INFORMATION MEMORY MEDIUM

Abstract: An optical disk (10) comprising a disk-like body (10) 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 one base plate. Each centering 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. The centering member (24) has a center hole (24a) defining the center of rotation of the body (16), and also three projections (36) formed in the surface thereof which faces away from the recording layer (20). The magnetic member (26) has three engaging holes (36) and is mounted on the cen­ tering member (24), with the projections (36) of the centering member fitted in the engaging holes (38). Since the optical disk (10) has magnetic members (26), one on each surface, it can be attracted to the turn­ table (54) of a drive mechanism (12) by means of the magnetic force exerted by the magnet (64) fitted in the recess (58) 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 EP-A-0 133 541, a flexible magnetic diskette has come to be known. The diskette comprises a flexible plastic disc sheet uniformly coated with magnetic material and mounted on a centering member for positioning said diskette on a turntable. Said centering member comprises a metallic member, said metallic member having engaging holes into which are inserted projecting members made on said centering member to fixedly attache said metallic member to said centering member. 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; and Fig. 4 is a plan view of an attractable member used in the information memory medium. 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. It has centering member 24 and magnetic member 26 attached to the surface of centering member 24. Centering member 24 is a discoid of thickness t, which is formed of synthetic resin and has center hole 24a. Further, either centering member 24 has ring-shaped 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. 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, while will be caused 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 boned to plate 18 do not distort each other even when the ambient temperature changes greatly. As shown in Figs. 1 to 4, magnetic members 26 of attractable members 22 are formed of metal in a disk shape having a through hole 26a at the center, and each magnetic member 26 has annular projection 32 coaxial with through hole 26a. Annular recess 34 coaxial with hole 24a is formed in the surface of centering member 24. Recess 34 has a width slightly larger than that of projection 32. Magnetic member 26 is arranged on centering member 24 such that projection 32 is fitted in recess 34. Magnetic member 26 is attached to centering member 24, cannot move in a direction perpendicular to the surface of base plate 18 since projecting members 36 are fitted in engaging holes 38 (described later), but can slightly move in a direction parallel to the surface of the base plate. As shown in Fig. 4, three projecting members 36 are formed on the bottom of recesses 34 of centering member 24, at equal intervals in the circumferential direction. Three engaging holes 38 are formed in magnetic member 26, at equal intervals in the circumferential direction of projection 32 of magnetic member 26. Magnetic member 26 is attached to centering member 24, as described above, since projecting members 36 are fitted in engaging holes 38. Each projecting member 36 has an elastically deformable detent 36a formed at the end thereof, and a support 36b for supporting detent 36a. Detent 36a has a diameter H₀ larger than diameter H₁ of support 36b. Each engaging hole 38 has a diameter H₂ larger than diameter H₁ and smaller than diameter H₀. Each detent 36a is positioned far from each engaging hole 38, and each support 36b is disposed in each engaging hole 38 such that projections 36 are fitted in engaging holes 38. Distance H₃ between the surface of magnetic member 26 and recess 34 is longer than height H₄ of projecting member 36 so that detent 36a may not project from the surface of magnetic member 26. To attach magnetic member 26 is attached to centering member 24, magnetic member 26 is so disposed that each engaging hole 38 opposes corresponding projecting member 36, and magnetic member 26 is pressed to centering member 24 until projection 32 of magnetic member 25 is contacted with the bottom of recess 34 of centering member 24. In this case, detent 36a is elastically deformed so that engaging hole 38 passes detent 36a to engage support 36b with engaging hole 38. Magnetic member 26 thus attached has it projection 32 interposed between detent 36a and the bottom of recess 34, and cannot move in a direction perpendicular to the surface of base plate 18, but can slightly move in a direction parallel to base plate 18 in a gap between engaging hole 38 and support 36b. 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 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 the attractable member 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 center hole 24a of only the attractable member facing turntable 54 when optical disk 10 is mounted on turntable 54. Hence, it is not required that center holes 24a of centering members 24 are aligned with high accuracy. If positioning portion 52a were fitted in center holes 24a of both centering members 24, these holes 24a should be coaxially aligned with high accuracy. 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 inevitably promotes the wear of centering members 24. 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 members 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. Thus, 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. In the embodiments described above, detent 36a of projecting member 36 is elastically deformed, and inserted in hole 38 thereby mounting magnetic member 26 on centering member. However, projecting member 36 can be columnar, projecting member 36 can be inserted into hole 38, and the end of the projecting member can form a detent. In the embodiments described above, three projecting members and engaging holes are formed. However, two projecting members and two engaging holes are sufficient.

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 plane body (16) having a base plate (18) supporting a recording portion (20) for recording information; an attractable member (22), provided on the center portion of said plane body (16), for holding said information memory medium onto said turntable (54), said attractable member (22) including a centering member (24) supported by said plane body (16) for centering said body (16) on said turntable (54), and a magnetic member (26) attached to said centering member (24) and adapted to be magnetically attracted to said magnetic attraction member (60), characterized in that, said centering member (24) having projecting members (36) and said magnetic member (26) having engaging holes (38) into which said projecting members (36) of said centering member (24) are inserted, each of said projecting members (36) having a supporting portion (36b) provided on said centering member (24) and a detent (36a) supported at the free end of said supporting portion (36b), wherein the diameter of said supporting portion (36b) is smaller than that of said engaging holes (38), and said supporting portion (36b) is movably engaged with each of said engaging holes (38), whereby said magnetic member (26) cannot move in a direction perpendicular to the surface of said base plate (18), but can slightly move in a direction parallel to said base plate (18). An information memory medium according to claim 1, characterized in that said centering member (24) has substantially the same thermal expansion coefficient as said base plate (18). An information memory medium according to claim 1, characterized in that said detent (36a) has an elastically formable body, and is inserted in the engaging hole (38), thereby engaging the support (36b) with the engaging hole (38). An information memory medium according to claim 1, characterized in that said detent (36a) is formed by inserting the projection member (36) into said engaging hole (38) and then machining the end of said projecting member (36). An information memory medium according to claim 1, characterized in that said magnetic member (26) is an annular body and is provided coaxially with the centerhole (24a). An information memory medium according to claim 5, characterized in that said centering member (24) has, in the surface thereof, an annular recess (34) coaxial with the centerhole (24a), said magnetic member (26) has an annular projection (32) extending along the circumferential direction thereof, said projecting member (36) is formed on the bottom of the recess (34), said engaging hole (38) is formed in the projection (32), and said magnetic member (26) is attached to the centering member (24), with the projection (32) engaged with the recess (34). An information memory medium according to claim 6, characterized in that three projecting members (36) and three engaging holes (38) are formed at equal intervals. An information memory medium according to claim 6, characterized in that the end of said projecting member (36) is receding from the outer surface of said portion of the magnetic member (26) other than the projection (32). 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 9, characterized in that said projection (28) has a height less than the thickness of said base plate (18). An information memory medium according to claim 1, characterized in that said body (16) further comprises another base plate (18), a recording portion (20) formed on this other base plate (18), and a spacer (21), and two base plates (18) are bonded, with said spacer (21) interposed therebetween, such that the information recording portions (20) face each other. An information memory medium according to claim 1, characterized in that said centering member (24) has an annular body.

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