Illumination device and image scanning device

An improved illumination device shortens a redundant area of insufficient light intensity close to a longitudinal end thereof. The device includes a casing, a bar-shaped light guide housed in the casing to cause a light-emitting surface thereof to be exposed, a light-emitting unit secured to an end section of the casing, wherein light from the light-emitting unit is introduced into the bar-shaped light guide through the end face thereof and is totally reflected within the bar-shaped light guide to be emitted through the light-emitting surface, and a shielding section provided to cover an end section of the bar-shaped light guide including the redundant area at the end section of the casing close to the light-emitting unit. A notch is formed at the end section of the bar-shaped light guide on the light-emitting surface side close to the light-emitting unit, and light from the light-emitting unit is reflected on a rear surface of the shielding section through a gap between this notch and the light-emitting unit to be introduced into the bar-shaped light guide.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority under 35 USC 119 based on Japanese patent application numbers 2004-354878, filed 08 Dec. 2004, and 2005-137732, filed 10 May 2005, the entire content of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illumination device for illuminating a document and an image scanning device (image sensor) in which the illumination device is incorporated.

2. Description of the Prior Art

A facsimile machine, a copying machine, a scanning device and the like are provided with an illumination device in which a bar-shaped light guide for irradiating a line-shaped light on a document is incorporated, and with an image scanning device provided with a lens array for causing the reflected light beams from the document to focus onto a line image sensor.

As shown in Patent Document 1 andFIG. 12, the illumination device is generally constructed in such a manner that the bar-shaped light guide101is fitted into a casing100with a C-shaped cross-section, and light from a light-emitting unit102secured to an end section of the casing is introduced into the bar-shaped light guide through the end face thereof and is caused to be totally reflected within the bar-shaped light guide and emitted from a light-emitting surface of the light guide

Referring to Patent Document 1, as shown inFIG. 13, a bottom section of the bar-shaped light guide101is provided with a scattering pattern103coated with a white paint and the like and each light-emitting element102a,102band102cof three primary colors of the light-emitting unit102is disposed by offsetting relative to a normal line from this bottom surface.

As a structure to prevent the bar-shaped light guide from dropping out from the casing, FIG. 4 of Patent Document 2 discloses that an engaging section is provided at an end section of the casing close to the light-emitting unit. Patent Document 3 also discloses a structure whereby a casing is divided in two parts in the longitudinal direction to prevent a gap from being formed between the end section of the casing and the light-emitting unit under the influence of heat.

In the case where the light-emitting elements of three primary colors are offset relative to the normal line from the bottom surface of the bar-shaped light guide as in Patent Document 1, the shape of the bar-shaped light guide becomes flat and as a result, the shape of the illumination device is also affected by the shape of light guide.

On the other hand, when each light-emitting element of three primary colors is disposed along the normal line from the bottom surface of the bar-shaped light guide, there are problems as described inFIGS. 14 and 15.

FIGS. 14(a) through (c) are views describing the condition in which light from a blue-color light-emitting element102a,a red-color light-emitting element102b,and a green-color light-emitting element102care incident on the bar-shaped light guide101, wherein light from each light-emitting element has light distribution characteristics of 180 degrees just before entering the bar-shaped light guide. However, when light is incident on a light guide made of acrylic, a radiation angle of the light from each light-emitting element has a spread of 84 degrees by Snell's law.

FIG. 15is a graph showing the relationship between displacement and light intensity of each light-emitting element in the main scanning direction (in the longitudinal direction of the light guide). As described above, since the radiation angle of light from each light-emitting element within the bar-shaped light guide101is equal (about 84 degrees), the light intensity of the blue-color light-emitting element102awhich is far from the bottom surface of the bar-shaped light guide101does not go over 80% unless a distance more than 5 mm is kept from the incident end face of the bar-shaped light guide101. Thus, when even one color has insufficient light intensity, that section becomes a redundant area which cannot be used as a light source.

