JPH0240138A - Objective lens driving device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an objective lens driving device used in an optical information processing device or the like.

(Prior Art) Conventionally, there are optical information processing devices that record and reproduce information by condensing a laser beam onto an information recording medium using an objective lens. Due to accuracy, surface runout and eccentricity occur on the information recording medium. Therefore, in this type of optical information processing device, focusing control is performed to drive the objective lens in the normal direction of the information recording medium, that is, in the focusing direction so that the light spot is always focused on the signal recording surface of the information recording medium; Tracking control to drive in the tracking direction is required.

As an example of an objective lens drive device that performs focusing control and tracking control, JP-A-62-4
No. 0627 discloses an apparatus shown in FIG.

This objective lens drive device consists of a base (1) made of a magnetic material.
A pair of leaf springs (3a) are attached to the support (2) provided above.
, (3b), a movable support part consisting of a hinge (4) and a movable body (5) is supported, the movable body (5) at the tip thereof supports an objective lens (6), and a leaf spring (3a).

The elasticity of (3b) enables displacement in the focusing direction and in the racking direction centering around the movable portion of the hinge (4). Further, focusing coils (7L (7)) are attached to both sides of the movable body (5), and tracking coils (8) (8) are attached to the outside thereof.

The inner yoke (9) supported by the base (1) is located inside the base (1).
), (9), but also outer yokes (10), (10
) is arranged, and inside the outer yoke (10) and (10), an inner yoke (9L (9) side is a magnet (11) with one polarity.

(11) is installed.

Therefore, this objective lens drive device uses a magnet (
11), a base (1) made of magnetic material, this base (1)
) A magnetic circuit is constituted by the corresponding inner yoke (9) and outer yoke (10) supported by a focusing coil (7) and a tracking coil (
8).

With the above configuration, this objective lens driving device detects a focus shift or a shift from a track with respect to an information recording medium using an error detection device (not shown), and sends a control signal obtained from the detected shift amount to a focusing coil (7).
(7), L-racking coils (8), and (8) to generate a driving force that displaces the objective lens (6) supported by the movable support in the focusing direction or the tracking direction. ing.

That is, the driving force in the focusing direction of this objective lens driving device is generated by the magnet (11) as shown in FIG.
) and the inner yoke (9) and the control signal obtained from the amount of deviation detected by the error detection device, the magnet (11) of the focusing coil (7)
A current I of a predetermined magnitude flows through the portion (13a) facing the
obtained by interaction with. Now, as shown in FIG. 8, for example, the inner yoke (9) side of the magnet (11) (
When the polarity of the focusing coil (7) side is N pole, the magnetic flux (14) supplied by the magnet (11) passes through the portion (13a) of the focusing coil (7) facing the magnet (11). , passes through a magnetic circuit consisting of an inner yoke (9), a base (1), and an outer yoke (10),
A driving force for moving the objective lens in the focusing direction is generated in the focusing coil (7).

However, this driving force in the focusing direction is obtained only in the portion (13a) facing the magnet (11), and not in other portions of the focusing coil (7). Rather, a part of the magnetic flux (14) supplied from the magnet (11) goes around to the part (13b) opposite to the part (13a) facing the magnets 1 to (11), and this part (13b) The current flowing through the part (13
Since the direction is opposite to the current I flowing through a), a driving force opposite to the driving force in the focusing direction is generated in this portion (13b), thereby reducing the driving force in the focusing direction.

(Problems to be Solved by the Invention) As described above, in the conventional objective lens drive device, the driving force for moving the objective lens in the focusing direction is generated only by the portion of the focusing coil that faces the magnet.
q and cannot be obtained in other parts. Rather, a driving force in the opposite direction to the driving force in the focusing direction is generated in a portion of the focusing coil opposite to the portion facing the magnet, thereby reducing the driving force in the focusing direction.

This invention was made in view of the above problems, and
The driving force in the focusing direction is also generated in the part of the focusing coil on the opposite side of the part facing the magnet, which was not previously used to generate the driving force in the focusing direction. This increases the efficiency of using the focusing coil and increases the driving force. The purpose is to increase

[Structure of the Invention] (Means for Solving the Problems) In an objective lens driving device for recording and reproducing information on an information recording medium, a movable lens that supports the objective lens so as to be movable at least in the normal direction of the information recording medium is provided. A focusing coil is supported by the support part, an inner yoke is placed inside the focusing coil, and a main magnet with one magnetic pole on the inner yoke side is arranged at a certain distance from the inner yoke, and the above-mentioned flap is aligned. An auxiliary magnet was disposed inside the casing coil and on the opposite side of the inner yoke to the side facing the main magnet so that the inner yoke side had the same polarity as the inner yoke side of the main magnet.

(Function) As described above, if an auxiliary magnet is placed on the opposite side of the inner yoke to the side facing the main magnet so that the inner yoke side has the same polarity as the inner yoke side polarity of main magnets 1~, focusing The driving force in the focusing direction can be generated by the magnetic flux supplied by the auxiliary magnets 1 to the part of the coil opposite to the part facing the main magnet where the current flows in the opposite direction. It is possible to increase the driving force in the focusing direction by 1q only.

(Example) Hereinafter, the present invention will be described based on an example with reference to the drawings.

FIGS. 1 and 2 show an objective lens driving device which is an embodiment of the present invention. In this objective lens drive device, a support (22) is fixed to one end of a base (2o) made of a magnetic material such as mild steel by a pair of pins (21), (21), and the objective is mounted on this support (22). A movable support part (23) that movably supports the lens (6) is attached.

The movable support part (23) includes a movable body (24) made of a non-magnetic material that supports the objective lens (6), and one end of which is fixed to the support body (22) to support the optical axis of the objective lens (6). a pair of leaf springs (25a) and (25b) facing each other in the direction;
A fixed part (26) supported by the other ends of the pair of leaf springs (25a) and (25b), and a hinge (27) made of synthetic resin attached to this fixed part (26). and a movable body balance part (28) attached to the opposite side of the fixed part (26) of this hinge (27), and the movable body (
24) and the movable body balance part (28) are integrally joined.

The hinge (27) has a thin portion (29) formed long in the same direction as the optical axis of the objective lens (6),
The fixed part (26) supported by a pair of leaf springs (25a) and (25b) can be bent at its thin wall part (29) and restored to its original state by the elastic action of the synthetic resin. It becomes. And this hinge (26
) Movable body (24) joined together by bending
By rotating the movable body balance section (28), the objective lens (6) can be displaced in the tracking direction. The movable body balance section (28) has one or more, in the illustrated example, two, in order to balance the movable body (24) and the objective lens (6) supported by the movable body (24). balancer (30a), (
30b) is buried. Further, a pair of leaf springs (25a), (25b) facing each other in the optical axis direction of the objective lens (6)
) is a fixed part (26) supported by its (I!2 end),
The objective lens (6) can be displaced in the focusing direction via the hinge (27), the movable body balance section (28), and the movable body (24).

Furthermore, a pair of cylindrical focusing coils (7), (7) are attached to both sides of the movable support part (23), and a pair of tracking coils (8),
(8) is installed. Inner yokes (9), (9) supported by the base (20) are located inside each of the focusing coils (7), (7), and correspond to each inner yoke (9L (9)). Outer yokes (32), (32) made by bending the base (20) at right angles and standing up are provided on both sides of the base (20). York (9),
Main magnet (33) with inner yoke (9) and (9) as one magnetic pole on the side facing (9), (33)
) is installed. Roughly speaking, the objective lens drive device in this example includes each focusing coil (7), (7)
and an auxiliary magnet (34) on the side opposite to the side facing the main magnet (33), (33) of each inner yoke (9), (9).

(34) is installed and pulled. This auxiliary magnet (
34), (34) is the inner yoke (9L) (9) side is the above main magnet (33), (33) inner yoke (9)
, has the same polarity as the magnetic pole on the (9) side.

Therefore, in this objective lens driving device, each main magnet 1 to (33), (33) and each inner yoke (9), (
9) Tracking coil (8) in the magnetic gap between
.

(8) and focusing coil (7), the - side of (7) is arranged, and the focusing coil (7L (7)
The inner yoke (9), (9
) and auxiliary magnets (311) and (3/I) are arranged.

Tracking control a3 and focusing control of this objective lens drive device are performed as follows.

That is, for example, as shown in FIG. 3, if the polarity of the main magnet (33) on the inner yoke (9) side and the polarity of the auxiliary magnet (34) on the inner yoke (9) side are N poles, then The control is based on the magnetic flux (14) supplied to the magnetic gap between the main magnet (33) and the opposing inner yoke (9), and the tracking error signal obtained from the amount of slippage detected by an error detection device (not shown). This is done by rotating the movable body around the thin part of the hinge by the electromagnetic force generated between the tracking coil (8) and the current i of a predetermined magnitude applied to the tracking coil (8).

On the other hand, regarding focusing control, similarly to the tracking control described above, the main magnet (33) supplies magnetic flux (1) to the magnetic gap between each opposing inner yoke (9).
4) and a current of a predetermined magnitude that is applied to the focusing coil (7) based on the focusing error signal obtained from the amount of deviation detected by the error detection device. )
In addition to the electromagnetic force a generated between the current and the current flowing in the opposing part (13a), the magnetic flux supplied from the auxiliary magnet (34) passes through the inner yoke (9) and the opposite side of this auxiliary magnet (34). The magnetic flux (36) flowing from the side and the part (1
3b) That is, the part facing the main magnet (33) (
An electromagnetic force generated between the current (1) and the current (1) flowing to the opposite side (13b) of the opposite side (13b) also acts. Moreover, the part facing the main magnet (33) of the sing twill (7) (
The magnetic flux (14) of the main magnet (33) passing through the main magnet (13a)
) and the part (13) on the opposite side of the focusing coil (7).
b) Magnetic flux (36) of auxiliary magnets 1 to (34) passing through
) is opposite in direction and faces the main magnet (33) of the focusing coil (7) (13
Since the current flowing through a) and the current flowing through the opposite part (13b) are in opposite directions, the generated electromagnetic forces a and b are in the same direction, and as a whole, the electromagnetic force a and the electromagnetic force is added.

To describe the relationship between the electromagnetic forces a and b in more detail, there is an objective lens drive device with a conventional structure without an auxiliary magnet as shown in FIG. 4, and an auxiliary magnet (
As a result of measuring the magnetic flux density at positions (P) and (Q) in the magnetic circuit of the objective lens drive device of this example equipped with 34) with a Gaussmeter, the data shown below was obtained.

(Margins below) Table In addition, the minus and minus signs in the table indicate that the polarity is N-pole or S-pole.

By the way, if the magnetic flux density that passes perpendicularly through the length g of a conductor through which a current of size ■ is flowing is B, then the electromagnetic force acting on the conductor is F=8・■・β... ...... It is given by (1).

Therefore, the current flowing through the focusing coil is I(A), and the current flowing through the focusing coil is I(A), and the current flowing through the focusing coil is
If the length of the part (13a) facing 3) and the part (13b) on the opposite side is ρ (m), then the electromagnetic force F1 ( N) and F2
(N) are respectively F1=4700X10-3I −
J) -500XIO"I -9-4200x 10-
3 I ◆9 ・・・・・・・・・ (2) F2
=3900xlO-3I-1-(-2300) xlO
-3I -fJ=6200x10-3I ・ρ
...Team...white... (3). In other words, when the auxiliary magnet is attached, the magnetic flux density at position (P) decreases, but due to the increase at position (0), the calculated driving force increases by approximately 48% as a whole compared to the case without the auxiliary magnet i~. I will do it. This calculated increase in driving force agrees well with the actually measured increase in driving sensitivity (about 41%), and the focusing driving force can be significantly increased by attaching the auxiliary magnet i~.

[Effects of the Invention] On the side surface opposite to the side surface facing the main magnet of the inner yoke inside the focusing coil supported by the movable support part that movably supports the objective lens, the inner yoke side has the polarity on the inner yoke side of the main magnet. When the auxiliary magnets are arranged so that the polarity is the same, in addition to the focusing driving force obtained in the part of the focusing coil facing the main magnet, the magnetic flux from the auxiliary magnet causes the part of the focusing coil facing the main magnet to have the opposite polarity. A focusing driving force in the same direction can be generated in the side portions, and the driving force for moving the objective lens in the focusing direction can be increased.

[Brief explanation of the drawing]

Figures 1 to 5 are detailed explanatory diagrams of this invention.
The figure is a perspective view showing the configuration of an objective lens driving device which is an example of the objective lens driving device, FIG. 2 is a sectional view taken along the line ■-■, and FIG. 3 (A)
Figures 4 (A) and (B) are a plan view of the magnetic circuit and a sectional view taken along the line ■-■ to explain the tracking control and focusing control, respectively.
The figures are diagrams for explaining the measurement of magnetic flux density in a magnetic circuit without an auxiliary magnet attached, and Figure 5 (A).
and (B) are diagrams for explaining the measurement of magnetic flux density in a magnetic circuit equipped with an auxiliary magnet, and FIG. 6 is a perspective view showing the configuration of a conventional objective lens drive device.
FIG. 7 is a plan view of the magnetic circuit, and FIG. 8 is a sectional view taken along the line ■-■. 6... Objective lens 7... Focusing coil 8... To racking coil 9... Inner yoke 20... Base 23... Movable support section 24... Movable bodies 25a, 25b... Leaf spring 26...fixed part 27...hinge 28...movable body balance 32...outer yoke 33...main magnet 34...auxiliary magnet

Claims (1)

[Claims] an objective lens that irradiates light for recording and reproducing information on an information recording medium; a movable support that supports the objective lens movably at least in the normal direction of the information recording medium; and a movable support that is attached to the movable support. an inner yoke supported by a base and disposed inside the focusing coil; and a main magnet constituting a magnetic circuit together with the inner yoke, and a main magnet arranged on the side surface of the inner yoke so that the inner yoke side has the same polarity as the inner yoke side of the main magnet, and the inner side of the focusing coil. An objective lens driving device characterized by comprising an auxiliary magnet located at.