JP2015023560A - Image sensor unit and image reading device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To illuminate a document surface over a range of focal depth of a rod lens array with illuminance which is stabilized and sufficient at all the time, in order to sharply form a document image on a light-receiving sensor in an image sensor unit or an image reading device.SOLUTION: An image sensor unit 14 comprises an illumination device 19 for illuminating a document surface, a light-receiving sensor 21, and a rod lens array 20 for forming an image of reflection light from the document surface onto the light-receiving sensor. An illumination axis 37 of illumination light 36 from the illumination device passes between a position A on a top face of platen glass 13 and a deepest point position B of focal depth furthest away from the rod lens array along an optical axis 30c of the rod lens array within a range of document-side focal depth. Over a full range from the position A to the position B, illuminance of illumination light is set within a predetermined range with respect to illuminance at an intersection position C between the illumination axis and the optical axis of the rod lens array.

Description

  The present invention relates to an image sensor unit used in an image reading apparatus such as an image scanner and other various optical devices, and an image reading apparatus including the image sensor unit.

  Conventionally, in image reading apparatuses such as facsimiles, copiers, image scanners, printers, and other various optical devices, the same-magnification imaging optical system is used to optically read an image of a document and convert it into an electrical signal. The contact image sensor (CIS) is widely used. The CIS includes a rod lens array in which a large number of cylindrical rod lenses are arranged between two substrates and arranged in one or more rows with their central axes parallel to each other (see, for example, Patent Document 1). ).

  The rod lens is designed to have a refractive index distribution in which the refractive index continuously decreases from the central axis toward the outer periphery. Initially, rod lenses are mainly glass lenses manufactured by spinning a rod-shaped glass material and imparting a refractive index distribution by ion exchange treatment or heat exchange of cations (for example, Patent Document 2). See).

  At present, many plastic rod lenses that can precisely control the refractive index distribution at a relatively low cost are employed (see, for example, Patent Document 3).

  The equal-magnification optical system rod lens has a feature that the focal depth is smaller than that of the reduction optical system lens. For this reason, when a transparent document such as a photographic film is placed slightly above the upper surface of the platen glass by guide means or the like, the focus may be blurred. In view of this, an image reading unit having two rows of lens arrays with different focal positions and two rows of image reading element arrays corresponding to them is proposed for reflective and transparent documents such as ordinary printed matter ( For example, see Patent Document 4).

  Furthermore, an image sensor unit is known in which two illumination devices are arranged opposite to each other on both sides of a rod lens array in order to suppress fluctuations in the amount of irradiation light on the document surface due to unevenness or floating of the document surface (for example, patents). (Ref. 4). The image sensor unit has a focal point on the document array side of the lens array, the intersection of the optical axis of one illumination device and the optical axis of the lens array is on the far side, and the optical axis of the other illumination device and the optical axis of the lens array. Are arranged at a distance of a / 2 or less with respect to the effective depth of field a of the lens array, respectively, and within the range of the effective depth of field a along the optical axis of the lens array. The light quantity fluctuation of the illuminating device is set to be within 10% to suppress the fluctuation of the high irradiation light quantity and the read light quantity.

JP 2012-244344 A Japanese Patent Laid-Open No. 10-139472 JP 2012-78750 A JP 2004-126284 A Table 2005-126284

  Basically, there is a strong demand for miniaturization of the optical device, and similarly, CIS is also required to be miniaturized by shortening the distance between a subject such as a document and an image, that is, the imaging distance. On the other hand, in CIS, it is necessary to set the focal depth of the rod lens as deep as possible so that a clear image can be read even if the distance between the original surface and the rod lens varies somewhat due to the floating of the original.

  As in the image reading unit described in Patent Document 4, when two lens arrays and image reading element arrays each having different focal positions are incorporated, first, the entire apparatus becomes larger and more complicated, and the number of parts increases. High price. In addition, since the lens array in any row remains small in depth of focus and does not change at all, it cannot cope with fluctuations in the floating amount of the document surface due to document folding or the like.

