US3731134A

US3731134A - Color picture tube utilizing a shadow mask which selects colors and detects the displacement of the beam

Info

Publication number: US3731134A
Application number: US00836424A
Authority: US
Inventors: T Iida
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1969-06-25
Filing date: 1969-06-25
Publication date: 1973-05-01
Anticipated expiration: 1990-05-01

Abstract

A color picture tube having a shadow mask which has, in addition to the function of selecting colors depending on the difference in incidence angles of a plurality of electron beams, a function of detecting the displacement of such electron beams. A signal thereby obtained is utilized so as to automatically correct vertical displacement and out-of-focussing of the electron beams thereby to increase the density of the electron beams impinging against the fluorescent screen and to improve the brightness and resolution of the picture obtained.

Description

Enited States Patent lida [75] Inventor: Teiji Iida, Chiba-ken, Japan [73] Assignees: Hitachi, Ltd., Tokyo; Teiji llida,

Chiba-ken, Japan [22] Filed: June 25, 1969 [21] Appl. No.: 836,424

[30] Foreign Appilcation Priority Data June 28, 1968 Japan ..43/45337 Oct. 24, 1968 Japan ..43/927l3 Oct. 24, 1968 Japan ...43/927l4 Nov. 11, 1968 Japan ....43/81915 Jan. 20, 1969 Japan ..44/3935 Jan. 20, 1969 Japan ..44/3936 Feb. 8, 1969 Japan ..44/9440 Mar. 14, 1969 Japan ....44/19369 Mar. 14, 1969 Japan ...44/22806 Apr. 9, 1969 Japan ...44/275l0 May 13, 1969 Japan ..44/36788 May 13, 1969 Japan ..44/36789 [52] U.S. Cl. "SIS/$1 C, 313/85 S [58] Field of Search ..31S/21 C; 313/85 S,

Primary ExaminerCarl D. Ouarforth Assistant Examiner-J. M. Potenza Att0rneyCraig, Antonelli and Hill [57] ABSTRACT A color picture tube having a shadow mask which has, in addition to the function of selecting colors depending on the difference in incidence angles of a plurality of electron beams, a function of detecting the displacement of such electron beams. A signal thereby obtained is utilized so as to automatically correct vertical displacement and out-of-focussing of the electron beams thereby to increase the density of the electron beams impinging against the fluorescent screen and to improve the brightness and resolution of the picture obtained.

24 Claims, 33 Drawing Figures PATENTEDMY Hm 373L134 SHEET 01 0F 14 INVENTOR TEI J I II DA ATTORNEYS PATENTEDHAY' 1 I915 SHEET 02 OF 14 m EEFFEBW INVENTOR TEIJ'I I PA ATTORNEYS PATENTEDHAY 1191a 3,731,134

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ATTORNEYS PATENTEU H915 3.731.134

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SHEET 08 {1F 14 INVENTOR TEITI IIDA FIG I? BY Md ATTORNEYS PATENTEU 11973 3.731.134

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INVENTOR TEI T I II DA QRIMQIMFHQM 1 1 1 l l lwl l m ATTORNEYS PATENTEDHAYHW 5,731,134

SHEET 11 OF 14 DENSITY INVENTOR fPOl l PUI DI I UI QI PQI JIQMI DI IM I PUI QI l I 1,71 IIDA ATTORNEYS PATENTEU W 1 1975 SHEET 13 0F 14 INVENTOR f/ZITI .IIDA

ATTORNEYS COLOR PICTURE TUBE UTKLIZING A SHADOW MASK WHECH SELECTS COLORS AND DETECTS THE DISPLACEMENT OF THE BEAM BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION This invention relates to color picture tubes and more particularly to a color picture tube in which displacement of a plurality of electron beams is detected by a shadow mask disposed in front of a fluorescent screen so that the displacement can automatically be corrected.

2. DESCRIPTlON OF THE PRIOR ART ln conventionally employed color picture tubes or shadow mask tubes, including those based on the Trinitron system of the SONY Corporation, the rate at which the electron beams pass through the shadow; mask, that is, the electron beam utility factor is quite low, i.e., of the order of percent to percent. Thus, the phosphors are caused to luminesce at a low rate by the electron beams that have passed through the shadow mask, resulting in a dark picture. It is therefore common practice to increase the anode voltage of the picture tube so as to raise the speed of electron beams passing through the shadow mask thereby to cause the phosphors to luminesce at a higher rate. However, the impingement of the high-speed electron beams against the phosphors generates X-rays and it is not yet possible to obtain a sufficiently bright picture even when the amount of X-rays so generated becomes as high as the allowable limit and might adversely affect the human body.

