Advantages The electronic let off and tack up are made to drive the warp beam and take roller on looms; .Let off keeps the tension of warp constant .take up realize a precise and on the fiy changeable weft density .Relax tension during looming stop time .Compensation of start marks .Lance functionSystem description Electronic let off and up work as gearboxes with adjustable gear ratio. The gear is set between the main shaft and the warp beam resp. take up roller. It manages the motion of warp and fabric. the gear ratio of take up is changed with the weft density and-in case of state Marks-during the starting period to compensate mechanical transient effect of the loom. The gear ratio of let off additionally is changed on each weft for regulation of warp tension. Manual and automatic motion is available for relax tension or changing fabric or warp beam；let off and tack up works as speed controlled positioning system. All parameter for motion （acceleration.speed.distance）are user adjustable.