JPH0395732A - Tracking system for optical disk - Google Patents

Abstract

PURPOSE:To realize a stable tracking servo system by forming a single feedback loop in a first actuator. CONSTITUTION:By feeding back an actuator displacement 16 of a first actuator 14 through a gain correcting means 17 and a filter 18, the properties of the first actuator 14 can be apparently changed. As a result, an open loop property can be improved from a tracking control signal 4 until the position of a light beam 20 and the stable tracking servo system can be constituted. Since the properties of the first actuator 14 corrected by the effect of the feedback depend on the property of the feedback loop, the influence of mechanical property fluctuation caused by disturbance such as a temperature change, etc., is hardly received and the stable servo system can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical disc tracking method for positioning a light beam on an information track on an optical disc.

[Conventional technology]

In a separable optical disk device, the high frequency component and the low frequency component of the tracking position error signal are respectively
In addition to the second actuator, a method for cooperatively controlling two actuators is disclosed by SBI Optical Storage Technologies and Applications, No. 899-02 January 1988, "High Speed Accessing Magnetic Optical Disk Drive (SPrE Optical
Storage Technology and App
lications, No. 899-02, Jan
．． 1988+″HighSpeed Accessi
ng Magneto-Optical Disk D
``live'')'' and Nikkei Electronics 1988.
4.18 No. 445pp. 211-224 r5.
25 inch magneto-optical disk device, average access time 50
Disclosed in ``Cut MS''.

In these documents, in the servo system of an optical disk,
A galvanometer mirror actuator is used as the first actuator, and a swing arm actuator is used as the second actuator.

The second actuator includes a Veriscope optical system and
The objective lens is moved generally in the radial direction of the optical disk to move the light beam over the entire recording/reproducing area, and the first actuator rotates the galvano ξ roller to tilt the optical axis of the light beam to move the light beam. It has the function of moving the optical disc in the radial direction within a minute range.

A second beam that moves the light beam over the entire recording and reproducing area.
It is difficult to obtain good mechanical properties that can be used alone in the tracking servo system of an optical disk, which requires a servo band of 1 kHz or more, and the galvanometer mirror actuator, which is the first actuator, has , good mechanical properties are obtained up to high frequency ranges, but if the optical beam is moved significantly by rotating the galvano ξ roller alone, the optical axis of the optical beam reflected from the optical disk will be emitted from the fixed optical system. Since it deviates significantly from the optical axis, signal detection by the fixed optical system is affected.

For this reason, in the conventional technology, the tracking position error signal is distributed to the first and second actuators using a high-pass filter and a low-pass filter, respectively, thereby realizing control that complements the characteristics of the individual actuators.

[Problem to be solved by the invention]

In conventional technology, in order to design good high-frequency characteristics of the galvanomirror actuator, which is the first actuator, if the galvanomirror is supported with a thin leaf spring, etc., the fundamental resonance frequency f due to the structure of the galvanomirror actuator. A resonance with a sharp peak appears. When a galvanometer mirror actuator with such characteristics is used as the first actuator, large vibrations tend to occur in the first actuator at the fundamental resonance frequency f0, and this vibration causes large optical axis deviations, which is a problem to be solved. was there.

Furthermore, even when optical axis misalignment is not a problem, when tracking servo is applied to position the light beam on the track of the optical disk, the fundamental resonance frequency f of the first actuator. The second actuator is driven in the opposite direction of the first actuator to position the light beam on the track, since the vibrations in the first actuator do not decay for a long time.
There was a problem to be solved in that the first actuator and the second actuator moved in opposite directions, reducing the stability of the servo system.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disc tracking method that solves the above problems and makes it possible to realize a stable tracking servo system.

