Abstract:
A disc cartridge is played by a drive device. The disc cartridge includes a recording disc and a case for rotatably receiving therein the recording disc. The drive device includes a cartridge holder for receiving the disc cartridge, a spindle for rotating the recording disc installed in the disc cartridge, and a recording/reading head unit for recording information on the recording disc and/or reading the information on the recording disc. A disc type discriminating apparatus is incorporated with both the disc cartridge and the drive device for discriminating the type of the recording disc in the disc cartridge when the disc cartridge is put into the drive device. The apparatus comprises a sensed member fixed to the disc cartridge, the sensed member being capable of representing the type of the recording disc in the is disc cartridge; and a sensing device fixed to the drive device for sensing the sensed member to discriminate the type of the recording disc when the disc cartridge is put into the drive device. The sensed member is not a through hole, and the sensing device is not a device which uses light as detecting medium. The sensed member is spaced away from the sensing device at the time when the sensing device is sensing the sensed member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to disc type discriminating apparatuses for use with a system including a disc cartridge and a drive device by which a recording disc in the disc cartridge is driven, and more particularly to the disc type discriminating apparatuses of a type using a sensed means fixed to the disc cartridge and a sensing means fixed to the drive device, so that when the disc cartridge is slid into the drive device, the sensing means senses the sensed means to discriminate the type (which represents the storage capacity or the like) of the recording disc in the disc cartridge. 
     2. Description of the Prior Art 
     Hitherto, in the data processing field using a memory storage, various disc cartridges have been proposed and put into practical use as a recording medium. The disc cartridge comprises a recording disc and a case (or cartridge) in which the recording disc is rotatably installed. As the recording disc, a magnetic disc, optical disc, optical/magnetic disc and the like are used in accordance with the data storage capacity needed in the data processing field. When the disc cartridge is slid into a drive device, the recording disc in the case becomes set on a spindle of the drive device and a shutter part of the case is opened exposing a recording surface of the disc to a recording/reading head unit (viz., pick-up) of the drive device. When the drive device is switched ON, the disc is turned at a given high speed to record thereon information from the head unit or to give information therefrom to the head unit. Usually, a measure is employed for automatically switching the drive device ON when the disc cartridge is sled into the drive device. 
     As is known, the disc cartridges of each category are classified into some groups depending on the storage capacity, that is, the recording density on the disc. For example, in case of 3.5″ microfloppy-disc cartridge, there are three groups, which are 1.44 MB-type, 1.2 MB-type and 720 KB-type. 
     For playing these different types of disc cartridges by a same drive device, there is need of inputting to a controller of the drive device an information on the type of the disc cartridge just before the disc cartridge is set to the proper position in the drive device. That is, upon receiving the information, the controller has to set the drive device to match to the type of the disc cartridge that is about to be set to the proper position. 
     One of known measures of producing such information is to provide the same portions of the disc cartridges with discrimination holes. For example, a first type of the disc cartridges is provided with a through hole, a second type of the disc cartridges is provided with a bottomed hole and a third type of the disc cartridges is provided with no hole. And, a detecting pin is provided to the drive device. When, upon insertion of a disc cartridge into the drive device, the detecting pin becomes engaged with a through hole, it is judged that the disc cartridge just set in the drive device is of the first type. That is, in case of the first type, the detecting pin is deeply inserted into the hole. In case of the second type, the detecting pin is shallowly inserted into the hole. While, in case of the third type, the detecting pin fails to detect the hole. That is, the moved distance of the detecting pin produces the information on the type of the disc cartridge. Usually, the information is electrically transmitted to the controller. 
     However, due to some reasons, the above-mentioned conventional measure has failed to provide users with satisfaction. That is, due to the compact construction of the disc cartridge, the area where the discrimination hole is provided is very limited, and the contacting engagement of the detecting pin with the discrimination hole is liable to cause abrasion of a periphery of the discrimination hole. Furthermore, the contacting engagement of the detecting pin with the discrimination hole tends to produce a noise. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a measure which is free of the above-mentioned drawbacks. 
     According to the present invention, there is provided a disc type discriminating apparatus for use with a system including a disc cartridge and a drive device, which apparatus comprises a sensed means fixed to a disc cartridge and a sensing means fixed to a drive device, wherein when the disc cartridge is slid into the drive device, the sensing means senses the sensed means to discriminate the type of the disc in the disc cartridge without touching the same. 
