1,721,052 research outputs found
Simplified model of a single-wheeled self-balancing robot in mathworks® simscape multibodyTM
No full textThe paper deals with a single-wheeled self-balancing mobile robot type, usually named ballbot. During the design process of a ballbot prototype a model with reduced complexity but effective performance is helpful to define and analyse features of the perceived solution. A model of a ballbot based on a simplified modelling approach is presented. Assumptions to describe the effects of force transmission between main inertial components of a ballbot are described. Appropriate kinematic constrains between the driving ball of the robot and its actuators are developed and implemented in a MathWorks® Simscape MultibodyTM environment. The software model is then tuned to the characteristic parameters of the ballbot prototype. Dynamics has been intrinsically evaluated by the software solver and an efficacious formulation of the frictional effects has been introduced with an all-inclusive equivalent friction torque. Two different tests have been carried out and used for reference: position control and force disturbance response. Comparison between experimental and simulation results are shown and analysed to validate the simplified modelling approach for the ballbot
Using a robot calibration approach toward fitting a human arm model
No full textIn the context of Industry 4.0, the human-robot interaction (HRI) can be improved by tracking the human arm in the workspace shared with the robot. This goal takes advantage of a customized human arm modeling and it should be conveniently achieved with a limited number of sensors and a reduced computational time. In this paper, considering the analogy between human and robotic arms, a new method for the identification of a custom-made human arm model was inspired by a robot calibration process. The Denavit-Hartenberg (DH) parameters of the arm model were estimated recording a suitable number of hand poses. Hence, a robotic arm was exploited to test the new method. To simplify the fitting procedure of a reliable robot model, the minimum number of the necessary end-effector (EE) poses was investigated. Through an optoelectronic system, the EE pose trajectory of a UR3 robot was recorded. The optimization of the DH parameters was repeatedly run decreasing the downsampling frequency of the acquired data and then the trajectory error was evaluated. A new reference dataset of robot configurations was acquired permutating the joints degrees of freedom among values of 0, +90, or −90°. Hence, the method to fit the model considering few EE poses was tested on six robot configurations randomly selected from the dataset. Overall, trajectory errors highlighted the applicability of this method in the context of HRI
Effetto della direzione del flusso di vapore acqueo sulla misura della permeabilità.
No full text....
Functional method for joints parameters assessment in human body modeling
Full text linkThe integration of proper algorithms and computer
graphics-based systems seems promising for the design of
biomechanical models and the relative motion analysis. Thus,
consequences on research fields as gait analysis are gathered,
focusing on joints kinematics. Human motion patterns are
indeed directly influenced from human model and associated
joints parameters, such as centers and axes of rotation. These, as
a matter of fact, determine the body segments coordinates
systems. Joints parameters are estimated with several methods.
The aim of this research is to evaluate the consistency of a
functional approach versus a the predictive one. A validation of
the algorithm used to estimate the lower limbs joints centers in
gait analysis is provided with a proper subject-specific multibody
model implemented in OpenSim space. Joints angles are
estimated using a global optimization method and a comparison
with the gold standard technique is also discussed. Overall the
obtained results are consistent for the two different
methodologies. The correlation of the curves is excellent in the
sagittal plane, and very good in the coronal and transversal
plane
Identification of the best strategy to command variable stiffness using electromyographic signals
No full textObjective. In the last decades, many EMG-controlled robotic devices were developed. Since stiffness control may be required to perform skillful interactions, different groups developed devices whose stiffness is real-time controlled based on EMG signal samples collected from the operator. However, this control strategy may be fatiguing. In this study, we proposed and experimentally validated a novel stiffness control strategy, based on the average muscle co-contraction estimated from EMG samples collected in the previous 1 or 2 s. Approach. Nine subjects performed a tracking task with their right wrist in five different sessions. In four sessions a haptic device (Hi-5) applied a sinusoidal perturbing torque. In Baseline session, co-contraction reduced the effect of the perturbation only by stiffening the wrist. In contrast, during aided sessions the perturbation amplitude was also reduced (mimicking the effect of additional stiffening provided by EMG-driven robotic device) either proportionally to the co-contraction exerted by the subject sample-by-sample (Proportional), or according to the average co-contraction exerted in the previous 1 s (Integral 1s), or 2 s (Integral 2s). Task error, metabolic cost during the tracking task, perceived fatigue, and the median EMG frequency calculated during a sub-maximal isometric torque generation tasks that alternated with the tracking were compared across sessions. Main results. Positive effects of the reduction of the perturbation provided by co-contraction estimation was identified in all the investigated variables. Integral 1s session showed lower metabolic cost with respect to the Proportional session, and lower perceived fatigue with respect to both the Proportional and the Integral 2s sessions. Significance. This study's results showed that controlling the stiffness of an EMG-driven robotic device proportionally to the operator's co-contraction, averaged in the previous 1 s, represents the best control strategy because it required less metabolic cost and led to a lower perceived fatigue
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
Wearable MIMUs for the identification of upper limbs motion in an industrial context of human-robot interaction
Full text linkThe automation of human gestures is gaining increasing importance in manufacturing. Indeed, robots support operators by simplifying their tasks in a shared workspace. However, human-robot collaboration can be improved by identifying human actions and then developing adaptive control algorithms for the robot. Accordingly, the aim of this study was to classify industrial tasks based on accelerations signals of human upper limbs. Two magnetic inertial measurement units (MIMUs) on the upper limb of ten healthy young subjects acquired pick and place gestures at three different heights. Peaks were detected from MIMUs accelerations and were adopted to classify gestures through a Linear Discriminant Analysis. The method was applied firstly including two MIMUs and then one at a time. Results demonstrated that the placement of at least one MIMU on the upper arm or forearm is suitable to achieve good recognition performances. Overall, features extracted from MIMUs signals can be used to define and train a prediction algorithm reliable for the context of collaborative robotics
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