Abstract:
It is an object of the present invention to provide an optical pickup apparatus appropriate for the notebook PC that can prevent structural resonance of the lens holder by arranging the focus coil and the tracking coil in a way to stabilize the weight balance, enable the tilt servo, and be composed in an extremely reduced thickness. An optical pickup apparatus composed to adjust the irradiation position of light beam to an optical disk by displacing an objective lens through a driving control of a lens holder holding the objective lens with a moving coil method, wherein an objective lens driving section is composed by arranging and fixing focus coils  7   a   , 7   b  so that a pair of coil main bodies be symmetrical about the objective lens  4  arranged at the middle of the lens holder  4 , and arranging a pair of tracking coils  8   a   , 8   b   , 8   c   , 8   d  at both sides of the respective focus coils.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention concerns an optical pickup apparatus for an optical disk apparatus improved in order to build in a personal computer (“PC” hereinafter), especially in a notebook PC. 
   2. Detailed Description of the Prior Art 
   In general, a PC is equipped as standard with an optical disk apparatus for reproducing record of or recording information in an optical disk abbreviated to CD (compact disk), DVD (digital versatile disk), which is essential for processing information powerfully and at the same time required to present a high accuracy and reliability according to the increase of storage density and the increase of readout speed, writing speed or others. 
     FIG. 9  shows an optical pickup apparatus for an optical disk apparatus adopted relatively largely for a desk top PC, and the same apparatus is so composed that, a light beam emitted from an semiconductor laser device  101  transmits a beam splitter  102  and enters an objective lens  104  installed in a lens holder  103 . Then, this objective lens  104  collects the light beam and spots of beam are formed in fine pits formed on a recording surface of an optical disk D. 
   The beam reflected from the recording surface of the optical disk D returns transmitting the objective lens  104  and is reflected in a right angle direction by the beam splitter  102 . Then, the light beam intensity detected by a photodiode  105  enables to read the record bits on the optical disk D. 
   By the way, as face run-out or eccentricity exist, for a rapidly rotating optical disk D, it is composed to irradiated the recording bit of the optical disk D with a spot of the beam correctly all the times, by making the objective lens  104  follow, in respect to this face run-out or eccentricity, by an objective lens driving apparatus. 
   This objective lens driving apparatus is the one where a focus coil  106  is wound on a side face of the lens holder  103  for holding the objective lens  104 , and further tracking coils  107  are disposed by one pair respectively on the opposite two faces. Then, a permanent magnet  108  and a yoke base  109  are arranged in a way to pinch these focus coils  106  and the tracking coil  107 , and compose a magnetic circuit. The lens holder  103  is supported by a suspension wire  110  and a suspension holder  111 , and the whole lens holder  103  is driven by a control current supplied to the focus coil  106  and the tracking coil  107 , so that the objective lens  104  can be positioned correctly. 
   Next, an optical pickup apparatus shown in  FIG. 10  has been developed for an optical disk apparatus to be built in a notebook PC and respective components are composed extremely flat, in order to integrate in a flat body of the notebook PC. In the same drawing, the symbol  112  is a lens holder, holding an objective lens  113  at the front end and a focus coil  114  at the rear end. Two tracking coils  115  are affixed to an open end face of the focus coil, and the focus coil  114  and the tracking coil  115  are supported by a suspension wire  118  and a suspension holder  119  so that they are positioned simultaneously in a magnetic circuit formed by permanent magnets  116 ,  117 . Then it is so composed that light beam incident transversely into a rising mirror  121  arranged in a frame body (not shown) under a yoke base  120  be incident to the objective lens  113 . 
