U.S. patent application number 11/907653 was filed with the patent office on 2008-02-21 for image reading apparatus.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Naoaki Ide.
Application Number | 20080043298 11/907653 |
Document ID | / |
Family ID | 32849517 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080043298 |
Kind Code |
A1 |
Ide; Naoaki |
February 21, 2008 |
Image reading apparatus
Abstract
An image reading unit according to the present invention
includes a lamp to incorporate a change in temperature conditions
to the emitting light amount, the lamp capable of illuminating an
reading object with a light of a predetermined intensity, an image
signal generation unit which generates an image signal
corresponding to the reflected light generated when a reading
object is illuminated, and a cooling unit which cools a
predetermined range of the lamp, so that the intensity change in
the light radiated from the lamp of the illumination unit, in the
length direction of the illumination unit can be suppressed.
Inventors: |
Ide; Naoaki; (Shizuoka-Ken,
JP) |
Correspondence
Address: |
FOLEY AND LARDNER LLP;SUITE 500
3000 K STREET NW
WASHINGTON
DC
20007
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
TOSHIBA TEC KABUSHIKI KAISHA
|
Family ID: |
32849517 |
Appl. No.: |
11/907653 |
Filed: |
October 16, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10354042 |
Jan 30, 2003 |
|
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11907653 |
Oct 16, 2007 |
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Current U.S.
Class: |
358/509 |
Current CPC
Class: |
H04N 1/02815 20130101;
H04N 1/00981 20130101; H04N 1/0287 20130101 |
Class at
Publication: |
358/509 |
International
Class: |
H04N 1/46 20060101
H04N001/46 |
Claims
1. An image reading apparatus comprising: an illumination unit
including a lamp to incorporate a change in temperature conditions
to the emitting light amount, the lamp extending in a predetermined
direction and having a predetermined length, the lamp illuminating
a reading object with a light of a predetermined intensity; an
image signal generation unit which generates an image signal
corresponding to a reflected light based on the reflected light
generated when the reading object is illuminated; and a light
intensity setting unit which sets a variation in the intensity of
the light radiated from the illumination unit within a
predetermined range in a length direction of the illumination
unit.
2. The image reading apparatus according to claim 1, wherein the
light intensity setting unit maintains the temperature distribution
in the length direction of the lamp of the illumination unit at a
predetermined condition.
3. The image reading apparatus according to claim 2, wherein the
light intensity setting unit includes at least two fans, the fans
provided at the positions satisfying the predetermined conditions
concerning the length direction of the illumination unit.
4. The image reading apparatus according to claim 3, wherein each
of the fans can be changed independently in the distance to the
lamp and/or the number of revolution.
5. The image reading apparatus according to claim 3, further
comprising an uniformalizing member which prevents the wind
generated by the fan from applying directly to the lamp of the
illumination unit.
6. The image reading apparatus according to claim 5, wherein the
uniformalizing member is made of metal with high thermal
conductivity.
7. A method for controlling a variation of light intensity of an
illumination lamp in a longitudinal direction comprising: detecting
a variety of light intensity of the illumination lamp in the
longitudinal direction based on a white reference marker which is
outputted from a CCD sensor and provide a reference for shading;
and cooling the illumination lamp by at least two fans provided at
positions separated in the longitudinal direction with variable
amounts of cooling wind to set the output signal outputted from the
CCD sensor and the variation of light intensity of the illumination
lamp in the longitudinal direction within a predetermined
range.
8. The method according to claim 7, wherein the amount of cooling
wind provided by each of the fans is controlled by the number of
rotations of the fan.
9. The method according to claim 7, wherein the amount of cooling
wind provided by each of the fans is determined based on a distance
between the fan and the illumination lamp.
10. An image reading apparatus comprising: an illumination unit
including a lamp to incorporate a change in temperature conditions
to the emitting light amount, the lamp extending in a predetermined
direction and having a predetermined length, the lamp illuminating
a reading object with a light of a predetermined intensity; an
image signal generation unit which generates an image signal
corresponding to a reflected light based on the reflected light
generated when the reading object is illuminated; and a light
intensity setting unit which includes at least two fans and sets a
variation in the intensity of the light radiated from the
illumination unit within a predetermined range in a longitudinal
direction of the illumination unit in accordance with a temperature
distribution in the longitudinal direction of the lamp.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional based upon U.S.
application Ser. No. 10/354,042, filed Jan. 30, 2003, the entire
contents of all of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an image reading apparatus
for obtaining image data for an electro-photographic image forming
apparatus, for example, and an image forming apparatus having the
image reading apparatus.
