Deflection unit for cathode ray tubes

#This invention relates generally to electron beams deflection systems for cathode ray tubes, and more particularly, to a magnetic deflection system having coil windings disposed in slots of a coil form.

#German patent reference DE-OS No. 28 07 978 teaches that it is difficult to achieve a suitable shape for a magnetic field produced by the windings of a cathode ray tube (CRT) deflection yoke of the type which conforms to the flared shape of the CRT envelope. The reference further states that the higher sensitivity of saddle-shaped coils with respect to toroid coils renders the production of suitable field shapes particularly difficult. Accordingly, the designers of CRT equipment have heretofore encountered difficult design choices. On the one hand, it is desirable to extend the portion of the electron beam axis throughout which the electron beam of the CRT is under the influence of the magnetic deflection field so as to achieve improved deflection sensitivity. However, such a technique would require either a lengthening of the neck of the envelope, which is generally undesirable, or the mounting of the deflection coils partially around the flared portion of the envelope. It is a further problem, however, that the mounting of the deflection coils over the flared portion of the envelope increases the distance between the coils and the electron beam, thereby diminishing the degree of influence of the magnetic field over the electron beam.

#The prior art has thrust at the problem of decreased sensitivity resulting from increased distance between the deflection coils and the electron beam by utilizing saddle-shaped coils. As indicated, although such coils have greater sensitivity than toroid coils, the production of a suitable magnetic field shape is difficult to achieve. In one prior art arrangement, saddle-shaped coils for one dimension of deflection are disposed in contact with the CRT envelope. The coils for the second dimension of deflection are disposed over the first set of coils, either as toroidal or as saddle-shaped coils. Accordingly, the second set of coils is disposed further from the electron beam than the first set of coils, thereby requiring much greater amounts of electric deflection power.

#Comprehension of the invention is facilitated by reading the following detailed description in conjunction with the annexed drawings in which:

#FIG. 1 is a cross-sectional representation of a coil form according to the principles of the invention;

#FIG. 2 is a front plan view of the coil form;

#FIG. 1 shows a cross-section view of a coil form 1 which has several slots 2 on its inside. In order to preserve the clarity of the drawing, only the slots on the upper half of the coil form are shown. Slots 2 are separated from one another by several ribs 3 which are shown shaded in the drawing. In this embodiment, coil form 1 is flared in the form of a horn so as to correspond to the shape of a CRT envelope. When the form is mounted on a CRT, ribs 3 are in contact with the CRT envelope. As will be described below, vertical and horizontal deflection coils (not shown in this figure) are wound on the coil form so as to be disposed in slots 2. The coil form is provided with a plurality of coil head chambers 4, 5, 6, and 7 which are formed from chamber walls 10, 11, 12, 13, 14, and 15. Wall 10 is shown in this embodiment to have a greater diameter than its associated chamber walls 15 and 14, so as to permit a yoke ring to be mounted thereon, as will be explained hereinbelow.

#The figure shows two winding turns 8 and 9 which are associated with one each of the horizontal and vertical deflection coils, respectively. Turn 8 which is illustratively associated with one of two horizontal deflection coils extends out of the plane of the figure at chamber 7, runs along a longitudinal slot, and into the plane of the paper at coil chambers 4. The other turns (not shown) of the horizontal deflection coils are correspondingly disposed in associated slot 2. Turn 9 which is associated with one of two vertical deflection coils extends out of the plane of the paper at chamber 6, runs along a slot 2, and reenters the plane of the paper at chamber 5. It is apparent from the figure that turns 8 and 9 are equidistant from a longitudinal central axis (not specifically shown) of the coil form, and therefore the completed coils have substantially equal diameters.

#FIG. 2 shows a frontal view of coil form 1, and shows the cross-section of section planes E and F along which the cross-sectional representation of FIG. 1 is presented. Longitudinal slots 2 are shown, and are provided with respective lower case letter designations which will facilitate the description, hereinbelow. The figure further shows the end faces of ribs 3 which merge into a front wall 11 of coil head chamber 7. Front wall 11 is shown to be discontinuous so as to permit communication between coil head chambers 7 and the slots 2. As can be seen from FIG. 1, predetermined ones of slots 2 which contain turns of wires to coil head chamber 7 run under a chamber 6, and therefore do not communicate with chamber 6. However, other ones of slots 2 which carry wires to chamber 6, such as turn 9 in FIG. 1, may communicate with either chambers 6 or 7. Chambers 6 and 7 are separated from each other by a partition wall 12. Partition wall 12 is visible through some of the slots in FIG. 2. A chamber wall 13, which is shown in cross-section in FIG. 1, is also visible through other slots in FIG. 2.