Magnetic disk drive

Abstract: A cartridge (234) for accommodating a magnetic recording medium (222) also accommodates an actuator (225) and a spindle (232). The spindle (232) accommodated in the cartridge (234) is driven by a spindle driving mechanism (236) provided in a driving device (235) so as to rotate the magnetic recording medium (322). The actuator (225) is driven by an actuator driving mechanism (237) provided in the driving device (235) so as to move a magnetic head approximately in the radial direction of the magnetic recording medium (222). The cartridge (234) includes a shutter mechanism (241) which is opened so as to expose at least a part of the spindle (232) and the actuator (225) in such a manner as to face the actuator driving mechanism (237) and the spindle driving mechanism (236), respectively, when the cartridge (234) is mounted on the driving device (235) and which is closed so as to enclose the spindle (232) and the magnetic head and the actuator (225) in the cartridge (234) in a sealed state when the cartridge (234) is removed from the driving device (235). The cartridge (234) further includes a ramp loading mechanism (229) for protecting the magnetic head from an external shock when the cartridge (234) is removed from the driving device (235).

Description: The present invention relates to a magnetic disk drive which is used as an external storage unit of a computer. Fig. 8 is a perspective view of an example of a conventional magnetic disk apparatus, which is shown in a catalogue of a microfloppy disk drive (3.5-inch flexible disk drive: MP-F11W) produced by SONY Corporation. This is a very general 3.5-inch flexible disk device (hereinunder referred to as "FDD"). In Fig. 8, the reference numeral 1 represents a magnetic head, 2 an arm to which the magnetic head 2 is fixed such that the magnetic head 2 exists within a predetermined azimuth, 3 a carriage to which the magnetic head 1 on the opposite side is fixed such that the magnetic head 2 exists within a predetermined azimuth, 4 a pressure spring for applying a predetermined pressure to the magnetic head 1 through the arm 2, 5 a fitting metal for fixing the pressure spring 4 to the carriage 3, 6 a lead screw which axially rotates and induces the linear reciprocal movements of the carriage 3, 7 a stepping motor for applying a driving force to the lead screw 6 and 8 a flexible printed circuit (hereinunder referred to as "FPC"). The reference numeral 9 denotes a loading mechanism having a function of mounting and removing a cartridge which is shown in Fig. 9, 10 a base to which various structures are fixed so as to be accommodated therein, 11 a front panel which is attached to the front surface of the disk drive, 12 a door provided on the front panel 11 so as to be opened and closed when the cartridge 18 is mounted or removed, 13 a push button which is pressed into the apparatus or released coupled with the movement of the loading mechanism 9, 14 a printed circuit board which is fixed to the bottom portion of the base 10, and 15 a mounting frame for mounting the drive on a system such as a personal computer. Fig. 9 is a perspective view of the cartridge 18. The reference numeral 16 represents a flexible recording medium on and from which information is written or read by the magnetic heads 1, 17 a shutter which is opened or closed coupled with the movement of the loading mechanism 9 so as to expose or cover the portion of the recording medium 16 with which the magnetic head 1 comes into contact, 19 a chucking plate magnetically attracted to the rotary portion of a spindle motor (not shown) which is provided in the disk drive shown in Fig. 8, 20 a center hole for receiving the centering shaft of the spindle motor and 21 a driving hole into which the driving pin of the spindle motor is inserted and to which the driving force is transmitted. The operation of this conventional magnetic disk drive will now be explained. When the cartridge 18 shown in Fig. 9 is inserted from the door 12 of the front panel 11, the shutter 17 is slid in the direction indicated by the arrow A in Fig. 9 by the loading mechanism 9, thereby exposing the portion with which the magnetic head 1 comes into contact. At the same time, the chucking plate 19 is attracted to the spindle chucking surface by the magnetic force of a magnet provided on the spindle chucking surface. The push button 13 projects coupled with the movement of the loading mechanism 9. The arm 2 is pushed down by the pressure spring 4 and the magnetic head 1 fixed on the arm 2 comes into contact with the recording medium 16, whereby the recording medium 16 is sandwiched between the magnetic head 1 fixed on the arm and the magnetic head 1 fixed on the carriage 3. When the recording medium 16 is normally chucked, the spindle motor starts to rotate, and the driving pin of the spindle motor comes into the driving hole 21 provided