1,720,998 research outputs found
A hybrid dynamical modeling framework for shape memory alloy wire actuated structures
No full textIn this letter, a hybrid model for single-crystal Shape Memory Alloy (SMA) wire actuators is presented. The result is based on a mathematical reformulation of the Müller-Achenbach-Seelecke (MAS) model, which provides an accurate and interconnection-oriented description of the SMA hysteretic response. The strong nonlinearity and high numerical stiffness of the MAS model, however hinder its practical use for simulation and control of complex SMA-driven systems. The main idea behind the hybrid reformulation is based on dividing the mechanical hysteresis of the SMA into five operating modes, each one representing a different physical state of the material. By properly deriving the switching conditions among those modes in a physically-consistent way, the MAS model is effectively reformulated within a hybrid dynamical setting. The main advantage of the hybrid reformulation is the possibility of describing the material dynamics with a simplified set of state equations while maintaining all benefits of the physics-based description offered by the MAS model. After describing the novel approach, simulation studies are conducted on a flexible robotic module actuated by protagonist-antagonist SMA wires. Through comparative numerical analysis, it is shown how the hybrid model provides the same accuracy as the MAS model while saving up to 80% of the simulation time. Moreover, the new modeling framework opens up the possibility of addressing SMA control from a hybrid systems perspective
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
A lumped parameter model for strip-shaped dielectric elastomer membrane transducers with arbitrary aspect ratio
No full textDielectric elastomer (DE) membrane transducers allow to achieve large strain, low energy consumption, low-noise, and highly compact mechatronic devices. To optimize the design of membrane DEs via numerically efficient software tools, as well as to develop accurate control and self-sensing algorithms, a lumped parameter model is required. In the case of rectangular DE strips clamped at both ends and subject to a uniaxial in-plane load, the resulting necking and inhomogeneous deformation turn out to be challenging to be described via standard lumped models, thus making it necessary to rely on numerically involved finite element (FE) tools. In this paper, we present a novel modeling framework that permits to accurately describe clamped DE membranes with generic aspect ratio in a control-oriented fashion. The model is grounded on an anisotropic free-energy function, which maps the inhomogeneities due to clamping within the constitutive membrane behavior. In this way, a lumped description of the DE can be obtained in terms of average stress and stretch quantities. After presenting the model, an extensive validation is performed by means of comparative studies with FE simulations as well as experimental results. It is observed how the proposed model permits to accurately describe the electro-mechanical response of clamped DE membranes for a wide range of aspect ratios, including nearly-uniaxial, nearly-pure shear, as well as intermediate configurations
Robust Interaction Control of a Dielectric Elastomer Actuator with Variable Stiffness
No full textThis paper presents an interaction control algorithm for a dielectric elastomer membrane actuator. The proposed method permits efficient exploitation of the controllable stiffness of the material, allowing to use the membrane as a 'programmable spring' in applications such as robotic manipulation or haptic devices. To achieve this goal, we propose a design algorithm based on robust control theory and linear matrix inequalities. The resulting controller permits to arbitrarily shape the stiffness of the elastomer, while providing robust stability and performance with respect to model nonlinearities. A self-sensing displacement estimation algorithm allows implementation of the method without the need of a deformation sensor, thus reducing cost and size of the system. The approach is validated on an experimental prototype consisting of an elastomer membrane preloaded with a bistable biasing spring
Bone remodelling around ceramic implants: a histomorphometrical evalua¬tion.Congresso congiunto IORS-SISC. Varese. 30 giugno-2 luglio 1996
No full textModel-based PID control of a dielectric electro-active polymer positioning system
No full textThis paper considers a micrometric positioning system based on a dielectric electro-active polymer membrane. The motion is generated by the deformation of the membrane caused by the electrostatic compressive force between two compliant electrodes applied on the surface of the polymer. The paper suggests various model-based design strategies (in both time and frequency domains) for PID control laws, which are able to compensate the nonlinear behavior of the actuator (caused by the characteristics of the material and the annular geometry of the membrane) and obtain very precise tracking of steps or sinusoidal reference signals. The various design strategies are discussed and compared both in simulations and experiments
Nonlinear Optimal Control of a Soft Robotic Structure Actuated by Dielectric Elastomer Artificial Muscles
No full textIn the field of soft robotics, Dielectric Elastomer Actuators (DEAs) represent a compact and efficient alternative to bulky pneumatic drives. Both soft robots and DEAs show highly nonlinear behaviours due to their intrinsic large deformations, making the design of dynamic controllers highly challenging. At present, the problem of position control of DEA soft robots has not yet been explored in the literature. In this paper, we directly account for the nonlinearities of a DEA-driven soft robotic structure using an Adaptive Dynamic Programming (ADP) approach. We develop for the first time a closed-loop optimal controllers for position regulation of a DEA soft robot, by approximating the solution of the Hamilton-Jacobi-Bellman equation with Neural Networks (NNs). We extend an existing model-based ADP approach to deal also with asymmetric input constraints. Simulation studies asses the improvements in positioning performance of the proposed approach, in comparison to traditional strategies
Smith-Predictor-Based Torque Control of a Rolling Diaphragm Hydrostatic Transmission
No full textRolling Diaphragm Hydrostatic Transmissions (RDHT) are high-performance low-cost solutions to delocalize heavy actuators away from the joints of robotic systems. Exploiting a low-cost pressure-based sensing technique, we propose here a Smith-predictor-based joint torque control of an RDHT-based actuation system. We also use a load-cell sensor for ground truth validation. The developed feedback controller is conveniently tuned based on an arbitrary pre-specified closed-loop natural frequency and damping ratio. This preserves the open-loop bandwidth while removing the intrinsic oscillations of the lightly damped highly transparent open-loop plant. Experimental tests validate the proposed control strategy, both in a stand-alone torque setpoint configuration and in a series of Human-Robot-Interaction tests confirming the significant advantages of the closed-loop control architecture
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