JPH10241425A - Lighting system and image reading system using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To illuminate a line region of an illumination object at high illumination intensity by arranging a prism sheet fit to part of the circumferential surface of a fluorescent tube, and a converging element which converges light emitted from the fluorescent tube and transmitted through the prism sheet and irradiates it to an irradiation object. SOLUTION: Light emitted from a straight tube-type fluorescent tube 101 is transmitted through a prism sheet 102 stuck on the circumferential surface of the fluorescent tube 101, and brightness in the vertical direction to the surface of the fluorescent tube 101 and in its adjacent direction is enhanced. Among the lights transmitted through the prism sheet 102, light emitted in the vertical direction to the tube surface and in its adjacent direction is converged with a cylindrical lens 103 which is a converging element, illuminated in line on the surface of an illumination object 104 such as a letter, and a line illumination region is illuminated. The cylindrical lens 103 is arranged so that the center axis of the fluorescent tube 101 is focused on the illumination region of the illumination object 104.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illuminating device for illuminating a linear area on an illuminated object and an image reading system using the illuminating device.

[0002]

2. Description of the Related Art An illuminating device for illuminating a linear area on an illuminated object such as a letter is mainly used in combination with a CCD line image sensor in an image reading system for reading an image on a document. An illumination device for such an image reading system generally uses a straight tube type fluorescent tube 201 as shown in FIG. That is, light from the fluorescent tube 201 is condensed by the concave reflecting mirror 202 and is irradiated on the illumination target 204 such as a letter, so that a linear region on the illumination target 204 is illuminated. The illuminated image of the linear region on the illumination target 204 is formed by an imaging lens 205 on a CCD line image sensor 206 provided in front of the illumination target 204 and read.

[0003] The fluorescent tube has a high luminous efficiency, is small in size, and inexpensive. However, since the amount of light is not so large, the structure using the fluorescent tube 201 as a light source as shown in FIG.
It is difficult to illuminate the area 4 with high illuminance. Among image reading systems, particularly in an industrial system that requires high-speed reading, it is required to illuminate an illumination target with high illuminance, and thus the illumination device in FIG. 8 is not suitable for such use.

Therefore, in a lighting device used in such a high-speed image reading system, as shown in FIG.
1, the light emitted therefrom is once condensed by a concave reflecting mirror 302, passed through an optical fiber bundle 303 via a heat ray cut filter (not shown),
In general, the light emitting end of the optical fiber bundle 303 is rearranged in a long and narrow manner to obtain a linear illumination pattern on the illumination target 305. The optical fiber bundle 303 and the line type light guide 304 are described in, for example,
148442, JP-A-6-51127, JP-A-6-51
128. Illuminated lighting object 3
The image formed on the imaging lens 05 is the same as that shown in FIG.
The image is formed on the CCD line image sensor 307 provided in front of the illumination object 305 via the, and is read.

However, a high-brightness lamp 301 such as a halogen lamp has a large amount of heat generation and power consumption, and requires a cooling fan and a large power supply. The optical fiber bundle 30
3 and the line type light guide 304 have a large shape,
Since the cost is high, the lighting apparatus as a whole becomes large and expensive in which the light source / power supply unit and the optical fiber bundle are connected, and miniaturization and cost reduction have been issues.

[0006]

As described above, the conventional illuminating device using a fluorescent tube has the advantages of high luminous efficiency, small size and low cost, but the amount of light is not so large. However, there has been a problem that the illuminance required as a lighting device for a high-speed image reading system cannot be sufficiently obtained.

On the other hand, an illuminating device using a light source including a high-intensity lamp such as a halogen lamp and a bundle of optical fibers can provide illumination with high illuminance, but generates a large amount of heat and consumes a large amount of power. There is a problem that a power source is required, and the shape is large and the cost is high.

An object of the present invention is to provide an illuminating device capable of illuminating a linear region on an illuminated object with high illuminance using a fluorescent tube, and an inexpensive and high-performance image reading processing device using the illuminating device. Aim.