SUMMARY OF THE lNVENTlON It is a primary object of the present invention to provide a color picture tube in which a shadow mask which is primarily used for the selection of colors depending on the difference in incidence angles of a plurality of electron beams has also a function of detecting a displacement of the electron beams and a signal thereby obtained is utilized so as to automatically correct vertical displacement and out-of-focussing of the electron beams thereby to increase the density of electron beams impinging against the fluorescent screen and to improve the brightness and resolution of the picture.

Another object of the present invention is to provide a color picture tube having such a shadow mask in which the electron beam passages are in the form of many slit-like openings arranged in the direction of beam scanning so as to improve the horizontal resolution and to control the extent of the beam directed to a phosphor among a plurality of phosphors which have a low luminous efficiency.

A further object of the present invention is to provide a color picture tube having such a shadow mask in which comb-shaped shadow mask sections are assembled tegether in such a manner that the ends of strip electrodes of each of the shadow mask sections are connected through an electrically insulating member to the base portion of the opposite shadow mask section, and the shadow mask sections are electrically insulated from each other so that the strip electrodes can act as means for detecting any displacement of the electron beams from their predetermined path.

Another object of the present invention is to provide a color picture tube having such a shadow mask in which many horizontally arranged slits are formed to serve as electron beam passages and a secondary electron emission layer is provided on each of the strips defining the slits for detecting any displacement of the electron beams.

Yet another object of the present invention is to provide a color picture tube in which beams emitted from electron guns are modulated and an MgO layer or a combination of spaced MgO segments and a signal wire is provided on each strip of a shadow mask for detecting any displacement of the modulated beams, the detected signal being then fed back through a feedback system so as to automatically correct the displacement.

A further object of the present invention is to provide a color picture tube having such a shadow mask in which many slits for allowing the passage of electron beams therethrough are formed in the horizontal scanning direction of the beams, and each strip defined between the adjacent slits is provided on its surface opposite to the electron guns an upper electrode and a lower electrode which extend in the longitudinal direction of the strip and are electrically insulated from each other as well as from the strip.

A yet a further object of the present invention is to provide a color picture tube having such a shadow mask which is disposed in front of a fluorescent screen having phosphor strips arranged in the form of horizontal stripes, which has many beam passage slits arranged opposite to the phosphor strips in a number substantially the same as the number of effective scanning lines, and in which a first electrode and a second electrode, vertically separated from each other, are provided through an electrical insulatorion an odd strip and an even strip of the shadow mask, respectively, for deriving a signal representing displacement of the electron beams.

A still further object of the present invention is to provide a color picture tube in which part of phosphor strips on a fluorescent screen can be used in common to both the odd field and the even field.

in accordance with the present invention, any displacement of a plurality of electron beams is detected by the shadow mask disposed in front of the fluorescent screen so as to automatically correct the displacement. Therefore, the electron beam utility factor can be increased to several times that of conventional shadow masks or aperture grills, thereby giving a very bright picture and a very satisfactory resolution. Further, by virtue of the increased electron beam utility factor, a sufficient intensity can be obtained with an anode voltage substantially the same as that used for black-andwhite television, thereby facilitating transistorization of color television receivers. Moreover, owing to the fact that the shadow mask according to the present invention has many horizontally arranged slits for the passage of electron beams therethrough, horizontal scanning by the electron beams is not in any way obstructed to ensure a satisfactory horizontal resolution. in the present invention, the electron gun for the red phosphor which has the lowest luminous efficiency among a number of phosphors may have a horizontally oval shape so that the amount of beam impinging against the red phosphor is larger than the amounts of beams impinging against other phosphors, thereby to improve the rate of luminescence of the red color and to enhance the color improvement. Since the shadow mask detects any displacement and out-of-focussing of a plurality of electron beams, the time for detecting electron beam displacement can be remarkably shortened compared with that in conventional apple tubes and Andromeda tubes, thereby facilitating feedback control and simplifying the structure of the feedback circuit.

Other objects, features and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS:

FIG. I is a schematic perspective view of part of an embodiment of the color picture tube according to the present invention.

FIG. 2 is an enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in the embodiment of the present invention shown in FIG. 1.

