Mask vibration damping in cathode ray tubes

A cathode ray tube which includes a faceplate having on its inner surface a centrally disposed phosphor screen, and a flat color selection electrode supported in tension, spaced from the screen. The electrode has a central apertured portion and a peripheral portion, and is susceptible to vibration. A vibration damping system is located on the peripheral portion of the electrode for damping vibrations in the electrode.

FIELD OF THE INVENTION 
This invention generally relates to cathode ray tubes and, particularly, to 
means for damping the resonant mask vibrations in tension mask color 
cathode ray tubes. 
BACKGROUND OF THE INVENTION 
As is known in the art, a color cathode ray tube generally is constructed 
with a glass envelope having a color phosphor screen or layer formed on 
the inner surface of a panel of the glass envelope. A color selecting 
electrode is located within the envelope opposing the phosphor screen. An 
electron beam is emitted from an electron gun located within a neck 
portion of the envelope, the electron beam being scanned by an 
electromagnetic deflecting device for impingement on a desired phosphor or 
phosphors of the phosphor screen. 
In conventional color cathode ray tubes having two-dimensionally curved 
color selecting electrodes or shadow masks, the curvature of the mask and 
its thickness causes it to be structurally self-supporting. Another type 
of commercial shadow mask is tensed on a cylindrical support frame and is 
not self-supporting as is the two-dimensionally curved type. It is used in 
conjunction with a cylindrically configured phosphor screen. A new type of 
shadow mask tube has a perfectly flat faceplate and an associated 
perfectly flat shadow mask. The shadow mask is a very thin foil maintained 
at a tension of tens of thousands of pounds per square inch. The 
afore-described cylindrical and flat tension shadow mask configurations 
are prone to vibrations, as may be caused by external pulses, or by a 
speaker in an associated television receiver, for example. The resonant 
frequency of vibration of the mask will vary depending on the mechanical 
parameters of and tension in the mask. Any vibration of the mask will 
cause electron beam landings to be out of registry with their respectively 
associated phosphor elements, causing color impurities in the reproduced 
images. 
Various means have been suggested for damping the resonant vibrations 
described above. For instance, in U.S. Pat. No. 3,638,063 to Tachikawa et 
al, dated Jan. 25, 1972, a damping wire or rod is stretched across grid 
elements of the tube. With such an arrangement, the grid elements are 
resiliently pressed by the damping rod and, therefore, are not likely to 
be caused to vibrate by external mechanical shocks or electron beam 
bombardment. In U.S. Pat. No. 4,504,764 to Sakamoto, dated Mar. 12, 1985, 
resonant vibrations are damped by making the resonant frequency of at 
least one aperture grid element of the color selecting aperture grill so 
as to be different from that of another grid element in the vicinity 
thereof. It should be noted that with such prior art systems, (1) the 
grids or grills are cylindrically curved, rather than being flat, and (2) 
the grill includes a number of parallel band-shaped grid elements. 
Therefore, with the system of Tachikawa et al, the damping rod can be held 
against the grid elements because of the curved nature of the cathode ray 
tube screen. In Sakamoto, the grid elements themselves can be selected of 
different resonant frequencies. Such solutions to the problem of resonant 
vibrations are not appropriate with color cathode ray tubes using 
apertured shadow masks which are flat and in high tension. A damping rod 
or wire cannot be held in engagement with a flat shadow mask. 
More particularly, a tension shadow mask is a rectangular membrane 
suspended in a high vacuum within the cathode ray tube envelope under high 
mechanical tension. The shadow mask is flat and, therefore, is capable of 
vibrating in so-called "membrane modes," i.e., the two-dimensional 
equivalent of the vibrations of a stretched string. This type of vibration 
is defined by the fact that the restoring force due to stiffness is 
negligible compared to that due to tension. The most prominent membrane 
mode is the fundamental one, with maximum amplitude in the center of the 
shadow mask. Elsewhere, the amplitude is a sinusoidal function of 
position. It is readily apparent that prior art mask damping devices, such 
as damping wires stretched in engagement with a cylindrically curved 
grill, are ineffective for use with a flat tension shadow mask. This 
invention is directed to providing a solution to the problem of damping 
resonant vibrations in a flat tension shadow mask. 
