Patent Application
20230412749
The present disclosure relates to an image reading device that causes convergence of light transmitted through or reflected from a reading target, that is, an irradiated body, with a lens array arranged in an array and that performs reading of the converged light with a sensor element array.
Some types of conventional image reading device, that is, some types of an image-reading line image sensor and an image input device including the image sensor, (i) emit light onto a reading target, (ii) converge light transmitted through or reflected from the reading target with rod lenses arranged in an array, and (iii) read the converged light with an array of linearly-arranged optical sensors (refer to, for example, Patent Literature 1). Such image reading device is used in an image reading apparatus such as a copier or a scanner that translates, into electronic information, images, characters, patterns, or the like on the reading target.
Examples of a lens array in an image reading device include a rod lens array and a microlens array for an erecting equal magnification optical system. Such a lens array is used in an apparatus such as a copier or a scanner that is used for digitization of information such as images, characters, and patterns printed on a paper medium or the like. Patent Literature 1 discloses an image reading device, that is, a line image sensor, that, with a rod lens array of rod-shaped lenses arranged in an array in accordance with a reading width, focuses reflection light or transmission light including information of a reading target illuminated by a line light source onto an optical sensor array arranged opposite to the reading target with respect to the lens array to perform reading.
The rod lens array disclosed in Patent Literature 1 includes rod lenses that are arranged in an array and that are formed from an inorganic material such as glass or from a resin or the like with a refractive index distributed in a radial direction thereof to form an erecting equal magnification optical system with a predetermined angular aperture and a predetermined conjugate length. Due to this configuration, a continuous linear image is obtainable.
Furthermore, in recent years, rod lens arrays have uses other than those in an input unit of a facsimile machine or the like such as those in backside-reading line image sensors installed in an automatic document feeder (ADF) in a document scanner or a copier, and those in a manufacturing line such as for printing inspection or film inspection in a commercial printing line. This is because a rod lens, although having a fixed focus, has a short conjugate length as the distance between focal points, and thus can form an image input system that is more compact than conventional optical systems that focus a reduced image onto a small sensor surface.
As the range of applications widens, attempts are considered, for yet wider application, to achieve improvement in shortness of the conjugate length that has been a contributing factor in miniaturization of image sensor products. For wider application, improvement in depth of field that is tolerance for a positional relationship between a focal position and a reading target, that is, by overcoming shallow or small depth of field, is required. In particular, in the case of image inspection, that is, in-line inspection of paper printing or film printing, a reading target may be conveyed at a high speed of 200 m/min or higher, and thus improvement is required with respect to a change in resolution of an image to be read that may possibly occur in response to flapping of the reading target due to the high-speed conveyance.
Against such background, various investigations are carried out to increase the depth of field in a line image sensor. For example, Patent Literature 1 discloses disposing an overlap limiter between lens elements in a lens element body to limit overlap of images formed by the lens elements, thereby controlling a diameter for image formation of each lens element to increase the depth of field, that is, improve the depth of field.
As another example, Patent Literature 2 discloses using an opaque, light-absorption layer around rod lenses to prevent occurrence of low resolution due to overlap of images formed by the rod lenses and to cause an array of the rod lenses to have depth-of-field characteristics close to the depth-of-field characteristics of a single rod lens, thereby increasing the depth of field, that is, improving the depth of field, of the rod lens array as a whole.
As still another example, Patent Literature 3 discloses arranging rod lenses with an opaque, light-absorption layer disposed around the rod lenses and with gaps left between the lenses to achieve uniform characteristics of the rod lens array, thereby reducing variations in an amount of light or in resolution between the lenses generated in the configuration disclosed in Patent Literature 2 and increasing the depth of field, that is, improving the depth of field.
Patent Literature 1: Unexamined Japanese Patent Application Publication No. H6-342131
Patent Literature 2: Unexamined Japanese Patent Application Publication No 2000-35519
Patent Literature 3: WO2013/146873
A line image sensor including a rod lens array has a problem in the securing of depth of field. Various techniques are developed heretofore for improvement in the depth of field to the same level as that of a single lens. The technique disclosed in Patent Literature 1 has a problem in that limitation to light incident on the limiter at a low incident angle is not provided.
