JPH01298531A - Focus servo controller - Google Patents

Abstract

PURPOSE:To prevent the generation of defocusing by inputting an objective lens driving signal to a focus offset control circuit, outputting a focus offset signal from the control circuit and inputting the output signal to a focus servo control circuit. CONSTITUTION:When an objective lens follows the track of an optical disk 1 and its position in an (r) direction is moved, an objective lens driving voltage corresponding to the moving distance is inputted from a tracking servo control circuit 4 to the focus offset control circuit 5. The circuit 5 converts the objective lens driving voltage outputted from the circuit 4 into a focus offset signal and input the signal to the focus servo control circuit 3. Thereby, the a servo operating point in the circuit 3 is moved in accordance with the focus offset signal and an accurate focus position can be controlled independently of the position of the objective lens in the (r) direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a focus servo control device for an optical disk device.

[Prior Art] Fig. 3 is a block diagram showing a conventional focus servo control device, in which (1) indicates an optical disk, (2)
is an optical head, (3) is a focus servo control circuit, (
4) is a tracking servo control circuit. On the information recording surface of the optical disc (1), information is arranged as pit rows (not shown) on concentric circles or spiral tracks, and light reflection conditions are different between parts where bits exist and parts where they do not exist. Therefore, the optical head (2) irradiates a spot light onto the track, receives the reflected light, and reproduces the recorded information from the modulation received by the received light signal. Therefore, the spot light must be adjusted so as to focus on the bits on the information recording surface. This adjustment is performed by adjusting the position of an objective lens (not shown) in the optical head (2), which is directed in a direction perpendicular to the information recording surface of the optical disc (1) (hereinafter referred to as two directions).
Control is performed by the focus servo control circuit (3) to move the objective lens in a direction perpendicular to the track on which information is recorded (radial direction of the optical disc (1), hereinafter referred to as r).
The tracking servo control circuit (4) controls the movement in the direction (referred to as "direction").

By the way, since the length of the radius from the center of rotation of the optical disk (1) to each track differs depending on each track, if the position of the objective lens is moved in the r direction according to the position of each track, the objective lens is If the bit is not moved in this direction, the focus of the objective lens will not be on the bit. This relationship is called focus offset. Figure 4 is a diagram showing the relationship of focus offset. Among the many tracks, the track located approximately at the center in the radial direction of the optical disc (1) is used as a reference, and the horizontal position in Figure 4 is The axis represents the position of the objective lens in the r direction, and the vertical axis corresponds to the change in position in the r direction.
It represents a change in position in a direction, that is, a focus offset.

FIG. 5 is a diagram showing the relationship between the objective lens drive voltage, which is the output of the tracking servo control circuit (4), and the position of the objective lens in the r direction.

[Problems to be Solved by the Invention] Since the conventional device is configured as described above, when the position of the objective lens in the r direction changes, the focal position of the spot light is shifted from above the bit. Therefore, the degree of modulation of the received light signal is lowered due to the presence of the bit, and the level of the tracking error signal obtained from the received light signal is also lowered, making tracking control difficult.

This invention was made in order to solve the above-mentioned problems in the conventional ones, and is a focus servo control that does not cause a focus shift even if the position of the objective lens in the r direction changes due to the operation of a tracking servo control circuit. The purpose is to obtain equipment.

[Means for Solving the Problems] In the present invention, an objective lens drive signal which is an output of a tracking servo control circuit is input to a focus offset control circuit, a focus offset signal corresponding to this input is outputted, and this focus offset is A signal is input to the focus servo control circuit, and the position of the objective lens in two directions is controlled by the focus servo control circuit.

[Operation] Since the focus of the spot light is accurately focused on the bit regardless of the position of the objective lens in the r direction, a tracking error signal of sufficient magnitude can always be obtained.

[Examples] Examples of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing an embodiment of the present invention. In the figure, the same reference numerals as in FIG. 3 indicate the same or corresponding parts, (5)
is a focus offset control circuit.

