GB1581279A

GB1581279A - Cathode ray tube

Info

Publication number: GB1581279A
Application number: GB2904877A
Authority: GB
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1976-07-19
Filing date: 1977-07-11
Publication date: 1980-12-10
Also published as: IT1114894B; FR2359504A1; FR2359504B1; JPS6051773B2; DE2732424B2; AU512080B2; JPS5310963A; CA1103299A; AU2699677A; DE2732424A1; DE2732424C3

Description

(54) CATHODE RAY TUBE (71) We, TOKYO SHIBAURA ELECTRIC COMPANY LIMITED, a Japanese Company, of 72, Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa-ken, Japan, 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 a colour cathode ray tubes of the beam indexing type.

A colour cathode ray tube of the beam indexing type has as part of the evacuated envelope an outwardly curved panel having a cathodo-luminescent screen on its inner surface, the screen comprising a plurality of different elemental colour phosphor stripes arranged cyclically in substantially parallel relation and a plurality of indexing stripes of radiation-emissive indexing material. The phosphor stripes and the indexing stripes are arranged with their length normal to the direction of scanning of the screen by an electron beam when the tube is in use. The indexing stripes emit radiation when the electron beam impinges thereon and the radiation is used in circuit means for synchronizing the colour moduration of the electron beam with the scan thereof.

In known cathode ray tubes having a screen of this type, the colour phosphor stripes and the correspondingly positioned indexing stripes have the same length and a hypothetical envelope curve connecting the ends of the phosphor stripes is barrel shaped as shown by line 32 in Figure 3 of the accompanying drawings. A hypothetical envelope curve connecting the ends of the indexing stripes is of the same shape and in Figure 3 this curve 30 is shown coinciding with the envelope curve of the phosphor stripes 32.

That is, in a conventional tube both the phosphor stripes and the indexing stripes are longest at the centre of the screen and the length of the stripes gradually reduces towards the side portions of the screen. This barrel shaped feature of the screen originates in the configuration of the glass panel on which the screen is formed. This panel is spherical or cylindrical for maintaining the strength of the evacuated envelope against atmospheric pressure.

Consequently, the indexing stripes at the horizontal edge portions of the screen have a length of V which at each end of the stripes is shorter by AV as compared with the indexing stripes at the screen centre. So, if when the tube is in use an electron beam is moved horizontally at a height V + AV from the horizontal centre of the tube, there are no indexing signals until the beam scans on the longest indexing stripe at the centre of the screen. Therefore, it is impossible to synchronize the colour moduration of the electron beam with the scan. A good colour reproduction can only be obtained over that part of the screen within a distance V from the horizontal centre thereof. This means that it is impossible to effectively use some portions of the phosphor screen area.

Further the prior art type of tubes have the defect that it can not partially obtain the indexing signals if there happens to be a vertical displacement between the phosphor stripes and the indexing stripes and also if the electron beam is scanned other than horizontally.

It is an object of the present invention to provide a cathode ray tube having an improved screen.

According to the present invention there is provided a colour cathode ray tube wherein the evacuated envelope thereof includes an outwardly curved panel portion having a cathodo-luminescent screen on its inner surface and a funnel portion provided with radiation detection means, said screen comprising a plurality of different elemental colour phosphor stripes arranged cyclically in substantially parallel relation and a plurality of indexing stripes of radiation-emissive indexing material arranged in predetermined substantially parallel relation with the phosphor stripes, said phosphor stripes and said indexing stripes being arranged with their length normal to the direction of scanning of the screen by an electron beam when the tube is in use, and said radiation detection means being adapted to pick up indexing signals generated by said indexing stripes when the electron beam sweeps across the screen, and wherein the ends of the phosphor stripes do not extend outwardly beyond the corresponding ends of the indexing stripes and at least at that side portion of the screen which is scanned first during each scan when the tube is in use the ends of the indexing stripes extend outwardly beyond the corresponding ends of the phosphor stripes.

