JPH01311426A - Objective lens driver - Google Patents

Abstract

PURPOSE:To perform focusing position with a wide band area by providing an objective lens to read information, a frame to fix the lens, and a coil to drive the objective lens, and forming the fixing frame of the objective lens with plastic in which fiber is mixed. CONSTITUTION:Two pairs of coils 12 and (13a-13d) are interposed in a magnetic gap, and they are displaced in a direction of Y by energizing the focusing coil 12, and are displaced in a direction of X by energizing the tracking coils (13a-13d). On a barrel 10, the objective lens consisting of three lenses is fixed at an end part near to the upper side of a disk, therefore, the center of gravity of a driven body consisting of the lens barrel 10, lens frames 11a and 11b, and the coils 12 and (13a-13d) exists at a part sided to the lens in the lens barrel 10. Here, it is desirable to form the frames 11a and 11b in light weight and with rigidity, and polycarbonate in which glass fiber is mixed is used. Since the driven body is formed in the light weight and with the rigidity and a resonance frequency in a high-pass area is increased, the focusing position control with a wide servo area can be performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention aims to read information optically recorded on a recording medium. The present invention relates to an objective lens driving device that drives in a direction.

[Conventional technology]

In optical reproducing devices that use laser light, signals are detected by focusing the laser light onto a minute spot using a lens, etc. However, in order to detect signals correctly, the light must be adjusted according to the irregularities and vibrations of the information recording carrier. Focusing control to focus the spot on the information recording carrier and tracking control to always make the light spot follow the correct signal track are required. Furthermore, if a time axis error occurs due to uneven rotation of the information recording carrier, control is required to correct this error. In order to perform these controls.

An error detection device that detects each error and an actuator that moves the optical system to cancel the error are required.
Conventionally, for this purpose, a so-called voice coil was provided on the driven body including the objective lens to make it movable in the optical axis direction, and mirrors with mutually orthogonal rotation axes were arranged in the optical path leading to the objective lens. A configuration is known in which the optical path is moved in two directions perpendicular to the optical axis by rotating these mirrors, thereby controlling the focal position in three independent directions.

In addition, Japanese Patent Laid-Open No. 52 No. 52 discloses a method in which an optical system using an objective lens with a narrow angle of view is supported by an elastic support member such as a plate spring, and is vibrated in the optical axis direction and in a direction perpendicular to the optical axis using a corresponding electrical signal. It has been proposed in No.-138903, etc.

In such a device that drives the objective lens two-dimensionally, possible methods for driving the objective lens include a method using an electromagnet, a voice coil method, and a method using a piezoelectric element, but focusing and tracking response performance In order to keep it in good condition, it needs to be small and lightweight.

[Problem that the invention seeks to solve]

In such an objective lens drive device, the rigidity of the drive coil becomes small, and it becomes extremely difficult to raise the high-frequency resonance frequency (f h) of the driven body including the drive coil to outside the servo usage band. There was a problem that precise focusing and tracking could not be performed.

In addition, in such an objective lens driving device, since the objective lens is fixed to the tip of the driven body on the disk side, the center of gravity of the driven body is aligned with the position of the center of gravity of the driven body in the optical axis direction of the objective lens. The center of the driving force in the tracking direction is biased toward the disk, that is, toward the objective lens. Especially CDs for compact discs with a diameter of 12 cm.
In the player, the spot diameter λ on the disc surface
/N^ (λ wavelength, NA: numerical aperture) is specified as a standard to be 1.75 μm or less. To meet this standard, the NA must be increased to 0.45 to 0.5.

Therefore, the objective lens has a structure of 3 to 4 elements, and the physical distance between the objective lens surface closest to the disk and the disk is 1i (working distance is 1, 5111m ~
It has to be small, about 2.0 inches.

Therefore, three to four objective lenses are arranged at the end of the lens barrel near the disk. Therefore, the center of gravity of the driven body including the objective lens is inevitably closer to the disk, that is, closer to the objective lens, and is inevitably closer to the disk, that is, closer to the objective lens than the center position of the driven body in the tracking direction. In other words, in the optical axis direction of the objective lens, the center of the driving force of the driven body is located on the opposite side of the disk, that is, the objective lens, from the weight Q of the driven body. Therefore, in such an objective lens drive device, when the drive device is driven in the tracking direction, unnecessary coupled resonance (ro
There is a problem in that accurate tracking error correction cannot be performed.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide an objective lens driving device for use in an optical reproducing device having a wide band servo response area.

