Soft Actuators and Robotic Devices for Rehabilitation and Assistance

Soft actuators and robotic devices have been increasingly applied to the field of rehabilitation and assistance, where safe human and machine interaction is of particular importance. Compared with their widely used rigid counterparts, soft actuators and robotic devices can provide a range of significant advantages; these include safe interaction, a range of complex motions, ease of fabrication and resilience to a variety of environments. In recent decades, significant effort has been invested in the development of soft rehabilitation and assistive devices for improving a range of medical treatments and quality of life. This review provides an overview of the current state-of-the-art in soft actuators and robotic devices for rehabilitation and assistance, in particular systems that achieve actuation by pneumatic and hydraulic fluid-power, electrical motors, chemical reactions and soft active materials such as dielectric elastomers, shape memory alloys, magnetoactive elastomers, liquid crystal elastomers and piezoelectric materials. Current research on soft rehabilitation and assistive devices is in its infancy, and new device designs and control strategies for improved performance and safe human-machine interaction are identified as particularly untapped areas of research. Finally, insights into future research directions are outlined. Corresponding author(s) Email: [email protected], [email protected]

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Hydraulically amplified self-healing electrostatic actuators with muscle-like performance

Science ◽

10.1126/science.aao6139 ◽

2018 ◽

Vol 359 (6371) ◽

pp. 61-65 ◽

Cited By ~ 228

Author(s):

E. Acome ◽

S. K. Mitchell ◽

T. G. Morrissey ◽

M. B. Emmett ◽

C. Benjamin ◽

...

Keyword(s):

High Speed ◽

Dielectric Breakdown ◽

Artificial Muscle ◽

Robotic Arm ◽

Soft Robotics ◽

Self Healing ◽

Electrostatic Actuators ◽

Robotic Devices ◽

Soft Actuators ◽

Wide Potential

Existing soft actuators have persistent challenges that restrain the potential of soft robotics, highlighting a need for soft transducers that are powerful, high-speed, efficient, and robust. We describe a class of soft actuators, termed hydraulically amplified self-healing electrostatic (HASEL) actuators, which harness a mechanism that couples electrostatic and hydraulic forces to achieve a variety of actuation modes. We introduce prototypical designs of HASEL actuators and demonstrate their robust, muscle-like performance as well as their ability to repeatedly self-heal after dielectric breakdown—all using widely available materials and common fabrication techniques. A soft gripper handling delicate objects and a self-sensing artificial muscle powering a robotic arm illustrate the wide potential of HASEL actuators for next-generation soft robotic devices.

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Shape-Memory Actuation of Individual Micro-/Nanofibers

MRS Advances ◽

10.1557/adv.2020.276 ◽

2020 ◽

Vol 5 (46-47) ◽

pp. 2391-2399

Author(s):

Yue Liu ◽

Oliver E. C. Gould ◽

Karl Kratz ◽

Andreas Lendlein

Keyword(s):

Shape Memory ◽

Shape Change ◽

Shape Memory Polymer ◽

Fiber Contact ◽

Physical Functions ◽

Robotic Devices ◽

The Stability ◽

Soft Actuators ◽

Working Distance

AbstractAdvances in the fabrication and characterization of polymeric nanomaterials has greatly advanced the miniaturization of soft actuators, creating materials capable of replicating the functional physical behavior previously limited to the macroscale. Here, we demonstrate how a reversible shape-memory polymer actuation can be generated in a single micro/nano object, where the shape change during actuation of an individual fiber can be dictated by programming using an AFM-based method. Electrospinning was used to prepare poly(ε-caprolactone) micro-/nanofibers, which were fixed and crosslinked on a structured silicon wafer. The programming as well as the observation of recovery and reversible displacement of the fiber were performed by vertical three point bending, using an AFM testing platform introduced here. A plateau tip was utilized to improve the stability of the fiber contact and working distance, enabling larger deformations and greater rbSMPA performance. Values for the reversible elongation of εrev = 3.4 ± 0.1% and 10.5 ± 0.1% were obtained for a single micro (d = 1.0 ± 0.2 μm) and nanofiber (d = 300 ± 100 nm) in cyclic testing between the temperatures 10 and 60 °C. The reversible actuation of the nanofiber was successfully characterized for 10 cycles. The demonstration and characterization of individual shape-memory nano and microfiber actuators represents an important step in the creation of miniaturized robotic devices capable of performing complex physical functions at the length scale of cells and structural component of the extracellular matrix.

