JPS63306537A - Optical recording and reproducing head device - Google Patents

Abstract

PURPOSE:To remove an offset error from a tracking servo by expanding and deflecting light by a cylindrical mirror mounted on a rotary sliding table and making the light incident upon a division type photodetector to detect the position of an objective lens in tracking and focusing directions. CONSTITUTION:The cylindrical mirror 9 arranged in the vicinity of the objective lens 3 so as to be driven together with the lens 3 and orientating its cylindrical axis direction rectangularly to the optical axis of the lens 3 deflects light right and left in accordance with the rotation of the lens 3 and in the vertical direction in accordance with the parallel advancement of the lens 3. The deflected light is detected by the division type photodetector 10 to detect the two-dimensional moving distance of the lens 3 fitted to an actuator 4, an offset generation variable at the time of detecting a tracking error due to the movement of the lens 3 is calculated based on the obtained objective lens moving distance and the calculated value is subtracted from a tracking error signal. Consequently, an error at the time of detecting the tracking error can be removed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used in CD players, optical video disc players, writable optical disc devices, etc., and is equipped with a detection means for detecting the amount of movement of an objective lens. The present invention relates to an optical recording/reproducing head device.

[Conventional technology]

Figure 3 shows, for example, the Optical Society of America (Optical 5o
April 1984, sponsored by the Society of America
The Optical Data Storage Committee (Topi
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3) The conventional optical recording/reproducing head IT, especially its objective lens movement amount/m detection device, is shown. In the figure, the objective lens (3)
) is attached to the actuator (4), and the light source (
8) enters the two-split photodetector (10) through the slit plate (12). The objective lens j3) is moved by a spring (
13), and the slit plate (12) is also fixed to a part that moves together with the objective lens (3).

With the above configuration, when the objective lens (13) is driven in the y direction, the slit plate (12) also moves in the y direction.

Therefore, among the light from the light source (8), the slit-transmitted light flux moves in the direction across the dividing line on the two-split photodetector (lO), so if you take the difference between the outputs of the two photodetectors, the objective It was possible to obtain a position signal corresponding to the y-direction flc of the lens (3).

Next, the reason why the above displacement signal is necessary will be explained. One K is I! Since the magnetic actuator is a second-order system in terms of servo response, the residual error will increase if the tracking range is large, but by adding this lens position signal to the servo loop, a zero-order system servo can be configured. This has the advantage of significantly reducing residual errors. Another useful feature will be explained with reference to FIG. Figure 4 shows the main parts of the optical system of an optical head device. Light (1) from a light source for recording and reproduction is guided by a beam splitter (2) toward an objective lens (3), and the light is The light is focused onto the track (6) of the disk (5). The reflected light from the disk (5) is detected by a two-split photodetector (7), and a tracking signal is obtained by a so-called push-pull method. In the case of the push-pull method, when the track deviates from the optical spot in the tracking direction of the disk (5) shown by the arrow (A) (X direction in Figure 3), the distribution of reflected light changes on the two-split photodetector. The symmetry breaks down around the dividing line, causing a difference in the output of the photodetector (7), and a tracking signal is obtained. However, if this tracking signal is applied to the actuator (4) and the objective lens (3) is servo-followed in the tracking direction [to the state shown by the broken line in Figure 4], the incident light on the photodetector (7) It can be seen that the pattern loses its balance with respect to the dividing line due to this following operation itself. In other words, an offset occurs in the servo operation. Since this offset has a correlation with the amount of movement of the objective lens (3), it can be corrected as long as the above-mentioned position signal is obtained. This is another reason why the position signal is necessary.

[Problem that the invention seeks to solve]

In the conventional optical recording/reproducing head device as described above.

Since the slit plate (12), which is the detection part, is fixed to the holding part of the objective lens (3), which originally moves only a minute amount, the sensitivity of position detection was low. Further, only a small portion of the total luminous flux from the light source (8) can be used as light transmitted through the slit, and from this point as well, there is a problem that the sensitivity is synergistically low.

