Patent Publication Number: US-6212038-B1

Title: Shutter mechanism for disk cartridge

Description:
This application is a divisional of application Ser. No. 08/958,900, filed Oct. 28, 1997, now U.S. Pat. No. 6,157,517, which application(s) are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a disk cartridge in which a disk-shaped recording medium such as an optical disk or a magnetic disk is housed rotatably relative thereto, and particularly relates to a shutter mechanism of the disk cartridge of a type in which a shutter thereof is slidable in both right and left directions from a neutral position at which a head access opening of the disk cartridge is closed by the shutter. 
     2. Description of the Related Arts 
     A cartridge case of a conventional disk cartridge, housing a disk-shaped recording medium such as a compact disk or the like therein, has a head access opening for access of a head. The head access opening is openable and closable by a shutter which is slidably mounted on a surface of the cartridge case. When the disk cartridge is loaded inside a disk drive system, the shutter of the disk cartridge is slid by a shutter drive pin of the disk drive system. This allows the shutter to open the head access opening so that the reading and/or writing relative to the disk-shaped recording medium is performed. 
     Meanwhile, there has been conventionally provided a disk cartridge which accommodates a disk-shaped recording medium that is readable and writable on both sides thereof, and which is possible to be set inside a disk drive system whichever either side thereof comes on top. In order to avoid any complication of the shutter drive mechanism on a side of the disk drive system, the shutter of the disk cartridge is so constructed as to be slidable in both right and left directions from a neutral position at which the head access opening is closed by the shutter, while the shutter drive pin of the disk drive system is so constructed as to be driven in one direction. 
     As this type of shutter mechanism, for example, Japanese Laid-Open Patent Publication No. 5-6758 discloses a disk cartridge with a shutter mechanism with the following construction. 
     That is, the disk cartridge has: 
     a shutter which is slidable relative to the cartridge case in which the shutter has a first slider able to be guided by a sliding groove, as guide means, that is formed on the cartridge case; 
     a stopper installed at a middle position relative to the cartridge case; 
     a pair of second sliders which are slidable on both sides of the stopper; and 
     a pair of torsion coil springs, as biasing means, which are mounted on both sides of the stopper and which bias the sliders inward to each other, 
     wherein the shutter has a pair of claws which are formed bent inward from a operational opening so that each claw contacts an inner surface of each second slider when both the second sliders contact the stopper. 
     With the mechanism, when the shutter is not driven by a disk drive system, the shutter remains at its neutral position with the shutter being biased to each other by the pair of torsion coil springs. On the other hand, when the shutter is slid, for example, in the right direction from the neutral position, the shutter is moved together with the right second slider in the right direction while the right torsion coil spring is being deformed or charged, whereas the left second slider remains stationary with the left second slider contacting the stopper. If the shutter is slid in the left direction, the operation is reversed. 
     According to the mechanism, the first slider of the shutter has only the function to guide the shutter relative to the cartridge case, but does not have the function to be biased or urged by the torsion coil spring as biasing means. 
     Meanwhile, as another shutter mechanism, there has been proposed a shutter mechanism (see Japanese Patent Publication No. 2508449 as a reference) with a pair of sliders which are able to slide on a metallic guide shaft. The guide shaft is arranged along a direction in which the shutter is slidable, and the pair of sliders are connected to each other with a tension coil spring. The shutter mechanism also has a stopper, formed centrally on the cartridge case, which contacts the pair of sliders from inside in which the stopper has a length that is greater than a free length of the tension coil spring. In the mechanism, the shutter has a pair of projecting parts that contact the two sliders from inside, respectively. 
     According to the mechanism, the shutter is normally held at the neutral position where the head access opening is closed by the shutter thus biased; on the other hand, the shutter is moved together with one of the sliders at time of sliding the shutter while the other of the sliders remains stationary. 
     Namely, the shutter mechanism according to the former prior art requires two torsion coil springs; and the shutter mechanism according to the latter related art requires a separate guide shaft, as components, respectively. In other words, the above shutter mechanisms require not a few assembling parts, thus leading to a high cost of production. In addition, shutter mechanism of the latter related art has another problem in which the shutter mechanism has to be assembled in such a way that the slider and shutter need to be first mounted on the separate guide shaft to form a subassembly and then the subassembly needs to be built on the cartridge case. That is, the assembling thereof is hard to perform. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide a disk cartridge, a shutter mechanism of which is constituted with a smaller number of assembling parts for easier assemblage and for prevention of high cost of production, the shutter being slidable relative to a cartridge case thereof from right to left with a neutral position at which the shutter closes a head access opening of the cartridge case. 
     In accomplishing this and other objects of the present invention, there is provided a disk cartridge comprising: a cartridge case which has an upper half-shell with an upper wall and a lower half-shell with a lower wall in which the cartridge case has a head access opening; a disk-shaped recording medium which is rotatably housed inside the cartridge case; a shutter which is slidable relative to the cartridge case in a sliding direction from right to left relative thereto with a neutral position therebetween corresponding to a position at which the shutter closes the head access opening; guide means which is provided on the cartridge case in the sliding direction; a first slider which is fixed to the shutter and which is guided by the guide means; and biasing means which exerts a biasing force upon the first slider so as to return the shutter to the neutral position when the shutter is moved to one of the right and left from the neutral position. 
     For example, in case of constructing the biasing means so that the biasing means is constituted by a pair of springs on both sides of the shutter so as to bias the shutter towards the neutral position, and in case of constructing the first slider so that the first slider is constituted by a single slider that is fixed to the shutter and that is guided by the guide means, a shutter mechanism being constituted with a smaller number of assembling parts for easier assemblage and for prevention of high cost of production is surely realized, in contrast with a former prior art (Japanese Laid-Open Patent No. 5-6758) in which a pair of coiled springs and a pair of sliders are used. That is, according to the mechanism, there is no need of two sliders. 
     Meanwhile, for example, in case of constructing the first slider so that the first slider is constituted by a single projection fixed to the shutter and in case of constructing the guide means so that the guide means is constituted by a groove that is defined between the upper half-shell and the lower half-shell and that is engaged with the single projection, a shutter mechanism being constituted with a smaller number of assembling parts for easier assemblage and for prevention of high cost of production is surely realized, in contrast with a latter prior art (Japanese Patent Publication No. 2508449) in which a guide rod made of metal is used. That is, according to the mechanism, there is no need of such a rod made of metal. 
     In the mechanism, the biasing means can further comprise: a pair of second sliders which are guided by the guide means, wherein one of the second sliders is arranged on one of a pair of sides of the first slider, and wherein the other of the second sliders is arranged on the other thereof of the first slider; spring means which attracts the pair of second sliders to each other; and a stopper, provided on the cartridge case, which has a pair of ends, wherein one of the ends is able to abut an inner surface of one of the second sliders, and wherein the other of the ends is able to abut an inner surface of the other of the second sliders from inside. 
     In the mechanism, the pair of second sliders and the stopper may be preferably so constructed that a position at which both the sliders contact the stopper corresponds to the neutral position of the shutter relative to the cartridge case. 