[Means for solving problems]

The above purpose is to use a frame for fixing the objective lens, and this frame is made of plastic mixed with fibers.

[Effect]

The fixed frame of the objective lens becomes a lightweight and rigid body and increases the high resonance frequency of the driven object, making it possible to control the focal position over a wide servo band.

〔Example〕

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

On the upper surface of the base 2 made of die-cast material with an opening 1 in the center shown in FIG.
Magnets 4a and 4b having a rectangular parallelepiped shape and magnetized in the thickness direction
The magnetic circuit members 17a and 17b consisting of the setscrew 5a
, 5b, etc., as shown in FIG. 1, so that the same polarity faces each other. Magnetic circuit member 17a, 1
The magnetism of 7b and the direction of the lines of magnetic force are as shown in FIG. 4, and magnetic fluxes are generated in the directions of the arrows in the magnetic gaps 6a and 6b, respectively. As shown in FIGS. 2 and 1, a support frame 7 is provided on the yoke plate 3a of one of the magnetic circuit members 17a.
and a terminal plate 14 are provided, and one end of each horizontal part of the support springs 88 to 8d is glued to the square with an adhesive, and the other ends of the support springs 88 to 8d are attached to the movable frame 9.
It is attached to the square with adhesive.

On the other hand, the lens barrel lO containing the objective lens is fixed by adhesive to lens frames 11a and 11b, which are fixed to each other by adhesive. A square focusing coil 1 is mounted on the outer surface of the square lens frame 11b.
2 is fixed with adhesive. Tracking coils 13a to 13d are fixed to the squares of the seven orcasing coils 12 with an adhesive.

Then, insert the focusing coil 12 into the lens frame 1.
1a, support (suspension) holder 18a on llb
, 18b are fixed with adhesive, and this support holder 18a
, 18b, the free ends a, b, c, d of the vertical portions of the support springs 88 to 8b shown in FIG. 1 are fixed with adhesive.

Here, the other end of each vertical portion of the support springs 8a and 8b is integrated with each horizontal portion, and is fixed to the movable frame 9 with an adhesive. The four tracking coils 13a to 1
3d are connected in series, and both ends thereof are connected to support springs 8a,
The free ends a and b of each vertical portion of 8b are soldered. Further, both ends of the focusing coil 12 are supported by support springs 8c.
, 8d are soldered to the free ends c and d of each vertical part. Therefore, each coil is electrically guided to the terminal plate 14 through the terminals 14a and 14b, and the tracking coils 13a to 8d are electrically guided through the copper foil surface of the terminal plate 14.
The focusing coil 12 is connected to the terminal 14c, 13b.
4d. This terminal plate 14 is fixed to the base 2 together with the support frame 7 with set screws 19 and the like.

With this configuration, two sets of coils 12, 1
3a''13d are present in the magnetic gaps 6a and 6b shown in FIG. 4, and are displaced in the Y direction by energizing the focusing 12, and displaced in the X direction by energizing the tracking coils 13a to 13d.

Here, as described above, the lens barrel 10 to which the objective lens is fixed has three lenses 20 as shown in FIG.
Objective lenses having configurations a, 20b, and 20c are arranged and fixed at the end near the disk R side (upper side).

Therefore, in FIG. 2, the lens barrel 10. Lens frame 11a
, 12.llb, and the center of gravity G of the driven body consisting of the coils 12.13a to 13d is located near the objective lens in the lens barrel 10. On the other hand, the center of the driving force of the driven body in the tracking direction is on a virtual plane including the center of the vertical portion of the tracking coils 13a to 13d, that is, D-E, and the center is at point F in the direction of the light beam of the objective lens. Become. On the other hand, the center of gravity G of the driven body will be located above this point F.

For this reason, it is fixed to the lower side of the lens frame 11b below the lens barrel 10 with an adhesive. The weight 15 lowers the position of the center of gravity G of the driven object itself by attaching the weight, and increases the center of gravity G of the driven object by the driving force F in the tracking direction of the driven object.
and the center of gravity G.

The weight 15 is made of a non-magnetic material such as brass or aluminum. Here, the retracted portions a to d of the support springs 8a to 8d are approximately equally spaced from the center F of the driving force in the tracking direction. Moreover, this weight 15 is in the state in which the setscrew 19 is not fixed in FIG.
8d, since it is configured so that it can be fixed later when it is fixed to the support frame 9, it can easily accommodate changes in the shape and weight of the objective lens.

In this figure, a cover 16 is provided to protect the objective lens driving device according to the present invention, and the cover 16 is fixed to the stepped portion 2a of the base 2 with an adhesive.

Here, it is desirable that the lens frames 11a and llb be lightweight and rigid, and it is necessary to select a material that satisfies the required performance. Good results have been obtained using polycarbonate or polybutylene terephthalate.

Flams 18a, 18b, 18c, 18 of lens frame 10a
d is for strengthening the four sides of the focusing coil 12.

It is fixed on the upper surface of the focusing coil 12.

On the other hand, the lens frame 11b is fixed to two sides of the lower surface of the focusing coil 12 for reinforcement. Since the lens frame is fixed to the objective lens at the center, the rigidity of the vibration system including the objective lens and the drive coil can be increased.

Cutouts 19a to 19d are provided on the four sides of the lens frame 11a. This is to confirm that the drive coil is correctly located in the magnetic gap of the magnetic circuit when assembling the objective lens drive device, and to pass it through the positioning jig.

FIG. 5 shows the amplitude frequency characteristic in one driving direction of the objective lens driving device according to the embodiment of the present invention. A in the diagram
is when the present invention is implemented, B is when the present invention is not implemented,
From this episode, it can be seen that the objective lens driving device according to the present invention has a wide frequency response range.

FIG. 6 is a vibration frequency characteristic diagram in the tracking direction of the objective lens driving device according to this embodiment. Tracking control is performed by passing a driving current through the tracking coils 13a to 13d to move the driving body including the objective lens in the tracking direction. In FIG. 6, the horizontal axis represents the frequency supplied to this driving current, and the vertical axis represents the frequency supplied to this driving current. The upper part shows the relative displacement characteristics of the amplitude, and the lower part shows the position characteristics. In the figure, fL is the support spring 88.
The minimum resonance frequency is determined by the rigidity of ~8d and the mass of the driven bodies 10-13, and f is the coupled resonance (rolling) frequency that is several times higher than the frequency f.

Further, FIG. 7 is an explanatory diagram when the objective lens driving device is driven in the tracking direction.

If the weight 15 is not attached, as shown in Fig. 7(a),
When the driving force F in the tracking direction is supplied to the driven object 10 including the objective lens 20, it will tilt.

Moreover, if the tilt direction is opposite to the driving force F, and the drive force in the tracking direction based on the tracking error signal causes the tilt as shown in FIG. 7(b), it will tilt away from the disk track. , the tracking error signal becomes larger, and therefore the spot produced by the objective lens deviates from the disk track.

Moreover, as shown in FIG. 6, the phase is delayed by 1.80 degrees or more at the frequency f2, so the tracking servo oscillates at the frequency f2, making servo impossible. Therefore, conventionally it has not been possible to perform accurate tracking control. In contrast, if a weight 15 is provided and the weight 15 is used to align the center of gravity G with the driving force F in the 1-racking direction as shown in FIG. 7(b), the solid line in FIG. So 18
Since a phase delay of 0 degrees or more does not occur, accurate tracking control can be performed.

〔Effect of the invention〕

As described above, according to the present invention, since the objective lens is fixed, the driven body becomes a light, heavy and rigid body, and the high resonance frequency of the driven body is increased, so that focal position control over a wide servo band becomes possible.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a two-dimensional objective lens drive device according to an embodiment of the present invention, Fig. 2 is a developed view thereof, Fig. 3 is a sectional view of the lens barrel, and Fig. 4 is a perspective view of a magnetic circuit member. , FIG. 5 is an amplitude frequency characteristic diagram of the objective lens driving device, FIG. 6 is an oscillation frequency characteristic diagram, and FIG. 7 is an explanatory diagram of driving the driven body in the tracking direction. 2... Base, 3... Yoke plate, 4...
Magnet, 7... Fixed frame, 8... Support spring,
9... Moving frame, 10... Lens barrel housing objective lens, 11... Lens frame, 12.13... Drive coil, 16... Cover, 18... Notch. Mistake 12 2nd Mistake 3 Illustration 4m 7K 5K 10K 3
0K (Hl) same release collection 6 closed S /Q

Claims (1)

[Claims] 1. It has an objective lens that reads information optically recorded on a recording medium, a frame that fixes this objective lens, and a drive coil that drives the objective lens, and the objective lens fixing frame is mixed with a fiber. An objective lens driving device characterized by being constructed of plastic.