JPH05342605A - Driving device for objective lens - Google Patents

Abstract

PURPOSE:To make the center of gravity of a movable part coincide with the driving point and to extend a frequency characteristic to a higher frequency range by constituting optical elements at the opposite position to an objective lens with regard to the bobbin of the objective lens driving device. CONSTITUTION:A 1/4 wavelength plate 22 is mounted at the lower surface opposite to an objective lens so that the center of gravity of the movable part coincides with the driving point. The elliptic shaped light beam emitted from a semiconductor laser 12 is made incident obliquely on the incident plane 14a of a prism 14 through a collimating lens 14, passes through a polarization film 14b to be changed into circular parallel beam, reflected by a raising prism 16 and gets to the objective lens driving device. The beam is focused on a recording medium 17 passing through the 1/4 wavelength plate 22 and the objective lens. The beam retrogresses, is reflected by the polarization film 14b and is made incident on a photodetector 21 through a reflection mirror 18, detecting lens 19 and a cylindrical lens 20 so as to obtain an RF signal of the medium 17. By utilizing the 1/4 wavelength plate 22 as a counter weight, the movable part is made thin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens driving device used in an optical head for recording / reproducing by irradiating a recording medium with a light beam.

[0002]

2. Description of the Related Art In recent years, an objective lens driving device for an optical head for an optical disk device adopts a method in which a bobbin fixing an objective lens is connected to a fixing member by a plurality of wire-shaped or plate-shaped supporting members and driven. Things are the mainstream.

An example of the above-mentioned objective lens driving device and an optical head device using the same will be described below with reference to the drawings.

FIG. 3 is a perspective view of a conventional objective lens driving device, FIG. 4 is a bottom perspective view of the movable portion of the conventional example, and FIG. 5 is a perspective view showing the structure of an optical head device using the conventional objective lens driving device. FIG. 6 and FIG. 6 are perspective views of movable parts of other conventional examples.

In FIGS. 3 and 4, reference numeral 1 denotes an objective lens, 2
Is a focus driving coil wound perpendicularly to the optical axis direction of the objective lens 1, 3 is a tracking driving coil wound perpendicularly to the tracking direction, 4 is the objective lens 1 for focus driving A bobbin for fixing the coil 2 and the tracking drive coil 3, 4a is a hole through which a supporting member 7 for connecting the bobbin 4 and the fixing member 9 is inserted, 5 is a magnet, 6 is a yoke, 7 is the bobbin 4 and the fixing member 9. A support member for connecting and supplying a drive current to the drive coils 2 and 3, and 8 is a relay board fixed to the bobbin 4 for relaying the drive coils 2 and 3 and the support member 7. Is fixed with solder or the like. Reference numeral 9 is a fixing member for fixing one end of the support member, 10 is a damping member for damping the support member 7, and 11 is a counterweight for balancing the movable portion.

In FIG. 5, 12 is a semiconductor laser which is a light source, 13 is a collimating lens, 14 is a polarizing prism,
14a is an incident surface, 14b is a polarizing film configured to transmit P-polarized light and reflect S-polarized light, and 15 is 1 /
4 wavelength plate, 16 a prism for start-up, 17 a recording medium,
Reference numeral 18 is a recording medium, a reflection mirror that changes the traveling direction of the return light reflected by the polarizing film, 19 is a detection lens, 20 is a cylindrical lens, and 21 is a photodetector divided into four parts.

In FIG. 6, 1, 2, 3, 4, 7, 8,
9 and 10 are the same as the component element names in FIG. Reference numeral 4c (hatched portion) is a bobbin extension portion configured to serve as a counterweight for the objective lens 1.

The operation of the conventional objective lens driving device and optical head device configured as described above will be described below.

In FIG. 3, the magnetic flux emitted from the magnet 5 into the space crosses the focus driving coil 2 and the tracking driving coil 3 formed on the bobbin and returns to the magnet 5 via the yoke again. Next, a driving force is generated in the coils by passing a current through the focus driving coil 2 and the tracking driving coil 3 through the supporting member 7 and the relay substrate 8 to move the objective lens in the optical axis direction and in the direction perpendicular to the recording track. Take control.

In FIG. 5, the elliptical light emitted from the semiconductor laser 12 is collimated by the collimating lens 13 into a parallel light beam and is incident on the prism 14 as P-polarized light. By obliquely entering the incident surface 14a of the prism 14, the elliptical parallel light flux is converted into a circular parallel light flux. Polarizing film 14
Since P polarized light is incident on b, the parallel light flux passes through the polarizing film 14b and further passes through the quarter wavelength plate 15 to be circularly polarized light. The circularly polarized light beam is reflected by the rising prism 16 and enters the objective lens 1 to focus on the recording medium 17 for recording, erasing, and reproducing. The direction of circularly polarized light of the light beam reflected by the recording medium 17 is opposite to that at the time of incidence, is reflected by the rising prism 16 again, is transmitted through the quarter wavelength plate 15, and is rotated by 90 ° when emitted from the semiconductor laser 12. It is converted into an S-polarized parallel light beam. Therefore, the light beam that has entered the prism 14 again is reflected by the polarizing film 14b and travels toward the reflection mirror 18. Then, the parallel light flux is reflected by the mirror 18 to be converged light by the detection lens 19, and the cylindrical lens 20 imparts astigmatism for focus error detection to the converged light to form a spot on the photodetector 21. The photodetector 21 is divided into four parts. An error signal for driving the objective lens driving device in the focus and tracking directions by performing arithmetic processing on the signals obtained from the divided photodetectors, and an RF signal which is a signal of the recording medium. The signal is obtained.

[0011]

Generally, in the objective lens driving device having the above-described structure, the driving force generation position and the center of gravity of the movable portion (the objective lens 1, the focus driving coil 2, the tracking driving coil 3, and the bobbin 4). Unless the positions are matched and the rotational moment is not applied to the movable portion, the movable portion makes a rotational movement, and the position control of the objective lens 1 cannot be performed, and correct recording / erasing / reproducing cannot be performed.

Since the objective lens made of glass having a large specific gravity is arranged at the upper end of the bobbin of the objective lens driving device described in the above-mentioned prior art, the center of gravity of the movable portion is at a high position. For this reason, the bobbin extension 4c is usually provided on the opposite side of the objective lens 1.
(Fig. 6) to lower the center of gravity to match the driving point,
Alternatively, the counterweight 11 is provided on the side opposite to the objective lens 1.
It was necessary to arrange (FIG. 4) to lower the center of gravity and match the driving points. Therefore, in the former case, the height of the bobbin 4 is increased, and the height of the objective lens driving device cannot be kept low. In the latter case, the counterweight 11 is used in order to prevent the light beam incident on the objective lens 1 from being blocked. Must be formed around the optical path hole portion 4b, and it is difficult to reduce the size of the bobbin 4, and the counterweight 11 is a separate member, leading to an increase in cost.

The present invention solves the above-mentioned conventional problems by extending the bobbin by arranging an objective lens and an optical element at both ends of the bobbin, and without using a counterweight, the center of gravity of the movable part and the driving point It is an object of the present invention to provide a small-sized objective lens driving device in which the frequency characteristics are extended to the high frequency range.

[0014]

In order to achieve this object, an objective lens driving device of the present invention comprises an optical element for transmitting light from a light source, an objective lens for converging a light beam on a recording medium, and The optical element and the objective lens each have a bobbin fixed to both ends thereof, and a support member that supports the bobbin so as to be movable in at least one axial direction.

[0015]

According to the present invention, the light from the light emitting source such as the semiconductor laser is transmitted through the optical element and focused on the recording medium by the objective lens to perform recording / erasing / reproducing.
The optical element serves as a counterweight of the objective lens and can be driven with the center of gravity of the movable portion and the driving point aligned, and as a result, the height of the movable portion can be reduced. Further, since it is not necessary to dispose a counterweight around the hole, a compact objective lens driving device can be constructed.

[0016]

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

FIG. 1 is a bottom perspective view of a movable portion of an objective lens driving device according to an embodiment of the present invention, and FIG. 2 is a perspective view showing a configuration of an optical head device using the objective lens driving device of the present embodiment.

