Disc player and focus search control method

Details Disc player and focus search control method Disc player and focus search control method

2001-03-20

2003-04-08

Edun, Muhammad (Department: 2655)

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

C369S044260, C369S053100

Reexamination Certificate

active

06545956

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technical field of disc players in which a disc-shaped recording medium such as a CD, a DVD or the like is set, a drive signal is applied to a pick-up, and an object lens can be controlled to move in a focussing direction with respect to the surface of the disc.
2. Description of the Related Art
In optical disc players such as, for example, CD players, a laser beam must be accurately converged on the information recording surface of a disc. To this end, by using a focus servo control device, the position of an object lens for pick-up is controlled with respect to the reflecting surface of the disc, such that the object lens is held at a focus position. In such a focus servo control device, a drive signal that corresponds to the distance between the object lens and the disc surface is supplied to the actuator of the object lens.
On the other hand, at the time of start-up of driving of the focus servo control device, the object lens is disposed very far away from the disc surface. Thus, when focus servo control is carried out, focus search must be carried out so that the focus is pulled in. Namely, a focus search signal having predetermined waveform pattern is applied to the actuator. After the object lens is moved to a vicinity of the focus position, processing moves on to focus servo control.
Recently, as more types of discs such as CDs, DVDs and the like have arisen, disc players which can be commonly used for plural types of discs have come to be demanded. In such a disc player, there is the need to drive the actuator in consideration of characteristics of plural discs.
However, comparing a CD with a DVD for example, the distance between the disc surface and the disc reflecting surface differs greatly. Thus, the focus positions of the object lens for focussing do not match with each other. As a result, when the CD and the DVD are driven by a common actuator and object lens, problems arise in that it is difficult to carry out operation for applying the focus search signal to pull-in the focus accurately for both CDs and DVDs, and much time is required for pulling in the focus. Thus, conventionally, there has been the problem that it is not easy to realize a disc player, which is applicable to plural types of disc-shaped recording media having different characteristics.
SUMMARY OF THE INVENTION
An object of the present invention, which was made in consideration of such problems, is to provide a disc player which, when different types of discs are used, can carry out focus searching by using a common actuator without the device structure becoming complicated.
In order to overcome the above-described problems, the first aspect of the present invention provides a disc player, which can be used in common for a plurality of types of discs having different focus positions of an object lens with respect to a recording surface, and which carries out focus servo control with respect to the discs and reads out recorded information, comprising: a judging device which judges a type of disc set at the disc player; a waveform setting device which, from a plurality of waveform information which are held in advance for use in focus searching for the plurality of types of discs, selectively sets a predetermined waveform information in accordance with results of judgement by the judging device; and a focus searching device which, at a time of start-up of the disc player, before the focus servo control is carried out, generates a focus search signal based on the waveform information set by the waveform setting device to carry out focus searching.
In accordance with this invention, when the disc selected from plural types of discs is set at the disc player, the type of the disc is judged, and predetermined waveform information corresponding to the results of judgement is selectively set. Then, the focus search signal based on the waveform information is generated. In this way, after focus searching has been carried out, processing moves on to focus servo and reading of recorded data from the disc is possible. Accordingly, even in a case in which the focus positions with respect to recording surfaces of plural discs are different, by adjusting the characteristic of the focus search signal, such a situation can be handled, and the focus searching can be carried out by providing an optimal characteristic for each disc while using a common actuator.
The second aspect of the present invention provides a disc player according to the first aspect, characterized in that in the disc player according to the first aspect, the waveform information is information for generating triangular, wave-shaped focus search signals, each of which has a predetermined peak value and a predetermined bottom value.
In accordance with this invention, at the time of the focus searching for a plurality of discs, triangular, wave-shaped focus search signals are used, and the peak values and bottom values thereof can be set individually. As a result, it is possible to set a peak value and a bottom value, which are suited for the focus position of each disc. The time for focus searching of each disc can be shortened, and the characteristics can be stabilized.
The third aspect of the present invention provides a disc player according to the first aspect, characterized in that the waveform information is information for generating triangular, wave-shaped focus search signals, for each of which a predetermined initial polarity is set.
In accordance with this invention, at the time of the focus searching for a plurality of discs, triangular, wave-shaped focus search signals are used, and the initial polarities thereof can be set individually. Namely, the initial voltage change direction of the focus search signal can be set to either the positive direction or the negative direction. Accordingly, the direction of the signal change can be freely set in accordance with the direction of the focus position for each disc. The degrees of freedom in the characteristics given to the focus searching can be increased even more.
The fourth aspect of the present invention provides a disc player according to the first aspect, characterized in that the plurality of waveform information include first waveform information set at a time when the type of the disc cannot be judged by the judging device, and the first waveform information has a variation range which corresponds to all of the plurality of types of discs.
In accordance with this invention, at the time when the disc is set at the disc player, if the type of disc cannot be judged, the first waveform information which is prepared therefor is selectively set, and the focus search signal which varies over a wide range during focus searching is used. Accordingly, by using a waveform that encompasses all of a plurality of focus positions of commonly-usable discs, it is possible to avoid a situation in which recorded information of a disc cannot be read.
In order to overcome the above-described problems, the fifth aspect of the present invention provides a focus search control method in a disc player which can be used in common for a plurality of types of discs having different focus positions of an object lens with respect to a recording surface, and which carries out focus servo control with respect to the discs and reads out recorded information, and the focus search control method comprises the steps of: judging a type of disc set at the disc player; selectively setting a predetermined waveform information in accordance with results of the judging, from a plurality of waveform information which are held in advance for use in focus searching for the plurality of types of discs; and generating a focus search signal based on the set waveform information to carry out focus searching, at a time of start-up of the disc player, before the focus servo control is carried out.
In accordance with this invention, when a disc selected from a plurality of types of discs is set at the disc player, the type of the disc i

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