JPH0471257B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an objective lens driving device for an apparatus for optically writing or reading information.

Conventional technology An objective lens drive device moves an objective lens along two axes, a focus direction and a tracking direction, in order to correct focus deviation due to vertical movement of a warped disk-shaped recording medium such as a compact disk, and tracking deviation due to eccentricity, etc. drive

A conventional objective lens driving device of this type has a structure as shown in FIG. 7, as shown in, for example, Japanese Patent Application Laid-Open No. 58-64649.

That is, the main body having the lens 14 supported by four leaf springs 18a to 18d is connected to the magnetic circuit 1.
9a, 19b and an electrodynamic transducer using the tracking coil 16 in the tracking direction T _r ,
Magnetic circuits 19a, 19b and focus coil 1
The focus direction is determined by an electrodynamic transducer using
Driving to F ₀ . Note that the leaf spring 18c is arranged on the opposite side of the leaf spring 18d with the lens 14 in the center. When driving in the tracking direction, driving forces T ₁ and T ₂ generated from the two magnetic circuits act on the center of gravity g ₀ of the movable part as shown in FIG. 8A.
It is supported by the deflection of the tracking leaf spring portion of the leaf spring and moves in the tracking direction. Similarly, when driving in the focus direction, the driving force is applied to the center of gravity _g0 of the movable part from the two magnetic circuits as shown in Figure 8B.
F ₁ and F ₂ act to move in the focus direction supported by the deflection of the focus leaf spring portion of the leaf spring.

Further, the entire objective lens driving device is access-driven by a motor in the access direction A _c (same direction as the tracking direction) on the recording medium.

Problems to be Solved by the Invention However, with such a structure, the objective lens may swing in the tracking direction due to movement in the access direction during high-speed access required for data transfer or other impacts. In other words, in Fig. 8A, the inertia force due to access drive to the center of gravity of the movable part
T ₃ works, like when driving in the tracking direction,
The objective lens is driven in the tracking direction.

As mentioned above, the objective lens drive unit itself is vulnerable to shocks, so even compact disc players can cause sound skips due to shocks while in operation, and data recording systems can cause recording errors when writing data. Therefore, the current situation is that a structure for absorbing the impact must be separately provided in the system in which the objective lens driving device is mounted.

Therefore, the present invention provides a stable objective lens driving device that is not affected by such impacts during driving.

Means for Solving the Problems The technical means of the present invention for solving the above-mentioned problems is to align the center of gravity of all movable parts with the support point from the fixed part, and to support the impact by the fixed part of the support system. It is something.

Effect The effect of this technical means is as follows.

In other words, by aligning the center of gravity of all movable parts in the tracking direction with the center of a support system such as an axis or pivot, movement in the tracking direction is controlled by the center of gravity of the movable part,
In other words, the rotating motion is made around the support system such as the shaft or pivot, and the position of the center of gravity of the movable part does not change even when the movable part moves, so that the impact is supported by the support system fixed part,
The base part and the movable part are shown assembled. Moreover, FIG. 9 is an exploded perspective view showing the movable part and the base part (fixed part) separately.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1A is a plan view of the objective lens driving device of this embodiment, and FIG. 1B is a front view thereof.

1 is an objective lens (hereinafter referred to as a lens) of a device that optically writes or reads information on a recording medium; 2 is a lens holder that holds the lens 1;
The lens 1 and lens holder 2 constitute a first movable part. Reference numeral 3 denotes a second movable part which is fixed by a shaft 5 so as to be rotatable only in the tracking direction, which is parallel to and radial to the surface of the recording medium, and the center of gravity of all movable parts is located at the center of the shaft 5. It is configured. 4a to 4d are plate springs that connect the first and second movable parts so that only the first movable part can move in the optical axis direction perpendicular to the recording medium surface, that is, in the focus direction; 6 is a bearing; 8 is a spring member for returning the first and second movable parts to their original positions after moving in the tracking direction; 9
a and 9b are magnetic circuits for driving the first movable part in the focusing direction; 9a and 9c are magnetic circuits for driving the first and second movable parts in the tracking direction; 10 is a support system fixed 11 is a focusing coil, 12 is a tracking coil, and 13 is a base.

In addition, as shown in FIG. 9, the magnetic circuits 9a, 9
b and 9c are made on the base 13 and consist of a yoke part and a magnet part. In each of the magnetic gaps between the yoke part and the magnet part,
A focusing coil and a tracking coil are arranged to obtain driving force.

The operation of this embodiment configured as above will be described below.

First, movement in the tracking direction will be explained.

FIG. 2 shows a simplified configuration of this embodiment in order to explain its operation. In FIG. 2, G is an axis, and the center of gravity of the entire system is on axis G. m ₁ and m ₂ are the masses of the first and second moving parts, I ₁ and I ₂
are the moments of inertia of the first and second movable parts around the axis G, l ₁ and l ₂ are the distances from the axis G to the points of application of the first and second tracking driving forces, and l _L is the distance from the axis G to the lens The distance to the center, F ₁ and F ₂ are the first and second tracking driving forces, and θ is the rotation angle of the movable part about the axis.

FIG. 3 shows the vibration mode in the tracking direction. FIG. 3A shows the vibration mode in the low frequency region, and the plate springs 4a to 4d have strong rigidity in the width direction, so the vibration mode in which the plate springs 4a to 4d bend does not occur, and the first and second movable parts are aligned with the axis G. rotate around,
The displacement in the tracking direction is obtained. FIG. 3B shows a vibration mode in a high frequency range. In the high frequency range, the leaf springs 4a to 4d bend in the width direction, so the first movable part is in a vibration mode in translation.

In order to obtain good displacement frequency characteristics of the lens 1 in the tracking direction, it is necessary to drive the lens 1 so that its acceleration characteristics are constant. Using the symbols explained in FIG. 2, the acceleration d ² y/dt ² of the lens 1 in the tracking direction is expressed as the following equation (1) in the low frequency region.

d ² y/dt ² =l _L d ² θ/dt ² =l _L・F ₁ l ₁ +F ₂ l ₂ /I ₁ +I ₂ …
...(1) Also, in the high frequency region, it is expressed as the following equation (2).

d ² y/dt ² =F ₁ /m ₁ (2) In other words, in order to obtain good displacement frequency characteristics, the acceleration must be constant in both the low frequency region and the high frequency region. That is, the following equation (3) must be satisfied.

l _L・F ₁ l ₁ +F ₂ l ₂ /I ₁ +I ₂ =F ₁ /m ₁ ...(3) In order to satisfy equation (3) in Fig. 4, the first and second
This figure shows the case where the current flowing through the tracking coils 22 and 23 is adjusted by adding a resistor 24R of resistance value to change each driving force. Figure 4A shows the case where each tracking coil is connected in series, and Figure 4B
is also the case when connected in parallel.

Furthermore, other methods to satisfy equation (3) include changing the number of turns of the tracking coil in order to adjust the driving forces F ₁ and F ₂ , changing the magnetic gap length of the magnetic circuit, and adjusting each drive force from the shaft. Distance to point of force application
By changing l ₁ and l ₂ or adding additional mass to the moving part.
There are methods such as changing I ₁ and I ₂ . Figure 5 shows the displacement frequency characteristics in the tracking direction,
Curve a is the case where the adjustment is made to satisfy equation (3), and curve b is the case when the arrangement is made so that equation (3) is not satisfied.

In the figure, ₀ is the lowest resonance frequency determined by the spring material 8 and the moment of the movable part, _h is the high cutoff frequency due to resonance of the lens holder, etc., and _r is mainly the mass of the first movable part and the width of the leaf springs 4a to 4d. It is the resonant frequency determined by the directional stiffness.

As described above, according to this embodiment, even if an impact is applied in the tracking direction T _r due to high-speed access, etc.
Since all the force exerted by the impact on the movable part is applied to the center of gravity G, the lateral rigidity of the fixed part and the leaf spring is reduced by fixing the center of gravity to the base 13 by the shaft 5, which is a support system. If the force is strong enough, it will be equivalent to having no impact on the moving parts at all.

Further, in the focus direction F ₀ , a magnetic circuit 9a,
The center of gravity g ₁ of the lens holder 2 including the lens is driven in the focus direction F ₀ by the driving force F ₃ generated by the coil 9 b and the coil 11 . At this time, the leaf springs 4a to 4b that support the movable part are connected on the extension line l from the center of gravity _g1 of the focus movable part as shown in FIG. 6, so there is no dynamic disturbance of the movable part due to driving. do not have.

Furthermore, the first movable part mass m ₁ , the moments of inertia around the axis G I ₁ , I ₂ , the distances from the axis G to the point of application of the tracking driving force l ₁ , l ₂ , and the distance from the axis G to the center of the lens 1 By adjusting the distance l _L and the first and second tracking driving forces F ₁ and F ₂ to satisfy equation (3), the displacement frequency characteristics of the lens 1 become flat and good acceleration characteristics in the tracking direction are obtained. be able to.

In order to suppress high-order resonance of the leaf spring, an elastic material such as rubber may be adhered to at least one of the front surface and the back surface of the leaf spring using an adhesive.

Effects of the Invention The present invention aligns the center of gravity of all movable parts in the tracking direction of an objective lens drive device with the center of a support system such as a shaft or pivot, and moves movement in the tracking direction by aligning the center of gravity of the entire movable part in the tracking direction with the center of the support system such as the shaft or pivot. By rotating the system around the system, it is supported by the support system fixed part against impacts perpendicular to the optical axis, so even when the objective lens drive device is in operation, it is completely unaffected by the above-mentioned impacts. Therefore, it is possible to easily design a system for mounting an objective lens driving device.

Furthermore, the displacement frequency characteristics of the lens are determined by the driving force in the first and second movable parts, so as to satisfy equation (3).
Flat characteristics can be obtained by adjusting the length and moment of inertia.

[Brief explanation of the drawing]

FIG. 1A is a plan view of an objective lens drive device according to an embodiment of the present invention, FIG. 1B is a front view of the same objective lens drive device, and FIG. 2 is a plan view of a main part showing the functions of the objective lens drive device. Figure 3A is a plan view of the main part showing the vibration mode in the low frequency range in the tracking direction of the objective lens driving device, Figure 3B is a plan view of the main part showing the vibration mode in the high frequency range of the objective lens drive device, and Fig. 4A is a circuit diagram showing the series connection of each tracking drive coil of the same objective lens drive device, FIG. 4B is a circuit diagram showing the same parallel connection, and FIG. 5 is the displacement frequency characteristic of the same objective lens drive device in the tracking direction. 6 is a front view of the main part showing the focus direction vibration mode of the objective lens drive device, FIG. 7 is a perspective view showing the conventional objective lens drive device, and FIG. 8A is a plan view of the main part.
FIG. 8B is a front view of the same essential parts, and FIG. 9 is an exploded perspective view showing the movable part and the base part (fixed part). DESCRIPTION OF SYMBOLS 1... Lens, 2... Lens holder, 3... Second movable part, 4a-4d... Leaf spring, 8... Spring material, 9a-9c... Magnetic circuit.

Claims (1)

[Claims] 1. A first movable part consisting of an objective lens and a lens holder of a device for optically writing or reading information on a recording medium, and a first movable part consisting of an objective lens and a lens holder; a second movable part that is rotatably fixed only in a certain tracking direction; the center of gravity of all the movable parts is located at the axis or pivot part;
one or more leaf springs connecting the first and second movable parts so that only the movable part can move in the focus direction, which is the optical axis direction perpendicular to the surface of the recording medium; , one or more spring members for returning the first and second movable parts to their original positions after moving in the tracking direction, and one spring member for driving the first movable part in the focus direction. Alternatively, it includes a plurality of focus magnetic circuits and one or more tracking magnetic circuits that drive the first and second movable parts in the tracking direction, and drives the first movable part in the tracking direction. The sum of moment forces represented by the product of the first driving force, the second driving force that drives the second movable part in the tracking direction, and the distance from the shaft or pivot part to the point of application of each driving force. is divided by the moment of inertia about the axis or pivot part, and multiplied by the distance from the axis or pivot part to the lens center, and the acceleration of the lens center in the tracking direction, and the first
Adjust the first and second driving forces or the masses of the first and second movable parts so that the accelerations represented by the driving force divided by the mass of the first movable part are equal. An objective lens driving device characterized by: 2 A first tracking drive coil that obtains a first driving force and a second tracking drive coil that obtains a second drive force are connected in series, and the first tracking drive coil or the second tracking drive coil The objective lens driving device according to claim 1, characterized in that a resistor having an appropriate resistance value is inserted in parallel for adjustment. 3 A resistor with an appropriate resistance value is connected in series to either the first tracking drive coil or the second tracking drive coil, and the first tracking drive coil and the second tracking drive coil are connected in parallel. 2. The objective lens driving device according to claim 1, wherein the objective lens driving device is adjusted as follows. 4. The objective lens drive device according to claim 1, wherein the length of the first tracking drive coil and the second tracking drive coil are adjusted by changing the lengths thereof. 5 The magnetic flux density generated in the magnetic air gap of the first magnetic circuit that drives the first movable part or the second magnetic circuit that drives the second movable part is determined by the air gap length, the thickness of the magnet, and the thickness of the yoke. The objective lens driving device according to claim 1, characterized in that the objective lens driving device is adjusted by changing, etc. 6. The objective lens driving device according to claim 1, wherein the adjustment is made by adding an appropriate mass to the first movable part or the second movable part.