JP3953173B2 - Contact image sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor for reading an image of a document, particularly a contact image sensor, as an input device for a computer, a facsimile machine, a copying machine or the like.
[0002]
[Prior art]
Image sensors are excellent in operability and versatility as image input devices, and have been widely used in recent years in fields such as OA equipment and information equipment. In particular, in recent years, demand for household facsimile machines has increased, and a compact and easy-to-use image sensor has been demanded. Therefore, a contact type using a light emitting diode (hereinafter referred to as “LED”) array or the like as a light source. Image sensors are becoming popular. FIG. 16 is a cross-sectional view of a conventional contact image sensor described in, for example, Japanese Patent Laid-Open No. 6-342131, and an outline thereof will be described.
[0003]
As shown in FIG. 16, the contact-type image sensor includes a light-receiving element array 124 including a document reading light-receiving element 121 in which a plurality of sensor pixels that perform photoelectric conversion are arranged, a protective film 122, and a substrate 123 on which the protective film 122 is mounted. An LED array 125 that is a linear light source that irradiates the document, a lens array 126 that forms an image of the document 129 on the light receiving element array 124 that is a light receiving unit, a transparent plate 127 on which the document 129 is placed, and the like It is comprised from the exterior case 128 which supports these members.
[0004]
In the operation of the contact type image sensor, the document surface is irradiated by the LED array 125, diffuse reflected light on the reading line of the document surface is imaged on the light receiving element array by the lens array 126, and the document which the reflected light has The light / dark information of 129, that is, the intensity of light, is converted into an electric signal by the sensor pixel of each original reading light receiving element 121 in the light receiving element array 124, and sent out for each reading line as a serial or parallel signal output. Then, the relative position between the document 129 and the sensor pixel array is moved in the direction perpendicular to the line, and data transmission for each line is repeated, thereby converting the two-dimensional image information into a time-series electrical signal.
[0005]
However, the above contact image sensor has the following problems. The lens array 126 is a compound eye lens composed of a plurality of rod lenses each having a condensing property arranged in a direction perpendicular to the drawing. Therefore, an image overlap occurs on the light receiving side, and a synthetic aperture angle increases. Therefore, there is a problem that the image quality deteriorates when the depth of field is shallow, the document is folded, or the document has irregularities such as cut and paste. Further, the spread part of the book cannot be read, and the application of the image sensor is limited.
[0006]
The state of image formation in the lens array 126 using the rod lens will be described with reference to FIG. The rod array shown in FIG. 16 has rod lenses 126a aligned in the line direction, and each rod lens 126a is made of a translucent material having a refractive index distribution in a direction perpendicular to the optical axis. As shown in FIG. 17A, each rod lens 126a forms an erecting equal-magnification image on the sensor surface on which the sensor pixels are arranged in the range of the diameter X0 on the document surface. Consider a light emitting point p and its imaging q. When p is at the reference position, it is assumed that there is a condensing point on the sensor surface, and the image formation q is not blurred. As shown in FIG. 17B, when the light emission point p moves by x to p ′, the condensing point also moves by x behind the sensor surface, and the image formation q on the sensor surface causes a blur of H amount. . The blur amount H is approximately H = θx when the rod lens 26a is used alone, and depends on the opening angle θ. When a plurality of rod lenses 126a are arranged as shown in FIG. 17C, the opening angle is θ ′ larger than θ, the amount of blur is H ′ larger than H, and approximately H ′ = θ′x. It becomes. As the number of arrangements of the rod lenses 126a increases, the aperture angle increases due to the overlap of the imaging range X0, and the blur increases. As described above, there is a problem that the aperture angle is wide, the relative depth of field is shallow, and the ratio of the amount of blurring of the imaging q to the movement of the light emitting point p is large.
[0007]
If an attempt is made to reduce the opening angle θ of each rod lens in order to eliminate such drawbacks, the optical path length from p to q becomes long, and the use of the contact image sensor increases the size of the apparatus. Further, such a rod lens itself is expensive. JP-A-6-342131 discloses a contact image sensor shown in FIG. 18 which is improved for the purpose of improving these drawbacks. In FIG. 18, reference numeral 110 denotes an aperture limiting member, which is disposed on the exit side corresponding to each rod lens 126a. The other points are the same as those of the image sensor shown in FIG. In this example, the aperture limiting member 110 limits the aperture angle of each rod lens 126a, limits the overlap of images between the rod lenses, and reduces the amount of blur.
[0008]
However, in this case, the positional relationship of the aperture limiting member 110 must be accurately matched to the individual rod lenses 126a, which is disadvantageous in terms of assembly. In addition, the amount of light passing through is restricted by the aperture limiting member 110, the intensity of incident light on the light receiving element array 124 is weakened, and the S / N ratio in photoelectric conversion tends to decrease and the noise of the generated signal tends to increase. .
[0009]
The present invention has the above-mentioned problems in the conventional contact image sensor, that is, in general, the problem that the aperture angle is wide and the depth of field is shallow, and using a rod lens having a large depth of field in order to improve this, The problem of increasing the size of the apparatus and the like, and the provision of an aperture limiting member for the rod lens are disadvantageous in assembly, and the problem of increasing the noise of the signal of the light receiving element is a problem to be solved. The present invention solves these problems, and provides a contact image sensor that can deal with various types of originals such as bent, uneven, double-page spread, can accurately read an image of an original, and can be easily assembled. Objective.
[0010]
[Means for Solving the Problems]
As a first means for solving the above-described problems, the present invention provides a transparent member that supports a document, a light source that illuminates the document, a lens array that guides reflected light from the document, and an exit side of the lens array. In the contact-type image sensor including an optical sensor array that receives and photoelectrically converts the image of the original, the lens array is formed by a collection of bifocal lenses.
[0011]
As a second means for solving the above-mentioned problems, in the first means, the bifocal lens of the lens array includes means for converting a wavefront of parallel incident light by diffraction and means for converting by refraction. And the first-order diffracted light is condensed on a first focal point and the first-order diffracted light is condensed on a second focal point separated from the first focal point.
[0012]
As a third means for solving the above-mentioned problems, the present invention is characterized in that, in the second means, a hologram is formed on at least one lens surface of the bifocal lens of the lens array.
[0013]
As a fourth means for solving the above-mentioned problems, in the third means, the hologram formed on the lens surface of the bifocal lens of the lens array has a light quantity of 0th-order diffracted light and first-order diffracted light. It is characterized by having a step between the lattices that can balance the amount of light.
[0014]
As a fifth means for solving the above-mentioned problem, in the first means, the bifocal lens of the lens array forms two types of holograms having different focal points of the first-order diffracted light on the lens surface. It is characterized by being.
[0015]
As a sixth means for solving the above-mentioned problem, in the present invention, in the first means, at least one lens surface of the bifocal lens of the lens array is constituted by two types of curved surfaces having different curvatures. It is characterized by that.
[0016]
As a seventh means for solving the above-mentioned problems, in the present invention, in any one of the first to sixth means, the light source for illuminating the document has R, G, B LEDs as light emitting elements. These LEDs are driven so as to be lit in time division sequentially for each color.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an example which is one of the preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a configuration of a contact image sensor according to the present embodiment, and FIG. 2 is a cross-sectional view taken along line AA of FIG. As shown in FIG. 1, the contact type image sensor of this example is a light receiving element comprising a document reading light receiving element 21 in which a plurality of sensor pixels for photoelectric conversion are arranged, a protective film 22, and a substrate 23 on which the protective film 22 is mounted. An array 24, an LED array 25 that is a linear light source that irradiates the document, a lens array 26 that forms an image of the document 29 on the light receiving element array 24 that is a light receiving unit, and a support frame 37 that holds the lens array 26. And a transparent plate 27 on which the document 29 is placed, and an outer case 28 that supports these members.
[00018]
In the operation of the contact image sensor, the document surface is irradiated by the LED array 25, and diffused and reflected light on the reading line of the document surface is imaged on the light receiving element array 24 by the lens array 26. The sensor information of each original reading light receiving element 21 in the light receiving element array 24 is converted into an electrical signal from the gray level information 29, that is, the intensity of light, and sent out as a serial or parallel signal output for each reading line. Then, the two-dimensional image information is converted into a time-series electric signal by moving the relative position between the document 29 and the sensor pixel row in the direction perpendicular to the line and repeating the data transmission for each line.
[0019]
As shown in FIGS. 1 and 2, the lens array 26 includes a plurality of rod lenses 36 arranged in a direction parallel to the reading line of the original surface, and is held by a lens holding frame 37. The rod lens 36 is a light receiving element. It consists of a hologram portion 36b having a hologram formed at the end facing the array 24 and a rod portion 36a connected to the hologram portion 36b, and has a substantially cylindrical shape as a whole. 3A and 3B are diagrams showing the shape of the rod lens 36, where FIG. 3A is a cross-sectional view and FIG. 3B is a bottom view. As shown in FIG. 3, a plurality of concentric grooves 36c are formed in the hologram portion 36b. The pitch interval of the grooves 36c becomes smaller toward the outer periphery of the circular end surface of the rod lens 36. The rod portion 36a is made of a translucent material having a refractive index distribution in a direction perpendicular to the optical axis, like the conventional rod lens 26a shown in FIG. 16, and has the same function itself.
[0020]
FIG. 4 is a diagram showing the action of optical path conversion when the hologram part 36b is single. As shown in FIG. 4, when light parallel to the optical axis incident on the surface opposite to the groove from the front exits from the grooved surface, the zero-order diffracted light s0 having a diffraction angle of 0, the pitch d of the groove 36c, and the light Is divided into first-order diffracted light s1 having a diffraction angle determined by a relationship of φ = sin ⁻¹ (λ / d). The 0th-order diffracted light s0 becomes light parallel to the optical axis similar to the incident light, but the 1st-order diffracted light s1 is bent away from the optical axis in the peripheral direction, and the angle is inversely proportional to the groove pitch d toward the periphery. It becomes large and becomes divergent light like light emitted from a virtual light emitting point Am like a concave lens. Conversely, when light is incident in the direction of focusing on Am from the side with the groove 36c, the light emitted from the hologram portion 36b is divided into zero-order diffracted light focused on Am and first-order diffracted light parallel to the optical axis. In this example, the groove 36c is formed in a shape so that the light amounts of the 0th-order diffracted light and the 1st-order diffracted light are substantially equal. The groove 36c can be formed simultaneously with the molding of the rod lens 36 by a molding die.
[0021]
FIG. 5 is a principle diagram showing the action of the optical path conversion in the rod lens 36 shown in FIG. 3, (a) is a sectional view showing the whole, (b) is a detailed view of a portion B in (a), (c) is It is CC arrow line view of (b). In FIG. 5A, the hologram portion 36b and the rod portion 36a are shown separately for convenience of explanation. In FIG. 5, the light emitted from the light emitting point A0 at the reference position is incident on the rod portion 36a, is emitted toward the 0th-order condensing point B00 that produces an equal-magnification erect image, and is emitted to the hologram portion 36b. Incident. The emitted light from the hologram part 36b is divided into 0th-order diffracted light s0 and 1st-order diffracted light s1, and the 0th-order diffracted light s0 is condensed at the 0th-order condensed light point B00, and the 1st-order diffracted light s1 is rearward from the 0th-order condensed light point B00. The light is condensed toward the primary condensing point B01 separated by d.
[0022]
The reason why the first-order diffracted light is condensed behind the condensing point B00 of the zero-order diffracted light is due to the divergence effect of the hologram part 36b already described with reference to FIG. 4, and a concave lens is disposed behind the convex lens. This is based on a principle similar to that in which the condensing point moves backward. Here, the sensor surface S is arranged so as to coincide with the primary condensing point B01. Assuming that the aperture angle viewed from the sensor surface is θ, the image formation by the 0th-order diffracted light is q0, and the image formation by the 1st-order diffracted light is q1, q0 and q1 are generated at the overlapping position, but the blur H0 of q0 is approximately H0 = θd. The q1 blur H1 is H1 = 0.
[0023]
Next, FIG. 6 is a diagram showing the relationship between the movement of the light emitting point and the blur, (a) is a sectional view showing the whole, (b) is an enlarged view of the D part in (a), (c) is a diagram of (b). It is an EE arrow line view. As shown in FIG. 6A, when the light emission point A0 moves from the reference point x0 to the point A0 ′ ahead by x, the zero-order light condensing point B00 moves to the point B00 ′ behind by x and the primary light condensing. Point B01 moves to B01 'point behind by approximately X. At this time, the blur amount B0 of the image formation q0 due to the 0th-order diffracted light is approximately B0 = θ | dx |, and the blur amount H1 of the image formation q1 due to the 1st-order diffracted light is approximately H1 = θ | x |. . FIG. 7 is a graph showing the relationship between the movement amount x of the light emitting point A0 from the reference position, the blur amount H0 of the zero-order diffracted light image q0, and the blur amount H1 of the first-order diffracted light image q1. Here, if the amount of blur for any one of the images is equal to or less than a predetermined value, the document reading light receiving element 21 arranged on the light receiving surface can be operated normally.
[0024]
Therefore, the smaller one of H0 and H1 shown in FIG. 7 is taken as the effective blur amount HE, and the blur amount of the conventional rod lens having no hologram portion shown in FIG. The graph compared with H is shown in FIG. In the figure, a solid line indicates HE and a broken line indicates H. In the case of the rod lens 36 of the present embodiment shown in FIG. 2, the effective amount of blurring with respect to the movement of the light emitting point can be kept small over a wider range than before. For example, when x is (3/2) d, the amount of blur can be reduced to 1/3 of the conventional one. Without reducing the aperture angle θ, it is possible to substantially increase the depth of focus and reduce the blur. This effect is the same in a lens array in which a plurality of rod lenses 36 are aligned, and the depth of focus is substantially increased without reducing the synthetic aperture angle corresponding to θ ′ in FIG. And blur can be reduced. Therefore, in this example, there is no need to provide a member for limiting the opening, or to reduce the diameter of the rod or increase the distance between the light emitting point and the light receiving point in order to reduce the opening angle.
[0025]
In this way, by providing the hologram part 36b on the rod lens 36, a bifocal lens that condenses the light from one light emitting point at two different positions is formed, and image formation by moving forward from the reference point Effective blur can be effectively reduced. In addition, there is no limiting member as described above, and a wide opening angle can be obtained, so that the apparatus can be miniaturized and a sufficient amount of light can be obtained on the light receiving surface. Thereby, in the contact image sensor according to the present embodiment shown in FIG. 1, a gap is formed between the transparent plate 27 and the document 29 due to bending or spread of the document 29, and the light emission point of the reflected light on the document surface is When the position is shifted forward from the position of the surface of the transparent plate 27, the amount of blur generated in image formation on the original reading light receiving element 21 arranged on the light receiving surface due to the shift can be significantly reduced as compared with the conventional case. In addition, in a small apparatus, the data on the original surface can be read with high accuracy by securing the amount of light on the light receiving surface.
[0026]
FIG. 9 is a principle diagram showing the action of optical path conversion when the rod lens 36 of the contact image sensor shown in FIG. 2 is arranged in the reverse direction so that the hologram portion 36b is on the transparent plate 27 side. In FIG. 8, the hologram portion 36b and the rod portion 36a are shown separately for convenience of explanation. As shown in FIG. 8, all the light emitted from the light emitting point A0 at the reference position is incident on the hologram portion 36b, and is diffracted by the same principle as already described, and is diffracted into the zeroth order diffracted light s0 and the first order. The light is divided into the folded light s1 and enters the rod portion 36a. At this time, the first-order diffracted light bends outward and takes the same angle as the light emitted from the virtual light spot Am behind the A0 by d. The 0th-order diffracted light s0 emitted from the rod portion 36a is condensed at a position B00 that is the same magnification as the light emission point A0, and the first-order diffracted light s1 is converged at a position Bm that is the same magnification as the virtual light spot Am by B0 to d. In this way, a bifocal lens is formed that produces two condensing points separated from one light emitting point, similar to the action of the rod lens 36 shown in FIG. Accordingly, this example also has the same operation and effect based on the same principle as that of the contact image sensor shown in FIG.
[0027]
FIG. 10 is a cross-sectional view showing a rod lens which is a modification of the rod lens 36 shown in FIG. The rod lens 36 includes a hologram portion 36b formed at an end portion facing the light receiving element array 24 and a rod portion 36a connected to the hologram portion 36b, and has a substantially cylindrical shape as a whole. The rod portion 36a is the same as the rod portion shown in FIG. A plurality of concentric grooves 36c are formed in the hologram portion 36b. The pitch interval of the grooves 36c becomes smaller toward the outer periphery of the rod lens 36 yen. The shape of the groove is a wave shape, and the second-order or higher-order diffracted light is completely cut so that the light intensities of the zeroth-order diffracted light and the first-order diffracted light are substantially equal. However, the direction of the wave-shaped gradient of the groove 36c is opposite to that of the rod lens 36 shown in FIG. 3, and the gradient of the groove 36c increases toward the inner periphery. As a result, the diffraction angle is reversed. For example, when a light beam parallel to the optical axis is incident on the hologram portion 36b, the first-order diffracted light is diffracted in a condensing direction like a convex lens.
