US2950969A - Method of producing controlled displacement of screen elements in cathode ray tubes - Google Patents

Description

- Aug. 30, 1-960 F. .1. BINGLEY 2,950,969

METHOD OF PRODUCING CONTROLLED DISPLACEMENT OF SCREEN ELEMENTS IN CATHODE RAY TUBES Filed Feb. 27, 1957 2 Sheets-Sheet 1 IN VEN TOR. FK/i/VA J BIA/61 E) Aug. 30, 1960 F. J. BINGLEY METHOD OF PRODUCING CONTROLLED DISPLACEMENT OF SCREEN ELEMENTS IN CATHODE RAY TUBES Filed Feb. 27, 1957 2 Sheets-Sheet 2 IN VEN TOR.

nited States Patent,

METHOD OF PRODUCING CONTROLLED DIS PLACEMENT OF SCREEN ELEMENTS IN CATH- ODE RAY TUBES Frank J. Bingley, Meadowbrook, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Feb. 27, 19 57, Ser. No. 642,848

3 Claims. (Cl. 96-41) This invention relates to the manufacture of cathode ray tubes and more particularly to the production of controlled displacement of screen elements in such tubes. The invention further relates to a method of producing a sub-master for use in the manufacture of cathode ray tubes wherein it is desired to effect controlled displacement of screen elements according to a predetermined pattern.

While not limited thereto, the invention is particularly applicable to the manufacture of color image-producing cathode ray tubes to be used in color television receivers employing a single cathode ray tube. The screen of such a tube has groups of elements thereon emissive of light of different colors, and it also has index elements for producing an indexing signal which is utilized to effect proper coordination between modulation and position of the image-producing beam, such coordination being requisite for proper color rendition. The cathode ray tube screen preferably comprises 7 parallel phosphor stripes arranged in color triplets, each triplet comprising three phosphor stripes which respond to electron impingement to produce light of three primary colors such as red, green and blue. The index elements preferably are in the form of spaced stripes and they are positionally related to said triplets. .The number of index elements may be equal to, greater or less than the number of groups of colored light-emissive elements.

In any cathode ray tube employing index elements, the electron impingement on said elements causes a flow of energy from each point of impingement to a common output point from which the indexing signal is derived and is fed to an external circuit. The flow of energy may be secondary electron emission, light emission, conductive flow of electrons, or of any other character. Thus, the index elements may be composed of a material, such as magnesium oxide, to emit secondary electrons to be collected by a collector electrode: or they may be composed of a material, such as zinc oxide, to emit light to be received by photo-electric means; or they may be composed of conductive material and may be connected to a common output lead.

In a co-pending application of R. G. Clapp, Serial No. 634,217, filed January 15, 1957, Patent No. 2,899,581, there is disclosed and claimed a screen structure wherein the index elements and the groups of colored light-emissive elements are relatively displaced to eliminate or minimize color error. Asset forth in the Clapp application, the color error is due to time variation between the electron impingement on the index elements and the performance of the aforementioned coordinating function, and according to the Clapp invention the screen elements are relatively displaced as a function of said time variation over the screen area. While it is possible to displace either the colored light-emissive elements or the index elements, it is usually simpler to displace the index elements.

In the preferred method of'manufacture of a cathode ray tube of the type here involved, as described in a copending application of M. Sadowsky et al., Serial No. 408,219, filed February 4, 1954, Patent No. 2,870,010, each set of screen elements is formed by first applying to the screen a coating of photosensitive material, then exposing to light the portions of the coating where the elements are to be provided, then applying the material which is to form the elements and finally Washing away the unexposed portions of the coating. In such method, the selective exposure of stripe portions to light is accomplished by projecting light through a master having spaced transparent stripes but being otherwise opaque.

In a co-pending application of J. B. Chatten, Serial No. 641,934, filed February 25, 1957, there is disclosed and claimed a method which provides zone-by-zone displacement of screen elements of a cathode ray tube. Thus, with respect to color error in a color image-producing tube of the character above-mentioned, the Chatten method may be employed to provide zone-b-y-zone displacement generally in accordance with the predetermined color error pattern. In accordance with the preferred form of that method, a sub-master is produced by successively exposing different zones or areas of a photographic plate to light through a master in such a manner as to effect zone-by-zone displacement of the master image on said plate. Then the plate is developed and it becomes a sub-master having the desired pattern of displacement, and it is used to expose to light those portions of the cathode ray tube screen where the displaced ele ments are to be formed.

