Modeling and control of an antagonistically actuated tendon driven anthropomorphic hand

Kurzfassung

Abstract: One of the major limitations of object manipulation with a robotic hand is the fragility of the hardware. This is one of the motivations for developing the new anthropomorphic and extremely robust Hand Arm System at the robotics and mecatronics center of DLR. The system is unique in terms of complexity, with 52 motors and more than 200 sensors, and also in terms of dynamics. Indeed, the system is mechanically compliant, thus offers the possibility to store and release energy, thereby providing two essential functions: The impacts are filtered and the dynamics are enhanced. This thesis focuses on the hand. It has 19 degrees of freedom, each being actuated by two flexible antagonistic tendons. Because the stiffnes of the tendons is not linear, it is possible to adjust the mechanical stiffness of the joints, similar to the co-contraction of human muscles, in order to adapt to a task. However, the stiffness adjustability rises new challenges in modeling and control. The state of the art usually focuses on the problems of tendon-driven systems or flexible joint robots but seldomly both simultaneously. In the first part, the modeling of the hand and the wrist is conducted. Several problems specific to tendon-driven systems are presented, such as the coupling matrices and the joint position estimation based on the tendon displacement. The second part focuses on the control of a single joint actuated by two flexible tendons. The distribution of the tendon forces and the correction of the effective stiffness are reported. Linear and nonlinear approaches are used and multiple experiments are realised to compare them. The major result is that the backstepping, a nonlinear control method,