Abstract:
There is disclosed an optical pickup apparatus in which an optical axis of an objective lens can be kept perpendicular to a recording surface of an optical disk regardless of a warp or a curvature of the optical disk. In this optical pickup apparatus, a lens holder can be moved in a focusing direction and a tracking direction. In order that the objective lens can be tilted in accordance with a skew of the optical disk in a radial direction, second magnets are mounted on the lens holder whereas second coils are mounted in opposed relation to the second magnets, respectively. The second magnets and the second coils cooperate with each other to tilt the objective lens.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an optical pickup apparatus used in an optical disk apparatus so as to record and reproduce information relative to an optical disk medium such as a high-density disk and a compact disk. More specifically, the invention relates to an optical pickup apparatus in which an optical axis of an objective lens can be kept perpendicular to a recording surface of the optical disk. 
     2. Description of the Related Art 
     A conventional optical pickup apparatus will now be described with reference to FIG.  10 . FIG. 10 is a perspective view of the conventional optical pickup apparatus, and FIGS. 11 to  14  are views explanatory of a skew of an objective lens developing when a conventional actuator device moves in a focusing direction and a tracking direction. More specifically, FIG. 11 is an enlarged view of a magnetic circuit portion, FIG. 12 is a cross-sectional view taken along the line A—A of FIG. 11, showing a tracking operation, FIG. 13 is a cross-sectional view taken along the line A—A of FIG. 11, showing a focusing-tracking operation, and FIG. 14 is a view explanatory of a skew of the pickup apparatus of FIG. 10 shown in FIG.  13 . 
     As shown in FIG. 10, the conventional optical pickup apparatus comprises an objective lens  1  for converging light onto an optical disk, a lens holder  2  to which the objective lens  1  is secured by an adhesive or the like, a focusing coil  3  adhesively secured to the lens holder  2  so as to move the lens holder  2  in a focusing direction, tracking coils  4  adhesively secured to the lens holder  2  so as to move the lens holder  2  in a tracking direction, four wires  5  which serve to feed electric current to the focusing coil  3  and the tracking coils  4 , and hold the lens holder  2  in a neutral position, relay boards  6  secured to the lens holder  2  by an adhesive or the like so as to relay the feeding of electric current to the focusing coil  3  and the tracking coils  4  from the wires  5 , a suspension base  7  to which the four wires  5 , holding the lens holder  2  in the neutral position, are fixedly secured, a yoke  9  fixedly secured to the suspension base  7  by an adhesive or screws, and magnets  8  fixedly secured to the yoke  9  by an adhesive or the like so as to impart a magnetic field to the focusing coil  3  and the tracking coils  4 . 
     After an optical axis of the objective lens  1  is adjusted, the pickup apparatus of this construction is precisely fixedly secured to a carriage (not shown) by an adhesive or solder. By changing the magnitude and direction of electric current flowing through the focusing coil  3  and the tracking coils  4 , the lens holder  2 , holding the focusing coil  3  and the tracking coils  4 , can be moved in a focusing direction and a tracking direction in accordance with Fleming&#39;s left-hand rule. 
     With the above conventional actuator device, the lens holder  2  can be moved only in the two directions (i.e., the focusing direction and the tracking direction), and therefore when reading and writing information relative to an optical disk having a tilt, a skew angle (i.e., an angle between the optical axis and a line perpendicular to the disk surface) develops, which has resulted in a problem that the reading and writing become unstable. 
     Next, the focusing-tracking operation of the conventional pickup apparatus will be described. The behavior of the lens holder  2  will now be described with reference to FIG. 11D which is a cross-sectional view taken along the line A—A of FIG. 11A, showing the magnetic circuit and the focusing and tracking coils of FIG.  10 . In FIGS. 12A,  12 B,  13 A and  13 B, the showing of the lens-holder  2  is omitted since the behavior of the lens holder  2  can be shown by the focusing coil  3  and the tracking coils  4 . 
     In FIG. 12A, the behavior of the lens holder  2  will be described, assuming that the direction of a magnetic field, formed by the magnets  8  and the yoke  9 , is a direction from the front side of the sheet of the FIG. 12A to the rear side thereof. As shown in FIG. 12A, the direction of upward and downward movement of the lens holder  2  is the focusing direction whereas the direction of right and left movement of the lens holder  2  is the tracking direction. When electric current is flowed in the tracking coils  4  in directions of arrows (FIG.  12 B), the lens holder  2  is moved left according to Fleming&#39;s left-hand rule. Then, in this condition of FIG.  12 B, when electric current is flowed in the focusing coil  3  in a direction of arrows (FIG.  13 A), the lens holder  2  is moved upward in the focusing direction according to Fleming&#39;s left-hand rule. 
     However, as a result of the movement in the focusing direction, the balance of the direction of the electric current in the focusing coil, existing in a magnetic field-existing region (indicated by hatching in FIG.  13 B), is lost, and therefore the lens holder  2  is not moved parallel in the focusing direction, but is angularly moved in a counterclockwise direction to be skewed as shown in FIG.  13 B. The amount of this skew increases as the amount of movement of the lens holder  2  in the focusing direction and the tracking direction increases. FIG. 14 is a view showing skew developing when the lens holder is moved in the focusing direction and the tracking direction. 
     The conventional optical pickup apparatus has the above construction, and therefore a tangential skew and a radial skew of the optical disk, which could be ignored in the conventional optical disk, can not be ignored in the recording and reproduction of a high-density optical disk in view of the reliability of a detection signal. For example, in a DVD, a dynamic skew margin is reduced in accordance with a short wavelength of a laser beam and a high NA (numerical aperture) of an optical system, and therefore a spindle motor for rotating the optical disk is skewed, or the skew is effected using a support shaft, supporting an optical pickup, and a guide shaft, and this adjustment margin prevents the achievement of the thin design. Non-standard optical disks have now been extensively marketed by various makers, and it has now become difficult to properly meet these various optical disks. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an optical pickup apparatus in which there is provided simple drive means for controlling tilt of an objective lens relative to an optical disk, and the tilt control of an optical pickup is effected so that the optical axis of the objective lens can be kept perpendicular to a recording surface of the optical disk. 
     According to the present invention, there is provided an optical pickup apparatus comprising: 
     lens holding means holding an objective lens; 
     lens drive means for driving the lens holding means in a focusing direction and a tracking direction; 
     elastic support members fixedly secured at one ends thereof to the lens holding means to support the lens holding means in a manner to allow movement of the lens holding means; and 
     a support fixing member supporting and fixing the elastic support members, the other ends of the elastic support members being fixedly secured to the support fixing member; 
     wherein the lens drive means is disposed between the lens holding means and the support fixing member; and 
     wherein second lens drive means for driving the lens holding means in a direction inclined relative to the focusing direction or the tracking direction is provided between the lens drive means and the support fixing member. 
     The second lens drive means comprises magnets, mounted on the lens holding means, and coils mounted on the support fixing member. 
