JP2006017951A - Document illuminating device, image reading unit, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that, in the case where a document illuminating device for reading images is composed of light emitting elements such as an LED, the emission of a luminous flux is large in a sbuscanning direction and high illuminance is not obtained even when a document surface (a surface to be illuminated) is directly illuminated by the plurality of light emitting elements arrayed in the subscanning direction and that a configuration for condensing a luminous flux in the subscanning direction by using a cylindrical lens causes partial condensing, resulting in nonuniform illuminance in the main scanning direction. <P>SOLUTION: A light conductive member 2 is disposed between the plurality of light emitting elements 1 and a surface 4 to be illuminated. A contact glass 3 is disposed between the conductive member 2 and the surface to be illuminated. The conductive member 2 is disposed at a prescribed angle θ to the normal of the contact glass. Selecting the number of light emitting elements, an array pitch, the shape of the conductive member, and the arrangement relative to the surface to be illuminated make it possible to obtain a flat part that is free from nonuniform illuminance in the main scanning direction and is almost flat in illuminance distribution in the subscanning direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  In recent years, a light emitting diode (hereinafter referred to as an LED) has been actively developed, and the brightness of the LED element has been rapidly increased. 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. 19 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. The line sensor 206 performs main scanning of the image.
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. Sub-scanning is performed by moving in the direction, and the entire original is read.
Normally, a document illumination device used for an image reading device requires a length approximately the same as the document width to illuminate a document. Therefore, as a method of using an LED as a document illumination device, an LED element is used for main scanning. A large number are arranged in the direction and used in an array.

However, although current LEDs have excellent characteristics as described above, the absolute brightness of each element is insufficient for use as an illuminating device of an image reading device, so that a low-speed reading device is used. In addition, it is used mainly for devices that emphasize compactness, and cold cathode fluorescent lamps are mainly used for high-speed reading devices and large devices.
FIG. 20 is a conceptual diagram showing a state in which the document surface is directly illuminated by the LED array. FIG. 4A is a cross-sectional view in the main scanning direction, FIG. 4B is a cross-sectional view in the sub-scanning direction, and the curve schematically shows the illuminance distribution.
In the figure, reference numeral 101 denotes an LED, 102 denotes a contact glass, and 103 denotes an illuminated surface such as a document surface.
An LED array composed of a plurality of LEDs 101 is arranged on the lower surface of the contact glass 102 and illuminates the upper surface of the contact glass as the document surface 103.
In order to make up for the above problem, for example, when the LED array is made to illuminate brightly by approaching the illuminated surface 103, even if the brightness unevenness of each LED indicated by the dotted line in FIG. As indicated by the solid line, illuminance unevenness appears in the main scanning direction. Conversely, when the LED array is moved away from the illuminated surface 103, the light diffuses and cannot be illuminated brightly.

21 and 22 are cross-sectional views of an illumination device using a rod-shaped light source.
In both figures, reference numeral 301 is a rod-like light source such as a cold cathode fluorescent lamp, 302 and 304 are mirror members having a partially cylindrical concave reflecting portion as an optical element, 303 is an illuminated surface such as a document surface, and 4 is an illuminated surface. The upper illuminance distribution curves in the sub-scanning direction are respectively shown. For the sake of simplification, the mirror surface member is replaced with only the reflective surface.
As shown in FIG. 21, the reflecting mirror for the rod-shaped light source can be used to illuminate the document surface broadly without collecting too much light, or to provide an appropriate illuminance distribution by combining a plurality of planes. Has been proposed (see, for example, Patent Document 1).
Here, how to increase the amount of light in the rod-shaped light source is as follows. As shown in both drawings, the light reflected from the rod-shaped light source 1 is reflected by the partially cylindrical mirror surface member 2, so The method of collecting light is mainly used. Here, the partial cylindrical shape is also called a cylindrical shape, and the cross section has a shape of a part of a quadratic curve such as a circle, an ellipse, a parabola, a hyperbola, or the like, or a shape close thereto, and the light source extends in the length direction of the rod-shaped light source. Or the length of the surface to be illuminated (the length of the main scanning region).

FIG. 23 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 305 denotes an imaging lens, 306 denotes a light receiving element, and 307 denotes a single light receiving unit.
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 unit 7 of the light receiving element 306 through the imaging lens 305. In the light receiving element 306 such as a CCD sensor, the width of the single light receiving portion 307 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 is shifted due to a shift in the illumination position due to a shift in the mirror angle or the like, and the amount of light reaching the single light receiving unit 307 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 side of the original image formed on the single light receiving unit 307 is, for example, even when a reduction optical system is used to reduce the image to 1/10. The problem is the same because it is only about 1 mm at most.

FIG. 24 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 portion is as narrow as about 0.1 mm, for example, if the center position of the illuminance distribution curve deviates from the reading portion 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 that purpose, in the vicinity of the maximum value of the illuminance distribution, the width required for reading (maximum of about 1 mm in the above example) plus a variation due to a mechanical error or the like (in the present invention, at least as an effective illumination range) It is preferable that there is a portion with less illuminance unevenness (ie, ± 1 mm is set), that is, a flat portion with illuminance.
The flat part means a part that falls within a 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.

