Characterisation and Control of a Woven Biomimetic Actuator for Wearable Neurorehabilitative Devices

Abstract

Twisted coiled actuators (TCAs) are a type of soft actuator made from polymer fibres such as nylon sewing thread. As they provide motion in a compact, lightweight, and flexible package, they provide a solution to the actuation of wearable mechatronic devices for motion assistance. Their limitation is that they provide low total force, requiring them to actuate in parallel with multiple units. Previous literature has shown that the force and stroke production can be improved by incorporating them into fabric meshes. A fabric mesh could also improve the contraction efficiency, strain rate, and user comfort. Therefore, this study focused on measuring these performance metrics for a set of TCAs embedded into a woven fabric mesh. The experimental results show that the stroke of the actuators scaled linearly with the number of activated TCAs, achieving a maximum applied force of 11.28 N, a maximum stroke of 12.23%, and an efficiency of 1.8%. Additionally, two control methods were developed and evaluated, resulting in low overshoot and steady-state error. These results indicate that the designed actuators are viable for use in wearable mechatronic devices, since they can scale to meet different requirements, while being able to be accurately controlled with minimal additional components.

Improved performance in temperature and speed of TCP artificial muscles for soft wearables robots by length modification

“…For instance, if an offset of 1 m is used, the final frequency will be 0.6477 Hz. This frequency improvement could be useful for physical rehabilitation therapy and low frequency ADLs, as the minimum frequency for these activities is 0.5 Hz [26,35].…”

“…However, one of the main disadvantages of TCPs is the low frequencies at which they can work (<1 Hz). A strategy to increase the response time could be to briefly apply a pulsed signal with high power peaks [12,26]. However, the continuation of a high-power pulse will produce an overheating of the actuator, causing it to break or burn out [27].…”

Paediatric ankle rehabilitation system based on twisted and coiled polymer actuators

“…Despite the challenges, the technology appears highly adaptable, and many approaches can be taken to improve the performance. To enhance torque, incorporating additional fibres, as seen in previous TCP studies, is a viable direction [40,41]. In this study, that approach was followed to get the required torque, as a single fibre would be insufficient to generate the necessary force.…”

Design and Fabrication of Embroidered Textile Strain Sensors: An Alternative to Stitch-Based Strain Sensors

“…This is especially important in the context of musculoskeletal rehabilitation, as textile strain sensors have the advantage of being able to be seamlessly integrated directly onto every-day garments, thus allowing for a continuous tracking of joint motions outside of a lab-constrained environment. Furthermore, when used alongside soft actuators, such as twisted coiled actuators [ 1 ], it would be possible to create a soft wearable mechatronic device that could be used during robot-assistive therapies. This would be possible because textile strain sensors are capable of reducing the overall bulkiness of the wearable robotic device by removing the need for bigger enclosures and reducing the number of wires required for communication with the mechatronic device.…”