JPH043043A - Overhead projector - Google Patents

Abstract

PURPOSE:To obtain a good liquid crystal image even if the temp. of liquid crystal display body rises by light incidence by detecting the quantity of the incident light on the liquid crystal display body and regulating the voltage impressed to the liquid crystal display body in accordance with the detected value. CONSTITUTION:This projector is provided with a light quantity detecting means 9 for detecting the quantity of the light source light with which the liquid crystal display body 7 is irradiated and a voltage control means 22 for regulating the voltage impressed to the liquid crystal display body 7 in accordance with the detected value from the light quantity detecting means 9. The temp. rise of the liquid crystal display body 7 is indirectly detected from the quantity of the incident light on the liquid crystal display body 7 and the control means 22 regulates the voltage impressed to the liquid crystal display body 7 in accordance with the detected voltage. The good liquid crystal image is obtd. even if the temp. of the liquid crystal display body 7 rises.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an over-rad projector that is used for research presentations, conferences, briefing sessions, etc. and projects an enlarged image onto a screen.

[Conventional technology]

Overhead projectors (OHPs) are traditionally used to project still images onto a screen.

FIG. 9 shows a perspective view of an over-rad projector which projects by a transmission type, and FIG. 10 shows a perspective view of an over-rad projector which projects by a reflection type. A transparent film is set on a Fresnel lens 51 that serves as a document table, and an image of the transparent film is placed on a projection lens 52 above the Fresnel lens 51.
After the image is enlarged, it is reflected by a projection mirror 53 and projected onto a screen provided in front of the projector.

The over-rad projector shown in FIG. 9 has a light source and a reflection mirror built into the housings 5 and 4 to which the front lens 51 is attached, and projects using light transmitted through the film on the front lens 51. 10th
The illustrated overherad projector has a projection lens 52 and a projection mirror 53 or a projection unit 55 attached to it.
A light source and a reflection mirror are built in, and the Fresnel lens 51 is irradiated with light from above, and the light reflected from the frame lens 51 is guided to the projection unit 5 for projection. Both of these overhead projectors have the same basic configuration for projecting still images, except for the difference in whether the Fresnel lens 51 is a transmissive type or a reflective type.

In contrast to such overhead projectors that project still images, overhead projectors that project moving images have been developed. In other words, with the recent development of liquid crystal technology, liquid crystal panels (including color liquid crystal panels) that can control the resolution of pixel-level images have been put into practical use. It is placed on a Fresnel lens and uses the transmitted light to project a moving image onto a screen. The development of such an over-the-top projector for projecting moving images has the advantage of increasing the convenience and demand for using over-the-top projectors.

FIG. 11 shows a liquid crystal display 60 developed for this purpose.
This liquid crystal display 60, which is an example, is used by being removably placed on a Fresnel lens of an overhead projector, and the lower end surface (bottom surface) is open, and the upper end surface has a liquid crystal panel. (LCD) 61 is installed.

Cooling air is allowed to pass under the liquid crystal panel 61, and a cooling fan 62 is provided at one end of the liquid crystal display 60.
The slit) 63 is opened.

In general, liquid crystal panels have the property of absorbing light and self-heating due to the absorption of light, and this self-heating makes image display unstable. Therefore, it is necessary to cool the liquid crystal panel 61, and cooling air for this purpose is directed below the liquid crystal panel 61.

FIG. 12 shows a perspective view of an overhead projector 70 that can switch and project both a liquid crystal image and a film image. A projection lens 72 whose focal length M is adjustable is attached to the front surface of the housing 71. Further, the side surface of the housing 71 is opened to form the document insertion lower 3. Reference numeral 80 is a document plate inserted into the document insertion lower 3, which includes a liquid crystal display 81 having a liquid crystal panel 82, and a film holder 8 into which a transparent film is inserted.
3 are connected by a hinge shaft 84. The overhead projector 70 with this structure can project a moving image on the liquid crystal when the liquid crystal display 81 is inserted into the document insertion lower 3, and when the film holder 83 is inserted into the document insertion lower 3.
It is also possible to project still images from film.

In this way, in the overhead projector shown in FIGS. 9 and 10, the liquid crystal display 60 shown in FIG.
By placing the image on the Fresnel lens 51, or by inserting the liquid crystal display 81 of the document plate 80 in the overhead projector shown in FIG. 12, it is possible to project a liquid crystal image.

[Conflicts that the invention attempts to solve]

However, in conventional overherad projectors, the image may become unstable or fluctuate during projection of the liquid crystal image, and a good image may not be projected. This is because the temperature of the liquid crystal increases due to absorption of light from the light source.

To explain this phenomenon with reference to FIG. 13, which shows a cross-sectional view of the liquid crystal panel 61, a color filter layer 61b is laminated on a liquid crystal layer 61a that displays an image, and a polarizing film 61 is placed above and below the liquid crystal layer 61a.
The liquid crystal panel 61 is constructed by covering the outer surface of the polarizing film 61 and coating the outer surface of the polarizing film 61 with a protective film 61 d. However, the color filter layer 61 b and the polarizing film 61 c easily absorb light, and this light absorption generates heat. , these layers 6
This is because the temperature of the liquid crystal layer 61a, which is in close contact with 1b and 61c, increases. The liquid crystal of the liquid crystal layer 61a has a characteristic that its fluidity increases as the temperature rises, and the voltage threshold for optical rotation changes as the fluidity fluctuates. Therefore, even if a low voltage is applied in a state of elevated temperature, the arrangement direction easily changes.
This causes the liquid crystal image to become distorted, making it impossible to project a high-quality image.

In such a state, the temperature of the liquid crystal layer 61a itself is measured,
It may be possible to adjust the applied voltage over the temperature range, but it is virtually impossible to measure the temperature of the stacked liquid crystal layers. Therefore, it is an object of the present invention to solve the problems caused by such temperature rise.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides an overhead projector that irradiates light from a light source onto a liquid crystal display and projects a liquid crystal image of the liquid crystal display onto a screen. The apparatus is configured to include a light amount detection means for detecting the amount of light, and a control means for adjusting the voltage applied to the liquid crystal display based on the detected value from the light amount detection means.

[For production]

According to such a configuration, the light amount detection means indirectly detects the temperature rise of the liquid crystal display due to light irradiation from the amount of light incident on the liquid crystal display, and the control means controls the temperature of the liquid crystal display based on this detected value. Since the voltage applied to the liquid crystal display is adjusted, it is possible to create a good liquid crystal image even if the temperature of the liquid crystal display increases.

〔Example〕

Hereinafter, practical examples of the present invention will be explained based on the drawings. 1 through 5 are diagrams showing one embodiment of an over-rad projector according to the present invention.

1 and 2 are a sectional view and a perspective view showing an example of an overhead projector 1 to which the present invention is applied. In the figure, a supporting member 3 is attached to a housing 2 serving as a base so as to be rotatable in an upright manner, thereby forming an over-the-top projector 1. The housing 2 has a built-in light source 4 such as a halogen lamp and a reflection mirror 5 that reflects the light from the light source 4 upward, and a Fresnel lens 6 is located in the housing 2 above the reflection mirror 5. installed. A liquid crystal display 7 is attached to the upper surface of the housing 2 located above the Fresnel lens 6, and the light from the light source 4 is reflected by a reflection mirror 5, transmitted through the Fresnel lens 6, and then displayed on the liquid crystal display. The liquid crystal display body 7 is configured so that the light reaches the body 7 and is emitted upward from the liquid crystal display body 7.
A liquid crystal image is formed by the applied voltage from i21 (see FIG. 4). Note that a pair of legs 8 are attached to both sides of the housing 2. The leg body 8 is constituted by a front leg 8a and a rear leg 8b connected by a bendable coupling leg 8c, and the angle of the housing 2 on the desk is adjusted by adjusting the bending of the coupling leg #8c.

The support member 3 directs the light transmitted through the liquid crystal display 7 to a screen (
It reflects toward the left (not shown).

The support member 3 includes a support arm 10 whose lower end is pivotally attached to the housing 2 so that its angle can be adjusted, and a stay 11 rotatably attached to the support arm 10.

A lens cover 13 is attached to the shaft portion of the stay 11, and a projection lens 14 for condensing and enlarging image light from the Fresnel lens 6 is provided within the lens cover 13.

A projection mirror 15 is attached to the front portion of the stay 11 to reflect the light transmitted through the projection lens 14 toward the screen.

This overhead projector 1 has a rectangular outer shape by folding the stay 11 into the support arm 10 and further folding the support arm 10 onto the housing 2. The overhead projector 1 has a rectangular outer shape, and can be stored in an atta V screen or the like and carried or carried. be exposed. Then, by raising the support arm 10 and rotating and deploying the stay 11, it becomes possible to project an image as shown in the figure.

In addition to the above configuration, a photosensor (light receiving element 9) is disposed within the housing 2.

The photosensor 9 is a light amount detection means for detecting the amount of light from the light source that enters the liquid crystal display 7, and is located in the optical path of the light from the light source and close to the liquid crystal display 7, as shown in FIG. It is set up so that The photosensor 9 may be disposed at a position that detects the amount of light incident on the liquid crystal display 7, for example, as shown in FIG. It can also be attached integrally to 7b. This photosensor 9 is designed to indirectly detect the temperature of the liquid crystal layer, which rises due to the incidence of light, by measuring the amount of light hitting the liquid crystal surface water body 7.

FIG. 4 shows a block diagram for controlling liquid crystal image formation on the liquid crystal display body 7. The liquid crystal image formation on the liquid crystal display body 7 is performed based on the voltage of the liquid crystal drive power supply 21.
The voltage 1 is applied to the liquid crystal display 7 after being adjusted by the voltage adjustment section 22. Voltage adjustment section 2
2 stores a table or a calculation program in which drive voltage values V to be applied with respect to variations in light intensity as shown in FIG. 5 are set. These tables empirically relate the amount of light I and the temperature of the liquid crystal that rises depending on the amount of light, and when the amount of light I is detected, the temperature of the liquid crystal that rises depending on the amount of light is indirectly calculated. I am now able to do some things.

The voltage adjustment unit 22 receives the amount of light incident on the liquid crystal display 7 detected by the photosensor 9, and adjusts the drive to be applied to the liquid crystal display 7 based on this amount of light, as shown in the characteristic diagram shown in FIG. Calculate the voltage value. Therefore, in such a configuration, even if the temperature of the liquid crystal of the liquid crystal display 7 rises due to the incidence of light,
Since the optimum voltage for fS can be applied to this increase, the liquid crystal image is not disturbed and a good W image can be projected.

6 and 7 illustrate an embodiment of the pond of the present invention for controlling liquid crystal imaging. In this embodiment, the amount of light detected by the photosensor 9 is input to the light amount integrating circuit 23. The light amount integrating circuit 23 calculates the integral value Q of the light amount and outputs the calculated value to the voltage adjustment section 22 . The voltage adjustment unit 22 stores a table or a calculation program of the driving voltage V corresponding to the integrated light amount Q as shown in FIG. 7, and determines the optimum driving voltage value based on the input integrated light amount Q. is calculated and applied to the liquid crystal display 7. Therefore, in this case as well, a liquid crystal image can be formed satisfactorily, but since the drive voltage value is calculated based on the integral value of the amount of light, it is possible to form an image with higher precision. In such control, the light amount integral value Q is cleared when the light source 4 is turned off or the detection level of the photosensor 9 falls below a certain level, and a new light amount integral value Q is set for the next projection.
is calculated. This state occurs when the temperature of the liquid crystal display 7 stops rising, and by clearing the integral value in this case, control failures during the next projection can be prevented.

In addition to such control, control as shown in FIG. 8 is also possible. FIG. 8 shows a case where the light source 4 is repeatedly turned on and off. In this case, the voltage originally applied to the liquid crystal display 7 is adjusted to increase or decrease by widening the OFF time interval of the light 'a4. That is, since there is a correlation between the OFF time interval of the light source 4 and the temperature drop of the liquid crystal display 7, highly accurate control is possible by performing such control.

Note that the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways, and can be similarly applied to, for example, the overhead projector shown in FIG. 9, FIG. 10, or FIG. 12.

〔Effect of the invention〕

As explained above, according to the present invention, the amount of light incident on the liquid crystal display is detected and the voltage applied to the liquid crystal display is adjusted based on the detected value. Even if the temperature rises, a good liquid crystal image can be formed.

[Brief explanation of drawings]

1 to 5 are diagrams showing one embodiment of an overhead projector according to the present invention, in which FIG. 1 is an overall cross-sectional view, FIG. 2 is a perspective view, and FIG. 3 is an example of the arrangement of photosensors. FIG. 4 is a front view of the liquid crystal display, FIG. 4 is a control block diagram, and FIG. 5 is a characteristic diagram showing the relationship between light amount and applied voltage. Fig. 6 is a control block diagram of another embodiment ρ1, Fig. 7 is a characteristic diagram showing the relationship between the light intensity integral value and the applied voltage in that embodiment, and Fig. 8 is a diagram showing the OFF time interval of the light source and the other control method. 9 and 10 are perspective views of examples of conventional overhead projectors, and 11 is a characteristic diagram showing the relationship between applied voltages.
The figure is a perspective view of a liquid crystal display used in these devices, section 12 is a perspective view of another conventional overhead projector, and FIG. 13 is a sectional view of the internal structure of the liquid crystal panel. 1... Over... L-do projector 2...
...Housing 4 ...Light source 7
...Liquid crystal display 9...Photo sensor (light amount detection means) 22...
... Voltage adjustment section (control means) 23 ... Mitsuzaka branch circuit (light amount detection means) Patent applicant Rico Co., Ltd. Figure 5 Light amount ■ Figure Time T

Claims (1)

[Claims] In an overhead projector that irradiates a liquid crystal display with light from a light source and projects a liquid crystal image of the liquid crystal display onto a screen, a light amount detection means detects the amount of light from the light source irradiated onto the liquid crystal display, and the light amount detection means An overhead projector comprising: a control means for adjusting a voltage applied to the liquid crystal display based on a detected value from the liquid crystal display.