Passive Constraints Research Articles

Loss-compensated non-reciprocal scattering based on synchronization

Breaking the reciprocity of wave propagation is a problem of fundamental interest, and a much-sought functionality in practical applications, both in photonics and phononics. Although it has been achieved using resonant linear scattering from cavities with broken time-reversal symmetry, such realizations have remained inescapably plagued by inherent passivity constraints, which make absorption losses unavoidable, leading to stringent limitations in transmitted power. In this work, we solve this problem by converting the cavity resonance into a limit cycle, exploiting the uncharted interplay between non-linearity, gain, and non-reciprocity. Remarkably, strong enough incident waves can synchronize with these self-sustained oscillations and use their energy for amplification. We theoretically and experimentally demonstrate that this mechanism can simultaneously enhance non-reciprocity and compensate absorption. Real-world acoustic scattering experiments allow us to observe non-reciprocal transmission of audible sound in a synchronization-based three-port circulator with full immunity against losses.

Passive Model-Predictive Impedance Control for Safe Physical Human–Robot Interaction

Various cognitive systems have been designed to model the position and stiffness profiles of human behavior and then to drive robots by mimicking the human’s behavior to accomplish physical human-robot interaction tasks through a properly designed impedance controller. However, some studies have shown that variable stiffness parameters of the impedance controller can cause the violation of the passivity constraint of the robot states, and make the robot’s stored energy exceed the external energy injected from the human user, thus leading to the unsafe human-robot interaction. To solve this problem, this paper proposes a novel passive model predictive impedance control method including two control loops. In the bottom-loop of the proposed controller, the robot is driven by a variable impedance controller to achieve the desired compliant interaction behavior. In the top-loop of the proposed controller, the model predictive control (MPC) is used to ensure that the robot states satisfy the passivity constraint by calculating a complementary torque to limit the stored energy of the robot. The passivity of the closed-loop robot system and the feasibility of MPC are guaranteed by theoretical analysis, ensuring the safety of the robotic movement in the human-robot interaction. The effectiveness of the proposed method is demonstrated by the simulation and experiment on the Franka Emika Panda robot.

On the Feasibility of Self-Powered Linear Feedback Control

A control system is called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">self-powered</i> if the only energy it requires for operation is that which it absorbs from the plant. For a linear feedback law to be feasible for a self-powered control system, its feedback signal must be colocated with the control inputs, and its input-output mapping must satisfy an associated passivity constraint. The imposition of such a feedback law can be viewed equivalently as the imposition of a linear passive shunt admittance at the actuation ports of the plant. In this paper we consider the use of actively-controlled electronics to impose a self-powered linear feedback law. To be feasible, it is insufficient that the imposed admittance be passive, because parasitic losses must additionally be overcome. We derive sufficient feasibility conditions which explicitly account for these losses. In the finite-dimensional, time-invariant case, the feasibility condition distills to a more conservative version of the Positive Real Lemma, which is parametrized by various loss parameters. Three examples are given, in which this condition is used to determine the least-efficient loss parameters necessary to realize a desired feedback law.

DESIGN OF VISCO-ELASTIC SUPPORTS FOR TIMOSHENKO CANTILEVER BEAMS

The appropriate design of supports, upon which beams are usually placed as structural components in many engineering scenarios, has substantial significance in terms of both structural efficacy and cost factors. When beams experience various dynamic vibration effects, it is crucial to contemplate appropriate support systems that will effectively adapt to these vibrations. The present work investigates the most suitable support configuration for a cantilever beam, including viscoelastic supports across different vibration modes. Within this particular framework, a cantilever beam is simulated using beam finite elements. The beam is positioned on viscoelastic supports, which are represented by simple springs and damping elements. These supports are then included in the overall structural model. The equation of motion for the beam is first formulated in the temporal domain and then converted to the frequency domain via the use of the Fourier Transform. The basic equations used in the frequency domain are utilized to establish the dynamic characteristics of the beam by means of transfer functions. The determination of the ideal stiffness and damping coefficients of the viscoelastic components is achieved by minimizing the absolute acceleration at the free end of the beam. In order to minimize the objective function associated with acceleration, the nonlinear equations derived from Lagrange multipliers are solved using a gradient-based technique. The governing equations of the approach need partial derivatives with respect to design variables. Consequently, analytical derivative equations are formulated for both the stiffness and damping parameters. The present work introduces a concurrent optimization approach for both stiffness and damping. Passive constraints are established inside the optimization problem to impose restrictions on the lower and higher boundaries of the stiffness and damping coefficients. On the other hand, active constraints are used to ascertain the specific values of the overall stiffness and damping coefficients. The efficacy of the established approach in estimating the ideal spring and damping coefficients of viscoelastic supports and its ability to provide optimal support solutions for various vibration modes have been shown via comparative experiments with prior research.

A refined finite element model for UHPC-filled FRP tube column

A sound finite element model is essential for the nonlinear structural analysis of FRP tube-confined UHPC columns, wherein an accurate constitutive model to characterize the mechanical behavior of UHPC under passive constraints is of utmost importance. This study presents a refined finite element modeling methodology for the UHPC-filled FRP tube column. The constitutive model for UHPC under passive constraint is developed, in which the yield criterion, hardening/softening law, plastic flow rule, and damage evolution law are determined based on the experimental results of UHPC under multiaxial loading conditions. Furthermore, a solid element model of FRP tube with definable layer information is utilized to simulate the behavior of FRP tubes under complex stress states. The proposed finite element model is implemented in ABAQUS and verified through available experimental results. The results indicate that the proposed model can accurately predict the stress–strain behavior of confined UHPC with varying fiber and coarse aggregate contents, and describe the damage progression of UHPC and FRP tubes. Particularly, the interaction process between FRP and UHPC can be well reflected. The proposed finite element model serves as a paradigm for numerical analysis of UHPC-filled FRP tube elements and provides a reference for simulations of UHPC structures.

Passivity-Based Decentralized Criteria for Small-Signal Stability of Power Systems With Converter-Interfaced Generation

With the increasing penetration of converter-interfaced generation, it would be advantageous to specify local grid-connectivity criteria to ensure small-signal stability of the interconnected system, rather than carrying out centralized stability studies every time the connection of a new device is contemplated. Passivity of the device admittance, which is an example of a local criterion, has been used previously to avoid resonances between converter-interfaced systems and the lightly damped oscillatory modes of the network, but it is unsuitable in general due to the conservative nature of passivity. Therefore, a composite set of criteria are proposed in this paper, which include time-scale separation (slow-fast clustering) constraints on the transient behaviour, and distinct passivity constraints for the slow and fast clusters. The application of these criteria is demonstrated using a case study.

Thermo-diffusion properties and active and passive control of migrated nanoparticles with zero and non-zero mass fluxes

Recently, the research in nanoparticles is widely focused by researchers owing to the role of such nanomaterials is various industrial and thermal systems. However, the control of thermal enhancement in heat transfer with interaction of nanoparticles is quite necessary in engineering processes to maintain the energy level. Following to such motivations, current research model communicates the thermal control of nanoparticles with applications of active and passive constraints. The flow is generated due to bidirectional nonlinear stretching surface. The heat transfer is studied with radiated chemical reaction effects subject to convective condition. The nanoparticles concentration distribution is assumed through Brownian motion and thermophoresis effects. The three-dimensional surface with nonlinear flow velocity originates the flow. The impulsion of tiny particles from the surface has been presented with zero and non-zero mass fluxes. The convergent simulation via homotopic analytical algorithm is performed against the formulated set of system. The heat and mass transfer effects are carried out through numerically and graphically for the various parameter of interest.

Variable stiffness locomotion with guaranteed stability for quadruped robots traversing uneven terrains.

Quadruped robots are widely applied in real-world environments where they have to face the challenges of walking on unknown rough terrains. This paper presents a control pipeline that generates robust and compliant legged locomotion for torque-controlled quadruped robots on uneven terrains. The Cartesian motion planner is designed to be reactive to unexpected early and late contacts using the estimated contact forces. Moreover, we present a novel scheme of optimal stiffness modulation that aims to coordinate desired compliance and tracking performance. It optimizes joint stiffness and contact forces coordinately in a quadratic programming (QP) formulation, where the constraints of non-slipping contacts and torque limits are imposed as well. In addition, the issue of stability under variable stiffness control is solved by imposing a tank-based passivity constraint explicitly. We finally validate the proposed control pipeline on our quadruped robot CENTAURO in experiments on uneven terrains and, through comparative tests, demonstrate the improvements of the variable stiffness locomotion.

Investigating Iraqi EFL Learners' Mastery of Passive Constraints in English

Investigating Iraqi EFL Learners' Mastery of Passive Constraints in English

Passive Decentralized Fuzzy Control for Takagi-Sugeno Fuzzy Model Based Large-Scale Descriptor Systems

This paper presents a decentralized control problem for stabilizing the nonlinear large-scale descriptor (LSD) systems that use the proportional-plus-derivative state (PD) feedback scheme. The descriptor systems have a great focus on the research because they can contain more physical characteristics than standard state-space systems. At first, each nonlinear subsystem in the LSD system can be represented by Takagi-Sugeno (T-S) LSD systems with interconnections. In order to be more realistic, we additionally consider external disturbances and perturbations that affect the system. Our goal is to design a decentralized (DPD) fuzzy controller, such that the T-S LSD system is stable while the external disturbances and perturbations that affect the system. For the controller design process, sufficient conditions were developed based on the quadratic Lyapunov approach, PD feedback scheme, robust constraint, passivity constraint, and linear matrix inequality (LMI) sufficient criteria. At last, two numerical examples are given to show the application of the main results.

