Attitude Control of Ornithopter Wing by Using a MIMO Active Disturbance Rejection Strategy.

This work proposes a mathematical solution for the attitude control problem of an ornithopter wing. An ornithopter is an artificial bird or insect-like aerial vehicle whose flight and lift movements are produced and maintained by flapping wings. The aerodynamical drag forces responsible for the flying movements are generated by the wing attitude and torques applied to its joints. This mechanical system represents a challenging problem because its dynamics consist of MIMO nonlinear equations with couplings in the input variables. For dealing with such a mathematical model, an Active Disturbance Rejection Control-based (ADRC) method is considered. The cited control technique has been studied for almost two decades and its main characteristics are the use of an extended state observer to estimate the nonmeasurable signals of the plant and a state-feedback control law in standard form fed by that observer. However, even today, the application of the basic methodology requires the exact knowledge of the plant's control gain which is difficult to measure in the case of systems with uncertain parameters. In addition, most of the related works apply the ADRC strategy to Single Input Single Output (SISO) plants. For MIMO systems, the control gain is represented by a square matrix of general entries but most of the reported works consider the simplified case of uncoupled inputs, in which a diagonal matrix is assumed. In this paper, an extension of the ADRC SISO strategy for MIMO systems is proposed. By adopting such a control methodology, the resulting closed-loop scheme exhibits some key advantages: (i) it is robust to parametric uncertainties; (ii) it can compensate for external disturbances and unmodeled dynamics; (iii) even for nonlinear plants, mathematical analysis using Laplace's approach can be always used; and (iv) it can deal with system's coupled input variables. A complete mathematical model for the dynamics of the ornithopter wing system is presented. The efficiency of the proposed control is analyzed mathematically, discussed, and illustrated via simulation results of its application in the attitude control of ornithopter wings.

Alternative approach to modal gait analysis through the Karhunen-Loève decomposition: An application in the sagittal plane.

This article uses the Karhunen-Loève decomposition (KL) technique, also known as proper orthogonal decomposition (POD) or principal component analysis (PCA), to introduce the concept of gait mode, which can be used as a tool to identify gait differences among subjects or groups and to approximate gait curves. The KL is a statistical pattern analysis technique for finding dominant structures in an ensemble of data. This technique can be used to decompose a spatiotemporal signal into time-independent, orthogonal, spatial components and time-dependent amplitudes. This study demonstrates the existence of a common gait mode through the analysis of the kinematics of 57 young, healthy subjects, and how they can be used to identify different walking patterns, for instance differentiating male and female subjects.

Análise da marcha pós-artroplastia total do joelho com e sem preservação do ligamento cruzado posterior / Gait analysis after total knee arthroplasty with and without posterior cruciate ligament preservation

Analisar a marcha de pacientes submetidos a artroplastia total do joelho, primária, com e sem preservação do ligamento cruzado posterior (LCP), visando avaliar qual dessas técnicas reproduz padrão de marcha mais próximo do normal. Material: No período de abril a novembro de 2000, foram analisados parâmetros cinemáticos e de eletromiografia dinâmica em 60 pacientes submetidos a artroplastia primária total do joelho, perfazendo um total de 70 casos. As artroplastias foram divididas em três grupos: grupo 1- próteses AMK e Osteonics com preservação do LCP (24 casos); grupo II - próteses Osteonics sem preservação do LCP (22 casos); grupo lII - próteses LCS, tipo plataforma, sem preservação do LCP (24 casos). Nessa avaliação foi utilizado o sistema Vicon 140, com três câmeras de infravermelho, duas plataformas de força Bertec e um sistema Motion Lab para análise eletromiográfica dinâmica. Os valores angulares de flexão da articulação do joelho durante a fase de suporte da marcha foram submetidos ao teste t para comparar a média dos ângulos de flexão do joelho com valores assumidos como padrão. Resultado: Os pacientes do grupo I foram os que mais se aproximaram do padrão de marcha considerado normal. Na avaliação gráfica, observou-se que em nenhum caso o padrão de marcha normal foi reproduzido. A co-contração ocorreu principalmente nos pacientes do grupo II (81,8 por cento). Ocorreram alterações de marcha na totalidade dos pacientes estudados. No grupo I, foram obtidos os melhores resultados, tanto na análise da marcha quanto na eletromiografia dinâmica. Conclusões: Em todos os pacientes estudados foram observadas alterações da marcha após a artroplastia total de joelho. No grupo em que se preservou o LCP, foram obtidos os melhores resultados, tanto do ponto de vista da análise da marcha quanto em relação à eletromiografia dinâmica

Modeling of a bipedal robot using mutually coupled Rayleigh oscillators.

The objective of the work presented here was the modeling of a bipedal robot using a central pattern generator (CPG) formed by a set of mutually coupled Rayleigh oscillators. We analyzed a 2D model, with the three most important determinants of gait, that performs only motions parallel to the sagittal plane. Using oscillators with integer relation of frequency, we determined the transient motion and the stable limit cycles of the network formed by the three oscillators, showing the behavior of the knee angles and the hip angle. A comparison of the plotted graphs revealed that the system provided excellent results when compared to experimental analysis. Based on the results of the study, we come to the conclusion that the use of mutually coupled Rayleigh oscillators can represent an excellent method of signal generation, allowing their application for feedback control of a walking machine.