JP2778094B2 - Optical disk tracking method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking method for an optical disk, and more particularly, to a light beam tracking method for controlling two actuators so that a light beam follows an information track.

[Conventional technology]

Some optical information recording and / or reproducing apparatuses using an optical disk use a separation type optical head.

The separation type optical head employs a configuration in which a condensing means for condensing a light beam on a recording medium is placed on a moving member, and a light source and an optical position error detecting means are placed on a fixed member. FIG. 4 shows an example of the configuration of the separation type optical head. The separation type optical head shown in FIG. 4 includes a light source for a recording / reproducing light beam 10, extracts information from the recording medium 11, and optically detects a relative position error between the light beam 10 and the recording medium 11. The optical system 12 is arranged on the fixed part 13. On the other hand, a focusing unit 14 for focusing the light beam 10 on the recording medium 11, a rising mirror 15, and a focus actuator 17 for moving the focusing unit 14 in the focal direction 16 include:
It is arranged on the movable part 19 of the positioner actuator 18,
The light beam 10 is moved over the entire range of the recording / reproducing area on the recording medium 11 by moving the entire movable portion 19 in the tracking direction 20 by the positioner actuator 18. In FIG. 4, reference numeral 21a denotes a mirror for reflecting the light beam 10, and reference numeral 6 denotes a tracking position error signal.

The light beam 10 is moved by the positioner actuator 18 in this manner, but the light beam
In an optical information recording / reproducing device that performs recording / reproducing according to 10,
In order to increase the density, it is required that the light beam 10 follow the information track with a required accuracy, for example, an accuracy of 0.1 μm or less. In this case, a tracking servo band of 1 kHz or less is required. Required. When it is desired to secure such a tracking servo band, the above-described method using only the positioner actuator 18 that moves the light beam 10 over the entire recording area, that is, a method using only the positioner actuator 18 is not sufficient. It is difficult to realize such a wide-band servo system due to mechanical characteristics.

On the other hand, as another method for moving the position of the light beam 10 on the recording medium 11, a method using a galvanomirror is known. FIG. 5 shows a method of moving a light beam by a galvanomirror. The principle of light beam movement by the galvanomirror actuator can be explained as follows.

That is, in FIG. 5, when the galvanomirror 21 for reflecting the incident light B is rotated clockwise by θ in the figure,
The light beam reflected by the galvanometer mirror 21 is reflected with the optical axis 23 inclined by 2θ from a reference position passing through the lens center 0 indicated by a broken line 24. For this reason, the light beam reflected by the rising mirror 15 and the objective lens used as a focusing means
The inclination of the optical axis 23 of the light beam with respect to 22 changes by 2θ,
As shown in the figure, the position of the light beam 10 on the recording medium 11 is
It moves by a fixed distance dx determined by the inclination of the optical axis of the light beam 10 and the focal length f of the objective lens 22. A galvanomirror actuator that drives such a galvanomirror 21
25 can be manufactured with good characteristics by the conventional technique, but as shown in FIG. 5, the inclination of the optical axis 23 of the light beam causes the optical axis 23 to move from the reference position (broken line 24). Due to the influence of the displacement and the influence of the aberration characteristics of the objective lens 22,
The inclination allowed for the optical axis 23 is limited, and thereby the moving distance dx of the light beam 10 on the recording medium 11 is limited.

Therefore, from such a point, as the conventional tracking servo method, the following documents, namely, Shimizu, and others:
"5.25-inch magneto-optical disk unit, average access time
Less than 50ms ”Nikkei Electronics, April 18, 1988 (No.45
5) As shown in PP. 211 to 224, a method of cooperatively controlling the positioner actuator 18 as shown in FIG. 4 and the galvano mirror actuator 25 as shown in FIG. 5 is known. I have.

In the above-mentioned reference, a rotary swing arm actuator is used as an actuator for moving the light beam over the entire range of the recording / reproducing area. However, in order to avoid confusion, this term is used as a positioner actuator. I do.

FIG. 6 shows a block diagram for realizing a conventional tracking method when the two actuators described above are controlled in a coordinated manner. In FIG. 6 showing the configuration of a conventional servo system, reference numeral 5 is a signal indicating the position of an information track, reference numeral 7 is a signal indicating the position of a light beam, and tracking signals obtained based on the signals 5, 7 are obtained. Position error signal 6
Is first applied to the phase compensation filter 30. The output obtained through the phase compensation filter 30 is output to the low-pass filter 3
1, given to the high-pass filter 32, respectively, the positioner actuator 18, the galvanomirror actuator 25
Is input to

In FIG. 6, when the open loop gain of the tracking servo system is considered to be included in the characteristics of each of the actuators 18 and 25, the characteristics of each element after the phase compensation filter 30 are as follows: It is represented by a function G _L , a high-pass filter transfer function G _H , a positioner actuator transfer function G _P, and a galvanomirror actuator transfer function G _G.

Here, omega _X cut-off frequency, the omega _N shows the servo band.

Assuming that the transfer function of the portion surrounded by the broken line 33 in FIG. 6 is Ga, Ga is expressed as follows using the above equations.

That is, Next, equivalent characteristics and a single actuator, which corresponds to the servo band omega _N is obtained.

This will be briefly described with reference to FIG.

FIG. 7 shows the characteristics and the like of the low-pass filter 31 and the high-pass filter 32 in the conventional servo system. The gain characteristics of the low-pass filter 31 and the high-pass filter 32 are the same as those of FIG. Figure (a), it has a characteristic to pass only the low-frequency side, of the high-frequency-side signal to the cut-off frequency omega _X gain curves 35 and 36 shown in (b). With such characteristics, in the tracking servo system shown in FIG. 6, a signal on a lower frequency side than the cut-off frequency ω _X is sent to the positioner actuator 18, and the cut-off frequency ω is sent to the galvanomirror actuator 25. Signals on the higher frequency side than _X are input, and the respective actuators 18 and 25 are driven. At this time, the low-pass filter 3
When the characteristic of 1 and the characteristic of the high-pass filter 32 are added,
As shown in the gain curve 37 shown in FIG. 7 (c), a flat characteristic with respect to the frequency is obtained, and the two actuators 18 and 25 are used to perform the A servo system equivalent to a servo system using a single actuator 34 as shown in FIG. 8 can be realized. That is, FIG. 8 is a diagram showing a configuration of a servo system using a single actuator.
Although the configuration is provided to the single actuator 34 via 30, such a servo system can be realized as an equivalent servo system.

[Problems to be solved by the invention]

However, the conventional one has the following disadvantages. In other words, in the conventional tracking method, the input signal to the actuator is frequency-separated, and the two actuators whose characteristics are complemented are moved in a coordinated manner, thereby enabling design as a single actuator and simplifying the handling of the servo system. However, in the conventional method, however, the number of filters inserted between the tracking position error signal and each actuator is large. As shown in FIG.
Since the phase compensation filter 30, the low-pass filter 31, and the high-pass filter 32 are used, there is a problem that the number of stages of the filter inserted in this way is large and the control system becomes complicated. Because of this, analysis of the control system is not always easy,
There is a problem that it is difficult to improve the characteristics of the control system, such as setting the initial value of the control system at the end of the access operation and improving the transient response.

An object of the present invention is to solve such a problem and provide a tracking system for an optical disk in which a tracking servo system having a simple and easy-to-analyze configuration controls two actuators whose characteristics are complemented to follow an information track with a light beam. Is to do.

