JP5657875B2 - Light guide, illuminating device and document reading apparatus including the same, light guide mold and method for manufacturing the same - Google Patents

Description

  In the present invention, in order to allow light emitted from a light source to enter from a light incident surface on one end side in the longitudinal direction and to exit from a light exit surface extending in the longitudinal direction, a projecting prism is guided to face the light exit surface. The present invention relates to a light guide provided with a plurality of prism forming surfaces formed side by side in the longitudinal direction of an optical body, an illumination device and a document reading device including the same, a light guide manufacturing die, and a method for manufacturing the same. .

  In a document reading apparatus that reads an image on a document surface, reflected light from the document surface illuminated by an illuminating device is received by a light receiving element such as a CCD and an image signal is output. Conventionally, an illumination device of this document reading device has generally used a fluorescent tube. However, in recent years, an illumination device using an LED as a light source is becoming widespread from the viewpoint of energy saving.

  In such an illumination device using LEDs as the light source, in addition to the configuration in which the LEDs are arranged over the entire width of the reading region, the light emitted from the LED light source using a light guide that extends over the entire width of the reading region. The light guide emits light emitted from the light source from the light incident surface on one end side in the longitudinal direction and exits from the light exit surface extending in the longitudinal direction. For this purpose, a prism forming surface is provided in which a plurality of protruding prisms are arranged in the longitudinal direction of the light guide so as to face the light emitting surface.

  However, the light guide is formed of a material having excellent translucency, such as an acrylic resin, but light attenuates in inverse proportion to the square of the distance as it is separated from the light source by light absorption. For this reason, in order to make the illuminance distribution of the light emitted from the light exit surface uniform over the entire longitudinal direction, it is necessary to gradually increase the reflection area by the prism from the light source side to the counter light source side. There is. Therefore, a technique is known in which the prism arrangement interval is gradually reduced from the light source side toward the counter light source side. In addition, a technique is known in which the width of the prism is gradually increased from the light source side toward the opposite light source side (see Patent Document 1).

JP-A-2005-204329

  However, in the technique of adjusting the illuminance distribution characteristics by the prism arrangement interval, the prism arrangement interval becomes extremely large at the end portion on the light source side, so that there is a problem that illuminance unevenness becomes remarkable. Further, in the technique of adjusting the illuminance distribution characteristic by the width of the prism, the width of the prism becomes extremely small at the end portion on the light source side, and accordingly, the irradiation width in the sub-scanning direction capable of ensuring the required illuminance becomes small. Therefore, when the positional relationship between the document surface and the light guide changes, there is a problem that the document surface cannot be properly illuminated.

  In addition, the document reading apparatus includes a contact type optical system that receives reflected light from the document surface by a reading sensor having the same width as the document, and reduces the reflected light from the document surface in the main scanning direction by a lens to the reading sensor. There is a reduction optical system that receives light. In this reduction optical system, the illuminance distribution on the light receiving surface of the reading sensor is highest at the center in the main scanning direction due to the cosine fourth law relating to the lens. It becomes the characteristic which becomes gradually lower toward.

  The problem of non-uniform illuminance on the light receiving surface of the reading sensor due to such characteristics of the reduction optical system can be solved by adjusting the illuminance distribution characteristic of the light guide, and the reflection area by the prism is long. If the light receiving surface of the reading sensor on which the characteristics of the reduction optical system and the characteristics of the light guide are superimposed, the reduction optical system is the smallest at the center of the direction and gradually increases from the center to the end. And the characteristics of the light guide are offset, and the illuminance on the light receiving surface of the reading sensor can be made uniform.

  However, when adjusting the illuminance distribution characteristic of the light guide so as to be suitable for such a reduction optical system, it is conceivable to use the technique for adjusting the illuminance distribution characteristic by the arrangement interval or width of the prism as described above. However, in the technology that adjusts the illuminance distribution characteristic by the arrangement interval of the prisms, there is a problem of uneven illuminance due to the extremely large arrangement interval of the prisms at the center, and the illuminance distribution characteristic is adjusted by the width of the prism In the technology, there is a problem that the irradiation width in the sub-scanning direction is insufficient due to the extremely small width of the prism at the center.

  The present invention has been devised in order to solve such problems of the prior art, and its main purpose is to solve the problem of uneven illumination and insufficient irradiation width in the sub-scanning direction. It is an object of the present invention to provide a light guide configured to obtain the following illuminance distribution characteristics, an illuminating device and a document reading device including the light guide, a mold for manufacturing a light guide, and a method for manufacturing the same.

  The light guide of the present invention has a projection facing the light emitting surface so that the light emitted from the light source is incident from the light incident surface on one end side in the longitudinal direction and is emitted from the light emitting surface extending in the longitudinal direction. A light guide having a prism forming surface in which a plurality of prisms are arranged in the longitudinal direction, wherein the prisms are arranged at regular intervals, and the prism forming surface has a required illuminance distribution characteristic. Accordingly, the top of the prism is positioned on the first reference plane constituted by one plane so that the height of the prism changes accordingly, and the distance from the first reference plane is along the longitudinal direction. In this configuration, the bottom of the valley between the prisms is positioned on the second reference plane arranged so as to change.

  The illumination device of the present invention includes a light source, a light guide that guides light emitted from the light source to a reading surface of a document, and a housing that integrally supports the light source and the light guide. It is an apparatus, Comprising: It is set as the structure provided with the said light guide.

  The document reading apparatus of the present invention includes the illumination device, a reading sensor that receives reflected light from the document and outputs an image signal, and a reduction optical system that guides the reflected light from the document to the reading sensor. It is set as the structure provided with.