OBJECTS OF THE INVENTION 
It is a general object of the invention to provide, for use in a color 
cathode ray tube having a color selection electrode supported in tension, 
means for avoiding a deterioration of picture quality caused by external 
vibrations. 
It is another object of this invention to provide for use in a color 
cathode ray tube a color selection electrode supported in tension and 
vibration damping means for damping vibrations in the electrode. 
It is an important object of this invention to provide such vibration 
damping means which maintains its effectiveness in spite of significant 
changes in the resonant frequency of the color selection electrode which 
may result from heating and cooling of the electrode. 
It is another object to provide such vibration damping means which does not 
occupy any portion of the scanned active area of the electrode and which 
therefore casts no shadow on the picture area of the screen. 
It is yet another object of the invention to provide such vibration damping 
means which is low in cost, easy to install and is not apt to damage a 
fragile foil electrode. 
It is still another object to provide such vibration damping means which is 
able to withstand the high temperatures encountered during tube processing 
and is compatible with the vacuum environment within a cathode ray tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to FIG. 1, there is shown a video monitor 10 that houses a 
color cathode ray tube 12. The design of the video monitor is the subject 
of copending design patent application Ser. No. 725,040, of common 
ownership herewith. The tube could as well be contained in a television 
console of the home entertainment type. The tube 12 shown is notable for 
the substantially flat imaging area 14 that makes possible the display of 
images in undistorted form. Imaging area 14 also offers a more efficient 
use of the screen area as the corners are relatively square in contrast to 
the rounded corners of the present-day home entertainment cathode ray 
tube. 
With reference also to FIGS. 2, 3 and 4, a front assembly 15 is depicted 
and includes a glass faceplate 16 noted as being flat, or alternately, 
"substantially flat," in that it may have finite horizontal and vertical 
radii, for example. Faceplate 16, depicted as being flangeless, is 
indicated as having on its inner surface 17 a centrally disposed phosphor 
screen 18 on which is deposited an electrically conductive film (not 
shown), typically composed of aluminum. The phosphor screen 18 and the 
conductive film comprise the electron beam target area. 
Screen 18 is shown as being surrounded by a peripheral sealing area 21 
adapted to be mated with a funnel 22. Sealing area 21 has, by way of 
example, three cavities: 26A, 26B and 26C therein. The cavities provide, 
in conjunction with complementary rounded indexing means, for indexing 
faceplate 16 with funnel 22. 
Funnel 22 has a funnel-sealing area 28 with second indexing elements 30A, 
30B and 30C therein in orientation alike to indexing elements 26A, 26B and 
26C. Indexing elements 30A and 30B are depicted in FIG. 4 as being 
V-grooves in facing adjacency with the cavities 26A and 26B. (Indexing 
elements 30C and 26C are similarly located.) The V-grooves of indexing 
elements 30A, 30B and 30C are preferably radially oriented, and the 
indexing elements are preferably located at 120 degree intervals in the 
funnel-sealing area 28. Ball means 32A, 32B and 32C, which provide the 
afore-described complementary rounded indexing means, are conjugate with 
the indexing elements 26A, 26B and 26C, and 32A, 32B and 32C for 
registering faceplate 16 and funnel 22. The indexing means set forth in 
the foregoing and their application to the foil tension mask technology is 
described and claimed in referent copending applications Ser. Nos. 572,088 
(now U.S. Pat. No. 4,547,696); 572,089; 727,486 (now U.S. Pat. No. 
4,695,523); 729,015; 754,786 (now U.S. Pat. No. 4,672,260); 754,787 (now 
U.S. Pat. No. 4,712,041); 758,174 (now U.S. Pat. No. 4,713,034) 831,697 
(now U.S. Pat. No. 4,692,660); and in U.S. Pat. No. 4,547,696 to Strauss, 
all of common ownership herewith. 
Front assembly 15 includes a tension foil shadow mask support structure 34, 
noted as being in the form of a frame secured to the inner surface 17 of 
faceplate 16 between the centrally disposed screen 18 and the peripheral 
sealing area 21 of faceplate 16, and enclosing screen 18. The shadow mask 
support structure 34 is preferably composed of sheet metal, and is secured 
to the inner surface 17 on opposed sides of screen 18, as indicated by 
FIG. 4. A foil shadow mask 35 is secured in tension on structure 34 at the 
locations indicated by asterisks in FIG. 4. Details of shadow mask support 
structure 34 can be derived from copending application Ser. No. 532,556 of 
common ownership herewith. 
As seen in FIGS. 1 and 2, a neck 36 extending from funnel 22 is represented 
as enclosing an electron gun 38 which is portrayed as emitting three 
electron beams 40, 42 and 44. The three beams serve to selectively excite 
to luminescence the phosphor deposits on the screen 18 after passing 
through the parallax barrier formed by shadow mask 35. 
Funnel 22 is indicated as having an internal electrically conductive funnel 
coating 43 adapted to receive a high electrical potential. The potential 
is depicted as being applied through an anode button 45 attached to a 
conductor 47 which conducts a high electrical potential to the anode 
button 45, which projects through the wall of funnel 22. The source of the 
potential is a high-voltage power supply (not shown). The potential may 
be, for example, in the range of 18 to 30 kilovolts, depending upon the 
type and size of cathode ray tube. Means for providing an electrical 
connection between the sheet metal frame 34 and the funnel coating 43 may 
comprise spring means 46, as depicted in FIG. 2. An internal magnetic 
shield 48 provides shielding for the electron beam excursion area and the 
front assembly 15 from the influence of stray magnetic fields. A yoke 50 
is shown as encircling tube 12 in the region of the junction between 
funnel 22 and neck 36. Yoke 50 provides for the electromagnetic scanning 
of beams 40, 42 and 44 across the screen 18. The center axis 52 of tube 12 
is indicated by the broken line. Items designated as "radially extending" 
extend radially outwardly from this axis. 
The above description of the video monitor, color cathode ray tube and 
shadow mask has been presented for exemplary purposes to illustrate one 
application of the vibration damping means of the invention. However, it 
should be understood that the invention is readily applicable for any 
color selection electrode other than a "shadow mask." 
In essence, a shadow mask of a color cathode ray tube or other color 
selection electrode of the type with which this invention is concerned 
comprises a rectangular membrane suspended in high vacuum under high 
mechanical tension. The mask therefore is capable of vibrating in 
"membrane modes" which are the two-dimensional equivalent of the 
vibrations of a stretched string. As illustrated in FIG. 5, a color 
selection electrode 56 is suspended under high mechanical tension between 
surrounding support rails 58. The rails are fixed to a glass faceplate 16' 
which is part of the glass envelope for the color cathode ray tube. A 
color phosphor screen or layer is formed on the inner surface of panel 
16', as at 60. The electron beam emitted from the electron gun of the 
cathode ray tube passes through color selection electrode 56 for 
impingement upon phosphor screen 60. 
FIG. 5 illustrates, in dotted lines, the resonant vibration of color 
selection electrode 56 as observed along a horizontal or vertical center 
line. It is apparent that the most prominent membrane mode is the 
fundamental one shown in FIG. 5, with maximum amplitude in the center of 
the electrode. Such vibration causes incorrect electron beam interception 
by the electrode. The resulting "landing errors" are most prominent at two 
points on the horizontal center line located approximately 55% of the 
distance from the center to the edge of both sides of the electrode, as 
indicated by lines 61. For instance, for a mask deflection of one mil at 
the center of mask 56, the landing errors at the two worst points are 
approximately 0.26 mils. In high resolution color cathode ray tubes, such 
resulting landing errors are not acceptable. Because of the absence of 
damping in high vacuum, the electrode, once excited by any kind of shock, 
may vibrate for a period of one minute or longer, corresponding to a "Q" 
in the order of 100,000. 
The amplitude of vibration of the electrode at points other than the center 
of the mask is a sinusoidal function of position. There may also be a 
problem with one of the first overtones. For instance, the frequency of 
the fundamental mode may be approximately 500 Hz. The first horizontal 
overtone (with a vertical nodal line) may be at approximately 750 Hz. 
FIGS. 3 and 3A show schematic locations for the electrode vibration damping 
means of the invention. In FIG. 3, the damping means are shown located 
intermediate the ends of the "long" sides of the color selection 
electrode, as at "X", the region of maximum peripheral motion for the 
fundamental mode and the first vertical overtone. FIG. 3A shows the 
location of the damping means intermediate the ends of the "short" sides 
of the color selection electrode, as at "Y", the region of maximum 
peripheral motion for the first horizontal overtone. 
