Patent Application
20060038475
The present invention relates to a cathode structure for cathode ray tube and, more particularly, to a “low consumption” cathode structure.
The electron guns for cathode ray tubes that use an oxide cathode are geared towards low cost, “low consumption” systems, this low consumption resulting from new designs of the parts that make up the gun or from the part assembly techniques. The reduction in power, which, according to the state of the art, is normally approximately 4.5 W for the three cathodes, to values approximating 2.1 W, entails introducing more compact and thermally optimized systems. The use of small filament and cathode are essential to achieving the low powers required but are still inadequate. To reduce said consumption, the thermal losses must be reduced while keeping the systems simple to avoid any cost overhead compared to the standard system.
A number of techniques have been explored to reduce the thermal losses of the filament cathode structure.
The first solution involves facilitating the thermal transfer between the filament and the cathode, for example by modifying the internal absorptivity of the skirt of the cathode sleeve.
To facilitate the thermal transfer between the filament and the cathode, the interior of the skirt of the cathode is blackened by deposition or treatment to promote the absorption of the heat by the skirt, the radiative transfer between the two entities then being more effective. This method is, for example, described in the U.S. Pat. No. 5,543,682.
This solution is effective in facilitating the filament-cathode transfer but requires a relatively complicated production process, such as vapour deposition and its application is therefore costly.
A second solution, as described in U.S. Pat. No. 4,558,254, consists in modifying the shape of the skirt of the cathode sleeve itself, by giving it an S-shape combined with reducing the thickness in this area, in order to augment the conduction path and reduce the passage section of the conductive flow between the hot zone of the cathode and its support.
Another solution proposed by the latter US patent consists in limiting the thermal losses by radiation towards the rear of the cathode using a long cathode with several diameters.
All these solutions are difficult to implement and are costly for producing cathode ray tubes particularly suited to television.
One object of the invention is to provide a simple and inexpensive system for assembling a cathode for electron gun with which to ensure low power consumption levels, preferably below 2.25 W for all three cathodes.
For this, the cathode for cathode ray tube electron gun according to the invention comprises:
The invention and its advantages will be better understood from the description below and the drawings, in which:
An electron gun for cathode ray tube comprises at least one emissive cathode designed to generate an electron beam to scan a screen of luminescent materials to generate a picture on the surface of the latter.
As illustrated by
Moreover, with this structure, the thermal expansions of the sleeve and the eyelet are compensated to avoid significant movements of the cathode towards the electrode 30 when the tube is operating.
Rigid support means 20, 21, 22, conventionally linked to the body of the gun, are used to keep the emissive surface of the cathode at the nominal distance from the electrode 30 disposed facing this surface. The cathode eyelets normally include, in their end opposite to the end linked to the sleeve, shoulders 25 designed to rest on the support means and be securely attached by welding to the latter.
The gun furthermore comprises a succession of electrodes 31, 32, etc, designed to shape the electron beams from the cathodes.
This structure gives a consumption of approximately 2.3 W to 2.4 W for the three cathodes of a typical colour cathode ray tube. Detailed analysis using simulation results shows the contribution of the various elements of the structure to the overall consumption:
With reference to
The two eyelets are concentric to each other and the facing surfaces are kept at a distance from each other, the two eyelets being in contact with each other only at their shouldered end part.
The eyelet structure according to the invention, compared to the state of the art illustrated by
Compared to the single-eyelet structure, experience shows that, to obtain a notable effect on the electrical consumption, the second, outer eyelet 106 should extend longitudinally so as to cover in this direction at least 50% of the length of the first eyelet 6.
In another embodiment of the invention derived from the above, the inner eyelet 6 has been subjected to a polishing process, preferably on both sides, to give the latter reflective-surface properties. It has been noted that, from a thermal point of view, a polished surface, the surface properties of which are characterized by low roughness, emits less heat flux than a surface having a high roughness, given equal temperature and area. Similarly, a polished surface receiving a heat flux from any source is less absorptive to the heat flux than a surface having a high roughness, given equal temperature and area, because a portion of the incident flux received is reflected by the surface and dissipates into the near environment.
Consequently, the radiative flux emitted by the inner surface of the first eyelet (6) of the cathode is mostly reflected towards the cathode sleeve; the outer surface of said eyelet (6), facing the second eyelet, is advantageously also polished, which limits the thermal emission towards the second eyelet (106) and therefore reduces the radiative losses towards the latter.
The polishing of the eyelet can be achieved mechanically or electrochemically.
The eyelets 6 and 106 are, for example, made of type 305 stainless steel which is an alloy commonly used because it is inexpensive. Their thicknesses are respectively 100 μm for the eyelet 6 and 122 μm for the eyelet 106 which gives sufficient rigidity for the assembly operations and, where appropriate, for the various steps in which the parts are handled by personnel.
For a cathode according to the invention, comprising a double eyelet 6 and 106 with polished surfaces for the innermost eyelet 6, a study of the power loss gives the following analysis:
It is thus possible to reduce the consumption of the three cathodes to the required level of 2.1 W in total, this without modifying the structure of the parts of the gun by replacing a single eyelet according to the state of the art with a double eyelet.
The embodiments described above are not limiting. Since the shapes of the eyelets must be suited to the structure of the gun in which they are inserted, their shape can, for example, be different from that of a straight cylinder.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0406738 | Jun 2004 | FR | national |
