Optical: systems and elements – Lens – With support
Reexamination Certificate
2000-11-09
2002-07-16
Ben, Loha (Department: 2873)
Optical: systems and elements
Lens
With support
C359S813000, C359S814000, C369S044150, C369S044140, C369S219100
Reexamination Certificate
active
06421191
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for driving an objective lens. More particularly, the invention relates to an apparatus which drives an objective lens in a direction parallel to the optical axis of the objective lens and also in a direction perpendicular to the optical axis of the objective lens, or parallel to the surface of a disk.
2. Prior Art
Optical pickups are known, each designed to record data on, and reproduce from, an optical disk or a magneto-optical disk.
An optical pickup comprises an optical system and an objective lens driving apparatus. The optical system has an objective lens. The objective lens driving apparatus drives the objective lens in a direction parallel to the optical axis of the objective lens and a direction perpendicular to the optical axis of the objective lens.
The optical system further has a light source, a detector and various optical components. The light source emits a laser beam, which is applied through the objective lens to the data-recording region of an optical disk. The detector detects the light reflected from the data-recording region of the optical disk.
The objective lens driving apparatus has a lens holder, a holder support, a plurality of elastic supports, and an electromagnetic circuit unit. The lens holder holds the objective lens. The holder support supports the lens holder, allowing the lens holder to move. The elastic supports support the lens holder, too, allowing the same to move. The electromagnetic circuit unit drives the lens holder in a focusing direction and in a tracking direction. The focusing direction is parallel to the optical axis of the objective lens. The tracking direction is perpendicular to the tracking direction or parallel to the surface of the optical disk.
The lens holder is made of, for example, resin material. The lens holder has a lens-holding part that holds the objective lens. The holder support has a holder-supporting part that holds the lens holder. The holder support has an opening, through which the optical axis of the objective lens extends.
The elastic supports are wires made of elastic metal. They are secured at one end to the lens holder and at the other end to the holder-supporting part of the holder support. Thus, the elastic supports connect the lens holder to the holder-supporting part of the holder support. The lens holder can therefore be moved.
The electromagnetic circuit unit has a drive magnet, a drive coil, and a yoke. The drive magnet and the drive coil cooperate, generating an electromagnetic force. The yoke defines a magnetic circuit. The drive coil comprises a focusing coil and a tracking coil. The focusing coil generates a force that drives the lens holder in the above-mentioned focusing direction. The tracking coil generates a force that drives the lens holder in the aforementioned tracking direction.
The electromagnetic circuit unit may be of either of two known types. In the first type (hereinafter called “moving magnet type”), the drive magnet is mounted on the lens holder that is a movable component. In the second type (hereinafter called “moving coil type”), the drive coil is mounted on the lens holder.
In the optical pickup having the structure described above, the objective lens driving apparatus drives the lens holder in the focusing direction and the tracking direction. The objective lens, which is held by the lens holder, focuses the laser beam on a desired track provided in the data-recording region of the optical disk. Data is thereby recorded on, or reproduced from, the optical disk.
An objective lens driving apparatus of moving magnet type is advantageous over an objective lens driving apparatus of moving coil type. This is because the lines for supplying power to the drive coil of the electromagnetic drive unit need not be lead from the lens holder that is a movable component and would not hinder the moving of the lens holder. Objective lens driving apparatus of moving magnet type are used in increasing numbers, as the speed at which the optical disk is rotated increases.
However, the objective lens driving apparatus of moving magnet type is disadvantageous. It may likely generate a rotation moment since its movable component is relatively heavy.
To reduce the influence of a rotation moment, the center of gravity of the movable component, i.e., the lens holder, must be located on the optical axis of the objective lens. To this end, two parts of the electromagnetic circuit unit are arranged symmetrically with respect to the optical axis of the lens in most conventional objective lens driving apparatuses of moving magnet type. (Hereinafter, an electromagnetic circuit unit having parts thus arranged will be referred to as “balanced electromagnetic circuit unit.”)
In the objective lens driving apparatus of moving magnet type that has a balanced electromagnetic circuit unit, the drive magnet and the yoke are mounted on the lens holder and positioned symmetrically with respect to the optical axis of the objective lens. Further, the drive coil is arranged on the holder support and opposes the drive magnet.
Two requirements must be fulfilled in the objective lens driving apparatus of moving magnet type that has a balanced electromagnetic circuit unit. First, the lens holder must be mounted on a shaft and needs to slides thereon. Second, the mirror that reflects the laser beam in the optical system must be arranged outside the drive coil of the electromagnetic circuit unit. Therefore, it is impossible to arrange the mirror right below the optical axis of the objective lens. The optical system including the mirror is inevitably large. This renders it difficult to provide a small and thin optical pickup.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an objective lens driving apparatus that is free of the problems described above.
According to the present invention, there is provided an objective lens driving apparatus including a lens holder, elastic supports, and a drive unit. The lens holds an objective lens. The elastic supports are secured at one end to the lens holder and at the other end to a fixed section, thereby allowing the lens holder to move. The drive unit drives the lens holder in a direction parallel to an optical axis of the objective lens and in a plane perpendicular to the direction parallel to the optical axis. The drive unit has at least two magnets provided on the lens holder, a coil section secured to the fixed section, and a yoke. The yoke constitutes, a closed magnetic circuit, along with the magnets. In the drive unit, said at least two magnets are arranged, opposing each other, the coil section is located in a gap between said at least two magnets, and a center of the gap is aligned with a center of the coil section.
According to the invention, there is provided an objective lens driving apparatus including a lens holder, elastic supports, and a drive unit. The lens holder holds an objective lens. The elastic supports are secured at one end to the lens holder and at the other end to a fixed section, thereby allowing the lens holder to move. The drive unit drives the lens holder in a direction parallel to an optical axis of the objective lens and in a plane perpendicular to the direction parallel to the optical axis. The drive unit has at least two magnets provided on the lens holder, a coil section secured to the fixed section, and a yoke. The yoke constitutes a closed magnetic circuit, along with the magnets. In the drive unit, said at least two magnets are arranged, opposing each other, the coil section is located in a gap between said at least two magnets, and a center of the coil section coincides with a gravity center of the lens holder.
REFERENCES:
patent: 5373496 (1994-12-01), Tomita et al.
patent: 5602808 (1997-02-01), Futagawa et al.
patent: 5691965 (1997-11-01), Jansen et al.
patent: 5719834 (1998-02-01), Futagawa et al.
patent: 6330120 (2001-12-01), Shibusaka et al.
Nagasaka Hideo
Osada Yasuo
Ben Loha
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sony Corporation
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