Abstract:
Disclosed are a pickup device assembly and an optical drive system. The assembly may comprise: a laser generator for generating laser beams; an objective lens; and at least one piezoelectric actuator for generating bending moments once applied with voltages, wherein the generated bending moments move the objective lens such that the laser beams are focused by the objective lens and then aim at concentric spiral data tracks of a disc with a strongest reflected signal of the laser beams from the disc.

Description:
TECHNICAL FIELD 
     The disclosure herein relates to an optical pickup assembly and an optical drive system with the same. 
     BACKGROUND 
     High definition (HD) videos and HDTV broadcasting become more popular in the entertainment industry. The HD videos and HDTV contents are generally recorded in an optical disc. The conventional optical drive for writing and playing back the HD videos and HDTV generally comprises a house, a disc/spindle assembly, an optical pickup assembly and a plurality of control circuits, in which the optical pickup assembly is a “heart” of the optical drive and is used for reading from and writing data into the optical disc. 
     The optical pickup assembly mainly comprises a laser generator (i.e. laser diode), a half-reflecting prism, an objective lens and a plurality of photodiodes. When reading the data from the optical disc, the laser generator generates and emits laser beams. The generated laser beams run through the half-reflecting prism and are converged into the objective lens, which in turn focuses the converged laser beams into small optical spots and sends the optical spots to the disc. Reflecting materials on the disc will reflect the optical spots. The reflected optical spots are transmitted through the objective lens and then reach the photodiodes via the half-reflecting prism. Since there are some pits in a surface of the disc to record the data, the laser beams are reflected from the surface of the disc in various directions. Signals of the laser beams in various directions may be represented as “0” or “1”. The photodiodes decode the data of “0” or “1” in a desirable format for playing back. 
     In the optical disc, data are recorded in concentric spiral tracks. When reading the data from the concentric spiral tracks, the error correction capability and reliability of the optical pickup assembly will directly depend on two motions of “tracking” and “focusing”. The “tracking” is to keep the laser beams aiming at the concentric spiral tracks. The called “focusing” is to accurately transmit the laser beams to the disc with the strongest reflected signal from the disc. The objective lens may be moved in a vertical direction to provide the motion of “focusing”, and moved in a horizontal direction to provide the motion of “tracking”. In order to maintain the “tracking” and “focusing” motions, a continuous adjustment of the lens-disc separation and of a radial position on the track are performed when reading and writing. 
     Currently large capacity optical disc formats such as Blu-ray and HD-DVD have been proposed. Accordingly, the optical drive is needed to be improved so as to quickly and precisely position optical detecting spots in tracking and focusing motions in optical pickup assembly. 
     SUMMARY 
     In a first aspect, there is provided a pickup device assembly comprising: 
     a laser generator for generating laser beams; 
     an objective lens; and 
     at least one piezoelectric actuator for generating bending moments once applied with voltages, 
     wherein the generated bending moments move the objective lens such that the laser beams are focused by the objective lens and then aim at concentric spiral data tracks of a disc with a strongest reflected signal of the laser beams from the disc. 
     According to one embodiment, two piezoelectric actuators generates bending moments once applied with voltages to move the objective lens in a horizontal direction such that the laser beams are focused by the objective lens and then aim at concentric spiral data tracks of a disc; and to move the objective lens in a vertical direction such that the laser beams are accurately transmitted through the lens to the disc with a strongest reflected signal of the laser beams from the disc. 
     Each of the two piezoelectric actuators may comprise a piezoelectric layer; and a shim arranged on one side of the piezoelectric layer. Alternatively, each of the two piezoelectric actuators is a piezoelectric bimorph actuator with two piezoelectric layers, and a shim is sandwiched between the two piezoelectric layers. There is provided a damping layer on one side of each actuator, and a constraining layer on one side of the damping layer. In another implementation, at least one segment of damping layer and the at least one segment of force transmission layer may be alternately sandwiched between the two piezoelectric layers. 
     In one embodiment, a lever beam is arranged between the two piezoelectric actuators to support the objective lens. 