     In the mechanism, the guide means can comprise a first guide groove which a part of the upper wall and a part of the lower wall cooperate to form therebetween, wherein the first slider can comprise a projecting part which is slidable inside the first guide groove, wherein the second slider slidably engages the first guide groove, and wherein the shutter can comprise an upper shutter plate and a lower shutter plate, in which the upper shutter plate and the lower shutter plate are divided at a location where the upper shutter plate and the lower shutter plate are connected to each other, and in which the upper shutter plate and the lower shutter plate are integrated to each other after the upper shutter plate and the lower shutter plate are mounted on the cartridge case. 
     According to the mechanism, for example, when one of the second sliders contacts the projecting part of the first slider so as to bias the shutter towards the neutral position, and when both the second sliders contact the stopper, the projecting part thereof is positioned between the pair of second sliders so that the shutter closes the head access opening of the cartridge case. On the other hand, when the shutter is moved in either direction of the right or left from the neutral position relative to the cartridge case, the projecting part pushes one of the pair of second sliders in the corresponding direction, while the other of the pair of second sliders remains stationary with the other thereof being held by the stopper. Because the spring means attracts both the second sliders to each other, the shutter is returned to the neutral position relative to the cartridge case at time of releasing any force to keep the shutter at a position that does not correspond to the neutral position relative thereto. 
     Also, according to the mechanism, the first guide groove is formed inside the cartridge case instead of mounting a guide rod thereon, and single spring means such as a spring coil which attracts the two second sliders to each other is used instead of mounting a pair of separate spring coils at different locations inside the cartridge case which bias a pair of different sliders to each other from outside respectively. Therefore, it is possible to reduce the number of parts constituting a disk cartridge of a type in which the shutter thereof can be slid laterally from the neutral position relative to the cartridge case, thus realizing a low cost of production. 
     Also, according to the mechanism, because there is no need of constructing the shutter mechanism as a subassembly before the shutter mechanism is assembled relative to a body of the cartridge case; in other words, because the disk cartridge is easily accomplished first by simply mounting each part thereof on the body of the cartridge case and then by fixing the upper shutter plate and the lower shutter plate to each other, it is possible to carry out the work to assemble the disk cartridge relatively easily. 
     In the mechanism, the projecting part of the first slider may comprise a first projecting part and a second projecting part that is separate from the first projecting part, in which the first projecting part is formed on one of a pair of sides of the shutter in the sliding direction, and in which the second projecting part is formed on the other of the pair of sides of the shutter in the sliding direction. 
     In the mechanism, it is preferable that one of is the upper wall and the lower wall comprises a projecting portion on an inner side thereof in which the projecting portion is formed in parallel with the first guide groove, and wherein the second slider comprises a sliding surface which is slidable relative to the projecting portion. 
     With the mechanism, the sliding movement of the second slider with respect to the one of the upper wall and the lower wall of the cartridge case is stabilized. Also, because it is possible to assemble the disk cartridge with the sliding surface of the second slider contacting the projection portion, the efficiency to assemble the disk cartridge is enhanced. 
     In the mechanism, it is preferable that the second slider comprises a wedge-like projection which projects in a direction in which the second slider contacts the stopper, while the stopper comprises a cutout portion with which the wedge-like projection of the second slider engages, wherein the wedge-like projection and the cutout portion comprise complementary frictional surfaces which contact with each other, and wherein the complementary frictional surfaces contact each other with the complementary frictional surfaces being pressed with each other when the second slider contacts the stopper under a biasing force exerted by the spring means. 
     According to the mechanism, the complementary frictional surfaces, of the second sliders and the stopper, contact to each other with the complementary frictional surfaces thereof being pressed to each other, when the pair of second sliders are assembled to one of the upper half-shell and the lower half-shell at time of assembling and when the spring means are installed between the pair of second sliders. Therefore, the second sliders are stably assembled relative to the stopper, and dislocation or disengagement of the second sliders from the stopper is effectively prevented. That is, the construction devotes itself to the enhancement of assembling work. 
     In the mechanism, it is preferable that the second slider further comprises a wedge-like groove which is formed tapering between a body of the second slider and the wedge-like projection, in which a surface that forms the wedge-like groove is formed generally in the sliding direction and is formed so as to be tapered in a direction opposite the stopper, while the stopper comprises a wedge-like part which is complementary with the wedge-like groove, and wherein the surface of the wedge-like groove and a surface of the wedge-like part contact each other when the second slider contacts the stopper under the biasing force exerted by the spring means. 
     According to the mechanism, because the second slider is held by the stopper at time of assembling so that not only the complementary frictional surfaces of the second slider and of the stopper contact to each other but also the surface of the wedge-like groove and the surface of the wedge-like part contact each other when the second slider contacts the stopper under the biasing force exerted by the spring means, the stability for assembling the second slider relative to the stopper is more enhanced. 
     In the mechanism, it is preferable that the part of the lower wall comprises a plank-like wall which has a projecting part that projects inside and which has a second guide groove on a side opposite a side on which the plank-like wall projects, in which the second guide groove exists in the sliding direction, wherein the second slider has a groove inside which the projecting part of the plank-like wall is slidably mounted, and wherein the second slider has a claw which projects inside the groove thereof and which slidably engages the second guide groove of the plank-like wall. 
     According to the mechanism, because the second slider is mounted on the lower wall, with the projecting part of the lower wall being embraced inside the groove of the second slider in which the claw of the second slider slidably engaging the second guide groove of the plank-like wall of the lower wall, the second slider is prevented from disengaging or being dislocated from the projecting part of the lower wall. 
     In the mechanism, it is preferable that one of the upper wall and the lower wall comprises a second guide groove which exists in parallel with the first guide groove and which exists opposite the first guide groove relative to the one of the upper wall and the lower wall, and wherein one, of the upper shutter plate and the lower shutter plate, which corresponds to the one of the upper wall and the lower wall comprises a projecting portion which slidably engages the second guide groove. 
     According to the mechanism, because the shutter is slidably guided on both sides of the cartridge case, the sliding movement of the shutter with respect to the cartridge case is more stabilized. 
     In accomplishing the above objects, there is also provided a disk cartridge comprising: a cartridge case which has an upper half-shell with an upper wall and a lower half-shell with a lower wall in which the cartridge case has a head access opening; a disk-shaped recording medium which is rotatably housed inside the cartridge case; a shutter which is slidable relative to the cartridge case in a sliding direction from right to left relative thereto with a neutral position therebetween corresponding to a position at which the shutter closes the head access opening; guide means which is provided on the cartridge case in the sliding direction; a first slider which is fixed to the shutter and which is guided by the guide means; and biasing means which exerts a biasing force upon the first slider so as to return the shutter to the neutral position when the shutter is moved to one of the right and left from the neutral position, wherein the guide means comprises a guide groove which a part of the upper wall and a part of the lower wall cooperate to form therebetween, wherein the first slider comprises a projecting part which is slidable inside the guide groove, and wherein the shutter comprises an upper shutter plate and a lower shutter plate, in which the upper shutter plate and the lower shutter plate are divided at a location where the upper shutter plate and the lower shutter plate are connected to each other, and in which the upper shutter plate and the lower shutter plate are integrated to each other after the upper shutter plate and the lower shutter plate are mounted on the cartridge case. 
     By the way, in a disk cartridge comprising: a cartridge case which has an upper half-shell with an upper wall and a lower half-shell with a lower wall in which the cartridge case has a head access opening; a disk-shaped recording medium which is rotatably housed inside the cartridge case; a shutter which is slidable relative to the cartridge case in a sliding direction from right to left relative thereto with a neutral position therebetween corresponding to a position at which the shutter closes the head access opening; guide means which is provided on the cartridge case in the sliding direction; a first slider which is fixed to the shutter and which is guided by the guide means; and biasing means which exerts a biasing force upon the first slider so as to return the shutter to the neutral position when the shutter is moved to one of the right and left from the neutral position, if a pair of coiled spring, or the like, as the biasing means, are mounted on both sides of the shutter so as to bias the shutter towards the neutral position relative to the cartridge case, there is no need of providing the first slider relative to the cartridge case. Even if the disk cartridge is so constructed, the shutter is held at the neutral position relative thereto when the shutter is not operated. Also with the mechanism, it is realized to reduce the number of assembling parts for the disk cartridge and to reduce the cost of production. In case that the disk cartridge is so constructed, there may be provided click means, for positioning the shutter relative to the cartridge case, which comprises: a projection on one of the shutter and the cartridge case, and a concave, which engages the projection, on the other of the shutter and the cartridge case. In the mechanism, the holding force, of the shutter relative to the cartridge case, exerted by the click means, may be set to such a degree as one that is smaller than a force exerted by a pin for driving the shutter. With the mechanism, a careless opening of the head access opening of the cartridge case is effectively prevented. 
     In accomplishing the above objects, there is also provided the following disk cartridge. 
     That is, there is provided a disk cartridge comprising: a cartridge case which has an upper half-shell with an upper wall and a lower half-shell with a lower wall in which the cartridge case has a head access opening; a disk-shaped recording medium which is rotatably housed inside the cartridge case; a shutter which is slidable relative to the cartridge case in a sliding direction from right to left relative thereto with a neutral position therebetween corresponding to a position at which the shutter closes the head access opening; guide means which is provided on the cartridge case in the sliding direction; a first slider which is fixed to the shutter and which is guided by the guide means; and biasing means which exerts a biasing force upon the first slider so as to return the shutter to the neutral position when the shutter is moved to one of the right and left from the neutral position, wherein the biasing means further comprises: a pair of second sliders which are guided by the guide means, wherein one of the second sliders is arranged on one of a pair of sides of the first slider, and wherein the other of the second sliders is arranged on the other thereof of the first slider; spring means which attracts the pair of second sliders to each other; and a stopper, provided on the cartridge case, which has a pair of ends, wherein one of the ends is able to abut an inner surface of one of the second sliders, and wherein the other of the ends is able to abut an inner surface of the other of the second sliders from inside, wherein the guide means comprises a guide rail which is integrated with an inner surface of one of the upper wall and the lower wall in the sliding direction, wherein the first slider slidably engages the guide rail, and wherein the second slider slidably engages the guide rail. 
     According to the mechanism, for example, when one of the second sliders contacts the first slider so as to bias the shutter towards the neutral position, and when both the second sliders contact the stopper, the first slider is positioned between both the second sliders so that the shutter closes the head access opening of the cartridge case. On the other hand, when the shutter is moved in either direction of the right or left from the neutral position relative to the cartridge case, the first slider pushes one of the pair of second sliders in the corresponding direction, while the other of the pair of second sliders remains stationary with the other thereof being held by the stopper. Because the spring means attracts both the second sliders to each other, the shutter is returned to the neutral position relative to the cartridge case at time of releasing any force to keep the shutter at a position that does not correspond to the neutral position relative thereto. 
     Also, according to the mechanism, the guide rail is integrated with the cartridge case and is not prepared as a member that is separate from the cartridge case; and each second slider of the two is not separately biased by a separate spring means from both sides of the cartridge case, but each second slider is mutually biased by a single spring means from inside of the cartridge case. Therefore, in a type of a disk cartridge in which a shutter is able to slide in either direction of the right or left from the neutral position relative to the cartridge case, the reduction of the assembling parts for the disk cartridge is surely realized, thus realizing the low cost of production. 
     In the mechanism, it is preferable that the guide rail comprises: a rail part; and a leg part which connects the rail part with the inner surface of the one of the upper wall and the lower wall, wherein the rail part is generally provided at a location which corresponds to a center line with respect to a direction of thickness of the cartridge case, in which the rail part has a thickness that is equal to or less than a thickness of the disk-shaped recording medium, and wherein the leg part is provided at a location outside the head access opening of the cartridge case. 
     A head for reading/writing data of a disk driving system gains an access to the disk-shaped recording medium through the head access opening of the cartridge case. Therefore, with the above mechanism of the present invention, interference of the guide rail relative to the access of the head is surely prevented. 
     In the mechanism, it is preferable that the rail part of the guide rail has a square cross section. 
     With the mechanism, because a rotation of the first slider relative to the guide rail and a rotation of the second slider relative thereto are surely prevented. Consequently, with the mechanism, there is no need of providing special, separate means for preventing the rotation therebetween. 
     In the mechanism, it is preferable that the first slider and the guide rail are so constructed that the first slider can be mounted on the guide rail in a direction generally perpendicular to a direction in which the guide rail extends, and/or that there is formed a space between one of a pair of ends of the guide rail and one of a pair of sides, of the cartridge case, extending in a direction perpendicular to the sliding direction, in which one of the second sliders can pass the space, and wherein there is formed a space between the other of the pair of ends of the guide rail and the other of the pair of sides, of the cartridge case, extending in the direction perpendicular to the sliding direction, in which the other of the second sliders can pass the space, and wherein the second slider has an engaging part which allows the second slider to be mounted on the guide rail in the sliding direction. 
     According to the mechanism, the work to mount the first and/or second slider(s) on the guide rail is facilitated. 
     Also, according to the mechanism, the spring means can be easily mounted on the second sliders before and after the second sliders are mounted on the guide rail. 
     Thus, with the mechanism, there is no need of preparing these parts as a subassembly beforehand, it is easy to assemble the disk cartridge. 
     In the mechanism, there may be further provided a retention part which is formed on an inner surface of the other of the upper wall and the lower wall in which the retention part constitutes an extension of the guide rail that corresponds to the space therebetween; and/or there may be further provided engaging means which makes the first slider and the second slider engage each other with the first slider and the second slider contacting each other, wherein the engaging means may comprise: a concave part which is provided on a contacting surface of one of the first slider and the second slider, and a convex part, able to engage the concave part, which is provided on a contacting surface of the other of the first slider and the second slider. 
     With the mechanism, it is possible to prevent a dislocation or disengagement of the second slider from the guide rail, even if the second slider is slid from the neutral position up to a position at which the second slider is disengaged from the guide rail as the shutter is forcibly moved from the neutral position. 
     In the mechanism, the second slider may have an engaging concave part which allows the second slider to be mounted on the guide rail in a direction perpendicular to the sliding direction, wherein the engaging concave part is defined inside an elastic hook-shaped part which is a part of the second slider. 
     With the mechanism, it is realized to facilitate the mounting of the second slider onto the guide rail. 
     In the mechanism, it is preferable that the elastic hook-shaped part comprises a tip part which has a guide sloping surface for assisting to mount the second slider onto the rail part of the guide rail. 
