Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-01-14
2001-08-14
Edun, Muhammad (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044140, C369S044150, C369S112040
Reexamination Certificate
active
06275454
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to optical disc drives, and particularly to high density optical disc drives that employ lenses supported on sliders that aerodynamically control head/disc spacing.
Run-out, in an optical disc drive, is the condition of variations in distance between the head and disc surface that leads to defocus of the objective lens. Run-out is caused by a lack of parallelism between the lens and disc surface, which in turn is caused by a number of factors, including unbalanced forces acting on the disc drive spindle, vibration, external noise, disc warpage, lack of perpendicularity of the disc spindle, and lateral motion of the spindle caused by ball bearing imperfections, to name a few. Many optical disc drives employ an objective lens positioned at a fixed location relative to the platform supporting the disc. Variations in the flatness in the disc, therefore, is the most common cause of run-out in such optical disc drives. Where the objective lens is mounted to a flying slider, disc run-out will be of less impact on lens focus because the slider follows undulations of the disc surface.
The density, or radial spacing, between concentric data tracks, on optical discs continue to increase, requiring greater precision of lens positioning. Conventional drives employing flying sliders accomplish lens positioning by operating an actuator arm with a large scale motor, such as a voice coil motor, to position a lens\slider on a gimbal at the end of the actuator arm. However, the large scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution lens positioning mechanism is necessary to accommodate more densely spaced tracks.
BRIEF SUMMARY OF THE INVENTION
A slider assembly for an optical disc drive in accordance with the present invention comprises a slider body having an aerodynamic surface arranged to fly a design distance from a recording surface of a recording medium when the recording medium is rotated about a medium axis at its operating velocity. An objective lens is supported by the slider and defines a focal point located at a fixed position relative to the lens. A microactuator is mounted to the slider body and supports the objective lens to selectively alter the radial position of the focal point relative to the medium axis.
In a preferred embodiment of the slider assembly, the microactuator includes a pad supported by the slider body. A micromotor beam, such as a pair of piezoelectric beams, are mounted to the pad and extend in spaced relation over the slider body. The objective lens is mounted to the micromotor beam as to be cantilevered over the slider body. The micromotor beam is operable to move the objective lens relative to the slider body to thereby rotate the objective lens about the roll axis and radially alter the position of the focal point.
In one form of the slider assembly, the pair of piezoelectric beams include conductive patterns to operate the piezoelectric beams to deflect in a direction along the yawl axis of the slider body. The first and second beams rotate the objective lens about the roll axis when operated at different voltages, and operate to rotate the objective lens about the pitch axis of the slider body to adjust the focus of the objective lens when operated at design polarities.
In another form of the slider assembly, the piezoelectric beans include conductive patterns having first portion to operate the piezoelectric beams to deflect in a direction along the yawl axis of the slider body to focus the objective lens relative to the recording surface, and a second portion to operate the piezoelectric beams to deflect in a direction along the pitch axis of the slider body to radially position the focal point.
In a preferred embodiment, the objective lens defines a light path through the slider body between the lens and the focal point, and a solid immersion lens is mounted to the slider body in the light path.
In accordance with another aspect of the present invention, an optical disc drive has a rotatable optical recording medium having a recording surface with a plurality of concentric radial tracks along which data may be recorded as marks having distinctive optical characteristics and along which data may be recovered by optically sensing marks when the recording medium is rotated at an operating velocity. An optical system has a light source for supplying light, an objective lens for directing light supplied by the light source at the recording surface, and a light detector operatively associated with the objective lens to receive light reflected from the recording surface. The objective lens defines a focal point at a position relative to the lens. A slider assembly supports the objective lens. An actuator arm supports the slider at a selected radial position adjacent the optical recording medium. The slider has an aerodynamic surface to fly a design distance from the recording surface when the recording medium is rotated at the operating velocity. A microactuator on the slider assembly is operable to selectively alter the radial position of the focal point relative to the slider.
Another aspect of the present invention is a method of radially positioning the focal point of an objective lens of a disc drive optical system in which the optical system includes an actuator arm having a slider which supports the objective lens and is arranged to fly a design distance from a recording surface of an optical recording medium when the recording medium is rotated at an operating velocity. The method comprises flying the slider a design distance from the recording surface, and selectively positioning the objective lens relative to the slider to selectively alter the radial position of the focal point relative to the recording surface.
The objective lens is advantageously mounted to a pair of cantilevered micromotor beams. In one embodiment, the beams are independently deflected in a direction along the yawl axis of the slider to rotate the objective lens about the roll axis.
In another embodiment, the beams are independently deflected in a direction along the pitch axis of the slider to move the objective lens along the pitch axis. In this embodiment, the beams may also be deflected along the yawl axis of the slider to focus the objective lens relative to the recording surface.
REFERENCES:
patent: 4914725 (1990-04-01), Belser et al.
patent: 5623461 (1997-04-01), Sohmuta
patent: 5764613 (1998-06-01), Yamamoto et al.
patent: 5828644 (1998-10-01), Gage et al.
Kusamuta, Yoshitoshi, NEC Corp, Patent Abstracts of Japan, Application No. 06-311597, Optical Disk Device, Jun. 25, 1996.
Berg Lowell James
Boutaghou Zine-Eddine
Edun Muhammad
Kinney & Lange
Seagate Technology Inc.
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