Preferably the ends of the indexing stripes extend outwardly beyond the corresponding ends of the phosphor stripes at both side portions of the screen.

In one embodiment of the invention the ends of the indexing stripes extend outwardly beyond the corresponding ends of the phosphor stripes across the entire width of the screen.

In a method of manufacturing the cathodo-luminescent screen of the outwardly curved panel portion of the colour cathode ray tube according to the invention, the plurality of different elemental colour phosphor stripes are arranged cyclically in substantially parallel relation on the panel portion by method steps which include projecting light from a light source onto the panel portion through apertures in a first mask, and the plurality of indexing stripes of radiationemissive indexing material are formed in predetermined substantially parallel relation with the phosphor stripes on the panel portion by method steps which include projecting light from a light source onto the panel portion through apertures in a second mask, the length of the apertures in the second mask being not less than those in the first mask and at least at one side portion of the second mask the length of the apertures being greater than those in the first mask.

In order that the invention may be more readily understood it will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view, partly cut away, of a colour cathode ray tube in accordance with the present invention; Figure 2 is a fragmentary enlarged perspective view of the screen of Figure 1 on the line 2-2; Figure 3 shows the hypothetical envelope curve of the ends of the phosphor stripes and the indexing stripes in a prior art beam indexing type colour cathode ray tube; and Figure 4 shows the hypothetical envelope curve of the ends of the phosphor stripes and the indexing stripes in a cathode ray tube according to the present invention.

Referring to Figures 1 and 2, a colour cathode ray tube has an evacuated envelope comprising a funnel portion 12 sealed to an outwardly curved rectangular-shaped panel portion 11. In the neck of the funnel portion 12 there is an electron gun assembly 14 and beam deflection means 15 is provided outside of the portion 12. A cathodoluminescent screen 20 is formed on the inside surface of the panel portion 11. The screen 20 comprises a plurality of different elemental colour phosphor stripes 21, 22 and 23 arranged cylcically in substantially parallel relation. Light absorbing stripes may be provided between the colour phosphor stripes.

A thin metal layer 27, for example of aluminium, is disposed on the back of the luminescent screen 20. A plurality of indexing stripes 25 of radiation-emissive indexing material are arranged in predetermined substantially parallel relation with the phosphor stripes on the layer 27. Both the phosphor stripes and the indexing stripes are arranged with their length normal to the direction of scanning of the screen by the electron beam emitted by the assembly 14 when the tube is in use. A phototube 13 located on the funnel portion 12 of the tube picks up indexing signals which are generated by the indexing stripes 25 when the electron beam sweeps across the screen 20. These signals provide information regarding the actual instantaneous position of the electron beam on the screen with relation to the colour phosphor stripes.The indexing signals are employed in a signal utilisation circuit 16 of a well known type to ensure that the proper electrical colour signal is supplied to the electron beam at all times.

In the embodiment illustrated in Figures 1 and 2, the indexing stripes 25 are spaced apart such that the space between adjacent stripes is four times that of the spacing between adjacent phosphor stripes.

A start signal generating stripe 26 of the same material as the indexing stripes is positioned at the side portion of the screen which first receives the scan of the. electron beam when the tube is in use. In the tube shown in Figure 1 the scan is from the right to the left when viewing the front of the panel portion 11 and consequently the stripe 26 is shown on the left hand side of the screen when viewed from the rear thereof.

According to the present invention the ends of the phosphor stripes do not extend outwardly beyond the corresponding ends of the indexing stripes and at least at the side portion of the screen which is scanned first during each scan when the tube is in use, the ends of the indexing stripes extend outwardly beyond the corresponding ends of the phos phor stripes. In the embodiment shown in Figures 1 and 2 the beam indexing stripes 25 extend beyond a hypothetical envelope curve 42 connecting the ends of the colour phosphor stripes in a vertical direction across the entire width of the screen. As shown in greater detail in Figure 2, the beam indexing stripes are longer than the respective phosphor stripes 21, 22, 23.

