JPS60106036A - Optical pickup device - Google Patents

Abstract

PURPOSE:To prevent the interference between focusing and tracking actions due to the shift of a reflected beam by turning the plate spring holding an objective toward the radial direction from a rotary center shaft of a pickup arm. CONSTITUTION:Plate springs 30 and 30 supporting an objective 13 at an end are turned toward the lengthwise direction of a pickup arm 11, i.e., in the radial direction of a rotary center shaft 12. While the other end of the spring 30 is fixed to the arm 11 by means of a fixing plate rectangular to the radial direction. Thus it is possible to prevent the interference of mechanical vibrations which causes the interference between focusing and tracking actions as well as the interference between the focusing and tracking actions due to the shift of the optical axis of the reflected beam given from an optical disk 15.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical pickup device used in optical information recording and reproducing devices for digital audio discs, video discs, image files, computer memories, and the like.

In order to read information from or record information on a rotating disk-shaped recording medium, a focus servo mechanism is used to accurately focus the laser beam on the pit surface of the disk, and a laser beam is constantly in tracking.・A tracking servo mechanism is required to keep track of the links.

Various optical devices that have both of these mechanisms have been proposed and put into practical use, but one of them is an integrated drive type picker.
A device called a pump device is known. Figures 1 and 2
The figure shows a conventional example of this type. Picka・
The pump arm 11 extends linearly on both sides of the rotation center shaft 12, and has an objective lens 13 mounted on one free end and a balance weight 14 fixed on the other free end. Center of rotation &h I 9 1-) +''+'I le mountain,
Iゝ, lf p −, /7 7,,, −/7 −
/, I I The objective lens 13 is fixed at a position where it moves approximately in the radial direction of the optical disk 15, that is, in the track direction Tr when rotated. A cavity 16 is formed in the pickup arm 11 on both sides of the rotation center shaft 12, and drive coils 17 are fixed to each of the cavities 16. An annular magnetic yoke 18 passing through the drive coil 17 and a magnetic yoke 20 to which an annular permanent magnet 19 is fixed are located. The magnetic yokes 18 and 20 are fixed outside the device, and the axial direction of the permanent magnet 19 is the magnetization direction.

That is, for example, the side facing the permanent magnet coil on the objective lens side is set as the north pole, and the side facing the permanent magnet coil on the balance window side is set as the south pole. Therefore, when a current is applied to the drive coil 17 in the opposite direction, the pickup arm 11 rotates about the rotation center axis 12 due to the electromagnetic interaction with the permanent magnet 19 and the magnetic yoke 18, 20, and the objective lens 13 rotates around the optical disk 15. It will move in the radial direction Tr.

By the way, in this conventional integrated drive type pickup device, in order to ensure weight symmetry with respect to the rotation center axis 12, the pickup arm 11 is extended on both sides of the rotation center axis 12, and a drive coil constituting the electromagnetic drive device is extended. 17, the permanent magnet 19 and the magnetic yoke 18.20 are connected to the rotation center axis 12
are provided on both sides. However, the rotation of the pickup arm 11 itself can be performed by providing this electromagnetic drive device only on one side of the rotation center axis. FIG. 3 shows an example of this, in which the cavity 16 of the pickup arm 11 and the drive coil 17 fixed to this cavity 16 are provided only on one side of the rotation center shaft 12, and the drive coil 17 is provided on the opposite side. The side pickup arm 11 supports an optical system consisting of a semiconductor laser light source 22 that irradiates the objective lens 13 with laser light, a polarizing beam splitter 23, a collimating lens 24, a quarter wavelength plate 25, and a mirror 26. The permanent magnet 19 and the magnetic yoke 18.20 are semicircular.

Furthermore, the example shown in FIG. 4 is an example in which the pick-up arm 11 itself is extended only to one side of the rotation center axis 12, and both the electromagnetic drive device and the laser optical system are provided on one side of the rotation center axis 12. In this example, an optical system that provides laser light to the objective lens 13 is arranged vertically, and an optical deflection element (for example, a Foucault prism) 27 and a light receiving element (for example, a photodiode) 28, which are not shown in FIG. 3, are arranged vertically. It is depicted. The Foucault prism 27 divides the light beam reflected by the optical disk 15 into two, and the light receiving element 28 receives this divided beam.

