JP2003098601A - Device for displaying screen image for image display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate speckles in a rear projection type laser scan image display device. SOLUTION: A screen 10 consists of a first optical diffusion plate 11 and a second optical diffusion plate 12, the first optical diffusion plate 11 consists of a light transmission surface 11a and an optical diffusion surface 11b, the second optical diffusion plate 12 also consists of a light transmission surface 12a and an optical diffusion surface 12b, and the first and second diffusion plates 11 and 12 are configured so that the optical diffusion surfaces 11b and 12b are opposite and in close contact to/with each other. Laser beams made incident from a light incident face 11c of the first optical diffusion plate 11 become a large number of small point light sources P1 and P2 on the optical diffusion surface 11b of the first optical diffusion plate 11, beams emitted from the point light sources P1 and P2 are made incident on a light diffusion surface (rough surface whose sand number is different from that of rough surface 11b) 12b of the second optical diffusion plate 12 to be point light sources again at the light diffusion surface 12b, and the point light sources become a wave front group to be emitted. At this time, such speckles that are generated on the optical diffusion surface 11b of the first diffusion plate 11 are not formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screen that enables display with less speckle noise in an image display device that scans a laser beam to display characters and images, and an image display device and image display using the screen. Regarding the method. In particular, the present invention relates to a screen that does not cause image blurring and realizes a speckle reduction effect at low cost, an image display device and a display method using the screen.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 2000-180973 (transmissive screen) proposes a transmissive screen on which an optical image formed on a light valve having image display portions arranged in a matrix is projected. However, the device targeted by the invention described in this publication forms an image by enlarging and projecting the matrix pixels obtained by the spatial modulator on the screen by the projection lens system. The light is projected all at once on the screen, and the light source is not intended for a high coherency object such as a laser. Therefore, the cause of speckle and moire in such a device is different from that in a display that scans a coherent laser. The screen described in this publication has a structure in which a light diffusing medium is embedded in the thickness direction of the screen, and when irradiated with a laser beam, the beam is diffused and the beam transmitted in the thickness direction of the screen has a large diameter. This causes a problem that pixels cannot be formed.

In the case of a laser scan display, laser light is scanned over the screen sequentially. At that time, 1
Since the frame is scanned at a speed of 60 Hz or higher, the scan line cannot be discerned by the human eye and is recognized as a continuous frame image. In the case of a projection type display using an incoherent light source, according to the above publication, the internal structure of the first and second light diffusion layers (the weight average particle diameter of the translucent fine particles contained in each diffusion layer is described. ,% By weight, thickness of the diffusion layer, etc.) is to prevent moire from occurring and the screen cost becomes high.

Further, Japanese Patent Application Laid-Open No. 55-65940 discloses a method of vibrating a screen to remove speckle noise. However, in this method, in the case of a large screen, the driving unit becomes large. , Power consumption also increases. In addition, Japanese Patent Publication No. 56-24922 discloses a method of inserting a quartz cell between a light source and a screen and removing speckle noise by ultrasonic waves. In this method, the resolution of laser light itself is disclosed. Will decrease.

[0005]

In the case of front projection in a laser scan display, the speckles of the individual flying spots themselves which are modulated and flickered on the screen are not so noticeable, and the reflection components of adjacent spots are the same. Speckle due to interference is also inconspicuous. On the other hand, in the case of the rear projection method, it is extremely dangerous for a scanning beam having a strong directivity to enter the eye, and therefore the directivity of the beam needs to be weakened by a diffusing screen. When the light is transmitted through the diffusing screen, there is a problem that speckles are generated due to interference of diffused waves between adjacent flying spots. This tendency is particularly noticeable when the generated image is a solid screen. An image with speckles has poor visibility and causes eyestrain, so improvement is required.

Several proposals have already been made for the method of eliminating speckles. For example, there is a method of vibrating the screen described above.
There is a problem that extra power is consumed for driving the vibration generator and the device, and implementation becomes difficult when the screen becomes large. Further, a method of modulating a laser at a frequency higher than the modulation frequency required for image formation has been proposed, but this method requires a special light source device and increases the device cost. In addition, a method of applying phase modulation to the light source has been proposed, but this also similarly complicates the light source and increases the device cost.

