Method of Forming a Deflection Yoke System

The present invention relates generally to television receivers, and more particularly to an improved deflection yoke system for such a receiver.

Present day television receivers generally utilize electromagnetic deflection, and incorporate a deflection yoke which fits over the neck of the cathode ray tube. This yoke contains a plurality of windings and a magnetic core positioned so that when signals are applied to the windings, magnetic fields are created to deflect the electron beam or beams in the cathode ray tube in the desired manner. These signals are applied to the yoke from deflection circuits in the television receiver chassis. The position of every windings and the shape of the coils which include the windings is of great influence to the homogeneity of the magnetic field and hence to the quality of the raster written by the electron beam or beams. Especially with color television receivers the displacement of a single winding about one diameter of the winding will lead to faults of the raster. Such displacement e.g. occurs if temperature increases during the winding procedure of mass production.

It is an object of the invention to reduce or to avoid faults in the form of the raster.

Another object is to provide a deflection coil having good performance even with wide deflection angles (e.g. 110.degree.) and multibeam deflection.

It is a further object of this invention to provide a production means and procedure to achieve saddle shaped deflection coils of improved construction.

This is accomplished, according to the above invention, by a saddle shaped deflection coil the longitudinal parts of which are formed in strands of several leads, and by providing a predetermined angle for the start of each strand. In the manufacture of said deflection coils the predetermined angle is achieved by quickly introducing means, e.g. pins, into the winding mandrel.

FIG. 1 is a perspective view of a saddle shaped deflection coil (prior art).

FIG. 2 is a cross section of the deflection coil shown in FIG. 1.

FIG. 3 is a cross section of a saddle shaped deflection coil according to the invention.

FIG. 4 is a schematic cross-sectional view of a winding mandrel as known for the manufacture of saddle shaped deflection coils.

FIG. 5 is another view of the mandrel shown in FIG. 4 and having pins for achieving coils according to the invention.

Referring now more paricularly to FIG. 1, the coil there is a product of a winding procedure as known in the art. It is one of a pair of identical coils which are assembled in a deflection yoke for establishing one of the deflection fields, for example, the horizontal field within a cathode ray tube. (The other pair of coils for establishing the vertical field may have a similar or indentical construction.) Each saddle shaped coil consists of longitudinal bundles 1 and 2 positioned around axis 5 and interconnected by lobes 3 and 4. Lobe 4 is the larger and shaped to fit the conical section of the tube envelope adjoining the neck section while the remaining lobe 3 is shaped closely to embrace the neck section. The coil is one continuous winding, which may consist of one or more parallel wires.

The said continuous winding is wound to constitute a succession of coils turns of generally similar configuration.

In FIG. 2 there is shown a cross-sectional view of a longitudinal bundle 2 of the coil shown in FIG. 1. Deflection coils of such configuration are usually wound in mandrels 10 shown in FIG. 4 and FIG. 5 in two different views. Such mandrels 10 consist of at least two portions 10a and 10b establishing a recess 15 defining a predetermined coil pattern for receiving a continuous wire and for forming the wire into consecutive coil turns having a shape corresponding to the pattern of the recess 15.

The mandrel 10 or a movable guide part (not shown) for feeding the wire into the recess is rotated or moved so that the successive coils turns are laid into said recess. After the required number of coils turns is achieved, the coil is mechanically compressed and, by application of heat, caused to integrate to one selfsustaining structure. By separating the portions 10a and 10b and loosening screw 12, the coil can be removed from the mandrel for assembling the yoke.

For achieving a homogeneous deflection field the deflection coil should be wound symmetrically. It has been found, however, that deflection coil manufactured by using mandrels as described are unsymmetrical ones. The present invention is based on the recognition that the winding mandrel 10 as presently used suffers in its winding properties as well from temperature and humidity as from variations in the "pull-of-wire" so that it is very difficult to manufacture deflection coils of equal behavior over the whole production series. With variations in the pull of wire it is possible that one longitudinal bundle is wound more loosely than the other bundle so that it will be broader than the other one. There is another disadvantage in tolerances of the diameter of the wire used. A change in the wire's diameter causes changes in the geometrical configuration of the coil because the required width of the recess is dependent on the wire's diameter. Changes in the coils configuration due to the above reasons cause faults in the raster. With color television receivers such faults are usually accompanied by chromatic aberrations. In the prior art variations in the coils configuration have been reduced by mechanically altering the width of the recess. Such procedure cannot overcome, however, changes caused by variations in humidity, temperature and different coatings of the wire.

In FIG. 3 there is shown a cross sectional view of a longitudinal bundle 2 of a deflection coil according to FIG. 1 when wound in accordance with the invention. The longitudinal bundles are distributed in different strands 16, 17, 18 and 19 being arranged at predetermined areas. This is achieved by providing starting points for each strand at predetermined angles 6, 7, 8, 9. With the manufacture of such coils said starting points are achieved by introducing pins 6, 7, 8, 9 into recesses 14, 15 at the lobes 3 and 4 which pins provide, after winding a predetermined number of turns, a starting point for the following strand. By using this construction according to the invention it is not possible that displacements of one wire can cause displacements of all following wires, too. Pins 6, 7, 8, 9 can be introduced by springs released e.g. by counters. Shooting-in the pins can be achieved mechanically or electrically by relays controlled by counters. Which kind of actuation will be of more advantage is dependent from the type of winding machines. With machines using rotating (axis 13) or movable mandrels electrical actuation will be preferred. In the foregoing description there is used the term strand for a group of coils turns being separated in at least part of the longitudinal bundles. In such a strand there are preferably used wires arranged in parallel.