Dynamic modeling and tension analysis of a 7-DOF cable-driven robotic arm

From shoulder to wrist, a person´s arm has a total of seven degrees of freedom (DOFs), which is the minimum number of DOF for the robot that needs to avoid obstacles and internal singularity. Compared to the traditional 7-DOF robot, the 7-DOF cable-driven robotic arm (CDRA) similar to human muscles parallel drive mode is the hybrid structure of serial-parallel, which can be seen as a four-link serial mechanism including base, upper arm, forearm and end-effector connected by the shoulder, elbow and wrist joint in series. However, the introduction of cables also increases the difficulty in dynamic analysis. In this paper, iteration Newton-Euler method is adopted to calculate the force and moment of each connecting rod acted by previous connecting rod. According to moment equilibrium, the tension of each cable can be calculated. In order to keep the cable tensional and also furthest reduce energy consumption, tension distribution algorithm is used to compute the driving force of each cable. To show the correctness of the robot dynamic model and the effectiveness of tension distribution algorithm, several simulation results are illustrated. These lay a good theory foundation for further research on effective control and performance improvement of the CDRA.