Safe physical human-robot interaction, conservation of energy, and adaptability are the main robotic applications that prompted the development of a number of variable stiffness actuators (VSAs). Implemented in a variety of ways, they use various technologies and feature the most diverse mechanical solutions, all of which share a fundamentally unavoidable nonlinear behavior. The control schemes proposed for these actuators typically aim at independent control of the position of the link and its stiffness. Although effective feedback control schemes using position and force sensors are commonplace in robotics, control of stiffness is at present completely open loop: The stiffness is inferred from the mathematical model of the actuator. We consider here the problem of estimating the nonlinear stiffness of VSA in agonistic-antagonistic configuration. We propose an algorithm based on modulating functions that allow us to avoid the need for numerical derivative and for which the tuning is then very simple. An analysis of the error demonstrates the convergence. Simulations are provided, and the algorithm is validated on experimental data.
The sustainability of social robotics and other ambitious research programs
depends on the identification of lines of research that are coherent with its
visionary goals while satisfying more stringent constraints of feasibility and near-
term pay-offs. These multiple constraints are naturally conducive to the idea of a
society of robots operating within the physical environments of everyday human
life, developing there rich robot-robot social exchanges, and yet refraining from
any physical contact with human beings.
Achieving the visionary goals of social robotics or its more realistic objectives
requires extensive multidisciplinary cooperation. Accordingly, social robotics
may come to play a significant coordinating role for the constellation of research
communities in robotics. This coordinating role is exemplified here by reference
to a principled approach to robotic hand control based on sensory-motor soft
synergies: pursued in some current investigations on artificial hands, this
approach promises to meet distinctive needs arising in social robotics in the way
of dexterous manipulation of objects that are primarily conceived for human use.
Measuring and monitoring through wearable technology parameters related to human movement, posture, and gesture are gaining momentum because of their wide range of potential applications in daily-life conditions. In previous studies, carbon elastomers (CEs) have been used as strain sensors. Recent developments of CE sensors mathematical modeling demonstrated that the CEs can be used as electrogoniometers. It was proved that for small local curvatures of CE layers, the resistance of a strip constituting a layer depends only on the total curvature of the same layer and not on the particular shape that the sensor keeps in adherence with a surface. Further, it was proved, theoretically and experimentally, that a double-layer configuration provides better accuracy with respect to a single-layer configuration. These results have been obtained under the hypothesis that the device was bent, but not extended. In this paper, we substituted the inextensible insulating layer in the sensors with an elastic one, allowing the system to extend its length. This improvement required further study to make it fit for biomechanical applications following epithelial deformations produced by joint movements and minimizes skin motion artifacts.
Abstract After passage through biological barriers, nanomaterials inevitably end up in contact with the vascular endothelium and physiological flow, and can induce cardiovascular damage. In this study the toxicity and sublethal effects of 6 nanoparticles, including 4 of industrial and biomedical importance, on human endothelial cells was investigated using different in vitro assays. The results show that all the particles investigated induce some level of damage to the cells and that silver particles were most toxic, followed by titanium dioxide. Furthermore endothelial cells were shown to be more susceptible when exposed to silver nanoparticles under flow conditions in a bioreactor. The study underlines that although simple in vitro tests are useful to screen compounds and to identify the type of effect induced on cells, they may not be sufficient to define safe exposure limits. Therefore, once initial toxicity screening has been conducted on nanomaterials, it is necessary to develop more physiologically relevant in vitro models to better understand how nanomaterials can impact on human health.
Measuring the viscoelastic behaviour of highly hydrated biological materials is challenging because of their intrinsic softness and labile nature. In these materials it is difficult to avoid pre-stress and therefore to establish precise initial stress and strain conditions for lumped parameter estimation using creep or stress-relaxation tests. We describe a method ($ε$M or epsilon dot method) for deriving the viscoelastic parameters of soft hydrated biomaterials which avoids pre-stress and can be used to rapidly test degradable samples. Standard mechanical tests are first performed compressing samples using different strain rates. The dataset obtained is then analysed to mathematically derive the material's viscoelastic parameters. In this work a stable elastomer, PDMS, and a labile hydrogel, gelatin, were first tested using the $ε$M, in parallel stress-relaxation was used to compare lumped parameter estimation. After demonstrating that the elastic parameters are equivalent and that the estimation of short time constants is more precise using the proposed method, the viscoelastic behaviour of porcine liver was investigated using this approach. The results show that the constitutive parameters of hepatic tissue can be quickly quantified without the application of any pre-stress and before the onset of time dependent degradation phenomena.
Collagen‐gelatin‐genipin‐hydroxyapatite composite scaffolds colonized by human primary osteoblasts are suitable for bone tissue engineering applications: In vitro evidences
