Light-supplying optical device

The line bow phenomenon is reduced by appropriately setting the reflective surface and/or the external shape of an optical element (e.g., a toric mirror) thereby realizing approximately linear illumination of the surface of the original document that is being read. In order to do this, optical elements can be formed so that the external shape of the reflective surface of the optical element is bow-shaped. Alternatively, the optical element can be arranged so that the optical axis of the reflective surface is parallel to the axis of the light reflected from the reflective surface.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an image input device that reads image 
information using photoelectric conversion elements. 
2. Description of Related Art 
FIG. 15 shows a conventional image input device, the light-supplying 
optical device of which is shown in FIG. 16. The light-supplying optical 
device shown in FIG. 16 has the optical arrangement illustrated in FIGS. 
17A and 17B, changing of the direction of the optical path being 
accomplished through the two mirrors 102 and 105 so that the 
light-supplying optical device can be housed in a limited space. 
In FIG. 16, one of the two mirrors used to change the optical path is a 
toric mirror 102. As shown in FIGS. 17A and 17B, the toric mirror 102 has 
a curved surface, which is curved in two perpendicular directions. As 
shown in FIG. 17A, the toric mirror 102 has a first radius of curvature 
R1, so that light rays produced by the light source 103 are supplied to a 
portion of the surface of the original document 101 so as to illuminate a 
width of one line (e.g., one page width). In addition, as shown in FIG. 
17B, a second radius of curvature R2 focuses the light emitted from the 
light source 103 to be formed into a point on the surface of the original 
document 101. Accordingly, radii of curvature R1 and R2 together result in 
the formation of a line of light on the original document, the line having 
a predetermined length in the R1 direction and a height extending in the 
R2 direction. 
As shown in FIG. 15, light rays produced by the light source 103 are 
incident on the toric mirror 102. These light rays are incident at angle 
111 relative to the axis (the optical axis) 110 of the toric mirror, in 
order to direct the optical axis of the light rays toward the next optical 
path changing mirror 105. Light rays reflected by the toric mirror 102 are 
formed into an image on the surface of the original document 101 via the 
optical path changing mirror 105. The light rays between the light source 
103 and the toric mirror 102 are at an angle 111 relative to the toric 
mirror optical axis, a downward angle in FIG. 15. Consequently, the light 
rays between toric mirror 102 and second mirror 105 are also at a downward 
angle relative to the toric mirror optical axis. 
Visible (image) information on the original document illuminated by the 
light rays is formed into an image on a linear image sensor 109 by a 
projection lens 108. Image sensor 109 can be, for example, a linear series 
of charge-coupled-devices (CCDs) that extend in a primary (or fast scan) 
direction. By moving the holder 107 that holds the original document in 
the direction indicated by the arrow in FIG. 15 (in what is known as the 
secondary or slow scan direction), all of the information on the surface 
of the original document can be read in succession by the linear image 
sensor 109. 
The light source 103 is constructed as shown in FIGS. 18A and 18b. A stem 
202 is soldered onto the top of a light source base 201. On this stem 202, 
a plurality of LED chips are arranged in rows 210a and 210b, and are 
bonded thereto. Around each LED chip is a conical reflector 202a that 
reflects the light produced in the sideways direction and projects it 
upward from the LED chip 201 (see FIG. 18B). 
In order to produce light in three colors, the light source 103 is 
comprised of two LED chip rows 210a and 210b. Blue LEDs that produce a 
small quantity of light per chip are arranged in one row 210a (e.g., 6 
chips). Red LEDs and green LEDs are arranged in a GRGGRG pattern in the 
other row 210b. After light from the rows 210a and 210b of LED chips is 
reflected by the reflectors 202a and emitted upward, the light is 
reflected by a blue-reflecting film 205a or by a wholly reflective mirror 
205b that are formed at a certain angle and spacing. The reflected light 
is emitted towards the front (to the right in FIGS. 18A and 18B, and to 
the left in FIG. 15), and is collected by the toric mirror 102 so as to 
extend linearly on the surface of the original document. 
