Presence Of Large Time Delay Research Articles

Network Synchronization Revisited: Time Delays in Mutually Coupled Oscillators

Coordinated and efficient operation in large, complex systems requires the synchronization of the rhythms of spatially distributed components. Such systems are the basis for critical infrastructure such as satellite navigation, mobile communications, and services like the precision time protocol and Universal Coordinated Time. Different concepts for the synchronization of oscillator networks have been proposed, in particular mutual synchronization without and hierarchical synchronization from a reference clock. Established network synchronization models in electrical engineering address the role of inevitable cross-coupling time delays for network synchronization. Mutual synchronization has been studied using linear approximations of the coupling functions of these models. We review previous work and present a general model in which we study synchronization taking into account nonlinearities and finite time delays. As a result, dynamical phenomena in networks of coupled electronic oscillators induced by time delays, such as the multistability and stabilization of synchronized states can be predicted and observed. We study the linear stability of nonlinear states and predict for which system parameters synchronized states can be stable. We use these results to discuss the implementation of mutual synchronization for complex system architectures. A key finding is that mutual synchronization can result in stable in- and anti-phase synchronized states in the presence of large time delays. We provide the condition for which such synchronized states are guaranteed to be stable.

PID controlled fully automated portable duodopa pump for Parkinson’s disease patients

Parkinson’s disease (PD) is a neurodegenerative disease that inhibits motor activities due to the impairment of brain cells which produce dopamine. Even though medications as well as Deep Brain Stimulations (DBS) are the two treatment options available to control parkinsonian symptoms, the first one is preferred mostly during the early stages of the disease. Continuous medication through Portable Duodopa Pump (PDP) without feedback is the existing method. This paper focuses on the development of a suitable closed-loop control strategy for traditional PDP; thereby ensuring fully automated drug infusion without wearing off. In fact, the drug infused by the controller is increased proportional to reduction in plasma level of dopamine. This results in the alleviation of side effects caused by incorrect dosages in medication therapy. The main control objective is set-point tracking of the closed-loop system with minimum settling time and good steady state accuracy even in the presence of large time delay, food and exercise disturbances as well as parameter variations present in the system. For achieving this objective, we modified the existing dose-effect model of Levodopa. The proposed model is enriched by (i) Levodopa to dopamine conversion factor, (ii) recirculation time delay and (iii) initial dopamine level present in patient’s BP (Blood Plasma). The in-silico analysis of oral medication is used to validate pharmacokinetics (PK), pharmacological activation (PA) and pharmacodynamics of Levodopa. The performance of the proposed fully automatic PDP has been evaluated by traditional Proportional Integral Derivative (PID) controller under two different tuning rules. It is revealed that, both Ziegler- Nichols (ZN) and Particle Swam Optimization (PSO) tuned PID controllers are robust regarding inter-patient variability and the dynamic performance of the later is superior in comparison with the former under intra-patient variability and disturbances.

Prediction-Based Adaptive Sliding Mode Control for Remotely Piloted System With Time Delay and Parameter Uncertainty

This paper proposes a state prediction adaptive sliding mode (SPASM) control method for the remotely piloted system (RPS). With consideration of the time delay caused by the large transmission delay existing in the RPS, a prediction algorithm is proposed to provide the state prediction by using the state transition matrix. To approximate the uncertain lag of the remotely piloted vehicle (RPV) control augmentation system, an adaptive law is proposed to estimate the parameter uncertainties, and the overestimating problem is resolved efficiently. Meanwhile, to deal with the unmodeled dynamics and the predicted errors, a sliding mode controller is designed to guarantee the robustness of the whole closed-loop system. The simulation results show that the SPASM controller can not only guarantee the stability of the RPS in the presence of large time delay but also has a desirable performance of tracking the pilot’s inputs while existing the unmodeled dynamics and parameter uncertainties.

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.

Projected predictive Energy-Bounding Approach for multiple degree-of-freedom haptic teleoperation

This paper presents a geometrically and dynamically transparent projected predictive Energy-Bounding Approach (EBA) for multiple degree-of-freedom (m-DOF) haptic teleoperation with time delays. The straightforward extension of a single-DOF teleoperation to m-DOF teleoperation suffers from a bad force distortion problem that becomes worse with the increase in communication time delays between master and slave sites. Due to this, geometry perception of remote m-DOF objects at master site is severely deteriorated. To solve this problem, a projected predictive m-DOF EBA is proposed by combining the m-DOF Predictive EBA and the projection method that can compensate the force distortion problem. The proposed approach also includes steps to get stably the information about the contact locations (geometry) of m-DOF remote objects without geometry detection sensors. In order to validate the proposed approach, some experiments performing surface contour-following are conducted using two Phantoms: (i) 2-DOF object (bobbin), and (ii) 3-DOF semi-spherical object in the presence of large time delays.

