Universal soft pneumatic robotic gripper with variable effective length

In this study, we built a four-fingered soft robotic gripper with tunable effective finger lengths. This robotic model is purely made of soft materials and allows two working modes that require very simple control: 1) deflate the soft fingers for bending to one direction therefore to open the gripper 'claw' and 2) inflate the fingers with compressed air for bending to the reverse direction, therefore to grip objects reversibly. Systematic tests of the gripping performance of the soft robotic model were conducted for 5 effective finger lengths ranging from 30 mm to 100 mm. Under each effective length, we measured the pull-off force of 8 sphere-shaped objects with diameters from 20 to 90mm, and five typical geometric shaped objects including sphere, cubic and cylinder etc. We also measured the pull-off force of gripping objects with different stiffness. Notably, we found that each object with different size prefer a 'sweet' effective finger length for generating maximum pull-off force. We show that tunable effective finger length for the soft robot can significantly improve the performance when gripping multiple objects. Current soft robotic prototype exhibits a simple-control, low-cost approach of grasping objects with different size, weight, and shape as well as material stiffness, and may open up new avenues for future industrial gripping.