JP2014017662A - Luminaire for image reading and image reader - Google Patents

Abstract

An illumination device for image reading and an image reading device capable of reducing unevenness in illuminance and achieving reduction in thickness at low cost are provided.
A plurality of light emitting elements provided apart from each other in the same direction as the long side of a long region on a document placement surface for image reading, and a light beam emitted from the light emitting element is condensed in a sub-scanning section, In addition, a condensing element that emits a light beam with an illumination optical axis whose angle with the original placement surface in the sub-scanning section is 5 degrees or more and 40 degrees or less, and an optical path length that reduces illuminance unevenness in the long side direction of the long region Is formed on the opposite side of the light emitting element and the light condensing element across the main scanning section, and has a reflecting element that reflects the light beam emitted from the light condensing element toward the long region.
[Selection] Figure 1

Description

  The present invention relates to an image reading illumination device that illuminates a long region on a document placement surface for image reading, and an image reading device using the same.

  In general, in an image reading apparatus such as an image scanner, a copying machine, or a facsimile, a document surface is illuminated using a tubular (linear) light source such as a fluorescent lamp, and an image is read in a line sequential manner. As the tubular light source 005, a cold cathode fluorescent tube or a xenon tube is mainly used. Xenon tubes are widely used as business equipment because of their good light quantity stability, but they are relatively expensive. For this reason, in particular, cold-cathode tubes with low cost are often used as household equipment with a low product unit price. However, cold-cathode tubes have a problem that light quantity stability is not good, and low-cost and light quantity stability is low. Development of a good linear illumination device is required.

As a result of recent technological development, the luminous efficiency of a light emitting diode (LED) is improved, and a technique for using a LED to form a linear illumination device has been developed.
When a point light source such as an LED is used as the light source, a plurality of point light sources are arranged separately from each other in the main scanning direction. When such a light beam emitted from each point light source is directly applied to an image reading surface such as a document surface, illuminance unevenness occurs in the main scanning direction, and density unevenness occurs in the read image. Therefore, various techniques for suppressing the occurrence of uneven illuminance have been developed in an image reading apparatus using a plurality of point light sources.

  In Patent Document 1, it is intended to eliminate unevenness in illuminance by providing a light diffusing unit that randomly diffuses light between a light source and an object (original). In Patent Document 2, a substrate having a front surface and a back surface as mounting surfaces is used, and a plurality of light emitting elements mounted on the front surface of the substrate are opposed to positions between the light emitting elements mounted on the back surface of the substrate. The structure to arrange in is taken. Thereby, the arrangement interval of the LEDs as the plurality of point light sources is made sufficiently narrower than the optical path length from the light source to the document surface. Further, in Patent Document 3, the light emission optical axis from the light source is laid so as to face upward from the horizontal direction, and the original surface is illuminated by being reflected by a reflecting member having a cylindrical curved surface.

JP-A-2005-156600 JP 2008-177918 A JP 2010-161536 A

  However, in the illumination device of Patent Document 1, since the light flux is randomly diffused, it is diffused in a region other than a predetermined illuminated region (long region), so that the light utilization efficiency of the light flux emitted from the light source is high. Not good. Moreover, in the illuminating device of patent document 2, a cost rise is caused by using the board | substrate which uses a surface and a back surface as a mounting surface. Further, in this conventional example, A shown in FIGS. 8 and 9 is 22 mm, B is 18 mm, and H is 30 mm. However, in order to reduce the illuminance unevenness shown in FIG. If the optical path length A is further increased, the apparatus height H is increased.

  Similarly, the illumination device of Patent Document 3 is also designed to increase the optical path length A from the light source to the illuminated region (long region) on the premise that the optical axis of the reading optical system is directly illuminated from one side. The length H is increased in size.

  The image reading apparatus is recently attached to the upper part of a laser printer or the like and is actively used as a multifunction machine. However, the thinning is a top priority from the viewpoint of barrier-free.

  An object of the present invention is to provide an image reading illumination device and an image reading device that can reduce unevenness in illuminance and achieve a reduction in thickness at a low cost.

  In order to achieve the above object, an image reading illumination device according to the present invention includes a plurality of light emitting elements provided apart from each other in the same direction as the long side direction of a long region on a document placement surface for image reading; A light beam emitted from the light emitting element is collected in a first cross section that includes a short side direction of the long region and is orthogonal to the document placement surface, and an angle formed with the document placement surface in the first cross section is 5 In order to form a condensing element that emits a light beam with an illumination optical axis that is not less than 40 degrees and not more than 40 degrees, and an optical path length that reduces illuminance unevenness in the long side direction of the long area, the Provided on the opposite side of the light emitting element and the light condensing element across a second cross section that includes the long side direction and is orthogonal to the document placement surface, and directs the light beam emitted from the light condensing element toward the long region And a reflective element that reflects the light.

  An image reading apparatus using the image reading illumination apparatus also constitutes another aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the illumination device for image reading which can reduce illumination intensity nonuniformity and can achieve thickness reduction cheaply, and an image reading apparatus using the same can be provided.

(A) is the schematic of the illuminating device for image reading which concerns on the 1st Embodiment of this invention, (b) is the largest optical path length from a light emitting element to a elongate area among the space | intervals adjacent to a light emitting element. It is explanatory drawing which shows the relationship of the angle width | variety which can obtain 60% or more of relative illuminance in the main scanning direction of a light emitting element at the space | interval Bmm, and (alpha) degrees. It is a graph which shows the main scanning illuminance distribution of the illuminating device for image reading which concerns on 1st Embodiment. It is the schematic of the illuminating device for image reading which concerns on 2nd Embodiment. It is a graph which shows the main scanning illuminance distribution of the illuminating device for image reading which concerns on 2nd Embodiment. It is the schematic of the illuminating device for image reading which concerns on 3rd Embodiment. It is a graph which shows the main scanning illuminance distribution of the illuminating device for image reading which concerns on 3rd Embodiment. It is sectional drawing which shows the structure outline | summary of the image reading apparatus carrying the illumination device for image reading which concerns on embodiment of this invention. It is the schematic of the conventional illuminating device for image reading. It is the schematic which shows the light source arrangement | positioning of the main scanning direction of the conventional illuminating device for image reading. It is a graph which shows the main scanning illuminance distribution of the conventional image reading illumination device.

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

<< First Embodiment >>
(Image reading device)
FIG. 7 is a cross-sectional view showing a schematic configuration of an image reading apparatus equipped with the image reading illumination device according to the embodiment of the present invention. Illumination light emitted from a light source 005 composed of a plurality of light emitting diodes LED (Light Emitting Diode) provided in the vertical direction (main scanning direction) in the drawing is irradiated on the original platen glass 001 which is the original placement surface. Illuminate the document placed in the.

  Then, the light beam having the image information reflected in the long region (the longitudinal direction is the same as the direction in which the light source 005 is arranged) on the document reading surface for image reading passes through the plurality of reflecting mirrors 006 and the imaging lens 007. Is imaged. That is, a long region is imaged on a one-dimensional photoelectric conversion element (for example, a CMOS array) 008 arranged in a direction perpendicular to the paper surface (main scanning direction). The carriage 001 reads the two-dimensional image of the document by the line sequential reading method while moving in the sub-scanning direction shown in the figure by the driving device 009.

(Image reading illumination device)
FIG. 1A is a schematic view of an image reading illumination device according to the first embodiment of the present invention. FIG. 1B shows the interval and angle characteristics of the light emitting element in the main scanning direction. That is, the optical path length from the light emitting element to the long region is A mm, the largest interval among adjacent intervals of the light emitting elements is B mm, and the angular width at which the relative illuminance is 60% or more in the main scanning direction of the light emitting elements is α °. Show the relationship. FIG. 2 is a graph showing the main-scanning illuminance distribution of the image reading illumination device according to this embodiment.

  In FIG. 1A, a plurality of LED chips 102 (side-view type LEDs) mounted on the substrate 101 emit light in the end face direction, and the positional relationship between the substrate 101 and the LED chips 102 is described in detail in FIG. It is the same as the conventional configuration. The light emitted from the LED chip 102 immediately enters the light collecting element 103 as a light distribution characteristic conversion element. The light condensing element 103 is a cylindrical lens surface having a flat incident surface facing the LED chip 102 and a curvature only in the sub-scan section (within the paper surface of FIG. 1A).

