JP2606422B2 - Track access device and track access method in optical disk device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a track access device in an optical disc device, and more particularly to a track access device for moving an optical head between tracks in order to enable access to a desired track.

[Conventional technology]

In an optical disc device that optically records / reproduces information on a disc-shaped record carrier, in order to perform recording / reproducing operations on a target track among a large number of concentric or spiral information tracks, It is necessary to move and position the optical head across multiple tracks. For this reason, similarly to a magnetic disk device or the like, generally, a speed control type movement control for following the speed of the head with respect to a reference speed signal that changes according to the distance to the target position of the head is performed. I have.

[Problems to be solved by the invention]

However, since the track pitch of the optical disk is much smaller than that of the magnetic disk, and the optical head is larger and heavier than the magnetic head, there are the following problems.

That is, in order to make the light spot follow a track of a minute width and to control the focus of the light beam, a lens for focusing the beam is attached to the lens actuator so as to be movable with respect to the optical head. Therefore, when the head is moved to move between tracks, the focusing lens vibrates, and accurate and stable movement of the light spot cannot be performed. Also, in order to accurately move and position the light spot on a fine track, it is necessary to perform high-precision speed control using a high-bandwidth control loop. However, since the head is large and heavy, It is difficult to configure a high-bandwidth control loop. To solve these problems and realize a high-speed, high-precision track access device,
For example, Japanese Patent Application Laid-Open No. Sho 60-131646 discloses a "tracking control device for an optical disk device", which includes a lens position detector, drives a focusing lens to move between tracks, and reduces the displacement of the head from the focusing lens. A method of following the lens position has been proposed. This is to try to control the movement at high speed and high bandwidth by adopting the track access method that moves the focusing lens, but operation becomes unstable if the displacement between the lens and the head becomes large, There is a disadvantage that the acceleration / deceleration of the lens must be kept within a range that the head can sufficiently follow. For this reason, the acceleration at the time of movement was suppressed to be smaller than the limit of the head drive mechanism (head actuator), and the maximum speed could not be achieved.

As another example, Japanese Patent Application No. 01-021665, entitled "Track Access Apparatus in Optical Disc Apparatus", includes a lens position detector, and moves the head while keeping the lens relatively stationary with respect to the head, thereby performing inter-track access. Are shown. This aims to stabilize access by moving the head by suppressing the vibration of the lens when moving the head.However, because the head is large, there is a limit to speed control with high accuracy and high bandwidth. However, there is a drawback that the arrival / stop to the target track cannot be performed sufficiently accurately and stably.

In addition to this, a method of externally providing a position scale and a speed detector to perform movement control is also generally used.However, since an external position scale cannot provide sufficient position accuracy, track access can be performed accurately. High-speed positioning and stopping due to the need for access control (fine seek) for correction and insufficient control loop bandwidth.
There is a drawback that it cannot be performed stably.

[Means for solving the problem]

The present invention relates to a track access device in an optical disc device for irradiating a concentric information track formed on a rotating disk-shaped record carrier with a light spot by a laser beam and positioning the information track on a predetermined information track. A track error detector that detects a displacement of the light spot with respect to the information track; a speed detection circuit that detects a track traversing speed of the light spot; and a position that detects an amount of movement of the light spot in the track traverse direction. An error signal generator, a reference speed signal generator for generating a reference speed signal from a position error signal indicating a difference between a target movement amount and an actual movement amount of the light spot, and an optical head in a radial direction of the record carrier. A head actuator to be moved, and a difference between the reference speed signal and a speed signal indicating a track traversing speed of the light spot. A first control loop configured to amplify a certain speed error signal to drive the head actuator and control a speed of the optical head so that the optical head reaches a target track; A lens position detector for detecting a displacement of the focusing lens to be focused with respect to the center of the laser beam,
A lens actuator for moving the focusing lens in the radial direction of the record carrier, a phase compensation circuit for phase-compensating the output of the lens position detector and feeding back to the lens actuator, and a power amplifier; A second control loop for controlling the position of the focusing lens so as to substantially stop the optical head at a standard position (the center of the optical axis) with respect to the optical head; A third control loop for amplifying the indicated velocity error signal via a power amplifier and supplying the amplified signal to the lens actuator to control the velocity of the lens so as to move the focusing lens to a target track; and detecting the lens position. Circuit that compensates the phase of the output of the And a fourth control loop for performing position tracking control of the optical head so as to reduce a displacement between the focusing lens and a standard position (center of the optical axis) of the optical head by moving a head actuator. It is characterized by.

