A Two-Chamber Soft Actuator with An Expansion Limit Line for Force Enhancement

Soft pneumatic actuators (SPAs) that can perform three-dimensional movements are being developed to perform more diverse tasks beyond simple bending. The conventional PneuNet actuators have expansion limit layers, which can obtain more tip force by limiting the expansion of the bottom. However, the presence of the expansion limit layer impedes other motions, such as rotation, when configured with multiple channels. In this study, we propose a two-chamber PneuNet actuator (TPA) to which the expansion limit line (ELLINE) is applied to obtain a force gain without a limitation on rotational motion due to the expansion limit layer. We perform a finite element analysis (FEA) on three designs that can rotate and bend using two-chamber to find the optimal design. The effects on twisting, bending, and tip force according to the width of the ELLINE on the selected design were then verified through an FEA. After measuring rotation and bending for the fabricated actuator with and without the ELLINE. In the case of the fabricated TPA with the ELLINE, the bending decreased by 19.8%. However, rotation increased by 22.8%, tip force increased by 1.53 times (with the ELLINE the force is 2.77 N in 70 kPa; without the ELLINE it is 1.8 N in 70 kPa), and grasping force increased by 5 times (with the ELLINE the force is 500 gf in 70 kPa, without the ELLINE it is 100 gf in 70 kPa). Furthermore, we fabricated a gripper using three actuators, capable of holding a weight of 505 g and objects of various shapes.