JPH10208256A - Optical disk device and access control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the moving speed of an optical spot relative to the target track follow precisely the target speed by generating the target speed of an optical spot at the time of the access operation which moves the light spot, detecting the moving speed, calculating the speed deviation by subtracting the moving speed from the target speed and adding the target speed of the light spot to the speed deviation. SOLUTION: A target speed generating means 50 determines the address which is used to access the ROM that stores the relation between the remaining number of tracks and the target speed from the output of a remaining-number- of-tracks coefficient means 571 to output the target speed. A subtraction means 51 outputs the speed deviation obtained by subtracting the light spot detection speed outputted from a light spot speed detection means from the target speed outputted from the target speed generating means, and a speed deviation amplifying means 520 amplifies the speed deviation. An adding means 501 adds the output of the speed deviation amplifying means 520 to the acceleration feed forward outputted from an acceleration feed forward generating means 500.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device such as a magneto-optical disk device or a CD-ROM device, and more particularly, to a light spot for recording or reproducing information from an arbitrary track to a desired track. The present invention relates to an apparatus and a method for performing a moving access operation.

[0002]

2. Description of the Related Art In an optical disk, tracks for recording information are formed spirally or concentrically on the disk recording surface. At the time of recording or reproducing information, a laser beam focused by an objective lens is radiated in a spot shape on a recording surface to precisely follow a desired track. Further, in order to perform recording / reproduction on tracks separated in the disk radial direction, that is, in the access direction, the light spot traverses a plurality of tracks at high speed. In order to achieve both high-precision tracking and high-speed access, the movable portion of the access mechanism equipped with the objective lens employs a so-called piggyback actuator system. That is, the movable part
A fine actuator that moves the objective lens finely is mounted on a coarse stage driven by a coarse actuator with a wide movable range. At the time of tracking, high-precision positioning is performed by the cooperative operation of the two, and at the time of access, the relative movement of the objective lens with respect to the course stage is suppressed, that is, the two are integrated, and the integrated movable part is moved at high speed. Hereinafter, the related art will be described with reference to several documents.

[0003] Table 3.10 on page 125 of "Basics and Application of Optical Disk Storage", supervised by Yoshito Tsunoda, published by the Institute of Electronics, Information and Communication Engineers in 1995, lists courses that are frequently used in current optical disk devices. The type of actuator is shown. Among them, the configuration of a double-sided coil type actuator suitable for high-speed access is shown. The course stage moves by receiving a thrust in the access direction from the course actuator. At this time, precise and smooth linear motion is possible by the bearing and the guide rail in the course / stage. Further, an objective lens, a fine actuator, and the like are mounted in the course stage. Regarding this, Table 3.1 on page 129 of the aforementioned document “Basics and Application of Optical Disk Storage”
1 shows the type of the fine actuator. Among them, the configuration of a biaxial orthogonal translation type actuator is shown. The fine stage on which the objective lens is mounted is supported like a cantilever by four parallel support springs protruding from the course stage. On both sides of the fine stage, there are a magnetic circuit, a tracking actuator coil, and an autofocus coil. With these magnetic circuits and coils, the objective lens moves in the access direction and the focus direction.

FIG. 16 is a schematic diagram showing a configuration of an optical system and an access mechanism of an optical disk device. Optical disk 10
Rotates about the disk rotation center 11. The number of revolutions differs depending on the type of optical disc device.
For an optical disc conforming to the International Standards Organization (ISO) standard of 130 mm in diameter and 2.6 gigabytes in capacity, the speed is constant at 3000 revolutions per minute. Laser light 4 emitted by laser diode 43
Numeral 9 is converted into parallel light by a coupling lens 44 and is incident on an objective lens 41 via a beam splitter 47, a 板 wavelength plate 48, and a rising mirror 42, where the light is incident on a light spot 40 on a recording surface. Narrowed down to The laser beam reflected by the recording surface enters the beam splitter via the objective lens, the rising mirror, and the quarter-wave plate, is bent there, and is split into two light detectors via a lens 46. 45 is irradiated. This photodetector outputs a tracking error signal (TES) corresponding to the amount of displacement of the light spot from the track center as an electric signal. TES
Is such that when the displacement amount of the light spot is 0, the signal value is also 0, and a sine wave of one cycle is generated every time one track moves from there. Further, regarding the access mechanism, the aforementioned 2
In the axis orthogonal translation type actuator, the coarse stage 33 and the fine stage 33 are used because of the parallel support spring.
, A restoring force of the spring 31 and a viscous force of the damper 32 are generated. Further, a displacement sensor (hereinafter, midpoint sensor 34) for detecting a relative displacement of the fine stage with respect to the course stage is used.

Next, conventional access control will be described. FIG. 17 is a diagram showing a basic configuration of conventional access control. This control system operates until the light spot moves from the current track to the desired track. The target speed generating means 50 generates a profile of the target speed that changes every moment. The subtracting means 51 outputs a speed deviation between a target speed and a light spot detection speed described later. The speed deviation compensating means 52 amplifies the speed deviation and outputs a control input to the actuator 53. The light spot moving means 54 moves by the driving force generated by the actuator. The two-segment photodetector 45 generates a tracking error signal (TES) according to the relative position of the light spot to the track eccentricity 55 as described above. TES is a sinusoidal signal during the access operation, and the light spot speed detecting means 56
The moving speed of the light spot is detected by measuring the cycle of TES and the like. Thus, since the access control system is a feedback control system, it can be said that the moving speed follows the target speed with a delay, and the driving force is generated by this speed deviation.

