JP2006067551A - Original lighting system, image scanner, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an original lighting system which is improved in lighting efficiency and set uniform in illuminance both in a main scanning direction and in an auxiliary scanning direction by using a light guide board of comparatively simple configuration. <P>SOLUTION: A polygonal light guide plate 2, which is inscribed (partial coincidence is included) on a rectangle 20 having a length/width ratio (it is called a squareness ratio) of 1 or more to 1 in a cross-sectional shape, is arranged so as to set its optical axis L0 at a prescribed angle with the surface 5 of an original. Side faces c1, c3, and c6 serve as reflecting surfaces. An LED 1 is set very close to the plane of incidence 2a of the light guide plate 2, the high illuminance part of a composite curve G obtained from the distributions of illuminance of direct light and reflected light from the reflecting surfaces is considered as a maximum reading width B on the surface of the original, and a reading region is set in the maximum reading width B. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a document illumination device used for a reading device such as a digital copying machine, an image scanner, or a digital laboratory.

  In recent years, light emitting diodes (hereinafter referred to as LEDs) are being actively developed, and the brightness of LED elements is rapidly increasing. LEDs generally have advantages such as long life, high efficiency, high G resistance, and monochromatic light emission, and are expected to be applied in many lighting fields. One of the applications is a document illumination device for an image reading device such as a digital copying machine or an image scanner.

FIG. 25 is a schematic diagram of an image forming apparatus having an image reading apparatus.
In the figure, reference numeral 100 denotes an image forming unit, and 200 denotes an image reading unit. Other symbols are directly cited in the description.
The image forming unit 100 includes a drum-shaped latent image carrier 111, and a charging roller 112 as a charging unit, a developing device 113, a transfer roller 114, and a cleaning device 115 are disposed around the image forming unit 100. A “corona charger” can also be used as the charging means. Further, an optical scanning device 117 that receives document information from the outside such as an image reading unit and performs optical scanning with the laser beam LB is provided, and “exposure by optical writing” is performed between the charging roller 112 and the developing device 113. To do.

  When forming an image, the image carrier 111, which is a photoconductive photosensitive member, is rotated at a constant speed in the clockwise direction, and the surface thereof is uniformly charged by the charging roller 112. An electrostatic latent image is formed upon exposure to the image. The formed electrostatic latent image is a so-called “negative latent image”, and the image portion is exposed. The cassette 118 containing the transfer paper P is detachable from the main body of the image forming apparatus 100, and when the transfer paper P is loaded as shown in FIG. The transfer paper P that has been fed and fed is caught by the registration roller pair 119 at its leading end. The registration roller pair 119 feeds the transfer paper P to the transfer unit at the timing when the toner image on the image carrier 111 moves to the transfer position. The transferred transfer paper P is superimposed on the toner image at the transfer portion, and the toner image is electrostatically transferred by the action of the transfer roller 114. The transfer paper P to which the toner image is transferred is sent to the fixing device 116, where the toner image is fixed in the fixing device 116, passes through the conveyance path 121, and is discharged onto the tray 123 by the discharge roller pair 122. The surface of the image carrier 111 after the toner image has been transferred is cleaned by a cleaning device 115 to remove residual toner, paper dust, and the like. The latent image carrier 111 is a photoconductive photoconductor, and an electrostatic latent image is formed by the uniform charging and optical scanning, and the formed electrostatic latent image is visualized as a toner image.

In the image reading unit 200, the document 202 is placed on the contact glass 201, and the document 202 is illuminated by an illumination unit (not shown) mounted on the first traveling body 203 disposed below the contact glass 201. The reflected light from the document 202 is reflected by the first mirror 203 a of the first traveling body 203, and then reflected by the first mirror 204 a and the second mirror 204 b of the second traveling body 204 and guided to the reduction imaging lens 205. The image is formed on the line sensor 206.
When reading the longitudinal direction of the document, the first traveling body 203 moves to the right in the figure at a speed of V, and at the same time, the second traveling body 204 moves to the right at a speed 1/2 V that is half that of the first traveling body 203. To scan the entire document.

FIG. 26 is a diagram for explaining the configuration of the scanner.
FIG. 27 is a view for explaining details of the vicinity of the light source unit.
In both figures, reference numeral 207 denotes a light source.
Normally, a document illumination device used for an image reading device requires a length substantially the same as the document width to illuminate the document 201. Therefore, a cold cathode fluorescent lamp or a cylindrical xenon lamp is mainly used as the light source 207. Is used. An example of an illuminance distribution on the surface of the contact glass 201 by a cylindrical lamp is indicated by a symbol G0 in FIG.
When irradiation light from the light source 207 is irradiated onto the original 202, the reflected light from the original 202 is converted into an electrical signal by a light conversion element (CCD, CMOS, etc.) 206a.
FIG. 28 is a diagram for explaining the relationship between the document surface and the imaging surface.
In the figure, reference characters R, G, and B indicate the distinction of colors to be read, red, green, and blue, respectively.
For color, as shown in the figure, since the image forming positions are different for R, G, and B, a uniform illuminance distribution with this width is required on the document surface. This width is about 1 mm in terms of actual size, and will be at most 2 to 3 mm even if an allowable range due to tolerance is considered. On the other hand, the rod-shaped lamp as described above can illuminate a relatively wide illumination area almost uniformly as shown by the curve G0, but it is compared with the illumination width required in practice. It can be said that it is too wide.

In order to meet the demand for miniaturization of the apparatus, a configuration using a light emitting element, that is, an LED element, which can be said to be a micro light source as a light source compared to the rod-shaped lamp has been put into practical use.
Although LEDs have various excellent characteristics, the absolute brightness of each element is insufficient for use as an illumination device for image reading devices. It has been used mainly in equipment.
In order to compensate for this problem, it is common to increase the amount of light in the LED array by using a large number of LED elements constituting the LED array. However, since the light diffuses widely, it is not very efficient. It goes against power saving. In addition, when a bullet-like LED with less diffusion is used, the efficiency is improved, but the directivity is high and unevenness occurs in the main scanning direction.
There is an example of a document illumination device that combines an LED array and a long lens for the purpose of improving light utilization efficiency (see, for example, Patent Document 1 and Patent Document 2). In these apparatuses, the efficiency of the light has been increased by converging the light of the LED on the sub-scan section of each LED.

However, when such a method is used, there is a problem that, as described in Patent Document 1, the central portion of the convergent light is bright, and light is diffused and darkened rapidly at a position off the center.
Of the light emitted from the LEDs, most of the light emitted at an angle with respect to the sub-scanning cross section is wasted. Therefore, if a large number of LEDs are not arranged, illuminance unevenness in the main scanning direction occurs.
There is an example in which a light guide plate or a counter reflector having a simple shape is used in order to make the light quantity distribution in the main scanning direction uniform (see, for example, Patent Document 3). However, this configuration is characterized in that a diffraction grating is provided on at least one of the entrance surface, the reflection surface, and the exit surface in order to make the light amount distribution uniform in the main scanning direction. It does not require uniformity.

FIG. 40 is a schematic diagram showing the positional relationship of light receiving elements of a digital copying machine or an image scanner.
In the figure, reference numeral 8 denotes an imaging lens, 6 denotes a light receiving element, and 7 denotes a single light receiving portion.
In the digital copying machine and the image scanner, as shown in the figure, the reflected light from the original is received by the single light receiving portion 7 of the light receiving element 6 through the imaging lens 8. In the light receiving element 6 such as a CCD sensor, the width of the single light receiving portion 7 is usually as narrow as about 0.05 to 0.1 mm. That is, in the case of equal magnification imaging, only a narrow area equal to that can be read on the original surface. If the light from the light source is collected sharply, the position of the illuminance distribution curve shifts due to the displacement of the illumination position due to a mirror angle shift or the like, and the amount of light reaching the single light-receiving unit 7 changes greatly, greatly affecting the formed image. Will be given.
This figure shows an example using an equal-magnification sensor, but the width of the illumination area on the document side that forms an image on the single light-receiving unit 7 even when the reduced optical system is used to reduce the image to 1/10, for example. The problem is the same because it is only about 1 mm at most.

FIG. 41 is a diagram showing the relationship between the change in the illuminance distribution curve and the reading position. FIGS. 4A and 4B show the case where the width of the illuminance distribution curve is relatively narrow, and FIGS. 3C and 3D show the case where the width of the illuminance distribution curve is relatively wide. Here, “relative” means a case where it is viewed in relation to the width of the reading area.
(A), (c) of the same figure shows the state illuminated normally.
In the case of a digital copying machine, since the width of the light receiving unit is as narrow as about 0.1 mm, for example, if the center position of the illuminance distribution curve deviates from the reading unit as shown in FIG. Illuminance falls. For this reason, in a digital copying machine or an image scanner, the illuminance distribution curve in the sub-scanning corresponding direction as shown in FIGS. 3C and 3D is wide, and the center position of the illumination is shifted from the reading unit. There is a need for a document illumination device that does not produce a difference in illuminance in the reading area. For this purpose, in the vicinity of the maximum value of the illuminance distribution, an illuminance unevenness of a width (for example, about 1 mm on one side) or more obtained by adding a fluctuation range due to a mechanical error or the like to a width necessary for reading (up to about 1 mm in the above example). There should be a small portion, that is, a flat portion with illuminance.
This flat part means a part that falls within the rate of change in a range that can be put into practical use by electrical correction such as AGC when handling a monochrome image even if the illuminance is not as designed when the mechanism is determined, The rate of change is acceptable up to about 30%. When a color image is handled, the rate of change is acceptable up to about 12% because it falls within a range in which the collapse of the color balance of the three primary colors can be corrected rather than the AGC problem.

FIG. 42 is a schematic diagram showing a state of illumination by a rod-shaped light source.
In order to satisfy this, as shown in the figure, the reflecting mirror for the rod-shaped light source can be used to illuminate the document surface extensively without collecting too much light, although it is low in efficiency. There has been proposed a configuration that creates an appropriate illuminance distribution by combining the above (see, for example, Patent Document 4). However, since this configuration is based on the premise that a rod-shaped light source is used, it is impossible to apply to a much smaller LED. The reason is mainly the difference in the ratio of the size of the surface to be illuminated and the light emitting part of the light source. The width of the illuminated surface in the sub-scanning direction is about several millimeters, but the size of the light emitting portion of the bar light source is larger than that, whereas the light emitting portion of the LED is smaller than the width of the illuminated surface. This difference causes a difference in the distance between the light source and the surface to be illuminated, the size of the reflecting mirror, and the like.
The use of the same configuration as that shown in the figure for using the LED array cannot achieve the original purpose of compensating for the insufficient brightness of the LEDs because the light utilization efficiency is too low.
A configuration for using an LED as an illumination light source has also been proposed (see, for example, Patent Document 5). However, the configuration shown in Patent Document 5 does not mention the illuminance distribution in the illuminated area.

43 and 44 are schematic views showing a state of illumination by a plurality of LEDs.
45 and 46 are schematic views when a light guide plate is disposed between the LED and the surface to be illuminated.
As described above, the method of illuminating the surface to be illuminated using a large number of LED elements has been described that light diffuses widely. To improve this, for example, when an LED array is brought close to the surface to be illuminated, FIG. As shown at 44, the brightness unevenness of each LED appears in the longitudinal direction.
Therefore, as a method of reducing the unevenness in the longitudinal direction while bringing the light source and the illuminated surface close to each other, the width in the longitudinal direction (main scanning direction) as shown in FIGS. The direction (sub-scanning direction) is a quadrangular prism that is about the short-side illumination width of the surface to be illuminated. The light emitted from the light source is incident on the light guide plate and is repeatedly reflected in the short direction, but is guided to the light exit surface of the light guide plate in the longitudinal direction without being affected except at the end, and illuminates the surface to be illuminated. If the light emitting surface of the light guide plate is regarded as a secondary light source, this method can reduce illumination unevenness in the longitudinal direction while bringing the light source and the surface to be illuminated closer. For the purpose of reducing illumination unevenness, it is desirable that the number of times of light reflection is large, so it is desirable that the short direction of the light guide plate is long, but if there is a length limitation on the layout, the mirror surface state is roughened Irradiation unevenness can be reduced by using a method of irregular reflection.

Japanese Patent Laid-Open No. 11-232912 (2nd page, FIGS. 1 and 9) JP-A-8-111545 (Page 4, FIG. 3) Japanese Patent Laid-Open No. 10-322521 (page 11, FIG. 11) Japanese Patent Laid-Open No. 6-22087 (page 3, FIG. 1) JP 2002-93227 A (page 4, FIG. 1)

SUMMARY OF THE INVENTION An object of the present invention is to solve these problems. A document illuminating apparatus that uses a plurality of light emitting elements and does not generate illuminance unevenness in the main scanning direction, has no uneven illuminance in the sub-scanning direction, and has high illumination efficiency. Is to provide.
In addition, the present invention proposes a configuration with improved light utilization efficiency to compensate for the lack of brightness of the LED elements. The surface to be irradiated is brightened with one LED or an LED array with a small number of elements. The purpose is to illuminate. An object of the present invention is to provide an illuminating device that has a wide illuminance distribution curve in the width direction of the surface to be illuminated, little illuminance unevenness, and little or no change in illuminance on the surface to be illuminated even if the illumination region is shifted within the error range of the mechanism And

  According to the first aspect of the present invention, the illuminated area having a length and a width for reading on the document surface, and the main scanning direction when the length direction is the main scanning direction and the width direction is the sub scanning direction. A plurality of light emitting elements arranged at predetermined intervals, and a light guide plate disposed between the plurality of light emitting elements and the document surface and guiding light beams from the plurality of light emitting elements to the illuminated area. In the illuminating device, the light guide plate has a length substantially equal to or longer than the length of the illuminated region in the main scanning direction, and the shape in the sub-scanning section has a ratio of the length to the width. A rectangle having a rectangular ratio of 1 or more, or a polygonal shape inscribed in the rectangle, the light emitting surfaces of the plurality of light emitting elements face one short side of the rectangle to form a light incident surface, and the other short Light is emitted with the side close to the illuminated area. And a plurality of surfaces corresponding to the two long sides of the rectangle connecting the exit surface and the entrance surface (hereinafter referred to as side surfaces) as light reflecting surfaces, and the optical axes of the plurality of light emitting elements are Arranged parallel to the long side of the rectangle, the optical axis is inclined at a predetermined angle with respect to the normal line of the document surface, out of the light flux from the exit surface of the light guide plate in the sub-scanning section, A reading area is set in an overlapping area between the direct light and at least one reflected light from at least two reflecting surfaces among the plurality of reflecting surfaces.

According to a second aspect of the present invention, in the document illuminating device according to the first aspect, at least one of the side surfaces has a predetermined inclination angle that is not parallel to the optical axis.
According to a third aspect of the present invention, in the document illuminating device according to the first or second aspect, the side surface has two surfaces that are connected to each other and have different inclination angles with respect to the optical axis.
According to a fourth aspect of the present invention, in the document illumination device according to the second or third aspect, the inclined direction of the side surface is a direction in which the exit surface side is farther from the optical axis than the incident surface side. It is characterized by.
According to a fifth aspect of the present invention, in the document illuminating device according to any one of the first to fourth aspects, the side facing the optical axis of the side surface is a surface subjected to high reflection treatment, and The optical axis side is hollow.

According to a sixth aspect of the invention, in the document illuminating device according to the fifth aspect of the invention, the distances from the light emitting element to the two end portions connected to the emission surface of the side surface are different.
According to a seventh aspect of the present invention, in the document illuminating device according to any one of the first to fourth aspects, the light exit surfaces of the light guide plate have different inclination angles with respect to the optical axis. It consists of two surfaces.
According to an eighth aspect of the present invention, in the document illuminating device according to the seventh aspect, the light exit surface of the light guide plate is asymmetric with respect to the optical axis.
According to a ninth aspect of the present invention, in the document illuminating device according to any one of the first to fourth aspects, the light emission surface is not orthogonal to the optical axis and has a predetermined inclination angle. It is characterized by that.
According to a tenth aspect of the present invention, in the document illuminating device according to the ninth aspect, the inclination direction of the light exit surface is a direction in which a corner portion of the light guide plate closest to the document surface is separated from the document surface. It is characterized by being.

According to an eleventh aspect of the present invention, in the document illuminating device according to any one of the first to fourth and seventh to tenth aspects, the light guide plate is made of a transparent member having a refractive index of 1.4142 or more. And
According to a twelfth aspect of the present invention, in the document illuminating device according to any one of the first to eleventh aspects, a part of a light beam that does not reach the reading region out of the light beam from the light guide plate is the reading region. A reflecting mirror is provided at a position facing the light exit surface of the light guide plate.
According to a thirteenth aspect of the present invention, in the document illuminating device according to any one of the first to eleventh aspects, a light guide plate having the same shape as the light guide plate combined with the plurality of light emitting elements is substantially related to the reading region. It is characterized by being provided symmetrically.
According to a fourteenth aspect of the present invention, there is provided an image reading apparatus using the document illumination device according to any one of the first to thirteenth aspects.
According to a fifteenth aspect of the present invention, an image forming apparatus using the image reading device according to the fourteenth aspect is characterized.

In the invention according to claim 16, when the illumination area has a length and a width for reading on the document surface, the length direction is a main scanning direction, and the width direction is a sub-scanning direction, the main scanning direction A plurality of light emitting elements arranged at predetermined intervals, a light guide plate having an incident surface on which light beams from the plurality of light emitting elements are incident, an output surface for emitting the light beams in a predetermined direction, and emitting the light guide plate An original illuminating device having a reflecting member that guides the luminous flux to the illuminated area, wherein the illumination distribution in the sub-scanning direction of the illuminated surface has a flat portion having a predetermined width or more.
In the invention according to claim 17, in the document illuminating device according to claim 16, the half value width L of the illuminance distribution in the sub-scanning direction is:
2 ≦ L ≦ 10
It is characterized by being in a range satisfying.
In the invention according to claim 18, in the document illumination device according to claim 17, when the thickness of the light guide plate is H, H and L are 0.5 ≦ L / H ≦ 30.
It is characterized by satisfying the relationship.

According to a nineteenth aspect of the present invention, in the document illumination device according to any one of the sixteenth to eighteenth aspects, the reflecting member is a reflecting member having a concave surface, and the concave surface is formed on the exit surface of the light guide plate. It is characterized by being directed.
According to a twentieth aspect of the present invention, in the document illumination device according to any one of the sixteenth to eighteenth aspects, the reflecting member is a pseudo concave reflecting member formed of a plurality of planes, and the emission surface of the light guide plate The quasi-concave surface is directed to the surface.
According to a twenty-first aspect of the present invention, in the document illuminating device according to any one of the sixteenth to twentieth aspects, the plurality of light emitting elements are arranged in one row, and the length of the element row and the light guide plate The vertical direction is arranged in parallel.
According to a twenty-second aspect of the present invention, in the document illuminating device according to any one of the sixteenth to twenty-first aspects, the plurality of light emitting elements are white LEDs.

According to a twenty-third aspect of the present invention, in the document illuminating device according to any one of the sixteenth to twenty-second aspects, at least two types of LEDs each having a different emission color are used for the plurality of light emitting elements. Are mixed when reflected multiple times in the light guide plate, and become white light on the exit surface of the light guide plate.
According to a twenty-fourth aspect of the present invention, in the document illuminating device according to any one of the sixteenth to twenty-third aspects, the light emitting surfaces of the plurality of light emitting elements are in close contact with the incident surface of the light guide plate. It is characterized by being.