[0003] An image reading apparatus or a scanner converts a reflected
light obtained by lighting a reading object such as a sheet-like
document, book and three-dimensional object, by an image reading
sensor such as a CCD sensor, and outputs the image data.
[0004] In many cases, in an image reading apparatus, a reflected
light from a reading object is transmitted to a CCD sensor
(illuminated by an illumination unit), by moving an optical element
set including an illumination unit and mirrors along a glass plate,
while remaining a reading object standstill at a predetermined
position in a document holding unit (a transparent glass
plate).
[0005] An illumination unit has a tubular exposing lamp formed to
be able to illuminate the reading width that is defined as a total
length of an optional one side of a transparent glass plate of a
document holding unit.
[0006] For example, in a scanner using a halogen lamp as an
exposing lamp, a fan is required for cooling a glass plate or a
document holding unit, a marker plate which provides a white
reference for shading correction, and the inside of a scanner. In a
scanner using a xenon lamp or a cold cathode-ray tube with small
amount of heat, a cooling fan is not necessarily required.
[0007] Although a lamp with small amount of heat such as a xenon
lamp is used, a higher illuminance is required to meet an apparatus
with a high reading speed (and image forming speed) or a color
copying apparatus, and the lamp is heated to a high temperature. In
a case where a specific position in a document holding unit is
illuminated like in a sheet-through system, the temperature of the
document holding unit rises high, and cooling is necessary.
[0008] Cooling or ventilation with a fan is necessary also to
prevent adhesion of dust to mirrors or the glass surface.
[0009] It is known that a lamp represented by a xenon lamp with a
phosphor applied to the inside of a tube changes in the
light-emitting efficiency of the phosphor, when the temperature in
the tube changes. Particularly, when the temperature in the tube is
lowered by cooling, the light-emitting efficiency increases and the
output light quantity increases. Thus, when a fan is mounted simply
for cooling, the luminance at an optional position in the reading
width defined in a document holding unit changes in the length
direction of the lamp depending on the direction and amount of the
wind from the fan.
[0010] When illuminance varies in the reading width of a document
holding unit, the image quality (level) of an image to be read
lowers. The S/N ratio of an image signal outputted from a CCD
sensor is deteriorated, and/or variations occur in the shading
correction.
BRIEF SUMMARY OF THE INVENTION
[0011] It is an object of the present invention is to improve the
image quality of the image information obtained by an image reading
sensor, by optimizing the distribution of the light radiated from a
lamp of an illumination unit in the length direction of the
illumination unit.
[0012] According to an aspect of the present invention, there is
provided an image reading apparatus comprising an illumination unit
including a lamp to incorporate a change in temperature conditions
to the emitting light amount, the lamp extending in a predetermined
direction and having a predetermined length, the lamp illuminating
a reading object with a light of a predetermined intensity; an
image signal generation unit which generates an image signal
corresponding to a reflected light based on the reflected light
generated when the reading object is illuminated; and a light
intensity setting unit (a cooling unit) which can set a change in
the intensity of the light radiated from the illumination unit
within a predetermined range in the length direction of the
illumination unit.
[0013] According to another aspect of the present invention, there
is provided an image reading apparatus comprising an illumination
unit including a lamp to incorporate a change in temperature
conditions to the emitting light amount, the lamp extending in a
predetermined direction and having a predetermined length, the lamp
illuminating a reading object to obtain the reflected light from
the reading object; a first control unit which changes the capacity
of the lamp of the illumination unit to illuminate the reading
object; an image signal generation unit which generates an image
signal by opto-electrically converting the reflected light; an
optical unit which inputs the reflected light to the image signal
generation unit; a second control unit which operates the image
signal generation unit; a white reference marker which provides a
reference for shading correction and illuminance of an illumination
light to illuminate the reading object; an image processing unit
which compensates a fluctuation in an image signal caused by any
one of or all of the image signal generation unit, the illumination
unit and the optical unit, and performs shading correction of the
output of the image signal generation unit to set a reference for
the output level of the image signal generation unit; a cooling
unit which cools the lamp of the illumination unit; a third control
unit which operates the cooling unit; and a control amount setting
unit which sets the cooling amount when operating the cooling unit
by the third control unit, and gives an instruction to the third
control unit.
