JPS61177648A - Tracking control system of optical head - Google Patents

Abstract

PURPOSE:To remove a beam shifting with a good follow-up characteristic by interlocking and controlling an actuator and a mirror so that the light shaft of an optical beam deflected by the mirror can always pass the focus at the rear side of the objective lens. CONSTITUTION:An actuator 300 and an actuator 200 are interlocked and the light axis always passes through an objective lens rear focus (P0 and P1). Namely, when an objective lens 2 is shifted from an L1 to an L2, the focus is shifted from 70 to 70', and at such a time, so that the light axis can pass a rear side focus P1, the shifting quantity and the deflecting quantity of the actuator 300 and the actuator 200 are interlocked and controlled. by executing the control, an optical beam always passes the rear side focus of the objective lens 2, the optical beam always returns to the same optical path, and then, the beam shifting is removed. Further, since it is not necessary to the rotating center of the mirror at the rear side focus surface, the mirror can be made small and light, and a response characteristic is also improved.

Description

[Detailed Description of the Invention] [Summary] Using a combination of an actuator that drives and controls an objective lens parallel to the optical disk surface and a mirror that deflects and controls the optical axis of a light beam, the light of the light beam deflected by the mirror is used. The actuator and mirror are controlled in conjunction so that the axis always passes through the rear focal point of the objective lens, making it possible to remove beam shifts with good followability.

[Industrial application field]

The present invention relates to a control method for an actuator used for focusing and tracking light spot control in an optical head of an optical disk device, and in particular, eliminates beam shift in tracking control with high precision and good tracking characteristics. This invention relates to a control method for actuators that can be used.

[Conventional technology]

A conventional control system for the seven actuators will be explained with reference to FIGS. 7 to 9.

The control method shown in Fig. 7 is described in the technical literature 'Natio
nal Technlea R@ptlt' VOl,
29. No.5. oat 1983, ``Optical start-up for compact disc players and its servo,'' and its control will be briefly explained here.

In FIG. 7, 1 is an optical disk, 2.2' is an objective lens, 3 is a magnetic circuit, 4 is a beam splitter, 5 is a two-split photodiode, 6.6' is an optical axis of a light beam,
7.7' is the focal point on the optical disk surface.

This figure shows only the portion of the optical head of the optical disc device that is related to the actuator for controlling the light spot.

In the control system shown in this figure, a two-dimensional drive type actuator is used as the actuator.

This two-dimensional drive type actuator performs two-dimensional drive in the illustrated tiger, king direction T (radial direction of the optical disc 1), and focusing direction F (direction perpendicular to the surface of the optical disc l), and is driven by a magnetic circuit 3. It is empowering.

Now, a light beam having an optical axis 6 emitted from a light beam source (not shown) passes through an objective lens 2 and is focused at a focal point 7.

Then, it is reflected by the optical disk surface and travels backward, and a part of it is reflected by the beam splitter 4 and enters the two-split photodiode.

Here, the reflected light beam is received at the center of the two-split photodiode, and in this state, a track error signal is detected by detecting the difference (A-B) in the intensity distribution of the light beam.

However, when the actuator receives the control signal, it moves the objective lens in the tracking direction T, and the objective lens moves 2' as shown by the dotted line.
When the objective lens moves to the position ■The optical axis of the beam is 6
'.

In such a case, the focus shifts to 7', the light beam that is reflected on the optical disk surface and passes through the beam splitter 4 illuminates the two divided photodiodes A and B as shown by the dotted line, and the amount of light to the photodiodes A and B is There will be a difference. In this state, movement of the light flux (beam shift) occurs in the true tracking error signal, causing an offset in the tracking error signal.

Therefore, in such a control system, even if tracking control is performed normally, the beam cannot always follow the center of the track, and normal track servo cannot be performed.

Next, the conventional control method ('APPLIE
D 0PTIC9'l No, 13. vol, 17.
l, July, 1978'video diak
player optics').

In this figure, 1 to 7 indicate the same parts as in FIG. 8 is a magnetic circuit, 9 is a mirror, P is the center of rotation of the mirror, and C is an arrow indicating the direction of rotation of the mirror. In addition, in this figure, the two-split photodiode 5 shown in FIG.
are omitted, and 6-1 and 6'-1 indicate the optical axes of the light beams in FIG.

