Structure for electrically connecting an annular corrugated tube

Electrical connection of an annular corrugated tube having an outer surface shape wherein grooves and ridges are alternately repeated in the axial direction of the tube in a wave form is carried out by cutting the tube at a groove, disposing a clamping member on each side of a ridge at the cut end of the tube and electrically connecting the tube to the clamping member positioned on the cut end of the tube side of the ridge by squashing the ridge with the clamping members.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a method and structure for electrically 
connecting an annular corrugated tube, and more particularly for example 
to a method and structure for electrically connecting a coaxial cable 
having an outer conductor with an annular corrugated outer surface as an 
annular corrugated tube when the end of the outer conductor is clamped by 
clamping members. 
2. Description of the Related Art 
Referring to FIG. 5, when a coaxial cable 100 is to be connected to an 
antenna or the like, a connector 50 is usually attached to its end. The 
coaxial cable 100 comprises an annular corrugated outer conductor 101 
formed as an annular corrugated tube. Here, for the convenience of the 
following description, the concave portions of the outer conductor 101 
will be referred to as grooves and the convex portions will be referred to 
as ridges. Accordingly, the outer conductor 101 has the shape of a tube 
wherein grooves and ridges are alternately periodically repeated in the 
axial direction of the tube. An inner conductor 102 having the shape of a 
straight pipe is disposed inside the outer conductor 101 coaxially 
therewith. An insulator 103 for electrically insulating the two conductors 
from each other is filled between the two conductors 101, 102. A corrosion 
prevention layer 104 for preventing corrosion of the coaxial cable 100 
covers the outside of the outer conductor 101. 
The connector 50 connected to the end of the coaxial cable 100 comprises a 
gripping flange 51, a connector proper 52, a connecting metal 53, an 
insulator 54, a contact 55, a support member 56 and a split clamp 57. 
By the coaxial cable 100 being connected to the connector 50, the end of 
the outer conductor 101 is clamped by the support member 56 and the split 
clamp 57 and the outer conductor 101 of the coaxial cable 100 is 
electrically connected to the connector 50. Therefore, it is necessary 
that the end of the outer conductor 101 be clamped by the support member 
56 and the split clamp 57. However, because the outer surface of the outer 
conductor 101 of the coaxial cable 100 is ridged and the pitch at which 
the grooves and ridges constituting the annular corrugated form are 
repeated is relatively long, the angle of slope of the ridges is also 
gentle. 
Consequently, when the end of the outer conductor 101 has not undergone any 
preparatory treatment, the work of clamping the end of the coaxial cable 
100 with the support member 56 and the split clamp 57 is not always easy. 
As a result, conventionally, to facilitate this clamping, the end of the 
outer conductor 101 has been widened radially outward. When it has been 
widened radially outward, the end of the outer conductor 101 can be easily 
clamped between the support member 56 and the split clamp 57. 
However, with this kind of conventional connection, the work of widening 
the end of the outer conductor 101 radially outward is time and labor 
consuming. Also, a specialized and costly tool is necessary for widening 
the end of the outer conductor 101. Furthermore, in order to widen the end 
of the outer conductor 101 radially outward it is necessary to cut the 
outer conductor 101 along a ridge using a cutting blade, and a complicated 
and expensive tool including members for guiding the cutting blade along 
the ridge is required for this. 
Thus with an annular corrugated tube like the outer conductor described 
above it is costly and not easy to clamp the end of the tube to a 
connecting member such as a connector with clamping members. 
SUMMARY OF THE INVENTION 
Accordingly, it is a main object of the invention to make it possible, 
without widening the end of the annular corrugated tube radially outward, 
to easily form at the end of the tube a connection part to be clamped when 
the tube is electrically connected. 
Another object of the invention is to make it possible without cutting a 
ridge part of the annular corrugated tube to easily form a connection part 
to be clamped when the tube is electrically connected. 
A further object of the invention is to provide a new method and structure 
for connecting a coaxial cable using an annular corrugated tube. 
Other and further objects, features and advantages of this invention will 
appear more fully from the following description. 
In this invention, electrical connection of an annular corrugated tube 
having an outer surface shape wherein grooves and ridges are alternately 
repeated in the axial direction of the tube in a wave form is carried out 
by cutting the tube at a groove, disposing clamping members on each side 
of a ridge at the cut end of the tube and electrically connecting the tube 
to the clamping member positioned on the cut end of the tube side of the 
ridge by squashing the ridge with the clamping members. 
The number of ridges squashed may be more than one, but the squashing can 
be carried out easily if only the first ridge is squashed. 