[0014] According to still another aspect of the present invention,
there is provided an image reading apparatus comprising an
illumination unit including a lamp to incorporate a change in
temperature conditions to the emitting light amount, the lamp
extending in a predetermined direction and having the distribution
of the emitting light amount in the length direction, the lamp
illuminating a reading object to obtain the reflected light from
the reading object; a lamp lighting circuit which changes the
capacity of the lamp of the illumination unit to illuminate the
reading object; a line CCD sensor which generates an image signal
by opto-electrically changing the reflected light; an optical unit
which transmits the reflected light to the light receiving surface
of the line CCD sensor; a CCD sensor driving unit which operates
the line CCD sensor; a white reference marker which provides a
reference for shading correction and illuminance of an illumination
light to illuminate the reading object; an image processing unit
which compensates a fluctuation in an image signal caused by any
one of or all of the line CCD sensor, the illumination unit and the
optical unit, and performs shading correction of the output of the
line CCD sensor to set a reference for the output level of the line
CCD sensor; a cooling fan which generates a cooling wind for
cooling the lamp of the illumination unit; an illuminance comparing
unit which compares the image signal outputted from both ends in
the length direction of the line CCD sensor and the image signal
outputted from the part close to the center in the length direction
of the line CCD sensor, among the reflected lights obtained when
the white reference marker is illuminated by the lamp, and sets the
wind amount of the cooling wind to be outputted by the cooling fan;
a motor driving unit which operates the cooling fan; and a control
amount setting unit which sets a value to be instructed to the
motor driving unit, to achieve the wind amount of the cooling wind
to be outputted by the cooling fan.
[0015] Additional objects and advantages of the invention will be
set forth in the description which follows, and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinafter.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0016] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention, and together with the general description given
above and the detailed description of the embodiments given below,
serve to explain the principles of the invention.
[0017] FIG. 1 is a schematic diagram explaining an example of an
image reading apparatus according to the present invention;
[0018] FIG. 2A is a schematic diagram explaining a layout of
cooling fans in the image reading apparatus shown in FIG. 1;
[0019] FIG. 2B is a schematic diagram explaining another layout of
cooling fans in the image reading apparatus shown in FIG. 1;
[0020] FIG. 3 is a block diagram explaining a signal processing
system and a driving control system incorporated in the scanner
shown in FIG. 1;
[0021] FIG. 4 is a view explaining the orientation characteristic
of an illumination lamp in the length direction, when cooling is
not performed;
[0022] FIG. 5 is a view explaining the changes in the orientation
characteristic of the light outputted from the illumination lamp,
when the illumination lamp which can output the light of the
orientation characteristic shown in FIG. 4 is cooled only at the
part close to the center in the length direction;
[0023] FIGS. 6 and 7 are views explaining an illuminance
distribution on a document table achieved by cooling with two
cooling fans arranged as explained in FIGS. 2A or 2B;
[0024] FIGS. 8A and 8B are schematic diagrams explaining an example
of another embodiment for cooling the illumination lamp in the
image reading apparatus shown in FIG. 1;
[0025] FIG. 9 is a view explaining still another embodiment for
cooling the illumination lamp in the image reading apparatus shown
in FIG. 1;
[0026] FIG. 10 is a view explaining an example of the output of a
CCD sensor obtained as a result of the cooling shown in FIG. 9;
and
[0027] FIG. 11 is a block diagram explaining an example of a
driving control system which can achieve the cooling shown in FIGS.
9 and 10.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Hereinafter, an image reading apparatus to which an
embodiment of the present invention is applicable, and an example
of an image forming apparatus in which the image reading apparatus
is incorporated, will be explained with reference to the
accompanying drawings. An embodiment will be explained taking an
example of a digital copier.
[0029] As shown in FIG. 1, an image reading apparatus (a scanner)
101 has a document table 11, which is made of optically transparent
material represented by a glass, and formed like a transparent
plate with the substantially uniform thickness.
[0030] Below the document table 11, at a predetermined position in
the image reading apparatus, a CCD sensor 12 which converts the
image information of a reading object 0 into an electric signal (an
image signal), is provided. The output from the CCD sensor 12 is
applied to an image processor circuit board 20.