FIG. 7 schematically shows the imaging of a conventional rod lens in an erecting equal-magnification imaging system. In the figure, a rod lens 1 is a cylindrical lens having a constant radius r ₀ and a lens length Z ₀ , and has an entrance surface 2 and an exit surface 3 that are flatly polished at its entrance end and exit end. The refractive index of the rod lens 1 continuously decreases in the radial direction from the refractive index N1 at the central axis. The light emitted from the point image P 0 on the document surface 4 is incident from the incident surface 2 of the rod lens 1, proceeds in a meandering manner in the optical axis direction at a constant period, and is emitted from the emission surface 3. Thus, a point image I0 is formed on the light receiving surface 5 of the light receiving element. Here, the distance between the point image P 0 and the incident surface 2, that is, the working distance L 0 is equal to the distance between the point image I 0 and the exit surface 3.

The depth of focus of the rod lens 1 is inversely proportional to the numerical aperture, the numerical aperture, the refractive index N1, the refractive index distribution constant in the center, and is proportional to the lens radius r _0. Accordingly, when the refractive index N1 and a refractive index distribution constant in the center is constant, in order to deepen the focal depth, it is necessary to reduce the lens radius r _0. However, if the lens radius r ₀ is reduced, handling and processing of the rod lens array become difficult, and the brightness of the rod lens 1 rapidly decreases in proportion to the square of the numerical aperture. There is a possibility that the reading performance is lowered.

Moreover, the working distance L0 of the rod lens 1, to the lens length Z ₀ changes to tangent, is inversely proportional to the square of the refractive index N1 and a refractive index distribution constant in the center. Therefore, the refractive index N1 and the lens radius r ₀ of the central constant, reducing the refractive index distribution constant, the lens length Z ₀ is in certain cases, the working distance L0 becomes longer. As a result, the conjugate length of the rod lens 1 (distance between object images = Z ₀ + 2L ₀ ) is increased, and the overall length of the optical system is increased. Therefore, the rod lens array and the image sensor including the rod lens array can be downsized. I can't. Therefore, if the lens length Z ₀ is shortened and the working distance L 0 is not lengthened, the field radius of the rod lens 1 is reduced. Therefore, there is a possibility that periodic uneven light intensity may occur, which is not preferable.

  Accordingly, the inventors of the present application arranged a plurality of columnar rod lenses having a refractive index distribution in which the refractive index continuously decreases from the central axis toward the outer periphery in at least one row with the central axes parallel. In each rod lens, the center refractive index of the incident side end region is equal to the center refractive index of the output side end region along the optical axis direction, and the center refractive index of the intermediate region is the center of both end regions. A rod lens array having a refractive index distribution characteristic higher than the refractive index has been devised. By providing such a refractive index distribution, in the intermediate region of the rod lens, light meanders and travels with a shorter cycle than both end regions, so that the optical path length is substantially increased. Therefore, even if the lens length of the rod lens in the optical axis direction is the same, the depth of focus can be set deeper than that of the conventional rod lens.

  When a rod lens array having a deep focal depth is used in this way, a clear image can be read even if the distance between the document surface and the rod lens varies greatly compared to the prior art due to the floating of the document. On the other hand, if the illuminance of the illumination light on the document surface varies, the amount of reflected light from the document surface varies, which may easily cause a density variation in the output image. In order to suppress or eliminate this density fluctuation, the illuminance of the illumination light on the document surface must always be stable and sufficiently large.

  In general, the illuminance of the diffused light decreases as the distance from the light source increases. Therefore, it is preferable to irradiate the illumination light from a position as close to the original surface as possible. However, the CIS of the equal-magnification imaging optical system does not have a space for arranging the optical components of the illumination system above the rod lens array. On the other hand, when the illumination light is irradiated from the side of the rod lens array at a shallow angle with respect to the document surface, the illuminance decreases at a larger rate as the distance from the optical axis of the illumination light increases to the periphery. Is required. A high-output light source may cause inconvenience such as that the emitted light is reflected directly or reflected on a surface other than the original surface and enters the rod lens array, or a large amount of heat is generated.

