Abstract:
A disc cassette comprises a case in which a recording disc is rotatably received. The case has an opening through which the disc is exposed. A bridge defined by the case extends across a mouth portion of the opening. A slide bar is arranged beside the bridge in a manner to move axially therealong. A shutter is connected to the slide bar to move therewith. The shutter selectively opens and closes the opening in accordance with axial movement of the slide bar. The slide bar has a base portion which comes beside the bridge when the shutter takes the open position, and the base portion is formed with a recess which faces in a direction away from the center of the disc recording medium.

Description:
This is a continuation of application Ser. No. 08/375,680 filed Jan. 20, 1995 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to disc cassettes for use in a photo-electromagnetic disc player, and more particularly to the disc cassettes of a type having a shutter. 
     2. Description of the Related Art 
     In order to clarify the object of the present invention, one conventional disc cassette DC of the above-mentioned type will be described with reference to FIGS. 9A and 9B of the drawings which figures show front and back perspective views of the disc cassette DC, respectively. 
     The disc cassette DC shown in the drawings is of a type which writes and read information onto and from a photo-electromagnetic disc using so-called “magnetic modulation overwrite method”. The disc cassette DC comprises a rectangular case  1  in which a photo-electromagnetic disc  2  is rotatably installed. To a center portion of the disc  2 , there is fixed a hub  2   a  which, upon need of playing the disc  2 , is held by a chucking member of a disc player (not shown). The case  1  comprises an upper half part  1   a  and a lower half part  1   b  which are coupled to have a thin space defined therebetween. As is seen from FIG. 9B which shows a back view of the disc cassette DC, the lower half part  1   b  is formed at its side rear portions with respective positioning openings  3 . Upon insertion of the disc cassette DC into the disc player, positioning pins of the disc player are brought into engagement with the positioning openings  3 , thereby to position the disc cassette DC relative to the disc player. The lower half part  1   b  of the case  1  has near one of the positioning openings  3  a slot in which a miss-write protection pawl  4  is slidably received. When the pawl  4  is moved to one given position, the disc  2  is prevented from recording or writing information thereon. The case  2  is formed at its side front portions with cassette pulling grooves  5 . That is, when the disc cassette DC is inserted into a certain position of the disc player, cassette pulling pins of the player become engaged with the grooves  5  and pull the disc cassette DC to a certain bottom position of the disc player. 
     As is seen from FIGS. 9A and 9B, the upper and lower half parts  1   a  and  1   b  of the case  1  are respectively formed with rectangular openings  6   a  and  6   b  through which upper and lower surfaces of the disc  2  are partially exposed. The lower opening  6   b  is larger than the upper opening  6   a  and is so sized as to expose the hub of the disc  2 . 
     Each opening  6   a  or  6   b  has a bridge  1   e  defined by the case  1 , which extends across a mouth portion of the opening, as shown. 
     A slide bar  8  is mounted on a front edge  1 C of the case  1  in a manner to slide in the direction of the arrow “A”. Connected to the slide bar  8  is a shutter  7  which comprises upper and lower shutter plates  7   a  and  7   b.  Thus, in response to the sliding movement of the slide bar  8 , the upper and lower openings  6   a  and  6   b  are selectively closed and opened by the upper and lower shutter plates  7   a  and  7   b.  Although not shown in the drawings, a torsion spring is installed in the case  1  to bias the shutter  7  in the direction to close the openings  6   a  and  6   b.  FIGS. 9A and 9B show a condition wherein the shutter  7  assumes its full open position. The slide bar  8  has a thickness somewhat smaller than that of the disc  2  in the case  1 . 
     FIG. 10 shows a condition wherein the disc cassette DC is properly set in the disc player. Under this condition, the shutter  7  of the disc cassette DC assumes its full open position and the hub  2   a  of the disc  2  is tightly held by the chucking member (not shown) of the disc player. Upon energization of a spindle motor (not shown) by which the chucking member is driven, the disc  2  is rotated about its axis. Within the disc player, there are installed a magnetic head  28  and an optical head  29  which are arranged to put therebetween the disc  2 . These heads  28  and  29  face the upper and lower openings  6   a  and  6   b  of the case  1 , respectively, and are mounted on a same head carriage  24  which is linearly movable in the direction of the arrow “B” in FIG. 10, that is, in the radial direction of the disc  2 . The head carriage  24  moves between an outermost position as shown by a phantom line and an innermost position as shown by a solid line. Due to movement of the carriage  24 , the two heads  28  and  29  are slid radially along the upper and lower openings  6   a  and  6   b  while making an interaction therebetween to write or read information on or from the disc  2 . 
