Patent Publication Number: US-2003235139-A1

Title: Head driving apparatus for disk apparatus

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a disk recording apparatus and particularly to a disk apparatus for recording or reproducing information onto or from a recording disk such as a compact disk (CD) and a digital versatile disk (DVD), and more particularly to a head driving apparatus for moving a pickup head with respect to a recording disk.  
       [0003] 2. Description of the Related Art  
       [0004] In resent years, development of an optical disk apparatus as a disk recording apparatus has proceeded. Particularly, a writing function has been additionally provided to a recording apparatus for an optical medium such as a CD-ROM, and, also for a driving apparatus for moving an optical pickup unit (OPU) as a pickup head for recording an information signal onto an optical disk in a radial direction of an optical disk, a function for feeding the optical pickup unit smoothly and accurately is demanded. At the same time, in order to achieve high-quality writing of writing data, an apparatus for adjusting the posture of the optical pickup unit so that an optical axis of laser light emitted from the optical pickup unit and a recording face of an optical disk may extend perpendicularly to each other is demanded.  
       [0005] As such an optical disk driving apparatus as described above, an apparatus is available which moves the optical pickup unit using a lead screw. FIG. 1 is a schematic view showing an appearance of a general configuration of an optical disk driving apparatus as viewed from the top face side, and FIG. 2 is a bottom plan view of the optical disk driving apparatus. A spindle motor  4  for rotationally driving an optical disk D indicated by a chain line in FIG. 1 is provided on a chassis  2  formed by working a metal plate or the like. A pair of main and sub guide rails  3   a  and  3   b  are supported in parallel in a predetermined spaced relationship from each other in a Y-axis direction on the chassis  2  such that they extend in an X-axis direction (radial direction of the optical disk) on a plane of X-Y coordinates. An optical pickup unit  1  is mounted for reciprocating sliding movement on the guide rails  3   a  and  3   b . Further, a lead screw  5  having screw threads formed on a circumferential face thereof is supported for rotation in parallel to the main guide rail  3   a  on one side of the chassis  2 . The lead screw  5  is rotatable in both of forward and reverse directions by a driving mechanism  6  including a motor not shown and a speed reduction mechanism  6   a . Further, a tooth unit  10  is provided on the optical pickup unit  1  and is held in meshing engagement with the lead screw  5 .  
       [0006] Referring to FIGS.  8 ( a ),  8 ( b ) and  9  which are a top plan view, a side elevational view and a perspective view, respectively, of the tooth unit  10 , the conventional tooth unit  10  is formed by integrally connecting a toothed member  102  held in meshing engagement with the screw threads of the lead screw  5  and a tooth base  101  fixedly supported on the optical pickup unit  1 . The tooth base  101  is fixed to the optical pickup unit  1  by a screw  106 . Further, two teeth  105  are formed on a front face of the toothed member  102  and held in meshing engagement with the screw threads of the lead screw  5 . The toothed member  102  is connected to the tooth base  101  by a pair of flexible connection pieces  103 . The toothed member  102  is resiliently pressed to the lead screw  5  by a tooth spring  104  interposed between the toothed member  102  and the tooth base  101 . Consequently, a meshing engagement state between the teeth  105  of the toothed member  102  and the screw threads of the lead screw  5  is kept.  
       [0007] In the optical head driving apparatus in which such a tooth unit as described above is used, if the lead screw  5  is rotated by the driving mechanism  6 , then force acting in an axial direction (X-axis direction) of the lead screw  5  is generated on the toothed member  102  held in meshing engagement with the screw threads of the lead screw  5 . Since the toothed member  102  is integrated with the optical pickup unit  1  through the tooth base  101 , the force in the axial direction is applied to the optical pickup unit  1  to move the optical pickup unit  1  along the guide rails  3   a  and  3   b . In particular, the optical pickup unit  1  is moved back and forth in the X-axis direction along the X-Y coordinate plane. Thereupon, laser light emitted from the optical pickup unit  1  is irradiated upon the optical disk D to allow recording or reproduction of data to be performed.  
       [0008] In the optical head driving apparatus, in order that the optical axis of the laser light emitted from the optical pickup unit  1  and the recording face of the optical disk D extend perpendicularly to each other in the Z-axis direction as described above, a skew adjustment portion  7   a  is provided at one end of the main guide rail  3   a  and a pair of skew adjustment portions  7   b  and  7   c  are provided at both ends of the sub guide rail  3   b . By the skew adjustment portions  7   a ,  7   b  and  7   c , the inclination of the guide rails  3   a  and  3   b  with respect to the chassis  2 , that is, the angle between them in the Z-axis direction, is adjusted to adjust the posture of the optical pickup unit  1  so that the laser light emitted from the optical pickup unit  1  can be irradiated perpendicularly in the Z-axis direction upon the recording face of the optical disk D.  
       [0009] However, in the optical head driving apparatus having such a configuration as described above, if the skew of the main and sub guide rails  3   a  and  3   b  is adjusted by the skew adjustment portions  7   a ,  7   b  and  7   c  so that the laser light of the optical pickup unit  1  may be directed perpendicularly to the recording face of the optical disk D, then there is the possibility that the parallelism between the main and sub guide rails  3   a  and  3   b  and the lead screw  5  in the Z-axis direction may be deteriorated. If the parallelism between the guide rails  3   a  and  3   b  and the lead screw  5  is deteriorated, then the teeth  105  of the toothed member  102  supported on the optical pickup unit  1  which moves along the guide rails  3   a  and  3   b  and the screw, threads of the lead screw  5  are brought out of meshing engagement with each other with a normal angle, resulting in generation of high drag or excessive frictional force between them. As a result, smooth movement of the optical pickup unit  1  along the guide rails  3   a  and  3   b  is obstructed. Therefore, the quality of writing by the optical disk recording apparatus, for example, onto a CD-ROM is degraded.  
       [0010] It is to be noted that Japanese Patent Laid-Open No. 2001-160272 discloses an apparatus wherein a rack (toothed member) provided on an optical pickup unit is resiliently pressed to a lead screw to achieve smooth movement of the optical pickup unit. However, the apparatus controls the inclination of the rack to secure a meshing engagement state between the rack and the lead screw and presupposes that a parallel state between the guide rails and the lead screw is secured. Therefore, it is difficult to solve such a trouble when the parallelism between the guide rails and the lead screw in the Z-axis direction is deteriorated as described above using the apparatus.  
       SUMMARY OF THE INVENTION  
       [0011] It is an object of the present invention to provide a head driving apparatus which can correctly adjust the posture of an optical pickup unit and can smoothly move the optical pickup unit.  
       [0012] In order to attain the object of described above, according to an aspect of the present invention, there is provided a head driving apparatus for a disk apparatus comprising a pickup head movable in an X-axis direction on a plane of X-Y coordinates along a guide rail for performing recording or reproduction of information onto or from a recording disk, a lead screw rotationally driven to move the pickup head in the X-axis direction, and a toothed member held in meshing engagement with the lead screw for moving the pickup head in the X-axis direction upon rotation of the lead screw, the toothed member being supported for pivotal motion on the pickup head within a range of a small angle on a plane of Z-X coordinates perpendicular to the X-Y coordinate plane on which the pickup head is moved.  
       [0013] Preferably, the toothed member is supported for pivotal motion on the pickup head within a range of a small angle also in the X-Y coordinate plane on which the pickup head is moved.  
       [0014] The toothed member may be disposed for pivotal motion with respect to the pickup head by means of a pivot extending in a Y-axis direction.  
       [0015] The head driving apparatus may further comprise a tooth base provided on the pickup head, and the toothed member may be supported for pivotal motion on the tooth base by the pivot extending in the Y-axis direction.  
       [0016] The head driving apparatus may further comprise a tooth spring interposed between the toothed member and the tooth base for resiliently pressing the toothed member to the lead screw and braking the pivotal motion of the toothed member. The tooth spring may be a coil spring arranged around the pivot.  
       [0017] Preferably, the pivot is formed from a boss provided on a rear face of the toothed member and inserted in a bush provided on a front face of the tooth base. Further preferably, the bush and the boss form a spherical bearing structure.  
       [0018] The head driving apparatus may be configured such that a pair of claw portions are provided on a rear face of the toothed member and inserted in a pair of slits, which are provided on a front face of the tooth base with clearances formed therebetween such that a pivotal motion of the toothed member within a small angle with respect to the tooth base is allowed by the clearances, and removal of the toothed member from the tooth base is prevented by the engagement between the claw portions and the tooth base.  
       [0019] The pickup head may be an optical pickup unit.  
       [0020] In the head driving apparatus for a disk apparatus, the toothed member can pivotally move within a range of a small angle on the Z-X coordinate plane rectangular to the X-Y coordinate plane on which the pickup head is moved. Therefore, even if the parallelism in the Z-axis direction between the guide rail and the lead screw is deteriorated, the toothed member is directed to a preferable angular position with respect to the lead screw so that the toothed member and the lead screw are brought into appropriate meshing engagement with each other. As a result, smooth movement of the pickup head is secured.  
       [0021] Further, the toothed member can pivotally move within a range of a small angle also on the X-Y coordinate plane on which the pickup head moves. Therefore, even if the parallelism in the Y-axis direction is deteriorated, the toothed member is pivotally moved in a follow-up manner so that the toothed member and the lead screw are brought into appropriate meshing engagement with each other. As a result, smooth movement of the pickup head is secured.  
       [0022] The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements are denoted by like reference symbols. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0023]FIG. 1 is a schematic view showing an appearance of an optical disk apparatus to which a head driving apparatus of the present invention can be applied as viewed from the top side;  
     [0024]FIG. 2 is a bottom plan view of the optical disk apparatus;  
     [0025]FIG. 3( a ) is a top plan view showing a tooth unit in the head driving apparatus;  
     [0026]FIG. 3( b ) is a side elevational view of the tooth unit;  
     [0027]FIG. 3( c ) is a sectional view taken along line A-A of FIG. 3( a );  
     [0028]FIG. 3( d ) is a sectional view taken along line B-B of FIG. 3( a );  
     [0029]FIG. 4 is an exploded perspective view of the tooth unit;  
     [0030] FIGS.  5 ( a ) and  5 ( b ) are schematic views of a toothed member of the tooth unit as viewed from the front side illustrating action of the head driving apparatus;  
     [0031]FIG. 6 is an exploded perspective view showing a modified head driving apparatus;  
     [0032] FIGS.  7 ( a ) and  7 ( b ) are schematic views of a toothed member as viewed from the top side illustrating action of the modified head driving apparatus;  
     [0033]FIG. 8( a ) is a top plan view showing a tooth unit in a conventional head driving apparatus;  
     [0034]FIG. 8( b ) is a side elevational view of the tooth unit in the conventional head driving apparatus; and  
     [0035]FIG. 9 is a perspective view showing the tooth unit shown in FIGS.  8 ( a ) and  8 ( b ). 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0036] A head driving apparatus according to the present invention is applied to the optical disk apparatus described hereinabove with reference to FIGS. 1 and 2. Thus, the optical disk apparatus is described in more detail.  
     [0037] A spindle motor  4  is supported on a chassis  2  formed in a rectangular shape on a plane of X-Y coordinates and rotates an optical disk D indicated by a broken line in FIG. 1 at a high speed. A head moving window  2   a  is provided in the chassis  2 . A pair of main and sub guide rails  3   a  and  3   b  are supported on the chassis  2  in parallel to each other and in a predetermined spaced relationship from each other in the Y-axis direction such that they extend in the X-axis direction (radial direction of the optical disk) and are exposed to the head moving window  2   a . An optical pickup unit  1  is mounted for sliding movement on the main and sub guide rails  3   a  and  3   b . For example, the optical disk apparatus is formed such that the guide rails  3   a  and  3   b  penetrate both side portions of a casing  1   a  of the optical pickup unit  1  so as to allow reciprocating movement of the optical pickup unit  1  in the X-axis direction along the guide rails  3   a  and  3   b , that is, along the X-Y coordinate plane.  
