ELECTRON-BEAM DEFLECTION SYSTEM FOR CATHODE-RAY TUBES

Abstract: Electron-beam deflection system (2) for cathode-ray tubes, which comprises a pair of vertical deflection coils (4), a pair of horizontal deflection coils and a rigid separator (2) which isolates the pairs of deflection coils from each other. The separator (2) includes, on its internal wall (11), attached additional pieces (21, 22) whose profile is matched to the profile of the deflection coils (4) that these pieces hold in position.

Description: ELECTRON-BEAM DEFLECTION SYSTEM FOR CATHODE-RAY TUBES The invention relates to an electron-beam deflection system for cathode-ray tubes, and more particularly to the device which both supports the deflection coils and ensures mechanical rigidity of the system. Such a deflection system, also called a deflector, generally consists of a pair of vertical deflection coils, a pair of horizontal deflection coils and an approximately frustoconical ring made of magnetic material intended to concentrate the flux created by the coils. The two pairs of deflection coils are electrically isolated by a separator, generally made of plastic, which furthermore makes it possible to improve the mechanical rigidity of the deflection device, to fasten the coils to each other and to adjust the assembly on the neck of the tube. The separator consists of an approximately funnel-shaped main body, made of one or more parts, and of a flexible rear part matching the neck of the tube and intended to fix the position of the deflection system along the longitudinal axis of the tube; this fastening is generally carried out by means of a clamping collar placed over the flexible rear part. In the case in which the coils have the shape of a saddle, the assembly of the various constituent elements of the deflection system takes place in the following manner: - the horizontal deflection coils are firstly placed inside the separator and generally held in place by clip-fastening and/or adhesive bonding; - next, the vertical deflection coils are placed on the external part of the separator; their front part is often fastened by introducing this part into a housing provided on the separator; - finally, the ring of ferromagnetic material is placed on the horizontal deflection coils which it covers partially. The rear part of the vertical deflection coils is immobilized so that the position of the ring of ferromagnetic material is precisely adjusted so that the fields created by the deflection coils have the desired shape for ensuring that the electron beams converge over the entire screen surface of the tube. Once this adjustment has been made, the ring is then definitively immobilized. After positioning, the constituent elements of the deflector must, in a final step, be definitively rendered integral with each other, for example, by adhesive bonding. A major problem consists in maintaining the relative position of the coils on the separator between the time when the adjustment is made and the time when they are definitively rendered integral with the body of the separator. In the case for example of saddle-shaped vertical deflection coils, it is known to fasten the front of the coil by clip-fastening it onto the front of the separator. This method remains effective as long- as the lateral harnesses of the coils connecting the front and rear bundles can bear on a ledge located on the surface of the separator and integral with the latter; this ledge is contained in the plane which separates the two coils of one and the same pair and extends from the front to the rear of the separator with a constant width ; it has the advantage of preventing the coil from rotating about the main axis of the deflector. However, this method is not very effective if the shape of the coil is such that most of the lateral harnesses, in particular at the front of the coil, no longer bear on the support ledge as in the prior art ; this is because the shapes of the deflection coils of the deflector fitted onto the neck of a cathode-ray tube determine the shapes of the field lines, and, likewise, the way in which the electron beams emanating from the gun are deflected. These coil shapes become more and more complex in order to maximize a deflection parameter and all differ from one deflection model to another. Furthermore, the separator is generally designed to be used with various sets of deflection coils for various types of tube. This is because, for reasons associated with optimizing the manufacturing costs, the separators being manufactured by injection- moulding plastic in expensive moulds, it is preferable to have a single type of mould. It is therefore not possible when moulding the separator to design a surface profile allowing the front of all types of coils to bear on this surface. In order to allow the use of a single separator model with several types of deflection coils, the invention proposes a structure for a deflector for cathode-ray tubes, which comprises a pair of vertical deflection coils (4) and a pair of horizontal deflection coils (3), at least one of these two pairs having the shape of a saddle, the saddle-shaped coils of at least one pair consisting of conductors forming a front bundle and a rear bundle which are connected to each other by lateral harnesses, the deflector furthermore including a rigid separator (2) which isolates the pairs of deflection coils from each other and means for holding the coils in position on the surface of the separator, characterized in that these means include attached additional pieces whose profile is matched to the profile of the coils that they hold in position. The invention will be more clearly understood with the aid of the description below and of the drawings among which: - Figure 1 illustrates a longitudinal section of a cathode-ray tube on the neck of which a deflector according to the prior art is fitted ; - Figure 2 illustrates one embodiment according to the prior art ; - Figure 3 is a rear view of one emoodiment of a deflector according to the invention ; - Figure 4 is a side view of a deflector according to the invention ; and - Figures 5a and 5b illustrate embodiments of the means according to the invention for holding the coils in position. Figure 1 illustrates a deflection system 1 comprising a pair of saddle-shaped horizontal deflection coils 3 and a pair of likewise saddle-shaped vertical deflection coils 4, which is isolated from the previous pair by a separator 2; a ring 5 of ferromagnetic material is placed around the coils 3 and 4. The assembly is placed on the neck 8 of the cathode- ray tube 6 so as to deflect the electron beams emanating from the gun 7 so that they scan the entire screen surface 9 of the tube. The various elements making up the system 1 may be held in place in an optimum adjustment position by adhesive bonding, the separator 2 providing both support for the various elements and ensuring mechanical rigidity of the assembly. During assembly of the constituent elements of the deflector, the deflection coils are placed on the body of the separator and their relative position is precisely adjusted so as to generate fields of desired conformation. Once this adjustment has been made, the coils must remain in place until the final adhesive- bonding step. Figure 2 illustrates one embodiment according to the prior art m which the vertical deflection coils 4 are held in place around the front bundle 10 by clip-fastening means 12, 13 and along the lateral harnesses by a separating ledge of constant width, extending from the front to the rear so that the harnesses can bear on the said wall. The rear bundle 11 of the coils is held m place on the separator, for example by using an adhesive tape 15. As illustrated m Figures 3 and 4, this separator structure is no longer suitable for holding in place the coils 4 including the lateral harnesses 18 which no longer bear on a ledge 14 of constant width. These lateral harnesses 18 have an internal edge 19 which, over a major portion of the front part of the coil, is raised and can no longer bear on the ledge 14. In the absence of other holding means, the coil 4 may undergo undesirable movements, particularly rotational movements about the main axis Z; the initial adjustment is therefore no longer guaranteed. As illustrated in Figures 3 and 4, a separator according to the invention comprises additional means (21, 22) for holding the coils in place in order to prevent in particular the rotational movement about the longitudinal axis Z which could occur before definitive fastening of the coils, for example by adhesive bonding to the separator. These means may consist of pieces 21 whose profile is designed to come into contact with the external edge 19 of the lateral harnesses 18. The pair of coils 4 is held in place so as to avoid any rotation by two flared pieces 21 of approximately triangular shape. Preferably, the piece 21 bears on that front end of the separator which lies approximately in a plane perpendicular to Z . In this way, the piece 21 is held in place more effectively with respect to the mechanical forces to which it may be subjected. Alternatively, or in addition to the pieces 21, and providing the same function, pieces 22 may hold the coils 4 in place by coming into contact with the internal edges 29 of the lateral harnesses 18. The profile of the pieces 21 and 22 matches the profile of the type of coils for which they ensure rotational immobilization about the longitudinal axis Z. The pieces 21 and 22 may be fastened to the surface of the separator by adhesive bonding. Alternatively, the pieces 21 may be fastened by clip-fastening them to moulded parts of the separator; for example, it is possible to keep the separating ledge 14 extending from the front to the rear on the surface of the separator, by adapting its cross section to the cross section 32 of the groove made in one surface of the piece 21 so as to ensure that it is held in place on the separator by clip-fastening, as illustrated in Figure 5a. In another embodiment, the surface of the separator is provided with a plurality of holes 31. These holes 31 are intended to house studs 33 of complementary shape with which that surface of the pieces 21 and 22 coming into contact with the separator may be provided, the pieces 21 and 22 being fastened to the surface of the separator by simply inserting the studs 33 into the holes 31. In this way, the means 31, 32, 33 for fastening the means 21 and 22 to the surface of the separator are decoupled from the shape of the said means 21 and 22. Thus, the profile of the means 21, 22 for holding the deflection coils 4 in place may be matched to the profile of various sets of coils without modifying the separator itself. It does not matter whether these holding means 21, 22 are placed on the internal surface or on the external surface of the separator so as to keep the horizontal or vertical deflection coils in position.

Claims: CLAIMS 1. Deflector for cathode-ray tubes, which comprises a pair of vertical deflection coils (4) and a pair of horizontal deflection coils (3), at least one of these two pairs having the shape of a saddle, the saddle-shaped coils of at least one pair consisting of conductors forming a front bundle (10) and a rear bundle (11) which are connected to each other by lateral harnesses (18), the deflector furthermore including a rigid separator (2) which isolates the pairs of deflection coils from each other and means for holding the coils in position on the surface of the separator, characterized in that these means include attached additional pieces (21, 22) whose profile is matched to the profile of the lateral harnesses that they hold in position. 2. Deflector according to Claim 1, characterized in that positioning means come into contact with the lateral harnesses of the coils of the same pair in order to hold them in place, over a length at least equal to 20% of the length of the said coils along the axis of revolution of the separator, in a radial angular position greater than or equal to 5°. 3. Deflector according to Claim 1 or 2, characterized in that the additional pieces come into contact with the deflection coils at points lying on the internal and/or external periphery of the coils. 4. Deflector according to one of the preceding claims, characterized in that the additional pieces include means (32) for rendering them integral with the surface of the separator by clip-fastening to moulded parts (14) on the said surface. 5. Deflector according to one of the preceding claims, characterized in that the additional pieces include protuberances (33) intended to be inserted into holes (31) made in the surface of the separator. 6. Deflector according to one of the preceding claims, characterized in that the additional pieces are placed on the flared part of the separator. 7. Cathode-ray tube whose deflector is in accordance with any one of the preceding claims .

Inventors: AZZI NACERDINE, MASSON OLIVIER, VOLATIER SEBASTIEN, AZZI, NACERDINE, MASSON, OLIVIER, VOLATIER, SEBASTIEN
Applicants: AZZI NACERDINE, MASSON OLIVIER, THOMSON TUBES & DISPLAYS, VOLATIER SEBASTIEN, AZZI, NACERDINE, MASSON, OLIVIER, THOMSON TUBES & DISPLAYS S.A., VOLATIER, SEBASTIEN
Application year: 2000
Main classification: H01J29
IPC codes: H01J29