Abstract:
An easily manufacturable optical disc drive that provides for accurate writing and reading of information signals to and from a disc loaded therein by maintaining the horizontal balance of its base during operation, and that provides for smooth loading and unloading of a disc. The optical disc drive includes a base formed of a single metal plate of 1.4–1.8 mm thickness. Major components of the base (i.e., a disc rotation driving mechanism, an optical pickup and a pickup feeding mechanism) are disposed on the base in such a way that the total weight of these components is nearly evenly distributed on the base. The optical pickup is adapted to move across an optical disc between its inner and outer circumferences, while the optical disc is rotated by the disc rotation driving mechanism. The base is supported by a plurality (i.e., at least three) of supporting members, each with an elastic support piece. These supporting members are disposed symmetrically with respect to a center line of the base along the direction of the optical pickup&#39;s movement. The symmetrical disposition of these supporting members, together with the vibration absorbing nature of the elastic support pieces and the balanced weight distribution on the base, eliminates weight shifts/imbalance caused by the optical pickup movement, thereby maintaining the horizontal balance of the base at all time during operation of the optical disc drive. The ease of manufacture can be achieved by selecting even numbers (e.g., four) of the supporting members for the base.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to disc drives and optical disc drives, and in particular, to disc drives and optical disc drives for loading and unloading discs and for writing and reading information signal to and from such discs. 
   2. Description of the Related Art 
   Conventionally, a disc drive is used in which a disc-like recording medium such as an optical disc, magneto-optical disc or magnetic disc is used as the recording medium. 
   The disc drives of this type include an optical disc drive in which an optical disc is used as the recording medium. In the optical disc drive, there are installed on a common base a disc rotation driver to drive the rotation of an optical disc and an optical pickup to scan, by a light beam, a signal recording area on the optical disc being rotated by the disc rotation driver, thereby reading an information signal recorded in the optical disc. 
   The base is formed from a thin metal plate, fixed to a support frame by means of supporting members each provided with a vibration-proofing elastic member, and fixed to a support pedestal by means of the support frame. 
   The support pedestal has movably installed thereon a disc tray which holds an optical disc and carries it into and out of the optical disc drive body in which the support pedestal is housed. The disc tray is supported on the support pedestal to be movable horizontally between a first position where the optical disc is projected out of the optical disc drive body and a second position where the optical disc is placed opposite to the disc rotation driving mechanism and loaded on a disc table of the disc rotation driving mechanism. The second position is a reading position. 
   The support frame on which the base is installed is pivoted in a direction in which the disc table of the disc rotation driving mechanism is moved towards and away from the optical disc held in the disc tray as the disc tray is moved into and out of the optical disc drive body. 
   In the optical disc drive constructed as in the above, as the disc tray holding an optical disc therein is moved by a tray moving mechanism from the first position towards the second position, the support frame pivots the disc table towards the optical disc held in the disc tray. When the disc tray arrives at the second position, the disc table is projected into the disc tray, the disc tray is a little levitated and the optical disc held in the disc tray is loaded on the disc table. When the optical disc is loaded onto the disc table, a clamping member provided at the optical disc drive body to be opposite to the disc table is pressed to the optical disc, so that the optical disc will be rotatable along with the disc table. 
   After the optical disc has become rotatable along with the disc table, the disc rotation driving mechanism is driven to move the optical pickup between the inner and outer circumferences of the optical disc being rotated along with the disc table. A signal recording area on the optical disc is scanned by a light beam emitted from the optical pickup to read an information signal recorded in the optical disc. 
   In the conventional disc drive, however, since the optical pickup is moved between the inner and outer circumferences of an optical disc when reading the optical disc, the weight balance of the base is varied with the movement of the optical pickup. Among others, in case the base on which the optical pickup is installed is made from a metal plate, the base will be deflected depending upon a moved position of the optical pickup and there will take place a skew with which a light beam will not be irradiated perpendicularly to a signal recording surface on the optical disc, with a result that no information signal can be read accurately. Especially, in an optical disc drive with a large and heavy optical pickup having a plurality of light sources and a plurality of photo-detectors provided therein, the base will be deflected considerably. Further, even with a little skew, no correct read of information signal can be made from an optical disc having image information, etc. recorded therein with a high density. 
   In an optical disc drive, in which the base is supported by supporting members each provided with an elastic member, when the weight balance of the base is changed, the weight applied to each supporting member varies, the supporting members are elastically deformed differently one from another, so that the base cannot be supported horizontally relative to a reference plane. If the base cannot be kept horizontal in an optical disc drive in which when the base is pivoted as the disc tray is pivoted, an optical disc is loaded onto the disc table, the disc tray will collide with the disc table, so that the optical disc cannot be loaded smoothly onto the disc table. 
   Also in a disc drive for any disc-like recording medium other than the optical disc, if the base on which the disc rotating mechanism and write and/or read head are installed is deflected as caused by the movement of the write and/or read head and thus deformed, the write and/or read head will not be able to correctly scan a recording track on the disc-like recording medium and thus to write and/or read any information signal with good writing and reading characteristics. 
   To prevent the base from being deflected due to a weight imbalance caused by the movement of the optical pickup and write and/or read head, it has been proposed to use a base formed from a thick metal plate which can assure a sufficient strength of the base. However, to form a base from such a thick metal plate by pressing or the like, a large force is needed. During production of a base from such a thick metal plate, the large pressure applied will cause a large internal stress in the metal plate. The internal stress will make it difficult to make the base highly flat. 
