JPS5918773B2 - Optical spot size control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a device for forming a light spot of a constant size on the surface of an object.

Recording or reproducing information using light spots is used in the color field. For example, there are devices that record information on microfilm using a light beam and read it out after development, or devices that record, for example, facsimile signals on photosensitive materials, and recent advances in materials that can optically record or reproduce high-density information. As a result, attempts have been made to record and reproduce large amounts of information at high density using minute light spots. In any of the above devices, it is desirable that the size of the light spot formed on the recording/reproducing object be kept constant so that information can be recorded or reproduced with good quality. This is particularly an important element in high-density recording and reproduction of a large amount of information using minute spots. In order to keep the above-mentioned light spot on the recording/playback surface small (for example, several μ) and at a constant size, the distance between the optical system that creates the small spot and the recording or playback object surface is generally kept constant. things will be done. Optical means, magnetic means, electrostatic means, hydrodynamic means, etc. are used to keep the above distance constant. The present invention provides an imaging control device that maintains a light spot at a constant size by detecting and controlling the distance between the optical system and the recording or reproducing object using optical means.

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

FIG. 1 shows an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a recording medium for recording or reproducing the above information, which moves in the direction of the arrow.

2 is a lens for forming a minute light spot at point A on the recording medium 1; 3 is a lens holder movable in the direction of the arrow; and 4 is a shift pulse generation circuit that generates a constant repetition of shift pulses.

Reference numeral 5 denotes a photodetection element array in which a large number of photodetection elements each having a size of, for example, about 30 μm are arranged, and their respective outputs are outputted in series by shift pulses from the above-mentioned pulse generation circuit 4.

6 is a shaping circuit that detects the electrical signals output in series from the photodetector array 5 and generates a rectangular wave having a pulse width proportional to the thickness of the light beam received by the photodetector array 5;
The output of the photoelectric converter array shown in FIG. 2b, which is output in response to the clock pulse train applied to the photoelectric converter array shown in FIG. 2, is converted into the pulse width output shown in FIG. 2e.

It generally consists of an integrating circuit and a waveform shaping circuit. 7 is a circuit that integrates the pulse width signal of the shaping circuit 6 and generates an output proportional to the pulse width; 8 is a circuit that detects and amplifies the difference between the output of 7 and the DC voltage applied to terminal B; 9 is 8 This circuit drives the lens holder 3 according to the difference signal output from the lens holder 3.

φIn represents an incident light beam, which enters with an optical axis shifted from the optical axis of the lens 2. Although parallel rays are shown in this figure, it can also be carried out with other than parallel rays. Furthermore, a coherent light source is generally used to obtain minute spots.
φIn is condensed by a lens 2 to generate a minute light spot A on the recording/reproducing medium 1. The light reflected at point A passes through lens 2 and generates a reflected light beam φ0ut. φ0
The thickness of ut is detected by the photodetecting element group 5. Also the first
In the figure, d indicates the distance between the lens and the recording/reproducing medium surface 1. The present invention compensates for fluctuations in the distance d caused by this movement when the recording/reproducing medium 1 and the lens system 2 move relative to each other in order to record or reproduce information, and maintains the distance d always at a constant distance. This is to maintain spot A at a constant size. Further, c in FIG. 1 indicates the optical axis of the lens 2. Figure 3 shows the configuration of Figure 1, and the variation of the distance d is reflected by the reflected light beam φ0.
It is a figure which shows that it can be detected by the thickness of ut.

Here, for ease of explanation, reflected light is also approximated as parallel rays. FIG. 3a shows an example in which the distance DO between the lens 2 and the recording/reproducing material 1 is a normal value and a minute light spot is generated at point A.

At this time, the diameter of the reflected light beam φ0ut is assumed to be D1. FIG. 3b shows the distance D mentioned above. The figure shows a case where the angle becomes (DO-Δd) due to the movement of either the lens 2 or the recording/reproducing material 1. Since the light point A becomes a minute light spot at point A symmetrical to the material surface, the diameter D of the reflected light beam φ0ut
2 is obviously smaller than D1 in figure a. Also, Figure 3c
is the distance D of a. The figure shows a case where Δd increases. In this case, as is clear from the figure, the reflected light is distributed as if it were generated from a point A that is symmetrical to point A with respect to the material surface, so the diameter D, of the reflected light beam φ0ut is larger than D. Therefore, the diameter of the reflected light beam is detected by the photodetecting element array 5 shown in FIG. If it is, an error voltage for driving the lens 2 is generated as the output of 8. An example of the relationship between this error voltage and the distance d is shown in FIG.
Therefore, by controlling the movement of the lens holder 3 using this error voltage, the distance d between the lens 2 and the recording/reproducing material 1 can be kept constant.

The movement of the lens holder is controlled by magnetic force, such as a driver for a voice coil of a speaker.
If low-speed control is sufficient, the vertical movement is controlled using, for example, a screw mechanism and a motor. FIG. 6 shows the relationship between the photodetector array and the reflected light beam, and the relationship between the clock pulse train of the clock pulse generator shown in FIG. 1 and the output electric pulse width of the photodetector array.

FIG. 5A shows an example of the arrangement of photodetecting elements, and FIG. 5B shows the relationship of reflected light beams incident thereon.

In general, each photodetector element (1
, 2...n), it is better to increase the length b in the vertical direction. FIGS. 5C and 5D show the relationship between the photodetector array and the reflected light beam shown in FIGS. 5A and B.
(In other words, the state in which the reflected light hits the 5th to (n-3)th photodetector elements), the clock pulse C applied to the photodetector array and the electrical pulse width output from the waveform shaping circuit shown in FIG. Show correspondence. That is, a rectangular pulse having a width from the fifth clock pulse to the (n-3)th clock pulse is output. Such pulses occur periodically depending on how the clock is applied. One embodiment of the present invention has been described above. FIG. 6 shows another embodiment of the invention. In the configuration shown in FIG. 1, the distance between the incident light beam φIn and the reflected light beam is generally so short that it may not be possible to insert a photodetecting element array.

In such a case, as shown in FIG. 6, a small hole is made in the total reflection mirror and the incident light beam is passed through the hole to hit the lens, and the reflected light beam is reflected to the left and hits the photodetector array 5. be. By using the apertured total reflection mirror in this manner, the utilization efficiency of the light energy irradiated onto the recording and reproducing material is increased, and moreover, high intensity reflected light can be obtained, allowing reliable detection. Furthermore, when the diameter of the reflected light beam is small, it is possible to magnify it using a lens system and irradiate the photodetecting element array. In the above embodiments, the light beam is incident on a position off the optical axis of the lens, and the light beam reflected from the surface of the recording or reproducing material is also made incident on a position off the optical axis of the lens. However, even when the light beam is made incident on the optical axis of the lens, the reflected light beam is also made incident on the optical axis of the lens, and the incident light beam and the reflected light beam are made to pass through the same path, By using a beam splitter or a half mirror, only the reflected light beam may be separated and guided to the photodetecting element.
As described above, according to the present invention, by appropriately controlling the distance between the lens and the imaging plane, the light beam irradiated through the lens is reliably irradiated onto the surface of the recording or reproducing material in a predetermined spot size. It is possible.

Note that the incident light beam φIn shown in the embodiment itself may be used as a recording or reproducing beam, or an incident light beam having a wavelength different from this incident light beam may be used as a recording/reproducing beam for recording through the lens. Alternatively, the surface of the recycled material may be irradiated.

[Brief explanation of the drawing]

Fig. 1 Light spot size in the air in one embodiment of the present invention
Figure 2 shows the main part signal waveform diagram, Figure 3 shows the block diagram of the control device.
Figures A, b, and c are diagrams of the operating principle of the present invention. Figure 4 is a diagram showing the relationship between distance fluctuation and error voltage. Figure 5 is a diagram showing the system of reflected light beams received by the photodetector array in electrical pulse width. FIG. 6 is a diagram for explaining a means for converting, and a diagram showing another embodiment of the present invention. 1...Recording and reproducing material, 2...Lens,
3...Movable lens holder, 4...
・Clock pulse generator, 5...Photodetection element array, 6...Waveform shaping circuit, 7...Integrator circuit, 8...Differential amplifier, 9 .....Luns holder drive circuit, A..... faint light spot, φIn
...Incident light beam, φ0ut...Reflected light beam.

Claims (1)

[Claims] 1. A light beam of a certain diameter is irradiated onto the surface of a recording or reproducing material through a lens, and the light beam reflected from the material surface is reflected through the lens into a light beam on which a plurality of photodetecting elements are arranged. irradiate a detection element array, create an electrical signal of a level corresponding to the number of the photodetection elements irradiated with the reflected light beam from the summed output of each output of the photodetection element, and according to the level of the electrical signal. A light spot size control device characterized in that the distance between the lens and the material surface is maintained constant by driving the lens.