Abstract: This article presented a four-fingered soft bionic robotic gripper with variable effective actuator lengths. By combining approaches of finite element analysis, quasi-static analytical modeling, and experimental measurements, the deformation of the single soft actuator as a function of air pressure input in free space was analyzed. To investigate the effect of the effective actuator length on the gripping per-formance of the gripper, we conducted systematical experiments to evaluate the pull-off force, the actuation speed, the precision and error tolerance of the soft gripper while grasping objects of various sizes and shapes. A combination of depressurization and pressurization in actuation as well as applying variable effective actuator length enhanced the gripper’s performance significantly, with no sensors. For example, with tunable effective actuator length, the gripper was able to grasp objects ranging from 2 mm – 170 mm robustly. Under the optimal length, the gripper could generate the maximum pull-off force for the corresponding object size; the precision and the error tol-erance of the gripper were also significantly improved compared to those of the gripper with full-length. Our soft robotic prototype ex-hibits a simple control and low-cost approach of gripping a wide range of objects and may have wide leverage for future industrial op-erations.

Key words: soft robotics, soft bionic gripper, pneumatic control, variable effective actuator length