JPS6032265B2 - Focus control device for optical playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In an optical video disc player, an objective lens focuses a laser beam on a recording track of a video disc, and the objective lens receives the reflected light and supplies it to a photoelectric element. , the video signal is being played back.

However, in this case, the video disc is rotated at a frame frequency, and there are 10
While there is vertical movement (surface wobbling) of about 0 to 500 ridges, the depth of focus of the objective lens is only about 1 Am. Therefore, in the video disk player, the objective lens system is configured as shown in FIG. 1 to automatically adjust the focus.

That is, in FIG. 1, 1 is a video disk, 2 is a permanent magnet, 3 and 4 are magnetic yokes, and 5 is an objective lens, and this lens 5 is housed in a lens barrel 6.
is attached through a support link 7 to a bobbin 9 on which a drive coil 8 is wound.

Furthermore, a leaf spring 11 is provided between the lens barrel 6 and the yoke 3, and a leaf spring 12 is provided between the bobbin 9 and the yoke 4. On the other hand, as shown by an arrow 15, the lens 5 is supported so as to be freely displaceable in all directions along the optical axis thereof. The magnet 2 and yokes 3 and 4 are supported by an arm (not shown),
During playback, the disk 1 is rotated at the frame frequency and the entire objective lens system moves in the radial direction of the disk.

During this reproduction, the distance between the lens 5 and the disk 1 is detected by a detection means (not shown), and the drive current of the coil 8 is controlled by the detection signal, so that the distance between the lens 5 and the disk 1 is adjusted. Constantly controlled. However, in such a configuration, mechanical resonance occurs in the leaf springs 11 and 12, and the frequency characteristics of the displacement of the lens 5 no longer have a flat (or constant slope) characteristic.
Sufficient focus control becomes impossible.

In addition, the leaf springs 11 and 12 support the lens 5 and at the same time act to prevent the lens 5 from being displaced.
It is necessary to increase the output of the amplifier for driving the lens 5 and also to increase the size of the magnetic circuit. This invention attempts to eliminate the above problems.

Let's explain one example below.

In FIGS. 2 and 3, the permanent magnet 2 is ring-shaped, and magnetic yokes 3 and 4 are fixed to the end faces thereof by adhesive.

In this case, the yoke 4 is ring-shaped, and the yoke 3 has a flange portion 3A and a cylindrical portion 3B, the flange portion 3A is in contact with the magnet 2, and the outer periphery of the free end of the cylindrical portion 3B is It is arranged to face the inner circumference of No. 4. Although not shown, the magnet 2 and yokes 3 and 4 are supported by arms and are moved in the radial direction of the disk 1 during reproduction. Furthermore, inside the cylindrical part 3B of the yoke 3,
A slide bearing 21 is provided.

As shown in FIGS. 4 and 5, the slide bearing 21 is made of, for example, polyacetal (Delrin: trade name) and is formed into a substantially cylindrical shape, and has a plurality of stripes extending in the axial direction on its inner circumferential surface. It has a groove 21A and a flange portion 21B at one end. The slide bearing 21 is fixed to the inside of the cylindrical portion 3B of the yoke 3 by press fitting or adhesive. Note that at this time, the flange portion 21B is in contact with the yoke 3, and the position of the slide bearing 21 with respect to the yoke 3 is regulated. A lens barrel 6 is provided inside this slide bearing 21.

In this case, the outer peripheral surface of the lens barrel 6 is subjected to, for example, Toughflam treatment or alumite treatment, and the lens barrel 6 is supported by the inner peripheral surface of the slide bearing 21 so as to be freely movable in its axial direction. Note that an objective lens (
combination lens) 5 is stored. Further, a ring-shaped holder 22 made of, for example, polyacetal is attached to the end of the lens barrel 6 on the yoke 4 side by adhesive, and a bobbin 9 is attached to the outer periphery of this holder 22 by adhesive. There is.

In this case, the position of the bobbin 9 is regulated by a flange portion 22A formed on the holder 22. Further, a driving coil 8 is wound around the bobbin 9, and this coil 8
is located between the opposing parts of the yokes 3 and 4.
Further, the holder 22 has, for example, eight through holes 22B formed in the direction of the bag, and two substantially Z-shaped stoppers 23, for example, are attached to the yoke 4 by adhesive.

One end of a pin 24 made of, for example, a stainless steel wire is press-fitted into a through hole formed in the idler of the stopper 23, and the other end passes through the through hole 22B of the holder 22 and passes through the cylindrical portion 3B of the yoke 3. It is placed in opposition to the free end of.
However, in this case, the through hole 228 of the holder 22 is
4 is said to be an idiot. According to such a configuration, the lens barrel 6 is connected to the magnet 2 by the slide bearing 21.
Since the lens 5 is slidably supported on the yokes 3 and 4, when a driving current is connected to the coil 8, the lens 5 is moved along the optical axis in all directions as shown by the arrow 15 together with the coil 8. The distance between the disk 1 and the disk 1 is controlled to be constant.

In this case, the lens 5 must be located at the reference position when there is no signal, but this is done by setting the DC level of the drive current of the coil 8 to a predetermined value.

Furthermore, the displacement range of the lens 5 is controlled by the holder 22, the cylindrical portion 3B, and the stopper 23.

Further, the pin 24 prevents the lens 5 from rotating around the optical axis, and the pin 24 prevents the lens 5 from rotating around the optical axis.
The one that is not penetrated acts as an air vent. In this way, the focus of the lens 5 is controlled, but in this case,
According to this invention, since the lens barrel 6 is supported by the slide bearing 21, the leaf spring 11 of the device shown in FIG.
, 12, and therefore the frequency characteristic of the displacement of the lens 5 has a constant slope of 11 phantom B/oct, so focus control can be performed reliably and sufficiently. can be done.

Further, in the device shown in FIG. 1, the leaf springs 11 and 12 are connected to the lens 5
However, according to the present invention, it is the friction of the slide bearing 21 that prevents the displacement of the lens 5, and this can be made sufficiently small by using the above-mentioned configuration, so that the lens 5 can be prevented from being displaced. There is no need to increase the output of the amplifier for driving 5, and it is possible to simplify the structure and also reduce the size of the magnetic circuit.

Furthermore, since it is supported by a slide bearing 21,
The displacement range of the lens 5 can be increased.

In addition, by simply changing the DC level of the drive current of the coil 8, the lens 5 can be positioned at the reference position with respect to the disk, so when supporting the magnet 2 and yokes 3 and 4 with the arm, mechanical errors can be avoided. Even if this occurs, it is easy to adjust or correct it. Furthermore, since there are no leaf springs 11, 12, no vibration noise is generated.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional example, Fig. 2 is a sectional view of an example of the present invention, Fig. 3 is a bottom view thereof, Fig. 4 is a plan view of a part thereof, and Fig. 5 is a sectional view thereof. . 2 is a permanent magnet, 3 and 4 are magnetic yokes, 5 is an objective lens,
8 is a coil, and 21 is a slide bearing. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A permanent magnet and a magnetic yoke, an objective lens, a lens barrel housing this objective lens, and this lens barrel,
A slide bearing slidably supports the permanent magnet and the magnetic yoke in the optical axis direction of the objective lens with as little friction as possible, and is located in a magnetic circuit formed by the permanent magnet and the magnetic yoke. and a stopper that limits the displacement range of the lens barrel in the optical axis direction of the objective lens with respect to the drive coil attached to the lens barrel, the permanent magnet, and the magnetic yoke; A focus control device for an optical device, comprising means for preventing the lens barrel from rotating about the optical axis of the objective lens with respect to the permanent magnet and the magnetic yoke.