JP2009176588A - Line illumination device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a line illumination device in which the size of the whole illumination device is shortened wherein a light guide body is shortened while securing a necessary illumination length. <P>SOLUTION: This is the line illumination device which has a rod-shaped light guide body 2 composed of a transparent member and a light source 1 arranged at both ends of the light guide body. A light-emitting face 3 of the light guide body is made as a cylindrical lens face of convex state, and on the side opposing to the light-emitting face, a parallel face 10 parallel to a cylindrical lens ridge line exists on the longitudinal most part excluding both ends, there are inclined faces 11 which become narrower toward the end parts at both end faces, reflecting patterns 4 are aligned and formed on the parallel planes, and a step-wise reflecting face 12 is formed on the inclined faces. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

Line lighting devices for facsimiles, electronic blackboards, electronic copiers, and other image reading devices include discharge tubes such as xenon fluorescent lamps, LED array bars with many light emitting diode (LED) chips arranged in an array, and the end of the light guide Light guide lighting with LEDs arranged in the part is used.
Among these, the light guide illumination method has excellent features such as no warming up, small size, low power consumption, low heat generation, and low cost. In particular, the illumination system that arranges LED chips with emission wavelengths of RGB three primary colors as one package on the end face of the light guide has a great advantage because full color image reading can be performed by switching and illuminating each RGB light emission, The use for various product uses, such as a small scanner for home use, has spread.

FIG. 1 illustrates the basic principle of the light guide illumination method. Light emitted from the LED 1 which is a light source disposed on the end face of the light guide 2 is taken into the light guide from the incident end face, and is propagated by total reflection repeatedly by internal reflection of the light guide. A reflection pattern 4 for extracting light is formed on one side of the light guide. The reflection pattern has a function of reflecting / diffusing light, and part of the light reaching the reflection pattern is emitted from the light exit surface 3 to the outside of the light guide. The light flux density in the light guide decreases as the distance from the incident end face increases, but a constant illuminance distribution is obtained in the longitudinal direction by gradually increasing the reflection pattern density in inverse proportion to the light flux density. Is possible.
The light exit surface 3 is a cylindrical lens surface, and can illuminate the elongated reading area of the document 5 efficiently by condensing the emitted light.

Although the light guide illumination system has many advantages, it has a problem in terms of downsizing the apparatus. This is because it is difficult to stabilize the illuminance in the vicinity of the incident end face of the light guide, and thus it is necessary to extend the light guide to the outside of the reading region. For example, Patent Document 1 proposes a method in which a reflection pattern (light diffusing portion) is not formed at a portion that is at least twice the diameter of the light guide from the end face of the light guide. In this case, the effective illumination area is further on the inner side, which is twice the diameter of the light guide.

JP 2002-101271 A

The reason why the illuminance at the end of the light guide is not stable is as follows.
As shown in FIG. 2, the light from the LED chip is incident after being refracted from the entrance surface of the light guide, and spreads radially and travels straight at a spread angle of approximately 40 degrees. When tracking the behavior of the light rays near the incident surface, the light reaching the reflection pattern is directly reflected from the incident surface 6, directly reflected by the inner surface 7, first reflected by the inner surface 7, and reflected twice by the inner surface. The secondary reflected light 8 arrives. In the range where the primary reflected light does not reach, the light flux on the reflecting surface is zero, in the range where the secondary reflected light does not reach, only the primary reflected light is reached, and in the range where the tertiary reflected light does not reach, the primary reflected light and the secondary reflected light are not. Become sum. Due to such a phenomenon, the light flux density fluctuates greatly in the vicinity of the incident end face depending on the position. Further, since the RGB LED chips are mounted at different positions, the positions where the direct light and the primary reflected light arrive also shift as shown in FIG. For this reason, it becomes impossible to adjust the reflection intensity of the reflection pattern in accordance with the light flux density.
Furthermore, the positional relationship between the light guide and the light source is affected by expansion due to temperature fluctuations and displacement due to vibration. In the vicinity of the incident, a slight change in positional relationship sharply changes the illuminance distribution.
As the distance from the incident surface increases, higher-order reflected light that has passed through various optical paths reaches the reflection pattern, so that the light flux density becomes uniform. In particular, in the range where the distance from the end surface is less than twice the diameter of the light guide. Since the next reflected light does not reach, the fluctuation of the light flux density becomes particularly remarkable.

An object of the present invention is to provide an illumination device that stabilizes illuminance in the vicinity of a light incident surface in a line illumination device using a rod-shaped light guide.

The illuminating device of the present invention is a line illuminating device having a rod-shaped light guide made of a transparent member and light sources arranged on both end faces of the light guide, and the light output surface of the light guide has a convex shape. The parallel surface parallel to the ridgeline of the cylindrical lens (X-axis direction of the light guide) occupies most of the longitudinal direction excluding both ends on the side facing the light exit surface. The both end portions have inclined surfaces that become narrower toward the end surface, the reflection pattern is arranged on the parallel surface, and the stepped reflection surface is formed on the inclined surface. Line lighting device.

Further, in the illumination device of the present invention, the reflection pattern is a pattern in which convex or concave portions having ridge lines (Y-axis direction of the light guide) parallel to the light incident side of the light guide are arranged, and the pitch, width, At least one of the heights is gradually changing.

According to the present invention, since the illuminance near the light incident end face of the rod-shaped light guide can be made uniform and stabilized, the length of the light guide can be shortened while ensuring the necessary illumination length, It becomes a line illuminating device which can shorten the longitudinal dimension of the whole illuminating device. Then, as in the case of FIG. 2, even if multi-color LED chips are arranged at different positions, it is possible to provide an illuminating device in which the chip position deviation is hardly reflected in the illuminance distribution.

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a perspective view for explaining the characteristics of the illumination device according to the present invention. Light sources 1 are disposed on both end faces of the rod-shaped light guide 2. The light exit surface 3 of the light guide is a convex cylindrical lens surface, and on the side facing the light exit surface, there is a parallel surface 10 parallel to the cylindrical lens ridge line, and the parallel surfaces are at both ends. It occupies most of the longitudinal direction excluding the portion of the inclined surface 11, and the inclined surface 11 is narrowed toward the end surface. Convex or concave reflective patterns 4 are arrayed on the parallel surfaces, and stepped reflective surfaces 12 are formed on the inclined surfaces. Hereinafter, the ridge line direction of the cylindrical lens surface is the X axis, the direction perpendicular to the parallel surface is the Z axis, and the direction perpendicular to both the X axis and the Z axis is the Y axis.

The outgoing light path will be described with reference to FIGS. 4 and 5 which are XZ cross-sectional enlarged views of the vicinity of the light incident end face in the illumination device of the present invention. In FIG. 4, the optical path from the adjacent light source is shown. A step-like reflecting surface 12 is formed on the inclined surface 11 at the end of the light guide, but light from the adjacent light source is not reflected by the step-like reflecting surface and emitted to the outside. Only after reaching the reflection pattern 4 formed on the parallel surface 10 after the inclined region is finished, the light is emitted in the direction of the document surface 5.

Next, FIG. 5 is a diagram showing an optical path from a light source arranged on the opposite side (far) from the proximity light source of FIG. The light propagating from the opposite side is emitted to the outside also by the reflection pattern 4, but is also emitted by the stepped reflection surface 12. Here, since the staircase-like reflecting surface has an effect of emitting light at a rate larger than that of the reflecting pattern, the luminous flux emitted from the inclined region becomes larger. That is, a large amount of light is emitted from the remotely located light source at the light guide end 11.

In the illumination device of the present invention, the light sources at both ends are turned on simultaneously. When switching RGB light emission, it is switched at the same timing. Therefore, the illumination light is the sum of the luminous fluxes from the light sources at both ends. In the light beam propagating through the light guide, the light beam propagated from a distant light source has a lower density than the light beam from a nearby light source, but has the effect of emitting a large proportion from the step-like reflection pattern, By optimizing the balance between the emitted light of FIG. 4 and the emitted light of FIG. 5, it is possible to make the illuminance distribution uniform up to the region near the light source (in some cases, to the outside of the light source).