The laser scan display is designed so that the eye-safe can be maintained when the beam is scanned at a predetermined speed. However, when an abnormality occurs in the scanning speed (for example, when the scanning is stopped), the beam power that is noticeable per unit time increases and an eye-safe problem occurs. However, no solution to this problem has yet been proposed.

The present invention has been made in view of the above-mentioned circumstances, and includes: a screen structure for eliminating image speckles of a rear projection type laser scan display; a laminated screen structure for not losing speckle reduction effect; -Screen configuration with high speckle reduction effect-Screen configuration that suppresses energy loss required for speckle removal-Screen configuration that can ensure eye-safe when scanning speed decreases, and these screens The present invention has been made for the purpose of providing an image display device and an image display method using the.

[0009]

According to a first aspect of the present invention, there is provided a screen which displays a character or an image by scanning a laser beam from the back surface of the screen, the screen having a rough surface on either the front surface or the back surface. Two processed light diffusion plates are laminated, and the roughness of the diffusion surface of each layer is not the same.

The invention of claim 2 is characterized in that, in the invention of claim 1, the opposing surfaces to be laminated are light diffusing surfaces.

According to a third aspect of the invention, in the second aspect of the invention, there is provided an adjusting means for adjusting the distance between the facing surfaces to be laminated.

According to a fourth aspect of the present invention, in the second aspect of the present invention, the stacking facing surface is bonded to the light diffusing plate with an adhesive having a different refractive index.

According to a fifth aspect of the present invention, there is provided two light diffusing plates, one surface of which is a diffusing surface, and the two light diffusing plates are laminated with the diffusing surfaces facing each other, and It is characterized in that the roughness of each diffusion surface of the two light diffusion plates is different.

According to a sixth aspect of the present invention, in the laser scan image display device for displaying a character or an image by scanning a laser beam from the rear surface of the screen, the screen is the first aspect.
It is characterized by being the screen according to any one of items 1 to 5.

According to a seventh aspect of the present invention, in the sixth aspect of the present invention, there is provided means for detecting a beam scanning speed, and when the beam speed detected by the beam speed detecting means falls below a predetermined speed, the surface spacing is reduced. It is characterized in that the adjusting means widens the distance between the surfaces which are laminated and adhered.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram for explaining the operating principle of a screen according to the present invention. In FIG. 1A, 10 is a screen according to the present invention, and the screen 10 is a first screen. It comprises a light diffusing plate 11 and a second light diffusing plate 12, and further, the first light diffusing plate 11 has a light transmitting surface 11a.
And the light diffusion surface 11b, and the second light diffusion plate 12 also includes the light transmission surface 12a and the light diffusion surface 12b (having a light diffusion degree (sand number) different from that of the light diffusion surface of the first light diffusion plate) 12b. The first light diffusing plate 11 and the second light diffusing plate 12 are configured such that the light diffusing surfaces 11b and 12b are in close contact with each other. Laser light L scanned on the screen 10
Is a light incident surface (non-diffusing surface) 11c of the first light diffusing plate 11.
From the light emitting surface (non-diffusing surface) 12c of the second light diffusing plate 12.

FIG. 1B is an enlarged view showing a part of the light diffusing surface 11b of the first light diffusing plate 11, which is incident from the light incident surface 11c of the first light diffusing plate 11. The laser light becomes a large number of minute point light sources on the light diffusing surface 11b of the first light diffusing plate 11, and is diffused and emitted from each of these point light sources. FIG. 1 (C) is an enlarged view showing the situation. The diffused beams Q ₁ and Q ₂ from the point light sources P ₁ and P ₂ generated as described above are at the positions S ₁ and S where the phases are aligned. _{At 2 and so on} , the light intensity increases and speckle noise occurs. This speckle noise becomes stronger as it gets closer to the screen, and becomes weaker in inverse proportion to the square of the distance as it goes away from the screen.

FIG. 1D schematically shows a state in which the light diffusing surface 11b of the first light diffusing plate 11 and the light diffusing surface 12b of the second light diffusing plate 12 are closely adhered to each other as described above. In the partially enlarged view shown, the beams emitted from the point light sources P ₁ and P ₂ generated on the light diffusing surface 11b of the first light diffusing plate 11 as described above, are emitted from the second light diffusing plate 12. Light diffusing surface (rough surface 11b
Is incident on a rough surface having a different sand number) 12b, where it again becomes a point light source and is emitted as a wavefront group from these point light sources. At this time, the speckle generated on the light diffusing surface 11b of the first light diffusing plate 11 is not established, and the second speckle
On the light diffusing surface 12b of the light diffusing plate 12, the coherency of the beam is lowered, the phase synchronization condition is hard to be established, and speckle noise is reduced.

