1. Field of the Invention
The present invention relates to a device for the insertion of cathodes in cathode tube guns, and especially for the simultaneous insertion of the three cathodes of a trichromatic tube.
2. Description of the Prior Art
One technique for fixing cathodes in cathode tube electron guns consists in the use of substantially sleeve-shaped "eyelets" which flare out on one side. The flared out part ends in a ring which is fixed to a supporting electrode placed just behind the first grid of the gun. The cathode is inserted in this eyelet and can move freely in it. This cathode is held at the end of a hollow rod (hereinafter called an insertion rod) connected to a vacuum tap. When the distance between the active side of the cathode and the first or second grid is adjusted to the desired value, the cathode is welded into the eyelet generally by spot or laser welding, at three or four spots.
However, despite all the care that may be taken in fixing eyelets, it often happens that these eyelets have position defects such as translational dislocations or tilts with respect to the theoretical axis. Faults of this type are detrimental to the proper positioning of the cathodes and to their adjustment, and entail the risk of damaging them when they are inserted in the eyelets or when the positioning instruments are withdrawn.
An object of the present invention is a device used to compensate for defects in the positioning and alignment of the three cathode eyelets of an electron gun cathode during the automatic positioning of the cathodes in the eyelets. This device should also enable the front-to-rear movement of the cathode in the eyelet in order to adjust the difference between the cathode and the first grid of the gun practically without any gap between the cathode and its eyelet, and should achieve this result during the simultaneous insertion of the three cathodes of a trichromatic tube.