Design, modeling, and control of underwater stiffness-enhanced flexible manipulator

A stiffness-enhanced flexible manipulator merges the high stiffness and load-bearing capacity of a rigid manipulator with the flexibility and safety of a soft manipulator, making it highly adaptable in unstructured environments. This design allows for various tasks, including inspections and grasping. However, existing stiffness-enhanced flexible manipulators often have complex structures, and factors like self-weight and external forces are commonly ignored during modelling, making precise motion control challenging. To address this, this paper introduces a stiffness-enhanced flexible manipulator designed for shallow water environments. It combines a tension spring skeleton with flexible pneumatic bellows, offering improved stability, rigidity, and large deformation capabilities. A stiffness model for the manipulator is developed, and based on this, a motion control strategy with deformation feedforward compensation is proposed. The proposed method reduces the complexity of controlling the stiffness-enhanced flexible manipulator while enhancing controllability. Experimental results demonstrate that the proposed methods deliver reliable control performance and effective operational capabilities.