Passivity-Based Model Predictive Control for Tethered Despin of Massive Space Objects by Small Space Tug

This paper studies the stable control of tethered despin of a massive rotating space object in a central gravity field by a small space tug. A control scheme under the passivity-based Model Predictive Control framework is designed to ensure the constraints of state and input (bounded libration angle, positive tether tension and bounded thrust) are satisfied. Furthermore, an additional passivity constraint is introduced into the passivity-based Model Predictive Control to guarantee the asymptotic stability of the closed-loop control system. The attainable equilibrium configuration of the tethered system is first analyzed. Then, a framework of the storage energy function is constructed by the potential energy shaping methodology to establish the passivity mapping of the tethered system from input to output. Finally, the strictly asymptotic stability of despinning control of the tethered system under the proposed control law is theoretically proved by the Invariance theorem and Lyapunov stability theory. The effectiveness of the proposed control scheme is verified by numerical simulation.

A Faster Passivity Enforcement Method via Chordal Sparsity

Passivity enforcement methods entail the solution of optimization problems characterized by significant computational complexity. Optimal solutions require the use of positive-real lemma constraints which do not rely on linearization but scale rapidly in size owing to auxiliary slack variables. This paper presents how a chordal sparsity pattern can be used to solve this passivity enforcement problem more efficiently. The proposed algorithm uses graph theory and convex optimization to achieve a suboptimal solution that reduces the computation time required for the solution of the positive-real lemma passivity constraints by constraining the auxiliary Lyapunov variable to have a banded pattern. We provide numerical results using actual power system equipment to show that the proposed method gives faster suboptimal solutions.

Novel Delay-Dependent Stabilization for Fuzzy Stochastic Systems with Multiplicative Noise Subject to Passivity Constraint

A novel delay-dependent stability criterion for Takagi-Sugeno (T-S) fuzzy systems with multiplicative noise is addressed in this paper subject to passivity performance. The general case of interval time-varying delay is considered for the practical control issue. For the criterion, an integral Lyapunov-Krasovskii function is proposed to derive some sufficient relaxed conditions and to avoid the derivative of the membership function. Moreover, a free-matrix inequality is adopted to deal with the delay terms such that the available derivative of time-varying delay is bigger than one. In order to employ a convex optimization algorithm to find the control gain, a projection lemma is applied to acquire the Linear Matrix Inequality (LMI) form of the sufficient conditions. With the obtained gains, a fuzzy controller is designed by the concept of Parallel Distributed Compensation (PDC) such that the delayed T-S fuzzy systems with multiplicative noise are asymptotically stable and passive in the mean square. Finally, a stabilization problem of the ship’s autopilot dynamic system and some comparisons are discussed during the simulation results.

Intelligent Fuzzy Control with State-Derivative Feedback for Takagi-Sugeno Fuzzy Stochastic Singular Systems

This document deals with the problem of passive fuzzy controller design with the state-derivative feedback approach for the nonlinear stochastic singular systems. Recently, the singular systems have a greater focus on literature because they can keep more physical system characteristics than conventional systems. At first, the Takagi-Sugeno fuzzy stochastic singular models are used to represent the nonlinear stochastic singular systems. Then, the state-derivative feedback approach and parallel distributed compensation method are employed to design the passive fuzzy controllers. In the design process, the Lyapunov stability conditions are developed subject to multiple performance constraints, including the passivity constraint and decay rate constraint. According to these Lyapunov stability conditions, the proposed fuzzy control problem can be effectively shifted into the linear matrix inequality problem that can be solved by using the convex optimal programming algorithm. At last, two examples are provided to verify the applicability and effectivity of the proposed passive fuzzy controller design approach.

Model Predictive Path Planning for an Autonomous Ground Vehicle in Rough Terrain

An autonomous ground vehicle (AGV) in rough terrain typically experiences uncertain environment. Because the uncertainty makes overall performance of autonomous navigation degrade, the AGV requires a suitable path to maintain or improve the performance against the uncertainty. In order to handle this problem, this study proposes a model predictive path planning algorithm by employing a passivity-based model predictive control (MPC) optimization setup. The model predictive path planning method is formulated as a finite optimization problem with an objective function and several constraints. In the cost function, environment perception result about the AGV’s own neighborhood is included and the only traversable region has low cost value. To reflect dynamic characteristics of the AGV, the proposed method utilizes dynamic and kinematic models of the AGV as equality constraints and limited range of states and control input as inequality constraints. In addition, the stability of the path planning method is improved by a passivity constraint. The solution of the optimization problem is obtained using the particle swarm optimization (PSO) method. Finally, field tests are conducted to validate the performance of the proposed algorithm, and satisfactory results of the autonomous navigation were obtained.

Kinestatic Analysis of General Parallel Manipulators

Robotic mechanisms in general can be of either serial-chain, parallel-chain, or hybrid (a combination of both parallel and serial chains) geometry. While it can be asserted that kinematic theories and techniques are well established for fully serial-chain manipulators, the same assertion cannot be made when it is considered in the general context. In this article, we present a general procedure for systematic formulation and characterization of the instantaneous kinematics for a robotic mechanism with a general parallel-chain geometry. A kinestatic approach based on screw system theory is adopted in this treatment. The resulting equation is a compact Jacobian matrix of the system which includes attributes from not only the active joints but also the passive constraints. An example has been provided to demonstrate the methodology as well as its theoretical feasibility.

Fuzzy controller design for nonlinear singular systems with external noises subject to passivity constraints

AbstractThis paper applies the state derivative feedback method and proportional plus derivative state feedback method to design the fuzzy controllers for the nonlinear singular systems with external noises. The Takagi‐Sugeno fuzzy modeling technology is employed in this paper to represent the nonlinear singular systems with external noise. Considering the singular Takagi‐Sugeno fuzzy model, the passivity constraint is chosen to treat the external noises for the controlled systems. By using the parallel distributed compensation method, the fuzzy controller is designed to satisfy the Lyapunov stability conditions and passivity constraints simultaneously. These sufficient conditions can be effectively solved in terms of linear matrix inequalities, which can be solved via the convex optimization technique. At last, some numerical examples are provided to verify the applicability and effectivity of the proposed fuzzy controller design methods.

Influence of soil-structure interaction (SSI) on optimal design of passive damping devices

Recently, the interest in research for optimization of viscous dampers in design of buildings has been increasing. In this study, the effect of soil-structure interaction has been taken into account for the purpose of optimal design of viscous dampers. A damper optimization method based on a target damping ratio and interstorey drift ratio found in literature has been adapted for a building structure model considering different types of sandy soils. While passive constraints have been taken as upper and lower limits of each damper, active constraints have been considered as a target damping ratio in terms of damping coefficients. The proposed algorithm includes time history analyses that test the designer’s optimal design. Interstorey drift ratios under design earthquakes have been checked at each design step. The first and second mode responses have been considered separately. According to the results obtained from this study, the negative impact of sandy soils on the dynamic behavior of superstructures can be overcome by optimal placement of dampers in buildings. The results of the analyses have shown that soil effects should be taken into account in solving damper optimization problems.

Autonomous platooning of multiple ground vehicles in rough terrain

AbstractThis study proposes an autonomous platooning algorithm, composed of velocity, and path planning systems, of multiple ground vehicles in rough terrain. The velocity planning system aims to maintain desired distance between preceding and rear vehicles, and the path planning system generates reliable path to make the vehicles move safely under the given rough environment. To supply a reliable velocity command for the maintenance of the predefined distance, a disturbance observer (DOB)‐based control method is employed. An uncertainty‐free longitudinal kinematic model is first utilized for a nominal velocity generator and the DOB is added to the nominal velocity planner for handling various uncertainties generated during the autonomous platooning. On the other hand, the path planning method is developed by employing a passivity‐based model predictive control method. With a derived passivity constraint, the stability of the platooning architecture, that is, the platooning performance, is improved. In addition, the proposed path planning method utilizes dynamic and kinematic models of the ground vehicle as equality constraints, and limited range of states and control input as inequality constraints, and perception result about the vehicle's own neighborhood is employed for generation of the path only in traversable region. Its solution is obtained using the particle swarm optimization method. Then, to follow the generated velocity and path commands, a well developed driving controller, commercially obtainable, is utilized. Finally, field tests are conducted to validate the performance of the proposed algorithm.

Robust control design for home pension service mobile robots with passive and servo constraints.

This paper presents a novel robust control design for a class of home pension service mobile robots (HPSMRs) with non-holonomic passive constraints, based on the Udwadia-Kalaba theory and Udwadia control. The approach has two portions: dynamics modeling and robust control design. The Udwadia-Kalaba theory is employed to deal with the non-holonomic passive constraints. The frame of the Udwadia control is employed to design the robust control to tracking the servo constraints. The designed approach is easy to implement because the analytical solution of the control force can explicitly be obtained even if the non-holonomic passive constraints exists. The uniform boundedness and uniform ultimate boundedness are demonstrated by the theoretical analysis. The effectiveness of the proposed approach is verified through the numerical simulation by a HPSMR.