JPH0281331A - Optical pickup - Google Patents

Abstract

PURPOSE:To stably carry out focus servoing by shifting a light source from the focal position of a collimator lens to control the distance between the focal position of the objective lens on the recording medium side and the convergent position of the light flux of the objective lens from the light source to 100-400mum. CONSTITUTION:The light source is shifted from the focal position of the collimator lens so that the distance between the focal position of the objective lens on the optical recording medium side and the convergent position of the light flux of the objective lens is controlled to 100-400mum. For example, the LED 3 as the light source is arranged slightly on this side of the focal position f0 of the collimator lens 4, and the light flux from the LED 3 is transmitted through a half mirror 5 and projected on an optical card 1 in its normal direction through the collimator lens 4, reflecting mirror 6, and objective lens 7. Accordingly, a focus error can always be detected with high sensitivity based on the illuminance distribution of the return light from the recording medium, and focus servoing is stably carried out at all times.

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]

As conventional optical pickups, for example, Japanese Patent Laid-Open Nos. 62-279523 and 63-9183 proposed by the applicant
There are those disclosed in Publication No. 0, Publication No. 63-117334, and the like. In these optical pickups, the optical pickup is illuminated from an oblique direction by an illumination means, and the reflected light is received by separate light-receiving areas in a direction that is displaced depending on the focus state. A focus error signal is obtained based on the output.

[Problems to be Solved by the Invention] However, as a result of studies by the inventors of the present invention, it has been found that the conventional optical pickup described above has the following points to be improved.

In other words, in the above-mentioned optical pickup, since the focus error signal is obtained by receiving the reflected light from the opposite peripheral areas of the illumination light projected onto the optical card, the illuminance of the reflected light incident on the light receiving area is As a result, the detection sensitivity is low and the focus servo is easily affected by noise.

The present invention was made in view of these problems, and an object thereof is to provide an optical pickup that is appropriately configured so that focus errors can always be detected with high sensitivity, and therefore focus servo can always be performed stably. shall be.

[Means and effects for solving the problem] In order to achieve the above object, the present invention includes a light source and an objective lens that projects a light beam from the light source onto an optical recording medium from the normal direction thereof through a collimator lens. The distance between the focal position of the objective lens on the optical recording medium side and the convergence position of the light beam by the objective lens is 100 μm to 400 μm.
The light source is arranged to be shifted from the focal position of the collimator lens so that the optical recording medium is illuminated in a defocused state.

〔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 moving the optical card 1 and the optical pickup 2 relatively in the track direction of the optical card 1. The LED 3 as a light source is at the focal position fO 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 l from the normal direction through the collimator lens 4, the reflection mirror 6, and the objective lens 7. The light beam is converged at a position 100 μm to 400 μIll apart from the focal point of the objective lens 7 on the optical card 1 side, so that the track of the optical card 1 is 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 bar mirror 5, and received by a photodetector 8. Here, the photodetector 8 is arranged at the focal position fO of the collimator lens 4 so that the image of the track illuminated by the LED 3 is formed by 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 focusing direction F, which is the optical axis direction of the objective lens 7, and a tracking direction perpendicular to the track of the optical card L. 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 opposing 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 and 17B, and a pair of outer yokes 18 facing these inner yokes 17A and 17B via focus coils 14A and 14B and tracking coils 15A and 15B, respectively.
A, 18B and 19A, 19B are provided, and permanent magnets 2OA, 20B and 21A, 21B are adhered to the inside of these outer yokes 18A, 18B and 19A, 19B, respectively, and the tracking coil 15A and focus coil are connected by the permanent magnets 2OA, 20B. The magnetic flux that crosses the tracking coil 15B and the focus coil 14B are generated by the permanent magnets 21A and 21B, respectively. In this way, by supplying focus error signals to the focus coils 14A and 14B via two of the four parallel wires 12, the objective lens 7 is displaced in the focus direction F together with the holder 11. to perform focus servo, and connect the tracking coils 15A and 1 via the other two wires.
By supplying a tracking error signal to 5B, the objective lens 7 is displaced in the tracking direction T together with the holder 11 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 and four pairs of focus tracking arranged 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. It is configured with error detection light receiving areas 331 to 33-8.

Here, as mentioned above, if the LED 3 is placed slightly in front of the focal position fo of the collimator lens 4 and the optical card 1 is illuminated in a defocused state, the illumination light will be directed ahead of the focal position of the objective lens 7. It is converged on. 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 is determined by the objective lens 7.
However, as is clear from FIG. A ring-shaped unchanging portion (indicated by reference numeral 35 in FIG. 4) is created, and the change in illuminance due to the change in the focal state of the objective lens 7 is opposite between the inside and outside of this unchanging portion 35. 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 it is in focus, but increases on the outside, and vice versa. As 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, whereas it decreases outside it.

In this embodiment, by arranging the LED 3 slightly in front of the focal position fo of the collimator lens 4, the optical card 1 is in the focused state located at the focal position of the objective lens 7, and the LED 3 is placed inside the unchanged portion 35. To ensure that the track 25 is sufficiently illuminated. In addition, in the photodetector 8, as shown in FIG.
inside the unchanged portion 35 of the spot image of the optical card 1 formed by the illumination light formed on the photodetector 8.
2 out of 4 pairs of focus/tracking error detection light receiving areas 33
-3.33-4 and 33-5.33-6 are arranged symmetrically so that their respective centers are located inside the unchanged portion 35 so as to mainly receive images of the inner periphery of the unchanged portion 35. and two other pairs of focus/tracking error detection light receiving areas 33-1, 33-2 and 33-7.
．． 33-8, the center of each of which is connected to the unchanged portion 35 so as to mainly receive the image of the outer periphery of the unchanged portion 35.
Arrange symmetrically so that it is located outside of. Further, the light receiving areas 32-1 to 32-12 for clock generation are the light receiving areas 33
-3.33-4 and 33-5.33-6. Note that the paired clock generation light receiving area 33-1
; 32-2.32-3; 32-4.・・－－－
--, 32-11; each interval of 32-12 is
17 of the black and white pattern images constituting the guide pattern 26
2 pitches. 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. It is configured to have a width that can sufficiently receive the reflected light from the white part (high reflectance part) between the guide pattern 26 and the data area, and the image of the outer peripheral part of the unchanged part 35. The light receiving areas 331, 33-2, and 33-7.
Since the illuminance of the incident light is low, the length of the area 33-8 is made longer than the length of the light-receiving areas 33-3 to 33-6 that receive the image of the inner peripheral part.

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 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 pitch is equal to the pitch of data on the optical card 1.

In this way, when the data pitch in the track width direction on the optical card 1 is 5 μl 1 l (track width 95 μm), the corresponding light receiving area 31-1 on the photodetector 8
The pitch of ~31-8 and 31-9 to 31-16 is 20
Since uI11, the photodetector 8 can also be manufactured easily.

As described above, one of the paired clock generation light receiving areas 32-1.32-3.32-5.32-7.32-
9 and 32-11, and the other clock generation light receiving area 32-2.32-4.32-6.32-8.
A clock signal is obtained based on the difference between the sum of the outputs of 32-10 and 32-12. In addition, the sum of the outputs of the light receiving areas 33-1, 33-3, 33-5 and 33-7 that receive the image of one edge in the width direction of the guide pattern 26, and the image of the other edge Light receiving area 3
3-2.33-4.33-6 A tracking error signal is obtained based on the difference from the sum of the outputs of 33-8, and the light receiving areas 33-3 to 33 whose centers are located inside the unchanged portion 35 -6 output sum and center unchanged part 3
Light receiving area 33-1.33-2.33 located outside of 5
A focus error signal is obtained based on the difference between the sum of the outputs of -7 and 338.

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 31-1. - Take in the output of 31-16 and read 16-bit data.

In the above configuration, the sum D of the outputs of the light receiving areas 33-3 to 33-6 whose centers are located inside the unchanged portion 35 in FIG.
1, when the optical card 1 is moved away from a position closer to the objective lens than the focal position (focus position) of the objective lens 7 through the focal position, the convergence position of the illumination light increases, but then decreases. . On the other hand, the sum D2 of the outputs of the light receiving areas 33-1, 33-2, 33-7 and 33-8, whose centers are located outside the unchanged portion 35, decreases until the illumination light converges position; After that, it increases. Therefore, these Dl
By processing the outputs of D and D2 so that the difference between them becomes zero at the in-focus position, it is possible to obtain a force error signal whose polarity is reversed before and after the in-focus position, as shown in FIG.

