a mechanism used to stop a loom automatically if a warp thread breaks. The most common type is mechanically operated.
The principle of operation of a warp stop-motion is as follows. A metal vane is fitted on each warp thread. Above the hole for the thread in the vanes there is a longitudinal slot through which two racks pass. The outer rack is fixed, and the inner is movable. The inner rack performs reciprocating motion inside the fixed rack. If a thread breaks, the vane drops and, by falling between the teeth of the racks, stops the motion of the movable rack which causes the loom to shut down. Warp stop-motions also exist that operate electromagnetically; in this case the fall of a vane when a warp thread breaks closes an electrical circuit and stops the loom. These mechanisms free the weaver from the need to watch for warp breakages, which is important when operating several automatic machines simultaneously, and prevent the occurrence of defects in the fabric.