DK144810B - SELF-CORRECTIVE COLOR REMOVAL VIEWING PLANT - Google Patents

Description

in 144810 o

The invention relates to a color television viewing system of the kind specified in the preamble of claim 1.

In most current color television receivers, a cathode ray tube is used in which a plurality of electron beams are produced by an electron gun assembly disposed within the tube at one end thereof, the electron beams being directed at a screen containing a plurality of different colored luminescent elements, at the other end of the tube.

An aperture mask or other color excitation means, such as an aperture grating or focusing grating, is arranged between the display screen and the electron gun assembly to shield the electron beams so that portions of each beam only hit the similarly colored luminescent elements. A deflection saw is arranged around the outside of the cathode ray tube, and this yoke is activated to produce a magnetic field to deflect the beams in the horizontal and vertical directions to form a scanned screen on the image screen. Such a basic display system is complemented by additional apparatus for providing dynamic convergence correction. A requirement for the display system is that the beams converge at all points of the scanned grid. The effect of non-convergence is an unwanted color fringing that occurs at the edge of objects in a television scene. A lack of convergence can be measured as the separation between the ideally superimposed red, green and blue lines in a cross-hatched pattern of lines appearing on the grid when an appropriate test signal is applied to the receiver.

It is common practice to cause the rays to converge statically at the center of the grid, e.g. Using 30 permanent magnets, the scan is placed around the neck of the image tube in a predetermined relationship with the rays. The rays do not remain converged when they deflect from the center of the screen because the screen is relatively flat and because the distance between the screen and the deflection center of the yoke increases as the beams 35 deflect away from the center of the screen. Furthermore, yoke monkeys cause rations, such as image field curvature, astigmatism, and coma.

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2 U4810 minor convergence error. It is common practice to use an apparatus to dynamically cause the rays to converge as they scan across the grid. Imaging tubes with a delta-type electron cannon assembly in which the three electron cannons 5 are disposed at the tips of an equilateral triangle are usually provided with an electromagnetic convergence assembly, in which electron magnets located outside the tube magnetize magnetic pole pieces inside the tube neck to move the rays in the radial direction. The electromagnets are activated by signals 10 with waveforms corresponding to the horizontal and vertical scanning speeds to produce the time-varying convergence fields as the rays are caused to scan. In addition, it is sometimes necessary to combine waveforms at the water and vertical scan rates such that waveforms at horizontal speed are modulated with verticals waveforms, and to add the resulting waveforms to convergence - electron magnets or to the coil coil set windings to improve the convergence of the rays in the corners of the raster.

Television receivers have previously been proposed, which include color image tubes with an electron gun assembly which produce three in-line beams which are usually located on a horizontal line. The rays must still be brought to converge. To this end, it is known that the rays can be dynamically converged in the horizontal direction by supplying appropriate signals with waveforms corresponding to the horizontal and vertical scanning rates of an electron magnetic or electrostatic convergence apparatus. A plant has been described in which the rays are caused to converge by means of the deflection saw. However, when the yoke is designed for that purpose, correction must be made for other yeast aberrations, such as coma. The apparatus used for dynamic coma correction offsets the cost savings achieved by avoiding the dynamic horizontal convergence apparatus.

It is known that the undesirable effects of coma and mangel on convergence can be mitigated by reducing the distance between the aligned rays in the deflection plane of the yoke.

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3 144810

This can be achieved by reducing the distance between the adjacent beam forming elements in the electron gun assembly. The closer the aligned beams are placed in the deflection plane, the less the electron beam aperture transmission 5 must be in order to maintain the screen tolerance between the irradiated spots and the fluorescent elements on the screen. When the mask transmission decreases, the output brightness of the picture tube decreases. Consequently, even if appropriate convergence and an acceptable degree of 10 coma can be provided at a plant employing relatively small spaced electron beams, the end result is unacceptable if the image does not have sufficient brightness to be conveniently capable of be observed under normal observation conditions.

It is the object of the invention to provide the design of a color television viewing system by which the need for a dynamic convergence apparatus and a coma correction apparatus is avoided and by means of which an image having commercially satisfactory brightness is produced.

The stated object is achieved by a plant of the kind specified in the preamble of claim 1, which according to the invention is designed as defined in the characterizing part of claim 1. As will be appreciated, the desired effect is obtained partly by selecting the winding distribution in the deflection coils based on a particular criterion for the convergence of the rays 25 in the different parts of the raster, and partly by selecting the electron gun aggregate from a criterion for the distance between the rays.

The invention is explained in more detail below with reference to the drawing, in which: FIG. 1 is a plan view of a longitudinal section through a color television display system according to the invention; FIG. 2 is the magnetic net deflection field produced by the means shown in FIG. 1, FIG. 3 shows the convergence of the electron beams in the embodiment of FIG. 1 35 under the influence of the device shown in FIG. 2 deflection field, FIG. 4 shows the winding distribution of a toroidal deflection saw suitable for use in the FIG. 1; FIG. 5 shows an electron gun assembly suitable for use in the embodiment of FIG. 1, and FIG. 6 shows an arrangement of an opening mask and a screen with luminescent elements suitable for use in the embodiment of FIG. 1.

FIG. 1 is a top view of a longitudinal section through a color television viewing system according to the invention. A color television viewing tube 10 includes an evacuated glass sheath 11. The front portion of the sheath 11 constitutes a screen and front plate 12, on the inside of which is provided a plurality of red, green and blue luminescent elements 13, 13a and 13b. Inside the tube, an aperture mask 14 including a plurality of apertures 15 is disposed near the luminescent elements so that the apertures 15 align with the luminescent elements to serve to shield the electron beams in such a way that portions of the electron beams passing through through the apertures 15, only the 20 hit similarly colored luminescent elements. At the other end of the glass sheath 11, there is an electron beam gun aggregate 15 for producing three aligned electron beams in the same plane. The electron gun assembly 16 is designed to cause the two outermost electron beams to converge with the middle beam at a centrally located point on the image screen. A more detailed discussion of the electron gun assembly 16 is given below in connection with FIG. 5th

Around the outside of the glass sheath 11, a deflection saw 17 is arranged along an extended portion thereof which is adapted to be actuated by appropriately shown sources of scanning currents to produce a magnetic field deflecting the electron beams to form a scanned raster on the screen. A more detailed description of the deflection saw 17 is given below in connection with FIG. 3 and 4.

Behind the deflection saw 17, a static convergence assembly 18 is mounted on the neck portion of the glass sheath 11. The static convergence assembly 18 includes magnets whose positions are adjustable to compensate for any errors related to the radiation escape and may cause the rays to converge in a point in the center of the screen when the beams are not deflected. A suitable static convergence assembly for use with an electron gun assembly in which the electron guns are aligned is disclosed in the specification of Danish Patent Application No. 203/73. Behind the beam convergence aggregate 18, a beam unit member 19 of conventional structure is provided, which serves to cause the beams to hit the similarly colored, luminescent elements.

As will be explained below, after a discussion of the components of the embodiment of FIG. 1, the deflection saw 17 and the electron gun assembly 16 cooperate to produce an acceptable convergence of the three electron beams at all points of the scanned grid without the use of an additional apparatus to dynamically cause the beams to converge or to correct for the effects. of coma.

FIG. 2 shows the predominant magnetic deflection field produced by the deflection saw shown in FIG. 1. Although the field uniformity in the horizontal and vertical directions will vary from point to point along the longitudinal axis of the pipe, the net effect of the field will be as shown in FIG. 2. A deflection field for deflecting the rays in the horizontal direction, which field 25 is produced by a pair of horizontal deflection coils, is shown by the fully drawn flux lines 21 extending in the vertical direction. It is noted that this magnetic field is concave distorted, since the flux lines are convex, seen from the center of the figure. This horizontal deflection field produces negative, horizontal, isotropic astigmatism for the electron beams.