FIG. 3 is a back view of the shadow mask shown in FIG. 2.

FIG. 4 is an enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in another embodiment of the present invention.

FIG. 5 is a back view of the shadow mask shown in FIG. 4.

FIG. 6 is an enlarged verticalsectional side elevational view of part of a shadow mask and phosphors in a further embodiment of the present invention.

FIG. 7 is an enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in a yet further embodiment of the present.

FIG. 8 is a block diagram of a control circuit for correcting the deflected beams by a signal representing electron beam displacement in a still further embodiment of the present invention.

FIG. 9 is a back view of a shadow mask in the embodiment shown in FIG. 8.

FIG. 10 is a schematic front elevational view of a shadow mask in another embodiment of the present invention.

FIG. 11 is a front elevational view of a shadow mask section in the shadow mask shown in FIG. 10.

FIG. 12 is an enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in still another embodiment of the present invention, showing means for detecting the arrival position of the electron beams.

FIG. 13 is a back view of the shadow mask shown in FIG. 12.

FIG. 14 is an enlarged back view of part of a shadow mask in yet another embodiment of the present invention.

FIG. I5 is an enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in a further embodiment of the present invention, showing means for detecting any displacement of electron beams.

FIG. 16 is a back view of the shadow mask shown in FIG. 15.

FIG. 17 is an enlarged back view of part ofa shadow mask in a yet further embodiment of the present invention.

FIG. 18 is an enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in a still further embodiment of the present invention, showing means for detecting the arriving position of electron beams.

FIG. I9 is a back view of the shadow mask shown in FIG. 18.

FIG. 20 is an enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in another embodiment of the present invention.

FIG. 21 is a back view of the shadow mask shown in FIG. 20.

FIG. 22 is an enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in still another embodiment of the present invention.

FIG. 23 is a back view of the shadow mask shown in FIG. 22.

FIG. 24 is a schematic enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in yet another embodiment of the present invention.

FIG. 25 is a schematic enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in another embodiment of the present invention.

FIGS. 26 and 27 are graphic illustrations of the density distribution of electron beam spots with respect to the shadow mask of the present invention.

FIG. 28 is a schematic enlarged vertical sectional side elevational view of part of a shadow mask and phosphors in a further embodiment of the present invention.

FIG. 29 is a back view of the shadow mask shown in FIG. 28.

FIG. 30 is a schematic view showing the state of beam scanning in the shadow mask shown in FIG. 28.

FIG. 31 is a schematic enlarged vertical sectional side elevational view of a shadow mask in another embodiment of the present invention.

FIGS. 32a and 32b are schematic enlarged vertical sectional side elevational views of part of a shadow mask and phosphors in a quadri-color picture tube embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 through 3, an embodiment of the color picture tube according to the present invention comprises three

electron guns

1, 2 and 3 for red, green and blue which are lined up in a vertical direction at the neck portion of a glass bulb 4. Each of the

electron guns

1, 2 and 3 is provided with a control grid, focussing electrodes and vertical deflecting electrodes.

The red, green and blue electron beams emitted from the respective electron guns I, 2 and 3 impinge against a fluorescent screen 5 which is formed by horizontally coating sets of red-, greenand blue-emitting phosphor strips G, R and B. The number of sets of the phosphor strips G, R and B is 490 or equal to the number of effective horizontal scanning lines. A shadow mask 6 is disposed opposite to the fluorescent screen 5 with a predetermined spacing defined therebetween. The shadow mask 6 is provided with horizontally running slits 7 for passage therethrough of the electron beams at positions opposite to the sets of the phosphor strips.

The width of each slit 7 is equal to one-third of the spacing between the scanning lines and the total number of the slits 7 is equal to the number of effective scanning lines or 490. In order to increase the mechanical strength of the shadow mask 6, strips 7 defining the slits 7 therebetween are connected to each other at a plurality of portions. The surface of the shadow mask 6 opposite to the electron guns is entirely covered by an electrically insulating layer 8 applied as a coating, and a metal layer for detecting vertical displacement and outof-focussing of the electron beams is formed on the insulating layer portion 8 covering each strip 7'. The odd metal layers are designated as first electrodes 9a, while the even metal layers are designated as second electrodes 9b. The first electrodes 9a are connected to a common signal lead 10 while the second electrodes 9b are connected to a common signal lead 11, so that, when the electron beams impinge against any one of the first electrodes 9a and second electrodes 9b, a signal is delivered through either lead for detecting vertical displacement and out-of-focussing of the electron beams.

