JP2012114759A - Line light source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a line light source which provides sufficient luminance and is less likely to cause luminance unevenness.SOLUTION: The line light source comprises: a light guide which comprises a columnar light guide part and a light emission part provided on the side surface of the light guide part and extending in the longitudinal direction of the light guide part; and a light emission device provided at the end of the light guide. The light emission part is a triangle-pole-shaped transparent region extending in the longitudinal direction.

Description

  The present invention relates to a line light source.

  Image scanners, facsimiles, copiers, etc., form a band-shaped light irradiation area (area irradiated with light) on the document surface and move the light irradiation area to convert the reflected light into an electrical signal with a line sensor. Convert and read image information. A light emitting diode array or a white fluorescent lamp is used to form the band-shaped light irradiation region.

  The light emitting diode array is a light source in which a plurality of light emitting diodes (LEDs) are arranged in a line, and is smaller and consumes less power than a white fluorescent lamp.

JP 2010-147592 A

  An LED array used for an image scanner or the like is usually provided with a large number of LEDs ranging from 30 to 40. With such a large number of LEDs, high luminance in the light irradiation region is ensured, and luminance unevenness in the light irradiation region is suppressed. This prevents an error in reading a document.

  However, an LED array composed of a large number of LEDs leads to an increase in size and complexity of the apparatus, which is not preferable for further miniaturization and low power consumption of an image scanner or the like. Accordingly, an object of the present invention is to provide a line light source (light source having an elongated light emitting portion) that can obtain sufficient luminance with a small number of light emitting elements (for example, LEDs) and hardly causes luminance unevenness.

  In order to achieve the above object, according to one aspect of the present invention, a columnar light guide unit and a light emitting unit provided on a side surface of the light guide unit and extending in a longitudinal direction of the light guide unit are provided. A line light source is provided that includes a light guide and a light emitting element provided at an end of the light guide, and the light emitting portion is a triangular prism-shaped transparent region extending in the longitudinal direction.

  According to the present invention, it is possible to provide a line light source capable of obtaining sufficient luminance with a small number of light emitting elements and hardly causing luminance unevenness.

2 is a plan view of the line light source according to Embodiment 1. FIG. It is sectional drawing along the II-II line of FIG. FIG. 3 is an example of a plan view illustrating a state where the line light source according to the first embodiment is mounted on an image scanner. It is an example of sectional drawing explaining the state which mounted | wore the image scanner with the line light source of Embodiment 1. FIG. It is a top view of a general line light source. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 5. It is a luminance distribution along the longitudinal direction of a light irradiation region illuminated by a general line light source. This is a viewing angle characteristic of a general line light source. It is a perspective view explaining the measuring method of the viewing angle characteristic of FIG. FIG. 6 is a plan view for explaining the operation of the line light source according to the first embodiment. FIG. 6 is a cross-sectional view illustrating the operation of the line light source according to the first embodiment. 3 is an example of a luminance distribution along a longitudinal direction of a light irradiation region illuminated by a pair of line light sources according to the first embodiment. 3 shows viewing angle characteristics of a pair of line light sources according to the first embodiment. It is a luminance distribution along the longitudinal direction of a light irradiation region illuminated by a pair of line light sources that do not have a triangular prism-shaped light emitting portion (prism). It is a viewing angle characteristic of a pair of line light source which does not have a triangular prism-shaped light emission part (prism). It is sectional drawing of the light guide of a pair of line light source which showed the characteristic in FIG.14 and 15. It is a figure explaining the relationship between incident light and an emitted light in the planar light-projection part which does not have a prism. It is a figure which shows the incident / exit relationship of the incident angle of the light which injects into a light-projection part, and an output angle in the line light source which does not have a prism. It is a figure explaining the relationship between the advancing direction of the light which injects into a triangular prism-shaped light-projection part (prism), and a light-projection surface. Explains the behavior of light incident on the light output part (prism) in a state inclined to the opposite side of the center line of the line light source and light incident on the light output part (prism) in a state inclined on the center line side of the line light source It is a figure to do. It is a figure explaining the relationship between the incident angle (theta) _in of light in the 1st light-projection surface and outgoing angle (theta) _{out on} the basis of the perpendicular of the 1st side surface. It is a figure explaining the incident / exit relationship of incident angle (theta) _{in of the} light which injects into a prism, and outgoing angle (theta) _{out of the} light radiate _| emitted from a prism. FIG. 2 is a schematic diagram illustrating an example of an image scanner having the line light source according to the first embodiment. 6 is a plan view of a line light source according to Embodiment 2. FIG. FIG. 25 is a sectional view taken along line XXV-XXV in FIG. 24. 6 is a plan view of a line light source according to Embodiment 3. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the matters described in the claims and equivalents thereof. In addition, the same code | symbol is attached | subjected to the corresponding part even if drawings differ, The description is abbreviate | omitted.

(Embodiment 1)
(1) Structure FIG. 1 is a plan view of a line light source 2 of the present embodiment. FIG. 2 is a cross-sectional view taken along the line II-II in FIG.

  As shown in FIG. 1, the line light source 2 includes a light guide 8 and a pair of light emitting elements (for example, LEDs) 10 a and 10 b provided at both ends of the light guide 8. The light guide is an optical member that propagates light incident on one end thereof toward the other end.

  As shown in FIG. 1, the light guide 8 is provided on the columnar light guide 4 and the side surface of the light guide 4 (the entire surface extending between both ends of the light guide 4). A light emitting portion 6 extending in the longitudinal direction 5 of the light portion 4. Here, as shown in FIG. 2, the light emitting portion 6 is a triangular prism-like transparent region extending in the longitudinal direction 5 of the light guide portion 4. The light guide unit 4 and the light emitting unit 6 are, for example, a transparent body integrally formed of polymethacrylic sanmethyl resin (refractive index n = 1.49).

  The light guide 4 has a prismatic shape (for example, a pentagonal prism shape) as shown in FIG. The light emitting unit 6 is provided in a region 16 that is a part of the first side surface 12 of the light guide unit 4 and is in contact with the long side 14 of the first side surface 12. Here, the region 16 is a region having a width less than half of the first side surface 12 (length in a direction perpendicular to the longitudinal direction 5). The first side surface 12 is a region included in the side surface of the light guide unit 4 (the entire surface between both end portions of the light guide unit 4).

  In addition, as shown in FIG. 2, the light guide 4 has a second side surface 18 adjacent to the first side surface 12. The second side surface 18 is integrated with the exposed one side surface 20 of the light emitting portion 6 to form a first light emitting surface 22. On the other hand, the other exposed side surface of the light emitting portion 6 is a second light emitting surface 24. Here, the light emitting surface is a surface through which light inside the optical member passes when it is emitted to the outside.

  Accordingly, the first light exit surface 22 is wider than the second light exit surface 24. Thus, the line light source easily emits more light on the side opposite to the center line 7 of the first side surface 12 (in the diagonally upper right direction in FIG. 2). Here, the center line 7 of the first side surface 12 is a line extending in the longitudinal direction 5 from the center of the first side surface 12. However, the first light emitting surface 22 may be formed only by the side surface 20 of the light emitting unit 6. That is, the second side surface 18 may not be provided in the light guide unit 4 and a third side surface 25 described later may be directly connected to the first side surface 12.

  Further, as shown in FIG. 2, the light guide unit 4 has a third side surface 25 that is inclined with respect to the first side surface 12 and faces the light emitting unit 6. The light propagating through the light guide 8 is reflected by the third side surface 25 and efficiently guided to the light emitting unit 6.

  In addition, as shown in FIGS. 1 and 2, the light guide 8 is a part of the side surface of the light guide unit 4 and the light emitting unit 6 is not provided (the first side surface 12 in the example of FIG. 2). And a diffuse reflection part 28 extending in the longitudinal direction 5 of the light guide part 4.

  Further, the light guide 8 is another part of the side surface of the light guide unit 4 and is not provided with the light emitting unit 6 and the diffuse reflection unit 28 (in the example of FIG. Part, the third side surface 25, and the fifth side surface 29) have a reflecting portion 30. That is, the side surface of the light guide 8 is covered with the diffuse reflection portion 28 or the reflection portion 30 except for the first light emission surface 22 and the second light emission surface 24. Here, the diffuse reflection part 28 is a member or a region that diffuses and reflects the light generated by the light emitting elements 10 a and 10 b and propagating through the light guide part 4. The reflection unit 30 is a member or region that reflects light generated by the light emitting elements 10 a and 10 b and propagating through the light guide unit 4. The same applies to the other embodiments.

  The diffuse reflection part 28 is, for example, a white paint printed on the fourth side face 26 by silk screen printing. Alternatively, the diffuse reflection unit 28 is a fine uneven group provided on the side surface of the light guide unit 4. The reflection unit 30 is, for example, an Al film. Alternatively, the reflecting unit 30 is a mirror-finished metal plate.

  FIG. 3 is an example of a plan view illustrating a state in which the line light sources 2a and 2b having such a structure are mounted on an image scanner. FIG. 4 is an example of a cross-sectional view illustrating a state in which the line light sources 2a and 2b are mounted on the image scanner. In the examples of FIGS. 3 and 4, the luminance of the light irradiation surface is increased by using a pair of line light sources. However, when the required luminance is low, only one line light source may be attached.

  In the image scanner, for example, as shown in FIG. 3, a pair of main line light sources 2 a and 2 b are arranged so that the light emitting portions 6 a and 6 b are adjacent and parallel to each other. For example, as shown in FIG. 4, the pair of line light sources 2a and 2b is stored in the light source case 32 so that the light emitting portions 6a and 6b are exposed.

  The light source case 32 is further provided with an imaging lens 34 and a line sensor 36. The line sensor 36 is a one-dimensional imaging device such as a CCD image sensor (Charge Coupled Device Image Sensor) or a CMOS image sensor (Complementary Metal Oxide Semiconductor Image Sensor). The light source case 32 storing the line light sources 2a, 2b and the like is arranged below the platen glass 35 (original table glass) as shown in FIG.

  Between the pair of line light sources 2a and 2b stored in the light source case 32, for example, a gap having a width of about 4 mm is provided. Lights 38a and 38b emitted from the pair of line light sources 2a and 2b are applied to the document 37, as shown in FIG. Lights 38a and 38b are diffusely reflected (irregularly reflected) by the irradiation region 41, and enter the imaging lens 34 through the line light sources 2a and 2b. The light incident on the imaging lens 34 is imaged on the line sensor 36 and converted into an electrical signal.

