Bio-Inspired Vibration Isolation: Methodology and Design

A quasi-zero-stiffness (QZS) vibration isolation system presents the characteristics of high-static-low-dynamic, which can effectively isolate ultralow-frequency vibrations. However, most QZS vibration isolation systems are highly susceptible to external loads, causing deviations from the equilibrium position, which degrades their vibration isolation performance and severely restricts the range of QZS. To overcome these limitations, a novel vibration isolator was proposed by integrating a QZS structure with a variable stiffness and variable damping (VSVD) structure. The stiffness and damping of the vibration isolation system can be regulated to resist variable mass loads, and the QZS vibration isolation band can be broadened using the nonlinear positive stiffness of the conical rubber spring to effectively suppress ultralow-frequency vibrations. The dynamic characteristics of the QZS-VSVD vibration isolator were analyzed using the harmonic balance method. The effects of damping coefficients, excitation amplitude, and mass load on the amplitude–frequency characteristics and displacement transmissibility of the vibration isolation system were investigated. A virtual prototype of the QZS-VSVD vibration isolator was established using the ADAMS software, and vibration simulations were conducted. The results indicate that the QZS-VSVD vibration isolator can achieve ultralow-frequency vibration isolation at approximately 1 Hz under variable mass loads ranging from 3300 N to 3700 N. When the mass load was 3500 N, the amplitudes of the isolated object were attenuated by 70.6% and 86.2% under displacement excitation at 3 Hz and 5 Hz, respectively. Compared to linear isolators and a typical QZS structure, the proposed QZS-VSVD vibration isolator exhibited a greater load-bearing capacity, stronger anti-interference capability, and broader vibration isolation bandwidth.

Many cities around the world are developing over-track buildings above metro depots to achieve efficient and economical land use. However, the vibrations generated by frequent train operations have a significant impact on the over-track buildings. Therefore, the analysis and control of vibrations at metro depots are of great importance. This paper focuses on the train-induced vibration propagation law and the application of vibration isolation trench measures of the over-track building in the metro depot. To this end, a typical metro depot is taken as the research object. The train-track model, used for simulating wheel-rail force, and the track-soil-building model, used for predicting structural response, are established, respectively. Then, the vibration response of the over-track building of the metro depot is explored, and the effects of vibration isolation measures of the open trench and infilled trench in the metro depot are studied. The results show that the train-induced vibration excitation of the metro is mainly concentrated in the range of 1 to 80 Hz, and the predominant frequency range of the floor vibration is 25 to 50 Hz. The vibration response of the floor is mainly affected by the stiffness. The larger the floor area, the smaller the vertical natural frequency, and the wider the range between the train vibration excitation areas, the more prone to resonance. In addition, the vibration isolation effect of the open trench is better than that of the infilled trench. The primary factor affecting the vibration isolation performance of open trenches is their depth; the influence of trench position and width on the vibration isolation performance is weaker compared to the depth. In the predominant frequency range of floor vibration, the overall vibration isolation effect of the flexible infilled trenches is better than that of the rigid infilled trenches. The main factor affecting the vibration isolation effect of the infilled trenches is the impedance ratio of the material. Among the six kinds of filling materials selected in this paper, the barrier effect of gravel is the worst, and the barrier effect of foam is the best. Using the measure of a foam infilled trench, Z-vibration levels of floors can be reduced by 8.6–13.9 dB.

Buildings are often constructed on a continuous layer of vibration isolation to reduce vibrations and structure-borne noise. There are many vibration isolation products (rubber mats, textiles, polymer foams), but none fulfils all requirements in terms of load-bearing capacity, performance, and cost. In previous work, we have shown that silica aerogel particle beds display a low resonance frequency and correspondingly high vibration isolation performance. Loose silica aerogel granules are not a practical vibration isolation solution. In order to guide the future development of dedicated vibration isolation products based on aerogels, we determine the vibro-acoustic properties of a variety of existing commercial and R&D stage mesoporous composites, that have been developed for thermal insulation applications. The sample set includes monolithic aerogels (polyurethane), silica aerogel composites (aerogel – fibers, aerogel impregnated foams, aerogel bound with polymer foam), glued fumed silica-fiber boards, and nanoporous polymer foam composite boards. The silica aerogel and fumed silica composites display low resonance frequencies (down to 8 Hz for 40 mm, strongly dependent on composite type) and a low dynamic stiffness and loss factor over a wide range of static loads. The polymer aerogel, nanoporous foam and polymer-bound silica aerogel granule board all display higher resonance frequencies, consistent with their higher static stiffness. Although optimized for thermal insulation rather than vibration isolation, many of the tested silica aerogel and fumed silica composites are competitive with the best vibration isolation products on the market in terms of vibration isolation performance. The diversity of materials tested informs on which approaches, materials, and materials combinations are most promising to target vibration isolation.

Joints are effective in absorbing the ground impact and isolating the vibrations caused by the impact when goats jump over the cliff to find food. A bionic vibration isolator for low-frequency vibration inspired by the goat hind limb joint is proposed. The quadrilateral mechanism of the bionic vibration isolator of varying sizes is used to mimic the vibration suppression effect of multiple joints in the hind limbs of goats. The rigid rods in the bionic mechanism are used to mimic the role of the bones in the joint, and the springs are used to mimic the function of the muscles or tendons near the joint. In addition, the slider mechanism of the bionic mechanism brings nonlinear damping and mass, which could effectively help the system to reduce the resonant frequency and enhance the vibration isolation performance. The natural frequency of the bionic mechanism is 1.2 Hz, while the natural frequency of the linear mechanism under the same conditions is 5.1 Hz. When the external vibration exceeds 2.4 Hz, the proposed bionic mechanism begins to perform vibration isolation performance. Compared with the linear vibration isolation device, the bionic mechanism has lower natural frequency, better vibration isolation performance, and wider vibration isolation frequency band. Therefore, this study creatively proposed a vibration control mechanism inspired by animal limbs and proposed a high-stability and low-cost bionic structures in the field of vibration control.

A compact X-shaped mechanism based 3-DOF anti-vibration unit with enhanced tunable QZS property

Taking single degree of freedom vibration isolation system under simple harmonic excitation as an example, and considering the energy, the vibration isolation performance in different conditions was studied theoretically and numerically. The results shows that when the simple harmonic excitation import energy is definite, the vibration isolation performance at the primary harmonic frequency of the nonlinear vibration isolation system is better than that of the linear system, and the vibration isolation performance of the nonlinear vibration isolation system in chaotic vibration state is much better than that in non-chaotic vibration state. For the same isolated object, if can let the vibration isolation system vibrate chaotically, the system will possess the best isolation performance at the primary frequency.

In order to improve the performance of the active vibration isolation system (AVIS) with electromagnetic actuator, several problems of vibration control are studied. Position control is a critical component in suspension systems, and the position sensor noise can extremely affect the stability of the system, so a tracking differentiator (TD) is proposed to obtain effective differential signal from relative position sensor. In vibration control, the feedback of acceleration combined with PD position feedback is presented to suppress transmission of periodic vibrations. Then, taking the acceleration transmission as the evaluation index, the acceleration transmission under the presented control method is derived, and the influence of control parameters on vibration isolation performance is discussed in detail. The vibration isolation performance is improved from 24.47 dB to 2.4 dB at resonance frequency, and −34 dB attenuation is achieved at 100 Hz with respect to vibration isolation mount system tested on the ground. The experimental results demonstrate that the performance of active vibration isolation system are improved by the proposed acceleration feedback control.

To improve the vibration isolation performance, a conventional passive two-parameter vibration isolator (VI) usually adopts the method of adding constant damping for energy dissipation. A compromise is made between the suppression of resonance peak and the rapid attenuation of transmissibility in the high-frequency band. A four-parameter-VI with frequency-dependent damping is a potential solution for this problem. The theoretical models of system transmissibility and equivalent damping are established by a normalization method, and the vibration isolation performance is compared with that of the two-parameter-VI and the three-parameter-VI. A novel four-parameter-VI with damping generated by a giant electrorheological fluid (GERF) damper is designed. The mechanical properties of the GERF damper are tested, and its damping effect is evaluated using an equivalent linearization method. Then, the vibration isolation performance of the four-parameter-VI is tested. The results show that: the vibration isolation performance of the four-parameter-VI can be affected by the damping ratio and the mass ratio. The four-parameter-VI exhibits the frequency-dependent damping characteristic of large damping in the low-frequency band and small damping in the high-frequency band by appropriately setting parameters. The vibration isolation ratio of the four-parameter-VI to white noise reaches 91.1% in the time domain with appropriate parameters, and the peak of the power spectral density curves decreases from 1.2 × 10−3 g2 Hz−1 to 0.16 × 10−3 g2 Hz−1 with a reduction of 1.04 × 10−3 g2 Hz−1 .

