Design, modeling, and characterization of a low-pressure dual-mode pneumatic soft actuator-gripper

Abstract

Soft pneumatic grippers show immense promise in grasping fragile, irregular, and unknown objects; however, simultaneously achieving high payload capacity and grasping flexibility under low actuation pressure remains a critical challenge. In this paper, we propose a low-pressure dual-mode pneumatic soft gripper, which is constructed by rigidly coupling a cylindrical enveloping module and a three-finger soft pneumatic network (PneuNet) bending module. The cylindrical module achieves an active enveloping grasp for heavy loads through inward radial expansion, whereas the three-finger module flexibly accommodates objects of various shapes and sizes via bending deformation. To characterize the actuation behavior of the cylindrical module, its deforming architecture is modeled as a thin-walled curved chamber, and the deformation process is conceptualized into two sequential stages: inversion and bulging. By combining analytical formulations and finite element analysis (FEA), a two-stage inflation mechanics model is established, augmented by a semi-empirical correction to account for non-ideal boundary constraints and material softening effects. Furthermore, FEA is utilized to predict the bending deformation of the PneuNet fingers, exhibiting excellent agreement with experimental measurements. Experimental results demonstrate that under a low actuation pressure of merely 20 kPa, the dual-mode gripper can achieve an exceptional vertical payload of up to 6.5 kg when grasping a 36-mm-diameter sphere. Moreover, the two grasping modules can synergistically interact to manipulate and reorient a single complex target, or independently grasp two distinct objects simultaneously. Ultimately, the proposed low-pressure, dual-mode soft gripper demonstrates substantial potential for versatile, safe, and highly efficient robotic manipulation.