  While repeating such a one-dimensional image reading operation, the line light sources 2 a and 2 b and the line sensor 36 move together with the light source case 32 in a direction 40 perpendicular to the strip-shaped light irradiation region 41. As a result, the document 37 is scanned by the belt-shaped light irradiation region 41, and the two-dimensional image data of the document 37 is read.

  By the way, it is preferable that the light emission wavelengths of the light emitting elements 10a and 10b provided at both ends of the light guide 4 are substantially equal. Or you may provide three types of light emitting elements which light-emit by R (red), G (green), and B (blue) in the both ends of the light guide part 4, respectively.

(2) Operation Next, the operation and characteristics of the line light source 2 will be described in comparison with a general line light source used for an image scanner. FIG. 5 is a plan view of a general line light source 2c. 6 is a cross-sectional view taken along line VI-VI in FIG.

  As shown in FIG. 5, the general line light source 2 c includes a columnar light transmitting body 46 and an LED array 42 provided on a side surface of the light transmitting body 46. As shown in FIG. 6, the translucent body 46 includes a translucent portion 48 and a light emitting surface 47 extending in the longitudinal direction 5 a of the translucent portion 48. Here, the light emitting surface 47 is an exposed side surface of the transparent body 46. The LED array 42 is a light emitting unit having a plurality of LEDs 44.

  The general line light source 2 c further includes light reflecting films (for example, Al reflecting films) 30 c and 30 d provided on the side surfaces of the light transmitting body 46. Note that such a general line light source 2c is different from the line light source 2 and is used alone.

  As shown in FIG. 6, the light 50 emitted from the LED 44 is reflected by the light reflecting film 30 c provided on the upper and lower side surfaces of the translucent body 46, and enters the light reflecting film 30 d facing the light emitting surface 47. Alternatively, the light 50 is directly incident on the light reflecting film 30d. The light 50 incident on the light reflecting film 30d is reflected and emitted from the light emitting surface 47 to the outside.

  Here, as shown in FIG. 5, the light emitting surface 47 is an elongated region extending in the longitudinal direction 5 a of the translucent body 46. Since light is emitted from such an elongated area, a band-shaped light irradiation area is formed on the document.

  FIG. 7 shows a luminance distribution along the longitudinal direction of the light irradiation region illuminated by such a general line light source 2c. The horizontal axis represents position coordinates along the longitudinal direction of the light irradiation region. The vertical axis represents the luminance (arbitrary unit) of the light irradiation area. This luminance distribution is obtained on the basis of an image photographed by a CCD camera from directly above the diffusion plate by arranging a diffusion plate with a transmittance of 40% 3 mm above the line light source 2c. FIG. 7 is a graph in which the brightest line is extracted from the captured image of the diffusion plate and the brightness of this line is graphed.

  A general line light source 2c used for measurement has a length of 320 mm and a width of 10 mm. The width of the light emitting surface 47 is 5 mm. The number of LEDs 44 is 36, and the total amount of power supplied to the LEDs 44 is 3.6 W.

  As shown in FIG. 7, the brightness of a general line light source 2c varies in a short cycle. This period coincides with the interval between the LEDs 44. The LED 44 and the light emitting surface 47 are close to each other as shown in FIG. For this reason, the light beam emitted from the LED 44 is emitted from the light emitting surface 47 before spreading. For this reason, as shown in FIG. 7, the luminance of the light irradiation region illuminated by the general line light source 2 c fluctuates in a short cycle corresponding to the interval between the LEDs 44.

  Such uneven brightness reduces the resolution of the image scanner and causes a document reading error. Therefore, in the general line light source 2c, a diffusion sheet is provided on the light emitting surface 47, and uneven brightness is suppressed. However, even in this way, it is difficult to sufficiently suppress luminance unevenness.

  On the other hand, the average luminance of the general line light source 2c in FIG. 7 is sufficiently high. The average illuminance on the document surface estimated from the luminance in FIG. 7 is 101,000 lx. This illuminance is sufficiently higher than the illuminance of 40,000 lx required for the light source of the image scanner.

  FIG. 8 shows viewing angle characteristics of a general line light source 2c. The radius r and the deviation angle θ in FIG. 8 correspond to the luminance of the line light source 2c and the light emission angle. The numerical values displayed on the bottom side and the outer periphery of FIG. 8 are the luminance of the line light source 2c and the light emission angle, respectively.

  Here, the luminance displayed on the bottom side of FIG. 8 is normalized by the maximum value. Further, the light emission angle displayed on the outer periphery of FIG. 8 is an angle θ formed by the perpendicular 54 (see FIG. 6) of the light emission surface 47 and the light emission direction. Here, the sign of the light emission angle θ is determined so as to be positive when the light emission direction is inclined to the opposite side of the center line of the transparent body 46.

  FIG. 9 is a perspective view for explaining a method of measuring the viewing angle characteristic. In order to measure the viewing angle characteristic, first, the line light source 2c is caused to emit light. Next, as shown in FIG. 9, the line light source 2 c is photographed by the CCD camera 52 while the CCD camera 52 is substantially half-rounded around the line light source 2 c. The distance between the line light source 2c and the CCD camera 52 is, for example, 1 m. A characteristic obtained by expressing the brightness of the line light source 2c and the rotation angle θ of the CCD camera 52 in a circular coordinate at this time is the viewing angle characteristic of FIG.

