A novel approach for stability and transparency control of nonlinear bilateral teleoperation system with time delays

In this paper, a novel control approach is presented to improve the stability and transparency of the nonlinear bilateral teleoperation system with time delays, where a four-channel (4-CH) architecture using modified wave reflection reduction transformation is explored in order to guarantee the passivity of the communication channels in the nonlinear bilateral teleoperation system; a sliding-mode controller is proposed to compensate for the dynamic uncertainties and enhance the system synchronization performance in finite time. The system stability has been analyzed using Lyapunov functions. The proposed method is validated through experimental work based on a 3-DOF bilateral teleoperation platform in the presence of time delays. The experimental results clearly demonstrate that the proposed control algorithm has superiority on system transparency over other wave-based systems.     

Model Predictive Control for Transparent Teleoperation Under Communication Time Delay

Prior efforts in bilateral teleoperation under communication delay have mainly yielded control algorithms that sacrifice performance in order to guarantee robust stability. In contrast, this paper proposes a multimodel predictive controller that can enhance the teleoperation transparency in the presence of a known constant delay. Separate controllers are designed for free motion/soft contact and contact with rigid environments, with switching between these mode-based control laws occurring according to the identified contact mode. Performance objectives such as position tracking and tool impedance shaping for free motion/soft contact, as well as position and force tracking for contact with rigid environments, are incorporated into a multi-input/multi-output state-space representation of the system dynamics. New Artstein-type state and measurement transformations are proposed to generate delay-free dynamics suitable for output-feedback control, based on the original dynamics with delays in various input and output channels. The application of the continuous-time linear quadratic Gaussian control synthesis to the resulting mode-based delay-free dynamics yields control laws that guarantee closed-loop stability and enhanced performance in each phase of teleoperation. The robustness of the mode-based controllers with respect to parametric uncertainty is analyzed. Experimental results with a single-axis teleoperation setup demonstrate the effectiveness of the proposed approach     

Adaptive neural network control of bilateral teleoperation with unsymmetrical stochastic delays and unmodeled dynamics

In this paper, adaptive NN control is proposed for bilateral teleoperation system with dynamic uncertainties, unknown external disturbances, and unsymmetrical stochastic delays in communication channel to achieve transparency and robust stability. Compared with previous passivity‐based teleoperation framework, the communication delays are unsymmetrical and stochastic. By partial feedback linearization using nominal dynamics, the nonlinear dynamics of the teleoperation system are transformed into two subsystems: local master/slave dynamics control and time‐delay motion tracking. By integrating Markov jump systems and adaptive parameters updating, adaptive NN control strategy is developed. The stability of the closed‐loop system and the boundedness of tracking errors are proved using Lyapunov–Krasovskii functional synthesis under specific linear matrix inequalities conditions. The proposed adaptive NN control is robust against motion disturbances, parametric uncertainties, and unsymmetrical stochastic delay, which effectiveness is validated by extensive simulation studies. Copyright © 2013 John Wiley & Sons, Ltd.     

Design and Implementation of Robust-Fixed Structure Controller for Telerobotic Systems

The controller design for bilateral teleoperation systems involves a delicate trade-off between performance and stability. To achieve high performance, high order robust controllers may not be feasible for real-time implementation because of hardware and computational limitations. The main purpose of this paper is to achieve stability and transparency in the presence of time delay in communication channel as well as model uncertainty. To address these problems, a novel robust fixed-structure controller is proposed for uncertain bilateral teleoperation systems. Here, the traditional conventional Proportional-Integral-Derivative (PID) controller is employed to achieve the requirements. The simplicity and straightforward design are the significant advantageous of the proposed method. Robust stability analysis of the proposed technique is also provided. Results demonstrate that the structure is effective in providing stability and transparency in teleoperation systems.     

