 111. The light is reflected by the second beam splitter 111, collected by the lens 115, and reaches the photodetector 117.

A reproduction signal can be obtained by taking the output of the photodetector. (Focus error signal detection optical system) Magneto-optical disk 51
Of the laser beams reflected by the second beam splitter 111 are reflected by the third beam splitter 121, condensed by the lens 123, and passed through the knife edge 125 to the two light receiving surfaces 127 a, To a split photodetector 127 having a 127b.

The method of detecting a focus error signal according to the present embodiment is called a knife edge method. For example,
If the objective lens 101 and the magneto-optical disk 51 are too close, the spot on the light receiving surface of the two-part photodetector 122
As shown in FIG. 5 (a), one of the light receiving surfaces 127a is biased,
If the objective lens 101 and the magneto-optical disk 51 are too far apart, as shown in FIG.
7b.

On the other hand, at the time of focusing, as shown in FIG. Therefore, by obtaining a difference signal between the light receiving surfaces 127a and 127b, the focus error (F
E) A signal is obtained.

(Track Error Signal Detection Optical System) Of the laser beam reflected by the magneto-optical disk 51, the laser beam transmitted through the third beam splitter 121
The light is condensed at 1 and reaches a split photodetector 133 having two light receiving surfaces 133a and 133b.

The method of detecting a track error signal according to the present embodiment is called a push-pull method. Using the fact that
This is for obtaining a track error signal.

That is, for example, when the spot of the laser beam is deviated inward from the track, the spot on the light receiving surface of the two-segment photodetector 133 is, as shown in FIG. When it is deviated toward the surface 133a and out of the track, as shown in FIG. 6C, it deviates toward the other light receiving surface 133b.

On the other hand, at the time of focusing, as shown in FIG. Therefore, by obtaining a difference signal between the light receiving surfaces 133a and 133b, a track error (T
E) A signal is obtained.

Next, the electrical configuration of the servo system of the optical pickup of this embodiment will be described with reference to FIG. The control unit 153 includes each light receiving surface 127 of the two-divided photodetector 127.
The focus error signal (FE) obtained by calculating the difference between the outputs of the a and 127b by the differential amplifier 151 is input.

The control unit 153 supplies the output of each light receiving surface 133a, 133b of the split photodetector 133 to the track error signal (T
E) is also entered.

The coil drive circuit 157 drives the coil 67 to move the main body 50 of the optical pickup device 55 in a direction crossing the track of the magneto-optical disk 51, thereby performing tracking of the optical pickup device 55.

The first and second piezoelectric element driving circuits 159 and 161 are connected to the first and second piezoelectric element bodies 201 and 161 respectively.
The voltage applied to 203 is changed. Next, the operation of the above configuration will be described.

When the magneto-optical disk 51 is not rotating, the slider 71 is pressed on the magneto-optical disk 51 by the urging force of the suspension 73. When the magneto-optical disk 51 is driven to rotate at a high speed by the spindle motor 53, a force (lift) that causes the slider 71 to fly is generated on the slider 71 by the airflow generated on the magneto-optical disk 51, and the suspension 73 is attached. Ascends against the power.

The principle will be described. As shown in FIG.
Velocity in free space: If there is a flat plate in a fluid flowing at U (in the present embodiment, it is air, but the same applies to water and oil), air on the flat plate surface due to the adhesive force of air Speed becomes zero. Since the velocity in free space is U, it has a unique velocity distribution called the wall law from the flat plate to free space. The area where the speed is up to 99% of U is called the boundary layer.

The state of the flow in the boundary layer is a laminar flow layer called a laminar boundary layer near the tip of the flat plate, but after a certain critical point, the flow state is disturbed. Instead, the fluid moves in a direction perpendicular to the flow, and the flow as a whole is transformed into a disturbed flow.

However, in the very vicinity of the wall in the turbulent boundary layer, there is an area called a laminar low layer or a viscous low layer in which the viscous force is dominant and the flow is in the state. The transition from laminar flow to turbulent flow is based on the Reynolds number: R = Ux / ν (x is the distance from the tip of the flat plate, ν is the kinematic viscosity of the fluid, and kinematic viscosity = viscosity / density). It is known that it can be organized.

FIG. 9 illustrates this phenomenon on a rotating disk.
It is. When one disk rotates with a constant angular velocity: ω around its central axis Oz in still air, the air near the disk is dragged by the disk due to the viscous force of air and rotates (also in this case) , The velocity of the air on the face of the disk is zero), and at the same time the dragged air moves outward due to the centrifugal force created by the rotation.

Therefore, the air near the disk flows outward while rotating in a spiral shape. Furthermore,
Depending on the continuous flow conditions, air flows in from the outside toward the center of the disk to fill the trace of the air that has flowed out, where a single circulating flow is formed.

Assuming now that the thickness of the layer of air dragged by the disk is δ, this δ is considered to have properties equivalent to the thickness of the boundary layer of the flat plate. Boundary layer thickness on a flat plate: Since δ is known to be proportional to x / √R,
Instead of the distance x from the leading edge in the flat plate and the velocity U of the boundary layer outflow, when the radius r and the peripheral velocity rω are used as the corresponding amounts in the case of a disk, the boundary layer thickness: δ Corresponds to √ (ν / ω) and is independent of r. That is, the thickness of the boundary layer on the disk rotating at a constant angular velocity in the stationary uniform air is the same on the disk.

Considering the actual case of the magneto-optical disk 51, when the 3.5-inch magneto-optical disk 51 is rotated at the highest speed of 7,200 (rpm), the outermost edge where the peripheral speed rω becomes the highest is r Since the peripheral velocity at 1.75 inches is 33.5 (m / sec) and the kinematic viscosity ν of air is 0.0000155 (m ² / sec), its Reynolds number: R is about 96,000.

Generally, the transition region from laminar flow to turbulent flow has a Reynolds number: R of about 300,000 to 500,000, so that the boundary layer on the magneto-optical disk 51 is laminar. Further, from the empirical formula for giving the thickness δ of the boundary layer: δ = 5r / √R = 5 / √ (ω / ν), the thickness of the boundary layer is about 0.7 (mm). Since a laminar flow is formed inside the boundary layer along the rotation direction of the disk, it is very easy to control the force generated on the object in the boundary layer. Because in the turbulent boundary layer,
Since the flow is in a very turbulent state, it is very difficult to analyze and control the force generated on the object placed therein.

In the case of a 3.5-inch magneto-optical disk, the Reynolds number R at the outermost edge of the magneto-optical disk exceeds 300,000 when the rotational speed exceeds 23,000 (rpm) (at this time, the thickness δ of the boundary layer is about 0.4 8 (mm)), the boundary layer gradually transitions to turbulent flow. You must use an area called the low rise.

Next, the force applied to an object having a wing-shaped cross section in the low-viscosity layer in the laminar boundary layer or the turbulent boundary layer will be described with reference to FIG. In the figure, the wing flows at an elevation angle α
When placed in U, lift L, drag D, and moment M around the leading edge O of the wing act.

The chord length is l, the wing surface is x, z (perpendicular to the paper)
Assuming that the area projected on the plane is the wing area A, L, D, and M are L =
(ρU ² AC _L ) / 2, D = (ρU ² AC _D ) / 2, M = (ρU ² AlC _m ) / 2,
C _L the lift coefficient, the C _D of the drag coefficient.

FIG. 11 shows an example of the most important lift coefficient C _L and drag coefficient C _D. FIG. 11 shows values of the lift coefficient: C _L and the drag coefficient: C _D with respect to the elevation angle α, and C _L increases linearly with both α.

[0051] If the airfoil is vertically symmetrical, the elevation angle: alpha but is C _L is also 0 0, when there is warping in the airfoil, as shown in FIG. 11, when the alpha = 0 C _L> It becomes 0. Α is 15-20
° CL near the highest and becomes at about 1.5, when α is further increased, C _L decreases abruptly. This is because the flow along the upper surface of the blade separates from the surface of the blade.

It is considered that the smaller the value of C _D / C _L is, the better the performance of the wing is. In this example, α is around 9 °. Therefore, the flying of the slider 71 stops at the position where the flying force of the slider 71, that is, the lift L acting on the wing 200, and the urging force of the suspension 73 are balanced.

When the control section 153 supplies a current to the voice coil motor 10 via the coil driving circuit 157, the main body 56 of the optical pickup device 55 moves in a direction crossing the track of the magneto-optical disk 51, and moves on a desired track. Stop.

The laser beam emitted from the laser light source 91 in the box 75 is applied to the slider 71 by the prism 97.
And is converged on the magneto-optical disk 51 by the objective lens 101 in the slider 71, and information is read / written from / to the magneto-optical disk 51.

The control unit 153 receives a focus error signal (FE) obtained by calculating the difference between the output of each of the light receiving surfaces 127 a and 127 b of the split photodetector 127 by the differential amplifier 151.

Based on the focus error signal (FE), the controller 153 applies the first and second piezoelectric element bodies 201 and 203 via the first and second piezoelectric element drive circuits 159 and 161. Change the voltage.

Then, the amount of expansion and contraction of each of the piezoelectric elements 201 and 203 changes, the elevation angle of the wing 200 changes, and the slider 7
The flying height H of 1 is moved to a position where the objective lens 101 is focused, and focusing is performed.

Further, the control section 153 supplies the output of each light receiving surface 133a, 133b of the two-split photodetector 133 with the track error signal (T
E) is also entered.

Based on the track error signal (TE),
The control unit 153 controls the coil 6 via the coil driving circuit 157.
7, the main body 50 of the optical pickup device 55 is moved in a direction crossing the track of the magneto-optical disk 51, and tracking of the optical pickup device 55 is performed.

According to the above configuration, the elevation angle of the wing portion 200 is changed by changing the voltage applied to the stacked piezoelectric element members 201 and 203 and changing the amount of expansion and contraction of the piezoelectric element members 202 and 203. Thus, the flying height of the slider 71 changes, and optimum focusing can be performed.

The present invention is not limited to the above embodiment. Although the optical pickup device of the above-described embodiment is a direct-acting optical pickup using a linear motor, it goes without saying that the present invention can be applied to a swing-type optical pickup.

[0062]

As described above, according to the present invention, the slider is provided with a wing portion whose elevation angle can be changed. By changing the elevation angle, the lift generated on the wing portion changes, and the flying height of the slider changes. In addition, optimal focusing can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an invention part of an embodiment, and FIG.
3 is a cross-sectional view taken along a cutting line AA.

FIG. 2 is a diagram illustrating an overall configuration of an optical pickup device according to an embodiment.

FIG. 3 is a top view of FIG. 1;

FIG. 4 is a diagram illustrating an optical system of the optical pickup shown in FIG.

FIG. 5 is a diagram illustrating a light receiving surface of the two-segment photodetector in FIG.

FIG. 6 is a diagram illustrating a light receiving surface of the two-segment photodetector in FIG.

FIG. 7 is a diagram illustrating an electrical configuration of a servo system of the optical pickup according to the embodiment.

FIG. 8 is a diagram illustrating a state of a fluid near a flat plate when the fluid includes a flat plate.

FIG. 9 is a diagram illustrating a state of a fluid near a rotating disk.

FIG. 10 is a diagram illustrating a wing.

FIG. 11 is a diagram illustrating an example of a relationship between a lift coefficient: CL, a drag coefficient CD, and an elevation angle.

FIG. 12 is a diagram illustrating an example of a conventional optical pickup.

[Explanation of symbols]

 51 Magneto-optical disk (recording medium) 71 Slider 200 Wing

Claims (2)

[Claims] 1. An optical pickup device having an objective lens and a slider which is held at a predetermined distance from a recording medium by an air flow generated by a rotating recording medium, wherein the slider can change an elevation angle. An optical pickup device comprising a wing. 2. The wing portion is composed of a plurality of piezoelectric elements stacked in a lift generation direction, and changes an elevation angle by changing a voltage applied to each piezoelectric element. 2. The optical pickup device according to 1.