JPH09311279A - Illuminator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an illuminator capable of obtaining uniform illuminance inside a required linear area without being affected by the irregularity of light quantity at an exit port where light emitted from a light source is emitted. SOLUTION: This illuminator guides the light emitted from the light source part to a linear light guide 104, and makes the light emitted from the plural lines of long exiting ports 121 provided in parallel at a specified pitch on a light emitting surface 105, condenses the emitted light by a cylindrical lens 106, and irradiates a face 107 to be irradiated with the condensed light. Provided that the focal distance of the lens 106 is defined as (f), a distance from the port 121 to the lens 106 is defined as (d), and a distance from the lens 106 to the face 107 is defined as L, an optical system is constituted to satisfy 1/f≠(1/d)+(1/L).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device, and more particularly to a lighting device suitable for illuminating a line-shaped area to be read in an image reading system.

[0002]

2. Description of the Related Art Generally, in an image reading system using a CCD line image sensor, it is necessary to illuminate a reading object such as a letter. Since the line image sensor has a line-shaped photosensitive area, it is desirable that the illumination area to be read is also line-shaped. Therefore, in an illumination device for such an application, after condensing light from a light source such as a halogen lamp, it is conventionally necessary to pass the light through a line type light guide using an optical fiber bundle in which the emitting end is arranged in a line. It has been adopted to irradiate an irradiation surface such as a reading target by arranging the lines in a line.

However, since the light emitted from the line-type light guide is emitted within a relatively large angle, even if the distance between the exit of the light guide and the illumination surface is about several cm, the light has a width of several cm. It will spread. Since the CCD line image sensor requires only a linear illumination area having a width of about 100 μm, this means that the light utilization efficiency is too low.

Further, since the illuminance distribution on the irradiation surface is such that the illuminance greatly decreases from the center to the peripheral portion, the image is obtained by illuminating the letter obliquely from above and reading the image with the line sensor from the front of the letter. In the reading system, if the letter moves back and forth even slightly in the thickness direction, the center of the irradiation surface shifts and the illuminance decreases.

FIG. 17 shows a conventional lighting device that solves this problem. In this illuminating device, a cylindrical lens is used in order to focus the light emitted from the line-type light guide, which is composed of optical fiber bundles arranged in a line, on a narrow line-shaped area on the irradiation surface. When the system is cut along a plane perpendicular to the lengthwise direction of the cylindrical lens, an image of the light guide exit is formed on the illuminated surface in order to concentrate the illuminance distribution on the illuminated surface as narrowly as possible. The layout is as follows. Assuming that the focal length of the cylindrical lens is f, the distance between the exit aperture and the cylindrical lens is d, and the distance between the cylindrical lens and the irradiation surface is L, the relationship of 1 / f = (1 / d) + (1 / L) Sometimes an image of the exit is formed on the illuminated surface. However, the thickness of the cylindrical lens is ignored here. By doing so, it is possible to concentrate the illuminance distribution in a linear region on the irradiation surface required for reading by the line image sensor, and improve the light utilization efficiency.

[0006]

As described above, in the conventional illuminating device, in order to concentrate the illuminating light on the narrowest possible line-shaped area on the irradiation surface, the emission port of the line-type light guide is provided with respect to the cylindrical lens. The system is arranged so that an image is formed on the irradiation surface. Therefore, there is a problem that the amount of light emitted from the emission port of the light guide has position-dependent unevenness, that is, if the amount of emitted light at each position within the emission port is different, the illuminance distribution on the irradiation surface also has unevenness. It was

The present invention provides an illuminating device capable of obtaining a uniform illuminance within a necessary line-shaped area on an irradiation target without being affected by unevenness in the amount of light at an emission port for emitting light from a light source. The purpose is to

[0008]

In order to solve the above-mentioned problems, the present invention completely forms an image of light from an emission port for emitting light from a light source on a line-shaped area on an irradiation surface to be illuminated. Do not focus with a lens so that the image of the exit on the irradiation surface is blurred, preventing uneven light amount at the exit from being reflected on the irradiation surface, without impairing the light utilization efficiency. The illuminance distribution is made uniform.

That is, in the illumination device according to the present invention, the light from the light source is emitted from a plurality of rows of long emission openings provided in parallel at a predetermined pitch, and is condensed by a cylindrical lens to be illuminated. 1 / f ≠ (1 / d) + (where f is the focal length of the cylindrical lens, d is the distance from the exit to the cylindrical lens, and L is the distance from the cylindrical lens to the illumination target. 1 / L) (1) is satisfied.

In this case, by further configuring the optical system so that the position of the image formation is shifted a little further from the irradiation surface by a predetermined amount found by the light source analysis, the gaps between the plurality of rows of the emission ports in the irradiation region are formed. The uneven illumination such as the appearance of dark streaks corresponding to is prevented, and a good lighting condition is realized.

Specifically, the focal length of the cylindrical lens is f, the distance from the exit to the cylindrical lens is d, the distance from the cylindrical lens to the illumination target is L, and the exit is on a plane separated by a unit distance from the exit. Assuming that the width of the illuminance distribution that one point in the mouth contributes is w, the parameter ε defined by the equation (2) of [Equation 1] should satisfy the condition of 0.632 <ε <1.48 (3). Just set it. By setting the parameter ε within this range, high illumination efficiency for the illumination target and uniform illuminance distribution on the illumination target are achieved.

