JPH0523663B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an image reading system in which an image is read by scanning a laser beam on a medium on which an image is recorded, such as an X-ray film, and detecting the transmitted or reflected light by photoelectric conversion. Regarding a reading device.

BACKGROUND OF THE INVENTION As is well known, in the medical field, diagnostic systems that diagnose diseases and the like by computer processing images read from X-ray film have become widespread. An example of the basic configuration of an image reading device for this purpose is shown in FIG. The beam emitted by the laser 1 passes through a reflecting mirror 2, is scanned by a polygon 3 (rotating polygon mirror), passes through an fθ lens 4, a reflecting mirror 5, and a cylindrical lens 6, and then passes over the image of the X-ray film 7 approximately in the transport direction. Operate on a perpendicular line. The cylindrical lens 6 is for tilt angle correction, and is for fθ
The lens 4 is used to focus the laser beam on the image and to make the movement of the spot on the image constant. The image scanning light undergoes a change in light intensity due to the change in density, which is taken into a photoelectric converter 9 via a condenser 8 and converted into an electrical signal according to the density, which is then introduced into a host computer or the like. The X-ray film 7 is sub-scanned in the Y direction by a feeding device 10.

Problems to be Solved by the Invention FIG. 13 shows the structure of the above-mentioned X-ray film 7, in which emulsion layers 12 are coated on both sides with a support 11 in between, and a protective layer 13 is coated on the outside of the emulsion layers 12. ing.

In beam scanning of such a film, reflection occurs at the interface between each layer of the film due to a change in refractive index. In particular, when the light enters the protective layer from the air or enters the air from the protective layer, the refractive index changes significantly, and normally about 4 to 5% of the reflected light is present. Therefore, as shown in FIG. 14, the incident light _L0 is divided into a component _L1 that passes through the film as it is and a component _L2 that passes through the film after being reflected at B and C. There is an optical path difference δ between L ₁ and L ₂ .

δ=(BC+CD)n-BE =2nh・cosφ′ However, n is the refractive index and h is the thickness.

When this optical path difference δ is an integer multiple of the wavelength of the reading laser beam, they strengthen each other most strongly, and when they are shifted by a half wavelength, they interact most weakly. Since the optical path difference δ changes depending on the scanning angle φ and the film thickness h, as a result, due to the combined optical path difference between the two,
The amount of transmitted light varies depending on the position of the film, resulting in interference fringes. As an example, FIG. 15 shows the change in phase difference depending on the scanning angle for a film with h=175 μm, λ=0.6328 μm, and n=1.52. In the figure, the horizontal axis shows the scanning angle, and the vertical axis shows the phase difference δ normalized by the wavelength λ. In other words, the light intensities strengthen each other where they intersect with the horizontal lines on the graph, and weaken each other between them, resulting in interference fringes that are wider at the center of the scanning width than the graph and become denser toward both ends.

Although changes in film thickness cannot be unconditionally defined, interference fringes are observed as contour lines for each film thickness. If there is no change in the thickness of the film, there is no need to consider this effect, but it is practically impossible to reduce the change in thickness to less than the wavelength order, and even if it were possible, the cost would increase significantly. It invites.

Furthermore, although the influence of such interference fringes can be prevented by lowering the reflectance of the film surface, it is not desirable to apply an anti-reflection film to the read image film, as this will lead to a significant increase in cost.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image reading apparatus that suppresses the generation of interference fringes due to the coherency of a laser beam when reading a film image.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention scans a laser beam on a medium on which an image is recorded, and reads the image from transmitted light or reflected light from the medium. In this image reading apparatus, a plurality of laser beams are incident on the medium at different angles and are located at the same scanning spot position.

Effect By overlapping multiple laser beams as a single spot on the medium, the positions of the laser beam that directly passed through the medium and the laser beam that passed through the film after being reflected twice on the film surface are changed. The generation of interference fringes is suppressed by varying the phase differences. This will be explained in detail below.

