Conventional Control Law Research Articles

Global stabilization of rigid formations in the plane

This paper considers the problem of distributed control of rigid formation shapes in the plane for multi-agent systems. A constructive perturbation method is proposed and combined with the conventional gradient control law. The proposed control law stabilizes the desired rigid formation in a global sense for all initial conditions except the case when a pair of communicating agents happen to have the same initial location. It also avoids collisions between any two communicating agents during the motion. Simulation results are provided to illustrate the effectiveness of the control algorithm.

Partial and total actuator faults accommodation for input-affine nonlinear process plants

In this paper, a new fault-tolerant control system is proposed for input-affine nonlinear plants based on Model Reference Adaptive System (MRAS) structure. The proposed method has the capability to accommodate both partial and total actuator failures along with bounded external disturbances. In this methodology, the conventional MRAS control law is modified by augmenting two compensating terms. One of these terms is added to eliminate the nonlinear dynamic, while the other is reinforced to compensate the distractive effects of the total actuator faults and external disturbances. In addition, no Fault Detection and Diagnosis (FDD) unit is needed in the proposed method. Moreover, the control structure has good robustness capability against the parameter variation. The performance of this scheme is evaluated using a CSTR system and the results were satisfactory.

Performance investigation of variable damping shock absorber combined with conventional semi-active vibration control logics

The shock induced by a rocket lift-off and pyrotechnic device actuation for interstage separation can cause damage to the on-board instruments of a spacecraft when the acceleration generated by the input shock exceeds their allowable acceleration value. The shock can be attenuated by mounting a shock absorber. In this paper, we propose a variable damping shock attenuation strategy combined with conventional semi-active vibration control laws derived from a two elements model composed of variable damping and spring stiffness that would attenuate the shock such that the main instrumentʼs input acceleration does not exceed the allowable acceleration value. The analysis results indicate that the combination of shock and conventional semi-active control logic attenuates the shock level better than an optimal passive and conventional semi-active control system. The strategy is also effective for suppressing the consequent vibration induced by the shock event.

21105 超広角レンズの広角特性を維持した特徴ベーストビジュアルサーボ(OS10-4【ロボティクス・メカトロニクス(4)】)

Abstract: Feature-based visual servo determines camera movement by comparing a current feature image and the goal feature image. This method does not require a geometric model of the object because it does not need a 3D information of the object. Therefore, it is robust to various disturbances. Various methods have been proposed. For example using a wide-angle lens enables the camera to capture the object in a wide range However, using a wide-angle lens in the conventional control law, the camera would conduct waste motion because of the peripheral distortion of the wide-angle lens. In addition, if the distortion is corrected, the wide-angle properties will be lost. This paper proposes a new Feature-based visual servoing control law by preserving wide-angle properties of super wide-angle lens.

Designing active flutter suppression for high-dimensional aeroelastic systems involving a control delay

Many linear control laws, such as optimal controllers and classical controllers, have seen their applications to suppressing the aeroelastic vibrations of the high-dimensional aeroelastic system. However, those conventional control laws may not work effectively if the high-dimensional aeroelastic system involves a control delay. The paper reveals the effect of input time delay on the stability of a controlled high-dimensional aeroelastic system in an incompressible flow field and presents a new optimal control law to suppress the flutter of the high-dimensional aeroelastic system with an input time delay in the control loop. The procedure of designing the proposed control law includes three steps as follows. The first step is to convert the system described by a set of differential equations with a time delay into a set of difference equations involving discrete delay terms by using zero-order holder. The second step, exhibiting the novelty of the study, is to transform the difference equations with delay terms into a set of delay-free difference equations via a state transformation. The third step is to use the theory of linear control, say, the theory of Linear Quadratic Gaussian (LQG), to complete the design of controller by solving an equivalent Riccati equation. The paper demonstrates the efficacy of proposed method in designing the flutter suppression controller for a wind-tunnel model of Multiple-Actuated Wing. The new method works much better than classical feedback and conventional LQG controllers, both of which do not take the input time delay into account and may induce instability, when the input time delay becomes significant.

Adaptive Failure Compensation of a Single Main-Rotor Helicopter

This paper develops an adaptive control strategy for failure compensation of a single main-rotor helicopter. The adaptive controller addresses the problem of instability due to failure in the main rotor or tail rotor assemblies, or unexpected variations in thrust or yaw due to damage to the rotor blades. An abstracted model of the helicopter is used for the development of the adaptive control laws. The effects of instability due to damage to the helicopter are modeled. A set of adaptive controllers are developed to stabilize the helicopter's states under failure. Simulation results establish the efficacy of the adaptive control scheme over the conventional control laws in providing stability.

Symplectic Transformation Based Analytical and Numerical Methods for Linear Quadratic Control with Hard Terminal Constraints

Feedback gain and feedforward input of conventional linear quadratic (LQ) hard terminal controllers tend to infinity at terminal time, so that the conventional controllers have to go open-loop for a short interval before the final time. This short interval is called blind time. To avoid the terminal infinite feedback control gain and feedforward input, new optimal control laws are proposed for hard terminal control of linear time-varying systems. Furthermore, a structure-preserving numerical method is also presented to evaluate the time-varying optimal feedback and feedforward control gains and corresponding optimal trajectory. The analytical and numerical methods being developed here are based on the application of symplectic (canonical) transformation and generating functions of Hamiltonian systems. Different from the existing generating function method for optimal control, the first type of generating function plays a key role in solving the associated Hamiltonian two-point boundary-value problem (TPBVP), while the second generating function is employed to recover the first type. This note uses the second and third types of generating functions to find novel optimal control laws by solving the Hamiltonian TPBVP, which eliminates the infinite control gains of conventional optimal control laws near terminal time. Since the optimal trajectory of the closed-loop system is a solution of the Hamiltonian TPBVP, by using symplecticity of the solution operator of the linear Hamiltonian system, this paper also derives a structure-preserving matrix recursive algorithm for the computation of time-varying optimal control gains and the systems optimal trajectories. Numerical simulations show that this structure-preserving algorithm gives accurate results for relative large discrete steps and keeps geometric properties of the solutions.

Feedforward linearization and disturbance rejection of mechanical systems using acceleration measurements

In this paper a time-delayed acceleration measurement is used to linearize a second order nonlinear system. A theoretical foundation is developed, and a control strategy is presented which handles the challenges related to classical linearization. Utilizing the acceleration measurement to directly cancel the nonlinearities constitute a feedforward approach which increases robustness with respect to unmodeled dynamics and model uncertainties. Due to the time-delay, one or more perturbation terms dependent on a previous state of the system appears. This work outlines a stability criterion which these terms must satisfy in order for the linearization to be valid, where it is shown that the performance of the scheme is dependent on the measurement time-delay. The proposed method proves feasible when compared to two other nonlinear control strategies, including a conventional linearization control law and a sliding mode control law. In comparison, the feedforward linearization features robust performance without aggressive control input.

Speed and Rotor Position Identification for PMSM Based on Improved Nonsingular Terminal Sliding-Mode

In this paper, an Improved Nonsingular Terminal Sliding-mode (INTSM) observer is proposed to estimate the speed of the permanent magnet synchronous motor (PMSM). The Nonsingular Terminal Sliding-mode (NTSM) not only inherits the good performance to track the state error, but also has the characteristic of limited time convergence. However, the conventional NTSM control law is too complex to apply in practice. The INTSM takes the thoughts of the fast Terminal Sliding-mode and uses a new nonlinear term to replace the conventional term. As a result, the new observer owns the characteristics of global fast convergence and simple control law. At last, the proposed method proves to be effective through the theoretical analysis and simulation test.

Comparison of Control Laws for Vibration Suppression Based on Energy Consumption

The research study presented here examines four conventional vibration suppression control laws and four hybrid modifications of these laws using a switching method. The motivation is to determine which of these eight controllers results in the least amount of power flow to the actuator to have the same settling time under free vibrations. The reason to look at reduced energy controllers is the idea that in some applications, very little energy is available for control, yet passive and semi-active methods cannot meet performance demands. In particular, the eventual goal is to reduce transient vibrations of smart structures using energy obtained from harvesting and/or low-power storage devices (batteries or super capacitors), as often desirable in aerospace systems. The four conventional active control systems compared in this study are Positive Position Feedback (PPF) control, Proportional Integral Derivative (PID) control, non-linear control, and Linear Quadratic Regulator (LQR) controls. A hybrid version of each controller is obtained by implementing a bang-bang control law (on-off control). The bang-bang control algorithm switches the control voltage between an external voltage supply and the feedback signal provided by the PPF, PID, non-linear, or LQR controllers. The purpose of combining the bang-bang control law with the aforementioned controllers is to reduce the power requirement for vibration suppression by providing an active controller with limited voltage input. Free vibrations of a thin cantilevered beam with a piezoceramic transducer are controlled by these eight controllers with a focus on the fundamental transverse vibration mode. Experimental results exhibit that the system with hybrid bang-bang-non-linear controller requires 67.3% less power than its conventional version. The hybrid versions require significantly less power flow compared to their conventional counterparts for the PPF, PID, and LQR controllers as well. Experiments also reveal the presence of substantial piezoelectric non-linearities in the transducer. The voltage-dependent behavior of the electromechanical coupling coefficient is identified empirically and represented by a curve-fit expression. A real-time adaptive control algorithm is developed to account for the voltage-dependent behavior of the coupling coefficient, enabling good agreement between the simulation and experimental results.

Enhancement of pointing performance by semi-active variable damping isolator with strategies for attenuating chattering effects

Semi-active control strategy is one of the most attractive approaches for space applications because of it provides better performance than passive systems and higher robustness than active systems. However, conventional semi-active approaches, such as skyhook and bang-bang control, cause the pointing accuracy of the on-board payload to degrade due to chattering effects created by the sudden variation of damping force when a semi-active isolation system is switched on or off. In this paper, we propose a semi-active strategy to minimize performance deterioration due to chattering effects. Numerical simulation result obtained using a simplified on-board payload model demonstrate that the proposed LQ semi-active control logic with variable damping achieves much better isolation performance than the conventional semi-active control laws under single and fly-wheel force excitation environments.

Chattering에 의한 위성 탑재체 지향성능저하 최소화를 위한 반능동제어기법 성능분석

수동형 진동제어 방식과 같이 시스템이 안정되며, 수동형에 비해 높은 제진 효과가 기대되는 반능동 진동제어 방식은 시스템의 안정화가 요구되는 우주구조물의 제진방법에 유효한 진동제어 방식중 하나이다. On-Off 제어방식에 근거한 반능동 제어는 On-Off 스위칭 시에 전달력의 불연속성으로 인한 chattering을 발생시킬 수 있으며, 이는 탑재체 구조물의 고유진동수와의 커플링으로 인하여 지향성능을 저하시키는 원인으로 작용할 수 있다. 본 논문에서는 chattering 영향 최소화를 통한 지향성능향상을 목적으로 LQ(Linear Quadratic)이론에 기반한 가변 감쇠형 반능동 제어기법을 제안하였다. 시뮬레이션 결과는 본 논문에서 제안한 반능동 제어기법은 기존의 skyhook와 LQ를 기반으로 하는 Bang-Bang 반능동 제어기법과 비교하여 높은 진동절연 성능을 나타내고 있다. Semi-active vibration control is one of the attractive control methods for space application due to its robustness as passive damping system and much higher damping performance than passive system. However, a chattering induced by the sudden variation of damping force at the time of On-Off switching of semi-active control device degrades pointing performance of the on-board payload. In this paper, to enhance the pointing performance of the on-board payload, we proposed a semi-active vibration isolation with a strategy for attenuating chattering effect. Numerical simulation results using simplified analysis model indicated that the proposed semi-active control strategy produced much better isolation performance than the conventional Bang-Bang control semi-active control laws derived from skyhook and LQ theories.

Reconfigurable magnetic attitude control of Earth-pointing satellites

Micro-, nano-, and pico-satellite designs are constrained by small power budget, weight, and size. The power constraint is taken care of by ensuring that all the systems onboard are optimized for low power consumption. Weight and size can be made small by reducing the number of sensors and actuators. However, the attitude control system, which constitutes one of the most important components of the satellite, often requires redundancy to make the satellite fail to be operational; but for such small satellites, low power, weight, and size limit the accommodation of redundancy in the attitude control system. Such small satellites are often magnetically actuated. The under-actuation problem of a satellite magnetic control torque in the presence of three magnetic coils has been extensively studied since 1970s. Moreover, the attitude control of a satellite using two actuators and time-dependent feedback control has been developed, but the magnetic attitude control of a satellite, which is already an under-actuated system, in the post-failure scenario of one of the three magnetic actuators, has not been developed. Failure of any one of the magnetic coils may render a satellite dysfunctional if proper control reconfiguration is not provided, keeping in view that the redundant attitude control system is not available. A new formulation for reconfiguring the control based on magnetic dipole moment modulation for the attitude control of Earth-pointing satellite has been presented in this article. In the post-failure scenario of one of the magnetic coils, the controlling capability of the system remains intact, which comes at the cost of high magnetic dipole moment in the functional magnetic coils but not at the cost of extra power. This also reduces the cross-coupling of the coils. The proposed magnetic dipole moment modulation in combination with the conventional control law is found to be very effective.

ACTIVE CONTROL OF ROLLING MANOEUVRES OF A ROBOTIC FINGER WITH HEMISPHERICAL TIP

In this paper we are concerned with the problem of sensory motor coordination of a robotic finger in order to evoke rolling maneuvers in a force-positioning task on a flat rigid surface. We use two different approaches to modeling the reaction of the soft fingertip with the contacted surface. Firstly, we assume that the environment imposes a purely kinematic rolling constraint on the end-effector motion in the tangent direction of the contacted surface. This implies no energy transfer or dissipation between the fingertip and the environment due to frictional forces. On the other hand, we assume that it is feasible for the fingertip to slip in which case pure rolling motion could be disturbed. The two different models are subsequently used to show by simulation that control laws, which have been designed on a rolling constraint dynamic model for frictional forces, fail to perform rolling in various environments. An extra control input that uses a reference rolling trajectory that is state dependent is proposed, which, if superimposed on a conventional force-position control law, can achieve rolling even on a surface with low friction characteristics. The proposed feedback signal does not utilize the modeling information in the control formulation, and thus permits easy implementation. Finally, the total controller is shown to achieve asymptotic convergence to the desired force-positioning task by simultaneously evoking pure rolling motion for the fingertip.

Stability analysis for a second-order continuous finite-time control system subject to a disturbance

In this paper, using finite-time control method, we consider the disturbance analysis of a second-order system with unknown but bounded disturbance. We show that the states of the second-order system will be stabilized to a region containing the origin. The radius of this region is determined by the control parameters and can be rendered as small as desired. The rigorous stability analysis is also given. Compared with the conventional PD control law, the finite-time control law yields a better disturbance rejection performance. Numerical simulation results show the effectiveness of the method.

State‐feedback disturbance attenuation for polytopic LPV systems with input saturation

AbstractThis paper proposes a state‐feedback control law for linear parameter‐varying (LPV) systems with input saturation and disturbances. The proposed control law employs two control parts: a main control part for reducing the restricted ℒ︁2 gain from the mismatched disturbance to the controlled output and an extra control part for eliminating the matched disturbance. Owing to this feature, the proposed control law provides a better disturbance attenuation performance than the conventional control law that deals with a unified disturbance regardless of the presence of matched and mismatched disturbances. Further, considering different forms of the feedback gain matrix K(θ(t)) and the Lyapunov function V(x(t)), three types of controllers are proposed. For each type, set invariance and the restricted ℒ︁2 gain performance conditions are first formulated in terms of parameterized linear matrix inequalities (PLMIs) and then converted into linear matrix inequalities (LMIs) by using a parameter relaxation technique. Results from the simulation of numerical examples confirm the effectiveness of the proposed controllers. Copyright © 2009 John Wiley & Sons, Ltd.

Antisway Tracking Control of Overhead Cranes With System Uncertainty and Actuator Nonlinearity Using an Adaptive Fuzzy Sliding-Mode Control

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> An adaptive fuzzy sliding-mode control (AFSMC) is presented for the robust antisway trajectory tracking of overhead cranes subject to both system uncertainty and actuator nonlinearity. First, a fuzzy sliding-mode control (FSMC) law is designed for the antisway trajectory tracking of the nominal plant. In association with a conventional trajectory tracking control law, this FSMC law guarantees asymptotic stability as well as improved transient response of the load sway dynamics while the trolley tracking error dynamics is rendered uniformly asymptotically stable. Second, a fuzzy uncertainty observer is designed to cope with system uncertainty as well as actuator nonlinearity present in an actual plant, and it is incorporated with the FSMC law for the development of the AFSMC law. In addition to stability analysis, the robust performance of the proposed AFSMC law is verified via numerical simulations and experiments. </para>

Plantwide Fault Isolation Using Nonlinear Feedback Control

Accurate detection and isolation of faults is a critical component of a reliable and efficient plantwide fault-tolerant control system. In a recent work (Ohran et al. AIChE J. 2008, 54, 223), we demonstrated that using a nonlinear controller to enforce a specific structure in the closed-loop system allows data-based detection and isolation of certain faults that would otherwise not be isolable using data-based techniques that do not impose the necessary closed-loop system structure. In this work, it is demonstrated through a multiunit chemical process example how this approach can be applied in a plantwide setting. By using nonlinear, model-based control laws to decouple certain states from faults of interest, unique fault responses in the state trajectories are obtained in the closed-loop system. On the basis of the unique responses, fault isolation becomes possible using data-based statistical process monitoring methods. The effectiveness of the method was tested through an extensive Monte Carlo simulation study of 500 runs for each of four fault scenarios and through comparison with a conventional (proportional−integral) feedback control law.

Two-dimensional simple proportional feedback control of a chaotic reaction system

The simple proportional feedback (SPF) control algorithm may, in principle, be used to attain periodic oscillations in dynamic systems exhibiting low-dimensional chaos. However, if implemented within a discrete control framework with sampling frequency limitations, controller performance may deteriorate. This phenomenon is illustrated using simulations of a chaotic autocatalytic reaction system. A two-dimensional (2D) SPF controller that explicitly takes into account some of the problems caused by limited sampling rates is then derived by introducing suitable modifications to the original SPF method. Using simulations, the performance of the 2D-SPF controller is compared to that of a conventional SPF control law when implemented as a sampled data controller. Two versions of the 2D-SPF controller are described: linear (L2D-SPF) and quadratic (Q2D-SPF). The performance of both the L2D-SPF and Q2D-SPF controllers is shown to be superior to the SPF when controller sampling frequencies are decreased. Furthermore, it is demonstrated that the Q2D-SPF controller provides better fixed point stabilization compared to both the L2D-SPF and the conventional SPF when concentration measurements are corrupted by noise.

Effect of wheel-slip prevention based on sliding mode control theory for railway vehicles

It is important to consider the robustness when designing brake control systems, because of the model's uncertainties that result from the nonlinear characteristics of wheel-to-rail adhesion forces and brake material friction coefficients. This paper presents the experimental results from the new wheel-slip prevention control using nonlinear robust control theory. The authors performed experiments for the proposed wheel-slip prevention control to compare it with the conventional control laws. The experimental results proved the comparative effectiveness of the proposed control and showed high brake performance under nonlinear characteristics of brake dynamics.