Vibration and impacts are essential features of many domestic and industrial hand-held machines. In many machines vibration cannot be avoided because of the vibro-impact nature of the working process. The only way to minimise an operator's exposure to harmful vibration in this case is to design the machine rationally. In this paper a percussion machine is considered as a multi-body vibro-impact system. The simplest structures have been found and investigated in which a strong vibro-impact process can be obtained with one body (casing/handle) being free of vibration. Computer simulations using Matlab-Simulink software and initial experiments validate the new approach. The main feature of the proposed new design is the use of a mechanism with zero differential stiffness. A hydro-pneumatic unit with zero stiffness was developed and tested. The new engineering solution was applied to a hydraulic breaker. Even a partial modification of the existing design and effective use of existing hydraulic power source demonstrated a significant improvement in performance. (c) 2007 Elsevier Ltd. All rights reserved.
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