FIELD OF THE INVENTION
The invention relates to a pick up unit for reading and/or writing data on a disk.
A pickup unit of this type is known from patent application US 2002/0009032 A1.
US 2002/0009032 A1 discloses a pickup unit for recording and reproducing information on and from an optical disk. The pickup unit comprises an objective lens provided in a lens holder which is connected to a frame by two pairs of elastic support members. The elastic support members extend parallel to each other and substantially parallel to the surface of the disk. In order to focus the lens with respect to the disk, the lens holder is movable towards and from the disk in a focus direction of the lens by a deflection of the elastic support members powered by a driving coil and a magnet. The lens and the portion of the frame closest to the surface of the disk both have about the same distance to the surface of the disk. As it is more and more desired to have a very small operating distance between the lens and the surface of the disk - smaller than the flatness tolerances of the disk, a risk of undesired collisions between the pickup unit and the disk exists, in particular between the disk and the portion of the frame closest to the surface of the disk. Collisions between the disk and the pickup unit may lead to serious damage to the surface of the disk.
In an attempt to solve this problem, a pickup unit known in the art comprises a lens holder having a lens mounted thereto by means of a pedestal. In this manner, the lens extends in an elevated position with respect to the frame of the pickup unit. As a result the lens can be positioned at a distance with respect to the surface of the disk which is smaller than the flatness tolerances of the disk, without the risk of collisions between the disk and the portion of the frame closest to the surface of the disk. However, mounting of the relatively heavy lens on the pedestal raised the center of mass of the lens holder with respect to the center of stiffness of the elastic support members accordingly. This leads to unfavorable dynamic properties of the lens holder which must be compensated by a counterweight mounted to the lens holder on the side opposed to the pedestal. Due to the additional mass of the pedestal and the counterweight, however, the movement of the lens holder needs to be powered by more powerful driving coils and magnets.
It is an object of the invention to provide an improved pickup unit for reading and/or writing data on a disk.
In order to accomplish that objective, the pickup unit according to the invention comprises a lens in a lens holder which is connected to a frame of the pickup unit by at least one elastic support member extending between a mounting position at the lens holder and a mounting position at the frame, the lens holder being movable with respect to the frame in a focusing direction of the lens towards and away from the disk by bending of the at least one elastic support member under the action of an actuator acting between the lens holder and the frame, wherein at least in an inactivated state of the actuator the mounting position of the at least one elastic support member at the lens holder is located closer to the disk than the respective mounting position of the at least one elastic support member at the frame, as seen in the focusing direction of the lens.
In the pickup unit according to the invention, it is possible to position the lens closer to the disk than the frame of the pickup unit without the need to use a counterweight. This is a result of the fact that in the invention not only the center of mass of the lens holder is raised but also the center of stiffness of the at least one elastic support member. Consequently it is not necessary to lower the center of mass of the lens holder again to coincide with the center of stiffness.
Due to the features as defined in claim 2 the desired effect can be obtained by a simple, substantially rectilinear support member.
Other embodiments of the pickup unit according to the invention are described in the claims 3 to 8.
The invention also relates to a disk drive unit comprising a disk drive and the pickup unit according to the invention.
Aspects and advantages of the invention will be apparent from the following description which is given with reference to the drawings.
The drawings show a preferred embodiment of the pickup unit according to the invention. This pickup unit 1 may be used in a device for reading and/or writing data on a disk, such as a compact disk player, which is adapted to read/and or write compact disks for audio and/or video by means of an optical or magnetic reading and/or writing member.
In a disk 2 for use in the previously described disk drive unit, data is encoded in one or more layers of the disk 2, shown schematically in
With reference to
The pickup unit 1 as a whole is movable in a tracking direction y with respect to the disk 2 by means of a slide mechanism (not shown). Under the action of an actuator 11, 12, 13 provided between the lens holder 6 and the frame 7, the lens 5 of the pickup unit 1 is movable with respect to the disk 2 and the frame 7 in the tracking direction y and a focusing direction z, and tiltable in a tangential direction x.
In the preferred embodiment of the pickup unit 1, the actuator 11, 12, 13 comprises a plurality of permanent magnets 11 connected to the frame 7 and a plurality of coils 12, 13 provided at the lens holder 6 and the permanent magnets 11 respectively, such that the coils 12, 13 and the permanent magnets 11 exert forces on the lens holder 6 by means of electric currents through the coils 12, 13. The movement of the lens holder 6 with respect to the frame 7 and the disk 2 is used to focus the laser light on the exact point on the data track 3 in the disk 2 and to position the lens holder 6 in such a way with respect to the disk 2 that the laser light is always locally perpendicular to the surface of the disk 2, despite an inclination of the surface of the disk 2 caused by deviations in the flatness of the surface of the disk 2.
The electric currents through the coils 12, 13 are provided by a control circuit (not shown) for an accurate control of the position and orientation of the lens holder 6 of the preferred embodiment of the pickup unit 1. In order to determine the actual position of the lens holder 6 with respect to the disk 2, the control circuit may use, for example, intensity parameters of the laser light received by the pickup unit 1. The control unit is not considered part of the invention, and a multitude of possible implementations of a control circuit for this purpose are known, so that no further description is given of the control unit.
With reference to
In
With reference to
It should be understood from the above description that the pickup unit 1 according to the invention comprises a lens 5 which is positioned closer to the disk 2 than its frame 7 in the focusing direction z of the lens, wherein both the center of stiffness of the wire members 8 and the center of mass of the lens holder 6 are positioned closer to the disk 2 by the same distance. As a result, a compensation of the position of the center of mass of the lens holder 6 to avoid unfavorable dynamic properties, for example by means of a counterweight at the lens holder known in the art, is not necessary. Accordingly, more powerful driving coils and magnets for moving such a compensated (heavier) lens holder are not necessary.
The invention is not restricted to the above-described embodiment as shown in the drawings, which may be varied in several ways without departing from the scope of the invention.
For example, the elastic support members may have any kind of shape between their mounting positions, and they may each have a different bending stiffness, as long as the center of stiffness of the wire members coincides with the center of mass of the lens holder. Accordingly, the number of elastic support members is not limited to four, and the pickup unit may thus also be provided, for example, with six elastic support members arranged in two cooperating groups of support members instead of two cooperating pairs of support members.
As a further example, the mounting positions of the elastic support members of each cooperating pair at the lens holder and the frame may be spaced apart by an equal distance and in the same direction, which may be any direction suitable for obtaining the (dynamic) properties of the movement of the lens holder as stated above.
In another variation, the elastic support members may extend at a slight angle with respect to a plane through the lens in the focusing direction and the tangential direction.
Moreover, several combinations of the features defined in the claims are possible.
In general it is noted that, in this application, the expression “comprising” does not exclude other elements, and “a” or “an” does not exclude a plurality. A single processor or unit may fulfill the functions of several elements in the appended claims. Reference signs in the claims shall not be construed as limiting the scope thereof.
Number | Date | Country | Kind |
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03104027.2 | Oct 2003 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB04/52197 | 10/25/2004 | WO | 4/25/2006 |