In another illumination device according to the present invention, the light from the light source is emitted from a plurality of rows of long emission openings provided in parallel at a predetermined pitch, and is condensed by a cylindrical lens. When illuminating an illumination target, the focal length of the cylindrical lens is f, the distance from the exit to the center of the cylindrical lens is d, and the distance from the center of the cylindrical lens to the illumination target is L.
Then, 1 / f ≠ (1 / d) + (1 / L) (4) is satisfied.

Also in this case, by configuring the optical system so that the position of the image formation deviates a little distance from the irradiation surface by a predetermined amount found by the light source analysis, dark streaks and the like appear in the irradiation area. Irregularity of illuminance is prevented and a good lighting condition is realized.

Specifically, the refractive index of the cylindrical lens is n, the radius is r, the pitch of the exit ports is p, the distance from the exit port to the center of the cylindrical lens is d, and the distance from the center of the cylindrical lens to the illumination target. Let L be the width of the illuminance distribution that contributes to one point in the emission port on a plane separated by a unit distance from the emission port,
paraxial focal length f given by f = r · n / 2 (n−1)
Is defined, the parameter ε defined by the equation (5) of [Equation 2] satisfies the condition of the equation (6) of [Equation 3], and (r / 2p)> 1 and 1 ≦ d / r It suffices to satisfy the condition of <2 (7).

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 is a diagram showing a configuration of an image reading system including an illumination device according to an embodiment of the present invention, and FIG. 2 is a diagram showing a configuration of a main part of the illumination device. is there.

The light source section 100 includes a lamp 101 and a reflecting mirror 10.
2 and the light emitted from the lamp 101 is reflected by the reflecting mirror 102.
And is incident on one end (incident end) of the guide portion 103 of the line-type light guide that is collected by the optical fiber bundle. The light emitted from the light emitting surface 105 of the line array portion 104 of the line-type light guide is irradiated onto an irradiation surface 107, which is an illumination target, for example, a surface of a letter, through a cylindrical lens 106 which is a condensing lens. 107
Illuminate the upper linear area. In the example of FIG. 1, the line-type light guides 104 are provided at two places so as to illuminate the surface of the irradiation surface 106 from diagonally above and below both sides.

Thus, the light is emitted from the light emitting surface 105 of the line type light guide, and the cylindrical lens 10 is further provided.
Irradiation surface 107 illuminated by the light condensed by 6
The upper image is imaged on a CCD line image sensor 109 provided in front of the irradiation surface 107 via an imaging lens 108, and the CCD line image sensor 109 reads the image on the irradiation surface 107 and outputs an image signal. Output to a processing unit (not shown).

Light emitting surface 105 of the line type light guide
Has a plurality of elongated (i.e., two rows in this example) emission ports 121 each having a long shape, that is, an elongated shape, provided in parallel at a predetermined pitch p as shown in FIG. Such an outlet 121
Specifically, the light emitting surface 105 having the above is realized by arranging the emitting ends 122 of the respective optical fibers of the optical fiber bundle forming the line type light guide in two rows as shown in FIG. You can

Here, when the light emitted from the emission port 121 is simply focused by the cylindrical lens 106 on a line-shaped region on the irradiation surface 107 to form an image as in the prior art, each column of each line is formed. The unevenness of the emitted light amount, that is, the unevenness of the light intensity distribution caused by the presence of the gaps between the exit ports 121, etc. is reflected as it is in the illuminance distribution on the irradiation surface 107, so that the illumination with uniform illuminance cannot be performed.

On the other hand, in the present invention, the irradiation surface 10
Illumination is performed by configuring the optical system so that the image of the emission port 121 on the image 7 is blurred by an appropriate amount. This blur prevents the unevenness of the light intensity distribution at the emission port 121 from being reflected on the irradiation surface 107, and further, the irradiation surface 107.
The illuminance distribution above can be made uniform. Moreover, not only the illuminance unevenness on the irradiation surface 107 is reduced, but also the illuminance distribution is almost uniform in a linear region of a certain width on the irradiation surface 107 without lowering the light utilization efficiency. Can be Hereinafter, this effect will be described.

First, as shown in FIGS. 2 and 3, a line type light guide having a plurality of rows of long emission openings 121 on a light emission surface 105 and a front surface of the light guide along the length direction of the emission openings 121. Cylindrical lens 106 arranged in parallel
Is in a positional relationship such that the image of the exit 121 is formed on the irradiation surface 107, that is, the focal length of the cylindrical lens 106 is f, the distance from the exit 121 to the cylindrical lens 106 is d, Let us consider a case where the distance from the cylindrical lens 106 to the irradiation surface 107 is L and these have a relationship of 1 / f = (1 / d) + (1 / L). Note that the aberration of the cylindrical lens 106 is assumed to be sufficiently small here.

At this time, the exit port 12 is formed on the irradiation surface 107.
An image of 1 is formed. In this case, the illuminance distribution on the irradiation surface 107 is as viewed in the axial direction of the cylindrical lens 106,
The unevenness of the light intensity distribution at the exit 121 is reflected as it is in an enlarged / reduced form. Of course, since the cylindrical lens 106 does not have a condensing function in the axial direction, the image of the exit 121 is not formed. Note that FIG.
At FWHM is full width at half maximum.

