JP2585782B2 - Reflective LCD overhead projector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal overhead projector for projecting and displaying the contents of a liquid crystal display element.

[Prior Art] In a conventional reflection type overhead projector (OHP), light L from a light source 1 passes through a film sheet 3 placed on a mirror Fresnel lens 2 as shown in FIGS.
The reflected light R is reflected by the mirror Fresnel lens 2. The reflected light R passes through the lens 4, is reflected by the mirror 5, and is projected and displayed on the projection surface. This is because it is complicated to take measures against dirt and preservation of the film sheet 3, and it is not easy to add or delete characters and figures on the original on the film sheet 3. However, there is an inconvenience that information cannot be exchanged with other devices.

In order to improve these points, a liquid crystal display (LCD) is replaced with a mirror Fresnel lens 2 instead of the film sheet 3.
A liquid crystal OHP has been proposed in which a personal computer or the like is used to provide data to the LCD and project and enlarge the contents of the LCD. Initially, as shown in FIG. 5, the LCD surrounds a liquid crystal panel 6 with a cabinet 7 and
In the cabinet 7, a drive unit such as an LCD driver circuit, a control circuit such as an interface, and a power supply circuit was incorporated. However, in this structure, there is a slight space between the liquid crystal panel 6 and the mirror Fresnel lens 2 as shown in FIG. 6, so that the incident light L from the light source 1 passes through the dots A of the liquid crystal panel 6, and The reflected light R is reflected by the mirror Fresnel lens 2 on the surface.
There is a problem that the data of the dot A and the dot B of 6a are overlapped when projected and displayed. In order to solve this problem, a structure has been proposed in which an approximate liquid crystal panel is tightly integrated with a mirror Fresnel lens.

"Problem to be Solved by the Invention" As shown in FIG. 7, there is a slight space between the liquid crystal cell 9 and the mirror Fresnel lens 2. Because of this interval, the liquid crystal cell 9
Incident light L1 and L2 pass through, are respectively reflected by the mirror Fresnel lens 2, and are emitted as emitted light R1 and R2. That is, since the incident light L1 passes through the polarizer 8a of the linear polarizer and passes only the component corresponding to the polarization direction and becomes linearly polarized light, the birefringence and alignment state of the liquid crystal in that portion by passing the dot C. When the polarization state changes, the intensity of the linear polarizer after passing through the polarizing plate 8b becomes in accordance with the state of the dot C of the liquid crystal cell 9, and this is reflected by the mirror Fresnel lens 2 to change the dot A. The emitted light R1 is emitted. Therefore, the emitted light R1 becomes linearly polarized light when passing through the polarizing plate 8b, and when the polarization state is changed by the birefringence and alignment state of the liquid crystal in that portion by passing through the dot A of the liquid crystal cell 9, the above-mentioned polarized light is emitted. The intensity after passing through the plate 8a depends on the state of the dot A of the liquid crystal cell 9.

That is, the intensity of the outgoing light R1 depends on the state of the dot C and the dot A.
And the intensity of the emitted light R2 also reflects the two states of the dot A and the dot B, and is displayed as a double image on the projection surface. There are drawbacks. When the liquid crystal panel and the mirror Fresnel lens are tightly integrated to solve these disadvantages,
The OHP and the liquid crystal panel must be formed as an integral structure, and there is a disadvantage that the degree of freedom in structure is reduced.

To solve this drawback, a liquid crystal display element with no polarizing plate on one side is provided on the mirror Fresnel lens so that the side where the polarizing plate is located is opposite to the mirror Fresnel lens, and a lens that collects the reflected light from the mirror Fresnel lens It was considered to provide a polarizing plate before or after the part.

