KR100260703B1 - Focus Servo Method for DVD Dual-Layer Discs - Google Patents

Abstract

PURPOSE: A focus servo method of a DVD dual layer disk is provided to perform a focus-on stably by giving an impulse focus driving signal(FOD) to a focus actuator, thereby stopping the actuator almost when an object lens is almost reached at object signal reflection layer. CONSTITUTION: An impulse focus driving signal(FOD) is supplied to a focus actuator through a driving unit in a layer jump(401). Thus, the driving force is decreased as zero and the progressing velocity to the focus direction is decreased, and an object lens is moved by an initial inertia only. A focus error detecting unit detects a focus error signal, and detects a focal point. A focus signal in the focal point is converted from a high level into a low level when a size of a high frequency(RF) signal read from a disk through a light pickup is more than a specific value. Also, a focus signal in the focal point is converted from a low level into a high level when the size of a high frequency(RF) signal is less than a specific value. It is detected whether the focus signal is a high level(402). A portion a focus zero cross signal(FZC) thereof is a falling edge is detected in a period the focus signal thereof is high level in the focal point(403). If the falling edge of the focus zero cross signal(FZC) is detected, a device controlling a focus servo operation senses as a reach at an object signal reflection layer and controls the driving unit. Thus, a focus-on is performed stably by applying a focus servo driving voltage to a focus coil(404).

Description

Focus Servo Method for DVD Dual-Layer Discs

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DVD disk having a dual layer structure, and more particularly, to stably jump when a layer jumps from a first signal reflection layer (second signal reflection layer) to a second signal reflection layer (first signal reflection layer). Focus It relates to a focus servo method of a DVD dual-layer disc that can be turned ″ on ″.

In general, in optical devices such as compact discs (CDs) and digital video discs (DVDs), a focus servo is wound around an optical pickup objective block placed in a magnetic field and moved in a direction of an optical axis by a servo signal. This means that the lens is positioned so that the reflective surface of the disk is within the depth of focus. However, in order to operate the servo device, a focus error (FE) signal is required. The focus error (FE) signal moves the objective lens up and down at a frequency of 1 to 2 Hz generated by the focus servo device immediately after the disc is inserted into the player. Doing so brings the disk's reflecting surface closer to the depth of focus of the lens, resulting in a noise-focused focus error (FE). Immediately after detecting the error signal, the focus servo is performed to bring the objective lens into the depth of focus. In the apparatus for controlling the focus servo operation, the focus state is determined based on whether the focus error (FE) signal detects the focus zero cross when focusing is performed.

On the other hand, research on DVD is being actively conducted as a next-generation information medium that will surpass current magnetic tapes and CDs in terms of information recording capacity and image quality. DVDs are made of a single-layered single-layer disc with a diameter of 120 mm, a thickness of 0.6 mm, and a storage capacity of 4.7 GB, or a dual-layer disc with a recording capacity of 9G, and two DVDs of the same structure. There is a double-sided double layer disk having a recording capacity of 10G or more. The structure of a dual DVD dual layer disc is shown in FIG.

FIG. 1 is a diagram showing the structure of a general DVD dual-layer disc. The thickness between the first signal reflection layer and the second signal reflection layer is approximately 40 탆, and is very close to each other. As a result, when using a general focus search method, a focus error (FE) signal as shown in FIG. 2 appears. This results in a fine level S-shaped curve due to the reflection of the disk substrate surface, and an S-shaped curve appears in turn by the two recording layers, that is, the first signal reflection layer and the second signal reflection layer. Recognizes the focus ″ ON / OFF ″ state from the Focus Zero Cross (FZC) detected by the focus error (FE) signal represented by the signal reflection layer, and controls the start and end of the focus servo. do.

However, since the two signal reflecting layers are located very close to each other, there is a possibility that an overshoot may occur due to a pull-in in the signal reflecting layer when the signal servo layer is jumped by a focus servo by a conventional analog method.

Accordingly, an object of the present invention is to provide an impulsive focus drive signal (FOD) to a focus actuator so that the actuator can be focused on stably while the objective lens reaches the target signal reflection layer. It is to provide a focus servo method.

1 is a diagram showing the structure of a general DVD dual-layer disc.

2 is a waveform diagram obtained when focus search is performed on the DVD of FIG.

