Patent Publication Number: US-6714491-B1

Title: Wire-suspended objective lens actuator structure and method of assigning current pathways thereto

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 89105442, filed Mar. 24, 2000. 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to an objective lens actuator structure. More particularly, the present invention relates to a wire-suspended objective lens actuator structure and a method of assigning current pathways. 
     2. Description of Related Art 
     Most photosensitive recording/regenerating devices contain an optical pickup head. To operate a recording/regenerating device, a beam of laser from a light source is passed into the object lens of an optical pickup head. The light beam forms a focus point at the data layer inside an optical disk. On reflecting from the data layer, the laser beam is intercepted by the optical pickup head again so that embedded data on the optical disk is retrieved. 
     The actuator device that drives the optical pickup head has a lens holder. In order for the optical pickup head to access data on an optical disk, a focusing coil for controlling the focus and a tracking coil for controlling the tracking must be installed on the lens holder. Currents are passed into these two coils to produce driving power in the magnetic field so that focusing and tracking are in control. Since the lens holder is the target of control for the focusing and the tracking system, inappropriate suspension renders control of the lens holder very difficult. Hence, it is important to take note of the method of channeling current into the lens holder because the current-position transfer function is likely to be affected. Most wire-suspended actuator device utilizes the conductive wires to suspend the lens holder and to input currents. 
     FIG. 1 is a perspective view of a conventional wire-suspended objective lens actuator structure. FIG. 2 is a side view of the conventional wire-suspended objective lens actuator structure in FIG.  1 . As shown in FIGS. 1 and 2, two U-shaped irons  101  are vertically erected on each side of a base plate  100 . The vertical branch of the U-shaped irons  101  closer to the edges of the base plate  100  is referred to as the outer branch. Similarly, the vertical branch of the U-shaped magnetic irons  101  closer to the middle of the base plate  100  is referred to as the inner branch. Two magnetic blocks  102  are attached to the respective inner sides of the outer branches of the U-shaped irons  101  for generating magnetic fields that cause the lens holder  104  to float on the base plate  100 . A focusing coil  106  and a tracking coil are attached to each side of the lens holder facing the U-shaped irons  101 . The wires inside the focusing coil  106  runs around in a plane that are parallel to the base plate  100 . The inner branch of the U-shaped irons  101  passes through the center of the respective focusing coil  106  assembly. On the other hand, the wires inside the tracking coil  108  runs around in a plane that are perpendicular to the base plate  100 . The tracking coils  108  are positioned between the magnetic block  102  and the inner branch of the U-shaped irons  101 . The lens holder  104  is suspended over the base plate  100  through the control wire  110  of the focusing coil  106 , the control wire  112  of the tracking coil  108 , the ground wire  114  of the focusing coil  106  and the ground wire  116  of the tracking coil  108 . 
     FIG. 3 is a sketch of the assigned current pathways in a conventional wire-suspended objective lens actuator structure. Amongst the four conductive wires shown in FIG. 3, two conductive wires are used for controlling the focusing coil  106  and the other two conductive wires are used for controlling the tracking coil  108 . Current flows into the focusing coil  106  via the control terminal  110  and emerges from the focusing coil  106  via the ground terminal  116 . Similarly, current flows into the tracking coil  108  via the control terminal  112  and emerges from the tracking coil  108  via the ground terminal  116 . 
     As data packing density inside an optical disk continues to rise, resolution of the optical reading system must also increase. Hence, desired perpendicularity between the light axis and the disk surface is correspondingly higher. To control the slant angle of the laser beam, an electrical servo system must be used. Otherwise, precision demanded by the optical system is so high that it is almost impossible to manufacture. In a conventional wire-suspended optical pickup head actuator structure, all four conductive wires are used up by the focusing coil and the tracking coil. Therefore, there is no wires left for installing slant adjustment coils. 
