Optical pickup device with a tilt adjusting actuator

An optical pickup device includes a lens, a base plate, a supporting wall substantially perpendicular extending from the base plate, at least one cantilever beam, and at least one piezoelectric member. The lens is configured for converging a light beam onto an optical disc. The cantilever beam includes a fixing end and a free end. The fixing end is fixed in/attached to the supporting wall, and the free end suspends the lens thereat. The piezoelectric member is sandwiched between the free end and the base plate. The piezoelectric member is electrically polarizable along a polarization pivot thereof, and thus the length thereof along the pivot direction may be adjusted electrically. The polarization pivot is substantially perpendicular to the base plate and the cantilever beam.

FIELD OF THE INVENTION

The present invention generally relates to an optical pickup device for irradiating a light beam onto a recording medium to read and/or record information from and/or to the recording medium and, more particularly, to an optical pickup device with a tilt adjusting actuator for adjusting an optical axis of a lens to compensate for the tilt of the recording medium.

BACKGROUND OF THE INVENTION

An optical disc has received attention as a memory medium that becomes a core in the recent rapid development of multimedia. The optical disc is loaded into an optical disc drive to perform reading/writing of data from/to the optical disc by means of an optical pickup head.

In order to improve the reliability of optical discs, it is necessary to store and reproduce high-quality signals to and from the optical discs. If there is a tilt angle of a recording surface of the optical disc with respect to an optical axis of a lens of the optical pickup head, then an aberration occurs in a light spot converged on the optical disc. As such, it becomes difficult to record and reproduce high-quality signals on the optical disc. Therefore, in order to record and/or reproduce high-quality signals to and/or from the optical disc, it is necessary to detect the aforementioned tilt angle accurately and to then correct this tilt angle.

As shown inFIG. 4, a conventional optical pickup head100includes a lens90, a lens holder80, several metal wires70, a bracket60, and a base50. The lens90is held by the lens holder80, and the lens holder80, in turn, is suspended by the metal wires70. The metal wires70are fixed in the bracket60extending upward from the base50. A pair of magnets81is respectively secured to two lateral sides of a bottom of the lens holder80. Opposite to the corresponding magnet81, a yoke51with a coil53wound thereon extends upwardly from the base50. Two ends of the coil53are connected to a power supply (not shown). A magnetic field may thereby be induced when a current is supplied to the coil53. When the optical pickup head100is reading or recording an optical disc (not shown), a detector (not shown) detects a tilt angle between the optical disc and an optical axis of the lens90, and a controller (not shown) controls a magnitude and direction of a current outputted by the power supply based on the detected tilt angle. As the output voltage of the power supply varies, the induced magnetic field of the coil53varies accordingly. An attraction interaction or a repulsion interaction between the magnet81and the coil53results in a position change of the lens holder80, so that a tilt adjustment is achieved.

The optical pickup head100adopts an electromagnetic tilt adjusting device. Besides the tilt adjusting device, most optical pickup heads also have a focus adjusting device and a track adjusting device. The focus adjusting device and the track adjusting device are usually electromagnetic adjusting devices. If the optical pickup100has another electromagnetic adjusting device besides the electromagnetic tilt adjusting device, a magnetic interference may arise between such electromagnetic devices.

SUMMARY OF THE INVENTION

Briefly described, one embodiment of a tray for a disc drive uses a piezoelectric element to eliminate any tilting of the optical lens of the optical pickup device.

An optical pickup device includes a lens, a base plate, a supporting wall substantially perpendicular extending from the base plate, at least one cantilever beam, and at least one piezoelectric member. The lens is configured for converging a light beam onto an optical disc. The cantilever beam includes a fixing end and a free end. The fixing end is fixed in and attached to the supporting wall, and the free end suspends the lens thereat. The piezoelectric member is sandwiched between the free end and the base plate, and configured to support the free end of the cantilever beam. The piezoelectric member is electrically polarizable along a polarization pivot thereof. The polarization pivot is substantially perpendicular to the base plate and the cantilever beam.

Other systems, methods, features, and advantages of the present optical pickup device will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present device, and be protected by the accompanying claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the drawing figures to describe the preferred embodiments of the present optical pickup device, in detail.

Referring toFIG. 1, an optical pickup device99includes a lens1, a lens holder2, a pair of cantilever beams3, several wires4, a supporting wall5, a base plate6, and a pair of piezoelectric member7. The supporting wall5perpendicularly extends from a side of the base plate6. Respective fixing ends32of the pair of cantilever beams3are fixed in and/or attached to the supporting wall5, while free ends34of the cantilever beams3are supported by a pair of piezoelectric members7. The piezoelectric members7are sandwiched between the base plate6and the free ends34of the cantilever beams3. The lens1is held by the lens holder2, while the lens holder2is suspended on the free ends34of the pair of cantilever beams3by the several wires4. Two polarizing ends72,74of the piezoelectric members7are respectively connected to an alterable/adjustable power supply (not shown). That is, the central polarization pivots of the piezoelectric members7are perpendicular to both the base plate6and the cantilever beams3.

