US2866125A - Cathode-ray tube - Google Patents

Description

Dec. 23, 1958 J. HAANTJES ETAL 6,125

CATHODE-RAY TUBE Filed Oct. 6, 1954 4 Sheets-Sheet 1 IN VEN TORS JOHAN HAANTJES GERRIT JAN LUBBEN AGENT Dec. 23, 1958 J. HAANTJES ET AL 2,866,125

CATHODE-RAY TUBE Filed 001.. 6. 1954 4 Sheets-Sheet 2 INVENTORS JOHAN HAANTJES GERRIT JAN LUBBEN AGENT Dec. 25, 1958 J. HAANTJES ET AL 2,86

CATHODE-RAY TUBE 4 Sheets-Sheet 3 Filed 001.- 6. 1954 i- Elli If:

INVENTORS JOHAN HAANTJES GERRIT JAN LUBBEN AGENT Dec. 23, 1958 J. HAANTJES Em 2,866,125

CATHODE-RAY TUBE Filed Oct. 5. 1954 4 Sheets-Sheet 4 1 INVENTORS JOHAN HAANTJES GERRIT JAN LUBBEN AGENT tats atent 2,866,125 Patented Dec. 23, 1958 cA'rnonE-aAY TUBE Johan ll-laantjes and Gerrit Jan Lubben, Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application October 6, 1954, Serial No.460,744

@iaims priority, application Netherlands February 9, 1954 It) Claims. (Cl. 31513) (l) The distortion proportional to a (2) The curvature of the image field and the astigmatism proportional to a 12, and

(3) The coma proportional to a17 wherein a is the deflection angle and b is the aperture angle or the diameter of the beam.

In a tube exhibiting a large diameter of the beamor a tube exhibiting three cathode rays which are considered together as a single beam, the errors in which the diameter b plays a part are interfenngly great if no particular steps are taken.

If care is taken that the electrons ofthe beam consist of one cathode ray only, or the electron of the beam constituted by three cathode rays are concentrated in the usual manner in the non-deflected position of the beam (a=) at one point, such is not the case in the deflected position. This is known as deliction defocussiug.

in colour television this would implythat the thrie colour images are not properly registered over the whole screen of the tube. It is noted thatthe distortion-which is not dependent upon the diameter b of the beam, such as barrel or pincushion distortion, maybe suppressed by providing, for example, magnets outside the tube. The curvature of the image field may be suppressed by modulating suitable components of pictureand. line fre quency on the concentrating field of .the focusing coil. However, astigmatism and coma then still remain as errors.

The primary object of the inventiomis to provide a cathode ray tube comprising a deflection coil system of the kind above described, in which the astigmatism is considerably reduced. A further. object of the'invention is to obtain a considerably decrezsed'coma.

The invention exhibits the characteristic that: in the tube the paths of the electrons after traversing a'con'- cenrating field andupon reachinguthe'fi'eld of the deflection coil system areconcentratedwithin a ribbon-like part of the space of the tube and lh6-(llIClIlGll= of the largest dimension of this ribbon-like'space ina-plane at right angles to the axis of the tube is substantiallyparallel to one direction of deflection and for thi dil'fiC1 tion of deflection the meridional image plane issubst-antially coincident with the surface of the screen and; for the other direction of deflection the sagital image plane is substantially coincident with the surface of the screen.

In order that the invention may be readily carried into effect, it will now be described with reterence to the accompanying drawings, given by way of example, in which:

Figs. 1 and 2 serve to explain the occurrence of errors inthe image and the decrease thereof.

Fig. 3 shows a cathode-ray tuie comprising a deflection system according to part of one embodirnmt of the invention for deflection in one direction.

Fig. 4 shows the associated system for deflection in the second direction.

Fig. 5 is a developed view of the coil of Fig. 3 in a flat plane.

Fig. 6 is a developed view of the coil of Fig. 4 in a fiat plane.

Fig. 7 serves to explain the magnitudes occurring with the coils of Figs. 3 and 4.

Fig. 8 is a side-view of another embodiment of the invention.

Figs. 9 and 9 are other side views of the same embodiment so far as one direction of deflection is concerned.

Figs. 10 and 10 are other side views of the embodiment of Fig. 8 so far as the second direction of deflection is concerned.

Fig. 11 shows one embodiment of a circuit arrangement for the parts of the coil shown in Fig. 8 and Fig; 12 shows a second embodiment of such a circuit arrangement.

