Design and Modeling of a Snake Robot Based on Worm-Like Locomotion

In this paper we restrict our attention to worm-like, vertical traveling wave locomotion and present detailed kinematics and dynamics of a planar multi-link snake robot. Lagrange's method is used to obtain the robot dynamics. Webots software is used for simulation and to experimentally investigate the effects of link shape on motor torques. Using the dynamics model and Webots simulation, a nine-link snake robot is designed and constructed. Physical experiments are carried out to validate the mathematical model. Webots software is also used to perform simulation and further validate theoretical results. Finally, stability of the snake robot is experimentally investigated.     

A multi-link system control strategy based on biological reaching movement

In the multi-link arm control process, the problems of trajectory planning and trajectory realization have been recognized as being of key importance. We developed a technique by which to realize a reaching movement control of the multi-link arm system, which was inspired by experimental results for reaching movements of macaques or human beings. The proposed method can treat the effect of the dynamics of the multi-link system and the trajectory planning of the end-effector, which has a bell-shaped speed profile, as well as the difficulties of redundancies of multi-link systems. Two-link arm reaching movement experiments revealed the same features, as demonstrated by the results of biological experiments on humans and macaques. In addition, the results obtained using a two-dimensional four-link model in a standing-up movement control experiment agreed well with 'standing-up from a chair' movement of human beings. Since the proposed method has a simple structure and its implementation process is simple, the proposed method will be effective for use in a multi-link system control strategy.     

Nonlinear generalized equations of motion for multi-link inverted pendulum systems

In this paper, the equations of motion for a general multi-link inverted pendulum system are derived. Assumptions previously employed to simplify such formulation are removed. The pendulum system is more general and includes nonlinear friction terms to suit various engineering applications. The generalized equations are first developed in the absolute coordinate system using Lagrange's technique, then a simple linear transformation is proposed to obtain the set of nonlinear equations in the DevanitHartenberg coordinate system. The equations of motion for double and triple link inverted pendulum systems are given as examples for such dynamics equations.     

多链路权值增大的动态最短路径算法

动态网络最短路径是交通、通信等系统中的重要问题。在处理多链路权值变大时,多链路权值增大的动态最短路径算法可有效地减少单链路权值增大动态最短路径算法的冗余计算。目前,多链路权值增大的动态最短路径算法的研究较少,尚未存在有效的多链路变大的动态最短路径算法。通过对现有动态最短路径算法的深入研究,提出了一种多链路权值增大的动态最短路径算法(DSPT-MLI)。算法复杂度分析和仿真结果显示,DSPT-MLI算法具有更少的节点更新次数和更高的时间效率。     

Multibody system dynamics simulator for process simulation of ships and offshore plants in shipyards

Since various existing simulation tools based on multibody system dynamics focus on conventional mechanical systems, such as machinery, cars, and spacecraft, there are some problems with the application of such simulation tools to shipbuilding domains due to the absence of specific items in the field of naval architecture and ocean engineering, such as hydrostatics, hydrodynamics, and mooring forces. Thus, in this study, we developed a multibody system dynamics simulator for the process simulation of ships and offshore structures. We based the simulator on six kernels: the multibody system dynamics kernel, the force calculation kernel, the numerical analysis kernel, the hybrid simulation kernel, the scenario management kernel, and the collision detection kernel. Based on these kernels, we implemented a simulator that had the following Graphic User Interfaces (GUIs): the modeling, visualization, and report GUIs. In addition, the geometric properties of blocks and facilities in shipyards are needed to configure the simulation for the production of ships and offshore plants, so these are managed in a database and connected to a specific commercial CAD system in shipyards. We used the simulator we developed in various cases of the process simulation of ships and offshore plants. The results show that the simulator is useful for various simulations of operations in shipyards and offshore industries.     

航空器多链路通信故障中断点云检测系统设计

为解决传统断点云检测系统中高频短消息传输精度较低、集成挖掘数据链长度受限等问题,提出设计一种航空器多链路通信故障中断点云检测系统。通过确定断点故障内点的方式,达到对多链路通信信道进行鲁棒性优化的目的,并根据待传输信息的总量限制条件,更新云检测流程,构建新型断点云检测模型。利用多链路通信寻址报文数据译码结果作为航空器多链路通信故障中断点的识别参数校验基准,并对上行报文进行显示识别处理,完成通信故障中断点的报文参数识别。将报文参数应用到新型断点云检测模型中,完成航空器多链路通信故障中断点的云检测。与传统检测系统段相比,应用新型断点云检测模型后,检测系统的高频短消息传输精度可以达到95%,集成挖掘数据链长度也得到大幅提升,确保了断点的云检测准确性。     

柔性关节机器人高精度自适应反步法控制

为实现多连杆柔性关节机器人的高精度运动控制,首先对其建立完整的动力学模型,包含了连杆和关节动力学的耦合项、LuGre动态摩擦模型和关节回差等因素．然后针对该模型设计带观测器的自适应反步法控制器,对不可测项进行在线估计和补偿．理论分析证明了观测器的收敛性和闭环系统的稳定性．该方法在一个3DOF（degree of freedom）柔性关节机器人上进行仿真,仿真结果验证了观测器的有效性,并表明该控制器能够降低连杆跟踪误差,实现良好的轨迹跟踪效果．     

