An online trajectory modifier for the base link of biped robots to enhance locomotion stability

Abstract

This puper proposes a n on-line trajectory modificution scheme f o r biped robots t o cope with uncertainty of their environment. For stable locomotion, brped robots should have robust properties against var-%ous disturbances such as ground irregularity and exter.rrul pushing or pulling forces. Since such uncertainty is not known a priori, biped robots should have the ability to adapt to t h e m on-line. In the proposed scheme, the trajectory of the base link in the vertical direction is modified depending o n the magnitude of ZMP deviation from its safety b o u n d a y such that appropriate angular m o m e n t is generated to maintain stable walking. The modified trajectory then graduully returns to the original trajectory using a 3rdor 5th-order interpolation polynomial. A n d this paper expunds the gravity-compensated inverted pendulum mode (GCIPM) to generate the base-link trajectory not only f o r single support phases but also double support phases. I n the simulations t o evaluate the proposed scheme, a n impedance controller is used to control a 6-dof biped robot and the environment of the biped robot is assumed to consist of nonlinear and linear compliant contact models. The simulation results show that the proposed on-line trajectory modification scheme effectively enhances the stability of locomotion.

Walking with perturbations: a guide for biped humans and robots

“…Kajita and colleagues, based on a humanoid robot HRP-2, calculated the minimal friction of the slippery surface needed to walk successfully, resulting in a friction coefficient of 0.14 [325]. Most solutions involve open loop control, yet some attempts were made for online trajectory control as well and this was shown to effectively enhance the stability of locomotion [326].…”