JPS62128030A - Position detector - Google Patents

Abstract

PURPOSE:To obtain the titled device with high-precision and wide detectable range by providing a reflecting piece consisting of a homing reflective material in such position that a detection signal is not affected even if a tracking actuator is changed in the focusing direction. CONSTITUTION:A tracking actuator 30 to which an objective lens 31 is set is turned around a revolving shaft 29 in the direction of an arrow 32. The rectangular reflecting piece is set to the side face of the tracking actuator 30, and a position detector 26 is provided in a position facing the reflecting piece. A differential signal 28 between respective outputs of light receiving sources P1 and P2, namely, a displacement signal of the actuator 30 is obtained by a differential amplifier 27. Respective outputs are added by an adding ampli fier 25, and the light emission power of a light emitting source is controlled in accordance with the magnitude of the addition signal by a power control circuit 24. Since the light reflected on the surface of the reflecting piece is returned toward the light source when the reflecting piece consisting of a hom ing reflective material is used, the detection range of angle change (turn change) is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for recording, reproducing, or erasing recorded information on an information recording medium (hereinafter referred to as a disk) using a light beam. The present invention relates to a position detection device that detects displacement of an actuator.

BACKGROUND ART FIG. 6 shows an example of a configuration for detecting displacement of a conventional tracking actuator. The drive signal 6 is amplified by a desired factor by the drive amplifier 1, voltage-to-current converted by the drive amplifier 2, and applied to the tracking actuator 3. Specifically, the drive current converted in step 2 is applied to the drive coil of the tracking actuator, and the tracking actuator 3 carrying the objective lens is moved to a desired position.

Now, the displacement of the tracking actuator 3 is detected electrically as shown below. The drive current applied to the drive coil of the tracking actuator 3 is detected and amplified by the amplifier 4 . Next, the signal amplified by the desired times is converted by an electric filter 6 having characteristics almost equivalent to the frequency characteristics of the tiger and king actuator 30,
A displacement signal 8 representing the displacement of the tracking actuator 3 is obtained. As described above, there is a method of monitoring the current applied to the drive coil and detecting displacement using the electric filter 5 having substantially the same frequency characteristics as the tracking actuator 3. In general, a tracking actuator has the characteristics of a second-order system having a resonance sieve of Q [dB] at the -order resonance frequency f0, as shown by solid lines 9 and 12 in FIG. For example, if a second-order active low-pass filter consisting of an amplifier 42 as shown in FIG. 8 is used, this characteristic can be obtained using the dashed line 10.
The characteristics shown in can be realized. As described above, there is a method of electrically detecting the displacement of the tracking actuator.

On the other hand, there is also a method of providing a separate detector to detect displacement. For example, Japanese Unexamined Patent Publication No. 56-163138 proposes several methods for detecting displacement of a rotary actuator. FIGS. 9a and 9b are diagrams showing an example thereof.

As shown in FIG. 9a, the two-split photodetector 17, which is divided into two at the center, is attached to the pickup support plate 13 (corresponding to the tracking actuator), and the light source 18 is attached as shown in FIG. The pickup 1 of FIG. 9a is fixed to the case 19 facing the two-split photodetector 17.
When the operating center 15 of 4 coincides with the operating reference line 21 shown in the figure, if the rain amount force difference of the two-split photodetector 17 is set to be zero, it will be integrated with the support plate 13. The two-split photodetector 17 also rotates about the rotation center 16 in response to the rotation of the pickup 14 in the arrow direction 22 in FIG. There is a difference in the amount of rotation of the pickup 14, and the amount of rotation of the pickup 14 can be detected. The arrow direction 22 in FIG. 9a indicates the tracking displacement direction.

In addition, means for detecting displacement optically and means for detecting displacement magnetically have also been proposed, but these are omitted here.

Problems to be Solved by the Invention However, the configuration of the conventional detection means as shown above has the following problems.

In the method of electrically detecting displacement, firstly, the sixth
In the tracking actuator 3 shown in the figure, the wQ value and fo shown in FIG. 7 change as the ambient temperature changes. The electric filter 5 naturally has temperature characteristics, but it is very difficult to make the temperature characteristics of the electric filter 5 equal to the temperature characteristics of the tracking actuator 3. Therefore, depending on the ambient temperature, accurate displacement detection may not be possible. There is a problem with it disappearing. Secondly, since it is necessary to match the electrical filter to the frequency characteristics of each tracking actuator 3, it is necessary to adjust it individually. Thirdly, it is extremely difficult to construct an active filter that can faithfully realize the frequency characteristics of the tracking actuator 30. In this way, the method of electrically detecting displacement has many problems, so
This is hardly a practical method.

On the other hand, conventional methods using detection means also have the following problems. The pickup support plate 13 (corresponding to a tracking actuator) shown in FIG. (omitted)).

That is, the structure is such that known tracking control is performed by rotating the support plate 13. Further, the pickup support plate 13 changes in the direction of the arrow in FIG. 9 so that the light beam is always focused on a desired track. That is, known focusing control is performed by vertically changing the support plate 13 with respect to the support shaft 1.

Now, in the configuration shown in FIG. 9, when the support plate changes in the direction of the arrow 23, the distance between the two-split photodetector 17 and the light source 18 also changes. When the interval changes, the output level of the displacement signal obtained from the two-split photodetector 17 changes.

In other words, there is a problem that the detection sensitivity changes. The other detection means proposed in JP-A-55-153138 also has the problem that the detection sensitivity changes as described above.

Further, in the detection means shown in FIGS. 9a and 9b, the weight of the support plate 13 is increased because the two-split photodetector 17 is mounted on the support plate 13. Further, wiring for distributing signals from the detector 17 is required. Generally, it is desirable for the movable part to be as lightweight as possible, and it is obvious that it is preferable to have no unnecessary wiring from the movable part.

As described above, all of the conventionally proposed detection means have problems in practical use.

Means for Solving the Problems In order to solve the above-mentioned problems, the position detection device of the present invention includes a detection means consisting of a light emitting source and a pair of light receiving sources adjacent to the light emitting source, and a detection means opposite to the means. , and even if the Track King actuator changes in the focusing direction,
A reflective piece made of retroreflective material and having a desired shape is provided at a position where the detection signal is not affected, and changes in the reflected light from the reflective piece are received by the pair of light receiving sources, and the tracking actuator receives the change in the reflected light from the reflective piece. It detects the displacement of

Effect The present invention has the above-described configuration to reduce the variation in detection sensitivity due to changes in the focus direction of the tracking actuator, which has been a problem in the past, and to utilize a reflective piece made of a retroreflective material to achieve a wide range of This provides a detectable range. Further, it is possible to provide more accurate displacement detection than the conventional method using an electric filter.

Embodiment Hereinafter, a position detection device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention. Rotation axis 29
A tracking actuator 30 to which an objective lens 31 is attached is configured to rotate in the direction of an arrow 32, with the objective lens 31 attached thereto. A rectangular reflective piece as shown in the figure is attached to the side surface of the tracking actuator 30 so that the reflectance is significantly different from that of the portion other than the reflective piece. A position detector 26 is installed at a position facing the reflective piece. Furthermore, LF shown in the figure
i Light emitting source P1. P2 is a light receiving source. When the tracking actuator 3o rotates in the direction of the arrow 32, the reflective piece also rotates, so that the light receiving source P1. A difference occurs between each output of P2. The differential amplifier 27 outputs the light receiving source P1. P2
A differential signal 28 of each output is obtained.

This differential signal 28 causes the actuator 3o to rotate.
is the displacement signal of Further, each output of the light receiving sources P1 and P2 is added by a summing amplifier 26, and the power control circuit 24
The light emitting power of the light source is controlled by the magnitude of the addition signal. This prevents the detection sensitivity from decreasing due to a decrease in the reflectance of the reflecting piece, clouding of the light receiving and emitting surfaces, etc., and always maintains a constant detection sensitivity.

In addition, tracking actuator 3, which has been a problem in the past,
As shown in the figure, changes in detection sensitivity due to changes in the focus direction 34 of zero can occur if the size of the reflective piece is made sufficiently long in the focus direction relative to the light emitting range from the light source that hits the reflective piece. I know it won't.

Now, a major feature of this device is the material used for the reflective piece shown below. In this position detection device, a retroreflective material is used for the reflective piece. Unlike general reflective materials, this material has the property of reflecting most of the incident light toward the light source.

A comparison with general reflective materials will be explained using FIG. 2. FIG. 2a shows a case where a reflective piece having a mirror surface is used, and FIG. 2b shows a case where a reflective piece made of a retroreflective material proposed in the present invention is used. When the surface of the reflective material is mirror-like as shown in Figure 2a, the law of reflection is followed, so a slight change in angle θ prevents the diverging light from the light source from reaching the light receiving element P2, and the amount of light incident on Pl decreases. It becomes very small. On the other hand, in case b, the light reflected on the surface of the reflective material travels in the direction of returning toward the light source, so even if the angle change θ is similar to that in a, some amount of light will return to P2. That is, this means that the detection range of angle changes (rotation changes) is wider in b than in a.

Figure 3 is a diagram showing how to check the size of both detection ranges,
FIG. 4 is a diagram showing the results. 24 to 28 in the figure have the same functions as in FIG. The rotor 37 is attached to the arrow 38 around the rotation shaft 36. FIG. 4 shows temporal changes in the displacement signal 28 obtained by the differential amplifier 27.

In FIG. 4, a portion 40 is due to the reflective piece 39, a portion 41 is due to the reflective piece 35, and t1 and t, respectively.
The part 2 is the displacement detection range. Since the rotor 37 rotates at a constant angular velocity, the horizontal axis t in FIG. 4 corresponds to displacement. Therefore, as is clear from the figure, the displacement detection range t1 obtained by the reflective piece made of a retroreflector is much wider than the displacement detection range obtained by the mirror-like reflective piece. The experimental results show a difference of several times. By using a reflective piece made of a retroreflective material in this way, a very wide detection range can be obtained.

In this embodiment, the displacement detection method for a rotating tracking actuator has been described, but it goes without saying that the present invention can be used not only for rotating type tracking actuators but also for other types of tracking actuators. It is also possible to detect displacement by using a configuration as shown in FIG. In this case, if the reflective piece is made long in the tracking direction (rotation direction) as shown in the figure, it will not be affected by the rotation.

Effects of the Invention As described above, the present invention provides higher accuracy and a wider detectable range than conventional displacement detection methods, and is very effective in practice.

Also, from a cost perspective, the fact that sufficient detection is possible by using inexpensive parts greatly contributes to reducing the cost of optical pickup.

Furthermore, simply by attaching the reflective piece to the movable part, there is almost no increase in weight, and there is no problem with wiring, so it is possible to obtain the effect that the dynamic characteristics of the actuator are hardly affected.

[Brief explanation of drawings]

Figures 1a and b are block diagrams and side views showing the position detection device according to the present invention, Figures 2a and b are front views showing the effect of using retroreflective pieces, and Figure 3 is a block diagram thereof. ,
Figure 4 is a signal waveform diagram, Figures 5a and b are front and side views with the position detection device centered in the focus direction, and Figure 6
The figure is a block diagram showing a conventional position detection device, Fig. 7a
, b is a characteristic diagram showing the frequency characteristics of the tracking actuator and the electrical filter, FIG. 8 is a circuit diagram showing an example of the electrical filter, and FIGS. 9 a and b show other examples of conventional position detection devices. They are a front view and a cross-sectional side view. 1... Drive amplifier, 2... Voltage-current conversion,
3... Tracking actuator, 4...
...Amplifier, 5...Filter, 6...Drive signal, 7...Displacement, 8...Displacement detection signal, 9...
...gain characteristics of tracking actuator,
1o...Gay 7% property of filter, 11...Phase characteristics of filter, 12...Phase characteristics of tracking actuator, 13...Pickup support plate, 14...・Pickup, 16... Center of operation, 16... Center of rotation, 1 end...
Two-split photodetector, 18...Light source, 19...
...Case, 2o...Support shaft, 21...
Operation reference line, 22...Rotation direction, 23...
... Focus direction, 24 ... Power control circuit, 25 ... Summing amplifier, 26 ... Position detector, 27 ... Differential amplifier, 28 ... ...
Differential signal, 29...Rotation axis, 30...
Tracking actuator, 31...Objective lens, 32...Rotation direction, 33...Reflection piece, 34...Focus direction, 35...Surface Reflective piece with mirror finish, 36...Rotation axis, 3
7-...Rotor, 38...Rotation direction, 39
... Reflective piece using retroreflective material, 40...
- Displacement signal change by 39, displacement signal change by 41...35, 42...amplifier. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 15

Claims (3)

[Claims] (1) an objective lens, a movable part that holds the objective lens, a drive means that drives the movable part so as to move the objective lens to a desired position, and at least two sides attached to the movable part. a reflective piece having a parallel shape; at least one light emitting source provided at a fixed position opposite to the surface of the reflective piece; and at least one light emitting source provided at a fixed position adjacent to the light emitting source. A position detecting device comprising at least a pair of light receiving sources, and the reflecting piece is made of a retroreflective material. (2) The position detection device according to claim 1, wherein the drive means drives the movable part in the focusing direction. (3) The position detection device according to claim 1, wherein the driving means drives the movable part in the tracking direction.