As described above, in the illumination device of the present invention, the light from the proximity light source is not emitted in the region where only the direct light 6 and the primary reflected light 7 in FIG. 2 reach, so even if the LED chips are arranged at different positions. Chip position deviation is hardly reflected in the illuminance distribution. In addition, the illuminance does not become unstable even if the positional relationship between the light guide and the light source slightly varies due to thermal expansion or vibration.

The length L from the incident surface (light guide end surface) to the parallel surface is suitably longer than the distance until the secondary reflected light reaches, and is approximately 2 to 3 times the height H1 of the incident surface. .
It is desirable that the size of the incident surface is a size that can efficiently take in the luminous flux from the LED light source to be used. For example, when a surface-mount package product having a light emitting area of φ4 mm is used, a size that can accommodate a φ4 mm circle is desirable. For example, if H1 is 4 mm, the desired distance L is 8 mm to 12 mm.

FIG. 6 is an XZ cross section of the step-like reflecting surface. The intensity of light emitted from the inclined region increases in proportion to D / P where D is the height of the stepped reflecting surface and P is the pitch. As shown in FIG. 6A, in the case where the step-like reflecting surfaces are connected in a horizontal plane in the X direction, the value of D / P becomes D / P = tanα when the inclination angle of the inclined region is α, and depends on the angle α. It is prescribed. Therefore, if α is too small, it is not possible to make the illuminance distribution uniform by using a light beam from a distant light source. The size of α is also constrained by the size of the incident end face and the cross-sectional shape suitable for condensing, so the intensity of light emitted from the step-like reflective surface is approximately the same as the intensity of light emitted from the parallel reflection pattern. In order to increase the strength, it is preferable in many cases to make the formation width (the length in the Y-axis direction) of the stepped reflection surface wider than the formation width of the reflection pattern. Further, as another method for increasing the intensity of light emitted from the stepped reflecting surface, there is a method of connecting the stepped reflecting surfaces by a surface inclined at an angle β as shown in FIG. 6B. In this case, D / P≈tan α + tan β, and D / P can be increased at the same angle α. However, if β is too large, the light beam from a nearby light source is not totally reflected and is emitted to the outside, which is not preferable. Β is preferably 5 degrees or less.
If the value of D is too large, uneven illuminance corresponding to each reflecting surface is generated, which is not desirable. On the other hand, if it is too small, an accurate shape cannot be formed at the time of molding. It is preferable to be in the range. The values of D and P do not need to be constant, and by gradually changing either or both, the intensity of the emitted light can be controlled to make the illuminance distribution uniform.

FIG. 7 is an XZ cross-sectional view enlarging one of the step-like reflecting surfaces 12. The outgoing angle distribution in which the light beam from the distant light source is reflected by the stepped reflecting surface varies depending on the angle γ of the reflecting surface. In order to realize a uniform illuminance distribution, it is necessary to smoothly overlap light emitted from a nearby light source with a reflection pattern and light emitted from a distant light source with a stepped reflecting surface. For this purpose, it is necessary that the light reflected from the step-like reflecting surface in FIG. Therefore, γ is desirably in the range of 45 degrees to 65 degrees. When γ is 45 degrees or less, the emission angle distribution does not spread to the right, and when it is 65 degrees or more, the ratio of the light that is reflected by the reflecting surface and emitted is small.

As a reflection pattern, a method of forming a fine concavo-convex pattern on the surface of a molded product and using reflection by the concavo-convex surface, and a method of using white (or light diffusive) ink and applying diffuse reflection by ink And are available.
In the printing method, the illuminance uniformity in the Y-axis direction can be obtained by arranging while gradually changing the density and size of minute circular and rectangular print patterns. In the concavo-convex method, illuminance uniformity can be obtained by gradually changing the density and size of the minute concavo-convex reflection pattern.