[0009]

In order to achieve the above object, the present invention improves the brightness of a fluorescent tube by optical means so as to illuminate a linear area on an illuminated object with sufficient illuminance. The main point is what you do.

That is, in the illumination device according to the present invention, a straight tube-type fluorescent tube, a prism sheet attached to at least a part of a peripheral surface of the fluorescent tube, and a light emitted from the fluorescent tube and transmitted through the prism sheet. A light condensing element for condensing light and irradiating the object to be illuminated.

As described above, in the present invention, the prism sheet, which is a lens sheet having an effect of optically improving the luminance in a specific direction, is attached to the peripheral surface of the fluorescent tube, so that the specific emission angle direction of the fluorescent tube can be improved. By improving the brightness of the light and further selectively guiding the light beam having the maximum brightness at each emission point on the fluorescent tube surface onto the illumination target by using the light condensing element, the light is high in the linear region on the illumination target. Illuminance can be obtained.

Here, the prism sheet typically has a plurality of ridges having a substantially triangular cross section on one surface,
The other surface is a sheet-like optical element having a prismatic uneven surface formed of a smooth surface. Such a prism sheet,
It has an optical angle selectivity such that light having an incident angle in a specific range is transmitted and light having an incident angle outside the specific range is diffused or reflected. Due to this property, when the prism sheet is attached to the peripheral surface of the fluorescent tube, which is a diffusive light source, the luminance in a specific direction, specifically, the luminance in the direction perpendicular to and near the tube surface of the fluorescent tube is improved. Can be done.

Further, when the prism sheet is attached to the peripheral surface of the fluorescent tube in such a direction that the ridge having a substantially triangular cross section is substantially parallel to the length direction of the fluorescent tube, Since the restriction on the light emission angle is relaxed, the effect of increasing the luminance in the direction perpendicular to the surface of the fluorescent tube and in the direction near the surface is more remarkably exhibited.

The prism sheet used in the present invention is a general term for a sheet-like optical element having a property of improving the luminance in a specific direction. In the prism sheet, the luminance in another direction decreases in exchange for the improvement in luminance in a specific direction. This decrease in luminance is not remarkable for light rays in the emission direction in a plane including the length direction of the ridge and the normal vector of the sheet, and is not significant for light rays in the plane perpendicular to the length direction of the ridge. Notable.

As an example of applying such a prism sheet to a lighting device, a backlight of a liquid crystal display is known. By placing a diffusion plate and a prism sheet on a light guide plate on which light from a light source is incident, the brightness in the front direction of the light guide plate can be improved, and the viewing characteristics of the liquid crystal panel can be improved. Comparing the luminance with and without the prism sheet on the diffuser plate arranged on the light guide plate, the luminance in the direction perpendicular to the surface of the light guide plate can be increased by placing the prism sheet. Are known. On the other hand, the present invention is different in that the prism sheet is attached to the peripheral surface of the fluorescent tube, and the light transmitted through the prism sheet is further condensed by a light condensing element and illuminated linearly on the illumination target. I have.

The light condensing element is an optical element having a function of deflecting light rays, in particular, a property of collecting light emitted from one point near another point, and is a cylindrical lens or a concave reflecting mirror (especially an elliptic cylindrical concave reflecting mirror). ) Is used.

When a concave reflecting mirror is used for the light-collecting element, especially when the fluorescent tube is a fluorescent tube with an aperture that emits light only from a part in the circumferential direction, the presence of a light-shielding mask for forming the aperture causes When the fluorescent tube casts a shadow,
There is a possibility that the illuminance on the illumination target may decrease, but in such a case, by installing the fluorescent tube at a position off the optical path of light reflected by the reflector and traveling toward the illumination target,
Shadows can be prevented.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows a configuration of an image reading system including a lighting device according to an embodiment of the present invention. The light emitted from the fluorescent tube 101 of the straight tube type passes through the prism sheet 102 attached to the peripheral surface of the fluorescent tube 101, and thereby emits light in the direction perpendicular to the surface of the fluorescent tube 101 and in the direction near the surface. Is enhanced.

