JPS5965945A - Focus control device - Google Patents

Abstract

PURPOSE:To obtain a titled device which scarcely causes a variation in characteristic due to surface swing and can execute easily an initial leading-in operation by coupling a fixed side and a moving side by a torsion bar which supports a slide bearing and also has a spring effect. CONSTITUTION:A coil holder 7 and a yoke 9a are connected by a torsion bar 11, and a spring constant term is added to a transfer characteristic. The transfer characteristic becomes a characteristic as shown in the figure, and has a resonance point f0=(K/M)1/2/2pi determined by a spring constant K and a moving part mass M. This spring constant term is a term of displacement and governs a characteristic in low frequency of vibration. Therefore, unless there is a spring term, surface swing dependability by which a term of friction depending greatly on a surface swing governs a characteristic of a low band is scarcely eliminated. Fron a surface swing value (scores of -seveval hundred microns) which is considered to be weight of a general objective lens 4, and a coefficient of friction (about 0.1-0.3) of a sliding part, a value of f0 can be selected within a range of several Hz-scores of Hz. As for the spring constant, it is desirable to make it small from the viewpoint of widening a linearity range and preventing high band resonance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus control device used for optical pickup in an optical information reproducing device or the like.

Conventional devices of this type include, for example, focus control devices for video disc players and digital audio disc players. Disks used in such devices generally have a track pitch of 1 to 2/Im and a track width of about 0.5 m.
They are as minute as 11rn, and in order to optically read such information signals, the reading light spot must be set at 1~1rn.
It is necessary to condense the light to about 21 InL. When the light is focused on such a small light spot, the depth of focus becomes as small as 1 to 2 am, and considering the surface wobbling caused by a rotating disk, the light spot is focused on a light beam orthogonal to the disk surface depending on the surface wobbling of the disk. A focus control device that performs tracking control in the axial direction is required. A conventional focus control device will be explained below with reference to FIGS. 1 and 2.

In FIG. 1, il+ is a disk, (2) is a light beam,
(3) is the focused light spot, (4) is the light beam (2
), 15) is a lens barrel joined to the objective lens (4), made of, for example, anodized aluminum, and (61 is a non-lubricated bearing, made of, for example, Teflon-based material). , (7) is a coil holder joined to the lens barrel (5), (81 is a coil, ((h),
(9.-)) is a yoke, and αQ is a magnet.

The objective lens (4) is fixed to a shaft (51) whose outer periphery is made of aluminized aluminum, etc. On the other hand, a Teflon-based dry bearing (6) is fixed to the inside of the yoke (9a), which is the fixed side. , and is held slidably in the optical axis direction +A+ with a gap of approximately several tens of microns by inserting the shaft 15+.

Further, a coil (8) is attached to the lens barrel (5) via a coil holder (7), and a yoke (
A coil (81) is arranged in a magnetic circuit formed by 9a), (9b) and a magnet (t(l).A light beam (2) is incident on the objective lens (4) of such a focus control device. A light spot (31) is placed on the disk (1).
form. When the disk (11) rotates, it causes surface deflection (several tens of microns to hundreds of microns) in the direction of the optical axis shown by the arrow (B).Therefore, such devices are equipped with a focus sensor (see Fig. (not shown)
is provided, and in order to convert this into an electrical signal and correct the focal shift, by applying a desired current to the coil (8), the objective lens (4) is moved along the optical axis in the direction of the arrow (/\).
The focus position was controlled by moving the .

Since the conventional focus control device is configured as described above, the position of the objective lens (4) cannot be determined and initial retraction at the start of operation is difficult. Further, in the transmission characteristics of the focus control device shown in FIG. 2, there was a phenomenon in which the characteristics changed depending on whether the surface runout of the disk (1) was large or small due to the influence of friction of the sliding portion. That is, as the disk surface runout becomes smaller, the gain decreases, and the degree of the decrease is approximately proportional to the change in the surface runout. So disk +11
The gain changes when reproducing the inner circumference and when reproducing the outer circumference.

The present invention has been made in order to eliminate the above-mentioned drawbacks of conventional focus control devices, and provides a device that is less likely to change characteristics due to surface runout and can perform an initial pull-in operation easily.

