Acceleration Feedback Research Articles

Comprehensive coverage of particle acceleration and kinetic feedback from the stellar mass black hole V404 Cygni

ABSTRACT We present analysis of comprehensive radio observations of the black hole V404 Cyg during its 2015 outburst. These data represent the best ever coverage of jet production and particle acceleration from any black hole. We report for the first time a clear and near-linear flux–rms correlation in the radio flux densities. Investigation of individual flares reveals in nearly all cases the peak corresponds to the transition from optically thick to thin to synchrotron emission, but an extended phase of particle acceleration is required in contrast to simple impulsive injection models. The largest radio flare is preceded by a phase of optical oscillations and followed one day later by a smaller but optically thin flare, likely due to ejecta interacting with the interstellar medium. Comparing the radio emission to contemporaneous X-ray and optical data, we find that the X-ray and radio measurements are correlated on all time-scales from seconds to one day. Correlation with the optical flux densities is weak at short time-scales, but becomes significant on time-scales greater than a few hours. We evaluate the physical conditions (size, magnetic field, and internal energy) associated with 86 individual radio flares, which in turn allows us to place a lower limit on the kinetic feedback over the 15 d of intense activity. If this energy was deposited locally to the source, as implied by the failure to detect jets on angular scales larger than milliarcsec, then we predict that a nova-like shell could have been formed.

Hopf bifurcation calculation in neutral delay differential equations: Nonlinear robotic arms subject to delayed acceleration feedback control

This study gives the derivation of the Hopf bifurcation calculation for neutral delay differential equations using the centre manifold reduction theorem and normal form calculation. The whole concept was inspired by a case study where a robotic arm subjected to nonlinear stiffness with delayed acceleration feedback controller is modelled. Two different configurations are distinguished depending on the location of the acceleration sensor, a collocated and a non-collocated one. After a brief investigation of the linear stability, the bifurcation occurring at the loss of stability is calculated with the presented analytic equations for neutral delay differential equations. Then, a nonlinear term is introduced in the control law that can modify the occurring subcritical behaviour and improve the robustness of the system. The analytic results are carefully analysed and validated via a numerical continuation software, which also provided useful information about the global behaviour of the bifurcations in addition to the locally valid analytic results.

Controlling mode-coupling instability in friction-induced vibration by acceleration feedback

Self-excited friction-induced oscillation, such as brake squeal, railway wheel squeal, chattering in machine tools, etc., is harmful in many mechanical systems. In the present study, the efficacy of acceleration feedback control with a second order filter is theoretically studied to mitigate friction-induced mode-coupling instability. Two different control strategies based on acceleration feedback are employed to control friction-induced mode-coupling instability of a two degrees-of-freedom linear system. Linear stability analysis near the equilibrium point of the system shows the efficacy of control laws to stabilize the system. The optimum filter parameters are determined by the pole crossover optimization method to attenuate the transient response as well as to achieve greater relative stability of the system. The Robustness study confirms the ability of the controller to stabilize the system in the presence of uncertainties in system parameters. Analytical results match closely with simulation results. Finally, nonlinearity in the form of stiffness is incorporated into the system for which the dynamics of the system show the presence of subcritical, supercritical Hopf bifurcation, and cyclic fold bifurcation. In the presence of nonlinearity, the feedback control is also able to reduce the range of instability of static equilibrium as well as the amplitude of the self-excited oscillation. The method of averaging is used to determine the stability and amplitude of the limit cycle. For the nonlinear system, the bifurcation diagram is constructed in AUTO and validated with results obtained from MATLAB SIMULINK and the method of averaging.

