Attenuating vibrations with negative stiffness

Many high-tech equipment demands a vibration free environment and can only operate at vibration levels much lower than typical ground vibrations. This high level of vibration isolation is difficult to achieve with conventional suspension solutions, especially in the range of low frequencies in the order of 1 Hz. The goal of the Kolibri project conducted at TNO is to develop an active vibration isolated tabletop system which excellent vibration attenuation properties at low frequencies: 60 dB attenuation at 1 Hz. The performance of the current Kolibri table does not meet this requirement by 30 dB and is to be improved. The current Kolibri set-up is analyzed to find the performance limiting functional sub-systems. The conclusion of this analysis is that a redesign of the suspension will provide a significant improvement of the vibration isolation performance. Reducing the natural frequency of the suspention from 10 Hz to 0.5 Hz will result in the desired performance improvement of the total Kolibri system. This reduction of natural frequency is to be achieved by reducing the suspension stiffness. The principle of negative stiffness is chosen to reduce the positive stiffness of the conventional spring. This will potentially result in a compact suspention mechanism at reasonable costs. Several concepts for this mechanism are analyzed. The configuration with three pre-tensioned radial flextures is chosen and completely worked out in detail. After manufacturing, the negative stiffness mechanism assembled to be tested. The performance of the negative stiffness mechanism is measured; the natural frequency of the mechanism is found to be X Hz, which is higher/lower than the specifications. Conclusions and recommendations are given for future developments on the Kolibri project, and for improving the negative stiffness mechanism.
Precision and Microsystems Engineering
Mechanical, Maritime and Materials Engineering