Secondary coating line

A secondary coating line for producing a secondary-coated optical fibre or bundle of fibres, the line including a feeding apparatus with a feed roll for feeding an optical fibre or bundle of fibres; an extruder for extruding an oversize secondary jacket around the fibre or bundle of fibres; a cooling apparatus for cooling the extruded secondary jacket, the distance between the extruder and the point where the cooling apparatus starts to cool being adjustable; and a winding apparatus for winding the finished secondary-coated fibre or bundle of fibres on a take-up roll. To maintain the high quality of the final product even as the line speed changes, the secondary coating line of the invention further including means for determining the point where the cooling apparatus starts to cool, means for determining the speed of the finished secondary-coated fibre or bundle of fibres, and means for adjusting the point where the cooling apparatus starts to cool in accordance with the speed of the finished secondary-coating fibre or bundle of fibres.

BACKGROUND 
The invention relates to a secondary coating line for producing a 
secondary-coated optical fibre or bundle of fibres, the line comprising a 
feeding apparatus with a feed roll for feeding an optical fibre or bundle 
of fibres; an extruder for extruding an oversize secondary jacket around 
the fibre or bundle of fibres; a cooling apparatus for cooling the 
extruded secondary jacket, the distance between the extruder and the point 
where the cooling apparatus starts to cool being adjustable; and a winding 
apparatus for winding the finished secondary-coated fibre or bundle of 
fibres on a take-up roll. 
A conventional secondary coating line with the basic structure described 
above is known e.g. from Finnish Patent 75,939, or corresponding British 
Patent Application 2,141,557. Conventionally, secondary coating lines like 
this have been controlled so that a product produced during the starting 
and speeding up of the line has not met the quality requirements. The 
reason for this is that when the speed of the line changes, the 
characteristics of the produced secondary coating also change; not until 
the normal running speed is achieved does the secondary coating reach the 
desired values. A rather large amount of valuable optical fibre has thus 
been wasted. 
Alternatively, optical fibres have not been thread into the tube provided 
by the secondary jacket until the production speed has been achieved. 
Plastic waste has been produced, and the production speed must have been 
adjusted to be so slow that it has been possible to thread the optical 
fibres into the secondary jacket at that rate. 
When optical fibres are thread into the secondary jacket at a rate that is 
slower than the normal running speed, the poor quality of the product is 
at least primarily due to the fact that the distance between the cooling 
apparatus and the extruders has not been suitable considering the rate. In 
practice, the plastic melt outlet from the press head forms after the 
press head a conical part in which the secondary jacket tube is drawn to 
its final measurements. If the water cooling conducted in the cooling 
apparatus is started at the conical part, the result is a brittle tube, 
i.e. the tensile strength of the tube in a tension test is small. If on 
the other hand the distance between the press head and the water cooling 
is too long, the hot plastic may run, causing faults in shape and 
variation in diameter. As the line speed increases, the tension cone 
following the press head becomes larger; by suitably adjusting the line 
speed, it has thus been possible to make the measurements of the secondary 
jacket comply with the quality requirements. 
In secondary coating, the type of plastic from which a secondary jacket is 
produced must also be taken into account. Since different plastic types 
have different characteristics, they behave differently in an extruder, 
and so the plastic melt also behaves differently and the line speed must 
be suitable in order that it might be possible to achieve the desired 
measurements. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a new kind of secondary 
coating line by which the quality of the secondary-coated optical fibre or 
bundle of fibres can be maintained high irrespective of the plastic type 
used, the line speed, or possible controlled changes in the line speed 
during the production process. This is achieved with the secondary coating 
line of the present invention, which is characterized by comprising means 
for determining the point where the cooling apparatus starts to cool, 
means for determining the speed of the finished secondary-coated fibre or 
bundle of fibres, and means for adjusting the point where the cooling 
apparatus starts to cool in accordance with the speed of the finished 
secondary-coated fibre or bundle of fibres. 
Thus the basic idea of the present invention is that if the point where the 
cooling is started is adjusted in accordance with the line speed, the 
final product always meets the quality requirements, irrespective of the 
line speed. Advantageously, the means for adjusting the point where the 
cooling apparatus starts to cool comprise a first memory means for storing 
product-specific secondary jacket data about the desired point for 
starting the cooling operation of the cooling apparatus at various speeds 
of the finished secondary-coated fibre or bundle of fibres. On the basis 
of the information obtained during the trial runs, it is possible to 
determine the conditions--which are dependent on the plastic type used and 
the desired measurements of the final product--under which a product with 
the desired characteristics is obtained. Accordingly, on the basis of the 
product specifications, it is thus possible to determine the point where 
the cooling is to be started, when the line speed is known. 
In order that all the possible factors affecting the quality of the product 
might be controlled, the secondary coating line of the invention 
advantageously also comprises a second memory means for storing 
product-specific secondary jacket data about the throughput of the 
extruder at different rotation rates of the pressing screw of the 
extruder, and means for adjusting the rotation rate of the pressing screw 
of the extruder to produce the desired throughput at various speeds of the 
finished secondary-coated fibre or bundle of fibres. This makes it 
possible to take into account any non-linearities of the operation of the 
extruder and to eliminate their effect. 
In accordance with the above, the secondary coating line of the invention 
makes it possible to reduce and increase the line speed without impairing 
the quality of the product. For optimal utilization of this 
characteristic, the line further comprises means for determining the 
length of a finished secondary-coated fibre or bundle of fibres wound on a 
take-up roll, and means for decelerating the speed of a finished 
secondary-coated fibre or bundle of fibres to a roll change speed as the 
desired length has been wound, and for accelerating it back to the normal 
speed after the change of rolls. 
In the following, the secondary coating line of the invention will be 
described in greater detail with reference to the attached drawing, which 
shows a schematic general view of a secondary coating line according to 
the invention.

DETAILED DESCRIPTION OF THE DRAWINGS 
For the sake of clarity, only those elements of the secondary coating line 
that are significant to the operation are shown in the figure. For 
example, elements conventionally contained in secondary coating lines such 
as a tension apparatus for directing a desired tensile force to the 
secondary jacket, or an apparatus connected with the extruder for feeding 
grease through the extruder into the secondary jacket so that it fills the 
jacket, or different measuring devices for measuring e.g. the diameter of 
the product are not depicted. Conventional line elements of this kind are 
disclosed e.g. in above-mentioned Finnish Patent 75,939 and corresponding 
British Patent Application 2,141,557. 
Basically, a secondary coating line according to the invention as shown in 
the figure comprises a feeding apparatus with a feed roll 1 for feeding an 
optical fibre or bundle of fibres 2, an extruder 3 for extruding an 
oversize secondary coating around the fibre or bundle of fibres 2, a 
cooling apparatus 4 for cooling the extruded secondary jacket, and a 
winding apparatus 5 for winding the finished secondary-coated fibre or 
bundle of fibres 6 on a take-up roll 7. As shown in the figure, the 
secondary coating line according to the invention further comprises a 
control computer 10 that contains storage areas and processors for 
performing different tasks. The control computer 10 comprises a storage 
area 11, in which the points where the cooling apparatus 4 starts to cool 
at various line speeds are stored. A block 15 of the control computer 10 
obtains the data indicating the line speed e.g. from a wheel 9 connected 
with the winding apparatus 5. Naturally, all conventional arrangements for 
measuring the line speed are suited for the purpose. On the basis of the 
measured line speed and the `recipe-specific` data in the storage area 11, 
an actuator 8 of the control computer 10 controls the cooling chute 17 
that is connected with the cooling apparatus 4 and has e.g. a telescopic 
structure, so that the distance between the cooling chute 17 and the 
extruder 3 is as desired. The cooling conditions of the secondary jacket 
can thus be held constant 30 irrespective of the length of the tension 
cone of the extruded secondary jacket, the length in turn depending on the 
desired measurements of the final product, the material of the secondary 
jacket, and the line speed. 
To control the position of the telescopic part 17 of the cooling chute, the 
control computer 10 naturally also needs information about the current 
position of the telescopic part, i.e. the point where the cooling is 
started. The control computer 10 obtains this information by conventional 
sensors in connection with the actuator 8. On the basis of both the point 
where the cooling is started and the line speed, and using the data stored 
in the memory means 11 concerning the product-specific point of the 
secondary jacket where the cooling operation of the cooling apparatus is 
to be started at various line speeds, the control computer 10 is able to 
give the actuator 8 a signal that moves the telescopic part 17 to the 
desired direction. Since the actuator 8 performs a continuous sensing 
operation, the control computer is continuously informed of the position 
of the telescopic part, and so the control computer can continuously 
modify the position of the telescopic part in accordance with the line 
speed. The modification can be performed so quickly that it is possible to 
start the line at a very low speed and even at this speed to meet the 
quality requirements set to the product, and further to accelerate the 
line until it reaches the desired speed without impairing the quality of 
the product. 
In the secondary coating line of the invention, it is also possible to take 
into account that the operation of the extruder may be non-linear. 
Accordingly, the control computer 10 comprises a second storage area or 
memory means 12 for storing the product-specific secondary coating data 
about the throughput of the extruder at different rotation rates of the 
pressing screw of the extruder. In order that the throughput of the 
extruder 3 might be made to comply with the varying line speeds, the 
control computer 10 comprises suitable software which--after receiving 
data about the line speed--gives the actuator 13 that adjusts the rotation 
rate of the pressing screw of the extruder a control signal that 
product-specifically sets the rotation rate of this pressing screw to the 
desired value at the various line speeds. This rectification of possible 
non-linearities of the extruder further enhances the operation of the line 
especially in situations where the line speed varies within a relatively 
large range. 
The characteristic of the secondary coating line according to the 
invention--that the line is able to produce a final product that meets the 
quality requirements irrespective of the line speed--is also. advantageous 
with respect to continuous operation: instead of a conventional double 
winder, the line can now be provided with a much cheaper single winder, 
since the change of rolls does not require that the line should be 
stopped. Accordingly, the winding apparatus 5 of the described line has an 
actuator 14, typically a separate production line actuator, measuring the 
length of the final product of the secondary coating line wound on the 
take-up roll 7. The data indicating the wound length is sent to a block 16 
of the control computer; by a program contained in the block and by 
utilizing other storage areas and processors of the computer 10, the speed 
of the secondary coating line can be decelerated to a roll change speed as 
the desired length has been wound, and accelerated back to the normal 
speed after the change of rolls. According to the invention, when the 
length of the product wound on the take-up roll reaches the desired value, 
block 16 of the control computer 10 can, if desired, slow the line speed 
down to a point where the take-up roll 7 can be changed in a single winder 
even without an accumulator. When the take-up roll has been changed, block 
16 controlledly accelerates the line speed back to the normal running 
speed; the production process has not been interrupted, nor has the 
quality of the product been impaired in any way by the change of rolls or 
associated changes in the speed. 
The secondary coating line of the invention has been described above by 
means of one illustrative and schematic solution, but it is to be 
understood that the line can be modified in many ways according to the 
need and that additional elements can be added without departing from the 
scope of the attached claims.