On the other hand, the optical system has the exit port 1 on the irradiation surface 107.
Even when the positional relationship is such that the image of 21 is not formed, by appropriately adjusting the focal length of the cylindrical lens 106 without changing the positional relationship of the elements, that is, 1 / f '= (1 / d ) + (1 / L) cylindrical lens 106 having a focal length of f ′
By replacing with, the image of the emission port 121 can be formed on the irradiation surface 107 without changing the enlargement / reduction ratio. The ratio of the size of the image of the emission port 121 to the size of the distribution area of the light emitted from the emission port 101, that is, the enlargement / reduction ratio, is calculated from the emission port 121 to the cylindrical lens 10.
6 and the distance L from the cylindrical lens 106 to the irradiation surface 107.

On the other hand, according to the present invention, when the image of the exit 121 is not formed on the irradiation surface 107, that is, the condition of 1 / f ≠ (1 / d) + (1 / L) is satisfied. In some cases, the irradiation surface 107
The image of the upper exit 121 is slightly blurred. The degree of blurring is determined by the intensity of directivity of light rays from each point in the emission port 121 and the intensity of image formation. On the irradiation surface 107, the illuminance distribution contributed by one point in the emission opening 121, that is, the distribution of the image formed on the irradiation surface 107 by each ray emitted from one point in the emission opening 121 in each direction is a point spread distribution. We will call it a point spread function. When the aberration can be ignored, the image on the irradiation surface 107 has the same size and the same shape at any point in the exit 121, and the illuminance of the image is the intensity of light emitted from that point. Proportional to. Therefore, the illuminance distribution on the irradiation surface 121 is calculated as follows:
It is obtained by calculating the convolution of the image of 1 and the point spread function.

The point spread function will be described in more detail. First, the spread distribution of the light emitted from the emission port 121 is approximated. The light emitted from each point on the emission port 121 is emitted with a certain solid angle spread. In order to evaluate how the outgoing light from the outgoing port 121 spreads, the outgoing port 121
The illuminance distribution of the light emitted from a certain point in the
When observed on a plane separated by a unit distance from
The illuminance takes a maximum value at a certain point and gradually decreases in the vicinity. When the distance from the point where the illuminance has the maximum value is | x | on a plane that is a unit distance from the emission port 121, the illuminance distribution I _dir (| x |) on that plane is
Is approximated by the following equation.

[0027]

(Equation 4) When the emission port 121 is formed by arranging the emission ends 122 of a large number of optical fiber bundles in a plurality of rows as shown in FIG. 4A, it is actually assumed that c = 2.8 and w = 0.24. It is possible to obtain the one close to the state of the exit of the optical fiber bundle. This distribution is shaped like a Gaussian distribution (in the case of c = 2) slightly closer to a rectangle. After that, these c = 2.8, w
The value is set to 0.24 for consideration.

When a lens that can be approximated to have no aberration is used as the cylindrical lens 106, and light emitted from one point inside the exit 121 is condensed by the cylindrical lens 106 and applied to the irradiation surface 107, the exit 121 is used. The image formed by one point on the irradiation surface 107 is a parallel translation of the image of the emission port 121 that is vertically / horizontally enlarged / reduced. Here, the coordinates (x, y) are taken on the irradiation surface 107. Irradiation surface 1
The origin in the point where the central axis (optical axis) of the optical system penetrates on 07, and the longitudinal direction of the exit port 121 (the cylindrical lens 1).
The y-axis is taken in the direction (06 axial direction), and the x-axis is taken in the direction perpendicular thereto. Then, the illuminance distribution I _dir (x, y) on a plane separated from the emission port 121 by a unit distance is represented by the following equation.

[0029]

(Equation 5) In this case, the illuminance distribution I _PSF (x,
y) is d in the x-axis direction compared to the illuminance distribution I _dir (x, y) on a plane separated by a unit distance from the emission port 121.
It is magnified or reduced by + L- (dL / f) times and in the y-axis direction by d + L times, respectively, to obtain the following expression.

[0030]

(Equation 6) The cylindrical lens 106 does not have a condensing function in the y-axis direction, which is the axial direction, that is,-(dL / f).
The light that has passed through the cylindrical lens 106 normally spreads in a range that is much wider in the y-axis direction than in the x-axis direction. Therefore, when the length direction of the emission port 121 and the axial length of the cylindrical lens 106 are sufficiently large, the illuminance distribution in the y-axis direction on the irradiation surface 107 is averaged and can be regarded as substantially uniform. Therefore, hereinafter, only the illuminance distribution in the x-axis direction will be described. In this case, the illuminance distribution I _PSF (x) can be expressed by the following equation.

[0031]

(Equation 7) Next, an image of the exit 121 will be described. Outlet 121
The above light intensity distribution also has unevenness depending on the position.
Here, as shown in FIG. 4A, when a line type light guide in which a plurality of optical fiber bundles are arranged is used, the emission port 12
The portion corresponding to the emission end 122 of each optical fiber that constitutes the optical fiber bundle within 1 (the portion indicated by ○ in the figure)
And a portion deviated from the emission end 122 (a portion not enclosed by ◯ in a portion enclosed by □ in the figure). Light is emitted from the former and its light intensity distribution is almost uniform, but light is hardly emitted from the latter.