Vertical Dynamic Response of the 2-DOF Maglev System considering Suspension Nonlinearity

In order to study the dynamic characteristics of the nonlinear system of the maglev train, a vibration model of the two-degree-of-freedom nonlinear suspension system of the maglev train is established in this paper. Based on the linearized model of the suspension control module, the suspension system is controlled by the state feedback method. Compared with the results of the Runge–Kutta method, the accuracy of the settlement results is verified. This paper analyzes the influence of system parameters and feedback control parameters on the system. The results show that the linear stiffness mainly affects the left-right migration of the resonance peak and the difference between the maximum and minimum of the resonance region of the suspension frame; the nonlinear stiffness mainly affects the slope of the resonance region of the car body and the suspension frame; displacement feedback control parameters can reduce the amplitude of the system, velocity feedback control parameters can make the state change of the suspension frame more smoothly, and acceleration feedback control parameters make the car body and the suspension frame have a strong coupling effect. According to the Hurwitz criterion of Hopf bifurcation, this paper deduces the conditions that the control parameters should satisfy when the equilibrium point is stable, and the instability produces periodic vibration under PID control. Through numerical simulation, it is found that the system has complex dynamic behavior, the results show that the system works under some conditions, and there are multiple stable and unstable limit cycles simultaneously. Therefore, the system will appear alternately between multiperiod and chaotic motion, which will affect the stability of the system.

A general class of optimal nonlinear resonant controllers of fractional order with time-delay for active vibration control – theory and experiment

The present article generalizes the classical integer-order resonant controllers for active vibration control. The proposed controller utilizes a second-order linear filter with response feedback and a control input in the form of a nonlinear, time-delayed function of the fractional derivative of the filter variable. Thereby, the proposed controller encompasses the integer-order resonant controllers, like positive position feedback, acceleration feedback, negative velocity feedback, etc. as special cases and allows an extra degree of freedom in terms of choosing the optimum form of the control input function. Theoretical analysis of the system is performed by the method of multiple time scales and finally, the results are verified by numerical simulations and experiments. Two new numerical methods of parameters optimization are discussed. Detailed parametric studies are performed to reveal the effects of different design parameters, viz. the control gain, time-delay, and the fractional-order of the input function on the system performance. The theoretical and experimental studies demonstrate the supremacy of the fractional-order control over integer-order resonant control, especially for higher control gain and delay. The existence of an optimal value of the fractional order of the control function is established.

Active auto-adaptive metamaterial plates for flexural wave control

In this paper, a novel design concept for active auto-adaptive metamaterial (AAAMM) plates is proposed based on an active auto-adaptive (AAA) control strategy guided by the particle swarm optimization (PSO) technique. The AAAMM plates consist of an elastic base plate and two periodic arrays of piezoelectric patches. The periodic piezoelectric patches placed on the bottom plate surface act as sensors, while the other ones attached on the top plate surface act as actuators. A two-dimensional (2D) simplified metamaterial (MM) plate model is established by the Hamilton principle. The finite element method (FEM) with quadratic shape functions is adopted for numerically solving the 2D simplified MM plate model, which is validated by two more accurate but also much more complicated FEM models using three-dimensional (3D) piezoelectric and 3D elastic solid elements, and by its 2D counterpart model solved by the plane wave expansion (PWE) method. The conventional displacement, acceleration and velocity feedback control methods are introduced and analyzed. Then, a novel AAA control strategy based on combining the displacement and acceleration feedback control methods and guided by the PSO technique is developed. The main objective of the present paper aims at the vibration or flexural wave suppression and isolation of elastic plate structures based on an auto-adaptive control strategy, which has wide-range engineering applications. Numerical results will be presented and discussed to show that the proposed AAAMM plates can automatically and intelligently evolve different feedback control schemes to adapt to different stimulations on demand. Compared to the conventional MM plates, the proposed AAAMM plates exhibit improved and enhanced band-gap characteristics and suppression performance for flexural waves at frequencies inside and outside the band-gaps.

Sliding Mode Bifurcation Control Based on Acceleration Feedback Correction Adaptive Compensation for Maglev Train Suspension System With Time-Varying Disturbance

In order to ensure the suspension stability of maglev train, the active control problems of static suspension and dynamic suspension are studied. First, the mathematical model of dynamic suspension characteristics of medium- and low-speed maglev train is established. Second, the PID controller is studied. The results show that the controller is very sensitive to time-varying disturbances such as nonuniformity and load, which leads to the decrease in system robustness. In order to suppress the disturbance effectively, a suspension control method based on the sliding mode reaching law is proposed. Based on the bifurcation phenomenon, the bifurcation point is solved to determine the main control parameters. On the basis of this, an acceleration feedback correction and adaptive control module based on the radial basis function (RBF) network is constructed to effectively suppress the vibration of the electromagnet. The controller consists of a sliding mode bifurcation control law, an acceleration feedback correction module, and an adaptive compensation loop. The simulation and experimental results show that the proposed control algorithm can significantly reduce the variation range of suspension gap with a smoother control current in the presence of complex disturbances and significantly suppress the coupled vibration.

