Design for damping

Implementation of energy dissipation that slows down motion (without introducing position uncertainty)

For a long time in the design of high-precision mechanisms, it was considered key to eliminate the disastrous effect of backlash and friction, and to design for high natural frequencies, i.e., light weight and stiff design, by putting material where it contributes most. Stiffness was the design paradigm in the 1950s. Recently, the implementation of passive damping was added to realize suppression of amplifications at resonances and thereby, sufficient exponential decay of undesired vibrations in uncontrolled DoFs. Passive damping, which was abandoned for a long time in view of the risk of position uncertainty by hysteresis, became a new design paradigm in the 2010s.

This section will elaborate on the system response to time-varying inputs, for which high stiffness, low mass and high damping are each necessary, both are not individually sufficient requirements for a precision machine. Damping implies energy dissipation to slow down motion as visualized in the so-called exponential decay function. Although high relative damping has the exact same impact on the exponential decay as high eigenfrequency, both are key, once resonant behavior is getting performance limiting.

Often, the potential energy dissipation within a part is seriously restricted as the material is selected based on criteria other than damping. In fact, design for high stiffness and damping usually implies a compromise, at least for single phase engineering materials. Instead of tailoring composite materials such as reinforcements, sandwich materials and laminates, damping is usually implemented at distinct locations, either as tuned mass or robust mass damper, or across larger surfaces through a viscous or viscoelastic layer damper, referred to as free layer damping or constrained layer damping. Characteristic properties will be elaborated upon, along with design rules and engineering examples. Finally, Eddy current damping and piezoelectric damping will be discussed. The latter resembles viscoelastic damping with respect to modeling, but shows hardly any temperature dependency, which makes it suitable for cryogenic conditions.


Design principles