Of the light transmitted through the prism sheet 102, light emitted from the fluorescent tube 101 in a direction perpendicular to the tube surface and in a direction near the tube surface is condensed by a cylindrical lens 103 which is a condensing element, and then illuminated. The surface of the target object 104, for example, a letter, is irradiated in a line shape, and the line-shaped irradiation area is illuminated. The cylindrical lens 103 is installed such that the central axis of the fluorescent tube 101 is focused on a linear irradiation area of the illumination target 104.

As described above, in the present embodiment, the fluorescent tube 101
And prism sheet 102 and cylindrical lens 1
The illumination device configured to illuminate the illumination object 104 in a line shape is configured by 03. In the example of FIG. 1, the illumination devices are provided at two locations so as to illuminate the surface of the illumination object 104 from obliquely above the left and right sides of the drawing.

The image on the illumination object 104 illuminated in this way is formed on a CCD line image sensor 106 provided in front of the illumination object 104 via an imaging lens 105. The CCD line image sensor 106
The image on the illumination target 104 is read, converted into an electric signal, and output to a processing unit (not shown) as an image signal.

Next, the configuration of the light source unit will be described in detail with reference to FIGS. FIG. 2 is a perspective view illustrating a configuration of a light source unit including a fluorescent tube 101 and a prism sheet 102.
FIG. 3 is a sectional view thereof. The fluorescent tube 101 applies a fluorescent substance 112 to the inner surface of a rod-shaped glass tube 111 having a circular cross section,
It is a straight tube fluorescent tube in which gas 113 is sealed. In this example, the prism sheet 102 is adhered to a part of the circumferential surface of the fluorescent tube 101 in the circumferential direction with a transparent adhesive 114.

The prism sheet 102 is shown in FIGS.
As shown in the figure, a number of protrusions having a substantially triangular cross-sectional shape are formed on one surface along the length direction, and the other surface is a sheet shape having a prismatic irregular surface made of a transparent sheet formed flat. An optical element, the flat side of which is a fluorescent tube 10
1 is attached to the peripheral surface. The prism sheet 102 having such a configuration has a so-called optical angle selectivity of transmitting light having an incident angle in a specific range and diffusing or reflecting light having an incident angle out of the specific range. .

That is, focusing on the light emitted from the fluorescent tube 101 and incident on one ridge of the prism sheet 102, the light having an acute angle of incidence with respect to the side of the triangle forming the ridge among these lights. That is, light in the direction perpendicular to the surface of the fluorescent tube 101 and in the direction near the surface of the fluorescent tube 101 passes through the prism sheet 102, but light having an obtuse incident angle is reflected or diffused by the prism sheet 102. On the other hand, light transmitted through the prism sheet 102 is emitted in a direction almost perpendicular to the prism sheet 102. As described above, the light that has entered the prism sheet 102 at an incident angle within a specific range and transmitted therethrough is condensed by the cylindrical lens 103, so that the object to be illuminated 104 is illuminated in a line, and the linear region is illuminated. You.

Next, the effects of the lighting device according to the present embodiment will be described. In order to obtain high illuminance when illuminating a letter or the like, light collection by a cylindrical lens or the like is not sufficient, and it is essential to improve the brightness of the light source. When performing illumination for reading an image, if illumination light is applied from directly above, the component regularly reflected on the paper surface directly enters the CCD image sensor, which is inconvenient. In addition, if the illumination light is applied from a very low angle, the influence of shadows due to irregularities on the paper surface increases, which is also inconvenient.

As described above, the irradiation angle (incident direction) suitable for irradiating the illumination light onto the object to be illuminated is limited to an area in a specific range. In general, a light-collecting element such as a cylindrical lens has an effect of increasing illuminance on an illumination target by widening an expected irradiation angle. However, under such conditions where the range of the irradiation angle is limited, there is a limit to improving the illuminance of the irradiation area on the illumination target simply by using the light condensing element. Need to improve. In achieving this requirement, the prism sheet 102 exerts a great effect.