Acceleration-feedback-based finite-time platoon control for interconnected vehicular system

The platoon control problem of interconnected vehicular systems is investigated in this paper studies. A finite-time adaptive sliding mode control (SMC) method based on acceleration feedback is developed to achieve platooning of interconnected vehicular systems subject to external disturbances and string stability of the closed-loop platoon system is analyzed. The string stability of the closed-loop system is achieved by applying the constant spacing (CS) strategy in the proposed adaptive sliding mode controller under zero initial steady-state error conditions. A novel error definition method is proposed to transform the non-zero initial steady-state error into the zero initial steady-state error so that the proposed algorithm can be independent of the initial steady-state errors and reduce the large transient response caused by non-zero initial steady-state errors. The salient feature of the proposed SMC law is that it does not need to know the disturbance boundary in advance. Finally, simulations and experiments are conducted to demonstrate the advantages and effectiveness of the proposed algorithm.

Steady-state performance and dynamic performance of heterogeneous platoons under a connected environment

Under the vehicle-to-vehicle (V2V) environment, the steady-state performance and the dynamic performance are both crucial for the traffic system. This paper proposes an in-depth methodology to provide some insights into the comprehensive changes of steady-state performance and dynamic performance of a heterogeneous platoon, which contains human-driven vehicles (HDVs) and connected and automated vehicles (CAVs). To further understand the impacts of various feedback information, an improved full velocity difference model that incorporates multiple feedback communicating information is developed. Based on the transfer function, the stability and steady-state error are proposed to characterize the steady-state performance, while the degree of fluctuation and duration of fluctuation are used to measure the dynamic performance. On the one hand, a key finding is that there are inconsistencies in steady-state and dynamic performance under particular feedback information. The acceleration or spacing feedback information can enhance the steady-state performance while degrading the dynamic performance. The speed difference feedback information yields the opposite result. On the other hand, it is discovered that compared to several types of feedback information, combining just one type of information is enough to boost the platoon performance. When the number of CAVs is considerable, combining two types of information will considerably increase the duration time. Therefore it is important to find the key feedback information for the platoon performance. The main purpose of this paper is to present a methodology of platoon performance analysis instead of discussing the various traffic scenarios. As a result, while certain results may alter in some specific scenarios, the proposed methodology and core contribution remain applicable to various traffic scenarios.

On the admissible control-loop delay for the inverted pendulum subject to detuned PDA feedback

In this paper, we consider the stabilization of φ̈(t)−a0φ(t)=−kpφ(t−τ−δp)−kdφ̇(t−τ−δd)−kaφ̈(t−τ−δa),which describes the control of an inverted pendulum by detuned proportional–derivative–acceleration (PDA) feedback. We show that the system can be stabilized using an appropriate choice of the control parameters kp, kd, ka and δp, δd, δa≥0 if τ is smaller than the critical delay τcrit=6/a0. This value is larger by a factor of 3≈1.73 than the critical delay of the proportional–derivative (PD) feedback with a single delay.

Bistability and delayed acceleration feedback control analytical study of collocated and non-collocated cases

Stability and bifurcation analysis of a non-rigid robotic arm controlled with a time-delayed acceleration feedback loop is addressed in this work. The study aims at revealing the dynamical mechanisms leading to the appearance of limit cycle oscillations existing in the stable region of the trivial solution of the system, which is related to the combined dynamics of the robot control and its structural nonlinearities. An analytical study of the bifurcations occurring at the loss of stability illustrates that, in general, hardening structural nonlinearities at the joint promote a subcritical character of the bifurcations. Consequently, limit cycle oscillations are generated within the stable region of the trivial solution. A nonlinear control force is then developed to enforce the supercriticality of the bifurcations. Results illustrate that this strategy enables to partially eliminate limit cycle oscillations coexisting with the stable trivial solution. The mechanical system is analysed in a collocated and a non-collocated configuration, depending on the position of the sensor.

Simultaneous damping and tracking control of a normal-stressed electromagnetic actuated nano-positioning stage

Normal-stressed electromagnetic actuated (NSEA) nano-positioning stage has become more and more promising in various fields due to its high actuation force density and large motion range. However, the intrinsic hysteresis of the actuator and the lightly-damped resonance of the mechanism hinder the stage for the high-accuracy and high-speed applications. To handle these two problems, the damping and tracking controllers are commonly adopted, as the inner and outer loops, respectively, to design a dual-loop controller. However, the existing sequential design approach limits the achievable performance of the controller. This paper proposes a simultaneous optimization approach for a dual-loop controller with the inner loop positive acceleration, velocity, and position feedback (PAVPF) damping controller and the outer loop proportional-integral (PI) tracking controller. The objective is to obtain a flat closed-loop frequency response with a large control bandwidth, and the parameters of the inner and outer loops are tuned simultaneously. Both the damping ratio and stiffness of the vibration mode are improved, and the obtained ± 3 dB control bandwidth exceeds the first resonant frequency of the open-loop system. Experiments are carried out on a custom designed NSEA nano-positioning stage. The tested bandwidth of the simultaneously optimized system agrees well with the theoretical one, and is 188.9% higher than that of the sequentially designed system. Step response tests, triangular wave tracking tests, and hysteresis reduction tests also demonstrate the effectiveness and advancement of the proposed approach.

Design of a contact‐force controller including airframe's velocity and acceleration feedback controllers for one‐degree‐of‐freedom propeller‐driven systems

AbstractContact‐force control of propeller‐driven systems achieves aerial tasks that require contact motions with objects. Conventional contact‐force controllers for propeller‐driven systems utilize a contact‐force feedback controller. Although the feedback gain should be high to achieve high target tracking performance, a high gain causes a large overshoot. This paper therefore proposes a novel contact‐force controller which utilizes an airframe's velocity and an airframe's acceleration. An estimated acceleration and an estimated velocity of the airframe are fed back to the contact‐force controller. A rotor angular velocity is utilized to estimate the acceleration. The validity of the proposed controller is verified through frequency analysis, simulation, and experiment.

Control Structure with Dual Acceleration Feedback for Positioning Machine with Semi-Closed Servo System

Control Structure with Dual Acceleration Feedback for Positioning Machine with Semi-Closed Servo System

Dynamic performance and stability analysis of an active inerter-based suspension with time-delayed acceleration feedback control

Dynamic performance and stability analysis of an active inerter-based suspension with time-delayed acceleration feedback control

Structural Design and Position Tracking of the Reconfigurable SCARA Robot by the Pre-Filter AFE PID Controller

The selective compliance assembly robot arm (SCARA) has been developed for decades and has been widely used in industry due to its light structure, quick response and high stiffness in a specific axis. In this work, we designed a reconfigurable SCARA robot with extensible physical space by adjusting the number of modular arms. Considering potential structural failure due to vibration, we employed a multi-objective optimization method based on the finite element method to optimize the bolt connectors between the modules. Compared with the classic finite element optimization method, this method focuses on the key factors affecting the precision of the reconfigurable robot; we used the fitting method of the multi-objective function to obtain the influential factors, which make the optimization results more consistent with a real situation. Then, exploiting the acceleration feedback enhanced (AFE) control strategy, a pre-filter AFE PID controller is proposed by introducing a pre-filter to effectively suppress the system disturbance, which is caused by gaps between the joints when the robot operates at high speed. Experiments show that the reconfigurable SCARA robot still has strong stability under the continuous disturbance of a 2 kg hanging plate weight.

Design of a Contact-force Controller Including Airframe's Velocity and Acceleration Feedback Controllers for One-degree-of-freedom Propeller-Driven Systems

Contact-force control of propeller-driven systems achieves aerial tasks that require contact motions with objects. Conventional contact-force controllers for propeller-driven systems utilize a contact-force feedback controller. Although the feedback gain should be high to achieve high target tracking performance, a high gain causes a large overshoot. This paper therefore proposes a novel contact-force controller which utilizes an airframe's velocity and an airframe's acceleration. An estimated acceleration and an estimated velocity of the airframe are fed back to the contact-force controller. A rotor angular velocity is utilized to estimate the acceleration. The validity of the proposed controller is verified through frequency analysis, simulation, and experiment.

Finite-Time Observer-Based Variable Impedance Control of Cable-Driven Continuum Manipulators

Human–robot interaction has been widely studied, where compliant and safe human–robot interaction of continuum manipulators in the constrained environment is one of the key issues that have not been well addressed. In this study, finite-time observer-based variable impedance control of cable-driven continuum manipulators (CDCM) is proposed to overcome the limitation of existing methods. First, the pseudo-rigid modeling method is utilized to establish the kinematics and dynamics of the CDCM. Then, a variable impedance controller with selected controller parameters for the CDCM is designed to realize compliant and safe human–robot interaction operations with force–position coupling constraint, which is rarely studied in the literature. In order to realize the closed-loop variable impedance controller, a finite-time observer is designed to estimate acceleration feedbacks, which can avoid the difficulty of directly sensing the interaction forces and shows excellent robust stability in noisy environments. On this basis, by combining the advantages of the variable impedance controller and finite-time observer, the finite-time observer-based variable impedance controller is proposed, and the stabilities of the proposed method are analyzed. Finally, the feasibility of the proposed control scheme for the CDCM is demonstrated by some numerical simulations.

Active Flutter Suppression and Aeroelastic Response of Functionally Graded Multilayer Graphene Nanoplatelet Reinforced Plates with Piezoelectric Patch

This paper investigates the aeroelastic flutter and vibration reduction of functionally graded (FG) multilayer graphene nanoplatelets (GPLs) reinforced composite plates with piezoelectric patch subjected to supersonic flow. Activated by the control voltage, the piezoelectric patch can generate the active mass and active stiffness that can accordingly increase the base plate’s stiffness and mass. As a result, it changes the GPLs reinforced plate’s dynamic characteristics. The motion equation of the plate-piezoelectric system is derived through the Hamilton principle. Based on the modified Halpin–Tsai model, the effects of graphene nanoplatelets weight fraction and distribution pattern on the dynamic behaviors of the plate are numerically studied in detail. The result illustrates that adding a few amounts of grapheme nanoplatelets can effectually enhance the aeroelastic properties of the plates. Two kinds of control strategies, including the displacement and acceleration feedback control, are applied to suppress the occurrence of the flutter of the plate. It shows that the displacement and acceleration feedback control can improve the critical flutter Mach number of the plate by attaching active stiffness and active mass, respectively. Furthermore, the combined displacement and acceleration feedback control has a better control effect than that of considering only one of them.

Discovering Stick-Slip-Resistant Servo Control Algorithm Using Genetic Programming.

The stick-slip is one of negative phenomena caused by friction in servo systems. It is a consequence of complicated nonlinear friction characteristics, especially the so-called Stribeck effect. Much research has been done on control algorithms suppressing the stick-slip, but no simple solution has been found. In this work, a new approach is proposed based on genetic programming. The genetic programming is a machine learning technique constructing symbolic representation of programs or expressions by evolutionary process. In this way, the servo control algorithm optimally suppressing the stick-slip is discovered. The GP training is conducted on a simulated servo system, as the experiments would last too long in real-time. The feedback for the control algorithm is based on the sensors of position, velocity and acceleration. Variants with full and reduced sensor sets are considered. Ideal and quantized position measurements are also analyzed. The results reveal that the genetic programming can successfully discover a control algorithm effectively suppressing the stick-slip. However, it is not an easy task and relatively large size of population and a big number of generations are required. Real measurement results in worse control quality. Acceleration feedback has no apparent impact on the algorithms performance, while velocity feedback is important.