The light condensing element 103 is in close contact with the plurality of LED chips 102 at the plane portion and is long in the main scanning direction (perpendicular to the paper surface), whereby all the light emitted from the LED chip 102 is taken into the light condensing element 103. . The light beam condensed in the sub-scanning direction by the condensing element 103 that is a cylindrical lens travels along the illumination optical axis 011 and intersects the reading optical axis 010.
The illumination optical axis is set at an angle of 15 ° upward with respect to the document surface 002 and is condensed at the sub-scan section (in the paper surface of FIG. 1A), so there is no light toward the slit 003. It is.

  Without such a contrivance, for example, when a rectangular parallelepiped having no light condensing power in the sub-scanning direction is provided instead of the light condensing element 103 which is a cylindrical lens, a light beam emitted downward from the exit surface exists, and the slit 003 enter. Then, the light beam entering the slit 003 is difficult to separate from the reading light beam along the reading optical axis 010 and appears as a flare on the read image.

  As described above, the light beam that has entered the reflecting element 104 facing the reading optical axis 010 via the light condensing element 103 is reflected by the reflecting element 104 and then centered on the intersection of the reading optical axis 010 and the document surface 002. The reading area (long area) is reached and the reading area (long area) is illuminated. The reflection element 104 is a bending mirror that reflects incident light from a light source incident on each reflection surface at a different angle to the same reading region (long region).

  Here, in relation to the illuminance unevenness, FIG. 1B shows the interval and angle characteristics of the light emitting element in the main scanning direction. That is, the optical path length from the light emitting element to the long region is A mm, the largest interval among adjacent intervals of the light emitting elements is B mm, and the angular width at which the relative illuminance is 60% or more in the main scanning direction of the light emitting elements is α °. Show the relationship. The condition that the light from the light emitting elements adjacent to each other at the maximum interval contacts in the long region satisfies the following expression.

B / (2A) = tan (α / 2)
Accordingly, the condition that the light from the light emitting elements adjacent at the maximum interval overlaps in the long region satisfies the following expression.

B / (2A) ≦ tan (α / 2) (1)
In the present embodiment, it is preferable that the following conditional expression is satisfied.

20 ≦ A ≦ 50 (2)
Here, if the lower limit value of Equation 1 is satisfied, the degree of freedom of arrangement of each element can be maintained high, and if the upper limit value is satisfied, an increase in the size of the device can be prevented. Moreover, if the lower limit value of Expression 2 is satisfied, the light emitting elements can be arranged with a sufficient interval, and if the upper limit value is satisfied, the performance related to high image quality can be maintained high.

  More preferably, the following expression is satisfied.

B / (4A) ≦ 0.9 tan (α / 2) (3)
25 ≦ A ≦ 50 (4)
In the present embodiment, the optical path length A from the light source represented by A1 + A2 to the reading region (long region) is 28 mm, and the maximum distance B in the main scanning direction of the light source is 18 mm. The LED is NSSW108T manufactured by Nichia Corporation. In the present embodiment, the characteristics of the main scanning illuminance distribution with less ripples can be obtained as shown in FIG. Furthermore, the height H of the lighting device is 23 mm, which is significantly thinner than the conventional one.

<< Second Embodiment >>
In this embodiment described with reference to FIGS. 3 and 4, a diffusion element 105 is added to the first embodiment. The diffusing element 105 of the present embodiment has a main scanning cross section (second cross section that includes the long side direction of the long region and is orthogonal to the document placement surface), and a diffusivity that is greater than the diffusivity in the sub-scanning cross section This is a film-like element having diffusion characteristics as described above, and is LSD40 × 0.2PC10 manufactured by Lumint. The diffusivity in the sub-scan section (first section including the short side direction of the long area and perpendicular to the document placing surface) of the element is extremely small, and other than the long area (illuminated area). The effect of lowering the illumination efficiency due to the illumination can be minimized.

  Further, by sufficiently securing the optical path length from the LED chip 102 to the diffusing element 105, the surface of the diffusing element 105 becomes a secondary light source surface that emits light uniformly in the main scanning direction. The illuminance distribution in the region (illuminated region) is also good.

  Here, in relation to the illuminance unevenness, the optical path length from the light emitting element to the diffusing element is Cmm, the largest distance between adjacent light emitting elements is Bmm, and the relative illuminance is 80% or more in the main scanning direction of the light emitting element. The angle width is shown as a relationship of β °. The condition that the light from the light emitting elements adjacent to each other at the maximum interval comes into contact with the diffusing element satisfies the following expression.

B / (2C) = tan (β / 2)
Accordingly, the condition that the light from the light emitting elements adjacent to each other at the maximum interval overlaps with the diffusing element satisfies the following expression.

B / (2C) ≦ tan (β / 2) (5)
In the present embodiment, it is preferable that the following conditional expression is satisfied.

5 ≦ A−C ≦ 15 (6)
By satisfying the range of Expression 5, high image quality can be maintained, and by satisfying the upper limit of Expression 6, it is possible to reduce the size. If the value is below the lower limit of Equation 6, the distance between the platen glass and the diffusing element becomes narrow, which increases the number of parts such as providing a contact prevention mechanism, which is not preferable.

  More preferably, the following range is satisfied.

B / (4C) ≦ tan 0.9 (β / 2) (7)
6 ≦ A−C ≦ 12 (8)
In the present embodiment, C represented by A1 + C1 is 20 mm, A represented by A1 + A2 is 25 mm, and B is 18 mm. The height H of the lighting device is also 25 mm, which is thinner than the conventional one. The LED is NSSW108T manufactured by Nichia Corporation.

  The illumination optical axis on the LED chip is an angle of 15 ° upward with respect to the document surface 002. Using this condition, it is possible to obtain the characteristics of the main scanning illuminance distribution with little ripple as shown in FIG.

<< Third Embodiment >>
In the present embodiment described with reference to FIGS. 5 and 6, the image reading illumination device having the configuration described in detail in the second embodiment is arranged in two sets, a first set and a second set, symmetrically across the reading optical axis. To do. The first set includes a light source 102 as a first light emitting element provided on the left side of FIG. 5, a first condensing element 103, and a first reflecting element 104. A light beam emitted from the light source 102 as the first light emitting element is condensed on a first cross section (parallel to the paper surface) that includes the short side direction of the long region and is orthogonal to the document placement surface. In addition, the first condensing element 103 emits a light beam with an illumination optical axis whose angle with the original placement surface in the first cross section is not less than 5 degrees and not more than 40 degrees.

  Then, in order to form an optical path length that reduces illuminance unevenness in the long side direction of the long region, a second cross section (main scanning cross section) that includes the long side direction of the long region and is orthogonal to the document placement surface is sandwiched. Thus, the first reflective element 104 is provided on the opposite side of the first light emitting element and the first light condensing element. The first reflecting element 104 reflects the light beam emitted from the first light collecting element 105 toward the long region.

  The second set includes a light source 103 as a second light emitting element provided on the right side of FIG. 5 and spaced apart from each other in the same direction as the long side of the long region with the long region interposed therebetween, 2 condensing elements 103. And a second reflecting element provided on the opposite side of the second light emitting element and the second light condensing element across the second cross section.

  In the present embodiment, the illumination optical axis on the LED chip is set to 30 ° upward with respect to the document surface 002 to prevent the interference of components and the occurrence of flare. In this embodiment, C represented by A1 + C1 is 20 mm, A represented by A1 + A2 is 25 mm, and the maximum distance B between the light sources is 18 mm. The LED in the present embodiment is NSSW108T manufactured by Nichia Corporation.

  According to this condition, in this embodiment, the height H of the lighting device can be made 28 mm, which is thinner than the conventional one. Further, the characteristics of the main scanning illuminance distribution with less ripples can be obtained as shown in FIG.

  The table in which each parameter and conditional expression of the example in each embodiment and the conventional example can be compared collectively is shown below.

(Modification)
In the embodiment described above, the light condensing element is a cylindrical lens surface having a light incident surface that is flat and a light exit surface that has a curvature in the sub-scanning section. An anamorphic optical element having different curvatures in the scanning section may be used. In this case, it is assumed that the curvature of the main scanning section is gentle (the curvature radius is large) compared to the curvature of the sub-scanning section. As a result, light distribution characteristics can be given independently in the main scanning direction and the sub-scanning direction, and in particular, the illuminance distribution unevenness on the document surface is improved in the main scanning direction, and the light condensing property is improved in the sub-scanning direction. The necessary and sufficient amount of light can be ensured by increasing it.

002 ..Original, 003 ..Slit, 010 ..Reading optical axis, 011 ..Illumination optical axis, 102 ..LED chip (light emitting element), 102 ..Condensing element, 104 ..Reflecting element, 105. Diffusion element

Claims (11)

A plurality of light emitting elements provided apart from each other in the same direction as the long side of the long region on the document placement surface for image reading;
A light beam emitted from the light emitting element is collected in a first cross section that includes a short side direction of the long region and is orthogonal to the document placement surface, and an angle formed with the document placement surface in the first cross section is 5 A condensing element that emits a light beam with an illumination optical axis that is at least 40 degrees and at most 40 degrees;
In order to form an optical path length that reduces illuminance unevenness in the long side direction of the long region, the second cross section including the long side direction of the long region and orthogonal to the document placement surface is sandwiched between A reflective element that is provided on the opposite side of the light-emitting element and the light-collecting element, and reflects a light beam emitted from the light-collecting element toward the long region;
An illumination device for reading an image characterized by comprising: The optical path length from the light emitting element to the long region is Amm,
The largest interval among adjacent intervals of the light emitting elements is Bmm,
When the angle width at which a relative illuminance of 60% or more can be obtained in a plane parallel to the second cross section of the light emitting element is α °,
The image reading illumination device according to claim 1, wherein the following conditional expression is satisfied.
B / (2A) ≦ tan (α / 2)
20 ≦ A ≦ 50 The image reading illumination device according to claim 2, wherein the following conditional expression is satisfied.
B / (4C) ≦ tan 0.9 (β / 2)
6 ≦ A−C ≦ 12   4. The image reading illumination device according to claim 1, wherein the condensing element is an anamorphic optical element having different curvatures in the first cross section and the second cross section. 5. .   5. The illumination device for image reading according to claim 4, wherein the anamorphic optical element is a cylindrical lens surface having a flat light incident surface and a curvature only in the second cross section.   6. The image reading illumination device according to claim 1, further comprising a diffusing element that diffuses a light beam reflected by the reflecting element toward the long region.   The diffusion element has different diffusion characteristics in the first cross section and the second cross section, and a diffusivity in the second cross section is larger than a diffusivity in the first cross section. The image reading illumination device according to claim 6. The largest interval among adjacent intervals of the light emitting elements is Bmm,
An optical path length from the light emitting element to the diffusion element is Cmm,
When the angle width at which a relative illuminance of 80% or more can be obtained in a plane parallel to the second cross section of the light emitting element is β °,
The image reading illumination device according to claim 6, wherein the following conditional expression is satisfied.
B / (2C) ≦ tan (β / 2)
5 ≦ A−C ≦ 15 The illumination device for image reading according to claim 8, wherein the following conditional expression is satisfied.
B / (4C) ≦ tan 0.9 (β / 2)
6 ≦ A−C ≦ 12 A plurality of first light emitting elements provided apart from each other in the same direction as the long side direction of the long region on the document placement surface for image reading;
The light beam emitted from the first light emitting element is collected in a first cross section including the short side direction of the long region and orthogonal to the document placement surface, and forms the document placement surface in the first cross section. A first condensing element that emits a light beam with an illumination optical axis having an angle of 5 degrees or more and 40 degrees or less;
In order to form an optical path length that reduces illuminance unevenness in the long side direction of the long region, the second cross section including the long side direction of the long region and orthogonal to the document placement surface is sandwiched between A first reflective element that is provided on the opposite side of the first light emitting element and the first light condensing element and reflects the light beam emitted from the first light condensing element toward the long region;
A plurality of second light emitting elements that are spaced apart from each other in the same direction as the long side of the long region across the long region;
The light beam emitted from the second light emitting element is condensed in the first cross section including the short side direction of the long region and orthogonal to the original document placement surface, and in the first cross section, the original document placement surface and A second condensing element that emits a light beam with an illumination optical axis that has an angle of 5 degrees to 40 degrees;
Provided on the opposite side of the second light emitting element and the second light condensing element across the second cross section in order to form an optical path length that reduces illuminance unevenness in the long side direction of the long region. A second reflecting element that reflects the light beam emitted from the second light collecting element toward the long region;
An illumination device for reading an image characterized by comprising: An image reading apparatus using the image reading illumination device according to claim 1.