The method using reflection by the uneven reflection pattern has an advantage that the reflection pattern can be simultaneously formed by injection molding using a mold having the corresponding unevenness, so that a printing process is unnecessary and the cost is low. Furthermore, while the printing method uses diffuse reflection, the emission angle cannot be controlled, whereas the uneven reflection method can control the emission angle by specular reflection by optimizing the shape of the unevenness, so that the light is collected efficiently. Can increase the illuminance.
In particular, by forming a pattern in which convex portions or concave portions having ridge lines on the Y axis (perpendicular to the longitudinal direction of the light guide) are formed, the controllability of the emission angle is enhanced. Such a concavo-convex reflection pattern can be used to cut a concavo-convex surface excellent in smoothness with high precision on the mold by cutting it in the Y-axis direction using a cutting tool having a tip shape corresponding to the mold. It can be processed, and an uneven shape in which the unevenness on the mold is reversed is transferred by an injection molding method.

A desirable embodiment in the case of forming a convex portion having a ridge line in the Y-axis direction will be described below with reference to FIG.
FIG. 8 is an XZ cross-sectional enlarged view of one convex portion. In order to realize a uniform illuminance distribution, it is necessary to smoothly overlap light emitted from a light source from a nearby light source with a convex portion and light emitted from a distant light source through a stepped reflection surface. For this purpose, it is necessary that the reflected light has an emission angle distribution that extends in the left direction, that is, in the direction of the proximity light source in FIG. Therefore, the angle δ with respect to the parallel surface (X-axis surface) of the convex protrusion in FIG. 8 is preferably in the range of 50 to 75 degrees. When δ is 50 degrees or less, the emission angle distribution does not spread to the left direction, and when it is 75 or more, the ratio of the light that is reflected by the reflecting surface and emitted is small.

If the height D of the protrusions is too large, it is not desirable because unevenness in illuminance corresponding to each protrusion occurs, and conversely, if it is too small, the exact shape is not transferred at the time of molding. It is preferable to be in the range of 02 mm to 0.2 mm.
When the ratio of E / D is too small when the width of the protrusion is E, it is impossible to emit a light beam having a small angle with the X-axis surface, and when it is too large, all light beams are emitted. The ratio to make becomes small. The proper range of E / D is approximately 3 to 6.
In order to emit light from the entire light-emitting surface of the light guide, convex portions having such a cross-sectional shape are arranged at an appropriate interval in the longitudinal direction (X-axis direction). At this time, the light flux density in the light guide decreases as the distance from the light incident surface decreases. Therefore, at least one of decreasing the X-direction formation pitch of the protrusions, increasing the Y direction, and increasing D is gradually changed. To balance the illuminance. In the present invention, since both ends of the light guide are light incident surfaces, the central portion in the X direction of the light guide is set to a maximum point (or minimum point).

Next, a preferred embodiment in the case of forming a recess having a ridge line in the Y-axis direction will be described with reference to FIG.
FIG. 9 is an XZ cross-sectional enlarged view of one recess. In order to realize a uniform illuminance distribution, it is necessary to smoothly overlap light emitted from a nearby light source by a recess and light emitted from a distant light source by a stepped reflecting surface. For this purpose, it is necessary to have an emission angle distribution in which the reflected light spreads in the left direction (the direction of the proximity light source) in FIG. Therefore, it is desirable that the cut angle ε with respect to the parallel surface of the recess is in the range of 50 to 75 degrees. When ε is 50 degrees or less, the emission angle distribution does not spread to the left side, and when it is 75 degrees or more, the ratio of the light that is reflected and emitted from the reflecting surface becomes small.
If the value of D is too large, uneven illuminance corresponding to each convex portion is generated, which is not desirable. Conversely, if it is too small, an accurate shape cannot be formed at the time of molding. It is preferable to be in the range.

In the illumination device of the present invention, the reflection pattern is not formed in the end region where only the direct light or the primary reflected light from the light source reaches inside the light guide, but the step-like reflection surface is formed. In the region near the incident surface, since the ratio of the direct reflected light from the light source and the primary reflected light to the reflection pattern together with the secondary reflected light or the higher order reflected light is large, uneven illuminance is likely to occur. In particular, this phenomenon becomes remarkable in an uneven reflection pattern using specular reflection. In order to alleviate the occurrence of such unevenness in the end region, it is preferable to form irregularities for appropriately diffusing light on the cylindrical lens surface. FIG. 10 shows a state in which the light diffusing irregularities 14 are formed on the cylindrical lens surface 3, and the position where the irregularities 14 are formed is preferably a position facing both ends of the parallel surface. By forming the unevenness, the light reflected by the reflective pattern is spread in the Y-axis direction, thereby eliminating the unevenness. The range in which the unevenness for light diffusion is formed in the longitudinal direction is preferably in the range of approximately 5 to 10 times the inside of H1 from the end of the parallel surface.

