Note: Descriptions are shown in the official language in which they were submitted.
- 1331979
ILLUMINATION DEVICE
Background of the Invention
Field of the Invention~
The present invention relates to an ~
illumination device to be used as a surface light source ~-
havlng uniform brightness, for example, as back light for -~
a liquid crystal cell. -
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The prior art will be discussed in detail -~
~f hereinbelow.
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~ Summary of the Invention
A primary object of the present invention is to
provide an illumination device comprising a reflecting
plate, linear light sources arranged closely to said ; ;~
reflecting plate and a diffusing plate arranged on the
opposite side of said reflecting plate with regard to
said light sources, sectional surface of said reflecting
. . .
plate on the plane perpendicular to the longitudinal
dlrection of said light sources having a shape of a
;~ concave curve whose curvature is continuously varying so
~ 20 as to assure uniform luminance distribution on said ~ ;
i diffusing plate.
Another object of the present invention is to
provide an illumination device characterized in that said~
!~ ~ reflecting plate is composed by bonding a metal foil
~ 25 forming a reflecting surface to said reflecting pla~e ;
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body made of a synthetic resin in said illumination
device.
A third object of the present invention is to
provide an illumination device wherein said reflecting
plate is formed as a member integral with a metal foil by
injection molding of a reflecting plate body made of a
synthetic resin.
A fourth object of the present invention is to
provide an illuminat~ion device formed by combining a .
plural number of members which are obtained by dividing,
along surfaces perpendicular to the longitudinal -
direction of said light sources, a reflecting plate made
as a member integral with a metal foil by injection
molding of a reflecting~plate body made of a synthetic
resin.
Brief Description of the Drawinqs
Fig. 1 and Flg. 2 show partially broken
perspective views illustrating the conventional
illumination devices respectively;
Fig. 3 shows a curve illustrating luminance
distribution on the diffusing plate o~ the illumination
device shown in Fig. 2; - ;
Fig. 4 shows a sectional view illustrating an `~
embodiment of the illumination device according to the ~-
25~ present lnvention;
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Fig. 5 shows a graph illustrating relationship
between position of the light source and luminance
distribution of the conventional illumination device;
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Fig. 6 shows a graph illustrating luminance
distribution obtained by the embodiment shown in Fig. 4;
Fig. 7 shows a sectional view of an apparatus
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for molding the reflecting plate used in the illumination ~ ;
device according to the present invention; ;~`
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~ Fig. 8 shows a sectional view on an enlarged ~
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soale illustrating the metal foil sheet for forming the
mirror surface of the reflecting plate;
,.
Fig. 9 shows a perspective view of the
illumination device using the reflecting plate body ~-~
formed integrally with a frame;
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Fig. 10 shows a perspectlve view of the
illumination device shown in Fig. 9 as seen from the
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bottom surface thereof;
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Fig. 11 shows a perspective view of a divided
member of the reflecting plate body; `
Fig. 12 shows an assembly diagram of the
`,~ divided refleating plate body; and
~ Fig. 13 and Fig. 14 show sectional views
ii ~ illustrating joined portions of the reflecting pIate body
in the assembIed condition thereof.
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As the conventional illumination device for
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1331979
illuminating a plane surface at a uniform brightness over
a relatively wide range, the illumination device having
the composition shown in Fig. 1 is already known. This
illumination device comprises two sets of parallelly ~ ~
arranged illumination systems; each consisting of a : -
fluorescent tube 1 designed as a linear light source and ~ --
a reflecting mirror 2 which is arranged under the
fluorescent tube 1, has a sectional shape of arc or ~
quadratic curve and elongated in the longitudinal ~;
;10 dlrectlon of the fluorescent tube 1; and a rectangular
diffusing plate 3 arranged on the illumination systems.