Also, in the track access method in the optical disk device according to the present invention, in the optical disk device described above, the first optical head speed control loop and the second focusing lens position control loop are operated, and the focusing lens is moved. A first head movement control mode for bringing the optical head closer to the target track while holding the optical head substantially stationary with respect to a standard position of the optical head; a third focusing lens speed control loop and the fourth light Operating a head position tracking control loop to move the optical head toward the focusing lens target track while following the movement of the focusing lens; and a position error to the target track. The light spot is moved to the target track by switching and operating according to the size of And it said that there was Unishi.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.
In FIG. 1, a laser diode 18 disposed in an optical head 2 is supplied with a current from a laser drive circuit 20 to emit laser light. The divergent laser light emitted from the laser diode 18 is converted into parallel light by the collimator lens 17, passes through the beam splitter 16, is bent in the optical path by the reflecting mirror 13, and enters the focusing lens 12. The focusing lens 12 focuses the light beam and forms a minute light spot on the surface of the record carrier 1. In addition, the focusing lens 12 and the reflecting mirror 13
Are mounted on a common arm and are moved together by a lens actuator 11. Then, by moving the focusing lens 12 in the radial direction of the record carrier 1 with the lens actuator 11, the focused light spot moves in the radial direction (traverse direction of the track), and tracking control can be performed. Conversely, the lens actuator
By appropriately controlling 11, the position of the focusing lens 12,
That is, the position of the light spot can be stopped at a fixed position with respect to the optical head 2. The lens position detector 14 is
The focusing lens 12 is disposed inside the optical head 2 so as to face the movable portion (arm) of the lens actuator 11, and detects a relative displacement of the focusing lens 12 with respect to the optical head 2. The beam splitter 16 separates a part of the reflected light that has been reflected by the record carrier 1 and returned through the focusing lens 12 and the reflecting mirror 13 and makes the reflected light enter the track error detector 15. The track error detector 15 receives a change in the intensity of the reflected light modulated by the track position information on the record carrier 1 and outputs a current corresponding to the displacement of the light spot with respect to the track center. The optical system, the lens actuator 11, the lens position detector 14, and the track error detector 15 that reach the focusing lens 12 from the laser diode 18 are incorporated in the optical head frame to constitute the optical head 2 as a whole. The optical head 2 is moved in the radial direction of the record carrier 1 by a head actuator 40 composed of a linear motor or the like. The output of the track error detector 15 is input to a track error amplifier 21 having a differential input, and the track error amplifier 21 outputs a track error signal 201 indicating the displacement of the light spot with respect to the track center. At the time of a track access in which the light spot moves between tracks, the track error signal 201 has a sinusoidal waveform that periodically changes every time the track is traversed. By detecting the 0 cross of 201 and pulsing it, a track pulse 202 is generated every time the track is crossed. The position error signal generator 32 receives a target movement signal 101 indicating the required movement amount (the number of tracks) of the light spot from the host device, and outputs the track cross pulse 2
The difference is subtracted (countdown) by 02, and a position error signal 102 indicating a position shift (residual error) of the moving light spot to the target track is output. The reference speed signal generator 33 receives the position error signal 102 and generates a reference speed signal 103 whose value changes according to the value. When the value of the position error signal 102 is X, the reference speed signal 1
The value V of 03 is, for example, It is calculated according to an equation close to On the other hand, the track cross pulse 202 is input to the speed detection circuit 23. The speed detection frequency 23 performs F / V (frequency-voltage) conversion on the track cross pulse 202, and generates a speed signal 203 indicating the track traversing speed of the light spot. The speed error amplifier 24 obtains the difference between the reference speed signal 103 and the speed signal 203, and outputs a speed error signal 204 indicating the difference between the set speed and the actual speed. Then, the speed error signal 204 is input to the power amplifier 26, and the head actuator 40 is corrected so as to correct the error.
, A first control loop (optical head speed control loop) is configured to move the head 2 by controlling the speed so that the head 2 follows the reference speed. In this case, the switch 25 is turned on on the side through which the speed error signal 204 passes.

On the other hand, the speed error signal 204 is input to the power amplifier 31,
When the lens actuator 11 is moved so as to correct the speed error, a third control loop (lens speed control loop) that is a speed control loop that moves the focusing lens 12 according to the reference speed is configured. In this case, the switch 30 is turned on on the side where the speed error signal 204 passes. However, as will be easily understood, if the first control loop and the third control loop are turned on at the same time, the operation becomes unstable.

Next, the output of the lens position detector 14 is input to a differential input lens position amplifier 27, and the lens position amplifier 27 outputs a lens position signal 210 indicating the deviation of the focusing lens 12 from the standard position. Then, the lens position signal 210 is
Enter 8 and 29 respectively. The phase compensation circuits 28 and 29 perform phase lead compensation on the lens position signal 210 in order to secure the stability of the position control loop.
A lead-lag filter is used. The output of the phase compensating circuit 28, that is, the lens position signal compensated for the phase lead is input to the power amplifier 31 and the lens actuator 11 is driven to set the position of the focusing lens 12 to the standard position with respect to the optical head 2. A second control loop (lens position control loop) for stopping is configured. In this case, the switch 30 is turned on to pass the output of the phase compensation circuit 28.

When the optical head 2 is driven to approach the target position by the above-described first control loop, the focusing lens 12 is not fixed, so that the head 2 moves to generate vibration. For this reason, the track error signal 201 is disturbed, and the position signal 102 and the velocity signal 203 generated based on the track cross pulse 202 do not accurately represent the movement of the optical head 2 but include fluctuations. Therefore, under such a condition that the focusing lens 12 vibrates, the track error signal 20
It is difficult to control the access of the optical head 2 based on 1 stably and accurately.

On the other hand, in the access device of the present invention, when the head 2 is moved in the first control loop by operating the second control loop and keeping the focusing lens 12 stopped with respect to the head. There is no vibration of the focusing lens 12
Stable and accurate head movement control is performed.

Next, the output signal of the phase compensation circuit 29, that is, the lens position signal whose phase advance has been compensated is input to the power amplifier 26 to drive the head actuator 40, so that the head 2 follows the movement of the focusing lens 12. A fourth control loop (a position control loop in which the head follows the lens position), which is a head position control loop, is configured. In this case, the switch 25 is turned on so that the output of the phase compensation circuit 29 passes.

When only the focusing lens 12 is moved in the target direction by the above-described third control loop, only a very small distance can be moved because the movable range of the focusing lens 12 is small. Further, a slight displacement of the focusing lens 12 with respect to the center of the light beam of the optical head 2 causes a reduction in the convergence of the light spot and a decrease in the detection characteristics of the track error signal 201, and thus the allowable movement range of the lens 12 is extremely small. Therefore, when the focusing lens 12 is moved in the target direction, it is necessary to move the optical head 2 accordingly. The second control loop drives the optical head 2 according to the lens position signal 210 to follow the movement of the converging lens 12, and serves to keep the optical head 2 small in displacement of the lens 12. This control loop allows the focusing lens 12
When the optical head moves at high speed, the optical head follows the movement and moves to the target position together.

As can be seen from the above description, the focusing lens 12 is stopped by the second control loop and the optical head 2 is moved by the first control loop, or the optical head 2 is moved by the fourth control loop. While following the focusing lens 12
The optical head 2, that is, the focused light spot can reach the target position by any method of moving the focusing lens 12 by the third control loop. However, since the optical head 2 is large and heavy, it is difficult to increase the frequency band of the control loop when the optical head 2 is moved by the first control loop. In addition, since the track pitch is very small in an optical disc device, the speed must be controlled accurately and the speed must be sufficiently low on the target track to accurately stop the optical head on the target track. It is difficult to perform such high-precision control if is sufficiently high.

