JPS62145541A - Objective lens driving device - Google Patents

Abstract

PURPOSE:To obtain a device in which the inclination of an objective lens hardly occurs even when driving is simultaneously driven in two directions by including a magnetic field generating means to give a magnetic field to the first and second coils of a movable part at the time of driving in the optical axis of the objective lens or the direction perpendicular to the optical axis direction. CONSTITUTION:With the length of the direction perpendicular to a uniform magnetic field 20 generated by a magnetic circuit out of a Focus coil 13 as l1, with the length of the part of the uniform magnetic field 20 as 2Xl2, and with the ratio of 2Xl2 as a parameter, the movable part is shifted in the radial direction and then, the ratio of a counterclockwise moment Ml and a clockwise moment Mr in the center of gravity of the movable part when the part is driven in the FOCUS direction is obtained. When Ml/Mr=1 is established, the objective lens is hardly inclined to the optical axis. In short, by constituting it so as to obtain 2.l2/l1=0.5, even when driving is simultaneously executed, the objec tive lens is hardly inclined to the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an objective lens driving device for an optical pickup that reads information on a recording medium.

[Technical background of the invention and its problems]

In an optical disk device, an optical pickup focuses light emitted from a light source (laser) onto a disk using an objective lens, and uses this focused light to record a signal on the disk, and also records signals on the disk using reflected light from the disk. It is a device that reads signals that have been recorded. However, actual discs have warpage and eccentricity, and the light from the light source must be adjusted to these warps and eccentricity in order to be properly focused on the disc's tracks. Various proposals have been made for this method, including a system in which the light from the optical pickup is driven in a direction perpendicular to the disk surface (pocus direction), and a system in which the track moves due to the eccentricity of the disk (Radia 1 direction). Optical pickups equipped with a driving system are the most common and are in practical use.

However, with the drive system in the FOCLIS direction and the drive system in the dia1 direction described above, the word υ is driven according to the amount of error, and the objective lens of the optical pickup is tilted with respect to the optical axis. However, there was a gap between the two, which caused aberrations (optical deviations) and made it impossible to focus the light well.

In order to solve this problem, attempts have been made in the past to correct the above-mentioned inclination by using a configuration called a short voice coil and by attaching a counterweight below the bobbin that holds the objective lens.

However, no matter which method is used, the Radi
There is no problem when driving only in the al direction or when the Radial direction is at the neutral position and only the pOcus direction is driven, but when driving in the B'ocus direction when the Radial direction is not at the neutral position, there is a problem. When driving both the p pOcus direction and the Radia 1 direction at the same time, a tilt in the Radia 1 direction/＼ will occur. As a countermeasure to this problem, a configuration was adopted in which several objective lenses were moved so that no aberrations would occur even when the objective lens was tilted to a certain degree, but this method naturally increased the weight, so 1. The drive chamber deteriorates, and configuring the objective lens itself to correct aberrations poses a problem in terms of cost. Achieving optical pickup has long been a technical challenge.

[Purpose of the invention]

The present invention has been made to solve the above problems, and its purpose is to provide an objective lens drive device that does not cause the objective lens to tilt even when driven in two directions simultaneously.

[Summary of the invention]

The present invention includes a lens that focuses light, a bobbin that holds the objective lens, and first and second coils that drive the bobbin at least in the direction of the optical axis of the objective lens or in a direction perpendicular to the direction of the optical axis. a first movable part of the movable part so that the moment of the small force at the center of gravity of the movable part always matches about 9 when driven in at least the optical axis direction of the objective lens or a direction perpendicular to the optical axis direction. and a magnetic field generating means for applying a magnetic field to the second coil.

Furthermore, in the objective lens driving device, the length of the magnetic field generating means in the direction perpendicular to the optical axis direction is approximately half the length of the first coil in the direction perpendicular to the optical axis direction. .

〔Effect of the invention〕

According to the present invention, it is possible to provide an objective lens driving device that does not cause tilting of the objective lens, so the burden of aberration correction on the objective lens itself is reduced, and a lightweight and inexpensive objective lens can be used. It is possible to improve the sensitivity and reduce the cost of optical pickup, and it is also possible to make the device even more compact in a device that does not require moderate drive sensitivity.

[Practical side of the invention]

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

FIG. 1 is a perspective view of the structure 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 the dotted line 20, and is held by a bobbin 12. And centering on this bobbin 12,
The objective lens 11 should be driven in the pOcus direction (, B
'0Cu3 coil 13 is the center pole 18a which will be described later.
, 18b is wound into a rectangular shape. Further, on the surface of this B"ocus coil 13, there is a Rad coil wound in a flat shape to drive the objective lens 11 in the adia1 direction.
ial: Four ff files 14a to 14d are pasted. (Only 14G and 14d L are visible in the figure) Below, objective lens 11, bobbin 12, pOcus: ff
The coil 13.1'l, radial coil 14 is generally referred to as a movable part. As conventionally used, the movable part is supported by four suspensions 15 so as to be movable in two directions: the pOcus direction and the Radia 1 direction. Center poles 18a, 1 on the left and right of the bobbin 12
8b, and permanent magnets 163 to 16d are provided on the sides facing the center poles 18a and 18b, sandwiching the radial coils 14a to 14d, respectively.
~16d are yokes 17a~17d with four protruding parts
It is attached to this protrusion. Below, permanent magnet 1
6a, yoke 17a, center ball 18a and permanent magnet 16b, yoke 17b1 center pole b and permanent magnet 1
6C1 yoke] 7C1 center ball a and permanent magnet 1
6d, yoke 17d, and center ball d are respectively referred to as first to fourth magnetic circuits. The first to fourth magnetic circuits always generate a uniformly distributed magnetic field.

The arrangement method, which is one of the features of the present application, will be described in detail later. In these configurations, the force generated by Fleming's left-hand rule can be reduced in the portion of each coil that is in a uniform magnetic field by passing current in accordance with the error amount through the pOcus coil 13 and the Radial coils 14a to 14d, respectively. Use this to focus the objective lens 11.
It is designed to drive in each of the s direction and the Radia 1 direction. Further, a counterweight 19 is attached to the lower part of the bobbin 12. This counterweight 1
9 will be explained in detail later.

Conventionally, an objective lens driving device has been constructed as shown in FIG. The bobbin 71 holding the objective lens 70 is provided with four protrusions, and the suspension 7
2 was provided to support the bobbin 71. A permanent magnet 73a is provided inside the suspension, and a permanent magnet 73b is further provided at a position facing the permanent magnet 73a with the bobbin 71 sandwiched therebetween. In other words, the permanent magnet 73a
, Suspension 7 is equipped with a pair of 73b.
2 must be provided in a portion that protrudes from the bobbin 71. On the other hand, in the case of the present application, the permanent magnet 17 in FIG.
By providing two pairs of a to 17d, suspension 1
5 can be provided inside this. In other words, it is clear that it will be smaller than the conventional one. Also, permanent magnet 1
The reason for configuring 72 to 17d in this way will be explained in detail later.

In FIG. 2, the first to fourth magnetic circuits described above are B
The 'ocus coil 13 is arranged so that the outermost part of the portion in the direction perpendicular to the uniform magnetic field (dotted line 20) and the outermost part of the uniform magnetic field (20) coincide with each other. Now, in the FOCuS coil 13, the uniform magnetic field (20
) is 11, and the length of the uniform magnetic field (20) is 2×12. 11 and 2×12Radi
When shifting in the a1 direction, the pOcus direction (
Moment of counterclockwise rotation at the center of gravity of the movable part when attempting to drive it in the vertical direction (direction perpendicular to the page) MA! and clockwise moment) Find the ratio of Mr.

Figure 4 shows the results of the experimental data. Rad on the horizontal axis
The amount of shift in the ial direction is taken as the vertical axis K Ml/Mr.

Take 0.4, 0.5, 0.6, and 0.7. Ml/
When Mr = not 1.0, if S[l/Mr > 1, it will be driven counterclockwise, and if Ml/Mr < 1, it will be driven clockwise, and the movable part will be driven in the pOcus direction. This causes the objective lens to be tilted with respect to the optical axis, causing the problem described in the conventional example. However, as can be seen from the figure, when Ml/Mr = 1 holds, when the movable part is shifted in the dia1 direction, even if the movable part is driven in the pOcus direction, the objective lens will not be aligned with the optical axis. Never lean against it. In other words, 2.12/l,
= 0.5, so by configuring, FOc
It is possible to realize a highly stable device in which the objective lens does not tilt with respect to the optical axis even if it is simultaneously driven in two directions, the US direction and the Radia 1 direction.

In FIG. 3, the height of the permanent magnet 16 is FOcus.

In order that the driving force in each direction of Badial always acts on the center of gravity of the movable part,
ial: higher than the film 14 so that the effective part of each coil does not protrude from the uniform magnetic field generated by the magnetic circuit. Furthermore, 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 biased due to the objective lens 11 protruding above the variable part.

As mentioned above, the objective lens);'ocus, Radia
By realizing an objective lens drive device in which the objective lens does not tilt with respect to the optical axis even when driven in two directions, the lens configuration is simplified because the burden of correcting aberrations of the objective lens is reduced. This makes it possible to use inexpensive objective lenses. Therefore, since the movable part is lighter, drive sensitivity can be improved, and the cost of the optical pink amplifier can also be reduced. Of course, it goes without saying that the optical characteristics of the optical pickup are improved because the aberration is reduced by the fact that no tilt occurs. Further, since the offset in one direction of 1 adia does not affect the assembly accuracy, the requirement for assembly accuracy is eased, and the configuration as in the present application has great effects, such as ease of assembly.

[Other embodiments of the invention]

A second embodiment of the present invention will be described below 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 the part corresponding to the center pole 18 in the embodiment shown in FIG. 1 is omitted. By doing this, although the magnetic field from the permanent magnet is weaker than in the above embodiment, it becomes easier to satisfy the condition that the objective lens does not tilt, and it is also possible to The movable range of the spectral big amplifier can be sufficiently moved without being hindered by the center pole, and the material is generally made of ferromagnetic material (high density). The effect of being able to speed up the access speed of pick-up is tremendous. In addition, in the past, the center pole acted as the iron core of the coil, increasing the inductance of the coil and causing poor frequency characteristics of the objective lens drive device. By eliminating the cause of this, it is also possible to improve the frequency characteristics of the objective lens driving device.

[Brief explanation of drawings]

FIG. 1 is a structural perspective view showing an embodiment of the device according to the present invention;
2 is a plan view of the embodiment device shown in FIG. 1, FIG. 3 is a side view of the embodiment device shown in FIG. 1, FIG. 4 is a diagram for explaining the embodiment device shown in FIG. 1, and FIG. The figure is a perspective view of the configuration of a conventional embodiment of the device, and FIG. 6 is a perspective view of the configuration of another embodiment of the device according to the present invention.

Claims (2)

[Claims] (1) an objective lens that focuses light; a bobbin that holds the objective lens; and first and second bobbins that drive the bobbin at least in the optical axis direction of the objective lens or in a direction orthogonal to the optical axis direction. a movable part composed of a coil, and a movable part so that the moment of the driving force at the center of gravity of the movable part is always balanced at least when the objective lens is driven in the optical axis direction or in a direction orthogonal to the optical axis direction. An objective lens driving device comprising: magnetic field generating means for applying a magnetic field to first and second coils. (2) A patent claim characterized in that the length of the magnetic field generating means in the direction orthogonal to the optical axis direction is approximately half the length of the first coil in the direction orthogonal to the optical axis direction. The objective lens driving device according to item 1.