Walking pattern generation for a humanoid robot with compliant joints

Abstract

This work presents a walking pattern generator based on the control of the center of mass (COM) states and its experimental validations on the compliant humanoid robot COMAN powered by intrinsically compliant joints. To cope with the inaccuracies of the joint position tracking resulted by the physical compliance, the proposed pattern generator uses the feedback states of the COM and on-line computes the updated COM references. The position and velocity of the COM are the state variables, and the constrained ground reaction force (GRF) limited by the support polygon is the control effort to drive the real COM states to track the desired references. The frequency analysis of the COM demonstrates its low frequency spectrum that indicates the demand of a low control bandwidth which is suitable for a robot system with compliant joints. The effectiveness of the proposed gait generation method was demonstrated by the experiments performed on the COMAN robot. The experimental data such as the COM position and velocity tracking, the GRF applied on feet, the measured step length and the walking velocity are analyzed. The effect of the passive compliance is also discussed.

Imitation of Dynamic Walking with BSN for a Humanoid Robot

“…The mean values of the hip pitch angle error can indicate similarity between the movements of a human subject and the robot because the knee pitch angles were constrained to be within a predefined range by one of the artificial constraints in (15). Therefore, without significant changes in the knee pitch angles, leg movements were mainly affected by the changes in the hip pitch angles.…”

“…Czarnetski et al [14] controlled NAO robot's walking by using the preview controller and closed loop control with sensor feedback. Li et al [15] generated walking patterns for COMAN, a compliant humanoid robot, by controlling the center of mass. However, these methods involve computation of joint trajectories for robot's motion by imposing stability constraints, but the resulting movement may not be natural or human-like because not all degrees of freedom (DOFs) are used.…”

A passivity based compliance stabilizer for humanoid robots

“…The effectiveness of the proposed stabilizer was validated when the simulated robot performed walking in place with a fixed walking pattern by the method in [16] [17]. The reason walking in place is chosen as a further validation is that the robot's base frame B coincides with the global frame W during gait.…”

A compliant humanoid walking strategy based on the switching of state feedback gravity compensation controllers

“…The step length during walking was 12 cm and the trajectory was generated at a frequency of approximately 0.8 Hz. Explicit details regarding the trajectory generation framework may be found in [22] [23]. In order to assess the robot's overall stability, an inspection of the joint tracking and Cartesian CoM position during the trajectory was required, as portrayed by Figs.…”