The present applicant has previously proposed an illuminating device that can perform uniform illumination with high light utilization efficiency by a substantially plate-shaped light guide plate (see Patent Document 2). According to the proposal, it is possible to make the illuminance distribution uniform in the main scanning direction by providing diffraction gratings on the reflection surfaces on both sides.
However, providing a diffraction grating on such a transparent member increases the cost, and an illuminance flat portion cannot be formed in the sub-scanning direction unless it is appropriately arranged.

Japanese Patent No. 0994148 Japanese Patent Laid-Open No. 10-322521

In the present invention, the reflecting member (referred to as a light guide plate in the present invention) shown in Patent Document 2 can produce an illuminance flat portion having a width of 2 mm or more in the sub-scanning direction without uneven illuminance in the main scanning direction. A basic composition and arrangement is proposed. In particular, regarding the characteristics in the main scanning direction, according to the present invention, a range in which the occurrence of illuminance unevenness in the main scanning direction can be suppressed without providing a diffraction grating is defined.
Furthermore, when the light guide plate is used in a document illumination device, it is naturally desirable that the light guide plate be as small as possible. However, if the light guide plate is reduced in size unnecessarily, the number of times the light is reflected inside the light guide plate. And causes uneven illumination in the sub-scanning direction. The present invention also prescribes the size of the light guide plate that is less likely to cause uneven illumination in the sub-scanning direction.

According to the first aspect of the present invention, when a surface to be illuminated having a length and a width, the length direction is a main scanning direction, and the width direction is a sub-scanning direction, a plurality of light emitting elements are arranged in the main scanning direction. An original illuminating apparatus comprising: a light source unit arranged; and a light guide plate disposed between the light source unit and the illuminated surface and guiding a light beam from the light emitting element to the illuminated surface, wherein the light guide plate Has a length, a width, and a thickness, the length direction coincides with the main scanning direction, an incident surface on which a light beam from the light emitting element is incident, and an exit that is opposed to the incident surface and emits the light beam And a plurality of light-emitting surfaces that are connected to each other in the thickness direction and are inclined at a predetermined angle θ with respect to the surface to be illuminated. Among the elements, on the illuminated surface corresponding to the midpoint of any two light emitting elements. The difference between the illuminance and the illuminance on the illuminated surface corresponding to the front of any one of the two light emitting elements is within 12% of the larger of the illuminances. Thus, the width and thickness of the light guide plate are set as described above.
According to a second aspect of the present invention, in the original illuminating device according to the first aspect, the width of the light guide plate is L, the thickness of the light guide plate is ε, and the light guide plate corresponds to the half-value angle in the light distribution of the light emitting elements. When the refraction angle in the medium is α and the constant related to the number of times the light beam corresponding to the half-value angle repeats reflection in the light guide plate is k,
k = (L / ε) × tan α
It is characterized in that L / ε is determined so that k determined by the above formula becomes 3.5 or more.

According to a third aspect of the present invention, in the document illumination device according to the first or second aspect, a contact glass is further disposed between the illuminated surface and the light guide plate, and the thickness of the contact glass is D. When the distance from the light emitting plate thickness direction center of the light guide plate to the contact glass surface is M, and the refraction angle of the light incident on the contact glass at an incident angle θ is θ ′,
Mtan θ + Dtan θ ′ − (ε / 2) × cos θ ≧ 2
The shape and arrangement of the light guide plate are determined so as to satisfy the above.
According to a fourth aspect of the present invention, in the original illuminating device according to any one of the first to third aspects, the light guide plate is a material satisfying nd ≧ 1.35 when the refractive index with respect to the d-line is nd. It is characterized by comprising.

According to a fifth aspect of the present invention, when a surface to be illuminated having a length and a width, the length direction is a main scanning direction, and the width direction is a sub-scanning direction, a plurality of light emitting elements are arranged in the main scanning direction. An original illuminating apparatus comprising: a light source unit arranged; and a light guide plate disposed between the light source unit and the illuminated surface and guiding a light beam from the light emitting element to the illuminated surface, wherein the light guide plate Is a hollow body having two reflectors having a length and a width, matching the length direction to the main scanning direction, extending in the length direction, and reflecting surfaces facing each other at a predetermined interval The hollow body has an incident opening for allowing a light beam from the light emitting element to enter and an exit opening for emitting a diplomatic beam toward the illuminated surface, and the reflecting surface is inclined at a predetermined angle θ with respect to the illuminated surface. Of any two of the plurality of light emitting elements. The illuminance difference between the illuminance on the illuminated surface corresponding to a point and the illuminance on the illuminated surface corresponding to the front of any one of the two light emitting elements is large among the illuminances. The width of the light guide plate and the predetermined interval are set so as to be within 12% of the direction.
According to a sixth aspect of the present invention, in the original illuminating device according to the fifth aspect, the light guide plate is configured such that the width of the reflection plate is L ′, the interval between the two reflection plates is ε ′, and the light distribution of the light emitting elements is performed. When the half-value angle in the distribution is α ′, and the constant involved in the number of times the light beam corresponding to the half-value angle repeats reflection in the light guide plate is k,
k = (L ′ / ε ′) × tan α ′
It is characterized in that L ′ / ε ′ is determined so that k determined by the above formula becomes 3.5 or more.