in the chucking plate 19, so that the recording medium 16 also rotates. The rotation of the stepping motor 7 is transmitted to the carriage 3 through the lead screw 6 and the carriage 3 linearly reciprocates by the distance which is proportional to the rotational angle of the stepping motor 7, so that the magnetic head 1 is positioned at the desired track position of the recording medium 16 in accordance with the command from the system. When the positioning of the magnetic head 1 is finished, the magnetic head 1 starts to write or read information on or from the magnetic recording medium 16. When the user presses the push button 13 in order to take out the cartridge 18 after the end of the writing/reading of necessary information, the loading mechanism 9 operates the other way around. That is, the arm 2 is pushed up, and the cartridge 18 is pushed out of the door 12 of the front panel 11. This FDD operates in the same way with respect to any other recording medium 16. In addition, in order to enable the recording medium 16 to operate normally in any other disk drive, namely, to impart compatibility between drives to the recording medium 16, the magnetic head 1 is fixed to the arm 2 within a predetermined azimuth in any disk drive. An FDD as a conventional magnetic disk drive in which a recording medium is replaceable has the above-described structure. Such an FDD must be free from the non-uniformity in the chucking accuracy at which a recording medium is chucked by the spindle and the non-uniformity in the rotational accuracy due to the non-uniformity in the chucking accuracy so as to write and read information on and from any recording medium in the same way. For this reason, the FDD must have a compatibility between recording mediums and impart a compatibility between drives to a recording medium. If these demands are satisfied, the increase in the recording density is checked and it is difficult to reduce the size of the disk drive in spite of a small capacity. In addition, since the disk drive does not have a sealed structure so as to make a recording medium replaceable, the dust which has entered the apparatus goes between the magnetic head and the recording medium and damages the recording medium or adheres to the driving mechanism such as the lead screw, thereby deteriorating the positioning accuracy and lowering the reliability. WO 90/05974 already discloses a magnetic disk drive including a spindle motor assembly having a magnetic clutch plate and an actuator. The disk drive receives a hermetically sealed cartridge containing a plurality of disks with associated heads mounted in the cartridge. Associated with an arm assembly which supports the heads is a component for use with the actuator. With the cartridge inserted in the drive, the actuator operates to cause the heads to traverse relative to the disk as the spindle motorassembly uses a magnetic field to engage a magnetic plate associated with the cartridge in order to spin the disk. Data transfer connectors are associated with both the drive and the cartridge in order to allow for the transfer of data between the cartridge and the drive. However, the cartridge has not a completely sealed structure, because part of the arm assembly projects via an opening of the cartridge. Through this opening dust may enter into the cartridge, which can cause the magnetic head to crash. JP-A-61074188 shows a disk cartridge including a case. In order to prevent the entry of dust or corrosive atmosphere into the case, it is closed at the side opposite to the insertion port of a drive shaft and simultaneously a flexible seal member is disposed on the interior of the insertion port forming case. JP-A-2139781 describes a magnetic disk device comprising means for reducing noise. Since vibration caused by a driving mechanism for a spindle and an access mechanism is transmitted to a base of a head disk assembly, a sound absorbing material is arranged on the outer surface of the base. From JP-A-2 094 192 a magnetic disk device is known which comprises a base plate for housing a carriage including the magnetic heads, and spindle and magnetic disks in a sealed state. In order to electromagnetically shield the magnetic disk device from external electromagnetic noise and also to prevent leakage of a magnetic flux from the device, the inner surface of the base plate is coated with a magnetic substance. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to solve the above-described problems in the related art and to provide a magnetic disk drive which allows the replacement of a recording medium, which has high reliability. For solving this object, a magnetic disk drive as known from WO 90/05974 comprises the features of the characterizing part of claim 1. Preferred embodiments of the magnetic disk drive according to the present invention are defined in the subclaims. In this structure according to the invention, the loading mechanism opens and closes the shutter mechanism when the cartridge is mounted on the driving device and removed therefrom, respectively. The loading mechanism opens the shutter mechanism when the cartridge is mounted on the driving device and exposes at least a part of the actuator and the spindle in the cartridge. In this state, the spindle driving mechanism and the actuator mechanism drive the spindle and the actuator, respectively. When the spindle is driven, the magnetic recording medium rotates and when the actuator is driven, the magnetic head is positioned. In this state, it is possible to write desired information at a given position on the magnetiv recording medium by the magnetic head or to read from a given position on the recording medium by the magnetic head the information written at that position. On the other hand, when the cartridge is removed from the driving device by the loading mechanism, the loading mechanism closes the shutter mechanism. In other words, the cartridge assumes a sealed state. In this way, according to the present invention, a small-sized magnetic disk drive which has higher reliability and a high recording density is realized at a low cost while maintaining easiness in handling. These advantages are ascribed to the fact that since the cartridge has a sealed structure, the cartridge is unsusceptible to dust and the recording density is enhanced, and that since the number of elements which are to be disposed in the cartridge in a sealed state is small, it is possible to reduce the size of the cartridge. The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings. Fig. 1 is perspective view of an embodiment of a magnetic disk drive according to the present invention; Fig. 2A is a plan view of the embodiment shown in Fig. 1; Fig. 2B is a B-B sectional side elevational view of the embodiment shown in Fig. 2A; Fig. 3A is a plan view of the bottom of the cartridge in the embodiment shown in Fig. 1, in the state in which the shutter mechanism is open; Fig. 3B is a plan view of the bottom of the cartridge of the embodiment shwon in Fig. 1, in the state in which the shutter mechanism is closed; Fig. 4 is a perspective view of the actuator in the embodiment shown in Fig. 1; Figs. 5A and 5B are a sectional side elevational view and a plan view, respectively, of the spindle in the embodiment shown in Fig. 1; Figs. 5C and 5D are a sectional side elevational view and a plan view, respectively, of the spindle driving mechanism in the embodiment shown in Fig. 1; Fig. 6 shows another embodiment of a magnetic disk drive according to the present invention; Fig. 7 is a perspective view of the actuator and the actuator driving portion in a conventional magnetic disk drive shown in Fig. 8; Fig. 8 is a perspective view of the conventional magnetic disk drive; and Fig. 9 is a perspective view of the cartridge in the conventional magnetic disk drive. An embodiment of the present invention will be explained hereinunder with reference to the accompanying drawings. Fig. 1 is a perspective view of an embodiment of the present invention. The reference numeral 232 represents a spindle on which a recording medium 222 of substantially not more than 76 mm mounted and which rotates with high accuracy, 233 a moving magnet fixed to one end of an actuator 225 which is opposite to the end at which a suspension 224 is fixed, and 234 a cartridge composed of a cover 230 and a base 210 and accommodating various elements therein. The cartridge 234 has a height of about less than 10 mm, a width of about less than 70 mm and a length of about less than 106 mm. The reference numeral 235 denotes a driving device into which the cartridge 234 is integrally inserted, and 236 a spindle motor driving mechanism which is composed of a plurality of flat coils 236a and which is disposed in the driving device 235 at the position which opposes the bottom portion of the spindle 232. The reference numeral 237 represents an actuator driving mechanism disposed in the driving device 235 at the position which opposes the bottom portion of the actuator 225, 238 a slot cover for covering the upper portion of the driving device 235 in the state in which the cartridge 234 is inserted thereinto, 239 a slot door provided at one end of the slot cover 238 so as to be opened and closed when the cartridge 234 is inserted or removed, 240 a loading mechanism provided in the driving device 235 so as to mount and remove the cartridge 234 on and from the driving device 235, 240a an L-shaped end portion of the loading mechanism 240, 240b the other end portion of the loading mechanism 240 and 241 a shutter mechanism which is composed of a magnetic shielding material and which slides so as to expose or cover the bottom portion of the actuator 225 and the bottom portion of the spindle 232 coupled with the operation of mounting or removing the cartridge 