Unfolding Textile-Based Pneumatic Actuators for Wearable Applications

Abstract

Textile based pneumatic actuators have recently seen increased development for use in wearable applications thanks to their high strength to weight ratio and range of achievable actuation modalities. However, the design of these textile-based actuators is typically an iterative process due to the complexity of predicting the soft and compliant behavior of the textiles. In this work we investigate the actuation mechanics of a range of physical prototypes of unfolding textile-based actuators to understand and develop an intuition for how the geometric parameters of the actuator affect the moment it generates, enabling more deterministic designs in the future. Under benchtop conditions the actuators were characterized at a range of actuator angles and pressures (0-136 kPa), and three distinct performance regimes were observed, which we define as Shearing, Creasing, and Flattening. During Flattening, the effects of both the length and radius of the actuator dominate with maximum moments in excess of 80 Nm being generated, while during Creasing the radius dominates with generated moments scaling with the cube of the radius. Low stiffness spring like behavior is observed in the Shearing regime, which occurs as the actuator approaches its unfolded angle. A piecewise analytical model was also developed and compared to the experimental results within each regime. Finally, a prototype actuator was also integrated into a shoulder assisting wearable robot, and on-body characterization of this robot was performed on five healthy individuals to observe the behavior of the actuators in a wearable application. Results from this characterization highlight that these actuators can generate useful on-body moments (10.74 Nm at 90°a ctuator angle) but that there are significant reductions compared to bench-top performance, in particular when mostly folded and at higher pressures.

Restoring arm function with a soft robotic wearable for individuals with amyotrophic lateral sclerosis

“…Moreover, from past characterization studies, we expected the robotic wearable to provide minimal assistive torque beyond about 105° of arm elevation (fig. S2) ( 35 ). In future iterations, actuator size, geometry, or inflation pressure could be adjusted and customized to increase the level of assistance.…”

“…τ act was calculated by interpolating with current measured actuator pressure and arm angle from the inertial measurement units, a 3D surface (see fig. S4), output of the characterization of the bifurcated actuator using a previously designed testing rig ( 35 ) on n = 1 healthy individual. τ bio was calculated using the arm angle from the inertial measurement units, a simplified arm kinematic model, and literature-averaged anthropometric data ( 41 , 42 ).…”

Soft Wearable Robots: Development Status and Technical Challenges

“…The driving force was transmitted to the corresponding joint via a Bowden cable. O’Neill et al [ 14 ] developed an abduction-assisted system that placed a textile-based pneumatic actuator under the armpit. The main purpose was to study how structural parameters of the actuator affected its moment characteristics.…”

Contraction model of skeletal muscle capable of tetanus and incomplete tetanus for design and control of biohybrid actuators

“…Unlike conventional industrial actuators that use electromagnetic induction, electrostatic induction, and piezoelectric effect, soft actuators and soft robots have distinctive characteristics, such as flexibility and elasticity (Bao et al, 2018;Lipson, 2014). They are particularly expected to be used in medical devices (Runciman et al, 2019), welfare applications (Bodenhagen et al, 2019) and wearable devices (Bützer et al, 2021;O'Neill et al, 2021) owing to their human-friendly characteristics, safety, and complex deformation capabilities. Soft actuators based on silicon rubbers driven by pneumatics or hydraulics (Polygerinos et al, 2017;KurumayaShunichi et al, 2019) are the mainstream of this field, and few of them have been developed based on the bioinspired design (Kovač, 2014;Kim et al, 2013).…”