   Still needed in the field, therefore, is a disc drive and an optical disc drive that provides for accurate writing and reading of information signals to and from a disc loaded therein by maintaining the horizontal balance of its base despite the weight shift caused by a movement of an optical pickup and a writing and/or reading means. In addition, the disc drives and the optical disc drives should provide for smooth loading and unloading of a disc. The disc drives and the optical disc drives should have a highly flat base and should also be easily manufactured. 
   SUMMARY OF THE INVENTION 
   It is an objective of the invention to provide a disc drive and an optical disc drive that can maintain the horizontal balance of its base during operation, thereby enabling information signals to be more accurately recorded on and/or reproduced from a disc loaded therein. 
   It is a further objective of the invention to provide a disc drive and optical disc drive that can smoothly load and unload a disc. 
   It is an additional objective of the invention to provide a disc drive and optical disc drive that has a highly flat base. 
   It is an additional objective of the invention to provide a disc drive and optical disc drive that can be simply and easily manufactured. 
   Features of the invention include balanced weight distribution on a base of a disc drive and an optical disc drive, symmetrical disposition of a plurality of supporting means on the base along its center line, location-dependent provision of an elastic member with different elasticity to each of the supporting members on the base, and location-dependent provision of differential height support among the supporting means on the base. 
   Advantages of the invention include elimination of weight shifts/imbalance during operation of the disc drive and the optical disc drive, smooth loading/unloading of a disc, and ease of manufacture of the disc drive and the optical disc drive. 
   According to one aspect of the invention, an optical disc drive includes a base, disc rotation driving means disposed on the base for rotating an optical disc loaded in the base, an optical pickup disposed on the base for recording data on and/or reproducing data from the optical disc, guide means disposed on the base for movably supporting the optical pickup between inner and outer circumferences of the optical disc during rotation of the optical disc, a feeding mechanism disposed on the base for feeding the optical pickup along the guide means, and a plurality of supporting means (e.g., four) disposed on the base, each with an associated elastic member for elastically supporting the base, wherein the supporting means and the associated elastic members are disposed symmetrically on the base with respect to a center line of the base along the direction of movement of the optical pickup. 
   According to another aspect of the invention, an optical disc drive includes a support pedestal, a base supported by the support pedestal, disc rotation driving means disposed on the base for rotating an optical disc loaded in the base, a disc tray movably disposed on the support pedestal between a first position where the optical disc is removable and a second position where the optical disc is at the disc rotation driving means, an optical pickup disposed on the base for recording data on and/or reproducing data from the optical disc, guide means disposed on the base for movably supporting the optical pickup between inner and outer circumferences of the optical disc during rotation of the optical disc, a feeding mechanism disposed on the base for feeding the optical pickup along the guide means, and a base support member for supporting the base with a plurality of supporting means disposed symmetrically with respect to a center line of the base along the direction of the movement of the optical pickup, wherein each of the supporting means includes an elastic member. 
   Of the plurality of supporting means, at least one disposed near the disc rotation driving means has a different supporting elasticity from at least another one disposed away from the disc rotation driving means, so that any imbalance of the weight caused by the movement of the writing and/or reading means is absorbed by the supporting means to keep the base horizontal. Further, at least one of the supporting means disposed near the disc rotation driving means supports the base at a different height relative to a reference plane from a height at which at least another one of the supporting means disposed away from the disc rotation driving means supports the base, so that these supporting means are elastically deformed correspondingly to the magnitude of the weight applied thereto, thereby maintaining the base horizontal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings, of which: 
       FIG. 1  is an exploded perspective view of an optical disc drive according to the present invention. 
       FIG. 2  is a plan view of an optical disc drive according to the present invention with a disc tray moved to a position that allows loading and unloading of an optical disc. 
       FIG. 3  is a plan view of an optical disc drive according to the present invention with a disc tray moved to another position that allows reading from, and writing to, of an optical disc. 
       FIG. 4  is an exploded perspective view of a base of an optical disc drive in accordance with the present invention. 
       FIG. 5  is a side elevation view of a base of an optical disc drive in accordance with the present invention. 
       FIG. 6  is a plan view of a base of one embodiment of an optical disc drive according to the present invention. 
       FIG. 7  is a cross-sectional view illustrating a supporting member of the base of  FIG. 6 . 
       FIG. 8  is a plan view of a base of another embodiment of an optical disc drive in accordance with the present invention. 
       FIG. 9  is a cross-sectional view illustrating a support member of the base of  FIG. 8 . 
       FIG. 10  is a side elevation view of an optical disc drive according to the present invention, with a disc tray moved to a first position and a base support moved downward below a support pedestal, for loading and unloading of an optical disc. 
       FIG. 11  is a side elevation view of an optical disc drive according to the present invention, with a disc tray moved to a second position and a base support moved upward to a level with a support pedestal, for writing to and reading from an optical disc loaded therein. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2  illustrate an optical disc drive according to the present invention in an exploded perspective view and a plain view, respectively. The optical disc drive includes a support pedestal  1  disposed inside a casing (not shown). The support pedestal  1  constitutes a main body of the optical disc drive, is formed by molding a synthetic resin, and has a support foot  2  disposed at each corner of the bottom thereof. 