3A to 3D are waveform diagrams for explaining a focus servo method of a DVD dual-layer disc according to the present invention.

4 is a flowchart illustrating a focus servo method of a DVD dual-layer disc according to the present invention.

The focus servo method of the DVD dual-layer disk according to the present invention for achieving the above object comprises the steps of: (1) supplying an impulsive focus drive signal to the focus actuator during layer jump, and (2) the input focus signal (Fok) (3) detecting a focus state, and (3) if a predetermined edge portion is detected from a focus zero cross (FZC) signal input on the focus point, recognizing that the target signal reflection layer has been reached and focus-on. Include.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a waveform diagram illustrating a focus servo method of a DVD dual-layer disc according to the present invention. FIG. 3 (a) is an impulsive focus drive signal FOD supplied to a focus actuator when layer jumping. b) is a focus error (FE) signal detected from the reflecting surface of the disc during focus servo. FIG. 3 (c) shows the focus signal Fok detected on the focal point, and FIG. 3 (d) shows the focus zero cross FZC signal detected from the focus error FE signal of FIG. 3 (b).

4 is a flowchart illustrating a focus servo method of a DVD dual-layer disc according to the present invention.

First, in the focus servo apparatus (not shown), an impulsive focus driving signal FOD of FIG. 3 (a) is supplied to the focus actuator through the driver during layer jump (step 401). Impulsive waveforms are unit area and time (t) On the basis of the characteristic that it rapidly decreases to zero at the place where 0, the impulsive focus driving signal (FOD in FIG. 3 (a)) is supplied to the focus actuator, and the driving force rapidly decreases to zero. As a result, the speed that progresses in the focus direction is attenuated so that the objective lens moves only by the initial inertia. Therefore, even if the thickness between the two signal reflecting layer is as small as about 40㎛, the actuator is almost in the state of speed until the current signal reflecting layer to jump to the target signal reflecting layer. The focus error detection unit (not shown) detects a focus error (FE) signal as shown in FIG. 3 (b) and detects a focus point therefrom. That is, the focus signal (Fok waveform in FIG. 3 (c)) on the focal point is ″ high ″ at the ″ low ″ level when its magnitude is greater than or equal to a certain value in the high frequency (RF) signal read from the disc through the optical pickup. It is changed to a high level, and when it is below a specific value, it is changed from a ″ high ″ level to a ″ low ″ level. It is determined whether this focus signal is a ″ high ″ level (step 402). The portion of the focus zero cross (FZC waveform in FIG. 3 (d)) falling edge is shown in a section in which the focus signal Fok on the focal point of FIG. 3 (c) is at the ″ high ″ level. Is detected (step 403). When the falling edge of the focus zero cross (FZC) signal of FIG. 3 (d) is detected, the apparatus for controlling the focus servo operation recognizes that the target signal reflection layer has been reached and controls the driving unit. Therefore, the focus servo driving voltage is applied to the focus coil. To stably focus on (step 404).

As described above, in the focus servo method of the DVD dual layer disc according to the present invention, considering that the two signal reflection layers of the dual layer disc are located very close to each other, the objective lens is applied by applying an impulsive focus drive signal (FOD) to the focus actuator. As time goes by, the speed decreases, so that when the layer is jumped, the target is accurately focused on the target signal reflection layer, thereby stably pulling in.

Claims (3)

A focus servo method of a DVD dual layer disc, comprising: (1) supplying an impulsive focus drive signal to a focus actuator when layer jumping; (2) detecting a focal point state from the input focus signal Fok; And (3) recognizing that the target signal reflection layer has reached the target signal reflection layer when the predetermined edge portion is detected from the focus zero cross (FZC) signal input on the focal point, and focusing on the DVD dual layer disc. . The method of claim 1, wherein the step (1) includes supplying an impulsive focus driving signal to the focus actuator so that the objective lens moves only by initial inertia so that the layer is jumped from the current signal reflection layer to reach the target signal reflection layer. Focus servo method for a DVD dual-layer disc, characterized in that the actuator is in a state of almost no speed. 3. The focus servo method of claim 2, wherein the step (2) determines whether the input focus signal Fok is at a predetermined level, and detects the focus point if it is at a predetermined level. .