   SUMMARY OF THE INVENTION 
   In the optical pickup apparatus composed as shown in  FIG. 9 , there is globally no mass-bias, because the focus coil  106  and the tracking coil  107  are arranged point-symmetrically about the objective lens  104 . The driving force generated by the coil act equally to the center of gravity, the lens holder  103  would not tilt even if tracking servo or focus servo is performed with low driving frequency. Moreover, the lens holder  103  does not resonate, advantageously, even if tracking servo or focus servo is performed with a high driving frequency. 
   Nonetheless, in the optical pickup apparatus of such composition, as the light beam is incident from the bottom face of the lens holder  103 , it is necessary to arrange optical components in a lower portion of the yoke base  109 . Such a composition increases the thickness of the whole optical disk apparatus and is inappropriate for the notebook PC, but may be admitted for the desktop PC having a large cabinet capacity. 
   On the other hand, according to a remarkable tendency of thinning the notebook PC, the composition of the optical pickup apparatus as shown in  FIG. 10  comes to be adopted largely, in order to cope with this thinning. In case of this composition, the lens holder  112  should be formed as flat as possible. On the other hand, an extremely expensive material such as highly elastic liquid crystal polymer or the like should be adopted in order to prevent the resonance. 
   In addition, this composition biases the weight balance, because on one side there is only one pair of tracking coils  115  to be attached to the focus coils  114  fixed to the lens holder  112 . Moreover, as the coil portion and the objective lens  113  are positioned at an extreme end in the longitudinal direction, the composition of the whole does not become a point symmetrical composition about the objective lens as the optical pickup apparatus as shown in  FIG. 9  adopted for the desktop PC, but becomes a cantilever support structure presenting an extremely inferior weight balance. 
   In such a composition that can not constitute a composition making the coil arrangement point symmetrical and cantilevers the lens holder  112  having a long distance between the objective lens  113  and the coil becoming the driving source and an inferior weight unbalance, when a tracking servo or focus servo is executed, the lens holder  112  tilts at a low driving frequency, the lens holder  112  generates a high order resonance at a high frequency, that can not be controlled even if a material of high elasticity such as liquid crystal polymer or others are adopted. 
   There, when a resonance is generated in the lens holder  112 , the beam spot by the objective lens comes naturally in the resonance state, disabling a correct focus servo or tracking serve. Especially for a higher speed, high record density DVD of about 0.74 μm in track width, there is every possibility that the resonance generation provokes read and write errors. 
   Moreover, in the optical pickup apparatus of the desktop PC in  FIG. 9 , while a tilt servo is enable for making the objective lens follow in parallel with the warping of an optical disk, the optical pickup apparatus of the notebook PC in  FIG. 10  can not perform this tilt servo, as the number of coil is limited, constituting a factor of inhibition to cope with a high speed, high record density of the optical disk. 
   The present invention has been devised in order to solve such problems of the prior art and has a first object of arranging the focus coil and the tracking coil to be point symmetrical by installing the objective lens at the center of them, stabilizing the weight balance and preventing the resonance from generating by the structure. 
   A second object of the present invention is enabling the tilt servo, which was impossible with the notebook PC of the prior art. 
   A third object of the present invention is allowing optical components to be arranged at a height position equivalent to the lens holder so that the thickness of the optical pickup apparatus be equal or inferior to 8.5 mm, in order to achieve an optical disk apparatus of 15 mm or less in thickness. 
