Design of vibration isolation systems that incorporate axial to rotary motion conversion mechanisms

Abstract

In this thesis, compliant axial to rotary motion conversion mechanisms are ex amined to generate isolation band gaps. To achieve low frequency phononic band gaps, LADD mechanism is examined, and its the effective inertia is aimed to be amplified. Moreover, to increase the isolation band gap of this structure, helical wire theory is investigated, and both analytical and finite element models of the mechanism are cre ated and validated with experiments. Then, by applying prestress and optimizing the cross section area of the helical wires, the phononic band gap is maximized at low frequencies. A quite wide band gap with ω1/ω2=0.215 is obtained with the use of idealized roller boundary conditions. However, this type of boundary condition is com pliantly realized via wires, the frequency ratio (ω1/ω2) increased to 0.5 and the band gap became narrower. Therefore, a novel axial to rotary motion conversion mechanism is proposed. In the proposed unit cell, a stop band is governed by two different types of modes. The lower and the upper natural frequencies of stop band is limited by the coupled axial-torsional and bending modes, respectively. For stop band maximization, cross and spiral flexures are used due to their high bending stiffness and low axial stiff ness. Besides, helical wires with large pitch angle are utilized to create large rotational motion from axial translations. Thus, the effective inertia of the mechanism is ampli fied. By using analytical and finite element models, band structure and the dynamic response attributes of the structure are examined, and parametric studies are con ducted. 3D printing and laser cutting is used during prototyping. Finally, comparison of the analytical, computational and experimental frequency response results is held for validation. In conclusion, a very wide phononic band is obtained with ω1/ω2=0.221.