US3760698A

US3760698A - Light exposure apparatus for forming fluorescent screens of color picture tubes

Info

Publication number: US3760698A
Application number: US00186217A
Authority: US
Inventors: T Fujimura
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1970-10-17
Filing date: 1971-10-04
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25
Also published as: GB1374124A; NL7114214A; DE2151519B2; DE2151519A1

Abstract

The disclosed apparatus includes a point source of light irradiating progressively the face plate for shadow mask color picture tubes from one end to the other through a slit on a douser reciprocating in parallel with the face plate. For forming phosphor dots of the particular color, the slit elongates in a direction to displace the corresponding gun from the tube axis and reciprocates perpendicularly to that direction at a higher rate for the central portion than for the lateral edge portions of the face plate. In synchronization with the movement of the slit, the light source depicts a closed curve as determined by the shape and speed of movement of the slit.

Description

United States Patent Fujimura Sept. 25, 1973 [75] Inventor: Takeo Fujimura, Kyoto, Japan [73] Assignee: Mitsubishi Denki Kabushiki Kaisha,

Tokyo, Japan 22 Filed: Oct. 4, 1971 [21] App]. No.: 186,217

[30] Foreign Application Priority Data UNITED STATES PATENTS 3,259,038 7 i9 66 Burdick 95/1 Primary ExaminerJohn M. Horan Att0rneyE. F. Wendcroth et a].

[57] ABSTRACT The disclosed apparatus includes a point source of light irradiating progressively the face plate for shadow mask color picture tubes from one end to the other through a slit on a douser reciprocating in parallel with the face plate. For forming phosphor dots of the particular color, the slit elongates in a direction to displace the corresponding gun from the tube axis and reciprocates perpendicularly to that direction at a higher rate for the central portion than for the lateral edge portions of the face plate. In synchronization with the movement of the slit, the light source depicts a closed curve as determined by the shape and speed of movement of the slit.

7 Claims, 18 Drawing Figures PMENTEU W255" FIG. 4

' FIG. 50

TAKEO FUJ [MURA ATTORNEY TAKEO FUJIMURA,

O 1: INVENTOR FIG. 6b

' ATTORNEY s LIGHT EXPOSURE APPARATUS FOR FORMING FLUORESCENT SCREENS OF COLOR PICTURE TUBES BACKGROUND OF THE INVENTION This invention relates to a light exposure apparatus for forming the fluorescent screen of color television picture tubes.

Color television picture tubes include a face plate the internal surface of which should have formed thereon a mosaic of different-color phosphors in the form of dots or strips. One serious problem encountered in disposing such a mosaic of phosphor dots or strips on the face plate is to substantially eliminate or minimize the mis-register for phosphor dots, that is, the deviation of the actual position of each phosphor dot or its equivalent from the desired position in which a corresponding beam of electrons is to land. In the past, a photographic technique has been generally utilized to form the particular mosaic of different-color phosphor dots on the internal surface of the face plate of color picture tubes by having a correction lens of special structure disposed on an optical path along which a beam of light travels toward a phosphor layer with a suitable photosensitive material disposed on the internal plate surface. This method has been theoretically impossible to fully compensate for the mis-register for phosphor dots throughout the entire surface of the face plate so long as the correction lens has a smooth surface or surfaces. In addition, it has been difficult to form such a correction lens even though it would have a curved surface or surfaces effecting a relizable or compromised correction because the curved surface or surfaces would be required to be complicated in curvature, that is, aspherical or asymmetrical. This has resulted in the use of expensive jigs for forming the lens and has made it impossible to adjust the particular curvature simply by varying the specification of the lens.

Also in color picture tubes of the three gun type, ex

. posures for red, blue and green phosphor dots must be effected through respective correction lenses which are required to be essentially different in configuration from one another. In addition, color picture tubes of higher performance could be generally manufactured only after experimental color picture tubes and correction lenses therefor had been repeatedly prepared with expensive cost and time.

On the other hand, any exposure to light is frequently required to be effected such that the exposure is more on the peripheral portion than on the central portion of the particular face plate. This is because, for example, in phosphor dot, shadow mask type color picture tubes, it is required to render the central portion of the face plate equal in a size of phosphor dot to the peripheral.

portion thereof in spite of the associated shadow mask including holes decreased in diameter from the central portion toward the peripheral portion of the face plate. For this reason, conventional exposure apparatus have included a neutral light filter on the optical path of the exposing light to suitably modify the distribution of the illumination on the face plate. Such a filter, however, usually has a transmission coefficient of 50 percent or less to that beam of light directed to the center of the face plate. This has resulted in the disadvantages that a proportion of the optical energy lost by the neutral light filter is increased to render the corresponding exposure time longer.

SUMMARY OF THE INVENTION It is another object of the invention to provide an exposure apparatus of the type as described in the preceding paragraph capable of satisfactorily correcting the mis-register through the use of an inexpensive correction lens of simple structure operatively associated therewith.

It is still another object of the invention to provide an exposure apparatus of the type as described in the preceding paragraph capable of readily changing the extent to which the mis-register is corrected.

It is a further object of the invention to provide an exposure apparatus of the type as described in the preceding paragraph capable of readily correcting the misregister with a minimum possible increase in exposure time.

