Human-Inspired Eigenmovement Concept Provides Coupling-Free Sensorimotor Control in Humanoid Robot

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.

Evidence in Support of the Independent Channel Model Describing the Sensorimotor Control of Human Stance Using a Humanoid Robot

“…The main purpose of the study was to show the functionality of the IC model in real world situations using robot experiments. Similar approaches have been used to test other balance control concepts, like the Disturbance Estimation and Compensation concept or the Eigen movement concept (Hettich et al, 2014 ; Alexandrov et al, 2017 ). Here, the IC model was able to control the robot in the time domain when adjusting the estimated neural controller parameters (i.e., the reflexive stiffness and damping) to the mass and weight of the robot.…”

Human-Derived Disturbance Estimation and Compensation (DEC) Method Lends Itself to a Modular Sensorimotor Control in a Humanoid Robot

“…This neurorobotics approach will allow neuroscientists and roboticists to compare different models both with respect to specific and general performance criteria (e.g., versatility, failsafe robustness, etc.). For example, a concept of how humans may deal with inter-link coupling forces using Eigenmovements has recently been tested in a robot of this laboratory, where it successfully passed the “real world” test (Alexandrov et al, 2017 ). The DEC concept provides an alternative solution for the problem of inter-segmental force coupling in terms of a bundle of counter measures, which include the DEC mechanisms for T ext and T acc in Figure 1 , modulation of passive stiffness and damping, and the use of waveforms for commanded movement trajectories, which are optimized for low acceleration and jerk (compare waveform in Figure 6 ).…”

“…Noticeably, however, the number of required synergies in complex movements may reach the number of DoFs. This may happen for example when movement control is organized in terms of eigenmovements (Alexandrov et al, 2017 ) where the aim is to free the control from coupling forces stemming from other movements. Certain synergies studied in humans, such as torque synergies, are so far largely neglected in robotics.…”

Analysis of balance control methods based on inverted pendulum for legged robots

“…Conclusions and summary about analyzed methods are presented in Table 2. The method presented in [13] was tested on the real robot and showed the best balance control of a humanoid robot. However, this method is very resource-intensive one.…”

“…The paper [13] considers the possibility of controlling the movement of a two-link anthropomorphic robot on the basis of coordination of natural synergies. The authors explore an approach demonstrating the advantages of motor control, which is based on the management of their own movements, which is a natural synergy.…”