that the cylinder 22 extends over the entire travelling distance of the dragging element 2a it is however also possible to divide the cylinder 22 and to limit it as shown in fig1 to the extreme positions of the oscillating system instead of the coil the cylinder can also be connected to a hydraulic fluid system which can serve to provide a controlled energy supply fig9 and fig1 show another dragging element 2b which is provided with a rod 32 on which two piston shaped elements 34 and 36 are mounted between arresting devices 12b and 14b which are mounted in block type arrangement in this case the arresting device 12b which marks the upper extreme position and to which the piston shaped element 34 adheres is located at the bottom and the arresting device 14b which marks the lower extreme position and to which element 36 adheres at the top the arresting devices 12b and 14b consist of permanently magnetic rings 38 arranged in such a way that their identical poles are facing each other within each ring 38 there are electromagnets 40 which can be operated by the above mentioned control unit 16 as soon as the extreme position is reached the piston shaped elements 34 and 36 adhere to the respective arresting devices 12b and 14b and are released only upon activation of the electromagnets 40 to perform another oscillating movement fig1 shows the device illustrated in fig9 and fig1 the arresting devices 12c and 14c however being arranged at a distance from each other which defines the travelling.