Abstract: In order to find the solution which helps to reduce the changes of warp tension in loom, the rules of warp path changing by shedding is researched, the influence on warp elongation caused by shedding is analyzed quantitatively, the rule of activity back roller swing which is needed to offset the warp tension changing during shed opening is obtained. At the same time, the difference of activity back roller swing needed by warp on different healds is analyzed comparatively. The result indicates that it is better to alleviate the changes of warp tension in loom by designing an activity back roller system. In this system the activity back roller swings as shed opening. Moreover, its effect is greatly related to the number of healds, the shed parameters, as well as the fabric structure. It is better to compensate the warp tension changes caused by fabric structure changes by adjusting the warp tension testing cycle in electronic let-off system. As a result, it is adaptive that we use symmetric shed and design the activity back roller system when the structure of fabric is simple and the elasticity of fiber is lower, such as plain fabric, glass fiber and high strength polyester.

Key words: loom, warp tension, shedding, back rest swing rule