JP2006344274A - Optical head - Google Patents

Abstract

A spherical aberration amount can be adjusted while performing stable tracking control.
An optical head includes a main shaft 8 including a piezoelectric element 7, a spherical aberration correcting optical element 5 held on the main shaft 8, and a sub shaft 10 holding the spherical aberration correcting optical element 5. The surface determined by the sub-axis 10 is the first surface, the surface perpendicular to the optical axis of the spherical aberration correcting optical element 5 is the second surface, and the intersection of the first surface and the second surface is on the recording medium. The projection direction and the track direction on the recording medium 1 are configured to be parallel to each other.
[Selection] Figure 1

Description

  The present invention relates to an optical head capable of ensuring the stability of tracking control when adjusting the light beam focusing position and spherical aberration.

  With the recent increase in the density of optical discs, optical heads used for recording and reproduction have been made to shorten the wavelength of laser light and increase the NA of objective lenses. When the numerical aperture of the light beam emitted from the optical head is increased and the wavelength of the emitted light is shortened, the amount of spherical aberration caused by the error in the thickness of the protective layer formed on the optical disk increases rapidly. Therefore, it is indispensable to provide means for correcting the amount of spherical aberration.

  FIG. 9A shows the main part of the conventional example.

  In FIG. 9A, 1 is a recording medium, 1a is a substrate, and 1b is a cover layer. A recording layer 1c is disposed between the cover layer 1b and the substrate 1a. A laser light source 3 emits laser light 4. 5 is a collimator lens, and 6 is an objective lens. Reference numeral 16 denotes a light spot that is condensed and irradiated on the recording layer 1c. The collimator lens 5 also serves as a spherical aberration correction optical element for correcting the spherical aberration of the light spot 16. A piezoelectric element 7 expands in the direction A when a positive voltage is applied to the + terminal, and contracts when a negative voltage is applied. Reference numeral 13 denotes a power source for applying a voltage to the piezoelectric element 7. Reference numeral 8 denotes a cylindrical main shaft which is arranged in parallel to the optical axis 9 of the laser light 4 incident on the collimator lens 5 and fixed to one end of the piezoelectric element 7.

  The piezoelectric element 7 is used as a means for giving an acceleration to the main shaft 8 and moving it. The other end of the piezoelectric element 7 opposite to the main shaft 8 is fixed to a part of the optical head. Reference numeral 10 denotes a sub-axis, which is arranged in parallel to the optical axis 9 and both ends are fixed to a part of the optical head. A lens holder 11 is a fixing means for fixing the collimator lens 5. A friction holder 12 as a coupling means is fixed to the main shaft 8 side of the lens holder 11, and the friction holder 12 is frictionally connected to the main shaft 8. The lens holder 11 is provided with a guide hole 11a, and the auxiliary shaft 10 is disposed so as to penetrate the guide hole 11a.

  The frictional force between the guide hole 11a and the counter shaft 10 is sufficiently smaller than the frictional force between the friction holding body 12 and the main shaft 8.

  The collimator lens 5, the lens holder 11, and the friction holder 12 are slidable in the optical axis direction except that the collimator lens 5, the lens holder 11, and the friction holder 12 are fixed to the main shaft 8 by a frictional force. For convenience, the side closer to the recording medium 1 in the optical axis direction is referred to as A direction, and the side away from the recording medium 1 is referred to as B direction.

  Since the movable part 100 is supported by two mutually parallel axes of the main axis 8 and the auxiliary axis 10, it can move in parallel to the direction of the optical axis 9 without rotating.

  When a voltage is gradually applied to the piezoelectric element 7, the piezoelectric element 7 expands in the direction A. Then, the main shaft 8 gradually moves in the direction A, and the friction holding body 12 frictionally coupled to the main shaft 8 also moves in the direction A together with the main shaft 8. Here, since the frictional force between the countershaft 10 and the guide hole 11a is sufficiently small, the movable part 100 including the friction holding body 12 gradually moves in the direction A, and as a result, the collimator lens 5 moves in the direction A. To do.

  When the voltage applied to the piezoelectric element 7 is suddenly removed from this state, the piezoelectric element 7 is rapidly shortened in the direction B, and the main shaft 8 is also suddenly moved in the direction B. However, when the movable part 100 tries to accelerate in the B direction, an inertial force corresponding to the mass of the movable part 100 acts. Since the friction holding body 12 is frictionally coupled to the main shaft 8, if the inertial force exceeds the static friction force, the friction holding body 12 slides on the main shaft 8 and moves to a dynamic friction region where the force is relatively small. As a result, the collimator The movable part 100 including the lens 5 remains almost in place regardless of the displacement of the main shaft 8 in the direction B.

  As a result of this one cycle, the collimator lens 5 has moved in the direction A by the extension of the piezoelectric element 7. Since the extension amount of the piezoelectric element 7 is very small, the movement amount of the collimator lens 5 per cycle is very small. By repeating this cycle, the collimator lens 5 is moved to an arbitrary amount (amount for correcting aberration) by A. It can be moved in the direction.

  Further, after the collimator lens 5 is moved by an arbitrary amount, the collimator lens 5 is fixed to the main shaft 8 by the friction holding body 12.

