JPH04243026A - Objective lens position detector - Google Patents

Abstract

PURPOSE:To miniaturize the position detector for an objective lens for recording and reproducing information on and from an optical recording medium and to lower the optical output thereof. CONSTITUTION:This position detector is constituted by disposing a spectroscope 101 which divides an incident luminous flux to two fluxes and emits the fluxes in different directions on a movable holder 31 which is mounted with the objective lens 17 and executes tracking control and providing at least one photodetector 103a which detects the quantity of the divided luminous fluxes so as to detect the position of the above-mentioned objective lens from a change in the output of this photodetector.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens position detecting device for an optical recording and reproducing apparatus that optically reproduces information or records and reproduces information.

0002

2. Description of the Related Art Optical disk devices require a tracking servo to record or reproduce signals concentrically or spirally on an information recording medium in a non-contact manner. Various methods have been proposed for this tracking servo sensor method, and there is a method called a push-pull method that utilizes diffracted light from a signal pit or a guide groove.

The principle of the push-pull tracking sensor method will be explained using FIG. 5. In FIG. 5A, the information recording medium 1 has a guide groove 2 in the center of the surface on the objective lens 3 side. The objective lens 3 forms a condensing spot 4 at the center of the guide groove 2 . The convex lens 5 is arranged parallel to the objective lens 3 on the side opposite to the information recording medium 1.

The two-split photodetector 6 has two light-receiving surfaces 6a,
6b, and is arranged on the opposite side of the convex lens 5. The differential amplifier 7 has input terminals +, which are respectively connected to the two light receiving surfaces 6a and 6b of the two-split photodetector 6.
-, and generates a tracking error signal TS based on the output from the light receiving surfaces 6a and 6b.

When the focused spot 4 is diffracted by both edges of the guide groove 2, it produces diffracted light distributions 8 and 9, and is also projected onto the surface of the two-split photodetector 6 to produce diffracted light distributions 10 and 11. arise. When the objective lens 3 is located at the center of the guide groove 2, the diffraction light distribution 1 follows the above-mentioned diffraction light distributions 8 and 9.
The intensities of 0 and 11 become equal, and the output TS of the differential amplifier 7
becomes zero.

However, if the relative positional relationship between the objective lens 3 and the guide groove 2 shifts due to eccentricity of the information recording medium 1, etc., the diffracted light distributions 8 and 9 will no longer be uniform, so that the differential amplifier The output TS of 7 is positive or negative. Therefore, a servo operation is performed to make this output TS zero, and the objective lens 3 is translated in the X direction shown in the figure.

Next, problems with the push-pull method will be explained. FIG. 5(b) is a diagram showing a state in which the guide groove 2 and the objective lens 3 are displaced by a distance d with respect to the neutral point of the objective lens 3. In this state, although the focused spot 4 is located at the center of the guide groove 2, the projected diffracted light distributions 10 and 11 on the surface of the two-split photodetector 6 correspond to the two light-receiving surfaces 6a and 6b. As a result, the output TS of the differential amplifier 7 does not become zero. That is,
This results in a state where a tracking offset occurs.

FIG. 5(c) is a diagram showing the tracking error signal TS with respect to the displacement d of the objective lens 3, and as the displacement d increases, the amount of tracking offset also increases.

As described above, the push-pull method is a simple method that uses diffracted light, but an offset occurs in the tracking error signal due to the displacement of the objective lens 3 in the tracking direction. The disadvantage was that it could not be wide enough.

[0010] Conventionally, there has been an objective lens position detection device disclosed in, for example, Japanese Patent Application Laid-open No. 198436/1983 as an attempt to improve such drawbacks.

This conventional objective lens position detection device is shown in FIG.
This will be explained using FIGS. FIG. 6 is a diagram showing the configuration of a conventional objective lens position detection device, in which a light beam emitted from a light source 12 such as a semiconductor laser is made into a parallel light beam by a collimator lens 13. The emitted light beam 14 from the collimator lens 13 passes through the first beam splitter 19 and is split by the second beam splitter 15, and the split light beam 16 passes through the objective lens 17 and becomes information. Recording medium 1
8, and travels backward along the optical path to the first beam splitter 1.
9 and enters a two-split photodetector 20 for tracking error detection, which has two light receiving surfaces 20a and 20b.

The differential amplifier 21 is connected to the two-split photodetector 20 for tracking error detection, and generates a tracking error signal TS based on outputs from its two light receiving surfaces 20a and 20b.

The other beam 22 that has passed through the second beam splitter 15 is reflected by a mirror 23 and then passes through the objective lens 1.
A slit 25 provided in a movable holder 24 that holds 7
, and is received by the two-split photodetector 26 for detecting the position of the objective lens, which has two light-receiving surfaces 26a and 26b. The differential amplifier 27 is connected to the two-split photodetector 26 for detecting the position of the objective lens, and its two light receiving surfaces 26a and 26b
The objective lens position detection signal LPS is generated based on the output from the objective lens position detection signal LPS.