It is an additional object of the invention either to eliminate the use of a neutral light filter previously employed to adjust the distribution of illumination on the screen or to simplify the construction thereof.

The invention accomplishes the above cited objects by the provision of a light exposure apparatus for forming a fluorescent screen of a color television shadow mask picture tube, comprising a face or screen plate for the color picture tube having coated on the internal surface thereof a photosensitive material containing phosphor layer, a shadow mask disposed oppositely to the internal surface of the face plate, and a point source of light disposed on that side of the shadow mask remote from the face plate, in addition a light shading plate is disposed between the shadow mask and the point source of light, the light shading plate including a strip-shaped slit therein, means are provided for reciprocating the light shading plate in substantially parallel relationship with the internal surface of the face plate so that a beam of light from the point source falls upon the phosphor layer on the internal surface of the face plate through the moving slit on the light shading plate to irradiate progressively the internal surface in a shape similar to that of the slit from one end to the other. I

Preferably, the light shading plate maybe disposed with respect to the face plate such that the slit has a lengthwise direction coinciding with a direction in which a particular one of the electron beam sources for stimulating that set of phosphor dots then to be formed is displaced from the longitudinal axis of the color picture tube.

Advantageously, the slit on the light shading plate may be of such a shape that the central portion is narrower in width than both end portions thereof while causing the light shading plate to be moved perpendicularly to the lengthwise direction of the slit at a higher rate for the central portion of the face plate than for the lateral edge portion thereof.- 7

BRIEF DESCRIPTION OF THE DRAWINGS The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic elevational view, partly in section of a light exposure apparatus constructed in accordance with the principles of the invention with a part broken away;

FIG. 2 is a perspective view of one portion of the apparatus shown in FIG. 1 with parts cut away;

FIG. 3a is a diagrammatic plan view illustrating relative positions of three guns to a face plate of a color picture tube;

FIGS. 3b through d are diagrammatic plan views illustrating the position and direction of movement of the slit on the light shading plate shown in FIGS. 1 and 2 with respect to the face plate shown in FIG. 3a for forming different-color phosphor dots;

FIG. 4 is a diagram useful in explaining the misregister for color picture tubes;

FIGS. 5a and b are view similar to FIGS. 3a and b respectively but illustrating a different arrangement of the three guns;

FIGS. 6a-6c are graphs illustrating the relationship between the shape and speed of movement of the slit shown in FIG. 3;

FIG. 7 is a perspective view of the details of the driving mechanism shown in FIG. 1 with parts broken away for the purpose of illustrating the internal construction;

FIG. 8 is a fragmental diagram illustrating in vectorial manner the mis-register at typical points on a fluorescent screen of a color picture tube formed by light exposure apparatus of the prior art type including a correction lens with the X and Y components of the vector also denoted;

FIG. 9 is a diagram similar to FIG. 8 but illustrating the mis-register obtained with another light exposure apparatus of the prior art type including a correction lens better in performance than that used with FIG. 8;

FIG. 10 is a diagram similar to FIG. 8 but illustrating the invention; and

FIGS. 11a and 11b are graphs illustrating a magnitude of movement of a particular point source of light relative to the slit of the present exposure apparatus used in plotting data shown in FIG. 10 withthe upper and lower portion representing movements along the X and Y axes respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings and FIG. 1 in particular, there is illustrated a light exposure apparatus for forming the fluorescent screen of color picture tubes in accordance with the principles of the invention. For the purpose of illustration only, the invention will be described in terms of the phosphor dot screen of shadow mask type color picture tubes but it is to be understood that the same is not restricted thereby or thereto. The arrangement illustrated comprises a framework 10 and a screen 12 for a color television picture tube fixedly secured in place to the framework 10 on the upper apertured wall surface by means of locating claws 14 one of which is shown in FIG. 1. The face plate 12 is pro vided on the internal surface with a light sensitive layer or coating 16 of a phosphor material of a particular color having mixed therewith a photoresist or a photosensitive material as for example polyvinyl alcohol suitably sensitized with ammonium dichromate, and a shadow mask 18 is disposed oppositely to the layer 16 with a suitable gap formed therebetween. This arrangement of the shadow mask 18 and layer 16 is well known in the art as shown by US. Pat. No. 3,259,038 to Burdick et al.

A correction lens 20 is disposed upon an apertured horizontal shelf transversing the interior of the framework 10 for the purpose well known in the art. Below the correction lens 20 and therefore the shelf there is disposed a light shading plate or douser 22 in parallel thereto. The douser 22 has an elongated window or slit 24 extending therethrough in a direction perpendicular to the plane of FIG. 1 and also one end, in this case, the righthand end as viewed in FIG. 1, mechanically connected through a pair of parallel arms 26(as best shown in FIG. 2) to a driving mechanism 28 disposed on the bottom of the framework 10. The driving mechanism 28 is operative to move the douser 22 and hence the slit 24 in the opposite directions shown at the double headed arrow in FIG. 1 at a predetermined speed and with a predetermined amplitude in the manner as will be described hereinafter. The douser 22 reciprocates in substantially parallel relationship with the internal face of the face plate 12.

