Ordinary Feedback Research Articles

BiDFDC-Net: a dense connection network based on bi-directional feedback for skin image segmentation.

Accurate segmentation of skin lesions in dermoscopic images plays an important role in improving the survival rate of patients. However, due to the blurred boundaries of pigment regions, the diversity of lesion features, and the mutations and metastases of diseased cells, the effectiveness and robustness of skin image segmentation algorithms are still a challenging subject. For this reason, we proposed a bi-directional feedback dense connection network framework (called BiDFDC-Net), which can perform skin lesions accurately. Firstly, under the framework of U-Net, we integrated the edge modules into each layer of the encoder which can solve the problem of gradient vanishing and network information loss caused by network deepening. Then, each layer of our model takes input from the previous layer and passes its feature map to the densely connected network of subsequent layers to achieve information interaction and enhance feature propagation and reuse. Finally, in the decoder stage, a two-branch module was used to feed the dense feedback branch and the ordinary feedback branch back to the same layer of coding, to realize the fusion of multi-scale features and multi-level context information. By testing on the two datasets of ISIC-2018 and PH2, the accuracy on the two datasets was given by 93.51% and 94.58%, respectively.

A Novel Hybrid (PID + MRAC) Adaptive Controller for an Air Levitation System

The air levitation system belongs to a class of systems with fast dynamics and low damping. Such characteristics make the plant intrinsically unstable and respond in a non-linear form. Thus, it is prohibitive to use classic control techniques, such as the PID (Proportional-Integral-Derivative) controller, to track the position of the sphere. The control system must be able to compensate the non-linearities, high oscillation and reject disturbances. Thus, this research proposes to create a new approach for the hybrid controller (PID + MRAC) present in the literature. The topological character of the proposed MRAC (Model Reference Adaptive Controller) consists of three parts: a feedforward controller, a derivative portion and an ordinary feedback. The feedforward portion has the purpose of rejecting undesirable disturbances. The derivative portion increases the stability of the system and the ordinary feedback makes the error null in steady state. Due to the convergence time of the adjustment parameters, MRAC performs poorly during reference changes and in the rejection of disturbances. Thus, it is common practice to use the MRAC with the PID controller. In its methodological aspect, the control law was created from Lyapunov's theory, with the purpose of ensuring asymptotic stability for the system. As a result, the proposed controller (Hybrid-MRAC or H-MRAC) showed better results than a literature reference (A-PID), in terms of mean absolute (MAE), mean square (MSE) and root mean square (RMSE) errors. In MAE simulations it was 51,25% lower on average, MSE was 51,65% and RMSE 31,40%. In the experiments, the MAE was on average 19,72% lower, the MSE 42,92% and the RMSE 18,58%.

Controlling of jerk chaotic system via linear feedback control strategies

In this paper, the strategies of linear feedback control for jerk system is considered. These strategies consist of four strategies (ordinary feedback control, dislocated feedback control, speed feedback control, and enhancing feedback control). We propose to combine between these strategies and obtained a better result from this combine. Numerical solution achieved the same results.

The Application of Some Linear Feedback Control Strategies on 3D Chaotic System

This paper tackles to some linear feedback control strategies, where we take a 3D chaotic system with a five critical point of unstability, which is discovered by scientist [Zhu Congxu, 2010]. So we applied some linear feedback strategies: first strategy Ordinary Feedback Control and the second strategy Dislocate Feedback Control on this system at origin point and we noticed that a necessary condition for suppression is getting positive feedback coefficient; but this condition fails at some strategies. For this reason, we focused on these cases in our search, and design more than a strategy for studying these different situations. Theoretical analysis and numerical simulation check the validity of the results obtained.

Probabilistic Approach to Finite State Mean Field Games

We study mean field games and corresponding N-player games in continuous time over a finite time horizon where the position of each agent belongs to a finite state space. As opposed to previous works on finite state mean field games, we use a probabilistic representation of the system dynamics in terms of stochastic differential equations driven by Poisson random measures. Under mild assumptions, we prove existence of solutions to the mean field game in relaxed open-loop as well as relaxed feedback controls. Relying on the probabilistic representation and a coupling argument, we show that mean field game solutions provide symmetric $$\varepsilon _N$$-Nash equilibria for the N-player game, both in open-loop and in feedback strategies (not relaxed), with $$\varepsilon _N\le \frac{\text {constant}}{\sqrt{N}}.$$ Under stronger assumptions, we also find solutions of the mean field game in ordinary feedback controls and prove uniqueness either in case of a small time horizon or under monotonicity.

Some Problems of Feedback Control Strategies and It’s Treatment

This paper extends and improves the feedback control strategies. In detailed, the ordinary feedback, dislocated feedback, speed feedback and enhancing feedback control for a several dynamical systems are discussed here. It is noticed that there some problems by these strategies. For this reason, this Letter proposes a novel approach for treating these problems. The results obtained in this paper show that the strategies with positive feedback coefficients can be controlled in two cases and failed in another two cases. Theoretical and numerical simulations are given to illustrate and verify the results.

Yet another four-dimensional chaotic system with multiple coexisting attractors

The study of nonlinear system with coexisting chaotic attractors is of recent interest. In this letter, we introduce a new four-dimensional chaotic system with coexisting attractors. The system has three quadratic nonlinearities and only one unstable fixed point. Basic dynamics of the system are analyzed, including dissipativity, equilibria, etc. The coexisting attractors in the system is investigated by numerical simulation. The control problem of the system is also considered. By using an ordinary feedback controller and a speed feedback controller, the chaotic behavior of the system can be well suppressed.

Controlling Neimark-Sacker Bifurcation in Delayed Species Model Using Feedback Controller

Based on the stability and orthogonal polynomial approximation theory, the ordinary, dislocated, enhancing, and random feedback control methods are used to suppress the Neimark-Sacker bifurcation to fixed point in this paper. It is shown that the convergence rate of enhancing feedback control and random feedback control can be faster than those of dislocated and ordinary feedback control. The random feedback control method, which does not require any adjustable control parameters of the model, just only slightly changes the random intensity. Finally, numerical simulations are presented to verify the effectiveness of the proposed controllers.

Improvement of Transient Response in Signal Transformation Approach by Proper Compensator Initialization

In this brief, the transient performance of the signal transformation approach (STA) is considerably enhanced by initializing the state vector of the compensator to appropriate values. For triangular reference tracking, it is shown that the proposed method is identical to the impulsive state multiplication (ISM) approach. Through simulations and experiments, we also show that the proposed method can be equally applied to improve the STA for arbitrarily shaped desired signals, where ISM is not applicable. Tracking efficacy of the proposed method compared with that of an ordinary feedback loop with a similar noise rejection performance is also demonstrated.

An unusual chaotic system and its control

This paper reports the finding of a new chaotic system in a simple three-dimensional (3D) autonomous system with two nonlinear terms, which has rich and complex dynamical behaviors, and its control. Of particular interest is the fact that new chaotic system has a chaotic attractor, one stable node-focus and one unstable saddle-focus. To understand the complex dynamics of the system, some basic dynamical properties, such as equilibria, stability, the complete mathematical characterizations for Hopf bifurcation are rigorously derived and studied. Furthermore, the existence of singularly degenerate heteroclinic cycles for a suitable choice of parameters is investigated. Finally, the control problem of a new unusual chaotic system is investigated using negative feedback control. The ordinary feedback control, dislocated feedback control, enhancing feedback control and speed feedback control are used to suppress chaos to unstable equilibrium. The design is also illustrated with both simulations and experiments.

Application of a dead time compensator as a PID controller

In this paper, the application of Dominant Gain Concept for controlling time delay processes is considered from a new viewpoint. In this viewpoint, time delay is considered as function with infinite Right Half Plane (RHP) zeros which are transferred to the Left Half Plane by adding a proper transfer function to the open loop function. Furthermore, by defining a new concept, called minimum-gain frequency, the propositions for control system stability and the manner of choosing order and gain of the added transfer function are proved. Also, the application of this method is studied in order to simultaneously compensate for the Right Half Plane zeros and time-delay. Finally, easy application of this method is shown in an ordinary feedback loop as a PID controller.

A new hyperchaotic system from the Lü system and its control

This paper presents a 4D new hyperchaotic system which is constructed by a linear controller to a 3D Lü system. Some complex dynamical behaviors such as Hopf bifurcation, chaos and hyperchaos of the simple 4D autonomous system are investigated and analyzed. The corresponding hyperchaotic and chaotic attractor is first numerically verified through investigating phase trajectories, Lyapunove exponents, bifurcation path, analysis of power spectrum and Poincaré projections. Furthermore, the design is illustrated with both simulations and experiments. Finally, the control problem of a new hyperchaotic system is investigated using negative feedback control. Ordinary feedback control, dislocated feedback control and speed feedback control are used to suppress hyperchaos to an unstable equilibrium. Numerical simulations are presented to demonstrate the effectiveness of the proposed controllers.

Magnetic telemanipulation device with mass uncertainty: Modeling, simulation and testing

Recently, magnetic telemanipulation devices have shown a great deal of promise in such areas as semi-conductor manufacturing, wind tunnels, drug delivery, and many more. However, these devices are generally associated with problems caused by payload variation and uncertainties in the parameters of the system which in turn, have limited the development and application of magnetic telemanipulation technology to its full capacity. This paper addresses and deals with these is sues by implementation of a precise position control method for a magnetic telemanipulation system with high level of uncertainties in its parameters. The levitation system used in this study is p rimarily designed for performing remote pick and place operations. The levitated object is a 28 gr microrobot capable of grasping and releasing payloads as heavy as 8 gr. To cope with the uncertainties in the modeling and payload variation, a model reference adaptive feedback linearization (MRAFL) controller is designed and its performance compared with an ordinary feedback linearization (FL) controller. Through experimental results it is shown that the MRAFL controller enables the microrobot to grasp and transport a payload as heavy as 30% of its own weight without a considerable effect on its positioning accuracy. In the presence of the payload, the MRAFL controller resulted in a RMS positioning error of 8 µm compared with 27.9 µm of the FL controller. The approach presented in this work is versatile as it leads to the modeling and control of a highly nonlinear system through a modular approach that can be applied to a variety of magnetic levitation and telemanipulation systems.

Controlling hyperchaos in hyperchaotic Lorenz system using feedback controllers

In this paper, the control strategies for hyperchaotic Lorenz system is investigated. The ordinary, dislocated, enhancing and speed feedback controls are used to suppress hyperchaos to unstable equilibrium. The Routh–Hurwitz criterion is used to derive the conditions of stability of the controlled hyperchaotic systems. It is found that the coefficients of enhancing feedback control and dislocated feedback control may be smaller than those of ordinary feedback control, so, the complexity and cost of the system control are reduced. Numerical simulations are given to illustrate the effectiveness of the proposed controllers.

Controlling friction-induced instability by recursive time-delayed acceleration feedback

A novel time-delayed acceleration feedback method of controlling friction-induced instability is proposed. A single degree-of-freedom mechanical oscillator on a moving belt represents the basic friction-driven system. The control force is synthesized based on an infinite weighted sum of the acceleration of the vibrating mass measured at regular intervals in the past. Such a control force can be effectively produced by the recursive summation of the time-delayed acceleration and the time-delayed control signal, and hence the technique is termed as the recursive time-delayed acceleration feedback control. The local stability analysis of the equilibrium reveals nontrivial and beneficial influences of the recursive gain on the system performance. Robustness of the control is shown to improve with the increasing value of the recursive gain. A multiple time scale based analysis of the system elucidates the role of the recursive gain in enhancing the amount of dissipation produced by the control action. The influences of the time-delay and the control gain on the optimized performance of the system are also discussed. Numerical simulations of the system equations corroborate the analytical results. The present method is believed to be applicable to any self-excited system having a large degree of instability that is not removable by an ordinary time-delayed feedback.

Sufficient Conditions for Closed-Loop Asymptotic Controllability and Stabilization by Smooth Time-Varying Feedback Integrator

For general finite-dimensional time-varying nonlinear systems, we derive sufficient conditions for closed-loop asymptotic controllability and asymptotic stabilization by means of a smooth ordinary time-varying feedback integrator. The main hypotheses are based on the existence of an almost smooth time-varying control Lyapunov function. The corresponding results generalize earlier works in the literature concerning dynamic stabilization for autonomous systems.

Feedback control strategies for the Liu chaotic system

This Letter proposed three strategies of the dislocated feedback control, enhancing feedback control and speed feedback control of the Liu chaotic system to its unstable equilibrium points. It is found that the coefficients of enhancing feedback control and speed feedback control are smaller than those of ordinary feedback control, so, the complexity and cost of the system control are reduced. Theoretical analysis and numerical simulation are given, revealing the effectiveness of these strategies.

Preview Control for Road Following of Vision Guided Intelligent Vehicle

The vision-guided intelligent vehicle acquires the road information by machine vision,and follows the road automatically. Ordinary feedback control only uses the present road information,so the intelligent vehicle can hardly work efficiently in complicated or emergent conditions.By previewing the on-line acquired road information,future navigation information can be utilized in order to improve safety and efficiency.So road information is classified into present information and future information, and they can be used in feedback and preview respectively.A preview-feedback controller is designed.The controller can automatically adjust the preview distance and the vehicle speed according to the previewed road,so tracking accuracy and driving stability can be improved.The simulation and experiments show that this controller has better accuracy and stability than the ordinary feedback controller.

Three control strategies for the Lorenz chaotic system

This paper suggests three strategies of the dislocated feedback control, so that enhancing feedback control and speed feedback control of the Lorenz chaotic system to its unstable equilibrium points can be enhanced. When the coefficients of enhancing feedback control and speed feedback control are smaller than those of ordinary feedback control, the complexity and cost of the system control are reduced. Theoretical analysis and numerical simulation are given, revealing the effectiveness of these strategies.

Non‐Lipschitzian control algorithms: application to a nanofriction model

AbstractRecently we proposed a new feedback control algorithm for quantities describing global features of non‐linear dynamical systems. The performance of the algorithm, which is based on the concepts of non‐Lipschitzian dynamics and global targeting, has been successfully demonstrated for systems confined to one spatial dimension and for a specific targeted global quantity, namely the velocity of the centre of mass. In this paper we extend the scope of the non‐Lipschitzian control scheme to multi‐dimensional systems and different targeted quantities. We illustrate the efficiency of the non‐Lipschitzian feedback w.r.t. the ordinary (Lipschitzian) feedback, as well as the robustness and accuracy of the algorithm in a broad variety of control scenarios on the 2‐d Frenkel‐Kontorova model for nanofriction. Published in 2005 by John Wiley & Sons, Ltd.