Patent Publication Number: US-7216357-B2

Title: Disc cartridge having a shutter that includes a convex portion protruding into a center hole of the disc

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 10/292,570, filed Nov. 12, 2002 now U.S. Pat. No. 6,983,477, which is a Continuation of International Application No. PCT/JP02/00110 with an international filing date of Jan. 10, 2002, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a disc cartridge for use to store a disk-shaped signal storage medium such as an optical disc or a magnetic disk therein in a rotatable state. 
     2. Description of the Related Art 
     Various disc cartridges have been proposed as protective cases for disk-shaped signal storage media. 
     For example, Japanese Laid-Open Publication No. 9-153264 discloses a disc cartridge in which a disk-shaped storage medium having a single or double signal recording sides (which will be herein referred to as a “disc” simply) is completely enclosed in a disc storage portion. The disc storage portion is defined inside a cartridge body that is made up of upper and lower halves. The cartridge body includes chucking openings and a head opening. The chucking openings allow the turntable of a spindle motor and a clamper to chuck a disc inserted, while the head opening allows a head to read and/or write a signal from/on the disc. The lower one of the chucking openings is continuous with the head opening. Accordingly, while the operator carries such a cartridge, dust easily enters the inside of the cartridge through these openings and the disc is also easily soiled with finger marks. For that reason, the disc cartridge further includes a shutter for closing these openings up. 
     A disc cartridge having such a structure, however, has the following drawbacks. Firstly, such a disc cartridge cannot be so thin. This is because the disc storage space, defined between the upper and lower halves, should be thick enough to allow a disc drive to accurately read or write a signal (or information) from/onto the disc stored in such a disc cartridge. The reasons why the disc storage space should be relatively thick include the expected flutter or warp of the disc being rotated and an error that may occur in disposing the disc cartridge at a predetermined position inside the disc drive. 
     Secondly, the shutter for closing up these chucking and head openings at the same time cannot be formed at a low cost, thus increasing the overall manufacturing cost of such a disc cartridge. The reason is as follows. Specifically, the lower half of the disc cartridge is provided with an opening for the turntable of the spindle motor and a head opening, while the upper half thereof is provided with another opening for the clamper. Thus, to close these three openings up at a time, the shutter needs to be formed in a U-shape, which is not so cheap to make. 
     Thirdly, the disc stored inside such a disc cartridge is not fixed in many cases, thus possibly causing dust or fine particle deposition and scratching problems. Specifically, although a disc with a metal hub can be attracted and fixed in position via a magnetic force so as not to move inconstantly, an optical disc with no hub, e.g., a CD or a DVD, is normally not fixed, and movable freely, inside the disc cartridge. Accordingly, when the shutter of the disc cartridge is opened inside the disc drive, dust may enter the cartridge through its openings and be deposited on the disc easily. Also, if the disc is shaken so much as to contact with the inner walls of the disc cartridge, the signal recording side of the disc may get scratched or fine particles may be stirred up and deposited on the disc. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to overcome the problems described above, an object of the present invention is to provide a disc cartridge that has a reduced thickness and a simplified, much less expensive shutter for a single-sided disc, in particular. Another object of the present invention is to provide a disc cartridge that can drastically reduce the dust to be deposited on the disc stored therein by getting the disc firmly held inside the disc cartridge and eliminating the inconstant movement of the disc. A third object of the present invention is to provide a disc cartridge of a good design by displaying the label side of the disc stored therein. 
     Briefly stated, the present invention is a disc cartridge comprising a cartridge body. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion has a disc window and a bottom and stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. A shutter is supported to, and movable with respect to, the cartridge body so as to expose or cover at least the head opening. 
     A disc cartridge according to the present invention includes a cartridge body, a shutter and a disk holding member. The cartridge body includes: a disc storage portion that stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed; a chucking opening that is formed on the bottom of the disc storage portion so as to get the disc chucked externally; and a head opening that is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The shutter is supported to, and movable with respect to, the cartridge body so as to expose or cover at least the head opening. The disc holding member holds or releases the disc onto/from the cartridge body. 
     The disc holding member preferably holds the disc by pressing the second side of the disc against the bottom of the disc storage portion. Also, the disc holding member preferably brings at least the outer periphery and its surrounding portion of the second side of the disc into contact with the bottom of the disc storage portion. 
     In one embodiment, the disc cartridge includes a plurality of disc holding members, including the disc holding member. Each of the disc holding members is disposed so that a portion thereof is located on the outer periphery of the disc. At least two of the disc holding members may have the same shape. The disc holding members may be interlocked together to perform an operation of holding or releasing the disc. 
     In one embodiment, the disc holding member is an ellipsoidal ring made of an elastic material. The ring is deformable so as to have an inside diameter that is greater than the diameter of the disc. 
     The disc holding member preferably has a slope that contacts with the disc. Preferably, by disposing the disc holding member on the cartridge body so that the slope of the disc holding member overhangs the outer periphery of the disc, the slope is brought into contact with a side surface or edge of the disc, thereby gripping the disc thereon, pressing the disc against the bottom of the disc storage portion, and holding the disc thereon. 
     In one embodiment of the disc cartridge, the cartridge body includes a pair of positioning holes that engages with positioning pins. The positioning pins are provided for a disc drive to define an insert position when the disc cartridge is loaded into the disk drive. 
     In another embodiment of the disc cartridge, the disc cartridge body includes a concave portion that engages with a convex portion provided for a disk drive and that is used to prevent the disc cartridge from being inserted erroneously. 
     In another embodiment of the disc cartridge, the disc cartridge body includes a concave portion that engages with a convex portion provided for a disk drive when the disc cartridge is inserted into the disk drive. 
     While the disc cartridge is being loaded into, and fixed at the insert position inside, the disk drive, the disc holding member may release the disc that the disc holding member has held thereon. 
     Alternatively, as the positioning pins of the disk drive engage with the positioning holes of the disc cartridge, the disc holding member may release the disc that the disc holding member has held thereon. 
     As another alternative, as the convex portion that is provided for the disk drive to prevent the disc cartridge from being inserted erroneously engages with the concave portion provided for the disc cartridge, the disc holding member may release the disc that the disc holding member has held thereon. 
     As still another alternative, as the convex portion provided for the disk drive engages with the concave portion of the disc cartridge, the disc holding member may release the disc that the disc holding member has held thereon. 
     The disc cartridge may include a pair of disc holding members, each holding the disc thereon at two points. Each of the pair of disc holding members may engage with one of the pair of positioning pins provided for the disk drive, thereby performing the operation of holding or releasing the disc at the two points of the disc holding member substantially simultaneously. 
     The shutter may include a member that engages with the disc holding member so that the disc having been held is released as the shutter is going to be closed or opened. 
     The disc holding member may include a deformable elastic portion that has been molded so as to form an integral part of the cartridge body. The disc may be either held or released by deforming the elastic portion. 
     In one embodiment, the disc cartridge further includes a locking mechanism for fixing and supporting disc holding member onto the cartridge body while the disc holding member is holding the disc thereon. 
     In one embodiment of the disc cartridge, one of the disc holding members includes a locking mechanism for fixing and supporting the disc holding members onto the cartridge body while the disc holding members are holding the disc thereon. 
     In one embodiment of the disc cartridge, the disc holding member further includes a stopper portion for preventing the disc from dropping down from the storage portion of the disc cartridge when the disc holding member releases the disc. 
     In one embodiment, the head opening reaches a side surface of the cartridge body. 
     In one embodiment, the disc cartridge includes a protective layer for preventing the disc from getting scratched on the bottom of the disc storage portion that contacts with the second side of the disc. The protective layer is preferably selected from the group consisting of an anti-scratching nonwoven fabric, a dustproof nonwoven fabric, an anti-scratching coating layer and a dustproof coating layer. 
     In one embodiment, the disc cartridge further includes a brush or a dust wiping member on one side of the shutter that moves across the head opening when the shutter is opened or closed. 
     In one embodiment, the dirt of the disc is removed by rotating the disc while the disc is in contact with the protective layer that is provided on the bottom of the disc storage portion. 
     In one embodiment, the disc cartridge further includes a disc holding/interlocking member, which is stored inside the disc storage portion to synchronize opening or closing of the shutter with the holding or releasing operation by the disk holding member. 
     In one embodiment, the shutter is substantially in a fan shape and is held so as to rotate and slide around the chucking opening, and opening or closing of the shutter is synchronized with the holding or releasing operation by the disk holding member. 
     The disk holding member preferably holds the disc thereon by pressing at least the outer periphery and its surrounding portion of the second side of the disc against the bottom of the disc storage portion, the disc holding/interlocking member or the shutter. 
     In one embodiment, the disc cartridge includes a plurality of disc holding members, including the disc holding member. Each of the disc holding members is disposed so that a portion thereof is located on the outer periphery of the disc. 
     The disc holding member preferably has a slope that contacts with the disc. Preferably, by disposing the disc holding member on the cartridge body so that the slope of the disc holding member overhangs the outer periphery of the disc, the slope is brought into contact with a side surface or edge of the disc, thereby gripping the disc thereon, pressing the disc against the bottom of the disc storage portion and holding the disc thereon. 
     In one embodiment, the disc holding member includes an elastic portion that has been molded so as to form an integral part of the cartridge body and that is deformable in such a manner as to either hold or release the disc. 
     In one embodiment, the disc holding member further includes a stopper portion for preventing the disc from dropping down from the storage portion of the disc cartridge when the disc holding member releases the disc. 
     In one embodiment, when the shutter opens to expose the head opening, the disk holding member releases the disc. 
     In one embodiment, the disc holding/interlocking member is substantially in a fan shape. 
     In one embodiment, the disc storage portion includes: a first inner surface to be the bottom of the disc storage portion; and a second inner surface that is substantially in a cylindrical shape and that surrounds the outer periphery of the disc when the disc is stored in the disc storage portion. 
     In one embodiment, the shutter is provided outside of the disc cartridge. 
     In one embodiment, the shutter is provided on the bottom of the disc storage portion. 
     In one embodiment, the shutter exposes or covers the chucking opening. 
     In one embodiment, the number of the shutters is one. 
     Another disc cartridge according to the present invention includes a cartridge body and a shutter. The cartridge body includes: a disc storage portion that stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion; a chucking opening that is formed on the bottom of the disc storage portion so as to get the disc chucked externally; and a head opening that is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The shutter is supported to, and movable with respect to, the cartridge body between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking opening and the head opening. 
     Still another disc cartridge according to the present invention includes a cartridge body, a shutter and a disk holding portion. The cartridge body includes: a disc storage portion that stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion; a chucking opening that is formed on the bottom of the disc storage portion so as to get the disc chucked externally; and a head opening that is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The shutter is supported to, and movable with respect to, the cartridge body so as to expose or cover the chucking opening and the head opening. The disc holding portion fixes the disc onto the shutter or the cartridge body when the shutter covers the chucking opening and the head opening synchronously with opening or closing of the shutter. 
     In one embodiment, the disc storage portion includes: a first inner surface to be the bottom of the disc storage portion; a second inner surface that is substantially in a cylindrical shape and that surrounds the outer periphery of the disc when the disc is stored in the disc storage portion; and a disc window through which the disc is inserted or removed. The disc storage portion stores the disc therein so that one side of the disc is exposed inside the disc window. 
     In one embodiment of the disc cartridge, the shutter includes a disc holding portion for fixing the disc onto the shutter when the shutter covers the chucking opening and the head opening synchronously with opening or closing of the shutter. 
     In one embodiment, the disk holding portion is provided as a portion of the shutter. 
     In one embodiment, the disc cartridge includes multiple disk holding portions, which include the disk holding portion and which are disposed on the shutter so as to hold the outer periphery and its surrounding portion of the disc. 
     In one embodiment, the disc is brought into plane contact with the shutter by the disk holding portion. 
     In one embodiment, the disk holding portion has a downwardly tapered slope, grips the disc thereon by bringing the slope into contact with a side surface or an edge of the disc, and holds the disc with respect to the cartridge body by bringing the disc into plane contact with the shutter. 
     In one embodiment, the disc cartridge further includes a locking mechanism for fixing and supporting the shutter onto the cartridge body while the shutter covers the chucking opening and the head opening. The second inner surface is preferably partially notched so as not to interfere with the operation of the shutter. 
     In one embodiment of the disc cartridge, the cartridge body includes a shutter storage portion that stores a portion of the shutter therein while the shutter exposes the chucking opening and the head opening. 
     In one embodiment, the disc cartridge further includes multiple stopper portions that protrude toward the disc window to prevent the disc from dropping down through the disc window. The stopper portions may move in a thickness direction of the disc cartridge as the shutter is going to be opened or closed. 
     In one embodiment, the disc cartridge may include a plurality of shutters, including the shutter. The plurality of shutters may cooperate with each other to expose or cover the chucking opening and the head opening. 
     In one embodiment, one of the shutters is provided with a locking mechanism that fixes the shutters onto the cartridge body while the shutters are covering the chucking opening and the head opening. 
     In one embodiment, the shutters cover the chucking opening and the head opening by partially overlapping with each other in a thickness direction of the shutters. 
     In one embodiment, the disc cartridge includes an erroneous insertion preventing mechanism for the disc cartridge. 
     In one embodiment, the head opening reaches a side surface of the cartridge body. 
     In one embodiment, the shutters rotate on multiple rotation shafts that are provided on the disc cartridge body. The rotation shafts are preferably provided in respective portions of the disc cartridge body other than the disc storage portion. Also, the head opening may reach a side surface of the cartridge body, and the rotation shafts may be provided near another side surface thereof that is opposed to the former side surface. 
     In one embodiment, the shutters include interlocking portions that open or close the shutters while being interlocked with each other. The interlocking portions may be cam-shaped or gear-shaped portions that are provided for the respective shutters. Alternatively, the interlocking portions may also be belts or links. 
     In one embodiment, the disc cartridge further includes an elastic member that applies a force in such a manner as to keep the shutters opened or closed. The elastic member is preferably provided in a portion of the disc cartridge body other than the disc storage portion. The elastic member may have been molded so as to form an integral part of the shutter. 
     In one embodiment, the stopper members may be removable and may have been molded so as to form integral parts of the cartridge body. 
     In one embodiment, the stopper members are provided so as to be removable from the cartridge body. 
     In one embodiment, the disc cartridge includes a protective layer for preventing the disc from getting scratched on a portion of the shutter that contacts with the second side of the disc. The protective layer is preferably selected from the group consisting of an anti-scratching nonwoven fabric, a dustproof nonwoven fabric, an anti-scratching coating layer and a dustproof coating layer. 
     In one embodiment, the dirt of the disc is removed by rotating the disc while the disc is in plane contact with the shutter. Alternatively, the dirt of the disc may also be removed by the opening or closing operation that is performed by the shutter to expose or cover the chucking opening and the head opening. 
     In one embodiment, the erroneous insertion preventing mechanism includes convex portions or concave portions that are provided on outer side surfaces of the cartridge body so as to be asymmetrically disposed in a direction in which the disc cartridge is inserted into an external apparatus. 
     In one embodiment, the locking mechanism includes: a locking hole that is formed through the disc cartridge body; and a locking protrusion portion that is provided for the shutter so as to engage with the locking hole when the shutter is located at such a position as to cover the chucking opening and the head opening. 
     In one embodiment, the locking protrusion portion is provided for the shutter by way of an elastic member and the elastic member applies a force to the locking protrusion portion toward the locking hole and makes the locking protrusion portion engage with the locking hole. 
     In one embodiment, the locking mechanism includes: a locking hole that is formed through the disc cartridge body; a locking protrusion portion that is provided so as to engage with the locking hole when the shutter is located at such a position as to cover the chucking opening and the head opening; a locking lever provided for the disc cartridge body; a first convex portion or first concave portion that is formed on the locking lever; and a second concave portion or second convex portion that is formed on the shutter so as to engage with the first convex portion or first concave portion at the covering position. 
     The locking lever may be provided for the disc cartridge body by way of an elastic member. The elastic member may apply a force to the locking protrusion portion toward the locking hole to make the locking protrusion portion engage with the locking hole. The elastic member may also apply a force to the first convex portion or first concave portion toward the second concave portion or second convex portion to make the first convex portion or first concave portion engage with the second concave portion or second convex portion. Also, the locking protrusion portion and the elastic member may have been molded so as to form integral parts of the shutter. Alternatively, the locking lever and the elastic member may have been molded so as to form integral parts of the disc cartridge body. 
     In one embodiment, the shutter includes a convex portion that is provided for the shutter so as to protrude into a center hole of the disc while the shutter is keeping plane contact with the disc and covering the chucking opening and the head opening. As the shutter is going to be opened, the convex portion lifts the disc in a thickness direction of the cartridge while contacting with the lower surface of the disc, thereby getting the disc and the shutter out of plane contact from each other. 
     In one embodiment, the disc cartridge includes a plurality of shutters, including the shutter. Each of the shutters includes a convex portion that is provided for the shutter so as to protrude into a center hole of the disc while the shutters are keeping plane contact with the disc and covering the chucking opening and the head opening. As the shutters are going to be opened, the convex portions lift the disc in a thickness direction of the cartridge while contacting with the lower surface of the disc, thereby getting the disc and the shutters out of plane contact from each other. 
     The convex portion may have a shape that is selected from the group consisting of a spherical shape, a conical shape, a ring shape and a shape made up of multiple spheres. 
     In one embodiment, the stopper members form integral parts of the shutter. The stopper members may be formed integrally with the shutter by way of flexible members or elastic members. Each of the stopper members may include a convex portion or a concave portion. An inner sidewall or an inner upper wall of the cartridge body may include a guide concave portion or a guide convex portion that engages with the convex portion or the concave portion of the stopper member. The stopper members may move in the thickness direction of the disc cartridge as the shutter is going to be opened or closed. 
     In one embodiment, the stopper members form integral parts of the cartridge body. The stopper members may be formed integrally with the cartridge body by way of elastic members. Each of the stopper members may be an elastic member that is obtained by separating a portion of the cartridge body via a slit. Each of the stopper members may include a first convex portion or a first sloped portion while the shutter may include a second sloped portion or a second convex portion. The first convex portion and the second sloped portion or the first sloped portion and the second convex portion may contact with each other. 
     Also, when the shutter exposes the chucking opening and the head opening, the first convex portion and the second sloped portion or the first sloped portion and the second convex portion may contact with each other. 
     A concave portion, which engages with the second convex portion or the first convex portion, may be provided near the first sloped portion or the second sloped portion. 
     In one embodiment, the stopper members hold the disc onto the cartridge body by pressing the disc in the thickness direction thereof and bringing the disc into plane contact with the shutter while the shutter covers the chucking opening and the head opening. 
     In one embodiment, an opening/closing lever for use to open or close the shutters and a locking mechanism for use to fix and support the shutters to the cartridge body when the shutters are located in such a position as to cover the chucking opening and the head opening are provided for two different ones of the shutters. 
     Still another disc cartridge according to the present invention includes a cartridge body, a shutter and a disc holding portion. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The shutter is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings, and defines a hole in a region corresponding to a center hole of the disc while the shutter is closed. The disc holding portion is provided for the shutter, presses the disc against the shutter, and holds the disc thereon while the chucking and head openings are covered with the shutter. 
     In one embodiment, the hole of the shutter has a diameter that is approximately equal to that of the center hole of the disc. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a shutter, a disc holding portion and a rim. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The shutter is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portion is provided for the shutter, presses the disc against the shutter, and holds the disc thereon while the chucking and head openings are covered with the shutter. The rim extends from an inner side surface of the disc storage portion toward the center of the disc and contacts with an outer edge portion of the disc while the shutter is closed. 
     In one embodiment, the shutter defines a hole in an area corresponding to a center hole of the disc while the shutter is closed. The rim may contact with the second side of the disc. The cartridge body may have a gap between the rim and the inner lower surface of the disc storage portion so that a portion of the shutter is stored in the gap while the chucking and head openings are exposed by the shutter. 
     In one embodiment, the disc cartridge further includes a convex portion around the hole of the shutter. The convex portion contacts with the second side of the disc while the chucking and head openings are covered with the shutter. 
     In one embodiment, the shutter includes a convex portion that closes a gap between the second side of the disc and the shutter while the shutter is closed. The convex portion may be located closer to the center of the disc storage portion than the rim is while the chucking and head openings are exposed by the shutter. The convex portion may be a protective layer that prevents the disc from getting scratched. 
     In one embodiment, a protective layer is provided on the rim to prevent the disc from getting scratched. The protective layer may be selected from the group consisting of an anti-scratching nonwoven fabric, a dustproof nonwoven fabric, an anti-scratching coating layer and a dustproof coating layer. 
     In one embodiment, the convex portion forms an integral part of the shutter. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters and a disc holding portion. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portion is provided for the shutters, presses the disc against the shutters, and holds the disc thereon while the chucking and head openings are covered with the shutters. The head opening reaches a side surface of the cartridge body. An operating portion for use to open and close the shutters is provided for the shutters and is located inside the head opening. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters and a disc holding portion. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portion is provided for the shutters, presses the disc against the shutters, and holds the disc thereon while the chucking and head openings are covered with the shutters. The shutters have first and second pairs of contact surfaces. Each pair of contact surfaces contacts with each other. The first and second pairs are not aligned with each other. 
     In one embodiment, the contact surfaces of each of the first and second pairs are sloped, and overlap with each other, in a thickness direction of the disc. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters and a number of disc holding portions. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. At least one of the disc holding portions is movable toward the center of the disc storage portion with respect to one of the shutters. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters, a number of disc holding portions and a number of stopper members. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters. Each of the disc holding portions has a downwardly tapered slope that presses the disc against the shutters and holds the disc thereon while the chucking and head openings are covered with the shutters. Each of the stopper members has a disc contact surface that prevents the disc from dropping down from the disc storage portion and provided for the cartridge body to protrude over the disc. A portion of the slope of each of the disc holding portions is located over the contact surface of each of the stopper members. 