The differential amplifier 28 is connected to the differential amplifiers 21 and 27, and detects the tracking error corrected by the tracking error signal TS obtained from the differential amplifiers 21 and 27, and the objective lens position detection signal LPS.
Generates signal C-TS.

Next, the operation of this conventional objective lens position detection device will be explained. FIG. 7 is a perspective view showing the main parts for detecting the objective lens position detection signal LPS in this conventional example. Movable holder 24 that holds objective lens 17
performs a tracking operation by rotating about the shaft 29 in the direction indicated by the arrow in the figure. Since the slit 25 provided in the movable holder 24 moves in conjunction with the tracking operation, the light beam 22a passing through the slit 25 is detected by a two-split photodetector 26 for detecting the position of the objective lens.
By receiving the light and taking its differential output, as shown in Figure 8(b)
The objective lens position detection signal LPS has the detection characteristics shown in
can be obtained.

Note that the tracking error signal TS by the normal push-pull method is obtained as the output of the differential amplifier 21 in FIG. 6, and as shown in FIG.
The waveform has a tracking offset with respect to the displacement d. These two signals are connected to a differential amplifier 28 shown in FIG.
As shown in FIG. 8(c), a corrected tracking error signal C-TS without tracking offset can always be obtained regardless of the displacement of the objective lens 17 in the tracking direction. It becomes possible to have a wide movable range in the tracking direction.

[0017]

[Problems to be Solved by the Invention] In the conventional objective lens position detection device, the light beam incident on the objective lens 17 and the slit 25 is split by the second beam splitter 15, so that the light beam incident on the objective lens 17 is In order to prevent this, an expensive light source with a high light output was required. In addition, the second beam splitter 15
It is necessary to guide the luminous flux divided by the slit 25 to the slit 25, which poses problems such as making it difficult to miniaturize the device. The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a small-sized objective lens position detection device that has a simple configuration and is highly reliable.

[0018]

[Means for Solving the Problems] An objective lens position detection device according to the present invention includes a spectroscopic means provided on a movable holder that holds an objective lens, and a light source provided on a fixed part facing the spectroscopic means. , first and second photodetectors that receive two beams of light emitted from the light source and split into two by the spectrometer, and the direction of the beam split into two by the spectrometer is controlled by the tracking control of the objective lens. It is characterized by being configured to be in the same direction as the direction of displacement due to operation.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a perspective view of this embodiment, and Figure 2 is Figure 1I.
It is a sectional view taken along the line I-II, and 12 to 14, 1 in the figure.
6 to 21, 27, and 28 are the same as those shown in FIGS. 7 and 8 of the conventional example.

Reference numeral 30 is for guiding the parallel light beam 14 converted by the collimator lens 13 to the objective lens 17. Reference numeral 31 denotes a movable holder, which has a bearing part 32 in the center thereof, and holds the objective lens 17 at a position offset by a predetermined distance from the axis of this bearing part 32. This movable holder 31 is provided with tracking control coils 33a, 33b and a focus control coil 34, and a control current is supplied to the tracking control coils 33a, 33b, and electromagnetic interaction with a magnetic circuit (not shown) is provided. Accordingly, the movable holder 31 is configured to rotate in the direction of arrow T about the axis of the bearing portion 32, thereby controlling the tracking of the objective lens 17.

Furthermore, a control current is supplied to the focus control coil 34, and the movable holder 31 is displaced in the direction of arrow F along the axis of the bearing portion 32 due to electromagnetic action with a magnetic circuit (not shown), and the objective lens 17 is moved. The lens is configured to perform focus control.

Reference numeral 101 denotes a branching triangular prism, which is a spectroscopy means, and is provided on the movable holder 31 at a position offset by a predetermined distance from the axis of the bearing 32. This branching triangular prism 101 has an apex angle of 90 degrees. The edges of these two reflective surfaces face in the opposite direction to the information recording medium 18 side, and the two reflective surfaces face in the tracking control direction (direction of arrow T). It is arranged in line with the

102 is a light source, and a triangular prism 10 for branching.
When the movable holder 31 is at the neutral point in the tracking control direction, the beam 104 emitted from the light source 102 has a beam cross section centered on the ridge of the branching triangular prism 101. It is configured to be symmetrically divided into two parts. 103a and 103b are
The light source 1 is a photodetector for detecting the position of the first and second objective lenses.
The light beams 105 and 106 are emitted from the branching triangular prism 101 and split into two by the branching triangular prism 101.

Next, the operation will be explained using FIG. 2. FIG. 2(a) shows the branching triangular prism 101 when the objective lens 17 is at the neutral point in the direction of tracking control operation.
, a light source 102 and a photodetector 10 for detecting the position of the objective lens.
3a and 103b, and FIG. 2(b) shows the positional relationship between the objective lens 17 and the tracking control operation.
The positional relationship between the triangular branching prism 101, the light source 102, and the objective lens position detection photodetectors 103a and 103b is shown when the branching triangular prism 101 is displaced by d.

As shown in FIG. 1, the outputs of the objective lens position detection photodetectors 103a and 103b are input to a differential amplifier 27, and as shown in FIG. When the lens 17 is at the neutral point, the light source 10
The light beam 104 emitted from the branching triangular prism 101
The photodetector 1 for detecting the objective lens position is divided into two equal parts.
Since the light is incident on the light receiving surfaces of 03a and 103b, the output LPS of the differential amplifier 27 becomes zero.

Further, as shown in FIG. 2(b), the branching triangular prism 101 is
When the displacement is 10, the light beam 10 is emitted from the light source 102
4 is unequally divided into two parts by the branching triangular prism 101, which enters the objective lens position detectors 103a and 103b, so that the output LPS of the differential amplifier 27 becomes positive.

In this way, the amount of light beams 105 and 106 split by the branching triangular prism 101 changes depending on the displacement d of the branching triangular prism 101 accompanying the tracking control operation of the objective lens 17.
The relationship between the displacement of LPS and the output LPS of the differential amplifier 27 changes from positive to negative as shown in FIG.

Note that since the light beams 105 and 106 split by the branching triangular prism 101 are received by the objective lens position detection photodetectors 103a and 103b, the diameters of the light beams 105 and 106 and the movement associated with the focus control operation are If the size of the objective lens position detection photodetectors 103a and 103b is set in consideration of the amount of displacement of the holder 31, the output LPS of the differential amplifier 27 can be changed by the displacement of the movable holder 31 accompanying the focus control operation of the objective lens 17. does not change, and there is no need for special position adjustment of the photodetectors 103a, 103b for detecting the objective lens position.

A tracking error signal TS based on the normal push-pull method is obtained as the output of the differential amplifier 21 shown in FIG. Therefore, as in the case of the conventional example shown in FIG. 6, a tracking error signal C-TS corrected by the differential amplifier 28 of FIG. 1 is obtained.

In the above embodiment, two photodetectors 103a and 103b were used as photodetectors for detecting the position of the objective lens, but as shown in FIG. 3, by receiving one of the light beams 105 by the photodetector 103a for detecting the position of the objective lens, inputting this output to one terminal of the differential amplifier 27, and inputting the bias V to the other terminal. This output LPS can be obtained, and the same effects as in the embodiment described above can be obtained.

In the above embodiment, a triangular prism with an apex angle of 90 degrees was used as the branching triangular prism, but any spectroscopic means may be used as long as it can split the light beam into two directions. A similar effect can be obtained.

[0032]

As described above, according to the present invention, the movable holder that holds the objective lens is provided with a spectroscopic means, and the light beam emitted from the light source provided opposite to the spectroscopic means is split into two by the spectroscopic means. The objective lens is simple, compact, and highly reliable because it separates the light beam into two beams and detects the position of the objective lens by receiving at least one of these two beams with a photodetector. A position detection device is obtained. Another advantage is that assembly and adjustment of the objective lens position detection device can be simplified.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of an objective lens position detection device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of this embodiment, and FIG.
FIG. 2 is a partial cross-sectional view taken along line II-II of FIG.

FIG. 3 is a characteristic diagram showing the relationship between the displacement of the objective lens in the tracking direction and the output LPS of the objective lens position detection device in this embodiment.

FIG. 4 is a perspective view of a second embodiment of the invention.

[Figure 5] Conventional tracking sensor using push-pull method
FIG. 2 is a diagram for explaining the principle of the Bosensor method.

FIG. 6 is a diagram showing the configuration of a conventional objective lens position detection device.

FIG. 7 is a perspective view of main parts of a conventional objective lens position detection device.

FIG. 8 is a signal waveform diagram of each part of a conventional objective lens position detection device.

[Explanation of symbols]

17 Objective lens 31 Movable holder 101 Triangular prism for branching 102 Light source

Claims (1)

[Claims] 1. A movable holder that holds an objective lens that focuses a tracking light beam to form a minute optical spot on a recording medium, and that displaces the position of the objective lens under the control of a tracking signal. , a spectroscopic means that is held by the movable holder and divides the incident luminous flux into two at its cross section; a light source that inputs the luminous flux into the spectroscopic means; and at least one of the luminous flux divided into two by the spectroscopic means. An objective lens position detection device comprising: a photodetector for receiving light, and configured such that a light beam divided into two by the spectroscopic means is divided into two in a direction in which the light beam is displaced in accordance with a tracking control operation of the objective lens.