The pickup device in which the electromagnetic drive device is provided on only one side of the pickup arm 11 is smaller and lighter than the conventional device shown in FIG. 1, and the moment of inertia can be reduced. It has the advantage that it can be driven in the track direction. For this reason, the applicant company is proceeding with research and development, but this type of pickup device has a new problem that is difficult to adjust the mechanical vibration characteristics due to poor symmetry (weight balance) around the rotation center axis 12. A problem arises. Among these problems, there is strong interference between the rotation of the pickup arm 11 (tracking) and the movement of the objective lens 13 in the optical axis direction (focusing). According to the tree inventor's analysis, there are two reasons for this.

One is interference due to mechanical vibration. That is, objective lens 1
When the pickup arm 11 moves in the lateral direction when the lens 3 performs a focusing operation, or conversely, when the pickup arm 11 performs a trunking operation, the objective lens 1-3 is twisted in the optical axis direction. be. This occurs strongly when the weight balance of the elements mounted on the pickup arm 11 around the rotation center axis 12 is unbalanced.

Another cause of interference is that the optical axis of the reflected light from the optical disk 15 moves due to the lateral movement of the objective lens 13, resulting in an offset in the tracking error signal, and the amount of offset is caused by the rotation of the optical disc 15. This is due to fluctuations in the same period as . The cause of this is that the objective lens 1
This comes from the support mechanism of No. 3. That is, the objective lens 13 is mounted on the pickup arm 11 to
Conventionally, the objective lens 13 is fixed to one end of the two lower leaf springs 30 and 30 of 4Z, as shown in FIGS. 1 and 5. The other end of this leaf spring 30, 30 is fixed to a halter 31 fixed on the pickup arm 11. The objective lens 13 is movably located in the free hole 32 of the holster 31, and therefore moves up and down around the linear fixed portion of the leaf spring 30.30 on the holter 31, that is, the rod-shaped fixed plate 33. can. The movement of the objective lens 13 around the fixed plate 33 can be viewed as approximately linear movement in the optical axis direction (focus direction). The specific movement mechanism for the objective lens 13 is based on an electromagnetic drive device similar to the tracking servo mechanism in principle. In this conventional device, a laser beam emitted from a semiconductor laser light source 22 forms an image on an optical disk 15 via a beam splinter 23, a collimator lens 24, and an objective lens 13, and the reflected light from the optical disk 15 conversely forms an image on an objective lens 13. , IJ meter lens 24
After entering the beam splitter 23 and being reflected there, it is split into two beams by the Foucault prism 27,
Each light is received by two light receiving elements 28. These two beams each consist of components reflected and diffracted on the left and right sides of the track 29 of the optical disc 15, so the drive coil 17 is arranged so that the intensity of the diffracted light on the left side of the track is equal to the intensity of the diffracted light on the right side of the track. When the servo is applied, the track 29 of the optical tisf 15 can be tracked. This method is called the far field method. Compared to a system in which the objective lens 13 is driven independently in two-dimensional directions, this integrally driven pickup device has a smaller amount of movement of the spot of the reflected light from the objective lens 13 on the light-receiving element 28, resulting in a tracking error. The advantage is that there is little offset in the signal.

However, in this conventional device, the objective lens 13 is fixed to one end of the two leaf springs 30.30, and the leaf spring 30.30 is aligned with the rotation center axis 1 of the pickup arm 11.
2 and is bent around the fixed plate 33 which is parallel to the radiation direction. Therefore, if the optical disc 15 has surface wobbling, the reflected light beam on the optical disc 15 is perpendicular to track 29,
In other words, movement in the radial direction Tr of the optical disc 15 is unavoidable. This problem will be explained in detail with reference to FIGS. 5 and 6. The objective lens 13 was originally made of a leaf spring 30.
30, and the leaf spring 30 does not expand or contract macroscopically, so it cannot move purely in the focus direction.If the objective lens 13 is driven downward, it will always move at right angles to the focus direction. Also move in the direction. That is, the objective lens 13 approaches the fixed plate 33 side.

Now, if there is surface wobbling in the optical disc 15 and the leaf spring 30 is bent by θ radians to follow this surface wobbling, then the length of the leaf spring 30 is L, and the amount of movement ΔZ of the objective lens 13 in the optical axis direction is ΔZ=Lsin O>LO(1) On the other hand, the amount of movement ΔX of the objective lens 13 toward the fixed plate 33 is 8v = T, (+ - rnc n ) is T, θz/
2 (2).

