JP4423095B2 - Document illumination device, image reading device, color document reading device, and image forming device - Google Patents

Description

The present invention relates to a document illumination device used for a digital copying machine or an image scanner .

In recent years, light emitting diodes (hereinafter referred to as LEDs) have been actively developed, and the brightness of LED elements has increased rapidly. LEDs generally have advantages such as long life, high efficiency, high G resistance, and monochromatic light emission, and are expected to be applied in many lighting fields.
As one of the applications, LEDs are used in a document illumination device of an image reading device such as a digital copying machine or an image scanner .

As an image forming apparatus having an image reading apparatus, the following is well known.
The image forming unit is provided with a charging roller, a developing device, a transfer roller, and a cleaning device as charging means around a drum-shaped latent image carrier. A “corona charger” can also be used as the charging means.
  An optical scanning device such as an image reading unit that receives external document information and performs optical scanning with a laser beam is provided, and “exposure by optical writing” is performed between the charging roller and the developing device.

When forming an image, the image carrier, which is a photoconductive photosensitive member, is rotated at a constant speed, the surface thereof is uniformly charged by a charging roller, and a negative electrostatic latent image is formed by optical writing of a laser beam of an optical scanning device. The negative electrostatic latent image is formed and reversely developed by a developing device to form a toner image.
  The uppermost sheet of transfer paper stored in a cassette that is detachably attached to the image forming apparatus main body is fed by a paper feed roller, fed to a transfer unit by a pair of registration rollers, and superimposed on the toner image in the transfer unit. After the toner image is electrostatically transferred by the transfer roller, the toner image is fixed by the fixing device, and is discharged onto the tray by the pair of discharge rollers through the conveyance path.
  The surface of the image carrier after the toner image is transferred is cleaned by a cleaning device to remove residual toner, paper dust, and the like.

The following are well known for reading images.
  In other words, the original is placed on the contact glass, the original is illuminated by an illumination unit integrated with the first traveling body disposed below the contact glass, and the reflected light from the original is reflected by the first traveling body. After being reflected in parallel with the traveling direction, the light is incident on a second traveling body in which two reflecting surfaces are orthogonally combined and reflected by the two reflecting surfaces in parallel with the traveling direction of the second traveling body. Then, the light is incident on a reduction imaging lens fixed in the apparatus and imaged on the line sensor.

The first traveling body is moved in parallel with the document surface at a speed: V, the original surface is illuminated and scanned, the second traveling body is moved at a speed: 1/2 V, and the imaging light flux reaches from the document surface to the reduction imaging lens. Keep the optical path length unchanged and read the entire document.
Normally, a document illumination device used for an image reading device requires a length substantially the same as the document width in order to illuminate a document. Therefore, as a method of using an LED as a document illumination device, a large number of LED elements are used. Use them in an array.
However, although LEDs have excellent characteristics as described above, since the absolute brightness of each element is insufficient for use as an illumination device of an image reading device, a low-speed reading device, It is mainly used for devices that emphasize compactness, and cold cathode fluorescent lamps are mainly used for high-speed reading devices and large devices.

In order to compensate for this problem, it is common to increase the amount of light in the LED array by using a large number of LED elements constituting the LED array. However, since the light diffuses widely, it is not very efficient. It goes against power saving. In addition, when a bullet-like LED with less diffusion is used, the efficiency is improved, but the directivity is high and unevenness occurs in the main scanning direction.
For the purpose of improving light utilization efficiency, there is a proposal for a document illumination device combining an LED array and a long lens (see, for example, Patent Document 1 and Patent Document 2). Usually, the light of an LED is intended to increase efficiency by converging on the sub-scan section of each LED. However, when such a method is used, there is a problem that the central portion of the convergent light is bright as shown in the drawing of Patent Document 1, and light is diffused and rapidly darkened at a position off the center. Of the light emitted from the LEDs, most of the light emitted with an angle in the sub-scanning cross section is wasted. Therefore, if a large number of LEDs are not arranged, illuminance unevenness in the main scanning direction occurs.
There is an invention of the present applicant that eliminates illuminance unevenness in the main scanning direction (see Patent Document 3). However, Patent Document 3 does not mention a condensing method in the sub-scanning direction. In addition, the present applicant has previously proposed a configuration in which an optical element has a light guide having an incident surface in the vicinity of a light beam exit surface of a point light source and an exit surface facing a reading region (Japanese Patent Application 2003). -140927). According to this configuration, the target illuminance distribution can be obtained satisfactorily. However, since the reflector is used in addition to the light guide, the configuration is somewhat complicated, and the cost tends to increase accordingly.

