Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-03-29
2004-03-23
Chow, Dennis-Doon (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S210000, C348S766000, C353S057000
Reexamination Certificate
active
06710762
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 the projection type display using a transmission type liquid crystal light valve.
2. Description of the Related Art
Among projection type displays using a valve for light modulation, a projection type display using a liquid crystal light valve, what is called, a liquid crystal projector can display a fine and large screen and therefore has a possibility to take the place of a display (CRT) for a home television or a personal computer (PC) in near future. Recently, along with an increase in display resolution required for the PC display, more fine and higher resolution for the liquid crystal projector is realized. The resolution proceeds from the conventional 640×480 dots (VGA) to 800×600 dots (SVGA) as a standard, and also to more fine 1024×768 dots (XGA) in future.
A schematic structure of the conventional liquid crystal projector
1
is briefly described with reference to
FIG. 15. A
projection optical system of the liquid crystal projector
1
comprises a lamp
2
, a liquid crystal light valve section
4
, and a projection lens
6
. Although a diagram is omitted, the projection optical system also comprises a plurality of dichroic mirrors for separating light from the lamp
2
into three colors of red, green and blue, and a dichroic prism (or a plurality of dichroic mirrors) for synthesizing the three separated colors. The separated three colors respectively enter a liquid crystal light valve for each color provided in the liquid crystal light valve section
4
, and are modulated according to an image signal, thereby emitting to the projection lens
6
after synthesized at the dichroic prism.
An image signal processing system in the liquid crystal projector
1
comprises a control circuit
8
to which a picture signal from the PC, the video equipment or the like inputs. The picture signal input to the control circuit
8
is converted to a predetermined voltage and supplied to each liquid crystal light valve in the liquid crystal light valve section
4
through a signal line
18
. A driving voltage according to the picture signal is applied to each pixel of the liquid crystal light valve, thus allowing to obtain an image on a screen by changing transmissivity of each pixel in response to the picture signal and modulating the light from the lamp
2
. Ordinary, 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
. Hence, a large electric power is supplied from a power supply
26
through a power line
24
and the lamp
2
produces heat to a high temperature.
The heat produced at the lamp
2
increases an internal temperature of the liquid crystal projector
1
(body) by radiation or heat conduction through air. Also, a liquid crystal in a liquid crystal panel forming the liquid crystal light valve, and a polarizing plate and the like mounted on a surface of the liquid crystal panel increase the temperature for themselves by absorbing the light as well. The conventional liquid crystal projector
1
flows air around the liquid crystal light valve section
4
to maintain temperatures of these liquid crystal, the polarizing plate and the like within a predetermined specification temperature, for example, approximately 60 degrees. An intake fan
10
and an exhaust fan
12
are provided on the body, as illustrated, for performing a forced air cooling to make a air flow around the liquid crystal light valve section
4
by rotating these fans
10
and
12
. Further, a filter
14
is mounted on the air inflow side of the intake fan
10
to prevent an entry of dusts and the like.
Also, a temperature detecting device
30
is mounted on the liquid crystal light valve section
4
to measure temperatures of the liquid crystal panel and the polarizing plate. A detecting signal from the temperature detecting device
30
is output to the control circuit
8
via a signal line
16
. The control circuit
8
compares the temperature detecting signal from the temperature detecting device
30
with a previously memorized reference value, thereby disconnecting the lamp
2
via a signal line
20
and the power supply
26
of the liquid crystal projector
1
via a signal line
22
, when the temperature detecting signal exceeds the reference value. Here, the reference value of the temperature memorized in the control circuit
8
is described with reference to
FIG. 16. A
lateral axis in
FIG. 16
shows a room temperature (° C.), while a vertical axis shows a temperature (° C.) detected based on the temperature detecting signal from the temperature detecting device
30
. As shown in
FIG. 16
, it its understood that a temperature in the liquid crystal light valve
4
increases along with an increase in room temperature in spite of the enforced air cooling by the fans
10
and
12
. Therefore, in the past, the reference value as an allowable temperature for the liquid crystal and the polarizing plate is adjusted to the specification temperature to protect the inner parts of the liquid crystal light valve. So, when the temperature in the liquid crystal light valve exceeds this reference value, the power supply
26
and the lamp
2
are disconnected.
Thus, the conventional liquid crystal projector
1
measures the temperature in the vicinity of the liquid crystal panel by means of the temperature detecting device
30
arranged at the liquid crystal light valve section
4
not to give a degradation or a malfunction to the liquid crystal or the polarizing plate by the heat or light from the lamp
2
, thereby disconnecting the power supply
26
and the lamp
2
by comparing the previously memorized reference value with the measurement result.
Now, as shown in
FIG. 16
, though the temperature in the liquid crystal projector
1
varies depending on a temperature in atmosphere wherein the liquid crystal projector
1
is arranged, the temperature in the liquid crystal projector
1
also varies from other causes, such as the extent of clogging of the filter
14
in front of the intake fan
10
. In short, some causes exist until the measurement result of the temperature detecting device
30
reached the above reference value. However, under a temperature control of the above-mentioned conventional liquid crystal projector, only if the temperature of the inner parts in the liquid crystal light valve section
4
exceeds the reference value or not is judged, thus preventing the temperature variation on the way to reach the reference temperature from being grasped. Therefore, it has a problem that it is difficult to find out the causes at the time of disconnection of the power supply
26
or the lamp
2
of the liquid crystal projector from the side of users.
Also, the conventional liquid crystal projector
1
has another problem that maintenance for easily discovering preventing the efficiency deterioration of the intake fan
10
caused by the clogging of the filter
14
, which is one of the causes by which the temperature of the inner parts in the liquid crystal light valve section
4
exceeds the reference temperature, is difficult.
The conventional liquid crystal projector
1
has a further problem that image quality degrades. Because even if a predetermined voltage is applied to the liquid crystal to gain a predetermined gradation in a half tone display, when the temperature of the liquid crystal panel in the liquid crystal light valve section
4
changes, transmissibity of the liquid crystal panel changes depending on it, so that the reproducibility of the half tone differs depending on the temperature.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a projector type display which can be easily maintained on the user side.
Above objects are achieved by a projection type display having a light valve for modulating and emitting an incident light from a light source, a projection lens for enlarging and projecting the emitted light form the light valve,
Chow Dennis-Doon
Fujitsu Limited
Greer Burns & Crain Ltd.
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