JPH02154331A - Optical pickup - Google Patents

Abstract

PURPOSE:To improve the accuracy of the tracking position control by forming a reference point which moves together with a condenser lens in a united state in a plane perpendicular to the optical axis passing through a point almost equal to the principal point of the condenser lens and providing a means which detects the position of the condenser lens to the surface of a recording medium by detecting the displacement of the reference point in the direction perpendicular to the optical axis of the condenser lens. CONSTITUTION:The height of the principal point of an object lens 1 is made coincident with the height of the center of the opening section 5a of a light shielding member 5 and centers of a light source 6 and a bisected photodetector 7 are made coincident with the center of the section 5a in Y direction. Accordingly, when a lens holder 2 makes parallel displacement in X direction, the position of the principal point of the lens 1 and sections 5a of the member 5 also make equivalent displacement in X direction and, moreover, even when the holder 2 makes rolling around Y axis, the principal point of the lens 1 and section 5a make equivalent displacement in X direction. Therefore, the accuracy of the tracking position control can be improved, since the displacement of a light spot on a recording medium can be detected accurately even when the holder 2 moves with rolling.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical pickup, and relates to an actuator that moves an objective lens parallel to the surface of a recording medium when recording or reproducing information on a recording medium. It is an optical pickup with

[Conventional example]

An optical pickup modulates light with a signal from an external information source to reproduce or erase information that is binary recorded or recorded on a recording medium.

In order to accurately record, reproduce, and erase this information, it is necessary to perform focus control so that the focal position of the objective lens is on the surface of the recording medium, and to perform position control in the focusing direction.

It is also necessary to control the position in the tracking direction so that the light spot on the surface of the recording medium is accurately positioned with respect to the guide groove formed on the recording medium.

The position of the objective lens in the tracking direction is controlled by moving the entire optical pickup in the case of a large movement, or by holding the objective lens by an actuator built into the optical pickup in the case of a minute movement. This is done by moving only the moving parts.

In order to accurately control the position in the tracking direction, an actuator equipped with a detector that detects the movement of the objective lens in the tracking direction with respect to the housing of the optical pickup is required.

FIG. 4 and subsequent figures show an optical pickup having the above-mentioned actuator. A lens holder I2 holding the objective lens 11 is provided on the optical pickup main body so as to be driven by an elastic wire 13. The main body is provided with a magnet 14 and yokes 15 and 16 to form a magnetic circuit, and by passing current through a coil 17 attached to the lens holder 12, the lens holder 12 can be moved in the X direction.

The lens holder 12 has a light shielding member 1 having an opening 18a.
8, and a light source 19 and a two-split photodetector 20 are provided at a predetermined interval with the light shielding member 18 in between, via the rising portion of the optical pickup main body.

The operation of the two-split photodetector 20 will be explained according to FIG. The light emitted from the light source 19 passes through the aperture 118a of the light shielding member 18 and enters the two-split photodetector 20.
When the lens holder 12 moves in the X direction, the light shielding member 18 also moves together, and the light spot 21 on the two-split photodetector 20 moves in accordance with the amount of movement. FIG. 5(A) shows the light spot 21 in a stationary state of the lens holder 12, and FIG.
) shows the light spot 21 moved in the X direction. When the light spot 21 moves, the two-split photodetector 20
A difference in output occurs between the divided parts. This difference is applied to the operational amplifier 2
2, the amount of movement in the X direction of the objective lens 11 held by the lens holder 12 can be detected.

[Problem to be solved by the invention]

By the way, when the actuator is shown in cross section, as shown in FIG. 6, the principal point 11a of the objective lens 11 and the center of the opening 18a of the light shielding member 18 are located at I! in the Z direction. 2. They are 1X apart in the X direction. Therefore, when the lens holder 12 moves in parallel in the X direction, the amount of movement in the X direction of the principal point 11a and the aperture 18a is equal, and the output of the operational amplifier 22 is the same in the X direction of the light spot transmitted through the objective lens 11 and condensed. Corresponding to the displacement (
Figure 7(A)).

However, as shown in FIG. 7(B), when the lens holder 12 rotates around the Y axis by an angle θ, the amount of movement of the principal point 11a in the X direction is ! , sin θ, whereas the aperture 18
The amount of movement of a in the X direction is β, (1-cos θ). Therefore, the displacement of the optical spot in the X direction and the output of the operational amplifier 22 do not correspond. The lens holder 12 is normally designed to move in parallel, but due to manufacturing errors or the like, the center of support or center of gravity of the lens holder 12 may be misaligned with the center of driving force, causing the lens holder 12 to actually move. If you do so, you will end up moving with a slight rolling motion.

It is difficult to detect the amount of movement of the light spot in accordance with the amount of movement of the lens holder 12 while rolling, and it has not been possible to improve the accuracy of tracking position control.

The present invention is proposed to solve the above problems,
The object of the present invention is to provide an optical pickup that can detect the amount of movement of a light spot corresponding to the rolling movement of the lens holder 12 and improve the accuracy of tracking position control.

[Means and effects for solving the problems] In order to achieve the above object, the present invention includes a movable member holding a condensing lens that irradiates a light spot onto the surface of a recording medium, and a movable member arranged on the optical axis of the condensing lens. In an optical pickup having a supporting member movably supported in orthogonal directions, a reference point that moves integrally with the condenser lens is formed on a plane orthogonal to the optical axis passing through approximately the principal point of the condenser lens; Means is provided for detecting the position of the condenser lens relative to the recording medium surface by detecting the displacement of the reference point in the direction perpendicular to the optical axis of the condenser lens.

