JP2006014081A - Image reader - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of forming a satisfactory image even when an original floats. <P>SOLUTION: This image reader 1 is provided with an illumination unit 3, a line image sensor 6 composed of photoelectric converters, and a lens array 4 being an erect life-size image-formation system for converging reflected light from an original in irradiated light from the illumination unit on the line image sensor 6, wherein the lens array 4 being the erect life-size image-formation system has the depth of focus of 1 mm or more. The illumination unit 3 is used, wherein illumination unevenness within the range of the depth of focus is within ±20% when a range on an optical axis where a modulation degree is ≥10% when a black and white periodical pattern of a spatial frequency 61p (line pair)/mm is subjected to erect life-size image-formation is defined as the range of the depth of focus. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image reading apparatus such as a facsimile, a copying machine, and a scanner apparatus.

  The contact type image sensor incorporating an erecting equal-magnification lens has fewer parts and can be made thinner than the reduction type, so it can be used as an image reading device (image sensor unit) for facsimiles, copiers, hand scanners, etc. It has been.

Patent Document 1 and Patent Document 2 disclose the above-described image reading apparatus, and a schematic configuration will be described based on FIG. 5. From a case 102 in which a light guide body 101 is housed in a housing 100 and a rod lens. The lens array 103 is disposed, the cover glass 104 is provided on the upper portion, the substrate 106 on which the line image sensor (light receiving element) 105 is disposed on the lower portion is attached, and the illumination light emitted from the emission surface of the light guide 101 is converted to the cover glass. By irradiating the document through 104 and detecting the reflected light by the line image sensor 105 through the lens array 103, the document is read.
JP 2001-358906 A US Pat. No. 6,259,082

  In the case of the contact-type image reading apparatus described above, there is a problem that the resolution is lowered due to the floating of the document. That is, when a book or the like is opened and placed on a glass plate (original table), the inter-page portion (throat portion) inevitably floats. Similarly, when the document has wrinkles or creases, the float is generated.

  However, the conventional image reading apparatus is designed so that the focal point of the lens array is positioned on a substantially glass plate (document table), and the irradiation light from the illumination device is approximately a glass plate (document table). Since it is designed to concentrate on the upper side, the amount of irradiation light is uneven at the portion of the document floating, the resolution is lowered, and an unnatural shadow is generated in the read image.

  FIG. 6 is a graph showing the relationship between the aperture angle of the lenses constituting the lens array, the depth of focus, and the amount of transmitted light. The depth of focus is the axial distance from the best image plane (the surface of the document table) to the plane where image blur is allowed. On the other hand, when the aperture angle of the lens is reduced, that is, the divergence angle of the light beam converging on the image plane is reduced, the depth of focus becomes deeper. However, when the aperture angle is reduced, the transmitted light amount is reduced and the light amount is insufficient.

  An object of the present invention is to minimize the deterioration of a read image on the assumption that the above-described problem, that is, the depth of focus and the amount of transmitted light are in a trade-off relationship.

  In order to achieve the above object, there is provided an erecting equal magnification imaging system capable of reading a space slightly apart from the upper surface of the document table (transparent plate) on which an original is placed, and a range read by the erecting equal magnification imaging system. An illumination unit that irradiates uniformly is required.

  For this reason, in the present invention, when an erect life-size image formation is performed with a black-and-white periodic pattern having a spatial frequency of 6 lp (line pair) / mm within a focal depth range in which image blur is allowed in an erect life-size imaging system. Is defined as a range on the optical axis in which the degree of modulation is 10% or more. Here, a 6 lp (line pair) / mm black-and-white periodic pattern is selected as the spatial frequency (a quantity representing the fineness of the periodic structure constituting the image), which is generally used for measuring the modulation degree. It is because it is a scale that is being used.

  The modulation degree is an index representing the depth of modulation. When the maximum value of the modulated light intensity is Imax and the minimum value is Imin, the modulation degree (m) = (Imax−Imin) / (Imax + Imin). Become. In the present invention, the range on the optical axis in which the modulation degree is 10% or more is set as the focal depth range, which is a limit value that can be clearly determined by humans. When the modulation degree is less than 10%, It is because it becomes impossible to judge.

  In the present invention, the erecting equal-magnification imaging system has a depth of focus of 1 mm or more. It is necessary to have a depth of focus of 1 mm or more in order to accurately read an image even if there are wrinkles or folds in the document, and the depth of focus is 1.6 mm or more to read even the throat of a book without any problem. It is preferable.

  Furthermore, it is desirable that there is as little illuminance unevenness as possible in the focal depth range. In the present invention, the illuminance unevenness is set within ± 20%. This is because electrical correction cannot be performed if it exceeds ± 20%.

  The erecting equal-magnification imaging system that can easily exhibit the above characteristics is configured by stacking a plurality of lens plates, and a large number of minute lenses are regularly arranged in a two-dimensional manner at a predetermined pitch on each lens plate. However, the present invention is not limited to this.

  The erecting equal-magnification imaging system is configured, for example, by superimposing two or three lens plates on top and bottom, and the center of the minute lens of the upper lens plate coincides with the center of the minute lens of the lower lens plate. And Further, by setting the single lens opening angle of the lens plate to 4 to 11 °, it is possible to satisfy both the transmitted light amount and the focal depth. Preferably, the opening angle is 4 to 6.8 °.

  In addition, the illumination unit that can easily exhibit the above characteristics includes a rod-shaped light guide that reflects light from a light source on both side surfaces and emits light from the output surface, and collects light reflected by one side surface. Although the position and the condensing position of the light reflected by the other side surface can be considered, it is not limited to this.

  As the rod-shaped light guide, a side shape parallel to the axis of the light guide may be an elliptical curved surface, a parabolic curved surface, or a composite curved surface thereof. In this case, the light guide may be integrally formed, or may be formed by bonding two halves, and an elliptical arc curved surface, a parabolic curved surface, or a composite curved surface thereof serving as a reflecting surface may be formed on each half.

  According to the image reading apparatus of the present invention, an erecting equal-magnification imaging system with a large focal depth is used, and an illumination unit with small illuminance unevenness in the focal depth range is used. Can be read as a simple image.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an image reading apparatus according to the present invention. In the image reading apparatus 1, line illumination devices 3 and 3 are arranged on the left and right sides of a housing 2. A lens array 4 which is a vertical magnification imaging system is arranged, a recess 5 is formed in the lower portion of the housing 2, a substrate 7 to which an image sensor (light receiving element) 6 is fixed is attached to the recess 5, and line illumination is performed. Above the devices 3 and 3 and the lens array 4, a transparent document table 8 on which a document is placed is provided. The image sensor (light receiving element) 6 is provided at a position substantially coincident with the position where the center line of the lens array 4 is lowered.

  Further, a part of the housing 2 below the lens array 4 is narrowed inward, and this portion is used as a ghost cut portion 9.

  The line illumination device 3 houses a rod-shaped light guide 31 made of acrylic resin or the like in a case 30. The light guide 31 has a cross-sectional shape in a direction perpendicular to the length direction, the bottom is a chamfered portion 31a, the left and right side surfaces 31b and 31c are elliptical curved surfaces, parabolic curved surfaces, or a composite curved surface thereof, and the outgoing surface 31d is a flat surface It is said.

  A light emitting element is provided at an end portion (perpendicular to the paper surface) of the light guide 31, and a light scattering pattern that scatters a light beam incident from the light emitting element into the light guide is formed in the chamfer 31 a.

  Further, the light rays that have entered the light guide and scattered by the light scattering pattern are reflected by the inner surfaces of the left and right side surfaces 31b and 31c, and are emitted from the emission surface 31d toward the document on the document table 8. By the way, in the present invention, the shapes and curvatures of the left and right side surfaces 31b and 31c are set so that the reflected lights from the left and right side surfaces 31b and 31c do not coincide with each other on the reading axis of the document and are shifted in the vertical direction. This range of deviation is a range in which uniform illuminance (within ± 20%) can be obtained in the focal depth range of the lens array 4 described later.

On the other hand, the lens array 4 is configured as an erecting equal-magnification lens by overlapping two lens plates 40 and 40 as shown in FIG. In each lens plate 40, a large number of microlenses 41 are regularly arranged in a two-dimensional manner at a predetermined pitch. The lens plate 40 is manufactured, for example, by press-molding a soft UV-effect resin using a transparent mold and hardening it by irradiating ultraviolet rays from the outside (2P molding method).
Further, as a molding method, glass or resin softened by heating may be press-molded or a pre-molded lens may be bonded.