Referring to FIGS. 4 and 5, another embodiment of the present invention comprises a shadow mask 6' disposed opposite to a fluorescent screen 4 having many sets of red-, greenand blue-emitting phosphor strips, R, G and B extending in a horizontal direction. The shadow mask 6' is provided with horizontally running slits 7a for passage therethrough of the electron beams at positions opposite to the sets of the phosphor strips as in the case of FIG. 2. The width of each slit 7a is equal to one-third of the spacing between the scanning lines and the total number of the slits 7a is equal to the number of effective scanning lines or 490. Each of the slits 7a is defined between adjacent strips 70'. Each of the odd strips 70' is provided on its surface opposite to the electron guns with 526 segments of MgO 7b which have a fixed width and are spaced at a fixed distance apart from each other in the longitudinal direction of the strip 70' to form segments of a predetermined pitch. Each of the even'strips 7a is provided on its surface opposite to the electron guns with 789 segments of MgO 70 which have a fixed width and are spaced at a fixed distance apart from each other in the longitudinal direction of the strip 7a to form segments having a pitch different from the segments on each of the odd strips. It will be noted that the number of the MgO segments 7c is 1.5 times that of the Mg() segments 712. A conductor wire 7e runs longitudinally above the series of the MgO segments 7b on the odd strip 7a with an electrically insulating support 7d interposed therebetween, while a conductor wire 7f runs longitudinally above the series of the MgO segments 7e on the even strip 7a with an electrically insulating support 7d interposed therebetween. The ends of the

conductor wires

7e and 7f are connected to a common external lead 73 and the potential of the

conductor wires

7e and 7f is kept at a higher value than that of the shadow mask 6'. Thus, when the horizontally scanning electron beams are displaced from the slit 7a to impinge against the MgO segments and secondary electrons are thereby emitted, the secondary electrons are arrested by the

conductor wire

7e or 7f to derive the electron beam displacement in the form of a frequency.

When, during horizontal scanning with the electron beams, the beams impinge against the MgO segments 7b whose number is 526, a frequency of 9.6 megacycles due to the stream of secondary electrons is derived from the conductor wire 7e, while a frequency of 14.4 megacycles is derived from the conductor wire 7f when the beams impinge against the MgO segments 7c whose number is 789.

FIG. 6 shows an improvement in the shadow mask structure shown in FIG. 2. In the shadow mask 6 shown in FIG. 6, a grid 6a for absorbing secondary electrons emitted by the impingement of electron beams is provided on each of the first and

second electrodes

9a and 9b through an electrical insulator 6b so as to prevent any undesirable color blur and reduction in the color purity due to the arrival of secondary electrons at the fluorescent screen.

In a further embodiment shown in FIG. 7 showing a modification of the structure shown in FIG. 6, a secondary electron absorbing grid is additionally provided through an electrical insulator 6d on each of the strip 7 at the surface opposite to the fluorescent screen 5 so as to absorb secondary electrons emitted from the aluminum metal back MB provided on the tri-color fluorescent screen 5 thereby to prevent undesirable color blur and reduction in the color purity. This arrangement is very important in a system adopted for the subsequent acceleration and focussing of electron beams.

Referring to FIG. 8, there is shown a block diagram of a feedback circuit for the detection of the arriving position of electron beams. The circuit is used in combination with the shadow mask of the kind described hereinabove so that the electron beam displacement signal detected by the shadow mask can be fed back to the beam control system for the electron guns to automatically correct the arrival position of the electron beams. Three

pilot carrier oscillators

19, 20 and 21 deliver three different pilot carrier signals at respective frequencies f f and f which are higher than 4.8 megacycles so as not to interfere with satisfactory television reception. The three pilot carrier signals are applied together with a picture signal from a television receiver 22 to the control grids of the

electron guns

1, 2 and 3 through red, green and

blue mixers

23, 24 and 25, respectively, to modulate the electron beams from the

electron guns

1, 2 and 3. The modulated electron beams scan along the slits 7 of the shadow mask 6. A modulated beam deflection control circuit 27 applies a deflecting voltage to the vertical deflecting electrodes of the

respective electron guns

1, 2 and 3 so as to forcedly deflect the modulated beams toward, for example, the upper edge of the slit 7 of the shadow mask 6, and thus the modulated beams impinge against the strip 7 of the shadow mask 6.