However, such an access control system has the following three problems. First, at the time of switching to the tracking control at the end of the access, the access time due to the movement speed not sufficiently decreasing due to the speed deviation and the light spot going over the target information track (hereinafter referred to as the target track). Is likely to increase. Second, in order to shorten the access time in this system, it is necessary to raise the target system speed and, at the same time, increase the loop gain of the feedback system in order to increase the bandwidth. But actually,
There is a phase delay due to a mechanical resonance of the light spot moving means or a detection delay of the light spot speed detecting means, and it may be difficult to increase the loop gain in order to secure stability against the delay. Third, during the access operation, in order for the laser beam having a certain distribution (spread, cross-sectional area) to correctly pass through the objective lens and to form a light spot on the recording surface stably, the fine stage must be positioned with respect to the coarse stage. Midpoint control to suppress relative displacement is required. In particular, in the aforementioned two-axis orthogonal translation type actuator, when the course stage receives a driving force from the course actuator,
Since the fine stage inevitably causes an inertial delay, that is, a relative displacement due to an inertial force due to its support structure, a control system for compensating for this is essential.

In order to solve the above problems, the following methods have been proposed.

Japanese Patent Publication No. 6-103536 discloses a technique in which a signal proportional to a target acceleration profile of an access operation is added to a speed deviation signal in a feed-forward manner, and this is used as a control input to a coarse actuator. ing. The target acceleration at this time is desirably a constant maximum acceleration and a constant maximum deceleration symmetrical at the center of the access range. In addition, a configuration is proposed in which the state feedback is provided for the course / stage movement speed and the fine stage relative displacement instead of feedback for the light spot movement speed. According to this technique, a control input during acceleration and deceleration is supplied by a feedforward signal of a target acceleration, and a feedback system acts to suppress a speed deviation.
It is possible to accurately follow the target speed without increasing the gain. However, this technique does not directly control the moving speed of the light spot, so if there is a large eccentricity in the rotation of the disk, the relative position between the light spot and the target track is changed at the time of switching to tracking control at the end of access control. Since the speed does not decrease sufficiently and a transient response such as overshoot occurs, there is a concern that the access time will increase. Furthermore, even if the target acceleration is set to a rectangular wave from a constant maximum deceleration at the end of access to a rectangular wave, it is possible to immediately position the light spot on the target track and set the moving speed to 0 at that time due to the effect of disturbance or the like. On the contrary, it is considered that a transient response is caused.

JP-A-5-11854 discloses a technique for stabilizing a two-stage control system by feeding back the relative speed of a fine stage with respect to a coarse stage to a control input to a fine actuator. . In this configuration, damping has the effect of suppressing the relative movement of the fine stage to some extent.
However, since the configuration does not generate a restoring force for suppressing the relative displacement, the above-described two-axis orthogonal translation type actuator cannot compensate for the relative displacement due to the inertia delay generated in the fine actuator during the access operation.

[0010]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems in the prior art regarding access control of an optical disk device, and to make the most of the capability of an actuator to achieve high-speed operation. It is to realize access control.

More specifically, one of the problems to be solved by the present invention is that, when accelerating the access operation, the maximum acceleration is performed by the coarse actuator, and during the retraction from the deceleration to the target track, the light spot of the light spot is increased. The purpose is to make the relative moving speed relative to the target track accurately follow a predetermined target speed. One of the other problems to be solved by the present invention is that the access control system can control the phase in the feedback loop such as the mechanism resonance of the moving means for moving the irradiation position of the light spot and the operation time of digital control. It is to be stable against delay. Further, another problem to be solved by the present invention is to compensate and suppress the midpoint shift of the fine stage due to the access operation.

[0012]

In order to solve the above-mentioned problems, a first means of the present invention is to mount an objective lens for irradiating a light spot on an optical disk having an information track, and to mount the objective lens on the optical disk. A fine stage that moves in the direction, a fine actuator that drives the fine stage, a course stage that carries the fine stage and the fine actuator and moves in the radial direction of the optical disk, and a course that drives the coarse stage・
An optical disc device having an actuator, comprising: a target speed generating means for generating a target speed of the light spot during an access operation for moving the light spot to another target information track; and a light for detecting a moving speed of the light spot. Spot speed detecting means, subtracting means for calculating a speed deviation by subtracting the moving speed from the target speed, target acceleration generating means for generating a target acceleration of the light spot, and a course actuator for adding the target acceleration to the speed deviation And a relative movement control means for suppressing the relative movement of the fine stage with respect to the course stage.

[0013] Further, the second means of the present invention comprises the first means.
A relative displacement detecting means for detecting a relative displacement amount of the fine stage with respect to the course stage; and a position deviation by subtracting the detected relative displacement amount from a target value of the relative displacement. Subtraction means, feedback compensation means which operates with the position deviation as input to suppress relative displacement and stabilize relative motion control means, and detects fine movement by detecting the acceleration of the course stage.
A feedforward compensator for generating a target acceleration of the stage, and an adder for calculating a control input to the fine actuator by adding an output of the feedforward compensator to an output of the feedback compensator. is there.

Further, a third means of the present invention is the above-mentioned first means.
Alternatively, in the access control method for controlling an optical disk device described in the second means, the target speed defines a constant speed and a speed of a deceleration operation after the light spot reaches the maximum speed, and the target acceleration is , The constant speed after the light spot reaches the maximum speed and the acceleration of the deceleration operation.

