JPH0223536A - Objective lens drive device in optical pickup - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an objective lens movement device in an optical pickup.

[Prior Art] Optical big amplifiers are well known in connection with optical disk systems. In recent years, optical disk systems, such as magneto-optical disk systems and write-once optical disks, which not only read but also write optical information, have strict tolerances for the tilt of the optical axis of the objective lens, and have a high tolerance for disturbances in the tracking state due to external disturbances. Tolerance is also strict. On the other hand, since high-speed access is required, the optical axis of the objective lens is likely to tilt in the tracking direction due to acceleration during access. conventionally,
In order to prevent this tilting of the optical axis in the tracking direction, the objective lens holder is supported by a leaf spring in the focusing direction and supported by a bearing in the tracking direction, making the support mechanism complicated. It had become

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a novel objective lens drive device that can simplify the support mechanism of an objective lens holder in an optical pickup. do.

[Means to solve the problem] The present invention will be explained below.

The objective lens IN movement device of the present invention is a device for driving an objective lens in an optical pickup, and includes a pair of thrust generating means, tilt detecting means, and signal processing means.

The pair of thrust generating means are disposed symmetrically with respect to the optical axis of the objective lens in the tracking direction, and are means for displacing the objective lens in the optical axis direction by thrust generated by electromagnetic force.

The tilt detection means is means for detecting the tilt of the optical axis of the objective lens in the 1-racking direction.

The signal processing means is means for obtaining a sum signal and a difference signal from the thrust signal for tilt correction and the focusing signal obtained from the tilt detecting means.

When the thrust to be generated by each of the pair of thrust generating means is F1 based on the focusing signal, and F2 is the thrust to be generated by each of the pair of thrust generating means based on the thrust signal for tilt correction. , the sum signal from the signal processing means is applied to one thrust generating means, and the difference signal is applied to the other thrust generating means. One of the thrust generating means generates a thrust of F1+F2, and the other thrust generating means generates thrusts of F1 and -F2, and the pair of thrust generating means performs focusing control and optical axis tilt correction control. at the same time.

In the above description, it goes without saying that the thrust force F2 to be generated by each of the thrust generating means by the thrust signal for tilt correction is opposite in direction in each thrust generating means, and constitutes a force couple.

[Function] As described above, in the present invention, it is assumed that the optical axis of the objective lens is tilted, and this is corrected. This correction is performed by a pair of thrust generating means for performing focusing. They are done at the same time.

[Example] Hereinafter, an example will be specifically described with reference to the drawings.

Referring to FIG. 5, this figure shows the objective lens and its driving mechanism.

In the figure, a support plate 5 is fixed upright on a base plate 10, and four springs 9A and 9B are attached to this support plate 5.
, 9C, and 9D are each planted with one end fixed.

The objective lens holder 4, which has a figure 8 shape when viewed from the Z direction, fixedly holds the objective lens L, and is connected to the four springs 9A.
~9D is supported. The direction in which the optical axis of the objective lens L should be is the Y direction in the figure, and the X direction is the tracking direction.

The objective lens holder 4 has coils 4 at both ends in the X direction in the figure.
A and 4B are fixed symmetrically to the optical axis of the objective lens L. These coils 4A and 4B are connected to the J5 plate lO
It is provided so as to surround the yokes 3A and 3B that are fixedly planted on the yokes 3A and 3B. Further, yokes 2A and 2B are fixedly planted on the substrate IO as shown in the figure, and each yoke 2A and 2
Magnets IA and 1B are fixed to B.

Therefore, the magnet IA and the yokes 2A and 3A form a magnetic circuit, and the magnetic flux of this magnetic circuit intersects with the coil 4A. Therefore, when a current is passed through the coil 4A, a thrust proportional to the current acts on the coil 4A. do. The direction of thrust is determined by the direction of current. Similarly, magnet IB, yokes 2B, and 3B form one magnetic circuit, and the magnetic flux of this magnetic circuit crosses coil 4B. Therefore, when current is passed through coil 4B, a thrust proportional to the current acts on coil 4B. do. Therefore, the magnet IA, yokes 2A, 3A, and coil 4A constitute one thrust generating means, and the magnet IB, yokes 2B, 3B, and coil 4B constitute the other thrust generating means. These pair of thrust generating means are configured symmetrically in the X direction, that is, in the tracking direction, with respect to the optical axis of the objective lens.