In order to solve these problems, the applicant of the present invention appropriately arranges a light source unit in which a plurality of LEDs having a predetermined light distribution is arranged and a long lens that does not converge in the sub-scanning cross-sectional direction. By converging the incident light not on the document surface position on the sub-scan section of each LED but on the document surface position having an angle in the main scanning direction with respect to the sub-scan section,
In the sub-scanning direction, the light convergence is high and the NA can be brightened.
In the main scanning direction, a document illumination device (Japanese Patent Application No. 2004-052253) has been proposed in which there is little loss due to light diffusion and less illuminance unevenness even with a relatively small number of LEDs.

JP-A-11-232912 JP-A-8-111545 Japanese Patent Laid-Open No. 10-322521

  However, although the present invention has the advantages as described above, it adopts a method of converging light sharply at the position of the original surface. There is a possibility that the amount of light that reaches will greatly change and greatly affect the formed image. For this reason, in a digital copying machine or an image scanner, it is desirable to have a document illuminating device in which the illuminance distribution curve in the sub-scanning-corresponding direction is wide to some extent and the illuminance difference in the reading area does not occur even when the center position of the illumination deviates from the reading unit. . For this purpose, in the vicinity of the maximum value of the illuminance distribution, a portion with a small illuminance unevenness that is a width (for example, about 1 mm on one side) or more obtained by adding a fluctuation width due to a mechanical error to a width necessary for reading, that is, a flat illuminance There should be a part.

According to the first aspect of the present invention, when a surface to be illuminated having a length and a width, the length direction is a main scanning direction, and the width direction is a sub-scanning direction, a plurality of LEDs emit light in the main scanning direction. a light source unit which is arrayed as elements, the disposed between the light source unit and the illumination target surface, the main scanning direction in the longitudinal direction of the convergence-matched long cylinder lens (hereinafter simply "long lens In the document illuminating apparatus that irradiates the irradiated surface with the light beam from the light source unit through the long lens, the passage of the light beam in the cross section in the sub-scanning direction of the long cylinder lens is provided. The surface facing the light source unit is R1, and on the cross section in the sub-scanning direction including the light emitting element end surface of the light source unit, the distance between the position of the light emitting element end surface and the R1 surface is D (LED), the R1 surface side When the distance from the focal position to the R1 surface and D (BF), formula D (LED) <D (BF)
It is characterized by satisfying .

According to a second aspect of the present invention, in the original illuminating device according to the first aspect, the emitted light of each of the plurality of light emitting elements is diverged by a long cylinder lens in a sub-scanning direction cross section including the end face of the light emitting element. In the direction of a predetermined afocal angle θp with respect to the cross section in the sub-scanning direction, the light becomes parallel light when viewed from the main scanning direction .

According to a third aspect of the present invention, in the original illuminating device according to the second aspect, the illuminance ratio is η (0 <η <1), and the illumination width of the illuminance ratio η in the sub-scanning section is W0 (η), When the illumination width of the illumination ratio η at the afocal angle is Wθp (η),
W0 (η) > Wθp (η)
Is satisfied .
According to a fourth aspect of the present invention, in the original illuminating device according to the second or third aspect, the afocal angle θp is set within a half-value angle of a light distribution of the light emitting element .

According to the fifth aspect of the present invention, a plurality of LEDs are arranged as light emitting elements in the main scanning direction when the illuminated surface having a length and a width, the length direction is the main scanning direction, and the width direction is the sub scanning direction. A light source unit, a long cylinder lens disposed between the surface to be illuminated and the light source unit, the longitudinal direction of which coincides with the main scanning direction, and the light beam from the light source unit is converted into the long cylinder lens. In the original illuminating apparatus that irradiates the irradiated surface with convergence by the light emitted from each of the plurality of light emitting elements is transmitted through the long cylinder lens and then parallel in the sub-scanning direction cross section including the end face of the light emitting element. becomes light, becomes convergent light as viewed from the main scanning direction in the sub scanning cross section with respect to a predetermined convergent angle θf becomes direction, the illumination light, in the sub-scanning direction, run sub at the convergence point to converge to the surface to be illuminated When the direction of the light-emitting element imaging magnification was beta,
β> 1
It is characterized by satisfying.
The invention according to claim 6 is characterized in that, in the document illuminating device according to claim 5, the convergence angle θf is set within a half-value angle of a light distribution of the light emitting element.

