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
  • G11B7/1384—Fibre optics
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
  • G11B11/16—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by mechanical cutting, deforming or pressing
  • G11B11/18—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by mechanical cutting, deforming or pressing with reproducing by optical means
• • 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
  • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
  • G11B7/005—Reproducing

Definitions

• the present invention relates to a process for the optical reading of a sound recording on an engraved support comprising at least one groove wound in a spiral on a disc, or in a helix on a cylinder, driven in rotation about an axis.
• the present invention proposes to provide a non-destructive method for reading these old recordings using optical techniques.
• the invention aims to overcome all the drawbacks of known techniques and to develop a device capable of implementing the method developed.
• the method of the invention is characterized in that an optical fiber is arranged substantially tangentially in said groove so that modulations etched in said groove cause displacements of the end of this fiber, in this that light is injected into said fiber, in that the light leaving the end of said fiber forms a light spot, in that an image of said spot is collected on an optical position sensor, and in that at least one component of the movements of said spot is analyzed in order to read said recording.
• the light leaving said fiber and forming the light spot is reflected at the end of the fiber and leaves laterally of the fiber.
• the movements of the reflected light spot are analyzed along two orthogonal axes and the results of this analysis are used, on the one hand to read said recording and on the other hand to control the movements of the fiber so that it follows the groove of said engraved support.
• the signal corresponding to the component is preferably broken down along one of the axes into two signals, one of which provides the sound recording engraved on the support and the other of which makes it possible to control the lateral displacement of the fiber to follow the groove, and preferably using the signal corresponding to the component along the other axis to control the height of the anchor point of the fiber relative to said engraved support.
• the orthogonal axes are respectively parallel and perpendicular to the surface of the engraved support.
• the orthogonal axes are arranged at 45 ° relative to the median plane passing through the bottom of the groove.
• the signal providing the sound recording and the signal making it possible to control the lateral displacement of the fiber advantageously correspond to the X axis parallel to the plane of the disc
• the signal making it possible to control the height of the point fiber anchoring advantageously corresponds to the axis Y perpendicular to the plane of the disc.
• the device for implementing the method is characterized in that it comprises an optical fiber disposed substantially tangentially in said groove, means for injecting light into the fiber, an optical system for collecting light leaving the fiber, an optical position sensor on which the optical system produces an image of the light spot formed by the light leaving the fiber, and means for analyzing the signals delivered by the position sensor and deducing therefrom the movements of the light spot in at least one direction for reading said recording.
• the optical fiber has a free end disposed in the groove, this end being arranged to reflect the light guided by its heart and to return it laterally with respect to its axis.
• the device preferably comprises two servo motors, one for moving the fiber laterally so that it follows the groove wound in a spiral on a disc or in a helix on a cylinder and the other so that it is maintained at a level substantially constant with respect to the surface of the disc.
• the optical position sensor comprises four electrodes corresponding in pairs to the two orthogonal axes.
• FIG. 1 represents a perspective view of a section of furrow of an engraved support
• FIG. 2 represents a cross-sectional view of this groove and the position of a conventional needle used for reading this recording
• FIG. 3 represents a view in longitudinal section of an end of optical fiber used in the context of the method according to the invention
• FIG. 4 represents a cross-sectional view of the groove and of the optical fiber used in the context of the method of the invention
• FIG. 5 is a schematic view illustrating the principle on which the method of the invention is based
• FIG. 6 represents a block diagram of the electronic circuit analyzing the light spot obtained on the optical position sensor
• FIG. 7 represents a detailed view of part of the circuit of FIG. 6,
• FIG. 8 represents a detailed view of another part of the circuit of FIG. 6, and
• FIG. 9 represents a view illustrating one of the advantages of the method according to the invention.
• the groove of a phonographic record which has been the only sound recording medium used for many years, has the shape of a spiral groove engraved directly or produced by pressing with a matrix. As shown in Figures 1 and 2, this groove 10 has a V-shaped profile open for example at 90 °. The lateral faces of this V are then inclined at 45 th relative to the vertical and are engraved either identically on the two faces 11 and 12 when the recording is monophonic, or differently when the recording is stereophonic. In the latter case, the face 11 corresponds to the right track and the face 12 corresponds to the left track.