     With this construction, there can be provided the optical pickup apparatus in which the lens holding means can be dynamically tilted so that the optimum signal reading can always be effected, thus achieving the tilt adjustment, and the optical axis of the objective lens can be kept perpendicular to a recording surface of an optical disk. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a preferred embodiment of an optical pickup apparatus of the invention; 
     FIG. 2 is a perspective view of a moving portion of the optical pickup apparatus of FIG. 1; 
     FIG. 3 is a perspective view of a fixed portion of the optical pickup apparatus of FIG. 1; 
     FIG. 4 is an exploded, perspective view of the fixed portion of FIG. 3; 
     FIG. 5 is a front-elevational view of a board in a second embodiment of the invention; 
     FIG. 6 is an exploded, perspective view of a tilt drive portion in a third embodiment of the invention; 
     FIG. 7A is an enlarged plan view of a magnetic circuit portion of FIG. 6; 
     FIG. 7B is an enlarged side-elevational view of the magnetic circuit portion of FIG. 6; 
     FIG. 7C is an enlarged front-elevational view of the magnetic circuit portion of FIG. 6; 
     FIGS. 8A and 8B are views explanatory of a tracking operation in FIG. 7; 
     FIGS. 9A,  9 C and  9 E are plan views explanatory of the focusing-tracking operation in FIG. 7; 
     FIGS. 9B,  9 D and  9 F are front-elevational views explanatory of the focusing-tracking operation in FIG. 7; 
     FIG. 10 is a perspective view of a conventional optical pickup apparatus; 
     FIG. 11A is an enlarged plan view of a magnetic circuit portion of FIG. 10; 
     FIG. 11B is an enlarged side-elevational view of the magnetic circuit portion of FIG. 10; 
     FIG. 11C is an enlarged front-elevational view of the magnetic circuit portion of FIG. 10; 
     FIG. 11D is a cross-sectional view taken along the line A—A of FIG. 11A; 
     FIGS. 12A and 12B are cross-sectional views taken along the line A—A of FIG. 11A, showing a tracking operation; 
     FIGS. 13A and 13B are cross-sectional views taken along the line A—A of FIG. 11A, showing a focusing-tracking operation; and 
     FIG. 14 is a view explaining a tilt of the optical pickup apparatus of FIG. 10 shown in FIGS.  13 A and  13 B. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     FIG. 1 is a perspective view of a preferred embodiment of an optical pickup apparatus of the invention. As shown in FIG. 1, this optical pickup apparatus comprises an objective lens  1  for converging light onto an optical disk, a lens holder (lens holding means)  10  to which the objective lens  1  is secured by an adhesive or the like, a focusing coil  3  adhesively secured to the lens holder  10  so as to move the lens holder  10  in a focusing direction, tracking coils  4  adhesively secured to the lens holder  10  so as to move the lens holder  10  in a tracking direction, four wires (elastic support members)  5  which serve to feed electric current to the focusing coil  3  and the tracking coils  4 , and hold the lens holder  10  in a neutral position, relay boards  6  secured to the lens holder  10  by an adhesive or the like so as to relay the feeding of electric current to the focusing coil  3  and the tracking coils  4  from the wires  5 , a board  11  which has the four wires  5  (holding the lens holder  10  in the neutral position) fixedly secured thereto, and is fixedly secured to a suspension base (support fixing member)  13  by a screw  12 , and a yoke  9  fixedly secured to the suspension base  13  by an adhesive or screws, and magnets  8  (which cooperates with the focusing coil  3  and the tracking coils  4  to form lens drive means) fixedly secured to the yoke  9  by an adhesive or the like so as to impart a magnetic field to the focusing coil  3  and the tracking coils  4 . The optical pickup apparatus of the first embodiment further comprises two tilt magnets  14   a  and  14   b  fixedly secured to the lens holder  10  (holding the objective lens  1 ) by an adhesive, and tilt coils  15   a  and  15   b  (which cooperate with the tilt magnets  14   a  and  14   b  to form second lens drive means) disposed in opposed relation to the tilt magnets  14   a  and  14   b , respectively. 
     FIG. 2 is a perspective view of a moving portion of the optical pickup apparatus of FIG.  1 . FIG. 3 is a perspective view of a fixed portion of the optical pickup apparatus of FIG. 1, and FIG. 4 is an exploded, perspective view of the fixed portion of FIG.  3 . In these Figures, the two tilt coils  15   a  and  15   b  are wound respectively on tilt coil bobbins  16   a  and  16   b  molded of a resin. Iron cores  17   a  and  17   b  are fixedly secured respectively to the tilt coil bobbins  16   a  and  16   b  by an adhesive or by insert molding (one-piece molding) and these iron cores  17   a  and  17   b  form magnetic fields when electric current flows in the tilt coils  15   a  and  15   b . The tilt coil bobbins  16   a  and  16   b  are precisely fixed to the suspension base  13 . 
     Next, the driving of the objective lens  1  by the optical pickup apparatus of the first embodiment will be described. First, the lens holder  10  is held in the neutral position by the four wires  5 , and electric current is flowed in the focusing coil  3  and the tracking coils  4  through the wires  5 , and by changing the magnitude and direction of this electric current, the lens holder  10 , having the objective lens  1  mounted thereon, can be moved in the focusing direction and the tracking direction. This operation is the same as the operation of the conventional actuator device. 
     The optical pickup apparatus of the first embodiment has the function of effecting a tilt control so as to correct a skew angle of the lens holder  10 . For example, when electric current is flowed in the tilt coils  15   a  and  15   b  in directions indicated in FIG. 4, the iron cores  17   a  and  17   b , provided respectively within the tilt coils  15   a  and  15   b , are magnetized as shown in FIG.  4 . Therefore, because of the magnetic attraction and repulsion between the magnetized iron cores  17   a  and  17   b  and the tilt magnets  14   a  and  14   b , mounted on the lens holder  10 , a force acts on the lens holder  10  as indicated by arrows in FIG. 2 to tilt the lens holder  10  so that a tilt angle due to a warp of the optical disk can be corrected. Naturally, by changing the direction and magnitude of the electric current flowing in the skew coils  15   a  and  15   b , the direction and angle of tilt of the lens holder  10 , having the objective lens  1  mounted thereon, can be changed. 
     Thus, in addition to the coils for effecting the focusing and tracking operation as in the conventional actuator device, the tilt coils  15   a  and  15   b  are provided for effecting the tilt operation. Therefore, variations in the driver does not need to be taken into consideration, and besides in the normal operation (in which the tilt operation is not effected), the actuator device operates in the same manner as the conventional actuator device, and therefore various characteristics of the actuator device will not be adversely affected. 
     Second Embodiment 
     A second embodiment of an optical pickup apparatus of the invention will be described with reference to FIG.  5 . FIG. 5 is a front-elevational view of aboard in the second embodiment. The optical pickup apparatus of the second embodiment is similar in construction to the optical pickup apparatus of the first embodiment, but differs therefrom in the construction of the board  11 . Four wires  5  are fixedly secured to the board  11 , and the four wires  5  are secured respectively to four end portions  11   a ,  11   b ,  11   c  and  11   d  of the board  11  by soldering. For effecting a tilt operation, two feeders for feeding electric current to a tilt coil  15   a  are soldered respectively to intermediate portions  11   e  and  11   f  of the board  11 , and similarly two feeders for feeding electric current to a tilt coil  15   b  are soldered respectively to intermediate portions  11   g  and  11   h  of the board  11 . Electric current is fed from an external flexible cable to feeders which feed electric current to the coils (focusing coil  3 , tracking coils  4  and tilt coils  15   a  and  15   b ). Thus, the tilt coils  15   a  and  15   b  are soldered to the same surface to which the conventional four wires are soldered, and with this construction the efficiency of the soldering operation in the assembling operation is enhanced. 
     Third Embodiment 
     A third embodiment of an optical pickup apparatus of the invention will be described with reference to FIG.  6 . FIG. 6 is an exploded, perspective view of a tilt drive portion of the third embodiment, and shows constituent elements of the invention added to the conventional actuator device. In the optical pickup apparatus of the third embodiment, the iron cores  17   a  and  17   b , provided for effecting the tilt operation, are so configured as to suppress a skew developing during the focusing operation and the tracking operation. 
     In the optical pickup apparatus of the third embodiment, iron cores  18   a  and  18   b  (corresponding respectively to the iron cores  17   a  and  17   b  in FIG. 4) have such a configuration that upper and lower portions of each iron core  18   a ,  18   b  has a generally L-shaped cross-section, and a projection of this L-shape is removed at an intermediate portion thereof. 
     Next, the behavior of a lens holder  10  will be described with reference to FIGS. 7A to  9 F. FIGS. 7A to  7 C are enlarged views of a magnetic circuit portion, and show only tilt magnets  14   a  and  14   b  and the iron cores  18   a  and  18   b . Since the movement of the lens holder  10  is the same as the movement of the tilt magnets  14   a  and  14   b , the showing of the lens holder is omitted. As shown in FIG. 7, the direction of upward and downward movement of the lens holder  10  is the focusing direction whereas the direction of right and left movement of the lens holder  10  is the tracking direction. 
     FIGS. 8A and 8B are views explanatory of the tracking operation of FIGS. 7A to  7 C. FIG. 8A shows an initial condition, and electric current is not flowed in a focusing coil  3  and tracking coils  4 , and the lens holder  10  is disposed in a neutral position. Then, electric current is flowed in the tracking coils  4 , so that the lens holder  10  (and hence the tilt magnets  14   a  and  14   b ) are moved in the tracking direction as shown in FIG.  8 B. 
     FIGS. 9A to  9 F are views explanatory of the focusing-tracking operation of FIGS. 7A to  7 C. In FIGS. 9A and 9B, electric current is flowed in the focusing coil  3  so that the lens holder  10  can be moved in the upward focusing direction (see FIGS. 7A to  7 C) from the condition of FIG.  8 B. The condition of the lens holder  10 , obtained when flowing this electric current, is shown in FIGS. 9C and 9D. In these Figures, the tilt magnets  14   a  and  14   b  are attracted by the iron cores  18   a  and  18   b , respectively. If the degree of attraction of the tilt magnet  14   a  is equal to that of the tilt magnet  14   b , the lens holder  10  is moved in the focusing direction while kept in a horizontal condition. However, when the lens holder  10  is moved in the tracking direction as shown in FIGS. 9A and 9B, the degree of attraction of the left tilt magnet  14   a  becomes different from the degree of attraction of the right tilt magnet  14   b . Those portions, indicated by hatching in FIG. 9B, represent regions where the tilt magnets  14   a  and  14   b  are liable to be attracted by the iron cores, respectively, and it will be appreciated from FIG. 9B that the attraction of the right tilt magnet is higher than that of the left tilt magnet. Namely, the fact that the attraction of the right tilt magnet is higher means that the right side portion of the lens holder  10  is less moved than the left side portion when the lens holder  10  is moved in the focusing direction. Therefore, the lens holder  10  is tilted as shown in FIG.  9 D. 
     This tilt occurs in a direction to cancel a skew tilt of the lens holder  10  which has been a problem with the behavior of the conventional actuator device (see FIG.  13 B), and by suitably determining the configuration of the iron cores  18   a  and  18   b  (iron cores  17   a  and  17   b  in FIG. 4) employed in the first embodiment, a skew (which has been a problem with the conventional actuator device) can be reduced. Such a skew increases as the amount of movement in the focusing direction increases, and in order that even this increase portion can be canceled, the projection is formed on one side portion of each of the upper and lower end portions of each iron core  18   a ,  18   b , so that these upper and lower end portion have a generally L-shaped cross-section, and the intermediate portion of each iron core  18   a ,  18   b  has a rectangular cross-section. 
     FIGS. 9E and 9F show a modified configuration in which a projection is formed on each iron core  18   a ,  18   b , and extends continuously from its upper end to the lower end, so that the iron core has a generally L-shaped cross-section. With this configuration, similar effects can be achieved. 
     Although the embodiments of the invention are directed to the optical pickup apparatus of the moving coil-type in which the coils are mounted on the lens holder, the invention is not limited to such a moving coil-type optical pickup apparatus. For example, even if the magnets are mounted on the lens holder, similar functions can be achieved. In this case, the wiring to the board end portions  11   a ,  11   b ,  11   c  and  11   d  is omitted. Thus, there can be achieved the optical pickup apparatus which is simple and sturdy in construction. 
     As described above, in the present invention, a skew angle, developing as a result of a warp of the optical disk, can be corrected, and the tilt control can be effected so that the objective lens can be always disposed in a posture best suited for reading signals, and therefore the ability of reading information from the optical disk is enhanced.