Types Of Control Laws Research Articles

Nonlinear Path Following Control of Autonomous Underwater Vehicles

A new type of control law is derived to steer an autonomous underwater vehicle (AUV) along a desired path. The methodology adopted for path following deals explicitly with vehicle dynamics. Furthermore, it overcomes stringent initial condition constraints that are present in a number of path following control strategies described in the literature. Controller design builds on Lypaunov theory and backstepping techniques. The resulting nonlinear feedback control law yields convergence of the path following error trajectories to zero. Simulation results illustrate the performance of the control system proposed.

Optimal synthesis in a two-dimensional problem with asymmetric constraints on the control

A two-dimensional optimal control problem is considered on the assumption that the terminal time of the process is not fixed and the integral objective functional depends on a parameter. Asymmetric constraints are imposed on the control parameter. Two cases are considered: constraints of the same sign and constraints of different signs. In the case of constraints of different signs, if the parameters of the problem satisfy certain relations, one obtains chattering control, alternating with a control with two switchings and a first-order singular are when these relations are violated. In the case of sign-definite control the controllability domain is part of the plane bounded by two semiparabolas. Three types of control law are then possible, in two of which the system will hit the boundary of the controllability domain and move along it, while the third features a first-order singular are. As the parameter of the problem is varied, the phase portrait undergoes evolution and one of these three types is interchanged with another. The optimality of these control laws is rigorously established using a dynamic programming method.

Effective Selection of Piezoceramic Actuators for an Experimental Flexible Wing

The effectiveness of individual or subsets of piezoceramic actuators are investigated in terms of their contributions to the joint controllability and observability for a e xed set of sensors. The method used is based on the decomposition of the Hankel singular values in terms of individual sensor and actuator combinations for e exible structures. The degree of participation of the individual structural modes in the e utter control problem is used to weigh the actuator selection metric in the feedback loop. Simulation results based on H2 and H1 control law designs indicate that closed loop performance can be improved signie cantly and the performance improvement is independent of the particular type of control law.

Variable structure robust control of uncertain time-delay systems

This paper introduces a variable structure output feedback robust control for uncertain time-delay systems. New types of switching manifolds with integral terms are implemented to consider larger class of linear systems by overcoming both the observability constraints of the reduced order system and the Kimura–Davison condition. Two types of control laws are introduced by which an estimate of a region of asymptotic stability to the origin and a region of attraction to the switching manifold are defined.

Time-invariant 2 DOF multivariable LQG predictive controllers

The multivariable generalized predictive control law is derived in a stochastic setting which closely follows the usual polynomial solution of the LQG problem. A constraint is applied that both the control and future predicted control are calculated using the same time-invariant controller. The conditions which must apply for a time-invariant controller to exist are discussed. The assumptions which must be made to ensure a GPC type of control law emerges are also clear from the analysis, which provides insights into the relationship between LQG and GPC control. The form of the two degree-of-freedom control law obtained closely parallels the GPC solution but ensures closed-loop stability. The solution of the multi-step cost-function problem is shown to provide an LQG type of control action and a set of predicted future controls and outputs. This is of importance when input and output constraints are to be applied based on the future predicted signals. The control signal can be found using the vector-matrix form of the solution and it is very similar to the GPC form of controllers. However, the stability properties for the feedback loop are much improved, relative to the traditional GPC or LRPC algorithms.

A pole placement adaptive control of a rapid thermal processor

Rapid thermal processing (RTP) techniques are often applied in microelectronic technology. The main characteristics of RTP techniques lie in single wafer treatments, fast thermal kinetics at low thermal cost and reduced contamination risks; moreover, many types of reaction can be realized with one single wafer treatment. Problems of measurement and control of space-time temperature profiles have not yet been solved in a satisfactory way; in particular, classical control algorithms (such as PID control) can give bad dynamics to the system if nominal temperature profiles must be modified. Modelling of the thermal behaviour of the process leads to very complex mathematical models. These are the reasons why adaptive control techniques are chosen. A CARIMA model is an interesting input-output model of the thermal processor, whose parameters can be estimated on-line, using an identification scheme which includes supervisory actions. The adaptive control algorithm is a full-state feedback pole-placement law with an adaptive observer. A partial-state reference model was included in the control law algorithm. This type of control law can be implemented even for non-minimum-phase systems, time-varying dynamics, a wrong assumption about the time delay of the system, and when disturbances on the load exist. Experimental results are presented which show a better performance when using an adaptive control strategy

General Active Micromotion Attenuator

This paper presents the one axis test bench of the microdynamic and accuracy pointing laboratory of the CNES and the preliminary results of a decoupling system which uses an inertial control mass to assume the decoupling function of a proof mass. The objective of this test bench is to compare on the same realisation, different types of control law in term of robustness versus external disturbances or modelling errors. The ability of real time implementation and the tuning facility will also be evaluated during this study.

Open-loop versus closed-loop control of processor loading

In many processing systems, the goodput (the number of succesfully completed tasks per time unit) may decrease as the offered load increases. Such systems need some form of overload control. We distinguish between open-loop control that limits the number of tasks in the system with a fixed maximum and closed-loop control that rejects new tasks if the observed processor loading is too high. In most control systems closed-loop control performs better than open-loop control. Here we present a remarkable illustration of the converse: we show that higher goodput can be obtained with an open-loop control-law. The results are obtained with a simplified analytical model of a multi-tasking processing system, such as the central processor of a telephone exchange. Compared to open-loop control, closed-loop control is more robust with respect to a change in task idle-time. Under conditions of overload, the mentioned differences between the two types of control law become more pronounced. The computed results are confirmed by the outcome of simulation runs. In the simulations we used a more realistic definition of goodput than was used in the analytical model.

A control weighted minimum-variance controller for non-minimum phase systems

A now minimum-variance type of control law is derived for use in self-tuning control schemes where the plant is non-minimum phase. The controller has some of the features of the minimum-variance controller and is related to the generalized or λ minimum-variance controller which includes control weighting terms. The controller has the advantage that when the control-weighting scalar tends to zero the system is assured of being asymptotically stable. The generalized minimum-variance controller, employed in the self-tuning control law, results in an unstable closed-loop system in this situation. The controller may also be used to stabilize plants which are both unstable and non-minimum phase (the closed-loop system corresponding to the generalized minimum variance controller may be unstable for all values of the weighting scalar in this situation)

Modal-Space Control of Large Flexible Spacecraft Possessing Ignorable Coordinates

One problem peculiar to spacecraft in free space is that of ignorable coordinates, which are present when the spacecraft has no natural ability of preventing rigid-body motions. Ignorable coordinates can be eliminated from the problem formulation by introducing a reduced state vector. However, this results in having the ignorable coordinates uncontrolled. This paper solves this problem by introducing a dual-level control. The firstlevel controls are designed to control the ignorable coordinates and they lead to a positive definite augmented system and the second-level controls are designed for the final control of the complete state vector, including the ignorable coordinates. The second-level controls are designed in modal space and can be based on several types of control laws. In particular, proportional control providing artificial viscous damping, proportional optimal control, and nonlinear on-off control are discussed. A numerical example, illustrating all of these control laws, is presented.