Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1999-04-19
2001-10-30
Tran, Thang V. (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S112250
Reexamination Certificate
active
06310840
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the field of optical scanning of high density disk-like information carriers.
BACKGROUND OF THE INVENTION
The invention relates to an optical scanning device for scanning an information track of an optically scannable information carrier, which scanning device includes a radiation source, an optical lens system with an optical axis for focusing a radiation beam supplied, in operation, by the radiation source into a scanning spot on the information carrier, and a first actuator for moving the lens system parallel to the optical axis, the lens system being provided with a main lens, an auxiliary lens, and a second actuator for moving the main lens and the auxiliary lens relative to each other.
The invention further relates to an optical lens system which can suitably be used in an optical scanning device in accordance with the invention.
The invention also relates to an optical player including a table which can be rotated about an axis of rotation, an optical scanning device for scanning an information track of an optically scannable information carrier which can be placed on the table, and a displacement device by means of which the scanning device can be moved, in operation, mainly in a radial direction relative to the axis of rotation.
An optical scanning device and an optical player of the types mentioned in the opening paragraphs are known from U.S. Pat. No. 5,712,842. The main lens of the optical lens system of the known optical scanning device is an objective lens, while the auxiliary lens is a relatively small, so-called solid immersion lens which is arranged between the objective lens and the information carrier to be scanned. By using the auxiliary lens, the lens system of the known scanning device has a relatively large numerical aperture, so that a relatively small scanning spot on the information carrier to be scanned is obtained. By virtue thereof, the known scanning device can suitably be used to scan information carriers having relatively small elementary information characteristics, that is information carriers having a relatively high information density, such as a high-density CD. By means of the first actuator of the known scanning device, the main lens and the auxiliary lens are jointly moved parallel to the optical axis, so that the scanning spot can be focused on the information layer of the information carrier. By means of the second actuator of the known scanning device, the auxiliary lens is moved relative to the main lens in a direction parallel to the optical axis, so that a spherical aberration of the radiation beam in a transparent protective layer of the information carrier present between the information layer and the scanning device can be corrected.
The above citation is hereby incorporated herein in whole by reference.
SUMMARY OF THE INVENTION
The inventors have recognized that a drawback of the known optical scanning device and the known optical player is that, as a result of the relatively large mass of the main lens, the first actuator must supply relatively large accelerating forces to correct high-frequency focusing errors which occur as a result of surface deviations present in the information layer of the information carrier to be scanned, in the direction of the information track to be scanned. As a result, the first actuator must have a relatively high power.
It is an object of the invention to provide an optical scanning device and an optical player of the types mentioned in the opening paragraphs, in which the accelerating forces, to be supplied by the first actuator, for correcting high-frequency focusing errors are limited, so that the necessary power of the first actuator is limited.
In the optical scanning device in accordance with the invention the auxiliary lens is secured in a fixed position to a housing of the lens system, which housing can be moved parallel to the optical axis by the first actuator, while the main lens, viewed parallel to the optical axis, is elastically suspended in the housing by means of an elastically deformable mounting unit, the main lens being movable relative to the housing by the second actuator in a direction parallel to the optical axis.
In operation, by displacements of the lens system parallel to the optical axis, both low-frequency focusing errors which have a relatively large amplitude and occur as a result of an oblique position of the information carrier to be scanned relative to the optical axis and/or by unevenness of the information carrier, and high-frequency focusing errors which have a relatively small amplitude and occur as a result of surface deviations present in the information layer of the information carrier in the direction of the information track to be scanned, must be corrected. Since the acceleration of the lens system is proportional to the amplitude of the focusing errors to be corrected and proportional to the square of the frequency of the focusing errors to be corrected, the accelerations of the lens system necessary to correct the high-frequency focusing errors are relatively large relative to the accelerations of the lens system necessary for correcting the low-frequency focusing errors. The elastically deformable mounting unit has a stiffness which, viewed parallel to the optical axis, is such that the main lens substantially completely follows the displacements of the lens system necessary to correct the relatively large low-frequency focusing errors, and substantially does not follow the displacements of the lens system necessary to correct the relatively small high-frequency focusing errors. In this manner it is achieved that the total mass, which is to be displaced by the first actuator to correct the small high-frequency focusing errors, is limited to mainly the mass of the housing of the lens system and the mass of the auxiliary lens, so that the accelerating forces for correcting the high-frequency focusing errors, which forces are to be supplied by the first actuator, and the necessary power of the first actuator are limited. The elastically deformable mounting unit also serves as a bearing of the main lens in the housing of the lens system.
In a particular embodiment of an optical scanning device in accordance with the invention, the mounting unit of the lens system includes two mounting elements which, viewed parallel to the optical axis, are arranged at some distance from each other and extend transversely to the optical axis, each mounting element, viewed parallel to the optical axis, being elastically deformable and, viewed at right angles to the optical axis, being mainly undeformable. By using the two mounting elements, viewed at right angles to the optical axis, a very rigid bearing of the main lens relative to the housing is achieved. By the co-operation between the two mounting elements, in addition, tilting of the main lens relative to the housing about tilting axes directed at right angles to the optical axis is precluded. In this manner, undesirable displacements of the main lens relative to the auxiliary lens, at right angles to the optical axis, and undesirable tilting of the main lens relative to the auxiliary lens about tilt axes directed at right angles to the optical axis are precluded, while displacements of the main lens relative to the auxiliary lens in a direction parallel to the optical axis are possible, thereby elastically deforming both mounting elements.
In a further embodiment of an optical scanning device in accordance with the invention is characterized in that the mounting elements are each provided with a first, substantially ring-shaped part which is secured to the housing, and a second substantially ring-shaped part which is secured to the main lens, the ring-shaped parts of a first one of the mounting elements being interconnected by at least three bendable bridges extending in a plane transverse to the optical axis and being arranged at regular distances from each other, while the ring-shaped parts of a second one of the mounting elements are interconnected by at least two
Aarts Jan W.
Baartman Jan P.
Tran Thang V.
U.S. Philips Corporation
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