1. Field of the Invention
The present invention relates to dobbies and other weaving mechanisms of the negative type for forming the shed in weaving looms, and more particularly to the spring systems which, in this type of mechanism, ensure return of the heddle frames.
2. History of the Related Art
Mechanisms of the negative type are known to operate positive control of the heddle frames acting only in one direction of the reciprocating stroke thereof, so that resilient elements should be provided, arranged so as to return the frames to the other end of the stroke. These resilient elements are most often constituted by two systems formed by parallel springs retained between two hooking elements of which one is mounted on a console or rack secured to the fixed structure of the loom, while the other is hooked either to the end of one of two cables provided for maneuvring each frame, or to a rocking guide lever associated with the cable.
It will be readily appreciated that the springs of each spring system are thus placed in tension during positive control of a frame by the weaving mechanism so that as the mechanism has arrived at the end of stroke the spring system will act on the cable or lever to return the frame to its initial position.
In practice and as illustrated in FIG. 1 of the accompanying drawings, each hooking element generally includes two parallel plates a assembled to one another by transverse ties b which are fixed by rivetting or crimping. For fastening the springs c, endpieces d in the form of hooks are conventionally provided and are adapted to cooperate in a removable manner with one of a row of small rods e rivetted on the plates a in a line oriented perpendicularly to the axis of the springs.
The prior art is illustrated by documents DE-A-3 533 336 (MURATA KIKAI), FR-A-2 626 013 (STAUBLI), GB-A-298 758 (HARLING and TODD) and EP-A-353 875 (YOKOI INDUSTRIES).
It should be observed that, due to the high operational speeds now conferred on weaving machines, more and more considerable forces are demanded of the spring systems, with the result that the springs break relatively frequently. Now, although it is fairly easy to replace a broken spring when the operation concerns one of the two side systems of the group of spring systems provided on one of the sides of a group of heddle frames. This is not so when it is question of extracting a broken spring and mounting a new one in the interior systems of the group. In fact, replacement involves dismantling and remounting a large number of systems and springs, all of which are in addition subjected to very high tension.
Furthermore, it is of interest to note that, due to their configuration, the hooks which connect the springs on the hooking elements, are subject to bending forces and are consequently the location of frequent breaks which stops the operation of a weaving machine.