JPS6027264A - Control method of intensity of light - Google Patents

Abstract

PURPOSE:To use effectively the output of a light source by providing a light intensity modulating means in the optical path of an optical beams and reducing the intensity of the incident optical beam while keeping a certain intesity stepwise. CONSTITUTION:An acoustooptic modulator 12 functioning as the light intensity modulating means is provided in the optical path of the optical beam. Laser light 13 from a light source 5 has only a desired intensity converted to a 0-order light 14 by the acoustooptic modulator 12, and an intensity corresponding to the difference is outputted as a 1-order light 15. This 0-order light 14 is reflected on a half mirror 16, and the quantity of this light is detected by a photodetector 17 to stabilize the 0-order light 14. Meanwhile, the light quantity of the 1- order light 15 is detected by a photodetector 19 and is compared with a set voltage; and if it is lower than the set voltage, a single pulse is generated. This pulse is counted, and a negative voltage corresponding to the counted value of pulses is outputted and is added to an initial set voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light intensity control method for controlling a light beam output from a reading light source for reading to a constant intensity.

Generally, in order to read all image information from a recording medium on which image information has been recorded, a light beam from a light source such as a laser is scanned two-dimensionally on the recording medium, and the reflected light from the recording medium is fully photoelectrically scanned. This is often done by detection.

When performing such reading, if the intensity of the reading light beam changes due to deterioration of the light source due to long-term use, it will have a very small effect on the quality of the read image.

For example, when a gas laser such as I-1e-Ne or Ar is used as a reading light source, the intensity of the light beam decreases to about 70% of the initial intensity after being turned on for 5,000 to 10,000 hours. Teshi Ushiu.

For this reason, conventionally, a light intensity modulation means was provided in the optical path of the light beam, the total intensity on the recording medium was monitored, and the light intensity modulation means was controlled so that this value was always stable at a constant level. As this constant level, for example, about 70% of the initial output intensity of this laser light source has been selected as the minimum allowable level necessary to obtain normal image quality. Therefore, in the initial stage of use of a laser light source, the intensity of the light beam was not fully utilized. In other words, if the intensity of the reading light beam incident on the recording medium is high, the quality of the read image will improve, but the light intensity must be set at a significantly lower level, which is extremely irrational. Ta.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a light intensity control method that fully supplies a light beam of stable intensity and makes effective use of the output of a light source.

The light intensity control method of the present invention monitors the intensity of the light beam from the reading moonlight σ shell for reading image information recorded on the recording medium, and keeps the intensity of the light beam incident on the recording medium constant. In the light intensity control method, a light intensity modulation means is provided in the optical path of the light beam, and the light intensity modulation means adjusts the intensity required for desired reading from a first intensity level close to the initial output intensity of the light source. Naj:l'! The main feature is that the intensity of the optical beam incident on the recording medium is gradually decreased up to intensity level 2 while maintaining a constant intensity.

In the present invention, the first intensity level close to the initial output intensity of the light source is, for example, about 95 times the initial output intensity, and the second intensity level necessary for desired reading is, for example, about 70% of the initial output intensity. Although it is preferable to set the value to , it is not limited to this value. Note that the first level is set to a value close to the initial output intensity of the light source because the laser light output of the light source itself has a noise component, and the first level is set to a level slightly lower than the minimum value of this noise component. It's for a reason. Furthermore, the relatively low level necessary to obtain the desired image quality is a value that can be changed each time depending on the purpose or various conditions, and does not necessarily indicate the minimum allowable level of image quality in a narrow sense. do not have.

Furthermore, the stepwise reduction in the present invention means that the light beam or intensity is decreased by a predetermined amount, and the light beam or intensity is stabilized at a certain level at each step, and the amount of reduction or the number of steps is Any value may be selected as needed.

Specifically, it may be carried out according to a preset program (the usage time of the light source and the amount of reduction in intensity), or the light beam intensity from the light source and the light beam intensity output from the light intensity modulation means may be adjusted. The difference may be monitored, and when the difference reaches a predetermined value, the intensity of the light beam incident on the recording medium may be reduced by a predetermined amount by means of total light intensity modulation means.

Furthermore, the light intensity modulating means according to the present invention may be any device that can arbitrarily reduce the total intensity of incident light and output it, such as an acousto-optic modulator, an electro-optic modulator, or a magneto-optic modulator. It is also possible to use a filter with a concentration gradient.

As described above, according to the light intensity control method of the present invention, the intensity of the light beam incident on the recording medium is adjusted by the light intensity modulating means in accordance with the light output from the light source, which decreases as the light source deteriorates over time. Since the light intensity is decreased stepwise from the first level to the second level, there is no need to drastically reduce the total light intensity from the initial state as in the conventional technology, so the light output from the light source can be reduced. It can be used efficiently, and therefore, a reading light beam with a higher light intensity than in the prior art can be made incident on the recording medium and image information can be read, so that all the read images can be made with good image quality. In addition, the light intensity at each stage set by the light intensity modulator is maintained at a constant and stable level, so even if noise components are superimposed on the light beam output from the light source, this The image quality is not affected by noise, and it is particularly effective in high-output Ar lasers and the like that have relatively large noise components, and its practical value is extremely great.

