Position adjusting method for deflecting yoke

A position adjusting method for a deflecting yoke of a color cathode-ray tube, where measurng equipment is positioned so that the measuring surface of the equipment is directed upwards, the color cathode-ray tube is positioned so that the panel surface of the tube directs downwards and the panel surface of the color cathode-ray tube is mounted on the measuring surface of the measuring equipment.

BACKGROUND OF THE INVENTION 
The present invention relates to a position adjusting method for a 
deflecting yoke of a color cathode-ray tube applied when the yoke is 
mounted on the tube, and especially to a position adjusting method 
comprising a special positioning of a color cathode-ray tube with respect 
to measuring equipment. 
A color cathode-ray tube has, on the inner surface of the panel of the 
tube, a stripe-shaped or dot-shaped fluorescent surface having colors of 
green, blue and red arranged in accordance with the slots formed in a 
shadow mask located in the tube. In mounting a deflecting yoke on the 
tube, the deflecting yoke is first adjusted in its position relative to 
the fluorescent surface, and then secured to the tube. The position 
adjusting process for the yoke includes a luster position adjustment, a 
purity adjustment and a convergence adjustment. The luster position 
adjustment is achieved by rotating the yoke around the deflection axis, 
the purity adjustment is achieved by shifting the yoke relative to the 
fluorescent surface in the direction of the central axis of deflection, 
and the convergence adjustment is achieved by shifting the yoke in a plane 
perpendicular to the central axis of deflection, i.e. parallel to the 
fluorescent surface of the tube, namely in a plane including X and Y 
directions as indicated in the drawings. These adjustments run into 
several dimensions, and require much labor. 
In the prior art, a cathode-ray tube is positioned in a state where the 
panel surface thereof faces in horizontal direction. Then, measuring 
equipment is attached to the cathode-ray tube, and the position of the 
yoke is adjusted. This method has problems as described below. 
First of the, the adjustment is influenced by earth magnetism. Heretofore, 
in carrying out a purity adjustment, when an adjustment achieved in the 
case where the tube panel faces east is selected as a standard adjustment, 
this standard adjustment is to be confirmed in other situations such as 
when the panel faces north or south. In this adjusting method, however, 
the electron beam through the tube is influenced by the vertical magnetic 
field of the earth, and the positional relation between the electron beam 
and the fluorescent surface is disturbed. 
Secondly, the dielectric strength of the tube against a high voltage 
becomes a problem. In a color cathode-ray tube having an electron gun of 
the multi-stage type where a high voltage is applied to each electrode, 
there is a risk that foreign matter which might exist in the tube may drop 
into the electron gun when the panel is directed horizontally for an 
adjustment, thereby deteriorating, due to the foreign matter, the 
dielectric strength against a high voltage which is applied to the 
electron gun. 
Thirdly, there is a problem with respect to handling of the measuring 
equipment. In case where the panel surface faces in a horizontal 
direction, the measuring equipment is required to be pressed against the 
panel surface where the equipment is to be attached to the panel. 
SUMMARY OF THE INVENTION 
An object of the present invention is to solve the above-mentioned problems 
of the prior art. 
Another object of the present invention is to provide a position adjusting 
method for a deflecting yoke which is not influenced by earth magnetism, 
involves no risk of injury to a cathode-ray tube having a electron gun of 
a multi-stage type, and facilitates the handling of the measuring 
equipment. 