Here, when the cylindrical lens 106 is a lens that can be approximated to be aberration-free and the irradiation surface 107 is at the image formation distance, such unevenness in the amount of light emitted from the emission port 121 remains on the irradiation surface 107. Appears as the illuminance distribution of. However, since the illuminance distribution is averaged in the y-axis direction, in the line-type light guide 104 in which a plurality of optical fiber bundles are lined up, the position x in the x-axis direction at the exit 121 is set.
The average light intensity distribution I _src (x) in is given by the following equation per column of the optical fiber bundle.

[0033]

(Equation 8) When this average light intensity distribution I _src (x) is projected onto the irradiation surface 107 by the cylindrical lens 106, the image is magnified L / d times, and the illuminance distribution I on the irradiation surface 107 is increased.
_scr (x) is given by the following equation.

[0034]

[Equation 9] Also, the illuminance distribution I when the optical fiber bundle has two rows
_scr (x) is given by the following equation (see FIG. 4B).

[0035]

(Equation 10) The design using the illuminance distribution I _scr (x) averaged in the y-axis direction according to the shape of the emission port 121 is effective regardless of whether the line-type light guide is configured with an optical fiber bundle or not. Such modifications are also included in the present invention. In addition, the above-mentioned semicircular illuminance distribution is directly changed to I _scr.
The approximation used as (x) also often provides a good design.

The illuminance distribution on the irradiation surface 107 when the cylindrical lens 106 is located at a position where the image of the exit opening 121 does not form an image on the irradiation surface 107 is obtained by convolving the image of the exit opening 121 and the point spread function. Decided.

Here, the full width at half maximum of the point spread function (1 / e
^1/2 full width) and the width of the image of the exit 121,
The parameter ε of the following equation is defined.

[0038]

[Equation 11] This is the same formula as the formula (2) of [Equation 1], f is the focal length of the cylindrical lens 106, d is the distance from the exit 121 to the cylindrical lens 106, and L is the distance from the cylindrical lens 106 to the irradiation surface 107. Distance, w
Is the width of the illuminance distribution contributed by one point in the emission port 121 on a plane separated from the emission port 121 by a unit distance. By using this parameter ε, the illuminance distribution on the irradiation surface 107 can be expressed by the following equation when the emission ports 121 have two rows.

[0039]

(Equation 12) In this equation, the function h (x ′, ε) is the two functions shown in the following equation.

[0040]

(Equation 13) Convolution of, that is,

[0041]

[Equation 14] Is defined as By using these, the point spread function becomes

[0042]

(Equation 15) And the image of the exit 121 is

[0043]

(Equation 16) It can be expressed as.

When the cylindrical lens 106 is not inserted, the illuminance distribution on the irradiation surface 107 is f → ∞, L / d →
Since the distribution is the same as 1, x → −x, h
By also using (−x ′, ε) = h (x ′, ε), the illuminance distribution when the exits 121 have two rows is given by the following equation.

[0045]

[Equation 17] Since w is a constant determined by the characteristics of the light source and p is also a constant according to the type of the light source system (pitch of the emission openings 121), if L / d is determined, the above equation is used to make the image size of the emission opening 121 the same. In this case, the shape of the illuminance distribution I _norm (x) is I _norm (x ′) = h (x′−1, ε) + h (x ′ + 1, ε) (24) And is determined only by ε. However, even if the sizes are different, if the vertical and horizontal scales are converted to the same shape, they are regarded as the same shape. When ε → 0, the image becomes closer to the completely imaged state, and the larger ε → ∞, the larger the image blur.

From the above, the cylindrical lens 106
When a lens with sufficiently small aberration is used as, the shape of the illuminance distribution can be specified by the parameter ε defined by the equation (15) of [Equation 11].

Next, the optimum range of the parameter ε will be described. For the case where the emission ports 121 are configured in two rows,
As illuminance distribution when ε is various, h (x-1, ε) + h
The result of obtaining (x + 1, ε) is shown in FIG. In addition, various ratios of the distribution shape at this time, that is, the ratio of the central value to the maximum value of the illuminance, the ratio of the peripheral value to the maximum value, the ratio of 90% full width to 10% full width, the ratio of 90% full width to 50% full width, As shown in FIG. However, in FIGS. 5 and 6, the constant c in the equation (7) that determines the spread distribution of the light on the optical axis is set to c = 2.8. Further, FIG. 7 shows various values of the illuminance distribution shape on the irradiation surface 107, that is, the maximum value, the peripheral value, the center value, 10% half width, 50% half width, and 90% half width of the illuminance.

From the curve shown in FIG. 5, it can be seen that when ε is small, a recess is formed at the position 0 (center portion) of the irradiation surface 107 and the uniformity is deteriorated. In a line sensor such as a CCD line image sensor, the most frequently read position is the central part, and the illuminance at this part greatly affects the illumination efficiency. Therefore, in order to obtain a sufficient illumination light ratio, the ratio between the maximum value and the central value in FIG. 6 is desired to be at least 0.85 or more, which requires ε> 0.632. .