     Usually, the disc players used as a supplemental memory device of a computer are restricted by size. As is seen from FIG. 10, assuming that the length of the disc player is “L” and a part “L 0 ” of the length “L” represents the length of a space for containing other mechanisms, the head carriage  24  has to be arranged within a limited zone having the length “L 1 ”. The length of an arm  27  through which the head  28  is connected to the head carriage  24  is so determined that when the head carriage  24  is located at the outermost position as shown by the phantom line, the head  28  is located at the outermost recording position of the disc  2 . Thus, the innermost position of the head  28  is automatically determined when the head carriage  24  comes into abutment with the slide bar  8  of the disc cassette DC. However, in this case, it sometimes. occurs that the innermost recording area (i.e., the area having the width “E”) of the disc  2  cannot be practically used, due to the limited movement of the heads  28  and  29  in the inward direction. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a disc cassette which can provide the head carriage of the disc player with a more satisfactory moving area, thereby permitting effective usage of the recording area of the disc. 
     According to a first aspect of the present invention, there is provided a disc cassette which comprises a case in which a disc recording medium is rotatably received, the case having an opening through which at least an information recording area of the medium is exposed; a bridge defined by the case, the bridge extending across a mouth portion of the opening; a slide bar arranged beside the bridge in a manner to move axially therealong; and a shutter connected to the slide bar to move therewith, the shutter selectively opening and closing the opening in accordance with axial movement of the slide bar, wherein the slide bar has a base portion which comes beside the bridge when the shutter takes the open position, the base portion being formed with a recess which faces in a direction away from the center of the disc recording medium. 
     According to a second aspect of the present invention, there is provided a disc cassette which comprises a case in which a disc recording medium is rotatably received, the case having an opening through which at least an information recording area of the medium is exposed; a bridge defined by the case, the bridge extending across a mouth portion of the opening; a slide bar arranged beside the bridge in a manner to move axially therealong; and a shutter connected to the slide bar to move therewith, the shutter selectively opening and closing the opening in accordance with axial movement of the slide bar, wherein the slide bar comprises a base portion which comes beside the bridge when the shutter takes the open position and a projection which is to be pressed by a shutter opening pin of a disc player, the projection protruding outward from the base portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which: 
     FIG. 1A is a front perspective view of a disc cassette of a first embodiment of the present invention; 
     FIG. 1B is a back perspective view of the disc cassette of the first embodiment; 
     FIG. 2 is an exploded view of a disc player with which the disc cassette of the first embodiment is incorporated; 
     FIG. 3 is a partially cut perspective view of the disc player, showing a condition wherein the disc cassette of the first embodiment is properly set therein; 
     FIG. 4 is a sectional view of the disc player, depicting an advantage obtained when using the disc cassette of the first embodiment; 
     FIG. 5 is an exploded view of a disc cassette of a second embodiment of the present invention; 
     FIG. 6A is a front perspective view of the disc cassette of the second embodiment; 
     FIG. 6B is a view similar to FIG. 6A, but showing a condition wherein the disc cassette is reoriented and a shutter of the disc cassette is opened; 
     FIG. 7A is a plan view of a disc cassette of the second embodiment of the present invention; 
     FIG. 7B is a bottom view of the disc cassette of the second embodiment; 
     FIG. 8A is a side view of the disc cassette of the second embodiment; 
     FIG. 8B is a view similar to FIG. 8A, but showing a different condition of the disc cassette; 
     FIG. 9A is a view similar to FIG. 1A, but showing a conventional disc cassette; 
     FIG. 9B is a view similar to FIG. 1B, but showing the conventional disc cassette; and 
     FIG. 10 is a view similar to FIG. 4, but showing a disadvantage obtained when using the conventional disc cassette. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1A and 1B, there is shown a disc cassette of a first embodiment of the present invention, which is generally designated by numeral  100 . 