  In the image sensor unit described in Patent Document 5, when a rod lens array having a deep focal depth is used, the intersection of the optical axis of the two illumination devices and the optical axis of the lens array is aligned with the optical axis of the lens array. Are farther apart from each other on the perspective side from the original side focus. For this reason, the combined light amount distribution of both illumination devices becomes sharp at the optical axis position of each illumination device, and the combined light amount may vary greatly within the depth of focus.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a range of focal depth of the rod lens array in order to clearly form a document image on the light receiving sensor using the rod lens array. It is an object of the present invention to provide an image sensor unit and an image reading apparatus capable of always stably illuminating a document surface with sufficient illuminance.

  According to the present invention, an illumination device that illuminates the document surface, a light receiving sensor, and a rod lens array that forms an image of reflected light from the document surface on the light receiving sensor, the optical axis of the illumination light from the illumination device is Passes between the position A of the document surface closest to the rod lens array and the position B of the document surface farthest from the rod lens array in the range of the focal depth on the document side along the optical axis of the rod lens array; In the entire range from position A to position B, the illuminance of the illumination light is within a predetermined range with respect to the illuminance of the illumination light at the intersection C between the optical axis of the illumination light and the optical axis of the rod lens array. A sensor unit is provided.

  By orienting the illumination light in this way, even in an image sensor unit using a rod lens with a deep focal depth, it is necessary and sufficient to read and output a clear and good image over the entire depth of focus range. It is possible to always ensure a stable illuminance. When the optical axis of the illumination light passes between the position A of the nearest original surface along the optical axis of the rod lens array and the position B of the farthest original surface, the optical axis of the illumination light is on the original surface. The case of passing through position A or position B is not included.

  In one embodiment, a portion of the illumination light emitted to the rod lens side with respect to the optical axis of the illumination light is partially shielded by the adjacent rod lens array, and an illumination range of the illumination light is The illumination light is oriented so as not to exceed the position A from the irradiation direction. As a result, the optical axis of the illumination light can be made to stand at a larger angle with respect to the document surface, so that the illumination light can be irradiated from a higher angle toward the document surface, and the emission light emission range can be narrowed down more narrowly. Can do. As a result, it is possible to illuminate the document surface with sufficient illuminance required in the entire range of the focal depth while suppressing the output of the illumination device.

  Further, according to the present invention, there is provided a platen glass for placing a document and the above-described image sensor unit of the present invention, and the position A of the document surface in the image sensor unit is defined by the document placement surface of the platen glass. An image reading apparatus is provided. Thereby, it is possible to always read and output a document image stably and clearly.

1 is a schematic perspective view of an image scanner including an image sensor unit of the present invention. It is a disassembled perspective view which shows typically the structure of the image sensor unit of this invention. (A) is a longitudinal sectional view of the lighting device, and (B) is a sectional view of the light guide rod taken along line III-III. It is a partially broken perspective view which shows a rod lens array typically. It is a figure explaining the image formation of the rod lens of FIG. It is a schematic diagram explaining arrangement | positioning of the illuminating device in the image sensor unit of this invention, and the orientation state of illumination light. It is a figure explaining the image formation of the conventional rod lens.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic perspective view of an image scanner equipped with an image sensor unit according to a preferred embodiment of the present invention. An image scanner 10 according to the present embodiment is a flat bed type image reading apparatus, and includes a substantially rectangular box-shaped main body 11 and a platen cover 12 attached to the main body at one end thereof by a hinge (not shown) so as to be opened and closed. Is provided.

  The main body 11 includes a platen glass 13 made of a large rectangular transparent glass plate fixed to the upper surface thereof, and a contact image sensor unit 14 according to the present invention. On the upper surface of the platen glass 13, a document to be read is placed with the document surface facing downward. When the platen cover 12 is closed, the original surface is brought into close contact with the upper surface of the platen glass by the pressing member 12a provided on the inner surface thereof.