[0028]
In FIG. 10, the light emitted from the light emitting point A0 at the reference position is incident on the rod portion 36a, is emitted toward the 0th-order condensing point B00 that produces an equal-magnification erect image, and is emitted to the hologram portion 36b. Incident. The light emitted from the hologram part 36b is divided into 0th-order diffracted light s0 and 1st-order diffracted light s1, and the 0th-order diffracted light s0 is condensed at the 0th-order condensed light point B00, and the 1st-order diffracted light s1 is forward from the 0th-order condensed light point B00. Is condensed toward the primary condensing point B01 separated by d1. The 1st-order diffracted light is condensed in front of the 0th-order diffracted light condensing point B00 because of the light condensing effect of the hologram part 36b already described, and the light is condensed by arranging a convex lens behind the convex lens. This is based on a principle similar to the point moving forward. In this manner, a bifocal lens is formed that produces two condensing points separated from one light emitting point, similarly to the action of the rod lens 36b shown in FIG. Accordingly, this example also has the same operation and effect based on the same principle as that of the contact image sensor shown in FIG.
[0029]
FIG. 11 is a view showing the shape of a rod lens which is another modification of the rod lens 36 shown in FIG. 3, wherein (a) is a cross-sectional view and (b) is a bottom view. The rod lens 36 shown in FIG. 10 includes a hologram part 36b having a hologram formed at the end facing the light receiving element array 24 shown in FIG. 2 and a rod part 36a connected to the hologram part 36b. . The rod part 36a is the same as the rod part 36a shown in FIG. The hologram portion 36b is divided into a first portion 36b1 and a second portion 36b2 each having grooves 36c1 and 36c2 having different shapes from each other with the diameter of the circle on the end face of the rod as a boundary. A plurality of circular grooves 36c1 and 36c2 are formed. The pitch interval of these grooves becomes smaller toward the outer periphery.
[0030]
However, the wave-shaped gradient directions of the grooves 36c1 and 36c2 are opposite to each other. That is, in the case of the groove 36c1, the depth increases in the direction of increasing toward the inner periphery, and as described above, the groove 36c1 has a light collecting property, whereas in the case of the groove 36c2, the depth decreases toward the inner periphery. It has a divergence with a gradient in the direction. Further, the grooves 36c1 and 36c2 have a shape that allows only the first-order diffracted light to pass without passing the zero-order diffracted light. As a result, the first portion 36b1 has a condensing function that bends incident light in the optical axis direction to produce first-order diffracted light, and the second portion 36b2 bends incident light in a direction away from the optical axis to produce first-order diffracted light. Has a divergent action.
[0031]
After the light from the light emitting point A0 at the reference position on the end surface opposite to the hologram part 36b is incident on the rod part 36a of the rod lens 36, in the direction toward B0 which is in the same positional relationship as A0. The light enters the hologram part 36b. Then, the light incident on the first portion 36b1 is subjected to the above-described condensing action and is condensed as the first-order diffracted light s11 at the first condensing point B11 that is a distance d before B0. The light incident on the second portion 36b2 receives the above-described divergence, and is condensed as a first-order diffracted light s12 at a second condensing point B12 behind the B0 by a distance d. In this way, a bifocal lens is formed that generates two condensing points at different positions with respect to one light emitting point. Accordingly, this example also has the same operation and effect based on the same principle as that of the contact image sensor shown in FIG.
[0032]
Hereinafter, an example which is another preferred embodiment of the present invention will be described with reference to the drawings. FIG. 12 is a cross-sectional view showing a configuration of a rod lens 36 that can also be used in a contact image sensor for color image reading described later. As shown in FIG. 12, the rod lens 36 includes a lens portion 36c having a convex curved surface formed at the end facing the light receiving element array 24, and a rod portion 36a connected to the lens portion 36c. Eggplant. The rod portion 36a has the same characteristics as the rod portion shown in FIG. The lens portion 36c has a first surface 36c1 made of a convex surface having a flat surface or low curvature on the inner side and a second surface 36c2 made of a convex surface having a curvature higher than that of the first surface 36c2 on the outer peripheral portion.
