JPH0425613B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a drive device for driving an objective lens of an optical disk or the like in the direction of the optical axis, and is particularly useful for suppressing vibration in a direction perpendicular to the optical axis. The present invention relates to a suitable objective lens driving device.

[Background of the invention]

An objective lens driving device that drives the objective lens only in the optical axis direction is disclosed in, for example, Japanese Patent Laid-Open No. 57-117133 and Japanese Patent Laid-Open No. 58-85939,
A spiral leaf spring supports the lens barrel to which the objective lens is fixed. An elastic member having a vibration absorbing effect is bonded to this spiral spring to reduce vibrations in the optical axis direction of the objective lens and in a direction perpendicular thereto, thereby improving focusing and track positioning accuracy. However, in the case of a spiral-wound leaf spring, the relationship between the driving force and displacement in the optical axis direction is highly nonlinear, resulting in the problem that the gain in the low frequency region of focusing control varies greatly depending on the position in the optical axis direction. There is.

On the other hand, there is a spring in which the spring shape is changed to a spiral shape, and is made into an elongated linear plate spring, as disclosed in, for example, Japanese Patent Application Laid-open No. 168021/1983. In this case, the relationship between the driving force in the optical axis direction and the displacement becomes close to linear, which is improved compared to a spiral leaf spring. However, when we assembled a head using this elongated linear leaf spring and measured the frequency characteristics of the amplitude of the objective lens in the track direction (track positioning direction), we found that if no vibration absorbing member such as rubber was bonded, Large tracking error peaks occurred near 2500 Hz and 3800 Hz, and when a vibration absorbing member such as rubber was bonded, a large tracking error peak occurred near 3800 Hz. 3800
Hz vibration is a mode of vibration in which one side of the spring facing the track direction is expanded and the other side is compressed. It has been found that this vibration cannot be damped even if a vibration absorbing member is attached to the leaf spring 1. On the other hand, 2500Hz
The vibration occurs when the leaf spring facing the track direction is initially deformed and when the leaf spring undergoes bending deformation vibration, the lens barrel attachment part of the leaf spring is displaced in the track direction. It is. This vibration can be reduced by joining a vibration absorbing member such as rubber.

As explained above, conventional objective lens support springs maintain good linearity of the driving force and displacement in the optical axis direction even when vibration-absorbing members such as rubber are used to reduce vibrations, and at the same time maintain vibrations in the track direction. It was difficult to suppress this.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an objective lens driving device that can maintain good linearity of driving force and displacement in the optical axis direction and at the same time reduce vibration amplitude in the track direction.

[Summary of the invention]

Vibration in the track direction of the objective lens caused by the leaf spring is caused by the in-plane deformation (stretching or bending) and out-of-plane deformation (bending) modes of the spring, but it is difficult to reduce vibration in the in-plane deformation mode. We decided to decide on a spring shape that focused on this countermeasure. In order to reduce vibration, it is necessary to increase the proportion of strain energy generated in vibration absorbing members such as rubber among the strain energy during vibration deformation, but measures for this must not degrade other characteristics. .
From this point of view, in order to maintain the advantages of a long and thin linear leaf spring while compensating for its disadvantages, one end of the spring should be bent.
By lowering the longitudinal stiffness of the spring during in-plane deformation mode, connecting both sides with vibration-absorbing members across this stiffness-reducing part, and increasing the strain energy generated in the vibration-absorbing members during in-plane deformation. We aimed to suppress the vibration of the in-plane deformation mode.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a schematic diagram of an optical disk device equipped with an objective lens driving device of the present invention.
A lens barrel 4 supporting an objective lens assembly 3 with an objective lens support member 2 is installed and coupled to the upper end of the head body 1. Light B emitted from the light source 5 passes through the beam splitter 6, is reflected by the galvanometer mirror 7 for adjusting the track position, passes through the objective lens assembly 3, is reflected by the optical disk 8, and passes through the same path again to the beam splitter. It passes through the pritter 6, enters the detection optical system 9, and outputs data on the surface of the optical disk 8, focusing error, and track position error.

In the apparatus shown in FIG. 1, the objective lens assembly 3 can be easily moved in the focusing direction, and the amount of movement in the track direction and jitter direction (direction perpendicular to the track direction and the focal direction) is within the allowable value (0.1 μm).
degree) or less. Since the jitter direction is approximately the same as the track direction, the following explanation will be given only in the track direction. In order to satisfy the above conditions, the lens support member 2 needs to satisfy the following conditions.

(1) The stiffness K _A in the focusing direction is small, the damping is large, and it is almost constant over the operating range.

(2) Large rigidity and damping in the track direction.

The objective lens assembly 3 receives a driving force F _A for focusing and accelerations α _T1 and α _T2 in the track direction from the lens barrel. The driving force F _A for focusing is the permanent magnet 1
0 and yokes 11 and 12. The head body 1 vibrates due to the reaction force of the force F _A of the voice coil 13 generated on the permanent magnet 10 and the yokes 11 and 12, and accelerations α _T1 and α _T2 in the track direction are generated in the lens barrel 4. This acceleration α _T1 , α _T2
is applied to the lens support member 2, causing the objective lens assembly 3 to vibrate in the track direction.

In order to satisfy the above conditions (1) and (2), the objective lens support member 2 has a structure as shown in FIG. 2, for example.

In FIG. 2, the objective lens support member 2 is provided with a hole 14 in the center into which the objective lens assembly 3 is inserted, and four leaf springs 17 are provided between the objective lens assembly side part 15 and the fixed side part 16. It is provided.
This leaf spring 17 extends in the same rotational direction on a tangent line centered on the optical axis of the objective lens, and is arranged in a pair of points. In this plate spring 17, a part of the longitudinal direction is bent at a right angle, and a part of the fixed side 19a in the longitudinal direction is bent at a right angle to form a longitudinal stiffness reduced part.

Further, a vibration absorbing member 18 made of an elastic material such as rubber is bonded to one side of the leaf spring 17, sandwiching the longitudinal stiffness reducing portion 17a and connecting the objective lens assembly and the fixed side portion. has been done. The reason why this lens support member is effective and the desirable conditions will be explained below.

FIG. 3 shows the deformed state of the leaf spring 17 and the vibration absorbing member 18 when the objective lens assembly 3 is displaced downward in the focusing direction. The leaf spring 17 is restrained by the vibration absorbing member 18, particularly the portion 18a. At the same time, a relatively large strain is generated in the rubber portion 18a, damping vibrations. Leaf spring 1
7 is restrained from deformation by the vibration absorbing member 18,
The portion of the leaf spring 17 that acts as a spring is the portion L _a -L _c of the leaf spring 17 . L _C is an equivalent length for correcting the increase in rigidity due to the leaf spring 17 being restrained by the vibration absorber 18, and is determined by the ratio of the rigidity of the leaf spring 17 and the vibration absorber 18. It changes. Now, the thickness of leaf spring 17 is
If t _a and Young's modulus are E _a , then the stiffness K _A of the leaf spring of length (L _a −L _c ) in the focusing direction is expressed as a Co constant by Equation (1), so other conditions and Make your selection so that K _A is small.

