Figure 19.1 illustrates the arrangement of elements in the needle bed of a machine having full mechanical selection. A separately-controlled arrangement may also be available on the other needle bed. In the tricks beneath each needle are selectors (two in the case of the double-cam system machine) whose tails are supported by a jacquard steel that extends across the full width of the needle bed.
There is a possible punched-hole position for each selector on every jacquard steel. The steels are hinged together to form an endless 'chain loop' which passes over the prism. The prism can turn whilst the cam-carriage is clear of the needle bed at the end of its traverse. This brings another steel onto its upper surface and thrusts it upward into contact with the protruding tails of the selectors. This produces a simultaneous selection at every needle trick, ready for the next carriage traverse. The prism can dwell to repeat a selection, or rack forwards or backwards by one or two positions.
An unpunched portion in a steel causes the corresponding selector to be pushed upwards in its trick, aligning its butt with a raising cam in the cam-carriage so that eventually the needle above it will be lifted, possibly to knit. A punched hole allows the selector tail to sink into the groove of the prism and thus be unaffected by the thrust of the prism so that its needle is left at an inactive level.
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