JP2000099972A - Optical pickup and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup and an optical disk device in which generation of dynamic skewness is suppressed. SOLUTION: The device is provided with a holding member 31, which holds a light converging means 22 in a moving capable manner in two axis directions, focusing coils 34 and tracking coils 35, which are arranged on the movable section including the means 22 and the member 31 or a fixed section 32, focusing magnets 36 and tracking magnets 37, which are arranged on the fixed section or the movable section so as to oppose these coils, and a two axis actuator 30 having the yokes related to these magnets and coils. Among these focusing coils and the tracking coils, at least a pair of plural coils are individually driven so that the driving currents are mutually unbalanced in the pair of coils.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in an optical disk device for recording and reproducing information signals on an information recording medium such as an optical disk, and an optical disk device using the same.

[0002]

2. Description of the Related Art Conventionally, reproduction or recording of information signals on an information recording medium such as an optical disk, for example, a so-called compact disk (CD) or magneto-optical disk (MO) is performed using an optical pickup. This optical pickup includes a semiconductor laser as a light source, an objective lens as a light focusing means, an optical system, a photodetector, and the like. In an optical pickup, a light beam emitted from a semiconductor laser is focused on a recording surface of an optical disk by an objective lens via an optical system. The return light beam from the optical disc is separated from the light beam emitted from the semiconductor laser by the optical system and guided to the photodetector.

A light beam emitted from a semiconductor laser is
The position of the objective lens in the optical axis direction is adjusted so that it is focused on the recording surface of the optical disk by following the displacement of the optical disk in the direction orthogonal to the surface direction of the optical disk that occurs due to the warp of the optical disk. Is done. At the same time, the position in the direction perpendicular to the optical axis of the objective lens is adjusted so that the position of the spot on the optical disk of the light beam emitted from the semiconductor laser follows the eccentricity of the optical disk or the meandering of the track formed on the optical disk. Is done. The in-focus position of the light beam emitted from the semiconductor laser and the spot position on the recording surface of the optical disk are adjusted by adjusting the position of the objective lens in the direction of the optical axis of the objective lens and in the direction perpendicular to the optical axis. Done by An electromagnetically driven actuator is used to adjust the position of the objective lens.

This actuator is called an objective lens actuator or a biaxial actuator, and has a holding member to which an objective lens is attached, a supporting portion for supporting the holding member movably in two axial directions, and a drive for generating a driving force. Department and contains. The holding member slides along a rotation axis provided on the fixed portion, whereby the position of the objective lens in the optical axis direction, that is, the focusing position is adjusted, and by rotating around the rotation axis, It is supported so that the position in the direction substantially perpendicular to the optical axis of the objective lens, that is, the tracking position is adjusted. Less than,
An example of this two-axis actuator will be described with reference to FIGS.

First, in FIGS. 6 and 7, a biaxial actuator 1 includes an objective lens 2, a holding member 3 for holding the objective lens, and the holding member 3 in two axial directions, ie, a focusing direction and a tracking direction. And a fixed portion 4 that is movably supported. The holding member 3 is supported so as to be rotatable around the axis and slidable along the axis with respect to a rotating shaft (main shaft) 4 a vertically planted near the center of the fixed portion 4. The lens 2 has substantially the symbol Tr
It is movably supported in a tracking direction indicated by k and a focusing direction indicated by reference Fcs.

The holding member 3 has a pair of focusing coils 3a and a pair of tracking coils 3b mounted on opposite surfaces thereof. And
On the fixed portion 4, so as to face the focusing coil 3 a and the tracking coil 3 b, respectively.
A focusing magnet 5 and a tracking magnet 6 are provided. Here, each magnet 5, 6
Are fixed to the yoke 4b raised from the side edge of the fixing portion 4 by bonding or the like.

When the focus coil 3a is energized, the magnetic flux generated in the coil 3a
The objective lens 2 moves substantially in the tracking direction indicated by the arrow Trk by interacting with the magnetic flux generated by the focusing magnet 5 attached to the main body, whereby the entire holding member 3 rotates about the main shaft 4a. Will be done. On the other hand, when the tracking coil 3b is energized, similarly, the magnetic flux generated in the coil 3b interacts with the magnetic flux generated by the tracking magnet 6 attached to the fixed part 4, so that the holding member 3 When the whole slides in the vertical direction along the main shaft 4a, the objective lens 2 is moved in the focusing direction indicated by the arrow Fcs.

According to the biaxial actuator 1 configured as described above, when a driving voltage is supplied to each of the coils 3a or 3b from the outside, the magnetic flux generated in each of the coils 3a and 3b causes the magnetic flux to be generated in the magnets 5 and 6 respectively. The holding member 3 rotates or slides with respect to the main shaft 4a by interacting with the magnetic flux generated by the main shaft 4a. Therefore, the objective lens 2 attached to the holding member 3 is appropriately moved in the focusing direction and the tracking direction. By performing focusing and tracking in this manner, the light beam from the light source of the optical pickup is irradiated on the signal recording surface of the optical disk via the objective lens 2, and the return light from the signal recording surface of the optical disk is The light again enters the optical detector of the optical pickup via the objective lens 2. Therefore, the information signal recorded on the signal recording surface of the optical disk is read.

The two-axis actuator 7 shown in FIG.
Is a mounting member 4 provided on the fixed portion 4 via an elastic holding member 8 such as a pair of left and right leaf springs and wires.
It is supported movably in two axial directions with respect to c. Further, in the two-axis actuator 7, a magnet 9 attached to the yoke 4d raised from the fixed portion 4 by bonding or the like is provided with a focusing coil 3a and a pair of tracking coils 3b provided on the holding member 3.
, Focusing or tracking is performed.

[0010]

However, the two-axis actuators 1 and 7 having such a configuration have the following problems. That is, in the two-axis actuator 1, the focusing coil 3a and the tracking coil 3b are respectively connected to a drive circuit. For example, as shown in FIG. 8, a pair of focusing coils 3a are connected in series to a driving circuit 3c, and a pair of tracking coils 3b are similarly connected to a driving circuit (not shown). They are connected in series. Thereby, for example, the same drive current flows from the drive circuit 3c to each of the focusing coils 3a, thereby generating a magnetic flux and interacting with the magnetic flux of the opposed magnet 5, thereby making the focusing coil 3a
Then, a force in the focus direction acts on the holding member 3.

At this time, the individual focusing coils 3a
The two magnetic circuits formed by the magnets 5 facing each other are unbalanced with each other because of variations. Further, the two-axis actuator 1 is configured as a so-called shaft sliding type, and a slight gap is required between the holding member 3 and the main shaft 4a so that the holding member 3 is driven to rotate with respect to the main shaft 4a. It is. Therefore, when the holding member 3 slides along the main shaft 4a, the holding member 3
, The gap causes a mechanical imbalance about the main shaft 4a. As a result, the objective lens 2 is slightly tilted due to variations in these magnetic circuits and mechanical imbalance due to the gap with respect to the main shaft 4a. That is, when the objective lens 2 is driven, the objective lens 2 ideally translates in parallel without tilting, but in reality, the objective lens 2 tilts with respect to the optical axis to have a small angle (hereinafter, referred to as a tilt angle). , Called dynamic skew).

In the two-axis actuator 7,
Focusing and tracking are performed by the elastic deformation of the elastic holding member 8 in the horizontal direction and the vertical direction. Therefore, the operations in the two directions interfere with each other, and the objective lens 2 is not moved (driven) to an appropriate position. There was a problem that would.

SUMMARY OF THE INVENTION In view of the above, it is an object of the present invention to provide an optical pickup and an optical disk device that can suppress the occurrence of dynamic skew.

[0014]

According to the present invention, there is provided a light source for irradiating a light beam emitted from the light source so as to be focused on a signal recording surface of a rotationally driven optical disk. Focusing means, a photodetector on which a return light beam from the signal recording surface of the optical disk is incident, a holding member for holding the light focusing means movably in two axial directions, and a movable member including the light focusing means and the holding member A focusing coil and a tracking coil disposed in a fixed portion or a fixed portion; a focusing magnet and a tracking magnet disposed in the fixed portion or the movable portion so as to face these coils; and the magnet and each coil An optical pickup comprising a two-axis actuator having a yoke associated with the focusing coil and the tracking coil. Of yl, be composed of an even number of coils to be at least one of pair, the coil comprising this pair is achieved by the drive current is driven individually so that the unbalanced to each other.

Further, according to the present invention, there is provided a drive unit for rotating an optical disk, and irradiating the rotating optical disk with light through a light converging unit, from a signal recording surface from the optical disk. An optical pickup for detecting the return light of the light through the light focusing means, a holding member for holding the light focusing means movably in two axial directions, and a movable or fixed part including the light focusing means and the holding member. 2 comprising a focusing coil and a tracking coil provided, a focusing magnet and a tracking magnet disposed on a fixed portion or a movable portion so as to face these coils, and a yoke associated with the magnet and each coil. A shaft actuator; a signal processing circuit for generating a reproduction signal based on a detection signal from the optical pickup; A servo circuit that moves the light focusing means in two axial directions based on a detection signal from an optical pickup, wherein at least one of the focusing coil and the tracking coil is paired with each other. This pair of coils is constituted by an even number of coils, and the paired coils are individually driven such that their drive currents are unbalanced with each other.

According to the above configuration, an even number of focusing coils or tracking coils forming a pair are individually driven such that their driving currents are unbalanced with each other, so that one of the coils is generated in one of the coils. The generated magnetic flux is larger than the magnetic flux generated in the other coil. As a result, an unbalance occurs in the driving force acting on the coil due to the interaction with the magnetic field of the focusing magnet or the tracking magnet. Therefore, when the holding member and the light focusing means move in the focus direction or the tracking direction,
By intentionally applying an unbalanced driving force, variations in the magnetic circuit including the coil on one side and the magnetic circuit including the coil on the other side and mechanical imbalance at the time of moving the holding member are cancelled. Become. As a result, the occurrence of dynamic skew during focusing or tracking is significantly suppressed. In the case of the shaft sliding type two-axis actuator, when the holding member moves along the main shaft, a slight inclination of the holding member with respect to the main shaft caused by a gap between the main member and the main shaft is suppressed. Will be. In the case of a two-axis actuator using an elastic holding member, mutual interference of driving in two directions is suppressed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Note that the embodiments described below are preferred specific examples of the present invention,
Although various technically preferable limits are given, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

FIG. 1 shows the basic configuration of an embodiment of an optical disk device incorporating an optical pickup according to the present invention. The optical disk device 10 includes an optical disk 11
Spindle motor 12 as a driving means for rotationally driving the motor
And an optical pickup 20 for irradiating a signal recording surface of the rotating optical disk 11 with a light beam to record a signal, reproducing a recorded signal by a return light beam from the signal recording surface, and a control unit 13 for controlling these. It has. Here, the control unit 13 includes an optical disk controller 14, a signal demodulator 15, an error correction circuit 16, an interface 1
7, a head access control unit 18 and a servo circuit 19 are provided.

The optical disk controller 14 controls the drive of the spindle motor 12 at a predetermined rotation speed. The signal demodulator 15 demodulates the recording signal from the optical pickup 20, corrects the error, and sends the signal to an external computer or the like via the interface 17. Thus, an external computer or the like can receive a signal recorded on the optical disk 11 as a reproduction signal. The head access control unit 18 moves the optical pickup 20 to a predetermined recording track on the optical disk 11, for example, by a track jump or the like. The servo circuit 19 moves the objective lens held by the biaxial actuator of the optical pickup 20 in the focusing direction and the tracking direction at the moved predetermined position.

FIG. 2 shows the structure of the optical pickup 20 incorporated in the optical disk device 10. The optical pickup 20 includes a light receiving / emitting element 21 and an objective lens 22. The light receiving and emitting element 21 is configured by integrating a semiconductor laser element as a light emitting element and a photodetector as a light receiving element. Objective lens 22
Is a convex lens, and forms an image of a light beam from the light receiving / emitting element 21 on a desired track on a signal recording surface of the optical disk 11 that is driven to rotate. Further, the objective lens 22
Is supported by a biaxial actuator according to the present invention described in detail below so as to be movable in two axial directions, that is, a tracking direction and a focusing direction.

