Linear illumination device

Abstract: A linear illumination device of the present invention includes: a guide made of a light transmitting material extending in a first direction, having a side face and at least one end face; at least one light emitter for allowing light to enter interior of the guide from the at least one end face of the guide; and a light diffusing section formed on part of the side face of the guide, for diffusing the light incident thereon, wherein at least part of the light entering the interior of the guide goes out from part of the side face of the guide facing the light diffusing section, thereby providing substantially linear illumination light along the first direction.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention: The present invention relates to a linear illumination device for illuminating a surface of a document in an optical image reading apparatus such as a direct contact type image sensor unit. 2. Description of the Related Art: Optical image reading apparatuses have been widely used in apparatuses such as a compact facsimile machine or a bar cord reader which optically read a document. Such an optical image reading apparatus illuminates the document, receives the light reflected by the document, and then obtains electric signals corresponding to an image on the document in accordance with the amount of the reflected light. As an illumination device of the apparatus of this kind, an LED array constituted by LED chips arranged in a line is used. With reference to the drawings, an example of the conventional linear illumination device used as the optical image reading apparatus will be described. Figure 19 shows the configuration of a conventional optical image reading apparatus. In Figure 19 , a document 141 is placed below the optical image reading apparatus. The optical image reading apparatus includes: an LED array as a linear illumination device 142 for illuminating the document 141; a rod lens array 143 for focusing light beams reflected by the document 141; and a photoelectric conversion element array 144 for receiving the focused light beams so as to convert the light beams into electric signals. As shown in Figure 20 , the LED array is constituted by arranging a plurality of LED chips 152 in a linear manner on a substrate 151 on which a circuit conductor layer is formed. The operations of the optical image reading apparatus and the linear illumination device having the above configurations will be described below. First, light beams emitted from the LED array 142 are radiated onto the document 141 to be read. The light beams reflected from the document 141 are focused by the rod lens array 143, and then are directed to the photoelectric conversion element array 144 so as to convert the light beams into electric signals corresponding to an image on the document 141 . In general, the document 141 is optically read while the optical image reading apparatus is scanning the document 141. In the case of using the LED array 142 as the illumination device, a direction along which the document 141 is scanned (hereinafter, simply referred to as a sub-scanning direction) is perpendicular to a direction in which the LED chips are arranged. In order to accurately read the document 141, the optical image reading apparatus requires that the illumination device illuminates a portion of the document 141 with a narrow width in the sub-scanning direction. In addition, illumination is required to be uniform in a direction perpendicularto the sub-scanning direction (hereinafter, referred to as a main scanning direction). In the case of using the LED array 142, however, it is difficult to illuminate the document 141 uniformly in the main scanning direction due to variation in the amount of light emitted from each of the LED chips 152 and effects of the directionality thereof. In order to reduce the adverse effect of the directionality of the LED chips 152, the number of the LED chips 152 needs to be increased. Alternatively, when the distance between the surface of the document 141 and the LED array 142 is made larger, the effects of the directionality of the LED chips 152 can be reduced. For example, in the case where an array of 24 LED chips is used as the illumination device, the distance between the document and the LED array should be setto be 9-10 mm in orderto illuminate an A4 sized document with a satisfactory uniform light. If illumination is not uniform in the main scanning direction, the electric signals obtained in accordance with the amount of light received by the photoelectric conversion element array 144 are also poor in uniformity (PRNU). The poor uniformity of the electric signals increases the production cost of the optical image reading apparatus in the case where the obtained electric signals are subjected to a signal correction processing (for example, shading correction). In addition, the electric signals with poor uniformity burden the signal correction processing ability. On the other hand, in the case where the signal correction processing is not performed, for example, when a uniformly gray document is read by the optical image reading apparatus, a brightly illuminated part may be displayed as white. Likewise, an insufficiently illuminated dark part may be displayed as black. Figures 22A and 22B show cross-sectional views of a direct contact type image sensor unit using the above-mentioned conventional illumination device. A document 64 is placed so as to be in close contact with one end of an optical fiber array 63 and is irradiated with light from an LED array 65 placed above. The reflected light which carries information of the document is directed toward a light receiving array 62 which is provided on the other end of the optical fiber array 63 so as to be converted into image signals. In the image sensor unit as described above, however, illuminance on the surface of the document greatly varies since the LED array 65 is used as the illumination device. Therefore, since senstivity of the sensor varies greatly, image reading performance is deteriorated. Moreover, since it is necessary to space the document 64 from the LED array 65 as described above, the unit itself becomes large. Therefore, a larger number of LED chips are required, thereby raising the cost of the unit. Moreover, when the LED array 65 is brought closer to the surface of the document 64 in order to increase an S/N ratio, PRNU of the electric signals are further deteriorated due to the adverse effect of the directionality of each of the LED chips. Next, another example of a conventional optical image reading apparatus will be described with reference to Figure 21 . Figure 21 shows the configuration of another conventional optical color image reading apparatus. In Figure 30 , three fluorescent lamps 142R, 142G and 142B are used as an illumination device. The three fluorescent lamps 142R, 142G and 142B are respectively for red light, green light and blue light (hereinafter, respectively referred to simply as R, G and B). The fluorescent lamps 142R, 142G and 142B are each fit separately in a time divided manner. A colored light beam emitted from one of the respective fluorescent lamps is reflected by a document 141 so as to be focused onto a photoelectric conversion element array 144 by a rod lens array 143. The photoelectric conversion element array 144 receives the focused light beam to convert it into an electric signal. The operation is successively repeated for R, G and B, thereby allowing the color of fhe document 141 to be analyzed. In this configuration, the document 141 can be illuminated uniformly in the main scanning direction. However, the three fluorescent lamps 142R , 142G and 142B respectively corresponding to R, G and B are required, making it difficult to realize low cost and reduction in size of the optical color image reading apparatus. From EP 0 663 756 A2 and from EP 0 607 930 A2 linear illumination devices in accordance with the preamble of claim 1 are known. Linear illumination devices of this kind, however, do not have a sufficiently linear illumination distribution. From JP-A-6-21940 and JP-A-7-14414 linear illumination devices according to the preamble of claim 1 are known. It is the object of the present invention to provide a linear illumination device and a direct contact type image sensor overcoming the disadvantages of the prior art, in particular providing a more linear illumination distribution. This object is achieved by a linear illumination device and a sensor in accordance with claims 1 and 45, respectively. The sub-claims define advantageous embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view showing a linear illumination device according to Example 1. Figure 2 is a light emitting distribution (directionality) of the light emitters according to Example 1. Figure 3 is a two-dimensional view showing the behavior of light beams entering the interior of a guide according to Example 1. Figures 4A through 4E are plan views respectively showing examples of the shape of a light diffusing section according to Example 1, and Figure 4F is a cross-sectional view of Figure 4E. Figure 5 shows the surface condition of the light diffusing section. Figure 6 shows the shape of an end cross-section of the guide. Figure 