JPH07119882B2 - Focus detection device for liquid crystal projector - Google Patents

Description

TECHNICAL FIELD The present invention relates to a focus detection device for a liquid crystal projector that magnifies and projects an image on a front screen by a projection lens, and enables autofocus by particularly simple focus detection. The present invention relates to a focus detection device for a liquid crystal projector.

“Prior Art” Conventionally, as a means for automatically detecting and adjusting focus, a means as shown in FIG. 4 is used in a camera or the like.

In FIG. 4, the focus detection device in the camera C is composed of a combination of an image pickup device 50 and a lens 5 for actually picking up an image, another optical system 51, and an electronic circuit 52 for distance measurement.

Further, in the camera C, the subject (for example, a person) 53 to be focused is not specified and the application range is wide, so that a complicated electronic circuit is required to adjust the position of the lens 50 and the measurement result in advance.

[Problems to be Solved by the Invention] In a liquid crystal projector, as a means for realizing autofocus, an optical system of the projector and another optical system for distance measurement and a complicated electronic circuit are used together as in the above-mentioned camera. However, there is a problem that the structure is complicated and the cost is increased significantly.

The present invention has been made in view of the above points, and an object thereof is to provide a focus detection device for a liquid crystal projector at low cost by using an optical system of the liquid crystal projector.

“Means for Solving the Problems” In order to solve the above problems, in the present invention, red,
A liquid crystal having a blue and green liquid crystal panel, and an image from the red liquid crystal panel is combined with an image from the blue liquid crystal panel and the green liquid crystal panel through a blue light synthesis dichroic mirror and a green light synthesis dichroic mirror and projected on a screen. In the projector, an infrared light emitting element and an infrared light receiving element are arranged in parallel at a position adjacent to the effective image area of the red liquid crystal panel, and the infrared light is emitted from the infrared light emitting element to hit the screen, The focus state on the screen is detected based on the amount of reflected light incident on the infrared light receiving element.

"Operation" In FIG. 1 showing an embodiment of the present invention, a light source lamp L
The images emitted from the three primary colors R, G, and B of the red liquid crystal panel 2, the green liquid crystal panel 3, and the blue liquid crystal panel 4 are optically combined into a color image by the light emitted from the screen, and enlarged and projected on the screen 6 as a colorful moving image. To be done.

At this time, the infrared light emitted from the infrared light emitting element 71 disposed adjacent to the effective image area of the red liquid crystal panel 2 passes through the dichroic mirrors DM3 and DM4 and the lens 5, and is reflected on the screen 6. .

The infrared light reflected by the screen 6 again passes through the lens 5 and the dichroic mirrors DM4 and DM3, and enters the infrared light receiving element 72.

The focus state is detected by the amount of infrared light incident on the infrared light receiving element 72.

[Example] Next, an example of an embodiment of the focus detection device for a liquid crystal projector according to the present invention will be described in detail with reference to FIGS.

FIG. 1 is a schematic configuration diagram showing an example in which a focus detection device for a liquid crystal projector according to the present invention is incorporated in a projection type liquid crystal projector.

In FIG. 1, a liquid crystal projector 1 includes liquid crystal panels 2, 3, 4 of three primary colors red, green, blue, mirrors M1, M2, M3 and dichroic mirrors DM1, DM2, DM3, DM4, a light source lamp L and a lens. It is composed of 5 and. 6 is a screen on which an image is projected.

The red liquid crystal panel 2 has a couple 7 of an infrared light emitting element and an infrared light receiving element arranged at a position adjacent to the effective image area.

The mirrors M1, M2, M3 are total reflection mirrors that reflect incident light.

The dichroic mirrors DM1 and DM2 are spectroscopic dichroic mirrors, which split red light and blue light, respectively.

The dichroic mirrors DM3 and DM4 are dichroic mirrors for color combination.

As the light source lamp L, for example, a metal halide lamp with a parabolic reflector is used.

The lens 5 is a projection lens that magnifies and projects an image in which the three primary colors are combined on the screen 6 as a colorful moving image.

Then, the light emitted from the light source lamp L is reflected by a reflection mirror.
Reflect on M1.

The light reflected by the reflecting mirror M1 is reflected only in red by the dichroic mirror DM1 for red reflection, and the remaining light is transmitted.

The light reflected by the dichroic mirror DM1 is reflected again by the reflection mirror M2, then passes through the red liquid crystal panel 2, passes through the color combining dichroic mirrors DM3, DM4, and is emitted to the lens 5.

Further, the light transmitted through the dichroic mirror DM1 is reflected only in blue by the blue reflection dichroic mirror DM2, and the remaining light is transmitted.

The light reflected by the dichroic mirror DM2 passes through the blue liquid crystal panel 4 and is then used for color combination.
The light is reflected by DM3, transmitted through the dichroic mirror DM4, and emitted to the lens 5.

The green light transmitted through the dichroic mirror DM2 is transmitted through the green liquid crystal panel 3, and then reflected by the reflection mirror M3 and the color combining dichroic mirror DM4 and emitted to the lens 5.

The light emitted to the lens 5 has already been color-synthesized, and is displayed as a colorful moving image on the screen 6 by the lens 5.

At this time, the infrared light emitted from the infrared light emitting element 71 of the couple 7 arranged adjacent to the red liquid crystal panel 2 passes through the lens 5, strikes the screen 6 and is reflected before passing through the lens 5. The light passes through and enters the infrared light receiving element of the couple 7.

FIG. 2 shows the red liquid crystal panel 2 in the focus detection device.
FIG. 6 is a front view showing a couple position of the infrared light emitting element and the infrared light receiving element.

In FIG. 2, the effective image area 21 of the liquid crystal panel 2 is shown.
The couple 7 is arranged at a position (upper part in the embodiment) adjacent to (illustrated by diagonal lines).

In the couple 7, an infrared light emitting element 71 and an infrared light receiving element 72 are arranged in parallel. This infrared light emitting element 71 and infrared light receiving element 72
Is shielded so that it emits light only in the front and receives light only from the front.

Therefore, as described above, the effective image area of the red liquid crystal panel 2
Infrared light emitted from the infrared light emitting element 71 arranged at a position adjacent to 21 passes through the dichroic mirrors DM3 and DM4 and the lens 5, and is reflected by the screen 6.

The infrared light reflected by the screen 6 again passes through the lens 5 and the dichroic mirrors DM4 and DM3 sequentially, and enters the infrared light receiving element 72 arranged in parallel with the infrared light emitting element 71.

The focus state is detected by the amount of reflected light that has entered the infrared light receiving element 72.

Then, the amount of light becomes maximum immediately before the optimum focus on the screen 6.

Therefore, autofocusing is performed by stopping the electric adjusting mechanism of the lens 5 at the position where the amount of light is maximum.

FIG. 3 is a functional block diagram of auto focus by applying the focus detection device of the liquid crystal projector according to the present invention.

In FIG. 3, the autofocus mechanism includes a couple 7 including an infrared light emitting element 71 and an infrared light receiving element 72,
Pulse generator PG, resistor R, gate GT, amplifier AM
P, a motor drive circuit 8, and a motor M.

Then, the pulse generator PG drives the infrared light emitting element 71 in a pulsed manner, and at the same time, this pulse causes the infrared light receiving element 72
Turns the output on / off.

As a result, an output signal with good noise resistance is obtained, and this output signal is output from the gate GT to the amplifier AMP, and the amplifier A
Amplify with MP.

The lens drive motor 8 is controlled by the output signal amplified by the amplifier AMP, and the motor M is driven to move the lens 5.

The motor M can be stopped at the maximum point of the signal and the lens 5 can be adjusted to the optimum focus.

[Advantages of the Invention] As described above, in the focus detection device for a liquid crystal projector according to the present invention, the infrared light emitting element and the infrared light receiving element are arranged adjacent to the effective image area of the red liquid crystal panel, and the infrared light is reflected on the screen. The focus amount is detected based on the amount of light thus generated.

Therefore, the focus measurement can be performed easily and inexpensively without the need for an optical system dedicated to the focus measurement as in the related art.

Further, the electric signal processing under the optimum focus condition is easy, and the autofocus is easy to adopt.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a projection type liquid crystal projector incorporating a focus detection device for a liquid crystal projector according to the present invention, and FIG. 2 shows a couple position of an infrared light emitting element and an infrared light receiving element of a red liquid crystal panel in the focus detecting device. A front view, FIG. 3 is a functional block diagram of the focus detection device, and FIG. 4 is a conventional autofocusing embodiment. 1 …… Liquid crystal projector 2 …… Red liquid crystal panel 5 …… Lens 6 …… Screen 7 …… Couple 71 …… Infrared light emitting element 72 …… Infrared light receiving element

Claims (1)

[Claims] 1. A red, blue and green liquid crystal panel, wherein an image from the red liquid crystal panel is combined with an image from the blue liquid crystal panel and the green liquid crystal panel through a blue light synthesis dichroic mirror and a green light synthesis dichroic mirror. In a liquid crystal projector for projecting on a screen with an infrared ray, an infrared light emitting element and an infrared light receiving element are arranged side by side in a position adjacent to the effective image area of the red liquid crystal panel, and infrared light is emitted from the infrared light emitting element. Then, the focus detection device of the liquid crystal projector is characterized in that the focus state on the screen is detected by the amount of the reflected light incident on the infrared light receiving element.