Performance improvement of the PD-based bilateral teleoperators with time delay by introducing relative D-control

In a force-reflecting bilateral teleoperator with a time delay, teleoperator stability is a serious problem. We have studied a bilateral teleoperator system with a time delay. We obtained stable conditions using proportional derivative-based (PD-based) control law. In this paper, PD-based control law is further studied. First, we study a PD control law with relative damping gain and its stabilizing effect that previously has not been studied quantitatively. A stable condition is derived with this PD-based controller with relative damping gain. Next, teleoperator performance by the PD control law with relative damping is evaluated and compared to PD control laws with only grounded damping using transparency analysis with a hybrid matrix. We showed that, the performance of the PD-based controller can be improved by introducing relative damping gain into the controller. As a controller design example, numerical simulations and 1-DOF experiments were conducted. Finally, peg-in-hole experiments and performance evaluations in realistic multi-DOF environments were conducted to demonstrate performance improvements by introducing the relative damping. A controller design that guarantees both stability and performance was achieved by iterating stable gain setting and performance evaluation.     

Stability of bilateral teleoperators with generalized projection-based force reflection algorithms

A general stability result for bilateral teleoperator systems with projection-based force reflection algorithms from a broad class is presented. It is shown that the overall stability of a teleoperator system can be achieved under mild assumptions on subsystem stability, properties of the communication channel, dynamics of the human operator, and the human force measurement/estimation process. In particular, the stability is achieved under a new general assumption on human dynamics which allows for both passive and nonpassive behaviour of the human operator. It is demonstrated that the use of projection-based force reflection algorithms effectively removes the constraints on subsystem gains that are typical for direct application of the small-gain design, thus solving the trade-off between stability, manoeuvrability, and high force reflection gain in bilateral teleoperation over communication networks.     

Nonlinear adaptive control for teleoperation systems with symmetrical and unsymmetrical time-varying delay

The stability and trajectory tracking control problem of passive teleoperation systems with the presence of the symmetrical and unsymmetrical time-varying communication delay is addressed in this paper. The proposed teleoperator is designed by coupling local and remote sites by delaying position signals of the master and slave manipulator. The design also comprises local proportional and derivative signals with nonlinear adaptive terms to cope with parametric uncertainty associated with the master and slave dynamics. The Lyapunov–Krasovskii function is employed to establish stability conditions for the closed-loop teleoperators under both symmetrical and unsymmetrical time-varying communication delay. These delay-dependent conditions allow the designer to estimate the control gains a priori in order to achieve asymptotic property of the position, velocity and synchronisation errors of the master and slave systems. Finally, simulation results along with comparative studies are presented to illustrate the effectiveness of the proposed method.     

A control scheme for stable force-reflecting teleoperation over IP networks.

The problem of force-reflecting teleoperation over Internet protocol networks is addressed. The existence of time-varying communication delay and the possibility of data losses are taken into consideration. Since significant data loss may result in discontinuity of the reference trajectory transmitted through the communication channel, the proposed control scheme includes a filter that provides a smooth approximation of a possibly discontinuous reference trajectory. The stability of the overall system is guaranteed by a version of the input-to-output stable small-gain theorem for functional differential equations. If the communication delay in the forward channel is an "approximately smooth" function of time, the proposed scheme guarantees that the slave manipulator tracks the delayed trajectory of the master within a prescribed small error.     

Implementation of position–force and position–position teleoperator controllers with cable-driven mechanisms

Bilateral teleoperation involves the motion control of a slave mechanism with a master mechanism that is capable of reflecting the sensory information such as force and torque signals captured from the master mechanism. Normally, the master and slave mechanisms in a teleoperator system are physically separated and are connected via some communication interface. As technology in robotic mechanism design continuously develops, advanced teleoperator systems are emerging. From the handling of hazardous and delicate materials in nuclear decommissioning to medical applications such as orthopedic and laparoscopic surgery, the demand for high bandwidth and fine-force reflecting bilateral teleoperator systems has become more and more important. This paper focuses on the implementation of an advanced master–slave teleoperator system using cable-driven WAM and PHANToM devices. Special emphasis is placed on the pragmatic issues on the implementation based two different designs of the teleoperator control schemes and the performance of the system under these two teleoperator control schemes.     

Cooperative control with distributed gain adaptation and connectivity estimation for directed networks

This paper addresses the problem of how to achieve superior performance by adaptively and distributively adjusting control gains of a cooperative control system. It is shown that according to distributed observations of changing network topologies and on the basis of online estimation of network connectivity, cooperative controls with adaptive gains can be synthesized to making the time derivative of the cooperative control Lyapunov function more negative and hence to improve stability and convergence of the overall system. For undirected networks, the proposed adaptive design reduces to improving the Fiedler eigenvalue (algebraic connectivity) as well as other eigenvalues. On the other hand, connectivity of a directed network is characterized by the property of the first left eigenvector(s) associated with its dominant eigenvalue, and in this paper, a distributed high‐gain observer design is proposed for each of the networked systems to utilize the same communication network among the systems. It is shown that even in the presence of transmission delays, the distributed estimators converge fast to the first left eigenvector(s) of the network. In addition, the expected consensus value(s) of the overall cooperative system under control is also estimated in a distributive manner. Rigorous analysis is carried out on estimation convergence and observer gain selection. It is shown that the proposed estimation and adaptive control designs are fully distributed, have guaranteed performance for all possible varying topologies as long as their dwelling times are bounded away from zero, and are robust with respect to excessively fast topology changes. Simulation results are included to demonstrate effectiveness of the proposed estimation and control schemes. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of quantization and saturation on performance in bilateral teleoperator

Quantization caused by communication channel and saturation caused by manipulator actuator can influence the synchronized motion of bilateral teleoperation system. The primary contribution of this paper is the consideration of quantization phenomenon when designing control law for teleoperator. Two types of control schemes are considered: position error feedback and slave torque feedback. We demonstrate that asymptotic stability is possible if a suitable relationship holds among the parameters of quantizer, controller, and saturation level. The secondary contribution of the paper is the estimation for the domain of attraction of teleoperator. Linear matrix inequality–based optimization conditions are established to guarantee the stability. The calculated region provides a basis when selecting the initial states. Finally, to further demonstrate validity of the proposed method, simulation and experiment are performed on a pair of robots, which have limited actuation capacity and communication channel.     

Control schemes for stable teleoperation with communication delay based on IOS small gain theorem

The problem of stabilization of a force-reflecting telerobotic system in presence of time delay in the communication channel is addressed. We introduce an approach that is based on application of the input-to-output stability (IOS) small gain theorem for functional differential equations (FDEs). A version of the stabilization algorithm as well as its two adaptive extensions are proposed. For all these control schemes, the input-to-state stability (ISS) of the overall telerobotic system is guaranteed in the global, global practical, or semiglobal practical sense for any constant communication delay under the assumption that the environmental dynamics satisfy a weak form of finite-gain stability property. As an intermediate step, we formulate and prove a general IOS (ISS) small gain result for FDEs.     

High‐gain nonlinear observer‐based impedance control for deformable object cooperative teleoperation with nonlinear contact model

Unmeasurable object deformation and local communication time delays between the slave robots influence the manipulation effect for multirobot multioperator teleoperation. In this article, a distributed control method based on high‐gain nonlinear observer, interactive identification, and impedance control is proposed for this problem. First, we use Hunt‐Crossley contact model and deduce the desired synchronizing object state in cooperative teleoperation. Second, an impedance item expressed by the internal position errors is presented to decrease object position tracking errors. For the unmeasurable object deformation, an interactive identification method is proposed for estimating unknown variables. Third, we consider both varying communication time delays and local time delays in the slave side. Two mirror high‐gain nonlinear observers are designed for estimating other slave robots' real‐time state. Finally, we build the system controllers and prove the stability of the closed‐loop system and the boundless of estimating errors using Lyapunov functions. Comparable simulation results executed by the physical system present that the position and internal force tracking errors of the object decrease in the designated cooperative tasks.     

新型机载机电管理系统网络化综合测试研究

针对新型机载机电管理系统功能性能测试需求,提出一种基于EtherCAT总线的网络化测试系统设计方案.该系统的设计采用模块化的设计思想,分别设计嵌入式主站、功能从站,主站与从站间通过EtherCAT总线实现数据通信.该系统具备仿真飞机机电子系统设备的各类输入输出信号与模拟飞管系统总线通信活动功能,可以实现对新型机载机电管理系统功能与性能的验证.测试结果表明,该系统测试覆盖率与测试效率高,运行稳定,可扩展性强.     

基于LQR的耦合动态互联系统分布式协作 负载均衡优化控制

针对一类非等同非线性耦合互联系统,提出分布式协作负载均衡优化控制方法.将子系统间的通信联系建模成有向图,借助输入输出反馈线性化技术,将耦合互联系统的分布式负载均衡控制设计问题转化为广义线性多智能体系统的同步跟踪问题;基于最近邻原则和LQR方法,设计增益可调的分布式协作负载均衡优化控制律,耦合强度依赖于通信拓扑,控制增益依赖于子系统模型;借助矩阵变换方法,整个闭环系统的渐近稳定性可以解耦成每个子系统的稳定性,在假定通信拓扑只含有生成树的条件下,借助李亚谱诺夫函数,可证明整个闭环系统是稳定的,且通过调节控制增益,可以得到期望的响应速度.仿真结果验证了所提出控制方法的有效性及可行性.     

Underlaid-D2D-assisted cooperative multicast based on social networks

In this paper, device-to-device (D2D) communication is integrated into cooperative multicast to elevate the multicast transmission rate from base station to users. To this end, a new optimization problem, aiming to maximize the overall cooperative multicast rate, is formulated with two essential features 1) D2D communication is exploited to accomplish the data forwarding in the second phase of cooperative multicast, which overcomes the performance bottleneck that time resource has to be bisected for original relay forwarding in conventional cooperative multicast. 2) Social tiers are also taken into account for relay user selection, which can be viewed as a kind of incentive mechanism to enable D2D communication. To solve the problem efficiently, a two-step scheme is presented, in which relay user selection by joint leveraging channel gains and social connections, and power allocation by quantum-behaved particle swarm optimization (QPSO), are carried out sequentially. Numerical simulations show that the proposed social network-based D2D-assisted cooperative multicast scheme performs well, and the performance gap between the proposed power allocation algorithm and upper bound could be limited within 5 % when the system is not heavily loaded. The performance gain over traditional cooperative multicast can reach up to 85 %.     

NASA laboratory telerobotic manipulator control system architecture

In support of the National Aeronautics and Space Administration (NASA) goals to increase the utilization of dexterous robotic systems in space, the Oak Ridge National Laboratory (ORNL) has developed the Laboratory Telerobotic Manipulator (LTM) system. It is a dexterous, dual-arm, force-reflecting teleoperator system with robotic features for NASA ground-based research. This article describes the overall control system architecture, including both hardware and software. The control system is a distributed, modular, and hierarchical design with flexible expansion capabilities for future enhancements of both hardware and software.     

Observer-based sliding mode impedance control of bilateral teleoperation under constant unknown time delay

Sliding mode control has been used extensively in robotics to cope with parametric uncertainty and hard nonlinearities, in particular for time-delay teleoperators, which have gained gradual acceptance due to technological advancements. However, since the slave teleoperator is in contact with a rigid environment, the slave controller requires a free of chattering control strategy, thus making first order sliding mode teleoperation control unsuitable. As an alternative, chatter free, higher-order sliding mode teleoperator control is proposed in this paper to guarantee robust tracking under unknown constant time delay. Moreover, complete order observers are proposed to avoid measurement of velocity and acceleration, along with a formal closed-loop stability proof of the observer-based controller. Experimental results are presented and discussed, which reveals the effectiveness of the proposed teleoperation scheme.     

力觉临场感遥操作机器人变增益力-位置型控制技术研究

为了实现良好的力觉临场感系统,在保证系统稳定性的基础上,提高操作透明性是其中的关键.通过对力-位置型力觉临场系统控制结构的透明性分析,提出了一种变增益力-位置型控制结构,通过改变从端的控制增益,来实现良好的透明性.并且还建立了一个单自由度的力觉临场感实验系统进行了实验研究,实验结果表明,这种控制结构在保证系统稳定的基础上实现了良好的控制透明性.     

