Abstract:
An objective lens actuator which mainly using an objective lens holder with a flat form facilitates manufacture and fabrication. Also the objective lens actuator controls the focusing direction, tracking direction and radial tilt direction of the optical pickup head. And, the objective lens actuator not only controls but also drives the optical pickup head.

Description:
FIELD OF THE INVENTION 
   The invention relates to an objective lens actuator for controlling and driving an optical pickup head. 
   BACKGROUND OF THE INVENTION 
   The technique of using a laser beam (such as a semiconductor laser) to read data recorded in a read-only optical recording medium (such as a CD or DVD) is well known in the art. The laser beam is focused on the track on the surface of the optical disc through an objective lens located in an optical pickup head, and a photo detector is then used to transform the return light reflected from the optical disc to regenerated signals so that the data recorded in the optical disc may be retrieved. During the data reading process, a tracking signal, focusing signal and radial tilt signal also have to be retrieved from the return light. The tracking signal and the focusing signal are used to control an actuator to move the objective lens in the optical axis direction (i.e. focusing direction), optical disc radial direction (i.e. tracking direction) and radial tilt direction so that the laser beam can accurately focus on a preset track on the optical disc surface. 
   While control of the radial tilt direction is not necessary in the reading operation of the read-only optical recording media, it is mandatory when the laser beam is used to write data on the writable optical recording media to control writing accuracy. The known technique at present for this purpose involves using an actuator that contains a plurality of coils on an objective lens bracket (or other elements), or forming a plurality of coils on a printed circuit board attached to an objective lens bracket to control the moving directions of the objective lens. Whatever designs are adopted for the coils, the locations of the coils are the same. 
   SUMMARY OF THE INVENTION 
   The primary object of the invention is to provide an objective lens actuator to control the focusing direction, tracking direction and radial tilt direction of the pickup head. 
   In order to achieve the foregoing object, the objective lens actuator according to the invention includes a ferromagnetic yoke, an objective lens holder, tracking coils, focusing coils, a magnetic element set, a suspension wire set, a damper holder and a printed circuit board. The ferromagnetic yoke has a cap that includes four inner yokes and an opening. The objective lens holder is movably located on the ferromagnetic yoke and has an objective lens holding port, and second openings. The objective holding port holds an objective lens. The second openings are located on the two opposite sides of the objective lens holder each two that correspond to each other and the second openings are allowing four inner yokes to pass through. The tracking coils are located on the other two opposite sides of the objective lens holder. The focusing coils are located on the periphery of the second openings each. The magnetic element set includes horizontal magnetic elements and vertical magnetic elements. The horizontal magnetic elements are located on the ferromagnetic yoke corresponding to the focusing coils to generate a magnetic flux orthogonal to the optical axis of the objective lens. The vertical magnetic elements are located on the ferromagnetic yoke corresponding to the tracking coils to generate a magnetic flux parallel to the optical axis of the objective lens. The suspension wire set is connected to the objective lens holder, tracking coils and focusing coils to hang the objective lens holder and channel current to the tracking coils and focusing coils. The damper holder is located on the ferromagnetic yoke to allow the suspension wire set to pass through. The printed circuit board is located on the damper holder and is coupled with the suspension wire set to provide current to the tracking coils and focusing coils to drive the objective lens holder. 
   The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of the invention; 
       FIG. 2  is a perspective view of the invention; 
       FIG. 3  is a schematic view of the objective lens holder of the invention; 
       FIG. 4  is a schematic view of magnetic flux directions according to the invention; 
       FIGS. 5A and 5B  are schematic views of the magnetic element set in one magnetic direction and a cross section taken on line I-I; 
       FIGS. 6A and 6B  are schematic views of the magnetic element set in another magnetic direction and a cross section taken on line II-II; and 
       FIGS. 7A and 7B  are schematic views of the vertical magnetic element of the magnetic element set and another embodiment thereof. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 ,  2  and  3 , the objective lens actuator according to the invention includes a ferromagnetic yoke  10 , an objective lens holder  20 , tracking coils  31   a  and  31   b , focusing coils  321 ,  322 ,  323  and  324 , a magnetic element set  40 , a suspension wire set  50 , a damper holder  60  and a printed circuit board  70 . 
   The ferromagnetic yoke  10  has a cap  11  and a plurality of flanges  12  located on lateral sides. The cap  11  includes four inner yokes  111  and an opening  112 . The inner yokes  111  are coupled on the objective lens holder  20 . The flanges  12  aim to hold the magnetic element set  40 , damper holder  60  and printed circuit board  70 . One of the flanges  12  has a screw hole  121 . 