Further, a fourth means of the present invention is the above-mentioned first means.
Alternatively, in the access control method for controlling an optical disk device described in the second means or the third means, the target speed generating means is configured to set a target speed according to a distance from a current irradiation position of the light spot to a target information track. The speed is generated, and the target acceleration generating means generates a target acceleration according to a distance from a current irradiation position of the light spot to the target information track, and a deceleration operation of the light spot is performed by the light spot. During a deceleration operation, a first deceleration section until reaching a predetermined position before the target information track, and a second deceleration until reaching the target information track from the predetermined position. The target speed and the target acceleration are decelerated at a constant acceleration in the first deceleration section, and the deceleration is increased in the second deceleration section. S in has been determined to be closer to 0, and, at the boundary of the first deceleration zone and the second deceleration zone,
The target speed and the target acceleration are respectively continuous.

Further, the fifth means of the present invention is characterized in that:
Alternatively, in the access control method for controlling an optical disk device according to the second means or the third means, the target speed generating means includes a target speed according to a distance from a current irradiation position of the light spot to a target information track. And the target acceleration generating means generates a target acceleration in accordance with the distance from the current irradiation position of the light spot to the target information track, and decelerates the light spot. Sometimes divided into a first deceleration section until reaching a predetermined position before the target information track and a second deceleration section until reaching the target information track from the predetermined position. The target speed is approximately a root function of the distance of the light spot to the target information track in the first deceleration section, and the second deceleration is performed. The distance between the light spots is almost a linear function of the distance to the target information track, and the target speed and the target acceleration are respectively continuous at the boundary between the first deceleration section and the second deceleration section. Things.

Further, the sixth means of the present invention is characterized in that:
Alternatively, in the access control method for controlling an optical disk device described in the second means, or in any one of the third to fifth means, the target acceleration generating means may control whether the light spot is in an accelerating operation or in a constant speed operation. , A target acceleration acting in the deceleration direction is generated.

Further, the seventh means of the present invention is characterized in that:
Alternatively, in the access control method for controlling an optical disk device described in the second means, or in any one of the third to sixth means, a time delay with respect to the target acceleration by the detection delay time of the light spot moving speed detecting means is obtained. Late
The target speed is generated.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a first embodiment of the present invention, an optical disk device which realizes an access control system by analog control will be described. FIG. 1 is a block diagram of an access control system according to a first embodiment of the present invention. Note that a tracking control system that operates after the end of the access operation is not shown.
In the illustrated embodiment, the target speed generating means 50, the subtracting means 51 connected to the output side of the target speed generating means 50, and the speed deviation amplifying means 520 connected to the output side of the subtracting means 51
And an adding means 501 connected to the output side of the speed deviation amplifying means 520; a coarse actuator driving amplifier 530 connected to the output side of the adding means 501; and an output of the coarse actuator driving amplifier 530. A coarse actuator 531, a coarse stage 540 driven by the coarse actuator 531, and a two-segment photodetector that outputs a tracking error signal (TES) corresponding to the amount of displacement of the light spot from the track center as an electric signal. 45, a light spot speed detecting means 56 and a track passage detecting means 570 connected to the output side of the two-divided photodetector 45, a remaining track number coefficient means 571 connected to the output side of the track passing detecting means 570, The output side of the remaining track number coefficient means 571 is connected to the output side of the adding means. 01 is a target acceleration generating means connected to the input side of the acceleration feedforward generator 50
0, a middle point deviation detecting means 538 which is a relative displacement detecting means for detecting a relative displacement amount of the fine stage with respect to the coarse stage, a subtraction means 535 connected to an output side of the middle point deviation detecting means 538, The middle point shift compensating means 536 which is a feedback compensating means connected to the output side of the means 535, the adding means 537 connected to the output side of the middle point shifting compensating means 536, and the output side of the adding means 537. Fine actuator drive amplifier 532
A fine actuator 533 controlled and driven by the output of the fine actuator drive amplifier 532;
A fine stage 541 driven by a fine actuator 533; and an inertia delay which is feed-forward compensating means connected to the output side of the coarse actuator driving amplifier 530 and having its output side connected to the input side of the adding means 537. And compensating means 534.

The input side of the target speed generating means 50 is connected to the output side of the remaining track number coefficient means 571, and the output side of the light spot speed detecting means 56 is connected to the subtracting means 5
1 input is connected to the negative side.

Relative displacement detecting means (middle point shift detecting means 53)
8), subtracting means 535, feedback compensating means (midpoint deviation compensating means 536), feedforward compensating means (inertial delay compensating means 534), and adding means 5
37, and relative motion control means is constituted.

The operation of the access control system will be described with reference to FIG. At the start of the access operation, the number of tracks in the distance from the track currently being followed by the light spot to the target track is set in the remaining track number coefficient means 571 as an initial value 572. The remaining track number coefficient means 571 is an up / down counter, and every time the track passage detecting means 570 detects that the light spot has passed through the track, the remaining travel distance (the number of remaining tracks) is counted down. This technology is based on the 1993 issue of Japan
Journal of Applied Physics, Volume 32, par
t1, Number 11B, pages 5371 to 5375. Suzuki et al., Advanced Direct
Seeding System for 5.25 "Magnetooptical
It is disclosed in detail in the Disk Drive. The target speed generating means 50 determines an address for accessing a read-only memory (ROM) storing the relation between the number of remaining tracks contained therein and the target speed from the output of the remaining track number coefficient means 571, The target speed is output based on the data in the memory. A method of designing a target speed profile (a graph defining the relationship between the number of remaining tracks and the target speed) stored in the ROM will be described later. The subtraction means 51 outputs a speed deviation obtained by subtracting the light spot detection speed output from the light spot speed detection means 56 from the target speed output from the target speed generation means 50.

The speed deviation amplifying means 520 amplifies the speed deviation. Acceleration feed forward generating means 500
Has a read-only memory (ROM) in which the relationship between the number of remaining tracks and the acceleration feedforward is stored, determines an address for accessing the ROM from the output of the remaining track number coefficient means 571, Is output. A method of designing an acceleration feed forward profile (a graph defining the relationship between the number of remaining tracks and the acceleration feed forward) stored in the ROM will be described later. The adding means 501 adds the output of the speed deviation amplifying means 520 and the acceleration feedforward output from the acceleration feedforward generating means 500, and outputs the result of the coarse actuator drive amplifier 53.
Output as control input to 0. The coarse actuator driving amplifier 530 supplies a driving current having a value corresponding to the control input to the coarse actuator 531. The coarse actuator 531 generates a driving force proportional to the driving current supplied from the driving amplifier 530. ,course·
The stage 540 is moved in the access direction.

The midpoint deviation detecting means 538 detects the relative displacement of the fine stage 541 in the access direction with respect to the course stage 540, that is, the midpoint deviation amount. During the access operation, it is desired to always set the middle point deviation amount to 0, so the subtraction means 535 subtracts the middle point deviation detection amount from the target value = 0 and outputs the position deviation. The midpoint deviation compensating unit 536 is a control element that operates to suppress the relative displacement and stabilize the relative motion control unit with the position deviation as an input in order to stabilize the control system and suppress the midpoint deviation. And can be realized as a phase compensator. The characteristics will be described later.

The inertia delay compensating means 534 is provided in the course
The actuator drive current is detected, and the acceleration of the course stage 540 is calculated and output based on the detected drive current. The configuration of the inertia delay compensating means 534 will be described later. Addition means 537
Adds the output of the midpoint deviation compensating means 536 and the output of the inertial delay compensating means 534 and outputs the result as a control input to the fine actuator drive amplifier 532. That is, the control input to the fine actuator drive amplifier 532 includes a signal for compensating for the midpoint shift and a feedforward signal of the acceleration of the coarse stage 540 output from the inertia delay compensating means 534 (the acceleration feed of the fine stage 541). (Which becomes a forward signal). Therefore, the fine stage 541 is driven so as to generate the same acceleration as that of the course stage 540 and not to cause a midpoint shift. The fine actuator 533 is provided with the fine actuator drive amplifier 5.
A drive force proportional to the drive current supplied from the drive stage 32 is generated, and the fine stage 541 is positioned at a position where the shift of the center point is zero.

The absolute position of the light spot on the stationary coordinate system is the sum of the amount of movement of the course stage 540 and the amount of deviation of the midpoint of the fine stage 541. The relative position of the light spot with respect to the target track is obtained by subtracting the track eccentricity 55 from the absolute position of the light spot. The two-segment photodetector 45 generates a sinusoidal tracking error signal (TES) according to the relative position of the light spot, as described in the section of “Prior Art”. The light spot speed detecting means 56 detects the relative speed of the light spot with respect to the target track, as described in the section of "Prior Art". The detected relative speed is fed back to the target speed by the aforementioned subtracting means 51. The track passing means 570 detects an edge of a signal (cross track signal) binarized by positive and negative of TES,
Generates a pulse each time it passes through a track.

FIG. 2 shows a target speed profile according to the first embodiment of the present invention. In this graph, the horizontal axis represents the number of remaining tracks, and the target speed at each remaining access distance is plotted on the vertical axis. FIG. 3 is an acceleration feedforward profile according to the first embodiment of the present invention. In this graph, the number of remaining tracks is plotted on the horizontal axis, and the acceleration feed forward at each remaining access distance is plotted on the vertical axis. The method for designing both profiles will be described with reference to these drawings.

As shown in FIG. 2, the target speed defines the light spot moving speed during the deceleration of the access operation. Therefore, during acceleration, since the speed deviation from the target speed is very large, the course actuator driving current is saturated at the maximum value, and the course stage 540 moves at the maximum acceleration. The target speed is obtained by connecting a plurality of functions as follows. In a section relatively close to the target track, the target speed Vr1 is a linear function of the number of remaining tracks Xe. That is, the target speed Vr1 is represented by the following function, using Vo as the target speed when the number of remaining tracks is 0, and KVr as a coefficient.

[0029]

(Equation 1)

In a section relatively far from the target track,
Constant deceleration is performed at the maximum deceleration αMAX. αMAX is a negative value. The target speed Vr2 at this time is the target speed Vr2.
Is represented by the following function, where e1 is the number of remaining tracks at which Eq.

[0031]

(Equation 2)

Further, there is a case where a constant maximum value VMAX of the target speed is set in a section apart from the target track. This is, for example, the case where the frequency of the tracking error signal is prevented from becoming excessively high and exceeding the processing capability of the signal processing integrated circuit. As shown in FIG. 2, the target speed profile is designed so that the first target speed Vr1 (Xe) and the second target speed Vr2 (Xe) are smoothly connected at the point of the remaining track number e2. That is, αMAX, V
o, three values of KVr, Xe = e2, Vr1 (e2) = Vr2 (e2), and

[0033]

(Equation 3)

E1 and e2 satisfying the above are solved as unknowns. Than this,

[0035]

(Equation 4)

[0036]

(Equation 5)

Is as follows. Also, the second target speed Vr2 (X
e) and the constant maximum speed VMAX are connected at the point of the remaining track number e3. That is, e3 is

[0038]

(Equation 6)

## EQU1 ## The target speed is calculated for each remaining track by one track using the equations (1) and (2) and stored in the ROM of the target speed generating means 50.