     According to a first aspect of the present invention, there is provided a disc type discriminating apparatus used in a system including a disc cartridge and a drive device, the disc cartridge including a recording disc and a case for rotatably receiving therein the recording disc, the drive device driving the recording disc in the disc cartridge and including a cartridge holder for receiving the disc cartridge, a spindle for rotating the recording disc installed in the disc cartridge, and a recording/reading head unit for recording information on the recording disc and/or reading the information on the recording disc. The disc type discriminating apparatus discriminates the type of the recording disc in the disc cartridge when the disc cartridge is put into the drive device. The disc type discriminating device comprises a sensed means fixed to the disc cartridge, the sensed member being capable of representing the type of the recording disc in the disc cartridge, the sensed member being other than a through hole; and a sensing means fixed to the drive device for sensing the sensed means to discriminate the type of the recording disc when the disc cartridge is put into the drive device, the sensing means being other than means which uses light as a detecting medium, wherein the sensed means is spaced away from the sensing means at the time when the sensing means is sensing the sensed means. 
     According to a second aspect of the present invention, there is provided a disc type discriminating apparatus which comprises a disc cartridge including a recording disc; a case for rotatably receiving therein the recording disc, the case having therein an annular ridge by which a receiving portion for rotatably receiving the recording disc is defined and having thereabout a peripheral wall; and an identification metal piece fixed to the case at a position between the annular ridge and the peripheral wall, the identification metal piece being capable of representing the type of the recording disc; and a drive device for driving the recording disc in the disc cartridge, the drive device including: a cartridge holder for receiving the disc cartridge; a spindle for rotating the recording disc installed in the disc cartridge; a recording/reading head unit for recording information on the recording disc and/or reading the information on the recording disc; and a metal sensor for sensing the identification metal piece to discriminate the type of the recording disc in the disc cartridge when the disc cartridge is put into the drive device. 
     According to a third aspect of the present invention, there is provided a disc type discriminating apparatus which comprises a disc cartridge including a recording disc; a case for rotatably receiving therein the recording disc, the case having therein an annular ridge by which a receiving portion for rotatably receiving the recording disc is defined and having thereabout a peripheral wall; and an identification magnet piece fixed to the case at a position between the annular ridge and the peripheral wall, the identification magnet piece being capable of representing the type of the recording disc; and a drive device for driving the recording disc in the disc cartridge, the drive device including a cartridge holder for receiving the disc cartridge; a spindle for rotating the recording disc installed in the disc cartridge; a recording/reading head unit for recording information on the recording disc and/or reading the information on the recording disc; and a magnetic sensor for sensing the identification magnet piece to discriminate the type of the recording disc in the disc cartridge when the disc cartridge is put into the drive device. 
     According to a fourth aspect of the present invention, there is provided a disc cartridge which comprises a recording disc; a case in which the recording disc is rotatably held; and an identification metal piece fixed to the case, the identification metal piece being capable of representing the type of the recording disc. 
     According to a fifth aspect of the present invention, there is provided a disc cartridge which comprises a recording disc; a case in which the recording disc is rotatably held; and an identification magnet piece fixed to the case, the identification magnet piece being capable of representing the type of the recording disc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view showing a disc cartridge and a drive device, to which a first embodiment of the present invention is practically applied, and showing one conventional disc cartridge; 
     FIG. 2 is a back view of the disc cartridge of FIG. 1 to which the first embodiment is applied; 
     FIG. 3 is an exploded view of the disc cartridge of FIG. 1 to which the first embodiment is applied; 
     FIG. 4 is an enlarged sectional view taken along the line IV—IV of FIG. 3; 
     FIGS. 5 and 6 are views similar to FIG. 4, but showing modifications of the first embodiment respectively; 
     FIG. 7 is an exploded view of the drive device of FIG. 1 to which the first embodiment is applied; 
     FIG. 8 is a schematic illustration of a disc type discriminating apparatus which constitutes an essential portion of the present invention; 
     FIG. 9 is a sectional view of the drive device of FIG. 1 under a condition wherein the drive device has set therein the disc cartridge of FIG. 1 to which the first embodiment is applied; 
     FIG. 10 is a view similar to FIG. 9, but showing a condition wherein the drive device of FIG. 1 has set therein the conventional disc cartridge; 
     FIG. 11 is a perspective view showing two disc cartridges and a drive device, to which a second embodiment of the present invention is practically applied, and showing one conventional disc cartridge; 
     FIGS. 12A,  12 B and  12 C are sectional views of the drive device of FIG. 11 with first type (viz., high density type), second type (viz., medium density type) and third type (viz., low density type) disc cartridges set therein respectively; 
     FIG. 13 is a perspective view showing two disc cartridges and a drive device, to which a third embodiment of the present invention is practically applied, and showing one conventional disc cartridge; 
     FIGS. 14A,  14 B and  14 C are sectional views of the drive device of FIG. 13 with first type (viz., high density type), second type (viz., medium density type) and third type (viz., low density type) disc cartridges set therein respectively; 
     FIG. 15 is a partial sectional view of a disc cartridge, showing an identification metal piece fixed to a lower half of the disc cartridge; 
     FIG. 16 is a view similar to FIG. 15, but showing the identification metal piece fixed to an upper half of the disc cartridge; 
     FIG. 17 is an exploded view of the disc cartridge with the identification metal piece fixed to a different position of the disc cartridge; 
     FIG. 18 is a view similar to FIG. 15, but showing the identification metal piece fixed to another different position of the disc cartridge; 
     FIG. 19 is a view similar to FIG. 15, but showing the identification metal piece fixed to still another different position of the disc cartridge; 
     FIG. 20 is a partial perspective view of a lower half of the disc cartridge with the identification metal piece fixed to a further different position of the disc cartridge; and 
     FIG. 21 is a schematic illustration of another disc type discriminating apparatus which is replaceable with the disc type discriminating apparatus of FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to FIGS. 1 to  10 , particularly FIG. 1, there is shown a first embodiment of the present invention. 
     In FIG. 1, there are shown a disc cartridge  1  and a drive device  101  to which the first embodiment is practically applied. In the drawing, a conventional disc cartridge  201  is also shown for reference. 
     The disc cartridge  1  comprises a recording disc  2  which serves as a recording medium and a rectangular case (or cartridge)  3  which rotatably receives therein the recording disc  2 . In the illustrated embodiment, the recording disc  2  is an optical/magnetic disc. The disc cartridge  1  has at a front portion thereof a shutter  4  which is slidably mounted on the case  3 . As is seen from FIG. 2, the disc cartridge  1  is equipped at its back side with an identification metal piece  5 . In the illustrated embodiment, the identification metal piece  5  is positioned near one of two rear corners of the rectangular case  3 . As will be described in detail hereinafter, the identification metal piece  5  is a member for representing the type (viz., storage capacity) of the disc cartridge  1  to which the metal piece  5  is attached. 
     Referring back to FIG. 1, the drive device  101  comprises a cartridge holder  102  which receives and holds therein the disc cartridge  1 , a spindle  103  which rotates the recording disc  2  in the disc cartridge  1  set in the cartridge holder  102 , a recording/reading head unit (viz., pick-up)  104  which, under rotation of the recording disc  2 , records information on a recording surface of the recording disc  2  or reads the information recorded on the recording surface of the recording disc  2 , a bias coil  105  which provides the recording surface of the recording disc  2  with an external magnetic field when the recording/reading head unit  104  records the information on the disc  2 , and a metal sensor  106  which can sense the identification metal piece  5  when the disc cartridge  1  is properly set in the drive device  101 . 
     Detailed construction of the disc cartridge  1  will be described with reference to FIG. 3 which shows an exploded view of the disc cartridge  1  turned upside down. 
     As is shown, the optical/magnetic disc  2  comprises a disc proper  21  and a metallic hub  22  which is fixed to a center of the disc proper  21 . As will become apparent as the description proceeds, the metallic hub  22  is caught by a catching member of the drive device  101  when the disc cartridge  1  is properly set in the drive device  101 . 
     The rectangular case  3  of the disc cartridge  1  comprises upper and lower rectangular halves  31  and  32  which are assembled to constitute a hollow rectangular structure. 
     The upper half  31  has at its inside center portion a smaller annular ridge  31   a  which rotatably receives therein the hub  22 , and at its inside outer portion a larger annular ridge  31   b  which rotatably receives therein the disc proper  21 . The smaller and larger annular ridges  31   a  and  31   b  are concentric with each other. The upper half  31  has further a rectangular cut  31   c  which extends radially outward from the smaller annular ridge  31   a  and terminates at a front edge of the upper half  31 . In the illustrated embodiment, a bridge member (no numeral) extends across the front part of the rectangular cut  31   c.  The upper half  31  has on its outer surface (viz., the surface facing downward in FIG. 3) both a smaller rectangular recess  31   d  which constitutes a slide area for the shutter  4  and a larger rectangular recess  31   e  to which a rectangular label (not shown) is stuck. 
     As is seen in FIG. 3, the lower half  32  has, at a portion facing to both the smaller annular ridge  31   a  and the rectangular cut  31   c  of the upper half  31 , an elongate cut  32   a  which extends radially outward from a center of the lower half  32  and terminates at a front edge of the lower half  32 . As shown, an inner end portion of the elongate cut  32   a  has a rounded periphery. The lower half  32  has at its inside outer portion a larger annular ridge  32   b  which, upon assembly of the upper and lower halves  31  and  32 , abuts against the larger annular ridge  31   b  of the upper half  31  to constitute an enclosed circular space for the disc  2 . The lower half  32  has on its outer surface (viz., the surface facing upward in FIG. 3) both a rectangular recess  32   d  which constitutes a slide area for the shutter  4  and an elongate recess  32   e  to which an elongate label (not shown) is stuck. 
