Notable advancements have been achieved in providing amputees with sensation through invasive and non-invasive haptic feedback systems such as mechano-, vibro-, electrotactile and hybrid systems. Purely mechanical-driven feedback approaches, however, have been little explored. In this paper, we now created a haptic feedback system that does not require any external power source (such as batteries) or other electronic components. The system is low-cost, lightweight, adaptable and robust against external impact (such as water). Hence, it will be sustainable in many aspects. We have made use of latest multimaterial 3D printing technology (Stratasys Objet500 Connex3) being able to fabricate a soft sensor and a mechano-tactile feedback actuator made of a rubber (TangoBlack Plus) and plastic (VeroClear) material. When forces are applied to the fingertip sensor, fluidic pressure inside the system acts on the membrane of the feedback actuator resulting in mechano-tactile sensation. We present the design, fabrication and validation of the proposed haptic feedback system. Our ∅7 mm feedback actuator is able to transmit a force range between 0.2 N (the median touch threshold) and 2.1 N (the maximum force transmitted by the feedback actuator at a 3 mm indentation) corresponding to force range exerted to the fingertip sensor of 1.2 − 18.49 N.
Nowadays, there is a growing awareness on the social and economic importance of the ocean. In this context, being able to carry out a diverse range of operations underwater is of paramount importance for many industrial sectors as well as for marine science and to enforce restoration and mitigation actions. Underwater robots allowed us to venture deeper and for longer time into the remote and hostile marine environment. However, traditional design concepts such as propeller driven Remotely Operated Vehicles (ROVs), Autonomous Underwater Vehicles (AUVs), or tracked benthic crawlers, present intrinsic limitations, especially when a close interaction with the environment is required. An increasing number of researchers are proposing legged robots as a bioinspired alternative to traditional designs, capable of yielding versatile multi-terrain locomotion, high stability, and low environmental disturbance. In this work, we aim at presenting the new field of underwater legged robotics in an organic way, discussing the prototypes in the state-of-the-art and highlighting technological and scientific challenges for the future. First, we will briefly recap the latest developments in traditional underwater robotics from which several technological solutions can be adapted, and on which the benchmarking of this new field should be set. Second, we will the retrace the evolution of terrestrial legged robotics, pinpointing the main achievements of the field. Third, we will report a complete state of the art on Underwater Legged Robots (ULRs) focusing on the innovations with respect to the interaction with the environment, sensing and actuation, modelling and control, and autonomy and navigation. Finally, we will thoroughly discuss the reviewed literature by comparing traditional and legged underwater robots, highlighting interesting research opportunities, and presenting use case scenarios derived from marine science applications.
Legged robots are a promising technology whose use is limited by their high energy consumption. Biological and biomechanical studies have shown that the vibration generated by elastically suspended masses provides an energy advantage over rigidly carrying the same load. The robotic validation of these findings has only scarcely been explored in the dynamic walking case. In this context, a relationship has emerged between the design parameters and the actuation that generates the optimal gait. Although very relevant, these studies lack a generalizable analysis of different locomotion modes and a possible strategy to obtain optimal locomotion at different speeds. To this end, we propose the use of articulated legs in an extended Spring-Loaded Inverted Pendulum (SLIP) model with an elastically suspended mass. Thanks to this model, we show how stiffness and damping can be modulated through articulated legs by selecting the knee angle at touch-down. Therefore, by choosing different body postures, it is possible to vary the control parameters and reach different energetically optimal speeds. At the same time, this modeling allows the study of the stability of the defined system. The results show how suitable control choices reduce energy expenditure by 16% at the limit cycle at a chosen speed. The demonstrated strategy could be used in the design and control of legged robots where energy consumption would be dynamically optimal and usage time would be significantly increased.
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