When the line type light guide is composed of a plurality of rows of emission ports 121, the irradiation surface 107
The shape of the illuminance distribution I _norm (x ′) above is

[0050]

(Equation 18) However, the skirt of the distribution is too gentle, and the illuminance h (± 2, ε) or h at the position of the image of the adjacent or next exit port is
If (± 4, ε) is too large, the distribution I _norm (x ′) becomes
This is inconvenient because the illuminance distribution is not uniform because it is small at x ′ = 0 or x ′ = 2 (m−1) in the peripheral portion and becomes large at x ′ = m−1 in the central portion. However, x ′ in this equation is a scale conversion of the actual length x on the irradiation surface 107 so that x′pL / 2d = x.

FIG. 8 shows the illuminance distribution on the irradiation surface 107 when the emission openings 121 are in a line. Further, the solid line in FIG. 9 similarly represents the illuminance distribution on the irradiation surface 107 when the emission openings 121 are in one row, and the broken line represents the illuminance distribution on the irradiation surface contributed by the emission openings 121 in the adjacent row. . From FIG. 9, in order to make the illuminance distribution flat, the value obtained by adding twice the value of x = p to the value of x = 0 in the illuminance distribution on the irradiation surface 107 contributed by one row of the emission ports 121 is It can be seen that the value should be approximately equal to twice the value of x = p / 2 in the illuminance distribution on the one line of the emission port 121.

However, for this purpose, it is necessary that the value of x = 2p in the illuminance distribution on one line of the emission port 121 is sufficiently smaller than the value of x = 0. If this condition is not satisfied, the point spread function will be blurred more than necessary, and it will interfere with the image area of the adjacent exit 121, and the distribution will not be uniform as a whole. Further, even if the number of rows of the emission ports 121 is increased, it is not possible to increase the area where the illuminance is uniform by the increased number.

X in the illuminance distribution on one line of the emission port 121
It is desirable that the ratio between the value of = 2p and the value of x = 0 is sufficiently small, but it is necessary to be 0.005 or less in order to realize sufficient practicality. From this, the condition of ε <1.48 is required.

From the above discussion, the parameter ε is 0.6
It is preferably within the range of 32 <ε <1.48. In particular, there is a point that the central depression in the illuminance distribution disappears as ε increases, and finally the value at the central portion matches the maximum value. At c = 2.8, the point at which the central value of this illuminance distribution matches the maximum value is approximately ε = 0.87. Also, when c = 2.0, this point is approximately ε = 0.81.
It is. Under this condition (eg, ε = 0.87), the illuminance distribution has the highest uniformity around the straight line of x = 0. Here, such a condition that the illuminance distribution has a flat shape at the top is called an optimum condition.

As an example, the exit surface 121 to the irradiation surface 10
Consider a case where the optical system is assembled so that the distance to 7 is d + L = 30 mm and the width of the linear irradiation region on the irradiation surface 107 is 4.5 mm. However, p = 0.5, w =
0.24, and the fiber bundles are arranged in two rows as shown in FIG. Except in the case of ε >> 1, the width of the irradiation region is determined by pL / d, so that d + L = 30 and p
From the condition of L / d = 4.5, d = 3.3 mm, L = 27 m
m is decided.

The optimum condition is ε = 0.87 when c = 2.8.
Therefore, when f is calculated back from equation (15), the optimum focal length of the cylindrical lens 106 is f = 3.70.
815 mm can be obtained. By determining various parameters of the optical system in this way, it is possible to obtain a substantially uniform illuminance distribution over the entire line-shaped region having a width of 4.5 mm on the irradiation surface 107.

Next, in this way, the cylindrical lens 1
The illuminance distribution on the irradiation surface 107 in the case of optimizing the optical system including 06 is obtained when the cylindrical lens 106 is not provided and when the image of the exit 121 is completely formed on the irradiation surface 107 by the cylindrical lens 106. Compare with the illuminance distribution.

The cylindrical lens 106 is connected to the exit port 12
The illuminance distribution when it is inserted between 1 and the irradiation surface 107 is
As described above, the function h (x ′, ε) defined by the equations (17) and (18) can be expressed by the equation (16).

The function h (x ', ε) is expressed by the following equation, as defined by the equations (17), (18) and (19).

[0060]

[Equation 19] However, when ε = 0, the function h (x ′, ε) becomes the following equation by considering the limit of ε → 0 in the above equation.

[0061]

(Equation 20) In this equation, the coefficient applied to the square root term on the right side corresponding to g (x ') defined in equation (18) is 2.28113 when c = 2.8.

When optimization is performed based on these things,
When the cylindrical lens 106 is not provided, and when the cylindrical lens 106 is used, the image of the exit 121 is projected onto the irradiation surface 107.
FIG. 10 shows a graph of the illuminance distribution on the irradiation surface 107 when the image is perfectly formed on the upper side. In the figure, the solid line shows the case of the optimum conditions described above, the broken line shows the case where the cylindrical lens 106 is not inserted, and the dotted line shows the case where the cylindrical lens 106 is inserted and the image of the exit 121 is completely formed on the irradiation surface 107. X of the illuminance distribution on the irradiation surface 107
Axial direction (direction orthogonal to the cylindrical lens 106)
The cross-sections at are shown respectively.