An unusual characteristic of certain crystalline minerals has been discovered in1880. When subjected to a mechanical force, the crystals become electrically polarized. Tension and compression generate voltages of opposite polarity, in proportion to the applied force. The converse of this relationship has also been confirmed: if one of these voltage-generating crystals is exposed to an electric field it lengthens or shortens, according to the polarity of the field and in proportion to the strength of the field. These behaviors are labeled the piezoelectric effect and the inverse piezoelectric effect, respectively.

According to the inverse piezoelectric effect, when an output voltage of the power supply varies, heights of the piezoelectric members7vary accordingly. As the heights of the piezoelectric members7change, the free ends34of the cantilever beams3rise or fall, so that an angle of the lens1suspended on the cantilever beams3with respect to the base plate6changes. Thus, a tilt angle can be adjusted.

Now referring toFIG. 2A, when the optical pickup device99is reading from and/or recording to an optical disc8, the optical pickup device99irradiates a light beam (not labeled) towards the optical disc8. The lens1converges the light beam and forms a focus spot (not shown) on a recording surface82of the optical disc8. An optical axis of the lens1should be substantially perpendicular to the recording surface82of the optical disc8. If the optical disc8is not positioned horizontally, a tilt angle θ, between the recording surface82of the optical disc8and a surface perpendicular to the optical axis of the lens1, is induced. Due to the presence of this tilt angle θ, an aberration may occur in the focus spot on the recording surface82. The optical pickup device99irradiates a detecting light beam together with the reading light beam to the optical disc8, and the optical disc8returns a light beam to a detector (not shown). The detector analyzes the return light beam, calculates the tilt angle θ, and sends out a tilt error signal. The tilt error signal is sent to the power supply of the piezoelectric members7, and the output voltage of the power supply changes, corresponding to the tilt error signal.

Now referring toFIG. 2B, when the power supply is supplied to the piezoelectric members7, the piezoelectric members7lengthens or shortens corresponding to the power supply. A displacement δ is induced to the free ends34of the cantilever beams3, since the free ends34are supported by the piezoelectric members7. As a result of the displacement6, a displacement angle ψ is induced relative to the lens holder2, as well as the lens1. If the displacement angle ψ of the lens1equals the tilt angle θ of the optical disc8, the displacement angle ψ successfully compensates for the tilt angle θ, and a tilt adjustment is actualized. It is to be understood that any system that compensates at least partially for the tilt angle θ by inducing some displacement angle ψ through the use of at least one piezoelectric member7is considered to be within the scope of the present optical pickup device.

In order to obtain an accurate displacement angle, the following equation is applied.
δ=PL3/3EI[1]
where:

P is the load that the piezoelectric members7apply on the cantilever beams3;

L is a length of the cantilever beams3;

E is Young's modulus of the cantilever beams3;

I is the moment of inertia of the cantilever beams3; and

δ is the maximum deflection of the cantilever beams3.

It is known that the displacement angle ψ is in proportion to δ/L, therefore the following formula can be derived:
ψ∝PL2/EI[2]

Further, the moment I of inertia depends on a cross section of the cantilever beams3. As shown inFIG. 3AtoFIG. 3C, the cantilever beams3can have different cross sections. The cantilever beam3can, for example, have a rectangular cross section (shown inFIG. 3A), an I-shaped cross section (shown inFIG. 3B), or a frame-shaped cross section (shown inFIG. 3C). The rectangular cross section is used as an example in the following text to calculate the moment of inertia of the cantilever beams3. The moment I of inertia of the cantilever beams3can be expressed with the following equation:
I=bh3/12  [3]
where:

b is the width of the rectangular cross section; and

h is the height of the rectangular cross section.

According to equation [2] and formula [3], the following formula can be derived:
ψ∝PL2/Ebh3[4]

The parameters E, L, b, h rely on the material and shape of the cantilever beams3. If the length and the cross section of cantilever beams3are predetermined, the displacement angle ψ of lens1is in proportion to the load P applied on the cantilever beams3. It is easy to adjust the displacement angle ψ of the lens1by directly adjusting the load P applied on the cantilever beams3by the piezoelectric members7. The cantilever beams3are made of a piezoelectric material, such as ZnO, LiNbO3, LiTaO3, and BaTiO3, or a combination thereof.

In alternative embodiments, another pair of piezoelectric members may be positioned respectively between a plate parallel to the base plate6, above the cantilever beams7, and the cantilever beams3. One of the piezoelectric member7under the cantilever beams3and the piezoelectric member7above the cantilever beams3lengthens, while the other shortens. Further, the lens1may also be directly suspended at the free end34of one of the cantilever beams3. Accordingly, the other cantilever beam3and the wires4can be omitted.

It should be emphasized that the above-described embodiments of the present invention, including any preferred embodiments, are merely possible examples of implementation of the principles of the invention, and are merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and be protected by the following claims.