Stripping apparatus for fibre-optical cables

The invention relates to a stripping apparatus for fibre-optical cables (31), having rotatable stripping knives (1033) and rigid centering jaws (1040) which, in the operating position, are arranged between the stripping knives and the end of the cable (31). The centering jaws (1040) are furthermore located in the immediate vicinity of the stripping knives (1033) and hold the cable (31) to be stripped, in such a way that any torques acting on the cable (31) are absorbed and twisting or breakage of the cable (31) is avoided. Furthermore, modifications of the stripping machines are described which disclose the lateral insertion of a cable (31) into the particular stripping position inside a stripping station (1,2,3) by means of a manipulator (35), a novel stripping station (3) for stripping coating layers for optical waveguides and a novel conductor stop apparatus (80) and a drive-saving arrangement of several stripping stations (1,2,3) on a carriage (912).

The invention relates to a stripping apparatus for cables, in particular 
fibre-optical cables, having at least one radially acting, rotatable 
stripping knife. 
Such stripping apparatuses have been the subject of various publications 
and are used in particular for the automatic stripping of cables having 
several sheath layers. 
U.S. Pat. No. 3,881,374 describes such an apparatus in which knives 
associated with centering jaws are capable of cutting into a cable and 
stripping off the sheath layer. Centering jaws are located on that side of 
the knives which faces the end of the cable, which, in conjunction with 
their rotatability, achieves a specific effect required in the U.S. 
Patent: the ends of the cables are twisted. However, this twisting causes 
damage and is undesirable, particularly in the case of thin cables or 
cables which are liable to break. 
A considerable time ago, the applicant proposed an invention in which, 
inter alia, the twisting of the cable ends and the associated risk of 
breakage are reduced. There, the centering jaws are shifted to that side 
of the stripping knives which are opposite the end of the cable and are 
positively controlled independently of the stripping knives. See U.S. Pat. 
No. 4,745,828, for which there are a number of continuation applications, 
and U.S. Pat. No. 5,010,797. It is pointed out that all patent 
applications and publications cited in this patent application, and the 
prior art documents cited in each of these, are considered to have been 
disclosed for the purpose of this patent application. The stripping 
apparatuses described in the last two U.S. Patents make it possible in 
principle to carry out well defined, high-quality stripping steps. A 
similar structure is described in JP-A-64-3608. 
With increasing reduction in the diameter of cables to be stripped and in 
particular with the need to be able also to strip fibre-optical cables 
completely and by an automated method, it is found, however, that the 
conventional stripping apparatuses can still lead to undesirable twisting 
or even to breakage (particularly in the case of glass fibres) of the 
conductors. The reason for this is that, through friction, the 
simultaneously rotating centering jaws additionally apply a torque to the 
conductor end which is already subjected to a critical and unacceptable 
torsional load by the stripping knives in the cutting region. 
Since none of the known stripping apparatuses solve this problem, the 
object of the invention is to provide a stripping apparatus in which very 
thin and easily broken cables can be stripped. This object is achieved for 
the first time by the instant invention. Even thin glass fibre sheaths can 
easily be cut and the corresponding layers stripped off. The resulting 
torsional moments are absorbed in an optimal manner by the centering jaws. 
In addition, various stripping arrangements have been disclosed in which 
several stripping stations effect complete stripping of a cable to be 
stripped. However, these arrangements have various disadvantages. 
U.S. Pat. No. 4,601,093 describes a stripping apparatus in which cables of 
different diameters are stripped by a method in which an operator first 
pushes the cable into an insertion orifice of a first station and then 
pulls it out from there and pushes it into a second station, pulls it out 
again, etc. The process requires the constant presence of an operator and 
a fair degree of skill on the part of the latter. 
U.S. Pat. No. 3,881,374 previously cited above also states that the cables 
are cut into pieces at one station and then transported by a conveyor belt 
to a processing station which then approaches in an axial direction the 
particular cable section to be processed, in order to strip said section. 
The cable thus moves in a radial direction relative to its axis, while the 
stripping apparatus must execute axial movements relative to the same 
axis. This requires complicated control means and is time-consuming. A 
similar apparatus is described in U.S. Pat. No. 4,879,926. 
An apparatus having a laterally pivotable manipulator arm and axially 
movable stripping stations was exhibited under the designation "Dr. 
Schleuniger Productronic AG, ASM 9500" at an exhibition in 1989. 
Moreover, a relatively new development in this area is the apparatus 
described in JP-3-15211 of January 1991. In this apparatus, a manipulator 
carriage is provided which is capable of transporting the cable ends to 
various stripping stations. The stripping stations themselves are adjacent 
to one another in a plane and are also guided by means of carriages in the 
axial direction of the cable. As in the case of the stripping apparatuses 
described above, this arrangement in JP-3-15211 gives rise to problems in 
the control and guidance of the cable ends; not least in the insertion of, 
for example, a flexible cable end in the axial direction. The curvature 
often results in incorrect positioning of the cable end and therefore 
sometimes leads to failure of the stripping apparatuses. 
It is therefore a further object of the instant invention to make it 
possible to introduce those cables to be stripped laterally into the 
working position without then additionally having to move the entire 
relevant working station in the axial direction. This should, if required, 
also permit rapid and reliable changing of the cable to several stripping 
stations. It should be possible for even flexible or curved cables, such 
as, for example, fibre-optical cables, to be brought without problems in a 
particular required working position from one working station to the 
other. On inspection of the cable, the latter should be held by means of 
clamping jaws in the immediate vicinity of the end of the working station, 
in order to reliably position flexible or curved conductors. The direct 
insertion of a cable into the particular working station should be 
possible by means of a manipulator arm. 
These objects are achieved, according to the instant invention by the 
lateral insertion, of the cable ends that are to be stripped. The cable 
ends are then in the immediate vicinity of the clamping jaws, in the 
correct position for making the first cut in the course of a cutting 
series when the manipulator has conveyed the cable to the particular 
working station. Additional axial movement of the manipulator or of the 
relevant working station can then be dispensed with, and as a result the 
stripping process is accelerated. In particular, fibre-optical cables or 
similar, flexible or curved cables can thus be inserted into the 
particular stripping stations without problems. 
Furthermore, stripping apparatuses for stripping a coating from optical 
waveguides have been disclosed, which apparatuses have profiled knives 
which correspond to the internationally standardised diameters of the 
glass fibres (e.g. 125 .mu.m). These known apparatuses are hand tools 
which are not suitable for the use in or on automatic stripping 
apparatuses. It is therefore the further object of the invention to 
develop the apparatus according to the instant invention by inventive 
measures to include the possibility of stripping a coating by an automated 
method. This project is achieved by apparatus that may also be used by 
itself, independently of the stripping apparatus described at the outset. 
Further embodiments and variants of this invention are evident from the 
description of embodiments illustrated in the accompanying drawings. The 
resulting advantages and potential applications are described briefly 
below. 
The direct lateral cable feed into the working region in the interior of a 
stripping station by means of a manipulator makes it possible for the 
first time to introduce curved, long conductors of varying shape into the 
working region of stripping stations, something which was previously 
possible only by hand from the end. The insertion process according to the 
invention is also faster. 
Both the insertion of the cable and the establishment of the required 
stripping length thereof are achieved rapidly and reproducibly by the 
combination of the manipulator with the conductor stop according to the 
invention, having a thrust sleeve and a stop rod. This combination itself 
can also be used in a novel and advantageous manner outside the scope of 
the invention. 
The variant having several working stations on a carriage--preferably 
together with a stop rod--saves additional controlled linear drives and 
helps to reduce the cable feed time. This variant, too, could be used by 
itself, independently of the other variants, in particular the means for 
copying the carriage movement towards the stop rod and the independent 
control for the thrust sleeve being novel and inventive. 
In addition to the nonrotatable centering apparatus, a second centering or 
tensioning apparatus absorbs all torsional stresses and helps to avoid 
damage to the conductor as a result of cutting by the stripping knives. In 
every case, clamping jaws fix axial positions of the cable. The embodiment 
having the rotating body according to FIG. 10 is very compact. 
The embodiment of the coating stripping head having the adjusting slides 
and centering plates is very compact and permits precise gripping of the 
optical waveguide, the variant having the sliding clutch permitting the 
individual adjustment of the contact force of the centering plates against 
the conductor. 
The use, known per se, of a heating element for the coating reduces its 
resistance to stripping. 
The cone-controlled drive for the centering apparatus constructed according 
to the invention, is robust. Both the stripping knives and the centering 
jaws preferably correspond to the variants which are described by the 
inventor in U.S. Pat. Nos. 5,010,797 and 4,745,828.

It should be stated beforehand that design elements from the applicant's 
patents U.S. Pat. No. 4,745,828 (as well as all continuation applications) 
and U.S. Pat. No. 5,010,797 are preferably used for achieving control of 
the centering jaws and stripping lines. These patents are herewith 
incorporated by reference in this disclosure. 
