02034nas a2200145   4500008004100000245005100041210005100092260001200143520161600155653001301771100001701784700002301801700001501824856004901839       2017                        eng d00aChoosing Poses for Force and Stiffness Control0 aChoosing Poses for Force and Stiffness Control  c06/20173 a<p class="rtejustify">In humanoids and other redundant robots interacting with the environment, one can often choose between different configurations and control parameters to achieve a given task. A classic tool to describe specifications of the desired force/displacement behavior in such problems is the stiffness ellipsoid, whose geometry is affected by the choice of parameters in both joint control and redundancy resolution—namely, gains and angles. As is well known, impedance control techniques can regulate gains to realize any desired shape of the Cartesian stiffness ellipsoid at the end-effector, so that robot geometry selection could appear secondary. However, humans do not use this possibility: To control the stiffness of our arms, we predominantly use arm configurations. Why is that, and does it makes sense to do the same in robots? To understand this discrepancy, we provide a more complete analysis of the task-space force/deformation behavior of compliant redundant arms to illustrate why the arm geometry plays a dominant role in interaction capabilities of robots. We introduce the notion of allowable Cartesian force/displacement (“stiffness feasibility”) regions (SFR) for compliant robots with given torque boundaries. We show that different robot configurations modify such regions and explore the role of robot geometry in achieving an appropriate SFR for the task at hand. The novel concepts and definitions are first illustrated in simulations. Experimental results are then provided to verify the effectiveness of the proposed Cartesian force and stiffness control.</p>
10aRobotics1 aAjoudani, A.1 aTsagarakis, N., G.1 aBicchi, A.  uhttp://ieeexplore.ieee.org/document/7951027/01909nas a2200181   4500008004100000245009500041210006900136260001200205520135300217653001301570100001401583700001101597700001101608700001701619700001501636700001201651856006401663       2017                        eng d00aCoordination Control of a Dual-arm Exoskeleton Robot Using Human Impedance Transfer Skills0 aCoordination Control of a Dualarm Exoskeleton Robot Using Human   c06/20173 a<p class="rtejustify">This paper has developed a coordination control method for a dual-arm exoskeleton robot based on human impedance transfer skills, where the left (master) robot arm extracts the human limb impedance stiffness and position profiles, and then transfers the information to the right (slave) arm of the exoskeleton. A computationally efficient model of the arm endpoint stiffness behavior is developed and a co-contraction index is defined using muscular activities of a dominant antagonistic muscle pair. A reference command consisting of the stiffness and position profiles of the operator is computed and realized by one robot in real-time. Considering the dynamics uncertainties of the robotic exoskeleton, an adaptive-robust impedance controller in task space is proposed to drive the slave arm tracking the desired trajectories with convergent errors. To verify the robustness of the developed approach, a study of combining adaptive control and human impedance transfer control under the presence of unknown interactive forces is conducted. The experimental results of this paper suggest that the proposed control method enables the subjects to execute a coordination control task on a dual-arm exoskeleton robot by transferring the stiffness from the human arm to the slave robot arm, which turns out to be effective.</p>
10aRobotics1 aHuang, B.1 aLi, Z.1 aWu, X.1 aAjoudani, A.1 aBicchi, A.1 aLiu, J.  uhttp://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7944582