     In a second aspect, there is provided a pickup system comprising: 
     a laser generator for generating laser beams; 
     an objective lens; and 
     at least one first actuator once applied with voltages to move the objective lens in a horizontal direction so as to implement a primary tracking motion; 
     at least one second actuator for generating bending moments once applied with voltages to move the objective lens in a horizontal direction so as to implement a second tracking motion, wherein the first tracking motion co-acts with the secondary tracking motion such that the laser beams are focused by the objective lens and then aim at concentric spiral data tracks of a disc; and 
     wherein the bending moments from the second actuator further make the objective lens to move in a vertical direction such that the laser beams are accurately transmitted through the lens to the disc with a strongest reflected signal of the laser beams from the disc. The movement amount of the objective lens caused by the first actuator may be more than that caused by the second actuator. 
     In a third aspect, there is provided a pickup unit, comprising: two piezoelectric actuators; a lever beam arranged between the two piezoelectric actuators; an objective lens arranged on the lever beam; wherein there is provided with a damping layer on one side of each of the piezoelectric actuators, and there is provided with a constraining layer on one side of the damping layer. 
     In a fourth aspect, there is provided a pickup unit, comprising: two piezoelectric actuators; a lever beam arranged between the two piezoelectric actuators; an objective lens arranged on the lever beam; wherein each of the two piezoelectric actuators comprises two piezoelectric layers, and wherein at least one segment of damping layer and at least one segment of force transmission layer are alternately sandwiched between the two piezoelectric layers. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a perspective view of a piezo-based optical pickup system according to one embodiment of the application. 
         FIG. 2  illustrates a perspective view of a piezo-based optical pickup system according to another embodiment of the application. 
         FIG. 3  illustrates an optical pickup system according to one embodiment of the application. 
         FIGS. 4A and 4B  are perspective views illustrating in two sides a piezo-based optical pickup device according to one embodiment of the application. 
         FIG. 5  is an exploded view of a piezo-based optical pickup device as shown in  FIGS. 4A and 4B . 
         FIGS. 6A and 6B  illustrate the movement relationship between the bimorph actuators and the objective lens according to one embodiment of the application. 
         FIGS. 7A-7D  illustrate different shapes of the constraining layer without a hinge according to different embodiments of the application. 
         FIGS. 8A-8D  illustrate different shapes of the constraining layer with a hinge according to different embodiments of the application. 
         FIG. 9  illustrates a perspective view of a piezo-based optical pickup system according to another embodiment of the application. 
         FIG. 10  is a cross-sectional view of the bimorph actuator according to one embodiment of the application as shown in  FIG. 9 . 
         FIG. 11  illustrates a perspective view of a piezo-based optical pickup system according to another embodiment of the application. 
         FIG. 12  is a cross-sectional view of the bimorph actuator according to one embodiment of the application as shown in  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, the exemplified embodiments in the application will be discussed in reference to the accompanying drawings. 
       FIG. 1  illustrates a perspective view of a piezo-based optical pickup system  200  according to one embodiment of the application. The system  200  comprises an arm body  203 , which may has an acute triangular shape as shown in  FIG. 1 . In a substantive center of the arm body  203 , the arm body  203  is pivotally connected with a pivot bearing  202 . A pickup device assembly  20  is arranged on one side of the arm body  203  and is provided with an optical pickup system  204 . For example, the optical pickup system  204  may include an objective lens  26 , a half-reflecting prism  2041  and a laser generator and photo-detector assembly  2042 , as shown in  FIG. 3 . For purpose of clarity, the laser generator and photo-detector assembly  2042  and half-reflecting mirror prism  2041  are omitted in  FIG. 1 . 
     There is provided a hollow hole on the side of the arm body  203  that is adjacent to the bottom of the triangular shape. Arranged around the internal sides of the hole is a voice coil motor (VCM)  201 . One or more permanent magnets (not shown) are arranged above or under the VCM  201 . When applied with voltages, the VCM  201  generates a magnetic field. The magnetic field co-acts with the magnetic field generated by the permanent magnets so as to enable the arm body  203  to rotate around the pivot bearing  202 , which in turn makes the objective lens  26  arranged on the pickup device assembly  20  to move in a horizontal direction. 
