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.     

Observer-based sliding mode control for bilateral teleoperation with time-varying delays

In this paper, a tracking control scheme is investigated for a bilateral teleoperation system with time-varying delays and dynamic uncertainties. The tracking control scheme is based on an extended state observer (ESO), a time-delay part observer and a continuous terminal sliding mode control (CTSMC) strategy. The dynamic uncertainties are dealt with by the ESO for the bilateral teleoperation system. The time-varying delays with unmeasurable derivatives are estimated by the two time-delay part observers. The CTSMC strategy is used to ensure finite-time convergence for the bilateral teleoperation system without knowing the second derivatives of tracking errors. Finally, experiment results are shown for the bilateral teleoperation system to demonstrate effectiveness of the developed tracking control scheme.     

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.     

A design of bilateral teleoperation systems using composite adaptive controller

This paper presents a synchronization scheme of bilateral teleoperation systems using composite adaptive controller. To design a controller for bilateral teleoperation systems, all the parameters of the master and the slave robots need to be known. However, there exist parameter uncertainties in the robot manipulators. A composite adaptive controller is designed for convergence of states and parameters of the master and the slave robots in the presence of parameter uncertainties. Consequently, position and force tracking problems in free and contact motion are solved in a synchronized manner. Through a number of simulations, the superiority of the proposed method over existing works is illustrated. Furthermore, for the validation of utility of the proposed method in an actual embedded system, the algorithms are implemented and tested in FPGA-based hardware controller.     

Adaptive finite‐time control for bilateral teleoperation systems with jittering time delays

In this paper, we present a robust adaptive control algorithm for a class of bilateral teleoperation systems with system uncertainties and jittering time delays. The remarkable feature of jittering delays is that time delays change sharply and randomly. Conventional controllers would fail because jittering time delays introduce serious chattering. To address the jittering issue, a novel jittering‐free scheme is developed by relaxing and extending the frequently used constant upper bound. Moreover, an adaptive law was incorporated with the Chebyshev neural network to deal with the system uncertainties. To obtain finite‐time synchronization performance, a fast terminal sliding mode controller is proposed through the technique of “adding a power integrator.” With the proposed control scheme, the robust finite‐time convergence performance is guaranteed. The settling time can be further calculated with the controller parameters. The simulation and experiment results have demonstrated the effectiveness of the proposed method.     

遥操作机器人系统带记忆的鲁棒反馈控制

针对遥操作机器人系统的通信通道中存在通信时延，以及机器人模型存在不确定性，可能造成系统不稳定和操作性能降低的问题，提出在环境模型未知的条件下，利用鲁棒控制理论，采用力、位置和速度反馈的控制方法，使得系统稳定，并且具有良好的透明性，控制参数可通过Matlab的LMI工具箱方便地求取，仿真结果表明了该方法的有效性。     

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.     

PD-like controller for delayed bilateral teleoperation of wheeled robots

This paper proposes a proportional derivative (PD)-like controller applied to the delayed bilateral teleoperation of wheeled robots with force feedback in face of asymmetric and varying-time delays. In contrast to bilateral teleoperation of manipulator robots, in these systems, there is a mismatch between the models of the master and slave (mobile robot), problem that is approached in this work, where the system stability is analysed. From this study, it is possible to infer the control parameters, depending on the time delay, necessary to assure stability. Finally, the performance of the delayed teleoperation system is evaluated through tests where a human operator drives a 3D simulator as well as a mobile robot for pushing objects.     

Human-centered control scheme for delayed bilateral teleoperation of mobile robots

Teleoperation task performance strongly depends on how well the human operator’s commands are executed. In this paper, we propose a control scheme for delayed bilateral teleoperation of mobile robots that considers user’s commands execution in order to achieve a high-performance teleoperation system in some important aspects like time to complete the task, safety, and operator dependence. We describe some evaluation metrics that allow us to address these aspects and a quantitative metric is proposed and incorporated in the control scheme to compensate wrong commands. A force feedback is applied to the master at the local site as a haptic cue. In addition, the system stability is analyzed taking into consideration the master and remote robot dynamic models and the asymmetric time-varying delays of the communication channel. Multiple human-in-the-loop simulations were carried out and the results of the evaluation metrics were discussed. Additionally, we present experiments where a user teleoperates a mobile robot via the Internet connection between Argentina and Italy.     

Passivity-based control for bilateral teleoperation: A tutorial

This tutorial revisits several of the most recent passivity-based controllers for nonlinear bilateral teleoperators with guaranteed stability properties. These schemes, which include scattering–based, damping injection and adaptive controllers, ensure asymptotic stability in multiple situations that range from constant to variable time-delays, with or without scattering transformation and with or without position tracking capabilities. Although all controllers exploit the basic property of passivity of the teleoperators, they have been developed invoking various analysis and design tools, which complicates their comparison and relative performance assessment. The objective of this paper is to present a unified theoretical framework—based on a general Lyapunov–like function—that, upon slight modification, allows to analyze the stability of all the schemes.     

