Abstract:
A disk chucking device for use in a disk player, in which the supporting shafts of clamping members are held in holding portions of a hinge provided on the top-surface side of a turntable in such a manner as to be coaxial with a cylinder and to slide along therewith, so that each of the supporting shafts is in opposed contact with the inner side surface of a center boss and a corresponding cam provided thereabove. Moreover, the clamping members, each of which has a chuck end portion formed on the top end thereof, are adapted to be able to vertically slide and radially swing. The clamping members are pushed by first and second spring members in the downward direction and in the direction of the outer circumference of a disk. When a disk installed in the device is detached therefrom, the clamping members are raised. Pins attached to the clamping members abut against the cams provided in the center boss. Then, the clamping members are inwardly tilted. Thus, the disk is detached from the device. Subsequently, the clamping members automatically return to initial positions thereof.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a disk chucking device for chucking a disk placed on a turntable of a disk player such as an optical disk player or a magnetooptical disk player. More particularly, the present invention relates to a disk chucking device suitable for reducing the thickness of the disk player. 
     2. Description of the Related Art 
     Hitherto, a disk chucking device illustrated in, for example, FIGS. 5,  6 A and  6 B has been used for chucking an optical disk, such as a compact disk (trade name), on a turntable. 
     As shown in FIG. 5, this chucking device  10  has a center boss  12  that is disposed above a turntable  11  in such a manner as to be coaxial therewith. Three pressing pieces  13  and three steel balls  14  are disposed under this center boss  12 . Each of the pressing pieces  13  and the steel balls  14  is partly exposed therefrom. The pressing pieces  13  are arranged at an angular interval of 120°, and the steel balls  14  are arranged at the same angular interval. 
     Further, the chucking device  10  is connected to a spindle motor  1  mounted on a chassis (not shown), and is driven by the motor  1  to rotate. 
     As illustrated in FIGS. 6A and 6B, an O-shaped ring (hereunder referred to as an O-ring)  16  made of an elastic material is mounted on the outer surface of a sleeve  15  coaxially connected to a central portion in the center boss  12 . This O-ring  16  outwardly pushes the pressing pieces  13  and the steel balls  14  (namely, in the directions of arrows a and b shown in FIGS.  6 A and  6 B). 
     Further, each of the pressing pieces  13  is connected to the bottom portion of a corresponding sleeve  15  through a corresponding elastic piece  13   s  formed on the bottom portion thereof. 
     In the case of the aforementioned chucking device  10 , when a disk D, whose central hole has engaged the center boss  12  as shown in FIG. 6A, is downwardly moved, the pressing pieces  13  inwardly move (namely, in the direction of an arrow a′). Thus, the inner edge of the central hole of the disk D is pressed outwardly (namely, in the direction of the arrow a) by an elastic restoring force of the O-ring  16 . Consequently, the disk D is centered on the turntable  11 . 
     Further, when the disk D is downwardly moved, the inner edge of the central hole of the disk D surmounts the steel balls  14  pushed outwardly (namely, in the direction of the arrow b) by the O-ring  16 , as illustrated in FIG.  6 B. The steel balls  14  push down the inner edge portion of the disk D (in the direction of an arrow C), so that the disk D is caught on the balls  14  and held by the turntable  11 . 
     Namely, the chucking of the disk D is performed by the steel balls  14 . 
     The steel balls  14 , however, push the inner edge portion of the disk D from an upwardly slanting direction, as illustrated in FIG.  6 B. Thus, the aforementioned conventional chucking device  10  has drawbacks in that the pressing forces of the steel balls  14  against the disk D vary with the shape of the chamfered inner edge thereof and that the adjustment of the pressing forces is difficult. 
     Moreover, the disk D is installed therein against the pressing forces of the steel balls  14 . Thus, the conventional disk chucking device  10  has another drawback in that, if the pressing forces of the steel balls  14  against the disk D are increased, a large force is needed when the disk D is inserted thereinto or removed therefrom. 