A point source of light 30 has a casing 32 including therein a suitable electric lamp and a collecting lens system therefor(not shown). The source of light 30 is disposed above and mechanically connected through arm means 34 to the driving mechanism 28. The point source 30 emits a divergent beam of light toward the internal surface of the face plate 12. The driving mechanism 28 is also operative to move the point source of light 30 along a predetermined closed curve in synchronization with the reciprocating movement of the slit 24 in the manner as will be described hereinafter.

FIG. 2 wherein like reference numerals designate the components identical to those illustrated in FIG. 1 shows the positional relationship among the face plate 12, the douser 22 and the point source of light 30 with the face plate 12 and douser 22 partly broken away. For purposes of illustration only, the phosphor layer 16 on the internal surface of the face plate 12, the shadow mask 18 and the correction lens 20 are omitted from FIG. 2.

The divergent beam of light emitted from the point source of light 30 travels toward the face plate 12 but a great part thereof is interrupted by the douser 22 while a small portion thereof is permitted to pass through the slit 24 on the douser 22 as shown by the thin solid line labelled LIGHT BEAM in FIG. 2 until it falls upon the internal surface of the face plate 12 to form an image or a projected area of the slit 24 on that surface. That area or strip irradiated with light on the internal surface of the face plate 12 and, strictly, on the phosphor layer 16 is defined by two dotted lines and designated by the reference numeral 24 in FIG. 2. As above described, the driving mechanism 28 is operative to move the slit 24 on the douser 2 2 with respect to the internal surface of the face plate 12 in the opposite directions shown at the double headed arrow in FIG. 2. As a result, the internal surface of the face plate 12 in the form of a strip is progressively irradiated with light having a substantially uniform intensity averaged with time. Thus the entire area of the face plate 12 is substantially uniformly irradiated with the light.

It is now assumed that the slit 24 on the douser 22 elongates in parallel to the so-called horizontal central line of the face plate 12. Considering a Cartesian orthogonal coordinate system having its origin 0 positioned at the center of the face plate 12 and the x and y axes thereof disposed on the so-called horizontal and vertical central lines of the face plate, the .r y plane thereof lies in a plane generally determined by the face plate 12 and therefore in a plane parallel to the plane of the douser 22 and passing above the point source 30 from which the divergent beam of light originates. The

y axis extends in a direction in which the electro gun corresponding to phosphor dots to be printed is displaced from the longitudinal axis of the color picture tube. In operation, the driving mechanism 28 is operated to move the point source of light 30 in a plane parallel to the x y plane in synchronization with the reciprocating movement of the douser 22 and in the manner as will be described later. It is assumed thatwhen the point source 30 occupies its position having coordinates AX and AY with respect to another orthogonal coordinate system having the X and Y axes parallel to the x and y axes as above described and the origin 0 suitably selected, the center of the irradiated strip24 on the internal surface of the face plate has an abscissa (x) with respect to the x y coordinate system. This origin O is selected to coincide with a deflection center for an electron path from that electron gun for emitting a beam of electrons stimulating phosphor dots of the particular color being formed. Under these circumstances, the point source 30 has its position (AX, AY) capable of being expressed by functions f(x) and g(x) ofx. Those functions f(x) and g(x) can be mainly determined with experiments so as to minimize the misregister for phosphor dots in consideration of the optical characteristics of the correction lens as shown in FIG. 1.

Referring now to FIG. 3a, there is shown three guns 36 to be incorporated into the associated tube arranged at vertices of an equilateral triangle whose center lies on the longitudinal axis 0" of the picture tube or a normal to the internal surface of the face plate 112 at its center. The guns are respectively labelled B, G and R" and adapted to stimulate the blue, green and red phosphor dots in the well known manner respectively from which blue, green and red lights are emitted.

According to the principles of the invention, the slit 24 on the douser 22 has its lengthwise direction disposed in parallel relationship with a direction in which the center of that gun of the associated picture tube to stimulate phosphor dots of a particular color being formed has been displaced from the longitudinal axis of the tube while the slit is caused to reciprocate perpendicularly to that direction. For example, in order to form the blue phosphor dots, the slit 24 is disposed in parallel relationship with a direction in which the center of the blue gun 36 has been displaced from the tube axis 0 as shown in FIG. 3b wherein also the slit 24 is shown at the double heated'arrow as reciprocating perpendicularly to that direction or to the axis. Therefore the slit 24 reciprocates along the x axis as shown in FIG. 3b. From FIG. 3b it will be seen that the arrangement of FIG. 2 is used for printing the blue phosphor dots for color picture tubes including the three guns disposed as shown in FIG. 3a.

FIG. shows the position and direction of movement of the slit 24 relative to the face plate for forming the green phosphor dots with the associated green gun 36 displaced from the tube axis 0 along the y axis. Similarly FIG. 3d illustrates an arrangement suitable for forming the red phosphor dots wherein the associated red gun36 has displaced from the tube axis 0 along the y axis and the slit 24 is adapted to reciprocate perpendicularly to the y axis or in parallel to the x axis.

In FIG. 4 et seqq and the description therefor either of the cordir'iate systems as shown in FIG. 2 is used, as the case may be, only for the purpose of illustration.

FIG. 4 is a diagram corresponding to that shown in any one of FIGS. 3b, 0 and d excepting that the face plate 12 is of a circular profile with the slit omitted. For purpose of illustration, the polar coordinate system is utilized, in addition to the Cartesian orthogonal x y coordinate system as shown in FIG. 2. The mis-register as above described will now be discussed with reference to FIG. 4 in terms of those phosphor dots adapted to emit light having a selected one of the primary colors.

For any given point (r, 6) shown in FIG. 4, a magnitude of mis-register required to be corrected can be considered to approximate the vectorial sum of the following components:

A. a first component having a direction of G? and a magnitude expressed by a function of the radius vector r thereof alone;-

B. a second component having a direction of W and a magnitude expressed by a function of its radius vector r multipled by cosO where 0 is an angle between the y axis and the radius vector r;

C. a third component having a direction of (TF and a magnitude expressed by a function of the radius vector r multiplied by sinO;

D. a fourth component having a direction perpendicular to the w direction and a magnitude expressed by a function of the radius vector r multiplied by cos0; and

E. a fifth component having a direction perpendicular to the O P direction and a magnitude expressed by a function of the radius vector r multipled by sin6.

Among them, the first component is very large in magnitude and can be theoretically corrected to a null value by a correction lens. In order to completely correct the first component, the correction lens involved is generally required to include a rotation-symmetrical aspheric surface facing the face plate. However, the correction can be, in many cases, substantially satisfactorily accomplished with the spherical surface for practical purposes.

The second and third components are small in magnitude and can be substantially completely corrected in view of the theoretical standpoint. Either one of these components is possible to be relatively easily decreased to a negligible magnitude by modifying the deflection yoke used in operating color picture tubes. For practical purposes, the remaining one of the second and third components is possible to be sufficiently corrected through the use of a modification of the correction lens employed in correcting the first component wherein one of the opposite surfaces thereof is formed to undulate in apredetermined direction. For practical purposes in almost all cases, that correction may be substantially satisfactorily accomplished with the one surface of the correction lens formed into a plane merely tilted at a suitable angle to the plane normal to the optical axis of the lens.

The fourth component is as small as negligible in almost all cases and particularly for blue phosphor dots because the associated gun is disposed symmetrically with respect to a plane passing through the longitudinal axis of the color picture tube and the vertical central line of the face plate (see FIG. 3b).

The fifth component is not only large in magnitude after, the first component, but also of such a nature that in view of the theoretical standpoint it is possible to be scarcely corrected by a correction lens. If it is attempted to correct the fifth component by using a particular collection lens have a smooth surface, then the other component or components as above described and particularly the second component will tend to occur with the result that, in many cases, the overall characteristics of the resulting screen is rather deteriorated. In order to prevent this deterioration of the characteristics of the screen, it is necessary to design a special correction lens so that a considerable magnitude of the mis-register is evenly distributed over the entire area of the screen. This measure is not only subject to a certain limit but also a design of such a correction lens itself is troublesome. In addition, the correction lens thus designed will include an aspherical, asymmetric surface resulting in a complicated configuration and therefore the correction lens becomes very troublesome to be produced.

Upon developing a new type of color picture tube, it is generally required simultaneously to develop a deflection yoke used in combination with that type of color picture tube. The standard plan for developing a new type of color picture tube is alternately to improve the deflection yoke and color picture tube in repeated manner. Thus, for a given deflection yoke, it is required .to produce that color picture tube best matching in characteristics the yoke within a short period of time.

. Under these circumstances, the preparation of the parsion picture tubes. The convergence of three beams of electrons generally tends to be deteriorated particularly on the peripheral portion of the screen of the tube. If the particular deflection yoke is changed in design to improve the dynamic convergence then the resulting mis-register also varies. This will lead to the necessity of re-designing the correction lens previously prepared to be fitted to the preceding deflection lens. Furthermore, that type of the mis-register is most changed in connection with the dynamic convergence represented by the fifth component as above described. It is recalled that, the fifth component is most difficult to be corrected by the correction lens.

From the foregoing it will be appreciated that it is desirable to provide means for correcting only the type of mis-register represented by the fifth component as above described independently of the associated correction lens as far as possible while being able to readily change the magnitude of correction. This gives the basis on which there has been-determined the position and direction of movement of the slit on the douser relative to the face plate as above described in conjunction with FIGS. 3b through d. While this means alone can not serve to completely correct the fifth component of the misqegister in view of the theoretical standpoint, the results of experiments have indicated that color picture tubes having a considerably wide angle of deflection and capable of being put to practical use can be provided as long as one uses a more practical means for suitably moving a point source of light such as shown by 30 in FIG. 2 in both directions of the X and Y or x and y axes thereby to collectively correct the mean magnitude of the mis-register at each of the incremental strip-shaped areas of the face plate irradiated by the moving source through the moving dousers slit, the dominant component thereof being the fifth as above described. This measure is effective even with a considerably broad slit on a douser and with a correction lens having a simple structure rather than a complicated structure such as a rotation-symmetric, aspherical lens of asymmetry of rotation type.

While the invention has been described in conjunction with the formation of the fluorescent screen of color picture tubes including a triad of guns disposed at vertices of an equilateral triangle as shown in FIG. 3a it is to be understood that the same is equally applicable to color picture tubes including a triad of guns disposed in a pattern different from that shown in FIG. 3a. For example, the invention is equally applicable to color picture tubes including a triad of guns disposed in aligned relationship as shown in FIG. 5a wherein like reference numerals and characters designate the components corresponding to those shown in FIG. 3a. As an example, FIG. 5b is a view corresponding to FIG. 3b and illustrating the position and direction of movement of the slit 24 relative to the face plate 12 suitable for forming blue phosphor dots adapted to be stimulated by the blue gun 36 or the lefthand gun B as viewed in FIG. 5a among the three aligned guns 36.

The invention further contemplates to minimize the increase in exposure time required for the incremental strip-shaped area of the face plate by the provision of a dousers slit formed into a unique shape and effecting a unique movement relative to the face plate. This leads inevitably to the necessity of decreasing somewhat the width of the slit which is caused to increase the exposure time. However, it is desirable to render the exposure time as short as possible.

In general, the point source of light 30 as shown in FIG. 1 or 2 has a density of luminous flux which decreases from a high value on the central portion of the face plate 12 to a low value on the peripheral portion thereof, assuming that the douser and its slit are not disposed. On the other hand, the face plate is frequently required to be exposed to light such that the peripheral portion thereof is exposed to a larger quantity of light than the central portion thereof. This is because, for example, in phosphor clot, shadow mask type color picture tubes, a shadow mask involved includes holes decreased in diameter from the fact that the central portion toward the peripheral portion and notwithstanding theassociated screen is required to include phosphor dots having the same size on the central portion as on the peripheral portion.

For these reasons, conventional exposure apparatus of the type using no douser nor a slit have usually included a suitable neutral light filter disposed on the optical path of exposing light to control the distribution of illumination on the face plate. For example, a correction lens involved may have one surface evaporated with any suitable metal for this purpose. For deflection color picture tubes, this type of neutral light filter has normally a transmission coefficient of 50 percent or less to a beam of light directed to the center of the face plate. This means that a very large proportion of energy of light incident upon the entire area of the face plate is lost through the absorption by the light filter.

The invention also contemplates to minimize or substantially eliminate this loss of optical energy. To this end, the slit on the douser is caused to move with respect to the face plate to permit an incremental stripshaped portion such as designated by 24' in FIG. 2 of the face plate irradiated by the point source of light through the slit to pass at a higher rate through the central portion of the face plate and at a lower rate through the lateral edge portions thereof. Simultaneously, the width of the slit is gradually increased from its minimum value on the middle portion to its maximum value at each end. This arrangement permits either the elimination of the neutral light filter previously employed or the substitution of a neutral light filter high in transmission coefficient therefor resulting in a decrease in loss of optical energy caused from the light filter. Also the arrangement ensures that the exposure time is not very increased with a slit narrow in width.

It will readily be understood that the profile of the strip-shaped area such as shown by 24' in FIG. 2 on the face plate is approximately an enlarged replica of that of the slit on the douser. Therefore, assuming that the face plate is put in the position of the douser, the profile of the irradiated strip-shaped area of the face plate will now be discussed.

The point source of light commonly used in light exposure apparatus to which the invention is concerned has very often a pattern of density ofliminous flux having a symmetry of rotation and the necessary pattern of exposure required for the face plate is, in many cases, of rotation-symmetrical. On the other hand, neutral light filters can be easily formed having a consistency characteristic of symmetry of rotation. In many cases, therefore, .it is desirable to correlate the shape of the slit with the speed of movement thereof so that the resulting pattern of exposure on the face plate is of a symmetry of rotation.

FIGS. 6a c are useful in explaining the relationship between the shape and speed of movement of the slit. It has been found that with satisfactory results, the slit has a width W expressed by WS Km where K is the width of the slit at the central portion and A is a constant as will be described later(see curve 6c)and a speed of movement expressed by S, K A where S, is the reciprocal of the speed of movement of i the slit, and K is the reciprocal of that speed of movement at which the slit passes through the y axis or x= (see curve 6a). The shape of the slit thus determined is shown in FIG. 6b as resembling a cross sectional profile of a concave-concave lens symmetrical with respect to the axis orthogonal to the optical axis thereof.

With the slit shaped as shown in FIG. 6b, a quantity of light falling upon any point (x, y) on the face plate through the moving slit for an interval of time sufficiently long as compared with the period of time for which the slite effects one complete reciprocating movement is proportional to a quantity expressed by That is, the resulting pattern of exposure is of a symmetry of rotation.

The source of light has generally a pattern of density of liminous flux smoothly decreasing from the central portion of the face plate toward the peripheral portion thereof. By properly selecting the constant A appearing in the above equations, the substantially desired pattern of exposure can be obtained without the use of a neutral light filter such as above described. A neutral light filter low in consistency may be used only when the screen should be locally controlled to a slight amount.