     [0038] An objective lens  1   b  is provided on the optical pickup unit  1  and laser light is emitted from an optical device mounted in the optical pickup unit  1  to the optical disk D through the objective lens  1   b  to perform recording or reproduction of information. However, detailed description thereof is omitted herein because it does not directly relate to the present invention. Further, a skew adjustment portion  7   a  is provided at one end of the main guide rail  3   a , and a pair of skew adjustment portions  7   b  and  7   c  are provided at both ends of the sub guide rail  3   b . By the skew adjustment portions  7   a ,  7   b  and  7   c , the supporting heights of the one end of the main guide rail  3   a  and both ends of the sub guide rail  3   b  are adjusted so that the inclination of the guide rails  3   a  and  3   b  in a Z-axis direction with respect to the chassis  2  can be adjusted. Since an adjustment mechanism by such skew adjustment portions is generally known, detailed description thereof is omitted herein.  
     [0039] A lead screw  5  having screw threads formed on a circumferential face thereof is supported for rotation at both ends thereof on one side of the chassis  2  such that it extends in the X-axis direction. The lead screw  5  is arbitrarily rotatable in both of forward and reverse directions by a screw driving mechanism  6  including a motor not shown and a speed reduction mechanism  6   a . Further, a tooth unit  10  is provided on the casing  1   a  of the optical pickup unit  1  and is held in meshing engagement with the lead screw  5  as hereinafter described.  
     [0040] The tooth unit  10  includes a tooth base  11  and a toothed member  12  separate from the tooth base  11 . The tooth base  11  is integrally fixed to the casing  1   a  of the optical pickup unit  1  by a screw  13 . Further, a plurality of teeth  14  are provided on the toothed member  12  in such a manner as herein after described. The teeth  14  are held in meshing engagement with the screw threads of the lead screw  5 .  
     [0041] Referring now to FIGS.  3 ( a ) to  3 ( d ) and  4 , the tooth base  11  is fixedly fastened to part of the casing  1   a  of the optical pickup unit  1 by the screw  13  inserted in a screw hole  111  formed at part of the tooth base  11 . A tooth supporting portion  112  curved in an L shape in a downward direction is formed on one side of the tooth base  11 . A bush  113  having a cylindrical shape is integrally formed in a projecting manner at a substantially central position in the leftward and rightward longitudinal direction of a front face of the tooth supporting portion  112 . Further, left and right ends  114  of the front face of the tooth supporting portion  112  are bulged forwardly, and slits  115  are individually formed at the bulged portions. Further, ribs  116  are formed in a projecting manner on the front face of the tooth supporting portion  112  in a slightly spaced relationship on both left and right sides of the bush  113 .  
     [0042] The toothed member  12  includes a vertical front plate portion  121  and vertical left and right side plate portions  124  formed by bending a plate piece into a U shape in plan. On the front face of the front plate portion  121 , two inclined teeth  122  for engaging with the screw threads of the lead screw  5  are formed in parallel to each other with an angle equal to the flank angle of the screw threads of the lead screw  5 . A circular boss  123  projects at a central position of the rear face of the front plate portion  121  such that it can be inserted into the bush  113  of the tooth base  11 . Further, claw portions  125  are formed in a projecting manner in a downward direction at tip ends of the left and right side plate portions  124  such that they can be inserted from above into the left and right slits  115  of the tooth base  11 . Since the thickness of the left and right claw portions  125  is smaller than the width of the slits  115 , if the left and right claw portions  125  are inserted into the slits  115 , then a slight space is formed between the claw portions  125  and the slits  115 . However, since the bottom ends of the left and right claw portions  125  are engaged with the rear face of the left and right ends  114  projecting from the tooth supporting portion  112 , inadvertent removal of the toothed member  12  from the tooth base  11  can be prevented.  
     [0043] When the left and right claw portions  125  and the left and right slits  115  are set in such a relationship as described above, the boss  123  of the toothed member  12  is inserted into the bush  113  of the tooth base  11 . In the state just described, the boss  123  is rotatable in the bush  113 , and a slight space is formed between the left and right claw portions  125  and the slits  115  in such a manner as described above. Consequently, the toothed member  12  can pivotally move, using the boss  123  and bush  113  as a pivot, within a predetermined small angler range on a plane of Z-X coordinates perpendicular to the tooth base  11 .  
     [0044] Further, a tooth spring  14  in the form of a compression coil spring is provided around the pivot formed from the boss  123  and the bush  113  and between the rear face of the front plate portion  121  of the toothed member  12  and the front face of the tooth supporting portion  112  of the tooth base  11 . The tooth spring  14  biases the toothed member  12  toward the lead screw  5 .  
     [0045] With the optical disk apparatus having the configuration described above, if the lead screw  5  is rotated by the driving mechanism  6  similarly as in the conventional apparatus, then since the teeth  112  are held in meshing engagement with the screw threads of the lead screw  5 , the toothed member  12  is moved in an axial direction of the lead screw  5 , that is, in the X-axis direction. By the fitting between the boss  123  and the bush  113  and the fitting between the left and right claw portions  125  and the left and right slits  115 , the toothed member  12  is integrated with the tooth base  11  in the X-axis direction. Therefore, the tooth base  11  is moved together with the toothed member  12 , and the optical pickup unit  1  which fixedly supports the tooth base  11  thereon is moved in the X-axis direction along the guide rails  3   a  and  3   b . The toothed member  12  is resiliently pressed to the lead screw  5  by the tooth spring  14 , and, at the same time, a posture of the toothed member  12  is maintained by frictional force generated by pressure contact between an end of the tooth spring  14  and the rear face of the toothed member  12 . As a result, a preferable meshing engagement state between the teeth  122  and the screw threads is secured. Consequently, the optical pickup unit  1  is moved in a radial direction of the optical disk D rotated at a high speed by the spindle motor  4  so that recording or reproduction of information onto or from the optical disk D is performed by the optical device internally mounted in the optical pickup unit  1 .  
     [0046] Incidentally, in the optical pickup unit  1 , it is preferable that the laser light emitted from the optical device internally mounted in the optical pickup unit  1  is projected perpendicularly to a recording face of the optical disk D as described above. Therefore, the inclination of the guide rails  3   a  and  3   b  in the Z-axis direction with respect to the plane of the chassis  2  is adjusted by the skew adjustment portion  7   a  provided at one end of the main guide rail  3   a  and the skew adjustment portions  7   b  and  7   c  provided at the both ends of the sub guide rail  3   b . Therefore, if the parallelism in the Z-axis direction between the main and sub guide rails  3   a  and  3   b  and the lead screw  5  is deteriorated, then since the toothed member  12  is supported by the optical pickup unit  1  which moves along the guide rails  3   a  and  3   b , the toothed member  12  and the lead screw  5  are brought out of meshing engagement with each other with a correct angle. As a result, smooth movement of the optical pickup unit  1  is obstructed.  
     [0047] However, when the parallelism between the lead screw  5  and the guide rails is deteriorated in such a manner as described above, in the head driving apparatus of the present embodiment, if a drag generated on a meshing face from an angle difference between the teeth  122  and the screw threads of the lead screw  5  is applied to the toothed member  12 , then the toothed member  12  is pivotally moved on the vertical Z-X coordinate plane around the pivot formed from the boss  123  and the bush  113  as exaggeratedly shown in FIG. 5( b ) against the frictional force by the tooth spring  14 . The pivotal motion of the toothed member  12  is allowed only within a range within which the both of the claw portions  125  can rock in the slits  115 , that is, only within a small angular range. Then, if the toothed member  12  is pivotally moved to a position at which the drag is smallest, then the teeth  122  of the toothed member  12  are directed to an angle same as the flank angle of the screw threads of the lead screw  5  and are automatically corrected so that the teeth  122  and the screw threads of the lead screw  5  enter into an appropriate meshing engagement state. Such a correction operation as described above performed by pivotal motion of the toothed member  12  is performed anywhere within a period of time within which the optical pickup unit  1  moves along the guide rails  3   a  and  3   b . Consequently, smooth movement of the optical pickup unit  1  is secured regardless of deterioration of the parallelism between the lead screw  5  and the guide rails  3   a  and  3   b.    
     [0048] Further, the tooth spring  14  brakes the pivotal motion of the toothed member  12  to prevent destabilization of the meshing engagement state between the toothed member  12  and the lead screw  5  caused by excessive pivotal motion of the toothed member  12 . Furthermore, since the toothed member  12  and the tooth base  11  are format as the single tooth unit  10 , attachment and detachment of the tooth unit  10  to and from the optical pickup unit  1  can be easily performed. It is to be noted that naturally the tooth base  11  may be unitarily formed with the casing la of the optical pickup unit  1 .  
     [0049]FIG. 6 shows a tooth unit of a modification to the embodiment described above. In the modification shown, the toothed member  12  is formed for pivotal motion not only on the Z-X coordinate plane with respect to the tooth base  11  but also on the X-Y coordinate plane on which the optical pickup unit  1  is moved.  
     [0050] In particular, not such a mere circular boss as described above but a boss  126  having a spherical end is formed in a projecting manner at a central position of the rear face of the front plate portion  121  of the toothed member  12 . Further, corresponding to the configuration just described, not such a mere cylindrical bush as described above but a spherical bush  117  having an inside circumferential face formed as a spherical surface is formed in a projecting manner on the tooth base  11 . Further, the spherical end of the boss  126  of the toothed member  12  is fitted in the spherical bush  117  of the tooth base  11  to form a spherical bearing structure. It is to be noted that the spherical bush  117  has some room wherein the spherical end of the boss  126  can be moved in an axial direction. Further, similarly as in the embodiment described above, the both side claw portions  125  of the toothed member  12  are inserted in the both side slits  115  of the tooth base  11  such that a space is formed between the claw portions  125  and the slits  115 .  
     [0051] According to the modification, similarly as in the embodiment described above, the toothed member  12  can pivotally move in a small angle on the Z-X coordinate plane perpendicular with respect to the tooth base  11  by the spherical bearing structure formed from the boss  126  and the spherical surface bush  117 . Consequently, smooth movement of the optical pickup unit  1  is achieved regardless of deterioration of the parallelism between the guide rails  3   a  and  3   b  and the lead screw  5  in the Z-axis direction.  
     [0052] Further, since the spherical bearing structure is formed from the boss  126  and the spherical bush  117 , the toothed member  12  can pivotally move also on the X-Y coordinate plane as seen in FIG. 7( a ) and  7 ( b ). The pivotal motion of the toothed member  12  is allowed only within a range within which the both side claw portions  125  can be rocked in the both side slits  115  in a widthwise direction thereof. Accordingly, where an axial line of the main guide rail  3   a  is inclined in the Y-axis direction on the X-Y coordinate plane with respect to an axial line A 1  of the lead screw  5  to deteriorate the parallelism, the toothed member  12  is pivotally moved on the X-Y coordinate plane with respect to the tooth base  11  as shown in FIG. 7( b ) by a drag which is generated between the teeth  122  of the toothed member  12  and the screw threads of the lead screw  5  when the optical pickup unit  1  moves along the guide rails  3   a  and  3   b . Consequently, since the teeth  122  can be usually directed to the direction along the axial direction of the lead screw  5 , smooth movement of the optical pickup unit  1  can be achieved also in this case.  
     [0053] It is to be noted that the present invention is not limited to an optical head driving apparatus for an optical disk apparatus, but can be applied also to a recording disk apparatus which includes a function for adjusting the skew of guide rails in order to adjust the angle of a pickup head with respect to a recording disk. Also, for example, in a magneto-optical disk apparatus, since a function for adjusting the angle of a magneto-optical head with respect to a magneto-optical disk is demanded, the present invention can be applied also to the magneto-optical head driving apparatus.  
     [0054] While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.