     With the mechanism, the mounting of the second slider onto the guide rail can be done more easily. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This and other objects and features of the present invention will become clear from the following description taken in conjunction with preferred embodiments thereof with reference to the accompanying drawings, in which: 
     FIG. 1 is a partly exploded perspective view of a disk cartridge according to a first embodiment of the present invention; 
     FIG. 2 is a partial inside view of a half-shell on a side of an upper wall of the disk cartridge shown in FIG. 1; 
     FIG. 3 is a partial top view of the half-shell of FIG. 2; 
     FIG. 4 is a partial inside view of a half-shell on a side of a lower wall of the disk cartridge shown in FIG. 1; 
     FIG. 5 is a partial top view of the half-shell of FIG. 4; 
     FIG. 6 is a sectional view taken along the line VI—VI of FIG. 4 in a state in which both shells and a shutter mechanism are assembled together; 
     FIG. 7 is a sectional view taken along the line VII—VII of FIG. 4 in a state in which both shells and the shutter mechanism are assembled together; 
     FIG. 8 is a perspective view of a left side slider of the disk cartridge shown in FIG. 1; 
     FIG. 9 is a perspective view of a right side slider of the disk cartridge shown in FIG. 1; 
     FIG. 10 is a sectional view of a modification of FIG. 7; 
     FIG. 11 is an explanatory view for explaining a motion of the sliders of the first embodiment, showing a state in which the shutter is at the neutral position; 
     FIG. 12 is an explanatory view for explaining the motion of the sliders of the first embodiment, showing a state in which the shutter is moved to the left; 
     FIG. 13 is a perspective view of a slider according to a modification of slider of the first embodiment; 
     FIG. 14 is a main-part plan view of a state in which the slider of FIG. 13 is assembled to the half-shell on the side of the lower wall; 
     FIG. 15 is a main-part front view of the state in which the slider of FIG. 13 is assembled to the half-shell on the side of the lower wall; 
     FIG. 16 is a perspective view of a slider of another modification of slider of the first embodiment; 
     FIG. 17 is a main-part plan view of a state in which the slider of FIG. 16 is assembled to the half-shell on the side of the lower wall; 
     FIG. 18 is a main-part front view of the state in which the slider of FIG. 16 is assembled to the half-shell on the side of the lower wall; 
     FIG. 19 is a main-part perspective view of a shutter plate on the side of the upper wall; 
     FIG. 20 is a main-part perspective view of a shutter plate on the side of the lower wall; 
     FIG. 21 is a perspective view of a modification of an engaging pin which is provided on the slider of the first embodiment; 
     FIG. 22 is a perspective view of another modification of the engaging pin which is provided on the slider of the first embodiment; 
     FIG. 23 is a sectional view of another modification, of FIG. 7, in which the slider of FIG. 22 is used; 
     FIG. 24 is a plan view showing a half-shell on a side of an upper wall of a disk cartridge according to a second embodiment of the present invention; 
     FIG. 25 is an inside view of the half-shell shown in FIG. 24; 
     FIG. 26 is a plan view showing a half-shell on a side of a lower wall of the disk cartridge according to the second embodiment; 
     FIG. 27 is an inside view of the half-shell shown in FIG. 26; 
     FIG. 28 is a sectional view taken along the line XXVIII—XXVIII of FIG. 25 in a state in which the half-shell on the side of the upper wall shown in FIGS. 24 and 25, the half-shell on the side of the lower wall shown in FIGS. 26 and 27, and a shutter mechanism are assembled together; 
     FIG. 29 is a sectional view taken along the line XXIX—XXIX of FIG. 25 in a state in which the half-shell on the side of the upper wall shown in FIGS. 24 and 25, the half-shell on the side of the lower wall shown in FIGS. 26 and 27, and the shutter mechanism are assembled together; 
     FIG. 30 is a plan view of an inner slider shown in FIG. 28; 
     FIG. 31 is a front view of the inner slider shown in FIG. 28; 
     FIG. 32 is a side view of the inner slider shown in FIG. 28; and 
     FIG. 33 is a perspective view of an outer slider shown in FIG.  29 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before the description of the present invention proceeds, it is to be noted that like or corresponding parts are designated by like reference numerals throughout the accompanying drawings. 
     Hereinafter, a first embodiment and a second embodiment of the present invention are described below in detail with reference to FIGS. 1 to  33 . 
     First, a disk cartridge according to the first embodiment is described below with reference to FIGS. 1 through  9 ,  11  and  12 . 
     The disk cartridge illustrated in the figures, has a quadrangular, thin-plate-shaped, hollow cartridge case in which a digital video disk (DVD) is rotatably housed as a disk-shaped recording medium. The cartridge case is so constructed that a half-shell on a side of an upper wall (hereinafter also referred to as an “upper wall side half-shell” (side A)), and a half-shell on a side of a lower wall (hereinafter also referred to as a “lower wall side half-shell” (side B)), which are both plastic molded and equal in thickness to each other, are overlaid on each other. 
     FIG. 1 is a partly exploded perspective view of the disk cartridge; FIG. 2 is a partial inside view of a half-shell on a side of an upper wall of the disk cartridge shown in FIG. 1; FIG. 3 is a partial top view of the half-shell of FIG. 2; FIG. 4 is a partial inside view of a half-shell on a side of a lower wall of the disk cartridge shown in FIG. 1; FIG. 5 is a partial top view of the half-shell of FIG. 4; FIG. 6 is a sectional view taken along the line VI—VI of FIG. 4 in a state in which both shells and a shutter mechanism are assembled together; FIG. 7 is a sectional view taken along the line VII—VII of FIG. 4 in a state in which both shells and the shutter mechanism are assembled together; FIG. 8 is a perspective view of a left side slider of the disk cartridge shown in FIG. 1; and FIG. 9 is a perspective view of a right side slider of the disk cartridge shown in FIG.  1 . 
     In the figures, a reference numeral  10  denotes the half-shell on the upper wall side,  20  denotes the half-shell on the lower wall side,  30  denotes a shutter, made of plastic, of the shutter mechanism,  40  denotes sliders (a left side slider and a right side slider), and  50  denotes a spring. The upper wall side half-shell  10  and the lower wall side half-shell  20 , are basically identical in configuration to each other except a portion constituting a guide groove, as described below, for sliding the shutter  30 . Peripheral walls  12 ,  22  defining a disk-housing space, and side walls  13 ,  23  extending along side edge portions of an upper wall  11  and a lower wall  21 , are formed integrally with the upper wall side half-shell  10  and the lower wall side half-shell  20 , respectively. The two shells  10 ,  20  are provided with head access openings  14 ,  24  which forms in a direction in which the disk cartridge is loaded to a disk drive (not shown) upward from the central portions of the upper wall  11  and the lower wall  21 . These openings  14 ,  24  are covered with the shutter  30 , and the shutter  30  is adapted to be slid to both right and left from a neutral position where the shutter  30  covers the openings  14 ,  24 . 
     The two shells  10 ,  20  differ from each other in the position of their upper-end walls  15 ,  25 , so that when the two shells  10 ,  20  are connected to each other, a guide groove  60  extending along an opening/closing direction of the shutter is formed on the lower wall  21  side between the two upper-end walls  15 ,  25  (see FIGS. 6,  7 ). Namely, both the two upper-end walls  15 ,  25  cooperate with each other to form the guide groove  60 . 
