Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
1998-10-02
2001-04-10
Tran, Thang V. (Department: 2753)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044290, C369S044120, C369S119000
Reexamination Certificate
active
06215738
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device for reading from and/or writing to optical recording media.
BACKGROUND OF THE INVENTION
A device of this type is disclosed in EP-B1-0 258 450. In this device, a beam is focused by a focusing means onto an optical recording medium at a focal point. The focal point is guided along data tracks of the recording medium by a displacement means which displaces the position of the focal point on the recording medium. The position of the focal point on the recording medium is displaced by the displacement means indirectly in this device, that is to say by way of the displacement of a lens of the focusing means, which results in displacement of the position of the focal point on the recording medium. The direction of movement is in this case perpendicular to the direction of the tracks present on the recording medium, the focal point being moved both in the positive direction and in the negative direction, depending on the requirement, while the tracks move away under the focal point in their longitudinal direction on account of the rotary movement of the recording medium. Due to inaccuracies, for example in the eccentricity of the recording medium designed as a disk, for example a CD, and tolerances in the securing of the recording medium in the device, it is necessary to displace the focal point virtually at all times in order to keep it on the track. In order to achieve a higher data transfer rate, it is expedient to increase the reading speed of the device. The consequence of this is that the displacements of the focal point on the recording medium which are necessary for the purpose of tracking have to be effected at an increased frequency. The known device may be regarded as having the disadvantage that it is unable, owing to the inertia of the focusing means, to achieve a desired high data transfer rate since tracking of the focal point on a track of the recording medium is no longer ensured correctly at a high reading speed.
SUMMARY OF THE INVENTION
The object of the present invention, therefore, is to improve the known device to the effect that a higher data transfer rate can be achieved with an acceptable outlay.
This object is achieved by means of the features specified in the characterizing part of claim
1
, according to which a beam influencing means is arranged in the beam path and, in dependence on an actuating signal of the regulator, influences the position of the focal point on the recording medium, in accordance with the same direction of movement which is also achieved by the displacement means. This has the advantage that a second beam influencing means, which co-operates with the first and influences the focal point in a direction of movement, ensures an increased accuracy and an increased speed of the desired and/or necessary displacement of the position of the focal point on the recording medium. Consequently, a higher data transfer rate can be achieved according to the invention. A movable mirror, for example, is provided as the beam influencing means. The direction of movement in which the focal point is displaced on the recording medium preferably lies in the plane of the recording medium, preferably essentially perpendicularly to the tracks of the recording medium, in order to enable tracking. A direction of movement which is essentially perpendicular to the plane of the recording medium is also provided according to the invention in order to enable exact focusing of the beam on the recording medium. In this case, the present invention is not restricted to optical recording media in the form of circular disks; other types of recording media, for example those in tape form, also lie within the scope of the invention.
The invention provides for one of the actuators or beam influencing means to have a large adjusting distance with a small bandwidth, while the corresponding other has a small adjusting distance with a large bandwidth. This has the advantage that optimization of the respective actuator to one of the properties “large adjusting distance” or “large bandwidth” makes it possible to use actuators of simple construction. Simultaneous optimization of both properties, on the other hand, can generally be achieved only with a disproportionately high outlay. Bandwidth is in this case essentially understood to mean the width of the frequency band of the actuating signal for which the actuator is designed, that is to say, for example, for which it can follow the actuating signal virtually with no delay and with no resonance. In general, the bandwidth is limited by an upper frequency which is influenced inter alia by the inertia of the actuator. It is advantageous, therefore, to design the actuator having a relatively large inertia as that with the small bandwidth.
An advantageous configuration of the present invention is to arrange a high-pass filter between the detector and the actuator with a large bandwidth, or to arrange a low-pass filter between the detector and the actuator with a small bandwidth. It is advantageous to employ both measures simultaneously. These measures have the advantage that it is consequently possible to split the regulating signals between the two actuators in a simple manner. In this context, a first variant provides for the regulating signal output by the detection means to be the one to be forwarded to the regulator by means of a corresponding filter. The said regulator consists of two isolated, mutually independent, separate regulators for each actuator, or advantageously consists of a coupled regulator in which both regulating paths influence one another. Another variant provides for an output signal of the regulator to be split by means of high-pass and/or low-pass filters and fed to the respective actuator. The band ranges of high-pass and low-pass filters advantageously overlap at least partially.
According to the invention, the beam influencing means is a movable micromirror. This has the advantage that the beam influencing means is small, that is to say has a low mass, and is thus able to carry out rapid movements. A large bandwidth of the beam influencing means is thus ensured. It is likewise advantageous that moving the micromirror requires only a small driving power, which ensures an economical energy consumption, little evolution of heat and other advantages which can be obtained by a low power consumption. In this case, the mirror is designed as a tilting mirror in order to enable tracking, for example as an electrostatically driven silicon mirror. For the purpose of focus following, the mirror is designed as a parallel-displaceable mirror. The resulting path difference of the beam reflected at the mirror leads to a displacement of the focal point in the direction of the optical axis; focusing on the recording medium is possible in this way. The micromirror is driven electrostatically, by means of a piezoelectric element or by similar suitable drive means.
The invention provides for beam generating means, detection means and beam influencing means to be provided integrated on a single semiconductor substrate. This has the advantage that adjustment of the individual elements arranged on the semiconductor substrate is already effected during the production of the substrate; when the device is assembled, all that is then necessary is a single adjustment of the semiconductor substrate, comprising a plurality of elements, in the device. The compactness of such an integrated semiconductor substrate can also be regarded as advantageous. The substrate can advantageously be integrated in devices of existing designs, without necessitating a redesign; a qualitative increase in the value of existing devices is thus possible. The semiconductor substrate is advantageously a silicon-based substrate since such substrates can be produced cost-effectively. Other elements are advantageously integrated on the semiconductor substrate as well, such as, for example, further optical elements, parts of the regulator, for example high-pass and/or low-pass filters, signal pre-ampl
Richter Hartmut
Uhde Dietmar
Deutsche Thomson-Brandt GmbH
Kiel Paul P.
Tran Thang V.
Tripoli Joseph S.
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