Abstract
Control of a multi-body system in both robots and humans may face the problem of destabilizing dynamic coupling effects arising between linked body segments. The state of the art solutions in robotics are full state feedback controllers. For human hip-ankle coordination, a more parsimonious and theoretically stable alternative to the robotics solution has been suggested in terms of the Eigenmovement (EM) control. Eigenmovements are kinematic synergies designed to describe the multi DoF system, and its control, with a set of independent, and hence coupling-free, scalar equations. This paper investigates whether the EM alternative shows “real-world robustness” against noisy and inaccurate sensors, mechanical non-linearities such as dead zones, and human-like feedback time delays when controlling hip-ankle movements of a balancing humanoid robot. The EM concept and the EM controller are introduced, the robot's dynamics are identified using a biomechanical approach, and robot tests are performed in a human posture control laboratory. The tests show that the EM controller provides stable control of the robot with proactive (“voluntary”) movements and reactive balancing of stance during support surface tilts and translations. Although a preliminary robot-human comparison reveals similarities and differences, we conclude (i) the Eigenmovement concept is a valid candidate when different concepts of human sensorimotor control are considered, and (ii) that human-inspired robot experiments may help to decide in future the choice among the candidates and to improve the design of humanoid robots and robotic rehabilitation devices.
Highlights
Most human skeletal movements involve several interconnected body segments
A kinematic aim is to maintain the center of mass (COM) of all body segments supported by the ankle joints above the base of support, which is the area under and between the feet, in order to
Dysfunction in the matching of timing and torque magnitudes across the chain of segments results in inappropriate compensation for body segment masses and inertia and neural time delays, imposing clinically for the kinematic chain as balance problems (Massion, 1992; Mergner, 2012) and for the kinetic chain as irregular and oscillating movements, a pathological symptom called ataxia that is typically found in cerebellar patients (Bastian, 1997)
Summary
Most human skeletal movements involve several interconnected body segments. Starting from buttressing segments such as the feet when standing, a chain of segments interleaves to the end effector such as the hand in reaching. A kinematic aim is to maintain the center of mass (COM) of all body segments supported by the ankle joints above the base of support, which is the area under and between the feet, in order to. A kinetic aim of movement coordination is to minimize effects of inter-segmental coupling torques. Dysfunction in the matching of timing and torque magnitudes across the chain of segments results in inappropriate compensation for body segment masses and inertia and neural time delays, imposing clinically for the kinematic chain as balance problems (Massion, 1992; Mergner, 2012) and for the kinetic chain as irregular and oscillating movements, a pathological symptom called ataxia that is typically found in cerebellar patients (Bastian, 1997). Neuroscientists devoted considerable attention to the neural mechanisms underlying human kinematic coordination (Massion, 1992), but paid less attention to the neural mechanisms underlying kinetic coordination, on which this paper focuses
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