JPH0281338A - Optical pickup - Google Patents

Abstract

PURPOSE:To simplify the constitution of an optical system and to miniaturize the whole by illuminating a recording medium in a defocusing condition, arranging a photo detector to the focus position of a collimator lens and forming the image of the recording medium. CONSTITUTION:The title pickup provides a light source 3, an objective lens 7 to project the light from the power source 3 through a collimator lens 4 to an optical type recording medium after a beam splitter is transmitted or reflected and a photo detector 8 to reflect, transmit or receive the reflecting light at an optical type recording medium through an objective lens 7 and the collimator lens 4 with a beam splitter. The light source 3 is dislocated and arranged from a focus position f0 of the collimator lens 4 and the light detector 8 is arranged to the focus position f0 of the collimator lens 4, an optical type recording medium is illuminated in the defocus condition and the image is formed at the photo detector 8. Thus, the constitution can be simplified, miniaturized and made inexpensive.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup for reading information recorded on an optical recording medium such as an optical card, a compact disc, or a video disc.

[Conventional technology]

Various types of optical pickups have been proposed in the past. For example, Japanese Patent Application Laid-Open No. 57-205833 discloses a system in which light from a light source is passed through a diffraction grating, a polarizing beam splitter, a collimator lens, a quarter-wave plate, and an objective lens. The reflected light passes through an objective lens, a 1/4 wavelength plate, a collimator lens, a polarizing beam splitter, a concave lens, and a cylindrical lens, and then is received by a photodetector to read information, as well as a focus error signal. Also disclosed is a device that detects a tracking error signal.

[Problem to be solved by the invention]

However, in the conventional optical pickup described above, a concave lens is used to separate the three beams of return light from the recording medium on the photodetector, and a concave lens is used to separate the return light of the information reading beam to detect focus errors. Since a cylindrical lens or the like is required to provide point aberration, there are problems in that the configuration is complicated and large, and the cost is high. In addition, by placing the light source at the focal position of the collimator lens, the light from the light source is projected onto the recording medium at the focal position by the objective lens as a parallel beam of light, so the spot of the reading light on the recording medium is extremely small (for this reason, for example, JP-A-63-7
When the width of one track is large and a plurality of pieces of data are recorded in the width direction, as in the optical card disclosed in Japanese Patent No. 533, it becomes difficult to read the information accurately.

This invention was made by focusing on these conventional problems, and can be made simple, compact, and inexpensive, and is also suitable for reading tracks that have multiple data in the track width direction. The object of the present invention is to provide an optical pickup that is appropriately configured so that it can always read accurately.

[Means and effects for solving the problem] In order to achieve the above object, the present invention includes a light source, and the light from the light source is transmitted or reflected through a beam splitter and then projected onto an optical recording medium through a collimator lens. an objective lens for
a photodetector that receives reflected light from the optical recording medium through the objective lens and the collimator lens, reflected or transmitted by the beam splitter, and the light source is arranged to be shifted from the focal position of the collimator lens. In addition, the photodetector is arranged at the focal point of the collimator lens to illuminate the optical recording medium in a defocused state and to form an image thereof on the photodetector.

〔Example〕

FIGS. 1 and 2 are a cross-sectional plan view and a cross-sectional front view showing the configuration of essential parts of an embodiment of the present invention. In this embodiment, data recorded on the tracks of the optical card 1 is read by relatively moving the optical card 1 and the optical pickup 2 in the track direction of the optical card 1. The LED 3 as a light source is at the focal position r0 of the collimator lens 4.
The light beam from the LED 3 is transmitted through the half mirror 5, and then projected onto the optical card 1 from the normal direction through the collimator lens 4, the reflection mirror 6, and the objective lens 7. The tracks of an optical card 1 are illuminated in a defocused state. Further, the reflected light from the optical card 1 is condensed by an objective lens 7, passed through a reflecting mirror 6 and a collimator lens 4, reflected by a half mirror 5, and received by a photodetector 8. Here, the photodetector 8
is placed at the focal position f0 of the collimator lens 4, and the LE
The image of the track illuminated by D3 is formed through the objective lens 7 and the collimator lens 4. Note that the light emitted from the LED 3 reflected by the half mirror 5 is received by the light receiving element 9, and the drive of the LED 3 is controlled so that the amount of light emitted from the LED 3 is thereby constant.

Above LED 3, half mirror 5, collimator lens 4
, the reflecting mirror 6, the photodetector 8, and the light receiving element 9 are mounted on a holding frame 10 fixed to a base (not shown) of the optical pickup 2.
Attach to.

On the other hand, the objective lens 7 is held in a holder 11, and the holder 11 is connected via four parallel wires 12 to a focus direction F, which is the optical axis direction of the objective lens 7, and a tracking direction perpendicular to the tracks of the optical card 1. It is supported on a wire stand 13 fixed to a base (not shown) so as to be movable in a direction T.