An embodiment of the present invention will be described below with reference to the drawings.

gJ3 and FIG. 4, the same numbers as in the conventional example indicate the same members. Ql) connects the coil holder (7) and the yoke (worm) with a torsion bar, and the member is made of, for example, a stainless steel wire for a spring.

That is, by connecting the fixed side and the movable side through the torsion bar (11) lζ which has a spring effect in addition to supporting the slide bearing, it is possible to add a spring constant term to the transmission characteristic, which was not available in the conventional linear type. When communicating with your heart! 1, the characteristics are as shown in Figure 5, and the resonance point 10 is determined by the number of springs and the moving part quality 1.↑)・4.
= , /" The dependence of the surface runout (velocity term) that dominates the low-frequency characteristics almost disappears.This tendency becomes more pronounced as the spring constant increases, but Runout value (several tens of microns)
The value of 10 is from several H2 to several tens of H, based on the Mazza coefficient (about 01 to 03) of the sliding part, which can be realized without difficulty (several hundred microns).
It can be selected within a range of about z. It is desirable to have a wide spring constant linearity range and to make it small in order to prevent high-frequency resonance. It is desirable for the spring structure to minimize the stiffness of the sliding portion as much as possible, and it is desirable to have a spring that generates almost no force in the direction perpendicular to the optical axis. Furthermore, even if there is almost no damping of the spring material, the increase in gain at the resonance point is due to the damping effect of the friction term and the gain peak at the resonance point.
Almost no damage occurs. Further, since the spring is used to generate a spring constant term K, there is no need to support the objective lens (4), and various types of springs can be selected. Further, by providing a spring effect, the midpoint position of the objective lens (4) is determined, and the sequence of the initial retracting operation is also simplified.

In Figures 3 and 4, four wooden torsion bars αυ are glued to the fixed side yoke and coil holder (7), respectively, but this is not limited to four wooden torsion bars, for example, it can be composed of two pieces. It is clear that similar effects can be achieved by

Further, FIGS. 6 and 7 show other embodiments of spring support.

That is, by joining one end of the spiral spring (121) to the coil holder (7) and the other end to the yoke (9b), it is possible to support the spring without interfering with the linearity of operation.

As described above, according to the focus control device of the present invention, the characteristics do not change due to surface deflection, and since the elastic body does not need to support the lens barrel, the spring constant of the elastic body can be reduced, so that the linearity range is wide. A focal-side S device with good damping characteristics at the resonance point and a simple initial pull-in operation can be realized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a conventional focus control device, FIG. 2 is a diagram showing the transmission characteristics of a conventional wave nail, FIG. 3 is a sectional view showing an embodiment of the present invention, and FIG. 4 5 is a front view (view from arrow C) showing one embodiment of the present invention, FIG. 5 is a diagram showing transfer characteristics of a focus control device according to the present invention, and FIG. 6 is a focus control device according to another embodiment of the present invention. FIG. 7 is a front view (view from arrow D) of the device shown in FIG. 6. In the figure, (41 is the objective lens, (5) is the lens barrel, (6 is
) is a non-lubricated bearing, (81 is a coil, (9a) (
9b) is a yoke, aO++ is a magnet, and αυα2 is an elastic body. Note that the same reference numerals in the figures indicate the same or equivalent parts. 9jl message to the agent - Figure 1? fl Han number figure 3 figure 4゜ figure 5'Fflfi&

Claims (1)

[Scope of Claims] (1) A condensing means for condensing a light beam, a lens barrel for holding the condensing means, and a sliding member for slidably supporting the lens barrel in the optical axis direction of the light beam. means, an elastic body stretched between the lens barrel and the non-sliding portion to elastically support the lens barrel, and a drive for driving the lens barrel to a desired position in the optical axis direction of the light beam. a focus control device having means. Place. (3) As a driving means, a magnetic circuit consisting of a yoke and a magnet is formed, a coil formed to wind the lens barrel is disposed in the magnetic flux, and a desired current is applied to this coil. 2. A focus control device according to claim 1 or 2 of the patent, characterized in that the device is driven. (4) The elastic body is a focus control device that is stretched between the end face of the lens barrel and the non-sliding part. (The elastic body 51 is a focus control device stretched between the end surface of the lens barrel and the non-sliding part.