JPS6145422A - Rotary actuator - Google Patents

Abstract

PURPOSE:To obtain high sensitivity in both focusing and tracking directions by uniforming the directions of rotational moment generated on coil parts in two magnetic gaps corresponding to a tracking coil. CONSTITUTION:The external periphery part of an objective lens holding cylinder 1 and a focusing coil 16 are arranged in a magnetic gap 17 between a york 12 and an intermediate york 14 to control the movement of the cylinder 1 in accordance with the direction and size of current flowing into the coil 16 and to attain focusing. On the other hand, parts 15a, 15b of a tracking coil 15 are arranged in the magnetic gaps 17, 19 respectively to control the movement of the cylinder 1 in the turning direction on the basis of the direction and size of current flowing into the coil while receiving the turning force of the same direction from respective magnetic circuits 18, 20. Consequently, a half or more of the whole length of the coil 15 is contributed to the tracking operation and the whole length of the coil 16 is contributed to focusing to obtain high sensitivity in both the tracking and focusing.

Description

Detailed Description of the Invention Field of the Invention The present invention relates to a rotary actuator used in a pickup for recording and reproducing various optical discs such as optical video discs, compact digital audio discs, and still image disc files. It is.

A conventional rotary actuator will be described with reference to the drawings. Figure 1 is an external view of a conventional rotary actuator, Figure 2 is a sectional view in the X direction of Figure 1, and Figure 3 is a cross-sectional view of a conventional rotary actuator.
FIG. 3 is a cross-sectional view in the y direction of the figure.

Reference numeral 1 denotes an objective lens holding cylinder, in which an objective lens 2 is provided at a position eccentric from the center of rotation. Reference numeral 3 denotes a rotation shaft vertically erected from the yaw 5, and a bearing provided inside the center of the objective lens holding cylinder 1 is fitted inside the portion 4. The objective lens holding cylinder 1 performs a tracking operation by rotating around this rotation axis 3, and performs a focusing operation by sliding in the axial direction. A magnetic circuit for performing focusing and tracking operations will be described below.

A ring-shaped magnet 6 is attached to the outer circumference of the yoke 5, and an outer circumferential yoke 7 is attached thereon.

The outer yoke 7 consists of a domain wall 7a and a notch 7b, and these domain walls 7a and notches 7b are provided in pairs at symmetrical positions divided by 9a in the circumferential direction. The yoke 5 also consists of a domain wall 5a and a notch 5b, and the yoke 5 and the outer yoke 7 are arranged so that the domain walls 5a and 7a and the notches 5b and 7b face each other.

A magnetic rotation ff is formed between the domain wall 5a, the magnet 6, and the domain wall 7a.
18 is constructed, and the outer peripheral portion of the objective lens holding cylinder 1 is fitted into the magnetic gap 11 between the domain walls 5a and 7a. A focusing coil 9 and a tracking coil 10 are mounted on the outer periphery of the objective lens holding cylinder 1. The focusing coil 9 is wound in the circumferential direction, and by passing a current through it, a force is applied to the coil 9 in the axial direction of the rotating shaft 3.
Focusing is performed by controlling the axial movement of the rotating shaft 3 of the objective lens holding barrel 1 depending on the direction and magnitude of the current. The tracking coil 10 is wound into a rectangular shape and is mounted on the circumference of the objective lens holding cylinder 1.

The tracking coil 10 is composed of parts 10a and 10b wound in the axial direction of the rotating shaft 3 and parts 10c and 10d wound in the circumferential direction. belongs to the magnetic gap 11, and the remaining half belongs between the notches 5b and 7b. When a current is passed through the coil 10, currents flow in opposite directions in the circumferential direction in the portions 10c and 106, so that the magnetic circuit 8 receives forces in opposite directions, and the forces cancel each other out. The portion 10a located in the magnetic gap 11 is subjected to a circumferential force by the magnetic circuit 8. A current flows in the portion 10b in the opposite direction to that in the portion 10a and receives a force in the opposite direction, so that the portion 10b is disposed corresponding to the cutout portions 5b and 7b where the magnetic circuit 8 is not provided. Generally, four tracking coils 10 are installed at substantially symmetrical positions, and the direction of the current is taken into consideration so that each coil 10 receives a force in the same direction. In this way, the direction and magnitude of the current flowing through the tracking coil 10 controls the rotation of the objective lens holding cylinder 1 around the rotation '@@3, thereby performing tracking.

However, in the conventional example described above, the focusing direction,
There is a problem in that the acceleration in both the tracking directions is insufficient, especially in the tracking direction.

The fundamental reason for the lack of acceleration is that both the focusing coil 9 and the tracking coil 10 contribute to driving the objective lens holding cylinder 1 by only a portion of the total coil length. Focusing coil 9 also has half of its total length as yoke 5.
．． Since both the notches 5b and 7b of No. 7 pass through a place where there is no magnetic field, only half of the total length of the coil contributes to the focusing drive. In the case of tracking coil 10,
Since only the coil 10a passes through the magnetic air gAii, only about 1/4 of the total coil length contributes to the tracking drive. For the reasons mentioned above, the lack of sensitivity in the conventional example 114 is due to the structure itself, and it is extremely difficult to increase the sensitivity.

Purpose of the Invention The present invention newly configures the magnetic circuit, yoke shape, tracking coil, etc., greatly increases the contribution of both the focusing coil and the tracking coil to driving the objective lens holding tube, and increases the contribution of both the focusing coil and the tracking coil to the driving direction of the objective lens holding tube. The purpose is to obtain a rotary actuator whose sensitivity can be folded.

Structure of the Invention The rotary actuator of the present invention is characterized in that the first magnetic gap and the tracking coil form a magnetic circuit, and the first magnetic gap is arranged along the outer periphery of the objective lens holder. and a second magnetic gap is formed so as to be located in a circumferential direction radially outward from the first magnetic gap, and is composed of the tracking coil and the first magnetic gap. The rotational moment generated by the first magnetic circuit and the second magnetic circuit including the tracking coil and the second magnetic gap is configured so that the directions of rotational moments about the rotating wheel are equal to each other. It is something.

According to this, the tracking coil effectively contributes to driving the objective lens holding cylinder, and the effective length of the focusing coil becomes long, so that high sensitivity can be obtained in both the focusing direction and the tracking direction.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 4 and subsequent figures. Reference numeral 1 denotes an objective lens holding cylinder, 2 an objective lens, 3 a rotating shaft, and 4 a bearing for the rotating shaft 3, which have the same structure as the conventional example.

Reference numeral 12 denotes a yoke that supports the rotating shaft 3. A ring-shaped magnet 6 is attached to the periphery of the yoke 12, and an outer yoke 13 is further provided on the outer periphery of the yoke. A middle circumference yoke 14 is mounted on the ring-shaped magnet 6, and this middle circumference yoke 14 has a relief part 1 for winding a tracking coil 15.
4a and a cutout 14b for inserting the yoke 14 into the coil 15, and a yoke piece 14c that closes the cutout 14b after insertion into the coil 15. In this embodiment, there is a pair of middle circumference yokes 14 symmetrically arranged, and a full circumference yoke is formed by attaching the yoke pieces 14c.
has been completed.

1G is a focusing coil, which is wound around the outer circumference of the objective lens holding cylinder 1 in the circumferential direction. Objective lens holding tube 1
The outer periphery of and the focusing coil 16 are placed in a first magnetic gap 17 between the yoke 12 and the middle yoke 14 . When current flows through the focusing coil 1G, a force is generated in the recoil 16 in the axial direction of the rotating shaft 3 in the magnetic circuit 18 composed of the yoke 12, the magnet 6, and the middle yoke 14, so that the coil 1G Focusing can be performed by controlling the movement of the objective lens holding cylinder 1 depending on the direction and magnitude of the current passed through the lens.

The tracking coil 15 wound in a rectangular shape is arranged in an annular shape on the outer periphery of the objective lens holding cylinder 1 and is mounted on the focusing coil 16, and is configured such that the intermediate yoke 14 can be inserted into the inside of the coil 15. There is. Needless to say, the gap between the coil 15 and the intermediate yoke 14 is designed to prevent the coil 15 from coming into contact with each other even if the coil 15 moves in the axial direction of the rotating shaft 3 and in the rotating direction of the objective lens holding cylinder 1. stomach. The tracking coil 15 is the rotation axis 3
It consists of parts 15a and 15b wound in the axial direction of the rotating shaft 3, and parts 15c and 15d wound in the direction perpendicular to the rotation axis 3, and the part 15a is wound in the first magnetic gap 17 in the same way as the focusing coil 16. , and the portion 15b is within the second magnetic gap 19. When a current is applied to the coil 15, the portion 15a is removed from the magnetic circuit 18 and the portion 15b is removed from the magnetic circuit 18.
receive a force from the magnetic circuit 20, but since the direction of the current and the direction of the magnetic field in the magnetic gap are opposite to each other, the portions 15a and 15b receive a rotational force in the same direction. Since portions 15C and 15d are not in the magnetic field, no force is generated.

Therefore, depending on the direction and magnitude of the current flowing through the tracking coil 15, the rotational movement of the objective lens holding cylinder 1 can be controlled to perform tracking.

