Classical Feedback Research Articles

Boosted Flight Controller for Quadrotor Navigation under disturbances

Lightweight Unmanned Aerial Vehicles (UAV) are usually very sensitive to the external disturbances during outdoor experimentations. These adverse conditions make both the dynamic modeling and the control tasks more complex. Thus, it is necessary to employ an efficient control technique with acceptable performance without a complete knowledge of the disturbed model. This is because, in the classic feedback linearization control, the deviations between the model and the real plant may produce poor performance. Throughout the present paper, Dynamic Sliding Mode Control (DSMC) technique is designed to deal with the disturbances and which has never been used for quadrotors. Unlike the existing sliding mode techniques, the designed one uses an input-dependent sliding surface in order to enhance the robustness level of the classical feedback linearization control law. The effectiveness of this approach that ensures 3D trajectory tracking of quadrotor is demonstrated through numerical simulations.

Signal-to-Noise Ratio Requirements for Discrete-time PID Controllers

In networked control a channel model is explicitly considered in discrete-time within the classic feedback loop scheme. It is well known by now that the channel model signal-to-noise ratio (SNR) happens to be an important parameter related to the overall stabilisability of the output feedback loop. In this paper we offer the rules for the design of discrete-time proportional-integral-derivative (PID) controllers for given closed loop bandwidth that quantifies the SNR requirement for the memoryless additive white Gaussian noise (AWGN) channel over the feedback path, which is a common used communication channel model. The design is centered on a PID controller structure due to its wide use in the industry. Since we focus on a PID controller structure, we then reduce the analysis to plant models of first and second order which are the structures more compatible with the PID controller design.

An Enhanced Smith Predictor Based Control System Using Feedback-feedforward Structure for Time-delay Processes

This paper presents enhanced Smith predictor based control systems (SPBCSs) for processes with a time-varying or fixed time delay. This work focuses on improving the arrangement and asynchrony of SPBCS components rather than the design of the predictor and the feedback controller, which have been well discussed in the literature. The proposed control system advances SPBCS through implementation of two design recommendations: (i) replacing the classical feedback controller by a feedback-feedforward control system, and (ii) synchronizing the reference signal and the predicted output. As a result, common shortcomings of SPBCSs or control systems based on Pade approximation, i.e. the trade-off between performance and steady-state error, and instability associated with non-minimum-phase systems do not exist in the proposed SPBCS. The superior performance of the proposed control system is demonstrated with two examples: temperature control of an infrared dryer (a system with fixed time-delay) and air-fuel ratio of a lean-burn spark-ignition engine (a system with time-varying delay and lag). The proposed control system is shown to clearly outperform the conventional SPBCS and Internal Model Control (IMC) PID based on Pade approximation for aforementioned examples and performs satisfactorily in the presence of noises, actuator saturations, and severe model inaccuracies.

The asymmetric relationship between returns and implied volatility: Evidence from global stock markets

We investigate the asymmetric relationship between returns and implied volatility for 20 developed and emerging international markets. In particular we examine how the sign and size of return innovations affect the expectations of daily changes in volatility. Our empirical findings indicate that the conditional contemporaneous return-volatility relationship varies not only based on the sign of the expected returns but also upon their magnitude, according to recent results from the behavioral finance literature. We find evidence of an asymmetric and reverse return-volatility relationship in many advanced, Asian, Latin-American, European and South African markets. We show that the US market displays the highest reaction to price falls, Asian markets present the lowest sensitivity to volatility expectations, while the Euro area is characterized by a homogeneous response both in terms of direction and impact. These results may be safely attributed to cultural and societal characteristics. An extensive quantile regression analysis demonstrates that the detected asymmetric pattern varies particularly across the extreme distribution tails i.e., in the highest/lowest quantile ranges. Indeed, the classical feedback and leverage hypotheses appear not plausible, whilst behavioral theories emerge as the new paradigm in real-world applications.

Improving video event retrieval by user feedback

In content based video retrieval videos are often indexed with semantic labels (concepts) using pre-trained classifiers. These pre-trained classifiers (concept detectors), are not perfect, and thus the labels are noisy. Additionally, the amount of pre-trained classifiers is limited. Often automatic methods cannot represent the query adequately in terms of the concepts available. This problem is also apparent in the retrieval of events, such as bike trick or birthday party. Our solution is to obtain user feedback. This user feedback can be provided on two levels: concept level and video level. We introduce the method Adaptive Relevance Feedback (ARF) on video level feedback. ARF is based on the classical Rocchio relevance feedback method from Information Retrieval. Furthermore, we explore methods on concept level feedback, such as the re-weighting and Query Point Modification (QPM) methods as well as a method that changes the semantic space the concepts are represented in. Methods on both concept level and video level are evaluated on the international benchmark TRECVID Multimedia Event Detection (MED) and compared to state of the art methods. Results show that relevance feedback on both concept and video level improves performance compared to using no relevance feedback; relevance feedback on video level obtains higher performance compared to relevance feedback on concept level; our proposed ARF method on video level outperforms a state of the art k-NN method, all methods on concept level and even manually selected concepts.

Tuning of PID Controller Based on Phase Margin for Stable Processes Via IMC Principles

A novel IMC (internal model control) PID tuning method is proposed for stable processes with time delay in the frequency domain. In the paper, the IMC controller is originally transformed into a classical feedback PID controller without approximating the time delay. The phase margin is used for an analytical approach of selecting controller parameter which is directly related to the dynamic performance and robustness of the system in IMC. The resulting analytical IMC-PID controller achieves almost the same control effect as IMC controller.

Investigations of an Accelerometer-based Disturbance Feedforward Control for Vibration Suppression in Adaptive Optics of Large Telescopes

Adaptive Optics (AO) systems in large telescopes do not only correct atmospheric phase disturbances, but they also telescope structure vibrations induced by wind or telescope motions. Often the additional wavefront error due to mirror vibrations can dominate the disturbance power and contribute significantly to the total tip-tilt Zernike mode error budget. Presently, these vibrations are compensated for by common feedback control laws. However, when observing faint natural guide stars (NGS) at reduced control bandwidth, high-frequency vibrations (>5 Hz) cannot be fully compensated for by feedback control. In this paper, we present an additional accelerometer-based disturbance feedforward control (DFF), which is independent of the NGS wavefront sensor exposure time to enlarge the “effective servo bandwidth”. The DFF is studied in a realistic AO end-to-end simulation and compared with commonly used suppression concepts. For the observation in the faint (>13 mag) NGS regime, we obtain a Strehl ratio by a factor of two to four larger in comparison with a classical feedback control. The simulation realism is verified with real measurement data from the Large Binocular Telescope (LBT); the application for on-sky testing at the LBT and an implementation at the E-ELT in the MICADO instrument is discussed.

Discrete approximate optimal vibration control for nonlinear vehicle active suspension

This paper presents the approximate optimal vibration control methodology for discrete nonlinear vehicle active suspension subject to persistent road disturbances. Based on a dynamic model of nonlinear vehicle active suspension and a linear exogenous system model of the persistent road disturbances, a nonlinear two-point boundary value (TPBV) problem is introduced. By introducing a sensitive parameter, the original TPBV problem is reformed as a series of TPBV problems without nonlinear items. A discrete approximate optimal vibration controller (DAOVC) can be obtained by solving a Riccati equation, Stein equation, and nonlinear compensation item, respectively. An iteration algorithm is designed to realize the computational realizability of DAOVC based on the control performance. It is demonstrated that the control performance of ride comfort, road holding ability, and suspension deflection under the DAOVC are much smaller than the ones under the classical feedforward and feedback optimal vibration controller (FFOVC) and open-loop vehicle suspension system.

A New Method for PID Tuning Including Plants Without Ultimate Frequency

The classical relay feedback method for tuning proportional-integral-derivative (PID) controllers cannot be applied to plants whose Nyquist diagrams do not cross the negative real axis; these are customarily tuned based on the reaction curve experiment. In this brief, we propose a tuning method based on a modified relay feedback experiment. In this experiment, a transfer function of constant phase in an arbitrarily large range of frequencies is inserted in the loop. The proposed methodology thus unifies the Ziegler-Nichols-like tuning methods, by allowing PID tuning based on relay feedback for a class of plants without ultimate frequency.

Control Under Stochastic Multiplicative Uncertainties: Part II, Optimal Design for Performance

This paper studies the optimal control design problem for linear discrete-time systems with stochastic multiplicative uncertainties. These uncertainties are assumed to be present in the control inputs and modeled as independent and identically distributed (i.i.d.) random processes. The optimal performance under study is defined in the mean-square sense, referred to as the mean-square optimal H 2 performance. It is shown that the mean-square optimal H 2 control problem via state feedback can be solved using a mean-square stabilizing solution to a modified algebraic Riccati equation (MARE). A necessary and sufficient condition for the existence of this solution is presented, which constitutes a generalization of the solution to the classic optimal H 2 state feedback design problem, whereas the latter can be obtained by solving an algebraic Riccati equation (ARE). It is also proven that the optimal control design problem can be cast as an eigenvalue problem (EVP). For the output feedback case with possible input delays, we show that the mean-square optimal H 2 control problem also amounts to solving an MARE, when the plant has no nonminimum phase zeros from the inputs to the measurement outputs. That is, the global optimal solution is obtained by solving an MARE incorporating the delays. The implication is that in this case a separation principle still holds.

A Lyapunov Stability Theory-Based Control Strategy for Three-Level Shunt Active Power Filter

The three-phase three-wire neutral-point-clamped shunt active power filter (NPC-SAPF), which most adopts classical closed-loop feedback control methods such as proportional-integral (PI), proportional-resonant (PR) and repetitive control, can only output 1st–25th harmonic currents with 10–20 kHz switching frequency. The reason for this is that the controller design must make a compromise between system stability and harmonic current compensation ability under the condition of less than 20 kHz switching frequency. To broaden the bandwidth of the compensation current, a Lyapunov stability theory-based control strategy is presented in this paper for NPC-SAPF. The proposed control law is obtained by constructing the switching function on the basis of the mathematical model and the Lyapunov candidate function, which can avoid introducing closed-loop feedback control and keep the system globally asymptotically stable. By means of the proposed method, the NPC-SAPF has compensation ability for the 1st–50th harmonic currents, the total harmonic distortion (THD) and each harmonic content of grid currents satisfy the requirements of IEEE Standard 519-2014. In order to verify the superiority of the proposed control strategy, stability conditions of the proposed strategy and the representative PR controllers are compared. The simulation results in MATLAB/Simulink (MathWorks, Natick, MA, USA) and the experimental results obtained on a 6.6 kVA NPC-SAPF laboratory prototype validate the proposed control strategy.

Disturbance Observer-Based Input-Output Finite-Time Control of a Class of Nonlinear Systems

This paper is concerned with disturbance observer-based input-output finite-time control of a class of nonlinear systems with one-sided Lipschitz condition, as well as multiple disturbances. Firstly, a disturbance observer is constructed to estimate the disturbance generated by an exogenous system. Secondly, by integrating the estimation of disturbance with a classical state feedback control law, a composite control law is designed and sufficient conditions for input-output finite-time stability (IO-FTS) of the closed-loop system are attained. Such conditions can be converted into linear matrix inequalities (LMIs). Finally, two examples are given to show the effectiveness of the proposed method.

Overexpression of suppressor of cytokine signaling 3 in dorsal root ganglion attenuates cancer-induced pain in rats.

BackgroundCancer-induced pain (CIP) is one of the most severe types of chronic pain with which clinical treatment remains challenging and the involved mechanisms are largely unknown. Suppressor of cytokine signaling 3 (SOCS3) is an important intracellular protein and provides a classical negative feedback loop, thus involving in a wide variety of processes including inflammation and nociception. However, the role of SOCS3 pathway in CIP is poorly understood. The present study was designed to investigate the role of SOCS3 in dorsal root ganglion (DRG) in the development of CIP.MethodCIP was established by injection of Walker 256 mammary gland tumor cells into the rat tibia canal. Whole-cell patch clamping and Western blotting were performed.ResultsFollowing the development of bone cancer, SOCS3 expression was significantly downregulated in rat DRGs at L2–L5 segments. Overexpression of SOCS3, using lentiviral-mediated production of SOCS3 at spinal cord level, drastically attenuated mechanical allodynia and body weight-bearing difference, but not thermal hyperalgesia in bone cancer rats. In addition, overexpression of SOCS3 reversed the hyperexcitability of DRG neurons innervating the tibia, and reduced abnormal expression of toll-like receptors 4 in the DRGs.ConclusionsThese results suggest that SOCS3 might be a key molecular involved in the development of complicated cancer pain and that overexpression of SOCS3 might be an important strategy for treatment for mechanical allodynia associated with bone cancer.

Non linear control of a robotic arm for pipeline reparation

This article presents a non-linear control system for a robotic arm that will be used for pipeline reparation. It starts with the mechanical description of the arm, its parameters and how the arm will repair the pipelines. This arm needs a control law that is non-linear. The proposed control strategy is obtained through the interpolation of classic feedback quadratic controllers that are computed for each operation point in a trajectory. This design is based on a numerical model that avoids computing an analytical model which is very useful for this kind of application. The technique is validated through simulations.

MEMS Inertial Sensors-Based Multi-Loop Control Enhanced by Disturbance Observation and Compensation for Fast Steering Mirror System.

In this paper, an approach to improve the disturbance suppression performance of a fast steering mirror (FSM) tracking control system based on a charge-coupled device (CCD) and micro-electro-mechanical system (MEMS) inertial sensors is proposed. The disturbance observation and compensation (DOC) control method is recommended to enhance the classical multi-loop feedback control (MFC) for line-of-sight (LOS) stabilization in the FSM system. MEMS accelerometers and gyroscopes have been used in the FSM system tentatively to implement MFC instead of fiber-optic gyroscopes (FOG) because of its smaller, lighter, cheaper features and gradually improved performance. However, the stabilization performance of FSM is still suffering a large number of mechanical resonances and time delay induced by a low CCD sampling rate, which causes insufficient error attenuation when suffering uncertain disturbances. Thus, in order to make further improvements on the stabilization performance, a cascaded MFC enhanced by DOC method is proposed. The sensitivity of this method shows the significant improvement of the conventional MFC system. Simultaneously, the analysis of stabilization accuracy is also presented. A series of comparative experimental results demonstrate the disturbance suppression performance of the FSM control system based on the MEMS inertial sensors can be effectively improved by the proposed approach.

Decentrailized formation flight control of quadcopters using robust feedback linearization

In this paper, a decentralized formation flight control scheme is proposed for a group of quadcopters using classical feedback linearization. Existing works typically involve a complicated design of nonlinear formation control laws, whereas the present work uses a linear control law for under-actuated nonlinear quadcopters. This linear formation control approach has a strong merit, in that it can be easily designed in a way to clearly guarantee the stability and performance of the collective nonlinear system quantitatively in terms of classical measures (e.g. stability and robustness margins). In this paper, the feedback linearization can transform nonlinear quadcopters dynamics into simple fourth-order and double integrators, for which a linear formation control law is designed to achieve a desired formation and heading synchronization through local information exchanges only. Moreover, a sliding-mode compensator is designed for possible dynamics inversion errors during the feedback linearization. Simulation results including a comparison with a recently proposed control law are presented to demonstrate the practical usefulness of the present work.

Electrotactile EMG feedback improves the control of prosthesis grasping force

Objective. A drawback of active prostheses is that they detach the subject from the produced forces, thereby preventing direct mechanical feedback. This can be compensated by providing somatosensory feedback to the user through mechanical or electrical stimulation, which in turn may improve the utility, sense of embodiment, and thereby increase the acceptance rate. Approach. In this study, we compared a novel approach to closing the loop, namely EMG feedback (emgFB), to classic force feedback (forceFB), using electrotactile interface in a realistic task setup. Eleven intact-bodied subjects and one transradial amputee performed a routine grasping task while receiving emgFB or forceFB. The two feedback types were delivered through the same electrotactile interface, using a mixed spatial/frequency coding to transmit 8 discrete levels of the feedback variable. In emgFB, the stimulation transmitted the amplitude of the processed myoelectric signal generated by the subject (prosthesis input), and in forceFB the generated grasping force (prosthesis output). The task comprised 150 trials of routine grasping at six forces, randomly presented in blocks of five trials (same force). Interquartile range and changes in the absolute error (AE) distribution (magnitude and dispersion) with respect to the target level were used to assess precision and overall performance, respectively. Main results. Relative to forceFB, emgFB significantly improved the precision of myoelectric commands (min/max of the significant levels) for 23%/36% as well as the precision of force control for 12%/32%, in intact-bodied subjects. Also, the magnitude and dispersion of the AE distribution were reduced. The results were similar in the amputee, showing considerable improvements. Significance. Using emgFB, the subjects therefore decreased the uncertainty of the forward pathway. Since there is a correspondence between the EMG and force, where the former anticipates the latter, the emgFB allowed for predictive control, as the subjects used the feedback to adjust the desired force even before the prosthesis contacted the object. In conclusion, the online emgFB was superior to the classic forceFB in realistic conditions that included electrotactile stimulation, limited feedback resolution (8 levels), cognitive processing delay, and time constraints (fast grasping).

In Vivo Conditions Enable IFNAR-Independent Type I Interferon Production by Peritoneal CD11b + Cells upon Thogoto Virus Infection

Type I interferons (IFNs) crucially contribute to host survival upon viral infections. Robust expression of type I IFNs (IFN-α/β) and induction of an antiviral state critically depend on amplification of the IFN signal via the type I IFN receptor (IFNAR). A small amount of type I IFN produced early upon virus infection binds the IFNAR and activates a self-enhancing positive feedback loop, resulting in induction of large, protective amounts of IFN-α. Unexpectedly, we found robust, systemic IFN-α expression upon infection of IFNAR knockout mice with the orthomyxovirus Thogoto virus (THOV). The IFNAR-independent IFN-α production required in vivo conditions and was not achieved during in vitro infection. Using replication-incompetent THOV-derived virus-like particles, we demonstrate that IFNAR-independent type I IFN induction depends on viral polymerase activity but is largely independent of viral replication. To discover the cell type responsible for this effect, we used type I IFN reporter mice and identified CD11b(+) F4/80(+) myeloid cells within the peritoneal cavity of infected animals as the main source of IFNAR-independent type I IFN, corresponding to the particular tropism of THOV for this cell type. Type I IFNs are crucial for the survival of a host upon most viral infections, and, moreover, they shape subsequent adaptive immune responses. Production of protective amounts of type I IFN critically depends on the positive feedback amplification via the IFNAR. Unexpectedly, we observed robust IFNAR-independent type I IFN expression upon THOV infection and unraveled molecular mechanisms and determined the tissue and cell type involved. Our data indicate that the host can effectively use alternative pathways to induce type I IFN responses if the classical feedback amplification is not available. Understanding how type I IFN can be produced in large amounts independently of IFNAR-dependent enhancement will identify mechanisms which might contribute to novel therapeutic strategies to fight viral pathogens.

On Feedback Architectures With Zero-Vibration Signal Shapers

The classical and recent feedback solutions for signal shapers are reviewed and critically analyzed in this paper. Based on this assessment, a new effective feedback control architecture is proposed, suitable for manipulation of weakly damped flexible structures. More specifically, we propose to include the inverse of a signal shaper's dynamics in the feedback path, and we justify this architecture by analysis of important feedback loop channels, namely the feedback responses from input disturbance to output and from reference to output. Both the classical ZV shaper with one lumped delay, and more recent shapers with distributed delays are considered and analyzed. The most appreciated features of suitable distributed-delay shapers are retarded characteristics—the closed-loop spectrum does not exhibit high-frequency roots close to the imaginary axis (in contrast to ZV shapers)—and at the same time reduced sensitivity of the closed loop interconnection to output disturbances. Feedback performance is demonstrated by two laboratory experiments.

A review of progress towards understanding the transient global mean surface temperature response to radiative perturbation

The correct understanding of the transient response to external radiative perturbation is important for the interpretation of observed climate change, the prediction of near-future climate change, and committed warming under climate stabilization scenarios, as well as the estimation of equilibrium climate sensitivity based on observation data. It has been known for some time that the radiative damping rate per unit of global mean surface temperature increase varies with time, and this inconstancy affects the transient response. Knowledge of the equilibrium response alone is insufficient, but understanding the transient response of the global mean surface temperature has made rapid progress. The recent progress accompanies the relatively new concept of the efficacies of ocean heat uptake and forcing. The ocean heat uptake efficacy associates the temperature response induced by ocean heat uptake with equilibrium temperature response, and the efficacy of forcing compares the temperature response caused by non-CO2 forcing with that by CO2 forcing. In this review article, recent studies on these efficacies are discussed, starting from the classical global feedback framework and basis of the transient response. An attempt is made to structure different studies that emphasize different aspects of the transient response and to stress the relevance of those individual studies. The implications on the definition and computation of forcing and on the estimation of the equilibrium response in climate models are also discussed. Along with these discussions, examples are provided with MIROC climate model multi-millennial simulations.