According to a seventh aspect of the present invention, in the document illuminating device according to any one of the first to sixth aspects, a length connecting both ends of the plurality of light emitting elements is longer than a length of the illuminated surface. Features.
According to an eighth aspect of the present invention, in the document illuminating device according to any one of the first to sixth aspects, an interval between the plurality of light emitting elements is P0, which is the distance between the light emitting elements closest to the center. N ≧ 1, and when the interval between any light emitting elements up to the light emitting element closest to the end is Pn,
Pn-1 ≧ Pn
0.2 ≦ Pn / P0 ≦ 1
It is characterized by satisfying the relationship of
According to a ninth aspect of the present invention, in the document illuminating device according to any one of the first to eighth aspects , the LED as the light emitting element is a one-chip type white light emitting diode using a phosphor. Features.

According to a tenth aspect of the present invention, in the document illuminating device according to any one of the first to eighth aspects , the LED as the light emitting element uses two or more chips each having a different light emission color. It is a white light emitting diode that emits white light by mixing colors.
According to an eleventh aspect of the present invention, in the document illuminating device according to any one of the first to tenth aspects, the long cylinder lens has a cross section of at least one of the light incident surface and the light exit surface of the sub-scanning section. It has an elliptic arc shape .
According to a twelfth aspect of the present invention, there is provided an image reading apparatus using the document illumination device according to any one of the first to eleventh aspects.
According to a thirteenth aspect of the present invention, there is provided a color original reading device using the original illumination device according to any one of the first to eleventh aspects.
According to a fourteenth aspect of the present invention, there is provided an image forming apparatus using the image reading device according to the twelfth aspect.
According to a fifteenth aspect of the present invention, there is provided an image forming apparatus using the color original reading device according to the thirteenth aspect.

  According to the present invention, the illuminance unevenness in the main scanning direction in the document illumination device having a linear illuminated area is further reduced as compared with the conventional art, and the document and image can be read with high quality.

1 and 2 are views for explaining the operation of the long lens of the present invention. 1 is a longitudinal sectional view, and FIG. 2 is a transverse sectional view.
In the figure, reference numeral 1 denotes a point light source, 2 denotes a cylinder lens as a long lens, and 3 denotes a contact glass placed in front of the surface to be illuminated.
The light incident surface 2a of the long lens 2 is disposed in the vicinity of the light emitting surface of the point light source 1, and the illuminated surface is disposed at a position away from the light emitting surface 2b of the lens by a predetermined distance. The surface to be illuminated is made to coincide with the surface 3b (hereinafter referred to as the back surface) of the contact glass 3 opposite to the point light source.
The point light source 1 is a light source having a very small light emission point, such as an LED, and the light emission point size can be regarded as a point as compared to the paper width when an A4 size or the like is considered as an illuminated surface. .

As shown in FIG. 2, the long lens 2 is long in one direction and the cross section orthogonal to the longitudinal direction has the same lens shape in all positions as shown in FIG. . That is, the long lens is a “long cylinder lens”. Hereinafter, the long lens may be simply referred to as a lens.
Such an illuminating device is used in a digital copying machine or an image scanner. In that case, one direction of the document is made to coincide with the longitudinal direction of the long lens 2 and is brought into close contact with the back surface 3b of the contact glass 3. Since the illumination light is condensed into a line along the longitudinal direction, the entire document surface cannot be read simultaneously. Therefore, the document surface and the illumination device must be moved relatively along the other direction of the document. Here, the linear direction of illumination light is called a main scanning direction, and the relative movement direction is called a sub-scanning direction. FIG. 1 shows a “cross section in the sub-scanning direction”. The section in the sub-scanning direction simply exists infinitely, but in the following description, it is “a section in the sub-scanning direction including the light emitting source in the light source unit” . Hereinafter, the “sub-scanning direction cross section” is also referred to as “sub-scanning cross section”.