     For assembling the disc cartridge  1 , the two halves  31  and  32  are put on each other with the optical/magnetic disc  2  installed therebetween, and four connecting screws  33 ,  34 ,  35  and  36  are used for securing the two halves  31  and  32 . For receiving the connecting screws  33 ,  34 ,  35  and  36 , the two mated halves  31  and  32  have at their four corners four aligned bores, the bores of the upper half  31  being threaded for fastening the screws as shown. When the two halves  31  and  32  are assembled in the above-mentioned manner, slide guide grooves  31   f  and  31   g  are defined at a front edge of the assembled rectangular case  3 . 
     As is understood from FIGS. 2 and 3, the shutter  4  is slidably disposed to the assembled rectangular case  3 . As is seen from FIG. 3, the shutter  4  comprises an upper blind plate  4   a  which is slidably put on the rectangular recess  31   d  formed on the upper side of the disc cartridge  1 , a lower blind plate  4   b  which is slidably put on the rectangular recess  32   d  formed on the lower side of the assembled rectangular case  3  and a bridge plate  4   c  by which the two blind plates  4   a  and  4   b  are united. The upper blind plate  4   a  has such a size as to sufficiently cover the rectangular cut  31   c  and the lower blind plate  4   b  has such a size as to sufficiently cover the rectangular cut  32   a.  An bar-like slide member  43  is connected through connecting screws  41  and  42  to an inner surface of the bridge plate  4   c,  so that the slide member  43  and the shutter  4  move or slide as a unit. The slide member  43  has at its axial ends leg portions  43   a  and  43   b  which are slidably engaged with the above-mentioned slide guide grooves  31   f  and  31   g  of the assembled rectangular case  3 . Thus, the shutter  4  slides on the rectangular case  3  in a direction parallel with the front edge of the case  3 . Due to sliding of this shutter  4 , the two cuts  31   c  and  32   a  of the case  3  are synchronously closed and synchronously opened by the blind plates  4   a  and  4   b  respectively. The lower blind plate  4   b  has an inward leading end which is slidably received in a guide slot defined by an elongate guide plate  44  fixed to the lower half  32 . Due to provision of the guide plate  44 , the leading end of the lower blind plate  4   b  is suppressed from being lifted out of the outer surface of the lower half  32 . 
     The shutter  4  is biased by a return spring  45  in a given direction, that is, a direction of the arrow “C” in FIG. 3, to close the two cuts  31   c  and  32   a  with the blind plates  4   a  and  4   b.  Thus, when the shutter  4  is moved in the other direction against the return spring  45 , the two cuts  31   c  and  32   a  become opened exposing upper and lower surfaces of the recording disc  2  therethrough. That is, the shutter  4  is movable between a close position wherein the two cuts  31   c  and  32   a  are closed and an open position wherein the two cuts  31   c  and  32   a  are opened. 
     As shown in FIG. 3, the discriminating metal piece  5  is positioned at one end of the elongate recess  32   e  of the lower half  32  near the connecting screw  36 . The discriminating metal piece  5  is circular in shape and is constructed of a stainless steel or the like. 
     As is seen from FIG. 4, the discriminating metal piece  5  is tightly received in a circular recess  32   f  formed in the bottom of the elongate recess  32   e  of the lower half  32  of the case  3 . If desired, as is seen from FIG. 5, an exposed upper surface of the metal piece  5  may be covered with a protection sheet  37 , and as is seen from FIG. 6, the protection sheet  37  may be received in a recess  32   h  so that an upper surface of the protection sheet  37  is flush with the bottom surface of the elongate recess  32   e  of the lower half  32 . With provision of the protection sheet  37 , disconnection of the discriminating metal piece  5  from the recess  32   f  is assuredly prevented. Furthermore, if desired, the discriminating metal piece  5  may be a sheet piece. In this case, the metal piece  5  can be connected to the elongate recess  32   e  by means of an adhesive double coated tape or the like. 
     Detailed construction of the drive device  101  will be described with reference to FIG. 7 which shows an exploded view of the drive device  101 . For ease of understanding, the assembled disc cartridge  1  is also shown in the drawing. 
     The drive device  101  generally comprises a loading assembly  111  and a base assembly  112  which supports thereon the loading assembly  111 . 
     The loading assembly  111  comprises the above-mentioned cartridge holder  102  and a frame  113  in which the cartridge holder  102  is vertically movable. For this vertical movement, the cartridge holder  102  has at its side walls two pairs of guide pins  115  which are accommodated in vertically extending openings  114  formed in side walls of the frame  113 . Although not shown in the drawing, a holder operating plate having a sloped surface is incorporated with the guide pins  115 , so that sliding of the holder operating plate in fore-and-aft directions induces upward and downward movement of the cartridge holder  102  relative to the frame  13 . 
     The cartridge holder  102  is equipped with a shutter opening arm  116  which is pivotally connected to a front portion of the cartridge holder  102  from which the disc cartridge  1  is inserted. A pin  117  is fixed to a leading end of the arm  116 . The above-mentioned bias coil  105  is connected to a middle portion of the cartridge holder  102 . 
     When the disc cartridge  1  is slid into the cartridge holder  102 , the pin  117  of the shutter opening arm  116  pushes the lead portion  43   a  of the slide member  43  to move, against the force of the return spring  45 , the shutter  4  to the open position wherein the two cuts  31   c  and  32   a  of the disc cartridge  1  are opened. When thereafter the disc cartridge  1  is brought to a proper position in the cartridge holder  102 , the above-mentioned operating plate is actuated to put down the cartridge holder  102  onto the base assembly  112 . Upon this, the hub  22  of the optical/magnetic disc  2  is caught or chucked by the spindle  103  of the base assembly  112 . Thereafter, the spindle  103  is rotated to rotate the disc  2  in such a manner as will be described hereinafter. 
     The base assembly  111  comprises a chassis  121  to which the spindle  103  and the recording/reading head unit (viz., pick-up)  104  are mounted. 
     The recording/reading head unit  104  generally comprises an optical fixed part  131 , an optical movable part  132  and a voice coil motor (VCM)  133 . The voice coil motor  133  is positioned below the optical/magnetic disc  2  and functions to move the optical movable part  132  in a radial direction of the disc  2 . Although not shown in the drawing, a laser diode is possessed by the optical fixed part  131 . An objective lens  134  is held by the optical movable part  132 , which faces upward. A half-mirror is installed in the movable part  132  just below the objective lens  134 . 
     To read information recorded on the recording surface of the optical/magnetic disc  2 , a laser beam “B” from the laser diode of the optical fixed part  131  is led into the optical movable part  132 , reflected by the half-mirror and emitted from the objective lens  134  to the information recording surface of the disc  2  to read the information on the recording surface. The laser beam thus including the information is led back through the same path to an information reading section possessed by the optical fixed part  131 . 
     To record information onto the recording surface of the optical/magnetic disc  2 , a powered laser beam is produced by the laser diode, which is irradiated from the objective lens  134  to the recording surface of the disc  2  to heat the same at the Curie point to remove magnetism therefrom. During this, the bias coil  105  is kept energized to apply a bias magnetic field to the recording surface to provide the same with a so-called “S-N” configuration for recording the information. 
     To the chassis  121 , there is mounted a base plate  135  which has a rounded recess for accommodating the spindle  103 . The base plate  135  has first and second disc cartridge positioning pins  136  and  137  fixed thereto. 
     The base plate  135  has near the positioning pin  137  the metal sensor  106  mounted thereto. As will be described hereinafter, the metal sensor  106  senses the identification metal piece  5  attached to the disc cartridge  1 . 
     As is seen from FIG. 8, the metal sensor  106  comprises generally a detecting coil  106   a  and a high-frequency oscillating circuit  106   c  which allows the detecting coil  106   a  to produce a high-frequency magnetic field  106   b.  When, with the detecting coil  106  producing the high-frequency magnetic field  106   b,  the identification metal piece  5  is brought to the area of the magnetic field  106   b,  induced current is forced to flow through the metal piece  5  to change the impedance of the detecting coil  106   a  and thus the oscillation is forced to stop. Thus, by sensing the stop of the oscillation, discrimination is so made by the controller that the disc cartridge  1  is of a type carrying the identification metal piece  5 . 
     The disc cartridge  1  and the drive device  101 , to which the first embodiment is practically applied, have the above-mentioned constructions. 
     Accordingly, when, in operation, the disc cartridge  1  is slid into the cartridge holder  102  of the drive device  101 , the shutter  4  of the disc cartridge  1  is opened by the shutter opening arm  116  of the cartridge holder  102 , and then, as is shown in FIG. 9, the disc cartridge  1  is lowered down together with the cartridge holder  102  to a properly set position wherein the optical/magnetic disc  2  is caught or chucked by the spindle  103  and the identification metal piece  5  of the disc cartridge  1  faces the metal sensor  106  of the drive device  101 . Upon this, the metal sensor  106  senses the identification metal piece  5  in the above-mentioned manner and determines that the disc cartridge  1  is of a type carrying the identification metal piece  5 , that is, for example, a high density type. 
