Actuators2016, 5(1), 3; doi:10.3390/act5010003 - published 4 January 2016 Show/Hide Abstract
Abstract: This paper presents the invention and development of a new fundamental type of hydraulic actuator, aimed at delivering better actuation efficiency. This actuator is a flexible tube, composed of two different materials, which deflects while applying inner pressure. This concept is simple to produce, and allows adaptation of the deflected shape by the design parameters (radius, wall thickness, geometry, etc.). Among other applications, it is mostly suitable for the activation of fins of nature-like marine robots. Theoretical formulation, production of prototypes and actuation experiments are presented, as well as material hysteresis research and an application example.
Actuators2016, 5(1), 2; doi:10.3390/act5010002 - published 30 December 2015 Show/Hide Abstract
Abstract: Recent advances in phase transition transduction enabled the design of a non-resonant broadband mechanical energy harvester that is capable of delivering an energy density per cycle up to two orders of magnitude larger than resonant cantilever piezoelectric type generators. This was achieved in a  oriented and poled domain engineered relaxor ferroelectric single crystal, mechanically biased to a state just below the ferroelectric rhombohedral (FR)-ferroelectric orthorhombic (FO) phase transformation. Therefore, a small variation in an input parameter, e.g., electrical, mechanical, or thermal will generate a large output due to the significant polarization change associated with the transition. This idea was extended in the present work to design a non-resonant, multi-domain magnetoelectric composite hybrid harvester comprised of highly magnetostrictive alloy, [Fe81.4Ga18.6 (Galfenol) or TbxDy1-xFe2 (Terfenol-D)], and lead indium niobate–lead magnesium niobate–lead titanate (PIN-PMN-PT) domain engineered relaxor ferroelectric single crystal. A small magnetic field applied to the coupled device causes the magnetostrictive element to expand, and the resulting stress forces the phase change in the relaxor ferroelectric single crystal. We have demonstrated high energy conversion in this magnetoelectric device by triggering the FR-FO transition in the single crystal by a small ac magnetic field in a broad frequency range that is important for multi-domain hybrid energy harvesting devices.
Actuators2016, 5(1), 1; doi:10.3390/act5010001 - published 23 December 2015 Show/Hide Abstract
Abstract: In this paper, we present the design and development of the UC-Softhand. The UC Softhand is a low cost, Bionic and adaptive hand that takes advantage of compliant joints. By optimization of the actuation strategy as well as the actuation mechanism, we could develop an anthropomorphic hand that embeds three actuators, transmission mechanisms, controllers and drivers in the palm of the hand, and weighs only 280 g, making it one of the lightest bionic hands that has been created so far. The key aspect of the UC Softhand is utilization of a novel compact twisted string actuation mechanism, that allows a considerable weight and cost reduction compared to its predecessor.
Actuators2015, 4(4), 336-352; doi:10.3390/act4040336 - published 11 December 2015 Show/Hide Abstract
Abstract: Artificial muscles define a large category of actuators we propose to analyze in a systemic framework by considering any artificial muscle as an open-loop stable system for any output which represents an artificial muscle dimension resulting from its “contraction”, understood in a broad meaning. This approach makes it possible to distinguish the artificial muscle from other actuators and to specify an original model for a linear artificial muscle, according to the theory of linear systems. Such a linear artificial muscle concept exhibits a constant stiffness independent on its control value. It is shown that a biomimetic actuator, made of two antagonist artificial muscles, requires that artificial muscle static characteristic, even in its most simplified form, is non-linear in the meaning of systems theory, to make possible the control of both actuator position and stiffness. However, we also attempt to show that a linear viscous damping can be a practical way for the dynamic behavior of the artificial muscle to be in relatively good accordance with the so-called Hill curve, interpreted as the dynamic characteristic linking the maximum contraction velocity of the artificial muscle to varying loads lifted against gravity.
Actuators2015, 4(4), 314-335; doi:10.3390/act4040314 - published 8 December 2015 Show/Hide Abstract
Abstract: The challenges of an HVDC breaker are to generate impulsive forces in the order of hundreds of kilonewtons within fractions of a millisecond, to withstand the arising internal mechanical stresses and to transmit these forces via an electrically-insulating device to the contact system with minimum time delay. In this work, several models were developed with different levels of complexity, computation time and accuracy. Experiments were done with two mushroom-shaped armatures to validate the developed simulation models. It was concluded that although the electromagnetic force generation mechanism is highly sensitive to the mechanical response of the system, the developed first order hybrid model is able to predict the performance of the breaker with good accuracy.