Knitting technology, Third Edition

19.11.6
Stitch pressing-down devices
The object of the presser foot and other similar devices (such as knock-over bits
and holding-down sinkers) is to keep the old (fabric) loops low down on the needle
stems. They are thus prevented from rising (‘riding-up’) and staying on the latch
spoons as the needles rise for clearing or yarn feeding. This ensures a ‘clean’ knit-
ting action, irrespective of the variable tensions within the knitted structure or the
lack of takedown tension operating onto the fabric from below.
Interest in this concept was regenerated in 1968 by the development work of
Frank Robinson
and 
Max Betts
of 
Courtaulds
, whose ‘presser foot’ patents were
licensed by 
Dubied, Bentley-Cotton
and 
Shima Seiki
for use on their flat knitting
machines. Other companies also employed stitch pressing-down devices of various
types on their machines.
The original presser foot consisted of a piece of wire bent at either end to form
a foot (Fig. 19.5). The centre of the wire is carried on the underside of a pivoted arm
that hangs downwards from a cross member so that it brushes against the upper
surface of the fabric loops as it moves with the cam-carriage. At the end of each tra-
verse, the pivoted arm is tilted to incline in the opposite direction, lifting one foot
out of action and lowering the foot on the other end to trail across the needle beds
for the return traverse
There is a device working with each cam system and its yarn carrier. Different

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Automatic power flat knitting
233
diameters of wire can be employed for varying machine gauges and yarn counts,
and it is possible to fit specially-angled feet of triangular cross-section for use during
single-bed knitting or loop transferring, if necessary.
The foot acts slightly in advance of the yarn carrier and the rise of the needles
for tucking or clearing. It enters the space between the needle beds to gently stroke
the old loops down the needle stems as it trails, at a slight decline to their upper
surface. Accommodation to differing degrees of knitting tightness can be achieved
with a spring-loaded, self-compensating presser foot, which rides-up the support
arm when the structure is knitted to a tighter quality.
As the presser foot does not create tension on loops already formed, loops may
be held on inactive needles for many knitting cycles and stitch concentrations can
be varied across the fabric width. It also enables separate garment panels to be com-
menced on empty needles and to be pressed-off on completion. The reduced take-
down tension removes the problem of shape distortion and the bowing of courses
caused by relaxation of the structure, often eliminating the need for first pressing.
The structures tend to be heavier, and rib knitted on two-cam systems shows a
slightly racked appearance because the presser foot causes yarn to flow into the 
first limb of each loop that it contacts. Two courses made in the same direction of
traverse emphasise the inclination of the loops. To produce a conventional elon-
gated loop instead of a round loop it is important to maintain some take-down
tension.