   The objective lens holder  20  is movably located on the ferromagnetic yoke  10  and has an objective lens holding port  21 , and second openings  23 . The objective lens holding port  21  corresponds to the opening  112  to hold an objective lens  80 . The second openings  23  are located on the two opposite sides of the objective lens holder  20  each two that correspond to each other and the second openings  23  are to allowing the four inner yokes  111  to pass through. The inner yokes  111  are located on the opposite sides of the second openings  23  corresponding to each other. 
   The objective lens holder  20  may be a flat board or a printed circuit board. If the objective lens holder  20  is a flat board, the tracking coils  31   a  and  31   b  and the focusing coils  321 ,  322 ,  323  and  324  are attached thereon. The objective lens  80  may be directly attached to the holding port  21 , or be held on the objective lens holder  20  through a coupler  120  and a counter weight  130 . The coupler  120  is located on one side of the objective lens holder  20  and includes a holding bore  120   a  to hold the objective lens  80 . The counter weight  130  which is corresponding to the coupler  120  is located on the other side of the objective lens holder  20  to adjust the center of gravity for the objective lens holder  20  and enable the center of gravity for the suspension wire set  50  to correspond to the printed circuit board  70 . If the objective lens holder  20  is a printed circuit board, the tracking coils  31   a  and  31   b  and the focusing coils  321 ,  322 ,  323  and  324  may be coated thereon. The objective lens  80  may be directly attached to the holding port  21 , or be held on the objective lens holder  20  through a coupler  120  and a counter weight  130 . The coupler  120  is located on one side of the objective lens holder  20 , and includes a holding bore  120   a  to hold the objective lens  80 . The counter weight  130  which is corresponding to the coupler  120  is located on the other side of the objective lens holder  20  to adjust the center of gravity for the objective lens holder  20  and enable the center of gravity for the suspension wire set  50  to correspond to the printed circuit board  70 . 
   Moreover, when the objective lens holder  20  is a flat board, the tracking coils  31   a  and  31   b  are formed on the other two opposite sides of the objective lens holder  20 , while the focusing coils  321 ,  322 ,  323  and  324  are formed on the periphery of the second openings  23  each, and the focusing coils  321 ,  322 ,  323  and  324  are connected in a serial and parallel fashion. 
   The magnetic element set  40  includes a horizontal magnetic element  41  and a vertical magnetic element  42 . The horizontal magnetic element  41  is located on the ferromagnetic yoke  10  corresponding to the focusing coils  321 ,  322 ,  323  and  324  to generate a magnetic flux orthogonal to the optical axis of the objective lens  80 . The vertical magnetic element  42  is located on the ferromagnetic yoke  10  corresponding to the tracking coils  31   a  and  31   b  to generate a magnetic flux parallel to the optical axis of the objective lens  80 . The magnetic flux direction is shown in  FIG. 4 . 
   The horizontal magnetic element  41  includes a first horizontal magnetic element  411  and a second horizontal magnetic element  412  that are located respectively on the outer sides of the focusing coils  321 ,  322 ,  323  and  324 , and the flanges  12  with a magnetic flux direction orthogonal to the horizontal moving direction of the objective lens holder  20 . Referring to  FIGS. 5A and 5B , the magnetic flux direction from N pole to S pole of the first horizontal magnetic element  411  is in the direction from the flange  12  to the inner yoke  111 . The magnetic flux direction from N pole to S pole of the second horizontal magnetic element  412  also is in the direction from the flange  12  to the inner yoke  111 . Another design may be adopted as shown in  FIGS. 6A and 6B  with another magnetic flux direction of the magnetic elements. The magnetic flux direction from N pole to S pole of the first horizontal magnetic element  411  is in the direction from the flange  12  to the inner yoke  111 , and from the inner yoke  111  to the flange  12 . The magnetic flux direction from N pole to S pole of second horizontal magnetic element  412  is in the direction from the flange  12  to the inner yoke  111  (corresponding to the first horizontal magnetic element  411  that has a magnetic flux direction from N pole to S pole in the direction from the flange  12  to the inner yoke  111 ), and from the inner yoke  111  to the flange  12  (corresponding to the first horizontal magnetic element  411  that has a magnetic flux direction from N pole to S pole in the direction from the inner yoke  111  to the flange  12 ). 
   The vertical magnetic element  42  includes two first vertical magnetic elements  421  and two second vertical magnetic elements  422  corresponding respectively to the two tracking coils  31   a  and  31   b . The two first vertical magnetic elements  421  are located on two opposite sides of one tracking coil  31   a  and have the same magnetic flux direction. That is, the magnetic flux direction from N pole to S pole of the first vertical magnetic elements  421  is in the direction from the cap  11  to the objective lens holder  20 . The two second vertical magnetic elements  422  are located on two opposite sides of the other tracking coil  31   b  and have the same magnetic flux direction. That is, the magnetic flux direction from N pole to S pole of the second vertical magnetic elements  422  is in the direction from the cap  11  to the objective lens holder  20 . 
   Moreover, the inner yokes  111  are positioned in such a manner so that the magnetic flux generated by the horizontal magnetic element  41  and the vertical magnetic element  42  of the magnetic element set  40  between the inner yokes  111  and the flanges  12  are coincided. Namely, the air gaps have magnetic fields to allow the tracking coils  31   a  and  31   b  and the focusing coils  321 ,  322 ,  323  and  324  to generate magnetic fluxes. 
   The suspension wire set  50  includes a suspension wire  51  that has one end connected to the objective lens holder  20 , tracking coils  31   a  and  31   b , and focusing coils  321 ,  322 ,  323  and  324  to hang the objective lens holder  20  and channel current to the tracking coils  31   a  and  31   b  and focusing coils  321 ,  322 ,  323  and  324 . 
   The damper holder  60  is located on the ferromagnetic yoke  10  and has a notch  61  to allow the suspension wire set  50  to pass through. The damper holder  60  also has a screw hole  62 . 
   The printed circuit board  70  is located on the damper holder  60  and is coupled with the suspension wire set  50  on the other end of the suspension wire  51  to provide current to the tracking coils  31   a  and  31   b  and the focusing coils  321 ,  322 ,  323  and  324  to drive the objective lens holder  20 . The printed circuit board  70  also has a screw hole  71 . 
   For assembly of the invention, when the objective lens holder  20  is a flat board, the tracking coils  31   a  and  31   b  are located on the other two opposite sides of the objective lens holder  20 , and the focusing coils  321 ,  322 ,  323  and  324  are located on the periphery of the second openings  23  each. If the objective lens holder  20  is a printed circuit board, the tracking coils  31   a  and  31   b  and the focusing coils  321 ,  322 ,  323  and  324  are coated on the printed circuit board, and no other action is needed. Place the objective lens  80  on the objective lens holding port  21  (or dispose the coupler  120  on one side of the objective lens holder  20 , and the counter weight  130  on the other side of the objective lens holder  20 , and attach the objective lens  80  to the holding bore  120   a ). Couple the inner yokes  111  of the cap  11  on the second openings  23  of the objective lens holder  20  with the opening  112  corresponding to the objective lens  80  held in the objective lens holding port  21 . Mount the first horizontal magnetic element  411  and the second horizontal magnetic element  412  of the magnetic element set  40  onto two opposite flanges  12 , and place the two first vertical magnetic elements  421  on two opposite sides of one tracking coil  31   a , namely the ferromagnetic yoke  10  and the cap  11 , and place the second vertical magnetic elements  422  on two opposite sides of the other tracking coil  31   b , namely the ferromagnetic yoke  10  and the cap  11 . Connect one end of the suspension wire  51  of the suspension wire set  50  to the objective lens holder  20 , tracking coils  31   a  and  31   b , and focusing coils  321 ,  322 ,  323  and  324 , and pass the other end of the suspension wire  51  through a damper  90  and connect to the printed circuit board  70 . Then a screw  100  runs through a washer  110 , the screw hole  121  of the flange  12 , the screw hole  62  of the damper holder  60  and the screw hole  71  of the printed circuit board  70  to couple the flange  12 , damper holder  60  and printed circuit board  70  together. 
   After assembling the invention as such, current can flow through the printed circuit board  70  and the suspension wire  51  to the tracking coils  31   a  and  31   b  and focusing coils  321 ,  322 ,  323  and  324  so that the air gaps between the inner yokes  111  and the flanges  12  have a magnetic field to enable the tracking coils  31   a  and  31   b  and focusing coils  321 ,  322 ,  323  and  324  to generate magnetic fluxes. While the current flows through the focusing coils  321 ,  322 ,  323  and  324 , magnetic fluxes are generated to move the objective lens holder  20  vertically. In the event that the magnetic fluxes generated by the focusing coils  321 ,  322 ,  323  and  324  are different, the variation of the magnetic fluxes drives the objective lens holder  20  in a tilted movement so that the incident light projected on the data storage medium may be kept as orthogonal as possible to obtain a desired signal. 
   Refer to  FIGS. 7A and 7B  for another embodiment of the vertical magnetic element of the invention. The magnetic element set  40  may adopt another design. The vertical magnetic element  42  includes a first vertical magnetic element  421  and a second vertical magnetic element  422  located on the same side of the two tracking coils  31   a  and  31   b . Then the two tracking coils  31   a  and  31   b  also can generate magnetic fluxes. 
   While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.