Active Vibration Isolation System Research Articles

Control performance simulation and tests for Microgravity Active vibration Isolation System onboard the Tianzhou-1 cargo spacecraft

The Microgravity Active vibration Isolation System (MAIS), which was onboard China’s first cargo-spacecraft Tianzhou-1 launched on April 20, 2017, aims to provide high-level microgravity at an order of 10-5–10-6g for specific scientific experiments. MAIS is mainly composed of a stator and a floater, and payloads are mounted on the floater. Sensing relative motion with respect to the stator fixed on the spacecraft, the floater is isolated from vibration on the stator via control forces and torques generated by electromagnetic actuators. This isolation results in a high-level microgravity environment. Before MAIS was launched into space, its control performance had been simulated on computers and tested by air-bearing platform levitation and aircraft parabolic flight. This article first presents an overview of the MAIS’s hardware system, particularly system structure, measurement sensors, and control actuators. Its system dynamics, state estimation, and control laws are then discussed, followed by the results of computer simulation and engineering tests, including the test of the six-degree-of-freedom motion by aircraft parabolic flight. Simulation and test results verify the accuracy of the control strategy design, effectiveness of the control algorithms, and performance of the entire control system, paving the way for operation of MAIS in space. This article also presents the steps recommended for the control performance simulation and tests of MAIS-like devices. These devices are expected to be used on China’s Space Station for various scientific experiments that require a high-level microgravity environment.

Experimental study on sliding mode variable structure control of active vibration isolation system of floating raft under multiple excitations

The frequency components of vibration signal in vibration isolation system under multiple excitations are quite complex.Self-adaptive feedforward control method based on Least Mean Square algorithm has strict requirements for reference signal, which results in a certain restriction on its practical application. Sliding mode variable structure control method needs neither complicated reference signal nor accurate mathematical model. It has the strong robustness for external disturbance and system parameter perturbation, and the physical implementation is simple. To this end, application of sliding mode variable structure control method is studied. First, mathematical model of the control channel through system is established for identification. Second, the discrete sliding mode variable structure controller based on state-space model is designed to carry out simulation and experiment. The experimental result indicates that root mean square value of vibration signal after control is decreased by 57.90%, of which the amplitudes of two main frequency components 17 and 25 Hz reduce by 42.66 and 72.71%, respectively. This shows that sliding mode variable structure control is an effective control method for active vibration isolation of floating raft under multiple excitations.

Design of Active Controller for Low-Frequency Vibration Isolation Considering Noise Levels of Bandwidth-Extended Absolute Velocity Sensors

The low-frequency performance of active vibration isolation system depends on the low-frequency measurement ability of inertial sensor such as geophone. Bandwidth extension-based methods may serve as a cost-effective solution to increase the low-frequency measurement accuracy of geophone, but suffered the deteriorations of the noise. Traditionally, the available extension bandwidth of geophone is merely based on the measured noise level or sensor dynamic, which may result in a degraded vibration isolation performance due to geophone's over- or undercompensation. In this paper, an integrated approach to hybrid controller design and compensation of geophone dynamic is developed by weighing the influences of sensor dynamic and noise on vibration isolation performance, and sets low-frequency design rules to moderately utilize the noisy responses of sensor. In feedback controller design, the aimed frequency is selected by the stability condition, the signal-to-noise ratio of sensor gives the design constraint to avoid the overuse bandwidth of geophone, while in feedforward control, the analyses are reversed, and consequently different aimed frequencies are achieved. The effectiveness of the designed controller was validated by experiments, indicating that the results were good consistencies with the analysis models, and the deteriorations by noise were avoided at low frequencies.

Desired Compensation Adaptive Robust Control of an Active Vibration Isolation System

Active vibration isolation system (AVIS) has attracted increasing attention of researchers in precision engineering. In this paper, a desired compensation adaptive robust controller (DCARC) is proposed for an AVIS developed in our laboratory. The AVIS composed of one platform and three active isolators is required to achieve high-performance vibration isolation as well as low trajectory tracking error for positioning. The vertical three degrees of freedom (DOFs) and horizontal three DOFs are decoupled by the joint bearing of the isolators. The dynamic model of the system is built and is simplified to three single-input-single-output (SISO) systems. The DCARC control scheme is then proposed, which contains a deterministic robust control (DRC) term and an adaptive control (AC) term. The high performance in vibration isolation and positioning can be subsequently achieved, even the actual load and system stiffness are unknown and there exists direct bounded disturbance on the platform. The AC term is designed to estimate the unknown parameters of the system. The DRC term can improve the robustness of the system, which is used to reject the direct disturbance and the parameter estimation error. Furthermore, the computing time and the influence of the measurement noise can be reduced effectively by reason of desired compensation. The numerical simulation and comparative experiments are carried out under the conditions of using DCARC, DRC, and AC controllers. The experimental results validate that the proposed DCARC control strategy outperforms other control method and possesses both high-performance vibration isolation and low tracking error.

Energy efficient active vibration control strategies using electromagnetic linear actuators

Energy efficient current control methods in electromagnetic linear actuators are required to minimize the electrical power requirements imposed by active vibration control strategies. In this paper an efficient bidirectional buck-boost converter is discussed in two scenarios: an active vibration isolation system and an active dynamic vibration absorber ( ADVA ) using a voice coil motor (VCM) actuator. An electrical analogous circuit of an experimental test platform is used as part of the simulation model. This test platform is based on a vibration shaker that provides the based excitation required for the single Degree of-Freedom (1DoF) vibration model under study. The proposed bidirectional non-isolated buck-boost converter can recover the energy when the VCM acts as a generator and store it for future use. Simulation results prove that this type of topology is far more efficient than linear amplifiers typically used in active vibration control. Within the context of slender structures, this efficient current control method improves the viability of using active vibration control in flexible structures such as beams.

Stacked dielectric elastomer actuator (SDEA): casting process, modeling and active vibration isolation

In this paper, a novel fabrication process of stacked dielectric elastomer actuator (SDEA) is developed based on casting process and elastomeric electrode. The so-fabricated SDEA benefits the advantages of homogenous and reproducible properties as well as little performance degradation after one-year use. A coupling model of SDEA is established by taking into consideration of the elastomeric electrode and the calculated results agree with the experiments. Based on the model, we attain the method to optimize the SDEA’s parameters. Finally, the SDEA is used as an isolator in active vibration isolation system to verify the feasibility in dynamic application. And the experiment results show a great prospect for SDEA in such application.

Investigation of microvibration levels in a laser interferometer with an active vibration isolation system

Vibration perturbations occurring during the operation of a laser interferometer with passive and active vibration isolation are investigated using a microvibration sensor based on micromechanical accelerometers. A description of the workstation is provided, and the optical layout of the device and the method of measurement are described. Analysis of the measurement results showed that, under the influence of random microvibration, the amplitudes of the surface vibrations and the vibrations of the microscope head are different, and the difference reaches values comparable to the resolution of the laser interferometer. It is shown that, in order to reduce the measurement errors of a laser interferometer, it is useful to perform active vibration isolation during the measurement.

Feedforward Feedback Linearization Linear Quadratic Gaussian With Loop Transfer Recovery Control of Piezoelectric Actuator in Active Vibration Isolation System

Hysteresis exists widely in intelligent materials, such as piezoelectric and giant magnetostrictive ones, and it significantly affects the precision of vibration control when a controlled object moves at a range of micrometers or even smaller. Many measures must be implemented to eliminate the influence of hysteresis. In this work, the hysteresis characteristic of a proposed piezoelectric actuator (PEA) is tested and modeled based on the adaptive neuro fuzzy inference system (ANFIS). A linearization control method with feedforward hysteresis compensation and proportional–integral–derivative (PID) feedback is established and simulated. A linear quadratic Gaussian with loop transfer recovery (LQG/LTR) regulator is then designed as a vibration controller. Verification experiments are conducted to evaluate the effectiveness of the control method in vibration isolation. Experiment results demonstrate that the proposed vibration control system with a feedforward feedback linearization controller and an LQG/LTR regulator can significantly improve the performance of a vibration isolation system in the frequency range of 5–200 Hz with low energy consumption.

Experimental estimation of transmissibility matrices for industrial multi-axis vibration isolation systems

Abstract Vibration isolation is essential for industrial high-precision systems to suppress external disturbances. The aim of this paper is to develop a general identification approach to estimate the frequency response function (FRF) of the transmissibility matrix, which is a key performance indicator for vibration isolation systems. The major challenge lies in obtaining a good signal-to-noise ratio in view of a large system weight. A non-parametric system identification method is proposed that combines floor and shaker excitations. Furthermore, a method is presented to analyze the input power spectrum of the floor excitations, both in terms of magnitude and direction. In turn, the input design of the shaker excitation signals is investigated to obtain sufficient excitation power in all directions with minimum experiment cost. The proposed methods are shown to provide an accurate FRF of the transmissibility matrix in three relevant directions on an industrial active vibration isolation system over a large frequency range. This demonstrates that, despite their heavy weight, industrial vibration isolation systems can be accurately identified using this approach.

Model reaching adaptive-robust control law for vibration isolation systems with parametric uncertainty

Adaptive control has been used for active vibration isolation and vehicle suspensions systems. A model reference adaptive control law is used for the plant to track the ideal reference model. In a model reaching adaptive control approach, the ideal of a skyhook target without using a reference model is achieved. In this paper, a novel approach, a model reaching adaptive-robust control law is studied for active vibration isolation systems. A dynamic manifold for ideal system is defined using the ideal of a skyhook target model system parameters. First, a new Lyapunov function is defined. Based on the Lyapunov stability theory, a model reaching adaptive and a robust control laws are derived for the uncertain system to reach the ideal manifold. Parameters and upper bounding functions are estimated as a trigonometric function depending on the relative displacements, velocities and the defined manifold. The developed adaptive and the robust compensators are combined and this combination is proposed as an adaptive-robust control law. After that, the controller is applied to a vehicle suspension system and the ideal of a skyhook target without using a reference model is achieved. The results also show that the proposed robust control law can increase the comfort of the vehicle active suspension systems and the ride comfort is remarkably increased.

Decentralized vibration control of a voice coil motor-based Stewart parallel mechanism: Simulation and experiments

In pursuit of a better working performance of the precise instruments equipped in spacecraft, vibration control systems are essential for preventing them from being disturbed. This paper studies the decentralized vibration control problems of a voice coil motor-based Stewart parallel mechanism. The Newton–Euler Method is used to formulate the dynamical equations of the Stewart platform in joint space. The decentralized control theory is employed to design the controller for the linearized system. A prototype of the voice coil motor-based Stewart platform was designed and tested to validate the vibration attenuation performance of the decentralized system. The effectiveness of active vibration isolation system is revealed by both the simulation and real-time experiments.

Ultra-low frequency active vibration control for cold atom gravimeter based on sliding-mode robust algorithm

An ultra-low frequency vibrational noise isolation apparatus from external vibration can be a critical factor in many fields such as precision measurement, high-technology manufacturing, scientific instruments, and gravitational wave detection. To increase the accuracies of these experiments, well performed vibration isolation technology is required. Until recently the cold atom gravimeter has played a crucial role in measuring the acceleration due to gravity and earth gravity gradient. The vibration isolation is one of the key techniques in the cold atom gravimeter. To reduce the vibrational noise caused by the reflecting mirror of Raman beams in the cold atom gravimeter, a compact active low-frequency vibration isolation system based on sliding-mode robust control is designed and demonstrated. The sliding-mode robust control active vibration isolation method is used to solve the vibration problem of Raman mirror in the cold atomic gravimeter. The purpose of vibration control is that the controller enables the system to be at zero state as the system states are away from the equilibrium due to vibration disturbance. In this system, the mechanical setup is based on a commercial passive isolation platform which only plays a role at higher frequency. A sliding-mode robust control subsystem is used to process and feed back the vibration measured by a seismometer which can measure the velocity of the ground vibration. A voice coil actuator is used to control and cancel the motion of a passive vibration isolation platform. The simulation and experiment results of vibration isolation platform show, on the one hand, that the vibration noise power spectral density decreases by up to 99.9%, and that the phase noise in cold atom interferometry produced by vibration decreases by up to nearly 85.3% compared with the results of the passive vibration isolation platform. On the other hand, compared with the lead-lag control method, the vibration noise power spectral density decreases by up to 83.3% and the phase noise in cold atom interferometry produced by vibration decreases by nearly 40.2%. Therefore, the sliding-mode robust control has the advantages of less tuning parameters, strong anti-interference ability, and more obvious vibration isolating effect.