     Central portions  15   a ,  25   a  of the two upper-end walls  15 ,  25 , i.e., portions corresponding to the width of the head access openings, are smaller in the thickness of the cartridge case than that of the other portions  15   b ,  25   b , and they are equal to or smaller than the thickness of the disk-shaped recording medium so as not to disturb or interfere the running of the head during access of the head to the disk  1  (i.e. disk-shaped recording medium) with the disk drive being loaded with the disk cartridge. Correspondingly to this, surfaces of the upper wall  11  and the lower wall  21  are so formed that central portions  11   a ,  21   a  of their upper end portions are recessed relative to the left and right portions  11   b ,  21   b  thereof. In the cartridge case, a slider/spring guide space  61  forms inside the cartridge case so as to communicate with the guide groove  60  when the two shells  10 ,  20  are combined together. 
     The shutter  30  comprises a shutter plate  31  on a side of the upper wall (hereinafter also referred to as an “upper wall side shutter plate”), and a shutter plate  32  on a side of the lower wall (hereinafter also referred to as a “lower wall side shutter plate”) which is connected to the upper wall side shutter plate  31  by a connecting plate  33 . The connecting plate  33  forms into a U-shape in cross section and fitted to the cartridge case so as to sandwich the upper wall  11  and the lower wall  21  thereof. The shutter  30 , having a projecting shape or appearance as viewed from the front side thereof as shown in FIG. 1, has recessed portions  37 ,  37  formed on its right and left shoulder portions. These recessed portions  37 ,  37  are used to open the shutter  30  by being engaged with a shutter drive pin when the disk cartridge is loaded to the disk drive. 
     The lower wall side shutter plate  32  and the connecting plate  33  are integrally molded as an L-shaped member, while the upper wall side shutter plate  31  is fixed to an end face of the connecting plate  33 . The lower wall side shutter plate  32  has a projecting part  34  which is slidably fitted to the guide groove  60  of the cartridge case. By the way, the projecting part  34  of the shutter  30  may be formed as a first projecting part  34   a  with a narrow width arranged on one side of the shutter  30 , and as a second projecting part  34   b  with a narrow width arranged on the other side of the shutter  30 , respectively, as shown by an imaginary line in FIG.  1 . 
     Meanwhile, in order that the upper wall side shutter plate  31  and the connecting plate  33  are integrated after being assembled to the cartridge case, a positioning projection  35  is formed at an end face of the connecting plate  33 , while a positioning recess  36  is formed in the upper wall side shutter plate  31 . The upper wall side shutter plate  31  and the connecting plate  33  can be fixed, for example, by ultrasonic welding after the positioning projection  35  is inserted into the positioning recess  36 . 
     Between the upper wall side half-shell  10  and the lower wall side half-shell  20 , is formed a guide space (groove)  61  for guiding the sliders  40 ,  40  and the spring  50 . Each of the two sliders  40 ,  40  housed in this guide space  61  has, on the upper end portion as shown in FIG. 1, an engaging portion  41  which slidably engages the guide groove  60 . The two engaging portions  41 ,  41  are arranged on both right and left sides of the shutter  30  so as to sandwich the projecting part  34  of the shutter  30  (see FIG. 11) therebetween. 
     Also, each of the sliders  40 ,  40  (the left side slider shown in FIG.  8  and the right side slider shown in FIG. 9 are symmetrical with respect to the shutter  30 ) has a positioning portion  43  provided with a pin  42  for supporting a tension coil spring  50 . The tension coil spring  50  is coupled with the spring locking pins  42 ,  42  so that the two sliders  40 ,  40  are biased so as to attract each other. In addition, each engaging portion  41  of the sliders  40 ,  40  is constituted by an upper wall  41   a  and a side wall  41   b.    
     Among these upper wall  41   a , side wall  41   b  and positioning portion  43 , is formed a groove  41   c  to which the upper-end wall  25  of the lower wall side half-shell  20  engages. Preferably, the pins  42 ,  42  are L-shaped as shown as a modification in FIG. 21 in order that end portions of the spring  50  are not easily disengaged or dislocated. In this modification, components or parts corresponding to those of the slider shown in the first embodiment are designated by the reference numerals used in the first embodiment and suffixed by an alphabetical character, “E”. 
     Each positioning portion  43  of the two sliders  40 ,  40  has a convex portion or a projecting portion  44  that projects in a direction opposite to the pin  42  which engages the spring  50 . And, on the lower wall side half-shell  20  of the cartridge case, is formed a stopper  26  that contacts an inner surface of the projecting portion  44  of each of the sliders  40 ,  40 , so that when the sliders  40 ,  40  are positioned relative to the stopper  26  with the projecting portions  44 ,  44  of the sliders  40 ,  40  contacting the stopper  26  of the cartridge case, the shutter  30  comes to the neutral position relative to the cartridge case, thus causing the head access openings  14 ,  24  of the cartridge case to be closed. 
     By the way, the stopper  26  which is a projection for limiting the running or movement of the sliders  40 ,  40  relative to the cartridge case, may be formed on the upper wall side half-shell  10  so as to contact the engaging portions  41 ,  41  of the sliders  40 ,  40 . 
     Furthermore, there is provided a projection streak  16  which extends in parallel with the guide groove  60 . The projection streak  16  forms on the upper wall side half-shell  10  of the cartridge case, the bottom surface (or inner surface) of the projection streak  16  forming circular so as not to interfere the tension coil spring  50 . Each of the sliders  40 ,  40  has a sliding surface  45  which slidably contacts with the upper surface of the projection streak  16 . 
     In the above arrangement, the disk cartridge can be assembled by arranging the lower wall side shutter plate  32  of the shutter  30  on the surface of the lower wall side half-shell  20  so that the projecting part  34  engages the guide groove  60 , by arranging the pair of sliders  40 ,  40  on the lower wall side half-shell  20  and connecting both ends of the spring  50  to the pair of pins  42 ,  42  of the two sliders  40 ,  40 , by thereafter fixing the shells  10 ,  20  to each other, and by fixing the upper wall side shutter plate  31 E to the connecting plate  33 . 
     With the disk cartridge assembled in this way, as shown in FIGS. 11 and 12, the pair of sliders  40 ,  40  are in contact with the projecting part  34  of the shutter  30  from both the right and left sides (see FIG.  11 ), while the sliders  40 ,  40  are positioned by the stopper  26  formed on the cartridge case, so that the projecting part  34  of the shutter  30  is positioned at the center of the guide groove  60 , and so that the shutter  30  comes to the neutral position, thus causing the head access openings  14 ,  24  to be closed. By the way, the stopper  26  contacts with the inner surface of the projecting portion  44  of each slider  40 . 
     Meanwhile, when the shutter  30  is slid from the neutral position to either right or left direction (FIG. 12 shows a state in which the shutter  30  is moved in the left direction), the projecting part  34  of the shutter  30  moves together with one, of the sliders  40 ,  40 , which is being pushed by the projecting part  34  of the shutter  30 . During this movement, the other of the sliders  40  is held stationary in position by the stopper  26  so that the tension coil spring  50  is stretched. The two sliders  40 ,  40  are attracted to each other by the tension coil spring  50 ; therefore, if releasing the force to keep the shutter  30  at a position in which the shutter opens, the shutter  30  returns to the neutral position. 
     In the above arrangement, since the components or parts thereof can be easily assembled to the shells without need of arranging the shutter mechanism in the form of a sub-assembly beforehand, the assembling of the disk cartridge can be done conveniently. Further, since only one spring is used, and since no metallic parts are used, it is possible to realize a reduction of its production cost and, and to realize a lightweight disk cartridge 
     Next, a modification shown in FIG. 10 is described below. 
     In this modification, components or parts corresponding to those of the disk cartridge of the first embodiment are designated by the reference numerals used in the first embodiment and suffixed by an alphabetical character, “A”. 
     FIG. 10 is a view corresponding to FIG. 7 of the first embodiment. In this example, a second guide groove  62 A, which is parallel to the guide groove  60 A, is formed on a surface of an upper wall  11 A, in which the second guide groove  62 A is formed opposite to the guide groove  60 A with respect to the upper wall  11 A. And a second projecting part  38 A that slidably fits to the second guide groove  62 A is formed on an inner surface of the upper wall side shutter plate  31 A. 
     As described above, the central portion of the upper wall  11 A (a portion corresponding to  11   a  of the first embodiment) is recessed relative to both the right and left side portions (portions corresponding to  11   b  of the first embodiment). Accordingly, the second guide groove  62 A is formed only on the right and left side portions (portions corresponding to  11   b  of the first embodiment) as indicated by imaginary lines in FIG.  3 . Alternatively, the second guide groove  62 A may be formed continuously so as to cover the central portion (a portion corresponding to  11   a  of the first embodiment) from the right and left portions. 
     Providing the second guide groove  62 A makes it possible to guide the shutter  30 A relative to the cartridge case more stably, with both sides of the shutter being guided by both sides of the cartridge case. 
     Next, three modifications of sliders and stoppers are described below with reference to FIGS. 13,  14 ,  15 , FIGS. 16,  17 ,  18  and FIGS. 22,  23 . 
     In these modifications, components or parts corresponding to those of the disk cartridge of the first embodiment are designated by the reference numerals used in the first embodiment, and suffixed by an alphabetical character, “B”, “C” or “F”, respectively. 
     As shown in FIG. 13, this slider  40 B has the same basic constitution as that of the first embodiment. That is, the slider  40 B comprises a positioning portion  43 B provided with a spring locking pin  42 B, an engaging portions  41 B and a projecting portion  44 B. A characteristic of the modification is that a frictional projection  44 B a  is formed on an inner surface of the projecting portion  44 B. This frictional projection  44 B a  has a tilted frictional surface  44 B b.    
     On the other hand, on a corresponding end portion of the stopper  26 B that engages the slider  40 B, as shown in FIG. 15, is formed a cutout  26 B a  which is so shaped as to accept the frictional projection  44 B a  of the slider  40 B. Further, on this cutout  26 B a,  a tilted frictional surface  26 B b  corresponding to the tilted frictional surface  44 B b  is formed. These frictional surfaces  44 B b,    26 B b  are tilted with respect to the direction of the sliding movement. Accordingly, when the shutter  30 B is in the neutral position, as shown in FIG. 15, the slider  40 B, is biased in the left direction in the figure so that the frictional projection  44 B a  of the slider  40 B is contacted with the cutout  26 B a  of the stopper  26 B. In this state, the frictional surfaces  44 B b,    26 B b  of the frictional projection  44 B a  and the cutout  26 B a  are both tilted; therefore, the frictional projection  44 B a  bites into the cutout  26 B a  like a wedge so that their frictional surfaces are brought into close contact to each other. 
     In addition, as shown in FIG. 14, the sliders  40 B,  40 B are exerted upon with the biasing force of the coil spring  50 B. Therefore, the slider tends to be rotated in a direction shown by an arrow Y in the figure. As a result, with the structure of the sliders and the stopper according to the first embodiment, the sliders may happen to be disengaged or dislocated from the guide groove  60  and the upper-end wall  25  in the assembling process, which incurs a disadvantage of poor assembling efficiency. 
     By contrast, according to the modification of FIGS. 13,  14 ,  15 , even if such a rotating force in the direction of arrow Y is exerted upon the sliders, the frictional force exerting between the two frictional surfaces is a resistance to the rotation thereof. That is, because the position and posture of the sliders are kept stationary and stable relative thereto, the assembling work of the sliders get more efficient and advantageous. 
     Another modification of a slider and a stopper for making the installation of sliders more stable than in the above modification, is shown in FIGS. 16,  17 ,  18 . In this modification, components or parts corresponding to those of the disk cartridge of the first embodiment are designated by the reference numerals used in the first embodiment and suffixed by an alphabetical character, “C”. This modification is basically the same as the modification of FIGS. 13,  14 ,  15 . Besides, in this modification, a cutout  44 C c  is formed on a side of the positioning portion  43 C of the frictional projection  44 C a.  Further, in correspondence to this cutout  44 C c,  a projection  26 C c  is formed on an end portion of the stopper  26 C. 
     Accordingly, also in this modification, a frictional force exerting between the frictional surfaces  26 C b  and  44 C b,  produces a resistance to the rotation of the slider relative to the stopper as shown in FIGS. 17 and 18. 
     Furthermore, the projection  26 C c  of the stopper bites into the cutout  44 C c  of the sliders as shown in FIG.  17 . Therefore, against the rotating force which is exerted upon the sliders in the direction of arrow Y as shown in the figure, the sliders are surely prevented from rotating by direct engagement of the projection  44 C c  with the projection  26 C c.  Therefore, in this modification, the sliders can be prevented from being disengaged or dislocated from the stopper almost 100%. 
     FIGS. 22 and 23 show another modification of a slider and a stopper for making the installation of sliders more stable as well. In this modification, components or parts corresponding to those of the disk cartridge of the first embodiment are designated by the reference numerals used in the first embodiment and suffixed by an alphabetical character, “F”. 
     A characteristic of the slider of the modification is that there is provided an upper wall extension  41 F d  formed by extending a part of the upper wall  41 F a  and that an engaging claw  41 F e  is formed from this upper wall extension  41 F d.  In correspondence to this engaging claw  41 F e,  a groove  25 F c  is formed on the upper surface of the upper-end wall  25 F of the lower wall side half-shell  20 F. As apparent from FIG. 23, in the state that the sliders  40 F,  40 F are assembled to the lower wall side half-shell  20 F, the upper wall extension  41 F d  extends on the upper-end wall  25 F, and the engaging claw  41 F e  slidably engages the groove  25 F c.  Accordingly, the slider of this arrangement, once mounted on the upper-end wall  25 F, is not easily dislocated or disengaged from the upper-end wall  25 F. 
     The mounting of the sliders onto the upper-end wall is forcedly carried out from the left side in FIG.  23 . In this mounting work, the upper wall of the sliders and the extension  41 F d  thereof are flexed upward, so that the sliders can be fitted onto the upper-end wall  25 F without problem. 
     Although the upper wall extension  41 F d  is an extension of part of the upper wall  41 F a,  it may otherwise be formed by extending the entire upper wall  41 F a  as indicated by an imaginary line as shown in FIG.  22 . 
     Alternatively, the modification shown in FIGS. 22 and 23 may be used in combination with the modifications described above and shown in FIGS. 13,  14 ,  15 ,  16 ,  17  and  18 . 