  The image sensor unit 14 is disposed immediately below the platen glass 13 and is held by a holding member 15 with its upper surface in close contact with the lower surface of the platen glass. At the time of reading the original, the image sensor unit is driven by the drive motor 16 via the wire 17 or the like, and moves along the slide shaft 18 in the original reading direction, that is, the sub-scanning direction.

  FIG. 2 schematically shows a basic configuration of the image sensor unit 14 of the present embodiment. The image sensor unit 14 includes a lighting device 19, a rod lens array 20, and a light receiving sensor 21. Further, the image sensor unit 14 has a housing (not shown) for mounting and holding the illumination device, the rod lens array, and the light receiving sensor at predetermined positions.

  The light receiving sensor 21 has a large number of photoelectric conversion elements 23 mounted in a line on the sensor substrate 22. For the photoelectric conversion element 23, for example, a solid-state imaging element such as a CMOS image sensor or a CCD image sensor is used. The rod lens array 20 is disposed so that the emission surface at the lower end thereof is aligned with the photoelectric conversion element. The rod lens array 20 can also be attached to the light receiving sensor 21 integrally. The illumination light emitted from the illuminating device 19 is reflected by the original surface of the original 24 and is incident on the incident surface at the upper end of the rod lens array 20, and is emitted from the emission surface and forms an image on the photoelectric conversion element 23.

  As shown in FIGS. 3A and 3B, the illumination device 19 includes a light guide rod 25, a frame 26 that holds the light guide rod, and a light emitting element 27. The light guide rod 25 has a length corresponding to the reading line width of the image sensor unit 14 and is a transparent material having high translucency such as glass, acrylic resin, epoxy resin, etc., and is uniform over the entire length. The cross-sectional shape is formed. The light guide rod 25 of this embodiment has a generally fan-shaped cross section as shown in FIG. 3B, and has an emission surface 25a on the top surface and a light scattering surface 25b on the bottom surface corresponding to the short bottom of the opposite trapezoidal cross section. . The exit surface 25a is processed into a lens surface that is a convex curved surface. The light scattering surface 25b is processed to be uneven so as to diffusely reflect the light introduced into the light guide rod.

  The frame 26 includes a holder portion 26a having a groove having a cross-sectional shape that substantially corresponds to the inverted trapezoidal portion of the light guide rod 25, and the end portions of the light guide rod 25 are provided at both ends 26b and 26c, respectively. A recess is provided at the opposite position to hold the A light emitting element 27 is attached to one end portion 26b toward the other end portion 26c, and a reflecting surface 28 is provided in the recess of the other end portion 26c. The light guide rod 25 is mounted on the frame 26 so that the inverted trapezoidal portion of the cross section is accommodated in the groove of the holder portion 26a and the emission surface 25a is exposed. Each end portion of the light guide rod 25 has one end surface 25c abutting against the reflecting surface 28 in the recess of the frame end portion 26c, and the other end surface 25d is the exit surface of the light emitting element 27 in the frame end portion 26b. Place it close to.

  For example, an LED is used for the light emitting element 27. When the image scanner 10 outputs only a monochrome image, a white LED is used, and when a color image is output, red, green, and blue LEDs are used corresponding to the three primary colors of RGB. Instead of these three color LEDs, a color image can be read by combining a white LED and red, green, and blue optical color filters.

  In FIG. 3, only one LED is drawn as the light emitting element 27. In another embodiment, a plurality of LEDs can be arranged at the end 26b of the frame 26. Further, instead of the reflecting surface 28, an LED can be arranged at the end 26c on the opposite side of the frame. As a matter of course, various known light-emitting elements such as organic or inorganic EL (electric luminescence) and LD (laser diode) can be adopted as the light-emitting element 27 in addition to the LED.

  In the illuminating device 19 of FIG. 3, the light emitted from the light emitting element 27 is introduced into the light guide rod 25 from the end surface 25d, and is guided in the longitudinal direction while being reflected by the inner surface. The light reaching the opposite end face 25c is reflected by the reflecting surface 28, and is similarly guided in the light guide rod 25 in the reverse direction in the longitudinal direction. When the frame 26 is white, light leaking from the light guide rod 25 to the outside in the groove and both end portions 26b and 26c of the holder portion 26a can be reflected and returned to the inside of the light guide rod. Loss is reduced.

  The light reflected by the light scattering surface 25b is emitted from the emission surface to the outside when the incident angle on the emission surface 25a is smaller than a predetermined critical angle. When the incident angle to the emission surface 25a is equal to or greater than the predetermined critical angle, the light is reflected by the emission surface and returns into the light guide rod 25. By forming the unevenness of the light scattering surface 25b at an appropriate pitch, illumination light with a uniform light amount is irradiated from the exit surface 25a over the entire length of the light guide rod 25.

  FIG. 4 schematically shows a configuration of a rod lens array 20 for line scanning used in the image sensor unit 14. The rod lens array 20 includes a large number of rod lenses 30 arranged between two substrates 31 and 32 and spacers 33 and 34 so that the central axes of the rod lenses are parallel to each other. One rod lens array arranged along the scanning direction is provided. The gaps between the rod lens 30 and the substrates 31, 32 and the spacers 33, 34 are filled with, for example, a thermosetting black silicon resin 35, thereby bonding and fixing the rod lens.

  In the present embodiment, the adjacent rod lenses 30 are arranged so as to be in close contact with each other, but in another example, they can be arranged with a certain gap. The rod lens rows can be arranged in two or more rows.

  Further, the two substrates 31 and 32 can be extended by a predetermined length along the axial direction of the rod lens 30 toward the emission side. The lengths of the extended portions 31 a and 32 a of the substrates 31 and 32 are set according to the working distance of the rod lens 30, for example. 2, when the rod lens array 20 is positioned with respect to the light receiving sensor 21 in FIG. 2, the lower ends of the extended portions 31 a and 32 a of the substrate are brought into contact with the upper surface of the sensor substrate 22. It can be matched to the conversion element 23. Further, by providing a recess on the upper surface of the sensor substrate 22 and inserting the lower ends of the extension portions 31a and 32a into the recess, the positioning accuracy can be increased not only in the height direction but also in the plane direction.

  The rod lens 30 is a cylindrical lens having a uniform circular cross section with a radius r1 along the central axis, that is, the optical axis, and having both end surfaces orthogonal to the optical axis polished flat. Each rod lens 30 has a refractive index distribution in which the refractive index continuously decreases from the central axis toward the outer periphery. Furthermore, the rod lens 30 of this embodiment has a refractive index distribution characteristic in which the refractive index continuously changes along the optical axis direction.

  Further, the rod lens 30 can change the size and shape of the circular cross section along the axial direction. Furthermore, the cross-sectional shape of the rod lens 30 can be various shapes other than a circle such as a polygon or a cross.

  As shown in FIG. 5, in the rod lens 30, the refractive index of the central axis, that is, the central refractive index is equal to N1 between the end region X1 on the incident side and the end region X2 on the outgoing side along the optical axis direction. It has the same refractive index distribution Q1. On the other hand, the intermediate region X3 between them is designed so that the central refractive index N2 is larger than N1 and has a refractive index distribution Q2 different from the incident side and outgoing side end regions X1 and X2. Thereby, the light reflected from the point image P1 on the document surface 24a advances meandering from the incident surface 30a of the rod lens 30 through the incident side end region X1 according to the refractive index distribution Q1, and enters the intermediate region X3. The light travels meandering according to the refractive index distribution Q2. Further, the laser beam advances in a meandering manner in accordance with the first refractive index distribution Q 1 and exits from the emission surface 30 b to form a point image I 1 on the light receiving surface 23 a of the photoelectric conversion element 23.

  The refractive index distribution in the optical axis direction can be set so that the refractive index gradually changes between the incident side and outgoing side end regions X1, X2 and the intermediate region X3. In another embodiment, the refractive index can be set to change steeply between the incident and exit side end regions X1, X2 and the intermediate region X3. In the intermediate region X3, the refractive index can be set so as to continuously change along the optical axis direction. In this case, the maximum center refractive index N2 is not necessarily the center position in the optical axis direction of the rod lens 30.