The Figures are described in relation to one another; identical parts are 
provided with identical reference symbols and similar parts bear identical 
reference symbols with different indices. FIG. 1 shows a stripping 
apparatus according to the invention, having a housing 7 which carries, in 
its upper region, an electronic control, a display and an input unit 17. 
Three working or stripping stations 1,2,3, a manipulator arm 35 having 
clamping jaws 36 and a conductor stop 80 are located in the lower region. 
The clamping jaws (36) serve for gripping the cable (31) which, in the 
starting position, can initially be pushed between the clamping jaws 36 
and against the conductor stop 80. 
The novel conductor stop 80 according to the invention, shown in FIG. 5 to 
7, serves for defining a required stripping length Y on the cable 31. It 
is displaceably mounted in stub sleeve (917) in the housing wall 52. The 
longitudinal stop in the axial direction is achieved by means of a stop 
rod 92 which is longitudinally displaceable in a thrust sleeve 91. In the 
position according to FIG. 5, the stop rod 92 is in its outermost position 
which corresponds to a 0 stripping length. A cable 31 can be forced 
against the freely projecting end face (95) of said rod 92. In the 
position shown, this end face lies on an imaginary line 916, which 
simultaneously passes through all relevant working regions of relevant 
stripping stations (1,2). 
FIG. 6 shows the length-measuring position--the line 916 has moved by the 
preset stripping length Y in that stop rod 92 has been retracted by 
carriage 912 moving to the right from its position in FIG. 5. The stop rod 
92 is extended in a backward direction and connected there to an adjusting 
ring 911 which is capable of copying (following) any movement of carriage 
912. For this purpose, the stop rod 92 is also kept retracted in the 
direction of the thrust sleeve 91 by means of a tension spring 915. The 
carriage 912 is displaceable by means of linear drive 99 mounted in a 
fixed manner in the housing. FIG. 7 shows the subsequent stripping 
position in which the conductor stop 80 has retracted completely behind 
the housing wall 52 and the stripping stations 1,2 travel back to the 
working position (916). The required stripping length has thus been set 
and the lateral displacement path for the cable 31 transported by the 
manipulator 35 has been freed. A thrust sleeve 91 is retracted in the 
axial direction by means of a linear drive 913 mounted in a fixed manner 
in the housing. 
Alternatively, the stripping stations 1,2 could also remain in the position 
shown in FIG. 5, but the thrust sleeve 91 and the stop rod 92 and all 
stripping stations 1, which themselves also have to execute retraction 
movements for stripping a cable sheathing section, would then have to be 
provided with separate linear drives 58. 
The thrust sleeve 91 is bevelled in a funnel-like manner at its end facing 
the manipulator 35, in order to facilitate the introduction of a cable. A 
further advantage, essential to the invention, is the determination of the 
length of, for example, a curved conductor 31 by the thrust sleeve 91, 
since said conductor is straightened in the inner bore of the sleeve 91, 
thus ensuring that the length determination is dimensionally correct. 
The usual functional sequence is thus as follows: When the clamping jaws 36 
of the manipulator 35 are opened, the cable 31 is pushed manually into the 
bore of the thrust sleeve 91 until it touches the preset stop rod 92. 
Either by means of a sensor, which is not shown, or as a result of a 
random start command, for example from a foot switch (not shown), the 
clamping jaws 36 close and the thrust sleeve 91 travels back in order to 
free the cable 31. The manipulator arm 35 then swivels into the required 
position, in which the cable end is held in the particular stripping 
station 1,2,3 (cf. for example station 2 for cutting through Kevlar fibres 
30, as in the patent application (P-2554-GB) submitted on the same date 
and considered herein as having been disclosed). 
Of course, the invention also relates to other manipulator designs, 
including those which are not pivotable or those which pivot about only 
one axis. In any case, the essential feature of all arrangements is that 
the cable ends are introduced laterally into the relevant stripping 
station. The invention also relates to those stripping stations which do 
not necessarily have a physical slot but in which the relevant stripping 
tools, such as knives, etc., are so far apart that cables can be 
introduced laterally. However, it should be noted that in various 
extensive test series it has been found that virtually only an arrangement 
having at least three knives 1033 is capable of applying sufficient axial 
tensile forces to the buffer (layer of a fibre-optical cable above the 
coating). In many cables, this layer in fact adheres so firmly that only 
parts of the buffer are torn off and only one or two knives are used. 