Under the optimum conditions, there is no dent in the center, and the illuminance in the vicinity of the center is about twice as high as in the case where the cylindrical lens 106 is not inserted, and the width 4 near the center on the irradiation surface 107 is 4 as designed. It can be seen that the illuminance of the line-shaped irradiation area of 0.5 mm is almost uniform. It should be noted that if the irradiation area is further narrowed, the illuminance can be further increased in inverse proportion thereto, and the superiority to the case where the cylindrical lens 106 is not inserted becomes clearer.

In the above description, the cylindrical lens 1
Although the discussion has been made assuming that it can be approximated when there is no aberration of 06, the condition of the parameter ε obtained as a result has practically sufficient performance even if it is applied when there is aberration of the cylindrical lens 106. A lighting device can be realized.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 11 is a diagram showing a configuration of a main part of the illumination device according to the present embodiment. The same parts as those in FIG. 2 will be designated by the same reference numerals, and in the present embodiment, a cylindrical lens 2 will be used instead of the cylindrical lens as the condenser lens.
The point that 06 is used is different from the first embodiment.

The cylindrical lens 206 basically has a light-collecting function similar to that of a non-aberration cylindrical lens, but it is difficult to express its behavior by a simple mathematical expression because of the size of aberration. Equation (5) of [Equation 5] (same as Equation (2) of [Equation 1]) when aberration can be approximated even if the aberration is large
If the parameter ε _abr can be defined by a simple equation similar to the parameter ε shown in (1), the condition that ε is approximately 1 is the same as in the case of no aberration. It is considered that the illuminance distribution can be obtained.

[0067]

(Equation 21) Strictly speaking, when a condenser lens having large aberrations such as the cylindrical lens 206 is used, the point image is deformed depending on the emission position. Even if this dependence is small, the full width of the point spread function of the numerator in the above expression is generally slightly different from that in the case of no aberration and becomes a slightly smaller value. For these reasons, defining and using ε _abr is not practical.

However, ε _{abr in the} case of using a cylindrical lens with large aberration should approach ε in the case of no aberration in the limit of small aberration. Therefore, even when the aberration is large, it is expected that ε defined by the equation (5) functions as a good index for expressing the behavior of the system. As described below, this was confirmed by actually performing a ray tracing simulation.

In order to know the influence of aberration, specifically, the cylindrical lens 20 is emitted from one point inside the exit 121.
A path of a light ray which passes through 6 and reaches the irradiation surface 107 will be examined. The light ray incident near the center of the cylindrical lens 206 travels in the same direction as in the case where there is no aberration, and is focused at the image formation distance in the case of no aberration. However, the ray incident on the peripheral portion of the cylindrical lens 206 is curved inward more largely than in the case of no aberration because of the large spherical aberration, and is closer to the lens 206 than the image forming distance in the case of no aberration. Focus on. As a result, the thickness of the beam that has passed through the cylindrical lens 206 and the total width of the point spread function become slightly thinner than in the case of an aplanatic lens.

In general, when considering an optical system having a large aberration, it cannot be discussed using a simple imaging formula, and ray tracing must be performed for each ray. Therefore, in the case of the cylindrical lens 206, the radius r of the cylindrical lens 206 and the emission port 12 of the line-type light guide
1, the distance d from the center of the objective lens 206 to the center of the objective lens 206 and the distance d + L from the exit 121 to the irradiation surface 107 are variously changed to perform a simulation calculation of ray tracing. Many combinations of parameters were investigated when a large illuminance distribution was obtained.

As a result, the parameters recognized as optimum are shown in the table of FIG. These are the system parameters that provide the optimum illuminance distribution in the case of a cylindrical lens. Epsilon calculated from these using Expression (5) is plotted in FIG. In FIG. 13, the horizontal axis is d / (2p) and the vertical axis is ε. The round dots in the figure correspond to each data in the table of FIG. As a result, the points of each data in FIG.
It was found that it was distributed in a certain area in the graph of.
When the achromatic cylindrical lens 106 is used as in the first embodiment, the optimum condition is expressed as ε = constant regardless of d / (2p) in the graph of FIG. When the cylindrical lens 206 is used as described above, the value of ε is not constant due to the influence of aberration, and has a strong variation with a strong correlation with d / (2p).

In this simulation, the refractive index of the glass forming the cylindrical lens 206 is n = 1.4.
8. The direction distribution of the light emitted from one point in the emission port 121 is r when the screen is placed perpendicular to the light emission surface of the light guide at a point separated by a unit distance from the emission point. As exp (-| r / w | c /
The distribution is 2). The values of c = 2.8 and w = 0.24 were used for these parameters c and w. When c = 2, a Gaussian distribution is obtained, but in this simulation, a distribution that is slightly squared from the Gaussian distribution was used with c = 2.8.

As described above, regardless of whether the aplanatic cylindrical lens 106 or the cylindrical lens 206 is used, the system parameters are set from the imaging conditions so that the irradiation surface 107 is slightly before the imaging position. By slightly shifting, the size of the point spread function is adjusted and
It is possible to smooth the unevenness in the amount of light emitted from No. 1 and prevent uneven illuminance such as the appearance of dark stripes in the irradiation area.

