JPS63288425A - Optical head device - Google Patents

Abstract

PURPOSE:To perform initial focusing in a short time by providing a pair of slits extending in the tracking direction on the outer peripheral part of an objective lens in a mobile part and transmitting the peripheral light, which does not pass the objective lens, through slits and arranging a photodetector which detects the light transmitted through slits. CONSTITUTION:A pair of slits which are extended from the outer peripheral part of an objective lens 3 in the tracking direction and face each other are formed in a mobile part 9 holding the objective lens 3. The peripheral light which does not pass the objective lens 3 out of the divergent luminous flux from a light source 1 is transmitted through the pair of slits 11 and 12 and is made incident on a pair of photodetectors 13 and 14 which are stuck to the rear face of a protective cover 20 of an optical head and are divided in the tracking direction. Consequently, the sum signal output of photodetectors 13 and 14 is increased or reduced by the quantity of light which does not pass the objective lens 3. Thus, initial focusing is performed in a short time, and the offset of a tracking error signal due to the deviation of the objective lens in the tracking direction is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head device for an optical disc device such as an optical disc playback device or a recording/playback device.

[Conventional technology]

FIG. 7 shows a conventional optical head device as shown in, for example, Japanese Utility Model Application Publication No. 61-68522. ), and is projected onto the information carrier (4) by the objective lens (5), and when in focus forms a minute light spot with a diameter of about 1 μm. In the head device, information carriers (4
) In order to accurately record and reproduce information on the information carrier (4), the objective lens (3) is driven in the direction of the arrow (F) in the figure so that it is always in focus on the information carrier (4). Focusing control is performed and the information track (2) on the information carrier (4) is tracked by the objective lens (3).
Tracking control is performed by driving in the direction of arrow (T).

FIG. 7 shows an optical path for obtaining a tracking error signal for tracking control.

The reflected light from the information carrier (4) passes through an objective lens (3) and a half mirror (2) to a two-split photodetector (s) and (6).
), and the signal processing unit (C) detects the tracking error signal of the minute light spot on the information carrier (4) based on the distribution of the amount of light incident on the two-split photodetector. This is a tracking error signal detection method called (push-pull method) etc. Note that the objective lens (3) is supported by a movable member (8).

With the above configuration, in order to focus the light spot on the information carrier (4), the objective lens (3) is driven in the focus direction, which is the arrow (p) direction in FIG. The light is guided to a photodetector (not shown) for detecting a focus error signal, the objective lens (3) is moved to an area where focus braking can be performed, and then focusing control is performed.

Also, in order to follow the track on the information carrier (4),
As mentioned above, the two-split photodetector (5) and (6) capture the amount of incident light, the signal processing unit (C) calculates the difference in light amount, the tracking error signal is detected, and the objective lens (5)
) in the direction of arrow (T) to perform tracking control.

[Problem that the invention seeks to solve]

The conventional optical head device is configured as described above.
As shown in FIG. 8, when the objective lens (31 is deviated by δ from the base position in the tracking direction and is following the normal track, the two-split photodetector (5) for detecting the tracking error signal, There was a problem that a deviation occurred in the light beam incident on the objective lens (6'), an offset occurred in the tracking signal, and tracking control could not be performed accurately.Also, since there was no information on the current position of the objective lens (6) in the focus direction, When adjusting the initial focus, etc., it is difficult to know whether to move the objective lens (3) upward or downward, so I end up moving it either upward or downward, which takes time for initial focus adjustment. There were also problems.

This invention was made in order to solve the above-mentioned problems, and it is possible to correct the offset in the tracking direction caused by the deviation of the objective lens from the base position in the tracking direction, and to correct the offset in the tracking direction when the objective lens is initially focused. ,
To provide an optical head device capable of detecting the position of an objective lens in a tracking direction and a focus direction so that the direction in which the objective lens is moved can be found and initial focusing can be performed accurately and in a short time.

[Means for solving problems]

The optical head device according to the present invention has a pair of slit holes extending in the tracking direction on the outer periphery of the objective lens of a movable part to which the objective lens is attached, and allows peripheral light overflowing from the objective lens to pass through the slit hole. (A pair of photodetectors are arranged to detect the light transmitted through each Nislit hole.

[For production]

In this invention, the deviation from the reference position of the objective lens in the tracking direction or the position of the objective lens in the focusing direction is detected by detecting the deviation of the objective lens from the reference position in the tracking direction or the position of the objective lens in the focusing direction. It can be easily detected using light, and it can correct the offset of the tracking signal caused by the deviation of the objective lens from the basic position in the tracking direction, and when adjusting the focus, the current position of the objective lens can be determined, and the objective lens can be moved up or down. : Information that allows you to decide whether to move or not, making it possible to shorten the time for initial focusing.

〔Example〕

FIGS. 1 and 2 show an embodiment of the present invention, in which a pair of opposing movable members (9) l: which hold an objective lens (3) extend from the outer periphery of the objective lens (3) in the tracking direction. Slit holes (11) and (12) are formed.

This slit hole (11) e (12) is the objective lens (
3) Allows ambient light to pass through. (10) is the center of rotation of the objective lens (3). Photodetectors (13) and (14) divided into a pair of tracking directions are attached to the back side of the protective cover (20) of the optical head.
The light transmitted through the slit holes (11) and (12) enters the photodetector (1331 (14)), respectively.

The first signal processing section (15) has a photodetector (15) e (
14) Take the sum signal output. Second signal processing unit (16)
takes the difference signal output of the photodetectors (13) and (14). The third signal processing section (17) is capable of division processing.

In addition, the same reference numerals as in FIG. 7 indicate the same parts.

In the optical head device configured as described above, out of the divergent light flux from the light source (1) directed toward the objective lens (3), the peripheral light overflowing from the objective lens (3) is transferred to a pair of slit holes (11). , (12), and a pair of photodetectors (13J) divided into tracking directions attached to the back side of the protective cover (20) of the optical head.

(14), so when the objective lens (3) is located above as shown in FIG. 3, the amount of light overflowing from the objective lens (6) will be large, and the light will be incident on the photodetector (1!i).

The sum signal output of (14) becomes large.

On the other hand, when the objective lens (6) is located downward as shown in Fig. 4, the amount of light overflowing from the objective lens (3) is small, and the sum signal output of the photodetectors (ts) and (14) is becomes small.

These calculations are performed by a signal processing unit (15) that outputs a sum signal as shown in Fig. It is possible to detect whether the objective lens (3) is above or below the base position set in advance.

In addition, as shown in Fig. 5, if the objective lens (3) deviates from the reference position in the tracking direction,
3) is shifted to the right by δ, the amount of light incident on the photodetector (16) becomes larger than the amount of light incident on the photodetector (14).

Conversely, as shown in Figure 3, if the objective lens (3) is shifted by δ to the left, the amount of light incident on the photodetector (13) will be smaller than the amount of light incident on the photodetector (14). .

That is, a difference signal output is generated in the photodetectors (13) and (14) in accordance with the deviation of the objective lens (3) from the basic position in the tracking direction. As shown in Figures 3 and 4, as the objective lens (3) moves in the focus direction, the sum signal level of the light beams incident on the photodetectors (13) and (14) changes, so the photodetector Vessel (13), (14
By dividing the difference signal output of J by the sum signal output, the deviation of the objective lens (6) from the base position in the tracking direction can be detected regardless of the vertical position of the objective lens (3) in the focusing direction.

Now, the output of the photodetector (13) is A, and the output of the photodetector (14) is
If the output becomes
The higher the objective lens (3) is, the larger the value becomes. Further, information on the deviation from the base head position in the tracking direction is provided to the signal processing unit (15).

(16) , (1υ given by (A-Bn/(A-1)).

In the above embodiment, the objective lens position detection device (the light emitted by two people is configured so that the light beam overflowing from the objective lens is transmitted through a slit hole extending in the tracking direction that sandwiches the objective lens, but there is no problem even if the sensitivity decreases. For example, the same effect can be obtained by using holes that are symmetrical in the tracking direction of the objective lens and sandwiching the objective lens.Furthermore, the same effect can be obtained by condensing the light flux overflowing from the objective lens using a lens.

〔Effect of the invention〕

As described above, according to the present invention (2), the position information of the objective lens in the focus direction and the deviation information from the reference position in the tracking direction are transmitted to the objective lens without using a special light source. Since the light is transmitted through a pair of slits provided on both sides in the tracking direction, and the amount of light is detected, the device can be made inexpensive, initial focusing can be done in a short time, and tracking caused by objective lens deviation in the tracking direction can be avoided. This has the advantage that it is easy to create an objective lens position detection device that can correct the offset of the error signal.

[Brief explanation of the drawing]

FIG. 1 is a side view of the essential parts of an embodiment of the present invention, FIG. 2 is a plan view of the essential parts, and FIGS. 3, 4, 5, and 3 are explanatory diagrams of the operation of the embodiment. FIG. 7 is an optical path diagram of a conventional optical head device, and FIG. 8 is an explanatory diagram of its operation. (1)...Light source, (3)...Objective lens, (4)...Information carrier, (9)...Movable member, (1)...
Slit hole, (13), (14J...photodetector, (
15)...first signal processing section, (16)...second signal processing section, (17)...third signal processing section. In each figure, the same reference numerals indicate the same or corresponding parts. 1 illustration, 5 illustrations of rhinoceros, 8 illustrations of fans

Claims (3)

[Claims] (1) A focus drive device that focuses diverging light from a light source with an objective lens and follows a track provided on an information carrier, and brakes the objective lens in the focal direction to record and reproduce information, and a focus drive device that tracks the track. In an optical head device equipped with a tracking drive device, a pair of slit holes are formed in a movable part to which the objective lens is mounted and extend in the tracking direction from an outer periphery of the objective lens, and a pair of slit holes are formed in a movable part to which the objective lens is mounted, and a pair of slit holes are formed in the movable part to which the objective lens is attached, and a pair of slit holes are formed in the movable part to which the objective lens is mounted, and a pair of slit holes extend from the outer periphery of the objective lens in the tracking direction; An optical head device comprising: a pair of photodetectors that receive peripheral light overflowing from the objective lens and transmitted through the slit hole. (2) The optical head device according to claim 1, which includes a first signal processing section that calculates the sum output of a pair of photodetectors, and obtains position information in the focus direction of the objective lens. (3) In addition to a first signal processing unit that calculates the sum output of a pair of photodetectors, a second signal processing unit that calculates the difference output, and a third signal processing unit that divides these two signals. 3. The optical head device according to claim 2, further comprising: detecting a deviation of the objective lens from a reference position in the tracking direction.