This invention was made to solve the above-mentioned problems.In addition to optically expanding the movement of the light flux and increasing the detection sensitivity, since no slit is used, the amount of incident light can be used without attenuation. It is an object of the present invention to provide an optical recording/reproducing head device equipped with a lens position detecting means capable of detecting the position of an objective lens not only in the tracking direction but also in the focusing direction.

[Means for solving problems]

An optical recording/reproducing head device according to the present invention includes a cylindrical mirror that is arranged near an objective lens so as to move together with the objective lens, and whose cylindrical axis is perpendicular to the optical axis of the objective lens; It includes a second light source that projects light onto the mirror, and a split-type photodetector that detects the movement of the light beam emitted from the second light source and reflected by the cylindrical mirror.

[For production]

In this invention, the cylindrical mirror can deflect the light left and right according to the rotation of the objective lens, and can deflect the light vertically according to the translation of the objective lens.

By detecting this deflected light with a split photodetector, it is possible to detect the two-dimensional movement of the lens attached to the actuator.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In the 11th g, the light beam (1) emitted from the first light source such as a semiconductor laser passes through the beam splitter (2),
Objective lens (3) K enters. The actuator (4) drives the objective lens (3) in the tracking direction (X) and the focusing direction (y) K. Optical disc (5
) on which a signal track (6) is formed. The photodetector (7) detects the light reflected from the optical disc (5),
A tracking signal, a tracking signal, and an information signal are obtained. The cylindrical mirror (9) is connected to a second light source (8) such as an LED mounted on the table (4a) of the actuator (4).
) is reflected and made incident on a 4-split photodetector (10). The direction of the cylindrical axis of the cylindrical mirror (9) is determined by the objective lens (
3) is perpendicular to the optical axis.

The actuator (4) is composed of a table (4a) on which the objective lens (3) is placed and a shaft (4b), and the table (4a) can freely rotate and slide in the axial direction around the shaft (4b). The objective lens (3) is moved in the tracking direction (X) by rotation of the table (4a) and in the focusing direction (y) by sliding in the axial direction. The table (4a) is mechanically coupled to an actuator (not shown) such as a voice coil motor, and track tracking and focusing control are performed by focusing and tracking signals from the photodetector (7). The surface of the zero cylindrical mirror (9) used for this purpose is typically cylindrical with a flat surface in the X direction and a concave surface in the Y direction.

Also, the focus of the objective lens (3) is on the optical disk (5), and the table (4m) is at the center of its operation [the center of rotation of the table (4a) is determined by a spring (not shown)]. At some point, the second light source (8)
The light from the 4-split photodetector (10) is configured so that the light comes to the center of the 4-split photodetector (10).

With the above configuration, when the light spot created by the objective lens (3) tracks the track (6) in the OC direction and the table (4a) rotates, the reflected light from the light source (8) is divided into four parts. The photodetecting elements (10a) (10b) (D sum signal and (xoc) (lo
The balance between the sum signals in d) is lost. Therefore, by taking the difference between both signals, a position signal in the tracking direction can be obtained. At this time, the light from the light source (8) is deflected by twice the rotation angle due to the law of reflection with respect to the rotation of the cylindrical mirror (9), so the detection sensitivity is doubled. Furthermore, since a slit or the like as in the conventional case is not used, the light from the light source (8) can be used effectively.

In addition, the detection sensitivity can be further improved by making the 1 cylindrical mirror (9) concave in the X direction with an appropriate degree of concaveness so that the reflected light forms a blur on the 4-split photodetector (10) K. do.

