Demagnetization and earthing device for a picture tube and machine for manufacturing same

A device for demagnetization of the picture tube of a television receiver and earthing of the conductive coating applied to the cone of the tube includes a demagnetization coil system (4) constituted by a bundle of insulated electric wires held together and forming at least one loop applied to the cone of the tube. The wires of the strand are held together by a tape of plastic material wound helically around them, while a bare electric wire (1) is wound helically with the same pitch as the tape. This wire is connected to earth (15, 16).

BACKGROUND OF THE INVENTION 
The invention relates to a device for the demagnetization of a picture tube 
of a television receiver and for earthing a conductive coating applied to 
the cone of the tube. The device includes a demagnetization coil system 
constituted by a bundle of electrically insulated wires held together and 
forming at least one loop applied to the cone of the tube as well as an 
electrical conductor connected to earth and arranged so as to be in 
electrical contact with the coating. 
A device fulfilling this function and comprising the aforementioned 
elements is described, for example, in the German Utility Model No. 
7030109. The device described in this document utilizes a metallic piece 
in the form of a spider, whose legs are fixed to gaps of the band of the 
picture tube by means of hooks and noses and are themselves provided with 
fingers for fixing the demagnetization coil as well as with recesses which 
permit of hooking a conductive tape for earthing provided with a tension 
spring. 
This device comprises a mechanical support, whose cost price is added to 
that of the coil and of the earthing tape, while the mounting of the 
assembly requires hooking the legs and positioning the noses, then the 
coil and finally the tape and its spring. 
SUMMARY OF THE INVENTION 
The invention has for its object to provide a device, which in itself is 
inexpensive and whose positioning is considerably simplified. For this 
purpose, the device according to the invention is characterized in that 
the earthing conductor encloses the wire bundle of the demagnetization 
coil system. Thus, this conductor does not require any specific fixing 
member and does not require a specific mounting operation either; it is 
fixed simultaneously with the coil. Moreover, the contact between this 
conductor and the coating is ensured along several distinct lines in 
different regions of the coating, which reduces its electrical resistance. 
In a preferred embodiment, in which the wires of the bundle are held 
together by a tape of plastic material helically wound around them, the 
conductor is advantageously a bare electric wire wound helically with the 
same pitch as the tape. Thus, it is possible to manufacture the coil 
system without the addition of the conductor requiring supplementary 
operations, while the cost price of the just-mentioned electric wire is 
substantially negligible. 
In another embodiment, in which the wires of the bundle are held together 
by a sheath of plastic material enclosing them, the conductor is 
advantageously constituted by the sheath itself, which is made conductive 
at least at the surface. 
Moreover, the device has an indirect advantage. The good isolation of the 
coil system connected to the mains is very important and standards provide 
for the testing of this isolation. Unfortunately, in order to carry out 
this test, an electrical contact surface has to be provided around the 
bundle; therefore, this test could be carried out according to the prior 
art only by taking samples at random at the expense of safety. With the 
device according to the invention, each coil system is provided with an 
earthing conductor enclosing it, while an isolation test over 100% of the 
members can be readily carried out. 
In order to ensure without supplementary material and in a single operation 
that the coil is fixed, the earthing conductor is fixed and also the band 
of the tube is earthed, in the case of a tube intended to be fixed by 
means of ears with which it is provided, the bundle of the coil system 
provided with the earthing conductor advantageously passes in front of the 
ears and is fixed by only these means. Moreover, this affords the 
advantage of ensuring without supplementary means that the antiimplosion 
band of the tube is earthed. When the device is provided with a conductor 
for the electrical connection of the demagnetization coil, the conductor 
may advantageously be also connected to one of the terminals of the said 
conductor. 
