Method and apparatus for compensating warp thread tension or elongation

Abstract

Different groups of warp threads are subject to different variations of warp thread tension during shed changes, especially when weaving a fabric having portions such as fabric edges with different weave binding patterns. To provide different warp thread tension compensation for the different thread groups, a cam-like first tensioning module is arranged protruding from the circumferential surface of the backrest along the entire operating width thereof. Second and third tensioning modules are arranged and engaged over the first tensioning module at particular selected axial locations on the backrest. While the second and third tensioning modules provide a constant deflection path distance for second and third warp thread groups guided thereover, the first tensioning module provides a varying deflection path distance for the first warp thread group guided thereover, depending on the oscillating rotational angular position of the backrest. The backrest oscillatingly rotates under a passive compensating spring tension and/or under a positive actuation mechanism coupled to the main loom shaft. The respective warp thread tension of each group of warp threads can be compensated differently or independently from the other groups. The arrangement can be easily reconfigured in a modular fashion to be adapted to the needs of weaving different product articles.