  Learning from Demonstration (LfD) approaches empower end-users to teach
robots novel tasks via demonstrations of the desired behaviors, democratizing
access to robotics. However, current LfD frameworks are not capable of fast
adaptation to heterogeneous human demonstrations nor the large-scale deployment
in ubiquitous robotics applications. In this paper, we propose a novel LfD
framework, Fast Lifelong Adaptive Inverse Reinforcement learning (FLAIR). Our
approach (1) leverages learned strategies to construct policy mixtures for fast
adaptation to new demonstrations, allowing for quick end-user personalization,
(2) distills common knowledge across demonstrations, achieving accurate task
inference; and (3) expands its model only when needed in lifelong deployments,
maintaining a concise set of prototypical strategies that can approximate all
behaviors via policy mixtures. We empirically validate that FLAIR achieves
adaptability (i.e., the robot adapts to heterogeneous, user-specific task
preferences), efficiency (i.e., the robot achieves sample-efficient
adaptation), and scalability (i.e., the model grows sublinearly with the number
of demonstrations while maintaining high performance). FLAIR surpasses
benchmarks across three control tasks with an average 57% improvement in policy
returns and an average 78% fewer episodes required for demonstration modeling
using policy mixtures. Finally, we demonstrate the success of FLAIR in a table
tennis task and find users rate FLAIR as having higher task (p<.05) and
personalization (p<.05) performance.
