1. a Robotics Laboratory, Jacobs University, Campus Ring 1, 28759 Bremen, Germany
2. b Robotics Laboratory, Jacobs University, Campus Ring 1, 28759 Bremen, Germany;, Email: a.birk@jacobs-university.de
3. c Robotics Laboratory, Jacobs University, Campus Ring 1, 28759 Bremen, Germany
4. d Robotics Laboratory, Jacobs University, Campus Ring 1, 28759 Bremen, Germany