Quasi-active suspension design using magnetorheological dampers

Quasi-active damping is a method of coupled mechanical and control system design using multiple semi-active dampers. By designing the systems such that the desired control force may always be achieved using a combination of the dampers, quasi-active damping seeks to approach levels of vibration isolation achievable through active damping, whilst retaining the desirable attributes of semi-active systems. In this article a design is proposed for a quasi-active, base-isolating suspension system.Control laws are firstly defined in a generalised form, where semi-active dampers are considered as idealised variable viscous dampers. This system is used to demonstrate in detail the principles of quasi-active damping, in particular the necessary interaction between mechanical and control systems. It is shown how such a system can produce a tunable, quasi-active region in the frequency response of very low displacement transmissibility.Quasi-active control laws are then proposed which are specific for use with magnetorheological dampers. These are validated in simulation using a realistic model of the damper dynamics, again producing a quasi-active region in the frequency response. Finally, the robustness of the magnetorheological, quasi-active suspension system is demonstrated.     

Robust control synthesis for seat suspension systems with actuator saturation and time-varying input delay

The control synthesis problem is investigated in this paper for a class of semi-active seat suspension systems with norm-bounded parameter uncertainties, time-varying input delay and actuator saturation. A vertical vibration model of human body is introduced in order to make the modeling of seat suspension systems more precise. By employing a delay-range-dependent Lyapunov function and exploring the property of the saturation nonlinearity, the existence conditions of the desired state-feedback controller are derived in terms of linear matrix inequalities (LMIs). The controller is derived by solving the LMIs and the corresponding closed-loop system is asymptotically stable with a guaranteed H_∞ performance. A design example is presented to show the usefulness and advantages of the developed theoretical results.     

一种提高RS422通信BIT可靠性的设计方法

电动静液作动器是飞机操纵系统的关键部件,要求有较好的速度平稳性。系统内存在泄漏非线性和摩擦非线性等影响速度平稳性的因素。滑模控制可以有效抑制系统内非线性因素的影响,但是由于抖振现象的存在限制了速度平稳性的进一步提升。针对固定切换增益的滑模控制方法的不足,提出一种基于变结构滤波器的自适应滑模控制方法。采用变结构滤波器估计系统状态信息,估计的系统状态信息用于构建滑模面,采用自适应切换增益来导出控制率,有效减小了抖振幅度。仿真结果证明了自适应滑模控制方法的有效性,采用这种方法提高了电动静液作动器的速度平稳性。     

Enhanced switching law for synchronized switch damping on inductor with bimodal excitation

Piezoelectric shunt damping is an emerging field of research. In recent years, a multitude of different electrical circuits have been developed aiming to increase the damping performance and robustness. Synchronized switch damping on inductor (SSDI) is a semi-active control technique that utilizes a passive inductance to build-up a voltage on the piezoceramics that is synchronized with the mechanical vibration. For a single mode excitation the voltage inversion should occur at the moments of maximum deformation, but for multimodal vibrations such a switching law may not be optimal.In this paper a novel switching law for bimodal vibrations is presented using a modal observer. An enhanced voltage build-up is generated by utilizing the vibration energy of the second mode. The amplification of dissipated energy is calculated in an analytical way using normalized parameters, yielding a general result which includes the influence of the frequency and amplitude ratio of the excitation signal. Measurements on a clamped beam test rig are conducted in order to validate the proposed method. An increase of nearly 350 percent in energy dissipation compared to the classical SSDI has been achieved. Furthermore, the increase in energy dissipation is higher than for a previously suggested, comparable switching law.     

Seismic test of least-input-energy control with ground velocity feedback for variable-stiffness isolation systems

A variable-stiffness isolation system, whose isolation stiffness can be altered instantaneously in response to the seismic load, is able to provide better seismic protection for vibration-sensitive equipment or facilities than a conventional isolation system with a fixed stiffness. To determine its time-variant isolation stiffness, this system usually requires an effective on-line control law. In this study, a control strategy called the least input energy control (LIEC) is proposed for a general variable-stiffness isolation system. With the feedback of the ground velocity, at each time step the LIEC is able to determine the optimal isolation stiffness that minimizes the input seismic energy transmitted onto the isolated object. In order to evaluate its control performance, the LIEC was physically implemented on a leverage-type variable-stiffness isolation system, and tested in a seismic simulation test. The experimental response of the LIEC was then compared to the uncontrolled response, as well as the simulated responses of two semi-active control laws derived from the widely used LQR control and modal control. A comparison of the results demonstrates that, among all the control cases considered, the LIEC transmits the least seismic input energy to the isolated system, and thus has the best isolation performance. In addition, the test data also show that the LIEC requires the least control force and control energy. This indicates that the LIEC is also a very efficient control method for variable-stiffness isolation systems.     

High frequency energy transfer in semi-active suspension

This paper investigates the effect of unintended high frequency excitations generated by the semi-active sky-hook control algorithm on the isolation properties of a car suspension. Using a quarter car model, an energy transfer from low to high frequency is established. An alternative algorithm is presented in this paper, in order to achieve smooth variations of the control force. Compared with the continuous semi-active sky-hook, the algorithm has been found to provide a similar damping of the body resonance, but also a better isolation at high frequency and global comfort.     

Aeroelastic dynamic response and control of an airfoil section with control surface nonlinearities

Nonlinearities in aircraft mechanisms are inevitable, especially in the control system. It is necessary to investigate the effects of them on the dynamic response and control performance of aeroelastic system. In this paper, based on the state-dependent Riccati equation method, a state feedback suboptimal control law is derived for aeroelastic response and flutter suppression of a three degree-of-freedom typical airfoil section. With the control law designed, nonlinear effects of freeplay in the control surface and time delay between the control input and actuator are investigated by numerical approach. A cubic nonlinearity in pitch degree is adopted to prevent the aeroelastic responses from divergence when the flow velocity exceeds the critical flutter speed. For the system with a freeplay, the responses of both open- and closed-loop systems are determined with Runge-Kutta algorithm in conjunction with Henon’s method. This method is used to locate the switching points accurately and efficiently as the system moves from one subdomain into another. The simulation results show that the freeplay leads to a forward phase response and a slight increase of flutter speed of the closed-loop system. The effect of freeplay on the aeroelastic response decreases as the flow velocity increases. The time delay between the control input and actuator may impair control performance and cause high-frequency motion and quasi-periodic vibration.     

An inverse model of MR damper using optimal neural network and system identification

Magnetorheological (MR) damper is one of the more promising new devices for vibration control of structures. External energy required by the adjustable fluid damper is minuscule while speed of its response is in the order of milliseconds. The MR damper is a semi-active control device and has been characterized by a set of non-linear differential equations which represent a forward model of the MR damper, i.e., the model can generate a force to a given displacement and applied voltage.This paper presents an inverse model of the MR damper, i.e., the model can predict the required voltage so that the MR damper can produce the desired force for the requirement of vibration control of structures. The inverse model has been constructed by using a multi-layer perceptron optimal neural network and system identification, which are Gauss-Newton-based Levenberg-Marquardt training algorithm, optimal brain surgeon strategy and autoregressive with exogenous variables (ARX) model. Based on the data from numerical simulation of the MR damper, the trained optimal neural networks can accurately predict voltage. If the inverse model is used in a control system, the semi-active vibration control can be implemented easily by using the semi-active MR damper.     

Self-powered active vibration control using a single electric actuator

The authors have proposed self-powered active vibration control systems that achieve active vibration control using regenerated vibration energy. Such systems do not require external energy to produce a control force. This paper presents a self-powered system in which a single actuator realizes active control and energy regeneration.The system proposed needs to regenerate more energy than it consumes. To discuss the feasibility of this system, the authors proposed a method to calculate the balance between regenerated and consumed energies, using the dynamical property of the system, the feedback gain of the active controller, the specifications of the actuator, and the power spectral density of disturbance. A trade-off was found between the performance of the active controller and the energy balance. The feedback gain of the active controller is designed to have good suppression performance under conditions where regenerated energy exceeds consumed energy.A practical system to achieve self-powered active vibration control is proposed. In the system, the actuator is connected to the condenser through relay switches, which decide the direction of the electric current, and a variable resistor, which controls the amount of the electric current. Performance of the self-powered active vibration was examined in experiments; the results showed that the proposed system can produce the desired control force with regenerated energy, and that it had a suppression performance similar to that of an active control system using external energy. It was found that self-powered active control is attainable under conditions obtained through energy balance analysis.     

双层板腔结构声传输及其有源控制研究

利用子系统模态综合方法,结合阻抗-导纳矩阵法,建立了双层板腔结构向自由空间声传输及其在入射板PZT控制、辐射板PZT控制,和腔中次级声源作动等多种控制策略下,系统物理模型的统一的分析模型,导出了系统模态响应及最优次级源强度的统一的阻抗-导纳矩阵表达式。该模型表达式各部分物理意义清晰、明确,便于进行系统耦合理论、有源控制及其机理的分析和数值研究。然后,在此基础上对双层板腔结构声传输有源控制进行了全面深入的数值计算和分析研究,重点探讨了控制方法策略及系统参数对有源控制效果的影响及其对应的控制机理。结果表明:入射板PZT作动辐射声功率最小控制策略是通过入射板、声腔和辐射板三个子系统的模态抑制或重组达到消声的目的,涉及多种复杂控制机理,对入射板、辐射板和声腔模态均有效,但对入射板模态更有效;在低频段声腔(0,0,0)模态在系统耦合响应中起主导作用,因此利用腔中次级声源作动能获得较理想的控制效果,是一种较好的控制策略;由于声腔模态与结构模态间复杂的耦合关系,使得某些频率处腔中声势能一定程度上的降低并不一定导致系统声传输损失的增加,因此,腔中声势能最小控制策略不一定能够获得理想的声传输控制效果。      

Semi-active friction tendons for vibration control of space structures

Semi-active vibration control systems are becoming popular because they offer both the reliability of passive systems and the versatility of active control without high power demands. In this work, a new semi-active control system is proposed and studied numerically. The system consists of variable-friction dampers linked to the structure through cables. Auxiliary soft springs in parallel with these friction dampers allow them to return to their initial pre-tensioned state. Using cables makes the system suitable for deployable, flexible and lightweight structures, such as space structures (spacecraft). A control system with three control laws applied to a single-degree-of-freedom structure is studied. Two of these laws are derived by using Lyapunov theory, whereas the third one is developed heuristically. In order to assess the performance of the control system, a parametric study is carried out through numerical simulations. An application of the proposed method to multi-degree-of-freedom structures is also presented and demonstrated through a numerical example. The system in semi-active mode is more effective than in passive mode and its effectiveness is less sensitive to loss of pre-tension.     

Performance analysis of a semi-active mount made by a new variable stiffness spring

A new variable stiffness mount (VSM), is created and its performance is experimentally measured and analyzed. VSMs have extensive applications in the vibration control of machineries including automotive industry. The variable stiffness in this design is realized by the prestress stiffness of a cable-based mechanism at a singular configuration. Changing the prestress, through a piezo actuator and a simple on-off controller, results in significant stiffness change in short time and at low energy costs. The stiffness of the VSM is characterized through static and dynamic tests. The performance of the VSM is then evaluated and compared with an equivalent passive mount in two main areas of transmissibility and shock absorption. The response time of the semi-active VSM is also measured in a realistic scenario. A summary of the performance tests are presented at the end.     

A STOCHASTIC OPTIMAL SEMI-ACTIVE CONTROL STRATEGY FOR ER/MR DAMPERS

A stochastic optimal semi-active control strategy for randomly excited systems using electrorheological/magnetorheological (ER/MR) dampers is proposed. A system excited by random loading and controlled by using ER/MR dampers is modelled as a controlled, stochastically excited and dissipated Hamiltonian system with n degrees of freedom. The control forces produced by ER/MR dampers are split into a passive part and an active part. The passive control force is further split into a conservative part and a dissipative part, which are combined with the conservative force and dissipative force of the uncontrolled system, respectively, to form a new Hamiltonian and an overall passive dissipative force. The stochastic averaging method for quasi-Hamiltonian systems is applied to the modified system to obtain partially completed averaged Itô stochastic differential equations. Then, the stochastic dynamical programming principle is applied to the partially averaged Itô equations to establish a dynamical programming equation. The optimal control law is obtained from minimizing the dynamical programming equation subject to the constraints of ER/MR damping forces, and the fully completed averaged Itô equations are obtained from the partially completed averaged Itô equations by replacing the control forces with the optimal control forces and by averaging the terms involving the control forces. Finally, the response of semi-actively controlled system is obtained from solving the final dynamical programming equation and the Fokker-Planck-Kolmogorov equation associated with the fully completed averaged Itô equations of the system. Two examples are given to illustrate the application and effectiveness of the proposed stochastic optimal semi-active control strategy.     

Experiment and analysis of a fuzzy-controlled piezoelectric seismic isolation system

Because a conventional seismic isolation system is usually a long-period dynamic system, it may easily incur an excessive seismic response when subjected to near-fault earthquakes, which usually contain strong long-period wave components. In order to alleviate this near-fault isolation problem, this paper investigates the possible use of a fuzzy-controlled semi-active isolation system, called a piezoelectric seismic isolation system (PSIS), whose seismic response is attenuated by a variable friction damper driven by an embedded piezoelectric actuator. The studied PSIS adopts a fuzzy controller whose control logic is similar to that of the anti-lock braking systems (ABS) widely used in the automobile industry. This ABS-type fuzzy controller has the advantages of being simple and easily implemented, because it only requires the measurement of the PSIS sliding velocity. In order to investigate its feasibility and isolation effectiveness, in this work both theoretical and experimental studies were carried out on a prototype PSIS. It is observed that the experimental responses of the PSIS can be well predicted by the theoretical responses simulated by the mathematical model and numerical procedure. Furthermore, both theoretical and experimental results have demonstrated that in either a near-fault or a far-field earthquake, the PSIS with the ABS-type fuzzy controller is very effective in suppressing simultaneously the isolator displacement and the acceleration response of the isolated object.     

基于平面声源的三层有源隔声结构物理机制研究

次级源为平面声源的三层有源隔声结构,深入理解有源隔声的物理机理有助于挖掘降噪潜力及实现系统优化设计。首先对三层有源隔声结构建模并求解系统的振动响应。然后,对控制前三层结构中声能量的传输规律进行深入分析。最后,在辐射板声功率最小条件下,通过分析控制前后声能量传输特性的变化阐述了隔声的物理机理。结果表明,声能量在三层结构中传输形成四个等效的传输通道,中间板与两腔的作用类似带通滤波器,不同的传输通道具有相似的带通特性。有源隔声机理在于,通过控制抑制了通带内的能量传输,显著提高了三层结构整体的隔声性能,从而有效阻止了声波的向后传播。      

Actuation of a discontinuous structure with piezoelectric actuators

An alternate approach to exciting a one-dimensional structure with discontinuities using a piezoelectric actuator is presented and examined. Instead of being bonded to the uniform side of a beam, the piezoelectric actuator is attached such that it spans two adjacent rib discontinuities. In this configuration, the actuator generates an eccentric actuation force on the structure and induces both axial and transverse motions. The goal of this work is to first model the axial and transverse response caused by the piezoelectric actuator. Then, the change in that response is examined for the case where an external disturbance force is present. The system is modeled by coupling the piezoelectric strain and structural dynamic response. The characteristics of the voltage-generated piezoelectric forces are discussed through numerical examples. The structural response found using the dynamic force–voltage model for the actuator is then compared to the response when the actuator model is approximated by its static or zero-frequency value. Furthermore, the ability of the actuator to potentially provide better control authority by using this alternate configuration is examined. The numerical study shows that when the actuator spans two discontinuities, there is potential for greater control authority than when that same actuator is placed on the uniform side of the structure.     

ACTIVE CONTROL OF FLEXIBLE STRUCTURES USING PRINCIPAL COMPONENT ANALYSIS IN THE TIME DOMAIN

Principal component analysis is used to simplify the extraction of the natural frequencies and their corresponding orthonormal mode shapes directly from experimental data of unknown flexible structures. A control law is designed using a state-space modal model and is tested on different structures. The results are extremely encouraging and demonstrate successful implementation of the active control strategies. The controller actuator as well as the detection sensor locations are examined throughout the structure length.     

A disk-pivot structure micro piezoelectric actuator using vibration mode B11

Micro piezoelectric actuator using vibration mode B(11) (B(mn), where m is the number of nodal circles, n is the nodal diameters) is designed. Different from conventional wobble-type ultrasonic motor using piezoelectric rod or cylinder, piezoelectric disc is used to excite wobble modes and metal cylinder stator is used to amplify the transverse displacement, metal rod rotor is actuated to rotate. The outer diameter of the actuator is 14mm. There are features such as low drive voltage, micromation, and convenient control of wobble state by modifying the structure of stator, etc. Finite element analysis (FEA) of the stator has been made. It is found that the resonant frequency of vibration mode B(11) is 49.03kHz, which is measured at 45.7kHz by the laser vibrometer and impedance analyzer. The rotation speed has been measured, which could be as high as 10,071rpm under an alternating current 100V. Such piezoelectric actuator can be optimized and adjusted to fit practical conditions. It can be applied in the fields of precise instrument, bioengineering and other micro actuator system.     

Local feedback control of light honeycomb panels

This paper summarizes theoretical and experimental work on the feedback control of sound radiation from honeycomb panels using piezoceramic actuators. It is motivated by the problem of sound transmission in aircraft, specifically the active control of trim panels. Trim panels are generally honeycomb structures designed to meet the design requirement of low weight and high stiffness. They are resiliently mounted to the fuselage for the passive reduction of noise transmission. Local coupling of the closely spaced sensor and actuator was observed experimentally and modeled using a single degree of freedom system. The effect of the local coupling was to roll off the response between the actuator and sensor at high frequencies, so that a feedback control system can have high gain margins. Unfortunately, only relatively poor global performance is then achieved because of localization of reduction around the actuator. This localization prompts the investigation of a multichannel active control system. Globalized reduction was predicted using a model of 12-channel direct velocity feedback control. The multichannel system, however, does not appear to yield a significant improvement in the performance because of decreased gain margin.     

Multifunctional design of inertially-actuated velocity feedback controllers

The vibration of a structure can be controlled using either a passive tuned mass damper or using an active vibration control system. In this paper, the design of a multifunctional system is discussed, which uses an inertial actuator as both a tuned mass damper and as an element in a velocity feedback control loop. The natural frequency of the actuator would normally need to be well below that of the structure under control to give a stable velocity feedback controller, whereas it needs to be close to the natural frequency of a dominant structural resonance to act as an effective tuned mass damper. A compensator is used in the feedback controller here to allow stable feedback operation even when the actuator natural frequency is close to that of a structural mode. A practical example of such a compensator is described for a small inertial actuator, which is then used to actively control the vibrations both on a panel and on a beam. The influence of the actuator as a passive tuned mass damper can be clearly seen before the feedback loop is closed, and broadband damping is then additionally achieved by closing the velocity feedback loop.