Abstract:
Disclosed in a lens actuator for an optical pickup apparatus, including: a movable holder to hold a lens; and an actuator to move the holder in a tracking direction and a focusing direction, wherein the actuator comprises a yoke and a magnet, and the holder contacts with the yoke before the holder contacts with the magnet, when the holder moves in the tracking direction.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a lens actuator for an optical pickup apparatus and an optical pickup apparatus, particularly to a lens actuator and an optical pickup apparatus suitable for actuating an objective lens and the like. 
         [0003]    2. Description of Related Art 
         [0004]    Optical pickup apparatuses have been developed, which can record and/or reproduce information on an optical disk as typified by a CD and DVD. Also, development of an optical pickup apparatuses which can record/reproduce information on an optical disk such as a Blu-ray Disc and HD DVD by using blue-violet semiconductor laser of about 400 nm wavelength has been promoted rapidly. Regarding an objective lens of an optical pickup apparatus to form a focal spot, required are focusing operation to image a focal spot appropriately on an image recording surface of an optical disk in recording and/or reproducing information and tracking operation to follow a track of an optical disk appropriately. 
         [0005]    For example, JP 2005-216357A discloses a lens actuator in which two wire suspension members in each side (four in total) support a lens holder with being capable of performing focusing operation, tracking operation and tilt operation. The suspension members have functions of elastically supporting the lens holder and of supplying electricity to generate magnetism required for each operation. 
         [0006]    When a holder holding an objective lens is moved in a tracking direction in a lens actuator, it is necessary to provide a stopper for preventing the holder from moving over an allowable range. It may be possible that a holder contacts with a magnet of an actuator so as to function as a stopper, when the holder moves a predetermined distance. However, according to such structure, when the holder swiftly contacts with the magnet, defective operation may occur because the magnet may slide or drop from a yoke. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention has been made in consideration of the above problem, and it is one of objects of the present invention to provide a lens actuator and an optical pickup apparatus in which defective operation is prevented. 
         [0008]    In order to attain the above object, according to a first aspect of the invention, a lens actuator for an optical pickup apparatus, comprises: a movable holder to hold a lens; and an actuator to move the holder in a tracking direction and a focusing direction, wherein the actuator comprises a yoke and a magnet, and the holder contacts with the yoke before the holder contacts with the magnet, when the holder moves in the tracking direction. 
         [0009]    According to a second aspect of the invention, an optical pickup apparatus comprises: a lens actuator for an optical pickup apparatus, comprising a movable holder to hold a lens, and an actuator to move the holder in a tracking direction and a focusing direction; and a housing to fix the lens actuator, wherein the actuator comprises a yoke and a magnet, and the holder contacts with the yoke before the holder contacts with the magnet, when the holder moves in the tracking direction. 
         [0010]    According to the lens actuator and optical pickup apparatus of the present invention, the actuator comprises the yoke and the magnet. When the holder moves in the tracking direction, the holder contacts with the yoke before it contacts with the magnet. Accordingly, since the holder is prevented from contacting with the magnet, it is possible to prevent the magnet from being slided or dropping from the yoke. Even when the magnet contacts with the holder after the holder contacts with the yoke, it is still advantageous because the impact on the contact is suppressed to some extent. However, it is preferable that the magnet does not contact with the holder. 
         [0011]    Preferably in the lens actuator and optical pickup apparatus, a length of the yoke in the tracking direction is longer than a length of the magnet in the tracking direction. 
         [0012]    Preferably in the lens actuator and optical pickup apparatus, an interval between the yoke and the holder in the tracking direction is shorter than an interval between the magnet and the holder. 
         [0013]    Preferably in the lens actuator and optical pickup apparatus, the yoke and the magnet are disposed in an opening of the holder, and a width of the opening in the tracking direction is narrower at a position facing with the yoke than a position facing with the magnet. 
         [0014]    Preferably in the lens actuator and optical pickup apparatus, in the opening, a protrusion is formed at a position facing with the yoke. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein; 
           [0016]      FIG. 1  is a perspective view of a lens actuator of the present embodiment; 
           [0017]      FIG. 2  is a view around the magnet  10 A and yoke  8 A watching from the direction of arrow II in  FIG. 1 ; 
           [0018]      FIG. 3  is a similar view with  FIG. 2 , showing a modification of the present embodiment; 
           [0019]      FIG. 4  is a similar view with  FIG. 2 , showing another modification of the present embodiment; and 
           [0020]      FIG. 5  is a similar view with  FIG. 2 , showing another modification of the present embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    Hereinafter, the present invention is described in detain with reference to the drawings.  FIG. 1  is a perspective view of a lens actuator of the present embodiment. A plate-like base  1  which also works as a yoke is fixed on a housing of an unillustrated optical pickup apparatus. A case  2  is fixed on the base  1 . A base board  3  is attached on the front side of the case  2  in the figure. One ends of wires  4  are fixed on the base board  3 , where the number of the wires  4  are three in each side and six in total. The wires  4  are aligned in each side in parallel at even interval in the vertical direction, and are laid along with the base  1 . The other sides of the wires  4  are soldered or caukled on a side wall of a holder  5  through a holder base  14  made of glass epoxy. The wires  4  have functions of supporting the holder  5  movably with respect to the base  1  and of supplying electric power from the base board  3  to which an unillustrated wiring is connected to a coil described below. The case  2  is filled up with gel (not shown) having dumping effect. 
         [0022]    The resin-made holder  5  has tabular shape of approximately pentagon, and an objective lens  6  is attached in a circular opening (not shown) located at the rear side in the figure. The objective lens  6  is used to focus a laser beam on a information recording surface of an optical disk in the optical pickup apparatus. The holder  5  forms two rectangular openings  5   a  and  5   b  at the front side in the figure, and has a balancer  5   c  adjacent to the rectangular openings  5   a  and  5   b . It also can be said that the holder  5  couples the side of the objective lens  6  and the opposite side thereof by columns  5   d  and  5   e  disposed at both sides of the rectangular opening  5   a  and by columns  5   e  and  5   f  disposed at both sides of the rectangular opening  5   b . According to such structure, it is possible to retain high rigidity of the holder  5  even when the cross section of the rectangular openings  5   a  and  5   b  are large. When the central axis of the shared column  5   e  located at the center intersects with the optical axis (and the extension thereof) of the objective lens  6 , the holder  5  can achieve a good balance. 
         [0023]    Inside the rectangular opening  5   a , a pair of magnets  9 A and  10 A are disposed to be opposite to each other, where yokes  7 A an  8 A which are formed by folding a part of the base  1  adheres and supports the magnets  9 A and  10 A from the backside. A first coil assembly G 1  (inner coil  12 A and outer coil  13 A) is disposed to wind around the magnet  9 A and yoke  7 A. A tracking coil  11 A whose coil axis is perpendicular to that of the first coil assembly G 1  is disposed between the first coil assembly G 1  and magnet  10 A. 
         [0024]    Inside the rectangular opening  5   b , a pair of magnets  9 B and  10 B are disposed to be opposite to each other, where yokes  7 A an  8 A which are formed by folding a part of the base  1  support the magnets  9 B and  10 B from the backside. A second coil assembly G 2  (inner coil  12 B and outer coil  13 B) is disposed to wind around the magnet  9 B and yoke  7 B. A tracking coil  11 B whose coil axis is perpendicular to that of the first coil assembly G 2  is disposed between the second coil assembly G 2  and magnet  10 B. The first coil assembly G 1  is attached to the rectangular opening  5   a  through a holder  15 A holding the both sides thereof, and the second coil assembly G 2  is attached to the rectangular opening  5   b  through a holder  15 B holding the both sides thereof. 
         [0025]      FIG. 2  is a view around the magnet  10 A and yoke  8 A watching from the direction of arrow II in  FIG. 1 . The rectangular opening  5   a  comprises steps  5   x  and  5   x  in both upper sides thereof in  FIG. 2 , and the width is narrower at the side of the objective lens. The steps  5   x  and  5   x  face with the yoke  8 A in a tracking direction (shown by an arrow Tr in  FIG. 2  or later), but do not face with the magnet  10 A. 
         [0026]    Next, operation of the lens actuator of the present embodiment is described. In  FIG. 1 , the direction of magnetic field across the outer coil  13 A is same as that across the outer coil  13 B. When electric power is supplied through the wire  4 , the electric current flows in the same direction (clockwise direction in the figure) and the same current value between the outer coils  13 A and  13 B, and magnetism upward in the figure is generated in the outer coils  13 A and  13 B according to Fleming&#39;s left-hand rule. Accordingly, the holder  5  to which the first coil assembly G 1  and second coil assembly G 2  are fixed moves upwardly in the figure so that the objective lens  6  moves in the optical axis direction. Thus, a focusing operation can be realized. When the direction of the electric current flow reverses, the holder moves downward. 
         [0027]    On the other hand, when electric current of clockwise direction is applied to the inner coil  12 B, and that of anticlockwise direction to the inner coil  12 B, magnetism upward in the figure is generated in the inner coil  12 A and magnetism downward in the figure is generated in the inner coil  12 B, according to Fleming&#39;s left-hand rule. Accordingly, a moment around its central axis acts on the holder  5 . Thus, by tilting the holder  5  with the moment, tilt operation of the objective lens  6  can be realized. When electric current directions of the inner coils  12 A and  12 B are both clockwise direction and electric current directions of the outer coils  13 A and  13 B are different each other, it is advantageous that a clockwise magnetic circuit is formed and gap magnetic flux density increases. 
         [0028]    Further, the holder  5  with the objective lens  6  can move in the direction perpendicular to the optical axis by applying electric current to the tracking coils  11 A and  11 B. Thus, tracking operation can be realized. 
         [0029]    According to the present embodiment, when the holder  5  moves more than a predetermined distance in any tracking direction, the step  5   x  at the moving direction contacts with the opposing surface of the yoke  8 A so as to work as a stopper. Thus, it is possible to prevent the holder  5  from moving more. On the other hand, since the step  5   x  does not directly contact with the magnet  10 A, the magnet  10 A is prevented from sliding or dropping out from the yoke  8 A. The step may be or may not be provided at the rectangular opening  5   b.    
         [0030]      FIG. 3  is a similar view with  FIG. 2 , and shows a modification of the present embodiment. In this modification, the rectangular opening  5   a  does not form a step. Instead, the width W 8  of the yoke  8 A in the tracking direction is longer than the width W 10  of the magnet  10 A in the tracking direction, where the protrusion of the yoke  8 A with respect to the magnet  10 A is the same between the both sides thereof. 
         [0031]    According to this modification, when the holder  5  moves more than a predetermined distance in any tracking direction, the side wall of the rectangular opening  5   a  at the moving direction contacts with the opposing surface of the yoke  8 A so as to work as a stopper. Thus, the holder is prevented from moving more. On the other hand, the side wall of the rectangular opening  5   a  does not directly contact with the magnet  10 A, the magnet  10 A is prevented from sliding and dropping from the yoke  8 A. 
         [0032]      FIG. 4  is a similar view of  FIG. 2  showing another modification of the present embodiment. According to the modification, a single opening  5   a  having no step is formed, and a yoke  8 A, a magnet  10 A, a yoke  8 B and a magnet  10 B are disposed in parallel. Here, the width W 8  of the left yoke  8 A in the tracking direction is longer than the width W 10  of the magnet  10 A in the tracking direction, and the yoke  8 A protrudes only on left side with respect to the magnet  10 A. On the other hand, the width W 8 ′ of the right yoke  8 B in the tracking direction is longer than the width W 10 ′ of the magnet  10 B in the tracking direction, and the yoke  8 B protrudes only on the right side with respect to the magnet  10 B. 
         [0033]    According to this modification, when the holder  5  moves more than a predetermined distance in the right direction, the left-side wall of the rectangular opening  5   a  contacts with the opposing surface of the yoke  8 A so as to work as a stopper. Thus, the holder  5  is prevented from moving more. 
         [0034]    On the other hand, the side wall of the rectangular opening  5   a  does not directly contact with the magnet  10 A, the magnet  10 A is prevented from sliding and dropping from the yoke  8 A. Further, when the holder  5  moves more than a predetermined distance in the left direction, the right-side wall of the rectangular opening  5   a  contacts with the opposing surface of the yoke  8 B so as to work as a stopper. Thus, the holder  5  is prevented from moving more. On the other hand, the side wall of the rectangular opening  5   a  does not directly contact with the magnet  10 B, the magnet  10 B is prevented from sliding and dropping from the yoke  8 B. Even when the width of the magnets  10 A and  10 B in the tracking direction is equal or longer than the width of the yoke  8 A and  8 B, similar advantage can be obtained by being the interval between the yokes  8 A and  8 B and the holer  5  shorter than the interval between the magnets  10 A and  10 B and the holder  5  (see the dashed line in  FIG. 4 ). 
         [0035]      FIG. 5  is a similar view with  FIG. 2 , showing another modification of the present embodiment. The modification is different from the embodiment of  FIG. 2  in that semispherical protrusions  5   y  and  5   y  are provided to face with the yoke  8 A instead of providing the steps with the rectangular opening  5   a . According to this modification, when the holder  5  moves more than a predetermined distance in any direction, any of the protrusions  5   y  contacts with the opposing surface of the yoke  8 A so as to work as a stopper. Thus, the holder  5  is prevented from moving more. On the other hand, the side wall of the rectangular opening  5   a  including the protrusion  5   y  does not directly contact with the magnet  10 A, the magnet  10 A is prevented from sliding and dropping from the yoke  8 A. 
         [0036]    Although the present invention is described with reference to the embodiment, the present invention is not limited to these embodiments and optional modification or alternation can be given. For example, the above-described embodiment and the modifications thereof can be carried out in combination. 
         [0037]    The entire disclosure of Japanese Patent Application No. 2006-6213 filed on Jan. 13, 2006, including description, claims, drawings and summary are incorporated herein by reference.