Referring now to Figure 4, the upper part of the screen is illustrated and the line 40 indicates a hypothetical envelope curve connecting the vertical ends of the indexing stripes and the line 42 indicates a hypothetical envelope curve connecting the ends of the colour phosphor stripes. In no position do the ends of the phosphor stripes extend beyond the ends of the indexing stripes and at both side portions of the screen the indexing stripes extend beyond the ends of the phosphor stripes. In the arrangement shown in Figures 1 and 2 the ends of the indexing stripes extend beyond the ends of the phosphor stripes across the entire width of the tube.

Where the length of the indexing stripes are only greater than the length of the phosphor stripes at one side portion of the screen, that side portion of the screen is the one which the electron beam first scans during each scan.

In the embodiment illustrated in Figures 2 and 3 the phosphor stripes are shown as a barrel shape which is determined by the inside configuration of the glass pane portion 11 and the indexing stripes are shown as having equal vertical lengths along the horizontal axis. In practice, however, the indexing stripes extend into the flange portion 17 of the panel portion 11.

The advantage of the present invention is that the entire area of the phosphor screen can be used as an effective screen with a correct colour synchronization action.

In order to produce a cathodo-luminescent screen on a curved panel portion 11 ultimately to form part of a colour cathode ray tube, two different masks are used in a manufacturing process. In the first stages of the process the colour stripes are formed on the panel portion by projecting light from a light source through the apertures of a first mask in which the apertures are arranged at the occurrence rate of the three phosphor groups in a horizontal direction. Subsequently the beam indexing stripes are formed by projecting light from the same light source through apertures of the second mask and these apertures are arranged at the horizontal occurrence rate of the indexing stripes. The apertures in the second mask are longer than those in the first mask.

By designing these masks, various configurations of the indexing stripes and the phosphor stripes can be obtained. For example, indexing stripes having a hypothetical envelope 40 having a similar barrel shape to the hypothetical envelope of the phosphor stripes can be obtained.

WHAT WE CLAIM IS: 1. A colour cathode ray tube wherein the evacuated envelope thereof includes an outwardly curved panel portion having a cathodo-luminescent screen on its inner surface and a funnel portion provided with radiation detection means, said screen comprising a plurality of different elemental colour phosphor stnpes arranged cyclically in substantially parallel relation and a plurality of indexing stripes of radiation-emissive indexing material arranged in predetermined substantially parallel relation with the phosphor stripes, said phosphor stripes and said indexing stripes being arranged with their length normal to the direction of scanning of the screen by an electron beam when the tube is in use, and said radiation detection means being adapted to pick up indexing signals generated by said indexing stripes when the electron beam sweeps across the screen, and wherein the ends of the phosphor stripes do not extend outwardly beyond the corresponding ends of the indexing stripes and at least at that side portion of the screen which is scanned first during each scan when the tube is in use the ends of the indexing stripes extend outwardly beyond the corresponding ends of the phosphor stripes.

2. A colour cathode ray tube as claimed in claim 1 wherein the ends of the indexing stripes extend outwardly beyond the corresponding ends of the phosphor stripes at both side portions of the screen.

3. A colour cathode ray tube as claimed in claim 1 wherein the ends of the indexing stripes extend outwardly beyond the corresponding ends of the phosphor stripes across the entire width of the screen.

4. A colour cathode ray tube as claimed in any preceding claims wherein the phosphor stripes are of a maximun length at the centre of the screen and are of progressively shorter length towards the opposite side portions thereof.

5. A colour cathode ray tube as claimed in claim 4 as appended to claim 2 or 3 wherein the length of the indexing stripes is uniform across the width of the screen, the length of each stripe being equal to or greater than the maximum length of the phosphor stripes.

6. A colour cathode ray tube substantially as herein before described with reference to the accompanying drawings.

7. A method of manufacturing the cathodo-luminescent screen of the outwardly curved panel portion of the colour cathode ray tube according to claim 1, wherein the plurality of different elemental colour phosphor stripes arranged cyclically in substan

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. phor stripes. In the embodiment shown in Figures 1 and 2 the beam indexing stripes 25 extend beyond a hypothetical envelope curve 42 connecting the ends of the colour phosphor stripes in a vertical direction across the entire width of the screen. As shown in greater detail in Figure 2, the beam indexing stripes are longer than the respective phosphor stripes 21, 22, 23. Referring now to Figure 4, the upper part of the screen is illustrated and the line 40 indicates a hypothetical envelope curve connecting the vertical ends of the indexing stripes and the line 42 indicates a hypothetical envelope curve connecting the ends of the colour phosphor stripes. In no position do the ends of the phosphor stripes extend beyond the ends of the indexing stripes and at both side portions of the screen the indexing stripes extend beyond the ends of the phosphor stripes. In the arrangement shown in Figures 1 and 2 the ends of the indexing stripes extend beyond the ends of the phosphor stripes across the entire width of the tube. Where the length of the indexing stripes are only greater than the length of the phosphor stripes at one side portion of the screen, that side portion of the screen is the one which the electron beam first scans during each scan. In the embodiment illustrated in Figures 2 and 3 the phosphor stripes are shown as a barrel shape which is determined by the inside configuration of the glass pane portion 11 and the indexing stripes are shown as having equal vertical lengths along the horizontal axis. In practice, however, the indexing stripes extend into the flange portion 17 of the panel portion 11. The advantage of the present invention is that the entire area of the phosphor screen can be used as an effective screen with a correct colour synchronization action. In order to produce a cathodo-luminescent screen on a curved panel portion 11 ultimately to form part of a colour cathode ray tube, two different masks are used in a manufacturing process. In the first stages of the process the colour stripes are formed on the panel portion by projecting light from a light source through the apertures of a first mask in which the apertures are arranged at the occurrence rate of the three phosphor groups in a horizontal direction. Subsequently the beam indexing stripes are formed by projecting light from the same light source through apertures of the second mask and these apertures are arranged at the horizontal occurrence rate of the indexing stripes. The apertures in the second mask are longer than those in the first mask. By designing these masks, various configurations of the indexing stripes and the phosphor stripes can be obtained. For example, indexing stripes having a hypothetical envelope 40 having a similar barrel shape to the hypothetical envelope of the phosphor stripes can be obtained. WHAT WE CLAIM IS:

1. A colour cathode ray tube wherein the evacuated envelope thereof includes an outwardly curved panel portion having a cathodo-luminescent screen on its inner surface and a funnel portion provided with radiation detection means, said screen comprising a plurality of different elemental colour phosphor stnpes arranged cyclically in substantially parallel relation and a plurality of indexing stripes of radiation-emissive indexing material arranged in predetermined substantially parallel relation with the phosphor stripes, said phosphor stripes and said indexing stripes being arranged with their length normal to the direction of scanning of the screen by an electron beam when the tube is in use, and said radiation detection means being adapted to pick up indexing signals generated by said indexing stripes when the electron beam sweeps across the screen, and wherein the ends of the phosphor stripes do not extend outwardly beyond the corresponding ends of the indexing stripes and at least at that side portion of the screen which is scanned first during each scan when the tube is in use the ends of the indexing stripes extend outwardly beyond the corresponding ends of the phosphor stripes.

tially parallel relation are formed on the panel portion by method steps which include projecting light from a light source onto the panel portion through apertures in a first mask, and the plurality of indexing stripes of radiation-emissive indexing material are formed in predetermined substantially parallel relation with the phosphor stripes on the panel portion by method steps which include projecting light from a light source onto the panel portion through apertures in a second mask, the length of the apertures in the second mask being not less than those in the first mask and at least at one side portion of the second mask the length of the apertures being greater than those in the first mak.