JPH03256227A - Focus pulling-in device - Google Patents

Abstract

PURPOSE:To realize the pulling-in of a focus smoothly, safely and surely by driving a focus actuator in a state that servo gain is lowered for a definite period. CONSTITUTION:When the focus actuator 6 reaches a just focus point, a detection circuit 2 outputs a just focus signal, and a input signal to a driving circuit 4 is switched from the output signal of a waveform generation circuit 1 to the output signal of a focus servo circuit 3a by an analog switch 7. Simultaneously, a timer circuit 8 makes the analog switch 9 activate for a definite period. During this operation, a resistor 304 is connected in parallel with the resistor 303, and the servo gain of the circuit 3a is lowered. Even if the focus error signal of a large level is inputted immediately after the input signal to the circuit 4 is switched to the signal from the circuit 3a, the actuator 6 is pulled-in smoothly, and it can be surely given focus servo.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a focus pull-in device for an optical disc device.

2. Description of the Related Art In recent years, optical disk devices have been widely used in various fields as audio and video playback, recording and playback, and storage devices for OA equipment.

A focus pull-in device in a conventional optical disc device has a configuration as shown in FIG.

In Fig. 3, 1 is a waveform generation circuit that generates a control signal to drive the focus actuator up and down in response to a focus-on signal input when the device is started, and 2 is a waveform generation circuit that detects a just focus point from a focus error signal from an optical head and generates a just focus signal. 3 is a focus servo circuit that outputs a control signal to drive a focus coil and control a focus actuator so that the laser disc light is always focused on the optical disc based on the focus error signal; 4 is a waveform generator A drive circuit that drives the focus coil based on a control signal from the circuit 1 or the focus servo circuit 3; 5 a focus coil that generates a magnetic field by driving the drive circuit 4 and drives the focus actuator 6; 7 a focus coil of the detection circuit 2; This is an analog switch for switching the control signal to the drive circuit 4 based on the output signal. Regarding the focus pull-in device having the above-mentioned configuration, the relationship and operation of the configuration will be explained below using FIGS. 3 and 4.

In the focus pull-in device shown in FIG. 3, when the device is started, the focus coil 5 is driven by the output signal from the waveform generation circuit 1 via the drive circuit 4, and the focus actuator 6 is driven up and down.

At the same time, the detection circuit 2 detects the just focus point, outputs the just focus signal when the focus actuator 6 reaches the focus point on the just focus 1 (point A in Fig. 4), and closes the analog switch 7b. death,
The analog switch 7a is opened, and the focus actuator 6 is switched from being controlled by the waveform generating circuit 1 to being controlled by the focus servo circuit 3 at this point, and thereafter the position is controlled by the focus servo circuit 3.

Problems to be Solved by the Invention However, in the above configuration, when the focus actuator 6 reaches the just focus point and the control is switched to the focus servo circuit 3 based on the focus error signal, the focus error signal immediately after switching is Because the movement of the actuator 6 is large, the signal is often larger than the signal level during normal focus servo operation, and in such cases, a large driving force is suddenly applied to the focus actuator 6, resulting in failure of servo retraction. Alternatively, the focus actuator 6 may collide with the optical disk.

In order to solve the above problems, the present invention provides a focus pull-in device that can smoothly and safely realize focus pull-in.

Means for Solving the Problems In order to solve the above problems, the focus pull-in device of the present invention is provided with a configuration in which the servo gain is reduced for a certain period from the time when the drive of the focus actuator is switched to the focus servo circuit. It is.

Effect of the Invention With the above-described configuration, the present invention drives the focus actuator with the servo gain reduced for a certain period of time from the time when the focus servo circuit is switched to drive, so even if the signal level of the focus error signal of the human input signal is large, the focus This allows smooth focus pull-in without suddenly applying a large driving force to the actuator.