[Means for Solving the Problems] The present invention has a light source for a light beam that performs recording and reproduction on an optical disk, a fixed optical system that detects information signals and servo signals from the optical disk, and a fixed optical system that makes the light beam minute on the optical disk. A separated optical system comprising a first actuator for moving, a movable optical system for focusing a light beam on an information track of an optical disk, and a second actuator for moving the movable optical system over the entire recording and reproducing area of the optical disk. Using a head, the position error between the information track on the optical disk and the light beam is detected as a tracking position error signal, and
By causing the first actuator to follow the high frequency signal of the tracking position error signal and causing the second actuator to follow the low frequency signal of the trunking position error signal, the two actuators are cooperatively controlled to produce a light beam. In the second tracking method for optical discs that performs tracking control, the optically detected tracking position error signal is applied to a high-pass filter and a low-pass filter through a phase compensation filter that improves the closed-loop stability of the entire tracking servo system. generate two control signals,
The control signal output from the low-pass filter is
gain correction means for setting the loop transfer characteristics between the actuators. gain correction means for setting the open-loop transfer characteristic of the first actuator by applying the control signal output from the high-pass filter to the second actuator via an amplification means for driving the actuator; The human power is applied to the first actuator through the amplification means, the displacement of the actuator is detected by the displacement detection means, and the human power is applied to the amplification means corresponding to the first actuator through the filter and the gain correction means. By doing so, a single feedback loop is formed in the first actuator.

According to the present invention, the fundamental resonance frequency of the first actuator is r0, the equivalent feedback band frequency of a single feedback loop for the first actuator is fI, and the tracking position error signal via the phase compensation filter is 2. When f2 is the cutoff frequency of the high-pass filter and low-pass filter that separate the two control signals, and f3 is the servo band frequency of the entire tracking servo system, the following relationship is required: fo < f+ < rz < fz.

[Effect]

According to the optical disk tracking method of the present invention, even when the first actuator is an actuator with sharp resonance characteristics such as a spring support structure, a displacement detection means for detecting the displacement of the first actuator is provided, and the first By configuring a feedback loop for the actuator, an active damping effect can be given to the first actuator, and the characteristics of the entire feedback loop can be designed to be almost flat without using a damping member or the like in the actuator body. .

In addition, since a feedback loop provides a damping effect to the basic resonance characteristics of the first actuator, it suppresses the influence of mechanical characteristic fluctuations caused by external disturbances such as temperature changes, and provides optical disk trunking servo with good characteristics. It becomes possible to control the system.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an optical disc tracking servo device to which an optical disc tracking method according to the present invention is applied.

This tracking servo device has a light source of a light beam that performs recording and reproduction on an optical disk 21, a fixed optical system 1 that detects information signals and servo signals from the optical disk, and a first optical system that moves the light beam minutely on the optical disk. actuator 14 is installed on a fixed part of the optical disc device, and a movable optical system consisting of a focusing means 25 for focusing the light beam 20 onto the information track of the optical disc 21 and a periscope optical system 19; Using a separate optical head equipped with a second actuator 11 that moves over the entire recording/reproducing area of the optical disk 21, the position error between the information track on the optical disk and the light beam is detected as a tracking position error signal, and the first The actuator 14 is made to follow the high frequency component of the tracking position error signal, and the second
By making the actuator 1l follow the low frequency component of the tracking position error signal, the two actuators 11. An optical disc tracking method is adopted in which optical beam tracking is controlled by controlling the optical disc 14 in a coordinated manner.

This tracking method further adds two optically detected tracking position error signals to a high-pass filter 5 and a low-pass filter 6 via a phase compensation filter 3 that improves closed-loop stability for the entire tracking servo system. A gain correction stage 9 for generating a control signal and applying the control signal output from the low-pass filter 6 to set an open loop transfer characteristic of the second actuator 11; and an amplification means 10 for driving the second actuator 11. gain correction means 12 for setting a loop transfer characteristic between the control signal outputted from the high-pass filter 5 and the first actuator 14; the first actuator 14 via the amplifying means 13;
In addition, the actuator displacement with respect to the first actuator 14 is detected by the displacement detection means 15, and the filter 17, the gain correction means . 18 to the amplifying means 13 corresponding to the first actuator 14, thereby providing a single feedbank loop for the first actuator.

Next, the operation of this embodiment will be explained. In the following explanation, the fundamental resonance frequency of the first actuator 14 is
, the equivalent feedback band frequency of a single feedback loop for the first actuator is rI,
It is assumed that the cutoff frequency of the high-pass filter 5 and low-pass filter 6 that divide the trunking position error signal passed through the phase compensation filter 3 into two control signals is r2, and the servo band frequency of the entire trunking servo system is -f.

A tracking position error signal 2 optically detected from a fixed optical system 1 in a separated optical head is passed through a phase compensation filter 3 corresponding to a tracking servo band frequency f, and then sent to a high-pass filter 5 as a tracking control signal 4.
and is input to the low-pass filter 6. The control signal 8 that has passed through the low-pass filter 6 is input to the second actuator 11 via the 1,000-stage gain correction 9 and the amplification means 10.

On the other hand, the control signal 7 that has passed through the high-pass filter 5 is applied to the human power of the first actuator 14 via a thousand stages of gain correction 12 and a thousand stages of amplification l3. At this time, the actuator displacement 16 of the first actuator 14 is detected by the displacement detection means 15 and fed back to the human power of the first actuator l4 via the filter 17, the gain correction means 18, and the amplification means 13.

The second actuator {1 is the Veriscope optical system 19
, the light beam 20 is moved over the entire recording area of the optical disc 21 by driving the condensing means 25. In the tracking servo system shown in FIG.
actuator 14. Trunking servo operation is realized by cooperatively controlling 11.

Here, the effectiveness of the optical disc tracking method according to the present invention will be explained. FIG. 2(b) shows the independent transfer characteristic when a galvanometer mirror with a structure such as a spring support is used as the first actuator 14 on the curve 30 of FIG. 2(a).
) shows the transfer characteristics of the second actuator 11 alone for moving the light beam over the entire recording/reproducing area, including the gain corresponding to the servo band frequency f of the entire tracking servo system. Figure 2(a)
, (b), the first actuator 14 exhibits good transfer characteristics even in the high frequency range, but the fundamental resonance frequency 10 is high, and the resonance frequency fo is 25 to 40.
A large gain peak of about dB appears.

As shown in FIG. 1, similarly to the prior art, a first-order high-pass filter 5 and a first-order low-pass filter 6, whose gain curves intersect at the cutoff frequency f2, are used to convert the tracking control signal 4 to the control signal 7.8. and generates the first and second actuators 14. 11, the transfer characteristic of the control signal 7 passing through the bypass filter 5 is shown by a curve 32 in FIG. 3, and the transfer characteristic of the control signal 8 passing through the low-pass filter 6 is shown by a curve 33 in FIG. , it can be seen from FIG. 3 that at frequencies lower than the cant-off frequency f2, the control signal 8 input to the second actuator 11 via the low-pass filter 6 is large, and at frequencies higher than the cant-off frequency f2, the control signal 8 is input to the first actuator via the high-pass filter 5. It is shown that the magnitude of the control signal 7 inputted to 14 is large.

A curve 34 in FIG. 4 shows the open-loop transfer characteristic from the tracking control signal 4 to the position of the light beam 20, including the characteristics of the high-pass filter 5 and the low-pass filter 6. In FIG. 4, a broken line 35 indicates the transmission characteristic of the light beam 20 to the position of the first actuator 14 alone;
6 shows the transfer characteristic of the second actuator 11 alone. In FIG. 4, the solid line 34 indicates that the gain for the second actuator 11 is large on the lower frequency side than the cutoff frequency f2 with respect to the gain characteristics of the entire servo system, except for the vicinity of the fundamental frequency f0 of the first actuator 14. It is shown that the second actuator 11 moves dominantly in the figure, and the first actuator 14 similarly moves dominantly on the higher frequency side than the cutoff frequency f2.

However, the fundamental resonant frequency f of the first actuator 14
. Near the frequency f0, the gain of the first actuator 14 is larger than the gain of the second actuator 11 despite fo<fz, and the first actuator 14 moves dominantly near the frequency f0. Therefore, as described above, a problem arises due to the fundamental resonance of the first actuator l4.