According to a twenty-fifth aspect of the present invention, there is provided an image reading apparatus using the document illumination device according to any one of the sixteenth to twenty-fourth aspects.
According to a twenty-sixth aspect of the present invention, there is provided a color original reading device using the original illumination device according to any one of the sixteenth to twenty-fourth aspects.
According to a twenty-seventh aspect of the present invention, there is provided an image forming apparatus using the image reading device according to the twenty-fifth aspect or the color original reading device according to the twenty-sixth aspect.

  According to the illumination device of the present invention, by using a light guide plate having a relatively simple configuration, it is possible to obtain a document illumination device that has high illumination efficiency and little illuminance unevenness in both the main scanning direction and the sub-scanning direction. .

FIG. 1 is a side sectional view showing the basic concept of the illumination device of the present invention.
FIG. 2 is an exploded perspective view of the light source unit of the illumination device of the present invention.
In both figures, reference numeral 1 denotes an LED as a light source, 2 denotes a light guide plate, 3 denotes a light source device, 4 denotes a contact glass, and 5 denotes a document surface.
The plurality of LEDs 1 are arranged at a predetermined interval in the longitudinal direction of the elongated substrate 1a. A combination of a plurality of LEDs 1 and a substrate 1a is referred to as a light source unit. A light guide plate 2 made of a plate-like transparent material is disposed along the longitudinal direction. In the light guide plate 2, the surface 2a facing the LED 1 is a light incident surface, the opposite surface 2b is a light emitting surface, and at least two other surfaces (referred to as side surfaces) along the longitudinal direction are light reflecting surfaces 2c. Used as. When the light is incident at an angle of the total reflection region, the reflection surface 2c is not particularly required as long as it is a smooth surface, but if not, is total reflection treatment such as aluminum vapor deposition performed, for example? Alternatively, a bright aluminum plate should be adhered.
The predetermined interval at which the LEDs are arranged refers to an arrangement interval in which the illuminance unevenness on the document surface falls within, for example, 12% allowed for a color document. Since this interval varies depending on the light emission distribution of the LED, the size of the light guide plate, and the like, it is determined based on the actually measured value.
Although the light emitting surface of the LED and the incident surface 2a of the light guide plate 2 are shown in close contact with each other, they may be separated as necessary.
In FIG. 2, the light guide plate 2 and the light source unit are shifted from each other for easy understanding.

FIG. 3 is a diagram for explaining the distribution of light emitted from the LED. The figure (a) is a figure which shows ideal light distribution, and the figure (b) is a figure which shows an example of the specification of LED currently used practically.
In FIG. 2A, reference numeral 1L denotes a light exit surface, and Q1 denotes a light emission distribution curve.
In principle, the LED 1 has a maximum light amount in the normal direction of the light exit surface 1L. A normal line standing on the light emission surface at the light emission center of the LED 1 is referred to as an optical axis of the LED 1. The light amount level with respect to the inclination angle θ from the optical axis is generally represented by f (θ). For an ideal light distribution,
f (θ) = cos θ
When the light quantity levels are connected by a curve, the cross section becomes a circle as shown in the figure. In this figure, the light quantity level on the optical axis is 1, and the others are represented by relative values. When the LED can be regarded as a point light source, the distribution curve Q1 has a spherical shape with a diameter of 1 when viewed three-dimensionally. This distribution is called Lambertian distribution. The light emission angle from the normal line at which the light amount level is halved is called a half-value angle. In this distribution, the half-value angle is 60 °.
FIG. 2B shows one of many standards. In the figure, reference sign Q2 indicates a light amount distribution curve representing a standard value. This standard value can be approximated by the equation (cos θ) ^1.5 . In this standard, the half-value angle is approximately 51 °.
The actual product is usually made so as not to fall below the standard value, and in some cases, the output may be larger than the standard value.

  The combination of the LED 1 and the light guide plate 2 is such that the optical axis of the LED 1 is inclined at an angle of about 30 ° to 45 ° with respect to the normal of the contact glass 4 on which the document surface is placed as the light source device 3 attached to the frame. Has been placed. In principle, the reading direction is made to coincide with the normal of the contact glass at a position where the illuminance distribution on the original surface is maximized, and the reflected light from the original is reflected in a predetermined direction by the first mirror 3 a held by the light source device 3. Is done.

FIG. 4 is a diagram for explaining a basic configuration example of the present invention.
The manner in which the light beam from the LED 1 is guided by the light guide plate will be described with reference to FIG.
The shape of the cross section perpendicular to the longitudinal direction of the light guide plate 2 is a rectangle in which the lengths of the incident surface 2a and the light emitting surface 2b are equal, and the length of the reflecting surface 2c is set to be twice that length, The LED 1 was brought into close contact with the central portion of the incident surface 2 a of the light guide plate 2. Thus, the ratio of the length to the width of the rectangle is referred to as the rectangle ratio. In this example, the rectangular ratio is 2. In this configuration, since the incident surface 2a and the reflecting surface 2c are orthogonal to each other, the optical axis L0 of the LED 1 is parallel to the reflecting surface 2c.
When the LED 1 and the incident surface 2a are not in close contact with each other, the light flux from the LED is once emitted into the air and then incident on the light guide plate 2. Therefore, refraction based on the refractive index of the light guide plate 2 occurs at the time of incidence. The spread angle of the light beam becomes smaller than that in the air. When the LED 1 and the light guide plate 2 are in close contact, there is no apparent refraction phenomenon, but the spread of the light beam in the light guide plate is the same as the spread of the light beam resulting from refraction. In the same figure, the refractive index is shown as 1.5 considering the use of glass or acrylic as the light guide plate 2 and the convenience of calculation. In this case, the critical angle of the light guide plate 2 with respect to the air is about 41.8 °, and even if a light beam having an emission angle of 90 ° from the LED 1 enters the light guide plate 2, the light guide plate 2 enters the light guide plate with respect to the optical axis. The incident angle is 41.8 ° and there is no light beam with a larger angle. Incidentally, the light ray entering at this maximum angle has an incident angle of 90 ° -41.8 ° = 48.2 ° with respect to the reflecting surface 2c, and this angle is larger than the critical angle 41.8 °, so that the 2c surface is Even if no reflective treatment is performed, total reflection occurs. Other light rays have an angle of incidence of less than 41.8 ° when incident on the 2a plane, so that the incident angle is greater than 48.2 ° with respect to the 2c plane, resulting in total reflection. As described above, when all the light rays incident on the side surface are totally reflected as a result, the side surface is called a mirror surface for convenience.

The above phenomenon is based on the premise that the refractive index of the medium is 1.5. Here, consider a case where the refractive index is even lower.
The condition that a light beam incident at a critical angle θ from an LED becomes a totally reflected light beam on a reflection surface orthogonal to the incident surface is 90 ° −θ = θ, using the above formula. Therefore, θ = 45 ° is obtained. The refractive index of the medium whose critical angle is 45 ° is
n = sin45 °
Sought in
n = √ (2) ≈1.4142
It becomes.
In other words, if a medium having a refractive index of about 1.4142 or more is used, the light flux of the LED entering from the incident surface is always totally reflected to the side surface orthogonal to the incident surface, even if the 2c surface is not subjected to a particularly reflective process. It becomes a luminous flux.

Considering a material that is practically available as a transparent member, the smallest refractive index is approximately n = 1.35. The critical angle of this medium is about 47.8 °. When this medium is applied to this configuration example, a light beam incident at a critical angle has an incident angle of 90 ° -47.8 ° = 42.2 ° with respect to a reflecting surface orthogonal to the incident surface, which is not a total reflection condition. . On the contrary, a light ray incident on the incident surface at 42.2 ° becomes a total reflection condition on the side surface. Therefore, the light beam outside the light source emission angle of about 65 ° corresponding to this angle of 42.2 ° does not become totally reflected light on the side surface, but exits from the side surface. Since this amount of light is lost to the illumination device, the light amount level at an emission angle of 65 ° is about 0.27 when the light distribution is (cos θ) ^1.5 . The amount of light included in an angle larger than that angle is only about 2% even when both sides of the optical axis symmetry are combined. Accordingly, if only the light loss is considered, the side surface reflection processing may be omitted in any transparent medium. However, if the light rays coming out from the side surface become stray light and affect the image quality degradation, it is necessary to take countermeasures.

The luminous flux in the range of the angle α1 directly directed from the LED 1 to the emission surface 2b diverges and exits in the range indicated as “direct luminous flux” in FIG. The light beam in the range of the angle α2 that is emitted from the LED 1 to the outside of the direct light beam is reflected by the reflecting surface 2c and exits from the emitting surface 2b as a reflected light beam once. Only the light beam up to α3 indicating the angle up to the critical angle is reflected twice as the outer light beam.
There are two reflecting surfaces 2c. For convenience of description, the two reflecting surfaces 2c are distinguished from each other as the c1 surface and the other as the c2 surface.
Since the reflecting surface c1 is a mirror surface, a virtual image 1 ′ of the LED 1 is generated at a predetermined position. The light beam in the range of the angle α2 is reflected as if it were a light beam from this imaginary light source. After exiting from the exit surface 2b, the light exits in the range shown as "c1 surface once reflected light beam" in the figure.
Reflected light from the c2 plane also emerges as divergent light similar to the above with respect to the optical axis.
If the reflectivity of the reflecting surface is 100%, the light beam reflected several times should be taken into consideration. In practice, however, the light quantity level decreases as the emission angle from the light source increases, and the twice reflected light. Is only in the range of the angle α3, and the contribution rate to the illuminance on the original surface is drastically reduced. Therefore, even if a large number of judgments are basically made up to one reflection, there is no great error.
In the figure, the hatched area is an area where the direct light and the one-time reflected light pass in common. This area is called a light flux overlapping area. Therefore, if a reading area is placed in this area, illumination with a relatively high illuminance should be obtained.

FIG. 5 is a diagram showing the illuminance distribution when the optical axis of the LED is tilted by 30 ° with respect to the normal of the document surface.
Assume a reading surface in which the normal N is inclined by γ = 30 ° with respect to the optical axis L0 of the light source device. However, in the figure, the thickness of the contact glass and the accompanying light refraction are omitted. Therefore, if the distance between the light guide plate 2 and the document surface is too small, the contact glass may not be sufficiently thick. Even in such a case, it can be used for an image forming apparatus of a document moving type with a fixed reading position. Further, the document surface is set at a limit position where the reading area is not blocked by the light guide plate 2 itself.
In the figure, symbol G is a curve indicating the relative illuminance on the document surface. The calculation of the illuminance assumes that the illuminance by direct light from the LED at the position P where the exit surface 2b intersects the optical axis is 1, and the light distribution of the light source is (cos θ) ^1.5, and each point on the document surface is calculated. The relative distance and the incident angle on the document surface are taken into consideration. The same applies to all the following drawings.
The discontinuous portion of the illuminance distribution curve G is formed by a limit light beam of a direct light beam or a once reflected light beam.
The area having the width where the reading surface (document surface) and the hatched area in FIG. 4 intersect has the highest illuminance, and the region in the normal N direction (reading direction) standing on the reading surface at this position is the maximum reading beam width B. Become. In the drawing, B is about 0.18 times the thickness (cross-sectional width) of the light guide plate 2. If the maximum reading light beam width B is 2 mm, the cross-sectional size of the light guide plate 2 is about The width may be 11 mm and the length may be 22 mm.
In the same figure, the angle of the light beam included until one-time reflection is larger than the half-value angle and is 64 ° on one side, and the light amount level at that angle assumes that the light amount distribution is (cos θ) ^1.5 distribution. The light amount level at the angle is approximately 0.29. Even assuming a Lambertian distribution, it is only about 0.44.

Here, the distance between the light guide plate 2 and the document surface will be considered.
In the case of a light source moving type scanner, the contact glass as the document placement surface needs to be at least about 3 mm. On the other hand, in the case of a document moving type scanner, the load applied to the contact glass is relatively small, so that it can be used even if it is thinner than the above. However, considering the mechanical strength, it is not preferable to make it too thin. If possible, we want to ensure a thickness of at least 2 mm.
Since the contact glass (including the case of synthetic resin) has a certain refractive index, it is not necessary to set the distance between the light guide plate 2 and the document surface in FIG. For example, when a medium having a thickness of 2 mm and a refractive index of 1.35 is used as the contact glass, the distance in the thickness direction corresponds to about 1.5 mm in the air.
Therefore, when the maximum reading light beam width B is considered to be 2 mm, it can be considered that the light guide plate 2 can be used if the distance between the light guide plate 2 and the document surface is two-thirds or more.
Conversely, when the distance between the light guide plate 2 and the original surface is not more than two-thirds of the maximum reading beam width B, the maximum reading beam width B is set to an appropriate value of 2 mm or more. It can be configured to be usable with.

6 and 7 are diagrams showing the illuminance distribution when the optical axis of the LED is inclined by 45 ° with respect to the normal of the document surface. FIG. 6 is a diagram showing a sub-scan section similar to FIG. 1, and FIG. 7 is a diagram showing a section including LEDs and inclined by 45 ° with respect to the sub-scan section.
In FIG. 6, the optical axis L0 is inclined at γ = 45 ° with respect to the normal N established at the point where the optical axis L0 intersects the document surface 5. Reference numeral G denotes an illuminance distribution curve on the document surface in this configuration. For comparison, the illuminance distribution curve shown in FIG. 5 is indicated by a dotted line as G ′. The curve G has a maximum illuminance greater than G ′, and the maximum reading width B is also larger than that shown in FIG. In FIG. 6, B is about 0.45 times the thickness (cross-sectional width) of the light guide plate 2. If the maximum reading light beam width B is 2 mm, the cross-sectional size of the light guide plate 2 is about The width is 4.5 mm and the length is 9 mm.
FIG. 7 shows the state of the light beam reaching the document surface in a direction inclined by 45 ° with respect to the main scanning direction. Since the light beam passes through the light guide plate at an angle of 45 °, the optical path extends to about 1.4 times the length in the case of FIG. Since the light beam tilted with respect to the main scanning direction is refracted in the main scanning direction on the entrance surface and the exit surface, the light beam has a three-dimensional deviation. It was simplified for the sake of explanation.
Reference numeral G ₄₅ indicates an illuminance distribution curve in this cross section. The calculation method of the illuminance distribution is the same as that in FIG. In the same position of the document surface 5, since the light beam is also superposition of a plurality of LED on the closer position, the contribution rate of the illuminance distribution of the G ₄₅ becomes smaller, affecting the size of the maximum reading beam width B There is no.
However, looking at the change in illuminance within the range of the maximum reading light beam width B, the ratio of the minimum value to the maximum value is 85.3%, which is close to 15% in terms of illuminance unevenness. In order to solve this problem, it is preferable to place a reflecting mirror (not shown) at an appropriate angle on the opposite side of the light guide plate 2 across the reading width, and to fold back the light beam that illuminates the document surface wastefully. By turning back, the gradient of illuminance is reversed, and the ratio between the maximum value and the minimum value shown earlier becomes smaller.

FIG. 8 is a diagram illustrating a configuration example for eliminating unevenness in illuminance.
In this configuration, a light guide plate 2 ′ having the same shape as the light guide plate 2 including a plurality of light emitting elements shown in FIG. 6 is arranged almost symmetrically across the reading region.
The illuminance distribution curve G on the document surface 5 is a combination of the illuminance distribution curves G ′ and G ″ (both indicated by broken lines) by the respective light guide plates 2 and 2 ′. Each before the combination is symmetric with respect to the reading area. Therefore, the portion where the reverse gradient portions overlap is almost flat, and the problem of uneven illumination is almost eliminated.
By the way, although the above configuration example has been described by using a transparent medium having a refractive index of 1.5, an illumination system device can be made even with a configuration in which two simple reflecting mirrors are arranged facing each other in the air. .

FIG. 9 is a diagram for explaining another configuration example of the present invention.
The optical axis L0 of the light emitting element 1 is disposed at a predetermined angle with respect to the document surface 5 and inclined at 45 ° in order to correspond to FIG.
In this configuration example, two reflecting mirrors c <b> 1 and c <b> 2 are disposed oppositely symmetrically with respect to the optical axis L <b> 0 of the light emitting element 1. Since this configuration can be regarded as almost the same as the refractive index of the light guide plate in FIG. 6 determined as n = 1, the two reflecting mirrors c1 and c2 in this configuration example are regarded as one body and are referred to as the light guide plate 2. To. Accordingly, although the light incident surface 2a and the light exit surface 2b have no substantial surface, the same definition as shown in FIG. 4 is used.
The light guide plate 2 of this configuration example has a rectangular ratio of 2 as in the configuration example of FIG. Moreover, since the refractive index of the medium of the light guide plate 2 in FIG. 6 is 1.5 as a whole, the size of the light guide plate 2 is formed to be 1.5 times in this configuration example. In this way, it is easy to compare the difference in document surface illuminance distribution. 9, the illuminance distribution curve according to this configuration example is indicated by a solid line G, and the illuminance distribution curve shown in FIG. 6 is indicated by a broken line G ′. Both curves are shown with the original surface and the center of the maximum reading area width B aligned. Both have a slight difference in the illuminance level, and the discontinuous positions are slightly shifted, but the trends are very similar.

In this configuration example, the reflective surfaces c1 and c2 are shown with the same length, but in this configuration, the same length is not necessarily required. Although not particularly shown, the lengths of the respective lengths may be changed according to the design needs. That is, the distances from the light emitting elements that reach the two end portions of the side surface that are continuous with the emission surface 2b may be different.
As can be seen from FIG. 9, the difference in refractive index within the light guide plate is not an essential problem for the present invention. In the various configuration examples of the present invention described below, the refractive index is treated as n = 1.5 for the sake of explanation. However, as long as a shape such as a rectangular ratio is selected, a medium having a refractive index n = 1 is basically used. apply. The configuration in which the light reflecting surface described later is inclined with respect to the optical axis can be easily configured by, for example, an aluminum drawing material. However, when the shape of the light exit surface 2b described later is changed in the case of a medium of n = 1, there is no effect of the shape change.
In the configuration example shown in FIGS. 4 to 9, it is not particularly meaningful to set the rectangular ratio to 2. Therefore, the case where the rectangular ratio is smaller than 2 is considered below.

FIG. 10 is a diagram for explaining a light beam when a light guide plate having a rectangular ratio of 1 is used.
In the figure, the light beam from the imaginary light source 1 ′ becomes a light beam including a critical angle, and the light beam exiting the emission surface 2 b is emitted in a wide range shown as “c1 surface once reflected light beam” in FIG. The same applies to the virtual light source 1 ″ by the c2 plane. In this configuration example, there is no doubt that there is an overlapping region of light beams, but not only γ = 30 ° or 45 ° but also an arbitrary angle γ It is not possible to place an inclined document surface.
The reason is that even if the document surface is set so as to pass through the overlapping region, if the extension of the normal line standing on the document surface from any position in the region passes through the light guide plate 2, the light guide plate 2. This is because the reading area is shielded and cannot be used. In summary, the reading area cannot be set unless there is a sufficiently large overlapping area outside the arc R having both ends of the exit surface 2b of the light guide plate 2 as diameters. In the figure, it can be seen that the original surface near γ = 45 ° can be barely placed, but the reading area can hardly be secured. However, the thickness of the contact glass is not yet considered in the figure.
Therefore, a high-illuminance original illumination area cannot be secured with a light guide plate having a rectangular ratio of 1.

FIG. 11 is a view for explaining a light beam when a light guide plate having a rectangular ratio of 1.5 is used.
In the figure, a document surface inclined at γ = 45 ° can be placed in the overlapping region of light beams, but a reading area having a practical width cannot be set on the document surface inclined at γ = 30 °. This is related to the emission angle (β in the figure) of the light beam from the imaginary light source 1 ′ (or 1 ″) at the end of the emission surface 2b near the imaginary light source. The document surface cannot be set at an angle, because even if such a document surface is set, the light guide plate 2 itself cannot get in the way to obtain the read light beam from the overlapping region of the light beam. However, when the emission angle β is 30 °, for example, even if the document surface inclination angle γ is set to 30 °, the width of the reading light beam is 0, and a practical reading light beam width cannot be obtained. Γ> β Since the document surface and the reading direction are orthogonal to each other, even if the emission angle is within a settable range when viewed from the reading area (for example, when β = 30 °, γ = 60 °) even if the original surface is in contact with the light guide plate 2 Therefore, not only the direct relationship between γ and β, but also the remainder angle of γ is related to β, that is, the relationship of 90 ° −γ> β is required.
When γ = 45 °, the remainder angle is also 45 °. Therefore, the inclination angle of 45 ° is the angle that is most easily set as the document surface. When the maximum reading width B is secured, the conditions for securing the above-mentioned minimum distance as the contact glass space are exactly the configurations shown in FIG. Therefore, when the refractive index is 1.5, it is desirable to use a rectangular ratio of 1.5 or more in principle. However, as the refractive index decreases, β becomes smaller, so that even a smaller rectangular ratio can be used.

FIG. 12 is a diagram for explaining another configuration example of the present invention.
This figure shows an example in which the thickness of the light guide plate shown in FIG. 4 is changed.
FIG. 12 is the same except that the thickness (width in the cross section) of the light guide plate 2 is one third of that of FIG. That is, the rectangular ratio is 6.
In the case of this shape, the luminous flux up to the fourth reflection is in the same angular range as the luminous flux of the single reflection in the shape shown in FIG. However, the light beams reflected by the third and fourth reflections have a considerably large exit angle from the exit surface 2b and do not reach the vicinity of the center of the original surface, so that the maximum reading beam width is not affected. Omitted.

FIG. 13 is a diagram showing the illuminance distribution when the optical axis of the LED is inclined by 30 ° with respect to the normal of the document surface.
Since the light beam reaching the reading surface is basically the same as described above, detailed description thereof is omitted.
In the drawing, B is approximately 0.3 times the thickness (cross-sectional width) of the light guide plate 2.
If the maximum reading light beam width B is 2 mm, the cross-sectional size of the light guide plate 2 may be approximately 6.7 mm wide and 40 mm long.
Also, in the figure, the angle of the light beam included by the second reflection is smaller than the half-value angle and is 35.2 ° on one side, and the light quantity level at that angle is approximately 0.74 in the case of (cos θ) ^1.5 distribution. is there.
That is, the configuration shown in the figure cannot be made much smaller than the configuration shown in FIG. 5, and the light utilization efficiency is considerably reduced.

FIG. 14 is a diagram showing the illuminance distribution when the optical axis of the LED is tilted 45 ° with respect to the normal of the document surface.
In this configuration example, if a document surface with an inclination angle γ = 45 ° is placed on the light guide plate 2 shown in FIG. 12, the maximum reading light beam width B is slightly wider than the case where γ = 30 °. Since the thickness is 0.45 with respect to the thickness of the light plate, in order to make this width 2 mm, the size of the cross section of the light guide plate 2 may be about 4.5 mm wide and 27 mm long. .
However, looking at the change in illuminance within the range of the maximum reading light beam width B, the ratio of the minimum value to the maximum value is 84.2%, which is close to 16% in terms of illuminance unevenness. In order to solve this problem, the reflecting mirror M indicated by a two-dot chain line in FIG. 14 is placed at an appropriate angle on the opposite side of the light guide plate 2 across the reading width, and the original surface is not used without entering the reading area. It is better to fold back the light beam that is illuminating. By turning back, the gradient of illuminance is reversed, and the ratio between the maximum value and the minimum value shown earlier becomes smaller. Alternatively, as shown in FIG. 8, the light guide plate 2 including the LEDs 1 may be arranged substantially symmetrically with respect to the reading area.
As a precaution, when examining the reflection up to the third time, the direction of the light beam after leaving the light emitting surface 2b is too far from the optical axis, and the reading width including the third reflection cannot be obtained. However, if folding is performed by the reflecting mirror as described above, at least a part of one side (the reflection surface c1 side) can be effectively used for three times reflection and sometimes four times reflection.

FIG. 15 is a diagram for explaining still another configuration example of the present invention.
In this configuration example, the illuminance distribution when the rectangular ratio is further increased to 15 is examined. Also in this example, because of the maximum reading beam width B, the inclination angle of the optical axis was set to γ = 45 °.
In this configuration, up to three reflections contribute to the maximum reading light beam width B. However, as in FIG. 14, the ratio of the minimum value to the maximum value in the width B is 86.5%, and the illuminance unevenness is 13.5%. Therefore, even in this configuration, it is necessary to take measures to eliminate uneven illuminance, such as providing a counter reflector M (not shown) at a position facing the light guide plate 2. In each of the following configurations, the illuminance unevenness is almost the same, and although not particularly illustrated, it is desirable to provide an opposing reflecting mirror or to symmetrically arrange the light guide plate 2 including the LEDs 1.

FIG. 16 is a diagram for explaining still another configuration example of the present invention.
In this configuration, a part of the light guide plate shown in FIG. 4 is modified. That is, the side close to the exit surface 2b of the reflecting surface 2c is left as it is, and the side close to the entrance surface 2a is configured as surfaces c3 and c4 inclined with respect to the optical axis. The lengths of the c1 and c2 surfaces were set to one third of the light guide plate cross-sectional length, and the degree of inclination of the c3 and c4 was determined so that the virtual image of the LED 1 could be formed on the extension of the reflecting surfaces c1 and c2. In the case of such a shape as well, the previous rectangular ratio is used by using the ratio of the maximum length to the maximum width. The same applies to the following various modifications. Therefore, the rectangular ratio of this configuration is 2. In other words, the present configuration example is a hexagon inscribed in the rectangle 20 having the rectangle ratio 2 shown by a one-dot chain line in FIG. However, the inscribed here includes a case where some sides coincide with a rectangle.
Such a light guide plate was arranged with an inclination of γ = 45 ° with respect to the document surface, as shown in FIG. With this configuration, the light beam included at the angle α3 and further outside the light beam included at the angles α1 and α2 illustrated in FIG. 4 also exits the emission surface 2b after being reflected once. After being emitted, this light beam diverges in a range that completely includes the maximum reading light beam width B, and the amount of light is added by that amount compared to the case of FIG.
As can be seen from the comparison between FIG. 5 and FIG. 6, when the inclination angle of the optical axis is set to 30 °, the maximum reading light beam width B cannot be made very large. Therefore, in this configuration example and below, in the case of the rectangular ratio 2, all the inclination angles of the optical axis are shown as 45 °.

With this configuration, the light beam that has not contributed to the single reflection in FIG. 6 provides an effective light beam in the range of the maximum reading light beam width B in this configuration.
This effect is because the inclination directions of the inclined reflecting surfaces c3 and c4 are such that when viewed from the light source side, the shape becomes wider toward the front. In other words, the inclination direction of the side surface is such that the exit surface side is farther from the optical axis than the entrance surface side.
As a result, the position of the maximum reading light flux width B is the same position as in FIG. 6, but the maximum illuminance value at that position is increased. The symbol G in the figure is a curve representing the illuminance distribution according to this configuration, and G ′ is a curve representing the illuminance distribution in FIG.
Further, in FIG. 16, the angle of the light beam included in the reflection on the c3 and c4 planes includes the critical angle for 90 ° emission from the light source, so the light amount level at that angle is 0 regardless of the light distribution. . In this configuration, the range of luminous flux that can be effectively used has reached the critical angle, so there is no need to consider up to twice reflection.
The inclination angles of the reflective surfaces c3 and c4 are set so that the respective imaginary light sources can be extended on the reflective surfaces c1 and c2 for convenience, but are set so that the imaginary light sources are closer to or further away from the real light sources. Also good.

FIG. 17 is a diagram for explaining still another configuration example of the present invention.
The figure shows an example in which the shape of the light guide plate in FIG. 16 is changed.
In FIG. 17, the shape of the exit surface of the light guide plate 2 has a surface b1 parallel to the entrance surface 2a, and a b2 surface connected to the surface b2 and inclined to the surface b1 on the side far from the document surface. The degree of inclination of the b2 surface is not particularly limited, but is set to 40 ° in the figure. This configuration example is a heptagon inscribed in a rectangle 20 having a rectangle ratio of 2.
Although all the configuration examples described so far have used light guide plates that are symmetric with respect to the optical axis, this configuration example is configured asymmetrically with respect to the optical axis. The aim of this configuration is to allow a light beam reaching far from the light guide plate 2 to be irradiated near the reading area by changing the shape of the exit surface. With this configuration, a part of the direct light that has not contributed to the reading area has entered the reading area, but conversely, the c2 surface once reflected light beam that has been in the reading area until now is partially read. Thus, the light beam reflected once on the c4 surface is almost totally reflected from the surface b2 of the exit surface, and does not go out to the document surface side. As a result, the reduction in the amount of light has become larger, so this configuration reduces the maximum illuminance instead. In the figure, a light beam and imaginary light source that do not contribute illuminance to the maximum reading light beam width B are omitted. The same applies to the following drawings.
In this configuration example, the distance between the light guide plate 2 and the document surface 5 is less than two-thirds of the maximum reading light beam width B. Therefore, by setting the width of the maximum reading light beam width B to 3 mm, for example, the distance can be secured to 1.5 mm or more.

FIG. 18 is a diagram for explaining still another configuration example of the present invention.
The figure shows an example in which the shape of the light guide plate in FIG. 17 is further changed.
In FIG. 18, the shape of the light guide plate 2 is such that the emission surface b1 is also inclined with respect to the reflection surface c1, and is composed of a c6 surface instead of the c2 and c4 surfaces. The b1 surface and the b2 surface are connected on the optical axis L0 and are inclined to face each other. The b1 surface is inclined by 10 ° with respect to the incident surface 2a, and the b2 surface is inclined by 20 ° in the opposite direction. Even in this configuration, the rectangular ratio of the circumscribed rectangle 20 including the incident surfaces 2a and c1 is set to be 2 as before.
The c6 surface was set so that a virtual image 1 ″ ″ of the LED 1 could be formed on the extension of the surface of the circumscribed rectangle facing the c1 surface (c2 surface in FIG. 4).
By adopting this configuration, the contribution of the luminous flux from the imaginary light source 1 ′ to the maximum reading width B by the c1 plane is eliminated, but that by the c3 plane and that by the c6 plane are increased, resulting in FIG. The illuminance on the original surface is larger than the configuration example shown.
When the reading area is set in an area where both the direct light and the one-time reflected light pass, the maximum reading light flux width B is 0.37 with respect to the thickness of the light guide plate 2. The cross-sectional size of the light guide plate 2 may be approximately 5.5 mm in width and 11 mm in length.

FIG. 19 is a diagram for explaining still another configuration example of the present invention.
The figure shows an example in which the shape of the light guide plate in FIG. 18 is further changed. In the following drawings, the circumscribed rectangle 20 is omitted.
In FIG. 19, the b2 surface and the c6 surface are the same as the shape shown in FIG. In this configuration example, the optical axis L0 is symmetrical.
According to this configuration, the contribution ratio of the one-time reflected light beam by the reflection surface c5 is increased with respect to the maximum reading light beam width B, and the absolute value of the original surface illuminance is not much different from that in FIG. Is getting bigger. Since the maximum reading light flux width B is 0.53 with respect to the thickness of the light guide plate, in order to make this width 2 mm, the size of the cross section of the light guide plate 2 is approximately 3.7 mm in width and length. It should be 7.4 mm.
When both side surfaces are inclined in the opening direction when viewed from the incident surface 2a as in this configuration example, even when the refractive index n of the medium is smaller than n = 1.4142 shown above, the side surface is subjected to reflection treatment. Total reflection occurs even without applying. Considering a material that is practically available as a transparent member, the smallest refractive index is approximately n = 1.35 as described above. The critical angle of this medium is about 47.8 °. Accordingly, the condition that a light beam entering at a critical angle from the incident surface 2a becomes a critical angle also on the side reflecting surface is that the tilt angle of the reflecting surface is (90 ° -47.8 °) −47.8 ° = −5. 6 °. Therefore, the reflecting surfaces c5 and c6 on the side surfaces only need to be inclined by about 5.6 ° with respect to the incident surface 2a. This angle is applicable when the rectangular ratio is approximately 2.5 in the configuration shown in FIG. When the rectangular ratio is larger than that, a special reflecting surface treatment on the side surface is not necessary in an arbitrary medium.
In other words, when the reflecting surface is inclined as described above, the refractive index n at which no special reflecting surface treatment is required is determined according to the angle. The value of n is naturally smaller than 1.4142.

FIG. 20 is a diagram for explaining still another configuration example of the present invention.
In the description of FIG. 11, it was concluded that a rectangular ratio of 1.5 or more is preferable based on the relationship between the emission angle β of outgoing light reflected once by the c1 surface or the c2 surface and the document surface inclination angle γ. As shown in the configuration example of FIG. 17, when the emission surface 2b is deformed as b1 and b2, particularly when the angle of the surface is changed as in b2, the relationship between β and γ is as follows. It doesn't hold true. Accordingly, the lower limit of the rectangular ratio cannot be specified. Furthermore, as shown in FIG. 18, when the b1 plane is also inclined and the c2 plane disappears and the c6 plane is used, as shown in FIG. 19, the c1 plane disappears and the c5 plane is used. In the case, the same can be said.
FIG. 20 shows an example in which the concept of the configuration example shown in FIG. 19 is applied to a rectangle 20 with a rectangle ratio of 1.
As can be seen from the figure, in this configuration, the document surface inclination angle γ = 45 ° can be set while the rectangular ratio is 1. However, the contribution ratios of the virtual images 1 ′ and 1 ″ to the document surface illuminance distribution are not so large. Therefore, with such a configuration, it is possible to set a desired reading region without necessarily focusing on the overlapping region of light beams. become.

FIG. 21 is a diagram for explaining still another configuration example of the present invention.
In this configuration example, the shape of the light guide plate 2 is such that the c1 surface in the shape shown in FIG. 6 is replaced with the c5 surface shown in FIG. 19, and the LED 1 is moved to the c2 surface side. The amount brought close was set so that the optical axis L0 passed through a position of one third of the length in the cross section of the emission surface 2b.
Although this configuration has a relatively simple shape, the light beam can be used effectively, and the maximum reading light beam width B and the maximum value of the illuminance distribution curve G are both the largest in the configuration example of the rectangular ratio 2. ing. For comparison, the original surface illuminance distribution curve of the configuration shown in FIG. 16 is indicated by a broken line as G ′. In this configuration, the maximum reading light flux width B is 0.57 with respect to the thickness of the light guide plate. In order to make this width 2 mm, the size of the cross section of the light guide plate 2 may be approximately 3.5 mm wide and 7 mm long.
When the distance between the light guide plate 2 and the document surface 5 becomes too small, as described above, if the maximum reading light beam width B is set to 3 mm or 4 mm, each dimension increases according to the ratio, and is practical. Can be set to any size.
Even when only one side surface is inclined with respect to the incident surface 2a as in this configuration example, at least the inclined surface is refracted by the medium used as the light guide plate as shown in the explanation of FIG. Depending on the relationship between the rate and the inclination angle, a special reflecting surface treatment for the surface is not necessary.

FIG. 22 is a diagram for explaining still another configuration example of the present invention.
In this configuration example, based on the configuration example of FIG. 16, in the light guide plate having a rectangular ratio of 6, a part of the reflective surfaces c1 and c2 on the side close to the LED is an inclined surface. The setting of the inclined surface was the same as the concept of FIG.
As can be seen from FIG. 14, when the rectangular ratio is large, the number of imaginary light sources contributing to the reading area is large and the maximum reading width B is not so large, so that the illuminance on the original surface is ensured. For the purpose, the method of dividing the exit surface 2b as shown in FIGS. 17 to 19 is not a good idea. Therefore, when the rectangular ratio is large, the method of FIG. 16 in which the imaginary light source is formed near the real light source is considered advantageous.
Looking at the results, the illuminance distribution on the original surface is 15% or more higher than that of the configuration shown in FIG. Further, the maximum reading light flux width B is also 15% or more, which is 0.6 with respect to the thickness of the light guide plate. Therefore, in order to set the maximum reading light beam width B to 2 mm with this configuration, the size of the cross section of the light guide plate 2 may be about 3.3 mm in width and 20 mm in length.

FIG. 23 is a diagram for explaining still another configuration example of the present invention.
In this configuration, the shape of the light guide plate 2 is further simplified. The exit surface 2b is not divided, and the reflection surfaces c5 and c6 are formed in the same way as the reflection surfaces c5 and c6 in FIG.
In this configuration, the illuminance on the original surface is slightly smaller than that in the configuration example of FIG. 21, but is about 10% higher than that in the configuration example shown in FIG. Further, the maximum reading light flux width B is also about 6% larger than that in the configuration example shown in FIG.

FIG. 24 is a diagram for explaining still another configuration example of the present invention.
In this configuration, the exit surface 2b of the light guide plate in FIG. 6 is inclined to one side to be b3. The direction of inclination is a direction in which the corner portion closest to the document surface of the light guide plate 2 is separated from the document surface side. Although there is no particular condition for the angle value, the inclination angle is 10 ° in FIG. In general, when the inclination angle of the exit surface is changed, the emitted light beam is bent relatively to the opposite side to the direction of change of the normal of the exit surface as compared to before the change. Accordingly, the illuminance distribution curve G on the document surface moves the high illuminance portion to the left in the drawing as compared to before the change.
If the inclination angle of the exit surface is too large, the overlapping region of the light beams by the imaginary light source 1 ′ and the imaginary light source 1 ″ is not preferable.

The light guide plate in the present invention that has been described above, as shown in part by the configuration example, can appropriately select the shape of the light guide plate according to various conditions of the installation location of the light source unit. . Here, the rectangular ratios 2, 6, 15 and the optical axis tilt angle γ = 45 ° given as examples are numerical values used for convenience of explanation, and the present invention is not limited to these numerical values. .
Next, a method for providing a flat portion in the illuminance distribution on the surface to be illuminated will be described.

FIG. 29 is a diagram showing a configuration outline of the embodiment described below.
In the figure, symbol H denotes the thickness of the light guide plate, L denotes the effective illumination width of the illuminated surface, and O denotes the optical axis.
The LEDs 1 as light sources are arranged in an array in a direction perpendicular to the paper surface of FIG. The light guide plate 2 also extends long in the light source arrangement direction. LED1 is arrange | positioned in the center part of one short side of the rectangular cross section of the same figure of the light-guide plate 2, and it is closely_contact | adhered to an end surface with a slight clearance gap. If it is in direct contact with the end face, all the light beams emitted from the LED 1 are incident on the light guide plate regardless of the light emission distribution characteristics of the LED 1. The center of the LED 1 is arranged to coincide with a straight line passing through the center of two upper and lower long sides (hereinafter referred to as side surfaces). With this straight line as the optical axis O, the luminous flux from the LED 1 is arranged so that the direction of the maximum light quantity coincides with the optical axis O.
The light flux from the LED 1 is incident from one end surface of the light guide plate 2, a part is directly emitted from the other end surface, and the other part is reflected one or more times on the side surface and is emitted as divergent light from the other end surface. . With such a configuration, the light beam spreads as if a new light source exists on the exit end face, and this exit end face is sometimes called a secondary light source.
The emitted light beam reaches the concave mirror 3, and the degree of divergence is reduced by reflection, and reaches the document surface (illuminated surface) 5 of the contact glass 4.
The light guide plate 2 basically has a rectangular parallelepiped shape having a length, a width, and a thickness. The length is approximately equal to or longer than the so-called main scanning direction of the surface to be illuminated. The width is a length extending in the left-right direction (hereinafter referred to as the sub-scanning direction) in the figure, and an arbitrary length can be selected depending on design conditions. The thickness is the short side of the rectangular cross section as indicated by the symbol H in FIG. In principle, the light guide plate 2 is arranged so that the optical axis O is parallel to the document surface.
As shown in FIG. 40, the illuminance distribution on the surface to be illuminated 5 is generally a so-called bell shape in which the vicinity of the center is large and decreases toward the end. Here, the effective illumination width L in the figure is defined as a half-value width of the illuminance distribution in the sub-scanning direction (a width exceeding a half value of the maximum illuminance).

30 and 31 are diagrams for explaining an embodiment of the present invention. 30 is a sub-scan sectional view, and FIG. 31 is a plan view of the contact glass as viewed from below the light guide plate.
The specifications of this example are shown below.
LED
Number 7 Output 1W / piece Characteristics Lambert distribution Light emitting surface Uniform light emitting surface light guide plate of 0.5mm x 0.5mm Length 35mm
Width 10mm
3mm thickness
Concave mirror diameter 10mm
Curvature radius 8mm
Slope of concave mirror optical axis with respect to optical axis of light guide plate
26 °
Distance between secondary light source and concave mirror reflecting surface center
6mm on the optical axis of the light guide plate
Contact glass thickness 3.2mm
Material nd = 1.517
Distance from light guide plate optical axis
5.6mm
Illuminated surface Position Contact glass upper surface Size 20 mm (main scanning direction) × 10 mm (sub-scanning direction)

32 and 33 are diagrams showing the illuminance distribution of this embodiment. 32 is a cross section in the sub-scanning direction passing through the center of the illuminated surface, and FIG. 33 is an illuminance distribution in the cross section in the main scanning direction.
In these figures, a surface to be illuminated of 20 mm × 10 mm is divided into 1 mm square meshes, and the illuminance values at each mesh are plotted. The same applies to the following embodiments.
As can be seen from FIG. 32, a moderate illuminance distribution region having a width of about 2 mm could be obtained. If the uneven illuminance in the sub-scanning direction can be allowed up to 12% from the peak value, this distribution can be sufficiently put into practical use. Incidentally, the illuminance distribution in the main scanning direction in FIG. 33 is well within 12%.
When the effective illumination width is read from this graph, it is about 5.7 mm, and L / H≈1.9 when the ratio to the thickness H of the light guide plate 2 is taken.

FIG. 34 is a view for explaining another embodiment of the present invention.
In the figure, reference numerals 91, 92 and 93 denote plane mirrors, respectively.
The specifications of this example are shown below. However, in the coordinate system, the vertical direction in the figure is the Y-axis direction, the horizontal direction is the Z-axis direction, and the center of the emission end face of the light guide plate 2 is the origin (Y = 0, Z = 0).
LED
Number 7 Output 1W / piece Characteristics Lambert distribution Light emitting surface Uniform light emitting surface light guide plate of 0.5mm x 0.5mm Length 35mm
Width 10mm
Thickness 2mm
Plane mirror 1
Width 3.5mm
Plane tilt with respect to the optical axis of the light guide plate
47 °
Center position coordinates Z = 3, Y = 1.35
Plane mirror 2
Width 1.5mm
Plane tilt with respect to the optical axis of the light guide plate
72 °
Center position coordinates Z = 5.15, Y = 0.65
Plane mirror 3
Width 2mm
Plane tilt with respect to the optical axis of the light guide plate
90 °
Center position coordinates Z = 5.4, Y = 2.36
Contact glass thickness 3.2mm
Material nd = 1.517
Distance from light guide plate optical axis
4.5mm
Illuminated surface Position Contact glass upper surface Size 20 mm (main scanning direction) × 10 mm (sub-scanning direction)

In this embodiment, the diffused light emitted from the secondary light source can be secured to a flat portion having a width of about 3 mm that is necessary for scanner illumination in the short direction by the pseudo-concave reflecting member composed of a plurality of plane mirrors. It is intended to converge and lead to the illuminated surface. Basically, a predetermined concave mirror is assumed, and after determining the number of divisions (for example, three divisions), the midpoint of the reflection surface (or its vicinity) in the cross section in the sub-scanning direction of each plane mirror (for example, 91, 92, 93) Is arranged at a point on the concave mirror (the center position coordinate) assumed so that the reflecting surface becomes a tangent at that point. In general, it is preferable to finely divide the concave mirror having a large curvature. The combination of the plane reflecting mirrors configured as described above will be referred to as a pseudo concave surface. The pseudo concave surface is composed of at least two plane reflecting mirrors. Although it is desirable that the reflecting surfaces of adjacent plane mirrors are substantially continuous, there is no particular problem other than light loss even if there is a slight gap.
This can be said to be a means close to a method of guiding light source light to an image display element by an integrator rod and a relay lens of a projection type image display apparatus as known in the prior art. The most different point from the integrator rod method is that the integrator method regards the secondary light source as an object, images the image display element as an image, and focuses the emitted light from the secondary light source on the image display element surface. In the method of the present invention, if the secondary light source is regarded as an object, diffused light is applied to the surface to be illuminated without imaging the light source itself, or the secondary light source light is divided into a plurality of light sources on the surface to be illuminated. It is in the lead. However, this is also an image limited to the cross section in the short direction, and does not consider refraction and reflection in the longitudinal direction. In addition, the present invention not only collects light, but also when the H of the light guide plate is small. May be divergent and may be said to be a completely different optical system.

35 and 36 are diagrams showing the illuminance distribution of this embodiment. FIG. 35 is a cross section in the sub-scanning direction passing through the center of the illuminated surface, and FIG. 36 is an illuminance distribution of the cross section in the main scanning direction.
As can be seen from FIG. 35, a moderate illuminance distribution region having a width of about 4 mm could be obtained. If the uneven illuminance in the sub-scanning direction can be allowed up to 12% from the peak value, this distribution can be sufficiently put into practical use. Incidentally, the illuminance distribution in the main scanning direction in FIG. 36 is also within approximately 12%.
When the effective illumination width is read from this graph, it is about 7.9 mm, and L / H≈4 when compared with the thickness H of the light guide plate 2.

FIG. 37 is a view for explaining still another embodiment of the present invention.
The specifications of this example are shown below.
LED
Number 7 Output 1W / piece Characteristics Lambert distribution Light emitting surface Uniform light emitting surface light guide plate with a length of 0.3mm x 0.3mm Length 35mm
Width 10mm
Thickness 0.3mm
Concave mirror diameter 9.5mm
Curvature radius 13mm
Slope of concave mirror optical axis with respect to optical axis of light guide plate
26 °
Distance between secondary light source and concave mirror reflecting surface center
6mm on the optical axis of the light guide plate
Contact glass thickness 3.2mm
Material nd = 1.517
Distance from light guide plate optical axis
5.6mm
Illuminated surface Position Contact glass upper surface Size 20 mm (main scanning direction) × 10 mm (sub-scanning direction)

38 and 39 are diagrams showing the illuminance distribution of this embodiment. 38 is a cross section in the sub-scanning direction passing through the center of the illuminated surface, and FIG. 39 is an illuminance distribution in the cross section in the main scanning direction.
As can be seen from FIG. 38, a moderate illuminance distribution region having a width of about 3 mm could be obtained. If the uneven illuminance in the sub-scanning direction can be allowed up to 12% from the peak value, this distribution can be sufficiently put into practical use. Incidentally, the illuminance distribution in the main scanning direction in FIG. 39 is also within 12%.
Since this graph cannot take half of one value, the effective illumination width cannot be read from this graph. It was found that the effective illumination width was about 8 mm by separately performing simulation exceeding this width. Therefore, L / H≈26.7 when taking a ratio with the thickness H of the light guide plate 2.

Here, the effective illumination width L will be considered.
As described above, it is desirable that a flat portion of the illuminance exists in the vicinity of the peak value of the illuminance distribution. The width is determined by the relationship with the light receiving element or the like of the reading optical system, but usually at least about 1 mm is required for the flat portion. As described above, when a mechanical tolerance is taken into consideration, it is necessary to provide a slight margin, and when this is expressed by the half-value width L, at least about 2 mm is required.
On the other hand, increasing L means that the width of the flat portion becomes larger than necessary, which leads to a loss of spectral quantity. Practically, 10 mm is sufficient.
This can be summarized as the following equation.
2 ≦ L ≦ 10

On the other hand, the thickness H of the light guide plate 2 cannot be made too small due to the material strength. If the material is made of synthetic resin, at least 0.3 mm is required.
On the other hand, when viewed in relation to the effective illumination width, for example, when H is about 0.3, it is necessary to diverge the emitted light from the light guide plate 2 by the reflecting member 3 in order to obtain a desired flat portion. At this time, it was found that when L = 8 or L = 9, a desired flat portion can be easily obtained. Therefore, it is preferable to satisfy L / H ≦ 30.
Further, it was found that when H = 4 or so, high efficiency can be obtained by irradiating the surface to be illuminated with a light beam that is equal or slightly converged by the reflecting member 3. Therefore, considering the minimum value of L, 0.5 ≦ L / H.
This can be summarized as the following equation.
0.5 ≦ L / H ≦ 30

Next, a light source that can be used in the present invention will be described.
In the present invention, the light source is most suitably a light emitting diode (LED). Among them, it is preferable to use a white LED in order to be able to handle reading of any document.
There are several types of white LEDs. One of them is a one-chip type white LED using a phosphor. A light emitting unit called a chip is sealed in a transparent enclosing member mixed with a YAG phosphor. The chip emits blue light made of InGaN. Thereby, when the chip emits blue light, the phosphor is simultaneously excited to emit yellow fluorescence. Since blue and yellow are complementary to each other, when both go out together, they are recognized as white light.
As another type, there is a white light-emitting diode that does not use a phosphor and uses two or more chips that emit different colors and emits white light by color mixture. The plurality of chips are arranged on the same surface, and are combined to be recognized as white when all the emission colors are mixed.
For example, in the case of two chips, chips that emit blue and yellow light are used as described above. In the case of three chips, chips that emit red, green, and blue corresponding to so-called three primary colors are used.
When light emission of a plurality of colors is performed, the color mixture is performed before the light flux is emitted from the LED and is usually treated as a white LED. In the present invention, the light flux is emitted a plurality of times in the light guide. Therefore, the color mixing may be completed to the extent that it can be regarded as white when the LEDs of different emission colors are arranged and emitted from the emission end side of the light guide.
Any of the document illumination devices described above can be used for an image reading device or a color document reading device, and these devices can form an image forming device.

It is a sectional side view which shows the basic concept of the illuminating device of this invention. It is a disassembled perspective view of the light source unit of the illuminating device of this invention. It is a figure for demonstrating distribution of the emitted light of LED. It is a figure for demonstrating the example of a basic composition of this invention. It is a figure which shows illuminance distribution when the optical axis of LED is inclined 30 degrees with respect to the normal line of a document surface. It is a figure which shows illuminance distribution when the optical axis of LED is inclined 45 degrees with respect to the normal line of a document surface. It is a figure which shows illuminance distribution when the optical axis of LED is inclined 45 degrees with respect to the normal line of a document surface. It is a figure which shows the structural example for eliminating illuminance nonuniformity. It is a figure for demonstrating the other structural example of this invention. It is a figure explaining the light beam at the time of using the light-guide plate of rectangular ratio 1. It is a figure for demonstrating the light beam at the time of using the light-guide plate of the rectangular ratio 1.5. It is a figure for demonstrating the other structural example of this invention. It is a figure which shows illuminance distribution when the optical axis of LED is inclined 30 degrees with respect to the normal line of a document surface. It is a figure which shows illuminance distribution when the optical axis of LED is inclined 45 degrees with respect to the normal line of a document surface. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. It is a figure for demonstrating the further another structural example of this invention. 1 is a schematic diagram of an image forming apparatus having an image reading apparatus. It is a figure for demonstrating the structure of a scanner. It is a figure for demonstrating the detail of the light source part vicinity. It is a figure for demonstrating the relationship between a manuscript surface and an image plane. It is a figure which shows the structure outline | summary of embodiment shown below. It is a figure for demonstrating a certain Example of this invention. It is a figure for demonstrating a certain Example of this invention. It is a figure which shows the illumination intensity distribution of a present Example. It is a figure which shows the illumination intensity distribution of a present Example. It is a figure for demonstrating the other Example of this invention. It is a figure which shows the illumination intensity distribution of a present Example. It is a figure which shows the illumination intensity distribution of a present Example. It is a figure for demonstrating the further another Example of this invention. It is a figure which shows the illumination intensity distribution of a present Example. It is a figure which shows the illumination intensity distribution of a present Example. It is a schematic diagram which shows the positional relationship of the light receiving element of a digital copying machine or an image scanner. It is a figure which shows the relationship between the change of an illumination intensity distribution curve, and a reading position. It is a schematic diagram which shows the mode of the illumination by a rod-shaped light source. It is a schematic diagram which shows the mode of the illumination by several LED. It is a schematic diagram which shows the mode of the illumination by several LED. It is a schematic diagram at the time of arrange | positioning a light-guide plate between LED and a to-be-illuminated surface. It is a schematic diagram at the time of arrange | positioning a light-guide plate between LED and a to-be-illuminated surface.

Explanation of symbols

1 LED
2 Light guide plate 3 Light source device 4 Contact glass 5 Document surface

Claims (27)

  An illuminated area having a length and a width for reading on a document surface, and a plurality of light emitting elements arranged at predetermined intervals in the main scanning direction when the length direction is a main scanning direction and the width direction is a sub scanning direction In the document illuminating apparatus, the light guide plate includes: an element; and a light guide plate disposed between the plurality of light emitting elements and the document surface and guiding light beams from the plurality of light emitting elements to the illuminated area. The main scanning direction has a length that is approximately equal to or longer than the length of the illuminated region, and the shape in the sub-scanning section is a rectangle having a rectangular ratio that represents a ratio of the length to the width of 1 or more, Alternatively, it has a polygonal shape inscribed in the rectangle, the light emitting surfaces of the plurality of light emitting elements face one short side of the rectangle as a light incident surface, and the other short side approaches the illuminated area. Arranged as a light exit surface, and A plurality of surfaces (hereinafter referred to as side surfaces) corresponding to the two long sides of the rectangle connecting the incident surface are light reflecting surfaces, and the optical axes of the plurality of light emitting elements are parallel to the long sides of the rectangle. The optical axis is inclined at a predetermined angle with respect to the normal line of the original surface, and direct light and the plurality of reflections out of the light flux from the exit surface of the light guide plate in the sub-scanning section. An original illuminating apparatus characterized in that a reading area is set in an overlapping area with at least one reflected light from at least two reflecting surfaces among the surfaces.   2. The document illuminating apparatus according to claim 1, wherein at least one of the side surfaces has a predetermined inclination angle that is not parallel to the optical axis.   3. The document illuminating device according to claim 1, wherein the side surface has two connected surfaces having different inclination angles with respect to the optical axis.   4. The document illumination device according to claim 2, wherein the side surface is inclined in a direction away from the optical axis on the exit surface side than on the incident surface side.   5. The document illumination device according to claim 1, wherein the side facing the optical axis of the side surface is a surface subjected to high reflection processing, and the optical axis side is hollow from the side surface. A document illumination device.   6. The document illuminating device according to claim 5, wherein distances from the light emitting element to two end portions connected to the emission surface of the side surface are different from each other.   5. The document illumination device according to claim 1, wherein the light emission surface of the light guide plate includes two surfaces having different inclination angles with respect to the optical axis. Document illumination device.   8. The document illumination device according to claim 7, wherein the light exit surface of the light guide plate is asymmetric with respect to the optical axis.   5. The document illuminating apparatus according to claim 1, wherein the light emission surface is not orthogonal to the optical axis and has a predetermined inclination angle.   10. The document illumination device according to claim 9, wherein an inclination direction of the light emission surface is a direction in which a corner portion of the light guide plate closest to the document surface is away from the document surface. apparatus.   11. The document illuminating device according to claim 1, wherein the light guide plate is made of a transparent member having a refractive index of 1.4142 or more.   12. The document illuminating device according to claim 1, wherein a reflecting mirror that folds a part of a light beam that does not reach the reading region out of the light beam from the light guide plate to the reading region is provided in the light guide plate. A document illuminating device provided at a position facing the light exit surface of the document.   12. The document illumination device according to claim 1, wherein a light guide plate having the same shape as the light guide plate combined with the plurality of light emitting elements is provided substantially symmetrically with respect to the reading area. Document illumination device.   An image reading apparatus using the document illumination device according to claim 1.   An image forming apparatus using the image reading apparatus according to claim 14.   An illuminated area having a length and a width for reading on a document surface, and a plurality of light emitting elements arranged at predetermined intervals in the main scanning direction when the length direction is a main scanning direction and the width direction is a sub scanning direction A light guide plate having an element, an incident surface on which light beams from the plurality of light emitting elements are incident, and an output surface for emitting the light beam in a predetermined direction; and the light beam emitted from the light guide plate is guided to the illuminated area. A document illuminating device having a reflecting member, wherein the illuminance distribution in the sub-scanning direction of the illuminated surface has a flat portion having a predetermined width or more. The document illumination device according to claim 16, wherein the half-value width L of the illuminance distribution in the sub-scanning direction is
2 ≦ L ≦ 10
A document illumination device characterized by satisfying the requirements. 18. The document illuminating apparatus according to claim 17, wherein when the thickness of the light guide plate is H, the H and the L are 0.5 ≦ L / H ≦ 30.
A document illuminating device characterized by satisfying the above requirements.   19. The document illuminating device according to claim 16, wherein the reflecting member is a reflecting member having a concave surface, and the concave surface is directed to the emission surface of the light guide plate. Lighting device.   19. The document illumination device according to claim 16, wherein the reflecting member is a pseudo-concave reflective member including a plurality of planes, and the pseudo-concave surface is directed to the emission surface of the light guide plate. A document illumination device characterized by the above.   21. The document illuminating device according to claim 16, wherein the plurality of light emitting elements are arranged in one row, and the length direction of the element rows and the light guide plate are arranged in parallel. A document illumination device characterized by the above.   The document illumination device according to any one of claims 16 to 21, wherein the plurality of light emitting elements are white LEDs.   23. The document illuminating device according to claim 16, wherein the plurality of light emitting elements include at least two kinds of LEDs each having a different emission color, and each color light is subjected to multiple reflection within the light guide plate. An original illuminating apparatus characterized in that the color is sometimes mixed and white light is emitted on the light exit surface of the light guide plate.   24. The document illuminating device according to claim 16, wherein the light emitting surfaces of the plurality of light emitting elements are in close contact with the incident surface of the light guide plate. .   An image reading apparatus using the document illumination device according to any one of claims 16 to 24.   25. A color original reading apparatus using the original illuminating device according to any one of claims 16 to 24.   An image forming apparatus using the image reading apparatus according to claim 25 or the color original reading apparatus according to claim 26.

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