     In this implementation, VCM  201  severs as a first actuator to make the objective lens  26  to move considerably in the horizontal direction so as to carry out a first stage and coarse “tracking” motion; while a second stage and fine “tracking” motion will be carried out in the pickup device assembly  20 , which will discussed below in reference to  FIGS. 4 and 5 . The first stage and coarse “tracking” motion and the second stage and fine “tracking” motion cooperate and form a dual-stage servo system for track seeking. 
       FIG. 2  illustrates a perspective view of a piezo-based optical pickup system  300  according to another embodiment of the application. The system  300  comprises two yokes  302 A and  302 B, which are opposite to each other, and a pair of magnetic flux insulators  305 A and  305 B. The two yokes  302 A and  302 B, and insulators  305 A and  305 B form a structure of rectangular frame. The yokes  302 A and  302 B may be made of magnetic conduction materials such as pure iron or silicon steel, and the insulators  305 A and  305 B may be made of non-magnetic conduction materials such as aluminum. 
     Two magnets  303 A and  303 B are arranged in the internal sides of the two yokes  302 A and  302 B, respectively. There are provided a pair of guiding rods  304 A and  304 B between the insulators  305 A and  305 B. The guiding rods  304 A and  304 B are separated from each other and extend along the extending direction of the magnets  302 A and  302 B. The guiding rods  304 A and  304 B may be made of magnetism-conductive materials. A VCM  301 A is housed on the guiding rod  304 A and a VCM  301 B is housed on the guiding rod  304 B. A pickup device assembly  20  is arranged between the VCM  301 A and the VCM  301 B. The pickup device assembly  20  may include an optical pickup system  204  as shown in  FIG. 3 . Again, the members  2041  and  2042  are omitted in  FIG. 2  for purpose of clarity. 
     When applied with voltages, each of the VCM  301 A and the VCM  301 B generates a magnetic field. The generated magnetic field co-acts with the magnetic field generated by the magnets  303 A and  303 B so as to move the pickup device assembly  20  in a horizontal direction, which in turn move the objective lens  26  thereon accordingly. In this implementation, VCMs  301 A and  301 B make the objective lens  26  to move considerably in the horizontal direction so as to carry out a first stage and coarse “tracking” motion; while the pickup device assembly  20  will carry out a second stage and fine “tracking” motion, which will discussed below in reference to  FIGS. 4 and 5 . The first stage and coarse “tracking” motion and the second stage and fine “tracking” motion cooperate and form a dual-stage servo system for track seeking. 
     Hereinafter, the pickup device assembly  20  according to the embodiments of the application will be discussed in reference to the accompanying drawings. 
     In general, the pickup device assembly  20  may carry out the secondary stage and fine “tracking” motion by moving the objective lens  26  therein in a horizontal direction, and the “focusing” motion by moving the objective lens  26  therein in a vertical direction. In the pickup device assembly  20 , there are provided two oppositely arranged piezoelectric actuators, such as bimorph actuators, between which the objective lens  26  is arranged. Take the piezoelectric bimorph actuators as an example, when applied with voltages, one piezoelectric layer of the each bimorph actuator extends and the other piezoelectric layer thereof contracts, and thus the piezoelectric bimorph actuator deforms, which in turn makes the objective lens  26  to move in a horizontal and radial direction such that the laser beams from the laser generator may be aimed at the concentric spiral tracks of the disc (i.e. the secondary stage “tracking” motion), and to move in a vertical direction such that the laser beams may be accurately transmitted to the disc with the strongest reflected signal from the disc (i.e. “focusing” motion). 
     In particular, a lever beam may be supported between the two bimorph actuators, and the objective lens may be arranged on the lever beam. Once applied with voltages, the bimorph actuators deform, and then generate forces and bending moments to move the lever beam in horizontal direction or vertical direction. The horizontal or vertical movements of the lever beam make the objective lens to move accordingly so as to complete the “tracking” or “focusing” motion. 
     The more details for the pickup device assembly  20  will be discussed in reference to  FIGS. 4-12 . 