For achieving the above-mentioned objects, the position adjusting method 
for a deflecting yoke according to the present invention comprises the 
steps of positioning a measuring equipment in a position where the 
measuring surface thereof faces upwards, positioning a color cathode-ray 
tube on the measuring equipment with the panel surface of the tube facing 
downwards, and adjusting the position of the deflecting yoke.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 shows a position adjusting method for a deflecting yoke of the prior 
art. For adjusting the position of the deflecting yoke 4, a color 
cathode-ray tube 1 is disposed in a position where the panel 2 of the tube 
faces in a horizontal direction, and then, measuring equipment 3 is 
attached to the panel surface 2. Usually, at first, the tube 1 is 
transferred by transfer means such as a conveyer (not shown) to a position 
opposite the measuring equipment 3, and then the measuring equipment 3 is 
shifted towards the tube 1. Next, the relative positions between the tube 
and the measuring equipment are adjusted with respect to X and Y 
directions perpendicular to the central axis of deflection, i.e. parallel 
to the fluorescent surface of the tube, with respect to Z direction 
parallel to the central axis of deflection, i.e. perpendicular to the 
fluorescent surface, and with respect to a rotation around the deflection 
axis. For holding the above-mentioned relative positions constant between 
the tube 1 and the measuring equipment 3 during the adjusting process in a 
situation where the panel 2 of the tube 1, faces in a horizontal 
direction, the measuring equipment 3 is required to be pressed on the 
panel 2 with a force F. In this situation, the position of the deflecting 
yoke 4 is adjusted as follows. First of all, a purity adjustment is 
achieved by adjusting the yoke position relative to the tube 1 mainly in 
the Z direction in situation where the panel of the tube faces east, and 
then the adjustment thus obtained is confirmed in the situations where the 
panel of the tube faces north and south, respectively. FIG. 3A shows a 
positional relation between fluorescent bodies 6 and electron beams 5 
obtained on the panel surface 2 by an adjustment of the tube situation 
with the panel facing east. This positional relation obtained by the 
above-mentioned purity adjustment varies as shown in FIGS. 3B and 3C, when 
the tube is turned for the panel to face north and south, respectively, 
due to the influence of the vertical magnetic field of the earth magnetism 
on the electron beams 5. A convergence adjustment includes a static 
control process (STC) where the deflecting yoke is inactive and a dynamic 
control process (DYC) where the deflecting yoke is active, and is achieved 
by shifting the position of the deflecting yoke 4 relative to the tube 1 
in X and Y directions passing through the central axis of deflection and 
by rotating the deflecting yoke in .theta. direction around the same 
central axis (refer to FIG. 1B). A luster position adjustment is achieved 
by rotating the deflecting yoke in .theta. direction around the central 
axis of deflection. 
FIG. 1A shows an arrangement of a tube and a measuring equipment according 
to the present invention. In FIG. 1, the measuring equipment 3 is fixed in 
a predetermined position with its measuring surface facing upwards, and 
the cathode-ray tube is transferred by transfer means (not-shown) such as 
a conveyer, and mounted on the measuring equipment with the panel 2 of the 
tube 1 facing downwards. After the position of the tube 1 is adjusted 
relative to the measuring equipment with respect to X, Y and .theta. 
directions as shown in FIG. 1B, the position of the deflecting yoke 4 will 
be adjusted relative to the tube 1 in the situation where the tube and the 
yoke are as shown in FIG. 1A. 
A positional adjustment of the yoke 4 carried out with the panel 2 of the 
tube 1 facing downwards has the following advantages. First of all, the 
adjustments are not influenced by the vertical magnetic field of the 
earth. In consequence, the positional relation between a fluorescent body 
and an electron beam is maintained constant independently of the facing 
direction of the panel, thereby making it unnecessary to adjust the 
position of the yoke 4, as in the prior art, in tube situations having 
specified panel directions. Secondly, since the panel of the tube is 
facing downwards during adjustment, there is no risk of any foreign matter 
existing in the tube dropping into the electron gun, which may cause a 
decrease of the dielectric strength of the tube. Thirdly, since the panel 
surface 2 of the tube 1 is pressed on the measuring surface of the 
measuring equipment 3 by virtue of the gravity force g, no other force is 
required for pressing the panel 2 against the measuring equipment 3, such 
as required in the prior art as shown by letter F in FIG. 2. Further, 
since the measuring equipment is fixed, it becomes unnecessary to move the 
measuring equipment 3 towards the tube 1 and to adjust the position of the 
measuring equipment relative to the tube 1 in the Z direction. 
While the invention has been described in its preferred embodiments, it is 
to be understood that the invention is not limited thereto but may be 
variously embodied within the scope of the following claims.