US2936400A - Compensation device for misaligned deflection plates in cathode ray tubes - Google Patents

Description

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. ATTORNEY 'Y Unit v tteS Thomas H. Tatham, Jr., San Diego, Calif., assignor to General Dynamics Corporation, Rochester, NY., a fcorporation of Delaware Application September 30,` 1958, Serial No. v764,388

' .s claims. (Crais-24) The present invention pertains to a compensation device for misaligned electrostatic deflection :plates in cathode'ray ytubes and more jspeciiically, concerns anY electrical circuit which substantially eliminates' distortion in cathoderay tube displays causedi by electrostatic plates not being properly aligned.

vIn'cathode ray tubes, the electro-responsive screen`,.on Whichthe electron `beam creates image displays, may be referred to in terms of an X-Y coordinate plot, with the X'axis called the horizontal axis and the Y axis called the vertical axis. Electrostatic deliectionv plates vpositioned in pairs in a `quadrature arrangement `in the neck of cathode ray tubesfuriction to deect the `electron beam .relative to the screen along the aforesaid Ahorizontal axis or .vertical axis or in combinations of the two. Each plate cfa pair `of electrostatic deflection plates, when Icorrectly aligned, lies in a plane that is parallel with but `displaced from lthe other plate of the respective pair. The vpairof plates are normally positioned at a 90 angle with another Vpair of plates giving the quadrature arrangement; This normal arrangement of pairs of electrostaticdeflection plates is shown in Patent No. 2,829,302 to Thomas Tatharn and assigned to the common assignee hereof. y

.In Ainserting and securing pairs of electrostatic -plates in the neck of cathode ray tubes, it is many -times diflicult to correctly align the pairs Aof plates so that the respective planes of each pair `are vat the desired 90 angle -to the plane of the other pair, thereby giving the quadrature relationship. This diculty arises because minor misalignment of the plates may only become apparent after the cathode ray tube is completely assembled and operatving, at which time the plates are Vinaccessible for adjustment. The misalignment condition that is normally tencountered is where one pair of plates lies in a plane 'that is at an angle other than v90 Vwith respect to the com-A mon -plane of the -other pair of plates. This causes the quadrature relationship of the pairs of plates to have a rhombicorientation rather than a Vsquare orientation. When 'the pairs of electrostatic deflection plates have 'a ,rhombic relationship they are then incapable, through normal separate signal control, of correctly deecting an electron beam along either the horizontal or vertical "axis of the cathode ray tube, 'or combinations of the two.

y ing displays, such misalignment of electrostatic deflection plates can cause the displayed picturey to 'have a slanted appearance, since the electron .beam may not be deflected on a true vertical or horizontal axis line. In the type of .cathode ray .tubes known as shaped beam v cathode ray tubes, the misalign'ment of electrostatic de-` `response to changes in the deection potential applied ectionjplates lcan bek extremely detrimental as it`causes' distortions in the display of 4thejcharacter images.

Shaped beam cathode'ray tubes use 'an electronbeam f i that has .a relatively* largeA cross-sectional area=which`is shaped by a beam shaping matrix into character images; I

This character shaped electron beam whenV contacting the electro-responsive screen causes an image bnl-the screen to be illuminated having the character shape.

Should an Yelectron beam of the shaped beam type be de 'llected by misaligned electrostatic deflection Vfplates, the

character image of the. electron beam will be rolled over, slanted or otherwisel distorted, and will, accordingly,

cause to -be displayed on th'e screenrofl the tube adistorted character image .which may have the' general shape of a parallelogram for `rhombic iigurel This', ofcourse, is detrimental to the qualityof ithe display as-it-dis'- tracts vfrom its vlegibilityA and desirability. Acoordiingly,v i. a need exists for Vthe present invention to provide a'. sim'- ple circuit arrangement capable of correctingthismisa alignment 'ofthe electrostatic deection plates, inasmuch as it is quite diicult to provide correctlyalig'ned electrostatic deflection plates in the neck of thecathode ray tube and `still maintain large volumepproduction of such tubes. vide .acircuit to. bel used in Acombination with cathode ray'tubes that is capable of substantially eliminating ydis;V tortions that Amay occur from electrostatic `dellection plates that are not properly aligned. y f

In accordance with the present-invention, whenv the condition exists in a `cathode ray tube wherein-oneV pair of electrostatic deflection plates is positioned askew, circuit means are provided which supply a correcting potential to the misaligned plates creating an electrostatic eld between the plates 4capable of deecting the ,electron f beam in 'a'manner as `if the'` plates were correctly aligned'.

