JPH0450657B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement of an automatic tracking device in an optical disk device.
This invention relates to improvements in track jump circuits for automatic tracking devices.

<Prior Art> FIG. 4 is a block diagram of a conventional optical disk device. In the figure, 1 is a laser light source such as a laser diode, 2 is a collimator lens that converts the light from light source 1 into parallel light with an appropriate diameter, 3 is a half mirror, and 4 is provided via this half mirror. A condensing (objective) lens that condenses light onto a track 5n on the disk 5;
A tracking servo actuator that is followed by n, for example, a voice coil motor is used. As a result, the objective lens 4 is moved in the in-plane direction of the disk, and tracking control of the light spot on the disk 5 is performed.

7 is a half mirror that distributes the reflected light from the disk 5 to the tracking servo circuit A side and the focus servo circuit B side, and 8 is a condensing lens that focuses the light from this half mirror. 9
is a photodetector whose light-receiving surface is divided into at least two regions (two in this example), so that a signal corresponding to the position of the detection spot can be read out.

In this specific example, the focus error signal and the tracking error signal are separated by a half mirror 7 and extracted by separate photodetectors.
Both signals may be extracted by the same photodetector using a split sensor.

Reference numeral 10 denotes an adder for detecting the sum of signals from two photodetecting elements 9a and 9b constituting the light receiving surface of the photodetector 9, and detects a signal component of the reflected light from the track 5n. 11 is focus servo circuit B
An actuator, for example, using a voice coil motor, to which a signal is given from the objective lens 4
is moved upward and downward to control the focus of the light spot.

The tracking servo circuit A includes a photodetection element 9
Deviation amplifier 1 that detects the difference between signals from a and 9b
2, an amplifier 13, a phase compensation circuit 14 that compensates for the characteristics of the tracking actuator 6 and prevents system oscillation, a switch 15 that opens and closes the servo loop;
An amplifier 16 whose inputs are supplied with an output from a track jump pulse generating circuit, which will be described later, and a tracking error signal from an amplifier 13 via a switch 15, a track jump pulse generating circuit 17, and a tracking actuator. Power amplifier 1 that sends drive current to voice coil 6
It consists of 8.

In the steady state, the switch 15 is closed to form a negative feedback loop, and tracking servo is performed so that the deviation signal of the amplifier 12 becomes zero. As a result, the objective lens 4 follows the track 5n.

When changing the track position at a relatively low speed, the entire optical system is moved in the radial direction of the disk 5 by a predetermined means (not shown in this figure) to access the desired track. However, when performing a high-speed transition between tracks, open the switch 15, open the servo loop, apply the track jump pulse described below to the coil of the actuator 6, and move the objective lens 4 to the target track. I'm trying to make it move at high speed.

FIG. 5 is a circuit diagram showing a specific example of the track jump pulse generation circuit 17 in such a conventional device.
This is an inverting amplifier in which the output terminal and the inverting input terminal are connected via the feedback resistor, and the non-inverting input terminal is connected to a reference point.

The operation of the track jump pulse generating circuit having such a configuration will be explained with reference to the waveform diagram of FIG. 6. External pulses open and close 17b and 17c as shown in Figures a and b, generating symmetrical positive and negative current pulses as shown in Figure c. When this current pulse is applied to the coil of the actuator 6, the objective lens 4 moves at a speed as shown in FIG. d. In that case,
Drive so that the final speed after the current pulse is removed is zero. Figure e shows the change in the position of the objective lens 4. The width to of the track jump pulse is selected such that the distance traveled d is equal to the inter-track distance. Note that the waveform of the current pulse shown in FIG. c approximately corresponds to the waveform of the acceleration of the objective lens 4.

However, with this method, once to is determined, it cannot be changed thereafter. On the other hand, if the objective lens 4 is deviated from the equilibrium position, the positive and negative forces acting on the objective lens 4 will become unbalanced. FIG. 7 is an explanatory diagram schematically showing the objective lens 4 portion. The objective lens 4 can be equivalently represented as being supported by two springs 4a and 4b. In the case of Figure a, the object is in an equilibrium state, and the positive and negative forces acting on the objective lens 4 are balanced. On the other hand, as shown in Figure b, when the objective lens 4 is deviated from the equilibrium position, the deviation
A restoring force kxo related to xo and spring constant k works, and if a current pulse like that shown in Figure 6c, which is the same as in the equilibrium state, is applied to the coil of actuator 6, the moving distance d will change. Therefore, the objective lens 4 cannot be correctly jumped to the target track.

