Humanoid robot arms have attracted more and more attention since it is human-friendly with the same size and movement characteristics of a human arm. A new 7-DoF (Degrees of Freedom) humanoid robot arm is proposed in this paper. To achieve high torques while keeping down the weight, all the motors are coupled with tendons. 2 motor 2-DoF (2M2D) and 3 motor 3-DoF (3M3D) coupled tendon-driven joint modules are proposed as basic components for the robot arm. The 2M2D coupled tendon-driven joint module and the 3M3D coupled tendon driven joint module structures are analyzed and compared. The 7 DoFs of a human arm were divided into a 3-DoF shoulder joint module, a 2-DoF elbow joint module, and a 2-DoF wrist joint module. The developed robot arm weighed 2.2[kg], while being able to lift a 1.5[kg] load. A current consumption experiment was conducted to verify the torque transmission characteristics of the 2M2D and 3M3D joint modules. A path repeatability experiment and an experiment to imitate dexterous manipulations of a human arm with master-slave control were conducted to investigate the performance of the modularized humanoid robot arm. The experimental results showed that the joint modules realized motor reallocation via tendon coupling, and that the humanoid robot arm was capable of performing dexterous manipulations like a human arm.