     Next, a concrete example of the structure for positioning the two shutter plates  31 ,  32  relative to each other and for welding them to each other is described below with reference to FIGS. 19 and 20. 
     In the example of FIG. 1, a narrow positioning recess  36   e  which is open toward the inner surface is formed in the center of a projecting portion  37   a  between the two recessed portions  37 ,  37  of the lower wall side shutter plate  32 , while a plurality of large and small welding projections  35  are formed around the positioning recess  36  with a good balance. On the other hand, the upper wall side shutter plate  31  has a plurality of recessed portions  36  which correspond to the projections  35  of the lower wall side shutter plate  32 , while a positioning projection  35   e  corresponding to the positioning recess  36   e  is projected in the center of a projecting portion  37   b  which corresponds to the projecting portion  37   a  of the lower wall side shutter plate  32 . When the two shutter plates  31 ,  32  are connected to each other, the positioning projection  35   e  is inserted into the positioning recess  36   e,  while the welding projections  35  are inserted into the welding recessed portions  36 . With the construction, the two shutter plates  31  and  32  are stably positioned relative to each other. Subsequently, the welding projections  35  and the welding recessed portions  36  are integrated by ultrasonic welding or other means. The mutually engaging portions of the positioning projection  35   e  and the positioning recess  36   e  may also be welded to each other at the same time. 
     By the way, the present invention is not limited to the first embodiment and its modifications described above, and may be embodied in other various ways. 
     For example, it is possible that the projecting part  34  of the shutter  30  is formed slightly (e.g., about 1 to 2 mm) wider than the width of the stopper  26  so that only one of the sliders  40 ,  40  contacts the stopper  26  at the neutral position. In this arrangement, although the shutter  30  is slightly shifted to right or left at the neutral position, there will not arise any problem substantially if the shift is within about 1 to 2 mm. 
     Next, a disk cartridge according to the second embodiment is described below with reference to FIGS. 24 to  33 . 
     The disk cartridge illustrated in the figures, also has a quadrangular, thin-plate-shaped, hollow cartridge case in which a digital video disk  101  (DVD) is rotatably housed as a disk-shaped recording medium. The cartridge case is also so constructed that a half-shell on a side of an upper wall (hereinafter also referred to as an “upper wall side half-shell” (side A)), and a half-shell on a side of a lower wall (hereinafter also referred to as a “lower wall side half-shell” (side B)), which are both plastic molded and equal in thickness to each other, are overlaid on each other. 
     FIG. 24 is a plan view showing the half-shell on the side of the upper wall of the disk cartridge according to the second embodiment of the present invention; FIG. 25 is an inside view of the half-shell shown in FIG. 24; FIG. 26 is a plan view showing the half-shell on the side of the lower wall of the disk cartridge according to the second embodiment; and FIG. 27 is an inside view of the half-shell shown in FIG.  26 . The two shells  110 ,  120  are basically of the same construction, except a guide rail part for sliding the shutter which is described below. 
     Peripheral walls  112 ,  122  defining a disk-housing space, and side walls  113 ,  123  extending along side edge portions of an upper wall  111  and a lower wall  121 , are formed integrally with the upper wall side half-shell  110  and the lower wall side half-shell  120 , respectively. The two shells  110 ,  120  are provided with head access openings  114 ,  124  which forms in a direction in which the disk cartridge is loaded to a disk drive (not shown) upward from the central portions of the upper wall  111  and the lower wall  121 . These openings  114 ,  124  are covered with the shutter  130  (see FIGS.  28  and  29 ), and the shutter  130  is adapted to be slid to both right and left from a neutral position where the shutter  130  covers the openings  114 ,  124 . 
     FIG. 28 is a sectional view taken along the line XXVIII—XXVIII of FIG. 25 in a state in which the half-shell on the side of the upper wall shown in FIGS. 24 and 25, the half-shell on the side of the lower wall shown in FIGS. 26 and 27, and a shutter mechanism are assembled together; and FIG. 29 is a sectional view taken along the line XXIX—XXIX of FIG. 25 in a state in which the half-shell on the side of the upper wall shown in FIGS. 24 and 25, the half-shell on the side of the lower wall shown in FIGS. 26 and 27, and the shutter mechanism are assembled together. 
     In FIGS. 28 and 29, a reference numeral  115  denotes a guide rail which is provided on the upper-wall side half-shell  110 ;  140  denotes an inner slider; and  150  denotes an outer slider. There are provided a pair of outer sliders  150 , and the pair of outer sliders  150  are connected to each other by a spring  160  so as to be attracted to each other, as will be described later. 
     The guide rail  115 , which is formed integrally with an inner-surface upper end portion of the upper wall  111 , comprises a rail part  115   a  having a square cross section and extending along one side of the cartridge case, and a leg part  115   b  connecting to the rail part  115   a  and the inner surface of the upper wall  111 . The leg part  115   b  is formed only on a right side and a left side of the head access opening  114 , while the rail part  115   a  of the guide rail  115  is arranged on a center line in a direction of thickness of the cartridge case as shown in FIGS. 28 and 29, the thickness of the rail part  115   a  being equal to or less than that of the disk-shaped recording medium (not shown). With the construction, the guide rail  115  does not disturb or interfere the running of the head which gains access to the disk therein when the disk drive is loaded with the disk cartridge. 
     By the way, the rail part  115   a  of the guide rail  115  is slightly shorter than the interval between the two side walls  113 ,  113  of the upper-wall side half-shell  110 , thus forming spaces or gaps  162 ,  162  between both ends of the rail part  115   a  and both side walls  113  of the upper-wall side half-shell  110 . On the other hand, in the lower-wall side half-shell  120 , a retention part  125  constituting an extension of the guide rail  115  is formed integrally with upper end portions of both side walls  123 ,  123  so that when the two shells  110 ,  120  are connected to each other, the guide rail  115  becomes continuous between both the side walls of the cartridge case. 
     Reference numerals  116  and  126  denote support members for the inner slider  140 , in which the support members extend in parallel with the guide rail  115 , where the rail part  115   a  of the guide rail  115  and these support members  116 ,  126  only cross the head access openings  114 ,  124 . Both end portions of the upper surfaces of these support members  116 ,  126  are formed into steps  116   a,    116   a  and  126   a,    126   a,  as shown in FIGS. 25 and 27, so as to functions as stoppers for the outer sliders  150 ,  150 . 
     The shutter  130  is made of plastics and formed into a U-shape in cross section. The shutter  130  is constituted, in a square-shape in cross section, by a shutter plate  131  for closing the opening  114  of the upper wall  111 , a shutter plate  132  for closing the opening  124  of the lower wall  121 , and a connecting plate  133  which connect the two shutter plates  131 ,  132  to each other. The shutter is provided so as to sandwich the upper wall  111  and the lower wall  121  from outside. 
     On the inner surface of the connecting plate  133  of the shutter  130 , is provided the inner slider  140  which slidably engages the guide rail  115 . The inner slider  140  has a groove  141  inside which the guide rail  115  are mounted when the inner slider  140  gains access to the guide rail  115  perpendicularly toward the upper wall  111 . After the inner slider  140  is mounted onto the guide rail  115 , the shutter  130  can be fixed to the inner slider  140  by screwing, ultrasonic welding, or other optional means. 
     The inner slider  140  is shown in FIGS. 30,  31  and  32 , where FIG. 30 is a plan view of the slider  140 , FIG. 31 is a front view thereof, and FIG. 32 is a side view thereof. This inner slider  140  exhibits a protruding shape as viewed from the front, and has recessed portions  142 ,  142  on both right and left shoulder portions thereof. 
     In correspondence to these recessed portions  142 ,  142 , the shutter  130  also has recessed portions on right and left shoulder portions although they are not shown in the figures, and the shutter  130  is so shaped that its central portion is protruded. By the way, the recessed portions on both shoulders of the shutter  130  are used in such a way that the shutter  130  is opened by hooking it with a shutter drive pin of the disk drive system when the disk cartridge is loaded to the disk drive. 
     The pair of the outer sliders  150 ,  150  are slidably mounted onto the guide rail  115  so as to sandwich the inner slider  140  from both sides. One of these outer sliders  150 ,  150  is shown in FIG.  33 . The outer slider  150  has an engaging recess  151  for being axially inserted relative to the guide rail  115 . Each of the outer slider  150  is inserted into the rail part  115   a  from the spaces  162 ,  162  formed between both ends of the rail part  115   a  of the guide rail  115  and both side walls  113  of the upper-wall side half-shell  111 . 
     The engaging recess  151  of the outer slider  150  is formed or defined by a hook-shaped part  152 . Also, each outer slider  150  is provided with a hook  153  on a surface thereof confronting the inner slider  140 . The outer sliders  150  are formed symmetrical relative to the inner slider  140 . 
     The hooks  153 ,  153  of the two outer sliders  150 ,  150  support a tension coil spring  160  therebetween, so that the two outer sliders  150 ,  150  are attracted to each other. The tension coil spring  160  extends or exists, inside a recessed portion  143  formed on a front-face lower end side of the inner slider  140 , between the two outer sliders  150 ,  150 . Thus, in a state that the two outer sliders  150 ,  150  are in contact with the stoppers  116   a,    126   a  of the upper surfaces of the support members  116 ,  126  of the cartridge case, the inner slider  140  is positioned relative to the supporting members  116 ,  126 , where the shutter  130  comes to the neutral position so that the head access openings  114 ,  124  are closed by the shutter  130 . 
     In the above arrangement, the disk cartridge can be assembled through the following steps of: 
     mounting the inner slider  140  onto the guide rail  115 ; 
     inserting the outer sliders  150 ,  150  from both ends of the guide rail  115 ; 
     mounting the tension coil spring  160  between the pair of outer sliders  150 ,  150 ; 
     connecting both shells  110 ,  120  to each other with the disk-shaped recording medium  101  being sandwiched therebetween; and 
     fixing the shutter  130  to the inner slider  140 . 
     With the disk cartridge assembled in this way, the pair of outer sliders  150 ,  150  contact with the inner slider  140 , fixed to the shutter  130 , from both right and left sides thereof, while the two outer sliders  150 ,  150  are positioned by the steps i.e. the stoppers  116   a,    126   a  of the supporting portions  116 ,  126 , with the inner slider  140  being positioned in the center of the guide rail  115 . With the state, the shutter  130  comes to the neutral position, causing the head access openings  114 ,  124  to be closed by the shutter  130 . 
     According to the above mechanism, there is no need of arranging the shutter mechanism as a subassembly beforehand, and the components and parts can be easily assembled to the shells  110 ,  120 . Therefore, it is easy to carry out the work to assemble the disk cartridge. 
     Also, only one spring  160  is used, and no additional metallic parts are used. Therefore, it is possible to reduce the cost of production of the disk cartridge and to make the disk cartridge lightweight. 
     By the way, with the arrangement that the rail part  115   a  of the guide rail  115  is formed square-shaped or quadrangle-shaped in cross section, the guide rail  115  functions as a stopper for preventing the rotation of the inner slider  140  and for preventing the rotation of the outer sliders  150 ,  150 , relative to the guide rail  115 . Thus, with the arrangement, there is no need of providing any special means for preventing the rotation therebetween. 
     Meanwhile, when the shutter  130  is slid in either direction of right or left relative to the cartridge case from the neutral position, the inner slider  140  moves together with the shutter  130  in the corresponding direction while the inner slider  140  is pushing one of the outer sliders  150 ,  150 . During the movement thereof, the other of the outer sliders  150 ,  150  is kept stationary in position by the stoppers  116   a,    116   a;    126   a,    126   a  so that the tension coil spring  160  is stretched between the pair of outer sliders  150 ,  150 . As a result, the two outer sliders  150 ,  150  are attracted to each other by the biasing force of the tension coil spring  160 , and the shutter  130  is returned to the neutral position by the biasing force thereof from the position at which the shutter opens the head access opening of the cartridge case, when the force to keep the shutter at the same position is released. 
     The present invention is not limited to the above second embodiment, and may be embodied in other various modifications. For instance, instead of forming the retention part  125 , constituting an extension of the guide rail  115 , on the lower wall side half-shell  120 , for example, it is also possible to form a recessed portion on one of the contact surface of the inner slider  140  and the contact surface of the outer sliders  150 ,  150 , and to form a protruding portion (projection portion) on the other of the contact surface of the inner slider  140  and the contact surface of the outer sliders  150 ,  150  in which the recessed portion and the protruding portion, as engaging means, engage each other when the inner slider  140  and the outer slider  150  contact each other. 
     With this arrangement, as the above embodiment in which the retention part  125  is provided as an extension of the guide rail  115 , the outer slider  150  is prevented from disengaging or dislocating from the guide rail  115  when the shutter  130  is opened and the outer slider  150  is slid up to such a position at which the outer slider  150  may possibly disengage from the guide rail  115 . 
     Also, for example, in order to be able to mount the outer slider  150  onto the rail part  115   a  of the guide rail  115  in a direction which is perpendicular to the direction in which the guide rail extends, instead of mounting the outer slider  150  onto the rail part  115   a  thereof in the axial direction in which the guide rail extends, a tip part (tip end portion) of the elastic hook-shaped part  152 , defining the engaging recess portion  151 , of the outer slider  150  may be formed shorter as indicated by an imaginary line  152   a  in FIG.  29 . 
     With this arrangement, the mounting of the outer sliders  150 ,  150  to the guide rail  115  can be easily achieved without providing the spaces  162 ,  162  between the side walls  113 ,  113  of the cartridge case and the sides of the guide rail  115 . 
     Furthermore, if the tip end portion of the hook-shaped part  152  is formed as a guide sloping surface as indicated by an imaginary line  152   b  in the same figure, the efficiency to mount the outer slider  150  onto the rail part  115   a  of the guide rail  115  is further enhanced. 
     Also, the inner slider  140  may form so as to have a width which is slightly (e.g., about 1 to 2 mm) wider than a width of gap or spacing between the two stoppers  116   a,    126   a;    116   a,    126   a  of the support members  116 ,  126  so that only one of the outer sliders  150 ,  150  contacts one of the stoppers  116   a,    126   a  at the neutral position. With this construction, the shutter  130  may be slightly shifted in the right or left when the shutter is located at the neutral position; however, if the shift is within about 1 to 2 mm, no special problem will arise. 
     Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various other changes and modifications are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.