JPH03211518A - Light beam scanner - Google Patents

Abstract

PURPOSE:To allow scanning in a correctly multiplexed state even if plural light beams line up in the direction corresponding to sub-scanning by adjusting the disposition of a light source unit so as to minimize the fluctuation of a light spot in the sub-scanning direction by the plural light beams reflected from the respective reflecting surfaces of a rotary polyhedral mirror. CONSTITUTION:The light quantity in the direction corresponding to the sub- scanning direction on a body to be irradiated by the entire part of the plural light beams 14 emitted from the light source unit is monitored. The disposition of the light source unit 13 or the multiplexing optical system is so adjusted as to minimize the fluctuation of the light spot in the sub-scanning direction on the body to be irradiated by these plural light beams 14. The deviation in the position of the light spot by the influence of the rotary polyhedral mirror 15 is obviated in this way even if the plural light beams 14 line up in the direction corresponding to the sub-scanning direction. The scanning is thus executed in the correctly multiplexed state.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is used in, for example, image reading devices, laser printers, etc., and uses a rotating polygon mirror to reflect and deflect a light beam so that the light beam illuminates the target object. The present invention relates to a light beam scanning device that scans over the body.

(Prior art) A recording sheet on which an image is recorded is scanned with a light beam to obtain an image signal, this image signal is subjected to image processing, and the light beam is modulated based on the image signal subjected to image processing. Systems that scan a recording sheet exposed to the light beam and reproduce and record images on the recording sheet are used in various fields.

For example, recording an X-ray image using a low gamma X-ray film designed to be compatible with subsequent image processing;
The X-ray image is read from the film on which it is recorded, converted into an electrical signal, and after image processing is performed on this electrical signal (image signal), the contrast is reproduced as a visible image on a photosensitive film, etc. A system that can obtain reproduced images with good image quality performance such as sharpness and graininess has been developed (see Japanese Patent Publication No. 81-5193).

In addition, the applicant has proposed radiation (X-rays, α-rays).

When irradiated with β rays, γ rays, electron beams, ultraviolet rays, etc., a part of this radiation energy is accumulated, and then when irradiated with excitation light such as visible light, stimulable fluorescence exhibits stimulated luminescence depending on the accumulated energy. A radiation image of a subject such as a human body is photographed and recorded on a sheet of stimulable phosphor using a stimulable phosphor, and this stimulable phosphor sheet is scanned with excitation light such as a laser beam. The resulting photostimulated luminescence is read in a charging manner to obtain an image signal, and based on this image signal, a radiation image of the subject can be recorded on a recording material such as a photographic light-sensitive material, a CRT, etc. A radiation image recording and reproducing system that outputs a visual image has already been proposed (Japanese Unexamined Patent Publication No. 5
No. 5-12429, No. 5B-11395.

No. 55-163472, No. 5B-104845, No. 55-116340, etc.).

This system has the practical advantage of being able to record images over a much wider range of radiation exposure compared to conventional radiographic systems using silver halide photography. In other words, in a stimulable phosphor, it is recognized that the amount of emitted light that is stimulated to emit light due to excitation after accumulation is proportional to the amount of radiation exposure over an extremely wide range.
Therefore, even if the amount of radiation exposure varies considerably due to various imaging conditions, the amount of stimulated luminescence emitted from the stimulable phosphor sheet can be read by the charging conversion means by setting the reading gain to an appropriate value. By converting the radiation image into an electric signal and using this electric signal to output the radiation image as a visible image to a recording material such as a photographic light-sensitive material or a display device such as a CRT, a radiation image that is not affected by fluctuations in radiation exposure amount can be obtained. be able to.

In the above-mentioned systems that use X-ray film, stimulable phosphor sheets, etc., and various systems that handle general images, etc., in order to read images and obtain image signals, it is necessary to use A light beam is scanned over a stimulable phosphor sheet or other recording sheet, and the light (for example, X
An image reading device is used that obtains an image signal by receiving light transmitted through an X-ray film or reflected from an X-ray film, stimulated luminescence light emitted from a stimulable phosphor sheet, etc., with a photodetector. In order to obtain a visible image based on an image signal, an image recording apparatus is used that scans a recording sheet such as a photosensitive film for image recording with a light beam whose intensity is modulated based on the image signal.