  Further, the light guide manufacturing mold of the present invention is configured so that the light emitted from the light source enters from the light incident surface on one end side in the longitudinal direction and is emitted from the light emitting surface extending in the longitudinal direction. A light guide manufacturing mold for manufacturing a light guide having a prism forming surface in which a plurality of protruding prisms are formed side by side in the longitudinal direction. Concave portions corresponding to the prisms are arranged at regular intervals on the mold surface that forms the prism forming surface, and the mold surface has a height of the prism according to the illuminance distribution characteristics required for the light guide. The bottom of the recess corresponding to the top of the prism is positioned on a first reference plane constituted by one plane so that the depth of the recess corresponding to the height changes, and the first reference The second is arranged such that the distance to the surface varies along the longitudinal direction. A structure in which the surface corresponding to the valley portion between the prism onto reference plane is formed so as to be located.

  Further, in the method for manufacturing a light guide manufacturing die according to the present invention, the light emitted from the light source is incident from the light incident surface on one end side in the longitudinal direction and is emitted from the light emitting surface extending in the longitudinal direction. A manufacturing method of a light guide manufacturing die for manufacturing a light guide having a prism forming surface in which a plurality of protruding prisms are formed in a longitudinal direction so as to face a light emitting surface, In the mold, concave portions corresponding to the prisms are arranged at regular intervals on a mold surface that molds the prism forming surface of the light guide, and the mold surface is required for the light guide. The depth of the concave portion corresponding to the height of the prism changes according to the illuminance distribution characteristic, and the concave portion corresponding to the top portion of the prism is formed on the first reference plane constituted by one plane. The bottom is located, and the distance from the first reference plane is along the longitudinal direction A surface corresponding to the bottom of the valley between the prisms is formed on the second reference surface arranged so as to change, and the mold has a cross-sectional shape along the second reference surface. The first step of forming the material and the mold material obtained in the first step are arranged so that the feed direction of the cutting tool and the first reference plane are parallel to each other, and then the cutting direction The operation of advancing the cutting tool from the reference position by a predetermined distance in the cutting direction and the operation of moving the cutting tool in the feed direction at a constant pitch corresponding to the arrangement interval of the prisms, And a second step to be formed.

  According to the present invention, since the amount of emitted light per unit length is determined according to the height of the prism, the required illuminance distribution characteristics can be obtained by appropriately setting the height of the prism. Also, since the prism spacing is constant, there is a problem of illuminance unevenness due to an extremely large prism spacing, and a problem of insufficient irradiation width in the sub-scanning direction due to an extremely small prism width. A great effect can be obtained in realizing a light guide body that does not occur and has excellent optical characteristics.

Schematic diagram showing a document reading apparatus to which the present invention is applied Sectional drawing which shows the illuminating device shown in FIG. 1 is a block diagram showing a schematic configuration of a control unit of the document reading apparatus shown in FIG. The figure which shows each characteristic of a light guide, a reduction optical system, and a reading sensor The schematic diagram which shows the light guide which concerns on the 1st Embodiment of this invention. The schematic diagram which shows the metal mold | die for manufacturing the light guide shown in FIG. The schematic diagram which shows the manufacturing process of the light guide manufacture metal mold | die shown in FIG. Schematic diagram showing another example of the light guide Diagram showing illuminance distribution on the document surface The schematic diagram which shows the light guide which concerns on the 2nd Embodiment of this invention. Diagram showing illuminance distribution on the document surface The figure which shows each characteristic of a light guide, a reduction optical system, and a reading sensor

  According to a first aspect of the present invention, there is provided a light emitting device for causing light emitted from a light source to be incident from a light incident surface on one end side in a longitudinal direction and emitted from a light emitting surface extending in the longitudinal direction. Opposite the surface, a light guide having a prism forming surface formed with a plurality of protruding prisms arranged in the longitudinal direction, wherein the prisms are arranged at regular intervals, the prism forming surface, The apex of the prism is positioned on a first reference plane constituted by one plane so that the height of the prism changes according to the required illuminance distribution characteristics, and the first reference plane and In this configuration, a valley bottom between the prisms is positioned on a second reference plane that is arranged so that the distance between the prisms changes along the longitudinal direction.

  According to this, since the height of the prism is determined by the distance between the first reference surface and the second reference surface, and the reflection area by the prism, that is, the amount of emitted light is determined according to the height of the prism, the first reference surface By appropriately setting the position of the second reference plane with respect to the required illuminance distribution characteristics, it is possible to obtain the required illuminance distribution characteristics.

  In order to adjust the illuminance distribution characteristics according to the height of the prism in this way, it is only necessary to keep the prism arrangement interval constant, and the illuminance unevenness caused by the excessive prism arrangement interval and the prism width is too small. Thus, the problem of insufficient irradiation width in the sub-scanning direction that occurs can be solved.

  Further, when the light guide is manufactured using a mold, the mold material is formed into a cross-sectional shape along the second reference plane that defines the position of the valley bottom between the prisms, and then the cutting tool is fed. The concave portion corresponding to the cutting direction, i.e., the prism, by cutting the cutting tool by a certain distance from the reference position in the cutting direction after arranging the direction and the first reference plane defining the position of the top of the prism in parallel It is only necessary to repeat the operation of moving forward in the depth direction and the operation of moving the cutting tool in the feed direction at a constant pitch corresponding to the arrangement interval of the prisms to form the recess. At this time, the cutting direction and the feed direction Therefore, the mold surface of the mold can be accurately formed, and the prism forming surface of the light guide is also accurately formed accordingly. Improve body optical properties Rukoto can.

