Safe fall: Humanoid robot fall direction change through intelligent stepping and inertia shaping

Abstract

Although fall is a rare event in the life of a humanoid robot, we must be prepared for it because its consequences are serious. In this paper we present a fall strategy which rapidly modifies the robot's fall direction in order to avoid hitting a person or an object in the vicinity. Our approach is based on the key observation that during "toppling" the rotational motion of a robot necessarily occurs at the leading edge or the leading corner of its support base polygon. To modify the fall direction the robot needs to change the position and orientation of this edge or corner vis-a-vis the prohibited direction. We achieve it through intelligent stepping as soon as a fall is detected. We compute the optimal stepping location which results in the safest fall. Additional improvement to the fall controller is achieved through inertia shaping techniques aimed at controlling the centroidal inertia of the robot.We demonstrate our results through the simulation of an Asimo-like humanoid robot. To our knowledge, this is the first implementation of a controller that attempts to change the fall direction of a humanoid robot.

Generalized direction changing fall control of humanoid robots among multiple objects

“…The first reported work on humanoid fall direction change was in [1] and in the current paper we present a thorough generalization, extension and improvement of this approach. A sample of our current results is shown in Fig.…”

“…IV-A. b) Control Trigger: As described in [1] the Fall Trigger Boundary (FTB) of a robot encloses a region in the robot's state space in which a given balance controller is able to stabilize the robot. An exit through the FTB is an indication of a certain fall and this event was used to activate a switch from the robot's balance controller to a fall controller.…”

“…These represent the set of directions in which the robot can fall without hitting an object. The number of safe fall regions, n s f , is given by: n s f = n ob j − n int (1) where, n ob j is the number of non-intersecting objects and n int is the number of pairs of intersecting expanded objects. The set of all safe fall regions is given by SF = {SF 1 , ..., SF n s f }, where SF j represents the j th safe fall region (free cone).…”

“…This paper proposes a strategy for planning and control of fall. The controller's objective is to prevent the robot from hitting surrounding objects during a fall by modifying its default fall direction.We have earlier presented such a direction-changing fall controller in [1]. However, the controller was applicable only when the robot's surrounding contained a single object.…”

“…We have earlier presented such a direction-changing fall controller in [1]. However, the controller was applicable only when the robot's surrounding contained a single object.…”