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 in. Therefore, the reversal portion where the optical card l is too far away and the polarity of the focus error signal is reversed in FIG. 6 should be as small as possible within the driving range of the objective lens 7. Although it is desirable, if the distance l between the reverse position and the focus position is set longer than 800 μm, the amount of light incident on the photodetector 8 will decrease, making it more susceptible to noise. 2 shorter than 200 p m,
The focus servo is likely to come off due to noise in the signal processing system, defects on the optical card l, fluctuations in the output of the light receiving area for focus error detection during seek, and the like. For this reason, the distance l is 200 μm to 800 μ−1, that is, the distance from the focal position (focal position of the objective lens 7 on the optical card side) to the convergence position of the illumination light is 100 μm to 400 μm.
Take a breather.

With this configuration, focus errors can always be detected with high sensitivity, and focus servo can always be performed stably.

Therefore, when the focus is turned on, the optical card l is the 6th
In the figure, when the objective lens 7 is in the normal part I within ±2 from the in-focus position, the objective lens 7 enters the servo range after a certain period of time.
After turning on the servo, normal focus servo can be performed stably. Further, when the optical card 1 is in the normal portion H 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 1 and the servo comes off, but in the latter case, the focus is turned off once. and focus coil 14A so that optical card 1 is positioned within ±l.

By supplying a bias current of a predetermined polarity to 14B to displace the objective lens 7 by a predetermined amount and then turning on the focus again, normal focus servo can be performed stably. Similarly, when the optical card 1 is in the reversal position in FIG. Light card 1 is the master! After displacing the objective lens 7 by a predetermined amount so as to be located within, the focus is turned on again, so that normal focus servo can be performed stably.

That is, when focus is turned on and 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 optical card 1 When the optical card 1 is located at a position far away from the target, the objective lens 7 is detected and the focus is turned off, and then a bias current of the required polarity is supplied to the focus coils 14A and 14B so that the optical card 1 is located within ±2. After displacing the lens by a predetermined amount, the focus can be turned on again.

Note that the present invention is not limited to the above-described embodiments, and can be modified or modified in many ways. The light-receiving region whose center is located outside the unchanged portion can be configured with any number of light-receiving regions. In addition, in the embodiment described above, in order to also obtain a tracking error signal, the guide pattern 2
The light-receiving areas for focus/tracking error detection are provided in pairs in the track width direction so as to receive the images of No. There is no need to provide a light receiving area, and there is no need to arrange the image of the guide pattern 26 to receive light. 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. Furthermore, in the above embodiment, the half mirror 5 transmits the light from the LED 3 and reflects the return light from the optical card 1, but it is possible to reverse the positional relationship between the LED 3 and the photodetector 8. , the light from the LED 3 can be reflected and the return light from the optical card l can be transmitted. Furthermore, 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 fo of the collimator lens 4, but can also be arranged behind the focal position fo of the collimator lens 4, so that the recording medium is at the convergence position of the illumination light. The distance between the objective lens and the focal position on the recording medium side is 100 μl to 400 μl
It is also possible to illuminate in a defocused state so that μ■. Furthermore, in the embodiment described above, a bar mirror 5 is disposed between the LED 3 and the collimator lens 4, and the optical card 1
The reflected light from the lens passes through the objective lens 7, the collimator lens 4, and the half mirror 5, and forms an image on the photodetector 8. , a converging lens is disposed between the half mirror 5 and the photodetector 8, so that the reflected light from the optical card 1 passes through the objective lens 7, the bar mirror 5, and the converging lens, and forms an image on the photodetector 8. You can also.

〔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, and the distance between the recording medium side focal position of the objective lens and the convergence position of the light beam from the light source by the objective lens is is 100μ11~400μ-
Since the recording medium is illuminated in a defocused state, focus errors can always be detected with high sensitivity based on the illuminance distribution of the return light from the recording medium, and therefore focus servo can always be performed stably. becomes possible.

[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 for data reading 32-1 to 32-
12... Light-receiving area for clock generation detection light-receiving area 35... Unchanged portion

Claims (1)

[Claims] 1. A light source, and an objective lens that projects the light beam from the light source onto an optical recording medium from the normal direction thereof through a collimator lens, and the focal position of the objective lens on the optical recording medium side and the objective lens The light source is arranged to be shifted from the focal position of the collimator lens so that the distance between the convergence position of the light beam and the convergence position of the light beam is 100 μm to 400 μm, and the optical recording medium is illuminated in a defocused state. An optical pickup characterized by: