Postural stability of biped robots and the foot-rotation indicator (FRI) point
- Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Computer and Information Science
The focus of this paper is the problem of foot rotation in biped robots during the single-support phase. Foot rotation is an indication of postural instability, which should be carefully treated in a dynamically stable walk and avoided altogether in a statically stable walk. The author introduces the foot-rotation indicator (FRI) point, which is a point on the foot/ground-contact surface where the net ground-reaction force would have to act to keep the foot stationary. To ensure no foot rotation, the FRI point must remain within the convex hull of the foot-support area. In contrast with the ground projection of the center of mass (GCoM), which is a static criterion, the FRI point incorporates robot dynamics. As opposed to the center of pressure (CoP) -- better known as the zero-moment point (ZMP) in the robotics literature -- which may not leave the support area, the FRI point may leave the area. In fact, the position of the FRI point outside the footprint indicates the direction of the impending rotation and the magnitude of rotational moment acting on the foot. Owing to these important properties, the FRI point helps not only to monitor the state of postural stability of a biped robot during the entire gait cycle, but indicates the severity of instability of the gait as well. In response to a recent need, the paper also resolves the misconceptions surrounding the CoP/ZMP equivalence.
- OSTI ID:
- 354262
- Journal Information:
- International Journal of Robotics Research, Journal Name: International Journal of Robotics Research Journal Issue: 6 Vol. 18; ISSN IJRREL; ISSN 0278-3649
- Country of Publication:
- United States
- Language:
- English
Similar Records
A study of the passive gait of a compass-like biped robot: Symmetry and chaos
Sensor-based control of a nine-link biped