     To eliminate this drawback, there has been proposed a disk chucking device adapted to optionally set a clamping force by pressing down the edge portion of the central hole of a disk at an end of a clamping lever pushed by a tension spring. 
     (Configuration of the Proposed Disk Chuck Device) 
     As shown in FIG. 7, this proposed disk chucking device  20 A comprises a turntable  21 A, a center boss  31 C coaxially engaging therewith, and holding members  71  each of which includes a Γ-shaped clamping member  61  for chucking a disk and which accommodates and holds this clamping member  61 . 
     Three notches (or openings)  22  are disposed at an angular interval of 120° in an intervening portion between the outer and inner edges of the turntable  21 A. A cylinder  23  is disposed in a central portion of the turntable  21 A. Further, three catching bosses  29  are disposed on the bottom side of the turntable  21 A at an angular interval of 120° so that each of the catching bosses  29  is aligned with a corresponding one of the openings  22 . 
     Three notches (or openings)  32  are arranged at an angular interval of 120° in the center boss  31 C, which engages the cylinder  23 , in such a manner that each of the openings  32  is aligned with a corresponding one of the openings  22  of the turntable  21 A. Each of three projection pieces  33  for centering a disk D is disposed between a corresponding pair of the openings  32 . 
     In this proposed device, a cam  34  is provided on the inner surface of each of the openings  32  of the center boss  31 C in such a manner as to be in opposed contact with a pin  64  of a corresponding one of the clamping members  61 , as will be described later. 
     A chuck end portion  62  for chucking a disk is formed at the top portion of each of the clamping members  61  in such a manner as to project in the direction of the outer circumference of the turntable  21 A and as to have upper and lower inclined surfaces. The pin  64  is disposed under this chucking portion  62 . Further, a supporting shaft  63  is disposed at the bottom portion of each of the clamping members  61 . 
     Each of the clamping members  61  is coupled to a corresponding one of the catching bosses  29  through a tension spring  66  and is inserted into a corresponding one of the holding members  71  provided on the bottom side of the turntable  21 A. 
     The holding members  71  are mounted on the side surface of the cylinder  23  at an angular interval of 120° so that each of the members  71  is aligned with and partly exposed from a corresponding one of the openings  22  of the turntable  21 A. 
     Further, each of the clamping members  61  respectively inserted into the holding members  71  is disposed in such a way as to be able to be partly exposed from a corresponding one of the openings  32  of the center boss  31 C. 
     Incidentally, the chucking device  20 A illustrated in FIG. 7 is connected to the spindle motor  1  mounted on the chassis (not shown), and is driven by the motor  1  to rotate. 
     With the aforesaid configuration, the proposed chucking device  20 A is adapted so that, when no disk is installed therein, the chuck end portion  62  of each of the clamping members  61  is exposed from the corresponding opening  32  of the center boss  31 C in the direction of the outer periphery of the turntable  21 A, as illustrated in FIG.  8 A. 
     Further, each of the clamping members  61  is pushed downwardly (namely, in the direction of an arrow d shown in FIG. 8A) by the resilient force of the corresponding tension spring  66  stretched between the corresponding one of the catching bosses  29  provided on the bottom side of the turntable  21 A and a catching hole  65  of a corresponding one of the clamping members  61 . The corresponding supporting shaft  63  abuts against the bottom end of a guide groove  75  of a corresponding one of the holding members  71 . The corresponding one of the clamping members  61  is pushed clockwise (namely, in the direction of an arrow e), so that the corresponding pin  64  abuts against the catching portion  73  of the corresponding holding member  71 . 
     Incidentally, in FIGS. 8A to  8 C and  9 A to  9 C, the supporting shaft  63  of the corresponding clamping member  61  is denoted by a mark “+” indicating the center of rotation. The pin  64  is designated by a mark “×” indicating that the pin  64  is movable. 
