JPS59152535A - Automatic focus controller - Google Patents

Abstract

PURPOSE:To set an accurate focusing position of an objective lens on an information disk for irradiation of a laser beam by providing the line sensors at the positions corresponding to the front and the back of the focus point of the laser light reflected by the information disk and to obtain the difference between detection outputs of luminous fluxes of both line sensors. CONSTITUTION:Line sensors 21 and 22 are set equidistantly from the front and back positions of an image point obtained when an information disk 18 is set at the focal point of an objective lens 17. The laser beam delivered from a laser light source 11 condenses microspots on the disk 18, and the reflected light of the disk 18 is returned by a beam splitter 14 and irradiated simultaneously to the sensors 21 and 22 by a half mirror 19 and a mirror 20 respectively. These sensors perform the scan with a frequency higher than the band of the focus error signal of a scanning circuit 23 to detect a signal pulse. The number of detectors of those line sensors to which the light is irradiated by pulse number/ voltage converting circuits 26 and 27 is detected through comparators 24 and 25. The outputs of these detectors are applied to a differential amplifier 28 to extract the focus error signal. Then the lens 17 is made to follow the disk 18.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical information recording and reproducing apparatus that records and reproduces information by condensing a light beam with an objective lens.

In particular, the present invention relates to an automatic focus adjustment device that brings all objective lenses to the correct focal position.

[Technical background of the invention and its problems]

In recording and reproducing the original disk, the laser beam focuses light onto a minute spot of 14 mφ or less to record and reproduce information on the information disk. At this time, the objective lens must follow the vertical movement of the information disk within a depth of focus of 1 μm. ``As a conventional method for this, for example, there is a method in which a laser beam is incident on the objective lens with a deviation from the optical axis, and the reflected light is received by a two-split photodetector. As the information disk moves up and down, the reflected light shifts horizontally, and when this light is received by a two-split photodetector and the difference between each is taken,
A positive or negative error signal is obtained depending on the direction of the vertical shift.

However, although conventionally considered methods such as the above method and the astigmatism method can suppress fluctuations in the focal point position with respect to the information disk, they alone cannot provide an accurate focal point position. In the case of reproduction, it is necessary to adjust the position of the photodetector to the point where the reproduction signal is maximum, and in the case of recording, it is difficult to find the focal point position.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focusing device that can irradiate a laser beam onto an information disk by accurately focusing all objective lenses.

[Summary of the invention]

In the optical system of an information recording and reproducing device, the present invention arranges line sensors at positions corresponding to the focal point of the reflected laser beam from the information disk, detects the size of each luminous flux, and detects the By taking the difference in output, a focus error signal is obtained, and this signal is used to move the objective lens up and down to bring the correct focus position onto the information disk.

〔Effect of the invention〕

According to the present invention, the focal point of the objective lens that irradiates the laser beam onto the information disk can be automatically and immediately adjusted, eliminating the need for adjusting the focal position of the conventional device, and improving stability, especially in the case of recording.

[Embodiments of the invention]

FIG. 1 is a block diagram showing another embodiment of the present invention.

A laser beam emitted from a laser light source (11) is modulated in light intensity by an optical modulator (12) according to an information signal.

The beam is further expanded by a lens (13), a beam splitter (14), a 1/4 wavelength plate 5), and a mirror (1).
K enters the objective lens (1, 7) through 6) and focuses the light onto the information disk (18). Information disc (18
) The reflected light from above returns to the original optical path, is reflected by the beam splitter (14), and is sent to two line sensors (2], ) (2) by a half mirror (19) and a mirror (20).
2) are irradiated at the same time. This line sensor (21
) (, 22) is scanned by a scanning circuit (23) at a frequency higher than the band of the focus error signal, which will be described later, and outputs a signal pulse "fc4'A." Line sensor (21) (
The output of 22) is used to detect the number of detectors of the line sensor irradiated with light, that is, the magnitude of the luminous flux, by comparators (24), (25) and total correction pulse number and pressure conversion circuits (26) and (27). Add these outputs to a differential amplifier (28),
Extract the focus error signal. This is added to the objective lens drive system (30) through the drive circuit (29), and the objective lens (
17) to follow the information disk (18).

FIG. 21 is a principle diagram showing the arrangement of line sensors.

If the image point (this is called the focused image point) when the information disk (18) is at the focused point of the objective lens (17) is the α point shown in Fig. 2 (al), then two line sensors (21) (2
2) are arranged at equal distances d in front and back from point α. In reality, mirrors are used as shown in Fig. 1, or prisms are used to arrange them in equal numbers as shown in Fig. 2 (at).At this time, the front line sensor = (21,)
When scanned with high frequency, a pulse waveform as shown in FIG. 2 fbl is obtained from each sensor depending on the size of the irradiated light beam. When all pulses exceed the standard intraocular pressure using a comparator, a pulse train corresponding to the number of sensors irradiated with light is obtained as shown in FIG. 2(c). By counting the number of pulses within one scanning time and generating a voltage proportional to the number of pulses, an electrical signal corresponding to the size of the luminous flux is obtained. When the irradiated luminous flux becomes thicker, the number of extracted pulses increases, and conversely, when the luminous flux becomes thinner, the number of extracted pulses decreases.

Similar detection is performed with the rear line sensor (22).

When the information disk moves away from the position where the information disk (18) is located at the focal point of the objective lens (17), the imaging point moves forward/sideward and becomes point β.At this time, the line sensor ( 2
1) has a smaller luminous flux, and the line sensor (22) has a larger luminous flux. Conversely, when the information disk (18) approaches the objective lens (17), the imaging point becomes the γ point, and the line sensor (21) has a larger luminous flux.

FIG. 3 is a diagram showing the relationship between the size of the luminous flux and the position of the line sensor. As mentioned above, the size of the luminous flux differs depending on the shift of the imaging point, so two line sensors (21
, ) If we take the difference between outputs 1 and 2 of (22), we get Figure 31 (
A positive output is obtained in the case of ``al'' in FIG. 3(b), zero when the focus is on, and a negative output is obtained in the case of FIG. 'ri so that the difference signal becomes zero when added to the proboscis lens driver (30).
It is possible for lJ to focus on moving songs. In this way, it becomes possible to focus immediately without adjusting the position of the Ze detector.

Although this method is shown here for the information recording device f3: column, it can also be used for information reproducing devices such as video discs and DADs.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, and Fig. 2 is a principle diagram showing the entire arrangement of the line sensor. FIG. 3 is a diagram showing the size of the luminous flux and the positional relationship of the line sensor. 11... Laser light source, 12... Optical modulator, 13...
·lens. I4...Beam splitter-115...1/4i long plate, 16...Mirror, 17...Paired snout lens, 18
...Information disc, 19...Half mirror-120...
Mirror, 21, 22... line sensor. 23...Scanning circuit, 24, 25...Specific softener, 26, 27...Pulse number tunsho conversion circuit, 28.
...Difference degree 1 amplifier, 29...Drive circuit, 3 (3...
Objective lens drive device. Representative Patent Attorney Kensuke Chika (and 1 other person) No. 1
figure? 3 ■ 201- Figure 3

Claims (1)

[Claims] a light source, an objective lens that focuses a light beam emitted from the light source onto an information medium, an optical system that divides a reflected beam from the information medium into two, and focusing one of the two divided beams of the reflected beam. A first line sensor placed in front of the image point, a second line sensor placed after the other in-focus image point of the two-split source, and an image obtained by the first and second line sensors. What is claimed is: 1. An automatic focus adjustment device comprising means for comparing outputs obtained by the means and extracting a focus error signal, and a drive device for moving an objective lens using the focus error signal obtained by the means.