As described above, the screen according to the present invention is obtained by closely laminating two light diffusing plates whose surfaces have been subjected to a diffusion (rough surface) treatment and which have different mesh numbers (sand numbers) on the light diffusing surfaces. Although the coherency of the flying beam is lost by the first light diffusing plate provided on the light beam incident side, speckles are generated in the image viewed from the emission side. When the diffusing surface of the second light diffusing plate is brought into close contact with the diffusing surface of the first light diffusing plate, the light diffused by the diffusing surface of the first light diffusing plate is absorbed by the diffusing surface of the second light diffusing plate. Then, the interference condition is again received by the diffusing surface of the second light diffusing plate, and the interference condition established from the relation between the mesh number and the wavelength of the diffusing surface of the first light diffusing plate is the second light diffusing plate. Since the sand number, that is, the surface roughness of the diffusion surface of the diffusion plate is different, it does not hold, and as a result, the interference wave front is disturbed and diffused. That is, since the coherency of the light incident on the diffusing surface of the second light diffusing plate is lost, even if there is an interference condition established by the sand number, that is, the surface roughness of the diffusing surface of the second light diffusing plate. , The light is incoherent so there is no interference. That is, no spectrum is generated.

When two sheets of diffusing screens having the same sand number, that is, the same surface roughness as the comparative example were piled up, there was no effect of eliminating speckles. From this, it is considered that if the sand number, that is, the surface roughness is the same, the coherence condition does not collapse and the interference condition is maintained, so that the speckle does not disappear.

In the screen shown in FIG. 1, an example is shown in which the diffusion surfaces of two light diffusion plates constituting the screen are in close contact with each other, but in this way, the diffusion surfaces are in close contact with each other. In this case, the thickness of the joining region in the light transmitting direction becomes extremely thin, so that the diameter of the beam that has been subjected to the diffusion action does not spread, and a good pixel can be formed. That is, since the distance between the diffusing surfaces is very short, the scanning beam diameter does not spread due to the diffusion. However, it is not always necessary to bring them into close contact, and they may be stacked close to each other with some space. By the way, when the second light diffusing plate is separated from the first light diffusing plate by about 1 mm, the point image due to the flying spot becomes blurred and the image resolution is significantly reduced.

As described above, in the present invention, the position of the point light source generated in the second light diffusing plate is in the light transmitting direction with respect to the position of the point light source generated in the first light diffusing plate. Proximity is important in terms of image resolution,
As shown in FIG. 1, it is not always necessary that the diffusion surfaces are in close contact (or close proximity) to each other. If the thickness of the light transmission surface of the second light diffusion plate can be made sufficiently thin, this second
The light transmitting surface 12a of the light diffusing plate 12 of the first light diffusing plate 11
The light diffusing surface 11b may be closely joined.

FIG. 2 is a block diagram showing another embodiment of the screen according to the present invention, in which the first light diffusion plate 11 and the second light diffusion plate 12 described in FIG. The light diffusing plate is adhered to the light diffusing plate with an adhesive 13 having a different refractive index. By providing a refractive index difference, a diffusion phenomenon can be generated on the diffusing surface, and a speckle elimination effect can be obtained.

As described above, when the second light diffusing plate 12 is separated from the first light diffusing plate 11, the point image due to the flying spot is blurred. Guard) can be secured.
For example, when the first light diffusing plate 11 and the second light diffusing plate 12 are separated by 1 mm, the spot diameter is expanded by about 10 times, so the beam power per unit area is reduced to about 1/100. However, if the distance is further increased, a greater extinction effect can be obtained.