FIG. 1 shows a structure in which a laser beam deflected by a polygon 21 passes through an imaging lens 22 located at a focal length f from the deflection point and forms an image on a film 23 at a distance f. In this structure, the laser beam deflected by the polygon 21 passes through the imaging lens 22 so that it is incident perpendicularly to the film 23 at any scanning angle. Further, the parallel light incident on the imaging lens 22 is focused on the film 23 surface. Here, when two parallel laser beams are incident on the polygon 21, the beams A and B are parallel to each other until they enter the imaging lens 22.
2, they overlap on the surface of the film 23 at an angle of θ. At this time, due to the difference in the angle of incidence of both beams A and B on the film 23, the optical path difference between the beams _L1 and _L2 in FIG. 14 described above is different for the beams A and B. By appropriately setting this optical path difference, that is, by setting the angle θ, the phase difference between the two beams cancels each other out and interference fringes are suppressed. For example, the thickness h of the film 23 =
175 μm, the refractive index of the film protective layer n = 1.52, and the wavelength λ = 0.6328 μm. When determining the angle θ that produces the least interference fringes, the optical path difference δ between L ₁ and L ₂ is: δ = 2nh・cos {sin ^-1 ((sinφ)/n)} When δ(A) - δ(B) = λ/2, the phases of the interference fringes generated by laser beams A and B are shifted by exactly half a period, so the interference fringes cancel each other out. . In other words, δ(A)-δ(B)=2nh-2nh・cos{sin ^-1 ((sin
Interference fringes can be suppressed by determining the angle θ such that θ)/n)}=λ/2 and reading an image using a laser beam set at this angle. In the above equation, under the above conditions, the angle θ=3 degrees.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows an embodiment for obtaining a plurality of parallel laser beams, and mainly shows a laser beam splitting means for splitting a laser beam emitted from one laser light source (a gas laser or a semiconductor laser) into a plurality of parallel beams. Figure A shows the beam output from one laser light source 31 using a half mirror (beam splitter).
32 and mirror 33, the beam emitted from the laser light source 31 is split into two by the half mirror 32, and the beam reflected by the half mirror 32 is further divided into two by the mirror 33. The optical path is bent and adjusted so that it is parallel to the beam that has passed through the half mirror 32.

In Figure B, the upper half of one side of the parallel plane substrate is a half mirror, the lower half is a normal transparent material, and the lower half of the other side of the substrate is a mirror, and the upper half is transparent. This is a case where a half mirror 34 made of a raw material is used.

C in the same figure shows a case using a parallel plane substrate 35 whose both sides are half mirrors, and the ratio of the two light amounts is 1.
Although it cannot be made one-on-one, it can be expected to have some effect.

FIG. 3D shows a substrate 36 that also serves as a mirror for optical path deflection, with a half mirror for adjusting the incident angle of the beam, and a total reflection mirror on the back surface.

Figure E shows a configuration that splits and outputs three or more laser beams from one laser light source, in which the beam from the laser light source 31 is split by a diffraction grating 37, and among them, the 0th order light and the ±1st order light are split. This is a case where parallel light is obtained from a convex lens 38 located at a distance by a focal length. As a modification of this, the zero-order light may be cut into two beams, or the ±second-order light may be included, if necessary.

In FIG. 5F, an acousto-optic deflector (AOM) 39 is used as a beam splitting means, and the O-order light and the first-order light are extracted as parallel light by a convex lens 40.

G in the same figure uses two laser light sources to obtain two luminous fluxes, laser light sources 41 and 42.
Two mirrors 43 and 44 are provided to adjust the distance between the light beams.

The above embodiments have shown cases in which a plurality of light beams are parallel to each other, but this is not limited to parallel light, and each light beam has an angle θ on the film surface. Any device that can generate laser beams that intersect with each other may be used. Further, the distance between each light beam is determined by the angle θ on the film surface and the focal length f of the imaging lens.

FIG. 3 shows an example in which a parallel light beam is incident on the film surface at an angle θ, and two light beams A,
B is deflected and scanned by a polygon 45, and an image is formed on a film 47 through an fθ lens 46. With this configuration, polygon 4 as an imaging lens
The scanning beam emitted from 5 is incident on the film surface at a certain angle. In other words, the angle of incidence on the film differs depending on the scanning angle. A major feature of this configuration is that, compared to the imaging lens shown in FIG. 1, a more compact lens can be used to obtain the same scanning width.

