A low cost and lightweight wire driven robot arm by using elastic strings

This paper presents an elastic tendon driven robot arm intended for a low-cost, lightweight and highly compliant robot arm, with experimental results of a basic task execution. A winding device for elastic tendon and a low-cost two link arm with compliant joints were prototyped. By using these elements, a marionette style tendon driven robot arm system are composed. The developed winding device enables a simple force control through manipulating the take-up amount. By using a compliant rubber shaft, the joint has secondary parasitic degrees of freedom (DOF) in addition to the primary axis. As a result, the arm is highly adaptable to unknown environments. A simple feed forward force control low was developed for the task execution under holonomic constraints. Static equilibrium equations are derived divided into the direction of motion for task and constraint. By using these equations, take-up amount of each winding device is determined for the required applying force for task execution, while monitoring the constraint forces. By the benefit of the high elasticity of the tendons, the force controller was easily implemented without using force sensors.