In the conventional technology, the redundant area is long and the length of a section useless as the illumination device is great. Those problems can not be solved by the structures disclosed in Patent Documents 2 and 3.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an improved illumination device which has a short redundant area, and an improved image scanning device in which such an improved illumination device is incorporated.

To solve the problems described above, an illumination device according to a first aspect of the invention is provided, which comprises a casing, a bar-shaped light guide housed in the casing to cause a light-emitting surface thereof to be exposed, a light-emitting unit secured to an end section of the casing, wherein light from the light-emitting unit is introduced into the bar-shaped light guide through the end face thereof and is totally reflected within the bar-shaped light guide to be emitted through the light-emitting surface, and a shielding section is provided to cover an end section of the bar-shaped light guide at the end section of the casing close to the light-emitting unit and on the light-emitting surface side of the bar-shaped light guide, a notch is formed at the end section of the bar-shaped light guide on the light-emitting surface side close to the light-emitting unit, and light from the light-emitting unit is reflected on a rear surface of the shielding section through a gap between this notch and the light-emitting unit to be introduced into the bar-shaped light guide.

An illumination device according to a second aspect of the invention is provided, which comprises a casing, a bar-shaped light guide housed in the casing to cause a light-emitting surface thereof to be exposed, a light-emitting unit including multiple light-emitting elements and secured to an end section of the casing, wherein light from the light-emitting unit is introduced into the bar-shaped light guide through the end face thereof and is totally reflected within the bar-shaped light guide to be emitted through the light-emitting surface, and the end face of the bar-shaped light guide facing the light-emitting unit is provided with a section to enlarge the incident angle when light from at least one said light-emitting element is incident on the bar-shaped light guide at a location facing at least the light-emitting element which is furthest from a bottom surface of the bar-shaped light guide.

The illumination device according to the present invention is especially effective when each light-emitting element of three primary colors included with the light-emitting unit is disposed in the direction of a normal line from the center line of the bottom surface in the width direction of the bar-shaped light guide.

Available as the section to enlarge the incident angle when light from the light-emitting element specified by the illumination device according to claim2is incident on the bar-shaped light guide is at least one of semispherical concave surface, a halved cylindrical concave surface, a semispherical convex surface, a halved cylindrical convex surface, a saw-tooth concave surface, a saw-tooth convex surface, a rough surface or the like.

An image scanning device according to the present invention comprises the illumination device described above, and an erecting unit magnification imaging system (lens array) to cause the reflected light beams from a document of the light emitted from this illumination device to focus onto a line image sensor.

The image scanning device may be such that the erecting unit magnification imaging system has a focal depth of 1 mm or more and the illumination irregularity of the illumination device in the focal depth range is within ±20%. In this case, the focal depth range means a range on the light axis in which a modulation degree (m) when a black-and-white periodic pattern of a spatial frequency 61 p (line pair)/mm is given the erecting unit magnification imaging is 10% or more.

The black-and-white periodic pattern of 61 p (line pair)/mm is selected here as the spatial frequency (i.e., quantity to show fineness of a periodic structure forming an image) because this scale is generally used to measure the modulation degree.

The modulation degree is an index to show the depth of modulation. If the maximum value of the light intensity subject to modulation is I max and the minimum value thereof is I min, (m)=(I max−I min)/(I max+I min). In the present invention, the range on the light axis in which the modulation degree becomes 10% or more is set as the focal depth range because this is a limit value which a human being can clearly judge. If the modulation degree is less than 10%, we can not judge clearly.

In claim6, the erecting unit magnification imaging system is set to provide a focal depth of 1 mm or more. It is necessary to provide the focal depth of 1 mm or more to scan the image correctly even though there are wrinkles or fold lines on the document. To scan even a back margin of a book without any problem, it is desirable that the focal depth be 1.6 mm or more.

It is also desirable that the illumination irregularity be as small as possible in the focal depth range. In the present invention, the illumination irregularity is set to be within ±20% because electric correction can not be made if the illumination irregularity is beyond 20%.