Comparing the 1-racking coil 15 of this embodiment with the tracking coil 10 of the conventional example, the tracking coil 15 of this embodiment can be easily increased in both the number of windings and the coil length. ~ It is possible to contribute more than half of the total length of the focusing coil 15 to the tracking operation (m). Therefore, it is possible to obtain high sensitivity in the tracking direction. Focusing on the focusing operation, the middle circumferential yoke 14 contributes to the tracking operation. Since the coil 16 is located on the outer periphery of the focusing coil 16, the entire length of the coil 16 is within the magnetic gap 17, and all of the coils contribute to focusing.Therefore, it is possible to obtain sharp sensitivity in the focusing direction as well.

As described above, according to this embodiment, the tracking coil 15 is sandwiched between the two magnetic gaps 17 and 19, and the dragging coil 15. Since both the A-focusing coil 1°6 and its angle are effectively contributed to driving the objective lens holding barrel 1, it is possible to achieve high sensitivity for both focusing and focusing. In the above embodiment, the yoke 12, the middle yoke 14, and the outer yoke 13 are integrally constructed, but the structure of the yoke is not limited to an integral type, and each yoke part is made independently and screwed together. You can obtain exactly the same function by fixing or gluing. Further, although two tracking coils 15 are installed in the circumferential direction in the above embodiment, this number is not limited to two, and the same function can be obtained even if three or more tracking coils are installed. be able to.

FIG. 7 shows another embodiment, in which a magnet 21 is attached to the surface of the outer yoke 13 facing the tracking coil 15. In this way, the second magnetic, air gap 19
Since the magnetic flux density within the tracking coil 15 becomes larger and the force generated in the tracking coil 15 also becomes larger, it is possible to obtain a rougher sensitivity in the tracking direction.

Effect of Haro As is clear from the above explanation, in the rotary actuator of the present invention, two magnetic gaps correspond to the tracking coil provided on the circumference of the objective lens holding cylinder, and the The tracking coil is designed so that the directions of the rotation moments around the rotation axis generated in the coils are mutually exclusive, so the tracking coil effectively contributes to driving the objective lens holding tube, and also the focusing coil. Since there is no notch in the sandwiching yoke, the effective length of the focusing coil becomes longer, and it has the advantage of achieving high sensitivity in both the focusing and tracking directions, making it a high-performance actuator for optical pickups that perform recording and playback of optical discs, etc. It has the excellent effect of providing

[Brief explanation of the drawing]

Figure 1 is a perspective view showing the configuration of a conventional example, and Figure 2 is the same as above.
3 is a y-direction sectional view of the same as above, FIGS. 4 and 5 are assembled perspective views showing an embodiment of the rotary actuator of the present invention, and FIG. 6 is a sectional view in the two directions of FIG. 4. FIG. 7 is a sectional view of the second embodiment. 1... Objective lens holding tube, 2... Objective lens, 3...
... Rotation axis, 12 ... Yoke, 13 ... Outer circumference yoke, 14 ... Middle circumference yoke, 14a ... Relief part, 14b
... Missing part, 14c... Yoke piece, 15... Tracking coil, 16... Focusing coil, 1
7... First magnetic gap, 18... First magnetic circuit,
19... Second magnetic gap, 20... Second magnetic circuit agent Yoshihiro Morimoto Figure 1 (ν2 Figure 2 Figure 3 (ν)) Figure S Figure 4 Figure 7

Claims (1)

[Scope of Claims] 1. An objective lens holding tube externally fitted around the rotating shaft so as to be rotatable in the circumferential direction and slidable in the axial direction; A rotary actuator having an objective lens provided thereon, and a focusing coil and a tracking coil provided on the outer periphery of the objective lens holding cylinder, the first and second magnetic fields forming a magnetic circuit with the tracking coil. The air gaps are arranged such that the first magnetic air gap is located along the outer periphery of the objective lens holding cylinder, and the second magnetic air gap is located in the circumferential direction radially outward of the first magnetic air gap. a first magnetic circuit configured with the tracking coil and a first magnetic gap; and a second magnetic circuit configured with the tracking coil and a second magnetic gap. A rotary actuator characterized in that it is configured so that the directions of rotational moment about a moving axis are equal to each other. 2. The rotary actuator according to claim 1, wherein at least one of the first and second magnetic gaps constitutes a magnetic circuit together with a focusing coil. 3. A yoke provided around the objective lens holding tube to form the first and second magnetic gaps is inserted into an annular tracking coil fixed to the outer periphery of the objective lens holding tube. A rotary actuator according to claim 1 or 2. 4. In order to allow the yoke to be inserted into the tracking coil, a relief part for forming the yoke into a rod shape and a cutout part for dividing the yoke in the circumferential direction were formed in a part of the yoke. The rotary actuator according to claim 3, characterized in that: 5. The rotary actuator according to claim 4, wherein the defective portion is filled with a yoke piece so that a magnetic gap is formed all around the rotary shaft.