Since~the conventional illumination device of
this type uses the reflecting mirrors havlng the~
sectional shape of arc or quadratic curve, the
illumination device has large thickness~d and is designed
as a relatively large unit accordingly.` Therefore, the
conventional illumination device is not su~ited for use as ~-
- an illumination devlce for back light of liquid crystalcell. Further, the conventional illumination device
cannot assure uniform luminance on the diffusing plate 3 ;
and has a defect that lumlnance ls too low or the ~ ;~
diffusing plate is too dark. In order to obtain
relatively uniform luminannce distribution with thls ~ ;
il}umlnation device,~it ls sufficlent to reserve a wlde
~2~5 ~ distance between the illumination systems 10 and the
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diffusing plate 3, but such a corrective measure is
undesirable since it inevitably enlarges the illumination
device and lowers luminance.
Further, as an illumination device of this type
and having small thickness, the illumination device ~ -
having the composition shown in Fig. 2 is also known.
Speaking concretely, this illumination device comprises
fluorescent tubes 1 parallelly arranged in a reflecting -
.
member 4 which is composed by arranging inclined and
lo elongated plane reflecting mirrors 4b on both sides of a
plane reflecting mirror 4a, and a diffusing plate 3
arranged over the fluorescent tubes 1. Though this
~ illumination device can be thin and assure relatively ~
; high brightness, luminance distribution on the diffusing
plate 3 is not uniform as shown in Fig. 3. In addition,
since the boundary portion 4c between the bottom surface
4a and inclined surface 4b is folded, there are formed ~
portions at which luminance is varied relatively abruptly ~;
on the diffusing plate 3.
Now, an embodiment oP the illumination device
according to the present invention will be described
detailedly with reference to the accompanying drawings.
A sectional view illustrating the embodiment of
the present invention is shown in Fiy. ~ wherein the ~ ``
reference numeral 11 represents linear light sources such -
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1331979 -
as fluorescent tubes, the reference numeral 12 designates ;~.
a reflecting plate and the reference numeral 13 denotes
a diffusing plate~
In this embodiment of the illumination device, : -
the reflecting plate 12 has flat surfaces 12a (having -
linear sections) under the light sources and surroundings
; ~ ~ thereof, and concave surfaces 12b(having curved sections)
outside the points A relatively far from the light
sources 11. Moreover, the curve on the section of the
concave surface 12b has such a shape as to have différent .
centers of curvature and radii of curvature at different
points on the curve, and the flat surfaces 12a and curved
surfaces 12b are continuous at all points thereof. ..
The continuous shape of said reflecting plate is `.::f
different depending on the size, thickness, etc. of the
illumination device as a whole. In addition, luminance .`.
distribution on the difusing plate 13~can further be .~
uniformalized by designing the flat surfaces of the. ~....... ~`
: reflecting plate 12 as concave surfaces having small . `
curvature or other types of curved surfaces.
When the reflecting plate has flat surfaces only,~
luminance distribution on the diffusing plate is as
shown in Fig. 5. Speaking concretely, luminance is the .
highest at central portion 13a located right over the
light source, lowers from intermediate portions 13b toward ~.
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1331979 :
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end portions 13c and the lowest at the end portions 13c.
In Fig. 5, the reference symbol L corresponds to the
position of the light source and the reference symbol E
corresponds to the end position of the reflecting mirror.
In the embodiment of the illumination device ~
according to the present inventlon shown in Fig. 3, centers ~ .
of curvature and radii of curvature at different points
of the curve surfaces~l2b of the reflecting plate 12 are
so selected as to obtain a flat luminance distribution ~-
~ as whole by compensating luminance at the portions 13b
and 13c.
:
In this embodiment of the illumination~device ~-~
according to the present invention, luminance distribution
, . . .
on the diffusing plate 13 is as shown in-Fig.~6~ e.
; 15 very flat luminance distribution is obtained~by designing ;~
the reflecting plate 12 so as to have the above-desoribed
shape. Further, since the reflecting plate 12 has a shape
continuous over the entire range, the diffusing plate 13 ~as
no portion which causes abrupt variation of luminance `
distribution.