The invention also relates to a machine for manufacturing a demagnetization 
device according to the invention, by means of which the wire bundle of 
the demagnetization coil system is enveloped, this machine being provided 
with a rotatable magazine for supplying a tape of plastic material and 
winding it helically around the bundle, as well as advantageously with a 
second rotatable magazine taken along with the first magazine for 
supplying and winding a bare conductive wire in order to wind during one 
and the same winding operation the conductive wire and the tape of plastic 
material. Thus, only a slight increase of the investment with respect to 
the machine permits of obtaining a quasi gratuitous earthing means. For 
each television apparatus constructed, the price of an earthing bundle 
provided with a specific spring, of its fixing means and of the fixing 
operation itself is economized.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
The cathode-ray tube or picture tube shown in FIG. 1 is coated with a 
conductive coating 7, in general a graphite coating, on the major part of 
its cone 6. It is provided with a metallic anti-implosion band 5, which 
carries ears 31, 32, 33, 34 for fixing the tube. It must in addition be 
provided with a demagnetization coil system; this coil system comprises a 
plurality of insulated electrical wire turns constituting a bundle of 
wires held together, the whole resembling a kind of pipe which is applied 
to the cone 6 of the tube so as to form therein at least one loop. 
As shown in FIG. 2A, this pipe 4 can be arranged so as to form two loops, 
one of which is located on the upper half of the cone, while the other is 
located on the lower half thereof, the collar 13 of the tube not being 
included in a loop. 
As shown in FIG. 2B, the pipe 4 can also be arranged so as to form two 
loops, the collar of the tube being included in one of the two loops, 
which is larger than the other. 
Otherwise, an electrical conductor, in this case an electric bare wire 1, 
connected to earth is wound helically around the wire bundle 4. 
The band 5 of the tube is thus provided with ears 31 to 34, which permit of 
fixing the tube in a cabinet or a chassis. The bundle 4 provided with the 
earthing conductor 1 passes in front of the ear 31 (the term "in front of" 
means: "on the side of the front face of the tube", that is to say behind 
the ear in the Figure), follows the band to the ear 32, in front of which 
it passes, traverses diagonally the cone to the ear 34, passes in front of 
the ear 34, passes along the band and passes in front of the ear 33, then 
traverses again diagonally the cone whilst passing under the collar 13 to 
the ear 31, in which the starting point of this description of the path of 
the bundle is located. Thus, the bundle is fixed to the tube 6 solely due 
to the fact that it passes in front of the ears. A spring 8 (FIG. 2A) 
drawing the two diagonal arms of the path towards each other ensures a 
tension of the coil system by which it is applied to the graphite-coated 
cone, which thus permits of obtaining an electrical contact between the 
wire 4 wound helically around the bundle and the graphite coating of the 
tube. Two rings 14 (FIG. 2B) formed from a notched belt with irreversible 
clamping can also ensure the tension of the coil system. 
The coil system is provided with a connector 2, to which the ends of the 
insulated electrical wire are connected, which constitutes the coil 
system; it is interesting to utilize this connector to also connect 
thereto the earthing conductor 1, which provides a means for connecting 
this conductor to, for example, the mass of a chassis. 
FIG. 3 shows a section of the bundle of FIGS. 2. The isolated conductive 
wires 12 are enclosed by a tape 10 of plastic material wound helically 
around them and holding them together. The conductor 1 is a bare electric 
wire, for example of galvanized copper, which is helically wound around 
the plastic tape 10. Moreover, it is advantageous for simplifying the 
manufacture of the assembly that this wire is wound with the same pitch as 
the tape 10. 
FIG. 4 shows a section according to another variation of a bundle according 
to the invention: the bundle of isolated conductive wires 12 is enclosed 
in this case by a sheath 9, which holds the wires of the bundle together; 
this cylindrical sheath of plastic material can be welded at 11 along a 
generatrix, for example by means of ultrasonic welding. According to the 
invention, this sheath is made of a material charged with conductive 
particles, or it is metallized at the surface. It is connected to earth by 
any known means, for example by providing an earthing wire 16 with elastic 
pincers 15 (FIG. 2B), which clamp the bundle at a point of its length, or 
by connecting the spring 8 of FIG. 2A to earth. 
At least one connection means with earth of this kind always remains 
necessary, even in the case in which there is a wire 1 connected to the 
connector 2 because several masses have to be combined at the coating of 
the cone and it is necessary that they are taken to different points. 