In this configuration, in the sub-scan section, the emitted light from the LED becomes divergent light through the long lens and illuminates the document surface. That is, the virtual image of the point light source 1 by the lens 2 is formed below the point light source 1 in FIG.
On the sub-scan section including the light emitting element end surface of the light source unit, the distance between the LED end surface and the R1 surface: D (LED), and the distance from the focal position on the R1 surface side to the R1 surface: D (BF) is “D Since (LED) <D (BF) ”, the image of the LED end face by the lens 2 is a virtual image in the sub-scan section, and the light beam that has passed through the long lens is“ divergent on the sub-scan section ”. Become.
That is, in the sub-scan section, the light beam transmitted through the long lens 2 is divergent as shown by a solid line in FIG. The starting point of divergence when the divergent light beam is extended to the light source side while ignoring the long lens 2 is the “virtual image of the point light source 1”.
However, the light beam emitted in the “direction shown by the broken line” in FIG. 2 is not a divergent light beam after exiting the lens but rather a parallel light beam.
It was shown by the broken line in FIG. 1, a lens 2 ', a contact glass 3', and the light beam shows a state in cross-section along the dashed line in FIG. As described above, the phenomenon of parallel light originates from the fact that the curvature of the apparent incident surface and exit surface for the light beam increases because the light beam transmits obliquely through the long lens 2.
In FIG. 2, θp is shown as an angle at which the luminous flux is parallel on the surface to be illuminated (this angle is referred to as an afocal angle for convenience). Hereinafter, generally, the angle formed by the light beam emitted from the cross section perpendicular to the paper surface and the sub-scanning cross section in the figure is θ, and such a light beam is referred to as an oblique light beam.
As described above, according to this configuration, all the light beams emitted from the point light source do not become diverging light with respect to the document surface, but there are light beams that are parallel to the document surface. An outline of the change of the focal position in the main scanning direction is shown by a two-dot chain line in FIG.
As the angle θ of the oblique light beam emitted from the point light source increases, the image Ii of the point light source that was initially a virtual image gradually becomes farther, and finally becomes infinite (parallel light beam) at θp. This is the reason why θp is called an afocal angle. If θ becomes larger than the non-focal angle θp, this time, the image becomes a real image Ir and approaches the contact glass from infinity on the opposite side. Zp is an asymptotic line of Ii and Ir.

FIG. 3 is a diagram for explaining the configuration of the prior application.
In the prior application, when the skew angle θ is set to 0, the light beam becomes a parallel light beam, and the angle around the θp is named a convergence angle θf, and is set so that the light beam converges at θf. That is, the image I of the light source becomes infinite on the sub-scanning section including the light source, and as the skew angle becomes larger than that, the real image Ir approaches the contact glass 3 almost along the asymptotic line Zp and converges. It reaches the contact glass back surface 3b at the angle θf. As the skew angle θ further increases, the real image enters the contact glass surface.
However, there is a slight difficulty in obtaining a flat illuminance distribution in the main scanning direction because the energy concentrates too much at the convergence point where the luminous flux viewed from the main scanning direction converges on the back surface of the contact glass, that is, the illuminated surface. I understood that. There are two ways to solve this problem. That is, one of them is a method of preventing the convergence point in the main scanning direction from entering the effective area. This is the reason why the present invention employs the configuration shown in FIGS. The other one is to increase the magnification ratio of the light source image, that is, the light emitting element imaging magnification in the sub-scanning direction is set to β as an enlargement magnification (β> 1) so that the energy is not concentrated in a narrow range. It is a method to do. This method will be described in an example described later. In addition to this, a method of enlarging the light emitting element itself is also conceivable, but considering that a commercially available product is used as the light source, it is not a good idea to prepare an LED having a particularly large light emitting area.

FIG. 4 is a diagram showing a configuration in consideration of the actual use state.
In the figure, only the sub-scan section including the light source is shown. Since the scanning optical system needs to optically read the surface to be illuminated, the scanning optical system is configured to illuminate obliquely and read from the front. This figure also shows the configuration of Example 1 described later.
FIG. 5 is a schematic view showing a cross section along the optical path including the principal ray.
In the figure, only the surface to be illuminated is replaced with a view seen from the front. Such a diagram is hereinafter referred to as an irregular plan view for convenience. This figure also shows the basic configuration of the first embodiment.
The light beam on the sub-scanning cross section enters the surface to be illuminated as a divergent light beam. Then, the light enters the surface to be illuminated as a parallel light beam at a position of θp = 45 °.
The contact glass 3 is formed of a glass plate having a width of 20 mm and a length of 50 mm, for example, and a central portion of about 2 mm in width is used as a reading area. The width in the sub-scanning direction of the CCD as the image reading means is approximately 1 mm in terms of the position of the illuminated area in the case of a three-color CCD. In consideration of component manufacturing errors, assembly errors, etc., the illumination width has a margin and the reading area is 2 mm. Therefore, if this area is set within an allowable range of uneven illuminance, a high-quality image can be obtained. The illuminance unevenness uses a ratio of the difference between the maximum illuminance and the minimum illuminance to the maximum illuminance as a percentage, and the allowable value is preferably 12% or less when a color image is read. When reading monochrome images, up to about 30% is acceptable.
The chief ray is a ray passing through the optical axis of the lens, and usually the direction of emission of the maximum radiant energy of the light source is made to coincide with the optical axis of the lens.

