Optics: image projectors – Temperature control
Reexamination Certificate
1999-10-22
2001-11-27
Dowling, William (Department: 2851)
Optics: image projectors
Temperature control
C353S057000
Reexamination Certificate
active
06322218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection type display using a light valve, particularly to a projection type display using a transmission type liquid crystal light valve.
2. Description of the Related Art
Among projection type displays using a light valve for a light modulation, a projection type display using a liquid crystal light valve called a liquid crystal projector has the potential to replace the display device (CRT) of home televisions and personal computers (PC) in the near future because the liquid crystal projector allows the display of a fine and large image screen. Recently, due to the increase in display resolution required for PC display, finer resolution of the liquid crystal projector has been realized. The resolution has increased from the conventional 640×480 dots (VGA) to 800×600 dots (SVGA) as a standard and it will proceed to the finer 1024×768 dots (XGA) in future.
A schematic structure of the conventional liquid crystal projector
100
is briefly described with reference to
FIG. 15. A
projection optical system of the liquid crystal projector
100
comprises a lamp
2
, three liquid crystal light valves
4
R,
4
G and
4
B and a projection lens
6
. Further, the projection optical system has dichroic mirrors DM
1
and DM
2
for separating a light from the lamp
2
into three colors of red, green and blue, dichroic mirrors DM
3
and DM
4
for synthesizing the separated three colors and mirrors M
1
and M
2
. The separated three color lights are incident on the liquid crystal light valves
4
R,
4
G and
4
B for each color respectively and are modulated according to the image signals, thereby emitting to the projection lens
6
after synthesized by the dichroic mirrors DM
3
and DM
4
.
An image signal processing system of the liquid crystal projector
100
comprises a control unit
80
to which a image signal from the PC or the video equipment and the like inputs. The image signal inputting to the control unit is converted to a predetermined voltage and supplied to each of the liquid crystal light valves
4
R,
4
G and
4
B. A driving voltage according to the image signal is applied to each pixel of the liquid crystal light valves
4
R,
4
G and
4
B, thus obtaining an image on the screen by changing the transmissivity of each pixel according to the image signal and modulating the light from the lamp
2
. Ordinarily, a light source capable of producing a large amount of light such as a metal halide lamp and the like is used as the lamp
2
. Therefore, a large electric power is supplied from a power supply
26
and the lamp
2
is heated up to a high temperature.
The heat produced at the lamp
2
increases an internal temperature of the body of the liquid crystal projector
100
by radiation or heat conduction through air. Further, a liquid crystal in the liquid crystal panel structuring the liquid crystal light valve and a polarizing plate attached on a surface of the liquid crystal panel and the like increase the temperature for themselves by absorbing the light. In conventional liquid crystal projector
100
air flows around the liquid crystal light valves
4
R,
4
G and
4
B so that the temperatures of the liquid crystal and the polarizing plate are maintained within a specification temperature determined, for example, at approximately 60° C. An intake fan
10
and an exhaust fan
12
are provided on the body of the liquid crystal projector
100
. In
FIG. 15
, the intake fan
10
is attached in the plane direction of the body and shown by dashed lines. The exhaust fan
12
is provided on the side of the body. An enforced cooling for making a air flow around the liquid crystal light valves
4
R,
4
G and
4
B is performed by rotating these fans
10
and
12
. Further, as shown in circular dashed lines in the figure, a filter
14
is mounted on the air inflow side of the intake fan
10
to prevent the dust from entering.
Also, if the temperature of the surrounding environment increases when the apparatus is working, or the filter
14
provided on the intake fan
10
for taking in the external air clogs due to dust and the like, the internal temperature of the apparatus extraordinarily increases, so that the members in the body, specifically, the structure members of the liquid crystal light valve may produce a deterioration in reliability. To avoid this, functions for alerting the operator and automatically stopping the apparatus by detecting the extraordinary temperature are provided to the control unit
80
of the liquid crystal projector
100
.
Therefore, a temperature detecting element
30
for detecting the temperatures of the liquid panel and the polarizing plate of the liquid crystal light valve
4
G is attached in the vicinity of the liquid crystal light valve
4
G. The detecting signal from the temperature detecting element
30
is output to the control unit
80
through a signal line. The control unit
80
compares the temperature detecting signal from the temperature detecting element
30
with the pre-memorized reference value. When the temperature detecting signal exceeds a reference value, the lamp
2
is disconnected or the power supply
26
of the liquid crystal projector
100
is disconnected. In the past, an allowable temperature at the liquid crystal members or the polarizing plate of the liquid crystal light valves
4
R,
4
G and
4
B is set as the reference value of an apparatus specification temperature. When this reference value is exceeded, the power supply
26
is disconnected and lamp
2
is also disconnected.
A thermistor is, for example, used as the temperature detecting element
30
for detecting the extraordinary temperature in the projector
1
. Though the temperature detecting element
30
is away from the position where the liquid crystal panel and the polarizing plate become the maximum temperature, it is arranged at the downwind side of the liquid crystal panel as a position which can detect the temperature as close as possible to the maximum temperature. Since the temperature detecting element
30
is away from the maximum temperature point of the members which are monitored, the temperature at the element
30
is increased less due to cooling of from maximum temperature point. Nonetheless, the temperature due to the heat transmitted from the members is actually measured where the temperature detecting element
30
is located.
Here, an operation for disconnecting the power source
26
and the like is described using a flow chart shown in FIG.
16
. In
FIG. 16
, first, a temperature t ° C. in the vicinity of the liquid crystal light valve
4
G based on the output from the temperature detecting element
30
(step S
100
). Next, by comparing a predetermined temperature t
OFF
for disconnecting the power source
26
with the measured temperature t (step S
101
). When the temperature t is larger than t
OFF
(t>t
OFF
), in short, the temperature t exceeds the temperature for disconnecting the power source
26
, and the process proceeds to step S
102
to process the disconnection of the power source
26
. When the temperature t is not larger than t
OFF
(t
C
=<t
OFF
), the process proceeds to step S
103
because disconnection of the power source
26
is not required. At step S
103
, a predetermined temperature t
ALARM
for displaying an alarm and the measured temperature t are compared. When the temperature t is larger than the temperature t
ALARM
(t>t
ALARM
), in short, the temperature t exceeds the temperature that triggers the alarm, and process proceeds to step S
104
to trigger the alarm and then return to step S
100
. When the temperature t is not larger than t
OFF a
(t=<t
OFF
) at step S
103
, the alarm display is turned off at step S
105
and the process moves to the control of the fans
10
and
12
(step S
106
). Thereafter, whether or not to complete operation is determined. When the operation is continued, the step returns to step S
100
and a new temperature t is acquired.
Thus, the conventional liquid cry
Kobayashi Tetsuya
Sugawara Mari
Suzuki Toshihiro
Dowling William
Fujitsu Limited
Greer Burns & Crain Ltd.
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