JPH0360148B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a beam penetrating cathode ray tube (beam penetrating cathode ray tube).
(penetration cathode ray tube), and in particular, to cancel the displacement of the spot position when changing the variable accelerating voltage to change the color development.

Beam-penetrating color cathode ray tube (CRT)
In this method, by changing the speed at which the electron beam collides with the fluorescent material on the front panel, it is possible to change the color of the area where the electron beam emits light (hereinafter referred to as the trace). can. The required velocity change is created by varying the accelerating voltage to which the electron beam is subjected. In some CRTs, this is done by varying a single voltage applied to both the funnel and face plate of the CRT's outer tube. In so-called "split anode" CRTs, the aforementioned speed changes are obtained by varying the voltage applied only to the front plate and keeping the voltage applied to the funnel constant. In either case, currently available fluorescent materials require a voltage change of several thousand volts to obtain a sufficient color change.

A long-standing problem with beam-penetrating color CRTs is that changing the color of the trace changes the deflection rate by as much as 40%. As the color is changed, the vertical direction of the CRT (hereinafter, the direction perpendicular to the front panel is referred to as the vertical direction, or the direction of a straight line passing through the vertical axis of the CRT and perpendicular to the vertical axis is referred to as the radial direction). ) direction component changes, so the time during which electrons are deflected by the deflection mechanism changes. As a result, even if the deflection electric field or magnetic field is the same, when the color development changes, the trace position on the front plate also changes. As the longitudinal velocity decreases, the radial displacement increases and the deflection rate (V/cm) decreases. If no compensation is made, these changes will cause a change in image size to occur at the same time as the color development is changed. Naturally, it is desirable that the size of the image is not affected by its color.

A conventional solution to the problem of color dependence of deflection ratio has been to change the gain of the deflection amplifier as the color is changed. This complicates both the deflection amplifier circuit and the overall control of the beam-penetrating color CRT. This is because the required gain change is a function of a high applied voltage, which can take several values, and the gain must track that voltage precisely. It would be desirable if this change in deflection factor could be canceled out within the CRT itself, allowing the deflection amplifier to operate at a fixed gain regardless of the value of the high variable voltage applied to the CRT.

When compensation is made for the horizontal and vertical deflection factors, the sum of these compensations must also provide the correct compensation in the diagonal direction, such as the main diagonal extending from the center of the front plate to its corners. Improper diagonal compensation results in barrel or pincushion distortion in the displayed pattern. In a CRT with an expansion mesh, the horizontal and vertical diffusivity can be adjusted by varying the electric field strength surrounding the expansion mesh. The required deflection rate compensation can be obtained by such a change in the degree of diffusivity. However, the diffusion mesh does not simply affect the horizontal and vertical lateral velocities independently; any radial diffusion takes place. Therefore, distortion-free deflection rate compensation must be achieved by selecting and realizing an appropriate diffusivity for each radial direction.

Therefore, the main object of the present invention is to provide a beam-penetrating color CRT in which the horizontal and vertical deflection rates remain constant even as the trace color changes.

Another object of the present invention is to provide a beam-penetrating color CRT whose horizontal and vertical deflection rates are automatically and continuously kept constant even with arbitrary changes in the applied high voltage within a range corresponding to maximum color change. The goal is to provide the following.

Another object of the present invention is to provide a constant deflection ratio in an electrostatically deflected beam penetrating color CRT with a diffusing mesh, thereby eliminating barrel or pincushion distortion due to variations in color development.

According to the present invention, these and other objects are achieved in an electrostatic deflection split anode beam penetrating color CRT by placing a correction lens centered on the axis of the tube. In a preferred embodiment, the correction lens is constituted by a conductive region inside a conical section at the entrance of the funnel region of the outer tube of the CRT in the vicinity of the diffusing mesh. This correction lens is electrically connected to the split anode front plate and both are subjected to the same switched high voltage. The shape of the correction lens interacts with the action of the diffusion mesh to vary the compensation of radial velocity in the horizontal, vertical, and diagonal directions (i.e., to provide a different amount of diffusion in each of these directions). selected. These changes in radial velocity counteract the changes in deflection rate caused by changes in longitudinal acceleration. This compensation operation is correct not only for selected voltages, but for all voltages applied to the front plate. Thus, even if the color development is changed, the vertical and horizontal deflection rates do not change as a whole and are automatically kept constant. The selected amount of correction is performed in all radial directions, including diagonal directions, and no distortion is induced in the displayed image.

Horizontal and vertical deflection factor correction for magnetically deflected split anode beam penetrating CRTs is also performed by a correction lens centered on the tube axis and placed inside the neck of the CRT near the entrance end of the deflection yoke. . The voltage of the correction lens is changed according to the high voltage of the front plate. The longitudinal velocity variation of the electron beam in the magnetic deflection region is controlled to compensate for the longitudinal velocity variation in the front plate region. This changes the amount of deflection in the magnetic deflection region, and as a result, the deflection rate ultimately becomes constant.

The present invention will be explained in detail below based on the drawings. FIG. 1 is a diagram showing a CRT according to the present invention. In FIG. 1, a "mesh can" 5 is located at the exit end of the electron gun assembly 6 of the CRT 1.
A supported diffusion mesh (itself not visible) is placed on top of it. Inside the CRT outer tube, near the entrance of the diffusion mesh and funnel,
A slightly tapered cylindrical conductive correction lens 3 with round protrusions at four locations is placed. The correction lens 3 is electrically connected to the segmented anode front plate by an external conductor (not shown). A dielectric coating gap 4 of essentially constant width separates the correction lens 3 from the conductive coating 2 inside the remainder of the funnel of the CRT 1 (hereinafter referred to as funnel coating). The funnel coating 2 is the same as before, except that the shape of its narrow end is such that it complements the shape of the end of the correction lens 3 with the dielectric coating gap 4 interposed therebetween. Further, the funnel covering 2 is electrically insulated from the front plate of the CRT 1.

CRT1 is intended for use in small, high quality color graphic display devices. Its front panel has an observation area approximately 127 mm (5 inches) wide (horizontally), 101.6 mm (4 inches) high (vertically), and approximately 381 mm (15 inches) long. CRT1
In order to make it easier to draw the shape of each part of the CRT 1, the CRT 1 is shown rotated 1/4 of the way around the vertical axis from its normal use position in FIG. The spatial relationship between the horizontal and vertical axes is therefore reversed here. In this way the wide side of the tube is illustrated,
Explanatory features are drawn larger.

The CRT shown in Figure 1 was not designed for oscillographic applications requiring maximum vertical deflection sensitivity, but rather for applications where approximately equal horizontal and vertical deflection sensitivities are most advantageous. Intended. Therefore, this
In a CRT, horizontal deflection occurs first (furthest from the front panel), followed by vertical deflection. It will be clear to those skilled in the art that the invention is equally applicable to CRTs designed so that one axis of deflection is much more sensitive than the other.

In contrast to the CRT 1 of FIG. 1, FIG. 2 is a cross-sectional view of a portion of a conventional split anode beam penetrating color CRT 7. In such a CRT 7, the inside of the funnel portion of the outer tube 8 is coated with a conductive funnel portion coating 10. This funnel covering is the diffusion mesh 1.
It extends from the front of 1 to quite close to the front panel. Another electrically conductive area 9 is coated over the fluorescent material on the front plate. The funnel cladding 10 is connected to a fixed high voltage source, while the conductive front plate cladding 9 is connected to a variable high voltage source.

The basic principle of the color dependence of the deflection rate in conventional split anode beam penetrating CRTs can be easily understood by looking closely at FIG. Dotted line 12 in Figure 2
For a to 12d, each front plate voltage is +15kV.
(for the green trace), the trajectories of the electron beam are shown for various amounts of deflection a to d. The trajectories 12a to 12d form a strain-free pattern made with a certain deflection rate. On the other hand, the second
The trajectories represented by solid lines 13a to 13d in the figure are significantly different from trajectories 12a to 12d, but the difference in conditions is that the front plate voltage is +9kV (for red trace).
It only decreased to .

Trajectories 12a to 12d and 13a to 13d
are essentially the same for the first two-thirds of their journey after leaving the diffusion mesh. The electrons corresponding to each trajectory are accelerated by the funnel coating 10 by virtually the same amount. Also, the radial velocity is once given by the deflection plate and the diffusion mesh, and then kept constant during the above two-thirds of the stroke. For trajectories 12a to 12d, the longitudinal component of the electron's velocity, once accelerated by the conductive funnel coating 10, remains essentially unchanged until the electron hits the front plate. The respective radial velocities remain constant after leaving the area of the diffusion mesh. Therefore, the trajectories 12a to 12d are approximately straight lines. However, when the front plate voltage is reduced, the longitudinal velocity of the electrons gradually decreases as they approach the front plate, while the radial velocity remains approximately constant (in fact, it increases slightly). As the electrons slow down axially, the more time they can travel radially before impacting the front plate. Therefore, the last portion of the trajectories 13a to 13d becomes more curved as it approaches the front plate. As a result, the deflection rate is significantly reduced (ie, the deflection sensitivity is increased) and a larger image is created with essentially no pincushion or barrel distortion.

FIG. 3 is a cross-sectional view of the upper part of a CRT 14 similar to FIG. 2 but made according to FIG. 1. Conductive coatings 17 (corresponding to the correction lens 3 in FIG. 1), 15 (corresponding to the funnel coating 2 in FIG. 1), and 16 (divided anodes on the front plate) are provided on the inside of the outer tube. There is. Resilient contact, pop-through
electrically connected to the conductive coating 17 for the correction lens by various conventional means such as through, a through-hole-like structure with a sealed hole (for connecting the front and back sides), and a metal anode button. You can get in touch. A layer 18 of insulating paint is applied to the gap 4 separating the conductive coatings 17 and 15. A similar insulating layer covers the conductive coating 15 of the funnel part.
and the conductive coating 16 of the front plate. In this example, the width of gap 4 is approximately 2.5
mm (1/10 inch). A conductor 19 connects the conductive sheathing 15 of the funnel to a fixed high voltage power supply, ie +15 kV in this example. The other conductor 20 is
Both the conductive coating 16 of the front plate and the conductive coating 17 for the correction lens are connected to a variable high voltage source having a value between +9 and +15 kV. In addition, the electron gun assembly 2
A diffusion mesh 21 at the outlet end of 2 is also shown.

The interior of the outer tube, in which the conductive coating 17 for the correction lens is placed, consists of two conical surfaces. The left side of the funnel near the gap 4 has an 8° conical surface, while the immediate left adjacent portion (the so-called "reducer") has a 38° conical surface. Since it is convenient to explain the following figures, we will mention the circle that is the intersection line of two conical surfaces in FIG. 3 (it is a straight line in FIG. 3, but it is a circle in three-dimensional space).

According to FIG. 3, the tip of the diffusion mesh 21 is located approximately 5.1 mm (0.2 inch) beyond the plane of the circular intersection along the longitudinal axis of the CRT.

The shape of the narrowest opening in the 38° portion of the conductive coating 17 for the correction lens has little or no effect. This is because the position of this opening is far away from the electrons exiting from the diffusion mesh 21. The shape may be circular. The shape where two conical surfaces intersect has already been described as a circle. The shape of the edge on the other end of the 8° conical surface side of the conductive coating 17 for the correction lens (Fig. 3) and the corresponding shape of the left edge of the conductive coating 15 of the funnel part are so simple. is not explained. As mentioned above and as seen in FIG. 1, this has a shape with four round protrusions.
This protruding shape is explained by the shape of the gap 4 between the conductive coating 17 and the funnel coating 15 for the correction lens. The reason for this is that the dimensions and shape of the gap 4 are much easier to draw than the shape of what it separates. gap 4
Of course, if you know the shape of , you can clearly and reliably know the shape of the rest.

Before discussing the nature of the shape of gap 4 and why it provides the desired correction, a final note is in order. It is immediately clear that the gap 4 is not only limited to an 8° conical surface, but also extends to a 38° conical surface in four places. 5th B
A quick look at the figure shows that the gap 4 is provided with four bent ears 24 to 27, if the gap 4 is considered as a surface in itself. As far as is known, these bent regions of the gap do not have particularly desirable properties due to their bending. This is due to the fact that the entry and exit of the four protrusions must be of a certain length and must be placed in a particular position with respect to the diffusion mesh in order to obtain the desired result. That is, since the line of intersection of the reducer and the funnel came within the range of their entry and exit, the last portion of the protrusion was bent. This CRT is a modification of an existing CRT, and it was outside the scope of this project to redesign the position of the diffusion mesh and the shape of the outer tube to eliminate these bends. On other CRTs, the curved ears of this gap may be missing, or they may have sharp edges. Book
In CRTs, this bending was simply ignored without any noticeable negative effects.

Figures 4A and 4B are similar to Figures 1 and 3.
This is a diagram illustrating a drawing method for showing the exact shape of the gap 4 for the specific CRT shown in the figure. Illustrated is a planar shape which, if made of a suitable medium such as paper or mylar, is cut out, joined at its edges and bent along dotted lines to form the gap 4. Construct actual three-dimensional shapes. That is, the 4th A
Figures 4B and 4B basically show how the shapes are made. Most of the shapes created in this way lie on the surface of an 8° cone.

In Figure 4A, dotted line 23 has a radius of 271.8mm.
(10.7 inches) and corresponds to the circular intersection of two cones. Angle O is approximately 51° and was chosen to create an 8° cone. To create the shape shown in Figure 4B, proceed as follows. First, make concentric sectors with radii of 266.7 mm (10.5 inches), 271.8 mm (10.7 inches), 276.9 mm (10.9 inches), 288.3 mm (11.35 inches), and 298.5 mm (11.75 inches). These sector segments must face the same 51° central angle. Divide the central angle into four equal parts corresponding to the horizontal and vertical axes. Subdivide each of the four equal parts to correspond to the position of its main diagonal (as defined by the aspect ratio). The angle α is smaller than the angle β in FIG. 4A because the symmetries about the different main diagonals are different. For a tube with a square front plate, α=β. Create eight parts by drawing nine radial lines from the center to the outermost segment. Along these radial straight lines are the illustrated centers of various small circle segments of defined radius, and a small circle is drawn. Each of these small circles intersects the associated large circle at a point on the associated radial straight line. Therefore, draw a tangent line connecting the continuous small circles along the inner and outer edges of this gap shape. Then, H, V and D signals are applied to the shape of this gap as shown in the figure. The resulting shape is cut out and corresponding edges are joined along the first and ninth radial lines. and radius 271.8mm
(10.7 inch) circle with a radius of 6.4 mm (0.25 inch) bent inward.

The annular wire piece made in this manner forms a conical surface having four protrusions as shown in FIG. 5B without distortion. By the symbols H, V and D, FIGS. 5A and 5B indicate the orientation of the gap 4 in the CRT of FIGS. 1 and 3. This is important because the protrusion marked V is 6.4 mm (1/4 inch) longer than the protrusion marked H.

I think it goes without saying that Figures 4A and 4
The specific values stated in Figure B are dependent on the size and shape of the CRT envelope and its diffusion mesh. However, once those skilled in the art know the shape of the correction lens, they can refer to this example and draw similar diagrams for different CRTs with different diffusion meshes. A method for selecting the shape of the correction lens for any CRT will be briefly explained below.

Before explaining the reason for the operation of this general shape, a method of assembling such a correction lens will be briefly explained. Both the correction lens and the conductive coating on the funnel are formed by vapor deposition of aluminum. The gap-shaped masking fixture is made of stainless steel sheet. It is held in place by gravity relative to the interior of the reducer.
It is thin enough to follow any slight eccentricity of the conical surface. The front plate and the outer tube of the electron gun extraction are placed in an aluminum evaporator and conductive coatings (3 and 2, or 17 and 15) are applied. The insulative coating 18 can then be applied by any convenient means, such as by hand application with a brush.

FIG. 6 is a diagram showing the compensation effect of the correction lens 17 on the electron beam when it exits the diffusion mesh 21. Similar to that shown in FIG.
It shows the trajectory of the electron beam for various deflection amounts while maintaining the voltage at 15kV. The solid lines 29a-29d represent the trajectories for the same amount of deflection when the split anode front plate voltage is reduced to +9 kV. As can be seen from the figure, for various amounts of initial deflection, the location where the electron beam finally impinges on the front plate is not affected by the front plate voltage.

When the front plate 16 is operated at the same voltage as the conductive coating 15 of the funnel, the correction lens 17 will also be at the same voltage. After all, the entire CRT is the same as having a uniform internal conductive coating without a separate segmented anode or a separate correction lens. Diffusion mesh 21 operates normally. That is, the area immediately outside the diffusion mesh 21 (for example +100V) and the CRT
The electric field between the adjacent part of the outer tube (+15 kV) is of high gradient. This high gradient electric field maximizes the magnification of the diffusion mesh 21.

However, if the voltage on the front plate 16 is +9kV or +
When decreasing to any convenient voltage between 15 kV and +9 kV, the voltage at the correction lens 17 decreases accordingly. This reduces the electric field gradient around the diffusion mesh 21. The effect of any voltage applied to the front plate is to properly reduce the magnification for all deflection angles experienced by the electron beam as it exits the diffusing mesh 21. The amount of reduction in magnification is selected so as to balance this reduction with the longitudinal axis deceleration and slight radial acceleration experienced by the electron beam as it approaches the front plate. No matter how the front plate voltage changes, the reduction in magnification described above will also follow correctly. What is shown in FIG. 6 is a part of the plan view of the CRT, so what is shown here is the trajectory of the electron beam with respect to horizontal deflection. Therefore, the correction lens 17
The above article regarding the operation of , implicitly assumes that there is no vertical deflection. That is, pattern correction along the diagonal is not considered. However, such considerations are necessary to prevent large pattern distortions in off-axis directions.

As mentioned above, if one looks closely at FIG. 4, it can be seen that the protrusions of the correction lens in the vertical direction are longer than those in the horizontal direction. If this reason is explained, the following explanation regarding the pattern correction method in the diagonal direction will be easier to understand.

If the voltage on the correction lens element 3 or 17 is reduced, the magnification of the diffusing mesh 21 will be reduced accordingly. Snell's law, which is the basis of this, will be explained very briefly below.

Give the following definition.

V ₁ : Potential of the interior and surface area of the diffusion mesh.

V ₂ : Potential near the outer region of the diffusion mesh.

Q ₁ : Complementary angle of the angle between the path of the electron passing through the mesh and the tangent to the mesh at the passing point.

Q ₂ : Complementary angle of the angle between the path of the electron that has just passed through the mesh and the tangent to the mesh at the passing point.

Then, the following formula holds true.

√ ₁ sinQ ₁ =√ ₂ sinQ ₂ …(1) Now, the potential on the surface of the diffusion mesh is about +100V
It is. The potential outside the diffusion mesh is mainly due to the conductive coating 2 or 15 of the funnel part. The purpose of the correction lens is first to operate at high pressure, such as a conductive coating on the funnel in a conventional polarized anode beam penetrating CRT, and then to operate at low pressure to create an area of low pressure that can be By doing so, the diffusion mesh 21 is partially shielded from the influence of high voltage appearing on the conductive coating of the funnel part, thereby
This is to reduce the effective value of the potential V ₂ in the equation.

If the distance between a point on the diffusion mesh and the point on the conductive coating of the funnel section closest to that point on the diffusion mesh is constant, then the physical The greater the separation, the greater the shielding and the greater the reduction in the effective value of the potential _V2 . However, those who are familiar with the properties of electric fields know that as the point we are considering on the mesh gets closer to the funnel (i.e., when the "constant distance" in the previous sentence becomes smaller), the physical It will be seen that the same degree of shielding can be obtained even if the separation is smaller. A low value of the potential V ₂ means that the magnification of the electron beam entering the region where the potential V ₂ is distributed is low. Obviously, the different values of the potential V ₂ radially distributed outside the diffusing mesh can be varied by varying the shape of the corrective lens element 3 or 17. That is, the degree of reduction in magnification in the horizontal and vertical axes when leaving a diffusion mesh in any radial direction is a function of at least two things: (1) the correction in that radial direction; the width of the lens; and (2) the distance measured along the radial direction from the center of the diffusing mesh to the point where the beam exits the mesh. The second condition is important for the same reasons as the first condition. That is, this condition affects the degree of separation between the conductive coating 2 or 15 of the funnel part to which high pressure is applied and the mesh part, and therefore affects the effective value of the potential _V2 . Second
Note that the condition (distance from the center of the mesh to the point where the beam exits) is essentially a function of the degree to which the deflector plate influences the beam before it passes through the diffuser mesh.

The reason why the vertical protrusion of the correction lens is larger than the horizontal protrusion will be explained next.

Consider horizontal deflection. As mentioned above, in the CRT described here, horizontal deflection is first performed so that the horizontal direction of the front plate is wider than the vertical direction, and the difference between the horizontal deflection rate and the vertical deflection rate is minimized. This is because it is desirable. This means that, with full horizontal deflection (but no vertical deflection), the beam passes through the diffuser mesh sufficiently far from the center of the diffuser mesh (i.e., at a large radial distance).

On the other hand, even with maximum vertical deflection (no horizontal deflection), the beam will not pass through the diffusing mesh at large radial distances.
The reason for this is that the vertical deflection plate is closer to the mesh (less time for deflection due to vertical radial velocity), and requires less deflection to begin with (the vertical dimension of the front plate is smaller than the horizontal dimension). ).

Assume that when switching the front plate to low pressure, both the horizontal and vertical deflection rates decrease at a rapid rate (in reality, the decrease in the vertical deflection rate tends to be several percentage points larger).Then, the required The result is an equal reduction in horizontal and vertical magnification by the diffusing mesh (or perhaps a somewhat larger reduction in vertical magnification), but when the electron beam is subjected to maximum vertical deflection, Even though the distance between the exit point from the diffusion mesh and the center of the diffusion mesh is smaller than in the case of horizontal deflection, and the voltage gradient associated with vertical deflection is not as large as that associated with maximum horizontal deflection. , the correction device must be able to act far away from where the beam exits the diffuser mesh and give the same result as a horizontal correction device that acts from a closer location (slightly larger results are required). (This is especially true if the Therefore, in order to achieve the required correction, the vertical projection of the correction lens element must be made longer.

Let us now consider the deflection in the main diagonal direction. This occurs when maximum vertical deflection and maximum horizontal deflection occur simultaneously. Under this condition, when the electron beam passes through the mesh, the distance from the center of the diffusing mesh to the exit point of the deflected electron beam is maximized. Since the exit point of this electron beam is close to the high voltage of the conductive coating of the funnel part, only a narrow intervening voltage is required to obtain the required change in the effective value of the potential V ₂ . The width of the correction lens element is therefore minimum in the main diagonal direction. These minimum values are equal because the radial distance is the same for each main diagonal. Furthermore, between the four minimum diagonal width portions, there are horizontal and vertical portions that are large and have different sizes. As shown in FIGS. 1 and 5, the correction lens determined by the above has a shape with a scallop-like edge at the edge.

Variations in the width of the gap 4 between the correction lens element and the conductive coating of the funnel can also influence the contour of the correction lens itself. These changes can be changes from one constant overall width to another, or local changes in width from one position of the gap 4 to another.

Although the correction lens described herein is constructed to accurately correct any given CRT, the shape of the correction lens depends in part on the size and shape of the CRT's outer tube. If you do not pay attention to the tolerances of the outer tube, some CRTs may
However, the shape of the correction lens that provides the correct correction effect may not necessarily provide the correct correction effect for other CRTs.
If suitable tolerances regarding the size and shape of the outer tube cannot be maintained, it may be desirable anyway to provide a deflection amplifier circuit with an adjustable amount of electrically variable gain. However, the variability here is 2
A ~3% gain change is much easier than getting a 40% change. The exact amount of gain change is adjusted during the calibration process after the CRT is installed, but this is because the amount is
This is because it can change for each CRT.

Based on my experience with this CRT, the tolerances of the outer tube would not be required to be particularly strict.
Furthermore, if the CRTs are of the same type, it is expected that almost accurate correction will be made even if the CRTs are replaced without paying special attention to tolerances.

The operating principle of the correction lens element will be explained in detail below using FIGS. 7 to 9.

FIG. 7 is a cross-sectional view of a conventional electrostatic deflection CRT 30 including a diffusion mesh 31. As shown in FIG. As mentioned above,
The potential of the diffusion mesh 31 is about +100V, and the potential of the conductive coating 32 of the funnel and the front plate 33 are each +15kV. Also shown in the figure are various equipotential lines between the diffusion mesh 31 and other parts within the CRT. As can be seen from the figure, the electric field gradient and the curvature of the equipotential lines are maximum at the closest portion of the diffusion mesh 31. Most of the diffusion effect on the electron beam trajectories 34a to 34d occurs before the electrons on the trajectories reach the 11.9 kV equipotential line.
By the time the 13.9kV equipotential line is reached, all diffusion except for a very small portion has been completed. From this point on, the electron enters the drift region and its trajectory becomes almost a perfectly straight line.

FIG. 8 is a cross-sectional view of a conventional CRT 35 similar to the CRT 30 shown in FIG. 7, but it differs from the CRT shown in FIG. different. The diffusion mesh 36 of FIG. 8 is the same as the diffusion mesh 31 of FIG. 7, and the electric field around it is also the same (perhaps almost, but not completely) as that of FIG. Therefore, up to the edge of the drift region, the eighth
In both the CRT 35 shown in the figure and the CRT 30 shown in FIG. 7, the same diffusion occurs for any given amount of deflection.

However, in the CRT 35 of FIG. 8, the drift region ends well before the front plate 38 at a curved equipotential line near the front plate 38, which has a reduced voltage. Various trajectories 39a to 39d
It is within this region that the electrons are slightly accelerated in the radial direction and greatly decelerated in the longitudinal direction.
Various symbols Δa to Δd indicate the amount of error in the final trace position.

FIG. 9 is a diagram illustrating how an example of the present invention operates in conjunction with and modifying the context of FIGS. 7 and 8. In the figure, the electrostatic deflection beam penetrating color CRT 40 includes a conductive correction lens element 4 electrically connected to a split anode front plate 43.
1 is provided. Between them is a conductive coating 42 of the funnel portion, which is electrically insulated from each. In the left part of FIG. 9, the equipotential lines of the electric field around the diffusion mesh 44 are shown. In contrast to the corresponding electric fields of FIGS. 7 and 8, the electric field around the diffusion mesh 44 of FIG. 9 has a lower electric field gradient and a lower degree of curvature of the equipotential lines. Comparing these figures, it can be seen that the gradient of the electric field is essentially the same in the immediate vicinity of the vertical axis, but there is a clear decrease in the gradient along the periphery of the diffusion mesh 44, with the equipotential lines becoming closer to the mesh. It no longer follows curvature. The reduction in curvature occurs by "pulling" these equipotential lines below about 9 kV toward the gap between the conductive correction lens element 41 and the conductive coating 42 of the funnel. Obviously, the amount of diffusion at each point on the diffusion mesh 44 moves away from the center due to the decrease in the electric field gradient that becomes more noticeable as you move from the center to the periphery of the diffusion mesh 44 and the accompanying decrease in the equipotential line curvature. As time goes on, Figures 7 and 8
It becomes even less than the spread of the corresponding points of the spread mesh in the figure. It is also clear that the position of the gap plays an important role in determining the reduction in the amount of diffusion. As mentioned above, in some types of CRTs, it is required to vary the amount of reduction in the amount of diffusion by the correction lens depending on the direction of deflection.
Therefore, the shape of this correction lens changes regularly according to the direction of deflection and is symmetrical.

Therefore, each of trajectories 45a-45d is diffused by a lesser amount than corresponding trajectories 39a-39d of FIG. 8. Trajectories 45a to 45
The longitudinal deceleration and slight radial acceleration that d undergoes as it passes through the equipotential lines surrounding front plate 43 offsets the reduction in diffusion just mentioned, resulting in trajectory 34a in FIG. 34d (where symbols a to d indicate the same amount of initial deflection in FIGS. 7 to 9, respectively).

Each of the curved equipotential lines surrounding the diffusion mesh 44 and the curved equipotential lines near the front plate 43 can be considered a lens. The refractive power of each lens is determined by the voltage difference between the elements that make up the lens and the shape of these elements. Since the voltages of these elements, the correction lens element 41 and the front plate 43, are equal and change together, and are always greater than the mesh voltage and less than the funnel voltage, the voltage difference of the "diffusion mesh lens" (correction lens 41
and the diffusing mesh 44) reduces the optical power of that lens, but the same voltage change (in this case between the funnel conductive coating 42 and the front plate 43) reduces the optical power of that lens.
increases the refractive power of the "front plate lens". The change in optical power of these lenses is a complex function of voltage difference. Roughly speaking, refractive power is the ability of an electric field to accelerate or decelerate electrons.

As you can easily understand, the correction lens element (9th
In the figure, the size and shape of the correction lens 41) are as follows:
When applying the correct correction when swinging the front plate voltage to its lowest voltage (e.g. from a high voltage of +15kV to +9kV), it is desirable that the selection be made so that even intermediate voltage values will basically operate correctly automatically. The ability to reduce the radial acceleration caused by the diffusive mesh lens by lowering the correction element voltage is
This is very similar to the ability of the front plate lens to reduce axial velocity and increase radial velocity.
By adjusting the dimensions of the corrective lens element,
The diffusive mesh lens function can be tailored to match the combined effect of the front plate lens function, not only at the lowest voltages, but also at intermediate values. Changes in one lens are then automatically canceled out by complementary changes in the other lens for any given voltage change.

Although not shown in FIG. 9, it will be appreciated that the electric field between the conductive coating 42 of the funnel and the front plate 43 has the greatest curvature at the corners of the front plate.
In other words, the electric lines of force (not equipotential lines) coming out from the conductive coating 42 of the funnel part and reaching the front plate 43 are concentrated together when the "vertical side" and "horizontal side" surfaces intersect and form one. This is because the outer tube bends in the area that forms the edge. Therefore, the refractive power of the front plate lens is greatest at the corners. Nevertheless, in the particular tube of this example, I am quite certain that this was not a significant source of the pattern distortion seen with some earlier corrector configurations. For example, with this CRT,
Reducing the front plate voltage without any corrective lens elements functioning changes the deflection factor significantly, but no pattern distortion in the corners is discernible. Therefore, the barrel distortion due to the shape of these early correction lenses appears to have resulted from overcorrection in the diagonal direction of deflection.

For the corner region electron beam, the diffusing mesh lens must achieve the same amount of magnification reduction as for the main axis. Figures 4B and 5
The four regions labeled "D" in Figure B are positions on the correction lens element corresponding to the corners of the front plate. On the one hand, a correction lens element (correction lens 4 in FIG.
1, conductive coating 17 for the correction lens in FIGS. 6 and 3, these points of the correction lens 3) in FIG. Although it is tempting to argue that The far end position of the diagonal electron beam in the diffusing mesh places the electron beam closest to the electric field emanating from the conductive coating of the funnel, so that even relatively small intervening electric fields can still have an obvious effect. have. Second, the minimum width point marked "D" is not completely isolated by itself. They are surrounded on both sides by rather sharp projections. Since the edges of these protrusions interact with the locations marked "D", the diagonal electric field disturbances in the diffusion mesh may be the result of the correction element "appearing wider than it is". . For these two reasons, therefore, the above-described geometry for the correction lens elements 41, 17, 3 actually provides the same nominal amount of magnification reduction in the diagonal direction at maximum deflection as in the other deflection directions.

It comes as a surprise to those skilled in the field of electro-optics that when performing motion analysis using an analytical model, even when using a computer, it is not always possible to obtain the most accurate and reliable information. I don't think so. This modeling approach is often only useful at predicting trends. As in the case of developing the shape of the correction lens element for the CRT in this example,
Much trial and error was required to find the required size, shape, and location.

Initial studies using computer models suggesting the feasibility of on-axis magnification correction were confirmed in empirical trials. Through empirical estimation and detailed trials, a generally cylindrical corrective lens element with two protrusions at the end along the vertical axis was created. This correction lens well compensated for on-axis deflection index changes at all intermediate voltages. However, although the shapes of these various early correction lenses were considered promising, they resulted in unexpected barrel distortion. As a result of searching for the cause of barrel distortion, the above-mentioned characteristic of the diffusive mesh regarding the radial distance from the center of the diffusing mesh to the location where the electron beam exits was found. Based on the elucidation of this property, a shape with four protrusions was obtained. The effects of these protrusions interact significantly. Therefore, in order to select its size and position, it is necessary to select a shape that allows appropriate deflection rate correction at all voltages and at the same time appropriate pattern correction by repeating trial and error several times.

The development work was completed with the following results. The +9kV voltage for red color slightly overcorrects the displayed image. That is, a red image and the same green image (+
15kV) is only slightly noticeable (1/4 of the trace line width, or approximately 127βm (0.005 inch)
Only, the size is different. As the front plate voltage increases, the error tapers off from this maximum and disappears completely by the time the amber trace is displayed. And this error correction is basically perfect from amber to green. No matter what color it is in, there is no discernible pattern distortion.

The shape was determined through a combination of trial and error and computer analysis using the finite element method.
Any of a number of well-known computer programs are useful in this regard. One such program is William B. Hermansfurth's "Electron Orbital Program," published in 1973 by the Stanford Linear Accelerator Center in the United States, Publication No.
SLAC-166(A)UC-28, which was developed for AEC under Contract No. 14T(04-3)-515. This FORTRAN program is
It is available from the National Technical Information Service (NTIS), part of the U.S. Department of Commerce, Springfield, Virginia.

Once the final shape was known, it was speculated by inspection that there might be some kind of relationship between the shape of the correction lens element and the shape of the front plate. While acknowledging that it is unclear how certain it is that this relationship can be generalized and applied to CRTs with significantly different designs, some speculation about this relationship is provided below.

The shape of the edge of the corrector lens element was observed to be the same or similar to the projection of the rectangular shape of the front plate onto the conical surface adjacent to the funnel portion of the outer tube of the CRT. To explain this, let us consider a right circular truncated cone made from an 8° right circular cone, which has dimensions corresponding to the CRT outer tube near the diffusion mesh. Then, select a first point on the axis of this right circular cone. In many cases the point will be closer to the narrow end of the cross section than the wide end. Furthermore, consider a rectangle with a similar shape to the front plate. The rectangle lies in a plane perpendicular to the axis of the right truncated cone, and its center often lies on the axis of the right truncated cone closer to its wide end than its narrow end. Furthermore, consider a straight line that is pivotally supported at the first point and intersects with the edge of the aforementioned rectangle, and makes this straight line go around the edge of the aforementioned rectangle. As a result, the locus of the intersection of this straight line and the surface of the truncated cone is the trajectory of the correction lens 4 shown in FIGS. 1 and 5.
The shape of the edges will be similar to numbers 1, 17, and 3.

The principles of the present invention have been used to correct for the effect of a diffusion mesh in another electrostatic deflection CRT having a diffusion mesh. The CRT was a monochrome CRT that operated at a fixed acceleration voltage, and was originally designed without a diffusion mesh. It was desired to include a standard, readily available diffusion mesh in the tube to increase its deflection sensitivity. Although the desired increase in sensitivity was obtained, the trade-off was a noticeable amount of pattern distortion due to an inadequate amount of diagonal diffusion. This distortion was eliminated by the use of a corrective lens element, essentially similar to that described above, but operated at a fixed voltage.

The corrective lens elements described herein are not necessarily
It will be appreciated that this need not be a conductive coating on the inside of the CRT's outer tube (although this is often the most convenient method). Other means of influencing the trajectory of the electron beam may be used, such as shapes made of thin metal plates and placed appropriately around the path of the beam. For example, the single color in the previous section
In the CRT example, a metal tab was attached to the mesh can by a dielectric separator.

Although the above explanation was about an electrostatic deflection type CRT, similar corrections can be made with a magnetic deflection type CRT.

FIG. 10 shows a magnetically deflected beam penetrating collar CRT 46 with a segmented anode front plate 47 separated from a conductive coating 48 of the funnel, a conductor 49 connecting the segmented anode front plate 47 to a first variable high voltage source (not shown). Another lead 50 connects the funnel conductive sheathing 48 to a fixed high voltage source (also not shown). Electron gun assembly in the CRT46 network (not shown)
emits a focused electron beam 51. Magnetic deflection yoke assembly 52 includes both horizontal and vertical deflection coils, which are driven by suitable deflection amplifiers (not shown).

As in the case of electrostatic deflection CRTs, color changes in the traces are accomplished by deflecting a high positive voltage applied to the segmented anode front surface. In this example, the conductive coating on the funnel operates at a fixed high voltage of +20 kV, and the split anode front plate operates at a fixed high voltage of +10 kV to +
Operates in the 20kV range.

A broken line 53 shows the locus of the electron beam for a given initial deflection amount of the electron beam 51, provided that the front plate is swung to the maximum voltage of +20 kV. Assuming that there is no correction lens of any kind, the initial deflection amount is similar to that of the locus 53 above, and the voltage of the divided anode front plate 47 is set to +10 kV.
The locus in the case where the temperature is lowered to this level becomes as shown by a dotted line 54. As with electrostatically deflected CRTs, the deflection process induces a radial velocity in the electron beam. The reduced front plate voltage reduces the longitudinal velocity of the electron beam as it approaches the front plate. The resulting increase in travel time results in a higher radial velocity and therefore a higher deflection.

Consider now the effect of a correction lens 55 in the form of an annular conductive surface, which is placed inside the neck of the CRT 46 and axially centered on the path of the electron beam 51. This correction lens 5
5 is placed, the electron beam 51 is placed on the yoke 5.
This is before entering the region of magnetic deflection created by 2. A lead 56 connects the correction lens 55 to a second variable high pressure source (not shown). As the color development of the trace changes, the first and second high pressure sources change simultaneously as follows. That is, as the voltage applied to the divided anode front plate 47 decreases, the positive high voltage applied to the correction lens 55 increases. By increasing the voltage across the correction lens 55, the electron beam 51 is accelerated in the longitudinal direction by the amount necessary to keep its travel time constant. As a result, the point of impact of the trajectory 57 of the electron beam on the front plate 47 is the trajectory 5
As shown in Figure 3, the deflection rate is constant. Similarly, split anode front plate 47
As the voltage applied to the correction lens 55 increases, the positive high voltage applied to the correction lens 55 decreases. If the magnetic deflection CRT is equipped with an autofocus circuit, it may be desirable to also couple the autofocus circuit to the circuit that controls the voltage applied to the correction lens.

It will be appreciated by those skilled in the art that the alternative embodiments described above are also applicable to electrostatic deflection CRTs without diffusion meshes.

[Brief explanation of drawings]

Figure 1 shows a beam penetrating collar according to the present invention.
A perspective view of a CRT, FIG. 2 is a partial cross-sectional view of a conventional beam-penetrating color CRT, and FIG.
Beam penetrating collar according to the invention shown in the figure
A cross-sectional view of the CRT, Figures 4A and 4B are diagrams explaining the shape of the gap in Figure 1, and Figure 5 is a diagram explaining the shape of the gap in Figure 1.
Figure 6 is a diagram explaining the three-dimensional shape of the gap in the figure, Figure 6 is a diagram explaining the action of the correction lens when the electron beam exits the diffusion mesh, and Figure 7 is a diagram explaining the conventional electrostatic deflection.
A diagram showing the internal potential and trajectory of the electron beam in a CRT, Figure 8 is a conventional beam penetrating color
FIG. 9 is a diagram explaining the variation of the electron beam trajectory in a CRT, FIG. 9 is a diagram explaining the correction effect in the beam penetrating color CRT according to the present invention, and FIG.
The figure shows an electromagnetic deflection beam penetrating collar according to the present invention.
FIG. 3 is a diagram illustrating the operation of a CRT. 2: Funnel portion coating, 3: Correction lens, 4: Gap, 6: Electron gun assembly, 15: Conductive coating on funnel portion, 16: Conductive coating on front plate, 17: Conductive coating for correction lens, 21 : Diffusion mesh, 4
7: Split anode front plate, 48: Conductive coating on funnel portion, 52: Magnetic deflection yoke assembly, 55:
correction lens.

Claims (1)

[Scope of Claims] 1. An evacuated outer tube having a narrowed end, a front plate, and a funnel-shaped part provided between the narrowed end and the front plate, the front plate being A voltage corresponding to the desired color development is applied to the outer tube, and an outer tube whose inner surface is made up of a beam-penetrating phosphor coating, and an outer tube provided at the narrowed end and arranged along the main axis of the outer tube. an electron beam generating means for sending an electron beam toward the front plate part; a deflection means for deflecting the electron beam in the directions of first and second deflection axes perpendicular to the main axis; provided on the inner surface of the funnel-shaped part; a funnel-shaped conductive coating, which is insulated from the beam-penetrating phosphor coating of the front plate portion and to which a predetermined voltage is applied; and a funnel-shaped conductive coating provided between the funnel-shaped conductive coating and the narrow end portion. four protrusions insulated from the funnel-shaped conductive coating and extending toward the front plate portion, the protrusions being arranged around the main axis in the directions of the first and second deflection axes; and a conductive film to which a voltage is applied that is linked to the voltage corresponding to the color development. 2. The beam penetration type cathode ray tube according to claim 1, wherein the inner surface of the front plate part further has a conductive coating, and a voltage corresponding to the color development is applied to the conductive coating. . 3. The beam penetration cathode ray tube according to claim 1 or 2, wherein the voltage applied to the conductive film is the same as the voltage depending on the color development.