? Here, the effect of the feedback loop on the first actuator 14 in the optical disc device shown in FIG. 1 will be described. The detection gain of the trunking position error signal 2 output from the fixed optical system 1 is set to 1, and the high pass filter 50
Assuming that the gain for the passband is 1, the detection gain of the actuator displacement 16 of the displacement detection means 15 is 1, and the transfer characteristic for the displacement of the light beam 20 on the optical disk 21 due to the displacement of the first actuator 14 is 1. ,
The vicinity of the first actuator 14 after the high-pass filter 5 can be expressed in an equivalent block diagram as shown in FIG. 5(a). In FIG. 5(a), considering the tracking servo band frequency f, the transfer characteristic of the gain correction means 12 is determined as Gg. , the transfer characteristic of the amplification means 13 is G
all1, the transfer characteristic of the first actuator 14 is G
act, the transfer characteristic of the gain correction means 17 is G9■, the transfer characteristic of the filter 18 is Gt, the transfer characteristic G lsp of the amplifying means 13 is G map -K a .
(1), what are the main points of the block diagram shown in FIG. 5(a)? As an example of the transfer characteristic, the following transfer characteristic can be determined.

G■ =ω:+”/(K■・ω.')...
(2)G. ct=ωo”/(s”+2・ξ
・ω.・S ten ω. ′)...(3) G9■ =ω,”/ (K.・ω.′)...
・(4) Gr = (3 ・s+ω+) / (s
+ 3 ・ω+)・ ・ ・(5) (However, ω.=f0/2・π ω,=f,/2 ・π ω2 = f z/ 2 ・π ω3 = r */ 2 ・π ξ is Attenuation constant at the fundamental resonance frequency of the first actuator) In FIG. 5(a), the transmission characteristic G1 ignoring the feedback loop from the control signal 7 to the first actuator l4 is (1)2 to (3) By the formula, G,=ω,27
(s2+2·ξ·ω.·S+ω.′)····(6) This is equivalent to the characteristic of the first actuator 14 according to the prior art shown in FIG. 2(a).

(4L (5) When the characteristics of the 1,000 stages of gain correction l7 and the filter 18 are determined as shown in 2, FIG.
As shown in Figure (b), it can be rewritten by the equivalent gain correction means 22, the 1,000-stage equivalent actuator 23, and the filter 18, and the transfer characteristics of the equivalent gain correction means 22 and the 1,000-stage equivalent actuator 23 can be changed to GX and Gy, respectively.
Then, Cκ-ω32/ωI2...
(7) Gy = ω1” / (s 2+ 2 ・ξ・
ωo − s + (1). ”)・・・・(8)

Ignoring the control signal 7, the feedback node loop shown in FIG. 5(b) is
For the actuator 14 of , a feedback loop of band f is equivalently established. At this time, Figure 5 (
In b), considering the effect of the 1,000-stage equivalent gain correction 22 on the control signal 7, the transfer characteristic of the first actuator is obtained as shown by the curve 41 in FIG.

As shown here, in the optical disk tracking servo device shown in FIG.
The actuator displacement 16 of the gain correction means 17. By feeding back through filter 18, the first
The apparent characteristics of the actuator 14 are shown by the broken line 4 in FIG.
0 to 0 as shown by the curve 41 in FIG. As a result, the open loop transfer characteristic from the tracking control signal 4 to the position of the light beam 20 can be improved as shown by the curve 42 in FIG. 7, and the broken line 43 in FIG. 44
the first and second actuators 14. from the trunking control signal 4 to the position of the light beam 20, respectively. As shown in the transfer characteristics of 11, the first
By suppressing the gain peak at the fundamental resonance frequency f0 of the actuator 14, it becomes possible to maintain a stable tracking servo system.

Furthermore, as shown in FIG. 6, the characteristics of the first actuator 14 corrected by the effect of the feed hack are
Since it depends on the characteristics of the feedback loop shown in Figures (a) and (b), it is possible to realize a stable servo system that is less susceptible to changes in mechanical characteristics due to disturbances such as temperature changes.

