In the following description, for purposes of simplicity it is assumed that only one needle bar is being employed. Essentially, the principles remain the same for double needle bar machines which are described later in the book (Chapter 29).
When the needle bar is observed in plan view from above, it can be seen that the guides of a guide bar are required to execute a compound movement composed of two separately derived motions (Figures 23.1 and 23.3):
A swinging motion (A-A) and a shogging movement (B-B) act at right-angles to each other in order for their threads to form overlap and underlap paths that combine as one thread path around the needles.
The swinging motion is in an arc from the front of the machine to the hook side and a later return swing. It occurs between adjacent needles and is a fixed, collective, and automatic action for all the guide bars as they pivot on a common rockershaft. It is derived, in a similar manner to the needle and other element bar motions, from the main cam-shaft and is adapted via levers, pivots and linkages. The two swinging movements produce the two side limbs when combined with the overlap
shog. When the overlap is omitted, the guides swing idly between adjacent needles and achieve no useful purpose.
On some machines, such as mechanical jacquard raschels and some multi guide bar and double needle bar machines, it is more convenient to swing the needle bar and trick-plate between the guide bars after they have shogged for the overlap and underlap. This considerably reduces the complexity of movement of the heavy guide bar assembly to only that necessary for shogging and thus increases the speed and efficiency of the machine.
The sideways shogging movement that occurs parallel to the needle bar produces the underlaps and overlaps. The occurrence, timing, direction and extent of each shog is separately controlled for each guide bar by its pattern chain links or pattern wheel attached to a horizontal pattern shaft driven from the main cam-shaft but set at right angles to it at one end of the machine. The guide bars are shogged independently sideways, parallel to each other, along linear bearings that support them in the swinging frame assembly, which is keyed to the guide bar rocker-shaft.
A shogging movement can occur when the guides have swung clear of the needle heads on the back or front of the machine. On the hook side it will produce an overlap and on the side remote from the hooks it will produce an underlap. The timing of the shog during the 360 degrees of the main cam-shaft revolution will thus determine whether an overlap or underlap is produced.
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