Design of reduced DOF parallel cable-based robots

In this paper, a new approach for the study and design of cable-based robots are presented. In the cable-based robots, a telescopic element is used to apply a force to the end-effector in order to maintain tension in all cables. As a result, cables tensions or internal forces in the manipulator appear in the design procedure which in turn makes the design procedure more complex than rigid-link robots. The main focus of this work is to introduce a geometrical approach for the study of this problem. In this approach, the capability of the end-effector for applying force and torque to external object is called force/torque capacity and is considered as the main target of the design process. The force and torque capacity of the manipulator is illustrated in a 3D space whose axes are force or torque components. It is shown that the force and torque capacity have a convex cone and parallelepiped shape, respectively. The design problem is then reduced to the sizing of these shapes according to the design requirements and manufacturing limitations. The approach is applied to the design of DeltaBot, a 3DOF cable-based parallel manipulator and the results are presented.