[0031] At a predetermined position close to one side of the
document table 11, a white reference marker (a white reference
plate) 13 is provided to set a white reference value of the CCD
sensor 12, and to control the distribution of illuminance at the
reading position of the reading object 0 set on the document table
11.
[0032] In the space under the document table 11, first and second
carriages 14 and 15 are provided.
[0033] At predetermined positions in the first carriage 14, an
illumination lamp (an exposing unit) 16 which illuminates the
reading object 0 placed on the document table 11, an image light
take-out mirror 14a which guides the light reflected from the
reading object 0 illuminated by the light from the illumination
lamp 16, that is, the image light in a predetermined direction, and
a lamp lighting circuit (an exposure control circuit) 17 which
lights the illumination lamp 16 so that it can radiate a light with
a predetermined intensity. The illumination lamp 16 is replaceable
by a xenon lamp or a cold cathode-ray tube, for example.
[0034] In the second carriage 15, first and second mirrors 15a and
15b are provided to guide the image light reflected from the image
take-out mirror 14a toward the CCD sensor 12.
[0035] Between the second carriage 15 and the CCD sensor 12, a lens
18 is provided to give a predetermined optical characteristics and
an image-forming magnification to the image light, which is
reflected by the second mirror 15b and guided to the CCD sensor
12.
[0036] Under the document table 11, at the position capable of
supplying an air current to the first and second carriages 14, 15
and the document table 11, first and second cooling fans (flat
cooling mechanism) 19a and 19b are provided.
[0037] The fans 19a and 19b are arranged with a predetermined
distance in the direction along the length direction of the
illumination lamp 16, as shown in FIG. 2A. The fans 19a and 19b may
also be arranged with difference distances from the lamp 16,
according to the space saved between the illumination lamp 16, in
the state viewed from the plane direction of the document table 11,
as shown in FIG. 2B.
[0038] FIG. 3 is a block diagram explaining a signal processing
system and a driving control system incorporated in the scanner
shown in FIG. 1.
[0039] In the scanner 101 shown in FIG. 1, the first and second
carriages 14 and 15 are moved by the rotation of a driving motor
21, to a home position not described in detail, or a position where
at least the white reference marker 13 can be illuminated by the
light from the illumination lamp 16. Therefore, the output of the
CCD sensor 12 corresponds to the intensity of the reflected light
from the white reference marker 13.
[0040] Since the white reference marker 13 is usually controlled
with a predetermined range of brightness (color and density),
reflectivity and surfaceness (diffuse reflection) over all areas
illuminated by the light from illumination lamp 16, when the output
of the CCD sensor 12 is not flat, it is seen that one of the
factors, such as the output level of each pixel of the CCD sensor
12 (the conversion efficiency), uneven lighting of the lamp 16, out
of the optical axis on the lens 18 or out of position of the lens,
and stains in the image take-out mirror 14a, first and second
mirrors 15a, 15b, and document table 11, is deviated from the
allowable reference value or the set value by more than the
specified value.
[0041] The CCD sensor 12 is a line sensor in which 7,500 pixels are
arranged like a straight line. The sensitivity of each pixel of the
CCD sensor is not constant, and has intrinsic variations.
[0042] The intensity of the light radiated from the illumination
lamp 16 is also not constant in the length direction (the
orientation distribution or the deviation in the light intensity in
the length direction of the lamp is different for each lamp, and
controlled as an individual difference).
[0043] The lens 18 has the characteristic that when the enlarging
angle viewed from the center of the lens 18 is assumed to be
.theta., the intensity of the light passing through the lens 18 is
decreased proportional to cos .sup.4.theta.. Therefore, when the
intensity of the light radiated from the illumination lamp 16 is
uniform over all areas in the length direction of the illumination
lamp 16, the intensity of the light passing through the periphery
of the lens 18 is decreased.
[0044] Because of these factors, in many cases, even if the image
of the reading object O is substantially equal in the image density
along the length direction of the illumination lamp 16, the density
level of the image signal outputted from the CCD sensor 12 is not
necessarily reproduced evenly along the length direction of the
illumination lamp 16.
[0045] Thus, before the image of the reading object O is inputted
into the individual pixels of the CCD sensor 12, the sensitivity of
each pixel of the CCD sensor 12 is corrected. Namely, the
sensitivity of the CCD sensor 12 is calibrated based on the black
reference image (lamp off) and white reference image (white
reference marker).
