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This paper presents the work addressing the issue of standing up after falling down for a novel three-legged mobile robot STriDER (Self-excited Tripedal Dynamic Experimental Robot). The robot is inherently stable when all three feet are on the ground due to its tripod stance, but it can still fall down if it trips while taking a step or if unexpected external forces act on it. The unique structure of STriDER makes the simple task of standing up challenging for a number of reasons; the high height of the robot and long limbs require high torque at the actuators due to its large moment arms; the joint configuration and length of the limbs limit the workspace where the feet can be placed on the ground for support; the compact design of the joints allows limited joint actuation motor output torque; three limbs do not allow extra support and stability in the process of standing up. This paper examines four standing up strategies unique to STriDER: three feet, two feet and one foot pushup, and spiral pushup. For all of these standing up strategies, the robot places its feet or foot at desired positions and then pushes the feet against the ground thus, lifting the body upwards. The four pushup methods for standing up were analyzed and evaluated considering the constraints such as, static stability, friction at the feet, kinematic configuration and joint motor torque limits, thus determining the suggested design and operation parameters. The motor torque trends as the robot stands up using pushup methods were investigated and the results from the analysis were validated through experiments.Copyright © 2009 by ASME |
