Modeling and control of an antagonistically actuated tendon driven anthropomorphic hand

Computer science in real time, Robotics, Automation

 

The thesis of Maxime Chalon focuses on the hand. It has 19 degrees of freedom, each being actuated by two flexible antagonistic tendons. Because the stiffness 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.

                                                         
Modeling and control

In this thesis, the modeling and the control of a complex and novel hand has been presented. The modeling followed an incremental approach and, starting with the motor modeling, provided a comprehensive and complete model of the system. Each phase of the modeling has been verified with simulations and experiments. The model established is the basis for the future work on the system. The specificities of antagonistically tendon driven systems have been presented in detailed with the help of the coupling matrices.

                                                         

The coupling matrices appeared to be a fundamental tool in understanding and manipulating the equations of such a system. Because of the system complexity, the work presented in this thesis had to be restricted and further research on some subsystems is still open. The control part aimed at identifying a suitable control approach for the finger. It has been demonstrated that advance control theory can be successfully applied. Because there is no need to use a complex control scheme if a simple one provides a correct answer, the first control approaches were linear ones. Then, according to the identified weaknesses, several controllers have been derived and implemented. Finally, the backstepping method provided a performant controller. The extension of the backstepping controller to an antagonistic structure was successful. Similar to the modeling part, each controller was derived, simulated and implemented. This provided valuable feedback about the quality (or possible errors) in the models.
Maxime Chalon
is proud to say that the complete Hand Arm System, used as a leading research platform for dexterous manipulation is currently using the models and the controllers created in this work.

                               
52 motors and 200 sensors

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 centre of Deutsches Zentrum fûr Luft- und Raumfahrt (DLR). The system is unique in terms of complexity, with 52 motors and more than 200 sensors, and also in terms of dynamics. It 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.

For changing the world

Maxime Chalon is a Research Engineer in robotics. He obtained a master from the Ecole des Mines d'Alès (EMA), France. In 2008, he started his research career at the Institute of Robotics and Mecatronics of the German Aerospace Center. In 2011, after gaining several years of experience in the field of robotic research he wanted to benefit from the robotic speciality course of Robotics Centre (MINES ParisTech - CAOR) and started a PhD in robotic control, at MINES ParisTech. He defended his thesis on October 2nd 2013. His research interests include robotic modeling and control, nonlinear control theory, grasping and space robotics.

Whether it is about colonizing distant planets or more simply performing hazardous or repetitive tasks, humanoid robots are the answer. They still lack intelligence but their physical performance is getting more impressive every year. There is little doubt that the tipping point for this technology is going to happen in this century. Maxime Chalon believe that his work in robotic research will contribute to change the world, just as the internet did in less than 50 years.