[Means for solving the problem]

The present invention controls a first actuator for moving a light beam over the entire area of a recording medium and a second actuator for moving the light beam in a very small area, so that the light beam is moved on the recording medium. In a tracking method for an optical disc positioned on an information track, a tracking position error signal is applied to a first actuator via a low-pass filter, and a tracking position error signal is applied to a second actuator via a high-pass filter. in a first actuator of the high pass filter and a second low-pass filter of the actuator cut-off frequency 3 · ω _N, the transfer function of the first actuator is omega ₁ / s cutlet omega ₁ ² = omega _N ^2/3, each of the actuator transfer function of the second actuator is omega ₂ / s cutlet ^{_{ω 2 2 = 3 · ω N}} 2 Using the data, servo bandwidth ω _N
Wherein the phase compensation effect in the vicinity of the servo band is generated by the second actuator.

[Action]

According to the optical disk tracking method of the present invention, a tracking position error signal can be added to each of the first and second actuators through a low-pass filter and a high-pass filter, respectively. According to the method of the present invention, an input signal to each actuator can be easily analyzed. In addition, the fact that the number of filter stages is smaller than that of the conventional method makes it easy to set the initial value of the filter for the purpose of improving transient characteristics, and also simplifies the configuration of the servo system. This is effective for reducing costs such as adjustment of the servo system compared to the conventional method.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of a tracking system for an optical disk according to the present invention. The tracking system for an optical disk having the configuration shown in FIG. 1 is a separation type optical system in which a focusing means for focusing a light beam on a recording medium is placed on a moving member and a light source and an optical position error detecting means are placed on a fixed member. This is applied to an optical disk tracking system in an optical disk device using a head, and a separation type optical head having a structure basically shown in FIG. 4 can be used.

Therefore, the tracking position error signal 6 in FIG. 1 is detected by, for example, the optical system 12 as shown in FIG. As a method of detecting a position error for obtaining an optical position error by using the signal 5 of the position information of the information track and the signal 7 of the position information of the light beam, specifically, a method such as a push-pull method is well known. The details are omitted here.

The tracking position error signal 6 is applied to the first and second actuators 3 and 4 via the low-pass filter 1 and the high-pass filter 2, respectively. Here, specifically, the first actuator 3 transmits the light beam 10 to a recording medium like the positioner actuator 18 described above with reference to FIG.
11 is an actuator for moving over the entire range of the recording / reproducing area on
For example, the aforementioned galvanomirror actuator 25 (fifth
As shown in the figure, the actuator moves the light beam over a small area on the recording medium 11. In the tracking servo system shown in FIG. 1, the first actuator 3 for moving the light beam over the entire area of the recording medium and the second actuator 4 for moving the light beam in a minute range are used. Each actuator 3, 4
Are coordinated so that the light beam is positioned on the information track on the recording medium. The tracking position error signal is supplied to the first and second actuators 3 and 4 that compensate for such characteristics. 6 is added directly to the low-pass filter 1 and the high-pass filter 2.

That is, in the configuration of the conventional servo system shown in FIG. 6, the tracking position error signal 6 is supplied to the low-pass filter and the high-pass filter by interposing the phase compensation filter 30 therebetween. In FIG. 1, the low-pass filter 3 and the high-pass filter 41 are applied to the first and second actuators 3 and 4, respectively.
The tracking position error signal 6 is added via a stage.

As described above, in the tracking servo system of FIG. 1, the first actuator 3 for moving the light beam over the entire area of the recording medium and the second actuator 4 for moving the light beam in a minute range are controlled in a coordinated manner. Accordingly, in the tracking method of the optical disk in which the light beam is positioned on the information track on the recording medium, the tracking position error signal 6 is applied to the first actuator 3 via the low-pass filter 1, and at the same time, the tracking position error signal 6 Is applied to the second actuator 4 via a high-pass filter, so that the phase compensation effect near the servo band is generated by the second actuator 4, and the number of filters used is smaller than in the conventional method. , The tracking position error signal 6 to the low-pass filter 1 and the high-pass filter 2 First and, by adding directly to the second actuator 3 and 4, the single actuator equivalent servo system is achieved with a simple configuration compared with the conventional method.

That is, in the optical disk tracking system of FIG. 1 according to the present invention, each of the first and second actuators 3 and 4, which complement the characteristics, is provided with one low-pass filter 1 and one high-pass filter 2 respectively. , The tracking position error signal 6 is added thereto, so that the input signals to the actuators 3 and 4 can be easily analyzed in this tracking method. Further, since the number of filter stages is smaller than that of the conventional method, it is easy to set the initial value of the filter for the purpose of improving the transient characteristics, and the configuration of the servo system is simplified. Cost reductions such as servo system adjustment can be achieved. This is based on the following viewpoints. First, in the tracking servo system shown in FIG.
It is assumed that the characteristics are included in the characteristics of the actuators 3 and 4 described above.

In FIG. 1, the transfer functions of the low-pass filter 1, the high-pass filter 2, the first actuator 3, and the second actuator 4 are represented by G _LA , G _HA , G _1A , and G _2A , respectively, as follows: Determined as follows.

Next, the open loop characteristics of the entire tracking servo
Then, Gb is expressed by the following equation from the above equations.

Here, the servo bandwidth of the tracking servo system as _{ω N, ω f = 3 ·} ω N ...... (11) relative to the transfer function of the above-described characteristics of the components ^{_{ω 1 2 = ω N 2/}} 3 ...... (12) ω ₂ ² = 3 · ω _N ² (13), the transfer function Gb of the entire tracking servo band
Is given by applying equations (11) to (13) to equation (10).

From this equation (14), embodiment of the tracking method of the optical disc with the present invention shown in FIG. 1, in the tracking servo system with a single actuator 34 shown in FIG. 8, the servo band and omega _N, and Its phase compensation filter
The servo system 30 has a servo system equivalent to a case where the transfer function G _RL is a lead-lag filter represented by the following equation.

That is, _GRL represented by equation (15) corresponds to the multiplication term on the left side in equation (14), and as indicated by equation (5), dashed line 33 in FIG. The transfer function Ga of the enclosed portion, that is, the portion excluding the phase compensation filter 30 is represented by ω _N / s ² , which is the one that can obtain characteristics equivalent to those of a single actuator corresponding to the servo band ω _N. Since the multiplication term on the right side in the expression (14) is such Ga, that is, ω _N / s ² , Gb in the expression (14)
The tracking servo system of FIG. 1 (actually, a phase compensation filter is not interposed unlike the conventional system) in which the transfer function of the entire tracking servo band is expressed by the following formula is simpler than the conventional system. A servo system including a single actuator can be realized.

 The above equation (14) means this.

Note that the above-described equations (6) to (9) and equations (11) to
From (13), the transfer functions G _LA , G _HA , G _1A , and G _2A are respectively as follows.

Regarding the phase compensation effect in the vicinity of the servo band ω _N , as described later, the high-pass filter 2 is used as the second actuator 4, that is, the actuator that moves the light beam 9 in a minute range. through effective use of the second actuator 4 where the tracking position error signal 6 is applied to, particularly, the effect of the phase compensation for the servo band omega _N is first from the differentiation effect of the high-pass filter 2 2 Can be generated by the actuator 4.

Further, the operation of the first and second actuators 3 and 4 in the embodiment of FIG. 1 will be specifically described with reference to FIGS. 2 and 3 as follows.

FIG. 2 is a diagram showing the open-loop frequency characteristic of the entire tracking servo system, that is, the open-loop characteristic of the servo system when the optical disk tracking method according to the present invention is implemented. 3 shows the gain characteristics and phase characteristics of the above. FIG. 3 shows the open-loop frequency characteristics of the first and second actuators 3 and 4 shown in FIG. 1, that is, the first and second actuators 3 and 4 when the optical disk tracking method of the present invention is implemented. FIG. 4 is a diagram showing an open loop characteristic, wherein curves 42 and 43 show the gain characteristic and the phase characteristic of the first actuator 3, respectively,
4 and 45 are gain characteristics of the second actuator 4, respectively.
The phase characteristic is shown.

The open loop frequency characteristic of the entire servo system shown in FIG.
As described above, the single actuator 34 shown in FIG.
In contrast, a frequency characteristic equivalent to the case where the phase compensation filter 30 is constituted by a lead-lag filter is obtained. In FIG. 3, the characteristic of the first actuator 3 is dominant on the low frequency side from the intersection P where the curves 42 and 44 indicating the gain characteristics of the first and second actuators 3 and 4 intersect. In this case, the characteristics of the second actuator 4 are dominant. In other words, the first actuator 3 operates for a slow large movement, and the second actuator 4 performs a tracking operation for a fine fast movement. For this reason, the mechanical characteristics required for the first actuator 3 are relaxed, and the first actuator 3 that moves the light beam 10 over the entire recording area on the recording medium 11 is easily realized. .

Further, as shown by the gain curve 42 in FIG. 3, the first actuator 3 has the servo band ω _N because the servo band ω _N is lower than the cutoff frequency ω _f of the low-pass filter 1.
_f , the tracking position error signal 6
Is performing a proportional operation. On the other hand, the servo band ω _N
The effect of phase lead compensation on
By applying the tracking position error signal 6 to the second actuator 4 via the high-pass filter 2, the second actuator 4
Generated by

As described above, the tracking position error signal 6 is passed through the low-pass filter 1 and the high-pass
By adding to the second actuators 3 and 4, a servo system equivalent to the single actuator 34 can be realized with a simpler configuration than the conventional system.

As in the conventional method, there is no problem that the number of filters inserted between the tracking position error signal and each actuator is large and the control system becomes complicated, and the initial value of the control system is not changed at the end of the access operation. Can be easily adapted to the improvement of the characteristics of the control system in the case where the transient response is improved by setting the control signal, the configuration is simple, and the analysis of the control system becomes easy.

〔The invention's effect〕

As described above, according to the optical disk tracking method of the present invention, it is possible to make the light beam follow the information track by controlling the two actuators in an emphasized manner by the tracking servo system having a simple configuration. In addition, this makes it easy to analyze the operation of the servo system, and it is also possible to easily calculate the initial value of the servo system.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an optical disk tracking system according to the present invention. FIG. 2 is a diagram showing an example of an open loop characteristic of a servo system when the optical disk tracking system is implemented according to the present invention. FIG. 3 is a diagram showing an example of the open-loop characteristics of the first and second actuators of FIG. 1 when the optical disk tracking method according to the present invention is implemented, and FIG. 4 is also used as the first actuator of the present invention. FIG. 5 is a view showing a configuration of a separation type optical head including a positioner actuator which can be applied. FIG. 5 is a view for explaining the principle of light beam movement by a galvanomirror actuator which can also be applied as a second actuator of the present invention. FIG. 7 is a block diagram showing the configuration of a conventional servo system. FIG. 7 is a low-pass filter and a high-pass filter of the conventional servo system. Shows characteristics of a motor, FIG. 8 is a diagram showing a configuration of a servo system with a single actuator. DESCRIPTION OF SYMBOLS 1 ... Low-pass filter 2 ... High-pass filter 3 ... 1st actuator 4 ... 2nd actuator 6 ... Tracking position error signal 10 ... Light beam 11 ... Recording medium

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein the first actuator for moving the light beam over the entire area of the recording medium and the second actuator for moving the light beam in a very small area are controlled in a coordinated manner so that the light beam is transmitted on the recording medium. A tracking position error signal is applied to a first actuator via a low-pass filter and a tracking position error signal is applied to a second actuator via a high-pass filter. and a first actuator of the high pass filter and the cutoff frequency of the low pass filter of the second actuator 3 · omega _N, the transfer function of the first actuator is omega ₁ / s cutlet omega ₁ ² = omega _N ^2/3, each of actuator transfer function of the second actuator is omega ₂ / s cutlet ^{_{ω 2 2 = 3 · ω N}} 2 Using chromatography data, next servo band omega _N, an optical disk tracking method characterized by causing a phase compensation effect in the vicinity of the servo band is generated by the second actuator.