The reflecting plate 12 of this embodiment has ~ ~ -
curved portions of special shapes and cannot be~manufac~
tured easily. However, manufacturing of the reflectlng
plate 12 can be facilitated by forming the reflecting ;~
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~plate body of a synthetic resin and arranging a metallic
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`~ layer having high reflectance such as aluminium on the
inside surface of the reflecting plate body. Moreover,
mass production of the reflecting plate with very high
precision is made possible by preparing metal dies having
high precision for molding the reflecting plate body made
of a synthetic resin.
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In order to arrange the metallic~reflecting layer
in the reflecting plate body made of a synthetic resin,
it is possible to adopt a method to plate or evaporation-
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coat the reflecting plate body with a metal, or a methodto bond a metal foil to the reflecting plate body. The
former plating or evaporation-coating method has defects -`
that metals can hardly adhere directly to the surface of --
a synthetic resin and that the reflecting layer formed by ; ;-`~
lS this method can easily be cracked or peeled off due to ~ , `
variations of temperature and humidity. The latter method -
uses a bonding tape having adhesive surfaces on both sides
to bond a metal foil to the surface of the reflecting
plate body, requires tedious bonding work and easily
allows the metal foil to be furrowed. Since;a furrowed
mirror surface will produce ununiform luminance distri-
bution on the diffusing plate of the illumina~tion device, ~;
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the latter method is undesirable. ;~
One of the characteristics of the present
invention lies in the molding method to form the reflecting ~
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plate made of a synthetic resin integral with the metal
foil.
An embodiment of the molding method for forming
the reflectlng plate to be used in the illumination device
according to the present invention will be described below.
An apparatus for carrying out the molding method -~
for the reflecting plate is illustrated in Fig. 7 wherein
the reference numeral 21 represents a molding press, the
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reference numeral 22 designates a nozzle of the molding
`~ 10 press, the reference numerals 23 and 24 denote molding
dies, the reference numeral 25 represents a ribbon .
consisting of a transparent film (base) 25a, a foil of a `
metal 25b such as aluminium and a layer of a bonding agent
25c formed thereon as shown in Fig. 8 in its sectional
view, the reference numeral 26 designates a ribbon ~eed
spool and the reference numeral 27 denotes a take-up spool. ;
- By using the molding apparatus having the composi- ~
tion descrlbed above, the ribbon 25 is stretched between ;;;
the molding dies 23 and 24 in the open condition of the
dies, and then the dies are closed. With the ribbon 25
sandwiched between the molding dies 23 and 24 by using a
clamp, a resin is injected into the cavity`of the molding
dies through the nozzle 22. Under the pressure produced ~ `
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by the injection of the resin, the base 25a of the ribbon
; 25 25 is pressed onto the core (having convex surfaces when
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the reflecting surface of the reflecting plate is concave)
of the upper die 24, the bonding agent layer 25c on the
opposite side is brought into close contact with the resin
injected into the cavity, the bonding agent is melted by
the heat of the resin, the metal foil 25b is made integral
with the resin, whereby a reflecting plate having a metal
foil made integral on the surface (for example, a concave - ;
~` surface) of the reflecting plate body made of the synthetic
resin is formed after the resin is cooled~and~set. Then, -
the reflecting plate is obtained by opening the~molding ~ ;-
dies and taking out the molding. Since the metal foil 25b
has been peeled off at this stage, a definite length of
the base is wound around the take-up spool 27 to posit}on
the next ribbon 25 between the molding dies 23 and 24.
Successively, the reflecting plate can be forme~d once -
again by repeating the processes described above~
When the reflecting plate having the shape shown `~
in Fig. 4 is to be formed by this method, it is desirable ; `
to use molding dies which sets the gate at the position 35
on the rear surface of the reflecting plate 32 shown in
Fig. 10. In other words, a weld line is produced at the
confluence position of resin flow, thereby furrowing the
metal foil in case of synthetic resin moldings. When the
gate is located at the position shown in Fig. IO, however
, ~
~ 25 the weld line 36 is produced in the direction perpendicular ~
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1331979
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to the longitudinal direction of the light sources as
shown in Fig. 9. Therefore, individual points on this
weld line are located at different distances from the
light sources even when the metal foil is furrowed by the
.
weld line. Accordingly, since the portions reflecting
; light ununiformly due to the furrow are not located at a ~
~ definite distance from the light sources, no ununiform -
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luminance distribution is produced on the diffusing plate.