Such technique as disclosed in Patent Literature 1 commonly uses a general-purpose product as a lens array and limits optical paths of light emitted from lenses by use of a light blocking member prepared in advance as a light blocking member having a pitch matching a pitch of fixed lenses, for improvement in depth of field. On the other hand, an optical system is formed by combining the blocking member and a lens array 1 in which, based on the assumption of forming a group of light blockers in one member or of combining multiple groups of light blockers, rod lenses are disposed on a flat plate with managed-arrangement as an array but without individual management of the position of each of the rod lenses.
For this reason, such technique as disclosed in Patent Literature 1 has a problem of difficulty in the accurate arranging of the light blocking member at a predetermined position in accordance with dimensional variability that a rod lens array including rod lenses with an actual diameter of 0.3 to 1.0 mm may possibly have, such as variation in a thickness of each rod lens and variation in an arrangement pitch.
Furthermore, since the light blocking member is included as a separate component, continually maintaining a constant positional relationship between the light blocking member and the rod lenses in response to a change in dimensions due to thermal expansion or contraction of the lens array due to a change in a temperature or humidity that may possibly occur in performing image capturing by a sensor system with lenses having configuration as that disclosed in Patent Literature 1 is difficult. Additionally, prevention is difficult of the occurrence of a severe decrease in quality of an image due to occurrence of a multiple image or shading image due to changes in a position of each lens of the lens array and a position of the blocking member.
The present disclosure is made to solve the aforementioned problems and relates to an image reading device having a highly-accurate structure that enables an easy increase in the depth of field, that is, improvement in the depth of the field, without need for a change in basic characteristics of lenses.
An image reading device according to the present disclosure includes (i) a lens array including lenses that are sandwiched between two fixing plates extending along a main scanning direction and are arranged in an array along the main scanning direction, (ii) a sensor element array including sensor elements that are arranged in an array along the main scanning direction and are each to receive light converged by the lenses, and (iii) an overlap preventer disposed between the lens array and the sensor element array to prevent overlap of images formed by the lenses. The overlap preventer is a slit section including a plurality of slit plates arranged in the main scanning direction and extending in a sub-scanning direction to partition off a space, and the slit plates are fixed to the fixing plates.
As described above, according to the present disclosure, an image reading device is obtainable in which limitation to the optical path is provided with high-accuracy positional configuration to prevent light that is specific light incident at a low incident angle from directly entering the sensor elements, and thus an increase in the depth of field, that is, improvement is the depth of field, can be achieved while suppressing a decrease in an amount of light.
In Embodiments 1 and 2, explanation of basic configuration of a slit section and explanation of a specific-light blocking member that can be used in an image reading device according to Embodiment 3 are provided. In Embodiment 3, explanation relating to fixation of the slit section is provided.
Hereinafter, Embodiment 1 is described with reference to
In
In
In
That is, the image reading device according to Embodiment 1 can be said to be a line image sensor that includes the light sources 10 and the sensor element array 3 with the rod lens array 1 located in between and in which the light sources 10 illuminate a portion of the reading target 9 at the center of reading for the rod lens array 1 and the sensor element array 3 converts a medium image formed by the rod lens array 1 into an electric signal. The role of the slit section 5 in the image reading device according to Embodiment 1 that is the line image sensor and the basic functions of the slit section 5 are described in detail below.
First, the role of the slit section 5 is described in detail. The point to be improved of the line image sensor using the rod lens array 1, as in the above description of the problem to be solved, is the securing of depth of field. An entire image formed by an imaging optical system, that is, by lenses, is not formed with a single rod lens 2 alone. As illustrated in
A low depth of field is mainly caused, rather than by the characteristics of each single lens, by arrayed lenses with which, as illustrated in
Since the rod lenses 2 are arrayed, as illustrated in
As illustrated on the left side in
The low depth of field resulting from the low resolution due to a greater distance of the position of the reading target 9 from the conjugate point, that is, from the focal position, is not mainly caused by the characteristics of each rod lens 2. The reduced depth of field is mainly caused by the rod lens array 1 that is an array of the rod lenses 2, that is, caused through forming of a blurred image resulting from images formed by the rod lenses 2 on the sensor element array 3 that are not superimposed at a regular position and deviate from each other due to (i) the difference in characteristics of the adjacent rod lenses 2 defined by the aforementioned overlap degree m, (ii) misalignment of the optical axes of the adjacent rod lenses 2 due to assembly errors, and (iii) enlargement or reduction of images due to deviation of the reading target 9 from the focal position. Thus, as illustrated in
Next, the basic functions of the slit section 5 of the image reading device according to Embodiment 1 are described in detail with reference to
The slit section 5 illustrated in
In the slit section 5, the slit plates 7 are fixed with the sidewall plates 6 so as to be held with a regular distance kept between each slit plate. More specifically, the slit plates 7 are fixed with two sidewall plates 6. Thus, the sidewall plates 6 can also be referred to as spacers 6. In other words, the sidewall plates 6 that are spacers 6 are two components that extend in the main scanning direction and face each other in the sub-scanning direction intersecting the main scanning direction. The multiple slit plates 7 extend in the sub-scanning direction between the two sidewall plates 6 to partition off the space between the two sidewall plates 6 to form the slit portions of the slit section 5. As illustrated in
Mechanical dimensions of the slit section 5 are preferably determined in the manner described below when the overlap degree that is a half of the value obtained by dividing by the lens diameter Φ the diameter of an area to which a single rod lens 2 transfers an image at the conjugate point is taken to be m and an angular aperture is taken to be θ for the rod lens 2. The pitch e between adjacent slit plates 7 of the multiple slit plates 7 is smaller than or equal to a value obtained by multiplying the overlap degree m and the lens diameter Φ by 0.6. The length of the slit section 5, that is, the length of the slit plates 7 on the optical path, is greater than or equal to a value obtained by dividing the pitch e by a tangent θ when the rod lens 2 has an angular aperture θ. That is, from the relationships for the pitch e of the slit plates 7, e≤0.6×m×Φ, and the height H of the slit plate 6, H≥e/tan(θ), the pitch e is about 2.0 mm from 0.5×m×1 mm, and the height of the slit plate 6, that is, the height of the slit section 5, is about 20 mm from 2.0/tan(6°) with a restriction of 6° allowing margin for the lens angular aperture. The height of the slit plate 6, that is, the height of the slit section 5, is a dimension in the optical axis direction that is a reading optical axis direction. One of the solid lines in
In Embodiment 3 described below, the pitch e between adjacent slit plates 7 of the multiple slit plates 7 is taken to be equal to the lens diameter Φ, and the length of the slit section 5, that is, the length of the slit plates 7 on the optical path, is greater than or equal to a value obtained by dividing the pitch e by a tangent θ when the rod lens 2 has an angular aperture θ. That is, from the relationship for the height H of the slit plate 6, H≥e/tan(θ), the pitch e is 1 mm, and the height of the slit plate 6, that is, the height of the slit section 5, is about 10 mm from 1.0/tan(9°) with a restriction of 9° lens angular aperture.
The solid lines in
To block light more stably, the slit section 5 described above in the image reading device according to Embodiment 1 preferably further includes the specific-light blocking members 8 as illustrated in
Multiple specific-light blocking members 8 as illustrated in
As illustrated in
Due to the specific-light blocking members 8 that are the beam-like members, the conditions of the surface, that is, a wall surface, of the slit section 5 are less likely to have an effect, and stable characteristics become obtainable. Providing of the specific-light blocking members 8 that are the beam-like members, although producing a slight decrease in the peak resolution at the focal position, enables a great improvement in the depth of field in reaction to the positional deviation of the reading target 9 in the reading optical axis direction. The depth of field can be increased by about three times.