FIG. 6 is a diagram illustrating an example in which the light distribution of the point light source is a Lambertian distribution.
In the figure, reference numeral 8 denotes a point light source, and 9 denotes a light distribution.
When the intensity distribution of the light energy emitted from the point light source is spherical Q, it is called a Lambertian distribution. The distribution in the figure shows a cross-sectional view. In the case of this distribution, the maximum energy is emitted in the direction normal to the surface of the light source. Assuming that the radiation direction of the maximum energy E is θ = 0 °, as the θ increases, the light energy of the luminous flux radiated in the angular direction decreases, and becomes 1 / 2E (half value) of the maximum value at θh = 60 °. The solid angular energy emission is reduced by a factor of four. θh = 60 ° is called a half-value angle of this distribution. Most of the radiant energy is radiated within this half-value angle.

The specifications of this example are shown below.
Cylinder lens R1 = ∞
R2 = −4.3 (ellipsoidal, conical multiplier K = −0.467)
Center thickness: 7.2 (mm)
Width in the main scanning direction: 100 (mm)
Material: nd = 1.491 νd = 57.2
LED light distribution: Lambert distribution
Intensity distribution on light emitting surface: uniform
Light emitting surface size: 1 (mm) x 1 (mm)
Quantity: 9 (pieces), 10 (mm) pitch
Efficiency: 1 (W) x 9
Contact glass Center thickness: 3.2 (mm)
Material: nd = 1.517 νd = 64.2
Positional relationship D (LED): 1 (mm)
D (BF): 3.93 (mm)
Distance between cylinder lens R2 surface and contact glass: 10 (mm)
Cylinder lens optical axis and contact glass tilt: 30 degrees Illuminated surface (document surface): on contact glass surface
Width 20mm, length 50mm
D (BF) is uniquely determined from the specifications of the cylinder lens .

FIG. 7 is an irregular plan view showing the configuration of the first embodiment.
In the present embodiment, the afocal angle θp is set to 45 °. That is, the light emitted from each LED in the direction of θp = 45 ° with respect to the sub-scanning cross section becomes parallel light after exiting the lens, and passes through the contact glass back surface 3b as the illuminated surface as parallel light. Is set. The reason why θp is set to 45 ° is that the relationship with the half-value angle θh of the light distribution of the light emitting element is taken into consideration. This is because the Lambert distribution has a half-value angle θh = 60 °, and if θp is set to be larger than this, the illuminance in the main scanning region having an angle larger than θp may be significantly reduced. The degree of the relationship between θp and θh depends on other conditions and cannot be uniquely determined, but at least θp ≦ θh is required.
FIG. 8 is a diagram for explaining the illuminance distribution of the first embodiment.
In this figure, the light emitted from the light source in consideration of the light distribution is regarded as the illuminance of the area by the number of light incident on each area obtained by equally dividing the surface of the contact glass into a 1 mm square mesh. is there.

Curves Gm1 and Gm2 represent the illuminance distribution in the main scanning direction by selecting the area having the highest illuminance on average in the main scanning direction as the center area of the illumination and determining the central area of the illumination. Each curve represents a width of 1 mm in the sub-scanning direction. Accordingly, the illuminance state of the reading area of 2 mm width can be understood from these two curves.
The ratio of the minimum value of illuminance to the maximum value in the region of Gm1 to Gm2 was 89.6%. This is 10.4% in terms of illuminance unevenness, and the illuminance unevenness allowed when reading a color document is about 12%. In the present embodiment, a reading area having a width of 2 mm can be secured.
FIG. 9 is a diagram for explaining the illuminance distribution in the sub-scanning direction.
The illuminance distribution in the sub-scanning direction at the center position in the main scanning direction is a curve Gs1. The illuminance distribution at a position 3 mm away from the center position toward the end in the main scanning direction is the curve Gs2, and the illuminance distribution at a position further 2 mm away (5 mm from the center) is the curve Gs3. Since the arrangement pitch of the LEDs is 10 mm intervals, the illuminance distribution repeats substantially the same distribution at the same 10 mm intervals. Accordingly, the graph is replaced in reverse order beyond the position of 5 mm, and this is equivalent to repeating the graph. Therefore, if the range of the main scanning direction region of 0 to 5 mm is confirmed, almost the entire illuminance distribution can be estimated. However, it is a condition that the illuminance distribution in the main scanning direction is stable from end to end. The illuminance unevenness in the 5 mm width range is less than 10%. In this graph, it can be seen that an area having a width of 2 mm including the maximum value at the center can be used as a reading area.