(inter alia the mass of a "focus spark cap" situated near the neck of the 
picture tube need not be connected to the same point of the sheath of the 
strand as the other masses). For this purpose, metallic rings 14 may also 
be imagined, which would be provided with eyelets for connecting thereto 
an earthing wire of the kind of the wire 16. 
A machine for enveloping a bundle as shown in FIG. 3 is shown 
diagrammatically in FIGS. 5 and 6. In FIG. 5, a coil 17 supplies a tape 
10, which is taken along and guided by pulleys 18 and then traverses an 
element 19 for measuring the supplied length and a cutting system 20. The 
tape is then positioned on a circular rotatable magazine 25 constituted by 
a wheel carrying near its rim a plurality of fly-wheel pulleys 41 to 48. 
The coiled bundle 4 to be enveloped traverses the magazine at its centre 
parallel to the axis of rotation of the magazine, i.e. perpendicularly to 
the plane of the drawing. 
FIG. 6 shows with the same reference symbols as FIG. 5 the elements in the 
region of the magazine 25 viewed from the side, that is to say that the 
observer is situated substantially in the plane of the wheel. The dotted 
loop 39 indicates that the coil system 4 is a ring, which is closed whilst 
passing through the exterior of the magazine 25. The coil system 4 is 
introduced into the magazine before the machine is made operative whilst 
passing through a groove 24 in the wheel of the magazine and it is 
stretched so as to be firmly held at the centre of the magazine 25. 
In order to start the winding operation, for example, the beginning part of 
the plastic tape is taken manually to the coiled bundle 4 and, for example 
it is fixed thereto by means of an adhesive tape. The magazine 25 is then 
caused to rotate in the sense of the arrow 38 so that the tape is 
simultaneously wound around the coil system at 27 and tape is disposed on 
the fly-wheel pulleys, as indicated by 26. A pincer system 40 ensures the 
tension of the tape. The coil system 4 is advanced synchronously in a 
direction indicated by the arrow 35 of FIG. 6, which leads to a helical 
winding operation. Of course the length of tape used for each turn around 
the coil system 4 is considerably shorter than that wound at 26 with the 
given diameter ratio. Consequently, the tape has to be cut with the 
cutting system 20 when the length necessary for enveloping the whole coil 
system 4 has been measured by the aforementioned measuring element 19. The 
magazine then continues to rotate and the fly-wheel pulleys rotate in 
themselves (in this case in the counterclockwise direction) in order to 
permit the tape of advancing with respect to the wheel 25. 
The machine as described thus far is known and is commercially available 
and therefore need not be further explained. Especially the various 
supports and motors providing for ordinary mechanical solutions are not 
shown. 
According to the invention, a second magazine is added to this machine for 
supplying and winding a bare conductive wire, which magazine is 
constituted advantageously in this case by a set of second fly-wheel 
pulleys arranged on the same axes as the first pulleys. They are shown in 
FIG. 6, in which the reference numerals 41 to 48 of the pulleys of FIG. 5 
are repeated with an additional reference symbol "A" or "B" (only a 
certain number of these pulleys are represented for the sake of clarity of 
the Figure). 
The pulleys provided with the reference symbol "A" correspond to the prior 
art and support the plastic tape, while those provided with the reference 
symbol "B" constitute the second magazine. 
A coil 21 of wire 1 supplies the bare electric wire through guides 22 
followed by a system analogous to that intended for the tape, in which the 
reference numerals 23, 29, 30 correspond to the reference numerals 18, 19 
and 20, respectively. 
Thus, the wire 1 and the tape 10 are wound during one and the same winding 
operation. 
The reference numerals 1, 36, 37 of FIG. 6 for the wire correspond to the 
reference numerals 10, 26 and 27, respectively, for the plastic tape. 
At the beginning of the winding, a few turns are made with the tape and the 
wire is fixed on the coiled bundle 4 only then. This procedure permits of 
the wire not being covered by the next turn of the tape.