[0033]
As shown in FIG. 12, after the light emitted from the light spot A0 at the reference position enters the rod part 36, the light passes through the rod part 36a toward the condensing point B0 having the same-upright relationship with the light spot A0. After exiting and entering the lens portion 36c, the light exits from the lens surface, but the light exiting from the first surface 36c1 is condensed at substantially the position of the condensing point B0, and the light exiting from the second surface 36c2 is due to refraction. Due to the light condensing effect, the light is condensed at a position B2 ahead of the condensing point B0 by dc. This is due to the difference in the condensing effect at each exit surface. In this way, a bifocal lens is formed that generates two condensing points at different positions with respect to one light emitting point. Accordingly, this example also has the same operation and effect based on the same principle as that of the contact image sensor shown in FIG.
[0034]
In the rod portion 36a, the compensation portion 36d adjacent to the second surface 36c2 distributes the refractive index in a direction that is square and perpendicular to the optical axis, and is similar to an achromatic lens when combined with the second surface 36c2. This reduces the spectral characteristics with respect to the wavelength of the lens surface, and even when used in a contact image sensor for color image reading, which will be described later, the condensing points corresponding to R, G, and B light coincide with B2. Have the effect of
[0035]
13A and 13B are diagrams showing the configuration of a contact image sensor for color image reading. FIG. 13A is a sectional view thereof, and FIG. 13B is a sectional view taken along the line DD in FIG. FIG. 14 is a cross-sectional view showing the structure of a rod lens used in the contact image sensor shown in FIG. As shown in FIG. 14, the rod lens 36 is provided with a hologram portion 36b in the peripheral portion of the end portion facing the light receiving element array 24, and the inner peripheral portion of the end portion is a rod portion 36a. The hologram portion 36b is provided with concentric 36c grooves, but the pitch interval of the grooves becomes smaller toward the outer periphery. The direction of the corrugated gradient of the groove 36c is a gradient in the direction in which the depth of the groove decreases toward the inner periphery, and has a divergence as already described. Furthermore, the shape of the groove 36c1 is a shape that allows only the first-order diffracted light to pass without passing the zero-order diffracted light. As a result, the hologram part 36b has a divergence action that bends the incident light in a direction away from the optical axis to produce first-order diffracted light.
[0036]
As shown in FIG. 14, the light emitted from the light spot A0 at the reference position enters the rod portion 36, and then exits from the hologram portion 36b at the end and the rod end 36a1 on the inner periphery. The light emitted from the rod end portion 36a1 is collected at a condensing point B0 that is at the same magnification as A0, and the light emitted from the hologram portion 36b is emitted from the condensing point B0 due to a divergence effect by diffraction. Also, the light is condensed at the rear position B2 by d. This is due to the difference in the condensing effect at each exit surface. In this way, a bifocal lens is formed that generates two condensing points at different positions with respect to one light emitting point.
[0037]
The rod portion 36a has the same characteristics as the rod portion shown in FIG. In the rod portion 36a, the compensation portion 36d close to the hologram portion 36b distributes the refractive index in a direction square to the optical axis and in a direction perpendicular to the optical axis. Thereby, the spectral characteristics with respect to the wavelength of the hologram part 36b are reduced by the combination with the hologram part 36b by the principle similar to the achromatic lens, and when used in the contact image sensor for color image reading shown in FIG. All the condensing points corresponding to R, G, and B light to be described later substantially coincide with B2 at a fixed position. That is, the diffraction angle in the hologram part 36b increases in proportion to the wavelength, and the divergence effect increases. Accordingly, the position of the condensing point B2 as it is corresponds to the light of R, G, B, and the distance d from B0 increases in the order of R, G, B, and the same spectral action as that of the convex lens tends to occur. As a result, the spectral properties are reduced by a method similar to the achromaticity of the convex lens.
[0038]
The operation of the contact image sensor for color image reading shown in FIG. 13 will be described. As shown in FIG. 13B, the LED array 25 that is a linear light source for irradiating a document has an LED (R LED) 25R that emits substantially red light and an LED that emits substantially green light on an LED substrate 25c. Three types of LEDs (G LED) 25G and a substantially blue light emitting LED (B LED) 25B are mixed and arranged in a line in the direction of the reading line. These LEDs are lit in a time-sharing manner for each color when a driving voltage is applied between driving electrodes (not shown) by a light source driving circuit (not shown), and illuminate a reading line on the original surface, and colors R, G, B Each time, reflected light of the corresponding color component on the original surface is generated.
