Pneumatic Hyperelastic Robotic End-Effector for Grasping Soft Curved Organic Objects

Pneumatically-driven soft robotic grippers can elastically deform to grasp delicate, curved organic objects with minimal surface damage. However, common actuators have complex geometries and are fabricated with ultra-soft hyperelastic elastomers not originally intended for scientific applications. The complexity of the actuator geometry and extreme nonlinearity of their material’s stress-strain behaviour make it difficult to predict the actuator’s deformation prior to experimentation. In this work, a compact soft pneumatic gripper made with polydimethylsiloxane (PDMS) is developed for grasping delicate organic objects, analyzed through computational modelling and experimentally validated. COMSOL Multiphysics is used to simulate the impact of geometrical parameters on the actuator’s behaviour, allowing for the refinement of the proposed geometry prior to fabrication. Optimal parameters are selected for fabrication, with experimental tests matching simulations within ± 1 mm. Gripper performance is evaluated for three actuator wall thicknesses in terms of contact area with target, contact force, and maximum payload before slippage. The comparative assessment between simulations and experiments demonstrate that the proposed soft actuators can be used in robotic grippers tailored for grasping delicate objects without damaging their surface. Furthermore, analysis of the actuators provides additional insight on how to design simple but effective soft systems

Pneumatic Hyperelastic Actuators for Grasping Curved Organic Objects

Soft robotic grippers often incorporate pneumatically-driven actuators that can elastically deform to grasp delicate, curved organic objects with minimal surface damage. The complexity of the actuator geometry and the nonlinear stress–strain behavior of the stretchable material during inflation make it difficult to predict actuator performance prior to prototype fabrication. In this work, a scalable modular elastic air-driven actuator made from polydimethylsiloxane (PDMS) is developed for a mechanically compliant robotic gripper that grasps individual horticultural plants and fungi during automated harvesting. The key geometric design parameters include the expandable surface area and wall thickness of the deformable structure used to make contact with the target object. The impact of these parameters on actuator displacement is initially explored through simulation using the Mooney–Rivlin model of hyperelastic materials. In addition, several actuator prototypes with varying expandable wall thicknesses are fabricated using a multistep soft-lithography molding process and are inserted in a closed ring assembly for experimental testing. The gripper performance is evaluated in terms of contact force, contact area with the target, and maximum payload before slippage. The viability of the gripper with PDMS actuators for horticultural harvesting applications is illustrated by gently grasping a variety of mushroom caps

Model uncertainty in ancestral area reconstruction: a parsimonious solution?

Increasingly complex likelihood-based methods are being developed to infer biogeographic history. The results of these methods are highly dependent on the underlying model which should be appropriate for the scenario under investigation. Our example concerns the dispersal among the southern continents of the grass subfamily Danthonioideae (Poaceae). We infer ancestral areas and dispersals using likelihood-based Bayesian methods and show the results to be indecisive (reversible-jump Markov chain Monte Carlo; RJ-MCMC) or contradictory (continuous-time Markov chain with Bayesian stochastic search variable selection; BSSVS) compared to those obtained under Fitch parsimony (FP), in which the number of dispersals is minimised. The RJ-MCMC and BSSVS results differed because of the differing (and not equally appropriate) treatments of model uncertainty under these methods. Such uncertainty may be unavoidable when attempting to infer a complex likelihood model with limited data, but we show with simulated data that it is not necessarily a meaningful reflection of the credibility of a result. At higher overall rates of dispersal FP does become increasingly inaccurate. However, at and below the rate observed in Danthonioideae multiple dispersals along branches are not observed and the correct root state can be inferred reliably. Under these conditions parsimony is a more appropriate model

ESC Guidelines for the diagnosis and treatment of acute and chronic heart failure 2008: The Task Force for the Diagnosis and Treatment of Acute and Chronic Heart Failure 2008 of the European Society of Cardiology. Developed in collaboration with the Heart Failure Association of the ESC (HFA) and endorsed by the European Society of Intensive Care Medicine (ESICM)

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