Selection area arrangement

Dependent upon the type of device, four arrangements of the selection areas around the fabric tube are possible:

1 Full jacquard selection can produce a selection area of theoretically unlimited depth and a width equal to the number of needles in the cylinder, so that the design exactly surrounds the fabric tube without repeating.

2 Pattern wheels have a circumference selection that is not an exact factor of the number of cylinder needles, so that their selection areas follow the spiral path of the feeder courses around the fabric tube. In the starting wale of each machine revolution, the base of the areas will thus have risen by the number of feeder courses knitted in one machine revolution compared with its position in the same starting wale at the previous machine revolution (X in Fig. 11.4a).

3 Fixed geometric selection devices (step jack devices) provide only one selection width at each device, which is unchanged from one machine selection to the next (Fig. 11.4b). Machines employing this type of device are termed small-area or intermediate jacquards; although their pattern area potential is limited, they have

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Fig. 11.4 The development of design areas using selection devices.

sufficient feeders and speed to be employed in the production of single colour and plain structures as well as jacquards.

A complete design depth is thus produced at each machine revolution, composed of the number of active feeder courses, so that the base of the design will have risen by that number of courses each time it is recommenced in the starting wale, but no displacement of design is noticeable between the adjacent finishing and starting wales of the fabric tube.

4 Non-fixed geometric selection devices hold a limited number of different selection widths so that a new selection width may be presented, commencing in the starting wale of each machine revolution (Fig. 11.4c). Single-jersey and rib machines using non-fixed selection are termed large-area jacquards. A design depth is thus developed that is a multiple of the number of machine revolutions in the sequence of selection presentations.These devices produce a displacement line between the starting and finishing wales of the tube in the form of a rise by the number of feeder courses in one revolution. Usually, the tube is split open along this line during finishing.

The potential depth of non-fixed selection devices is increased by the ability to dwell (retain) a selection for a number of machine revolutions, and to rack the selection sequence forwards or backwards by one or two steps.

Only in the case of full jacquard selection on machines with stationary needle bed tricks (certain flat machines and revolving cam-box circular machines) can a successive row of selection decisions be kept in permanent alignment with each trick. On other revolving cam-box machines and flat machines, the selection devices pass across the tricks with their associated cam-sections or, in the case of revolving cylinder machines, they remain with their cam-sections as the cylinder revolves past them.

Pattern wheels or discs turn in continuous alignment but in the opposite direction to the cylinder, so that each trick in turn receives a decision from the selection sequence around the wheel periphery. The element butts being selected may be set-out at the same height. Although the selection is in a fixed set-out in a pattern wheel, the pattern depth is spirally developed over a number of machine revolutions. On machines with selector wheels, a tape may rearrange the selection set-out for the next machine revolution, or a different disc selection may be switched into operation.

With multi-butt selection, the selection butt at each trick can be placed at one of a number of different heights, usually in a geometric set-out, which together will determine the pattern width (Fig. 11.4). As either the selection device or the needle cylinder is revolving, the selection is transferred from the device by a bank of spring-loaded plates or electronically-controlled selectors that pivot across to contact any selection butts at that height as they pass (Fig. 11.5).

Instead of one pattern key (comb) at each selection, it is possible to have four different selection keys on a spindle so that, when the machine has a pattern

Selectors, operate on Jack butts

Selectors, operate on Jack butts

Fig. 11.5 Fixed pattern key selection.

Pattern key lock

Pattern key

Fig. 11.5 Fixed pattern key selection.

change, the spindle is turned at each feed to introduce a new pattern-selection key.

On mechanical selection devices, a vertical row of selection teeth or pegs at each station pushes the respective height plates towards the needle bed. With non-fixed selection, a different selection row may be aligned at the start of each machine revolution at each device in turn.

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