Briefly, the invention contemplates in one preferred embodiment an improved 
color selection electrode damping system incorporating a dynamic vibration 
damper which avoids frequency tracking problems by using the electrode 
tension to determine the resonant frequency not only of the electrode but 
also of the damper device. The damper includes rigid means secured to the 
edge of the tensed electrode and dissipative or resistive means connected 
to the rigid means and spaced from the tensed electrode. In this preferred 
embodiment, resistive loading of the rigid means is achieved by lossy 
flexural means. In essence, the system involves the use of coupled 
resonators. 
More particularly, FIG. 6 shows one possible construction of the coupled 
resonator vibration damping means, generally designated 62, of the 
invention which includes a channel-shaped elongated member in the form of 
a bar 64 for amplifying the vibration in the electrode 56. Bar 64 is 
secured to a bracket 66 which, in turn, is secured to tensed color 
selection electrode 56 on the marginal portion of the electrode, 
immediately inside supporting rail 58. Bracket 66 is in the form of an 
angle-bracket to provide rigid support for rigid channel-shaped bar 64. 
The bracket preferably is fabricated of relatively heavy metal material, 
such as 0.020 inch steel, so as not to flex. Bar 64 is made of thinner 
material such as 0.015 inch steel in order to reduce its moment of 
inertia, but it is channel-shaped to optimize its flexural rigidity. The 
bracket 66 may be spot welded to electrode 56, with the bar 64 spot welded 
to the bracket, or a one-piece construction may be provided. The two-piece 
construction shown may be preferred because the projecting bar may make 
handling of the electrode during photoscreening of the cathode ray tube 
more difficult. Making bar 64 and bracket 66 rigid, i.e., keeping their 
compliance negligible compared to the compliance of electrode 56 to which 
the means 62 is secured, ensures frequency tracking when the electrode 
tension changes, as will now be described. 
It can be noted in FIG. 6 that bracket 66 and the attached channel-shaped 
bar 64 are angled relative to the faceplate in order to accommodate a 
magnetic shield which will be mounted on rail 58 over the color selection 
electrode. The angle must not be too great so as not to interfere with the 
electron beams as they are scanned to the edge of the screen. In addition, 
it can be seen that bracket 66 has a low profile versus the higher bar 64. 
The bracket is deliberately kept low in profile because it is attached to 
the electrode before it goes through the screen exposure process steps. A 
tall bracket could catch on an operator's clothing or otherwise cause 
interference. Therefore, the bar is welded to the bracket after all 
screening operations are completed. In this manner, amplification of 
vibration is achieved without having a high bracket throughout the 
screening processing. 
FIG. 7 illustrates schematically the condition when a moment is applied to 
rigid means 62 (here shown as bracket 66 and bar 64). The bar and bracket 
remain rigid and rotate together about axis of rotation 68, while 
electrode 56 stretches to permit such rotation. The angular stiffness, 
defined as the applied moment divided by the angular displacement, is a 
function of the size and shape of the bracket support area (i.e., the area 
defined by the spot welds between the bracket and the electrode), and also 
is proportional to the tension in electrode 56. The resonant frequency of 
angular vibration of bar 64 and bracket 66 about axis 68 is therefore 
proportional to the square root of the electrode tension. This same 
relationship, however, is true for the resonant frequency of the electrode 
itself. Consequently, as the tension relaxes when the electrode is heated 
by the electron beam during tube operation, the resonant frequencies of 
the electrode and the bar decrease at the same rate, and frequency 
tracking is ensured. 
How the bracket-bar assembly 62 functions as a dynamic vibration damper for 
a selected resonant mode, e.g., the fundamental membrane mode of electrode 
56, will now be explained. 
If assembly 62 were held in a fixed position, vibration of the electrode 
would result in the portion of the electrode adjacent to bracket edge 70 
(FIG. 7) moving u and down while turning about edge 70 as its axis. Since 
the electrode is under tension, it would exert an alternating force upon 
assembly 62, attempting to set it into angular vibration. 
Conversely, if the electrode were held in a fixed position at its center, 
angular vibration of assembly 62 would displace edge 70 up and down, 
attempting to set electrode 56 into vibration. Electrode 56 and assembly 
62 thus represent two coupled resonators. As previously stated, their 
resonant frequencies are made substantially alike. As is well-known, a 
pair of coupled resonators exhibits two new resonant frequencies; for an 
experimental structure consisting of electrode 56 and barbracket assembly 
62 as described, each separately resonant at 70 Hz, the two coupled 
resonances were observed to occur at 447 Hz and 494 Hz. 
