JPS60201541A - Objective lens device - Google Patents

Abstract

PURPOSE:To rotate smoothly an objective lens holding barrel by setting a ratio of a product between the number of windings and a current of each tracking coil so as to be equal to a ratio of distance between each tracking coil and a support shaft. CONSTITUTION:The ampere-turn ratio of the tracking coils 17, 17', that is the ratio of the product between a current and the number of windings, is selected to a value so as to generate F1, F2 proportional to distances r1, r2 from a support shaft 2 to each acting point and obtaining the relation of F1.r2=F2.r2 thereby rotating smoothly the objective lens holding barrel 9. Since the drive forces F1, F2 generated from the tracking coils 17, 17' are exerted vertically on a normal of the support shaft 2 at all times in this way, even when the turning angle of the objective lens holding barrel 9 is larger, no side pressure is exerted on the support shaft 2 and then the objective lens holding barrel 9 is rotated more smoothly.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an objective lens device used in an optical disc player.

Background Art> A conventional objective lens device of this type is disclosed in Japanese Patent Application Laid-Open No. 57-2104.
As seen in Publication No. 57, an objective lens holding tube supporting an objective lens is pivoted at its center, and a magnetic circuit means provided in relation to this objective lens holding tube is used to adjust the focus direction (optical axis direction of the objective lens). ) and tracking direction (radial direction of the disc).

By the way, in an objective lens device having such a structure, in order to be able to adjust the tracking direction sufficiently, it is necessary to increase the amount of eccentricity of the objective lens from the center of the holding tube, and therefore the diameter of the lens holding tube must be increased. This has the disadvantage that it increases the size of the device as a whole.

OBJECTS OF THE INVENTION The present invention was devised in view of the drawbacks of the above-mentioned conventional devices, and by providing a supporting shaft for pivotally supporting the objective lens holding cylinder at a position eccentric from the center of the objective lens holding cylinder, To provide an objective lens device capable of sufficiently adjusting the tracking direction without increasing the diameter of the objective lens holding tube, and further to enable smooth rotation of the objective lens holding tube even in such a structure. It is something.

<Embodiment of the present invention> Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 to 4 are a perspective view, a plan view, a front sectional view, and an exploded perspective view of an objective lens device according to the present invention. The body is provided with arc-shaped first yokes 3 and 3' at left and right positions sandwiching the support shaft 2, and stopper holes 5a, 5a are provided so as to sandwich the support shaft 2 in the front and rear directions perpendicular to these yokes. '
and a support protrusion 4.4' having a support shaft 2 and a first
A through hole 6 that allows the light beam to pass through the plate surface between the yoke 3 and the yoke 3.
is installed.

7 and 7' are magnets mounted and fixed on the base body l on the outside of the first yokes 3 and 3', and the upper surface thereof has an arc along the arc of the first yoke 3 and 3'. A second yoke 8°8' with surfaces 8a, 8a' is fixed.

Reference numeral 9 denotes an objective lens holding tube made of a cylindrical body with an open bottom surface, and the closed end surface thereof, that is, the back surface of the upper wall surface, is inserted into the above-mentioned support shaft 2 at a position offset from the center O of the upper wall surface. It has a bearing part 10 to be supported, and has a position on the upper wall surface opposite to the bearing part IO with a line connecting the center O and the center of the bearing part IO (the center of the support shaft 2) above. It has a lens holding opening 11 into which the objective lens 14 is fitted, and an insertion opening 12 that sandwiches the center O in a direction orthogonal to the line t connecting the center O and the center of the bearing part IO.
．． 12' is open.

Further, the objective lens holding cylinder 9 has a peripheral edge of the upper wall surface opposite to the side having the lens holding opening 11 cut out +3, and a balance weight I5 is fixed to this portion.

16 is a focusing coil directly wound around the outer periphery of the objective lens holding cylinder 9, and 17 and 17' are tracking coils fixed to the outer periphery of this focusing coil.

Reference numeral 18 denotes a neutral holder made of an elastic material such as rubber, and includes a main body part 18a to be inserted into the bearing part IO, a stopper hole +8c extending horizontally in front and behind this main body part 18a, and a stopper hole +8c at the tip.
It consists of a holding arm portion 18b, +8b' having a diameter of 18c'.

The objective lens holding tube 9 is attached to the objective lens 14 as described above. Each coil 16 and I'7. IT' is fixed and the neutral holder 1 is attached to the bearing part 10 with the main body part 18a.
8 is inserted, and the neutral holder 18 is inserted and supported by the support shaft 2 using the bearing part 10 so that the holding arms 18b and 18b' rest on the support protrusions 4 and 4', Furthermore, the stopper member 1 is inserted through the insertion hole 12.12' provided on the upper wall surface.
9. Attach 19' to the neutral retainer and support projection hole +8c, +
Removal is stopped by inserting into 8c', 5a, and 5a'.

In this state that the objective lens holding cylinder 9 is inserted and supported on the support shaft 2, it can move up and down (in the focus direction) and rotate (in the radial direction) along the support shaft 2.
and a second yoke, and the objective lens 14 is opposed to the through hole 6 on the base body l.

