JP2001092015A - Projection display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively cool a polarizing plate and to reduce noise of a cooling fan by accurately grasping the temperature of the polarizing plate without using a special sensor to control the rotation of the fan, with respect to the projection display device. SOLUTION: A projection display device controls the airflow of the cooling means on the basis of the quantity of a black level signal included in a video signal detected at a prescribed time or the integral value of the luminance level of a video signal at a prescribed time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type display device, and more particularly to a liquid crystal projection type display device which projects light from a light source through a liquid crystal panel.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration of a conventional projection display device. In the figure, 1 is a light source, 2 is a polarization conversion system, 3 is a liquid crystal panel, 4 is a drive circuit, 5 is a polarizing plate, 6 is a cooling fan, 7 is a temperature sensor, and 8 is a fan control circuit.
The light emitted from the light source 1 includes linearly polarized light having a constant vibration direction and unnecessary light having a phase different from that by 90 °.
The unnecessary light is removed by the polarization conversion system 2. The liquid crystal panel 3 is driven by a drive circuit 4 based on an input video signal. The polarizing plate 5 disposed on the emission side absorbs the phase of the linearly polarized light incident on the liquid crystal panel 3, and transmits the phase when the phase is rotated by 90 °.

In displaying a signal corresponding to white as a video signal, the phase of linearly polarized light incident on the liquid crystal panel 3 is rotated by 90 ° in the liquid crystal layer. The light whose phase has been rotated by 90 ° transmits through the polarizing plate 5 which transmits the phase.
On the other hand, when displaying a signal corresponding to black, the liquid crystal panel 3
Is incident on the liquid crystal panel 3 with the same phase as that at the time of incidence, and is shielded by the polarizing plate 5 which absorbs the phase. As described above, in the image formed by the video signal, a portion corresponding to white passes through the polarizing plate, and a portion corresponding to black is shielded from light, whereby an image is projected on a screen (not shown).

Therefore, when a dark image is projected on the screen for a long time, the light shielded by the polarizing plate increases and the temperature of the polarizing plate increases. The polarizing plate has low heat resistance and needs to be kept at about 100 ° C. or lower in order to guarantee long-term performance. For this reason, a cooling fan 6 is mounted to cool the polarizing plate 5. Since a liquid crystal projector is often used in a conference room or a presentation room, it is required to suppress noise caused by a fan while improving cooling efficiency. Therefore, as shown in FIG. And a method of controlling the number of revolutions of the fan by a fan control circuit 8 based on the temperature near the polarizing plate or the temperature of the air taken in has been attempted.

[0005]

However, the temperature sensor in the above-mentioned projection type display device cannot sense the temperature of the air mainly sucked by the fan and cannot monitor the temperature of the polarizing plate itself. Since the polarizing plate generates a large amount of heat and has low heat resistance as compared with other optical components, it is ideal that the temperature is controlled as accurately as possible and cooled so as to be kept at or below the heat resistant temperature. At the same time, it is necessary to minimize fan noise caused by cooling.

The projection type display device provided by the present invention can effectively detect the temperature rise of the polarizing plate without using a special sensor and control the rotation of the fan to effectively cool and cool the polarizing plate. It is an object to reduce fan noise.

[0007]

According to the present invention, there is provided a projection display apparatus comprising: a liquid crystal panel driven based on a video signal; and an optical device for condensing light from a light source onto the liquid crystal panel. System, a polarizing plate on which the light transmitted through the liquid crystal panel is incident, and a projection display device having a wind cooling means for cooling the polarizing plate by air, based on information obtained from the video signal based on an air volume of the wind cooling means. Control.

A liquid crystal panel driven based on a video signal, an optical system for condensing light from a light source on the liquid crystal panel, a polarizing plate on which the light transmitted through the liquid crystal panel is incident, and a wind filter on the polarizing plate. In a projection display device having an air cooling means for cooling, the light amount of the light source is controlled based on information obtained from the video signal.

The information obtained from the video signal is the amount of the black signal detected in a predetermined time or the integrated value of the luminance level in the predetermined time. A liquid crystal panel driven based on a video signal; an optical system for condensing light from a light source on the liquid crystal panel; a polarizing plate on which the light transmitted through the liquid crystal panel enters; and a wind for cooling the polarizing plate. In a projection display device having a cooling means, when an image whose luminance level is equal to or lower than a predetermined value continues for a predetermined time, the liquid crystal panel is driven based on an image signal other than the image.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. Note that the same or corresponding parts as those described in the above related art are denoted by the same reference numerals, and description thereof is omitted.

Embodiment 1 FIG. 1 shows a configuration of a projection display device according to the present embodiment. Here, a structure in which one liquid crystal panel is used is shown, but the present invention can be applied to a case where three RGB panels are used or a case where a plurality of other panels are used.

In FIG. 1, a detection circuit 9 detects a black signal or a signal whose luminance level is close to black (hereinafter, referred to as a black level signal) contained in a video signal. Control the number of revolutions of the cooling fan 6 based on the command from When a video signal containing a large amount of black level signal is input for a long time, the polarization plate 5
Increases the amount of light absorbed, and the temperature rises. Detection circuit 9
Gives an instruction to increase the rotation speed of the cooling fan 6 to the fan control circuit 8 when the integrated value of the black level signal detected at a predetermined time exceeds the set threshold value. When the integrated value of the black level signal detected in a predetermined time becomes equal to or less than the threshold value, the detection circuit 9 gives a command to the fan control circuit 8 immediately or after a certain time to reduce the rotation speed of the cooling fan 6. .

Here, the operation of the detection circuit 9 will be described. The detection circuit 9 counts, as a black level signal, a signal whose luminance level is equal to or lower than a preset level among the input video signals, and an integrated value of the black level signal detected in a predetermined time exceeds a threshold value. Fan control circuit 8
Send a command to Alternatively, an integral value of the luminance level of the video signal at a predetermined time may be obtained, and a command may be sent to the fan control circuit 8 when the integral value falls below a set value.

Here, the brightness level of the video signal detected as the black level signal, the threshold value of the black level signal amount detected during a predetermined time when the rotation speed of the cooling fan 6 is changed, and the rotation speed of the fan are changed. The parameters such as the timing of the operation can be arbitrarily set. By setting these parameters in consideration of a rise in the temperature of the optical system being used, it becomes possible to cool the polarizing plate more effectively.

According to this embodiment, the temperature rise of the polarizing plate is estimated based on the black level signal included in the video signal,
By controlling the number of revolutions of the fan, noise reduction of the fan can be realized.

When three RGB liquid crystal panels are used,
Of these, the cooling fan may be controlled by monitoring the black level of the video signal of the one on which the temperature rise of the output side polarizing plate is the largest. The cooling fan may be controlled by monitoring the black level included in the video signals of all the liquid crystal panels.

As shown in FIG. 2, a cooling fan 10 which is always operated is provided with a cooling auxiliary fan 11 which is operated only at a high temperature.
May be provided. Here, the driving of the auxiliary cooling fan 11
The rotation speed control during stop or drive is performed based on the amount of the black level signal detected in a predetermined time as described above.

Embodiment 2 FIG. FIG. 3 shows the configuration of the projection display device according to the present embodiment. In the figure, reference numeral 12 denotes a power control circuit, which is connected to the light source 1. In addition, the detection circuit 9 ′ in the present embodiment detects a black level signal included in the video signal, and at the same time, checks a change in the video signal to determine whether the image is a moving image or a still image.

In the present embodiment, as in the first embodiment, the detection circuit 9 'monitors the black level signal included in the video signal,
The power control circuit 12 suppresses the output of the light source 1 itself when the amount of the black level signal detected in a predetermined time exceeds a threshold value.

The detection circuit 9 'detects a black signal included in the video signal, and when the amount of the black level signal detected in a predetermined time exceeds a set threshold value, the power control circuit 12
To the power source 1. The power control circuit 12 lowers the power input to the light source 1 within a range in which the light emission characteristics of the light source 1 do not significantly change (for example, 80% or more of the normal output) based on the command, thereby increasing the temperature of the polarizing plate 5. To reduce. Also, it is determined from the change in the video signal that the video is in the temporary stop state. If this state continues for a long time, the power of the light source 1 is reduced to 0 or the power is reduced so that the screen becomes sufficiently dark by this control. You may. Accordingly, it is possible to prevent the polarizing plate 5 from being damaged when the pause state continues for a long time with a dark image.

Embodiment 3 FIG. 4 shows the configuration of the projection display device according to the present embodiment. In FIG. 4, reference numeral 12 denotes a built-in signal pattern, which is an all-blue screen (blue background);
A video signal pattern such as a gray screen is stored.

In this embodiment, as in the second embodiment, the detection circuit 9 'monitors the black level signal and simultaneously checks the change in the video signal to determine whether the image is a moving image or a still image. When the detection circuit 9 ′ detects a black level signal of a threshold value or more for a predetermined time and determines that the image is in a pause (pause) state, the projected image is stored in the built-in signal pattern 12. It is configured to switch to.

The main video signal after switching can be arbitrarily set, and may be a still image or a moving image. Accordingly, it is possible to prevent the polarizing plate 5 from being damaged when the pause state continues for a long time with a dark image.

[0024]

According to the present invention, by detecting the black level signal included in the video signal, it is possible to monitor the temperature rise of the polarizing plate without using a special sensor.
Further, since the number of rotations of the cooling fan is controlled based on the amount of the black level signal detected in a predetermined time, it is possible to efficiently cool the polarizing plate whose temperature rise largely depends on the type of the input signal.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a projection display device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating another configuration of the projection display device according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a projection display device according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a projection display device according to a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a configuration of a conventional projection display device of this type.

[Explanation of symbols]

Reference Signs List 1 light source, 2 polarization optical system, 3 liquid crystal panel, 4 drive circuit, 5 polarizing plate, 6 cooling fan, 7 temperature sensor, 8 fan control circuit, 9 detection circuit, 9 'detection circuit, 10 cooling fan, 11 auxiliary cooling fan , 12
Power control circuit, 13 Built-in signal pattern.

Claims (4)

[Claims] A liquid crystal panel driven based on a video signal; an optical system for condensing light from a light source onto the liquid crystal panel;
In a projection type display device having a polarizing plate on which the light transmitted through the liquid crystal panel is incident, and a wind-cooling unit for cooling the polarizing plate, the airflow of the wind-cooling unit is controlled based on information obtained from the video signal. Projection type display device characterized by performing. 2. A liquid crystal panel driven based on a video signal, an optical system for condensing light from a light source on the liquid crystal panel,
In a projection type display device having a polarizing plate on which the light transmitted through the liquid crystal panel is incident, and a wind cooling unit for cooling the polarizing plate, controlling the light amount of the light source based on information obtained from the video signal. A projection display device characterized by the following. 3. The projection display according to claim 1, wherein the information obtained from the video signal is an amount of a black signal detected in a predetermined time or an integrated value of a luminance level in the predetermined time. A projection display device characterized by the following. 4. A liquid crystal panel driven based on a video signal, an optical system for condensing light from a light source on the liquid crystal panel,
In a projection type display device having a polarizing plate on which the light transmitted through the liquid crystal panel is incident, and a wind-cooling unit for cooling the polarizing plate, when an image having a brightness level of a predetermined value or less continues for a predetermined time, the liquid crystal is removed. A projection display device, wherein the panel is driven based on a video signal other than the video.