   The present invention solves the aforementioned problems by a first composition of optical pickup apparatus composed to adjust the irradiation position of light beam to an optical disk by displacing an objective lens through a driving control of a lens holder holding the objective lens with a moving coil method, wherein: 
   an objective lens driving section is composed by arranging and fixing focus coils so that a pair of coil main bodies be symmetrical about the objective lens arranged at the middle of the lens holder, 
   a second composition of the aforementioned first composition, wherein the coil main body of the focus coil is composed independently in a current path, 
   a third composition of the aforementioned first composition, wherein the coil main body of the focus coils is composed integrally in the current path, 
   a fourth composition of the aforementioned first or second composition, wherein respective sides of the lens holder is cantilever-supported by three suspension wires, and each individual focus coil and a tacking coil are supplied with driving current from the suspension wire, 
   a fifth composition, wherein the suspension wire to be arranged between the upper and lower suspension wires is made softly, 
   a sixth composition of an optical pickup apparatus composed to adjust the irradiation position of light beam to an optical disk by displacing an objective lens through a driving control of a lens holder holding the objective lens with a moving coil method, wherein coil main body of the focus coils is arranged in the lens holder symmetrically about the objective lens, a notch for securing an optical path is formed in an intermediate portion which is a side of the lens holder where the objective lens is positioned, 
   a seventh composition of an optical pickup apparatus composed to adjust the irradiation position of light beam to an optical disk by displacing an objective lens through a driving control of a lens holder holding the objective lens with a moving coil method, wherein: 
   the lens holder is formed in a box so that a space be formed at the lower face of the objective lens, and a rising mirror for reflecting light beam incident from the side of the lens holder is received just under the objective lens in the space, 
   an eighth composition of the aforementioned seventh composition, wherein a clearance groove is formed on the inner wall face of the lens holder corresponding to the top of the rising mirror, 
   a ninth composition of the aforementioned seventh composition, composed so that the lowest portion of the objective lens is positioned more under the uppermost part of the rising mirror, when the lens holder holding the objective lens shifts downward, concerning the disposition relation between the objective lens and the rising mirror, 
   tenth composition, wherein a stopper is installed on the lens holder, in a way to prevent the lens holder from oscillation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and others and advantages of the present invention will become clear from following description with reference to the accompanying drawing, wherein: 
       FIG. 1  is a plan view showing the arrangement state of an optical pickup apparatus and optical components of the present invention; 
       FIG. 2  is a plan view showing a lens holder of the present invention; 
       FIG. 3  illustrates the inner structure of the optical pickup apparatus of the present invention; 
       FIG. 4  is a partial section side view for illustrating the composition of the lens holder of the present invention; 
       FIG. 5  illustrates the inner structure of the lens holder of the present invention; 
       FIG. 6  is a perspective view showing a focus coil and tracking coil used for the present invention; 
       FIG. 7  is a perspective view showing another embodiment of focus coil and tracking coil used for the present invention; 
       FIG. 8  shows the comparison of frequency response characteristics during the tracking direction driving of optical pickup apparatus of the present invention and the prior art; 
       FIG. 9  is a perspective view showing the structure of the optical pickup apparatus adopted for the desktop PC of the prior art; and 
       FIG. 10  is a perspective view showing the structure of the optical pickup apparatus adopted for the notebook PC of the prior art. 
     
       
         
               
               
             
               
               
               
             
           
               
                   
                   
               
               
                   
                 SYMBOLS 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  1 
                 Lens holder 
               
               
                   
                  2 
                 Suspension holder 
               
               
                   
                  3a, 3b, 3c 
                 Suspension wire 
               
               
                   
                  4 
                 Objective lens 
               
               
                   
                  5, 6 
                 Coil reception section 
               
               
                   
                  7a, 7b 
                 Focus coil 
               
               
                   
                  8a, 8b, 8c, 8d 
                 Tracking coil 
               
               
                   
                  9 
                 Notch 
               
               
                   
                 10 
                 Rising mirror 
               
               
                   
                 11 
                 Yoke base 
               
               
                   
                 12 
                 Clearance groove 
               
               
                   
                 13, 14 
                 Yoke piece 
               
               
                   
                 15 
                 Permanent magnet 
               
               
                   
                 16 
                 Optical component 
               
               
                   
                   
               
             
          
         
       
     
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Now, the present invention shall be described in detail.  FIG. 1  shows an arrangement state of an optical pickup apparatus A of the present invention, a semiconductor laser device B for DVD and a semiconductor laser device C for CD. The light beam emitted from the respective semiconductor laser devices forms light path to an objective lens of the optical pickup apparatus A passing through optical components of a plurality of mirror systems and lens systems. 
   For the optical pickup apparatus A, as shown in  FIG. 2  and  FIG. 3 , a lens holder  1  is cantilevered with three suspension wires  3   a ,  3   b ,  3   c  per one side by a suspension holder  2 . The lens holder  1  holds an objective lens  4  in the middle, and coil reception section  5 ,  6  are formed up and down symmetrically in  FIG. 2  about the objective lens. There, this coil reception section  5 ,  6  receives focus coil  7   a ,  7   b  and tracking coils  8   a ,  8   b ,  8   c ,  8   d  as shown in  FIGS. 4–6  and  7 . Thereby, an objective lens driving section is composed, respective arrangement of the focus coil and tracking coil become a point symmetrical arrangement about the objective lens  4 , making the whole one excellent in weight balance. It should be appreciated that the focus coil and the tracking coil are affixed with glue, and furthermore, both coils are affixed with glue in the coil reception section. 
   The suspension wires  3   a ,  3   b ,  3   c  are provided with a function as lead constituting a power supply path to respective coils, one coil is connected to two of suspension wires of one side, while the other focus coil is connected to two of suspension wires of the other side. Then four tracking coils  8   a ,  8   b ,  8   c ,  8   d  are connected in series, and the terminal thereof is connected to the right and left suspension wires one by one. Consequently, respective tracking coils  8   a ,  8   b ,  8   c ,  8   d  are supplied with an identical control current; however, as the focus coil  7   a ,  7   b  can be supplied with different control currents individually, the tilt servo becomes possible so that the objective lens be parallel all the times even when the optical disk is biased. It should be appreciated that, though the focus coil and tracking coil of this embodiment are composed individually as shown in  FIG. 6 , it is also possible to compose integrally with an identical current path as shown in  FIG. 7 . In this case, the tilt servo can not be performed using the focus coil, but two suspension wires on one side will be sufficient. 
   By the way, when the lens holder is cantilevered by three suspension wires on one side as in this embodiment, it was confirmed that the suspension wire  3   b  arranged in the middle ends up to be a resistive element against the flexion of upper and lower suspension wires  3   a ,  3   c , generating an unstable resonance in the focus direction. There, it is necessary to prevent an effect to the flexion from occurring by increasing the flexibility of this intermediate suspension wire  3   b  than the upper and lower suspension wires  3   a ,  3   c.    
   To cope with this problem, for instance, by making the diameter of the intermediate suspension wire  3   b  equal or inferior to 80% in diameter than the upper and lower suspension wires  3   a ,  3   c , the spring constant thereof becomes about 41% allowing to deform flexibly, Also, in case of composing the intermediate suspension wire  3   b  by adopting those of the same diameter as the upper and lower suspension wires  3   a ,  3   c , flexibility can be imparted by creasing an intermediate portion thereof. 
   Next, as for the lens holder  1  supported by an end portion of the suspension wires  3   a ,  3   b ,  3   c , a notch  9  is formed on a side face introducing the light beam into the objective lens  4  as shown in  FIG. 4 . This lens holder  1  is formed into a box so that a space is formed on the lower face of the objective lens as shown in  FIG. 5 , and the rising mirror  10  fixed to a frame body (not shown) arranged under the yoke base  11  is received in the space. Then, a clearance groove  12  is formed on the inner wall face of the lens holder  1  so that this polarizing lens  10  can be arranged at a high position in the space, and it is so composed that the top  10   a  of the mirror  10  fits into this clearance groove. Thereby, even when the lens holder  1  descends in the focus serve, a sufficient distance thereof can be obtained by the clearance groove  12 , allowing to arrange relatively the rising mirror  10  at the high position in the space, and contribute to the flattening of the whole optical pickup apparatus. It should be appreciated that it constitutes a composition allowing the lowermost portion of the objective lens  4  held by the lens holder to shift in order to be positioned lower than the top (uppermost portion) of the rising mirror. 