The objective lens follows the track of the optical disk (1) and r
When the position in the direction moves, an objective lens drive voltage (drive in the r direction) corresponding to the amount of movement is input from the tracking servo control circuit (4) to the focus offset control circuit (5). The focus offset control circuit (5) converts the objective lens drive voltage, which is the output of the tracking servo control circuit (4), into a focus offset signal according to the relationship shown in FIGS. Enter in (3). Therefore, the operating point of the servo in the focus servo control circuit (3) moves in accordance with the focus offset signal, and is controlled to an accurate focal position regardless of the position of the objective lens in the r direction.

FIG. 2 is a block diagram showing a method for creating a conversion (objective lens drive voltage - focus offset signal) table used in the focus offset control circuit (5). In the embodiment shown in the figure, the focus offset control circuit is in measurement mode. and an operation mode (the mode changeover switch is not shown), and when in the operation mode, it operates as explained in Figure 1, and when it is in the measurement mode, it operates as shown below to create and store a conversion table. do.

First, an objective lens drive signal is input from the focus offset control circuit (5) to the tracking servo control circuit (4), the objective lens is moved by a predetermined amount in the r direction, and in this state, the focus servo control circuit (3) is activated to focus. An offset signal is input, and the magnitude of the focus offset signal is adjusted so that the tracking error signal from the tracking servo control circuit (4) is maximized.

When this adjustment is completed, a pair of focus offset signals is obtained that corresponds to the objective lens drive voltage (objective lens drive voltage output from the tracking servo control circuit (4) at that time) to be stored as a conversion table. By repeating such measurements, a conversion table can be created and stored. In the operation mode, the objective lens drive voltage is input and the corresponding focus offset signal is read from the conversion table.

[Effects of the Invention] As described above, according to the present invention, the focus position can always be controlled to be accurate regardless of the position of the objective lens in the r direction, thereby preventing a drop in the tracking error signal and achieving stable tracking. This has the effect of allowing servo control.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the invention, FIG. 3 is a block diagram showing a conventional device, and FIGS. 4 and 5 is a diagram showing the relationship between objective lens drive voltage and focus offset signal. (1) is an optical disk, (2) is an optical head, (3) is a focus servo control circuit, (4) is a tracking servo control circuit, and (5) is a focus offset control circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (2)

[Claims] (1) A spot light is irradiated onto an optical disc through an objective lens, the reflected light from the optical disc is received through the objective lens, and the modulation received by this received light signal is detected to record on the optical disc. When reproducing information recorded on the optical disc, a focus error signal is obtained from the light reception signal in order to match the focus of the spot light on the information recording surface of the optical disc, and the position of the objective lens is adjusted based on the focus error signal to record the information. In a focus servo control device that performs control in a direction perpendicular to the surface, a tracking error signal is obtained from the light reception signal in order to align the focus of the spot light with the center of a track on which information is recorded on the information recording surface of the optical disk. a tracking servo control circuit that controls the position of the objective lens in a direction perpendicular to the track on the information recording surface based on the tracking error signal; and a focus offset that generates a focus offset signal corresponding to the output of the tracking servo control circuit. A focus servo control device comprising: a control circuit; and means for applying an offset to the input of the focus servo control device using the output of the focus offset control circuit. (2) In the focus servo control device according to claim 1, the focus offset control circuit has a measurement mode and an operation mode, and in the measurement mode inputs an objective lens drive signal to the tracking servo control circuit; Find the focus offset signal that produces the maximum tracking error signal and the objective lens drive voltage output from the tracking servo control circuit at that time, and create a correspondence table between the objective lens drive voltage and focus offset signal in this way. A focus servo control device characterized in that in an operation mode, an objective lens drive voltage is inputted from the tracking servo control circuit, read from the correspondence table, and outputted as a focus offset signal.