  According to a second aspect of the present invention for solving the above-mentioned problems, in the first aspect, the second reference surface is composed of a plurality of planes, and the prisms have heights on the light source side and the anti-light source side. It is set as the structure which became small gradually from the edge part of this to the center part.

  According to this, since the illuminance characteristic of the light guide can be approximated to the reverse characteristic of the transmission characteristic of the reduction optical system that guides the reflected light from the original to the reading sensor in the original reading apparatus, at the position of the reading sensor, The characteristics of the reduction optical system and the characteristics of the light guide are offset, and the illuminance distribution in the reading sensor can be made substantially uniform. As a result, high-precision reading can be realized, and light use efficiency can be increased to reduce power consumption.

  Furthermore, since the second reference surface is composed of a plurality of planes, a mold surface corresponding to the valley bottom between the prisms in the light guide mold can be manufactured with high accuracy. Since the valley bottom between the prisms of the optical body is also accurately formed, the optical characteristics of the light guide can be further improved.

  In this case, the second reference plane is preferably composed of at least two planes having different inclinations in the light source side region and the counter light source side region with the central portion in the longitudinal direction interposed therebetween.

  According to a third aspect of the present invention for solving the above-described problems, in the first aspect, the second reference surface is configured by a curved surface that is curved in a substantially arcuate shape, and the height of the prism is on the light source side. And it is set as the structure which became gradually small toward the center part from the edge part by the side of a counter light source.

  According to this, the illuminance characteristic of the light guide can be approximated with high accuracy to the reverse characteristic of the transmission characteristic of the reduction optical system that guides the reflected light from the original to the reading sensor in the original reading apparatus. At the position, the characteristics of the reduction optical system and the characteristics of the light guide are canceled, and the illuminance distribution at the reading sensor can be made uniform with high accuracy. As a result, high-precision reading can be realized, and light use efficiency can be increased to reduce power consumption.

  According to a fourth aspect of the present invention for solving the above-mentioned problems, in the first to third aspects of the present invention, the prism is formed so that a cross section has a triangular shape or a trapezoidal shape.

  According to this, when manufacturing a light guide using a metal mold | die, die cutting becomes easy.

  According to a fifth aspect of the present invention, there is provided a light source, a light guide that guides light emitted from the light source to a reading surface of a document, and a housing that integrally supports the light source and the light guide. It is an illuminating device provided with the body, Comprising: Let the said light guide be the structure which is a light guide based on the said 1st-4th invention.

  A sixth invention made to solve the above-described problem is a document reading device, the illumination device according to the fifth invention, and a reading sensor that receives reflected light from the document and outputs an image signal. And a reduction optical system that guides reflected light from the original to the reading sensor.

  A seventh invention made to solve the above-mentioned problems is that, in the sixth invention, in the main scanning direction at the position of the reading sensor where the characteristics of the reduction optical system and the characteristics of the light guide are superimposed. The light guide is set to a characteristic in which the illuminance is increased in the central part in the main scanning direction with respect to the characteristic opposite to the characteristic of the reduction optical system so that the illuminance is maximum in the central part of Only the output signal of the light receiving element located at the center in the main scanning direction of the sensor is monitored, and the peak hold control is performed to keep the maximum value of the output signal of the reading sensor constant.

  According to this, it is only necessary to monitor the output signal of the light receiving element located at the center of the reading sensor, so that peak hold control is facilitated.

  In an eighth aspect of the present invention made to solve the above-described problems, the light emission is performed so that light emitted from the light source is incident from a light incident surface on one end side in the longitudinal direction and is emitted from a light emitting surface extending in the longitudinal direction. A light guide manufacturing die for manufacturing a light guide having a prism forming surface in which a plurality of protruding prisms are formed in a longitudinal direction so as to face the surface, Concave portions corresponding to the prisms are arranged at regular intervals on the mold surface that forms the prism forming surface, and the mold surface is provided on the prism according to the illuminance distribution characteristics required for the light guide. The bottom of the concave portion corresponding to the top of the prism is positioned on the first reference plane constituted by one plane so that the depth of the concave portion corresponding to the height changes, and the first Arranged so that the distance from the reference surface changes along the longitudinal direction. Surface it is corresponding to the valley portion between the prism to the second reference plane on a structure that is formed so as to be positioned that.

  According to a ninth aspect of the present invention for solving the above-described problems, the light emission is performed so that light emitted from a light source is incident from a light incident surface on one end side in the longitudinal direction and is emitted from a light emitting surface extending in the longitudinal direction. A manufacturing method of a mold for manufacturing a light guide for manufacturing a light guide having a prism forming surface in which a plurality of protruding prisms are formed in a longitudinal direction so as to face the surface, In the mold, concave portions corresponding to the prisms are arranged at regular intervals on a mold surface that molds the prism forming surface of the light guide, and the mold surface has an illuminance required for the light guide. The bottom of the concave portion corresponding to the top of the prism is formed on the first reference plane constituted by one plane so that the depth of the concave portion corresponding to the height of the prism changes according to the distribution characteristic. Located at a distance from the first reference plane along the longitudinal direction. The surface corresponding to the bottom of the valley between the prisms is positioned on the second reference plane arranged so as to change, and the gold has a cross-sectional shape along the second reference plane. The first step of forming the mold material and the mold material obtained in the first step are arranged so that the feed direction of the cutting tool and the first reference plane are parallel to each other, and then cutting is performed. Repeating the operation of moving the cutting tool forward in the cutting direction by a predetermined distance from the reference position in the direction and the operation of moving the cutting tool in the feed direction at a constant pitch corresponding to the arrangement interval of the prisms. And a second step of forming the structure.

