JPH0223849B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to, for example, a light beam deflection mirror of an optical disk type recording/reproducing device, and in particular to an oscillating light beam whose rotation center is the intersection line of the mirror with the light source side focal plane of an objective lens. Regarding the structure of a deflection mirror.

A device that records information by using a laser beam to make minute holes in a thin film on a rotating disk, and reproduces information by irradiating the disk with a laser beam and depending on the intensity of the reflected light is called an optical disk, and there are various types of disks. A method has been proposed. In an optical disk, the part that has the function of focusing the laser beam onto the disk and precisely positioning it in the radial direction is called an optical head. One of the methods for precisely positioning a laser beam in the radial direction (referred to as tracking) is an oscillating mirror method. In the oscillating mirror method, the optical path from the light source to the mirror and the optical path when the light reflected from the disk returns after being reflected by the mirror generally do not match, resulting in tracking errors. In order to prevent this, a method has been proposed in which the rotation center axis 8 of the mirror is provided near the intersection line between the light source side focal plane 7 of the objective lens 2 and the surface of the mirror 3, as shown in FIG.
No. 55-108554). In this method, the light source 4
The laser beam emitted from the mirror passes through the semi-transparent mirror 5, is reflected by the mirror 3, passes through the objective lens 2, is reflected by the disk 1, passes through the objective lens 2 again, is reflected by the mirror 3, and is reflected by the semi-transparent mirror 5. The tracking deviation detector 6 is reached. At this time, if the optical path of the light reflected by the mirror 3 and reaching the semi-transparent mirror 5 changes depending on the angle of the mirror 3, the tracking deviation detection value will deviate. In order to prevent this, it is effective to provide the rotation axis 8 of the mirror 3 near the line of intersection between the light source side focal plane 7 of the objective lens 2 and the reflective surface of the mirror 3 as described above. This method is Mirror of Rotation Axis in, Focus
Plane, hereinafter referred to as the MIRAF method.

Next, we will discuss the conditions required for the light beam deflection mirror used in the MIRAF system.

1 Generally, the light source side focal point of the objective lens 2 is located inside the objective lens 2, so the rotation axis 8 of the mirror 3 must be above the bottom surface 2b of the objective lens.

2 Mirror 3 must be below objective lens 2. However, this occurs when the optical system is located below the disk as shown in Figure 1.

3. There must be no play in the rotating shaft 8 of the mirror 3.

4. Mirror 3 does not undergo unnecessary deformation caused by vibrations up to sufficiently high frequencies.

As shown in FIG. 2, a conventional light beam deflection mirror has a spring 10 made of rubber or metal on the back surface of a mirror 9, and coils 11a and 11b for driving the mirror to swing are attached to both ends of the mirror 9. The mirror swing drive coils 11a and 11b are interposed within the magnetic gap of the magnets 12a and 12b, respectively. The end of the spring 10 opposite to the mirror 9 and the magnets 12a and 12b are fixed to the substrate 13. This deflection mirror is rotated as shown by the broken line in FIG. 3 by the rotational moment M acting on the mirror swing drive coils 11a and 11b.
Assuming that the length of the spring 10 is L and the bending rigidity is EI,
The displacement δ and the rotation angle θ at the connection point between the spring 10 and the mirror 9 are determined by the following equation.

δ=ML ² /2EI ...(1) θ=ML/EI ...(2) From the above two equations, the rotation center 14 of the mirror 9 is the spring 1
It can be seen that it is in the center of 0. In addition, the spring 10 has high rigidity in the longitudinal direction (X' direction in Figure 2), but low rigidity in the direction perpendicular to it (Y' direction in Figure 2), so acceleration in directions other than the X' direction is reflected by the deflection mirror. , the spring 10 is deformed, the mirror 9 is displaced, and the center of rotation of the mirror 9 is shifted as a result.

As described above, conventional deflection mirrors have the disadvantage that the center of rotation is not within a plane that includes the reflective surface of the mirror, and that the center of rotation is easily shifted due to external disturbances.

SUMMARY OF THE INVENTION An object of the present invention is to provide a light beam deflection mirror that has a rotation center within a plane that includes a reflecting surface of the mirror, and whose rotation center does not shift due to disturbances.

The present invention includes a mirror, a mirror support that supports the mirror, a fixing block that connects the mirror support via a spring, and a drive means that drives the mirror support. In a mirror that deflects a light beam incident on the mirror by driving a support, a plurality of leaf springs are arranged approximately perpendicular to each other, one end of each leaf spring is connected to the mirror support, and the other end is connected to a fixed block to form a cross. The present invention is characterized in that a spring is formed, and the mirror support body is rotatably supported by the cross spring about a substantially orthogonal point of the leaf springs.

