JPS60136924A - Objective lens driver - Google Patents

Abstract

PURPOSE:To decrease a read error, to improve the S/N and to speed up the read time by adopting the structure that the twist rigidity of the entire elastic support member of a lens system is increased and the generation of an asymmetrical or inverse symmetical mode is suppressed to decrease excessive vibration. CONSTITUTION:The plate width of two plate springs 20a at the upper side of the plate springs 20a, 20b displacing an objective lens 12 only in the automatic focus direction is taken large, a gap narrower than the plate spring width is formed between the plate springs so as to connect the plate springs with a flexible member 22 made of a rubber or the like. That is, if one plate spring tends to move upward or downward, the vibration is attenuated by the flexible member 22 and a force is delivered to the other plate spring. Thus, the deforming state of the plate springs is uniformed for the left and right parts so as to suppress the asymmetrical mode and the inverse symmetrical mode and also generate the damping effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an apparatus for reading out information by focusing light on minute information recording portions recorded on concentric or spiral tracks on a disk, and in particular for an apparatus for reading information from the same disk. The present invention relates to an optical information reading device that can read information with less noise from portions of upper tracks having significantly different radii.

[Background of the invention]

Optical recording is performed on a disc or a sticker on a disk in a size of around 1 micron, and the phase or amplitude of this part (called a pit) is made different from other parts to record all video signals and digital information. It is already well known that regeneration technology has been developed.

FIG. 1 shows the basic structure of this type of optical information reading device. 1 is an optical information recording medium in which information is recorded concentrically or spirally around a certain point at approximately the same density. 2 is an information medium drive mechanism for reading, and 3 is a pit from which information is about to be read. 4 is an optical means for reading information from the pit, such as an objective lens; 5 is an automatic focusing drive mechanism that focuses the light irradiated through the objective lens 4 onto the pit surface; and 6 is an objective lens. 1 is a supporting ring spring, a VFi adjuster, 8 is a lens, 9 is a light source such as a laser, and 10 is an actuator that drives the objective lens 4 in a direction perpendicular to the track 3 and moves it to another track.

The beam irradiated from the light source 9 passes through the lens 8 and the objective lens 4.
and a polarizer 7, the information medium 1
The laser beam is focused and irradiated onto minute recording portions (pits) lined up on track 3. Next, the diffracted light reflected (or transmitted) by the pit is read out by the optical information reproducing means 11.

Reproduction is performed as described above, but the focused light must first be moved to the desired pit. That is, the actuator 1° is used in the track direction, and the automatic focusing drive mechanism 5t is used in the focusing direction. An example of an MD device for such an objective lens is the
As disclosed in Japanese Patent No. 2030, there is a structure in which the objective lens system is supported using a leaf spring that displaces only in the autofocus direction and a leaf spring that displaces only in the tracking direction. Figure 2 shows its structure. As shown in FIG. 2, the objective lens system 12 is supported by a fixed support member 13, four leaf springs 14 that are displaced only in the autofocus direction, and four leaf springs 15 that are displaced only in the tracking direction. has been done. The objective lens system 12 includes an automatic focusing drive mechanism consisting of a magnet provided on the fixed side and a drive coil 16 provided on the movable side, and a drive mechanism consisting of a magnet provided on the fixed side and a drive coil 16 provided on the movable side. It is driven in the multifocal direction and the tracking direction by a tracking drive mechanism consisting of A-17. The intermediate holder 18 is connected to this drive and the leaf spring 14
It functions to separate the direction in which the plate spring 15 moves. Among the members constituting this drive mechanism, the leaf springs 14 and 1
5 requires free movement in two directions, so it needs to be very flexible. For this reason, the leaf springs 14 and 15 are made of a spring material such as copper, and are extremely thin at 50 to 100 μm. This plate spring 14.15 is therefore
It already has a plate bending resonance point at several hundred Hz, and its modes are very complex, including a mode that causes the lens to vibrate minutely in the tracking direction. In order to suppress the vibration, conventionally, for example, a thin rubber sheet is pasted on the surface of the plate springs 14 and 15.

That is, when the automatic focus drive mechanism is used to perform automatic focusing on the pit portion and the objective lens system 12 is driven, the leaf springs 14 and 15 are excited by the force, and the objective lens system 12 is moved in the above-mentioned tracking direction. It will begin to vibrate at a minute vibration frequency. As a result, the pits were not irradiated with well-focused light, resulting in a bladder ejection error and a decrease in the S/N ratio.

[@Ming's purpose]

The present invention has been made based on the above-mentioned problem.When an objective lens is driven in the focusing direction for automatic focusing or in the tracking direction, extra vibrations occur in the automatic focusing direction or in the tracking direction. The purpose is to reduce the readout error, improve the S/N ratio, and increase the readout time.

[Summary of the invention]

When a leaf spring is used as an elastic support member for supporting an objective lens system, the characteristics required of the leaf spring are summarized as follows. In other words, in order to focus on the bit surface of the disk, it follows the ridges in the out-of-plane direction of the disk.
It should also have a similar degree of freedom (flexibility) in the tracking direction (radial direction of the disk), and it should generate as little unnecessary vibration as possible when driven in the autofocus direction or tracking direction. (Because there is a risk that force cannot be fully controlled as a disturbance factor when automatic control is used.) Furthermore, it should not be damaged or bent even after long periods of use.

As a result of investigation, it has become clear that in the leaf spring shape shown in FIG. 2, the mode of microvibration in the tracking direction is mainly an asymmetric mode or an antisymmetric mode with respect to the horizontal or vertical direction of the leaf spring. Therefore, a component that causes the objective lens system as a whole to be twisted relative to the fixed support member is generated, which results in minute vibrations in the tracking direction. Therefore, in the present invention,
The elastic support member of the lens system is characterized by having a structure that increases the screw rigidity as a whole and suppresses the occurrence of asymmetric or antisymmetric modes.

[Embodiments of the invention]

Embodiments of the objective lens driving device of the present invention are shown in FIGS.
This will be explained with reference to FIG.

FIG. 3 is a diagram showing a support structure for supporting an objective lens system in an embodiment of the objective lens driving device of the present invention.

Although not shown, the objective lens system 12 includes a drive coil that is disposed in a magnetic circuit and constitutes a drive mechanism for driving in the focal direction, and an MA drive that constitutes a drive mechanism for IKwJ in the tracking direction. It is fixed to the upper part of the driven member 19 including the coil.

The objective lens 12fr includes a driven member 19 having two upper and two lower elastic support members, for example, plate blades 20a, which are displaced only in the autofocus direction by the fixed support member 13.

20b and two left and right elastic members, for example, leaf springs 21, which are displaced only in the tracking direction.

18 is an intermediate holder that holds leaf springs 2Qa, 20b and leaf spring 21.
The function is to separate the direction of movement of the

In the above-mentioned leaf springs that are displaced only in the autofocus direction, the width of at least the upper two leaf springs 20a is larger than that in the conventional structure shown in FIG. A space is formed that is narrower than the width of the leaf spring. In this narrow space, the upper plates are connected to each other by a flexible member 22 made of rubber or the like.

FIG. 4 is a diagram showing a support structure in another example of the present invention. In this example, the width of the upper and lower leaf springs 20a and 20b, which are displaced only in the autofocus direction, is the same as that shown in FIG. It is similar to the example.

As shown in the conditions required for leaf springs, this leaf spring needs to be extremely soft, but in order to suppress extra minute vibrations, the stiffness of the leaf itself must be increased, or damping action must be applied. It is necessary to add it effectively.

Now, if the plate width of the leaf spring is b1 and the plate thickness is 6h, the element that maintains the degree of freedom is quantified as static rigidity, and dynamically is quantified as the first-order natural frequency. In contrast, it is quantified by the ^-order mode of the plate. The first-order natural frequency fI is f+! oe bhs , ... (1) The higher-order mode is fllI section αIbhs ... (2) However, the field & of the screw mode is when the cross section is rectangular. (1
) and (2) both have a term proportional to hl, and increasing the plate thickness is effective in increasing the rigidity, but from equation (1), increasing the plate thickness is effective. Increasing fl can also be considered as a method of increasing the board width, and in this case (3)
It can be seen from the formula that the coefficient can be made larger than the method of increasing the plate thickness. The above is the basic idea behind increasing the board width, as shown in Figure 3.

In Figure 4, they are arranged three-dimensionally, making the effect even more like that of a large Buddha.

The above is a description of a method for improving the overall screw stiffness without increasing the ft-t-laxity, but this method alone cannot reduce the asymmetrical and antisymmetrical modes and improve the damping described above. For example, in FIG. 8, when one of the two upper leaf springs 20a exhibits an upward resonance mode, the other leaf spring moves downward (antisymmetric mode). ) or when only one leaf spring moves (asymmetric mode).

For this purpose, a very soft member 22 connected with 22 leaf springs in the horizontal plane provides effective plowing. In other words, when one leaf spring tries to push up or down, it transmits a force of 1 - weakening to the other leaf spring. At this time, the strain in the flexible member 2z is large, and a vibration damping effect occurs. Since the force from one leaf spring is transmitted to the other leaf spring, the deformation state of the leaf spring becomes fairly uniform on the left and right sides, and as a result, the asymmetric mode and antisymmetric mode are As well as being suppressed, a damping effect occurs.

FIG. 5 shows an example of the effects of the present invention. This is a display of the vibration level expressed in the tracking direction when the drive mechanism is driven in the autofocus direction. The horizontal axis represents the number of sputum, and the vertical axis represents the total relative displacement level.Characteristics shown by the dotted line in Figure 0 Characteristics of the conventional structure shown in Figure 2 for a person, and Characteristics B shown for actual clothes are the implementation shown in Figure 3. It shows the characteristics in the example.

It is clear that in the case of the present invention 1, the peak level is reduced by 20 dB or more. It is also clear that the damping effect has also increased.

As mentioned above, the following effects can be obtained by using the structure shown in FIGS. 3 to 5.

As shown in Figs. 3 and 4, at least two O-plate springs in the same plane are connected, making it difficult for them to vibrate, so it is possible to reduce the vibration to an extremely small level.

(2) Due to the wide leaf spring structure, overall screw mode is less likely to occur.

(3) Depending on the member that connects the two plates, it is possible to successfully improve the damping effect.

In addition, in the embodiments shown in Figures 3 and 4, the vibration reduction effect as described above is not limited, and it is possible to also use the lead St, which reduces the number of parts and simplifies assembly. There is almost no need to consider matters such as cutting lines, and reliability can be improved.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to suppress the extra high-order MilIJt generated when the objective lens is driven, and it is possible to reduce the continuous exposure error and improve the 8/N ratio. This makes it possible to increase the speed of successive outputs.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram illustrating the principle of a conventional optical information reading device, FIG. 2 is a diagram illustrating an example of a conventional objective lens drive device, and FIGS. 3 and 4 are objective lens drive devices of the present invention. FIG. 5 is a diagram illustrating the main part of the embodiment, and FIG. 5 is a diagram showing the relative displacement level between the support structure of the present invention and the conventional row. 12... Objective lens system, 13... Fixed support member, 1
8... Intermediate holder, 19... Driven member, 20...
- Auto focus direction support plate spring, 21... Tracking direction support lln 2nd Yu J2 Wood 3rd t Sai 4 3') r-5th same sentence number (Saw 71K)

Claims (1)

[Scope of Claims] 1. The objective lens system is configured to include an autofocus direction support member in which a plurality of plate-shaped first elastic members that are displaceable in the autofocus direction are provided at arbitrary intervals, and an autofocus direction support member that is displaceable in the tracking direction. A magnetic circuit that supports a fixed support member by a plurality of plate-shaped second elastic members and tracking direction support members provided at arbitrary intervals, and controls the displacement of the objective lens system in the autofocus direction and the tracking direction; In the objective lens driving device including a drive coil, the width dimension of the surface including the spacing portion of the plurality of plate-shaped first elastic members forming at least the autofocus direction support member em among the objective lens system support members is the same. An objective lens driving device characterized in that a distance between the first elastic member and another elastic member disposed on a plane is set to be smaller than the width dimension of the first elastic member. Z Claim 1 characterized in that a flexible member is disposed on at least one surface of the plurality of elastic members located in the same plane, at least in the space between them.
The objective lens driving device described in .