Andreas Kugi Christian Ott Alin Albu-Schäffer Gerd Hirzinger On the Passivity-Based Impedance Controlof Flexible Joint Robots. 416-429 2008 24 IEEE Transactions on Robotics 2 http://dx.doi.org/10.1109/TRO.2008.915438 db/journals/trob/trob24.html#KugiOAH08