Showing papers by "Cornel Sultan published in 2009"

Tensegrity motion control using internal mechanisms

Abstract: Key properties of tensegrity structures are reviewed and illustrated on a representative structure. These properties reveal an ideal way of motion using infinitesimal internal mechanisms. Consequently, a new motion control strategy which exploits these mechanisms is introduced.

Nonlinear modeling and output feedback control design for a small-scale helicopter

Abstract: This paper presents a helicopter dynamic model controlled by a nonlinear output feedback controller. Particular emphasis is placed on the mathematical modeling of the main rotor dynamics, i.e., modeling the individual dynamics of the blades and the dynamics of the main rotor stabilizing bar. Since the derived model is highly nonlinear, an output feedback controller that uses a nonlinear observer is derived and used for both stabilization and trajectory tracking. The effectiveness of the proposed control scheme is verified through numerical simulations.

Applications of Calculus of Variations to Aircraft and Spacecraft Path Planning

Abstract: The problem of finding the trajectory for an aerospace vehicle moving between two fixed points is investigated using Calculus of Variations (CV), which can provide necessary and sufficient conditions for trajectories that optimize a cost index. Within the framework of a systematic study aimed at tackling analytically the trajectory generation problem, this paper presents applications of the CV to find trajectories that optimize kinetic energy, energy consumption, and fuel consumption considering several environmental conditions.

Design of Structures for Proportional Damping Approximation Using the Energy Gain

Abstract: NLIKE inertial and stiffness characteristics, which can be easily measured in static conditions, damping, a dynamic characteristic, is more difficult to quantify. Hence, in many cases the artificial Rayleigh damping model, which assumes that the damping matrix is a linear combination of the mass and stiffness matrices, is used. Rayleigh damping (or a generalization of it) is preferred because it leads to the ideal situation of a proportionally damped linear model of the structure’s dynamics, but it is neither a physics based nor a data based model. When the source of damping can be identified and accurately modeled using physics principles the Rayleigh damping assumption (or any artificial damping model for that matter) is not recommended. One example is that of tensegrity structures: the major damping sources can be easily identified, the joints and the tendons, and for these elements reliable physics based damping models can be built. However, in most cases the resulting linearized dynamics models are not proportionally damped. In general, the likelihood of obtaining non-proportionally damped models will increase due to our enhanced ability to accurately model damping using physics principles. Even if a system is not proportionally damped, one would still like to be able to approximate it with a proportionally damped system. For structures, usually described using models with many degrees of freedom, such models are very advantageous because they allow the replacement of non-proportionally damped models with decoupled models, which can be easily used for control design, fast computations, etc. This paper, which is strongly related to Ref. 6, pursues the idea of designing the structure such that it yields a linearized dynamics model that is “close” to a proportionally damped one. In Ref. 6 the design of structures for proportional damping approximation was investigated by exploiting only one, indirect factor that influences the accuracy of the approximation, namely the separation between natural frequencies. It was ascertained that separation