FIG. 9B is a view of FIG. 9A viewed from above. In the figure, a shaft 14 of a motor for rotating the recording medium 1 is shown. The recording medium 1 is formed with a plurality of spiral or concentric tracks. Reference numeral 15 denotes one of a plurality of formed tracks.
Japanese Patent Laying-Open No. 2004-39068 (page 3-5, FIG. 1)

  However, the other end of the main shaft 8 opposite to the piezoelectric element 7 is not fixed to improve sliding, that is, there is a slight backlash, so when moving the movable part 100 in the direction of A, A moment force is applied to the main shaft 8 such that the sub shaft 10 side moves with a delay relative to the main shaft 8 side of the movable portion 100. For this reason, the main shaft 8 is swung, and the movable portion 100 is inclined with respect to the optical axis 9 within a plane determined by the main shaft 8 and the sub shaft 10. As shown in FIG. 9B, the surface determined by the main shaft 8 and the sub shaft 10 holding the collimator lens is the first surface, the surface perpendicular to the optical axis 9 is the second surface, and the first surface and the second surface When the intersecting line of the two surfaces is projected onto the recording medium 1 and the direction of the track on the recording medium 1 is orthogonal, the light spot 16 on the recording medium 1 Displacement in the direction to go straight. As a result, tracking control may become unstable.

  The optical head of the present invention includes a light source that emits light, a condensing unit that condenses light on a recording medium having a track, and a spherical aberration correcting unit that corrects spherical aberration of light emitted from the condensing unit. The spherical aberration correction means includes a main axis provided with a drive means, a spherical aberration correction optical element held on the main axis, and a sub-axis holding the spherical aberration correction optical element, and the main axis and the sub-axis The surface determined by the axis is the first surface, the surface perpendicular to the optical axis of the spherical aberration correcting optical element is the second surface, and the intersection of the first surface and the second surface is on the recording medium. The projection direction and the track direction on the recording medium are configured to be parallel. As a result, the above object is achieved.

  The optical head of the present invention includes a light source that emits light, a condensing unit that condenses light on a recording medium having a track, and a spherical aberration correcting unit that corrects spherical aberration of light emitted from the condensing unit. The spherical aberration correction means includes a main axis provided with a first drive means, a spherical aberration correction optical element held on the main axis, the spherical aberration correction optical element, and a second drive means. And the displacement of the spherical aberration correction optical element by the first drive means is equal to the displacement of the spherical aberration correction optical element by the second drive means. As a result, the above object is achieved.

  The optical head of the present invention includes a light source that emits light, a condensing unit that condenses light on a recording medium having a track, and a spherical aberration correcting unit that corrects spherical aberration of light emitted from the condensing unit. The spherical aberration correction means includes: a spherical aberration correction optical element held on a shaft; a first piezoelectric element disposed at an end of the shaft and fixed at the other end opposite to the shaft; A second piezoelectric element disposed at the other end of the shaft opposite to the first piezoelectric element and fixed at the other end opposite to the shaft; and the shaft and the first piezoelectric element. The first piezoelectric element and the second piezoelectric element are driven so that the entire lengths of the element and the second piezoelectric element are equal. As a result, the above object is achieved.

  An optical head according to the present invention includes a light source that emits light, and a condensing unit that condenses the light on a recording medium having a track, and the condensing unit is held by the main shaft including a driving unit and the main shaft. A surface determined by the main axis and the sub-axis is defined as a first surface, and a surface perpendicular to the optical axis of the light-collecting element is defined as a second surface. The first surface and the second surface are configured such that the direction when the intersecting line of the first surface and the second surface is projected onto the recording medium is parallel to the direction of the track on the recording medium. As a result, the above object is achieved.

  An optical head according to the present invention includes a light source that emits light and a condensing unit that condenses light on a recording medium having a track, and the condensing unit is held by a main shaft that includes a first driving unit. Consists of a condensing element and a secondary shaft that holds the condensing element and includes a second driving means, and the displacement of the condensing element by the first driving means and the second driving means It is driven so that the displacement of the condensing element is equal. As a result, the above object is achieved.

  The optical head of the present invention includes a light source that emits light, and a condensing unit that condenses the light on a recording medium having a track. The condensing unit includes a condensing element held on a shaft, A first piezoelectric element disposed at an end and fixed at the other end opposite to the axis; and disposed at the other end of the axis opposite to the first piezoelectric element and opposite to the axis And the second piezoelectric element having the other end fixed to the first piezoelectric element so that the entire length of the shaft, the first piezoelectric element, and the second piezoelectric element is equal. The second piezoelectric element is driven. As a result, the above object is achieved.

  According to the present invention, the movable portion is configured such that the direction when the intersecting line of the first surface and the second surface is projected onto the recording medium and the direction of the track on the recording medium are parallel to each other. Even if 100 is inclined with respect to the optical axis within the plane determined by the main axis and the sub axis, the light spot on the recording medium is displaced in a direction parallel to the track, so that off-track does not occur and tracking control is performed. Can be stable.

  In addition, since the spherical aberration correction optical element is driven by applying a voltage to the first driving unit and the second driving unit, the movable unit 100 has an optical axis within a plane determined by the main axis and the sub axis. Since the light spot on the recording medium is not displaced, off-track does not occur and tracking control can be stabilized.

  Further, the spherical surface is controlled by controlling the voltage applied to the first piezoelectric element and the second piezoelectric element so that the entire lengths of the shaft, the first piezoelectric element, and the second piezoelectric element are equal. Since the aberration correction optical element is driven, the axis does not tilt and the light spot on the recording medium is not displaced, so that off-track does not occur and tracking control can be stabilized.

  Further, the condensing element is configured such that the direction when the intersecting line of the first surface and the second surface is projected onto the recording medium and the direction of the track on the recording medium are parallel, Even if the optical spot is tilted with respect to the optical axis within the plane determined by the main axis and the sub axis, the light spot on the recording medium is displaced in a direction parallel to the track, so that off-track does not occur and tracking control can be stabilized. .

  Further, since the condensing element is driven by applying a voltage to the first driving means and the second driving means, the condensing element is placed on the optical axis within a plane determined by the main axis and the sub axis. In contrast, the light spot on the recording medium is not displaced, and therefore no off-track occurs, and the tracking control can be stabilized.

  Further, the voltage applied to the first piezoelectric element and the second piezoelectric element is controlled so that the entire lengths of the shaft, the first piezoelectric element, and the second piezoelectric element are equal to each other. Since the optical element is driven, the axis does not tilt and the light spot on the recording medium is not displaced, so that off-track does not occur and tracking control can be stabilized.

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Note that the present invention is not limited to the present embodiment.

(Embodiment 1)
FIG. 1 shows a main part of an optical head according to Embodiment 1 of the present invention. FIG. 1A is a sectional view thereof. In FIG. 1A, the recording medium 1, the laser light source 3, the collimator lens 5, the objective lens 6, the light spot 16, the piezoelectric element 7, the power source 13, and the main shaft 8 are the same as those described in the conventional example (FIG. 9). Detailed description will be omitted. FIG.1 (b) is the figure which looked at Fig.1 (a) from the top. Reference numeral 15 denotes one of the plurality of formed tracks. The difference from the conventional example is that the surface determined by the main axis 8 and the sub-axis 10 is the first surface, the surface perpendicular to the optical axis 9 is the second surface, and the intersection line of the first surface and the second surface is recorded. This is that the direction when projected onto the medium 1 and the direction of the track on the recording medium 1 are parallel to each other.

  The operation of the first embodiment configured as described above will be described below.

  The laser light 4 emitted from the laser light source 3 passes through the collimator lens 5, passes through the objective lens 6 and the cover layer 1 b, and forms an image on the recording layer 1 c. When the recording medium 1 is rotationally moved with surface deflection or eccentricity, the objective lens 6 operates two-dimensionally, and the light spot 16 is focused on the recording layer 1c in a predetermined state. And the light spot 16 is controlled so as to follow the track 15.

  FIG. 2 shows the change over time of the drive voltage applied to 7. It is a positive voltage that varies linearly between voltage 0 and voltage E. The drive voltage waveform is such that the value of T1 with respect to T2 is not 1. In FIG. 2, T1> T2.

  As shown in the period of T1, when the voltage is gradually applied to the piezoelectric element 7, it expands in the direction of A. Then, the main shaft 8 gradually moves in the direction A, and the friction holding body 12 frictionally coupled to the main shaft 8 also moves in the direction A together with the main shaft 8. Here, since the frictional force between the countershaft 10 and the guide hole 11a is sufficiently small, the movable part 100 including the friction holding body 12 gradually moves in the direction A, and as a result, the collimator lens 5 moves in the direction A. To do. If the voltage applied to the piezoelectric element 7 is suddenly removed from this state as shown in the period T2, the piezoelectric element 7 is rapidly shortened in the direction B, and the main shaft 8 is also suddenly moved in the direction B. However, when the movable part 100 tries to accelerate in the B direction, an inertial force corresponding to the mass of the movable part 100 acts. Since the friction holding body 12 is frictionally coupled to the main shaft 8, if the inertial force exceeds the static friction force, the friction holding body 12 slides on the main shaft 8 and moves to a dynamic friction region where the force is relatively small. As a result, the collimator The movable part 100 including the lens 5 remains almost in place regardless of the displacement of the main shaft 8 in the direction B. As a result of this one cycle, the collimator lens 5 has moved in the direction A by the extension of the piezoelectric element 7. Since the extension amount of the piezoelectric element 7 is very small, the movement amount of the collimator lens 5 per cycle is very small. By repeating this cycle, the collimator lens 5 is moved to an arbitrary amount (amount for correcting aberration) by A. It can be moved in the direction.

  When the collimator lens 5 is moved in the reverse direction, that is, in the direction of B, the voltage applied to the piezoelectric element 7 is switched to a voltage that satisfies T1 <T2. Accordingly, the drive voltage to the piezoelectric element 7 increases rapidly and gradually decreases. Then, the main shaft 8 rapidly moves in the direction of A, but the movable portion 100 does not move, and the main shaft 8 gradually moves in the direction of B, so that the movable portion 100 also moves in the direction of B. As a result, the collimator lens 5 moves in the direction B.

  When the cover layer 1b has a thickness variation or the like and spherical aberration occurs, the aberration correction is performed by moving the collimator lens 5 in the direction in which the spherical aberration is reduced by the above method.