   The optical disc drive also includes a disc tray  4  disposed on the support pedestal  1  for holding and carrying an optical disc  3  in and out of the support pedestal  1 . The disc tray  4  contains a disc receiving concavity  5  on its upper surface for selectively position and securely hold a optical disc of two different sizes. Rails  6  are disposed along opposite sides of the disc tray  4 . The support pedestal  1  has a plurality of rail supports  7  disposed along opposite sides thereof. The rails  6  of the disc tray  4  are movably supported on the rail supports  7  of the support pedestal  1  in the directions of arrows A 1  and A 2 . That is, the disc tray  4  is movably supported between a first portion inside the casing (not shown), as illustrated in  FIG. 2 , and a second position outside the casing (not shown), as illustrated in  FIG. 3 . At the first position, the disc tray  4  with the optical disc  3  in the disc receiving concavity  5  is drawn out of the casing, thereby allowing the optical disc  3  to be removed from the disc receiving concavity  5 . At the second position, an information signal can be read from the optical disc  3 . Thus, the first position is a disc loading/unloading position, while the second position is a disc reading/writing position. A plurality of rollers  9 , which are connected to each other by a shaft  8 , are disposed at the front side of the support pedestal  1 . The rollers  9  support the lower side of the disc tray  4  and enable the disc tray  4  to move smoothly. 
   The disc tray  4  is moved between the first position (see  FIG. 2 ) and the second position (see  FIG. 3 ) by a tray feeding mechanism  11  disposed on the support pedestal  1 . As shown in  FIG. 1 , the tray feeding mechanism  11  includes a drive motor  12  fixed to the lower surface of the support pedestal  1 . The drive motor  12  has a drive shaft  12   a  projecting out to the upper surface of the support pedestal  1 . The tray feeding mechanism  11  also includes a pulley gear  15  connected by a belt  14  to a pulley  13 , which is fixed on the drive shaft  12   a . The pulley gear  15  has a gear  15   a , which is meshed with a coupling gear  16 , installed rotatably to the support pedestal  1 . The coupling gear  16  has a small-diameter gear  16   a , which is meshed with a coupling gear  17   a  of a tray feeding gear  17 , which is installed rotatably to the support pedestal  1 . The tray feeding gear  17  has a large-diameter gear  17   b  at its outermost circumference that is meshed with a rack gear  18 , which is disposed along one side of the lower surface of the disc tray  4 . 
   In the tray feeding mechanism  11  thus constructed, when the drive motor  12  is put into run, the pulley gear  15  is rotated and the tray feeding gear  17  is rotated by means of the coupling gear  16 . As the tray feeding gear  17  is rotated, the large-diameter gear  17   b  of the tray feeding gear  17 , being meshed with the rack gear  18  of the disc tray  4 , is rotated to move the disc tray  4  in the direction of arrow A 1  (i.e., from the first position to the second position) as illustrated in  FIGS. 1 and 2 . Alternatively, the large-diameter gear  17   b  is rotated to move the disc tray  4  in the direction of arrow A 2 , as illustrated in  FIGS. 2 and 3  (i.e., from the second position to the first position), correspondingly to the rotating direction of the drive motor  12 . 
   A disc drive unit  21  is disposed on the support pedestal  1 , on which the disc tray  4  is movably provided, to rotate the optical disc  3  on the disc tray  4 , as well as to read an information signal recorded therein. 
   As will be seen from  FIGS. 1 and 4 , the disc drive unit  21  includes a base  22 , which is formed from a flat metal plate by stamping and pressing. The base  22  is formed to have a rectangular shape and has formed in a position deviated to one end thereof from the center thereof a generally rectangular opening  24 , in which an optical pickup  23  is disposed. The base  22  has installed at one end thereof a disc rotation driving mechanism  25  which drives to rotate the optical disc  3  carried on the disc tray  4 . The disc rotation driving mechanism  25  includes a spindle motor  26  having a spindle  27 , and a disc table  28  fixed integrally on the free end of the spindle  27 . The spindle motor  26  is fixed to the lower surface of the base  22  with the spindle  27  thereof projected out to the upper surface of the base  22 . The spindle motor  26  has a motor housing  26   a  fixed to the base  22  with fixing screws  30 . The disc table  28  has provided in the center thereof a socketed projection  28   a  in which the freed end of the spindle  27  is fitted, so that the disc table  28  is rotatable with the spindle  27 . In the center of the upper surface of the disc table  28  on which the optical disc  3  is placed, there is provided a centering boss  29  which is to be engaged in a center hole  3   a  in the optical disc  3  in order to make the center of the optical disc  3  coincide with the center of rotation of the disc table  28 . The centering boss  29  is smaller in diameter as it goes from the base thereof towards the free end. By engaging the optical disc  3  at the center hole  3   a  thereof onto the free end of the centering boss  29  and lowering it towards the base end of the centering boss  29 , the optical disc  3  is loaded on the disc table  28  with the center thereof made to coincide with the center of rotation of the disc table  28 . 
   As shown, the optical pickup  23  installed to the base  22  includes an optical block  31  incorporating a light source, such as a semiconductor laser, to emit a light beam by which a signal recording area on the optical disc  3  loaded on the disc table  28  and driven to rotate, optical parts such as a beam splitter, etc. to guide the light beam emitted from the light source to an objective lens and split the light beam incident upon the objective lens, and a photo-detector to detect the light beam reflected from the optical disc  3 . On the upper surface of the optical block  31  opposite to the optical disc  3 , there is provided an objective lens  32  to converge the light beam emitted from the light source and focus it on the signal recording area on the optical disc  3 . The objective lens  32  is supported on an objective lens moving mechanism (not shown), which moves the objective lens  32  in two axial directions perpendicular to each other, namely, in a focusing direction parallel to the optical axis of the objective lens  32  and a tracking direction perpendicular to the optical axis of the objective lens  32 , namely, a direction extending radially of the optical disc  3 . The objective lens moving mechanism works as follows. Namely, a light beam emitted from the light source is irradiated to the optical disc  3 , a return light component of the irradiated light beam from the optical disc  3  is detected to provide a focus error signal and/or tracking error signal, the objective lens  32  is moved in the focusing direction and/or tracking direction based on the focus error signal and/or tracking error signal. Thus, the light beam irradiated through the objective lens  32  to the optical disc  3  is focused on the signal recording area on the optical disc  3 , thereby scanning a predetermined recording track in the signal recording area. 
   The objective lens moving mechanism is constructed on a yoke  33  forming a magnetic circuit for the objective lens moving mechanism, and covered with a lid  34  installed on the optical block  31 . The lid  34  has formed in the upper surface thereof a window  35  through which the objective lens  32  faces the optical disc  3 . 
   The optical pickup  23  thus constructed is supported on the base  22  to be movable radially of the optical disc  3  being positioned inside the opening  24  and rotated on the disc rotation driving mechanism  25  as shown in  FIG. 1 . Further, the base  22  has installed thereon a main guide shaft  36  and sub guide shaft  37 , on which the optical pickup  23  is movably supported. As shown in  FIG. 4 , the main and sub guide shafts  36  and  37  are fixed to the lower surface of the base  22 , supported at the ends thereof on shaft supports  38 , and extend along the opposite edges, respectively, of the opening  24  and in parallel to each other. The main guide shaft  36  forms a reference guide shaft for movement of the optical pickup  23 , and it is installed highly parallel to a center line P 1 , shown in  FIG. 2 , passing through the center of the spindle  27  being the center of rotation of the disc rotation driving mechanism  25  installed to the base  22 . 
   As shown in  FIGS. 1 and 2 , the optical block  31  has a pair of projecting guide shaft support pieces  39  provided at one side thereof optical pickup  23 . The guide shaft support pieces  39  has guide shaft insertion holes  40 , respectively, formed through them. Also the optical block  31  has guide supports  41  provided at the side thereof opposite to the side where the projecting guide shaft support pieces  39  are provided. Each of the guide supports  41  has a generally C-shaped section (not shown). The optical pickup  23  is supported on the base  22  with the main guide shaft  36  inserted through the guide shaft insertion holes  40  in a pair of guide shaft support pieces  39 , respectively, and with the guide supports  41  engaged on the sub guide shaft  37 . The optical pickup  23  is supported with the objective lens moving mechanism including the objective lens  32  being positioned on the upper surface of the base  22  and the optical block  31  being positioned on the lower surface of the base  22 . Namely, the optical pickup  23  extends to both above and below the base  22 . 
   As shown in  FIGS. 1 and 4 , the optical pickup  23  supported on the main and sub guide shafts  36  and  37  fixed to the base  22  is moved by the pickup feeding mechanism  45  disposed on the side of the base  22  on which the main guide shaft  36  is fixed, in the directions of arrows B 1  and B 2  shown in  FIG. 3  between the inner and outer circumferences of the optical disc  3  set and rotated in the disc rotation driving mechanism  25 , namely, along the main guide shaft  36 . As shown in  FIGS. 4 and 5 , the pickup feeding mechanism  45  includes a drive motor  47  having a drive shaft  46  and fixed to the lower surface of the base  22  with the drive shaft  46  projected to the upper surface of the base  22 , a drive gear  48  fixed to the drive shaft  46 , a coupling gear  49  having a small-diameter gear  49   a  and being meshed with the drive gear  48 , and a feeding gear  50  meshed with the small-diameter gear  49   a  of the coupling gear  49 . As shown in  FIG. 1 , in the optical pickup  23 , a rack gear  51  fixed to the side of the optical block  31  at which the latter is installed on the main guide shaft  36  is meshed with a feeding gear  50  of the pickup feeding mechanism  45 . Thus, the optical pickup  23  is fed in the direction of arrow B 1  or B 2  in  FIG. 3  between the inner and outer circumferences of the optical disc  3  correspondingly to the rotating direction of the drive motor  47 . 
   The rack gear  51  includes two rack plates  51   a  and  51   b  superposed on each other. There is provided a helical compression spring  52  between the rack plates  51   a  and  51   b . Thus the rack plates  51   a  and  51   b  will be forced away from each other by the spring  51 . So, a backlash caused between the feeding gear  50  of the pickup feeding mechanism  25  and the rack gear  51  of the optical pickup  23  when the optical pick-up  23  is fed, is absorbed to attain an accurate feeding of the optical pickup  23 . 