  The operation of the lens array 4 converges the light from the exit surface 31b of the light guide 31 reflected by the document surface to the image sensor (light receiving element) 6 via the lens array 4 as shown in FIG. In this case, since the lens array 4 is formed with a plurality of rows of fine lenses 41 in the sub-scanning direction, the light amount level is not lowered due to the deviation between the lens optical axis and the image sensor 6 as in the prior art.

FIG. 4 is a graph showing the relationship between the depth of focus and the degree of modulation. As is apparent from this graph, the degree of modulation decreases as the depth of focus increases. If the degree of modulation is less than 10%, the image cannot be clearly determined by the human eye, so the degree of modulation needs to be maintained at 10% or more. Therefore, a deeper depth of focus can cope with the floating of the original, but a restriction is also imposed on the depth of focus due to the degree of modulation. In other words, the lens array 4 having a focal depth of 1 mm while maintaining a modulation degree of 10% or more can sufficiently deal with wrinkles and folding of the document, and is 1.6 mm while maintaining a modulation degree of 10% or more. If the lens array 4 has a focal depth, it is possible to cope with the throat lift of the document (book).

Here, as a reference for measuring the degree of modulation, the degree of modulation when a black-and-white periodic pattern with a spatial frequency of 6 lp (line pair) / mm is imaged at an equal magnification is used.

  Also, as shown in FIG. 6, there is a certain relationship with the aperture angle of the lenses 41 constituting the lens array 4, and for example, in order to obtain a focal depth of 1 mm or more, the aperture angle must be 6 ° or less. There is a fixed relationship between the aperture angle and the transmitted light amount, and the transmitted light amount increases as the aperture angle increases. In particular, when the lens array 4 including the two lens plates 40 shown in the embodiment is used, the amount of transmitted light is larger than that of the conventional rod lens array. Considering the above points, the opening angle of the microlens 41 is set in the range of 4 to 11 °, preferably in the range of 4 to 6 °.

  The image reading apparatus according to the present invention is effectively used as a copying machine, a facsimile, or the like.

Sectional view of an image reading apparatus according to the present invention Perspective view of erecting equal-magnification imaging system with overlapping lens plates The figure which shows the relationship between the depth of focus of the erecting equal-magnification imaging system with a lens plate superimposed Graph showing the relationship between depth of focus and modulation depth Sectional view of a conventional image reading apparatus Graph showing the relationship between aperture angle, depth of focus and transmitted light

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image reading apparatus, 2 ... Housing | casing, 3 ... Line illumination apparatus, 4 ... Lens array which is an erecting equal magnification imaging system, 5 ... Recessed part, 6 ... Image sensor (light receiving element), 7 ... Substrate, 8 ... Document platen, 9 ... Ghost cut part, 30 ... Case, 31 ... Bar light guide, 31a ... Bottom part of light guide, 31b, 31c ... Side face of light guide, 31d ... Output surface, 40 ... Lens plate, 41 ... Micro lens.

Claims (3)

An illumination unit, a line image sensor composed of photoelectric conversion elements, and an erecting equal-magnification imaging system for condensing reflected light from the original of the irradiation light from the illumination unit toward the line image sensor. In the image reading apparatus, the erecting equal-magnification imaging system has a depth of focus of 1 mm or more, and the illumination unit has an illuminance unevenness within ± 20% in the depth of focus range. .
However, the focal depth range refers to a range on the optical axis where the modulation degree is 10% or more when a black and white periodic pattern with a spatial frequency of 6 lp (line pair) / mm is imaged at an equal magnification. 2. The image reading apparatus according to claim 1, wherein the erecting equal-magnification imaging system is configured by stacking a plurality of lens plates, and each lens plate has a number of minute lenses regularly two-dimensionally at a predetermined pitch. An image reading apparatus that is arranged in an array. 2. The image reading apparatus according to claim 1, wherein the illumination unit includes a rod-shaped light guide that reflects light from a light source on both side surfaces and emits the light from an output surface, and a light collection position of the light reflected by one side surface. And a light collecting position of light reflected by the other side surface is different.