JP2001273656A - Objective lens driving device for optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid cost increase due to the use of an optical position detecting sensor and to avoid necessity of large electric power. SOLUTION: The device is constituted such that the magnet 5 constituting a magnetic circuit for driving an objective lens 2 is magnetized in the manner that magnetic fluxes vary in a direction for detecting the position of the objective lens 2 in the tracking direction, and that a magnetic detection sensor 30 mounted on a coil unit 3 is arranged in the magnetic gap 5g of the magnetic circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens driving device of an optical pickup which constitutes an optical disk device capable of optically reading information by projecting a light spot on a recording medium on a disk.

[0002]

2. Description of the Related Art An optical pickup constituting an optical disk apparatus generally comprises an objective lens driving device having an objective lens and an optical system for transmitting and receiving light to and from the objective lens. It has a structure in which an objective lens driving device is arranged. The objective lens driving device includes an objective lens, a focus coil, a movable unit including a tracking coil, and a fixed unit including a magnetic circuit.
The movable part is supported by the fixed part with four wires partially surrounded and held by an elastic damper material such as a viscoelastic material.

In an optical disk device that performs high-speed seek, an objective lens driving device constituting an optical pickup moves at high speed between different tracks in the radial direction of the optical disk to access and retrieves information from an information track. At this time,
The objective lens driving device moves at a high speed with the tracking servo turned off, but the movable portion supported by the four wires in a cantilever manner from the fixed portion cannot follow the movement of the fixed portion.
As a result, the objective lens mounted on the movable part vibrates in the track direction, vibrates even when it reaches the vicinity of a required track, and the speed detection of the optical pickup becomes inaccurate, or the tracking servo needs to be restarted. When making a withdrawal,
There is a problem that the tracking servo becomes unstable.

As means for suppressing such unnecessary vibration of the objective lens, means for detecting the amount of movement of the objective lens in the tracking direction and applying tracking servo has been proposed (for example, Japanese Patent Application Laid-Open No. 2-281431). .

More specifically, as shown in FIGS. 7 and 8, light emitting diodes 32 and 36 as light emitting elements, photodiodes 33 and 37 as light receiving elements, and a slit 34 provided on the front surface of the photodiodes 33 and 37. And detectors 30 and 35 for detecting the position of the unit 18 for holding the objective lens 3 in the directions of the arrows X ₁ and X _2.
Are provided on the base 23 at regular intervals in the directions of the arrows X ₁ and X ₂ , and between the light emitting diodes 32 and 36 and the photodiodes 33 and 37, the arrows X ₁ and X of the unit 18 are provided.
_It is provided in _two directions, and when the base 23 is stopped and the objective lens 3 is held at a predetermined position on the base 23, the positions are set so that the light receiving amounts of the photodiodes 33 and 37 become equal. The light shielding plates 16 and 17 provided in the directions of the arrows X ₁ and X _{2 of} the unit 18 are set.

[0006] Then, when the seek operation example on the base 23 starts to move in the arrow X ₁ or X ₂ direction at a high speed, the position of the base 23 and the unit 18 is displaced, the amount of light received by the photodiode 33, 37 is not equal to one another . Based on the difference, the tracking coils 4, 5, 7, and 8 are energized via a differential amplifier, a driver circuit, and the like, to return the objective lens 3 to a predetermined position on the base 23. 7 and 8, 6 and 9 are focus coils, and 12, 13, and 15 are leaf spring members.

[0007]

However, in this prior art, an optical position detection sensor is used to detect the position of the objective lens 3 in the tracking direction, and a new light emitting element or the like is prepared. Because of the necessity, the cost was increased. Another problem is that a large amount of power is required to drive the light emitting element.

The present invention has been made for the purpose of solving such problems of the prior art.

[0009]

Means for solving the above problems will be described below with reference to FIG. 1 corresponding to an embodiment.
explain. According to the present invention, a magnet 5 constituting a magnetic circuit for driving the objective lens 2 is magnetized so that a magnetic flux density changes in a direction of detecting a position of the objective lens 2 in a tracking direction, and a coil unit. 3
The magnetic detection sensor 30 mounted on the magnetic circuit is disposed in the magnetic gap 5g of the magnetic circuit.

In such a configuration, when the objective lens 2 moves in the tracking direction T, the magnetic detection sensor 30 also moves, and the magnetic flux density detected by the magnetic detection sensor 30 changes. Since the position of the objective lens 2 in the tracking direction T is detected from the amount of change, the magnetic detection sensor 30 functions as a position detection sensor in the tracking direction T.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a perspective view showing an embodiment of the present invention. In FIG. 1, 1 is a lens holder, 2 is an objective lens, 3 is a coil unit, 5 is a magnet, 5 g
Is a magnetic gap, and 30 is a magnetic detection sensor.

The lens holder 1 is made of a light metal having a high flexural modulus, for example, a magnesium alloy or a resin made of carbon fiber. Through the use of such materials,
The bending elastic modulus of the lens holder 1 itself increases, and the higher-order resonance frequency increases. Thereby, it is possible to cope with an increase in the speed of the optical disk device.