That is, since the surface of the fluorescent tube 101 is regarded as a surface of a substantially diffused light source, light emitted therefrom is emitted in almost all directions on the front side of the tube surface. However, of those lights, the light that reaches the vicinity of the irradiation area on the illumination target 104 and is effectively used as the illumination light is limited to light emitted in a limited emission direction. Therefore, if the luminance can be improved only in this direction, the illuminance in the irradiation area should be improved.

Also, if the brightness can be improved in a certain direction by any method, even if the direction is not conveniently directed to the direction of the irradiation area, the light in that direction is collected by a light condensing element such as a cylindrical lens 102. By guiding to the vicinity of the irradiation area by using, the effect of improving the illuminance in the irradiation area can be obtained.

As in this embodiment, the prism sheet 102
Is used, the luminance in a specific emission direction is improved. As described above, the prism sheet 102 has an optical angle selectivity of transmitting light having an incident angle in a specific range and diffusing or reflecting light having an incident angle outside the range. Therefore, when the prism sheet 102 is attached on the peripheral surface of the fluorescent tube 101, which is a diffusive light source, light in a direction other than the specific emission direction is reflected again toward the light source and re-diffused.
Recycling occurs. Thereby, the luminance in a specific direction can be improved.

Then, the prism sheet 1
The light whose luminance in a specific direction has been increased by 02 is linearly guided on the illumination target 104 by the cylindrical lens 103, thereby effectively improving the luminance of the linear region that is the irradiation region on the illumination target 104. be able to.

As shown in FIG. 2, the prism sheet 102 is attached to the peripheral surface of the fluorescent tube 101 in such a manner that a ridge having a substantially triangular cross section is substantially parallel to the length direction of the fluorescent tube 101. Have been. Thus, the prism sheet 10
2 is attached to the peripheral surface of the fluorescent tube 101,
Therefore, the above-described effect is more remarkably exhibited because the limitation on the emission angle of light in the length direction is reduced.

Next, the fluorescent tube 101 and the prism sheet 10
Another configuration example of the light source unit composed of the two light sources will be described. FIG.
In the light source section shown therein, the fluorescent tube 101 is of a general full-surface emission type, and a part of its peripheral surface, that is, the illumination target 1
Although the prism sheet 102 is adhered only to the linear irradiation area side (cylindrical lens 103 side) on the portion 04, the configuration of the light source section is not limited to this, and is shown in FIGS. 4 and 5, for example. It can also be configured as follows.

FIG. 4 shows an example in which the fluorescent tube 101 is of a full-surface emission type, and a prism sheet 102 is attached to the entire peripheral surface. Even with such a configuration, the same effect as the configuration shown in FIGS. 2 and 3 in which the prism sheet 102 is attached to only a part of the circumferential surface of the fluorescent tube 101 in the circumferential direction can be obtained.

FIG. 5 shows an example in which the fluorescent tube 101 has an aperture and a prism sheet 102 is attached to the aperture. The fluorescent tube with an aperture is, as shown in the figure, covered with a light shielding mask 115 to cover a part of the circumferential surface of the glass tube 111 in a circumferential direction, so as to block light so that light is not emitted, and is covered with the light shielding mask 115. A fluorescent tube in which the luminance of the light emitting portion is improved by making the portion where there is no light into the aperture 116 so that light is emitted only from the aperture 116.

In the fluorescent tube with an aperture shown in FIG.
The fluorescent substance 112 is located at the position of the aperture 116 which is the emission part.
A similar effect can be obtained by using an apertured fluorescent tube to which a fluorescent substance has been applied, although not coated. Also, the aperture 116 may be transparent or opaque.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 6 is a cross-sectional view illustrating a configuration of an image reading system including the illumination device according to the present embodiment. Explaining the elements corresponding to those in FIG. 1 with the same reference numerals, the present embodiment is different from the first embodiment in that an elliptic cylindrical concave reflecting mirror 107 is used as a condensing element.