When the modulated beams deflected by the control circuit 27 impinge against the upper or lower edge of the slit 7 of the shadow mask 6, a signal including the frequency components f,, f, and f; of the three pilot carrier signals corresponding to the impinged beams is derived from the shadow mask 6, and the signal is amplified by an amplifier 28 which is connected to the shadow mask 6 through a capacitor C. The signal output from the amplifier 28 is separated by red, green and blue band-

pass filters

29, 30 and 31, and the signals delivered from the

filters

29, 30 and 31 are applied to red, green and

blue detectors

32, 33 and 34, respectively, to be demodulated by the latter. The demodulated reproduced signals are applied to red, green and blue

vertical deflecting amplifiers

35, 36 and 37, respectively, to operate the latter. The output signals from the

amplifiers

35, 36 and 37 are then applied to the vertical deflecting electrodes for the

electron guns

1, 2 and 3 for further suppressing the upward deflection of the electron beams. Thus, any further deflection of the electron beams by the modulated beam deflection control circuit 27 can be prevented. Such an operation is repeated each time the electron beams impinge against the shadow mask 6 by being deflected by the deflecting voltage supplied from the control circuit 27. Therefore, the locus of the beams will be as shown by the broken line in FIG. 9.

Even if vertical displacement of the beams tends to develop in the above operation, that is, when the beams tend to be displaced toward the lower edge of the slit 7 of the shadow mask 6 for some reason, downward displacement of the beams would not occur since the beams are forcedly deflected toward the upper edge of the slit 7 by the control circuit 27.

On the other hand, when the beams tend to be further displaced toward the upper edge of the slit 7, this displacement is combined with the forced deflecting action on the electron beams with the result that the electron beams are deflected to an excessive degree and impinge against the upper edge of the slit 7 at a rapid rate. However, impingement of the electron beams results in detection of frequency components included therein and the control feedback system is immediately operated to suppress deflection by the control circuit 27. Therefore, the beams are pulled back toward the lower edge of the slit 7. The locus of beams running in the slit 7 does not take a periodic waveform as shown in FIG. 9 but assumes an irregular waveform.

Another embodiment of the present invention includes a shadow mask 45 as shown in FIGS. 10 and 11. The shadow mask 45 consists of a pair of comb-shaped shadow mask sections 41 of structure as seen in FIG. 11. Each shadow mask section 41 is provided with (n 1/2) elongated strip electrodes 42 the width of which is equal to or larger than the spacing between scanning lines. (n represents the number of effective scanning lines.) The strip electrodes 42 of the shadow mask section 41 are parallelly spaced from each other at a distance of, for example, 2d which is two times the width d of each strip electrode 42. The shadow mask sections 41 are combined together in a flat fashion in such a manner that any one of the strip electrodes 42 of each shadow mask section 41 extends into the space defined between the adjacent strip electrodes 42 of the opposite shadow mask section 41, and the ends of the strip electrodes 42 of each shadow mask section 41 are connected through electrically insulating members 43 to the base portion A of the opposite shadow mask section 41, thereby defining electron beam passage slits 44 between the strip electrodes 42 so interlaced.

The shadow mask 45 constructed in the above manner is secured opposite to a fluorescent screen formed by arranging red-, greenand blue-emitting phosphor strips R, G and B in a horizontally striped pattern on the from inner wall face of a glass bulb so that the slits 44 run horizontally in front of the fluorescent screen. The strip electrodes 42 of the shadow mask sections 41 constituting the shadow mask 45 are operated as electrodes for deriving a beam displacement signal which, when detected, is fed back to an electron beam control circuit through a feadback system so as to correct displacement of electron beams and to improve the picture brightness and resolution.

While, in the present embodiment, the width of the strip electrodes 42 and the spacing between the strip electrodes 42 have been specified, the shadow mask according to the present invention is in no way limited to such specific values and many changes may be made therein as required. Further, as a means for preventing mechanical vibration of the strips of the shadow mask, suitable strips or narrow band-like members may be bonded or secured to one or both faces of the shadow mask in such a relationship that they cross perpendicularly with respect to the strip of the shadow mask.

