Thanapat Wanichanon - Academia.edu (original) (raw)

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Papers by Thanapat Wanichanon

AIAA SPACE 2011 Conference & Exposition, 2011

International Journal of Control, 2013

cooperative force-reflecting teleoperator system based on a version of the nonlinear small-gain t... more cooperative force-reflecting teleoperator system based on a version of the nonlinear small-gain theorem. The controls are assumed to be of the proportional-derivative (PD) type and the parameters are fine-tuned, so the interconnected system is stable.

Numerical Algebra, Control and Optimization, 2013

This paper develops a new, simple, general, and explicit form of the equations of motion for gene... more This paper develops a new, simple, general, and explicit form of the equations of motion for general constrained mechanical systems that can have holonomic and/or nonholonomic constraints that may or may not be ideal, and that may contain either positive semi-definite or positive definite mass matrices. This is done through the replacement of the actual unconstrained mechanical system, which may have a positive semi-definite mass matrix, with an unconstrained auxiliary system whose mass matrix is positive definite and which is subjected to the same holonomic and/or nonholonomic constraints as those applied to the actual unconstrained mechanical system. A simple, unified fundamental equation that gives in closed-form both the acceleration of the constrained mechanical system and the constraint force is obtained. The results herein provide deeper insights into the behavior of constrained motion and open up new approaches to modeling complex, constrained mechanical systems, such as those encountered in multi-body dynamics.

Nonlinear Approaches in Engineering Applications 2, 2013

Nonlinear Approaches in Engineering Applications, 2011

Chapter 11 Explicit Equation of Motion of Constrained Systems Applications to Multi-body Dynamics... more Chapter 11 Explicit Equation of Motion of Constrained Systems Applications to Multi-body Dynamics Firdaus E. Udwadia and Thanapat Wanichanon Abstract This chapter develops a new, simple, general, and explicit form of the equations of motion for general nonlinear ...

Journal of Guidance, Control, and Dynamics, 2014

A two-step formation-keeping control methodology is proposed that includes both attitude and orbi... more A two-step formation-keeping control methodology is proposed that includes both attitude and orbital control requirements in the presence of uncertainties. Based on a nominal system model that provides the best assessment of the real-life uncertain environment, a nonlinear controller that satisfies the required attitude and orbital requirements is first developed. This controller allows the nonlinear nominal system to exactly track the desired attitude and orbital requirements without making any linearizations/approximations. In the second step, a new additional set of closed-form additive continuous controllers is developed. These continuous controllers compensate for uncertainties in the physical model of the satellite and in the forces to which it may be subjected. They obviate the problem of chattering. The desired trajectory of the nominal system is used as the tracking signal, and these controllers are based on a generalization of the concept of sliding surfaces. Error bounds on tracking due to the presence of uncertainties are analytically obtained. The resulting closed-form methodology permits the desired attitude and orbital requirements of the nominal system to be met within user-specified bounds in the presence of unknown, but bounded, uncertainties. Numerical results are provided, showing the simplicity and efficacy of the control methodology, and the reliability of the analytically obtained error bounds.

Applied Mathematics and Computation, 2010

a b s t r a c t This paper deals with an explanation of a paradox posed by Hamel in his 1949 book... more a b s t r a c t This paper deals with an explanation of a paradox posed by Hamel in his 1949 book on Theoretical Mechanics. The explanation deals with the foundations of mechanics and points to new insights into analytical dynamics.

Journal of Applied Mechanics, Transactions ASME, 2014

ABSTRACT Descriptions of real-life complex multibody mechanical systems are usually uncertain. Tw... more ABSTRACT Descriptions of real-life complex multibody mechanical systems are usually uncertain. Two sources of uncertainty are considered in this paper: uncertainties in the knowledge of the physical system and uncertainties in the "given" forces applied to the system. Both types of uncertainty are assumed to be time varying and unknown, yet bounded. In the face of such uncertainties, what is available in hand is therefore just the so-called "nominal system," which is our best assessment and description of the actual real-life situation. A closed-form equation of motion for a general dynamical system that contains a control force is developed. When applied to a real-life uncertain multibody system, it causes the system to track a desired reference trajectory that is prespecified for the nominal system to follow. Thus, the real-life system's motion is required to coincide within prespecified error bounds and mimic the motion desired of the nominal system. Uncertainty is handled by a controller based on a generalization of the concept of a sliding surface, which permits the use of a large class of control laws that can be adapted to specific real-life practical limitations on the control force. A set of closed-form equations of motion is obtained for nonlinear, nonautonomous, uncertain, multibody systems that can track a desired reference trajectory that the nominal system is required to follow within prespecified error bounds and thereby satisfy the constraints placed on the nominal system. An example of a simple mechanical system demonstrates the efficacy and ease of implementation of the control methodology.

This paper presents a new reference-tracking control methodology for nonlinear dynamical systems ... more This paper presents a new reference-tracking control methodology for nonlinear dynamical systems in the presence of unknown, but bounded, uncertainties in the system. To this end, two controllers are combined. A nonlinear controller is first developed to exactly track the desired reference trajectory assuming no uncertainties in the nonlinear nominal system. The entire nonlinear dynamics of the nominal system is included and no approximations/linearizations are made. Next, an additional continuous controller is developed in closed form to compensate for uncertainties in the physical model by generalizing the concept of sliding surfaces. Unlike conventional sliding mode control, this Lyapunov-based approach eliminates the chattering problem by replacing a signum function with a set of continuous functions that may have different forms depending on practical considerations related to actuator implementation. Among these possible forms, special attention is paid to a controller with a PID form. By using Lyapunov stability theory it is shown that this additional controller forces the tracking errors that arise because of the uncertainties in the system to move into a small, user-specified region around the generalized sliding surface. Once these tracking errors enter this small region, if the original nonlinear system is assumed to be linearizable, then linear control theory will ensure that they will further converge to even smaller values. A numerical example is provided, in which a satellite in the presence of air drag is required to maintain a specific, circular orbit around the Earth whose gravity field is imprecisely known. The example demonstrates the accuracy, efficiency, and ease of implementation of the control methodology.