In a system of two coupled resonators, energy originally present in one 
resonator is rapidly transmitted to the other, and the entire system can 
be damped by applying damping to just one of the resonators. Assembly 62 
functions to extract vibratory energy from electrode 56 and render it 
accessible to resistive means 72 (FIG. 6) wherein it may be dissipated. 
In the preferred embodiment, the resistive means 72 includes flexural means 
for applying resistive damping to bar 64. The flexural means is capable of 
propagating energy in the form of flexural waves. In an environment where 
viscous liquids or eddy current damping devices cannot be used, such as in 
the vacuum environment of a color cathode ray tube, it is difficult to 
produce a well-defined mechanical resistance. However, the invention 
illustrates various forms of suitable flexural means such as that shown in 
FIG. 6. More particularly, a flexural wave transmission line 74, such as a 
wire or a thin, flat strip, is connected between bar 64 and a support 76. 
The wire preferably may be stranded in order to provide increased 
flexibility as well as internal frictional resistance. The propagation 
velocity of flexural waves in a given wire or strip is proportional to the 
square root of frequency, and it decreases as flexibility increases. Low 
propagation velocity is desirable because, to obtain sufficient damping, 
the transmission line should be approximately 2-4 wavelengths long. To 
allow convenient placement of the line inside a cathode ray tube, the 
wavelength should therefore not exceed 2-3 inches. At 500 Hz this requires 
a maximum propagation velocity of 1,000-1,500 inches per second. In 
practice, a stainless steel wire rope which is stranded with seven strands 
of 0.011 inch wire has been used successfully. The wire is attached to the 
top of bar 64 by a small flexible clip made of 0.005 inch thick steel. Its 
measured propagation velocity at 470 Hz is approximately 25 meters (1,000 
inches) per second. 
It has been found that if wire 74 is made approximately 40 inches long, its 
natural losses (presumably friction between strands) suffice to provide 
the desired resistive behavior: A flexural wave at 400-500 Hz, launched at 
one end and reflected from the other, is sufficiently attenuated upon its 
return to the launching end to make the mechanical impedance of the line 
substantially resistive, equal to its characteristic impedance which is 
the product of flexural wave velocity and mass per unit length. However, 
the same effect can be obtained with a six-inch wire (approximately three 
wavelengths long) by loosely stringing light objects upon the wire. When 
the wire vibrates in flexure, these objects rattle and thereby extract 
energy from the vibration, converting it to random vibrations and 
eventually into heat, resulting in damping the bar 64 and electrode 56 
vibrationally coupled thereto. 
FIG. 6 shows one embodiment wherein steel bushings 78 are strung on wire 
74, with some clearance between the bushings so that they can vibrate 
freely. The resulting damping action has been found to be 
indistinguishable from that observed when the wire was loosely wrapped 
with sound-absorbent textile or paper-based material which, of course, 
cannot be used in a cathode ray tube. When the electrode is caused to 
vibrate in its lowest frequency mode by a brief driving pulse, the time 
constant of amplitude decay is on the order of 20 milliseconds. In actual 
practice, 23 steel bushings, 1/4 inch long, having 0.040 inch I.D. and 
0.078 inch O.D. were strung on the stranded wire 74. 
FIG. 8 illustrates another embodiment wherein a coil spring 80 is 
positioned in loose surrounding relationship about wire 74. Such a spring 
can also be used for vibration damping and may have advantages, from a 
manufacturing standpoint, over multiple small parts such as bushings 78. 
There may be instances wherein it is impractical to place a supporting bar 
76 at a corner of the cathode ray tube envelope. FIG. 9 shows an alternate 
form of the invention wherein wire 74' is doubled-back toward means 62 
whereby one end 82 of the flexural transmission line is secured to the top 
of bar 64, and an opposite end 84 of the line is secured to bracket 66. 
The line is folded back onto itself, as at 86. Again, loose objects, such 
as bushings 78, are strung along both portions of the line which may be 
shaped as a triangle, as shown. The transmission line thereby becomes 
self-supporting. 
