Evaluation on Implementing an Active Braking System in Wheelchair Rear-Mounted Power-Assisted Device

Power-Assisted Devices (PADs) for wheelchairs are becoming popular tools to enhance propulsion capabilities and to assist wheelchair users to perform daily activities. PADs include Pushrim Activated Power-Assisted Wheelchairs, joy-stick-driven wheels, front-end attachments, and rear-end attachments. Considering the latest, they are not equipped with any active braking system. This could affect the handling of the wheelchair and introduce safety concerns. The paper aims to assess the performance of a rear add-on during driving and braking conditions, and to investigate the implementation and effectiveness of a servo braking system. A dynamic multibody model of a wheelchair has been developed and the dynamic of the system has been analyzed. To enhance the braking effectiveness, an additional preload torque between the wheelchair and the device has been modelled. Simulations have been performed for different braking torques. The results show that the introduction of a mounting preload positively affects the braking effectiveness, and it assists the user to perform part of the braking action

Collection and analysis of human upper limbs motion features for collaborative robotic applications

Background: The technologies of Industry 4.0 are increasingly promoting an operation of human motion prediction for improvement of the collaboration between workers and robots. The purposes of this study were to fuse the spatial and inertial data of human upper limbs for typical industrial pick and place movements and to analyze the collected features from the future perspective of collaborative robotic applications and human motion prediction algorithms. (2) Methods: Inertial Measurement Units and a stereophotogrammetric system were adopted to track the upper body motion of 10 healthy young subjects performing pick and place operations at three different heights. From the obtained database, 10 features were selected and used to distinguish among pick and place gestures at different heights. Classification performances were evaluated by estimating confusion matrices and F1-scores. (3) Results: Values on matrices diagonals were definitely greater than those in other positions. Furthermore, F1-scores were very high in most cases. (4) Conclusions: Upper arm longitudinal acceleration and markers coordinates of wrists and elbows could be considered representative features of pick and place gestures at different heights, and they are consequently suitable for the definition of a human motion prediction algorithm to be adopted in effective collaborative robotics industrial applications

Estimation of Force Effectiveness and Symmetry During Kranking Training

The third Sustainable Development Goal of the 2030 Agenda promotes healthy lives and well-being for all people of all ages. A good way to ensure a healthy lifestyle is to perform daily physical activity. Among different exercises of cardiovascular training, kranking is a program that involves arm-cranking gesture performed on a stationary handbike. In order to correctly perform this activity, biomechanical parameters have to be monitored. The present pilot study aimed at developing a setup for the quantitative evaluation of the force effectiveness and symmetry during different conditions of upper limbs kranking. One healthy young subject performed different tasks of steady-state cycling on varying cadence, braking torque, and motion pattern. Strain gauges positioned on the handles of a commercial arm-cranking machine allowed the estimation of total and effective forces applied by the user. Moreover, an optical motion capture system was adopted to evaluate the kinematics of the upper limbs during the movement. Comparing the total and the effective forces, the effectiveness of the gesture was evaluated for all testing conditions. Overall, results suggest that the developed setup is adequate to efficaciously identify possible alterations of performance parameters during upper limbs kranking

Simplified model of a single-wheeled self-balancing robot in mathworks® simscape multibody™

The 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 Multibody™ 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

In 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

Chiral algebras, localization and surface defects

Four-dimensional N = 2 superconformal quantum field theories contain a subsector carrying the structure of a chiral algebra. Using localization techniques, we show for the free hypermultiplet that this structure can be accessed directly from the path integral on the four-sphere. We extend the localization computation to include supersymmetric surface defects described by a generic 4d/2d coupled system. The presence of a defect corresponds to considering a module of the chiral algebra: our results provide a calculational window into its structure constants.Comment: 47 pages; minor typos correcte

Exact Bremsstrahlung functions in ABJM theory

In this paper we study the Bremsstrahlung functions for the 1/6 BPS and the 1/2 BPS Wilson lines in ABJM theory. First we use a superconformal defect approach to prove a conjectured relation between the Bremsstrahlung functions associated to the geometric ($B^{\varphi}_{1/6}$) and R-symmetry ($B^{\theta}_{1/6}$) deformations of the 1/6 BPS Wilson line. This result, non-trivially following from a defect supersymmetric Ward identity, provides an exact expression for $B^{\theta}_{1/6}$ based on a known result for $B^{\varphi}_{1/6}$. Subsequently, we explore the consequences of this relation for the 1/2 BPS Wilson line and, using the localization result for the multiply wound Wilson loop, we provide an exact closed form for the corresponding Bremsstrahlung function. Interestingly, for the comparison with integrability, this expression appears particularly natural in terms of the conjectured interpolating function $h(\lambda)$. During the derivation of these results we analyze the protected defect supermultiplets associated to the broken symmetries, including their two- and three-point correlators.Comment: 43 pages, 3 figures. Minor changes. Published versio