The reflecting plate shown in Fig. 9 and Fig. lO
has a structure wherein the reflecting plate body 30 is
made integral with a frame 32 and 33. Therefore, this -
structure makes it unnecessary to assemble the reflecting
; plate with the frame, thereby facilitating assembly of the
illumination device. The reflecting plate 30 must be thin-~
to enhance accuracy of the reflecting surface. It is
therefore desirable to mold reinforcing ribs 34 as Lntegral ~ ;
members as shown in Fig. 10. In this case, the reinforcing
ribs should preferably be elonged in the direction per-
:: .
pendicular to the longitudinal direction of the light ~ ~
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soruces. That is to say, even if the metal foil on the
reflecting surface is furrowed at the portions on the ;~
opposite side o~ the ribs 34 due to sink marks, etc. at
~' the molding stage, the furrows are formed in the ;
longitudinal direction of the ribs and do not produce
~ 25 ununiform luminance distribution for the same reason as
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that due to the furrows produced by the weld line ~
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~; described above. ;Now, descriptions will be made on another method -
to form the reflecting plate consisting of a reflecting
;~ 5 plate body made of a synthetic resin and having a metal :
foil bonded to the surace~thereof.
First, a reflecting plate body is~formed by -~
njection molding so as to have high accuracy on the side
of the reflecting surface. A metal foil coated with a
bond1ng agent on one surface theréof is brought into
contact with one surface of the reflecting plate body in -~
such a direction that the bonding agent is set on~the~side
of the reflecting plate body,- pressed and heated, whereby -`
a reflecting plate integral with a metal foil is formed.
This method has a defect that the means to mold
the reflecting plate body and the means to fix the~metal
foil as an integral member of the reflecting plate~body ;~
require separate processes. However, the metal foil~
cannot be furrowed when the reflecting plate body;is made
of a synthetic resin with high precision. Therefore, the~
illumination device using this type of reflecting plate
~` is more desirable to assure uniform luminance distribution
` on the diffusing plate.
The reflecting plate having the above-described
reflecting plate body made of a synthetic resin can hardly
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` 1331979
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be molded with high precision, when it has a large size, -~ -
due to the sink mark, etc. formed at the cooling stage.
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When a large reflecting plate is to be molded, it is
therefore desirable to cut the reflecting plate body along
~;~ 5 the planes perpendicular to the longitudinal direction of
the light soruces and combine a plural number of divided -
members. In other words, it is desirable to mold a plural
number of the moldings 30';having the~shape shown in Fig.
11, and bond the moldings on the sides of 30'a and 30'b ;~ -~
so as to form a large~refleoting plate body.
In order to bond a plural number of the members
of the reflecting plate to form a large reflecting plate,
the bonding means illustrated in Fig. 12 ~hrough Fig. 14
can be used in addition to the bonding method of the
. -
reflecting plate members.
In Fig. 12, the reference numerals 41 and 42 ;~
:
represent reflecting plate members as cut or divided parts
of the reflecting plate shown in Fig. 9 and Fig. 10.
Formed on the end surface 41a of the reflecting plate
~member 41 are an elastlc piece 43a having upward hook at
the tip thereof at a position a little rightward in the ; ~`~
~` vicinity the center of the end surface and a notch 43b at
~; a position a little leftward from the center of the end
surface 41a. Further, formed on the end surface of the
reflecting plate member 41 are a protrusion 45a having a -~
hole 45a' at the left end~thereof and a downward boss 45b having a
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133~97~ ;
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tapped hole 45b' into which a screw can be forcibly
screwed at the right end thereof. Similarly, the
reflecting plate member 42 has an elastic piece 44a having
an upward hook, notch 44b, a protrusion 46a having a hole
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46a' and a boss 46b having a tapped hole 46b'.
