Deflection System for Color Picture Tubes

The invention pertains to a deflection system for color picture tubes in general and to a deflection system for a color picture tube having an in-line gun system in particular.

One such deflection system is known from the German Pat. No. 28 51 014. That system includes two deflection coils which are independent of each other. The deflection coil for the vertical deflection field is wound on a core. The field formers for forming the vertical deflection field consist of four arms. These arms, are disposed within the front area of the deflection system outside the deflection coils, and extend substantially parallel in relation to the Z-axis of the color picture tube. The arms project with one half over the deflection system, and with the other half over this system in the direction of the screen of the color picture tube and are intended to conduct the stray or leakage fluxes produced by the vertical deflection coil in such a way that the vertical deflection field exhibiting a pincushion distortion.

It is one object of the invention to provide a self-converging and distortion-free deflection system for the use with color picture tubes.

In accordance with the invention, to prevent a deflection system for a color picture tube provided with an in-line gun system from causing pincushion distortions in the east-west direction on the screen, at least two plane, thin field formers are provided for on the end face of the core for the vertical deflection coils. These field formers are made from a soft-magnetic material and are substantially in the shape of ring segments.

The invention will be better understood from a reading of the following detailed description in conjunction with the drawing in which:

FIG. 1 is the sideview of a deflection system disposed on the neck of a color picture tube;

FIG. 2 is a top view of field formers; and

FIG. 3 is the top view of a second embodiment of the field formers.

In FIG. 1, only a part of the cone 1 and the neck 2 of a color picture tube are shown. In-line gun system 3 is schematically denoted in the neck 2. Deflection system 4 is slipped on to the neck 2 of the color picture tube and is connected to the cone 1 of the color picture tube with the aid of adjustable mounting elements 5.

In the coordinate system shown in the drawing, the X-axis indicates the horizontal line, and the Y-axis indicates the vertical line of the color picture tube. The Z-axis is the longitudinal axis of the deflection system or of the color picture tube respectively. In FIG. 1, the X-axis is perpendicularly on the drawing plane.

The deflection system 4 comprises a deflection coil within a coilform 6 for the horizontal deflection field. The deflection coil 7 for the vertical deflection field is disposed on the coilform 6. The deflection coil 7 includes two winding halves 7a and 7b which are both wound on to a common core 8. This core is a conical toroid. In front of the end face 14 of the core 8 are two field formers 9 of which only one is visible. These plane (flat), thin field formers 9 of a soft-magnetic material are both in the same plane extending through both the X- and the Y-axis, which is perpendicular to the Z-axis. When looked at in the direction of the Z-axis, the field formers 9 are covered almost by one half by the end face 14 of the core 8. The field formers 9 are disposed mirror-symmetrically in relation to both the X- and the Y-axes, so that their centers lie on the X-axis.

FIG. 2 shows a first embodiment of the field formers 9 in a top view. The shown field former essentially has the shape of a ring segment, with the segment angle thereof amounting to 120.degree.. The width of the ring segment amounts to approximately 15 mm. the field former 9 is shown in its position relative to the coordinate system in such a way as it is disposed on the end face 14 of the core 8 within the deflection system 4. This implies that the bisecting line of the segment angle coincides with the X-axis. For the sake of clarity, the core 8 is shown without the deflection coil for the vertical deflection field. The field former 9 includes one hole near each end of the ring segment. These holes 10 are engaged by pins 13 provided for on the coilform 6 and serving to keep the field formers in position within the deflection system 4 as shown in FIG. 1.

A top view of a second embodiment of the field formers 9 is shown in FIG. 3. This type of field former has a polygonal outer contour. There are four corners which are all mirror-symmetrical in relation to the X-axis. The first pair of corners 11 is .+-.18.degree. away from the X-axis, and the second pair of corners 12 is about .+-.45.degree. away from the X-axis. The line connecting the corner 11 and the corner 12 forms an angle of about 26.degree. with a line which is perpendicular to the X-axis.

The field formers 9 may also be of polygonal design on their inner contours. It is also possible for both the outer and the inner contours to have a polygonal design.

To diminish the effects of the field formers, it is also possible to cut out of the field formers 9 a segment symmetrically in relation to the X-axis. The four field formers resulting therefrom, assume within the deflection system 4 the same position as the two field formers described with reference to FIG. 1. When four field formers are used, they may also be arranged in pairs in different X-Y planes.

The deflection field produced by the vertical deflection coil is an inhomogeneous field which exhibits a pincushion distortion in the front part, and a barrel distortion in the rear part of the deflection system. This inhomogeneous field can be described by the superposition of a dipole with a sextipole and with multipoles of higher order. The field formers 9 reinforce the sectipole and the multipoles of higher order in such a way that a strong pincushion field will result in the front part of the deflection system. In this way it is achieved that there will be no pincushion distortions on the screen of the color picture tube in the X direction (east/west direction). The corners 11, 12 in the outer or the inner contours of the field formers respectively, reinforce the multipoles of higher order.