Patent Publication Number: US-2005125817-A1

Title: Optical disk device and carriage feed mechanism therefor

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical disk device and a carriage feed mechanism for the optical disk device.  
      2. Description of the Related Art  
      An optical disk, which records information in an optical disk such as a CD, a CD-ROM, or a DVD-ROM, reproduces recorded information, or performs recording and reproduction, generally includes: a spindle motor that is disposed on a chassis and drives to rotate an optical disk; a carriage mounted with an optical pickup; a main shaft and a counter shaft that guide the carriage in a radial direction of the optical disk; a screw shaft that is disposed on the chassis; a feed motor that drives to rotate the screw shaft; and a gear member that is disposed on the carriage, meshes with the screw shaft, and moves the carriage in the radial direction of the optical disk along the main shaft and the counter shaft according to the rotation of the screw shaft.  
      In recent years, the optical disk device realizes a very small light spot through a reduction in a wavelength of a semiconductor laser and an increase in NA (Numerical Aperture) of an object lens and makes it possible to perform high-density large capacity recording/reproduction.  
      On the other hand, in the case in which there is tilt (skew) of a lens optical axis of an optical pickup with respect to an optical disk surface, large comatic aberration occurs in proportion to the cube of NA. Consequently, installation of tilt correction means is required.  
      In addition, since a distance between an object lens and an optical disk surface constituting an optical pickup (working distance) is reduced due to the increase in NA, adjustment of height of the optical pickup is required in order to prevent the object lens and the optical disk from colliding with each other.  
      Therefore, conventionally, there has been proposed an optical disk device in which a spindle motor is disposed on a chassis, a base block is provided on the chassis to face the spindle motor, and the carriage, the main shaft, the counter shaft, the screw shaft, and the feed motor are disposed on this base block to perform adjustment of tilt and height of a lens optical axis of an optical pickup by adjusting tilt and height of the base block (see, for example, JP-A-2002-269768).  
      According to the conventional technique described above, since tilt and height of the base block itself, in which the carriage, the main shaft, the counter shaft, the screw shaft, the feed motor, and the like are incorporated, are adjusted, biting and disengagement of the screw shaft and the gear member do not occur. In addition, adjustment of tilt and height of the lens optical axis of the optical pickup can be performed without changing a meshing state of the screw shaft and the gear member. Therefore, the technique is advantageous in reducing a load on the feed motor and realizing a reduction in a size of the feed motor.  
      However, since the base block separated from the chassis is required, the technique is disadvantageous in realizing a reduction in a size and a reduction in a weight of the optical disk device.  
     SUMMARY OF THE INVENTION  
      The invention has been devised in view of the circumstances, and it is an object of the invention to provide an optical disk device and a carriage feed mechanism that are advantageous in reducing a load on a feed motor and realizing a reduction in a size of a motor and advantageous in realizing a reduction in a size and a reduction in a weight.  
      In order to attain the object, the invention is an optical disk device that performs recording and/or reproduction of information in an optical disk using an optical pickup, including: a spindle motor that is disposed on a chassis and drives to rotate an optical disk; a carriage mounted with the optical pickup; a screw shaft that is disposed on the chassis and has a drive gear formed on an outer peripheral surface thereof; a feed motor that drives to rotate the screw shaft; a support mechanism that supports the carriage so as to be movable in a radial direction of the optical disk; an adjustment mechanism that adjusts tilt and height of the carriage with respect to a recording surface of the optical disk; and a gear member that is disposed on the carriage, has a driven gear meshing with a drive gear of the screw shaft, and moves the carriage in the radial direction of the optical disk via the support mechanism according to the rotation of the screw shaft, characterized in that the gear member is supported on the carriage so as to be rotatable around an imaginary axis substantially perpendicular to an axis of the screw shaft.  
      In addition, the invention is an optical disk device that drives to rotate an optical disk disposed on a chassis and moves a carriage mounted with an optical pickup in a radial direction of the optical disk on the chassis to perform recording and/or reproduction of information in the optical disk, characterized in that a carriage feed mechanism, which moves the carriage in the radial direction of the optical disk, includes: a screw shaft that is disposed on the chassis and has a drive gear formed on an outer peripheral surface thereof; a feed motor that drives to rotate the screw shaft; a support mechanism that supports the carriage so as to be movable in a radial direction of the optical disk; an adjustment mechanism that adjusts tilt and height of the carriage with respect to a recording surface of the optical disk; and a gear member that is disposed on the carriage, has a driven gear meshing with a drive gear of the screw shaft, and moves the carriage in the radial direction of the optical disk via the support mechanism according to the rotation of the screw shaft, characterized in that the gear member is supported on the carriage so as to be rotatable around an imaginary axis substantially perpendicular to an axis of the screw shaft.  
      In the invention, even if tilt and height of the carriage with respect to the recording surface of the optical disk are adjusted by the adjustment mechanism, the gear member rotates while a meshing state of the drive gear and the driven gear is maintained, and the meshing state of the drive gear and the driven gear does not change.  
      Therefore, the invention is advantageous in reducing a load on the feed motor and realizing a reduction in a size of the motor. Moreover, an optical disk device and a carriage feed mechanism for the optical disk device, which are advantageous in realizing a reduction in a size and a reduction in a weight, are obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a plan view of a chassis of an optical disk device;  
       FIGS. 2A  to  2 C are explanatory diagrams of tilt adjustment for a main shaft;  
       FIGS. 3A and 3B  are explanatory diagrams of a gear member;  
       FIG. 4  is an explanatory diagram of a meshing state of the gear member and a screw shaft; and  
       FIG. 5  is a block diagram of the optical disk device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The invention attains the above-mentioned objects by supporting a gear member, which meshes with a drive gear of a screw shaft and moves a carriage in a radial direction of an optical disk according to rotation of the screw shaft, on the carriage so as to be rotatable around an imaginary axis substantially perpendicular to an axis of the screw shaft.  
      An embodiment of the invention will be hereinafter explained with reference to the drawings.  
       FIG. 1  shows a plan view of a chassis of an optical disk device,  FIGS. 2A  to  2 C show explanatory diagrams of tilt adjustment of a main shaft,  FIGS. 3A and 3B  show explanatory diagrams of a gear member,  FIG. 4  shows an explanatory diagram of a meshing state of the gear member and a screw shaft, and  FIG. 5  shows a block diagram of the optical disk device.  
      An optical disk device  10 , which records/reproduces information in an optical disk, includes a chassis  12  disposed in the inside of a not-shown case.  
      As shown in  FIG. 1 , a rectangular opening  1202  is formed in the center of the chassis  12 , and a spindle motor  14  is attached in one side portion constituting an edge of the opening  1202 . In the figure, reference numeral  1402  denotes a turntable that is located on an upper surface of the chassis  12  and driven to rotate by the spindle motor  14 . An optical disk is mounted on the turntable  1402  such that a recording surface thereof faces the opening  1202 .  
      As shown in  FIG. 1 , a carriage  22  mounted with an optical pickup  20 , a screw shaft  24 , and a support mechanism  26  for the carriage  22  are provided so as to face the opening  1202  on a lower surface of the chassis  12 , a leaf spring  28  is attached to the carriage  22 , and a gear member  30  is attached to the leaf spring  28 . The carriage  22  is moved in a radial direction of the optical disk via the support mechanism  26  and the gear member  30  according to rotation of the screw shaft  24 .  
      In addition, a feed motor  40 , which drives to rotate the screw shaft  24 , and an adjustment mechanism  42 , which adjusts tilt and height of the carriage  22  with respect to the recording surface of the optical disk, are provided on a lower surface of the chassis  12  on the outside of the opening  1202 .  
      In this embodiment, a carriage feed mechanism, which moves the carriage  22  mounted with the optical pickup  20  in the radial direction of the optical disk, includes the screw shaft  24 , the support mechanism  26 , the leaf spring  28 , the gear member  30 , the feed motor  40 , and the adjustment mechanism  42  and the like.  
      The optical pickup  20  is disposed in the center on an upper surface of the carriage  22 , a bearing hole  2202  is formed on one side of the carriage  22 , and a C-shaped engaging portion  2204  opened on an outer side is formed on the other side of the carriage  22 .  
      In this embodiment, the support mechanism  26  includes a main shaft  44  and a counter shaft  46  that are supported by the chassis  12  at an interval in a direction perpendicular to a direction, in which the carriage  22  is moved, and extend in a direction parallel to the moving direction of the carriage  22 . The main shaft  44  is inserted slidably through the bearing hole  2202  of the carriage  22 , and the counters haft  46  is inserted through the engaging portion  2204  of the carriage  22 .  
      Both ends of the main shaft  44  and the counter shaft  46  are supported movably only in a thickness direction (vertical direction) of the chassis  12  by a not-shown guiding mechanism, respectively. As shown in  FIG. 2 , those ends are placed on heads  48 A of male screws  48  that threadedly engage with female screws of the chassis  12 .  
      In addition, compression springs  50  are disposed between both the ends of the main shaft  44  and the counter shaft  46  and the lower surface of the chassis  12 , and both the ends of the main shaft  44  and the counter shaft  46  are always in abutment against the heads  48 A of the male screws  48  by these compression springs  50 .  
      In this embodiment, plural adjustment portions  4202 , which adjust positions of both the ends of the main shaft  44  and the counter shaft  46  with respect to the recording surface of the optical disk, are constituted by the male screws  48  and the compression springs  50 . The adjustment mechanism  42  is constituted by these plural adjustment portions  4202 .  
      When the male screws  48  at both the ends of the main shaft  44  are rotated, tilt of the main shaft  44  changes and radial skew is adjusted. When the male screws  48  at both the ends of the counter shaft  46  are rotated, tilt of the counter shaft  46  changes and tangential skew is adjusted. When all the male screws  48  in the four positions are rotated by an identical amount, height of the carriage  22  with respect to the recording surface of the optical disk is adjusted, and height of the optical pickup  20  is adjusted.  
      Note that  FIG. 2B  shows a state in which tilt of the main shaft  44  is adjusted by +A degrees from a state of  FIG. 2A .  FIG. 2C  shows a state in which tilt of the main shaft  44  is adjusted by −A degrees from the state of  FIG. 2A .  
      The screw shaft  24  is provided near the main shaft  44  to extend in parallel with the main shaft  44 , and a drive gear  2402  is formed on an outer peripheral surface of the screw shaft  24 .  
      The feed motor  40  is disposed to be directly connected to one end of the screw shaft  24 , and the other end of the screw shaft  24  is supported rotatably by a not-shown bearing portion of the chassis  12 .  
      The leaf spring  28  is formed of a spring steel plate and disposed on a side of the carriage  22  facing the screw shaft  24 .  
      As shown in  FIG. 3A  as a front view and in  FIG. 3B  as a side view, the leaf spring  28  includes a first plate portion  2802 , a base of which is attached to the upper surface of the carriage  22  and a tip of which extends toward the screw shaft  24 , and a second plate portion  2804 , which is formed to bend at a right angle from the tip of the first plate portion  2802  and faces the drive gear  2402 . A hole  2806  is provided through the center of the second plate portion  2804 . Note that, in  FIG. 1 , reference numeral  2812  denotes a screw that attaches the first plate portion  2802  to the upper surface of the carriage  22 , and reference numeral  2814  denotes a baffle pin.  
      The gear member  30  includes a main body  3002  of a rectangular plate shape, a driven gear  3004  that is formed to swell out on one surface of this main body  3002  and is capable of meshing with the drive gear  2402 , and a columnar shaft portion  3006  that is protrudingly provided from the other surface of the main body  3002 .  
      As shown in  FIGS. 1 and 4 , the driven gear  3004  meshes with the drive gear  2402 , the other surface of the main body  3002  is brought into abutment against the second plate portion  2804 , and the shaft portion  3006  is inserted through the hole  2806  and an end thereof is melted by heat to be formed as a swelled portion  3010  having a diameter larger than an inner diameter of the hole  2806 , whereby the gear member  30  is disposed on the second plate portion  2804  to be rotatable around the hole  2806  and the shaft portion  3006 . Consequently, the gear member  30  is supported on the carriage  22  to be rotatable around an imaginary axis substantially perpendicular to the axis of the screw shaft  24  (or around an imaginary axis substantially perpendicular to a longitudinal direction of the screw shaft  24 ).  
      Moreover, the gear member  30  is always biased in a direction, in which the driven gear  3004  meshes with the drive gear  2402 , by, in particular, the second plate portion  2804  of the leaf spring  28 . In this embodiment, biasing means, which biases the gear member  30  in the direction in which the driven gear  3004  meshes with the drive gear  2402 , is constituted by the leaf spring  28 .  
      In this embodiment, the carriage  22  moves in the radial direction of the optical disk by rotation drive of the feed motor  40 , a light beam is irradiated on the optical disk such as a CD, a CD-ROM, or a DVD-ROM from the optical pickup  20 , and information is recorded in the optical disk or recorded information is reproduced, or recording and reproduction is performed.  
      More specifically, as shown in  FIG. 5 , the optical disk device  10  includes a controller  200  and a signal processing circuit  300  in addition to the spindle motor  14 , the optical pickup  20 , the feed motor  40 , and the like.  
      The controller  200  is constituted to perform rotation control for the spindle motor  14  and the feed motor  40 , servo control for a focusing direction and a tracking direction of the optical pickup  20 , output control for a light beam of the optical pickup  20 , decoding processing for a reproduction signal, and the like.  
      The signal processing circuit  300  is constituted to perform reproduction of information recorded in an optical disk  100  on the basis of the reproduction signal and perform recording of information, which is inputted from the outside, in the optical disk  100  via a controller  106 .  
      Next, actions and advantages will be explained.  
      When the male screws  48  at both the ends of the main shaft  44  are rotated, radial skew is adjusted, when the male screws  48  at both the ends of the counter shaft  46  are rotated, tangential skew is adjusted, and when all the male screws  48  in the four positions are rotated by an identical amount, height of the optical pickup  20  is adjusted.  
      Then, tilt of the carriage  22  changes at the time of adjustment of radial skew and, when it is assumed that the gear member  30  is fixed to the carriage  22 , a meshing state of the drive gear  2402  and the driven gear  3004  changes, and biting and disengagement of these gears  2402  and  3004  occur. However, in this embodiment, the gear member  30  is supported so as to be rotatable around an imaginary axis perpendicular to the axis of the screw shaft  24  via the hole  2806  and the shaft portion  3006 . Thus, even if tilt of the carriage  22  is adjusted, the gear member  30  rotates while a meshing state of the drive gear  2402  and the driven gear  3004  is maintained, and the meshing state of the drive gear  2402  and the driven gear  3004  does not change.  
      In this embodiment, as shown in  FIG. 4 , a diameter D of a bottom of the drive gear  2402  of the screw shaft  24  is about 2 mm, and a depth E at which the drive gear  2402  and the driven gear  3004  mesh with each other is 0.25 mm. Despite the fact that the drive gear  2402  and the driven gear  3004  have only the very small meshing depth E, smooth meshing of the drive gear  2402  and the driven gear  3004  is guaranteed.  
      Therefore, even if the main shaft  44  is tilted to adjust radial skew, a meshing state of the drive gear  2402  and the driven gear  3004  does not change. Consequently, biting and disengagement of gears are prevented, and it is possible to move the carriage  22  smoothly in the radial direction of optical disk using the feed motor  40  without causing large torque fluctuation.  
      This also makes it possible to move the carriage  22  at high speed between a retracted position apart from the optical disk and a recording and reproduction position facing the bottom of the recording surface of the optical disk. This is advantageous in improving operability of the optical disk device  10 .  
      Since it is possible to maintain a meshing state of the drive gear  2402  and the driven gear  3004  in a uniform state, fluctuation in a load applied to the feed motor  40  can be controlled to be minimum, and a load applied to the feed motor  40  can be reduced. This is advantageous in realizing a reduction is a size of the feed motor  40 .  
      Since it is possible to attain the above-mentioned advantages with the simple structure in which the gear member  30  is rotatably supported on the carriage  22 . This is advantageous in realizing a reduction in the number of components and a reduction in a size of the optical disk device  10 .  
      In addition, in this embodiment, the driven gear  3004  is always biased in the direction, in which the driven gear  3004  meshes with the drive gear  2402 , by the leaf spring  28 . This is advantageous in preventing disengagement of the driven gear  3004  and the drive gear  2402 .  
      Note that, in the case in which the driven gear  3004  is biased in the direction in which the driven gear  3004  meshes with the drive gear  2402 , for example, it is also possible that a block is provided on a side of the carriage  22  in a direction in which the block separates from and approaches the drive gear  2402  of the screw shaft  24 , the gear member  30  is rotatably attached to this block, and this block is biased in the direction of drive gear  2402  by a coil spring or the like. However, it is advantageous in realizing a reduction in the number of components and a reduction in a weight if the leaf spring  28  is used as in the embodiment.  
      In addition, it is possible to use various mechanisms, which are publicly known conventionally, as the support mechanism  26  that supports the carriage  22  so as to be movable in the radial direction of the optical disk and the adjustment mechanism  42  that adjusts tilt and height of the carriage  22  with respect to the recording surface of the optical disk. The support mechanism  26  and the adjustment mechanism  42  are not limited to the constitution of the embodiment.