Sami Haddadin Alin Albu-Schäffer Gerd Hirzinger The role of the robot mass and velocity in physical human-robot interaction - Part I: Non-constrained blunt impacts. 1331-1338 2008 ICRA http://dx.doi.org/10.1109/ROBOT.2008.4543388 conf/icra/2008 db/conf/icra/icra2008.html#HaddadinAH08