FluNet: A hybrid internet simulator for fast queue regimes

Motivated by the scale and complexity of simulating large-scale networks, recent research has focused on hybrid fluid/packet simulators, where fluid models are combined with packet models in order to reduce simulation complexity as well as to track dynamics of end-sources accurately. However, these simulators still need to track the queuing dynamics of network routers, leading to considerable simulation complexity in a large-scale network model. In this paper, we propose a new hybrid simulator – FluNet – where queueing dynamics are not tracked, but instead, an equivalent rate-based model is used. The FluNet simulator is predicated on a fast-queueing regime at bottleneck routers, where the queue length fluctuates on a faster time-scale than end systems. This allows us to simulate large-scale systems, where the simulation “time step-size” is governed only by the time-scale of the end-systems, and not by that of the intermediate routers; whereas a queue-tracking based fluid simulator would require decreasingly smaller step-sizes as the system scale size increases. We validate our model using a ns-2 based implementation. Our results indicate a good match between packet systems and the associated FluNet system.     

Flexible Links Manipulators: from Modelling to Control

This paper relates recent results obtained in the field of modelling and control of flexible link manipulators and proposes an investigation of the problem raised by this type of systems (at least in the planar case). First, adopting the modal floating frame approach and the Newton–Euler formalism, we propose an extension of the models for control to the case of fast dynamics and finite deformations. This dynamic model is based on a nonlinear generalisation of the standard Euler–Bernoulli kinematics. Then, based on the models recalled we treat the end-effector tracking problem for the one-link case as well as for the planar multi-link case. For the one-link system, we propose two methods, the first one is based on causal stable inversion of linear non-minimum phase model via output trajectory planning. The other one is an algebraic scheme, based on the parametrization of linear differential operators. For the planar multi-link case the control law proposed is based on causal stable inversion over a bounded time domain of nonlinear non-minimum phase systems. Numerical tests are presented together with experimental results, displaying the well behaved of these approaches.     

Contact control for advanced applications of light weight arms

Many applications of robotic and teleoperated manipulator arms require operation in contact and noncontact regimes. This paper deals with both regimes and the transition between them with special attention given to problems of flexibility in the links and drives. This is referred to as contact control. Inverse dynamics is used to plan the tip motion of the flexible link so that the free motion can stop very near the contact surface without collision due to overshoot. Contact must occur at a very low speed since the high frequency impact forces are too sudden to be affected by any feedback generated torques applied to a joint at the other end of the link. The effects of approach velocity and surface properties are discussed. Force tracking is implemented by commands to the deflection states of the link and the contact force. This enables a natural transition between tip position and tip force control that is not possible when the arm is treated as rigid. The effects of feedback gain, force trajectory, and desired final force level are of particular interest and are studied. Experimental results are presented on a one-link arm and the system performance in the overall contact task is analyzed. Extension to multi-link cases with potential applications are discussed.     

大时延对拥塞控制系统性能的影响及补偿方法

针对大时延对计算机网络拥塞控制系统性能的影响,设计了一种基于Smith预估器的拥塞控制算法,并将其推广到多条链路的情况;该算法实现简单,适合计算机控制系统实现,在大时延网络中具有实际应用价值#仿真结果表明,该算法动态响应快,能够有效克服大时延对系统性能的不利影响,大大抑制了队列的不稳定振荡,提高了链路利用率。     

Evaluation of driver’s behavior with multibody-based driving simulator

This paper deals with a driving simulator with a multibody vehicle model. Driving simulators require a real-time calculation of vehicle dynamics in response to driver’s inputs, such as a steering maneuver or a brake pedal operation. The authors realized a real-time calculation with a multibody vehicle model by approximating the calculation of constraint equations, and developed a driving simulator with 6-axes motion system. Drivers can feel the multibody analysis results through body sensory information such as the acceleration produced by the motion system and the visual information generated by computer graphics with the developed MBS simulator system. In this paper, a closed-loop test of a human-automobile system was investigated with the developed MBS driving simulator. In this evaluation, the driving simulator system and driver’s behavior were included in a multibody dynamics analysis, so it consists of a hardware- and human-in-the-loop simulation. It was observed from test results that the driving behavior was changed according to the parameters of the multibody vehicle model.     

Predictive end-point trajectory control of elastic manipulators

This article presents an approach to end-point trajectory control of elastic manipulators based on the nonlinear predictive control theory. Although this approach is applicable to manipulators of general configuration, only planar flexible multi-link manipulators are considered. A predictive control law is derived by minimizing a quadratic function of the trajectory error of the end-points of each link, elastic modes, and control torques. This approach avoids the instability of the zero dynamics encountered in the controller design using feedback linearization and variable structure control techniques for end-point control. Furthermore, the derived predictive controller is robust to uncertainty in the system parameters. Simulation results are presented for a one-link flexible manipulator to show that in the closed-loop system accurate end-point trajectory control and vibration damping can be accomplished. © 1996 John Wiley & Sons, Inc.     

Dynamic Modeling Based on Real-Time Deflection Measurement and Compensation Control for Flexible Multi-Link Manipulators

The problem of tip trajectory tracking control is considered in this paper for flexible multi-link manipulators. An integrated optical laser sensor system is utilized to measure the tip deformations of the flexible links. The Lagrangian assumed-mode method incorporating the measured linear displacements and angular deflections of flexible links is used to derive the dynamic model of the flexible manipulator. To reduce as far as possible the tip tracking/positioning errors caused by the link flexibility, an error compensation approach is proposed. The additional compensation amounts of joint variables are calculated kinematically in terms of the measured deformations, and are added to the nominal commands generated by the computed torque controller. The simulation results demonstrate the effectiveness of the proposed approach.     

Adaptive neural network output feedback control for flexible multi-link robotic manipulators

In this paper, a novel approach for adaptive control of flexible multi-link robots in the joint space is presented. The approach is valid for a class of highly uncertain systems with arbitrary but bounded dimension. The problem of trajectory tracking is solved through developing a stable inversion for robot dynamics using only joint angles measurement; then a linear dynamic compensator is utilised to stabilise the tracking error for the nominal system. Furthermore, a high gain observer is designed to provide an estimate for error dynamics. A linear in parameter neural network based adaptive signal is used to approximate and eliminate the effect of uncertainties due to link flexibilities and vibration modes on tracking performance, where the adaptation rule for the neural network weights is derived based on Lyapunov function. The stability and the ultimate boundedness of the error signals and closed-loop system is demonstrated through the Lyapunov stability theory. Computer simulations of the proposed robust controller are carried to validate on a two-link flexible planar manipulator.     

Constraint-Defined Manifolds: a Legacy Code Approach to Low-Dimensional Computation

If the dynamics of an evolutionary differential equation system possess a low-dimensional, attracting, slow manifold, there are many advantages to using this manifold to perform computations for long term dynamics, locating features such as stationary points, limit cycles, or bifurcations. Approximating the slow manifold, however, may be computationally as challenging as the original problem. If the system is defined by a legacy simulation code or a microscopic simulator, it may be impossible to perform the manipulations needed to directly approximate the slow manifold. In this paper we demonstrate that with the knowledge only of a set of “slow” variables that can be used to parameterize the slow manifold, we can conveniently compute, using a legacy simulator, on a nearby manifold. Forward and reverse integration, as well as the location of fixed points are illustrated for a discretization of the Chafee-Infante PDE for parameter values for which an Inertial Manifold is known to exist, and can be used to validate the computational results     

Modeling of flexible-link manipulators with prismatic joints

The axially translating flexible link in flexible manipulators with a prismatic joint can be modeled using the Euler-Bernoulli beam equation together with the convective terms. In general, the method of separation of variables cannot be applied to solve this partial differential equation. In this paper, we present a nondimensional form of the Euler-Bernoulli beam equation using the concept of group velocity and present conditions under which separation of variables and assumed modes method can be used. The use of clamped-mass boundary conditions lead to a time-dependent frequency equation for the translating flexible beam. We present a novel method to solve this time-dependent frequency equation by using a differential form of the frequency equation. We then present a systematic modeling procedure for spatial multi-link flexible manipulators having both revolute and prismatic joints. The assumed mode/Lagrangian formulation of dynamics is employed to derive closed form equations of motion. We show, using a model-based control law, that the closed-loop dynamic response of modal variables become unstable during retraction of a flexible link, compared to the stable dynamic response during extension of the link. Numerical simulation results are presented for a flexible spatial RRP configuration robot arm. We show that the numerical results compare favorably with those obtained by using a finite element-based model.     

Constraint-defined manifolds: A legacy code approach to low-dimensional computation

If the dynamics of an evolutionary differential equation system possess a low-dimensional, attracting, slow manifold, there are many advantages to using this manifold to perform computations for long term dynamics, locating features such as stationary points, limit cycles, or bifurcations. Approximating the slow manifold, however, may be computationally as challenging as the original problem. If the system is defined by a legacy simulation code or a microscopic simulator, it may be impossible to perform the manipulations needed to directly approximate the slow manifold. In this paper we demonstrate that with the knowledge only of a set of “slow” variables that can be used toparameterize the slow manifold, we can conveniently compute, using a legacy simulator, on a nearby manifold. Forward and reverse integration, as well as the location of fixed points are illustrated for a discretization of the Chafee-Infante PDE for parameter values for which an Inertial Manifold is known to exist, and can be used to validate the computational results.     

基于动态规划的多链路出口路径选择算法

针对多链路接入问题,选取链路成本及影响网络性能的路由跳数作为多链路出口路径选择的优化对象,通过建立多目标优化模型,将多链路出口路径选择转化为动态规划问题,提出一个基于动态规划的多链路出口路径选择优化算法。模拟结果表明,该算法能有效提高网络性能,降低网络链路成本。