234. The reference numeral 242 represents a positioning pin A provided on the driving device 235 so as to determine the position of the cartridge 234 when the cartridge 234 is inserted, 243 a positioning pin B provided on the driving device 235 similarly to the positioning pin A 242, and 244 a connector A which is provided in the driving device 235 so as to come into contact with a connector B 245 (shown in Fig. 3A) in electric conduction which is provided on the bottom portion of the cartridge 234 in electrical connection with an FPC 208 which transmits a signal of a magnetic head 223. The reference numeral 246 represents a system connector which is attached to a printed circuit board 214 at one end of the driving device 235 so as to connect the driving device 235 to the system. In Fig. 3A, the reference numeral 253 denotes a retracting cam A which is provided on the bottom surface of the cartridge 234 and which is rotated by means of a spring or the like. The reference numeral 254 in Fig. 1 represents a retracting cam B which is provided in the cartridge 234 and which has the same rotational shaft as the retracting cam A 253. The reference numeral 226 denotes a pivot and 229 a ramp loading mechanism. Fig. 2A is a plan view of the embodiment shown in Fig. 1 in the state in which the cartridge 234 is integrally inserted into the driving device 235 and Fig. 2B is a sectional side elevational view thereof. In Figs. 2A and 2B, the reference numeral 247 represents a spindle housing which constitutes a bearing of the spindle 232, 248 a subbase to which the spindle housing 247 and a bearing portion 225a of the actuator 225 are fixed, 249 a subplate to which the subbase 248 is fixed through a column 252, 250 a buffer material with which the gap between the subbase and the inner wall of the cartridge 234 and the gap between the subplate 249 and the inner wall of the cartridge 234 are filled. The reference numeral 251 represents a rotor which constitutes the bottom portion of the spindle 232. The rotor 251 is composed of a magnet which has a plurality of magnetic poles in the circumferential direction in correspondence with number of the flat coils 236a of the spindle driving mechanism 236. The reference numeral 255 in Fig. 4 denotes a yoke which constitutes the moving magnet 233, 256 a pair of magnets fixed to both ends of the yoke 255, and 257 a coil wound around the actuator driving mechanism 237 in a flat shape. The reference numeral 213 represents a push button and 223 the magnetic head in Figs. 2A and 2B. Figs. 3A and 3B show the cartridge 234 and Fig. 4 shows the structure of the actuator 225 and the vicinity thereof. Figs. 5A to 5D show the structure of the spindle 232, the spindle motor driving mechanism and the vicinity thereof. The operation of this magnetic disk drive will now be explained. When the user pushes the cartridge 234 into the slot cover 238 while pressing the cartridge 234 against the slot door 239 in the direction indicated by the arrow A in Fig. 1, the slot door 239 swivels inwardly and downwardly around the axis B to clear the entrance. The cartridge 234 is then inserted into the slot cover 238 along the L-shaped end portions 240a of the loading mechanism 240 with the slot door 239 pressed under the cartridge 234 until the cartridge 234 abuts against the positioning pin A 242 and the positioning pin B 243 and is stopped thereby. Simultaneously, the loading mechanism 240 is lowered, and the cartridge 234 is also lowered by virtue of the L-shaped end portions 240a, thereby being united with the driving device 235 into one body. When the cartridge 234 is inserted, the end portions 240b of the loading mechanism 240 slide the shutter mechanism 241 in the opposite direction to the direction of cartridge insertion in correspondence with the amount of horizontal movement of the cartridge 234. As a result, the shuttering mechanism 241 exposes a part of the actuator 225 in the vicinity of the moving magnet 233 and a part of the spindle 232 in the vicinity of the bottom portion of the rotor 251, both of which have been covered by the shutter mechanism 241 on the base 210, and the connector B 245, as shown in Fig. 3A. In this way, the cartridge 234 is united with the driving device 235 into one body with the bottom portion of the rotor 251 of the spindle 232 facing the spindle motor driving mechanism 236, and the magnetic poles of the pair of magnets 256 of the moving magnet 233 facing the actuator driving mechanism 237. In this state, the connector A 244 of the driving mechanism 235 comes into contact with the connector B 245 of the cartridge 234 and they are electrically connected with each other. When a command such as writing and reading is transmitted from the system to the driving device 235 through the system connector 246, a current flows to the spindle driving mechanism 236 in accordance with the command, so that the spindle 232 is rotated by the electromagnetic induction produced between the spindle driving mechanism 236 and the rotor 251. When the number of revolutions of the spindle 232 reaches a stationary number of revolutions and the spindle 232 rotates normally, a control current flows to the actuator driving mechanism 237, and the electromagnetic induction by a magnetic circuit constituted by the actuator driving mechanism 237 and the moving magnet 233 produces the force for moving the moving magnet 233. As a result, the actuator 225 with the suspension 224 mounted on the ramp loading mechanism 229 rotates around the pivot 226, so that the suspension 224 leaves the ramp loading mechanism 229 and the magnetic head 223 moves to the outer periphery of the recording medium 222 while floating thereabove at a slight height. In this state, it is possible to rock the actuator 225 by varying the direction of the current flow, and it is possible to position the magnetic head 223 at a desired position on the recording medium 22 for the writing/reading operation by controlling the amount of current. The written/read signal is transmitted to the connector A 244 through the FPC 208, and to the connector B 245 which is electrically connected to the connector A 244. The signal is then subjected to a predetermined processing by the printed circuit board 214 provided on the bottom portion of the driving device 235 and transmitted to the system through the system connector 246. The operation of removing the cartridge 234 from the driving device 235 after the end of a predetermined operation will now be explained. When the push button 213 is pressed, the loading mechanism 240 is raised and the cartridge 234 is also raised therewith. The connecter A 244 is separated from the connector B 245, whereby the bottom portion of the rotor 251 of the spindle 232 is moved from position which faces the spindle motor driving mechanism 236 and the magnetic poles of the pair of magnets 256 of the moving magnet 233 are moved from the position which faces the actuator driving mechanism 237. In this state, it is possible to remove the cartridge 234 from the driving device 235. When the cartridge 234 is drawn, the shutter mechanism 241 slides in the opposite direction to the direction of cartridge removal in correspondence with the amount of horizontal movement of the cartridge 234. The shutter mechanism 241 thus covers the part of the actuator 225 in the vicinity of the moving magnet 233, the part of the spindle 232 in the vicinity of the bottom portion of the rotor 251, and further the connector B 245, as shown in Fig. 3B. In the base 210, the vicinity of the moving magnet 233 and the vicinity of the rotor 251 of the spindle 232 are composed of a nonmagnetic material and the other portion is made of a magnetic shielding material. In addition, in the cartridge 234 which is removed from the driving device 235, the portions of the nonmagnetic material in the vicinity of the moving magnet 233 and in the vicinity of the rotor 251 of the spindle 232 of the base 210 are covered with the shutter mechanism 241 composed of a magnetic shielding material. Accordingly, there is no fear of the information written on the recording medium 222 being damaged due to external influence. Although the moving magnet 233 and the actuator driving mechanism 237 are coupled in a non-contacting state by electromagnetic induction in order to rock the actuator 225 in this embodiment, they may be coupled in a contacting state as in another embodiment shown in Figs. 6 and 7. In this embodiment, a turntable 358 composed of a magnetic material is attached to one end of a pivot 326. An elastic thin-film seal 359 which is deformable in the rotational direction of the pivot 326 so as not to obstruct the rocking movement of the pivot 326 is provided between the pivot 326 and a base 310. An actuator driving mechanism 337 is provided with a coupling member 360 composed of a magnet in such a manner as to be removably coupled with the turntable 358. The actuator driving mechanism 337 is composed of magnets 361 and a coil 362 so as to rotate the coupling member 360. In this structure, when a cartridge 334 is inserted into a driving mechanism, the coupling member 360 is magnetically coupled with the turntable 358 into one body while rotating such that the end surface of a notched portion 364 provided on the turntable 358 of an actuator 325 shown in Fig. 7 abuts against the end surface of a notched portion 363 provided on the coupling member 360. Consequently, the actuator 325 to which the driving force of the actuator driving mechanism 337 is transmitted is rocked. At this time, the elastic thin-film seal 359 repeats clockwise or counterclockwise deformation in correspondence with the rotation or reverse rotation of the turntable 358. Thus, this embodiment has similar advantages to those of the first embodiment.

Claims: A magnetic disk drive system comprising: A) a cartridge (234) including: a) a planar magnetic recording medium (222); b) a spindle (232) fixed to the central part of the magnetic recording medium (222); c) a magnetic head (223) which is fixed to an actuator (225) and which magnetically writes information on the magnetic recording medium (222) and reads the information written on the magnetic recording medium (222); and d) an actuator (225) which supports the magnetic head (223) which supports the magnetic head (223) at one and thereof and which rocks around the pivot (226) in a plane parallel to the recording surface of the recording medium (222); and B) a driving device (235) including: e) a loading mechanism (240) for mounting the cartridge (234) on the driving device (235) while opening a shutter mechanism (241) and for removing the cartridge (234) while closing the shutter mechanism (241); f) a spindle driving mechanism (236) for rotating the magnetic recording medium (222) by rotating the spindle (232) in the state in which the cartridge (234) is mounted; and g) an actuator driving mechanism (237) for moving the position of the magnetic head (223) by rocking the actuator (225) in the state in which the cartridge (234) is mounted, characterized in that the cartridge (234) has a sealed structure and that the shutter mechanism (241), when it is closed, accomodates the magnetic recording medium (222), spindle (232), magnetic head (223) and actuator (225) in the cartridge (234) in a sealed state and, when it is opened, exposes at least a part of the actuator (225) and that an elastic thin-film seal (359) which is an annular member composed of a plurality of scale-like pieces covers the peripheral edge of the exposed pivot (326), which is deformed by the rotational force around the pivot (326) and which absorbs the rotational force by the deformation and seals at least the peripheral edge of the exposed pivot (326); a turntable (358) is opposed to one end of the pivot (326) in such a manner as to seal the exposed pivot (326) in the axial direction when the cartridge (234) is mounted on the driving mechanism (235) and the shutter mechanism (241) is open; and a coupling member (360) is engaged with the turntable (358) so as to transmit the rotational force of the actuator driving mechanism (337) and rotate the turntable (358). A magnetic disk drive system according to claim 1, wherein the shutter mechanism (241) is composed of a magnetic shielding material. A magnetic disk drive system according to claim 1, wherein the surface of the cartridge (234) except the surface which faces the spindle driving mechanism (236) and the actuator driving mechanism (237, 337) is covered with a magnetic shielding material. A magnetic disk drive system according to claim 1, wherein the cartridge (234) includes further a means for covering the the surface which faces the spindle driving mechanism (236) and the actuator driving mechanism (237, 337) with a nonmagnetic material when the shutter mechanism (241) is closed. A magnetic disk drive system according to claim 1, wherein the cartridge (234) further includes a cartridge connceting mechanism (245) and the actuator (225, 335), respectivelly, from a driving circuit and transmitting and receiving an electric signal between the magnetic head (223) and the driving circuit; and the driving device (235) further includes a driving device connecting mechanism (244) which is connected to the cartridge connecting mechanism (245) and which is separated from the cartridge connecting mechanism (245) when the cartridge (234) is removed from the driving device (235). A magnetic disk drive system according to claim 1, wherein the cartridge (234) further includes: a case which is composed of a base (210) and a cover (230) and which constitutes the outer frame of the cartridge (234); a subbase (248) for fixing the spindle (232) and the pivot (226, 326) of the actuator (225, 325); a subplate (249) which is supported by the subbase (248) and which covers the magnetic recording medium (222); and a buffer material (250) with which the gap between the subbase (248) and the inner wall of the case and the gap between the subplate (249) and the inner wall of the case are filled. A magnetic disk drive system according to claim 1, wherein the cartridge (234) further includes: a suspension (224) which is a leaf spring with one end being fixed to the actuator (325) and the other end supporting the magnetic head (223) in such a manner as to enable the magnetic head (223) to be pushed up vertically relative to the actuator (325); a means for moving the magnetic head outside of the recording surface of the magnetic recording medium (222) in a plane which is parallel to the recording surface of the magnetic recording medium (222) by rotating the actuator (325) when the shutter mechanism (241) is closed>; a retracting cam (253) for pushing up the suspension (224) when the shutter (241) is closed; and a ramp loading mechanism (29) for receiving the suspension (224) and holding the vertical position of magnetic head (223) when the magnetic head (223) moves outside of the recording surface of the magnetic recording medium (222) and the suspension (224) is pushed up.

Inventors: KAMO MASAYOSHI, KAWADA JUNJI, SHOJI KENJI, KAMO, MASAYOSHI, KAWADA, JUNJI, SHOJI, KENJI, Kamo, Masayoshi, c/o Mitsubishi Denki K. K., Kawada, Junji, c/o Mitsubishi Denki Engin. K. K., Shoji, Kenji, c/o Mitsubishi Denki K. K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: G11B25
IPC codes: G11B25, G11B19, G11B23, G11B5, G11B33, G11B17