The light from the blue LEDs is reflected by the blue-reflecting film 205a, 
while the light from the red LEDs and green LEDs is reflected by the 
wholly reflective mirror 205b, so that when viewed from the front of the 
light source (to the right in FIGS. 18A and 18B, and to the left in FIG. 
15), it appears that the three colors of light have all been produced from 
the same position. Switching between the red, green and blue colors is 
controlled electronically, making high speed reading of the original 
document possible. 
With the conventional light-supplying optical device described above, 
because the toric mirror 102 has a radius of curvature R1, and light rays 
from the light source 103 form an angle 111 with respect to the optical 
axis 110 of the toric mirror 102, the angle at which the light is 
reflected by toric mirror 102 differs between the center and the perimeter 
(i.e., the ends) of the toric mirror 102. As a result, the image of the 
light source on the surface of the original document 101 is shaped like a 
bow (i.e., a curved line) as shown by line 120 in FIG. 23, rather than in 
a straight line as shown by broken line 121. 
In addition, the toric mirror 102 also has radius of curvature R2. Because 
of this bow-shaped image of the light source on the surface of the 
original document 101, the so-called line bow phenomenon results in the 
output of the line sensor 109. Consequently, the line on the surface of 
the original document 101 that is read by the linear image sensor 109 is 
not uniformly illuminated, creating the problem that the amount of light 
at the center and at the ends of the line that is read are not uniform. 
The amount of light shown in FIG. 24 indicates that uniform light 
quantities cannot be obtained, because the amount of light at the center 
is smaller, while the amount of light at the ends is greater. 
SUMMARY OF THE INVENTION 
In this regard, it is an object of the present invention to reduce the line 
bow phenomenon by appropriately designing the reflective surface and 
external form of the reflective, optical element (e.g., a toric mirror), 
so as to realize approximately linear illumination of the surface of the 
original document that is being read and thereby to obtain uniform 
illumination. 
In order to achieve the above and other objects, and to overcome the 
shortcomings detailed above, a first aspect of the invention reduces the 
line bow phenomenon by using an optical element that includes a reflective 
surface having a bow shape to reflect light from the light source. The bow 
shape of the optical element is such that the image of the optical 
element, when viewed from the position of the original document, is 
straight, rather than bow-shaped. The light from the light source is 
incident on the reflective surface at a certain angle as in previous 
devices. However, because the reflective surface is formed having a 
bow-shaped external form, the reflected light is linear, rather than 
bow-shaped. 
According to a second aspect of the invention, the reflective surface of 
the optical element is arranged so that light that is incident on the 
reflective surface at a certain angle is reflected in a direction that is 
parallel to the optical axis of the reflective surface. 
According to a third aspect of the invention, the shape of the reflective 
surface of the optical element lies on an ellipsoid of revolution formed 
by reverse projecting a straight image reading line from the focus point 
(e.g., the line sensor) of an optical system (that focuses light from the 
original document to the line sensor) through the optical system. 
With all aspects of the invention, the reflective surface can be a toric 
mirror, a cylindrical mirror or a Fresnel mirror, for example. 
With the light-supplying optical device having the above structure, the 
shape of the reflective surface is a shape that cancels the line bow 
phenomenon. In addition, the external shape of the reflective surface is a 
curved shape that cancels the line bow phenomenon. By this means, the line 
bow phenomenon is mitigated when using a reflective surface such as a 
toric mirror, and it becomes possible for the supply of light on the 
surface of the original document being read to be approximately linear, 
and to obtain a supply of light in which the amount of light is uniform.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
An explanation of embodiments of the present invention is provided 
hereafter, with reference to the drawings. 
FIGS. 1A and 1B are a top view and a side view showing a first embodiment 
of a light-supplying optical device according to the present invention. 
In FIGS. 1A and 1B, the shape and position of the toric mirror 11 are as 
described below. Conventionally, as shown in FIG. 13A, the shape and 
position of toric mirror 21 are such that the normal line N-N' at the 
position of reflection on the optical axis A-A' of toric mirror 21, and 
the external form lines X-X' and Y-Y' of the toric mirror 21 are parallel, 
the light reflected from the toric mirror 21 being at an angle to lines 
N-N', X-X', and Y-Y'. In this case, the external form (i.e., the front 
view) of the toric mirror 21 has a slightly curved shape, as seen from the 
surface of original document 101, after reflection by mirror 105, as shown 
in FIG. 14. In other words, because light is reflected at an angle to the 
optical axis of toric mirror 21, the image of the toric mirror (and of a 
line of light reflected by the toric mirror 21) reflected to mirror 105 
and then to the original document 101 is curved. This yields the same 
results as if a curved light source were supplying the light to the 
original document 101. 
In contrast, in the first embodiment of the present invention, as shown in 
FIGS. 1A and 1B, the mirror 11 as a whole is inclined more than in the 
example of FIGS. 13A-13B, so that the direction L-L' of the reflected 
light is parallel to the optical axis A-A' and to the external form lines 
X-X' and Y-Y' of the toric mirror 11. Consequently, when viewed from the 
surface of the original document, the mirror 11 has an approximately 
linear shape, as shown in FIG. 2. Through this structure, the curvature 
(line bow) of the illuminating light at the position of the surface of the 
original document is reduced. Accordingly, non-uniformity of illumination 
is reduced. 
FIG. 3 is a side view showing a second embodiment of a light-supplying 
optical device according to the present invention. With the prior art 
light-supplying optical device (as shown in FIGS. 6A-6D) and in the first 
embodiment of the invention, the point of reflection of light from the 
center portion 61 of the reflective surface and from the end portions 62 
of the reflective surface of the toric mirror are shifted vertically in 
relation to each other. This is shown in FIGS. 6C and 6D, which show the 
points of reflection at the center and at one end, respectively, of the 
toric mirror. As seen from these figures, the angle of reflection is 
different at the center and at the ends of the toric mirror because the 
incident light reflects from different portions of the toric mirror in the 
vertical (i.e., short) direction of the toric mirror. Accordingly, the 
center A and the ends B of the toric mirror are not optically identical. 
In other words, the angle between the incident light and the reflected 
light at the center A is small as shown in FIG. 6C, while, in contrast, 
the angle between the incident light and the reflected light at the ends B 
becomes larger, as shown in FIG. 6D. 
In the second embodiment of the present invention, the toric mirror 63 is 
shaped so that the light reflects from the same portion of the toric 
surface relative to the vertical (short) direction of the toric mirror at 
the center and at the ends of the toric mirror. In other words, the angle 
between the incident light and the reflected light at the center A of the 
toric mirror 63 is the same as the angle between the incident light and 
the reflected light at the ends B of the toric mirror 63 and, preferably, 
at all points between A and B, as shown in FIGS. 4A and 4B. In addition, 
so that the mirror has an approximately linear shape when viewed from the 
surface of the original document, the external form of the reflective 
surface of the toric mirror 63 is not linear, but rather is approximately 
bow-shaped (curved) as shown in FIG. 5. By this means, the curvature (line 
bow) of the supply of light at the position of the original document 
surface is reduced without the non-uniformity of illumination increasing, 
and in addition the non-uniformity of illumination is further decreased 
because the center and the ends of the toric mirror are optically 
identical. 
FIG. 7 is an oblique view of a third embodiment of a light-supplying 
optical device according to the present invention. FIGS. 8A-8C are a top 
view, a front view and a side view of the third embodiment of a 
light-supplying optical device according to the present invention. In 
addition, FIG. 9 is a side view showing the third embodiment of the 
light-supplying optical device according to the present invention. As with 
the previous embodiments, light emitted by light source 103 is reflected 
by optical element 71 and mirror 105 to illuminate a portion of an 
original document 101. 
In the third embodiment, the reflective surface of the optical element 71 
is not comprised of a toric surface, but rather of an elliptical Fresnel 
surface 72 having two axes of curvature. FIG. 8A illustrates that the 
Fresnel surface 72 is curved in the horizontal direction (i.e., the same 
direction as curvature R1 in FIG. 17A). FIG. 8C illustrates that the 
Fresnel surface 72 is curved in the vertical direction (i.e., the same 
direction as the curvature R2 in FIG. 17B). The Fresnel surface 72 is 
comprised of concentric ellipses. The Fresnel surface 72 having the band 
pattern of concentric ellipses can be mounted on a flat base plate, 
forming a compact reflective optical element. 
Because the Fresnel surface 72 functions in a manner similar to a toric 
surface, the positioning and external form of the mirror can be the same 
as in the first and second embodiments, it being possible to reduce the 
line bow phenomenon if the arrangement is set so that the mirror has an 
approximately linear shape when viewed from the direction of the surface 
of the original document. 
FIG. 10 is an oblique view showing a fourth embodiment of a light-supplying 
optical device according to the present invention. FIGS. 11A-11C are a 
front view, a bottom view and a side view showing the fourth embodiment of 
a light-supplying optical device according to the present invention. In 
addition, FIG. 12 is a side view showing the fourth embodiment of the 
light-supplying optical device according to the present invention. 
In the fourth embodiment, a Fresnel mirror is formed from a plurality of 
component Fresnel mirrors 73a, 73b, 73c, 73d and 73e. A base plate 75 is 
supported by a support shaft 76 so that the angle of the Fresnel mirror 
relative to the light rays output from the light source can be adjusted. A 
curved surface 75a is formed on the surface of the base plate 75 facing 
the light source. Curved surface 75a has a radius of curvature extending 
in the same direction as curvature R1 of FIG. 17A, which is parallel to 
the surface of the original document. 
The illustrative Fresnel mirror is comprised of five separate component 
Fresnel mirrors 73a-73e, which are attached, e.g., adhered or screwed, 
onto the curved surface 75a of the base plate 75 so as to form a single 
Fresnel mirror. The component Fresnel mirrors are comprised of rectangular 
mirror surfaces. In this example, each rectangular mirror surface is flat. 
As shown in FIG. 10, the component Fresnel mirrors are lined up in the 
direction of the Y axis (horizontally) on the curved surface 75a. As shown 
in FIG. 11C, each of the component Fresnel mirrors 73a-73e has a curved 
surface with a specified radius of curvature extending in the direction of 
the X axis (i.e., vertically, perpendicular to the surface of the original 
document). 
On the curved surfaces, a uniform Fresnel shaped Fresnel pattern is formed 
only in the direction of the X axis. That is, a plurality of reflective 
surfaces are arranged adjacent to each other in the X-axis direction, with 
each reflective surface being arranged to reflect a ray of light at a 
slightly different angle than an adjacent reflective surface. This is 
illustrated in FIG. 11C, which shows that adjacent reflective surfaces are 
arranged at slightly different angles. As shown in FIG. 11C, the 
reflective surfaces near the center of each component Fresnel mirror are 
perpendicular to a center line L extending through the center of the 
component Fresnel mirror, whereas the reflective surfaces spaced away from 
the center are arranged at a slight angle to the perpendicular, the slight 
angle gradually increasing for reflective surfaces located farther from 
center line L. 
