肌电假手感觉反馈机理研究

基于振动电机的肌电假手感觉反馈首次应用在HIT多自由度假手中。对肌电信号的拾取方式和肌肉动作分配作了规定,概述了假手的整体工作模式,着重在机理研究的基础上利用振动电机进行了感觉反馈的应用。在满足应用功能和所占空间小的前提下实现了假手整体系统的可靠运行,避免了各模块间信号的干扰。     

采用压缩感知的协作多点信道反馈算法研究

协作多点技术（ Coordinated Multiple Points,CoMP）作为LTE-A的最重要候选技术之一,已经得到广泛的关注。在协作多点中,有很多种传输方案,其中一种基于联合传输下的全局预编码方案能够获得极佳的系统性能,而实现该方案的前提是基站可以得到较为完整的信道状态信息。因此在信道反馈时选择显式反馈,因为相比较其他反馈方式,它可以反馈更为完整的信道状态信息,而显式反馈的缺点为需要的反馈量过大。文中利用一种采用压缩感知的信道反馈新方法对联合传输下的全局预编码方案信道显式反馈信息进行压缩,仿真结果显示在不影响系统性能的前提下,能够有效地减少反馈量,使得系统发挥最佳性能。     

Constrained control of SISO bilinear systems

Relative degree and nonminimum phase difficulties limit the applicability of input-output feedback linearization; hence the need for approximations. Earlier work on predictive control of bilinear systems overcame these problems by means of interpolation between feedback linearization and state feedback, the former providing optimality and the latter guaranteeing feasibility and stability through the use of invariant/feasible polytopes. The current work also makes use of polytopes in preference to ellipsoids but achieves distinctly different objectives. First, it is shown that feedback linearization can be used over particular polytopes without needing to resort to either approximation or interpolation. Then, it is shown that invariant polytopes based on bilinear controllers can be much larger. These two approaches are combined in an algorithm that guarantees stability over much larger initial condition sets and gives much improved closed-loop performance.     

基于非线性力反馈模型的软组织变形仿真

虚拟手术仿真研究中反馈力一般采用线性模型,但软组织的反馈力往往呈现出非线性的特点.通过对软组织生物力学特性的分析,将非线性性质应用到软组织力反馈模型的研究.在保持原线性反馈力方向不变的前提下,加入非线性扰动,建立了反馈力的非线性模型,从而使反馈力更加真实.首先构建了人体肝脏物理模型,然后给出了非线性力反馈模型方程,并对人体肝脏物理模型变形和反馈力进行了仿真.为了减小计算量采用了整体刚度矩阵缩减算法.仿真结果表明该模型有较好的非线性和可调节性.     

Stabilization of the PVTOL aircraft based on a sliding mode and a saturation function

This study presents a feedback control strategy for the regulation of a planar vertical takeoff and landing aircraft. To this end, two controllers that work simultaneously were designed. The first controller is devoted to stabilizing the vertical variable and is based on a simple feedback‐linearization procedure in combination with a saturation function. The second controller – based on a combination of the traditionally PD‐controller and a sliding mode controller – stabilizes both the horizontal and angular variables to the desired rest position. The performance of the closed‐loop system is demonstrated through simulation results. Copyright © 2016 John Wiley & Sons, Ltd.     

A sampled normal form for feedback linearization

This paper discusses the problem of preserving approximated feedback linearization under digital control. Starting from a partially feedback linearizable affine continuous-time dynamics, a digital control procedure which maintains the dimension of the maximally feedback linearizable part up to any order of approximation with respect to the sampling period is proposed. The result is based on the introduction of a sampled normal form, a canonical structure which naturally appears when studying feedback linearization.This work was supported by an Italian 40% M.U.R.S.T. grant and a French M.E.N.-D.R.E.D. grant.     

Feedback passivity approach to output feedback disturbance attenuation for uncertain nonlinear systems

The problem of output feedback disturbance attenuation for a class of uncertain nonlinear systems is studied based on output feedback passification. Previous work on output feedback disturbance attenuation is extended to the case where (1) the nominal system is not transformable into the normal form and (2) the uncertainty is parameterized nonlinearly. An adaptive output feedback controller is also provided that makes a nonlinear system passive. The paper then considers the output feedback disturbance attenuation problem for a class of uncertain nonlinear systems in the normal form and of relative degree one. The difference is that the result is applicable to nonlinear systems that include the uncertainty in the input matrix and do not satisfy the matching condition.     