     SUMMARY OF THE INVENTION 
     Accordingly, one object of the present invention is to provide a wire-suspended objective lens actuator structure whose lens holder is able to bear not only a focusing coil for focusing and a tracking coil for tracking, but also a slant adjustment coil for adjusting the slant angle. The wire-suspended actuator structure can be applied to a high-density optical disk and a high-precision optical system. When the optical disk somehow moves away from the optical axis during spinning, the slant adjustment coil is able to adjust the lens holder so that the lens holder remains parallel to the optical disk. Hence, correct data can be read from the optical disk as usual. 
     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for assigning current pathways to the wire-suspended actuator structure. Four conductive wires are used to control three sets of coils. Each of the three conductive lines is used for controlling the focusing coil, the tracking coil and the slant adjustment coil respectively. The fourth conductive wire is a common ground terminal for three sets of coils. 
     This invention also provides a wire-suspended objective lens actuator structure and a method of assigning current pathways such that the ground terminal of the original independent focusing coil and tracking coil are combined. The freed-up ground wire is used as a conductive wire that leads to one of the terminals of a slant adjustment coil. The other terminal of the slant adjustment coil is connected to the common ground terminal of the focusing and tracking coil. The control terminal of the focusing coil, the tracking coil and the slant adjustment coil are each connected to a differential voltage-output current amplifier circuit or to a differential voltage-output voltage amplifier circuit respectively. Using a small differential voltage, focusing, tracking and slant adjustment of the lens holder are possible. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
     FIG. 1 is a perspective view of a conventional wire-suspended objective lens actuator structure; 
     FIG. 2 is a side view of the conventional wire-suspended objective lens actuator structure in FIG. 1; 
     FIG. 3 is a sketch of the assigned current pathways in a conventional wire-suspended objective lens actuator structure; 
     FIG. 4 is a perspective view of a wire-suspended objective lens actuator structure according to this invention; 
     FIG. 5 is top view of the wire-suspended objective lens actuator structure in FIG. 4; 
     FIG. 6 is a sketch of the assigned current pathways in the wire-suspended objective lens actuator structure of this invention; 
     FIG. 7A is a block diagram showing a first method of assigning the current pathways to the wire-suspended objective lens actuator structure of this invention; 
     FIG. 7B is a diagram showing the differential voltage-output current amplifier circuit shown in FIG. 7A; 
     FIG. 8A is a block diagram showing a second method of assigning the current pathways to the wire-suspended objective lens actuator structure of this invention; and 
     FIG. 8B is a diagram showing the differential voltage-output voltage amplifier circuit shown in FIG.  8 A. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     FIG. 4 is a perspective view of a wire-suspended objective lens actuator structure according to this invention. FIG. 5 is top view of the wire-suspended objective lens actuator structure in FIG.  4 . As shown in FIGS. 4 and 5, four U-shaped irons  201  are vertically positioned on a base plate  200 . The U-shaped irons occupy mutually perpendicular directions near the edges of the base plate  200 . The vertical branch of the U-shaped irons  201  closer to the center of the base plate  200  is referred to as the inner branch. Similarly, the vertical branch closer to the edges of the base plate  200  is referred to as the outer branch. Four magnetic blocks are attached to respective inner surfaces of the outer branches of the U-shaped iron  201 . Two magnetic blocks  202   a  are used for focusing and tracking while the other two magnet blocks  202   b  are used for adjusting slant angle. The two focusing and tracking magnets  202   a  are positioned on a pair of U-shaped irons  202  facing each other near the edges of the base plate  200 . The two slant adjustment magnets  202   b  are positioned on another pair of U-shaped irons  202  facing each other again near the edges of the base plate  200 . The four magnets together provide the necessary magnetic fields so that a lens holder  204  is able to float near the center of the base plate  200 . The lens holder  204  is also suspended on top of the base plate  204  through a focusing coil control wire  210 , a tracking coil control wire  212 , a slant adjustment coil control wire  220  and a common ground wire  224 . The conducting wire inside each focusing coil  206  and each slant adjustment coil  218  runs around in a plane parallel to the base plate  200 . The inner branch of the U-shaped irons  201  pass through the focusing coils  206  and the slant adjustment coils  218  respectively. The two focusing coils  206  face each other on each side of the lens holder  204  in the direction where the control wires  210 ,  212 ,  220  and  224  are run. Together with the focusing and tracking magnets  202   a , the focusing coils  206  control the focus. The two slant adjustment coils  218  also face each other on another pair of sides of the lens holder  204 . Together with the slant adjustment magnets  202   b , the slant adjustment coils  218  control the slant angle. The conducting wire inside each tracking coil  208  runs around in a plane perpendicular to the base plate  200 . The tracking coils  208  are inserted between the focusing and tracking magnet  202   a  and the inner branch of the U-shaped iron  201 . Each tracking coil  208  is attached to the focusing coil  206  on each side of the lens holder  204 . 
     FIG. 6 is a sketch of the assigned current pathways in the wire-suspended objective lens actuator structure of this invention. Three conductive wires are connected to the focusing coil  206 , the tracking coil  208  and the slant adjustment coil  218  respectively. The remaining conductive wire is connected to the other ends of the focusing coil  206 , the tracking coil  208  and the slant adjustment coil serving as a common ground terminal  224 . Current for controlling the focusing coil  206  flows into the coil from the control wire  210  and out through the common ground terminal  224 . Similarly, current for controlling the tracking coil  208  flows into the coil from the control wire  212  and out through the ground terminal  224 , and current for controlling the slant adjustment coil  218  flows into the coil from the control wire  220  and out through the ground terminal  224 . 
     FIG. 7A is a block diagram showing a first method of assigning the current pathways to the wire-suspended objective lens actuator structure of this invention. The loads of the coils are R L1 , R L2  and R L3  respectively. The control terminal of each load resistor is connected to the amplifying circuit  301 . The amplifying circuit  301  is in turn connected to individual differential voltage-output current amplifier circuits  300 . 
     FIG. 7B is a diagram showing the differential voltage-output current amplifier circuit shown in FIG.  7 A. Each differential voltage-output current amplifier circuit  300  includes two operational amplifiers OP 1  and OP 2  and five resistors R 1 , R 2 , R 3 , R 4  and R 5 . According to the circuit arrangement, the following can be computed:            V4   -   V5     =         (       R2   R1     -     R4   R3       )        V3     +     (         R4   R3        V2     -       R2   R1        V1       )         ;               I   load     =         V4   -   V5     R5     =           (       R2   R1     -     R4   R3       )        V3     +     (         R4   R3        V2     -       R2   R1        V1       )       R5         ;               if                   R2   R1       =     R4   R3       ,                  then                   I   load       =         V2   -   V1     R5     .                       
     Hence, the load current depends only on the differential voltage (V 2 -V 1 ) and is unaffected by load reactance. 
     FIG. 8A is a block diagram showing a second method of assigning the current pathways to the wire-suspended objective lens actuator structure of this invention. The loads of the coils are R L1 , R L2  and R L3  respectively. The control terminal of each load resistor is connected to the amplifying circuit  401 . The amplifying circuit  401  is in turn connected to individual differential voltage-output voltage amplifier circuits  400 . 
     FIG. 8B is a diagram showing the differential voltage-output voltage amplifier circuit shown in FIG.  8 A. Each differential voltage-output current amplifier circuit  400  includes an operational amplifier OP 3  and four resistors R 1 , R 2 , R 3  and R 4 . According to the circuit arrangement, the following can be computed:          V0   =       R2   R1          [         (     1   +     R1   R2       )                     V2     1   +     R3   R4           -   V1     ]         ;               if                   R3   R4       =     R1   R2       ,                  then                 V0     =       R2   R1            (     V2   -   V1     )     .                         
     Hence, the output voltage depends only on the differential voltage (V 2 -V 1 ). 
     In summary, four conductive wires are used to control three current pathways in this invention. Three conductive wires are used for controlling the focusing coil, the tracing coil and the slant adjustment coil respectively. In fact, (N+1) conductive wires can be used to control N current pathways. Hence, more flexibility and degree of freedom can be conferred to any system having multiple of controlling coils. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.