the stop 31 for the purpose of moving toward the reference position independently of the initial position the crank 14 together with this stop element 33 is thus moved against the stop 31 thereupon the drive shaft is moved by one step of the stepper motor in the opposite direction whereby the stop element 33 is clear off the stop 31 this is then the reference position from which the stepper motor is moved for instance by 88 steps in order that the two end positions corresponding to fig2 and 4 are assumed to form the particular desired weave using the thread guide elements 2 3 in order to move the stepper motor into a desired position suitable control and latching currents are applied to the stepper motor the terminals of the stepper motor are so associated with the stop 31 that the stepper motor will move by one step away from the stop 31 into the reference position when its terminals are loaded with corresponding voltage pulses because the angle of rotation undergone by the drive motor 12 is limited the path of the thread guide elements 2 3 may be predetermined if the path is selected to be between the positions shown in fig2 and 4 optimal advantage is taken of a limited torque to form an open shed 10 and to hold the selvage threads 8 9 at an open shed in the embodiment of fig5 and 6 the cranks 14 15 are part of a crankshaft 37 driven by the drive motor 12 the crankshaft is composed of a crank 15.