In addition, in such a state, the final velocity of the objective lens 4 after the current pulse is removed is not zero, so when the tracking servo state is entered after the jump, the transient response is poor and the stabilization time is long. Ta.

<Problems to be Solved by the Invention> The technical problems to be solved by the present invention are such that the moving distance of the track jump does not always change even if the objective lens is not in an equilibrium state, and the settling after the jump is fixed. The objective is to realize a fast track jump pulse generation circuit.

<Means for solving the problem> Light from a light source is focused on a disk through an objective lens, a light spot on the disk is detected by a photodetector having multiple light-receiving surfaces, and this detection signal is In an optical disk device that detects a signal component, controls the focus of the light spot, and controls the tracking of the light spot based on (b) tracking error signal detection means for guiding a tracking error signal using the detection signal; (b) generating a track jump pulse and adding a low-frequency signal component extracted from the tracking error signal to the pulse; (c) a track jump pulse generating means for generating a track jump pulse corrected for an error due to a deviation from the equilibrium position of the lens; (c) a track jump pulse from the track jump pulse generating means; , an amplifying means to which the tracking error signal from the tracking error signal detecting means is added as an input, and (d) a switch provided between the amplifying means and the tracking error signal detecting means, In the tracking control state, the switch is closed and the output of the amplifying means is applied to an actuator that drives the objective lens within the track plane to form a negative feedback loop to perform tracking control and track jump. During control, the switch is opened and the track jump pulse from the track jump pulse generating means is applied to the actuator via the amplifying means without using the negative feedback loop.
The reason is that jump control is performed.

<Operation> The above technical means operates as follows. That is, the signal component extracted from the output of the detector is a signal component corresponding to the deviation of the objective lens from the equilibrium state, and by adding this to the track jump pulse, the deviation can be corrected. The error term based on this is removed. As a result,
Regardless of the equilibrium state of the objective lens, the moving distance of the track jump does not change, and the target track can be correctly jumped.

<Examples> Examples of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an optical disk device which is an embodiment of the present invention, and FIG. 2 is a specific example of a track jump pulse generation circuit used in this embodiment. In the figure, the same elements as those in FIG. 4 are given the same reference numerals, and explanations thereof will be omitted.

The track jump pulse generation circuit 19 is
It is comprised of an inverting amplifier 19a, a low-pass filter 19b for extracting low-frequency components from the tracking error signal from the amplifier 13, switches 19c, 19d, and 19e, and an OR circuit 19f as switch control means. The reference voltages -Vref and Vref are connected to the inverting input terminal of the inverting amplifier 19a and the switches 19c,
19d and the input resistor, and
The low frequency component from the low frequency filter 19b is sent to switch 1.
9e and an input resistor, the non-inverting input terminal is connected to a reference point, and the inverting input terminal and output terminal are connected via a feedback resistor.

Prior to explaining this circuit, the movement of the objective lens 4 when it is out of an equilibrium state will be explained.
When it is not in an equilibrium state, due to the restoring force of the springs 4a and 4b, it is not possible to accurately move the objective lens 4 to the target track by applying symmetrical current pulses of positive and negative as shown in FIG. 6c. Can not. This state can be expressed numerically as follows. However, m: mass of the objective lens 4, Ai: force acting on the objective lens 4 based on the drive current pulse (the amplitude of the drive current pulse is i, and the proportionality constant is A), x: displacement of the objective lens 4.

In section a of the current pulse in Fig. 6c, the relationship of the force applied to the objective lens 4 is mx = Ai - kxo (1), and the acceleration x is x = (1/m)・( Ai−kxo) …(2) Therefore, the moving speed x can be expressed as x=(1/m)・(Ai−kxo)t…(3) The displacement x is /m)・(Ai−kxo)・(t ² /2) …(4)

On the other hand, in section b of the current pulse in Figure 6c, the acceleration x... can be expressed as x=(1/m)・(-Ai−kxo)...(5), and the moving speed x・Adding the initial velocity in section a, it can be expressed as x・={(−Ai−kxo)t +(Ai−kxo)to}・(1/m) (6), and the displacement x is x = {(−Ai−kxo)・(t ² /2)+(Ai−kxo)・to
・t + (Ai−kxo)・(to ² /2)}・(1/m)…(7
) can be expressed as

As a result, the final velocity x・d of the objective lens 4 is: x・d=(−2kxo)・to・(1/m) …(8) The final moving distance xd is: xd={Ai・to ² −2kxo・to ² }・(1/m) …(9).

As is clear from equation (8), when the objective lens 4 is not in an equilibrium state, the restoring force by the spring acts,
The final velocity x·d is no longer zero.

When the final moving distance in the equilibrium state is xdo, this can be expressed as xdo=Ai·to ² ·(1/m) (10). To is selected, and xdo is preset to be equal to the distance between tracks, but the final moving distance xd when not in an equilibrium state will not be the same as this xdo, and it will not be possible to move accurately to the target track. do not have.

In the present invention, focusing on the fact that the positional deviation of the detection spot on the photodetector 9 corresponds to the deviation of the objective lens 4 from the equilibrium position, the tracking error signal which is the output of the amplifier 13 is sent to the low-pass filter 19b. Through this, a signal component corresponding to the deviation of the objective lens 4 from the equilibrium position is obtained, and this is added to the drive current pulse.

FIG. 3 is an explanatory diagram of the operation of the track jump pulse generation circuit shown in FIG. 2. switch 19
The switches 19c and 19d are opened and closed by the pulses shown in FIGS. Ru.

As a result, during the period when the track jump pulse is being applied, the signal from the low-pass filter 19b is added to the drive current pulse with a polarity that cancels out the error term kxo in equation (1), and the current pump as shown in Figure d is added. I am getting . With this current pulse, the amplitude increase/decrease Δi is
By making it equal to kxo, the error term can be removed.

<Effects of the Invention> According to the present invention, since the actuator 6 is driven by the drive current pulse from which the error has been removed, the correct moving distance can be obtained regardless of the position of the objective lens 4, and the final velocity can be adjusted. can be reduced to zero, making it possible to achieve excellent response characteristics.

In the above description of the present invention, the photodetector 9 that detects the tracking error signal is used to detect the deviation of the objective lens 4 from the equilibrium position, but the present invention is not limited to this. A displacement detector for direct detection may be provided, and the output thereof may be added to the drive current pulse.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of a track jump pulse generation circuit used in the device according to the embodiment shown in FIG. An explanatory diagram of the operation of the track jump pulse generation circuit shown in the figure, FIG. 4 is a configuration diagram of a conventional device, and FIG. 5 shows a specific example of the track jump pulse generation circuit used in the conventional device shown in FIG. 6 is an explanatory diagram of the operation of the track jump pulse generation circuit shown in FIG. 5, and FIG. 7 is an explanatory diagram schematically showing the objective lens 4 portion. 5... Disk, 5n... Track, 6... Actuator, 9... Photodetector, 19... Track jump pulse generation circuit, 19a... Inverting amplifier, 19b... Low pass filter, 19c-19
e...Switch.

Claims (1)

[Claims] 1. Light from a light source is focused on a track on a disk through an objective lens, a light spot on the disk is detected by a photodetector having a plurality of light receiving surfaces, and a signal is generated based on this detection signal. component detection, focus control of the light spot,
Further, in an optical disk device configured to perform tracking control of the light spot, the tracking servo circuit includes: (a) tracking error signal detection for guiding a tracking error signal using a plurality of detection signals detected by the photodetector; (b) generating a track jump pulse and adding a low-frequency signal component extracted from the tracking error signal to this pulse to correct an error due to a deviation of the objective lens from the equilibrium position; track jump pulse generating means for generating a track jump pulse; (c) a track jump pulse from the track jump pulse generating means and a tracking error signal from the tracking error signal detecting means; (d) a switch provided between the amplification means and the tracking error signal detection means, and in a normal tracking control state, the switch is closed and the The output of the amplifying means is applied to an actuator that drives the objective lens in the track plane to form a negative feedback loop to perform tracking control. For track jump control, the switch is opened and the negative feedback loop is activated. The track jump pulse from the track jump pulse generating means is applied to the actuator via the amplifying means without using the track jump pulse generating means.
An automatic tracking device characterized by performing jump control.