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Design and Control of a Recovery System for Legged Robots

Falling is usually avoided in legged robotics. A robot is supported if it falls lower than a set height. In contrast, when children first learn to walk, a parent is close behind and catches the child if it is necessary. As the child learns to walk, the parent intervenes less and less. A recent paper on arXiv.org proposes similar assistance to legged robots.

Image credit: Pxhere, CC0 Public Domain

The proposed system replicates the parent’s helping hand for planar robots. It can have a minimal effect on the robot’s dynamics or help in the form of a controlled vertical force. If failure is detected, the system intervenes immediately and resets the robot for the next experiment.

A mechatronic planarizer, as well as several controllers, are developed to implement the recovery system. It can reduce the likelihood of damage to robots and increase trial speed. These benefits are useful for machine learning applications.

This paper describes the design and control of a support and recovery system for use with planar legged robots. The system operates in three modes. First, it can be operated in a fully transparent mode where no forces are applied to the robot. In this mode, the system follows the robot closely to be able to quickly catch the robot if needed. Second, it can provide a vertical supportive force to assist a robot during operation. Third, it can catch the robot and pull it away from the ground after a failure to avoid falls and the associated damages. In this mode, the system automatically resets the robot after a trial allowing for multiple consecutive trials to be run without manual intervention. The supportive forces are applied to the robot through an actuated cable and pulley system that uses series elastic actuation with a unidirectional spring to enable truly transparent operation. The nonlinear nature of this system necessitates careful design of controllers to ensure predictable, safe behaviors. In this paper we introduce the mechatronic design of the recovery system, develop suitable controllers, and evaluate the system’s performance on the bipedal robot RAMone.

Research paper: Green, K., Smit-Anseeuw, N., Gleason, R., and Remy, C. D., “Design and Control of a Recovery System for Legged Robots”, 2021. Link: https://arxiv.org/abs/2111.14972

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