INFORMATION MEMORY MEDIUM

Abstract: An optical disk (10) comprising a disk-like body (16) having two base plates (18) made of synthetic resin and two recording layers (20) formed on the base plates (18), respectively. The body (16) is formed by bonding the base plates (18), with a spacer (21) interposed therebetween, such that the recording layers (20) face each other. The disk (10) further comprises two cen­ tering members (24), each projecting from the surface of the center portion of each base plate. Each cen­ tering member (24) is made of synthetic resin, and one magnetic member (26) is mounted on the centering member. The centering member (24) is inserted in a hole (19) formed in the center portion of the body (16). The cen­ tering member (24) has a center hole (24a) defining the center of rotation of the body (16), and also a recess (32) for holding the magnetic member. Four through-­ holes (44) are formed in the bottom of the recess (32). The magnetic member (26) has four projections (45) and is held in the recess (32), with the projections (45) inserted into the through-holes (44) of the bottom of the recess (32). Since the optical disk (10) has mag­ netic members (26), one on each surface, it can be attracted to the turntable (54) of a drive mechanism (12) by means of the magnetic force exerted by the magnet (64) fitted in the recess formed in the surface of the turntable (54).

Description: The present invention relates to an information memory medium, such as an optical disk, for use in an information processing apparatus, on which information can be recorded and from which it can be reproduced or erased when irradiated by an optical beam, such as a laser beam. Nowadays, information processing apparatuses which employ an optical disk as a memory medium are in widespread use. During the use of the information processing apparatuses, the information memory medium is held on a turntable. A conventional magnetic memory medium is held on the turntable by a magnet clamper. The clamper has a magnet, and the turntable is formed of magnetic material. Thus, conventional magnetic memory medium is held on the turntable by the magnetic attraction produced by the clamper. The same type of a magnet clamper is used to hold an optical disk on the turntable of the information processing apparatus. From the document EP-A-0 195 330 A2, a flexible magnetic diskette used for magnetical storing various information which is recorded and read by a magnetic head, has come to be known. The diskette comprises a flexible plastic disc sheet uniformly coated with magnetic material and having a mount hole at the center thereof, and a holder for securing the disk sheet of the periphery of the mount hole. The holder is also made of a plastic material for holding the flexible disk sheet over the peripheral portion of the mount hole via a double-sided adhesive ring. A core member is made of a magnetic metal having a high abrasive resistance and rigidly attached to the holder over at the surface of the holder, with which a drive unit is engaged. From the document GB-A-2 163 887, a disk cassette comprising an envelope containing an information disk has come to be known, having two parallel major walls in one or each of which are formed a central opening for the passage of the drive spindle of a drive apparatus for driving the disk and the slot through which the disk can be scanned by information-recording and/or -reproducing means of the drive apparatus. The information disk can be read on both sides and carries a hub on both sides by means of which it can be driven by a suitable drive apparatus. Each hub comprises a plastics hub portion and a metal hub portion which is adapted to cooperate with a magnetic retaining device on the drive apparatus. The information memory media according to prior art as mentioned above have the disadvantage that tolerances of the adjustment of the magnetic member relative to the centering member will cause severe eccentricy of the base plate. Moreover, thermal expansion effects will cause deformations of the diskette if the core member made of metal exhibits a substantial different thermal expansion coefficient compared with the thermal expansion coefficient of the plastic disc sheet. This condition narrows the palette of possible materials, which may be choosen for the diskette, in a disadvantageous fashion. Object of the invention is to provide an information memory medium which can by magnetical means be securely mounted on or attached to the turntable of an information processing apparatus, exhibiting an excellent precision of centering on the shaft of said turntable, even if the ambient temperature changes greatly. This object is solved by an information memory medium according to the characterizing portion of the main claim. Further improvements of the subject-matter of the main claim are given with subclaims 2-10. A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained, as the same become better understood by reference to the following detailed description, when considered in connection with the accompanying drawings, in which: Fig. 1 is a partially cross-sectional side view of an information processing apparatus in which an information memory medium of this invention can be used; Fig. 2 is a partially cross-sectional side view of the same information processing apparatus, in which the information memory medium of the invention is attached to a drive mechanism; Fig. 3 is a sectional view of an essential portion of the information memory medium according to an embodiment of the present invention; Fig. 4 is a plan view of an attractable member used in the information memory medium; Fig. 5 is a perspective view of a centering member; and Fig. 6 is a perspective view of a magnetic member. Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. As shown in Fig. 1, an information processing apparatus comprises optical disk 10 used as an information memory medium, and drive mechanism 12 for rotating optical disk 10. Disk 10 contained in cartridge 14 (indicated by two-dot and dash line), is inserted into the apparatus through a medium slot cut in a housing of the apparatus. Thereupon, disk 10 is automatically introduced horizontally into a predetermined position by a medium guiding/loading mechanism. During this process, part of cartridge 14 is open so that the center portion of disk 10 is exposed. Thereafter, cartridge 14 is moved along the plane of disk 10, so that the disk is mounted automatically on drive mechanism 12. Optical disk 10 comprises body 16 and a pair of attractable members 22. Body 16 comprises two disk-shaped base plates 18, two information recording layers 20, inside spacer 21, an outside spacer (not shown). Either base plate 18 has bore 19 and is made of transparent synthetic resin, such as acrylic resin or polycarbonate, by means of injection molding. Information recording layers 20 are formed on base plates 18, respectively. The spacers, both shaped like a ring, are interposed between those surfaces of base plates 18 which face away from layers 20. The spacers are bonded to each other and also to plates 18 by means of ultrasonic curing, whereby base plates 18 are coupled concentrically. As is shown in Figs. 1 to 3, either attractable member 22 is fixed to the center portion of the associated base plate 18. Attractable member 22 has centering member 24 and magnetic member 26 contained in centering member 24. As is shown in Figs. 1 to 5, centering member 24 consists of annular frame 41 and four spokes 42, and has thickness t. Spokes 42 are connected together at the center of frame 41, thereby forming a center portion 43 of centering member 24. The center portion 43 has center hole 24a. Further, either centering member 24 has ring-shaped projection 28 coaxial with hole 24a. While projection 28 is fitted in bore 19 of its corresponding base plate 18, it is fixedly bonded to the outer surface of the base plate, or the opposite surface thereof to that surface on which information record layer 20 is formed. Thus, centering member 24 is coaxially positioned relatively to base plate 18. As is shown in Fig. 1, either centering member 24 has been made by cutting recess 32 in a disk, and then by cutting four through holes 44 in the bottom of recess 32. Centering member 24 is bonded to the corresponding base plate 18 by bonding agent, such as epoxy resin, which has no adverse influence on base plate 18. In order to shorten the working time for base plates 18, bore 19 of each plate 18 is formed during the process of injection molding. Base 19 formed in this manner is formed, as shown in Fig. 3, in a stepwise shape having a large-diameter portion 19a and a small-diameter portion 19b formed by exfoliating by a punch in case of cutting by the punch of an injection molding machine. Large-diameter portion 19a of bore 19 is formed with higher dimensional accuracy than small-diameter portion 19b. Therefore, height h1 of projection 28 of each centering member 24 is shorter than axial length h2 of portion 19a so that projection 28 can engage only portion 19a of higher accuracy. Thus, members 24 are fixed with high positional accuracy, without being substantially eccentric to base plates 18. Bore 19 of each base plate 18 is worked with high accuracy, so as to be coaxial with a spiral pre-groove (not shown) for recording and reproduction, formed on the base plate. Likewise, the outer peripheral surface of projection 30 and center hole 26a of each centering member 26 are worked with high accuracy, so as to be coaxial with each other. Thus, when member 24 is fixed to base plate 18, the center of the pre-groove is accurately in alignment with that of hole 24a or the center of rotation of base plate 18. It is therefore possible to prevent lowering of recording/reproducing accuracy or increase of access time, which will result in if the pre-groove is eccentric to the rotational center of base plate 18. Both centering members 24 are made of the same synthetic resin as base plates 18, and have substantially the same thermal expansion coefficient as base plates 18. Therefore, either base plate 18 and centering member 24 bonded to plate 18 do not distort each other even when the ambient temperature changes greatly. Each magnetic member 26 is made of metal. As is shown in Figs. 1 to 4 and Fig. 6, magnetic member 26 is shaped like a disk, and has through hole 26a at the center. Four projections 45 are formed on either magnetic member 26, and fitted in four through holes 44 of centering member 24 Magnetic member 26 has outer flange 46 and inner flange 47. Step portions 48, 49 are formed at the inner periphery of outer frame 41 and outer periphery of center portion 43, respectively, and are formed at the interface of base plate 18. Magnetic member 26 is held in recess 32 of centering member 24 in the state that projection 45, outer flange 46 and inner flange 47 are respectively engaged with through hole 55, step portions 48 and 49. In this case, height H₁ of projections 45 is substantially equal to or slightly less than thickness H₂ of centering member 24. A narrow gap is formed between projection 45 and through hole 44, and flange 46 and flange 47 have a slightly smaller width than step portions 48 and 49 or substantially the same thickness as step portions 48, 49. Accordingly, magnetic member 26 cannot move in a direction perpendicular to the surface of base plate 18, but can move slightly in a direction parallel to the surface of base plate 18. In this way, magnetic member 26 can easily be attached to centering member 24 since the mechanism required is simple. As shown in Figs. 1 and 2, drive mechanism 12 for driving optical disk 10 includes brushless DC motor 50 of an outer-rotor type, for use as a drive source, and turntable 54 mounted on rotating shaft 52 of motor 50 and adapted to be rotated by motor 50. Tip end portion 52a of shaft 52 is inserted into center hole 26a of disk 10, as will be mentioned later, thus constituting a positioning portion for positioning the disk relatively to turntable 54. Motor 50 is supported by frame 55, which is fitted to control board 56 for controlling the operation of the motor. Turntable 54, which is formed of nonmagnetic metal, has support surface 54a extending perpendicular to shaft 52 of motor 50. Also, turntable 54 is formed with circular depression 58, which is coaxial with shaft 52, and opens to surface 54a. Diameter D3 of depression 58 is greater than diameter D1 of centering member 24 of optical disk 10. Depression 58 contains magnetic attraction member 60 which magnetically attracts one of attractable members 22 of disk 10. Attraction member 60 includes ring-shaped yoke 62 and magnet 64, which are arranged coaxially with shaft 52. Yoke 62 has inner and outer peripheral walls 62a and 62b, coaxial with each other, and magnet 64 is located between the peripheral walls. The top faces of yoke 62 and magnet 64 are located at distance T from support surface 54a of turntable 54. Distance T is greater than height t of projection of centering members 24 of optical disk 10. Thus, housed in depression 58, magnetic attraction means 60 can fully exhibit its force of attraction for mounting disk 10 on turntable 54, and prevent magnetic leakage to the outside. As described above, diameter D1 and height t of centering member 24 are smaller than diameter D2 of depression 58 and distance T, respectively. Therefore, if optical disk 10 is set on turntable 54 so that positioning portion 52a of shaft 52 is inserted in one of center holes 24a of attractable members 22, as shown in Fig. 2, one of attractable members 22 is housed fully in depression 58. As a result, magnetic member 25 of attractable member 22 is attracted to magnet 64, so that disk 10 is mounted in direct contact with support surface 54a of turntable 54. Thus, base plate 18 having information record layer 20 thereon is held securely to turntable 54, so that vibration of base plate 18 perpendicular to its surface can be minimized. Accordingly, information can be recorded and reproduced correctly. If attractable member 22, not base plate 18, contacted support surface 54a of turntable 54, optical disk 10 would vibrate greatly, unless the surface of member 24 and base plate 18 are very accurately parallel to each other. Therefore, member 24 and the layer of adhesive must have a uniform thickness. It is very difficult, however, to form member 24 and the adhesive layer which have uniform thicknesses. The length of positioning portion 52a of shaft 52 is such that portion 52a can be fitted in only center hole 24a of the turntable-side attractable member when optical disk 10 is mounted on turntable 54. There will be no substantial projection even if center holes 24a of centering members 24 are not aligned with high accuracy. To fit positioning portion 52a in center holes 24a of both centering member 24, these holes 24a must be coaxial with each other. However, it is very difficult to align bores 19 of base plates 18 or center holes 24 of members 24. If positioning portion 52a is too long, it takes a long time to set optical disk 10 on turntable 54. This helps wear the disk. Magnetic attraction means 60 is housed in depression 58 formed in turntable 54, so that magnetic leakage is reduced to a low level. Accordingly, iron filings or powder of other magnetic material does not hinder the engagement of shaft 52 and center hole 24a by sticking to shaft 52. As mentioned above, height t of projection of either centering member 24 is less than distance T between the top faces of yoke 62 and magnet 64 and support surface 54a of turntable 54. When optical disk 10 is mounted on table 54, therefore, gap G is defined between attractable member 22 and magnetic attraction means 60. Gap G has is so broad that the disk is magnetically attracted to turntable 54. Therefore, as turntable 54 rotates, disk 10 is reliably rotated, and disk 10 can be removed easily from turntable 54 by only lifting cartridge 14. In this embodiment, gap G has such a size that force of attraction of about 700 g acts on attractable member 24. In Fig. 2, numeral 66 designates a head, which is moved in the radial direction of optical disk 10 by head moving means, such as a linear motor. Head 66 can record information on, and reproduce information from, on information record layer 20 formed on lower-side base plate 18. Since base plate 18 and centering member 24 are formed of synthetic resins having substantially the same thermal expansion coefficient, and magnetic member 26 is further mounted on centering member 24, the base plate and the centering member do not distort each other even if the ambient temperature changes greatly. Therefore, information can be correctly recorded on, or reproduced from, the disk. Further, since magnetic member 26 can slightly move in parallel with the surface of base plate 18 with respect to centering member 24, the difference of thermal expansion coefficients between centering member 24 and magnetic member 26 can be compensated for, and the distortion of the base plate can be further reduced. However, the base plate may be made of materials other than resins, such as glass, or ceramics. Further, the centering member can be made of any material other than synthetic resin. The centering members can be made of any material having substantially the same thermal expansion coefficient as the material of the base plate. If the base plates are made of glass, the centering members may be formed of glass or ceramic material. The embodiments described above are optical disks having two disk base plates. Alternatively, the disk may have only one plate. Further, magnetic attraction means 60 may be formed only of a magnet. Depression 58 in turntable 54 can be hexagonal or rectangular, not circular. Each attractable member 22 must only have shape and size so that it can be housed in the depression. In the aforementioned embodiments, moreover, the yoke of the magnetic attraction means has inner and outer peripheral walls. Alternatively, it may be provided with only an inner peripheral wall, or only an outer peripheral wall. Centering member 24 and magnetic member 26 are not necessarily limited to the above-mentioned shape, but magnetic member 26 may, in summary, be contained in centering member so as to be slightly movable in a direction parallel to the surface of base plate 18.

Claims: An information memory medium adapted to be driven by a drive mechanism (12) having a turntable (54) for rotating said medium, and a magnetic attraction member (60) for magnetically attracting said medium to said turntable (54), said information memory medium comprising; a) a body (16) having a disk-like base plate (18), and a recording portion (20) for recording information; b) a centering member (24) formed on the center area of said body (16), for centering said body on said turntable (54), said centering member (24) having a center portion, a recess (32) formed in said center portion, and a through-hole (44) formed in the bottom of said recess (32), and said centering member (24) having substantially the same thermal expansion coefficient as said base plate (18); c) a magnetic member (26) held in said centering member (24) and adapted to be attracted to said magnetic attraction member (60), having a projection (45) fitted into said through-hole (44) of said centering member (24), characterized in that d) said recess (32) is opening to said base plate (18); e) said centering member (24) has a step portion (48,49), and said magnetic member has an engaging portion (46,47) fitted in said step portion (48,49) for preventing said magnetic member from moving in a direction perpendicular to said base plate (18); f) said projection (45) and said engaging portion (46,47) are shorter than said through-hole (44) and said step portion (48,49), respectively, measured in the direction parallel to said base plate (18); g) said magnetic member (26) is mounted on said centering member (24) such that said magnetic member (26) is unable to move in a direction perpendicular to the surface of said base plate (18), and able to move in a direction parallel to said surface thereof. An information memory medium according to claim 1, characterized in that said step portion (48,49) is formed in that portion of said centering member (24) which faces said base plate (18), and said engaging portion (46,47) is interposed between the step portion (48,49) and said base plate (18). An information memory medium according to claim 1, characterized in that said projection (45) has a height less than the thickness of said centering member (24). An information memory medium according to claim 1, characterized in that said centering member (24) has an annular body. An information memory medium according to claim 1, characterized in that said projection (45) of said magnetic member (26) has an outer surface located flush with, or receding from, the outer surface of said centering member (24). An information memory medium according to claim 1, characterized in that said centering member (24) has a projection (28) fitted in the through-hole (19) of said base plate (18). An information memory medium according to claim 6, characterized in that the projection (28) of said centering member has a height less than the thickness of the base plate (18). An information memory medium according to claim 1, characterized in that said centering member (24) has a ring-shaped frame (41), a center portion (43) having said center hole (24a), and a plurality of spokes (42) connecting the center portion (43) to the ring-shaped frame (41), said spikes (42) defining the bottom of said recess (32), and said ring-shaped frame (41), said center portion (43) and said spokes (42) defining said through-hole (44). An information memory medium according to claim 8, characterized in that said centering member (24) has four spokes (42), and said centering member (24) has four through-holes (44), and said magnetic member (26) has four projections (45) fitted into the through-holes (44) of said centering member (24), respectively. An information memory medium according to claim 1, characterized in that said body (16) comprises another base plate (18), an information recording portion (20) formed on this other base plate (18), and a spacer (21), and the two base plates (18) are bonded, with the spacer (21) interposed therebetween, such that the information recording portions (20) face each other.

Inventors: INAGE, NOBUO, ODAWARA, KAZUHARU C/O PATENT DIV. K.K. TOSHIBA
Applicants: KABUSHIKI KAISHA TOSHIBA, TOSHIBA INTELLIGENT TECHNOLOGY LTD.
Application year: 1987
Main classification: G11B23
IPC codes: G11B7, G11B17, G11B23