     While, as is seen from FIG. 10, when a conventional disc cartridge  201  (viz., low density type) having no identification metal piece  5  is put into the drive device  101  in the above-mentioned manner, the metal sensor  106  fails to sense the metal piece  5  and thus the impedance of the detecting coil  106  does not change. Thus, discrimination is so made by the controller that the disc cartridge just set in the drive device  101  is of a type carrying no identification metal piece  5 , that is, the conventional low density type. 
     Referring to FIGS. 11,  12 A,  12 B and  12 C, particularly FIG. 11, there is shown a second embodiment of the present invention. In this second embodiment, two, that is, first and second metal sensors  106  and  107  are mounted to separate portions of the drive device  101 . In this case, three types of disc cartridges can be discriminated. 
     In FIG. 11, three types of disc cartridges  1 ,  1 ′ and  201  are shown. The upper disc cartridge  1  is of the above-mentioned high density type, the middle disc cartridge  1 ′ is of a medium density type and the lower disc cartridge  201  is of the above-mentioned low density type (or conventional type). As shown, the high density type disc cartridge  1  is equipped with an identification metal piece  5  of stainless steel at a position that, when the disc cartridge  1  is put into the drive device  101 , faces the first metal sensor  106 , the medium density type disc cartridge  1 ′ is equipped with an identification metal piece  5  of stainless steel at a position that, when the disc cartridge  1 ′ is put into the drive device  101 , faces the second metal sensor  107 , and the low density type disc cartridge  201  is not equipped with the identification metal piece  5 . 
     Accordingly, as is seen from FIG. 12A, when the high density type disc cartridge  1  is put into the drive device  101 , the first metal sensor  106  senses the stainless steel metal piece  5  and thus discrimination is so made by the controller that the disc cartridge  1  just set in the drive device  101  is of the high density type. As is seen from FIG. 12B, when the medium density type disc cartridge  1 ′ is put into the drive device  101 , the second metal sensor  107  senses the stainless steel metal piece  5  and thus discrimination is so made that the disc cartridge  1 ′ just set in the drive device  101  is of the medium density type, and as is seen from FIG. 12C, when the lower density type disc cartridge  201  is put into the drive device  101 , either of the first and second metal sensors  106  and  107  fails to sense the metal piece  5  and thus discrimination is so made that the disc cartridge  201  just set in the drive device  101  is of the low density type. 
     Referring to FIGS. 13,  14 A,  14 B and  14 C, particularly FIG. 13, there is shown a third embodiment of the present invention. In this third embodiment, three types of disc cartridges are discriminated by only one metal sensor  106  mounted to the drive device  101 . 
     In FIG. 13, three types of disc cartridges  1 ,  1 ′ and  201  are shown. The upper disc cartridge  1  is of the above-mentioned high density type, the middle disc cartridge  1 ′ is of a medium density type and the lower disc cartridge  201  is of the above-mentioned low density type. The high density type disc cartridge  1  is equipped with an identification metal piece  5  of stainless steel at a position that, when the disc cartridge  1  is put into the drive device  101 , faces the metal sensor  106 , the medium density type disc cartridge  1 ′ is equipped with an identification metal piece  5 ′ of aluminum at a position that, when the disc cartridge  1 ′ is put into the drive device  101 , faces the metal sensor  106 , and the low density type disc cartridge  201  is not equipped with an identification metal piece  5 . 
     Accordingly, as is seen from FIG. 14A, when the high density type disc cartridge  1  is put into the drive device  101 , the metal sensor  106  senses the stainless steel metal piece  5  and thus discrimination is so made by the controller that the disc cartridge  1  just set in the drive device  101  is of the high density type. As is seen from FIG. 14B, when the medium density type disc cartridge  1 ′ is put into the drive device  101 , the metal sensor  106  senses the aluminum metal piece  5 ′ and thus discrimination is so made that the disc cartridge  1 ′ just set in the drive device  101  is of the medium density type. 
     It is now to be noted that due to essential difference in property between aluminum and stainless steel by which the metal pieces  5  are produced, a frequency produced by the high-frequency oscillating circuit  106   c  of the metal sensor  106  when sensing the aluminum metal piece  5 ′ is different from that produced when sensing the stainless steel metal piece  5 . Thus, by processing this frequency difference, discrimination as to whether the disc cartridge is of the high density type or the medium density type is carried out by the controller. 
     As is seen from FIG. 14C, when the low density type disc cartridge  201  is put into the drive device  101 , the metal sensor  106  fails to sense the metal piece  5  and thus discrimination is so made that the disc cartridge  201  just set in the drive device  101  is of the low density type. 