Because the curved surfaces are formed only in the direction of the X axis 
in the component Fresnel mirrors, the radius of curvature of the line bow 
from the Fresnel mirror formed by the five component Fresnel mirrors 
73a-73e is increased. Accordingly, the mirror composed of the five 
component Fresnel mirrors 73a-73e is capable of forming an image of the 
light source with diminished generation of the line bow phenomenon, and, 
therefore, is capable of forming an image of the light source more 
linearly on the surface of the original document, and on the CCD, thereby 
realizing a more uniform illumination of the original document. In 
addition, because the component Fresnel mirrors 73a-73e have a Fresnel 
pattern only in the direction of the X axis and are flat in the direction 
of the Y axis, their manufacture is relatively easy. Therefore it is 
possible to produce the component Fresnel mirrors 73a-73e through the 
mechanical processing of metal or through the injection molding of 
plastic. 
In order to completely prevent generation of the line bow phenomenon, it 
would be appropriate to form the component Fresnel mirrors 73a-73e so that 
the Fresnel shape of each of the component Fresnel mirrors 73a-73e is 
different. This would compensate for the position of the image of the 
reflected light rays. In this case, each Fresnel shape would be symmetric 
with respect to the center line L of the mirror. 
The surface in the embodiment described above will be more nearly curved as 
the number of component Fresnel mirrors used increases. It also would be 
appropriate to use a single curved surface Fresnel mirror instead of 
separate component Fresnel mirrors (i.e., each reflective surface in the 
single component Fresnel mirror would curve in the direction of the Y 
axis). 
Because this structure functions in a manner similar to a toric surface, 
the positioning and external form of the mirror can be the same as in the 
first and second embodiments, it being possible to reduce the line bow 
phenomenon if the arrangement is set so that the mirror has an 
approximately linear shape when viewed from the direction of the film 
surface. 
In addition, when the Fresnel surface is divided into strips (i.e., 
components 73a-73e) and the positions of the component Fresnel mirror 73a 
in the center and the component Fresnel mirrors 73b, 73c, 73d and 73e 
toward the ends are (vertically) shifted so that they are essentially 
linear in shape when viewed from the direction of the original document 
surface, it is possible to make adjustments to create a more linear, more 
uniform image of the light source. Additionally, it is possible to place 
the Fresnel mirror without it being inclined, while still reducing the 
line-bow phenomenon present in conventional devices. The Fresnel surface 
in the third embodiment shown in FIGS. 7-9 can also be comprised of 
strips, thereby making it possible to obtain the same results as with the 
fourth embodiment. 
FIGS. 19-22 are an oblique view, a side view, a top view and an oblique 
view showing a fifth embodiment of a light-supplying optical device 
according to the present invention. 
In FIG. 19, the shape and position of the toric mirror 91 are determined as 
described hereafter. 
The toric mirror 91 is created with the external form of the toric surface 
having a bow shape (as shown, e.g., in FIG. 5) using part of an ellipsoid 
of revolution 92. The shape of the ellipsoid of revolution 92 is 
established as described hereafter. 
As shown in FIG. 20, by positioning the light source 103 at the position of 
focus A' on the x axis and the entrance pupil of the projection lens 108 
at the other position of focus A, because of the properties of the 
ellipsoid of revolution 92, light rays produced by the light source 103 
are concentrated at the entrance pupil of the projection lens 108. In 
addition, the optical axis center point of the toric mirror 91 is 
positioned at point Q on the ellipsoid of revolution, the center of one 
line being read from the surface of the original document 101 being 
positioned at point P on the line segment QA. 
Line segment DE, which passes through point P and is parallel to the Y 
axis, is positioned as shown in FIG. 21. The length of line segment DE 
corresponds to the length of one line being read from the surface of the 
original document 101. Referring to the semi-major axis of the ellipse as 
"a", and the semi-minor axis as "c", the formula for the ellipsoid of 
revolution is as follows: 
EQU x.sup.2 /a.sup.2 +(y.sup.2 +z.sup.2)/c.sup.2 =1 (1) 
In addition, from the relationship: 
EQU segment AQ+segment QA'=2a, (2) 
we get: 
EQU c.sup.2 +.xi..sup.2 =a.sup.2, (3) 
wherein .xi. is the distance from the origin to points A and A'. 
