Reduction of Whole Body Vibration in a Wide Frequency Range Using Inflation Pressure Control of Air Bladder Cushion

Several types of interfaces like foam and inflated air cells exist to reduce the effect of mechanical vibration experienced in human-machine interfaces in different scenarios such as transportation. However, their vibration attenuation performance in a wide frequency range relevant to whole body vibration (1–80 Hz) leaves much to be desired. In this study, we investigate the effect of inflation pressure on the vibration attenuation behavior of an air cell cushion. An experimental setup capable of conducting frequency sweep tests and regulating inflation pressure in an air cell array cushion was developed. Frequency sweep tests were conducted at various inflations and the vibration transmissibilities at static inflations were plotted. A dynamic inflation scheme was developed based on the apriori knowledge of inflation dependent transmissibilities. Furthermore, the closed loop behavior of the inflation scheme was evaluated with a frequency sweep test. The resulting closed loop transmissibility indicated better vibration attenuation performance than any single static inflation for the air cell array cushion in the range of frequencies relevant to whole body vibration. This result lays the groundwork for potential air cell cushions which modify their inflation dynamically through a direct feedback from sensors like accelerometers to attenuate vibration in a wide frequency range.

Experimental Study of a Variable Stiffness Seat Suspension Installed With a Compact Rotary MR Damper

Traditional MR seat suspension without stiffness control is not able to avoid the resonance between the excitation and the seat, though it can dampen the vibration energy. To solve this problem, this paper proposed a variable stiffness (VS) magnetorheological (MR) damper to implement an advanced seat suspension. Its natural frequency can be shifted away from the excitation frequency through the variations of stiffness, thereby realizing the non-resonance control. The new seat suspension is designed and prototyped first, and then its dynamic property under different energizing current, excitation amplitude, and excitation frequency was tested using an MTS machine. The testing results verified its stiffness controllability. The vibration attenuation performance of the seat suspension was also evaluated on a vibration shaking table. The vibration reduction performance of the seat suspension was evaluated under two kinds of excitations, i.e., harmonic excitation and random excitation; the experimental results indicate that the new seat suspension outperforms passive seat suspensions regarding their ride comfort.

Finite Frequency Robust Vibration Control of Flexible-Rigid Coupled Spacecraft

This paper is concerned with robust vibration control of flexible-rigid coupling spacecraft with finite frequency constraint. Considering that the major vibration energy of flexible structure is induced by the vibration modes located in a specific frequency range, the dynamics of the considered spacecraft are derived as a system with given vibration modes. A novel robust finite frequency controller is proposed by using output feedback method, which focuses on suppressing the vibration modes in given frequency region. Compared with the classic entire frequency controller, the newly proposed controller can achieve better vibration attenuation performance. Finally, illustrative simulation results are provided to demonstrate the effectiveness and superiority of our proposed control method.

Comfort-enhanced vibration control for delayed active suspensions using relaxed inequalities

This paper presents a comfort-enhanced vibration control design approach for vehicle active suspensions with control delay. By introducing some novel relaxed inequalities, a less conservative bounded real lemma is derived such that the suspension system is asymptotically stable and has an enhanced vibration attenuation performance in the presence of road disturbance and control delay. In the control design, an augmented Lyapunov–Krasovskii functional is proposed to enlarge the degree of freedom of design. A suitable controller can be obtained via a sufficient condition with linear matrix inequality constraints. Compared with the previous methods based on frequently used inequalities and the traditional Lyapunov–Krasovskii functional, the proposed controller can provide better comfort performance for different control delays. Finally, the advantages of the proposed method are demonstrated using numerical examples.

A six degree of freedom passive vibration isolator with quasi-zero-stiffness-based supporting

A six degree of freedom nonlinear passive vibration isolator is proposed based on Stewart platform configuration with the quasi-zero-stiffness structure as its legs. Due to the high static stiffness and low dynamic stiffness of each leg, the proposed six degree of freedom system can realize very good vibration isolation performance in all six directions while keeping high static load-bearing capacity in a pure passive manner. The mechanic model of the proposed six degree of freedom isolator and the dynamic equation of the isolator are established successively. Theoretical analysis on cross coupling stiffness reveals that the system can demonstrate quasi-zero-stiffness property in all six degree of freedom. Moreover, an analysis on stability shows that the condition of structural parameters for the isolator to realize quasi-zero-stiffness is also the stability boundary of the system. A series of numerical simulations on displacement transmissibilities in coupled degree of freedoms, the coupling effects of transmissibility, and a dynamic response in random excitation are carried out to show the effectiveness of the proposed six degree of freedom isolator, as well as the influence of structural parameters on vibration attenuation performance. Considering its high performance in a simple passive manner, it can be foreseen that the proposed six degree of freedom isolator will be applied in various engineering practices with multi-degree of freedom vibration isolation.

State observation–based control algorithm for dynamic vibration absorbing systems featuring magnetorheological elastomers: Principle and analysis

Based on state observation, a rapid, stable, and effective control algorithm for magnetorheological elastomer (MRE)–based dynamic vibration absorbers (DVAs) applied to automobile powertrain mount systems is proposed and investigated in this article. The state-space model for powertrain mount systems with MRE-based DVAs is established using the rank criterion method for observable systems. According to the principle of system reconfiguration, a full state observation model using an adaptive Kalman filter with Sage–Husa noise estimator is developed. With the state vectors estimated by the Kalman filter, the phase difference between the displacement of the dynamic mass of the MRE-based DVA relative to the powertrain and the absolute displacement of the powertrain is updated continuously based on Simpson’s rule. By adjusting the applied current to the MRE-based DVA with fuzzy logic control corresponding to the cosine value of the phase difference, the natural frequency of the MRE-based DVA could track the excitation frequency of the powertrain well, which results in vibration attenuation of the powertrain mount system. With consideration of excitation noise, time delays, and parametric uncertainties, the simulation experiments of vibration attenuation performance of the MRE-based DVA for the powertrain mount systems when under time-varying excitation are carried out to verify the effectiveness and the stability of the proposed algorithm with fuzzy steps. The simulation results show that when using the proposed algorithm with fuzzy steps, the MRE-based DVA could attenuate the powertrain vibration rapidly and effectively, and the vibration attenuation performance will not be influenced by noise, time delays, and parametric uncertainties.

Magnetic Nonlinear Energy Sink for Vibration Attenuation of Unbalanced Rotor System

A novel nonlinear energy sink (NES) consisting of permanent magnetic springs and coil springs is proposed, and the vibration attenuation performance of the NES for unbalanced rotor system is investigated. Firstly, the nonlinearity of the magnet spring is analyzed and the structure of the NES is introduced. Then, the dynamic model of the rotor system with the NES is built, and the responses and stabilities of the system are studied by applying Complexification-averaging method. The strongly modulated responses (SMR) behavior, which is the most important performance characteristic of the NES, is analytically studied by combining Complexification-averaging method and multiscale method and numerically verified by Runge-Kutta method. The results show that the NES is effective in attenuating the vibration of unbalanced rotor, and the SMR occurrence range can be broadened by increasing the nonlinearity of the NES. And also, the NES has better performance over a wider frequency range than the linear absorber.

Principle, modeling, and control of a magnetorheological elastomer dynamic vibration absorber for powertrain mount systems of automobiles

This article proposes and validates the principle of a new magnetorheological elastomer (MRE) dynamic vibration absorber (DVA) for powertrain mount systems of automobiles. The MRE DVA consists of a vibration absorption unit and a passive vibration isolation unit. The vibration absorption unit composed of a magnetic conductor, a shearing sleeve, a bobbin core, an electromagnetic coil, and a circular cylindrical MRE is utilized to absorb the vibration energy, and the passive vibration isolation unit is used to support the powertrain. The finite element method is employed to validate the electromagnetic circuit of the MRE DVA and obtain the electromagnetic characteristics. The theoretical frequency-shift principle is analyzed via the established constitutive equations of the circular cylindrical MRE In order to demonstrate how the parameters of the MRE influence the vibration attenuation performance, the MRE DVA is applied to a powertrain mount system to replace the conventional passive mount. The frequency-shift property of the vibration absorption unit and the vibration attenuation performance of the MRE DVA on the powertrain mount system are experimentally tested. To validate and improve the vibration attenuation performance for the semi-active powertrain mount systems, an optimal variable step algorithm is proposed for the MRE DVA and numerical experiments are carried out.