WO2005038785A2

WO2005038785A2 - Improved arrangement for dual lens actuator

Info

Publication number: WO2005038785A2
Application number: PCT/IB2004/052132
Authority: WO
Inventors: Sjoerd Stallinga
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2003-10-21
Filing date: 2004-10-19
Publication date: 2005-04-28
Also published as: TW200519897A; WO2005038785A3

Abstract

A disk drive for writing and/or reading information into/from an optical multiple data layer disk (DSK), comprising a lens system comprising a first (OL0) and a second (OL1) lens for focusing light onto a first (L0) and a second (L1) data layer, respectively, of the disk (DSK), and an actuator (AC) for moving the lens system along a radial direction (R) of the disk (DSK). The first (OL0) and second (OL1) lenses are positioned in a way that an imaginary centre line (IC) through the at least first (OL0) and second (OL1) lenses is parallel to the disk (DSK) when present and perpendicular to the direction of radial movability of the actuator (AC). Preferably, the shortest distance of the optical axis (k0) of the first lens (OL0) to the centre of the disk (DSK) is approximately equal to the shortest distance of the optical axis (k1) of the second lens (OL1) to the centre of the disk (DSK).

Description

Improved mounting method for dual lens actuator

The invention relates to a disk drive for writing/reading information into/from an optical multiple data layer disk, comprising a lens system comprising a first and a second lens for focusing light onto a first and a second data layer, respectively, of the disk, and an actuator for at least moving the lens system along a radial direction of the disk. As is commonly known, an optical storage disk comprises at least one track, either in the form of a continuous spiral or in the form of multiple concentric circles, of storage space where information may be stored in the form of a data pattern. Optical disks may be read-only type, where information is recorded during manufacturing, which information can only be read by a user. The optical storage disk may also be a writable type, where information may be stored by a user. For writing information in the storage space of the optical storage disk, or for reading information from the disk, an optical disk drive comprises, on the one hand, rotating means for receiving and rotating an optical disk, and on the other hand optical means for generating an optical beam, typically a laser beam, and for scanning the storage track with said laser beam. For rotating the optical disk, an optical disk drive typically comprises a motor, which drives a hub engaging a central portion of the optical disk. Usually, the motor is implemented as a spindle motor, and the motor-driven hub may be arranged directly on the spindle axle of the motor. For optically scanning the rotating disk, an optical disk drive comprises a light beam generator device (typically a laser diode), an objective lens for focussing the light beam in a focal spot on the disk, and an optical detector for receiving the reflected light reflected from the disk and for generating an electrical detector output signal. During operation, the light beam should remain focused on the disk. To this end, the obj^'ective lens is arranged axially displaceable, and the optical disk drive comprises focal actuator means for controlling the axial position of the objective lens. Further, the focal spot should remain aligned with a track or should be capable of being positioned with respect to a new track. To this end, at least the objective lens is mounted radially displaceable, and the optical disk drive comprises radial actuator means for controlling the radial position of the objective lens. For portable applications both the disk and the disk drive need to have small dimensions. In order to achieve sufficient data capacity on a small disk the use of a dual layer disk is quite favorable for this application. Figure 1 shows, in part, a dual layer optical disk system. A lens system comprises first and second objective lenses OL0 and OLI. The lens system is attached to an actuator AC for radial and/or vertical movement for the purpose of tracking and focusing, respectively. In a disk DSK a first data layer L0, is located at a depth d below an entrance surface S of the disk DSK. A second data layer LI is located at a depth d+s. A top layer of thickness d is called the cover layer CL. The intermediate layer of thickness s is called the spacer layer SL. For a high Numerical Aperture (NA) readout system, such as the so called Blu-ray Disk (BD) or Portable Blue (PB) systems, compensation of so-called spherical aberration is needed. Spherical aberration is the phenomenon that the rays in the converging cone of light scanning the disk DSK that are close to the optical axis have a different focal point than the rays in the converging cone that make an angle with the optical axis. This results in blurring of the spot and loss of fidelity in reading out the bit stream. The amount of spherical aberration that needs to be compensated for is proportional to the depth of the data layer (first data layer L0 or second data layer LI) that is focused on. A fixed amount of spherical aberration can be compensated for by the objective lens producing the converging cone of light. However in a dual layer disk system compensation for the spherical aberration related to focusing through the spacer layer is also needed. This may be achieved by the use of two objective lenses, each of the two objective lenses compensated for the spherical aberration related to the first data layer and the second data layer, respectively. The two lenses may be replaced by a monolithic component, manufactured by plastic injection molding, where the mold contains the shape of two adjacent objective lenses, each of the two objective lenses optimized for read-out of one of the two layers of a dual layer disk. The two lenses must be mounted to the actuator, which is the part of the drive that can move in the radial and focus direction in order to keep the scanning spot on track and in focus. As there are two lenses adjacent to each other the actuator occupies a relatively large area in the plane parallel to the disk. This has the disadvantageous effect that the smallest diameter of the disk which can be used for writing/reading information into/from the disk is restricted by the dimensions of the lens system. As a consequence the amount of data which can be recorded and/or retrieved on/from one of the two data layers is less than in the case of a single data layer disk. This is especially a problem for portable applications where disks with a small diameter are used. Therefore it is an object of the invention to increase the storage capacity for a multiple data layer disk (e.g. a dual layer disk). To achieve the object of the invention a disk drive as defined in the opening paragraph is characterized in that at least the first and second lenses are positioned in a way that an imaginary centre line through the at least first and second lenses is parallel to the disk and perpendicular to the direction of radial movability of the actuator. It is to be noted that the wording "parallel" also covers the wording "approximately parallel" or "substantially parallel". Further it is to be noted that the wording "perpendicular" also covers the wording "approximately perpendicular" or "substantially perpendicular ". Due to the fact that the two lenses are no longer positioned in the conventional way, that is to say in a radial direction (of the disk), but in an inventive way, that is to say in a tangential direction, the focus points of the lenses can now be closer to the centre of the disk. This is because in the conventional way there must be sufficient area in between the rotation motor and the inner diameter of the disk in order to accommodate the inner lens (e.g. the first lens) when the inner diameter of the second data layer (the data layer corresponding to the second lens) is read out with the second lens. In the inventive way of positioning the lens system there is no need for accommodating one of the lenses while the other one is used for focusing. An embodiment of the invention is characterized in that the shortest distance of the optical axis of the first lens to the centre of the disk is approximately equal to the shortest distance of the optical axis of the second lens to the centre of the disk. Although the inventive way of positioning the lens system is advantageous in respect of getting an increased storage capacity the tracking of a focal spot may be more complicated in case the so-called well known 3 -spots push-pull tracking method is used. This is caused by the so- called yo and yi errors meaning that the optical axes of the first and second lenses are a distance +yo and -yi away from the radial line of the disk, respectively. The tracking is improved however by making the shortest distance of the optical axis of the first lens to the centre of the disk equal to the shortest distance of the optical axis of the second lens to the centre of the disk, or in other words by making y₀ = yi.

