Expressive Whole-Body Control for Humanoid Robots
(2402.16796)Abstract
Can we enable humanoid robots to generate rich, diverse, and expressive motions in the real world? We propose to learn a whole-body control policy on a human-sized robot to mimic human motions as realistic as possible. To train such a policy, we leverage the large-scale human motion capture data from the graphics community in a Reinforcement Learning framework. However, directly performing imitation learning with the motion capture dataset would not work on the real humanoid robot, given the large gap in degrees of freedom and physical capabilities. Our method Expressive Whole-Body Control (Exbody) tackles this problem by encouraging the upper humanoid body to imitate a reference motion, while relaxing the imitation constraint on its two legs and only requiring them to follow a given velocity robustly. With training in simulation and Sim2Real transfer, our policy can control a humanoid robot to walk in different styles, shake hands with humans, and even dance with a human in the real world. We conduct extensive studies and comparisons on diverse motions in both simulation and the real world to show the effectiveness of our approach.
Overview
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The paper introduces an expressive whole-body control policy, ExBody, aimed at making humanoid robots move with greater expressiveness akin to human motion through the use of human motion capture data and deep Reinforcement Learning (RL).
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ExBody employs motion retargeting techniques to adapt human motion data to fit robotic models, specifically using the Unitree H1 robot, overcoming differences in degrees of freedom and physical capacity.
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The control policy, trained in randomized environments, enables the robot to execute diverse and expressive movements, such as dancing and walking with gestures, demonstrating significant nuance in robotic movement.
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ExBody's robust sim-to-real transfer capability allows the humanoid robot to interact dynamically with human partners and navigate various terrains, presenting potential implications for enhancing human-robot interaction, entertainment, and assistive technologies.
Expressive Whole-Body Control for Humanoid Robots
Introduction
Recent advances in humanoid robotics have sought to bridge the gap between the mechanical movements traditionally associated with robots and the expressive, nuanced motions observed in living beings. In the presented work, a notable contribution towards this aim has been made through the development of an expressive whole-body control policy, referred to as ExBody, for humanoid robots. This initiative not only aims to enhance the robots' ability to perform a wider range of movements but is also designed to imbue them with a level of expressiveness that is closely akin to human motion.
Methodology
Learning from Human Motion Capture Data
The foundation of ExBody's approach lies in utilizing large-scale human motion capture data from the graphics community, integrating this with deep Reinforcement Learning (RL) in a simulated environment. This methodology enables the derivation of a control policy that can subsequently be transferred to a real humanoid robot, facilitating movements that are rich in expressivity.
Motion Retargeting
A key challenge in this process is the inherent difference in degrees of freedom (DoF) and physical capacity between the human models used in motion capture data and the actual robotic hardware. ExBody addresses this by employing motion retargeting techniques, adapting human motion data to fit the robotic model utilized in this study, the Unitree H1 robot.
Reinforcement Learning Framework
The RL framework constitutes the core of the ExBody approach, where the humanoid robot is trained to follow command-conditioned locomotion alongside achieving specified expressive motion goals. These goals are derived from the human motion capture data, focusing on the upper body to ensure a practical level of expressivity without overly constraining the robot's movement capabilities. The policy is trained in highly randomized environments to ensure robustness and feasibility of sim-to-real transfer.
Results and Discussion
Policy Effectiveness
The study demonstrates the effectiveness of ExBody in several key areas. The robot is capable of executing diverse movements with significant expressiveness, such as dancing and walking with varied gestures. The behavior of the robot in these instances showcases an unprecedented level of nuance in robotic movement that is both diverse and human-like.
Sim-to-Real Transfer
Crucial to the success of ExBody is its robust sim-to-real transfer capability. The control policy, once trained in simulation, exhibits high compliance and effectiveness when deployed in the real world, enabling the humanoid robot to interact dynamically with human partners and navigate various terrains with expressive motions.
Potential Implications and Future Directions
The implications of this research are significant for the future development of humanoid robots. By enabling robots to perform more expressive and varied movements, ExBody opens up new possibilities for human-robot interaction, entertainment, and assistive technologies. The approach also presents a scalable framework that could potentially be adapted for other robotic form factors.
However, the study also recognizes the limitations inherent in the current implementation, such as the challenges related to motion retargeting and the risks associated with robot falls. Future work will need to address these challenges, further refining the control policy and exploring protective measures for the robots.
Conclusion
The presented work on ExBody represents a significant step forward in the quest for more expressive and human-like movement in humanoid robots. By leveraging extensive human motion capture data and employing a refined RL framework, the study not only enhances the robots' movement capabilities but also enriches their ability to interact with the surrounding environment in a way that is both meaningful and engaging.
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