Computational Fluid Dynamics Study of a Soft Actuator for Use in Wearable Mechatronic Devices

Mechatronic rehabilitative devices have been proven to provide cost effective solutions to long term physical therapy for patients with musculoskeletal disorders. However, current actuator technologies limit the minimization of the overall size and weight of these devices preventing innovation into unobtrusive wearable form factors that are also effective and comfortable. This study is focused on a recently discovered smart actuator made from flexible nylon thread, which has exhibited a great potential for use in wearable mechatronic devices. This is known as the twisted coiled actuator (TCA) due to the hyper twisting and induced coiling involved in its fabrication process. One of the limiting factors of the TCA, is the thermal activation mechanism, which results in a slow cooling phase and a low working bandwidth. This paper is focused on optimizing an active cooling design using numerical analysis. To do this, a simple pipe geometry was designed and tested using fluid dynamics software. Three off-the-shelf fluidic pumps were simulated using varying tube diameters to find a sufficient cooling rate, a minimum fluid volume, and to select a proper pump for future testing. The results indicate that a global maximum cooling rate exists for each specific pump at a unique tube diameter. Additionally, the speed of cooling was under 500 ms concluding that the pumps tested can sufficiently provide the cooling rates required to assist motion in wearable devices. Furthermore, the process developed here provides quantitative support for the optimal selection of initial design parameters and can be translated to designs using different form factors and fluid properties.