Method and device for controlling a hydraulically operated power screwdriver

摘要

The method involves determining nominal pressure by an electronic evaluation unit (18). A piston-cylinder unit (2) is pressure-loaded to perform a pre-stroke until the nominal pressure is reached and followed by a return stroke. A time interval from the beginning of pressure loading up to the arrival of the nominal or initial pressure after pressure relief, is measured. The pressure loading and measuring steps are repeated. The measured time intervals are compared. Pressure loading cycles are stopped when a last measured time interval is shorter than a penultimate measured time interval. An independent claim is also included for a hydraulically operated power wrench comprising an adjustable pressure valve.