1,720,996 research outputs found
Fiber pumps for wearable fluidic systems
No full textIncorporating pressurized fluidic circuits into textiles can enable muscular support, thermoregulation, and haptic feedback in a convenient wearable form factor. However, conventional rigid pumps, with their associated noise and vibration, are unsuitable for most wearables. We report fluidic pumps in the form of stretchable fibers. This allows pressure sources to be integrated directly into textiles, enabling untethered wearable fluidics. Our pumps consist of continuous helical electrodes embedded within the walls of thin elastomer tubing and generate pressure silently through charge-injection electrohydrodynamics. Each meter of fiber generates 100 kilopascals of pressure, and flow rates approaching 55 milliliters per minute are possible, which is equivalent to a power density of 15 watts per kilogram. The benefits in design freedom are considerable, which we illustrate with demonstrations of wearable haptics, mechanically active fabrics, and thermoregulatory textiles
Peeling in electroadhesion soft grippers
Full text linkElectroadhesion endows robots with super-human abilities: mechanical geckoes that climb vertical walls and soft grippers that grasp the most delicate objects. Based on electrostatics, the adhesion forces are turned on and off by an electrical signal, promising extremely fast operation, from silent fully solid-state devices. Practical applications of electroadhesion have however been limited to date by two main challenges: (1) the adhesion forces can vary over 1000x by simply changing the angle between the electroadhesive tape and the object, (2) release is often slow due to residual adhesion when voltage is removed.This paper describes a solution to both these issues by understanding and leveraging peeling in electroadhesion. We present simple models for peeling of electroadhesive tapes, predicting a change in peeling force from < 1 mN to over 1 N by changing the angle between the tape and the object from 90 degrees to 0 degrees. The models are in excellent agreement with our peeling experiments with 30 mm long, 20 mm wide, 300 tm thick electroadhesion tapes made of silicone rubber with carbon electrodes.We demonstrate an electroadhesion soft gripper that uses motorized fingers to control the peeling angle, as a practical application of our peeling models. By moving the fingers to ensure a low peeling angle (0 degrees) when grasping, the same gripper can successfully pick up from a 10 g cherry tomato (2.5 cm wide) to a 600 g Mango (9 cm wide). By then setting a high peeling angle (> 30 degrees), the gripper reliably and rapidly (< 300 ms) releases those objects, despite residual adhesion.Electroadhesion soft grippers have many advantages, including grasping without squeezing, silent operation, low power consumption (< 1 W) and low weight (1 g per soft finger). Understanding and modelling contact mechanics in electroadhesion devices was an essential missing step for practical applications of electroadhesion in robots and grippers. This paper sheds light on how peeling influences electroadhesion and provides practical tools to design and operate electroadhesion systems
Stiffening in soft robotics: A review of the state of the art
No full textThe need for building robots with soft materials emerged recently from considerations of the limitations of service robots in negotiating natural environments, from observation of the role of compliance in animals and plants [1], and even from the role attributed to the physical body in movement control and intelligence, in the so-called embodied intelligence or morphological computation paradigm [2]-[4]. The wide spread of soft robotics relies on numerous investigations of diverse materials and technologies for actuation and sensing, and on research of control techniques, all of which can serve the purpose of building robots with high deformability and compliance. But the core challenge of soft robotics research is, in fact, the variability and controllability of such deformability and compliance
Modelling the nonlinear response of fibre-reinforced bending fluidic actuators
No full textSoft actuators are receiving increasing attention from the engineering community, not only in research but even for industrial applications. Among soft actuators, fibre-reinforced bending fluidic actuators (BFAs) became very popular thanks to features such as robustness and easy design and fabrication. However, an accurate modelling of these smart structures, taking into account all the nonlinearities involved, is a challenging task. In this effort, we propose an analytical mechanical model to capture the quasi-static response of fibre-reinforced BFAs. The model is fully 3D and for the first time includes the effect of the pressure on the lateral surface of the chamber as well as the non-constant torque produced by the pressure at the tip. The presented model can be used for design and control, while providing information about the mechanics of these complex actuators
Comparison of Optimization Algorithms for the Indirect Encoding of a Neural Controller for a Soft Robotic Arm
No full textAbstract
With their dexterity, robustness and safe interaction with humans, soft robots bode to revolution the field of robotics. However, featuring structures undergoing nonlinear deformations and under-actuated mechanisms, traditional control techniques are usually unsuccessful. Artificial neural networks have instead shown to be a suitable solution to control soft robots in several cases. Among the different classes of algorithms to train neuro-controllers, one that recently experienced a wide spread consists of optimization with genetic algorithms (GAl through indirect encoding. Main advantages are: the ability to produce networks with functional regularities that exploit the geometry of the domain; the decoupling of problem complexity from its resolution. The predominant use of GA has several reasons, ranging from bio-inspiration to some undeniable technical advantages. However, two main issues suggest the need to explore different and possibly more efficient algorithms to train neuro-controllers for soft robots: the high computationaI cost of mathematical models to simulate soft robots and evidences of unsuccessful global convergence of GA if not carefully tuned. In this study, we compared the performance of GA with those of other optimization algorithms in training an artificial neural network to control a soft robotic arm inspired by the octopus, simulated through a non-linear dynamic mathematical mode
Delicate yet strong: characterizing the electro-adhesion lifting force with a soft gripper
No full textCompliant grippers are one of the most promising soft robotic devices for industrial tasks. Soft grippers dramatically simplify grasping control because the gripper automatically conforms to the object's shape. A common limitation of soft structures is that they can only generate low forces, limiting grasping ability. One approach to increase the holding force is to increase the shear force by using controlled adhesion: the lifting force is thus increased, while the clamping force can be kept low, important for manipulating delicate objects. In this work, we explore the lifting force generated with a soft gripper using electroadhesion. We show that this force is highly dependent on the holding posture, which depends on both the shape of the gripper and the shape of the object. For a 1 cm(2) electroadhesion area, we measure maximum lifting forces up to 16 N, strongly dependent on object's shape. Reliability is also an essential feature to move soft robots into industrial scenarios. The gripper survived over 100 cycles at high load with no damage, showing its high robustness. Combining electroadhesion and dielectric elastomers actuators, our soft gripper generates grasping forces so high that we reach the structural limits of the rigid plastic frame, yet it is delicate enough to gently pick up and release a cherry tomato.LMT
Actuating droplets with electrowetting: Force and dynamics
Full text linkAbstract Electrowetting on dielectric (EWOD) allows rapid movement of liquid droplets on a smooth surface, with applications ranging from lab‐on‐chip devices to micro‐actuators. The in‐plane force on a droplet is a key indicator of EWOD performance. This force has been extensively modeled but few direct experimental measurements are reported. We study the EWOD force on a droplet using two setups that allow, for the first time, the simultaneous measurement of force and contact angle, while imaging the droplet shape at 6000 frames/s. For several liquids and surfaces, we observe that the force saturates at a voltage of approximately 150 V. Application of voltages of up 2 kV, that is, 10 times higher than is typical, does not significantly increase forces beyond the saturation point. However, we observe that the transient dynamics, localized at the front contact line, do not show saturation with voltage. At the higher voltages, the initial front contact line speed continues to increase, the front contact angle temporarily becomes near zero, creating a thin liquid film, and capillary waves form at the liquid–air interface. When the localized EWOD forces at the contact line exceed the capillary forces, projectile droplets form. Increasing surface tension allows for higher droplet forces, which we demonstrate with mercury
Soft Robotic Grippers
Full text linkAdvances in soft robotics, materials science, and stretchable electronics have enabled rapid progress in soft grippers. Here, a critical overview of soft robotic grippers is presented, covering different material sets, physical principles, and device architectures. Soft gripping can be categorized into three technologies, enabling grasping by: a) actuation, b) controlled stiffness, and c) controlled adhesion. A comprehensive review of each type is presented. Compared to rigid grippers, end-effectors fabricated from flexible and soft components can often grasp or manipulate a larger variety of objects. Such grippers are an example of morphological computation, where control complexity is greatly reduced by material softness and mechanical compliance. Advanced materials and soft components, in particular silicone elastomers, shape memory materials, and active polymers and gels, are increasingly investigated for the design of lighter, simpler, and more universal grippers, using the inherent functionality of the materials. Embedding stretchable distributed sensors in or on soft grippers greatly enhances the ways in which the grippers interact with objects. Challenges for soft grippers include miniaturization, robustness, speed, integration of sensing, and control. Improved materials, processing methods, and sensing play an important role in future research
Conduction Electrohydrodynamics with Mobile Electrodes: A Novel Actuation System for Untethered Robots
No full textElectrohydrodynamics (EHD) refers to the direct conversion of electrical energy into mechanical energy of a fluid. Through the use of mobile electrodes, this principle is exploited in a novel fashion for designing and testing a millimeter-scale untethered robot, which is powered harvesting the energy from an external electric field. The robot is designed as an inverted sail-boat, with the thrust generated on the sail submerged in the liquid. The diffusion constant of the robot is experimentally computed, proving that its movement is not driven by thermal fluctuations, and then its kinematic and dynamic responses are characterized for different applied voltages. The results show the feasibility of using EHD with mobile electrodes for powering untethered robots and provide new evidences for the further development of this actuation system for both mobile robots and compliant actuators in soft robotics
Evolving Optimal Swimming in Different Fluids: A Study Inspired by batoid Fishes
No full textFor their efficient and elegant locomotion, batoid fishes (e.g. the manta ray) have been widely studied in biology, and also taken as a source of inspiration by engineers and roboticists willing to replicate their propulsion mechanism in order to build efficient swimming machines. In this work, a new model of an under-actuated compliant wing is proposed, exhibiting both the oscillatory and undulatory behaviors underlying batoid propulsion mechanism. The proposed model allowed an investigation of the co-evolution of morphology and control, exploiting dynamics emergent from the interaction between the environment and the mechanical properties of the soft materials. Having condensed such aspects in a mathematical model, we studied the adaptability of a batoid-like morphology to different environments. As for biology, our main contribution is an exploration of the parameters linking swimming mechanics, morphology and environment. This can contribute to a deeper understanding of the factors that led various species of the batoid group to phylogenetically adapt to different environments. From a robotics standpoint, this work offers an additional example remarking the importance of morphological computation and embodied intelligence. A direct application can be an under-water soft robot capable of adapting morphology and control to reach the maximum swimming efficiency
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