1,720,978 research outputs found
Musculoskeletal Modeling of the Human Lower Limb Stiffness for Robotic Applications
Full text linkThis research work presents a physiologically accurate and novel computationally fast neuromusculoskeletal model of the human lower limb stiffness. The proposed computational framework uses electromyographic signals, motion capture data and ground reaction forces to predict the force developed by 43 musculotendon actuators. The estimated forces are then used to compute the musculotendon stiffness and the corresponding joint stiffness. The estimations at each musculotendon unit is constrained to simultaneously satisfy the joint angles and the joint moments of force generated with respect to five degrees of freedom, including: Hip Adduction-Abduction, Hip Flexion-Extension, Hip Internal-External Rotation, Knee Flexion-Extension, and Ankle Plantar-Dorsi Flexion. Advanced methods are used to perform accurate muscle-driven dynamic simulations and to guarantee the dynamic consistency between kinematic and kinetic data.
This study presents also the design, simulation and prototyping of a small musculoskeletal humanoid made for replicating the human musculoskeletal structure in an artificial apparatus capable to maintain a quiet standing position using only a completely passive elastic actuation structure. The proposed prototype has a total mass of about 2 kg and its height is 40 cm. It comprises of four segments for each leg and six degrees of freedom, including: Hip Adduction-Abduction, Hip Flexion-Extension, Knee Flexion-Extension, Ankle Plantar-Dorsi Flexion, Ankle Inversion-Eversion, and Toe Flexion-Extension. In order to reconstruct the continuous state space parameters proper of the assembly's control of quiet standing, a hybrid non-linear Extended Kalman Filter based technique is proposed to combine a base-excited inverted pendulum kinematic model of the robot with the discrete-time position measurements.
This research work provides effective solutions and readily available software tools to improve the human interaction with robotic assistive devices, advancing the research in neuromusculoskeletal modeling to better understand the mechanisms of actuation provided by human muscles and the rules that govern the lower limb joint stiffness regulation. The obtained results suggest that the neuromusculoskeletal modeling technology can be exploited to address the challenges on the development of musculoskeletal humanoids, new generation human-robot interfaces, motion control algorithms, and intelligent assistive wearable devices capable to effectively ensure a proper dynamic coupling between human and robot
How different human muscle models affect the estimation of lower limb joint stiffness during running
No full textThe dynamics of muscle force generation is directly related
to the movement dynamics of the skeletal system. Thus, modelling muscle dynamics is important to fully understand the control of movement
in humans. Abnormal movements caused by neuromuscular diseases such
as stroke, Parkinson's disease, or multiple sclerosis to name a few have all
in common the presence of some abnormal muscle tone. Muscle tone can
be effectively represented via short-range stiffness. Since stiffness is difficult to measure in real time, it is convenient to use numerical models to
assess muscle stiffness as function of muscle dynamics. In this work, two
different implementations of the Hill-type muscle model are considered
to estimate the lower limb joint stiffness during running. The obtained
results are discussed to evaluate how the choices of muscle models affect the estimation of lower limb joint stiffness. We found that stiffness
estimates are strongly dependent on the adopted muscle model. We observed different magnitude and timing of the estimated stiffness time
profile with respect to each gait phase, as function of the model used.
Furthermore, the two models produced substantially different joint stiffness time profiles for the ankle joint
Effects of Reserve Actuators on Optimization Solutions: from Muscle Force to Joint Stiffness
No full textThis work presents a comparison between two
optimization methods used to compute the muscle activation
levels and corresponding forces that drives a set of generalized
coordinates towards a set of desired trajectories. To improve the
performance of musculoskeletal optimizations a supplemental
set of actuators is often included in addition to the modeled
muscles. Given a dynamic musculoskeletal model and five sets
of reserve actuators, a series of numerical simulations have been
performed using experimental data from a healthy male subject
who executes a running movement at three different speeds.
This is the first work to investigate the incidence of different
reserve actuator sets on muscle activation-to-force optimization
solutions, with respect to the estimation of the human lower
limb muscle forces and corresponding joint stiffness. The results
show significant differences between the obtained estimates,
indicating a greater accuracy on the Computed Muscle Control
solutions than pure Static Optimization solutions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
An Integrated System to approach the Programming of Humanoid Robotics
Full text linkThis paper describes a set of laboratory experiences focused on humanoid robots offered at the University of Padua. Instructors developed an integrated system through which students can work with robots. The aim is to improve the educational experience introducing a new learning tool, namely a humanoid robot, and the Robots Operating System (ROS) in a constructivist framework. This approach to robotics teaching lets students exploiting up-to-date robotic technologies and to deal with multidisciplinary problems, applying a scientic approach. By using humanoid robots, students are able to compare human movements
to robot motion. The comparison brings out human/robot similarities, pushing students to solve complex motion problems in a more natural way while discovering robot limitations. In this paper, the learning objectives of the project, and the tools used by the students are presented. A set of evaluation results are provided in order to validate the authors'
purpose. Finally, a discussion about designed experiences and possible future improvements is reported, hoping to encourage further spread of educational robotics in schools at all levels
Socio-economic impact of medical lower-limb Exoskeletons
No full textA constructive debate is ongoing among experts and academics about the social and economic impacts of advanced robotics. Exoskeleton robotic suits represent one of the most significant examples of what Human-Oriented Robotics is. After recent technological advances, the range of application fields of these devices has widened with respect to the first applications about teleoperation and power amplification. The aim of this paper is to contribute to the ongoing discussion by offering a vision of the possible future developments in terms of socio-economic impacts, resulting from the increasing use of Exoskeleton Robots, especially with regard to their applications in lower limb medical rehabilitation. In order to provide a concrete contribution to the current state-of-the-art, we are working on an alternative exoskeleton design approach to overcome the identified limits to the diffusion of this new technology. The achieved results are presented in the final part
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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