FIG. 10 shows another embodiment of a coupled resonator system of the 
invention wherein, instead of using a lossy flexural transmission line, 
the vibration damping means comprises a flexurally resonant stranded wire. 
Two stranded wires 88 are shown secured to opposite sides of bar 64. As is 
known, stranded wire i much more flexible than solid wire of the same 
cross-section. When stranded wire flexes, the individual strands slide 
against each other, causing friction which extracts vibratory energy, and 
thereby provides damping. Dimensioning the wire to be at least 
approximately resonant increases its amplitude and facilitates energy 
loss. Alternatively, a lossy fibrous mass may be attached to bar 64 to 
provide damping. see FIG. 10A 
FIG. 11 shows another embodiment of the invention wherein a plurality of 
resonators are provided which resonate at different frequencies with the 
range of frequencies at which electrode 56 is expected to resonate as it 
heats up during tube operation. Specifically, a plurality of compliant 
reeds 90 are secured to bracket 66. As a reed bends as it vibrates, the 
bending of the lossy material extracts energy from the system. The 
compliance of the reeds, in combination with the compliance provided by 
the electrode, establish different resonant frequencies for the different 
reeds. The reeds can be of different lengths, as shown, and/or of 
different thicknesses to resonate at different frequencies. The reeds 
should be at least somewhat lossy. For example, they may be made of pure 
magnesium which is known to have vibration-damping properties. 
Whereas the embodiment of FIG. 6 provides a self-tracking system, as 
described, with excellent damping regardless of frequency, FIG. 12 shows a 
version which will not track electrode resonance changes, but is simple 
and employs a single lossy, compliant reed resonator 90'. This version 
offers the advantages of low cost and easy execution. 
It should be noted that the resonant frequency of reed 90' is determined by 
the effective mass of the reed in combination with its total compliance, 
i.e., the sum of the compliances of the reed itself and the compliance 
prevailing at bracket 66 on which the reed is mounted. The latter 
compliance varies inversely with the tension of electrode 56. Therefore, 
the resonant frequency of reed 90', while unable to track the 
temperature-engendered variations of the resonant frequency of electrode 
56 completely, it follows these variations at least in part. 
FIG. 13 shows an embodiment of the invention wherein, instead of using a 
mechanical transmission line, a lossy reed or the like, a form of 
"friction brake" 92 is used to extract energy from the system by a rubbing 
action. The friction brake must be detuned, i.e., it does not resonate 
with bracket 66 and bar 64. The brake is secured to rail 12, as at 94, and 
includes a torsional spring portion 96. Friction between bar 64 and brake 
92 is controlled by the torsional spring portion and will extract energy 
from the system. 
FIG. 14 shows another embodiment of the invention, again using the coupled 
resonator principles. A relatively massive rod or wire 98 is welded to the 
peripheral portion near the apertured area of the electrode. Wire 98 
provides mass to the vibration damping means the same as bracket 66 
described above. By properly selecting the mass of the wire, the wire can 
be set into resonance at the same resonant frequency as electrode 56. 
Since the electrode tension provides the compliance for both the electrode 
resonance and the resonance of the wire, this system also will have the 
frequency tracking feature. To extract energy from the system, an overlaid 
braid 100 is provided. The braid is not secured to the wire but vibrates 
or "rattles" against it. The braid can be welded to the electrode near the 
weld line of the electrode to rail 12. 
FIG. 15 shows an embodiment of the invention wherein electrode 56 is 
coupled to a lossy reed resonator 102 by means of a weak, bent leaf spring 
104. The reed is not mounted on electrode 56 but on rail 12, as shown at 
106. Operation of this embodiment is analogous to that described in 
connection with FIG. 12, except that the resonant frequency of reed 102 
does not track that of electrode 56 even in part. 
Lastly, FIG. 16 shows a simple embodiment of the invention wherein a simple 
energy absorber 108 is secured along the peripheral portion of electrode 
56 to damp vibrations in the electrode. The energy absorber can be of 
braided material, for instance. 
It will be appreciated that numerous modifications in the described 
embodiments of the invention will be apparent to those skilled in the art 
without departing from its true spirit and scope. For example, damping of 
a resonator by resonant stranded wires (FIG. 10), friction (FIG. 13) or 
contact with a braid (FIG. 14) may be used in embodiments other than those 
where it is illustrated. The invention is to be limited only as defined in 
the claims.