  By providing the refractive index distribution in the optical axis direction as described above, the period of light meandering the incident side end region X1 and the emission side end region X2 in the optical axis direction is equal. On the other hand, the period of light meandering the intermediate region X3 in the optical axis direction is shorter than that of the incident side and emission side end regions X1 and X2. Here, the distance between the point image P1 and the incident surface 30a, that is, the working distance L1, is equal to the distance between the point image I1 and the exit surface 25b.

This is compared with the conventional rod lens 1 of FIG. It is assumed that the rod lenses 1 and 30 have the same lens radii r0 and r1 and the same focal depth, that is, the working distances L0 and L1 are equal. Since the length of the intermediate region X3 of the rod lens 30 of this embodiment is shorter than the corresponding intermediate region of the conventional rod lens 1, the lens length Z1 is correspondingly larger than the lens length Z0 of the conventional rod lens 1. Is also shortened. As a result, since the conjugate length (= Z ₁ + 2L1) of the rod lens 30 is shorter than that of the conventional rod lens 1 while maintaining the same depth of focus, the rod lens array 20 and the image sensor 14 are downsized. be able to. Further, since the lens radii are the same, there is no possibility that the image reading performance is deteriorated.

  The rod lens 30 can be manufactured using conventional techniques. For example, in the case of manufacturing with germanium-doped quartz glass material, different refractive index distributions can be given in the optical axis direction by changing the intensity of ultraviolet light irradiated to give the refractive index distribution along the optical axis direction. It is known. In the case of a plastic material, it is known that the refractive index can be changed in the optical axis direction by adjusting the condensing region of the laser beam irradiated to the polymer material.

  FIG. 6 shows the arrangement of the illumination device 19 in the image sensor unit 14 and the orientation state of the illumination light applied to the document surface 24a. The rod lens array 20 is arranged such that the optical axis 30 c of the rod lens 30 is orthogonal to the upper surface of the platen glass 13 and the focal position is set slightly above the upper surface of the platen glass 13.

  By using the rod lens array 20 including the rod lenses 30 of FIG. 5, a depth of focus ΔL that is larger than the conventional one can be set above the upper surface of the platen glass 13. The document 24 is read between the position A where the optical axis and the upper surface of the platen glass 13 intersect along the optical axis 30c of the rod lens 30 and the position B at the deepest point of the focal depth ΔL from the upper surface of the platen glass 13. Thus, a clear output image can be obtained.

  Further, the rod lens array has the optical axis 30c of the rod lens orthogonal to the upper surface of the sensor substrate 22 of the light receiving sensor 21 and is aligned with the photoelectric conversion element 23, and the exit surface 20b is a working distance L1 from the photoelectric conversion element. It arrange | positions so that it may become. Since the working distance L1 of the rod lens 30 is longer than before, a larger space than before is secured above the sensor substrate 22.

  In this embodiment, the illuminating device 19 is arranged on one side (right side in the figure) of the rod lens array 20 in the sub-scanning direction with the emission surface 25a of the light guide rod 25 facing the position A on the upper surface of the platen glass 13. The By using the large space secured above the sensor substrate 22, the illuminating device 19 makes the optical axis of the illuminating light 36 irradiated from the emission surface 25 a, that is, the illuminating axis 37 a larger angle with respect to the platen glass 13. It becomes possible to stand up. It is also possible to provide the illumination device 19 on the sensor substrate 22.

  The illumination light 36 is oriented so that the illumination axis 37 intersects the optical axis 30c of the rod lens at a position C between the position A and the position B. Here, the position C between the position A and the position B means that the case where the position C matches the position A or the position B is not included. The illumination device 19 is configured so that the illumination light 36 always includes the position A and the position B in the irradiation range, and the desired sufficient illuminance is obtained in the entire range of the focal depth ΔL from the position A to the position B. Determine the setting conditions. This design condition includes, for example, the output and characteristics of the light emitting element 27, the optical performance of the light guide rod 25 and the exit surface 25a, the structure of the illumination device 19, the arrangement of each component, and the like.

