Innovation from Siemens: Active vibration dampers for container cranes
Nuremberg, Germany, 2010-Nov-30
Siemens Drive Technologies Division is offering a system for damping the vibration on a container crane. The company has developed a technique for active damping using a linear motor with "intelligent" motion. It is mounted on the girder and a weight is attached, but it is many times lighter than for a conventional, passive vibration damper. A sensor detects the vibration of the girder and algorithms use these values to precisely calculate how the linear motor has to be moved to neutralize the natural oscillation of the girder. Through intelligent acceleration and braking of the linear motor, the forces are directed into the girder. The vibration is reduced much more quickly and effectively than when using conventional techniques.
For loading and unloading container ships, container cranes are normally used. Containers are hoisted from a ship by a container crane, transported to the shore by a trolley where it is set down for onward transport. When the crane trolley moves, a vibration is generated in the container crane in the direction of travel of the crane trolley. When the container bridge is vibrating too much, it is not possible for the crane driver to load or unload with any precision. The dynamic response of the motion then has to be reduced considerably in order to keep the excitation of vibration to a minimum. This consumes a great deal of time when containers are being transferred and, due to the additional costs that it causes, it is undesirable.
The innovation presented by Siemens Drive Technologies is a system for effective damping of vibration in the mechanical structure of the crane that can be easily integrated into a container crane.
"Higher, faster, better: For crane builders, this means installing their container bridges in a minimum of space, but still catering to a higher clearance, while at the same time ensuring faster throughput in freight handling. With the power drive damper Siemens provides an opportunity to fully compensate for the increased vibration susceptibility under these conditions. This opens up new perspectives in terms of speed and throughput of freight transfer using container cranes", said Dr. Elmar SchÃ¤fers, Manager of Mechatronics R&D at Siemens Drive Technologies. The power drive damper can be integrated in existing container cranes generally without the need for structural modifications. "Siemens wants to launch active vibration damping with linear motors on the market by the middle of next year in cooperation with a crane builder", said Joachim Zoll, Manager for Cranes at Siemens Drive Technologies.
Modern harbor cranes are of a lighter construction than their predecessors, and taller. They must also not take up too much quay space, allowing space for transport vehicles to drop the freight. If the vibration has to be reduced on a container crane, the crane structure for example can be constructed stiffer. When constructing a more stiff crane structure, crane span, cross-sectional area and overhead clearance must be modified on the container crane. This is difficult to realize in most container cranes. To reduce vibration, passive mass dampers are often used today. A weight of up to 60 tonnes is often suspended on a pendulum device. The vibration frequency is set by the length of this pendulum and energy is removed from the vibrating mass via a damper which finally damps the disturbing vibration of the crane. A passive mass damper of this type is, however, extremely costly to integrate in the structure of the crane, the materials required are considerable and the damping effect is limited.
A picture accompanies this Press Release. You can find the picture on the Internet at: www.siemens.com/dt-picture/3014