The control system shown in this figure has two actuators.

One is a focus actuator that includes a magnetic circuit 3, which moves the objective lens 2 in the focusing direction F.
and performs focusing control.

The other is an actuator comprising a magnetic circuit 8 and a mirror 9, which directs the incident light beam in the track direction (radial direction of the optical disk l).

is deflected to perform tracking control.

That is, the focus actuator receives the focus error signal and performs focusing control, and the track actuator receives the track error signal and drives the magnetic circuit 8 to move the mirror f' 9 along the arrow C around the rotation center P. It rotates to the l position to perform tracking control.

In this control system, when tracking control is performed from the focal point 7 to 7' for a light beam having an optical axis 6-1, the optical axis of the light beam becomes 6'-1. For this reason, the method shown in this figure also has the disadvantage that a beam shift occurs and the track following characteristics deteriorate, similar to the method shown in FIG. 7.

The two control methods described above with reference to FIGS. 7 and 8 are the mainstream of conventional methods.

On the other hand, the method shown in FIG. 9 has been conventionally proposed for the purpose of eliminating the beam shift in these two control methods. (Proceedings of the Japan Society of Applied Physics, April 1983)
7P-X-8, r Image fixed tracking method for optical discs) In this figure, 1, 2, 3. is the same as that shown in Fig. 7, 6-2.6'-2 is the optical axis, 10 is the back focus of the objective lens, 11 is the back focal plane, 12 is the center of rotation,
13 is a mirror, and 14 is a magnetic circuit. Further, the arrow mark indicates the rotation direction of the mirror B, and the arrow mark E indicates the inner peripheral side of the optical disc 1.

In the control system shown in this figure, in order to eliminate beam shift, the center of rotation of the mirror 13 is set at the rear focal plane of the objective lens 2 (including the focal point opposite to the focal point on the surface of the optical disc 1, and The optical axis is controlled so that the optical axis always passes through the rear focal point.

When such control is performed, the optical axis 6'-2 of the optical beam subjected to the laser beam control coincides with the incident optical axis 6-2 by passing through the rear focal point 10, so that the beam shift is eliminated. In the control system shown in this figure, the actuator including the magnetic circuit 3 only performs focusing control in the direction Flζ perpendicular to the surface of the optical disk 1, and does not perform control in the parallel direction.

Further, the movement of the rear focal point due to focusing control can be ignored. This point will be briefly touched on below with specific numerical values.

Assume that in the configuration shown in FIG. 9, the objective lens 2 is moved by Δf in the direction of F for focusing control. In this case, the beam shift amount χ is given by the track eccentricity Δε.

Now, the amount of movement due to one casing control is 100 μm.

Optical disc eccentricity is 300μ 1-15+++ town f34.311111 town, χ-14μ network becomes.

This is approximately 0.003μ as a tracking deviation detection error.
This corresponds to the current situation and is a negligible value.

For reference, in the sense of comparison with the control system of the configuration shown in Figures 7 and 8, tiger and king control (
Fig. 7) and beam shift amounts when tracking control is performed using only the mirror (Fig. 8) are as follows: Only the objective lens (No. 7 wJ)...χ! 2Δg (6
00μm) Mirror only (Figure 8) χ=2t・Δt
/f (2093μ layer).

In principle, this beam shift amount χ becomes χ 0 in the control system shown in FIG.

However, in the control system shown in FIG. 9, the actuator including the mirror 13 magnetic circuit 14 is large and heavy;
The following disadvantages are that the followability of the control speed is poor, and as will be described later, the follow-up range is narrow from the viewpoint of lens aberration, and the accuracy is poor.

[Problem that the invention seeks to solve]

As described above, in the conventional system, a beam shift occurs in principle, and when a configuration in which the beam shift is eliminated, control followability and accuracy deteriorate.

The present invention provides a control method that eliminates these drawbacks.

[Means for solving problems]

FIG. 1 is a diagram for explaining the present invention in detail.

In this figure, l is an optical disk, 2 is an objective lens, 3 is a magnetic circuit, 21 is a mirror, and 22 is a magnetic circuit.

The magnetic circuit 3 constitutes a part of a first actuator 300 that controls the position of the objective lens 2, and
．． The magnetic circuit 22 controls the optical beam deflection of the optical axis 60.

A light beam having an optical axis 60 focuses a light beam 70 on a track of the optical disc 1.

The first actuator controls the position of the objective lens in a direction T parallel to the optical disc surface and a direction F perpendicular to the optical disc surface.

The center of rotation 72 of the mirror 21 constituting the second seven cutter 200 is a focal point P that faces the focal point 70 via the objective lens 2. is set at a position away from the focal plane 71 that includes. What is the preferred setting position?

This is the center position of the mirror 21.

Actuator 1 and actuator 2 work together to perform control so that the optical axis always passes through the rear focal point (Po, P+) of the objective lens.

In other words, for tracking control (when the ζ objective lens is moved to the opposite direction, the focal point moves by 70'Cζ, but
At this time, the movement and deflection amounts of the single actuator 1 and the actuator 2 are controlled in conjunction so that the optical axis passes through the rear focal point P□.

Now, as shown in FIG. 1, the distance between the center of the objective lens 2 and the focal point P0 is defined as the distance j between the Zoy focal point P0 and the reflection point of the mirror.

At this time, the rotation angle of the mirror and the amount of movement of the lens are: When trying to follow the eccentricity ε of the track, the rotation angle of the mirror θ
Then, the amount of movement of the objective lens is j tanθ, so t'' (j + f) tanθ, θ-tan-'
(g/ (j +f>) Therefore, the rotation angle of the mirror is
tan-" (g/(1+f)) The amount of movement of the objective lens may be controlled to be εj/(j+f).

[Effect]

By performing the above-mentioned control, the light beam always passes through the back focus of the objective lens, and the light beam always returns along the same optical path, eliminating beam shift. .

Moreover, since it is not necessary to set the rotation center of the mirror on the rear focal plane, the mirror can be made smaller and lighter, and its response characteristics can be improved.

The table shows a comparison between the conventional example shown in FIG. 9 and the mirror in the configuration of the present invention.

From this table, it can be seen that the shape is smaller, the TL amount is lighter, and the responsiveness is improved.

Another control factor is the problem of lens aberration. Normally, when a light beam is deflected by a mirror, if the deflection angle θ is increased, aberration occurs in the lens.

This limit is θ. Then, the eccentricity followability is f in the case of Fig. 9.
tanθ. is its limit.

However, according to the method of the present invention, θ. The limit value of the eccentricity tracking amount l when applying the restriction is C'+f)tanθ.

Then I tan θ. can only be increased.

If it is f-4.3nma l -20111111, it becomes 1/f-4.6 times, and it is possible to improve the eccentricity followability by 4.6 times.

Furthermore, in the present invention, the influence of movement of the focal point accompanying focusing control can be reduced as follows.

That is, the influence of the focus movement in the control method shown in FIG. 9 is χ-"-child t is -.

If we enter the same parameter value, it becomes χ-3,1μ lock,
The effect of the present invention is 71 times (Cf+l') (4
Can be made smaller (゜5 times).

〔Example〕

FIG. 2 shows an embodiment of the invention.

In this figure, 1. 2. 3. 7, 21, and 22 are the same as those in FIG. 1, 23 is a beam splitter, 24 is a collimating lens, 25 is a light source, and 26 is a 4-split photodiode.

The light beam emitted from the light source 25 is converged by a collimating lens, passes through a beam splitter 23, and is directed to a mirror 21.
The light is polarized by the objective lens 2 and reaches a focal point 701ζ.

The beam reflected by the surface of the optical disk 1 is transmitted through the objective lens 2.
．． A portion of the light is reflected by the beam splitter 23 via the mirror 21 and enters the 4-split photodiode 26 .

The driving force for controlling the objective lens 2 is applied two-dimensionally by the magnetic circuit 3 in the directions T and F shown in the figure.

Now, after the light beam is incident on the four-divided photodiode, the amount of light irradiated by each of the photodiodes A, B, C, and D (therefore, it is controlled by the drive system shown in FIG. 3).

In this book 11nlζ, 31 is a drive circuit for performing electric focusing control, 32 is a focus coil v for focusing control of the magnetic circuit 3, 33 is a mirror drive circuit for driving a mirror, and 34 is a magnetic circuit. 22 mirror coil, 35 and 36 equivalent filter, 37 differential amplifier,
38 is a lens drive circuit, and 39 is a lens moving coil.

The terminal T1 receives a focus error signal represented by (A+D) - (B+C) of the amount of light compared to the photodiodes A, B, C, and D, and the terminal Telζ receives a focus error signal (A+B) - (C).
+D) is input.

The control is as follows.

A track error signal is transmitted through the drive circuit 31, and at the same time as the mirror is moved, the position of the mirror is determined from the mirror coil current through the equivalent filter 35, and with this mirror position as a target value, a current flows through the lens coil. A lens position signal obtained through an equivalent field 36 is obtained, and the lens is driven through a differential amplifier 37.

FIG. 4 shows another embodiment of the present invention, and FIG. 5 shows its drive system. In this figure, 1. 2. 3.70.2122,
23.24.25.26.31, 32.33.34.3
9 is the same as that shown in FIGS. 2 and 3, 27 is a light source, 2
8 is a detector, 41 is a differential amplifier, and 42 is a lens drive circuit.

This figure differs from Figures 2 and 3 in that the mirror position detection system is composed of a light source 27 and a light detector 28, and the output P of the detector 28 shown in Figure 4 is used to detect the mirror position. Detecting a position signal, detecting a lens position signal based on a signal P2 indicating the amount of movement of the lens, and detecting a fifth position signal.
Control is performed by inputting to terminals TPI and TPI in the figure, respectively.

The control operation is similar to that shown in FIGS. 2 and 3.

FIG. 6 is a block diagram of the control system of the present invention, in which reference numeral 51 indicates the transfer function of the mirror, and 52 indicates the transfer function of the lens.

The control operation is as follows.

At point A, the target value (track center) and the track error signal are compared, and the residual difference moves the mirror.
Aiming at the position of the galvano mirror found at point B,
Point D is compared with the position of the lens in the parallel direction, and the lens is driven.

At point 0, the lens and lens movement amounts are added together, and feedback is applied to point A as a tracking error signal.

Note that the target value is input from terminal T, and the output is output from terminal 1.

〔Effect of the invention〕

As described above, the present invention has the advantage of being able to eliminate beam shifts, realizing an optical head with good followability, and improving accuracy.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention. 2 to 6 are detailed explanatory diagrams of the present invention. FIGS. 7 and 8 are explanatory diagrams of conventional examples. In Figure 1, l stands for an optical disc. 2 is the objective lens. 3.22 is a magnetic circuit. 21 is a mirror. Book i;I:11! Reiri ml Shen Ming Tomoe Figure 1 Unexploded Go Lost Man n Sha Ming l Figure 2 Figure 3 Ten Orchard π Flower ν'Js Shumeime 114 Figure Cow IEti Monthly Spring Se L Town/l Eishiq [H Fig. 5 g145 - IFJqt, 1C
≧1 No. 6 Flash at the end of the lawn (g) Fig. 7 Hakabo &/ltLgFI Fig. 8 Conventional method> Explanatory drawing Fig. 9 Procedural amendment form G) % formula % 2. Name of the invention Optical head Tracking control method 3, [Relationship with the corrective person case Patent applicant address 1015 Kamiodanaka, Nakahara-ku, Yozaki City, Kanagawa Prefecture (
522) Name Fujitsu Ltd. 4. Agent postal code 211 5. Date of amendment order May 28, 1985 (shipping date) 6. Number of inventions increased by amendment None 7. Subject of amendment (1) Details The statement on page 18, line 4 of the book is amended as follows. "Figures 7 to 9 are explanatory diagrams of conventional examples."

Claims (1)

[Claims] In an optical head of an optical disc device that focuses a light beam on a track on an optical disc surface, a first actuator (300) drives and controls an objective lens (2) of the optical head in parallel to the optical disc surface; A second actuator (200) for deflection control is provided, and the first focus (70, 7) of the light beam is placed at a predetermined position on the track.
0') and the optical axis of the light beam passes through a second focal point (P_0, P_1) facing each other with the objective lens in between. A tracking control method for an optical head, which is characterized by: