EP1077468A1 - Colour cathode ray tube with tension mask - Google Patents

Abstract

The image tube has an essentially rectangular shadow mask (25) and a frame carrying the mask. The mask is tensioned in two essentially mutually perpendicular directions and is clamped into the frame on two opposing sides, both of the other sides not being connected to the frame. The sides not connected to the frame are strengthened at the edges (29) wrt. the inner surface and have an inward curvature. Independent claims are also included for a colour TV and for a colour monitor.

Description

The invention relates to a color television set or a color monitor and in particular a color picture tube with a tension mask, which is a bias in vertical and has horizontal direction.

Color television sets and (computer) monitors are used to convert electrical Signals in color images. Color televisions and monitors now have one Interface for various video signal formats (such as composite signals, analog or digital component signals). These signals are in a television set or a monitor to control a color picture tube in analog RGB signals converted. In doing so, they are sent to a television set or a monitor Video signals are converted so that each individual pixel has a Certain brightness or color values can be assigned to the display screen can. For the playback of an image contained in a video signal in a color picture tube contained in a color television or monitor, three Generates electron beams. Each of these electron beams corresponds to one of the three Basic colors of the additive color mix: red, green, blue. Depending on the Playback position is the pixel information, i.e. the brightness and color information, of the video signal a corresponding pixel on a fluorescent screen assigned to the color picture tube.

By overlaying three color separation images pixel by pixel, one comes with one Color tube an additive color mixture. The fluorescent screen of a color picture tube contains approx.400,000 triple colors, i.e. fluorescent dots arranged in groups of three with one glowing red, one glowing green and one glowing blue Fluorescent dot. The diameter of such a light spot is in about 0.3 mm.

When playing a video signal, each of these points becomes one of the three Electron beams controlled and made to glow. The electron beams are from an electron gun in the neck of a color picture tube generated. Such a color picture tube is shown in cross section in FIG. Essentially a color picture tube consists of a glass body 15. On the inside of the Front screen 16 of the color picture tube is a phosphor layer 17 with the phosphor dots arranged. The electron beams to control the phosphor dots are generated by an electron gun 18 in the neck of the color picture tube. there are the electrical signals for controlling the electron gun via contact pins 20 of the electron gun supplied from the outside. By a not shown Deflection unit, which is attached to the outside of the color picture tube, become the electron beams so distracted that all the pixels of the luminescent screen are driven in succession become. At a distance of approximately 15 mm from the fluorescent screen 17 away there is a shadow mask with a inside the color picture tube Mask frame 19. In the shadow mask there is every color triplet on the fluorescent screen assigned its own opening. These openings or holes have one Diameter of about 0.25 mm and are at regular intervals in the shadow mask / shadow mask etched. In each case through the common beam deflection controlled hole of the shadow mask meet the three electron beams and fall on the fluorescent spots of the fluorescent screen 17 lying behind a large part of the electrons generated by the electron gun are landing on the shadow mask. This leads to heating and corresponding thermal expansion of the shadow mask. The position of the in openings in the shadow mask opposite those assigned to them Fluorescent dots. Due to such a shift, the deteriorates Color purity of the reproduced pixels. Such deterioration does especially noticeable in the holes on the edge of the mask.

Shadow masks are not only in the form of shadow masks, they are are also used in the form of stripe masks. With these stripe masks is the fluorescent screen 17 of a color picture tube not with individual phosphor dots, but with fluorescent strips running in the direction of the stripes of the shadow mask Mistake. Accordingly, the shadow mask has stripes Openings for the individual electron beams, each of which the stripe on the Luminous screen are assigned. Such a stripe mask often consists of parallel trending "wires".

As shown in Fig. 4, the shadow mask is held by a mask frame 19, to give the mask mechanical stability and manageability. The In modern color picture tubes, mask frames are also made of thin sheet metal.

Because of the lower thermal expansion, shadow masks are used nowadays also made of iron-nickel alloys with a very low coefficient of thermal expansion manufactured. Because such iron-nickel alloys are many times more expensive than iron, mask frames are made of iron. Problematic is the combination of shadow masks and mask frames that are made of materials with different coefficients of thermal expansion exist. When heating such mask-frame combinations are deformations of the shadow mask possible. This makes the position of the openings in the shadow mask relative changed to the location of the assigned phosphor dots or phosphor strips.

Shaped, self-supporting shadow masks have found the greatest distribution. Such a shadow mask is shown in Fig. 1. The behind the fluorescent screen 1 Arranged shadow mask contains hole-like or strip-like openings 3, which the Match the arrangement of the fluorescent colors on the fluorescent screen. The mask is attached to a frame 2. The contour of such a mask can be vertical as well as being varied in the horizontal direction. The holding frame must be used do not absorb large forces for the mask. The material of the frame can therefore be selected essentially according to economic considerations.

Another type of color picture tube is biased in the vertical direction on. Such shadow masks, so-called tension masks, are essentially spread through the Trinitron tube. These shadow masks are on their top and the lower edge firmly connected to the mask frame. The preload of the Shadow mask is required to ensure that the distance between the Illuminated screen and the shadow mask in the direction of the longitudinal axis 21 of the color picture tube remains constant. The vertical alignment is achieved by the preload "Wires" put under tension. This gives the stripe mask its mechanical Stability. High tensile forces are required for the preload, the values of several can accept kN. The mask frame is therefore very solid. When choosing the material, the high process temperatures are particularly important To consider the manufacturing process of a color picture tube. Have such masks however the advantage that they have a high transparency and the mask contour has a high thermal stability. However, a disadvantage of such masks is that in principle they only have a cylindrical curvature of the mask. Also tend the tensioned mask wires to mechanical vibrations with strong To respond to vibrations.

Such a tension mask with tension in the vertical direction is shown in Fig. 2. Also this mask has a fluorescent screen 1 and a mask frame 2. The wires 5 the mask are biased in the vertical direction. This bias is through the arrows 7, 8 indicated in Fig. 2. To avoid vibration of the wires and in order to keep the distances between the wires constant, are across the tensioned mask wires 5 so-called damping wires 6 placed. Have this the task of suppressing mechanical vibrations of the mask wires 5 and keep the distances between the wires constant. These damping wires 6 have the disadvantage that they are displayed on the screen of the color picture tube and to be recognized there as permanent horizontal dark lines in the picture are.

In the case of such masks which are prestressed in the vertical direction, the mechanical Stability can also be improved by having small webs between the wires to be ordered. These webs prevent that every single mask wire for can swing. Through a uniform arrangement of such webs Gaps between the wires are kept constant and appear on the screen a homogeneous, non-distracting structure, like that of shaped shadow masks is known.

However, the use of such bars has the opposite of the mask wires Disadvantage that there is a coupling of the wires in the horizontal direction and itself the shadow mask thereby also in the horizontal direction during thermal heating expands. Such an expansion in turn leads to a shift the landing points of the electron beams on the fluorescent screen. This Displacement results in a deterioration in the image reproduction quality. Around Keeping this effect small is used as the material for the shadow mask and the mask frame preferably uses Invar or another iron-nickel alloy, which have a low coefficient of thermal expansion. Thereby However, the manufacturing costs of such a color picture tube are significantly increased.

To prevent deterioration in image quality due to thermal expansion in Avoiding the horizontal direction is - as described - a possible way out to use special alloys as mask material. However, it is an alternative also possible, in addition, a prestress on the mask in the horizontal direction exercise. This causes the mask to bulge when heated in the longitudinal direction avoided the color picture tube. 3 shows such a mask with a mask frame 2 shown. Arrows 7-10 indicate that the mask is both vertical and is biased in the horizontal direction. In this way, the consequences a thermal expansion of the webs located between the holes 3 in horizontal direction can be compensated.

In order to create such a horizontal bias, the shadow mask in the simplest case also attached to the side of the mask frame. A horizontal one Alternatively, bias can also be done without connecting the shadow mask with the side elements of the mask frame. For this, the Shadow mask in the horizontal direction through a narrow, non-perforated surface extended. By stretching the shadow mask in the vertical direction, it becomes non-perforated sections extended in the direction of stretch. At the same time there is a constriction in the middle of these sections, i.e. these sections will due to the narrowing, the strongest in the middle. This will make the punched Inner surface of the shadow mask that is not punched between the two Edge sections lies, pulled outwards. So it is simultaneously with the vertical Bias creates an additional horizontal bias. This method is commonly referred to as the semi-stretch tension technique, or SST technique for short.

The principle of this technique is explained with reference to FIG. 5. Only a part of it of the entire shadow mask, and that is only one half in FIG. 5 the shadow mask with one of the non-perforated, additional side surfaces shown. The shadow mask 25 has a perforated section 26 and additional Sections 27 in which no holes are provided. To the bias in vertical direction, the mask will be attached to the mask frame stretched in the vertical direction. This will attach the shadow mask a permanent prestress in the mask frame on the shadow mask 25 exercised in the vertical direction. This pretension prevents the curvature of the Mask due to the longitudinal axis of the color picture tube during operation thermal expansion in the vertical direction. 5 shows how the shape of the edge portion 27 of the shadow mask, which has no openings has changed in this aspect ratio. The shape of the shadow mask in front of the Stretching is shown by the solid lines, the shape after stretching is represented by the broken line 30. When stretching the width of the edge portion 27 is reduced, the greatest decrease in width in midway between the top and bottom. The one that occurs maximum decrease in width of the edge section 27 is referred to as necking C. With the shift of the boundary line 28 between the punched and the not perforated section 27 by the constriction in the direction of the outer edge 29 of the shadow mask 25, the mask inner surface 26 is also pulled outwards. As a result, the perforated section 26 is stretched in the horizontal direction and at the same time creates a pretension in the horizontal direction.

In other words, stretching the mask in the vertical direction also has an effect a horizontal tensile force that is directed outward. The height this tensile force depends on the strength of the constriction C. The wider the section 27 before vertical stretching, the greater the constriction created C and thus the horizontal traction. The width of the additional, Non-perforated sections 27 can, however, only be increased to a very limited extent without that the screen area in the horizontal direction by disturbing, not as a display area usable areas must be widened. Are accordingly the horizontal tensile forces that can be generated are very low.

With the horizontal tensile forces that can be generated in this way today only the thermal expansion of mask materials with a special low thermal expansion coefficients can be absorbed. This one Mask materials such as Invar, especially expensive, it is desirable to have such to replace expensive mask materials with cheaper ones.

The object of the invention is known color television sets and color monitors and in particular to develop color picture tubes such that the shadow masks of the Color picture tubes can also be made from a cheaper mask material can.

This object is achieved for a color picture tube having the features of claim 1, for a color television set with the features of claim 8 and for one Color monitor with the features of claim 9.

According to the invention, an expensive mask material that has a low thermal Has expansion coefficients, then by a cheaper mask material such as. Replace iron if the tensile forces are significantly higher in the horizontal direction than can be generated so far. Because then even the much larger ones can thermal expansion of the cheaper materials in operation compensated become. To do this, the sides of the shadow mask that are not with the mask frame are connected, arcuate, the arcuate outer Edge has a higher strength than the shadow mask inner surface. For Generation of an outward pull on the inner surface of the shadow mask the arc shape of the side edges must point inwards. Through vertical Stretching the mask also stretches the arc shape, i.e. their curvature diminishes yourself. This moves all points on the outer, reinforced edge to the outside and thus also the inside of the mask in a corresponding manner. Even when the shadow mask is stretched, the outer ones on the side keep Edges have an arch-like shape, but with significantly less curvature. The Size of the constriction in the middle of the shadow mask between the upper and lower Edge results from the arch shape (curvature) of the reinforced edge before and after stretching the shadow mask. After stretching, the outer, reinforced edge of the shadow mask take an almost straight shape. In this way, a constriction can be achieved, the larger the larger the differences in the arc shape before and after the vertical stretching of the shadow mask are. Because this results in more severe constrictions than conventional can be achieved are also the horizontal tensile forces that can be generated in this way significantly larger.

These higher tractive forces allow a stronger horizontal than usual Expansion of the shadow mask can be compensated. That has the special Advantage that materials are also used for the shadow mask can, which do not have a particularly low coefficient of thermal expansion. Because of the particularly high horizontal pretension according to the invention can nevertheless be prevented that a curvature of the shadow mask in the longitudinal direction the picture tube occurs. This means that cheaper mask materials can also be used Fabrics such as Use iron without sacrificing image quality over conventional ones Masks is deteriorating. The production of color picture tubes, and thus also of monitors and televisions, can be done with the same quality cheaper.

Advantageously, the shadow mask has an arcuate shape to reinforce it Sides on these have a larger material cross section than in the inner surface of the mask. In this way, the firmness of the mask can be increased simple way to increase.

When making a shadow mask, the mask is used to create the openings usually subjected to an etching process. During this etching process the material cross section of the entire mask is reduced. An increased material cross section on the arcuate edge areas to be reinforced can be particularly produce simply by largely removing these edge areas from the etching process to be left out. As a result, these sections point after the etching process a larger material cross section than the perforated mask area.

It is also possible to increase the strength in the arcuate edge areas achieve that the shadow mask in these areas a changed material composition having. By changing the material composition higher strength can be achieved in the edge areas. To this In this way, the increase in cross-section of the mask can be smaller in edge areas or completely disappear.

The higher strength or the larger material cross section can also be produced by this be that an additional element in the edge areas to be reinforced is provided. The advantage of this procedure is that the masks initially can be produced in the usual way and finally with additional, separately manufactured elements can be combined. The invention can be based on this Easily in the usual manufacturing process of a color picture tube to get integrated. If this additional element is made of a material with increased Strength can be produced, the material cross section of this additional element turn out to be particularly low.

It is particularly advantageous if the shadow mask is made of iron can.

Fig. 1 eine geformte, selbsttragende Schattenmaske,

Fig. 2 eine Spannmaske mit Zug in vertikaler Richtung,

Fig. 3 eine Spannmaske mit Zug in horizontaler und vertikaler Richtung,

Fig. 4 den prinzipiellen Aufbau einer Farbbildröhre,

Fig. 5 einen horizontalen Verlängerungsabschnitt einer Schattenmaske im gestreckten und nicht gestreckten Zustand,

Fig. 6 einen erfindungsgemäß ausgestalteten seitlichen Randabschnitt einer Schattenmaske im gestreckten und nicht gestreckten Zustand, und

Fig. 7 das Verhältnis zwischen der Durchbiegung der erfindungsgemäß ausgestalteten seitlichen Ränder in Abhängigkeit von deren Dickenverhältnis.

An embodiment of the invention is explained with reference to the drawings. Shows in detail

1 is a shaped, self-supporting shadow mask,

2 is a tension mask with train in the vertical direction,

3 is a tension mask with tension in the horizontal and vertical directions,

4 shows the basic structure of a color picture tube,

5 shows a horizontal extension section of a shadow mask in the stretched and non-stretched state,

6 shows a lateral edge section of a shadow mask designed according to the invention in the extended and non-extended state, and

7 shows the relationship between the deflection of the lateral edges designed according to the invention as a function of their thickness ratio.

6 shows an embodiment of a shadow mask designed according to the invention 25 reproduced. The shadow mask consists of a perforated section 26 and a non-perforated section 27. Section 27 consists of two differently designed parts A and B. Part A corresponds in its Strength, especially in its material cross-section, that of the perforated / slotted Section 26 of the shadow mask. Part B, however, is in his Strength increased, for example due to an increased material cross section. The A part marked with A can by so-called etching in cross section be reduced so far that it strengthens the perforated / slotted Mask part 26 corresponds. The part marked with B, however, is designed so that it has a significantly higher mechanical strength. In section B it can either be a so-called "full material" without etching or additional material, for example by attaching another Element.

The solid lines in FIG. 6 represent, as in FIG. 5, the state of the shadow mask 25 before stretching in the vertical direction. The width of the part A of the arcuate edge is designated by x ₁ in the middle between the upper and lower edge of the shadow mask , the width of part B with x ₂ . The inward-facing radii of parts A and B of section 27 are denoted by R ₁ for the outer edge of part B, R _M for the center radius between parts A and B and R ₂ for the boundary line between part A and the perforated section 26 of the shadow mask 25.

The state of the edge region 27 of the shadow mask 25 designed according to the invention after the stretching in the vertical direction is shown in FIG. 6 with the broken line. The arch shape of the reinforced part B is straightened by the stretching. This means that the edge lines of part B have only a slight curvature compared to the radii R ₁ and R _M , which can even approach a straight line. However, an exact straight shape cannot be achieved by the stretching, so that the reinforced edges B always have a "residual curvature" in the direction of the arc shape before the stretching.

By stretching the arch shape of the reinforced edges B in turn Constriction C creates. Unlike in FIG. 5, the section is constricted 27 this time, however, not on both sides of section 27, but only on the side of section 27, which is on the perforated surface 26 of the shadow mask borders. With the shadow mask designed according to the invention, therefore, only takes place a one-sided constriction takes place, so that the total width reduction of the section 27 benefits the generation of horizontal traction. The stronger one Constriction can result in a greater horizontal bias of the shadow mask cause.

The maximum preload that can be generated depends in particular on the radii of the reinforced one B marginal areas. The greater the difference between the radii before and after the vertical stretching of the shadow mask, the larger that can be generated horizontal preload.

An exemplary embodiment of a color picture tube designed according to the invention, which can be installed in color television sets and color monitors according to the invention, has approximately the following dimensions: Height of the shadow mask about 414 mm, Shadow mask material Iron, Aspect ratio in about 4: 3, Shadow mask thickness about 0.1 mm (with the exception of the reinforced edge areas), x ₁ + x ₂ about 5 mm, R ₁ about 3.35 m, R _M approximately 12.0 m.

With such a color picture tube, horizontal tensile forces in the order of about 1000 N / mm ² can be achieved. For the effects according to the invention it is not necessary for the shadow mask of a color picture tube to have exactly these dimensions. Similarly high horizontal tensile forces can also be achieved with a shadow mask if the radius R _{1 is} less than about 4.5 m, in particular less than 4 m, and the radius R _{M is} less than 20 m, in particular less than 15 m, the Shadow mask otherwise has the dimensions given above. In the case of differently dimensioned color picture tubes, the parameters must also be varied accordingly in order to obtain sufficiently high horizontal tensile stresses.

As shown in Fig. 6, a significantly higher constriction can be inventively C than achieve with previously known methods, so that a stronger horizontal thermal expansion can be compensated for as conventional. Thereby it is only possible with shadow masks that are only on two opposite Sides are attached to the mask frame, use other mask materials, especially those that have a higher coefficient of thermal expansion. In this way, the relatively expensive Invar can be used as a manufacturing material replace with iron. Although iron has a higher coefficient of thermal expansion, but the higher horizontal bias according to the invention can Compensate for greater thermal expansion of iron so that no curvature the shadow mask occurs in the longitudinal direction of the color picture tube.

The achievable constriction C (and thus the horizontal traction) is not only from Radius of the reinforced outer lateral edges of the shadow mask, but also the degree of their reinforcement. The gain can be increased of the material cross section. The degree of reinforcement results then from the thickness ratio of the reinforced edge to the non-reinforced part the shadow mask. The horizontal tensile force that can be achieved by stretching Shape change of the arch shape of the reinforced outer edge B is based, depends on how much the extension of the arc shape of the outer Claim margins against the opposing forces of the inner surface of the mask can. The inner surface of the mask also tries to stretch in the vertical direction compensate by contraction in the horizontal direction. As a result of that the strength of the outer edge or both opposite outer edges is increased so that this essentially the shape of the inner surface of the mask Forcing on vertical stretching will increase the horizontal acting tensile force achieved.

In Fig. 7 it is indicated how with the given parameters for the shadow mask the deflection by varying the thickness ratio of parts A and B. i.e. the constriction C can vary (in mm). With increasing differences in thickness from part A to part B, i.e. with increasing material cross section of part B with the same thickness of part A, the achievable deflection and thus increases the achievable horizontal traction increases significantly. So with a shadow mask with the parameters given above with a thickness ratio of A to B of about 0.7 achieve 0.2 mm deflection. With a thickness ratio from A to B of 0.2 the deflection that can be achieved can be doubled to about 0.4 mm.

The invention is basically directed to a second bias, which is indirect is generated via a first bias. The second Bias generated in a direction that is substantially perpendicular to the direction the first bias. Due to an inward arch shape of the lateral mask edges and their reinforcement, the achievable second bias increase significantly.

Claims (9)

Color picture tube with a shadow mask (25) essentially having a rectangular shape and a mask frame (19) carrying the shadow mask (25), that the shadow mask (25) is pretensioned in two directions which are essentially perpendicular to one another, that the shadow mask (25) is clamped on two opposite sides in the mask frame (19) and the other two sides of the shadow mask (25) are not connected to the mask frame (19), and that the outer edges (29) of the sides of the shadow mask (25) which are not connected to the mask frame are strengthened in relation to the inner surface of the shadow mask and have an arc shape pointing towards the inside of the shadow mask (25). Color picture tube according to claim 1, characterized in that the reinforcement the strength of the outer edges (B) of the arcuate sides of the shadow mask (25) is achieved through an increased material cross section. Color picture tube according to claim 2, characterized in that the edges (B) of the Shadow mask (25) are reinforced by the fact that the material cross section of the Shadow mask (25) is not reduced by etching during mask production becomes. Color picture tube according to claim 1 or 2, characterized in that the edges (B) the shadow mask (25) are reinforced by the fact that the strength a changed composition of the mask material on the outer edges (B) is increased. Color picture tube according to one of claims 1 to 4, characterized in that the edges (B) of the shadow mask (25) are reinforced by the fact that additional Elements can be arranged in the border areas. Color picture tube according to claim 5, characterized in that the additional Elements consist of a material with increased strength. Color picture tube according to one of claims 1 to 6, wherein the shadow mask (25) is made of iron. Color television set with a color picture tube according to one of Claims 1 to 7. Color monitor with a color picture tube according to one of claims 1 to 7.

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