According to a seventh aspect of the present invention, in the document illumination device according to the fifth or sixth aspect, the light guide is provided with a dustproof structure.
According to an eighth aspect of the present invention, in the document illuminating device according to any one of the fifth to seventh aspects, a contact glass is further disposed between the illuminated surface and the light guide plate, When the thickness is D, the distance from the exit aperture center of the light guide plate to the contact glass surface is M, and the refraction angle of the light incident on the contact glass at an incident angle θ is θ ′,
Mtan θ + Dtan θ ′ − (ε / 2) × cos θ ≧ 2
The shape and arrangement of the light guide plate are determined so as to satisfy the above.
In the invention according to claim 9, in the document illumination device according to any one of claims 3, 4, and 8,
D ≧ 2
θ ≧ 20 °
It is characterized by satisfying.

According to a tenth aspect of the present invention, in the document illumination device according to any one of the third, fourth, eighth, and ninth aspects, the contact glass has nd ≧ 1 when a refractive index with respect to d-line is nd. .35 material.
According to an eleventh aspect of the present invention, in the document illuminating device according to any one of the first to tenth aspects, the light emitting element is a white LED.
According to a twelfth aspect of the present invention, in the document illuminating device according to any one of the first to tenth aspects, the light emitting element includes at least two kinds of LEDs each having a different emission color, and each color light is The light is mixed by multiple reflection in the light guide plate, and can be regarded as white light at the exit position of the light guide plate.
According to a thirteenth aspect of the present invention, there is provided an image reading device using the original illumination device according to any one of the first to twelfth aspects.
According to a fourteenth aspect of the present invention, there is provided an image forming apparatus using the image reading device according to the thirteenth aspect.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an original illuminating apparatus using a plurality of light emitting elements such as LEDs and having a simple configuration and less unevenness in illuminance in the main scanning direction and the sub scanning direction on the original surface.

FIG. 1 is a diagram schematically showing the configuration of the present invention. FIG. 4A is a cross-sectional view in the main scanning direction, FIG. 4B is a cross-sectional view in the sub-scanning direction, and the curve schematically shows the illuminance distribution.
In the figure, reference numeral 1 denotes an LED, 2 denotes a light guide plate, 3 denotes a contact glass, and 4 denotes an illuminated surface.
In the configuration shown in FIG. 20 above, the LED 101 is disposed relatively close to the contact glass 102. Therefore, when trying to obtain high illuminance, illuminance unevenness occurs remarkably. When the LED 101 is separated from the contact glass 102, the illuminance is significantly reduced and it cannot be used. However, in the present configuration using the light guide plate 2 shown in FIG. 1, among the light beams from the individual LEDs 1, the light beams diverge greatly when the LED 1 is far from the contact glass 3 in the main scanning direction. The illuminance unevenness of the LED becomes smooth, and the result of the synthesis is almost free from local unevenness. In addition, in the sub-scanning direction, the light beam is repeatedly reflected in the light guide 2 and reaches the vicinity of the contact glass 3 before being emitted from the light guide. Therefore, the degree of divergence is smaller than that in the main scanning direction. Thus, the illuminance does not decrease so much.

However, in order to have the effect shown in the figure, it is necessary to appropriately set the arrangement / light distribution of the LEDs arranged in the light source unit (LED array). That is, even if a light guide plate is arranged between the LED array and the document surface, the width of the light guide plate can be reduced even if the light distribution of LEDs is steep, the distance between adjacent LEDs is long, or the distance between the LEDs is close to some extent. Naturally, unevenness of illuminance occurs when the value is short. Although it is not impossible to make the illuminance unevenness almost zero, considering the manufacturing cost, the above-described allowable range, that is, a condition that the illuminance unevenness is within 12% is obtained on the premise of the color image.
In general, the brightness of a single light source in a direction having an angle θ from the normal to the brightness in the normal direction of the light emitting surface decreases in accordance with the angle θ. As an ideal light source, a distribution in which the luminance in the θ direction is represented by cos θ is called a Lambert distribution. The LED that is actually ^sold, distributed and which can be approximated by ^{cos 1.5} theta, there is a distribution that can be approximated by cos ² theta.
When these LEDs are aligned in the normal direction and arranged in a direction orthogonal to the normal direction, and the illuminance distribution in the array direction at the illuminated position separated by a predetermined distance is examined, the position where the normal of each LED passes ( There are cases where the illuminance distribution at the point P0 (hereinafter referred to as point P0) shows the maximum value, and the position (hereinafter referred to as the point Ph) just corresponding to the intermediate point of the adjacent LED shows the maximum value.