FIG. 10 is a diagram showing the illuminance distribution by one light source.
This figure shows the relative illuminance distribution on the surface to be illuminated when one LED is placed in the center of the main scanning direction. The contours are drawn equally with a maximum illuminance of 1 and no illuminance of 0, and an illuminance ratio of 0.1 unit. The thick line is a contour line with an illuminance ratio of 0.5. The horizontal axis (x coordinate) is the coordinate in the main scanning direction where the light source position is x = 0. The vertical axis (y-coordinate) is the coordinate in the sub-scanning direction where the center in the width direction of the contact glass is y = 0.
From this figure, the difference in illumination width in the main scanning direction with a single LED can be seen well. Here, the illumination width is defined as the width seen in the sub-scanning direction in the designated contour line region in FIG. In order to express the designated contour line, the illuminance ratio is displayed in% and written before the illumination width. For example, the 50% illumination width of the position (x = 0) of the surface to be illuminated corresponding to the position of the light source is approximately 14 mm, one of which is cut at the edge of the contact glass. In contrast, the 20% illumination width is 20 mm because both sides are cut at the edge of the contact glass. In this case, the 10% illumination width is the same 20 mm.
In order to see the illumination width corresponding to the afocal angle θp, it is only necessary to look at the contour line in the sub-scanning direction at the position of x = 16.5 mm. Since the thick line shown above is not applied to this position, the 50% illumination width is 0 mm and the 20% illumination width is approximately 11 mm. Incidentally, when the 10% illumination width is seen, it is about 12 mm.
Since the illumination width is a function of the illuminance ratio with respect to the maximum illuminance in this way, the illumination width in the sub-scan section is set as W0 (η) with the illuminance ratio being η (<1), and the illumination width at the non-focal angle θp is Wθp ( η), at any η, W0 (η)> Wθp (η)
Is true.

In Example 2, only the R2 surface (= -4.3) of the cylinder lens in the specification of Example 1 was changed to increase the light collecting ability.
R2 = -3.4mm
As a result of this change, D (BF) = 2.1 mm.
As a result of this change, the light flux in the sub-scanning section is slightly divergent although it is divergent light. The afocal angle θp in this configuration is θp = 37 °, and the position in the main scanning direction where the light beams are parallel is 12.9 mm from the center.
11 to 13 are diagrams for explaining the results of Example 2. FIG. These drawings correspond to FIGS. 8 to 10 in the first embodiment.

14 and 15 are diagrams for explaining the results of Example 3. FIG. These figures correspond to FIGS. 8 and 9 in the first embodiment.
In the third embodiment, the curvature specification of the surface of the cylinder lens and the distance to the contact glass are changed among the specifications of the first embodiment.
Cylinder lens R1 = 10
R2 = −2.887 (ellipsoidal, conical multiplier K = −0.837)
Distance between cylinder lens R2 surface and contact glass: 20 (mm)
With the above change, the convergence angle θf is θf = 35 mm, and the position of the convergence point in the main scanning direction is 19 mm from the center.
As shown in FIG. 14, in the present embodiment, when the both ends of the main scanning direction exceeds ± 17 mm, the illuminance is clearly reduced. Therefore, in order to expand the effective illumination area, it is necessary to take measures such as further increasing the number of light sources on the peripheral side or increasing the arrangement density of the light sources toward the periphery.
In the region of ± 17 mm, as shown in FIG. 15, when a reading area of 2 mm is secured, the illuminance unevenness is about 11% and can be used as a reading area.

16 to 18 are diagrams for explaining the fourth embodiment.
As shown in FIG. 16, in the present embodiment, the module is reduced in size by inserting a reflecting mirror M between the cylinder lens of the third embodiment and the document surface.
Reflector related specifications are shown.
Between cylinder lens and reflector: 15.6 mm
Reflector size: 100 mm (main scanning direction) × 10 mm (sub-scanning direction)
Reflector tilt: 26.57 degrees Contact glass position:
The 3a surface is arranged parallel to the optical axis of the cylinder lens and 15 mm from the optical axis. When converted into the same expression as in Example 3 based on these conditions, the distance between the cylinder lens R2 surface and the contact glass: 34.4 ( mm)
The optical axis of the cylinder lens and the inclination of the contact glass: 36.86 degrees. Even with this change, the convergence angle θf did not change, and the convergence point became far. The distance from the center of the convergence point in the main scanning direction was 32.7 mm.

