Optical fiber proof testing equipment

Optical fiber proof testing equipment has a rotary drive and two pulleys directly coupled to the drive. A fiber is taken from fiber drawing equipment around part of the circumference of the first pulley, along a guide track and around part of the circumference of the second pulley. Respective continuous belts apply a resilient bias to clamp the fiber to the pulleys, the resilient bias being adjustable. The second pulley is marginally greater in diameter than the first pulley so as to establish a predetermined tensile stress in fiber moving between the two pulleys. The test equipment is used after fiber has been drawn in a drawing tower and then coated and before the fiber is stored on reels. The tensile force on the fiber can be changed by changing the diameter of the first or second pulleys. In addition some incremental change in the tensile force can be obtained by adjusting the resilient bias provided by the continuous belt.

This invention relates to a fiber proof testing equipment and particularly 
to such equipment adjusted for in-line use in a fiber manufacturing plant. 
In the manufacture of optical waveguides for use in optical communication 
systems conventionally a large diameter glass preform is made with the 
desired composition and the cylindrical preform is then heated to 
softening and fiber of the order of 125 microns in diameter is drawn from 
one end of the cylindrical preform. The fiber is taken to a fiber winding 
station where it is wound onto reels. At a stage intermediate the pulling 
of fiber and its storage the fiber is coated with a protective layer of a 
plastic such as silicone or acrylate and is coated with a powder so that 
the fiber can move easily relative to supporting parts of an optical cable 
when the fiber is made up into cable. 
In order to assess whether the fiber is suitable for cabling, tests must be 
performed on it. One of the primary tests is to ensure that the fiber can 
stand up to tensile stresses which can occur while the fiber is being 
cabled or when the cable is being installed. A convenient way of testing 
all fiber made during a production run is simply to draw fiber from the 
fiber pulling and coating stations using drawing equipment which 
automatically introduces a predetermined tensile force in the fiber as the 
fiber passes through the drawing equipment. If the fiber is weak, it 
breaks. 
Conventionally known equipments for in-line drawing and testing of optical 
fiber are of the type described in U.S. Pat. No. 4,148,218. This patent 
shows a first tractor assembly driven by a variable speed drive motor with 
the belt extending to a constant torque device, the output of which drives 
a second tractor assembly. The constant torque device includes a clutch 
and a drive including a shaft connected to a belt wheel of the second 
tractor assembly. The unloaded speed of this drive is faster than the 
rotational speed of the first tractor assembly. However when the second 
tractor assembly pulls the fiber, its speed is reduced by causing the 
constant torque device to overload and the clutch to slip. In order for 
the tension to stay uniform the performance of the constant torque device 
should not vary. However with wear, it is inevitable that the particular 
torque at which the clutch starts to slip will change and then either the 
fiber will not be tested at the right tensile stress level or the 
equipment must be periodically adjusted to restore the torque level. 
According to the present invention there is provided an optical fiber proof 
testing equipment comprising a drive means, first and second pulleys 
directly coupled to the drive means, first resilient means for bearing 
down on a fiber located between the first resilient means and the pulley 
over part of the circumference of the first pulley to fix the fiber 
against that circumferential part of the first pulley, second resilient 
means for bearing down on a fiber located between the second resilient 
means and the second pulley over part of the circumference of the second 
pulley to fix the fiber against that circumferential part of the second 
pulley, guide means for guiding the fiber from the first pulley part to 
the second pulley part, the second pulley being larger in diameter than 
the first pulley. 
Preferably the pulleys are fixed at the same vertical height with axes 
thereof parallel to one another. Each resilient means is preferably a 
continuous belt extending around three pulleys, a part of the continuous 
belt extending between two of the pulleys bearing against said 
circumferential part of the respective pulley. The position of the third 
pulley within the continuous belt can be moved towards or away from the 
length of belt in order to change the tension within the belt and so alter 
the pressure exerted by the length of the belt on the fiber extending 
around the pulley surface. 
The guide means can be a grooved body. The grooved body can include a drop 
piece moveable away from the fiber to enable a direct measurement of fiber 
tension to be made. The fiber entry and take up positions are preferably 
such that the fiber extends around a quarter of the circumference of each 
pulley. 
Preferably drive to the main pulleys is by means of a toothed band which 
engages a toothed drive gear. 
The surface of the primary first and second pulleys can be anodized 
aluminum but may be coated for example with polyurethane of shore hardness 
of the order of 90 durometers.

Referring in detail to the Figures, there is shown a pair of pulleys 10, 
12. Optical fiber from a drawing and coating tower 13 is fed between the 
pulley 10 and a continuous flexible band 14 which presses the fiber 
against the pulley 10. The fiber passes along a horizontal track to the 
take up pulley 12 against which the fiber is pressed by a resilient band 
16. The fiber extending between the two pulleys 10 and 12 is subjected to 
a tensile force which depends on the difference between diameters of the 
two pulleys and to some extent on the clamping force between the 
respective pulleys 10, 12 and the bands 14, 16 which bear against them. 
The tensile test equipment is mounted on a panel 18. To the rear of the 
panel and mounted on a platform is a motor DC 20 which acts through a 
coupling 22 to a shasft 24 on which is mounted a toothed gear wheel 26 and 
elements 40 cooperate to permit adjustment of the shaft being mounted in a 
bearing housing 28. The toothed gear wheel 26 is secured to the shaft 24 
on which is mounted the take up pulley 12. A toothed transmission band 30 
extends around the toothed gear and around an identical toothed gear (not 
shown) which is secured to a shaft 32 on which is mounted the pulley 10. 
The toothed interengagement between the band 30 and the two gear wheels 
ensures that regardless of change in motor speed, the two pulleys 10 and 
12 rotate at identical rotational velocities. The pulleys 10, 12 can be 
made of an apertured lightweight aluminum alloy to minimize their moments 
of inertia. 
In use, fiber extends around part of the circumference of both pulleys and 
occassionally in use the fiber will slip relative to the pulley surfaces. 
To prevent any wear to the pulley surfaces especially if relatively hard 
fiber coating such as acrylate are used, the surface of the pulleys is 
coated with 90 durometer polyurethane. The fibers are pressed against the 
surface of the pulleys by the continuous bands 14 and 16 which are made of 
layered synthetic rubber material which is reinforced with nylon. Suitable 
material is available under the trade mark Habasit. The bands 14 and 16 
each extend around a pair of fixed rollers 34 and a third roller 36 which 
is mounted on a carriage 38. The positions of carriages 38 can be adjusted 
in a direction radial to the associated pulleys 10, 12 by turning an 
adjusting screw 40. Between the two pulleys 10, 12 the fiber extends along 
a grooved guide having two fixed sections 42 and a central section 44 
which can be detached and dropped out of the line of the guide way to 
allow the actual tensile force within the fiber to be routinely measured 
using a tensiometer (not shown). 
The panel 18 is bolted to a framework 46 to maintain the pulleys 10, 12 at 
the desired height relative to a drawing tower 13 and a fiber winding unit 
including reel 15 as shown in FIG. 3. The diameter of the right hand or 
take up pulley is made 1.19 mm greater than the diameter of the left hand 
pulley for a fiber stress level of 50 Kpsi. This diameter difference can 
be changed to vary the fiber stress level if greater or lesser stresses 
are anticipated during installation or cabling. The fiber is firmly held 
against the pulley 10 by the band 14 and since the two pulleys 10, 12 are 
turned at exactly the same rotational velocity then there must be some 
slippage of fiber on the take up pulley 12. Depending on the extent to 
which the fiber is biassed against a circumferential arc of pulley 12 by 
the band 16, this slippage is translated into a tensile force within a 
part 17 of the fiber stretching between the two pulleys 10, 12. To 
increase the tension in the fiber, the roller 36 associated with take up 
pulley 12 can be moved radially outward to increase the bias of band 16 
against the take up roller. Adjustment screw 40 can be turned in the 
opposite direction to reduce tension. Alternatively, slippage promoting 
tension within the fiber can take place at the input pulley 10. Again by 
moving the reciprocal roller 36 to change the bias of the band 14 against 
the pulley surface lesser or greater tension within fiber part 17 can be 
achieved. 
FIG. 3 shows the fiber being collected by the input pulley 10 from a fiber 
drawing and coating tower 13 and shows also the fiber leaving the output 
pulley 12 and being taken to the fiber take-up reel 15. 
The equipment therefore not only applies a tensile stress to a fiber but is 
also the mechanism by means of which fiber is pulled from a preform within 
the pulling tower 13 down through a fiber coating unit. The equipment is 
normally used in conjunction with monitoring equipment located upstream of 
the tensile testing unit, the monitoring equipment functioning to 
continuously monitor the diameter of fiber and the concentricity both of 
the fiber core within the fiber cladding material and of the fiber itself 
within an applied plastic jacketing material. If there is any variation in 
diameter of the fiber, then the tensile testing unit can be adjusted to 
retard or advance the speed of drawing fiber from the preform. 
As shown in FIG. 3, in the event that there is a weakness in the fiber 
which causes it to fracture under the applied tension, then by the fall of 
a dancer 47 a photodetector 48 mounted on frame 46 monitors the existence 
of a break and triggers an alarm. However the fiber drawing equipment 
continues to function. Thus the trailing section of fiber is retained by 
gravity within the guide groove 42 and when it reaches and is taken up by 
the take up pulley 12, the test tension is again applied to the remaining 
fiber. The alarm triggers personnel or automatic winding equipment to 
initiate a fiber reel transfer and reduce the pulling speed. Known tensile 
testing equipment of the two-pulley type have used tractor assemblies 
mounted one above the other so that when the fiber breaks a dangling end 
portion of the remaining fiber is fed from a top tractor assembly down 
into a bottom tractor assembly. This is inferior for three reasons. 
Firstly, static electricity tends to cause the fiber to wrap around the 
bottom pulley. Secondly, it is more difficult for the operator to rethread 
the fiber. Lastly, the fiber path has more bends. 
What is claimed is: