Delays In Communication Channels Research Articles

Optimal control in teleoperation systems with time delay: A singular perturbation approach

The main goal of controller design in teleoperation systems is to achieve optimal performance, transparency and stability in presence of factors such as time delay in communication channel and modeling uncertainties. The teleoperation systems usually have complex dynamic. Consequently, differential equation solution of optimal control problem is difficult and complex for them. This paper presents a novel method for designing optimal controller based on singular perturbation framework for these systems. Firstly, we use the Taylor expansion to model the time delay, with considering time delay term; we derive a singular perturbation formulation for the teleoperation system. Using singular perturbation model and Chang decoupling transformation, singularly perturbed differential equations of optimal control problem is decomposed into the reduced order slow and fast differential equations. A formula is obtained that produces the solution of original differential equations of optimal control problem in terms of solutions of the slow and fast reduced order matrix differential equations. The reduced-order differential equations decrease the complexity of the optimal control problem for teleoperation systems. The simulations verify the effectiveness of the proposed control method and excellent performances tracking with high speed and small control signal.

Increasing stability in model-mediated teleoperation approach by reducing model jump effect

Model-mediated teleoperation is a predictive control approach for controlling haptic teleoperation systems whereby the environment force is virtually located on master side in order to increase the stability and transparency of the system. This promising approach, however, results in new challenges. One pivotal challenge is the model jump effect, which stems from the delay in correct creation of the virtual environment. Previous works have endeavored to reduce this effect; however, they either led to transparency decrease or assumed simplified environment models. In this paper, we propose a control approach for this aim based on the idea of decoupling. This means that when a new environment has been identified, the operation is interrupted and no signal is transmitted between master and slave sides. During this time, both sides are controlled by their own sliding mode controllers until the system reaches stability. The main advantage of this method is its independence from environment type, which makes it usable for different kinds of applications. To verify the effectiveness of the proposed approach simulation tests are conducted. The results show the system is stable in interaction with hard and soft environments in presence of large time delays in communication channels.

Delay-Dependent Algebraic Riccati Equation to Stabilization of Networked Control Systems: Continuous-Time Case.

In this paper, a delay-dependent algebraic Riccati equation (DARE) approach is developed to study the meansquare stabilization problem for continuous-time networked control systems. Different from most previous studies that information transmission can be performed with zero delay and infinite precision, this paper presents a basic constraint that the designed control signal is transmitted over a delayed communication channel, where signal attenuation and transmission delay occur simultaneously. The innovative contributions of this paper are threefold. First, we propose a necessary and sufficient stabilizing condition in terms of a unique positive definite solution to a DARE with Q > 0 and R > 0. In accordance with this result, we derive the Lyapunov/spectrum stabilizing criterion. Second, we apply the operator spectrum theory to study the stabilizing solution to a more general DARE with Q ≥ 0 and R > 0. By defining a delay-dependent Lyapunov operator, we propose the existence theorem of the unique stabilizing solution. It is shown that the stabilizing solution, if it exists, is unique and coincides with a maximal solution. Third, as an application, we derive the explicit maximal allowable delay bound for a scalar system. To confirm the validity of our theoretic results, two illustrative examples are included in this paper.

Teleoperation Control Based on Combination of Wave Variable and Neural Networks

In this paper, a novel control scheme is developed for a teleoperation system, combining the radial basis function (RBF) neural networks (NNs) and wave variable technique to simultaneously compensate for the effects caused by communication delays and dynamics uncertainties. The teleoperation system is set up with a TouchX joystick as the master device and a simulated Baxter robot arm as the slave robot. The haptic feedback is provided to the human operator to sense the interaction force between the slave robot and the environment when manipulating the stylus of the joystick. To utilize the workspace of the telerobot as much as possible, a matching process is carried out between the master and the slave based on their kinematics models. The closed loop inverse kinematics (CLIK) method and RBF NN approximation technique are seamlessly integrated in the control design. To overcome the potential instability problem in the presence of delayed communication channels, wave variables and their corrections are effectively embedded into the control system, and Lyapunov-based analysis is performed to theoretically establish the closed-loop stability. Comparative experiments have been conducted for a trajectory tracking task, under the different conditions of various communication delays. Experimental results show that in terms of tracking performance and force reflection, the proposed control approach shows superior performance over the conventional methods.

Impact of phase-locked loop on system dynamics of a CCGT incorporated diverse source system employed with AC/DC interconnection

Nowadays, research on renewable generation penetration in a power system has facilitated the use of power electronics with improved grid-support functionalities. This article addresses the automatic generation control of a three-area interconnected system with combined cycle gas turbine and two thermal generating units in area1 and a wind and two thermal units in other areas. All areas are employed with delayed communication channels, and appropriate generation rate constraints and governor deadband are provided in thermal systems. A recent metaheuristic algorithm, namely stochastic fractal search (SFS), is applied for optimization of secondary controller gains and other system parameters. The performance of various two-degrees-of-freedom proportional-integral-derivative (2DOF PID) controller structures are compared with single-degree-of-freedom proportional-integral-derivative controllers, and results explore the superiority of 2DOF PID controllers. An attempt to explore the impact of AC/DC links considering delayed phase-locked loop (PLL) dynamics during coordination with diverse source interconnected AC systems is presented and discussed. Results clearly outline overshoots and settling time of frequency, tie-power, and temperature deviation increases owing to the inclusion of PLL. A detailed numerical analysis is presented to understand the system dynamic responses due to parametric changes in PLL function. However, with optimum parametric selection, the deviations and settling time decrease. Last, sensitivity analysis implies that SFS optimized controller parameters need not be reset for ±25% changes in loading condition; inertia constant; and ±10%, ±20%, and –25% changes in tie-power synchronizing co-efficient. But system responses deteriorate during +25% changes in the latter owing to very strong ties between the areas, which are not recommended.

Passivity-based PI control of first-order systems with I/O communication delays: a frequency domain analysis

ABSTRACTIn this paper, the proportional integral (PI) control of first-order linear passive systems through a delayed communication channel is revisited in light of the relative stability concept called σ-stability. Treating the delayed communication channel as a transport partial differential equation (PDE), the passivity of the overall control-loop is guaranteed, resulting in a closed-loop system of neutral nature. Spectral methods are then applied to the system to obtain a complete stability map. In particular, we perform the -subdivision method to declare the exact σ-stability regions in the space of PI parameters. This framework is then utilised to analytically determine the maximum achievable exponential decay rate σ*d of the system while achieving the PI tuning as explicit function of σ*d and system parameters.

A Passivity-Based Approach for Stable Patient–Robot Interaction in Haptics-Enabled Rehabilitation Systems: Modulated Time-Domain Passivity Control

In this paper, a novel passivity-based technique is proposed to 1) analyze and 2) guarantee the stability of haptics-enabled robotic/telerobotic systems when there is a possibility of having a source of nonpassivity (namely, a nonpassive environment) in addition to the conventional nonpassive component in teleoperation systems (namely, a delayed communication channel). The need for the proposed technique is motivated by safe and optimal implementation of the haptics-enabled robotic, cloud-based, and remote rehabilitation systems. The objective of the controller proposed in this paper is to perform minimum alteration to the system transparency, in a dynamic and patient-specific manner, by utilizing quantifiable biomechanical capability of the user’s limb (i.e., excess of passivity) in dissipating interactive energies to guaranteeing human–robot interaction safety, in the context of the strong passivity theorem. The proposed controller is named modulated time-domain passivity control (M-TDPC) approach and is a new member of the family of the state-of-the-art TDPC techniques. Simulations and experimental results are presented in support of the proposed technique and the developed theory.

Improving teleoperation system performance in the presence of estimated external force

Teleoperation systems have been developed in order to manipulate objects in environments where the presence of humans is impossible, dangerous or less effective. The presence of force signals plus position signals in the control scheme could effectively improve transparency. However, the main restriction is force measurement in some applications. A new modified strategy for estimating the external forces acting on the master and slave robots is developed. The main advantage of this strategy is that the necessity for force sensors is eliminated, leading to lower cost and further applicability. A novel control algorithm with estimated force signals is proposed for a general nonlinear bilateral teleoperation system with time delay. The stability condition in the teleoperation system with the new control algorithm is verified by means of Lyapunov stability analysis. The designed control algorithm guarantees stability of the teleoperation system in the presence of an estimated operator and environmental force. Experimental results confirm the efficiency of the novel control algorithm in position tracking and force reflection. Design a control scheme for bilateral teleoperation via estimated external force.Transparency improvement of the system in contact condition.Considering the effect of time delays in communication channels between master and slave robot.Demonstrating stability of closed loop system theoretically and experimentally.

A novel multilateral teleoperation scheme with power-based time-domain passivity control

Multilateral teleoperation systems, which are extended from the traditional bilateral teleoperation, have become subject to increasing attention in current years, with increasing industrial requirements, such as the remote operation of larger objects and more complex tasks. In this paper, a general multilateral teleoperation control problem is discussed, in which n masters remotely control n slaves through delayed communication channels. A novel communication structure is proposed to satisfy the multiple master–slave communication requirement, in which weighting coefficients are chosen freely to perform the weighted effects of different masters or slaves. Power-based time-domain passivity control is subsequently developed for the complex multiple master–slave communication channel, to achieve the passivity of multilateral teleoperation systems under time delay. Experiments on a teleoperation system with two masters and two slaves are described; the results verify the effectiveness of the proposed control scheme.

A Practical Coordinated Trajectory Tracking for A Group of Mixed Wheeled Mobile Robots with Communication Delays

Coordination between a specific mobile robot type has been widely investigated, e.g coordination between unicycles. To extend the applicability of the system, a coordinated trajectory tracking of mixed type of mobile robots is considered. We prove that if a certain type of wheeled mobile robot is able to individually track its own reference, then coordination in tracking with other type of robots can be achieved simply by sharing individual tracking errors. Using two types of wheeled mobile robots, namely unicycle type (a nonholonomic mobile robot) and omni wheels type (a holonomic mobile robot), a coordinated control algorithm can achieve a global asymptotically stable condition of the error dynamics of the systems. Under bidirectional communication between robots as a constraint, the group is able to maintain individual tracking while coordinating the movements with other robots regardless occurring perturbations in the system and delays in communication channels. Simulation results suggest that information sharing between the robots increase the robustness in coordinating individual trajectories. Results also show that delays cause drop in performance similar to the case of no information sharing.

An Exact Stability Condition for Bilateral Teleoperation With Delayed Communication Channel

In this correspondence paper, an exact method is developed to guarantee asymptotic stability of a bilateral teleoperation system that is subjected for a time-delayed communication. This extends the prior art of searching for the maximum upper bound of time delay. In order to improve the flexibility in controller design and obtain better performance, a fractional-order PD $^{ {\alpha }}$ controller is proposed. The exactly stable regions of delays are explored for both integral-order and fractional-order controllers. Compared with conditions in most previous works which are deduced by the Lyapunov–Krasovskii functional and rely on the solution of some linear matrix inequalities, the stability conditions proposed in this paper are established from the frequency domain point of view, and thus, the results are not only sufficient but also necessary. To illustrate accuracy of the conditions, they are simulated on a delayed teleoperation system composed of a pair of robots.

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.

A linear programming framework for networked control system design

This paper considers stability and performance for a sampled data system with a distributed controller, time-varying delay, quantization, saturation, and external disturbances. We decompose the overall system into two subproblems. The first is a linear subsystem containing a distributed controller satisfying information sharing constraint between sensor and actuator. The second involves nonlinear error dynamics comprised of sampling, quantization, delay and saturation errors. We show how to construct an invariant set of the error dynamics using a linear program. Our method enables the design of distributed/localized controllers and delayed communication channels with linear programming, enhancing both implementation and design scalability. The use of l∞ signal/l1 operator norm appears essential to capture communication error and facilitate scalable computation. We also analyze the suboptimality gap and the feasibility condition of the proposed linear program.

Optimal synchronization of teleoperation systems via cuckoo optimization algorithm

The main goal of controller design in bilateral teleoperation systems is to achieve stability and transparency in presence of different factors such as time delay in communication channel and modeling uncertainties. The contribution of this paper is designing an optimal controller for synchronization of bilateral teleoperation systems with the objectives of reducing the factors. This requires optimizing a set of parameters of the so-called synchronization control law. To this reason, a novel meta-heuristic algorithm namely cuckoo optimization (CO) algorithm was employed. Comparative simulations are performed to demonstrate the feasibility of the proposed control technique. The results indicate that CO is a powerful search and optimization technique that may yield better solutions to the problem in hand than those obtained using other algorithms including biogeography-based optimization, imperialist competitive and artificial bee colony.

Experimental comparison of backdrivability for time-delayed telerobotics

After stability, transparency is the major goal in teleoperation system design. This transparency goal of the overall system depends on the master/slave manipulator backdrivability. However, time delay in communication channel severely affects the backdrivability of a bilateral teleoperation system in practice. This study investigates the effects of communication delays on the backdrivability of a teleoperation system for wave-variable-based control techniques. The controllers are compared on position and force tracking performance using two identical linear robots coupled via network model that allowed random transmission round-trip delays. Overall, the comparison study reports a deteriorating effect in the system backdrivable performance (i.e., larger position errors and lower fidelity of contact information) from delays. In addition, wave-variable-based controller with position compensation is shown to make better system backdrivability.

Adaptive Fuzzy Control for Multilateral Cooperative Teleoperation of Multiple Robotic Manipulators Under Random Network-Induced Delays

In this paper, an adaptive fuzzy control is investigated for multilateral teleoperation of two cooperating robotic manipulators that manipulate an object with constrained trajectory/force in the presence of dynamics uncertainties and random network-induced delays. First, the interconnected dynamics that consist of two master robots and cooperating slave robots are formulated. To consider multiple stochastic delays in communication channels, Markov processes are used to model these random network-induced delays. The interconnected dynamics of the teleoperation are divided into a local master/slave position/force subsystem and a stochastic-delayed motion synchronization subsystem. Then, an adaptive fuzzy control strategy, which is based on linear matrix inequalities (LMIs) that combine adaptive update techniques, is proposed to suppress the dynamics uncertainties, the external disturbances, and the multiple stochastic delays in communication channels. The control approach ensures that the defined synchronization errors converge to zero. The stochastic stability in mean square of the closed-loop system is proved using LMIs based on Lyapunov-Krasovskii functional synthesis. The proposed controls are validated using extensive simulation studies.