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Flexible shape memory alloy actuators for soft robotics: Modelling and control

International Journal of Advanced Robotic Systems ◽

10.1177/1729881419886747 ◽

2020 ◽

Vol 17 (1) ◽

pp. 172988141988674 ◽

Cited By ~ 4

Author(s):

Dorin-Sabin Copaci ◽

Dolores Blanco ◽

Alejandro Martin-Clemente ◽

Luis Moreno

Keyword(s):

Shape Memory Alloy ◽

Shape Memory ◽

Linear Models ◽

Complex Dynamics ◽

Weight Ratio ◽

Model Free ◽

Wearable Robots ◽

Robotic Devices ◽

Soft Actuators ◽

And Control

One of the limitations in the development of really soft robotic devices is the development of soft actuators. In recent years, our research group has developed a new flexible shape memory alloy actuator that provides more freedom of movements and a better integration in wearable robots, especially in soft wearable robots. Shape memory alloy wires present characteristics such as force/weight ratio, low weight, and noiseless actuation, which make them an ideal choice in these types of applications. However, the control strategy must take into account its complex dynamics due to thermal phase transformation. Different control approaches based on complex non-linear models and other model-free control methods have been tested on real systems. Some exoskeleton prototypes have been developed, which demonstrate the utility of this actuator and the advantages offered by these flexible actuators to improve the comfort and adaptability of exoskeletons.

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MXene artificial muscles based on ionically cross-linked Ti3C2Tx electrode for kinetic soft robotics

Science Robotics ◽

10.1126/scirobotics.aaw7797 ◽

2019 ◽

Vol 4 (33) ◽

pp. eaaw7797 ◽

Cited By ~ 28

Author(s):

Sima Umrao ◽

Rassoul Tabassian ◽

Jaehwan Kim ◽

Van Hiep Nguyen ◽

Qitao Zhou ◽

...

Keyword(s):

Structural Reliability ◽

Artificial Muscle ◽

Response Speed ◽

Input Voltage ◽

Artificial Muscles ◽

Wearable Electronics ◽

Bending Strain ◽

Kinetic Art ◽

Robotic Devices ◽

Soft Actuators

Existing ionic artificial muscles still require a technology breakthrough for much faster response speed, higher bending strain, and longer durability. Here, we report an MXene artificial muscle based on ionically cross-linked Ti3C2Tx with poly(3,4 ethylenedioxythiophene)-poly(styrenesulfonate), showing ultrafast rise time of within 1 s in DC responses, extremely large bending strain up to 1.37% in very low input voltage regime (0.1 to 1 V), long-term cyclic stability of 97% up to 18,000 cycles, markedly reduced phase delay, and very broad frequency bandwidth up to 20 Hz with good structural reliability without delamination under continuous electrical stimuli. These artificial muscles were successfully applied to make an origami-inspired narcissus flower robot as a wearable brooch and dancing butterflies and leaves on a tree as a kinetic art piece. These successful demonstrations elucidate the wide potential of MXene-based soft actuators for the next-generation soft robotic devices including wearable electronics and kinetic art pieces.

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Open Loop Position Control of Soft Hydraulic Actuators for Minimally Invasive Surgery

Applied Sciences ◽

10.3390/app11167391 ◽

2021 ◽

Vol 11 (16) ◽

pp. 7391

Author(s):

Mark Runciman ◽

James Avery ◽

Ara Darzi ◽

George Mylonas

Keyword(s):

Minimally Invasive Surgery ◽

Minimally Invasive ◽

Invasive Surgery ◽

Position Control ◽

High Volume ◽

Open Loop ◽

Low Profile ◽

Potential Applications ◽

Robotic Devices ◽

Soft Actuators

Minimally invasive surgery (MIS) presents many constraints on the design of robotic devices that can assist medical staff with a procedure. The limitations of conventional, rigid robotic devices have sparked interest in soft robotic devices for medical applications. However, problems still remain with the force exertion and positioning capabilities of soft robotic actuators, in conjunction with size restrictions necessary for MIS. In this article we present hydraulically actuated soft actuators that demonstrate highly repeatable open loop positioning and the ability to exert significant forces in the context of MIS. Open loop position control is achieved by changing the actuator volume, which causes contraction. In one degree of freedom (DOF) configurations, root mean square error (RMSE) values of 0.471 mm, 1.506 mm, and 0.350 mm were recorded for a single actuator against gravity, a single actuator with a pulley, and a horizontal antagonistic configuration, respectively. Hysteresis values of 0.711 mm, 0.958 mm, and 0.515 mm were reported in these experiments. In addition, different numbers of soft actuators were used in configurations two and three DOFs to demonstrate position control. When deactivated, the soft actuators are low-profile and flexible as they are constructed from thin films. As such, a robot with a deployable structure and three soft actuators was constructed. The robot is therefore able to reversibly transition from low to high volume and stiffness, which has potential applications in MIS. A user successfully controlled the deployable robot in a circle tracing task.

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