That is, as shown in FIG. 1, the liquid crystal panel 10 is, for example, of the TN type, the STN type, the BCB type or the SSFLC type utilizing the birefringence of the liquid crystal. The incident light L1 is reflected by the mirror Fresnel lens 2, and then passes through the polarizing plate 8b → the dot A of the liquid crystal cell 9 → the polarizing plate 8c. At this time, since the incident light L1 is light emitted from, for example, a normal OHP halogen lamp, the polarization state is random, so that the incident light
Even if L1 is influenced by the birefringence and the orientation state of the liquid crystal of the dot C of the liquid crystal cell 9, the light passing through the liquid crystal cell 9 has a drammed polarization state. Even if it passes, the polarization state does not substantially change,
And the light intensity does not change. This random light passes through, for example, a polarizing plate 8b of a linear polarizer to become linearly polarized light, is reflected by the mirror Fresnel lens 2, and passes through the polarizing plate 8b as it is. When this linearly polarized light passes through the dot A of the liquid crystal cell 9, the polarization state is changed depending on the birefringence and alignment state of the liquid crystal in that part, for example, the inclination of the linearly polarized light is changed,
Or it becomes elliptically polarized light. In this state, the light intensity does not change. This light is, for example, a linear polarizer polarizer
After passing through the liquid crystal cell 8c, the intensity of the light after passing through the liquid crystal cell changes depending on the change in the polarization state. In this way, the incident light L1 becomes the emission direction R1 that reflects the birefringence and alignment state of the liquid crystal of the dot A of the liquid crystal cell 9 and is projected on the projection surface. Therefore, only the birefringence and the alignment state of the liquid crystal of the dot A are reflected on the emitted light R1, but not the birefringence and the alignment state of the liquid crystal of the dot C.

On the other hand, considering incident light L2, incident light L2 is also incident light.
Like L1, the polarization state is random, so the incident light
With exactly the same operation as L1, even when the light passes through the dot A of the liquid crystal cell 9, the polarization state does not substantially change, and the light intensity does not change. The incident light L2 becomes the outgoing light R2 reflecting only the birefringence and alignment state of the liquid crystal of the dot B of the liquid crystal cell 9 and is projected on the projection surface. Therefore, only the birefringence and the alignment state of the liquid crystal of dot B are reflected on the outgoing light R2.
The birefringence and alignment state of the liquid crystal are not reflected.

Therefore, outgoing light R1 passing through dot A, incident on dot A, and outgoing light R2 passing through dot B, only outgoing light R1 is reflected as the birefringence of the liquid crystal of dot A and the intensity of the alignment state. And the image of the projected display is not doubled.

In this configuration, since the distance between the liquid crystal panel and the mirror Fresnel lens is not affected at all, the degree of freedom of the configuration of the liquid crystal panel is increased. That is, by attaching a polarizing plate to an OHP using a conventional film sheet, both a conventional display using a film sheet and a display using a liquid crystal panel having no polarizing plate on the upper surface can be performed. Also, there is an advantage that the projected display image is brighter than the conventional example. That is, in the conventional example, the light passes through the polarizing plate a total of four times because the light reciprocates between the two polarizing plates. In the present invention, however, the light only needs to pass through the polarizing plate a total of three times. Light absorption is reduced.

Even if the liquid crystal layer contains a dichroic dye, one of the double images will become thinner if the liquid crystal is also mainly used for refraction, for example, if the dye is added by the TN or STN method. The double image can be made inconspicuous. If the dye itself has no optical anisotropy, no double image is produced.

Overhead projectors are characterized in that they can be projected and displayed on large screens, and from this point the view angle is wide.
STN type liquid crystal is excellent. However, when attempting to display black and white using this STN type liquid crystal display device, the wavelength of the light causes a phase difference due to the length of the birefringence, and this phase difference causes color to appear on the display characters on the projection surface, for example. Poor nature.

The present invention eliminates the conventional disadvantages of characters and the like being displayed as a double image on a projection surface and the occurrence of colors in black-and-white display characters on the projection surface. It is an object of the present invention to provide a reflection type OHP which is configured without having an integral structure.

According to the present invention, an STN mode liquid crystal display element having no polarizing plate on one side of the mirror Fresnel lens is provided on the mirror Fresnel lens such that the side where the polarizing plate is located and the mirror Fresnel lens are opposed to each other, and A second polarizing plate is provided in front of or behind a lens unit that collects reflected light from the mirror Fresnel lens, and a phase compensator is provided in the liquid crystal display element or the second polarizing plate.

FIG. 2 shows an embodiment of the present invention.

A liquid crystal cell 9 of a so-called double STN type in which a liquid crystal cell or a film is opposed to or bonded to a driving liquid crystal cell as a phase compensating plate. When a film is used as the phase compensator 11, it is generally called a phase film system, but in the present invention, since the phase compensator is exactly the same in both the liquid crystal cell and the film,
Both are collectively called the double STN method.

In this double STN mode, the phase compensator may be composed of a large number of liquid crystal cells or films, and this phase compensator completely compensates for the phase difference of light caused by the birefringence of the STN mode liquid crystal display element. can do.

It is assumed that the incident light L1 passes through the phase compensator 11 and the driving liquid crystal cell 9 in the order of D → C → A → F as shown in FIG.
For the same reason as without the phase compensator 11, the light intensity on the projection plane is affected only by the alignment state of the liquid crystal or film at points A and F. Similarly, for incident light L2, B, G
The intensity of light on the projection plane is affected only by the orientation of the liquid crystal or film at the point. From this, the projected display image becomes 2
It turns out that it does not overlap. Also, even if the outgoing light R1, R2 of the incident light L1, L2 has a phase difference due to the length of the wavelength depending on the birefringence and alignment state of the STN liquid crystal, the phase difference is automatically compensated by the phase compensator. Therefore, it is possible to prevent the display characters and the like on the projection plane from being colored.

As shown in FIG. 3, the phase compensating plate 11 may have a structure separated from the driving liquid crystal cell 9. In this case, the phase compensator
11 is advantageous in that it is downsized and the manufacture of the phase compensator is facilitated. Instead of separating the entire phase compensating plate from the driving liquid crystal cell, it is also possible to adopt a structure in which a part of the phase compensating plate is separated from the driving liquid crystal cell.

The present invention is effective even if the phase compensating plate contains a dye.

[Effects of the Invention] As described above, according to the present invention, it is possible to eliminate the double image of the projection display without bringing the liquid crystal panel and the mirror Fresnel lens into close contact with each other in the reflection type liquid crystal OHP, and use the phase compensator to display the monochrome image. It is possible to eliminate the occurrence of color in characters. The present invention is applicable to the STN method and the double STN method in which the display method of the liquid crystal cell mainly uses the birefringence of the liquid crystal, and is effective even when a dye is added to the above method. According to the present invention, a liquid crystal OHP can be easily formed using a reflection type OHP using a conventional film sheet. In a transmissive OHP, a liquid crystal OHP can be configured in a similar configuration. Therefore, the liquid crystal OHP can be configured with the same liquid crystal panel for both the transmission type and the reflection type OHP using the conventional film sheet.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing another embodiment of the present invention, FIG. 3 is a sectional view showing still another embodiment of the present invention, FIG. Is a conventional reflective OHP
FIG. 4B is a side view of the vinyl sheet 3 and the mirror Fresnel lens 2, FIG. 5 is a perspective view showing a liquid crystal display element used in a conventional reflective OHP, and FIG. FIG. 7 is a side view of a conventional reflection type OHP mirror Fresnel lens and a liquid crystal display device using the liquid crystal display device shown in FIG. 7, and FIG. 7 is an enlarged view of FIG.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location G09F 9/00 358 G09F 9/00 358 (72) Inventor Toshihiro Yonemitsu 1-chome 21 Dogenzaka, Shibuya-ku, Tokyo No. 6 Inside Japan Aviation Electronics Industry Co., Ltd. (72) Inventor Akihiro Honma 1-21-6 Dogenzaka, Shibuya-ku, Tokyo Japan Inside Japan Aviation Electronics Industry Co., Ltd. (56) References , U) Japanese Utility Model Showa 63-191336 (JP, U)

Claims (1)

(57) [Claims] 1. A reflective overhead projector for reflecting light from a light source by a mirror Fresnel lens and projecting and displaying data on the mirror Fresnel lens, wherein the mirror Fresnel lens has no polarizing plate on one side.
An N-mode liquid crystal display element is provided so that the side where the polarizing plate is located and the mirror Fresnel lens face each other; and a second polarizing plate is provided before or after a lens unit that collects reflected light from the mirror Fresnel lens. A reflective liquid crystal overhead projector, wherein a phase compensator is provided on the element or the second polarizing plate.