Referring to FIGS. 12 and 13 showing another embodiment of the present invention, the color picture tube includes a fluorescent screen 51 which is formed by horizontally coating sets of red-, greenand blueemitting phosphor strips R, G and B. The number of sets of the phosphor strips is 480 or equal to the number of effective scanning lines. A shadow mask 52 is disposed opposite to the fluorescent screen 51 with a predetermined spacing defined therebetween. The shadow mask 52 is provided with horizontally running slits 53 for passage therethrough of electron beams at positions opposite to the sets of the phosphor strips. The width of each slit 53 is equal'to one-third of the spacing between the scanning lines and the total number of slits 53 is equal to the number of effective scanning lines or 480. In order to increase the mechanical strength of the shadow mask 52, strips 53 defining the slits 53 therebetween are connected to each other at a plurality of portions by connecting members 53". Each of the odd strips 53 is provided on its surface opposite to the electron guns with 526 segments of secondary electron emitting Mg0 54a which have a fixed width and are spaced apart at a fixed distance from each other in the longitudinal direction of the strip 53. Each of the even strips 53' is provided on its surface opposite to the electron guns with 789 segments of secondary electron emitting Mg0 54b which have a fixed width and are spaced apart at a fixed distance from each other in the longitudinal direction of the strip 53'. It will be noted that the number of the Mg0 segments 54b is 1.5 times that of the Mg0 segments 54a. A signal wire 56a runs longitudinally above the series of the Mg0 segments 54a on the odd strip 53 with an electrically insulating support 55a interposed therebetween, while a signal wire 56b runs longitudinally above the series of the Mg0 segments 54b on the even strip53' with an electrically insulating support 55b interposed therebetween. The ends of the

signal wires

56a and 56b are connected to a common signal lead 57 and the potential of the

signal wires

56a and 56b is kept at a higher value than that of the shadow mask 52. Thus, when the electron beams impinge against the Mg0 segments and the secondary electrons are thereby emitted, the secondary electrons are absorbed by the

signal wires

56a and 56b to derive the electron beam displacement in the form of a frequency,

and at the same time, to derive a pilot carrier signal contained in the secondary electrons.

When beam displacement takes place during scanning with the electron beams and the beams impinge against the Mg segments 54a whose number is 526, a frequency of 9.6 megacycles, due to the stream of secondary electrons, is derived from the signal wire 56a, while a frequency of 14.4 megacycles due to the stream of secondary electrons is derived from the signal wire 5612 when the beams impinge against the Mg0 segments 5412. None of these frequencies interferes with the video signal.

In a further embodiment of the present invention shown in FIG. 14, there is shown a shadow mask 52 which is similar in construction to that shown in FIGS.

12 and 13. The surface of each strip 53 opposite to the electron guns is separated into an upper portion and a lower portion along the longitudinal direction of the strip 53. The upper portion is coated with 789 segments of Mg0 63a which have a fixed width and are spaced apart from each other in the longitudinal direction of the strip 53', while the lower portion is provided with 526 segments of Mg0 63b which have a fixed width and are spaced apart at a fixed distance from each other in the longitudinal direction of the strip 53'. Centrally to each strip 53' and opposite to the electron guns, a signal wire 64, supported by an electrically insulated support, extends in the longitudinal direction of the strip 53'. The signal wires 64 are connected to a common signal lead 65 which is connected to bandpass filters (not shown) for three color pilot carriers in a feedback circuit (not shown). This arrangement can eliminate polarity switch-over circuits. Vertical displacement of electron beams can thus be detected by the

Mg0 segments

63a and 63b provided for the specific purpose.

In the embodiment described above, a potential difference may be established between the fluorescent screeen and the shadow mask as required so as to further accelerate andfocus the electron beams passed through the slits of the shadow mask, thereby avoiding blurring of the color.

Referring to FIGS. and 16 showing a yet further embodiment of the present invention, there is shown a fluorescent screen 71 which is formed by horizontally coating sets of red-, greenand blue-emitting phosphor strips R, G and B in horizontally striped pattern. The number of sets of the phosphor strips is 480 or equal to the number of effective scanning lines. A shadow mask 72 is disposed opposite to the fluorescent screen 71 with a predetermined spacing defined therebetween. The shadow mask 72 is provided with horizontally running slits 73 for the passage therethrough of electron beams at positions opposite to the sets of the phosphor strips; The width of each slit 73 is equal to one-third of the spacing between the scanning lines and the total number of the slits 73 is equal to the number of effective scanning lines or 480. In order to increase the mechanical strength of the shadow mask 72, strips 74a and 74b defining the slits 73 therebetween are connected to each other at a plurality of portions by connecting members 74. Each of the odd strips 74a is provided on the surface opposite to the electron guns with 526 secondary electron emitting segments 75a of material such as tin or carbon which emits less secondary electrons than the material, steel, of the shadow mask 72. The segments 750 have a fixed width and are spaced apart at a fixed distance from each other in the longitudinal direction of the strip 74a. Similarly, each of the even strips 74b is provided on the surface opposite to the electron guns with 7 89 secondary electron emitting segments b of material such as tin or carbon. The segments 75!; have a fixed width and are spaced apart at a fixed distance from each other in the longitudinal direction of the strip 7412. It will be noted that the number of the segments 75b is 1.5 times that of the segments 75a. The strips 74a and 74b, hence the shadow mask 72 itself serves as a signal delivering electrode and a lead 76 is connected to the shadow mask 72 for deriving a frequency due to the stream of secondary electrons emitted as a result of impingement of electron beams against the strips and for deriving a pilot carrier signal contained in the electron beams.

A shadow mask 72 shown in FIG. 17 has a structure similar to that shown in FIGS. 15 and 16. The surface of each of strips 74a and 74b is separated into an upper portion and a lower portion along the longitudinal direction of the strip. The upper portion is coated with 789 secondary electron emitting segments 82a of material such as tin or carbon. The segments 82a have a fixed width and are spaced apart at a fixed distance from each other in the longitudinal direction of the strip. Similarly, the lower portion is coated with 526 secondary electron emitting segments 82b of material such as tin or carbon. The segments 82b have a fixed width and are spaced apart at a fixed distance from each other in the longitudinal direction of the strip. The shadow mask 72 itself serving as a signal delivering electrode is connected to a lead 83 which is connected to band-pass filters (not shown) for three color pilot carrier signals. This arrangement can eliminate polarity switch-over circuits. Vertical displcement of electron beams can thus be detected by the secondary electron emitting segments 82a and 8212 provided for the specific purpose.

Referring to FIGS. 18 through 21 showing other embodiments of the present invention, a fluorescent screen 91, a shadow mask 92, electron beam passage slits 93, and strips 93 defining therebetween the slits 93 and connected to each other at a plurality of portions by connecting members 93" have a'structure similar to that of the preceding embodiments.

In FIGS. 18 and 19, each strip 93' of the shadow mask 92 is provided on the surface opposite to the electron guns with a layer of secondary electron emitting Mg0 94 for detecting the vertical displacement and out-of-focussing of electron beams. Centrally to the strip 93 and opposite to the Mg0 layer 94, a signal wire 95, supported by an electrically insulating support 96, extends above-the Mg0 layer 94 in the longitudinal direction of the strip 93'. The signal wires 95 corresponding to the odd strips 93' are connected to a common signal lead 97, while the signal wires 95 corresponding to the even strips 93' are connected to a common signal lead 98. These signal wires 95 are applied with a potential higher than that applied to the shadow mask 92. Thus, the signal wire 95 absorb the secondary electrons emitted as a result of the impingement of electron beams against the Mg0 layer 94 to derive a displacement signal contained therein thereby

Claims

1. A color picture tube comprising means for emitting a plurality of electron beams, a fluorescent screen formed by arranging sets of phosphor strips of a plurality of colors in the horizontal scanning direction of the electron beams in the same number as that of the effective scanning lines, and a shadow mask provided with electron beam passage slits defined between strips, said slits being arranged in the horizontal scanning direction of the electron beams at positions opposite to said sets of phosphor strips, said shadow mask serving as a means for detecting the vertical deflection of the electron beams with respect to the scanning Direction thereof.

2. A color picture tube as claimed in claim 1, in which said shadow mask is provided with a control circuit for deflecting said electron beams toward one of the lower and upper edges of said slit.

3. A color picture tube as claimed in claim 1, in which the odd strips of said shadow mask are electrically connected together to constitute a first electrode group while the even strips of said shadow mask are also electrically connected together to constitute a second electrode group, and said first and second electrode groups are electrically insulated from each other so as to detect displacement of the electron beams.

4. A color picture tube as claimed in claim 3, in which said electron beams are modulated by respective pilot carriers of different frequencies and the pilot carrier signals are derived from said electrode groups to detect displacement of the electron beams.

5. A color picture tube as claimed in claim 3, in which said electron beams are modulated by a common pilot carrier.

6. A color picture tube as claimed in claim 3, in which a grid for absorbing secondary electrons is disposed on at least one of the surfaces of each said strip of said shadow mask.