Conversely, when V-knives were used, there was a considerable disadvantage 
so that a double V-shaped groove was formed in the cut produced. The 
V-knives must slide against one another with their flat side, and the 
particular bevelled knife edge presses in the form of a wedge into the 
buffer and generates static friction there, which results in a torque. 
Hence, virtually only one arrangement of at least three knives which lie 
in a plane is universally applicable. 
To limit the opening distance of the clamping jaws 36, a micrometer screw 
77 (FIG. 1) is provided according to the invention in a particularly 
advantageous manner, which micrometer screw 77, via an active link, limits 
the possibility of axial movement of the clamping jaws and/or makes it 
possible to adjust the clamping pressure. 
Station 2, shown on the left of the conductor stop 80, is preferably a 
station for cutting pull-relief fibres and is not described in detail 
here. A preferred embodiment of this station is disclosed in the patent 
application (P-2554-GB) submitted on the same date. The total disclosure 
content of this application is also considered to have been disclosed in 
this application. 
A station 1 which essentially forms a stripping head for cutting through 
and stripping off layers of the cable (31) is shown to the right of the 
conductor stop 80. 
According to the invention, the stations 1,2 are such that the cable (31) 
can be inserted laterally into the stations by means of the manipulator 
arm (35). 
According to FIG. 2, the stripping station 1 has centering jaws 1040 which 
are arranged concentrically and nonrotatably with respect to the axis 1028 
of a cable (31) to be stripped and are radially adjustable by an adjusting 
drive (1056) via a two-armed lever (105) and a cone (109). Furthermore, 
the stripping knives (1033b) which can be rotated about the axis (1028) by 
means of a rotary drive (1055) are provided concentrically thereto. The 
radially acting swivel mechanism for the stripping knives (1033) and for 
the centering jaws is described in, for example, U.S. Pat. Nos. 4,745,828 
and 5,010,797. 
In contrast to the elements described there, the structure shown for 
mounting the centering jaws 1040 has a central holding element 1057, which 
is held concentrically and axially nondisplaceably relative to the 
stripping knives 1033. 
The radial movement of the centering jaws is effected by means of a 
two-armed lever (105b) which is controlled via a cone (109b) rigidly 
connected to a thrust rod (1023b). 
The thrust rod (1023b) is engaged by a brake element or block (1062) whose 
braking effect can be set by adjusting a spring (1064). The brake block 
(1062) is mounted in a holder (1065) which on the one hand cooperates with 
a threaded spindle (1063) of an adjusting drive (1056) and on the other 
hand is rigidly connected to a control rod (1050b) which extends in a 
tubular manner around the thrust rod (1023b). The control rod (1050b) 
carries, in its front region, on a bearing (1015b), a second cone (1058) 
which, together with second two-armed levers (1053), is responsible for 
the radial control of the stripping knives (1033b) which are formed on 
knife holders (1032b). 
Thus, the levers (1053) and the knives (1033) are also rotatable about the 
axis (1028) of rotation by means of the cone (1058). For this purpose, 
they are held in a rotary element (1014). The rotary element (1014) is 
equipped at one point with a pulley (1052) which can be set into rotation 
by means of a belt (1054) of a rotary drive (1055). 
When the adjusting drive (1056) is operated, the cones (109b) and (1058) 
are initially uniformly displaced. However, as soon as the centering jaws 
(1040b) meet resistance as a result of contact with a cable sheath, the 
thrust rod (1023b) slips through against the braking force of the brake 
element (1062). This prevents undesirable squeezing of the cable. However, 
the stripping knives (1033b) continue moving to the required stripping gap 
under positive control since control rod (1050b) is fixedly secured to 
both holder 1065 and the inner race of bearing (1015b). 
In contrast to the known insertion orifice, a lateral insertion orifice 
(29c5) is provided for introducing the cable end to be stripped, as can be 
more clearly seen in FIGS. 3 and 4. However, the invention also relates to 
any other knives which permit lateral introduction of the cable. 
The described parts of the stripping knives 1033 and controls therefor form 
the knife head, which is closed at its end face by a cover plate 1024. The 
cover plate has a lateral slot as in the case of the knife-holding plate. 
They form there a slot-like insertion orifice 29c for the cable 31. For 
automatic operation of the knife head, it is necessary for the insertion 
orifice 29c to be positioned or to be turned towards the manipulator 35 
prior to insertion of a cable. The position of the insertion orifice 102 
is determined via a sensor mark 1026 which is positioned beside a 
stationary sensor 1069 (FIG. 2). As soon as the sensor mark 1026 and the 
sensor 1069 coincide, the required insertion position has been reached and 
the rotary drive stops the pulley 1052 and hence the rotary element 1014 
or the knife head. 
Both the centering jaws (1040) and the stripping knife (1033) are formed 
approximately as described in U.S. Pat. No. 5,010,797. Alternative 
variants of these are, however, possible. 
The stripping station 3 for stripping a coating is located in the upper 
region of the apparatus and can be swivelled in towards a cable held in 
the clamping jaws 36. This facilitates the feed logistics of the 
manipulator arm 35. 
The position of station 3, shown in FIG. 1, corresponds to the rest 
position. In this position, the insertion orifice 29c6 is opposite an 
inventive brush arrangement 4 which is equipped with an axially 
displaceable brush for cleaning the stripping station 3. Such a brush 
arrangement could also be used in other stripping stations or stripping 
apparatuses. 
As can be more clearly seen in FIGS. 8-12, a drive 32 is connected to 
station 3 for the swivel movement of the latter, said drive being axially 
held at the other end, in a manner not shown, on the carriage 912 on 
bearing 28. 
The stripping station 3 has profiled knives 18 which are pivotable about a 
guide pin 38. They are each driven by means of an adjusting slide 16 
having a driver 13. The adjusting slides 16 are driven symmetrically and 
synchronously by means of control pins 37. The control pins 37 are held on 
a shaft 26 which can be rotated by means of a rotary drive 27. 
They are also connected to a sliding clutch having a spring assembly 21 
which is held pressed against an adjusting disc 20 by means of an 
adjusting collar 22. By turning the adjusting collar 22, the applied force 
or sliding force between the control disc 20 and the shaft 26 is 
determined. 
The control disc 20 carries control pins 15 which engage recesses in 
centering plates 14. Turning the control disc 20 leads to a longitudinal 
displacement of the centering plates 14. These are each equipped, on their 
side facing the cable 31, with two retaining surfaces which are parallel 
to the corresponding retaining surfaces of the other centering plate 14. 
The plates 14 are appropriately undercut in order to permit complete 
closing of the retaining surfaces. 
The stripping head 3 furthermore has two leg springs 23 which close the 
insertion orifice 29c6 under spring load. When a cable 31 is inserted, the 
spring force is overcome in order to snap in the cable. The leg springs 23 
therefore act as precentering means during longitudinal adjustment of the 
stripping station for reaching a cutting position close to the cable end 
(as can be seen, for example, in FIG. 13). They can advantageously be used 
in all stripping stations having a lateral insertion slot. 
Scraping plates 19 which are parallel to the profiled knives 18 and behind 
the edge of which the profiled knives 18 swivel back into the rest 
position are provided for scraping any coating residues from the profiled 
knives 18. At this edge, any coating still adhering is scraped off, the 
brush subsequently removing all remaining residues. 
On the guide pin 38, flat heating elements 24 are rotatably mounted in the 
axial direction of a cable to be stripped, which elements, if required, 
preheat the coating to make it easier to strip off. A spring 40 tensions 
the heating elements 24 in the closing direction of the profiled knives 
18, with which they are connected in a nonpositive manner by means of 
connecting pins 25. The process has approximately the following stages: 
insertion of the cable by means of the manipulator which is in the 
immediate vicinity of the end face of the stripping station; the springs 
23 grip and hold the cable 31; displacement of the stripping station 
towards the cable end to the required cutting position (the springs 23 
prevent the cable 31 from slipping away); closing of the profiled knives 
18 and heating elements 24; stripping of the coating with the profiled 
knives 18 closed, after a delay; opening said knives and swivelling back 
of the stripping head 3. 
Opening of the profiled knives 18 thus automatically leads to opening of 
the heating elements 24. 
The profiled knives themselves can easily be replaced. They are held only 
by spring force at the guide pins 38, so that they can easily be pulled 
out there manually. Holes or indentations are formed in the upper region 
to provide a more secure grip. The embodiment and arrangement of the 
profiled knives can advantageously also be used in other stripping 
apparatuses for coating. They are striking in their precision and do not 
damage the optical waveguide during stripping. 
Most of the apparatuses and apparatus details described herein are novel 
for stripping machines and are inventive performances per se. They 
increase the stripping speed and the precision during stripping of 
fibre-optical cables.