       FIGS. 4A and 4B  are perspective views illustrating in two sides a piezo-based optical pickup device  20  according to one embodiment of the application.  FIG. 5  is an exploded view of a piezo-based optical pickup device as shown in  FIGS. 4A and 4B . As shown, the optical pickup device  20  comprises a housing  27  on which there are arranged piezoelectric actuators  21 A and  21 B, damping layers  22 A and  22 B, and constraining layers  23 A and  23 B. Each of the actuators  21 A and  21 B comprises two piezoelectric layers, between which a shim is sandwiched. The shim may be formed of metal materials, such as brass or stainless steel, or composite materials. The damping layers  23 A and  23 B may be formed of viscoelastic materials and the constraining layers  22 A and  22 B may be formed of metal materials. It should be appreciated that the number of piezoelectric layers shall be less or more than two although the above are discussed in reference to the actuators  21 A and  21 B comprising two piezoelectric layers. In the case that each of actuators  21 A and  21 B is made of single piezoelectric layer, the shim may be arranged on one side of the single piezoelectric layer. Hereinafter, the discussion will be made in reference to the actuators  21 A and  21 B comprising two piezoelectric layers (also referred to “bimorph actuators”). 
     The housing  27  may have a cuboid body with configurations for holding the bimorph actuators  21 A and  21 B, the damping layers  22 A and  22 B, and the constraining layers  23 A and  23 B. In one example, the configurations may be two holding slots  28 A and  28 B symmetrically formed in the house. As shown in  FIGS. 4 and 5 , the bimorph actuators may be shaped as rectangular sheets, and the damping layers and constraining layers may be shaped as triangular sheets, respectively. One end of each of the bimorph actuators  21 A and  21 B, damping layers  23 A and  23 B, and constraining layers  22 A and  22 B is inserted into the slots. 
     As shown, a lever beam  25  is held between the two bimorph actuators  21 A and  21 B. According to one embodiment, the lever beam  25  may be held in the middle of the front ends of the bimorph actuators  21 A and  21 B. The lever beam  25  may be attached to each bimorph actuator  21 A and  21 B by an epoxy  24 A and an epoxy  24 B. It should be understood that the lever beam  25  may be attached or fixed to each bimorph actuator  21 A and  21 B by other available means. The lever beam  25  may be made of brass or stainless steel, which materials may be different from that of the constraining layers  23 A and  23 B. The materials of the lever beam  25  may be selected depending on the required stroke for the “focusing” motion. The objective lens  26  is substantively arranged in the center of the lever beam  25 . As shown in  FIG. 5 , an epoxy  30 A and an epoxy  30 B are used to connect the lever beam  25  to the lever bases  29 A and  29 B. 
     The bimorph actuators  21 A and  21 B have not only high resolution and bandwidth but also light weight and low power consumption compared with voice coil motors. When applied with voltages, the bimorph actuators  21 A and  21 B operate to generate forces and bending moments to move the lever beam  25  in a horizontal direction, which in turn moves the objective lens  26  thereon accordingly so as to carry out the secondary “tracking” motion, and to contract or extend the lever beam  25  to lift the objective lens upwards and downwards so as to carry out the “focusing” motion. 
     In particular, when the actuators  21 A and  21 B bend in the same direction, the lever beam  25  as well as the lens  26  thereon will be moved towards the tracking direction, as shown in  FIG. 6A . When the actuators  21 A and  21 B bend in opposite directions, for instance, both of the actuators  21 A and  21 B move towards the lens  26 , the lever beam  25  will be squeezed and then arched, which in turn lifts up the lens  26 . While both of the actuators  21 A and  21 B move far away from the lens, the lever beam  25  will be extended, which in turn makes the lens move down, as shown in  FIG. 6B . As discussed in the above, the “tracking” motion caused by the actuators  21 A and  21 B is referred to the secondary fine “tracking” motion, which co-acts with the first coarse “tracking” motion to keep the laser beams from the laser generator and photo-detector assembly  2042  ( FIG. 3 ) aimed at the concentric spiral tracks of the disc. On the other hand, the lens  26  is moved in a vertical direction such that the laser beams from the laser generator and photo-detector assembly  2042  may be accurately transmitted to the disc with the strongest reflected signal from the disc. When the laser beams are reflected from the disc, they will reach a plurality of photodiodes (not shown) in the optical pickup system  204 . The signals of reflected laser beams from each of photodiodes are added so as to form a focusing error signal. Only the focusing error signal is of zero, the focusing is accurate and the reflected signal will be the strongest one. 