Neural-adaptive control of single-master-multiple-slaves teleoperation for coordinated multiple mobile manipulators with time-varying communication delays and input uncertainties.

In this paper, adaptive neural network control is investigated for single-master-multiple-slaves teleoperation in consideration of time delays and input dead-zone uncertainties for multiple mobile manipulators carrying a common object in a cooperative manner. Firstly, concise dynamics of teleoperation systems consisting of a single master robot, multiple coordinated slave robots, and the object are developed in the task space. To handle asymmetric time-varying delays in communication channels and unknown asymmetric input dead zones, the nonlinear dynamics of the teleoperation system are transformed into two subsystems through feedback linearization: local master or slave dynamics including the unknown input dead zones and delayed dynamics for the purpose of synchronization. Then, a model reference neural network control strategy based on linear matrix inequalities (LMI) and adaptive techniques is proposed. The developed control approach ensures that the defined tracking errors converge to zero whereas the coordination internal force errors remain bounded and can be made arbitrarily small. Throughout this paper, stability analysis is performed via explicit Lyapunov techniques under specific LMI conditions. The proposed adaptive neural network control scheme is robust against motion disturbances, parametric uncertainties, time-varying delays, and input dead zones, which is validated by simulation studies.

Trilateral Teleoperation of Adaptive Fuzzy Force/Motion Control for Nonlinear Teleoperators With Communication Random Delays

In this paper, an adaptive fuzzy control scheme is proposed for hybrid motion/force of trilateral teleoperation systems with a dual-master-single-slave configuration under stochastic time-varying delays in communication channels. Different from previous works on bilateral teleoperation systems, this paper addresses dual-master trilateral control of a single holonomic-constrained robotic manipulator, where the communication delays are modeled as multiple Markov chains, and the motion/force controls are investigated under consideration of unsymmetric stochastic time-varying delays and system dynamical uncertainties. Using partial feedback linearization, the whole trilateral teleoperation system, which consists of both master and slave manipulator dynamics, is transformed into three subsystems. By integrating Markov jump systems to handle random delays, adaptive fuzzy control strategies are developed for the nonlinear teleoperators with modeling uncertainties and external disturbances by using the approximation property of the fuzzy logic systems (FLSs). It is proven that the trilateral teleoperation system is stochastically stable in mean square under specific linear matrix inequality (LMI) conditions, and all the signals of the resulting closed-loop system are uniformly bounded. The proposed scheme is validated by extensive simulations.

Bilateral Teleoperation of Holonomic Constrained Robotic Systems With Time-Varying Delays

In this paper, adaptive control is proposed for hybrid position/force synchronization of master-slave teleoperation systems with time-varying delays in communication channels. Different from previous works on bilateral teleoperation systems, we investigate position/force control of bilateral teleoperation systems subject to time-varying delays and dynamical uncertainties. Using partial feedback linearization, the dynamics of both master and slave are transformed into two subsystems: local master/slave position/force control with unmodeled dynamics and delayed position/force synchronization. An adaptive control is proposed to deal with the dynamical uncertainties and robust against time delays, which guarantees the position/force synchronization trajectories converge to the desired manifolds with prescribed performance. The stability of the closed-loop system and the boundedness of synchronization tracking errors are proved using linear matrix inequalities based on Lyapunov stability synthesis. The position/force tracking error up to an ultimately bounded error is achieved. The proposed adaptive controls are robust against relative motion disturbances, parametric uncertainties, and time delays, and are validated by experimental studies.

Delay-dependent stability for transparent bilateral teleoperation system: an LMI approach

There are two significant goals in teleoperation systems: Stability and performance. This paper introduces an LMI-based robust control method for bilateral transparent teleoperation systems in presence of model mismatch. The uncertainties in time delay in communication channel, task environment and model parameters of master-slave systems are called a model mismatch. The time delay in communication channel is assumed to be large, unknown and asymmetric, but the upper bound of the delay is assumed to be known. The proposed method consists of two local controllers. One local controller namely local slave controller is located on the remote site to control the motion tracking and the other one is located on the local site namely local master controller to preserve the complete transparency by ensuring force tracking and the robust stability of the closed-loop system. To reduce the peak amplitude of output signal respect to the peak amplitude of input signal in slave site, the local slave controller is designed based on a bounded peak-to-peak gain controller. In order to provide a realistic case, an external signal as a noise of force sensor is also considered. Simulation results show the effectiveness of proposed control structure.