JPS62231429A - Objective lens driver for optical disk - Google Patents

Abstract

PURPOSE:To widen the stable operating range by adopting the mechanism wherein a tracking correction servo based on a position sensor is used for a tracking servo so as to cancel the DC offset of a tracking error. CONSTITUTION:The optical axis of an objectivelens 1 of an objective lens actuator A is kept perpendicular to the face of an optical disk D and an objective lens support 6 supporting the objective lens 1 elastically to a support base 5 being the main body freely slidably in a plane in parallel with the face of an optical disk 5 is provided so as to make the optical disk D movable freely in the radial direction. A position sensor P.S is provided to the objective lens actuator A and the slide change of the objective lens support 6 is picked up. The servo mechanism consists roughly of the tracking servo mechanism 31 at the outside and the inner tracking correction servo mechanism 32, the objective lens 1 is tracked and scanned to the track of the optical disk D in the tracking servo mechanism 31 and the tracking correction servo corrects the tracking scanning of the objective lens 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an objective lens driving device for an optical disc.

Needless to say, in this type of objective lens drive device, in order to extract information recorded on the disk, the objective lens is placed at a position facing the disk, and this objective lens allows the information recorded on the disk to be retrieved at a high density. It is configured to accurately focus a light beam on the track position, which is the formed recording section. Therefore, the objective lens is driven by a tracking servo mechanism so that the light beam can always accurately track and scan the track position.

This tracking servo mechanism uses a push-pull method as a tracking error signal detection method. In this push-pull method, an error signal can be obtained with one beam, and the configuration is very simple as shown in FIG. That is, a bipolar tracking servo error signal can be obtained by simply taking the difference between the beams from the disk D via the objective lens ◯ using a photodetector PD divided into 1/2. As shown in FIG. 5, the intensity distribution of the light that is diffracted and reflected by the pits P formed on the disk D and enters the objective lens O again is different from the pit P and the spot S.
It takes advantage of the fact that it changes depending on the relative position change.

When the positions of the beam spot S and the pit P exactly match as shown in FIG. 7(A), an equal intensity distribution is shown on the left and right sides as shown in FIG. 7(II), but this positional relationship is If there is a shift as shown in (A) in the figure, the left and right intensity distribution becomes asymmetrical as shown in (CB) in Figure 6. Since this asymmetry is reversed depending on the positional relationship between the beam spot S and the pit P, the polarity of the deviation can be determined.

The problem that Akira is trying to solve By the way, if the tracking scan is performed by moving only the lens, the spot S will be located on the photodetector PD.
The tracking error signal will have a DC offset. This has the problem of shifting the positions of the track and the beam, narrowing the range in which stable operation can be achieved.

Furthermore, in order to shorten the access time, the objective lens ◯ is moved at high speed in the radial direction of the optical disc. However, when the system is brought to a sudden stop, vibrations occur, and it takes a considerable amount of time for the vibrations to dampen and stabilize, making it impossible to meet short-term demands.

11''1 Means for Solving the Problems Therefore, the present invention has been made to solve the problems of the prior art, and the objective lens is connected to the track of an optical disk by a tracking servo mechanism using a push-pull method. In an objective lens drive device for an optical disc that performs tracking scanning.

an objective lens holder that maintains the optical axis of the objective lens perpendicular to the surface of the optical disk and elastically supports the objective lens on a main body so as to be slidable in a plane parallel to the surface of the optical disk; an objective lens actuator that is movable in a radial direction; a position sensor that is provided on the objective lens actuator to detect sliding changes of the objective lens holder; and a tracking correction that corrects the tracking scan using a signal from the position sensor. This is an objective lens drive head for optical discs consisting of a servo mechanism.

This invention will be explained below based on the drawings. Figures 1 to 4
The figure shows an embodiment of the present invention.

The objective lens drive device for an optical disk uses a combination of a pair of tracking servo leaf springs 2, 2 and a pair of focus servo leaf springs 3.3 to support the objective lens 1.

In the figure, reference numeral 4 denotes a spring support member, and the respective ends of the pair of tracking servo leaf springs 2, 2 and the pair of focus servo leaf springs 3, 3 are fixed to the spring support member 4 by gluing or the like. It is. The objective lens 1 is supported at the tips of the focus servo leaf springs 3, 3. On the other hand, the tips of the tracking servo leaf springs 2, 2 are fixed to protrusions 5a, 5a provided on the support base 5, respectively 6 Therefore, the spring support member 4 supports the tracking servo leaf springs 2, 2. It is elastically supported by a support base 5, which is the main body, in a slidable manner.

The objective lens 1 is directly connected to the focus servo plate spring 3,
The objective lens holder 6 containing the objective lens 1 is supported by the focus servo leaf springs 3, 3, instead of being supported by the focus servo leaf springs 3, 3. The objective lens holder 6 has track coil bobbins 6a, 6a protruding in the track direction (disc radial direction), and the track coil bobbins 6a, [ia] have tracking coils 7.
At the same time, a focusing coil bobbin 6b is provided protruding downward, and a focusing coil 8 is wound around the focusing coil bobbin 6b. These, objective lens 1, objective lens holder 6, tracking coil 7.
7 and focusing coil 8 to form the objective lens unit U.
It consists of:

A tracking yoke 9 is fixed to the protrusion 5a of the support base 5, and a tracking magnet 10 is attached to the tracking yoke 9. The tracking magnet 10 and the tracking coil 7 are combined to form a tracking servo linear motor V. Furthermore, the support stand 5
Focusing yokes lla, llb and a focusing magnet 12 are buried approximately in the center of the yoke, and these focusing yokes lla, llb, focusing magnet 12, and the focusing coil 8 are combined to form a linear focusing servo. The motor W is omitted.

In order to read the information recorded on the optical disc D,
The laser beam must be focused on the disk surface and trace a track on the disk.

When the focus of the laser beam deviates from the disk surface,
The error signal is detected, and the objective lens unit U is moved by the focus servo linear motor W in the focus direction (direction perpendicular to the disk surface) to the position where the laser beam is focused, that is, to the position where the error signal becomes 0. Ru. In this case, the focus servo leaf springs 3, 3 supporting the objective lens unit U are bent around the ends where the focus servo leaf springs 3, 3 are supported by the spring support member 4, so that the objective lens unit U is bent. Also, the lens unit U is moved in the focus direction. When the focal position of the laser beam deviates from the track, the error signal is detected and the linear motor V for tracking servo
The objective lens unit U is slidably moved in the track direction until the laser beam is located on the track, that is, until the error signal becomes 0. In this case, since the spring support member 4 is supported by the tracking servo leaf springs 2, 2, the tracking servo leaf springs 2, 2 are bent and the spring support member 4 is moved in the vertical direction in FIG. , movement of the objective lens unit U in the track direction is permitted.

Therefore, the objective lens actuator A keeps the optical axis of the objective lens 1 perpendicular to the surface of the optical disc D, and elastically supports the objective lens 1 on the support base 5, which is the main body, so that it can freely slide in a plane parallel to the surface of the optical disc 5. The objective lens holder 6 is movable in the radial direction of the optical disc D.

The PS shown in Figures 1 to 3 is a position sensor.

It is provided in the objective lens actuator A, and detects the sliding change of the objective lens holder 6.

That is, the position sensor PS in this embodiment is composed of a light emitting diode LED, a reflecting member M, and a 172-divided photodetector PD, for example, a light emitting diode LI.
The ED and the 1/2-split photodetector PD are provided on a support base 5, and a reflecting member M is attached to the outside of the objective lens holder 6. Therefore, when the objective lens 1 is subjected to tracking servo and is elastically supported by the tracking servo spring 2 and slides from the neutral position shown in FIG. Provide a signal to subtractor 35 which outputs the position to the lens actuator.

As another example of the position sensor PS, the reflecting member M may be formed as a part of the objective lens holder 6 instead of being made separately, or as shown in FIG. The difference in the light intensity distribution can be made clearer by giving a different reflectance from the rest of the surface.

Next, FIG. 4 is a block diagram of the tracking servo system. This servo mechanism includes a tracking servo mechanism 31 on the outside of Oji and a tracking correction servo mechanism 3 on the inside.
It is composed of 2. The tracking servo mechanism 31 causes the objective lens 1 to perform tracking scanning with respect to the track of the optical disk D, and the tracking correction servo causes the tracking scanning of the objective lens 1 to be corrected. 33 is a photodetector that detects a tracking error using the push-pull method; 34 is a subtractor that creates a tracking error using signals from the two photodetectors 33; and 35 is a signal from the photodetector PD of the position sensor PS. This is a subtracter that outputs the sliding change position of the objective lens holder 6. The output from the subtracter 34 and the output from the subtracter 35 multiplied by an appropriate coefficient by an amplifier 36 are connected to a DC offsetler 37 with a tracking error via a phase compensation circuit 38, a switch 39, and an amplifier 40 to an adder. 41. On the other hand, the output from the subtracter 35 is directly input to the adder 41 in an opposite phase to apply negative feedback via the amplifier 42. The switch 39 is connected to the access voltage generator 43, and is opened from the normally closed state by a signal from the access voltage generator 43 in response to an access command. The adder 41 is connected to a driver 44 that drives the objective lens holder 6, and the output of the driver 44 is input to an objective lens actuator A that moves the objective lens holder 6.

Next, the operation will be explained.

When the optical disc D rotates normally, the focusing servo operates, and a normal signal is reproduced from the optical disc D,
A tracking servo loop is formed when a tracking ON command is received.

In order to read the information of the pit P of the optical disc D by the reading optical system, while tracking and scanning the track, for example, if the beam spot S deviates slightly from the pit P as shown in FIG.
The light intensity distribution differs depending on the photodetector 33, and the subtractor 34
The tracking error is output by Based on this output, the objective lens actuator A is driven by the output of the driver 44 by the outer tracking servo mechanism 31. That is, the objective lens holder 6 is moved by the objective lens 4 due to the deflection of the tracking servo leaf spring 2.
slides a little. With such feedback, the beam spot S is moved from the shifted overlap with the pit P in FIG. 6(A) to the overlap shown in FIG. 7(A).

If there is no offset, it will be a sine wave signal centered on the 0 level as shown in Figure 8, but since it is offset by the DC component, it will change and stabilize including the DC component as shown in Figure 9. become. Therefore, the objective lens actuator A is driven, and the sliding displacement of the objective lens holder 6 is detected by the position sensor PS (for example, FIG. 1, FIG. 2, and FIG. 3). In this position sensor PS, the amount of light received by one of the pair of photodetectors PD increases, the amount of light received by the other decreases, and a signal is generated to cancel the offset.

The light from the light emitting diode LED is reflected by the reflecting member H attached to the outer peripheral surface of the objective lens holder 6 shown in Figs. The slide change position of the body 6 is outputted by a subtracter 35. Another subtracter 37 subtracts the output from the subtracter 35 multiplied by an appropriate coefficient by the amplifier 36 from the output from the subtracter 34, and the phase compensation circuit 38 compensates the phase of this difference. The signal is amplified by an amplifier 40 and input to an adder 41. On the other hand, the output from the subtracter 35 is suitably amplified by an amplifier 42 and similarly input to an adder 41. Based on the result of the adder 41, a drive signal is output from the driver 44 to drive the objective lens actuator A. In this way, tracking correction servo is applied by the tracking correction servo mechanism 32 to eliminate the DC offset and widen the stable operation range.

Further, when accessing, the access voltage generator 43 is caused to generate a voltage according to an access command, and the switch 39
from normally closed to open. Therefore, if no countermeasures are taken in the case of high-speed access and sudden stop, the objective lens actuator A will vibrate greatly as shown by the solid line in FIG. 10. However, in this invention, the vibration of the objective lens holder 6 is detected by the position sensor PS, the pair of photodetectors PD generates a signal to maintain the neutral position, and this signal is input to the subtracter 35. Ru.

The output from the subtracter 35 is amplified by the amplifier 42, inputted to the adder 41 in opposite phase, and fed back to the objective lens actuator A by the driver 44.
Even large vibrations caused by a sudden stop will quickly attenuate as shown by the broken line in FIG.

As described above, according to the present invention, since the tracking servo uses a tracking correction servo based on a position sensor, the DC component of the tracking error that is a problem with the push-pull method tracking servo can be reduced. The offset can be canceled and the stable operation range can be widened. Furthermore, even when access is made, the vibration of the objective lens holder is quickly damped, so access time can be shortened. Normal track servo ON
Sometimes parasitic resonance components can be damped, and unnecessary resonance caused by tracking can be damped.

[Brief explanation of drawings]

FIG. 1 is a plan view of an objective lens drive unit for an optical disk showing an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 1, and FIG. 3 is a schematic diagram showing the objective lens unit. Part perspective view,
Fig. 4 is a block diagram of the tracking servo system, Fig. 5 is a schematic explanatory diagram of the tracking servo using the push-pull method, and Fig. 6 shows the misaligned relationship between the beam spoiler 1~ and the pit and the intensity distribution of the light. Figure 7 is a diagram showing the consistent relationship between the beam spora 1- and pitch 1- and its light intensity distribution, Figure 8 is a diagram showing the tracking error signal, and Figure 9 is a diagram showing the tracking error signal, and Figure 9 includes the DC offset component. FIG. 10 is a diagram illustrating the attenuation of vibration during access. 1... Objective lens 2... Leaf spring for tracking servo 5... Support stand (main body) 6... Objective lens holder PS... Position sensor L [ED... Light emitting diode PD... Photodetector A
...Objective lens actuator M...Reflection member No. 1 - Fig. 2 Fig. 3 Fig. 5 Fig. 6 (A) +8) Fig. 7 (A) Old) Fig. 8 Fig. 9 Fig. 10L3 Procedure Jizuo, January 8, 1986, W.J.? A8. . 1. Indication of the case 1986 Patent Application No. 073614 2. Name of the device Objective lens drive device for optical disks 3. Person making the correction Relationship to the case Patent applicant address 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Issue name (05
2) Asahi Optical Industry Co., Ltd. 4, Agent 103 Telephone 669-4421 Address 1-13-125 Kakigara-cho, Nihonbashi, Chuo-ku, Tokyo Target of amendment Drawing 6, Contents of amendment (1) No. 8 in the drawing 9 and 10 are corrected according to the attached drawings. Figure 8 Figure 9 Figure 10

Claims (1)

[Scope of Claims] In an objective lens drive device for an optical disc, in which an objective lens performs tracking scanning with respect to a track of an optical disc by a tracking servo mechanism using a push-pull method, the optical axis of the objective lens is set perpendicular to the surface of the optical disc. an objective lens actuator having an objective lens holder elastically supporting the objective lens on a main body so that the objective lens can be slid freely in a plane parallel to a plane parallel to a plane of the optical disc, and that is movable in a radial direction of the optical disc; An objective lens drive device for an optical disc, comprising: a position sensor provided on the objective lens actuator to detect sliding changes of the objective lens holder; and a tracking correction servo mechanism that corrects the tracking scan using a signal from the position sensor.