  As shown in FIG. 17, as compared with Example 3, the amount of light in the periphery is more noticeable as the cylinder lens is further away from the contact glass. Instead, the spread of the light beam in the sub-scanning direction is increased, and the change in the sub-scanning direction is very small in the 2 mm width as the reading area. As shown in FIG. 18, there is not much difference in the range from 0 mm to 5 mm, and the influence of the arrangement pitch of the light sources is hardly seen.

FIG. 19 is a diagram illustrating an example of the interval between the light emitting elements of the light source unit.
In the same figure, the code | symbol P shows the light emitting element interval.
The arrangement interval of the plurality of light emitting elements is set such that the interval between the light emitting elements closest to the center is P0, n ≧ 1, and the interval between arbitrary light emitting elements to the light emitting element closest to the end is Pn.
Pn-1 ≧ Pn
0.2 ≦ Pn / P0 ≦ 1
It is configured to satisfy the above relationship at the same time.
Even in the illuminance distribution shown in FIG. 17, the illuminance is slightly reduced at both ends in the main scanning direction. This is considered to be because the main scanning direction end of the illuminated surface receives only the light beam from the center side of the position. In order to solve this problem, the above configuration is adopted.
In the embodiments so far, the target is to make the illuminance of the illuminated surface uniform. However, depending on the characteristics of the reading optical system, there may be a shortage of peripheral light amount called so-called shading. This configuration can also be used to obtain a lighting device that takes shading correction into account. As described above, by increasing the arrangement density of the light emitting elements toward the end in the main scanning direction, the peripheral light amount is made larger than the central portion, and as a result, the light amount that has passed through the reading optical system is made uniform.

The specific example of arrangement | positioning which makes the illumination intensity distribution in a to-be-illuminated surface uniform is shown.
The total number of light emitting elements is 15, and the arrangement interval P0 of the light sources closest to the center is 6.2 mm.
From the next light emitting element toward the end, the interval is reduced by 0.3 mm each up to the second one, and the outside is successively narrowed by 0.4 mm. Therefore, the distance between the outermost (seventh) light emitting element and the innermost light emitting element is 4 mm, and the distance between the centers of the outermost light emitting elements is 72.2 mm, which is longer than the length of the illuminated surface (50 mm). . As a result, the edge in the main scanning direction of the surface to be illuminated receives light from a light source having a high arrangement density and also receives light from the outside as well as from the center, thereby eliminating peripheral illuminance reduction. The
In the above description, the length of the surface to be illuminated has been discussed as 50 mm. However, when actually applied to a reading device or the like, measures such as increasing the number of light emitting elements so as to correspond to a desired document width are used. Take.

Next, a light source that can be used in the present invention will be described.
In the present invention, the light source is most suitably a light emitting diode (LED). Among them, it is preferable to use a white LED in order to be able to handle reading of any document.
There are several types of white LEDs. One of them is a one-chip type white LED using a phosphor. A light emitting unit called a chip is sealed in a transparent enclosing member mixed with a YAG phosphor. The chip emits blue light made of InGaN. Thereby, when the chip emits blue light, the phosphor is simultaneously excited to emit yellow fluorescence. Since blue and yellow are complementary to each other, when both go out together, they are recognized as white light.
As another type, there is a white light-emitting diode that does not use a phosphor and uses two or more chips that emit different colors and emits white light by color mixture. The plurality of chips are arranged on the same surface, and are combined to be recognized as white when all the emission colors are mixed.
For example, in the case of two chips, chips that emit blue and yellow light are used as described above. In the case of three chips, chips that emit red, green, and blue corresponding to so-called three primary colors are used.

It is a figure for demonstrating an effect | action of the elongate lens of this invention. It is a figure for demonstrating an effect | action of the elongate lens of this invention. It is a figure for demonstrating the structure of a prior application. It is a figure which shows the structure which considered the actual use condition. It is the schematic which shows the cross section along the optical path containing a chief ray. It is a figure which shows the example whose light distribution of a point light source is a Lambert distribution. 3 is an irregular plan view showing the configuration of Example 1. FIG. It is a figure for demonstrating the illumination intensity distribution of Example 1. FIG. It is a figure for demonstrating the illumination intensity distribution of a subscanning direction. It is a figure which shows the illumination intensity distribution by one light source. It is a figure for demonstrating the result of Example 2. FIG. It is a figure for demonstrating the result of Example 2. FIG. It is a figure for demonstrating the result of Example 2. FIG. It is a figure explaining the result of Example 3. FIG. It is a figure explaining the result of Example 3. FIG. FIG. 10 is a diagram for explaining a fourth embodiment. FIG. 10 is a diagram for explaining a fourth embodiment. FIG. 10 is a diagram for explaining a fourth embodiment. It is a figure which shows the example of the space | interval of the light emitting element of a light source unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emitting element 2 Long lens 3 Contact glass

Claims (15)

A surface to be illuminated having a length and a width; and a light source unit in which a plurality of LEDs are arranged as light emitting elements in the main scanning direction when the length direction is a main scanning direction and the width direction is a sub scanning direction. And a converging long cylinder lens disposed between the illuminated surface and the light source unit, the longitudinal direction of which coincides with the main scanning direction, and emits light from the light source unit to the long cylinder In a document illumination device that irradiates the irradiated surface through a lens,
The light-emitting element on the cross-section in the sub-scanning direction including the light-emitting element end face of the light source unit, where R1 is a surface facing the light source unit among the light beam passage planes in the cross-section in the sub-scanning direction of the long cylinder lens. When the distance between the position of the end surface and the R1 surface is D (LED) and the distance from the focal position on the R1 surface side to the R1 surface is D (BF), the formula D (LED) <D (BF)
Document illumination device characterized by satisfying the above . The document illumination device according to claim 1,
The light emitted from each of the plurality of light emitting elements becomes divergent light in a sub-scanning direction section including the end face of the light emitting element by a long cylinder lens, and in a direction having a predetermined afocal angle θp with respect to the sub-scanning direction section. Is a document illuminating device characterized by being parallel light as viewed from the main scanning direction . The document illumination device according to claim 2,
When the illumination ratio is η (0 <η <1), the illumination width of the illumination ratio η in the cross section in the sub-scanning direction is W0 (η), and the illumination width of the illumination ratio η at the non-focal angle is Wθp (η) , At any η
W0 (η) > Wθp (η)
Document illumination device characterized by satisfying the above. In the document illumination device according to claim 2 or 3,
The document illuminating apparatus characterized in that the afocal angle θp is set within a half-value angle of a light distribution of the light emitting element. A surface to be illuminated having a length and a width; and a light source unit in which a plurality of LEDs are arranged as light emitting elements in the main scanning direction when the length direction is a main scanning direction and the width direction is a sub scanning direction. A long cylinder lens disposed between the surface to be illuminated and the light source unit, the longitudinal direction of which coincides with the main scanning direction, and the light beam from the light source unit is converged by the long cylinder lens. In a document illuminating device that irradiates the irradiated surface with a characteristic,
The light emitted from each of the plurality of light emitting elements passes through the long cylinder lens and then becomes parallel light in the sub-scanning direction cross section including the light emitting element end face, and has a predetermined convergence angle θf with respect to the sub-scanning direction cross section. In the direction, it becomes convergent light as seen from the main scanning direction ,
When the light emitting element imaging magnification in the sub-scanning direction at the convergence point where the illumination light converges on the illuminated surface in the sub-scanning direction is β,
β> 1
Document illumination device characterized by satisfying the above. The document illumination device according to claim 5,
The original illuminating apparatus characterized in that the convergence angle θf is set within a half-value angle of a light distribution of the light emitting element. The document illumination device according to any one of claims 1 to 6,
An original illuminating apparatus, wherein a length connecting both ends of the plurality of light emitting elements is longer than a length of the illuminated surface. The document illumination device according to any one of claims 1 to 6,
The arrangement interval of the plurality of light emitting elements is set such that the interval between the light emitting elements closest to the center is P0, n ≧ 1, and the interval between arbitrary light emitting elements to the light emitting element closest to the end is Pn.
Pn-1 ≧ Pn
0.2 ≦ Pn / P0 ≦ 1
A document illumination device characterized by satisfying the above relationship at the same time. In the document illumination device according to any one of claims 1 to 8,
The LED as the light emitting element is a one-chip type white light emitting diode using a phosphor. In the document illumination device according to any one of claims 1 to 8,
The LED , which is the light emitting element , is a white light emitting diode that emits white light by color mixture using two or more chips that emit different colors. The document illumination device according to any one of claims 1 to 10,
The document illuminating apparatus according to claim 1, wherein the long cylinder lens has an elliptic arc shape in a cross section of at least one of the light incident surface and the light emitting surface in the sub-scanning section.   An image reading apparatus using the document illumination device according to claim 1. A color document reading apparatus using the document illumination device according to claim 1 .   An image forming apparatus using the image reading apparatus according to claim 12.   An image forming apparatus using the color document reading device according to claim 13.

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