7 is a perspective view showing a guide of a linear illumination device according to Example 2. Figure 8A is a perspective view showing a linear illumination device according to Examples 3 of the present invention; and Figure 8B is a cross-sectional view thereof. Figures 9A to 9D are plan views respectively showing examples of the shape of the light diffusing section according to Example 3, and Figure 9E is a cross-sectional view of Figure 9D . Figure 10A is a perspective view showing a truncated cone shaped guide of a linear illumination device according to Example 4 and Figure 10B is an end cross-sectional view thereof. Figures 11A to 11F are plan views showing examples of the shape of a light diffusing layer according to Example 4. Figure 12A a perspective view showing another truncated cone shaped guide according to Example 4; and Figure 12B is an end cross-sectional view thereof. Figure 13 shows a cross-section of the guide. Figure 14 is a perspective view showing a cone shaped guide according to Example 5. Figure 15A shows a front view showing a light emitter included in a linear illumination device according to Example 6; and Figure 15B is a side view thereof. Figure 16 is a perspective view showing another configuration of a light emitter in a linear illumination device according to Example 6. Figure 17 is a perspective view showing still another configuration of a guide of a linear illumination device according to Example 6. Figures 18A to 18D are plan views respectively showing examples of the shape of the light diffusing section according to Example 6; and Figure 18E is a side view of Figure 18D . Figure 19 shows the configuration of a conventional optical image reading apparatus. Figure 20 shows the configuration of a conventional LED array serving as a linear illumination device. Figure 21 is a side view showing the configuration of a conventional optical image reading apparatus. Figures 22A and 22B are cross-sectional views showing a conventional image sensor unit. Figures 23A to 23E are cross-sectional views respectively showing linear illumination devices according to Example 7. Figure 24A is a cross-sectional view showing a modification of Example 7 of the present invention, taken along a main scanning direction; and Figure 24B is another cross-sectional view of the linear illumination device, taken along a sub-scanning direction. Figure 25A is a cross-sectional view showing another modification according to Example 7 of the present invention, taken along a main scanning direction; and Figure 25B is another cross-sectional view of the linear illumination device, taken along a sub-scanning direction. Figures 26A and 26B are cross-sectional views respectively showing modifications of Example 7. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described by way of illustrative examples. The present invention is realised in those embodiments shown in Figures 8A, 8B, 9B, 11A, 11C, 17 and 18B. Example 1 A linear illumination device according to Example 1 will be described. Figures 1 through 6 show the configuration of a cylindrical linear illumination device according to Example 1. Figure 1 is a perspective view showing a linear illumination device according to Example 1. The linear illumination device includes: a guide 1; a light diffusing section 2; and light emitters 3. As shown in Figure 1, the guide 1 includes end faces 4a and 4b and a light emitting face 5. Figure 2 shows a light emitting distribution (directionality) of the light emitters 3. Figure 3 two-dimensionally shows the behavior of light beams entering the interior of the guide 1. Figure 4A through 4E show examples of the shape of the light diffusing section 2 formed on the surface of the guide 1. Figure 5 shows the surface condition of the light diffusing section 2 formed on the surface of the guide 1. Figure 6 shows the shape of a cross-section of the guide 1. Throughout the above-mentioned drawings, the same components are denoted by the same reference numerals. The operation of the linear illumination device having the above configuration will be described with reference to Figures 1 to 6. In Example 1, a cylindrical linear illumination device is shown as an example of a pillar shaped linear illumination device for convenience. The guide 1 is made, by injection molding or extrusion, of a material having a light transmittance of 80% or higher (according to ASTM measurement method D1003) and a refractive index in the range of 1.4 to 1.7. As such a material, for example, a resin such as acrylic resin, polycarbonate resin, polystyrene resin or polyvinyl chloride or a light transmitting material such as glass can be used. The light diffusing section 2 is formed on part of a cylindrical side face of the guide 1. Since the surface of the guide 1 except the light diffusing section 2 should be smooth, if necessary, a process such as polishing is conducted for the surface of the guide 1 except the light diffusing section 2. Alternatively, the light diffusing section 2 can be fabricated by forming a groove on part of the side face of the guide 1 and then providing a light diffusing layer on the groove. The light emitters 3, each of which includes a light emitting element such as light emitting diodes, are attached to and in contact with the end faces 4a and 4b. The light emitters 3 have a light emitting angle distribution (directionality), for example, in the range of 30 to 150 degrees as shown in Figure 2. When the light emitters 3 are lit, light beams emitted from the light emitters 3 pass through the end faces 4a and 4b so as to enter the interior of the guide 1 . Inside the guide 1, the light beams behave as shown in Figure 3, in accordance with the Snell's law expressed by the following Formula 1. [Formula 1] sin i sin n = n r n i i: Angle between light beams 31 travelling into air from the interior of the guide and the normal of the surface of the guide r: Refractive angle when the light beams 31 are emitted into air n r : Refractive index of air (i.e., 1) n i : Refractive index of guide (1.4 to 1.7) More particularly, light beams, which are incident on the side face of the guide 1 at angles smaller than a critical angle (i 0 = sin -1 (1/n j )), are refracted by the side face of the guide 1 so as to pass into air, as shown as 31 in Figure 3. On the other hand, light beams which are incident on the side face of the guide 1 at angles equal to or larger than the critical angle are totally reflected by the side face of the guide 1. This is shown as 32 in Figure 3 as light beams travelling through the interior of the guide 1 while being repeatedly totally reflected by the side surface thereof. When part of the light beams 32 are incident on the light diffusing section 2, that part of the light beams 32 is diffused instead of totally reflected. The diffused light beams also behave in accordance with the Snell's law at the surface of the guide 1 which is a next destination of the light beams. Part of the diffused light beams, the incident angle of which with respect to the side face of the guide 1 is smaller than the critical angle, goes out into air so as to serve as illumination light beams 34. On the other hand, the remaining part of the light beams, the incident angle of which with respect to the side face of the guide 1 is equal to or larger than the critical angle, are totally reflected as shown as 33 in Figure 3. The same phenomenon as described above occurs in a longitudinal direction of the guide 1 depending on whether a next destination of the light beam is the light diffusing section 2 or the side face of the guide 1 excluding the light diffusing section 2. Moreover, the same phenomenon repeatedly occurs in the cross-sectional direction of the guide 1 . Although the cylindrical guide 1 as shown in Figure 1 is described as an example, the guide 1 can have other shapes such as a polygonal pillar shape. Furthermore, although the light diffusing section 2 is formed on the surface of the side face of the guide 1 as one continuous part so as to have a constant width, a width or an area of the light diffusing section 2 can be varied as moving from both ends of the guide 1 toward the central portion thereof in order to obtain uniform illumination light beams. Figures 4A through 4E show examples of other possible shapes of the light diffusing section 2. Figure 4A shows the light diffusing section 2 having a gradually increasing width as moving from both end faces 4a and 4b toward the central portion, which is formed as one continuous part. Figure 4B shows the light diffusing sections 2 having a constant width formed on the side face of the guide 1 at constant intervals. Figure 4C shows the light diffusing sections 2 formed at constant intervals, which has a gradually increasing width as moving from both end faces 4a and 4b of the guide 1 toward the central portion. Figure 4D shows the light diffusing sections 2 having a constant width formed at gradually decreasing intervals as moving from both end faces 4a and 4b of the guide 1 toward the central portion. Figure 4E shows the light diffusing section 2 formed on the side face of the guide 1 in the case where a total reflection layer 41 is formed on the side face of the guide 1 except the light outgoing face 5 and the end faces 4a and 4b being in contact