Passive bilateral control and tool dynamics rendering for nonlinear mechanical teleoperators

We propose a passive bilateral teleoperation control law for a pair of n-degree-of-freedom (DOF) nonlinear robotic systems. The control law ensures energetic passivity of the closed-loop teleoperator with power scaling, coordinates motions of the master and slave robots, and installs useful task-specific dynamics for inertia scaling, motion guidance, and obstacle avoidance. Consequently, the closed-loop teleoperator behaves like a common passive mechanical tool. A key innovation is the passive decomposition, which decomposes the 2n-DOF nonlinear teleoperator dynamics into two robot-like systems without violating passivity: an n-DOF shape system representing the master-slave position coordination aspect, and an n-DOF locked system representing the dynamics of the coordinated teleoperator. The master-slave position coordination is then achieved by regulating the shape system, while programmable apparent inertia of the coordinated teleoperator is achieved by scaling the inertia of the locked system. To achieve this perfect coordination and inertia scaling, the proposed control law measures and compensates for environment and human forcing. Passive velocity field control and artificial potential field control are used to implement guidance and obstacle avoidance for the coordinated teleoperator. The designed control is also implemented in an intrinsically passive negative semidefinite structure to ensure energetic passivity of the closed-loop teleoperator, even in the presence of parametric model uncertainties and inaccurate force sensing. Experiments are performed to validate the properties of the proposed control framework.     

Neural network-based synchronization of uncertain chaotic systems with unknown states

In this paper, synchronization of chaotic systems with unknown parameters and unmeasured states is investigated. Two nonidentical chaotic systems in the framework of a master and a slave are considered for synchronization. It is assumed that both systems have uncertain dynamics, and states of the slave system are not measured. To tackle this challenging synchronization problem, a novel neural network-based adaptive observer and an adaptive controller have been designed. Moreover, a neural network is utilized to approximate the unknown dynamics of the slave system. The proposed method imposes neither restrictive assumption nor constraint on the dynamics of the systems. Furthermore, the stability of the entire closed-loop system in the presence of the observer dynamics has been established. Finally, effectiveness of the proposed scheme is demonstrated via computer simulation.     

Control of Teleoperators with Communication Time Delay through State Convergence

This paper describes a new control method of teleoperation systems with communication time delay. This method models the teleoperation system in the state space, considering all the possible interactions that could appear in the operator‐master‐slave‐environment set, and it uses the Taylor expansion to model the time delay. The control system allows that the slave manipulator follows the master in spite of the time delay in the communication channel. The tracking is achieved by state convergence between the master and the slave. The method is also able to establish the desired dynamics of this convergence and the dynamics of the slave manipulator. Furthermore, a simple design procedure is provided to obtain the control system gains. These control gains are calculated solving a set of seven equations. The control method is robust to the uncertainty of the design parameters, so it is not necessary to obtain good estimations of these parameters. Simulations and experiments with a one DOF teleoperation system are presented to verify the control method. © 2004 Wiley Periodicals, Inc.     

Exploiting distinctive visual landmark maps in pan–tilt–zoom camera networks

Pan–tilt–zoom (PTZ) camera networks have an important role in surveillance systems. They have the ability to direct the attention to interesting events that occur in the scene. One method to achieve such behavior is to use a process known as sensor slaving: one (or more) master camera monitors a wide area and tracks moving targets so as to provide the positional information to one (or more) slave camera. The slave camera can thus point towards the targets in high resolution.In this paper we describe a novel framework exploiting a PTZ camera network to achieve high accuracy in the task of relating the feet position of a person in the image of the master camera, to his head position in the image of the slave camera. Each camera in the network can act as a master or slave camera, thus allowing the coverage of wide and geometrically complex areas with a relatively small number of sensors.The proposed framework does not require any 3D known location to be specified, and allows to take into account both zooming and target uncertainties. Quantitative results show good performance in target head localization, independently from the zooming factor in the slave camera. An example of cooperative tracking approach exploiting with the proposed framework is also presented.     

遥操作旋转运动梁系统多目标优化控制研究

本文以旋转运动柔性梁为对象,采用基于胞映射的多目标优化方法进行遥操作系统双边控制研究.首先建立遥操作旋转运动柔性梁系统动力学方程,其次考虑信号传输时滞和系统主从端跟踪误差信号设计主端控制器和从端控制器,并利用Lyapunov稳定性理论获得保证闭环控制系统稳定的控制增益所需要满足的条件.由于满足稳定性条件并不意味着好的控制性能,最后利用基于胞映射的多目标优化方法进行优化控制设计,得到同时满足多个不同目标的控制增益的Pareto最优解集.仿真结果表明所获得的控制增益能够有效实现遥操作系统主从端的信号跟踪,并且操作者能够及时感受到从端环境的变化.