  If the illuminance distribution changes abruptly within the range of the focal depth ΔL along the optical axis 30c of the rod lens 30, the original 24 is sufficiently placed on the upper surface of the platen glass 13 even if the original density (reflectance) is uniform. If it is not in close contact, the output obtained by the light receiving sensor 21 changes, and the output image is uneven in the sub-scanning direction. This can be solved by keeping the amount of change in illuminance within a certain range over the entire range of the focal depth ΔL.

  The illumination light 36 is diffuse light, and its illuminance generally has a peak on the illumination axis 37 and attenuates as it moves away from the illumination axis toward the outer edge. For this reason, the illumination axis 36 is not aligned with the position A on the upper surface of the platen glass 13 but with the position of the illumination light 36 according to the position C between the position A and the position B as described above. As a whole, fluctuations in the illuminance distribution can be reduced. In this embodiment, it is preferable that the fluctuation range of the illuminance distribution between the position A and the position B is set to ± 5%, where the illuminance at the position C on the illumination axis 37 is 100%.

  Normally, shading correction of the image reading apparatus is performed by placing a reference white reference plate on the upper surface of the platen glass. Since the white reference plate used as a product that can actually be mass-produced has a reflectance of 90% to 95%, when shading correction is performed with this white reference as a full range, a document with a higher reflectance than that is All the output of the read data is saturated on the white side. After the shading correction is performed with the white reference as a full range, if the ambient temperature of the light source of the illumination light changes and the illuminance increases, a document with the same reflectance as the white reference similarly outputs all of the read data. Saturates on the white side. In order to avoid these inconveniences, an output of 255 × 0.9≈230 gradations is usually obtained with a target of about 90% of the full range with respect to the output of the read data obtained from the white reference. Perform shading correction.

  In the present embodiment, as described above, the illuminance at the position A on the upper surface of the platen glass 13 where the white reference for performing shading correction is arranged is within a range of ± 5% with respect to the illuminance on the illumination axis 37. Assuming that the illuminance at position A is 95% of the minimum value, the output of the read data obtained on the upper surface of the platen glass 13 is 95% of the output at position C on the illumination axis 37. Here, shading correction is performed on the data obtained from the white reference on the upper surface of the platen glass 13 with a target of 90% of the full range, and after reading the actual document at the position A on the upper surface of the platen glass 13, the document is illuminated with the illumination axis. Suppose that it has risen to position C at 37. At this time, the output of the data read from the position C is + 5% different from the data read at the position A. This difference is 230 × 0.05≈12 gradations. When the document read at position C has the same reflectance as the white reference on the upper surface of the platen glass 13, the output is 230 + 12 = 242 gradations and does not saturate on the white side. Further, the 12-tone output difference with respect to the reference output is within an allowable range of output variation required for a general scanner.

  Further, consider a case where the illuminance at position A is 95% of the illuminance at position C and the illuminance at position B is 105% of the maximum value. Similarly, after reading an actual document at position A on the upper surface of the platen glass 13, it is assumed that the document has lifted up to position B at the deepest point of the focal depth. At this time, the output of the data read from the position B has a difference of + 10% from the data read at the position A. This difference is 230 × 0.10 = 23 gradations. When the document read at the position B has the same reflectance as the white reference on the upper surface of the platen glass 13, the output is 230 + 23 = 253 gradations, and in this case, the white side is not saturated.

  In this embodiment, the fluctuation range of the illuminance distribution between the position A and the position B is set to ± 5% of the illuminance at the position C on the illumination axis 37, but the present invention is not limited to this. The illuminance distribution between the position A and the position B is, for example, an illumination axis 37 according to the design specifications and usage conditions of the image scanner 10, the performance and characteristics of the rod lens array 20 and the light receiving sensor 21 constituting the image sensor unit 14, for example. An appropriate range such as 90%, 85% or ± 10% of the above illuminance can be set.

  In general, diffused light attenuates as the illuminance peaks on the illumination axis and moves away from the outer edge side, and greatly decreases at the outer edge portion. As described above, since the illumination light 36 of the present embodiment is also diffused light, it is difficult to secure desired illuminance at the position A and / or position B if the emission range from the emission surface 25a is excessively narrowed. There is. Therefore, it is preferable that the emission range of the illumination light 36 from the emission surface 25a is set so as to include a region somewhat outside the positions A and B.

  At this time, as shown in FIG. 6, the portion 36b of the illumination light 36 closer to the rod lens array 20 than the illumination axis 37 is partially shielded by the side wall of the adjacent rod lens array 20, and the irradiation range is platen. Orientation is performed so that the position A on the upper surface of the glass 13 does not exceed the left side in the drawing, that is, in the direction opposite to the irradiation direction of the illumination light. Thereby, the illumination axis 37 can be arranged to stand at a larger angle with respect to the platen glass 13. As a result, the illumination light 36 can be irradiated from a higher angle toward the document surface 24a, so that the emission range of the illumination light 36 can be narrowed down. Thereby, the illuminating device 19 can illuminate the original surface with sufficient illuminance that is always required stably over the entire depth of focus while suppressing the output of the light emitting element 27 as a light source.

  In another embodiment, the image sensor unit 14 may include two lighting devices 19 having the same configuration. In this case, one illumination device 19 is arranged symmetrically on both sides in the sub-scanning direction with the rod lens array 20 interposed therebetween. Thereby, it is possible to ensure sufficient illuminance necessary for reading and outputting a clear image over the entire range of the focal depth while reducing the size of each lighting device 19 with a low output.

  The image scanner of the above embodiment is a line sensor that reads a document as a one-dimensional image by arranging rod lenses and photoelectric conversion elements in one row, but is not limited to this. The present invention can be similarly applied to a surface sensor in which a plurality of photoelectric conversion elements are arranged to read a document as a two-dimensional image.

  As mentioned above, although this invention was demonstrated in relation to the preferred embodiment, this invention is not limited to the said embodiment, In the technical scope, it can implement with a various change or deformation | transformation. Needless to say. For example, the illuminating device and the light guide rod have been proposed in various structures so far as the illumination device and the light guide rod can irradiate a uniform amount of illumination light along the reading width of the document.

DESCRIPTION OF SYMBOLS 10 Image scanner 11 Main body part 12 Platen cover 14 Image sensor unit 19 Illuminating device 20 Rod lens array 21 Light receiving sensor 22 Sensor substrate 23 Photoelectric conversion element 24a Original surface 25 Light guide rod 25a Outgoing surface 26 Frame 27 Light emitting element 30 Rod lens 30c Optical axes 31, 32 Substrate 33, 34 Spacer 36 Illumination light 37 Illumination axis

Claims (3)

An illumination device for illuminating the document surface;
A light receiving sensor;
A rod lens array that focuses reflected light from the document surface on the light receiving sensor;
The position of the original surface closest to the rod lens array in the range of the focal depth on the original side along the optical axis of the rod lens array, and the rod lens of the illumination light from the illumination device, and the rod lens Passing between the position B of the document surface furthest from the array, and
The illuminance of the illumination light in a whole range from the position A to the position B is predetermined with respect to the illuminance of the illumination light at an intersection position C between the optical axis of the illumination light and the optical axis of the rod lens array. Image sensor unit within range.   The portion of the illumination light emitted to the rod lens side with respect to the optical axis of the illumination light is partially shielded by the adjacent rod lens array, and the illumination light irradiation range is the illumination light irradiation The image sensor unit according to claim 1, wherein the illumination light is oriented so as not to exceed the position A from a direction. An image reading device comprising: a platen glass for placing a document; and the image sensor unit according to claim 1, wherein a position A of the document surface in the image sensor unit is defined by a document placement surface of the platen glass. apparatus.

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