     The damping layers  22 A and  22 B and the constraining layers  23 A and  23 B may extend along the lengthwise direction of the bimorph actuator  21 A and  21 B. The damping layers  22 A and  22 B are specially shaped in order to tackle a critical vibration mode arisen during the device  20  operates or the external shock impacts. As the bimorph actuators  21 A and  21 B swing to provide the “tracking” and “focusing” motions, they expand or contract one side of the damping layer while the constraining layer constrains the other side of the damping layer from moving. The relative motion between two sides of the damping layer generates a shear deformation to dissipate the vibration energy. 
     According to another embodiment, a hinge  54  is linked between the lever beam  25  and at least one of constraining layers  23 A and  23 B to adjust the stiffness of the pickup device and hold the lever beam  25  in the middle of the front ends of the bimorph actuators in the assembly, as shown in  FIGS. 8A-8D . In another embodiment, the hinge  54  is connected to the at least one of constraining layers  23 A and  23 B. In the case that the lever beam  25  is attached to the bimorph actuator  21 A and  21 B by epoxy at the beam bases  29 A and  29 B, the hinge  54  may be provided between the constraining layers  23 A and  23 B and the lever bases  29 A and  29 B. 
     According to another embodiment of the optical pickup device  20 , only one hinge  54  is provided between the lever beam  25  and one of constraining layers  23 A and  23 B, or between the lever beam  25  and both of constraining layers  23 A and  23 B. In this embodiment, each of the damping layers  22 A and  22 B and constraining layers  23 A and  23 B may be shaped with a triangular sheet, as shown in  FIG. 7A . Alternatively, the damping layers  22 A and  22 B and constraining layers  23 A and  23 B may be shaped in different way. For example, each of the damping layers  22 A and  22 B and constraining layers  23 A and  23 B may be shaped as a curved triangular sheet as shown in  FIG. 7B , a curved trapezoid sheet as shown in  FIG. 7C , and an elliptic sheet as shown in  FIG. 7D . 
       FIG. 9  illustrates a piezo-based optical pickup device  90  according to one embodiment of the application.  FIG. 10  is a cross-sectional view of the bimorph actuator as shown in  FIG. 9 . As shown, the optical pickup device  90  comprises two piezoelectric actuators  91 A and  91 B, each of which is inserted in a slot on the housing  97 . The above mentioned lever beam  25  is provided between the two bimorph actuators  91 A and  91 B, and an objective lens  26  is arranged on the lever beam  25 . 
     Each of bimorph actuators  91 A and  91 B has a first piezoelectric layer  911 A and a second piezoelectric layer  911 B, between which there are sandwiched a viscoelastic damping layer  912 , and an epoxy layer  914  for increasing the transmissibility of active action of each bimorph actuator. Between the first piezoelectric layer  911 A and the second piezoelectric layer 911 B, the viscoelastic damping layer  912  and the conductive epoxy layer  914  form a separation  913  that is used as a reserving space for the shearing changes of the damping layer  912 . The epoxy layer  914  is conductive and connects the opposite sides of the layers  911 A and  911 B. 
     Alternatively, as shown in  FIGS. 11 and 12 , a plurality of segment of viscoelastic damping layers  1012 A,  1012 B and  1012 C and a plurality of segment of conductive epoxy layers  1014 A,  1014 B,  1014 C may be alternately sandwiched between the first piezoelectric layer  911 A and the second piezoelectric layer  911 B, in which each viscoelastic damping layer and the conductive epoxy layer adjacent thereto form separations  1013  that are used as reserving spaces for the shearing changes of the respective damping layer  1012 A,  1012 B and  1012 C. 
     According to this embodiment, the viscoelastic damping layers are used as a shim of the bimorph actuator to gain the damping effect. As the viscoelastic shimmed bimorph actuator swings to provide the tracking and focusing motions, one of the piezoelectric layers  911 A and  911 B expands one side of the viscoelastic layer while the other piezoelectric layer contracts the other side of the viscoelastic layer. The relative motion between two sides of the viscoelastic layer generates a shear deformation in the viscoelastic layer to dissipate the vibration energy in the pickup device. 
     The embodiments according to the application have been described in reference to the accompanying drawings, but the present invention is not limited thereto. Various modifications and changes can be made by those skilled in the art according to the disclosure herein, which should be within the scope of the present invention.