On hosiery machines without positive feed, the distance between the top of the needle head at knock-over and the loop-supporting belly of the sinker will determine the length of loop that is drawn.
On single-cylinder machines, the sinkers are in a bed fixed to the head of the needle cylinder so that any raising or lowering of the cylinder will affect the loop length.
A gradual lowering of the cylinder produces graduated stiffening. On electronically-controlled machines, this is achieved by step motors which are employed to raise and lower the stitch cams and also for introducing the stitch cams. This is particularly useful on tights machines for precisely placed spliced areas of elastane yarns to give selective comfort support whilst saving expensive yarn.
In single-cylinder tights production, Matec has developed the VPS (Variable Profile Stitch Cam). The angular position of the step motor-controlled stitch cam is adjusted to the speed requirements in different parts of the tights. A ten degree difference can enable an increase in speed by 130rpm in that section of the tights.
On mechanically-controlled machines, levers scanning tracks on the control drum operate through adjustable set-screws to raise or lower the cylinder. Separate tracks on the drum may be responsible for adjustment of the loop length for the waste courses, toe, heel, panel, ankle and foot, graduated stiffening, etc. Graduated stiffening is operated from a rotary eccentric cam that is racked independently of the control shaft and allows the cylinder to be gradually lowered during the knitting of the calf, so that loops gradually become smaller and the leg tube is narrowed.
On double-cylinder machines, loop length adjustment is achieved by adjusting the stitch cams and thus the needle height.
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