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

FIG. 1 is a schematic diagram showing an example in which the light intensity control method according to the present invention is applied to a radiation image information reading device.

This device has a magnetic layer 2af laminated on the surface of an endless belt 2 that is drivably suspended around a pair of rollers], a, 11), and a stimulable fluorescent layer on which radiation image information is stored and recorded. 3 are brought into close contact with each other by magnetic force, and all rollers of the endless belt 2], a, 1
At the same time, a light beam 4 is scanned from above this phosphor sheet 3 through a galvanometer 6 in a direction perpendicular to the moving direction A of the endless belt 2 (arrow 13). The sheet 3 is irradiated with light beam 4 and the sheet 3 is scanned two-dimensionally with the light beam 4. That is, sub-scanning is performed in the endless bell l-2c7]tl moving direction A, and the main water 4F is scanned in the direction B perpendicular to this.
I'm L. The endless heald 2 has a magnetic layer 2a on a flexible endless belt-like support 2b.
(It is made by laminating i7 layers.

Next to the laser light source 5 (gas laser tube of He-Ne, Ar, etc.), a 1" acoustic optical modulator 12 is arranged as a light intensity modulating means, and a stabilized zero
It outputs secondary light.

Note that the difference output between the laser light output from the light source 5 and this 0th order "r" is simultaneously generated from the acousto-optic modulator 12 as approximately first order light. This first order light is constantly monitored by a photodetector. The output from this photodetector is input to a control loop circuit (#', not shown in the figure).This control loop circuit will be described later.Also, the laser light source 5 and galvanometer 6
Beam expanders 9a and 9b made of two convex lenses are provided on the optical path between the two to expand the beam diameter.

Between the galvanometer 6 and the phosphor sheet 3, there is an imaging lens 1 that focuses the laser beam onto the phosphor sheet 3.
1 is arranged so that the laser beam from the laser light source 5 is expanded in beam diameter by beam expanders 9a and 9b, and focused onto the phosphor sheet 3 by the imaging lens 11. It is composed of

The phosphor sheet 3 includes a magnetic layer 3a and a bond-storing phosphor layer 3b.
f, and the image of the object transmitted by the radiation has been stored and recorded in the erotic phosphor layer 3b. When this phosphor sheet 3 is irradiated with a light beam 4, the irradiated part emits all stimulated luminescence, and this stimulated luminescence is emitted by a total reflection light guide plate 7 made by completely molding an acrylic plate, for example. The light is focused and detected by a photoelectric detector 8 such as a photomultiplier, and an image signal is obtained. The image signal is obtained as a time-series image signal according to two-dimensional scanning, and is used for image processing and reproduction.

FIG. 2 is a schematic diagram showing the control loop circuit used in the example of FIG.

Laser light 13 generated from light source 5 is transmitted to acousto-optic modulator 1
2, only the desired light intensity is converted as 0-dimensional 14,
The light intensity approximately corresponding to the difference is output as one-dimensional 15. A portion of this zero dimension 14 is reflected by a half mirror 16 disposed on this optical path, and the amount of light is detected by a first photodetector 7. The first photodetector 17 and amplifier 18 form the entire first control loop and stabilize the light intensity of the 0th order light 1/I. On the other hand, the first dimension 15 is optically fitted by the second photo detector 19.
is detected, converted into an electrical signal, and input to the comparator 20. The electrical signal corresponding to the one-dimensional light intensity is compared with a fixed set voltage, and when it becomes smaller than this set voltage, a single pulse is generated. do. . That is, this comparator 2
0 constantly determines whether the difference in light intensity between the laser beam 13 from the light source 5 and the zero dimension 14 is greater than or equal to a predetermined value. This pulse is absolved by the counter 21 at the next stage, and a negative voltage corresponding to the cumulative number of pulses up to that point is transferred to the D/A converter 22.
The voltage is then outputted, added to the initial setting voltage (negative voltage), and input into the first control loop.

The detection of the one-dimensional 15 described above; the control circuit forms a second control loop. As a result, the 0-dimension 14 is maintained at a stable light intensity at a certain level at one stage, but as the light source 5 deteriorates over time, the intensity of the laser beam decreases and the 0-dimension 14 is When the light intensity difference falls below a predetermined level, the O-order light is successively reduced by 2 to 5 degrees of the initial laser light intensity from the light source. This is 9
The zero-order light 14, that is, the excitation light, can always maintain a light intensity substantially close to the output of the light source 5, and the output of the light source 5 can be used effectively.

FIG. 3 is a graph showing the intensity control pattern of zero-order light when the control loop circuit shown in FIG. 2 is used, together with the intensity attenuation curve of the laser beam from the light source. Note that the horizontal axis indicates the laser lighting time, and the zero-order light intensity control pattern 23 is the intensity attenuation curve 24095% of the laser light from the light source.
The curve 24 is initially set to 1°, so it becomes a straight line, but as the light source 5 deteriorates, the curve 24 becomes lower and the pattern 23
When the difference between the two and It becomes a graph. Furthermore, 1-1: minimum allowable image quality level 25 (usually about 70% of the initial laser beam intensity) is shown in FIG. 3, and the light source 5 can be used until the pattern 23 reaches this level 25. means. Note that the light intensity difference between the pattern 23 and the curve 24, which is a condition for reducing the light intensity in the ( ) dimension, may be set to an arbitrary amount as necessary.

FIG. 4 shows an example of a zero-order light intensity control pattern 26 in which the time and amount of reduction are set in advance, and the total light intensity of the zero-order light is reduced accordingly.The intensity of the laser light from the light source is This is a graph shown together with the attenuation curve 27.The horizontal axis shows 1f41'e when the laser is turned on.

If the state of attenuation of the laser beam intensity due to deterioration of the light source 5 can be determined in advance, the time (t,) at which the intensity of the zero-order light is completely reduced can be determined in advance.

12, 13) and the amount of decrease (ΔII, Δ12°Δi3)' at that time may be set. However, each condition must be set so that the light intensity control pattern 26 of the zero-order light falls within a region between the intensity attenuation curve 27 of the laser light from the light source 5 and the minimum allowable image quality level 28.

Note that when the light intensity control method of the present invention described above is actually applied to an image information reading device, the entire intensity of the light beam incident on the recording weight body is must be kept constant. That is, it is necessary to ensure that the timing at which the intensity of the light beam incident on the recording medium is gradually reduced does not coincide with the time when the recording medium is read.

Therefore, if you want to control the light intensity according to this program by setting the usage time of the reading light source and the amount of reduction in the intensity of the light beam at that time in advance, for example, you can monitor the entire usage time of the light source and set the remaining usage time. The intensity of the light beam may be reduced to the next level when the time required to read one recording medium becomes shorter. The difference between the light beam intensity from the light source and the light beam intensity output from the light intensity modulation means (to make the intensity of the light beam incident on the recording medium constant) is monitored, and this difference is measured. In the case of the method described above, in which the total intensity of the optical beam incident on the recording medium is reduced when the beam becomes a predetermined value, the beam intensity is controlled to reduce the total intensity of the beam incident on the recording medium for the time required to read one recording medium. The predetermined value is set to a value larger than the estimated amount of decrease in the intensity of the light source, and even if the difference output reaches the predetermined value while reading the recording medium, the The intensity of the light beam incident on the recording medium may be controlled to be kept constant until reading is completed. Alternatively, since the decrease in intensity of the laser light source is not rapid, the intensity of the light beam may simply be reduced from the next reading once the differential output reaches a predetermined value.

Furthermore, when reading a series of recording bodies on which image information is recorded by applying the light intensity control method of the present invention, there is a difference in the reading light beam intensity between the first recording body and the last recording body. If this occurs, it is necessary to read or correct the read signal. To correct this, the sensitivity of the photodetector that detects reflected light or transmitted light from the recording medium is increased in accordance with the amount of decrease in the intensity of the reading light beam, and the same image information is treated as a signal amount of the same level. The same image information is the same level signal! There are methods such as performing image processing to make it look like a seedling. However, although the laser light source attenuation detection as described above can be performed at all times, it is necessary to
Alternatively, this can be done at every appropriate number of readings or at the same time as checking the device every day when the device is used.

[Brief explanation of drawings]

Part i IRJ is a schematic diagram showing an example in which the light intensity control method according to the present invention is applied to a radiation image information reading device; :(l'Xl is 1 using the control loop circuit shown in Figure 2.
1. Intensity control pattern of ()-order light of "j" Graph shown together with the intensity attenuation curve of laser light from all light sources, No. 41J is the 0-order light by setting the time and amount of decrease for all ()-dimensional light in advance. 3 is a graph showing an intensity control pattern of zero-order light when controlling the intensity of , together with an intensity attenuation curve of a laser beam from a light source.

Claims (1)

[Claims] ([) The intensity of a light beam from a reading light source for reading image information recorded on a recording medium is monitored, and the intensity of the light beam incident on the recording medium is entirely constant. In one method, a light intensity modulation means is provided in the optical path of the light beam, and the light intensity modulation means reads a desired reading from a first intensity level close to the initial output intensity of the light source. The intensity of the light beam incident on the recording medium is decreased stepwise while maintaining a constant intensity until the second intensity level required for q! 2. The light intensity control method according to claim 1, characterized in that: (2) the stepwise reduction of the light beer is performed according to a preset program. (3) The stepwise reduction of the light beam is achieved by monitoring the difference between the light beam intensity from the light source and the light beam intensity output from the light intensity modulating means, and when this difference reaches a predetermined value. The light beam according to claim 1, characterized in that this is carried out by reducing the total intensity of the light beam incident on the recording medium by a predetermined amount by the light intensity modulating means. Strength control method.