FIG. 3 and FIG.
0 shows the configuration of a two-axis actuator incorporated in the actuator. In FIG. 3, the biaxial actuator 30 is configured as a shaft sliding type, and has a holding member 31 for holding the objective lens 22, and the holding member 31 can be moved in two axial directions, that is, in a focusing direction and a tracking direction. And a fixing portion 32 for supporting the fixing portion. The holding member 31
The objective lens 22 is substantially supported by being supported so as to be rotatable around the axis and slidable along the axis with respect to a rotation shaft (main shaft) 33 vertically implanted near the center of the fixed portion 32. The tracking direction and the code Fcs indicated by the code Trk
Are supported so as to be movable in the focusing direction indicated by. In addition, the holding member 31 has surfaces opposite to each other,
A pair of focusing coil 34 and tracking coil 35 are attached to each. Each of these coils 34 and 35 is configured to be flat in the illustrated case.

The focusing coils 34
A pair of focusing magnets 36 and a pair of tracking magnets 37 are provided on the fixed portion 32 so as to face the tracking coils 35, respectively. Here, the focusing magnet 36 is formed in a substantially square shape and is divided into two equal parts by a vertical dividing line. For example, the right side is an S pole and the left side is an N pole when viewed from the main shaft 33 side. It is magnetized in two poles. Then, the focusing magnet 36 is fixed to the fixed portion 3.
2 is fixed to the yoke 32a raised from the side edge by bonding or the like. Thus, the pair of focusing magnets 36 are arranged point-symmetrically about the main shaft 33.

On the other hand, the tracking magnet 37 has a substantially square outer shape,
It is divided into two equal parts by a horizontal dividing line, and is, for example, magnetized in two poles such that the lower side is an S pole and the upper side is an N pole when viewed from the main shaft 33 side. And the tracking magnet 37
Is similarly fixed to the yoke 32b raised from the side edge of the fixing portion 32 by bonding or the like. As a result, the pair of tracking magnets 37 is
Are arranged symmetrically about the point. The fixed portion 32 is entirely made of a magnetic material, so that the yokes 32a and 32b constitute a magnetic circuit.

When the focus coil 34 is energized, the magnetic flux generated in the coil 34 is
2 interacts with the magnetic flux from the focusing magnet 36 attached to the lens 2, whereby the entire holding member 31 rotates around the main shaft 33, so that the objective lens 22 substantially moves in the tracking direction indicated by the arrow Trk. Will be moved. On the other hand, when the tracking coil 35 is energized, similarly, the magnetic flux generated in the coil 35 interacts with the magnetic flux generated by the tracking magnet 37 attached to the fixed portion 32, thereby causing the holding member 31. When the whole slides vertically along the main shaft 33, the objective lens 22 moves in the direction of the arrow Fcs.
Is moved in the focusing direction indicated by.

The above configuration is substantially the same as the conventional optical pickup and the conventional two-axis actuator 1 shown in FIGS. 6 and 7, but the optical pickup 20 according to the present embodiment has the two-axis actuator The driving circuit of the focusing coil 34 and the tracking coil 35 in 30 has a different configuration in that it is configured as follows. First, the focus coil 3
4, as shown in FIG. 4, the two pairs of coils 34 a and 34 b include a servo circuit 1 in series with each other.
9, two resistors connected in series to each other, variable resistors 41, 4 in the illustrated case.
2 are connected in parallel, and furthermore, the center, that is, the coils 34a,
A controllable power supply 43 is connected between the variable resistor 34b and the variable resistors 41 and 42. Thereby, each coil 34
a, 34b and variable resistors 41, 42 and a controllable power supply 4
3 constitutes a bridge circuit.

The variable resistors 41 and 42 are connected to the individual coils 34
a and 34b are relatively adjusted in current level. The controllable power supply 43 includes two coils 34a, 34
A DC (direct current) offset is superimposed relatively between b, and this offset is appropriately adjusted. Thus, by adjusting the variable resistors 41 and 42 and controlling the controllable power supply 43, each of the coils 34a and 34b is controlled.
Are adjusted to be unbalanced with each other. The drive circuit 40 can be easily and inexpensively configured by a simple configuration in which variable resistors 41 and 42 and a controllable power supply 43 are added to the conventional drive circuit. . The tracking coil 37 is also driven by a drive circuit (not shown) similarly configured as a bridge circuit.

The optical disk device 10 according to the present embodiment
When the optical disk 11 is reproduced, the light receiving / emitting element 2 of the optical pickup 20 is configured as described above.
One semiconductor laser element emits light, and this light beam is focused on the signal recording surface of the optical disk 11 via the objective lens 22. The return light from the optical disc 11 again enters the photodetector of the light emitting / receiving element 21 via the objective lens 22.
As a result, a reproduction signal, a focusing error signal, and a tracking error signal relating to the optical disk 11 are detected based on the detection signal from the photodetector, and the recording signal of the optical disk 11 is reproduced.

At this time, the servo circuit 1 is controlled based on the focusing error signal and the tracking error signal.
9 is a focusing coil 34 of the biaxial actuator 30
By controlling the drive current to the tracking coil 35, the tracking and focusing of the objective lens 22 are performed. That is, currents based on the focusing servo signal and the tracking servo signal are supplied to the focusing coil and the tracking coil of the two-axis actuator 30, respectively. As a result, the magnetic flux generated from the focusing coil 34 and the tracking coil 35 and the magnets 36, 3
7, the interaction with the magnetic flux by the coils 34, 35
As a result, a driving force in the direction of the main shaft 33 and a rotating force around the main shaft 33 are generated, and the holding member 31, that is, the objective lens 22 is driven in the focusing direction Fcs and the tracking direction Trk.

In this case, the focusing coil 34 includes a pair of coils 34a and 34b,
Adjustable and controllable power supply 43 for zero variable resistors 41 and 42
, The drive currents are adjusted so as to be unbalanced with each other. Thereby, each coil 34a, 34b
Due to the interaction between the magnetic flux and the focusing magnet 36, the driving forces acting on the coils 34a and 34b become unbalanced with each other. Therefore, even if there is a variation in the magnetic circuits of the coils 34a and 34b and a mechanical imbalance due to the gap between the holding member 31 and the shaft 33, the variations and dynamics of these magnetic circuits are caused by the unbalanced driving force described above. Since the imbalance is canceled, the inclination of the objective lens 22 held by the holding member 31 with respect to the optical axis, that is, the occurrence of dynamic skew is greatly suppressed. As a result, the signal quality of the optical pickup 20 and the optical disk device 10 when recording or reproducing the optical disk is improved. Further, with respect to the tracking coil 35, the variation of the magnetic circuit and the mechanical imbalance are similarly canceled.

Here, the adjustment of the currents of the individual coils 34a and 34b by the drive circuit 40 is performed as follows. The drive circuit 40 is represented as an equivalent circuit shown in FIG.
4b are Z1 and Z2, and the variable resistor 4b
Assume that the impedances of the power supplies 1 and 42 are Z3 and Z4, the internal resistance of the controllable power supply 43 is Rg, and the voltage is Eg. Further, a current flowing through a closed circuit including the coil 34a, the controllable power supply 43 and the variable resistor 41 is denoted by j1, and a current flowing through a closed circuit including the coils 34a and 34b and the variable resistors 42 and 41 is denoted by j2. Further, the drive voltage by the servo circuit 19 is E and the drive current is j3.

The currents j1 and j2 are respectively

(Equation 1)

(Equation 2) It is represented by Where Δ is

(Equation 3) , And from these equations, each coil 34a, 34b
Are obtained, I1 = j1 + j
2, I2 = j2, so from the closed circuit equation, Δ is
That is, the above equation (3) is obtained.

(Equation 4)

(Equation 5) Therefore, the currents I1 and I2 are determined by the impedances Z3 and Z4 of the variable resistors 41 and 42 and the voltage Eg of the controllable power supply 43, respectively. Therefore, it can be understood that the current flowing through each of the coils 34a and 34b can be adjusted by adjusting the variable resistors 41 and 42 and controlling the controllable power supply 43.

In the above-described embodiment, the drive circuit 40 for the focusing coil 34 and the tracking coil 35 includes the variable resistors 41 and 42. Obviously, a fixed resistance may be used if the mechanical imbalance is canceled. In the above-described embodiment, the two-axis actuator 30 is configured as a shaft sliding type. However, the present invention is not limited to this, and at least one of the focusing coil and the tracking coil is an even number of pairs. If it is composed of individual coils, it can be applied to a two-axis actuator having a configuration in which the elastic holding member such as a wire or a leaf spring or the holding member is supported by a resin elastic holding member so as to be movable in two axial directions. The present invention can be applied. In the embodiment described above, the optical disk device 10 and the optical pickup 20
Is an example, and the present invention can be applied to other configurations, for example, an optical disk device or an optical pickup for recording / reproducing a magneto-optical disk.

[0033]

As described above, according to the present invention, the occurrence of dynamic skew can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical disk device incorporating an optical pickup according to the present invention.

FIG. 2 is a schematic diagram showing a configuration of an embodiment of an optical pickup in the optical disk device of FIG. 1;

FIG. 3 is a schematic perspective view showing a configuration of a biaxial actuator in the optical pickup of FIG. 2;

FIG. 4 is a block circuit diagram showing a driving circuit of a focusing coil in the two-axis actuator of FIG. 3;

FIG. 5 is a circuit diagram showing an equivalent circuit of the drive circuit shown in FIG. 4;

FIG. 6 is a schematic perspective view showing an overall configuration of an example of a conventional two-axis actuator for an optical pickup.

FIG. 7 is a schematic plan view of the biaxial actuator of FIG. 7;

FIG. 8 is a circuit diagram showing a drive circuit of a focusing coil in the biaxial actuator of FIG. 7;

FIG. 9 is a schematic perspective view showing the overall configuration of another example of a conventional two-axis actuator for an optical pickup.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Optical disk apparatus, 11 ... Optical disk apparatus, 12 ... Spindle motor, 13 ... Control part,
14 ... optical disk controller, 15 ... signal demodulator, 16 ... error correction circuit, 17 ... interface, 18 ... head access control unit, 19 ...
Servo circuit, 20 ... Optical pickup, 21 ...
Light receiving / emitting element, 22 ... objective lens, 30 ... biaxial actuator, 31 ... holding member, 32 ... fixed part, 32a, 32b ... yoke, 33 ... spindle, 3
4 ... Focusing coil, 35 ... Tracking coil, 36 ... Focusing magnet, 37
..Tracking magnets, 40... Drive circuits,
41, 42: variable resistor, 43: controllable power supply

Claims (4)

[Claims] A light source; a light converging means for irradiating a light beam emitted from the light source so as to focus on a signal recording surface of a rotationally driven optical disk; and returning light from the signal recording surface of the optical disk. A light detector on which a beam is incident; a holding member for holding the light focusing means so as to be movable in two axial directions; a focusing coil and tracking disposed on a movable or fixed part including the light focusing means and the holding member And a two-axis actuator having a focusing magnet and a tracking magnet disposed on the fixed portion or the movable portion so as to face these coils, and a yoke associated with the magnet and each coil. An optical pickup, wherein at least one of the focusing coil and the tracking coil is an even pair. It is composed of a number of coils, coil, an optical pickup, characterized in that the drive current is driven individually so that the unbalanced with each other to be the pair. 2. A bridge comprising the pair of coils connected in series with each other, and connected to the coil by two resistors connected in series with each other and having a centrally controllable power supply. A circuit is configured.
An optical pickup according to item 1. 3. The optical pickup according to claim 2, wherein the resistor is a variable resistor. 4. A driving means for rotating and driving the optical disc, and a light irradiating means for irradiating the rotating optical disc with light through a light focusing means, and returning light from a signal recording surface from the optical disc through the light focusing means. Pick-up, a holding coil for holding the light focusing means movably in two axial directions, a focusing coil and a tracking coil disposed on a movable or fixed part including the light focusing means and the holding member A two-axis actuator having a focusing magnet and a tracking magnet, and a yoke associated with each of the magnets and each coil, which are disposed on the fixed or movable portion so as to face these coils; A signal processing circuit for generating a reproduction signal based on the signal; and a detection signal from the optical pickup. And a servo circuit for moving the light focusing means in two axial directions based on the following: an even number of coils in which at least one of the focusing coil and the tracking coil is paired. An optical disk device, wherein the paired coils are individually driven such that their drive currents are unbalanced with each other.