Here, f o, f +, when implementing the present invention
Considering the relationship between fZ and r3, as in the past, the movement of the light beam in the high frequency region within the tracking servo band is controlled by the first actuator, and the movement of the light beam in the low frequency region is controlled by the second actuator. Since the control is performed by the actuator 11, a relationship of fZ < f3 is obtained between the cutoff frequency f2 of the high-pass filter 5 and the low-pass filter 6 and the servo band frequency f3 of the entire trunking servo system. Moreover, the band frequency r1 of the feedback system shown in FIG. 5 with respect to the fundamental resonance frequency f0 of the first actuator l4 is fo < f. Since the effect of improving the characteristics of the first actuator 14 is obtained when r
The relationship o < fl is obtained. Further, as shown in FIG. 7, in order to obtain the characteristics of the entire tracking servo system similar to those of a single actuator, the relationship fI<fz is required, and the relationship f,<f2 is obtained.

To summarize the above, in order to realize the tracking servo system according to the present invention, f. , f,, f2, and f3 are required to have the following relationships: fQ < f, < f2 < (3).

In the embodiment shown in FIG. 1, a swing arm actuator shown in the prior art is used as the second actuator, but the present invention is not particularly limited to the arrangement of the first and second actuators. It is also effective when a direct-acting actuator is used as the first actuator.

(Effects of the Invention) As described above, according to the present invention, in a tracking servo system that moves two actuators in a coordinated manner,
The first one follows the high frequency signal of the tracking position error signal.
Even if the actuator has mechanical resonance with a steep gain peak, the mechanical resonance can be suppressed without providing a damper member to the actuator, making it possible to realize a stable servo system that is less susceptible to temperature changes.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an optical disc tracking servo device implementing the optical disc tracking method 2 of the present invention, Fig. 2 is a diagram illustrating the transfer characteristics of the first and second actuators, and Fig. 3 is a low-pass filter. ．． FIG. 4 is a diagram illustrating the transfer characteristics of the tracking control signal that has passed through the high-pass filter. FIG. 5 is a block diagram equivalently showing the transfer characteristics of an embodiment of feedback to the first actuator according to the present invention; FIG. 7 is a diagram illustrating the effect of feedback on the first actuator according to the present invention, and FIG. 7 is a diagram illustrating a transfer characteristic that combines the characteristics of the first and second actuators according to the present invention. 2 ・ 5 ・ 6 ・ 11 ・ 14 ・ 15 ・ 20 ・ 42 ・

Claims (2)

[Claims] (1) A fixed optical system that has a light source for a light beam that performs recording and reproduction on an optical disk, and that detects information signals and servo signals from the optical disk, a first actuator that minutely moves the light beam on the optical disk, and a light beam. using a separate optical head comprising a movable optical system for condensing light onto an information track of an optical disc, and a second actuator for moving the movable optical system over the entire recording/reproducing area of the optical disc;
The position error between the information track on the optical disk and the light beam is detected as a tracking position error signal, and the first
A second actuator is made to follow the high frequency component of the tracking position error signal, and a second actuator is made to follow the low frequency component of the tracking position error signal, thereby cooperatively controlling the two actuators to perform tracking control of the light beam. In an optical disk tracking method, two control signals are generated by applying an optically detected tracking position error signal to a high-pass filter and a low-pass filter via a phase compensation filter that improves closed-loop stability for the entire tracking servo system. ,
The control signal output from the low-pass filter is
gain correction means for setting an open-loop transfer characteristic of the actuator, and amplification means for driving the actuator to the second actuator, and the control signal output from the high-pass filter is transmitted to the first actuator in an open-loop manner. is applied to the first actuator via a gain correction means for setting characteristics and an amplification means for driving the actuator, and a displacement detection means detects actuator displacement with respect to the first actuator, and a filter and a gain correction means are applied to the first actuator. A tracking method for an optical disc, characterized in that a single feedback loop is formed in the first actuator by inputting the input to the amplifying means corresponding to the first actuator through the amplification means. (2) In the optical disc tracking servo system according to claim 1, the fundamental resonance frequency of the first actuator is f_0, and the first
f_1 is the equivalent feedback band frequency of a single feedback loop for the actuator, a high-pass filter that divides the tracking position error signal via the phase compensation filter into two control signals, f_2 is the cutoff frequency of the low-pass filter, and tracking servo system. A tracking method for an optical disc characterized by having the following relationship: f_0<f_1<f_2<f_3, where f_3 is the overall servo band frequency.