EP0164230B1

EP0164230B1 - Electron gun electrode and method of manufacturing the same

Info

Publication number: EP0164230B1
Application number: EP85303457A
Authority: EP
Inventors: Ikuya Takahara; Yoshihiro Fujimoto
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1984-05-18
Filing date: 1985-05-16
Publication date: 1989-08-09
Also published as: KR850008554A; DE3572252D1; KR910002972B1; EP0164230A1; JPS60243949A

Description

This invention relates to methods of manufacturing electron gun electrodes of cathode ray tubes, for example electrodes for in-line electron gun assemblies of color picture cathode ray tubes. In such electron gun assemblies, end walls of the electrodes must be parallel to a reference plane perpendicular to the axis of the electron gun assembly. When an electrode is prepared by laser welding flanges of first and second electrode portions, the degree of parallelism ofthe end walls of the two electrode portions with respect to the reference plane influences the precision of the completed electrode and hence of the electron gun assembly.
A conventional in-line convergence electrode is shown in longitudinal section in Figure 1. The convergence electrode is assembled such that a cylindrical upper convergence electrode portion 1 is welded by laser radiation at a plurality of positions with a cylindrical lower convergence electrode portion 2 at out-turned flanges 1 a and 2a, respectively. Reference numeral 3 denotes a welded portion. References numerals 1 and 2b denote the end walls of the upper and lower convergence electrode portions 1 and 2, respectively. The end walls 1 b and 2b have electron beam apertures 1c and 2c, respectively. An axis I of the apertures 1 and 2c is parallel with the axis of the electron gun assembly.
The upper and lower convergence electrode portions 1 and 2 are prepared by press drawing a stainless steel plate having a thickness of about 0.3 mm, and the resultant structures must be heat- treated in a hydrogen atmosphere at a temperature of 1,000 to 1,100°C so as to perform degassing and to eliminate stress. Under these circumstances, errors in parallelism of the end walls 1 b and 2b are caused by the pressing and the heat treatment. In particular, the error in each cylindrical electrode portion along its major axis is larger than that along the minor axis thereof, thereby causing an error h1 in parallelism between the upper and lower surfaces of the electrode portion.
Certain further details and design factors concerning prior art electron gun assemblies are described in GB-A-2068163 and in US-A-4234814.
The prior art describes a method of manufacturing an electron gun electrode of a cathode ray tube, comprising:

providing first and second electrode portions each comprising an end wall having the same number of electron beam apertures, a side wall extending peripherally of said end wall, and an out-turned flange extending peripherally of the free end of said side wall in a plane parallel to the end wall and perpendicular to the axes of each associated pair of said electron beam apertures; and
welding said flanges together to form the electron gun electrode.

The present invention is characterized by: prior to said welding step, locating each said electrode portion in a polishing machine having upper and lower parallel reference bases and polishing the surface of said flange remote from the end wall to improve the degree of parallelism of said surface in relation to said end wall.
An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a longitudinal sectional view of a conventional electron gun electrode;
Figure 2 is a sectional view showing deformation of a flange of an upper electrode portion so as to explain the degradation of parallelism in an electron gun electrode; and
Figure 3 is a sectional view showing the main part of a polishing machine for carrying out a method according to the present invention.

In order to best understand the present invention, a parallelism error in a conventional upper electrode portion will be described. Fig. 2 is a central sectional view showing an upper convergence electrode portion 1 obtained by drawing in the same manner as in Fig. 1. Part of a flange surface 1 a of the portion 1 is deformed by a height h2. In this manner, a parallelism error in the flange surface 1a occurs with respect to a plane A - A' perpendicular to the axis of each electron beam aperture 1c.
In order to correct such an error, the flange surface 1a is polished by a portion corresponding to the height h2, and the flange surface 1a can be precisely parallel to the ideal plane. The flange surface of the lower electrode half can also be polished to obtain a convergence electrode having polished surfaces as the lens formation surfaces.
A method of polishing the surface described above will be described with reference to Fig. 3. Referring to Fig. 3, reference numerals 4 and 5 denote bases of a commercially available polishing machine, respectively. This polishing machine has a mechanism for rotating the upper and lower bases 4 and 5 while the lower and upper surfaces of the upper and lower bases 4 and 5 are keptto be parallel with high precision. The upper base 4 has a mechanism forvertically moving the lower surface of the upper base 4 and the upper surface of the lower base 5 relative to each other while the upper and lower surfaces are kept parallel with high precision. The upper base 4 has a compressing mechanism for compressing an electrode half toward the lower base 5.
The electrode half 1 is held between the upper and lower bases in the polishing machine to polish the flange surface 1a a and a bottom surface 1 b. In orderto stably and precisely polish each surface, a polishing jig 6 is mounted on the lower surface of the upper base 4. The polishing jig 6 has at least two (three in this embodiment) cores 6b extending vertically on a table 6a fixed on the base 4. A diameter of each of the cores 6b is smaller by 0.01 mm than that of the beam aperture 1c. The tolerance of the diameter of the core 6b is 0.01 mm in the same as in the beam aperture 1c.
In operation, the cores 6b of the polishing jig 6 are fitted in the electron beam apertures 1c, respectively. The flange surface 1a deformed as shown in Fig. 2 is fixed on the base 5. The upper and lower bases 4 and 5 are rotated relative to each other while a pressure of 0.3 to 0.4 kg/cm² is applied to the surface to be polished. The polished flange surface 1a becomes precisely parallel to the ideal plane perpendicular to the axis of the electron beam aperture 1c.
Subsequently, the bottom surface 1 b is polished using the polished flange surface 1a as a reference surface, thereby obtaining a flat bottom surface 1b which is precisely parallel to the ideal plane.
In the embodiment described above, the flange surface is polished to be perpendicular to the axis of the electron beam aperture, and then the polished flange surface is used to as the reference surface to polish the bottom surface, thereby obtaining the flat flange and bottom surfaces precisely parallel to the ideal plane perpendicular to the axis of the electron beam aperture. However, when recent laser welding is performed, the flange surface often need not have higher precision than that of the bottom surface. It is important to obtain the flat bottom surface precisely parallel to the ideal plane.
As is apparent from the above description, the surface of the flange remote from the end wall and optionally also the outer surface of the end wall are polished to be parallel to the ideal plane perpendicular to the axis of the electron beam aperture, thereby improving the precision of the electron gun using such an electrode. The surfaces to be polished can be easily located using a jig having cores entering the electron beam apertures.
In this manner, when the surfaces are polished to obtain smooth, flat surfaces, the lens characteristics themselves are also improved.

Claims

1. A method of manufacturing an electron gun electrode of a cathode ray tube, comprising:

providing first and second electrode portions (1, 2) each comprising an end wall (1b, 2b) having the same number of electron beam apertures (1c, 2c), a side wall extending peripherally of said end wall, and an out-turned flange (1a, 2a) extending peripherally of the free end of said side wall in a plane parallel to the end wall and perpendicular to the axes of each associated pair of said electron beam apertures; and

welding said flanges together to form the electron gun electrode;
characterized by:

prior to said welding step, locating each said electrode portion (1, 2) in a polishing machine having upper and lower parallel reference bases (4, 5) and polishing the surface of said flange (1a, 2a) remote from the end wall (1b, 2b) to improve the degree of parallelism of said surface in relation to said end wall.

2. A method according to Claim 1, characterized by, subsequent to said step of polishing the surface of the flange (1a, 2a), polishing the outer surface of the end wall (1b, 2b) using the previously polished flange surface (1a, 2a) as a reference surface, to further improve the degree of mutual parallelism of said flange surface and said end wall outer surface of each said electrode portion (1, 2).

3. A method according to Claim 1 or Claim 2, characterized in that said step of locating each said electrode portion (1, 2) in a polishing machine is effected by fitting at least two cores (6b) of a jig through said electron beam apertures (1c, 2c), thereby polishing the surfaces to be polished perpendicular to the longitudinal axes of said electron beam apertures.

4. A method according to Claim 3, characterized in that said electron beam apertures (1c, 2c) are circular and each said core (6b) has a diameter smaller by 0.01 mm. than that of the relevant aperture.

5. A method according to any one of Claims 1 to 4, characterized in that the or each polishing step is effected by relative rotation of said located electrode portion (1, 2) and a polishing member (5) of said polishing machine under an applied pressure of 0.3 to 0.4 kg/cm².