and controller means 33 preferably equipped with a closed electronic control system the hydraulic setting device 12 is provided with a hydraulic pump 30 and a tank 31 to serve a servo valve 32 the hydraulic setting device 12 also includes other hydraulic components of known construction such as an overflow valve filter and an accumulator to absorb pressure shocks etc the closed electronic control system of controller means 33 comprises an electronic unit connected by wires 34 and 35 to the sensor 26 and servo valve 32 of setting device 12 respectively the electronic control system of controller means 33 actuates the servo valve 32 and is arranged to regulate the pattern of movement acceleration and speed of the nozzle 4 the servo valve 32 is in connection with two pressure chambers 43 44 of the nozzle oscillating means 25 via hydraulic conduits 36 37 respectively the hydraulic conduits 36 37 between servo valve 32 and nozzle oscillating means 25 should be as short as possible to give the control system high rigidity accordingly the servo valve 32 is preferably mounted directly on the nozzle oscillating means 25 the electronic control system of controller means 33 operates with a closed control circuit in which a signal concerning the current angular position.