title: Kinematic feedback control laws for generating natural arm movements.
abstract: We propose a stochastic optimal feedback control law for generating natural robot arm motions. Our approach, inspired by the minimum variance principle of Harris and Wolpert (1998 Nature 394 780-4) and the optimal feedback control principles put forth by Todorov and Jordan (2002 Nature Neurosci. 5 1226-35) for explaining human movements, differs in two crucial respects: (i) the endpoint variance is minimized in joint space rather than Cartesian hand space, and (ii) we ignore the dynamics and instead consider only the second-order differential kinematics. The feedback control law generating the motions can be straightforwardly obtained by backward integration of a set of ordinary differential equations; these equations are obtained exactly, without any linear-quadratic approximations. The only parameters to be determined a priori are the variance scale factors, and for both the two-DOF planar arm and the seven-DOF spatial arm, a table of values is constructed based on the given initial and final arm configurations; these values are determined via an optimal fitting procedure, and consistent with existing findings about neuromuscular motor noise levels of human arm muscles. Experiments conducted with a two-link planar arm and a seven-DOF spatial arm verify that the trajectories generated by our feedback control law closely resemble human arm motions, in the sense of producing nearly straight-line hand trajectories, having bell-shaped velocity profiles, and satisfying Fitts Law.
authors.affiliation: School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Korea.
authors.forename: Donghyun
authors.initials: D
authors.lastname: Kim
authors.forename: Cheongjae
authors.initials: C
authors.lastname: Jang
authors.forename: Frank C
authors.initials: FC
authors.lastname: Park
mesh_terms: D000465:Algorithms; D001132:Arm / Q000502:physiology*; D032701:Biomimetics / Q000379:methods*; D003198:Computer Simulation; D025461:Feedback, Physiological / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D012371:Robotics / Q000379:methods*; D013647:Task Performance and Analysis