Focus coils 14A and 14B are attached to the holder 11 on opposite end faces in the tracking direction T, and tracking coils 15A and 15B are attached to the outside of these focus coils 14A and 14B, respectively.

Also, a focus coil 14A is provided on the base (not shown).
, 14B to provide inner yokes 17A, 17B, and a pair of outer yokes 18A, 18B and opposing inner yokes 17A, 17B via focusing coils 14^, 14B and tracking coils 15^, 15B, respectively. 19^, 19B are provided, and these outer yokes 18A, 18B and 19A, 1 are provided.
Permanent magnets 20^, 20B and 2 are placed inside 9B, respectively.
1A and 21B are glued together to create permanent magnets 2OA and 20.
Magnetic flux that crosses the tracking coil 15A and the focus coil 14^ by the permanent magnets 21A and 21
B generates magnetic fluxes that cross the tracking coil 15B and the focus coil 14B, respectively. In this way, two of the four parallel wires 12
Focus coil 14A, 14 through main wire
By supplying a focus error signal to B, the objective lens 7 is displaced in the focus direction F together with the holder 11 to perform focus servo, and the tracking error signal is sent to the tracking coils 15A and 15B via the other two wires. By supplying the holder 11, the objective lens 7 is displaced in the tracking direction T to perform tracking servo.

FIG. 3 shows an example of the track format of the optical card 1 shown in FIG. A guide pattern 26 consisting of a black and white pattern is formed in the center of the track 25 and extends in the track direction, and 8-bit data is recorded on each side of the guide pattern 26 in the track width direction. .

FIG. 4 shows the configuration of an example of the photodetector 8 shown in FIG. 2. In FIG. The photodetector 8 has data reading light receiving areas 31-1 to 31-16 arranged corresponding to 16 data recording positions in the track width direction, and is spaced apart in the track direction so as to receive the image of the guide pattern 26. 6
Pairs of clock generation light receiving areas 32-1 to 32-12;
It is composed of four pairs of focus/tracking error detection light-receiving areas 33-1 to 33-8 arranged spaced apart and facing each other in the track width direction so as to receive images of both edge portions of the guide track 26 in the track width direction. .

Here, as described above, the LED 3 is placed slightly in front of the focal position f0 of the collimator lens 4, and the optical card 1
When illuminated in a defocused state, the illumination light is converged ahead of the focal position of the objective lens 7. Therefore, in a focused state in which the focal position of the objective lens 7 is located on the optical card 1, the illuminance distribution of the illumination light on the optical card 1 is as shown by the solid line in FIG. 5, for example, and the optical card 1 is When approaching the objective lens side from the focal position of the objective lens 7, the spot diameter becomes larger, so the illuminance distribution becomes as shown by the two-dot chain line in FIG. It will be shown as follows. in this way,
The illuminance distribution of the illumination light on the optical card 1 changes depending on the distance between the objective lens 7 and the optical card 1, but as is clear from FIG. A ring-shaped unchanging part (indicated by reference numeral 35 in FIG. 4) is created in which the illuminance hardly changes even if the distance between the optical card 1 and the optical card 1 changes. The change in illuminance due to the change in the focal state in No. 7 is reversed. That is, when the optical card 1 approaches the objective lens side rather than the focal position of the objective lens 7, the illuminance decreases on the inside of the unchanged portion 35 compared to when in focus, but increases on the outside, and vice versa. When the optical card 1 moves away from the focal position of the objective lens 7, the illuminance increases inside the unchanged portion 35 compared to when it is in focus, but decreases outside it.

In this embodiment, by arranging the LED 3 slightly in front of the focal position r0 of the collimator lens 4, in the focused state where the optical card 1 is located at the focal position of the objective lens 7,
Enable sufficient illumination of the track 25 inside the unchanged portion 35. Moreover, in the photodetector 8, the fourth
As shown in the figure, the data reading light-receiving areas 31-1 to 3146 corresponding to the data recording positions of the track 25 are set inside the unchanged portion 35 of the spot image of the optical card 1 by the illumination light formed on the photodetector 8. are arranged along the diameter direction of the unchanged portion 35, and two of the four pairs of focus/tracking error detection light receiving regions 33-3.
33-4, 33-5, and 33-6 are arranged symmetrically so that their respective centers are located inside the unchanged portion 35 so as to mainly receive images of the inner peripheral portion of the unchanged portion 35, The other two pairs of focus/tracking error detection light receiving areas 33-1, 33-2 and 337, 33-
8 are arranged symmetrically so that their centers are located outside the unchanged portion 35 so as to mainly receive images of the outer periphery of the unchanged portion 35.

Further, the clock generation light receiving areas 32-1 to 32-12 are arranged between the light receiving areas 33-3, 33-4 and 33-5, 33-6.

Note that the paired clock generation light receiving areas 32-1;
2, 32-3; 32-4,..., 32-
11; 32-12 is set to 1/2 a pinch of the image of the black and white pattern constituting the guide pattern 26. Further, each of the focus/tracking error detection light receiving areas 33-1 to 33-8 has a length that is an integral multiple of the pitch of the black and white pattern so that it can receive the image of the edge portion in the track width direction of the black and white pattern. And the white part (high reflectance part) between the guide pattern 26 and the data part
The light-receiving areas 33-1, 33-2 and 33-7, 33-8 are configured to have a width sufficient to receive reflected light from
Since the illuminance of the incident light is low, the inner peripheral portion is made longer than the length of the light receiving areas 33-3 to 33-6 that receive light.

Here, the magnification of the optical system is determined by the ratio of the emission diameter of the LED 3 to the diameter of the unchanging portion 35 of the illumination light on the optical card 1, and the pitch of the data image of the track 25 formed on the photodetector 8. For example, the ratio of the focal lengths of the collimator lens 4 and the objective lens 7 is set to 1:4 so that the ratio of the pitch of the data on the optical card l is equal to the pitch of the data on the optical card l. In this way, the data pitch in the track width direction on the optical card 1 is 5μII+
(track width 95 μm), the corresponding light receiving areas 31-1 to 31-8 and 31-9 on the photodetector 8
Since the pitch of 31-16 is 20 μm, the photodetector 8 can also be manufactured easily.

As described above, one of the paired clock generation light receiving areas 32-1.32-3.32-132-7.32-9
and the sum of the outputs of 32-11 and the other clock generation light receiving area 32-2.32-4.32-6.32-8.3
A clock signal is obtained based on the difference between the sum of the outputs of 2-9 and 3210. In addition, the guide pattern 26
The sum of the outputs of light-receiving areas 33-1, 33-3, 33-5 and 33-7 that receive an image of one edge in the track width direction, and the light-receiving area 33 that receives an image of the other edge.
-2. Obtain a tracking error signal based on the difference between the sum of the outputs of 33-4° 33-6 and 33-8, and
A light receiving area 33- whose center is located inside the unchanged portion 35
Focusing is performed based on the difference between the sum of the outputs of 3 to 33-6 and the sum of the outputs of light receiving areas 33-1, 33-2, 33-7 and 33-8 whose centers are located outside the unchanged portion 35. Try to get an error signal.

In this embodiment, focus servo is performed by displacing the objective lens 7 in the optical axis direction so that the optical card 1 is located at its focal position based on the focus error signal obtained as described above, and the tracking error signal is While performing tracking servo so that the spot center of the illumination light is located at the widthwise center of the desired track 25 of the optical card 1, the objective lens 7 is moved in synchronization with the clock signal to the data reading light receiving area 33-1. - Take in the output of 31-16 and read 16-bit data.

According to this embodiment, the sum D1 of the outputs of the light receiving areas 33-3 to 33-6 whose centers are located inside the unchanged portion 35 in FIG.
When moving away from a position closer to the objective lens than the focal position through the focal position, the illumination light increases up to the convergence position of the illumination light, but decreases thereafter. On the other hand, the light receiving area 33-1.33-2.33 whose center is located outside the unchanged portion 35
The sum D2 of the outputs of −7 and 33 to 8 decreases up to the convergence position of the illumination light, but increases thereafter. Therefore, by processing the outputs of Dl and D2 so that the difference between them becomes zero at the in-focus position, it is possible to obtain a focus error signal whose polarity is reversed before and after the in-focus position, as shown in Figure 6. .

Here, the position where the focus error signal becomes zero occurs not only at the in-focus position but also at a position conjugate to the in-focus position with respect to the convergence position of the illumination light, and when the optical card 1 is moved away from this position, the focus error signal becomes zero. The polarity is reversed and focus cannot be pulled. Therefore, it is desirable that the reversal portion where the optical card 1 is too far away and the polarity of the focus error signal is reversed in FIG. 6 be as small as possible within the driving range of the objective lens 7. When the distance Mi between them is increased, the amount of light incident on the photodetector 8 decreases, making it more susceptible to noise. Also, distance! If it is shortened, the focus servo is likely to come off due to noise in the signal processing system, defects on the optical card 1, fluctuations in the output of the light receiving area for focus error detection during seek, etc. For this reason, the distance Ml is 200 μm ~ 8
00 μm, that is, the distance from the focal position (focal position of the objective lens 7) to the convergence position of the illumination light is 100 μm to 4
It is preferable to set the thickness to 00 μm.

In this way, when the focus is turned on, if the optical card 1 is in the normal area ■ within ±2 from the focus position in Fig. 6, the objective lens 7 will enter the servo range after a certain period of time and the servo will be turned on. After that, normal focus servo can be performed stably. Further, when the optical card 1 is in the normal part (2) in FIG. 6, the servo is turned on when the objective lens 7 enters the servo range. At this time, there are cases where the focus servo is performed calmly and stably, and cases where the objective lens 7 enters the reversal section due to inertia separating from the optical card l and the servo comes off, but in the latter case, the focus is turned off once. Then, after displacing the objective lens 7 by a predetermined amount by supplying a bias current of a predetermined polarity to the focus coils 14A and 14B so that the optical card 1 is positioned within ±2, normal focus is achieved by turning on the focus again. Servo can be operated stably. Similarly, when the optical card 1 is in the reversal position in FIG. After the objective lens 7 is displaced by a predetermined amount so that the optical card 1 is positioned within ±l, the focus is turned on again, thereby stably performing normal focus servo. In other words, focus on,
When the objective lens 7 is close to or away from the optical card 1 without changing the focus error signal even after a certain period of time has elapsed, or when the focus error signal becomes zero twice and the objective lens 7 is at a position away from the optical card 1. Sometimes, after detecting them and once focusing off, the focus coil 14A is moved so that the optical card l is positioned within ±2.
It is sufficient to supply a bias current of a desired polarity to 14B to displace the objective lens 7 by a predetermined amount, and then turn on the focus again.

Note that this invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, is there a light-receiving area whose center is located inside the unchanged portion for detecting focus errors, or a light-receiving region whose center is located outside the unchanged portion? Area (1) can be configured with any number of light-receiving areas. In addition, in the above-described embodiment, in order to obtain a trunking error signal, the light-receiving areas for focus/tracking error detection were provided in pairs in the track width direction so as to receive the image of the guide pattern 26; If you only want to detect errors, use
It is not necessarily necessary to provide the light-receiving areas in pairs in the track width direction, and it is also not necessary to arrange them so as to receive the image of the guide pattern 26. Therefore, the present invention can be effectively applied not only to optical cards but also to other optical recording media such as CDs that do not have guide patterns. In addition, in the embodiment described above, the half mirror 5
In the above, the light from the LED 3 is transmitted through and the return light from the optical card 1 is reflected. However, by reversing the positional relationship between the LED 3 and the photodetector 8, the light from the LED 3 is reflected, and the light from the optical card 1 is reflected. It is also possible to allow the return light from to pass through. Further, the light source is not limited to an LED, but a semiconductor laser or the like can also be used, and its arrangement is not limited to the front of the focal position r0 of the collimator lens 4, but can also be arranged behind the focal position r0 to illuminate the recording medium in a defocused state. You can also do it.

〔Effect of the invention〕

As described above, according to the present invention, the light source is arranged offset from the focal position of the collimator lens to illuminate the recording medium in a defocused state, and the photodetector is arranged at the focal position of the collimator lens. Since the image of the recording medium is formed without using a lens, the configuration of the optical system can be simplified, the whole can be made smaller and cheaper, and focus errors can be detected with high sensitivity. This can always be read accurately even when reading a track with multiple pieces of data.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional plan view showing the configuration of essential parts of an embodiment of the present invention, FIG. 2 is a cross-sectional front view, and FIG. 3 is a diagram showing an example of the track format of the optical card shown in FIG. 1. Figure 4 is a diagram showing the configuration of an example of the photodetector shown in Figure 2. Figure 5 is a diagram showing changes in the illuminance distribution of illumination light on the optical card in Figure 1. Figure 6 is a diagram showing focus error. It is a figure which shows a signal. 1... Optical card 2... Optical pickup 3... LED 4... Collimator lens 5... Half mirror 6... Reflection mirror 7...
- Objective lens 8... Photodetector 25... Track 26... Guide pattern 31-1
~31-16... Light receiving area 32-1 for data reading
~32-12...Clock generation light receiving area 33-1~
33-8... Light receiving area for focus/tracking error detection 35... Unchanged portion Fig. 1 Fig. 2 Fig. 4

Claims (1)

[Claims] 1. A light source, an objective lens that transmits or reflects the light from the light source through a beam splitter and then projects it onto an optical recording medium via a collimator lens, and transmits the reflected light from the optical recording medium to the objective lens and the collimator. a photodetector that receives light reflected or transmitted by the beam splitter through a lens, the light source is placed offset from the focal position of the collimator lens, and the photodetector is placed at the focal position of the collimator lens. An optical pickup characterized in that the optical pickup is configured to illuminate the optical recording medium in a defocused state and form an image thereof on the photodetector.