Next, the bow shape in the external form of the toric surface of the toric 
mirror 91 is formed as described below. 
By tracing back light rays from the position (point A) of the entrance 
pupil of the imaging lens 108, the path on the ellipsoid of revolution 
traced by light rays that pass through the (straight) line segment DE 
becomes the basis for the bow shape in the external form of the toric 
surface. 
Vector f and vector P are defined as shown in FIG. 20. 
vector f=(.xi.,0,0) 
vector P=(.alpha.,.beta.,.GAMMA.). Here, .alpha. and .GAMMA. are constants. 
In addition, using "k" as a parameter, we get: 
vector AQ=k*vector P=k(.alpha.,.beta.,.GAMMA.) 
vector OQ=vector f+k*vector P=(.xi.+k.alpha., k.beta., k.GAMMA.) 
EQU =(x,y,z) (4) 
The components of this vector OQ fulfill the conditions of equation (1). 
In addition, as shown in FIG. 21, substituting the components of vector OQ 
into equation (1), within the range -b.ltoreq..beta..ltoreq.b, we get: 
EQU (.xi.+k.alpha.).sup.2 /a.sup.2 +k.sup.2 (.beta..sup.2 
+.GAMMA..sup.2)/c.sup.2 =1, (5) 
and solving for k, we arrive at: 
##EQU1## 
and one need only graph the path of vector OQ using parameter k, which has 
.beta. as a variable. 
AP=42.02 
PQ=49.20 
QA'=40.95 
From equation (2), a=66.09 
Using the law of cosines,.xi.=25.74 
From equation (3), c=60.87 
In addition, calling QAA'=.THETA., the X component .alpha. of vector P is: 
.alpha.=-41.58 
.GAMMA.=6.03 
Substituting these values into equation (6) and finding the path, the 
result is the toric mirror 91 of FIG. 19. Here, b=12.225, so we have 
-12.225.ltoreq..beta..ltoreq.12.225. 
In addition, by positioning a slit having the same shape as the illuminated 
region of the linear surface of the original document 101 so that it is 
perpendicular to line segment AQ and also includes line segment DE, the 
path on the ellipsoid of revolution 92 traced by the light rays that pass 
through the slit after being traced back from point A forms the bow shape 
of the external form of the toric surface of the toric mirror 91. 
It is also possible to divide the bow shape of the external form of the 
toric surface into strips as in the fourth embodiment. Furthermore, when 
the shape in the direction of the minor axis, as shown in FIG. 22, is set 
as described below, the light quantity on the line being read on the 
surface of the original document 101 is increased. In other words, on a 
cross section including AQ' A', calling P' the intersection between cross 
section AQ' A' and line segment DE, by creating the ellipse that passes 
through point Q' and has A' and P' as foci and creating the part of the 
ellipse centered at point Q' so that it is formed in the direction of the 
minor axis, the quantity of light on the line being read on the surface of 
the original document 101 is increased. 
With the embodiments explained above, an explanation was provided for a 
device with at least one toric mirror having a toric surface with two 
major meridian, but the advantages of the present invention could be 
obtained even if the device had a cylindrical mirror and cylindrical lens 
with a so-called cylindrical surface that is comprised of a toric surface 
having one major meridian. 
With the present invention, as explained above, the line bow phenomenon is 
reduced by appropriately setting the reflective surface and external shape 
of the toric mirror. Therefore it is possible to realize approximately 
linear illumination of the surface of the original document that is being 
read, thereby obtaining illumination in which the amount of light is 
uniform. 
While this invention has been described in conjunction with specific 
embodiments thereof, it is evident that many alternatives, modifications 
and variations will be apparent to those skilled in the art. Accordingly, 
the preferred embodiments of the invention as set forth herein are 
intended to be illustrative, not limiting. Various changes may be made 
without departing from the spirit and scope of the invention as defined in 
the following claims.