A rotating polygon mirror is often used in the image reading device, image recording device, etc. to scan a light beam onto a recording sheet. By rotating the rotary polygon mirror at high speed, main scanning can be performed repeatedly at high speed, and by relatively moving the recording sheet (sub-scanning) in a direction approximately perpendicular to the main scanning direction, the recording sheet can be scanned two-dimensionally. scanned at high speed,
Therefore, a high-speed image reading device or image recording device can be realized. In addition, in these image reading devices and image recording devices, when the light intensity of the light beam emitted from one light source is weak, multiple light sources are provided,
A plurality of light beams emitted from the plurality of light sources may be combined to form the same spot on the recording sheet.

(Problem to be Solved by the Invention) A rotating polygon mirror has slightly different distances from its rotation axis to its respective reflecting surfaces, so it is difficult to determine which reflecting surface the light beam emitted from the light source is reflected and deflected by when it reaches the recording sheet. Therefore, the optical path lengths may differ slightly from each other. For example, in the case of a single light beam emitted from a single light source, this variation in optical path length only causes a variation in the spot diameter on the recording sheet, and the spot position does not change.
Combining multiple light beams may cause variations in the spot position that require more precise adjustment than the spot diameter. This variation in spot position will be explained below with reference to FIGS. 3 and 4.

Figure 3 shows an example of a multiplexing optical system. When the reflecting surface that actually reflects and deflects the light beam of the rotating polygon mirror is in the normal position (case (a)), the reflecting surface is in front of the normal position. FIG. 4 is a diagram showing the optical path in the case (case (b)) and in the case (case (C)) when it is recessed from the normal position.

The two light beams 2a and 2b emitted from the two light sources La and lb pass through the first imaging optical system 3 and onto the reflecting surface 4 (reflecting surface 4' represents the same reflecting surface) of the rotating polygon mirror. Once combined, the beam is reflected and deflected (in this figure, the light beam 2a,
2b is depicted as being transmitted, but this figure shows that the light incident on the reflective surface 4 is reflected by the same reflective surface 4' as the reflective surface 4. ), which are multiplexed onto the recording sheet 6 via the second imaging optical system 5 into two light beams 2a.

2b forms a single light spot.

However, when the reflective surface 4 is located in front of the normal position (case (b)), the light beam 2
b is irradiated with a shift in the X direction from the light beam 2a, and on the other hand, when the reflecting surface 4 is recessed from its normal position, (C
), the light beam 2a is irradiated onto the recording sheet 6 with a shift in the X direction from the light beam 2b. Here, if the light intensities of the two light beams 2a and 2b are different from each other, a positional shift of the light spot occurs.

FIG. 4 is an enlarged view showing the light intensity distribution of the two light beams 2a and 2b shown in FIG. 3 in the X direction on the recording sheet 6. As shown in FIG.

Here, for simplicity, we will explain the X of the two light beams 2a and 2b.
The curves representing the directional light intensity distribution are given the same numbers as the corresponding light beams 2a and 2b. Also, Figures 4(a), (b), and (c) are respectively similar to Figure 3(a).
, (b).

It corresponds to (C). Further, it is assumed here that the first beam 2b has a stronger light intensity than the first beam 2a.

When the two light beams 2a and 2b completely overlap as shown in Fig. 3(a), the irradiation position of the combined spot becomes the regular irradiation position 0, but as shown in Fig. 3(b). When the reflective surface 4 is located in front of the normal position as shown in Figure 4 (
If the reflective surface is shifted in the X direction as shown in b) and the reflective surface is retracted as shown in Figure 3 (C), the result will be a shift in the opposite direction to the X direction as shown in Figure 4 (C). Become.

