Abstract: An optical disk apparatus of the present invention forms, in a first embodiment, two laser beams for erasure of data and irradiates the two laser beams from a single erasing head 102 so that focuses 207 and 208 thereof may be disposed on a same track of an optical disk 206. In order to construct the erasure head so as to provide two beams, either a two beam semiconductor laser 201 may be used or a beam from a semiconductor laser 215 may be divided into two beams. For the means for dividing the beam into two beams, a Wollaston polarizing prism 216, a Bragg diffraction grating 218, a Foucault prism 219 or some other suitable element can be used. Meanwhile, in a second embodiment, data are reproduced by an optical equivalence method using an optical disk 82, 100 or 206 of a phase change medium which exhibits a phase difference smaller than 180 degrees in reflected light therefrom based on recorded data. The phase difference preferably ranges from 120 degrees to 150 degrees.

Abstract: According to a method and apparatus for detecting a tracking error signal for an optical disk of this invention, the tracking error signal is detected from a differential output of a pair of first photosensors arranged in areas in which a 0th-order component and .+-.1st-order components of a reflected beam incident on a track groove of a grooved optical disk are superposed. An offset signal of the tracking error signal is detected on the basis of outputs from a pair of second photosensors arranged between the first photosensors at a center of an area, of the 0th-order component, in which the 0th-order component is not superposed on the .+-.1st-order components, and the first and second photosensors are aligned in a tracking servo direction. The first and second photosensors are controlled to move on the basis of the detected offset signal.

Abstract: It is the object of the invention to decrease the gain peak of an objective lens holder at a natural frequency of a biaxial objective lens actuator used in an optical disc a system using a reproducing-only-disc, a write-once-disc or a erasable disc. The out-line of a construction is that each of support for an objective lens holder is composed of plural elastic wires surrounded damping material (silicone, for example), and a damping effect can be achieved by shearing stress caused in damping material, and each of support springs passes through a hole of a damping box, wherein the clearance between the support spring and the inner wall of the hole is filled with gelled damping material. A further improvement of damping can be achieved by the damping box.

Abstract: An optical composite unit is provided to receive a light focused by a focusing lens for receiving a light reflected from an optical disc. The optical composite unit comprises a cylindrical lens and side-wedge prisms or side-cylindrical lenses which are provided on both sides of the cylindrical lens. The cylindrical lens has a height including a diameter of the focused light and a width narrower than the diameter, and an axis which is rotated by 45.degree. relative to a long axis of a cylindrical beam formed by the cylindrical lens. The side-wedge prisms or side-cylindrical lenses form side beams separated from the cylindrical beam. The cylindrical beam is for detecting a focus error, and the side beams are for detecting a tracking error.

Abstract: It is the object of the invention to provide the actuator for the objective lens, suitable for the optical disc apparatus with high speed access property and high drive sensitivity especially in the track drive direction, and to solve problems concerning with manufacturing processes, by using metallic leaf springs with high reliability for supporting the lens holder to make its movements to be translation motions in both focus and tracking drive directions. The lens holder 22, a movable object, is supported by four leaf springs 21a to 21d, thereby its movements is pure translation motions in both focus and tracking drive directions. The drive sensitivity in the track drive direction is largely increased by designing and improving configurations of the magnetic circuit and the focus and tracking drive coils.

Abstract: A focus drive coil is wound on an outer periphery of a lens holder, and two tracking drive coils are provided on the focus drive coil. Magnetic chips are preferably interposed between each of the two tracking drive coils. First to third magnets are provided on an actuator base. The first magnet faces the adjacent half portions of the two tracking drive coils, and the second and third magnets face the outer half portion of the two tracking drive coils. The lens holder is supported on the actuator base by using upper and lower parallel triangular plate springs.

Abstract: A concurrent recording and reproducing optical disc has a magneto-optical medium film coated on a ROM disc having rows of pits. The magneto-optical film is arranged by a predetermined interval between the two adjacent rows of the pit rows. The predetermined interval is determined by a dark Airy disc circle band of a beam spot obtained by focusing a light beam on the concurrent recording and reproducing optical disc. Preferably, two light beams are focused on the optical disc to provide first and second beam spots. The first beam spot is focused on one of the pit rows, and the second beam spot is focused on an area between two selected pit rows.

Abstract: Disclosed is a process for the preparation of a modified methacrylic resin molding material, wherein a volatile component is removed from a methacrylic polymer composition containing a volatile component including an unreacted monomer, a solvent or a by-product, and a modifying polymer is added to the methacrylic polymer composition to prepare a modified molding material.

Abstract: A dot printer wherein a bearing member is movably attached to each of two shafts disposed in parallel with a platen, and a plurality of electromagnets are secured to the bearing members together with a head which houses therein a plurality of needles driven by the electromagnets. In this arrangement, the necessity of employing a carrier can be eliminated to simplify the structure as well as to reduce both the dimensions and the weight of the whole while ensuring a high-speed printing operation with another advantage of facilitating the assembling process.