Loop Signals Research Articles

Adaptive Fuzzy Control for Nonlinear State Constrained Systems With Input Delay and Unknown Control Coefficients

In this paper, an adaptive fuzzy controller is investigated for a class of strict-feedback nonlinear state constrained systems with both input delay and unknown control coefficients. Nussbaum gain technique is employed in the design progress to deal with the unknown time-varying control coefficients. Pade approximation and an intermediate variable are applied to compensate for the effect of the input delay and the barrier Lyapunov functionals (BLFs) are used to guarantee the states to remain within their constraint sets. The unknown functions are approximated by Fuzzy logic systems (FLSs). It is proved that the tracking error can converge to a compact set of the origin without violating the state constraint, and all closed loop signals remain bounded. The effectiveness of the proposed controller is illustrated through two examples.

On Operational Space Tracking Control of Robotic Manipulators With Uncertain Dynamic and Kinematic Terms

In this study, a continuous robust-adaptive operational space controller that ensures asymptotic end-effector tracking, despite the uncertainties in robot dynamics and on the velocity level kinematics of the robot, is proposed. Specifically, a smooth robust controller is applied to compensate the parametric uncertainties related to the robot dynamics while an adaptive update algorithm is used to deal with the kinematic uncertainties. Rather than formulating the tracking problem in the joint space, as most of the previous works on the field have done, the controller formulation is presented in the operational space of the robot where the actual task is performed. Additionally, the robust part of the proposed controller is continuous ensuring the asymptotic tracking and relatively smooth controller effort. The stability of the overall system and boundedness of the closed loop signals are ensured via Lyapunov based arguments. Experimental results are presented to illustrate the feasibility and performance of the proposed method.

Nonlinear adaptive fuzzy output-feedback controller design for dynamic positioning system of ships

This paper develops a nonlinear adaptive fuzzy output feedback controller for dynamic positioning (DP) system of ships in the presence of unmeasured states of ships, unknown dynamic model parameters, unknown time varying environment disturbances and input saturation. It is the first time that all the conditions above are simultaneously dealt with in the DP control design. By combining adaptive fuzzy system and auxiliary dynamic system, a control scheme with high-gain observer is developed via vectorial backstepping method. It is proved that the proposed nonlinear adaptive fuzzy output feedback controller can maintain the ship at desired position and heading with arbitrary accuracy, while guaranteeing the uniform ultimate boundedness of all closed loop signals in the DP system. Finally, simulations are carried on a supply ship to demonstrate the effectiveness of the proposed control approach.

Adaptive fuzzy output feedback stabilization control for the underactuated surface vessel

This paper designs an adaptive fuzzy stabilization controller for the underactuated surface vessel in the presence of unknown time varying environment disturbances and input saturation. By combining adaptive fuzzy system and auxiliary dynamic function, a stabilization control scheme is developed via vectorial backstepping technique and Lyapunov direct method. To begin with, based on the diffeomorphism equivalent transformation, the stabilization problem of underactuated surface vessel can be transformed into the stabilization analysis of two subsystem. Further, the adaptive fuzzy system is employed to approximate the uncertain term induced by the unknown time varying environment disturbances in the control law. In particularly, an auxiliary dynamic function is exploited to deal with the input saturation. It is proved that the proposed adaptive fuzzy output feedback controller can stabilize the vessel to desired equilibrium origin, while guaranteeing the uniform ultimate boundedness of all closed loop signals in the underactuated system. Finally, simulation results are given to demonstrate the effectiveness of the proposed control approach.

A robust interaction control approach for underwater vehicle manipulator systems

In underwater robotic interaction tasks (e.g., sampling of sea organisms, underwater welding, panel handling, etc) various issues regarding the uncertainties and complexity of the robot dynamic model, the external disturbances (e.g., sea currents), the steady state performance as well as the overshooting/undershooting of the interaction force error, should be addressed during the control design. Motivated by the aforementioned considerations, this paper presents a force/position tracking control protocol for an Underwater Vehicle Manipulator System (UVMS) in compliant contact with a planar surface, without incorporating any knowledge of the UVMS dynamic model, the exogenous disturbances or the contact stiffness model. Moreover, the proposed control framework guarantees: (i) certain predefined minimum speed of response, maximum steady state error as well as overshoot/undershoot concerning the force/position tracking errors, (ii) contact maintenance and (iii) bounded closed loop signals. Additionally, the achieved transient and steady state performance is solely determined by certain designer-specified performance functions/parameters and is fully decoupled from the control gain selection and the initial conditions. Finally, both simulation and experimental studies clarify the proposed method and verify its efficiency.

Adaptive nonlinear gain based composite nonlinear feedback controller with input saturation

This article proposes for the first time a novel adaptive nonlinear gain based composite feedback controller. In the proposed method an adaptive nonlinear gain is introduced in the composite feedback controller to improve the system dynamic response. Using the Lyapunov analysis and the adaptive law for the nonlinear gain, it is shown that all the closed loop signals of the system are bounded. Finally, we use a double integrator single-input single-output system and twin rotor multi-input multi-output (MIMO) system to demonstrate the application of the proposed scheme. In both the applications, the improvement in settling time and root mean square error is scalable by the adaptive nonlinear gain based composite feedback control. Further the controller is successfully tested for a set of desired set points for MIMO system example which will create large initial errors.

Adaptive stabilization of high-order time-delay nonlinear systems with unknown state-dependent growth rates

This paper investigates the problem of adaptive stabilization by state feedback for a class of high-order nonlinear systems with time-varying delays. Compared with the existing relevant literature, a distinguishing feature of the systems under investigation is that the growth rates are unknown functions of system states. This renders the existing control methods inapplicable to the control problems of the systems. By skillfully using the method of adding a power integrator, an adaptive state-feedback controller independent of the time delay is explicitly constructed with the help of appropriate Lyapunov–Krasovskii functionals. It is proved that the states of the time-delay nonlinear systems can be regulated to the origin, while all the closed loop signals are globally uniformly bounded. Finally, both physical and academic examples are provided to illustrate the effectiveness of the proposed scheme.

Nonlinear power system excitation control using adaptive wavelet networks

A wavelet network-based nonlinear excitation control is designed to enhance the transient stability of a power system. The power system model used to improve the transient stability via excitation control can be written in the canonical form. The resulting excitation control signal that achieves a prescribed tracking performance is shown to include unknown nonlinear terms. A wavelet network is constructed to generate an approximation of these nonlinear terms and hence facilitate the design of the nonlinear excitation controller. Based on the wavelet network approximation, suitable adaptive control and appropriate parameter update algorithm are developed to force the nonlinear uncertain power system to track a prescribed trajectory with desired dynamic performance. It is shown that the proposed controller achieves ultimately bounded tracking error and boundedness of the closed loop signals. A single machine infinite bus system with uncertain fault location is presented to illustrate the proposed design procedure and exhibit its performance. The performance of the proposed excitation controller is compared with the classical IEEE-type ST1A static exciter equipped with a power system stabilizer.

The global build-up to intrinsic ELM bursts and comparison with pellet triggered ELMs seen in JET

We focus on JET plasmas in which ELMs are triggered by pellets in the presence of ELMs which occur naturally. We perform direct time domain analysis of signals from fast radial field coils and toroidal full flux azimuthal loops. These toroidally integrating signals provide simultaneous high time resolution measurements of global plasma dynamics and its coupling to the control system. We examine the time dynamics of these signals in plasmas where pellet injection is used to trigger ELMs in the presence of naturally occurring ELMs. Pellets whose size and speed are intended to provide maximum local perturbation for ELM triggering are launched at pre-programmed times, without correlation to the occurrence times of intrinsic ELMs. Pellet rates were sufficiently low to prevent sustained changes of the underlying plasma conditions and natural ELM behaviour. We find a global signature of the build-up to natural ELMs in the temporal analytic phase of both the full flux loops and fast radial field coil signals. Before a natural ELM, the signal phases align to the same value on a 2–5 ms timescale. This global build up to a natural ELM occurs whilst the amplitude of the full flux loop and fast radial field coil signals are at their background value: it precedes the response seen in these signals to the onset of ELMing. In contrast these signals do not clearly phase align before the ELM for ELMs which are the first to occur following pellet injection. This provides a direct test that can distinguish when an ELM is triggered by a pellet as opposed to occurring naturally. It further supports the idea [–] of a global build up phase that precedes natural ELMs; pellets can trigger ELMs even when the signal phase is at a value when a natural ELM is unlikely to occur.

Abstract 5091: Synergistic apoptosis induced by combined PI3 kinase and bcl-xl inhibition in genotypic subsets of prostate cancer is attenuated by a feedback signaling loop via the alpha-5 integrin

Abstract Background: Integrin-mediated cellular adhesion to extracellular matrix components is a crucial regulator of tumor cell survival and chemoresistance. The integrin alpha 5 (ITGA5) plays a vital role in the migration and adhesion of prostate cancer (PCa) cells to fibronectin secreted by bone-derived mesenchymal stromal cells (Joshi, 2015), architects of a metastatic niche (Shiozawa, 2011). Hypothesis: The mechanism(s) whereby ITGA5 regulates the survival and chemoresistance in PCa may define novel therapeutic approaches. Methods and Results: To assess the pro-survival function of ITGA5 in PCa, we found that ITGA5 shRNA reduced bcl-2 and bcl-xl expression, and induced apoptosis in PC-3 cells. In these PTEN-mutant (mt) AR-negative(-) cells, pharmacological inhibition of the PI3K signaling pathway (BKM120) in combination with ITGA5 knockdown synergistically induced apoptosis as assessed by induction of cleaved caspase-3 and cleaved PARP. Similarly, BKM120 in combination with pharmacological inhibition of bcl-2/bcl-xL (ABT263) also induced apoptosis in synergistic fashion in PC-3 cells. Synergistic apoptosis with PI3-kinase inhibitors (BKM120, pictilisib) and ABT-263 was restricted to PTEN-mt PC-3 and LNCaP cells and was not observed in PTEN-wt, AR- DU145 cells. The pan-Akt-inhibitor GDC-0068 in combination with ABT263 induced apoptosis specifically in PTEN-mt AR+ LNCaP and C4-2B cells. By contrast, there was diminished evidence of synergy of PI3-Kinase inhibitors and bcl-2 specific inhibition with ABT199 pointing toward the requirement of bcl-xl inhibition. However, resistance to longer-term therapy with PI3K and bcl-xl/bcl-2 inhibition was observed in PC-3 but not LNCaP cells. Although single-agent PI3K inhibitor therapy downregulates ITGA5 expression in PC-3 cells, by contrast bcl-2/bcl-xl inhibitor therapy, alone or in combination with PI3K inhibitor therapy, strongly upregulates ITGA5 expression together with Akt activation suggesting that ITGA5 represents a pathway of resistance to combinatorial therapy through feedback loop signals generated with bcl-xl inhibition. In support of this hypothesis, ITGA5 knockdown together with BKM120 and ABT263 combinatorial therapy blocked the upregulation of ITGA5 and associated Akt activation, further reduced bcl-xl expression, and enhanced apoptosis in PC-3 cells. In PTEN-wild type AR-positive VCAP cells, evidence for synergistic apoptosis with PI3K and bcl-2/bcl-xl inhibition was also obtained suggesting that the TMPRSS2-ERG fusion may phenocopy the pro-survival pathways of PTEN-deficient cells. Conclusions: These data point toward a personalized pharmacological strategy combining PI3-kinase or Akt inhibition with bcl-2/bcl-xL inhibition in genotypic subsets of prostate cancer and identify a potential resistance pathway mediated by ITGA5-mediated signaling. Citation Format: Wenying Ren, Raghav Joshi, Paul Mathew. Synergistic apoptosis induced by combined PI3 kinase and bcl-xl inhibition in genotypic subsets of prostate cancer is attenuated by a feedback signaling loop via the alpha-5 integrin. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5091.

Observer-based adaptive fuzzy controller for nonlinear systems with unknown control directions and input saturation

This paper addresses design of an observer-based adaptive fuzzy controller for a class of single-input–single-output (SISO) nonlinear systems with unknown dynamics subject to input nonlinearity and unknown direction. The proposed controller is singularity free. A high-gain observer is designed to estimate the unmeasured states, and the Lipschitz condition for proving boundedness of the estimated states is relaxed. The Nussbaum function is used to handle the unknown virtual control directions and the backstepping technique has been applied for controller design. It is proved that all closed loop signals are semi-globally uniformly ultimately bounded (SGUUB) and the output tracking error converges to a small neighborhood of the origin by choosing the design parameters appropriately. Numerical example illustrates effectiveness of the proposed method even for the system with a change in control direction.

Fault tolerant finite-time leader–follower formation control for autonomous surface vessels with LOS range and angle constraints

In this work, we present a novel fault tolerant leader–follower formation control scheme for a group of underactuated autonomous surface vessels with partially known control input gain functions, where the line-of-sight (LOS) range and angle tracking errors are required to be constrained. Both parametric system uncertainties with time-varying unknown functions and nonparametric system uncertainties satisfying norm-bounded conditions are discussed. To address LOS range and angle constraints and finite time convergence, time-varying tan-type barrier Lyapunov functions (BLFs) are incorporated with the control scheme. For the formation control, only measurements of LOS range and angle are used for control implementation, no other information about the leader is required. We show that under the proposed control method, despite the presence of actuator faults and system uncertainties, the formation tracking errors can converge into arbitrarily small neighborhoods around zero in finite time, while the constraint requirements on the LOS range and angle will not be violated. All closed loop signals are bounded. Simulation results further demonstrate the effectiveness of the proposed method.

Centering the Organizing Center in the Arabidopsis thaliana Shoot Apical Meristem by a Combination of Cytokinin Signaling and Self-Organization

Plants have the ability to continously generate new organs by maintaining populations of stem cells throught their lives. The shoot apical meristem (SAM) provides a stable environment for the maintenance of stem cells. All cells inside the SAM divide, yet boundaries and patterns are maintained. Experimental evidence indicates that patterning is independent of cell lineage, thus a dynamic self-regulatory mechanism is required. A pivotal role in the organization of the SAM is played by the WUSCHEL gene (WUS). An important question in this regard is that how WUS expression is positioned in the SAM via a cell-lineage independent signaling mechanism. In this study we demonstrate via mathematical modeling that a combination of an inhibitor of the Cytokinin (CK) receptor, Arabidopsis histidine kinase 4 (AHK4) and two morphogens originating from the top cell layer, can plausibly account for the cell lineage-independent centering of WUS expression within SAM. Furthermore, our laser ablation and microsurgical experiments support the hypothesis that patterning in SAM occurs at the level of CK reception and signaling. The model suggests that the interplay between CK signaling, WUS/CLV feedback loop and boundary signals can account for positioning of the WUS expression, and provides directions for further experimental investigation.

Implementation of a new iterative learning control algorithm on real data

In this paper, a newly presented approach is proposed for closed-loop automatic tuning of a proportional integral derivative (PID) controller based on iterative learning control (ILC) algorithm. A modified ILC scheme iteratively changes the control signal by adjusting it. Once a satisfactory performance is achieved, a linear compensator is identified in the ILC behavior using casual relationship between the closed loop signals. This compensator is approximated by a PD controller which is used to tune the original PID controller. Results of implementing this approach presented on the experimental data of Damavand tokamak and are consistent with simulation outcome.

Adaptive control of nonlinear systems with full state constraints using Integral Barrier Lyapunov Functionals

In this study, a controller design for nonlinear strict feedback systems with full state constrains is presented. A backstepping stable controller is designed by using the Integral Barrier Lyapunov Functionals (iBLF). Compared with the previous designs, the systems are required to contain the unknown parameters. Under the backstepping control-based iBLF, the output tracking is well achieved without violation of any constraint and the closed loop signals are bounded. The stability of the closed-loop system is analyzed by using the Lyapunov theorem. Finally, a simulation example is used to verify the effectiveness of the proposed design.

Prescribed performance fuzzy backstepping control for nonlinear large-scale systems

In this paper, a fuzzy backstepping control (BSC) is proposed in order to design a controller that guarantees a prescribed tracking error performance for nonlinear large-scale systems. A virtual error constraint variable whose basic idea originates from funnel control is defined for the purpose of a constraint variable in the recursive BSC design steps. In addition, an adaptive fuzzy system is considered to compensate for the unknown nonlinear dynamics and differentiated variables of the BSC system, which give rise to a complex controller structure because the repeated differentiation of the virtual control variable is used in the design procedures. Satisfaction of a prescribed performance and boundedness of the overall closed loop signals are evaluated via simulation and experiment.

Adaptive stabilization of high-order time-delay nonlinear systems with unknown state-dependent growth rates

This paper investigates the problem of adaptive stabilization by state feedback for a class of high-order nonlinear systems with time-varying delays. Compared with the existing relevant literature, a distinguishing feature of the systems under investigation is that the growth rates are unknown functions of system states. This renders the existing control methods inapplicable to the control problems of the systems. By skillfully using the method of adding a power integrator, an adaptive state-feedback controller independent of the time delay is explicitly constructed with the help of appropriate Lyapunov–Krasovskii functionals. It is proved that the states of the time-delay nonlinear systems can be regulated to the origin, while all the closed loop signals are globally uniformly bounded. Finally, both physical and academic examples are provided to illustrate the effectiveness of the proposed scheme.

Adaptive sliding mode fuzzy control for unknown robots with arbitrarily-switched constraints

This article addresses the control problem of robots with unknown dynamics and arbitrarily-switched unknown constraints. Such kind of robots will be shown to be unknown hybrid systems with arbitrary switching and an Adaptive Sliding Mode Fuzzy Control (ASMFC) strategy is proposed that handles the unknown dynamics of the robot along with the unknown constraints arbitrary switching. The ASMFC is a synergy of finding a Common Lyapunov Function (CLF) between the resulted switched subsystems of the considered robots, employing the Fuzzy Logic Systems (FLS), and the use of the Sliding Mode Control (SMC). The CLF accommodates the constraints arbitrary switching, the SMC adds robustness against possible parameters drift, and the FLS approximates the unknown robot dynamics. All unknown parameters are adapted online and all closed loop signals are guaranteed to be bounded. The proposed strategy is validated by conducting an experiment on a KUKA Lightweight Robot (LWR) doing a typical force-guided peg-in-hole assembly task that falls in the category of robot systems under consideration. Excellent tracking performance is obtained when using the ASMFC strategy. Comparison is conducted with the performance of a PD controller that is widely used in commanding industrial robots and the superiority of the proposed strategy is shown.

The global build-up to intrinsic edge localized mode bursts seen in divertor full flux loops in JET

A global signature of the build-up to an intrinsic edge localized mode (ELM) is found in the temporal analytic phase of signals measured in full flux azimuthal loops in the divertor region of JET. Toroidally integrating, full flux loop signals provide a global measurement proportional to the voltage induced by changes in poloidal magnetic flux; they are electromagnetically induced by the dynamics of spatially integrated current density. We perform direct time-domain analysis of the high time-resolution full flux loop signals VLD2 and VLD3. We analyze plasmas where a steady H-mode is sustained over several seconds during which all the observed ELMs are intrinsic; there is no deliberate intent to pace the ELMing process by external means. ELM occurrence times are determined from the Be II emission at the divertor. We previously [Chapman et al., Phys. Plasmas 21, 062302 (2014); Chapman et al., in 41st EPS Conference on Plasma Physics, Europhysics Conference Abstracts (European Physical Society, 2014), Vol. 38F, ISBN 2-914771-90-8] found that the occurrence times of intrinsic ELMs correlate with specific temporal analytic phases of the VLD2 and VLD3 signals. Here, we investigate how the VLD2 and VLD3 temporal analytic phases vary with time in advance of the ELM occurrence time. We identify a build-up to the ELM in which the VLD2 and VLD3 signals progressively align to the temporal analytic phase at which ELMs preferentially occur, on a ∼2−5ms timescale. At the same time, the VLD2 and VLD3 signals become temporally phase synchronized with each other, consistent with the emergence of coherent global dynamics in the integrated current density. In a plasma that remains close to a global magnetic equilibrium, this can reflect bulk displacement or motion of the plasma. This build-up signature to an intrinsic ELM can be extracted from a time interval of data that does not extend beyond the ELM occurrence time, so that these full flux loop signals could assist in ELM prediction or mitigation.

Space‐interweaving‐time‐convolutional space–time codes for full‐duplex MIMO relay networks

AbstractIn this paper, a space‐interweaving‐time‐convolutional space–time coding (SITC‐STC) scheme is proposed to collect cooperative diversity gain for full‐duplex multiple‐input multiple‐output (MIMO) relay systems. It is shown that because of the loop channel interference and crosstalk interference caused by different transmit and receive antenna pairs of the MIMO relay, the full‐duplex mechanism cannot be achieved effectively in MIMO relay networks by directly adopting relaying methods for half‐duplex systems. The traditional method to deal with this issue is removing the interference as much as possible. While, the proposed SITC‐STC scheme only needs to cancel partial interference signals and then amplify together with interweaving in space by a power control matrix. That is, the loop signals are not directly cancelled but used for coding in the SITC‐STC scheme. Simulation results verify the proposed SITC‐STC scheme by comparing it with existing STC schemes and show that it can collect most of the diversity gain in MIMO relay networks. Copyright © 2015 John Wiley & Sons, Ltd.