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This paper describes an avoidance behavior against unknown forces acting from outside the system on a biped vehicle. External forces that act on a biped vehicle can be divided into two categories: disturbances from the rider of the vehicle and disturbances from outside the system. Disturbances from the rider are measured by a force sensor placed between the rider's seat and the pelvis, while disturbances from outside the system are estimated from zero moment point (ZMP) errors. To guarantee walking stability, the waist position is adjusted to match the measured ZMP to the reference ZMP and the position of the landing foot is adjusted such that the waist trajectory does not diverge. On implementing the developed method on the human-carrying biped robot in an experimental setup, the robot could realize a stable walk even while subjected to unknown external forces in the environment. On applying a pushing force to the walking robot, the robot moved in the pushed direction and away from the source of the externally generated forces. On pushing the robot that was walking forward, the robot stopped moving forward and avoided getting closer to the source of the externally generated forces. We confirmed the effectiveness of the proposed control through these experiments.
Hashimoto et al. (Sat,) studied this question.