In the following, as a typical case, the refractive index is n = 1.48, and the line type line guide is the light emitting surface 1.
It is assumed that the optical fibers having a diameter of 0.5 mm are arranged in two rows at a pitch of 0.5 mm in the emission port 121 of No. 05, and the width of the emission port 121 is 2p = 1 mm. Further, the solid angle spread of the light emitted from one point in the emission port 121 is
It is assumed that the half width at half maximum is about w = 0.24 on a plane separated from 1 by a unit distance. Furthermore, the exit 121
When the directional distribution of the light emitted from the light source, that is, the illuminance distribution of the light emitted from one point on the light output port 121 is examined on a plane separated from the light output port 121 by a unit distance, exp ( -| R / w | c / 2).

Here, the coordinate system (x, y, z) is defined. The optical axis is the z-axis, and the length direction of the cylindrical lens 206 is the y-axis. The irradiation surface 107 is assumed to be perpendicular to the z axis. Also, the x axis is taken perpendicular to the y axis and the z axis. Coordinate system (x,
The origin of y, z) is the exit 121 of the line type light guide.
Becomes the center point of. Note that FIG. 11 shows a cross section taken along the zx plane.

As an example, the exit 121 and the irradiation surface 107
And the distance d + L = 30 mm, and the width of the exit 121 is 20
Consider a case where a cylindrical lens 206 having a radius of 2 mm is placed in front of the exit 121 when the length is about 0 mm, which is sufficiently long.

In this case, since most of the light emitted from the emission port 121 is made incident on the cylindrical lens 206, the condition r <d <2r and r> 2p, that is, (r / 2p)> The condition of 1 and 1 ≦ d / r <2 is required. The former is a condition that limits the distance between the emission port 121 and the cylindrical lens 206 so that the number of light rays that do not enter the cylindrical lens 206 and squeeze the side thereof is sufficiently small. In the latter case, if the radius of the cylindrical lens 206 is too small, the size of the emission port 121 is too large as compared with the size of the cylindrical lens 206, so even if the cylindrical lens 206 is placed in contact with the emission port 121. However, this is a condition that comes from the fact that the number of rays that pass through the side of the cylindrical lens 206 still increases.

In the case where the cylindrical lens 206 is used as in this embodiment, a simulation calculation is performed,
The illuminance distribution shape on the irradiation surface 107 was obtained. As a result, the illuminance distribution in the x direction on the irradiation surface 107 when the position of the center of the cylindrical lens 206 (the distance d from the exit 121 of the line type light guide to the lens center) is used as a parameter is as shown in FIG. I found out.

In FIG. 15, the radius of the cylindrical lens 206 is r =
It is a three-dimensional representation of the illuminance distribution on the irradiation surface 107 in the case of 2.2 mm, and the height of the graph represents the magnitude of the illuminance.
Similarly, FIG. 16 three-dimensionally represents the illuminance distribution on the irradiation surface 107 when r = 3 mm, and the height of the graph also represents the magnitude of the illuminance. When r = 3 mm, the focal length is almost reached. According to FIG. 16, it can be seen that when r = 3 mm, there is a large depression in the center of the illuminance distribution, and a dark streak appears in the center of the irradiation area. This is because the light diverges in the length direction of the line array portion 104 of the line type light guide, while the light is directed in the direction (x direction) perpendicular to it, so that the center of the irradiation range. It has a dark streak.

On the irradiation surface 107, the region of the highest illuminance has the widest area, and the optimum parameter for preventing the dark line at the center from appearing is the cylindrical lens 20.
The position d of the central portion of 6 is 2.0 to 2.4 mm, particularly 2.2.
mm. According to FIG. 15 showing the illuminance distribution in the case of d = 2.2 mm, there is no dark streak in the center portion while condensing light to almost the same level as in the case of d = 3.0 mm, and the width of the top portion is about 6. It can be seen that the 3 mm line-shaped region has a substantially flat shape, and achieves uniform illuminance.

[0081]

As described above, according to the present invention, the light source emits the light from the emission port of the light emitting portion such as the line type light guide so that the image is not perfectly formed in the linear region on the irradiation surface. By condensing with a cylindrical lens or a cylindrical lens so that the image of the emission port on the irradiation surface is blurred, it is possible to prevent uneven light amount at the emission port from being reflected on the irradiation surface, and to improve the light utilization efficiency. It is possible to uniformly illuminate a linear irradiation region within a certain width on the irradiation surface with high illuminance without damaging it.

Further, in the lighting device according to the present invention,
Since a perfect image is not formed on the irradiation surface, sufficient performance can be exhibited even when a cylindrical lens or a cylindrical lens having large aberration is used as the condenser lens. Such a condenser lens having a large aberration can be manufactured at a very low cost.

Therefore, by using an illuminating device including such an inexpensive condenser lens in combination with a line image sensor, the illumination efficiency can be improved several times, and an inexpensive high-sensitivity line sensor can be used instead. Even if a line sensor with poorer performance is used,
A read output with N can be obtained. As a result, it is possible to realize an image reading system having a high performance-to-price ratio.