In the optical disk 15 with small surface runout, the value of θ is sufficiently small and the second-order minute amount ΔX can be ignored. However, if the surface deflection of the optical tisf 15 is large, ΔX cannot be ignored. According to the analysis of the present inventor, since the absolute value of this ΔX does not matter, the problem is the direction in which it occurs. If the reflected light beam is located perpendicular to the direction of radiation from the trunk 29, this ΔX causes the reflected light beam to move in the direction Tr perpendicular to the trunk 29, which may impede accurate tracking. That is, when the reflected light beam moves in the above direction, the beam is divided into two by the Foucault prism 27 at a position shifted from the beam center. As a result, even if the light beam incident on the optical disk 15 passes through the edge of the trunk 29, the amount of light received by the two light receiving elements 28 will not be equal due to the change in the vertical position of the objective lens 13.

In other words, an offset occurs in the tracking error, and the amount of offset changes depending on the position of the objective lens 13 in the optical axis direction. Therefore, if the tracking servo is operated in this state, the light beam incident on the optical disc 15 will meander over one track 29 at the same period as the wobbling of the optical disc 15. As a result, optical disk 15
The S/N ratio of the internal information reading signal is reduced, and since the light beam meanderes over the track and tracks it, it is easy to fall off the track even with the slightest impact.

The present invention solves the above-mentioned problems of optical pickup devices in which the electromagnetic drive device of the pickup arm is provided only on one side of the rotation center axis of the pickup arm. The above-mentioned problems can be solved by a simple change to the above-mentioned device, which is characterized in that a leaf spring that supports the pickup arm and fixes the other end to the pickup arm is oriented in a radial direction from the central axis of rotation of the pickup arm. I can do it.

The invention will now be described with reference to the illustrated embodiments. 7 to 9 show the present invention applied to a pick-up device of the type shown in FIG. 4. The difference from the pick-up device shown in FIGS. The leaf spring 30.30 supporting the pickup arm 11 in the longitudinal direction,
In other words, the only point is that the other end is fixed to the pickup arm 11 with a fixing plate 33 that is perpendicular to the radial direction and oriented in the radial direction of the rotation center axis 12. The rest of the structure is the same as that of the apparatus shown in FIG. 4, and the same parts are given the same reference numerals.

According to the apparatus of the present invention having the above configuration, the above two causes of interference between focusing and tracking can be eliminated. First, interference caused by mechanical vibration will be explained. When the pickup arm 11 performs a tracking operation, a lateral force is also applied to the objective lens 13 via the fixed plate 33 and the parallel leaf spring 30. When the objective lens 13 is vertically balanced, the objective lens 13 tries to move parallel to the pickup arm 11, but when the objective lens 13 is unbalanced, the response at the upper and lower ends of the objective lens 13 is different, and the upper and lower A force is applied to the leaf spring 30.30. If the leaf springs 30 are oriented in a direction perpendicular to the radial direction of the rotation center shaft 12 as in the conventional case, one of the upper and lower leaf springs 30 will be deflected more due to the unbalanced force acting vertically. This causes movement of the objective lens 13 in the optical axis direction. However, as in the present invention, the leaf spring 30 is
Even if a force is applied to the upper plate spring 30 due to tracking, a torsional force acts on the chain plate spring 30, and the objective lens 13 is oriented in the optical axis direction. Almost no movement occurs. In other words, in the conventional device, a force that tries to bend the plate spring in the thickness direction is applied due to tracking, but according to the present invention, a torsional force acts on the plate spring, and the plate spring bends in the direction of the plate thickness. Since the case where a torsional force is applied is much stronger than the case where a force in the thickness direction is applied and is not easily deformed, according to the present invention, interference between tracking and focusing can be minimized.

In addition, when focusing drive is performed, objective lens 1
3 moves a minute amount in the direction of the fixed plate 33 of the leaf spring 30. As a result, force is also applied to the pickup arm 11 via the fixing plate 33. As in the conventional device, the leaf spring 30 is the rotation center axis 1.
If the force is perpendicular to the radial direction of 2, this force will move the pickup arm 11 in the track direction, but
When the leaf spring 30 is oriented in the radial direction of the rotation center axis 12 as in the present invention, the force applied from the objective lens 13 to the pickup arm 11 via the fixed plate 33 is applied in the longitudinal direction of the arm 11, that is, the rotation Since the force is only applied in the radial direction of the central axis 12, it does not act as a force to rotate the pickup arm 11. Therefore, mechanical interference with the trough kink due to focusing can be minimized.