大时延遥操作系统的波变量双边自适应控制

针对通信时延对遥操作系统稳定性和透明性的影响,研究了一种基于双边自适应控制和波变量理论的控制方法。通过设计波控制器保证通信传输模块的无源性,在保证系统稳定的基础上,调节波阻抗系数来提高系统的透明性,并在时延10 s的情况下进行主从端速度、位置和力的跟踪仿真实验,结果表明该方法和已有的双边自适应方法相比既能保证系统稳定且透明性好,达到较好的控制效果。     

Bilateral parallel force/position teleoperation control

The extension of parallel force/position control to teleoperation systems is considered in this article. In the proposed four‐channel bilateral controller, higher priority is granted to position control at the master side and to force control at the slave side. The primary goal of this control architecture is the enhancement of force and position tracking performance in the presence of uncertainties in the system and environment. The stability and performance of the proposed controller is investigated by analyzing the three decoupled single‐degree‐of‐freedom systems obtained from decoupling and projecting the closed‐loop system dynamics onto the slave task‐space orthogonal directions. Experimental results demonstrate significant improvement in transparency. © 2002 Wiley Periodicals, Inc.     

Dynamic modeling and nonlinear tracking control of a novel modified quadrotor

In this article, a nonlinear tracking controller is designed based on Lyapunov stability for a novel aerial robot. The proposed 6‐rotor configuration improves stability and payload lifting capacity of the robot compared with conventional quadrotors while avoiding further complexities in the robot dynamics and steering principles. The dynamical model of the robot is derived using Newton‐Euler method. The model represents a nonlinear, coupled, and underactuated system. The proposed control strategy includes 2 main parts: an attitude controller and a position controller. Both the attitude and position controls are Lyapunov‐based nonlinear tracking controllers that guarantee the asymptotic convergence of the states' tracking errors to zero. Simulation results are presented to illustrate appropriate performance of the closed‐loop system in terms of position/attitude tracking even in the presence of wind disturbance.     

A novel control design for delayed teleoperation based on delay-scheduled Lyapunov–Krasovskii functionals

This paper addresses the controller design problem for bilateral teleoperation over unreliable networks. The stability and tracking performance analyses are presented for a novel force-reflecting emulator control scheme. The performance (stability, synchronisation, transparency) is guaranteed by H_∞ control theory and delay-scheduled Lyapunov–Krasovskii functionals (LKF), which could improve the existing stability criterion. The design is achieved by using linear matrix inequality optimisation. For the simulation, first, numerical examples are given to demonstrate the effectiveness and benefits of the delay-scheduled LKF-based stability results; second, the proposed controller design solution is illustrated by various simulations and compared with other recent approaches under different working conditions, e.g. abrupt tracking motion and wall contact.     

Absolute stability analysis of sampled-data scaled bilateral teleoperation systems

Stability of a bilateral teleoperation system may be jeopardized by controller discretization, which has been shown to involve energy leaks. This paper proposes a novel approach to analyzing the absolute stability of sampled-data bilateral teleoperation systems consisting of discrete-time controllers and continuous-time master, slave, operator, and environment. The proposed stability analysis permits scaling and delay in the master and the slave positions and forces. The absolute stability conditions reported here impose bounds on the gains of the discrete-time controller, the damping terms of the master and the slave, and the sampling time. A design-related application of these results is in proper selection of various control parameters and the sampling rate for stable teleoperation under discrete-time control. To explore the trade-off between the control gains and the sampling time, it is studied that how large sampling times, which require low control gains for maintaining stability, can lead to unacceptable teleoperation transparency and human task performance in a teleoperated switching task. This shows that the effect of sampling time must be taken into account because neglecting it (as in the absolute stability literature) undermines both stability and transparency of teleoperation. The resulting absolute stability condition has been verified via experiments with two Phantom Omni robots.     

欠驱动无人水下航行器三维轨迹跟踪的反步控制

针对欠驱动无人水下航行器(underactuated unmanned underwater vehicles,UUVs)三维轨迹跟踪控制问题,本文有别于传统反步法中基于视线法设计姿态角误差变量的思路,提出了一种定义虚拟速度误差变量的反步控制器设计方法,能够有效避免传统反步法控制律设计时存在的奇异值问题,简化了传统反步法复杂的计算过程;设计了欠驱动UUV的三维轨迹跟踪控制器,给出了系统的误差方程,基于Lyapunov稳定性理论证明了系统在定常外界扰动下的鲁棒性和稳定性;仿真结果表明本文提出的UUV三维轨迹跟踪反步控制方法收敛、有效,能够实现欠驱动UUV对时变三维轨迹的精确跟踪控制.     

Integrated adaptive robust control for multilateral teleoperation systems under arbitrary time delays

With the increasing industrial requirements such as bigger size object, stable operation, and complex task, multilateral teleoperation systems extended from traditional bilateral teleoperation are widely developed. In this paper, the integrated control design is developed for multilateral teleoperation systems, where n master manipulators are operated by human to remotely control n slave manipulators cooperatively handling a target object. For the first time, the control objectives of multilateral teleoperation including stability, synchronization, transparency, and internal force distribution are clarified systematically. A novel communication architecture is proposed to cope with communication delays, where the estimated environmental parameters are transmitted from the slave side to the master, to replace the traditional environmental force measurement in the communication channel. A kind of nonlinear adaptive robust control technique is used to deal with nonlinearities, unknown parameters, and modeling uncertainties existing in the master, slave, and environmental dynamics, so that the excellent tracking performance is achieved in both master and slave sides. The coordinated motion/force control is designed in the slave side by the optimal internal force distribution among n slave manipulators, and the impedance control is designed in the master side to realize the target transparency behavior. In summary, the proposed control algorithm can achieve the guaranteed robust stability, the excellent synchronization and transparency performance, and the optimal internal force distribution simultaneously for multilateral teleoperation systems under arbitrary time delays and various modeling uncertainties. The simulation is carried out on a 2‐master/2‐slave teleoperation system, and the results show the effectiveness of the proposed control design. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel adaptive robust control architecture for bilateral teleoperation systems under time‐varying delays

Bilateral teleoperation technology has caused wide attentions due to its applications in various remote operation systems. The communication delay becomes one of the main challenging issues in the teleoperation control design. Meanwhile, various nonlinearities, parameter variations, and modeling uncertainties existing in manipulator and environment dynamics need to be considered carefully in order to achieve good control performance. In this paper, a globally stable nonlinear adaptive robust control algorithm is developed for bilateral teleoperation systems to deal with these control issues. Namely, the unknown dynamical parameters of the environmental force are estimated online by the improved least square adaptation law. A novel communication structure is proposed where only the master position signal is transmitted to the slave side for the tracking design, and the online estimators of the environmental parameters are transmitted from the slave to the master to replace the traditional environmental force measurement. Because the estimated environmental parameters are not power signals, the passivity problem of the communication channel and the trade‐off limitation between the transparency performance and robust stability in traditional teleoperation control are essentially avoided. The nonlinear adaptive robust control is subsequently developed to deal with nonlinearities, unknown parameters, and modeling uncertainties of the master, slave, and environmental dynamics, so that the guaranteed transient and steady‐state transparency performance can be achieved. The experiments on two voice‐coil motor‐driven manipulators are carried out, and the comparative results verify that the proposed control algorithm achieves the excellent control performance and the guaranteed robust stability simultaneously under time delays. Copyright © 2014 John Wiley & Sons, Ltd.     

Adaptive Inverse Dynamics Four-Channel Control of Uncertain Nonlinear Teleoperation Systems

Most of the methods to date on bilateral control of nonlinear teleoperation systems lead to nonlinear and coupled closed-loop dynamics, even in the ideal case of perfect knowledge of the master, the slave, the human operator and the environment. Consequently, the transparency of these closed-loop systems is difficult to study. In comparison, inverse dynamics controllers can deal with the nonlinear terms in the dynamics in a way that, in the ideal case, the closed-loop systems become linear and decoupled. In this paper, for multi-d.o.f. nonlinear teleoperation systems with uncertainties, adaptive inverse dynamics controllers are incorporated into the four-channel bilateral teleoperation control framework. The resulting controllers do not need exact knowledge of the dynamics of the master, the slave, the human operator or the environment. A Lyapunov analysis is presented to prove the transparency of the teleoperation system. Simulations are also presented to show the effectiveness of the proposed approach.     

Adaptive neural integral sliding‐mode control for tracking control of fully actuated uncertain surface vessels

This paper develops a novel adaptive neural integral sliding‐mode control to enhance the tracking performance of fully actuated uncertain surface vessels. The proposed method is built based on an integrating between the benefits of the approximation capability of neural network (NN) and the high robustness and precision of the integral sliding‐mode control (ISMC). In this paper, the design of NN, which is used to approximate the unknown dynamics, is simplified such that just only one simple adaptive rule is needed. The ISMC, which can eliminate the reaching phase and offer higher tracking performance compared to the conventional sliding‐mode control, is designed such that the system robust against the approximation error and stabilize the whole system. The design procedure of the proposed controller is constructed according to the backstepping control technique so that the stability of the closed‐loop system is guaranteed based on Lyapunov criteria. The proposed method is then tested on a simulated vessel system using computer simulation and compared with other state‐of‐the‐art methods. The comparison results demonstrate the superior performance of the proposed approach.     

预估控制下的实时网络遥操作移动机器人

构建了能使操作者通过Internet远程实时控制的移动机器人系统．为了补偿网络时延和抵消其对遥操作系统的影响,基于我们以前提出的改进型Smith预估器原理,采用了预估控制策略．为了保证系统稳定性和透明性,基于主从端的传感器信息交换,设计了一个动态模型管理器,其中模型和力反馈误差调节通过模糊控制实现．除了力反馈外,为了增强遥操作的实时性,引入了预估的虚拟显示．为了精确地预测网络时延,提出了一个新颖的时钟同步算法．为了降低时延抖动,结合我们提出的两个算法,实现了数据缓冲策略．最后,通过长距离的网络遥操作实验验证了系统和控制策略的实用性和有效性．     

4‐Channel Sliding Mode Control of Teleoperation Systems with Disturbances

Sliding mode control can effectively account for the disturbances of a system. Among the different teleoperation architectures, 4‐channel architecture is the most successful for fulfilling transparency. In this paper, two sliding mode controllers are designed for nonlinear master and slave with external disturbances and are incorporated into a 4‐channel structure to achieve transparency. To this end, each of the controllers consists of a sliding mode position feedback law, a force feedback law, and two supplementary terms regarding gravity and contact force compensation. Stability and transparency of the overall system is studied via a Lyapunov function analysis. Simulations compared with the conventional adaptive control on teleoperation systems demonstrate the effectiveness of the proposed scheme.     

Time forward observer based adaptive controller for a teleoperation system

This paper presents a design of a teleoperation system using time forward observer-based adaptive controller. The controller is robust to the time-variant delays and the environmental uncertainties while assuring the stability and the transparent performance. A novel theoretical framework and algorithms for this teleoperation system have been built up with neural network-based multiple model control and time forward state observer. Conditions for stability and transparency performance are also investigated.     

Digital versus analog control of bilateral teleoperation systems: A task performance comparison

Controller discretization has the potential to jeopardize the stability of a bilateral teleoperation system. As reported in the literature, stability conditions impose bounds on the gains of the discrete-time controller and the sampling period and also a trade-off between the two. This paper shows a choice of task for which large sampling periods, necessitating low control gains for maintaining stability, lead to low teleoperation transparency and unacceptable task performance. It continues to show that users can successfully perform the same task if the controller is implemented using analog components. This highlights the advantages of analog haptics in tasks involving the display of highly stiff environments. The paper also highlights the constraints in designing analog haptic teleoperation controllers and proposes design guidelines to address them.     

Adaptive controller of a master–slave system for transparent teleoperation

This article presents an adaptive control scheme based on position-force architecture to achieve the stability and transparency for teleoperation in unknown or varying environments. Without any knowledge about the parameters of the slave robot and environment dynamics, the proposed scheme guarantees the robustness to the parameter uncertainties of the master robot as well as the stability of the whole teleoperation system. Numerical simulations are presented to demonstrate the transparency and robustness to the parameter uncertainties of the master robot. Experimental results to a master–slave system show the validity of the proposed scheme. © 1998 John Wiley & Sons, Inc.     

基于时域无源性控制的六足机器人双边触觉遥操作

随着六足机器人研究工作的深入,针对其遥操作系统的开发面临诸多挑战.为了弥补松软接触条件对系统可控性及稳定性的影响,提出一种基于时域无源性控制(time-domain passivity control,TDPC)的六足机器人双边触觉遥操作方法.其主从两端采取位置-速度的交互模式,通过分析足-地柔性接触的作用机理,构建无源观测器和无源控制律以补偿足底滑移所导致环境系统的潜在有源性,采用速度跟踪模式设计基于触觉力反馈的系统控制架构,并利用Llewellyn准则确定控制律参数的稳定范围.最后,搭建半物理仿真实验平台并验证所提出的双边触觉遥操作方法在松软地形条件下能够保证六足机器人遥操作系统的稳定,且兼具较好的持续跟踪能力.