Cascade design for formation control of nonholonomic systems in chained form

This paper presents a constructive method to design a cooperative state and output feedback to steer a group of nonholonomic mobile robots in chained form to form a desired geometric formation shape. The control methodology divides the resulting tracking error dynamics into a cascaded of linear and time-varying subsystems. A basic consensus algorithm is first applied to the linear subsystem which makes the states synchronize exponentially to zero. Once this first linear subsystem has converged, the second cascade can be treated as a linear time-varying subsystem perturbed by a vanishing term from its cascade. A dynamic state and output feedback is constructed to achieve synchronization of the rest of the states. The proof of stability is given using a result from cascade systems. Since time delay appears in many interconnection networks and particularly in cooperative control, its effect on the stability of the closed-loop system is analyzed using Razumikhim theorem. It is shown that the established cooperative controller work well even in the presence of time delay. Numerical simulations are performed on models of car-like mobile robots to show the effectiveness of the proposed cooperative state and output-feedback controllers.     

Simple algebraic criteria for stability of neutral delay-differential systems

The asymptotic stability of linear neutral systems with a single delay is investigated in this article. Based on the characteristic equation, new algebraic criteria for the stability of the system are derived in terms of the spectral radius of corresponding modulus matrices. The significance of our new criteria is that it takes into consideration the structure information of the system matrices, thus reducing the conservatism found in the literature. Numerical examples are given to demonstrate the new stability criteria and to compare them with the previous results in the literature.     

Global asymptotic stabilization for input-delay chained nonholonomic systems via the static gain approach

In this paper, a novel control strategy is proposed for asymptotically stabilizing chained nonholonomic systems with input delay. Firstly, by using the input-state-scaling technique and the static gain control method, the stabilization control problem of such systems is transformed into designing two gain parameters to stabilize a class of generalized feedback systems with state delay. Then, based on the Lyapunov–Krasovskii theorem, the stability analysis of the closed-loop systems is achieved by the appropriate selection of the gain parameters, and the state and output feedback controllers are constructed simultaneously. An illustrative example is also provided to demonstrate the effectiveness of the proposed strategy.     

On iterative refinement of triangular linear algebraic systems

In this paper the “convergence” of an iterative refinement procedure for solving triangular linear algebraic systems is proved. The application of this procedure to the “accurate” LU decomposition of near-singular systems is described. A simple numerical example illustrates the theory.     

Output feedback control for a class of high-order nonholonomic systems with complicated nonlinearity and time-varying delay

This paper considers the output feedback control problem for high-order nonholonomic time-delay system. Remarkably, the studied system allows the polynomial time-delay growing conditions. Moreover, the applicable power ranges of nonlinear drift and diffusion terms are further relaxed to be a interval rather than a fix point. By choosing a new Lyapunov–Krasovskii (L–K) functional, and by modifying the adding a power integrator method, a delay-independent output feedback controller is designed such that the system is globally asymptotically stable. A simulation example is given to show the validity of the proposed theory.     

Frequency-shifting-based stable on-line algebraic parameter identification of linear systems

In this paper a new approach to algebraic parameter identification of the linear SISO systems is proposed. The standard approach to the algebraic parameter identification is based on the algebraic derivatives in Laplace domain as the main tool for algebraic manipulations like elimination of the initial conditions and generation of linearly independent equations. This approach leads to the unstable time-varying state-space realization of the filters for the on-line parameter estimation. In this paper, the finite difference and shift operators in combination with the frequency-shifting property of Laplace transform is applied instead of algebraic derivatives. Resulting state-space realization of the estimator filters is asymptotically stable and doesn’t require switch-of mechanism to prevent overflow of the estimator variables. The proposed method is especially suitable for applications in closed-loop on-line identification where the stable behavior of the estimators is a necessary requirement. The efficiency of the proposed algorithm is illustrated on three simulation examples.     

A cost-effective wireless network migration planning method supporting high-security enabled railway data communication systems

As a typical railway Cyber-physical System (CPS), radio-based train control systems have been playing an increasingly important role in rail transit. The engaged network, Global System for Mobile Communications for Railway (GSM-R), which is an out-dated wireless communication technology, will be decommissioned due to diminishing support from industry, and a new generation successor, e.g. Long-Term Evolution (LTE), is urgently required to replace the current network. The radio-based train control systems must be safety critical, which relies on a high-security Data Communication System (DCS). In this paper, a novel wireless network migration methodology in DCS is proposed. By using this methodology, the high-security required DCS performance in radio-based train control systems is maintained and the network migration cost, e.g. the used number of base station (BS), is reduced when updating the GSM-R to LTE.     