FIG. 3 shows the first light diffusing plate 1 as described above.
The first and second light diffusing plates 12 are joined together so that the distance between them can be adjusted, in other words, a main part configuration diagram for explaining an example of a screen having a fail-safe mechanism. 11 is a first light diffusing plate, 12 is a second light diffusing plate, 1
Reference numeral 4 denotes a support member that supports the first light diffusion plate 11 and the second light diffusion plate 12, and 15 denotes the first light diffusion plate 11.
And the second light diffusing plate 12 is joined / separated by the joining / separation adjusting means, which is composed of, for example, a piezoelectric element.
By applying a voltage from the power source 16 of the piezoelectric element 15, the bonded state shown in FIG. 3 (A) is changed to the separated state shown in FIG. 3 (B). This separation amount can be adjusted by the voltage applied to the piezoelectric element 14.

In the above case, the separation adjusting mechanism 15
For example, the piezoelectric element 1 is not limited to the piezoelectric element.
An elastic member is used instead of the first light diffusion plate 11 and the second light diffusion plate 11.
A wedge-shaped member is formed on the joint surface of the light diffusing plate 12 so that the taper end abuts on the joint surface, and the wedge-shaped member is moved to the inside of the screen at the same time when an abnormal signal is detected to widen the surface interval. It is possible to adopt a desired configuration such as the above configuration.

As described above, the first light diffusion plate 11 and the second light diffusion plate 11
When the joining / separation adjusting mechanism of the light diffusing plate 12 of FIG.
In the joined state shown in (A), a spot image without blurring can be obtained on the screen, and FIG.
It is also possible to intentionally blur the spot by setting the separated state shown in (B). This also leads to the effect of ensuring eye safety when an abnormal scanning speed occurs. Further, since the beam spot can be greatly blurred by separating and contacting the facing surfaces in synchronization with the velocity abnormality signal sent from the beam scanning velocity detecting means, the beam power incident on the eye can be greatly reduced. Therefore, it is possible to obtain the effect of ensuring the eye-safe at the time of abnormal scanning. This is a particularly important function in scanning type displays.

FIG. 4 is a schematic configuration diagram of a main part for explaining an embodiment of the projection image display apparatus using the screen as described above. In the figure, 21 is a laser light source (subscript, R
Is red, G is green, B is blue), 22 is a condenser lens, 23 is an AOM, 24 is a collimating lens, 25 is a reflecting mirror, 26 is a dichroic mirror, 27 is a polygon mirror, and 28 is a tilt (45 °). ) A mirror, 29 is a galvanometer scanner, 30 is a scanning lens, and as is well known, the beam from the laser light source 21 is condensed by the condensing lens 22 to the AOM 23.
The light is condensed and incident on and modulated, the emitted light is collimated by the collimator lens 24, the total reflection mirror 25 and the dichroic mirror 26 match the optical axes of the three wavefronts, and the light is incident on the polygon mirror 27. The light beam scanned by the polygon mirror 27 is reflected by the tilted (45 °) mirror 28 toward the galvano scanner 29, vertically scanned (sub-scanned) by the galvano scanner 29, and then condensed by the scanning lens 30. The screen 10 is focused and scanned.

Further, in FIG. 4, 31 is an LD, 32 is a PD, 33 is a sync signal generator, 34 is a galvano drive mechanism controller, and 35 is a galvano drive mechanism. The scanning of one surface of the mirror 29 is detected, and the galvano scanner 29 is sub-scanned in synchronization with this scanning.

In order to evaluate speckle noise, a solid image was laser-scanned and drawn on the screen, and the light intensity distribution on the screen was measured. The larger the standard deviation value B with respect to the average light intensity A of the measurement area, that is, B / A, the more noise. The measurement conditions are as follows. (A) Speckle measurement of a laser scanning image was performed using a diffusing particle screen (Cinecoat screen) manufactured by Draper. (B) A screen in which the diffusing surface of a diffusing particle type screen (Cinecoat screen) made by Draper and the diffusing surface of a sand plate of sand number 240 are in close contact with each other is constructed, and a solid image is drawn by scanning a laser beam for measurement. did. The sand diffuser 240 has a BK7 glass surface with a diffusion treatment and is 5 m thick.
m was used. (C) The same measurement as in (b) was performed when the sand number was changed to 1500.

The resulting speckle noise was 0.385 in the case of (a): 0.385 in the case of (b): 0.290 in the case of (c). From the above results, (b) and (c) rather than (a)
Results in less speckle. From these results, although the values of (b) and (c) are slightly different, there is no great difference. The above is the result based on the evaluation method with higher accuracy than the visual speckle evaluation.