  As shown in FIG. 8, the line light source 2c has the maximum luminance in the direction of θ = + 15 °. Accordingly, the luminance of the line light source 2c is maximized in a direction slightly tilted outward from just above the line light source 2c.

  By the way, when light is emitted directly above the line light source 2c (θ = 0 °), the reflected light from the original is blocked by the line light source 2c, and the line sensor disposed obliquely below the line light source 2c. Will not reach. On the other hand, as the light emission direction is inclined, the original is irradiated obliquely, and the illuminance on the original surface is lowered. For this reason, the general line light source 2 c is designed so that light is emitted slightly obliquely outward from directly above the light emitting surface 47. Therefore, viewing angle characteristics as shown in FIG. 8 are obtained.

  10 and 11 are a plan view and a sectional view for explaining the operation of the line light source 2 of the present embodiment. In addition, the light emission part 6 is abbreviate | omitted in FIG. 10 so that drawing may not become complicated. On the other hand, FIG. 11 shows the light emitting elements 10a and 10b that are not present in the cross section of the light guide 8 so that the operation can be easily explained.

  As shown in FIG. 10, light 50a and 50b emitted from the light emitting elements 10a and 10b (for example, LEDs) are incident on the light guide 8 from the end thereof (that is, the light emitting elements 10a and 10b are light guides). 8 is supplied with light). The light 50a and 50b incident on the light guide 8 is reflected (including diffuse reflection) by the diffuse reflector 28 and the reflector 30 (see FIG. 11) provided on the side surface of the light guide 8, as shown in FIG. ) Is propagated through the inside of the light guide 8. As shown in FIG. 11, the lights 50a and 50b are gradually emitted from the light emitting unit 6 to the outside while propagating inside the light guide. As described above, the light emitting portion 6 is a region extending in the longitudinal direction of the light guide 8. Accordingly, the light beams 38 a and 38 b (see FIG. 4) emitted from the light emitting unit 6 form a band-shaped light irradiation region 41 on the document 37.

  FIG. 12 is an example of a luminance distribution along the longitudinal direction of the light irradiation region 41 illuminated by the pair of main line light sources 3 (see FIG. 3). The horizontal axis is the position coordinate along the longitudinal direction of the light irradiation region 41. The vertical axis represents the luminance of the light irradiation area. The measurement conditions for the luminance distribution are the same as in FIG.

  The length of the line light source 2 used for the measurement is 320 mm. The line light source 2 has a width of 12 mm and a thickness of 5 mm (see FIG. 2). The inclination angle of the third side surface 25 with respect to the fourth side surface 26 (bottom surface) of the light guide unit 4 is 45 °. The inclination angle of the first light exit surface 22 with respect to the first side surface 12 is 45 °. On the other hand, the inclination angle of the second light exit surface 24 with respect to the first side surface 12 is 34.28 °. As shown in FIG. 2, the fifth side surface 29 between the first side surface 12 and the fourth side surface 26 is perpendicular to the first side surface 12 and the fourth side surface 26. The total power supplied to the light emitting elements 10a and 10b is 3.0W.

  As is apparent from FIG. 12, according to the present line light source 2, uneven brightness does not occur. This is because, as shown in FIG. 11, the light beams emitted from the light emitting elements 10a and 10b are repeatedly reflected by the reflection unit 30 and the diffuse reflection unit 28, thereby being disordered and uniforming the spatial distribution of the light beams. It is. In particular, the diffuse reflection unit 28 efficiently suppresses uneven brightness by diffusely reflecting (diffuse reflection) the light emitted from the light emitting elements 10a and 10b. By the way, the luminance distribution of FIG. 12 is substantially flat except for the peaks at both ends. This is because the light density in the longitudinal direction 5 is made uniform by supplying light from both ends of the light guide 8. The flattening of the luminance distribution can also be realized by providing a light emitting element only at one end of the light guide 8 and gradually increasing the width of the diffuse reflection portion toward the other end.

The average luminance shown in FIG. 12 is 4,038 cd / cm ² . The average illuminance estimated from this luminance is 31,700 lx. This value substantially satisfies the required illuminance 40,000 lx of the image scanner. Therefore, the line light source 2 can satisfy the required illuminance of the image scanner. For this purpose, for example, the power supplied to the light emitting elements 10a and 10b may be increased by about 20 to 30%. Alternatively, the number of light emitting elements may be increased. As described above, according to the present line light source 2, sufficient luminance can be obtained and luminance unevenness hardly occurs. The reason why sufficient luminance can be obtained by the line light source 2 will be described later.

  FIG. 13 shows viewing angle characteristics of the pair of main line light sources 3 (see FIG. 3). The radius r and the deflection angle θ in FIG. 13 correspond to the normalized luminance and light emission direction. The way of viewing FIG. 13 is the same as FIG.

  As shown in FIG. 13, the luminance of the pair of line light sources 3 including the line light source 2 is maximized in the direction of approximately θ = ± 15 °. By the way, the present line light source 2 is designed so that the intensity of the emitted light is maximized in a direction slightly inclined outward. Further, the viewing angle characteristic of the pair of line light sources 3 is a superposition of the viewing angle characteristics of a pair of line light sources arranged so that the light emitting portions 6 are juxtaposed. Therefore, the viewing angle characteristics of FIG. 13 indicate that the luminance of the line light source 2 is maximized in a direction inclined approximately 15 ° to the oblique outer side of the light guide 8. This emission angle is substantially the same as the light emission angle of the general line light source 2c used in the image scanner described above. That is, the viewing angle characteristic of the line light source 2 is suitable for an image scanner.

  FIG. 14 is a luminance distribution along the longitudinal direction of a light irradiation region illuminated by a pair of line light sources that do not have a triangular prism-shaped light emitting portion (prism) 6. The horizontal axis represents position coordinates along the longitudinal direction of the light irradiation region. The vertical axis represents the luminance of the light irradiation area. The measurement conditions of the luminance distribution are the same as the luminance distribution shown in FIG.

  FIG. 15 shows the viewing angle characteristics of a pair of line light sources having no prism. The radius r and the deviation angle θ in FIG. 15 correspond to the normalized luminance and light emission angle, respectively. The view of FIG. 15 is the same as the viewing angle characteristic of FIG.

  FIG. 16 is a cross-sectional view of a pair of line light source light guides 8d that do not have a prism and whose characteristics are shown in FIGS. 14 and 15 (however, FIG. 16 shows one light guide of the line light sources arranged side by side. Only the body cross section is shown.) As shown in FIG. 16, the light guide 8d has a light guide part 4d, a planar light emitting part 47d (that is, a light emitting surface), and a diffuse reflection part 28 facing the light emitting part 47d. is doing. Furthermore, the light guide 8d includes a plurality of light reflecting portions 30 provided between the light emitting portion 47d and the diffuse reflecting portion 28, and light emitting elements (not shown) provided at both ends of the light guiding portion 4d. Have. Here, the width of the light emitting portion 47d is 5 mm, and the interval between the line light sources is 4 mm. The length of the light guide 4d is 320 mm.

As shown in FIG. 14, uneven brightness as shown in FIG. 7 does not occur in the light irradiation region illuminated by a pair of line light sources not having a prism. However, the average luminance of the light irradiation region is as low as 1,387 cd / cm ^2, which is only about 1/3 of the pair of line light sources 3 including the line light source 2. For this reason, the pair of line light sources not having the prism cannot satisfy the required illuminance of the image scanner.

  As shown in FIG. 15, the directivity of the pair of line light sources not having the prism is lower than the pair of line light sources composed of the line light source 2 shown in FIG. 13. By the way, the directivity of a pair of line light sources is a superposition of the directivities of line light sources arranged side by side. Accordingly, FIG. 15 shows that the directivity of the line light source having no prism is lower than that of the line light source 2.

  Thus, since the directivity of the line light source not having the prism is low, the area of the light irradiation region illuminated by the line light source not having the prism becomes wide. For this reason, the brightness | luminance of the light irradiation area | region illuminated by a pair of line light source which does not have a prism becomes small as shown in FIG.

  FIG. 17 is a diagram for explaining the relationship between the incident light 55 and the emitted light 56 in the light emitting unit 47d that does not have a prism. The refractive index n (for example, 1.49) of the light guide portion 4d made of resin or the like is larger than the external refractive index n (= 1.0). Therefore, the emission angle θ2 of the light 56a emitted from the light emitting portion (light emitting surface) 47d is larger than the incident angle θ1 in accordance with Snell's law (see FIG. 17). Therefore, the directivity of a line light source that does not have a prism is low.

  Next, the reason why the directivity of the line light source having no prism is lowered will be quantitatively explained according to Snell's law. FIG. 18 is a diagram showing the incident / exit relationship 58 between the incident angle θ1 and the outgoing angle θ2 of the light incident on the light emitting portion 47d in the line light source having no prism described with reference to FIG. The horizontal axis is the incident angle θ1. The vertical axis represents the emission angle θ2. The incident angle θ1 and the emission angle θ2 are angles measured clockwise from the perpendicular 54 of the light emitting portion 47d, as shown in FIG.

The input / output relationship 58 was derived according to Snell's law, where the refractive index n of the light guide 4d was 1.49. Here, the broken line 57 in FIG. 18 corresponds to the function θ2 = θ1. As is clear from the positional relationship between the broken line 57 and the incident / exit relationship 58, the output angle θ2 of the line light source not having the prism is larger than the incident angle θ1 (accurately, the absolute value is larger). The incident / exit relationship 58 is interrupted in a region where the absolute value of the incident angle θ _in is large. This is because the incident angle θ _in exceeds the critical angle in these regions.

  Incidentally, the light 55 incident on the light emitting portion 47d from the light guide portion 4d is concentrated in a substantially constant incident angle range (for example, −35 ° to + 35 °). In a line light source having no prism, incident light 55 within such a fixed angle range is emitted in a wider angle range (for example, −59 ° to + 59 °) in accordance with the input / output relationship 58 of FIG. . Therefore, the directivity of a line light source that does not have a prism is low. For this reason, the area of the region (light irradiation region) illuminated by the pair of line light sources is increased, and the luminance is decreased.

  On the other hand, the directivity of the line light source 2 of the present embodiment is higher than that of the line light source not having a prism, as shown in FIG. For this reason, the area of the region (light irradiation region 41) illuminated by the pair of main line light sources 3 is reduced, and the luminance of the light irradiation region 41 (see FIG. 4) is increased. Hereinafter, the reason why the directivity of the line light source 2 is higher than that of the line light source having no prism will be described with reference to FIGS. 19 to 22.

  FIG. 19 is a diagram for explaining the relationship between the traveling direction of light incident on the triangular prism-shaped light emitting portion (prism) 6 and the light emitting surfaces 22 and 24. The light incident on the light emitting unit 6 is classified into light 60 inclined to the opposite side of the center line 7 (see FIG. 1) of the line light source 2 and light (not shown) inclined to the center line of the line light source. Can do.

  As shown in FIG. 19, the light 60 inclined to the opposite side of the center line 7 of the line light source 2 intersects the first light emitting surface 22 (oriented in the direction opposite to the line light source 2) at a large angle. On the other hand, the light 60 inclined to the line light source 2 intersects the second light emitting surface 24 (facing the center line 7 side of the line light source) at a small angle. For this reason, the light 60 inclined to the opposite side of the center line 7 of the line light source 2 is emitted mainly from the first light exit surface 22. Similarly, light (not shown) inclined toward the center line 7 side of the line light source 2 is mainly emitted from the second light emission surface 24.

  FIG. 20 shows light 60 incident on the light emitting unit 6 (prism) in a state inclined to the opposite side of the center line 7 of the line light source 2 and light emitting unit 6 in a state inclined to the center line 7 side of the line light source 2. It is a figure explaining the behavior of the light 62 which injects into (prism). As described with reference to FIG. 19, the light 60 incident on the light emitting portion 6 while being inclined to the opposite side of the center line 7 of the line light source 2 is mainly incident on the first emitting surface 22. At this time, the incident light 60 is emitted in accordance with Snell's law as shown in FIG. 20 while changing the traveling direction toward the center line 7 side of the line light source 2.

  On the other hand, the light 62 incident on the light emitting portion 6 while being inclined toward the center line 7 side of the line light source 2 is mainly incident on the second emission surface 24. At this time, the incident light 62 is emitted in accordance with Snell's law as shown in FIG. 20 while changing the traveling direction to the side opposite to the center line 7 of the line light source 2. For this reason, the light 60a and 62a emitted from the line light source 2 travels in a direction offset in a direction (θ = 0) perpendicular to the first side surface 12 from the line light source having no prism. Therefore, the directivity of the line light source 2 is originally high.

Next, the reason why the directivity of the line light source 2 becomes high will be quantitatively explained according to Snell's law. FIG. 21 is a diagram for explaining the relationship between the incident angle θ _in and the outgoing angle θ _{out on} the first light exit surface 22 with the perpendicular 54a of the first side surface 12 as a reference. Here, the incident angle θ _in and the outgoing angle θ _out are angles measured clockwise from the perpendicular 54a of the first side surface 12, as shown in FIG.

The incident angle φ _in and the outgoing angle φ _out measured with respect to the perpendicular 54b of the first light emitting surface 22 can be expressed by the following equations using the incident angle θ _in and the outgoing angle θ _out .

φ _in = α-θ _in (1)
θ _out = α-φ _out (2)
Here, α is an inclination angle of the first light emitting surface 22 with respect to the first side surface 12. In the present line light source 2, α is 45 °.

On the other hand, φ _in and φ _out satisfy the following equation according to Snell's law.

1.49 × sinφ _in = sinφ _out (3)
Therefore, the emission angle θ _out can be expressed by the following equation.

θ _out = α-arcsin {1.49 × sin (α-θ _in )} (4)
The light exit angle θ _{out at} the second light exit surface 24 can also be expressed by Expression (4). However, the inclination angle β of the second light exit surface 24 with respect to the first side surface 12 is used instead of α. In this line light source 2, β is −34.28 °.

FIG. 22 illustrates the incident / exit relationship between the incident angle θ _{in of} the light 60 and 62 (see FIG. 20) incident on the prism and the outgoing angle θ _out of the light 60a and 62a (see FIG. 20) emitted from the prism. FIG. FIG. 22 shows an incident / exit relationship 64 at the first light exit surface 22 derived according to Equation (4) and an incident / exit relationship 66 at the second light exit surface 24 similarly derived according to Equation (4). FIG. 22 also shows an incident / exit relationship 58 (see FIG. 18) of a line light source having no prism. Here, the input / output relationship 64 on the first light output surface 22 is a curve obtained by translating the input / output relationship 58 of the line light source having no prism by (θ _in , θ _out ) = (+ 45 °, + 45 °). . Further, the incident / exit relation 66 on the second light exit surface 24 is a curve obtained by translating the incident / exit relation 58 by only (θ _in , θ _out ) = (− 34.28 °, −34.28 °). .

Now, it is assumed that the incident angle θ _{in of} light incident on the prism 6 is distributed in a range of −35 ° to + 35 °, for example. In this case, the emission angle θ _{out of} light _in which the incident angle θ _in is distributed from 0 ° to + 35 ° is distributed from −44 ° to + 30 ° according to the input / output relationship 64. Similarly, the emission angle θ _{out of} light _in which the incident angle θ _in is distributed from −35 ° to 0 ° is distributed from −35 ° to + 23 ° according to the input / output relationship 66. Therefore, according to the line light source 2, the emission angle θ _out of the light 60 and 62 incident on the prism 6 is −44 ° to + 30 °. On the other hand, in the line light source having no prism, the emission angle θ _out of the light incident on the flat light emission part 47d is distributed between −59 ° and + 59 ° as described above.

  As is apparent from the distribution of the emission angles, the width of the light emission angle of this line light source is 74 ° (= 44 ° + 30 °). On the other hand, the width of the light emission angle of the line light source having no prism is 118 ° (= 59 ° + 59 °). For this reason, the directivity of the present line light source 2 is higher than that of a line light source having no prism. Therefore, the luminance of the light irradiation area illuminated by the pair of main line light sources 3 is higher than that of the pair of line light sources not having the prism. Note that the width of the light emission angle is based on the above-described assumption, and is not an accurate simulation of the viewing angle characteristics of FIGS.

  In the above description, the inclination angles of the first light exit surface 22 and the second light exit surface 24 are 45 ° and −34.28 °, respectively. However, even if the inclination angles of the first light emitting surface 22 and the second light emitting surface 24 are changed, the directivity of the line light source 2 is higher than that of the line light source having no prism. That is, the inclination angle of the first light exit surface 22 and the second light exit surface 24 may be an angle other than 45 ° and −34.28 °.

  As described above, according to the present line light source 2, the luminance in the light irradiation region 41 is sufficiently high due to the small number of light emitting elements (for example, two), and luminance unevenness hardly occurs in the light irradiation region 41.

  FIG. 23 is a schematic diagram illustrating an example of an image scanner having the line light sources 2a and 2b. In the image scanner described with reference to FIG. 4, the line light sources 2a and 2b, the imaging lens 34, and the line sensor 36 are all stored in the light source case 32a. On the other hand, in the example shown in FIG. 23, the line sensor 36 and the imaging lens 34 are fixed not to the light source case 32a but to the casing 70 of the image scanner 68.

  The light diffusely reflected by the document 37 is converted into parallel rays by a collimator lens (not shown) stored in the light source case 32 a and guided to the imaging lens 34 by a plurality of mirrors 72. The light guided to the imaging lens 34 is imaged on the line sensor 36 and converted into an electrical signal. The two-dimensional image data of the document 37 is read by moving the line light sources 2a and 2b stored in the light source case 32a while repeating such photoelectric conversion.

  4 and 23, the document 37 is fixed and the line light source moves. However, the line light source and the line sensor may be fixed and the document may move.

(Embodiment 2)
FIG. 24 is a plan view of the line light source 2d of the present embodiment. 25 is a cross-sectional view taken along line XXV-XXV in FIG. As is clear from FIG. 24, the structure of the line light source 2d is substantially the same as that of the line light source 2 of Embodiment 1 (see FIG. 1). However, as shown in FIG. 25, unlike the line light source 2 of Embodiment 1, the light emitting part 6d of the line light source 2d has a right-angled triangular cross section. Further, the first inclined surface 74 of the light emitting portion 6d is perpendicular to the first side surface 12d. For this reason, the second slope 76 opposite to the long side 14 (see FIG. 24) of the first side surface 12 d is wider than the first slope 74. The other points are substantially the same as those of the line light source 2 of the first embodiment.

In the first embodiment, the operation of the line light source 2 is described on the assumption that the incident angle θ _{in of} light incident on the light emitting unit 6 is distributed in a relatively wide range (−35 ° to 35 °). did. However, when the incident angle theta _in the light incident on the light emitting portion 6 is distributed in a narrow range, the first light exit surface 22 is wider than the second light emitting surface 24, the line light source according to the first embodiment 2 ( 2) is not preferred.

For example, it is assumed that the incident angle θ _{in of} light incident on the light emitting unit 6 is distributed in a narrow range of −12 ° to 12 °. In this case, the incident angle θ _in of the light incident on the first emission surface 22 is distributed in the range of 0 ° to 12 ° as described with reference to FIG. The range of the emission angle θ _out corresponding to such a distribution is −44 ° to −9 ° according to the input / output relationship 64 of FIG. The light having such a negative emission angle θ _out travels in a direction inclined substantially toward the center line 7 side of the first side surface 12 of the light guide 4. Even if such light reaches the document 37 and is diffusely reflected, it is blocked by the line light sources 2a and 2b and does not reach the line sensor 36 (see FIG. 4). That is, almost all the light emitted from the first emission surface 22 is wasted.

On the other hand, the light emitted from the second light emitting part 24 travels _in the direction opposite to the center line 7 of the first side face 12 when the incident angle θ _{in of the} light incident on the light emitting part 6 is narrow, and is almost useless. do not become. For example, when the incident angle theta _in the light incident on the light emitting portion 6 is distributed in the range of -12 ° to 12 °, light incident on the second light emitting portion 24, input-output relation in Fig. 22 66 According to this, it is distributed in the range of −12 ° to 0 °. The range of the emission angle θ _out corresponding to such a distribution is 0 ° to 23 °. The light having such a positive emission angle θ _out travels substantially in the direction opposite to the center line 7 of the first side surface 12. For this reason, the light emitted from the second light emitting unit 24 is not wasted.

Thus, when the incident angle θ _{in of the} light incident on the light emitting portion 6 is distributed in a narrow range (centered around θ _in = 0 °), the second emitting surface 24 is changed to the first light emitting surface 22. By making it wider, useless emission of light can be suppressed.

  In the line light source 2d of the present embodiment, the second inclined surface 78 corresponding to the second light emitting surface 24 of the first embodiment is wider than the first inclined surface 74 corresponding to the first light emitting surface 22 of the first embodiment. It has become. Therefore, according to the line light source 2d, light incident on the second inclined surface 74 is reduced, and useless emission of light that does not reach the line sensor 36 is suppressed.

  In the line light source 2d, as shown in FIG. 25, the first slope 74 is perpendicular to the first side surface 12d. For this reason, the light incident on the first inclined surface 74 is easily totally reflected. For this reason, it is more difficult to emit unauthorized light.

  However, the first slope 74 may be inclined with respect to the first side surface 12d. Even in such a case, if the light emitting part 6d has the first inclined surface 74 on the long side 14 side and the second inclined surface 78 wider than the first inclined surface 74, it does not reach the line sensor 36. Useless light emission can be suppressed.

In the present embodiment, it is assumed that the incident angle θ _{in of} light incident on the light emitting portion 6d is distributed in a narrow range (for example, −12 ° to 12 °). Thus, whether θ _in is distributed in a narrow range or a wide range is determined by the shape of the light guide portion 4d and the like. Therefore, it is considered that a preferable structure of the light emitting portion also changes depending on the shape of the light guide portion 4d.

(Embodiment 3)
FIG. 26 is a cross-sectional view 2e of the line light source of the present embodiment. As shown in FIG. 26, the line light source 2e includes a reflecting portion 30e provided on the first inclined surface 74e of the light emitting portion 6e on the long side 14 side of the first side surface 12. Here, the reflecting portion 30e is a member that reflects light incident on the first inclined surface 74e, and is, for example, an Al film or a mirror-finished Al plate.
Thereby, useless light that does not reach the line sensor 3 is not emitted from the first inclined surface 74e. The other points are substantially the same as those of the line light source 2 of the first embodiment.

  In the second embodiment, the reflective portion 30e is not provided on the first slope 74, but the reflective portion 30e may be provided on the first slope 74 as in the present embodiment. Thereby, useless emission of light can be suppressed.

  In the above embodiment, the light emitting elements 10a and 10b are LEDs. However, the light emitting elements 10a and 10b are not limited to LEDs. For example, the light emitting elements 10a and 10b may be a surface emitting laser or an organic EL (electroluminescence) light emitting element.

  Moreover, in the above embodiment, the light guide 8 is formed with resin. However, the light guide 8 may be formed of other materials. For example, the light guide 8 may be formed of Pyrex (registered trademark).

  Moreover, in the above embodiment, the light guide part 4 has a prismatic shape. However, the light guide 4 may have other shapes. For example, the light guide 4 may have a semi-cylindrical shape with a semicircular cross section.

  Moreover, in the above embodiment, the light guide part 4 is integrally molded with the light emitting part 6. However, the light guide unit 4 and the light emitting unit 6 may be formed separately and then integrated.

  Moreover, in the above embodiment, this line light source is used as a light source of an image scanner. However, the line light source can also be used for other applications. For example, this line light source may be used as a light source for a facsimile, a copier, or the like. Or you may use this line light source for an illuminating device. Here, this line light source 2 is more suitable for a lighting device than a general line light source 2c having high directivity. In this case, the light output unit 6 may be provided at the center of the first side surface 12, for example.

2 ... line light source 4 ... light guide 6 ... light emitting part 8 ... light guides 10a, 10b ... light emitting element 28 ... diffuse reflection part 30 ... reflection part 44 ··LED

Claims (7)

A light guide having a columnar light guide and a light emitting part provided on a side surface of the light guide and extending in a longitudinal direction of the light guide;
A light emitting element provided at an end of the light guide,
The light emitting part is a line light source that is a triangular prism-shaped transparent region extending in the longitudinal direction. The line light source according to claim 1,
The light guide has a prismatic shape,
The line light source, wherein the light emitting part is provided in a region that is a part of the first side surface of the light guide unit and is in contact with a long side of the first side surface. The line light source according to claim 2,
The light guide has a second side surface adjacent to the first side surface;
The line light source according to claim 1, wherein one side surface of the light emitting unit and the second side surface are integrated to form one light emitting surface. The line light source according to claim 2,
The line light source according to claim 1, wherein the light emitting section includes a first slope on the long side and a second slope wider than the first slope. The line light source according to claim 4,
The line light source, wherein the first slope is perpendicular to the first side surface. The line light source according to claim 2,
The line light source further comprising a reflecting portion provided on the first slope on the long side of the light emitting portion. The line light source according to any one of claims 1 to 6,
The light emitting element is a light emitting diode,
The light guide has a diffuse reflection part extending in the longitudinal direction in a region which is a part of the side surface and is not provided with the light emitting part, and is the other part and the light emitting part. A line light source comprising: a reflection part in a region where the part and the diffuse reflection part are not provided.

Images