Holding the objective lens using four springs has the advantage that it has a simpler structure and is free from backlash compared to conventional support using temporary springs and bearings. However, when acceleration in the Y direction or Rotation and oscillation occur as a result. The optical axis of the objective lens L is tilted in the tracking direction.

Next, referring to FIG. 3, this FIG. 3 shows the basic optical configuration of an optical pick amplifier to which the present invention is applied.

The light emitted from the laser diode 20 is collimated by a collimating lens 22 and separated into two beams by a polarizing beam splitter 24. One of the separated beams passes through the 174-wave plate 26 and enters the objective lens L. Under the action of the objective lens L, it enters the disk medium 1oo such as a magneto-optical disk, and when reflected, it enters the objective lens L.
and a polarizing beam splitter 2 via a 174 wavelength plate 26.
4, the light beam is guided to the optical information detection system 38 by the polarizing beam splitter 24. A focusing signal, a tracking signal, and an R['' signal are obtained from this optical information detection system 38 using a known method.

The other beam separated by the polarizing beam splitter 24 is reflected by the beam splitter 32, enters the mirror 31 integrated into the objective lens holder 4, and upon reflection, passes through the beam splitter 32 and is condensed. lens 3
4 onto the position sensor 36.

In FIG. 4, when the optical axis of the objective lens L is not tilted, the reflected light from the mirror 31 enters the point A of the position sensor 36, as shown by the broken line in the figure. When the optical axis is tilted by φ, the mirror 31 is also tilted by φ, the direction of the light reflected by the mirror 31 is tilted by 2φ, and the light beam convergence position at this time becomes point B.

The distance 1 between points A and B is 1=2φh using h in the figure. If the resistance change with respect to the unit length displacement of the light condensing position in the position sensor is 8r (then, when the resistance changes by Δr according to the distance 1, 1=Δr/ΔR=2φ
h, the inclination angle φ of the optical axis can be known as φ=(1/2h)(Δr/ΔR).

Beam splitter 32, mirror 31, condenser lens 34
, the position sensor 36 constitutes tilt detection means.

FIG. 6 shows an example of a specific arrangement of the tilt detection means. The mirror 31 is fixedly installed on the bottom surface of the objective lens holder 4, and the beam splitter 32 and the condenser lens 34 are integrated with the substrate 10 together with the polarizing beam splitter 24 by suitable support means (not shown), and the position of the mirror 31 is fixed. sensor 3
6 is fixed to the substrate 10.

Incidentally, reference numeral 33 in FIG. 6 indicates a counterbalance for maintaining balance with the mirror 31.

Now, referring to FIG. 1, this figure shows the objective lens holder 4 viewed from the Z direction in FIG.

When the objective lens holder 4 is in the position shown by the broken line, the objective lens has no optical axis tilt and no focus error.

Now, consider a case where the objective lens holder 4 is deviated from the normal position (the position indicated by the broken line) as shown by the solid line. At this time, for focusing, the objective lens holder 4 is
It is necessary to displace the object upward in the figure by a distance @SF, and the thrust required for that purpose is assumed to be 2F1. In addition, in the position shown by the solid line, the optical axis of the objective lens is tilted by φ, so to correct this tilt of the optical axis, a clockwise couple is applied to the objective lens holder 4. The force constituting this couple necessary for the above correction is designated as F2 as shown in the figure.