The lens holder 1 has a tracking direction T
Are formed with two notches 1a. The thickness of the objective lens mounting portion 1b for holding the objective lens 2 is uniform.

The notch 1a has a reinforcing insulating protective film (not shown) formed on the surface thereof. This is because light metal having a high flexural modulus, such as a magnesium alloy, or a resin made of carbon fiber used for the lens holder 1 has a high conductivity, so that the insulating property of the coil unit 3 attached to the notch 1a is high. This is to ensure. When the insulating protective film for reinforcement is not formed on the surface of the cutout portion 1a of the lens holder 1, the insulating protective film for reinforcement (not shown) is provided on the coil unit 3 attached to the cutout portion 1a. Z)
Is formed to ensure the insulation of the coil unit 3.

The coil unit 3 is formed by laminating a required number of printed circuit boards 3p on which one tracking coil 3t and four focus coils 3f are formed. The tracking coil 3t is arranged at the center of the printed circuit board 3p, and the four focus coils 3f are arranged on both sides of the tracking coil 3t in upper and lower stages.
Note that the focus coil 3f may be composed of two pieces.

The coil unit 3 is fixed to the lens holder 1 by being inserted into and bonded to the notch 1a. Four V-grooves 3v are formed at both ends of the coil unit 3 in the tracking direction T, and one ends of the four conductive elastic bodies 4 are fixed to the V-grooves 3v by solder 3h.

A through hole (not shown) is formed in a hollow portion of the tracking coil 3t, and the magnetic detection sensor 30 is disposed and fixed so as to be embedded therein. As the magnetic detection sensor 30, a magneto-electric element such as a magneto-resistance effect element and a Hall element is used. The magnetic detection sensor 30 is less expensive than an optical position detection sensor composed of a light emitting element or the like, and does not require a large amount of power to drive. .

The magnet 5 is magnetized so that the magnetic flux density changes in the tracking direction T. When the magnetism detection sensor 30 moves in the tracking direction T, the magnet 5
The pole and the south pole are switched in the tracking direction, that is, as shown in FIG. 2, the two poles are magnetized by the boundary line 5b between the north pole and the south pole in the tracking direction T. 7 is adhered. A magnetic gap 5g is formed by the opposition of the two magnets 5,
In the tracking direction T of the magnetic gap 5g, the direction of the line of magnetic force B is reversed. Note that the magnet 5 is
It may be composed of individual pieces.

The magnetic flux density in the magnetic gap 5g is:
With the boundary 5b between the N pole and the S pole as a reference, the polarity increases toward the N pole, and the polarity reverses and increases as the position approaches the S pole.

As shown in FIG. 3, the width W of the magnet 5 at the stationary position of the movable portion movably supported by the conductive elastic body 4 in a cantilever manner, that is, at its own weight position in the focus direction F, When the coil unit 3 is disposed in the magnetic gap 5g, of the vertical sides parallel to the focus direction F of the focus coil 3f, the right and left outer vertical sides a and c are within the magnetic gap 5g (within the width W of the opposing magnet 5). (Refers to a gap). As shown in FIG. 3, the height H of the magnet 5 is parallel to the upper and lower inner horizontal sides b and d and the focus direction F of the tracking coil 3t among the horizontal sides perpendicular to the focus direction F of the focus coil 3f. Vertical side A,
C is set so as to be arranged in the magnetic gap 5g (refer to a gap within the height H of the opposed magnet 5). The boundary line 5b between the N pole and the S pole of the magnet 5 is located in the middle of the vertical sides A and C parallel to the focus direction F of the tracking coil 3t. The center of the magnet 5 is
It substantially coincides with the center of the coil unit 3.

In FIG. 3, a driving force is generated in the same direction in the tracking direction T by the current flowing through the vertical sides A and C parallel to the focus direction F of the tracking coil 3t.
The current flowing through the horizontal sides b and d perpendicular to the focus direction F of the focus coil 3f causes the focus direction F
, A driving force in the same direction is generated.

The magnet 5 constitutes a drive source in the focus direction F and the tracking direction T, and also constitutes a tracking direction position detection sensor without deteriorating the drive sensitivity of the objective lens driving device.

The above is the case where the magnet 5 is magnetized in two poles in the tracking direction T by the boundary line 5b between the N pole and the S pole. As shown in FIG. The same effect can be obtained even if two poles are magnetized by the boundary line 5b between the N pole and the S pole. In this case, as shown in FIG. 5, the focus coil 3f is connected to the printed circuit board 3p.
And the four tracking coils 3t are
It is arranged on both sides of the focus coil 3f in two upper and lower stages. The magnetic detection sensor 30 is not affected when the objective lens 2 moves in the focus direction F, and detects the position only when the objective lens 2 moves in the tracking direction T.
It is arranged away from the boundary line 5b between the pole and the south pole. Further, 4 ends are provided at both ends of the coil unit 3 in the tracking direction T.
One V-groove 3v is formed, and one end of each of the four conductive elastic bodies 4 is fixed to the V-groove 3v by solder 3h. Note that the tracking coil 3t may be composed of two pieces.

In this case, the width W of the magnet 5 is shown in FIG. 6 at the stationary position of the movable portion movably supported by the conductive elastic body 4 in a cantilever manner, that is, at its own weight position in the focus direction F. As described above, when the coil unit 3 is disposed in the magnetic gap 5g, of the vertical sides parallel to the focus direction F of the tracking coil 3t, the right and left inner vertical sides A and C are within the magnetic gap 5g (the width of the facing magnet 5). (Indicating a gap within W). The height H of the magnet 5 is
As shown in FIG. 6, vertical sides a and c parallel to the focus direction F of the focus coil 3f and the tracking coil 3
The horizontal sides B and D on the upper and lower sides of the horizontal sides perpendicular to the focus direction F of t are determined so as to be arranged in the magnetic gap 5g (indicating a gap within the height H of the opposed magnet 5). ing. The boundary line 5b between the N pole and the S pole of the magnet 5 corresponds to the focus direction F of the tracking coil 3t.
Are located in the middle between the lower side B and the upper side D of the horizontal sides B and D perpendicular to the horizontal side. The center of the magnet 5 substantially matches the center of the coil unit 3.

In FIG. 6, a driving force is generated in the tracking direction T in the same direction by currents flowing through the vertical sides A and C parallel to the focus direction F of the tracking coil 3t.
The current flowing through the horizontal sides b and d perpendicular to the focus direction F of the focus coil 3f causes the focus direction F
, A driving force in the same direction is generated.

The coil unit 3 is disposed in the magnetic gap 5g, and the other end of the conductive elastic body 4 is fixed to the base substrate 9 through the wire base 8 by soldering. Thereby, while the magnetic detection sensor 30 mounted on the coil unit 3 is arranged in the magnetic gap 5g,
The lens holder 1 is movably supported in a cantilever manner with respect to a fixed portion including a magnet 5, a yoke base 6, a yoke 7, a wire base 8, and a base substrate 9.

With such a configuration, the focus coil 3
f, if the tracking coil 3t is energized, a driving force is generated in the focus direction F and the tracking direction T, and the objective lens 2 can be moved in the focus direction F and the tracking direction T according to the surface deflection and eccentricity of the recording medium. it can.

Then, during the seek operation, when the fixed portion starts moving in the tracking direction T at a high speed, the positions of the magnet 5 and the magnetic detection sensor 30 are shifted, and the magnetic detection sensor 30 detects the position of the objective lens 2. Based on this detection,
By energizing the tracking coil 3t via a driver circuit or the like, the objective lens 2 is returned to a predetermined position of the fixed portion.

In the above description, the magnetic detection sensor 30 functions as a position detection sensor in the tracking direction T. By magnetizing the magnet 5 so that the magnetic flux density changes in the focus direction F, the magnetic detection sensor 30 Can also function as a position detection sensor.

[0031]

As described above, the present invention provides:
A magnet constituting a magnetic circuit for driving the objective lens is magnetized so that a magnetic flux density changes in a direction for detecting a position of the objective lens in a tracking direction, and a magnetism detection attached to a coil unit. A sensor is disposed in a magnetic gap of the magnetic circuit. Therefore, when the objective lens moves in the tracking direction, the magnetic detection sensor also moves, and the magnetic flux density detected by the magnetic detection sensor changes, and the position of the objective lens in the tracking direction is detected from the amount of change. Therefore,
According to the present invention, it is possible to obtain an effect that it is possible to avoid an increase in cost due to the use of an optical position detection sensor and a necessity of large power.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an embodiment of the present invention.

FIG. 2 is a plan view showing a magnetic circuit.

FIG. 3 is a layout diagram showing a positional relationship between a magnet and a focus coil / tracking coil at a position of its own weight in a focus direction according to an embodiment of the present invention.

FIG. 4 is a side view showing a magnetic circuit.

FIG. 5 is an exploded perspective view showing another embodiment of the present invention.

FIG. 6 is a layout diagram showing a positional relationship between a magnet and a focus coil / tracking coil at a position of its own weight in a focus direction in another embodiment of the present invention.

FIG. 7 is a perspective view of a conventional technique.

FIG. 8 is a plan view of a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens holder 2 Objective lens 3 Coil unit 3f Focus coil 3t Tracking coil 5 Magnet 5g Magnetic gap 30 Magnetic detection sensor

Claims (3)

[Claims] 1. A magnet constituting a magnetic circuit for driving an objective lens is magnetized so that a magnetic flux density changes in a direction of detecting a position of the objective lens in a tracking direction, and is provided in a coil unit. An objective lens driving device for an optical pickup in which a mounted magnetic detection sensor is disposed in a magnetic gap of the magnetic circuit. 2. The objective lens driving device for an optical pickup according to claim 1, wherein the magnet is magnetized to have two poles in the tracking direction. 3. The objective lens driving device for an optical pickup according to claim 1, wherein the magnet is magnetized to two poles in the focus direction.