Control Effort Constraints Research Articles

A Highly-Maneuverable Demining Autonomous Robot: an Over-Actuated Design

Based on the well-known advantages of using an over-actuated mechanism for robots, this research proposes a holonomic highly-maneuverable autonomous robot design for demining service applications. The proposed approach provides an interesting compromise between the design requirements of the demining robot applications and the over-actuated autonomous robots. The robot body is mainly divided into two parts: the first part provides the robot with its required locomotion and it consists of a driving/steering subsystem with four driving wheels (4WD), four steering mechanisms (4SW), and a passive suspension subsystem. The second part is a manipulator with three degrees of freedom that is designed based on two parallelogram mechanisms. The proposed design insures many advantages over existing designs, including stability, maneuverability, autonomous navigation, and simplicity of the control effort constraints. The robot model and its corresponding stability analysis were conducted and simulated in order to evaluate the motion of the robot over different environments rough terrains and slanted surfaces. Moreover, a prototype of the proposed robot was developed and built and different types of sensors were used in order to help it take precise actuation decisions for navigation and control. The prototype was experimentally tested for different scenarios and environments in order to validate the proposed design. The testing results demonstrated decent performance of the robot in autonomous navigation and in localizing the detected objects.

Dynamics Analysis and Robust Control for Electric Unicycles Under Constrained Control Force

This paper investigates the dynamics analysis and robust control law design for the proposed schematic design of electric unicycles. The schematic design of the proposed unicycle possesses a supportive seat for the rider and is also equipped with a handling rod for maneuvering, similar to a Segway device. First, this paper conducts an analysis and comparison of the dynamics properties and derivation of the nonlinear governing equation for the unicycle. Next, it emphasizes the development of an input-constrained robust controller design for the proposed configuration of the electric unicycle. The issues investigated in this paper include the dynamics property analysis and comparison, nonlinear dynamics derivation, robust control diagram formulation, controller synthesis regarding linear matrix inequalities (LMIs), and time response simulations and discussions. In this control law design via LMIs, the desired performances of: (1) relative stability or decay rate for command tracking capability; (2) disturbance attenuation for robustness against uncertainty parameters; and (3) an accommodation of control effort constraints under the regulation or command tracking of certain initial state condition are investigated and demonstrated using time response simulations of the controlled unicycle dynamics.

The influence of regularization on anechoic performance and robustness of sound zone methods

Recent attention to the problem of controlling multiple loudspeakers to create sound zones has been directed toward practical issues arising from system robustness concerns. In this study, the effects of regularization are analyzed for three representative sound zoning methods. Regularization governs the control effort required to drive the loudspeaker array, via a constraint in each optimization cost function. Simulations show that regularization has a significant effect on the sound zone performance, both under ideal anechoic conditions and when systematic errors are introduced between calculation of the source weights and their application to the system. Results are obtained for speed of sound variations and loudspeaker positioning errors with respect to the source weights calculated. Judicious selection of the regularization parameter is shown to be a primary concern for sound zone system designers—the acoustic contrast can be increased by up to 50 dB with proper regularization in the presence of errors. A frequency-dependent minimum regularization parameter is determined based on the conditioning of the matrix inverse. The regularization parameter can be further increased to improve performance depending on the control effort constraints, expected magnitude of errors, and desired sound field properties of the system.

Control of manipulators in a constrained workspace by means of linked invariant sets

AbstractWe propose a new technique for controlling manipulators in constrained environments. Based on recent developments on constrained control theory, our approach basically consists in covering the admissible region of the configuration space by partially overlapping convex polyhedra arbitrarily fixed and forming a connected family. Each of these polyhedra, defined in the configuration space, is suitably extended in the state‐space (i.e. configuration‐plus‐velocity space) in order to maintain all the original connections among regions and to be a tracking domain of attraction for the system, i.e. a set of initial states from which a reference signal can be asymptotically approached without constraints violation during the transient. The connection path is not generated a priori, but it is automatically produced on‐line by a hierarchical feedback controller. A high‐level controller selects the confining polyhedron, to which the current state has to be transferred, which is the closest to the one containing the target reference. A low‐level controller solves the problem of locally tracking a suitable crossing point to the desired new region under constraints. The robustness of the scheme as well as the control effort constraints are also taken into account. Copyright © 2004 John Wiley & Sons, Ltd.

Robust feedback control of flow-induced structural radiation of sound

A significant amount of the interior noise of aircraft and automobiles is a result of turbulent boundary layer excitation of the vehicular structure. In this investigation, the feasibility of active robust feedback control of the noise due to this type of excitation is studied. The structural sound radiation system investigated is comprised of a simply supported panel excited by turbulent flow. An analytical model of this system is developed to evaluate the robust feedback control system design strategy. The model consists of a modal description of the excitation of the plate by a turbulent boundary layer, a modal representation of the plate vibrations, and an acoustic model of the sound radiated from the plate. Parametric uncertainties of 1% variation in the natural frequencies and 5% variation in the damping ratio are considered. A frequency domain controller design approach is utilized to develop a robust controller. Performance objectives are specified which include output performance of the sound radiated by the plate and control effort constraints on the force applied to the plate by the controller. Plate acceleration feedback is used in an effort to reduce the sound-pressure level. Approximately 16 and 8 dB of sound-pressure level reduction were achieved at the first and third resonances, respectively.

Utilization of Control Effort Constraints in Linear Controller Design

A linear controller design procedure, which accounts for constraints on control effort, is developed by requiring that the control system utilize the maximum energy delivering capability of the final control elements under some specified test conditions (e.g., maximum step reference input). Results using this approach are available from previous studies for low-order single-input single-output controlled systems. This paper presents results for multi-input multi-output systems where the number of inputs is equal to the number of states. Both state variable feedback control for regulation, and integral plus state variable feedback control for tracking are considered and illustrated with an example problem.

On an inverse problem in optimal control

The problem of optimizing linear-stationary control systems subject to quadratic performance indices and bounded control effort constraints is studied. This problem was first proposed by Letov [1]. His solution, however, has been found to be valid only in some special cases [3]. In this paper, necessary and sufficient conditions for the existence of the optimal control laws of the saturation type are developed. It is shown that the weighting factors in the performance index have to be chosen in a particular manner, and the plants have to satisfy certain conditions to yield an optimal saturation type control law. As the weighting on the control effort in the performance index is decreased, the optimal solution approaches a bang-bang type singular control.