[0046] Assuming that k is a coefficient (magnification), S is an
image signal before correction, B is black data and W is white
data, based on the previously read black data or the output of the
CCD sensor 12 when the illumination lamp 16 is off, and the white
data or the output of the CCD sensor 12 against the reflected light
from the white reference marker 13, for example, calculate the
correction value I by the equation I=k {(S-B)/(W-B)}, whereby the
shading of the output signal from the CCD sensor 12 is
corrected.
[0047] More particularly, the white reference marker reading signal
outputted from the CCD sensor 12 is amplified to a predetermined
level by an amplifier circuit 71 in the image processor circuit
board 20, and applied to an A/D converter circuit 72, where the
signal is converted from analog to digital.
[0048] The A/D converted white reference marker reading signal is
corrected in the shading, based on the above-mentioned black data,
by calculating the correction value I in the shading correction
circuit 73.
[0049] As explained above, the illumination lamp 16 is a xenon lamp
or a cold cathode-ray tube, and the amount of the illumination
light radiated from the part cooled by the cooling fans 19a and 19b
is increases compared with the illumination lights from the other
parts.
[0050] For example, when the cooling fans 19a and 19b are not
provided, the illumination light radiated from the illumination
lamp 16 has the flat orientation characteristic all over the length
direction, as shown in FIG. 4, and only the part close to the
center of the lamp 16 is cooled by a fan, the illuminance at the
part close to the center of the document table 11 is increased to
be larger than the reference value Lx, as shown in FIG. 5. FIGS. 4
and 5 graphically shows the changes in the illuminance on the
document table 11, expressing the distance in the length direction
of the illumination lamp 16 along the horizontal axis, and the
intensity of the illumination light radiated from the lamp 16 along
the vertical axis. As to the orientation in the length direction of
the illumination lamp 16, there is a type in which the light amount
at both ends is set higher or lower than that at the center, but it
is needless to say that the amount of the light radiated from a
cooled part is larger than those radiated from the other parts.
[0051] Accordingly, as to the illumination lamp 16 having the
orientation characteristic shown in FIG. 4, the output of the CCD
sensor 12 can be made flat all over the length direction, by
increasing the amplitude against the output signal from the parts
(the output of the CCD sensor 12) with lower illuminance on the
document table 11.
[0052] However, in this method, the noise level is also amplified
at the ends of the CCD sensor 12, and the S/N ratio is
deteriorated. That is, if the output difference between the ends
and the center is double, the noise level is also doubled.
[0053] Further, when the light amount at the part close to the
center in the length direction of the illumination lamp 16 is
extremely increased by the cooling, there arises another problem
that the output at the part close to the center of the CCD sensor
12 is saturated. In this case, the shading correction becomes
incomplete (the correction limit is exceeded), and the image signal
becomes defective (an opaque defect occurs in the output
image).
[0054] Thus, as explained before with reference to FIG. 2A, the
first and second fans 19a and 19b are provided at both ends or
close to the both ends in the length direction of the illumination
lamp 16, and by the control of a scanner CPU 51, a predetermined
value (a voltage or the number of pulse corresponding to the number
of rotation) is instructed to a cooling fan driving circuit 53 to
control the amount of the cooling wind provided from each fan to
the illumination lamp 16, so that the white reference marker
reading signal outputted from the CCD sensor 12 becomes
substantially equal over all areas in the length direction of the
illumination lamp 16. By this instruction, the cooling fans 19a and
19b are driven at predetermined speeds to supply a predetermined
amount of cooling wind to the illumination lamp 16, and the
illuminance on the document table 11 is made substantially equal in
all parts in the length direction of the illumination lamp 16, as
shown in FIG. 6, at a level L1 a little higher than the reference
value Lx shown in FIGS. 4 and 5.
[0055] Owing to the structural feature of the scanner 101, as
explained before with reference to FIG. 2B, there may be the case
where the distance from the first and second cooling fans 19a and
19b to the illumination lamp 16 is not the same.
[0056] In this case, a predetermined value (a voltage or the number
of pulse corresponding to the number of rotation) is instructed to
the cooling fan driving circuit 53 independently for each of the
fans 19a and 19b, so that the white reference marker reading signal
outputted from the CCD sensor 12 becomes substantially equal over
all areas in the length direction of the illumination lamp 16,
according to the distance from the lamps 19a and 19b to the
illumination lamp 16.
[0057] As stated above, even if the distance from the first and
second cooling fans 19a and 19b to the illumination lamp 16 is not
the same, the illuminance on the document table 11 is made
substantially equal in all parts in the length direction of the
illumination lamp 16, as shown in FIG. 7, at a level L2 a little
higher than the reference value Lx shown in FIGS. 4 and 5.
[0058] In other words, the illumination distribution on the
document table 11 can be set to substantially equal, by setting the
amount of the cooling wind provided from the fan located near to
the lamp 16 smaller than that from the fan located far from the
lamp 16, so that the degrees of cooling the lamp 16 by the two fans
become substantially equal, as shown in FIG. 2B.
[0059] The positions of the cooling fans shown in FIG. 2B may be
previously set, and can easily be set also by making at least one
of the fans arranged as shown in FIG. 2A movable to a desired
position manually or by a fan moving mechanism includes a not-shown
moving guide and a moving unit or the like.
[0060] Further, since the cooling fans 19a and 19b are provided at
the position or close to the position where the fluctuation in the
light amount in the length direction of the illumination lamp 16,
the fluctuation in the illumination distribution at the position on
the document table 11 where the reading object 0 is illuminated,
can also be suppressed to small. However, in many cases, the fan
mountable position is controlled by the number of elements and
wiring materials disposed in the scanner 101 or the construction
cabinet, and a fan moving mechanism is not necessarily be
provided.
[0061] As described above, in the scanner in which the illumination
distribution on the document table 11 in the length direction of
the lamp 16 is made uniform by supplying a predetermined amount of
cooling wind from the first and second fans 19a and 19b, by the
control of the scanner CPU 51, a predetermined value is instructed
to the lamp lighting circuit 17, and the illumination lamp 16 is
lit to be able to radiate a light with a predetermined intensity
(light amount). When a not-shown control panel or an external unit
instructs to read the image of the reading object 0 set on the
document able 11, the lamp 16 may remain lighting (for the shading
correction).
[0062] In the above-mentioned scanner 101, when the illumination
lamp 16 radiates a light with a predetermined intensity, the
elongate area of the reading object 0 placed on the document table
11 along the direction where the illumination lamp 16 is extended
is illuminated, and the reflected light or the image light is
sequentially reflected by the image take-out mirror 14a, the first
mirror 15a and the second mirror 15b, and is guided to the lens 18.
The image light guided to the lens 18 is given a predetermined
image-forming magnification, and focused to the CCD sensor 12.
[0063] Thereafter, under the control of the scanner CPU 51, a
predetermined value or the number of motor driving pulses (or a
voltage) is applied to the motor driving circuit 52, and the
driving motor 21 is driven at a predetermined speed. Therefore, the
positions of the first and second carriages 14 and 15, to which the
rotation of the driving motor 21 is transmitted through a not-shown
driving force transmission mechanism, are continuously changed
along the document table 11. Namely, the first and second carriages
14 and 15 are moved along the document table 11.
[0064] Thus, the position of the reading object 0 illuminated by
the light from the illumination lamp 16 is sequentially changed
along the document table 11, and the reflected light is
sequentially focused to the CCD sensor 12. Therefore, the images of
the reading object 0 in all areas on the document table 11 are
guided to the CCD sensor 12.
[0065] The first and second cooling fans 19a and 19b are driven at
predetermined speeds to be able to supply the cooling wind of a
predetermined amount, when a predetermined value is instructed to
the cooling fan driving circuit 53 while at least the illumination
lamp 16 is lighting, that is, while the first and second carriages
14 and 15 are being reciprocated along the document table 11. The
fans 19a and 19b can supply the cooling wind with a desired amount,
according to the driving pulse or voltage supplied to the fan
driving circuit 53.
[0066] Therefore, the document table 11 and illumination lamp 16
are cooled, and adhesion of dust to the document table 11, white
reference marker 13, the mirrors 14a, 15a, 15b, and lens 18 can be
prevented.
[0067] The image signal, whose image information of the reading
object 0 outputted from the CCD sensor 12 has been read, is
converted into a digital signal by the A/D converter circuit 72,
corrected in the black and white levels by the shading correction
circuit 73, and gamma corrected by the image processor circuit 74
to meet the image output characteristic of an image forming unit
103, and the noise component is eliminated.