The acceleration feed forward αF (X
e) is a section where the number of remaining tracks is equal to or less than e2.

[0041]

(Equation 7)

In a section farther than e2, a constant value = αM
AX. Further, even during the acceleration of the access operation, the overshoot does not occur after the light spot moving speed reaches the target speed by applying the negative value, that is, the acceleration feedforward in the deceleration direction. By applying the acceleration feedforward (negative acceleration) in the deceleration direction, when the difference between the target speed and the detected relative speed becomes smaller, the negative acceleration becomes effective and the light spot moving speed becomes higher. Shooting is prevented. The acceleration feedforward for each remaining access distance of one track is calculated using Equation 7 and the constant deceleration αMAX, and stored in the ROM of the acceleration feedforward generating means 500.

Next, the midpoint deviation correction control will be described.
Fig. 4 shows the fine actuator with a two-axis orthogonal translation type actuator.
This is the transmission characteristic from the control input to the actuator to the fine stage displacement. About 55Hz,
There is main resonance due to the mass of the stage and the parallel support springs that support it. At frequencies above the main resonance, the gain characteristic
The slope is 40 dB / dec, and there is a higher-order mechanism resonance at about 29 kHz. In order to construct a stable control system for a control object having such characteristics, the above-mentioned midpoint deviation compensating means 53 is required.
Reference numeral 6 includes a phase compensator and a notch filter for suppressing higher-order mechanism resonance. This phase compensator includes a phase delay compensator for suppressing low-frequency disturbances, particularly 100 Hz or less, such as track eccentricity, and a phase lead near the gain crossover frequency of several kHz to stabilize the control system by increasing the phase lead. A phase lead compensator is connected in series. The transfer function C (s) of the phase compensator is expressed by the following equation.

[0044]

(Equation 8)

S: complex parameter of Laplace transform, kc: gain of phase compensator, aLG and bLG: coefficients defining phase delay characteristics, aLD and bLD: coefficients defining phase lead characteristics.

From the above, the loop transfer characteristic of this control system is as shown in FIG. At this time, the gain crossover frequency is 4.3 kHz and the phase margin is 44.3.
The degree and gain margin are 15 dB. The phase margin is
The difference between the phase at the frequency (4.3 kHz) corresponding to the gain of 0 dB (see the lower graph in FIG. 5) and -180 degrees (phase) is referred to as the gain margin. It refers to the difference between the gain at the time of FIG. 5 and the gain of 0 dB.

The characteristics of the inertia delay compensating means 534 are as follows. For the purpose of this description, the acceleration sensitivity of the coarse actuator, that is, the DC gain of the transfer characteristic from the coarse actuator drive current to the acceleration of the coarse stage is denoted by kAc, the acceleration sensitivity of the fine actuator, that is, the fine actuator drive. The DC gain of the transfer characteristic from the current to the acceleration of the fine stage is represented by the symbol kAf. The acceleration of the coarse stage is calculated from the detected value of the coarse actuator drive current, and the inertia delay compensating means 534 is used in order to use this acceleration as the acceleration feed forward of the fine stage.
Is the gain kAc / kAf.

The response waveform of the access operation using the above technique of the present invention is shown below. 6 to 8 are response waveforms according to the present invention, and FIGS. 9 to 11 are response waveforms of a conventional access control without using acceleration feedforward. Both are 1/3 full stroke access operations. FIG. 6 and FIG. 9 are time responses of the target speed and the light spot moving speed in each case. 7 and 10 show the time response of the speed deviation in each case. 8 and 11 show the waveforms of the course actuator drive current in each case, and the drive force is proportional to this.

In the conventional method, a braking force for deceleration is generated by a speed deviation after the moving speed overshoots the target speed. For this reason, it is necessary to increase the time constant of the low-speed section where the speed decelerates in an exponential manner, which causes an increase in access time. On the other hand, according to the present invention, since the braking force for deceleration is mainly generated by the acceleration feed forward, the speed deviation is always zero. In addition, since the time constant of the exponential function of the low-speed section can be reduced, the access time is reduced by about 30%. Furthermore, by adding a negative acceleration feedforward that acts in the deceleration direction during acceleration, there is no overshoot with respect to the target speed at the start of deceleration. In addition, the maximum speed of the light spot can be made smaller than in the conventional method. In FIG. 6, the target speed during the light spot acceleration (maximum target speed)
And the maximum value of the moving speed of the light spot. This is the effect of the negative acceleration feed forward that acts in the deceleration direction during acceleration. Acceleration in the acceleration direction occurs due to the difference between the target velocity maximum value and the detected light spot moving velocity (subtraction means 51 and velocity deviation amplification means 520).
Since this acceleration balances the negative acceleration feed forward, the acceleration stops, and the speed becomes constant with the speed deviation remaining.

Next, as a second embodiment of the present invention, an optical disk apparatus which realizes an access control system by digital control will be described. This digital control system is designed by converting the access control system of the first embodiment into a discrete time system.

FIG. 12 shows the configuration of the access control system according to the second embodiment of the present invention. The operation of the digital control system will be described with reference to FIG. A description will be given mainly of differences from the first embodiment. The illustrated apparatus includes a coarse stage 21 driven by a coarse actuator 20 and a fine stage 21.
A fine stage 33 driven by the actuator 30 to advance and retreat in the access direction on the course stage 21;
A spring 31 and a damper 32 interposed between the course stage 21 and the fine stage 33 to restrain relative movement in the access direction between the two, a midpoint sensor 34 disposed on the course stage 21, and a laser beam A laser diode 43 that emits, a coupling lens 44 that converts the laser light emitted from the laser diode 43 into parallel rays,
A beam splitter 47 adjacent to the coupling lens 44 on the optical axis, a quarter-wave plate 48 adjacent to the beam splitter 47 on the optical axis,
A rising mirror 42 disposed adjacent to the four-wavelength plate 48 on the optical axis thereof and reflecting the laser beam by bending the direction of the incident laser beam by 90 degrees, and reflected by the rising mirror 42 disposed on the fine stage 33. Objective lens 41 for irradiating light spot 40 on optical disc 40 by converging laser light
A lens 46 disposed adjacent to the beam splitter 47 and having a direction at 90 degrees to the optical axis of the laser beam incident on the beam splitter 47 as an optical axis; and a lens 46 disposed adjacent to and on the optical axis of the lens 46. An A / D converter 630 and a track passage detecting means 570 connected to the output of the two-split photodetector 45 and the two-split photodetector 45, respectively;
The position error signal linearizing means 631 connected to the output side of the converter 630, the remaining track number counting means 571 connected to the output side of the track passage detecting means 570, and the anti-error signal connected to the midpoint sensor 34. Alias filter 621
And A / connected to the anti-alias filter 621.
The data bus 604 connected to each output side of the D converter 622, the A / D converter 622, the remaining track number counting means 571 and the position error signal linearizing means 631, and the input side is connected to the data bus 604. D / A converters 610 and 620
The input side is connected to the output side of the D / A converter 610, and the output side is connected to the coarse actuator connected to the coarse actuator 20.
An actuator drive amplifier 530, an anti-alias filter 611 connected to another output side of the coarse actuator drive amplifier 530, an input side to the output side of the anti-alias filter 611, and an output side to the data bus 604. A / D converter 612 connected, an input side to the output side of the D / A converter 620, an output side to a fine actuator driving amplifier 533 connected to the fine actuator 30, and a data bus 60.
4 (hereinafter referred to as C)
PU) 600, RAM 601, ROM 602,
And an address bus 603 connected to the CPU 600, the RAM 601 and the ROM 602.

CPU 600 executes a program describing a procedure of access control. The algorithm of the access control program will be described later. RAM 601
Is used for temporary storage of variable values and the like when the access control program is executed. ROM 602 is
Constants for access control, such as the target speed profile and the acceleration feed forward profile, are stored in advance, and are used to read out the values when the program is executed. The address bus 603 is connected to the RA
A digital signal line for specifying an address of a desired data area in the M601 or the ROM 602. Data bus 604
Are the CPU 600, the RAM 601 and the ROM 60
2, the D / A converters 610 and 620, the A / D converter 6
12, 622, a signal line for transmitting and receiving digital data to and from the position error signal linearizing means 631 and the remaining track number counting means 571.

The D / A converter 610 is connected to the CPU 600
The digital signal of the control input to the coarse actuator 20 calculated in the above is converted into an analog signal,
It is input to the actuator drive amplifier 530. The A / D converter 612 converts a voltage signal proportional to the coarse actuator drive current into a digital signal,
Supply to 00. The anti-alias filter 611 is
This is an analog filter for preventing a high-frequency component included in a detection signal of a coarse actuator drive current from becoming a low-frequency alias noise due to sampling and adversely affecting access control.

The D / A converter 620 is connected to the CPU 600
The digital signal of the control input to the fine actuator 30 calculated in step (1) is converted into an analog signal and input to the fine actuator driving amplifier 533. A /
The D converter 622 converts the midpoint shift amount detection signal output from the midpoint sensor 34 into a digital signal and supplies the digital signal to the CPU 600. Anti
The alias filter 621 is an analog filter that removes alias noise due to sampling of the midpoint shift amount detection signal.

As described in the first embodiment, the remaining track number counting means 571 outputs the number of tracks remaining up to the target track. This signal is a digital signal, which the CPU 600 takes in. Further, since the tracking error signal (TES) has a sine wave shape, it is converted into an A / D signal.
After sampling by the converter 630, the position error signal linearizing means 631 generates a position error signal linear with respect to the position shift between 1 and the light spot in the rack using the arcsin function. The CPU 600 captures this signal. The above three A / D converters 612, 622, and 630 simultaneously perform sampling at a constant period.

FIGS. 13, 14 and 15 are flowcharts showing the processing procedure of the access control program.
The control algorithm will be described using this. FIG. 13 shows a timer interrupt processing algorithm. The CPU 60
0 executes a control program at a constant period by generating a timer interrupt at the same time as the sampling of the A / D converters 612, 622, and 630 described above. When an interrupt occurs, it is first determined whether the current control mode is access control or tracking control. The access control processing will be described later. Next, processing of the current control mode is executed according to the determination result. After the processing is completed, the process waits until the next timer interrupt.

FIGS. 14 and 15 show the algorithm of the access control process. First, the remaining track number counting means 571
, The data of the number of remaining tracks up to the target track is fetched (141). Next, a linearized position error signal of the light spot in one track is fetched from the position error signal linearizing means 631 (142). Next, a detection signal of the coarse actuator drive current is taken in from the A / D converter 612 (1).
43). Next, a detection signal of the fine stage middle point shift amount is taken in from the A / D converter 622 (144). Next, a target speed corresponding to the number of remaining tracks is read from the ROM 602 and set (145). Next, the position of the light spot with respect to the target track is calculated from the number of remaining tracks and the linearized position error signal (146). Next, the speed of the light spot is calculated (147). This includes
The backward difference method, that is, a method of calculating the difference between the light spot position at the current time and the light spot position one sample before, is the simplest. Alternatively, use of a state estimator that calculates the speed from the light spot position and the coarse actuator drive current detection signal may be considered. Next, a speed deviation, that is, a difference between the target speed and the light spot speed is calculated, and the difference is further integer-multiplied by a loop gain (148). Next, ROM6
From 02, an acceleration feedforward corresponding to the number of remaining tracks is read and set (149).

Next, the control input to the course actuator 20 is calculated by adding the acceleration feedforward to the speed deviation multiplied by an integer by the loop gain (150). Next, the control input is output to the D / A converter 610 (15).
1). Next, the output equation of the midpoint deviation compensating means is calculated (152). Next, the value (kAc / kAf) of the inertia delay compensation means is calculated from the coarse actuator drive current detection signal (153). Next, the control input to the fine actuator is calculated by adding the value of the inertia delay compensating means to the output of the midpoint deviation compensating means (154). Next, the control input is output to the D / A converter 620 (155).
Next, if the light spot velocity detecting means has a state equation like a state estimator, the state equation is calculated (156). Next, the state equation of the midpoint deviation compensating means is calculated (157).

As described above, the calculation order of the dynamic control elements is as follows: first, an output equation is calculated, its value is output via a D / A converter, and then a state equation is calculated. By performing the calculation in such a procedure, it is possible to reduce the dead time due to the calculation and prevent a decrease in the stability of the digital control system. When the above process is completed, the process returns to the timer interrupt process (158).

The output equation and the state equation of the above-mentioned midpoint shift compensating means used in this digital control algorithm are derived as follows. First, the transfer function of the phase compensator of Expression 8 is discretized by bilinear transformation to obtain the next pulse transfer function.

[0061]

(Equation 9)

Z is the complex parameter of the z-transform, C (z) is the pulse transfer function of the phase compensator, aD0, aD1, bD
0, bD1, and dD1 are coefficients that define the characteristics of the compensator, and are uniquely determined by bi-linearly transforming equation (8). A state space representation of Equation 9 is used in the above algorithm. As an example, if Equation 9 is expressed in observable canonical form,
The output equation is as follows.

[0063]

(Equation 10)

The state equation is as follows.

[0065]

[Equation 11]

ED (k) is the input to the compensator at the current sample time k, uD (k) is the output of the compensator at the current sample time k, and xD1 (k) and xD2 (k) are the compensations at the current sample time k. Vessel state variables.

In the access control system of digital control, the moving speed of the light spot is detected with a time delay from the actual one. This will be described with reference to FIG. Since the digitally controlled light spot speed detecting means 56 is a discrete time system, there is a detection delay inherent in the detection method. For example, in the backward difference method, the detection delay is 1/2 of the sample period.
In order to prevent a speed deviation due to such a detection delay from occurring, the target speed is generated by delaying the acceleration feedforward by the detection delay. Therefore, a dead time element equal to the detection delay is inserted between the target speed generating means 50 and the subtracting means 51. This dead time element can be realized by a linear element using first-order Paddy approximation. As another method, the target speed profile stored in the target speed generating means can be delayed by the detection delay without using the dead time element.

[0068]

As described above, according to the present invention, when accelerating the access operation, the maximum acceleration is performed by the coarse actuator, and the moving speed of the light spot is determined in advance from the start of the deceleration to the retraction into the target track. Since the target speed is accurately followed, a high-speed and stable access operation becomes possible. Further, even if the access operation is performed at a high speed, the objective lens does not shift due to the inertial delay, so that the light spot can be stably irradiated on the recording surface of the optical disk.

[Brief description of the drawings]

FIG. 1 is a block diagram of an access control system according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing an example of a profile of a target speed applied to the embodiment shown in FIG. 1;

FIG. 3 is a conceptual diagram showing an example of an acceleration feedforward profile applied to the embodiment shown in FIG. 1;

FIG. 4 shows a fine axis of a two-axis orthogonal translation type actuator.
9 is a graph showing an example of a transfer characteristic from an actuator control input to a fine stage displacement.

5 is a graph showing an example of a loop transfer characteristic of the midpoint deviation compensation control system of the embodiment shown in FIG. 1;

FIG. 6 is a graph showing an example of a time response of a target speed and a light spot moving speed in the embodiment shown in FIG. 1;

FIG. 7 is a graph showing an example of a time response of a speed deviation in the embodiment shown in FIG. 1;

FIG. 8 is a graph showing an example of a waveform of a course actuator drive current of the embodiment shown in FIG. 1;

FIG. 9 is a graph showing an example of a time response of a target speed and a light spot moving speed of a conventional access control.

FIG. 10 is a graph showing an example of a time response of a speed deviation of a conventional access control.

FIG. 11 is a graph showing an example of a waveform of a coarse actuator drive current in conventional access control.

FIG. 12 is a block diagram illustrating an access control system according to a second embodiment of the present invention.

FIG. 13 is a flowchart illustrating a timer interrupt processing algorithm according to the second embodiment of this invention.

FIG. 14 is a flowchart illustrating an access control processing algorithm according to the second embodiment of this invention.

FIG. 15 is a flowchart illustrating an access control processing algorithm according to the second embodiment of this invention.

FIG. 16 is a conceptual diagram showing a configuration example of an optical system and an access mechanism of the optical disc device.

FIG. 17 is a block diagram showing a basic configuration of a conventional access control system of the optical disk device.

[Explanation of symbols]

Reference Signs List 10 optical disk 11 disk rotation center 20 course actuator 21 course
Stage 30 Fine actuator 31 Spring 32 Damper 33 Fine stage 34 Midpoint sensor 40 Light spot 41 Objective lens 42 Start-up mirror 43 Laser diode 44 Coupling lens 45 Two-segment photodetector 46 Lens 47 Beam splitter 50 Target speed Generating means 51 Subtracting means 52 Speed deviation compensating means 53 Actuator 54 Light spot moving means 55 Track eccentricity 56 Light spot speed detecting means 500 Acceleration feed forward generating means 501 Adding means 520 Speed deviation amplifying means 530 Course actuator driving amplifier 531 Course actuator 532 Fine actuator drive amplifier 533 Fine actuator 534 Inertia lag compensation means 535 Subtraction means 536 Compensation for midpoint deviation Means 537 Addition means 538 Middle point deviation detection means 540 Course stage 541 Fine stage 570 Track passage detection means 571 Remaining track number detection means 572 Initial value 600 Microprocessor (CPU) 601 Random access memory (RAM) 602 Read only -Memory (ROM) 603 Address bus 604 Data bus 610 D / A converter 611 Anti-alias filter 612 A / D converter 620 D / A
Converter 621 Anti-alias filter 622 A / D
Converter 630 A / D converter 631 Position error signal linearizing means

Claims (7)

[Claims] 1. A fine stage mounted with an objective lens for irradiating a light spot on an optical disk having an information track and moving in a width direction of the information track,
A fine actuator for driving the fine stage, a coarse stage mounted with the fine stage and the fine actuator and moving in the radial direction of the optical disc, and a coarse actuator for driving the coarse stage. An optical disc device comprising: a target speed generating means for generating a target speed of a light spot during an access operation for moving the light spot to a target information track; and a light spot speed for detecting a moving speed of the light spot. Detecting means, subtracting means for subtracting the moving speed from the target speed to calculate a speed deviation, target acceleration generating means for generating a target acceleration of the light spot, and adding the target acceleration to the speed deviation, Adding means for calculating a control input to the coarse actuator; An optical disk device comprising: relative movement control means for suppressing relative movement of the fine stage with respect to the fine stage. 2. The optical disk device according to claim 1, wherein said relative movement control means includes a relative displacement detection means for detecting a relative displacement amount of said fine stage with respect to said coarse stage, and a relative displacement target value. Subtraction means for calculating a position deviation by subtracting the detected relative displacement amount, and feedback compensation operable to suppress the relative displacement and to stabilize the relative motion control means using the position deviation as an input. Means, a feed-forward compensating means for detecting the acceleration of the coarse stage to generate a target acceleration of the fine stage, and adding the output of the feed-forward compensating means to the output of the feedback compensating means. An optical disk device comprising an adding means for calculating a control input to the optical disk. 3. The access control method in an optical disk device according to claim 1, wherein the target speed defines a speed of a constant speed operation and a speed of a deceleration operation after the light spot reaches a maximum speed. And
The access control method according to claim 1, wherein the target acceleration defines acceleration of a constant speed operation and a deceleration operation after the light spot reaches a maximum speed. 4. The access control method in the optical disk device according to claim 1 or 2, or the access control method according to claim 3, wherein the target speed generating unit determines a target speed from a current irradiation position of a light spot. A target speed according to a distance from the current position of the light spot to a target information track, and a target acceleration according to a distance from the current position of the light spot to the target information track. The deceleration operation is a first deceleration section until the light spot reaches a predetermined position before the target information track during the deceleration operation, and reaches the target information track from the predetermined position. And the target speed and the target acceleration are decelerated at a constant acceleration in the first deceleration section. In the second deceleration section, the deceleration is determined so as to gradually approach 0, and at the boundary between the first deceleration section and the second deceleration section, the target speed and the target acceleration are: An access control method characterized by being continuous. 5. The access control method in the optical disk device according to claim 1 or 2, or the access control method according to claim 3, wherein the target speed generation unit determines a target position from a current irradiation position of the light spot. A target speed according to a distance from the current position of the light spot to a target information track, and a target acceleration according to a distance from the current position of the light spot to the target information track. The deceleration operation is a first deceleration section until the light spot reaches a predetermined position before the target information track during the deceleration operation, and reaches the target information track from the predetermined position. And a second deceleration section up to the target speed, and the target speed is a target information track of the light spot in the first deceleration section. In the second deceleration section, it is a substantially linear function of the distance of the light spot to the target information track, and the first deceleration section and the second deceleration The access control method according to claim 1, wherein the target speed and the target acceleration are continuous at a boundary between the sections. 6. The access control method in the optical disk device according to claim 1 or 2, or the access control method according to any one of claims 3 to 5, wherein the target acceleration generating means performs a light spot acceleration operation. An access control method characterized in that a target acceleration acting in a deceleration direction is generated even during middle or constant speed operation. 7. The access control method for an optical disk device according to claim 1 or 2, or the access control method according to any one of claims 3 to 6, wherein: The access control method, wherein the target speed is generated with a time delay with respect to the target acceleration.