JP5360646B2 - Line lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an illumination device in a line shape with stable illuminance, having excellent performance and of reduced cost. <P>SOLUTION: The illumination device includes a rod-shaped light guide body made of a transparent member and a light source arranged at both ends of the light guide body. Fine prisms with ridge lines parallel to the width direction are arranged on one face in the length direction of the light guide body, and an opposing light- emitting face is made as a cylindrical lens face. Further, one or more rugged lines with ridge lines in a length direction are formed in the area within &plusmn;20&deg; from the normal direction of the center of the fine prism. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

The present invention relates to a line illumination device used in an image reading apparatus.

Line-shaped illumination devices for facsimiles, electronic blackboards, electronic copiers, and other image reading devices include discharge tubes such as xenon fluorescent lamps, LED array bars in which a large number of LEDs (light emitting diodes) are arranged in an array, and ends of light guides Light guide lighting with LEDs arranged in the part is used.
Of these, the light guide illumination method does not require warm-up, and has excellent features such as small size, low power consumption, low heat generation, and low cost. Therefore, it can be used in various products such as small home scanners. It is coming.

A general problem in the light guide illumination system used in the image reading apparatus is to efficiently use the limited light from the light source arranged on the end face to maintain the illuminance uniformity over the entire reading area. .
A perspective view of a typical structure of a light guide in this method is shown in FIG. 1, and a side view for explaining the behavior of light rays is shown in FIG.
The light from the light source 1 is taken into the light guide from the end face of the light guide 2 and propagates through the light guide while repeating total reflection at the air interface. A reflection pattern 3 that reflects light in the direction of the light exit surface is formed on one side surface in the longitudinal direction of the light guide, and a part of the light hitting the reflection pattern is emitted from the light exit surface 4. The light exit surface is a curved surface of a cylindrical lens, and is condensed to illuminate the band-like area 6 on the document surface 5 serving as a reading unit. The light flux propagating in the light guide decreases as the distance from the light source decreases.However, the reflection pattern has a gradation that is rough in the vicinity of the light source and becomes denser as the distance from the light source increases, so that uniform illuminance can be obtained over the entire length. It is possible.

As a reflection pattern, typically, a micro prism is formed on the surface of a molded product and specular reflection is used, and white (or light diffusive) ink is printed and applied and diffuse reflection by ink is used. There is a method to do. A method using specular reflection by a fine prism has an advantage that the printing process is unnecessary and the cost is low. Furthermore, since the light is reflected in a specific direction, the light can be more efficiently collected in a narrow band-like range, which is advantageous in terms of illumination efficiency.

With an image reading light source, the illuminance is stable in a constant width in the short direction (sub-scanning direction) in order to cope with fluctuations in the reading position due to floating of the document (reading surface), machine shakiness and assembly accuracy limits. Sex is required. Especially in applications such as double-sided document scanners, electronic blackboards, and copiers where documents tend to float, illuminance stability over a wide range is required. FIG. 3 is a diagram showing an example of the illuminance distribution in the short direction (horizontal axis) of the light guide, but in the illuminance distribution having a sharp peak in the short direction like the distribution P shown here, The illuminance changes due to the floating of the original, resulting in uneven brightness in the read image. In addition, even if the unit is slightly misaligned, light and dark unevenness occurs.
In order to ensure illuminance stability in the short-side direction, the light collecting effect on the lens surface of the cylindrical shape is weakened or eliminated so that the emitted light has the distribution Q of FIG. 3 spread in the short-side direction. However, on the other hand, the reading surface illuminance is required to be as high as possible in order to increase the reading speed and reduce the noise. In such a case, the illuminance is remarkably lowered, which is not preferable. In order to satisfy the conflicting demands, the distribution as shown in R of FIG. 3 is used so that the change in illuminance is small within a certain range used for reading, and the light that is irradiated to the unused range and is wasted is minimized. It is required to produce.

However, it has been difficult to stabilize the short-side distribution as the distribution R shown in FIG. 3 by the irradiation by condensing by the specular reflection type reflection pattern and the cylindrical lens.
That is, when the cross section of the light exit surface of the light guide is a convex shape having a continuous curve and the same shape over the entire length, it is only necessary to control the pitch, height, width, etc. of the fine prism as shown in FIG. A short direction distribution such as R could not be obtained. Also, the short distribution cannot be made the same from near the light source to far. In particular, very strong unevenness occurs near the light source.

The inventor previously proposed a method for improving the distribution in the lateral direction by forming a plurality of projections and depressions on the light exit surface in the area near the light source to diffuse the emitted light to a certain extent (Patent Document 1). However, there is a limit in making the short distribution close to the ideal distribution as shown in R of FIG. 3 even at a position away from the light source.

JP 2008-140726 A

The present invention provides a stable line illuminating device for the above inconvenience while maintaining the illuminance within the range of the illuminance distribution in the short direction of the light guide over the entire length of the light guide. It is something to try.

The present invention provides a lighting device having a rod-shaped light guide body made of a transparent member and a light source disposed at an end of the light guide body. Are arranged in an array, the light exiting surface is a cylindrical lens surface, and the cylindrical lens surface further has a ridge line in the longitudinal direction within a range of ± 20 degrees from the normal direction of the center of the ridge line of the fine prism. A line illumination device characterized in that one or more concavo-convex lines are formed, and preferably the width or height of the concavo-convex lines is changed in the longitudinal direction, or the number of the concavo-convex lines is changed in the longitudinal direction. It is a line lighting device.
According to the present invention, the line illumination device is configured such that the angle formed by the concavo-convex line cross section and the cylindrical lens cross section is 140 degrees or greater, and the maximum angle formed by the adjacent concavo-convex line cross section is 110 degrees or greater.

According to the present invention, an ideal concavo-convex distribution is obtained by forming an uneven line having a ridge line in the longitudinal direction on the light exit surface of the light guide over its entire length. By changing the width or height in the longitudinal direction or changing the number of concave and convex lines in the longitudinal direction, it is possible to eliminate changes in the lateral direction distribution depending on the position in the longitudinal direction. A line illuminating device having a wide range of illuminance stability that can cope with backlash and assembly accuracy limits can be obtained.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 4 is a perspective view schematically showing a light guide and a light source which are features of the line illumination device of the present invention. One side surface of the light guide 2 in the longitudinal direction (X-axis direction) is a flat surface, and the fine prisms 8 are arrayed so as to form ridge lines 9 in the short-side direction (Y-axis direction). An LED light source 1 is disposed on the end face of the light guide. The light incident surface of the light guide is arranged close to the LED so that light emitted from the LED can be taken in efficiently. Light taken into the light guide from the light incident surface is propagated in the longitudinal direction while repeating total reflection at the air interface.
On one side surface of the light guide in the longitudinal direction, fine prisms having ridge lines in the short direction are arrayed, and a part of the light reaching the fine prism is reflected and is more constant than the light exit surface 4 of the light guide. The light is emitted in the positive direction of the Z axis with a width. Some of the light is refracted at the air interface of the fine prism and extracted to the back side of the prism, but if a light-reflective member is installed on the back side of the prism surface, the light that has escaped to the back side In addition, the light is again reflected from the light guide and returned from the light exit surface. Therefore, when it is desired to increase the illuminance, it is preferable to arrange a light reflective member on the back side of the fine prism.

On the light exit surface of the light guide, at least one concavo-convex line 10 having an arc cross section is formed.
Here, the function of the uneven line will be described.
The light emitted from the LED is refracted at the interface between the light guide and the air, and is incident with a spread of approximately (half angle) 40 degrees. Light that is taken into the light guide and reaches the surface other than the microprism is totally reflected, and only the light that reaches the microprism is emitted outside the lightguide, but the microprism is specularly reflective. The angle emitted from the light exit surface varies depending on the angle of light reaching the fine prism. In order to uniformly control the lateral distribution, the angle of light reaching the fine prism is important. First, in the vicinity of the light source, the light incident from the LED reaches the prism directly, or is reflected by a small number of times such as once or twice on the side surface of the light guide. As described above, the light passing through the specific optical path discontinuously reaches the fine prism, so that significant illuminance unevenness occurs in the vicinity of the light source.

Hereinafter, the illuminance distribution in the short direction of the light guide will be described with reference to FIG.
FIG. 5A shows the illuminance distribution in the short direction according to the distance from the light incident surface when using the light guide A (comparative example) in which the uneven surface is not provided on the light exit surface of the light guide. The horizontal axis is the position in the Y direction (short direction) (mm), and the vertical axis is standardized so that the illuminance in the normal direction (angle 0) of the fine prism surface forming surface (described later) is 1. Indicates the relative illuminance at each position of the hour. The light guide has a circular arc shape with a cross section of R = 2.2 mm, and a plane having a straight cross section is formed on one longitudinal side at a position 2.0 mm from the center of the arc. A light guide A (comparative example) is a microlens having a longitudinal dimension of 320 mm in which micro prisms having an isosceles triangle cross section with an angle of 120 degrees are arranged and having no cylindrical surface on the cylindrical lens surface (light exit surface).

5A shows a position 7.5 mm from the light exit surface of the light guide A (Y = 9.7 where R = 2.2 is the center of the cylindrical arc), and is horizontal to the surface where the fine prism is formed. When the light receiving surface is placed on the light receiving surface, the distance (X) from the light incident surface is 5-20 mm, 30-50 mm, 120-230 mm, 210-230 mm, 300-320 mm, and the illuminance distribution in the short direction is expressed as a light beam. This is a result of simulation using simulation software ("LIGHT TOOLS" manufactured by OPTICAL RESEARCH ASSOCIATES).
The upper part of FIG. 5A is a graph of the illuminance distribution with a width of 20 mm in the short direction, and the lower part shows a graph in which the illuminance distribution in the short direction of 6 mm is enlarged. From the graph of FIG. 5A, it can be seen that the distribution is significantly different at the measurement positions (five places) according to the distance from the light incident surface. As described above, the angular distribution of light propagating through the light guide varies depending on the longitudinal (X) position, and the angular distribution of the light beam reaching the fine prism also varies depending on the longitudinal position. This is thought to change the distribution in the short direction.

FIG. 5B shows the illuminance distribution in the short-side direction of the light guide B in which four kamaboko-shaped uneven lines having an arc cross section of R = 0.6 mm are formed over the entire length on the light exit surface of the light guide A. (Example 1). The center coordinates (Y, Z) of the four rounded arcs are (−0.56, 1.53) (−0.21, respectively) when the center coordinates of the arc R = 2.2 are (0, 0). 1.63) (0.21, 1.63) (0.56, 1.53), which is constant over the entire length in the longitudinal direction.
Comparing the two graphs of A and B in FIG. 5, the distribution in the short direction of the light guide B provided with the uneven lines is becoming uniform, and in B, ± 10% at Y = ± 0.5 mm. As a result, a certain degree of illuminance stability is secured.
In this way, by providing uneven lines on the light exit surface, the lateral direction distribution approaches the ideal shape and is made uniform.
However, the distribution in the range of X = 0 to 20 still has a sharp peak, which is insufficient to make the illuminance distribution uniform over the entire length in the length direction. In more detail, the peak is narrow at the position of X = 300 to 320, and there is room for further improvement.

Therefore, in order to further improve and stabilize the illuminance distribution of the light guide B, add a kamaboko-shaped concavo-convex line only to the part where the illuminance peak is further expanded in the light guide B, or increase the amount of protrusion to enhance the diffusion effect. This is the light guide C (Example 2).
In this case, six additional concave / convex lines are additionally provided on the light incident surface side. In each case X = 0, (Y, Z) is (−1.15, 1.25) (−0.73, 1.53) (−0.28, 1.68) (0.28, 1.68) (0.73, 1.53) (1.15, 1.25), and the center of Y = -1.15 is 0.19 degrees in the Y / X direction and 0.05 degrees in the Z / X direction. With a slope of 0.15 degrees in the Y / X direction, and a center of Y = -0.28 with a slope of -0.07 in the Z / X direction. The center of Y = 0.28 has an inclination of −0.07 degrees in the Z / X direction, and the center of Y = 0.73 has an inclination of −0.15 degrees in the Y / X direction. , Y = 1.15 has a center of inclination of −0.19 degrees in the Y / X direction and 0.05 degrees in the Z / X direction, and the height of the convex portion gradually increases as the distance from the light incident surface increases. It is set to be small. FIG. 4 schematically shows the light guide C.

In addition, on the incident light facing surface, two kamaboko-shaped concavo-convex lines in which (Y, Z) is (−0.6, 1.53) (0.6, 1.53) at X = 320 are added. , Y = −0.6 Camaboko center is provided with a −0.03 degree inclination in the Y / X direction, Y = 0.6 Camaboko center is provided with a 0.03 degree inclination in the Y / X direction. The height of the convex portion gradually decreases as the distance from the light incident facing surface increases.
Since the shape of these added concavo-convex lines overlaps with the concavo-convex line shape of the light guide B, the number of concavo-convex lines of the light guide C is 6 on the light incident surface side and 4 on the light incident opposite surface side. Become.
C in FIG. 5 is a graph showing the simulation result of the light guide C. When this is seen, the lateral direction distribution is made more uniform than in the case of the light guide B, and ± 1 at any X position. As a result, the illuminance stability was as high as about ± 4% at .5 mm, which was closer to the ideal distribution.

The effect of the uneven lines is schematically shown in FIG. The uneven line 10 has an effect of appropriately diffusing light in the short direction when the light reflected from the fine prism 8 is emitted from the emission surface. Thereby, the short direction distribution of illuminance can be optimized. Furthermore, the change in distribution can be suppressed by changing the width and height of each concavo-convex line according to the position in the longitudinal direction, or by additionally forming the concavo-convex line in a part in the longitudinal direction.

FIG. 7 shows the cross-sectional shape of the light incident end face of the light guide, and the shape of the concavo-convex line 10 is a squirrel-shaped type having an arc cross section as shown in FIG. Any shape such as a corrugation as shown may be used. What is important is the function of appropriately spreading the emitted light in the short direction, the maximum angle α formed with the cylindrical lens surface is 140 degrees or more, and the maximum angle β formed between adjacent concavo-convex line sections is 110 degrees or more. Is preferred. The larger the α and β angles, the stronger the light is diffused in the short direction. However, if the angle is too large, the light condensing at the reading position is excessively deteriorated and the illuminance near the normal direction is lowered, which is not preferable. In addition, the position of the concave / convex line is most effective in the vicinity of the normal direction of the fine prism in order to diffuse and stabilize the light in the short direction, and at least one is provided within a range of ± 20 degrees. Is preferred.

The diffused light of each concavo-convex line needs to be mixed and made uniform at the reading position, and if the short dimension K of one concavo-convex line is too large, light and dark unevenness corresponding to the concavo-convex occurs, which is inconvenient. is there. As the distance to the reading surface is shorter, unevenness in brightness and darkness due to the uneven line is more likely to occur. Therefore, it is necessary to reduce K. However, in a normal illumination device, K is approximately 1/5 or less of the short dimension W of the light guide. desirable.
In the embodiments, the cylindrical lens cross section of the light exit surface is a simple arc shape. However, the present invention is not limited to this, and a curved line or an ellipse in which a plurality of arcs are continuous is appropriately selected.

The present invention can be applied to a case where LEDs are arranged on one end face of a light guide or a case where LEDs are arranged on both end faces.

Next, the function of the fine prism will be described.
In the light guide plate of the present invention, fine prisms having ridge lines in the lateral direction (Y direction) are formed.
8 to 11 are side views for explaining a cross section of one fine prism and an optical path there.
As the cross-sectional shape of the fine prism, it is preferable that the prism cross-sectional shape is symmetrical in order to emit light from both ends symmetrically when the LEDs are arranged on both end faces. As described above, a part of the light reaching the fine prism is reflected on the light exit surface side, and a part is refracted and emitted on the back side of the prism, but even if a reflector is arranged on the back side of the prism, the normal direction In order to increase the illuminance, it is advantageous that the ratio of reflection from the prism is high, and a shape in which the two reflecting surfaces 13 are isosceles triangles having apex angles of about 120 degrees as shown in FIG. 8 is preferable. However, in such a shape, the angle of the emitted light is inclined to the opposite side to the light source on the XZ plane, so that the shadow appearance due to the unevenness of the original differs depending on the longitudinal position, and there is a problem that the shadow stands out depending on the position. . In order to avoid this problem, it is desirable to make the emission angle peak close to the normal direction. For this purpose, the trapezoidal shape as shown in FIG. 9 is used, and the angle γ of the reflecting surface 13 is set to 20 to 30 degrees. Is preferred. When the cross-sectional width of the fine prism is E and the height is D, the outgoing light rate is reduced if the ratio of E / D is too small or too large. The proper range of E / D is approximately 3 to 8.

On the other hand, when the LED is disposed only on one end surface of the light guide, the cross-sectional shape of the fine prism may be symmetrical as shown in FIGS. 8 and 9, but the first reflecting surface as shown in FIG. 14 and the second reflecting surface 15, the angle δ formed with the normal of the first reflecting surface is set to 75 to 85 degrees, and the angle ε formed with the second reflecting surface is set to 15 to 50 degrees. Is more preferred. Here, if it is desired to increase the illuminance by increasing the reflection ratio at the fine prism, ε is set to 40 to 50, and ε is set to 15 to 40 when the angle peak of the emitted light is to be in the normal direction of the fine prism. It is preferable.

Furthermore, in order to effectively emit the light reflected and returned from the incident light opposing surface side while giving priority to the light emitting function propagating from the light incident surface side, an asymmetric cross-sectional shape as shown in FIG. It is also suitable.

Such a fine prism shape can be used to cut a rough surface on the mold with high precision by cutting it in the Y-axis direction using a corresponding cutting edge (cutting tool) on the mold. It is possible to process and form a concavo-convex shape in which the concavo-convex on the mold is reversed by an injection molding method.

As the material of the light guide, one having a high transmittance at the emission wavelength of the LED to be used is desirable, and acrylic resin, polycarbonate resin, cycloolefin resin, and the like are preferably used.

The line illumination device of the present invention has features such as no warming up, small size, low power consumption, low heat generation, low cost, and stabilization of illuminance. The image reading apparatus can be used.

The perspective view which shows the structure of a typical light guide illumination system Side view explaining the behavior of light Diagram showing illuminance distribution in the short direction The perspective view which shows the characteristic of the illuminating device of this invention The figure which shows the transversal direction illumination distribution in a comparative example and an Example Sectional view schematically showing the effect of uneven lines Sectional drawing explaining the cross-sectional shape of an uneven | corrugated line Side view showing fine prism and optical path Side view showing fine prism and optical path Side view showing fine prism and optical path Side view showing fine prism and optical path

Explanation of symbols

1. Light source (LED)
2. 2. Light guide 3. Reflective pattern 4. 4. Light exit surface 5. Manuscript surface 6. Lighting area Light incident surface 8. Fine prism 9. 9. Fine prism ridge line Uneven line 13. Prism reflecting surface 14. First reflective surface 15. Second reflecting surface

Claims (3)

In a lighting device having a rod-shaped light guide made of a transparent member and a light source disposed at an end of the light guide, a fine one having a ridge line in the short side direction on one side surface in the longitudinal direction of the light guide The prisms are arrayed, and the light exit surfaces facing each other are cylindrical lens surfaces. Further, the cylindrical lens surfaces have ridge lines in the longitudinal direction within a range of ± 20 degrees from the normal direction of the ridge line center of the fine prism. A line illumination device for reading an image, wherein at least one uneven line is formed. Change the width of the concavo-convex line so that it becomes narrower as it goes away from the light incident surface in the longitudinal direction , or change so that the height of the convex portion becomes smaller gradually as it gets away from the light incident surface or the light incident facing surface in the longitudinal direction. The line illumination device according to claim 1, wherein the number of the uneven lines is changed in the longitudinal direction. The line illumination device according to claim 1 or 2, wherein the maximum angle α formed by the concavo-convex line cross section and the cylindrical lens cross section is 140 degrees or more, and the maximum angle β formed by the adjacent concavo-convex line section is 110 degrees or more. .

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