Figt'l shows a rectangular system of axes x, ij, z, the origin 0 of which coincides wiih the deflecim centre, imagined tobe concentrated at one print, of a deflection coil system which is not shown. This coil system serves for the deflection in the x and 1' directions of a beam which in the non-deflected prsition is concentrated around the axis of the tube, in this case the z-axis, and of which the electrons travel in the direction of the positive z-axis. The beam is constituted by three cathode rays provided by three electron guns 1, 2, 3 which are positioned symmetrically about the z-axis. The beam diverges till it reaches the concentrating field, the action of which is imagined to be concentrated in a plane at right angles to the z-axis and passing through point 5. The beam converges after having passed the concentrating field and subsequently traverses the deflection system at 0. The diameter of the beam occurring at 0 determines the magnitude of the errors occurring. If deflection does not take place, the beam converges at point 6 of the z-axis. The substantially plane screen of the cathode-ray tube is at right angles to the z-axis and passes through point 6. Of this screen only the intersecting line 7 with the plane x=o is shown.

The drawing furthermore shows what happens, for example,without taking particular steps, if the beam is deflected in the negative ij-direction in. the direction of the line 8 in. the plane x=o. Starting from the origin 0, there will be produced, in succession, a linear cross-section 9 of the beam, located in the plane x=0 an elliptical cross-section 10, of which the major axis is parallel to the line 9, a circular cross-section 11, then again an elliptical cross-section 12, of which the major axis is at right angles to the direction of the linear crosssection 9, and then finally a linear cross-section 13, which is at right angles to the linear cross-section 9 and hence at right angles to the plane x=o.

The linear cross-section 9 is located in an image plane, of which only the intersecting line 14 with the plane x=0 is shown. This image plane 14 is the sagital image plane for deflection in the ij-direction. When in this description and the appended claims reference is made to a defiection'device and the associated sagital image plane,

this is to be understood to mean that image plane in which a linear cross-section of the beam is produced, which linear cross-section is parallel to the direction of deflection concerned. I V

The circular cross-section 11 is located in the plane of the mean curvature of the image field, of which as before only the intersecting line 15 with the plane x5-b is shown. i

The linear cross-section 13 is located in the meridional image plane, of which only the intersecting line 16'with the plane x= is'shown. When in this description and the appended claims reference is made to a direction of deflection and the associated meridional image plane, this is to be understood to mean that image plane in which a linear cross-section of the beam is produced, which linear cross-section is at right angles to the direction of deflection concerned.-

Furthermore, in the definitions reference is made to a linear cross-section in the meridional plane or'the sagital plane, but this does not make it impossible for the linear cross-section to be reduced substantially to a point.

, From the foregoing it appears that, unless particular steps are taken, the beam which in the non-deflected position converges to a point 6 on screen 7, in the deflected position does not converge anywhere to one point on the screen. However, if the cross-section of the beam is not unduly large, the circular cross-section 11 in the plane of the mean curvature of the image field becomes very small. It is now furthermore known that with a suitable shape of the deflection coil system it is possible for the sagital image plane 14 and the meridional image plane 16 to; coincide in practice for the two directions of deflection with the image'plane 15 of the mean curvature of the image field. In this case a beam of a diameter which is not unduly large is thus concentrated substantially to a point in the plane 15. However, the plane 15 is a plane having a finite radius of curvature, so that it. does not coincide with the substantially plane screen 7, with the result that a substantially punctiform image does not appear on the screen 7. Consequently, it is commonpractice to control the strength of the concentrating field at as a function of .the deflection in the x and ij-directions.

The deflecting field H of the deflection coil system may be described by three relatively perpendicular components H (x, ij, z), H -(x, ij, z) and H (x, i]', z), all three of which may be dependent upon x, ij and 2, as shown. This field must satisfy the following conditions of symmetry:

1 f. I f, a: 7, z)

1 0 i, t1 i, Z)= z1 2) wherein H H and H, are coeflicients which are .only dependent uponz. An .accent meansa differentiation 7 with respect to z. Terms containing H 'are'notimportant for the present considerations, which are limitedto third order errors in the image. The components for the deflection in the x direction are of a similar form, which is found by interchanging x and ii in the righthand terms of the equations.

For the x component of the field strength there is found in the plane x=0 T,,(0,ij,z)=H +H ij H ij The values H and H may then be determined by measuring the magnetic field in the x direction in the plane x=o, and it will be found-that these values vary as a function of z. When these coefficients are known, then the total field distribution in the vicinity of the z-axis can be determined. H determines the sign of the direction of deflection. Hereinafter the sign of H always refers to that sign which occurs if H is positive.

The electron paths may be calculated with the aid of the Fermat principle that the paths chosen by the electrons between two points are the paths between these points for which the travelling time is a minimum. One

may thus start by calculating the paths for small deflections. When this calculation is made for determined initial conditions, that is to say the point x. yo: Z0, Where the beam with the direction x,,, ij,,', enters the deflecting field, which place is thus located at that end of the coil 'which is most remote from the screen, in Fig. 1 between the concentrating field and the plane z=0, it is found that the deflection I] in the ij-direction is independent of the initial conditions, viz.