   Further, on the lower surfaces of the spindle motor  26  and drive motor  47  fixed to the lower surface of the base  22 , there is fixed a printed circuit board  53 , in which there is formed a drive control circuit to control the driving of the motors  26  and  47 . The printed circuit board  53  has fixed at one side thereof connection terminals  54  for supplying a power and control signal to each of the spindle motor  26  and drive motor  47 . 
   As mentioned above, the base  22 , on which the disc rotation driving mechanism  25 , optical pickup  23  and optical pickup feeding mechanism  45  are installed, is fixed to a base support  55  supported pivotably on the support pedestal  1 , and forms the disc drive unit  21 . The base support  55  is formed by molding a synthetic resin to be a frame having a rectangular shape as shown in  FIG. 1 . 
   The base  22  has installed to the lower surface of the base support  55  thereof the disc rotation driving mechanism  25 , optical pickup  23  and optical pickup feeding mechanism  45  with the optical pickup  23  being exposed to above the base support  55  through an opening  155  formed in the center of the base support  55 . The base  22  is supported by the base support  55  by means of first to fourth supporting members  56  to  59  disposed symmetrically with respect to the center line P 0  of the base  22  extending in a direction in which the base  22  is guided by the main and sub guide shafts  36  and  37 . 
   More particularly, in one embodiment of an optical disc drive according to the present invention, a rectangular base  22  has first to fourth supporting member receiving holes  61  to  64  at each of its corners, respectively. The first to fourth supporting member receiving holes  61  to  64  are disposed on the base  22  symmetrically along a center line P 0  of the base  22  as shown in  FIG. 6 . Each of the supporting member receiving holes  61  to  64  is formed generally circular, and each of the support members  56  to  59  is partially fitted in each of the holes  61  to  64 . Among these supporting member receiving holes, the first and second supporting member receiving holes  61  and  62  are disposed on one side of the base  22 , while the third and fourth supporting member receiving holes  63  and  64  are disposed on the other side of the base  22 , thereby forming a symmetrical arrangement along the center line P 0  of the base  22 . Disposition of support members, supporting member receiving holes and supporting members (described below) in a symmetrical arrangement on the base  22  enables a simple and easy manufacturing process of an optical disc drive. 
   Each of the first to fourth supporting members  56  to  59  includes a cylindrical elastic support piece  65  formed from an elastic material such as rubber, a helical spring  66  to adjust the elasticity of the elastic support piece  65 , and a washer-based fixing screw  67  to fix the elastic support piece  65  along with the helical spring  66  to the base support  55 , as shown in  FIG. 7 . The elastic support piece  65  is hollow and includes a cylindrical small-diameter portion  65   a  and cylindrical large-diameter portion  65   b . The base support  55  has formed at each corner thereof a cylindrical support portion  68  projecting from the lower side thereof. The elastic support piece  65  is fitted at the cylindrical small diameter portion  65   a  on the cylindrical support portion  68 . As shown, the elastic support piece  65  is grooved at  69  in the cylindrical large-diameter portion  65   b  thereof. The elastic support piece  65  is fitted at the groove  69  thereof in each of the first to fourth supporting member receiving holes  61  to  64 . The large-diameter portion  65   b  of the elastic support piece  65  is recessed at the lower side thereof and along the outer edge thereof to form a spring retention projection  70 . The helical spring  66  is provided around the elastic support piece  65  and between a washer base  67   a  of the screw  67  and the spring retention projection  70  as shown in  FIG. 7 . 
   Each of the first to fourth supporting members  56  to  59  is fixed to the base  22  with the elastic support piece  65  being fitted at the groove  69  in each of the supporting member receiving holes  61  to  64 . After the supporting members  56  to  59  are fitted in the supporting member receiving holes  61  to  64 , respectively, the helical spring  66  is fitted on the elastic support piece  65  and retained by the washer base  67   a  of the fixing screw  67 , and the fixing screw  67  is screwed into the cylindrical support portion  68  of the base support  55 . Thus, the base  22  is fixed to the lower side of the base support  55 . 
   The base  22  is fixed to the base support  55  with the elastic support pieces  65  and helical springs  66 . So, a disturbance such as a vibration conveyed through the base support  55  is absorbed or attenuated by the elastic support pieces  65  and helical springs  66 . Thus, the disc rotation driving mechanism  25  and optical pickup  23  installed to the base  22  can be stably driven. 
   In an optical disc drive according to the present invention, main components of the base  22  such as the optical pickup  23 , disc rotation driving mechanism  25  and pickup feeding mechanism  45 , are disposed on the base  22  in such a way that their total weight is supported essentially evenly at the both sides of the base  22  relative to the center line P 0 , as shown in  FIG. 6 . For example, the optical pickup  23  and the disc rotation driving mechanism  25  can be disposed on one side of the base  22  relative to the center line P 0 , while the pickup feeding mechanism  45  can be disposed on the other side of the other side. Such an arrangement of these components prevents weight imbalance of the base  22 , by essentially evenly maintaining the weight applied to one side of the base  22  along the center line P 0  to the other. 
   To reduce the size of the disc drive itself using the base  22 , the base  22  is designed to have a sufficient size for installing thereon the optical pickup  23 , disc rotation driving mechanism  25  and pickup feeding mechanism  45 . To this end, the base  22  has installed at one end thereof heavy parts such as the spindle motor  26 , further a heavier part such as the disc rotation driving mechanism  25  in which the optical disc  3  is loaded. As shown in  FIG. 6 , the optical pickup  23  to scan the optical disc  3  set and rotated in the disc rotation driving mechanism  25 , is moved between the center of the base  22 , and a position near the disc rotation driving mechanism  25  and a generally central position of the base  22  indicated with a dashed line in  FIG. 6 . Therefore, the center of gravity Q 1  of the base  22  will be displaced to the center of the spindle  27  being the center of rotation of the disc rotation driving mechanism  25 , and the center of gravity Q 2  of the base  22  when the optical pickup  23  is moved to a position away from the disc rotation driving mechanism  25 , will also be displaced to the center of the spindle  27 . 
   Since the optical pickup  23  is supported on the base  22  to be movable parallel to the center line P 0  of the base  22 , even when the optical pickup  23  is moved to any position, the center of gravity Q of the base  22  always lies nearly along the center line P 0  of the base  22 . 
   Thus, since the center of gravity Q of the base  22  is displaced to one end of the base  22  at which the disc rotation driving mechanism  25 , a large weight will be applied to the base  22  at the first and third supporting members  56  and  58  provided at the one end of the base  22 . To horizontally support the base  22  with the base support  55  being a reference supporting plane, the supporting force of the first and third supporting members  56  and  58  is made larger than the supporting force of the second and fourth supporting members  57  and  59 . To this end, the helical spring  66  forming each of the first and third supporting members  56  and  58  has a larger spring constant than the helical spring  66  forming each of the second and fourth supporting members  57  and  59 . The base  22  is supported with a difference between the weight applied at one end of the base  22  and that applied at the other end being thus absorbed. Thus, the base  22  will be supported horizontally by the base support  55 . 
   The first to fourth supporting members  56  to  59  supporting the base  22  are disposed symmetrically with respect to the center line P 0 , where the center of gravity of the base  22  is approximately located. So, since the first and third supporting members  56  and  58  may have the same supporting force and the second and fourth supporting members  57  and  59  may have the same supporting force, the first to fourth supporting members  56  to  59  can be designed and manufactured more easily. 
   A plurality of supporting members need not be disposed at corners of the base  22 . Rather, these supporting members merely need to be symmetrically disposed along the center line P 0  of the base  22  in order to support the base  22 . For example, in another embodiment of the present invention, the second and fourth supporting members  57  and  59 , supporting the other end of the base  22  opposite to the one end where the disc rotation driving mechanism  25  is installed, may be disposed at positions deviated from the corners of the base  22 , as shown in  FIG. 8 . In this embodiment, main components of the base  22  such as the optical pickup  23 , disc rotation driving mechanism  25  and pickup feeding mechanism  45 , are also disposed on the base  22  in such a way that their total weight is supported essentially evenly at both sides of the base  22  relative to the center line P 0 , as shown in  FIG. 8 . More specifically, the optical pickup  23  and the disc rotation driving mechanism  25  are disposed on one side of the base  22  relative to the center line P 0 , while the pickup feeding mechanism  45  is disposed on the other side of the other side. Such an arrangement of these components prevents weight imbalance of the base  22 , by nearly evenly maintaining the weight applied to one side of the base  22  along the center line P 0  to the other. In addition, disposition of the support members in a symmetrical arrangement on the base  22  enables a simple and easy manufacturing process of optical disc drives in accordance with the present invention. 
   Also, the first to fourth supporting members  56  to  59  supporting the base  22  may be composed each of only a cylindrical elastic support piece  71  formed from an elastic material such as rubber and a washer-based fixing screw  72  to fix the elastic support piece  71  to the base support  55 , as shown in  FIG. 9 . The fixing screw  72  has a washer base  72   a . The elastic support piece  71  of each of the supporting members  56  to  59  is fitted on the cylindrical support portion  68  projecting from the lower surface of the base support  55 , and elastically compressed between the washer base  72   a  of the fixing screw  72  screwed into the cylindrical support portion  68  and the lower surface of the base support  55 . Namely, the elastic support piece  71  is installed under a predetermined elasticity. The elastic support piece  71  is grooved at  73  in a middle outer surface thereof. The base  22  is supported on the base support  55  by means of the first to fourth supporting members  56  to  59  with the elastic support piece  71  of each of the supporting members  56  to  59  being engaged at the groove  73  in each of the supporting member receiving holes  61  to  64  of the base  22 . 
   In case the first to fourth supporting members  56  to  59  thus constructed are used, the elastic support piece  71  forming each of the second and fourth supporting members  57  and  59  may have a larger hardness than the elastic support piece  71  forming each of the first and third supporting members  56  and  58 , to absorb a difference between a weight applied to one end of the base and a one applied to the other end, whereby the base  22  can be supported horizontally by the base support  55 . 
   Even when the first to fourth supporting members  56  to  59  constructed as shown in  FIG. 9  are used to support the base  22 , a disturbance such as a vibration transmitted via the base support  55  can be absorbed or attenuated by the elastic support piece  71 , so it is possible to prevent any vibration from being transmitted to the disc rotation driving mechanism  25  and optical pickup  23  installed on the base  22 , thus the disc rotation driving mechanism  25  and optical pickup  23  can be driven stably. In addition, instead of changing the supporting force of the support members  56  to  59 , it is possible to support the base  22  horizontally by changing the establishment of the support height of the base  22 . In other words, the first and third supporting members  56  and  58  support the base  22  at different height relative to a reference plane from that at which the second and fourth supporting members  57  and  59  support the base  22 , so that the base  22  is elastically deformed correspondingly to the magnitude of the weight applied to the supporting members  55  to  59  and thus it can be kept horizontal. 
   In an optical disc drive for the optical disc  3  as a recording medium, the light beam emitted from the optical pickup  23  has to be irradiated highly perpendicularly to the signal recording surface of the optical disc  23 . If such a skew that the optical axis of the light beam is oblique relative to the signal recording surface of the optical disc  3  takes place, a predetermined recording track can-not be scanned by the light beam, thus failing to correctly read an information signal recorded in the optical disc  3 . Especially in an optical disc for a high recording-density optical disc  3  having video information recorded herein, any inclination of the light beam relative to the signal recording area of the optical disc  3  will result in a failure to read an information signal from the optical disc  3 . 
   To prevent the light beam emitted from such an optical pickup  23  from being oblique relative to the signal recording area of the optical disc and irradiate the light beam highly perpendicularly to the signal recording area of the optical disc  3 , the base  22  on which the optical pickup  23  and disc rotation driving mechanism  25  has to be kept highly flat. 
   For example, in case the base  22  is used in an optical disc drive for a recording medium such as a digital video or versatile disc (DVD) having a diameter of 12 cm, dedicated for recording video information, it is necessary that the fixed portion of the spindle motor  26  forming the disc rotation driving mechanism  25 , both ends of the main guide shafts  36  and the end of the sub guide shaft  37  nearer to the disc rotation driving mechanism  25  should have a flatness of 0.03 or less in relation to first reference points S 1 , and S 2  near the shaft supports  38  supporting the opposite ends, respectively, of the main guide shaft  36  on which the optical pickup  23  is supported, and to a third reference points S 3  near the shaft supports  38  supporting the end of the sub guide shaft  37  near the disc rotation driving mechanism  25 , as will be seen from  FIG. 6 . 
   To this end, the base  22  has to be formed from a material strong enough to maintain a constant flatness without any deflection caused by reception of the weight of the optical pickup  23  and disc rotation driving mechanism  25  installed on the base  22 . In case the base  22  is made of a metal plate, the metal piece is stamped and bent by pressing. When a metal plate is worked by pressing to make the base  22 , a large internal stress will developed in the metal plate during the manufacture if the latter is relatively thick. The internal stress will make it difficult to work the base  22  for a high flatness. 
   According to the present invention, the base  22  is made of a metal plate having a thickness ranging from 1.4 mm to 1.8 mm. The metal plate having such a thickness was used to form a rectangular base  22  of which the width W, is about 80 mm and length L, is about 100 mm as shown in  FIG. 6 . Under the conditions of the disc rotation driving mechanism  25  weighing about 50 g, optical pickup  23  weighing about 40 g and the pickup feeding mechanism  45  weighing about 30 g are installed to the base  22 , the flatness, relative to the first to third reference points S 1  to S 3 , of the fixed portion of the spindle motor  26 , both ends of the main guide shaft  36  and the end of the sub guide shaft  37  near the disc rotation driving mechanism  25  could be kept to 0.03 or less. 
   The base  22  on which the disc rotation driving mechanism  25 , optical pickup  23  and pickup feeding mechanism  45  are installed as in the above is supported to the base support  55  with the first to fourth supporting members  56  to  59 . As shown in  FIG. 1 , with a pair of pivots  75  projecting from at the opposite sides, respectively, of the other end opposite to the one end of the base  22  at which the disc rotation driving mechanism  25  is positioned, being engaged in a pair of shaft supports  76  provided at both rear sides, respectively, of the support pedestal  1 , the base support  55  is installed to the support pedestal  1  pivotably about the pivots  75  in the directions of arrows Y 1 , and Y 2  relative to the support pedestal  1 , as illustrated in  FIG. 10 . The pivots  75  engaged in the shaft supports  76 , respectively, are supported by flanges  77   a  formed on fixing screws  77 , respectively, screwed in the shaft supports  76 , respectively, and thus prevented from being disengaged from the shaft supports  76 . The optical pickup  23 , disc rotation driving mechanism  25  and pickup feeding mechanism  45  installed to the base  22  are thus located extending to above and below the support pedestal  1  through an opening I a formed in the latter, as shown in  FIG. 10 . 
   As shown in  FIG. 1 , the base support  55  has an engagement piece  78  projecting from the lateral face at one end thereof. As also shown in  FIG. 1 , the base support  55  supported on the support pedestal  1  pivotably about the pivots  75  is engaged at the engagement projection  78  thereof in a cam recess  80  formed on the outer surface of a cam gear  79  rotated by the tray feeding mechanism  11 . The cam gear  79  is meshed with a tray feeding gear  17  located at the front portion of the support pedestal  1 , supported pivotably on a shaft (not shown) and forming the tray feeding mechanism  11 , so that it will be rotated as the disc tray  4  is fed between the first and second positions. 
   On the outer surface of the cam gear  79 , the cam recess  80  is formed spiral from the base end towards the free end of the cam gear  79 . The base support  55  is engaged at the engagement projection  78  thereof in the cam recess  80  thus formed on the cam gear  79  as mentioned above. As the earn gear  79  rotates, the engagement projection  78  is moved by the cam recess  80  axially of the cam gear  70  and thus the base support  55  is pivoted about the pivots  75  in the directions of arrows Y 1  and Y 2  in  FIG. 10  relative to the support pedestal  1 . 
   The support pedestal  1  has provided thereon a clamper  81  cooperative with the disc table  28  of the disc rotation driving mechanism  25  to have the optical disc  3  loaded on the disc table  28  rotate along with the disc table  28 . The clamper  81  is installed rotatably at the center of a clamper support plate  84  extending between opposite ends of the support pedestal  1  and fixed with screws  83  to supporting projections  82  studded on the support pedestal  1 . 
   In the optical disc drive constructed as in the above, when the disc tray  4  is drawn out of the casing to the first position where the optical disc  3  can be loaded or unloaded, the one end of the base support  55  where the disc rotation driving mechanism  25  is pivoted to a position under the support pedestal  1 , as shown in  FIG. 10 . 
   When the optical disc  3  for playing is put on the disc tray  4  drawn out of the casing and then driven by the drive motor  12  of the tray feeding mechanism  11  to move in the direction of arrow A, in  FIG. 2  into the casing, the cam gear  79  meshed with the tray feeding gear  17  is rotated. As the earn gear  79  is thus rotated, the base support  55  having the engagement projection  78  engaged in the cam recess  80  in the cam gear  79  is pivoted in the direction of arrow Y 1  in  FIG. 10  about the pivots  75  relative to the support pedestal  1 . That is, as the disc tray  4  is moved, the base support  55  will be pivoted towards the disc tray  4 . 
   When the disc tray  4  has been moved to midway between the first position and the second position inside the casing, the base support  55  is pivoted to a position where the disc table  28  of the disc rotation driving mechanism  25  is let to go into the disc tray  4 . When the base support  55  is pivoted until the disc table  28  goes into the disc tray  4 , the optical disc  3  held in the disc receiving concavity  5  will be raised from the bottom of the disc receiving concavity  5  and placed on the disc table  28 . Further as the disc tray  28  is moved to the second position where the optical disc  3  is read, the base support  55  will further be pivoted in the direction of arrow Y 1  in  FIG. 10  simultaneously with the movement of the disc tray  4  and take a horizontal position relative to the support pedestal  1  as shown in  FIG. 11 . When the base support  55  is pivoted to the horizontal position in relation to the support pedestal  1 , the clamp  81  will press the optical disc  3  placed on the disc table  28  and the optical disc  3  can be rotated along with the disc table  28 . At this time, the disc tray  4  will be held at the second position where it is locked by a locking mechanism (not shown). 
   When the disc tray  4  has been moved to the second position and the optical disc  3  held on the disc tray  4  has been loaded rotatably along with the disc table  28 , the disc rotation driving mechanism  25  is driven to drive to rotate the optical disc  3  and drive the optical pickup  23 . As the optical pickup  23  is fed by the pickup feeding mechanism  45  radially of the optical disc  3 , the signal recording area on the optical disc  3  is scanned by a light beam emitted from the optical pickup  23  to read an information signal recorded in the optical disc  3 . 
   When the tray feeding mechanism  11  is driven to move the disc tray  4  in the direction of arrow A 2  in  FIG. 3  after the optical disc  3  is read, the base support  55  is pivoted in the direction of arrow Y 2  in  FIG. 11  towards under the support pedestal  1  as the disc tray  4  is moved. When the base support  55  has been pivoted in the direction of arrow Y 2  in  FIG. 11 , the optical disc  3  on the disc table  28  will leave the disc table  28  and be held in the disc receiving concavity  5  of the disc tray  4 . The disc tray  4  will further be moved. When the disc tray  4  has been moved to the first position, the base support  55  will have left the support pedestal  1  as shown in  FIG. 10 . 
   In the optical disc drive according to the present invention, the base  22  on which the disc rotation driving mechanism  25  is installed is supported by the base support  55  to be highly flat. Therefore, the disc rotation driving mechanism  25  can be installed with an improved precision. When the base support  55  is pivoted towards and away from the disc tray  4  as the disc tray  4  is moved, the optical disc  3  can be loaded onto or unloaded from the disc table  28  with no possible collision between the disc tray  4  and disc rotation driving mechanism  25 . 
   In the foregoing, the present invention has been described concerning the embodiment for an optical disc as the recording medium. However, the present invention may be applied to an optical disc drive for any other disc-like recording medium than the optical disc, such as a magnetic disc as advantageously as in the above. 
   In the optical disc drive in which the disc rotation driving mechanism and the writing and/or reading means for a disc-like recording medium driven to rotate by the disc rotation driving mechanism are installed to the base, the base can be supported highly flat. Therefore, the signal recording surface of the disc-like recording medium can be scanned while a distance between the disc-like recording medium driven to rotate by the disc rotation driving mechanism and the writing and/or reading means is being kept constant. Thus, it is possible to write or read an information signal correctly to or from the disc-like recording medium. 
   As having been described in the foregoing, the present invention provides a disc drive and an optical disc drive in which the base on which the disc rotation driving mechanism and writing and/or reading means are installed can be kept highly flat and can be supported by the base support and the like with the high flatness, so that an information signal can be written or read correctly and a disc-like recording medium can be smoothly loaded in place. 
   It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that structures and methods within the scope of these claims and their equivalents be covered thereby.