Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2002-11-27
2004-12-28
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S628000, C362S035000, C362S330000
Reexamination Certificate
active
06836368
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a wedge plate type light guiding plate for a front light and a method for manufacturing the light guiding plate.
To reduce the power consumption, some conventional display units have a lighting device. When there is sufficient outside light such as sunlight or room lighting, this type of display unit uses outside light. When the outside light is insufficient, the display unit uses the lighting device. Such display units include a reflective display unit with a front light.
FIG. 6
shows a reflective display unit
50
with a front light. The display unit
50
includes a light source
51
, a light guiding plate
52
, and a reflective liquid crystal panel
60
. The light guiding plate
52
has an incident plane
54
, a first exit plane
53
, and a second exit plane
55
. The liquid crystal panel
60
is located below the first exit plane
53
. A considerable number of grooves
57
having saw-tooth cross-section are formed on the second exit plane
55
. Each groove
57
is defined by a light admission plane
57
a
and an inclined plane
57
b.
The light admission plane
57
a
is inclined by an angle &ggr; relative to the first exit plane
53
. The inclined plane
57
b
is inclined by an angle &agr; relative to the first exit plane
53
. The light admission plane
57
a
and the inclined plane
57
b
form an apex angle &bgr;.
To improve the visibility of the reflective liquid crystal panel
60
, it is desirable that the brightness of the panel
60
be enhanced and the brightness distribution of the panel
60
be uniform.
Brightness uniformity is an index representing the evenness of a brightness distribution. To compute the brightness uniformity, the values of brightness at specific points on the light guiding plate
52
are measured. The brightness uniformity is computed based on the maximum value and the minimum value of the measured brightness. Specifically, the brightness uniformity is computed in the following manner. First, the surface of the light guiding plate
52
is divided into sixteen sections by three parallel lines and another three lines perpendicular to the first three lines. The brightness at each of the nine intersection points L1 to L9 is measured. Then, the minimum brightness is divided by the maximum brightness. The resultant represents the brightness uniformity. The closer to one the resultant is, the smaller the difference between the minimum brightness and the maximum brightness is, that is, the more uniform the brightness distribution is.
However, since the amount of light that reaches regions far from the light source
51
is small, the amount of light reflected by the light admission planes
57
a
in the region is small. Accordingly, only a small amount of light exits from the first exit plane
53
in the regions far from the light source
51
. This results in a reduced brightness and an uneven brightness. In other words, the brightness distribution is uneven. Japanese Laid-Open Patent Publication No. 2000-21224 discloses a wedge plate type light guiding plate having improved brightness and brightness uniformity. Japanese Laid-Open Patent Publication No. 2000-111900 discloses a flat plate type light guiding plate having improved brightness and brightness uniformity.
Specifically, in the light guiding plate
52
of the publication No. 2000-21224, the pitch of the grooves
57
is randomly varied. The randomly varied pitch and the wedge shape of the light guiding plate make the brightness uniform. On the other hand, in the flat plate type light guiding plate of the publication No. 2000-111900, the depth of the grooves increases as the distance from the light source
51
increases, while the pitch of the grooves is constant. Also, as the distance from the light source
51
increases, the inclination angle a gradually increases from 0.5° to 3.5° or the inclination angle &bgr; increases from 40° to 60°.
In the light guiding plate disclosed in the publication No. 2000-21224 having a varying groove pitch, smaller pitch of the grooves
57
makes the brightness distribution uniform. However, if the pitch does not match the pixel pitch of the reflective liquid crystal panel
60
, interference patters will appear. Also, since the groove pitch randomly varies, emission lines appear in regions where the pitch is greatly varied. Interference patterns and emission lines both degrade the visibility.
In the flat plate type light guiding plate disclosed in the publication No. 2000-111900, the apex angle &bgr; changes if the groove depth increases and the angle &agr; or the angle &ggr; changes. In this case, since the angle &agr; or the angle &ggr; changes, the brightness distribution cannot be easily made uniform. Since the apex angle &bgr; changes, the brightness does not increase even if the groove depth increases. If the apex angle &bgr; changes, manufacture of a mold for forming the light guiding plate will be complicated, and the accuracy of the mold will be degraded.
SUMMARY OF THE INVENTION
Accordingly, it is a first objective of the present invention to provide a wedge plate type light guiding plate for front light, which waveguide increases the brightness and improves the uniformity of brightness distribution while preventing interference patterns from appearing.
A second objective of the present invention is to provide a method for manufacturing a wedge type light guiding plate for front light, which method facilitates forming of an accurate mold and permits apex angles defined by peaks and bottoms forming grooves in the light guiding plate to be accurately formed as designed.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the invention provides a wedge plate type light guiding plate for a front light mounted on a reflective display unit having a display portion. The light guiding plate guides light from a light source and irradiates the light onto the display portion. The light guiding plate has an incidence plane, an opposite end plane, an exit plane facing the display portion and a reflection-exit plane. The incidence plane permits light to enter the light guiding plate. The opposite end plane opposites to the incidence plane. Light entering the light guiding plate through the incidence plane exits through the exit plane toward the display portion. The reflection-exit plane opposites to the exit plane. Light reflected on the display portion passes through the exit plane and the reflection-exit plane. A plurality of grooves are formed on the reflection-exit plane. The grooves extend in a direction parallel to the direction in which the incidence plane extends, and are arranged at a predetermined pitch in a direction perpendicular to the direction in which the incidence plane extends. The depth of the grooves monotonously increases from the incidence plane toward the opposite end plane. Each groove is defined by intersecting first and second planes. The first plane is inclined such that the distance between the exit plane and the first plane increases as the distance from the light source increases. In each groove, the angle defined by the first plane and the exit plane is substantially equal to that of the other grooves. In each groove, the angle defined by the first plane and the second plane is substantially equal to that of the other grooves.
The invention also provides a method for manufacturing a wedge plate type light guiding plate for a front light mounted on a reflective display unit having a display portion. The light guiding plate includes an incidence plane for permitting light to enter the light guiding plate, an opposite end plane opposite to the incidence plane, an exit plane facing the display portion, and a reflection-exit plane opposite to the exit plane. A plurality of grooves having a saw-tooth cross-section are formed on the reflection-exit plane. The grooves extend in a direction parallel to the direction in which the incidence plane extends, and are arranged at a predetermined pitch in a direction perpendicular to the dir
Isogai Fumikazu
Mita Yasuya
Niida Eiki
Takeuchi Norihito
Dang Hung Xuan
Kabushiki Kaisha Toyota Jidoshokki
Martinez Joseph
Morgan & Finnegan , LLP
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