Embodiment 2 is described with reference to
With the specific-light blocking members 8 included in the image reading device according to Embodiment 2, since the hypotenuse of the right-angled triangle forming the profile of each of the specific-light blocking members 8 is inclined with respect to the optical axis direction, reflection of light by the specific-light blocking members 8 toward the sensor element 4 can be further reduced. Thus, in the case of employing, in the specific-light blocking members 8 that are the beam-like members in the image reading device according to Embodiment 2, the same thickness d (dimension d in the optical axis direction), the same pitch f (pitch for interval f), the same entire dimension t for the slit plates 7 including the specific-light blocking member 8 in the main scanning direction, and the same height a (dimension a in the main scanning direction or height a protruding in the main scanning direction) as the specific-light blocking members 8 in the image reading device according to Embodiment 1, due to the specific-light blocking members 8 that are the beam-like members having a shorter height a nearer the sensor elements 4, an image reading device with an increased depth of field and a more stable image quality is obtainable. The image reading device according to Embodiment 2 preferably also satisfy the relationship a/f≥tan(θ).
As described above, according to the image reading devices according to Embodiments 1 and 2, limitation is provided for the optical path to prevent light that is specific light incident at a low incident angle from directly entering the sensor elements 4. This configuration thus enables increasing the depth of field, that is, improving the depth of field, while suppressing a decrease in an amount of light.
The below described problem remains in improvement as disclosed in Patent Literature 2, that is, improvement of the depth of field in each single rod lens. That is to say, there is difficulty in achieving the uniform resolution or brightness in reaction to positional deviation of a reading target in the depth direction, as described in Patent Literature 3. Further, in the case of using a long line sensor with the technique disclosed in Patent Literature 2, a change in distribution of brightness occurs due to environmental changes, in particular, due to changes in relative positions of lenses and a sensor array due to a difference in thermal expansion caused by temperature changes. This change produces unevenness in illumination or sensitivity independently of whether shading compensation is performed in advance, thereby degrading the image quality. Moreover, improving the depth of field of each rod lens requires a reduction in the size of an area for a part functioning as a lens to allow the lens to be independent. This structure leads to a dark image due to a reduction in the amount of light for image formation or requires use of needlessly bright lighting, and thus a faster reading system is unlikely to be achieved.
The technique disclosed in Patent Literature 3 can achieve uniform resolution or brightness in reaction to the positional deviation of a medium, unlike the technique of Patent Literature 2. However, the technique disclosed in Patent Literature 3 requires a more reduction in the size of an area for a part functioning as a lens than with the technique of Patent Literature 2. This reduction leads to a dark image due to a reduction in the amount of light for image formation or the need for using needlessly bright lighting, and thus a faster reading system is unlikely to be achieved. Further, using lenses with basic characteristics thereof changed is required to use the techniques disclosed in Patent Literatures 2 and 3, and thus these techniques have difficulty in response to various operation distances (distance from a lens end to a reading medium) for various uses including inspection.
Contrary to Patent Literatures 1, 2 and 3, the image reading devices according to Embodiments 1 and 2 enable an easy increase in the depth of field, that is, improvement in the depth of the field, without need for a change in basic characteristics of lenses.
Embodiment 3 is described with reference to
The image reading device according to Embodiment 3 has the structure illustrated in
The fixing plates 13 in
The fitting portions 15 are multiple grooves 16 formed along the optical axis of the lens array 1 of which optical axis direction matches a cylindrical direction or the focal depth direction that is the direction of the depth of field as illustrated in
The structure illustrated in
The structure illustrated in
The structure illustrated in
Although cases in which the fixing legs 14 are formed in the slit plates 7 are described above, the fixing legs 14 may be formed in the sidewall plates 6 that are the spacers 6 described in Embodiments 1 and 2. In the case in which the fixing legs 14 are formed in the sidewall plates 6, the slit plates 7 are fixed to the fixing plates 13 via the sidewall plates 6. Further, configuration may be employed in which the fixing legs 14 are formed in both the slit plates 7 and the sidewall plates 6. That is, the fixing legs 14 are formed in at least one of the slit plates 7 or the sidewall plates 6. Moreover, the fixing legs 14 are included in the slit section 5 and thus may have black surfaces. In this case, at least surfaces of the fixing legs 14 that are contiguous with the slit plates are black surfaces. The black surfaces are, for example, black velvety surfaces.
