The shogging movement is initiated by varying the radius of the continuously-turning pattern shaft, either in the form of different heights of pattern links that pass over a pattern drum attached to the shaft, or in the form of carefully-shaped solid metal circular cams, termed pattern wheels, attached to it (Fig. 23.3).
An increase in height from one link to the next produces a thrust against the end of the guide bar, shogging it positively into the machine; a decrease will produce a negative shog towards the pattern shaft as the result of the action of a return spring. A constant height will produce no shog and the guide bar will continue to swing through the same needle space. The periphery of the pattern wheel or chain track is scanned by a roller that is linked by a flexible, ball-jointed push-rod to the end of a guide bar. The underside of the rod near the roller is supported on a slide that moves freely on a metal surface as shogging occurs.
The drive for the pattern shaft is obtained from the main cam-shaft, via bevel gears and a universal joint, to a worm that drives the worm-wheel of the pattern shaft. The ratio of cam-shaft speed to pattern shaft speed is usually 16:1; therefore, 1/16th of the surface of a pattern wheel would represent one course or knitting cycle.
Pattern wheels provide accuracy and smooth running at high speeds, but they are only economical for long production runs of the common, simple repeat structures. For fancy structures, frequent changes of pattern, and long pattern repeats, the shog-ging movements are obtained by assembling a chain of re-usable pattern links.
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