As an erecting unit magnification imaging system which can easily exhibit the characteristics described above, a structure whereby a plurality of lens plates is superposed and each lens plate is regularly provided with a number of minute lenses at a given pitch in a two-dimensional manner can be considered, but it is not limited to this structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.FIG. 1is a cross-sectional view of an image scanning device in which an illumination device according to the present invention is incorporated.FIG. 2is a perspective view showing a substantial part of the illumination device andFIG. 3is an exploded perspective view showing the substantial part of the illumination device.

An image scanning device comprises a frame1provided with a concave section1aand a concave section1b,a transparent top plate2adapted to cover the upper surface of the concave section1aand to mount a document thereon, a bar-shaped light guide3housed in a casing4to form a line illuminating device5which is obliquely secured within the concave section1a,a substrate8situated within the concave section1band provided with a line image sensor (photoelectric transfer element)6and a drive circuit7, and a lens array9for 1:1 imaging held within the frame1.

With this arrangement, the document mounted on the top plate2is irradiated by light emitted from a light-emitting surface of the line illuminating device5and the reflected light is caused to be incident on the image sensor6arranged in a line shape by the lens array9.

The casing4of the line illuminating device5is formed in a U-shape in its cross-section and the bar-shape light guide3is fitted into the opening of the casing4to allow the light-emitting surface3ato be exposed. A light-emitting unit10is fixed to one end of the casing4. A blue-color element10a,a red-color element10b,and a green-color element10care secured to the light-emitting unit10at regular intervals along a normal line from the center line of a bottom surface3bin the width direction of the bar-shaped light guide3.

The bar-shaped light guide3is formed from a transparent resin such as acrylic. One end face of the bar-shaped light guide3is situated to face the light-emitting unit10and the bottom surface3bthereof is provided with a scattering pattern11for allowing the light incident from the end face to reflect diffusely. The scattering pattern11is provided by applying a white paint or forming an irregularity (concavity and convexity).

A notch12is formed at an end section of the bar-shaped light guide3on the light-emitting surface3aside close to the light-emitting unit10. With this notch12, a gap13is formed between the light-emitting unit10and the end face of the bar-shaped light guide3. Referring to the notch12, any shape will do as far as the gap13is formed. For example, by providing a shorter light guide3than a normal light guide, a gap can also be formed between the light-emitting unit10and the end section of the light guide.

Further, a shielding section14is provided to cover the notch12. This shielding section14is integrally formed with the casing4, but can be formed integrally with or separately from the light-emitting unit10. It is desirable that the shielding section14be made of material with high reflectance. It is also desirable that at least a section of the shielding section14reflecting the light emitted from the light-emitting unit10have higher reflectance. For example, metal or white resin with high reflectance can be used as the shielding section14.

As shown inFIG. 4(a), the light emitted from a blue-color element10a,which is furthest from the bottom surface3bof the bar-shaped light guide3, of the light-emitting elements of the light-emitting unit10and entering the light guide directly from the end face of the light guide3as in the past has a long redundant area. However, as shown inFIG. 4(b), the light emitted from the blue-color element10aand passing through the gap13is reflected on a rear surface of the shielding section14to enter the light guide3from the surface of the notch12. Since the reflected light from this shielding section14become almost perpendicular, the redundant area becomes quite short.

Since the light from the blue-color element10ais combined with the light of the red-color element10(b) and the green-color element10(c) also shown inFIGS. 4(a) and (b), the redundant area becomes shorter as a whole.

FIG. 5is a graph showing the relationship between displacement and light intensity of each light-emitting element in the main scanning direction of the illumination device according to the present invention. As is obvious from a comparison betweenFIG. 5andFIG. 15, the light intensity of the blue-color element10aat a place close to the gap13rises sharply at a location close to the end face of the light guide and is almost at the same level as the light intensity of the remaining red-color element10band green-color element10c.Accordingly, the length of the redundant area is reduced to almost half of the conventional length.