[0068] After gamma corrected by the image processor circuit 74, the
image signal is stored line by line in a work memory (or an image
memory) or RAM 76 at a predetermined time interval through a shift
register 75 (or a buffer memory), for example. A predetermined
image processing is performed for the stored image signal, and the
image processed signal is outputted as an image signal to an
external memory or an external unit (a printer).
[0069] FIGS. 8A and 8B show another embodiment for cooling the
illumination lamp in the scanner shown in FIG. 1.
[0070] As shown in FIG. 8A, a scanner 201 has a document table 11,
a CCD sensor 12, an exposing unit (an illumination lamp) 16, a lamp
lighting circuit 17, and at least one cooling fan 219, as in the
scanner 101 explained before with reference to FIG. 1. The
illumination lamp 16 and first carriage 14 are partially covered by
a cover member 220, which prevents the cooling wind generated by
the cooling fan 219 from applying directly to the lamp 16.
[0071] The cover member 220 is provided except the area where the
illumination light from the illumination lamp 16 is blown toward
the document table 11. Namely, the cover member 220 can be used in
an optional form and structure, for example, it can be formed
cylindrical with an opening formed by cutting out the part located
between the illumination lamp 16 and document table 11. The cover
member 220 can be made of a metal plate with high thermal
conductivity, such as, a copper (Cu) and aluminum (Al).
[0072] As shown in FIG. 8A, by covering the illumination lamp 16
(and a part of the first carriage 14 which holds the lamp 16) by
the cover member 220, it can be prevented that a specific area of
the lamp 16 is extremely cooled. That is, by using the cover member
220, the cover member 220 is cooled, and the air around the lamp 16
is cooled. Thus, only a specific part in the length direction of
the illumination lamp 16 is cooled, and variations in the light
amount can be prevented. Further, as shown in FIG. 8A, by using the
cover member 220 to temporarily cool the air around the lamp, only
one cooling fan 219 is required.
[0073] FIG. 8B shows a modification example of providing the cover
member shown in FIG. 8A. In this example, at least the illumination
lamp 16 and lamp lighting circuit 17 are formed and sized to be
covered by the cover member. Namely, in the example shown in FIG.
8B, the first carriage 14 is provided with the lamp lighting
circuit 17 which functions as a heating source like a lamp, in
addition to the illumination lamp 16. Thus, as to the heat radiated
from the lamp lighting circuit 17, by cooling it simultaneously
with the heat from the lamp 16, unevenness in the temperature
around the lamp 16 can be prevented more efficiently than the
example shown in FIG. 8A. Therefore, variations in the illumination
light radiated from the lamp 16 are made smaller (decreased) than
the example shown in FIG. 8A.
[0074] FIG. 9 shows an example of another configuration for cooling
the illumination lamp in the scanner shown in FIG. 1. FIG. 10 shows
an example of the output of the CCD sensor obtained as a result of
the cooling shown in FIG. 9. FIG. 11 shows a block diagram
explaining the driving control system which can achieve the cooling
shown in FIGS. 9 and 10. In the example explained with reference to
the FIGS. 1, 2A, 2B, 3 to 7, the illumination lamp is cooled evenly
in the total length, for the purpose of uniforming the light
radiated from the illumination lamp in the length direction of the
lamp.
[0075] However, in the system using the lens 18, as the distance
from the center of the lens increases, the intensity of the light
guided to the CCD sensor 12 is decreased, and there are many cases
where the intensity of the light radiated from the illumination
lamp 16 to the reading object 0 is increased at both ends of the
lamp 16. Further, since the intensity of the light radiated from
the lamp 16 is gradually decreased depending on the total time (the
accumulated hours) of turning on the lamp, the thickness of the
light-emitting body (phosphor) or the phosphor amount at both ends
of the lamp is increased in many cases compared with the phosphor
thickness (amount) at the part close to the center of the lamp.
[0076] It is seen from the above description the intensity of the
light generated from the illumination lamp 16 changes (mostly,
decreases) depending on the total time of turning on the
illumination lamp 16. Therefore, when cooling the illumination lamp
16 by using the cooling fans 19a and 19b, if the total time since
the initial turning on of the scanner 301 is insufficient, the
light amount at the ends in the length direction of the lamp 16 is
increased to be larger than the reference value, and the image
information of the reading object 0 may be damaged. On the other
hand, as the total time of turning on the lamp 16 increases, the
base density of the image information at the positions
corresponding to both ends of the lamp 16 increases, and the
contrast may become dull compared with the image signal obtained
from the part close to the center of the lamp.
[0077] Thus, in the scanner 301 shown in FIGS. 9 and 10, the image
signal outputted from the CCD sensor 12 and converted into a
digital signal by the AID converter circuit 72, is applied to a
center illuminance extractor circuit 251 and an end illuminance
extractor circuit 252, where the illuminance at the part close to
the center and ends of the lamp 16 is taken out, and the signal is
applied to an illuminance distribution comparator circuit 253.
[0078] The illuminance distribution comparator circuit 253 outputs
the value to indicate the difference between the illuminance at the
part close to the center and ends of the lamp.
[0079] Thereafter, based on the instruction from the scanner CPU
51, a predetermined value (the number of rotation) is instructed
independently to the cooling fan driving circuit 53, so that each
of the fans 19a and 19b can be driven at predetermined speeds, that
is, capable of supplying the cooling wind of a predetermined
amount. Therefore, the ends of the illumination lamp 16 are cooled
by respective fans 19a and 19b, so that the intensity of the light
radiated from the ends of the illumination lamp 16 becomes to be
the predetermined intensity.
[0080] As stated above, the intensity of the light radiated from
the lamp 16, which changes depending on the accumulated turning on
hour, is held at the predetermined intensity. In this case, as
shown in FIG. 10, the intensity of the illumination light applied
to the light receiving surface of the CCD sensor 12 to form an
image, is held substantially equal at optional positions
corresponding to all areas in the length direction of the lamp
16.
[0081] Namely, concerning the length direction of the CCD sensor
12, a homogeneous reading signal can be obtained in all areas in
the length direction, without lowering the S/N ratio of the image
signal outputted from an optional position. In this case, both ends
of the illumination lamp 16 are cooled by the cooling fans 19a and
19b, respectively, so that the intensity of the light radiated from
the illumination lamp 16 is increased within a range that the
illumination of the illumination light on the document table 11 to
be inputted to the CCD sensor 12 is not saturated. The amount of
the cooling wind blown from the fans 19a and 19b to the
illumination lamp 16 can be easily changed by setting the number of
rotation of each fan or the motor driving current supplied to each
fan, based on the output corresponding to the reflected light from
the white reference marker 13, for example.
[0082] More particularly, when reading the reflected light from the
white reference marker 13 for the shading correction, for example,
the mean value of the 500 pixel outputs at the center and the mean
value of the 500 pixel outputs at both ends, among the image
signals outputted from the CCD sensor 12, are compared.
[0083] When the mean value of the pixel outputs at both ends is
lower than the mean value of the pixel outputs at the center, the
cooling fans 19a and 19b are rotated at a first predetermined
speed, and both ends of the lamp 16 are cooled. Then, the means
value of the 500 pixel outputs at the center is compared again with
the mean value of the 500 pixel outputs at both ends.
[0084] When the mean value of the outputs at both ends is lower
than the mean value of the outputs at the center, the driving
current supplied to the fans is increased, and the cooling fans are
rotated at a second predetermined speed faster than the first
speed. Namely, both ends of the lamp 16 are further cooled.
[0085] As described above, cooling both ends of the lamp 16 and
comparing the outputs at the center and both ends of the CCD sensor
12 are repeated until the output difference of the CCD sensor 12
comes in .+-.5%, and/or reaching a range of predetermined allowable
number, thereby the output level of the CCD sensor 12 is made
uniform in all areas in the length direction.
[0086] Further, the intensity of the light at both ends of the
illumination lamp 16 is increased by adding the phosphor amount or
changing the electrode form, and the lamp is more expensive than
the lamp with flat orientation. By cooling both ends with cooling
fans, the light intensity at both ends can be increased without
increasing the cost.
[0087] As explained hereinbefore, according to the present
invention, the flow of wind supplied by the cooling fans to cool
the illumination lamp is optimized, and variations in the
illuminance on the document table can be suppressed. Therefore, the
picture quality of the reading image is improved.
[0088] Moreover, according to the present invention, when there is
an intensity difference between the light radiated from both ends
in the length direction of the lamp and the light radiated from the
part close to the center of the lamp, owing to the structure of the
illumination lamp, a homogeneous reading signal can be obtained all
over the area in the length direction of the CCD sensor, without
lowering the S/N ratio of the image signal outputted from an
optional position.
[0089] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *