Patent Application
20090096957
The present application claims priority over Japanese Application JP2007-268412 filled on Oct. 15th, 2007, the contents of which are hereby incorporated into this application by reference.
(1) Field of the Invention
The present invention relates to a liquid crystal display.
(2) Related Art Statement
In recent years, use of light emitting plasma display panels and non-light emitting liquid crystal display devices instead of CRT's (cathode ray tubes) as displays has been increasing.
From among these, liquid crystal display devices use a liquid crystal panel as a transmission type light modulation element, and the rear surface is provided with an illuminating device (also referred to as backlight), and the liquid crystal panel is illuminated with light. In addition, the liquid crystal panel forms an image by controlling the transmittance of light emitted from the backlight.
One feature of liquid crystal display devices is that they can be made thin in comparison with CRT's, and in recent years, thinner liquid crystal display devices have been in demand. Thus, Patent Document 1, for example, discloses a technology for a sidelight system having a configuration where LED's (light emitting diodes) are used for the light source of the backlight, and this light source is placed to the side of the liquid crystal panel instead of on the rear of the backlight, so that the rear surface of the liquid crystal panel is illuminated with light by means of a light guiding plate.
(Patent Document 1) Japanese Unexamined Patent Publication 2006-156324 (see
In the above described sidelight system, there is a risk that the brightness may become inconsistent and the efficiency with which light enters may lower due to fluctuation in the dimensions as a result of thermal expansion of the components as the size of the liquid crystal panel increases.
In particular, the positional relationship between the light source and the light guiding plate tends to easily change due to the difference in temperature between when the light is on and when the light is off. Here, when the light source and the light guiding plate make close contact due to the change in the positional relationship resulting from thermal expansion, the conditions for total reflection are lost, and thus the uniformity of the brightness is affected. In addition, there is a risk that the light guiding plate may become warped when the light guiding plate makes close contact with the light source.
In addition, it has been desired to attach the light source directly to a heat releasing member provided in liquid crystal display devices in order to reduce the number of steps for attaching the light source and the number of members for attachment. In particular, LED's have excellent heat releasing properties, and therefore, though it is desirable to thermally fix LED's to a heat releasing member, the fluctuation in the dimensions resulting from thermal expansion of the above described components becomes significant, and thus, it becomes more difficult to set the positional relationship between the light source and the light guiding plate.
The present invention is provided in order to solve these problems, and an object is to provide a liquid crystal display device having excellent uniformity in the brightness, so that the display performance of the liquid crystal can be improved.
In order to solve the above described problems, the present invention provides a configuration where the above described light source is covered with a lens in the above described light source module, and the distance D between the above described lens and the above described entrance surface when the above described light source module is not driven is set within a range found using the following formulas (1) and (2):
{(□×L1)−(□×L2)}n×□T=D1 (1)
D1□D□D1×3 (2)
According to the present invention, an appropriate distance can be maintained between the lens of the light source module and the entrance surface of the light guiding plate, and thus, a liquid crystal display device having excellent uniformity in the brightness, so that the performance of displays of liquid crystal can be increased, can be gained.
a) is a diagram showing the arrangement of wires and drive circuits on a liquid crystal panel;
b) is a diagram showing the arrangement of a TFT and a pixel electrode;
a) is a diagram showing the arrangement of light sources and light guiding plates;
b) is a diagram showing a light source;
a) is a graph showing the lower limit value for the distance when the light source module is placed on the short side of the light guiding plate;
b) is a graph showing the lower limit value for the distance when the light source module is placed on the long side of the light guiding plate;
a) is a graph showing the relationship between the ratio of the thickness of the light guiding plate to the diameter of the lens and the efficiency with which light enters; and
b) is a graph showing the relationship between the ratio of the diameter of the lens to the size of the chip and the efficiency with which light enters.
1 liquid crystal display device
101 heat sink
107
a inlets
107
b outlets
120 liquid crystal panel
120
a signal wire driving circuit
120
b scanning wire driving circuit
120
c signal wire
120
d scanning wire
120
e TFT
120
f liquid crystal
120
g pixel electrode
120
h counter electrode
121 light guiding plate
121
a entrance surface
121
b exit surface
122 lower chassis (support member)
124 light source module
123 substrate
124 light source module
124
a LED
124
b wire pattern
124
c lens
125 drive portion
125
a control device
125
b DC/DC power supply
131 first rubber cushion
132 second rubber cushion
133 buffering body
134 optical sheet
135 first reflective sheet
136 second reflective sheet
137 first frame
137
a inlets
137
b outlets
138 second frame
139 upper chassis
D distance
In the following, the best mode for carrying out the invention is described in detail in reference to the drawings.
In the present embodiment, as shown in
As shown in
The light guiding plate 121, described in detail below, is placed on the rear surface of the liquid crystal panel 120, and substrates 123 which form light source modules 124 are placed on the left and right side in the direction of the length of the light guiding plate 121. That is to say, light beams from the light source modules 124 on the two sides, left and right, enter the light guiding plate 121. Here, the sides of the light guiding plate 121 along which the light source modules 124 are placed are referred to as entrance surfaces 121a. In addition, the surface of the liquid crystal panel 120 is referred to as exit surface 121b.
In addition, as shown in
The liquid crystal panel 120 has a configuration where liquid crystal is sandwiched between two glass substrates, and the orientation of the liquid crystal molecules which make up the liquid crystal is controlled so that the liquid crystal functions as an optical shutter for controlling transmission and blocking of light emitted from the light guiding plate 121.
As shown in
In addition, as shown in
The relationship between the opening and closing of the shutter for the liquid crystal 120f and the voltage applied to the liquid crystal (which is almost the same as the voltage between the pixel electrode 120g and the counter electrode 120h) depends on the so-called display mode of the liquid crystal 120f. In an example of the display mode for a liquid crystal panel 120 (see
In addition, in the case where a negative voltage is applied to the scanning wire 120d connected to a TFT 120e, the connection between the signal wire 120c and the pixel electrode 120g becomes of a state of high resistance, so that the voltage applied to the liquid crystal 120f can be maintained.
As described above, the liquid crystal 120f is controlled by the voltage applied across the scanning wire 120d and the signal wire 120c in the configuration.
The scanning wire driving circuits 120b function to scan the pixels with a certain period, so that a predetermined voltage is applied to the scanning wires 120d one by one from the top to the bottom, for example. In addition, signal wire driving circuits 120a apply a voltage corresponding to the respective pixels connected to the scanning wire 120d to which a predetermined voltage is applied by a scanning wire driving circuit 120b to the respective signal wires 120c.
In this configuration, the scanning wire 120d to which a voltage is applied can set bright pixels and dark pixels. In addition, as the scanning wire driving circuits 120b scan the pixels, the signal wire driving circuits 120a control the voltage applied to the respective signal wires 120c, and thus, bright pixels and dark pixels can be set for all of the scanning wires 120d, and an image can be formed on the liquid crystal panel 120.
Here, the signal wire driving circuits 120a and the scanning wire driving circuits 120b are controlled by a control device 125a (see
The control device 125a functions to manage an image signal to be displayed on the liquid crystal panel 120 as information on the brightness for each portion of the liquid crystal 120f (see
Returning to
Here, in the present embodiment, as shown in
In addition, as shown in
As shown in
Here, as shown in
As shown in
As described above, the present embodiment has such a configuration that the rear surface of the liquid crystal panel 120 is illuminated with light beams emitted through the exit surface 121b of the light guiding plate 121.
Returning again to
The first frame 137 is made of an aluminum alloy, for example, and placed on the front surface of the liquid crystal panel 120 so as to function also as a front cover for the liquid crystal display device 1. The first frame 137 is secured to the heat sinks 101 by means of screws 137c (see
When the first frame 137 and the lower chassis 122 are combined so that the housing for the liquid crystal display device is formed, the outlets 137b of the first frame 137 and the outlets 107b of the lower chassis 122 are connected, while the inlets 137a of the first frame 137 and the inlets 107a of the lower chassis 122 are connected in the configuration.
The first rubber cushion 131 is placed on the front surface of the liquid crystal panel 120 in such a manner as to function as a support member provided between the first frame 137 and the liquid crystal panel 120. In addition, the second rubber cushion 132 is placed on the rear surface of the liquid crystal panel 120 in such a manner as to function as a buffering member between the liquid crystal panel 120 and the second frame 138.
The second frame 138 functions as a support for the liquid crystal panel 120, and at the same time, intervenes between the heat sinks 101 and the liquid crystal panel 120 so as to function as a heat insulating material for preventing heat from the heat sinks 101 from being conveyed to the liquid crystal panel 120.
The optical sheet 134 is placed on the rear surface of the second frame 138 so as to function to provide directionality for light emitted from the light guiding plate 121, so that light becomes uniform within the plane and the brightness increases toward the front. Here, the number of optical sheets 134 is not limited, and in the present embodiment, three optical sheets 134 are provided, as shown in
The first reflective sheet 135 is placed on the rear surface of the optical sheet 134. The first reflective sheet 135 functions to reflect light beams which do not enter the light guiding plate 121 from among light beams emitted from the light source modules 124 and make reflected light beams enter the light guiding plate 121, and also functions to make light beams emitted through the exit surface 121b of the light guiding plate 121 in the vicinity of the light source modules 124 return into the light guiding plate 121. In the vicinity of the light source modules 124, light emission of RGB is inconsistent, and thus, this portion cannot be used as a display surface. Therefore, light beams in the vicinity of the light source modules 124 are returned into the light guiding plate 121 by the first reflective sheet 135, so that loss of light can be reduced.
The second reflective sheet 136 is placed on the rear surface of the light guiding plate 121. The second reflective sheet 136 functions to reflect light which does not directly enter the light guiding plate 121 from among light beams emitted from the light source modules 124 and makes reflected light enter the light guiding plate 121, so that the efficiency with which light beams can be used can be increased, and at the same time, functions to make light beams which exit through the lower surface of the light guiding plate 121 due to failure to meet the conditions for total reflection return into the light guiding plate 121.
The heat sinks 101 are formed of a material having excellent heat conductivity, for example a metal material, such as copper or aluminum, and functions to efficiently release heat generated in the light source modules 124. In addition, the heat sinks 101 are connected to the surface of the substrates 123 on which the LED's 124a are not mounted using a thermally conductive adhesive member 101a (see
Furthermore, the heat sinks 101 contain the liquid crystal panel 120 and the light guiding plate 121 inside a visual rectangular parallelepiped region that is circumscribed on the heat sinks 101, and thus, function to protect the liquid crystal panel 120 and the light guiding plate 121 when pressure is applied to the liquid crystal display device 1.
Here, the structure of the heat sinks 101 is in approximately L shape as viewed from the top, and as shown in
Heat generated in the light source modules 124 is conveyed to the heat sinks 101 and diffuses along the surface of the heat sinks 101 located on the rear surface of the light guiding plate 121, and after that released into the air that flows between the light guiding plate 121 and the lower chassis 122. The air flows between the light guiding plate 121 and the lower chassis 122 from the bottom to the top as a result of natural convection.
In addition, outside air is sucked into the liquid crystal display device 1 through the inlets 137a in the first frame 137 (see
As described above, in the present embodiment a space for releasing heat in the up-down direction relative to the display screen of the liquid crystal display panel 120, that is to say, an air path, is formed between the light guiding plate 121 and the lower chassis 122, as shown in
Furthermore, a drive portion 125 is provided with a control device 125a for controlling the liquid crystal display device 1 (see
As shown in
{(□×L1)−(□×L2)}n×□T=D1 (1)
D1□D□D1×3 (2)
Here, □ is the coefficient of thermal expansion of the light guiding plate 121, L1 is the length of the light guiding plate 121, □ is the coefficient of thermal expansion of the lower chassis 122, L2 is the length of the lower chassis 122 in the direction of the length of the light guiding plate 121, n is a variable (1 in the case where the entrance surface 121a is formed on one side, ½ in the case where the entrance surface 121a is formed on two sides; in the present embodiment, the entrance surface 121a is formed on the two sides, and therefore, the variable is ½), and □T is the difference in temperature (temperature of heat sinks 101−ambient temperature around liquid crystal display device 1).
The range for the distance D which is smaller than the value D1 gained using the formula (1) is excluded in the above described formula (2) because in the case where the distance D is set smaller than the value D1 gained using the formula (1), there is a risk that the lenses 124c and the entrance surfaces 121a of the light guiding plate 121 may make contact in spite of the design having a clearance between parts and the margin, thus making the efficiency with which light enters lower when the size of the light guiding plate 121 fluctuates as a result of thermal expansion when the light source modules 124 are driven.
Meanwhile, the range for the distance D which is more than three times greater than the value D1 gained using the formula (1) is excluded because in the case where the distance D is set greater than the value D1 as gained using the formula (1), there is a risk that the space between the lenses 124c and the entrance surfaces 121a of the light guiding plate 121 may become too large to lower the efficiency with which light enters when the size of the light guiding plate 121 fluctuates as a result of thermal expansion when the light source modules 124 are driven.
In contrast, in the case where the distance D is set within a range between the value D1 gained using the formula (1) an a value three times greater than D1, contact between the lenses 24c and the entrance surfaces 121a of the light guiding plate 121 can be avoided, and at the same time, the efficiency with which light enters can be prevented from lowering, even when the size of the light guiding plate 121 fluctuates as a result of thermal expansion when the light source modules 124 are driven.
Next, it is confirmed with concrete numeral values what conditions for the dimensions can allow for a necessary distance D in order to prevent interference between the entrance surfaces 121a of the light guiding plate 121 and the lenses 124c of the light source modules 124 between these.
Here, the lenses 124c are made of silicon, the heat sinks 101 are made of copper, and the lower chassis 122 is made of an aluminum alloy. In addition, the light guiding plate 121 is made of an acryl resin. The light source modules 124 having lenses 124c as described above are thermally secured to the heat sinks 101 through the substrates 123, and the lower chassis 122 is secured to the heat sinks 101 by means of screws 101b. That is to say, the light source modules 124 and the lower chassis 122 are secured via the heat sinks 101.
Here, the lower portion of the heat sinks 101 are formed so as to have a slit on the side facing the lower chassis 122, and thus, the heat sinks 101 and the lower chassis 122 are in such a state as to be almost completely thermally isolated. As a result, there is a difference in temperature between the heat sinks 101 and the lower chassis 122.
In addition, the light guiding plate 121 is made of acryl having a high coefficient of thermal expansion, as described above, and therefore, it is assumed that parts interfere when in an expanded state as a result of high temperatures. As a result of numeric analysis, it was found that the average temperature of the light guiding plate 121 is 63.6 □ when the LED's 124a emit heat at 50 W, and the average temperature of the lower chassis 122 is 73.1 □. Here, the ambient temperature is 25 □ at the time of assembly, and the temperature T1 of the light guiding plate 121 is 40 □ and the temperature □T2 of the lower chassis 122 53 □ when the difference in temperature from the ambient temperature of 25 □ is included as a margin of 10%.
The allowance in terms of the dimensions of the parts is as in Table 1. Here, a liquid crystal panel 120 of which the aspect ratio is 16:9 is used.
The total allowance in terms of the dimensions of the parts Ad of these parts is found as the sum of squares using the following formula (3).
Ad=√(dcp2+dcu2+dan2+dsi2+drp2)=0.516 mm (3)
Next, the amount of expansion □D at the time of high temperature on one side of the liquid crystal panel 120 is found. The amount of expansion □D can be found using the following formula (4).
□D=(□R−□W)/2+□C+□S+□L (4)
Here, □R is the amount of expansion of the light guiding plate 121, □W is the amount of expansion of the lower chassis 122, and “(□R−□W)/2” is the portion corresponding to the above described formula (1). □R can be found as □ (coefficient of thermal expansion of light guiding plate 121)×L1 (length of light guiding plate 121)×□T1, and □W can be found as □ (coefficient of thermal expansion of lower chassis 122)×L2 (length of lower chassis 122)×□T2.
In addition, □C is the amount of expansion of the heat sinks 101 in the length C1 between the surface of the heat sinks 101 where the substrates 123 are attached and the screw holes 101b for attachment (see
Table 2 shows the coefficient of thermal expansion of the object members.
When the amount of expansion □D at the time of high temperatures is found from the concrete dimensions in the liquid crystal display device using the above described formula (4), □D=(2.17−0.918)/2+0.002+0.0003+0.023=0.652 mm.
Accordingly, the distance D between the entrance surfaces 121a of the light guiding plate 121 and the lenses 124c of the light source modules 124 has a relationship with the above described total allowance in terms of the dimensions of parts Ad and the above described amount of expansion □D at the time of high temperatures which satisfies the following formula (5).
D>Ad+□D (5)
Here, as described above, Ad is 0.516 mm and □D is 0.652 mm, and therefore, D>1.168 mm.
An error margin of 20% is taken into consideration in the results for the thus gained distance D, and the value of the distance D is set as D=1.168×1.2=1.40 mm.
Thus, the amount of expansion at the time of high temperatures is confirmed on the basis of the distance D taking an error margin of 20% into consideration, so that the results shown in Table 3 are gained, and when the above described distance D and the amount of expansion □T′, which is the sum of the total allowance in terms of the dimensions of the parts Ad and the amount of expansion at the time of high temperatures, are compared, the relationship is as shown in the following formula (6).
D>Ad+□T═ (6)
Here, Ad is 0.516 mm and □T′ is 0.651 mm, as described above, and therefore, 0.516+0.651=1.167, and thus, D=1.4>1.167.
That is to say, the value of the distance D is greater than the amount of expansion □T′, which is the sum of the total allowance in the dimensions of the parts Ad and the amount of expansion at the time of high temperatures, and it could be confirmed that the distance D for preventing interference between the entrance surfaces 121a of the light guiding plate 121 and the lenses 124c of the light source modules 124 between these at the time of high temperatures was appropriate.
Meanwhile, in the above described formula (2), the range for the distance D is set between the value D1 gained using the formula (1) and a value three times greater than D1, and therefore, contact between the lenses 124c and the entrance surfaces 121a of the light guiding plate 121 can be avoided without fail in the case where the above described total allowance in terms of the dimensions of the parts Ad and the above described amount of expansion LED at the time of high temperatures are taken into consideration, even when the size of the light guiding plate 121 fluctuates as a result of thermal expansion when the light source modules 124 are driven.
In addition, the distance D secures a space which is effective at the time of assembly of the parts between the entrance surfaces 121a of the light guiding plate 121 and the lenses 124c of the light source modules 124, and thus, the efficiency of work increases, the productivity increases and the yield also increases. In addition, light emitted from the LED's 124a can be prevented from leaking out while maintaining the clearance between the entrance surfaces 121a of the light guiding plate 121 and the LED7s 124a small and constant, and thus, the efficiency with which light enters the light guiding plate 121 can be prevented from lowering. As a result, a preferable and predetermined brightness can be gained.
a) and 6(b) show concrete examples where the lower limit values are for the distance D required for each of the predetermined sizes for the liquid crystal panel 120 (for each size of the light guiding plate 121 used), and the solid line (I) in the graph indicates the arrangement of the light source modules 124 on the two sides of the light guiding plate 121 and the dashed line (II) in the graph indicates the arrangement of the light source module 124 on one side of the light guiding plate 121. In addition, the light guiding plate 121 used has an aspect ratio of 16:9, and
In the actual setting for the distance D, the total allowance in terms of the dimensions of the parts Ad is added to the value of the gained distance D, as described above, and an error margin of 20% is taken into consideration for this, and thus, the distance D for preventing interference between the entrance surfaces 121a of the light guiding plate 121 and the lenses 124c of the light source modules 124 is appropriate between these at the time of high temperatures.
Incidentally, as shown in
a) is a graph showing the relationship between the ratio of the thickness B of the light guiding plate 121 to the diameter A of the lenses 124c and the efficiency with which light enters, and shows that the greater the value of the ratio (B/A) of the thickness B of the light guiding plate 121 to the diameter A of the lenses 124c is, the higher the efficiency with which light enters is.
The present embodiment is formed so that the above described ratio (B/A) is 1 or greater, preferably 1.2 or greater. That is to say, the ratio of the thickness B of the light guiding plate 121 to the diameter A of the lenses 124c is 1 or greater, and therefore, as is clear from
In addition,
The present embodiment is formed so that the above described ratio (A/C) becomes 5 or greater (A/C □5), preferably 7 or greater (A/C □7). That is to say, the ratio (A/C) of the diameter A of the lenses 124c to the chip size C of the LED's 124a is 5 or greater, and therefore, as is clear from
In addition, in the present embodiment, optical sheets 134 are provided between the liquid crystal panel 120 and the light guiding plate 121, as described above, and the length L1 of the light guiding plate 121 is greater than the length L3 of the liquid crystal panel 120, and at the same time, the length L4 of the optical sheets 134 is greater than the length L1 of the light guiding plate 121 in the configuration, and therefore, the following working effects can be gained.
That is to say, the length L4 of the optical sheets 134 is greater than the length L1 of the light guiding plate 121, and therefore, light beams that are converted to light from a surface light source by the light guiding plate 121 enter the optical sheets 134 without leaking, and thus, appropriate correction is carried out on the optical sheets 134, so that a predetermined distribution can be gained in the brightness.
In addition, the length L4 of the optical sheets 134 is greater than the length L3 of the liquid crystal panel 120, and therefore, light passes uniformly through the liquid crystal panel 120, and thus, a liquid crystal display device 1 with high and uniform brightness in a plane can be gained.
In the following, the effects gained in the present embodiment are described.
(1) The distance D between the lenses 124c of the light source modules 124 and the entrance surfaces 121a of the light guiding plate 121 can be kept appropriate, and contact between these can be prevented even when the positional relationship changes due to the difference in temperature between when the light is turned on and when the light is turned off. Accordingly, a liquid crystal display device 1 having excellent uniformity in the brightness, so that the display performance of the liquid crystal can be increased, can be gained.
(2) Inconsistency in the brightness and lowering of the efficiency with which light enters due to fluctuation in the dimensions of the components resulting from thermal expansion can be prevented, even when the scale of the liquid crystal panel 120 is increased.
(3) The distance D between the lenses 124c of the light source modules 124 and the entrance surfaces 121a of the light guiding plate 121 is kept appropriate, and therefore, the problem with the light guiding plate 121 becoming warped when the light guiding plate 121 makes contact with the lenses 124c can be prevented.
(4) The light source modules 124 are thermally secured to the heat sinks 101 in the configuration, and therefore, heat from the light source modules 124 can be released through the heat sinks 101, and in addition, setting of the distance D, which would otherwise be troublesome, is easy with the structure where heat from the light source modules 124 can be released through the heat sinks 101, as described above.
(5) The distance D between the lenses 124c of the light source modules 124 and the entrance surfaces 121a of the light guiding plate 121 is kept appropriate, and therefore, an effective space can be secured when the parts are assembled, and the efficiency of operation increases, the productivity increases and the yield also increases. That is to say, the effects both of holding the distance D small and constant in order to increase the efficiency with which light enters and of increasing the ease of assembly by securing the clearance can be gained at the same time.
(6) The diameter A of the lenses 124c is set equal to or smaller than the thickness B of the light guiding plate 121, and therefore, loss of light can be prevented, and as a result, the efficiency with which light enters the light guiding plate 121 can be increased. Accordingly, when this is applied to a liquid crystal panel 120 for a large screen, for example, a liquid crystal display device 1 with high and uniform brightness on the surface can be gained.
(7) The ratio (A/C) of the diameter A of the lenses 124c to the chip size C of the LED's 124a is 5 or greater, and therefore, the efficiency with which light enters into the light guiding plate 121 can be kept high, and when this is applied to a liquid crystal panel 120 for a large screen, for example, a liquid crystal display device 1 with high and uniform brightness on the surface can be gained.
(8) The relationship between the length L1 of the light guiding plate 121, the length L4 of the optical sheets 134 and the length L3 of the liquid crystal panel 120 satisfies: length L4 of optical sheets 134>length L1 of light guiding plate 121>length L3 of liquid crystal panel 120, and therefore, appropriate correction can be carried out on the optical sheets 134, so that a predetermined distribution can be gained in the brightness and light from the optical sheets 134 uniformly passes through the liquid crystal panel 120, and thus, a liquid crystal display device 1 with high and uniform brightness on the surface can be gained.
Here, the materials and dimensions for the light guiding plate 121, the lenses 124c, the substrates 123, the heat sinks 101 and the lower chassis 122 are not limited to those described above, and appropriate ones can be selected.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2007-268412 | Oct 2007 | JP | national |
