Noise is not just a nuisance; it affects our health. No accepted financial data exist for the treatment costs of noise-related health problems, but several studies prove its direct relation to stress hormone levels or cardiovascular deceases, and many public organizations promote low-noise environment to protect health and comfort. Noise reduction has become major field of manufacturers’ competition: noise level data appear on domestic machines from mixers to dishwashers, brand names with ‘whisper’ or ‘silence’ are popular, aircrafts are successful due to their low noise levels. The efficient way to reduce noise is the elimination of its source that is usually vibration of some machine elements. Vibration elimination is relevant in the development of electric and self-driving cars where control panels and MEMS devices are sensitive for high-frequency excitations in the same way as high-performance machine tools are with aims at (sub)micron cutting precision. Methods of vibration reduction are based on the so-called modal testing that identifies the machines’ dynamic properties like natural frequencies. The test requires accurate broadband excitation. Commercial exciters have several drawbacks; one of these is the limited applicability for moving targets, rotating shafts. In the ERC Advanced Grant “SIREN”, a patent application was submitted and the pre-prototype of a ball shooter was constructed to excite spindles of machining centres by ball impacts. Experiments with the pre-prototype proved that the contact time is one order of magnitude shorter than that of standard impulse tests, while the force signal is near ideal: prall-free impulses with 30 kHz bandwidth were generated. Potential industrial end-users and distributors expressed interest in case a prototype is developed with accurately tuneable impact time/location together with precise online detection of impact direction for moving objects. These tasks form the work packages and deliverables of the proposal.
The main idea of the PIEZOMACH project is to develop a fully passive nonlinear device for suppressing chatter vibrations in machine tools. These vibrations represent a major concern in industry, as they result, for instance, in waves on the machined surface. This project goes beyond the challenge of dealing with the nonlinear nature of chatter vibrations, to developing a device that can unlock the huge potential of nonlinearity to improve dynamic performance. More specifically, the linear characteristic of the absorber will be optimized to maximize its stability properties, while its nonlinear characteristic will be designed in order to avoid dangerous bistable behaviors and guarantee robustness. This technique, successfully implemented for the suppression of aeroelastic instabilities, will be adapted to machine tool vibrations, first analytically and then experimentally, paving the way to the industrial exploitation of the obtained results. The vibration absorber will be practically realized utilizing an RLC resonant circuit coupled to the mechanical structure through a piezoelectric patch. An important aspect of this project is that it exploits the complementary expertise of the Experienced Researcher, regarding nonlinear vibration absorbers, acquired in the framework of the ERC Starting Grant NOVIB, and of the Beneficiary, regarding machine tools vibrations, obtained in decades of activity in the field and in the recent ERC Advanced Grant SIREN. For these reasons, PIEZOMACH represents a unique possibility to join the knowledge developed in two different ERC Grants into a single project that will allow the Experienced Researcher to boost his career through an intensive transfer of knowledge with the Beneficiary, and that is aimed at the development of a product with a strong industrial and commercial potential.