The term deflection is to be understood in this case constant, wherein z=z is the plane 7 of the screen at whichthe deflection I] occurs. If, without deflection, the electrons impinge upon the surface 27:2 at one 'point, they thus keep doing so as a first approximation for small deflections.

In future formulas, the subscript s refers to points located at or values determined at the planar screen 7.

-For the sake of completeness it is mentioned that K is a constant. r

If the terms in the expressions for H H and H which are quadratic in x, ij and x', ij', are also taken into consideration in the calculation, deflections result which differ or deviate from the deflection I], which has been found to a first approximation and which is now indicated as U for the plane z=z,,, and also for deflection in the x direction differences or deviations occur from the deflection X=X which has been found as a first approximation.

The said differences or deviations Ax and Aij are in the case that the undeflected beam would have reached the point X,,=0, 1J,=o

image field, the deviations are given by It is noted that the sign of or, for a clearer recognition, in polar coordinates:

IJ, cos p and The electrons on the periphery of the beam having a radius r, which thus converged to the same point before passing the same field, now produce an elliptical crosssection. The rays of a beam intersect twice in a line, in the sagital and the meridional image planes. A circular cross-section alsooccurs somewhere between the said two lines, viz. in the plane of the mean curvature of the image field. The curvature. of the sagital image plane is as a first approximation that of the meridional image plane is and that of the mean curvature of the image field is rt-I 2 The image is called anastigmatic when the said planes are coincident and hence if :5 Now, it can be shown that:

image field determined by since this requires in addition that ea l-13 0. The integral with H does not occur in this sum and the other terms are together always positive.

From this it follows that it is not possible to design a deflection coil system by which a beam converging in the non-deflected position, is invariably caused to converge, after deflection, in a fiat plane so long as the beam is of arbitrary cross-section.

A first recognition underlying the invention is a choice of the cross-section of the beam such that it is yet possible to obtain a flat plane of convergence as far as astigmatism and coma is concerned. For this purpose the beam is given a ribbon-like shape. In a three-colour television tube, the three electron guns are arranged, for example, on one line,-which 1ine coincides with one direction. of deflection. The three beams together then constitute one ribbon-like beam.

If the ribbon-like shape is chosen in the ii-direction, as shown in Fig. 2, in which identical parts are indicated by the same reference numerals as in Fig. 1, go is substantially forv all points of the beam, so that the afore-mentioned difference Ax in the plane z=z is always zero. Consequently, the length of the meridional image .3 of Fig. 1, which .is located a little before the plane z=z is already substantially reduced to zero in the image plane 13 of Fig.2. In order to'obtain a flat plane of convergence," it is then necessary only that the meridional image. plane. becomes a flat plane and hence that [3 :0 It is noted that the remaining small length of the meridional'image' 13 is determinedby the width of the ribbon-like beam. For completeness sake, it is further noted that [3 :0 implies a deflection proportional to the field strength. A positive value of 3 means that the deflections of the beam at the screen are greater than proportional to the field strength and therefore to the current in the deflection coil. If 13., is negative, the deflection is less than proportional to this current.

If the ribbon-shape would have been chosen in the x-direction, it would be necessary upon deflection in the ij-direction to ensure thata ='O, which would result in a flat sagital image plane.

The meridional image plane thus must be a flat plane for the deflection coil bringing about deflection in a direction parallel to the largest transverse dimension of the ribbon-like beam, whereas the sagital image plane must be a flat plane for the 'deflection'coil bringing about deflection in a direction at right angles to thelargest transverse dimension.

In the expression (2) for 5 the first integral is positive, so that the second integral must be negative, in order that 5 :0. This implies that H must be substantially positive through the length of the coil, since' the deflection H is negative with a positive field in the x-direction. The variation of H as a function of z may be fairly arbitrary, provided that the value of the integral does not vary. The largest contribution to the integral is provided by the values of H at high value of z and hence at that end of the coil system which is adjacent the screen, since both I] and (zz increase quadratically with z. Consequently, at the said end of the coil, the mean value of H will have to be positive. This means that in avoiding this distortion, the ij-component of the field strength should increase a certain extent in the direction of deflection.

a must be equal to zero for the deflection coil system for the other direction of deflection and hence in the case of Fig. 2 for the x-direction. On the ground of analogous considerations, it follows that it is then necessary for this deflection system that the value H at the end of the coil system which is adjacent the screen should be substantially negative. This means that the x-cornponent of the field strength should decrease a certain extent in the direction of deflection.

If the complete deflection system satisfies the foregoing requirements, no perceptible astigmatism will occur upon deflection in the x-direction and no perceptible astigmatism will occur either upon deflection in the z'j-direo tion. Moreover, it is mentioned that now a flat image plane is obtained, so that it is no longer necessary to vary the strength of the concentrating field as a function of the deflection amplitude.

As mentioned before, there is still a certain freedom in the variation of H as a function of z.

This may be utilized for suppressing or greatly reducing the coma error. This error may be expressed by the equations In polar coordinates the said formulas become as follows:

In order to suppress the coma error, a ,8 and 6 would and 1 V 55- Zn 8 It appearsthat p and {3 become small enough to avoid any appreciable interference, if

a Hz( t) f dz-O 7 So that and B5=%.

In order to provide for the last-mentioned integral to be equal to zero, it is sufficient as a first approximation if the integral is substantially zero over the length of the coil. This may be obtained as follows:

The coil which deflects in the ij-direction and of which H in order to suppress astigmatism, must be substantially positive at the end adjacent the screen, requires a substantially negative H value at the other end of the coil.

The opposite applies for the coil bringing about deflection in the x-direction.

So far the two deflections have been dealt with separately. However, in practice, deflection takes place in both directions simultaneously. It appears that the expressions for the differences Ax and'Aij then become a little more elaborate.

The astigmatism is then representedby the equations:

and the 'coma by:

X and U therein arethe first-order deflections in the plane 2:2, in the x and ij-directions.

The A-coefl'icients are integral functions of the values H and H (hence H and H of coil [1 deflecting in the X-direction) and the B-coeflicients are integral functions of the values H and H (hence H and 1-1 of coil I deflecting in the ij-direction). The subscripts I refer to values associated with a coil I having a main field component in the x-direction, and the subscripts II with a coil II having amain field component in the ij-direction.

' .If, as before, the largest transverse dimension of the ribbon-like beam is parallel to the ij-axis and hence =90, we find for the astigmatism:

Now, it can be shown that:

The first three integrals together always provide a negative contribution with the conventional dimensions of the cathode-ray tubes and the coeflicients deflection coil systems. The two latter terms containing the H and the H thus have to provide together a positive contribution. With the latter two integrals the values of H at the end of the coil which is adjacent the screen of the coil.

are most important, as before. It is already necessary that H is negative and H is positive at the said end The first of the two integrals then becomes positive (since the deflection I] is' negative with a positive fieldin the x-direction) and the second integral, including the minus sign, becomes negative. If the sum of the two integrals must be positive, the absolute value of H is required to be higher than the absolute value of H at the corresponding end of the coil and hence in the vicinity of the screen 2 2 The cathode-ray tube .21 in Fig. 3 comprises three electron guns for producing three cathode rays 22, 23,

24, which guns are known per se and shown only diagrammatically,

The cathode rays pass on their way to a screen 25 through the field of a concentrating coil 26 of known is constant throughout the length of the coil.

the case with the coils shown in Figs. 3 and 4. Howa manner to form one deflection system, but they are shown separately for the sake of clearness.

Since the two coil halves 27a and 27b, as mentioned before, serve for deflection or the cathode rays in a vertical direction, it is necessary to ensure that the three cathode rays '22, 23, 24 upon entering the deflection space are located within a ribbon-like space, of which the largest dimension, as measured at right angles to the axis of the neck 29 of the tube, is also located in a vertical direction.

It is furthermore important to point out that, as a rule, the plane of the three electron guns does not coincide with the vertical plane, since a slight shift of the plane of the cathode rays still occurs as a result of the presence of the concentrating field of the coil 26.

The coil halves 27a and 2712 are formed in a shape such that the value is positive, as measured at the extremity of the coil halves which is adjacent the screen 25 of the tube.

The value h constitutes a proper approximation of the quotient for the form of the coils to be discussed.

In Fig. 7, the importance of the angle p and, of the radius R is shown more fully by a cross-section of an arbitrary deflection coil in a plane at right angles to the axis of a tube.

One half of the coil comprises conductors 29a and 291), which are usually constituted by a plurality of relatively insulated wires. The other half of the coil comprises conductors 30a and 30b. It is shown in dotted lines that, on the one hand, the conductors 29a and 2% are interconnected at the front and the rear side of the coil and on the other hand, the conductors 30a and 3%. The figure shows that the coil does not surround the tube completely and that the portion which is not embraced is equal to an angle 4 h.

If the neck of the tube is circular-cylindrical and if the conductors engage either the neck or a surface concentrical therewith, the distance R between the centre of each conductor and the axis of the neck of the tube This is ever, due to the asymmetric shape, this results in variation of the value of the angle 0, which angle thus has difie'rent values for cross-sections of the coil at different areas.

For the coil ha'lves 27a, 2712, the value it must be positive at the extremity 3l, which implies that the angle 4/ at this area is less than 30.

For the coil halves 28a and 2815, the value It must be negative at the extremity '32 and hence also on the side must be substantially zero for both pairs of coil halves 27a, 27b and 28a, 28b.

When'the coils surround a circular-cylindrical surface as assumed in the case under consideration, the coil halves27a and 28a have'the shape as shown in the developed state in Figs. 5 and 6, respectively.

In Figs. 5 and .6, dotted lines indicate the location :of the conductors of the coil halves which are active for the deflection, if it would invariably be zero throughout the length of the coil, which lines thus correspond to an angle 1/ of 30".

It is noted that the condition that h is, on the average, substantially zero throughout the length of the coil half is a first approximation of the condition that t f h(zz,)

is substantially zero.

If the two coil halves 27a, 27b and 28a, 28b are located on concentric surfaces, it immediately follows from the requirement that the absolute value of h for the coil 28a, 28b at the extremity concerned must be higher than that for the coil 27a, 27b that the coil halves 23a and 28b in the developed state are more trapezoidal than the coil halves 27a and 27b.

If the coils, instead of surrounding a circular-cylindrical portion of the neck of the tube, are located wholly or in part on a conical surface, not only the angle 1/ varies in the longitudinal direction of the coil, but also the radius R varies in the quantity In this case also the said conditions must be fulfilled.

A cathode-ray tube comprising a deflection coil system as described above permits of obtaining punctiforrn images of the cathode rays 22, 23, 24 on the screen 25, which images are also substantially free from coma. If the beams 22, 23, 24 occur simultaneously, they provide together only one punctiform image which is likewise substantially free from coma.

For the sake of completeness, it is observed that the shape of the coil halves is dependent upon the radius R of the coils halves, the length z z of the coil half and the distance 2 If the angle ,0 indicated in Fig. 7 for the coil half of Fig. 5 at the point is indicated as 1,0 and as & at the point Z and for the coil half of Fig. 6 is indicated at & at the point Z and as 1/ at the point Z1, then we have with the conventional dimensions:

With a 3 cm.-radius of the coil, a length of. 12.5 cms. of the coil and a distance 2 :44 cms., we have 34.52 =27.5, =ll.5 and b =36.5.

It is important to point out that the coil halves have a finite thickness also at the extremities, so that 10 and Z correspond to the area of the centre of the conductors.

Fig. 8 shows another embodiment of the deflection coil system. As before, it assumed that the largest transverse dimension of the ribbon-like cathode-ray beam extends in the ii-direction.

Two rings 33 and 34 of ferromagnetic material surrounding the neck of the cathode-ray tube (not shown) are located one after another along the axis of the tube. The rings have toroidally wound on them several coil packages. The deflection coil system for deflection in the x-direction is constituted by a first set of four coil packages wound on ring 33 and by a second set of four coil package wound on ring 34. Since Fig. 8 is a side view from the x-direction, only two packages 35 and 36 of the first set of four packages located on ring 33 can be seen.

.coil on ring 34 has a positive H -value.

11 These packages are also shown in Fig. 9a, which is a side view of ring 33 from the z-direction. Fig. 9a. also shOWs the location of the two other coil packages 37 and 38 of the first set of four.

Of the second set of four coil packages arranged on ring 34, Fig. 8 also shows only the packages 39 and 40. w

Fig. 9b is a side-view of ring'34 in the z-direction in which the other coil packages 41 and 42 of the second set of four are also seen. Figs. 9a' and 9b also indicate, on the ij-axis, the orientation of the ribbon-like beam produced by the three electron guns 1, 2 and 3. The coil packages are interconnected in a manner which will be described hereinafter. Consequently, the packages 35,

.36, 37, 38 provided on ring 33 are traversed by a current,

of which the direction is indicated in Figs. 9a and 9b in each package, on the inside of the ring, by a cross if the current flows inthe direction of the positive z-axis and by a dot if the current flows in the direction of the negative z-axis.

The current thus flows in opposite directions through two diametrically opposing packages 36, 37 or 35, 38

or 39,- 42 or 40, 41.

Such diametrically located packages are located in the case of ring 33 in planes which make an'angle smaller than 30, in this case an angle of 25, withthe plane ij=0, and in the case ring 34 in planes which make an angle larger than 30, in this case an angle asesnes system shown in Figs. 9a and 9b) has a predominant negative H -value on the side adjacent the screen. The

magnitude of the H -values may be varied by variation of the corresponding angles. Furthermore, the H -value may be controlled by suitable choice of the numbers of ampereturns on ring 33 and ring 34 for each coil system. It is thus also possible to ensure that the absolute value of H on the side adjacent the screen, of the coil system for deflection in tie x-direction is higher than the absolute value of H ,'on the side adjacent the screen, of the system for deflection in the ii-direction. Furthermore, it 7 can be ensuredthat the mean H -value throughout the length of the coil is substantially zero for each coil system.