Convergence analysis of Newton method without inversion for solving discrete algebraic Riccati equations

In this paper, we first introduce the necessary and sufficient conditions for the existence of the solution of discrete algebraic Riccati equation. Then we propose the Newton method without inversion to find the solution of the discrete algebraic Riccati equation. We show that the proposed method converges to a positive definite solution of the discrete algebraic Riccati equation. Finally, the accuracy and effectiveness of the proposed method in compare to some existing algorithms are demonstrated by various numerical examples.     

Stability-equation method for sampled-data systems

This paper presents a new transformation by which the stability-equation method can be applied for analysis and design of sampled-data systems. New stability criteria applicable to systems with transfer function having both real and complex coefficients are presented. Several kinds of examples are considered with computer results given.     

Fixed-time leader-following consensus of multiple uncertain nonholonomic systems: An adaptive distributed observer approach

This paper discusses the fixed-time leader-following consensus problem for multiple uncertain nonholonomic systems, which are widely used in engineering models. According to our literature review, either the system is assumed to be known, or the uncertainty only contains state information, which does not meet the actual requirements. For this reason, this paper investigates more general nonholonomic systems with uncertainties driven by inputs and states. First, a fixed-time adaptive distributed observer is proposed to estimate the leader’s state and structural parameters, which ensures that the estimation errors converge to zero within a fixed time. Second, two regulator equations based on the idea of cooperative output regulation are constructed, and a novel observer-based distributed switching control law is proposed. This control law overcomes the nonholonomic constraints and appropriately relaxes the assumptions of uncertain functions in the existing references. Finally, the simulation results verify the effectiveness of the proposed control scheme.     

Coordination of nonholonomic mobile robots for diffusive threat defense

This paper studies coordination of a team of nonholonomic mobile robots with smart actuators for defending against invasive threat to a planar convex area. The threat refers to a kind of harmful substance such as chemical pollutant appearing outside and moving towards the area. The invasion of threat can be modeled by a 2D unsteady reaction-diffusion process. To reflect the adverse effect of threat on the area, a so-called risk intensity field is introduced. The value of risk intensity is equal to the concentration of threat measured by a static mesh sensor network. Based on this risk intensity field, a coordination control scenario using Voronoi tessellation is formulated. In order to minimize the actuator performance loss and reduce the total average risk intensity simultaneously, a generalized centroidal Voronoi tessellation (CVT) algorithm including optimal motion control and risk mitigation control is designed. The proposed algorithm is gradient-based and guides mobile robots to track their optimal trajectories asymptotically. Meanwhile, two conditions of choosing control gains are derived to keep the total average risk intensity below a safety level. Several simulation examples with different cases of threat invasion are provided and the advantage of proposed algorithm over traditional control method is presented.     

多媒体处理器运动估计数据存取新方法

针对多媒体处理时运动估计引起的巨大计算量的问题,提出了一种简化的运动估计方法,当更新搜索窗口的数据时,仅更新搜索窗口移动后发生变化的一列宏块数据,从而减少更新量,提高多媒体处理的运算性能.     

Managing information systems for urban and regional planning in Asian metropolitan regions

Information management is a neglected function of urban and regional planning in Asian metropolitan regions. Although some kind of information systems exist, these are mostly used for general administration and not for urban and regional planning. The critical factors which appear to impede the implementation of information systems are the inability to define the information needs, lack of systematic and disaggregated data, reliance on secondary sources and administrative records, lack of effective data processing devices, shortage of skilled personnel for data analysis, inadequate and defective methods and procedures for monitoring and evaluation, and limited resources for the adoption of information systems and technology. Some international organizations are increasingly committed to assisting the developing countries in practical programmes and pilot demonstration projects geared to the development of information systems for planning.     

平面八连杆和九连杆机械臂关节角无偏差运动规划验证

基于平面三连杆,PUMA560,PA10等机械臂的计算机仿真结果证实了二次型性能指标方案用于冗余机械臂关节角无偏差运动规划的有效性。为了进一步验证该二次型性能指标优化方案,本文以高度冗余的平面八连杆和九连杆机械臂为例进行计算机仿真验证,仿真结果证实了该方案对解决高度冗余平面机械臂的关节角偏差问题是可行且有效的。     

A two-step iterative method for discrete-time systems reduction

A two-step iterative method (1,2) for a reduction in the order of linear continuous-time systems, given in the state equation or the transfer function, is extended to reduce discrete-time systems. The method requires the optimization of the residues and eigenvalues (or poles) belonging to an objective function. The objective function to be minimized is chosen as the finite sum of the squares of the error between the step responses of the reduced model and the original system. This scheme is continued cyclically until the objective function is satisfactorily minimized. By investigating the initial selection of the eigenvalues in the reduced-order model, it is found that the dominant eigenvalues of the original system give a good approximation. Further, the resulting model is always stable, assuming the original system is stable. As shown in a numerical example, the proposed method is superior to the other methods of model reduction in both steady-state and transient responses, and in the value of the sum of the squares of the error.     

A method for the integer-order approximation of fractional-order systems

A procedure for approximating fractional-order systems by means of integer-order state-space models is presented. It is based on the rational approximation of fractional-order operators suggested by Oustaloup. First, a matrix differential equation is obtained from the original fractional-order representation. Then, this equation is realized in a state-space form that has a sparse block-companion structure. The dimension of the resulting integer-order model can be reduced using an efficient algorithm for rational L₂ approximation. Two numerical examples are worked out to show the performance of the suggested technique.     

Interval approximation method for stability analysis of time-delay systems

This paper studies the stability analysis of linear systems with time-varying delay, which is supposed to be the trigonometric form. By utilizing the characteristics between time-varying delay and its derivative, a novel interval approximation method is proposed, which provides the new allowable delay sets. Then making use of Wirtinger inequality, reciprocally convex inequality and the looped Lyapunov–Krasovskii functionals, the stability criteria with less conservatism are obtained. Finally, two examples are used to show the effectiveness and efficiency of the stability criteria.     

Experimental validation of a practical nonlinear control method for hydraulic flight motion simulator

The hydraulic flight motion simulator (HFMS), as a key equipment for hardware-in-the-loop (HWIL) simulation in the field of aerospace, is required to have the ability to accurately simulate the aircraft attitude in the laboratory. However, three model uncertainties including nonlinear friction torque, unbalanced gravity torque and time-varying inertia existing in the outer frame of the HFMS at the same time become a main obstacle to achieving its high-precision position control effect. In this paper, according to identification results of friction torque and gravity torque from experiments, combining with simulation result of time-varying inertia of the outer frame from virtual prototype, a disturbance-observer-based nonlinear robust controller with the model compensation was designed on the basis of the mathematical model. Here, since the model compensation has eliminated the main mismatched uncertainties, dual disturbance observers are only necessary to suppress unmodeled mismatched uncertainties and matched uncertainties. Furthermore, the zero bias of the servo valve was also considered to help controller implementation. Finally, the effectiveness and the practicability of the proposed control method were validated by comparative experiments, which demonstrates that the proposed control method is promising and can be applied in the high-precision position control for the HFMS.     

Wearable skin-like optoelectronic systems with suppression of motion artifacts for cuff-less continuous blood pressure monitor

According to the statistics of the World Health Organization, an estimated 17.9 million people die from cardiovascular diseases each year, representing 31% of all global deaths. Continuous non-invasive arterial pressure (CNAP) is essential for the management of cardiovascular diseases. However, it is difficult to achieve long-term CNAP monitoring with the daily use of current devices due to irritation of the skin as well as the lack of motion artifacts suppression. Here, we report a high-performance skin-like optoelectronic system integrated with ultra-thin flexible circuits to monitor CNAP. We introduce a theoretical model via the virtual work principle for predicting the precise blood pressure and suppressing motion artifacts, and propose optical difference in the frequency domain for stable optical measurements in terms of skin-like devices. We compare the results with the blood pressure acquired by invasive (intra-arterial) blood pressure monitoring for >1500 min in total on 44 subjects in an intensive care unit. The maximum absolute errors of diastolic and systolic blood pressure were ±7/±10 mm Hg, respectively, in immobilized, and ±10/±14 mm Hg, respectively, in walking scenarios. These strategies provide advanced blood pressure monitoring techniques, which would directly address an unmet clinical need or daily use for a highly vulnerable population.