遥操作系统基于观测器的预测控制

在遥操作系统中需要主、从机械手间进行通信,但通信通道中存在较大的通讯时延,这会降低系统操作性能,甚至会使系统不稳定.为了解决这个问题,首先建立系统的状态空间模型,接着提出用时间前向观测器预测从机械手状态,并结合力、位置和速度反馈消除或减小时延对系统影响.系统反馈参数可方便地通过线性矩阵不等式求解.该方法能使系统渐近稳定而且具有良好的透明性.仿真结果表明该方法是有效的.     

变时延力反馈遥操作机器人系统的内模控制

针对遥操作机器人通讯信道变化时延破坏系统稳定性和透明性的问题,为力反馈遥操作系统建立了内模控制结构,设计了两端控制器,并给出了有界时延摄动下系统鲁棒稳定和满足鲁棒性能准则的控制器参数范围,使系统在变时延下依然稳定并具有良好的透明性．给出的控制方法不仅对时延状况适应性强,而且控制器参数少,相关度低,依据不同性能要求进行选取的灵活性大．     

工业机器人遥操作系统的空间映射与控制策略

针对工业机器人遥操作系统中存在的主从机器人工作空间差异以及运动控制精度与安全问题,提出了一种工作空间映射算法与位置—速度混合控制策略。首先,将遥操作划分为自由运动和交互两个阶段,在自由运动阶段采用映射算法使主从机器人的工作空间高度覆盖,使主机器人可操控的从机器人运动范围最大化。进一步,在交互阶段设计了一种位置—速度混合控制策略对工业机器人的运动进行准确的控制,使主从机器人的实际位置轨迹准确的跟随,并进一步引入反馈引导力以实现安全的控制。最后在Touch-ABB IRB120主从机器人遥操作实验平台上对所提控制方法进行验证,实验结果表明该方法使得主从机器人运动范围在高度覆盖的同时可以保证遥操作控制的精度。     

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.     

Application of wave-variable control to bilateral teleoperation systems: A survey

Teleoperation systems allow an operator to perform complex tasks in a remote environment. Stability of a bilateral teleoperation system is quite sensitive to time delays. One of the methods to guarantee the stability of bilateral telerobotics in the presence of time delays is wave variable control. A review of various applications of wave variable methods in telerobotics has been conducted. An evaluation of different methods proposed to compensate for the intrinsic problems associated with wave variable methods, including position drift, wave reflection and time varying delay, has also been carried out. In addition, different techniques developed to enhance the performance of the wave-based systems are also identified and reviewed. The research gaps in this field are identified and future directions for further research are proposed.     

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.     

Robust saturation‐based control of bilateral teleoperation without velocity measurements

This paper addresses the control design problem under no velocity measurements for nonlinear teleoperation system in the presence of asymmetric time‐varying delays. Based on the proposed proportional‐derivative‐like controller and nonlinear‐proportional‐derivative‐like controller, which correspond, respectively, to the actuator non‐saturation and actuator saturation, the control objectives of boundedness of velocities and position tracking errors for the master robot and the slave robot are obtained. These designed controllers do not rely on the velocity signals. The effectiveness of the proposed controller are finally verified by two numerical examples. Copyright © 2014 John Wiley & Sons, Ltd.     

Synchronization of bilateral teleoperators with time delay

Bilateral teleoperators, designed within the passivity framework using concepts of scattering and two-port network theory, provide robust stability against constant delay in the network and velocity tracking, but cannot guarantee position tracking in general. In this paper we fundamentally extend the passivity-based architecture to guarantee state synchronization of master/slave robots in free motion independent of the constant delay and without using the scattering transformation. We propose a novel adaptive coordination architecture which uses state feedback to define a new passive output for the master and slave robots containing both position and velocity information. A passive coordination control is then developed which uses the new outputs to state synchronize the master and slave robots in free motion. The proposed algorithm also guarantees ultimate boundedness of the master/slave trajectories on contact with a passive environment. Experimental results are also presented to verify the efficacy of the proposed algorithms.     

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.     

PD‐like controllers for delayed bilateral teleoperation of manipulators robots

This paper proposes a compensated PD‐like controller for delayed bilateral teleoperation of a manipulator robot. The scheme has a PD‐like remote controller, a damping into the master, and a compensation strategy. The proposed compensation removes part of potential energy of the user's command depending on the difference between the situation on the remote site and the situation as perceived by the human operator. In addition, the stability of the delayed teleoperation system is analyzed, and a comparison based on experiments is carried out in order to analyze the advantages of using the proposed compensation. Finally, results of a bilateral teleoperation including the proposed control scheme, where the master and slave exchange information by using a low‐cost connection of mobile Internet, are shown. Copyright © 2014 John Wiley & Sons, Ltd.