The light source section comprises a straight fluorescent tube 101 and a prism sheet 102 adhered to the peripheral surface thereof as in the first embodiment. Light emitted from the fluorescent tube 101 passes through the prism sheet 102. By doing so, the luminance in the direction perpendicular to the surface of the fluorescent tube 101 and in the direction near the surface is increased. In the present embodiment, of the light transmitted through the prism sheet 102, the light emitted from the fluorescent tube 101 in a direction perpendicular to the tube surface and in a direction near the tube surface is condensed by the elliptic cylindrical concave reflecting mirror 107. , Lighting object 1
For example, it is irradiated in a line on the surface of a letter which is 04,
This linear irradiation area is illuminated. The elliptic cylindrical concave reflecting mirror 107 is arranged such that the central axis of the fluorescent tube 101 is
4 so as to form an image on the linear irradiation area.

As described above, in this embodiment, the fluorescent tube 101
And prism sheet 102 and elliptic cylindrical concave reflecting mirror 10
7 constitutes an illumination device that illuminates the illumination target 104 in a line shape. This illumination device is provided at two places so as to illuminate the surface of the illumination target 104 from diagonally upper right and left sides in the figure, as in the first embodiment.

In this embodiment, the fluorescent tube 101 is of the full-surface light emitting type shown in FIG. 4, and a prism sheet 102 is attached to the entire peripheral surface. When the light source unit is configured in this manner, light emitted in all directions of the fluorescent tube 101 can be condensed by the elliptic cylindrical concave reflecting mirror 107 and irradiated onto the illumination target 104, so that the illumination efficiency is further improved. There are advantages to

The structure of the light source section is such that the fluorescent tube 101 is of a full-surface light emitting type as shown in FIG. 1 and is provided only on a part of its peripheral surface, that is, on the side of a linear irradiation area on the illumination object 104. The prism sheet 102 may be attached, or the fluorescent tube 101 may be provided with an aperture as shown in FIG. 5, and the light may be emitted only from the aperture 116 to improve the brightness of the emission section. A configuration in which the prism sheet 102 is attached only to the aperture portion may be adopted.

(Third Embodiment) Next, a third embodiment of the present invention will be described. FIG. 7 is a cross-sectional view illustrating a configuration of an image reading system including the illumination device according to the present embodiment. The elements corresponding to those in FIG. 6 will be described with the same reference numerals. In the present embodiment, the fluorescent tube 101 is located at a position deviated from the optical path of light toward the linear irradiation area of the illumination target 104. A different point from the second embodiment is that a fluorescent tube 101 and an elliptic column-shaped concave reflecting mirror 107 are installed in the second embodiment.

In the second embodiment, as shown in FIG. 6, since the fluorescent tube 101 is in the optical path, especially when a fluorescent tube with an aperture is used, the fluorescent tube 101 is shaded by the light shielding mask 115. As a result, the illuminance on the illumination target 104 may be reduced. On the other hand, in the present embodiment, as shown in FIG. 7, the fluorescent tube 101 is arranged at a position off the optical path to eliminate the influence of the shadow. By doing so, even when a fluorescent tube with an aperture is used as the fluorescent tube 101, a decrease in illuminance on the illumination target 104 can be avoided.

Also in this embodiment, an elliptic cylindrical reflecting mirror is used as the concave reflecting mirror 107. In this case, the fluorescent tube 101 is located at the two focal positions of the reflecting mirror 107.
And the linear irradiation region on the illumination target 104 are arranged, so that the light from the fluorescent tube 101 is efficiently condensed on the illumination region of the illumination target 104 by the reflecting mirror 107.

Although various embodiments of the present invention have been described above, the present invention is not limited to the configuration of the above-described embodiments. For example, in the above embodiment, the prism sheet 102 is arranged so that the length direction of the protrusion is parallel to the length direction of the fluorescent tube 101. It may be orthogonal to the direction.

The prism sheet is not limited to the shape shown in the figure, but transmits light having an incident angle within a specific range and diffuses light having an incident angle outside this specific range. Alternatively, any configuration may be used as long as it has optical angle selectivity for reflection.