Embodiment FIG. 1 is a block diagram of a focus pull-in device according to an embodiment of the present invention. Components having the same functions as those of the conventional example are given the same reference numerals and explanations will be omitted. In the figure, 8 is the detection circuit 2
31 is a servo amplifier of the focus servo circuit 3a, 303 is a resistor that determines the servo gain, and 9 is a timer circuit that generates a fixed time by using the focus signal from the timer circuit 8 as an input signal. This is an analog switch that connects or disconnects the resistor 304 in parallel with the resistor 303, and serves as means for reducing the servo gain of the focus servo circuit 3a together with the timer circuit 8 and the resistor 304. The parallel circuit of resistor 301 and capacitor 302 is for high frequency enhancement and phase compensation, capacitor 305 is for stabilization, and the circuit consisting of resistors 306, 307 and capacitor 307 is for reduction and enhancement. FIG. 2 is a timing chart that does not show the operation of the embodiment shown in FIG.

Regarding one embodiment of the present invention comprising the above-mentioned constituent elements, the relationship and operation of the structure will be explained below with reference to FIGS. 1 and 2. When the device is started, a focus on signal causes the waveform generation circuit 1 to output a control signal to drive the focus actuator 6 up and down, and this control signal causes the drive circuit 4 to send a drive current to the focus coil 5 to move the focus actuator 6 in the up and down direction. Drive. At the same time, the detection circuit 2 detects the just focus point from the focus error signal obtained from the optical head. When the focus actuator 6 reaches the just focus point, the detection circuit 2 outputs a just focus signal,
In response to this signal, the input signal to the drive circuit 4 is switched from the output signal of the waveform generation circuit 1 to the output signal of the focus servo circuit 3a by the analog switch 7. At the same time, the timer circuit 8 outputs an operating signal to the analog switch 9 for a certain period of time based on the just focus signal. While the analog switch 9 is operating, the resistor 304 is connected in parallel with the resistor 303, and while the analog switch 9 is operating, the servo gain of the focus sabot circuit 3a is the parallel resistance value of the resistors 303 and 304. This becomes the servo gain that can be determined. Therefore, the servo gain during this period is changed from the servo gain determined by the normal resistor 303 to the resistor 3
Since the servo gain is reduced to the servo gain determined by the parallel value of 03 and the resistor 304, even if a focus error signal of a higher level than usual is manually input immediately after the input signal to the drive circuit 4 is switched to the focus servo circuit 3a, The focus actuator 6 is pulled in smoothly without sudden movements, making it possible to reliably apply the focus servo.

Effects of the Invention As described above, according to the present invention, the focus pull-in operation can be performed smoothly and reliably, and is extremely effective in practical use without damaging the optical disc or the focus actuator.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a focus pull-in device according to an embodiment of the present invention, FIG. 2 is a timing chart showing its operation, FIG. 3 is a block diagram of a conventional example, and FIG. 4 is a block diagram showing its operation. This is a timing chart 1 shown in FIG. 1...Waveform generation circuit, 2...Detection circuit, 3a...Focus servo circuit, 4...
・Drive circuit, 5... Focus coil, 6...
...Focus actuator, 7...Analog switch, 8...Timer circuit, 9...
...Analog switch, 303.304...Resistance.

Claims (1)

[Claims] In an optical disk device that reads or writes recorded information using an optical disk, there is provided a waveform generation circuit that generates a control signal for driving a focus actuator up and down based on input of a focus-on signal when starting the device, and the waveform generation circuit. A drive circuit that drives a focus coil using a control signal from the circuit, a detection circuit that detects a just focus point from a focus error signal from an optical head and outputs a just focus signal when the focus actuator is driven up and down, and a focus A focus servo circuit outputs a control signal to drive the focus coil and control the focus actuator so that the laser diode light is always focused on the optical disk based on the error signal, and a drive circuit uses the just focus signal. A focus pull-in device comprising: an analog switch for switching a control signal from a waveform generation circuit to a focus servo circuit; and means for reducing the servo gain of the focus servo circuit for a certain period of time from the start of focus servo pull-in at a just focus point.