In this way, by making the position of the position detection point of the lens holder in the Z direction (focusing direction) almost coincide with the position of the principal point of the objective lens in two directions, the orthogonal coordinates with the rotation center of the lens holder as the origin (0) can be set. When considering x-Z, if the coordinates of the principal point of the objective lens are (0, 47,) and the coordinates of the detection point are (L, 1.), then the lens holder has an angle θra
When rotating by d (θ<<1), the displacement of the principal point in the X direction is 13 θ, and the displacement of the detector in the X direction is also β2θ, which coincides with each other.

〔Example〕

FIG. 1 shows a first embodiment of the present invention, and FIG. 1(A) is a plan view of an actuator.

A lens holder 2 holding an objective lens 1 is movably supported by four elastic wires 4 on a rising portion 3 of a base. A light shielding member 5 having an opening 5a in the center is integrally provided on the side of the lens holder 2. A light source 6 and a two-split photodetector 7 are arranged in the Y direction with the light shielding member 5 in between, and a differential amplifier 8 calculates the difference in the output of the light that has passed through the aperture 5a and is received by the two-split photodetector 7. I'm trying to detect it.

FIG. 1(B) is a sectional view taken along line A-A.
The height position of the principal point of the light shielding member 5 and the height position of the center of the opening 5a of the light shielding member 5 are made the same, and the light source 6 and the two-split photodetector 7 are
The center of each of the openings 5a and 5b are made to coincide with the center of the opening 5a in the Y direction.

With this configuration, when the lens holder 2 moves in parallel in the X direction, the principal point position of the objective lens 1 and the opening 5a of the light shielding member 5 also undergo the same displacement in the X direction. Further, even if the lens holder 2 moves around the Y axis, each of them is equally displaced in the X direction as described above.

This means that when considering Cartesian coordinates x-2 with the rotation center of the lens holder as the origin (0) as shown in FIG. 2, the coordinates of the principal point 1a of the objective lens are <0. β2), the coordinates of the position detection point of the objective lens (βo, β2), when the lens holder rolls by an angle θrad (θxl), the displacement of the principal point 1a in the X direction is p2 θ, the position detector This is because the displacement in the X direction is also 12θ, which is the same.

Next, depending on the displacement of the opening 5a of the light shielding member 5 in the X direction,
As the light spot 9 that passes through the aperture 5a and is received by the two-split photodetector 7 moves, the differential amplifier 8 detects the difference in the output of each of the split portions.

In this way, the amount of movement of the lens holder 2 in the X direction while rolling can be detected, and therefore the amount of movement of the principal point of the objective lens l in the X direction can be detected, and in turn, the displacement of the optical spot on the recording medium by the actuator can be detected. You will be able to know.

FIG. 3 shows a second embodiment of the invention. The same reference numerals are given to parts corresponding to those in the first embodiment. In this embodiment, as a means for detecting the amount of movement of the lens holder 2 in the X direction, the emitted light from the light source 6 is reflected by a small mirror lO provided on the lens holder 2, as shown in FIG. A method is used in which the reflected light is received by a two-split photodetector 7 and the difference in output between the divided portions is detected by a differential amplifier 8.

The mirror 10 is provided so as to move integrally with the lens holder 2 to the same height position as the principal point position 1a of the objective lens l in the Z direction (FIG. 3(B)). Therefore, when the lens holder 2 moves in parallel in the X direction, the X direction displacement of the principal point position 1a of the objective lens 1 and the X direction displacement of the mirror IO become equal.

Further, even if the lens holder 2 rolls around the Y axis, each of them is equally displaced in the X direction as described above.

The principle of this operation is the same as in the first embodiment, and since the light spot 9 moves on the two-split photodetector 7 in response to the displacement of the mirror IO, the objective The amount of movement of the principal point of the lens l in the X direction can be detected, and thus the displacement of the light spot on the recording medium caused by the actuator can be known.

In this embodiment, since a large light shielding member as in the first embodiment is not used, it is possible to reduce the weight of the movable part, and furthermore, the occurrence of harmful resonance can be avoided.

In the above embodiment, the supporting means for the movable member is a wire type, but it is needless to say that the present invention is not limited to this and can be applied to other supporting means.

〔Effect of the invention〕

As described above, according to the present invention, by locating the position detection point of the objective lens and the principal point of the objective lens on a plane perpendicular to the optical axis of the objective lens, recording is possible even when the lens holder moves while rolling. The displacement of the light spot on the medium can be accurately detected.

This makes it possible to improve the accuracy of tracking position control.

[Brief explanation of the drawing]

FIGS. 1(A) and (B) are a plan view and a sectional view taken along the line A-A of the first embodiment of the present invention; FIG. 2 is an explanatory diagram of the same; FIG. 3(A), B) is a sectional view showing the main part of the second embodiment of the present invention, FIG. 4 is an overall perspective view showing the conventional example, and FIGS. 5 (A) and (B) are views showing the conventional light detection method. FIG. 6 is a cross-sectional view showing the main parts of the conventional device, and FIGS. 7(A) and 7(B) are explanatory views of the same. ■...Objective lens la...Objective lens principal point 2...Lens holder 4...Elastic wire 5...
- Light shielding member 5a...opening 6...light source
7...Two-split photodetector Fig. 3 (A) CB) Fig. 1 Fig. 2 Fig. 4 Fig. 5

Claims (1)

[Claims] 1. A movable member that holds a condenser lens that irradiates a light spot onto the surface of a recording medium, and a support member that supports the movable member so that it can move in a direction perpendicular to the optical axis of the condenser lens. A reference point that moves together with the condenser lens is formed on a plane orthogonal to the optical axis passing through approximately the principal point of the condenser lens, and the reference point is orthogonal to the optical axis of the condenser lens. 1. An optical pickup comprising means for detecting the position of a condenser lens with respect to a recording medium surface by detecting displacement in the direction.