     Since the disc cassette  100  of this first embodiment is similar in construction to that of the above-mentioned conventional disc cassette DC of FIGS. 9A and 9B, only parts and construction which are different from those of the conventional disc cassette DC will be described in detail in the following for facilitation of the description the same parts and construction are designated by the same numerals. 
     In this first embodiment  100 , a recess  8   e  is formed at a front surface of the slide bar  8 , which permits the head carriage of the disc player to have an increased inward moving zone. As will become apparent as the description proceeds, the recess  8   e  is so constructed as to receive a front face of the head carriage of the disc player when the head carriage comes to its innermost position. 
     In FIGS. 2 and 3, there is shown a disc player by which the disc cassette  100  is operatively played. In these figures, particularly apparent in FIG. 2 there is denoted by numeral  10  a chassis on which a slide plate  11  is mounted to slide in the directions of the arrows X and X′. For this slide movement, the slide plate  11  is formed with two pairs of slots (no numerals) with which respective guide pins  12  fixed to the chassis  10  are slidably engaged. To the slide plate  11 , there is connected one end of a coil spring  13 , so that the slide plate  11  is biased toward a loading position, that is, in the direction of the arrow X′. It is to be noted that in FIG. 2, the slide plate  11  assumes the loading position, while, in FIG. 3, the slide plate  11  assumes an unloading position. 
     Designated by reference A is an auto-eject mechanism A which comprises an electric motor  14  mounted on the chassis  10 . The motor  14  drives an output gear  15  which is provided with an engaging pin  15   a.  When, upon energization of the motor  14 , the engaging pin  15   a  abuts against a lug  16  raised from the slide plate  11  and presses the same, the slide plate  11  is shifted from the loading position to the unloading position against the force of the coil spring  13 . 
     Designated by reference B is a disc rotating mechanism which comprises a motor carrying unit  17  which is vertically movably mounted on the chassis  10 . The motor carry unit  17  takes its lower position due to the force of coil springs  18  when the slide plate  11  is in the unloading position. In contrast, when the slide plate  11  is brought to the loading position, the motor carrying unit  17  is raised by sloped lugs  19  of the slide plate  11  thereby to take its upper position. The motor carrying unit  17  carries a spindle motor whose output shaft is provided with a chucking member  20 . When the motor carrying unit  17  is lifted to the upper position, the chucking member  20  holds the hub  2   a  of the disc cassette  100  which has been kept in the disc player. Thus, when, under this condition, the spindle motor is energized, the disc  2  is turned. 
     Designated by reference C is a cassette positioning mechanism which comprises a pin holding block  21  which is vertically movably mounted on the chassis  10 . The pin holding block  21  takes its lower position when the slide plate  11  is in the unloading position. In contrast, when the slide plate  11  is brought to the loading position, the pin holding block  21  is raised by sloped lugs  22  of the slide plate  11  to thereby take its upper position. The pin holding block  21  is provided at both ends with respective positioning pins  23 . When the pin holding block  21  is lifted to the upper position, the positioning pins  23  become engaged with the positioning openings  3  of the disc cassette  100  which has been kept in the disc player. With this, the positioning of the disc cassette  100  in the player is accomplished. 
     Designated by reference D is a head mechanism which comprises a head carriage  24  which is arranged on the chassis  10  to move in the directions of the arrows X and X′. For the movement of the head carriage  24 , a pair of guide rails  25  are mounted on the chassis  10 , along and on which the head carriage  24  slides. A pair of linear motors  26  are arranged beside the guide rails  25 . That is, when the linear motors  26  are energized, the head carriage  24  is moved in the direction of the arrow X or X′ along the guide rails  25 . The head carriage  24  carries an arm  27  of which leading end is equipped with a magnetic head  28 . At a lower position of the magnetic head  28 , there is arranged an optical head  29  which is also carried by the head carriage  24 . In practice, the optical head  29  is an objective lens, and a laser beam source (not shown) is mounted on a position of the chassis  10 . When the disc cassette  100  is properly set in the disc player, the disc  2  is placed between the magnetic and optical heads  28  and  29 . As is known in the art, due to the interaction between the two heads  28  and  29 , writing or reading of information onto or from the photo-electromagnetic disc  2  is achieved. 
