Design of 9-DOF humanoid arms inspired by the human’s inner shoulder to enhance versatility and workspace

Many humanoid arms have six degrees-of-freedom (DOFs), similar to the human joint configuration. Moreover, humanoid arms with 7-DOF or 8-DOF have been designed to enhance the range of motion or structural versatility. Notably, these arms exhibit structural limitations and thus cannot effectively implement versatile and complex motions such as valve closing motion. To address this problem, this paper proposes a novel 9-DOF humanoid arm, named RoK-Arm9, inspired by the human inner shoulder. Two additional joints are introduced inside the shoulder to increase the versatility and workspace. To demonstrate the superiority of RoK-Arm9 over the existing robots for complex dual-arm manipulation, we analyzed the corresponding manipulability measure, bimanual task areas, and dual-arm manipulability measure. Finally, we confirmed that the actual RoK-Arm9 can conduct the same motion as the simulation. •Necessity of scapulohumeral rhythm for versatility and a wide workspace of humanoid.•Analysis of upper body structure based on anatomy and Design of the 9-DOF humanoid dual-arm.•Verification versatility through analysis of manipulability measure and dual-arm manipulability measure in a workspace.