JPH05334704A - Servo circuit for optical disk device - Google Patents

Abstract

(57) [Summary] [Structure] A means for detecting the speed of the lens 3 moved by the fine actuator 5 is provided, and adders 17, 18 are provided between the input stage of the fine actuator 5 and the fine compensation circuit 12. Then, the speed signal detected by the speed detecting means is added to the adder 17, and the input signal of the secondary low-pass filter 11 is made the sum of the output signal 20 of the fine compensating circuit and the output signals of the adders 17 and 18. ,
Then, the Q value of the second-order low-pass filter 11 is raised to match the frequency at which the peak occurs with the disk rotation frequency. [Effect] In the constant rotation optical disk device, only the coarse system gain of the disk rotation frequency can be increased, so that the gain for suppressing the disk eccentricity can be secured without increasing the DC gain.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to tracking control in a disk radial direction by a fine actuator that moves a lens and a course actuator that moves the entire optical head, and more particularly to a course system circuit.

[0002]

2. Description of the Related Art FIG. 4 shows an outline of a conventional optical disk device. The optical disk device is a storage device that reads and writes data on a disk-shaped medium 1 by using a laser beam 2. The reading of data is performed by detecting the change in the amount of reflected light from the disc 1 or the optical activity of the reflected light. Writing is performed by increasing the output of the laser beam 2.

In order to increase the capacity of an optical disk, it is necessary to reduce the area for recording data. The area for recording data depends on the size of the laser beam 2 that hits the disk surface. Therefore, a light spot 4 of about 1 μm in which the laser light 2 is narrowed down to the diffraction limit by the lens 3 is used.

The ability to accurately position the light spot 4 on the disk 1 is a condition for reading the data written at that position without error, and the reliability of the data largely depends on the positioning performance of the light spot 4. ..

The light spot 4 is moved by a coarse actuator 6 that moves the entire head and a fine actuator 5 that moves only the lens 3. The coarse actuator 6 and the fine actuator 5 are brushless DC motors that generate force based on Fleming's left-hand rule. The two actuators 5 and 6 allow the light spot 4 to follow the target position of the disk with a tracking accuracy of several hundred nanometers or less.

The follow-up control of the optical disk device is as follows. The fine actuator 5 is current-driven through the fine compensating circuit 8 and the fine amplifier 9 by the track signal 7 indicating the relative position between the light spot 4 and the disc 1. The coarse actuator 6 is driven from a fine current command value 10 by a secondary low-pass filter 11 simulating the fine actuator 5, a compensation circuit 12, and a coarse current amplifier 13.

The track signal 7 is detected by the push-pull method. When the position 14 of the returning light is different, the push-pull detection type track signal is erroneous because a value substantially proportional to the optical axis shift is added. When the amount of movement of the lens 3 driven by the fine actuator 5 from the reference position is large, an optical axis shift 14-b occurs and an error occurs in the signal 7 for positioning. Therefore, it is necessary to make the coarse actuator 6 move well in the low range where the driving displacement is large, and to move the fine actuator 5 in the high range where the fluctuation displacement is minute.

Since the optical disc 1 is a portable medium, a disc eccentricity of about 50 μm occurs as the disc rotates. Since the disk eccentricity is generated by the rotation of the disk, the eccentricity frequency and the rotation frequency are equal. If the eccentricity is followed only by the fine actuator 5, an error occurs in the track signal 7 and the positioning is erroneous. Therefore, the disc eccentricity needs to be followed by the course actuator 6.

As a conventional technique, Japanese Patent Laid-Open Publication No. 64-13275 discloses a method in which a gain of a fine system of a disc eccentric frequency is increased, an error of a position signal due to an optical axis shift is estimated from an observer, and a tracking signal is calculated.

[0010]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In order to maintain a, it is necessary to prevent the lens 3 driven by the fine actuator 5 from being significantly displaced from the reference position of the lens. Then, one of the factors that deviates from the reference position of the lens is disk eccentricity.
The disc eccentricity is about 50 μm, and the deviation of the lens from the reference position must be suppressed to several μm.

Therefore, if the course actuator 6 can follow the disc eccentricity, the lens 3 driven by the fine actuator 5 will not be displaced from the reference position. Therefore, at the disc rotation frequency, it is necessary to make the gain larger than the gain of the fine system. This is possible by simply increasing the DC gain of the course system. However, due to the vibration characteristics of the coarse actuator, there is a limit to increase the gain of direct current, which cannot be so high.

An object of the present invention is to provide a servo circuit that suppresses disk eccentricity without increasing the DC gain of the course system.

[0013]

A signal indicating a relative displacement between a light spot and an optical disc is input to a fine compensating circuit, and an output signal of the fine compensating circuit is used as a drive signal of a fine actuator for driving a lens, A coarse actuator that inputs the drive signal of the fine actuator to a second-order low-pass filter, inputs the output of the second-order low-pass filter to a course compensator, and outputs the output signal of the course compensator to the entire fine actuator. In the servo circuit of the optical disc to be the drive signal of, the means for detecting the speed of the lens moved by the fine actuator is provided, and an adder is provided between the input stage of the fine actuator and the fine compensation circuit, and The speed signal detected by the speed detecting means is added to the adder. In addition, the input signal of the second-order low-pass filter is the sum of the output signal of the fine compensating circuit and the output signal of the adder, and the Q value of the second-order low-pass filter is raised to generate a peak frequency. To match the disk rotation frequency.

[0014]

Function Consider the condition for detecting the displacement of the fine actuator by the secondary low-pass filter. The input and output relationships for the fine actuator and the second-order low-pass filter can be represented by the same frequency response of the second-order lag system. The characteristics of the second-order delay system are determined by the main resonance and damping. Generally, the Q value is used as the value corresponding to the damping corresponding to the second-order low-pass filter. The Q value is almost proportional to the reciprocal of damping. If the respective constants are the same, the displacement of the fine actuator can be estimated from the value of the secondary low-pass filter by inputting the same input value to the fine actuator and the secondary low-pass filter.

Next, FIG. 3 shows a case where the damping of the secondary delay system is small (a) and a case where the damping is large (b). When damping is small (a), near the main resonance,
A sudden gain change occurs. Therefore, when the fine displacement is estimated from the drive value of the fine actuator by using the second-order low-pass filter, the same main resonance and damping as those of the fine actuator are required, and the allowable value is small with respect to the variation of the constant.

However, when the damping is large (b), there is no abrupt change in the gain and the allowable value increases with respect to the variation of the constants. Therefore, even if the main resonance and the damping are deviated, there is no large error and the fine actuator. The displacement of the lens due to can be estimated.

Therefore, in order to estimate the fine displacement by changing the constants of the fine and second-order low-pass filters, it is necessary to increase the damping. In order to handle a small damping fine actuator as a large damping actuator, it is necessary to electrically feed back the speed obtained by the speed detecting means via an adder.

With this velocity feedback loop,
The signal input to the adder is passed through a second-order low-pass filter to obtain an estimated value with few errors.

However, if an offset occurs in the circuit from the output of the adder to the fine actuator, the estimated value differs in terms of direct current. In order to compensate the estimated value of DC, the sum of the signal after the adder and the input signal of the adder is input to the second-order low-pass filter. This allows for variations in offset and main resonance.

Up to now, only the function of estimating the fine actuator displacement has been described in the second-order low-pass filter.
Furthermore, by reducing the damping of the second-order low-pass filter, it is possible to provide a gain amplifying function of a specific frequency. As shown by the second-order delay system in FIG. 3, the Q value is increased and the rising frequency is made to coincide with the disk rotation frequency. From the above, it is possible to increase the gain of the course system with respect to the disk rotation frequency without increasing the DC gain of the course system. For this reason, the lens does not need to be displaced much from the reference position, and erroneous positioning can be prevented.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

An optical disk device to which this method is applied is shown in FIG.
Is. The optical disk device includes an optical disk 1, a spindle motor 24 for rotating the optical disk 1, a head 25 for reading and writing data, a fine actuator 5 for moving a lens 3 mounted in the head 25, a course actuator 6 for moving the entire head 25, and , A circuit for controlling each of the actuators 5 and 6.

The optical disc is rotated at 2400 rpm by the spindle motor 24, and a disc eccentricity of about 50 μ occurs due to misalignment. Data is read and written by positioning the light spot 4 on the disk eccentricity. The fine actuator 5 moves the light spot 4.
And the course actuator 6, and the two actuators 5 and 6 are brushless DC motors.

The structure for tracking of the optical disk device is as follows. That is, the laser light 2 emitted from the light source 26 enters the lens 3 and becomes a light spot 4. The light spot 4 is reflected by the disc 1 and the return light 28 is incident on the detector 27. The return light 28 causes the detector 27 to detect the tracking signal 7 indicating the positional deviation between the light spot 4 and the optical disc. The detector 27 is composed of a two-divided photodiode, and the photodiode is an element through which a current flows when exposed to light. The amount of the return light 28 changes depending on the relative displacement between the light spot 4 and the disc 1. Therefore, the tracking amplifier 7, which is the amount of positional deviation, obtains the current of each photodiode generated by the amount of returned light by the differential amplifier 19 configured by an OP amplifier.

The tracking signal 7 is passed through the fine compensator 8 to produce an output signal 20. Fine compensator 8
Is an OP amplifier circuit having a function of position delay compensation and a function of phase lead compensation and consisting of a capacitor and a resistor.

The fine actuator 5 is an actuator with small damping. The output 20 of the compensator is passed through the adder 17 and the current amplifier 9 to cause a current to flow through the fine actuator 5, the speed sensor 30 for fine detects the speed, and the signal 16 is fed back to the adder 17. In this way, speed feedback is applied to increase the damping value.

The speed sensor 30 detects the speed by the voltage generated from the search coil attached to the lens 3. The current amplifier 9 has a function of converting the output voltage of the adder 17 into a current and generating a current 33 in the actuator 5, which is directly proportional to the input voltage value 32. The current amplifier 9 is
It is composed of semiconductor elements.

The coarse actuator 6 needs to be moved so that the fine actuator 5 does not deviate too much from the reference position. The sum of the output value 20 of the fine compensator added to the adder 17 and the voltage 21 proportional to the fine current is used as the input 22 of the secondary low-pass filter 15. Since the signal is derived from the current value 33 of the fine actuator 5, the influence of the fine system offset can be reduced. Further, since the velocity feedback system is configured, the influence of the characteristic variation of the actuator is small. The secondary low-pass filter 15 uses the same frequency as the disk rotation frequency as the main resonance frequency. Further, the Q value is increased to secure the gain. Therefore, the output of the second-order low-pass filter 15 has an estimated value in which the gain is amplified at the disk rotation frequency. The course actuator 6 is driven to the value 23 through the course compensator 12 and the current amplifier 13.

The open loop of the course system is shown in FIG. Due to the open loop characteristic, a gain that suppresses disk eccentricity is secured. Therefore, the fine actuator does not move due to the eccentricity of the disk, and the optical axis does not shift.

[0030]

According to the present invention, in the constant rotation optical disk device, only the coarse gain of the disk rotation frequency can be increased, so that the DC gain is not increased.
It is possible to secure a gain that suppresses disk eccentricity.

[Brief description of drawings]

FIG. 1 is a block diagram of a tracking circuit to which the present invention is applied.

FIG. 2 is an open loop characteristic diagram of a course system to which the present invention is applied.

FIG. 3 is a frequency characteristic diagram of a second-order lag system when damping is small (a) and when damping is large (b).

FIG. 4 is a block diagram of a conventional tracking circuit.

[Explanation of symbols]

3 ... Lens, 5 ... Fine actuator, 11 ... Secondary low-pass filter, 12 ... Course compensation circuit, 17 ...
Adder, 18 ... Adder, 19 ... Differential amplifier, 20 ... Output signal of fine compensation circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukio Sumitani 502 Jinritsucho, Tsuchiura-shi, Ibaraki Hiritsu Seisakusho Co., Ltd.

Claims (1)

[Claims] 1. A signal indicating a relative displacement between a light spot and an optical disc is input to a fine compensating circuit, and an output signal of the fine compensating circuit is used as a drive signal for a fine actuator for driving a lens, and the fine actuator A driving signal is input to a second-order low-pass filter, an output of the second-order low-pass filter is input to a course compensator, and an output signal of the course compensator drives a coarse actuator that drives the fine actuator. In the servo circuit of the optical disc to be a signal, means for detecting the speed of the lens moved by the fine actuator is provided, and an input stage of the fine actuator,
An adder is provided between the fine compensation circuits, and
The speed signal detected by the speed detecting means is added to the adder, and the input signal of the secondary low-pass filter is the sum of the output signal of the fine compensating circuit and the output signal of the adder. Servo circuit for optical disk device.