Receding horizon time-optimal control for a class of differentially flat systems

A closed-loop, time-optimal path-following control scheme is proposed for a class of constrained differentially flat systems. Within a receding horizon framework, a finite horizon optimisation problem is solved at each sample, using available state feedback and feedforward path information. Irrespective of horizon length, the proposed formulation guarantees exact path-following. Moreover, the requirements under which the proposed algorithm achieves minimum-time path-following are established. Simulations conducted with a rigid X–Y table model confirm the theoretical results.     

Indoor low-cost localization system for controlling aerial robots

This paper presents a low-cost localization system to guide an Unmanned Aerial Vehicle (UAV) in indoor flights, considering an environment with invariant texture and typical indoor illumination. The first contribution of the paper is the proposal of a system to estimate the position and orientation of the UAV, through a multi-sensor fusion scheme, dealing with data provided by a RGB-D sensor, an inertial measurement unit (IMU), an ultrasonic sensor and optical flow-based velocity estimates. A second contribution of the paper is the proposal of a high-level control system to guide the UAV in path-following tasks, involving two controllers: a kinematic one, responsible for generating reference velocities for the vehicle, and a PD one, responsible for tracking such reference velocities, thus characterizing a cascade controller. Experiments with such a localization and control systems, during which abrupt disturbances are applied, were carried out to check the effectiveness of the developed capture and control systems, whose results validate the proposed framework.     

两种连接形式的拖挂式移动机器人路径跟踪控制

拖挂式移动机器人是一种具有不同连接形式的多车体系统.本文对标准连接和非标准连接的拖挂式机器人,研究了前向和倒车路径的跟踪控制.首先,建立系统的运动学模型并进行运动特性分析;其次,基于Lyapunov方法提出一种与期望路径具有一致运动方向的单体机器人全局路径跟踪控制器;然后将其引入到两种拖挂式机器人的前向跟踪控制中,并分别通过运动学变换和反演控制实现了两种连接形式下的倒车跟踪控制,从而使多节车体始终保持一致的运动方向,避免了不合理位形的出现.仿真结果表明该方法的有效性.     

A quadratically convergent procedure for the calculation of stability points in finite element analysis

In this paper a new finite element formulation is given for the analysis of nonlinear stability problems. The introduction of extended systems opens the possibility to compute limit and bifurcation points directly. Here, the use of the directional derivative yields a quadratically convergent iteration scheme. The combination with arc-length and branch-switching procedures leads to a global algorithm for path-following.     

Quantized stabilizing control of state-dependent switching affine systems with control-input and state-measurement quantization

This paper addresses stability analysis and quantized stabilization of discrete-time state-dependent switching affine systems with quantized control inputs and state measurements. The employed controller is in a mode-dependent affine form to improve the adaptation to the mode of the controlled system and then to acquire less conservative results. The quantization scheme is considered to be logarithmic and synchronized with the mode switching of the switching affine system and the controller. Aiming at achieving lower conservative criteria, a mode-dependent Lyapunov function incorporating quantization uncertainties is constructed. Correspondingly, the stability analysis and the stabilizing control synthesis are implemented. In the end, the proposed quantized control strategy is applied to a vehicle path-following problem to exemplify its effectiveness and robustness against data quantization in control inputs and state measurements.     

自动测试系统自检方案设计

大型自动测试系统测试仪器、开关的种类、型号、数量都较多,因此全系统自检有较大难度。分析一般自动测试系统基于仪器自检的系统自检、基于仪器比对的系统自检、基于开关切换的系统自检等方案,给出一种综合自检方案。该方案分为仪器自检、关键仪器测试、开关系统测试和仪器比对4个步骤,能可靠地检验自动测试系统通用部分的可用性。     

非完整移动机器人全局路径跟踪控制

根据制导路径跟踪理论,提出了一种非完整移动机器人全局路径跟踪控制方法.这一方法首先在路径坐标系上计算实际位置与期望位置的误差,利用制导的路径跟踪理论,导出消除该误差所需的姿态角和路径参数更新律,然后据此求解角速度及实际控制.文中还给出了初始路径参考点的计算方法,分析了路径跟踪方向和反转方法.稳定性分析证明该方法没有控制奇异点,受控闭环系统全局一致渐近稳定.最后通过移动机器人典型路径跟踪实验验证了所提出方法的可行性.     

A highly scalable path-following controller for N-trailers with off-axle hitching

The paper presents a highly scalable nonlinear cascaded-like path-following feedback controller for N-trailer robotic vehicles equipped with arbitrary number of off-axle hitched trailers. In contrast to the other path-following control laws proposed in the literature for N-trailer robots, the presented control approach does not require determination of the shortest distance to a reference path. By introducing the so-called segment-platooning reference paths, and under the sign-homogeneity assumption for hitching offsets, the asymptotic following is guaranteed for both constant- and varying-curvature reference paths using either backward or forward vehicle motion strategy with a guidance point fixed on the last trailer. The paper contains experimental results obtained with a 3-trailer laboratory-scale vehicle.     

Path-following for nonminimum phase systems removes performance limitations

We highlight an essential difference between path-following and reference-tracking for nonminimum phase systems. It is well known that in the reference-tracking, for nonminimum phase systems, there exists a fundamental performance limitation in terms of a lower bound on the L/sub 2/-norm of the tracking error, even when the control effort is free. We show that this is not the case for the less stringent path-following problem, where the control objective is to force the output to follow a geometric path without a timing law assigned to it. Furthermore, the same is true even when an additional desired speed assignment is imposed.     

Path-following for linear systems with unstable zero dynamics

A constructive solution to the path-following problem for MIMO linear systems with unstable zero dynamics is developed. While the original control variable steers the system output along the path, the path parameter θ is used as an additional control to stabilize zero dynamics with a feedback law which is nonlinear due to the path constraint. A sufficient condition for solvability of the path-following problem is given in terms of the geometric properties of the path. When this condition is satisfied, an arbitrary small L₂ norm of path-following error can be achieved, thus avoiding performance limitations of the standard reference tracking problem imposed by unstable zero dynamics.     

Passivity-based designs for synchronized path-following

We consider a formation control system where individual systems are controlled by a path-following design and the path variables are to be synchronized. We first show a passivity property for the path-following system, and next, combine this with a passivity-based synchronization algorithm developed in Arcak [2007. Passivity as a design tool for group coordination. IEEE Transactions on Automatic Control, in press]. The passivity approach expands the classes of synchronization schemes available to the designer. This generality offers the possibility to optimize controllers to, e.g., improve robustness and performance. Two designs are developed in the proposed passivity framework: the first employs the path error information in the synchronization loop, while the second only uses synchronization errors. A sampled-data design, where the path variables are updated in discrete-time and the path-following controllers are updated in continuous time, is also developed.     

Frequency domain criteria for strict aperiodicity of linear interval systems

Interval systems arise when systems experience parameter variations. This paper derives frequency domain criteria for interval systems to be strictly aperiodic. The frequency domain criteria only requires one frequency domain plot to check for strict aperiodicity of linear interval systems. Furthermore, the largest allowable perturbation bounds can be graphically estimated from the same frequency domain plot.     

Motion coordination and reactive control of autonomous multi-manipulator systems

The emerging field of service robots demands new systems with increased flexibility. The flexibility of a robot system can be increased in many different ways. Mobile manipulation—the coordinated use of manipulation capabilities and mobility—is an approach to increase robots flexibility with regard to their motion capabilities. Most mobile manipulators that are currently under development use a single arm on a mobile platform. The use of a two-arm manipulator system allows increased manipulation capabilities, especially when large, heavy, or non-rigid objects must be manipulated. This article is concerned with motion control for mobile two-arm systems. These systems require new schemes for motion coordination and control. A coordination scheme called transparent coordination is presented that allows for an arbitrary number of manipulators on a mobile platform. Furthermore, a reactive control scheme is proposed to enable the platform to support sensor-guided manipulator motion. Finally, this article introduces a collision avoidance scheme for mobile two-arm robots. This scheme surveys the vehicle motion to avoid platform collisions and arm collisions caused by self-motion of the robot. © 1996 John Wiley & Sons, Inc.     

Simultaneous path-following and vibration control for uncertain nonlinear flexible mechanical systems without dependency on oscillatory mathematical model

Multibody System Dynamics - In this paper, a novel multiobjective algorithm for simultaneous path-following control (PFC) of multivariable flexible dynamical systems and maintaining...     

基于列表签名的安全电子投票方案

列表签名是群签名的一个推广,对用户签名的次数作了有效限制并增加了公开检测和公开身份验证。本文基于列表签名提出可用于大规模选举的电子投票方案,任何人都可以对不诚实投票行为进行验证;若不诚实投票者投出超过一张的选票,则任何人都可以通过选票中的签名进行检测并确定不诚实签名者的身份。该方案同时保证了选票的唯一性
性、秘密性、可验证性和公平性,具有较高的通信效率和安全性。     

A new electronic traveler’s check scheme based on one-way hash function

Nowadays, electronic commerce is booming on the Internet and becoming more popular. Many kinds of electronic services have been developed. The most successful are the electronic payment systems such as the electronic cash/check and wallet. Most electronic payment systems are based on an elaborate discrete logarithm that raises an important issue regarding efficiency. Therefore, Hsien et al. proposed an electronic traveler’s check system in 2001 using a discrete logarithm. In this paper, we propose a new electronic traveler’s check system based on one-way hash function to improve efficiency and cost. Furthermore, our proposed scheme supports an on-line and off-line electronic traveler’s check system of practical flexibility for use in the real world.     

Viscoelastic model based force control for soft tissue interaction and its application in physiological motion compensation

Controlling the interaction between robots and living soft tissues has become an important issue as the number of robotic systems inside the operating room increases. Many researches have been done on force control to help surgeons during medical procedures, such as physiological motion compensation and tele-operation systems with haptic feedback. In order to increase the performance of such controllers, this work presents a novel force control scheme using Active Observer (AOB) based on a viscoelastic interaction model. The control scheme has shown to be stable through theoretical analysis and its performance was evaluated by in vitro experiments. In order to evaluate how the force control scheme behaves under the presence of physiological motion, experiments considering breathing and beating heart disturbances are presented. The proposed control scheme presented a stable behavior in both static and moving environment. The viscoelastic AOB presented a compensation ratio of 87% for the breathing motion and 79% for the beating heart motion.     

Two-dimensional wave propagation in a nonlinear elastic half-space

Finite amplitude wave propagation in an elastic, isotropic half-space is investigated. A numerical scheme that was previously developed and shown to yield satisfactory accurate results whenever smooth solutions occur is modified here for the cases in which steep solutions are obtained. The stability analysis of the proposed numerical procedure is carried out, and the stability criteria are given in terms of the spectral radii of the matrices involved in the equations of motion. The hyperbolicity conditions of the equations of motion are derived and shown to impose restrictions on the possible values of displacement gradients so that the range of variation of the strength of the applied load is limited. As a first chek of the accuracy of the numerical results, a propagating shock wave is produced numerically and compared with the analytical solution. In a second check, propagating circularly polarized waves are numerically simulated and compared with the corresponding analytical solution. In each case good agreement is obtained. For the “quadratic material” adopted in this paper, it is shown that a compressive normal line force yields propagating pulses having larger amplitudes, broader widths and larger arrival times, as compared with those caused by a tensile one. The linear response is also shown for comparison.     

A new electronic traveler’s check scheme based on one-way hash function

Nowadays, electronic commerce is booming on the Internet and becoming more popular. Many kinds of electronic services have been developed. The most successful are the electronic payment systems such as the electronic cash/check and wallet. Most electronic payment systems are based on an elaborate discrete logarithm that raises an important issue regarding efficiency. Therefore, Hsien et al. proposed an electronic traveler’s check system in 2001 using a discrete logarithm. In this paper, we propose a new electronic traveler’s check system based on one-way hash function to improve efficiency and cost. Furthermore, our proposed scheme supports an on-line and off-line electronic traveler’s check system of practical flexibility for use in the real world.     

An Adaptive Control Technique for Motion Synchronization by On-line Estimation of a Recursive Least Square Method

This article presents an adaptive technique to tune controller gains for the motion synchronization of two gimbal systems by using a recursive least square method in the real-time fashion. In the master-slave configuration, the slave gimbal system follows the master’s motion while the master tracks the reference. In order for the slave gimbal system to synchronize with the motion of the master gimbal system, the dynamic difference between two systems is compensated by the controller gains. The controller gains of the slave are adaptively adjusted by the recursive least square method to cope with the deviation. The performances of three control schemes such as an independent PD control, a dependent torque control, and an RLS torque control scheme are evaluated by the experimental studies for the low cost gimbal systems. Experimental studies confirm that the RLS-based adaptive scheme actually outperforms by adjusting controller gains for the motion synchronization of the master and slave configuration.