Control-structure Interaction Research Articles

Deep reinforcement learning‐based active mass driver decoupled control framework considering control–structure interaction effects

AbstractControl–structure interaction (CSI) plays a significant role in active control systems. Popular methods incorporate actuator dynamics into an integrated control system to account for CSI, leading to a situation where existing structural control algorithms that ignore CSI cannot be applied directly. To address this issue, this study proposes a deep reinforcement learning (DRL) based active mass driver (AMD) decoupled control framework, in which a structural control algorithm is employed to generate the control force command without consideration of CSI, while a DRL agent is utilized to attenuate the CSI effects of AMD systems and achieve a desired control force. The DRL‐based AMD control framework is verified through a series of numerical experiments. Furthermore, the applicability of the control framework is confirmed in a wind‐excited 76‐story benchmark building. Comprehensive analysis indicates that the proposed control framework can effectively eliminate the CSI effects and apply accurate control force to the structure in various scenarios, which allows for an ideal structural response control.

Study on the interaction between shaking table and eccentric load

The control-structure interaction (CSI) between shaking table and eccentric load is one of the most important reasons causing the accuracy degradation of shaking table test. At present, the eccentric ratio (ER) of load and the coupling between actuators pose challenges to study the CSI. Thus, this paper establishes an analytical transfer function matrix of a shaking table and eccentric load. Based on the transfer function matrix, a comprehensive study is conducted to analyse the CSI effect under different eccentric ratio conditions. The analysis proves the influence of the CSI, and the CSI amplifies the actuator coupling more than 22 times at 20.00 Hz. Furthermore, a real-time CSI compensation strategy considering the actuator coupling is proposed. With the adopting of the proposed strategy, the coupling between two actuators is fully eliminated, and the correlation coefficients of ground motion records of two actuators are improved by 14.75% and 5.48%, respectively.

Improved Three-Variable Control for Electromagnetic Mass Damper System Considering Control–Structure Interaction

Current methods account for control–structure interaction (CSI) in structural control design, which may be unavailable in the preliminary design phase of actively controlled structures due to the unknown dynamic characteristic of an actuator. Therefore, it may result in significant difference in the design and evaluation of an active structural control system when ignoring or considering CSI at different phases. To eliminate the CSI effects of electromagnetic mass damper (EMD) system and thus decouple the tracking control of EMD from the control design of structure, in this paper, an improved three-variable control (ITVC) combining a signal convertor, a typical three-variable controller, and a voltage compensator is developed. The voltage compensator counteracts the influence of lower-order CSI including viscous damping force and Coulomb friction. The three-variable controller reduces the higher-order CSI effects, while the signal convertor converts all command and feedback signals to the relative coordinate system and eliminates the additional CSI effects. Performance tests and frequency response tests of the EMD system show that the CSI effects are basically eliminated by ITVC. In addition, shake table tests are performed on a one-story actively controlled structure to further verify ITVC. Experimental results suggest that ITVC can apply accurate control force on the structure and achieve ideal structural response control.

A composite control scheme for electromagnetic active mass damper against control-structure-interaction effects

Existing methods account for control-structure-interaction (CSI) in structural control design. However, their implementations may be challenging since the dynamic characteristics of actuator are unavailable in the preliminary design phase of actively controlled structures. In this study, a composite control scheme (CCS) is proposed to eliminate the CSI effects of electromagnetic active mass damper (AMD), and thus decouple the tracking control of AMD from the control design of structure. In the CCS, force compensation is performed to counteract the influence of lower-order CSI including the damping force and friction, while hierarchical control comprised of low-level feed-forward/feedback control and high-level sliding mode control is designed to reduce the higher-order CSI effect and achieve a high-performance force control. Performance tests and frequency response tests of the electromagnetic AMD system indicate that the CSI effects are significantly reduced by the proposed CCS. Furthermore, shake table tests are conducted on a two-story actively controlled structure to verify the effectiveness of CCS. Experimental results show that the proposed CCS can apply accurate control force to the structure, which contributes to an ideal structural response control.

A simple strategy for active structural control against control–structure–excitation effects: Concept, framework, and experiments

AbstractActive control is among the most effective control techniques for mitigating structural vibrations. Control–structure interaction (CSI) plays a significant role in modeling a control system. Popular methods incorporate the actuator dynamics and structure into the control system to account for CSI. The transfer function of the actuator can be identified through frequency response tests without physical modeling. However, this method ignores the effects of the excitation. Another approach is to create a physics‐based model of the actuator and include it in the control design, but its implementation may be challenging and requires a thorough understanding of the complex control system. In this study, the concept of control–structure–excitation effects (CSEE) is presented to account for the effects of the control, structure, and excitation on the transfer function of the actuator. In contrast to the existing control methods that consider CSI in system modeling, an improved control framework is proposed to eliminate the influence of CSI/CSEE on the control performance and thus decouple the tracking control of the actuator from the control design of the structure. This is achieved by introducing the control floor acceleration into the actuator controller and transforming the tracking of the absolute control force into that of the relative acceleration. The control strategy is simple and easy to implement based on conventional actuator control algorithms, such as three‐variable control. Frequency response tests and shake table tests were performed on a two‐story small‐scale structure to evaluate the effectiveness of the control strategy. It was confirmed that the improved control framework shows good tracking performance with respect to the control force and thus allows for ideal structural response control.

Effect assessment for the interaction between shaking table and eccentric load

Electro-hydraulic shaking table is an essential experimental apparatus to evaluate structural performance under actual vibration condition. The control-structure interaction (CSI) between shaking table and eccentric load has lately received considerable attention for causing the accuracy degradation of shaking table test. At present, the research gap of the influence of the eccentricity of load on the CSI makes it challenging to find the CSI effects. And an effect assessment is yet to be proposed to evaluate the CSI effects, which has impeded the development of test technology. To overcome those theoretical bottlenecks, in this research, an analytical transfer function matrix of shaking table and eccentric load is established to analyze the CSI effects. The analysis is conducted under such conditions as different mass ratio (MR), moment of inertia ratio (IR), and eccentric distance ratio (ER) conditions. Through the analysis, the role of the ER is identified, the sensitivities of the MR, IR, and ER to the transfer function matrix are revealed, and the CSI effects are found. Furthermore, a novelty effect assessment is proposed to appraise whether the CSI effects can be ignored in shaking table test. And the visualization expression of the effect assessment is obtained for convenient application.

A model predictive control for attitude stabilization and spin control of a spacecraft with a flexible rotating payload

Many Earth Observation missions, implementing space-based microwave sensing techniques for collecting surface information, employ spinning sensors to cover large swaths of terrestrial areas, thus improving the rate at which global maps of those measured data are generated. These spacecraft (as Soil Moisture Active Passive (SMAP) developed by NASA or Copernicus Imaging Microwave Radiometer (CIMR) currently under development by Thales Alenia Space) consist of a main non-spun platform and a rotating part composed of an antenna boom, a deployable reflector and a rotation mechanism. As the reflector is designated to rotate about the nadir axis producing conically scanned antenna beams with precise surface incidence angle, the payload pointing accuracy needs to be addressed at both spin subsystem and platform level. In this work, a representative model of the dynamic behaviour of SMAP satellite is developed as a study case to design the proposed control strategies; in particular, a SMAP-like payload structural model is built using FEM commercial codes. The spacecraft is equipped with a Reaction Wheels Assembly (RWA) to accomplish both momentum compensation for the spun element and three-axis attitude control and a motor for the spin mechanism. The objective of the study is to develop the spacecraft control architecture in the frame of Model Predictive Control (MPC) theory. MPC refers to a class of algorithms in which the control action is obtained by computing an open-loop optimal sequence of control moves over a predefined time horizon; moreover, the ability to set constraints on process inputs and outputs directly in the problem formulation allows to account for actuators’ limits. In the study two operative phases of the satellite are addressed: the Spin-up, in which the 6-meter diameter antenna is spun-up to the operative condition of 14.6 RPM, and the Science Phase, in which precise nadir pointing and stability of the flexible system must be kept for acquiring high-resolution measurements. To this purpose, control–structure interaction between attitude/spin control system and flexible dynamics, as well as system’s imbalances, are carefully addressed by the proposed control architecture. The nonlinear in-orbit dynamics of the flexible spacecraft is then used to evaluate the performance of the MPC controller in terms of pointing accuracy and robustness to uncertainties.

Effect of Control–Structure Interaction Using Torsional Servomotor for Active Tuned Mass Damper Control System

The control–structure interaction (CSI) affects the performance and robustness of protective structures in active control system, and it is important to consider the CSI effect to achieve high performance in structural vibration control. In this paper, the electro-mechanical model of the torsional servomotor is derived by establishing dynamic voltage equilibrium equation. Three different active control models (non-CSI, reduced-order CSI, and higher-order CSI model) which considering different accuracy requirements of the electro-mechanical relationship are established to investigate the influence of the CSI on active tuned mass damper (ATMD) control system. The frequency- and time-domain responses of a three-story steel frame structure during different excitations are investigated, and as a comparison, the responses of the uncontrolled and tuned mass damper (TMD) control system are also studied. It can be concluded that the control performance of the active control system is reduced due to the CSI effect, especially at resonance frequency region of the structure (around 2.7 Hz, 8.2 Hz, and 13.2 Hz). The input voltage, velocity of the top floor, velocity of active mass, and higher-order of control forces have an important influence on the servomotor output control force. Furthermore, it can be found that, to achieve the same control effect, the required control voltage has been significantly increased due to the CSI effect.

Modeling and nonlinear optimal control of active mass damper with rotating actuator for structural vibration control

An innovative nonlinear optimal control scheme based on θ-D approximation for structural vibration control with R-AMD (active mass damper with rotating actuator) is developed in this paper. In the R-AMD which was proposed in our previous work, rotating actuator rather than linear actuator is used to accelerate and decelerate the inertial mass, thus avoiding stroke-related problems. The rotational motion of the inertial mass makes R-AMD a special nonlinear AMD, which raises the level of difficulty in controller designing. Taking the control–structure interaction (CSI) effect into consideration, the modeling of target structure/R-AMD coupled system is fulfilled using the Lagrange equations. Regarding the nonlinearity in the R-AMD system, a nonlinear optimal control scheme is designed based on θ-D approximation, during which the important role of diffeomorphism transformation of coordinates is presented. Experiments are conducted to validate the effectiveness of the proposed control algorithm and the R-AMD device.

Improved Systemic Hazard Analysis Integrating With Systems Engineering Approach for Vehicle Autonomous Emergency Braking System

Abstract Safety analysis is a significant step for safety-critical system development. Compared with traditional vehicles, the system interactions for autonomous vehicles are more abundant and complex. Traditional hazard analysis methods, such as failure mode and effects analysis (FMEA) and fault tree analysis (FTA) which are based on the component failure and reliability theory, cannot identify the system hazards related to system interactions. An emerging hazard analysis method based on systems theory, systems theory process analysis (STPA) mainly focuses on identifying the control system hazards caused by system interactions. In this study, STPA method is used to identify the potential hazards and casual factors for autonomous emergency braking systems by concentrating on system interactions. To improve the consistency between system design and safety analysis, the workflow combining model-based systems engineering (MBSE) and STPA is proposed. The systems modeling language (SysML) is used to describe control structure and system interaction relationships. According to the identified casual factors, certain constraints and requirements can be derived, which can provide the guidance for system development with respect to system design. Furthermore, the quantitative analysis of certain unsafe control action is conducted by simulation, which shows effectiveness and feasibility of the proposed method in safety analysis and system design.

Multibody dynamics and robust attitude control of a MW-level solar power satellite

This paper addresses the multibody dynamics and robust attitude control of a MW-level solar power satellite, which mainly consists of an 800-m-length center truss, a 150-m-diam microwave-transmitting antenna and twenty-four 25 × 100 m solar subarrays. Based on the selected reference attitude and the floating frame formulation, the flexible multibody attitude dynamic model is firstly derived by Lagrange equations in terms of quasi-coordinates. The gravity-gradient, solar radiation pressure, and microwave radiation torques are also investigated to evaluate their influence on attitude control accuracy. Then, a hybrid high/low bandwidth robust controller is proposed. The rough attitude control of the center truss and solar subarrays is achieved by the low bandwidth control, which combines the feedback linearization with the disturbance observer and minimizes the control-structure interaction of the center truss. The precise antenna pointing control is achieved by the high bandwidth collocated control, where the optimal locations of actuators/sensors are obtained by minimizing the influence of the attitude control system on the structural vibration. The fully coupled nonlinear numerical simulation are finally provided. It is demonstrated that the proposed controller can guarantee attitude control performance of all component structures.

Analysis of the interaction effects between double shaking tables and test structure

Electrohydraulic shaking tables provide a direct means to evaluate structural performance under actual vibration conditions. The control–structure interaction is one of the most important reasons for the degradation of the control performance of the shaking table. This article establishes a series of novel analytical models to investigate the control–structure interaction effects between double shaking tables and test structure. These models are the model of shaking table, the model of control error signal, the flow requirement model of servo valve, the force requirement model of actuator, and the resonance response model of structure. Based on the analytical models of the flow requirement model of servo valve, force requirement model of actuator, and resonance response model of structure, a comprehensive simulation study is conducted under different structural conditions. The study reveals the influence trend and the influence degree of the control–structure interaction on the models. Furthermore, the applications in experiments, the suggestions for the designing of the shaking table, and the deeper explorations of the control–structure interaction are obtained.

Optimization Provenance of Whiplash Compensation for Flexible Space Robotics

Automatic controls refer to the application of control theory to regulate systems or processes without human intervention, and the notion is often usefully applied to space applications. A key part of controlling flexible space robotics is the control-structures interaction of a light, flexible structure whose first resonant modes lie within the bandwidth of the controller. In this instance, the designed-control excites the problematic resonances of the highly flexible structure. This manuscript reveals a novel compensator capable of minimum-time performance of an in-plane maneuver with zero residual vibration (ZV) and zero residual vibration-derivative (ZVD) at the end of the maneuver. The novel compensator has a whiplash nature of first commanding maneuver states in the opposite direction of the desired end state. For a flexible spacecraft simulator (FSS) free-floating planar robotic arm, this paper will first derive the model of the flexible system in detail from first principles. Hamilton’s principle is augmented with the adjoint equation to produce the Euler–Lagrange equation which is manipulated to prove equivalence with Newton’s law. Extensive efforts are expended modeling the free–free vibration equations of the flexible system, and this extensive modeling yields an unexpected control profile—a whiplash compensator. Equations of motion are derived using both the Euler–Lagrange method and Newton’s law as validation. Variables are then scaled for efficient computation. Next, general purposed pseudospectral optimization software is used to seek an optimal control, proceeding afterwards to validate optimality via six theoretical optimization necessary conditions: (1) Hamiltonian minimization condition; (2) adjoint equations; (3) terminal transversality condition; (4) Hamiltonian final value condition; (5) Hamiltonian evolution equation; and lastly (6) Bellman’s principle. The results are novel and unique in that they initially command full control in the opposite direction from the desired end state, while no such results are seen using classical control methods including classical methods augmented with structural filters typically employed for controlling highly flexible multi-body systems. The manuscript also opens an interesting question of what to declare when the six optimality necessary conditions are not necessarily in agreement (we choose here not to declare finding the optimal control, instead calling it suboptimal).

Adaptive control for smart-actuated base isolation structures regarding various reference-tracking strategies

An adaptive control framework considering servo-hydraulic dynamics is proposed for base isolation structures regarding various reference-tracking strategies. The reference-tracking-based adaptive controller is derived from a backstepping design methodology with Lyapunov stability analysis. Servo-hydraulic dynamics, including the control-structure interaction (CSI) and the actuator uncertainties, have significant effects on seismic control performance; accordingly, the critical issue of the control device dynamics-induced time-lag should be introduced in the control process. To drive a successful active control event, an inverse actuator model is integrated within the proposed controller. Such inverse dynamic models, with adaptive regulation characteristics, are expected to compensate the time-lag real-time. On the other hand, for a reference-tracking-based controller, control performance is determined by a reference model. Therefore, different reference generation strategies have been discussed in a comparative study by considering the effect of structure nonlinearity and substructure-interaction. To investigate the performance of the proposed controller in detail, the first example is a nonlinear single-degree-of-freedom (SDOF) system. Then, a multi-degree-of-freedom (MDOF) system with a nonlinear base isolation layer is employed in a comparative study with various reference-tracking strategies. Subsequently, the proposed control framework has been performed in a nonlinear base isolation benchmark problem; and, the control performance demonstrates the efficacy of the reference-tracking controller in a two-dimensional actuator control problem.

Backstepping adaptive control for real-time hybrid simulation including servo-hydraulic dynamics

Abstract A backstepping adaptive control method is proposed for on-line estimation of unknown servo-hydraulic dynamics and the compensation of time-varying lags in real-time hybrid simulation tests. The response tracking problem becomes a critical challenge when realistic experimental conditions are taken into consideration, such as control-structure interaction effects and sensor measurement noise. Unlike a conventional time-lag compensator, the proposed adaptive controller generates a command trajectory for the actuated system according to adaptive laws. Besides bringing response tracking error to zeros, the estimation of a first-principle actuator dynamic model is also facilitated in the proposed approach. Lyapunov stability analysis is systematically presented for designing the adaptive control law. Illustratively, a three-story seismically excited structure with different control strategies is utilized to demonstrate the efficiency and robustness of the proposed controller. A benchmark problem is then utilized for the verification of controller’s advancement. Four simulation cases with different damping/mass conditions and four ground excitation scenarios are selected for the application. As stated, favorable tracking performance has been observed with a remarkable improvement in performance evaluation.

Field stabilization control of the European Extremely Large Telescope under wind disturbance.

This paper discusses the field stabilization control of the M5 unit under wind disturbances. The first part is a literature survey of the spectral content of the wind disturbance. Next, a simplified model of a tip/tilt mirror control system is used to analyze the conditions for control-structure interaction. The influence of the asymptotic decay rate of the wind tilt disturbance on the magnitude and spectral content of the control torques is pointed out. A full telescope model is developed to justify a decoupled tip/tilt control design and to analyze the response of the primary mirror M1 to the disturbance generated by the control torques of the M5 unit.

Adopting Robotic Systems to Enhance Vibration Control of Footbridges

With innovation and aesthetics playing leading roles, the landscape of footbridge design continues to evolve towards lightweight, landmark structures, increasing the emphasis on mitigating lively dynamic responses. To satisfy architectural constraints, auxiliary control devices are being used to control the response under infrequent peak-loading events. Nearly all implemented control devices are permanent installations of passive systems, such as viscous dampers or tuned mass dampers (TMDs), that are tuned to a particular structural property and hence specific to the particular application. Recently, the concept of deployable, autonomous control systems has been presented, in which a robotic platform is combined with an active control device to yield a system that is capable of providing short-term control for a range of structures. This concept is particularly attractive in relation to footbridge applications, where the systems can be deployed during predictable peak-loading events such as marathons or used with temporary footbridges where the need for control depends on the intended use. In this paper, analytical modeling of a prototype system is presented to validate experimental identification. Furthermore, the role of the control–structure interaction (CSI) is described and compensated for through an active controller formulation and the use of a position feedback controller for disturbance rejection. The performance of the prototype system is evaluated experimentally and assessed relative to an equivalent passive TMD device. The experimental study validates the controller formulation and demonstrates the effectiveness of the prototype system.

Control-structure interaction in piezoelectric deformable mirrors for adaptive optics

This paper discusses the shape control of deformable mirrors for Adaptive Optics in the dynamic range. The phenomenon of control-structure interaction appears when the mirror becomes large, lowering the natural frequencies fi, and the control bandwidth fc increases to improve the performance, so that the condition fc < fi is no longer satisfied. In this case, the control system tends to amplify the response of the flexible modes and the system may become unstable. The main parameters controlling the phenomenon are the frequency ratio fc / fi and the structural damping s. Robustness tests are developed which allow to evaluate a lower bound of the stability margin. Various passive and active strategies for damping augmentation are proposed and tested in simulation.

Model-based framework for multi-axial real-time hybrid simulation testing

Real-time hybrid simulation is an efficient and cost-effective dynamic testing technique for performance evaluation of structural systems subjected to earthquake loading with rate-dependent behavior. A loading assembly with multiple actuators is required to impose realistic boundary conditions on physical specimens. However, such a testing system is expected to exhibit significant dynamic coupling of the actuators and suffer from time lags that are associated with the dynamics of the servo-hydraulic system, as well as control-structure interaction (CSI). One approach to reducing experimental errors considers a multi-input, multi-output (MIMO) controller design, yielding accurate reference tracking and noise rejection. In this paper, a framework for multi-axial real-time hybrid simulation (maRTHS) testing is presented. The methodology employs a real-time feedback-feedforward controller for multiple actuators commanded in Cartesian coordinates. Kinematic transformations between actuator space and Cartesian space are derived for all six-degrees-offreedom of the moving platform. Then, a frequency domain identification technique is used to develop an accurate MIMO transfer function of the system. Further, a Cartesian-domain model-based feedforward-feedback controller is implemented for time lag compensation and to increase the robustness of the reference tracking for given model uncertainty. The framework is implemented using the 1/5th-scale Load and Boundary Condition Box (LBCB) located at the University of Illinois at Urbana- Champaign. To demonstrate the efficacy of the proposed methodology, a single-story frame subjected to earthquake loading is tested. One of the columns in the frame is represented physically in the laboratory as a cantilevered steel column. For realtime execution, the numerical substructure, kinematic transformations, and controllers are implemented on a digital signal processor. Results show excellent performance of the maRTHS framework when six-degrees-of-freedom are controlled at the interface between substructures.

Attitude and vibration control of a satellite containing flexible solar arrays by using reaction wheels, and piezoelectric transducers as sensors and actuators

The primary purpose of this paper is to provide insight into control-structure interaction for satellites comprising flexible appendages and internal moving components. The physical model considered herein aiming to attend such purpose is a rigid-flexible satellite consisting of a rigid platform containing two rotating flexible solar panels. The solar panels rotation is assumed to be in a sun-synchronous configuration mode. The panels contain surface-bonded piezoelectric patches that can be used either as sensors for the elastic displacements or as actuators to counteract the vibration motion. It is assumed that in the normal mode operation the satellite platform points towards the Earth while the solar arrays rotate so as to follow the Sun. The vehicle moves in a low Earth polar orbit. The technique used to obtain the mathematical model combines the Lagrangian formulation with the Finite Elements Method used to describe the dynamics of the solar panel. The gravity-gradient torque as well as the torque due to the interaction of the Earth magnetic field and the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control and piezoelectric actuators to control the flexible motion of the solar arrays. Computer simulations are performed using the MATLAB® software package. The following on-orbit satellite operating configurations are object of analysis: i) Satellite pointing towards the Earth (Earth acquisition maneuver) by considering the initial conditions in the elastic displacement equal to zero, aiming the assessment of the flexible modes excitation by the referred maneuver; ii) the satellite pointing towards the Earth with the assumption of an initial condition different from zero for the flexible motion such that the attitude alterations are checked against the elastic motion disturbance; and iii) attitude acquisition accomplished by taking into account initial conditions different from zero for both attitude and elastic vibrations. Additionally, the control efforts for the three cases are compared. Results indicate that the attitude control is able to excite the solar panels' vibration modes and vice-versa. The piezoelectric vibration control shows significant performance improvement when compared to contributions of the attitude control to the vibration damping.