In FIG. 2 are also shown flux lines 22 which represent a magnetic deflection field for deflecting the rays in the vertical direction, which is produced by a pair of vertical deflection coils in deflection saw 17. It is noted that the vertical deflection field is substantially convex distorted, with flux lines concave, seen from the center of the figure. The vertical deflection field produces position 6

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146810 tive, vertical, isotropic astigmatism for the rays.

The purpose of generating the particular deflection fields discussed above is further explained in connection with FIG. Third

FIG. 3 shows the convergence of the electron beams in the embodiment of FIG. 1 under the influence of the device shown in FIG. 2 deflection field. FIG. 3a shows the mutual position of the green, red and blue rays 20a, 20b and 20c respectively as they appear in the deflection plane, i.e. the plane C in FIG. 1, for the yoke, seen from the front end of the picture tube. FIG. 3b shows, in excessive form, the state of convergence of the rays in the corner of the scanned grid and along the vertical and horizontal deflection axes 25 and 26. respectively, it is noted that each electron beam irradiates several luminescent elements of a particular color simultaneously. The luminescent elements are naturally separated from each other, but this is not shown in FIG. 3b, which illustrates the convergence of the entire rays in different regions of the front plate.

At the center of the grid, the green, red, and blue beam converge. This center convergence is achieved by the flushing of the jets provided by the design of the electron gun assembly and by the action of the static convergence assembly 18 shown in FIG. 1. Along the horizontal - the deflection axis 26 is the green, red and blue beam 25 as shown subconverged, i.e. that there is a gap between the rays along the horizontal axis and that their order is the same as the order of the rays in the deflection plane as shown in FIG. 3a. This condition occurs at both ends of the grid along the horizontal axis. It is understood that the under-convergence of the rays at the ends of the horizontal axis decreases as a function of the distance from the center of the raster, at which point the rays converge. The subconvergence of the horizontal rays is due to the particular horizontal deflection field shown in FIG. 2nd

35 At the ends of the vertical axis 25 of FIG. 3b, the red, green and blue rays are shown to be over converged,

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I.e., the blue and the green beam have intersected at some point so that the blue and green beam at the front plate containing the luminescent elements,. lies on the opposite side to their position in the yoke's 5 deflection plane. This overconvergence of the rays along the vertical axis decreases as a function of the distance from the center of the raster, at which point the rays converge. The overconvergence of the rays along the vertical axis is due to the particular vertical deflection field shown in FIG. 2. The convergence state of the jets is a result of the design of the deflection saw so that it exhibits some negative, horizontal, isotropic astigmatism and some positive, vertical, isotropic astigmatism. Although a state of convergence is shown in which the jets are over-converged along the vertical axis and under-converged along the horizontal axis, it is understood that other modes of non-convergence along the axes can be used to produce acceptable convergence over the entire raster.

It has been found that the rays can be caused to converge substantially at both the corners of the raster and at all 20 other points of the raster, as shown in FIG. 3b, by appropriately dimensioning the astigmatism in the deflection coils.

The corner convergence illustrated in the upper right corner of the grid of FIG. 3b, shows that the blue and green rays are slightly offset relative to the red rays in the vertical direction. The upper left corner shows that the blue and green beam are offset relative to the red beam in a direction opposite to the one in the right corner. The effect of this on the grid is known under the term "trap" in which, instead of being rectangular, the grids get a slightly trapezoidal contour. Attempts have been made in the past to produce line focusing shafts which, ideally, provide convergence of the rays along the deflection axes, but which generally cause an unacceptably large amount of trap in the corners, the corner convergence state being further characterized by a horizontal separation of the rays and by eir. relatively large vertical separation.

0 8 144810

An ideal line focusing coil set has negative, horizontal, isotropic astigmatism and positive, vertical, isotropic astigmatism. This type of astigmatism is necessary to maintain the convergence of the three horizontally aligned 5 rays along the horizontal and vertical deflection axis. This state of convergence on the axes will be extended to the corners of the raster and, ideally, will result in a convergence of the rays at all points of the raster. In practice, it has been found that this ideal line focusing mode 10 can only be realized by picture tubes whose screen diagonal has a length of approx. 35 cm or less. In picture tubes whose screen diagonal is larger, no line focusing mode will be provided and the result will be a trap mode as discussed above in connection with FIG. 3b. When traps occur, the positive and negative astigmatism must be weighed between the vertical deflection coil and the horizontal deflection coil by appropriately selecting the conductor winding distribution so that substantial convergence is achieved at all points of the grid.

By the term "substantial convergence" is meant herein a state of convergence which is commercially satisfactory.

It is common practice for a television receiver manufacturer to set boundary requirements for the lack of convergence in the design specifications of a particular television receiver. It is always desirable to keep the lack of convergence as close to zero as possible, but in practice, manufacturing variations mean that it is impossible to realize a zero convergence error.

One design goal set by a manufacturer is that the lack of beam convergence, measured at a distance of approx. 13 mm from the edges of the scanned grid, must be 30 smaller than 1.3 mm for a picture tube whose screen has a diagonal of 38 cm. This design limit is increased by a larger screen and is approx. 1.6 mm for a picture tube whose screen has a diagonal of 63 cm.

In practice, the above-mentioned manufacturing variations, especially the variations of the color image tube and the yoke, cause a variation of convergence errors from one receiver to the other.

144810 0 9

Many receivers have convergence errors which are much smaller than the 1.3 mm design dimension. On the other hand, other receivers made from the same series of components on the same production line will have a much greater lack of convergence. Recipients sold commercially have been found to have convergence errors greater than 3.2 mm. In the sense in which the term "in substantial convergence" is used herein is meant a lack of convergence not greater than 3.2 mm. The lack of convergence of the rays can be observed in the separation of the ideally superimposed red, blue and green lines in a cross-hatched pattern of lines appearing on the screen when a suitable test signal is applied to the television receiver.

It is possible that manufacturing variations of the yokes and image tubes in conjunction with a non-optimal assembly may result in 15 ± convergence errors up to 3.2 mm, but this condition does not occur frequently and thus does not show that the invention should not be used with advantage.

The deflection saw in question, which is discussed in more detail in the specification for Danish Patent Application No. 214/73, 20 produces a deflection field which results in the rays generally converging at all points of the grid by balancing the astigmatism between the horizontal deflection windings and the vertical. -afbøjningsviklingerne.

FIG. 4 shows the winding distribution in a toroidal-shaped deflection saw suitable for producing the convergence properties shown in FIG. 3b. The yoke includes conductors 31 forming a pair of vertical deflection coils and conductors 32 forming a pair of horizontal deflection coils wound in toroidal shape about a ferrite core 30. It is understood that the return conductors 30 will lie along the outside of the ferrite core 30 .

FIG. 5 shows an electron gun assembly 16 suitable for use in the embodiment of FIG. 1. Three separate cathodes 35a, 35b and 35c are used to generate three electron beams. The electrons emitted by the cathodes are then accelerated, formed into rays and focused by the other electrodes, including a G1 electrode 36, a G2 electrode 37, a G3 electrode 38, and a G4 electrode 39.

or 14 144810

Although not shown, it will be appreciated that the cathodes and other electrodes are held in their mutual positions by suitable common glass strips attached to the various electrodes. The electron gun assembly 16 produces the three electron beams that converge at the center of the front plate of FIG. 1 when a deflection field is not produced by deflection saw. In order to achieve this state of convergence, the escape of and the gap between the various electrodes, in particular electrodes G3 and G4, are critical to each other 10. It should be noted that all the electrodes have three openings and are common to the three rays. This monolithic type of construction greatly facilitates the building of an accurate electron gun, which produces the desired alignment of the rays, especially in the vertical direction. The spacing between the openings in the G3 and G4 electrodes allows the two outermost beams to converge with the middle beam at the imaging screen. Minor errors in the radiation escape, ie by the convergence in the center of the screen, is corrected by appropriate adjustment of the static convergence unit mentioned above.

20 In larger color image tubes, e.g. in a color image tube whose diagonal diagonal is 38 cm or larger, it may be desirable to provide coma correction such that the scans scanned by the outer beams are the same size as the scans scanned by the middle beam of 25 screen. The deflection saw may exhibit coma, and if so, this phenomenon will tend to become more troublesome to the observer as the size of the screen increases. In order to correct for the effects of coma, around the output openings of the G4 electrode, generally 30 annular screens 40 and 41 of magnetically permeable material such as nickel iron may be arranged. These screens effectively protect the two outer rays from a portion of the magnetic deflection field, thereby offsetting the effect of the deflection field on the three rays to produce three equal-size grids.

11 144810 d

It has been found that the space between adjacent rays in a self-converging color television viewing system according to the invention must be carefully selected.

The minimum gap between adjacent rays 5 is determined by the lowest acceptable output brightness requirement set for the picture tube. As the jets are produced at less and less spacing, the transmission of the mask must be diminished to maintain color uniformity. This results in a smaller output brightness from the picture tube. The lower bound of the interspace between adjacent rays, in order to provide satisfactory brightness in a given picture tube, can be calculated or determined empirically in known manner.

On the other hand, according to a feature of the present invention, there is a limit to the maximum mutual spacing between adjacent rays. This approach is approached when the deflection saw no longer scans the beams with satisfactory convergence at all points of the grid.

20 Referring again to the case. 1. It is seen that between the space between adjacent rays in a plane extending through a point C is denoted by S. The letter C indicates the deflection plane of the yoke. S is measured in the deflection plane at some distance from the electron gun assembly, but it is understood that S is determined by selection of an electron gun which produces the desired gap, measured in a plane located midway along the length of the yoke. The ratio of S to the opening gap of the beam-forming electrodes in the electron gun can be determined trigonometrically by first measuring the distance between openings and the distance between the center of the yoke and the openings along the path to the screen at which the rays converge. The deflection plane C is generally a plane located halfway along the longitudinal axis of the yoke and perpendicular thereto. The deflection saw is mounted around the outside of the casing of the picture tube, with only a relatively small clearance between the inside of the yoke and the glass casing. This clearance is generally 12 in the order of 6 mm or less. It has been found that a deflection saw of the kind in question can be moved in a direction perpendicular to the longitudinal axis of the picture tube to produce the best possible convergence of the rays. The static convergence-5 unit is first adjusted to produce convergence of the rays at the center of the grid. Next, the coil set is moved across the image tube until the best possible convergence in the grid is achieved. The yoke is then secured in place by means of appropriate mounting means, or in the abovementioned plant, the deflection saw, which directs the distribution of the deflection windings, is selected to produce negative, horizontal, isotropic astigmatism and positive, vertical, isotropic astigmatism, serving to maintain the convergence three electron beams at a satisfactory 15 degrees as long as the distance S does not exceed 5 mm. Color television viewing systems according to the invention have been successfully built using picture tubes whose diagonal screens have a length of 38 and 43 cm, and with an S spacing of approx. 4 mm. Such a combination, together with the gap-opening mask, also provides an appropriate output brightness for the picture tube. It has been found that the effects of coma, viz. regardless of the size of differently colored grids, increases proportionally to the square of the S distance. This is why S must not be increased to a relatively large value simply to obtain greater output brightness from the picture tube. At an S-distance not greater than approx. 5 mm, it is unnecessary to correct for coma if the diagonal of the screen does not exceed 35 cm. When larger image screens are used, the effects of coma grow proportionally with the increase in size and it is desirable to use coma screens as discussed in connection with FIG. 5th

Although a toroidal coil set has been used in connection with the disclosed embodiment, it is understood that a suitable deflection saw with saddle-type coils may as well be used.

It is known that the coma properties of saddle-type coils can be regulated by the distribution of the saddle-type windings at the input portion and at the middle portion of the deflection coils. Similarly, the astigmatism of saddle-type coils can be regulated by means of the winding distribution in the middle and at the output portions of the deflection coils. In some circumstances, it is possible to avoid the coma screens discussed in connection 5 with FIG. 5 because the coma properties of the saddle-type coil set can be regulated.

In certain embodiments of the color television viewing system of the invention, it may be desirable to reduce the convergence errors of the rays or to reduce the effects of coma by decreasing the S distance between adjacent rays until the point at which the output brightness is reaching below a satisfactory level in a picture tube using a picture screen with luminescent spots and a spot-opening shadow mask. In this case 15, the output brightness can be increased by using an arrangement of luminescent elements and aperture mask as shown in FIG. 6th

FIG. 6 shows an arrangement of an opening mask and a screen with luminescent elements of the line type, suitable for use in the embodiment of FIG. 1 illustrates 20 tubes. In FIG. 6, the three electron beams 20a, 20b and 20c are directed through elongated aperture slots 15 in an aperture mask 14 to hit, respectively, green, red and blue, luminescent elements of the line type deposited on the screen 12. A combination of this kind wherein the slot openings extending in the same direction as the vertical luminescent line elements may conveniently be used with an electron gun assembly of the kind in which the individual electron guns lie on the same horizontal line as discussed in connection with FIGS. 5 because the vertical alignment of the rays is not critical. This is because the luminescent elements extend continuously in the vertical direction of the screen, and it is not necessary to critically control the vertical tolerance of the rays, because they will always hit the desired color when shifting in the vertical direction. Thus, the elongated slot apertures 15 35 in the aperture mask 14 allow a greater portion of the jets to pass than would be the case if similar spotted apertures were used in conjunction with a down-screen with spot-shaped, luminescent elements. The result of the larger mesh transmission using the arrangement of elongate slot openings and vertical luminescent elements as shown in FIG. 6 is an increase in the output brightness of the image tube, thereby enabling a relatively small S-distance of the beams to be used to achieve substantially convergence of the electron beams when scanned by the deflection saw mentioned above. Unlike a similar delta-type electron-gun aggregate, it does not require dynamic convergence on the line-electron gun aggregate used in the combination of the invention, and thus does not result in separation of the three rays into a group. , ie an increase 15 of the mutual beam distances in the group of three jets as the jets deflect from the center of the raster. Thus, the lens structure associated with the printing of the luminescent elements is simplified.

The plant in question has the advantageous feature that it does not require dynamic correction for lack of convergence and for effects of coma. As the lack of convergence and the effects of coma increase as the size of the display screen grows, the invention can advantageously be used with color car articulating tubes with on-line electron cannon assemblies whose diagonal screen 25 has a size of 58-63 cm. However, in these circumstances it may be desirable to supplement the self-convergence with a simplified dynamic convergence apparatus. In this connection, an electrostatic or electromagnetic convergence means may be used which is located in the neck portion of the image tube and which is activated only at either the line or field scan rate. For example, the use of only horizontal dynamic convergence correction together with an electron gun aggregate in which the individual electron guns lie on a horizontal line, as discussed above, will result in a raster in which the jets converge satisfactorily at all points.

Claims (3)

144810 0 Patent Claims. A color television viewing system comprising a color television picture tube containing a) a front plate on which groups of three differently colored, luminescent elements are disposed to form a screen, b) an electron beam cannon assembly for generating three electron beams contained therein. a horizontal plane substantially perpendicular to the screen and along three generally converging lines extending toward the screen; c) an aperture mask including a plurality of apertures aligned with said groups of luminescent elements; and d) a deflection saw comprising a vertical axis. deflection coils and horizontal - deflection coils disposed around the image tube between the mask and the electron gun assembly for deflecting the jets to form a screen screen display characterized in that e) the winding distribution in the deflection coils is selected to generate positive vertical feed and negative 20 horizontal isotropic astigmatism dimensioned so that the convergence of the beams along the vertical and horizontal deflection axes is balanced against the convergence of the beams at the corners of the raster, wherein the f) electron gun assembly is further selected to produce a gap no greater than ca. 5 mm, between adjacent rays of the said rays, measured in a plane located midway between the ends of the deflection saw. Color television viewing system according to claim 1, characterized in that the electron gun assembly includes at least one common beam-forming electrode having three openings for the rays. Color television viewing system according to claim 1, characterized in that the electron gun assembly includes screen portions arranged around the path of the two outermost 35 of the three beams for shielding these beams from a portion of the deflection field.