Warp Let-Off Systems

The warp let-off motion is necessary to provide a sufficient amount of warp threads and to keep the warp tension as uniform as possible. In conjunction with the back rail (on flexible bearings), the warp let-off has to compensate for the increase in thread length caused by shedding (Fig. 4.15). A uniform warp tension is important for the quality of the final woven fabric. 

The warp let-off motion can either be passive with an intermittent flexible movement of the warp beam or active with a driven warp beam. According to the drawoff motion, either the distance between the weft threads (negative draw-off) or the distance of the center points between consecutive weft threads may be set at a constant value (Fig. 4.16). 

---