Transparent four-channel bilateral control architecture using modified wave variable controllers under time delays

SUMMARYStability and transparency are two critical indices of bilateral teleoperation systems. The wave variable method is a conservative approach to robustly guarantee system passivity under arbitrary constant time delays. However, the wave-variable-based reflection is an intrinsic problem in this method because it can significantly degrade system transparency and disorient the operator's perception of the remote environment. In order to enhance both the transparency and the stability of bilateral teleoperation systems in the presence of large time delays, a new four-channel (4-CH) architecture is proposed which applies two modified wave-transformation controllers to reduce wave-based reflections. Transparency and stability of the proposed system are analyzed and the improvement in these when using this method is measured experimentally. Results clearly demonstrate that the proposed method can produce high transparency and stability even in the presence of large time delays.

Control of intensified equipment: A simulation study for pH control in a spinning disc reactor

The majority of the research that has been carried out in the field of process intensification concentrated primarily on the feasibility of the underlying concepts and the resulting benefits in terms of productivity and efficiency, whilst little has been done to investigate the control and operation of intensified units. This contribution provides an overview of the potential difficulties encountered in controlling intensified processes. The investigation is focused on controlling pH in a spinning disc reactor (SDR), as an example of an intensified reactor technology, using a classical Proportional Integral (PI) controller. The simulation studies show that a PI controller applied to an example intensified system yields superior setpoint tracking performance in terms of integral of absolute error (IAE), compared to that achieved in a conventional system. However, the controller performance in the intensified system suffers from high overshoots which may be considered unacceptable for many processes. The results also show that the PI controller applied to control pH in a simulated SDR provides poor performance in the presence of large time delays. Two approaches of including a ‘pH characteriser’ and a ‘disturbance observer’ (DO) are examined to compensate for the pH process nonlinearity. The characteriser is successful in suppressing the limit cycles observed in the pH response whilst the DO scheme marginally improves the disturbance rejection performance of the PI controller in terms of IAE.

Four-Channel Control Architectures for Bilateral and Multilateral Teleoperation

The four-channel architecture in teleoperation with force feedback has been studied in various existing literature. However, most of them focused on Lawrence architecture and did not research other cases. This paper proposes two other four-channel architectures: passive four-channel architecture and passive four-channel architecture with operator force. Furthermore, two types of multilateral shared control architecture based on passive four-channel architecture, which exists in space teleoperation, are put forward. One is dual-master multilateral shared control architecture, and the other is dual-slave multilateral shared control architecture. Simulations show that these four architectures can maintain stability in the presence of large time delay.

Time-delayed control design for active control of structures: principles and applications

In this paper we develop the principles of time-delayed control design for the active control of structures in which the presence of large time delays in the control loop may make it difficult for their effects to be easily eliminated and/or compensated. A control design strategy is proposed that is different from what has been generally accepted hereto; it calls for taking advantage of these large, inherent time delays in the control design. The presence of large time delays in the control loop requires that we understand the infinite dimensionality of the system and so we introduce the concept of non-system poles. This is first done within the framework of an SDOF system with time-delayed velocity feedback control. Several new results are presented dealing with stability and performance issues. These results include and extend those available to date. Having developed control design principles with an SDOF system as the underlying basis, these principles are then developed for multi-actuator, multiple time-delay control of MDOF systems. A numerical example of a building structure modeled as an MDOF system that is subjected to strong earthquake ground shaking is presented. The control design based on the underlying principles shows good stability characteristics and effective performance behavior. We demonstrate its application to a structure subjected to strong earthquake ground shaking, thereby showing its usefulness in hazard mitigation. Copyright © 2005 John Wiley & Sons, Ltd.

APPLICATION OF ADAPTIVE CONTROLLERS FOR THE TEMPERATURE CONTROL OF A SEMI-BATCH REACTOR

This paper investigates experimentally the application of several adaptive control algorithms for the control of a semi-batch chemical reactor. These algorithms combine parameter estimation algorithms and conventional control design methods to update the coefficients of the control algorithm. To make practical use of these control strategies, simple computational procedures are presented. The control objective is to keep the reactor temperature within safe operating specifications by manipulating the electrical heating power. Experimental results demonstrate that this class of adaptive controllers works well in the presence of large time delay, hard constraints and disturbances.

FEEDBACK LINEARIZATION DESIGNS FOR UNCERTAIN NONLINEAR TIME-DELAY PROCESSES: A COMPARATIVE STUDY

This work concerns the phenomena in which the feedback linearization control is applied to uncertain nonlinear time-delay processes. Under the I/O linearization algorithm, both nonlinear controllers are used to stabilize the closed-loop system with transformed delay inputs. When the effect of input perturbations can converge to zero or asymptotically vanish, these nonlinear feedback designs with only an adjustable parameter can directly improve the tracking performance. The simple linearizing controller can directly regulate the system output at unstable operating point. Combined with deadtime compensation the nonlinear predictive controller with the aid of appropriate state prediction is valid for the real process in the presence of large time delay. Finally, via computer simulation and test of control ability of both feedback control designs the useful comparative results are presented.