     Further, for simplicity of drawing, only parts needed for describing the displacement of the clamping member  61  are denoted by reference characters in FIGS. 8B,  8 C,  9 B and  9 C. 
     As illustrated in FIG. 8B, when a disk D is installed therein, the inner edge portion thereof pushes the top surface  62 A of the chuck end portion  62  of each of the clamping members  61  in the inner circumference of the turntable  21 A with the descent of the disk D (in the direction of the arrow d). Thus, each of the clamping members  61  is turned counterclockwise as viewed in this figure, so that each of the pins  64  is detached from the catching portion  73  of the corresponding holding member  71 . 
     In a state of the device illustrated in FIG. 8B, each of the clamping members  61  remains pushed downwardly by the elastic force of the corresponding tension spring  66 . Thus, the corresponding supporting shaft  63  abuts against the bottom end of the guide groove  75  of the corresponding holding member  71 . 
     This state lasts until the disk D descends still more to a position where the inner edge of the top surface thereof surmounts the edge of the chuck end portion  62  of each of the clamping members  61 . 
     Then, as illustrated in FIG. 8C, when the disk D descends still more and the disk D is put on the turntable  21 A, the top surface of the disk D abuts against the inclined lower surface  62 B of each of the clamping members  61 . 
     In a state illustrated in FIG. 8C, each of the clamping members  61  remains pushed downwardly by the resilient force of the corresponding tension spring  66 . Thus, the corresponding supporting shaft  63  abuts against the bottom end of the guide groove  75  of the corresponding holding member  71 . Moreover, the supporting shaft  63  is pushed counterclockwise as viewed in this figure, so that the corresponding pin  64  abuts against the catching portion  73  of the corresponding holding member  71  again. 
     Thus, the inclined lower surface of the chuck end portion  62  of each of the clamping members  61  abuts against the inner edge portion of the disk D from above and pushes and clamps the disk D. Namely, the disk D is chucked. 
     Therefore, the setting of the elastic force of the tension springs  66  ensures a stable pressing force of each of the clamping members  61  when a disk D is installed in this proposed chucking device  20 A. 
     Moreover, the relatively simple structure of each of the clamping members  61  and the holding members  71  results in decrease in the cost of components and in the number of man-hours to fabricate the device  20 A. 
     Additionally, the supporting shaft  63  of each of the clamping members  61  is vertically rockably held in the guide groove  75  of the corresponding holding member  71 . Thus, even when, for instance, a mechanical shock causes the disk D to move in the direction in which the chuck end portion  62  of each of the clamping members  61  engages therewith, the chuck end portion  62  thereof rises with the result that the pressing force against the disk D is constant. 
     In the case that a disk D is released from the chucking device  20 A which is in the state where the disk is chucked as illustrated in FIGS. 8C and 9A, the bottom surface  62 B of the chuck end portion  62  of each of the clamping members  61  is upwardly pushed by the inner edge of the top surface of the disk D with ascent thereof. 
     Further, as illustrated in FIG. 9B, each of the clamping members  61  is raised against the resilient force of the tension springs  66 . The supporting shaft  63  thereof upwardly slides in the guide groove  75  of the corresponding holding member  71 . Moreover, the pin  64  of each of the clamping members  61  is detached from the catching portion  73  of the corresponding holding member  71  and then abuts against the inner slope of the corresponding cam  34  of the center boss  32 . 
     In the state of the device illustrated in FIG. 9B, the pin  64  of each of the clamping members  61  slides on the inner slope of the corresponding cam  34  of the center boss  32 . Thus, each of the clamping members  61  rotates counterclockwise, as viewed in this figure. 
     The amount of rotation of each of the clamping members  61  reaches a maximum value when the disk D rises still more to a position where the inner edge of the top surface thereof surmounts the edge of the chuck end portion  62  thereof, as illustrated in FIG.  9 C. 
