Abstract: The stopping mark is common fabric defects in warp knitting production, and it is considered that the mark is caused by tension of warp yarn when turning on and/or turning off the machine. In this paper, the motion curve of the main shaft of the machine and the beam motor of electronic let-off system was tested. The beam motor lags behind main shaft is tested in warp beam let-off system when turning on and/or turning off the machine. The lag time is reduced when turning on the machine, and the lag angle gradually increases with the main shaft speed increasing; Meanwhile the lag time changes a little when turning off the machine, and the lag angle is reduced. That caused the tension change “normal→the loose and tight changing in the state of partial loose→the loose and tight changing in the state of partial tight→normal” of warp yarn. In this paper, it is discussed that main factors which affect the lag performance of warp let-off system are those, such as main controller of let-off system, the software of control, the control mode of servo system, the servo performance, servo parameter setting, as well as main shaft encoder.

Key words: warp knitting, electronic let-off system, response characteristics, warp tension, stopping mark