  By the way, in the conventional example, the other end of the main shaft 8 opposite to the piezoelectric element 7 is not fixed. Therefore, when the movable portion 100 is moved in the direction A or B, the main shaft 8 side of the movable portion 100 is moved. On the other hand, a moment force is applied to the main shaft 8 such that the side of the sub shaft 10 moves with a delay. For this reason, there has been a problem that the main shaft 8 is swung and the movable portion 100 is inclined with respect to the optical axis 9 within a plane determined by the main shaft 8 and the sub shaft 10. However, in the present embodiment, as shown in FIG. 1B, the surface determined by the main shaft 8 and the sub shaft 10 is the first surface, and the surface perpendicular to the optical axis 9 is the second surface. Since the direction when the intersecting line of the surface and the second surface is projected onto the recording medium 1 and the direction of the track on the recording medium 1 are parallel to each other, the recording medium 1 can be used even if there is a backlash. The upper light spot 16 is displaced in a direction parallel to the track 15. As a result, since the light spot 16 is always positioned on the track 15, the tracking control does not become unstable.

  In the above description, the piezoelectric element 7, the main shaft 8, and the friction holding body 12 that is frictionally coupled to the main shaft 8 are used as means for displacing the collimator lens 5. However, the lead screw is rotated with the main shaft 8 as a lead screw. Similar effects can be obtained by using a DC motor or a stepping motor.

  In the above description, the collimator lens 5 is displaced as means for correcting the spherical aberration, but a beam expander may be used.

  FIG. 3 shows a configuration diagram of a main part of an optical head using a beam expander.

  Constituent parts similar to those in FIG. The beam expander is originally intended to use two lenses, a concave lens 50 and a convex lens 51, to enlarge or reduce the light diameter while maintaining the parallelism of the light rays. However, when the distance between the concave and convex lenses is intentionally shifted, weak diffused or condensed light can be obtained, and spherical aberration can be freely generated in combination with the objective lens 6. By using this function, it is used as spherical aberration correction means.

  The convex lens 51 is attached to the lens holder 11. The concave lens 50 and the collimator lens 5 are fixed to a part of the optical head.

  Similarly to the above description, the distance between the concave lens 50 and the convex lens 51 is changed by displacing the convex lens 51, and control is performed so that the spherical aberration of the light spot 16 is minimized.

(Embodiment 2)
FIG. 4 shows a main part of the optical head according to the second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. The difference from the first embodiment is that piezoelectric elements 60 and 61 are attached to both ends of the main shaft 8. The side opposite to the main axis 8 of the piezoelectric elements 60 and 61 is fixed to a part of the optical head. The piezoelectric elements 60 and 61 expand by applying a positive voltage to the + terminal, and contract by applying a negative voltage. The + terminal side of the piezoelectric element 60 is attached to the main shaft 8, and the − terminal side is fixed to a part of the optical head. The positive terminal side of the piezoelectric element 61 is attached to the main shaft, and the negative terminal side is fixed to a part of the optical head.

  The + terminal of the piezoelectric element 60 is connected to the OUT terminal of the power supply 13, and the − terminal is connected to GND. The negative terminal of the piezoelectric element 61 is connected to the OUT terminal of the power supply 13, and the positive terminal is connected to GND. The drive voltage applied to the piezoelectric elements 60 and 61 is the same as in FIG.

  Therefore, when the voltage is gradually applied to the piezoelectric element 60 as shown in the period of T1, it expands in the direction of A. At the same time, the piezoelectric element 61 shrinks in the direction A. Accordingly, the main shaft 8 gradually moves in the direction A, and the friction holding body 12 frictionally coupled to the main shaft 8 also moves in the direction A together with the main shaft 8. Here, since the frictional force between the countershaft 10 and the guide hole 11a is sufficiently small, the movable part 100 including the friction holding body 12 gradually moves in the direction A, and as a result, the collimator lens 5 moves in the direction A. To do.

  When the voltage applied to the piezoelectric element 60 is suddenly removed from this state as shown in the period T2, the piezoelectric element 60 rapidly contracts in the direction B. At the same time, the piezoelectric element 61 expands rapidly in the direction of A.

  Accordingly, the main shaft 8 also moves suddenly in the direction B. However, when the movable part 100 tries to accelerate in the B direction, an inertial force corresponding to the mass of the movable part 100 acts. Since the friction holding body 12 is frictionally coupled to the main shaft 8, if the inertial force exceeds the static friction force, the friction holding body 12 slides on the main shaft 8 and moves to a dynamic friction region where the force is relatively small. As a result, the collimator The movable part 100 including the lens 5 remains almost in place regardless of the displacement of the main shaft 8 in the direction B.

  As a result of this one cycle, the collimator lens 5 has moved in the direction A by the extension of the piezoelectric element 60.

  When the movable unit 100 is moved in the direction A by driving the piezoelectric elements 60 and 61, a moment force is generated on the main shaft 8 so that the sub-shaft 10 side moves with a delay relative to the main shaft 8 side of the movable unit 100. Even if added, both ends of the main shaft 8 are fixed to a part of the optical head via the piezoelectric elements 60 and 61, so that the main shaft 8 does not shake. Therefore, the movable part 100 does not tilt with respect to the optical axis 9 within a plane determined by the main shaft 8 and the sub shaft 10.