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

  As shown in FIG. 1, an original reading apparatus 1 to which the present invention is applied includes an illuminating apparatus 2 extending in the main scanning direction to illuminate an original A, and a reflected light from the original to receive an image signal. A reading sensor 3 for outputting and a reduction optical system 4 for guiding reflected light from the document A to the reading sensor 3 are provided.

  In the reading sensor 3, a light receiving element (CCD) that converts light into an electrical signal is arranged in the main scanning direction for each color of RGB to constitute a line sensor. The document A is fed between the document glass 6 and the document guide 7 by the transport roller 5, and the document A is transported to perform scanning in the sub-scanning direction.

  The reduction optical system 4 includes a plurality of mirrors 11, slits 12, and lenses 13. The slit 12 cuts unnecessary light. The lens 13 forms an image of the reflected light from the document A on the light receiving surface of the reading sensor 3 and reduces it in the main scanning direction so as to match the width of the reading sensor 3.

  As shown in FIG. 2, the illumination device 2 includes a light source 21, a light guide 22 that guides light emitted from the light source 21 to the reading surface of the document A, and a housing that integrally supports the light source 21 and the light guide 22. It has a body 23 and a radiator 24 that radiates heat generated by the light source 21.

  The light source 21 is provided with an LED chip on a ceramic substrate and a hemispherical lens so as to cover the LED chip. The light source 21 is a so-called one-chip white LED, the LED chip emits blue light, the lens is obtained by dispersing a yellow phosphor in a bonding material made of transparent silicon or the like, and the LED chip emits. The blue light is converted into yellow light by the yellow phosphor in the lens, and the blue light transmitted through the lens and the yellow light emitted from the yellow phosphor are mixed to become white light.

  The light guide 22 is provided so as to extend over substantially the entire width of the reading region, and the light emitting surface that extends in the longitudinal direction by causing the light emitted from the light source 21 to enter from the light incident surface 31 on one end side in the longitudinal direction. In order to emit light from 32, a prism forming surface 33 in which a plurality of protruding prisms are arranged in the longitudinal direction of the light guide 22 is provided opposite the light emitting surface 32. The light guide 22 is formed of a light-transmitting resin material such as acrylic resin (PMMA), and has a tapered shape in which the cross-sectional area gradually decreases from the light source side to the counter light source side.

  The light incident surface 31 is a flat surface, and the light emitting surface 32 is a curved surface having an elliptical cross section. In the prism forming surface 33, a prism having a triangular or trapezoidal cross section on a flat surface or a gently curved surface extends in a direction perpendicular to the longitudinal direction of the light guide 22, and the light guide A plurality of 22 are arranged in the longitudinal direction.

  The end of the light guide 22 on the light source side is held by the first holding member 25, and the end on the opposite light source side is held by the second holding member 26. A light reflector 28 that guides the light emitted from the light source 21 to the light incident surface 31 of the light guide 22 is provided at the end of the light guide 22 on the light source side. A mirror member 27 capable of contacting the end surface 34 of the light guide 22 is accommodated in the second holding member 26 that holds the end of the light guide 22 on the side opposite to the light source. The mirror member 27 is formed with a reflection surface on the end surface 34 side of the light guide 22, and light that reaches the end surface 34 of the light guide 22 while repeating refractive reflection inside the light guide 22 is reflected in the mirror member 27. The light is reflected by the reflection surface of the light and returned to the inside of the light guide 22.

  Here, two light guides 22 are provided in parallel with each other (see FIG. 1), and two light sources 21 are provided corresponding to the two light guides 22.

  As shown in FIG. 3, in the document reading apparatus 1, an analog image signal output from the reading sensor 3 is converted into digital image data by an A / D conversion unit 15. The image data output from the A / D converter 15 is subjected to required image processing by the image processor 16 and then transferred to the image memory 17 that holds the image data. The image processing unit 16 performs various types of image processing such as shading correction, pixel density conversion, and gamma correction.

  Further, in the light source 21 using LEDs, there is generally a change in the light amount of about 10% over the entire service life, and the light emission efficiency changes with a change in temperature. For this reason, the correction control unit 18 performs a process of correcting the light amount of the light source 21 so that the output signal of the light receiving element of the reading sensor 3 is always constant at the time of lighting or at the start of reading of the document. The correction control unit 18 compares the output signal of the light receiving element with a predetermined reference value, adjusts the control current supplied from the light source control unit 19 to the light source 21 based on the deviation, and adjusts the light amount of the light source 21. Is controlled to be constant.

  In this light amount correction, in order to measure the light amount of the light source 21, as shown in FIG. 2, a reference plate that reflects light emitted from the light emitting surface 32 of the light guide 22 and guides it to the reading sensor 3. 35 is provided. The reference plate 35 is made of, for example, a white sheet-like member, and is arranged outside the document reading area so as not to interfere with the reading of the document A.

  As shown in FIG. 1, here, a reduction optical system in which reflected light from the document surface is reflected by a mirror 11 and then reduced in the main scanning direction by a lens 13 so as to match the width of the reading sensor 3. 4 is adopted. In the reduction optical system 4, assuming that the illuminance of light emitted from the light guide 22 is uniform in the main scanning direction (longitudinal direction of the light guide 22), the illuminance distribution on the light receiving surface of the reading sensor 3 is as follows: As shown in FIG. 4 (A), the cosine fourth law relating to No. 13 shows a characteristic that changes in a bow shape, being highest at the center in the main scanning direction and gradually decreasing from the center toward the end. Can not be read accurately.