At this time, of the pair of thrust generating means shown in FIG.
The thrust generating means constituted by magnet IA, yokes 2A, 3A, and coil 4A generates a thrust of ['l+F2, and the thrust generating means constituted by magnet IB, yokes 2B, 3[1, and coil 4B generates thrust Fl. By generating -F2, it is possible to simultaneously perform a focusing operation and an operation for correcting the inclination of the optical axis with respect to the objective lens held by the objective lens holder 4 in the position shown by the solid line. In this case, the information that the thrust force F1 should be generated is obtained from the focusing signal, and the signal that the force F2 for correcting the tilt of the optical axis should be generated is obtained from the output from the position sensor of the tilt detection means. can get.

Therefore, assuming that the output signal for focusing from the optical information detection thread 38 is 81 and the output of the position sensor is 82, these signals S1 and S2 are each composed of a compensation block and an amplifier, as shown in FIG. Control signal generation circuit 50.6
Enter 0. The control signal generation circuit 50 generates a signal indicating that the above-mentioned thrust force F1 necessary for the focusing operation should be generated, that is, the focusing signal f1, in response to the signal S1, and the control circuit 60 generates a focusing signal f1 in response to the signal S2. A signal indicating that the thrust force F2 necessary for correction should be generated, that is, a thrust force signal f2 for tilt correction is generated. These signals f1, f
2 are input to an adder 70 and a subtracter 80, respectively, and the adder 70 obtains a sum signal corresponding to fl+f2, and the subtracter 80 obtains a difference signal corresponding to fl-f2. These signals are converted into current signals and applied to each of the pair of thrust generating means described above. Thus, one thrust generating means generates thrust F10F2, and the other thrust generating means generates thrust Fl-F2, and the objective lens 1 performs focusing control and optical axis tilt correction control at the same time. .

Adder 70. Subtractor 80 constitutes signal processing means.

[Effects of the Invention] As described above, according to the present invention, a novel objective lens driving device in an optical pickup can be provided.

As described above, this device has a function of correcting the tilt of the optical axis of the objective lens, so it is possible to hold the objective 1 nose in a way that causes the objective lens to tilt.
For example, it becomes possible to hold the objective lens using four bar springs as shown in the embodiment, and the holding mechanism for the objective lens is simplified. In addition, since the objective lens is controlled to correct the inclination of its optical axis, the objective lens has high stability in the optical axis direction and can sufficiently withstand high-speed access. Furthermore, since the tilt of the optical axis is corrected by a pair of thrust generating means for focusing, the control mechanism is also simple.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the present invention in detail. FIG. 2 is a diagram showing an example of the signal processing means, FIG. 3 is a diagram for explaining the optical configuration of an optical pickup to which the present invention is applied, and FIG. 4 is a diagram showing the inclination of the optical axis of the objective lens. FIG. 5 is a perspective view showing the objective lens folding mechanism in the embodiment, and FIG. 6 is a diagram illustrating an example of the arrangement of the tilt detecting means. be. Loo, objective lens, 4. ,, objective lens holder, 4A
, 4B, , Coil, l^, IB, , Magnet, 36. ,
, position sensor Fig. 4 Fig. 2

Claims (1)

[Claims] A device for driving an objective lens in an optical pickup, which is arranged symmetrically with respect to the optical axis of the objective lens in the tracking direction, and drives the objective lens in the optical axis direction using thrust generated by electromagnetic force. a pair of thrust generating means for displacement; a tilt detecting means for detecting the tilt of the optical axis of the objective lens in the tracking direction; and a thrust signal for tilt correction and a focusing signal obtained from the tilt detecting means. , a signal processing means for obtaining a sum signal and a difference signal between the two, the thrust force to be generated by each of the pair of thrust generation means is determined based on the focusing signal, and the thrust force to be generated by each of the pair of thrust generation means is determined based on the thrust force signal for tilt correction. When the thrust to be generated by each of the thrust generating means is F2, the sum signal from the signal processing means is applied to one thrust generating means, the difference signal is applied to the other thrust generating means, and the above One thrust generating means receives a thrust of F1+F2, and the other thrust generating means receives a thrust of F1−.
An objective lens drive device, characterized in that it generates a thrust of F2, and performs focusing control and optical axis tilt correction control using the pair of thrust generating means.