As the ridged tube, one of which the ratio of the depth of the grooves to 
the pitch of the ridges is 1.0:2.0 to 2.5, that is, one of which the width 
of the ridges is considerably lower than that of a normal annular 
corrugated tube (of which the same ratio is 6.0) and the surfaces of the 
side walls of the ridges are steep is used. By using an annular corrugated 
tube having ridges of this kind of shape, squashing of a ridge can be 
easily carried out with a small force. (The above-mentioned groove depth 
is the distance from the peak of a ridge to the bottom of a groove.) 
Cutting of the annular corrugated tube is carried out using a cutting blade 
only one side of the cutting edge of which has a sloping surface. In this 
way, by using a cutting blade having a cutting edge sharper than when a 
cutting blade having sloping surfaces on both sides of the cutting edge is 
used, cutting can be carried out more easily. 
The invention also employs the electrical connection described above for a 
method for connecting a coaxial cable, and in this case the annular 
corrugated tube is an outer conductor of a coaxial cable and the clamping 
member positioned on the cut end of the annular corrugated tube side of 
the ridge is a part of connector attached to the end of the coaxial cable; 
here, the clamping member on the opposite side of the ridge from the cut 
end of the annular corrugated tube is a split clamp fitted on the annular 
corrugated tube. 
The invention also provides a structure for electrically connecting an 
annular corrugated tube comprising: an annular corrugated tube having an 
outer surface shape wherein grooves and ridges are alternately repeated in 
the axial direction of the tube in a wave form and having one end cut at a 
groove; clamping members which are disposed on each side of the first 
ridge from the cut end of the annular corrugated tube; and a clamping 
member moving member for making the clamping members move toward each 
other, wherein by an operation of the clamping member moving member 
causing the clamping members to squash the first ridge the annular 
corrugated tube is electrically connected to the clamping member 
positioned on the cut end of the annular corrugated tube side of the 
ridge. The invention also provides a structure for connecting a coaxial 
cable employing this structure for electrically connecting an annular 
corrugated tube. 
In this structure for connecting a coaxial cable, squashing of a ridge of 
an outer conductor of a coaxial cable is effected by a cap nut screwed 
into a part of a connector being tightened. By this construction being 
adopted, by a ridge being squashed as the cap nut is tightened during 
connection of the coaxial cable to the connector, at the same time a 
connection part of the outer conductor is formed and therefore the work of 
separately squashing a ridge is eliminated. 
Also, the end of an inner conductor of the coaxial cable projects beyond 
the end of the outer conductor, an inner conductor connecting and fitting 
part for connecting and fitting with the inner conductor is provided 
inside the connector and by the end of the inner conductor engaging with 
the inner conductor connecting and fitting part as the outer conductor is 
connected with the connector the outer conductor and the inner conductor 
are connected simultaneously.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a coaxial cable 200 has as an annular corrugated tube 
an outer conductor 201 with ridges 20/B on its outer surface. A corrosion 
preventing layer 202 is formed on the outer surface of the outer conductor 
201. An insulator 203 is formed on the inner surface side of the outer 
conductor 201. An inner conductor 204 is disposed inside the insulator 
203. The outer conductor 201 and the inner conductor 204 are electrically 
insulated from each other by the insulator 203. The outer conductor 201 as 
seen from outside is formed as an annular corrugated tube wherein grooves 
201A and ridges 201B are alternately repeated. 
As the outer conductor 201 used in this preferred embodiment, for example 
one of which the internal diameter at the grooves 201A is 9.3 mm, the 
pitch of the ridges 201B is 3.0 mm and the depth of the grooves is 1.3 mm 
is used. That is, the width of the ridges 201B is small and the side wall 
surfaces thereof are steep. 
The following preparation of the coaxial cable 200 is carried out before it 
is connected to a connector 1: The end of the coaxial cable 200 is treated 
to make it straight over a predetermined length suited to the axial 
direction dimensions of the connector 1, for example about 100 mm. The 
corrosion preventing layer 202 constituting the outermost layer of the 
coaxial cable 200 and consisting of for example polyethylene is cut 
circumferentially and removed over a predetermined length from the end of 
the coaxial cable 200. The position of the cut end of the corrosion 
preventing layer 202 is so set that it is aligned with a central position 
of one of the grooves 201A of the outer conductor 201. The length of the 
corrosion preventing layer 202 so peeled off is determined according to 
the axial dimensions of the connector 1. 
After the corrosion preventing layer 202 is thus peeled off, the outer 
conductor 201 is cut from the end of the coaxial cable 200 over a 
predetermined length suited to the axial dimensions of the connector 1, 
for example 8 to 9 mm, the cutting being carried out at one of the grooves 
201A in a predetermined position. This cut state is shown in FIG. 2(b). 
The insulator 203 exposed as a result of this cutting is removed. As a 
result of the removal of this insulator 203 the inner conductor 204 is 
exposed as shown in FIG. 2(b). The exposed inner conductor 204 is 
chamfered using a flat file. 
The method by which the outer conductor 201 is cut will now be described. 
Cutting of the outer conductor 201 is carried out using a cutting tool 30 
shown in FIG. 3 and FIG. 4. 
The construction of the cutting tool 30 will now be described. The cutting 
tool 30 has an L-shaped support member 31. A pair of guide rollers 32, 32 
are mounted on one end 31a of the support member 31 a predetermined 
distance apart from each other. A pair of holding members 33, 33 are 
mounted on the other end 31b of the support member 31. The pair of holding 
members 33, 33 face each other across a predetermined gap with a rotary 
shaft 33a mounted therebetween. The pair of guide rollers 32, 32 and the 
pair of holding members 33, 33 are disposed facing each other across a 
predetermined vertical gap in front of an inner side surface 31c of the 
support member 31. A feed screw 34 serving as a relative movement 
mechanism is rotatably housed inside the end 31b of the support member 31. 
The pair of holding members 33, 33 are movable by this feed screw 34 in 
the length direction of the end 31b of the support member 31, i.e. the 
direction in which the holding members 33, 33 face the guide rollers 32, 
32. A disc-shaped cutting blade 35 is rotatably mounted on the rotary 
shaft 33a between the holding members 33, 33. As a result, the cutting 
blade 35 faces the pair of guide rollers 32, 32. The rotary shaft 33a on 
which the cutting blade 35 is mounted and rotary shafts not shown in the 
drawings on which the pair of guide rollers 32, 32 are mounted are 
parallel with each other and with the thickness direction of the support 
member 31, i.e. a direction perpendicular to the paper surface. 
A characteristic feature of the cutting tool 30 is the structure of the 
cutting blade 35. That is, of the two sides of the cutting edge 35c of the 
cutting blade 35, one cutting edge side 35a is sloping with respect to the 
radial direction of the cutting blade 35 and the other cutting edge side 
35b is perpendicular to the axial direction of the cutting blade 35. 
In cutting the outer conductor 201 of the coaxial cable 100 using this 
cutting tool 30, first, to make it possible to position the coaxial cable 
200, the feed screw 34 is operated and the pair of holding members 33, 33 
are moved in advance as far away from the guide rollers 32, 32 as they 
will go. The coaxial cable 200 with the corrosion preventing layer 202 
already peeled off and the outer conductor 201 thereby exposed is then 
positioned between the cutting blade 35 and the guide rollers 32, 32. 
During this positioning the cutting blade 35 is brought into line with a 
groove 201A at a predetermined position. The feed screw 34 is then 
operated and the cutting blade 35 is moved toward the guide rollers 32, 
32. Simultaneously with this movement, the position of the cutting tool 30 
is finely moved in the axial direction of the coaxial cable 200 until the 
cutting edge side 35b of the cutting edge 35c of the cutting blade 35 
almost abuts with the side wall surface of the ridge 201B adjacent to the 
groove 201A of the outer conductor 201 on the same side of the groove 201A 
as the axial center of the coaxial cable 200, that is, on the right side 
thereof in FIG. 4. When this is being done, because as described above the 
cutting edge side 35b is perpendicular to the axial direction of the 
cutting blade 35, the cutting blade 35 can be moved in the axial direction 
of the coaxial cable 200 until the cutting edge 35c of the cutting blade 
35 is positioned at the side wall of the ridge 201B. 
A knob 34a attached to the feed screw 34 is then further turned to rotate 
the feed screw 34 and cause the cutting blade 35 to cut to some extent 
into the surface of the groove 201A of the outer conductor 201 in said 
predetermined position. The outer conductor 201 is then cut by the cutting 
tool 30 in this state being rotated about the coaxial cable 200 by hand. 
This turning of the cutting blade 35 is carried out by hand as described 
above, but because the guide rollers 32, 32 rotate relative to the 
circumference direction of the outer conductor 201 and the cutting blade 
35 also rotates along the outer surface of the outer conductor 201, even 
with a relatively small force it is possible to rotate the coaxial cable 
200 easily by hand. 
In this way, the cut position of the outer conductor 201 cut from the 
coaxial cable 200 is not the middle of the groove 201A of the 
predetermined position but is a position near the ridge 201B adjacent to 
the groove 201A on the same side thereof as the axial center of the 
coaxial cable 200. 
The coaxial cable 200 having had its end prepared as described above is 
connected to the connector 1 as described below with reference to FIG. 1. 
The connector 1 comprises a cap nut 2 serving as a clamping member moving 
member fitting on the outside of the connection end of the coaxial cable 
200 and a main body 3 serving as one clamping member connected by a screw 
thread to the cap nut 2. A split clamp 4 serving as another clamping 
member is disposed between the cap nut 2 and the main body 3. The split 
clamp 4 is made up of a clamping part 4a, a pushed-upon part 4b and a 
joining part 4c joining these together. A coupling nut 5 is rotatably 
mounted on the outside of the main body 3. A central connector 6 is 
mounted inside the main body 3 with an insulator 7 disposed therebetween. 
A side of the central connector 6 to which the inner conductor 204 is 
connected constitutes a tubular part 208, and a plurality of slits 209 are 
formed in the tubular part 208 in the axial direction. The provision of 
these slits 209 make it possible for the tubular part 208 to widen; by 
widening, the tubular part 208 firmly holds the inner conductor 204 when 
it is fitted into the tubular part 208, and in this way electrical 
connection of the inner conductor 204 to the central connector 6 is stably 
effected. As a result of having the constitution described above the split 
clamp 4 has an inner surface shape which covers one of the ridges 201B of 
the outer conductor 201 of the coaxial cable 200, and the split clamp 4 is 
made up of a pair of circular arc shaped ringlike members not fully shown 
in the drawings fitting around the outside of the outer conductor 201 and 
a member which with the ringlike members positioned around the outer 
surface of one of the ridges 201B of the outer conductor 201 holds the 
ringlike members together on the outer surface of the ridge 201B as a 
split clamp. 
Connection of the coaxial cable 200 using the connector 1 will now be 
described. 
With the coaxial cable 200 inserted into the connector 1 through an opening 
in the main body 3, the split clamp 4 is fitted onto a second ridge of the 
ridges 201B of the outer conductor 201. This second ridge is the second 
ridge from the end of the coaxial cable 200. The cap nut 2 is then screwed 
into the main body 3 so that the split clamp 4 fitted over a ridge 201B of 
the outer conductor 201 is clamped from both sides. By this screwing 
action the split clamp 4 is clamped between a receiving seat 2a provided 
on the cap nut 2 and a receiving seat 3a provided on the main body 3. By 
tightening the cap nut 2 the split clamp 4 is moved toward the left in 
FIG. 1, and as a result of this a first ridge of the plural ridges 201B of 
the outer conductor 201 is clamped between the split clamp 4 and the 
receiving seat 3a of the main body 3 and as this clamping force increases 
the ridges is squashed into a flange shape. This squashing of the first 
ridge of the plurality of ridges 201B is effected smoothly with a small 
force because the width of the first ridge is small and the side wall 
surfaces of the ridges are steep. 
In this way, the outer conductor 201 of the coaxial cable 200 is firmly 
electrically and mechanically connected to the connector 1 by way of the 
main body 3. Also, simultaneously with this connection of the outer 
conductor 201, the inner conductor 204 fits into the tubular part 208 of 
the central connector 6 and connection of the inner conductor 204 is also 
effected. Thus, connection of the outer conductor 201 and the inner 
conductor 204 to the connector 1 is performed easily just by tightening 
the cap nut 2. 
The outer conductor 201 of the coaxial cable 200 is connected to the 
connector 1 in this way, and at the time of this connection the first 
ridge of the plurality of ridges 201B at the end of the outer conductor 
201 is squashed and becomes a flange portion 205 and the outer conductor 
201 is connected to the connector 1 by way of this flange portion 205. 
Therefore, the work of widening the end of the outer conductor 201 
radially outward as has been done conventionally becomes unnecessary. The 
flange portion 205 is automatically created when the cap nut 2 and the 
main body 3 of the connector 1 are joined together. 
In this point, the work of connecting the connector 1 to the coaxial cable 
200 is greatly reduced compared to a conventional case. Labor costs are 
also reduced as a result of this reduction in the connection work. 
Furthermore, because a special tool for widening the end of the outer 
conductor 201 radially outward becomes unnecessary, tooling costs can also 
be reduced. 
Also, because cutting of the outer conductor 201 is carried out at a groove 
201A, compared to when cutting of a ridge is carried out, because guiding 
members and the like not necessary, the cutting work is simple and cutting 
costs can be reduced. 
In particular, because the cutting position of the outer conductor 201 is a 
position near a ridge 201B, even if this ridge 201B is squashed as 
described above, the cut end of the outer conductor 201 is not positioned 
further on the radially inner side of the coaxial cable 200 than a groove 
201A. Therefore, even after the ridge 201B of the outer conductor 201 is 
squashed, the separation distance between the outer conductor 201 and the 
inner conductor 204 at the cut end of the outer conductor 201 remains 
substantially the same as the separation distance between the outer 
conductor 201 and the inner conductor 204 elsewhere in the cable, and high 
frequency transmission path impedance fluctuation caused by variations in 
this separation distance is suppressed. 
While the invention has been particularly shown and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that the foregoing and other changes in form and 
details can be made therein without departing from the spirit and scope of 
the invention.