Abstract: A spring drive mechanism has a spiral spring positioned in a spring encasement as a power source. Its ends are connected, on the one hand, to a spring encasement gear and, on the other hand, to a spring shaft gear. For the purpose of winding up the spring, the spring encasement gear is in mesh with a first drive pinion and the spring shaft gear is in mesh with a second drive pinion. These drive pinions has a stress-free connection to a wind down/wind up shaft across a unidirectional torque transmitters which each permits rotation in one direction; the directions being opposite. A reverse pinion has one pinion sprocket is mesh with the spring shaft gear. The other pinion sprocket is in mesh with the drive pinion in the wind up position. In this position, the spring drive mechanism is blocked in such a way that the tensioned driving spring cannot release.