Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
  • G11B7/1372—Lenses
  • G11B7/1374—Objective lenses
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
  • G02B1/14—Protective coatings, e.g. hard coatings
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B3/00—Simple or compound lenses
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
  • G02B7/02—Mountings, adjusting means, or light-tight connections, for optical elements for lenses
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
  • G11B7/121—Protecting the head, e.g. against dust or impact with the record carrier

Definitions

• the present invention relates to an objective lens for focussing a plurality of laser beams having different wavelengths onto an optical disc.
• optical recording media including CDs and DVDs. It is to be noted that there is a tendency to use a single objective lens for various kinds of discs, that is, to focus beams on, for example, a CD and a DVD using the same objective lens.
• a beam having a wavelength of 780 nm is focussed
• a beam having a wavelength of 650 nm is focussed, so that the so-called working distance between the disc and the objective lens differs according to the disc used.
• the working distance is 1.3 mm for the CD, and 1.1 mm for the DVD.
• a pick-up 101 moves vertically as the disc 100 moves vertically during rotation due to small warps in the disc 100, as shown in Fig. 1.
• the servo mechanism includes a feedback circuit comprising a focus error signal detection circuit 102 and a phase compensation drive amplifier 103. The servo mechanism maintains the proper working distance between the objective lens and the disc 100.
• the objective lens 101L moves vertically by the excitation of coils 10 lC.
• the focus servo maintains the proper working distance by moving the objective lens 101L towards the disc 100 and then moving the objective lens 101L away from the disc 100.
• an objective lens for focussing a plurality of laser beams having different wavelengths onto an optical disc.
• the objective lens comprises a lens main body and a protective protrusion integrally formed around the lens main body.
• the protective protrusion protrudes beyond the apex of the convex surface of the lens main body. At least the portion of the protective protrusion protruding beyond the apex of the convex surface of the lens main body is provided with a protective member.
• the protective member is provided at least partially in the periphery of the lens main body. According to a third aspect of the invention, the protective member is arranged to replace the entire protective protrusion of the lens main body.
• the protective member is arranged to replace the entire protective protrusion and is provided at least partially in the periphery of the lens main body.
• Fig. 1 is a block diagram of a focus servomechanism
• Figs. 2A and 2B are schematic views illustrating the focus servomechanism
• Figs. 3 A, 3B and 3C are sectional views of objective lenses
• Fig. 4 is a schematic view of a disc playback apparatus
• Fig. 5 is a schematic view of another disc playback apparatus.
• Figs. 3A through 5 the upper side of the lens is opposed to the back side of the disc.
• a protective member lb separate from a lens main body la is attached to a peripheral flat surface portion of the lens main body la of an objective lens 1 opposed to the back side of the disc.
• This protective member lb is formed as a ring surrounding the lens main body la and is high enough so as to protrude beyond a plane Id which is tangent to the apex of the convex surface lc of the lens main body la.
• the protective member lb is preferably formed of an elastic material having a fixed level of hardness, such as rubber, plastic or other suitable materials.
• suitable rubber materials include: natural rubber, butyl, polyurethane VitonTM and other synthetic rubbers.
• suitable plastics include: nylon, Teflon, Delrin, Torlon and polycarbonate.
• other suitable materials include: cotton, paper and other soft materials.
• Fig. 3B the top portion of a protective protrusion lp of the conventional objective lens 1 is cut away, and the protective member lb is attached to the surface of the portion of the protective protrusion lp.
• the protective member lb protrudes beyond a plane Id which is tangent to the apex of the convex surface lc of the lens main body la. That is, the protective member lb is only provided on the protective protrusion lp surrounding the lens main body la.
• the protective protrusion lp is integrally formed with the objective lens 1.
• the protective member lb is stacked on top of the protective protrusion lp.
• the protective member lb Due to the small working distance between the objective lens 1 and the disk, it is important to minimize the height of the protective member lb above the apex of the convex surface lc of the lens main body la. If the protective member lb protrudes to a larger degree than necessary it is liable to collide with the back surface of the disc, which is undesirable. That is, it is undesirable to simply stack the protective member lb on the protective protrusion lp well beyond the lens main body la since the protective member lb would forcibly rub against the back surface of the disc. Further, the reproduction of signals would be hindered and the focus mechanism could be damaged since focus servo is constantly operating during the rotation of the disc.
• Fig. 3C illustrates an embodiment of the present invention wherein the protective member lb is formed around the perimeter of the objective lens 1.
• the protective member lb may be molded or attached by other means including: bonding, adhesives and melting around the objective lens 1. Again the protective member lb protrudes beyond a plane Id which is tangent to the apex of the convex surface lc of the lens main body la.
• the protective member lb is formed continuously around the lens main body la, it is possible in other embodiments to provide a plurality of protective members lb at equal intervals or unequal intervals in the periphery of the lens main body la.
• the protective protrusion lp is a plurality of equal intervals or unequal intervals in the periphery of the lens main body la.
• the height of the stacked protective member lb and protective protrusion lp is the same as the previously described embodiments. Furthermore, even if collision occurs, it is not the protective protrusion lp but the protective member lb that collides with the back surface of the disc.
• This protective member lb may be formed by applying a protective material to the protective protrusion lp. Because the protective member lb is made of a soft material, damage to the lens 1 and disc are substantially reduced as compared with objective lenses not having a protective member lb.
• Figs. 4 and 5 show playback apparatuses for a disc 100 which includes: a laser beam source 10, an aperture, a beam splitter 12, a collimator lens 13, a focusing lens 14, a photodetector 15 and an objective lens 1.
• the laser beam source 10 can be: a laser diode, a semiconductor laser, or the any other suitable laser source.
• the beam splitter 12 separates incident light from the laser beam source 10 and reflected light from the disc 100.
• the collimator lens 13 produces a parallel beam for the objective lens 1.
• the focussing lens 14 focuses light onto the photodetector 15.
• the apparatus shown in Fig. 5 is similar to that shown in Fig. 4 except that in Fig. 5, the incident beam from the laser beam source 10 is transmitted through the beam splitter 12 and the output beam from the disk 100 is reflected by the beam splitter 12.
• the incident beam from the laser beam source 10 is reflected by the beam splitter and the output beam from the disk 100 is transmitted through the beam splitter 12.
• the objective lens 1 has a protective member around the periphery of the lens main body as illustrated in Figs. 3 A, 3B and 3C.
• the objective lens of this embodiment is applicable to any system in which a single objective lens is used to read from and/or write to a plurality of kinds of discs, requiring changes in the focal length and working distance.
• an objective lens has a protective member on its surface which protects it from colliding with the associated disc, whereby damage to the lens and disc is avoided.

Landscapes

• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• General Physics & Mathematics (AREA)
• Optical Head (AREA)
• Lenses (AREA)
• Window Of Vehicle (AREA)
• Optical Recording Or Reproduction (AREA)
• Glass Compositions (AREA)
• Optical Filters (AREA)

Priority Applications (10)

Applications Claiming Priority (2)

Publications (1)

Family

ID=12635252

Family Applications (1)

Country Status (15)

Cited By (2)

Families Citing this family (14)

Citations (2)

Family Cites Families (5)

• 1999
  • 1999-02-19 JP JP04240899A patent/JP4136160B2/ja not_active Expired - Fee Related
• 2000
  • 2000-02-18 CN CNB008040001A patent/CN1156719C/zh not_active Expired - Lifetime
  • 2000-02-18 DE DE60023852T patent/DE60023852T2/de not_active Expired - Lifetime
  • 2000-02-18 HK HK02102833.5A patent/HK1041314A1/zh unknown
  • 2000-02-18 MX MXPA01008393A patent/MXPA01008393A/es unknown
  • 2000-02-18 BR BR0010115-0A patent/BR0010115A/pt not_active Application Discontinuation
  • 2000-02-18 TW TW089102882A patent/TW525152B/zh not_active IP Right Cessation
  • 2000-02-18 AT AT00910251T patent/ATE309554T1/de not_active IP Right Cessation
  • 2000-02-18 CA CA002362902A patent/CA2362902A1/en not_active Abandoned
  • 2000-02-18 US US09/507,283 patent/US20020109925A1/en not_active Abandoned
  • 2000-02-18 KR KR1020017010573A patent/KR20010102271A/ko not_active Ceased
  • 2000-02-18 EP EP00910251A patent/EP1161701B9/en not_active Expired - Lifetime
  • 2000-02-18 WO PCT/US2000/004327 patent/WO2000049445A1/en not_active Ceased
  • 2000-02-18 AU AU32374/00A patent/AU3237400A/en not_active Abandoned
  • 2000-02-18 NZ NZ513218A patent/NZ513218A/xx not_active IP Right Cessation

Patent Citations (2)

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