Nonsmooth output feedback stabilization of a class of genuinely nonlinear systems in the plane

In this note, we address the problem of output feedback stabilization for a class of planar systems that are inherently nonlinear in the sense that the linearized system at the origin is neither controllable nor observable. Moreover, the uncontrollable modes contain eigenvalues on the right-half plane. By the well-known necessary condition, such planar systems cannot be stabilized, even locally by any smooth output feedback, and hence must be dealt with by nonsmooth output feedback. The main contribution of this work is the development of a non-Lipschitz continuous output feedback design method that leads to a solution to the problem. The proposed output feedback control scheme is not based on the separation principle but rather, relies on the design of a reduced-order nonlinear observer from an earlier paper with an appropriate twist, and the tool of adding a power integrator. A non-Lipschitz continuous output feedback controller is explicitly constructed, achieving global stabilization of the planar systems without imposing the high-order growth conditions required in a previous paper.     

Minimum entropy-based performance assessment of feedback control loops subjected to non-Gaussian disturbances

Control performance assessment (CPA) is a useful tool to establish the quality of industrial feedback control loops. While many current CPA techniques are developed solely for the controlled systems under the assumption of the Gaussian disturbance, the conventional minimum variance control (MVC) approach would not be applied when the disturbance distribution is non-Gaussian. In this paper, based on the information theory and the minimum entropy criterion, a more general CPA index for the feedback control loop subjected to unknown disturbance distribution is investigated. The fundamentals of MVC are first reexamined, and then an innovative performance index is given by incorporating the entropy. The feedback control algorithm based on minimum entropy, called MEC (minimum entropy control), is derived. MEC based CPA for the controlled system requires effective and systematic identification of the associated system models based on the closed-loop data. In this work, a new methodology based on the entropy criterion instead of the mean square error criterion is presented to estimate disturbances for the purpose of evaluating the performance of the control systems. To demonstrate the effective MEC based CPA method, both numerical and industrial examples are applied and compared with the MVC based CPA method.     

Tracking control and robustness analysis for planar vertical takeoff and landing aircraft under bounded feedbacks

We study feedback tracking problems for the planar vertical takeoff and landing (PVTOL) aircraft dynamics, which is a benchmark model in aerospace engineering. We provide a survey of the literature on the model. Then we construct new feedback stabilizers for the PVTOL tracking dynamics. The novelty of our work is in the boundedness of our feedback controllers and their applicability to cases where the velocity measurements may not be available, coupled with the uniform global asymptotic stability and uniform local exponential stability of the closed‐loop tracking dynamics and the input‐to‐state stable performance of the closed‐loop tracking dynamics with respect to actuator errors. Our proofs are based on a new bounded backstepping result. We illustrate our work in a tracking problem along a circle. Copyright © 2011 John Wiley & Sons, Ltd.     

Modern Wiener--Hopf design of optimal controllers Part I: The single-input-output case

An analytical feedback design technique is presented here for single-input-output processes which are characterized by their rational transfer functions. The design procedure accounts for the topological structure of the feedback system ensuring asymptotic stability for the closed-loop configuration. The plant or process being controlled can be unstable and/or nonminimum phase. The treatment of feedback sensor noise, disturbance inputs, and process saturation is another major contribution of this work. The cornerstone in the development is the selection of a performance index based on sound engineering considerations. It is these considerations, in fact, which ensure the existence of an optimal compensator for the system and make the performance index a natural one for the problem at hand.     

Whole-hand kinesthetic feedback and haptic perception in dextrous virtual manipulation

One of the key requirements for a Virtual Reality system is the multimodal, real-time interaction between the human operator and a computer simulated and animated environment. This paper investigates problems related particularly to the haptic interaction between the human operator and a virtual environment. The work presented here focuses on two issues: 1) the synthesis of whole-hand kinesthetic feedback, based on the application of forces (torques) on individual phalanges (joints) of the human hand, and 2) the experimental evaluation of this haptic feedback system, in terms of human haptic perception of virtual physical properties (such as the weight of a virtual manipulated object), using psychophysical methods. The proposed kinesthetic feedback methodology is based on the solution of a generalized force distribution problem for the human hand during virtual manipulation tasks. The solution is computationally efficient and has been experimentally implemented using an exoskeleton force-feedback glove. A series of experiments is reported concerning the perception of weight of manipulated virtual objects and the obtained results demonstrate the feasibility of the concept. Issues related to the use of sensory substitution techniques for the application of haptic feedback on the human hand are also discussed.     