FIG. 4 and FIG. 5 are calculation results showing how interference fringes are reduced based on the present invention. In Figure 4, 2
Opening angle of the book's luminous flux θ = 0.3 degrees, in Figure 5 θ =
The case of 0.2 degrees is shown. The horizontal axis is the scanning angle, which indicates the angle of incidence on the film surface. In other words, each 0 degrees of incidence means that the scanning beam is irradiated to the center of the image. The contrast of the interference fringes is shown on the vertical axis; when the contrast is 1, there is no interference fringe reduction effect, and when the contrast is 0, it means that they are completely canceled out. Therefore, since the angle of incidence of the scanning beam on the film surface varies depending on the scanning position, interference fringes cannot be removed over the entire scanning width, but the effect of reducing interference fringes can be seen within a certain range of scanning angles. , FIG. 4 shows that the interference fringes are reduced to less than half of the conventional level in the scanning range of 10 to 20 degrees. In addition,
Increasing the angle θ is effective in reducing interference fringes at the center of the scanning width, and increasing the number of light beams to three or more allows for more uniform interference fringe reduction over the entire scanning width.

FIG. 6 shows a case where an ultrasonic optical deflector (AOD) is used as the laser beam splitting means. The beam emitted from the laser light source 48 is redirected by a mirror 49 and enters an ultrasonic optical deflector 50, and the deflector 50 changes its first order diffraction angle according to the frequency applied thereto. The divided light beams are converted into parallel beams by a convex lens 51 located a focal length away from the divided beams. The subsequent optical system is the same as that shown in FIG. 3, and the two light beams are superimposed at one point on the film surface by the imaging lens 46.

In this embodiment, the angle θ is changed by the deflector 50 according to the scanning angle, thereby making it possible to reduce interference fringes over the entire scanning angle. The reason for this will be explained in detail below.

Figure 7 shows the situation when the scanning beam is incident on the image film.A is the scanning beam incident on the film, and B is the light beam that has been split once and superimposed on the film surface again to reduce the influence of interference fringes.
shall be. Furthermore, the light flux that directly passes through the film is L ₁ , and the light flux that passes through the film after being reflected is L 1 .
Let it be L ₂ . Further, in the same figure, A shows the situation at the center of the scanning width, and B shows the situation at the end of the scanning width. Here, the angle θ between the two luminous fluxes A and B is
When the optical path difference δ(A) between L ₁ (A) and L ₂ (A) and the optical path difference δ(B) between L ₁ (B) and L ₂ (B) are shifted by half a wavelength, that is, δ(A )−δ(B)=λ/2, the interference fringes are completely canceled. However, when the light beams are incident on the end of the scanning width at the same angle θ, the difference in the optical path difference between the two light beams A' and B' at B is not equal to half a wavelength. In other words, δ′=(A)−δ′(B)=λ/2 is not satisfied, and the difference in optical path difference becomes larger toward the end (as the scanning angle becomes larger).
Therefore, in order to make the difference in the optical path difference between the two beams λ/2 over the entire scanning width, it is necessary to change the beam angle θ according to the scanning angle. FIG. 8 shows the results. In the figure, the horizontal axis represents the scanning angle, and the vertical axis represents the optimal (difference in optical path difference λ/
The angle θ is set so that the angle becomes 2. From this characteristic, by changing the angle θ of the two beams, the difference in the optical path differences δ(A) and δ(B) of the beams A and B can always be kept at λ/2, and the entire scanning width Interference fringes can be suppressed over a period of time. In this way, by changing the carrier frequency according to the scanning angle using the ultrasonic optical deflector 50, the diffraction angle is changed, and the angle θ of the two beams is changed.
By changing the angle on the film surface, interference fringes can be reduced.