In FIG. 1 and FIG. 2, 22 is a quarter wave plate. The quarter-wave plate 22 is attached to the lower surface on the opposite side of the objective lens 1 so that the center of gravity of the movable portion and the driving point coincide with each other. The center of gravity is adjusted by the size and the mounting position of the quarter-wave plate, but since the specific gravity of glass and the specific gravity of the quarter-wave plate are about the same, they may be about the same. 2, 3, 4, 7, 8, 9, 10, 12, 13,
14,14a, 14b, 16,18,19,20,21
Is the same as the component name of the conventional example.

The operations of the objective lens driving device and the optical head device of the present embodiment having the above-described structure will be described below.

In FIG. 2, the elliptical light emitted from the semiconductor laser 12 is collimated by the collimator lens 13 to be a parallel light beam and is incident on the prism 14 as P-polarized light. By obliquely entering the incident surface 14a of the prism 14, the elliptical parallel light is converted into a circular parallel light flux. Polarizing film 14b
Since it is incident as P-polarized light, the parallel light beam passes through the polarizing film 14b, is reflected by the rising prism 16 and is directed to the objective lens driving device. The light flux passes through the quarter-wave plate 22 of the objective lens driving device, becomes circularly polarized light, enters the objective lens 1, is focused on the recording medium 17, and is recorded, erased, and reproduced. The direction of circularly polarized light of the light beam reflected by the recording medium 17 is opposite to that at the time of incidence, passes through the quarter-wave plate 22, is converted into an S-polarized parallel light beam, and is reflected by the rising prism 16. The light beam that has entered the prism 14 again is reflected by the polarizing film 14b and travels toward the reflection mirror 18. Then, the parallel light flux is reflected by the reflection mirror 18 to be converged light by the detection lens 19 and converged by the cylindrical lens 20, and astigmatism for focus error detection is given to form a spot on the photodetector 21. By arithmetically processing each signal obtained from each of the divided photo detectors, an error signal for driving the objective lens driving device in the focus and tracking directions and an RF signal which is a signal of the recording medium are obtained.

As described above, according to this embodiment, by using the quarter-wave plate as the counter weight, the movable part can be made thinner than the conventional bobbin shape method in which the center of gravity and the driving point are matched.

Further, in comparison with the conventional method of matching the center of gravity and the driving point with the counter weight, the quarter wave plate 22 formed on the fixed side is used as the counter weight to reduce the number of parts and man-hours. You can Moreover, since there are no parts between the polarizing prism 14 and the rising prism 16, the optical path length can be shortened and the optical head device can be downsized. Also, the bobbin optical path hole 4b
The bobbin 4 is reinforced because the 1/4 wavelength plate 22 is covered, and the frequency characteristic can be extended to a high frequency range.

In this embodiment, the quarter-wave plate is used as a substitute for the counter weight, but other optical elements such as a glass plate and a hologram may be used.

[0024]

As described above, according to the present invention, in the bobbin of the objective lens driving device, the center of gravity of the movable portion and the driving point are made coincident by forming the optical element at the position opposite to the objective lens, and the thin type is achieved. It has a feature that can be changed.

Further, since the optical element serving as the counter weight can be formed in the optical path hole portion of the bobbin of the movable portion, the counter weight and the bobbin can be downsized. Also,
Since the optical element covers the optical path hole portion of the bobbin, the rigidity of the bobbin is increased, the band of the objective lens driving device can be widened, and its practical effect is very large.

[Brief description of drawings]

FIG. 1 is a bottom perspective view of a movable portion of an objective lens driving device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration of an optical head device using an objective lens driving device according to an embodiment of the present invention.

FIG. 3 is a perspective view of a conventional objective lens driving device.

FIG. 4 is a bottom perspective view of a movable portion of a conventional objective lens driving device.

FIG. 5 is a perspective view showing a configuration of an optical head device using a conventional objective lens driving device.

FIG. 6 is a top perspective view of a movable part of a conventional objective lens driving device.

[Explanation of symbols]

 1 Objective Lens 2 Focus Drive Coil 3 Tracking Drive Coil 4 Bobbin 7 Support Member 22 1/4 Wave Plate

Claims (2)

[Claims] 1. An optical element for transmitting light from a light source, an objective lens for converging a light beam on a recording medium, a bobbin having the optical element and the objective lens fixed at both ends thereof, and at least one axis. An objective lens driving device having a support member for supporting the bobbin so as to be movable in a direction. 2. The objective lens driving device according to claim 1, wherein the optical element is a quarter-wave plate.