Patent ID: 7392915

Claim:
A method for controlling swaying and swinging of a spreader in a crane and the load attached thereto, the crane comprising: a trolley, hoist gears provided with hoist drums placed in the trolley, hoisting ropes arranged on the hoist drums, on which the spreader is suspended from the trolley and which are directed back to the trolley through sheaves arranged on the spreader, the swaying and swinging being controlled by control equipment comprising: four auxiliary gears provided with rope drums and including motors and motor control equipment placed in the trolley, auxiliary ropes arranged on the rope drums of the auxiliary gears, sheaves for the auxiliary ropes placed in the spreader, through which sheaves the auxiliary ropes passing obliquely from the rope drums of the auxiliary gears are directed to spaces arranged in the hoist drums for the auxiliary ropes, said method comprising; controlling forces exerted on the spreader by each auxiliary rope driven by a corresponding auxiliary gear based on torque instructions; determining said torque instructions by means of control logic which receives force data of the corresponding auxiliary rope and rotating speed data of the corresponding auxiliary gear, said control logic providing and maintaining the desired rope forces, controlling the rotation and the resistance of the swinging of the spreader using said motor in the corresponding auxiliary gear; forming said torque instruction in each corresponding auxiliary gear as sum of a static and a dynamic term; calculating the static torque instruction based on a reference value of the rope force in the auxiliary gear, a measuring data of the rope force and the rotating speed of the auxiliary gear; and a dynamic feed forward torque instruction T dyn, calc , based on a change occurring in the calculated rotating speed of each auxiliary gear.