Zero-Stiffness-SystemsCopyright: © IGMR
The implementation of a zero stiffness system for damping and isolation of large masses have great potential to achieve extremely low decoupling frequencies while maintaining a high load carrying capacity.
A conflicting goal in vibration decoupling is to achieve low decoupling frequencies while maintaining high bearing capacity. The stiffness of classic suspension systems can be reduced through the targeted preloading and arrangement of additional spring without significantly influencing the load-bearing capacity. The use of such so-called zero-stiffness systems thus holds great potential for isolating the vibration of large masses from the environment. To enable the implementation of these novel spring systems, IGMR is researching the design as well as the behavior of such systems in operation.
In order to reduce unwanted vibrations in large masses, the supporting structures must be decoupled from external disturbances. The aim is to achieve the lowest possible isolation frequency. Classical spring systems reach their limits here. On one hand, a low isolation frequency requires springs with the lowest possible stiffness. On the other hand, the mechanical stresses in the springs increase with decreasing stiffness, so that the fatigue strength is no longer given.
One way of resolving this conflict of aims is to use so-called zero-stiffness systems. The qualitative structure of a zero-stiffness system is shown in the figure at the end of the page. The system shown is an undamped single-mass oscillator that has been extended by two laterally preloaded springs. At the operating point shown, the load is carried exclusively by the vertical spring. In the event of a deflection in the vertical direction the preloaded lateral springs reinforce the motion instead of acting against the vertical deflection. Therefore, the lateral springs have a negative stiffness with respect to a vertical deflection. With the help of the combination of the positive stiffness of the vertical spring and the negative stiffness of the horizontal springs, the total stiffness can theoretically be significantly reduced for the same load capacity.
The approach by combining the positive stiffness of classical springs with a negative stiffness generated by suitable mechanisms has high potential for decoupling large masses. In this way, isolation systems with high load capacity and low isolation frequencies can be realized theoretically. In the context of this research topic, the design criteria of the system elements are analyzed in more detail and existing dependencies within them are identified. Furthermore, the system behavior outside the operating point is investigated.
Within the scope of this research, various technical approaches to vibration isolation using zero-stiffness systems are being researched and analyzed. As an extension of the work, calculation bases are derived for the most promising approaches and adapted in a simulation environment according to the modeling of the system. In this way, initial estimates for the design and dimensioning of the required elements of such a zero-stiffness system can be developed. Based on this, the influences and effects of various system parameters on system-specific properties will be investigated in order to further optimize the development.
The investigation of the system behavior outside the operating point will be carried out with the aid of multi-body simulation. Here, for example, the linearity of certain system properties as a function of the deflection is determined on the basis of suitable comparison criteria.
IGMR as Partner in Vibration Technology
Novel isolation systems for the decoupling of large, vibrating masses are investigated at the IGMR. Here, the many years of experience and expertise in vibration technology can be combined with the latest research methods.