[Brief description of drawings]

FIG. 1 is a perspective view showing an overall configuration of an image reading system including an illumination device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a main part of the lighting device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an emission port on a light emission surface in FIG.

FIG. 4 is a diagram showing a more detailed shape of the emission port shown in FIG. 3 and an illuminance distribution averaged in the emission port length direction on the irradiation surface.

FIG. 5 is a diagram showing an illuminance distribution shape on an irradiation surface when an aplanatic thin lens is used as a cylindrical lens lens in the same embodiment.

FIG. 6 is a diagram showing various ratios of the illuminance distribution shape on the irradiation surface when an aplanatic thin lens is used as the cylindrical lens lens in the same embodiment.

FIG. 7 is a diagram showing various values of the illuminance distribution shape on the irradiation surface when an aplanatic thin lens is used as the cylindrical lens lens in the same embodiment.

FIG. 8 is a diagram showing an illuminance distribution shape on an irradiation surface in the case of using a non-aberration thin lens for the cylindrical lens lens in the case of a single row of emission ports in the same embodiment.

FIG. 9 is an illuminance distribution on an irradiation surface contributed by an emission opening of a row of interest and an emission opening of an adjacent row when an aberration-free thin lens is used as a cylindrical lens lens in the case where the emission opening is in one row in the same embodiment. Diagram showing the shape

FIG. 10 is a diagram showing a comparison of illuminance distributions on an irradiation surface under optimum conditions, no cylindrical lens, and imaging conditions.

FIG. 11 is a cross-sectional view showing a configuration of a main part of a lighting device according to a second embodiment of the present invention.

FIG. 12 is a diagram showing various parameters for obtaining a flat illuminance distribution by simulation.

FIG. 13 is a diagram showing ranges of various parameters for obtaining a flat illuminance distribution by simulation.

FIG. 14 is a diagram showing an illuminance distribution when the radius is 2 mm and the screen distance is 30 mm.

FIG. 15 is a diagram showing an example of a preferable illuminance distribution on the irradiation surface in the present embodiment.

FIG. 16 is a diagram showing an example of an unfavorable illuminance distribution on the irradiation surface.

FIG. 17 is a sectional view showing a schematic configuration of a lighting device according to a conventional technique.

[Explanation of symbols]

 100 ... Light source part 101 ... Lamp 102 ... Reflector 103 ... Line type light guide guide part 104 ... Line type light guide line array part 105 ... Line type light guide light emitting surface 106 ... Cylindrical lens 107 ... Irradiation surface 108 ... Imaging lens 109 ... CCD line image sensor 110 ... Illuminance distribution 121 ... Ejection port 122 ... Optical fiber bundle exit end 206 ... Cylindrical lens 207 ... Illuminance distribution

Claims (5)

[Claims] 1. A light source, a light emitting means for emitting light from the light source through a plurality of rows of long emission openings provided in parallel at a predetermined pitch, and a light emission means for condensing the light emitted from the emission openings. And a cylindrical lens for irradiating an illumination target, wherein f is a focal length of the cylindrical lens, d is a distance from the exit to the cylindrical lens, and L is a distance from the cylindrical lens to the illumination target. At this time, 1 / f ≠ (1 / d) + (1 / L) (1) is satisfied. 2. A light source, light emitting means for emitting light from the light source from a plurality of rows of long emission openings arranged in parallel at a predetermined pitch, and light emitted from the emission openings. And a cylindrical lens for irradiating an illumination target, the focal length of the cylindrical lens is f, the distance from the exit to the cylindrical lens is d, the distance from the cylindrical lens to the illumination target is L,
Let w be the width of the illuminance distribution that a point in the emission port contributes on a plane separated from the emission port by a unit distance. An illumination device characterized in that the parameter ε defined by is satisfying the condition of 0.632 <ε <1.48 (3). 3. A light source, light emitting means for emitting light from the light source from a plurality of rows of long emission openings arranged in parallel at a predetermined pitch, and light emitted from the emission openings. And a cylindrical lens for irradiating an illumination target, the focal length of the cylindrical lens is f, the distance from the exit to the center of the cylindrical lens is d, and the distance from the center of the cylindrical lens to the illumination target. Where L is, 1 / f ≠ (1 / d) + (1 / L) (4) 4. A light source, light emitting means for emitting light from the light source from a plurality of rows of long emission openings arranged in parallel at a predetermined pitch, and light emitted from the emission openings. And a cylindrical lens for irradiating an illumination target, the refractive index of the cylindrical lens is n, the radius is r, the pitch of the exit ports is p, the distance from the exit port to the center of the cylindrical lens is d, Letting the distance from the center of the cylindrical lens to the illumination target be L, and the width of the illuminance distribution contributing to one point in the emission port on the plane that is a unit distance from the emission port be w, f = r · n / 2 ( When the paraxial focal length f given by n-1) is defined, The parameter ε defined by is The illuminating device satisfying the condition (1), and further satisfying the conditions (r / 2p)> 1 and 1 ≦ d / r <2 (7). 5. The light emitting means has a plurality of rows of optical fiber bundles arranged in parallel with one end facing the light source,
The illumination device according to any one of claims 1 to 4, wherein the other end of the optical fiber bundle is used as the emission port.