GB2051467A - Cathode ray tube funnel and method of making the same - Google Patents

Abstract

A cathode ray tube funnel has a pre-machined soldering edge 1 to which the screen is soldered, and a throat tube 2. At least three bosses 3 in a parabolic region of the funnel have surfaces are accurately ground so that one point on each surface 3' lies on a common circle centred at I and lying in a first reference plane A at d1 from edge 1. Three points on the inside or outside wall of the tube 2 lie in a second reference plane B on a common circle centred at b Plane B is at a greater distance d2 from the edge 1 than plane A. The plane of soldering edge 1 is perpendicular to the axis a-b. A recess in the ground surface of at least one boss 3 acts as a locating point for a deflection coil. Setting up and milling procedures to form the worked surfaces are discussed. Bosses may be provided near the soldering edge as in colour TV tubes. <IMAGE>

Description

SPECIFICATION Cathode ray tube funnel and method of making the same This invention relates to a funnel for a cathode ray tube, especially a colour television tube, and to a method of making such a funnel.

In funnels of the kind specified, an edge of the funnel provides the so-called soldering edge, to which the television screen is soldered and the funnel throat tube is adapted to accommodate the image ray-forming mechanism.

The deflection coil is fitted on the funnel, and more specifically in the parabolic region thereof, and also on a portion of the throat tube, and its exact and immovable location is vital.

A special problem in making such funnels is the exact, i.e. as nearly perpendicular as possible, alignment of the throat tube relative to the plane of the soldering edge. However, a direct exact i.e. perpendicular, soldering of the throat tube to the base of the funnel throat is not possible; therefore, a certain amount of fine adjustment work is always necessary after the deflection coil has been fitted in order to compensate somehow for positional and directional deviations of the throat tube relative to the plane of the soldering edge.

In recent times new concepts have been developed, e.g. for colour television tubes, with the aim to avoid the need for such final adjustment work. One essential condition for this is that reference surfaces must also be provided in the parabolic funnel region for the deflection coil (abutment or engagement surfaces for the deflection coil) which is centred on the throat tube thereby ensuring exact perpendicular alignment of the coil relative to the soldering edge plane.

Accordingly, it is the aim of the present invention to provide a funnel for a cathode ray tube which, by virtue of its mode of construction realises a geometric quality system of hitherto unreached accuracy.

According to the present invention, there is provided a cathode ray tube funnel whose funnel edge provides the soldering edge for the soldering of the screen thereto, whose funnel throat tube serves to house the image ray-forming mechanism, and on whose outer wall in the parabolic region thereof are formed at least three cams which are situated in a first reference plane extending substantially parallel with the soldering plane and spaced therefrom by a defined distance, characterised by the following features:: (1) the surface of said cams is worked; (2) one point on each of said worked surfaces lies on a first circle which is common to all of the said points, the points being arranged in precisely predetermined circumferentially spaced positions on said circle; (3) the said first circle is in the said first reference plane; (4) the centre of said first circle lies on a straight line, here called the funnel axis; (5) a second reference plane, likewise substantially parallel with said soldering edge plane, is defined at a greater distance from the latter than the first reference plane; (6) at least three points on the external or internal wall surface of the funnel throat tube lie on a second circle in said second reference plane; (7) the centre of said second circle likewise lies on the funnel axis; and (8) the said funnel axis is normal to the soldering edge plane.

For describing the alignment of the funnel throat cylinder relative to the plane of the soldering edge the following reference system is generally applied; A reference plane is defined at a given distance from the soldering edge of the funnel. By hitherto applicable tube design concepts a tolerance of + 0.7 mm can be accepted for the distance between the said reference plane and the soldering edge. Two further planes, spaced apart by a distance of 76 mm, are defined in the throat of the funnel. Hitherto applied standards allowed a tolerance of + 0.25 mm, in some cases even + 0.3 mm, in respect of dissimilarity in the distance of the said two planes relative to the soldering edge surface.

There are various machining procedures which may be adopted to satisfy hitherto applied quality standards within the terms of the described reference system. For example, it is quite common to engage the funnel in a cardanic chuck applied to the outer parabolic region thereof and press it against a rotating lapping wheel wetted with a suitable abrasive.

In this way, the initially rough pressed edge is lapped until an electric proximity switch operates. Taking into account all the mechanical and electrical inaccuracies, it is possible in this manner to achieve reference plane spacings relative to the soldering edge which are within the earlier mentioned tolerance range of + 0.7 mm but it is not possible to adhere to a tolerance of + 0.1 mm, as demanded by the new concept.

There is also another method which is frequently adopted: the funnel may be equally well engaged in a chuck or gripping device with the throat pointing downwards so that the glass part touches the work support of the machine at three points which are situated on the periphery of a circle having a diameter of 110 mm. The next step is to line up the funnel throat on the outside in such a way that the centre in a first reference plane as well as the centre of a second reference plane lies on the machine axis. The funnel, thus located in respect of said points may then be further supported in the region of the funnel body near the soldering edge by suitable hydraulic or pneumatic work supporting pins.

In the course of the actual machining process, the soldering edge is now milled exactly perpendicular to the defined axis of the said two points, it being immaterial whether such milling operation is carried out with the aid of one large or several small milling cutters combined in a "crown".

None of the hitherto known methods were able to secure the desired success regarding the close tolerances imposed by the new concept, not even when the funnel was filled with water in order to suppress oscillations.

The basic, new and improved quality system underlying and realised in the present invention is more particularly explained with reference to the accompanying drawing which shows a vertical section through a funnel according to the present invention and two cross-sections.

The funnel has a soldering edge 1 to which a television screen is subsequently attached by soldering. funnel tube 2 is adapted ultimately to accommodate the image ray-form- ing mechanism.

At least three cams 3 are formed on the exterior surface of the funnel, and more specifically in the parabolic region thereof, all of which lie in a first reference plane A which is spaced a defined distance d1 away from the plane of the soldering edge 1.

A second reference plane B is defined a greater distance d2 away from the plane of the soldering edge 1 in such a way that at least three points on the external or internal wall surface of the funnel throat tube 2 lie in this plane B and also on a common circle having its centre at b.

The essential characteristic of this invention resides in that the surfaces (3') of these cams 3 are worked, e.g. ground, in such a manner that one point on each of these machined surfaces 3' is situated on a circle which is common to all of said points and lies in plane A. The centre of this circle is designated a.

A straight line passing through points a and b, here called the "funnel axis", is required to be normal to the plane of the soldering edge 1 in accordance with the following condition: each point of said soldering edge 1 must be within two imaginary planes which are normal to a-b and mutually spaced apart by a distance of 0.2mm.

It is already known to provide cams on the surface of a television tube, not only in the parabolic region but particularly also in the region of the soldering edge. These known cams simply serve as abutments or stops for the subsequent positioning of the funnel but are not suitable in their hitherto known shape and form as reference elements for a geometric quality system.

According to one special embodiment of the present invention, the cams which are provided in the region of the soldering edge may be additionally included in the above defined quality system namely by working, e.g. grinding, the surfaces of these came also so that the resultant surfaces are at an exact desired distance from the axis a-b.

According to a further embodiment of the invention a recess or depression, e.g. a notch, may be provided in the surface 3' of at least one of the cams 3 to serve as a locating point for the subseqently fixed deflection coil.

The following method is specified for making a funnel according to the present invention.

The funnel, consisting of funnel body and throat or neck part attached thereto, is premachined or pre-worked at its soldering edge, it being immaterial whether by lapping or milling. The only thing which is required is that the machining treatment applied should produce a soldering edge which is already as nearly as possible perpendicular to the defined throat axis. The funnel, with the soldering edge thus prepared, is now placed on a machine table and lined up in plane B by means of a collet or the like in such a fashion that point b will be in the vertical axis of the machine. It is recommended to choose the material pairing between soldering edge and machine table in such a way that a minimum of friction is involved in the horizontal alignment operation despite the weight of the funnel. When the funnel is thus properly set up in the machine centre, it is fixed in this position.It is basically immaterial in which mechanical manner this is done. Such fixing may be obtained, for example by vacuum application, or by means of a horizontally floating ring which engages from the outside with the rotationally symmetrical part of the funnel and presses it down on the table.

An essential feature of the present invention however, is a working process applied to glass cams (or bosses) which were previously formed by pressing in the region of the coilcontact surfaces. Depending on the shape and design of the coil element, these surfaces on the pressed glass cams or bosses which are to be machined may be surfaces of a cone whereof the axis is identical with the axis a-b, or they may be plane surfaces made parallel to the tangential direction and spaced slightly away from the exterior surface of the funnel.

It was found very convenient to produce these surfaces by a milling operation using a high speed revolving diamond cutter. In the former case the funnel is set in rotation about the vertical axis which passes through b while a milling cutter automatically cuts down the cams in such a manner that point a will also come to lie on the machine axis, that is to say that the axis a-b thus produced extends nor mal to the soldering edge within the terms of funnel alignment accuracy. In the second case the rotating milling cutter is constrained, e.g.

by means of a driven longitudinal table, to pass tangentially along the cams to be ground. This method will produce plane surface.

Prior to the milling of the cams, the funnel is turned into the correct angular position for application of the milling cutter to the cams.

In this way virtually any desired number of flats or faces can be ground over a defined circumference.

With the same line-up and set-up that is to say the same work fixation, this kind of milling unit can also be used to machine the surfaces of further cams, generally provided in colour television tubes in the region of the soldering edge of the funnel, in the desired manner.

Claims (9)

1. A cathode ray tube funnel whose funnel edge provides the soldering edge for the soldering of the screen thereto, whose funnel throat tube serves to house the image rayforming mechanism, and on whose outer wall in the parabolic region thereof are formed at least three cams which are situated in a first reference plane extending substantially parallel with the soldering plane and spaced therefrom by a defined distance, characterised by the following features:: (1) the surface of said cams is worked; (2) one point on each of said worked surfaces lies on a first circle which is common to all of the said points, the points being arranged in precisely predetermined circumferentially spaced positions on said circle; (3) the said first circle is in the said first reference plane; (4) the centre of said first circle lies on a straight line, here called the funnel axis; (5) a second reference plane, likewise substantially parallel with said soldering edge plane, is defined at a greater distance from the latter than the first reference plane; (6) at least three points on the. external or internal wall surface of the funnel throat tube lie on a second circle in said second reference plane; (7) the centre of said second circle likewise lies on the funnel axis; and (8) the said funnel axis is normal to the soldering edge plane.

2. A funnel according to claim 1, wherein further cams are likewise surface worked in such a way that the resulting finished surfaces are spaced relative to the funnel axis by an exact desired distance.

3. A funnel according to claim 1 or 2, wherein the surface of at least one of the cams is formed with a recess serving as a locating and orientation point for the subsequently fitted deflection coil.

4. A funnel according to any of claims 1 to 3, wherein the soldering edge is preworked.

5. A funnel according to claim 4, wherein said soldering edge is lapped, milled or ground.

6. A method of making a funnel according to any one of claims 1 to 5, wherein the soldering edge of the funnel is pre-worked in such a way that the soldering edge plane is substantially normal to the funnel axis whereupon the funnel is placed on said pre-worked soldering edge and so arranged in the second reference plane at the throat tube that centre of the second circle is brought to lie in the vertical machine axis in which position the funnel is fixed, and then the cams which are formed on the parabolic funnel region are worked in such a way that they satisfy the conditions listed in claim 1.

7. A method according to claim 6, wherein with the same arrangement as described in claim 5, surface working is also applied to any cams which are provided in the region of the soldering edge.

8. A method according to claim 6 or 7, wherein recesses are formed in the cams which serve as locating means for the subsequently fitted deflection coil.

9. A cathode ray tube funnel substantially as hereinbefore described with reference to the accompanying drawing.

1 0. A method of making a cathode ray tube funnel substantially as hereinbefore described with reference to the accompanying drawing.