A symmetric cable-pulley based mechanism for gravity compensation of robotic manipulators: Static and dynamic analysis

In this paper, a novel design for gravity compensation of manipulators has been introduced and its effect on the static and dynamic performance has been studied. The gravity compensation mechanism (GCM) of this study deploys a symmetrical configuration for the pulleys and cable to reduce the tension in the cable without requiring additional space for longer springs and their displacements. The reduction of cable tension significantly increases the durability of the proposed GCM, which tackles one of the most critical issues of the cable-pulley based gravity compensating systems. The configuration of the proposed GCM also distributes equal internal forces and moments over the joints of the manipulator. As a key part of the design, the dynamic performance of the manipulator is evaluated before and after it is equipped with the GCM. The dynamic manipulability ellipse is used to measure the variations in dynamic performance. Implementation on a real multi-degree-offreedom (DOF) manipulator showed the effectiveness of the proposed GCM in gravity compensation and also its simplicity of extension and larger achievable workspace comparing to the previous works.