   Next, the yoke base  11  for fixing the suspension holder  2  at the end portion is provided with an upright yoke piece  13  . . . ,  14  . . . and a permanent magnet  15  is fixed to one yoke piece  13 . Therefore, a magnetic circuit is formed between the permanent magnet  15  . . . and the yoke piece  14  . . . , and the focus coil  7   a ,  7   b  and the tracking coil  8   a ,  8   b ,  8   c ,  8   d  are arranged by interposing in this magnetic circuit as shown in  FIG. 1 . Here, in case of interposing both coils in the magnetic circuit, they may be arranged so that all of both sides of the focus coils  7   a ,  7   b  receives the effect of the magnetic field; however, the tracking coil  8   a ,  8   b ,  8   c ,  8   d  are attached displacing from the center of the focus coil  7   a ,  7   b  as shown in  FIG. 1  and  FIG. 6 , so that they receive the effect of the magnetic field only at one side. 
   As described hereinabove, when the optical pickup apparatus of the present invention is assembled as shown in  FIG. 3 , the focus coil  7   a ,  7   b  and the tracking coils  8   a ,  8   b , 8   c ,  8   d  to be arranged point-symmetrically about the objective lens  4 . There, the focus coil  7   a ,  7   b  comes into a state being supplied with control current individually from the suspension wire, and the whole of the rising mirror  10  is received in the lens holder  1 . Thereby, lens or other optical components  16  to be disposed in the vicinity of the lens holder  1  also come to be received within the range of the thickness of the lens holder  1  and the yoke base  11 . 
   Also, the lens holder  1  of optical pickup apparatus of the present invention extends stoppers  1   a ,  1   b ,  1   c ,  1   d  from the main body thereof and makes them into contact with the permanent magnet  15 . This is to prevent the lens holder  1  in the floating state without any restriction from oscillating in the tracking direction when an impact is applied from the outside, and the suspension wire  3   a  . . . from plastically deforming. It should be appreciated that, during the normal and stable operation, as there is a clearance between the stopper and the permanent magnet, the stopper and the permanent magnet do not come into contact, even when the lens holder  1  oscillates in the tracking direction by the tracking operation during the control. 
   In short, by adopting such a composition, the suspension wire  3   a  . . . would not be affected even when the lens holder  1  comes into a state of oscillation by an impact from the exterior, because the range of this oscillation is limited to a range where the stopper  1   a ,  1   b ,  1   c ,  1   d  comes into contact with the permanent magnet  15  . . . In case of this embodiment, as stoppers are installed at four points approximately in point symmetry about the objective lens  4 , the stoppers of two points on one side come simultaneously into contact with the permanent magnet, and thereby prevent rotation moment from occurring. It should be appreciated that such stopper may further be installed over and under the lens holder, for example, without limiting to the four points. 
     FIG. 8  shows the comparison of frequency response characteristics during the tracking direction driving of optical pickup apparatus of the present invention and the prior art, the horizontal axis corresponds to the driving frequency in the tracking direction (Hz), the left vertical axis the gain (dB), the right vertical axis the phase (deg) and the characteristics of the portion improved by the present invention is shown by an alternate long and short dash line. 
   As evident from the same drawing, in the optical pickup apparatus of the prior art, there was a problem that lower resonance and higher resonance occur in addition to primary resonance, and gain and phase vary discontinuously, thereby lowering the tracking characteristics. In contrast, in the present invention, the focus coil and tracking coil are arranged symmetrically about the lens, and what is more, the suspension wire situated at the middle, among three suspension wires on respective side faces of the lens holder is made flexible, allowing to control the gain and phase variation in the lower resonance and the higher resonance, thereby improving the tracking characteristics. 
   It should be appreciated that, similarly as the frequency response characteristics during the tracking direction driving shown in  FIG. 8 , the frequency response characteristics are improved even during the focus direction driving, allowing to control the gain and phase variation in the lower resonance and the higher resonance, thereby improving the focus characteristics. 
   As described in detail hereinabove, according to the present invention, the inclination of resonance of the lens holder provoked by structural problems can be prevented, because the weight balance is stabilized by arranging the focus coil and tracking coil in point symmetry about the objective lens. Consequently, it becomes possible to make even the notebook PC cope with the high speed, and high record density. 
   In addition, according to the present invention, distinct focus coils can be supplied with different control current, because focus coils are composed to be arranged in symmetry by dividing about the objective lens, thereby enabling the tilt servo, and allowing to prevent read and write errors provoked by the warping of optical disk or others. 
   Still further, according to the present invention, as the light path to the objective lens is made to be formed on the side face of the lens holder, the arrangement of optical components can be arranged at a height equivalent to the lens holder, whereby the whole thickness of the optical pickup apparatus can be reduced extremely, and an optical pickup apparatus extremely useful particularly for the notebook PC can be provided. 
   While the presently preferred embodiment of the present invention has been shown and described, it will be understood that the present invention is not limited thereto, and that various changes and modification may be made by those skilled in the art without departing from the scope of the invention as set forth in the appended claims.