     In the state of the device illustrated in FIGS. 9B and 9C, the chuck end portion  62  of each of the clamping members  61  is upwardly exposed from the corresponding opening  32  of the center boss  31 C. 
     When the disk D rises still more from the position thereof shown in FIG. 9C to a position where the inner edge of the bottom surface thereof abuts against the top surface of the chuck end portion  62  of each of the clamping members  61 , the engagement of the disk D with the chucking portion  62  is canceled. 
     Then, the supporting shaft  63  of each of the clamping members  61  downwardly slides in the guide groove  75  of the corresponding holding member  71  and finally abuts against the bottom end thereof because the clamping members  61  are pushed clockwise (namely, in the direction of the arrow e) and downwardly (namely, in the direction of the arrow d) by the resilient force of the tension springs  66 . Moreover, each of the pins  64  abuts against the catching portion  73  of the corresponding holding member  71  again. Thus, the device  20 A automatically returns to the initial state where no disk is installed therein as illustrated in FIG.  8 A. 
     The aforementioned chucking device  20 A, however, cannot be applied to a slim disk apparatus, because the holding members  71  are placed under the turntable  21 A, as shown in FIGS. 7 to  9 C. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a disk chucking device which can stably ensure the pressing forces of clamping members when a disk is installed therein, and which has a simple configuration and can be easily reduced in thickness. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features, objects and advantages of the present invention will become apparent from the following description of a preferred embodiment with reference to the drawings in which like reference characters designate like or corresponding parts throughout several views, and in which: 
     FIG. 1 is a diagram showing the configuration of a disk chucking device embodying the present invention; 
     FIGS. 2A to  2 C are sectional diagrams illustrating an operation of installing a disk in the disk chucking device embodying the present invention; 
     FIGS. 3A to  3 D are sectional diagrams illustrating an operation of detaching the disk from the disk chucking device embodying the present invention; 
     FIGS. 4A and 4B are conceptual diagrams illustrating a chucking mechanism of the disk chucking device embodying the present invention; 
     FIG. 5 is a perspective diagram showing the configuration of a conventional disk chucking device; 
     FIGS. 6A and 6B are sectional diagrams illustrating a chucking operation of the conventional disk chucking device; 
     FIG. 7 is a perspective diagram showing the configuration of the proposed disk chucking device; 
     FIGS. 8A to  8 C are sectional diagrams illustrating an operation of installing a disk in the proposed disk chucking device; and 
     FIGS. 9A to  9 C are sectional diagrams illustrating an operation of detaching a disk from the proposed disk chucking device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, a disk chucking device embodying the present invention will be described in detail by referring to FIGS. 1 to  4 B. 
     (Configuration of Embodiment) 
     FIG. 1 shows the configuration of this embodiment of the present invention. Incidentally, the disk chucking device of the present invention is used in a disk recording/reproducing apparatus (not shown), such as an optical disk player or a magneto-optical disk player. 
     As shown in FIG. 1, the disk chucking device  120 S comprises a turntable  121 S, a center boss  131 C coaxially engaging therewith, clamping members  161  each shaped like a chevron, a hinge member  181  for holding the clamping members  161 , and a plate spring member  191 . 
     Three T-shaped notches (or openings)  122  are placed in an intervening portion between the outer and inner edges of the turntable  121 S at an angular interval of 120°. A cylinder  123  is disposed in the central portion of the turntable  121 S. Further, a fan-shaped concave portion  124  is formed around each of the three openings  122 . Three openings  125  are provided at an angular interval of 120° in the turntable  121 S. Each of the openings  125  is disposed between corresponding adjacent two of the concave portions  124 . 
     Three notches (or openings)  132  are placed in the center boss  131 C engaging with the cylinder  123  at an angular interval of 120° so that each of the openings  132  is aligned with a corresponding one of the openings  122  formed in the turntable  121 S. Each of three projection pieces  133  for centering a disk D is provided between corresponding adjacent two of the openings  132 . 
