Engenharia Mecânica
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/23
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17 resultados
Resultados da Pesquisa
Artigo 2 Citação(ões) na Scopus Using linear programming for the optimal control of a cartpendulum system(2011-01-05) PUGLIA, L. V.; Fabrizio Leonardi; Marko AckermannThis paper discusses the use of linear programming for the optimal control of a cart pendulum system. The objective function and the constraints are designed to minimize the control effort and the time duration of the operation. Simulations and experimental tests were performed. Restrictions of null angle and angular velocity at the extremes were incorporated in the design specification as well as other physical constraints. In order to compensate for the modeling errors and disturbances, the optimal trajectory was kept within a prescribed precision by means of a closed loop system. The obtained results illustrate that the technique is simple, powerful and always conclusive.Artigo de evento 0 Citação(ões) na Scopus Using linear programming for the optimal control of a cartpendulum system(2011) PUGLIA, L. V.; Fabrizio Leonardi; Marko AckermannThis paper discusses the use of linear programming for the optimal control of a cart pendulum system. The objective function and the constraints are designed to minimize the control effort and the time duration of the operation. Simulations and experimental tests were performed. Restrictions of null angle and angular velocity at the extremes were incorporated in the design specification as well as other physical constraints. In order to compensate for the modeling errors and disturbances, the optimal trajectory was kept within a prescribed precision by means of a closed loop system. The obtained results illustrate that the technique is simple, powerful and always conclusive.- A method to simulate motor control strategies to recover from perturbations: Application to a stumble recovery during gait(2011-09-03) FORNER-CORDERO, A.; Marko Ackermann; DE LIMA FREITAS, M.Perturbations during human gait such as a trip or a slip can result in a fall, especially among frail populations such as the elderly. In order to recover from a trip or a stumble during gait, humans perform different types of recovery strategies. It is very useful to uncover the mechanisms of the recovery to improve training methods for populations at risk of falling. Moreover, human recovery strategies could be applied to implement controllers for bipedal robot walker, as an application of biomimetic design. A biomechanical model of the response to a trip during gait might uncover the control mechanisms underlying the different recovery strategies and the adaptation of the responses found during the execution of successive perturbation trials. This paper introduces a model of stumble in the multibody system framework. This model is used to assess different feedforward strategies to recover from a trip. First of all, normal gait patterns for the musculoskeletal system model are obtained by solving an optimal control problem. Secondly, the reference gait is perturbed by the application of forces on the swinging foot in different ways: as an instantaneous inelastic collision of the foot with an obstacle, as an impulsive horizontal force or using a force curve measured experimentally during gait perturbation experiments. The influence of the type of perturbation, the timing of the collision with respect to the gait cycle, as well as of the coefficient of restitution was investigated previously. Finally, in order to test the effects of different muscle excitation levels on the initial phases of the recovery response, several muscle excitations were added to selected muscles of the legs, thus providing a simulation of the recovery reactions. These results pave the way for future analysis and modeling of the control mechanisms of gait. © 2011 IEEE.
- Influence of center of pressure estimation errors on 3D inverse dynamics solutions during gait at different velocities(2013-12-05) CAMARGO JUNIOR, F.; Marko Ackermann; LOSS, J. F.; SACCO, I. C. N.The aim of this study was to investigate the effect of errors in the location of the center of pressure (5 and 10 mm) on lower limb joint moment uncertainties at different gait velocities (1.0, 1.5, and 2.0 m/s). Our hypotheses were that the absolute joint moment uncertainties would be gradually reduced from distal to proximal joints and from higher to lower velocities. Joint moments of five healthy young adults were calculated by inverse dynamics using the bottom-up approach, depending on which estimate the uncertainty propagated. Results indicated that there is a linear relationship between errors in center of pressure and joint moment uncertainties. The absolute moment peak uncertainties expressed on the anatomic reference frames decreased from distal to proximal joints, confirming our first hypothesis, except for the abduction moments. There was an increase in moment uncertainty (up to 0.04 N m/kg for the 10 mm error in the center of pressure) from the lower to higher gait velocity, confirming our second hypothesis, although, once again, not for hip or knee abduction. Finally, depending on the plane of movement and the joint, relative uncertainties experienced variation (between 5 and 31%), and the knee joint moments were the most affected. © 2013 Human Kinetics, Inc.
- Modeling of gait adaptations to minimize plantar tissue strain during walking(2010) HALLORAM, L. P.; Marko Ackermann; ERDEMIR, A.; VAN DEN BOGET, A. J.
- A computational study of the swing phase of the gait with standard and spring-loaded crutches(2012-06-12) Marko Ackermann; TAISSUN, B. A.Crutches have suffered few functional modifications over their long history, with improvements largely limited to aesthetics and weight reduction aspects. The large energetic cost of the gait with crutches and problems associated to their long-term use impose a heavy burden to the users. In order to mitigate some of the mentioned problems, alternative designs have been proposed over the past few decades. Among them, the idea of incorporating an elastic element to the crutches to reduce impact forces transmitted to the upper extremities and to promote energy storage and release has been indicated in the specialized literature as a potential solution, in particular for the crutch gait styles more similar to the normative human gait such as the two-point and the swing-through. In fact, tendon elasticity has been shown to reduce energy consumption during animal and human locomotion by means of energy storage in the initial and mid stance-phase and release in the push-off phase of the gait cycle. In spite of the great potential of this idea, appropriate stiffness curves for the elastic element are poorly studied in the literature. This study aims at investigating appropriate stiffness values for the elastic element of spring-loaded crutches by means of computational simulations using a model of the swing phase of the swing-through gait style. The findings show that the stiffness should be tuned carefully to ensure improved gait quality. Spring-loaded crutches undoubtedly reduce impact forces transmitted to upper limbs and shoulder at touch down but they can deteriorate performance with respect to foot clearance and effort at the shoulder when compared to stiff crutches if stiffness is not carefully selected. © 2012 IEEE.
- Modeling and optimal control formulation for manual wheelchair locomotion: The influence of mass and slope on performance(2014-08-15) Marko Ackermann; Fabrizio Leonardi; COSTA, H. R.; FLEURY, A. T.A framework to generate predictive simulations is proposed to investigate the influence of system's mass on manual wheelchair locomotion. The approach is based on a model of wheelchair propulsion dynamics and an optimal control formulation. In this study, predictive simulations of steady-state wheelchair locomotion are generated for different combinations of model mass and uphill slope inclination angle. The results show that the influence of system's mass is negligible in level surfaces in steady-state, a finding which agrees with experimental observations in the literature. On the other hand, the results show that the influence of mass on slopes is critical, with large increases in propulsion effort with system's mass, even for slight inclination angles. This shows the importance of reducing wheelchair mass for improving locomotion performance, particularly in overcoming obstacles and ramps. Decreasing the wheelchair's mass may not be sufficient. Therefore, and on the light of these findings, we propose the reduction of system's apparent mass through the implementation of an impedance control scheme in powerassisted wheelchairs.
- A modeling framework to investigate the radial component of the pushrim force in manual wheelchair propulsion(2015-11-25) Marko Ackermann; COSTA, H. R.; Fabrizio Leonardi© Owned by the authors, published by EDP Sciences, 2015.The ratio of tangential to total pushrim force, the so-called Fraction Effective Force (FEF), has been used to evaluate wheelchair propulsion efficiency based on the fact that only the tangential component of the force on the pushrim contributes to actual wheelchair propulsion. Experimental studies, however, consistently show low FEF values and recent experimental as well as modelling investigations have conclusively shown that a more tangential pushrim force direction can lead to a decrease and not increase in propulsion efficiency. This study aims at quantifying the contributions of active, inertial and gravitational forces to the normal pushrim component. In order to achieve this goal, an inverse dynamics-based framework is proposed to estimate individual contributions to the pushrim forces using a model of the wheelchair-user system. The results show that the radial pushrim force component arise to a great extent due to purely mechanical effects, including inertial and gravitational forces. These results corroborate previous findings according to which radial pushrim force components are not necessarily a result of inefficient propulsion strategies or hand-rim friction requirements. This study proposes a novel framework to quantify the individual contributions of active, inertial and gravitational forces to pushrim forces during wheelchair propulsion.
- A comparison of different assistance strategies in power assisted wheelchairs using an optimal control formulation(2016-08-18) CUERVA, V. I.; Marko Ackermann; Fabrizio LeonardiPower assisted wheelchairs are a promising solution to overcome problems associated with manual wheelchair propulsion, such as the incidence of upper limbs injuries and muscle fatigue. However, there are still open questions regarding the most appropriate assistance strategy. The main goal of this paper is to compare three different types of assistance in power assisted wheelchairs: constant force, proportional force and a novel type of assistance inspired on the impedance control theory. The comparison was performed using a simple model and an optimal control formulation that searched for optimal user actuation and controller parameters so as to minimize the user effort. The fairness of the comparison was ensured by imposing an upper bound on the energy consumption by the motors. The results show that the proportional and impedance controlbased strategies are the most appropriate steady state conditions. In typical daily activities such as obstacle avoidance, the impedance control has advantage as it permits a faster system's response.
- Optimal control of the wheelchair wheelie(2016-08-18) DOS SANTOS, E. G.; Fabrizio Leonardi; Marko AckermannThe wheelchair wheelie is a maneuver employed to overcome obstacles and descend ramps, for instance. The task is similar to the stabilization problem of an inverted pendulum that is extensively described in the control theory literature. However, in this case, the goal is to maintain the user and the wheelchair in equilibrium on wheels, which is achieved when the center of mass of the system is aligned with the rear axle in the vertical direction. This work investigates a controller to perform the wheelie in power-assisted wheelchairs using optimal control theory and a model of the user and wheelchair system. The proposed approach leads to a controller capable of rising the wheelchair, which is able to reject perturbations and which is robust to typical parameter uncertainties.