In producing the sub-master, the preferred procedure is to first make a map of the screen area zoned according to the different degrees of displacement desired in the various zones. Thus, where the objective is to eliminate or minimize color error in a color image-producing cathode ray tube, the map is zoned according to the degrees of color error. Then zone plates or masks are made according to the zoning of the map, and the masks are used in conjunction with the aforementioned'master in making the desired sub-master.

With the foregoing in mind, the principal object of the present invention is to provide an improvement ofthe Chatten method. w v r .In accordance with this invention, onlytwo precisely- .formed zone masks are made regardless of'the number of zones, one of which zone masks is the exactconverse or negative of the other, and roughly-formedmasks corresponding in number to. the number of zones are made for use with the precisely-formed zone-masks. The precisely-formed masks serve accurately to define theborders of the various zones, and the roughly-formed masks serve in cooperation With the precisely-formed masks-to define the zones in succession- The masks are utilized in association with a master to produce a pattern of the various positioning of the screen elements in the zones successively defined by the masks. 1 a I The invention may be fully understood from'the following detailed description with reference to the accompanying drawings, wherein: W

Fig. 1 illustrates, by way of example, a pattern of displacement of index elements in a cathode ray tube;

Fig. 2 shows a set of masks employed according to the present invention; I

Fig. 3 is a perspective view showing how the displacement pattern is produced; and r Fig. 4 is a face view of a sub-master produced according to the preferred form of this invention.

It will be understood that the displacement of the index elements is with reference to a normal position representing zero displacement. In color television receivers in which the color-representative signal successively represents the primary colors red, green and blue, the previously mentioned color triplets of the cathode ray tube each may comprise three phosphor stripes emissive of light of the said colors in the order mentioned. Suppose that there is one index stripe for each color triplet and that the normal position of the index stripes is directly behind the red light-emissive stripes. Then if the space or distance between consecutive red light-emissive stripes is regarded as 360 electrical degrees, and if each red lightemissive stripe is regarded as positionally representing zero displacement, each green light-emissive stripe may positionally represent 120 displacement, and each blue light-emissive stripe may positionally represent 240 displacement. "Thus if an index stripe were displaced 120, it would be shifted from its normal position to a position directly behind the green light-emissive stripe.

Referring first to Fig. 1, there is illustrated a pattern of displacement of the index stripes which has been found to be suitable to compensate for varying transit time of secondary electrons in a cathode ray tube employing index elements emissive of secondary electrons. In this illustration, the area of the cathode ray tube screen which is visible to a viewer is represented as defined by the border line 10. The screen area is represented ash is seen by a viewer. The screen area is divided into zones wherein the displacement of the index stripes to the right'increases zone-by-zone in 5 increments. Thus within the central zone, the index stripes have zero displacement; within the immediately adjacent zone, the index stripes have 5 displacement; within the next zone the index stripes have displacement; and so on.

It will be realized that it is impossible to illustrate to scale the actual displacements which are very small. By way of example, two of the index stripes are shown at 11 and 12 with the displacement greatly exaggerated so as to be clearly visible. Since the index stripe 11 extends through the central zone, it has zero displacement within that zone, but in the other zones through which it extends, it is displaced to the right the number of degrees represented by each zone. Since the index stripe 12 does not extend through the central zone, it is displaced to the right in all of the zones through which it extends, the displacement in each zone being the number of degrees represented by that zone. 1

In the preferred practice of this invention, a map of the screen area is first made, with contour lines thereon as in Fig. 1, dividing the area into zones according to the desired pattern of displacement of the index stripes. Then the aforementioned masks are made according to the zone pattern of the map, and these masks are used in conjunction with a striped master to produce the desired pattern of displacement of the index stripes.

The method according to this invention may be clearly understood by considering it with reference to a simple pattern. Suppose, for example, that the screen area is divided into four simple zones-a central zone, two concentric annular zones, and an outer zone. According to this invention, two precisely-formed zone masks are made, as shown in Fig. 2 at 13 and 14, and four roughly-formed masks are made, as shown at 15 to 18.

The manner in whichthese masks are used to produce the desired pattern of displacement of the index stripes is simply illustrated in Fig. 3. In the preferred practice of the invention, a photographic plate 19 is subjected to successive exposures by employing the masks in conjunction with a striped mask or master 20. The latter has opaque stripes 21 and is otherwise transparent. It may consist of a photographic plate which has been selectively exposed and developed. The spacing of the opaque stripes 21 corresponds to the desired spacing of the index stripes on the screen of the cathoderay tube.

Light from a point source 22 passes through the master and through two of the masks, and produces an image on a ground glass plate 23. This image is projected through a lens 24 onto the photographic plate 19. The

projected image is displaced for each exposure of the photographic plate, preferably ;by displacement of the 28 free to transmit light.

master 20, although this could be accomplished in other ways, as by displacing the photographic plate or the lens or the light source.

Referring again to Fig. 2, the first precisely-formed zone mask 13 has accurately defined transparent zones 25 and 26, and is otherwise opaque. The second precisely-formed zone mask 14 is the exact converse or negative of mask 13, and it has accurately defined transparent zones 27 and 28, being opaque in the areas corresponding to the transparent zones 25 and 26 of mask 13. An important advantage of thismethod is that the two precisely-formedmasks may be made from a common mother plate by contact printing followed by ordinary development-of one mask plate and reversal development of the other mask plate. This insures that the glass supporting base will be on the same side of the gelatin emulsion in both masks, which is important because of the refraction of the glass.

The first roughly-formed mask 15 is to be used with mask 13 and its sole purpose is to cover the transparent zone 26 while leaving the transparent zone 25 free to transmit light. Accordingly, mask 15 has a transparent area 29 and is otherwise opaque. Obviously, the size of the transparent area 29 may vary within the limits imposed by the transparent zones 25 and 26 of mask 13. Therefore, the mask 15 maybe roughly-formed for its intended purpose stated above.

The second roughly-formed mask 16 is intended to be used with the zone mask 14, and its sole purpose is to cover the transparent zone 28 while leaving the transparent zone 27 free to transmit light. Accordingly, mask 16 has a transparent area 30, and it is otherwise opaque.

It will be seen that the size of the transparent area 30 may vary wtihin the limits imposed by zones 27 and 28 of mask 14, and therefore, the mask 16 may be roughlyformed for its intended purpose above indicated.

The third roughly-formed mask 17 is intended to be used with mask 13, and its sole purpose is to cover the transparent zone 25 while leaving the transparent zone 26 free to transmit light. Accordingly, mask 17 has an opaque area 31 and is otherwise transparent. Obviously, the size of the opaque area 31 may vary within the limits imposed by the transparent zones 25 and 26, and therefore, the mask 17-may be roughly formed.

The fourth roughly-formed mask 18 is intended to be used with the zone mask 14, and its sole purpose is to cover transparent zone 27 while leaving transparent zone Accordingly, mask 18 has an opaque area 32and is otherwise transparent. Obviously, the size of the opaque area 32 may vary within the limits imposed by the transparent zones 27 and 28, and therefore the mask 18 may be roughly formed.

Referring again to Fig. 3 and considering in detail the sequence of operations involving the masks of Fig. 2, the master 20 is initially in a position corresponding to zero displacement of the index stripes. The masks 13 and 15 are first placed between master 20'and the ground glass plate 23. Then the point source of light 22 is turned on. It will be seen that the central area 33 of photographic plate19 will be exposed except for stripes 34 which will remain unexposed.

The light source is then turned ofiand the masks 13 and 15 are replaced by masks 14 and 16. The master 20 preferably is moved slightly to the right a distance corresponding to the index displacement desired in the zone defined by the transparent area 28 of mask 14. The light source 22 is then turned on, exposing the next area of plate 19 except for stripes slightly offset in relation to the stripes 34.

The same procedure is followed with the masks 13 and.

17, and with the masks. 14 and 18, with the master 20 slightly displaced further to the right in each instance to effect the desired index displacement.