Referring now to FIG. 7, there is illustrated one form of the driving mechanism 28 shown in FIGS. 1 and 2. In FIG. 7, the driving mechanism has been turned through an angle of 90 from its position shown in FIGS. 1 and 2 to have its bottom side illustrated as the front side and a housing therefor is partly broken away to illustrate the internal construction. The arrangement illustrated comprises a housing 40 having a top wall 42 and an operating shaft 44 journalled to the top wall 42 through a bearing 46 whereby the shaft 44 can tilt in every direction about a point A on the axis thereof. The shaft 44 has secured to one end, or the upper end when the mechanism 28 is in its normal position as shown in FIGS. l and 2, the lamp casing 32 including the point source of light 30(shown in phantom in FIG. 7). The lamp casing 32 may be of a square cross section and is provided on the lower side or that side on which the shaft 44 is secured, with an L-shaped bracket 48 having an elongated hole 50 disposed in that arm thereof extending in parallel to the shaft 44. On the other hand, a support member 52 suitably fixed to the top housing wall 42 is provided on the free end portion with a pin 54 loosely extendingthrough the elongated hole 50 in the bracket 48. The pin 54 has a longitudinal axis lying in a line perpendicular to the axis of the shaft 44 and passing through the point A whereby the lamp casing 32 is permitted freely to tilt about the point A but prevented from rotating about the axis of the shaft 44.

As shown inFlG. 7, the shaft 44 has an L-shaped control member 56 including a pair of

legs

58 and 60 extending perpendicularly to each other and to the axis of the shaft 44 and rigidly secured at the junction of both legs to the other end of the shaft as by a set screw. The

legs

58 and 60 have individual rods 62 and 64 projecting from the respective free ends substantially parallel to the shaft 44 and provided at the free ends with respective rollers 66 and 68 subsequently engaging cam plates 70 and 72 which will be described hereinafter. The rods 66 and 68 are normally forced in engagement with the peripheral surfaces of the respective cam plates 70 and 72 by the action of a tensioning spring 74 spanned between the other end portion of the shaft 44 and a suitable point on one side wall 76 of the housing 40 as shown in FIG. 7.

It is to be noted that, when inoperative, the shaft 44 has its longitudinal axis 0' somewhat displaced in parallel from the longitudinal'axis O of color picture tubes whose screens are to be formed by the apparatus disclosed herein. The position of the shaft's axis 0' relative to the tube s axis 0 depends upon the gun arrangement in the associatee color picture tube. That is, the axis 0' is positioned on the longitudinal axis of that gun adapted to stimulate phosphor dots of a particular color to be formed. Also the

legs

58 and 60 of the control member 56 are initially. arranged to extend along the X and Y axes as shown in FIG. 7 and also in FIG. 2 respectively.

A pair of elongated guide slots 78 and 80 are dis-.

posed in parallel relationship on the top wall 42 of the housing 40 also in parallel to the x axis and have individual support rods 82 and 84 corresponding to the connection arms 26 as shown in FIGS. 1 and 2. Both I rods 81 and 84 are rigidly secured at one end to the douser 22 on one end portion and at the other ends to a frame 86 movably disposed within the housing 40 so as to be guided within the guide slots 78 and 80.

A pedestal 88 is fixed on the side wall 76 so as to be spaced away from and opposite to the shaft 44. Then an electric motor 90 is disposed upon the pedestal 88 so that its rotary shaft 92 extends toward to the top housing wall 42 in substantially coaxial relationship with the shaft 44. The rotary shaft 92 has mounted thereon the cam plate 70 for controlling the movement along the X axis of the point source of light 30, the cam plate 72 for controlling the movement along the Y axis of the source 30 and a cam plate 94 for controlling the reciprocating movement of the douser 22 and therefore the slit 24 in spaced relationship and in the named order starting with the free extremity of the rotary shaft 92. As above described, the rollers 66 and 68 engage the camming surfaces of the cam plates 70 and 72 respectively. The cam plate 94 for the slit 24 is in the form of a cardioid and mounted on the rotary shaft 92 to engage a roller 96 disposed at one end of a rod 98 having the other end fixed to the front side as viewed in FIG. 7 of the frame 86. The roller 96 is maintained in engagement with camming surface of the cam plate 94 by the action of a tensioning spring 100 spanned between the frame 86 and a suitable point on the top housing wall 42. v i

In operation, the motor 90 is rotated to roll the roller 96 along the camming surface of the cam plate 94 whereby the frame 86 is moved along the guide slots 78 and 80 to move the support rods 78 and 80. This results in the movement of the douser 22 with the slit 24 along the x axis in the manner as determined by the cam plate 94. Since the cam plate 94 is in the form of a cardioid as above described, the slit 24 on the douser 22 is permitted to be moved in front of the face plate 12(not shown in FIG. 7) along the x axis at a higher speed for the central portion of the face plate and at a lower speed for the lateral edge portions thereof as long as the cam plate 94 is properly mounted on the rotary shaft 92 of the motor 80.

The rotational movement of the motor 90 also causes the cam plates 70 and 72 to move the

control legs

58 and 60 in their longitudinal directions orthogonal to each other in their limits as determined by the cam plates 70 and 72 respectively. Due to the resultant movements of both

legs

58 and 60, the shaft 44 is caused to rock about the point A on the axis thereof within a range predetermined through the engagement of the pin 54 with theelongated hole 50 as above described. Therefore the point source of light 30 connected to the end of the shaft 44 effects a rocking movement within that predetermined range about the point A and also in synchronization with the reciprocating movement of the slit 24 on the douser.22 controlled by the cam plate 94 thereby to depict a predetermined closed curve about the longitudinal axis The profiles of the cam plates 70 and 72 depend upon the movement of the slit 24 and the type of misregister to be corrected and can be experimentally determined to establish easily and exactly the movement of the source 30 relative to the slit 24.

The effectiveness of the invention will now be demonstrated with reference to FIGS. 8 through 10 wherein the mis-register is illustrated for blue phosphor pictures reproduced by deflection color picture tubes usually called the 19V type and including a triad of color guns arranged as shown in FIG. 30. Since the reproduced picture is bilaterally symmetric, the mis-register is illustrated only at various typical points on the righthand half as viewed in FIGS. 8, 9 and 10 in terms of both the vector and also the x and y components thereof whose magnitudes are denoted in mm beside the associated points. In these Figures, the x and y axes coincide with those shown in FIG. 2.

FIG. 8 shows the results of experiments conducted with a conventional exposure method of simultaneously irradiating the entire area of the face plate by a point source of light through a correction lens having a relatively simple structure in which that surface thereof facing the face plate is spherical and rotationsymmetric while the other surface is in the form of a plane tilted to the plane normal to the optical axis thereof. In other words, FIG. 8 shows a deviation of the actual position of the source of light from the desired position in a plane normal to the longitudinal axis of the color picture tube in terms of the vector and the x and y components in mm occurring in the case the correction lens as above described is used. With the actual position of the source precisely coinciding with the desired position at the center of the screen on the face plate, the actual position of the source at a point, for example, on the lower righthand corner deviated from the desired position at that point by 0.95 and 0.87 mm in the lefthand and lower directions as viewed in FIG. 8 or along the x and y axes.

FIG. 9 shows the results of experiments conducted with the conventional exposure mehod as above described utilizing an improved correction lens designed and constructed on the basis of the principles that the mis-register in the radial direction such as the GFdirection shown in FIG. 5 is minimized while that portion of the mis-register remaining theoretically uncorrected is put out of the effective diameter of the screen as much as possible(wich is subject to some limitation due to lens-making technique) and by calculating according to the method of least squares. The resulting lens was a complicated structure having an aspherical, rotationasymmetric surface.

In FIGS. 8 and 9 it is to be noted that in FIG. 8 the correction lens is of a compromised design so that it can be used with each of the red, green and blue guns included in color picture tubes of the type as above described whereas in FIG. 9 the correction lens One effective approach to decrease the overall ribute tydescribed in conjunction with FIG. 8 is utilized, the rface. thod of point source of light may be preliminarily displaced ute tycorrection lenses for trial will amount to about ten rface. thod of the invention using the same correction lens as above te tyby selective crystallization, and provides a novel process for the preparation of optically active serine. c6. A process as claimed in claim 1 further including the steps of dissolving, at elevated temperature, additional DL-serine m-xylene-4- sulfoante in mother liquor obtained after the recovery of said crystallized one of said enantiomers thereby producing another supersaturated solution, allowing crystallization to take place and recovering the crystallized other one of said enantiomers. is of a special design particularly suitable for correcting the blue phosphor dots alone. From a comparison of FIGS.8 and 9, however, it will be seen that the use of the correction lens as described in conjunction with FIG. 9 does not contribute to a very noticeable progress.

The use of a correction lens of complicated structure such as described for FIG. 9 yields a distribution of observed vectors for the mis-register considerably dependent upon the particular design thereof such as the minimization of the radial mis-register in the example of FIG. 9. The results of calculations have indicated that for each design, the calculated vectors for the misregister are not greatly different in magnitude from those shown in FIG. 8.

One effective approach to decrease the overall misregister is to keep the mis-register somewhat uncorrected at the center of the picture or screen. For example, the method of least squares can be utilized to reduce the overall mis-register to a mean magnitude which is as small as possible. Also when the correction lens as above described in conjunction with FIG. 8 is utilized, the point source of light may be preliminarily displaced from the correct position by a short distance. This measure gives a considerable result. While the correction shown in each of FIGS. 8 and 9 can be improved in this way, the result obtained has not been so different from that shown in each of FIGS. 8 and 9.

Furthermore, when using the correction lens as above described in conjunction with FIG. 9 is not only necessary to use a different lens for each color but each lens is higher in original cost of trial manufacture than that used with FIG. 8 by a factor from three to five times for each color. Therefore, the total cost required I and Y components AX and AY(see FIG. 2) respec tively of the movement of the source of light were first determined on the basis of the movement of the slit as above described in conjunction with FIG. 3b. FIGS. 11a and b show by way of example, the magnitudes in mm of those X and Y components of movement of the source in ordinate plotted against the movement in abscissa of the slit according to which the camming surfaces of the cam plates 70 and 72 were determined. Then the driving mechanism 28 as shown in FIG. 7 including the cam plates 70 and 72 thus determined was operated to obtain the data shown in FIG. I0.

By comparing FIG. 10 with FIG. 9, it will be apparent that the correction effect provided by the invention is excellent as compared with the prior art practice and also that the excellent correction effect results from the slit arranged with respect to the face plate and the source of light as shown in FIG. 3b.

In addition, it has been found that the correction effect similar to that shown in FIG. 10 is exhibited by the invention using the same correction lens as above described for each of the red and green phosphor data with the arrangements shown in FIG. 30 or d.

The correction for green and red has been most difficult to be effected on the upper, righthand and lower lefthand corners and the lower righthand and upper lefthand corners as viewed in FIG. 3a of the screen respectively because the deflection angle or the radius vector r as shown in FIG. 4 is wide or large and because the fifth component of the mis-register is large. The invention can effect the substantially complete correction on each of those corners of the screen which is one of the great advantages of the invention.

It is noted that, due to the width of the slit 24, the use of a particular point source of light effecting the movement as shown in FIGS. 11a and b does not always convert theoretically the distribution of mis-register as shown in FIG. 8 to that illustrated in FIG. 10. However, since the point source of light is arranged in many cases to be moved monotonously with respect to the moving slit as will readily be understood from the illustration of FIGS. 11a and b, it has been found that a deviation of the actual correction from the theoretical correction is negligible even with the width of the slit as broad as several tenths of the lateral dimension of the fluorescent screen.

While the invention has been illustrated and described in conjunction with a single preferred embodiment thereof, it is to be understood that numerous changes and modifications may be resorted to without departing from the spirit and scope of the invention. For example, the slit and the point source of light may be effectively moved by any suitable driving mechanisms rather than the cam mechanisms, for example, servo driving mechanisms. The correction lens as above described in conjunction with FIG. 8 may be modified to be suitable for use wth the invention. In the latter case, the resulting lens will include similarly a curved surface of simple configuration exhibiting the correction effect superior to that shown in FIG. 8.

What is claimed is:

I. In a light exposure apparatus for forming a fluorescent screen of a color television shadow mask picture tube, said screen being formed from a face plate for the color picture tube having a light sensitive layer containing phosphors coated on its internal surface and wherein a shadow mask is positioned opposite said internal surface of said face plate, the improvement comprising a point source of light disposed on that side of said shadow mask remote from said face plate, a movable light shading plate dsposed between said point source of light and said shadow mask, a strip-shaped slit disposed in said light shading plate, and means for reciprocating said light shading plate in substantially parallel relationship with respect to said internal surface of said face plate, so that a beam of light emitted from said point source of light falls upon the said internal surface of said face plate through said slit on the moving light shading plate to irradiate progressively the internal surface of the face plate in a shape similar to that of the slit from one end to the other.

2. A light exposure apparatus as claimed in claim 1 wherein said light shading plate is positioned with respect to said face plate so that said slit elongates in the direction in which the electron beam source for stimulating the particular phosphor portion being formed on said internal suface of said face plate is displaced from the longitudinal axis of the color picture tube.

3. A light exposure apparatus as claimed in claim 1 wherein said strip-shaped slit on said light shading plate has a width which increases from a small value at the center to a large value at each end thereof and wherein means are provided to move said light shading plate perpendicular to the lengthwise directionof said slit such that the slit is moved at a higher rate for the central portion of the face plate than for the lateral edge portion thereof.

4. A light exposure apparatus as claimed in claim 1, wherein a correction lens is disposed between said point source of light and said light shading plate for controlling the optical path along which the beam of light from the point source of light travels.

5. A light exposure apparatus as claimed in claim 1, wherein a correction lens is disposed between said light shading plate and said shadow mask for controlling the optical path along which the beam of light from the point source of light travels.

nisms being mounted on a common shaft.

Claims

1. In a light exposure apparatus for forming a fluorescent screen of a color television shadow mask picture tube, said screen being formed from a face plate for the color picture tube having a light sensitive layer containing phosphors coated on its internal surface and wherein a shadow mask is positioned opposite said internal surface of said face plate, the improvement comprising a point source of light disposed on that side of said shadow mask remote from said face plate, a movable light shading plate dsposed between said point source of light and said shadow mask, a strip-shaped slit disposed in said light shading plate, and means for reciprocating said light shading plate in substantially parallel relationship with respect to said internal surface of said face plate, so that a beam of light emitted from said point source of light falls upon the said internal surface of said face plate through said slit on the moving light shading plate to irradiate progressively the internal surface of the face plate in a shape similar to that of the slit from one end to the other.

3. A light exposure apparatus as claimed in claim 1 wherein said strip-shaped slit on said light shading plate has a width which increases from a small value at the center to a large value at each end thereof and wherein means are provided to move said light shading plate perpendicular to the lengthwise direction of said slit such that the slit is moved at a higher rate for the central portion of the face plate than for the lateral edge portion thereof.

6. A light exposure apparatus as claimed in claim 1, further comprising means for moving said point source of light in synchronization with the movement of said light shading plate.

7. A light exposure apparatus as claimed in claim 1, wherein said means for reciprocating the light shading plate includes a cam mechanism for reciprocating the light shading plate and another cam mechanism for moving said point source of light along a predetermined closed curve in synchronization with the movement of said light shading means, both cam mechanisms being mounted on a common shaft.