The vehicle‐mounted equipment is easy to be disturbed by external vibration excitations during transportation, which is harmful to the measurement accuracy and performance of the equipment. Aiming at the vibration isolation of the vehicle‐mounted equipment, a semiactively controlled quasi‐zero stiffness (QZS) vibration isolator with positive and negative stiffness is proposed. The vertical spring is paralleled with a magnetorheological (MR) damper, and the semiactive on‐off control scheme is adopted to control the vibration. The analytical expression of the isolator’s displacement transmissibility is derived via the averaging method. Then, the vibration isolation performance under different road excitations and different driving speeds is simulated and compared with the uncontrolled passive QZS vibration isolator. In addition, the mechanical structure of the semiactive QZS isolator is designed and manufactured, and the test system is built by LabVIEW software and PXI embedded system. The isolation effect of the semiactive QZS isolator is verified through test data. It is found that the proposed semiactive QZS isolator shows excellent vibration isolation performance under various road excitations, while the passive QZS isolator is effective only under harmonic excitations. The vertical acceleration of vehicle‐mounted device can be decreased over 70% after isolation, and the vibration isolation effect is remarkable. The design idea and research results of the semiactive QZS isolator may provide theoretical guidance and engineering reference for vibration isolation.

A creative wide-frequency and large-amplitude vibration isolator design method based on magnetic negative stiffness and displacement amplification mechanism

Despite the significant engineering applications of vibration isolation structures, there remain challenges in adjusting low-frequency isolation performance. To tackle this issue, this study proposes a temperature-controlled quasi-zero stiffness vibration isolation structure utilizing NiTi shape memory alloys. The stiffness and vibration isolation performance of the structure can be adjusted by modifying the heat treatment process and temperature variations of the alloy. The vibration isolation system is composed of vertical and horizontal alloy beams, with structural mechanics analysis performed to develop both static and dynamic theoretical models. The study investigates the effects of the heat treatment process on the phase transition characteristics and mechanical properties of nickel-titanium alloys, and analyzes the correlation between the heat treatment parameters of alloy beams and the stiffness performance of vibration isolation structures. By applying temperature variations to the alloy beams, the stiffness and vibration isolation performance of the entire structure can be dynamically adjusted. This research provides theoretical guidance for achieving adjustable vibration isolation performance across low-frequency and wide ranges, offering promising prospects for the application of vibration isolation structures in dynamic environments.

To address the low-frequency vibration isolation at the load-bearing and operating ends of robots and thereby enhance precision, this paper proposes a quasi-zero-stiffness (QZS) vibration isolation joint based on disc springs. The joint employs reverse-stacked disc springs to provide low stiffness in the horizontal direction and negative stiffness in the vertical direction. By adjusting the pre-compression of the disc spring s, the stiffness can be actively tuned to achieve ultra-low-frequency vibration isolation. Mathematical models are established to analyse its mechanical properties and vibration isolation performance in various directions. The results show that the joint attains quasi-zero stiffness near the equilibrium position, exhibits excellent vibration isolation performance in multiple directions, and can adapt to different excitations through active control. The proposed structure is compact and offers high load-bearing capacity, making it suitable for a wide range of applications such as high-precision surgical robots and aerospace instruments.

This paper proposes a new spacecraft in-orbit launch design using a nonlinear configuration to utilize nonlinear dynamics for the enhancement of vibration isolation and launch performance. The in-orbit launch device has four springs, where the stroke directions of two springs are perpendicular to the launch direction so as to produce nonlinearity with negative stiffness for enhancing the launch velocity. The other two springs are designed to counterbalance the above negative stiffness when the launch outlet is shut down, leading to quasi-zero dynamic stiffness for vibration isolation enhancement. The dynamic equations of the in-orbit launch device for both the on- and off-launch are presented. Then the performance enhancement of both the vibration isolation and launch performance is thoroughly investigated via comparative study and parametric study. The resonance peak is reduced by 4.16 dB, the effective vibration isolation bandwidth is increased by 57%, and the launch speed is increased 1.64 times. This validates the performance improvement of the new launch device design and presents a useful guideline for application.

Six degree of freedom quasi-zero stiffness magnetic spring with active control: Theoretical analysis of passive versus active stability for vibration isolation

The active control technology was carried out on the marine diesel two-stage vibration isolation system (MDTVIS); the active control technology was able to make up for passive vibration isolation technology in the low-frequency range. The construction of a secondary path was one of the most important sectors, which had a full impact on active vibration isolation performance. Nonlinear components comprised the secondary path, which were principally the nonlinear vibration of multi-degrees of freedom in the practical MDTVIS and the nonlinear control path in the hydraulic servo actuator. The nonlinearity was not ignorable in coping with the second path, so that the vibration isolation performance was greatly influenced by the secondary path in the active control technology with the classic adaptive comb-type filter. By combining the model reference adaptive inverse control strategy with the nonlinear robust control technology, the linearity control algorithm was designed, and then the classic adaptive comb-type filter algorithm was carried out for the new system; herein the hybrid control strategy was constructed to apply to the secondary path in the practical MDTVIS. The proposed hybrid control strategy was able to improve the initial active vibration isolation control algorithm with an adaptive comb-type filter and overcome shortcomings of the vibration strengthened in some multi-harmonic-frequency sites in the low-frequency range. The total performance of vibration isolation coupling with multi-path was improved in balance.