The circuit means includesa summing amp'lirer circuit that may be placed in one of the lines carrying the control signals from the source to the deflectionplates.l This circuit means receives the control signals that would norv mally be applied to the Tdeilection plates and"provides a corrected potential output to the misaligned pair'of plates having a magnitude which compensates, in deecting the beam, for the misalig'nmen't of the electrostatic plates. The corrected potential has a magnitude that reilects changes in the magnitude of the controly signals supplied to the other pair of electrostatic deilection plates, which plates taken with the misaligned pair comprises the aforesaid quadrature arrangement. `A potentiometer means is incorporated in this circuit means for providing selective adjustment of the magnitude of the signal received b y the misaligned pair of plates in to the other set of electrostatic delection plates. Accordingly, in the present invention voltages may be sclectively ta-ken from the signals applied to one `set of plates and added to the signals applied tothe other incorrectly aligned set of plates, thereby correcting the resultant deflection of the electron beam by the incorrectlyV Figure 1 is a perspective view of a shapedr beam cathode ray tube;

Figure 2 is a schematic Villustration of thel circuit ar rangement for practicingthe present invention;V and Figure 3 illustrates the display screen of a cathodewrayl` Patentedl May l0, 19610 It .is accordingly an Aobject of this-inventionpto pro-V tube with the distorted display and the corrected display illustrated thereon.

Referring more particularly to the drawings, wherein like reference numerals refer to the same parts throughout the several views, in' Figure 1, a cathode ray tube 5 of the shaped beam type is-shown. This type of tube utilizes electrostatic deflection plates for deiiecting the electron beam at several points along its path from the beam generating and projecting unit 14 to the electroresponsive screen 13 in a manner disclosed in Patent No. 2,735,956, issued to Joseph T. McNaney and assigned to the same assignee hereof. Shaped beam tubes project a diiused type electron beam which, because of its relatively large cross sectional area, may be shaped to desired character images. Because the electron beam normally has a larger. cross sectional area than that encountered in ordinary cathode ray tubes, the misalignment problems in placing electrostatic. deflection plates in shaped beam cathode ray tubes is greater. Further inasmuch as the electron beam is shaped into character images the misalignment of electrostatic deflection plates can result in a slanted character image on the screen of the tube which is obviously undesirable. In tubes of this type as well as other cathode ray tubes, sets of electrostatic plates such as sets 6, 7 and 8, function to deflect an electron beam in an X, Y plane that is perpendicular to the longitudinal axis of the tube. These sets of plates may be utilized to deflect the electron beam at selective points along the neck of the tube or for iinally positioning the beams point of impact with the electro-responsive screen 13.

The misalignment condition of a set of plates will result in a detiection of the electron beam, when the electrostatic plates receive the correct potential, in a manner causing distortion in the nal display on the screen of the cathode ray tube. With reference to Figure 2, the electrostatic deflection plates shown schematically therein are in a normally encountered position of misalignment wherein the pair of electrostatic plates 11 are in the correct horizontal alignment and electrostatic plates 12 are misaligned in a direction oblique to the desired vertical deflection line.

When the electron beam is projected from the beam generating means 14 in a path along the longitudinal axis of the cathode ray tube and is deiiected by the misaligned plates 12 as shown in Figure 2, which could also be the pair of the set of plates 8 shown in Figure l, the beam will be deected correctly along the horizontal line 15. However, when the beam is deected by correctly aligned plates 11, it will be deected incorrectly along line 17 in the vertical direction. Therefore when the beam is deected in a vertical direction in any of the four X, Y, quadrants it will be deflected at an angle to the vertical axis 16 that corresponds substantially to line 17. The degree of variance from the vertical line 16 is dependent upon the amount of misalignrnent of the misaligned plates. The deection of the beam along the horizontal line 15 will be substantially correct inasmuch as electrostatic deflection plates 11 are positioned parallel to the horizontal axis line 15. Therefore, when the beam is caused to be deflected in a horizontal direction by a voltage change on electrostatic deection plates 12 only, it will maintain its correct position in a horizontal plane because it will maintain the same relative spacing between the plates 11 in its horizontal path, and the deflecting influence of the eld between plates 11 will remain the same. However, when the electron beam is deflected in a vertical direction by a change in the potential on electrostatic plates 1.1, the beam will be caused to be moved not only in a vertical direction, but also to a certain degree in a horizontal direction, giving a resultant direction Vof deflection that lies substantially along line 17. This condition results inasmuch as the beams relative distance between plates 12 is moving in a direction other than the vertical direction along line 16. Thus for the volts to 12 volts.

beam to maintain the same potential relationship between plates 12, it must move on a line substantially parallel to the plates 12. Accordingly, it may be expected when the plates are misaligned as shown in Figure 2, that any direct deection in the vertical direction will not follow a vertical path but ratherwill follow a path substantially parallel to the misaligned plates.