When these~reflecting plate member 41 and reflecting ~-~
plate member~42 are set in the positions shown;in Pig. 12,
the hook-shaped elastic piece 43a faces the notch 44b, the
notch 4~3b~faces the hook-shaped elastic piece 44a, the ~-
~ 10 ~protrusion~45a faces the~boss 46b and the protrusion 46a - ;
;~ faces the boss 45b.
n order to join the reflecting plate members 41
~; and 42 to each;other, the members ~are set and brought into
contact with each other in such positions that~the end ~
surfaces 41a and 42a cross each~other in an "X" shape, and
then turned in the directions oppcsite to each other until
the end surfaces are matched. Accordingly, the~hook-shaped~
elastic piece 43a is engaged with the engaging end of the
notch 44b and the hook-shaped elastic piece 44a lS engaged
with the engaging end of the notch 43b respectively as
shown in Fig. 13. Simultaneously, the protrusion 45a is
fitted into the boss 46b and the protrusion 46a is fitted
into the boss 45b respectively as shown in Fig. 14. By
this assembling procedure, the reflecting plate members
41 and 42~are joined to each other~, and a large reflecting~
plate is formed.
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1331979 ~ ~
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The joint can be made more secure by bonding both
the reflecting plate members with a bonding agent at the
joining stage described above. ~
As another method to join both the reflecting ~-
~ 5 plate members, it~is possible to form protrusions of the -
;` shape simiIiar to~that~of the protrusions~45a and 46a
shown in F1g. 12 but wlth no tapped~holes~and protrusions ~ ;
to be engaged therewith at opposite positions, assemble
both the~ reflecting plate members, and then make the
0 ~protrusions integral~by melting.
In any case of the joining, screwing and solvent
;~ welding of both the reflecting plate members, the joint
can be made more secure by bonding the end surfaces thereof
with a bonding agent.
Further, since the reflecting plate members 41 and
42 have the ~ame shape as shown in Fig. ~12,~two reflecting
plate members~of the ;same type can~be joined in the
opposite directions. Moreover, it~is possible to prepare
the reflecting plate body by forming the elastic pieces,~
protrusions and bosses on both the end surfaces of the
refIecting plate members, for ex;ample, in the arrangement
~. . . . .
on the reflecting plate~member 41~on one~end surface and
in the arrangement on the reflecting plate member 42 on
the other end surface, and joining a plural number of the
25 ~ reflecting plate~members on the same type.
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Though the above-described illumination device -~
~ according to the present invention has a concave surface
:~ on the reflecting plate, this surface may be designed as :~ .
Fresnel surface (a surface similar to the surface of
Fresnel lens). In this case, the reflecting plate has ~-
- ~
smaller thickness, thereby making it poss1ble to form a
thinner:illumination~device.
Since the illumination device according to the
~ present invention uses the reflecting plate havlng a
; :~ 10 central surface~deslgned as a plane surface or~nearly~
plane surface with large radii of curvature and a curved
. surface with radius of curvature gradually varying in the~
vicinity of its end as described above, the illuminati~on
device can be very thin~and assure unlform~lumlnance~
distribution on the dlffusing plate thereof. Further,
.
mass production of the illumination:device; is possible,
though th~ refleating plate has the special shape ~ `
;'~
described above, by formlng the reflecting plate body by
: injection molding of a synthetic resin. Furthermore, a : .
mirror surface from which the metal foil is not peeled cff
: can be formed easily by forming the reflecting plate body :
integral with the metal foil at the molding stage.
Moreover, when a large reflecting mirror is to be formed
by this method, it ls possible to prepare a~large ~
25 ~ reflecting plate, with little influence on luminance: ~-
; 133~ 97~
distribution of the diffusing plate, by molding re~lecting
mirror members in the shapes of the reflecting plate cut ~
or divided along the planes perpendicular to the longi- -. -
tudinal direction of the light sources and joining these ~ -~
reflecting plate members. ~ -
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