Consider a simple model. At an arbitrary position P on the illuminated surface, illuminance is obtained by combining light beams from a plurality of LEDs. Naturally, the light flux from the LED near the point P greatly contributes to the illuminance at the point P, and the light flux from the LED far away does not contribute much. Assume that the length of the LED array is sufficiently larger than the desired size as the surface to be illuminated, and the LEDs are arrayed at equal intervals. If the contribution ratio of the luminous flux from the LED at the end to the illuminance at the edge of the illuminated surface is small enough not to affect the illuminance unevenness, the illuminance unevenness at the illuminated surface is the position where the normal passes. It is only necessary to compare the two points of the point P0 and the position Ph point corresponding to the intermediate point of the adjacent LED. If the difference in illuminance when viewed from the larger of the illuminances at these two points is within 12%, it can be used safely for color images.
The change in illuminance at an arbitrary position P depends mainly on the ratio of the LED pitch to the distance from the LED to the surface to be illuminated. When this ratio is sufficiently large, the illuminance at the point P0 mainly depends on the luminous flux from the LED alone, and the contribution ratio from the adjacent LED does not become so large. On the other hand, the illuminance at the Ph point can be obtained mainly by the light flux from one LED on each side, but each light flux is considerably smaller than a half of the light flux reaching the P0 point. Is smaller than the illuminance at the point P0.
On the contrary, when the above ratio is considerably small, the illuminance at the Ph point may be larger than the illuminance at the P0 point. In that case, the tendency becomes stronger as the ratio becomes smaller.

When the larger of the illuminance at the P0 point and the Ph point is Emax and the smaller illuminance is Emin,
(Emax−Emin) / Emax <0.12
The number of LEDs, the arrangement pitch, and the distance from the LED to the illuminated surface may be determined so as to satisfy the above.
In the present invention, as shown in FIG. 1, the light guide plate 2 is used while being inclined with respect to the surface to be illuminated. It has been described that the light guide plate 2 causes the light beam in the sub-scanning direction to diverge after reaching the vicinity of the illuminated surface, so that the light amount loss is reduced in the sub-scanning direction. Regarding the main scanning direction, the point that the optical path length changes because the light guide plate 2 enters, and the point that the light beam is incident in an inclined state with respect to the illuminated surface are different from the explanation using the model, but these conditions are Basically, it appears only as a change in illuminance level, and has little effect on illuminance unevenness.

LED array Number of LEDs 7 Array One row in the main scanning direction Array pitch 8mm
Light distribution Distribution Lambert distribution Output 10mW / 1 unit Light emitting surface 0.5 × 0.5mm surface intensity distribution uniform surface light source light guide plate length × width × thickness 60 × 8 × 1mm
Material nd = 1.517
Side Reflective film (100% reflectance) coating arrangement LED light emitting surface-light guide plate first end surface spacing Adherence Length of perpendicular drawn from the center of the second end surface of the light guide plate to the document surface 6 mm
Angle formed by the second end surface perpendicular to the light guide plate and the above normal 60 ° contact glass thickness 3.2 mm
Material nd = 1.517
Document surface The surface of the contact glass that is 0.01 mm away (shifted upward) from the upper surface is the document surface. 41 mm (main scanning direction) x 31 mm (sub-scanning direction)

FIG. 2 is a diagram illustrating an illuminance distribution according to the configuration of the first embodiment. FIG. 4A shows the distribution in the sub-scanning direction, and FIG. 4B shows the distribution in the main scanning direction.
In the figure, the horizontal axis represents the position (unit mm) of the contact glass, and the vertical axis represents illuminance (unit μW / mm ² ). The same applies to the following illuminance distribution.
In this embodiment, the illuminance distribution is obtained by dividing the original surface into 41 × 31 grids, tracing 1 million rays as rays from the light source, and calculating the number of rays incident on each 1 × 1 mm square grid. Plotted as illuminance on the grid. Hereinafter, the calculation of the illuminance distribution is the same. FIG. 4A shows the illuminance distribution in the sub-scanning direction cross section including the light source, and FIG. 4B shows the illuminance distribution in the main scanning direction cross section including the peak value of the graph in the sub-scanning direction. As can be seen from FIG. 5B, there is almost no illuminance unevenness in the main scanning direction.

FIG. 3 is a diagram showing the illuminance distribution of the comparative example. FIG. 4A shows the distribution in the sub-scanning direction, and FIG. 4B shows the distribution in the main scanning direction.
The specification of a comparative example is shown. The configuration of the comparative example conforms to FIG.
LED array: Same light guide plate as in Example 1: None Arrangement Length of perpendicular drawn from the center of the LED light emitting surface to the document surface 6 mm
The angle formed by the center of the light emitting direction and the perpendicular line 60 degrees Contact glass: Same as in Example 1 Original surface: Same as in Example 1 As shown in FIG. It is 22.1%, indicating that it is not suitable for color images.

FIG. 4 is a diagram showing the illuminance distribution in the main scanning direction by two LEDs.
In Example 1, the illuminance distribution in the main scanning direction on the illuminated surface by the LED at the center position, that is, at the position of 21 mm in the main scanning direction, and one LED adjacent to the LED is as shown in FIG. The illuminance is higher in the middle than the corresponding position. The illuminance of the illuminated surface corresponding to the position in front of the LED is about 11.7% lower than the illuminance of the illuminated surface corresponding to the midpoint of the two LEDs. That is, the illuminance difference is about 12%.
This difference in illuminance can be made smaller by widening the LED interval than 8 mm in the above embodiment.
Although the figure shows the illuminance by only two LEDs, the illuminance from a plurality of adjacent LEDs is actually superimposed, and these illuminances contribute from the midpoint corresponding position to the LED front corresponding position. Since the rate is larger, the illuminance difference is further reduced.
In general, the light output of surface-mounted LEDs is expressed in terms of luminous intensity, and the luminous intensity of currently distributed LEDs is about 125 to 860 mcd at a forward current of 10 to 30 mA. As a result, in the present invention, the light output of all LEDs is set to a value of 10 mW, but as described above, the increase in the brightness of the LEDs is rapidly progressing, and if the increase in the brightness of the LEDs is advanced, the number of LEDs used is increased. It leads to decrease. The present invention that suppresses illuminance unevenness in the main scanning direction is further required by increasing the brightness of the LEDs.

<Experimental example 1>
In this embodiment, the size and the like of the light guide plate in Embodiment 1 are changed.
LED array Number of LEDs 11 Array One row in the main scanning direction Array pitch 5mm
Light distribution Distribution Lambert distribution Output 10 mW / unit Light emitting surface 0.5 × 0.5 mm surface intensity distribution uniform surface light source light guide plate length × width × thickness 100 × 5 × 1 mm
Material nd = 1.517
Side Reflective film (100% reflectivity) coating arrangement Perpendicular length drawn from the center of the LED light emitting surface to the document surface 8mm
The angle θ 30 ° formed by the center of the light emission direction and the perpendicular line
Contact glass Same document surface as Example 1 Same as Example 1

The illuminance distribution in the sub-scanning direction is likely to be uniform because the number of reflections in the thickness direction of the light guide plate is increased to increase the degree of superimposition of the light flux after being emitted from the light guide plate. For that purpose, it is better that the plate thickness ε is smaller than the distance L of the light incident / exit surface.
Here, when the light beam emitted from the LED into the light guide at an angle α is reflected k times,
L = k (ε / tan α) (1)
And can be put. In the equation, ε / tan α is the distance in the L direction of the light guide that travels from the one reflecting surface to the other reflecting surface. Since L can be set to an arbitrary length, k is not limited to an integer. Since the LED is arranged at the center of the light guide in the thickness direction, for example, when 0.5 <k <1.5, the light beam is emitted from the emission surface into the air only once. If 2.5 <k <3.5, the light is emitted three times.
If the half-value angle of the Lambertian LED is made to correspond to the angle α in the light guide,
sin α = sin 60 ° / nd
When nd = 1.517 is used, α≈34.8 °.
Since L = 5 mm and ε = 1 mm, k = L / (ε / tan α) ≈3.48
It becomes. Conversely, the value of L can also be determined after the value of k is determined in advance.

FIG. 5 is a schematic diagram for explaining the arrangement of Experimental Example 1.
FIG. 6 is a diagram showing the illuminance distribution in the sub-scanning direction at the center of the original surface according to Experimental Example 1.
The light beam corresponding to the half-value angle emitted from the LED at ± 60 ° is reflected three times in the light guide, and then travels in the direction of ± 60 ° from the exit surface of the light guide. When the light guide is inclined by 30 ° with respect to the contact glass as in this experimental example, one of the light rays of ± 60 ° is incident on the contact glass at an angle of 30 °, and the other light ray is parallel to the contact glass. Go in the right direction.
As is apparent from FIG. 6, in this experimental example, the illuminance unevenness in the sub-scanning direction is considerably large. That is, even if an attempt is made to take a width of 2 mm as a reading area near the center of the sub-scanning, a stable reading area cannot be set with this illuminance distribution. This is thought to be due to insufficient illuminance uniformity in the sub-scanning direction. In this experimental example, k = 3.48. That is, k was set to the upper limit of three times of reflection. Therefore, it is necessary to reset k to the range of reflection four times or more.

FIG. 7 is a schematic diagram for explaining the arrangement of the second embodiment.
FIG. 8 is a diagram showing the illuminance distribution in the sub-scanning direction at the center of the original surface according to the second embodiment.
In this embodiment, the light guide plate is defined such that k≈5.5, and the length of the light guide plate is determined by length × width × thickness 100 × 8 × 1 mm.
Other conditions are the same as in the experimental example.
When calculated backward from the size of the light guide plate, k≈5.563 is accurately obtained.
As shown in FIG. 8, in this embodiment, the illuminance unevenness in an effective illumination range (2 mm width) that can be used as a reading area is within about 4.0%.

<Experimental example 2>
I changed the thickness and length of the light guide plate.
Light guide plate length x width x thickness 100 x 9.5 x 2 mm
Other conditions are the same as those in the first embodiment.
When k is calculated under this condition, k≈3.3. Since this is a value smaller than that of Experimental Example 1, it is expected that the illuminance unevenness is further increased.

FIG. 9 is a schematic diagram for explaining the arrangement of Experimental Example 1.
FIG. 10 is a diagram showing the illuminance distribution in the sub-scanning direction at the center of the original surface according to Experimental Example 1.
As is apparent from FIG. 6, the illuminance distribution is very similar to the illuminance distribution shown in FIG. 6, and the illuminance unevenness is larger than that in FIG.

FIG. 11 is a schematic diagram for explaining the arrangement of the third embodiment.
FIG. 12 is a diagram showing the illuminance distribution in the sub-scanning direction at the center of the original surface according to the third embodiment.
The length of the light guide plate is further increased with respect to Experimental Example 2.
Light guide plate length x width x thickness 100 x 12 x 2 mm
Other conditions are the same as those in the first embodiment.
When k is calculated under this condition, k≈4.2, and reflection is four times.
As is apparent from FIG. 12, even if the thickness of the light guide is increased, the illuminance unevenness (about 3.0% in FIG. 12) can be reduced by increasing the width accordingly.

13 and 14 are diagrams for explaining the arrangement of the light guides.
Here, a general arrangement relationship of the light guides will be considered. FIG. 13 shows a state in which the center of the light exit surface of the light guide is further away from the lower surface of the contact glass having a thickness D by a distance M, and the light guide is inclined at an angle θ with respect to the normal of the contact glass surface. Show. A light beam incident on the contact glass at an angle θ is assumed to travel through the medium at an angle θ ′.
FIG. 14 is a schematic diagram assuming that the light beam from the light guide exit surface is completely diffused light, and the center of the exit surface is regarded as a point light source. The original document surface immediately above the point light source is set as the coordinate origin.
When the illuminance on the document surface is calculated according to the figure, the illuminance is inversely proportional to the square of the light path length and proportional to the Lambertian distribution. The Lambert distribution has the maximum radiation intensity in the angle θ direction shown in the figure, but since the ray path length is shorter in the direction closer to the origin, the closer to the origin is brighter. In general, a peak of illuminance distribution appears between them.
In FIG. 13, since the reading direction is a direction perpendicular to the document surface, the origin itself cannot be a reading area because it is blocked by the light guide plate. At least the range from the origin to ½ × cos θ of the plate thickness ε is blocked by the light guide plate and cannot be read.
As described above, since the width of 2 mm is desired as the reading area, it is necessary to set an effective area of at least 2 mm including a peak value in the range up to the point P on the original surface. When this relationship is expressed by a mathematical formula,
Mtanθ + Dtanθ ′ − (ε / 2) × cos θ ≧ 2 (2)
It becomes.

Since the thickness D of the contact glass is structurally limited, for example, in the document placement type and the optical system moving type, the thickness is usually 3 mm or more. In the case of a sheet document moving type with the optical system fixed, it can be made thinner, for example, 2 mm. Therefore, in the above formula, the lower limit of D may be regarded as 2 mm.
If the inclination angle θ of the light guide plate is too small, the effective area cannot be obtained sufficiently. Therefore, although not shown in the figure, as a result of simulation of several illuminance distributions under the condition of M + D ≧ 6, θ ≧ 20 ° is obtained. I found it desirable.
In FIG. 14, the light-guiding body exit surface having a thickness of ε mm is described as a point. However, when a difference in illuminance distribution between when a non-zero ε is given and when it is regarded as a point, ε ≦ 3 mm is satisfied. It turns out that there is no problem even if it is regarded as a point in practical use.

<Experimental example 3>
Light guide plate length x width x thickness: 100 x 12 x 2 mm
Arrangement of perpendicular line drawn from the center of the LED light emitting surface to the document surface: (M + D) 7 mm
The angle θ formed by the center of the light emitting direction and the normal of the contact glass is 20 degrees, and other specifications are the same as those in the third embodiment.
Under this condition, Mtanθ + Dtanθ′≈2.12 mm
(Ε / 2) × cos θ≈0.94
Therefore, the left side of Equation (2) is Mtanθ + Dtanθ ′ − (ε / 2) × cosθ≈1.2 mm
And does not satisfy the formula (2).

FIG. 15 is a schematic diagram for explaining the arrangement of Experimental Example 3.
FIG. 16 is a diagram showing the illuminance distribution in the sub-scanning direction at the center of the original surface according to Experimental Example 3.
Under the conditions of this experimental example, since the point P is at a position of about 2.12 mm from the origin, the peak value of the illuminance distribution in the sub-scanning direction occurs at a position closer to about 2.12 mm from the origin. Therefore, the necessary width as the effective illumination width is about 3 mm from the origin, but in this range, as shown in FIG. 16, the illuminance unevenness exceeds 15%.

FIG. 17 is a schematic diagram for explaining the arrangement of the fourth embodiment.
FIG. 18 is a diagram showing the illuminance distribution in the sub-scanning direction at the center of the original surface according to the fourth embodiment.
In the present embodiment, only the arrangement of the light guide plate in Experimental Example 3 is changed.
Arrangement of perpendicular line drawn from the center of the LED light emitting surface to the document surface (M + D) 7mm
The angle θ 30 ° formed by the center of the light emitting direction and the normal of the contact glass The other specifications are the same as in Example 3.
Under this condition, Mtanθ + Dtanθ′≈3.31 mm
(Ε / 2) × cos θ≈0.87
Therefore, the left side of Expression (2) is Mtanθ + Dtanθ ′ − (ε / 2) × cosθ≈2.45 mm.
Thus, the expression (2) is satisfied.
As shown in FIG. 18, the illuminance distribution in the sub-scanning direction according to the present embodiment is about 7.8% in the range of the effective illumination width of 2 mm, and can be sufficiently used as a reading area.

The experimental examples and examples shown so far have been based on the use of a light guide plate made of glass. However, making glass with a thickness of 2 mm or 1 mm with glass has a problem of breakage and is not practical. Therefore, consider making this with a transparent resin. In the case of a transparent resin, the refractive index is smaller than the refractive index 1.517 of glass shown in Examples and the like (for example, nd = 1.35 to 1.38 of polytetrafluoroethylene). As described above, the present invention has conditions related to the refractive index of the material of the light guide plate, but does not depend directly on the conditions. Therefore, it is completely free to use a transparent resin other than glass as the material of the light guide plate.
For the same reason, the material of the contact glass is not confused by its name, and a transparent resin can be used. Therefore, although nd = 1.517 was used as the refractive index of the contact glass in the experimental examples and examples, the value of 1.35 may be used for this value as well.

Further consideration of the light guide plate shows that the refractive index is 1, that is, the medium can be air. That the medium is air means that it may be a hollow body whose side surface is surrounded by a reflecting surface. There may be an opening on the incident side of the light beam and an opening on the emission side. However, in order to prevent dirt and dust from adhering to the reflecting surface, it is preferable to attach a dust-proof lid to the above-mentioned amount opening. However, the lid is formed of a transparent member so that it does not interfere with the incident / exit of the light beam.
In this case, when the width of the reflecting surface is L ′, the interval between the two reflecting plates is ε ′, and the half-value angle in the light distribution of the light emitting element is α ′,
k = (L ′ / ε ′) × tan α ′ (3)
It becomes. Further, the expression corresponding to the expression (2) is Mtanθ + Dtanθ ′ − (ε ′ / 2) × cosθ ≧ 2 (4)
It becomes.

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 ideally performed before the light beam is emitted from the LED, but in the case of the present invention, the light beam repeats reflection a plurality of times in the light guide. Color mixing may be completed to such an extent that it can be considered white at the time of emission from the emission end side of the light guide.

  Any of the document illumination apparatuses described above can be used for an image reading apparatus, and the image reading apparatus can form an image forming apparatus.

It is a figure which shows typically the structure of this invention of this invention. FIG. 3 is a diagram showing an illuminance distribution according to the configuration of Example 1. It is a figure which shows the illumination intensity distribution of a comparative example. It is a figure which shows the illuminance distribution of the main scanning direction by two LED. It is a schematic diagram for demonstrating arrangement | positioning of Experimental example 1. FIG. 6 is a diagram illustrating an illuminance distribution in a sub-scanning direction at the center of a document surface according to Experimental Example 1. FIG. FIG. 6 is a schematic diagram for explaining the arrangement of Example 2. FIG. 10 is a diagram illustrating an illuminance distribution in the sub-scanning direction at the center of the original surface according to the second embodiment. It is a schematic diagram for demonstrating arrangement | positioning of Experimental example 1. FIG. 6 is a diagram illustrating an illuminance distribution in a sub-scanning direction at the center of a document surface according to Experimental Example 1. FIG. 10 is a schematic diagram for explaining the arrangement of Example 3. FIG. FIG. 10 is a diagram illustrating an illuminance distribution in the sub-scanning direction at the document surface center according to the third embodiment. It is a figure for demonstrating arrangement | positioning of a light guide. It is a figure for demonstrating arrangement | positioning of a light guide. It is a schematic diagram for demonstrating arrangement | positioning of Experimental example 3. FIG. FIG. 10 is a diagram illustrating an illuminance distribution in the sub-scanning direction at the center of a document surface according to Experimental Example 3. 10 is a schematic diagram for explaining an arrangement of Example 4. FIG. FIG. 10 is a diagram illustrating an illuminance distribution in the sub-scanning direction at the document surface center according to the fourth embodiment. 1 is a schematic diagram of an image forming apparatus having an image reading apparatus. It is a conceptual diagram which shows the state which illuminates the original document surface directly with an LED array. It is sectional drawing of the illuminating device using a rod-shaped light source. It is sectional drawing of the illuminating device using a rod-shaped light source. 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.