with the light emitters 3. As the total reflection layer 41, a thin film made of metal such as palladium, iron, chromium, aluminum, silver or nickel or alloy thereof is used. Alternatively, the total reflection layer 41 is formed by processing ink containing these alloy fragments or alloy particles by vapor-deposition, sputtering, transferring, plating, painting, printing or the like. The surface of the light diffusing section 2 formed on the surface of the guide 1 may be roughene. In this case, it is preferred that the surface condition of the light diffusing section 2 is such that center line average roughness Ra is in the range of (100 to 0.013)a and the maximum height Rmax is in the range of (400 to 0.05)S in terms of surface roughness indicated in JIS standard B0601. Alternatively, the cross-section of the light diffusing section 2 may have a triangular wave shape (or a sawtooth surface) having a pitch in the range of 50 µm to 2000 µm and a height at the peak in the range of 20 µm to 800 µm, as shown in Figure 5. In either case, a light utilization efficiency can be enhanced as compared with the case where the light diffusing section 2 is not roughened or formed to have a triangular wave or a sawtooth shape. By roughening the surface of the light diffusing section 2 or forming the light diffusing section 2 to have a triangular wave or sawtooth shape, an incident angle of the light beams which are previously totally reflected by opposing side face of the guide 1 can be changed from the previous incident angle. This prevents the light beams which are once totally reflected at the side face of the guide 1 from remaining in the guide 1 while being repeatedly reflected, and therefore improves the light utilization efficiency. Accordingly, the illumination efficiency can also be improved. Alternatively, in the case where the guide 1 has a cylindrical shape as described in Example 1, two plane portions can be formed on the light outgoing face 5 of the guide 1 so that an angle formed by the two planes is 90 degree as shown in the cross-sectional view of Figure 6 . As described above, according to Example 1, the linear illumination device includes the guide made of a light transmitting material and the light diffusing section formed on the side face of the guide. The light emitters are arranged to be in contact with both end faces of the guide so that light beams emitted by the light emitters enter the guide from both end faces. Then, the light beams travel through the interior of the guide while being totally reflected by the side face of the guide. On the surface of the guide is formed the light diffusing section for diffusing the light beams incident thereon to pass into air. The light diffusion section is arranged along a longitudinal direction of the guide i.e., the main scanning direction. As a result, the guide emits light uniformly in the main scanning direction. Example 2 A linear illumination device according to Example 2 will be described. Figure 7 is a perspective view showing a guide of a linear illumination device according to Example 2. In Figure 7, components denoted by the same reference numerals as those in Figure 1 refer to the same components. However, the linear illumination device shown in Figure 7 differs from that shown in Figure 1 in that a light diffusing layer 71 is provided instead of the light diffusing section 2 . The light diffusing layer 71 is formed of a light diffusing material having a larger refractive index than that of the guide 1 and a light transmitting resin having approximately the same refractive index as that of the guide 1, on the part of the surface of the guide 1 by printing, coating using a roll coater, painting or the like. For example, titanium oxide, zinc oxide, magnesium oxide, calcium carbonate or silica is used as the light diffusing material, and silicon resin is used as the light transmitting resin. Alternatively, the light diffusing layer 71 can be fabricated in the same manner as that of the light diffusing section 2 shown in Figures 4A through 4F. Alternatively, the light diffusing layer 71 can be formed on the entire surface or part of the light diffusing section 2. In this case, light beams are more effectively diffused as compared with the case where the surface of the guide 1 on which the light diffusing layer 71 is formed (the interface between the light diffusing layer 71 and the guide 1 ) is smooth. Therefore, illumination efficiency of the linear illumination device is improved by 20% or more. Example 3 In Examples 1 and 2, a large part of light beams emitted from the light emitters 3 entering the interior of the guide 1 from one end face disadvantageously goes out from the opposite end face without being incident on the side face of the guide 1. Therefore, only part of the light beams emitted from the light emitters 3 serves as the illumination light beams 34. In other words, the light beams emitted from the light emitters 3 are not fully utilized, and therefore it is difficult to realize illumination in which the amount of illumination light is sufficient. Hereinafter, a linear illumination device which can provide a sufficient amount of light as illumination light will be described as a device according to Example 3. Figures 8A and 8B are a perspective view and a cross-sectional view showing a linear illumination device according to Example 3 of the present invention, respectively. The linear illumination device in Example 3 differs from that in Example 1 in that the linear illumination device has a V-shaped cut face 81. In Figures 8A and 8B , the other same components as those in Figure 1 are denoted by the same reference numerals as those in Figure 1. Although the light emitters 3 are arranged to be in contact with the end faces 4a and 4b of the guide 1 as shown in Figure 1, the light emitters 3 are omitted in Figures 8A and 8B for simplicity. The V-shaped cut face 81 is formed by cutting the cylindrical side face of the guide 1 so that both a width and a depth of the cut face gradually increases as approaching the central portion of the guide 1 from the end faces 4a and 4b and becomes maximum in the central portion. The operation of the linear illumination device having the above configuration will be described below. When the light emitters 3 are lit, light beams emitted by the light emitters 3 enter the interior of the guide 1 from the end faces 4a and 4b. Then, the light beams, which are incident on the side face of the guide 1, behave in the same manner as that of the linear illumination device described in Example 1 so as to serve as illumination light beams 34. A large part of the light beams which are not incident on the side face of the guide 1 is incident on the V-shaped cut face 81 formed on the side face of the guide 1. On the entire surface or part of the surface of the V-shaped cut face 81 is formed the light diffusing section 2. Therefore, the light beams incident on the V-shaped cut face 81 are also diffused so that part of them go out of the guide 1 as the illumination light beams 34. In this way, in Example 3, the light beams emitted by the light emitters 3 can be used for illumination more effectively than in Examples 1 and 2. In Example 3, the light diffusing section 2 is formed on the entire side face of the V-shaped cut face 81 as one continuous part. In order to obtain illumination light beams whose amount is uniform in main scanning direction, a width or an area of the light diffusing section 2 formed on the side face of the V-shaped cut face 81 can be varied as approaching the central portion between both end faces 4a and 4b of the guide 1 . Other possible shapes of the light diffusing section 2 are shown in Figures 9A through 9D. Figure 9A shows the light diffusing sections 2 having a constant width formed on the side face of the V-shaped cut face 81 at constant intervals. Figure 9B shows the light diffusing sections 2 having a gradually increasing width as approaching the central portion between both end faces 4a and 4b of the guide 1, which is formed at constant intervals. Figure 9C shows the light diffusing sections 2 having a constant width at gradually decreasing intervals as approaching the central portion from both end faces 4a and 4b. Figure 9D shows the light diffusing section 2 in the case where a total reflection layer 91 is formed on the surface of the guide 1 except the light diffusing section 2, the light outgoing face 5 and the end faces 4a and 4b . Furthermore, it is possible to replace the light diffusing section 2 shown in Figures 9A through 9D by the light diffusing layer 71, as in Example 2. Alternatively, the light diffusing layer 71 can be formed on the entire surface or part of the light diffusing section 2 formed on the entire side face or part of the V-shaped cut face 81 . As the total reflection layer 91, the thin film made of metal such as palladium, iron, chromium, aluminum, silver or nickel or alloy thereof is used. Alternatively, the total reflection layer 41 can be formed by processing ink containing these alloy fragments or alloy particles by vapor-deposition, sputtering, transferring, plating, painting, printing or the like. It is preferred that the surface condition of the light diffusing section 2 formed on the side face of the V-shaped cut face 81 is such that center line average roughness Ra is in the range of (100 to 0.013)a and the maximum height Rmax is in the range of (400 to 0.05)S in terms of surface roughness indicated in JIS standard B0601. Alternatively, the cross-section of the light diffusing section 2 formed on the surface of the guide 1 can have a triangular wave shape (or a sawtooth surface) having a pitch in the range of 50 µm to 2000 µm and a height at the peak in the range of 20 µm to 800 µm. In either case, the illumination efficiency of the illumination device can be improved as described in Example 1. As described above, the V-shaped cut face is formed by cutting the cylindrical side face of the guide so that a width and a depth of the cut face gradually increases as moving from the light incident faces of the guide toward the central portion and becomes maximum in the central portion. With such a configuration, not only light beams which are incident on the side face of the guide, but also a large part of the light beams, which are not incident on the side face of the guide, can be allowed to be diffused by the light diffusing section and/or layer. Therefore, the light beams travelling through the interior of the guide from one end face to the opposite end face without being reflected or diffused can be decreased, increasing the illumination efficiency of the illumination device. Example 4 Hereinafter, a linear illumination device according to Example 4 will be described. Figure 10A is a perspective view showing a truncated cone shaped guide of a linear illumination device according to Example 4 of the present invention, and Figure 10B is a cross-sectional view thereof. Figure 11A through 11F show various shapes of a light diffusing layer formed on the side face of the guide. Figure 13 shows a cross-section of the guide. Throughout Figures 10A and 10B , 11A through 11F and 13, the components as those shown in the aforementioned drawings are denoted by the same reference numerals. Although the light emitters 3 are arranged to be in contact with the end faces 4a and 4b of the guide 1, the light emitters 3 are omitted in Figures 10A and 10B for simplicity. The guide in Example 4 differs from those in Examples 1 through 3 in that the guide has such a truncated cone shape that a cross-sectional area of the guide 1 gradually decreases as approaching the central portion from both ends 4a and 4b of the guide 1 and becomes minimum in the central portion with an area of 70% or less of the cross-sectional area of one of the end faces 4a and 4b. Such a truncated cone shape of the guide improves the uniformity in the main scanning direction as compared with the shapes in Examples 1 through 3. Although the truncated cone shaped guide is described by way of example for convenience, the guide can have such a polygonal truncated cone shape that a cross-sectional area gradually decreases as approaching the central portion from both end faces of the guide and becomes minimum in the central portion while keeping the cross-sectional shape similar to that of the end face. The operation of the guide of the linear illumination device having the above configuration will be described. When the light emitters 3 are lit, light beams enter the interior of the guide 1 from both end faces 4a and 4b. The light beams are reflected and diffused in the same manner as in the linear illumination device described in Example 1. In addition, light beams travelling from one end face toward the opposite end face are gradually sharpened as moving toward the central portion. Therefore, the amount of illumination light beams 34 emitted from a portion in the vicinity of the central portion of the guide can be increased, thereby improving illumination efficiency and eliminating nonuniformity of illumination. As described above, the guide 1 has such a truncated cone shape that a cross-sectional gradually decreases as approaching the central portion between both end faces and becomes minimum in the central portion. The guide 1 includes the light diffusing section 2 formed on the side face of the guide 1 . With such shape and configuration, the amount of illumination light beams exiting the guide from a portion in the vicinity of the central portion can be increased. As a result, illumination efficiency can be improved while reducing the nonuniformity of illumination. The light diffusing section 2 having a constant width is formed on part of the side face of the guide 1 as one continuous part in Figure 10A. in orderto obtain illumination light beams whose amount is uniform in the main scanning direction (in the longitudinal direction), however, a width or an area of the light diffusing section 2 can be varied from both end faces toward the central portion of the guide 1 . Figures 11A through 11B show other possible shapes of the light diffusing section 2 . Figure 11A shows the light diffusing section 2 having a gradually increasing width as approaching the central portion from both ends 4a and 4b of the guide 1 , which is formed as one continuous part. Figure 11B shows the light diffusing sections 2 having a constant width, which are formed at constant intervals. Figure 11C shows the light diffusing sections 2 having a gradually increasing width as approaching the central portion between both ends 4a and 4b of the guide 1, which is formed at certain intervals. Figure 11D shows the light diffusing sections 2 having a constant width, which are formed at gradually decreasing intervals as approaching the central portion from both end faces 4a and 4b of the guide 1. Figure 11E shows the light diffusing section 2 in the case where a total reflection layer 111 is formed on the side face of the guide 1 except the light diffusing section 2 , the light outgoing face 5 and the end faces 4a and 4b . Figure 11F shows the light diffusing section 2 formed so that a ratio of a diameter of a cross-section of the guide 1 to a width of the light diffusing section 2 is kept constant along the longitudinal direction of the guide 1 . Moreover, it is possible to replace the light diffusing section 2 shown in Figures 10A and 10B by the light diffusing layer 71. Furthermore, the light diffusing layer 71 can be formed on the entire side face or part thereof of the light diffusing section 2 shown in Figures 10A and 10B . In the case of Figure 11E, as the total reflection layer 111 , a thin film made of metal such as palladium, iron, chromium, aluminum, silver or nickel or alloy thereof is used. Alternatively, the total reflection layer 111 can be formed by processing ink containing these alloy fragments or alloy particles by vapor-deposition, sputtering, transferring, plating, painting, printing or the like. It is preferred that the surface condition of the light diffusing section 2 formed on the surface of the guide 1 is such that center line average roughness Ra is in the range of (100 to 0.013)a and the maximum height Rmax is in the range of (400 to 0.05)S in terms of surface roughness indicated in JIS standard B0601. Alternatively, the cross-section of the light diffusing section 2 formed on the surface of the guide 1 can have a triangular wave shape (or a sawtooth surface) having a pitch in the range of 50 µm to 2000 µm and a height at the peak in the range of 20 µm to 800 µm. In either case, the illumination efficiency of the illumination device can be increased as compared with the case where the light diffusing section 2 is not roughened or is not to be formed to have a triangular wave or a sawtooth shape, as described in Example 1. Figure 12A is a perspective view showing another truncated cone shaped guide 1, and Figure 12B is a cross-sectional view thereof. Instead the shape shown in Figure 10A , the guide 1 can have a shape as shown in Figure 12A. As shown in Figure 12A , the guide 1 has such a truncated cone shape that a cross-sectional area in the longitudinal direction decreases between both end faces 4a and 4b of the guide 1 as approaching the central portion from both end faces 4a and 4b and becomes minimum in the central portion. Moreover, by connecting points on circumferences of cross-sections in the longitudinal direction of the guide 1, a straight line which extends substantially parallel to the axis of the guide 1 is obtained. The side face of the guide 1 containing the straight line is made to face the document. A portion in the vicinity of this straight line serves as a light outgoing surface 5. The entire surface or part of other side face serves as the light diffusing section 2. A cross-sectional shape of the guide 1 can be such a shape that two planes are formed on the light outgoing face 5 of the guide 1 so as to form an angle of 90 degrees therebetween as shown in Figure 13, as long as the guide has a truncated cone shape as described in Example 4 . In order to fully utilizing the light beams which enter from one end face of the guide 1 and go out from the other end face without being reflected and diffused, it is desirable that the guide 1 is configured as a shape obtained by attaching two cones together at their summits so that the guide 1 has a straight line facing the document as the shape shown in Figure 12A , instead of a truncated cone shape. However, in view of the strength of the guide 1, it is better that the central portion of the guide 1 is thick to a certain degree. The comparative data between the linear illumination device shown in Figures 12A and 12B according to Example 4 and a conventional linear illumination device will be shown. In the linear illumination device shown in Figures 12A and 12B , a diameter of each of the end faces 4a and 4b is 5 mm, a diameter of a cross-section in the central portion is 2.7 mm, a width of the light diffusing layer 71 is 1 mm, and a depth of a groove is 0.5 mm. Example 4 Conventional Illuminance on surface of document 600 lux 600 lux Nonuniformity of illumination on surface of document ∼ 7% ∼ 15% Distance between illumination system and surface of document 1 mm 9.5 mm Number of LED chips 8 24 As described above, a linear illumination device in Examples 1 through 4 includes light emitters on end faces of a guide made of a light transmitting material. The guide has a pillar shape or a truncated cone shape. Furthermore, a V-shaped cut face or a groove is formed on at least one surface of the guide. The V-shaped cut face or a groove is treated to be a roughened face or a triangular wave shape so as to form a light diffusing section. As a result, nonuniformity of illumination in the main scanning direction on the surface of the document to be illuminated is eliminated. Therefore, the illuminance can be increased without degrading uniformity of the illumination even when the linear illumination device approaches the surface of the document in close proximity thereof. Furthermore, since the linear illumination device can approach the surface of the document in close proximity thereof, the use of the linear illumination device according to Examples 1 through 4 is used for an illumination system of the optical image reading apparatus can contribute the reduction in size of the entire apparatus. Thus, it is possible to load the linear illumination device in machines required to be compact such as a portable facsimile machine. In addition, since the number of elements of the light emitters can be reduced, reduction in cost can be realized. Example 5 With reference to Figure 14 , Example 5 of an illumination device will be described. For simplicity, the light emitter 3 is omitted in Figure 14 . Examples 1 through 4 above describe the case where light is made to enter the guide 1 provided so as to extend along the main scanning direction from both end faces thereof. On the other hand, in Example 5, light is made to enter the guide 1 from one end face. In order to make the light enter from one of the end faces so as to obtain uniform illumination light in the main scanning direction, it is contemplated that the guide 1 is formed as a cone shape as shown in Figure 14. As in Figure 14, in the case where the guide 1 has such a shape that a side face thereof contains a straight light parallel to the longitudinal direction of the guide 1 and light beams are emitted from the vicinity of the straight line, the light diffusing section 2 or the light diffusing layer 71 is provided in the position substantially facing the straight light. The light entering the guide 1 behave in the same manner as that described in Example 1 to go out from a portion 5 in the vicinity of the straight line. In the case where light is made to enter from only one end face of the guide 1 extending in the main scanning direction, the shape of the guide 1 is not limited to that shown in Figure 14. Alternatively, the guide 1 can have such a shape that the guide 1 as shown in Examples 1 through 4 above is cut in the central portion and a cut face is made to be a reflective face or a mirror face. If the light is made to enter from one of the end faces of the guide 1 as described in Example 5, a ratio of a length of the part actually capable of emitting illumination light to a length of the entire illumination device in the longitudinal direction can be increased as compared with Examples 1 through 4. This is because the part which does not contribute to illumination in the illumination device can be reduced. Moreover, since only one light emitted is sufficient in the configuration of Example 5, the number of light emitters such as LED chips can be reduced. Furthermore, the light entering from one end face of the guide 1 is sharpened as travelling toward the other face in the shape shown in Figure 14. The light incident on the other end face is reflected in another shape. Thus, the light entering from one end face and going out from the other end face without being reflected and diffused can be eliminated. Therefore, in Example 5, the light utilization efficiency of light emitted from the light emitter can be further enhanced than that in Examples 1 through 4. Example 6 A linear illumination device according to Example 6 will be described below with reference to Figures 15A to 15B . While the light emitting element emitting light in a certain wavelength band is provided in one of the light emitters 3 in Examples 1 through 5, light emitting elements 21, 22 and 23 respectively emitting light of R, G and B are provided in a single light emitter 3 as shown in Figures 15A and 15B in Example 6. Except this point, Example 6 is the same as Example 1. Therefore, the description of the configuration of the illumination device of Example 6 is emitted. The light emitting elements 21, 22 and 23 are sequentially lit in a time divided manner, thereby emitting light beams of the respective colors in a time divided manner as the illumination light beams 34 . Instead of sequentially lighting the red light emitting element 21, the green light emitting element 22 and the blue light emitting element 23 included in each of the light emitters 3 in a time divided manner, the elements 21, 22 and 23 can be simultaneously lit. In this case, a color filter is provided in front of a light receiving portion (not shown) for receiving reflected light from the document so as to separate the light into respective colors. Furthermore, instead of the light emitters 3 configured to include the red light emitting element 21, the green light emitting element 22 and the blue light emitting element 23 as shown in Figure 2 , a light emitter can be independently formed for each color. In such a case, as shown in Figure 7 ; a red light emitter 71, a green light emitter 72 and a blue light emitter 73 can be brought in close contact with the guide 1 in a sequential manner by rotating a substrate 74 on which three light emitters 72, 73 and 74 are provided, thereby sequentially lighting the three light emitters. In this case, the red light emitter 71, the green light emitter 72 and the blue light emitter 73 can be LEDs respectively having their own color. As in Example 1, according to Example 6, the light diffusing section 2 is provided for the side face of the guide 1 made of a light transmitting material. Then, the light emitters 3 are arranged to be in contact with the light incident surfaces (the end faces) 4a and 4b perpendicularly crossing the axis of the guide 1 so as to sequentially light emitting elements for three colors of the light emitters 3 in a time divided manner. Therefore, for each color, there always exist a group of numberless light beams which are reflected by the boundary between the interior of the guide 1 and air so as to travel through the interior of the guide 1 and another group of numberless light beams diffused by the light diffusing section 2 so as to pass into air. Consequently, light beams free from nonuniformity of illumination are radiated from the light outgoing face 5 of the guide 1 in a time divided manner. As a result, a color document placed on the optical color image reading apparatus is uniformly illuminated for each color. Furthermore, by modifying Example 6, the light diffusing layer 81 can be provided as in Example 2. With this configuration, in the case where the three light emitting elements 21, 22 and 23 are provided in each light emitter 3 as shown in Figures 15A and 15B , and in the case where the light emitter is independently provided for each color as shown in Figure 16, light having each color can be efficiently diffused. As a result, an illumination efficiency of the linear illumination device can be improved by 20 % or more. Next, a further modification of an illumination device of the present Example 6 will be described. In this modification, as in Example 3, a V-shaped cut face 121 is formed on the side face of the guide 1 as shown in Figure 17. The V-shaped cut face 121 is formed by cutting the cylindrical side face of the guide 1 so that both a width and a depth of the cut face gradually increases as approaching the central portion of the guide 1 between the end faces 4a and 4b and becomes maximum in the central portion. The light diffusing section 2 is formed over the entire surface of the V-shaped cut face 121. The part of the side face of the guide 1 facing the V-shaped cut face 121 serve as the light outgoing face 5. Alternatively, the light diffusing section 2 can be formed into pattern as shown in any one of Figures 18A to 18C on part of the V-shaped cut face 121. Alternatively, a total reflection layer 131 can be provided on the side face of the guide 1 except the V-shaped cut face 121 and the light outgoing face 5. Furthermore, in Figures 17 and 18A through 18D, the illumination device of this modification similarly functions even if the light diffusing section 2 is replaced by the light diffusing layer 71 as described in Example 2. If the light diffusing layer 71 is formed on the entire surface or part of the light diffusing section 2, an illumination efficiency can be further enhanced. As a material of the total reflection layer 131, any of the materials described in the above examples as materials of the total reflection layer can be used. Also in this modification, if the surface of the light diffusing section 2 is roughened or formed into a triangular shape (a sawtooth surface) as mentioned above, an illumination efficiency can be further enhanced. Furthermore, as described in Example 4, the guide 1 can have a shape obtained by attaching two truncated cones together at their end faces having smaller diameters. With such a shape, the amount of illumination light emitted from the light outgoing surface 5 in the vicinity of the guide 1 can be increased as compared with the guide 1 merely having a V-shaped cut face is used. The reason for this is as follows. Since a cross-sectional area of the guide 1 gradually decreases as moving from the end faces 4a and 4b toward the central portion, the light beams travelling from the end faces 4a and 4b toward the central portion is gradually sharpened. As a result, the uniformity of illumination can be further increased. Also in the case where the guide 1 has such a shape, the light diffusing section 2 and/or the light diffusing layer 71 can be similarly formed. As described above, the linear illumination device of the present invention includes: the pillar shaped guide made of a light transmitting material; the light diffusing section formed on at least part of the side face of the guide; and the light emitter provided in the vicinity of both end faces approximately crossing the axis of the guide. The light emitted from the light emitter is allowed to enter the interior of the guide. Then, the light entering the guide 1 is repeatedly reflected until the light reaches the light diffusing section 2. When the light reaches the light diffusing section 2, the light is diffused by the light diffusing section 2 so as to go out from the face facing the light diffusing section 2 to the outside. The light diffusing section 2 is provided as one continuous part or is partially provided along the longitudinal direction of the guide 1. Therefore, the light going out from the guide 1 is uniform in the longitudinal direction of the guide 1, that is, in the main scanning direction. The light emitter is constituted so that red (wavelength in the range of 600 nm to 700 nm), green (wavelength in the range of 500 nm to 600 nm) and blue (wavelength in the range of 400 nm to 500 nm) are sequentially illuminated in a time divided manner. The colored light emitted from the light emitters enters the interior of the guide from the end faces, and behaves in accordance with the Snell's law. More specifically, the light beams, which are incident on the side face of the guide at angles smaller than the critical angle, pass through the side face of the guide so as to pass into air. On the other hand, the light beams, whose incident angles are out of the critical angle, do not pass through the side face of the guide while being repeatedly totally reflected at a boundary between the guide and air. If part of the light beams strikes on the light diffusing section, the part of the light beams is diffused instead of being totally reflected. The diffused light beams behave in accordance with the Snell's law at a boundary between the guide and air, which is a next destination of the diffused light beams. The diffused light beams which are incident on the next destination at angles smaller than the critical angle pass into air from the light outgoing face so as to contribute as illumination light beams. Since the similar phenomenon is repeated numberless time in all directions of cross-sections perpendicularly crossing the axis of the guide, illumination light beams going out from the light outgoing face becomes approximately uniform in the axial direction (the longitudinal direction) of the guide 1. The light beams having colors respectively corresponding to R, G and B are radiated in a time divided manner, colors of a color document can be separated on the illumination side. The guide is constituted so that a shape of a cross-section perpendicularly crossing the axis of the guide is approximately circular or polygonal and an area of the cross-section is constant. As a result, a shape of the guide is simplified so as to facilitate the production thereof. Moreover, the approximately V-shaped cut face is formed by cutting the side face of the guide in an oblique and planar manner so that a width of the cut face gradually increases as moving from the light incident faces. Then, the light diffusing section is formed on the approximately V-shaped cut face. As a result, the amount of the light entering one end face and leaking outside from the other end can be reduced so as to improve the illumination efficiency. Alternatively, the guide can have such an approximately truncated cone shape or an approximately truncated polygonal pillar shape that a shape of a cross-section perpendicularly crossing the axis is approximately circular or polygonal and an area of a cross-section gradually decreases as moving from both end faces of the guide toward the central portion so as to be minimum. Also in this case, the amount of light beams entering the interior of the guide from one end face of the guide and leaking outside from the other end face can be reduced, thereby improving the illumination efficiency. Furthermore, by connecting a point on an outer circumference of each cross-section perpendicularly crossing the axis through a line parallel to the axis of the guide, the light outgoing face of the guide becomes approximately linear, thereby forming a linear region illuminated by the illumination light. By forming two planes in the vicinity of the light outgoing face of the guide so as to form approximately 90 degree therebetween, the light outgoing face of the guide becomes planar. As a result, a region illuminated by the illumination light can be planar. Furthermore, by forming the light diffusing section having a constant width on the side face of the guide in the axis direction as one continuous part, or by forming the light diffusing sections in the axis direction at constant intervals, the formation of the light diffusing section is facilitated. Alternatively, by forming the light diffusing section so that a width increases as moving from both end faces of the guide toward the central portion, the amount of illumination light in the vicinity of the central portion of the guide 1 can be increased. As a result, the phenomenon that the amount of light generally decreases as moving away from the light emitter can be reduced. Alternatively, by forming the light diffusing sections on the side face of the guide in the axis direction at constant intervals so that a width increases as moving from both end faces of the guide toward the central portion, the amount of illumination light in the vicinity of the central portion of the guide 1 can be increased. Alternatively, the same effect can be obtained by forming the light diffusing section on the side face of the guide in the axis direction at constant intervals so that intervals decrease as moving from both end faces of the guide toward the central portion. Furthermore, by providing the total reflection layer in the region except the light diffusing section and the light outgoing faces, the light leaking outside from the region except the light diffusing section and the light outgoing faces can be eliminated so as to increase the amount of illumination light going out from the light outgoing face, thereby improving the illumination efficiency. If the light diffusing layer is provided instead of the light diffusing section, approximately uniform illumination light can be similarly emitted from the light outgoing face of the guide. By providing the light diffusing layer on the entire light diffusing section or part thereof, the amount of light which is diffused and then is refracted to pass into air, is increased. As a result, the illumination efficiency is improved. The light diffusing layer is made of a mixture of the light diffuser having a refractive index larger than that of the guide and a light transmitting resin having a refractive index approximately equal to that of the guide. Therefore, since the light diffusing layer has the approximately same properties as those of the guide, heat resistance, weather resistance and the like can be improved. By constituting the light emitter by the light emitting diode, time required to emit light beams of R, G and B in a time divided manner can be shortened. Since the linear illumination device of Example 6 and the modifications thereof has the effects as described above, nonuniformity of illumination in the main scanning direction can be reduced. Furthermore, according to Example 6 and the modifications thereof, illumination with three colors, i.e., R, G and B is made possible in one guide. Therefore, the optical color image reading apparatus which illuminates the document to be read by means of the illumination device can be reduced. Thus, it is possible to load the linear illumination device in a compact color facsimile machine or color copying machine, thereby contributing to the reduction of size of these machines. Furthermore, since the illumination system capable of emitting light beams of R, G and B in a time divided manner can be produced with a simple configuration, the cost can be lowered. Example 7 A linear illumination device according to Example 7 will be described. Figures 23A to 23E are cross-sectional views respectively showing linear Illumination devices according to Example 11. Figures 23A and 23E show cross-sections taken along a main scanning direction, and Figures 23B , 23C and 23D show cross-sections taken along a sub-scanning direction. The light incident face is configured as a triangular wave face having a predetermined angle and a predetermined pitch in Example 7. By this shape, the uniformity of the illumination light in the main scanning direction can be further improved. Also in the case where the light outgoing face is configured as a triangular wave face instead of the light incident face, the uniformity of the illumination light in the main scanning direction can be similarly improved. As shown in Figure 23A , if both light incident face and light outgoing face are configured as triangular wave faces, it is effective to improve the uniformity of the illumination light. In this case, a height at a peak of a triangular wave, an angle of a slope and a pitch of the light incident face and the light outgoing face can be either the same or different from each other. In any of the cases described above, a triangular wave face can be replaced by a face having a sawtooth cross-sectional shape. As shown in Figure 23B , the transparent plate 343 can have a barrel shape extending in the main scanning direction, and can be placed so that its curved face serves as the light outgoing face. The transparent plate 343 is provided with a lens function only in the sub-scanning direction by adopting such a shape, thereby further reducing a width in the sub-scanning direction of the light emitted from the transparent plate 343 . As shown in Figure 23C , the transparent plate 343 is configured so that a width in the sub-scanning direction becomes narrower in the direction away from the light emitting element array 342. Alternatively, as shown in Figure 23D , the transparent plate 343 is configured so that a width in the sub-scanning direction is kept constant to a certain distance from the light emitting element array 342 and then gradually decreases when exceeding the certain distance. In either case, since a width in the sub-scanning direction of the light entering the transparent plate 343 is gradually sharpened, illumination having a narrower width in the sub-scanning direction can be realized as compared with the illumination device including the transparent plate 343 having a constant width in the sub-scanning direction as in Example 10. Furthermore, as shown in Figure 23E , a refractive index of part in the transparent plate 343 can be varied by forming a plurality of cavities in the transparent plate 343. Each of the cavities can have, for example, a cylindrical shape or a triangular prism shape extending in the sub-scanning direction. In the case where the cavity has a triangular prism shape, the cavities are formed so that one side face is opposed to the light incident face of the transparent plate 343 and an edge (corresponding to one summit of a triangular cross-section) opposing the side face is closer to the light incident face than the side face. In this way, by providing the cavities having a pillar shape extending in the sub-scanning direction in the transparent plate 343, light is diffused in the transparent plate 343. Therefore, illumination light which is more uniform in the main scanning direction can be obtained. Hereinafter, two modifications of Example 7 will be described with reference to Figures 24A through 24B . In these modifications, the transparent plate 343 in Example 7 is replaced with transparent plates 343a and 343b. Each of the transparent plates 343a and 343b has substantially the same lengths as the circuit substrate 341 both in the longitudinal direction (the main scanning direction) and in the latitudinal direction (the sub-scanning direction) of the circuit substrate 341. In the direction perpendicular to the main scanning direction and the sub-scanning direction, a total length obtained by adding the length of the transparent plate 343a to the length of the transparent plate 343b, is substantially equal to a distance between the array of LED chips 342 and the document to be illuminated by the linear illumination device. In one modification, the light outgoing face of the transparent plate 343a, which is opposite to the face adjacent to the LED chips 342, is configured as a triangular wave face having a predetermined angle and a predetermined pitch as indicated with 344a in Figure 24A . Due to this shape, the uniformity of the illumination light in the main scanning direction can be further improved, as described in Example 1 with reference to Figure 5 . In the other modification, the light incident face of the transparent plate 343b, which is adjacent to the transparent plate 343a, is configured as a triangular wave face having a predetermined angle and a predetermined pitch as shown by 344b in Figure 25A . Therefore, the uniformity of the illumination light outgoing from the face opposite to the triangular wave face 344b can be also improved. Alternatively, both of the light outgoing face 344a of the transparent plate 343a and the light incident face 344b of the transparent plate 343b may be configured as triangular wave faces. In this case, a height at a peak of a triangular wave, an angle of a slope and a pitch of the light incident face and the light outgoing face can be either the same or different from each other. In any of the cases described above, a triangular wave face can be replaced by a face having a sawtooth cross-sectional shape. As shown in Figure 26A , the transparent plate 343b can have a barrel shape extending in the main scanning direction, and can be placed so that its curved face serves as the light outgoing face. The transparent plate 343b is provided with a lens function only in the sub-scanning direction by adopting such a shape, thereby further reducing a width in the sub-scanning direction of the light emitted from the transparent plate 343b. As shown in Figure 26B , both of the transparent plates 343a and 343b are configured so that a width in the sub-scanning direction becomes narrower in the direction away from the light emitting element array 342. Alternatively, the transparent plates 343a and 343b can be configured so that a width of the one transparent plate in the sub-scanning direction is kept constant while a width of the other transparent plate in the sub-scanning direction gradually decreases in the direction away from the LED chips 342. In the latter case, the light incident face of the transparent plate 343b has a narrower width than that of the light outgoing face of the transparent plate 343a. In either case, since a width in the sub-scanning direction of the light emitted by the LED chips 342 is gradually sharpened, illumination having a narrower width in the sub-scanning direction can be realized. Furthermore, also in the case where using two transparent plates for making light emitted from the LED chips 342 expand in the main scanning direction, a refractive index of part in at least one of the transparent plates 343a and 343b can be varied by forming a plurality of cavities therein. In this case, even when both of the light outgoing face of the transparent plate 343a and the light incident face of the transparent plate 343b are flat, illumination efficiency can be improved due to diffusion of light by the cavities. Each of the cavities can have, for example, a cylindrical shape or a triangular prism shape extending in the sub-scanning direction. In the case where the cavity has a triangular prism shape, the cavities are formed so that one side face is opposed to the light incident face of the transparent plate 343a and an edge (corresponding to one summit of a triangular cross-section) opposing the side face is closed to the light incidentface than the side face. In this way, by providing the cavities having a pillar shape extending in the sub-scanning direction in at least one of the transparent plates 343a and 343b, light is diffused while passing therethrough, leading to improvement of illumination efficiency and uniformity of illumination light in the main scanning direction. In addition, also in the modifications of Example 7, if concavities are formed on the substrate 341 and light diffusing elements are then attached onto the bottom faces of the concavities after the bottom faces and the peripheries of the concavities are made to be mirror faces or reflective faces, the uniformity of the illumination light in the main scanning direction as well as the illumination efficiency can be improved. Various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope of this invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be broadly construed.

Claims: A linear illumination device comprising: a guide (1) made of light transmitting material extending in a first direction, having a side face and at least one end face (4a, 4b); light emitting means (3) for allowing light to enter the interior of the guide (1) from the at least one end face (4a, 4b) of the guide (1); and a light diffusing section (2) formed on the side face of the guide (1) and extending in said first direction, for diffusing the light incident thereon, whereby at least part of the light entering the interior of the guide (1) goes out from part of the side face of the guide facing the light diffusing section (2), thereby providing substantially linear illumination light along said first direction, wherein the light diffusing section (2) is formed on said side surface of the guide (1) with a varied width crosswise to the first direction; and characterized in that the guide (1) is formed from a cylindrical shape in such a way that the light diffusing section (2) is formed so as to increase the width and depth as approaching a central portion of the guide (1) from said at least one end face. A linear illumination device according to claim 1, wherein the guide (1) has two end faces (4a, 4b) opposing each other, and the light emitting means (3) includes two light emitters for allowing the light to enter the guide (1) from the two end faces (4a, 4b). A linear illumination device according to claim 1, wherein the light diffusing section (2) includes a groove formed in said side face of the guide (1) and a light diffusing layer (71) provided on the groove. A linear illumination device according to claim 1, wherein the light diffusing section (2) has a rough surface. A linear illumination device according to claim 4, wherein the light diffusing section (2) has a center line average roughness Ra in the range of (100 to 0.013) a and the maximum convex height Rmax is in the range of (400 to 0.05)S in terms of surface roughness indicated in JIS standard B0601. A linear illumination device according to claim 1, wherein a surface of the light diffusing section (2) has a triangular wave shape or a sawtooth shape. A linear illumination device according to claim 6, wherein a surface of the light diffusing section (2) has a triangular wave shape having a pitch in the range of 50 µm to 2000 µm and a height at a peak in the range of 20 µm to 800 µm. A linear illumination device according to claim 1, wherein the light diffusing section (2) is formed on said side face of the guide (1) as one continuous part in the first direction. A linear illumination device according to claim 1, wherein a total reflection layer (111) is formed on the entire side face of the guide excluding the light diffusing section (2) and the part of said side face facing the light diffusing section. A linear illumination device according to claim 1, wherein the light diffusing section (2) comprises at least partly a diffusing layer. A linear illumination device according to claim 10, wherein the diffusing layer (2) is made of a light diffuser and a light transmitting resin. A linear illumination device according to claim 11, wherein a refractive index of the light diffuser is larger than that of the guide (1). A linear illumination device according to claim 11, wherein a refractive index of the light transmitting resin is substantially equal to that of the guide (1). A linear illumination device according to claim 11, wherein the light diffuser is TiO 2 . A linear illumination device according to claim 14, wherein the light transmitting resin is a silicon resin. A linear illumination device according to claim 1, wherein the light transmitting material has a light transmittance of 80 % or more according to ASTM measuring method D1003. A linear illumination device according to claim 1, wherein a refractive index of the light transmitting material is substantially in the range of 1.4 to 1.7. A linear illumination device according to claim 1, wherein the light transmitting material is an acrylic material. A linear illumination device according to claim 1, wherein the light transmitting material is a polycarbonate. A linear illumination device according to claim 1, wherein the guide (1) has two end faces opposing each other, and the light emitting means (3) allows the light to enter the guide (1) from one of the two end faces, the other end face being a mirror face or a reflective face. A linear illumination device according to claim 1, wherein the light emitting means (3) has at least one light emitting diode. A linear illumination device according to claim 2, wherein each of the two light emitters (3) has at least one light emitting diode. A linear illumination device according to claim 1, wherein the light emitting means (3) has a light emitting angle distribution in the range of 30 to 150 degrees. A linear illumination device according to claim 2, wherein the guide (1) has a pillar shape extending in the first direction. A linear illumination device according to claim 24, wherein the width of the light diffusing section (2) in a second direction perpendicular to the first direction gradually increases as approaching a central portion of the guide from the two end faces. A linear illumination device according to claim 24, wherein the light diffusing section (2) is formed at constant intervals in said first direction. A linear illumination device according to claim 24, wherein the light diffusing section (2) is formed in the first direction at intervals, the intervals gradually decreasing as approaching a central portion from the two end faces (4a, 4b) of the guide (1). A linear illumination device according to claim 10, wherein said diffusing layer is formed on an entire surface or a part of said light diffusing section (2). A linear illumination device according to claim 24, wherein two planes forming a predetermined angle therebetween are provided in the part of the side face of the guide (1) facing the light diffusing section (2). A linear illumination device according to claim 39, wherein the predetermined angle is 90 degrees. A linear illumination device according to claim 24, wherein a V-shaped cut face (81), which has such a shape that a width and a depth in a second direction perpendicular to the first direction gradually increase as approaching a central portion of the guide (1) from the two end faces (4a, 4b), is formed in the side face of the guide (1). A linear illumination device according to claim 31, wherein the light diffusing section (2) is formed on an entire surface or a part of said V-shaped cut face (81). A linear illumination device according to claim 2, wherein the guide (1) has such a shape that a cross-sectional area of the guide (1) gradually decreases as approaching a central portion between the two end faces (4a, 4b). A linear illumination device according to claim 33, wherein the light diffusing section (2) is formed in said first direction as one continuous part. A linear illumination device according to claim 34, wherein the width of the light diffusing section (2) in a second direction perpendicular to the first direction gradually increases as approaching a central portion of the guide (1) between the two end faces (4a, 4b). A linear illumination device according to claim 33, wherein the light diffusing section (2) is formed in the first direction at constant intervals. A linear illumination device according to claim 33, wherein the light diffusing section (2) is formed in the first direction at intervals gradually decreasing as approaching a central portion of the guide (1) between the two end faces (4a, 4b). A linear illumination device according to claim 33, wherein a cross-section of the guide (1) has a similar shape as that of each of the two end faces (4a, 4b), and each of the two end faces (4a, 4b) has a polygonal cross-section. A linear illumination device according to claim 38, wherein said cross-section is circular. A linear illumination device according to claim 39, wherein two planes forming a predetermined angle therebetween are provided in the part of the side face of the guide (1) facing the light diffusing section (2). A linear illumination device according to claim 40, wherein the predetermined angle is 90 degrees. A linear illumination device according to claim 33, wherein the cross-section of a central portion of the guide (1) is 70 % or less of an area than the cross-section of each of the two end faces (4a, 4b). A linear illumination device according to claim 1 to 42, wherein the light emitting means (3) emits red light, green light and blue light in a time divided manner. A linear illumination device according to claim 43, wherein the light emitting means includes three light emitting diodes (21, 22, 23) respectively emitting the red light, the green light and the blue light. A direct contact type image sensor unit comprising: an optical fiber array (201, 246) including a plurality of optical fibers for transmission of light from a document (251) to a light receiving element (242); a transparent plate (203, 247) placed so as to be in contact with the optical fiber array (201, 246), which has two end faces; a pair of opaque substrates (208, 248) placed so as to interpose the optical fiber array (201, 246) and the transparent plate (203, 247) therebetween; light emitting means (250) for allowing light to be incident on the transparent plate (203, 247) on one of the two end faces of the transparent plate (203, 247); a light blocking layer (252) formed on the other of the two end faces of the transparent plate (203, 247); and said light receiving element (242) array including a plurality of light receiving elements provided on one end of the plurality of optical fibers, wherein the light emitting means (250) is a linear illumination device as claimed in claim 1 to 44 and emits linear illumination light to the document (251) along said first direction. A direct contact type image sensor unit according to claim 45, wherein each of the plurality of optical fibers has a core (211), a cladding layer (212) provided on an outer surface of the core (211), and a light absorbing layer (213) provided on an outer surface of the cladding layer (212). A direct contact type image sensor unit according to claim 45, further comprising lens means disposed between one of the two end faces of the transparent plate (203) and the light emitting means (250), wherein the lens means converges the illumination light only in a second direction perpendicular to the first direction. A direct contact type image sensor unit according to claim 45 to 47, wherein a refractive index of the guide (1) of the linear illumination device is substantially equal to that of the transparent plate (203). A direct contact type image sensor unit according to claim 45, wherein the material of the transparent plate (203) is the same as the light transmitting material forming the guide (1) of the linear illumination device. A direct contact type image sensor unit according to claim 45, wherein the linear illumination device is connected to the transparent plate (203) using a transparent resin having substantially the same refractive index as those of the guide (1) and the transparent plate (203), while optically matching the guide (1) and the transparent plate (203). A direct contact type image sensor unit according to claim 47, wherein a refractive index of the lens means is substantially the same as that of the transparent plate (203). A direct contact type image sensor unit according to claim 47, wherein the lens means and the transparent plate (203) are made of the same material. A direct contact type image sensor unit according to claim 51, wherein the lens means is connected to the transparent plate (203) using a transparent resin having substantially the same refractive index as those of the lens means and the transparent plate (203), while optically matching the lens means and the transparent plate (203). A direct contact type image sensor unit according to claim 45, wherein an angle at which the illumination light from the linear illumination device is incident on the document is in the range of 0 to 50 degrees.

Inventors: FUJIWARA SHINJI, HONGOU KOUKI, KAJITA YUKA, MURATA TAKAHIKO, NAKAMURA TETSUROH, TANAKA EIICHIRO, FUJIWARA, SHINJI, HONGOU, KOUKI, KAJITA, YUKA, MURATA, TAKAHIKO, NAKAMURA, TETSUROH, TANAKA, EIICHIRO
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1996
Main classification: H04N1
IPC codes: H04N1