     Designated by numeral  30  is a cassette holder which is arranged above the chassis  10 . The cassette holder  30  is in the form of a rectangular frame and comprises an upper wall  30   a,  a lower wall  30   b  and two narrow side walls  30   c,  which are united to have the holder sized to receive therein the disc cassette  100 . The lower wall  30   b  is formed with a large cut (not shown) into which the motor carrying unit  17  and the optical head  29  are to be received when the disc cassette  100  is properly set in the disc player. The upper wall  30   a  is formed with a cassette stopper  32  against which a leading edge of the disc cassette  100  abuts when the cassette  100  is properly set in the cassette holder  30 . 
     As will be described in detail in the following, the cassette holder  30  is equipped with a shutter opening/closing mechanism E, an auto-eject mechanism F and a slide plate locking mechanism G. 
     As is seen from FIG. 2, the shutter opening/closing mechanism E comprises a curved cam slot  33  formed in the upper wall  30   a  of the cassette holder  30 , a shutter opening pin  34  slidably engaged with the cam slot  33 , and a torsion coil spring  35  having one end fixed to the pin  34  and the other end fixed to the upper wall  30   a.  Due to the force of the torsion coil spring  35 , the shutter opening pin  34  is biased to take one end position of the slot  33 , that is, the position as shown in FIG.  2 . 
     The auto-eject mechanism F comprises a first eject plate  36  which is arranged beneath a lower surface of the lower wall  30   b  of the cassette holder  30 . The first eject plate  36  is movable in the directions of the arrows X and X′ of FIG. 2 while being guided by guide pins  37  fixed to the lower wall  30   b.  That is, the guide pins  37  are slidably engaged with respective slots (no numerals) formed in the first eject plate  36 . A pivot shaft  38  is fixed to one end of the first eject plate  36  for rotatably holding a second eject plate  39 . The second eject plate  39  is formed with a curved cam slot  40  which is slidably engaged with one of the above-mentioned guide pins  37 . The second eject plate  39  is provided with a cassette drawing pin  41 , so that when the second eject plate  39  turns about the pivot shaft  38 , the pin  41  moves in the directions of the arrows Y and Y′. 
     Designated by numeral  42  is a third eject plate which is rotatable in the directions of the arrows Z and Z′ about a pivot shaft  43  fixed to the lower wall  30   b  of the cassette holder  30 . One end of the third eject plate  42  is engaged with an end of the first eject plate  36 . The third eject plate  42  is provided at the other end thereof with a hold pin  44  which is detachably engageable with a raised lug  45  of the slide plate  11 . Due to the force of a coil spring  46  arranged between the third eject plate  42  and a part of the lower wall  30   b,  the third eject plate  42  is biased to pivot about the pivot shaft  43  in the direction of the arrow Z. 
     The slide plate locking mechanism G comprises a latch plate  47  which is rotatably connected through a pivot shaft  48  to the chassis  10 . Thus, the latch plate  47  is rotatable about the pivot shaft  48  in the directions of the arrows H and H′. Due to the force of a torsion coil spring  49 , the latch plate  47  is biased to pivot in the direction of the arrow H and detachably engageable with a latch pin  50  fixed to the slide plate  11 . The latch plate  47  is formed with a release lever  51 . 
     In the following, operation of the disc player having the above-mentioned construction will be described with reference to FIG.  2 . 
     For ease of understanding, the description will be commenced with respect to a rest condition of the disc player. Under this rest condition, the slide plate  11  is latched relative to the chassis  10 . That is, the slide plate  11  assumes the unloading position having the latch pin  50  latched by the latch plate  47  and having the raised lug  45  pressed against the hold pin  44  of the third eject plate  42  in the direction of the arrow X, causing the cassette drawing pin  41  to assume a stand-by position, as shown in FIG.  2 . Furthermore, under this rest condition, the motor carrying unit  17  and the pin holding block  21  assume their lower positions. 
     When the disc cassette  100  is inserted into the cassette holder  30 , the disc cassette  100  pushes at its front end the shutter opening pin  34 . Thus, with insertion of the disc cassette  100  into the cassette holder  30 , the pin  34  is slid in and along the cam slot  33  toward a rear end thereof against the force the torsion coil spring  35 . During this movement of the shutter opening pin  34 , the pin  34  is slid on and along the front edge of the disc cassette  100  while pushing the slide bar  8  of the shutter  7 , thus opening shutter  7 . 
