Trunk postural tracking of assistive soft pneumatic actuator belt

Fiber-reinforced Soft Pneumatic Actuators (SPAs) are found in mobile robots, assistive wearable devices, and rehabilitative technologies. Being intrinsically compliant and readily manufacturable they are attractive for use where safety and customizability are a priority. While different types of SPAs can be found to match the force performance requirements of a variety of applications, outlying system-level issues of robustness, controllability, and repeatability are not traditionally addressed at the actuator level. The SPA pack architecture presented here aims to satisfy these standards of reliability as well as extend the basic performance capabilities of SPAs by borrowing advantages leveraged ubiquitously in biology; namely the structured parallel arrangement of lower power actuators to form the basis of a larger, more powerful actuator module. An SPA pack module consisting of a number of smaller SPAs will be studied using an analytical model and a physical prototype. For a module consisting of four unit actuators an output force over 112 N is measured, while the model indicates the effect of parallel actuator grouping over a geometrically equivalent single SPA scales as an increasing function of the number of individual actuators in the group. A 23% increase in force production over a volumetrically equivalent single SPA is predicted and validated, while further gains appear possible up to 50%, reasonably bounded by practical limitations from material properties and manufacturability. These findings affirm the advantage of utilizing a fascicle structure for high-performance soft robotic applications over existing monolithic SPA designs. An active wearable belt will be presented to demonstrate the capability of SPA pack modules to affect human trunk posture while standing, while further work may enable active modulation of trunk angle during walking to provide corrective assistance or gait modifying perturbations.