By way of numerical examplepitis mentioned that the coil system shown in Figs. 8, 9a, 9b, 10a, 10b, with of 43, with the plane ij=0, since. the magnitude H of a a set of four of these coil packages is determined, as before, by the magnitude ;3+4 cos 1,0

in which 1p represents half of the acute angle between two packages with the same direction of current and hence is, for example 25, in Fig. 9a. Since a coil package is wound toroidally and the long axis of the coil package is thus substantially parallel to the z-axis, the angle 41, in contra-distinction to the angle with the trapezoidal saddle coils shown in Figs. 3 to 7, is constant and hence no function of z. If l/=, h=0 and hence H =0. If the angle o is smaller than 30, H is positive.

The complete deflection coil for deflection in the x-direction thus comprisesa part which is remote from the screen, viz. ring 33 together with the packages 35, 36, 37,38, of which H is positive, and a part which is adjacent the screen, viz. ring 34 together with the packages 39, 40, 41, 42, of which H is negative. I

The coil system for deflection in the z'j-direction is arranged on the same rings 33 and 34. The ring 33 carries the four coil packages 45, 46, 47, 48, of which only two, viz. 4S and 46 are seen in Fig. 8 and are indicated in dotted lines in distinction from the other coil system.

Fig. 10a, as before, is a side-view in the z-direction of ring 33 and Fig. 101) of ring 34. The ring 34 carries four coil packages 49, 50, 51, 52.

The value H of the parts of this coil system is determined as before by the expression this angle, considering the directions of current indi-- the angles (p indicated therein permits of obtaining an image which does not exhibit any appreciable astigmatism or coma with the following proportioning.

The number of ampere-turns of the coil packages 45, 46, 47, 48 and 49, 50, 51, 52 were in a relationship of 8:5 and those of the coil packages 35, 36, 37, 38 and 39, 4h, 41, 42 in a relationship of 5:2. Inside the coils the largest transverse dimension of the ribbon-shaped beam is equal to 20 mms. The diameter of the coils, that is of the central layer of the rings, was 70 mms. The total length of the coil system and hence from point 53 to point 54 in Fig. 8 was 60 mms. and the distance between the centre of the coil system and the screen was 350 mms.

Fig. 11 shows a possible manner of feeding the coil packages of the system for deflection in the ij-direction. The coil packages 45, 46, 47, 48 arranged on ring 33 are connected in series, care being taken to connect each part in such manner that the direction of current in each coil package has the correct polarity relative to the direction of the z-axis. The coil packages 49, 50,

51, 52 arranged on ring 34 are also connected in series.

Each series-connection furthermore includes one half of a coil 55 having a slidable core 56. The resultant seriesconnections are connected in parallel between supply terminals 57 and S8, to which a sawtooth current is supplied. The distribution of current through the two parallel branches may be varied by sliding the core 56, so that the numbers of ampere-turns for the system on ring 33 and for the system on ring 34 are relatively varied. The coil 55 is arranged in such manner that the deflection of the beam is not influenced by it.

In the circuit shown in Fig. 12, the coil packages 45, 46, 47, 43 are included in one branch of a bridge circuit and the coil packages 49, 50, 51, 52 are included in a second branch thereof. The third branch is constituted by one half of a coil 59 and the fourth branch by the other half of coil 59, which, as before, comprises an adjustable core 60. A diagonal 63 of the bridge is connected between the centre of core 59 and the junction of the two sets of four coil'packages. The other diagonal has connected to it input terminals 61 and 62 for supply of the sawtooth current. If the bridge circuit is in equilibrium, which may be ensured by adjustment of the core 60, the diagonal 63 is currentless and the same cated in Figs. 10a and 1017, now corresponds to 33 in Y Fig. 100: and to 20 in Fig. 10b.

The part of the deflection coil on ring 33 thus exhibits a H -value which is negative and the part of the Thus, the requirement is fulfilled that the deflection system for the deflection parallel to the ribbon-shaped beam, that is to say the ii-direction (coil system shown in Figs. 10.1 and 10b) has apredorninantly positivefi current flows through the two sets of four coil packages. When the equilibrium of the bridge is disturbed, one set of packages is traversed by a current greater than that traversing the other. 7 As before, the coil 59 is arranged in such manner that the deflection of the beam is not influenced by it.

What is claimed is: I

1. In combination; a cathode-ray tube having a substantially planar electron-receiving screen extending substantially at right angles to the longitudinal axis of the tube and means including a plurality of electron guns for producing a common electron beam having a substantially ribbon-like shape along the axis of said tube;

13 and electromagnetic deflection'means'located between said electron guns and said screen for produci'nga deflecting field within the tube for deflecting said electron beam in two substantially perpendicular directions, whereby said beam may be caused to scan said screen, said ribbonshaped beam having a longer and a shorter dimension both at right anglesto one another and to the axis of the tube, said longer dimension of said beam extending parallel to one direction of deflection of the beam at said deflection means, said deflection means producing a deflection field causing the electron beam to form a linear cross-section perpendicular to said one direction of deflection and located in the meridional image plane which is substantially coincident with the surface of said screen, and to form a linear cross-section parallel to the other direction of deflection and located in the sagital image plane which is also substantially coincident with the surface of said screen.

2. In combination; a cathode r'ay tube having at one end a substantially planar electron-receiving screen extending'sub stantially at right angles to the longitudinal axis of the tube and at the other end a plurality of electron guns each producing a stream of electrons directed at said screen, said electron guns being located adjacent one another and extending substantially in a common plane, thereby jointly producing an electron beam having a substantially ribbon-like shape along the axis of said tube; means intermediate said guns and screen for producing a field for focussing said beam onto said screen; and electromagnetic deflection means located between said electron guns and said screen for producing a deflecting field within thetube for deflecting said electron beam in two substantially perpendicular directions, whereby said beam may be caused to scan said screen, said ribbon-shaped beam having a longer and a shorter dimension both at right angles to one another and to the axis of the tube, said longer dimension of said beam extending parallel to one direction of deflection of the beam at said deflection means, said deflection means including two sets of coils each producing a deflection in one of said two perpendicular directions and each producing a different field distribution within the tube, the one set of coils producing thedefiection field in saidone direction of deflection'of the beam establishing a field distribution within the tube causing the beam to form a linear cross-section perpendicular to said one direction of deflection and located'in the meridional image plane which is substantially coincident with the surface of said screen, the other set of coils establishing a field distribution within the tube causing the beam to form a linear cross-section parallel to the other direction of deflection and located in the sagital image plane which is also substantially coincident with the surface of said screen.

3. In combination; a cathode-ray tube having a substantially planar electron-receiving screen extending substantially at right angles to the longitudinal axis of the tube and a plurality of electron guns each producing a stream of electrons directed at said screen, said electron guns being located adjacent one another and extending substantially in a common plane, thereby jointly producing an electron beam having a substantially ribbon-like shape along the axis of said tube; and electromagnetic deflection means located between said electron guns and said screen for producing a deflecting field within the tube for deflecting said electron beam in two substantially perpendicular directions, whereby said beam may scan said screen, said ribbon-shaped beam having a longer and a shorter dimension both at right angles to one another and to the axis of the tube, said longer dimension of said beam extending parallel to one direction of deflection of the beam, wherein said tube axis corresponds to the z axis of a rectangular system of coordinates, said one direction of deflection corresponds to the ij axis and said other direction of deflection corresponds to the x axis,

oII( 'i- Z I- 0 and in which the integral is substantially zerofor both field components, "where the coefficients H Hb H and H are functionsof'z and Z is the coordinate of the end of the deflection means remote from the screen, Z is the coordinate of the end of the deflection means adjacntthescreen, and z is'the distance between the screen and'the coordinate z the value of the term at the end of said coil systemadjacentsaid screen being positive and the value of the term at said end being negative,- said term having an absolute value which exceeds the absolute value of the term where the coefficients H ,H H H are determined by measuring the x-component Hx of the'magnetic field in the plane x=0 at a particular ij-point and substituting in the equation H =H +H ij and by measuringithe ij-component H of the magnetic fieldin the plane ij=0 at a particular x-point and substituting in the equation H H -l-H x whereby the meridional image plane for said one direction of deflection produced by said deflecting field is substantially coincident with the surface of the screen, and the sagital image plane for the other direction of deflection produced by said deflecting field is also substantially coincident with the surface of the screen.

4. In combination; a cathode-ray tube having a substantially planar electron-receiving screen extending substantially at right angels to the longitudinal axis of the tube and means including a plurality of electron guns for producing a combined electron beam having a substantially ribbon-like shape along the axis of said tube; and electromagnetic deflection means located between said electron guns and said screen for producing a deflecting field within the tube for deflecting said electron beam in two substantially perpendicular directions, whereby said beam may be caused to scan said screen, said ribbon-like beam having a longer and a shorter dimension both at right angles to one another and to the axis of the tube, said longer dimension of said beam extending parallel to one direction of deflection of the beam at said deflection means; said deflection means including first and second ferromagnetic annular members surrounding the tube with the second member being closer to the screen than the first member, a first coil system for deflecting said beam in said one direction of deflection comprising a first set of four coils wound toroidally on the first an- 15 nular memberand a second set of four coils wound toroidally on the second annular member, a second coil system for deflecting said beam in the other direction comprising a third set of four coils Wound toroidally on the first annular member and a fourth set of four coils wound toroidally on the second annular member, two

coils of each set of four coils being mounted substantially diametrically opposite one another and being connected so as to be traversed by deflection currentin opposite senses, whereby said deflection means produce a deflection field 'in which the meridional image plane for said 7 one direction is substantially coincident with the surface of said screen, and the sagi-tal image plane for the other direction of deflection is also substantially coincident with the surface of said screen.

5. The combination set forth in claim 4 wherein the angles subtended by adjacent coils of each set traversed tion of an impedance and the two sets and their associated portion of the impedance are connected in parallel, said impedance being variable to control the relative magnitude of the current through the coil sets.

8. The combination set forth in claim 6 wherein the coils of both sets are connected in series, and all the coils are connected in parallel with a variable impedance, an intermediate portion of said impedance being connected to the junction of the two sets of coils.

9. In combination; a cathode-ray tube having a sub stantially planar electron-receiving screen extending-substantially at right angles to the longitudinal axis of the tube and means including a plurality of electron guns for producing an electron beam having a substantially ribbonlike shape along the axis of said tube; and electromagnetic deflection means located between said electron guns and said screen for producing a deflecting field within the tube for deflecting said electron beam in two substantially perpendicular directions, whereby said beam may be caused to scan said screen, said ribbon-like beam having a longer and a shorter dimension both at right angles to one another and to the axis of the'tube, said longer dimension of said beam extending parallel to one direction of deflection of the beam at said deflection means; said deflection means including a first pair of coil halves diametrically surrounding the tube for deflection in said one direction and a second pair of coil halves diametrically surrounding the tube between and symmetrically relative to the first pair for deflection in the other direction, the coils of said first pair having a shape producing a field at which the value h measured at the coil ends adjacent the screen is positive, the coils of said second pair having a shape producing a field at which the value h at said coil ends is negative and has an absolute value higher than the h for said first pair, wherein -3+4 cos :1

R R is the radius from the tube axis to the coil halves, and 11/ is equal to one-quarter of the angle of the tube not embraced by the coil halves, said two pairs of coil halves producing a field wherein the integral first pair having its wide end adjacent the screen and with the second pair having its narrow end adjacent the screen,

the non-parallel sides of the trapezoidal coil halves of the second pair defining a larger angle than that of the first pair.

' References Cited in the file of this patent I UNITED STATES PATENTS V 2,165,028 Blumlein July 4, 1939 2,170,944 Glass et a1. Aug. 29, 1939 2,172,733 Federmann et al Sept. 12, 1939 2,455,171 Haantjes Nov. 30, 1948 2,595,548 Schroeder May, 6, 1952 Neeteson Nov.,4, 1952 STATES PATENT OFFICE Certificate of Correction Patent No. 2,866,125 December 23, 1958 Johan Haantjes et a1.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, lines 52 and 53 should read m shown below instead of as in the patent- HA2, ij,?z)=H (x, ijfz) =H,(w,-'ij,tz) H,,(z, 'ij, z)=-H,,(m, t'j, z)==-H,,(x, -ij, 2) lines 69 to 71, should read as shown below instead of as in the patentcolumn 4, line 7, for T, read --H,--; line 8, strike out HQ/ 3; line 58, for =0, final occurrence, read =o:--; column 7,1me 64, for t at portlon of the equation reaading A X, read +A,,X,; column 10, line 63, for it assumed read -it is assume Signed and sealed this 28th day of April 1959.

Atheist: T. B. MORROW, ROBERT C. WATSON, Attesfing Oficcv. H I Commissioner of Patents.

UNITED STATES PATENT OFFICE Certificate of Correction Patent No. 2,866,125 December 23, 1958 J ohen Haentjes et el.

It is hereby certified that error appears in the printed specification of the above numbered atent requi g correction and that the said Letters Patent should read as correcte below.

Column 3, lines 52 and 53 should read as shown below instead of as in the patent- A j,-? 20% if z( ifi HUGE: 0 lj("' 1 'jr l!( i .7 lines 69 to 71, should read as shown below instead of as in the patent- I III )x +z1;zi

3 6 column 4, line 7, for T, reed --H,; line 8, strike out Hgz""+ line 58, for

o, final occurrence, read =o:-; column 7, line (it, for t at portion of the equat1on reading AX, reed +A,X,; column 10, line 63, for it assumed read -it is assumed--.

Signed and sealed this 28th day of April 1959.

Attesfi: T. B. MORROW, ROBERT C. WATSON, Atteszxing Ofliaer. Commissioner of Patents.

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