An embodiment of the present invention will be described below with reference to FIGS. 4 to 9. FIG. 4 is a diagram illustrating the configuration of the light beam deflection mirror including its peripheral portion. There is a mirror 3 directly below the objective lens 2, and the mirror support 15 that supports this mirror 3 is rotatable around the rotation center O by a cross spring 16 (however, it is not completely free and cannot rotate around the rotation center O). The natural frequency is approximately 50Hz). The cross spring 16 is fixed to a fixed block 17. Drive coils 18a and 18b are provided on the back side of the mirror 3 and apply force to the mirror 3 and the mirror support 15 in the X' direction.
A magnet 19 is provided on the back side of the mirror 3 for applying a magnetic field to the drive coils 18a, 18b. A balancer 2 is installed on the side opposite to the drive coil of the mirror support 15.
0 is attached, and moments are balanced in the X and Y directions around the rotation center O. The sketch of the state with objective lens 2 removed is shown in Figure 5.
As shown in the figure. Since the state of the cross spring 16 is difficult to understand in FIGS. 4 and 5, the cross spring 16 is shown in FIG. The shaded area in FIG. 6 is welded to the mirror support 15. The other end of each spring 16a-16d is welded to a fixed block 17. The welded parts may be connected by adhesion or brazing depending on the combination of materials and assembly method. Generally, cross springs require time to assemble, but one solution to this problem is to use four springs 16a as shown in Figure 7.
There is a method in which the pieces 21a to 21c, in which the parts 21a to 21c are connected to each other, are formed into a single plate by etching or the like, and the plate is bent at the bending part P to form a cross spring shape. According to this method, since the springs 16a to 16d are connected to each other, if only one location is fixed, positioning of the remaining welding locations becomes very easy. As a result, assembly time can be shortened.

Let the forces acting on the drive coils 18a and 18b in FIG. 4 be Fa and Fb in FIGS. 8 and 9. Ideally, whatever the forces Fa and Fb are, it is desirable that the mirror support 15 rotate rigidly about the rotation center O as shown in FIG. Force Fa,
While the frequency of Fb is low, the mirror support 15 deforms as shown in FIG. The deformation is mirror support 1
5 may occur. At this time, the angle of the mirror 3 is determined by the elastic deformation of the mirror support 15 shown in FIG. 9 in addition to the rigid body rotation shown in FIG. It's bigger. Therefore, the angle of the light beam is governed by elastic deformation due to resonance at the natural frequency of the mirror support 15, and the phase of the deflection angle of the light beam with respect to the force also lags, which is detrimental to control of the deflection angle of the light beam. Therefore, it is necessary to suppress resonance at the natural frequency of the mirror support 15 as much as possible. One method is to apply driving forces Fa and Fb on both sides of the node of the natural vibration mode at the natural frequency of the mirror support 15, as shown in FIG.
There are ways to cancel each other out. When the mirror 3 is located at the tip of the mirror support 15 as in this embodiment, the point of application of the driving force is generally placed near the mirror 3 in order to match the phase of the acceleration of the mirror and the driving force as much as possible. be. Further, one of the natural vibration modes of the mirror support 15 has a shape similar to the vibration mode of a beam with both ends free, as shown in FIG. 9, and a vibration node is generated at the tip. When two forces with the same phase are applied to both sides of a node, the two forces cancel out their vibration modes, so the vibration at that frequency can be reduced more than when only one of the two forces is applied. In order to determine the conditions under which the two forces completely cancel each other out, it is necessary to measure each deflection mirror, but it is possible to approximately determine these conditions through calculations or simple experiments. Parameters to be changed at this time include the position of the force application point and the magnitude of the force, but specifically, the positions of the coils 18a and 18b, the magnetic flux density applied to the coils 18a and 18b,
Possible factors include the length of the magnetic gap.

In addition, in this embodiment, the balancer 20
The moments in both directions are balanced, and Y
Since it is symmetrical about the axis, the moment in the Z direction is balanced, so even if disturbance acceleration is applied to the deflection mirror in the X, Y, and Z directions from the outside, the moment of the disturbance applied to the deflection mirror is small, so the light beam is deflected. The angle shifts only slightly.

Another method is to apply the driving force Fc to the node of the vibration mode in Fig. 9, but in this method, only one driving means can be provided, so the amount of movement of the light beam per unit input is It has the disadvantage of low sensitivity. However, it can be used for some applications even with low sensitivity.

According to the present invention, by using a cross spring to support the light beam deflection mirror, the rigidity other than rotation around one axis can be sufficiently increased, so that the precision of light beam deflection angle control can be improved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of a light beam position control system in which the rotation center of the mirror is set near the intersection of the focal plane of the objective lens on the light source side and the mirror, and Fig. 2 is a diagram showing an example of a conventional light beam deflection mirror. 3 is an explanatory diagram of the operating state of FIG. 2, FIG. 4 is a side view of an embodiment of the light beam deflection mirror of the present invention, FIG. 5 is a sketch of FIG. 4, and FIG. 6 is a cross sectional view of the embodiment of the present invention. spring sketch,
FIG. 7 is a developed view of the cross spring in the present invention, and FIG.
The figure is an explanatory diagram of an ideal vibration mode of the embodiment of the present invention, and FIG. 9 is an explanatory diagram of an undesirable vibration mode of the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Disk, 2... Objective lens, 3... Mirror, 15... Mirror support, 16... Cross spring,
18a, 18b...driving means, 20...balancer.

Claims (1)

[Scope of Claims] 1. Comprising a mirror, a mirror support that supports the mirror, a shank fixing block that supports the mirror support via a spring, and a drive means that drives the mirror support, In the light beam deflecting mirror in which the mirror support is driven by the driving means to deflect the reflection angle of the light beam incident on the mirror, a plurality of leaf springs are arranged substantially orthogonally to each other, and each leaf spring is A cross spring is provided with one end connected to the mirror support and the other end connected to the fixing block, and the cross spring allows the mirror support to rotate around a substantially orthogonal point of the plurality of leaf springs. A light beam deflecting mirror characterized by supporting.