Signal shaper with a distributed delay: Spectral analysis and design

Input shapers with time delays have proved useful in many applications related to controls for various oscillatory devices, for example flexible manipulators and cranes. In the paper, a novel approach for designing a zero-vibration signal shaper based on equally distributed delay is proposed. The parameter assessment of the shaper is based on the spectral approach. Various characteristics of the shaper are analyzed and compared with the classical zero-vibration shaper with a lumped delay. The analysis shows that the novel shaper is a slower, but more robust alternative to the classical shaper. Besides, the discrete implementation of the shaper is proposed and tested. It includes zero placement based parameter adjustment with the objective to preserve full compensation of the oscillatory mode by the discrete algorithm.     

Adaptive input shaping for maneuvering flexible structures

In the control of flexible structures many methods are used to reduce residual vibration due to the excitation of flexible modes. Input shaping, a feed-forward method, typically convolves the input with a sequence of impulses that are independent of the system maneuver. While reducing the residual vibration, input shaping extends the duration of the maneuver command by the length of the input shaper. This paper explores the idea of adaptive input shaping which allows a fast input shaper to be used while providing robustness to parameter uncertainty by tuning the shaper to the flexible mode frequency. The adaptive input shaping method presented can adapt between maneuvers or during maneuvers. Analysis yields a large range of convergence that is verified by simulation and shows this method to be less complex than other adaptive approaches.     

Active vibration control of a fluid/plate system using a pole placement controller

We consider the problem of active reduction of the structural vibrations induced by the sloshing of large masses of fuel inside a partly full tank. The proposed study focuses on an experimental device mimicking an aircraft wing made of an aluminium rectangular plate equipped with piezoelectric patches at the clamped end and with a cylindrical tip tank, more or less filled with liquid. After deriving a representative finite-dimensional model of the complete system, containing the first five structural modes of the plate and the first three liquid sloshing modes, a controller is computed. Since our main scope is to control the most energetic mode of the structure, a full state-feedback method coupled with an observer is used. Finally, the controller is also tested for different initial conditions/perturbations and the results are compared with the ones obtained with an H _∞ controller. Experimental results illustrate the relevance of the chosen strategy.     

Dynamic modelling, simulation and control of a manipulator with flexible links and joints

The paper presents a dynamic modelling technique for a manipulator with multiple flexible links and flexible joints, based on a combined Euler–Lagrange formulation and assumed modes method. The resulting generalised model is validated through computer simulations by considering a simplified case study of a two-link flexible manipulator with joint elasticity. Controlling such a manipulator is more complex than controlling one with rigid joints because only a single actuation signal can be applied at each joint and this has to control the flexure of both the joint itself and the link attached to it. To resolve the control complexities associated with such an under-actuated flexible link/flexible joint manipulator, a singularly perturbed model has been formulated and used to design a reduced-order controller. This is shown to stabilise the link and joint vibrations effectively while maintaining good tracking performance.     

Singular perturbation analysis of high-frequency filter design

The control design of systems with lightly damped high frequency oscillatory modes is treated. Systems exhibiting these lightly damped modes include turbine generators and large flexible structures. Frequently the dynamics of these high-frequency modes are not known very accurately. As a result, the design objective is to improve the slow dynamics without destabilizing the high-frequency modes. From a classical frequency domain design viewpoint, this is in part a filtering problem requiring some kind of high-frequency filter. The singular perturbation method is used to systematically develop a two-time-scale method to design these high-frequency filters and provides guidelines on the kind of high-frequency filter to be used. In addition, the method provides an asymptotic error analysis. The design is illustrated with an example representative of a power system model with a two-mass turbine-generator model.     