  Therefore, since the light spot 16 is always located on the track 15, the tracking control does not become unstable.

  In the present embodiment, the spherical aberration is corrected by the collimator lens 5, but a beam expander may be used.

(Embodiment 3)
FIG. 5 shows a main part of the optical head according to the third embodiment of the present invention. The same blocks as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. The difference from the first embodiment is that piezoelectric elements 65 and 66 are attached to both the main shaft 8 and the sub shaft 67, respectively. Further, the lens holder 11 is fixed to the main shaft 8 and the sub shaft 67 by friction force via the friction holding bodies 12 and 68.

  The piezoelectric elements 65 and 66 expand by applying a positive voltage to the + terminal, and contract by applying a negative voltage. The + terminal side of the piezoelectric element 65 is attached to the main shaft 8, and the − terminal side is fixed to a part of the optical head. The + terminal side of the piezoelectric element 66 is attached to the sub shaft 67, and the − terminal side is fixed to a part of the optical head. The + terminal of the piezoelectric element 65 is connected to the OUT terminal of the power supply 13, and the − terminal is connected to GND. Further, the + terminal of the piezoelectric element 66 is connected to the OUT terminal of the power supply 13, and the-terminal is connected to GND. The auxiliary shaft 67 is disposed in parallel to the optical axis 9. The other end of the sub shaft 67 opposite to the piezoelectric element 66 is not fixed. A friction holding body 68 serving as a coupling means is fixed to the lens holder 11 on the side of the auxiliary shaft 67, and the friction holding body 68 is frictionally connected to the auxiliary shaft 67. The collimator lens 5, the lens holder 11, and the friction holding bodies 12 and 68 are fixed to the main shaft 8 and the sub shaft 67 by a frictional force. Accordingly, the movable portion 70 constituted by the collimator lens 5, the lens holder 11, and the friction holders 12 and 68 can slide in the optical axis direction within a plane determined by the main shaft 8 and the sub shaft 67.

  The drive voltage applied to the piezoelectric elements 65 and 66 is the same as in FIG.

  Therefore, when the voltage is gradually applied to the piezoelectric elements 65 and 66 as shown in the period of T1, it expands in the direction of A. Accordingly, the main shaft 8 and the sub shaft 67 are gradually moved in the direction A, and the friction holding bodies 12 and 68 frictionally coupled to the main shaft 8 and the sub shaft 67 are also moved in the direction A together with the main shaft 8 and the sub shaft 67. As a result, the movable part 70 moves in the direction A.

  If the voltage applied to the piezoelectric elements 65 and 66 is suddenly removed from this state as shown in the period of T2, the piezoelectric elements 65 and 66 contract rapidly in the direction of B. Accordingly, the main shaft 8 and the sub shaft 67 are also suddenly moved in the direction B. However, when the movable part 70 tries to accelerate in the B direction, an inertial force corresponding to the mass of the movable part 70 acts. Since the friction holding bodies 12 and 68 are frictionally coupled to the main shaft 8 and the sub shaft 67, when the inertial force exceeds the static friction force, the friction holding bodies 12 and 68 slide on the main shaft 8 and the sub shaft 67 for comparison. As a result, the movable part 70 including the collimator lens 5 remains almost in place regardless of the displacement of the main shaft 8 and the sub shaft 67 in the direction B.

  As a result of this one cycle, the collimator lens 5 has moved in the direction A by the extension of the piezoelectric elements 65 and 66.

  When the movable unit 70 is moved in the direction A by simultaneously driving the piezoelectric elements 65 and 66, a moment force is generated such that the side of the sub shaft 67 moves with respect to the side of the main shaft 8 of the movable unit 70 with a delay. Therefore, the main shaft 8 will not swing. Therefore, the collimator lens 5 of the movable portion 70 does not tilt with respect to the optical axis 9 within the plane determined by the main shaft 8 and the sub shaft 67.

  Therefore, since the light spot 16 is always located on the track 15, the tracking control does not become unstable.

  In the above description, the piezoelectric elements 65 and 66, the main shaft 8, the sub shaft 67, and the friction holding bodies 12 and 68 are used as means for displacing the collimator lens 5. However, the main shaft 8 and the sub shaft 67 are used as lead screws, and leads are used. The same effect can be obtained by using a DC motor for rotating the screw or a stepping motor.

  In the present embodiment, the spherical aberration is corrected by the collimator lens 5, but a beam expander may be used.

(Embodiment 4)
FIG. 6 shows a main part of an optical head according to Embodiment 4 of the present invention. The same blocks as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  The difference from the first embodiment is that the object to be driven is not the collimator lens 5 but the objective lens 6. That is, not the spherical aberration of the spot 16 but the condensing state is adjusted.

  In FIG. 6A, reference numeral 80 denotes a lens holder which is a fixing means for fixing the objective lens 6. A friction holder 12 as a coupling means is fixed to the main shaft 8 side of the lens holder 80, and the friction holder 12 is frictionally connected to the main shaft 8. The lens holder 80 is provided with a guide hole 80a, and the auxiliary shaft 10 is disposed so as to penetrate the guide hole 80a. A movable part composed of the objective lens 6, the lens holder 80, and the friction holding body 12 is referred to as a movable part 81.

  The laser light 4 emitted from the laser light source 3 passes through the collimator lens 5, passes through the objective lens 6 and the cover layer 1 b, and forms an image on the recording layer 1 c. When the surface shake occurs in the recording medium 1, the objective lens 6 is moved, and the condensing state of the light spot 16 on the recording layer 1c is controlled to be a predetermined state. FIG. 6B is a view from above. Reference numeral 15 denotes one of the plurality of formed tracks. A plane determined by the main axis 8 and the sub axis 10 is defined as a first plane, a plane perpendicular to the optical axis 9 is defined as a second plane, and an intersection line between the first plane and the second plane is projected onto the recording medium 1. The direction of the track and the direction of the track on the recording medium 1 are parallel to each other.

  The operation of the fourth embodiment configured as described above will be described below.

  The drive voltage applied to the piezoelectric element 7 is the same as in FIG.

  As shown in the period of T1, when the voltage is gradually applied to the piezoelectric element 7, it expands in the direction of A. Then, the main shaft 8 gradually moves in the direction A, and the friction holding body 12 frictionally coupled to the main shaft 8 also moves in the direction A together with the main shaft 8. Here, since the frictional force between the countershaft 10 and the guide hole 80a is sufficiently small, the movable portion 81 including the friction holding body 12 gradually moves in the direction A, and as a result, the objective lens 6 moves in the direction A. To do.

  If the voltage applied to the piezoelectric element 7 is suddenly removed from this state as shown in the period T2, the piezoelectric element 7 is rapidly shortened in the direction B, and the main shaft 8 is also suddenly moved in the direction B. However, when the movable portion 81 tries to accelerate in the B direction, an inertial force corresponding to the mass of the movable portion 81 acts. Since the friction holding body 12 is frictionally coupled to the main shaft 8, when the inertial force exceeds the static friction force, the friction holding body 12 slides on the main shaft 8 and moves to a dynamic friction region where the force is relatively small. The movable portion 81 including the lens 6 remains almost in place regardless of the displacement of the main shaft 8 in the direction B. As a result of this one cycle, the objective lens 6 has moved in the direction A by the extension of the piezoelectric element 7.

  When the objective lens 6 is moved in the direction B, the voltage applied to the piezoelectric element 7 is switched to a voltage that satisfies T1 <T2. Accordingly, the drive voltage to the piezoelectric element 7 increases rapidly and gradually decreases. Then, the main shaft 8 moves rapidly in the direction of A, but the movable portion 81 does not move, and the movable portion 81 also moves in the direction of B as the main shaft 8 gradually moves in the direction of B. As a result, the objective lens 6 moves in the direction B.

  When surface vibration or occurrence occurs in the recording medium 1, the focusing state of the light spot 16 on the recording layer 1c is always set to a predetermined state by moving the objective lens 6 by the above method according to the surface vibration. Can do.

  By the way, the other end of the main shaft 8 opposite to the piezoelectric element 7 is not fixed in order to improve sliding, that is, there is some backlash, so that the movable portion 81 is moved in the direction of A or B. A moment force is applied to the main shaft 8 such that the sub shaft 10 moves with a delay relative to the main shaft 8 of the movable portion 81. For this reason, the main shaft 8 is swung, and the movable portion 8 is inclined with respect to the optical axis 9 within a plane determined by the main shaft 8 and the sub shaft 10. However, in the present embodiment, as shown in FIG. 6B, the surface determined by the main shaft 8 and the sub shaft 10 is the first surface, and the surface perpendicular to the optical axis 9 is the second surface. Since the direction when the intersecting line of the surface and the second surface is projected onto the recording medium 1 and the direction of the track on the recording medium 1 are parallel, the light spot 16 on the recording medium 1 is It is displaced in a direction parallel to the track 15. As a result, since the light spot 16 is always positioned on the track 15, the tracking control does not become unstable.

(Embodiment 5)
FIG. 7 shows the main part of the optical head according to the fifth embodiment of the present invention. Blocks similar to those in Embodiments 2 and 4 are given the same numbers, and description thereof is omitted.

  In the present embodiment, the object to be driven is the objective lens 6 as in the fourth embodiment. That is, the light collection state of the spot 16 is adjusted.

  This embodiment is different from the second and fourth embodiments in that piezoelectric elements 60 and 61 are attached to both ends of the main shaft 8. The side opposite to the main axis 8 of the piezoelectric elements 60 and 61 is fixed to a part of the optical head.

  A movable portion 81 composed of the objective lens 6, the lens holder 80, and the friction holder 12 is driven by the piezoelectric elements 60 and 61. The drive voltage applied to the piezoelectric elements 60 and 61 is the same as in FIG. Therefore, when the voltage is gradually applied to the piezoelectric element 60 as shown in the period of T1, it expands in the direction of A. At the same time, the piezoelectric element 61 shrinks in the direction A. Accordingly, the main shaft 8 gradually moves in the direction A, and the friction holding body 12 frictionally coupled to the main shaft 8 also moves in the direction A together with the main shaft 8. Here, since the frictional force between the countershaft 10 and the guide hole 80a is sufficiently small, the movable portion 81 including the friction holding body 12 gradually moves in the direction A, and as a result, the objective lens 6 moves in the direction A. To do.

  When the voltage applied to the piezoelectric element 60 is suddenly removed from this state as shown in the period T2, the piezoelectric element 60 rapidly contracts in the direction B. At the same time, the piezoelectric element 61 expands rapidly in the direction of A.

  Accordingly, the main shaft 8 also moves suddenly in the direction B. However, when the movable portion 81 tries to accelerate in the B direction, an inertial force corresponding to the mass of the movable portion 81 acts. Since the friction holding body 12 is frictionally coupled to the main shaft 8, when the inertial force exceeds the static friction force, the friction holding body 12 slides on the main shaft 8 and moves to a dynamic friction region where the force is relatively small. The movable portion 81 including the lens 6 remains almost in place regardless of the displacement of the main shaft 8 in the direction B.

  As a result of this one cycle, the objective lens 6 has moved in the direction A by the extension of the piezoelectric elements 60 and 61.

  When surface vibration or occurrence occurs in the recording medium 1, the focusing state of the light spot 16 on the recording layer 1c is always set to a predetermined state by moving the objective lens 6 by the above method according to the surface vibration. Can do.

  When the movable portion 81 is moved in the direction A by driving the piezoelectric elements 60 and 61, a moment force is generated on the main shaft 8 such that the side of the sub shaft 10 moves with respect to the main shaft 8 side of the movable portion 81 with a delay. Even if added, both ends of the main shaft 8 are fixed to a part of the optical head via the piezoelectric elements 60 and 61, so that the main shaft 8 does not shake. Therefore, the movable portion 81 does not tilt with respect to the optical axis 9 within a plane determined by the main shaft 8 and the sub shaft 10.

  Therefore, since the light spot 16 is always located on the track 15, the tracking control does not become unstable.

(Embodiment 6)
FIG. 8 shows a main part of an optical head according to the sixth embodiment of the present invention. The same blocks as those in the third and fourth embodiments are denoted by the same reference numerals and description thereof is omitted.

  In the present embodiment, the object to be driven is the objective lens 6 as in the fourth embodiment. That is, the light collection state of the spot 16 is adjusted. This embodiment is different from the third and fourth embodiments in that piezoelectric elements 65 and 66 are attached to both the main shaft 8 and the sub shaft 67, respectively. Further, the lens holder 80 is fixed to the main shaft 8 and the sub shaft 67 by friction force via the friction holding bodies 12 and 68.

  The movable part 82 including the objective lens 6, the lens holder 80, and the friction holders 12 and 68 is driven by the piezoelectric elements 65 and 66.

  The drive voltage applied to the piezoelectric elements 65 and 66 is the same as in FIG.

  Therefore, when the voltage is gradually applied to the piezoelectric elements 65 and 66 as shown in the period of T1, it expands in the direction of A. Accordingly, the main shaft 8 and the sub shaft 67 are gradually moved in the direction A, and the friction holding bodies 12 and 68 frictionally coupled to the main shaft 8 and the sub shaft 67 are also moved in the direction A together with the main shaft 8 and the sub shaft 67. As a result, the movable part 82 moves in the direction A.

  If the voltage applied to the piezoelectric elements 65 and 66 is suddenly removed from this state as shown in the period of T2, the piezoelectric elements 65 and 66 contract rapidly in the direction of B. Accordingly, the main shaft 8 and the sub shaft 67 are also suddenly moved in the direction B. However, when the movable portion 82 tries to accelerate in the B direction, an inertial force corresponding to the mass of the movable portion 82 acts. Since the friction holding bodies 12 and 68 are frictionally coupled to the main shaft 8 and the sub shaft 67, when the inertial force exceeds the static friction force, the friction holding bodies 12 and 68 slide on the main shaft 8 and the sub shaft 67 for comparison. As a result, the movable portion 82 including the objective lens 6 remains almost in place regardless of the displacement of the main shaft 8 and the sub shaft 67 in the direction B.

  As a result of this one cycle, the objective lens 6 has moved in the direction A by the extension of the piezoelectric elements 65 and 66.

  When surface vibration or occurrence occurs in the recording medium 1, the focusing state of the light spot 16 on the recording layer 1c is always set to a predetermined state by moving the objective lens 6 by the above method according to the surface vibration. Can do.

  When the movable unit 80 is moved in the direction A by simultaneously driving the piezoelectric elements 65 and 66, a moment force is generated such that the side of the sub shaft 67 moves with respect to the side of the main shaft 8 of the movable unit 80 with a delay. Therefore, the main shaft 8 will not swing. Therefore, the objective lens 6 of the movable portion 80 does not tilt with respect to the optical axis 9 within the plane determined by the main shaft 8 and the sub shaft 67.

  Therefore, since the light spot 16 is always located on the track 15, the tracking control does not become unstable.

  In the above description, the piezoelectric elements 65 and 66, the main shaft 8, the sub shaft 67, and the friction holding bodies 12 and 68 are used as means for displacing the objective lens 6. However, the main shaft 8 and the sub shaft 67 are used as lead screws. The same effect can be obtained by using a DC motor for rotating the screw or a stepping motor.

  As described above, the present invention has been exemplified using the preferred embodiment of the present invention, but the present invention should not be construed as being limited to this embodiment. It is understood that the scope of the present invention should be construed only by the claims. It is understood that those skilled in the art can implement an equivalent range based on the description of the present invention and the common general technical knowledge from the description of specific preferred embodiments of the present invention. Patents, patent applications, and documents cited herein should be incorporated by reference in their entirety, as if the contents themselves were specifically described herein. Understood.

  INDUSTRIAL APPLICABILITY The present invention is useful as an optical head capable of adjusting the amount of spherical aberration that provides the best reproduction signal quality while performing stable tracking control.

1 is a block diagram showing a configuration of an optical head according to a first embodiment of the present invention. Diagram showing drive voltage waveform of piezoelectric element Block diagram showing the configuration of an optical head using a beam expander FIG. 3 is a block diagram showing a configuration of an optical head according to a second embodiment of the present invention. Block diagram showing the configuration of an optical head according to a third embodiment of the present invention. Block diagram showing a configuration of an optical head according to a fourth embodiment of the present invention. Block diagram showing a configuration of an optical head according to a fifth embodiment of the present invention. Block diagram showing a configuration of an optical head according to a sixth embodiment of the present invention. Block diagram showing the configuration of a conventional optical head

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording medium 3 Laser light source 4 Laser light 5 Collimator lens 6 Objective lens 7 Piezoelectric element 8 Main axis 9 Optical axis 10 Sub axis 11 Lens holder 11a Guide hole 12 Friction holder 13 Power supply 14 Motor shaft 15 Track 16 Light spot

Claims (12)

A light source that emits light, a light condensing unit that condenses the light on a recording medium having a track, and a spherical aberration correcting unit that corrects the spherical aberration of the light emitted from the light converging unit. Comprises a main axis provided with a driving means, a spherical aberration correction optical element held on the main axis, and a sub-axis holding the spherical aberration correction optical element, and a surface determined by the main axis and the sub-axis is a first one. And a direction perpendicular to the optical axis of the spherical aberration correcting optical element as a second surface, and an intersection line of the first surface and the second surface projected onto a recording medium and recording. An optical head characterized in that the direction of tracks on a medium is parallel. A light source that emits light, a light condensing unit that condenses the light on a recording medium having a track, and a spherical aberration correcting unit that corrects the spherical aberration of the light emitted from the light converging unit. Includes a main shaft provided with a first driving means, a spherical aberration correction optical element held on the main axis, and a secondary axis holding the spherical aberration correction optical element and provided with a second driving means. An optical head comprising: the displacement of the spherical aberration correcting optical element by the first driving means and the displacement of the spherical aberration correcting optical element by the second driving means are equal to each other . 3. The optical head according to claim 1, wherein the driving means is constituted by a piezoelectric element that displaces the main axis in the first plane. 3. The optical head according to claim 1, wherein the main shaft is constituted by a lead screw and the driving means is constituted by a motor for rotating the lead screw. A light source that emits light, a light condensing unit that condenses the light on a recording medium having a track, and a spherical aberration correcting unit that corrects the spherical aberration of the light emitted from the light converging unit. Is opposite to the first piezoelectric element, a spherical aberration correcting optical element held on the axis, a first piezoelectric element disposed at the end of the axis and fixed at the other end opposite to the axis. And a second piezoelectric element disposed at the other end of the shaft on the side and fixed at the other end opposite to the shaft, the shaft, the first piezoelectric element, and the second piezoelectric element. An optical head characterized in that the first piezoelectric element and the second piezoelectric element are driven so that the overall length is equal. 3. The optical head according to claim 1, wherein the spherical aberration correcting optical element is constituted by a collimator lens. 3. The optical head according to claim 1, wherein the spherical aberration correcting optical element is constituted by a beam expander. A light source that emits light; and a condensing unit that condenses the light onto a recording medium having a track, wherein the condensing unit includes a main shaft that includes a driving unit, a condensing element that is held by the main shaft, and The first axis is a plane determined by the main axis and the sub axis, and the second plane is a plane perpendicular to the optical axis of the condensing element. An optical head characterized in that a direction when a line of intersection of the first surface and the second surface is projected onto a recording medium and a direction of a track on the recording medium are parallel to each other. A light source that emits light; and a condensing unit that condenses the light onto a recording medium having a track. The condensing unit includes a condensing element that is held on a main shaft that includes a first driving unit; It is composed of a secondary shaft that holds an optical element and is provided with a second driving means, and the displacement of the condensing element by the first driving means and the displacement of the condensing element by the second driving means An optical head that is driven so as to be equal to each other. 10. The optical head according to claim 8, wherein the driving means is constituted by a piezoelectric element that displaces the main axis in the first plane. 10. The optical head according to claim 8, wherein the main shaft is constituted by a lead screw, and the driving means is constituted by a motor for rotating the lead screw. A light source that emits light, and a condensing unit that condenses the light onto a recording medium having a track, the condensing unit being disposed on a concentrating element held on a shaft, and an end of the shaft, and A first piezoelectric element having the other end opposite to the axis fixed; and the other end of the axis opposite to the first piezoelectric element, and the other end opposite to the axis fixed. The first piezoelectric element and the second piezoelectric element so that the entire length of the shaft, the first piezoelectric element, and the second piezoelectric element is equal. An optical head that is driven.

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