than two intersections 48 without holes in each row 49 as seen in fig5 the machine drive motor 43 is coupled between power lines 55 56 through any of normally open relay contacts 57 a normally closed cam operated switch 58 or a normally open manually operated switch 59 the normally closed cam operated switch 58 is periodically opened by a cam 60 driven by motor 43 through transmission 44 see fig4 at a frequency equal to the intermittent rotary advance of the pattern spool 51 such that the switch 58 is opened in synchronism with the orientation of any turning worm 28 in the turned heddle position 28a the light source 19 is continuously energized producing the beam of light 38 directed toward the light beam receiver 37 which in this fig5 is shown as a photoelectric device 61 when the beam of light 38 is detected by the photoelectric device it produces a signal closing a circuit to relay coil 62 thereby opening relay contacts 57 the machine drive motor 43 is stopped if the cam operated switch 58 is simultaneously open this stops the entire warp drawing operation and only occurs when no portion 22c of any heddle 22 is in the heddle turned position when any of the turning worms 28 is in turned heddle position 28a the motor 43 remains idle until the faulty condition has been corrected or the switch 59 is manually closed fig6.