Time Delay In Communication Channel Research Articles

Towards Cyber–Physical Systems Robust to Communication Delays: A Differential Game Approach

Collaboration between interconnected cyber-physical systems is becoming increasingly pervasive. Time-delays in communication channels between such systems are known to induce catastrophic failure modes, like high frequency oscillations in robotic manipulators in bilateral teleoperation or string instability in platoons of autonomous vehicles. This paper considers nonlinear time-delay systems representing coupled robotic agents, and proposes controllers that are robust to time-varying communication delays. We introduce approximations that allow the delays to be considered as implicit control inputs themselves, and formulate the problem as a zero-sum differential game between the stabilizing controllers and the delays acting adversarially. The ensuing optimal control law is finally compared to known results from Lyapunov-Krasovskii based approaches via numerical experiments.

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.

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.

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.

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.

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.

Bilateral control of master–slave manipulators with constant time delay

This paper presents a novel teleoperation controller for a nonlinear master–slave robotic system with constant time delay in communication channel. The proposed controller enables the teleoperation system to compensate human and environmental disturbances, while achieving master and slave position coordination in both free motion and contact situation. The current work basically extends the passivity based architecture upon the earlier work of Lee and Spong (2006) [14] to improve position tracking and consequently transparency in the face of disturbances and environmental contacts. The proposed controller employs a PID controller in each side to overcome some limitations of a PD controller and guarantee an improved performance. Moreover, by using Fourier transform and Parseval’s identity in the frequency domain, we demonstrate that this new PID controller preserves the passivity of the system. Simulation and semi-experimental results show that the PID controller tracking performance is superior to that of the PD controller tracking performance in slave/environmental contacts.

A Simple Structure for Bilateral Transparent Teleoperation Systems With Time Delay

This paper presents a simple structure design for bilateral teleoperation systems with uncertainties in time delay in communication channel. The goal is to achieve complete transparency and robust stability for the closed-loop system. For transparency, two local controllers are designed for the bilateral teleoperation systems. One local controller is responsible for tracking the master commands, and the other one is in charge of force tracking as well as guaranteeing the stability of the closed-loop system in the presence of uncertainties in time delay. The stability analysis will be shown analytically for two cases: (I) the possibly stability and (II) the intrinsically stability. Moreover, in Case II, in order to generate the proper inputs for the master controller in the presence of uncertainties in time delay, an adaptive finite impulse response (FIR) filter is designed to estimate the time delay. The advantages of the proposed method are threefold: (1) stability of the closed-loop system is guaranteed under some mild conditions, (2) the whole system is transparent, and (3) design of the local controllers is simple. Simulation results show good performance of the proposed method.

FEASIBILITY TEST RESULTS OF BILATERAL TELEOPERATION USING THE ENERGY-BOUNDING ALGORITHM

Time delays in communication channels usually make teleoperation systems unstable. To cope with this, we apply the energy-bounding algorithm (EBA) that had been proposed for stable haptic interaction. The EBA restricts the energy generated by the sample and hold operator to consumable energy by the energy-consuming physical damping in the haptic system and some part of human arm to guarantee the passivity condition of whole system. This algorithm always guarantees stable haptic interactions, but compromises the displayable impedance range of the virtual environment.The EBA can be straightforwardly applied for bilateral teleoperation due to the analogy between the haptic simulation system and the teleoperation system. The video shows some feasibility test results of the EBA for bilateral teleoperation. Various test results for free, contact, and abrupt motions show that the EBA can ensure stable bilateral teleoperation for the fairy large amount of constant/variable time delays (2.5 sec (one-way) for free motion and 300 msec (one-way) for contact motion).