JPH0415533B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to optical information processing in which information is optically recorded or read out by irradiating light onto a rotating disc-shaped recording medium (hereinafter referred to as a disk). Regarding equipment.
More specifically, it is an automatic system that automatically detects the focal shift of the light irradiated onto the recording medium, operates the control system so that this becomes zero, and keeps the irradiated light always focused on the recording medium. The present invention relates to an optical information processing device equipped with a focusing device.

[Background of the Invention] Conventionally, as an optical information processing device, a device that irradiates light onto a disk that stores information in a concentric circle or a spiral shape and reads out the signal is known from Philips Technical Review Vol. 133, 1973, No. 7. It is being In such devices, the rotating disk vibrates in the axial direction due to distortion of the disk surface or deviation of the axis of the turntable on which the disk is placed, making it difficult to maintain the correct positional relationship between the objective lens and the disk at all times. It's impossible. As a result, the diameter of the spot irradiating the disk changes greatly, making it impossible to read information accurately, so it is important to always maintain the correct positional relationship between the objective lens and the disk.

Conventionally, in order to automatically focus laser beams, etc., the distance between the objective lens that constricts the laser beam to a fine focus and the surface of the object to be focused is measured using electrical capacitance. , there is a method of making the objective lens follow such that this distance matches the focal length of the objective lens.

FIG. 1 is a principle diagram of a conventional automatic focusing device that focuses using capacitance. In the figure, a laser beam emitted from a laser beam 1 passes through a first lens 2 and a semi-transparent mirror 3, is reflected by a reflecting mirror 4, is stopped by an objective lens 5, and is focused on the surface of a moving object 6. Note that the moving object 6 rotates in a direction perpendicular to the plane of the paper. Also, the objective lens 5 is attached to the holder 7.
The electrode 8 is further fixed to this and together constitute a movable part.

Here, since the capacitance between the electrode 8 and the moving object 6 is inversely proportional to the distance between the two, by utilizing this relationship, the position detection circuit 9 detects the distance between the electrode 8 and the moving object 6.
Measure the distance to. The current control circuit 10 takes into account the distance from the electrode 8 to the objective lens 5, compares the distance between the moving object 6 and the objective lens 5, and the focal length of the objective lens 5, and determines whether the focal point is on the surface of the moving object. A current is applied to the voice coil 11 attached to the holder 7 as shown in FIG.

The voice coil 11 includes a permanent magnet (not shown).
etc., a constant DC magnetic field is always applied from the outside, and an electromagnetic force proportional to the current is generated, which moves the voice coil 11, holder 7, and objective lens 5 in the optical axis direction, and connects the objective lens 5 and the moving object 6. change the distance between. (In the following examples, it is assumed that a DC magnetic field is applied to the voice coil from the outside, and a description of this DC magnetic field will be omitted.) Thus, the laser beam is always focused on the surface of the moving object. The information on the moving object is read out by this laser beam and detected by the photodetector 12.

In this way, the focusing method using capacitance can perform focusing without contacting a moving object, but in practice it has the following major drawbacks.

The first drawback is that since the distance between the objective lens and the moving object is measured by capacitance, the moving object must also be a conductor. That is,
If the moving object is not a conductor, this method is useless unless the surface is coated with a metal film, such as by plating.

The second drawback is a fatal drawback of this conventional method, which arises from measuring the distance between the objective lens and the moving object and focusing the objective lens based on this value. In other words, the distance between the objective lens and the focal point is given in the form of a voltage in order to compare it with the measured value, but if this value changes due to fluctuations in the power supply voltage, the focal point will no longer be on the surface of the moving object. It deviates from the

Furthermore, the following drawbacks also occur. This will be explained using a diagram.

FIG. 2 is an enlarged view of the vicinity of the objective lens in FIG. 1. In the conventional method, since there is a distance v between the objective lens 5 and the electrode 8, the distance u between the electrode 8 and the moving object 6 is measured, and u+v is the distance between the objective lens 5 and the focal point A.
The focal point A is controlled to be on the surface of the moving object 6 by controlling the distance w to match the distance w (focal length if the light incident on the objective lens 5 is a parallel ray).

However, the distance between the electrode 8 and the objective lens may change due to thermal expansion of the holder 7 due to changes in ambient temperature, deformation of the electrode 8 due to vibration, etc. In this case, even if the distance w between the objective lens and the focal point is given accurately, (u+v) will not match w,
The focal point A is shifted from the surface of the moving object 6 as shown.

Another conventional example is to vibrate a reflecting mirror installed in the optical path between the objective lens and the light source along the optical axis direction, thereby effectively vibrating the light source, and changing the intensity of the light from the disk and changing the intensity of the reflecting mirror. Method of obtaining defocus signal by detecting phase difference with vibration (U.S. Patent No.
No. 3,673,412), but the amount of vibration of the optical member for detecting defocus is large, and sufficient accuracy cannot be obtained to control a disk rotating at high speed.
Moreover, it is necessary to provide a reflecting mirror to detect a focal shift, which also has the disadvantage of complicating the structure of the optical head.

[Object of the Invention] An object of the present invention is to eliminate the above-mentioned drawbacks and provide an optical information processing device equipped with an automatic focusing device that always focuses on an object.

[Summary of the invention] In order to achieve the above object, in the present invention,
An objective lens for focusing light from a light source on a rotating recording medium, a photodetector for detecting reflection from the recording medium, and an optical element for separating the irradiated light are integrated, and a constant frequency A small vibration is applied sinusoidally and in the direction of the optical axis, the reflected light from the recording medium is received by a photodetector, and the magnitude and direction of the defocus are detected from the strength and weakness of the output, thereby keeping the recording medium always in focus. It is something that connects.

[Embodiments of the Invention] The present invention will be described in detail below with reference to the drawings.

FIG. 3 is an explanatory diagram showing one embodiment of the present invention.

A laser beam sent out from a laser light source 51 passes through a first lens 52 and a semi-transparent mirror 53 and then passes through a reflecting mirror 54.
The light is reflected by the object lens 55 and focused on the surface of the video disk 57. This laser light is reflected by the surface of the video disk 57 and returns to the original optical path, is reflected by the semi-transparent mirror 53, passes through an aperture having a pinhole (not shown), and is received by a photodetector 58. Note that when the light receiving surface of the photodetector 58 is extremely small, an aperture is not necessarily necessary. The optical information thus recorded on the video disk 57 becomes an output signal from the photodetector and is applied to an information source terminal (not shown).

Next, FIG. 4 shows the characteristics of the photodetector 58 with respect to its focal position. In the figure, the horizontal axis x is the distance between the objective lens and the video disk surface, and the vertical axis E is the output voltage of the photodetector.

In FIG. 3, the aperture (not shown) is positioned so that when the laser beam projected from the objective lens 55 is focused on the surface of the video disk 57, the output of the photodetector 58 is maximized. There is. In this case, if _{the distance between the objective lens 55 and the surface of the video disk 57 is x 0 , then} in FIG. , and the portion of the horizontal axis where x>x ₀ indicates that the focal point is closer to the objective lens than the video disk surface. Furthermore, when x is changed, the output voltage of the photodetector is almost symmetrical around _x0 .

When the focal position of the projected laser beam is closer to the objective lens than the video disk, that is, when the objective lens is vibrated in the optical axis direction at a point x _A that is larger than x ₀ ,
The output voltage of the photodetector appears as a vibration waveform with a phase difference of 180° compared to the phase of the vibration of the objective lens. Conversely, when x _A is smaller than x ₀ , a vibration waveform with a phase matching the vibration phase appears. Furthermore, the output voltage from the photodetector increases as x _A is farther away from x ₀ .

In this example, based on these phenomena, in order to detect x _A - x ₀ , that is, the amount and direction of focus shift, synchronous rectification is performed by multiplying the output voltage of the photodetector by a value corresponding to the vibration waveform of the objective lens. Use the method of This will be explained with reference to FIG.

First, a sine wave output is sent out from the oscillator 60, amplified by the current amplifier 67, and then applied to the voice coil 56 to cause the objective lens 55 to vibrate minutely in the optical axis direction. In this embodiment, the objective lens 55 and other optical systems such as an aperture, a photodetector 58, a first lens 52, a semi-transparent mirror 53, and a reflecting mirror 54 are integrated into a compact structure, which is vibrated by a voice coil. let Due to this vibration, as shown in FIG. 4, a strong and weak output is generated in the photodetector 58.

The output of the photodetector 58 contains components other than the vibration frequency of the objective lens 55, such as the video disk 57.
Since the above video signal and the like are superimposed, the bandpass filter 59 passes only signals near the vibration frequency of the objective lens. The objective lens 55 is driven by a sine wave signal from an oscillator 60, but its operation is somewhat delayed in phase compared to the sine wave signal from the oscillator. Therefore, the sine wave current from the oscillator 60 is brought into phase with the minute vibrations of the objective lens 55 through the phase adjuster 61, and is applied to the switching device 62.

A switching device 62 selects three contact positions according to the output of the phase adjuster 61. FIG. 5 shows each voltage waveform of the input/output signal of the switching device 62, E is the output voltage of the phase adjuster 61, and when the instantaneous value of E is above a certain voltage value, the switching device 62 contacts contact a. . At this time, the output voltage of the switching device 62 is F, and its waveform is J.

Conversely, when E is below a certain voltage, switching device 62 contacts contact C. At this time, the output voltage of the switching device 62 is G, and its waveform is L. When E is of intermediate magnitude, switching device 62 contacts contact point b and no output is sent. Such a switching device can be easily constructed using conventional techniques.

The signals phase-differentiated by the switching device 62 in this manner pass through a first reduction filter 63 and a second reduction filter 64, respectively. First reduction filter 63
The output of is the average value K at the output voltage F in Figure 5.
Similarly, the output of the second filter filter 64 is the average value M of the output voltage G. These signals are subtracted by subtracter 6
Added to and subtracted from 5.

The output voltage of the subtracter 65 is negative if the focus of the objective lens is closer to the lens than the video disk surface, and positive if it is closer to the video disk. Note that the absolute value of the output voltage is proportional to the amount of defocus.

Therefore, a control signal is sent from the control circuit 66 based on the output of the subtracter 65, and after being amplified by the current amplifier 67, the objective lens 55 is moved in addition to the voice coil 56, and the focus shift (x _A - x ₀ ) is is zero,
That is, control is performed so that the focal point always coincides with the surface of the video disk. In this case as well, the distance to the video disk 57 can be changed by moving the objective lens in response to a control signal using not only the voice coil 56 but also other means, as in the previous embodiment.

In the above embodiment, a control signal sent from the control circuit 66 is applied to the voice coil 56, and other optical systems are integrated with the objective lens 55 to move a compact object. without limitation, using any other means to move the objective lens in response to the control signal;
The distance to a moving object can be changed.

In the present invention, the compact optical system integrated with the objective lens is vibrated in the axial direction, but the amount of displacement due to this vibration is actually very small, so in practice this can be ignored and there is no defocusing at all. It can be assumed that this does not occur. for example,
For an objective lens with a depth of focus of 1 μ, the magnitude of vibration may be set to less than that, for example, about 0.5 μ.

[Effects of the Invention] As described above, according to the present invention, the optical system that irradiates the recording medium with light from the light source and the optical system that detects the reflected light from the recording medium are integrated, and minute vibrations are applied to the optical system. Due to this minute vibration, there is no positional deviation between the optical components constituting each optical system. There is no need to provide a special optical element for defocus detection, and the structure of the optical head is simple. In addition, since the vibration frequency component is extracted from the photodetector output and the defocus signal is detected using the oscillator output whose phase is adjusted to match the phase of this vibration frequency component, the defocus signal is not affected by recorded information or tracking deviation, etc.
Highly reliable defocus detection and control becomes possible.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of a conventional automatic focusing device, Fig. 2 is an enlarged explanatory diagram of the vicinity of the objective lens, Fig. 3 is an explanatory diagram of an embodiment of the present invention, and Fig. 4 and Fig. 5 are illustrations of the present invention. FIG. 3 is a characteristic diagram for explaining the principle of the invention. 1,51...laser light source, 2,52...first
Lens, 3, 53...Semi-transparent mirror, 4, 54...Reflector, 5, 55...Objective lens, 6, 57...Moving object (video disk), 7...Holder, 8
... Electrode, 9 ... Position detection circuit, 10 ... Current control circuit, 11,56 ... Voice coil, 12,5
8... Photodetector, 60... Oscillator, 61... Phase adjuster, 59... Bandwidth filter, 63, 64... Reduction filter, 66... Control circuit, 67... Current amplifier, 62 ...Switching device, 65...Subtractor.

Claims (1)

[Claims] 1 Irradiate the rotating recording medium on which information is recorded with light focused by an objective lens along the rotational direction,
In an optical information processing device that converts reflected light from the recording medium into an electrical signal by a photodetector and reproduces the information from the electrical signal, at least the objective lens and the photodetector are integrated; means for vibrating with a first signal of a predetermined frequency in the optical axis direction of the objective lens; phase adjustment means for adjusting the phase of the first signal of the predetermined frequency; and a means for vibrating the first signal of the predetermined frequency in the optical axis direction of the objective lens; a switching device for phase-discriminating the second signal at timing according to the phase-adjusted first signal; and a switching device for inputting the phase-discriminated signal from the switching device. and a subtracter for subtracting the outputs of the two reduction filters, and a distance from the objective lens to the recording medium is controlled by the output of the subtracter. Optical information processing device.