     It is to be noted that in addition to the above-mentioned stainless steel and aluminum, other metals such as copper, brass and the like are usable as the material of the identification metal pieces  5  and  5 ′. 
     If desired, a measure depicted by FIGS. 15 and 16 may be employed for discriminating a disc cartridge set in the drive device  101 . That is, in the high density type disc cartridge  1  shown in FIG. 15, the identification metal piece  5  is fixed to the lower half  32  of the disc cartridge  1 , while, in the medium density type disc cartridge  1 ′ shown in FIG. 16, the identification metal piece  5  is fixed to the upper half  31  of the disc cartridge  1 ′. Thus, when the high density type disc cartridge  1  (see FIG. 15) is put into the drive device  101 , the identification metal piece  5  faces the metal sensor  106  keeping a shorter distance of “D1” therebetween. While, in case of the medium density type disc cartridge  1 ′ (see FIG.  16 ), the identification metal piece  5  faces the metal sensor  106  keeping a longer distance of “D2” therebetween. Due to difference of the distance, frequencies produced by the high-frequency oscillating circuit  106   c  of the metal sensor  106  when sensing the metal pieces  5  and  5  are different. Thus, by processing this frequency difference, discrimination as to whether the disc cartridge is of the high density type  1  or the medium density type  1 ′ is carried out by the controller. 
     Furthermore, if desired, a measure depicted by FIGS. 17,  18  and  19  may be employed for discriminating a disc cartridge set in the drive device  101 . That is, in this measure, the depth of a recess for putting therein the identification metal piece  5  changes for each type of the disc cartridges. As is seen from FIG. 17, a cylindrical hollow boss  51  is formed on the inner surface of the lower half  32  of the rectangular case  3  at a position between the larger annular ridge  32   b  and an outermost peripheral wall  32   i.  The identification metal piece  5  is put into the boss  51 . Another cylindrical hollow boss  52  is formed on the inner surface of the upper half  31 , which, when the two halves  31  and  32  are coupled to constitute the case  3 , abuts against a top of the metal piece  5  put in the hollow boss  51 . 
     The detail of this measure is depicted by FIGS. 18 and 19. In the high density type disc cartridge  1  shown in FIG. 18, the depth of the hollow boss  51  for the metal piece  5  is relatively large, while, in the medium density type disc cartridge  1 ′ shown in FIG. 19, the depth of the hollow boss  51  is relatively small. Thus, when the high density type disc cartridge  1  (see FIG. 18) is put into the drive device  101 , the identification metal piece  5  faces the metal sensor  106  keeping a shorter distance of “D1” therebetween. While, in case of the medium density type disc cartridge  1 ′ (see FIG.  19 ), the identification metal piece  5  faces the metal sensor  106  keeping a longer distance of “D2” therebetween. For the reason as mentioned hereinabove, discrimination as to whether the disc cartridge is of the high density type  1  or the medium density type  1 ′ is carried out by the controller. 
     Furthermore, if desired, a measure depicted by FIG. 20 may be employed for discriminating a disc cartridge set in the drive device  101 . That is, in this measure, a mounting member  52  is integrally provided to the outermost peripheral wall  32   i  of the lower half  32  of the case  3 . A rectangular parallelepiped identification metal piece  5 ″ is held by the mounting member  52 . The material of the metal piece  5 ′ changes for each type of the disc cartridges. As shown, the metal sensor  106  mounted in the drive device  101  is oriented to face in a direction parallel with a major surface of the lower half  32 . 
     Furthermore, if desired, one of the four connecting screws  33 ,  34 ,  35  and  36  (see FIG. 3) for connecting the upper and lower halves  31  and  32  may be used as the identification metal piece  5 . For example, in the high density type disc cartridge  1 , the connecting screw  36  is constructed of aluminum, and the other three connecting screws  33 ,  34  and  35  are constructed of iron coated with zinc. The metal sensor  106  in the drive device  101  is placed at a position that, when the disc cartridge is put into the drive device  101 , faces the connecting screw  36 . Thus, when the disc cartridge  1  having the above-mentioned connecting screws is put into the drive device  101 , the metal sensor  106  senses the connecting screw  36  (viz., identification metal piece) and discrimination is so made that the disc cartridge  1  just set in the drive device  101  is of the high density type. Furthermore, if desired, the four connecting screws  33 ,  34 ,  35  and  36  may be used as the identification metal pieces  5 . That is, these four connecting screws are constructed of different metals and four metal sensors are mounted to the drive device  101  for sensing the four metal pieces  33 ,  34 ,  35  and  36 . In this case, numerous types of disc cartridges can be discriminated. 
     Furthermore, if desired, in place of the above-mentioned disc type discriminating apparatus of FIG. 8 which includes the identification metal piece  5  and the metal sensor  106 , another type disc type discriminating apparatus may be used, which is shown in FIG.  21 . 