When a change in the position of the light spot occurs in the sub-scanning direction in the image reading device, the image carried by the image signal obtained by reading the image will have uneven density in the sub-scanning direction, with one rotation of the rotating polygon mirror being one cycle. This causes a problem in that the image quality of the visible image reproduced based on the image signal deteriorates and becomes difficult to see. In addition, a similar phenomenon occurs in image recording devices, and when a change in the position of the light spot occurs in the sub-scanning direction during image recording, the underlying image signal does not contain the density unevenness described above. However, the result is that density unevenness occurs in the sub-scanning direction in the image recorded on the recording sheet.

As a means to solve the above problem, it is possible to arrange multiple light beams in a line in the direction corresponding to the main scanning, but when multiple light beams are combined, it is recommended to arrange them only in the direction corresponding to the main scanning. It becomes difficult to construct a compact light source unit that includes many light sources that generate these many light beams, and the optical system that combines the many light beams emitted from the light sources becomes large. The problem before considering the influence of the rotating polygon mirror is that the accuracy of multiplexing will deteriorate.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a light beam scanning device that can perform scanning in a correctly combined state even when a plurality of light beams are lined up in a direction corresponding to sub-scanning. be.

(Means for Solving the Problems) A forward beam scanning device of the present invention includes a light source unit that emits a plurality of light beams, and a plurality of light beams emitted from the light source unit form a single light point on an irradiated object. a combining optical system that combines the plurality of light beams so as to form a single light beam, and a rotating polygon mirror that reflects and deflects the plurality of light beams; a main scanning optical system that repeatedly scans the plurality of waveformed tip beams over the irradiated object, the irradiated object or the main scanning optical system relative to a sub-scanning direction substantially perpendicular to the main scanning direction; a sub-scanning means for moving the plurality of light beams, a monitoring means for monitoring the center of gravity of the amount of light in a direction corresponding to the sub-scanning direction on the irradiated object by the entire plurality of light beams;
Based on the monitored center of gravity, the light source unit or the light source unit or the light source unit is configured to minimize the variation of the light spot in the sub-scanning direction due to the plurality of light beams reflected from each reflecting surface of the rotating polygon mirror. The present invention is characterized in that it includes an adjusting means for adjusting the arrangement position of the wave optical system.

Here, the above-mentioned "direction corresponding to the sub-scanning direction on the irradiated object" refers to the direction in which the two light beams emitted from the light source unit are reflected and finally irradiated onto the irradiated object. Assuming that two light beams are lined up in the sub-scanning direction, the two light beams can be placed at any position on the optical path from when they are emitted from the light source unit until they are irradiated onto the irradiated object. The direction in which the lines are lined up.

(Function) The present invention conventionally provides a light source unit and an optical system so that the geometric center of a plurality of light beams emitted from the light source unit coincides with the optical axis of the optical system extending from the light source unit to the irradiated object. The above problem occurs when the light intensities of the plurality of light beams emitted from the light source unit differ from each other due to the relative position with respect to the light source unit being determined, and the plurality of light beams emitted from the light source unit This was done based on the knowledge that by aligning the center of gravity of the entire light amount with the optical axis, the position of the combined light spot on the irradiated object does not change regardless of whether the reflective surface of the rotating polygon mirror moves in or out. be.

That is, the light beam scanning device of the present invention includes a monitor unit that monitors the center of gravity of the amount of light in a direction corresponding to the sub-scanning direction on the irradiated object by all of the plurality of light beams, and a unit that monitors the center of gravity of the light amount in a direction corresponding to the sub-scanning direction on the irradiated object. Equipped with adjustment means for adjusting the placement position of the light source unit or the multiplexing optical system so that the fluctuation of the waved light spot in the sub-scanning direction is minimized, so multiple light beams are lined up in the direction corresponding to the sub-scanning direction. Even when the object is irradiated, the position of the light spot on the object to be irradiated is scanned without changing in the sub-scanning direction.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an example of an image reading device using an embodiment of the light beam scanning device of the present invention. Here, an example of an image reading device that obtains an image signal by reading a radiation image stored and recorded on the above-mentioned stimulable phosphor sheet will be described.

A radiation imaging device (not shown) irradiates a subject with radiation, and the radiation that has passed through the subject is irradiated onto a stimulable phosphor sheet, whereby a radiation image of the subject is stored and recorded on the stimulable phosphor sheet. The stimulable phosphor sheet on which the image has been stored is stored in the image reading device 10.
is set in the specified position.