     In this embodiment, a cam  134  is provided on the inner surface of each of the openings  132  of the center boss  131 C. Further, as will be described later, the cam  134  is in opposed contact with a pin  164  of the corresponding clamping member  161  when a disk is detached from the chucking device  120 S. 
     A chuck end portion  162  for chucking a disk is formed at the top portion of each of the clamping members  161  in such a manner as to project in the direction of the outer circumference of the turntable  121 S and has upper and lower inclined surfaces thereof. A pin  164  is disposed under each of the chuck end portions  162 . A supporting shaft  163  is disposed at the bottom portion of each of the clamping members  161 . 
     Further, the circular hinge member  181  has a cylindrical portion  182  in the central portion thereof, and slidably engages the cylinder  123 . Three sets of holding portions  183  are formed along the edge of the hinge member  181  at an angular interval of 120°. Each of the holding portions  183  consists of two U-shaped bent pieces. The supporting shaft  163  of each of the clamping members  161  is rotatably held by the bent pieces of a corresponding one of the holding portions  183 . 
     Further, in another embodiment which is not shown, it is possible that the circular hinge member  181  and the clamping members  161  are composed as a unit member. 
     Furthermore, each of the clamping members  161  is disposed in such a way as to be able to be partially exposed from the corresponding opening  132  provided in the center boss  131 C. 
     Additionally, a compression coil spring  184  for obtaining the pressing forces of the clamping members  161  is placed between the center boss  131 C and the cylindrical portion  182  of the hinge member  181  in such a way as to be coaxial with the cylindrical portion  182 . 
     On the other hand, the plate spring member  191  is disposed under the turntable  121 S. Three L-shaped elastic pieces  192  are formed along the edge of this plate spring member  191  at an angular interval of 120°. Each of three J-shaped elastic pieces  193  is formed between corresponding two of the adjacent L-shaped elastic pieces  192 . 
     The plate spring member  191  is attached to the bottom side of the turntable  121 S by thermal fusion utilizing small holes  194  provided therein. Then, each of the L-shaped elastic pieces  192  penetrates through a corresponding one of the openings  122  provided in the turntable  121 S and is in opposed contact with the inner surface of a corresponding one of the clamping members  161 . Each of the J-shaped elastic pieces  193  penetrates through a corresponding one of the openings  125  provided in the turntable  121 S and is in opposed contact with the inner surface of the corresponding projection piece  133  of the center boss  131 C. Thus, an outward radial resilient force is imparted to each of the L-shaped elastic pieces  192  and the J-shaped elastic pieces  193 . 
     Incidentally, the chucking device  120 S is connected to a spindle motor (not shown) mounted on a chassis (not shown) to which the cylinder  123  is fitted, and is driven by the motor  1  to rotate. 
     (Chucking Mechanism of Embodiment) 
     Next, a chucking mechanism of this embodiment of the present invention will be described hereinbelow with reference to FIGS. 2A to  4 B. 
     With the aforementioned configuration, when a disk D is installed in the chucking device  120 S, each of the L-shaped elastic pieces  192  of the plate spring member  191  is in opposed contact with the inner surface of the corresponding clamping member  161 S, as illustrated in FIG. 2A, and is pushed clockwise (namely, in the direction of an arrow X shown in this figure). The pin  163  of each of the clamping members  161  abuts against the inner surface  135  of the side edge portion of the corresponding opening  132  of the center boss  131 C. The chuck end portion  162  of each of the clamping members  161  is partly exposed in the direction of the outer circumference of the turntable  121 S from the corresponding opening  132  of the center boss  131 C. 