FIG. 6is a view similar toFIG. 4showing another embodiment. In the embodiment described above, the notch12is linearly formed, but in this embodiment, the notch12is formed in a curve. By making the notch12linear, it is possible to keep the balance of each color as described above, but it is possible to control the directional characteristics of each color by making the notch12curved.

FIG. 7is a view similar toFIG. 4showing still another embodiment andFIG. 8is a perspective view showing an end face of a light guide of the embodiment shown inFIG. 7. In this embodiment, the notch is not formed, but the end face of the bar-shaped light guide3is formed flat. A semispherical concave surface15ais formed, as a part to enlarge the incident angle of the light incident on the bar-shaped light guide, on the surface of the end face facing the blue-color element10a. Referring to the scattering pattern11, a halved cylindrical concave surface is formed on the bottom surface3bin this embodiment.

By forming this semispherical concave surface15a,part of the light from the blue-color element10ais refracted outwards to expand when entering the bar-shaped light guide3through the semispherical concave surface15a.The light entering the light guide directly from the end face of the light guide3not through the semispherical concave surface15ahas a long redundant area, but the incident light through the semispherical concave surface becomes almost perpendicular and as a result, these light beams are combined to make the redundant area extremely short.

FIG. 9is a graph showing the relationship between displacement and light intensity of each light-emitting element, in the main scanning direction, of the illumination device according to the embodiment as shown inFIG. 6. According to this graph, the illumination device according to this embodiment also has a redundant area of which the length is almost half of the conventional length as in the previous embodiment.

FIG. 7is a view similar toFIG. 4showing still another embodiment.FIG. 8is a perspective view showing an end face of a light guide showing yet another embodiment, similar to the embodiment shown inFIG. 7. In these embodiments, the notch is not formed, but the end face of the bar-shaped light guide3is formed flat. A semispherical concave surface15ais formed, as a part to enlarge the incident angle of the light incident on the bar-shaped light guide, on the surface of the end face facing the blue-color element10a. Referring to the scattering pattern11, a halved cylindrical concave surface is formed on the bottom surface3bin the embodiment ofFIG. 7. The embodiment ofFIG. 8includes a plurality of halved cylindrical concave surfaces11bdisposed along the bottom surface3bof the light guide3that act as light scattering devices, in a similar manner to the painted light-scattering pattern11of the embodiment shown inFIG. 3. This arrangement of halved cylindrical concave surfaces11bdisposed on the bottom surface3bof the light guide3is also shown inFIGS. 10 and 11.

In the embodiment as shown inFIG. 11(a), halved cylindrical concave surfaces15dand15eare formed as sections to enlarge the incident angle of light incident on the bar-shaped light guide. A semispherical convex surface, a halved cylindrical convex surface or rough surface can also be formed in place of the semispherical concave surface or the halved cylindrical concave surface as shown in the figure.

In an embodiment as shown inFIG. 11(b), saw-tooth concave surfaces15f,15gand15hare formed as a part to enlarge the incident angle of light incident on the bar-shaped light guide. In an embodiment as shown inFIG. 11(c), concave surfaces15fand15gprovided with continuous minute saw-tooth concave surfaces are formed. A saw-tooth convex surface can also be used in place of the saw-tooth concave surface.

EFFECTS OF THE INVENTION

According to the present invention, a redundant area of an illumination device in which a bar-shaped light guide is incorporated can be shortened. In this manner, even though the length of the illumination device is shortened, it is possible to obtain the light intensity equivalent to the conventional device. Since the interference with another device becomes less, it is advantageous in terms of design.

INDUSTRIAL APPLICABILITY

An illumination device and an image scanning device according to the present invention can be incorporated and effectively used in a copying machine, a facsimile machine, and the like.

Although there have been described what are the present exemplary embodiments of the invention, it will be understood that variations and modifications may be made thereto within the spirit and scope of the appended claims.