     In one embodiment, the pair of shutters is locked together while closed. 
     In one embodiment, the disc cartridge further includes a shutter contact portion that regulates the positions of the shutters being closed. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters and a number of disc holding portions. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. Each of the disc holding portions includes a first portion with a first height and a second portion with a second height that is lower than the first height. An upper surface of the cartridge body has a recessed portion to receive the top of the first portion of each disc holding portion that moves as the shutters are going to be opened or closed. The recessed portion is thinner than another portion of the upper surface of the cartridge body under which the second portion of the disc holding portion moves. 
     In one embodiment, as the shutters are going to be closed, the first portion contacts with the disc earlier than the second portion. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters, a number of disc holding portions and a stopper member. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The disc storage portion also has a disc window through which the disc is inserted or removed into/from the disc storage portion. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. The stopper member is secured to the cartridge body so as to be movable between a state of protruding into the disc window and a state of not protruding into the disc window. 
     In one embodiment, the stopper member is movable on a plane that is parallel to the upper surface of the cartridge body. The stopper member may be rotatable on the upper surface of the cartridge body. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters, a number of disc holding portions and a disc receiving portion. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. The disc receiving portion is provided along the inner circumference of an inner lower surface of the disc storage portion so as to contact with an outer edge portion of the second side of the disc that is being held while the shutters are closed. 
     In one embodiment, at least a part of the disc receiving portion is parallel to the inner lower surface of the disc storage portion and contacts with the other side of the disc. The disc receiving portion may be a taper that is provided between an inner side surface and the inner lower surface of the disc storage portion. While the shutters are closed and the disc is held, the outer edge of the disc may be in contact with the disc receiving portion. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters and a number of disc holding portions. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. An inner lower surface of the disc storage portion includes first regions, through which respective bottoms of the disc holding portions pass while the shutters are going to be opened or closed. The first regions are recessed. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters and a number of disc holding portions. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. An inner lower surface of the disc storage portion includes second regions that are located in the vicinity of the outer periphery of the shutters while the shutters are closed. The second regions are recessed. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters and a number of disc holding portions. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. An inner lower surface of the disc storage portion includes third regions that are located around the chucking and head openings and/or near an inner side surface of the disc storage portion. The third regions are recessed. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a shutter, a number of disc holding portions and first and second operating portions. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The shutter is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutter, press the disc against the shutter and hold the disc thereon while the chucking and head openings are covered with the shutter. The first and second operating portions are used to open and close the shutter. 
     In one embodiment, the first and second operating portions are respectively provided for first and second side surfaces of the cartridge body. The first and second side surfaces may be adjacent to each other. The first operating portion may be a protrusion that is connected to the shutter, and the shutter may be opened or closed by sliding the first operating portion along a portion of the first side surface. Also, the second operating portion may be a rotational member that is engaged with the shutter. Then, the shutter may be opened or closed by rotating the second operating portion. Alternatively, the second operating portion may also be a sliding link member that is engaged with the shutter. Then, the shutter may be opened or closed by sliding the second operating portion along the second side surface. 
     In one example, the second operating portion may also be a belt member that is connected to the shutter. Then, the shutter may be opened or closed by sliding the second operating portion along the second side surface. 
     In one example, the disc cartridge includes a pair of shutters, including the shutter. The first and second operating portions may be connected to, or engaged with, the pair of shutters, respectively. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters, a number of disc holding portions and a rotation stopper member. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. The rotation stopper member is provided for at least one of the disc holding portions to prevent the disc from rotating while the shutters are closed. 
     In one example, the rotation stopper member is made of a material having a large coefficient of friction and is provided for the at least one of the disc holding portions so as to contact with the disc while the shutters are closed. 
     In one example, the rotation stopper member is made of rubber. 
     Yet another disc cartridge according to the present invention includes a cartridge body, a pair of shutters, a number of disc holding portions and at least one stopper member. The cartridge body includes a disc storage portion, a chucking opening and a head opening. The disc storage portion has a disc window and stores a disc, having first and second sides, therein so that the disc is rotatable in the disc storage portion and that the first side of the disc is exposed inside the disc disc window. The chucking opening is formed on the bottom of the disc storage portion so as to get the disc chucked externally. The head opening is also formed on the bottom of the disc storage portion so as to allow a head, which reads and/or writes a signal from/on the second side of the disc, to access the second side of the disc. The pair of shutters is supported, and movable with respect to the cartridge body, between the second side of the disc and the bottom of the disc storage portion so as to expose or cover the chucking and head openings. The disc holding portions are provided for the shutters, press the disc against the shutters, and hold the disc thereon while the chucking and head openings are covered with the shutters. The at least one stopper member is provided for the cartridge body so as to protrude at least partially into the disc window. The head opening reaches a side surface of the cartridge body. An operating portion for use to open and close the shutters is provided for the shutters and is located inside the head opening. 
     In one example, the shutters have first and second pairs of contact surfaces, each pair contacting with each other. The first and second pairs are not aligned with each other. The contact surfaces of each of the first and second pairs may be sloped, and overlap with each other, in a thickness direction of the disc. In the first pair of contact surfaces, the contact surface of one of the two shutters may be located over the contact surface of the other shutter. In the second pair of contact surfaces on the other hand, the contact surface of the one shutter may be located under the contact surface of the other shutter. While closed, the shutters may define a hole in a region corresponding to a center hole of the disc. Specifically, the hole defined by the shutters may have a diameter that is approximately equal to that of the center hole of the disc. 
     In one example, the disc holding portions are provided at two ends of the shutters, and each of the disc holding portions has a downwardly tapered slope. At least one of the disc holding portions may be provided so as to be movable toward the center of the disc. 
     In one example, each of the disc holding portions includes a first portion with a first height and a second portion with a second height that is lower than the first height. An upper surface of the cartridge body has a recessed portion to receive the top of the first portion of each of the disc holding portions that moves as the shutters are going to be opened or closed. The recessed portion is thinner than another portion of the upper surface of the cartridge body under which the second portion of each of the disc holding portions moves. 
     As the shutters are going to be closed, the first portion may contact with the disc earlier than the second portion. 
     In one example, the stopper member has a contact surface that contacts with the disc  100 . A portion of the slope of at least one of the disc holding portions is located over the contact surface of the stopper member. 
     In one example, the shutters rotate on a pair of rotation shafts that are provided for the disc cartridge body. The shutters may include interlocking portions that interlock with each other to open or close the shutters. The disc cartridge may further include an elastic member that applies a force to the shutters to keep the shutters closed. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
       In the drawings: 
         FIG. 1  is a perspective view illustrating an overall configuration for a disc cartridge according to a first embodiment of the present invention. 
         FIG. 2  is a perspective view of the disc cartridge shown in  FIG. 1  as viewed from below it. 
         FIG. 3  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 1 . 
         FIG. 4  is a cross-sectional view illustrating a disc holding member and a surrounding portion of the disc cartridge shown in  FIG. 1 . 
         FIG. 5  is a cross-sectional view illustrating another disc holding member and a surrounding portion of the disc cartridge shown in  FIG. 1 . 
         FIG. 6  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 1  in which its shutter is opened and positioning pins have been inserted. 
         FIG. 7  is a cross-sectional view illustrating the disc holding member and its surrounding portion shown in  FIG. 6 . 
         FIG. 8  is a perspective view illustrating the disc holding member and its surrounding portion shown in  FIG. 6 . 
         FIG. 9  is a plan view illustrating an overall configuration for a disc cartridge according to a second embodiment of the present invention. 
         FIG. 10  is a plan view illustrating a state of the disc cartridge shown in  FIG. 9  in which the disc has been released. 
         FIG. 11  is a plan view illustrating an overall configuration for a disc cartridge according to a third embodiment of the present invention. 
         FIG. 12  is a plan view illustrating a state of the disc cartridge shown in  FIG. 11  in which the disc has been released. 
         FIG. 13  is a plan view illustrating an overall configuration for a disc cartridge according to a fourth embodiment of the present invention. 
         FIG. 14  is a plan view illustrating a state of the disc cartridge shown in  FIG. 13  in which the disc has been released. 
         FIG. 15  is a plan view illustrating an overall configuration for a disc cartridge according to a fifth embodiment of the present invention in a state where its shutter is closed. 
         FIG. 16  is a cross-sectional view of a disc holding member of the disc cartridge shown in  FIG. 15 . 
         FIG. 17  is a plan view illustrating an overall configuration for the disc cartridge shown in  FIG. 15  in a state where its shutter is opened. 
         FIG. 18  is a cross-sectional view of the disc holding member of the disc cartridge shown in  FIG. 17 . 
         FIG. 19  is a plan view illustrating an overall configuration for a disc cartridge according to a sixth embodiment of the present invention in a state where its shutter is closed. 
         FIG. 20  is a plan view illustrating an overall configuration for the disc cartridge shown in  FIG. 19  in a state where its shutter is opened. 
         FIG. 21  is a plan view illustrating an overall configuration for a disc cartridge according to a seventh embodiment of the present invention in a state where its shutter is closed. 
         FIG. 22  is a plan view illustrating an overall configuration for the disc cartridge shown in  FIG. 21  in a state where its shutter is opened. 
         FIG. 23  is a perspective view illustrating an overall configuration for a disc cartridge according to an eighth embodiment. 
         FIG. 24  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 23 . 
         FIG. 25  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 23  in which its shutters are closed with its cartridge upper shell and the disc removed. 
         FIG. 26  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 23  in which its shutters are opened with its cartridge upper shell and the disc removed. 
         FIG. 27  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 23  in which its shutters are closed with the disc removed. 
         FIG. 28  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 23  in which its shutters are opened with the disc removed. 
         FIG. 29  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 23  that passes the center of the disc. 
         FIG. 30  is a cross-sectional view illustrating a portion of the shutter of the disc cartridge shown in  FIG. 23 . 
         FIG. 31  is a partial plan view illustrating an operating portion and its surrounding portion of the disc cartridge shown in  FIG. 23 . 
         FIG. 32  is a perspective view illustrating a stopper member of the disc cartridge shown in  FIG. 23 . 
         FIG. 33  is a front view of the disc cartridge shown in  FIG. 23  as viewed from a direction in which the cartridge is inserted into a drive. 
         FIG. 34  is a perspective view illustrating an overall configuration for a disc cartridge according to a ninth embodiment of the present invention. 
         FIG. 35  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 34 . 
         FIG. 36  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 34  in which its shutters are closed with the disc removed. 
         FIG. 37  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 34  in which its shutters are opened with the disc removed. 
         FIG. 38  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 34  that passes the center of the disc to show a state where its shutters are closed. 
         FIG. 39  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 34  that passes the center of the disc to show a state where its shutters are opened. 
         FIG. 40  is a cross-sectional view illustrating a disc outer peripheral cross section of the disc cartridge shown in  FIG. 34  that passes the center of the disc to show a state where its shutters are closed. 
         FIG. 41  is a cross-sectional view illustrating a disc outer peripheral cross section of the disc cartridge shown in  FIG. 34  that passes the center of the disc to show a state where its shutters are opened. 
         FIG. 42  is a perspective view illustrating an overall configuration for a disc cartridge according to a tenth embodiment of the present invention. 
         FIG. 43  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 42 . 
         FIG. 44  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 42  in which its shutters are closed with the disc removed. 
         FIG. 45  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 42  in which its shutters are opened with the disc removed. 
         FIG. 46  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 42  that passes the center of the disc to show a state where its shutters are closed. 
         FIG. 47  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 42  that passes the center of the disc to show a state where its shutters are opened. 
         FIG. 48  is a cross-sectional view illustrating a disc outer peripheral cross section of the disc cartridge shown in  FIG. 42  that passes the center of the disc to show a state where its shutters are closed. 
         FIG. 49  is a cross-sectional view illustrating a disc outer peripheral cross section of the disc cartridge shown in  FIG. 42  that passes the center of the disc to show a state where its shutters are opened. 
         FIG. 50  is a perspective view illustrating an overall configuration for a disc cartridge according to an eleventh embodiment of the present invention. 
         FIG. 51  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 50 . 
         FIG. 52  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 50  in which its shutters are closed with the disc removed. 
         FIG. 53  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 50  in which its shutters are opened with the disc removed. 
         FIG. 54  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 50  that passes the center of the disc to show a state where its shutters are closed. 
         FIG. 55  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 50  that passes the center of the disc to show a state where its shutters are opened. 
         FIG. 56  is a cross-sectional view illustrating a portion of the shutter of the disc cartridge shown in  FIG. 50 . 
         FIG. 57  is a partial plan view illustrating an operating portion and its surrounding portion of the disc cartridge shown in  FIG. 50 . 
         FIG. 58  is a perspective view illustrating a state of a disc cartridge according to a twelfth embodiment of the present invention in which its shutters are closed with the disc removed. 
         FIG. 59  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 58  that passes the center of the disc to show a state where its shutters are closed. 
         FIG. 60  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 58  in which its shutters are opened with the disc removed. 
         FIG. 61  is a partial cross-sectional view illustrating a cross section of the disc cartridge shown in  FIG. 58  that passes the center of the disc to show a state where its shutters are opened. 
         FIG. 62  is a perspective view illustrating a modified example of the disc cartridge shown in  FIG. 58  to show a state where its shutters are closed with the disc removed. 
         FIG. 63  is a perspective view illustrating a state of the disc cartridge shown in  FIG. 61  in which its shutters are opened with the disc removed. 
         FIG. 64  is a perspective view illustrating an overall configuration for a disc cartridge according to a thirteenth embodiment of the present invention. 
         FIG. 65  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 64 . 
         FIG. 66  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 64  in which its shutters are closed. 
         FIG. 67  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 64  in which its shutters are opened. 
         FIG. 68  is a detailed perspective view of a shutter locking portion. 
         FIG. 69  is a detailed cross-sectional view of a disc holding portion of the shutter. 
         FIG. 70  is a cross-sectional view illustrating the shapes of a pair of contact surfaces of the two shutters. 
         FIG. 71  is a cross-sectional view illustrating the shapes of another pair of contact surfaces of the two shutters. 
         FIG. 72  is a perspective view illustrating an overall configuration for a disc cartridge according to a fourteenth embodiment of the present invention. 
         FIG. 73  is a perspective view illustrating the shutters of the disc cartridge shown in  FIG. 72 . 
         FIG. 74  is an enlarged perspective view illustrating the disc holding portions and their surrounding members of the disc cartridge shown in  FIG. 72 . 
         FIG. 75  is an enlarged perspective view illustrating the disc holding portion and its surrounding portion of the disc cartridge shown in  FIG. 72 . 
         FIG. 76  is an enlarged cross-sectional view illustrating the disc holding portion and its surrounding members of the disc cartridge shown in  FIG. 72 . 
         FIG. 77  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 72  in which its shutters are closed. 
         FIG. 78  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 72  in which its shutters are opened. 
         FIG. 79  is a cross-sectional view taken along the line B—B shown in  FIG. 78 . 
         FIG. 80  is a cross-sectional view taken along the line C—C shown in  FIG. 78 . 
         FIG. 81  is a cross-sectional view taken along the line A—A shown in  FIG. 77 . 
         FIG. 82  is a cross-sectional view illustrating a modified example of the disc receiving portion. 
         FIG. 83  is an exploded perspective view illustrating an exploded state of a disc cartridge according to a fifteenth embodiment of the present invention. 
         FIG. 84  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 83  in which its shutters are closed. 
         FIG. 85  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 83  in which its shutters are opened. 
         FIG. 86  is a cross-sectional view taken along the line D—D shown in  FIG. 84 . 
         FIG. 87  is a cross-sectional view taken along the line E—E shown in  FIG. 85 . 
         FIG. 88  is a perspective view illustrating an overall configuration for a disc cartridge according to a sixteenth embodiment of the present invention. 
         FIG. 89  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 88 . 
         FIG. 90  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 88  in which its shutters are closed. 
         FIG. 91  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 88  in which its shutters are opened. 
         FIG. 92  is a schematic plan view illustrating a modified example of the disc cartridge shown in  FIG. 88  to show a state where the shutters of the disc cartridge are closed. 
         FIG. 93  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 92  in which its shutters are opened. 
         FIG. 94  is a perspective view illustrating an overall configuration for a disc cartridge according to a seventeenth embodiment of the present invention. 
         FIG. 95  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 94 . 
         FIG. 96  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 94  in which its shutters are closed. 
         FIG. 97  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 94  in which its shutters are opened. 
         FIG. 98  is a perspective view illustrating an overall configuration for a disc cartridge according to an eighteenth embodiment of the present invention. 
         FIG. 99  is an exploded perspective view illustrating an exploded state of the disc cartridge shown in  FIG. 98 . 
         FIG. 100  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 98  in which its shutters are closed. 
         FIG. 101  is a schematic plan view illustrating a state of the disc cartridge shown in  FIG. 98  in which its shutters are opened. 
         FIG. 102  is an exploded perspective view illustrating an exploded state of a disc cartridge according to a nineteenth embodiment of the present invention. 
         FIG. 103  is an enlarged cross-sectional view illustrating a disc holding portion and its surrounding members of the disc cartridge shown in  FIG. 102 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiment 1 
     Hereinafter, a disc cartridge  301  according to a first embodiment of the present invention will be described with reference to  FIGS. 1 ,  2  and  3 .  FIG. 1  is a perspective view illustrating an overall configuration of the disc cartridge  301 , including a disc  100  stored, as viewed from above the cartridge  301 .  FIG. 2  is a perspective view of the disc cartridge  301  as viewed from below the cartridge  301 .  FIG. 3  is an exploded perspective view illustrating respective parts of the disc cartridge  301 . 
     The disc  100  includes first and second sides. The first side of the disc  100 , on which its label, for example, is normally printed, is illustrated in  FIG. 1 , while the second side of the disc  100 , i.e., the signal recording side  100 A, is illustrated as the back surface in  FIG. 3 . 
     As shown in  FIG. 1 , the disc cartridge  301  includes a cartridge lower shell  11 , a cartridge upper shell  12 , disc holding members  13 ,  14  and a shutter  21 . 
     As shown in  FIG. 3 , the cartridge lower shell  11  includes a chucking opening  11   c  and a head opening  11   h . The chucking opening  11   c  is provided to allow a chucking member (e.g., a spindle motor for rotating the disc  100 ) to enter the disc cartridge  301  externally. The head opening  11   h  is provided to allow a head, which reads and/or writes a signal from/on the signal recording side  100 A of the disc  100 , to enter the disc cartridge  301  and access the signal recording side  100 A. The cartridge lower shell  11  also includes two positioning holes  11   w , which engage with cartridge positioning pins  210  of a disc drive, thereby defining the position of the disc cartridge  301  with respect to the disc drive. The cartridge lower shell  11  faces the signal recording side  100 A of the disc  100 . 
     The cartridge upper shell  12  includes a circular disc window  12   w , through which the disc  100  can be introduced and removed into/from the disc cartridge  301  and which expands over the entire projection area of the disc  100  to expose the upper surface of the disc  100 . The cartridge upper and lower shells  12  and  11  are adhered or welded together at their outer periphery, thereby forming a cartridge body  10 . 
     A disc storage portion  10   d  for storing the disc  100  therein (see  FIG. 1 ) is defined by a first inner surface  11   u  of the cartridge lower shell  11  and a second inner surface  12   i  of the cartridge upper shell  12 . The first inner surface  11   u  is opposed to the signal recording side  100 A of the disc  100 , while the second inner surface  12   i  has a substantially cylindrical shape and defines the disc window  12   w  inside. That is to say, the first inner surface  11   u  becomes the bottom of the disc storage portion  10   d . The first inner surface  11   u  of the cartridge lower shell  11  is provided with a protective layer  11   p  for the purpose of preventing the disc  100  from getting scratched or any dust from reaching the signal recording side  100 A. 
     The protective layer  11   p  may be appropriately selected from the group consisting of an anti-scratching nonwoven fabric, a dustproof nonwoven fabric, an anti-scratching coating layer and a dustproof coating layer. In this embodiment, a sheet of a dustproof nonwoven fabric is adhered or ultrasonic welded as the protective layer  11   p.    
     In the disc storage portion  10   d , a gap, which is wide enough to allow the disc  100  to rotate freely, is provided between the second inner surface  12   i  and the disc  100 . Also, the top of the disc storage portion  10   d  is the disc window  12   w  so that the disc  100  stored in the disc storage portion  10   d  has one side thereof exposed inside the disc window  12   w.    
     As shown in  FIG. 3 , the disc cartridge  301  includes two disc holding members  13  of the same shape. Each of the disc holding members  13  includes a pair of elastic portions  13   d  and a hole portion  13   w  that runs obliquely through the disc holding member  13 . When the elastic portions  13   d  of the disc holding members  13  are sandwiched between the cartridge upper and lower shells  12  and  11 , an elastic force is applied to the respective ends of the disc holding members  13  in the direction indicated by the arrows  13 B in  FIG. 3 . As a result, the disc  100  is pressed against the first inner surface  11   u . Also, these two disc holding members  13  are disposed so that the hole portions  13   w  thereof are located substantially over the positioning holes  11   w.    
     The disc holding member  14  includes a rotation shaft  14   s  and two elastic portions  14   d . The disc holding member  14  is secured to the cartridge body  10  so as to rotate on the rotation shaft  14   s . When the elastic portions  14   d  are sandwiched between the cartridge upper and lower shells  12  and  11 , an elastic force is applied to the respective ends of the disc holding member  14  in the direction indicated by the arrow  14 B. As a result, the disc  100  is pressed against the first inner surface  11   u.    
     The shutter  21  is externally fitted with the cartridge lower shell  11  so as to face the signal recording side  100 A of the disc  100 . As shown in  FIGS. 1 and 2 , when the shutter is moved in the direction indicated by the arrow  21 A or  21 B, the chucking opening  11   c  and the head opening  11   h  are exposed or covered. A shutter spring  31  is extended between the shutter  21  and the cartridge body  10  to apply an elastic force to the shutter  21  in such a direction as to close the shutter  21 . 
     As shown in  FIG. 2 , a label plane or concave portion  10   f , on which the contents that have been written on the disc  100  being stored can be noted down, is provided on the surface of the cartridge body  10  (i.e., the cartridge lower shell  11 ). Also, a pair of concave portions  10   c , provided on the right- and left-hand sides of the cartridge body  10 , may be used as either pull-in notches or positioning recesses when the disc cartridge  301  is pulled in and loaded into a disk drive or when the disc cartridge  301  is stored in a changer. Another concave portion  10   g , provided on just one side, has such a shape as to prevent erroneous insertion of the disc cartridge  301 . That is to say, this concave portion  10   g  is just fitted with a convex portion provided for the disc drive only when the disc cartridge  301  is inserted in the correct direction. Suppose the disc cartridge  301  is being inserted into the disc drive upside down or the wrong way round by mistake. In that case, these concave and convex portions are never fitted with each other and the disc cartridge  301  cannot be inserted thereto correctly. In this manner, the erroneous insertion can be prevented. 
     Next, it will be described in further detail with reference to  FIGS. 4 and 5  how the disc holding members  13  and  14  hold the disc  100  thereon.  FIG. 4  is a cross-sectional view of the disc holding member  13  in a state where the disc  100  has been mounted thereon as shown in  FIGS. 1 through 3 , while  FIG. 5  is a cross-sectional view of the disc holding member  14  in the state where the disc  100  has been mounted thereon.  FIGS. 4 and 5  are both taken in a disc radial direction. 
     As shown in  FIGS. 4 and 5 , the disc holding members  13  and  14  include slopes  13 ′ and  14 ′, which overhang a portion of the projection area of the disc  100  (i.e., over the outer periphery of the disc  100 ), at the respective ends thereof. An elastic force is applied from the elastic portions  13   d  or  14   d  to the disc holding member  13  or  14  in the direction indicated by the arrow  13 B or  14 B. In that situation, the slope  13 ′ or  14 ′ contacts with the outer edge  100   c  of the disc  100 , thereby gripping the disc  100  thereon and pressing the disc  100  in a thickness direction  100   t  thereof. As a result, the signal recording side  100 A is brought into plane contact with the sheet  11   p . In this manner, the disc  100  is held and fixed inside the cartridge body  10 . In this state, the outer periphery of the signal recording side  100 A of the disc  100  keeps a close contact with the sheet  11   p . Thus, no dust will be deposited on the signal recording side  100 A. 
     Next, it will be described in detail with reference to  FIGS. 6 ,  7  and  8  how the disc  100  is released from the disc holding members  13  and  14 . 
       FIG. 6  is a perspective view illustrating the disc cartridge with the cartridge upper shell  12  and the disc  100  removed therefrom. As shown in  FIG. 6 , the shutter  21  has its L-shaped portion  21   s  pressed by a shutter opening mechanism (not shown) of the disc drive in the direction indicated by the arrow  21 A. As a result, the chucking opening  11   c  and the head opening  11   h  are now exposed. Also, the pair of cartridge positioning pins  210  of the disc drive is engaged with the positioning holes  11   w  of the cartridge body  10 . 
       FIG. 7  is a cross-sectional view of the disc holding member  13  in the state shown in  FIG. 6  and is taken in a disc radial direction.  FIG. 8  is an enlarged view illustrating the main parts, or the disc holding member  14  and the shutter  21  in the state shown in  FIG. 6 . 
     As shown in  FIG. 7 , when the cartridge positioning pin  210  of the disc drive is inserted into the positioning hole  11   w , the cartridge positioning pin  210  engages with the obliquely running hole portion  13   w  of the disc holding member  13 . As a result, the disc holding member  13  is lifted in the direction  13 A, and the disc  100  is released from the grip of the slope  13 ′ and is now freely rotatable. At this point in time, the rim  13   e  at the end of the disc holding member  13  still overhangs a portion of the projection area of the disc (i.e., the outer periphery thereof). Accordingly, even if the disc  100  is released in a disk drive that is so constructed as to mount the disc  100  vertically, the disc  100  will not drop down from the disc cartridge  301 . 
     On the other hand, when the shutter  21  is opened, a guide rib  21   x  provided on the shutter  21  enters a concave portion  14   w  of the disc holding member  14 , thereby lifting the ceiling of the concave portion  14   w  as shown in  FIG. 8 . As a result, the disc holding member  14  is lifted to the direction  14 A and the disc  100  is released from the grip of the slope  14 ′ and becomes freely rotatable. At this point in time, the rim  14   e  at the end of the disc holding member  14  still overhangs a portion of the projection area of the disc (i.e., the outer periphery thereof). Accordingly, even if the disc is released in a disk drive that is so constructed as to mount the disc  100  vertically, the disc  100  will not drop down from the disc cartridge  301 . 
     Also, to remove the disc intentionally, the operator must release the disc from the three disc holding members  13  and  14  at the same time. Accordingly, it is possible to prevent the operator from removing the disc accidentally. 
     In this embodiment, the end  21   r  of the shutter  21 , which is opposed to the disc  100 , may be provided with a brush or a dust cleaning member as shown in  FIG. 2  so that dust is removed from the signal recording side  100 A of the disc  100  every time the shutter  21  is opened and closed. Optionally, the disc cartridge  301  may further include a locking mechanism for fixing and supporting the disc holding members onto the cartridge body  10  when the disc is held. 
     Embodiment 2 
     Hereinafter, a disc cartridge  302  according to a second embodiment of the present invention will be described with reference to  FIGS. 9 and 10 . Specifically,  FIG. 9  is plan view illustrating an overall configuration for the disc cartridge  302  in which the disc  100  is held.  FIG. 10  is a plan view illustrating an overall configuration for the disc cartridge  302  in which the disc  100  has been released. In  FIGS. 9 and 10 , each member equivalent to the counterpart of the first embodiment described above is identified by the same reference numeral and the description thereof will be omitted herein. 
     The disc cartridge  302  is different from the disc cartridge  301  of the first embodiment in the disc holding members. Specifically, the disc cartridge  302  includes two pairs of disc holding members  15  and  16 , which slide in the direction indicated by the arrow  15 A or  15 B, as shown in  FIG. 9 . 
     Each of the disc holding members  15  includes an elastic portion  15   d , which applies an elastic force to the disc holding member  15  in the direction indicated by the arrow  15 B. Just like the disc holding members  13  and  14  of the first embodiment, a slope  15 ′ provided at the end thereof holds and fixes the disc  100  onto the cartridge body  10 . 
     Each of the disc holding members  16  includes a rotation shaft  16   c . That is to say, the disc holding member  16  is provided for the cartridge body  10  so as to rotate on its rotation shaft  16   c . Just like the disc holding members  13  and  14  of the first embodiment, a slope  16 ′ provided at the end of each disc holding member  16  holds and fixes the disc  100  onto the cartridge body  10 . Each of the disc holding members  15  further includes a coupling pin  15   p , which is engaged and interlocked with a groove  16   g  provided for its associated disc holding member  16 . 
     When the two cartridge positioning pins  210  of the disc drive are engaged with the positioning holes  11   w  of the cartridge body  10 , respective protrusions  15   s  of the disc holding members  15  are pushed by the positioning pins  210  as shown in  FIG. 10 . As a result, the disc holding members  15  are moved in the direction indicated by the arrow  15 A and the disc  100  is released from the grip of the slopes  15 ′. In the meantime, as the disc holding members  15  are moved, the disc holding members  16  are rotated to the direction indicated by the arrow  16 A. Consequently, the disc  100  is also released from the grip of the slopes  16 ′. 
     Embodiment 3 
     Hereinafter, a disc cartridge  303  according to a third embodiment of the present invention will be described with reference to  FIGS. 11 and 12 . Specifically,  FIG. 11  is plan view illustrating an overall configuration for the disc cartridge  303  in which the disc  100  is held.  FIG. 12  is a plan view illustrating an overall configuration for the disc cartridge  303  in which the disc  100  has been released. In  FIGS. 11 and 12 , each member equivalent to the counterpart of the first embodiment is identified by the same reference numeral and the description thereof will be omitted herein. 
     The disc cartridge  303  is different from the disc cartridge  301  of the first embodiment in the disc holding members. Specifically, the disc cartridge  303  includes two pairs of disc holding members  17  and  18 , to which an elastic force is applied in the directions indicated by the arrows  17 B and  18 B, respectively, as shown in  FIG. 11 . These disc holding members  17  and  18  have been molded together with the cartridge body  10  so as to form integral parts of the cartridge body  10 . 
     Each of the disc holding members  17  includes an elastic portion  17   d , which applies an elastic force to the disc holding member  17  in the direction indicated by the arrow  17 B. Just like the disc holding members  13  and  14  of the first embodiment, a slope  17 ′ provided at the end of each disc holding member  17  holds and fixes the disc  100  onto the cartridge body  10 . 
     Each of the disc holding members  18  also includes an elastic portion  18   d , which applies an elastic force to the disc holding member  18  in the direction indicated by the arrow  18 B. A slope  18 ′ provided at the end of each disc holding member  18  also holds and fixes the disc  100  onto the cartridge body  10 . 
     When this disc cartridge  303  is inserted into a disc drive  200 , a pair of disc releasing pins  217 , provided for the disc drive  200 , presses protrusions  17   s  of the disc holding members  17 . As a result, the disc  100  is released from the disc holding members  17  as shown in  FIG. 12 . At the same time, another pair of disc releasing pins  218 , also provided for the disc drive  200 , contacts with the side surfaces  18   s  of the disc holding members  18 . Consequently, the disc  100  is also released from the disc holding members  18 . 
     Embodiment 4 
     Hereinafter, a disc cartridge  304  according to a fourth embodiment of the present invention will be described with reference to  FIGS. 13 and 14 . Specifically,  FIG. 13  is plan view illustrating an overall configuration for the disc cartridge  304  in which the disc  100  is held.  FIG. 14  is a plan view illustrating an overall configuration for the disc cartridge  304  in which the disc  100  has been released. In  FIGS. 13 and 14 , each member equivalent to the counterpart of the first embodiment is identified by the same reference numeral and the description thereof will be omitted herein. 
     The disc cartridge  304  is different from the disc cartridge  301  of the first embodiment in the disc holding member. Specifically, the disc cartridge  304  includes a ringlike disc holding member  19 . 
     As shown in  FIG. 13 , the disc holding member  19  is a ringlike elastic member, which is made of rubber, for example, and which can change its shape freely. When no force is externally applied thereto, the disc holding member  19  has an ellipsoidal shape. However, by applying an external force thereto, the disc holding member  19  may be deformed into a substantially completely round shape. When the disc holding member  19  is deformed into a substantially completely round shape, the inside diameter thereof is greater than the diameter of the disc  100 . 
     As shown in  FIG. 13 , the ellipsoidal disc holding member  19  is in contact with the disc  100  at multiple points, thereby holding and fixing the disc  100  onto the cartridge body  10 . However, when this disc cartridge  304  is inserted into a disc drive  200 , a pair of convex portions  219 , provided for the disc drive  200 , presses the major axis portion of the ringlike disc holding member  19 , thereby deforming the disc holding member  19  as shown in  FIG. 14 . As a result, the disc holding member  19  is deformed into an approximately completely round shape and is no longer in contact with the disc  100 . That is to say, the disc  100  is released from the disc holding member  19 . 
     To release the disc  100  from the disc holding member  19 , the force that deforms the disc holding member  19  may also be applied from the convex portion of the disc drive, which engages with the concave portion  10   g  (see  FIG. 2 ) provided for preventing the erroneous insertion, to the disc holding member  19 . Alternatively, that force may also be applied from a pair of convex portions of the disc drive, which engages with the concave portions  10   c  (see  FIG. 2 ) provided on the right- and left-hand sides of the disc cartridge  1  for pulling in the disc cartridge  304 , to the disc holding member  19 . 
     Embodiment 5 
     Hereinafter, a fifth embodiment of the present invention will be described with reference to  FIGS. 15 through 18 .  FIGS. 15 and 17  are plan views illustrating the structure of a portion of a disc cartridge  305  according to this embodiment from which the cartridge upper shell has been removed. Specifically,  FIG. 15  illustrates a state where the shutter  21  covers the openings  11   h  and  11   c , while  FIG. 17  illustrates a state where the shutter  21  exposes the openings  11   h  and  11   c .  FIGS. 16 and 18  illustrate states of a disc holding portion  43  when the shutter  21  is closed and when the shutter  21  is opened, respectively. 
     In this embodiment, each member equivalent to the counterpart of the disc cartridge of the first embodiment is identified by the same reference numeral. 
     The disc cartridge of this embodiment is characterized in that the disc holding and releasing operations by disc holding members  43  are synchronized with the opening and closing operations by the shutter  21  by way of a disc holding/interlocking member  44 . 
     The disc holding/interlocking member  44  is provided over the first inner surface  11   u  of the cartridge lower shell  11  so as to rotate and slide around the chucking opening  11   c  of the cartridge lower shell  11  as indicated by the arrow  44 A in  FIGS. 15 and 17 . The disc holding/interlocking member  44  has a fan shape, or in the shape of a partially notched ring that has an inside diameter equal to the diameter of the chucking opening  11   c.    
     The disc holding/interlocking member  44  includes an engaging pin  47  that extends toward the cartridge lower shell  11  (i.e., in the direction going into the paper of  FIGS. 15 and 17 ). The cartridge lower shell  11  and the shutter  21  are respectively provided with guide grooves  11   m  and  21   m  that both engage with this engaging pin  47 . Also, multiple protrusions  45 , which extend outward and toward the cartridge upper shell (i.e., in the direction coming out of the paper of  FIGS. 15 and 17 ), are provided on the outer periphery of the disc holding/interlocking member  44 . Furthermore, the upper surface of the disc holding/interlocking member  44  is covered with a nonwoven fabric or a coating to prevent the disc  100  from getting scratched or dust from being deposited on the signal recording side thereof. 
     A number of disc holding members  43  are disposed at predetermined intervals on respective regions of the cartridge lower shell  11  so as to hold the outer edge portion of the disc thereon when the disc is stored in the disc cartridge. In  FIGS. 15 and 17 , three disc holding members  43  are provided. Alternatively, two, four or more disc holding members  43  may also be provided. In any case, each of those disc holding members  43  is secured to the cartridge lower shell  11  so as to rotate on the rotation shaft  43 A thereof. 
     As shown in  FIG. 16 , the disc holding member  43  is located at such a position as to partially overlap with the outer periphery and its surrounding portion of the disc holding/interlocking member  44 . Also, a mechanism (not shown in  FIG. 16 ) such as the elastic portion  14   d  shown in  FIG. 5 , for example, presses the disc holding member  43  in the direction  43 B (i.e., toward the cartridge lower shell  11 ). Accordingly, while contacting with the edge of the disc  100 , the slope  43 ′ of the disc holding member  43  not only presses the disc  100  in the direction  43 B so that the disc  100  is brought into contact with the disc holding/interlocking member  44  but also holds the disc  100  thereon. 
     As shown in  FIG. 15 , when the disc cartridge holding the disc (not shown) thereon is inserted into a disc drive  200  in the direction indicated by the arrow  1 A, a shutter opening/closing lever (not shown), provided for the disc drive  200 , moves the shutter  21  in the direction  21 A, thereby opening the shutter  21 . When the shutter  21  starts to move in the direction  21 A, a force is also applied in the arrowed direction  21 A to the engaging pin  47  of the disc holding/interlocking member  44  that is inserted into the guide groove  21   m  of the shutter  21 . As a result, the engaging pin  47  is moved along the guide groove  11   m  of the cartridge lower shell  11 , and the disc holding/interlocking member  44  starts to rotate around the chucking opening  11   c  as indicated by the arrow  44 A. The guide groove  11   m  preferably extends approximately in the direction in which the shutter  21  is moved so that the disc holding/interlocking member  44  moves synchronously with the shutter  21 . 
     When the shutter  21  is completely open, the protrusions  45  on the outer periphery of the disc holding/interlocking member  44  are located under the disc holding members  43  as shown in  FIG. 17 . Then, as shown in  FIG. 18 , the disc holding members  43  are pushed up by the protrusions  45  and the slopes  43 ′ of the disc holding members  43  separate themselves from the outer edge of the disc  100 . As a result, the force  43 B that has pressed the disc  100  vertically to the disc plane is removed and the disc  100  is released to be freely rotatable. At this point in time, the rim  43   e  at the end of the disc holding member  43  still overhangs a portion of the projection area of the disc  100  (i.e., the outer periphery thereof). Accordingly, even if the disc  100  is released in a disc drive that is supposed to mount the disc thereon vertically, the disc will not drop down from the cartridge. 
     In the disc cartridge  305  of this embodiment, the disc can be released even if the disc cartridge is not inserted into the disc drive  200 . For example, if the shutter  21  is opened manually, the disc holding members  43  will release the disc  100  synchronously with the movement of the shutter  21 . Thus, the user can remove the existing disc from the cartridge and insert another disc thereto intentionally. 
     Embodiment 6 
     Hereinafter, a sixth embodiment of the present invention will be described.  FIGS. 19 and 20  are plan views illustrating the structure of a portion of a disc cartridge  306  according to this embodiment from which the cartridge upper shell has been removed. Specifically,  FIG. 19  illustrates a state where the shutter covers the head opening, while  FIG. 20  illustrates a state where the shutter exposes the head opening. In  FIGS. 19 and 20 , each member equivalent to the counterpart of the disc cartridge of the first or fifth embodiment is identified by the same reference numeral. 
     The disc cartridge of this embodiment is characterized in that the disc holding/interlocking member of the fifth embodiment described above also functions as a shutter. The shutter  46  is provided over the first inner surface  11   u  of the cartridge lower shell  11  so as to rotate and slide around the chucking opening  11   c  of the cartridge lower shell  11  as indicated by the arrow  46 B in  FIGS. 19 and 20 . The shutter  46  has a fan shape, or in the shape of a partially notched ring that has an inside diameter equal to the diameter of the chucking opening  11   c.    
     The shutter  46  includes an engaging pin  46   p  that extends toward the cartridge lower shell  11  (i.e., in the direction going into the paper of  FIGS. 19 and 20 ). The cartridge lower shell  11  is provided with a guide groove  11   m  that engages with this engaging pin  46   p . When the engaging pin  46   p  is located at one end of the guide groove  11   m , the head opening  11   h  is closed up by the shutter  46 . And when the engaging pin  46   p  is located at the other end of the guide groove  11   m , the head opening  11   h  is exposed. The guide groove  11   m  is provided along a portion of an arc that is concentric with the chuck opening  11   c . The guide groove  11   m  preferably extends approximately in the direction  1 A in which the disc cartridge is inserted so that the shutter  46  is opened as the disc cartridge is inserted into the disc drive. 
     Multiple protrusions  46   c , which extend outward and toward the cartridge upper shell  12  (i.e., in the direction coming out of the paper of  FIGS. 19 and 20 ), are provided on the outer periphery of the shutter  46 . Furthermore, the upper surface of the shutter  46  is covered with a nonwoven fabric or a coating material to prevent the disc  100  from getting scratched or any dust from being deposited on the signal recording side thereof. 
     A number of disc holding members  43 , having a structure similar to that of the disc holding members of the fifth embodiment, are disposed at predetermined intervals on respective regions of the cartridge lower shell  11 . The disc holding members  43  and the protrusions  46   c  of the shutter  46  together hold or release the disc synchronously with the movement of the shutter  46  as already described for the fifth embodiment. 
     When the disc cartridge of this embodiment is inserted into the disc drive  200  as indicated by the arrow  1 A in  FIG. 19 , the engaging pin  46   p  of the shutter  46  will soon contact with a contact member  201  provided for the disc drive  200 . And when the disc cartridge is inserted deeper into the disc drive  200 , the engaging pin  46   p  is pressed by the contact member  201  to start to move along the guide groove  11   m . Then, the shutter  46  starts to rotate around the chucking opening  11   c  of the cartridge lower shell  11  as indicated by the arrow  46 B. As the shutter  46  rotates, the head opening  11   h  is opened little by little. 
     As shown in  FIG. 20 , when the disc cartridge has been fully inserted into the disc drive  200 , the engaging pin  46   p  will reach the other end of the guide groove  11   m . As a result, the head opening  11   h  is completely exposed. At this point in time, as already described for the fifth embodiment, the protrusions  46   c  are located under the disc holding members  43 . Then, the disc holding portions are pushed up by the protrusions  46   c  toward the cartridge upper shell  12  (i.e., in the direction coming out of the paper of  FIG. 20 ). As a result, the disc  100  that has been held by the disc holding members  43  is released and now freely rotatable. 
     The disc cartridge of this embodiment needs no disc holding/interlocking member. Thus, compared to the disc cartridge of the fifth embodiment, the disc cartridge can be thinner. Also, if the engaging pin  46   p  is moved manually along the guide groove  11   m , the shutter  46  can be opened and the disc can be released from the disc holding members and removed. 
     In this embodiment, the shutter  46  rotates clockwise as viewed from over the cartridge upper shell. However, the shutter  46  may also be rotated counterclockwise if the position of the guide groove  11   m  is changed. 
     Embodiment 7 
     Hereinafter, a seventh embodiment of the present invention will be described.  FIGS. 21 and 22  are plan views illustrating the structure of a portion of a disc cartridge  307  according to this embodiment from which the cartridge upper shell has been removed. Specifically,  FIG. 21  illustrates a state where the shutter covers the head opening, while  FIG. 22  illustrates a state where the shutter exposes the head opening. In  FIGS. 21 and 22 , each member equivalent to the counterpart of the disc cartridge of the third or sixth embodiment is identified by the same reference numeral. 
     The disc cartridge of this embodiment is different from the disc cartridge of the sixth embodiment in the structure of the disc holding members. Specifically, as shown in  FIGS. 21 and 22 , the disc cartridge of this embodiment includes a plurality of disc holding members  17 . Just like the disc holding members of the third embodiment described above, each of these disc holding members  17  also includes an elastic portion  17   d . While the shutter  46  is closed, the elastic force applied from the elastic portions  17   d  holds the disc in such a manner as to press the disc  100  toward the center of the disc ( 17 R). In this embodiment, the disc holding members  17  form integral parts of the cartridge lower shell  11 . Alternatively, the disc holding members  17  may also be formed separately from the cartridge lower shell  1 . 
     When a cross section thereof is taken in the disc radial direction, each of these disc holding members  17  also has a slope that tilts to overhang a portion of the projection area of the disc (i.e., the outer periphery of the disc) just like the disc holding member  43  shown in  FIG. 18 . Accordingly, if the disc gets held by the disc holding members  17  so as to have its outer edge contact with the respective slopes, then the disc is pressed against the shutter  46 . 
     The shutter  46  includes a plurality of protrusions  46   c  on the outer periphery thereof. In this embodiment, the protrusions  46   c  protrude outward. Also, the protrusions  46   c  are located at such positions on the outer periphery of the shutter  46  as to contact with the elastic portions  17   d  of the disc holding members  17  when the shutter  46  is opened. 
     As shown in  FIG. 22 , when the shutter  46  is opened, the protrusions  46   c  dominate the elastic force of the elastic portions  17   d , thereby pushing the elastic portions  17   d  outward from the disc  100  (i.e., in the directions  17   s ). As a result, the disc  100  is released. However, each of the disc holding members  17  also includes a rim  17   e  at the end thereof. Even after the disc  100  has been released, the rim  17   e  still overhangs a portion of the projection area of the disc. Accordingly, even if the disc cartridge has been loaded into the disk drive  200  that is supposed to mount the disc  100  thereon vertically, the disc  100  will not drop down from the disc cartridge. 
     The disc cartridge of this embodiment has all the features of the sixth embodiment described above. In addition, the disc holding members  17  may form integral parts of the cartridge lower shell  11 . Thus, the disc cartridge can have a simplified structure and its manufacturing cost can be reduced. 
     Embodiment 8 
     Hereinafter, a disc cartridge  308  according to an eighth embodiment of the present invention will be described with reference to the drawings. 
     First, the structure of the disc cartridge  308  will be outlined with reference to  FIGS. 23 and 24 . As in the first embodiment, the disc  100  shown in  FIGS. 23 and 24  also includes first and second sides. The first side of the disc, on which its label, for example, is normally printed, is illustrated in  FIG. 23 , while the second side of the disc  100 , i.e., the signal recording side  100 A, is illustrated as the back surface in  FIG. 24 . 
     As shown in  FIGS. 23 and 24 , the disc cartridge  308  includes a cartridge lower shell  11 , a cartridge upper shell  12 , a pair of shutters  21  and  22  and stopper members  23 . 
     As shown in  FIG. 24 , the cartridge lower shell  11  includes a chucking opening  11   c  and a head opening  11   h . The chucking opening  11   c  is provided to allow a chucking member (e.g., a spindle motor for rotating the disc  100 ) to enter the disc cartridge  308  externally. The head opening  11   h  is provided to allow a head, which reads and/or writes a signal from/on the signal recording side  100 A of the disc  100 , to enter the disc cartridge  308  and access the signal recording side  100 A. The cartridge lower shell  11  faces the signal recording side  100 A of the disc  100 . Also, the head opening  11   h  reaches a side surface of the cartridge lower shell  11 . 
     The cartridge upper shell  12  includes a circular disc window  12   w , through which the disc  100  can be introduced and removed into/from the disc cartridge  308  and which expands over the entire projection area of the disc  100  to expose the upper surface of the disc. The cartridge upper and lower shells  12  and  11  are adhered or welded together at their outer periphery, thereby forming a cartridge body  10 . 
     A disc storage portion  10   d  for storing the disc  100  therein is defined by a first inner surface  11   u  of the cartridge lower shell  11  and a second inner surface  12   i  of the cartridge upper shell  12 . The first inner surface  11   u  is opposed to the signal recording side  100 A of the disc  100 , while the second inner surface  12   i  has a substantially cylindrical shape and defines the disc window  12   w  inside. That is to say, the first inner surface  11   u  becomes the bottom of the disc storage portion  10   d.    
     In the disc storage portion  10   d , a gap, which is wide enough to allow the disc  100  to rotate freely, is provided between the second inner surface  12   i  and the disc  100 . Also, the top of the disc storage portion  10   d  is the disc window  12   w  so that the disc  100  stored in the disc storage portion  10   d  has one side thereof exposed inside the disc window  12   w.    
     The stopper members  23  are provided in a removable state for the cartridge upper shell  12  so as to partially protrude into the disc window  12   w . In this embodiment, two stopper members  23  are provided as shown in  FIGS. 23 and 24 . On the other hand, a stopper portion  12   s  is provided for the cartridge upper shell  12  so as to protrude into the disc window  12   w . The stopper portion  12   s  forms an integral part of the cartridge upper shell  12 . The two stopper members  23  and the stopper portion  12   s  are arranged approximately at regular intervals around the circumference of the disc window  12   w  for the purpose of preventing the disc  100  from dropping down from the disc window  12   w . These stopper members  23  and stopper portion  12   s  can prevent the dropping particularly effectively when this disc cartridge is vertically loaded into a disc drive and used. 
     The shutters  21  and  22  are disposed between the signal recording side  100 A of the disc  100  and the inner surface  11   u  of the disc storage portion  10   d . The shutters  21  and  22  include rotation holes  21   u  and  22   u , respectively. These rotation holes  21   u  and  22   u  are engaged in a freely rotatable state with a pair of rotation shafts  11   s , which is located outside of the disc storage portion  10   d  of the cartridge body  10  and opposite to the head opening  11   h . Thus, the shutters  21  and  22  rotate on the rotation shafts  11   s  in such a manner as to expose or cover the chucking and head openings  11   c  and  11   h.    
     A cam  21   c  and a follower  22   c  are provided near the rotation holes  21   u  and  22   u  of the shutters  21  and  22 , respectively. The cam  21   c  and the follower  22   c  have mutually engaging shapes and together make up an interlocking mechanism  20   c  for opening and closing the shutters  21  and  22  while interlocking them with each other. 
     The respective surfaces of the shutters  21  and  22 , which are opposed to the signal recording side  100 A of the disc, are covered with protective layers  21   p  and  22   p  for the purpose of preventing the disc  100  from getting scratched or any dust from entering the signal recording side  100 A thereof. 
     The protective layers  21   p  and  22   p  may be appropriately selected from the group consisting of an anti-scratching nonwoven fabric, a dustproof nonwoven fabric, an anti-scratching coating layer and a dustproof coating layer. In this embodiment, sheets of a dustproof nonwoven fabric are adhered or ultrasonic welded as the protective layers  21   p  and  22   p.    
     Shutter springs  31  and  32  are provided outside of the disc storage portion  10   d  for the shutters  21  and  22 , respectively. These springs  31  and  32  apply an elastic force to the shutters  21  and  22  in such a direction as to close the shutters  21  and  22 . Optionally, the elastic force may also be applied from any other type of elastic members to the shutters  21  and  22  in that closing direction. 
     As shown in  FIG. 24 , the disc cartridge  308  includes disc holding portions  21   a ,  21   b ,  22   a  and  22   b  at both ends of the shutters  21  and  22 . Each of these disc holding portions  21   a ,  21   b ,  22   a  and  22   b  has a downwardly tapered slope at the end of the shutter  21  or  22  to grip the outer edge of the disc  100  while the shutters  21  and  22  are closed. The structure and operation of the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  will be described in further detail later. 
     As shown in  FIG. 23 , the upper surface of the cartridge body  10  (or the cartridge upper shell  12 ) has a label plane  10   f , on which the contents that have been written on the disc  100  being stored can be noted down, and embossed arrow marks (or concave portions)  10   a  that indicate the direction (the arrow  1 A) in which this disc cartridge  308  should be inserted into a disc drive. In addition, two concave portions  10   c  are further provided on two of the side surfaces of the cartridge body  10  that are parallel to the direction  1 A in which the cartridge body  10  is inserted. These concave portions  10   c  may be used as either pull-in notches or positioning recesses when the disc cartridge  308  is loaded into a disk drive or when the disc cartridge  308  is stored in a changer. 
       FIG. 25  is a perspective view illustrating a state where the shutters  21  and  22  cover the chucking and head openings  11   c  and  11   h  with the cartridge upper shell  12  and the disc  100  removed. In  FIG. 25 , the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  of the shutters  21  and  22  are located at such positions as to grip the outer edge of the disc  100  (not shown). 
       FIG. 26  is a perspective view illustrating a state where the shutters  21  and  22  expose the chucking and head openings  11   c  and  11   h  with the cartridge upper shell  12  and the disc  100  removed. As a result of the rotation of the shutters  21  and  22  on their rotation holes  21   u  and  22   u , respectively, the chucking and head openings  11   c  and  11   h  are now exposed. Also, as the shutters  21  and  22  have rotated, the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  have also rotated on the rotation holes  21   u  and  22   u . Consequently, the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  are now separated from the outer edge of the disc  100  (not shown). 
       FIG. 27  is a perspective view illustrating a state where the shutters  21  and  22  cover the chucking and head openings  11   c  and  11   h  with the disc  100  removed. As shown in  FIG. 27 , the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  protrude into the disc storage portion  10   d  to hold the disc  100  (not shown) thereon. On the other hand,  FIG. 28  is a perspective view illustrating a state where the shutters  21  and  22  expose the chucking and head openings  11   c  and  11   h  with the disc  100  removed. As shown in  FIG. 28 , while the shutters  21  and  22  are opened, the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  are stored outside of the disc storage portion  10   d  of the cartridge body. 
     Next, the structure and the operation of the shutters  21  and  22  will be described in further detail with reference to  FIGS. 29 ,  30  and  31 .  FIG. 29  is a cross-sectional view as viewed along a plane that passes the center of the disc  100 . As shown in  FIG. 29 , the second inner surface  12   i  of the disc storage portion  10   d  of the cartridge body  10  is provided with a notch  10   w  so as not to interfere with the opening and closing operations of the shutter  22  or  21 . Also, the cartridge body  10  further includes a shutter storage portion  10   s  for storing a portion of the shutter  22  or  21  being opened. Furthermore, at least the edge portions  21   f  and  22   f  of the shutters  21  and  22 , which are butted against each other over the head and chucking openings  11   h  and  11   c  while the shutters are closed, overlap with each other in the thickness direction of the disc  100  as shown in  FIG. 29 . 
     On the other hand, as shown in  FIG. 30 , each of the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  includes a slope  21   a ′,  21   b ′,  22   a ′ or  22   b ′, which overhangs a portion of the projection area of the disc and overlaps with the outer edge of the disc  100 . That is to say, the slope  21   a ′ has a downwardly tapered shape and leans toward the disc  100 . While the chucking and head openings  11   c  and  11   h  are covered with the shutters  21  and  22 , the slope  21   a ′ is allowed to contact with the outer edge  100   c  of the disc  100 , thereby gripping the disc  100  thereon and pressing the disc  100  in the thickness direction  100   t . In this manner, the signal recording side  100 A is brought into plane contact with the sheets  21   p  and  22   p  of the shutters  21  and  22  and the disc  100  is held and fixed onto the cartridge body  10 . In such a state, the signal recording side  100 A of the disc  100  is in close contact with the sheets  21   p  and  22   p . Thus, no dust will be deposited on the signal recording side  100 A. 
     Also, if the exposed side of the disc  100  is rotated manually or if the shutters  21  and  22  are opened or closed intentionally, then dust, finger marks or any other dirt that has adhered onto the signal recording side  100 A of the disc  100  may be wiped away. 
     Furthermore, as shown in  FIG. 31 , the shutter  21  includes a shutter opening/closing portion  21   t , an elastic portion  21   v  and a locking protrusion portion  21   k . These portions  21   t ,  21   v  and  21   k  form integral parts of the shutter  21 . Specifically, the shutter opening/closing portion  21   t  is for use to open and close the shutters externally. The locking protrusion portion  21   k  is connected to the shutter  21  by way of the elastic portion  21   v . While the shutter  21  covers the chucking and head openings  11   c  and  11   h , the locking protrusion portion  21   k , to which an elastic force is being applied from the elastic portion  21   v , engages with a locking hole  10   k  of the cartridge body  10 , thereby preventing the shutter  21  from rotating and fixing and supporting the shutter  21  to the cartridge body  10  as shown in  FIG. 31 . When the shutter  21  is fixed, the other shutter  22 , which is interlocked with the shutter  21  via the interlocking mechanism  20   c , is also fixed. 
     Accordingly, only by getting the locking protrusion portion  21   k  pressed externally by a protrusion, for example, in the direction indicated by the arrow  20 A and disengaged from the locking hole  10   k  while pressing the opening/closing portion  21   t  in the direction indicated by the arrow  20 B at the same time, the shutters  21  and  22  can be rotated to expose the chucking and head openings  11   c  and  11   h  and the disc  100  can be released from the disc holding portions  21   a ,  21   b ,  22   a  and  22   b . Thus, it is possible to prevent the operator from removing the disc accidentally. 
     Next, the structure and operation of the stopper members  23  will be described in further detail with reference to  FIGS. 24 and 32 .  FIG. 32  is a perspective view illustrating the removable stopper member  23  upside down. The convex portions  23   a ,  23   b  and  23   c  of the stopper member  23  are respectively engaged with concave portions  12   a ,  12   b  and  12   c  provided for the cartridge upper shell  12  near the disc window  12   w  thereof as shown in  FIG. 24 . Thus, the stopper member  23  can be removed from the cartridge upper shell  12 . 
     Next, a mechanism for preventing the erroneous insertion of the disc cartridge  308  into a disc drive will be described in further detail with reference to  FIG. 33 .  FIG. 33  is a front view of the disc cartridge  308  shown in  FIG. 23  as viewed in the direction in which the disc cartridge  308  is inserted into a disk drive (i.e., arrow  1 B). As shown in  FIG. 33 , the cartridge body  10  includes a concave portion  10   g  on one side surface thereof and is asymmetric in the direction  1 A in which the disc cartridge  308  is inserted into the disc drive (see  FIG. 23 ). The concave portion  10   g  is not located at the center of thickness. 
     According to such a structure, only when a convex portion, provided for the disc drive, is fitted with this concave portion  10   g , the disc cartridge  308  can be inserted into the disc drive correctly and the disc drive can operate normally. 
     Stated otherwise, even if one tries to insert the disc cartridge  308  into the disc drive upside down by mistake, he or she cannot insert the cartridge  308  into the disc drive. This is because the convex portion of the disc drive interferes with the opposite side surface with no concave portion  10   g . Also, even if one tries to insert the disc cartridge  308  into the disc drive upside down and in the wrong way by mistake, he or she cannot insert the cartridge  308  into the disc drive, either. This is because the convex portion of the disc drive also interferes with the non-recessed portion of the side surface with the concave portion  10   g . Thus, the erroneous insertion can be prevented. 
     The disc cartridge  308  of this embodiment may be modified in various manners. 
     For example, the thickness of the cartridge body  10  may be further reduced to such an extent that the stopper members  23  will not protrude from the upper surface  12   f  of the cartridge upper shell  12  (see  FIG. 24 ) while the shutters  21  and  22  are closed. On the other hand, while the shutters  21  and  22  are opened, the stopper members  23  may be protruded from the upper surface  12   f  of the cartridge upper shell  12  in the following manner. Specifically, as the shutters  21  and  22  are going to be opened, the disk holding portions  21   a  and  22   a , for example, may push the convex portions  23   a  of the stopper members  23  upward while passing under the stopper members  23 . Then, the stopper members  23  are protruded from the upper surface  12   f  of the cartridge upper shell  12 . According to such a structure, a sufficiently broad space can be allowed the disc  100  to rotate inside the disc storage portion  10   d  and yet the disc cartridge can have its thickness further reduced. 
     Also, the stopper members  23  may form integral parts of the cartridge body  10 . In that case, the stopper members  23  may be able to be folded and unfolded. 
     Furthermore, the shutter springs  31  and  32  may apply an elastic force in such a direction as to open the shutters  21  and  22 . If the shutters can operate almost completely synchronously by way of the interlocking mechanism, just one of the shutter springs  31  and  32  may be provided. 
     The locking protrusion portion  21   k  forms an integral part of the shutter  21 . Alternatively, a locking lever, including a locking protrusion portion and a convex portion at the end thereof, may be connected to the cartridge body  10  via an elastic portion, and an associated concave portion may be provided for the shutter so that the convex and concave portions engage with each other. In that case, by pressing the locking protrusion portion through a locking hole of the cartridge body, these convex and concave portions may be disengaged from each other so as to allow the shutters to rotate freely. Optionally, the locking lever, as well as the shutter springs (i.e., elastic members), may be resin springs that form integral parts of the cartridge body  10 . 
     Embodiment 9 
     Hereinafter, a disc cartridge  309  according to a ninth embodiment of the present invention will be described with reference to the drawings. 
     As shown in  FIGS. 34 and 35 , the disc cartridge  309  includes a cartridge lower shell  41 , a cartridge upper shell  42 , stopper members  42   a ,  42   b ,  42   c  and  42   d , and a pair of shutters  51  and  52 . 
     As shown in  FIG. 35 , the cartridge lower shell  41  includes a chucking opening  41   c  and a head opening  41   h . The chucking opening  41   c  is provided to allow a chucking member (e.g., a spindle motor for rotating the disc  100 ) to enter the disc cartridge  309  externally. The head opening  41   h  is provided to allow a head, which reads and/or writes a signal from/on the signal recording side  100 A of the disc  100 , to enter the disc cartridge  309  and access the signal recording side  100 A. The cartridge lower shell  41  faces the signal recording side  100 A of the disc  100 . Also, the head opening  41   h  reaches one side surface of the cartridge lower shell  41 . 
     The cartridge upper shell  42  includes a circular disc window  42   w , through which the disc  100  can be introduced and removed into/from the disc cartridge  309  and which expands over the entire projection area of the disc  100  to expose the upper surface of the disc. The cartridge upper and lower shells  42  and  41  are adhered or welded together at their outer periphery, thereby forming a cartridge body  40 . 
     A disc storage portion  40   d  for storing the disc  100  therein is defined by a first inner surface  41   u  of the cartridge lower shell  41  and a second inner surface  42   i  of the cartridge upper shell  42 . The first inner surface  41   u  is opposed to the signal recording side  100 A of the disc  100 , while the second inner surface  42   i  has a substantially cylindrical shape and defines the disc window  42   w  inside. That is to say, the first inner surface  41   u  becomes the bottom of the disc storage portion  40   d.    
     In the disc storage portion  40   d , a gap, which is wide enough to allow the disc  100  to rotate freely, is provided between the second inner surface  42   i  and the disc  100 . Also, the top of the disc storage portion  40   d  is the disc window  42   w  so that the disc  100  stored in the disc storage portion  40   d  has one side thereof exposed inside the disc window  42   w.    
     The stopper members  42   a ,  42   b ,  42   c  and  42   d  form integral parts of the cartridge upper shell  42  so as to partially protrude into the disc window  42   w . Each of these stopper members  42   a ,  42   b ,  42   c  and  42   d  is separated from the cartridge upper shell  42  via a slit. These stopper members  42   a ,  42   b ,  42   c  and  42   d  are used to prevent the disc  100  from dropping down from the disc window  42   w . The stopper members  42   a ,  42   b ,  42   c  and  42   d  can prevent the dropping particularly effectively when the disc cartridge is vertically loaded into a disc drive and used. Optionally, these stopper members  42   a ,  42   b ,  42   c  and  42   d  may be integrated with the cartridge upper shell  42  by way of elastic members. 
     The shutters  51  and  52  are disposed between the signal recording side  100 A of the disc  100  and the inner surface  41   u  of the disc storage portion  40   d . The shutters  51  and  52  include rotation holes  51   u  and  52   u , respectively. These rotation holes  51   u  and  52   u  are engaged in a freely rotatable state with a pair of rotation shafts  41   s , which is located outside of the disc storage portion  40   d  of the cartridge body  40  and opposite to the head opening  41   h . Thus, the shutters  51  and  52  rotate on the rotation shafts  41   s  in such a manner as to expose or cover the chucking and head openings  41   c  and  41   h.    
     A cam  51   c  and a follower  52   c  are provided near the rotation holes  51   u  and  52   u  of the shutters  51  and  52 , respectively. The cam  51   c  and the follower  52   c  have mutually engaging shapes and together make up an interlocking mechanism  50   c  for opening and closing the shutters  51  and  52  while interlocking them with each other. 
     The respective surfaces of the shutters  51  and  52 , which are opposed to the signal recording side  100 A of the disc, are covered with protective layers  51   p  and  52   p  for the purpose of preventing the disc  100  from getting scratched or any dust from reaching the signal recording side  100 A thereof. 
     The protective layers  51   p  and  52   p  may be appropriately selected from the group consisting of an anti-scratching nonwoven fabric, a dustproof nonwoven fabric, an anti-scratching coating layer and a dustproof coating layer. In this embodiment, sheets of a dustproof nonwoven fabric are adhered or ultrasonic welded as the protective layers  51   p  and  52   p.    
     Shutter springs  61  and  62  are provided outside of the disc storage portion  40   d  for the shutters  51  and  52 , respectively. These springs  61  and  62  apply an elastic force to the shutters  51  and  52  in such a direction as to close the shutters  51  and  52 . Alternatively, the shutter springs  61  and  62  may apply an elastic force to the shutters  51  and  52  in such a direction as to open the shutters  51  and  52 . Also, if the shutters can operate almost completely synchronously by way of the interlocking mechanism, only one of the shutter springs  61  and  62  may be provided. 
     As in the eighth embodiment, the shutters  51  and  52  include disc holding portions  51   a ,  51   b ,  52   a  and  52   b  at the ends thereof as shown in  FIG. 35 . Furthermore, as will be described in detail later, convex portions  51   e  and  52   e  are provided on respective regions of the shutters  51  and  52  so as to be located under the center hole of the disc  100 . 
     As shown in  FIG. 34 , the upper surface of the cartridge body  40  (or the cartridge upper shell  42 ) has embossed arrow marks (or concave portions)  40   a  that indicate the direction (the arrow  1 A) in which the disc cartridge  309  is inserted into a disc drive. The cartridge body  40  further includes two concave portions  40   c  on a pair of its side surfaces that are parallel to the inserting direction  1 A. These concave portions  40   c  may be used as either pull-in notches or positioning recesses when the disc cartridge  309  is loaded into a disk drive or when the cartridge  309  is stored in a changer. Optionally, just one side surface of the cartridge  309  may include the concave portion  40   c . In that case, the concave portion  40   c  may be used as a mechanism for preventing erroneous (e.g., upside down) insertion when the disc cartridge  309  is inserted or loaded into a disk drive. The upper surface of the cartridge body  40  further includes a grip portion  40   e  that allows the operator to grip this disc cartridge  309 . This grip portion  40   e  has an antislip embossed shape. 
       FIG. 36  is a perspective view illustrating a state where the shutters  51  and  52  cover the chucking opening  41   c  and the head opening  41   h  with the disc  100  removed.  FIG. 37  is a perspective view illustrating a state where the shutters  51  and  52  expose the chucking opening  41   c  and the head opening  41   h  with the disc  100  removed. 
     Hereinafter, the structure and the operation of the shutters  51  and  52  will be described in further detail. As shown in  FIGS. 34 and 35 , the disc holding portions  51   a ,  51   b ,  52   a  and  52   b  provided for the shutters  51  and  52  also have such a shape as including a slope that tilts in such a manner as to overhang the projection area of the disc and to overlap with the outer periphery of the disc  100  as in the eighth embodiment. That is to say, the slope is downwardly tapered and leans toward the disc  100 . Thus, the same effects as those of the eighth embodiment are also achieved. 
     Also, the shutter  52  includes an opening/closing portion  52   t  for use to open and close the shutters externally, while the shutter  51  includes an elastic portion  51   v  and a locking protrusion portion  51   k  as integral parts thereof. The locking protrusion portion  51   k  is connected to the shutter  51  by way of the elastic portion  51   v . Thus, while the chucking and head openings  41   c  and  41   h  are covered with the shutters  51  and  52 , the locking protrusion portion  51   k , to which an elastic force is applied from the elastic portion  51   v , engages with a locking hole  40   k  of the cartridge body  40 , thereby fixing and supporting the shutter  51  in a non-rotatable state to the cartridge body  40 . When the shutter  51  is fixed, the other shutter  52 , which is interlocked with the shutter  51  via the interlocking mechanism  50   c , is also fixed. 
     Accordingly, only by getting the locking protrusion portion  51   k  pressed externally by a protrusion, for example, in the direction indicated by the arrow  50 A and disengaged from the locking hole  40   k  while pressing the opening/closing portion  52   t  in the direction indicated by the arrow  50 B at the same time as shown in  FIG. 36 , the shutters  51  and  52  can be rotated to expose the chucking and head openings  41   c  and  41   h  and the disc  100  can be released from the disc holding portions  51   a ,  51   b ,  52   a  and  52   b . Thus, it is possible to prevent the operator from removing the disc  100  accidentally. 
     Also, unlike the eighth embodiment, the locking protrusion portion  51   k  and the opening/closing portion  52   t  are provided for the two different shutters  51  and  52 . Such a structure is particularly effective for a disc cartridge for a disc of a small diameter. This is because a disc cartridge for a disc of a small diameter and the shutters thereof should have relatively small sizes and it is normally difficult to provide the locking protrusion portion and opening/closing portion for a single shutter out of design considerations. Also, even when a single shutter can include both the locking protrusion portion and the opening/closing portion, a very narrow gap would be allowed between a shutter opening/closing mechanism and an unlocking mechanism on the disc drive side or these two mechanisms need to be provided within a very limited space, thus making it hard to design the disc drive as intended. 
     The locking protrusion portion  51   k  forms an integral part of the shutter  51 . Alternatively, a locking lever, including a locking protrusion portion and a convex portion at the end thereof, may be connected to the cartridge body  40  by way of an elastic portion, and an associated concave portion may be provided for the shutter so that the convex and concave portions engage with each other. In that case, by pressing the locking protrusion portion through a locking hole of the cartridge body, these convex and concave portions may be disengaged from each other so as to allow the shutters to rotate freely. Optionally, in that case, the locking lever, as well as the shutter springs (i.e., elastic members), may be resin springs that form integral parts of the cartridge body  40 . 
     Next, it will be described how the convex portions  51   e  and  52   e  on the shutters  51  and  52  work.  FIG. 38  is a cross-sectional view illustrating the center of the disc and its surrounding portions as viewed along a plane that passes the center of the disc  100 . As shown in  FIG. 38 , while the shutters  51  and  52  are closed, the convex portions  51   e  and  52   e  protrude into the center hole  100   h  and the disc  100  is now in plane contact with the shutters  51  and  52 . 
     As shown in  FIG. 39 , while the shutters  51  and  52  are going to be opened, the convex portions  51   e  and  52   e  slide from inside the center hole  100   h  into under the lower surface of the disc  100 , thereby lifting the disc  100  and bringing the disc  100  out of plane contact with the shutters  51  and  52 . In this manner, while the shutters  51  and  52  are going to be opened or closed, the signal recording side  100 A will not get scratched by the shutters  51  and  52 . Also, it is inside the signal recording area of the signal recording side  100 A that the convex portions  51   e  and  52   e  move along with the shutters  51  and  52  being opened or closed. Accordingly, the convex portions  51   e  and  52   e  never contact with, or scratch, the signal recording area. 
     Next, the structure and operation of the stopper members will be described with reference to  FIGS. 40 and 41 .  FIG. 40  is a cross-sectional view illustrating a portion surrounding the disc outer periphery as viewed along a plane that passes the center of the disc  100 . A convex portion  42   c ′, ( 42   a ′,  42   b ′ or  42   d ′) has been formed on the bottom of the stopper member  42   c , ( 42   a ,  42   b  or  42   d ). While the shutters  51  and  52  are closed, the stopper member  42   c  is substantially parallel to the disc  100  and falls within the thickness of the cartridge  309  as shown in  FIG. 40 . An appearance of the disc cartridge  309  in such a state is illustrated in  FIG. 36 . 
     On the other hand, while the shutters  51  and  52  are opened, the slope portions  52   f ,  51   f ,  51   d  and  52   d  of the shutters  51  and  52  contact with the convex portions  42   a ′,  42   b ′,  42   c ′ and or  42   d ′, respectively, thereby lifting the stopper members  42   a ,  42   b ,  42   c  and  42   d  to above the disc  100  as shown in  FIG. 41 . An appearance of the disc cartridge  309  in such a state is illustrated in  FIG. 37 . By using such a structure, particularly in an interval after the disc cartridge  309  has been vertically loaded into a disc drive and before the disc  100  gets chucked, it is possible to prevent the disc  100  from dropping down from the cartridge  309 . In addition, while the disc  100  is being chucked, the disc  100  can move in a broader space. Furthermore, this structure also contributes to further reducing the thickness of the cartridge body. 
     It should be noted that to keep the shutters  51  and  52  temporarily opened for a while, the slope portion  52   f , ( 51   f ,  51   d  or  52   d ) may have a convex or concave portion that engages with the convex portion  42   a ′, ( 42   b ′,  42   c ′ or  42   d ′). 
     Embodiment 10 
     Hereinafter, a disc cartridge  310  according to a tenth embodiment of the present invention will be described with reference to the drawings. The disc cartridge  310  of this embodiment is mainly characterized in that stopper members are provided for the shutters. 
     As shown in  FIGS. 42 and 43 , the disc cartridge  310  includes a cartridge lower shell  71 , a cartridge upper shell  72 , stopper members  81   d ,  81   f  and  82   d , and a pair of shutters  81  and  82 . 
     As shown in  FIG. 43 , the cartridge lower shell  71  includes a chucking opening  71   c  and a head opening  71   h . The chucking opening  71   c  is provided to allow a chucking member (e.g., a spindle motor for rotating the disc  100 ) to enter the disc cartridge  310  externally. The head opening  71   h  is provided to allow a head, which reads and/or writes a signal from/on the signal recording side  100 A of the disc  100 , to enter the disc cartridge  310  and access the signal recording side  100 A. The cartridge lower shell  71  faces the signal recording side  100 A of the disc  100 . Also, the head opening  71   h  reaches one side surface of the cartridge lower shell  71 . 
     The cartridge upper shell  72  includes a circular disc window  72   w , through which the disc  100  can be introduced and removed into/from the disc cartridge  310  and which expands over the entire projection area of the disc  100  to expose the upper surface of the disc  100 . The cartridge upper and lower shells  72  and  71  are adhered or welded together at their outer periphery, thereby forming a cartridge body  70 . 
     A disc storage portion  70   d  for storing the disc  100  therein is defined by a first inner surface  71   u  of the cartridge lower shell  71  and a second inner surface  72   i  of the cartridge upper shell  72 . The first inner surface  71   u  is opposed to the signal recording side  100 A of the disc  100 , while the second inner surface  72   i  has a substantially cylindrical shape and defines the disc window  72   w  inside. That is to say, the first inner surface  71   u  becomes the bottom of the disc storage portion  70   d.    
     In the disc storage portion  70   d , a gap, which is wide enough to allow the disc  100  to rotate freely, is provided between the second inner surface  72   i  and the disc  100 . Also, the top of the disc storage portion  70   d  is the disc window  72   w  so that the disc  100  stored in the disc storage portion  70   d  has one side thereof exposed inside the disc window  72   w.    
     The shutters  81  and  82  are disposed between the signal recording side  100 A of the disc  100  and the inner surface  71   u  of the disc storage portion  70   d . The shutters  81  and  82  include rotation holes  81   u  and  82   u , respectively. These rotation holes  81   u  and  82   u  are engaged in a freely rotatable state with a pair of rotation shafts  71   s , which is located outside of the disc storage portion  70   d  of the cartridge body  70  and opposite to the head opening  71   h . Thus, the shutters  81  and  82  rotate on the rotation shafts  71   s  in such a manner as to expose or cover the chucking and head openings  71   c  and  71   h.    
     A cam  81   c  and a follower  82   c  are provided near the rotation holes  81   u  and  82   u  of the shutters  81  and  82 , respectively. The cam  81   c  and the follower  82   c  have mutually engaging shapes and together make up an interlocking mechanism  80   c  for opening and closing the shutters  81  and  82  while interlocking them with each other. 
     The respective surfaces of the shutters  81  and  82 , which are opposed to the signal recording side  100 A of the disc, are covered with protective layers  81   p  and  82   p  for the purpose of preventing the disc  100  from getting scratched or any dust from entering the signal recording side  100 A thereof. 
     The protective layers  81   p  and  82   p  may be appropriately selected from the group consisting of an anti-scratching nonwoven fabric, a dustproof nonwoven fabric, an anti-scratching coating layer and a dustproof coating layer. In this embodiment, sheets of a dustproof nonwoven fabric are adhered or ultrasonic welded as the protective layers  81   p  and  82   p.    
     Shutter springs  91  and  92  are provided outside of the disc storage portion  70   d  for the shutters  81  and  82 , respectively. These springs  91  and  92  apply an elastic force to the shutters  81  and  82  in such a direction as to close the shutters  81  and  82 . Alternatively, the shutter springs  91  and  92  may apply an elastic force to the shutters  81  and  82  in such a direction as to open the shutters  81  and  82 . Also, if the shutters can operate almost completely synchronously by way of the interlocking mechanism, only one of the shutter springs  91  and  92  may be provided. 
     As in the eighth embodiment, the shutters  81  and  82  include disc holding portions  81   a ,  81   b ,  82   a  and  82   b  at the ends thereof as shown in  FIG. 43 . Convex portions  81   e  and  82   e  are also formed on the shutters  81  and  82 , respectively. 
     Furthermore, as will be described in detail later, the stopper members  81   f ,  81   d  and  82   d  are provided as integral parts of the shutters  81  and  82  near the disc holding portions  81   a ,  81   b  and  82   b  of the shutters  81  and  82 , respectively. Alternatively, these stopper members  81   f ,  81   d  and  82   d  may be integrated with the shutters  81  and  82  by way of elastic members. 
     As shown in  FIG. 42 , the upper surface of the cartridge body  70  (or the cartridge upper shell  72 ) has embossed arrow marks (or concave portions)  70   a  that indicate the direction (the arrow  1 A) in which this disc cartridge  310  should be inserted into a disc drive. The cartridge body  70  further includes two concave portions  70   c  on a pair of its side surfaces that are parallel to the inserting direction  1 A. These concave portions  70   c  may be used as either pull-in notches or positioning recesses when the disc cartridge  310  is loaded into a disk drive or when the cartridge  310  is stored in a changer. Optionally, just one side surface of the cartridge  310  may include the concave portion  70   c . In that case, the concave portion  70   c  may be used as a mechanism for preventing erroneous (e.g., upside down) insertion when the disc cartridge  310  is inserted or loaded into a disk drive. The upper surface of the cartridge body  70  further includes a grip portion  70   e  that allows the operator to grip the cartridge  310 . This grip portion  70   e  has an antislip embossed shape. 
       FIG. 44  is a perspective view illustrating a state where the shutters  81  and  82  cover the chucking opening  71   c  and the head opening  71   h  with the disc  100  removed.  FIG. 45  is a perspective view illustrating a state where the shutters  81  and  82  expose the chucking opening  71   c  and the head opening  71   h  with the disc  100  removed. 
     Hereinafter, the structure and the operation of the shutters  81  and  82  will be described in further detail. As shown in  FIGS. 42 and 43 , the disc holding portions  81   a ,  81   b ,  82   a  and  82   b  provided for the shutters  81  and  82  have such a shape as including a slope that tilts in such a manner as to overhang the projection area of the disc and to overlap with the outer periphery of the disc  100  as in the eighth embodiment. That is to say, the slope is downwardly tapered and leans toward the disc  100 . Thus, the same effects as those of the eighth embodiment are also achieved. 
     Also, the shutter  82  includes an opening/closing portion  82   t  for use to open and close the shutters externally, an elastic portion  82   v  and a locking protrusion portion  82   k  as integral parts thereof. The locking protrusion portion  82   k  is connected to the shutter  82  by way of the elastic portion  82   v . Thus, while the chucking and head openings  71   c  and  71   h  are covered with the shutters  81  and  82 , the locking protrusion portion  82   k , to which an elastic force is applied from the elastic portion  82   v , engages with a locking hole  70   k  of the cartridge body  70  as shown in  FIG. 44 , thereby fixing and supporting the shutter  82  in a non-rotatable state to the cartridge body  70 . When the shutter  82  is fixed, the other shutter  82 , which is interlocked with the shutter  82  via the interlocking mechanism  80   c , is also fixed. 
     Accordingly, only by getting the locking protrusion portion  82   k  pressed externally by a protrusion, for example, in the direction indicated by the arrow  70 A and disengaged from the locking hole  70   k  while pressing the opening/closing portion  82   t  in the direction indicated by the arrow  70 B at the same time as shown in  FIG. 44 , the shutters  81  and  82  can be rotated to expose the chucking and head openings  71   c  and  71   h  and the disc  100  can be released from the disc holding portions  81   a ,  81   b ,  82   a  and  82   b . Thus, it is possible to prevent the operator from removing the disc accidentally. 
     The locking protrusion portion  82   k  forms an integral part of the shutter  82 . Alternatively, a locking lever, including a locking protrusion portion and a convex portion at the end thereof, may be connected to the cartridge body  70  by way of an elastic portion, and a concave portion may be provided for the shutter so that the convex and concave portions engage with each other. In that case, by pressing the locking protrusion portion through a locking hole of the cartridge body, these convex and concave portions may be disengaged from each other so as to allow the shutters to rotate freely. Optionally, in that case, the locking lever, as well as the shutter springs (i.e., elastic members), may be resin springs that form integral parts of the cartridge body  70 . 
     Next, the structure and operation of the stopper members  81   f ,  81   d  and  82   d  will be described in further detail. While the shutters  81  and  82  are closed, the stopper members  81   f ,  81   d  and  82   d  are substantially parallel to the disc  100  and do not protrude from the upper surface of the disc cartridge  310  as shown in  FIGS. 46 and 48 . An appearance of the disc cartridge  310  in such a state is illustrated in  FIG. 44 . 
     On the other hand, while the shutters  81  and  82  are going to be opened, the stopper members  81   f ,  81   d  and  82   d  are guided by a slit  70   s  and a sloped portion  72   s  of the cartridge body  70  so as to be lifted to above the disc  100  as shown in  FIGS. 47 and 49 . The slit  70   s  is formed in the inner sidewall portion of the cartridge body  70 , while the sloped portion  72   s  is formed on the inner upper wall of the cartridge body  70 . Also, the cartridge upper shell  72  is provided with notched portions  72   a ,  72   b  and  72   c  so as not to interfere with the stopper members  81   f ,  81   d  and  82   d  that have been lifted up. An appearance of the disc cartridge  310  in such a state is illustrated in  FIG. 45 . 
     While the shutters  81  and  82  are closed, the stopper members  81   f ,  81   d  and  82   d  overhang the projection area of the disc  100  and are located over the disc  100 . Thus, the stopper members  81   f ,  81   d  and  82   d  press the disc  100  against the shutters  81  and  82  in the thickness direction, thereby holding the disc  100  thereon. Accordingly, the disc holding portions  81   a ,  81   b ,  82   a  and  82   b  may be omitted from the shutters  81  and  82 . 
     According to such a structure, particularly in an interval after the disc cartridge  310  has been vertically loaded into a disc drive and before the disc  100  gets chucked, it is possible to prevent the disc  100  from dropping down from the disc cartridge  310 . In addition, while the disc  100  is being chucked, the disc  100  can move in a broader space. Furthermore, this structure also contributes to further reducing the thickness of the cartridge body. 
     Embodiment 11 
     Hereinafter, a disc cartridge  311  according to an eleventh embodiment of the present invention will be described with reference to the drawings. 
     As shown in  FIGS. 50 and 51 , the disc cartridge  311  includes a cartridge lower shell  11 , a cartridge upper shell  12 , a pair of shutters  21  and  22  and stopper members  23 . As shown in  FIGS. 52 through 56 , the structures and functions of all of these members are the same as those already described for the eighth embodiment and the detailed description thereof will be omitted herein. 
     Unlike the disc cartridge  308  of the eighth embodiment, the shutters  21  and  22  of the disc cartridge  311  of this embodiment have a hole  20   h  as shown in  FIGS. 50 and 51 . 
     More specifically, while the shutters  21  and  22  of the disc cartridge  311  are closed, the shutters  21  and  22  define the hole  20   h  just under the center hole  100   h  of the disc  100 . The hole  20   h  is made up of two notches  21   h  and  22   h  provided for the shutters  21  and  22 , respectively. 
     If the disc cartridge  311  is left with the upper surface of the disc  100  exposed upward as shown in  FIG. 50 , dust may pass through the center hole  100   h . Even so, in this structure, the dust should pass and go out through the hole  20   h  of the shutters  21  and  22  without remaining inside the disc cartridge  311 , or without being deposited on the shutters  21  and  22 . Thus, when the shutters  21  and  22  are opened (i.e., when this disc cartridge  311  is loaded into a disc drive), no dust will have been deposited on the signal recording side  100 A of the disc. 
     Considering the disc cartridge  311  may be left either upside up as shown in  FIG. 50  or upside down (i.e., with the cartridge lower shell  11  facing upward), the hole  20   h  preferably has a diameter that is approximately equal to that of the center hole  100   h . This is because if such a relationship is satisfied, dust will be deposited neither on the shutters  21  and  22  when the disc cartridge  311  is left upside up nor on the signal recording side  100 A of the disc  100  when the disc cartridge  311  is left upside down. 
     In this disc cartridge  311 , the opening/closing portion for use to open and close the shutters  21  and  22  is provided for the shutter  22  unlike the disc cartridge  308  of the eighth embodiment. More specifically, as shown in  FIGS. 51 and 57 , the opening/closing portion  22   t , elastic portion  22   v  and locking protrusion portion  22   k  are provided as integral parts of the shutter  22 . The locking protrusion portion  22   k  is connected to the shutter  22  by way of the elastic portion  22   v . Accordingly, unlike the eighth embodiment, the opening/closing portion  22   t  is located on the right-hand side of the head opening  11   h  with respect to the disc  100 . The function and the operation of the opening/closing portion  22   t  are the same as those described for the disc cartridge  308  of the eighth embodiment. 
     Embodiment 12 
     Hereinafter, a disc cartridge  312  according to a twelfth embodiment of the present invention will be described with reference to the drawings. 
     Unlike the disc cartridge  311  of the eleventh embodiment, the disc cartridge  312  includes a rim  12   t  around the inner side surface  12   i  of the disc storage portion  10   d  and a convex portion  20   w  around the hole  20   h  defined by the shutters  21  and  22 . These features will be described below. 
     As shown in  FIG. 58 , the rim  12   t  protrudes from the inner side surface  12   i  of the cartridge upper shell  12  toward the inner periphery of the disc  100  and substantially surrounds the outer periphery of the disc storage portion  10   d .  FIG. 59  shows a cross section of the disc cartridge  312  in a state where the disc  100  is stored in the disc storage portion  10   d . While the shutters  21  and  22  are closed, the outer edge of the signal recording side  100 A of the disc  100  contacts with the rim  12   t  as shown in  FIG. 59 . As a result, the gap between the outer periphery of the disc  100  and the cartridge body is closed, thereby preventing any dust from reaching the signal recording side  100 A. 
     Also, a gap  10   w  is provided between the rim  12   t  of the cartridge body  10  and the cartridge lower shell  11 . Thus, when the shutters  21  and  22  are opened, respective portions of the shutters  21  and  22  enter the gap  10   w  as shown in  FIGS. 60 and 61 . In this manner, it is possible to prevent the shutters  21  and  22  from interfering with the cartridge body  10 . 
     In such a structure, however, while the shutters  21  and  22  are closed, another gap  10   z  that leads to the open air is also created between the disc  100  and the shutters  21  and  22  as shown in  FIG. 59 . To close this gap  10   z , the shutters  21  and  22  include convex portions  21   w  and  22   w , respectively, around the center hole  100   h  of the disc. As shown in  FIG. 58 , when the shutters  21  and  22  are closed, these convex portions  21   w  and  22   w  are in tight contact with each other, thereby forming the convex portion  20   w  that closes the gap  10   z  around the entire disc center hole  100   h . As a result, no dust will reach the signal recording side  100 A of the disc  100  through the disc center hole  100   h.    
     However, the top of these convex portions  21   w  and  22   w  might contact with the signal recording side  100 A of the disc  100 . Accordingly, the edge of the convex portions  21   w  and  22   w  should preferably be round so as not to scratch the disc. Optionally, the convex portions  21   w  and  22   w  may form integral parts of the shutters  21  and  22 , respectively. In that case, an anti-scratching nonwoven fabric is preferably adhered or ultrasonic welded to that portion of the convex portion  20   w  that contacts with the disc  100  or an anti-scratching coating is preferably formed on that portion. Alternatively, the convex portions  21   w  and  22   w  themselves may be made of an anti-scratching nonwoven fabric or an anti-scratching coating and directly ultrasonic welded or bonded to the shutters  21  and  22 , respectively. 
     Also, as shown in  FIG. 59 , while the shutters  21  and  22  are closed, the disc  100  is held by the shutters  21  and  22  so as to be lifted by the convex portion  20   w  and the rim  12   t  over the shutters  21  and  22  with the gap  10   z  left between them. That is to say, most of the signal recording side  100 A of the disc  100  is not in plane contact with the shutters  21  and  22 . Accordingly, even if the shutters  21  and  22  are subjected to no treatment (e.g., even when no anti-scratching nonwoven fabric is attached thereto), the signal recording side  100 A still will not get scratched. 
       FIGS. 62 and 63  illustrate a disc cartridge including alternative convex portions  21   w ′ and  22   w ′ that have been expanded toward the outer periphery of the disc  100 . Specifically,  FIG. 62  illustrates a state where the shutters  21  and  22  are closed, while  FIG. 63  illustrates a state where the shutters  21  and  22  are opened. 
     As shown in  FIGS. 62 and 63 , while the shutters  21  and  22  are opened, the convex portions  21   w ′ and  22   w ′ are preferably located inside the rim  12   t  of the disc storage portion  10   d  (i.e., closer to the center of the disc storage portion). Then, the convex portions  21   w ′ and  22   w ′ will not contact with, or interfere with, the rim  12   t.    
     Optionally, the convex portions  21   w ′ and  22   w ′ may form integral parts of the shutters  21  and  22 , respectively. In that case, an anti-scratching nonwoven fabric is preferably adhered or ultrasonic welded to those portions of the convex portions  21   w ′ and  22   w ′ that contact with the disc  100  or an anti-scratching coating is preferably formed thereon. Alternatively, the convex portions  21   w ′ and  22   w ′ themselves may be made of an anti-scratching nonwoven fabric or an anti-scratching coating and directly ultrasonic welded or bonded to the shutters  21  and  22 , respectively. 
     Embodiment 13 
     Hereinafter, a disc cartridge  313  according to a thirteenth embodiment of the present invention will be described with reference to the drawings. 
     First, the structure of the disc cartridge  313  will be outlined with reference to  FIGS. 64 and 65 . As in the eighth embodiment, the disc  100  shown in  FIGS. 64 and 65  also has first and second sides. The first side, on which the label of the disc, for example, is normally printed, is illustrated in  FIG. 64 , while the second side of the disc  100 , i.e., the signal recording side  100 A, is illustrated as the back surface in  FIG. 65 . 
     As shown in  FIGS. 64 and 65 , the disc cartridge  313  includes a cartridge lower shell  11 , a cartridge upper shell  12 , a pair of shutters  21  and  22  and stopper members  23 . 
     As shown in  FIG. 65 , the cartridge lower shell  11  includes a chucking opening  11   c  and a head opening  11   h . The chucking opening  11   c  is provided to allow a chucking member (e.g., a spindle motor for rotating the disc  100 ) to enter the disc cartridge  313  externally. The head opening  11   h  is provided to allow a head, which reads and/or writes a signal from/on the signal recording side  100 A of the disc  100 , to enter the disc cartridge  313  and access the signal recording side  100 A. The cartridge lower shell  11  faces the signal recording side  100 A of the disc  100 . The cartridge lower shell  11  is formed by molding a synthetic resin. 
     The head opening  11  reaches one side surface of the cartridge lower shell  11 . To minimize a decrease in rigidity of the cartridge lower shell  11  due to the presence of the head opening  11   h , the cartridge lower shell  11  includes a bridge portion  11   b  that links both ends of the head opening  11   h  together. 
     The bottom of the cartridge lower shell  11  further includes two positioning holes  11   w  into which cartridge positioning pins of a disc drive are inserted. 
     The cartridge upper shell  12  includes a circular disc window  12   w , through which the disc  100  can be introduced and removed into/from the disc cartridge  313  and which expands over the entire projection area of the disc  100  to expose the upper surface of the disc  100 . The cartridge upper and lower shells  12  and  11  are adhered or welded together at their outer periphery, thereby forming a cartridge body  10 . The cartridge upper shell  12  is also made of a synthetic resin. 
     A disc storage portion  10   d  for storing the disc  100  therein is defined by a first inner surface  11   u  of the cartridge lower shell  11  and a second inner surface  12   i  of the cartridge upper shell  12 . The first inner surface  11   u  is opposed to the signal recording side  100 A of the disc  100 , while the second inner surface  12   i  has a substantially cylindrical shape and defines the disc window  12   w  inside. That is to say, the first inner surface  11   u  becomes the bottom of the disc storage portion  10   d.    
     In the disc storage portion  10   d , a gap, which is wide enough to allow the disc  100  to rotate freely, is provided between the second inner surface  12   i  and the disc  100 . Also, the top of the disc storage portion  10   d  is the disc window  12   w  so that the disc  100  stored in the disc storage portion  10   d  has one side thereof exposed inside the disc window  12   w.    
     The stopper members  23  are provided in a removable state for the cartridge upper shell  12  so as to partially protrude into the disc window  12   w . As shown in  FIGS. 64 and 65 , two stopper members  23  are provided in this embodiment. On the other hand, a stopper portion  12   s  is provided for the cartridge upper shell  12  so as to protrude into the disc window  12   w . The stopper portion  12   s  forms an integral part of the cartridge upper shell  12 . The two stopper members  23  and the stopper portion  12   s  are arranged approximately at regular intervals around the circumference of the disc window  12   w  for the purpose of preventing the disc  100  from dropping down from the disc window  12   w . Also, two convex disc contact portions  12   s ′ are formed on the stopper portion  12   s . For the disc  100 , these disc contact portions  12   s ′ are as high as the disc contact portions  23   a  of the stopper members  23 . 
     According to this structure, even if the disc cartridge  313  is mounted vertically or upside down, the disc  100  still can be kept in a fixed position. That is to say, when the disc cartridge  313  is inserted vertically or upside down into a disc drive, the dropping can be prevented particularly effectively. It should be noted that the stopper members  23  do not have to be removable from the cartridge body  10 . Alternatively, as long as the stopper members  23  can be rotated or turned inside the disc storage portion  10   d  to such an extent as to allow the operator to remove the disc  100  from the cartridge body  10 , the stopper members  23  may also be secured to the cartridge upper shell  12 . 
     The shutters  21  and  22  lie on a single plane between the signal recording side  100 A of the disc  100  and the inner surface  11   u  of the disc storage portion  10   d . The shutters  21  and  22  include rotation holes  21   u  and  22   u , respectively. These rotation holes  21   u  and  22   u  are engaged in a freely rotatable state with a pair of rotation shafts  11   s , which is located outside of the disc storage portion  10   d  of the cartridge body  10  and opposite to the head opening  11   h . Thus, the shutters  21  and  22  rotate on the rotation shafts  11   s  in such a manner as to expose or cover the chucking and head openings  11   c  and  11   h . The shutters  21  and  22  are also made of a synthetic resin. 
     A ring-shaped portion  21   c  and a pin-shaped portion  22   c  are provided near the rotation holes  21   u  and  22   u  of the shutters  21  and  22 , respectively. The ring-shaped portion  21   c  and the pin-shaped portion  22   c  have mutually engaging shapes and together make up an interlocking mechanism  20   c  for opening and closing the shutters  21  and  22  while interlocking them with each other. The interlocking mechanism  20   c  may also be any other interlocking mechanism such as a cam mechanism or a gear mechanism. 
     The respective surfaces of the shutters  21  and  22 , which are opposed to the signal recording side  100 A of the disc, are covered with protective layers  21   p  and  22   p  for the purpose of preventing the disc  100  from getting scratched or any dust from entering the signal recording side  100 A thereof. 
     The protective layers  21   p  and  22   p  may be appropriately selected from the group consisting of an anti-scratching nonwoven fabric, a dustproof nonwoven fabric, an anti-scratching coating layer and a dustproof coating layer. In this embodiment, sheets of a dustproof nonwoven fabric are adhered or ultrasonic welded as the protective layers  21   p  and  22   p.    
     A locking protrusion portion  21   k  is provided for the shutter  21 , while a locking engaging portion  22   k , which engages with the locking protrusion portion  21   k , is provided for the shutter  22 . The locking protrusion portion  21   k  and locking engaging portion  22   k  together make up a locking mechanism  20   k  for locking and unlocking the shutters  21  and  22  to/from each other. By using this structure, the shutters  21  and  22  can be locked and unlocked, thus preventing the operator from opening the shutters accidentally. In addition, the signal recording side  100 A of the disc  100  can be protected from dust, finger marks or scratches. The locking protrusion portion  21   k  and the locking engaging portion  22   k  form integral parts of the shutters  21  and  22 , respectively. 
     Furthermore, the shutters  21  and  22  are provided with notches  21   h  and  22   h , respectively. When the shutters  21  and  22  are closed, these notches  21   h  and  22   h  contact with each other to form a hole  20   h . While the shutters  21  and  22  are closed, the hole  20   h  is located just under the center hole  100   h  of the disc  100 . The diameter of the hole  20   h  is approximately equal to that of the center hole  100   h  of the disc  100 . In such a structure, even if this disc cartridge  313  is left with the upside up, no dust will be deposited on the shutters  21  and  22 . Also, even if the disc cartridge  313  is left upside down, no dust will be directly deposited on the signal recording side  100 A of the disc  100 , either. 
     As described for the eighth embodiment, the shutters  21  and  22  include disc holding portions  21   a ,  21   b ,  22   a , and  22   b  for holding the disc  100  thereon while the shutters are closed. The disc holding portions  21   a ,  21   b ,  22   a  and  22   b  have been molded integrally with the shutters  21  and  22  so as to be dispersed around the circumference of the disc. Each of these disc holding portions  21   a ,  21   b ,  22   a  and  22   b  has a downwardly tapered slope to contact with the disc  100 . By providing these slopes, the disc  100  can be held firmly and pressed against the shutters  21  and  22  while the shutters  21  and  22  are closed. 
     In this embodiment, only the disc holding portion  21   b  is not secured to the shutter  21  but is connected thereto via an elastic portion  21   d  and is freely rotatable in the radial direction of the disc  100  (i.e., toward the center of the disc). Accordingly, the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  can firmly hold a disc  100  having any of various diameters or thicknesses without allowing the disc  100  to move inconstantly. 
     A shutter opening/closing portion  22   t  for use to open and close the shutter  22  is formed as an integral part of the shutter  22  so as to be opposed to the rotation hole  22   u , i.e., near the disc holding portion  22   a . When the shutters  21  and  22  are attached to the cartridge body  10 , the shutter opening/closing portion  22   t  is located under the bridge portion  11   b  and inside the head opening  11   h . In opening or closing the shutters  21  and  22 , the opening/closing portion  22   t  is moved along the bridge portion  11   b  inside the head opening  11   h . In this arrangement, there is no need to separately provide any gap for allowing the shutter opening/closing portion  21   t  to move therein for the cartridge body  10 . In other words, since there is no need to provide an extra gap for the cartridge body  10 , no dust will enter the cartridge body  10  unnecessarily. Furthermore, the shutter opening/closing portion  22   t  can be disposed inside the head opening  11   h  of the cartridge body  10 , thus providing a cartridge of a good design. 
     As shown in  FIG. 66 , the shutters  21  and  22  are not entirely in contact with each other along a line but have a plurality of contact surfaces that are not aligned with the line. More specifically, the shutters  21  and  22  have a first pair of contact surfaces  21   f  and  22   f  over the chucking opening  11   c  and a second pair of contact surfaces  21   g  and  22   g  over the head opening  11   h , respectively. In this embodiment, the contact surfaces  21   f  and  22   f  contact with each other along the center-of-symmetry line of the disc cartridge  313 . On the other hand, the contact surfaces  21   g  and  22   g  contact with each other along a line that defines a predetermined angle (e.g., approximately 15 to 16 degrees) with the center-of-symmetry line. When the shutters  21  and  22  have such shapes, the shutter  22  can have an integral shape from the vicinity of the shutter opening/closing portion  22   t  and can have sufficiently high rigidity. 
     Shutter springs  31  and  32  are provided outside of the disc storage portion  10   d  for the shutters  21  and  22 , respectively. These springs  31  and  32  apply an elastic force to the shutters  21  and  22  in such a direction as to close the shutters  21  and  22 . The shutter springs  31  and  32  are inserted into two spring poles  11   t  provided for the cartridge lower shell  1 . In this embodiment, torsion coil springs are used as the shutter springs  31  and  32 . Springs of the same shape are used as the shutter springs  31  and  32  to reduce the cost. Examples of other elastic members that may be used as the shutter springs include compression springs, leaf springs and elastic resin springs. 
     As shown in  FIG. 65 , the disc cartridge  313  includes a write protect member  40 , which is inserted into a groove portion  11   v  of the cartridge lower shell  11  so as to slide along the groove portion  11   v . By sliding the write protect member  40 , the convex portion  40   t  thereof is displaced. Thus, in accordance with the position of the convex portion  40   t , a sensor switch provided for a disc drive is turned ON or OFF. In this manner, writing on the disc  100  may be either prohibited or allowed. 
     This disc cartridge  313  is made up of the cartridge body  10  consisting of the cartridge lower and upper shells  11  and  12 , stopper members  23 , shutters  21  and  22 , shutter springs  31  and  32 , and write protect member  40 . 
     When the cartridge lower and upper shells  11  and  12  are joined together, the two rotation shafts  11   s  of the cartridge lower shell  11  are engaged with two concave portions  12   h  of the cartridge upper shell  12 . In this manner, the rotation shafts  11   s  can have their rigidity increased. Thus, even when the shutters  21  and  22  are open, reduced torsion is created around the respective centers of rotation of the shutters by the elastic force applied from the shutter springs  31  and  32 . As a result, the shutters can be opened to the intended angle. 
     The upper surface of the cartridge body  10  (or the cartridge upper shell  12 ) has a label plane  10   f , on which the contents that have been written on the disc  100  stored can be noted down, and an embossed arrow mark (or concave portion)  10   a  that indicates the direction (the arrow  1 A) in which this disc cartridge  313  is inserted into a disc drive. 
     The cartridge body  10  further includes two pairs of concave portions  10   c  and  10   e  on two side surfaces thereof that are parallel to the inserting direction  1 A. These concave portions  10   c  and  10   e  may be used as either pull-in notches or positioning recesses when the disc cartridge  313  is loaded into a disk drive or when the disc cartridge  313  is stored in a changer. The cartridge body further includes a slit portion  10   b  on one of its side surfaces. The slit portion  10   b  may be used as a recess to identify the upside and downside of the disc cartridge  313  when this disc cartridge  313  is inserted into the disc drive. 
     Hereinafter, it will be described with reference to  FIGS. 66 ,  67 ,  68  and  69  how this disc cartridge  313  operates.  FIGS. 66 and 67  illustrate a state where the shutters are closed and a state where the shutters are opened, respectively.  FIG. 68  illustrates the details of the shutter locking portion. And  FIG. 69  illustrates the details of the disc holding portion of the shutter. 
     First, a storage state of the disc cartridge  313 , i.e., a state of the disc cartridge  313  that has not been loaded into a disc drive yet, will be described. In that state, the shutters  21  and  22  are closed as shown in  FIG. 66 . Also, as shown in  FIG. 69 , the sloped portion  22   a ′ of the disc holding portion  22   a  of the shutter  22  contacts with the outer edge of the disc  100 , thereby holding the disc  100  thereon and pressing the disc  100  in the thickness direction  100   t . In this manner, the signal recording side  100 A is brought into plane contact with the sheet  22   p  of the shutter  22  and the disc  100  is held and fixed onto the cartridge body  10 . The other disc holding portions  21   a ,  21   b  and  22   b  also have their own sloped portions  21   a ′,  21   b ′ and  22   b ′, respectively. Thus, just like the sloped portion  22   a ′, these sloped portions  21   a ′,  21   b ′ and  22   b ′ also hold and fix the disc  100  onto the cartridge body  10 . 
     In this state, the signal recording side  100 A of the disc  100  is in close contact with the sheets  21   p  and  22   p . Thus, no dust will be deposited on the signal recording side  100 A. Also, if the exposed side of the disc  100  is rotated manually or if the shutters  21  and  22  are opened or closed intentionally, then dust, finger marks or any other dirt that has adhered onto the signal recording side  100 A of the disc  100  may be wiped away. 
     Furthermore, since the shutters  21  and  22  are locked by the locking mechanism  20   k , the operator cannot open the shutters  21  and  22  accidentally. Thus, the signal recording side  100 A of the disc  100  can be protected from dust, finger marks or scratches. 
     Furthermore, the hole  20   h , which is defined by the notches  21   h  and  22   h  provided for the shutters  21  and  22 , respectively, is provided in the regions of the shutters  21  and  22  that are located under the center hole  100   h  of the disc  100 . In such a structure, even if the cartridge  313  is left, dust may pass through the center hole  100   h  but will not be deposited on the shutters  21  and  22 . 
     Also, while the shutters  21  and  22  are closed, at least the two pairs of contact surfaces  21   f ,  22   f  and  21   g ,  22   g  of the shutters  21  and  22 , which are butted with each other over the head and chucking openings  11   h  and  11   c , each overlap with each other in the thickness direction of the disc  100  as shown in  FIGS. 70 and 71 . Accordingly, even if the shutters  21  and  22  have been closed incompletely because a disc  100  having a non-regular diameter has been mounted or because the shutters  21  and  22  have not been locked completely, no gap will be created between the contact surfaces of the shutters  21  and  22 . Thus, even in such a situation, the disc  100  can also be protected from dust, finger marks or scratches. 
     Also, as shown in  FIG. 70 , the shutters  21  and  22  are in contact with each other around the head opening  11   h  so that the contact surface  22   g  of the shutter  22  is located over the contact surface  21   g  of the shutter  21 . On the other hand, as shown in  FIG. 71 , the shutters  21  and  22  are in contact with each other around the chucking opening  11   c  so that the contact surface  21   f  of the shutter  21  is located over the contact surface  22   f  of the shutter  22 . In this manner, the angle defined by one of multiple contact surfaces of the shutter  21  or  22  may be different from the angle defined by another one of the contact surfaces of the shutter  21  or  22 . In such a structure, the two shutters  21  and  22  can be tightly engaged with each other in the thickness direction of the disc. Thus, neither the shutter  21  nor the shutter  22  will be raised unintentionally. In addition, while the shutters  21  and  22  are closed, the contact surfaces of the shutters  21  and  22  can have increased rigidity. 
     In this embodiment, the shutters  21  and  22  have the contact surfaces  21   g ,  22   g ,  21   f  and  22   g  shown in  FIGS. 70 and 71 . However, the shutters  21  and  22  may also have contact surfaces at different locations or may contact with each other in a different manner from those shown in  FIGS. 70 and 71 . For example, the contact surfaces  21   g  and  22   g  shown in  FIG. 70  may be shifted to a location around the head opening  11   h  and contact with each other. Alternatively, the contact surfaces  21   f  and  22   f  shown in  FIG. 71  may be shifted to a location around the chucking opening  11   c  and contact with each other. Then, the shutters  21  and  22  can exhibit even higher rigidity when closed, and the gap between the contact surfaces can be further reduced, thus preventing any dust from entering the inside of the cartridge. 
     Also, while the shutters  21  and  22  are closed, convex portions  21   j  and  22   j , provided for the shutters  21  and  22  as shown in  FIG. 68 , are in contact with two shutter stopper portions  12   f  provided for the cartridge upper shell  12  as shown in  FIG. 65 . Accordingly, the shutters  21  and  22  have its rotation regulated and cannot move from their locked positions. As a result, the shutters will not move inconstantly. In addition, it is possible to prevent the operator from breaking the shutters intentionally. Furthermore, since the shutters  21  and  22  have their rotation regulated, the shutter opening/closing portion  22   t  is not displaced. Accordingly, when this disc cartridge  313  is loaded into a disc drive, the shutter opening/closing portion  22   t  can be engaged with the shutter opening/closing mechanism of the disc drive just as intended. 
     Next, it will be described how this disc cartridge  313  is loaded into the disc drive. As shown in  FIG. 66 , when the disc cartridge  313  is inserted into the disc drive in the direction  1 A, the cartridge positioning pins of the disc drive engage with the positioning holes  11   w  of the disc cartridge  313 , thereby determining the horizontal and vertical positions of the disc cartridge  313  inside the disc drive. 
     Then, a shutter opening/closing member of the shutter opening/closing mechanism provided inside the disc drive engages with the shutter opening/closing portion  22   t  shown in  FIG. 68 . At the same time, an unlocking member of the shutter opening/closing mechanism presses a locking press portion  21   y , which is connected to the shutter  21  by way of a locking elastic portion  21   e , in the direction  20 A. As a result, the locking protrusion portion  21   k  of the locking mechanism  20   k  is disengaged from the locking engaging portion  22   k  thereof, thereby unlocking the shutters  21  and  22  from each other. In such a state, the shutter opening/closing member moves the shutter opening/closing portion  22   t  in the direction  20 B at the same time. Consequently, the shutter  21  rotates on the rotation shaft  11   s  while overcoming the elastic force applied from the shutter spring  31  as shown in  FIG. 67 . Synchronously, the other shutter  22 , which is interlocked with the shutter  21  via the interlocking mechanism  20   c , also rotates while overcoming the elastic force applied from the shutter spring  32 . Accordingly, when the shutter  21  has been opened, the shutter  22  will have also been opened. 
     By this point in time, the locking protrusion portion  21   k  and the locking press portion  21   y  will have recovered their original shapes and returned to their home positions along with the locking elastic portion  21   e . Thus, the locking elastic portion  21   e  made of a resin is not deformed plastically. In this manner, the signal recording side  100 A of the disc  100  is exposed through the chucking and head openings  11   c  and  11   h . Also, the disc  100 , which has been held by the disc holding portions  21   a ,  21   b ,  22   a  and  22   b , is released therefrom as the shutters  21  and  22  rotate. As a result, the disc  100  is now freely rotatable inside the disc storage portion  10   d.    
     Subsequently, the spindle motor and the turntable of the disc drive enter the chucking opening  11   c  and the head thereof enters the head opening  11   h . Consequently, the disc drive is now ready to perform a write or read operation on the disc  100 . 
     As described above, only by getting the locking protrusion portion  21   k  pressed externally by a protrusion, for example, in the direction  20 A and disengaged from the locking engaging portion  22   k  while pressing the shutter opening/closing portion  22   t  in the direction indicated by the arrow  20 B at the same time, the shutters  21  and  22  can be rotated to expose the chucking and head openings  11   c  and  11   h  and the disc  100  can be released from the disc holding portions  21   a ,  21   b ,  22   a  and  22   b . Thus, it is possible to prevent the operator from opening the shutters or removing the disc accidentally. As a result, the disc  100  can be protected from dust, finger marks or scratches. 
     Hereinafter, it will be described how the disc cartridge  313  is ejected from the disc drive. When an ejecting mechanism of the disc drive starts to operate, the shutter opening/closing member, which has been engaged with the shutter opening/closing portion  22   t , disengages itself from the shutter opening/closing portion  22   t . As a result, the shutters  21  and  22  cannot be kept opened anymore. That is to say, the shutters  21  and  22 , to which an elastic force is being applied from the shutter springs  31  and  32  in such a direction as to close the shutters  21  and  22 , start to rotate in the closing direction. Consequently, the shutters  21  and  22  close up the head and chucking openings  11   h  and  11   c . In this case, the shutters  21  and  22  are locked to each other by the locking mechanism  20   k . In the meantime, the disc  100  gets held by the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  again to recover its original state. In such a state, the disc cartridge  313  is ejected from the disc drive. 
     In the disc cartridge  313 , the disc contact portion  23   a  of the stopper members  23  provided for the cartridge body  10  and the disc contact portion  12   s ′ of the cartridge upper shell  12  are located at the same vertical level as shown in  FIG. 69 . Also, the top of the sloped portions  21   a ′,  21   b ′,  22   a ′ and  22   b ′ of the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  of the shutters  21  and  22  is higher in level than the bottom of the disc contact portions  23   a  and  12   s ′ in the direction  100   u  in which the disc  100  is moved upward. Accordingly, although the disc cartridge  313  may be used either vertically or upside down depending on the type of the disk drive, the shutters  21  and  22  still can hold the disc  100  firmly thereon. For example, particularly when the disc  100  is used upside down, the disc  100  that is no longer chucked contacts with the disc contact portions  23   a  and  12   s ′ and still can maintain its horizontal position. And when the shutters  21  and  22  are closed in such a state, the disc  100  contacts with the slopes  21   a ′,  21   b ′,  22   a ′ and  22   b ′ this time. Then, the disc  100  will slide along the slopes smoothly to be held firmly by the disc holding portions  21   a ,  21   b ,  22   a  and  22   b.    
     As described above, in the disc cartridge of this embodiment, the cartridge body thereof has a disc window and covers only one side of the disc. Also, a shutter opening/closing portion is provided inside a head opening of the cartridge body, and therefore, there is no need to provide any unnecessary gap for the cartridge body. As a result, no dust will enter the inside of the cartridge body. 
     In addition, the two shutters are made to contact with each other along the centerline of the disc over the chucking opening and along a line, which defines a predetermined angle with the centerline of the disc, over the head opening. Accordingly, these shutters can have an integrated structure from the vicinity of the shutter opening/closing portion and can exhibit sufficiently high rigidity. 
     Furthermore, since the two shutters are locked or unlocked to/from each other, the operator cannot open or close the shutters accidentally. Thus, the disc can be protected from dust, finger marks or scratches. 
     Moreover, at least one of multiple disc holding portions is not secured to the shutter but is just connected thereto via an elastic portion. As an elastic force is also applied from a shutter spring, the disc holding portion can be deformed elastically in the disc radial direction. For that reason, even if a disc of a non-regular diameter has been mounted, such a disc can also be held firmly without allowing it to move inconstantly. 
     Embodiment 14 
     Hereinafter, a disc cartridge  314  according to a fourteenth embodiment of the present invention will be described with reference to  FIGS. 72 through 81 . In the disc cartridge  314  of this embodiment, the same member as the counterpart of the disc cartridge  313  of the thirteenth embodiment is identified by the same reference numeral. 
     The disc cartridge  314  is different from the disc cartridge  313  of the thirteenth embodiment in the respective shapes of the inner upper surface  12   u  of the cartridge upper shell  12  (see  FIG. 79 ), the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  (see  FIGS. 72 through 79 ) and the stopper members  53  (see  FIGS. 72 ,  77  and  78 ). In addition, the disc cartridge  314  further includes a disc receiving portion  60  (see  FIGS. 72 and 81 ). Thus, the following description of the disc cartridge  314  will be focused on these differences. 
     In the disc cartridge  313  of the thirteenth embodiment, the respective tops of the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  thereof are located at substantially the same vertical levels along the outer periphery of the disc  100 . In contrast, in the disc cartridge  314  of this embodiment, protrusions are formed on the disc holding portions  21   b ,  22   a  and  22   b  as shown in  FIGS. 73 and 79 . More specifically, each of the disc holding portions  21   b ,  22   a  and  22   b  includes: a first portion  121   b ,  122   a  or  122   b  that has a protrusion thereon and has a first height h 1 ; and a second portion  221   b ,  222   a  or  222   b  that has a second height h 2 . The other disc holding portion  21   a  consists of a second portion  221   a  that has the second height h 2 . 
     The first height h 1  is greater than the second height h 2  and is approximately equal to the height of the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  of the disc cartridge  313  of the thirteenth embodiment. That is to say, the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  of this embodiment are lower than the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  of the disc cartridge  313  of the thirteenth embodiment except their first portions  121   b ,  122   a  and  122   b.    
     Also, as shown in  FIGS. 74 and 75 , a step  223  is formed on the upper surface of the first portion  122   a  of the disc holding portion  22   a . Specifically, the step  223  is provided along the outer periphery of the disc so that a part of the first portion  122   a  that is closer to the disc is higher than the other part thereof. A similar step is also formed on the upper surface of the first portion  121   b  of the disc holding portion  21   b  and on the upper surface of the first portion  122   b  of the disc holding portion  22   b.    
     As the shutters  21  and  22  are going to be closed, the first portion  121   b ,  122   a  or  122   b  of the disc holding portion  21   b ,  22   a  or  22   b  contacts with the disc  100  earlier than any other portion thereof (i.e., earlier than the second portion  221   b ,  222   a  or  222   b  thereof). 
     The disc holding portions  21   a ,  21   b ,  22   a  and  22   b  move as the shutters  21  and  22  are opened or closed.  FIG. 77  illustrates the respective positions of the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  while the shutters  21  and  22  are closed. On the other hand,  FIG. 78  illustrates the respective positions of the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  while the shutters  21  and  22  are opened.  FIGS. 79 and 80  illustrate cross sections that are respectively taken along the lines B—B and C—C shown in  FIG. 78 . 
     As shown in  FIGS. 77 ,  78  and  79 , the regions  12   y ,  12   x  and  12   z  on the inner upper surface  12   u  of the cartridge upper shell  12 , through which the first portions  121   b ,  122   a  and  122   b  of the disc holding portions  21   b ,  22   a  and  22   b  pass as the shutters  21  and  22  are opened or closed, are recessed. On the other hand, the regions  12   y ′,  12   x ′ and  12   z ′, through which the second portions  221   b ,  222   a  and  222   b  thereof pass, are not recessed. Accordingly, the cartridge upper shell  12  is thinner in the regions  12   x ,  12   y  and  12   z  than in the regions  12   x ′,  12   y ′ and  12   z ′ and the other regions. 
     As shown in  FIGS. 76 and 79 , the top of the first portion  122   a  is located at a vertical level higher than the bottom of the stopper member  53 . Also, the top of the first portion  122   a  of the disc holding portion  22   a  enters the recessed region  12   x  on the inner upper surface  12   u  of the cartridge upper shell  12 , and the recessed region  12   x  receives the top of the first portion  122   a . Since the step  223  is formed at the top of the first portion  122   a , just a part of the upper surface of the first portion  122   a  is in contact with the inner upper surface  12   u . On the other hand, the second portion  222   a  is not in contact with the inner upper surface  12   u  of the cartridge upper shell  12 . 
     To open and close the shutters  21  and  22  smoothly, the friction caused by the contact between the top of the first portion  122   a  of the disc holding portion  22   a  and the inner upper surface  12   u  of the cartridge upper shell  12  is preferably small. For that purpose, the top of the first portion  122   a  of the disc holding portion  22   a  has a convex arc-shaped cross section when taken in the radial direction of the disc  100 . This step  223  is provided to compensate for shortage in strength, which would be caused by a sharpened top, and to make that top moldable more accurately and more easily. 
     As shown in  FIG. 80 , the top of the first portion  122   b  of the disc holding portion  22   b  is also located at a vertical level higher than the bottom of the stopper member  53 . And the top of the first portion  122   b  enters the recessed region  12   z  on the inner upper surface  12   u  of the cartridge upper shell  12  (i.e., the recessed region  12   z  receives the top of the first portion  122   b ). Although not shown, the top of the first portion  121   b  of the disc holding portion  21   b  is also located at a vertical level higher than the bottom of the stopper member  53 , and enters the recessed region  12   y  on the inner upper surface  12   u  of the cartridge upper shell  12 . 
     As described above, the regions  12   x ,  12   y  and  12   z  on the inner upper surface  12   u  of the cartridge upper shell  12  are recessed to receive portions of the disc holding portions. Thus, the overall thickness of the disc cartridge  314  can be reduced by the depth of those recessed regions  12   x ,  12   y  and  12   z.    
     Even if the cartridge having such a structure is used either vertically or upside down, the disc  100  that is no longer chucked never fails to contact with the sloped portion  122   a ′ of the first portion  122   a  of the disc holding portion  22   a  as the shutters  21  and  22  are going to be closed. Thereafter, the disc  100  will slide smoothly along the sloped portion  122   a ′ to contact with the sloped portion  222   a ′ of the second portion  222   a  of the disc holding portion  22   a  (see  FIG. 74 ). At the same time, the disc  100  also contacts with the sloped portion  221   a ′ of the second portion  221   a  of the disc holding portion  21   a  including no protrusion. In this manner, the disc holding portions  21   a  and  22   a  hold the disc  100  thereon cooperatively. The two other disc holding portions  21   b  and  22   b  also hold the disc  100  thereon through similar operations. Accordingly, although this disc cartridge has a reduced thickness, the disc cartridge can close the shutters in any position and can hold the disc thereon just as intended. 
     If this disc cartridge had its overall thickness just reduced without changing the shapes of the disc holding portions (or using the disc holding portions of the first embodiment as they are), the regions  12   x ,  12   x ′,  12   y ,  12   y ′,  12   z  and  12   z ′ on the inner upper surface  12   u  of the cartridge upper shell  12 , through which the disc holding portions  22   a ,  21   b  and  22   b  pass, should all be recessed as can be seen from  FIG. 78 . In that case, the cartridge upper shell  12  would have a reduced thickness over a rather wide area and such a disc cartridge would have a decreased strength. In contrast, the disc cartridge  314  can have its thickness reduced without decreasing its overall strength because the regions  12   x ,  12   y  and  12   z  with a reduced thickness are relatively narrow. 
     In this embodiment, protrusions are provided for three of the four disc holding portions to define the first portions. However, any other number may be selected depending on the number of disc holding portions or the shapes of the shutters. 
     The disc cartridge  314  of this embodiment is also different from the disc cartridge  313  of the thirteenth embodiment in the shape of the stopper members  53 . 
     As shown in  FIG. 72 , the stopper members  53  have the shape of a notched circular plate. Specifically, notches  54  having substantially the same shape as the stopper members  53  are provided along the disc window  12   w  of the cartridge upper shell  12  and the stopper members  53  are engaged in a rotatable state with the notches  54 . As shown in  FIG. 77 , the stopper members  53  are held in such a manner as to partially protrude into the disc window  12   w  of the cartridge upper shell  12  when rotated. Also, as shown in  FIG. 78 , by rotating the stopper members  53 , the stopper members  53  may also be held in such a manner as to be stored inside the cartridge upper shell and not to protrude into the disc window  12   w . If the stopper members  53  are easily disengaged from the notches  54  unintentionally, then the side surfaces of the stopper members  53  and the notches  54  of the cartridge upper shell  12  may have mutually engaging concave and convex portions, for example. 
     In such a structure, the thickness of the stopper members  53  may be substantially equal to that of the upper part of the cartridge upper shell  12 . Thus, the disc cartridge  314  can have a reduced overall thickness. 
     The disc cartridge  314  of this embodiment is also characterized by including a disc receiving portion  60  at the bottom of the inner periphery of the disc storage portion. The disc storage portion is defined by the inner lower surface  11   u  and the inner side surface  11   i  of the cartridge lower shell  11  as shown in  FIGS. 72 ,  77 ,  78  and  81 . The disc receiving portion  60  has an upper surface  60   a , which is parallel to the inner lower surface  11   u  of the cartridge lower shell  11 . 
     While the shutters  21  and  22  are closed and the disc  100  is held by the disc holding portions, the outer edge and its surrounding portion of the signal recording side  100 A of the disc  100  are in contact with the upper surface  60   a  of the disc receiving portion  60 . Thus, no dust will be deposited on the signal recording side  100 A of the disc  100  or accumulated on the inner lower surface  11  of the cartridge lower shell. 
     Alternatively, the disc receiving portion  60  may have any shape other than that shown in  FIG. 81 . For example, as shown in  FIG. 82 , a disc receiving portion  76  having a tapered shape may be formed so as to contact with the inner lower surface  11   u  and the inner side surface  11   i  of the cartridge lower shell. In that case, while the shutters  21  and  22  are closed and the disc  100  is held by the disc holding portions, the outer edge of the signal recording side  100 A of the disc  100  contacts with the disc receiving portion  76 . 
     Embodiment 15 
     Hereinafter, a disc cartridge  315  according to a fifteenth embodiment of the present invention will be described with reference to  FIGS. 83 through 87 . In the disc cartridge  315  of this embodiment, the same member as the counterpart of the disc cartridge  314  of the fourteenth embodiment is identified by the same reference numeral. 
     As shown in  FIG. 83 , the disc cartridge  315  is different from the disc cartridge  314  in that the disc cartridge  315  includes four types of recesses  85 ,  86 ,  87  and  88   a  through  88   c  on respective regions of the inner lower surface  11   u  of the cartridge lower shell  11  that contact with the shutters  21  and  22  and on the lower surfaces  21   v  and  22   v  of the shutters  21  and  22 . These four types of recesses will be described one by one. Where the disc cartridge is supposed to hold a 12 cm disc, these recesses may have a depth of about 0.1 mm to about 0.3 mm, for example. 
     As can be seen from  FIGS. 84 and 85  illustrating a state where the shutters  21  and  22  are closed and a state where the shutters  21  and  22  are opened, respectively, the first type of recesses  86  are formed on respective regions of the inner lower surface  11   u  of the cartridge lower shell  11  that contact with the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  of the shutters  21  and  22  being opened or closed. 
     The disc holding portions  21   a ,  21   b ,  22   a  and  22   b  are sandwiched between the cartridge upper and lower shells  12  and  11  with almost no gap left between them. Accordingly, when respective members of the disc cartridge  315  are assembled together or if any of those members of the disc cartridge  315  has a size that is greatly different from the designed one, the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  might contact with the cartridge upper and lower shells  12  and  11  strongly. In that case, excessive friction would be created between the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  and the cartridge upper or lower shell  12  or  11 . As a result, the shutters  21  and  22  might be unable to be opened or closed so easily or dust might be stirred up due to the friction. 
     However, by providing the first type of recesses  86 , gaps are provided under the disc holding portions  21   a ,  21   b ,  22   a  and  22   b , thus reducing such friction. Then, the shutters  21  and  22  can always be opened or closed smoothly and the dust to be stirred up due to the friction can be reduced. 
     The second type of recesses  87  are formed on those regions where the respective outer edges of the shutters  21  and  22  are located while the shutters  21  and  22  are closed. As shown in  FIGS. 84 and 86 , the second type of recesses  87  preferably include the lines on the inner lower surface  11   u  of the cartridge lower shell  11  that correspond to the outer edges of the shutters  21  and  22  and are preferably present both inside and outside the lines. 
     The disc cartridge  315  is supposed to store the disc therein with one side thereof exposed, and the disc  100  can be pressed in the direction indicated by the arrow A in  FIG. 86 . To protect the signal recording side  100 A of the disc  100 , the nonwoven fabrics  21   s  and  22   s  are provided but the outer edges of the shutters  21  and  22  are not completely covered with the nonwoven fabrics  21   s  and  22   s . Accordingly, if the disc  100  is pressed in the arrowed direction A, then the outer edges of the shutters  21  and  22  contact with the signal recording side  100 A of the disc  100 , thus possibly scratching the signal recording side  100 A. 
     However, if the second type of recesses  87  are provided, the shutters  21  and  22  may be deformed in such a manner that the outer edges thereof are partially forced into the second type of recesses  87 . Then, the pressing force can be dispersed, and the outer edges of the shutters  21  and  22  will not contact with the signal recording side  100 A of the disc  100  too strongly. 
     The third type of recesses include: the third type of recesses  88   a  that are provided on the inner lower surface  11   u  so as to surround the chucking and head openings  11   c  and  11   h ; the third types of recesses  88   b  that are formed on those regions of the inner lower surface  11   u  that are not overlapped by the shutters  21  and  22  being closed; and the third type of recess  88   c  that is provided on a region of the inner lower surface  11   u  that is overlapped by the shutters  21  and  22  being closed. The third type of recesses  88   b  and  88   c  are provided as arcs along the inner side surface of the disc storage portion. In this embodiment, the number of the recesses  88   a  of the third type is three. 
     This disc cartridge  315  is also provided with various types of structures (e.g., a disc receiving portion) for preventing dust from entering the disc cartridge or being deposited on the signal recording side of the disc. However, it is difficult to totally eliminate that entering or deposition of dust. 
     Thus, the third type of recesses are provided to accumulate the dust that has entered the disc cartridge  315 . Specifically, as the shutters  21  and  22  are going to be opened or closed, the dust is collected in these recesses of the third type. Once collected in the third type of recesses, the dust never contacts with the shutters  21  and  22  and remains in the third type of recesses without going out of the third type of recesses. Accordingly, by accumulating the dust in the third type of recesses in this manner, the dust will not interfere with the operation of the shutters or will be stirred up to a much lesser degree due to the friction. 
     It should be noted that these effects are also achievable by the first type of recesses  86  or the second type of recesses  87 . Accordingly, the disc cartridge  315  does not have to include all of the first, second and third types of recesses  86 ,  87 ,  88   a ,  88   b  and  88   c  but may include just one type of recesses. Even so, the shutters will not be interfered with their operation by the dust and almost no dust will be stirred up due to the friction to say the least. 
     Also, to remove the dust that has entered the gap between the shutters  21  and  22  and the inner lower surface  11   u  of the cartridge lower shell  11  and accumulate it in the second type of recesses  87 , for example, even more effectively, the respective lower surfaces  21   v  and  22   v  of the shutters  21  and  22  may be provided with the recesses  85  along the outer edges thereof. In that case, when the shutters  21  and  22  are closed, these recesses  85  are preferably located inside the second type of recesses  87  (i.e., closer to the center of the cartridge) as shown in  FIG. 84 . Also, as shown in  FIG. 86 , while the shutters  21  and  22  are closed, the recesses  85  of the shutters  21  and  22  are preferably discontinuous from the second type of recesses  87  on the inner lower surface  11   u  of the cartridge lower shell  11 . 
     When the recesses  85  are provided, the outer edge portions of the shutters  21  and  22  are deformed more easily. Accordingly, even when a force is externally applied to the disc  100  in the arrowed direction A, the outer edge portions of the shutters  21  and  22  will much less likely contact with the signal recording side  100 A so strongly as to scratch it. Optionally, a nonwoven fabric, for example, may be welded or adhered to these recesses  86 ,  87 ,  88   a ,  88   b  and  88   c . Then, the gaps of the cartridge body can be filled and entering of extraneous dust can be prevented with even more certainty. 
     In this embodiment, the various types of recesses are provided for the disc cartridge  314  of the fourteenth embodiment. Alternatively, these recesses may also be provided for the disc cartridge according to any of the eighth through thirteenth embodiments. 
     Embodiment 16 
     Hereinafter, a disc cartridge  316  according to a sixteenth embodiment of the present invention will be described with reference to  FIGS. 88 through 93 . In the disc cartridge  316  of this embodiment, the same member as the counterpart of the disc cartridge  313  of the thirteenth embodiment is identified by the same reference numeral. 
     As shown in  FIG. 88 , the disc cartridge  316  of this embodiment includes: a first opening/closing portion  22   t  on a first side surface  10   p  of the cartridge body that extends substantially vertically to the direction  1 A in which this disc is inserted; and a second opening/closing portion  93  on a second side surface  10   q  thereof. The first opening/closing portion  22   t  has the same structure as the opening/closing portion  22   t  of the disc cartridge of the thirteenth embodiment. 
     As shown in  FIG. 89 , the second opening/closing portion  93  is formed in the shape of a gear having a hole that can be inserted into a rotation shaft  11   q  provided for the cartridge lower shell  11 . A side surface of the cartridge lower shell  11  has an opening  11   r  to expose a portion of the second opening/closing portion  93  through the second side surface  10   q  of the cartridge body  10  when the second opening/closing portion  93  is inserted into the rotation shaft  11   q . Alternatively, the rotation shaft  11   q  may be provided for the cartridge upper shell  12 . 
     Two shutters  21  and  22  are also provided to expose or cover the head and chucking openings  11   h  and  11   c  of the cartridge lower shell  11 . The first opening/closing portion  22   t  forms an integral part of the shutter  22  (i.e., the first shutter member). On the other hand, a sector gear  21   m , which engages with the second opening/closing portion  93  having the gear shape, is formed on the outer side surface of the shutter  21  (i.e., the second shutter member) and is located near the disc holding portion  21   b . The center of the sector gear  21   m  is the rotation hole  21   u  of the shutter  21 . A concave portion  21   n  is provided adjacent to the sector gear  21   m . This concave portion  21   n  is formed to define a space in which the second opening/closing portion  93  having the gear shape engages with the sector gear  21   m.    
     The shutters  21  and  22  may be opened or closed by using the first opening/closing portion  22   t  in the following manner. First, as shown in  FIG. 90 , the locking protrusion portion  21   k  and the locking engaging portion  22   k , which together make up the locking mechanism  20   k , are disengaged from each other. Then, the first opening/closing portion  22   t  is slid along the first side surface  10   p  of the cartridge as indicated by the arrow  22 W. As a result, the movement of the shutter  22  is transmitted to the shutter  21  by way of the interlocking mechanism  20   c  and these two shutters  21  and  22  expose the head and chucking openings  11   h  and  11   c  cooperatively as shown in  FIG. 91 . 
     The shutters  21  and  22  may also be opened or closed by using the second opening/closing portion  93  in the following manner. First, the locking mechanism  20   k  is unlocked as shown in  FIG. 90 . Next, the second opening/closing portion  93  is rotated to the direction indicated by the arrow  93 A. Then, the sector gear  21   m  gets engaged with the geared second opening/closing portion  93  and starts to rotate around the rotation hole  21   u , thereby opening the shutter  21 . Since the movement of the shutter  21  is transmitted to the shutter  22  by way of the interlocking mechanism  20   c  and these two shutters  21  and  22  expose the head and chucking openings  11   h  and  11   c  cooperatively. When the head and chucking openings  11   h  and  11   c  are completely exposed by the shutters  21  and  22  as shown in  FIG. 91 , a portion of the second opening/closing portion  93  is located inside the concave portion  21   n  of the shutter  21 . 
     In closing the shutters  21  and  22 , the first opening/closing portion  22   t  may be slid in the direction opposite to the direction  22 W or the second opening/closing portion  93  may be rotated to the direction opposite to the direction  93 A. In this embodiment, the shutter springs  31  and  32  are provided to apply an elastic force to the shutters  21  and  22  in such a direction as to close the shutters  21  and  22 . Accordingly, unless a force that is strong enough to open, or keep opened, the shutters  21  and  22  against the elastic force of the shutter springs  31  and  32  is applied to the first or second opening/closing portion  22   t  or  93 , the shutters  21  and  22  close themselves automatically even without performing the operations described above. 
     In the disc cartridge  316  of this embodiment, the opening/closing portions are provided for the shutters  21  and  22  both on a surface that is perpendicular to the disc inserting direction and on a surface that is parallel to the disc inserting direction. Accordingly, no matter whether the disc drive used is compatible with only a disc cartridge including a shutter opening/closing portion on a side surface that extends perpendicularly to the disc cartridge inserting direction or only a disc cartridge including a shutter opening/closing portion on a side surface that extends parallelly to the disc cartridge inserting direction, the disc drive can always write or read a signal on/from the disc in the disc cartridge of this embodiment. 
     Also, in the disc cartridge  316  of this embodiment, the second opening/closing portion  93 , provided for the side surface parallel to the direction in which the disc cartridge  316  is inserted, has a gear shape. Accordingly, a shutter opening/closing mechanism to be provided for the disc drive may also be any of various shapes of gears that can engage with the second opening/closing portion  93 . Thus, the disc drive may use a relatively simple mechanism to open or close the shutters  21  and  22  of the disc cartridge  316 . 
     In the embodiment described above, the sector gear  21   m  is provided near the disc holding portion  21   b . This is because the distance between the sector gear  21   m  at such a position and the rotation hole  21   u  of the shutter  21  is relatively short and because the sector gear  21   m  needs to have a relatively short length to open the shutter  21  fully. However, the sector gear  21   m  does not have to be provided at this position. Alternatively, the sector gear  21   m  and the second opening/closing portion  93  may also be provided at such positions as shown in  FIGS. 92 and 93 . In  FIGS. 92 and 93 , the sector gear  21   m  is located at such a position that when extended, a circular trace drawn by the sector gear  21   m  will substantially intersect with the center of the disc, while the second opening/closing portion  93  is provided at such a position as to engage with the sector gear  21   m . When the second opening/closing portion  93  is provided at such a position, the sector gear  21   m  should be relatively long to open the shutter  21  fully, but the distance between the sector gear  21   m  and the rotation hole  21   u  may also be relatively long. That is to say, since there is a longer distance between the fulcrum and the application point in that case, a lighter force is needed to rotate the second opening/closing portion  93  and open or close the shutters  21  and  22 . 
     Embodiment 17 
     Hereinafter, a disc cartridge  317  according to a seventeenth embodiment of the present invention will be described with reference to  FIGS. 94 through 97 . In the disc cartridge  317  of this embodiment, the same member as the counterpart of the disc cartridge  316  of the sixteenth embodiment is identified by the same reference numeral. 
     As shown in  FIG. 94 , the disc cartridge  317  of this embodiment includes a second opening/closing portion  94  on its second side surface  10   q  instead of the second opening/closing portion  93  of the disc cartridge  316  of the sixteenth embodiment. 
     As can be seen from  FIG. 95 , the second opening/closing portion  94  is a link member that can slide along the opening  11   r  on the side surface of the cartridge lower shell  11  and is bent approximately at the center thereof. Also, the second opening/closing portion  94  includes a protrusion  94   a  at one end thereof. This protrusion  94   a  engages with a groove  21   i  that is provided on the shutter  21  near the disc holding portion  21   b  thereof. 
       FIGS. 96 and 97  illustrate two states of the disc cartridge  317  in which the shutters  21  and  22  thereof are closed and opened, respectively. As already described for the thirteenth and sixteenth embodiments, the shutters  21  and  22  can be opened or closed by sliding the first opening/closing portion  22   t  in the direction indicated by the arrow  22   w.    
     The shutters  21  and  22  may also be opened or closed by using the second opening/closing portion  94  in the following manner. First, the locking mechanism  20   k  is unlocked as shown in  FIG. 96 . Next, the second opening/closing portion  94  is slid in the direction indicated by the arrow  94 B. As a result of this operation, a force is applied to the second opening/closing portion  94  in such a direction as to move the protrusion  94   a  of the second opening/closing portion  94  in the direction indicated by the arrow  94 B. Thus, the shutter  21  is rotated around the rotation hole  21   u  and opened. Since the movement of the shutter  21  is transmitted to the shutter  22  by way of the interlocking mechanism  20   c , these two shutters  21  and  22  expose the head and chucking openings  11   h  and  11   c  cooperatively. As in the sixteenth embodiment, the shutters  21  and  22  can also be closed by sliding the second opening/closing portion  94  in the direction opposite to the direction  94 B, and the shutter springs  31  and  32  also apply an elastic force to the shutters  21  and  22  in the same direction. 
     Just like the disc cartridge of the sixteenth embodiment, no matter whether the disc drive used is compatible with only a disc cartridge including a shutter opening/closing portion on a side surface that extends perpendicularly to the disc cartridge inserting direction or only a disc cartridge including a shutter opening/closing portion on a side surface that extends parallelly to the disc cartridge inserting direction, the disc drive can always write or read a signal on/from the disc in the disc cartridge of this embodiment. 
     Also, as shown in  FIGS. 96 and 97 , the direction  94 B in which the second opening/closing portion  94  is slid to open the shutters  21  and  22  is antiparallel to the disc cartridge inserting direction  1 A. Accordingly, if a protrusion that engages with the second opening/closing portion  94  is provided for a disc drive, that protrusion engages with the second opening/closing portion  94  and opens the shutters  21  and  22  of the disc cartridge while the disc cartridge of this embodiment is going to be inserted into the disc drive. Thus, a simplified shutter opening/closing mechanism may be provided for the disc drive. 
     Embodiment 18 
     Hereinafter, a disc cartridge  318  according to an eighteenth embodiment of the present invention will be described with reference to  FIGS. 98 through 101 . In the disc cartridge  318  of this embodiment, the same member as the counterpart of the disc cartridge  316  of the sixteenth embodiment is identified by the same reference numeral. 
     As shown in  FIG. 98 , the disc cartridge  318  of this embodiment includes a second opening/closing portion  96  on its second side surface  10   q  instead of the second opening/closing portion  93  of the disc cartridge  316  of the sixteenth embodiment. 
     As can be seen from  FIG. 99 , the second opening/closing portion  96  is a belt member that is connected to the disc holding portion  21   a  of the shutter  21 . This belt member has a protrusion  96   a  at one end thereof. And the protrusion  96   a  can slide along the opening  11   r  on the side surface of the cartridge lower shell  11 . Alternatively, the second opening/closing portion  96  may form an integral part of the shutter  21 . 
       FIGS. 100 and 101  illustrate two states of the disc cartridge  318  in which the shutters  21  and  22  thereof are closed and opened, respectively. As already described for the sixteenth and seventeenth embodiments, the shutters  21  and  22  can be opened or closed by sliding the first opening/closing portion  22   t  in the direction indicated by the arrow  22   w.    
     The shutters  21  and  22  may also be opened or closed by using the second opening/closing portion  96  in the following manner. First, the locking mechanism  20   k  is unlocked as shown in  FIG. 100 . Next, the protrusion  96   a  of the second opening/closing portion  96  is slid in the direction indicated by the arrow  96 B. As a result of this operation, a force is applied to the shutter  21  in such a direction as to rotate the shutter  21  on the rotation hole  21   u  and pull the end of the shutter  21  to the direction indicated by the arrow  96 C. Since the movement of the shutter  21  is transmitted to the shutter  22  by way of the interlocking mechanism  20   c , these two shutters  21  and  22  expose the head and chucking openings  11   h  and  11   c  cooperatively. To close the shutters  21  and  22 , the opposite operation is performed. 
     Just like the disc cartridge of the sixteenth embodiment described above, no matter whether the disc drive used is compatible with only a disc cartridge including a shutter opening/closing portion on a side surface that extends perpendicularly to the disc cartridge inserting direction or only a disc cartridge including a shutter opening/closing portion on a side surface that extends parallelly to the disc cartridge inserting direction, the disc drive can always write or read a signal on/from the disc cartridge of this embodiment. 
     If the second opening/closing portion  96  forms an integral part of the shutter  21 , the number of members that make up the disc cartridge can be reduced. As a result, the manufacturing cost of the disc cartridge can be reduced or the manufacturing process thereof can be simplified. 
     In the sixteenth through eighteenth embodiments described above, the second opening/closing portion is provided on the left-hand side with respect to the disc cartridge inserting direction. However, the location of the second opening/closing portion is not limited to the left-hand side described above. Alternatively, the second opening/closing portion may be provided on the right-hand side  10   r  with respect to the disc inserting direction as shown in  FIG. 88 . As another alternative, the second opening/closing portion may also be provided on the back surface  10   t  of the disc cartridge as shown in  FIG. 88 . In that case, the belt-shaped second opening/closing portion  96  of this eighteenth embodiment is preferably used because the disc cartridge can have the second opening/closing portion on its back surface without changing its details so much. 
     Embodiment 19 
     Hereinafter, a disc cartridge  319  according to a nineteenth embodiment of the present invention will be described with reference to  FIGS. 102 and 103 . In the disc cartridge  319  of this embodiment, the same member as the counterpart of the disc cartridge  313  of the thirteenth embodiment is identified by the same reference numeral. 
     The disc cartridge  319  of this embodiment is characterized by providing rotation stopper members  97  for the disc holding portions  21   b ,  22   a  and  22   b  and concave portions  89  for the shutters  21  and  22 , respectively. The concave portions  89  are used to ultrasonic weld a nonwoven fabric to the shutters  21  and  22 . 
     More specifically, the disc holding portions  21   b ,  22   a  and  22   b  include holes  21   q ,  22   r  and  22   q , in which the rotation stopper members  97  are embedded. As shown in  FIG. 103 , the rotation stopper member  97  partially protrudes from the slope  21   b ′, ( 22   a ′ or  22   b ′) of the disc holding portion  21   b , ( 22   a  or  22   b ) and contacts with the outer edge of the disc  100  while the disc  100  is held by the disc holding portions  21   a ,  21   b ,  22   a  and  22   b . The rotation stopper members  97  are preferably made of a material that has some elasticity and a large coefficient of friction. For example, rotation stopper members  97  made of rubber are preferably used. 
     It should be noted that at least one of the disc holding portions  21   a ,  21   b ,  22   a  and  22   b  should be provided with the rotation stopper member  97  to stop the rotation effectively. However, to prevent the unintentional rotation of the disc  100  with more certainty, the three rotation stopper members  97  are preferably provided as shown in  FIG. 102 . 
     In this structure, while the disc  100  is held by the disc holding portions  21   a ,  21   b ,  22   a  and  22   b , the rotation stopper members  97  that are in tight contact with the disc  100  do not allow the operator to rotate the disc  100  so easily. Accordingly, even if the operator tries to rotate the disc  100  intentionally while pressing the disc  100  against the shutters  21  and  22 , the disc  100  will not rotate. Thus, even if relatively stiff dust has adhered to the nonwoven fabric provided for the shutters  21  and  22 , the disc will not get scratched by the operator&#39;s operation such as that described above. 
     In addition, by providing the rotation stopper members  97 , it is also possible to prevent the disc  100  from moving inconstantly inside the disc holding portions. 
     As shown in  FIG. 102 , the shutters  21  and  22  include the concave portions  89 , which are used to ultrasonic weld a nonwoven fabric to those portions of the shutters  21  and  22  that will contact with the signal recording side of the disc  10 . In  FIG. 102 , the concave portions  89  are formed so as to surround the outer periphery of those portions of the shutters  21  and  22  that will contact with the signal recording side. The concave portions  89  are also formed inside the concave portions  89  that surround the outer periphery. However, the regions where the concave portions  89  are provided are not limited to those illustrated in  FIG. 102  as long as the nonwoven fabric can be adhered to the shutters  21  and  22  just as intended. At these concave portions  89 , the nonwoven fabric is ultrasonic welded to the shutters  21  and  22 . The nonwoven fabric might be partially cured or the resin material of the shutters  21  and  22  might partially protrude from the nonwoven fabric during the ultrasonic welding process. Even so, when these concave portions  89  are provided, those cured or protruding portions are received by the concave portions  89  and do not contact with the disc. Thus, the disc does not get scratched. When a nonwoven fabric is provided, these concave portions  89  are also preferably formed on the shutters in any of the first through eighteenth embodiments described above. 
     In the first through nineteenth embodiments described above, a nonwoven fabric is ultrasonic welded or adhered to the shutters. However, if the disc has some anti-scratching structure (e.g., if the signal recording side of the disc is covered with a stiff hard coating), then the nonwoven fabric does not have to be attached thereto, but the shutters may contact with the disc directly. Also, not the entire surface of the shutters has to be in plane contact with the signal recording side of the disc, but the shutters may have such a structure that at least a portion of the shutters contacts with the signal recording side of the disc. That is to say, not the entire surface but just a portion of the surface of the shutters may be in plane contact with the disc. In that case, some anti-scratching structure (e.g., a nonwoven fabric) may be provided for only that portion being in plane contact with the disc. 
     In the first through nineteenth embodiments described above, the disc  100  to be stored in the disc cartridge has just one signal recording side. However, a single-sided disc like this is used for illustrative purposes only. This is because the disc cartridge of the present invention has such a structure as to expose one side of the disc and because a single-sided disc is best suited to a structure of that type. Thus, even a disc having two signal recording sides may be appropriately stored in the disc cartridge of the present invention and may be loaded into a disc drive to write or read a signal thereon/therefrom. It should be noted, however, that where a double-sided disc is stored and housed in the disc cartridge of the present invention, dust may be deposited on the exposed one of the two signal recording sides. Accordingly, in that case, some mechanism for preventing the unwanted dust deposition should preferably be provided. 
     Also, in the first through nineteenth embodiments described above, the size of the disc  100  is not particularly specified. However, the present invention may be implemented as a disc cartridge for accommodating a disc having a size of 12 cm or any of various other sizes. 
     Furthermore, in the first through nineteenth embodiments described above, the disc cartridge is illustrated as having an outer dimension that is slightly greater than the size of the disc. However, the size relationship between the disc and the disc cartridge is not limited to the illustrated one. For example, even when the disc cartridge has an outer dimension that is large enough to store a 12 cm disc therein, the disc storage portion and the disc holding portions of the disc cartridge may have their sizes and structures defined in such a manner as to store an 8 cm disc. Such a disc cartridge may be used as an adapter for getting write and read operations performed on an 8 cm disc by a disc drive for writing or reading a signal on/from a 12 cm disc. 
     The various features as described for the first through nineteenth embodiments may be combined appropriately. For example, the rotation stopper members as described for the nineteenth embodiment may be provided for the disc cartridge of the sixteenth embodiment. Also, the recesses for use to collect dust therein as described for the fifteenth embodiment may be provided for the disc cartridge of the sixteenth embodiment. As can be seen, the first through nineteenth embodiments may be combined in numerous other ways and not all of those possible combinations of embodiments have been described herein. However, it is quite possible for those skilled in the art to carry out those various possible combinations of embodiments by reference to the description of the present application. Thus, it is intended that all of those various possible combinations of embodiments fall within the scope of the present invention. 
     The disc cartridge of the present invention can be used particularly effectively to store a disc having only one recording side. The cartridge body thereof has such a structure as to cover only the signal recording side of the disc and expose the other side thereof. Thus, the cartridge can have a reduced thickness. Also, the shutters thereof are formed in such a shape as to cover just one side of the disc cartridge. Accordingly, the shutters can have a simplified structure and can be formed at a lower cost. In addition, the disc holding portions or disk holding members thereof hold a disc thereon by pressing the disc against the shutters or the cartridge body. Thus, the disc will not move inconstantly inside the cartridge body and no dust will be deposited on the signal recording side of the disc. Furthermore, since the label side of the disc is displayed inside the disc window, the disc cartridge can also have a good design. 
     Thus, the present invention provides a thinner and highly dustproof disc cartridge of a good design that is applicable for use in various types of disc drives. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.