     Furthermore, the hinge member  181  is downwardly pushed by the resilient force of the compression coil spring  184  and thus is in opposed contact with the largest-diameter top surface of the cylinder  123 . Each of the clamping members  161  having the supporting shaft  163  held by a corresponding one of the U-shaped holding portions  183  of the hinge member  181  is downwardly pressed by the pressing force of the spring  184 . The top surface of each of the clamping members  161  is placed under the top surface of the center boss  131 C. 
     Incidentally, in FIGS. 2A to  3 D, the supporting shafts  163  of the clamping members  161  are denoted by the mark “+” representing the center of rotation, and the pins  164  are designated by the mark “×” indicating that the pins  164  are rotatable, similarly as in FIGS. 8A to  9 C described previously. 
     As illustrated in FIG. 2B, when the disk D is installed in this device, the top surface  162 A of the chuck end portion  162  of each of the clamping members  161  is pushed by the inner edge of the disk D in the direction of the inner circumference of the turntable  121 S during the descent of the disk D. Each of the clamping members  161  is rotated counterclockwise (namely, in the direction of an arrow Y shown in FIG.  2 B). Thus, each of the pins  164  is detached from the inner surface  135  of the corresponding opening  132  of the center boss  131 C. Moreover, each of the L-shaped elastic pieces  192  of the plate spring member  191  is pushed anticlockwise (namely, in the direction of the arrow Y shown in FIG.  2 B). 
     In the state of the device illustrated in FIG. 2B, the hinge member  181  remains pushed downwardly by the resilient force of the compression coil spring  184  and is in opposed contact with the top surface of the largest-diameter portion of the cylinder  123 . 
     This state lasts until the disk D descends still more to a position where the inner edge of the top surface thereof surmounts the edge of the chuck end portion  62  of each of the clamping members  61 . 
     Then, in the state in which the disk D descends still more to a position where the disk D is put on the turntable  121 S as illustrated in FIG. 2C, the top surface of the inner edge of the disk D abuts against the bottom surface  162 B of the chuck end portion  162  of each of the clamping members  161 . 
     In the situation illustrated in FIG. 2C, the chucking device  120 S returns to nearly the same state as illustrated in FIG. 2A except the position of the disk D. 
     Namely, the pin  164  of each of the clamping members  161  is pushed clockwise (that is, in the direction of the arrow X) by the corresponding L-shaped elastic piece  192  of the plate spring member  191  and abuts against the inner surface  135  of the side edge portion of the corresponding opening  132  of the center boss  131 C. 
     Furthermore, the supporting shafts  163  of the clamping members  161  are pushed downwardly by the resilient force of the compression coil spring  184  through the U-shaped holding portions  183  of the hinge member  181 . The bottom surface  162 B of the chuck end portion  162  of each of the clamping members  161  abuts against the inner edge of the disk D from above. Thus, the disk D is pressed and clamped. In other words, the disk D is put between the turntable  121 S and each of the chuck end portions  162  of the clamping members  161 , and is thus chucked. 
     Therefore, in the case of the chucking device  120 S of this embodiment, the pressing forces exerted by the clamping members  161  at the time of installing a disk are stably ensured by setting the resilient force of the compression coil spring  184 . 
     Moreover, each of the supporting shafts  163  of the clamping members  161  is held by the corresponding U-shaped holding portions  183  of the hinge member  181  which can slide upwardly and downwardly along the cylinder  123  serving as a guide axis of sliding motion. Consequently, even when, for instance, a mechanical shock causes the disk D to move in the direction in which the chuck end portion  162  of each of the clamping members  161  engages therewith, the chuck end portion  162  thereof rises with the result that the pressing force against the disk D is constant. 
     Further, all of the clamping members  161  and the compression coil spring  184  are placed above the turntable  121 . Thus, the height of the entire device is reduced. Consequently, a slim device is realized. 
     Furthermore, the structures of the clamping members  161 , the hinge member  181  and the plate spring member  191  are relatively simple. Thus, the cost of components and the number of man-hours to fabricate the device are decreased. 
     Additionally, in the case of this embodiment, the distance from the supporting shaft  163  of each of the clamping members  161  to the center of the turntable  121 S is set as being nearly equal to the radius of the central hole of the disk D. Thus, the supporting shaft  163  of each of the clamping members  161  is placed just under the point of contact between the disk D and the chuck end portion  162  of the corresponding clamping member  161 . Consequently, the pressing forces of the clamping members  161  against the disk D are ensured. Moreover, the resilient forces of the Lshaped elastic pieces  192  of the plate spring member  191  are decreased. 
     Incidentally, as illustrated in FIG. 2C, the chuck end portion  162  of each of the clamping members  161  is exposed in the direction of the outer circumference of the turntable  121 S from the corresponding opening  132  of the center boss  131 C even when the disk D is chucked. 
     Further, the top portions of the clamping members  161  are placed under the top surface of the center boss  131 C. In FIGS. 4A and 4B, the disk is not shown, for ready understanding. 
     When the disk D is detached from the device in which the disk D is chucked as illustrated in FIGS. 2C and 3A, the bottom surface  162 B of the chuck end portion  162  of each of the clamping members  161  is upwardly pushed by the inner edge of the top surface of the disk D during the descent thereof. 
     Then, with the upward displacement of the clamping members  161 , the supporting shafts  163  thereof are displaced in the direction of the axis of the cylinder  123  while being respectively held in the holding portions  183  of the hinge member  181 . Moreover, the pins  164  of the clamping members  161  are upwardly displaced while sliding along the inner surfaces of the side edge portions of the openings of the center boss  131 C. 
     Incidentally, as a result of the fact that the holding portions  183  of the hinge member  181  are upwardly placed, the coil spring  184  is compressed still more. 
     Subsequently, the pins  164  of the clamping members  161  are detached from the inner surfaces  135  of the side edge portions of the openings of the center boss  131 C and come to slide on the inner slopes of the cams  134  of the center boss  132 , as illustrated in FIG.  3 C. Thus, the coil spring  184  is compressed still more, and each of the clamping members  161  rotates counterclockwise (namely, in the direction of the arrow Y). 
     The amount of rotation of each of the clamping members  161  reaches a maximum value when the disk D ascends still more and the inner edge of the top surface of the disk D surmounts the edges of the chuck end portions of the clamping members  161  as illustrated in FIG.  3 D. 
     In the state illustrated in FIGS. 3C and 3D, the top portions of the clamping members  161  are upwardly exposed from the openings  132  of the center boss  131 C as shown in FIG.  4 B. Incidentally, in FIG. 4B, the disk is not shown, for ready understanding. 
     When the disk D ascends still more from the position shown in FIG. 3D to a position where the bottom surface of the disk D abuts against the top surface  162 A of the chuck end portion  162  of each of the clamping members  161 , the engagement of the disk D with this chuck end portion  162  is canceled. 
     Then, as the hinge member  181  pushed by the resilient force of the compression coil spring  184  returns downwardly to the initial position, the clamping members  161  having the supporting shafts  163  respectively held in the holding portions  183  are downwardly displaced. Moreover, the pin  164  of each of the clamping members  161  is pressed clockwise by the corresponding L-shaped elastic piece  192  of the plate spring member  191  and thus abuts against the inner surface  135  of the corresponding opening of the center boss  131  again. Consequently, the device automatically returns to the state where no disk is installed as illustrated in FIG.  2 A. 
     As described above, according to the present invention, the pressing forces of the clamping members can be stably ensured. Moreover, the device can be reduced in thickness. 
     Furthermore, according to an embodiment of the present invention, the elastic force of the first elastic piece of the plate spring member can be decreased. 
     Although the preferred embodiment of the present invention has been described above, it should be understood that the present invention is not limited thereto and that other modifications will be apparent to those skilled in the art without departing from the spirit of the invention. 
     The scope of the present invention, therefore, should be determined solely by the appended claims.