  Therefore, the illuminance distribution characteristic of the light guide 22 is a characteristic opposite to the characteristic of the reduction optical system 4, that is, a characteristic that is low at the center in the main scanning direction and high at the end, and changes in a bow shape opposite to the characteristic of the reduction optical system. Set as shown. As a result, the characteristics of the reduction optical system 4 and the characteristics of the light guide 22 are offset on the light receiving surface of the reading sensor 3 where the characteristics of the reduction optical system 4 and the characteristics of the light guide 22 are superimposed. As shown in (B), the illuminance at the reading sensor 3 is made uniform.

  Here, the error in the output value caused by the difference in illuminance on the light receiving surface of the reading sensor 3 can be corrected by signal processing (shading correction), but the illuminance on the light receiving surface of the reading sensor 3 as described above. It is possible to realize highly accurate reading by making the signal uniform. Moreover, since it is not necessary to cut unnecessary light with the slit 12 of the reduction optical system 4, the light quantity of the light source 21 can be used efficiently.

<First Embodiment>
As shown in FIG. 5, in the light guide 22 according to the first embodiment of the present invention, the prisms 41 are arranged at regular intervals. In the prism forming surface 33, the apex 41a of the prism 41 is positioned on the first reference surface 42 constituted by one plane so that the height of the prism 41 changes according to the required illuminance distribution characteristics. In addition, a valley bottom 44 between the prisms 41 is formed on the second reference surface 43 that is arranged so that the distance from the first reference surface 42 changes along the longitudinal direction.

  Here, the height of the prism 41 is determined by the distance between the first reference surface 42 and the second reference surface 43, and the reflection area by the prism 41, that is, the light exit surface 32 is emitted according to the height of the prism 41. Since the amount of emitted light per unit length is determined, the required illuminance distribution characteristic can be obtained by appropriately setting the position of the second reference surface 43 with respect to the first reference surface 42.

  The prism 41 has a triangular or trapezoidal cross section, and is formed in a state extending in a direction orthogonal to the longitudinal direction of the light guide 22. The length in the extending direction is the length of the light guide 22. The same is true for a plurality of prisms arranged in the direction. Further, the distance between the first reference surface 42 and the second reference surface 43 is constant in the direction orthogonal to the longitudinal direction of the light guide 22, and the height of the prism 41 is the height of the light guide 22. It is constant in the extending direction perpendicular to the longitudinal direction.

  The second reference plane 43 is formed of a plurality of planes so that the illuminance distribution characteristic suitable for the reduction optical system 4 can be obtained, and the height of the prism 41 is the center from the end on the light source side and the counter light source side. It is getting smaller gradually toward. In particular, here, the second reference surface 43 is composed of at least two planes having different inclinations in the light source side region and the counter light source side region with the longitudinal center portion interposed therebetween. The plane 43a in the first region, the plane 43b in the second region at the center, and the plane 43c in the third region on the side opposite to the light source.

  In the first region on the light source side, the plane 43a is arranged so that the distance from the first reference surface 42 gradually decreases from the light source side toward the central portion, and therefore the height of the prism 41 is set on the light source side. It gradually decreases from the center toward the center. In the second region at the center, the flat surface 43b is arranged so as to be parallel to the first reference surface 42, so that the height of the prism 41 is constant. In the third region on the side opposite to the light source, the flat surface 43c is arranged so that the distance from the first reference surface 42 gradually increases from the center toward the side opposite to the light source. It gradually increases from the center toward the opposite light source.

  Note that the prism 41 is shown enlarged from the actual dimensions for the convenience of illustration, and is actually a minute one such as a height of 0.06 mm to 0.12 mm and a width of 0.42 mm. A large number of such prisms 41 are formed with an arrangement interval of 0.46 mm, for example.

  Further, when the prism 41 has a triangular cross section, the cross-sectional shapes of the prisms 41 arranged in the longitudinal direction of the light guide 22 are similar. When the prism 41 has a trapezoidal cross section, the width of the apex 41a is constant between the prisms 41 having different heights. Therefore, although strictly not similar, the angle of the inclined surface is constant. It can be said that the relationship is similar.

  Next, as shown in FIG. 6, a mold 51 for producing the light guide 22 will be described. The mold 51 is for molding the prism forming surface 33 of the light guide 22 and is set in an injection molding machine together with a mold for molding a surface other than the prism forming surface 33 of the light guide 22 and is made of acrylic resin or the like. The light guide 22 is manufactured by injection molding of the resin material.

  In this mold 51, recesses 53 corresponding to the prisms 41 are arranged at regular intervals on a mold surface 52 for molding the prism forming surface 33 of the light guide 22, and the mold surface 52 is a single plane. The bottom 53a of the recess 53 corresponding to the top 41a of the prism 41 is positioned on the first reference surface 42 to be configured, and the distance from the first reference surface 42 is changed along the longitudinal direction. A surface 54 corresponding to the valley bottom 44 between the prisms 41 is formed on the second reference plane 43.

  Here, since the prism 41 is formed so that the cross section has a triangular shape or a trapezoidal shape, it is easy to perform die-cutting by extracting a molded product from the mold 51.

  Next, as shown in FIG. 7, a method for manufacturing the mold 51 will be described. Here, first, as shown in FIG. 7A, the mold material 61 is formed into a cross-sectional shape along the second reference plane 43 that defines the position of the valley bottom 44 between the prisms 41 by cutting or the like. The first step is performed.

  Next, as shown in FIG. 7B, the mold material obtained in the first step is used to define the feed direction (Y direction) of the cutting tool 62 and the position of the top 41a of the prism 41. After being arranged so as to be parallel to the reference surface 42, the cutting tool 62 is moved from the reference position in the cutting direction (X direction) by a certain distance LX in the cutting direction (X direction), that is, the concave portion 53 corresponding to the prism 41. A second step of forming the recess 53 by repeating the operation of moving forward in the depth direction and the operation of moving the cutting tool 62 in the feed direction (Y direction) at a constant pitch LY corresponding to the arrangement interval of the prisms 41. Is implemented. When a cutting tool 62 smaller than the prism 41 is used, one of the prisms 41 is moved and processed in the XY direction, and this is used as a unit, and the prism processing is repeated after moving at an equal pitch in the feed direction (Y direction). Thus, the recess 53 may be formed.

  Accordingly, the concave portions 53 for forming the prisms 41 are formed at regular intervals on the mold surface 52 for forming the prism forming surface 33 of the light guide 22, and the bottom 53 a of the concave portion 53 that becomes the top 41 a of the prism 41 is the first. Are arranged on the reference plane 42.

  It should be noted that a mold matching surface or the like is preferably formed on the mold block 61 in advance. The mold block 61 may be made of a low-hardness material, such as brass, which is easy to cut in order to increase processing accuracy, and brass may be plated with copper. In addition, a high hardness super steel material such as an SKD material or high-speed steel may be used for a mold for molding a surface other than the prism forming surface 33 of the light guide 22.

  Here, the movement control of the cutting tool 62 at the time of sequentially cutting the concave portion 53 may be performed only in the X direction (cutting direction) and the Y direction (feed direction) orthogonal to each other, particularly from the reference positions in the X direction and the Y direction. Since the movement control is performed only in one direction, the movement amount in the X direction and the Y direction is constant, and the constant operation is repeated regardless of the depth of the recess 53, so that the processing accuracy is improved and the prism 41 is formed. The recessed part 53 can be shape | molded accurately.

  In the first step shown in FIG. 7A, the second reference surface 43 is formed into three planes 43a, 43b, and 43c by cutting or the like along the second reference surface 43. Therefore, the processing accuracy is improved, and the surface 54 of the mold surface 52 that forms the valley bottom 44 between the prisms 41 can be accurately formed.

  Thus, since the mold surface 52 for molding the prism forming surface 33 of the light guide 22 can be accurately formed, the molding accuracy of the prism forming surface 33 of the light guide 22 is improved, and in particular, the light guide. Since the height of the prism 41 having a great influence on the illuminance distribution characteristic of 22 can be managed with high accuracy, an accurate illuminance distribution characteristic can be obtained.

  Next, the illuminance distribution on the document surface is compared between the light guide 22 according to the first embodiment and the light guides 71 and 81 shown in FIGS. In the light guide 71 shown in FIG. 8A, a first reference surface 73 that defines the position of the top portion 72a of the prism 72, and a second reference surface 75 that defines the position of the valley bottom portion 74 between the prisms 72, The first reference surface 73 and the second reference surface 75 are parallel to each other, and the height of the prism 72 is constant over the entire length. In the light guide 81 shown in FIG. 8B, a first reference surface 83 that defines the position of the top portion 82 a of the prism 82, and a second reference surface 85 that defines the position of the valley bottom portion 84 between the prisms 82. Are configured as one plane, and the distance between the first reference surface 83 and the second reference surface 85, that is, the height of the prism 82 is gradually increased from the light source side toward the counter light source side. .

  As shown in FIG. 9, since the light guide 71 shown in FIG. 8A attenuates due to light absorption, the illuminance on the document surface shows a characteristic that gradually decreases from the light source side toward the non-light source side. In the light guide shown in FIG. 8B, the prism area per unit length gradually increases from the light source side to the counter light source side, so that there is no influence of attenuation due to light absorption, and the illuminance on the document surface is The characteristic is that the illuminance is substantially uniform over the entire main scanning direction (longitudinal direction of the light guide). This is an ideal form in the case of a contact type optical system.

  On the other hand, in the light guide 22 according to the first embodiment of the present invention, the height of the prism 41, that is, the prism area per unit length, gradually increases from the end on the light source side and the opposite light source side toward the center. Therefore, the characteristics of the reduction optical system based on the cosine fourth law are canceled and uniform as shown in FIG. Illuminance distribution can be obtained.

<Second Embodiment>
As shown in FIG. 10, in the light guide 91 according to the second embodiment of the present invention, the first reference surface 93 that defines the position of the top portion 92a of the prism 92 is similar to the first embodiment. The second reference plane 95 that defines the position of the valley bottom portion 94 between the prisms 92 has a substantially arcuate shape so that the illuminance distribution characteristic suitable for the reduction optical system 4 can be obtained. The prism 92 is configured by a curved surface, and the height of the prism 92 is gradually reduced from the end on the light source side and the opposite light source side toward the center. Other configurations are the same as those of the first embodiment.

  Here, as shown in FIG. 5, in the light guide 22 according to the first embodiment, the intersection line of the first to third three planes 43 a, 43 b, and 43 c constituting the second reference plane 43 is obtained. In correspondence with the position, as shown in FIG. 11, an inflection point at which the change rate of the illuminance (gradient in the figure) changes greatly appears.

  On the other hand, in the light guide 91 according to the second embodiment, the inflection point of the illuminance distribution as in the case of the light guide 22 according to the first embodiment does not appear. For this reason, the illuminance distribution in the reading sensor 3 can be made more uniform due to the reverse characteristic that cancels out the optical characteristic of the reduction optical system in which the illuminance changes in a curve based on the cosine fourth law. can do.

  Note that, in the light guide 91 according to the second embodiment, the position of the valley bottom portion 94 between the prisms 92 is defined at the time of manufacturing the mold for forming the prism forming surface 33 as in the example of FIG. When forming a cross-sectional shape along the second reference surface 95, it is necessary to finish the curved surface corresponding to the second reference surface 95 composed of a curved surface, molding of this curved surface is likely to cause processing errors, Ensuring accuracy is troublesome, and the light guide 22 according to the first embodiment is more advantageous in terms of mold fabrication.

  By the way, as shown in FIG. 3, the correction controller 18 performs a process of correcting the light amount of the light source 21 so that the output signal of the light receiving element of the reading sensor 3 is always constant. Control so that the maximum value of the output signal becomes constant, so-called peak hold control is performed. In this peak hold control, if the output signal of the light receiving element located at the center of the main scanning direction (light receiving element arrangement direction) in the reading sensor 3 is set to always show the maximum value, It is only necessary to monitor the output signal of the light receiving element located at the center, and control becomes easy.

  Therefore, as shown in FIG. 12, the illuminance characteristics of the light guide 22 are compared with the characteristics (indicated by B in the figure) opposite to the characteristics of the reducing optical system 4 (indicated by A in the figure). It is set to a characteristic (indicated by C in the figure) corrected so that the illuminance increases at the center of the direction.

  As shown in FIG. 4, the transmission characteristic of the reduction optical system 4 is substantially arcuate, which is high at the center in the main scanning direction, low at the end, and convex toward the high illuminance side based on the cosine fourth law. A characteristic that changes so as to draw a curved curve is shown, and the illuminance characteristic of the light guide 22 is opposite to that of the reduction optical system, that is, a curved line that is curved in a substantially arcuate shape that protrudes toward the low illuminance side. If the characteristics change in this way, the light receiving surface of the reading sensor 3 on which the characteristics of the reduction optical system 4 and the illuminance characteristics of the light guide 22 are superimposed has a characteristic in which the illuminance is uniform in the main scanning direction (D in the figure). Show).

  On the other hand, as described above, the illuminance characteristic of the light guide 22 is corrected so as to increase the illuminance at the center in the main scanning direction with respect to the characteristic opposite to the characteristic of the reduction optical system 4. When set to (indicated by C in the figure), an illuminance characteristic (indicated by E in the figure) at which the illuminance becomes maximum at the center in the main scanning direction can be obtained on the light receiving surface of the reading sensor 3. Therefore, by monitoring only the output signal of the light receiving element located at the center in the main scanning direction in the reading sensor 3, it is possible to perform peak hold control that keeps the maximum value of the output signal of the light receiving element constant. Easy to control.

  In the above example, the scanning is performed in the sub-scanning direction by transporting the document. However, the illumination device and the mirror are moved in the sub-scanning direction with respect to the document placed on the document glass. Thus, the scanning in the sub-scanning direction may be performed.

  Although not particularly mentioned in each of the above examples, the height of the light guide prism may be set in consideration of the attenuation due to light absorption.

  The light guide according to the present invention, the illuminating device and the document reading device including the light guide, the light guide manufacturing die, and the manufacturing method thereof cause problems of uneven illuminance and insufficient irradiation width in the sub-scanning direction. In order to allow the light emitted from the light source to enter from the light incident surface on one end side in the longitudinal direction and to exit from the light exit surface extending in the longitudinal direction. A light guide provided with a prism forming surface in which a plurality of protruding prisms are arranged in the longitudinal direction of the light guide so as to face the emission surface, an illuminating device including the prism, a document reading device, and a light guide It is useful as a body manufacturing mold and its manufacturing method.

DESCRIPTION OF SYMBOLS 1 Document reading device 2 Illumination device 3 Reading sensor 4 Reduction optical system 11 Mirror 12 Slit 13 Lens 21 Light source 22/91 Light guide 31 Light incident surface 32 Light output surface 33 Prism formation surface 41/92 Prism, 41a / 92a Top part 42・ 93 First reference surface 43, 95 Second reference surface 44, 94 Valley bottom 51 Mold 52 Mold surface 53 Recess, 53a Bottom 54 Surface 61 Mold material 62 Cutting tool A Document

Claims (9)

In order to make the light emitted from the light source enter from the light incident surface on one end side in the longitudinal direction and exit from the light emitting surface extending in the longitudinal direction, a plurality of projecting prisms face the light emitting surface in the longitudinal direction. A light guide having prism forming surfaces formed side by side,
The prisms are arranged at regular intervals, and the prism forming surface is on a first reference surface configured by one plane so that the height of the prism changes according to required illumination distribution characteristics. And the valley bottom between the prisms is positioned on a second reference plane that is arranged so that the distance from the first reference plane changes along the longitudinal direction. Formed,
The second reference surface is formed by a curved surface that is curved in a substantially arcuate shape, and the height of the prism is gradually reduced from the end on the light source side and the opposite light source side toward the center portion. A light guide. In order to make the light emitted from the light source enter from the light incident surface on one end side in the longitudinal direction and exit from the light emitting surface extending in the longitudinal direction, a plurality of projecting prisms face the light emitting surface in the longitudinal direction. A light guide having prism forming surfaces formed side by side,
The prisms are arranged at regular intervals, and the prism forming surface is on a first reference surface configured by one plane so that the height of the prism changes according to required illumination distribution characteristics. And the valley bottom between the prisms is positioned on a second reference plane that is arranged so that the distance from the first reference plane changes along the longitudinal direction. Formed,
The light guide according to claim 1, wherein the prism is formed so that a cross section has a triangular shape or a trapezoidal shape. An illumination device comprising a light source, a light guide that guides light emitted from the light source to a reading surface of a document, and a housing that integrally supports the light source and the light guide,
The said light guide is a light guide of any one of Claim 1 thru | or 2 , The illuminating device characterized by the above-mentioned.   The illumination apparatus according to claim 3, comprising: a reading sensor that receives reflected light from a document and outputs an image signal; and a reduction optical system that guides the reflected light from the document to the reading sensor. Document reading device. In the position of the reading sensor where the characteristics of the reduction optical system and the characteristics of the light guide are superimposed, the light guide has the reduction optical system so that the illuminance is highest at the center in the main scanning direction. Is set to a characteristic that the illuminance increases at the center in the main scanning direction,
Only the output signal of the light receiving element located at the center in the main scanning direction of the reading sensor is monitored, and peak hold control is performed to keep the maximum value of the output signal of the reading sensor constant. The document reading device according to claim 4. In order to make the light emitted from the light source enter from the light incident surface on one end side in the longitudinal direction and exit from the light emitting surface extending in the longitudinal direction, a plurality of projecting prisms face the light emitting surface in the longitudinal direction. A mold for manufacturing a light guide for manufacturing a light guide having prism-formed surfaces formed side by side,
Concave portions corresponding to the prisms are arranged at regular intervals on a mold surface that molds the prism forming surface of the light guide, and the mold surface has an illuminance distribution characteristic required for the light guide. Accordingly, the bottom of the concave portion corresponding to the top of the prism is positioned on the first reference plane constituted by one plane so that the depth of the concave portion corresponding to the height of the prism changes. And it is formed so that the surface corresponding to the bottom of the valley between the prisms is located on the second reference plane arranged so that the interval with the first reference plane changes along the longitudinal direction,
The second reference surface is formed by a curved surface that is curved in a substantially arcuate shape, and the height of the prism is gradually reduced from the end on the light source side and the opposite light source side toward the center portion. A mold for manufacturing a light guide. In order to make the light emitted from the light source enter from the light incident surface on one end side in the longitudinal direction and exit from the light emitting surface extending in the longitudinal direction, a plurality of projecting prisms face the light emitting surface in the longitudinal direction. A mold for manufacturing a light guide for manufacturing a light guide having prism-formed surfaces formed side by side,
Concave portions corresponding to the prisms are arranged at regular intervals on a mold surface that molds the prism forming surface of the light guide, and the mold surface has an illuminance distribution characteristic required for the light guide. Accordingly, the bottom of the concave portion corresponding to the top of the prism is positioned on the first reference plane constituted by one plane so that the depth of the concave portion corresponding to the height of the prism changes. And it is formed so that the surface corresponding to the bottom of the valley between the prisms is located on the second reference plane arranged so that the interval with the first reference plane changes along the longitudinal direction,
A mold for manufacturing a light guide, wherein a cross section of the prism is formed in a triangular shape or a trapezoidal shape. In order to make the light emitted from the light source enter from the light incident surface on one end side in the longitudinal direction and exit from the light emitting surface extending in the longitudinal direction, a plurality of projecting prisms face the light emitting surface in the longitudinal direction. A method of manufacturing a light guide manufacturing mold for manufacturing a light guide having prism-formed surfaces formed side by side,
In the mold, concave portions corresponding to the prisms are arranged at regular intervals on a mold surface that molds the prism forming surface of the light guide, and the mold surface is required for the light guide. The depth of the concave portion corresponding to the height of the prism changes according to the illuminance distribution characteristic, and the concave portion corresponding to the top portion of the prism is formed on the first reference plane constituted by one plane. A surface corresponding to the bottom of the valley between the prisms is positioned on a second reference plane that is positioned such that the bottom is positioned and the distance from the first reference plane varies along the longitudinal direction. Formed,
A first step of forming a mold material in a cross-sectional shape along the second reference plane;
The mold material obtained in the first step is arranged so that the feed direction of the cutting tool and the first reference surface are parallel, and the cutting tool is fixed from the reference position in the cutting direction. A second step of forming the recess by repeating the operation of moving forward in the cutting direction by a distance and the operation of moving the cutting tool in the feed direction at a constant pitch corresponding to the arrangement interval of the prisms. ,
The second reference surface is formed by a curved surface that is curved in a substantially arcuate shape, and the height of the prism is gradually reduced from the end on the light source side and the opposite light source side toward the center portion. A method for manufacturing a mold for manufacturing a light guide. In order to make the light emitted from the light source enter from the light incident surface on one end side in the longitudinal direction and exit from the light emitting surface extending in the longitudinal direction, a plurality of projecting prisms face the light emitting surface in the longitudinal direction. A method of manufacturing a light guide manufacturing mold for manufacturing a light guide having prism-formed surfaces formed side by side,
In the mold, concave portions corresponding to the prisms are arranged at regular intervals on a mold surface that molds the prism forming surface of the light guide, and the mold surface is required for the light guide. The depth of the concave portion corresponding to the height of the prism changes according to the illuminance distribution characteristic, and the concave portion corresponding to the top portion of the prism is formed on the first reference plane constituted by one plane. A surface corresponding to the bottom of the valley between the prisms is positioned on a second reference plane that is positioned such that the bottom is positioned and the distance from the first reference plane varies along the longitudinal direction. Formed,
A first step of forming a mold material in a cross-sectional shape along the second reference plane;
The mold material obtained in the first step is arranged so that the feed direction of the cutting tool and the first reference surface are parallel, and the cutting tool is fixed from the reference position in the cutting direction. A second step of forming the recess by repeating the operation of moving forward in the cutting direction by a distance and the operation of moving the cutting tool in the feed direction at a constant pitch corresponding to the arrangement interval of the prisms. ,
A method for producing a mold for producing a light guide, wherein the prism has a cross-section formed in a triangular shape or a trapezoidal shape.

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