In this process, ;it,is important that the precisely-formed masks be precisely positioned since their .purposeis to stripe portions of the screen.

i define accurately the borders of the successive zones. On the other hand, the roughly-formed masks need notbe precisely positioned since they merely serve to cover or tn'as'k portions of the precisely-formed masks. In practice, the process may be carried out by means of a projector having provision for precise location of the pre cisely-formed masks and also having provision for precise displacement of the master. It will be realized, of course, that Fig. 3 is intended to illustrate clearly the method involved and is not intended to represent actual dispositions of the elements.

As a result of this process, the photographic plate 19, after development, has transparent stripes as shown in Fig. 4 and is otherwise opaque. At its central portion, the plate 19 has the transparent stripes 34 which have zero displacement. The next zone of the plate 19 has transparent stripes 35 which are slightly displaced to the right. The next zone of the plate 19 has transparent stripes 36 which are further slightly displaced to the right. The outermost zone on the plate 19 has transparent stripes 37 which are still further slightly displaced to the right.

As previously mentioned, the preferred method of manufacture of a cathode ray tube of the type here involved is that described in the aforementioned Sadowsky et a1. application. The index stripes are provided on the screen of the cathode ray tube according to said method, using the plate or sub-master 19 to expose to light stripe portions of the screen corresponding to the stripes 34 to 37 in Fig. 4. Thus the index stripes are provided on the screen according to the pattern of the transparent stripes of sub-master 19.

While in practice the pattern of displacement of the index stripes, such as shown in Fig. 1, involves a much greater number of zones than the simple displacement pattern of Fig. 4, it will be understood that the production of a sub-master having the displacement pattern of Fig. 1 simply requires a greater number of roughlyfortned masks, in addition to the two zone masks, and a greater number of successive exposures of the photographic plate which is to constitute the sub-master. In the case of a pattern such as shown in Fig. 1, each of the roughly-formed masks from the third one on will have an opening or transparent area through which a particular zone may be exposed. The last several masks will have openings or transparent areas for exposure of the similar corner zones.

It will be apparent that this method is applicable no matter how many zones there are in the desired pattern. In any case, one of the precisely-formed zone masks is transparent in the odd-numbered Zones, while the other precisely-formed zone mask is transparent in the evennumbered zones. Of course, the roughly-formed masks correspond in number to the total number of different zones, as their puropse is to expose the zones in succession when employed in conjunction with the zone masks, as described above with reference to Fig. 2.

-As above described, in the preferred practice of this invention the displacement pattern of the screen elements is produced on a sub-master which is then used to produce the same pattern on the screen of a cathode ray tube. Once the sub-master is produced it can be used to produce the pattern on screens of successive cathode ray tubes.

It will be apparent, however, that the displacement pattern could be produced directly on the screen of a cathode ray tube by this method. Thus in Fig. 3, instead of successive exposure of zones of the plate 19, a photosensitive coating on the screen of a cathode ray tube could be exposed zone-by-zone, utilizing a striped master having transparent stripe portions so as to expose However, this procedure would be time-consuming and expensive because each cathode ray tube would require the multiple exposure process.

gara es 6 From the foregoing description, it will be'seen that the method according to this invention comprisesproducing a pair of zone masks, one havingtransparent zones corresponding to the odd-numbered zones of the screen area, and the other having transparent zones cor: responding to the even-numbered zones ofthe screen area, producing other masks successively cooperable wi-th said zone masks alternately to define in succession zones corresponding to the zones of the screen area, and utiliz ing said masks in association with a master to produce'a pattern according to the desired positioning of screen elements in the successive zones of the screenarea.

This method has the advantage that, regardless of the number of zones into which the screen area is divided, only two precisely-formed zone masks are required and these may be made from a common mother plate as hereinbefore described. 7

The roughly-formed masks may be cheaply made from any opaque material. Thus in the array of Fig. 2, the masks 15 and 16 could consist of opaque paperwith holes cu t therein, and the masks 17 and 18 could consist of opaque paper disks. It should be noted, however, that if glass is used, it should be of the best grade to avoid diiferences of refraction.

While the invention has been described with reference to specific forms and applications, it is to be understood that the invention is not limited thereto but contemplates such modifications and other applications as may be resorted to by those skilled in the art.

I claim:

1. In the manufacture of color image-reproducing cathode ray tubes having colored light-emissive elements and index elements on the screen thereof, wherein an index signal is produced by flow of energy from successively scanned points of the screen area to a common output point, and wherein for proper color rendition it is desired that said light-emissive elements and said index elements shall have different predetermined relative positions in predetermined successive zones of the screen area,

a method of establishing desired difierent positioning of elements in said zones which comprises producing a pair of precisely-formed zone masks, one having transparent zones corresponding precisely to alternate ones of said zones and being otherwise opaque, and the other being an exact negative of the first mask, said masks being adapted to be used alternately, producing other masks which when placed individually and in succession adjacent to the alternately-used zone masks serve in cooperation with the latter to define in succession transparent zones corresponding respectively to the successive zones of the screen area, ar ranging a photosensitive surface for exposure from a light source, interposing said zone masks alternately and said other masks in succession between said surface and said light source to define for exposure successive zones of said surface corresponding respectively to the successive zones of the screen area, and at the same time projecting through said masks onto the successively-defined zones of said surface images of the screen elements according to the desired dififerent positioning of said elements in the successive zones of the screen area, and finally developing said v stripes according to the desired pattern of the index stripes over the screen area, which comprises making a map of the screen area with lines on the map dividing it into the said successive zones, producing according to said map 7 a pa n xs sel -fe med one masks, on a n t n nar tzqne cp tssn ndin p q s lt 1tmet 9ns said and be n herwise o a ue n h ethe being an exact negative of the first mask, said masks being adapted to be used alternately, producing according to said map other masks which when placed individually and in succession adjacent to the alternatelyused zone masksserve in cooperation with the latter to define iii-succession transparent zones corresponding respectiyely to the successive mapped zones of said screen area, arranging a photographic plate for exposure from a light source, inte posing said zone masks alternately and said other masks in succession between said plate and said light source to define for exposure successive zones of said plate corresponding respectivelyto the successive mapped zones ofsaid screen area, and at the same time projecting through said masks onto the successiveiy-de fined zones of said plate images of the index stripes according to the desired different positioning of the index stripes in the different zones of said screen area, and finally developing said plate so that it has transparent stripes ac- References Cited in the file of this patent UNITED STATES PATENTS 853,072 Morikoa Apr. l2, 1 932 2,462,150 Wilkinson Feb. 22, 1949 2,617,337 Snyder NOV. 11, 1952 Tondreau et al Sept. 8 1953 OTHER REFERENCES Clerc Photography, Theory & Practice, page 342, Greenwood & Co. Ltd., 1937, London; Clerc Photography, Theory & Practice, page 99,-Green: wood & Co. Ltd, 1937, London. i H

Claims (1)

1. IN THE MANUFACTURE OF COLOR IMAGE-REPRODUCING CATHODE RAY TUBES HAVING COLORED LIGHT-EMISSIVE ELEMENTS AND INDEX ELEMENTS ON THE SCREEN THEREOF, WHEREIN AN INDEX SIGNAL IS PRODUCED BY FLOW OF ENERGY FROM SUCCESSIVELY SCANNED POINTS OF THE SCREEN AREA TO A COMMON OUTPUT POINT, AND WHEREIN FOR PROPER COLOR RENDITION ITIS DESIRED THAT SAID LIGHT-EMISSIVE ELEMENTS, AND SAIS INDEX ELEMENTS SHALL HAVE DIFFERENT PREDETERMINED RELATIVE POSITIONS IN PREDETERMINED SUCCESSIVE ZONE OF THE SCREEN AREA, A METHOD OF ESTABLISHED DESIRED DIFFERENT POSITIONING OF ELEMENTS IN SAID ZONES WHICH COMPRISES PRODUCING A PAIR OF PRECISELY-FORMED ZONE MASKS, ONE HAVING TRANSPARENT ZONES CORRESPONDING PRECISELY TO ALTERNATE ONES OF SAID ZONES AND BEING OTHERWISE OPAQUE, AND THE OTHER BEING AN EXACT NEGATIVE OF THE FIRST MASK, SAID MASK BEING ADAPTED TO BE USED ALTERNATELY, PRODUCING OTHER MASKS WHICH WHEN

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