     When the disc cassette  100  is further inserted into the cassette holder  30 , the disc cassette  100  pushes the release lever  51 . Following this, the latch plate  47  is turned in the direction of the arrow H′, releasing the latch pin  50 , thereby cancelling the latched condition of the slide plate  11  to the chassis  10 . Thus, due to the force of the coil spring  13 , the slide plate  11  is moved in the direction of the arrow X to the loading position. During this movement of the slide plate  11 , the raised lug  45  is moved away from the hold pin  44 , and thus the third eject plate  42  is turned in the direction of the arrow Z due to the force of the coil spring  46 . With this, the first eject plate  36  is slid in the.direction of the arrow X′ and at the same time the second eject plate  39  is turned in the direction of the arrow Y. With this turning of the second eject plate  39 , the cassette drawing pin  41  is put into the cassette pulling groove  5 . Thus, thereafter, the disc cassette  100  is automatically drawn into a deeper position in the cassette holder  30  with the movement of the first eject plate  36  in the direction of the arrow X′. The inward movement of the disc cassette  100  continues until the disc cassette  100  abuts the cassette stopper  32  of the cassette holder  30 . Under this condition, the disc cassette  100  is fully received in the cassette holder  30  and the shutter  7  of the disc cassette  100  is fully opened. 
     When the slide plate  11  is shifted from the unloading position to the loading position in the above-mentioned manner, the motor carrying unit  17  and the pin holding block  21  are lifted from the lower positions to the upper positions by the sloped lugs  19  and  22 . Thus, the chucking member  20  of the motor carrying unit  17  holds the hub  2   a  of the disc  2  in the disc cassette  100 , permitting the disc  2  to rotate upon energization of the spindle motor. Furthermore, the positioning pins  23  of the pin holding block  21  are put into the positioning openings  3  (see FIG. 1B) of the disc cassette  100 , so that the disc cassette  100  is positioned relative to the disc player. When, under rotation of the disc  2 , the linear motors  26  are energized, the head carriage  24  is moved in the directions of the arrows X and X′, thereby moving the magnetic and optical heads  28  and  29  in the radial direction of the disc  2 . During the movement of the two heads  28  and  29 , writing or reading of information onto or from the disc  2  is carried out. 
     As has been described hereinabove, under rotation of the photo-electromagnetic disc  2 , the head carriage  24  moves on and along the paired guide rails  25  in the directions of the arrows X and X′ of FIG.  2  and thus the two heads  28  and  29  move in the radial direction over the photo-electromagnetic disc  2 . Writing or reading of information onto or from the disc  2  is carried out by the heads  28  and  29  in a so-called “Magnetic Field Modulation Overwrite Process”. 
     As is seen from FIG. 4, the head carriage  24  defines, at a portion from which the arm  27  extends toward the head  28 , a front face  24   b  which faces a front end of the disc cassette  100  which is properly set in the disc player. That is, the radially moved distance of the two heads  28  and  29  relative to the disc  2  depends on the distance defined between the front face  24   b  of the head carriage  24  and the front end of the disc cassette  100 . If, for increasing the distance, the length of the arm  27  is increased, the head carriage  24  and the arm  27  are projected significantly rearward when the head carriage  24  comes to its outermost position. This creates a need of providing the disc player with a space for containing such projected members, and thus the disc player becomes bulky in construction. 
     In the following, an advantage obtained by the first embodiment  100  will be described with reference to the drawings, particularly FIGS. 2 and 4. 
     That is, in accordance with the present invention, such a disadvantage is solved by the recess  8   e  of the slide bar  8  of the disc cassette  100 . The reason will become apparent from the following. 
     As is seen from FIG. 4, assuming that the length of the disc player is “L” and a part “L 0 ” of the length “L” represents the length of a space (or dead space) for containing the other mechanisms, the head carriage  24  has to be arranged within a limited zone having the length “L 1 ”. The length “S” of the arm  27  is so determined that when the head carriage  24  is located at the outermost position as shown by the phantom line, the head  28  is located at the outermost recording position of the disc  2  in the disc cassette  100 . 
     At the outermost position of the head carriage  24 , a rear face  24   a  of the head carriage  24  is located at the front end of the dead space having the length “L 0 ”; at the innermost position of the head carriage  24 , the front face  24   b  is in contact with the slide bar  8  of the disc cassette  100 . However, in the present invention, the recess  8   e  formed in the slide bar  8  can receive the front face  24   b  of the head carriage  24 , thereby increasing the stroke “L 2 ” of the head  28  in the inward direction. That is, when the disc cassette  100  of the invention is used, the magnetic head  28  and the optical head  29  can be moved to a more inward position of the disc  2  than that of the above-mentioned conventional disc cassette DC. Thus, in the invention, the recording area of the disc  2  can be fully used. 
     Referring to FIGS. 5,  6 A,  6 B,  7 A,  7 B,  8 A and  8 B, there is shown a disc cassette of a second embodiment of the present invention, which is generally designated by numeral  200 . 
     In the following description, parts and construction substantially the same as those of the first embodiment  100  are designated by the same numerals and detailed explanation of such will be omitted. 
     In the second embodiment of the invention, as is seen from FIG. 5, the slide bar  8  of the disc cassette  200  comprises a bar proper  8   d  and an enlarged head portion  8   b.  The head portion  8   b  has a projection which is projected in the direction away from the case  1 . That is, as is seen from FIGS. 7A and 7B, the projection of the head portion  8   b  protrudes from the bar proper  8   d  in the direction of the arrow X of the drawings. 
     That is, in this second embodiment  200 , the gap located on the front surface of the bar proper  8   d  and between the projected head portion  8   b  and where the shutter  7  is connected to the side bar  8  corresponds to the recess  8   e  of the first embodiment  100 , which functions to receive the front face  24   b  (see FIG. 4) of the head carriage  24  when the head carriage  24  is moved to the innermost position. 
     Referring back to FIG. 5, to the bar proper  8   d,  there is fixed the shutter  7  which comprises the upper and lower shutter plates  7   a  and  7   b.  The slide bar  8  is slidably put in a grooved construction of the front edge of the case  1 , so that in response to the sliding movement of the slide bar  8 , the upper and lower shutter plates  7   a  and  7   b  selectively close and open their corresponding upper and lower openings  6   a  and  6   b.  Between the slide bar  8  and the lower half part  1   b  of the case  1 , there is disposed a torsion coil spring  60  by which the shutter  7  is biased in the direction to close the openings  6   a  and  6   b.  In the illustrated embodiment  200 , the lower opening  6   b  for receiving the optical head  29  and a circular opening  6   c  for receiving the chucking member  20  are independently formed in the lower half part  1   b  of the case  1 . 
     As is seen from FIGS. 6A and 6B, the case  1  is formed at its front side portion with a projection  1   d  of which inside wall faces an opposed face  8   c  of the head portion  8   b  of the slide bar  8 . Designated by numeral  9  is a pin holding recess into which the shutter opening pin  34  of the disc player drops when the disc cassette  200  is fully received in the cassette holder  30 . 
     When, as will be understood from FIG. 6A, the disc cassette  200  is inserted into the cassette holder  30  of the disc player, the shutter opening pin  34  of the player is led into a space defined between the projection  1   d  of the disc cassette  200  and the head portion  8   b  of the same. With insertion of the disc cassette  200  into the cassette holder  30 , the pin  34  is slid on and along the front edge of the disc cassette  200  while pushing the head portion  8   b  of the slide bar  8 . Thus, against the force of the torsion coil spring  60 , the slide bar  8  is moved in the direction of the arrow Y in FIGS. 7A,  8 A and  8 B. When the disc cassette  200  is fully inserted into the cassette holder  30 , the shutter  7  fixed to the slide bar  8  fully opens the upper and lower openings  6   a  and  6   b  of the disc cassette  200 . 
     Because the head portion  8   b  and the bar proper  8   d  constitute a gap which corresponds to the recess  8   e  of the first embodiment  100 , the recording area of the disc  2  can be fully utilized similar to of the first embodiment  100 . When the size of the head portion  8   b  is increased, the sliding engagement between the head portion  8   b  and the shutter opening pin  34  during the shutter opening process is much improved. 
     Although the above description is directed to a disc cassette which contains a photo-electromagnetic disc, the prevent invention is not limited to such disc cassette. That is, the present invention is applicable to various types of disc cassettes. 
     Although in the above-mentioned embodiments  100  and  200 , the slide bar  8  and the shutter  7  are depicted separate members, they may be constructed as an integrated member.