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Modelling the Physical Human-Exoskeleton Interface
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Modelling friction at the mechanical interface between the human and the exoskeleton
Full text linkIn virtual assessments of exoskeletons, often, friction is not modelled even though the actual interface consists of straps or moulded surfaces, where friction could play a significant role. In this work, the human-exoskeleton interaction during the use of a passive lower limb exoskeleton is modelled in three test cases through two different interface models. In particular, a model introducing friction at the human-exoskeleton interface is compared with a more conventional model that uses a kinematic joint to simulate the interface forces. Both the models show a good match between the empirical and predicted distribution of body weight between the subject and the exoskeleton. However, the results also show different trends of the moment required at the assisted joint by the different interface models, highlighting the importance of a realistic interface model to investigate the effectiveness of the exoskeleton in virtual assessments
An observational method for Postural Ergonomic Risk Assessment (PERA)
Full text linkMonotonous, repetitive work characterizes production lines. Repetitive movements and awkward postures are the most prominent physical risk factors in the workplace. Various legislations have been enacted along with technical standards for ergonomic risk evaluation to ensure the safety of the operators. There are numerous methods to assess the ergonomic risk at work. However, most methods are not meant to be used for assessing cyclic work. This paper proposes a method, Postural Ergonomic Risk Assessment (PERA), which is suitable to evaluate the postural ergonomic risk of short cyclic assembly work. Its key features are simplicity and compliance with standards. The added value of the method is that it provides an analysis of every work task in the work cycle, which facilitates the identification of sources of high risk to the operator. The method has been verified on nine work cycles, constituted by 88 work tasks, and it demonstrates accordance with the European Assembly Worksheet (EAWS), which has been developed to comply with the relevant standards and is one of the most comprehensive tools for ergonomic risk assessment. Industrial relevance: The simplicity and the compliance with standards of the proposed method would allow for a quick check of every work task of the work cycle and identification of problem areas. With further work, it would be possible to integrate the method along with work design tools used in the industry
Simulating the dynamics of a human-exoskeleton system using kinematic data with misalignment between the human and exoskeleton joints
Full text linkMusculoskeletal model-based simulation can be a powerful tool in the design and evaluation of exoskeletons. They are used extensively during the virtual prototyping stage using motion data of the human without the exoskeleton. An ideal exoskeleton model, perfectly aligned with the human joint axes, can be used to co-simulate the human and exoskeleton dynamics. However, misalignment between the human and exoskeleton joints is commonly observed during the use of an exoskeleton, potentially leading to a loss in the effective assistance received by the user. Motion data collected with the user wearing the exoskeleton should, normally, be able to capture the misalignment between the human and exoskeleton joints. Using misaligned motion data in the combined human-exoskeleton model can lead to complications in the virtual model and unrealistic outputs. One way to tackle these complications is to assume alignment between the human and exoskeleton joints in the model by kinematically constraining it.
This work presents a new method that facilitates the analysis of misaligned human-exoskeleton systems. This is achieved by introducing artificial segments between the human and exoskeleton models. These artificial segments, the so-called dummy segments, ensure kinetic alignment between the human and exoskeleton joints in the model without altering the observed kinematics from the actual trial. The method is demonstrated using an active lower-limb exoskeleton that aims to assist the elderly in stair negotiation. A single subject performed eight trials with the exoskeleton in a laboratory. Motion data of both the subject and exoskeleton were recorded using an optical marker-based motion capture system. Further, the measured ground reaction force and the exoskeleton assistive force were used as inputs in the combined human-exoskeleton model. The outputs from the inverse dynamics analysis of the model with the dummy segments were compared to those from a reference model, where the measured external forces were applied directly to the human model at the corresponding reference points, bypassing the human-exoskeleton interface model completely. The results of the knee compression force, knee flexion moment, and activation of vastus lateralis from the model with the dummy segments showed good agreement with the reference model. The use of the dummy segments allows the study of aligned kinetics and misaligned kinematics from the same model
Physical and Virtual Assessment of a Passive Exoskeleton
No full textThe paper describes the testing activity carried out on a commercial
passive lower limb exoskeleton: the Chairless Chair, a wearable sitting support
that allows workers to switch between a standing and a sitting posture. Tests
were carried out with FCA workers who volunteered for the study. Laboratory
trials served to familiarize the users and to obtain an initial feedback on the
usability of the device in the assembly line. At a second step, virtual modelling
of a few static postures was carried out, reproducing the anthropometry and the
postural angles of the worker while using the exoskeleton. A main output of the
model is the estimate of what forces are exchanged between the subject and the
exoskeleton. In the case of the lower limb exoskeleton, an important parameter
to consider is the percentage of the subject’s weight that is sustained by the
exoskeleton frame. The higher is this percentage, the lower will be the strain on
the subject’s lower limbs. First comparison between experimental and simulated
results showed good agreement and auspicious advantages of exoskeletons in
relieving the strain on workers
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
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
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