在离散观测和反馈延迟下的混杂随机系统镇定

对混杂随机系统的状态反馈控制近年来引起了广泛的关注. 一个更现实也更经济的情况是对状态的观测 不是连续时间而是离散时间的. 同时, 现实中绝大多数的观测和反馈系统都或多或少会存在时滞现象. 因此, 讨论 这种基于离散时间观测同时带有观测反馈时滞的混杂随机系统的反馈控制是很有意义的. 特别地, 通过使用一个 李雅普诺夫泛函, 不仅可以得到H无穷稳定、渐近稳定和指数稳定, 而且还能显著地改善对时滞上界的要求. 本文是 文献[20]工作的深入和推广.     

Sampled-data feedback and stability for a class of uncertain nonlinear systems based on characteristic modeling method一类非线性不确定系统基于特征建模方法的采样控制及稳定性研究

In this paper, we investigate the tracking problem for a class of second-order uncertain nonlinear systems using sampled-data output feedback. Our controller is designed based on the characteristic modeling method. We first derive the corresponding characteristic model and then give the sampled-data feedback control law, which is referred to as “golden-section adaptive control based on characteristic models”. The closed-loop system is shown to be stable and, concurrently, it is demonstrated that the tracking error can be made arbitrarily small by taking a sufficiently small sampling period. Our results improve upon the findings of previous work by removing the persistent excitation condition, and also lay certain theoretical foundations for practical applications of golden-section adaptive control.     

Linearizing feedforward–feedback control of pH processes based on the Wiener model

This paper examines the control of pH processes based on the Wiener model construct (a dynamic linear element representing the mixing dynamics of the process in series with a static nonlinearity representing the titration curve). Conditions under which the pH process behaves like an exact Wiener system are examined. Linearization by output transformation using both the true inverse of the titration curve and an estimate of the inverse is employed to make the pH process appear linear enabling the application of a linear feedback (PI) controller. Although many others have utilized an identified nonlinearity for linearizing feedback control of pH processes, much less work has been done on using the nonlinearity for linearizing feedforward control. Here, a simple linearizing feedforward controller is proposed based on a current estimate of the inverse titration curve. Simulated closed-loop results demonstrate the superiority of the linearizing feedforward–feedback strategy versus linearizing feedback only, when the inverse titration curve is accurately estimated.     

Stabilization of a chemostat model with Haldane growth functions and a delay in the measurements

The stabilization of equilibria in chemostats with measurement delays is a complex and challenging problem, and is of significant ongoing interest in bioengineering and population dynamics. In this paper, we solve an output feedback stabilization problem for chemostat models having two species, one limiting substrate, and either Haldane or Monod growth functions. Our feedback stabilizers depend on a given linear combination of the species concentrations, which are both measured with a constant time delay. The values of the delays are unknown. Instead, one only knows an upper bound on the delays, and we allow the upper bound to be arbitrarily large. The stabilizing feedback depends on the known upper bound for the delays as well. Our work is based on a Lyapunov-Krasovskii argument.     

Minimizing the feedback matrix norm in modal control problems

In this work, we propose algorithms for optimizing the choice of feedback in the modal control problem in multidimensional linear systems with the criterion of minimizing the norm of the feedback matrix. The proposed approaches to solving this problem are based on representing the original system in an orthonormal basis. In particular, representing controllability in a block form lets us divide a high dimensional optimization problem into optimization subproblems of lower dimension. We pay special attention to finding the initial value of the feedback matrix with suboptimal search procedures. We give recommendations on constructing numerical search procedures for suboptimal solutions with gradient-based methods. The efficiency of the developed algorithms is demonstrated with numerical examples.     

A separation principle for distributed dissipative bilinear systems

The problem of input-output stabilization is generalized from finite dimensional bilinear systems to a class of distributed bilinear systems. The solution is based on the nonlinear feedback stabilization results given previously by the authors (1999), with the observers presented by the same authors (1997) in another work.     

Output feedback control of nonlinear systems subject to sensor data losses

In this work, we focus on output feedback control of nonlinear systems subject to sensor data losses. We initially construct an output feedback controller based on a combination of a Lyapunov-based controller with a high-gain observer. We then study the stability and robustness properties of the closed-loop system in the presence of sensor data losses for both the continuous and sampled-data systems. We state a set of sufficient conditions under which the closed-loop system is guaranteed to be practically stable. The theoretical results are demonstrated using a chemical process example.