7. A color picture tube as claimed in claim 1, in which each of the odd strips and each of the even strips of said shadow mask are provided on the surface opposite to said electron beam emitting means with secondary electron emitting segments of different pitches, respectively.

8. A color picture tube as claimed in claim 7, in which a signal wire for absorbing secondary electrons extends in the longitudinal direction of each said strip over the surface which is provided with said secondary electron emitting segments, said signal wires being connected to a common signal lead.

9. A color picture tube as claimed in claim 1, in which each said strip is provided with an upper series and a lower series of secondary electron emitting segments of different pitches arranged in the longitudinal direction of said strip.

10. A color picture tube as claimed in claim 9, in which a signal wire for absorbing secondary electrons extends in the longitudinal direction of each said strip over the surface which is provided with said secondary electron emitting segments, said signal wires being connected to a common signal lead.

11. A color picture tube as claimed in claim 1, in which a layer for emitting secondary electrons is deposited on the surface of said shadow mask opposite to said electron beam emitting means, and a signal wire for absorbing secondary electrons extends in the longitudinal direction of each said strip over the surface which is provided with said secondary electron emitting layer, the odd signal wires being connected to a common signal lead while the even signal leads being connected to another common signal lead.

12. A color picture tube as claimed in claim 1, in which each said strip is provided with a pair of separate electrodes arranged on the upper and lower portions of the strip for detecting the deflection of electron beams, respectively.

13. A color picture tube comprising means for emitting a plurality of electron beams, a fluorescent screen formed by arranging sets of phosphor strips of a plurality of phosphors, in a fixed pattern so that the suitable phosphors among the set of phosphors can be used in common to both the odd field and the even field, each phosphor strip in said sets of phosphor strips having a width which is one-half of the spacing between the scanning lines, and a shadow mask disposed opposite to said fluorescent screen and provided with electron beam passage slits defined between strips, said slits being arranged in the horizontal scanning direction of the electron beams in the same number as that of effective scanning lines and having a width which is one-half of the spacing between the scanning lines, said shadow mask serving as a means for detecting the position of the electron beams.

14. A color picture tube as claimed in claim 13, in which said shadow mask is provided with a control circuit for deflecting said electron beams toward one of the lower and upper edges of said slit.

15. A color picture tube as claimed in claim 13, in which the odd strips of said shadow mask are electrically connected together to constitute a first electrode group while the even strips of said shadow mask are also electrically connected together to constitute a second electrode group, and said first and second electrode groups are electrically insulated from each other so as to detect displacement of the electron beams.

16. A color picture tube as claimed in claim 15, in which said electron beams are modulated by respective pilot carriers of different frequencies and the pilot carrier signals are derived from said electrode groups to detect displacement of the electron beams.

17. A color picture tube as claimed in claim 15, in which said electron beams are modulated by a common pilot carrier.

18. A color picture tube as claimed in claim 15, in which a grid for absorbing secondary electrons is disposed on at least one of the surfaces of each said strip of said shadow mask.

19. A color picture tube as claimed in claim 13, in which each of the odd strips and each of the even strips of said shadow mask are provided on the surface opposite to said electron beam emitting means with secondary electron emitting segments of different pitches, respectively.

20. A color picture tube as claimed in claim 19, in which a signal wire for absorbing secondary electrons extends in the longitudinal direction of each said strip over the surface which is provided with said secondary electron emitting segments, said signal wires being connected to a common signal lead.

21. A color picture tube as claimed in claim 13, in which each said strip is provided with an upper series and a lower series of secondary electron emitting segments of different pitches arranged in the longitudinal direction of said strip.

22. A color picture tube as claimed in claim 21, in which a signal wire for absorbing secondary electrons extends in the longitudinal direction of each said strip over the surface which is provided with said secondary electron emitting segments, said signal wires being connected to a common signal lead.

23. A color picture tube as claimed in claim 13, in which a layer for emitting secondary electrons is deposited on the surface of said shadow mask opposite to said electron beam emitting means, and a signal wire for absorbing secondary electrons extends in the longitudinal direction of each said strip over the surface which is provided with said secondary electron emitting layer, the odd signal wires being connected to a common signal lead while the even signal wires being connected to another common signal lead.

24. A color picture tube as claimed in claim 13, in which each said strip is provided with a pair of separate electrodes arranged on the upper and lower portions of the strip for detecting the deflection of electron beams, respectively.