Design and analysis of cable-driven robotic arm with variable stiffness modular joint

This paper describes a robotic arm that allows for safe human-robot interaction. The robotic arm is essentially a cable-driven robotic arm with passive variable stiffness features; the cable-driven section of the arm maintains high stiffness and strength by utilizing a unique lightweight tension amplification system. The stiffness of the joints, which is intimately related to the performance of motion control, is quadratically amplified. We propose a 1-DOF and 3-DOF joint mechanism using the tension amplification method, which we combine to construct the robotic arm's elbow and wrist. Modular joints with variable stiffness are used in the 3-DOF shoulder. The passive compliant parts of the variable stiffness modular joint with progressive stiffness could make the actuator inherently soft at low contact torque levels and significantly stiffer at higher interaction torque levels, resolving common design trade-offs in linear series elastic actuators. To assess the workspace of the robotic arm, a kinematic model of the 7-DOF robotic arm is built. Finally, a cable-driven robotic arm prototype with variable stiffness joint module is developed.