other side of the pivot pint 9 i e below the pivot point 9 the other end of the decelerating string 8 has a similar tensioning means 15 as the pull string 2 in the vicinity of the pivot arm 1 stop 16 is fastened to the decelerating string 8 and bears against an abutment 17 and lifts off the abutment 17 during deceleration the motion of the pivot arm 1 is controlled by way of a toggle lever 4 by two cams 6 and 7 one arm of the toggle lever is connected to the pivot arm 1 while the other one is linked to the frame of the loom in the vicinity of the point of articulation of the toggle lever 4 a roll 18 is located which is moved by the cams 6 and 7 the toggle lever 4 is suitably linked to the pivot arm 1 in the vicinity of the pivot point 9 in order that its movement consumes a minimum of energy the first cam 6 serves to tension the pull string 2 and has an approximately spiral periphery with one step it is arranged above the toggle lever 4 and urges it downwardly beyond its dead center the toggle lever 4 is thereby stretched and urges the pivot arm 1 counterclockwise to the left the second cam 7 has a circular periphery with one nose 19 and is so arranged that the roll 18 on the toggle lever 4 bears against the circular peripheral portion of the second cam 7 when the toggle lever 4 is moved beyond its dead center slightly in downward direction both cams.