EoW January 2012

EuroWire – January 2012

Technical article

In another experiment, the process set

points of one twinner were changed,

but the lay set point was left constant.

In this case, pretwist ratio and twinner

bow speeds were changed.

Figure 3

shows distinct differences in the resultant

lay as a result of process set points.

With conventional manual or visual

measurement techniques, changes this

small would be quite difficult to discern.

In another experiment, two twinning

machines were set to the same lay set

point, and the pairs from each machine

measured.

Figure 4

is an example from that

experiment and shows the shift in nominal

from one machine to another. In several

other cases, changes on the order of a

millimetre or two were readily discernable

in the histogram.

2.1.3 FFT of individual pair lays

The ability of the equipment to sample at

a high data rate allows lay variations to be

seen on a scale of about each lay length.

A surprising outcome was that a number

of other variation signatures were also

captured in addition to the primary lay

length signature.

Waterfall analysis is a way to capture

frequency signatures over time and

display in an understandable format. For

instance, waterfall displays are commonly

used in measuring and troubleshooting

SRL on primary extrusion lines. For this

analysis, we also used waterfall analysis

tools to better capture the variation of the

pair lay over the length of the spool.

Figure 5

is an example of a waterfall FFT,

with time on the horizontal axis, frequency

on the vertical axis, and shading as the ‘z’

axis. For the ‘z’ axis, the lighter the colour

the more intense the frequency signature

is.

An expected outcome was the frequency

signature from the primary lay length. A

surprising outcome was the additional

signature content found in the FFT

waterfall. A signature is clearly visible from

both the twinner bow RPM (2x lay length,

½ frequency) as well as the pretwist (at

pretwist %) imparted on the wire before

twinning. There are also a number of

other unexpected signatures found within

the FFT waterfall that indicate other

mechanical patterns of the manufacturing

equipment.

Figure 6

shows the difference in the FFT

pattern when a change in the pretwist

ratio is implemented. In this diagram, the

signature of the primary lay and the bow

speed is the same as

Figure 5

However, the signature for the pretwist has

a shift that is consistent with the changes

in the set points on the twinning machine.

2.1.4 Relationship of Process Set Points

to Nominal Lay Length

Using DOE techniques with the nominal

lay length as an output and a 2x2 matrix

of process set points as the inputs, the

relationship of set points to nominal lay

could be determined. The main effect

plots in

Figure 7

show that there is a

strong relationship between the pretwist

ratio and the lay length. The bow speed

relationship is not as strong.

Interestingly there is also a sign of an

interaction effect of bow speed and

pretwist ratio on lay length as shown by

the interaction plot in

Figure 8

This means that how the lay length is

affected by pretwist ratio depends on

what setting for bow speed has been

chosen.

It should be noted that the amount of

change in lay length accounted for by the

process pretwist ratio is still very small.

Normally this might not be considered

significant to crosstalk performance.

Without replication of the test matrix,

statistical significance of this change

cannot be determined. But it does give

initial indication that there may be some

cause and effect in this relationship.

2.2 Pair Lays at Cabling Studies

Extending the experimentation of pair lays

into the cabling process was necessary to

confirm previous findings of individual

pairs and to measure the lays of at least

two individual pairs going into the cabling

process at the same time.

Using the process set points described

in Section 2.1.2, a simple 2x2 test matrix

was set up to compare the signatures of

various pairs at the chosen set points of

pretwist ratio and bow speed. Only two

of the pairs in the cable were subjected

to the 2x2 test matrix while the remaining

▲

Figure 5

FFT showing measured frequency pattern at lay, bow speed, and

pretwist ratio

▲

Figure 6

FFT showing same lay as above, but with a different pretwist ratio and

the resultant shift in the FFT pattern

Primary Lay Signature

Bow Signature

Pretwist Signature

Lay Length Signature

Bow Signature –

Lay

Pretwist Signature % of lay