Bi-level model reduction for coupled problems

In this work a methodology is proposed for the optimization of coupled problems, and applied to a 3D flexible wing. First, a computational fluid dynamics code coupled with a structural model is run to obtain the pressures and displacements for different wing geometries controlled by the design variables. Secondly, the data are reduced by Proper Orthogonal Decomposition (POD), allowing to expand any field as a linear combination of specific modes; finally, a surrogate model based on Moving Least Squares (MLS) is built to express the POD coefficients directly as functions of the design variables. After the validation of this bi-level model reduction strategy, the approximate models are used for the multidisciplinary optimization of the wing. The proposed method leads to a reduction of the weight by 6.6%, and the verification of the solution with the accurate numerical solvers confirms that the solution is feasible.     

Designing feedforward command shapers with multi-objective genetic optimisation for vibration control of a single-link flexible manipulator

This paper presents investigations into the design of a command-shaping technique using multi-objective genetic optimisation process for vibration control of a single-link flexible manipulator. Conventional design of a command shaper requires a priori knowledge of natural frequencies and associated damping ratios of the system, which may not be available for complex flexible systems. Moreover, command shaping in principle causes delay in system's response while it reduces system vibration and in this manner the amount of vibration reduction and the rise time conflict one another. Furthermore, system performance objectives, such as, reduced overshoot, rise time, settling time, and end-point vibration are found in conflict with one another due to the construction and mode of operation of a flexible manipulator. Conventional methods can hardly provide a solution, for a designer-oriented formulation, satisfying several objectives and associated goals as demanded by a practical application due to the competing nature of those objectives. In such cases, multi-objective optimisation can provide a wide range of solutions, which trade-off these conflicting objectives so as to satisfy associated goals. A multi-modal command shaper consists of impulses of different amplitudes at different time locations, which are convolved with one another and then with the desired reference and then used as reference (for closed loop) or applied to system (for open loop) with the view to reduce vibration of the system, mainly at dominant modes. Multi-objective optimisation technique is used to determine a set of solutions for the amplitudes and corresponding time locations of impulses of a multi-modal command shaper. The effectiveness of the proposed technique is assessed both in the time domain and the frequency domain. Moreover, a comparative assessment of the performance of the technique with the system response with unshaped bang–bang input is presented.     

Preshaping input trajectories of industrial robots for vibration suppression

This paper presents several novel methods that improve the current input shaping techniques for vibration suppression for multi-degree of freedom industrial robots. Three different techniques, namely, the optimal S-curve trajectory, the robust zero-vibration shaper, and the dynamic zero-vibration shaper, are proposed. These methods can suppress multiple vibration modes of a flexible joint robot under a computed torque control based on a rigid model. The time delays for each method are quantified and compared. The optimal S-curve trajectory finds the maximum jerk to obtain the minimum vibration. The robust zero-vibration shaper can suppress multiple modes without an accurate model. The delay of the dynamic zero-vibration shaper is smaller than the existing input shaping techniques. Our analysis is verified both by simulation and experiment with a six degrees-of-freedom commercial industrial robot.     

Adaptive Tracking Filter for Stabilizing a Flexible Launch Vehicle

The flight control system designer is increasingly concerned with the problem of providing adequate stability of the elastic modes of the flight vehicle. The problem of stabilizing bending modes can be solved by the use of different bending filters. But continuously changing behavior of the elastic modes frequencies makes it impossible to suppress the elastic modes. In this paper, adaptive tracking filter is used to solve this problem. Where it can track the frequency of predominant oscillator…     

Optimization process for configuration of flexible joined-wing

An optimized configuration design utilizing both structural and aerodynamic analyses of a flexible joined-wing configuration is presented in this paper. The joined-wing aircraft concept fulfills a proposed long-endurance surveillance mission and incorporates a load-bearing antenna structure embedded in the wing skin. Aerodynamic, structural, and optimization analyses are completed a number of times. A range of joined-wing configurations were trimmed for critical flight conditions and then structurally optimized for trimmed flight and gust loads to achieve a minimum weight for each configuration. A response surface statistical analysis was then applied to determine optimal joined-wing aircraft configurations. The response surface showed trends in the design of lightweight joined-wing aircraft. The revised version of this paper was presented at the 10th MAO Multidisciplinary Analysis and Optimization Conference, August 30–September 1, 2004.     