[0046]

As described above, according to the present invention, the brightness of the light from the fluorescent tube in the specific direction is improved by the prism sheet, and only the light having the improved brightness is condensed on the object to be illuminated by the condensing element. Even when illumination is performed using the same fluorescent tube by irradiating the irradiation part in a concentrated manner,
Higher illuminance can be obtained in the linear irradiation area.

Accordingly, the required illuminance can be sufficiently obtained in an image reading system that requires high-speed reading even though an inexpensive fluorescent tube is used, and the cost is significantly reduced as compared with an illumination system using an optical fiber or the like. This makes it possible to reduce the size of the device and save energy. In addition, by slightly modifying a conventional lighting device using a fluorescent tube, it is possible to improve the illuminance of a linear irradiation area with the same power consumption.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an image reading system including a lighting device according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing an example of a configuration of a light source unit including a fluorescent tube and a prism sheet according to the present invention.

FIG. 3 is a sectional view showing a configuration of the light source unit.

FIG. 4 is a cross-sectional view showing another configuration example of a light source unit including a fluorescent tube and a prism sheet according to the present invention.

FIG. 5 is a cross-sectional view showing another configuration example of a light source unit including a fluorescent tube and a prism sheet according to the present invention.

FIG. 6 is a sectional view showing the configuration of an image reading system including a lighting device according to a second embodiment of the present invention.

FIG. 7 is a sectional view showing a configuration of an image reading system including a lighting device according to a third embodiment of the present invention.

FIG. 8 is a perspective view showing the configuration of a conventional image reading system including an illumination device using a straight tube fluorescent tube.

FIG. 9 is a perspective view showing a configuration of a conventional image reading system including a lighting device using an optical fiber bundle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Fluorescent tube 102 ... Prism sheet 103 ... Cylindrical lens 104 ... Illumination object 105 ... Imaging lens 106 ... CCD line image sensor 107 ... Reflecting mirror 111 ... Glass tube 112 ... Fluorescent substance 113 ... Filling gas 114 ... Transparent adhesive 115 … Light shield 116… Aperture

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G02B 5/08 G02B 5/08 G03B 27/54 G03B 27/54 Z H04N 1/04 101 H04N 1/04 101

Claims (9)

[Claims] 1. A fluorescent tube of a straight tube type, a prism sheet attached to at least a part of a peripheral surface of the fluorescent tube, and a light radiated from the fluorescent tube and transmitted through the prism sheet is collected. And a light-collecting element for irradiating the object to be illuminated. 2. The prism sheet according to claim 1, wherein the prism sheet has an optical angle selectivity for transmitting light having an incident angle in a specific range and diffusing or reflecting light having an incident angle outside the specific range. Item 2. The lighting device according to Item 1. 3. The prism sheet is a sheet-like optical element in which a plurality of ridges having a substantially triangular cross-sectional shape are formed on one surface along a length direction, and the other surface is formed flat. The illumination device according to claim 1, wherein the other surface is attached to a peripheral surface of the fluorescent tube. 4. A prism sheet according to claim 3, wherein said prism sheet is attached to a peripheral surface of said fluorescent tube such that said ridge is substantially parallel to a length direction of said fluorescent tube. Lighting equipment. 5. The illuminating device according to claim 1, wherein a cylindrical lens is used as the light-collecting element. 6. The lighting device according to claim 1, wherein a concave reflecting mirror is used as the light-collecting element. 7. The apparatus according to claim 1, wherein a concave reflecting mirror is used as said light-collecting element, and said fluorescent tube is installed at a position deviated from an optical path of light reflected by said reflecting mirror and directed toward an object to be illuminated. The lighting device according to any one of claims 4 to 4. 8. The lighting device according to claim 1, wherein the fluorescent tube has an aperture for emitting light only from a part in a circumferential direction. 9. An image reading system comprising: the illumination device according to claim 1; and reading means for reading an image on the illumination target.