Flexible Actuators for Soft Robotics

169

Soft robotics has experienced an exponential growth in publications in the last two decades. [1] Unlike rigid conventional manipulators, [2,3] soft robots based on hydrogels, [4,5] electroactive polymers, [6,7] and elastomers [7-9] are physically resilient and can adapt to delicate objects and environments due to their conformal deformation. [10,11] They also show increased safety and dexterity can be lightweight and used within constrained environments with restricted access. [12,13] Many soft robots have a biologically inspired design coming from snakes, [14-17] worms, [18-20] fishes, [21-24] manta rays, [25,26] and tentacles. [27-29] The scope of applications includes minimally invasive surgery, [30,31] rehabilitation, [32,33] elderly assistance, [34] safe human-robot interaction, [35,36] and handling of fragile materials. [37,38] Important features of soft robotics design, fabrication, modeling, and control are covered in the soft robotics toolkit. [39,40] The building blocks of soft robots are the soft actuators. The most popular category of soft actuator is the soft fluidic actuator (SFA), where actuation is achieved using hydraulics or pneumatics. [8,41] These actuators are usually fabricated with silicone rubbers following a 3D molding process, [42] although directly 3D printing the soft actuators is also possible. [43,44] Silicone rubber is a highly flexible/extensible elastomer with high-temperature resistance, lowtemperature flexibility, and good biocompatibility. [45] Elastomers can withstand very large strains over 500% with no permanent deformation or fracture. [46] For relatively small strains, simple linear stress-strain relationships can be used, and two of the following parameters can be used to describe the elastic properties: bulk compressibility, shear modulus, tensile modulus (Young's modulus of elasticity), or Poisson's ratio. [45] For large deformations, nonlinear solid mechanic models using hyperelasticity should be considered. [8,32,47-50] Due to the strong nonlinearities in SFAs and their complex geometries, analytical modeling is challenging. [51] A brief review of the analytical methods for modeling of soft robotic structures is provided in the following. 1.1. Analytical Modeling of Soft Actuators The majority of soft/continuum robots with bending motion can be approximated as a series of mutually tangent constant curvature sections, i.e., piecewise constant curvature. [52] This is a result of the fact that the internal potential energy is uniformly distributed along each section for pressure-driven robots. [53] This approach has also been validated using Hamilton's principle by Gravagne et al. [54] As discussed by Webster and Jones, [52] the kinematics of continuum robots can be separated into robotspecific and robot-independent components in this approach. The robot specific mapping transforms the input pressures P or actuator space q to the configuration space κ, ϕ, l, and the robot-independent mapping goes from the configuration space to the task space x. The actuator space contai...

Section: Introductionmentioning

confidence: 99%

Finite Element Modeling of Soft Fluidic Actuators: Overview and Recent Developments

Xavier

Fleming

Yong

2020

169

“…Moreover, a wide range of electrode materials have been studied including metallic films/diaphragms, carbon-based materials (carbon powders, graphene, CNTs), nanoparticles, liquid metals, ion/hydro gels, and different composite materials. [263,[266][267][268][269][270][271] Carbon-based materials are most commonly used due to their conductivity even under high applied levels of stress/strain, whereas CNTs are the most common among all carbon-based materials. For instance, Zhao et al designed rolled DEAs which utilizes CNTs-based electrodes developed using a stamping process from polytetrafluoroethylene (PTFE) filter.…”

Section: Electrodes For Soft Actuatorsmentioning

confidence: 99%

Soft Actuators for Soft Robotic Applications: A Review

El‐Atab

Mishra

Al‐Modaf

et al. 2020

325

224

The compliant, continuum, and configurable robotics field in general has gained growing interest in the past years especially with the exciting advances in artificial intelligence technology, [1] which could enable various valuable applications ranging from manufacturing to safety and healthcare. [2,3] Soft robots are of notable interest because, unlike their rigid counterpart, they can easily deform while being mechanically resilient, [4,5] adapt to the outer environment without harm to humans, [6] and finally, enable low-cost manufacturing. [7] For robots to interact with the outer environment and complete tasks, a set of sensors and actuators need to be integrated into the system. Soft robots, in specific, present additional challenges because their sensing and actuation devices are generally highly integrated within the body of the robot and its whole functionality. These challenges become even more critical when the soft robot is scaled down to sub-centimeter size as the sensing, power, and data analysis units are moved off-board. As a result, miniaturized soft actuators that respond to various stimuli and show large deformations in addition to mechanical resilience are crucial. These would be particularly promising for application in artificial muscles, microrobots, and micro-manipulators. [8-10] Active and soft materials are promising for this task as they can be actuated through various external stimuli, such as photons, thermal, magnetic and/or electric field. Such materials range from particles, to polymers (either electroactive or shape memory), papers, fluids, shape memory alloys (SMAs), liquid metals, hydrogels, 2D materials, or a combination of these. [6-25] Nevertheless, some materials can be more suitable for a specific set of applications than others; for instance, materials stimulated by the near-infrared (NIR) spectrum are promising for biomedical applications, whereas sunlight-stimulated materials are suitable for nature-inspired soft robots used in outside environments. Various useful metrics are generally used to assess the performance of the actuators; these include the generated stress and strain, Young's modulus or measured stiffness, in addition to their power, work, energy, and force density. In this Review article, however, we focus on the application of the soft actuators in soft robotics where the reported metrics include mode and speed of actuation (or locomotion), power, voltage, current (of the driving signal), lifting force, and weight among others. In this Review article, different active materials that have been developed and used in soft actuators for soft robotics are discussed and grouped by the stimulus that generates the actuation response as shown in Figure 1. The physics of operation, resulting deformations, mechanical resilience, and their pros and cons are presented with a focus on the applications of the different soft

“…There have been significant advances in the design, actuation, and control methods of this technology, opening up new avenues for wearable systems to provide improved task assistance and feedback for various applications. [1][2][3][4][5] The capabilities of these soft, elastomeric material-based robots allow further development of intimate human-robot interaction through haptic feedback. [2,6] Tactile feedback plays an important role in human-robot interaction.…”

Section: Introductionmentioning

confidence: 99%

Soft Touch using Soft Pneumatic Actuator–Skin as a Wearable Haptic Feedback Device

Sonar

Huang

Paik

2021

Understanding the external environment depends heavily on vision, audition, and touch. Like vision and audition, the human sense of touch is complex. Tactile perception is composed of multiple fundamental and physical experiences felt as changes in stiffness, texture, shape, size, temperature, and weight by the skin. While researchers and industries have made continuous efforts to abstract and recreate these haptic experiences, haptic devices are still limited in invoking intricate and rich sensations. Herein, the design, model, and experimental validation of a wearable skin-like interface, able to recreate the roughness, shape, and size of a perceived object is presented; a platform for an interactive "physical" experience. The cogency of immersion through tactile feedback on moldable clay by the user response from the active haptic feedback, is examined. For the experimental test, a soft pneumatic actuator (SPA)-skin interface (90 Hz bandwidth) with a complex actuation pattern is prototyped. The SPA-skin's performance using three sets of simulated textures (<300 μm) and for reconstructing simulated contours (of a rectangle, circle, or trapezoid) in the virtual reality (VR) platform is investigated. The experimental results demonstrated for the first time how artificially created tactile feedback can indeed simulate physical interaction, with 83% average accuracy for contour reconstruction.