The invention will be described in more detail with reference to the accompanying drawings, in which: Figure 1 shows, in part, a dual layer optical disk system; Figure 2 shows a monolithic dual lens component in an actuator; Figure 3 shows a known method for mounting a dual lens for an optical disk apparatus; and Figure 4 shows the inventive method for mounting a dual lens for an optical disk apparatus.

In these figures parts or elements having like functions or purposes bear the same reference symbols. Figure 2 shows a monolithic dual lens component in an actuator AC. The actuator AC comprises a lens system provided with lenses OLn and OLi for focusing light to an optical data layer. The optical axes of the lenses OLo and OLi are indicated by ko and ki, respectively. The radial direction of movement of the actuator AC for tracking purposes is indicated by rd. The vertical direction of movement of the actuator AC for focusing purposes is indicated by fc. An imaginary centre line through the at least first and second lenses OLo, OLi is indicated by IC. This centre line IC is perpendicular to the optical axes ko and ki. Figure 3 shows a known method for mounting a dual lens for an optical disk apparatus. The actuator AC containing lenses OLo and OLi is used in the read -out of a track T on a dual layer optical disk DSK with inner diameter ID and outer diameter OD. The actuator AC can move in the radial direction R. The optical axes ko and ki (see figure 2) of both lenses OLo and OLi are perpendicular to the radial direction R. The disk DSK is rotated by rotation means RM (i.e. a motor) at the center of the disk DSK. Both lenses OLo and OLi must be able to reach the inner diameter ID. When the data layer LI is read out with lens OLi the other lens OLo will be in the area AR within the inner diameter ID. Therefore the area AR cannot be used for recording/retrieving data into/from the disk DSK. The centre line IC is parallel to the radial direction R. In Figure 3 the centre line IC coincides with the dashed line R. Figure 4 shows the inventive method for mounting a dual lens for an optical disk apparatus. An importance difference compared to the known method shown in figure 3 is that the lens system is now mounted such that the centre line IC is perpendicular to the radial direction R. As a consequence there is no need for accommodating one of the lenses OLo, OLj while the other one is used for focusing. Therefore the area AR which cannot be used for recording/retrieving data into/from the disk DSK is smaller, or in other words the inner diameter ID is smaller. As a direct consequence there is more space left on the disk DSK for recording/retrieving data. Thus the storage capacity for the dual data layer disk DSK is increased significantly, especially for portable applications where both the disk DSK and the disk drive need to have small dimensions. Preferably, the shortest distance of the optical axis ko of the first lens OLo to the centre of the disk DSK is equal to the shortest distance of the optical axis ki of the second lens OLi to the centre of the disk DSK, or in other words the distance between the first lens OLo and the dashed line R is equal to the distance between the second lens OLi and the dashed line R.

Claims

CLAIMS:

1. A disk drive for writing and/or reading information into/from an optical multiple data layer disk (DSK), comprising a lens system comprising a first (OLo) and a second (OLi) lens for focusing light onto a first (Lo) and a second (Li) data layer, respectively, of the disk (DSK), and an actuator (AC) for moving the lens system along a radial direction (R) of the disk (DSK), characterized in that the first (OLo) and second (OLi) lenses are positioned in a way that an imaginary centre line (IC) through the at least first (OLo) and second (OLi) lenses is parallel to the disk (DSK) when present and perpendicular ^■ to the direction of radial movability of the actuator (AC).

2. A disk drive according to claim 1, characterized in that the shortest distance of the optical axis (k₀) of the first lens (OLo) to the centre of the disk (DSK) is approximately equal to the shortest distance of the optical axis (ki) of the second lens (OLj) to the centre of the disk (DSK).