Depending on the shape of the LED package used, as shown in FIG. 11A, a part of the light emitted from the LED 1 is not taken into the light guide, but becomes a leaked light 15 from the gap with the incident end face of the light guide. It reaches the effective area of 5. In such a case, since an illuminance peak is partially generated, it is preferable to cover the light exit surface near the incident end face with a cover 16 for blocking leakage light as shown in FIG. 11B.

As shown in FIG. 12, an end parallel surface 17 that is parallel to the ridgeline of the cylindrical lens surface may be provided outside the inclined surface. Since there is no function to emit light on the end parallel surface, the effective irradiation area will be somewhat narrowed, but the distance L to the parallel surface will be as small as possible while ensuring the emitted light intensity from the stepped reflective surface. This is advantageous for preventing the emission from the region where the light flux density is unstable. Further, when the cover 16 is provided, since the reflected light from a position very close to the incident surface is blocked by the cover, there is an advantage that the light can be used more efficiently.

It is desirable that the surfaces of the light guide other than the reflection pattern and the stepped reflection surface are all smooth. When the smoothness is poor, light scattering at the interface occurs, so that not only the leakage light that is not controlled is generated and the efficiency is deteriorated, but also the light guide that is long in the X-axis direction emits light far from the light source. Since it is not transmitted, the whole cannot emit light.

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.

In the reflection pattern and the stepped reflection surface, not all the light is reflected to the light exit surface side, but a certain amount of light leaks to the back side. It is desirable to arrange via. If the reflecting member is in close contact with the back surface of the light guide, the light reflected and returned to the light guide side is also effectively collected and emitted by the cylindrical lens surface.

General configuration diagram of light guide illumination method The figure explaining the optical path of a light guide end part The perspective view which shows the characteristic of the illuminating device of this invention The figure explaining the optical path from near LED The figure explaining the optical path from a distant LED The figure explaining the shape of a step-like reflective surface The figure explaining the reflected light path in a step-like reflective surface The figure explaining the optical path at the time of forming a convex part as a reflective pattern The figure explaining the optical path at the time of forming a recessed part as a reflective pattern The perspective view which shows the structure which provided the unevenness | corrugation which diffuses light in the light emission surface The figure explaining the leak light and cover from LED The figure which shows the structure which provided the parallel surface outside the inclined surface

Explanation of symbols

1 Light source (LED)
2 Light guide 3 Light exit surface 4 Reflective pattern 5 Document surface 6 Direct light 7 Primary reflected light 8 Secondary reflected light 10 Parallel surface 11 Inclined surface 12 Stepped reflective surface 14 Light diffusion unevenness 15 Light leaked from LED 16 Cover 17 End parallel surface

Claims (3)

A line illumination device having a rod-shaped light guide made of a transparent member and light sources arranged on both end faces of the light guide, wherein the light output surface of the light guide is a convex cylindrical lens surface. The parallel surface parallel to the cylindrical lens ridge line occupies most of the longitudinal direction excluding both ends on the side facing the light exit surface, and inclined surfaces that narrow toward the end surface are formed at both ends. A line illumination device characterized in that a reflection pattern is arranged on the parallel surface, and a stepped reflection surface is formed on the inclined surface. The reflective pattern is a pattern in which convex or concave portions having ridge lines parallel to the light incident side of the light guide are arranged, and at least one of the pitch, width, and height is gradually changed. The line lighting device according to claim 1. The formation width of the step-like reflection surface formed on the inclined surface (the length in the Y-axis direction of the light guide) is wider than the formation width of the reflection pattern formed on the parallel surface. 2. Line illumination device.

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