Therefore, when current is applied to the focusing coil 16 and the tracking coil 17, 17', the objective lens holding cylinder 9 moves up and down in the focusing direction along the spindle 2 at a rate proportional to the current value. It rotates in the radial direction about the support shaft 2, and in cooperation with circuit means and other mechanical means (not shown) can direct the light beam emitted from the objective lens 14 to a predetermined position on a track on the disk.

By the way, in the present invention, the positions of the tracking coils 17 and 17' with salts 9 are shown in FIG.

Special consideration has been taken as shown in Figures 2 and 5.

That is, as is clear from Fig. 4, the tracking coil 17, 17' is a planar annular body consisting of vertical portions a, a' and horizontal portions b, b'. The center Ql, Q in the width direction of one vertical portion a
2 is the above 1st. A second yoke is fixed to the outer circumferential surface of the focusing coil 16 so that the line connecting the center 0 of the objective lens holding cylinder 9 and the center of the support shaft 2 is located above the second yoke. By fixing the tracking coil 17.17' on the focusing coil 16 in this way, the point of action of the magnetic field based on the tracking coil 17.17' on the objective lens holding cylinder 9 is at the center Ql.

Q2, and the driving force Fl (Fl' and F2CF2') acts in the direction perpendicular to the line t, that is, in the tangential direction of the objective lens holding cylinder 9. Therefore, the driving force F
lCF+') and F2 (F2') do not include any force that distorts the support shaft 2, and the objective lens holding cylinder 9 can be smoothly rotated about the support shaft 2.

Note that the above point of action is, for example, the objective lens holding tube 9 in FIG.
If the arrangement of the tracking coil, each yoke, and the magnet is set so that they are located at points PI and P2, the driving force fl at each point of action is set.

Needless to say, the component forces fll and f12 of f2 act as side pressures that distort the support shaft 2, and the smooth rotation of the objective lens holding cylinder 9 is obstructed.

Further, in the present invention, the tracking coils 17 and 17'
The ampere-turn ratio of , that is, the ratio of the product of the current and the number of turns, is proportional to the ratio of the distances rl and r4 from the support shaft 2 to each of the above points of application, and the following formula % formula % is obtained. , F2 are selected to generate values, and the objective lens holding cylinder 9 is configured to rotate smoothly.

In addition, in the present invention, as shown in FIG. 6 as another embodiment, the radius of curvature r', R ' and r.

By making the center of R the center of the support shaft 2, the direction of the magnetic lines of force is formed radially around the support shaft 2.

As a result, the driving forces Fl and F2 generated by the tracking coils 17° and 17' always act perpendicular to the normal line from the support shaft 2, so the rotation angle of the objective lens holding tube 9 becomes large. Since no lateral pressure is applied to the support shaft 2, the objective lens holding cylinder 9 can be rotated more smoothly than in the case shown in FIG.

Furthermore, in the present invention, as shown in FIG. 7, on the outer peripheral surface of the objective lens holding cylinder 9, a large number of ribs 20 are provided at equal intervals extending in the vertical direction over the entire outer periphery, so that the focusing coil 16
A gap is provided between the coil and the objective lens holding cylinder 9 to improve the heat dissipation effect against heat generated in each coil portion.

<Effects of the present invention> Since the present invention is configured in an upwardly slanted manner, the tracking direction can be adjusted by increasing the amount of eccentricity from the rotation center of the objective lens without increasing the diameter of the objective lens holding cylinder. Moreover, since the ratio of the product of the number of turns of each tracking coil and the current is made equal to the ratio of the distance between each tracking coil and the support shaft, the objective lens holding tube can be rotated smoothly. This is an excellent invention.

[Brief explanation of the drawing]

1 to 4 show a perspective view, a plan view, a front sectional view, and an exploded perspective view of an objective lens device according to the present invention, FIG. 5 is an explanatory diagram of its operation, and FIG. Floor plan, 7th
The figure is a perspective view showing a different embodiment of the objective lens holding cylinder in the objective lens device. l: base body, 2: support shaft, 3 (3'): first yoke,
7 (7'): Magnet, 8 (8'): Second yoke. 9: Objective lens holding cylinder, 14: Objective lens, 16: Focusing coil, +7 (17'): ) Racking coil. Agent Patent Attorney Aihiko Fukushi (and 2 others) Figure 7 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. First yokes are provided on both sides of the support shaft on a base body having a support shaft, and magnets and second yokes are provided outside of these first yokes in correspondence with each of the first yokes. An objective lens holding cylinder holding an objective lens is inserted into the support shaft so that its peripheral surface is positioned between the first yoke and the second yoke, and the objective lens In a lens holding tube in which focusing and tracking coils are fixed to the outer peripheral surface of the lens holding tube, the support position of the objective lens holding tube by the support shaft is a position offset from the center of the objective lens holding tube. At the same time, the tracking coil is fixed to the outer peripheral surface of the objective lens holding cylinder so that the point of action is located on a line connecting the center of the objective lens holding cylinder and the support shaft, and the number of turns and current of each tracking coil are fixed. An objective lens device in which the ratio of the products of is set to be equal to the ratio of the distance between each tracking coil and the above-mentioned support shaft.