The stimulable phosphor sheet 11 set at a predetermined position is conveyed (sub-scanned) in the direction of arrow Y by a sheet conveyance means 15 such as an endless belt driven by a drive means (not shown). On the other hand, a plurality of light beams 14 are emitted close to each other and in parallel with each other from a light source unit 13 containing a plurality of laser light sources (in FIG. 1, the plurality of light beams are collectively shown as one beam). ) passes through a first optical system 16 configured to combine a plurality of light beams 14 on the reflecting surface of a rotating polygon mirror 15 and enters the rotating polygon mirror 15 . This rotating polygon mirror 15 is driven by a motor 7 and rotates at high speed in the direction of arrow Z. The plurality of light beams 14 incident on the rotating polygon mirror 15 are reflected and deflected by the rotating polygon mirror 15, and the plurality of light beams 14 are combined into one light spot on the sheet 11, and the light spot is After passing through the second optical system 18, which is configured to maintain that state even when it scans the sheet 11, the optical path is changed by the mirror 21 and the beam enters the sheet 11,
Main scanning is repeatedly performed in the direction of arrow X, which is substantially perpendicular to the direction of sub-scanning (direction of arrow Y).

From the point where the light beam 17 of C) 11 is irradiated,
Stimulated luminescence light 22 is emitted in an amount corresponding to the stored X-ray image information, and this stimulated luminescence light 22 is guided by a light guide 23 and photomultiplier (photomultiplier tube) 24 converts it into a photoelectron. detected.

The light guide 23 is made by molding a light-guiding material such as an acrylic plate, and is arranged so that a linear incident end surface 23a extends along the main scanning line on the stimulable phosphor sheet ll. The light receiving surface of the photomultiplier 24 is coupled to the annularly formed exit end surface 23b. The stimulated luminescent light 22 entering the light guide 23 from the input end surface 23a travels through the interior of the light guide 23 through repeated total reflection, exits from the exit end surface 23b, is received by the photomultiplier 24, and is converted into a radiographic image. The expressed stimulated luminescent light 22 is converted into an electrical signal by a photomultiplier 24.

The analog signal S^ output from the photomultiplier 24 is logarithmically amplified by the log amplifier 25 and then
The signal is input to the D converter 26 and sampled to obtain a digital image signal SD.

This image signal So is sent to an image processing device (not shown), where appropriate image processing is performed on the image signal So, and then sent to an image reproduction device, where a visible image based on the image signal SO is reproduced and displayed.

Here, the plurality of light beams 14 are arranged at the starting point position of main scanning.
ive devlce) 31 for each main scan.

This PSD 31 detects the position of the center of gravity of the light intensity in the sub-scanning direction (direction of arrow Y) of a combined spot consisting of a plurality of light beams 14, and outputs a monitor signal S representing the position of the center of gravity.
N is input to the control circuit 32.

FIG. 2 is a diagram showing an example of the monitor signal sM input to the control circuit 32 shown in FIG. 1. The horizontal axis represents time t, and the vertical axis represents the spot position in the sub-scanning direction (the position of the center of gravity of the amount of light) carried by the monitor signal sM. Further, the numbers shown in the figure correspond to the respective reflecting surfaces (first to sixth surfaces) of the rotating polygon mirror 15 shown in FIG. Although the distance from the rotation axis of the motor 17 differs for each reflective surface, since the rotation axis of the motor 17 also vibrates in synchronization with each rotation, the fluctuation of the light spot on the sheet 11 in the sub-scanning direction is As shown in this figure, it is often a substantially sinusoidal waveform in which one revolution of the rotating polygon mirror is synchronized.

The sheet 11 is conveyed from the upstream side in the conveyance direction (arrow Y direction in FIG. 1), and before the leading edge of the sheet 11 reaches the scanning line formed by the plurality of light beams 14, the PSD 31 scans the light beams 14 from the plurality of light beams 14. The center of gravity of the spot in the sub-scanning direction is monitored. Here, it is assumed that the center of gravity is vibrating as indicated by the solid line A shown in FIG. At this time, the drive circuit 33 that slightly moves the light source unit 13 in the direction of arrow C corresponding to the sub-scanning direction is controlled by the control circuit 32.
The light source unit 13 is moved in the direction of the arrow C so that the variation in the center of gravity of the light spot passing through the SD 31 is minimized, for example, as shown by the broken line B in FIG. In this manner, the radiation image stored and recorded on the sheet 11 is read after the variation in the center of gravity of the light spot becomes the minimum. Therefore, the obtained image signal SD carries a high-quality image with extremely small density unevenness in the sub-scanning direction.

In the above embodiment, the position of the light source unit 13 is finely adjusted in order to adjust the center of gravity of the light spot; instead, the position of the first optical system 16 may be finely adjusted.

Further, although the above embodiment is an image reading device that reads radiation images stored and recorded on a stimulable phosphor sheet, the light beam scanning device of the present invention can also be applied to a more general image reading device. It goes without saying that there is.

Further, the light beam scanning device of the present invention can be applied not only to an image reading device but also to an image recording device.

For example, in FIG. 1, a photosensitive film on which an image is recorded by the light beam I4 is set in place of the stimulable phosphor sheet 11, and a plurality of light beams 14 emitted from the light source unit 13 are transmitted by the AOM based on the image signal. Even in the case where the photosensitive film is scanned by intensity modulation, it is desirable that the light spot on the photosensitive film caused by the plurality of light beams (4) does not fluctuate in the sub-scanning direction.
In this case as well, variations in the light spot in the sub-scanning direction can be minimized in the same manner as in the above embodiment.

(Effects of the Invention) As described above in detail, the light beam scanning device of the present invention has the following advantages: the amount of light in a direction corresponding to the sub-scanning direction on an irradiated object by all of the plurality of light beams emitted from the light source unit; The position of the light source unit or the combining optical system is adjusted so that the variation in the sub-scanning direction of the light spot on the object to be irradiated by these multiple light beams is minimized. Even if a plurality of light beams are lined up in the corresponding direction, the position of the light spot will not shift due to the influence of the rotating polygon mirror, and scanning will be performed in a correctly combined state.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image reading device using an embodiment of the light beam scanning device of the present invention, and FIG. 2 shows a plurality of lights reflected and deflected from each reflective surface of a rotating polygon mirror. FIG. 3 is a diagram showing an example of the fluctuation of the center of gravity position of the light spot obtained by receiving the light spot consisting of the entire beam with a PSD. Figure 4 shows the optical path when the reflective surface that is actually reflecting and deflecting is at the normal position, when it is in front of the normal position, and when it is recessed from the normal position. FIG. 3 is an enlarged view showing the light intensity distribution of the two light beams shown in FIG. 1 in the X direction on the recording sheet. 10... Image reading device 11... Stimulable phosphor sheet 13... Light source unit 14... Plural light beams 15... Rotating polygon mirror 22... Stimulated luminescent light 24... Photo Multiplier 31-=PSD (position 5ens
H1ve device )32...control circuit
33...Drive circuit diagram 0

Claims (1)

[Claims] a light source unit that emits a plurality of light beams; a combining optical system that combines the plurality of light beams so that the plurality of light beams emitted from the light source unit form one light spot on an irradiated object; A rotating polygon mirror that reflects and deflects the plurality of light beams is provided, and the plurality of light beams that are combined to form one light spot on the irradiated object are repeatedly main-scanned on the irradiated object. a main-scanning optical system that moves the irradiated object or the main-scanning optical system relatively in a sub-scanning direction substantially perpendicular to the main-scanning direction; monitoring means for monitoring the center of gravity of the amount of light in a direction corresponding to the sub-scanning direction on the body;
Based on the monitored center of gravity, the light source unit or the light source unit or the light source unit is configured to minimize the variation of the light spot in the sub-scanning direction due to the plurality of light beams reflected from each reflecting surface of the rotating polygon mirror. A light beam scanning device characterized by comprising an adjustment means for adjusting the arrangement position of a wave optical system.