JPH04325927A - Focus pull-in device - Google Patents

Abstract

PURPOSE:To smoothly and surely execute a focus pull-in operation by resolving the problem of suddenly giving large drive force to a focus actuator when changing a control state at a just focus position in an optical disk device to read or to read/write recorded information by using an optical disk. CONSTITUTION:After the drive of a focus actuator 6 is switched to a focus servo circuit 3a, an analog switch 10 is turned on for the fixed time, the servo gain of the focus servo circuit 3a is reduced so as not to suddenly give the large drive force to the focus actuator 6, and focus pull-in is smoothly executed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus pull-in device for an optical disc device.

0002

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 office automation 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 generating 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 generating circuit that detects a just-focus point from a focus error signal from an optical head and performs just-focusing. 3 is a detection circuit that outputs a signal; 3 is a focus servo circuit that drives a focus coil and outputs a control signal to control a focus actuator so that the laser disc light is always focused on the optical disc; 4 is a focus servo circuit that outputs a control signal to control a focus actuator; A drive circuit that drives a focus coil based on a control signal from the waveform generation 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 a focus actuator 6, and 7 a detection circuit. 2
This is an analog switch for switching the control signal to the drive circuit 4 based on the output signal of the drive circuit 4.

Regarding the focus pull-in device having the above-mentioned structure, the relationship and operation of the structure will be explained below with reference to FIGS. 3 and 4.

In the focus pull-in device shown in FIG. 3, when the device is started, a focus coil 5 is driven via a drive circuit 4 by an output signal from a waveform generation circuit 1, and a 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 just focus point (point A in FIG. 4), closes the analog switch 7b, and closes the analog switch 7b.
At this point, the focus actuator 6 is switched from being controlled by the waveform generating circuit 1 to being controlled by the focus servo circuit 3, and thereafter the focus servo circuit 3 performs position control.

[0007]

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 occurs immediately after the switch. The signal is often higher than the signal level during normal focus servo operation, and in such cases, if the servo is applied with the normal gain, a large driving force will suddenly be applied to the focus actuator 6, resulting in servo pull-in failure. , or the focus actuator 6 may collide with the optical disk.

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

[0009]

[Means for Solving the Problems] In order to solve the above problems, the focus pull-in device of the present invention reduces the servo gain for a certain period from the time when the drive of the focus actuator is switched to the focus servo circuit, and has a reduction compensation function. It has a configuration that invalidates the .

0010

[Operation] With the above-described configuration, the present invention reduces the servo gain for a certain period of time after switching to driving the focus servo circuit, and drives the focus actuator with the reduction compensation function disabled. Even if the signal level of the focus error signal is high,
A large driving force is not suddenly applied to the focus actuator, allowing smooth focus pull-in.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 FIG. 1, reference numeral 8 denotes a timer circuit which generates a fixed time by using the just focus signal from the detection circuit 2 as an input signal, 31 a servo amplifier of the focus servo circuit 3a, 303 a resistor that determines the servo gain,
9 is an analog switch that connects or disconnects the resistor 304 in parallel with the resistor 303 according to the output signal from the timer circuit 8, and, together with the timer circuit 8 and the resistor 304, serves as a means for reducing the servo gain of the focus servo circuit 3a. ing. The parallel circuit of resistors 300, 301 and capacitor 302 is for high frequency compensation and phase compensation, capacitor 305 is for stabilization, and the circuit consisting of resistors 306, 307 and capacitor 307 is for reduction compensation. Reference numeral 10 denotes an analog switch that shorts or enables the capacitor 308 according to the output signal from the timer circuit 8, and serves as a means for disabling the reduction compensation function by shorting the capacitor 308. FIG. 2 is a timing chart showing the operation of the embodiment shown in FIG.

[0013] Regarding one embodiment of the present invention comprising the above-mentioned components, the relationship and operation of the configuration will be explained below using 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, and based on this signal, the input signal to the drive circuit 4 is changed from the output signal of the waveform generation circuit 1 to the focus servo by the analog switch 7. The signal is switched to the output signal of the circuit 3a. At the same time, the timer circuit 8 outputs operation signals to the analog switches 9 and 10 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 servo circuit 3a is the same as that of the resistors 303 and 304. The servo gain is determined by the parallel resistance value. Therefore, the servo gain during this period is reduced from the servo gain determined by the normal resistor 303 to the servo gain determined by the parallel value of the resistors 303 and 304. At the same time, the analog switch 10 operates and the capacitor 308 is shorted. Since the reduction compensation function is disabled, even if a focus error signal of a higher level than usual is input immediately after the input signal to the drive circuit 4 is switched to the focus servo circuit 3a, the focus actuator 6 will not suddenly move. It is pulled in smoothly without any movement, making it possible to reliably apply the focus servo.

[0016]

As described above, according to the present invention, the focus pull-in operation can be performed smoothly and reliably, and is extremely effective in practice without damaging the optical disk or the focus actuator.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a focus pull-in device in an embodiment of the present invention.

[Figure 2] Timing chart showing the operation of the device

[Figure 3
]Block diagram of conventional example

[Figure 4] Timing chart showing the operation of the conventional example

[Explanation of symbols]

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] 1. In an optical disk device that reads or writes recorded information using an optical disk, a waveform generation circuit generates a control signal for driving a focus actuator up and down based on input of a focus-on signal when starting the device; A drive circuit that drives a focus coil using a control signal from the waveform generation circuit, and 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. , a focus servo circuit that 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 focus error signal, and a just focus signal. An analog switch that switches the control signal to the drive circuit from the waveform generation circuit to the focus servo circuit, reduces the servo gain of the focus servo circuit for a certain period of time from the start of focus servo pull-in at the just focus point, and disables the reduction compensation function. A focus pull-in device equipped with a means for