On the other hand, since the following operation of the optical head 2 with respect to the movement of the lens 12 by the fourth control loop has a delay time,
When the focusing lens 12 is moved by the third control loop, an excessively rapid acceleration / deceleration leads to a shortage of the following operation, and the operation becomes unstable. Therefore, the moving speed of the focusing lens 12 must be set to a low level with a sufficient margin. This is a disadvantage that the access speed to the target track cannot be sufficiently increased.

In the access device of the present invention, the head access operation is performed by combining the first control mode in which the optical head 2 is moved by the first control loop and the second control mode in which the focusing lens 12 is moved by the third control loop. , A high-speed and stable track access operation is realized by taking advantage of only the two control methods. That is, when the optical head 2 (light spot) is moving at a high speed far away from the target position (target track), the optical head 2 operates in the first control mode, follows the target position and becomes slow, and the speed is reduced. In a situation where accuracy and stable deceleration stop are required,
It operates in the second control mode. The focusing lens 12 is stopped in the second control loop, and the optical head 2 is stopped in the first control loop.
In the first control mode for driving the optical head 2, the high-bandwidth optical head 2
Although it is difficult to control the movement of the optical head 2, the maximum acceleration and deceleration that can be generated by the head actuator 40
It is possible to move. On the other hand, in the vicinity of the target track, the speed control with high accuracy and stability is performed by the second control mode in which only the focusing lens 12 is moved. By the combination of such two control modes, an access device that performs a high-speed and stable track access operation can be realized.

FIG. 2 is a waveform diagram showing an example of a signal in the embodiment of FIG. In FIG. 2, a waveform A shows a waveform of the reference speed signal 103 at the time of track access. Reference speed signal 103
Is commonly used for the first control mode and the second control mode, and changes continuously even when the mode is switched. Value of the movement start time t ₀ criterion from the point D the rate signal 103 of the optical head 2 indicates the maximum speed V _H. The deceleration is started at a point D where the optical head 2 approaches a certain distance from the target position (target track), and the value of the reference speed signal 103 decreases.
During this time, the optical head 2 is driven in the first control mode.
The approach to distance sufficiently close to the target track, the speed was reduced point switches the control mode to the second control mode at time t _1, thereby driving the focusing lens 12. At this time,
The speed of the focusing lens 12 becomes _VL , does not change more rapidly than before, and substantially continuous deceleration is performed. Thereafter, the standard speed signal 103 further lowers the value to stop the focusing lens 12 the value at the target arrival time t ₂ to 0.

A waveform B indicates a waveform of the speed signal 203. Although the reference speed signal 103 becomes _VH from the start of the movement of the optical head 2, the speed of the optical head 2 does not rise instantaneously but approaches _VH at a substantially constant acceleration. The deceleration is started from the deceleration start point D, and the optical head is decelerated as the reference speed signal 103 decreases. While the optical head 2 is operating in the first control mode, the control band is slightly lower, so that a slight speed error occurs during deceleration. When the mode is switched to the second control mode at the point E, the speed error becomes extremely small because the control band becomes high. Thereafter, since the speed error is small at the time of reaching the target, the focusing lens 12 stably stops almost immediately when the reference speed signal 103 becomes 0.

Waveform C shows the waveform of the lens position signal 210. Since the focusing lens 12 is vibrated at each point where the acceleration changes, the position of the focusing lens 12 slightly shifts, but the vibration is suppressed by the function of the second control loop (lens position holding loop). Can be Further, at the point E where the control mode is switched, the optical lens 2 is strongly decelerated to correct the speed error, which causes a lens position shift. However, the following operation of the optical head 2 by the fourth control loop causes
The level is small and stable. While stopping the target track reaches time t ₂ focusing lens 12, is almost completely, the optical head 2 has a slight speed, t ₂ hereinafter also minor lens - the position deviation between the head occurs, it Is also reduced by the fourth control loop.

〔The invention's effect〕

As described above, the present invention provides a first control loop for moving the optical head to the target position, a second control loop for stopping the focusing lens with respect to the optical head, and a second control loop for moving the focusing lens to the target position. And a fourth control loop for causing the optical head to follow the movement of the focusing lens, a first control mode for moving the optical head to the target at the time of track access, and moving the focusing lens to the target. By operating in combination with the second control mode to be performed, there is an effect that it is possible to realize an access device that performs high-speed, stable, and accurate track access that maximizes the capability of the head actuator.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram showing an example of a signal in the embodiment of FIG. DESCRIPTION OF SYMBOLS 1 ... Record carrier, 2 ... Optical head, 11 ... Lens actuator, 12 ... Converging lens, 13 ... Reflection mirror, 14 ... Lens position detector, 15 ... Track error detector, 16 ...
Beam splitter, 17… Collimate lens, 18… Laser diode, 20… Laser drive circuit, 21… Track error amplifier, 22 …… Track pulse generation circuit, 23…
… Speed generator, 24… speed error amplifier, 25,30… switch, 26,31… power amplifier, 27… lens position amplifier, 28,29… phase compensation circuit, 32… position error signal generation Device, 33: Reference speed signal generator, 40: Head actuator, 101: Target movement amount signal, 102: Position error signal, 103: Reference speed signal, 201: Track error signal, 202: Track Cross pulse, 203 ... speed signal,
204: Speed error signal, 210: Lens position signal.

Claims (2)

(57) [Claims] 1. A track access in an optical disk device for irradiating a concentric information track formed on a rotating disk-shaped record carrier with a light spot by a laser beam and positioning the information track on a predetermined information track. In the apparatus, a track error detector that detects a displacement of the light spot with respect to the information track, a speed detection circuit that detects a track traversing speed of the light spot, and detects an amount of movement of the light spot in a track traverse direction A position error signal generator, a reference speed signal generator for generating a reference speed signal from a position error signal indicating a difference between a target movement amount and an actual movement amount of the light spot, and an optical head in a radial direction of the record carrier. And a difference between the reference speed signal and a speed signal indicating a track traversing speed of the light spot. A first control loop for controlling the speed of the optical head so that the optical head reaches a target track, the first control loop comprising: a power amplifier that amplifies a speed error signal, and drives the head actuator; A lens position detector for detecting a positional shift of the focusing lens for focusing the laser beam relative to the center of the laser beam, a lens actuator for moving the focusing lens in the radial direction of the record carrier, and phase-compensating the output of the lens position detector. A second control unit configured by a phase compensation circuit and a power amplifier that feeds back to the lens actuator, and controls the position of the focusing lens so that the position of the lens is substantially stopped at a standard position (center of the optical axis) with respect to the optical head. A difference between the reference speed signal and the track traversing speed of the light spot. A speed error signal indicative amplified through the power amplifier, by feeding to the lens actuator,
A third control loop for controlling the speed of the lens so as to move the focusing lens to the target track; and a circuit for phase-compensating the output of the lens position detector and inputting the output to a power amplifier, and A fourth position control of the optical head is performed by moving the head actuator so as to reduce the displacement between the focusing lens and a standard position (center of the optical axis) of the optical head.
A track access device in an optical disk device, comprising: a control loop; 2. A track access method by a track access device in an optical disk device according to claim 1, wherein said first optical head speed control loop and said second focusing lens position control loop are operated. A first head movement control mode for bringing the optical head closer to the target track while holding the focusing lens so as to be approximately stationary with respect to a standard position of the optical head; a third focusing lens speed control loop; Operating a fourth optical head position tracking control loop to move the focusing lens toward a target track while causing the optical head to follow the movement of the focusing lens; and a second lens movement control mode. By switching and operating according to the magnitude of the position error to the track, the light spot can be moved to the target track. Track access method in an optical disk device being characterized in that so as to perform the movement.