GB1578310A

GB1578310A - Projection display apparatus

Info

Publication number: GB1578310A
Application number: GB20853/78A
Authority: GB
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1977-10-31
Filing date: 1978-05-19
Publication date: 1980-11-05
Also published as: IT1159148B; DE2843191A1; FR2410326B1; CA1113619A; DE2843191C2; FR2410326A1; JPS5631013B2; JPS5468117A; IT7828244A0

Description

(54) PROJECTION DISPLAY APPARATUS (71) We, INTERNATIONAL BUSINESS MACHINES CORPORATION, a Corporation organized and existing under the laws of the State of New York in the United States of America, of Armonk, New York 10504, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement : This invention relates to projection display apparatus.

According to the invention, such apparatus comprises means to produce an image of a light valve formed by visible light of specified wavelengths on a projection screen, means to produce a translatable cursor image on the screen having a spectral component distinct from those of the light valve image, and a light pen device sensitive to the spectral component of the cursor image and substantially insensitive to the components of the light valve image.

The scope of the invention is defined by the appended claims; and how it can be carried into effect is hereinafter particularly described with reference to the accompanying drawings, in which: - Fig. 1 is a schematic view of projection display apparatus according to this invention, Fig. 2 illustrates a typical light spectrum for a projection lamp used in the apparatus, Fig. 3 is a view of a cursor wire arrangement, Fig. 4 is a part-sectional view of a light pen device, Fig. 5 illlstrates the interaction of a light pen and cursor, Fig. 6 is a schematic view of an embodiment of interactive display apparatus according to this invention, and Fig. 7 is a schematic of a second embodiment of apparatus according to this invention.

Projection display apparatus (Fig. 1) has a projection system 10 which projects an image from a light valve (not shown) and images 14 and 16 of translatable cursor wires on a rear projection screen 12. The images 14 and 16 intersect at point 18 as a crosswire image to indicate reference coordinates on the screen 12.

The image from the light valve provides legible data in the form of areas of contrast in the visible light spectrum. The data may, for example, be in the form of characters and digits, graphs and/or pictures. The background area may be light or dark and the data areas dark or light, or the contrast may be obtained by using different coloured wavelengths.

The light valve may be either subtractive or additive. With a subtractive light valve the screen will normally be luminous and written areas of the image will be darker.

With an additive light valve, the screen will normally be dark and written areas of the image will be luminous. In either case, the dark areas of the screen image will not be black because of the limited contrast ratio of the image.

The images of the cursor wires are provided by cursor wires which are opaque to radiation which provides a contrast background to the images, and which has a spectral component distinct from the visible light used to form the image of the light valve, though it may include such visible light in addition.

A light pen 20 has an end 22 which interacts directly with the projection screen 12.

The light pen 20 is not sensitive to visible light, but is sensitive to the distinct spectral component of the cursor wire image background.

During operation of the light pen 20, the light pen is activated and positioned on the screen 12, the images 14 and 16 of the cursor wires are translated rapidly across the screen 12 in succession. The light pen 20 detects the passage of the image 14 and 16 of the cursor wires, because of the absence of the spectral component to which it is sensitive. The position of the light pen end 22 on the screen 12 may thus be determined by knowledge of the positions of the cursor wires at the times the images 14 and 16 are intercepted by the light pen 20.

The provision of a visible light background for the cursor wire images enables the images to be visible for use as an adjustable crosswire cursor when the light pen is not being used. If the background for the cursor wire images was only in the visible spectrum, that is without the distinct spectral component, it might be thought that the position of the point 18 on the screen could be detected by a light pen sensitive to the visible spectrum. However, the signal level would vary widely from dark to luminous areas of the screen.

Accordingly, the cursor wires are flooded uniformly with an additional spectral component which is distinct from the visible light used to form the image of the light valve.

The light or radiation output from the projection system 10 is critical for the successful operation of the cursor wire images and the light pen.

A typical lamp used in projection display systems has an output which covers the spectrum shown in Fig. 2, that is, it contains ultra violet light having wavelengths less than 04 microns, visible light in the range of 04 to 07 microns, near infra red light having a wavelength between 0'7 and 2 0 microns and infra red radiation or heat having a wavelength greater than 2 microns. In general, the data image in the projection display system on the screen is formed with the visible light. This visible light is also used to form the image of the cursor wires. In addition, the cursor wire image contains an additional spectral component. In the preferred embodiment, this additional spectral component is in the near infra red wavelength, that is, between 0 7 and 10 microns. The light pen is only sensitive to this additional spectral component.

It will be appreciated that the additional spectral component is not limited to the near infra red band, but could be a band of visible light, for example, red light, if this is not included in the light valve image, which could be formed with the remainder of the visible spectrum, namely, cyan light.

The light pen would be sensitive to red light only.

The images 14 and 16 of the cursor wires are derived from cursor wires 14A and 16A (Figure 3). Preferably, the cursor wire 14A is mounted to project the image 14 on a horizontal transverse line across the screen 12 and is movable normal to its length up and down the screen in the Y axis by a system of belts and pulleys driven by a motor whose position is indicated in encoder means 26. Similarly, the cursor wire 16A is mounted to project the image 16 on a vertical transverse line across the screen 12 and is movable normal to its length across the screen in the X axis by a system of belts and pulleys driven by a motor whose position is indicated in encoder means 24.

The light pen 20 (Fig. 4) has an opening 22A which is positioned directly on the projection screen. The pen 20 contains a lens 24, an aperture 26, a filter 28, and a photo-diode 30 connected to conductors 32.

The filter 28 transmits only the spectral component of the cursor image. When the light pen end 22 is placed on the screen, the lens 24 images a small area of the screen 12 exposed through the opening 22A onto the aperture 26.

The illuminated background of the cursor wire images includes the spectral component to which the photodiode 30 is sensitive, due to the filter 28. There is, therefore, an output 34 (Fig. 5) from the photodiode 30, which is unaffected by variations in illumination of the visible light of the light valve image. As the image 16 of the X-cursor wire 1 6A crosses the area of the screen, the spectral component is removed and the output of the photodiode 30 momentarily dips at 40 (Fig. 5). This dip in the output is used to read the position of the X-cursor wire 16A from the encoder means 24, so that the X coordinate of the light pen on the screen is known. Immediately following this, the Y-cursor wire 14A can be moved in order to determine the Y-coordinate of the light pen in a similar way.

The essential characteristics of the light pen 20 is that the photodiode 30 is responsive to the distinct spectral component which is used to form the translatable crosswire image on the projection screen.

The preferred spectral component is in the near infra red spectrum portion, that is, between 07 microns and 1 0 microns.

The interaction between the light pen and the translating cursor wire image is illustrated in Fig. 5. The upper curve shows the output of the photodiode against time. The lower curve 36 shows the Xcoordinate location of the image of the X-cursor on the screen against time. The position information is provided by a shaft encoder on the motor which drives the Xcursor, or by timing information, or by the use of a stepper motor. When the image of the X-cursor crosses the position of the light pen at 38, the output of the photodoide will momentarily drop. The known position of the X-cursor at this time T, is the X-coordinate of the light pen.

A subsequent and similar operation of the Y-cursor will provide the Y-coordinate of the light pen.

The light valve may be a transmissive, light valve (Fig. 6). A projection lamp 42 having an output comprising visible light 44 represented by an arrow with a single line, near infra red radiation 46 represented by an arrow with a double line, and infra red radiation 48 represented by an arrow with a wavy line. The radiations 44, 46 and 48 are collimated by the condenser lens 50.

The collimated radiations are directed to a hot mirror 52 which transmits the visible light 44 and reflects the infra red radiation 46 and the near infra red radiation 48.

Radiations 46 and 48 are directed to a cold mirror 54 which transmits the infra red radiation 48 and reflects the near infra red radiation 46 to a condenser lens 56. The near infra red radiation 46 is reflected by a folding mirror 58 to a hot mirror 60. The visible light 44 which is passed through the hot mirror 52 passes through a condenser lens 62 and a light valve which is located in plate 64. It is this light valve which provides the legible data areas on the screen.

The visible light then passes through hot mirror 60 and continues along with the near infra red radiation 46 to relay lens 66 which relays a visible light image of the light valve in plane 64 and the near infra red radiation into the plane of the cursor wires located at 68. The wires are opaque to the visible light and the near infra red radiation. The light and radiation then proceed through a field lens 70 which images the aperture of the relay lens 66 into the aperture of a projection lens 72. The projection lens 72 images plane 68 onto the screen. Hence, the screen displays an image of the light valve whose image was relayed into plane 68 and also an image of the cursor wires which are located in plane 68.

The embodiment described uses the near infra red radiation as the spectral component which passes through the plane 68 to form an image of the cursor wires on the screen which is subsequently sensed by a light pen sensitive to the near infra red radiation.

Various modifications of this embodiment are possible. For example, the mirror 60 may also be used for directing on to the light valve in the plane 64 a near infra red laser, such as Nd: YAG for the purpose of writing on the light valve. It will also be understood that instead of using a portion of the lamp spectrum for the near infra red radiation, a separate narrow bandwidth source could be used. For example, the cold mirror 54 could be removed and replaced by a GaAs infra red diode.

In another embodiment (Fig. 7), a reflective light valve is used. A lamp 80 transmits visible light 82, near infra red radiation 84 and infra red radiation 86 through a condenser lens 88 which collimates the light from the lamp 80. The light passes through the condenser lens 89 and forms an image of the lamp filament on an elliptical mirror 90 on an aperture plate 94. The elliptical mirror 90 reflects visible light but transmits infra red and near infra red radiation. The aperture plate 94 contains an aperture 91 and a front surface mirror 92 on the opposite side to the elliptical mirror 90. Aperture plate 94 is suitable for a subtractive light valve. Alternatively, an aperture plate 94A may be used for an additive light valve and has an elliptical mirror 90A, a front surface mirror 92A on the opposite side to the elliptical mirror 90A and an opaque stop 93A. The near infra red radiation 84 and the infra red radiation 86 which passes through the elliptical mirror 90 or 90A continues and passes through condenser lens 96 to a cold mirror 98 which transmits the infra red heat 86 but reflects the near infra red radiation 84. The near infra red radiation 84 that is reflected by the mirror 98 passes through the condenser lens 96 and forms an image of the lamp filament on mirror 92 or 92A.

The visible light 82 is reflected by mirror 90 or 90A and passes through a telecentric schlieren lens 100 to a reflective light valve 102. The reflective light valve 82 reflects visible light 82 through a lens 100 to the aperture 91 on aperture plate 94 (or around the opaque stop 93A on aperture plate 94).

The visible light 82 and the near infra red radiation 84 pass through a relay lens 103 which along with lens 100 forms an image of the light valve 102 in plane 104, the location of the cursor wires. Field lens 106 images the aperture of relay lens 103 into the aperture of projection lens 108 which images plane 104 onto the screen.

It will be understood that the invention could be used with an image from a CRT or similar photoemissive display element when used in a projection display mode.

This invention is particularly useful for projection systems employing a reflective liquid crystal light valve.

If information about only one coordinate of the light pen is needed, then only one cursor is required. The cursor images could be provided by distinct spectral component images on a background not containing such spectral component.

WHAT WE CLAIM IS:- 1. A projection display apparatus comprising means to produce an image of a light valve formed by visible light of specified wavelengths on a projection screen, means to produce a translatable

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the Y-cursor will provide the Y-coordinate of the light pen. The light valve may be a transmissive, light valve (Fig. 6). A projection lamp 42 having an output comprising visible light 44 represented by an arrow with a single line, near infra red radiation 46 represented by an arrow with a double line, and infra red radiation 48 represented by an arrow with a wavy line. The radiations 44, 46 and 48 are collimated by the condenser lens 50. The collimated radiations are directed to a hot mirror 52 which transmits the visible light 44 and reflects the infra red radiation 46 and the near infra red radiation 48. Radiations 46 and 48 are directed to a cold mirror 54 which transmits the infra red radiation 48 and reflects the near infra red radiation 46 to a condenser lens 56. The near infra red radiation 46 is reflected by a folding mirror 58 to a hot mirror 60. The visible light 44 which is passed through the hot mirror 52 passes through a condenser lens 62 and a light valve which is located in plate 64. It is this light valve which provides the legible data areas on the screen. The visible light then passes through hot mirror 60 and continues along with the near infra red radiation 46 to relay lens 66 which relays a visible light image of the light valve in plane 64 and the near infra red radiation into the plane of the cursor wires located at 68. The wires are opaque to the visible light and the near infra red radiation. The light and radiation then proceed through a field lens 70 which images the aperture of the relay lens 66 into the aperture of a projection lens 72. The projection lens 72 images plane 68 onto the screen. Hence, the screen displays an image of the light valve whose image was relayed into plane 68 and also an image of the cursor wires which are located in plane 68. The embodiment described uses the near infra red radiation as the spectral component which passes through the plane 68 to form an image of the cursor wires on the screen which is subsequently sensed by a light pen sensitive to the near infra red radiation. Various modifications of this embodiment are possible. For example, the mirror 60 may also be used for directing on to the light valve in the plane 64 a near infra red laser, such as Nd: YAG for the purpose of writing on the light valve. It will also be understood that instead of using a portion of the lamp spectrum for the near infra red radiation, a separate narrow bandwidth source could be used. For example, the cold mirror 54 could be removed and replaced by a GaAs infra red diode. In another embodiment (Fig. 7), a reflective light valve is used. A lamp 80 transmits visible light 82, near infra red radiation 84 and infra red radiation 86 through a condenser lens 88 which collimates the light from the lamp 80. The light passes through the condenser lens 89 and forms an image of the lamp filament on an elliptical mirror 90 on an aperture plate 94. The elliptical mirror 90 reflects visible light but transmits infra red and near infra red radiation. The aperture plate 94 contains an aperture 91 and a front surface mirror 92 on the opposite side to the elliptical mirror 90. Aperture plate 94 is suitable for a subtractive light valve. Alternatively, an aperture plate 94A may be used for an additive light valve and has an elliptical mirror 90A, a front surface mirror 92A on the opposite side to the elliptical mirror 90A and an opaque stop 93A. The near infra red radiation 84 and the infra red radiation 86 which passes through the elliptical mirror 90 or 90A continues and passes through condenser lens 96 to a cold mirror 98 which transmits the infra red heat 86 but reflects the near infra red radiation 84. The near infra red radiation 84 that is reflected by the mirror 98 passes through the condenser lens 96 and forms an image of the lamp filament on mirror 92 or 92A. The visible light 82 is reflected by mirror 90 or 90A and passes through a telecentric schlieren lens 100 to a reflective light valve 102. The reflective light valve 82 reflects visible light 82 through a lens 100 to the aperture 91 on aperture plate 94 (or around the opaque stop 93A on aperture plate 94). The visible light 82 and the near infra red radiation 84 pass through a relay lens 103 which along with lens 100 forms an image of the light valve 102 in plane 104, the location of the cursor wires. Field lens 106 images the aperture of relay lens 103 into the aperture of projection lens 108 which images plane 104 onto the screen. It will be understood that the invention could be used with an image from a CRT or similar photoemissive display element when used in a projection display mode. This invention is particularly useful for projection systems employing a reflective liquid crystal light valve. If information about only one coordinate of the light pen is needed, then only one cursor is required. The cursor images could be provided by distinct spectral component images on a background not containing such spectral component. WHAT WE CLAIM IS:-

1. A projection display apparatus comprising means to produce an image of a light valve formed by visible light of specified wavelengths on a projection screen, means to produce a translatable

cursor image on the screen having a spectral component distinct from those of the light valve image, and a light pen device sensitive to the spectral component of the cursor image and substantially insensitive to the components of the light valve image.

2. Apparatus according to claim 1, in which the cursor image spectral component is in the near-infra red light waveband.

3. Apparatus according to claim 2, in which the cursor image spectral component has a wavelength between 0-7 slm and 1-0 ,am.

4. Apparatus according to claim 1, in which the cursor image spectral component has a visible light wavelength not present in the light valve image.

5. Apparatus according to any preceding claim, in which the cursor image also includes visible light of wavelengths present in the light valve image.

6. Apparatus according to any preceding claim, in which the cursor image producing means produces two images transverse to each other and translatable in directions transverse to their lengths, to produce a crosswire image.

7. Apparatus according to claim 6, in which the cursor images are separately translatable.

8. Apparatus according to claim 5 including means to measure the amounts of translation of the cursor images.

9. Apparatus according to any preceding claim, in which the light valve image is an image of a transmissive light valve.

10. Apparatus according to any of claims 1 to 8, in which the light valve image is an image of a reflective light valve.

11. Apparatus according to any of claims 1 to 8, in which the light valve image is an image of a photoemissive display element.

12. Apparatus according to any preceding claim in which the light valve image and the cursor image are derived from the same radiation source.

13. Apparatus according to any of claims 1 to 11, in which the light valve image and cursor image are derived from separate radiation sources.

14. Apparatus according to any preceding claim, in which the light pen device includes a filter adapted to transmit radiation having substantially the same spectral component as the cursor image, and a photodiode sensitive to the radiation transmitted by the filter

15. A projection display apparatus substantially as hereinbefore described and as illustrated in Figures 1 to 6 of the accompanying drawings.

16. A projection display apparatus substantially as hereinbefore described and as illustrated in Figures 1 to 5 and 7 of the accompanying drawings.