K _A = CoE _a・B _a・t _a ³ / (L _a − L _c ) ³ ………(1) To reduce the change (nonlinearity) of stiffness K _A depending on the position of the focal direction (L _a − It is desirable to increase L _c ) and t _a . In addition, in order to increase the damping of vibrations in the focusing direction of the objective lens assembly 3, the objective lens assembly 3 is
As shown in the figure, it is necessary to increase the proportion of strain energy generated in the vibration absorbing member 18 among the total strain energy when the state is displaced from the state shown by dotted line A to the state shown by solid line B, and the larger L _c is, the more desirable. If the thickness t _b of the vibration absorbing member 18 is large, or if the width D _c of the gap 18 a of the vibration absorbing member 18 is small, the restraint by the vibration absorbing member 18 is too large, and the deformation of the vibration absorbing member 18 is small, causing the vibration Absorbing member 1
8, the distortion generated is too small for damping to be effective. In this case, the rigidity K _A also increases, which is not desirable from this point of view. Conversely, if t _b is small or D _c
When is large, the stress generated in the vibration absorbing member 18 is small and damping is not effective, but the rigidity K _A is small, which is desirable from this point of view. There is a range between these where damping is effective to some extent and the stiffness K _A is below the allowable value. As mentioned before, L _a −L _c
It is desirable to increase the length of From this point,
The intersection of the perpendicular line drawn from the center of the objective lens assembly 3 to the leaf spring 17 and the leaf spring 17 is sandwiched between the junction point of the leaf spring 17 with the objective lens assembly side part 16 and the junction point with the fixed side part 15. It is best to place it on the opposite side.

FIG. 4 shows the deformation state of the leaf spring 17 and the vibration absorbing member 18 in the in-plane deformation mode. In order to suppress the displacement in the track direction to a sufficiently small level, the resonant frequency in the track direction is sufficiently high and damping is sufficient. is required to be large. As long as the above two conditions are required as characteristics in the focusing direction and the condition that the resonant frequency in the track direction is sufficiently high, a structure consisting of a long and thin linear leaf spring and a vibration absorbing member bonded to this leaf spring may be sufficient. However, this method was not able to suppress vibrations in the in-plane deformation mode. This is because the part where the vibration absorbing member is joined is close to the fixed point of the leaf spring, so when the vibration absorbing member undergoes in-plane deformation, the strain on the vibration absorbing member is small, and damping is not effective because the strain energy absorbed is small. be. In order to improve this, the shape of the spring should be changed so that the amount of deformation at the part where the vibration absorbing member is joined is increased, and the fixed side 17a of the leaf spring 17 can be bent at a right angle as shown in Fig. 2. This can be achieved by Leaf spring 17 and vibration absorbing member 18
is deformed as shown in Fig. 4, the vibration absorbing member 1
The strain is large in the gap portion 18a of No. 8, and this portion contributes most to vibration suppression. The leaf spring 17 is elongated in order to reduce the stiffness K _A in the focusing direction, so the bending stiffness in the in-plane direction is small, and the stiffness in the longitudinal direction is sufficiently large, so it is displaced in the T _R direction in Figure 4. The stiffness K _TR in this case can be roughly determined by equation (2). C ₁ is a constant.

K _TR = C ₁ = E _a・t _a・B _b ³ /L _b ³ ………(2) Also, the resonant frequency F _TR is calculated by assuming that the mass per spring of the objective lens assembly 3 is M ₂ ( 3) It is expressed by the formula.

In order to make the resonant frequency F _TR more than the target value,
Although K _TR must be increased, the gap 18a of the vibration absorbing member 18 in the track direction (x
In order to increase the displacement in the direction), K _TR must be small. The rigidity K _TR of the fixed side 17a of the leaf spring 17 is determined to be an appropriate value that is neither too large nor too small. The value of K _TR includes vibration absorbing member 1
8 is also added, but normally it is smaller than the rigidity of the leaf spring 17, so it is mostly determined by the leaf spring 17.

FIG. 5 shows the out-of-plane deformation mode of the leaf spring 17 and the vibration absorbing member 18. The amplitude of the out-of-plane deformation mode is largest near the center of the leaf spring 17 in the length direction when the width and thickness of the leaf spring 17 are similar; however, in the leaf spring 17 in FIG. The amplitude increases near the part that curves at a right angle. The vibration absorbing member 18 receives strain by restraining the leaf spring 17 near the bent portion thereof, thereby suppressing vibration.
Even in the out-of-plane deformation mode, the gap portion 18a of the vibration absorbing member 18 receives the largest strain and therefore contributes most to vibration suppression.

The fixed side 17a of the leaf spring 17 is bent in the second direction.
It is not preferable to turn the spring in the opposite direction as shown in the figure because it increases the outer diameter of the spring.

In addition to the embodiments described above, other embodiments based on the same principle are possible. FIG. 6 shows a case where the fixed side 17a of the leaf spring 17 of the embodiment shown in FIG. 2 is moved to the objective lens assembly 3 side. In the figure, 19 is a leaf spring, 19a
is a portion corresponding to 17a above. In this case, since the fixed side and the objective lens assembly are exchanged, if the vibration absorbing member 20 is also placed on the objective lens assembly side, the same function as in the embodiment shown in FIG. 2 can be provided. If the vibration absorbing member 20 is made circular, the leaf spring 17 will be restrained quite far to the outside, and unless the leaf spring 19 is long, the rigidity in the focusing direction will be reduced.
K _A becomes too large. FIG. 7 shows a case where the fixed side portion 17a of the leaf spring 17 in FIG. 2 is changed from a cantilever type fixed side portion 17b to a double supported type fixed side portion 17b. Even in this case, the same effect as in FIG. 2 can be obtained. In the example shown in FIG. 8, the fixed side 2 of the leaf spring 21 is
1a is not directly joined to the fixed side part, but is fixed via the part 21c bent at right angles again, and the in-plane deformation caused by the spring 21b is inserted in the middle of the spring having the sum of the length of the leaf springs 21 and 21c. It can be considered that a stiffness-reduced portion is provided, and it can be considered that the leaf spring 17 of FIG. 2 is further generalized.

All of the above examples have four leaf springs, but in principle, the objective lens support members extending in the same rotational direction on the tangents of concentric circles centered on the optical axis of the lens are arranged at equal angles on one plane. If they are arranged apart from each other, other than four, if there are three or more, it is possible to give them isotropic properties. In the case of two springs, the characteristics will change in the longitudinal direction and the width direction of the spring, so it is generally not preferable.

Although the vibration absorbing members shown in FIGS. 2 and 6 to 8 are all bonded to one side of the leaf spring, the same effect can be achieved even if the vibration absorbing members are bonded to both sides. Furthermore, as explained in the embodiment shown in FIG. 2, the planar shape of the vibration absorbing member can be any shape as long as it includes the part that contributes most to vibration damping, as long as it does not have any other negative effects on the characteristics. may be multiple.

〔Effect of the invention〕

According to the present invention, the rigidity is low in a specific direction (focusing direction), the linearity is excellent, and it has appropriate damping, and the amplitude in other directions (track direction, jitter direction) is suppressed to a sufficiently small value. Since a support spring can be provided, high track positioning accuracy can be achieved, and furthermore, an optical disk device with high track density can be realized.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an optical disk device equipped with an objective lens driving device of the present invention, FIG. 2 is a plan view illustrating in detail an example of the objective lens support member in FIG. 1, and FIG. 4 and 5 are diagrams illustrating the in-plane deformation mode and out-of-plane deformation mode of the objective lens support member shown in FIG. 2, respectively. , FIGS. 6 to 8 are diagrams illustrating other examples of the objective lens support member in the objective lens driving device of the present invention. 2... Objective lens support member, 3... Objective lens assembly, 4... Lens barrel, 17, 19, 21... Leaf spring, 1
8, 20... Vibration absorbing member.

Claims (1)

[Scope of Claims] 1. An objective lens drive device comprising a plurality of objective lens support members extending in the same rotational direction on a tangent to a concentric circle centered on the optical axis of the objective lens, comprising: a spring serving as the objective lens support member; A spring portion that is arranged in a substantially straight line at equal angles on the same plane, and that is bent in a direction perpendicular to the longitudinal direction of the substantially straight spring. A stiffness reducing portion is provided on one side of the spring, and the stiffness reducing portion is sandwiched between a longitudinal portion of the spring that continues from one end of the stiffness reducing portion and continues from the other end of the stiffness reducing portion. An objective lens driving device characterized in that a vibration absorbing member is provided which connects between the fixed parts of the spring and absorbs vibrations of the rigidity reduced part.