that the holding current has a value of 0 at the time t 4 or slightly later this enables the stopper element 13 to start its motion exactly at t 4 at a later time t 5 the stopper element 13 has reached its original position again in yarn stopper magnets according to the state of the art there is usually a force close to the end position that is strong in many cases stronger than desirable this means that the requirements of the damping capability of the end positions are small in the new method described above for reduction of input energy amount and final speed kinetic energy of the stopper element 13 the voltage is controlled and thereby also the force to a desirable level with the object on one hand to minimize the amount of input energy and on the other hand to minimize the final speed the voltage is held on the smallest possible level at the end of the motion this will mean compared with the prior art that the force that is available for bounce damping in the end position will decrease two dampers and an inter mediate counter mass in each end position for example according to fig1 will give good results a low current at the end of the motion can be achieved with a small bounce being kept an even more sophisticated method for controlling the motion of the stopper magnet 2 is shown in fig3 it aims particularly at compensating for deviations in the motion time in the prior art there is no compensation for deviations in motion time that depends on variations in load or friction there is compensation for temperature dependence but this will.