• the needle or stylet 13 follows the groove of the disc driven in rotation by a turntable turntable and bears on the lateral faces of this groove in zones 11a and 12a which are located near the bottom.
• An electromagnetic, electrodynamic or piezoelectric cell is mechanically coupled to the needle and converts the movements of the latter into electrical signals.
• optical fiber 14- see FIG. 3
• This conventional technique is totally abandoned within the framework of the process defined above and the needle is replaced by an optical fiber 14- (see FIG. 3), or more exactly a section of optical fiber which is disposed substantially tangentially or at an angle. weak in the groove 10.
• This fiber comprises a core 15 conducting light surrounded by an envelope 16, commonly called “cladding”. Its end 17 is cut in such a way that the light injected into the heart 15 undergoes a total reflection on the fiber-air diopter and is returned laterally through the envelope
• Figure 4- shows the optical fiber seen in section in the groove 10.
• the horizontal displacements "X” are due to the modulation of the groove, that is to say that they correspond to the recording engraved in the groove
• the vertical displacements "Y" correspond to the flatness defects of the disc.
• the reflected beam 18 corresponding to arrow A is focused by an optical system 19 ' on an optical position sensor 20, in the form of a light spot 21.
• the movement of this light spot 21 according to the X axis corresponds to the horizontal displacement of the fiber and the displacement of the light spot 21 along the Y axis corresponds to the vertical displacement of this fiber.
• the sensor 20 supplies two currents per axis. If the light spot is in the center of the sensor, these two currents are equal but with opposite signs.
• the circuit illustrated in FIG. 6 in the form of a block diagram represents the sensor 20 provided with two position electrodes 20x1 and 20 X 2 for detecting the position of the spot 21 on the X axis and two position electrodes 20 y ⁇ and 20 y2 to detect the position of spot 21 on the Y axis.
• These detectors provide electrical signals in the form of intensities I x ⁇ , I xZ , I y and I y 2 which are converted into voltage , U x2 , U y x and U Y 2.
• I o is the total intensity of the current supplied by the detectors on the X axis
• the currents Ixi and l ⁇ 2 are converted into voltages Uxi and U 2
• R represents the load resistance
• the two signals Ux and U y are independent of the brightness of spot 21.
• Signal X corresponds to the sound recorded by the groove. It is also used to control the horizontal displacement of the optical head, that is to say of the fiber, one free end of which is housed in the groove and the other end of which is anchored on a support controlled by two motors 22 and 23 one of which 22 moves the optical head horizontally and the other of which 23 generates the vertical guide.
• the Y-axis signals correspond to sound.
• it is also possible to use the method for playing stereophonic discs by tilting the X and Y axes at 4-5 ° relative to the plane of the disc.
• the signal X is divided into two parts (see FIG. 7).
• the part 26a of the signal which has passed through a low-pass filter 24 is used to control the lateral displacement of the fiber to ensure the "tracking" of the groove and to maintain on average the light spot in the middle of the X axis. A this effect, this part of the signal is transmitted to the motor 22 through a regulation circuit 27.
• the part 26b of the signal which has passed through a high-pass filter 25 having a cut-off frequency of the order of 20 Hz, corresponds to the oscillations side of the light spot around the middle central position.
• This part 26b of the signal corresponds to the sound recording which can be reproduced by a loudspeaker 28.
• the signal Y corresponds to the vertical displacement of the fiber which results from the flatness defects of the disc.
• This signal passes through a low-pass filter 29 with a cut-off frequency of 10 Hz and is directed to the motor 23 via a regulation circuit 30 which controls the vertical movement of the fiber to maintain the light spot in the middle of the Y axis.
• the stress that the end of the fiber exerts on the groove is of the order of 50 to 60 mg, that is to say much lower than that exerted by any conventional needle or stylus .
• the reduction in stress is at least a factor of 40 to 50. As a result, it becomes possible to read cracked and cracked discs.
• FIG. 9 makes it possible to compare the reading positions of a conventional needle and of the optical fiber. Due to the different geometry of these two elements and the appropriate choice of the diameter of the fiber, the contact zones of said elements with the faces 11 and 12 of the groove 10 are not located in the same places. The contact areas 11a and 12a of the needle are often damaged due to the multiple readings of the disc. The contact areas 11b and 12b of the optical fiber 14 are located higher than the previous ones, that is to say in places where there has practically never been contact with a needle. This eliminates a significant part of the parasitic noise.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Recording Or Reproduction (AREA)
• Optical Head (AREA)

Priority Applications (1)

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Publications (1)

Family

ID=4189769

Family Applications (1)

Country Status (2)

Citations (1)

• 1993
  • 1993-02-22 EP EP93903773A patent/EP0591479A1/de not_active Withdrawn
  • 1993-02-22 WO PCT/CH1993/000045 patent/WO1993017418A1/fr not_active Application Discontinuation

Patent Citations (1)

Non-Patent Citations (4)

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