     The disc type discriminating apparatus of FIG. 21 comprises a magnetic sensor  1106  which is mounted in the drive device  101  and an identification magnet piece  1005  which is fixed to the disc cartridge. The magnetic sensor  1106  comprises a fixed contact  1106   a  and a movable contact  1106   b  which are housed in a case (no numeral). When the identification magnet piece  1005  is brought to a position near the magnetic sensor  1106 , the movable contact  1106   b  is brought into contact with the fixed contact  1106   a  to turn the sensor  1106  ON. 
     Thus, when the disc type discriminating apparatus of FIG. 21 is practically employed in the above-mentioned first embodiment of FIG. 1 in place of the discriminating apparatus of FIG. 8, such changes are needed that the identification magnet piece  1005  is fixed to the disc cartridge  1  in place of the identification metal piece  5  and the magnetic sensor  1106  is connected to the drive device  101  in place of the metal sensor  106 . 
     Thus, when the disc cartridge  1  carrying the identification magnet piece  1005  is sled into the drive device  101 , the magnetic sensor  1106  of the drive device  101  senses the magnet piece  1005  and determines that the disc cartridge  1  is of a type carrying the identification magnet piece  1005 , that is, for example, a high density type. 
     When the disc type discriminating apparatus of FIG. 21 is practically employed in the above-mentioned second embodiment of FIG. 11 in place of the discriminating apparatus of FIG. 8, the following changes are needed. 
     That is, respective identification magnet pieces  1005  are fixed to the disc cartridges  1  and  1 ′ in place of the identification metal pieces  5  and  5 . And, first and second magnetic sensors  1106  are mounted to the drive device  101  in place of the two metal sensors  106  and  107 . 
     Thus, when the high density type disc cartridge  1  carrying the identification magnet piece  1005  is put into the drive device  101 , the first magnetic sensor  1106  senses the identification magnet piece  1005  and thus discrimination is so made that the disc cartridge  1  just set in the drive device  101  is of the high density type. While, when the medium density type disc cartridge  1 ′ carrying the identification magnet piece  1005  at a different position is put into the drive device  101 , the second magnetic sensor  1106  senses the identification magnet piece  1005  and thus discrimination is so made that the disc cartridge  1 ′ just set in the drive device  101  is of the medium density type, and when the low density type disc cartridge  201  having no identification magnet piece carried thereon is put into the drive device  101 , either of the first and second magnetic sensors  1106  and  1106  fails to sense the identification magnet piece and thus discrimination is so made that the disc cartridge  201  just set in the drive device  101  is of the low density type. 
     When the disc type discriminating apparatus of FIG. 21 is practically employed in the above-mentioned third embodiment of FIG. 13 in place of the discriminating apparatus of FIG. 8, the following changes are needed. 
     That is, the identification magnet piece  1005  is fixed to the disc cartridge  1  in place of the stainless steel identification piece  5 , a less-powered identification magnet piece is fixed to the disc cartridge  1 ′ in place of the aluminum identification piece  5 ′, and the magnetic sensor  1106  is mounted to the drive device  101  in place of the metal sensor  106 . 
     Thus, when the high density type disc cartridge  1  carrying the identification magnet piece  1005  is put into the drive device  101 , the magnetic sensor  1006  senses the identification magnet piece  1005  and thus discrimination is so made that the disc cartridge  1  just set in the drive device  101  is of the high density type. While, when the medium density type disc cartridge  1 ′ carrying the less-powered identification magnet piece is put into the drive device  101 , the magnetic sensor  1006  senses the less-powered identification magnet piece and thus discrimination is so made that the disc cartridge  1 ′ just set in the drive device  101  is of the medium density type. When the low density type disc cartridge  201  having no identification magnet piece is put into the drive device  101 , the magnetic sensor  1106  fails to sense the identification magnet piece and thus discrimination is so made that the disc cartridge  201  just jet in the drive device  101  is of the low density type. 
     When the disc type discriminating apparatus of FIG. 21 is practically employed in the above-mentioned measures of FIGS. 15,  16 ,  17 ,  18 ,  19  and  20  in place of the discriminating apparatus of FIG. 8, the following changes are needed. 
     That is, respective identification magnet pieces  1005  are fixed to the disc cartridges  1  and  1 ′ in place of the identification metal pieces  5  and  5  (or  5 ″), and the magnetic sensor  1106  is mounted to the drive device  101  in place of the metal sensor  106 . Due to the difference in distance between the identification magnet piece  1005  and the magnetic sensor  1106 , the magnetic sensor  1106  senses the difference in magnetic force and thus discriminates the types of the disc cartridges.