Integrated aerodynamic-structural-control wing design

The aerodynamic-structural-control design of a forward-swept composite wing for a high subsonic transport aircraft is considered. The structural analysis is based on a finite-element method. The aerodynamic calculations are based on a vortex-lattice method, and the control calculations are based on an output feed-back control law. The wing is designed for minimum weight subject to structural, performance/aerodynamic and control constraints. Efficient techniques are developed to calculate the control-deflection and control-effectiveness sensitivities which appear as second-order derivatives in the control constraint equations. To suppress the aeroelastic divergence of the forward-swept wing, and to minimize the take-off gross weight of the design aircraft, two separate cases are studied: (1) combined application of aeroelastic tailoring and active controls; and (2) aeroelastic tailoring alone. For the particular example problem considered in this study, the aeroelastic tailoring was found to have a substantially greater influence than active controls on weight minimization and divergence suppression.     

Design of dual-dimensional controller based on multi-objective gravitational search optimization algorithm for amelioration of impact of oscillation in power generated by large-scale wind farms

This paper studies the impact of high penetration of wind generation technology on dynamic stability of power networks. A mathematical model of a multi-machine power system, including Large-scale Wind Power Generation System (LWPGS) incorporating active power oscillation due to tower shadow and wind shear phenomena is developed. Based on this model, an extended Small-Signal Scrutiny (SSS) procedure to study the impact of oscillatory modes on mechanical vibrations is proposed. The critical operating points that can be dangerous for power system performance are detected. The study is based on modified 16-machine 5-area network with lightly damped electromechanical modes. A dual-dimensional controller for LWPGS is proposed. The first and second dimensions of the designed controller are based on wide-area and local signals, respectively. Selection of the best input of the LWPGS is based on Singular Value Decomposition (SVD) analysis, while the qualified remote control signal is found by geometric approach. Multi-Purpose Gravitational Search Algorithm (MPGSA) based on fuzzy decision making is applied for the coordinated design of LWPGS controller and accelerating power PNS (PNS2B) of the synchronous machines. The simulation results are presented to elucidate the effectiveness of the well-tuned damping controller of the LWPGS.     

基于滑模控制的折叠翼飞行器辅助机动研究

基于滑模控制策略,研究了折叠翼飞行器辅助机动问题.分析了系统折叠角与气动参数的关系,把机翼折叠角看成额外的控制输入,构造了包含折叠辅助机动的飞行器动力学模型.针对非线性系统,加入混合干扰,设计了非奇异动态终端滑模控制(NDTSMC)器,能够较好地抑制折叠翼飞行器的不确定性,同时完成姿态跟踪控制.仿真结果表明,NDTSMC改善了折叠翼飞行器的控制精度和鲁棒性能,具有较好的抖振消除效果.与传统飞行器相比,加入折叠辅助机动的折叠翼飞行器拥有更高的机动性和抗干扰能力.     

A Digital Input Shaper for Stable and Transparent Haptic Interaction

This paper presents frequency-dependent digital damping referred to a digital input shaper (DIS). Compared to the previously proposed analog input shaper, the DIS makes the implementation of damping much more flexible and significantly reduces the electrical noise. Moreover, the DIS incorporates a position control method at the initial contact to improve the perceived contact hardness. Then, through a series of simulations and benchmark virtual wall experiments, we show that the DIS can significantly increase the impedance range that a haptic interface can stably display and that the initial contact hardness that a user perceives can be noticeably improved by using the proposed position control method. Finally, the DIS is applied to scaled teleoperation using an atomic force microscope and through contact experiments it is shown that it can indeed increase the scaled impedance of a real environment that can be stably displayed. ©     

Adaptive input shaping for manoeuvring flexible structures using an algebraic identification technique

Input shaping is an efficient feedforward control technique which has motivated a great number of contributions in recent years. Such a technique generates command signals with which manoeuvre flexible structures without exciting their vibration modes. This paper presents a novel adaptive input shaper based on an algebraic non-asymptotic identification. The main characteristic of the algebraic identification in comparison with other identification methods is the short time needed to obtain the system parameters without defining initial conditions. Thus, the proposed adaptive control can update the input shaper during each manoeuvre when large uncertainties are present. Simulations illustrate the performance of the proposed method.     

飞翼飞行器的操纵面故障自适应补偿控制

本文针对具有操纵面卡死、失效故障以及执行器饱和的飞翼飞行器纵向运动,考虑系统的预定动态性能,提出了一种自适应反步补偿跟踪控制方案.设计预定动态性能(prescribed performance bound,PPB)边界以保证系统的跟踪误差,采用二阶指令滤波器限制执行器的饱和,通过控制分配避免执行器故障后对横侧向运动的影响.所设计的自适应反步补偿跟踪控制律能够保证系统对参考信号的渐近跟踪.仿真结果表明了本文方法的有效性.     

Aeroservoelastic model based active control for large civil aircraft

A modeling and control approach for an advanced configured large civil aircraft with aeroservoelasticity via the LQG method and control allocation is presented.Mathematical models and implementation issues for the multi-input/multi-output(MIMO) aeroservoelastic system simulation developed for a flexible wing with multi control surfaces are described.A fuzzy logic based optimization approach is employed to solve the constrained control allocation problem via intelligently adjusting the components of output v...     

Control of a Non-uniform Flexible Beam: Identification of First Two Modes

This paper presents an experimental study implementing the input shaping control of the first two modes of the vibration of a non-uniform flexible cantilever beam having a translating base. Examples of a moving cantilever beam appear in many industrial systems. Vibration suppression of the beam has important implications for improving the effectiveness of such systems. The equations of motion of the cantilever beam, including the moving base, are developed using the extended Hamilton principle. The partial differential equation representing the beam’s dynamics is then transformed into a finite-dimensional model using the Galerkin method. Accordingly, the modal parameter identification procedure is established based on experimental modal analysis. Under the estimated modal parameters, including the natural frequency and damping ratio, single- and two-mode input shaping controllers of three different types (zero vibration, zero vibration derivative, and zero vibration derivative-derivative) are designed for vibration suppression of the beam. Experimental results are discussed, reporting that the two-mode shaper’s vibration suppression was superior to the single-mode shaper. In contrast, the two-mode shaper’s settling time has slightly increased compared to that of the single-mode shaper.

     

基于分布估计算法的弹性飞翼飞行器多操纵面控制分配

针对弹性飞翼飞行器多操纵面控制分配问题,提出了衡量弹性震动的机振力指标,建立了完整的控制分配模型,提出了采用分布估计算法（EDA）对模型进行求解。首先进行舵面结构设计,分析各气动舵面的工作方式及控制能力,并依据气动数据中升降副翼、余度舵、副翼的舵面控制效率,进行舵面功能配置。在进行控制分配时,分析控制分配的主要性能指标,确立总体多目标优化评价函数,并结合等式和不等式约束条件。采用性能优越的EDA进行求解。通过建立概率模型来估计真实分布,在EDA的进化过程中,各个舵面会根据偏转效率进行分配,结合优化函数最终收敛到最优解。最后分析机翼气动弹性对系统静态操纵效能的影响。从不考虑气动弹性系统响应曲线和考虑气动弹性之后的系统响应曲线比较结果可以看出,有弹性情况下系统响应曲线超调量和过渡时间都减小,飞翼式飞行器飞行品质得到显著提高,优化之后系统效能提高了10%。仿真结果表明,EDA能够较好地解决控制分配问题,并能提高系统动态品质,验证了多操纵面控制分配模型和算法的有效性。