JPH05249427A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To reduce variance in white balance due to variance of a dichroic mirror, a light source, etc., by adjusting color purity and the quantity of light by a 1/2-wavelength plate whose rotational angle is finely adjustable. CONSTITUTION:The dichroic mirror which demultiplexes light into light beams of the primary colors R, G, and B, and multiplexes the decomposed light beams, three liquid crystal panels 4 which impose modulation on incident light, and an optical system which projects transmitted composite light on the liquid crystal panels are arranged in an optical path. The 1/2-wavelength plate 43 is provided between the projection light side of the liquid crystal panel 4, which imposes modulation on, at least, the G component, and the dichroic mirror for multiplexing in parallel to the liquid crystal panel planes rotatably in a plane parallel to the panels.

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, and more particularly to a white balance adjusting mechanism for a liquid crystal projector.

[0002]

2. Description of the Related Art Since a liquid crystal panel can modulate transmitted light, a projector which is remarkably miniaturized as compared with a conventional one has been developed and put into practical use by combining it with an optical system.

FIG. 5 schematically shows the optical path of a conventionally used device of this type. In the figure, three liquid crystal panels 3, 4, and 5 are arranged corresponding to the R, G, and B primary color components of the projected image. A modulation signal is supplied to each of the liquid crystal panels 3 to 5 from the main body of the image processing apparatus, and the transmitted light from the light source 1 is modulated according to an image and emitted to the optical system.

The light emitted from the light source 1 has its optical path adjusted by the cold mirror M1 and the long and short wavelength regions such as infrared rays and ultraviolet rays are removed by the filter F, and then R, G by the first dichroic mirror D1. The component is reflected and the B component is transmitted.
The reflected light is made incident on the second dichroic mirror D2, and the transmitted light is made incident on the B-modulated liquid crystal panel 5 with its optical path bent by the total reflection mirror M2. The second dichroic mirror D2 has a characteristic of reflecting the R component and transmitting the G component, splits the incident light into R and G, and separates each light into the R modulation liquid crystal panel 3,
It is incident on the G modulation liquid crystal panel 4. Three liquid crystal panels 3
Each of the modulated lights that have passed through .about.5 is then combined with the three primary colors by the third and fourth dichroic mirrors D3, D4 and transmitted through the projection lens 2 to be projected as a color image on a screen or the like. In the figure, M3 is a total reflection mirror for changing the optical path of the G component transmitted through the G modulation liquid crystal panel.

In the liquid crystal projector having the above structure, it is necessary to adjust the white balance in order to improve the quality of the projected color image. In the conventional device, in particular, in order to increase the accuracy of each component having a color-determining action or to adjust the G light amount with high relative luminous efficiency,
A method of arranging a polarizing plate for adjusting the light amount on the modulation liquid crystal panel is adopted. Since the former is not economical, the latter is usually adopted.

FIG. 6 shows the structure of the G modulation liquid crystal panel 4 in which the latter polarizing plate for adjusting the light quantity is arranged. In this liquid crystal panel 4, an incident polarizing plate 41 and an outgoing polarizing plate 42 are superposed on the light incident side and the light emitting side via a liquid crystal layer.
A light amount adjusting polarizing plate 6 is attached to a metal fitting 7 on the emission side of 2. The metal fitting 7 is inserted into a guide pin 8 which is erected on a mount supporting the liquid crystal panel 4, and rotatably supports the light quantity adjusting polarizing plate 6 on a plane parallel to the liquid crystal panel 4. The metal fitting 7 adjusted by rotation is screw 9
Fixed by.

[0007]

In order to adjust the white balance of the G component by rotating the light quantity adjusting polarizing plate 6 in a plane parallel to the panel and adjusting the polarization angle between the polarizing plate 6 and the emitting polarizing plate 42. The light amount is adjusted to an arbitrary value and the screw 9 is fixed at the adjusted position.

In the light quantity adjusting system using the polarizing plate as described above, since the polarizing plate is additionally inserted, the transmittance of light is reduced by about 15% by the insertion of the polarizing plate, and the illuminance of the whole is reduced. The decrease is inevitable, and it cannot be said that it is a preferable white balance adjusting mechanism for a projector that requires as much light as possible. Further, in the adjusting mechanism described above, it is necessary to design in advance the light amount balance of the R, G, and B components in consideration of the decrease in illuminance, and there is a problem that the design is not easy.

The present invention has been made in view of the above problems of the liquid crystal projector, and provides a mechanism capable of finely adjusting variations in optical elements such as a dichroic mirror without lowering the amount of light.

[0010]

In order to achieve the above-mentioned object, the present invention decomposes light into three primary colors of R, G and B, or dichroic mirror for combining the decomposed light, and adds modulation to incident light. In a liquid crystal projector having three liquid crystal panels and an optical system for projecting the combined light transmitted through the liquid crystal panels, between the outgoing light side of the liquid crystal panel for modulating at least the G components of the three primary colors and the combining dichroic mirror. To
A half wave plate is provided in parallel with the plane of the liquid crystal panel,
A liquid crystal projector is constructed by rotatably supporting a wave plate in a plane parallel to the plane of a liquid crystal panel.

[0011]

[Function] By inserting the half-wave plate, the color purity and the amount of light are adjusted to reduce the white balance variation due to the variations of the dichroic mirror and the light source, and the half-wave plate is rotated for adjustment. As a result, it is possible to make fine adjustments and reduce individual differences between devices.

[0012]

EXAMPLE The liquid crystal projector in this example has the same optical path as that shown in FIG. 5 of the device shown in a model, but the structure of the liquid crystal panels 3, 4 and 5 arranged in the optical path is different.
That is, as shown in FIG. 5, the light from the light source 1 is separated into R, G and B by the dichroic mirrors D1 and D2, and the respective light components are modulated by the liquid crystal panels 3, 4 and 5, and again by the dichroic mirrors D3 and D4. Although combined and projected from the projection lens 2 onto the screen, at least the G modulation liquid crystal panel 4 has a structure shown in FIG. 1, which is different from the structure of the conventional device.
Since the light amount of the G component is the most important component in determining the white balance of the device, this embodiment is adopted to adjust this light amount.

FIG. 1 shows a G modulation liquid crystal panel 4 according to this embodiment.
2 shows an upper plane of the liquid crystal panel 4. Figure 1
In the liquid crystal panel 4, the incident polarization plate 41 and the emission polarization plate 42 are laminated and adhered to both surfaces sandwiching the liquid crystal layer. A ½ wavelength plate 43 for adjusting the amount of light supported by the metal fitting 44 is disposed on the emission side of the emission polarizing plate 42. As shown in FIG. 2, the metal fitting 44 has a guide pin 4 that is set up on a mounting base that supports the liquid crystal panel 4.
5, a guide hole 46 for inserting 5 is formed, and the guide hole 46 is attached to the half-wave plate 4 attached to the metal fitting 44.
It is formed in an arc shape so that 3 can be rotated in a plane parallel to the liquid crystal panel 4. Further, a fixing piece 47 for fixing the position adjusted by rotation with the main body of the projector is integrally formed on the metal fitting 44. By fixing the fixing piece 47 with a screw 48, the liquid crystal panel 4 is fixed. The position of the half-wave plate 43 with respect to is fixed.

In the plan view of FIG. 2, the half-wave plate 43 is used.
Of the three directions (1) to (3), the direction is the plane of polarization of the light beam emitted from the output polarizing plate 42, the direction is the optical axis of the crystal of the half-wave plate 43, and the direction is the half-wave plate 43. 2 shows the plane of polarization of the light beam that exits. Here, when the angle formed by the polarization plane (direction) of the light beam emitted from the emission polarizing plate 42 and the crystal optical axis (direction) of the half-wave plate 43 is θ, the half-wave plate 43 expressed by the above direction. The plane of polarization of the light beam emitted from
It is rotated by 2θ with respect to the direction. Therefore, it is enlarged with respect to θ, and it becomes possible to finely adjust the angle.

The color purity of the G component modulated by the liquid crystal panel 4 is determined by the fourth dichroic mirror D4, and the characteristics of p wave and s wave of this dichroic mirror D4 are shown in FIG. As shown in this figure, the transmission band of the s wave is narrowed from both sides of the p wave. Therefore, by adjusting the angle of the half-wave plate 43 shown in the above direction, the color purity of the G component can be adjusted and the amount of light can be continuously changed, and since 2θ appears with respect to the direction, Fine adjustment is possible.

In the above embodiment, the G component contributes the most to the white balance, so that the G modulation liquid crystal panel 4 is described. However, the same applies to the R modulation liquid crystal panel 3.
It can be configured by stacking wave plates and providing an angle adjusting mechanism. FIG. 4 shows the p-wave and s-wave characteristics of the third dichroic mirror D3 that determines the color purity of the R component in this case. By adjusting the direction of the half-wave plate, the light amount and color purity of the R component can be adjusted.

[0017]

As described above, according to the present invention, by inserting the rotatably supported half-wave plate, variations in the cut wavelength region at the time of transmission and reflection of the dichroic mirror, variations in the color tone of the light source, etc. It is possible to adjust the white balance variation caused by the above, and to improve the quality of the projected image of the liquid crystal projector. Also R,
It is possible to reduce the variation in monochromatic purity of G and B.

[Brief description of drawings]

FIG. 1 is a side view showing the structure of a G modulation liquid crystal panel of a liquid crystal projector according to an embodiment of the present invention.

FIG. 2 is a plan view of the liquid crystal panel of FIG.

FIG. 3 is a characteristic diagram of p waves and s waves of a fourth dichroic mirror mounted in the same embodiment.

FIG. 4 is a characteristic diagram of p waves and s waves of a third dichroic mirror mounted in the embodiment.

FIG. 5 is a diagram schematically showing an optical path of a conventional liquid crystal projector.

FIG. 6 is a side view showing a light amount adjustment mechanism of a liquid crystal panel used in a conventional device.

[Explanation of symbols]

 D1 to D4 Dichroic mirror 3, 4, 5 Liquid crystal panel 41 Incident polarization plate 42 Emission polarization plate 43 1/2 wavelength plate 45 Guide pin 46 Guide hole

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04N 9/31 A 8943-5C

Claims (1)

[Claims] 1. A dichroic mirror for separating projection light from a light source into three primary colors of R, G, and B, and three liquid crystal panels for applying modulation for projection images to each of the separated three primary colors,
In a liquid crystal projector including a dichroic mirror that synthesizes modulated light that has passed through a liquid crystal panel and an optical system that projects the synthesized light, a dichroic mirror for synthesizing the outgoing light side of the liquid crystal panel that modulates G components of at least three primary colors And a half wave plate in parallel with the liquid crystal panel plane,
A liquid crystal projector in which the half-wave plate is rotatably supported in a plane parallel to the plane of the liquid crystal panel.