- Award ID(s):
- NSF-PAR ID:
- Date Published:
- Journal Name:
- Wearable Technologies
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Upper limb mobility impairments affect individuals at all life stages. Exoskeletons can assist in rehabilitation as well as performing Activities of Daily Living (ADL). Most commercial assistive devices still rely on rigid robotics with constrained biomechanical degrees of freedom that may even increase user exertion. Therefore, this paper discusses the iterative design and development of a novel hybrid pneumatic actuation and Shape Memory Alloy (SMA) based wearable soft exoskeleton to assist in shoulder abduction and horizontal flexion/extension movements, with integrated soft strain sensing to track shoulder joint motion. The garment development was done in two stages which involved creating (1) SMA actuators integrated with soft sensing, and (2) integrating pneumatic actuation. The final soft exoskeleton design was developed based on the insights gained from two prior prototypes in terms of wearability, usability, comfort, and functional specifications (i.e., placement and number) of the sensors and actuators. The final exoskeleton is a modular, multilayer garment which uses a hybrid and customizable actuation strategy (SMA and inflatable pneumatic bladder).more » « less
Soft intelligent structures that are programmed to reshape and reconfigure under magnetic field can find applications such as in soft robotics and biomedical devices. Here, a new class of smart elastomeric architectures that undergo complex reconfiguration and shape change in applied magnetic fields, while floating on the surface of water, is reported. These magnetoactive soft actuators are fabricated by 3D printing with homocomposite silicone capillary ink. The ultrasoft actuators easily deform by the magnetic force exerted on carbonyl iron particles embedded in the silicone, as well as lateral capillary forces. The tensile and compressive moduli of the actuators are easily determined by their topological design through 3D printing. As a result, their responses can be engineered by the interplay of the intensity of the magnetic field gradient and the programmable moduli. 3D printing allows us to fabricate soft architectures with different actuation modes, such as isotropic/anisotropic contraction and multiple shape changes, as well as functional reconfiguration. Meshes that reconfigure in magnetic fields and respond to external stimuli by reshaping could serve as active tissue scaffolds for cell cultures and soft robots mimicking creatures that live on the surface of water.
In the world of soft-robotic medical devices, there is a growing need for low profile, non-rigid, and lower power actuators for soft exoskeletons and dynamic compression garments. Advanced compression garments with integrated shape memory materials have been developed recently to alleviate the functional and usability limitations associated with traditional compression garments. These advanced garments use contractile shape memory alloy (SMA) coil actuators to produce dynamic compression on the body through selective heating of the SMA material. While these garments can create spatially- and temporally-controllable compression, typical SMA materials (e.g., 70°C Flexinol) consume considerable power and require considerable thermal insulation to protect the wearer during the heating phase of the SMA actuation. Alternative SMA materials (e.g., NiTi #8 by Fort Wayne Metals, Inc.) transform below room temperature and do so using no applied electrical power and generate no waste heat. However, these materials are challenging to dynamically control and require active refrigeration to reset to material. In theory, low-temperature SMA actuators made from materials like NiTi #8 may maintain additional dynamic actuation capacity once equilibrated to room temperature (i.e., the material may not fully transform), as the SMA phase transformation temperature window expands when the material experiences applied stress. This paper investigates this possibility: we manufactured and tested low-temperature NiTi coil actuators to determine the magnitude of the additional force that can be generated via Joule heating once the material has equilibrated to room temperature. SMA spring actuators made from NiTi #8 consumed 84% less power and stabilized at significantly lower temperatures (26.0°C vs. 41.2°C) than SMA springs made from 70°C Flexinol, when actuated at identically fixed displacements (100% nominal strain) and when driven to produce equal forces (∼3.35N). This demonstration of low-power, minimal-heat exposure SMA actuation holds promise for many future wearable actuation applications, including dynamic compression garments.
Assistive wearable soft robotic systems have recently made a surge in the field of biomedical robotics, as soft materials allow safe and transparent interactions between the users and devices. A recent interest in the field of soft pneumatic actuators (SPAs) has been the introduction of a new class of actuators called fabric soft pneumatic actuators (FSPAs). These actuators exploit the unique capabilities of different woven and knit textiles, including zero initial stiffness, full collapsibility, high power-to-weight ratio, puncture resistant, and high stretchability. By using 2D manufacturing methods we are able to create actuators that can extend, contract, twist, bend, and perform a combination of these motions in 3D space. This paper presents a comprehensive simulation and design tool for various types of FSPAs using finite element method (FEM) models. The FEM models are developed and experimentally validated, in order to capture the complex non-linear behavior of individual actuators optimized for free displacement and blocked force, applicable for wearable assistive tasks.
Soft actuators are typically designed to be inherently stress‐free and stable. Relaxing such a design constraint allows exploration of harnessing mechanical prestress and elastic instability to achieve potential high‐performance soft robots. Here, the strategy of prestrain relaxation is leveraged to design pre‐curved soft actuators in 2D and 3D with tunable monostability and bistability that can be implemented for multifunctional soft robotics. By bonding stress‐free active layer with embedded pneumatic channels to a uniaxially or biaxially pre‐stretched elastomeric strip or disk, pre‐curved 2D beam‐like bending actuators and 3D doming actuators are generated after prestrain release, respectively. Such pre‐curved soft actuators exhibit tunable monostable and bistable behavior under actuation by simply manipulating the prestrain and the biased bilayer thickness ratio. Their implications in multifunctional soft robotics are demonstrated in achieving high performance in manipulation and locomotion, including energy‐efficient soft gripper to holding objects through prestress, fast‐speed larva‐like jumping soft crawler with average locomotion speed of 0.65 body‐length s−1(51.4 mm s−1), and fast swimming bistable jellyfish‐like soft robot with an average speed of 53.3 mm s−1.