Next, position detection in the focusing direction (y) will be explained. Now, if the table (4a) is moved upward in order to move the objective lens (3) upward in the figure (to move it closer to the optical disk), the cylindrical mirror (9) will similarly move upward. Figure 2 shows the reflected optical path at this time, and when the cylindrical mirror (9) is at the center position (solid line) K, the photodetector (
The reflected light beam is incident on the center of the dividing line of 1O), but when the cylindrical mirror (9) is displaced upward (dashed line), the reflected light passes through the photodetecting elements (10a) (10c) according to the law of reflection of concave mirrors.
deflect in the direction of When the objective lens (3) is displaced downward from the equilibrium position, it is deflected in the direction of reflection, and the light detection element (
10b) Deflect in the (10d) direction. Therefore, a displacement signal in the focusing direction can be obtained by creating a sum signal of the photodetecting elements (10a) and (IOC) and a sum signal of the photodetecting elements (10b) (10d) and taking the difference between the two signals.

As a result of the above, the objective lens (3) explained earlier in the conventional device
This makes it possible to eliminate the offset that occurs in the push-pull tracking detection method due to the movement of the object. That is, based on the amount of objective lens movement obtained above, the amount of offset generated in tracking error detection due to objective lens movement is calculated, and the error in tracking error detection can be eliminated by subtracting it from the tracking error signal. . As mentioned above, the tracking servo and focusing servo control constitute a secondary system in terms of servo control, and when the tracking amount is large, the residual error becomes large. However, with this invention, the objective lens (3
) positional information, that is, zero-order system information, can be incorporated into the servo system, and residual errors can be reduced. Furthermore, if you know the position in the focusing direction, it will be easier to control the initial retraction of the focus servo, and what to do when the focus servo comes off due to some disturbance.
This greatly facilitates the processing of electronic circuits.

In the above embodiment, a cylindrical concave mirror is used as the cylindrical mirror (9), but a cylindrical convex mirror may also be used. In addition, in the above embodiment, a four-split photodetector (10)
Although position detection in two directions, one in the tracking direction and the other in the tracking direction, is performed simultaneously using
Instead of the divided photodetector (1G) O, a commercially available 8i position detection photodetector whose output varies linearly depending on the position of the incident light may be used.

〔Effect of the invention〕

As described above, according to the present invention, the position of the objective lens in the tracking and focusing directions can be adjusted using the cylindrical mirror provided on the rotating and sliding table of the two-dimensional actuator.
Since the light is magnified and deflected by an angle IEK corresponding to the position of the objective lens and made incident on the split-type photodetector for detection, it is possible to eliminate the offset error of the tracking servo.

By incorporating the zero-order system servo information, residual errors can be reduced. Further, it has great effects, such as detecting out-of-focus and facilitating initial focus pull-in.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part of an embodiment of the present invention, FIG. 2 is a partial side view for explaining the operation of the device shown in FIG. 1, and FIG. 3 is a perspective view of a conventional optical recording/reproducing head device. FIG. 4 is a partial side view for explaining the operation of the device shown in FIG. 3. (1)...Light flux from the first light source, (2)...Beam splitter, (3)...Objective lens, (4)...Actuator, (4a)...Table, (4b)...Shaft, (5)...Optical disc, (6)...Signal track, (
7)...Photodetector, (8)...Second light source, (9)...
Cylindrical mirror, (10)...4-split (split type) photodetector. In addition, the same reference numerals in each (2) indicate the same or corresponding parts.

Claims (1)

[Claims] a first light source, an objective lens that focuses the light beam from the first light source onto an optical disk having an information track recorded in an optically readable form, and detects reflected light from the optical disk to generate an information signal. and an optical recording/reproducing head device comprising: a photodetector for obtaining a servo signal; and an actuator for controlling the objective lens using the servo signal to correct a deviation between the focus of the objective lens and the information track. a cylindrical mirror disposed near the lens to co-move with the objective lens and whose cylindrical axis direction is perpendicular to the optical axis direction of the objective lens; and a second light source that projects light onto the cylindrical mirror. , a split-type photodetector for detecting movement of the light beam emitted from the second light source and reflected from the cylindrical mirror in at least one of the optical axis direction of the objective lens and the direction perpendicular to the optical axis; An optical recording/reproducing head device characterized in that the amount of movement of the objective lens is detected based on a difference in the outputs of split-type photodetectors.