[0039]
The reflected light also enters the rod lens 36 corresponding to the reflection point in a time-sharing manner for each of R, G, and B colors. The light of each color incident on the rod lens 36 is condensed toward two points almost in a fixed position even if the color changes according to the principle already explained for each color. Therefore, in the case of this example, regarding the reading of each color of the color image of the document, the color image can be read accurately with the same operation and effect by the same principle as that of the contact image sensor shown in FIG.
[0040]
As for the lenses constituting the lens array according to the embodiment of the contact image sensor of the present invention described above, a lens having a lens surface having a different hologram or curvature on one end surface of the rod lens has been described. The present invention is not limited to this, and even in the case where these are provided on the other end face instead of one end face, or on the end faces on both sides as necessary, the same effects as those of the embodiments described above can be obtained. Have. In addition to the rod lens, a hologram 40b is provided on at least one surface of the convex lens 40 as shown in FIG. 15, or at least one surface of the convex lens is composed of two types of surfaces having different curvatures although not shown. Therefore, similar effects can be obtained by configuring the lens array.
[0041]
【The invention's effect】
As described above, according to the present invention, in the contact-type image sensor, an imaging angle of the light receiving unit due to the floating of the original is reduced without limiting the opening angle, and a small-sized and high reading accuracy apparatus is provided. Can do.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of a contact image sensor that is one embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along the line AA of FIG.
3A and 3B are diagrams showing a structure of a rod lens used in the contact image sensor shown in FIG. 1, wherein FIG. 3A is a cross-sectional view, and FIG. 3B is a bottom view.
4 is a diagram illustrating an operation of the rod lens illustrated in FIG. 3. FIG.
FIG. 5 is a diagram showing an operation of the rod lens shown in FIG. 3;
6 is a diagram showing an operation of the rod lens shown in FIG. 3. FIG.
7 is a diagram illustrating an operation of the rod lens illustrated in FIG. 3. FIG.
8 is a diagram showing the action of the rod lens shown in FIG. 3;
FIG. 9 is a diagram illustrating an operation of the rod lens illustrated in FIG. 3;
10 is a diagram showing the structure and operation of a modified example of the rod lens shown in FIG. 3. FIG.
11A and 11B are diagrams showing the structure and operation of a modified example of the rod lens shown in FIG. 3, wherein FIG. 11A is a cross-sectional view, and FIG.
FIG. 12 is a cross-sectional view showing the structure of a rod lens used in a contact image sensor that is one embodiment of the present invention.
13A and 13B are diagrams showing a configuration of a contact image sensor that is one embodiment of the present invention, in which FIG. 13A is a cross-sectional view, and FIG. 13B is a cross-sectional view taken along line DD in FIG.
14 is a diagram showing the structure and operation of a rod lens used in the contact image sensor shown in FIG.
FIG. 15 is a cross-sectional view showing the structure of a bifocal convex lens used in a contact image sensor that is one embodiment of the present invention.
FIG. 16 is a cross-sectional view showing a configuration of a conventional contact image sensor.
17 is a diagram showing the action of a rod lens used in the contact image sensor shown in FIG.
FIG. 18 is a cross-sectional view showing a configuration of a conventional contact image sensor.
[Explanation of symbols]
24 light receiving element array 25 LED array 26 lens array 27 transparent plate 28 outer case 36 rod lens 36b hologram part 36c lens part

Claims (2)

A transparent member that supports the original, a light source that illuminates the original, a lens array that guides reflected light from the original, and an optical sensor array that receives and photoelectrically converts the image of the original on the exit side of the lens array The lens array includes a plurality of rod lenses arranged in a direction parallel to a reading line on the document surface, and the rod lenses have a refractive index distribution in a direction perpendicular to the optical axis. A rod portion made of a translucent material and a hologram portion having a plurality of concentric grooves connected to the emission side of the rod portion are integrally formed, and has an erecting image forming function and emits emitted light 2 contact image sensor, characterized in that focused on the focal point of the. An LED light source for illuminating the original, a lens array for guiding reflected light from the original, and a light receiving element array, and a color image reading contact for imaging the reflected light of the original on the light receiving element array In the type image sensor, the rod lens used in the lens array is integrated with a rod portion and other optical path changing means, and the rod portion has a refractive index in a direction parallel to and perpendicular to the optical axis. A distributed compensation portion is provided in the vicinity of the optical path changing means to form a bifocal lens that generates a condensing point at two different positions in the optical axis direction with respect to one light emitting point, and the operation of the compensation portion. R, G , B A contact image sensor for reading a color image, characterized in that the condensing points for the light of the color are matched.

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