Explanation of symbols

1 LED
2 Light guide plate 3 Contact glass 4 Illuminated surface

Claims (14)

  A surface to be illuminated having a length and a width; a light source unit in which a plurality of light emitting elements are arranged 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 disposed between a unit and the surface to be illuminated and guiding a light beam from the light emitting element to the surface to be illuminated, wherein the light guide plate has a length, a width, and a thickness. Having a length direction coincident with the main scanning direction, an incident surface on which a light beam from the light emitting element is incident, an exit surface facing the incident surface and emitting the light beam, and connecting both surfaces thereof; Two reflective surfaces facing each other in the thickness direction, and the reflective surfaces are arranged to be inclined at a predetermined angle θ with respect to the illuminated surface, and any two of the plurality of light emitting elements emit light. Illuminance on the illuminated surface corresponding to the midpoint of the element and the above two light emission The width of the light guide plate so that the illuminance difference with the illuminance on the illuminated surface corresponding to the front of any one light emitting element of the children is within 12% with respect to the larger of the illuminances. An original illuminating device having a set thickness. The document illumination device according to claim 1, wherein the width of the light guide plate is L, the thickness of the light guide plate is ε, and the refraction angle in the light guide plate medium corresponding to the half-value angle in the light distribution of the light emitting elements is α, When k is a constant related to the number of times the light beam corresponding to the half-value angle repeats reflection in the light guide plate,
k = (L / ε) × tan α
An original illuminating apparatus characterized in that L / ε is determined so that k determined by the formula of is equal to or greater than 3.5. 3. The document illuminating device according to claim 1, wherein a contact glass is further disposed between the illuminated surface and the light guide plate, the thickness of the contact glass being D, and the exit surface thickness of the light guide plate. When the distance from the center of the direction to the contact glass surface is M, and the refraction angle of the light beam incident on the contact glass at an incident angle θ is θ ′,
Mtan θ + Dtan θ ′ − (ε / 2) × cos θ ≧ 2
An original illuminating apparatus characterized in that the shape and arrangement of the light guide plate are determined so as to satisfy the above.   4. The document illumination device according to claim 1, wherein the light guide plate is made of a material satisfying nd ≧ 1.35 when a refractive index with respect to d-line is nd. apparatus.   A surface to be illuminated having a length and a width; a light source unit in which a plurality of light emitting elements are arranged in the main scanning direction when the length direction is a main scanning direction and the width direction is a sub scanning direction; And a light guide plate disposed between the unit and the surface to be illuminated and guiding a light beam from the light emitting element to the surface to be illuminated, wherein the light guide plate has a length and a width. A hollow body having two reflectors whose length direction coincides with the main scanning direction and extending in the length direction and whose reflecting surfaces are opposed to each other at a predetermined interval, the hollow body from the light emitting element The plurality of light emitting elements, and the reflecting surface is inclined at a predetermined angle θ with respect to the illuminated surface. The illuminated surface corresponding to the midpoint of any two of the light emitting elements And the illuminance difference on the illuminated surface corresponding to the front of any one of the two light emitting elements is within 12% of the larger of the illuminances. In this way, the width of the light guide plate and the predetermined interval are set as described above. 6. The document illuminating device according to claim 5, wherein the light guide plate has a width of the reflection plate as L ′, an interval between the two reflection plates as ε ′, and a half-value angle in a light distribution of the light emitting elements as α ′, When k is a constant related to the number of times the light beam corresponding to the half-value angle repeats reflection in the light guide plate,
k = (L ′ / ε ′) × tan α ′
An original illuminating apparatus characterized in that L ′ / ε ′ is determined so that k determined by the equation of 3.5 is 3.5 or more.   7. The document illumination device according to claim 5, wherein the light guide has a dustproof structure. 8. The document illuminating device according to claim 5, further comprising a contact glass disposed between the illuminated surface and the light guide plate, wherein the thickness of the contact glass is D, and the light guide plate. When the distance from the center of the exit aperture to the contact glass surface is M, and the refraction angle of the light incident on the contact glass at an incident angle θ is θ ′,
Mtan θ + Dtan θ ′ − (ε ′ / 2) × cos θ ≧ 2
An original illuminating apparatus characterized in that the shape and arrangement of the light guide plate are determined so as to satisfy the above. The document illuminating device according to any one of claims 3, 4, and 8,
D ≧ 2
θ ≧ 20 °
Document illumination device characterized by satisfying the above.   10. The document illumination device according to claim 3, wherein the contact glass is made of a material satisfying nd ≧ 1.35 when a refractive index with respect to d-line is nd. Document illumination device.   11. The document illuminating apparatus according to claim 1, wherein the light emitting element is a white LED.   11. The document illuminating apparatus according to claim 1, wherein the light emitting element includes at least two kinds of LEDs each having a different emission color, and each color light is multiple-reflected within the light guide plate. The original illuminating apparatus, wherein the light is mixed and the white light can be regarded at the emission position of the light guide plate.   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 13.

Images