The circuit arrangement disclosed in Figure 2 operates substantially as follows. Control signals are supplied in the form of voltages to the electrostatic deection plates 11 and 12 from the source of control signals as shown. The normal supply voltage signal that would be supplied to electrostatic deiiection plates 12 from the source of control signals, if they Were correctly aligned, is the voltage E1 which is supplied'to line 19. The normal supply voltage supplied to electrostatic plates 11 is the potential E2 which is supplied to line 18. Since the plates 12 are misaligned, as shown in Figure 2, the beam when deflected moves in a vertical direction along line 17. To correct this, circuitry including a summing amplifier 24 is inserted into the line 19. The summing amplifier 24 operates as stated on page 664, Figures l849 in Electronic and Radio Enigneering by Frederick E. Turman, published by McGraw-Hill in 1955, and is capable of summing two or more voltage waves and providing an output voltage that is proportional to the sum of the independent voltages supplied to the summing amplilier. Because of the feed-back arrangement in the summing amplifier, it constitutes substantially a zero impedance. Accordingly, the output voltage is substantially immune to minor variationsV in changes in the input Voltage.

Voltage El is supplied to the summing amplifier through limiting resistor 2i) as voltage E4. A portion of voltage E2, that is supplied directly to the horizontal deflection plates 11, is tapped off by potentiometer '21 providing a voltage E3 through limiting resistor 23 to the summing amplilier 24. By varying potentiometer 21, the magnitude of the potential E3 may be varied as desired. Generally the limiting resistors 20 and 23 have substantially the same resistance valves. The output voltage E5 to the misaligned plates 12 has a magnitude that is proportional to the sum of input voltages E3 and E4. Accordingly, the potential on electrostatic plates 12 is dependent upon the input potential El and the tapped off voltage E3. Inasmuch as the tapped ott voltage E3 is proportional `to the magnitude of the voltage E2 in line 18, the voltage E5 thus reects any changes in the potential E2 that is applied to electrostatic deflection plates 11.

For example if initially the drop across the pair of plates 11 is 10 volts and the drop across the pair of plates 12 is 10 volts, the electron beam may be caused to strike the screen 37, see Figure 3, of a cathode ray tube at point 31. If in this situation the potential drop across plates 11 is increased to 20 Volts and the potential across plates 12 held at 10 volts, the beam would then strike the screen 37 at point 32. However, in accordance with the invention, the aforesaid circuit arrangement would cause the voltage drop across plates 12 to increase from 10 This increase would cause the electron beam to strike the screen at point 33, which, as desired, is along the vertical axis. Therefore, when the potential on electrostatic deflection platesv 11 is increased, the potential on electrostatic deection plates 12 is also increased. Conversely when the potential on electrostatic deection plates 11 is decreased, the potential on electrostatic deflection plates 12 is also decreased.

The aforesaid circuit and voltage arrangement causes the electron beam to be deilected in a correct vertical direction 34 and horizontal direction 35, as shown in Figure 3, rather than along the oblique line 36 with the accompanying distortion in the character images.

In Figure 2 if E5, the potential applied to electrostatic deilection plates 12, is varied byvarying E1 and E2 is held constant, the beam will then be deilected in a horizontal direction with no change in its deflection resulting from the addition of the voltage E3 inasmuch as potential E2 has not been altered. However, Yif the potential E2 is variedand potential E1 remains constant, the output voltage E5 is then varied in'magnitude in proportion to the change of the potential magnitude E2, which results v rin E5 being increased in accordance with the increase in Y'value of potential E3.

Potentiometer 21 provides an external and easily accessible means for varying the value of E3 and thus establishing by direct view of the screen converse could be true where the vertical plates 11 would be misaligned and the horizontal plates 12 would be in a direction parallel to the vertical'line 16. Also, the device would .operate when both the horizontal and vertical plates may be misaligned at which point two summing amplifiers would be present, one in each of lines A18 and 19 and could be so correlated as to provide a correct vertical and horizontal deection of the beam regardless of the potential applied to the respective plates.

Obviously many modifications and variations of the f present invention are possible in the light of the above'k teachings. 'It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise Ythan as specically described.

.I claim:

1.`In a cathode ray tube display system wherein an electron beam is deected to predetermined positions on the screen of the cathode ray tube in accordance with X-Y potentials being applied to pairs of electrostatic deilection plates when one of the pairs of plates may be positioned askew, the improvement comprising adjustable ysumming amplier means for varying the potential supplied to the askew pair of plates in response to variations inthe magnitude of the potentials applied to the other pair of said deflection plates.

f 2. In a cathode ray tube display system wherein an electron beam is deflected to predetermined positions on the screen of the cathode ray tube in accordance with deection potentials being applied to pairs of electrostatic deflection plates from a source of control signals, when one of the sets of plates may be positioned askew, the improvement comprising summing ampliiier means for receiving potentials from said source of control signals and providing an adjustable output signal to said askew set of deflection plates, said output signal Ahaving a magnitude corresponding to the sum of the magnitude of the signal normally applied to the askew deflection plates from said source of control signals andthe magnitude of a second pulse which varies inl accordance with the magnitude of the potential applied to said other set of plates Y from said source of control signals but of a lesser ratio of magnitude, a potentiometer being positioned between said other setv of deection plates and said summing amplier for selectively adjusting the magnitude of said I signal received from said other deflection plates in responsevto the change in the deection potentials applied to said other set of said deiection plates.

x3., In a cathode ray tube display system wherein an electronbeam is deflected to predetermined positions on j the-screen of the cathode ray tube in accordance with amplifier means responsive to the magnitude of Vdeflection control signals supplied to said correctly aligned pair of deection plates for applying a corrected deilection signal magnitude to said pair of askew plates. l t

4. In a cathode ray tube display means having deilection means responsive to control signals for deecting an electron beam to predetermined positions on the screen of a cathode ray tube wherein the deilection means in cludes two pairs of electrostatic deilection plates .posif tioned in the form of a rhombus with one'pair having' substantially a correct alignment and the other pair' having an incorrect alignment, the improvement compris-- ing a summing amplifier for combining a portion of a control signal to said correctlyV aligned plates with a control signal to said incorrectly aligned plates, providing an output signal to said incorrectly aligned plates having a magnitude that varies in accordance with the deilection magnitude of said control signal to said incorrectly aligned plates and the magnitude of the deflection signal to said correctly aligned plates.

`5. In a cathode ray tube having beam generating meansfor generating and projecting an electron beam toward an electro-responsive screen and deflection means for de ecting said beam, said deflection means including a.

pair of misaligned electrostatic plates and a pair of cor-- rectly aligned electrostatic plates, a source of first control signals lfor supplying separate deection signals to eacht of said pairs of plates, summing ampliier meansresponsive to the magnitude of control signalsfto'both ofsait pairs of deection plates for providing second control signals to said misaligned pair of plates having a magnitude that varies with the magnitude of said first control signals to both of said pairs of plates.

6. In a system lfor displaying characters on screens of cathode ray tubes including a shaped beam cathode ray tube having deilection plates for positioning a shaped electron beam relative to the longitudinal axis of said shaped beam cathode ray tube, the improvement comsignals to one of said plates of said -deection means, said control signals having a magnitude that varies in correspondence with the magnitude of the control signal applied to other of said deection plates.

7. In a cathode ray tube display system wherein an electron beam is deflected by pairs of electrostatic detlection plates in accordance with X-Y potentials being applied to said pairs of electrostatic deflection plates positioned in quadrature when one of said pairs oflplates may be positioned at an angle other than 96 relative to the other of said pairs of plates, the improvement comprising summing amplifier means for varying the potential applied to one pair of said platesin proportion to variations in the magnitude of potentials applied to the other pair of said deection plates for causing said electron beam to be dellected in a ydesired X-Y plot irrespective of angular positioning of one of said pair of plates v relative to the other of said pair of plates.'

8. In combination a cathode ray tube display system having electrostatic deflection means for deflecting an electron beam, said deflection means being positioned in misalignment, summing amplifier means for receiving portions or control signals supplied to said ldeflection means for providing new control signals to said deilection means, said deliection means in response to said new control signals deecting said beam in a manner similar to that deflection of an electron beam that would occur if said deection system had been correctly aligned.

References Cited in the le of this patent UNITED STATES PATENTS 2,244,748 Walker Iune'lO, 1941 2,496,283 Gall Feb. 7, 1950 2,600,463 Bertein June 17. 19521

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