NONLINEAR DYNAMIC ABSORBER TO REDUCE VIBRATION IN HAND-HELD IMPACT MACHINES

Hand-held impact machines have been used since the early 20th century. Up to day still a little has been changed in their fundamental design. Despite them being robust and efficient,vibration, noise, dust and poor ergonomics cause a large number of injuries to the operators, especially in the stone industry. In this paper, vibration dynamics of a pneumatic hand-held impact machine (HHIM) equipped with a nonlinear tuned vibration absorber (NLTVA) is in focus. The considered HHIM has the same parameters as the existing conventional one with respect to piston weight, impact energy and operating frequency. The paper presents the mathematical and computational models of vibration dynamics of the HHIM with NLTVA as well as the experimental set-up developed for model validation. The advantage of using a nonlinear spring is shown and how the effective vibration reduction frequency of the NLTVA can be made to follow the excitation frequency and thereby in principal achieving the same conditions as is the case for tuned pendulum absorbers for torsional vibrations where the resonance frequency follows the engine order. Using the verified and validated computational model, the sensitivity analysis of vibration dynamics has been performed in a broad set of feasible operational scenarios with respect to structural parameters of the HHIM equipped with NLTVA. Sensitivity analysis results have formed the base for optimisation of the parameters of NLTVA. It was shown by simulations as well as it was proved by experiment that the vibration of the HHIM equipped with NLTVA can be reduced significantly in a broader range of operating frequencies compared to the vibration of the same machine equipped with linear tuned vibration absorber. The results obtained confirm the possibility to design a user friendly low vibration impact machine efficiently operating in a broad frequency range. Optimised NLTVA combined with vibration isolation has shown to significantly reduce the vibration on the operator