Since the image reading device according to Embodiment 3 has the structure illustrated in
To avoid such failure to obtain uniform images across the whole length of the sensor element array 3, in processing of the lens array 1 with respect to the side plates that are the fixing plates 13, a number and dimension of the lenses 2 for a total reading length are measured and an average pitch is calculated, to eliminate the effect of lens pitch variations of the lenses 2 between multiple lens arrays 1. Then, after determining a starting point, a group of the fitting portions 15, that is, the groves 16, the holes 17, or the grooves 18, are formed at regular intervals with the average pitch of the lens array 2. The group of the fitting portions 15 formed in the aforementioned manner enables prevention of the center positions of the slit plates 7 from being located with deviation relative to the lenses 2 at or greater than the degrees of variations in arrangement of the lenses 2.
Preventing occurrence of variations in arrangement of the lenses 2 enables forming the fitting portions 15, that is, the groves 16, the holes 17 or the grooves 18, with, even at a maximum, a deviation of 0.03 mm from an ideal arrangement for a thickness of 0.1 mm, that is, an arrangement in which each slit plate 7 overlaps each of adjacent lenses by 0.05 mm. In the case in which a higher accuracy is required, alignment of the fitting portions 15 may be performed when forming the fitting portions 15, that is, the groves 16, the holes 17 or the grooves 18, while checking positions of the lenses 2 using an imaging device such as a camera.
The slit plates 7 of the image reading device according to Embodiment 3 are formed by (i) to ensure strength while achieving a thin thickness to increase the aperture ratio of the lenses 2, performing fitting of stainless plates with a thickness of 0.1 mm so as to have a width of 4.0 mm, a height of 10 mm in the optical axis direction corresponding to the height of the slit plates 7, with portions with a length of 5 mm corresponding to the fitting portions 15 and (ii) performing blackening and low-reflectivity processing to both sides thereof so as to be the aforementioned black surfaces. Specifically, since a stainless material is used, surfaces of the stainless plates are processed by sandblasting to form textured surfaces, and then black plating processing is performed for low light reflectivity. The slit plates 7 are fixed to the lens array 1 by (i) fitting the slit plates 7, more specifically, the fixing legs 14, to the fitting portions 15 that are holes or grooves in side surfaces of the lens array 1 and (ii) applying an adhesive to insertion portions, that is, the fitting portions.
Due to the aforementioned configuration, an occupation area of the slit plates 7 in the image reading device according to Embodiment 3 can be smaller, that is, dimensions of the slit plates 7 in the width direction can be smaller, and thus assembly without a major change in a conventional sensor module mechanism is achievable. Further, since the slit plates 7 stand independently without the sidewall plates 6 that are the spacers 6 as structural components at portions connecting the slit plates 7 therebetween, that is, holding the slit plates 7 along the main scanning direction of the lens array 2, near-surface reflection effect of emitted light can be easily eliminated.
Although the slit plates 7 described above have a width of 4.0 mm that is almost the same as the width of the lens array 1, similar effects are obtainable by the slit plates 7 having any width that provides light-blocking portions having the same width as the diameter of the lenses 2, and thus the width can be modified to match the mounting mechanism. Although a stainless plate may be used as abase material of the slit plates 7 to ensure strength, resin that has high workability and is easy to process into a shape for attachment may be used as the material of the slit plates 7, with processing of surfaces thereof so as to have a low-reflectivity. Further, although the slit plates 7 described above have a thickness of 0.1 mm in view of availability as a material, reducing the thickness while ensuring shape stability as the slit plates 7 leads to a narrower area providing limitation to light emitted from the lens array 1 and thus enables reducing a decrease in brightness as an optical system.
In the case as illustrated in
In the present embodiment, to arrange the lens array 1 and the slit plates 7 at predetermined positions so as to have a one-to-one correspondence, the slit plates 7 are fixed to the rows of the holes 17 that (i) have a diameter of 0.2 mm and a depth of 5 mm that correspond to 0.2 mm that is the thickness of the slit pates and (ii) are formed in surfaces of the side plates on the lens-light emission side with alignment so as to be arranged at positions between adjacent lenses 2. The holes 17 for fixing the silt plates 7 may have any diameter that allows the side plates of the lens array 2 that are the fixing plates 13 to have a thickness sufficient for maintaining strength. For example, a diameter Φ of 0.2 mm can be used for about 1.9 mm thickness of the side plates that are the fixing plates 13. The permissible increase is to approximately a half or less of the thickness of the side plates of the lens array 2.
As described above, the fitting portions 15 of the image reading device according to Embodiment 3 are formed through processing to the fixing plates 13 that are sidewalls of the lens array 1 so as to have a structure that enables alignment and arrangement of the slit section 5, that is, alignment and arrangement of the group of the slit plates 7. According to this structure, a mechanism for improvement in depth of field can be arranged without an increase in area occupied by a lens system in a cross section and without a major change to mechanical portions of a conventional image reading device.
With regard to the configuration of the lens array 1 in which the lenses 2 are arranged in an array along the main scanning direction and the lenses 2 are sandwiched between the two fixing plates 13 extending along the main scanning direction, the fixing plates 13 need not be included in the lens array 1 and instead may be formed outside the lens array 1. Note that this structure can also be described by saying “the lenses 2 are sandwiched by the two fixing plates 13”. That is, the lens array 1 may be formed integrally with, or be formed separately from, the fixing plates 13, that is, may be formed as a separate component.
In the case in which the lens array 1 and the fixing plates 13 are formed integrally, processing to the lens array 1 is required to form the fitting portions 15. This requires an increase in amount of time for processing and an increase in processing accuracy, and thus may possibly lead to a relatively high manufacturing cost. Thus, configuration for alignment and attachment of the slit section 5, that is, alignment and attachment of the group of the slit plates 7, as a structure for forming the lens array 1 and the fixing plates 13 separately, is described below with reference to
The fitting portions 15 that are illustrated in
Due to the pitch of the grooves 16 of the rubber plate 13 that is smaller than the pitch of the lenses 2, at one end of the lens array 1, the lens array 1 and the rubber plate 13 are fixed to each other with the groove 16 aligned. Then, for positional adjustment of the lenses 2 and the grooves 16 across the whole length of the lens array 1, the lens array 1 and the rubber plate 13 are bonded with the rubber plate 13 extended such that positions of the grooves 16 match the positions of the lenses. By performing this operation on the opposite surface, processing for arrangement and fixation of the slit plates 7 at predetermined positions between the lenses 2 is achieved. On condition that a thickness of the rubber plates 13 is appropriately selected, the rubber plates 13 may have the holes 17 illustrated in
Alignment and retention of the slit plates 7 are achievable by inserting into the fitting portions 15 formed in the rubber plates 13 the slit section 5, that is, the slit plates 7 or the sidewall plates 6. Since the rubber plates 13 processed to have grooves are obtainable by rubber molding processing, positional alignment of the lenses 2 and the fitting portions 15 is ensured by post-molding extensibility that is a change in length of about 5% of the whole length, and manufacture as a separate component creates cost benefits.
Although configuration suitable for attaching the slit section 5, that is, the slit plates 7, to the lens array 1 in post-processing is described above, the configuration of the image reading device according to Embodiment 3 is not limited to this configuration. Another alignment of the slit section 5, that is, slit plates 7, is described below. The lens array 1 is manufactured by arranging on a flat plate made of fiber reinforced plastic (FRP) the lenses 2 in parallel and in close contact and by sandwiching by bonding and fixing two FRP plates. In the case of forming the fixing plates 13 integrally with the lens array 1, the FRP plates correspond to the fixing plates 13. Checking a position of each lens 2 in post-processing is difficult since (i) variations in a lens system and bending, inclination or the like of rods occur during arrangement and (ii) both ends of the lens array are the only references for arrangement of the lenses.
Thus, a structure for arrangement of the lenses 2 may be formed in the side plates in advance for arrangement thereto of the lenses 2, and additionally, a structure indicating in the lens array 1 positions between adjacent lenses 2 may be used by using FRP plates that have, on surfaces thereof opposite to the surfaces for arrangement of the lenses 2, a structure indicating positions between pairs of lenses. Configuration suitable for achievement of the aforementioned structures is illustrated in
Specifically, (i) a structure of a row of protrusions that each have a triangular cross-sectional shape to hold the lens 2 by contacting a side surface thereof is formed on a side of the FRP plate to which the lenses 2 are to be fixed, that is, on a side of the side plate for holding lenses, at a pitch corresponding to a fiber diameter of the lenses 2 and (ii) structures that each indicate an arrangement position of the lens 2, for example, structures that each have a concave triangular shape, are formed on the opposite surface of the FRP plate at positions deviating by a half of the pitch from the row of the protrusions to hold lenses. The lens array 1 is formed using two side plates formed in the aforementioned manner. According to this configuration, positions of the lenses 2 with respect to the side plates are determined independently of diameter or skew in placement of the lenses as illustrated in
In the case of forming the fixing plates 13 illustrated in
As described above, in the lens array 1 of the image reading device according to Embodiment 3, each of the side plates that are the fixing plates 13 for holding the lenses 2 has a structure for alignment of the lenses 2 and has, on the opposite surface, an alignment structure corresponding to the structure for alignment of the lenses 2. Further, in the lens array 1 having a structure in which the lenses 2 arranged in a row are fixed by the two side plates that are the fixing plates 13, each of the side plates that are the fixing plates 13 (i) has, on a surface thereof to which the lenses are fixed, fixing structures for fixing positions of the lenses that have a height less than one-third of the diameter of the lenses and that are arranged at the pitch of the lenses so as to contact side surfaces of the lenses 2 and (ii) has, on the outer side surface thereof, a structure for fixing the slit plates 7 at positions between adjacent lenses 2, and the lenses 2 are bonded by these side plates.
Furthermore, the image reading device according to Embodiment 3 includes (i) an array of the lenses 2 as the lens array 1 that are sandwiched and bonded by thin plates that have, on one surfaces thereof, structures for alignment and retention of the slit plates 7 that are the light blocking members and (ii) the group of the slit plates 7 arranged at the predetermined positions corresponding to the group of the lenses 2. The thin plates that are the fixing plates 13 having the structures for alignment and retention of the slit plates 7 that are the light blocking members may be made of a material having high extensibility. The portions for alignment and retention of the slit plate 7 may be arranged at a pitch lower than or equal to a minimum lens pitch of the lenses 2.
Furthermore, to ensure positional accuracy of the lenses and structures for installation of the light blocking members across the entire length, the lens array 1 of the image reading device according to Embodiment 3 may be formed by, after aligning the lenses 2 and the fitting portions 15 that are the structures for installation of the slit plates 7, fixing to one end or a center portion of the lens array 1 the thin plates that are the rubber plates 13 having extensibility and having a group of structures that are the group of the fitting portions 15 for holding the slit plates 7, and then sticking other portions of the thin plates in order while extending the thin plates.
As described above, according to the image reading devices according to Embodiments 1 to 3, since high-accuracy positional alignment of the slit section 5, that is, high-accuracy positional alignment of the slits 7, can be easily achieved by fitting, that is, inserting, the fixing legs 14 into the fitting portions 15 formed in the fixing plates 13, an image reading device with stably increased depth of field and stable quality of an image is obtainable.
Furthermore, according to the image reading devices according to Embodiments 1 to 3, light transmission cylinder portions 5 or light transmission cylinder portions 13 provide limitation for the optical path to prevent light that is specific light incident at a low incident angle from directly entering the sensor elements 4. Due to this configuration, an image reading device with a stably increased depth of field and stable quality of an image is obtainable without need for a change in basic characteristics of lenses.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-160321 | Sep 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/020886 | 6/1/2021 | WO |