Therefore, even if a weight imbalance occurs by providing the electromagnetic drive device for the pickup arm 11 only on one side of the rotation center axis 12, mechanical interference between focusing and tracking can be prevented.

Next, the reason why it is possible to prevent interference between focusing and tracking due to movement of the optical axis of the reflected beam from the optical microscope 15 will be explained. When the focusing is performed, the objective lens 13 moves in the focus direction and in a direction perpendicular to the focus direction according to equations (1) and (2). However, in the present invention, since the leaf spring 30 is oriented in the radial direction of the rotation center axis 12, the objective lens 13 is moved in the focus direction, and the track 29 is different from the conventional example.
move in the tangential direction Ta. That is, in the present invention, the "direction perpendicular to the focus direction" is the tangential direction Ta of the track. Therefore, from the semiconductor laser light source 22 to the beam splitter 23, the collimator lens 24, and the objective lens 1,
Even if the focus servo acts on the objective lens 13 and moves it in the focus direction, the reflected light beam of the laser beam focused on the track 29 of the optical disk 15 via After passing through and being reflected by the beam splinter 23, it moves on the ridge line 35 of the Foucault prism 27. Even if the beam moves up and down the ridge line 35 of the Foucault prism 27, 2
The division ratio of the tree into beams does not change. As a result, the difference signal between the photocurrents of the two light receiving elements 28 depends on whether the light beam incident on the optical disk 15 is accurately tracking the track 29 or not. That is, an offset component corresponding to the lower part of the objective lens does not occur in the tracking error, and the difference signal represents only the deviation of the optical beam from the track due to the tracking error. Therefore, when the tracking servo is operated, the objective lens 13 will accurately track directly above the track even on a disk with large surface wobbling. As a result, the disc information read signal S
/N ratio is maintained high, and stable servo operation can be performed that is resistant to external shocks.

Although the present invention has been described above using reading of information from the optical disc 15 as an example, the present invention is also effective for devices that write information optically.

As described above, the optical pickup device of the present invention has a very simple configuration in which the leaf spring supporting the objective lens is oriented in the radial direction from the rotation center axis of the pickup arm, and the reflected light beam is It is possible to prevent interference between focusing and tracking due to the movement of
<Even if the lance collapses, interference between mechanical focusing and tracking can be effectively prevented, making it possible to achieve accurate tracking with a lighter and more compact pickup device. be.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of the main parts of an example of a conventional optical pickup device, Fig. 2 is a plan view of the main parts, and Figs. 3 and 4 are each one side of the central axis of rotation of the pick-up arm. FIG. 5 is a cross-sectional view showing an example of a pickup device equipped with an electromagnetic drive device; FIG. is an explanatory diagram exaggerating the movement in the direction perpendicular to the focus direction that occurs as the objective lens moves in the focus direction, and FIGS. 7 to 9 show embodiments of the optical pickup device of the present invention. The first
FIG. 5 is a perspective view, a plan view, and a perspective view corresponding to FIGS. DESCRIPTION OF SYMBOLS 11...Pickup arm, 12...Rotation center axis, 13...Objective lens, 15...Optical disc, 17
... Drive coil, 18.20 ... Magnetic yoke, 19
...Permanent magnet, 22...Semiconductor laser light source, 23.
...Beam splitter, 24...Collimator lens,
27... Foucault prism, 28... Light receiving element, 29
...Trunk, 30...Leaf spring, 33...Fixing plate. Patent applicant: Asahi Optical Industry Co., Ltd. Agent: Kunio Miura Figure 2 Figure 3/, '5 Figure 4 Figure 5

Claims (1)

[Claims] (1) A pickup arm rotatably supported on a rotation center axis, an electromagnetic drive device that rotationally drives the pickup arm, a leaf spring with one end fixed to the free end of the pickup arm, and a supported at the other end. It is equipped with an objective lens that focuses the laser beam on the optical disk, and the objective lens is moved approximately in the radial direction of the optical disk by the rotation of the pickup arm mentioned above, and the objective lens is moved in the optical axis direction by the elasticity of the leaf spring. In the optical pickup device, the electromagnetic drive device of the pickup arm is provided only on one side of the rotation center axis of the pickup arm, and the leaf spring is oriented in a radial direction from the rotation center of the pickup arm. An optical pickup device characterized in that it is provided with: