JPH06194621A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To surely and individually control the temperature of plural liquid crystal panels, to reduce faulty gradation and irregular color based on the temperature dependency of the transmissivity characteristic of the panel and to improve the quality of a projected image by providing a cooling means in each of the panels. CONSTITUTION:Cooling fans 15 to 17 are respectively provided at the positions of three liquid crystal panels 5, 9 and 13 through which R light, G light and B light respectively pass. The cooling fans 15 to 17 are controlled and driven in accordance with the temperature of the corresponding liquid crystal panels 5, 9 and 13, so that the temperature of the panel is controlled to be kept at specified temperature. A diode for detecting temperature is provided in the panels 5, 9 and 13, and connected to the input side of an operational amplifier. The output side of the operational amplifier is connected to a microcomputer(CPU), and connected to a driving circuit for the fans 15 to 17. A power source is connected to the driving circuit and the microcomputer is connected thereto. Thus, the panels 5, 9 and 13 are controlled to be at the optimum temperature suited to ambient temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector having a plurality of liquid crystal panels, and more particularly to a temperature control mechanism for the liquid crystal panels.

[0002]

2. Description of the Related Art As a liquid crystal display device, (R) (G)
A liquid crystal projector having three liquid crystal panels of three color systems (B) is used. Each liquid crystal panel transmits R light, G light, and B light, and combines these lights through a projection lens to display liquid crystal of a predetermined color. Each liquid crystal panel of a liquid crystal projector having such a plurality of liquid crystal panels has temperature dependence of transmittance characteristics.

FIG. 3 shows an example of the transmittance characteristic of such a liquid crystal panel and shows a graph of the relative transmittance with respect to the voltage applied to the liquid crystal in the normally white mode of the TN mode liquid crystal panel. As can be seen from the figure, the γ characteristic and the threshold value at the temperature T ° C change ± ΔT ° C, so that the transmittance decreases when the temperature rises and the transmittance rises when the temperature lowers. Change greatly as you do.

Such a change in the transmittance characteristic directly affects the image projected through the projection lens, resulting in defective gradation or coloring due to the gradation due to the difference in the γ characteristic for each color. In order to prevent such a problem, it is necessary to keep the temperature of the liquid crystal panel constant.

In a conventional liquid crystal projector having a plurality of liquid crystal panels, a single fan cools the entire interior of the liquid crystal projector including the liquid crystal panel, as disclosed in, for example, Japanese Patent Laid-Open No. 4-427. The temperature was controlled. That is, in the conventional liquid crystal projector,
An air supply fan and / or an exhaust fan is provided as a cooling means for the liquid crystal panel and circuits, the temperature is detected at one point in the projector (for example, the metal part of the optical chassis), and based on the ambient temperature of this part. The temperature was controlled by driving the fan.

[0006]

However, in the conventional liquid crystal projector, since the temperature inside the projector is controlled by cooling the entire inside of the projector by using a single fan, the temperature control of each liquid crystal panel becomes insufficient. It is not possible to sufficiently prevent the change of the transmittance characteristic due to the temperature change of the liquid crystal panel, and therefore the gradation defect of the projected image and (R) (G)
This is a cause of causing color unevenness and poor white uniformity due to the temperature difference between the panels of FIG.

The present invention has been made in view of the above-mentioned drawbacks of the prior art. In a liquid crystal projector having a plurality of liquid crystal panels, the temperature of each liquid crystal panel can be individually and reliably controlled, and the transmittance characteristic of the panel can be controlled. An object of the present invention is to provide a liquid crystal projector that improves the projected image quality by reducing gradation defects and color unevenness due to temperature dependence.

[0008]

To achieve the above object, in the present invention, in a liquid crystal projector having a plurality of liquid crystal panels, a cooling means is provided for each of the plurality of liquid crystal panels. In a preferred embodiment to which the present invention is applied, the plurality of liquid crystal panels are composed of three plates that respectively transmit R light, G light and B light.

In a further preferred embodiment, the cooling means comprises a fan. In a further preferred embodiment, a control circuit for driving and controlling the cooling means is provided, temperature detection means is provided for each of the plurality of liquid crystal panels, and each temperature detection means is connected to the control circuit.

[0010]

A cooling means such as a fan is provided for each liquid crystal panel of the plurality of liquid crystal panels, and the fan is drive-controlled for each panel to individually control the temperature of each liquid crystal panel.

[0011]

1 is a block diagram of a liquid crystal projector according to an embodiment of the present invention. This liquid crystal projector includes a white lamp 1 and dichroic mirrors 2 and 3 that reflect R light.
A liquid crystal panel (LCD) 5 and an optical lens system 4 that transmit the R light, dichroic mirrors 6 and 7 that reflect the G light, and a liquid crystal panel (LCD) that transmits the G light.
9 and an optical lens system 8, dichroic mirrors 10 and 11 for reflecting B light, a liquid crystal panel 13 and an optical lens system 12 for transmitting the B light, and a projection lens for transmitting the separated RGB lights by combining them. 14 are provided.

The white light emitted from the white lamp 1 is separated into R light, G light and B light of predetermined wavelengths by the dichroic mirrors 2, 3, 6, 7, 10 and 11, and the liquid crystal panel 5 on each optical path. , 9, 13 are passed. At this time, each liquid crystal panel acts as an optical shutter for the image component signal of each light of R, G, B, and controls the drive of each liquid crystal panel to control the composition ratio of R light, G light, and B light. The projection lens 14 synthesizes them to obtain an image signal of a predetermined color tone.

Cooling fans 15, 16 and 17 are provided at the positions of the three liquid crystal panels 5, 9 and 13 through which the R light, G light and B light respectively pass. Each cooling fan 1
5, 16 and 17 are corresponding liquid crystal panels 5, 5, respectively.
The driving is controlled according to the temperatures of 9 and 13, and the temperature of each panel is controlled to be maintained at a predetermined temperature.

FIG. 2 shows an example of the control circuit configuration of the cooling fan. A diode 18 for temperature detection is provided on the liquid crystal panel 5 for R light, and the diode 18 is connected to the input side of an operational amplifier 19. The output side of the operational amplifier 19 is connected to the microcomputer (CPU) 21 and the drive circuit 20 of the cooling fan 15. The drive circuit 20 is connected to the power supply 22 and the microcomputer 21. The set temperature of the liquid crystal panel 5 can be arbitrarily set by changing the value of the resistor connected to the operational amplifier 19.

In the control circuit having the above-mentioned structure, the drive circuit 20 of the fan 15 is controlled through the operational amplifier 19 according to the temperature detected by the diode 18, and the air volume and the like are adjusted according to the difference from the set temperature, thereby the liquid crystal panel. Keep 5 at the desired temperature. In this case, high-precision temperature control is achieved by setting the air flow rate by controlling the drive circuit 20 based on a program previously incorporated in the microcomputer 21 in consideration of the ambient temperature and the like. The operational circuit 19 and the drive circuit 20 for the fan 5
It may be connected only via the microcomputer 21 without directly connecting with. Further, it is also possible to drive and control the fan 5 with a predetermined output via the drive circuit 20 according to the output of the operational amplifier 19 without using the microcomputer 21.

Further, in the microcomputer 21, similarly to the circuit of the liquid crystal panel 5 for R light, the temperature detection signals of the liquid crystal panel 9 for G light and the liquid crystal panel 13 for B light are respectively operational amplifiers (not shown). And a cooling fan 16 for cooling the liquid crystal panels 9 and 13,
A drive circuit (not shown) for driving 17 is connected.
With such a configuration, each liquid crystal panel is controlled to an optimum temperature in accordance with the ambient temperature, and a relative temperature difference is provided between the liquid crystal panels so that the relative transmittances are different from each other.
It is possible to control the composition ratio of light to obtain an image having a desired color tone.

[0017]

As described above, in the liquid crystal projector according to the present invention, the cooling means (fan) is provided for each of the plurality of liquid crystal panels, and the temperature control is performed for each liquid crystal panel. Control reliability is improved, each liquid crystal panel can be maintained at a constant temperature or a desired set temperature accurately, and gradation defects and color unevenness due to the temperature dependence of the liquid crystal panel can be reduced to improve the quality of the projected image. You can

Further, the degree of freedom in designing the ventilation path is increased as compared with the conventional structure in which the entire device is cooled, and various shapes according to the application place can be realized and the size can be reduced. Further, since each liquid crystal panel is intensively cooled, cooling efficiency is increased, power consumption is saved, and fan noise is reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of a liquid crystal projector according to an embodiment of the present invention.

FIG. 2 is a temperature control circuit diagram of the liquid crystal projector of FIG.

FIG. 3 is a characteristic diagram showing temperature dependence of transmittance of a liquid crystal panel.

[Explanation of symbols]

1: White lamp, 2, 3: Dichroic mirror, 5:
R light liquid crystal panel, 6, 7: dichroic mirror,
9: Liquid crystal panel for G light, 10, 11: Dichroic mirror, 13: Liquid crystal panel for B light, 14: Projection lens, 1
5, 16 and 17: cooling fan, 18: temperature detection diode, 19: operational amplifier, 20: fan drive circuit, 2
1: Microcomputer, 22: Power supply.

Claims (4)

[Claims] 1. A liquid crystal projector having a plurality of liquid crystal panels, wherein each of the plurality of liquid crystal panels is provided with a cooling means. 2. The liquid crystal projector according to claim 1, wherein each of the plurality of liquid crystal panels includes three plates that transmit R light, G light, and B light, respectively. 3. The liquid crystal projector according to claim 1, wherein the cooling unit includes a fan. 4. A control circuit for driving and controlling the cooling means, a temperature detecting means is provided for each of the plurality of liquid crystal panels, and each temperature detecting means is connected to the control circuit. The liquid crystal projector according to item 1.