A birefringent film in which molecules oriented in a direction parallel to the film plane and molecules oriented in the direction of the thickness of the film are present in a mixed state. Also, a process for producing the birefringent film, which comprises laminating a resin film on one or both sides thereof with a shrinkable film, thereby preparing a laminate, and then heat stretching the laminate, thereby performing stretching treatment of the resin film while imparting to the resin film the ability to shrink in the direction crossing the stretching direction. A retardation film is formed by using at least one birefringent film and has refractive indexes, n x and n y , in two directions parallel to the plate plane and crossing each other at right angles and a refractive index, n z , in the direction of the thickness of the plate, said refractive indexes n x , n y , and n z satisfying the following equation: 0<(n.sub.x -n.sub.z)/(n.sub.x -n.sub.y)<1 provided that n x >n y . Also, an elliptically polarizing plate comprises a laminate of the retardation film with a polarizing plate. Additionally, a liquid crystal display comprises a liquid crystal cell and a polarizing plate disposed at least on one side of said liquid crystal cell through the retardation film.

Birefringent film with nx >nz >ny, process for producing the same, retardation film, elliptically polarizing plate, and liquid crystal display

An optical disc system including a focusing mechanism and a tracking mechanism, wherein the mechanisms are controlled by feedback loops having electronic circuits for generating a servo error signals. The error signals are communicated in the feedback loop for effecting corrections of the focusing mechanism and the tracking mechanism. The optical disc system is provided with digital lead/lag compensation circuit assembly including a servo loop having servo loop transfer function and an error signal. The circuit assembly includes a motor or actuator having a mechanical resonance frequency being less than a predetermined sampling frequency and a compensation circuit for stabilizing the servo loop. The error signal of the servo loop is sampled at the pre-determined sampling frequency. Normalization of the error signals to the information signal occurs during sampling. The compensation circuit has a compensation transfer function including a single lead and a complex lag for producing a notch filter with a notch. The compensation transfer function is formulated so that the notch occurs at approximately one half the predetermined sampling frequency thereby reducing amplitude of the mechanical resonance frequency in the servo loop transfer function. The optical disc system also includes a mechanical isolator for vibration isolation and accommodation of thermal expansion, an oscillator with a tank circuit having an increased resistance, an improved focus capture system, and means for identifying blank sectors in a storage medium.

Servo control system for information storage device

An optical system supporting device in which an optical system holding member is supported by springs to be movable in focusing and tracking directions; and each of the springs has at least one portion which is oriented parallel with a tangential direction and one bending portion which is bent toward an optical axis of the optical system. Therefore, the holding member is made small in width with respect to the tracking direction; and thus the holding member can be made light in weight such that the driving sensitivity of the holding member is improved.

Optical system supporting device

An assembly for controlling the position of a lens in an optical data storage and retrieval drive includes a carriage that suspends a lens holder using a plurality of flexures. A lens is mounted in the lens holder such that the center of mass of the suspended lens holder lies on the optical axis of the lens, and also coincides with the center of mass of the lens. The lens holder is capable of relative motion with respect to the carriage with at least one degree of freedom. The center of mass of the carriage lies within 0.1 mm of the optical axis, proximate the center of mass of the lens holder. Suspensory forces acting on the lens holder are symmetric about the optical axis. A coarse magnetic drive moves the carriage in a tracking direction, and exerts forces on the carriage that are balanced and symmetric about the optical axis, so that moments about the center of mass of the carriage are effectively absent. Inertial forces acting on the carriage, and forces reactive to the magnetic drive forces are also balanced and symmetric with respect to the optical axis, and produce insubstantial moments about the center of mass of the carriage. There is a fine tracking and a focusing drive for the lens holder. Both of these drives produce balanced and symmetric forces about the optical axis, such that moments about the optical axis are absent. Inertial forces and reactive forces acting on the suspended lens holder are also symmetric about the optical axis. As a result the objective lens moves along its optical axis, and in its tracking direction without change in attitude, and its focal point can be precisely controlled with respect to the surface of a storage medium being read or written.

Seek actuator for optical recording

An optical head which includes a movable bobbin having an objective lens and tracking coils for tracking operation, a carriage guided in such a manner to be able to move in the tracking direction and a state transformation mechanism for transforming the state of the bobbin and carriage between a first state, in which the objective lens can move in the tracking direction but the carriage does not move in the tracking direction, and a second state, in which the movable bobbin and the carriage moves in the tracking direction as one body. When effecting a tracking operation, the state transformation mechanism transforms the state of the bobbin and the carriage into the first state, in which the objective lens can move in the tracking direction but the carriage does not move in the tracking direction, and a tracking drive current is then made to flow through the tracking coils to perform the tracking operation. This results in that the objective lens is supported by a system of a single degree of freedom, of which characteristics are determined by the mass of the movable bobbin and the spring constant of the bobbin supporting means. In contrast, when effecting an access operation, the state transformation mechanism transforms the movable bobbin and the carriage into the second state, in which the bobbin and the carriage move in the tracking direction in one united body, and an access drive current is then made to flow through the tracking coils to effect the access operation. Thereby, tracking performance can be increased and a seeking operation can be performed at a high speed. Further, the tracking coil can be used to effect the access drive operation. Thus, there can be less weight of a movable part of the optical head and lower power consumption.

Miniaturized low-power-consumption optical head provided with a state transformation mechanism

An objective lens for optical disks comprises a first lens component and a second lens component and, when the distance on an optical axis from an entrance face of the first lens component disposed in a position farthest from an optical disk to the center of gravity of the objective lens is taken as gc, the overall length of the objective lens as Σ d, and the focal length as f, the following conditions are satisifed and any of surfaces of the lens components is configured as an aspherical surface: g c<Σd<0.5 0.9<Σd/f<2.2 Thus, the use of the objective lens makes it possible to reduce the load to a driving device for moving the objective lens and to provide the driving device small in size and light in weight.

Objective lens for optical disks

An apparatus for supporting an objective lens projecting a light beam upon an optical record disc having a data track recorded therein, movably in a focusing direction parallel to an optical axis of the objective lens as well as in a tracking direction perpendicular both to the optical axis and to the track in order to effect focusing and tracking servo controls, including four resilient wires arranged between a lens holder and a stationary base member, said resilient wires being not in parallel with each other. Two resilient wires provided nearer to the optical record disc are arranged such that extensions of these wires intersect with each other at a first point to make a first apex angle and the remaining two wires are arranged such that extensions of these wires intersect with each other at a second point to form a second apex angle, the first and second points being aligned in the focusing direction and the first apex angle being smaller than the second apex angle.

Apparatus for supporting objective lens movably in two orthogonal directions

PURPOSE:To improve the rigidity of a movable member, to raise a resonance frequency, and to execute stable servo by forming a reinforcing member for improving the rigidity of the movable member integrally under a protruding state from an optical system supporting member positioned at the approximately center of the movable member. CONSTITUTION:An opening 4b to be formed with an outer peripheral part 4c and a cylindrical part (optical system supporting member) 4d of a movable member 4 is partitioned into four with ribs 4a and bulkheads 4e formed from the outer peripheral part 4c to the cylindrical part 4d, and two pairs of inner yokes 7a and 7b are positioned here. Further, for the inner yokes 7a and 7b, while their surfaces opposite to the cylindrical part 4d are chamfered, the center of the inner yokes 7a and 7b and the center of an objective lens 1 are made into a mutually approaching state. Since the ribs 4a are formed from the cylindrical part 4d to the outer peripheral part 4c of the movable member 4 in this manner, the rigidity of the opening 7b is improved. Thus, the rigidity of the movable member 4 can be improved, the resonance frequency can be raised, and the stability of servo can be improved.

Optical driving device

PURPOSE:To attain easy and proper positioning of an elastic support member by forming a hole and a slot larger than the cross section width of the elastic support member and inserting and fixing the elastic support member end to the hole and the slot. CONSTITUTION:Round holes 11, 12 are formed to a moving member 4 and a stationary member 9 with a tilt of angles theta1, theta2 with respect to the axial line of a metallic wire 10. Only part of the cross section of the holes when viewing the axial direction of the metallic wire 10 is regarded to be penetrated and the diameter of a through-part E in the axial line direction of the elastic support member is selected to be a minimum diameter sufficiently affording the insertion of the metallic wire 10. With the metallic wire 10 inserted to the through-part E, the wire is supported in a way of two point contact and positioned properly. Thus, proper positioning is simply realized.

Optical system support for optical system recording and reproducing device

PURPOSE:To shorten a access time by forming a spring in such constitution where a mobile member does not tilt even though the force is applied to the centroid of the mobile member in the desired direction. CONSTITUTION:An objective lens 1 is struck to an objective lens holding member 3. The member 3 is supported movably in a body by a fixing member 9 via four plate springs 10a-10d set in parallel to an XY plane together with a mobile member 4. A stopper 11 made of an impact absorbing material like the synthetic resin, for example, is set on an end face of an inner yoke 7 set in the tracking direction. In such constitution, the optical axis of the lens 1 is never tilted even though the force of inertia is applied to the member 4 in the focusing or tracking direction by properly selecting those springs 10a-10d. As a result, a light spot can be quickly applied onto a target information track. Then the access time is shortened.

Supporting device for optical system

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