Note that a movable element to which a mirror can be attached, such as a galvanometer mirror or a piezo element, can also be used as a means for changing the angle θ of the two light beams according to the scanning angle. For example, as shown in FIG. 9, two beams are obtained by a half mirror 52 and a mirror 53, and the reflection angle is changed according to the scanning angle by attaching the mirror 53 to a rotatable element. It passes through a convex lens 54 located approximately the focal length away from that position.

When adjusting the angle according to the scanning position, it may be difficult to obtain the designed value with the configuration of the embodiment, but even if the contrast of the interference fringes does not become 0, it is possible to obtain an effect close to it. I can do it.

FIG. 10 is a side view of the optical system in FIG. 3 described above, and in this configuration, the film 47 is slightly tilted from a state perpendicular to the optical axis as shown by a broken line to a state shown by a solid line. This is the arrangement. This configuration reduces interference fringes over the entire scanning width. That is, in FIG. 3, since the angle θ is fixed, it is difficult to maintain the optical path difference at λ/2 even when the incident angle changes, but by tilting the film 47, the scanning beam can be changed. The angle of incidence on the film is biased to reduce the substantial change in the angle of incidence due to change in the scanning angle, thereby expanding the range in which interference fringes are reduced. For example, when the film 47 is tilted by 30 degrees, the effective angle of incidence with respect to the scanning angle Y (0 to 25) is: Y(0)=30.000 Y(5)=30.375 Y=(10)=31.475 Y=( 15) = 33.226 Y = (20) = 35.531 Y = (25) = 38.290, and even though the scanning beam is swung from 0 to 25 degrees, the angle of incidence on the film only changes by about 30 to 38 degrees. , the interference fringe suppression range can be widened.

FIG. 11 is a characteristic diagram showing the above-mentioned effect,
It can be seen that when the film 47 is tilted at 30 degrees and the angle θ between the two light beams is 0.14, the contrast of the interference fringes is suppressed to 0.2 or less over the scanning angle of 0 to 24 degrees.

Effects of the Invention As described above, according to the present invention, since image reading is performed in which a plurality of laser beams are incident on a medium at different angles and are configured to be at the same scanning spot position, direct light on the medium is used. This has the effect of effectively suppressing the occurrence of interference fringes due to the optical path difference between the reflected light and the reflected light.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of main parts of the present invention, FIG. 2 is a block diagram showing an embodiment of the laser beam generating means in the present invention, FIG. 3 is a block diagram showing an embodiment of the beam deflection means in the present invention, 4 and 5 are contrast characteristic diagrams based on the present invention, FIG. 6 is a configuration diagram showing an embodiment of the beam deflection means in the present invention, and FIG. 7 is an optical path difference diagram for explaining the operation in FIG. 6. 8 is an optimal angle characteristic diagram in FIG. 6, FIG. 9 is a block diagram showing an embodiment of the beam deflection means in the present invention, and FIG. 10 is a block diagram for suppressing the optical path difference in the present invention. 11 is a contrast characteristic diagram in FIG. 10, FIG. 12 is a configuration diagram of the image reading device, FIG. 13 is a cross-sectional view of the film, FIG. 14 is a diagram showing the optical path difference between incident light and reflected light,
FIG. 5 is a characteristic diagram of the order of occurrence of interference fringes due to the optical path difference. 21...Polygon, 22...Combined lens, 23
...Film, 31...Laser light source, 37...Diffraction grating, 50...Ultrasonic optical deflector.

Claims (1)

[Scope of Claims] 1. An image reading device that scans a medium on which an image is recorded with a laser beam and reads the image from transmitted light or reflected light from the medium, in which a plurality of laser beams are scanned onto the medium. An image reading device characterized in that the beams are incident on the image at different angles and are scanned at substantially the same spot position. 2. The image reading device according to claim 1, wherein the laser beams are configured such that the angle of incidence between them is always constant. 3. The image reading device according to claim 1, wherein the laser beams have a mutual incident angle that changes depending on the scanning angle. 4. The image reading device according to claim 1, wherein the laser beam is obtained by a laser beam splitting means that splits a laser beam emitted from one light source into a plurality of beams. 5. The image reading device according to claim 1, wherein the medium angle is such that the laser beam has an incident angle deviating from the perpendicular direction of the medium.