JP2575354B2 - Objective lens drive - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to an optical pickup objective lens driving device for reading information on a recording medium.

[Technical background of the invention and its problems]

In an optical disk apparatus, an optical pickup focuses light emitted from a light source (laser) on a disk by an objective lens, and records a signal on the disk using the focused light, or records the reflected light from the disk. Or read a signal that has been transmitted. However, an actual disk has warpage or eccentricity, and light from a light source must be appropriately focused on the track of the disk in accordance with the warpage or eccentricity. Various proposals have been made for this method. Among them, a system for driving the light from the optical pickup in a direction perpendicular to the disk surface (Focus direction) and a direction in which the track moves due to the eccentricity of the disk (Radial The optical pickup having a system for driving in the direction (i.

However, the drive system in the Focus direction and Radia
By driving according to the amount of each error by the driving system in the l direction, the objective lens of the optical pickup is tilted with respect to the optical axis, causing aberration (optical shift) and focusing the light well. There was a problem that it could not be done.

In order to solve this problem, conventionally, there has been an attempt to correct the above-mentioned inclination by using a configuration called a short voice coil or attaching a counter weight below a bobbin holding an objective lens.

However, no matter which of these methods you use, Radial
Drive only in the direction or when the Radial direction is in the neutral position
When driving only in the s direction, there is no problem at all, but R
When driving in the Focus direction when the radial direction is not at the neutral position, that is, when driving both the Focus direction and the Radial direction at the same time, a tilt in the Radial direction occurs. As a countermeasure, a configuration was adopted in which several objective lenses were combined so that no aberration would occur even if the objective lens was tilted to a certain degree. However, this method naturally increased the weight, and the drive sensitivity was deteriorated. In addition, configuring the objective lens itself to correct aberrations is problematic in terms of cost, and is compact, lightweight, low-cost, and
It has been a conventional technical problem to realize an optical pickup that can be accurately driven to a predetermined position.

[Object of the invention]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and an object of the present invention is to provide an objective lens driving device which does not tilt the objective lens even when driven in two directions simultaneously.

[Summary of the Invention]

An objective lens driving device according to the present invention includes an objective lens that focuses light, a bobbin that holds the objective lens, a first coil that drives the bobbin in an optical axis direction of the objective lens, and an optical axis direction. A movable section comprising a plurality of second coils provided close to the first coil for driving in a direction orthogonal to each other and provided symmetrically with respect to the optical axis; In order to drive the lens in the optical axis direction and in a direction orthogonal to the optical axis direction, a common magnetic field is applied to both the first and second coils of the movable section, and the first and second coils are provided. The length of the surface that generates the magnetic field with respect to the second coil arranged in a direction orthogonal to the optical axis direction in the direction orthogonal to the optical axis is opposite to the second coil. 1 coil in a direction orthogonal to the optical axis. It is approximately half of the, in the same number as the plurality of second coils and is characterized by comprising a magnetic field generating means symmetrical configuration with respect to the optical axis.

〔The invention's effect〕

According to the present invention, it is possible to provide an objective lens driving device in which the objective lens does not tilt, so that the burden of aberration correction on the objective lens itself is reduced, and a lightweight and inexpensive objective lens can be used, and the drive sensitivity can be improved. And the cost of the optical pickup can be reduced, and in a device that does not require much drive sensitivity, the device can be made smaller.

(Example of the invention)

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

FIG. 1 is a perspective view showing the configuration of an objective lens driving device for an optical pickup according to the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a side view thereof. The objective lens 11 has an optical axis on a dotted line 20, and the objective lens 11 is held by a bobbin 12. In order to drive the objective lens 11 in the Focus direction with the bobbin 12 as a center, the Focus coil 13 is wound in a rectangular shape so as to cover center poles 18a and 18b described later. Also, a radial coil wound flat on the surface of the focus coil 13 to drive the objective lens 11 in the radial direction.
Four coils 14a to 14d are attached. (14 in the figure
c, 14d only), objective lens 11, bobbin 12, F
The ocus coil 13 and the radial coil 14 are generally called a movable part.
The movable portion is supported by four suspensions 15 so as to be movable in two directions, a Focus direction and a Radial direction, as conventionally used. Center poles 18a and 18b are provided on the left and right sides of the bobbin 12, and a permanent magnet 1 is provided on the side facing the center poles 18a and 18b with the radial coils 14a to 14d interposed therebetween.
6a to 16d are provided, and the permanent magnets 16a to 16d are attached to the protrusions of the yokes 17a to 17d having four protrusions. Hereinafter, the permanent magnet 16a, the yoke 17a, the center pole 18a and the permanent magnet 16b, the yoke 17b, the center pole 1
8b, permanent magnet 16c, yoke 17c, center pole 18c
And, permanent magnet 16d, yoke 17d, center pole 18d,
Are respectively called first to fourth magnetic circuits.
The first to fourth magnetic circuits always generate a magnetic field having a uniform distribution. The arrangement method, which is one of the features of the present invention, will be described in detail later. In these configurations, currents are applied to the Focus coil 13 and the Radial coils 14a to 14d in accordance with the amount of error, thereby generating a portion of each coil in a uniform magnetic field according to Fleming's left-hand rule. Using the force, move the objective lens 11 in the Focus direction,
It is a mechanism to drive in each direction of al direction. or,
A counterweight 19 is attached to a lower portion of the bobbin 12. The counterweight 19 will be described later in detail.

Conventionally, an objective lens driving device has been configured as shown in FIG. That is, the bobbin 71 holding the objective lens 70 is provided with four protrusions, and the suspension 72 is provided here to support the bobbin 71. A permanent magnet 73a is provided inside the suspension, and a permanent magnet 73b is provided at a position facing the permanent magnet 73a across the bobbin 71. That is, by providing the pair of permanent magnets 73a and 73b, the suspension 72 must be provided at a portion protruding from the bobbin 71. In contrast, in the case of the present application,
By providing two pairs of the permanent magnets 17a to 17d in FIG. 1, the suspension 15 can be provided inside the permanent magnets 17a to 17d. That is, it is obvious that the size becomes smaller than the conventional one.
The reason for configuring the permanent magnets 17a to 17d in this manner will be described in detail later.

In FIG. 2, the first to fourth magnetic circuits described above include:
The focus coil 13 is arranged so that the outermost part in the direction orthogonal to the uniform magnetic field (dotted line 200) coincides with the outermost part of the uniform magnetic field (200). Now, in the Focus coil 13, the length l ₁ in the direction orthogonal to the uniform magnetic field (200) generated by this magnetic circuit, and the length of the uniform magnetic field (200) portion are 2 × l ₂ . I do. l ₁ and the ratio of 2 × l ₂ When the movable part shifts in the Radial direction with the parameter as a parameter, when trying to drive in the Focus direction (perpendicular to the plane of the paper), the leftward moment Ml and the rightward moment Mr at the center of gravity of the movable part are calculated. Find the ratio.

FIG. 4 shows the results of the experimental data. Radial on horizontal axis
The direction shift amount and the vertical axis represent Ml / Mr. Also, parameter as sample Are taken as 0.3, 0.4, 0.5, 0.6, 0.7. If Ml / Mr is not 1.0 and Ml / Mr> 1, it is driven counterclockwise, and if Ml / Mr <1, it is driven clockwise, and the movable part is driven in the Focus direction. The objective lens is inclined with respect to the optical axis, that is, the problem described in the conventional example occurs. However, as can be seen from the figure, when Ml / Mr = 1 holds,
When the movable part is shifting in the Radial direction,
Even when driven in the Focus direction, the objective lens does not tilt with respect to the optical axis. In other words, by configuring so that 2 · l ₂ / l ₁ = 0.5, the objective lens does not tilt with respect to the optical axis even if it is simultaneously driven in both the Focus direction and the Radial direction. An excellent device can be realized.

In FIG. 3, the height of the permanent magnet 16 is set so that the driving force always acts on the center of gravity of the movable part in the respective directions of Focus and Radial.
The focus coil 13 and the radial coil 14 are made higher so that the effective portion of each coil does not protrude from the uniform magnetic field generated by the magnetic circuit. In addition, Focu
The effective portion of the s coil 13 is a region that generates a driving force necessary for movement in the focus direction, and is located between a magnetic field region formed by the permanent magnets 16a and 16c and a magnetic field region formed by the permanent magnets 16b and 16d. It corresponds to the located part. Also, Ra
The effective portion of the dial coil 14 is a region for generating a driving force necessary for the movement in the radial direction and a region for generating a driving force for suppressing the rotational moment generated by the Focus coil 13,
Between the magnetic field regions by the permanent magnets 16a, 16c and the permanent magnets 16b, 1
This is a portion existing between the magnetic field regions according to 6d. further,
A counterweight 19 is attached to the lower part of the bobbin 12 in order to correct the weight balance of the movable part which is deflected due to the object lens 11 protruding above the variable part.

As described above, even if the objective lens is driven in the two directions of Focus and Radial, the objective lens driving device in which the objective lens does not tilt with respect to the optical axis is realized, thereby reducing the burden of correcting the aberration of the objective lens. Therefore, a lightweight and inexpensive objective lens having a simplified lens configuration can be used. Therefore, the drive sensitivity is improved by the weight reduction of the movable part, and the cost of the optical pickup can be reduced. It goes without saying that the optical characteristics of the optical pickup are improved because the aberration is reduced by the amount of no inclination. In addition, since the offset in the radial direction does not affect, the requirement of the assembly accuracy is eased, and the assembly is facilitated.

[Another embodiment of the invention]

Hereinafter, a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a perspective view of the objective lens driving device. Here, the same reference numerals as in FIG. 1 indicate the same parts. In other words, the feature of this embodiment is that a component corresponding to the center pole 18 in the embodiment shown in FIG. 1 is omitted. By doing so, although the magnetic field from the permanent magnet is weakened as compared with the above embodiment, it becomes easier to satisfy the condition for preventing the tilt of the objective lens, and the movable range in the radial direction Can be taken without being disturbed by the center pole,
Since the material of the spectral pickup, in which the center pole made of a ferromagnetic material (high density) is generally eliminated, is reduced, the effect that the access speed of the optical pickup can be increased is enormous. In the past, the center pole acted as the core of the coil, increasing the inductance of the coil and causing a deterioration in the frequency characteristics of the objective lens driving device. This means that the frequency characteristics of the objective lens driving device can be improved.

[Brief description of the drawings]

FIG. 1 is a configuration perspective view showing an apparatus according to an embodiment of the present invention,
2 is a plan view of the embodiment of FIG. 1, FIG. 3 is a side view of the embodiment of FIG. 1, FIG. 4 is a view for explaining the embodiment of FIG. FIG. 6 is a perspective view showing the structure of a conventional apparatus, and FIG. 6 is a perspective view showing the structure of another embodiment according to the present invention.

Claims (1)

(57) [Claims] An objective lens for converging light; a bobbin for holding the objective lens; a first coil for driving the bobbin in the optical axis direction of the objective lens; and a first coil for driving the bobbin in the optical axis direction. A movable section comprising a plurality of second coils which are provided close to the first coil for driving and are provided symmetrically with respect to the optical axis; Direction and a direction perpendicular to the optical axis direction, while applying a common magnetic field to both the first and second coils of the movable unit, facing the first and second coils, The total length of the surface that generates the magnetic field in the direction orthogonal to the optical axis with respect to the second coil arranged side by side in the direction orthogonal to the optical axis direction is equal to the length of the first coil. Approximately half the length in the direction perpendicular to the optical axis. The plurality of second
And a magnetic field generating means having the same number of coils as those of the above and having a configuration symmetrical with respect to the optical axis.