An inerter-based active vibration isolation system

This paper presents a theoretical study on passive and active vibration isolation schemes using inerter elements in a two degree of freedom (DOF) mechanical system. The aim of the work is to discuss basic capabilities and limitations of the vibration control systems at hand using simple and physically transparent models. Broad frequency band dynamic excitation of the source DOF is assumed. The purpose of the isolator system is to prevent vibration transmission to the receiving DOF. The frequency averaged kinetic energy of the receiving mass is used as the metric for vibration isolation quality. It is shown that the use of inerter in the passive and active vibration isolation schemes considered enhances the isolation effect.

Study on active vibration isolation system using neural network sliding mode control

In this paper, an active vibration isolation system based on hybrid algorithm is presented in a wide frequency band. Initially, a nonlinear magnetostrictive actuator model is used to establish the appropriate parameters by experiments, which make the actuator using in vibration isolation system work in a better linear dynamic performance, then the sliding mode algorithm modified by neural network, a hybrid algorithm is proposed as the active control controller, and its stability is also analyzed by Lyapunov theory. Furthermore, a dynamic virtual prototype model of active vibration isolation is established to carry out the co-simulation with Adams and Matlab/Simulink, and the results show that under the difference excitations, the neural network sliding mode controller exhibits a good control performance, and the active vibration isolation can effectively improve the vibration isolation effect, reduce the force transmitted to the base and broaden the vibration isolation bandwidth.

Modeling and analysis of the disturbance about an active vibration isolation system

PurposePrecision active vibration isolation system (AVIS) is crucial for the mechanical processing equipment in the field of precision manufacturing. Working reliability and efficiency of the system directly influence operating condition of the equipment and the quality of work pieces.Design/methodology/approachA complete structure of the AVIS includes two parts: the excitation part and the passive vibration isolation system (PVIS). The excitation part consists of voice coil motors (VCMs). In this paper, the working process of AVIS is studied particularly via linear simplification on the decoupling model and the mechanical dynamic equations to solve the vibration problem, and they are validated by the experiments.FindingsAccording to dynamic analysis and experiment on an AVIS on different reference points, the VCMs are used as actuators in the AVIS to excite the PVIS, and the performance characteristics of the whole AVIS is well reflected by the amplitude–frequency curves, the bode diagrams and the power spectral density curves.Originality/valueThis study has provided a way for obtaining the inner structure and working condition of the AVIS, which are essential to better control of the AVIS and to further study it in precision manufacturing application.

Passive and active vibration isolation systems using inerter

This paper presents a theoretical study on passive and active vibration isolation schemes using inerter elements in a two degree of freedom (DOF) mechanical system. The aim of the work is to discuss basic capabilities and limitations of the vibration control systems at hand using simple and physically transparent models. Broad frequency band dynamic excitation of the source DOF is assumed. The purpose of the isolator system is to prevent vibration transmission to the receiving DOF. The frequency averaged kinetic energy of the receiving mass is used as the metric for vibration isolation quality. It is shown that the use of inerter element in the passive vibration isolation scheme can enhance the isolation effect. In the active case, a feedback disturbance rejection scheme is considered. Here, the error signal is the receiving body absolute velocity which is directly fed to a reactive force actuator between the source and the receiving bodies. In such a scheme, the so-called subcritical vibration isolation problems exist. These problems are characterised by the uncoupled natural frequency of the receiving body larger than the uncoupled natural frequency of the source body. In subcritical vibration isolation problems, the performance of the active control is limited by poor stability margins. This is because the stable feedback gain is restricted in a narrow range between a minimum and a maximum. However, with the inclusion of an inerter in the isolator, one of the two stability margins can be opened. This enables large, theoretically unlimited negative feedback gains and large active damping of the receiving body vibration. A simple expression for the required inertance is derived.

Non-parametric identification of multivariable systems: A local rational modeling approach with application to a vibration isolation benchmark

Abstract Frequency response function (FRF) identification is often used as a basis for control systems design and as a starting point for subsequent parametric system identification. The aim of this paper is to develop a multiple-input multiple-output (MIMO) local parametric modeling approach for FRF identification of lightly damped mechanical systems with improved speed and accuracy. The proposed method is based on local rational models, which can efficiently handle the lightly-damped resonant dynamics. A key aspect herein is the freedom in the multivariable rational model parametrizations. Several choices for such multivariable rational model parametrizations are proposed and investigated. For systems with many inputs and outputs the required number of model parameters can rapidly increase, adversely affecting the performance of the local modeling approach. Therefore, low-order model structures are investigated. The structure of these low-order parametrizations leads to an undesired directionality in the identification problem. To address this, an iterative local rational modeling algorithm is proposed. As a special case recently developed SISO algorithms are recovered. The proposed approach is successfully demonstrated on simulations and on an active vibration isolation system benchmark, confirming good performance of the method using significantly less parameters compared with alternative approaches.

Self-tuning MIMO disturbance feedforward control for active hard-mounted vibration isolators

This paper proposes a multi-input multi-output (MIMO) disturbance feedforward controller to improve the rejection of floor vibrations in active vibration isolation systems for high-precision machinery. To minimize loss of performance due to model uncertainties, the feedforward controller is implemented as a self-tuning generalized FIR filter. This filter contains a priori knowledge of the poles, such that relatively few parameters have to be estimated which makes the algorithm computationally efficient. The zeros of the filter are estimated using the filtered-error least mean squares (FeLMS) algorithm. Residual noise shaping is used to reduce bias. Conditions on convergence speed, stability, bias, and the effects of sensor noise on the self-tuning algorithm are discussed in detail. The combined control strategy is validated on a 6-DOF Stewart platform, which serves as a multi-axis and hard-mounted vibration isolation system, and shows significant improvement in the rejection of floor vibrations.

Simultaneous topology optimization of supporting structure and loci of isolators in an active vibration isolation system

We developed a new multi-objective and multi-level optimization method to design an active vibration isolation system. Both the layout of the continuum (i.e. the supporting structure) and the loci of the isolators are designed using topology optimization technique in a unified formulation for the first time. The static, dynamic and vibration-isolation characteristics are taken into account simultaneously in the present model. Due to their different roles in the system it may be appropriate and advantageous to treat the design of the continuum layout and isolator loci as different sub-problems with different objectives in separate stages. The multi-level optimization technique, where the optimization of the supporting structure and the isolator loci are incorporated into a closed-loop, is proposed and implemented so that the interactions between these two sub-problems can be fully taken into account. Numerical results demonstrate the validity of the proposed design cycle. Comparisons show that the overall static, dynamic and vibration-isolation performance of the optimized system outperforms the ones designed by traditional methods.

Verification of the Microgravity Active Vibration Isolation System based on Parabolic Flight

The Microgravity active vibration isolation system (MAIS) is a device to reduce on-orbit vibration and to provide a lower gravity level for certain scientific experiments. MAIS system is made up of a stator and a floater, the stator is fixed on the spacecraft, and the floater is suspended by electromagnetic force so as to reduce the vibration from the stator. The system has 3 position sensors, 3 accelerometers, 8 Lorentz actuators, signal processing circuits and a central controller embedded in the operating software and control algorithms. For the experiments on parabolic flights, a laptop is added to MAIS for monitoring and operation, and a power module is for electric power converting. The principle of MAIS is as follows: the system samples the vibration acceleration of the floater from accelerometers, measures the displacement between stator and floater from position sensitive detectors, and computes Lorentz force current for each actuator so as to eliminate the vibration of the scientific payload, and meanwhile to avoid crashing between the stator and the floater. This is a motion control technic in 6 degrees of freedom (6-DOF) and its function could only be verified in a microgravity environment. Thanks for DLR and Novespace, we get a chance to take the DLR 27th parabolic flight campaign to make experiments to verify the 6-DOF control technic. The experiment results validate that the 6-DOF motion control technique is effective, and vibration isolation performance perfectly matches what we expected based on theoretical analysis and simulation. The MAIS has been planned on Chinese manned spacecraft for many microgravity scientific experiments, and the verification on parabolic flights is very important for its following mission. Additionally, we also test some additional function by microgravity electromagnetic suspension, such as automatic catching and locking and working in fault mode. The parabolic flight produces much useful data for these experiments.