Apparatus for erasing information from optical recording tape with a thermo-deforming layer

Abstract: A method and apparatus for erasing information from optical recording tape having a thermo-deforming layer 2 is disclosed in which information is recorded by forming bumps 4 with residual stress deformed viscoelastically by way of heating portions of said layer 2, and is erased by making said bumps 4 planar by re-heating the bumps 4 in order to remove the residual stress. The information is erased by forming a focal line L f on the tape T using optical elements 11 and 12 for emitting and condensing light of a certain thermal energy, and re-heating the thermo-deforming layer 2 including the bumps 4 on the focal line L f . The information is effectively erased by means of an erasing optical device which forms a focal line L f , and information is recorded without noise, during the erasing and recording operation of an optical recording tape having a thermo-deforming layer. Lower power consumption is achieved by the efficient use of light.

Description: The present invention relates to an apparatus for erasing information from optical recording tape with a thermo-deforming layer, and particularly to an apparatus for optically erasing information using an optical system which scans a tape with focused light. Referring to Japanese laid-open patent publication No. 1-294238 and U.S. Patent No. 4,398,203, an information medium is introduced in which information is optically recorded and read. Different from conventional magnetic, optical, or magneto-optical media, the information medium has a thermo-deforming layer which is viscoelastically thermo-deformed, and records information according to the arrangement of bumps created by heating portions of the thermo-deforming layer. The basic structure and record/playback principle of the medium are illustrated in Figs.1A, 1B and 1C. Referring to Fig.1A, the medium comprises a supporting layer 1, a thermo-deforming layer 2, and protective layer 3 which are stacked in order. When laser light 5 is projected on thermo-deforming layer 2, the portion which is irradiated by laser light 5 is heated by its thermal energy and expands viscoelastically as shown in Fig.1B. Then, when cooled, the expanded portion contracts by viscoelastical deformation to render a bump 4 having a different residual stress than the original planar form as shown in Fig.1C. Thus, it is possible to optically record information by discontinuously forming the bumps while projecting modulated laser light. In addition, when laser light is induced to the degree where the thermo-deforming layer does not yet expand from the heat, optical reproduction of the information can be done by detecting light modulated and reflected by the bumps. Further, since the thermo-deforming layer becomes planar by being heated to remove the residual stress of the bumps, erasing the information is also possible by means of a heater capable of evenly heating the entire thermo-deforming layer. Optical recording media with such a thermo-deforming layer may be manufactured in cassette tape form, and their wide application for computer memory devices to process a great quantity of information, as well as audio and video players, is expected. Referring to Fig.2 as a prior art, tape T (an aforementioned optical recording medium) is wound on two reels R and R' in a cassette C. A heater EH as an erase head and an optical means OH as a record/playback head are provided in close proximity to tape T which travels between the two reels R and R', and passes very near the heater EH which is in the form of a plate or a rod and installed so as not to make direct contact with tape T. In other words, the conventional erasing method is to perform the aforementioned erasing by radiant heat from the heater EH which heats tape T as it passes, and cooling as it proceeds past the influence of heater EH. Erasing by heat, however, is disadvantageous in that first, since the environment influences the heater, maintaining a proper and uniform heating temperature is difficult; secondly, the erasing operation is delayed because the heater requires time to come up to a predetermined temperature; and finally, while cooling, an additional heat shielding means or a cooler is required in order to interrupt the influence of radiant heat from the heater. An apparatus for erasing information from optical recording tape with the help of the thermal energy of light is described in GB-A-1 409 534. This prior art reflects the apparatus defined in the preamble of claim 1. It is an object of the present invention to provide an improved optical erasing apparatus enabling an effective erasing operation. This object is achieved with an apparatus having the features of present claim 1. To achieve the object, an optical means is employed to scan a running tape with focused light of a certain thermal energy. According to the present invention, thermal energy of light can be effectively utilized in that light is concentrated on the focal line by means of the optical device, while the tape, to be more precise, the thermo-deforming layer, meets the focal line more exactly. Since the thermal energy of light depends on the optical system including the light source and the lens element for condensing the light, the thermal energy is far from the environmental influences. Accordingly, the present invention facilitates control of the temperature required to remove the residual stress of the bumps in order to make the bumps of the thermo-deforming layer planar, which needs no additional cooler because the peripheral temperature on the tape does not rise, acquiring rapid response and solving the delay problem. Furthermore, to erase the information completely, during the erasing operation, the present invention enables the control of part of or the whole optical system for correcting an error caused by the tape's horizontal and vertical vibration so that the focal line of the optical system coincides with that of the tape. Brief Description of the Drawings The above object and other advantages of the present invention will become more apparent by describing in detail a preferred embodiment of the present invention with reference to the attached drawings in which: Figs.1A, 1B and 1C are cross sections illustrating the structure of optical recording tape with a thermo-deforming layer and the record/playback principle thereof; Fig.2 is a plan view of a tape playing portion illustrating a conventional erasing device using the tape shown in Fig.1; Fig.3 is a plan view of a tape playing portion illustrating an erasing device of the present invention; Fig.4 is an enlarged plan view of the erasing optical device shown in Fig.3; Fig.5 is a perspective view illustrating another embodiment of the erasing device shown in Fig.3; and Fig.6 is a Gaussian beam distribution chart of the embodiment shown in Fig.4. Detailed Description of the Invention Referring to Fig.3, the erasing device of the present invention is different from the conventional one of Fig.2 in that an erasing optical device 10 is provided as an erasing head. The erasing optical device 10 as shown in Fig.4, comprises a laser diode 11 for emitting laser light as a light source, a semi-cylinder lens 12 for concentrating the laser light on focal line L f , a square incidence aperture 13 which is positioned between laser diode 11 and semi-cylinder lens 12 to pass only the central portion of the laser light, and a collimating lens 14 for converting the light passing through the aperture to parallel light. The square incidence aperture 13 passes the central portion of the laser light, intercepts the low-intensity peripheral light, and simultaneously squares the cross-section of the parallel light from collimating lens 14. When the square beam of parallel light is incident to semi-cylinder lens 12, the beam becomes horizontally concentrated, thus focusing along focal line L f vertically (see Fig.5). Tape T runs on the plane including the focal line and is heated by the thermal energy of the focused light, erasing the tape. Detecting and driving optical devices are provided so that tape T may precisely coincide with the focal line L f . Briefly, reflected light from tape T is used to sense the focal line's exact location according to the tape's vibration. Then, using a correction signal obtained from the reflected light, either the semi-cylinder lens 12 or the entire optical device itself is driven horizontally and/or vertically. A detailed description of the optical devices will be herein abbreviated since detecting and driving devices of this nature are commonly used in the art. Referring to Fig.5, three laser diodes 11a, 11b and 11c are used as light sources in the embodiment. Laser diodes 11a, 11b and 11c are spaced apart from one another and in parallel with focal line L f formed on the tape. The purpose of this arrangement of the three diodes is to obtain high and even gain distribution of the Gaussian beam within a square region A of the parallel light incident to semi-cylinder 12. Referring to Fig.6, overlapping parabolic distributions Ga, Gb and Gc of the Gaussian beam of each laser diode 11a, 11b and 11c acquire an effective Gaussian beam distribution G' having a uniform maximum value and a broad circular region B. As square region A inscribed with circular region B meets semi-cylinder lens 12, low power consumption is achieved as well as efficiency. As described above, the present invention makes it possible to effectively erase information by means of an erasing optical device which forms a focal line and to repeatedly record information without noise, during the erasing and recording operation of an optical recording tape having a thermo-deforming layer. In addition, the present invention achieves low power consumption by the efficient use of light.

Claims: An apparatus for erasing information from an optical recording tape (T) having a thermo-deforming layer (2) in which information is recorded by forming bumps (4) with residual stress deformed viscoelastically by way of heating portions of said layer, and erased by making said bumps (4) planar by re-heating said bumps (4) in order to remove the residual stress, said erasing apparatus (1) comprising: at least one light source (11,11a,11b,11c) generating light; a square incidence aperture (13) passing a central portion of the light generated from said at least one light source, characterized by a collimating lens (14) converting light passing through said square incidence aperture (13) into a square beam (A) of parallel light; and a semi-cylinder lens (12) concentrating the square beam of parallel light on said tape (T) to form a focal line (L f ). An apparatus for erasing information from an optical recording tape having a thermo-deforming layer as claimed in claim 1, wherein at least two light sources (11a,11b,11c) are provided parallel to said focal line (L f ).

Inventors: HWANG WEON-JAE, HWANG, WEON-JAE
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO. LTD.
Application year: 1991
Main classification: G11B7
IPC codes: G11B7