[0032]

As is apparent from the above description, according to the present invention, as compared with the conventional method of vibrating the screen, a mechanism required for generating the vibration is unnecessary, and particularly in the case of a large screen,
It is possible to avoid complication of the mechanism required for vibration generation and increase of energy consumption loss. -The device configuration does not become complicated. -The energy loss required for speckle removal can be suppressed. -Effect can be obtained even if a general CW oscillation laser is used.・ Can maintain images without blur.・ The cost required for speckle removal is low.・ Contributes to low cost of equipment without speckles. And so on.

Further, the coherency of the beam is lowered on the first diffusing surface, and speckles generated on the first diffusing surface can be eliminated by the light diffusing effect of the second diffusing surface. By joining the diffusing surfaces to each other, the diffusing can be performed twice in a narrow area, the spot diameter of the scanning beam does not become large, image blur does not occur, and the speckle reduction effect can be obtained.・ A good image without blurring speckles
It can be realized with a simple screen configuration.

At the same time that a spot image without blur can be obtained on the screen, it is possible to intentionally blur the spot, and further, eye safe can be secured when an abnormal scanning speed occurs.・ Because the beam spot can be greatly blurred by performing the operation of separating and contacting the facing surfaces in synchronization with the speed abnormality signal sent from the scanning speed detection means, the beam power incident on the eyes can be greatly reduced. It is possible to obtain the effect of ensuring the eye safety at the time of abnormal scanning.

[Brief description of drawings]

FIG. 1 is a conceptual diagram for explaining an operating principle of a screen according to the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the screen according to the present invention.

FIG. 3 is a main part configuration diagram for explaining an example of a screen including a fail-safe mechanism.

FIG. 4 is a schematic configuration diagram of a main part for explaining an embodiment of a projection image display device using a screen.

[Explanation of symbols]

10 ... Screen, 11 ... 1st light diffusing plate, 11a, 1
2a ... Light transmitting surface, 11b, 12b ... Light diffusing surface, 11c ...
Light incident surface (non-diffusing surface), 12 ... Second light diffusing plate, 12c
... Light emitting surface (non-diffusing surface), 13 ... Adhesive agent, 14 ... Support member, 15 ... Bonding / separation adjusting means, 16 ... Power source, 21 ... Laser light source, 22 ... Condensing lens, 23 ... AOM, 24 ... Collimator Lens, 25 ... Reflective mirror, 26 ... Dichroic mirror, 27 ... Polygon mirror, 28 ... Inclination (45
) Mirror, 29 ... Galvano scanner, 30 ... Scan lens, 31 ... LD, 32 ... PD, 33 ... Sync signal generator,
34 ... Galva 1 drive mechanism controller, 35 ... Galva 1 drive mechanism.

Continued front page    (72) Inventor Keinobu Osaka             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 2H021 BA27 BA28

Claims (7)

[Claims] 1. A screen for displaying a character or an image by scanning a laser beam from the back surface of the screen, wherein the screen comprises two light diffusing plates, one of the front surface or the back surface of which is roughened. An image display screen, characterized in that the layers are laminated and the diffusion surfaces of the layers are not the same. 2. The image display screen according to claim 1, wherein the facing surface to be laminated is a light diffusing surface. 3. The image display screen according to claim 2, further comprising adjusting means for adjusting a gap between the facing surfaces to be stacked. 4. The image display screen according to claim 2, wherein the stacking facing surface is bonded to the light diffusing plate with an adhesive having a different refractive index. 5. A light diffusing plate having two surfaces, one surface of which is a diffusing surface, wherein the two light diffusing plates are laminated with the diffusing surfaces facing each other, and the two light diffusing plates are stacked. An image display screen characterized in that the roughness of each diffusion surface of the plate is different. 6. A laser scan image display device for displaying a character or an image by scanning a laser beam from the back surface of the screen, wherein the screen is the screen according to any one of claims 1 to 5. Scan image display device. 7. The apparatus according to claim 6, further comprising means for detecting a beam scanning speed, and when the beam speed detected by the beam speed detecting means is lower than a predetermined speed, the surface spacing adjusting means laminates the layers closely. A laser scan image display device characterized by widening the distance between surfaces.